COLUMBIA LIBRARIES OFFSITE HEALTH SCIENCES STANDARD ^: *'''h ' •■■■ J,. -• . .... -J, •J I-- ■ ;^ m iT'S' lA , '( ' ■^n^^;^"^^: -'V'- ' ■^'.^' ! ".<■ ' ','-^'1' "-ivi" ' ■-..V.J,'', cil'.nf > " - "^r QnZ2. C. Jamieson and Mr. A. R. Maclean. ARTHUR ROBINSON. June 8, 1917. ^H '"WSit Oliver Sheppard, R.H.A., fecit. DANIEL JOHANNES CUNNINGHAM ADHUC LOQUITUR. Demonstrator ok Anatomy, University of Edinburgh, 1874-1882. Professor of Anatomy, Royal College of Surgeons, Dublin, 1882-1883. Professor of Anatomy, Trinity College, Dublin, 1883-1903. Professor of Anatomy, University op Edinburgh, 1903-1909. LIST OF COXTKIl^LTOKS RICHARD J. A. BERRY, M.D., F.R.C.S. Ed., Professor of Anatomy, University of Melbourne. {The Respiratory System.) A. FRANCIS DIXON, M.B., D.Sc. (Dubl.), Professor of Anatomy, Trinity College, Dublin. {The Uro-genital Sysievi.) A. CAMPBELL GEDDES, M.D., Professor of Anatomy, University of Montreal. (The Ductless Glands.) DAVID HEPBURN, M.B., F.R.S.E., Professor of Anatomy, University College, Cardiff'. {Arthroloyy.) ROBERT HOWDEN, M.A., M.B., Professor of Anatomy, University of Durham. {The Organs of Sense and the Integument.) A. M. PATERSON, M.D., F.R.C.S., Professor of Anatomy, University of Liverpool {Myology, The Spinal and Cerebral Nerves, The Sympathetic Nervous System.) ARTHUR ROBINSON, M.D., F.R.C.S. Ed., Professor of Anatomy, University of Edinburgh. {General Embryology, The Vascular System.) Q. ELLIOT SMITH, M.D., F.R.S., Professor of Anatomy, University of Manchester. {The Central Nervous System.) HAROLD J. STILES, M.B., F.R.C.S. Ed., Surgeon to the Royal Hosjiital for Sick Children, Edinburgh. {Surface and Surgical Anatomy.) ARTHUR THOMSON, LL.D., M.A., M.B., F.R.C.S., Profe.ssor of Human Anatomy, University of Oxford. {Osteology.) DAVID WATERSTON, M.A., M.D., F.R.C.S. Ed., Professor of Anatomj-, University of St. Andrews. {Tlie Digestive System.) CONTENTS. Glossary of Variations between International and Old Terminology Introduction PAGE xvii GENERAL EMBRYOLOGY. PAGE The Animal Cells 7 Reproduction of Cells ... 8 Amitotic and Mitotic Division of Cells 9 The Ovum 13 Its Structure 13 Its Maturation ..... 15 The Spermatozoon 17 Fertilisation 20 Segmentation 21 Formation of Blastula . . . . 21 Ectoderm and Entoderm . . . 21 Embryonic Area .... 22 Extra-Embryonic Coelom ... 22 Differentiation of the Embryonic Area . 23 Neural Groove 23 Formation of Notochord and Secondary Mesoderm ..... 24 The Paraxial Mesoderm .... 28 Mesodermic Somites .... 28 Early Stages in Development of the Nervous System .... 30 Nerve Ganglia and Chromaffin Tissues 32 Differentiation of the Neural Tube . 33 Fate of Walls of Primitive Brain Vesicles ..... 33 Fate of Cavities of Primitive Brain • 36 Folding off of the Embryo ... 37 Professor Arthur Robinson. Formation of the Embryo Development of the Limbs Primitive Alimentary Canal . The Fore -Gut — Pharynx and Stoma todaium ..... Visceral Clefts and Arclie^s Rudiments of Respiratory System External Ear, Tympanic Cavity and Auditory Tube The Tongue .... Derivatives of the Mid-Gut . The Hind-Gut, Anal Passage, and Post anal Gut .... Derivatives of the Stomatodseum— The Nose and Mouth . The Internal Ear . ". . . Protection and Nutrition of the Embryo during its Intra-uterine Existence FcEtal Membranes and Appendages Chorion .... Amnion .... Body-Stalk Allantois .... Umbilical Cord Yolk-Sac or Umbilical Vesicle The Placenta .... Primitive Vascular System and FcEtal Circulation Summary of the External Features of the Human Embrj^o and Fcetus at different periods of Development . PAGE 39 39 41 42 43 44 44 45 47 48 48 50 53 53 53 54 54 54 55 55 56 63 74 OSTEOLOGY. The Skeleton . Composition of Bone Structure of Bone Os.sification and Growth o The Vertebral Column A Typical Vertebra Cervical Vertebra; Thoracic Vertebra^ . Lumbar Vertebra} Fal.se or Fixed Vertel>ra; The Sacrum The Coccyx The Vertebral Column as a w Professor Arthur Thomson. 81 82 83 )i' Bones 85 87 88 ! 90 93 95 j 96 ! 96 99 vhole 100 Development of the Vertebral Column The Cartilaginous Column Ossification of the Vertebrae The Sternum . The Ribs The Costal Cartilages The Thorax as a wliole The Bones of the Skull Frontal Bone Parietal Bones . Occipital Bone . Temporal Bones Sphenoid Bone. 102 102 104 106 109 113 113 115 115 118 120 125 133 CONTENTS. XI Ethmoid Bone . Inferior Condue The Lacrimal Bones The Vomer .... Nasal Bones Sutiiral Bones . Bone.s of the Face . Ma.xilhe .... Palate Bones Zygomatic Bones ^Iandible .... The Hyoid Bone . The Skull a.s a whole The Skull from the Front The Skull from the Side . Posterior Asjiect x)f the Skull Uj)per Aspect of Skull Base of the Skull . The Skull in Section Upper Surface of the Base of the Skull Medial Sagittal Section of Skull . Nasal Fossae Nasal Septum Air-sinuses in Nasal Fosspe . Frontal Sections of the Skull Horizontal Section of the Skull Sexual Differences in the Skull The Skull at Birth Differences due to Age . Bones of the Upper Extremity Clavicle .... Scapula .... Humenis .... connexion with the PAOK 139 142 U3 144 145 14r, 146 14G l.'iO ir)3 154 158 159 160 164 171 171 172 179 179 183 183 185 185 186 192 193 194 197 197 197 200 .204 THE ARTICULATIONS OR JOINTS. Syndesmology ..... 299 Synarthroses 299 Diartiiroses or Movable Joints . . 300 Structures which enter into the Formation of Joints . . . 301 The Different Kinds of Movement at Joints 303 The Development of Joints . 304 Morpliology of Ligaments . . 305 Ligaments of the Vertebral Column and Skull . . . . .305 Articulation between the Athis and Epistropheus .... 309 Articulation between the Atlas and the Cranium .... 310 Mandibular Joint 312 Cranial Ligaments not directly as.so- ciated with Articulations . 313 The Joints of the Thorax . . .' 313 Joint^s of the Heads of the Kibs 313 Costo-transverse Joints . . . 314 Articulations between the Ribs and their Cartilages .... 315 Interchondral Joints 315 Sterno-costal Joints . . . : 315 Sternal Articulations . . . 317 The Articulations of the Superior Ex- tremity 317 THE MUSCULAR SYSTEM. The Muscular System . Fascite ..... Description of the Muscles 363 364 365 Ulna .... PAOE 210 Radius .... . 214 Tin; Carpus 217 Tin: Carpus as a wlnjle 222 The Metacarj)us 223 Tlie Phalanges . •2-2(i ye.samoid Bones . 228 Bones of the Lower Limb . 228 The Pelvic Ginlle and the Lowi M K.x- tremity .... 228 The Hip Bone . 228 The Pelvis 235 The Femur 239 The Patella 245 The Tibia . 246 The Fibula 250 Tarsus 254 Talus 254 Calcaneus .... 2.59 Navicular Bone of the Fool 261 Cuneiform Bones 261 Cuboid Bone 263 The Tai-siLS as a whole . 264 The Metatarsus . . 265 Phalanges of the Foot 267 Sesamoid Bones of the Foot . 269 Appendices — Architecture of the Bones of the Skeleton . 270 Variations in the Skeleton 275 Serial Homologies of the Vertebrie . 283 Measurements and Indices emj (loved in Physical Anthropology . 284 Developmentof the Chondro-cranium and Morphology of the Skul I 290 Morphology of the Limits 294 Professor David Hepburn. Articulations of the Clavicle . 317 Stemo-clavicular Joint 317 Acromio-clavicular Joint . 318 Ligaments of the Scapula 320 Shoulaer-joint 320 Elbow-joint .... 323 The Radio-ulnar Joints . 326 The Radio-carpal Joint . 328 Carpal Joints 329 Intermetacarpal Joints . 332 Carpo-metacar])al Joints 332 Melacarpo-phalangeal Joints 3.33 Interphalangeal Joints . . 334 Articulationsand Ligaments of the '. ^elvis 334 Lumbo-sacral Joints . 335 Sacro-iliac Joint 335 Symphysis Pubis . 337 Articulations of the Inferior Ext re mitv 339 The Hip-joint . ■ . 339 The Knee-joint 342 The Tibio-liliular Joints . 349 The Joints of the Foot 351 The Ankle-joint 351 The Intertarsal Joints 354 The Tai-so-metatarsal Joints 359 Intermetatarsal Joints 360 Metatai-so-phalangeal Joints 360 Interphalangeal Joints . 361 Professor A. Mklvillf PATKR.SOX. Appendicular Muscles . . 365 Fascia- and Sui>erficial Muscles o f the Back .365 xu CONTENTS. Fasciae of the Back The Superficial Muscles of the Back The Fascite and Muscles of the Pectoral Region Fasciae of the Pectoral Region Muscles of the Pectoral Region Fascite and Muscles of the Shoulder Muscles of the Shoulder Fasci te and Muscles of the Arm Fasciae and Muscles of the Forearm and Hand The Muscles of the Front and Medial Aspect of the Forearm Superficial Muscles . Intermediate Layer . Deep Layer Short Muscles of the Hand Muscles of the Thumb . Muscles of the Little Finger The Interosseous Muscles of the Hand The Muscles on the Dorsal Surface of the Forearm Suijerficial Muscles . Deep Muscles . The Lower Limb . Fasciae and Muscles of the Thigh and Buttock . . . . , Fasciae of the Thigh and Buttock , Muscles of the Thigh and Buttock The Muscles on the Anterior Aspect of the Thigh . The Muscles on the Medial Side of the Thigh . Tlie Muscles of the Buttock The Muscles on the Posterior Aspect of the Thigh . The Fasciae and Muscles of the Leg and Foot Fasciae of the Leg and Foot The Muscles on the Front of the Leg and Dorsum of the Foot PAGE 365 365 369 369 369 373 373 378 382 385 385 388 388 391 392 393 394 395 396 398 402 402 402 405 405 411 414 418 422 422 424 THE CENTRAL NERVOUS SYSTEM. Elements of the Central Nervous System 497 Outline of Development of the Central Nervous System .... 499 Neurone Theory ..... 503 Nerve Components . . . 505 Nerve-cells . . ■ . . . 506 Nerve-fibres ...... 508 Neuroglia . . . . . .511 The Nature of tlie Brain . . .512 The Spinal Medulla .... 517 Internal Structure of Spinal Medulla 523 Characters presented by the Spinal Medulla in its Different Regions . 524 Component Parts of the Gray Matter of the Spinal Medulla . . .527 Component Parts of the White Matter of the Spinal Medulla . . . 531 The Encephalon or Brain . 539 General Appearance of the Brain . 539 Parts of Encephalon derived from the Hind-ljrain 543 Medulla Oljlongata .... 643 Pons 548 The Fourth Ventricle ... 549 Internal Structure of Medulla Ob- longata and Pons . . . .551 Internal Structure of tlie Pons . 565 PAGE The Muscles on the Lateral Side of the Leg 426 The Muscles on the Posterior Aspect of the Leg 428 The Muscles in the Sole of the . oot . 432 Axial Muscles 437 The Fasciae and Muscles of the Back . 437 The Fasciae of the Back .... 437 The Muscles of the Back . . . 438 First Group 438 Second Group 439 Third Group 442 Fourth Group ..... 444 The Fasciae and Muscles of the Head and Neck 446 Fasciae of the Head and Neck . . 44.. The Muscles of the Head . . .448 Superficial Muscles .... 448 The Muscles of the Scalp . . .448 The Muscles of the Face . . .450 The Fasciae and Muscles of the Orbit . 452 Muscles of Mastication .... 454 The Muscles of the Neck . . .458 The Muscles of the Hyoid Bone . . 458 • The Muscles of the Tongue . . ., 462 The Muscles of the Pharynx . . . 464 The Muscles of the Soft Palate . . 466 Deep Lateral and Praevertebral Muscles of the Neck 467 The Muscles of the Thorax . . .470 Muscles of Respiration .... 470 Fasciae and Muscles of the AbdominalWall 474 Fasciae of the Abdominal Wall . . 474 The Muscles of the Abdominal Wall . 476 Fasciae and Muscles of the Perineum and Pelvis 485 Fasciae of the Perineum .... 485 The Muscles of the Perineum . . 486 The Fasciae of the Pelvis . . . 489 Muscles of the Pelvis .... 493 The Development and Morphology of the Skeletal Muscles . . . 495 Professor G. Elliot Smith. The Cerebellum The Structure and Connexions of the Cerebellum . . The Mesencephalon .... Internal Structure of the Mesence- phalon The Deep Connexions of the Cerebral Nerves attached to the Medulla Oblongata, Pons, and Mesence- phalon ...... Prosencephalon or Fore-brain Development of Parts derived from Fore -brain ..... Parts derived from the Dience- phalon Thalamus Hypothalamic Region Pineal Body Trigonum Habenulae Corpora Mamillaria .... Hypophysis Third Ventricle .... Cerebral Connexions of the Optic Tract Parts derived from the Telencephalon . Cerebral Hemispheres The Connexions of the Olfactory Nerves 570 576 581 584 592 607 608 609 609 613 614 614 615 615 616 619 620 620 623 CONTENTS. Xlll The Cerebral Commissures and the: Sej)tum Pellucidum . . . 628 Tlie Corpus Callosuin . . .629 Tlie Lateral Ventricle . . .632 13a.sal Ganglia of the Cerebral Hemi- sphere 637 Intimate Structure of Cerebral Hemi- sphere 644 The Cerebral Cortex .... 644 The Neopallium .... 645 The White Matter of the Cerebral Hemispheres 647 THE PERIPHERAL NERVOUS SYSTEM. Spinal Nerves 677 Development of the Peripheral Nerves . 679 Development of the Sympathetic System 681 Development of the Cerebral Nerves . 682 The Spinal Nerves . . . . .685 Posterior Rami of the Spinal Nerves . 687 Posterior Rami of the Cervical Nerves . 688 Posterior Rami of the Thoracic Nerves . 690 Posterior Rami of the Lumbar Nerves . 690 Posterior Rami of the Sacral and Coccy- geal Nerves 691 Morphology of the Posterior Rami . 691 Anterior Rami of the Spinal Nerves . 692 Cervical Nerves 692 Cervical Plexus 694 Phrenic Nerve 699 Morphology of the Cervical Plexus . 700 Brachial Plexiis 700 Branches of Brachial Plexus . . 701 Anterior Thoracic Nerves . . 703 Musculo-cutaneous Nerve . 704 Median Nerve 705 Ulnar Nerve 708 Medial Cutaneous Nerve of the Fore- arm 709 Medial Cutaneous Nerve of the Arm 710 Axillary Nerve 710 Radial Nerve 710 Superficial Ramus of Radial Nerve . 712 Deep Ramus of Radial Nerve . . 712 Subscapular Nerves . . . .713 Thoracic Nerves 713 Lumbo-sacral Plexus .... 718 Lumbar Plexus 719 Obturator Nerve .... 722 Femoral Nerve ..... 724 Sacral Plexus 727 Sciatic Nerve . ... 728 The Nerves of Distribution from the Sacral Plexus .... 728 The Sulci and Gyri of the Cerebral Hemispheres The Acoustic Area and Fibre Tracts The Visual Area and Fibre Tracts The Parietal Region of the Bniii Tlie Frontal Region . Weight of the Brain . Meninges of the Encephalon and Spina Medulla .... Dura Mater .... Arachnoidea .... Pia Mater 653 657 658 662 665 667 667 667 670 673 Professor A. Melville Paterson. Common Peroneal Nerve . Deep Peroneal Nerve Superficial Peroneal Nerve Tibial Nerve .... Medial Plantar Nerve Lateral Plantar Nerve Pudendal Plexus .... Pudendal Nerve Morphology of the Pudendal Plexus Morphology of the Limb-plexuses . Distribution of Spinal Nerves to Muscles and Skin of Limbs Variations in Position of the Li ml plexuses .... Significance of the Limb-plexuses . Sympathetic Nervous System . Cervical Part of Sympathetic Trunk Superior Cervical Ganglion Middle Cervical Ganglion Inferior Cervical Ganglion Thoracic Part of Sympathetic Trunk Abdominal Part of Sympathetic Trunk Pelvic Part of Sympathetic Trunk Sympathetic Plexuses ... Coeliac and Pelvic Plexuses Cerebral Nerves Olfactory Nerves Optic Nerve .... Oculo-motor Nerve . Trochlear Nerve Trigeminal Nerve Abducens Nerve Facial Nerve .... Acoustic Nerve .... Glossopharyiigeal Nerve . Vagus Nerve .... Thoracic Plexuses of . Accessory Nerve Hypoglossal Nerve . Development of Cerebral Nerves . Morphology of Cerebral Nerves 730 730 731 732 734 734 735 738 740 741 744 752 753 753 756 756 759 759 759 761 762 763 763 767 767 768 769 770 771 781 781 784 785 786 789 791 791 795 796 ORGANS OF SENSE AND THE INTEGUMENT. Professor Robert Howden. Olfactory Organ Cartilages of Nose Nasal Cavity . Organ of Sight . Bulb of the Eye . Sclera Cornea . Vascular and Pigmented Tunic Retina Refracting Media of Eveball . Eyelids . . . " . Lacrimal Apparatus Development of the Eye Auditory Organ . 799 800 801 806 806 807 808 810 814 819 821 824 825 827 External Ear .... Auricle .... External Acoustic Meatus Tympanic Cavity . Tympanic Antrum and Mastoid Air cells .... Auditory Tube . Auditory Ossicles Internal Ear .... Osseous Labyrinth . Membranous Labyrinth . Development of Labyrinth Organs of Taste . The Integument or Skin . 827 827 830 832 836 837 838 843 843 846 853 854 856 XIV CONTENTS. Appendages of the Skin .... Development of the Skin and its Appendages THE VASCULAR SYSTEM. PAGE PAOK 858 Endings of Nerves of General Sensa- tion 863 861 Special End Organs .... 863 Professor Arthur Robinson. Structure of Blood-vessels 868 1 The Heart .... 870 ' The Chambers of the Heart . 873 Structure of the Heart . 878 Pericardium .... 880 Arteries .... 882 Pulmonary Artery . 882 The Systemic Arteries . 884 1 Aorta 884 Thoracic Aorta 884 1 Abdominal Aorta . 885 ! Branches of the Ascending Aorta 887 i Coronary Arteries 887 Branches of the Arch of the Aorta 888 , Innominate Artery 888 , The Arteries of the Head and Neck 888 Common Carotid Arteries 888 External Carotid Artery 891 Branches of External Carotid Arterj ' 891 Internal Carotid Artery 900 Branches of Internal Carotid Artery 902 Vertebral Ai'tery 905 Arteries of the Upper Extremity . 909 Subclavian Arteries 909 Branches of the Subclavian Artery 910 Axillary Artery .... 914 j Branches of the Axillary Artery 916 917 Branches of Bracliial Artery 918 Radial Artery .... 919 Ulnar Artery .... 921 The Arterial Arches of the Wrist anc Hand 923 Branches of Descending Thoracic Aorta 924 Visceral Branches of the Descending Thoracic Aorta 925 Parietal Branches of the Descending Thoracic Aorta 925 ! Branches of Abdominal Aorta 927 '■ The Paired Visceral Branches of the Alxiominal Aorta 927 The Unpaired or Single Viscera Branches of the AMominal Aorta 928 Parietal Branches of the Abdomina Aorta 933 Common Iliac Arteries 935 i Hypogastric Artery 936 Branches of the Posterior Division 938 Branches of the Anterior Division 939 Visceral Branches 939 Parietal Branches of the Anterio Division .... 940 The Arteries of the Lower Extremity 944 The External Iliac Artery 944 The Femoral Artery . 946 Popliteal Artery .... 951 Posterior Tibial Artery . . 952 Plantar Arteries . 954 Anterior Tibial Artery . 955 Tnv. Veins . . ." . . 958 The Pulmonary Veins . . 958 Systemic Veins .... 959 Coronary Sinus and V(uns of Heart . 959 Superior Vena Cava and its Tril)u taries 960 Azygos Veins 960 Innominate Veins .... Veins of the Head and Neck . The Veins of the Scalp Veins of the Orbit, Nose, and Infra- temporal Region . . . . Venous Sinuses and Veins of the Cranium, and its Contents . Diploic and Meningeal Veins . Veins of the Brain .... Sinuses of the Dura Mater Veins of the Spinal Medulla Veins of the Superior Extremity . Deep Veins of the Upper Extremity Axillary Vein ..... The Superficial Veins of the Superior Extremity Inferior Vena Cava and its Tributaries Common Iliac Veins Veins of the Lower Extremity Deep Veins of the Lower Extremity Superficial Veins of the Lower Extre- mity The Portal System Mesenteric and Splenic Veins . The Ltmph Vascular System The Terminal Lymph Vessels Lymph Glands of the Head . Lymph Glands of tlie Neck . Lymph Vessels of the Head and Neck . Lymph Glands of the Superior Extre- mity ...... Lymph Vessels of the Superior Extre- mity The Lymph Glands of the Thorax The Lymjjh Vessels of the Thorax Lymph Glands and Vessels of the In- ferior Extremity .... Lym^^h Vessels of the Inferior Extremity Lymph Glands of the Pelvis and Ab- domen ...... Lymph Vessels of the Pelvic Viscera Lymph Glands of the Abdomen Development of the Blood-Vasculau System The Primitive Aortte and Primitive Heart The Primitive Veins Development of Heart, of first part of Aorta, and of Pulmonary Artery . Division of Heart into its different Chambers, and Division of Aortic Bulb The Aortic Arches — Formation of Chief Arteries . . • . Primitive Dorsal Aortte — Formation of Descending Aorta Branches of Primitive Dorsal Aorta; Arteries of Limbs .... Development of the Veins The Vitelline and Umbilical Veins . Formation of the Portal System The Anterior Cardinal Veins . The Post(;rior Cardinal Veins, tlie Subcardinal Veins, and the Inferior Vena Cava ..... Veins of Limbs 962 964 967 968 969 969 970 972 977 977 977 977 978 980 983 985 986 990 988 992 993 996 998 1000 1003 1006 1009 1010 1013 1013 1014 1015 1017 1019 1025 1025 1026 1031 1033 1027 1028 1029 1031 1035 1036 1036 1038 1040 1042 CONTENTS. XV MoUPHOLOQY OF THK VASCHIiAR SysTKM The Segmental Arteries and their Anastomoses ..... Aorta, Pulmonary Artery, and otlier Chief Stem Vessels The Liml) Arteries .... Morphology of tlie Veins . Abnoumamties and Variations of THK Vascular Systk.\i Abnormalities of tlie Heart .VKnormalities of Arteries THE RESPIRATORY SYSTEM. Tiie Organs of Respiration and Voice The Laiynx Cartilages of the Larynx Articuhitions, Ligaments, and Mem branes of the Larynx Cavity of tlie Larynx Muscles of the Larynx Trachea ...... THE DIGESTIVE SYSTEM. Digestive System, General Arrangement of Month Palate and Isthmus Faucium Teeth Permanent Teeth Deciduous Teeth Structure of the Teeth Tongue Glands Salivary Glands The Pharynx The Palatine Ton.sils The CEsophagus .... Structure of the CEsophagus The Abdominal Cavity . Subdivisions of the Abdominal Cavity The Peritoneum .... Stomach ...... Relations and Connexions of Stomach .... Position of Stomach . Structure of the Stomacli THE URINO-GENITAL SYSTEM. The Urinary Organs . The Kidneys ..... The Ureters The Urinary Bladder . The Urethra (Female) . The Male Reproductive Organs The Testis The Deferent Duct Descent of the Testis Spermatic Funiculus Scrotum ...... Penis ...... Prostate ...... Bulbo-urethral Glands . The Male Urethra The Female Reproductive Organs THE DUCTLESS GLANDS. The Chromapliil and Cortical Systems The Suprarenal Glands Ductless Glands of Entoderinal Origin The Thyreoid Gland The Para thyreoid Glands PAor. -1042 The Branches of the Aorta 10.50 The Arteries of the Head and Neck . 1053 1042 The Arteries of the Up )er Limb The Iliac Arteries and t leir Bi-anche.s 10.54 1055 1046 The Arteries of the J^jwi-r Limb 1056 1047 Al)normalities of Veins .... 1057 1047 The Superior Vena Cava . 1057 The Veins of the Uj)per Extremity . The Inferior Vena Cava . 1058 1049 10.58 lono The Veins of the Lower Extremity . 1059 10.^)0 Abnormalities of tlie Lymph Vessels 1059 Profe.s.sor RicHAHi) J. A. 1 iERRY. 1061 Bronchi ..... 1082 1061 Thoracic Cavity 1083 1062 Pleurae 1U84 Mediastina ...... 1089 1065 The Lungs 1091 1068 Root of th(' Lung .... 1096 1072 Structure of the Lungs 1098 1078 Developmentof the Respiratory Apparatus 1099 Professor David Waterston. 110.3 Intestines 1177 1106 Structure of Intestines 1178 1110 Duodenum 1182 1113 Liver ....... 1187 1115 Structure of Liver .... 1198 1121 Vessels of Liver .... 1199 1122 Gall-Bladder and Bile Pa.s.sages 1201 1124 Pancreas 1203 1131 Jejunum and Ileum .... 1208 1133 Large Intestine 1210 1140 Caecum and Vermiform Proces.s 1213 1145 Colon ....... 1219 1150 Rectum ....... 1224 1153 Anal Canal 1228 1155 Peritoneum 12.34 Development of Digestive System . 1244 1158 Development of the Teeth 1244 1160 Morphology of Teeth .... 1248 1163 Development of the Pharyn.x of the (Esophagus, Stomach, and 1248 1169 Intestines 1249 1172 of the Peritoneum .... 1252 1174 of the Liver and Pancreas 1254 Professor A. Francis Dixon. 1257 Ovary 1310 1257 Uterine Tubes ..... 1314 1265 Uterus ....... 1316 1271 Vagina 1321 1284 Female External Genital Organs . 1324 1286 Larger Vestibular Glands 1327 1286 Development of the Urino-genital 1289 Organs 1327 1295 The Wolffian Duct and Embryonic 1296 1 Secretory Organ .... The Ureter and Permanent Kidney 1329 1297 1331 1298 The Urethra 1332 1.301 Sexual Glands and Generative Ducts 1333 1.304 External Genital Organs . 1335 1.304 The Mammary Glands .... 1336 1310 Development of the Mammae 1339 Professor A. Campbell Geddes. 1341 The Thymus 1350 1343 Ductless Glands associated with tht- 1347 Vascular System .... 1352 1.347 Spleen ....... 1352 1348 Glomus Coccygeum .... 1.353 XVI CONTENTS. SURFACE AND SURGICAL ANATOMY. Harold J. Stiles, F.RC.S. Ed. Head and Neck .... PAGE 1357 PAGE The Upper Extremity .... 1444 Cranium ..... 1357 Shoulder .... 1444 Face 1374 Axilla 1446 Neck Thorax 1385 1395 Arm .... 1447 The Lungs and Pleurie . 1398 Elbow 1449 The Heart and Great Vessels . 1403 Forearm and Hand . 1450 Abdomen 1407 The Lower Extremity . 1455 The Anterior Abdominal Wall 1407 The Buttock . 1455 AMominal Cavity . 1411 The Back of the Thigh 1456 The Abdominal Viscera . 1415 The Popliteal Fossa . . 1457 Male Perineum .... 1427 The Front of the Thigh 1458 Prostate 1429 The Knee . 1460 Female Pelvis .... 1434 The Leg . . 1461 Back 1436 The Foot and Ankle 1463 INDEX '. . 1467 A GLOSSARY OF THK INTERNATIONAL (B.N.A.) ANATOMICAL TERMINOLOGY Longitudirralis Longitudinal Verticalis Vertical { Anterior Posterior Anterior ) Posterior j Ventral Ventran 1 Dorsal Dorsal J \ Cranial Cranial ] i Caudal Caudal j i Superior Inferior Superior) Inferior j r I Proxiinalis Distalis Proximal) Distal j Sagittalis Sagittal { Frontalis Frontal Horizontalis Horizontal Medianus Median { Medialis Lateralis Medial \ Lateral / { Intennedius Intermediate { Superficialis Profundus Superficial \ Deep ) f Externus External ] Internal J 1 Internus \ Uliraris Radialis Ulnar \ Radial/ I Tibial Fibular Tibial \ Fibular/ r GENEEAL TEEMS. Terms indicating Situation and Direction. Referring to the long axis of the body. /Referring to the position of the long axis of tire body in the erect posture. Referring to the front and back of tlie body or the limbs. Referring to the anterior and posterior aspects, respectively, of the body, and to the flexor and extensor aspects of the limbs, respectively. Referring to position rrearer the head or the tail end of the long axis. Used only in reference to parts of the head, neck, or trunk. Cephalic is sometimes used instead oi cranial. Used in reference to the head, neck, and trunk. Equivalent to cranial and caudal respectively. Used only in reference to the limbs. Proximal, nearer tlie attached end. Distal, nearer the free end. Used in reference to planes parallel witli the sagittal suture of the skull, i.e. vertical antero-posterior planes. Used in reference to planes parallel with the coronal suture of the skull, i.e. vertical transverse planes. Used in reference to planes at right angles to vertical planes. Referring to the median vertical antero-posterior plane of the body. Referring to structures relatively nearer to or further away from the median plane. Referring to structures situated between more medial and more lateral structures. Referring to structures nearer to and further away from the surface. Referring, with few exceptions, to tire walls of cavities .-md hollow organs. Not to be used as synonymous with medial and lateral. Used iir reference to tlic medial and lateral borders, respectively, of tire forearnr and hand. Used in reference to the medial and lateral borders, respectively, of the leg and foot, xvii XVlll GLOSSARY. THE BONES. B.N. A. Terminolouy. VertebrsB Fovea costalis superior Fovea costalis interior Fovea costalis trans- versalis Radix arcus vertebrre Atlas Fovea deutis Epistroplieus Dens Sternum Corpus steriii Processus xiphoideus Incisura jugularis Planum sternale Ossa Cranii. Os frontale Spina frontalis Processus zygomati- cus Facies cerebralis Facies frontalis Pars orbitalis Os parietale Linese temporales Sulcus transversus Sulcus saffittalis Os occipitale Canalis hypoglossi Foramen occipitale magnum Canalis condyloideus Sulcus transversus Sulcus sagittalis Clivus Linea nuchre suprema Linea nuclifc sujjerior Linea nuchce inferior Os sphenoidale Crista infratemporalis Sulcus chiasmatis Crista splienoidalis Spina angularis Lamina medialis jiro- cessus pterygoidei Lamina lateralis jiro- cessus pterygoidei Canalis pterygoideus [Vidii] Fossa hypophyseos Old Terminology. Vertebrae Incomplete facet for bead of rib, upper Incomplete facet for head of rib, lower Facet for tubercle of the rib Pedicle Atlas Facet for odontoid process Axis Odontoid process Sternum Gladiolus Eusiforni process Supra-sternal notch Anterior surface Bones of Skull. Frontal Nasal s^Jine External angular process Internal surface Frontal surface Orbital plate Parietal Temporal ridges Groove for lateral sinus Groove for sup. longi- tudinal sinus Occipital Anterior condyloid foramen Foramen magnum Posterior condyloid foramen Groove for lateral sinus Groove for sup. long. sinus Median part of upper surface of basi-occi- pital Higliest curved line Hujterior curved line Inferior curved line Sphenoid. Pterygoid ridge Optic gi'oove Ktbmoidal crest Spinous process Internal pterygoid plate External pterygoid plate Vidian canal Pituitary fossa B.N. A. Terminology. Sulcus caroticus Conchte spbenoidales Hamulus ptery- goideus Canalis pharyngeus Tuberculum selbii Fissura orbitalis superior Os temporale Canalis facialis [Fal- lopii] Hiatus canalis facialis Vagina processus sty- loidei Incisura mastoidea Impressio trigemini Eminentia arcuata Sulcus sigmoideus Fissura petrotym- panica Fossa mandibularis Semicanalis tubre auditivse Os ethmoidale Labyrinthus etli- moidalis Lamina papyracea Processus uncinatus Os lacrimale Hamulus laurimalis Crista lacrimalis pos- terior Os nasale Sulcus ethmoidalis Maxilla Facies anterior Facies infratempor- alis Sinus maxillaris Processus frontalis Processus zygomati- cus Canales alveolares Canalis naso-laeri- malis Os incisivum Foramen inci.sivum Os palatinum Pars jierjieiidiculaiis Crista conclialis Crista etbmoidalis Pars horizontalis Old Terminology. Cavernous gi'oove Sphenoidal turbinal bones Hamular process Pterygo - palatine canal Olivary eminence Sphenoidal fissure Temporal Bone Aqueduct of Fal- lopius Hiatus Fallopii Vaginal process of tympanic plate Digastric fossa Impression for Gas- serian ganglion Eminence for sup. semicircular canal Sigmoid fossa. Glaserian fissure Glenoid cavity Eustachian tube Ethmoid Lateral mass Os planum Unciform process Lachrymal Bone Hamular process Lachrymal crest fTasal Bone Groove for nasal nerve Superior Maxillary Bone Facial or external surface Zygomatic surface Antrum of Highmore Nasal process Malar process Posterior denial canals Lachrymal groove Premaxilla Anterior jjalatine foramen Palate Bone Vertical plate Inferior turbinate crest Superior turbinate crest Horizontal plate GLOSSARY. XIX B.N. A. TEKMI.NOI.OIiY. Os zygomaticam I'rocessus temporalis I'rocessiis tVoiito- splienoidulis Foramen zygoma- tico-orbitale Foramen zygomatico- faciale Mandibula Spina mentiilis Linea obliqua Linea mylohyoidea.. Incisura niandibulae Foramen mandibulare Canalis mandibuliE I'rotuberantia men- talis <)I,U TKK.MI.NUr.lMlY. Malar Bone Zygomatic process Frontal process Temporo-malar canal Millar foramen Inferior Maxillary Bone (ienial tnliercle or spine Kxternal oblique line Internal oblique line Sigmoid notch Inferior dental foia- men Inferior dental canal Mental process The Skull as a Whole. Ossa suturarum Foveolte granulares (Pacchioni) Fossa pterygo-pala- tina Canalis pterygo- palatinus Foramen laceruni Choanse Fissura orbitalis su- perior Fissura orbitalis in- ferior Wormian bones Pacchionian depres- sions Spheno-maxillary fossa Posterior palatine canal Foramen laceruni medium Posterior uares Sphenoidal fissure Spheno-ma.\illary fissure Clavicula Tuberositas coracoi- dea Tuberositas costalis Scapula Incisura scapularLs Angulus lateralis Angulus medialis Humerus Sulcus iutertubercu- laris Crista tuberculi majoris Crista tuberculi minoris Facies anterior medi- alis Facies anterior later- alis Margo medialis Margo lateralis Sulcus nervi radialis Capitulum Epicondylus medialis Epicondylus lateralis Ulna Incisura semilunaris Upper Extremity. Clavicle Impression for conoid ligament Impression for rhom- boid ligament Scapula Supra-scapular notch Anterior or lateral angle Superior angle Humerus Bicipital gi'oove External lip Internal lip Internal surface External surface Internal border External border Musculo-spiral groove Capitellum Internal condyle External condyle Ulna Greater sigmoid cavity IJ. N.A. TKUMi.\o(,erior lingualis Fascia diaphragmatis Deep layer of triangu- superior urogenitalis lar ligament Longitudinalis Inferior lingualis superior inferior Fascia diaphragmatis Superficial layer of Transversus linguie Transverse fibres urogenitalis in- the triangular liga- Verticalifl lingu* Vertical fibres ferior ment Arcus tendineus White line of pelvis fasciae pelvis Muscles of the Pharynx. Ligamenta pubo - Anterior and lateral prostatica true ligaments of Pharyngo-palatinus Palato-pharyngeus bladder M. uvula Azygos uvulae Fascia diaphragmatis Visceral layer of Levator veli palatini Levator palati pelvis superior pelvic fascia Tensor veli palatini Tensor palati Fa.scia diaphragmatis Anal fascia Glosso-palatinus Palato glossus pelvis inferior J 4 GLOSSARY. XX 11 1 THK ^NERVOUS SYSTEM. Spinal Medulla. B.N. A. Tkh,min()I.()(;v. Fasciculus anterior pro- prius (Flechsig) Fasciculus lateralis l)ro}>rius Nucleus dorsalis I'ars tlioracalis Old Tkuminoujuy. Auterior ground or basis bundle Lateral grovind bundle Clarke'.s coluuui Dorsal ]iart oi' sj)iiial medulla Paramedian furrow Sulcus intermedius ])osterior The Brain or Eucephalon is divided into [larts as follows B.N. A. Tkkminulogy. Column;uanteriores,etc. Fasciculus cerebro - spinalis anterior Fasciculus cerebro - spinalis lateralis (pyramidalis) Fa.sciculus cerebelio - si)inalis Fasciculus antero-later- alis superHcialis Oi.D Tkumi.volocv. Anterior grey horns, etc. Direct pyramidal tract Crossed tract pyramidal Direct cerebellar tract (•owers' tract RHOMBENCEPHALON = Myelencei)lialon (medulla oblongata) (after-brain) lo * • -i Meteucei.halon (pons and cerebelluu,) (hind-brain) /Posterior primary vesicle. Mesencephalon (mid-brain — peduncles, corpora quadrigemina, etc. — ) Middle primary vesicle CEREBRUMS 'Diencephalon = (inter-brain) Thalainencephalon , Thalamus (optic thalamus). -Metathalamus (geniculate bodies). Epithalamus (i)ineal body, etc.). PROSENCEPHALON j (fore-braiii) Telencephalon Mamillary portion of hyimthalamus. \_ Posterior part of 3rd veutricle. Optic portion of hypothalamus (hypophysis). x^ Optic nerves. Anterior part of 3rd ventricle. Pallium (cortex cerebri). Lateral ventricles. Brain. Rhombencephalon Eiainentia medialis Ala cinerea Area acustica Nucleus nervi ab- ducentis Nuclei n. acustici Fasciculus lougi- tudiualis medialis Corpus trapezoideum Incisura cerebelli anterior Incisura cerebelli posterior Sulcus horizontalis cerebelli Lobulus centralis Folium vermis Tuber vermis Lobulus quadrangu- laris Brachium conjuncti- vum cerebelli Brachium pontis Restiform body Lobulus semilunaris superior Lobulus semilunaris inferior Eniinentia teres Trigonum vagi Trigonum acus- ticum Nucleus of 6th nerve Auditory nucleus Posterior longitudinal bundle Corpus trapezoides Semilunar notch (of cerebellum) Marsupial notch Great horizontal tis- sure Jjobus centralis Folium cacuminis Tuber valvule Quadrate lobule Superior cerebellar peduncle Middle cerebellar peduncle Inferior cerebellar peduncle Postero - superior lobule Postero - inferior lobule Cerebrum Pedunculus cerebri CoUiculus superior CoUiculus inferior Aquseductus cerebri Foramen interven - triculare Hypothalamus Sulcus hypothalami- cus Massa intermedia Fasciculus thalamo- maiuillaris Pars opercularis Thalamus Pallium Gyri transitivi Fissura cerebri later- alis Gyrus temporalis su- perior Gyrus temporalis medius Gyrus temporalis in- ferior Sulcus centralis (Ro- landi) Sulcus temporalis su- perior Crus cerebri Anterior corpus quadrigeminum Posterior corpus quadrigeminum Iter e tertio ad quar- tum ventriculum, oraqued. of Sylvius Foramen of Monro Subthalamic region Sulcus of Monro Middle commissure Bundle of Vicqd'Azyr Pars basilaris Optic thalamus Cortex cerebri Annectant gyri Fissure of Sylvius First temporal gyrus Second temporal gyi-us Third temporal gyrus Fissure of Rolando Parallel sulcus XXIV GLOSSAKY B.N. A. Terminology. Sulcus temporalis me- dius Sulcus circularis Sulcus temporalis in- ferior Gyrus fusiformis Sulcus interparietalis Sulcus corj)oiis callosi Sulcus cinguli Fissura hippocampi Gyrus cinguli Stria terminalis Trigonum coUaterale Hippocampus Digitationes liippo - campi Fascia dentata liij^po- campi Columna fornicis Septum pellucidum Cornu inferius Commissura hippo- campi Nucleus lentiformis Pars frontalis capsulcC internse Pars occipitalis cap- sulse internae Kadiatio occipito - thalamica Radiatio corporis callosi ' Pars frontalis Pars occipitalis Old Tekminologt. Second temporal sul- cus Limiting sulcus of Reil Occipito -tempo r a 1 sulcus Occipito -temporal convolution Intraparietal sulcus Callosal sulcus Galloso-marginal fis- sure Dentate fissure Callosal convolution Taenia semicircularis Trigonum veutriculi Hippocampus major Pes hippocampi Gyrus dentatus Anterior pillar of fornix Septum lucidum Descending horn of lateral ventricle Lyi'a Lenticular nucleus Anterior limb (of internal capsule) Posterior limb (of internal capsule) Optic radiation Radiation of corpus callosum Forceps minor Forceps major Membranes of Brain. Cisterna cerebello-me- dullaris Cisterna interpeduncu- laris Granulationes arachnoi- deales Tela chorioidea veu- triculi tertii Tela chorioidea vcn- triculi quarti Cerebral N. oculomotorius N. trochlearis N. trigeminus Ganglion semi- lunare (Oasseri) N. naso-ciliaris N. maxillaris N. meningeus (me- dius) N. zygomaticus Rami alveolares superiores i)OS - teriores Rami alveolares su- periores medii Cisterna magna Cisterna basalis Pacchionian bodies Velum interpositum Tela choroidea inferior Nerves. Third nerve Fourth nerve Fifth nerve Gasserian ganglion Nasal nerve Superior ma.xillary nerve Recurrent menin- geal nerve Temporo - malar nerve Posterior superior dental Middle superior dental B.N. A. Terminology. Rami alveolares superiores an- teriores Ganglion spheno- palatinum N. palatinus me- dius N. mandibularis Nervus spinosus N. alveolaris in- ferior N. abducens N. facialis N. intermedius N. acusticus Ganglion superius N. recurrens Ganglion jugulare Ganglion nodosum Plexus cesophageus^ anterior [ Plexus oesophageus j posterior J Nervus accessorius Ramus internus Ramus externus Old Terminology. Anterior superior dental Meckel's ganglion External palatine nerve Inferior maxillary nerve Recurrent nerve Inferior dental Sixth nerve Seventh nerve Pars intermedia of Wrisberg Eighth or auditory nerve Jugular ganglion of 9th nerve Recurrent laryngeal nerve Ganglion of "j root I of Ganglion of j vagus trunk J Plexus gulae Spinal accessory Accessory portion of spinal accessory nerve Spinal portion Spinal Nerves. Rami posteriores Rami anteriores N. cutaneus colli Nn. supraclavicular es anteriores Nn. supraclaviculares medii Nn. supraclaviculares posteriores N. dorsalis scapula Nn. intercosto - brachiales N. thoracalis longus N. thoraco-dorsalis N. cutaneus brachii medialis N. cutaneus brachii lateralis Fasciculus lateralis Fasciculus medialis N. cutaneus anti- brachii lateralis N. cutaneus anti- brachii medialis Ranms volaris Ramus ulnaris N, axillaris Posterior primary divisions Anterior primary di^asions Transverse superficial cervical nerve Suprasternal nerves Supraclavicular nerves Supra - acromial nerves Nerve to the rhom- boids Intercosto - humeral nerve Nerve of Bell Long subscapular nerve Lesser internal cu- taneous nerve Cutaneous branch of circumflex nerve Outer cord (of plexus) Inner cord Cutaneous branch of musculo- cutaneous nerve Internal cutaneous nerve Anterior branch Posterior branch Circumflex nerve GLOSSARY. XXV B.N. A. Terminology. N. interosseus volaris Kaimis j)aliiiaris N. mediani Nil. digi tales volares proprii K a III u s (I o r 8 a 1 i s mail us Ramus cutaneus pal maris N. radialis N. cutaneus luachii posterior N. cutaneus anti- brachii dorsalis Ramus superficialis N. interosseus dor- salis Nil. digitales dorsales N. ilio-hypogastricus Ramus cutaneus lateralis Ramus cutaneus anterior cutaneous of ulnar Old Tkrminoi.ooy. Anterior interosseous I'almar cutaneous branch of the me- dian nerve ('ollateral palmar digital branches of median nerve Dorsal cutaneous branch of ulnar nerve Palmar branch nerve Musculo-spiral nerve Internal cutaneous branch of mus- culo-spiral nerve External cutane- ous branches of musculo- sjtiral nerve Radial nerve Posterior interos- seous nerve Dorsal digital nerves Ilio - hypogastric nerve Iliac branch of ilio - hypogastric nerve Hypogastric branch of ilio - hypo- gastric nerve B.N. A. Tehminoi.ogy. N. genito-femoralis N. lumbo - in - guinalis N. spermaticus ex- ternus N. cutaneus femoris lateralis N. femoralis N. saphenus Ramus infrajiatel- laiis N. ischiadicus N. peronffius com - munis Ramus anasto - moticus pero- najus N. peronteus super- ficialis N. peroniEus pro- fundus N. tibialis N. cutaneus sura? medialis N. sural is N. plantaris medialis N. plantaris lateralis N. pudendus Oi.u Tehmin()I.(m;v. Genito-crural nerve Crural branch of genito - cniral nerve Genital branch of genito - crural nerve External cutane- ous nerve Anterior crural nerve Long saphenous nerve Patellar branch of long saphenous nerve Great sciatic nerve External popliteal nerve Nervus communi- cans fibularis Musculo-cutaneous nerve Anterior tibial nerve Internal popliteal and posterior tibial nerves Nervus communi- cans tibialis Short saphenous nerve Internal plantar External jilantar Pudic nerve THE HEART AND BLOOD-VESSELS. Heart. Atrium Auricula cordis Incisura cordis Trabeculae carneje Tuberculum inter- venosum Sulcus longitudinalis anterior Sulcus coronarius Limbus fossaj ovalis Valvula veniv cava' Valvula sinus coio- narii Auricle Auricular appendix Notch at apex of heart Columnfe carneae lutervenous tubercle of Lower Anterior interven- tricular groove Auriculo - ventricular groove Annulus ovalis Eustachian valve Valve of Thebesius Arteries. Sinus aortfe A. profunda liugu.'e A. maxillaris externa A. alveolaris inferior Ramus meningeus ac- cessorius A. buccinatoria A. alveolaris superior posterior Aa. alveolares su - periores anteriores Ramus carotico-tym- panicus Sinuses of Valsalva Rauine artery Facial artery Inferior dental artery Small meningeal artery Buccal artery Posterior superior den- tal artery Anterior superior den- tal arteries Tympanic branch of int. carotid A. chorioidea A. auditiva interna Rami ad pontem A. pericardiac o- phrenica Rami intercostales Truncus thyreo-cervi- calis A. transversa scapula; A. intercostalis sii- prema A. transversa colli A. thoracalis suprenia A. thoraco-acromialis A. thoracalis lateralis A. c i r c u m H e x a sea pu lie A. profunda brachii A. coUateralis radi- alis A. coUateralis ulnaris superior A. collaterals ulnaris inferior Ramus carpeus vol- aris Anterior choroidal artery Auditory artery Transverse arteries (branches of basilar artery) Arteria comes nervi phrenici Anterior intercostal arteries Thyroid axis Suprascapular artery Superior intercostal Transversalis colli Superior thoracic artery Acromio - thoracic artery Long thoracic artery Dorsalis scapulie Superior profunda Anterior branch of superior jirofunda Inferior profunda Anastomotica magna Anterior radial carpal XXVI GLOSSAKY. B.N. A. Terminology. Ramus carjieus dorsalis Aa. metacarpefe dor- sales A. volaris indicis radialis Arcus volaris supcr- ficialis Arcus volaris pro- fundus A. interossea dorsalis A. interossea recurrens A. interossea volaris Ramus carpeus dorsalis Ramus carpeus volaris Aa. digitales volares communes Aa. digitales volares propriae ArteriiB intestinales A. suprarenalis media A. hypogastrica A. umbilicalis A. pudenda interna A. e{)igastrica inferior A. sj>ermatica externa Aa. pudendffi externha»ricus Recessus ellipticus Paries jugiilaris Paries labyrinthica Fenestra vestibuli Fenestra cochlea' Paries mastoidea Antrum tympani- cum Paries carotica Processus lateralis Processus anterior External semicircular canal Canalis reuniens Membranous cochlea Fovea hemispherica Fovea hcmi-elliptic^ Floor of tympanum Inner wall Fenestra oval is Fenestra rotunda Posterior wall Mastoid antrum Anterior wall Processus brevis malleus) Processus gracilis (of TEXT-BOOK OF ANATOMY. INTRODUCTION. Anatomy is a comprehensive term, which inckides several closely related branches of study. Primarily it is employed to indicate the study of the parts which build up the body, and the relationship which these present to each other. But tlie structure of an individual is not the same at all stages of its life, for many changes occur during the period of its existence. The ovum and the spenuatozoon, which are the starting-points of every individual, are very different from the finished organism as represented by the adult, and the series of changes through which the organism passes until its structure is perfected and full growth is attained constitute the phenomena of development. The general term "development" includes not only the various and striking structural changes which occur during the intra-uterine life of the individual, to the study of which the term embryology is more specially applied, but also many growth processes which occur after birth, such as the later stages in the ossification and growth of the bones, the eruption of the two series of teeth, the adjustment of the vascular system to its new require- ments, etc. The actual observation of the processes by which the parts of the body are gradually formed, and of the structural arrangements by means of which a ten;porary connexion is established between the ovum and the mother, through which an interchange of nutritive and other matters between the two takes place, renders embryology one of the most interesting of all the departments of anatomy. The term ontogeny also is used to denote the development of the individual. There is, however, another form of development, slower, but just as certain in its pro- cesses, which affects not only the individual, but all the members of the animal group to which it belongs. The theory of descent or evolution leads us to believe that between man of the present day and his remote ancestors there is a wide structural gap, which, if the geological record were perfect, would be seen to be completely occupied by long-lost intermediate forms. In the process of evolution, therefore, structural changes have gradually taken place which have modified ;he entire race. These evolutionary phases constitute the ancestral history or phylogeny of the race. Ontogeny and phylogeny are intertwined in a re- marka)>le manner, and present certain extraordinary relationships. In other words, the ancestral evolutionary development appears to be so stamped upon an individual that it repeats certain of the phylogenetic stages with more or less clear- ueaa during the process of its own individual development. Thus, at an early period in the embryology of man evanescent gill-pouches appear which are comparable with those of a fish, whilst a study of the development of his heart shows that it passes through transitory structural conditions similar, in many respects, to the permanent 1 1 2 TEXT-BOOK OF ANATOMY. conditions of the heart in certain of the lower animals. It is in connexion with this that the phrase has arisen that every animal in its individual development or ontogenv climbs up its own genealogical tree — a saying which, taking it even in the broadest sense, is only partially true. The broader conceptions of anatomy, which are obtained by taking a general Bur^'ey of the structural aspects of the entire animal kingdom, constitute morphology. The morphologist investigates the laws of form and structure, and in his generalisa- tions he gives attention to detail only in so far as this is necessary for the proper establishment of his views. The knowledge of anatomy which is required by the student of medicine is different. It is essentially one of detail, and often details important from the practical and utilitarian points of view have little or no morphological value. This want of balance in the interest attached to anatomical facts, according to the aspect from which they are examined, so far from being unfortunate, affords the teacher the means of making the study of anatomy at once fascinating and instructive. Almost every fact which is brought under tht notice of the student can be accompanied by a morphological or a practical application. These possibilities of application lighten a study which, presented to the student of medicine in any other way, would be at once dry and tedious. Certain terms employed in morphology require early and definite explanation. These are homology, serial homology, and homoplasy. The same organ repeated in two different animals is said to present a case of homology. But Jhe morphological identity between the two organs must be proved beyond dispute before the homology between them can be allowed. In deciding the identity the great and essential test is that the two organs in question should have a similar develop- mental origin. Thus, the fore-limb of a quadruped is homologous with the upper limb of man ; the puny collar-bone of a tiger, the fibrous thread which is the only representative of this bone in the horse, and the strongly marked clavicle of the ape or man, are all, strictly speaking, homologous with one another. Homologous orcrans in different animals usually occupy a similar position and possess a similar structure, but not invariably so. It is not uncommon for a muscle to wander somewhat from its original position, and many cases could be quoted in which parts have become completely transformed in structure, either from disuse or for the purpose of meeting some special demand in the animal economy. In the study of the muscles and ligaments instances of this will be brought under the notice of the reader. Often organs which perform totally different functions are yet perfectly homologous. Thus the wing of a bat or the wing of a bird, both of which are subservient to flight, are homologous with the upper limb of man, the Office of which is the different one of prehension. Identity or correspondence in the function performed by two organs in two different animals is not taken into consideration in deciding questions of homology. The gills of a fish and the lungs of a higher vertebrate perform very much the same physiological office, and yet they are not homologous. The term analogy is often used to express functional correspondence of this kind. In the construction of vertebrates and certain other animal groups a series »>f similar parts are repeated along a longitudinal axis, one after the other. Thus the series of vertebrae which build up the backbone, the series of ribs which gird round each side of the chest, the series of intercostal muscles which fill up the intervals between the ribs, the series of nerves which arise from the brain and spinal medulla, are all examples of this. An animal exhibiting such a condition of parts is said to present the segmental type of organisation. In the early stages of development this segmentation is much more strongly marked, and is to be seen in parts which INTKODUCTION. 3 subsequently lose all trace of such a subdivision. The parts thus repeated are said to be serially homologous. But there are other instances of serial homology besides those which are manifestly produced by segmentation. The upper limb is serially homologous with the lower limb : each is composed of parts which, to a large extent, are repeated in the other, and the correct adjustment of this comparison between the several parts of the upper and lower limbs constitutes one of the most difficult and yet interesting problems of morphology. Homoplasy is a term which has been introduced to express a form of corre- spondence between organs in different animals which cannot be included under the term homology. Two animal groups, which originally have sprung from the same stem-form, may independently develop a similar structural character which is altogether absent in the ancestor common to both. Thus the common ancestor of man and the carnivora in all probability possessed a smooth brain, and yet the human brain and the carnivore brain are both richly convoluted. Not only this, but certain anatomists seek to reconcile the convolutionary pattern of the one with the convolutionary pattern of the other. What correspondence there is does not, in every instance, constitute a case of homology, because there is not in every case a community of origin. Correspondence of this kind is included under the term " homoplasy." Another example is afforded by the heart of the mammal and that of the bird. In both of these groups the ventricular portion of the heart consists of a right and a left chamber, and yet the ventricular septum in the one is not homologous with the corresponding septum in the other, because the common ancestor from which both have sprung possessed a heart with a single ventricular cavity, and the double-chambered condition has been a subsequent and independent development in the two groups. Systematic Anatomy. — The human body is composed of a combination of several systems of organs, and the several parts of each system not only present a certain similarity in structure, but also fulfil special functions. Thus there are — 1. The skeletal system, composed of the bones and certain cartilaginous and mem- branous parts associated with them, the knowledge of which is known as osteology. 2. The articulator!/ system, which includes the joints or articulations, the knowledge of which is termed arthrology. 3. The muscular system, comprising the muscles, the knowledge of which con- stitutes myology. 4. The nervous system, in which are included the brain, the spinal medulla, the ganglia of the spinal and cerebral nerves, the sympathetic ganglia, and the various nerves proceeding from and entering these. The knowledge of these parts is ex- pressed by the term neurology. In this system the organs of sense may also be included. 5. The hlood vascular and lymphatic system, including the heart, blood-vessels, the lymph vessels, and the lymph glands. Angeiology is the term applied to the knowledge of this system. 6. The respiratory system, in which we place the lungs, windpipe, and larynx. 7. The digestive system, which consists of the alimentary canal and its associated glands, and parts such as the tongue, teeth, Hver, pancreas, etc. ' 8. The urogenital system, composed of the urinary organs and the reproductive organs — the latter differing in the two sexes. The term splanchnology denotes the knowledge of the organs included in the respiratory, digestive, and urogenital systems. 9. The integumentary system consists of the skin, nails, hair, etc. The know- ledge of this system is termed dermatology. 4 TEXT-BOOK OF ANATOMY. The numerous organs which form the various systems are themselves built up of tissues, the ultimate elements of which can be studied only by the aid of the microscope. The knowledge of these elements and of the manner in which they are grouped together to form the various tissues of the body forms an important branch of anatomy, which is termed histology. The structure of the human body may be studied in two different ways. The several parts may be considered with reference to their relative positions, either as they are met with in the course of an ordinary dissection, or as they are seen on the surface of a section through the body. This is the topogfaphical method. On the other hand, the several systems of organs may be treated separately and in sequence. This constitutes the systematic method, and it is the plan which is adhered to in this treatise. Descriptive Terms.— Anatomy is a descriptive science founded on observa- tion, and in order that precision and accuracy may be attained it is necessary that we should be provided with a series of well-defined descriptive terms. It must Fig. 1. — Horizontal Section through the Trunk at the Level of the First Lumbar Vertebra. be clearly understood that all descriptions are framed on the supposition that the body is in the erect position, with the arms by the side, and the hands held so that the palms look forwards and the thumbs laterally. An imaginary plane of section, passing longitudinally through the body so as to divide it accurately into a right and a left half, is called the median plane. Fig. 1 (M.P.). When the right and left halves of the body are studied it will be found that both are to a large extent formed of similar parts. The right and left limbs are alike ; the right and left halves of the brain are the same ; there are a right and a left kidney and a right and a left lung, and so on. So far the organs are said to be symmetrically arranged. But still a large amount of asjrmmetry may be observed. Thus, the chief bulk of the liver lies to the right side of the median plane, and the spleen is an organ which belongs wholly to the left half of the body. Indeed, it is well to state that perfect symmetry never does exist. There always will be, and always must be, a certain want of balance between symmetrically placed parts of the body. Thus the right upper limb is, as a rule, constructed upon a heavier and more massive plan than the left, and even in those organs where the symmetry appears most INTRODUCTION. 5 perfect, as for instance the brain and spinal medulla, it requires only a closer study to reveal many points of difference between the right and left halves. The line on the front of the body along which the median plane reaches the surface is termed the anterior median line ; whilst the corresponding line behind is called the posterior median line. It is convenient to employ other terms to indicate other imaginary planes of section through the body. The term. sagittal, therefore, is used to denote any plane which cuts through the body along a path which is parallel to the median plane (S S') ; and the term coronal or frontal is given to any vertical plane which passes through the body in a path which cuts the median plane at right angles (C C). The term horizontal, as applied to a plane of section, requires no explanation. Any structure which lies nearer to the median plane than another is said to be medial to it ; and any structure placed further from the median plane than another is said to lie lateral to it. Thus in Fig. 1, A is lateral to B ; whilst B is medial to A. The terms internal and external are applied to the walls of hollow cavities or organs ; thus, the ribs possess external surfaces, that is, surfaces away from the cavity of the thorax, and internal surfaces adjacent to the cavity. The terms anterior and ventral are synonymous, and are used to indicate a structure (D) which lies nearer to the front or ventral surface of the body than another structure (E) which is placed nearer to the back or dorsal surface of the body, and which is thus said to be posterior or dorsal. In some respects it would be well to discard the terms " anterior " and " posterior " in favour of " ventral " and " dorsal," seeing that the former are only applicable to man in the erect attitude, and cannot be applied to an animal in the prone or quadrupedal position. They are, however, so deeply ingrained into the descriptive language of the human anatomist that they cannot be entirely discarded. A similar objection may be raised to the terms superior and inferior, which are employed to indicate the relative levels at which two structures lie with reference to the upper and lower ends of the body. The equivalent terms of cephalic or cranial and preaxial are, therefore, some- times used in place of "superior," and caudal and postaxial in place of " inferior." The terms proximal and distal should be applied only in the description of the limbs. They denote relative nearness to or distance from the root of the limb. Thus, the hand is distal to the forearm, whilst the arm or brachium is proximal to the forearm. HUMAN EMBRYOLOGY. By A. H. Young and Arthur Kobinson. Eewritten by Arthur Kobinson. The ontogenetic or developmental history of every human individual is separable into two main periods, pre-natal and post-natal. It is to the knowledge of the phenomena of the earlier or pre-natal period that the term human embryology is applied, and as pre-natal development takes place in an organ called the uterus, it is frequently spoken of as intra-uterine development. The period of pre-natal development extends through nine lunar months, and may be divided into three sub-periods : (1) the pre-embryonic period, during wliich the zygote, from which the embryo is formed, shows no definite separation into embryonic and non-embryonic portions. This period lasts about fourteen days ; (2) the period of the embryo, in which the zygote is definitely separated into embryonic and non-embryonic portions, but the embryonic part has not yet assumed a clearly human form. This period terminates at the end of the second month ; (3) the foetal period, which commences at the end of the second month, when the embryo assumes a definitely human form and is called, thenceforth, a foetus. The fcetal period ends at birth, when the fwtus becomes a child and post- natal development commences. Only the general phenomena of the pre-natal period of development are considered in this section ; the details of the pre- and post-natal development of the various organs and systems will be dealt with in the sections devoted to the descriptions of their adult conditions. THE STEUCTURE OF ANIMAL CELLS. The human body is formed by the multiplication and differentiation of animal cells, therefore it is essential that the student should possess a knowledge of the main features and capabilities of such cells before he commences the study of the details of human embryology. Animal cells differ from each other in minor points of structure, in association with the positions they occupy and the functions they perform ; nevertheless, they all possess some common and essential structural features, and, in the younger stages of their history, some common capabilities. The following are the constituent parts of a typical animal cell : — The cell body : — containing (a) The nucleus with its nucleolus ; (&) The centrosome with the centrioles ; (c) The mitochondria. All the essential parts of the cell consist of a substance caUed protoplasm. In its simplest form protoplasm is the semifluid, viscous, irritable, and con- 7 Nucleolus Nucleus Spongioplasin (cyto-reticulum) Hyaloplasm Attraction sphere Centrosome Fig. 2. — Diagram of an Animal Cell. 8 HUMAN EMBEYOLOGY. tractile substance which forms the "physical basis of life." It consists of C, H., N., 0., and S., combined together in different ways and in differing proportions to form various modifications of protoplasm which possess definite physical and chemical characteristics, and which receive, therefore, different names. The cell body consists of a kind of protoplasm called cytoplasm, separable into two parts ; the spongioplasm or cyto-reticulum, which forms a network or spougework ; and a more fiuid part, the hyaloplasm or cytolymph, which occupies the interstices of the reticulum. The nucleus hes in the cytoplasm. It consists of a form of protoplasm, called karyoplasm, which is separable into a more fibrillar part, the karyo-reticulum, and a more fiuid part, the karyo-lymph or nuclear juice. The reticulum also consists of two parts, the achromatic or non-stainable part formed of a substance called linin, and a part called chromatin, which is readily stainable. Chromatin varies in appearance at various stages of the cell life. During the resting periods, which intervene between the periods of cell division, it is broken up into small particles which either are embedded in or are in close association with the linin network. When cell division commences the chromatin particles are, in many cases, aggregated to form a thread-like strand, which ultimately breaks up into a number of segments called chromosomes. The chromosomes are probably of definite number in the body cells of any given species of animal. In the human subject the typical number is probably 24. According to Winiwarter's recent observations tlie number of cliromosomes in eacli oocyte I (see p. 12) is 48, and in each spermatocj^te I (see -p. 12) it is 47. Eacla mature ovum (see p. 13), therefore, has 24 chromosomes, but some spermatids (see -p. 17) have 24 and others 23. If a spermatozoon (see p. 17) with 24 chromosomes unites with a mature ovum a female results, but if a sj^ermatozooii with 23 chromosomes unites with a mature ovum a male results. During the resting period the nucleus is bounded by a distinct nuclear mem- brane, wiiich is continuous on the one hand with the karyo-reticulum, and on the other wdth the cyto-reticulum. The nucleolus is a spherical vesicle which lies in the karyo-lymph during the resting periods of the ceU. It disappears entirely during the periods of division. The protoplasm of which it is formed is called pyrenin. In some cases several nucleoli are present. The nodes of the karyo-reticulum are sometimes called false nucleoli. The cen,trosome is a clear spherical area of the cytoplasm which lies usually in the neighbourhood of the nucleus. Around it the granules of the cytoplasm are arranged in radial lines, and in its interior he one or two minute, deeply staining bodies, the centrioles. The centrosome appears to play a very important part in cell multiplication ; and, in the more ordinary form of cell division, it divides before the division of the cell takes place, but in certain cases it disappears before the cell divides. The mitochondria are minute particles. They are demonstrable in the majority of cells during life ; or by means of certain stains, after special methods of fixation and preservation have Ijeen used. They are believed to play an important part in the economy and life-history of the cells, and they form a very definite part of the structure of the spermatozoon or male gamete. THE LIFE-HISTOKY AND CAPABILITIES OF ANIMAL CELLS. Every animal cell is formed by the division of a pre-existing cell called the mother cell. The mother cell divides into two equal parts — the dmighter cells, each of which, under ordinary conditions, possesses all the capaljilities of its mother. Reproduction of Cells. — Ordinary tissue cells increase in number by the division ot the pre-existing cells into equal parts, and each part possesses similar capa))ilities. Every new cell has a definite life- history ; it grows, performs its proper function, and ceases to exist, either by dividing into two daughter cells, or by dying and Itreaking up into fragments whicli disappear. Wliilst the multiplication rate exceeds the death-rate in any given tissue or organ, that tissue or organ grows. When tlie multiplication rate and the death- MITOTIC DIVISION OF CELLS. / >< CentrosomH witli contriolcs Xucleus Flu, 3. — Schema of Animal Cell in Resting Stage. Nucleus with chromatic[- substance in skein form 7 rate are equal, the tissue or organ is in a state of equilibrium. As soon as the death-rate exceeds the multiplication rate, decay and atrophy set in ; and when the decay and atrophy have proceeded to such an extent that an important tissue or organ can no longer i)ertbrm its proper functions, general death ensues. General decay and death are, therefore, the natural results of the loss ot multi}»lication power o( the cells of the body, but life may jjersist after multiplica- tion power is lost, so long as the cells last ])roduced retain their capaliilities, and death may result whilst multiplication power of the cells is retained, if the newly produced cells are incapable of performing their proper functions. Nevertheless, speaking generally, it may be said that cell niultii)lication is a vital necessity, and it takes ])lace in two ways — (1) by amitotic and (2) by mitotic division of pre-existing colls. Amitotic Division. — The phenomena of amitotic division, so far as they are known, are much simpler than those of mitotic division. First the nucleus is constricted and divided ; then the cell body is constricted and divided, and two similar daughter cells, each half the size of the mother cell, are produced. The part played by the centrosome during the process is not definitely known, but each daughter cell eventually possesses a centrosome. The appar- ently simple process of amitotic division occurs at some periods of growth, and the more com- plicated process of mitotic division at other periods, but the laws which govern the alterna- tions are unknown. Mitotic Division ; Mitosis, or Karyokin- esis. — Mitotic or karyokiuetic division is not only the more complicated, but it appears also to be the more imytortant form of cell division. It takes place in all rapidly growing tissues, especially in the embryonic and foetal stages of life, and it is the main form of cell division which occurs in the earliest embryonic periods. There are, however, two forms of mitosis, the homotype and the heterotype. Of the two, homotype is so much the more common that it may be looked upon as the ordinary form, for heterotype mitosis appears to be limited to one of the two cell divisions which occur during the maturation of the germ cells, and to some of the cell divisions which are associated with the production of malignant tumours. Homotype Mitosis. — The phenomena of homotype mitosis occur in four phases, (1) the prophase, (2) the metaphase, (3) the anaphase, and (4) the telophase. The Prophase. — During the prophase both the centrosome and the nucleus undergo very obvious transformations. The centrosome and its contained centriole divide into two parts, of which one passes to one pole and the other to the opposite pole of the nucleus. The nuclear transformations concern the nucleolus, the chromatic substance, and the nuclear membrane. Tlie nucleolus disappears. In some cases it passes from the nucleus into the cytoplasm, where it breaks up ; in other cases the details of its disappearance are entirely unknown. Fig. 4. — Schema of Animal Cell in Eakly Part ok Pkophase ok Homotype Mitosis. Daughter centrosome Achromatic spindlr Chromosomes I- at equator 1 of siiiudlP . ■h^ I Fig, 5. — Schema of Animal Cell at Com- pletion OK Prophase of Homotype Mitosis. 10 HUMAN EMBKYOLOGY. Daughter centrosoiiie Cliromosomes dividing into equal parts Fig, 6. — Schema of Animal Cell in Meta- phase of homotype mitosis. Daughter centrosonie Chromosomes at ^^■ pole of spindle yf^ Achromatic / . ':" spindle/^:;. ' .. :/■.•,. A The chromatic substance is aggregated to form first a fine and afterwards a thicker thread or spirem. At the same time, a spindle of achromatic fibrils appears between the two daughter centrosomes, and the nuclear membrane disappears. As soon as the achromatic spindle is definitely established the chromatic thread breaks up into a number of segments, the chromosomes, which arrange themselves around the equator of the achromatic spindle. The chromosomes may be V-shaped, rod-like, cuboidal or spheroidal, and each may be a single structure, or it may consist of two or four parts which are closely bound to- gether. There is evidence which tends to sup- port the belief that, whether the chromosome appears to consist of one, two, or more seg- ments, its constituent particles are derived partly from the maternal and partly from the paternal ancestor of the cell ; and it is believed that the maternal and paternal portions undergo similar division during the last three phases of mitosis. In any case, whether the chromosomes are single or compound structures, each becomes attached to, or very closely associated with, one of the fibrils of the achromatic spindle. At the end of the prophase the nucleus as such, and the nucleolus, have entirely dis- appeared, and the cell body contains, in their place, two centrosomes, an achromatic spindle, and the chromosomes. The centrosomes lie at the opposite poles of the achromatic spindle with the granules of the protoplasm grouped radially around them, and the chromosomes are grouped round the equator of the achromatic spindle. The Metajphase. — During the metaphase each chromosome divides into two equal parts, the rods or loops dividing longitudinally ; and the division, in all cases, commences at the point where the chromosome is in relation with the fibrils of the achromatic spindle. The Anaphase. — In the anaphase the halves of the chromosomes, i.e. daughter chromosomes, move towards the opposite poles of the achro- matic spindle, and when they reach the vicinity of the daughter centrosomes the anaphase ends and the telophase begins. The Telophase. — At the end of the anaphase, or the commencement of the telophase, a con- striction appears around the periphery of the cell, at the level of the equator of the achro- matic spindle. After its appearance the con- striction gradually deepens until the cell is completely divided into two halves, the daughter cells, each of which contains the typical number of chromosomes, and a portion of the achromatic spindle. The Resting Stage.— During the resting stage, which lasts for a variable period, a nucleus is formed in each daughter cell by the appearance of a nuclear membrane around the chromosomes, as they repass first to the thread-like and then to the granular form of chromatic substance, and by the reappearance of a nucleolus. The cell increases in size also. The Period of Cell Life. — The period of cell life varies, but in all cases it ultimately ends in death ; for a time comes when cells no longer transmit to their Vllf^ Fig. 7. — Schema of Animal Cell at End OK Anaphase of Homotype Mitosis. Centrosome Nucleus Fig. 8. — Sche.ma ok Animal Cell at End ok Telophase ok Homotype Mitosis. The cell has divided into two daughter cells. Red and blue indicate the original paternal and maternal derivatives. HETEKOTYPE MITOSIS OF CELLS. 11 descendants the power of division, or the capability of growth and function. If it were not so, growth and function, or at least inaLiitenance and function, would continue uninterruptedly, and in the absence of accident or disease individual life would continue for ever, and " old age" would be unknown. It appears, therefore, that the ancestors of certain tissue cells are capable of producing only a certain number of descendants, which grow to the normal size and perform their pro})er functions for a more or less fixed period, whilst in other cases the power of division appears to bo transmitted continuously, but the more remote descendants become less and less capalde of performing their proper functions. The result in both cases is the same; gradual decay, terminating in death. Heterotype Mitosis. — In ordinary or homotyi)e mitosis the chromosomes are divided into (upial parts, and, when the process of cell division is completed, each daughter cell possesses the same number and same kind of chromosomes as the mother cell from wliich it was derived (Figs. 3-8). In heterotype mitosis, the number of chromosomes is reduced during the cell division, and each daughter cell possesses only half the number of chromosomes that was present in the mother cell. The details of the division of the chromosomes during heterotype mitosis differ in different groups of animals, but the end is the same in all cells in which the process occurs, and is the reduction of the number of the chromosomes in the daughter cells to half tlie number typical for the ordinary cells of the animal. The most typical form of heterotype mitosis is seen during the first maturation division of many germ cells, in which, during the spirem or thread-like stage of the chromatic substance, careful examination of the thread shows that it consists of a number of alternate segments attached end to end, the number of segments corresponding with the number of the chromosomes typical for the ordinary cells of the animal. Towards the end of the prophase, the segments of the thread become attached together in pairs which form a number of twin chromosomes. These arrange themselves around the equator of the achromatic spindle, and it is obvious that the number of twin chromosomes is only half the number of the chromosomes originally present in the cell (Figs. 12 and 13). (See note 1, p. 79.) The total number of chromatic segments is still the same, for each twin chromosome consists of two ordinary chromosomes attached side to side. The process of reduction takes place during the metaphase, when the two segments of each twin chromosome become separated from one another. During the anaphase the separated segments pass to the opposite poles of the achromatic spindle, and when the telophase is completed the number of chromosomes in each daughter cell is half that which was present in the mother cell (Figs. 12-19). In some cases, at the commencement of heterotype mitosis, the chromosomes are not arranged in pairs as twins, but in groups of four, called tetrads, each tetrad consisting of a pair of dyads. In those cases the two dyads of each tetrad are separated from one another during the metaphase, and when the telophase is com- pleted each daughter cell possesses only half the number of chromatic particles which were present in the mother cell. It is known that a cell which contains only half the typical number of chromo- somes can divide once, therefore from each original cell which underwent heterot}^ mitosis four grand-daughter cells may be produced. It is still uncertain, ho%vever, whether or not cells which contain only half the typical number of chromosomes can further subdivide, or whether they can continue to live and function. So far as the observations made can he relied upon, it appears that such cells either die or they unite with another cell containing half the typical number of chromosomes to prod uce a new cell which contains the typical number of chromosomes and which possesses also the capability of reproducing itself by division. The Gametes. — The gametes are the germ elements by whose union, in pairs, new individuals are produced. They are of two kinds, female gametes or ova and male gametes or spermatozoa. Both female and male gametes are modified cells, by means of which hereditary characteristics are transmitted from generation to generation, and they are derived from cells called primitive germ cells, whose origin will be considered in association with the development of the germinal layers. 12 HUMAN EMBRYOLOGY. The germ cells reach their full development in special sex glands, the ova in the ovaries of the female and the spermatozoa in the testes of the male. After the descendants of the primitive germ cells have increased, by ordinary primitive germ cell Young oocytes Oocyte II and first polar body Mature ovum and polar bodies Period of Division during which numerous de- scendants are formed from the primitive germ cell. Period of Growth of oocytes I. Period of Matura- tion during which four descendants are formed from each oocyte I, i.e. the mature ovum and three polar bodies (the number of polar bodies is i r - regular). Fig. 9. — Schema of the Developmental History of the Mature Ovum. Primitive genu cell Young Spermatocyte II Spermatids Spermatozoa I Period of Division dur- ing which many de- scendants are formed from each primitive germ cell. Period of Growth spermatocytes I. of Period of Maturation during which four spermatids are pro- duced from each sper- matocyte I. Period of Transforma- tion during whicli each spermatid be- ■ comesaspermatozooii. r/fj. 10. — Schema ok the Developmental Hi.story of Spermatozoa. cell division, to a number which is probably fixed and unchangcaljle, but which is not definitely known, they begin to increase in size, that is, they enter upon a period of growtli, and at this time the female germ cells are called oocytes of the first order, oocytes I, and the male germ cells are called spermatocytes of the first order, sperma- tocytes I. Both the oocytes I and the spermatocytes I possess all the essential THE OVUM. 13 parts of a typical animal cell, and, in addition, each has special peculiarities which differentiate it both from the geriri-cells of thu opposite sex and also from ordinary animal cells. Therefore the oocyte and the spermatocyte nmst be considered separately ; but before this is done it must be noted that each oocyte I and each spermatocyte I is capaljle of producing only four descendants. The mitotic cell divisions by which th(! descendants art; produced are called the maturation divisions, and they result, in the case of the oocyte, in the formation of om; large functional cell — the mature ovum, and three small impotent cells — the polar bodies ; whilst in the case of the spermatocyte the four descendants are of equal size and each becomes transformed into a presumably potent spermatozoon. THE OVUM. An ovum presents all the characteristic structural features of an animal cell, but it is peculiar on account of its relatively large size, the large size of its nucleus, and the possession of an investing membrane, the oolemma. As the young ova or oocytes of the first order enter upon their period of growth, each is enclosed by a single layer of special cells, the stratum granulosum, which constitute, together with the oocyte, a primary ovarian follicle (O.T. Graafian follicle). The cells of the stratum granulosum multiply rapidly until they form a layer, several cells thick. At the same time, the oocyte increases in size and becomes surrounded by the membrane, called the oolemma, which intervenes between it and the innermost cells of the stratum cjranulosum. Whilst the growth of the oocyte and the thickening of the oolemma are still proceeding, a fluid-filled cavity appears in the stratum granulosum. Whether the cavity is due to the imbibition of fluid or to the dehiscence of the cells of the stratum granulosum is still uncertain, but, after its appearance, the cavity with its surrounding walls and the enclosed oocyte is spoken of as a vesicular ovarian follicle. The cavity of the vesicular follicle gradu- I- corona radiata ,, . '' 1 •j_ ■ "• Granular layer, ally increases, and, as it grows, It separates 11. — The Ovum and its Coverings (Diagrammatic). The corona radiata, which completely surrounds the ovum, is only represented in the lower part of the figure. .'). Vitellus or Yolk. li. Nucleus (germinal vesicle). 3. Vitelline membrane. 7. Nucleolus terminal spot), the oocyte and the celts of the stratum 4. oolemma (zona pelludda). S. Nuclear membrane. granulosum immediately around the oocyte from the remainder of the cells of the stratum, except in a small area where the two parts of the stratum granulosum still remain in direct continuity. When this condition is attained the cells of the stratum granulosum which immediately surround the oolemma are spoken of as the ovular cumulus ; they enclose the oocyte, and, together with it, they form a bold promontory which projects into the cavity of the follicle. When its full growth is attained each oocyte I is a comparatively large cell, which measures 200/a in diameter. It con.sists of a cell body which is surrounded by a definite enclosing membrane, the oolemma, and it contains (1) a nucleus^, (2) a centrosome, (3) numerous granules called deutoplasmic or yolk granules, and (4) mitochondria. The Oolemma. — The limiting membrane or oolemma is also called the zojia pellucida, on account of its appearance under low magnifying powers, and the zona striata, because, under certain conditions, radial striae are seen in it when it is highly magnified. It is a strong, elastic membrane, which not only protects the oocyte from pressure, but probably also prevents the impregnated oocyte or zygote 14 HUMAN EMBEYOLOGY. Oolemma from coming into close contact with the maternal tissues until it has attained the proper stage of development. The exact origin of the oolemma is unknown. It must be formed either by the action of the cells of the stratum granulosum, or by the action of the oocyte, or by interaction between the two ; but, up to the present, opinions regarding the origin are divided. It is stated that processes of the cells of the ovular cumulus pass through the oolemma, forming the radial striae,and become continu- ous with or lie in close association with the protoplasm of the oocyte ; and it is probable either that the processes are used as pabulum by the growing oocyte, or that they transmit nutritive material to the oocyte. The Body of the Ovum.— The cell body, originally called the yolk, consists of spongio- FiG. 12.-SCHEMA OF MATURATION OF OvuM, plasm aud hyaloplasm. Early Part of Prophase of First Division. ^ „, .^ -^ , ^ rm t . ^ The Deutoplasm. — Ihe deutoplasm con- sists of a number of more or less highly refractile granules, of varying size, which are embedded in the cytoplasm. They are largest in size and are most closely aggregated to- gether in the region around the nucleus, where they form a definite deutoplasmic zone. But in the human ovum and in the ova of the majority of mammals, as contrasted with the ova of birds, reptiles, and amphibia, the amount of deutoplasm is relatively small ; and for this reason the human ovum is classified as oligolecithal, the term telolecithal Fig. 13.— Schema ok Maturation of Ovum in being apphed tO OVa in which the deutoplasm Prophase of First Division. The cliromatic is present in considerable amount, as in the Oolemma Nucleus Chromosome thread has divided into twin chromosomes Each twin may be assumed to consist of a maternal and a paternal part. Oolemma Achromatic spindle Twin chromo- ova of the frog; whilst the ova of birds, many reptiles, and the monotremes amongst mammals, in which the deutoplasm greatly preponderates over the cell protoplasm, are termed eutelolecithal. The deutoplasmic granules are believed to serve as a store of nutritive material which is utilised during the early stage of the growth of the zygote, during which they disappear. (See note 2, p. 79.) The Nucleus. — The nucleus, formerly called the germinal vesicle, is a spherical vesicle of comparatively large size ; its diameter, which measures 50/x, being one- fourth of the diameter of the oocyte. It usually lies excentrically in the cytoplasm. Its constituent parts are a nuclear mem- brane, surrounding the haryoplasm, which is separable, as in ordinary animal cells, into (1) an achromatic reticulum, the linin ; (2) chromatic substance, which is embedded in or closely connected with the strands of the linin ; and (3) the nuclear juice, which fills the meshes of the reticulum ; and it contains usually one, but sometimes several nucleoU. The Centrosome. — The centrosome is not always very evident. It is usually present during the growth stage of the oocyte, and it disappears when the first maturation division commences. It may contain one or two centrioles, and it Fig. 14. — Schema of Maturation of Ovum at End of Prophase of First Division. The twin chromosomes lie at the equator of the achromatic spindle. THE OVUM. 15 Oolemma Achromatic !ii>iiidle ,. Twin cliromo- somes at coimiieiice- meiit or Heparatioii of paternal and maternal parts I W. ^ Fio. 15. — Schema of Matlkatki.n ok Ovcm in Metai'ha.se ok Fikst Division. One pole of the spindle projects into tlie first polar bud, and the matenial and paternal parts of the chromosomes are separating from each other. Oolemma Polar bud with chr iiiosoin Achromatic. spindle lies in the region of the larger deutoplasmic granules Ity which its presence is frequently obscured. The Mitochondria. — These minute particles can he demonstrated by suitable methods of fixation and staining. The Maturation of the Ovum.— The process of maturation consists of two mitotic divisions, of which the first is hetero- typical, and results in the reduction of the number of chromosomes, and the second is homotypical. Tlie phenomena of the two divisions differ in some of their details from those of ordinary cell divisions, therefore a short account of them is necessary. In the prophase of the first maturation division, the centrosome, the nucleolus, and the nucleus vanish, and an achromatic spindle appears at one pole of the oocyte, wliere it lies, at iirst, parallel with the surface ; and the chromosomes are gathered around its equator. The number of the chromosomes is only half tlie typical number, and they are probably twin chromosomes (p. 11). There are no centrosomes at the poles of the spindle. After a short time the spindle rotates until it lies at right angles to its original position, and one pole, surrounded by a small amount of the cytoplasm, forms a projection, the first polar projection, on the surface of the oocyte (Fig. 14). During the metaphase the twin chromo- somes divide. In the anaphase the daughter chromosomes travel to the opposite poles of the spindle, and at the end of the anaphase one-half of the daughter chromosomes lies in the first polar projection and the other half in the body of the oocyte (Fig. 16). ~' -- In the telophase the first polar projection Fig. 16.— Schema of Maturation of Ovum at is separated from the body of the oocyte and oocyte I ceases to exist, being converted into an oocyte of the second order, or oocyte II, and the first polar body, each of which contains half the typical number of chromo- somes. The second maturation division occurs without the intervention of a restini^ stage, i.e. without the reappearance of a nucleus in oocyte II. A new achromatic spindle appears with the daughter chromosomes at its equator; it rotates, and one pole, sur- rounded by a small amount of cytoplasm, projects on the surface of the oocyte as the second polar projection (Fig. 17). In the metaphase the daughter chromosomes divide homotypically into equal parts, and during the anaphase the grand-daughter chromo- somes move towards the poles of the spindle, one-half entering the second polar projection and the other half remaining in the body of the oocyte. During the telophase the second polar projection is separated as the second polar body and the larger remaining part of the oocyte II becomes the mature ovum (Figs. 17 and 18). Chromosomes which remain in oocyte II End of the Anaphase of the Fiust Divi- sion. Two chromosomes (paternal or maternal) lie in the fir.st polar bud and two in the larger part of the ovum which becomes oocyte II. Oolemma ^^^f'""^ polar bud First polar bo>.^ Mesodermal somite Notochord ^ Intermediate cell tract _ ^ Amnion cavity . _ Amnion _ Somatic mesoderm Coeloni _, - Splanchnic mesodenn _ ^ - Primitive gut ^ - ' Extra-embryonic coelonr '' Wall of yolk-sac ^ ' Cavity of yolk-sac Fig. .39. — Transverse Section of the Zygote shown in Fig. 38, showing the differentiation of the mesoderm. of a triangular prism with the apex directed ventro-medially, towards the notochord, and the base dorso-laterally, towards the surface ectoderm. The cephahc portion of each paraxial bar, as far caudalwards as the middle of the hind-brain, remains unsegmented, but the remainder is cut into a number of Chorion Scleratogenous mesoderm Muscle plates Cutis lamella Wolffian duct Intermediate cell tract Amnion Amnion cavity Neural tube Spinal ganglion Sympathetic ganglion ^ Aorta Intra-embryonic crelom Extra-embryonic ccelom ~, Gut Cojlom Umbilicus Yolk-sac Fig. 40.— Schema of a Transverse Section of a Zygote, showing differentiation of mesoderm and extension of amnion. segments, the mesodermal somites, by a series of transverse clefts (Fig. 38). The first cleft appears in the region of the hind-brain, and the others are formed successively, each caudal to its predecessor. Only three or four somites lie in the THE MESODERM. 29 region of the head ; tlie remainder are in the hody area of the embryonic region. The segmentation of the paraxial bars commences before their elongation is com- pleted, and tlie posterior somites are separated off as the paraxial bars are extended by the continued proliferation from the nodal point at the anterior end of the primitive streak. Wlien they are tirst defined the somites are solid masses of cells, but in a short time a cavity — the cadom of the somite or myocoele — is developed in each mass. -Me80derm of aninion — ^ — ■ -Bctodcrm of amuion — Neural crest Roof-plate Lateral wall of neural groove '- Floor- plate Mesoderm of entoderm vesicle Entoderm Cavity of entoderm vesicle Aninion cavity Notochord jlesodenii of chorion 'roplioblast of chorion Fig. 41. A. Transverse section of a zygote, showing the constituent parts. B. Diagram of embrj'onic area sliowing parts of neural plate and j)riniitive streak. The apical portion of the hollow mesodermal somite is its scleratogenous segment. The cells of the scleratogenous section of the somite undergo rapid proliferation. Some of the newly formed scleratogenous cells invade the myoccele ; others migrate towards the notochord ; finally, the scleratogenous cells separate from the remainder of the somite, and as they increase in number they migrate along the sides of Trophoblast of chorion Mesoderm of chorion Mesoderm of amnion Ectoderm of amnion Neural crest " Roof-plate ■ Lateral wall of neural groove " Floor-plate Primitive Entoderm streak Mesodei-m of ' entoderm vesicle Cavity of entoderm vesicle Amnion cavity Paraxial mesoderm Notochord Fio. 42. A. Diagram of a transverse section of a zygote, showing.the formation of a neural groove in the embryonic area. B. Diagram of a surface view of the embryonic area of the same zygote. the notochord and the neural tube, which has been formed in the meantime ffom the neural groove, and join with their fellows of the opposite side, and with their cephalic and caudal neighbours. In this way is formed, around the neural tube and the notochord, a continuous sheath of mesoderm, the membranous vertebral column, from which are differentiated, in later stages, the vertebral colunm and its ligaments, and the membranes of the brain and the spinal medulla. 30 HUMAN EMBEYOLOGY. After the separation of the scleratogenous segments of the mesodermal somites, the remainders of the somites, each of which consists of a fiat plate with incurved dorsal and ventral margins, constitute the muscle plates from which the striped muscle iibres are derived. In tlxe opinion of some observers tlie outermost portion of each of the above-described plates is developed into subcutaneous connective tissue cells ; consequently it is sjjoken of as the cutis lamella. According to this view the muscle cells are formed from the innermost cells and the incurved margins of the jjlates. The Intermediate Cell Tracts. — The intermediate cell tracts are the rudiments of the internal organs of the genital system and the temporary and permanent urinary system, \\-ith the exception of the urinary bladder and the urethra. The Lateral Plates. — From the cells of the lateral plates are formed the lining endothelial cells of the great serous cavities of the body — the pleurae, the peri- cardium, and the peritoneum ; the majority of the connective tissues, with the exception of those of the vertebral column and the head, the greater part or all the mesoderm of the limbs, and, probably, the unstriped muscle fibres of the walls of the alimentary canal and the blood-vessels. Position of otic vesicle Embryonic arc Keural crest Neural tube- Ectoderm amnion Jlesoderm amnion Tropboblast of chorion paraxial mesoderm ntermediate cell tract Splanchnic and ^omatic layers of lateral plate nieso. Amnion Xeural crest ^' Caudal neuropore Notochord Mesoderm of yolk-sac ' Entoderm of yolk-sac xtra-em- bryonic coelom Alimentary canal Yolk-sac Fig. 43. A. Diagram of a transverse section of a zygote, in which the neural tube has formed but has not separated from the surface ectoderm. B. Diagram of embryonic area of same zygote. Compare with surface view of embryo in Fig. 38. The Cephalic Mesoderm. ^ — It has already been noted that the mesoderm of the head Ijecomes segmented only in the region of the caudal part of the hind-brain, where four cephalic mesodermal somites are formed on each side. From the scleratogenous portions of these somites are developed the occipital part of the skull and the corresponding portions of the membranes of the brain, and from their muscle plates the intrinsic muscles of the tongue. The unsegmented part of the cephalic mesoderm gives rise to the remaining muscles and connective tissues of the head region. Early Stages of the Development of the Nervous System. — No definite trace of the nervous system is present until the primitive streak has formed and the emVjryonic area has passed from a circular to an elongated form. Then an area of thickened ectoderm, the neural plate, appears in the anterior part of the embryonic area. It commences a short distance posterior to the anterior end of the area, and its posterior extreuiity embraces the anterior end of the primitive streak. Its lateral margins fade into the surrounding ectoderm, and, in the earliest stages, cannot be definitely defined ; but, as the elongation of the plate continues coinci- dently with the elongation of the embryonic area, the lateral margins of the plate are elevated as the mesoderm beneath them thickens, and so they become distinct. THE EARLY NERVOUS SYSTEM. 31 As the lateral inargius of the neural plate are raised the plate is necessarily lolded longitudinally, and the sulcus so furnied is called the neural groove. Each side wall of the neural groove, formed by the corresponding half of the neural plate, is a neural fold. At a very early period the neural folds unite anteriorly to form the anterior ))oundary of the neural groove, and, somewhat later, they unite posteriorly, caudal to the neurenteric canal and across the anterior end of the primitive streak. After the lateral boundaries and the anterior and posterior extremities of the neural groove are defined, the lateral margins of the neural folds converge until they meet and fuse in the median plane, and the neural groove is thus converted into the neural tube, which possesses a floor or ventral wall, formed by the central part ol Surface / Neural crest \ ectoderm ,- /Roof- plate ,^ y^ Primitive ganglion Surface ectoderm Koof- plate Surface ectoderm ,Floor-plate- (1) Sympathetic ganglion Cbroinalliii cells Roof-plate Ependyma cells Posterior nerve-root Spinal ganglion Posterior nerve -root Anterior nerve-root Sympathetic ganglion Chromaffin cells Basal lamina with neuroblasts (3) Roof-plate \ Central canal Ependyma cells Mantle layer Peripheral laver Gut Anteriorlnerve-root Sympathetic ganglion Chromaffin cells ■ Gut Roots of sympathetic ganglion Sympathetic nerve (4) Secondary sympathetic ganglion Fig. 44.— Diaor.\ms illustrating the formation of (1) the rudiments of the primitive ganglion from the neural crest. (2) The differentiation of different parts of the primitive ganglion into permanent ganglion root, sympathetic ganglion, and masses of chromaffin cells. (3) The formation of the anterior and posterior nerve-roots. (4) The differentiation of the walls of the neural tube into ependvmal matter and peripheral layers. The cells of the primitive ganglion which form the primitive sheaths of the nerves are not shown in the diagrams. the original neural plate and called the basal plate or floor-plate ; a dorsal wall or roof-plate, and two lateral walls formed by the lateral parts of the neural plate. The fusion of the lateral margins of the neural plate to form the roof-plate of the neural tube commences in the cervical region, and from there extends cranialwards and caudalwards, therefore the last parts of the roof-plate which are formed are its anterior and its posterior extremities ; consequently, for a time, the neural canal, which is the cavity of the tube, opens on the surface at its anterior and posterior ends; the anterior opening being called the anterior neuropore, whilst the open part at the posterior end is termed the posterior neuropore (Fig. 43). Eventually, however, about the third week of embryonic 32 HUMAN EMBEYOLOGY. life both apertures are closed and, for a time, the neural canal becomes a completely closed cavity. As the margins of the neural groove rise and converge they carry with them the adjacent ectoderm to which they are attached, and which forms part of the surface covering of the embryo ; consequently, when the lateral margins of the folds meet and unite, the tube, which is completed by their fusion, is embedded in the body of the embryo, but, for a time, its dorsal wall is attached to the surface ectoderm by a ridge of cells, formed by the fused lateral margins of the neural plate. This ridge is called the neural crest (Figs. 41-44). The neural crest is the rudiment of the cerebral and spinal nerve ganglia, the sympathetic gangha, the chromaffin cells of the chromaffin organs, and the cellular sheaths of the peripheral nerves; whilst the walls of the neural tube become transformed into the various constituent parts of the central nervous system, the brain and spinal medulla, the retinae of the eye-balls, and the optic nerves.^ The Formation of the Nerve Ganglia, the Chromaffin Tissues, and the Primitive Nerve Sheaths. — The primitive ganglia grow as cell buds from the neural crest which, for a time, connects the dorsal wall of the neural tube with the surface ectoderm. In the body region they correspond in number with the spinal nerves and with the primitive segments into which the^ mesoderm becomes divided, but in the cephaUc region their arrangement is more irregular, and some of the gansha of the cerebral nerves receive additional cell elements from the surface ectoderm. Simultaneously with the appearance of the cell buds which form the primitive gangha, the neural crest disappears, and directly after the ganglia are formed they lose their connexion with both the neural tube and the surface ectoderm and become isolated cell clumps. At this period, therefore, the nervous system consists of the neural tube and the primitive ganglia. After the primitive gangha have lost their connexion with the neural tube they increase in size by the proHferation of their constituent cells, and they migrate ventrally along the sides of the neural tube, but the migration ceases before the ventral ends of the gangha reach the level of the ventral wall of the tube. As the migration proceeds clumps of cells are budded off* from the ventral ends of the gangha. These secondary cell buds are the rudiments of the sympathetic ganghon cells and of the chromaffin tissue which is found in the sympathetic nerve plexuses, the medulla of the suprarenal glands, and in the carotid glands. In the first instance the secondary cell buds which form the sympathetic gangha wander ventrally and medially, from the ventral ends of the primitive ganglia, until they attain the positions afterwards occupied by the ganglia of the sympathetic trunks on the ventro-lateral aspects of the vertebral coluum. From the primary sympathetic gangha, buds of cells are given off"; these buds wander still further ventrally to become the cells of the gangha of the cardiac, coehac, and other great ganghonic nerve plexuses, as well as to form the chromaffin cells of the chromaffin organs. The exact manner in which the cells of the primitive sheaths of the nerves originate from the primitive gangha is not known, but it has been shown by Harrison, in the case of the frog, that if the primitive ganglia are destroyed, the primitive sheaths of the nerves are not formed. Presumably, therefore, in the frog the cellular sheaths of the nerves are derived from cells produced by the primitive gangha, and it may be assumed that they have a similar origin in the human subject. After the rudiments of the sympathetic system, the chromaffin cells, and the cellular sh(;aths of the nerves have separated, the remains of the primitive ganglia become the permanent spinal and cerebral nerve gangha. In the early stages these ganglia are completely isolated structures which lie along the sides of the neural tube between the lateral walls of the tube medially, and the mesoderm somites laterally. Some time after the ganglia of the cerebral and spinal nerves l)ecome isolated ' It is stated that some of tlie sympathetic nerve-cells are derived from the ventral parts of the lateral walls of the neural tube, Vjut the evidence on this point is not entirely satisfactory. THE NEUEAL TUBE. 33 their cells give off processes which become nerve-fibres. These fibres grow out both from tlie dorsal and the ventral ends of the ganglia, and, together with the ganglia, they form, in the cranial region, certain of the cerebral nerves, and, in the spinal region, tiie posterior roots of the spinal nerves. The fibres which grow out of the dorsal ends uf the ganglia enter the walls of the neural tube, and by their means the gangHa regain connexion with the tube. The fibres which grow out from the ventral end of each spinal ganghou unite with the fibres of the corresponding anterior nerve-root, which, in the meantime, has grown out from the cells of the ventral part of the lateral wall of the spinal portion of tlie neural tube, and form with them a spinal nerve-trunk. The Differentiation of the Neural Tube. — Before the neural groove is con- verted into a closed tube, an expansion of its anterior part indicates the separation of tlie neural rudiment into cerebral and spinal sections, the dilated portion being the rudiment of the brain and undilated part the rudiment of the spinal medulla. Whilst the cere})ral portion is still unclosed, three secondary dilatations of its walls indicate its separation into three sections, the primitive fore-brain, the mid-brain, and the hind-brain ; the primitive fore-l)rain being the most cephalward or anterior and the liind-brain the most caudal or posterior of the three (Fig. 38). Shortly after the tln*ee segments of the brain are defined, and Itefore it becomes a closed tube, a vesicular evagination forms at the cephalic end of each lateral wall of the primitive fore-brain region. These evaginations arc the primary optic vesicles, and they are the rudiments of the optic nerves, the retinae, and the posterior epithelium of the ciliary body and the iris of the eye-ball. When the cere])ral portions of the neural folds meet and fuse dorsally the cerebral dilatations become the primitive brain vesicles, each vesicle possessing its own cavity and walls, but the cavities of the three vesicles are continuous with one 'another, and the cavity of the hind-brain vesicle is continuous, caudally, with the central canal of the spinal part of the neural tube. After the primitive brain vesicles are formed, a diverticulum grows out from the cephalic end of the primitive fore-brain vesicle. This is the rudiment of the secondary fore-brain. Its cephaUc end soon divides into two lateral halves, which are the rudiments of the cerebral hemispheres of the adult brain (Fig. 45). After their formation the cerebral hemispheres expand rapidly in all direc- tions. They soon overlap the primitive fore-brain and mid-brain (Fig. 63), and, eventually, the liind-brain also, and each gives off from the cephaUc end of its ventral wall a secondary diverticulum, the olfactory diverticulum, which becomes converted, later, into the olfactory bulb and olfactory tract. When they first appear the rudiments of the cerebral hemispheres are con- nected together, across the median plane, by a part of the cephalic end of the wall of the secondary fore-brain dilatation, which is called the lamina terminalis. This primitive connexion between the two cerebral hemispheres persists through- cut the whole of hfe, and it is supplemented, at a later period, by the formation of three secondary commissures, the corpus callosum and the fornix, which grow across the space between the cerebral hemispheres and connect their medial walls together, and the anterior commissure which grows through the lamina terminalis and connects the temporal portions of the two hemispheres. The Fate of the Walls of the Primitive Brain Vesicles.— The primitive hind-brain, which is also called the rhomltencephalon, is separated in the later stages of development into two parts. (1) A caudal portion which is connected with the medulla spinalis, and which becomes the medulla oblongata or myelen- cephalon of tlie adult brain. (2) A cephalic portion which is continuous at one end with the medulla oblongata and at the other with the mid-brain. The ventral wall of the cephalic portion of the primitive hind-brain is ultimately converted into the pons, and its dorsal wall differentiates into two parts — a caudal part which becomes the cerebellmn ; and a cephaUc part which is converted into the anterior medullary velum and the brachia conjunctiva. The brachia conjunctiva connect the cerebellum with the ventral part of the mid-brain. The pons and cerebellum form the metencephalon of the adult, whilst the brachia conjunctiva 3 34 HUMAN EMBRYOLOGY. DORSALIS and tlie anterior medullary velum constitute parts of the isthmus rhombencephali (Figs. 45, 63). The ventral portion of the primitive mid-brain is converted into the two peduncles of the cerebrum of the adult l)rain, and the dorsal portion is transformed into four rounded elevations, the colhculi or corpora quadrigemina. The transformations which take place in the region of the primitive fore-brain or prosencephalon are numerous and comphcated; therefore its ventral, lateral, and dorsal walls require separate consideration. By the expansion of its cephalic (anterior) extremity is formed the secondary fore-brain, which becomes di\'ided, as already explained, into the two secondary vesicles which are the rudiments of the cerebral hemispheres of the completed brain. After the formation of the rudiments of the cerebral hemispheres, which constitute the tel- encephalon of the adult, the primi- tive fore-brain and the undivided stalk of the second- ary fore-brain diverticulum be- come the dience- phalon. The cephalic or anterior end of the diencephalon is closed by the lamina terminahs (see p. 33), in association with which are subse- quently developed Fig. 45. — Diagrams to illustrate the Alar and Basal Lamina. In both two columns cases the embryonic brain is represented in mesial section (His). which run dorSO- A. The different subdivisions of the brain are marked off from each other by dotted VCntrally, the lines, and the dotted line running in the long axis of the neural tube indicates the polriTTiTio of the separation of the alar from the basal lamina of the lateral wall. . /pk m B. Medial section through the brain of a human embryo at the end of the first . •ii ' A 1 month. Dotted lines mark ofi" the different regions and also the alar and basal tSriOI pillarsj, anCl laminae from each other. twO tranSVerse H, Buccal part of hypophysis cerebri ; RL, Olfactory lobe ; C.Str, Corpus striatum ; COmmisSUres, One A, Entrance to optic stalk ; 0, Optic recess ; I, Infimdibular recess ; T, Tuber q^ wbicb COnnectS cinereum ; M, Mamillary eminence. , ,■, i.i j. •^ together the two cerebral hemispheres and is called the anterior commissure, whilst the other is the optic chiasma in which the medial fibres of the optic nerves decussate. From the cephalic or anterior end of the ventral wall of the diencephalon a diverticulum is projected ventrally towards the dorsal wall of the primitive mouth. The ventral end of this diverticulum becomes the posterior lobe of the hypophysis (O.T. pituitary body) of the adult, tlie dorsal end becomes the tuher cinereum, and the intermediate part is the infundihulum which connects the tuber cinereum of the adult brain with the posterior lobe of the hypophysis. Caudal to the hypophyseal diverticulum a single elevation appears in the ventral wall of the diencephalon. It is the corpus mamillare, which afterwards separates into the paired corpora mamillaria of the adult lirain. Still more caudally tlie ventral wall of the diencephalon takes part in the formation of the substantia perforata posterior, which lies between the two peduncles of tlie cerebrum and is partly developed from the cephalic or anterior end of the ventral wall of the ]:)rimitive mid-brain. The greater part of the dorsal wall of the diencephalon is ultimately reduced to a single layer of epithelial cells, but near its caudal end a diverticulum is projected dorsally. This is the epiphysis or pineal body, which remains quite THE NEURAL TUBE. 35 Spon^oblast / Roof-plato Spongioblast Floor- plate Fl(i. 46. A. Diagram of a trausveise section of a spinal medulla wliicli liaH not difl'erentiatetl into groups of cells. B. Diagram of a transverse section of a spinal medulla showing positions of germinal cells. rudinientaiy in man as contrasted: witli many otlier animals. At a later period two transverse bands of fil)res appear in the dorsal wall of the diencei)halon, one in front of and the other immediately hehiiid the root of tlie einphyseal recess. The anterior hand is the dorsal or habenular commissure, and the posterioi- is the ]>osterior commissure of the adult hrain. These structures, collectively, together with a small diverticulum of the epithelial roof, which appears anterior to the dorsal com- missure, and is called the supra-pineal recess, constitute the so-called epithalamus. Eacli lateral wall of the diencephalon is diflJerentiated into a dorsal and a ventral part. The dorsal part forms a large gray mass called the thalamus, and on the posterior end of the thalanuis are de- veloped two rounded eleva- tions, the medial and the lateral geniculate bodies, which constitute the meta- thalamus of the adult brain. The ventral or basal portion of the lateral wall of the diencephalon, together with the adjacent part of the ventral wall, forms the hypothalamus of the fully developed l)rain. The Fate of the Spinal Portion of the Primitive Neural Tube.— The spinal portion of the neural tul)e, during the first three months of intra- uterine life, develops equally in its whole extent, but after that period a longer cephalic or anterior (superior in the erect posture) and a shorter caudal portion are recognisable. The cephalic portion undergoes still further development and is converted into the spinal medulla of the adult, but in the smaller caudal or posterior portion retrogressive changes occur, and it is trans- formed into the non-functional filum terminale of the completed medulla spinalis. Histological Differentiation of the Walls of the Neural Tube. — In the earUest stages of its de- velopment the walls of the neural tube consist of a mass of nucleated protoplasm, more or less distinctly differentiated into cell areas, of columnar form, which extend be- tween and are connected with an internal limiting membrane, bound- ing the neural canal, and an ex- ternal limiting membrane, which surrounds the whole t\ibe. At this time the outline of a transverse section of the primitive neural tube is somewhat ovoid. The cavity of the tube is compressed laterally into a dorso- ventral cleft, which is bounded by dorsal, ventral, and lateral walls. In the dorsal and ventral walls, called respectively the roof- and tioor-plates, the columnar character of the primitive epithehal elements of the medulla spinalis is retained throughout the whole of life, but the peripheral parts of some of the cells are converted into fibrils. In the lateral walls of the embryonic medulla spinalis some of the cells soon Columnar cells of roof-plate Peripheral layer • - Neuroblasts Mantle layer Spongioblast -; Ependyuia cells Neuroblast Fio. 47.- Coluuinar cells of floor-plate -SHOWIxNG ELE.MENTS OF CeNTUAL NERVODS SYSTEM. 36 HUMAN EMBEYOLOGY. assume a spherical form. These spherical cells have large deeply staining nuclei, and they are termed germinal cells. For many years it was Iteheved that the germinal cells were the predecessors of the primitive nerve elements or neuroblasts, and that the remaining cells, called spongioblasts, became transformed into the reticular sustentacular tissue of the central nervous system. It appears, however, from the results of more recent researches, that some of the descendants of the germinal cells become spongioblasts whilst others become neuroblasts or primitive nerve-cells. Moreover, there appear to be two groups of germinal cells ; the descendants of one group are directly transformed into the ependymal or lining cells of the central canal, whilst those of the other group form in the first instance indifferent cells, some of whose descendants become neuroblasts and others spongioblasts. The fate of the cells present before the germinal cells appear, and which do not become germinal cells, is uncertain, but they probably take part in the formation of the spongioblastic tissue. It is beheved, therefore, that all the nerve-cells are the descendants of the germinal cells, and that the spongioblasts which become developed into the cells of the neurogha or sustentacular reticulum are derived partly from the non- germinal cells of the primitive neural tube and, partly, they are descendants of the germinal cells. As differentiation proceeds three layers and two membranes are gradually defined in the walls of the neural tube : (1) a central layer of columnar ependyma cells immediately surrounding the central canal ; (2) an intermediate or mantle layer consisting of neuroblasts and their processes, the nerve-fibres, intermingled with spongioblasts ; (3) a peripheral reticular layer consisting, at first, of processes of the bodies of the spongioblasts. The membranes are an external limiting membrane, surrounding the exterior of the tube, formed by the fused outer ends of the spongioblastic cells, and an internal limiting membrane bounding the central canal and continuous with the inner ends of the ependyma cells. Through- out the whole of the spinal medulla and the brain, the ependyma cells become transformed into the columnar cihated cells which hne the cavities of the adult Ijrain and spinal medulla. The mantle layer becomes converted into the gray matter of the adult central nervous system. The peripheral reticular layer, in the spinal region, becomes permeated by nerve-fibres, which are merely processes of the nerve-cells, and it is thus converted into the white matter of the adult spinal medulla. In the brain region it is either transformed in the same way into white matter, or it remains in a more rudimentary condition as a thin peripheral layer of neuroglia on the surface of the gray matter. On the other hand, in the brain region white matter is formed internal to the gray matter by the growth of nerve-fibres which insinuate' themselves between the mantle layer externally and the bodies of the ependyma cells internally. As the histological differentiation of the walls of the neural tube is proceeding each lateral wall is divided into a dorsal part, the alar lamina, and a ventral part, the basal lamina, by a sulcus-like dilatation of the central canal called the sulcus limitans. After the limiting sulci are formed the parts of the walls of the neural tube are a roof-plate, a floor-plate, and two lateral walls, each of which consists of an alar lamina, essentially sensory in function, and a basal lamina, essentially motor in function (Tig. 44). The Fate of the Cavities of the Primitive Brain. — The cavity of the spinal portion of the primitive neural tube becomes the central canal of the spinal medulla of the adult. The cavities of the yjrimitive brain vesicles are transformed into the ventricles, foramina, and aqueduct of the adult brain. The cavities of tlie teleuoephalic divisions of the secondary fore-ln'ain become the right and left lateral ventricles of the adult brain. The cavity of the undivided portion of the secondary fore-brain vesicle, together with the cavity of the primary fore-brain, become the third ventricle or cavity of the diencephalon, and the apertures of communication l)etween the third ventricle and the cerebral hemispheres are the interventricular foramina CO.T. foramina of Monro). The cavity of the hind-J^rain vesicle Itecomes the fourth ventricle, and the THE FORMATION OF THE EMBRYO. 37 cavity of the primitive mid-brain is converted into the aqueductus cerebri, which connects the third with the fourth ventricle. After the anterior and posterior neuropores (p. 31) are closed, the cavity of the neural tube is, for a time, a completely enclosed space. Subsequently the mesoderm, which in the meantime has surrounded the tulte, becomes differentiated, in its immediate neighbourhood, into three membranes. The innermost of the three is closely connected with the walls of the neural tu])e and is called the pia mater. The outermost, known as the dura mater, is dense and resistant, and the intermediate menil)rane is a thin lamella called the arachnoid. As the membranes are formed, spaces are differentiated between them. The space between the dura mater and the arachnoid is the subdural space, and that between the arachnoid and the pia mater is the subarachnoid space. After a time a median yjcrforation, the median aperture of the fourth ventricle (O.T. foramen of Magendie), and two lateral perforations pierce the dorsal wall of the fourth ventricle and the pia mater which covers it, and thus the fourth ventricle becomes connected with the subarachnoid space. It is stated also that a perforation passes through the medial wall and the covering pia mater of a portion of each lateral ventricle which is called its inferior horn, throwing those portions of the lateral ventricles also into communication with the subarachnoid space, but it is doubtful if the statement is correct. THE FORMATION OF THE EMBRYO. Neural plate Ectoderm of amnion Mesoderm of amnion Primitive streak Body stalk Allantoic diverticulum from entoderm vesicle mesoderm Jlesoderm o entoderm vesicle Entoder Notochor Fig. 48. — Schema of Sagittal Section of Embryonic Area and Amnion before the Folding of the Area has commenced. The transformation of the relatively flat embryonic area f; into the form of the embryo is due, in the first instance, to the rapid extension of the median part of the area, as contrasted with the slower growth of its mar- gins, and the later modeUing of the various parts of the y^ \ / embryo is due to different rates cephalic end of -^ \ j c 4-1 • j-cc i. J. r embr>onicarea._™ 01 growth in dinerent parts oi Pericardial the embryonic region. By the rapid proliferation of cells from the nodal grow- ing point, at the cephalic end of the primitive streak, the cephalo-caudal length of the area is increased, whilst the cephahc and caudal ends of the area remain relatively fixed, conse- quently the area be- comes folded longitu- dinally. At the same time, the cephahc end of the neural groove is pushed away from the nodal point, until it Ues at first dorsal and then cephalad to the cephalic border of the area. As a result of this move- ment the bucco-pharyn- geal and the pericardial areas become reversed in position, and a cephalic or head fold is formed. This fold is bounded, dorsally, by what is now the cephalic portion of the embryo, ventrally, by the reversed pericardial region, and its cephahc end is formed by the extremity of the head region and the bucco-pharyngeal membrane. AmnioQ_ cavity Ectoderm of amnion Amnio! :ic mesoderm Chorionic mesoticrm k > Re^tion of K^ posterior Xeural tub^^ ^_I'H " dium i not sh( Reffion of A' _^C^^mmm ■iih-'ttJ'I^J^'l ^ . neuropore neuropore V \^/\^S Bucco-pharyngeaV // V membrane | Pericar Fore-gut (heart 1 1 i Mid-gut 3wn) Hind -gut ^^K- membrane *^^ Body stalk ^*art in the formation in the body of the embryo. On the other band, its mesodermal and entodermal constituents represent a cUverticulum from the wall of the hind-gut, present in many mammals and known as the allantois ; it might with advantage, therefore, be termed the allantoic stalk. At first the umbihcal orifice is relatively large as contrasted with the total size THE LIMBS. 39 of the embryo, liut as the embryo rapidly extends, in all directions, from the margin of the orifice, the latter soon becomes relatively small. Ultimately the various parts of the mtfrgiu of the orifice are approximated until they fuse together, closing the opening and forming a cicatrix on the ventral wall of the abdomen which is known as the umbilicus or navel. THE EMBRYO. Whilst the embryonic area is being folded into the form of the embryo, the neural groove on the surface of the area is being converted into the neural tube. After the neural tube is completely closed and separated from the surface, during the third week, the embryo is an elongated organism possessing a larger cepbalic end, a smaller caudal entl, attached by the body stalk to the chorion (Fig. 49), a continuous and unbroken dorsal surface, a ventral surface separated into cephahc and caudal portions by the umbilical orifice, two lateral surfaces right and left, and it contains within its interior three cavities : (1) The cavity of the neural tube, whicli becomes the cavities of the brain and the spinal medulla (Fig. 50) ; (2) the primitive alimentary canal, which is a portion of the entodermal vesicle constricted otf during the folding of the eml)ryonic area (Figs. 37, 40); (3) the embryonic cojloni. The coelom consists of right and left portions which communicate at the margin of the umbilicus with the extra-embryonic coelom, and with each other through the pericardial portion of the intra-embryonic ccelom in the ventral wall of the fore -gut of the embryo (Figs. 49, 90). At this period the embryo is easily distinguished from the remainder of the zygote, and it is so far developed that indications of its general plan of organisa- tion are discernible. It has, as yet, no limbs, but the general contour of the head and body are defined. It possesses a notochord or primitive skeletal axis, afterwards replaced by the permanent vertebral column. On the dorsal aspect of the notochord lies the neural tube, which is the rudiment of the future brain and the spinal medulla. At the sides of the neural tul^e and the notochord are the mesodermal somites and the nerve ganglia (Figs. 40, 43). Ventral to the notocliord is the primitive ahmentary canal (Fig. 50), closed at its cephalic end by the bucco-pharyngeal membrane, and at its caudal end by what was originally the caudal portion of the primitive streak, but which is now called tlie cloacal membrane l)ecause it separates the caudal end of the hind-gut, which l)ecomes the entodermal cloaca, from the amniotic cavity (Fig. 50). At the sides of the primitive alimentary canal are the right and left lateral parts of the ccelom, and l)etween the dorsal angle of each half of the ccelom and the mesodermal somites of the same side lies the intermediate cell tract which is the rudiment of the greater part of the genito-urinary system (Figs. 39, 40). Ventral to the fore-gut is the pericardial mesoderm, traversed by the pericardial portion of the coelom, which is connected dorsally, on each side, witli the corre- sponding lateral portions of the ccelom ; and ventral to the hind-gut is the cloacal membrane. Between the pericardial region at the one end and the cloacal membrane at the other lies the umbihcal orifice, through which the mid-gut communicates with the yolk sac, the intra-embryonic part of the ccelom with the extra-embryonic coelom, and the allantoic diverticulum with the cloaca (Figs. 39, 50). THE LIMBS. When it is first defined the embryo is entirely devoid of Umbs (Fig. 51). During the third week a superficial ridge appears on each side, along the line of the intermediate cell tract in the interior. This is the Wolffian ridge, and upon it the rudiments of the fore and hind limbs, the limb buds, are formed, as secondary elevations ; the fore-Hmb buds preceding the hind-limb buds in time of appearance (Fig. 52). 40 HUMAN EMBEYOLOGY. Shortly after it has appeared, each hmb bud assumes a semilunar outline ; it projects at right angles from the surface of the body, and it possesses dorsal and ventral surfaces,' and cephalic or preaxial, and caudal or postaxial borders. The Fig. 51. — View of Dorsal Aspect of a Human Embryo — 1'38 mm. Long, before the appearance of the limbs. (From Keibel and Elze, Normo.Uafeln. ) Fig. 52.— Dorsal lateral View of A Human Embryo — 2'4 mm. Long. The Wolffian ridge is seen at the lateral border of the meso- dermal somites. (Keibel and Elze, Normaltafeln. ) bud is the rudiment of the distal segment of the future limb, the hand in the case of the fore-hmb, and the foot in the case of the hind-limb. As the limb-rudiment increases in length the more proximal segments of the limb are differentiated, the forearm and arm in the case of the fore-hmb, and the leg and the thigh in the case of the hind -limb. At the same time the Kmbs are folded ven- trally, so that their original ventral surfaces become medial and their original dorsal surfaces lateral, and the convexities of the elbows and knees are directed laterally. At a later period, on account of a rotation which takes place in opposite directions in the fore- as contrasted with the hind- liml)8, the convexity of the elbow is turned towards the caudal end of the body and that of the knee towards the cephalic end. It is only at much later periods of de- velopment, as tlie erect posture is assumed, that theconvexity of the elbow is directed dorsally and the convexity of the knee ventrally. The terminal or distal seg- ment of each hmb is, at first, a flat plate with a rounded margin, l)ut it soon diflerenti- ates into a proximal or basal part and a more flattened marginal portion. It is along the line where these two parts arc continuous that tlic rudiments of the digits appear. Th(;y )>ecome evident as small elevations on the dorsal surface of the limb bud about the filth week ; they extend peripherally, and by the sixth week the fingers project beyond the margins of the hand segment, but the toes do not attain to a corresponding stage of development until the early part of the seventh week. \' Fig. 53.— Lateral View ok a Human Embryo— 2-1 mm. greatest length, showing limb buds projecting from the Wolflian ridge. (Keibel and Elze, Normcdtafeln.) THE PRIMITIVE ALIMENTARY CANAL. 41 Thu nails are later developraeijts. They appear at the third month and reach the ends of the digits at the sixth month. Each Hmb bud is essentially an extension of a definite number of segments of the body. It consists, at first, of a core of mesoderm covered by ectoderm. As it Krows tilt! anterior branches of the spinal nerves of the correspondmg segments are prolonged into it, together with a number of blood- vessels. The nerves remain as the nerves of the fully developed liml), but the blood-vessels are reduced in number and are modified until a smaller number of permanent main trunks is estabhshed. The greater part, if not the whole, of the mesodermal core ol' the primitive limb-rudiment seems to V>e produced by the somatic mesoderm of the lateral plate. As the development proceeds it is differentiated into the cartilagin- ous, muscular, and other connective tissue elements which are the rudi- ments of the skeletal framework and the muscles and fasciae of the adult liml). It is not yet decided whether or not the muscle elements of the mesodermal core are derived from the lateral plate mesoderm, or from muscle cells which have migrated into the limb, from the muscle plates of the segments from which the limb is formed and from which muscles of the body wall are developed ; and although it is generally beUeved that the bone which replaces the cartilaginous skeletal rudiments is produced by mesodermal cells, it has been asserted that the bone-producing cells originate in the ectoderm and migrate from the surface into the interior. Fig. 54. — Lateral View of a Human Embryo — 9 5 ram. Long. (Keibel and Elze, iVonn«^te/e^n. ) Note that the limb rudiments no longer project at right angles from the side of the body but that they are bent ventrally. THE EARLIER MODIFICATIONS OF THE PRIMITIVE ENTODERMAL ALIMENTARY CANAL AND THE FORMATION OF THE STOMA- TOD^UM AND PROCTODEUM. The greater part of the permanent alimentary canal is derived from the ento- dermal sac and is therefore lined by entoderm cells. This part is enclosed in the embryo as the latter is folded off from the remainder of the zygote (Fig. 50), but the cephalic and caudal portions of the alimentary canal are formed by the enclosure of part of the external space and are, therefore, lined by ectoderm. The cephahc part is a portion of a space called the stomatodaeum which lies, at first, between the ventrally bent extremity of the head and the bulging pericardial region (Fig. 50). At a later period it is enclosed laterally by the rudi- ments of the maxillae or upper jaws, and caudally by the mandi])ular rudiments. When it first appears the stomatodaeum is separated from the cephahc end of the entodermal portion of the primitive canal by the Imcco-pharyngeal membrane, but when that septum disappears, during the third week, the stomatodaeum communicates with the fore-gut. Subsequently, it is separated into nasal and oral portions, and the oral portion forms that part of the mouth in which the gums and teeth are developed. The caudal part of the permanent canal is formed by the elevation of a surface 42 HUMAN EMBEYOLOGY. fold round a pit-like hollow called the proctodseum (Fig. 60), which is separated from the caudal part of the ento- Amnion .-..vity, ^''"'^"] ^"V^^'""' piasuiodiai trophobiast dcrmal portloii of tlic alimentary canal, until about the fourth week, by a membrane called the anal membrane, a portion of the more extensive cloacal mem- brane mentioned on p. 39. Celliilar troplioblast Mt^i'iierm of chorion ,'Eut. of amnion Body stalk AUan- tois Differentiation of the Fore-gut. Derivatives of the Lateral "Wall. — Shortly after the fore- gut is enclosed, and whilst it is still separated from the stomato- daeum by the bucco-pharyngeal membrane, its cephaHc extremity dilates to form the primitive pharynx and thereafter, a series of eight pouches are formed in its walls, five in each lateral wall ; the pharyngeal or branchial pouches ; two in its ventral wall, one near the cephahc extremity, the rudiment of the thyreoid gland, and a second situated more caudally, which is the germ of the respiratory system, that is, of the larynx, the trachea, the bronchi, and the epithelial lining of the lungs. The eighth pouch, Seessel's pouch, is formed in the dorsal wall, immediately caudal to the dorsal end of the bucco-pharyngeal membrane, and it projects into the floor of the primitive cranium. Wall of yolk-sac Fig. 55. — Sagittal Section of Zygote showx in Fig. 38. 1st Brancliial - cleft 2iid Branchial pouch \^ 2nd Branchial cleft 3rd Bi-anchial pouch 4th Branchial pouch-' 4th Branchial cleft Pharyngo-branchial duct, 5th Branchial bar 5th Branchial pouch -- Separating membrane - l.st cleft = tympanum i and tube '/ Lower Upper- parathyreoid parathyreoid Upijer Lower parathyreoid paratliyreoid .Thyreoid gland -Tlivmu- Nxhyi - - Hyoid bone • - Thyreo-glossal duct Thyreoid cartilage Thymus Fig. 56. — Schema showing the branchial pouches, the branchial clefts, the branchial bars, and the thyreo- glossal duct and some of their derivatives. I., II., III., IV., and V., the five branchial bars. Simultaneously with the formation of the pharyngeal pouches internally a series of clefts appear externally. They correspond- in position with the first four pharyngeal pouches, and they are called the pha>r3mgeal or branchial clefts. By means of the pharyngeal pouches and clefts the lateral boundary of the cephahc part of the fore-gut, on each side, is divided into a series of bars, the pharyngeal or branchial bars, five in number, but the fifth is distinctly visible only in the inner aspect of the pharynx. THE PRIMITIVE ALIMENTARY CANAL. 43 The first of the pharyngeal bars is the rudiment of the maxillary and mandiljular regions. It is called tlie mandibular arch. The second is the hyoid arch, and the remainder are the branchial arches proper. When they first appear, the arches extend from the level of the dorsal wall of the fore-gut to tlie ])ericardiuni but, as growth proceeds, and the neck is developed between Uie head and the pericardium, the ventral ends of the arches of opposite sides meet in the ventral wall of the primitive pharynx. The growth of the mandi- Kudiiiient of I■l^spirato^y system Ectoderm of embryo I Meilulla spinalis Ectoderm of amnion | I / Notochonl Mnnrlrnii nfiiiini"" ^ \ | I / Dorsal pancreas nuliment Thyreo-glossal (li]jjKi^ ( •' Peritoneal ]iart of C(»-'loni Hind-brail] Seessers pouch Mid-brain Rathke's pouch Cerebral hemisphere" Pericardium Rudiment of liver Septum transversum Rudiment of gall-bladder | Ventral pancreas rudiment Vitello-intestinal duct Peritoneal part of ccelom oacal membrane "ail-fcut diverticulum lorion Allantoic diverticulum Fig. 57. — Schema of a Longitddinal Section of an Embryo dorsal and ventral divertricula for alimentary canal. (After Mall, modified.) Showing The heart is not shown. bular and the hyoid arches soon greatly exceeds that of the branchial arches proper, and the latter gradually recede from the surface until, on each side, they Ue at the bottom of a depression, the precervical sinus, which is overlapped by the caudal border of the hyoid arch. As the overgrowth of the hyoid arch continues the open- ing of the precervical sinus to the surface is reduced to a narrow channel, the precer- vical duct. Afterwards this is obliterated, the sinus becomes the precervical vesicle, 1st cleft- — ind cleft --'\^^=^ 3rd cleft- Precervical duct' 4th cleft ' Branchial duct Precervical sinus Precervical duct 4th pouch Fig. 58.— Schema showing the formation of the precervical sinus, the branchial ducts, and the precervical sulcus. but the position of the original aperture of the precervical duct is temporarily indicated by a sulcus, the precervical sulcus which soon disappears. The precervical vesicle lies at the side of the third pharyngeal cleft, and it is associated with the second and fourth clefts by narrow canals, the branchial ducts, which are the remains of the branchial clefts. Ultimately the precervical vesicle and the branchial ducts disappear, but it has been suggested that before the vesicle disappears a part of the lobe of the thymus of the same side is formed from its wall. 44 HUMAN EMBEYOLOGY. The portion of the wall of the primitive pharynx which lies between each pair of visceral arches and separates the clefts externally from the pouches internally is called the separating membrane. In the earliest stages it consists of ectoderm, mesoderm, and entoderm ; then, for a time, the mesoderm disappears to re-appear again between the two epithehal strata at a still later period. Eound the margins of the dorsal part of the first pharyngeal or mandibular cleft are formed a series of tubercles which develop into the auricle of the external ear, and the cavity of the cleft becomes the external acoustic meatus (see p. 52). The first pharyngeal pouch and the adjacent part of the cavity of the primitive pharynx becomes the tympanic cavity and the auditory (O.T. Eustachian) tube. A part of the cavity of the second pharyngeal or hyoid pouch is represented in the adult by the supra-tonsillar recess, which lies in the side wall of the pharynx above the palatine tonsil (Fig. 56). The third pharyngeal pouch opens like the first and second directly into the cavity of the fore-gut, but the fourth and fifth pouches lie in the lateral wall of a common recess which opens by a single aperture, the pharyngo-branchial duct, into the cavity of the primitive jjharynx (Fig. 56). The cavities of the third, fourth, and fifth pouches ultimately disappear, but before the disappearance takes place diverticula which, at first, are hollow but, after- wards, become solid are given off from the ventro-lateral parts of each, and sohd epithehal outgrowths, the epithehal bodies, are formed from the dorso-lateral walls of the third and fourth pouches (Fig. 56). The ventral diverticulum from the third pouch, on each side, forms the main part of the corresponding lobe of the thymus, and the ventral diverticulum of the fourth pouch either takes part in the formation of the thymus or it entirely disappears. The rudiment of the thymus is formed in the neck, but as the gland differentiates it extends and it migrates caudally, until its cephalic end hes near the caudal end of the thyreoid gland, at the level of the sixth ring of the trachea, and its caudal end is in the thorax at the level of the fourth costal cartilage. The epithehal bodies derived from the third and fourth pharyngeal pouches form the structures known in the adult as the paratliyreoid bodies. That derived from the third pouch migrates caudally more rapidly than its fellow formed from the fourth pouch ; consequently the parathyreoid derived from the fourth pharyngeal pouch lies at the middle of the dorsal border of the corresponding lobe of the adult thyreoid gland, and the parathyreoid formed from the third pharyngeal pouch is situated at the caudal end of the corresponding. lobe of the thyreoid gland and close to the cephahc end of the thymus. The diverticulum formed from the ventral part of the fifth pharyngeal pouch is the ultimo-branchial body. After it separates from the pouch it becomes sohd and is associated with the corresponding lobe of the thyreoid gland, but, apparently, in the human subject, it takes no part in the formation of that gland. Derivatives of the Ventral Wall. — The diverticulum from the ventral wall of the primitive fore-gut, which is situated nearest the cephalic or anterior end of the gut, is the rudiment of the thyreoid gland. It commences in the median plane, between the ventral ends of the mandibular and hyoid arches, and grows ventrally, into the substance of the neck, then turns caudally, ventral to the cartilages which form in the second, third, and fourth arches, from which the hyoid bone and the cartilages of the larynx are developed. When the caudal end of the diverticulum reaches the region where the cephalic or anterior portion of the trachea will be formed it becomes bilobed, and thus is differentiated into the isthmus and the two lobes of the permanent gland. The stalk of the diverticulum, which extends from what becomes the oral part of the primitive pharynx to the isthmus of the gland, is the thyreoglossal duct. Its cephahc end remains as the foramen caecum, which is situated in the dorsum of the tongue, at the junction of the ventral two-thirds with the dorsal third. The caudal end sometimes persists and is transformed into the third or pyramidal lobe of the thyreoid gland, which is attached to the dorsal border of the isthmus (Figs. 56, 61). The more caudally situated diverticulum from the ventral wall of the fore-gut is the rudiment of the respiratory system (Figs. 59, 60). When it first appears THE PKIMITIVE ALIMENTAEY CANAL. 45 Tuberculuin iinpiir Sinus arciiatiis Kurcula it has the form of a longitudinal groovt^ hounded at its cranial end and laterally Vjy an elevated ridge, named hy His the furcula (Fig. 59). The caudal end ol" the groove soon dilates into a pouch, and then the pouch and groove are separated hy a con- striction, which ])asses from the caudal towards tlic cranial end, from tlie more dorsal jtart of the fore-gut, which he- comes the oesophagus. The constricting process ceases before the separation reaches the cranial extremity of the re- spiratory rudinu-nt, which remains, there- fore, in communication witli the pharynx and forms the permanent laryngeal aper- ture. The tube farmed In' the separation of the groove is dififerentiated into the larynx and the trachea, and the caudal terminal dilatation soon divides into two lateral lobes, each of whicli is the rudi- ment of the epithelial lining bronchi and the lung of the corresponding side. The Tongue. — The tongue is formed hy four separate rudiments which lie in the ventral part of the cranial end of the primitive pharynx. Two of these are eleva- tions formed on the caudal surfaces of the ventral ends of the mandibular arches, Co.-loii Fig. 59. — View ok Flook ok Phi.mitive Phakynx, .'ihowiiif? the furcula witli tlie groove, from which arise the cavities of the larynx, the trachea, the bronchi, and the alveoli of the lungs. Small intestine Pancreas | Cwcuni Stomach Bile-duct Liver Intestinal loop I Large intestine Lung yNotocliord CEsophagus Trachea Heart Pharynx Pericardium Vertebra Spinal medulla Uladder Wolffian duct Tongue Hind-brain Allantoic diverticulum Miii-braiu | Vitello-intestinal duct Fore -brain Fig. 60.— Further Development ok the Alimentary Canal, as seen jn a Human Embryo ABOUT Five Weeks Old (Diagrammatic). The tongue is well formed, the trachea and oesophagu.s are separated, the bronchi have commenced to branch ; the duodenal curve is well formed, and the caecum has appeared in the loop of the mid-gut. The cloaca is partially separated into genito-urinary and rectal portions. one on each side. The third is a median elevation, the tuberculum impar, which is situated immediately caudal to the conjoined ventral ends of the mandibular arches, 46 HUMAN EMBEYOLOGY. and the fourth, called the copula, formed by the conjoined ventral ends of the second arches, is separated from the tuberculum impar by the orifice of the thyreoid rudiment (Fig. 61). The two lateral elevations on the mandibular arches unite to form the greater part of the ventral or anterior two-thirds of the tongue, upon which all the papillae Mandibular rudiments / Tuberculum ^ \ . impar Foramen c tecum >/ Furcula Aperture of larynx Labio-dental sulcus Mandibular rudiment Tuberculum impar Hyoid rudiment Germ and subst. eburnea Foramen caecum Precervical sinus Aperture of larynx Fig. 61. — Schema showing stages in the development of the tongue. are developed. The tuberculum impar either disappears or it forms the median part of the anterior two-thirds of the organ. The posterior or dorsal third of the tongue, which lies in the ventral or anterior wall of the permanent pharynx, is formed from the copula of the second arches. It follows from what has been said Esophagus Rudiment of respiratory system \ Notochord ', I Medulla spinalis Bctoderm of embryo Liver diverticulum branching in septum transversura f Stomach Dorsal pancreas rudiment Ventral pancreas rudiment "k^ Peritoneal part of coelum ,V Csecum Peritoneal part of ,' coelum Wolffian duct Rectum -f Tail gut >^ Genito-urinary ^ r^ chamber Cloacal membrane Allantoic diverticulum Rathke's pouch Ectoderm of amnion Mesoderm of amnion Pericardium Umbilical cord Placental mesoderm V oik -sac eptum transversum Fig. 62. — Schema showing further stages in the development of the diverticula from the jiriniitive gut and modifications of the mid-gut and tlie mid-gut regions. Tlie Ix-art is not .shown. (After Mall, modified.) that the commencement of the thyreoid rudiment, which persists in the adult as the foramen ctecum of the tongue, must lie at the junction of the dorsal third with the ventral two-thirds. In many cases it appears to lie in the dorsal end of the ventral two-thirds, a position which may be associated with the fact that, in some cases, the rudiment of the thyreoid passes through the substance of the tuberculum THE PRIMITIVE ALIMENTARY CANAL. 47 impar anil not from l)etween the tuberculum impar and the ventral ends of the hyoid arches. Derivative of the Dorsal Wall (Seeesel's Pouch). — The dorsal diverticulum from the cranial end of the fore-gut, to wliicli tlie al)ove term is applied, enters the Ijase of the occipital region of the primitive head. The ultimate fate of the pouch is unknown in the huuum sul»ject, hut it has been suggested that it is represented by a depression in the mucous membrane of the cranial part of the pharynx, close to the pharyngeal tonsil, which -is known as the pharyngeal bursa. The reader who has followed this description will have noted that from the cranial portion of the fore-gut are formed the caudal or inferior part of the mouth (with the exception of the lips, teeth, and gums), the pharynx, the thyreoid gland, the thymus, the parathyreoids, the respiratory organs, and the cesophagus. 'J'he more caudally situated portion of the fore-gut is differentiated into the stomach and the fiist and second parts of the duodenum. The stomach is formed from the part of the fore-gut immediately adjacent to Rudiiii<>nt of thyreoid gland Trachea Notochord \ \ Qisophagus Medulla spinalis Ectoderm of e-.«bryo Foramen ca-cum Stomach Pancreas rudiment / Peritoneum Cerebellar part of hind-brai Hypophysis . Mid-brain Mesoderm of amnion Ectoderm of amnion Ductus deferens rinary bladder Cerebral hemisphere Proctodwuin Genito-urinary chamber Allantoic diverticulum Chorion Mandibular arch Pericardium j Liver diverticulum Mesoderm of placenta I Yolk-sac Diverticulum of peritoneum Fig. 63. — Schema showing complete separation of cloaca into dorsal and ventral parts and the temporary ventral hernia of a portion of the gut through the umbilical orifice. The heart is not shown. (After Mall, modified.) the oesophagus, and the duodenum from the more caudally placed portion, which is directly continuous with the mid-gut. The Liver and Pancreas. — When the embryo is about three weeks old and has attained a length of 2*5 mm. a ventral diverticulum appears in the ventral wall of the duodenal part of the fore-gut, and when the age of the embryo is about four weeks and its length increased to aliout 4 mm. a diverticulum is formed in the dorsal wall a little nearer the cranial end. The ventral pouch is the rudiment of the liver, the flail bladder, the hile-ducts, and a portion of the pancreas, and the remainder of tlie pancreas is formed from the dorsal diverticulum (Figs. 57, 62, 63). The Derivatives of the Mid-Gut.— The mid-gut is tbat part of the primitive alimentary tract which lies between the more definitely enclosed fore-gut and hind-gut, and it is in free communication with the yolk-sac by the vitello-intestinal duct. It is transformed into the greater part of the small intestine. The Derivatives of the Hind-Gut. — The parts formed from the hind-gut are: — (1) Tlie terminal part of the ileum; (2) the whole of the large intestine, except a small portion of the anal canal ; (3) the urachus, the urinary bladder, the urethra in the female, and the greater part of the urethra in the male.^ 1 T. B. Johnston, Jcurn. o/Anat., Oct. 191.3 ; H. v. Berenberg-Gossler, Anat., Heft. 1913. 48 HUMAN EMBEYOLOGY. As development proceeds the mid-gut and the cephahc (anterior) part of the liind-gut form a U-shaped tube which possesses a cranial (anterior) and a caudal (posterior) limb, and a ventral extremity which is connected with the yolk-sac by a narrowed and elongated canal, the vitello-intestinal duct (Fig. 57). Upon the caudal hmb of the loop, about the middle of its dorso-ventral height, an enlargement appears wMch is the rudiment of the caecum and vermiform process of the adult. After this rudiment has formed the caudal limb of the loop under- goes rotation, being carried first to the left, then cranially, and finally to the right. As it is carried to the right it crosses the cranial (later ventral) aspect of the cranial hmb of the loop, and when the rotation is completed the regions of the jejunum and ileum, the csecum, the ascending and the transverse colon are defined. After the rotation has occurred the tubular intestine formed from the mid-gut and the anterior part of the hind-gut, undergoes rapid elongation and is thrown into a number of coils. When the embryo has attained the length of 10 mm., and is a little over a month old, the greater portion of the coiled gut passes through the umbihcal orifice into an expansion of the coelom formed in the proximal part of the umbihcal cord (see fj. 47) (Fig. 63), which has replaced the allantoic or body-stalk as the medium by wMch the embryo is attached to the chorion. The herniated coils remain in the root of the umbilical cord until the embryo is about 40 mm. long, and about ten weeks old, when they return to the abdomen, and the coelomic space in the umbihcal cord disappears. The Derivatives of the Posterior Part of the Hind-Gut. — When the caudal portion of the liind-gut is first enclosed its terminal extremity and its ventral wall are bounded by the caudal portion of the primitive streak, which is bent ventrally during the folding -off of the embryo. The terminal part of this portion of the gut becomes expanded, forming a chamber called the entodermal cloaca, into the ventral parts of which the ducts of the primitive kidneys, the pronephric or Wolffian ducts, open, one on each side. The ventral part of the cephahc end of the cloaca is continuous with the allantoic diverticulum, and the dorsal part with a tubular portion of gut which forms the descending and possibly also the iliac and pelvic portions of the colon. As the temporary tail is formed and projected first caudally and then ventrally, by the growth energy of the nodal point situated at the caudal end of the neural tube, a diverticulum of the caudal end of the dorsal part of the cloaca is prolonged into it, forming the tail gut. This soon becomes shut off from the cloaca. It entirely disajjjjears before the temporary tail is absorbed into the caudal end of the body (Figs. 57, 62, 63). At a later period the cloaca itself is separated into a dorsal part, the rectum, and a ventral jjart, the urino-genital chamber, by the formation of a septum, which commences in the angle between the allantoic diverticulum and the ventral wall of the cloaca, and is prolonged caudally till it reaches and fuses with the internal surface of the cloacal membrane, which thus becomes separated into urino-genital and anal portions, both of which disappear about the eighth week. In both sexes the urino-genital section of the cloaca is separable into three parts : (1) a cranial part, which is converted into the urachus or middle umbihcal ligament; (2) an intermediate part, which becomes the urinary bladder; and (Z) a caudal part, which, in the female, is transformed into the urethra and the vestibule of the vagina, whilst in the male it is developed into the urethra. Derivatives of the Stomatodseum. — When the stomatodeeum is first definitely established, it is bounded cranially (anteriorly) by the caudal surface of the ventrally bent terminal part of the head, caudally by the conjoined ventral ends of the mandilmlar arches, and laterally by the dorsal parts of the mandibular arches, and the maxillary processes, which grow ventrally from the dorsal parts of the mandibular arches. The space is open ventrally, and it is closed dorsally by the bucco-pharyngeal membrane, which separates it from the fore-gut (Fig. 55). THE STOMATODtEUM 49 Prosencephalon Globular proceaa Olfactory pit StomaUxlienm Fig. 64. — Anteriok View of BotrNDAtuEs of Stomatod.«um befoke Completion of Primi- tive Upper Lip. The bucco-pliaryngtal membrane disappears about the third week, and about the twL-nty-first day a divt-rticuhim from the stomatod.neum is projected into the caudal surface of the liead, from the point where that surface originally joined the dorsal end of the external surface of the bucco-pharyngeal membrane. The diver- ticulum is Bathke's pouch. The cranial extremity of thu pouch comes into relation with the hypophyseal diverticulum from the Hoor of the third ventricle, and dilates. The stalk which connects the dilated terminal part of the diverticulum with the stomatodajum disappears, and the terminal vesicle becomes the anterior lobe of the hypophvsis (O.T. pituitary body) (Figs. 57, 62, 63). The Separation of the Stomatodaeum into Nose and Mouth. — In the cephalic boundary of the stomatodseal space lies the ventral end of the head, which is called the fronto-nasal process. In the fronto-nasal process, on each side of the median plane, is situated a shallow pit, the olfactory pit, and by the pits the process is divided into a median part, the median nasal process, and two lateral parts, the lateral nasal processes. Further, the margin of the median process is divided by a median cleft into right and left globular processes (Fig. 64). The orifices of the olfactory pits are directed laterally, therefore the lateral nasal processes lie dorsal to the median nasal process in the cranial boundary of the stomatodffial space, and as their margins increase in height the pits deepen (Fig. 69). At this period the cranial boundary of the stomatodaeum is divided by the median sulcus and the olfactory pits into four projections — the two globular processes, each of which hes between the median sulcus and an olfactory pit, and the two lateral nasal processes, which form the dorso-lateral borders of the olfactory pits. The lateral boundaries are formed by the maxillary processes and the dorsal parts of the mandibular bars, and the caudal boundary is formed by the medi- ally turned and conjoined ventral parts of the mandibular bars. Immediately cranial to the maxillary process, on each side, is the projecting eye ; and leading from it, between the maxillary process and the lateral nasal process, is the naso-lacrimal sulcus. As growth proceeds and each maxil- lary process grows ventrally, its ex- tremity fuses with the caudal or pos- terior border of the lateral nasal process, and then, carrying the lateral nasal process with it, it fusas with the globular process of the same side. After tlie fusion of the maxillary processes, and the posterior or caudal borders of the lateral nasal processes, with the globular processes has occurred, the olfactory pits are completely separated, for a time, from the stomatodagum^ and they lie in the ledge which now forms the cranial boundary of the stomato- daeum. This ledge consists of the two globular processes, fused into a single mass, and the two maxillary processes, the caudal or posterior ^ edges of the lateral nasal ' Inferior in erect posture. , - Cerebral hemisphere -Eye -Lens — Lateral nasal process -Maxillary process -Mandibular arch -Hyoid arch -Third arch —Pericardial region Fio. 65. — Schema of Anterior View of the Head OF A Human Embryo showing the Co.mpletion OF THE Primitive Upper Lip. 50 HUMAN EMBEYOLOGY. Anterior nasal orifice \ Globular process processes beintr shut off from the margin of the ledge by the maxillary processes (Fig. 65). After the ledge is completed the dorsal ends ot the oliactory pits are separated from the stomatodteum by a thin membrane, but this soon disappears, and the pits open again into the stouiatodseal space, through apertures which are called the primitive choanse. After the formation of the primitive choanse a ledge grows from the medial surface of each maxillary process towards the median plane, caudal to the choanse. These ledges, the palatine processes, meet and fuse during the third month of foetal life, the fusion commencing ventrally and being completed dorsally in the region of the uvula. As the ledges meet and fuse, the stomatodseum is separated into a cranial and a caudal portion. The cranial part is the nasal cavity ; it is soon divided into two lateral halves by a septum which passes caudally from the base of the cranium. The caudal portion of the stomatodseum blends with the ventral part of the primitive pharynx and it forms the vestibule of the mouth and its derivatives, and the gums and teeth. The details of the process by which the primitive lips are separated into the permanent lips, and the gums are defined, are described in the section dealing with the digestive system. The Derivative of the Proctodaeum. Embryo about 2^ months old (His). The lips _The proctodeum is a surface depression are separated from the gums, and the line of the i • i •- • • j. ^i ^ j.- i- common dental germ is visible in the latter. The ^hich OWCS its OrigUl to the clcvatlOn ot palatine processes are growing inwards from the the SUrfaCC rOUnd the margin of the anal maxillary processes. membrane. It forms the lowest portion of the pars analis recti of the adult. Urino-genital System. — The formation of the internal parts of the urino-genital system from the intermediate cell tract, the urino-genital chamber, and the differentiation of the external genitals in the region of the cloacal membrane are described in the account of the urino-genital system. The development of the auditory organ is so intimately associated with the development of the pharyngeal portion of the primitive gut that a short considera- tion of the chief phenomena may with advantage be introduced here ; but for the details of the development of the internal, middle, and external portions of the ear the student must refer to the account of the development given in association with the description of the auditory organ. Palatine process Fig. 66. — Portion of Hypophyseal depression THE Head of a Human THE INTERNAL EAR, THE TYMPANUM AND AUDITORY TUBE, AND THE EXTERNAL EAR. In tlie human subject, as in other mammals, the auditory organ consists of the internal ear or la})yrinth, the middle ear or tsrmpanum, with which is associated the auditory tube (O.T. Eustachian) ; and the external ear, which consists of the external acoustic meatus witli the auricle at its lateral end. Tlie internal ear itself consists of two parts — the cochlea, which is tlie true organ of hearing, and tlie vestibule and the three semicircular canals connected witli it, whicli are associated witli the recognition of alterations in the position of the head, and, therefore, with the recognition and maintenance of equilil)rium. The whole of the internal ear is lined with ectodermal-epithelium, the auditory epithelium, which is derived from the surface of the head of the embryo. It is recognisable in embryos of about 26 mm. (Fig. 67) as a thickened and slightly depressed plate of ectodermal cells which lies on the surface of the head, in the region of the hind-brain, dorsal to the second branchial cleft. As development THE INTERNAL EAR. 51 proceeds the plate is gradually iuvaginated iuto the substance of the head, and is Hind-brain Auditory ganglion Rudiment of otic vesicle Pa rax Hyoinand SoM First cephal Fig. 67. — Transverse Section of a Rat Embryo. Showing the relation of the paraxial niesoderni of the head to the lateral plates, the commencenieiit of the formation of the otic vesicles and hyoniandibular clefts, and the relation of the primitive heart to the pericardium and fore-gut. EC. Ectoderm. SoM. Somatic mesoderm, SpM. Splanchnic mesoderm. transformed into a pear-shaped vesicle, the otic vesicle, which remains for a time in communication with the ex- m^ terior by means of a short tubular stalk, the recessvs Idbyrinthi, which is subse- quently converted into the ductus endolymphaticus.^ After it is separated from the surface the otic vesicle alters its position, until its ventral end lies in close re- lation to the dorsal wall of the pharynx, and, at the same time, it undergoes alteration of shape. The ventral part of the vesicle grows towards the median plane, along the ventral wall of the hind-brain. It forms the cavity and the lining epithelium of the coch- lea ; l)ut it remains in con- nexion with the dorsal part by means of a narrow tulje, the canalis reuniens, and as it grows in length it becomes converted into a spiral tube. The portion of the dorsal section of the primitive Vesicle, which lies to the lateral side of the recessus labyrinthi, first ' See note 3, p. 79. 4a -Transverse Section thkoi- OF AN EmBRTO. H THE Head Showing the rudiments of the three parts of the ear and their relation to the hyomandibular cleft. BY. Blood-vessels. C. Cochlea. EM. Ext. acoustic meatus. ET. Auditory tube. HB. Hind-brain. HM. Hyomandibular cleft. N. Notochord. OV. Otic vesicle. P. Pharynx. RL. Reces.sus labyrinthi SC. Semicircular canal. T. Tympanum. expands and then becomes compressed 1 See note 3, p. 79. and 52 HUMAN EMBEYOLOGY. constricted into the form of three flat purse-hke diverticula which, by the partial obliteration of their cavities, become converted into the three semicircular canals (see Sense Organs). The more ventral part of the dorsal section of the vesicle is divided, by a constriction of its lateral wall, into a dorsal part, the utricle, which remains in connexion with the semicircular canals, and a ventral part, the saccule, which is united to the cochlea by the canalis reuniens. The apex of the constriction which separates the utricle from the saccule passes into the mouth of the ductus endo- lymphaticus, which is thus transformed into the Y-shaped canal which connects the utricle with the saccule. At a later period the closed extremity of the ductus endolymphaticus dilates and forms a small saccule, the saccus endolympliaticus. In the adult the saccus endolymphaticus lies in the posterior fossa of the skull, in relation with the posterior surface of the petrous part of the temporal bone and ex- ternal to the dura mater. The tympa- num and the auditory tube (O.T. Eustachian) are developed from the flrsl; visceral pouch. The ventral part of the pouch disappears at an early stage. The dorsal extremity expands and is converted into the cavity of the tympanum, whilst the stalk of connexion with the pharynx is gradually con- stricted off from its lateral to- wards its medial end, and is converted into the auditory tube. The constriction commences when the embryo has attained a length of about 20 mm., that is about the beginning of the eighth week, and is completed about the end of that week when the embryo is about 25 mm. long. After the auditory tube is defined it grows rapidly in length, and cartilage appears in its walls during the fourth month. As the tympanic cavity increases in size the auditory ossicles — stapes, incus, and malleus, which are differentiated from the dorsal ends of the cartilages of the first and second branchial arches, are invaginated into it. The membrana tjrmpani, which separates the tympanum from the external acoustic meatus, is formed from the separating membrane which intervenes between the first branchial pouch and the first cleft. It consists, therefore, of an external covering of ectoderm, an internal lining of entoderm, and an intervening layer, of fibrous tissue, derived from the mesoderm. The external ear is developed from the cavity and the boundaries of the first branchial cleft. The cavity of the cleft is transformed into the cavity of the external acoustic meatus, and on the mandibular and on the hyoid margins of the Fig. 69.- -FlGURES, MODIFIED FROM HiS, ILLUSTRATING THE FORMATION OF THE Pinna. 1. Tuberculum tragicura = Tragus. 2. ,, anterius helicis 3. ,, intermedium helicis 1-Heli.x. 4. Cauda helicis 5. Tuberculum anthelicis = Antihelix. 6. Tuberculum antitragicum=Anti- tragus. 7. Tuberculum lobulare = Lobule. HM. Hyomandibular cleft. OV. Otic vesicle. THE MEMBEANES AND APPENDAGES OF THE FCETUS. 53 cleft tliree eminences appear. From the eminences on the two arches, and the skin immediately posterior to the eminences on the hyoid arch, are formed the various parts of tlie auricle, but the exact part played by the individual eminences in the human subject is as yet a matter of some doul>t. THE PROTECTION AND NUTRITION OF THE EMBRYO DURING ITS INTRA-UTERINE EXISTENCE. Whilst it is passing down the uterine tube, and for a brief period after it enters the uterus, the zygote, or impregnated ovum, depends for its nutrition upon the yolk granules (deutoplasm) embedded in its cytoplasm, and upon the fluid medium surrounding it which is secreted by the walls of the uterine tube and the uterus. As the liuman ovum is very small, and as it contains but little deutoplasm, its nutrition is practically dependent, almost from the first, upon external sources of supply. The urgent necessity for the formation of adequate arrangements whereby the external sources may be utilised leads to the early establishment of an intimate connexion between the zygote and the mother, which is one of the characteristic features of the development of the human embryo. During the third week after fertilisation, as the embryo is beginning to be moulded from the embryonic region, and before the paraxial mesoderm commences to separate into mesodermal somites, a primitive heart and the rudiments of some well-defined blood-vessels are distinguishable in the embryo; but the details of the development of the vascular system and the establishment of the embryonic circulation cannot be well understood until the formation and structure of a group of closely associated extra-embryonic organs or appendages, derived from the zygote, has been considered. This group includes the chorion, the placenta, the amnion, the umbilical cord, and the yolk-sac. THE MEMBRANES AND APPENDAGES. The Chorion. — It has already been noted that when the zygote becomes a blastula it consists of three vesicles, a large vesicle enclosing two smaller vesicles and a mass of primary mesoderm (Fig. 29). The wall of the large vesicle is composed of trophoblast (trophoblastic ectoderm), and its inner surface is in direct contact with the primary mesoderm. A Uttle later a cavity, the extra-embryonic coelom, appears in the primary mesoderm, separating it into two layers, one lining the inner surface of the tropho- blast and the other covering the outer surfaces of the two inner vesicles (Figs. 70, 71). As soon as the extra-embryonic crelom is estabhshed the chorion is formed ; it consists of the trophoblast and its inner covering of mesoderm. In the meantime the trophoblast has differentiated into two layers, an inner cellular layer, and an outer plasmodial layer. In the plasmodial layer cell territories are not defined, and it consists, therefore, of nucleated protoplasm. The dilferentiation of the trophoblast into two layers occurs after the zygote is embedded in the mucous membrane of the uterus which is modified for its reception and which, after the modification has occurred, is called the decidua. As development proceeds the trophoblast increases in thickness and it invades the decidua. As this invasion occurs the plasmodial layer of the trophoblast becomes permeated with spaces which are continuous with the lumina of the maternal blood-vessels in the decidua, and are filled with maternal blood. By means of the spaces the plasmodial trophoblast is separated into branching processes which intervene between the blood-filled spaces. The processes are the primary chorionic villi, and they soon develop cellular interiors (Fig. 72). After a time the primary villi are invaded by the chorionic mesoderm, and are thus converted into the secondary chorionic villi, which become vascularised by the 54 HUMAN EMBEYOLOGY. Anterior end of npiiral fold _,/^~y«. .ria.sinoiUal trophoblast •• ..l^^^^r^ ._■- Cellular trophoblast Amnion cavity [blast -.- ilesoderm lining of tropho- -; — - Mesoderm of amnion - - Ectoderm of amnion i^ Allanloiu diverticulum ,'r of entoderm vesicle I'S' Body stalk mesoderm Extra-embryonic coelom Entoderm Mesoderm covering of entoderm vesicle eurenteric canal Cavity of entodermal vesicle Fig. 70. — Schema of Sagittal Section of Zygote along Line A. /' growth of foetal vessels into the foetal mesodermal cores. The secondary villi, therefore, consist of a mesodermal core covered by a layer of cellular trophoblast and a layer of plasmodium, the latter lying outside the former. Still later the secondary villi send out numer- ous branches into the blood spaces, and thus increase greatly in complexity (Figs. 75, 76, 77). As development progresses still further a part of the chorion is converted into the foetal portion of an organ called the placenta, and thus the chorion is divided into placental and non- placental regions. Upon the placental part the vilh con- tinue to increase, but they dis- appear entirely from the non- placental part, which is then called the chorion laeve (Fig. 77). The Amnion, the Body- Stalk (Allantoic Stalk), and the Umbilical Cord.— The amnion is formed from that portion of the wall of the larger of the two inner vesicles of the zygote, the ecto- mesodermal vesicle (p. 22), which does not take part in the formation of the embryo. It consists of ectoderm cells covered exter- nally by a layer of extra-em- bryonic mesoderm, and it is continuous with the margin of the embryonic area (Figs. 70, 71). The cavity of the ecto- mesodermal vesicle, enclosed between the amnion and the embryonic area, is the cavity of the amnion ; it is filled with fluid, which raises the amnion in the form of a cupola over the embryonic region (Fig. 70). The Body-Stalk (Allantoic Stalk).— It has been noted already that the mesoderm of the median part of the posterior or caudal portion of the amnion becomes Plasmodial trophoblast Neural groove Chorion ■' Cellular trophoblast \ I, Mesoderm lining of trophoblast Amnion cavity Extra-embrj'onic coslom Mesoderm of amnion Ectoderm of amnion Jlesoderm covering entoderm Entoderm Cavity of entodermal vesicle "' Fig. 71. Notochord -Schema of Transverse Section of Zygote along Line B (Fig. 31). Plasmodia! trophoblast Plasmodial trophoblast Cellular trophoblast' McsodiTHi Ectodi-rm of amnion Plasmodial trophoblast Cellular trophoblast "" Efl'erent vessel -- of villus Fused nii'soilemi , of chorion j/iCy - and amnion ^/ Ectoderm / of amnion «^ Afferent vessel of villus ,^ Fused mesoderm of ~t amnion and chorion il Ectoderm of amnion Fi'i. 72.— Schema of Three Stages in the formation of a Chorionic Villus. thickened. In the thickened strand lies the allantoic diverticulum of the entodermal vesicle (Fig. 70), whilst through it, on either side of the allantoic diverticulum, pass the umbilical arteries and veins, by means of which blood is conveyed between the embryo and the chorion. This segment of the wall of the amnion vesicle was termed by His the body-stalk. It takes no direct part in the formation of the embryo, and as it THE MEMBRANES AND APPENDAGES. 55 contains the rudinicntary allantoic diverticulum and represents the much uiore highly developed allantois of other forms, it would, perhaps, he hetter to term it the allantoic stalk. For the. ])resent purpose it is imi)ortant to note that the hlood- vessels which pass through the hody-stalk enter or leave the hody through the umbilical oritice, which is, at first, a relatively large aperture (Fig. 50). As the embryonic area is folded into the form of the embryo the amnion increases in extent, tilling more and more of the extra-embryonic coelom, and the embryo rises into the interior of its cavity. In other words, the walls of the amnion bulge ventrally round the cranial and caudal extremities and the lateral borders of The embryo (Figs. 75, 76, 77). As the distension of th<^ amnion still continues, the ventral bulging, round the margin of the umbilical orifice, l^ecomes more pro- nounced, the yolk-sac is forced farther and farther away from the embryo, the vitello-intcstinal duct is elongated, and it is surrounded by a hollow tul)e. The cavity of the tube is an elongated part of the extra-embryonic cadom, and its walls Afleix-nt vessf of villu: I'liisinoilial tioplioblasl Cellular Irophoblast Afferent veHSel of villus Mestxlenn . of villus Efferent vessel of villus Fig. 73. — Sch1';ma ov a Tkaxsvekse Section ok a Secondary Chokiomc Villds. A loop of tlie afferent vessel has been cut at two points. are formed by the amnion (Figs. 57, 62, 63) The caudal wall of the tube neces- sarily consists of the elongated body-stalk (allantoic stalk). As the distension of the amnion still continues, the walls of the tube are forced against the vitello- intestinal duct, and the amniotic mesoderm fuses with the mesoderm of the vitello-intestinal duct. When the fusion is completed, a solid cord, the umbilical cord, is formed (Figs. 77, 78, 80). It consists of an external covering of amniotic ectoderm, and a core of mesoderm in which lie the two umbilical arteries of the body-stalk, a single umbilical vein formed by the fusion of the two primitive veins, and the remains of the vitello-intestinal duct and the vitelline vessels. The proximal end of the umbilical cord is connected with the embryo ; the distal end is attached to the chorion, and in its neighbourhood lies the now relatively small vesicular yolk-sac (Fig. 62). As the amnion grows still larger, all that part of its outer surface which does not take part in the formation of the umbilical cord is ultimately pressed into contact with the inner surface of the chorion, with which it fuses, and the cavity of the extra-embryonic part of the coelom is obliterated (Fig. 78). The outer wall of the zygote now consists of the fused chorion and amnion, and it contains in its interior the amniotic cavity and the embryo, which is attached to the chorion by the umbilical cord. When it is first formed the umbilical cord is comparatively short, but, as the amniotic cavity increases, the cord elongates, until it attains a length of from 18 to 20 inches, a condition which allows the embryo to float freely in the fluid in the amniotic cavity, whilst its nutrition is provided for by the flow and return of blood, through the umbilical cord, to and from the placenta, where interchanges take place between the maternal and the fa?tal blood. The Yolk-Sac or Umbilical Vesicle. — When the embryonic area is folded into the form of the embryo, the entodermal vesicle is differentiated into three parts : (1) a part enclosed in the embryo, where it forms the primitive entodermal alimentary canal; (2) a part which lies external to the embryo in the extra- embryonic ctelom — this is the yolk-sac or umbilical vesicle ; (3) the third portion is the vitello-intestinal duct, which connects the primitive alimentary canal and the yolk-sac together (Figs. 40, 62). The walls and the cavity of the yolk sac are, therefore, continuous with the walls of the primitive alimentary canal, and the structural features of the two are identical, each consisting of an internal layer of entodermal cells and an external layer of splanchnic mesoderm. Free communication between the yolk-sac and the primitive alimentary canal 56 HUMAN EMBEYOLOGY. appears to exist in the human subject till the embryo is three weeks old and about 2 '5 mm. long. During the fourth week the vitello-intestinal duct is elongated into a relatively long narrow tube, which is lodged in the umbiUcal cord and the yolk-sac, which has become a relatively small vesicle, is placed between the outer surface of the amnion and the inner surface of the chorion, in the region of the placenta (Fig. 62). During the latter part of the fourth or the early part of the fifth week, when the embryo has attained a length of about 5 mm., the vitello- intestinal duct separates from the intestine and commences to undergo atrophy, but remnants of it may be found in the umbihcal cord up to the third month. The yolk-sac itself persists until birth, when it is, relatively, a very minute object which lies either between the amnion and the placenta or between the amnion and the chorion leeve. At a very early period, before the paraxial mesoderm has commenced to divide into mesodermal somites, a number of arteries, the primitive vitelline arteries, are distributed to the yolk-sac from the primitive arterial trunks of the embryo, the primitive aortas, and the blood is returned from the yolk-sac to the embryo by a pair of vitelline veins (Fig. 81). After a time the arteries are reduced to a single pair, and after the two primi- tive dorsal aortse have fused into a single trunk, the pair of vitelline arteries also becomes converted into a single trunk, which passes through the umbilical orifice along the vitello-intestinal duct to the yolk-sac (Fig. 83). The vitelline veins also pass through the umbihcal orifice on their way to the heart of the embryo, and they become connected together, in the interior of the body of the embryo, by transverse anastomoses, which are described in the account of the development of the vascular system. After the umbilical cord is formed, the extra-embryonic parts of the vitelline veins disappear, and can no longer be traced in the cord. The same fate overtakes the extra-embryonic and a portion of the intra-embryonic part of the vitelline artery, and the remainder of the artery persists as the superior mesenteric. THE PLACENTA. The placenta is an organ developed for the purpose of providing first the embryo and later the foetus with food and oxygen, and for removing the effete products produced by the metabolic processes which take place in the growing organism. It is formed partly from the zygote and partly from the mucous membrane of the uterus of the mother. In the placenta the blood-vessels of the embryo of the earlier stages and the foetus of the later stages and the blood of the mother are brought into close relationship with one another, so that free interchanges may readily take place between the two blood streams ; and the modifications and transformations of the uterine mucous membrane and the chorion of the zygote, by which this intimate relationship is attained, constitute the phenomena of the development of the placenta. The details of the develojjment of the human zygote for the first ten or twelve days after the fertilisation of the ovum are not known, but the knowledge of what hapi^ens in other mammals justifies the belief that during that time the zygote is formed, in the ovarian, or the middle part of the uterine tube, by the union of a spermatozoon with the mature ovum. During the first ten to fourteen days after its formation it passes along the uterine tube, towards the uterus, whilst, at the same time, it undergoes the divisions which convert it into a morula. The Formation of the Placenta. — Before the zygote reaches the uterus the mucous membrane which hues the cavity of that organ undergoes changes, in preparation for its reception and retention, and when the changes are completed the modified mucous membrane is known as the uterine decidua. The changes which take jjlace are, for the most part, hypertrophic in character ; the vascularity of the mucous membrane is iucreased, mainly by the dilatation of its capillaries; the tubular glands of the membrane are elongated, they become THE PLACENTA. 57 tortuous, and dilatations form in their walls a short distance from their outer closed extremities. At the same time the interglandular tissue increases in amount, and as a result of the various processes the decidua is thicker, softer, more spongy, and more vascular than the mucous membrane from which it was evolved. Partly on account of the dilatation of the deep part of the glands and partly on account of ditterences in texture of the internal as contrasted with the external part of the decidua, the membrane may be looked upon as consisting of three layers. (1) An internal layer, next the cavity, the stratum compactum. (2; An intermediate layer, the stratum spongiosum, formed largely by the dilated parts of the gli^tids. (3) An external layer, the unchanged layer, in which lie the com- parativf iy unaltered outer ends of the glands. "VVnen the zygote, in the morula stage, reaches the uterus, from the tenth to ♦■lie fourteenth day, -it acts as a parasite, it eats its way through the epithelium on the surface of the decidua, and implants itself in the stratum compactum. The zygote may penetrate the decidua at any point of the wall of the uterine cavity, but it usually enters at some point of the dorsal or the ventral wall. The entrance gener- ally takes place between the mouths of adjacent glands, which are pushed aside, and the zygote be- comes at once surrounded by the interglandular tissue of the stratum com- pactum of the decidua. The aperture through which it passes may be closed by a fibrinous plug or its margins may con- verge rapidly and fuse together. The portion of the de- cidua in which the zygote is embedded is thicker than the other parts of the membrane, and it is separ- ated by the zygote into an internal part, the decidua capsularis, and an external part, the decidua basalis. The junction of the decidua capsularis with the decidua basalis is the decidua marginalis, and the remainder of the decidua, by far the larger portion, is the decidua vera. As soon as the zygote becomes embedded in the decidua its trophoblast under- goes rapid proliferation. The superficial part of the growing trophoblast becomes converted into a mass of nucleated protoplasm, the plasmodial or syncytial layer, but the inner part remains more or less distinctly cellular. The plasmodial portion of the trophoblast invades and destroys the surrounding maternal tissue, and at the same time spaces appear in its substance. As the Plasmodium destroys the walls of the dilated maternal blood-vessels, channels are made through which the maternal blood flows into the spaces in the plasmodium, and thus maternal blood begins to circulate in the tropholdast of the zygote. In the meantime the extra-embryonic ccelom has appeared in the primary mesoderm of the zygote, and the outer layer of the mesoderm has associated itself with the trophoblast to form the chorion. The spaces in the plasmodium enlarge rapidly after the maternal blood Cavity cervix ute Fio. 74. — ScHEM.\ OF A Frontal Section of the Utebcs, showing the various parts of the decidua ami a zygote embedded in the decidua. 58 HUMAN EMBKYOLOGY. begins to circulate within them and the plasmodium becomes divided into three series of Spongy layei I Placental area Intervillous space ; Unchanged layer of decidua Maternal blood-vessel '.^ *<-^ Stratum spongiosum Muscular wall of uterus Uterine tube Mesoderm linin trophobla: Trophoblas^ Unchanged part o; glan Dilated part glan Cavity of uterus Secondary villus Amnion cavity Amnion Embryonic ar parts. (1) The parts which lie between adjacent blood spaces, the primary chorionic vUli. (2) The parts which lie in con- tact with the mesoderm of the chorion, and which form with the mesoderm the chorion plate. (3) The parts which cover the maternal tissues and form the outer boun- daries of the blood spaces, the basal layer. The blood spaces themselves are called the in- tervillous spaces (Figs. 76, 79). After a time each primary villus differenti- and plasmodial periphery, and thereafter the villi are invaded Unchanged layer Maternal blood-vessels '» Placental area j Body-stalk Allantoic diverti- -culum Primitive streak Neurenteric canal Cavity of entoderm sac Extra-embryonic coeloin Decidua capsularis Decidua vera Spongy layer Fig. 75. — Schema of a Section of a Pregnant Uterus after the formation OF THE Intervillous Spaces. ates into a cellular core by the mesoderm of the chorion and are thus converted into secondary vUli (Fig. 76). The first-formed villi are non-vascular, but by the time the secondary villi have developed the um- bilical arteries have grown through the body-stalk (allantoic stalk) into the meso- derm of the chorion, and branches from them enter the meso- dermal cores of the vilU, which thus be- come vascular. When the second- ary villi are fully developed each con- sists of a vascular mesodermal core con- tinuous with the mesoderm of the chorion. The meso- dermal core is covered Troplioblast- of chorion Amnion" Amnion, cavity Trophoblast • Decidua, capsularis Decidua vera" Spongy layer Extra-em bryuiiiC ccfelom Muscular wall of uten Intervillous spaces Absorbing chorionic villi rerine tube Body-stalk Hind-gut Allantoic diverticulum Pericardium Bucco- pharyngeal membrane Yolk-sac Fig. 76. — Schema of a Frontal Section (;f a Pregnant Uterus at the I'EHiou OF THE FORMATION OF THE EMBRYO. Note extension of amnion as contrasted ^sith stage .shown in Fig. 75. THE PLACENTA. 59 by a layer of cellular trophoblast, Langhati's layer, vviiich lies next the mesoderm, and a layer of plasmodium external to the cellular layer. The proximal end of each villus is continuous with the chorion plate of the interN-illous spaces, formed by tlie chorion, and the distal extremity is connected with the plasmodial basal layer of the trophoblast, which forms the outer boundary of the intervillous spaces and which is fused with the maternal decidual tissue. After a time branches are projected from the sides of the secondary villi into the intervillous spaces. In this way two sets of secondary villi are differentiated, (1) the anchoring villi (Fig. 79), which cross from the chorion to the Yolk-sac Secondary villuH rViiclioriiiK villus ^latfrnal artery Umbilical cord - Temporarily herniated small intestine Uterine tube Unchanged part of uterine gland [JUilated part of uterine ^laiid eeidua capsularis Decidua capsulari rophoblast esoderm lining of chorion Iseve ~THeso^' ^[^/■"Amnion cavity mt-^ P^^M -?^ ^1 ^ . cord '^^,^ \inm ^^m ^W >4-?^ Compact layer of decidua IT m^ ter"^ <-- Troplioblast uterine tube . ^^^Jf 1 ^^ ' m^ 1 l^Rn^ Fused mesoderm \H^^^ ^of chorion and 1^ ««""amnion Vitello- intestinal- duct JPI^H kSHk -^ J i f'"' \ wHtM Ectoderm of mk. .JL r.^ ■^^ jl ^ L. . -^ I MB J Spongy layer Cloaca Rectum - Small intestine / Amuioi; cavity Liver Stomach" Trachea Pericardium Fig. 78. — Schema of a Section op a Pregnant Uterus after Fusion of Amnion and Chorion. part in the formation of the so-called foetal portion of the placenta, the maternal part of that organ being formed by the decidua basalis. The placenta, therefore, is formed partly by the zygote and partly by maternal tissues, but the interchanges between the foetal and the maternal blood take place in the substance of the zygote through the trophoblast which covers the surfaces of the villi. As the growth of the embryo and the distension of the amnion continue, the outer surface of the amnion is gradually forced against the inner surface of the chorion, with which it fuses. When this fusion is completed the extra- embryonic coelom is obliterated and the zygote contains only one extra-embryonic cavity, the amniotic cavity, in which the foetus floats in the amnion fluid (Fig. 78). At this period the amnion cavity is bounded by a wall formed by the fused amnion chorion and decidua. In the meantime the chorion has differentiated into the chorion Iseve, fused with the decidua capsularis, and the chorion frondosum, fused witli the decidua basilis. As the distension of the amnion proceeds to a still greater extent, the part of the wall of the cavity formed by the fused amnion chorion Iseve and the decidua capsularis projects more and more into the cavity THE PLACENTA. 61 of the uterus, until it is forced against the surrounding wall of the uterine cavity, where it fuses with the decidua vera, and thus the cavity of the uterus is obliterated. This fusion takes place towards the end of the second month, and as soon as it has occurred the discoid mass of placental tissue is continuous at its margin with the fused amnion, chorion, and decidua vera (Fig. 78). After the second month the iVetus lies in the amnion cavity, which is bounded by the fused chorion and uterine wall, except at the lower end of the uterus, where, over the oriticium internum, the cavity of the body of the uterus communicates with the cavity of the neck of the uterus; there the amniotic cavity is bounded by a mem- brane formed by the fused anmion chorion heve and the decidua capsularis only. And at the end of pregnancy this i)ortion of the membrane is ruptured by the increased pressure of the amnion Huid ]»roduced by the contraction of the muscular wall of the uterus (-Fig. 88). Uiii-h.-iiiKeil part of uterine gland Muscular wall of utefiis | Matf rnal vein Matj'Tiial artery Dt'ciilua l)asilis— uncliaiigHii part .Viiclinrinj; villus l>eciiiua-str.ituiu spoiiijiosnni Unchanged part of uterine glaml ailiilical gut • n.i llUlbili- ilis impar bllical srt«ry Umbilical cord Unchanged layer I I I I Ectoderm of amnion Spongy layer I | Fused mesoderm of amnion and chorion Comi)act layei' Trophoblast of chorion Fui. 79. — Schema (1f Stkdctuke of Completed Placenta. Completion of the Placenta. — It has already been stated that each secondary villus consists of a vascular mesodermal core covered by a cellular and a plasmodial layer of trophoblast, the latter lying next the maternal blood in the intervillous spaces. As development proceeds and the intervillous spaces become larger, the villi become longer and more complicated, and at the same time the cellular layer of the trophoblast largely disappears, until in the majority of the villi the plasmodial layer alone covers the vascular mesodermal core. In still later stages, degenerative changes occur not only in the villi, but also in the chorionic plate of the intervillous spaces and in the basal trophoblast which closes the spaces externally. One of the results of the degenerative pro- cesses is the deposit of fibrinoid material in the place originally occupied by the trophoblast, the object of this process is still unknown ; another is the adhesion of the fibrinous layers on the surfaces of adjacent villi, and the fusion of the villi thus connected into masses of intermingled fibrinous and vascular tissue. When the chorionic part of the placenta is completed it consists of (1) the 62 HUMAN EMBRYOLOGY. chorion plate closing the intervillous spaces internally ; (2) the villi ; (3) the intervillous spaces; and (4) the basal layer of the trophoblast, which closes the intervillous spaces externally, and is perforated by the maternal vessels passing to and from the spaces. The maternal portion of the completed placenta consists from within outwards of (1) the basal layer of the decidua ; (2) the remains of the spongy layer of the decidua ; and (3) the unchanged layer. Placenta Spongy layer Umbilical cord Betoderm of amnion Fused rpesoderni of amnion and chorion Trophoblast Spongy layer, of decidua Muscular wall of uterus Compact layer, of decidua Uterine tube — Amnion cavity Spongy layer of decidua Fused mesoderm of amnion and chorion Fig. 80. — Schema ov Pregnant Uterus immediately after Birth of the Child, showing commencing separation of the placenta. Part of the umbilical cord is shown in section and part in surface view. The blue streaks in the former part indicate the position occupied by the vitello-intestinal duct in earlier stages. The basal layer of the decidua is the remains of the compact part of the decidua basalis of earher stages. It is fused internally with the basal plate of the tropho- blast, and is continuous externally with the spongy layer. The spongy layer con- sists of a series of cleft-like spaces. These spaces are the compressed remains of the earlier dilated portions of the glands of the stratum spongiosum, from which the epithelial lining has, to a great extent, disappeared. The spongy layer is con- tinuous externally with the unchanged layer, in which lie the unaltered outer parts of the glands and the intervening interglandular tissue. THE PRIMITIVE VASCULAR SYSTEM. 63 The maternal hlijod-vessels pass from the muscular wall of the uterus into the sul)- mucous tissue, and tiience into the placenta, where they traverse the maternal portion and the hasiil plate of the decidua and open into the intervillous spaces. The arteries usually open on or near the septa and the veins in the intermediate areas. In addition, however, to the constituent parts already described, the chorionic part of the placenta contains some strands of maternal tissue, and in the maternal part there are portions of trophohlast. The parts of the decitlua found in the chorionic part of the placenta are a series of fibrous strantls, the remains of parts of the stratum compactum which were not destroyed by the trophoblastic invasion. They are continuous externally with fibrous strands of the maternal part of the placenta, and serve to separate the placenta into a series of lol»es, from 15 to 20 in number. The portions of trophoblast met with in the maternal part of the placenta are variable pieces of plasmodium which appear to have wandered from the general mass. They may lie found in any of the strata of the maternal part, and even in the submucous tissue. At the enil of pregnancy, when intra-uterine life terminates, the fused amnion chorion and decidua capsularis are ruptured, in the region of the internal orifice of the uterus, and the amniotic fiuid is expelled through the vagina. Next the foetus is extruded, and as soon as it is born it becomes a child. After the child is born it remains attached to the placenta by the umbilical cojd (Fig. 80), which is usually hgatured in two places and then divided, between the ligatures, by a medical man or an attendant. Afterwards the placenta is expelled from the uterus. Detachment of the placenta is probably caused by contraction of the muscular substance of the uterus, and it takes place by rupture of the strands of the spongy layer of the decidua (Fig. 80). As the detached placenta is expelled the decidua vera is torn through along the line of the spongy layer, and the fused amnion and chorion Iseve and the inner part of the decidua vera, which are attached to the margin of the placenta and which constitute the membranes, are expelled with it. At birth the placenta weighs about 500 grm., it has a diameter of about 16 to 20 cm., and is about 3 cm. thick. Its inner surface is covered with the amnion which fused with the chorion towards the end of the second month of pregnancy. Its outer surface is rough, it is formed by the remains of the spongy layer of the decidua, and is di\dded into a number of areas by a series of fissures which correspond in position with the septa by which the organ is divided into lobes. THE PRIMITIVE VASCULAR SYSTEM AND THE FCETAL CIRCULATION. As the zygote travels along the uterine tube, from the ovarian towards the uterine end, it exists either upon the yolk granules derived from the ovum or upon substances absorbed from the fluids by which it is surrounded. After it enters the uterus it must depend, for a time, upon the same sources of nutriment, but as it penetrates the decidua it is probable that the cells of the trophoblast actually devour the cells of the decidua which they invade. This source of food is only sufficient for a short period, whilst the zygote remains relativel}' small, and substances absorbed by its surface cells can be transmitted easily to all parts. Whilst the period exists, however, not only are the decidual tissues utihsed as a food-supply, but fluids are absorbed from them and transmitted into the interior of the zygote to fill the expanding cavities of the amnion and the ccelom. In all probal)ility the fluids passed into the zygote contain nutritive materials which suffice for the requirements of the embryonic and non-embryonic parts of the zygote so long as both consist of comparatively thin layers of cells, Itut when the embryonic area increases in thickness, and begins to be moulded into the embryo, its association with adjacent fluids becomes less intimate, and as the development of its various parts progresses, a supply of food and oxygen is required which is greater than can be provided by osmosis from the adjacent fluid media. Thus an imperative necessity arises for a method of food-supply adequate to the in- creasing requirements upon which the continued development and growth depend. 64 . HUMAN EMBRYOLOGY. To meet this necessity the blood vascular system is formed. The system is essentially an irrigation system. In its earliest stages it consists of a series of vessels, the blood-vessels, all of which contain a corpuscle-laden fluid, called blood. The blood is kept circulating, in the early stages, by the rhythmical contraction of the walls of the vessels, but, after a short time, parts of the vessels are developed into a muscular organ called the heart. After the heart is estabhshed the continuance of the circulation of the blood depends upon the regular con- tractions of the nmscular substance of its walls. The corpuscular portions of the blood and the walls of the blood-vessels are formed from the cells of the zygote, but it is obvious, in the early stages at all events, that the fluid portion of the blood must be obtained from the mother. It is necessary, therefore, both for this purpose and for the facihtation of interchanges between the foetal and maternal blood streams, that the fcetal blood-vessels should be brought into close association with the maternal blood at an early period. It is for this purpose, among others, that large spaces appear in the trophoblast ; that the spaces become filled with blood from maternal vessels which have been opened up by the destructive action of the trophoblast cells ; and that the spaces are afterwards invaded by the chorionis villi, which carry in their interiors branches of the blood-vessels of the embryo. As soon as the intimate relationship between the chorionic vilh and the maternal blood is established fluids can readily pass from the^ maternal to the foetal vessels, and there can be no doubt that both food and oxygen pass from the maternal to the fcetal blood through and by the agency of the trophoblastic epithelium, whilst, at the same time, waste products of foetal metabolism pass from the fcetal to the maternal blood. The germs of the vascular system are a series of cells arranged in strands which constitute, collectively, the angioblast. They appear between the entodermal and the mesodermal layers of the wall of the yolk-sac, and, therefore, entirely outside the embryo ; but it is not certain whether they are derived from the mesoderm or from the entoderm. Origin of Blood Corpuscles. — After a time the angioblast separates into two parts, (1) the peripheral cells of the strands which form the endothelial walls of the primitive blood-vessels, and (2) the central cells which become the primitive blood corpuscles or mesamoeboids (Minot). The mesamoeboids are colourless cells with large nuclei and a relatively small amount of protoplasm ; from them are formed, either by transformation or division, (1) the erythrocytes, which are coloured blood corpuscles, and (2) nucleated colourless corpuscles. The erythrocytes are nucleated cells with a homogeneous protoplasm which contains the substance, called haemoglobin, upon which the yellowish-red colour of the cells depends, and from them are derived the fully developed red corpuscles. The primitive erythrocytes, the ichthyoid cells of Minot, are transitory structures in mammals, but they are the permanent red blood cells of the ichthyopsida (fishes and amphibia). They are succeeded by the sauroid blood cells (Minot), which represent the permanent corpuscles of reptiles and birds, and which are distinguish- able from the ichthyoid cells by their smaller size and more deeply-staining nuclei. The sauroid blood cells are replaced by the blood plastids, which are young non- nucleated red corpuscles. According to some observers the blood plastids are sauroid cells which have lost their nuclei, whilst other investigators believe the blood plastids to be the nuclei of sauroid cells. Whatever their origin, they become converted into permanent red blood corpuscles by transformation from the spherical to a cup-shaped and later to a biconcave form. The young red blood cells are therefore the ichthyoid cells, those progressively older are sauroid cells, blood plastids, and blood corpuscles. The colourless, nucleated corpuscles — white blood corpuscles — are much less numerous than the coloured corpuscles in the adult blood. They appear to be derived from the mesamoeboids, though it is possible that they are also formed by ordinary mesoderm cells, and as regards tho.'^e formed from mesamoeboids it is not certain whether a mesamoeboid cell can by division produce both erythrocytes and white corpuscles, or whether it must produce one or the other. (See note 5, p. 79.) THE PKIMITIVE VASCULAR SYSTEM 65 Dorsal intorscg^nental branch(>8 Dorsal aorta- 1st aortii' arcli Common trunk form by umbilical and yolk-sac veins ena umbilicalis mpar Umbilical arteries Fl( Vitelline arteries 81. — Schema of Circulation of an Embkyo, 1"35 mm. i.dng, with Six SoMiTKS. (After Felix, moilitied.) The primitive mesamceboids ate formed in the wall of the yolk-sac, and there some of them produce erythrocytes ; many, however, migrate into the embryo, where some of them take part in the formation of the walls of the em- bryonic blood-vessels, and others .liecome enclosed in the liver, the lymph glands, and the l)0ue marrow, -where they become foci for the formation of blood corpuscles. During the hrst two months the primitive forms of red lilood cells predominate. In the second month the sauroid cells in- crease considerably in number, and from the third month the blood plastids become more and more numerous, until, at the eighth month (Minot), the majority of the l)lood cells are blood plastids underfjoing conver- sion into blood cor- puscles. At this time the colourless cells are present in a very distinct minority. Formation of the Primitive Blood Vascular System of the Embryo. — Tlie earliest stage of the formation of the heart and Ijlood- vessels in the human subject are not known, but, judging by what occurs in other mammals, it is probable that the first- lormed vessels appear in the splanchnic mesoderm before the embryonic area begins to fold. It is presumed that they are formed by angioblastic cells which have migrated into the embryonic area from the walls of the yolk-sac. From their seat of origin they extend towards the caudal end of the embryonic area, one on each side of the notochord, and from the caudal end of the embryonic region they pass along the body-stalk into the chorion. (See note 5, p. 79.) As the cephalic Dor«il intersegmental branches end of the CmbryOnic Dprsalaort* ^rca is foldcd, tO enclose the fore-gut, the corresponding parts of the primi- tive arteries are bent into a c-shaped form. The ventral limb of the c, which lies in the dorsal wall of the pericardium and the ventral wall of the fore-gut, is the primi- tive ventral aorta. The bend of the c is the first aortic arch, which passes along the lateral margin of the bucco-pharyngeal meml)rane. The dorsal hmb of the c is the cranial part of the primitive dorsal aorta. The primitive dorsal aorta passes posteriorly into the tail and gives off in the region of the tail fold the primitive umbilical arteiy, which runs along the body-stalk to the chorion. The caudal parts of the primitive ventral aortae are the rudiments of the heart. At first they he, quite separate from each other, in the dorsal wall of the pericardium, but soon they approach one another and fuse together to form a single tubular 5 Anterior cardinal veil Ist aortic arch Heart Stem formed by union of lateral umbilical and vitelline veins Vena umbilicalis impar Umbilical arteries Fk;. Vitelline veins 82. — ScHE.MA OF Vascular System ok an Embryo, 2 "6 .mm. long, with Fourteen Somites. (Arteries after Feli.x, moditied.) 66 HUMAN EMBEYOLOGY. Posterior cardinal veins Yolk-sac artery (later = superior mesenteric) 2ud aortic arche 1st aortic arches Anterior cardinal vein; Sinus venosus Umbilical arteries ' Vena umbilicalis impar Fig. 83. -Schema, of Vascular System of an Embryo with twenty- three Somites. (Arteries after Felix, modified. ) heart. The more cranially situated parts of the primitive ventral aortse remain separate and take part in the formation of ventral roots of the aortic arches. Before the single heart is formed other blood-vessels have appeared, which return blood from the chorion and the yolk-sac. to the heart. These vessels are the primitive veins. Two veins pass from the chorion into, the body-stalk, where they fuse together to form the vena umbilicalis impar. This divides, at the caudal end of the embryo, into the two lateral umbilical veins, which run to the heart, one along each lateral margin of the embryo. In an embryo 1'3 mm. long (Eternod), in which the paraxial mesoderm had not yet commenced to segment into meso- dermal somites, each lateral umbihcal vein received, as it entered the embryo, a large efferent vein from the yolk-sac. This condition, if regular, is very transitory. After a very short time the connexion of the vitelline veins with the caudal ends of the lateral umbilical veins is lost, and the blood is returned from the yolk-sac directly to the heart by two vitelhne veins, one on each side, which run along the sides of the vitello-intestinal duct and receive the lateral umbilical veins close to the heart (Fig. 81). In the meantime a number of branches have been developed from both the dorsal and the ventral walls of the nh pair of inter- primitive dorsal aortffi ; the former are the somatic pre-segmental and inter- segmental arteries, and the latter are the primitive vitelline arteries. In a human embryo which has de- veloped six distinct mesodermal somites the vitelhne arteries form a plexus on the sides of the hind-gut area of the wall of the entodermal vesicle, from which the umVjilical arteries appear to spring (Felix). The plexus is re- presented in Fig. 81 by the bulbous dilatations. The vessels which enter this plexus arise from the ventral aspects of the primitive dorsal aortte, some distance from their caudal ends. It is probable, however, that the caudal ends of the primitive dorsal aortse are connected with the caudal part of the plexus at tlie points of origin of the umbilical arteries, though segmental arteries Vertebral arteries 1st pair of inter- segmental arteries IsL cBphalic aortic arch 2nd cephalic aortic arch 3rd ceplialic aortic arch 4tli cephalic aortic arch (5th cephalic aortic arch Bulbns cordis Ventricle Atrium Sinus venosus Fig. 84. — Diagram showiiif; stage of five aortic arclies. the connexions are not visible; in the sections of the embryo mentioned (Fig. 81). Practically tlie same condition is present in an embryo 1-6 mm. long possessing fourteen distinct somites, except that the main rootlets of the umbilical artery, on each side, are situated farther caudalwards than in tlie younger embryo, and lie in the region of the most caudal somites (Fig. 82). Further Development of the Arterial System. — When the embryo possesses twenty-thrtic mesodermal soinites, liut is still devoid of limbs, the arterial system has THE PKIMITIVE VASCULAR SYSTExM. 67 Srd'arches 4th archcM ; 6th arches 6th arcties DorHal aprta Pulmonary arteries External carotids / I Ventral root of 3r(l arch ' Ventral root of 4tli and 5th arches J Tnincus arteriosus Fig. 85. — Schema of Aoktic Arches of an Embkyo, 9 mh. long. (After Tandler, modified.) The second and third arches have atrophied and the transitory fifth has appeared. advanced considerably in development. Two aortic arches, on each side, now connect the cephalic end of the heart with 'the primitive dorsal aorta. Tiie umhihcal artery and vitelline arteries are quite separate, and each umbilical artery springs, l)y a number of roots which anastomose together, from the caudal part of the C(jrre- sponding dorsal aorta. The vitelline arteries are still numerous, l)ut that which rises opposite the twelfth mesodermal somite is becoming the main artery of the yolk-sac; eventually its ])roximal , ■ ^ c 1 • . '-nd arches atrophied part IS transtormed into ' °- •- the superior mesenteric artery of the ftetus. When the embryo has attained a len^fth of 5 mm., and is about live weeks old, it possesses about thirty-eight mesodermal somites, and ist arches atrophied five aortic arches are present on each side. Commencing from the cranial end, they are the first, second, third, fourth, and sixth ; the fifth arcli appears sul*- sequently between the fourth and the sixth. All five arches pass to the corresponding dorsal aorta, but the three most caudal, on each side, spring from the cranial end of the heart, which is now called the aortic trunk, whilst the two most cranial rise from a common stem which constitutes their ventral roots, and which springs, also, from the aortic trunk (Fig. 84). A little later the aortic trunk gives off only two branches on each side, (1) a stem common to the first five arches, for the fifth has now appeared, and (2) the sixth arch (Fig. 85). The fifth arch is very transitory. Whilst it is present it runs from the common ven- tral stem, caudal I ^ T-.,;r.., nf ,li,/.tii..- ut.tor-;i-v.:iiw tO tn6 lOUrtll arch,' to the dorsal part of the sixth arch. It soon disap- pears, and no traces of it are left in the adult (Fig. 85). The portion of the common ventral stem which lies caudal to each of the arches is Internal carotid Internal carotid • Internal carotid Arch of aorta i Right subclavi.in artery I j Left subclavian artery Right subclavian artery j Union of ductus arteriosus ■with aorta Union of dorsal roots of Cth arches Dotsal aoila External carotid External carotid Left common carotid Right common carotid nionary artery Left pulmonary artery Innominate artery Right 6th arch Left 6th arch Ascending aorta Fi(i. 86. — Schema ok paut of the Ahteriai. System of a Fcetus .seen from the Left Side. Parts of the first and second arches, the dorsal roots of the third arches, the dorsal part of tlie right sixth arch, and the dorsal roots of the right fourth and fifth called tllO VCn- arches have atrophied. The position of tte fifth arch is not indicated ; see Fig. 84. + 1 ^ f f 1 p arch, and the parts of the primitive dorsal -Aoxi-x wliich lie caudal to the dorsal ends of tlie arches are called their dorsal roots. Tlie fir.st two arches, on each side, disappear, and their ventral roots become the external carotid arteries of the adult. The ventral root of the third arch becomes the common carotid, whilst the tliird arch and the dorsal roots of the first and second arclies are transformed into the internal carotid. The ventral root of the fourth arch on the right side becomes the innominate artery, and the right fourth arch forms the proximal part of the right subclavian artery. The remainder of the 5 a 68 HUMAN EMBRYOLOGY. External carotids right subclavian is developed from the seventh right somatic inter-segmental artery. The ventral root of the left fourth arch and the arch itseK form the arch of the aorta. The fifth arch, as already stated, is quite transitory ; it leaves no remains, therefore it is not necessary to speak of any part of the ventral stem as its ventral root. The ventral part of the sixth arch on the right side becomes the extra-pulnionary part of the corresponding pulmonary artery. On the left side it practically disappears. On the right side the dorsal part disappears, but on the left side it persists, till birth, as the ductus arteriosus, which connects the pulmonary artery with the aorta, and after l^irth it is converted into the ligamentum arteriosum. The truncus arteriosus is cleft into two parts by a spiral septum ; one part, which remains continuous with the ventral roots of the fourth arches and therefore with the innominate artery and the aortic arch, becomes the ascend- ing aorta, and the other, which remains associated with the sixth arches, becomes the stem of the pulmonary artery. Whilst the changes mentioned have been taking place in the cephahc part of the arterial system, the primitive dorsal aortse have fused together from a point immediately caudal to their seventh dorsal branches to a point immediately cranial to the origins of the umbilical branches from their ven- tral aspects, and their ventral Vjranches have fused together into single stems, some of which have been converted into the coeliac, the superior mesenteric, and the inferior mesenteric arteries. The fusion of the dorsal aortse commences in embryos about 2'5 mm. long. When the embryo has' attained a length of 5 mm. the fusion has extended to the caudal ends of the aortse and the single stem is continued into the rudimentary tail as the caudal artery, which after- wards becomes the middle sacral artery. After the fusion is completed the um- bilical arteries spring from the ventral aspect of the single dorsal aorta. (For iiG. 8/. -Schema of Part of the Vascular System , ^ fm-thpr hi^tnrv of tbp artPrial svsfpm OK A F(ETDs SEEN FROM THE Front. Showing the "^^6 luiiner nistory 01 tne arterial system, origin of the positions of the first and second arches, See under Vascular System.) the dorsal roots of the third arches on both sides, •J'-J^q Primitive VenOUS System. The and the dorsal roots of the fourth and fifth arches r. , i„r> -.^ „ 4. 1 „ <. ,^, „ on the right side are shown in dotted lines. The A^St definite venous trunks tO appear positions of the fifth arches are not shown. are the umbilical veins, returning blood from the chorion, and the vitelline veins, which convey the blood from the yolk-sac. Two umbilical veins enter the body-stalk and unite to form the vena umbilicalis impar (Fig. 81). This divides, at the posterior margin of the umljilicus, into the right and left lateral umbilical veins, which run round the lateral margins of the umbilical orifice, in the lateral margins of the body wall of the embryo. At the cranial margin of the umbilicus they turn medially, enter a transverse bar of mesoderm which forms the caudal boundary of the pericardium and is known as the septum transversum, and jjass through it into the caudal end of the heart (Figs. 81, 82). The l)lood from the yolk-sac passes, for a short time, into the lateral umbilical veins at the posterior margin of the umbilicus. This is a very transitory arrange- ment, and it is soon replaced by the formation of two proper vitelline veins, one on each side, which ascend, along the vitello-intestinal duct, to the cranial margin 1st arch 2nd arclv Internal carotid" Internal carotid Internal carotid Kight common carotid--" Dorsal root of Srdarcli '^' Right sub-, clavian artery Innominate artery ^c Right pulmonarj^^" artery 1', Ascending aorta- ■>' Pulmonary arterj— t — Dorsal root of right (3th arcli Internal carotid External carotid External carotid Dorsal root of left 3rd arcli Left common carotid Arch of aorta arch) Left subcla- ' vian artery - Arch of aorta \Ductus arteriosus \ Arch of aorta '\ Left pulmon- ary artery Dorsal aorta -• Dorsal aorta THE PRIMITIVE VASCULAK SYSTEM. 69 of the uiiibilicua, where they enter. the Heptuiu transversuni, in which each vitelline vein joins the corres])onding umbilical vein, forming a common vitello-intestinal trunk, which enters the sinus venosus (Fig. 81). This trunk also receives the primitive head vein, or anterior cardinal vein, whicli returns tin* Idood from the craniul \nirl of the cmliryo (Fig. 82). Iiitoriial jugulur veiti-^ Kxleriial jiigulai- V('iir-|l Vertobial artery - Left iiinoininale vein Subclavian art pry -ifi' Subclavian \ lin Riglit pulmonary arli'ry Superior vena cava "^ Right atrium Vena azygos Uight ventricle Inferior vena cava, vitelline vein portion Inferior vena ca\a, down- growtli from vitelline vein - Right and Irl't l)ranches _. of portal vein Portal vein — Remains of vitelline vein Inferior \ena cava (subcarericardiuni Duct of Cnvier Pleuro-pericardial canal Lung bud Q-^KOpliagus y Lung bud Commencing lateral jiart of diaphragm Septum trans\ersuni ^--1- Peritoneum Heart Fig. 91. — Schema of Later Stage ok Differentiation OF CcELOM. A, from above. B, transverse section cut Fig. 92. — Schema of a Transverse Section level of lung bud in A. at the level of the Lung Bud in Fig. 91. pericardial canal (Fig. 91). As the lung buds grow the cavities of the pleuro- pericardial canals increase in size, and each passes ventrally, round the side of the pericardium towards the ven- tral wall of the body, until it is separated from its fellow of the op- posite side only by a median meso- derm-filled interval, which becomes the anterior mediastinum and the anterior part of the superior media- pieurai cavity stinuin (Fig- 94). At the same time Closed aperture tetween thc cavity of cacli plcuro-pcricardial pleura and iieiicardiuiu , ''. , '■ . ^ . , , canal, and the growing lung bud in its interior, grow towards the cephalic end of the embryo (Fig. entary canal Duct of Cuvier Lung B-if--- Lateral part of diaphragm converging I , ,1 towards dorsal '■ • '' mesentery Septum transversum Peritoneum Spinal medidla (Esophagus Fig. 93. — Schema of still later Stage of Ccelom DiKFEREXTUTiox. The pleurae are separated from the pericardia, but still communicate with the peritoneum. Fig. 94. — Schema of Tr.vxsverse Section o? Embrto at Level of Line B, Fig. 93, showing ventral ex- tension of the pleurae. 93). As it passes cephal wards the growing lung lies to the lateral side of the duct of Cuvier, which is thus forced against the cephalic end of the pleuro- p^i(;af(Ji9') f^Dal, compressing it towards the median plane, against the sides 74 HUMAN EMBEYOLOGY. of the trachea and the oesophagus, until its cavity is obliterated. When this occurs the pericardial cavity is entirely shut off from the remainder of the coelom, and it becomes a completely closed space (Fig. 93). As the closure of the pericardial cavity is taking place two wing-like folds of mesoderm, connected ventrally with the septum transversum and laterally with the body walls, appear, caudal to the lungs (Figs. 91, 93). These folds are the rudiments of the lateral parts of the diaphragm, and each passes medially until it fuses with the mesoderm of the side wall of the fore-gut and with the dorsal mesentery. When this fusion is completed the cavity of the portion of the ccelom surrounding the lung, the original pleuro-pericardial canal, is separated from the more caudal part of the ccelom, which now becomes the peritoneal cavity. Only the broad outlines of the processes by which the pleuro-peritoneal canals are separated from the pericardium and the peritoneum are mentioned in the preceding paragraphs. The details of the processes are too complicated for description in an ordinary text-book of anatomy. The Formation of the Diaphragm. — There are four main parts of the diaphragm, a ventral, a dorsal, and a right and a left lateral. The ventral part is formed from the septum transversum, which is gradually differentiated into a caudal, an intermediate, and a cephalic part. The caudal part is transformed into (1) the mesodermal tissue of the liver, which grows towards the abdomen, (2) the falciform and coronary ligaments, and (3) the small omentum. The cephahc part becomes the caudal or diaphragmatic wall of the pericardium. The intermediate part is transformed into the ventral portion of the diaphragm. The dorsal part of the diaphragm is developed from the mesoderm of the dorsal mesentery of the fore-gut. Each lateral part is derived from a lateral ingrowth which springs ventrally from the septum transversum and laterally from the body wall. The two lateral portions grow towards the median plane till they fuse with the dorsal portion ; but in some cases, especially on the left side, the fusion is not completed. In such cases an aperture of communication remains, between the pleural and the peritoneal cavities, through which a portion of the abdominal contents may pass into the pleural sac, constituting a diaphragmatic hernia. SUMMAEY OF THE EXTEENAL FEATUEES OF THE HUMAN EMBEYO AND FGETUS AT DIFFEEENT PEEIODS OF DEVELOPMENT. During the first fourteen days after the impregnation of the ovum the human zygote descends through the uterine tube, assumes the morula condition, enters the uterus, penetrates into the decidua compacta, and differentiates into three vesicles and a mass of primitive mesoderm ; but, probably, it is not until the beginning of the third week, if Bryce's calculations are correct, that a definite embryonic area is present. By that time the zygote is an ovoid vesicle measuring 2-4 by 1-8 mm. Its wall is formed by the trophoblast, and it contains two inner vesicles, the ecto-mesodermal and the entodermal vesicles. The inner vesicles are surrounded by a mass of primary mesoderm in which the extra-embryonic portion of the coelom is beginning to appear. At this period the embryonic area is the region where the walls of the two inner vesicles lie in relation with one another, and it is '19 mm. long (Fig. 30). By the eighteenth or nineteenth day the area has attained a length of 1"17 mm. and it is '6 mm. broad. It is pierced, about the centre of its length, by the neurenteric canal ; the primitive streak has appeared on the dorsal surface of the area ; the primitive groove is distinct, and the neural groove is indicated. The body-stalk is bent dorsally, at right angles with the area, and it contains the allantoic diverticulum, which has already been projected from the wall of the entodermal vesicle (Fig. 95). During the next twenty-four hours the length of the embryonic area increases to 1 "54 mm.; the neurenteric canal is moved caudally, to a point well behind the middle of the length of the area, and the posterior part of the area is bent ventrally, forming the posterior boundary of the hind-gut region and indicating the position of the future cloacal membrane. The head fold has begun to form, and the pericardial region lies in the ventral wall of the rudimentary fore-gut (Fig. 96). By the middle of the third week the head and tail folds are distinctly formed and THE HUMAN EMBRYO AT DIFFERENT PERIODS. iO the length of the embryo is 19 mm., the neunil folds are well developed, the neural groove is still completely open, and six pairs of mesodermal somites are visible (Fig. 97). In the next few days the length increases to 2 5 mm., the neural groove closes except in the cranial and caudal regions, the number of mesodermal somites is increased to four- teen pairs, and the cranial region begins to bend ventrally as the cervical flexure forms (Fig. 98). By the end of the first month the greatest length of the embryo is about 2"6 rnm., the head is bent at right angles to the body, the Wolffian ridges have appeared along the ventral martrins of the mesodermal somites and indications of the limb rudiments Fig. 95. — Frassi's Zygote. Estimated to be 18-19 days old (Bryce). The embryonic area is 1'17 mm. long ami "6 mm. broad. Copied from Xor- malta/eln, Keibel and Elze, representing a recon- struction. The chorion is not shown. The upper part of the amnion is cut away, and the dorsal aspect of the embryonic area is seen from above. In the centre of tlie area is the neurenteric canal and caudal (inferior in the Fig.) to it is the primitive groove. Cephalwards of the neurenteric canal is the neural groove, in the middle of the neural plate. At the lower (caudal) end of the Fig. is seen a section of the body stalk containing the allantoic diverticulum, and the nodulated area seen at the upper and right lateral part of the Fig. is a portion of the yolk-sac. Fig. 96. — Si'Ee's Zygote. (From Keibel and Elze's Xormaltafeln.) Length of embryonic area 1"54 mm. Estimated age 19-20 days (Bryce). At the lower end of the Fig. (caudal end of the embryo) is seen a portion of the chorion attached to the embryo by the body stalk. A portion of the amnion is still attached to the margin of the embryonic area, and the dorsal surface of the embryonic area is exposed. In the median plane of the area is the neural groove, and at the caudal end of the groove is the neur- enteric canal. The caudal part of the area is bent ventrally, and upon it is the remains of the primitive groove. The yolk-sac is seen at the upper and right part of the Fig. are present. The rudiments of the otic vesicles have appeared as slight depressions in the region of the hind-brain. The anterior and posterior neuropores are still open (Fig. 99). In the latter part of the fourth or the beginning of the fifth week the embryo attains a length of about 5 mm., when measured from the vertex of the head to the base of the tail, the mesodermal somites increase to thirty-five ; the rudiments of the fore- and hind- limbs become quite distinct ; the otic vesicles sink into the interior of the head but remain connected with the surface by the recessus labyrinthi, the tail becomes a very definite appendage, and the bulgings caused by the otic vesicles are quite obvious on the surface of the head. The cervical flexure remains acute, and the head bends at right angles upon itself in the region of the mid-brain, forming the cephalic flexure, with the result that the frontal extremity of the head is turned caudally (Fig. 100). By the end of the fifth week the length of the embryo has increased to 1 1 mm. (CR) ^ ^ CR indicates the crown-rump or crown-breech measurement which corresponds with the sitting height (Mall). 76 HUMAN EMBEYOLOGY. (Mall). Forty-three mesodermal somites are present, but only about twenty-one are visible on the surface. During the fifth week the lens of the eye appears as a thickening of the surface ectoderm ; sinks into the interior of the eyeball ; becomes a vesicle and separates from the surface. The three segments of the fore-limb become visible, and the rudiments of the fingers appear. The hind-limb is less advanced ; the thigh segment is not distinct, and the rudiments of the toes are not yet visible. The third and fourth visceral arches disappear from the surface and lie in the depths of the precervical sinus, a depression between the neck and the anterior part of the body ; this is overlapped, superficially, by the caudal margin of the second arch, which grows tailwards and forms the operculum of il Ite*' Fig. 97. — Krcembr - Pfannenstiel Zr- GOTE. (From Keibel and Elze's Nmiiialtafeln. ) The embryonic region is folded into the form of an embryo, which is 1 "9 mm. long, and it is possibly about three weeks old. At the lower end of the Fig. (the caudal end of the embryo) are seen portions of the chorion and body- stalk. The cerebral portion of the neural rudiment is defined. Six pairs of mesodermal somites are present, but there are no signs of limbs. Fig. 98. — Balle's Embryo. (From Keibel and Elze's Normoltafeln.) Length after hardening in alcohol 2 '5 mm. The neural groove is closed from the sixth somite to within a short distance of the caudal end, but it is open anteriorly. The hind-, mid-, and fore- brain regions and the optic vesicle can be distinguished. At the lower end of the Fig. is tlie body-stalk, and at the right side a part of the yolk-sac. Fig. 99. — Pfannenstiel's Em- bryo. (From Keibel and Elze's NoTimdtafdn. ) Length of embryo about 2 '6 mm. The rudiment of the otic vesicle is seen in the Fig. above the second branchial cleft. The heart and peri- cardium from the bulging eminence below the head and the Wolffian ridge is seen at the lateral border of the meso- dermal somites. the sinus (Figs. 101, 102). During the fiftli week the head grows rapidly, and becomes relatively very large as contrasted with the body. During this week also the olfactory pits appear, and grow dorsally in the roof of the stomatodajum, separating the median from the lateral nasal processes ; the median process is divided into the two globular processes ; and the maxillary processes of the mandibular arches, growing towards the median plane, fuse with the lateral nasal and the globular processes, so completing the lateral parts of the primitive cranial lip (Figs. 64, 65, 66). The nodular outgrowths which form the rudiments of the auricles appear on the margins of the hyo-mandibular cleft and fuse together, and by the end of the week traces of the tragus, the holi.x, and the antitragus are visible (Fig. 103). By the seventh week the embryo has attained a length of 17 mm. (CR). The cervical flexure has begun to unfold. The rudiments of the eyelids have appeared. The globular processes have fused together, but there is still a distinct notch in the middle of the cephalic or upper lip. The margins of the auricles are now well defined ; the hands are THE HUMAN EMBRYO AT DIFFERENT PERIODS. 77 I ( Fig. 100. — Sidk view ok an Embryo, measuring about 5 mm. from the root of the neck to the base of the tail, and about 47 mm. from the crown or mid-brain region to the base of the tail, that is to the breech or rump. (From Keibel and Elze's Normaltafehi.) The neural tube is closed. The limb buds are quite distinct, and the maxillary process of the mandibular bar has grown forward below the eye (dorsal to the eye in the Fig.). Fig.' 101. — Embkyo of 7'2 mm., CR Mea-sukkment. 8"5 mm. greatest length. (From Keibel and Elze's Normaltafehi. ) llie fore-limb is distinctly in advance of the hind-limb. The second branchial arch has begun jto overlap the third and fourth and to enclose the precervical sinus. The tip of the maxillary process is in contact with the lateral and medial nasal processes at the margins of the olfactory pit. Fig. 102. — Embhyo, ~"1 mm. ^CKj, and 8 mm. greatest length. (From Keibel and Elze's Xonnaltafeln.) The limbs have begun to fold ventrally. The second arch has completely overlapped the third and fourth which now lie in the precervical sinus, and the sinus still opens on the surface at the posterior border of the second arch. The lens of the eyeball is very evident, and rudiments of the auricle of the e.xtemal ear have appeared on the mamlibular or tirst, and the hyoid or second arch. Fig. 103. — Embkto, 10-9 mm. (CR) and 11 "5 mm. greatest length. (From Keibel and Elze's Xonualta/dn). The pre- cervical sinus is closed and additional rudiments of the auricle of the external ear are present on the first and second arches. The anterior nares are no longer visible from the side. 78 HUMAN EMBEYOLOGY. folded medially; the tips of the fingers are free, and the palms rest on the cranial part of the distended abdomen. The thighs and the toes have appeared, and the tail has begun to fuse with the caudal end of the bod}^ (Fig- 104). At the end of the eighth week, when the embryo becomes a foetus, it has attained a length of about 25 mm. (CR). The auricles project from the sides of the head, the tail has almost disappeared from the surface, and the toes are free fi-om one another. The cervical flexure is now very slight, and although the head is still relatively large, the disproportion between it and the body has begun to decrease (Fig. 105). Third Month. — The head grows less rapidly, and, though it is still large, it is relatively smaller in proportion to the whole body. The eyelids close, and their margins fuse Fig. 104. — EiiBRyo (CR) greatest length 18"5 mm. Probably between seven and eight weeks old. (From Keibel and Elze's Normaltafeln.) The abdomen is very prominent on account of the rapid increase of the liver. The digits of the hand and foot are distinct but not separated from one another. The margin auricle of the external ear is completed. The eyelids have begun to form. Fig. 105. — Homan F(etus eight and a half WEEKS OLD. (After His. ) GE. Genital eminence ; UC. Umbilical cord. together. The neck increases in length. The various parts of the limbs assume their definite proportions, and nails appear on the fingers and toes. The proctodseum is formed and the e.xtemal generative organs are difl'erentiated, so that the sex can be distinguished on external examination. The skin is a rosy colour, thin and delicate, but more consistent than in the preceding stages. By the end of the third month the total length of the foetus, excluding the legs, is 7 cm. (24 in.), including the legs, 9-10 cm. (3f-4 in.), and it weighs from 100-125 grammes (3^-4| oz.). Fourth Month. — In the fourth month the skin becomes firmer, and fine hairs are developed. The disproportion between the fore- and hind-limbs disappears. If the foetus is born at this period it may live for a few hours. Its total length from vertex to heels is 16-20 cm. (6r-8 in.), from vertex to coccyx 12-13 cm. (4^-5^ in.), and it weighs from 230-260 grammes (81-91 oz.). Fifth Month. — The skin becomes firmer, the hairs are more developed, and sebaceous matter appears on the surface of the body. The legs are longer than the arms, and the umbilicus is farther from the pubis. At the end of the month the total length of the THE HUMAN EMBRYO AT DIFFERENT PERIODS. 79 fa'tus, from vertex to heels, is 25-27 cm. (10-1011 in.), from vertex to coccyx 20 cm. (8 in.), and its average weight is about half a kilogramme (1 ,'(j lbs.). Sixth Month. — The skin is wrinkled and of a dirty reddish colour. Tlie hairs are stronger and darker. The deposit of sebaceous matter is greater, especially in the axillie and groins. The eyelashes and eyebrows appear. At the end of the month the toUil length of the fcetus, from vertex to heels, is from 30-32 cm. (12-12? in.), and its average weight is about one kilogramme (2^ lbs.). Seventh Month. — The skin is still a dirty red colour, but it is lighter than in the previous inonth. The body is more plump on account of a greater deposit of sub- cutaneous fat. The eyelids re-open, and the foetus is capable of living if born at this period. Its total length at the end of the month, measured from vertex to heels, is 35-36 cm. (14-14': in.), and its weight is about one and a half kilogrammes (3.1 lbs.). Highth Month. -The skin is completely covered with sebaceous deposit, which is thickest on the head and in the axilla) and groins, and its colour changes to a bright flesh tint. The umbilicus is farther from the pubis, but it is not yet at the centre of the body. The total length of the fa3tus, from vertex to heels, is 40 cm. (16 in.), and its weight varies from 2 to 2\ kilogrammes (4^-5.'; lbs.). Ninth Month. — The hair begins to disappear from the body, but it remains long and abundant on the head. The skin becomes paler, the plumpness increases, and the umbilicus reaches the centre of the body. At the end of the ninth month, when the fcetus is born, it measures about 50 cm. from vertex to heels (20 in.), and it weighs from 3-3i kilogrammes {^i%-'iyq lbs.). The age of a foetus may be estimated, approxiniately, by Hasse's rule, viz., Up to tlie fifth month the length in centimeters, the lower limbs being included, equals the square of the age in months, and after the fifth month the length in centimeters equals the age multiplied by five. Note 1.— Evidence is gradually accuniulating which tends to show that the reduction of the number of chromosome.s may take place during the last divisions of the germ mother cell, that is before the growth of the oocyte or spermatocyte I commences, and therefore before maturation commences. NoTK 2. — There is evidence which jjoints to conclusions somewhat different from those stated ou p. 14, regarding the dentoplasni in mammalian ova, but it is not yet sufficient or sufficiently conclusive to justify its incorporation in a text-book account. Note 3. — The recent observations of (J. Fineman, A7iat. Hefte, 159 H. (53 B. H.), 1915, show that the ductus enilolymphaticus is not derived from the original canal of communication with the exterior, but is formed independently by a process of evagination. Note 4. — Evidence which has accumulated since this statement was made tends to show that bluod corpuscles and the endothelial cells which form the walls of the primitive blood-vessels are derived from different ancestors, the endothelial cells from mesencliyme cells, and the red blood corpuscles form angioblasts which may be derived, as some observers believe, from mesenchyme cells, or, as others thhik more probable, from entoderm cells. Note 5. — The origin of the white blood corpuscles is still uncertain ; according to some investigators they and the red corpuscles have common ancestors and the same ancestoi's may produce endothelium also ; this is the so-called monophyletic view. It appears jjrobable, however, that, in some vertebrates, the white corpuscles are derived from one set of mesoderm cells, the red corpuscles from another, and the endothelium of the blood-vessels from a third set of mesodermal cells, each set of mesoderm cells being capable of pro- ducing only one kind of descendant ; this is the polyphyletic view. OSTEOLOGY. THE SKELETON. By Arthur Thomson, F.K.C.S. Professor of Anatomy, University of Oxford. The term skeleton (from the Greek, o-KeAeros, dried) is applied to the parts which reiuaiu after the softer tissues of tlie body have been disintegrated or removed, and iuchides not only the bones, but also the cartilages and ligaments which bind them together. In the restricted sense of the word the skeleton denotes the osseous framework of the body. It is in this sense that it is generally employed in human anatomy. The skeleton serves to support the softer structures which are grouped around it, and also affords protection to many of the delicate organs which are lodged within its cavities. By the articulation of its several parts, its segments are con- verted into levers which constitute the passive portion of the locomotory system. Kecent research has also proved that certain cells found in bone -marrow are intimately associated with the development and production of some of the corpuscles of the blood. Bone may be regarded as white fibrous tissue which, having become calcified has undergone subsequent changes, so as to be converted into true osseous tissue. Most probably all bone is of membranous origin, but it may pass through a stage in which cartilage plays an important part in its development. In many instances the cartilage persists, and is not converted into bone, as in the case of the articular cartilage which clothes the joint surfaces, the nasal septum, the cartilages of the nose, and the cartilages of the ribs. A persistence of the membranous condition is met with in man in the case of the tentorium cerebelli, which in some groups of animals (Carnivora) is converted into a bony partition. Skeletal structures may be derived from each of the three layers of the trilaminar blastoderm. The exo-skeleton includes structures of ectodermal, and some of mesodermal origin, in the shape of hair, nails, feathers, teeth, scales, armour- plates, etc., whilst the endo-skeleton, with which we are more particularly concerned, is largely derived from the mesodermal tissue, but also includes the notochord, an entodermal structure which forms the primitive endo-skeleton, around which the axial skeleton is subsequently developed in the Vertebrata. The endo-skeleton is divisible into an axial portion, appertaining to the trunk and head, and an appen- dicular part, associated witli the limbs. It also includes the splanchnic skeleton, which comprises certain bones developed in the substance of some of the viscera, such as the os cordis and os penis of certain mammals. In man, perhaps, the cartilaginous framework of the trachea and bronchi may be referred to this system. The number of the bones of the skeleton of man varies according to age. Owing to a process of fusion taking place during growth, the number in the adult .is less than the number in the child. The following table does not include the sesamoid bones, which are frequently developed in tendons, the most constant ossicles of this description being those in relation to the metacarpo-phalangeal joint of the thumb, and the metatarso-phalangeal joint of the great toe. 81 6 82 OSTEOLOGY. life The table represents the number of bones distinct and separable during adult Axial skeleton Appendicular skeleton The ossicles of the ear 'The vertebral column The skull . The sternum The ribs . The hyoid bone (The upper limbs (The lower limbs Single Bones. 26 6 1 34 Pairs. 12 32 31 3 86 Total. 26 22 1 24 1 64 62 6 206 Bones are often classified according to their shape. Thus, long bones, that is to say, bones of elongated cylindrical form, are more or less characteristic of the limbs. Broad or flat bones are plate-like, and serve as protective coverings to the structures they overlie ; the bones of the cranial vault display this particular form. Other bones, such as the carpus and tarsus, are termed short bones ; whilst the bones of the cranial base, the face, and the vertebrae, are frequently referred to as irregular bones. Various descriptive terms are applied to the prominences commonly met with on a bone, such as tuberosity, eminence, protuberance, process, tubercle, spine, ridge, crest, and line. These may be articular in their nature, or may serve as points or lines of muscular and ligamentous attachment. The surface of the bone may be excavated into pits, depressions, fovece, fossae, cavities, furrows, grooves, and notches. These may be articular or non-articular, the latter serving for the recep- tion of organs, tendons, ligaments, vessels, and nerves. In some instances the substance of the bone is hollowed out to form an air space, sinus, or antrum. Bones are traversed hj foramina and canals ; these may be for the entrance and exit of nutrient vessels, or for the transmission of vessels and nerves from one region to another. A cleft, hiatus, or fissure serves the same purpose ; channels of this kind are usually placed in the line of a suture, or correspond to the line of fusion of the primitive portions of the bone which they pierce. Composition of Bone. — Bone is composed of a combination of organic and inorganic substances in about the proportion of one to two. Organic matter (Fat, etc., Collagen) . . . 31 '04 Mineral matter — Calcic phosphate .... 58*23'^ Calcic carbonate Calcic fluoride Magnesic phosphate Sodic chloride 7-32 1-41 1-32 •69 68-97 100-00 The animal matter may be removed by boiling or charring. According to the completeness with which the fibrous elements have been withdrawn, so the brittle- ness of the bone increases. "When subjected to high temperatures the earthy matter alone remains. By soaking a bone in acid the salts may be dissolved out, leaving only the organic part. The shape of the bone is still retained, but the organic suljstance which is left is soft, and it can be bent about in any direction. The toughness and elasticity of bone depends therefore on its organic constituents, whilst its hardness is due to its mineral matter. Bone may be examined either in the fresh or dry condition. In the former state it retains all its organic parts, which include the fibrous tissue in and around it, the blood-vessels and their contents, together with the cellular elements found within the substance of the bone itself, and the marrow which occupies the lacunar spaces and marrow cavity. In the dried or macerated bone most of these have disappeared, though a considerable portion of the organic matter still remains, even in bones of great antiquity and in a more or less fossil condition. Con- sidering its nature and the amount of material employed, bone possesses a remark- able strength, equal to nearly twice that of oak, whilst it is capable of resisting a STKUCTURE OF BONE. 83 greater crushing strain ; it is stated that a cubic inch of bone will support a weight of over two tons. Its elasticity is remarkable, and is of the greatest service in enabling it to withstand the shocks to which it is so frequently subjected. In regions vvliere wood is scarce the natives use the ribs of large mammals as a sub- stitute in tlie construction of their bows. Its hardness and density vary in different parts of the skeleton, and its permanency and durability exceed that of any other tissue of the body, except the enamel and dentine of the teeth. The osseous remains of a race over eighty centuries old have been excavated in Egypt. Structure of Bone (Macroscopic). — To obtain an idea of the structure of a bone it is necessary to examine it both in the fresh or recent condition and in the macerateil state. In the former the bone is covered by a memltnine wliich is with dilHculty torn olf, owing to the abundance of tine fibrils which enter the sul)8tance of the bone from. its deep surface. This membrane, called the periosteum, overlies the bone, except where the bone is coated with cartilage. This cartilage may form a bond of union between contiguous bones or, in the case of bones united to each other by movable joints, may be moulded into smooth articular surfaces called the articular cartilages. The attachment of the various ligaments and muscles can also be studied, and it will be noticed that where tendon or ligament is attached, the bone is often roughened to form a ridge or eminence ; where fleshy muscular fibres are attached, the bone is, as a rule, smooth. In the macerated condition, when the cartilage and fibrous elements have been destroyed, it is possible, however, to determine with considerable accuracy the parts of the bone covered with articular cartilage, since the bone here is smooth and conforms generally to the curves of the articular areas of the joint ; these areas are referred to as the articular surfaces of the bone. The bone, stripped of its periosteal covering, displays a dense surface finely pitted for the entrance of the processes derived from the periosteum, which thus establish a connexion between the bony substance and that vascular layer ; here and there, more particularly in the neighbourhood of the articular extremities, these pits increase in size and number and allow of the trans- mission of small blood-vessels. If careful examination is made, one or two foramina of larger size will usually be noticed. These vascular foramina or canals allow the passage of arteries of considerable size into the interior of the bone, and are called the canales nutricii or nutrient canals or foramina of the bone. There are also corresponding channels for the escape of veins from the interior. In order more fully to ascertain the structure of bone it will be necessary to study it in section. Taking first a long bone, such as one meets with in the limbs, one notices on longitudinal section, that the bone is not of the same density throughout, for, whilst the external layers are soUd and compact, the interior is made up of loose spongy bone called suhstantia S2wngiosa (cancellous tissue). Further, it will be observed that in certain situations this spongy substance is absent, so that there is a hollow in the interior of the bone called the medullary cavity. In the recent condition this cavity is filled with the marrow and is hence often called the marrow cavity. This marrow, which fills not only the marrow cavity but also the interstices between the fibres of the spongy substance, consists largely of fat cells, together with some marrow cells proper, supported by a kind of retiform tissue. The appearance and constituents of the marrow differ in dilVerent situations. In the medullary cavity of long bones the marrow, as above described, is known as medulla ossium flava (yellow marrow). In other situations, viz., in the diploe of the cranial bones (to be hereafter descrilied), in the spongy tissue of such bones as the vertebrae, the sternum, and the ribs, the marrow is more fluid, less fatty, and is characterised by the presence of marrow-cells proper, which resemble in some respects colourless blood corpuscles. In addition to these, however, there are small reddish -coloured cells, akin to the nucleated red corpuscles of the blood of the embryo. These cells (erythroblasts) are concerned in the formation of the coloured corpuscles of the blood. Marrow which displays these characteristic appearances is distinguished from the yellow variety, already described, by being called the medulla ossinm rubra (red marrow). The marrow met with in the spongy tissue of the cranial bones of aged individuals often undergoes degenerative changes and is sometimes referred to as gelatinous marrow. 84 OSTEOLOGY. A better idea of the disposition of the bony framework of a long bone can be obtained bj the examination of a section of a macerated specimen. In such a specimen the marrow has been destroyed and the osseous architecture of the bone is consequently better displayed. Within the body of the bone is seen the marrow cavity extending towards, but not reaching, eitlier extremity of the bone. This cavity is surrounded on all sides by a loose spicular network of bone, which gradually increases in compactness until it reaches the circumference of the shaft, where it forms a dense surrounding wall. In the shaft of a long bone the thickness of this outer layer is not the same throughout, but tends to diminish as we approach the extremities, nor is it of uniform thickness on all sides of the bone. All the long bones display curves in varying degree, and it is a uniform rule that the thicker dense bone is found along the concave surface of the curve, thus assisting in materially strengthening the bone. Towards the extremities of the long bone the structure and arrangement of the bone undergoes a change. There is no marrow cavity, the spongy tissue is not so open and irregular, and the external wall is much thinner than in the shaft ; indeed in many instances it is little thicker than stout paper. A closer examination of the arrange- ment of this spongy tissue throughout the bone suggests a regularity in its arrangement which might escape notice ; and if, in place of one bone only being examined, sections of other bones are also inspected, it will be observed that the spicules of this tissue are so arranged as best to withstand the strains and stresses to which the bone is habitually subjected. From what has been said it will be obvious that the arrangements above described are those best adapted to secure the maximum of strength with the minimum of material, and a consequent reduction in the weight of the skeleton. The same description applies, with some modification, to bones of flattened form. Taking as an example the expanded plate-like bones of the cranial vault, their structure, as displayed on section, exhibits the following appearance : The outer and inner surfaces are formed by two compact and dense layers, having sandwiched between them a layer of spongy tissue called the diploe, containing red marrow. Note that there is no medullary cavity, though in certain situations and at certain periods of life the substance of the diploe may become absorbed and converted, by the evagination of the mucous membrane of the respiratory tract, into air-spaces or air-sinuses. Structure of Bone (Microscopic). — True bone differs from calcified cartilage or membrane in that it not merely consists of the deposition of earthy salts within its matrix, but displays a definite arrangement of its organic and inorganic parts. Compact bone merely differs from loose or spongy bone in the denseness of its tissue, the characteristic feature of which is the arrangement of the osseous lamellae to form what are called Haversian systems. These consist of a central or Haversian canal, which contains the vessels of the bone. Around this the osseous lamellae are arranged concentrically, separated here and there by interspaces called lacunae, in which the bone corpuscles are lodged. Passing from these lacunae are many fine channels called canaliculi. These are disposed radially to the Haversian canal, and pass through the osseous lamellas. They are occupied by the slender processes of the bone corpuscles. Each Haversian system consists of from three to ten concentric rings of osseous lamellae. In addition to the lamellae of the Haversian systems there are others which are termed the interstitial lamellae ; these occupy the intervals between adjoining Haversian systems, and consist of Haversian systems which have undergone a process of partial absorption. Towards the surface of the bone, and subjacent to the peri- osteal membrane which surrounds the shaft, there are lamellae arranged circum- ferentially ; tliese are sometimes referred to as the outer fundamental lamellae. The periosteal membrane wliich surrounds the bone, and which plays so important a part in its development, sends in processes through the various Haversian systems, which carry with them vessels and cells, thus forming an organic meshwork around wliich the earthy salts are deposited. Ossification of Bone. — For an account of the earlier development of the skeleton the reader should consult a manual of embryology. Concerning the OSSIFICATION AND GROWTH OF BONES. 85 subsequent changes which take place, these are dependent on the conversion of the scleratogenous tissue into membrane and cartilage. A characteristic of this tissue is tliat it contains elements whicli become formed into bone-produchig cells, called osteoblasts. These are met with in the connective tissue from wliich the membrane bones are formed, whilst they also appear in the deeper layers of the investing tissue of the cartilage (perichondrium), and so lead to its conversion into the bone- producing layer or periosteum. All true bone, therefore, may probably be regarded as of membranous origin, though its appearance is preceded in some instances by the deposition of cartilage ; in this case calcification of the cartilage is an essential stage in the process of bone formation, but the ultimate conversion into true bone, with characteristic Haversian systems, leads to the absorption and disappearance of this primitive calcified cartilage. In considering the development of bone an inspection of the skeleton of a foetus will enable the student to realise that much of what is ijone in the adult is preformed in cartilage, whilst a part of the fully developetl skeleton is represented only by membrane : hence, in regard to this ossiticatiou, bones have been described as of cartilaginous and membranous origin. If the development of a long bone is traced through successive stages from the cartilaginous condition in which it is preformed, it will be noticed that ossification begins in the body ; the part of the bone ossified from this centre is referred to as the diaphysis, and, since it is the first to appear, the centre is spoken of as the primary centre of ossification. As yet, the ends of the body are cartilaginous knobs, but at a later stage one or more ossific centres appear in these cartilaginous extremities. These centres, which are independent of the diaphysis and appear much later, at vari- able periods, are termed secondary centres, and from them the epiphyses are formed. If there is more than one such centre at the end of a bone, the associated centres unite, and at a later stage the osseous mass so formed joins with the body or diaphysis, and in this way the formation of the bone is completed. Complete fusion by osseous union of the epiphyses with the diaphyses occurs at variable periods in the life of the individual. Prior to this taking place, the two are bonded together by a cartilaginous layer which marks the position of the epiphyseal line. If the bone is macerated at this stage of growth, the epiphysis falls away from the diaphysis. In the case of the articular ends of bone it will be noticed that the surfaces exposed by the separation of the epiphysis from the diaphysis are not plane and smooth, but often irregular, notched, and deeply pitted, so that when the two are brought together they interlock, and, as it were, dovetail into each .other. In this way the extremities of the bone as yet ununited by osseous growth are, during youth and adolescence, able to withstand the shocks and jars to which during life they are habitually subjected. A long bone has been taken as the simplest example, but it by no means follows that these epiphyses are confined to the articular extremities of long bones. They are met with not only in relation to the articular surfaces of bones of varied form, but also occur where bones may be subjected to unusual pressure or to the strain of particular muscles. For this reason epiphyses of this nature have been called pressure and traction epiphyses (Parsons). There occur, however, secondary independent centres of ossification, which cannot be so accounted for. Possibly these are of phylogenetic interest only, and may accordingly be classed as Atavistic. Ossification in Membrane. — Membrane bones are such as have developed from fibrous tissue without having passed through a cartilaginous stage. Of this nature are the bones of the cranial vault and the majority of the bones of the face, viz., the maxillte, zygomatic (malar), nasal, lacrimal, and palate bones, as well as the vomer. The medial lamina of the pterygoid process (internal pterygoid plate) is also of membranous origin. In the course of the development of a bone from membrane, as, for example, the parietal bone, the fibrous tissue corresponding to the position of the primary centre becomes osteogenetic, because here appear the bone-forming cells (osteoblasts), which rapidly surround themselves with a bony deposit more or less spicular in arrangement. As growth goes on these osteoblasts become embedded in the ossifying matrix, and remain as the corpuscles of the future bone, the spaces in which they are lodged corresponding to the lacunie and canaliculi of the fully developed osseous tissue. From the primary centre ossifica- 86 OSTEOLOGY. tion spreads eccentrically towards the margins of the bone, where ultimately the sutures are formed. Here the growth rendered necessary by the expansion of the cranium takes place through the agency of an intervening layer of vascular connective tissue rich in osteoblasts ; but in course of time the activity of this is reduced until only a thin layer of intermediate tissue persists along the line of the suture ; this may eventually become absorbed, leading to the obliteration of the suture by the osseous union of the contiguous bones. Whilst the expansion of the bone in all directions is thus provided for, its increase in thickness is determined by the activity of the underlying and overlying strata. These form the periosteum, and furnish the lamellne which constitute the inner and outer compact osseous layers. Ossification in Cartilage. — Cartilage bones are those which are preformed in cartilage, and include most of the bones of the skeleton. Their growth is often described as endochondral and ectochondral, the former term implying the deposition of membrane bone in the centre of the cartilage, while the latter signifies a deposit of membrane bone on the surface of the cartilage, the osteo- genetic layer on the surface of the cartilage being named the perichondrium till once bone has been formed, when it is called the periosteum. In a cartilage bone changes of a similar nature occur. The cartilage, which may be regarded histologically as white fibrous tissue + chondro-sulphuric acid and a certain amount of lime salts, undergoes the following changes : — First, the cartilage cells being arranged in rows, become enlarged ; secondly, the matrix between the cartilage cells becomes calcified by the deposition of an additional amount of lime salts ; thirdly, the rows of cells become confluent ; and, fourthly, into the spaces so formed extend the blood-vessels derived from the vascular layer of the periosteum. Accompanying these vessels are osteoblasts and osteoclasts, the former building up true bone at the expense of the calcified cartilage, the latter causing an absorption of the newly formed bone, and leading to its conversion into a marrow cavity, so that in due course all the cartilage or its products disappear. At the same time that this is taking place within the cartilage, the perichondrium is undergoing conversion into the periosteum, an investing membrane, the deeper stratum of which, highly vascular, furnishes a layer of osteoblast cells which serve to develop the circumferential lamellae of the bone. It is by the accrescence of these layers externally, and their absorption internally through the action of the osteoclast cells, that growth takes place transversely. A transverse section of the shaft of a long bone shows this very clearly. Centrally there is the marrow cavity, formed primarily by the absorption of the calcified cartilage; around this the spongy tissue produced by the partial erosion of the primary periosteal bone is disposed, whilst externally there is the dense envelope made up of the more recent periosteal growth. Growth of Bone. — The above description, whilst explaining the growth of bone circumferentially, fails to account for its growth in length ; hence the necessity in long bones for some arrangement whereby ossification may take place at one or both extremities of the body. This zone of growth is situated where the ossified body becomes continuous with the cartilaginous epiphysis. In addition, within these epiphysial cartilages calcification of the cartilage takes place centrally, just as in the diaphysis. The two parts of the bone, viz., the diaphysis and epiphysis, are thus separated by a layer of cartilage, sometimes called the cartilage of conjuga- tion, as yet uncalcified, but extremely active in growth owing to the invasion of vessels and cells from a vascular zone which surrounds the epiphysis. The nucleus of the epiphysis becomes converted into true bone, which grows eccentrically. This arrangement provides for the growth of the shaft towards the epiphysis, and the growth of the epiphysis towards the shaft ; so that as long as the active intervening layer of cartilage persists, extension of growth in a longitudinal direction is possible. As might be expected, experience proves that growth takes place more actively, and is continued for a longer time, at the end of the bone where tlie epiphysis is the last to unite. In consequence, surgeons sometimes term this the " growing end of the bone." Subsequently, however, at variable periods the intervening layer of cartilage becomes calcified, and true bony growth occurs within it, thus leading to complete osseous union between the shaft and epiphysis. When this has taken place all further growth in a longitudinal VERTEBRAL COLUMN. 87 direction ceases. lu cases where the epiphysis enters into the formation of a joint, the cartilage over the articular area persists and undergoes neither calcification nor ossitication. Vascular, Lymph, and Nervous Supply of Bone. — From what has been said it will 1)6 gatherod that the vascular Hiipply of the bone is derived from the vessels of the periosteum. These consist of Hue arteries which enter the surface of the diaphysis aud epiphysis ; but in addition there is a larger trunk which enters the diaphysis aud reaches the medullary cavity. This is called the nutrient artery of the bone. The direction taken by this vessel varies in different bones. In the upper limb the artery runs distally in the case of the humerus and proxinuilly in the radius and ulna ; in the lower limb the nutrient vessel of the femur is directed towards the proximal extremity of the shaft, whilst in the tibia and fibula it follows a distal course. The direction of the nutrient artery in the bone is a mechanical restilt of the uuequal growth of the two extremities of the bone. During the greater part of intra-uteriue life the principal nutrient arteries of the long bones are directed towards the distal extremity of the limb. In the process of development the point of entrance of the artery is turned away from the epiphysis which furnishes the greatest amount of bone, and thus, together with tlie nutrient canal, acquires an obliquity directed towards the extremity of the bone which develops last (Piollet, J. de I'Anat. et de la Phys., 1905, p. 57). It may assist the memory to point out that when all the joints are flexed, as in the position occupied by the fcetus in utero, the direction taken by the vessels is the same, and corresponds to a line passing from the head towards the tail-end of the embryo. Consequently, in the upper limb the vessels run towards the elbow, whilst in the lower limb they pass from the knee. The veins which permeate the spongy texture of the bone are large and thin- walled. They do not accompany the arteries, and, as a rule, in long bones they escape through large openings near the articular surfaces. In flat bones they occupy channels witliin the diploe, and drain into an adjacent sinus, or form communica- tions with the superficial veins of the scalp. The lymph vessels are mainly periosteal, but enter the bone along with the blood-vessels and become perivascular. The nerves which accompany the arteries are probably destined for the supply of the coats of these vessels. Whether they end in the bony tissue or not is unknown. The attention of anatomists has long been directed to the elucidation of the laws which regulate bone-growth. Our present knowledge of the subject may be briefly summarised in the following generalisations : — 1. In bones with a shaft and two epiphyses, the epiphysis towards which the nutrient artery is directed is the first to unite with the shaft. 2. In bones with a shaft and two epiphyses, as a rule the epiphysis which com- mences to ossify latest unites soonest with the shaft. (The fibula is a notable exception to this rule.) 3. In bones with a shaft and one epiphysis the nutrient artery is directed towards the end of the bone which has no epiphysis. (This arrangement holds good in the case of the clavicle, the metacarpus, metatarsus, and phalanges.) 4. When an epiphysis is ossified from more than one centre, coalescence takes place between the separate ossific nuclei before the epiphysis unites with the shaft. Highly suggestive, too, are the following propositions — That ossification first commences in the epiphysis which ultimately acquires the largest relative propor- tion to the rest of the bone, and that the ossification of the epiphysis is also correlated with its functional importance. In cases of long bones with only one epiphysis, the epiphysis is placed at the end of the bone where there is most movement. . COLUIVINA VERTEBRALIS. The vertebral column of man consists of thirty-three superposed segments or vertebrae. In the adult, certain of these vertebrie have become fused together in the process of growth to form bones, the segmental arrangement of which 88 OSTEOLOGY. is somewhat obscured, though even in their fully developed condition sufficient evidence remains to demonstrate their compound nature. The vertebne so blended are termed the fixed or false vertebrse, whilst those between which osseous union has not taken place are described as the movable or true vertebrae. This fusion of the vertebral segments is met with at each extremity of the vertebral column, more particularly the lower, where the column is modified to adapt it for union with the girdle of the lower limb, and where also man's degenerated caudal appendage is situated. But a partial union of the vertebral segments also takes place at the upper end of the column, between the highest two vertebra?, in association with the mechanism necessary to provide for the movements of the head on the column. For descriptive purposes the vertebral column is subdivided according to the regions through which it passes. Thus the vertebrte are described as cervical (vertebrae cervicales), thoracic (vertebrae thoracales), lumbar (vertebrae lumbales), sacral (vertebrae sacrales), and coccygeal (vertebrae caudales), according as they lie in the regions of the neck, thorax, loins, pelvis, and tail. The number of vertebrae met with in each region is fairly constant, though, as will be hereafter pointed out, variations may occur in the number of the members of the different series. The vertebrae in man are thus apportioned — 7 cervical, 12 thoracic, 5 lumbar, 5 sacral, and 4 or 5 coccygeal ; the former three groups comprise the true or mov- able vertebrae, the latter two the false or fixed vertebrae. The vertebral formula may be thus expressed : — Movable or True Vertebrae. Fixed or False Vertebrae. Cervical. Thoracic. Lumbar. Sacral. Coccygeal. 7 12 5 5 4 =33. The vertebrae, though displaying great diversity of characters in the regions above enumerated, yet preserve certain features in common. All possess a solid part, corpus vertebrae or body (centrum) ; all have articular processes by which they articulate with their fellows ; most have muscular processes developed in connexion with them ; whilst the majority display a vertebral foramen formed by the union of a bony arcus vertebrae (vertebral arch) with the body. These common characters may best be studied by selecting for description an intermediate member of the series. For this purpose one of the middle or lower thoracic vertebrae may be chosen. A typical vertebra may be described as consisting of a body composed of a mass of spongy bone, more or less cylindrical in form. The size and shape of the body is liable to considerable variation according to the vertebra examined. The superior and inferior surfaces of the body are very slightly concave dorso- ventrally and from side to side, due to the thickening of the bone around its margins. In the recent condition these surfaces afford attachment for the inter- vertebral fibro-cartilages, which are placed like pads between the bodies of the movable members of the series. The circumference of the body, formed as it is of more compact bone than the interior, is usually slightly concave from above downwards, though the dorsal surface becomes flat, where the body forms the anterior boundary of the vertebral foramen, at which point it is usually slightly concave from side to side. The vertical surfaces of the body are pierced here and there by foramina for the passage of nutrient vessels, more particularly on the dorsal surface, where a depression of considerable size receives the openings of the canals through which some of the veins which drain the body of the bone escape. Connected with the body posteriorly there is a bony vertebral arch, which, by its union with the body, encloses a foramen of variable size, called the vertebral foramen. When the vertebrae are placed on the top of each other these, foramina form, with the uniting ligaments, a continuous canal — vertebral canal — in which the spinal medulla, with its coverings, is lodged. The vertebral arch, which is formed by the union of the roots of the vertebral arches (pedicles) and laminae, besides enclosing the vertebral foramen, also supports the spinous and trans- verse processes, which may be regarded as a series of levers to which muscles are VEllTEBRAL COLUMN. 89 Fovea cosUilis tnumversuliH Fovea coslaliH Hiiiierior Hoi of t... v.rt..b,«i ..rci. cesses are united to the arcli. Each root is compressed from side to siile, and luxs rounded superior and in- ferior borders. Since the vertical breadth of the roots is not as great as the heiglit of the body to which they are attached, it follows that when the vertebrie are placed one above the other a series of intervals is left between the roots of the vertebral arches of the difl'ereut vertebrie. These spaces, enclosed anteriorly by the bodies of tiie verte- bra3 and their intervertebral libro- cartilages and posteriorly by the coaptation of the articular processes, form a series of holes communicat- ing with the vertebral canal ; they are called the intervertebral foramina, and allow the transmission of spinal nerves and vessels. As each inter- vertebral foramen is bounded above and below by one of the roots of the vertebral arch, the grooved surfaces in correspondence with the upper aud lower borders of the roots are called the incisurae vertebrales superior et inferior (upper and lower intervertebral notches). Posteriorly, the two roots of each vertebral arch are united by two somewhat flattened plates of bone — the laminae — which converge towards the median plane, and become fused with the root of the projecting spinous process. The vertical lengths or heights of the laminae and their sloping arrangement are such, that, when the vertebrae are articulated together, they leave little space between them, thus enclosing fairly completely the vertebral canal, of which they form the posterior wall. The edges and inner surfaces of the laminae are rough for the attachment of the ligaments which bind them together. The muscular processes are three in number, viz., two processus transversi — one on either side — and one central or median, the processus spinosus. The transverse processes project laterally on either side from the arch at the point where the root of the vertebral arch joins the lamina. The spinous process extends backwards in the median plane from the point of fusion of the lamime. The spinous processes display much variety of length and form. The articular processes (zygapophyses), four in number, are arranged iu pairs — one superior, the other inferior ; the former are placed on the upper part of the arch where the roots of the arch (pedicles) and lamime join, the latter on the lower part of the arch in correspondence with the superior. Whilst differing mucii in the direction of their articular surfaces, the upper have generally a backward tendency, whilst the lower incline forwards. Fovea cos talis trans- verealis Superior articular process Uoiit of the vertebral arch Fovea costalis inferior Fig. 106. — Fifth Thoracic Vektebka, (A) as viewed from the riglit side, (B) as viewed from above. 90 OSTEOLOGY. THE TRUE OR MOVABLE VERTEBRAE. Vertebrae Cervicales. The cervical vertebrae, seven in number, can be readily distinguished from all the other vertebrae by the fact that their transverse processes are pierced by a foramen. The highest two, and the lowest, require special description ; the remaining four conform to a common type. Their bodies, the smallest of all the true vertebrae, are oblong in shape, the transverse width being much longer than the antero- posterior diameter. The superior surface, which slopes from behind forwards and downwards, is concave from side to side, owing to the marked projection of its lateral margins. Its anterior lip is rounded off, whilst its posterior edge is sharply defined. The inferior surface, which is more or less saddle-shaped, is directed downwards and backwards. It is convex from side to side, and concave from before backwards, with a slight rounding off of the projecting anterior lip. The vertical diameter of the body is small in proportion to its width. The anterior surface is flat in the middle line, but furrowed laterally. The posterior surface, which is rough and pierced by many small foramina, is flat from side to side and above downwards ; it forms part of Bifid spine Superior articular process Superior notch Foramen transversarium Inferior notch Inferior articular process . ^ /#i Foramen transversarium I iSpinous process Anterior tubercle A g Fig. 107. — Focbth Cervical Vertebra, (A) from above, and (B) from the right side. the anterior wall of the vertebral foramen. The lateral aspect of each body, par- ticularly in its upper part, is fused with a root of the arch and with the costal part of a transverse process, and forms the medial wall of a foramen transversarium. The roots of the vertebral arcbes, which spring from the posterior half of the lateral aspects of the body, about equidistant from their superior and inferior margins, are directed horizontally backwards and laterally. The superior and inferior notches are nearly equal in depth. The laminae are long, and about as high as the bodies of the bone. The vertebral canal is larger than in the thoracic and lumbar regions ; its shape is triangular, or more nearly semilunar. The transverse processes, so called, are pierced by the foramen transversarium (vertebrarterial or transverse foramen). They consist of two parts — the part behind the foramen, which springs from the vertebral arch and is the true transverse process, and the part in front, which is homologous with a rib in the thoracic portion of the column. These two processes are united laterally by a bridge of bone, which thus converts the interval between them into a foramen, and they terminate, beyond the bridge, in two tubercles, known as the anterior and posterior tubercles. The general direction of the transverse processes is laterally, slightly forwards, and a little downwards, the anterior tubercles lying medial to the posterior. The two tubercles are seY)arated above by a groove directed laterally, downwards, and forwards ; along this the spinal nerve trunk passes. The foramen transversarium is often subdivided by a spicule of bone. In the recent condition and in the cases of the upper six vertebrae it is traversed by the vertebral artery and vein. The spinous processes, which are directed backwards, are short, compressed vertically, and Ijifid. The articular processes are supported on cylindrical masses of CERVICAL VEKTEBRiE. 91 bone fused with the arch where the roots of the vertebral arches and tlie lamiuaj join. These cylinders are sliced away obliquely above and Ijelow, so that the superior articular facets; more or less circular in form, are directed upwards and backwards, whilst the corresponding inferior surfaces are turned downwards and forwards. The Atlas or First Cervical Vertebra. — This bone may l)e readily recognised by the aljsenci^ of the Inxly and spinous process. It consists of two lateral masses, wliich support the articular and transverse processes. The lateral masses are them- selves united by two curved bars of bone, the anterior and posterior arches, of whicli the former is the stouter and shorter. Each lateral mass is irregularly six-sided, and so placed that it lies closer to its fellow of the opposite side in front than behind. Its upper surface is excavated to form an elongated oval facet called the superior articular fovea, wliich is concave from ])efore backwards, and inclined obliquely medially ; not infrequently this articular surface displays indications of division into two parts. The superior articular fovete are for the reception of the condyles of the occipital bone. The inferior articular foveae or facets are placed on the inferior surfaces of the lateral masses. Of circular form, they display a slight side-to-side con- cavity, though Hat in the antero- posterior direction. Their disposition is such that their surfaces incline downwards and slightly medially. They rest on the superior articular processes of the second cervical vertebra or epistropheus. Springing from the an- terior and medial aspects of the lateral masses, and uniting them in front, is a curved bar of bone, the arcus anterior (anterior arch); compressed on each side, and thickened centrally so as to form on its an- terior aspect the rounded tuberculum anterius (an- terior tubercle). In corre- spondence with this, on the posterior surface of this arch is a circular (fovea dentis) for articulation with the dens of the epistropheus. The medial surface of the lateral mass is rough and irregular, displaying a tubercle for the attachment of the transverse ligament of the atlas, which passes across the space included between the two lateral masses and the anterior arch, thus holding the dens of the epistropheus in position. Behind each tubercle there is usually a deep pit, opening into the bottom of which are the canals for the nutrient vessels. Laterally to the lateral mass, and principally from its upper half, the transverse process arises by two roots which include between them the foramen trans- versarium. The transverse process is long, obliquely compressed, and down-turned ; the anterior and posterior tubercles have fused to form one mass. The posterior arch arises in part from the posterior surface of the lateral mass, and in part from the posterior root of the transverse process. Compressed from above downwards anteriorly, where it bounds a groove which curves around the posterior aspect of the superior articular process, which groove is also continuous laterally with the foramen transversarium, the posterior arch becomes thicker medially, at which point it displays posteriorly a rough irregular projection — the tuberculum posterius (posterior tubercle), the feeble representative of the spinous process. A prominent little tubercle, arising from the posterior extremity of the superior articular process, overhangs the groove above mentioned, and not in- FiG. 108.- 1. Posterior arch. 2. Transverse process. 3. Tubercle for transverse ligament. 4. Anterior arch. 5. Anterior tubercle. -The Atlas kuom above. 6. Surface for articulation with dens. 7. Superior articular surface. 8. Foramen for vertebral arterj'. 9. Groove for vertebral artery. 10. Posterior tubercle. facet 92 OSTEOLOGY. frequently becomes developed so as to form a bridge of bone across it, converting the groove into a canal through which the vertebral artery and the posterior ramus of the suboccipital nerve pass — a condition normally met with in many animals. It is noteworthy that the grooves traversed by the highest two spinal nerves lie behind the articular processes, in place of in front, as in other parts of the column. The ring furmed by the lateral masses and the anterior and posterior arches is of irregular outline. The anterior part, cut off from the rest by the transverse ligament, serves for the lodgment of the dens of the epistropheus ; the larger part behind corresponds to the upper part of the vertebral canal. Epistropheus or Second Cervical Vertebra. — This is characterised by the presence of the tooth-like dens (O.T. odontoid process) which projects upwards from the superior surface of the body. Slightly constricted where it joins the body, the dens tapers to a blunt point superiorly, on the sides of which there are surfaces for the attachment of the alar ligaments. When the atlas and epistropheus are articulated this process lies behind the anterior arch of the atlas, and displays on its anterior surface an oval or circular facet which rests on that on the posterior surface of the anterior arch of the atlas. On the posterior aspect of the neck of the dens there is a shallow groove in which lies the transverse ligament of the atlas, which holds the dens in position. Dens Groove for transverse ligament of the atlas ^ / Superior articular surface Articular surface for anterior arch of atlas Dens Foramen for vertebral artery rm Inferior articular ^^ .i . i,mi -i t, J„arked. ^^^h lor the twelfth rib. Its S. Superior "| Tubercles corre- sponiliiig to I. Inferior E. Latf!ral f Mamillary. J Accessory. I Transverse of lumbar. transverse processes, short and stunted, have no facets, and are broken up into smaller tubercles, called the lateral, superior, and inferior tubercles. These are homologous with the trans- verse, mamillary, and accessory processes of the lumbar vertebrae. Indica- tions of these processes may also be met with in the tenth and eleventh thoracic vertebrae. The twelfth thoracic vertebra may usually be distinguished LUMBAK VERTEBRAE. 95 from the eleventh hy the arran^'omcnt of its inferior articular Y)rocesses, which resemble those of the lumbar series in being turned laterally ; V)ut the eleventh occasionally displays the same arrangement, in which case it is not always easy to distinguish between them. Inferior articular process Mamillary process / Vertebrae Lumbales. The lumbar vertebrae, live in number, are the largest of the movable vertebra3. They have no costal articular facets, nor are their transverse processes pierced by a foramen. In this way they ca,n be readily distinguished from the members of the cervical and thoracic Spinous process series. The body is kidney- shaped in outline, and of large size, exhibiting a gradual transition from the thoracic form in the hitjher sei^ments. The transverse diameter is usually about a half greater than the antero- posterior. The anterior vertical thickness is slightly greater than the posterior, being thus adapted to the anterior convex curve of the column in this region. The roots of vertebral arches (O.T. pedicles), directed horizontally back- wards, are short and stout; the superior notches are shallow, but deeper than in the thoracic region; the inferior grooves are deep. The laminae are broad and nearly vertical, sloping but little. They support on their inferior margins the inferiorarticular processes. The vertebral foramen is large and triangular. The spinous processes, spatula shaped, with a thickened posterior mar- gin, project backwards and slightly downwards. The transverse processes, more slender than in the thor- acic region, pass horizon- tally laterally, with a , i » • • r *i slicrht backward inclination and usually with an upward tilt. Arising Iron) the junction of the roots of the vertebral arches with the laminse in the higher members of the series, they tend to advance so as to become fused with the lateral side of the root and posterior aspect of tlie body in the lower two lumbar vertebrae. In these latter vertebra the superior intervertebral grooves are carried obliquely across the superior surfaces of the bases of the transverse processes. The transverse processes lie in line with the lateral tubercles of the lower thoracic vertebrae, with Bo.iy Superior articular process Mamillary process Transverse jirocess profess Inferior articular process Fig. 111. — Third Lumbar Vertebra, (A) from above, and (B) from the left side. 96 OSTEOLOGY. which they are serially homologous, and are to be regarded as representing the costal elements. Placed on their bases posteriorly, and just lateral to and inferior to the superior articular processes, are the small accessory processes, which are in series with the inferior tubercles of the lower thoracic vertebrse. The superior articular processes are stout, oval, curved plates of bone, fused in front with the roots and laminae, and having their concave articular surfaces vertical and turned medially. Laterally, and on their posterior edge, the bone rises in the form of an elongated oval tubercle, the processus mamillaris (mamillary process) ; these are in correspondence with the superior tubercles of the lower thoracic transverse processes. The inferior articular processes lie on either side of the root of the spinous process, supported on the inferior margin of the laminse. Their articular surfaces, oval in outline, convex from side to side, and plane from above downwards, are turned laterally. The inferior articular processes are much closer together than the superior ; so that when the vertebrae are articulated the superior articular processes of the lower vertebra embrace the inferior articular processes of the higher vertebra. The fifth lumbar vertebra is characterised by the size of its body, which is the largest of all the vertebrae. Further, the inferior surface of the body is cut away at the expense of its posterior part : hence the thickness of the body in front much exceeds the vertical diameter behind. By its articulation with the first sacral segment the inferior border of the body of this bone assists in the formation of the sacro-vertebral angle. The transverse process is pyra- midal in form, and stouter than those of the other lumbar vertebrae. It arises by a broad base from the side of the back of the body, as well as from the pedicle, and is directed laterally and a little backwards and upwards. Its upper surface is slightly grooved by the superior intervertebral notch. A deep notch separates it posteriorly from the superior articular processes, which are less in-turned than in the other members of the series, their articular surfaces being directed more backwards than inwards, and displaying less concavity. The inferior articular processes are further apart than is the case with the other members of the series : they lie in line with the superior. The spinous process is shorter and narrower than the other lumbar spines, particularly so in the female. The vertebral canal is somewhat compressed at its lateral angles. THE FALSE OR FIXED VERTEBRAE. Os Sacrum. The sacrum, of roughly triangular shape, is formed normally by the fusion of five vertebrae. The anterior surface of the bone is slightly hollow from side to side and concave from above downwards, the curve being usually most pronounced opposite the third sacral segment. The central part corresponds to the bodies of the sacral vertebrae, the lines of fusion of which are indicated by a series of four parallel ridges which cross the median part of the bone at gradually diminish- ing intervals from above downwards ; on each side these ridges disappear on the medial walls of the four anterior sacral foramina. The size of these holes decreases from above downwards. The upper and lower border of each foramen is formed by a stout bar of bone, of which there are five oh each side, corre- sponding in number with the vertebrae present. These unite laterally so as to form the pars lateralis (O.T. lateral mass), thus enclosing the foramina to the lateral side, though there the edge is not abrupt, but sloped so as to pass gradually into the canal. The large anterior rami of the sacral nerves pass through these foramina and occupy the shallow grooves. The bone is broadest across the first sacral vertebra, tends to narrow opposite the second, and again usually increases in width opposite the third. When this condition is well marked, the edge has a notched appearance (sacral notch) wliich assists in the interlocking of the sacro- THE SACRUM. 97 iliac joint ; this feature is common in the Simiidic and some of the lower races of mankind (Puterson). The surface of bone between and lateral to the first, second, third, and fourth foramina affords attachment to the ftbres of origin of the piriformis, wliich may in some instances extend on to the bodies of the second and third segments (Adolphi), whilst on the edge lateral to and below the fourth foramen the coccygeus is inserted. The posterior surface is rough and irregular. Convex from above downwartls, it displays in the median plane the crista sacralis media, a crest whereon are seen four elongated tubercles — the spines of the upper four sacral vertebrte. Lateral to these the bone forms a groove — the sacral groove — the floor of which is made up of the confluent lamime of the corresponding vertebra.'. In line with the intervals between the spines, and wider apart above than below, another series of tubercles is to be Superior articular processes Transverse process of first sacral vertebra Ala Anterior siicral foramen Inferior lateral angle. Groove for tifth sacnil nerve C^ - . .'n'.ai- surface Fig. 112. — The Sacrum (anterior view). seen. These are due to the fusion of the articular processes of the sacral vertebr?e, which thus form faint interrupted ridges on each side of the bone (cristae sacrales articulares). Normally, the spine of the lowest sacral segment is absent, and the laminse do not coalesce medially, thus leaving a gap in which the sacral canal is exposed (Matus sacralis) ; whilst interiorly the tubercles corresponding to the inferior articular processes of the last sacral vertebra form little down-projecting processes — the sacral comua — by means of which the sacrum is in part united to the coccyx. Just wide of the articular tubercles are the posterior sacral foramina, for the transmission of the posterior rami of the sacral nerves. These are in correspondence with the anterior foramina, so that a probe can be passed directly through both openings; but be it noted that the posterior are much smaller, and their margins much sharper, than is the case with the anterior. The surface of the pars lateralis (lateral mass) lateral to the posterior sacral foramina is rough and irregular, owing to the presence of four more or less elevated tubercles, which constitute the lateral ridges on either side of the bone (cristae sacrales 7 98 OSTEOLOGY. laterales), and which are serially homologous with the true transverse processes of the lumbar vertebrie. The posterior surface of the bone furnishes an extensive surface for the origin of the sacro- spinalis, whilst the edge of the bone lateral to the third and fourth foramen gives attachment to the glutaeus maximus. The base of the bone displays features more in accordance with a typical vertebra. Centrally, and in front, is placed the body, the superior surface of which articulates with the last lumbar vertebra through the medium of an intervertebral fibro-cartilage. The anterior margin is thin and projecting, overhanging the general concavity of the pelvic surface of the bone, and forming what is called the promontory. Posterior to the body, the sacral canal, of triangular form but slightly compressed dorso-ventrally, is seen, whilst still more posteriorly is the short spinous Superior aperture of sacral canal Superior articular process Transverse process '^ ^^/i \>;,„ Posterior sacral forampn -^^ '■''' Inferior lateral angle- - Sacral cornu Inferior ajierture of sacral canal Groove for fifth sacral nerve Coccygeal articular surface Fig. 113. — The Sacrum (posterior view). process, forming the highest tubercle of the median crest. Spreading out from the sides, and partly from the back of the body on each side, is a fan-shaped mass of bone, the upper surface of which is slightly concave from side to side, and convex from above and behind downwards and forwards. This, the ala sacralis, corresponds to the thick upper border of the lateral part, and is formed, as will be explained hereafter, by elements which correspond to the roots of the vertebral arches (O.T. pedicles) and the transverse processes of the sacral vertebrae, together with superadded structures — the sacral ribs. The lateral margin of the lateral part, as seen from above, is sharp and laterally convex, terminating posteriorly in a prominent tubercle — the highest of the series of elevations seen on the posterior surface of the bone, which have bee"n already described as serially homologous with the true transverse processes of the lumbar vertebrae. Fused with the dorsal surface of each lateral part, and separated from it laterally by a narrow but deep notch, is the superior articular process. This supports a vertical articular surface, which is of circular or oval form, and con- cave from side to side, having a general direction backwards and a little medially. The borders of the sacrum are thick above, where they articulate with the ilia. THE COCCYX. 99 tliia ami taperiug below, wiiere they furnish attachments for the powerful sacro- tuberous ligaments (O.T. great 'sacro-sciatic). The iliac articiilar surfaces are described as auricular in shape (facies auricularis), and overlie the lateral parts formed by the Hrst three sacral vertebra-, tliou;^di this arrangement is liable to con- siderable variation. Posterior to the auricular surface the bone is rough and pitted by three distinct depressions for the attachment of the strong Siicro-iliac ligaments. Inferiorly, the edge formed by the lateral parts of the fourth and fifth sacral vertebrae becomes gradually thinner, and at the inferior lateral angle changes its direction and sweeps medially towards the body of tiie hfth sacral segment. The apex, or lower end of the sacrum, is formed by the small oval body of the fifth sacral vertebra, which articulates with the coccyx. The sacral canal follows the curve of the bone ; more or less triangular in shape above, it becomes compressed and flattened dorso-veutrally below. Inferiorly, its posterior wall is deficient owing to the imperfect ossification of the laminte of the fifth, and, it may be, of the fourth sacral segments. Passing obliquely downwards and laterally from this canal into the lateral parts on either side are the four pairs of intervertebral foramina, each of which is connected laterally with a V-shaped canal which terminates in front and behind in the anterior and posterior sacral foramina. The posterior limb of the V is shorter and narrower than the anterior. The female sacrum is proportionately broader than the male, its curves are liable to great individual variation ; usually it is flattened above, and somewhat abruptly curved below, as contrasted with the male sacrum, in which the curve is more uniformly distributed throughout the bone. In the female the absolute depth of the curve is less than in the male. The iliac articular surface of the female sacrum is smaller than, and of a different shape from, that of the male ; in the majority of cases it only extends over two sacral segments, whereas in the male it invariably includes a part, and at times the whole of the third segment (Derry). The variation in the proportions of the breadth to the length of the sacrum is expressed by the formula — ^ -, = Sacral Index. Sacra with an index above ^ -^ length 100 are platyhieric and are generally characteristic of the higher races, those with an index below 100 are dolichohieric and are more commonly met with in the lower races of men. The average European index is 1124 for males and 11G"8 for females. Os Coccygis. The coccyx consists of four — sometimes five, less frequently three — rudimentary vertebrse, which tend to become fused. The first piece is larger than the others ; it has an oval hollow 34 34 facet on its superior sur- face, which articulates with the body of the last sacral segment. Pos- teriorly, two processes, comua coccygea, which lie in series with the articular processes of the sacrum, extend upwards and unite with the sacral comua, thus bridging over the notch for the exit of the fifth sacral nerve, and converting it into a foramen, the last of the intervertebral ^- Transverse process, series. From the sides of the body project rudimentary transverse processes, which may, or may not, unite with the sacrum close to the lower lateral angles ; in the latter case the fifth anterior sacral foramina are enclosed. Inferiorly, the body of the bone articulates with the succeeding vertebra. The second coccygeal vertebra displays Fio. 114. — The Coccyx. A. Posterior Surface. B. Anterior Surface. 2. Transverse process. 3. For Sacrum. 4. Coriiu. 100 OSTEOLOGY. slight traces of a transverse process and the rudiments of roots of the vertebral arch. The succeeding segments are mere rounded or oval-shaped nodules of bone. Fusion between the lower elements occurs normally in middle life, whilst union between the first and second segments occurs somewhat later. It is not unusual, however, to find that the first coccygeal vertebra remains separate from the others. Though very variable, as a rule, fusion occurs more commonly in the male, and at an earlier age, than in the female. Szawlowski has recorded a case in which a curved pi'ocess arose from the ventral surface of the first coccygeal segment. He regards this as possibly the homologue of a ventral arch {Anat. Am. Jena, vol. xx. p. 320). From the posterior surface of the coccyx the glutseus maximus arises, whilst to it is attached the filum terminale of the spinal medulla. To its borders are attached the coccygei and levatores ani muscles; and from its tip spring the fibres of the sphincter ani externus. THE VERTEBRAL COLUMN AS A WHOLE. When all the vertebrae are articulated together, the resulting column displays certain characteristic features. The division of the column into a true or movable part, comprising the members of the cervical, thoracic, and lumbar series, and a false or fixed portion, including the sacrum and coccyx, can be readily recognised. The vertebrae are so disposed that the bodies form an interrupted column of solid parts anteriorly, which constitutes the axis of support for the head and trunk; whilst the vertebral arches posteriorly provide a canal for the lodgment and protection of the spinal medulla and its membranes. In the movable part of the column both the anterior supporting axis and the vertebral canal are liable to changes in their disposition, owing to the movements of the head and trunk. Like the bodies and vertebral arches, the spinous and transverse processes are also supeq^osed, and fall in line, forming three series of interrupted ridges — one (the spinous) placed centrally and behind, the others (the transverse) placed laterally. In this way two vertebral grooves are formed which lie between the central and lateral ridges. The floor of each groove is formed by the laminae and articular processes, and in these grooves are lodged many of the muscles which serve to support and control the movements of the column. Further, the column so constituted is seen to display certain curves in an antero- posterior direction. These curves are, of course, subject to very great variation according to the position of the trunk and head, and can only be satis- factorily studied in a fresh specimen ; but if care is exercised in the articulation of the vertebrae, the following characteristic features may be observed, assuming, of course, that the column is erect and the head so placed that the axis of vision is directed towards the horizon. There is a forward curve in the cervical region, which gradually merges with the backward thoracic curve ; this becomes con- tinuous below with an anterior convexity in the lumbar region, which ends more or less abruptly at the union of the fifth lumbar with the first sacral vertebra, where the sacrum slopes suddenly backwards, causing the column to form a marked projection — the sacro-vertebral angle. Below this, the anterior concavity of the front of the sacrum is directed downwards as well as forwards. Of these four curves, two — the thoracic and sacral — are primary, they alone exist during foetal life ; whilst the cervical and lumbar forward curves only make their appearance after birth — the former being associated with the extension and elevation of the head, whilst the latter is developed in connexion with the use of the hind limb in the hyper-extended position, which in man is correlated with the assumption of tlie erect posture ; this curve, therefore, only appears after the child has begun to walk. For these reasons the cervical and lumbar curves are described as secondary and compensatory. Not infrequently there is a slight lateral curvature in the thoracic region, the convexity of the curve being usually directed towards the right side. This may be associated with a greater use of the muscles of tlie right upper limb, or may depend on the pressure exercised by the upper part of the tlioracic aorta on the THE VEETEBRAL COLUMN AS A WHOLE. 101 vertebrie of the thonicic region, thus causing a slight lateral displacement, together with a flattening of the side of the fifth thoracic vertebra (impressio aortica) as was first pointed out by Wood {Journ. Anat. and Physiol. vol. iii.). Above and below this curve there are slight compensatory curves in the opposite direction. The line wliich unites the tips of the spinous pro- cesses is not a repetition of the curves formed Vjy the bodies. This is due to the fact that the length and direction of thespinous processes vary much in different regions ; thus, in the neck, with the exception of the second, sixth, and seventh, they are all short (absent in thecaseof theatlas). In the thoracic region the spinous processes, though long, are obliquely placed — a circum- stance which mucli reduces their prominence ; that of v the seventh thoracic vertebra is usually the longest and most slanting. Below that point their length gradually decreases, and their position more nearly approaches the horizontal. In the loins the spinous processes have all a slight downward direction. The spinous processes of the upper three or four sacral vertebrae form an osseous ridge with interrupted tubercles. The ridge formed by the vertebral spines is an important determinant of the surface form, as it corresponds to the median furrow of the back, and there the individual spines may be felt and counted from the seventh cervical down to the sacral region. That is best done when the back is well bent forwards. Taken as a whole, the spinous ])i'ocesses of the movable vertebrte in man have a downward inclination — a character which he shares with the anthropoid apes and a few other animals. This character serves to distinguish his column from those of lower mammals in which the spines of the lumbar vertebrae are directed head wards towards the "centre of motion," which is usually situated near the caudal extremity of the thorax, where a vertebra is placed the direction of whose spine is vertical to the horizontally disposed column ; this vertebra is often referred to as the anticlinal vertebra. As viewed from the front, the vertebral bodies increase in width from the second cervical to the first thoracic ; thence a reduction in breadth takes place to the level of the fourth thoracic, below which there is a gradual increase in their transverse dia- meters until the sacrum is reached. There a rapid reduction in width takes place, terminating interiorly in the nodules of the coccyx. The transverse processes of the atlas are wide and outstanding. The succeeding four cervical vertebras have transverse processes of nearly equal width ; the seventh, however, displays a marked increase in its transverse diameter, and is alDout equal in width to the first thoracic vertebra. Below this a gradual and regular diminution in width characterises the trans- verse processes of the thoracic vertebrae, until in the case of the eleventh and twelfth they are merely represented by the small lateral tubercles. In the luml)ar region the transverse processes again appear outstanding, and of nearly equal length. The transverse diameter of the lateral parts of the first sacral vertebra forms the widest part of the column. Below that, a decrease in width occurs until the 7a Fig. 115. — Vertebkal Column FROM THE Left Side. 102 OSTEOLOGY. level of the third sacral segment is reached, at which point the transverse diameter is somewhat abruptly diminished, a reduction in width which is further suddenly accentuated opposite the fifth sacral segment. As viewed from the side, the bodies display a gradual increase in their antero-posterior extent until the second lumbar vertebra is reached, below which, that diameter is slightly reduced. In the sacral region the reduction in the antero-posterior diameter is great in the first and second sacral segments, more gradual and less marked in the last three segments. The facets for the heads of the ribs in the upper thoracic region lie on the sides of the bodies ; those for the tenth, eleventh, and twelfth are placed farther back on the roots of the vertebral arches. The intervertebral foramina increase in size from above downwards in the movable part of the column, being largest in the lumbar region. In the sacral region they decrease in size from above downwards. In the cervical region the highest two cervical nerves pass out behind the articular ^, processes of the atlas and epistropheus, and lie, therefore, ^ klJ behind the corresponding transverse processes of those vertebrge. The succeeding cervical nerves pass out through the intervertebral foramina, which are placed between the transverse processes and anterior to the articular processes. In the thoracic and lumbar vertebrse the intervertebral foramina lie anterior to both the articular and transverse processes. The arrangement of the intervertebral foramina in the sacrum has been already sufficiently explained. The vertebral canal for the lodgment of the spinal medulla and its meninges is largest in the cervical and lumbar regions, in both of which it assumes a triangular form ; whilst it is narrow and circular in the thoracic region. These facts are correlated with the movements of the ^^■^. column which are most free in those regions where the canal is largest, i.e. the neck and loins. The average length of the vertebral column is from 70 to 73 centimetres, or from 21\ to 28| inches. Of this the cervical part measures from 13 to 14 cm. ; the thoracic, 27 to 29 cm.; lumbar, 17 to 18 cm.; and the sacro- coccygeal, 12 to 15 cm. The individual differences in the length of the column are less than one might expect, the variation in height of different individuals being often largely dependent on the length of the lower limbs. In the female the average length of the column is about 60 centimetres, or 23| inches, and the curve in the lumbar region is usually move pronounced. DEVELOPIVIENT OF THE VERTEBRAL ys COLUMN. The Cartilaginous Column. As has been already stated (p. 37), the neural tube and the notochord are enveloped by a continuous sheath of mesodermal tissue which forms the membranous vertebral column It is by the chondrification of this that the car- Co^Z^L\VZl7oZ^l^... tilaginous column is developed. This process commences about the end of the first or the beginnmg of the second month of foetal life. In correspondence with each vertebral segment, two symmetrical nodules of 'cartilage appear on either side of the notochord; these rapidly surround and constrict it. By their fusion they constitute the body of a r^ I Coccy- ^geal 4-5 THE CARTILAGINOUS COLUMN. 103 cartilaginous vertebra, and are so disposcid that they alternate in position with the muscle plates which are lying on either side. In tliis way a vertebral body corre- sponds in positi(m to the caudal halt' of the anterior myotome, and the ceplialic half of the posterior myotome, the intermyotomic intervals, which contain the connective tissue plates separating the muscle segments, lie in line laterally with the mid- points of the sides of the cartilaginous vertebrae. It is by chondri- fication of these intersegmental layers that in certain regions the ribs are ultimately devidopod. Meanwhile, the scleratogenous tissue between the chondri- fying vertebral bodies undergoes little change and persists as the intervertebral fibro-cartilage. Here the embedded notochord undergoes but slight compression and enlarges, so that if a length of the column be examined in longitudinal section the notochord displays a moniliform appearance, the constricted parts correspond- ing to the bodies, the enlarged portions to the fibro-cartilages. The I'ormer disappear at a later stage when ossification begins, but the latter persist in •the adult as the pulpy core in the centre of the intervertebral fibro-cartilage. The portions of the scleratogenous tissue which lie lateral to the notochord have next to be considered ; these extend dorsalwards around the vertebral canal, and ventralwards beneath the notochord. The former is sometimes called the vertebral bow, the latter the hypochordal bow. The vertebral bow begins to chondrify on each side, and forms the lateral portions of the cartilaginous vertebral VertebKil canal Vertebral bow Notochord Slieatli Hypochordal bow Myotome I -Septum I5ody of vertebra Hypochordal liOW Rib N'otocliord Fig. 117. — The Dkvelopment of the Membranous Basis of a Vertebra (after Keith). A, in transverse section, B, iu horizontal section, showing the relation of the vertebrte to the primitive segments. arch, the extremities of which usually unite dorsally about the fourth month of foetal life ; if from defective development this union should fail to occur a deformity known as spina bifida is the result. From the cartilaginous vertebral arch, so formed, arise the chondrified rudiments of the spinous, transverse, and articular processes. The chondrification of the vertebral arch is variously described as being in- dependent of the body or an extension from it ; in any case, union between it and the body is rapidly effected. The scleratogenous tissue between the cartilaginous vertebral arches which does not undergo chondrification persists as the ligaments uniting the vertebral laminae. As regards the so-called hypochordal bow, for the most part it disappears. By some it is regarded as being represented by a fibrous strand in the inter- vertebral fibro - cartilage on the cephalic side of the vertebra to which it belongs. It is, however, noteworthy that in the case of the atlas vertebra there is an exception to this arrangement; for here the hypochordal bow chondrifies and subsequently by ossification forms the anterior arch of that bone — an arch which lies ventral to, and embraces the dens of the epistropheus {q.v. p. 91). It is only in the thoracic region that the ribs, developed as stated above by the chondrification of the intersegmental septa, attain their full dimensions. In the cervical, lumbar, and sacral regions they exist only in a rudimentary or modified form, as has been described elsewhere. In the construction of the chest wall the ribs are supported ventrally by the sternum, as to the development of which there is some difference of opinion. Ruge has described this bone as formed by the fusion of two cartilaginous bands produced by the coalescence of the expanded ends of the first five 104 OSTEOLOGY. or seven cartilaginous ribs. Paterson, on the other hand, regards the sternum as arising independently of the ribs by the union of a right and left sternal bar in the median ventral line. There are also reasons for supposing that the presternum is intimately associated with the development of the ventral part of the shoulder girdle. Ossification of the Vertebrae- — The vertebrae are developed by ossification of the cartilage which surrounds the notochord and which passes dorsally over the sides of the vertebral canal. The centres for the bodies first appear in the lower thoracic vertebrse about the tenth week. An oval nucleus develops in each body. At first it is placed dorsal to the notochord, but subsequently surrounds and causes the disappearance of that structure. Occasionally, however, the primitive centre appears to be formed by the coalescence of two primary nuclei. Support is given to this view by the occasional occurrence of vertebne in which the body is developed in two collateral halves, or in cases where only one-half of the body persists (Turner) ; normally, however, it is impossible to make out this division. From these single nuclei the bodies are developed, the process extending up and down the cohimn until, by the fifth month, all the bodies possess ossific nodules, except the coccygeal segments. About the seventh Aveek a single centre appears in the vertebral arch on either side. These commence first to ossify in the upper cervical region and extend rapidly downwards throughout the column. They first appear near the bases of the superior articular processes, and extend backwards into the laminae, laterally into the transverse processes, and forwards into the roots of the vertebral Centre arclies. These latter project anteriorly and form a considerable portion for of the postero-lateral aspects of the body, from which, however, they brai*^ are separated by a cartilaginous strip — the neuro-central synchondrosis arch — which docs uot entirely disappear until about the fifth or sixth year. It is important to note that in the thoracic region the costal facets lie ^Centre for behind the neuro-central synchondrosis, and are therefore borne on the ^°'^^ lateral aspects of the roots of the vertebral arches. Fusion of the F 118 — o laminae in the median plane posteriorly begins, after birth, in the lumbar ' OF Vertebra region and extends upwards, so that by the fifteenth month or there- abouts the arches in the cervical region are completed posteriorly. In the sacral region ossification is slower, the vertebral canal not being enclosed till the seventh to the tenth year. The spinous processes are cartilaginous at birth, but they become ossified by the extension into them of the bony laminse. At puberty certain secondary or epiphyseal centres make their appearance ; these are five in number. One caps the summit of the spinous process, except in the cervical region. A single centre on each side appears at the extremity of the transverse process, and in the thoracic region assists in forming the articular surface for the tubercle of the rib. Two epiphysial plates are formed — one for the superior, and the second for the inferior surface of the body, including also that part which lies posterior to the neuro-central synchondi'osis and is formed by the root of the vertebral arch ; from these the thickened circumference of both upper and lower aspects of the body are derived. Fusion of these centres with the rest of the bone is not complete till the twenty-fifth year. In the cervical region independent centres are described as occvirring in the anterior roots of the transverse processes of the sixth and seventh vertebrae. These correspond to the costal element, and may occasionally persist in the form of cervical ribs. Elsewhere they are formed by lateral extensions from the root of the vertebral arch. In the lumbar region the transverse process of the first lumbar vertebra is occasionally associated with an independent costal centre, which may blend with it, or persist as a lumbar rib. The mamillary processes are derived from separate centres. The vertebral arch of the fifth lumbar vertebra is occasionally developed from two centres on each side, as is demonstrated by the fact that the arch is sometimes divided by a synchondrodial joint running obliquely across between the superior and inferior articular processes. (See ante, p. 91; also Fortschritte av,f dem, Gehiete der Rontgenstrahlen. Erganzungsheft i. ; "die Entwickelung des menschlichen Knochengeriistes wahrend des fotalen Lebens," von Lambertz.) At the eighteenth year there are two epiphyses at the end of the costo- transverse process of the fifth lumbar vertebra ; one caps the transverse element, the other caps the costal element (Fawcett). Atlas. — The lateral masses, transverse processes, and posterior arch are developed from two centres — one on each side — which correspond with the centres from which the vertebral arches of the other members of the series are developed. These make their appearance about the seventh week, and do not unite posteriorly till after the third year. Their point of union is sometimes preceded by the formation of a distinct spinal OSSIFICATION OF THE VERTEBRAE. 105 nucleus (Quain). Tlio transverse processes are completed by epiphyses about the eight- eenth year (Fawcett). The anterior arch is developed from centres variously described as single or double, which appear in the hypochordal arch of cartilage described by Froriep {Arch. /. Anat. u. Physiol., Anat. Ahth. 1886) which here persists. In this cartilage ossification conuiiences during the first year of life. Union with the lateral masses is delayed till six or eight years after birth. The lateral extremities of the anterior arch assist in forming the anterior part of the superior articular processes. Epistropheus. — Tlie epistroplieus ossifies from five primitive centres. Of these, two — one on each side — apjjcar about the seventh week, and form the articular and transverse processes, together with the lamiuje and spinous process. One, or it may Vje two, nuclei appear in the inferior part of the body about the fifth month. The superior part of the body, including a small part of the superior articular process, and the base of the dens, S 14 16 Fig. 119. Cei-vic(d vertebra. 1. Centre lor body. 2. Superior epiphysial plate. 3. Anterior bar of transverse process developed by lateral extension from root of vertebral arch. 4. Neuro-central synchondrosis. 5. Inferior epiphysial plate. Lumbar vertebra. 6. Body. 7. Superior ejnjdiysial plate. 8. Epiphysis for mamillary proce.ss. 9. Epiphysis for transverse process. 10. Epiphysis for spinous proces"s. 11. Neuro-central synchondrosis. 12. Inferior epiphysial plate. Thoracic vertebra. Centre for V)ody. Superior epiphysial plate, appears about puberty ; unites at 25th year. Neuro-central synchondrosis does not ossify till 5th or 6th year. 16. Appears at puberty ; unites at 25th year. 17. Appears at puberty ; unites at 25th year. 18. Appears about 6th week. Epistropheus. 19. Centre for transverse process and verteV)ral arch ; appears about 8th week. 20. Synchondroses close about 3rd year. 13. 14. 15 Ossification of VERTEBUiK. 21. Centre for summit of dens ; appears 3rd to 5th year, fuses Sth to 12th year. 22. Ai>pears about 5th or 6th month ; unites with opposite side 7th to Sth month. 23. Synchondrosis closes from 4th to 6th year. 24. Inferior epiphysial plate ; appears about puberty, unites about 25th year. 25. Single or double centre for body ; appears about 5th month. Atlas. 26. Posterior arch and lateral masses developed from a single centre on either side, which appears about 7th week. In this figure the posterior arch is represented complete by the union posteriorly of its posterior elements. 27. Anterior arch and portion of superior articular surface developed from single or double centre, appearing during 1st year. Thoracic vertebra. 28. Epiphysis for transverse process ; appears about puberty, unites aliout 25th year. 29. Epiphysis appears about puberty ; unites about 25th or 27th year. 30. Centre for vertebral arch on either side ; appears aliout 6th or 7th week, the laminae unite from birth to 15th month. The arch is here shown complete posteriorly. 31. Centre for body ; apjiears about 6th week, unites with vertebral arcli from 5th to 6th year. are developed from two laterally-placed nuclei which appear shortl}' after, and fuse together at the seventh or eighth month, so that at birth the bone consists of four pieces. Fusion between these parts takes' place in the following order : — The dens unites with the body and lateral parts about the third or fourth year ; union between the two lateral portions posteriorly and. the body and lateral parts anteriorly, is complete at from four to six years. The summit of the dens is developed from a separate centre, occasionally double, which appears from the third to the fifth year, and fuses with the rest of the bone from the eighth to the twelfth year. About puberty an annular epiphysis is developed on the inferior surface of the body, with which it is completely united during the twentieth to the twenty-fifth year. Some authorities state that a few granules between the base of the dens and the superior sui-face of the body represent the superior epiphysial plate ; but 106 ■ OSTEOLOGY. as fusion between the dens and the body occurs before the time for the appearance of these secondary epiphysial plates, this can hardly be regarded as correct. The line of fusion of the dens with the body is defined by a small disc of cartilage which persists within the substance of the bone till an advanced period of life. A pair of epiphyses placed over the tubercles of the spinous process, if not always present, are at least frequent. Sacrum. — Each of the sacral segments is ossified from three centres : one for the body, and two for the vertebral arch — that for the body, which makes its appearance in the first three sacral vei'tebrse about the end of the third month, about the fifth to the eighth month for the last two segments. From the two centres for the vertebral arches, which make their appearance about the fifth or sixth month in the higher segments, the laminse, articular processes, and the posterior half of the alee on either side are developed. The sacral canal is not enclosed till the seventh to the tenth year, the laminfe usually failing to meet in the lowest segment, and occasionally, to a greater or less extent, in some of the higher segments. The anterior portion of the lateral parts is developed from separate centres which represent the costal elements (Gegenbauer). These appear about the sixth to the eighth month, and may develop in relation to the upper four sacral segments ; more usually they are met with in connexion with the first three, and exceptionally they may be found only in the upper two. It is by fusion of these with the posterior arches that the lateral parts, which support the hip bones,, are formed. The costal elements fuse about the second to the fifth year with the vertebral arches, prior to their union with the bodies ; and the segments of the lateral parts unite with each other sooner than the union of the bodies is effected. The latter only takes place after puberty by the fusion of the epiphysial plates, a pair of which make their appearance between the bodies of each segment. The lower segments begin to unite together about the eighteenth year, but fusion between the first ^"'- ''°;:;:StS" t'r.lrr!i°;.r and second sacral vertebra is not completed till Arrangement of the Costal and Trans- VERSE Epiphyses at the Eighteenth 'tbe twenty-fifth year or after. Year. T., Epiphysis of transverse process. C.V., Ventral epiphysis of costal process. CD., Dorsal epiphysis. In addition to the foregoing there are costal and transverse epi- physes. According to Fawcett they are arranged as follows. Costal epiphyses : The costal pro^ cesses of the I. and II. sacral segments bear at their The numbers indicate the segments to which lateral ends inferiorly two such epiphyses, one . the epiphyses belong. j , , . i ii. i, ^i. • r • ^ ^ •' ^ dorsal and one ventral ; these, by their fusion and expansion mainly in an upward direction, form a plate — the auricular facet. The III. and IV. costal processes have only one epiphysis each, viz., the ventral. All these appear about the eighteenth year. Transverse epiphyses : Epiphyses are developed on all the transverse processes of the sacral vertebrae except the II. Those of the IV. and V. play an important part in the moulding of the lower lateral region of the sacrum. Thus, the transverse epiphysis of the IV. segment becomes comma-shaped by downward and lateral growth, the head of the comma fuses with the costal epiphysis of the III. sacral segment, which in turn unites with the epiphysis of the transverse process of the V. segment, the ultimate result being a Z-like arrangement on the posterior and inferior aspect of the sacrum. The extremities of the superior spinous processes are occasionally developed from independent epiphyses. On making a median section of an adult bone the persistence of the intervertebral fibro-cartilages between the bodies is indicated by a series of oval cavities. Coccygeal Vertebrae. — These are cartilaginous at birth. Each has a separate centre ; the first appears from the first to the fourth year, the second from the sixth to the tenth year, the third and fourth segments at or about puberty. Secondary centres, for the coccygeal cornua and epiphysial plates for the bodies are also described. Fusion of the various segments begins below and proceeds upwards, but is liable to great indi- vidual variation. In advanced life the coccyx is often ossified to the sacrum. THE STERNUM. The sternum occupies the middle of the upper part of the thoracic wall anteriorly. It is connected on each side with the cartilages of the first seven ribs, and supports, superiorly, the clavicles. It consists of three parts, named respectively THE STERNUM. 107 Incisura jugularis Clavicular fac«t III. Rib cartilage — the manubrium or handle ; the corpus stemi or body ; aud the processus xiphoideus (or xiphoid cartilage). Of these the body is formed by the fusion in early life of four setoid aii-cellb Facial nerve Facial canal laid open, displaying the facial nerve within Fig. 139. Preparation to display tlie position and relations of the tympanic antrum. The greater part of the posterior wall of the external acoustic meatus has been removed, leaving onlj' a bridge of bone at its medial ex- tremity ; under this a bristle is displayed, passing from the tympanic antrum through the iter to the cavity of the tympanum. in front of this, and in line with the angle formed by the anterior border and the squamous part, is the slit-like opening of the hiatus canalis facialis, within the projecting lip of which two small orifices can usually be seen. These are the openings of the canalis facialis; if a bristle is passed through the more medial of the two openings it will be observed to pass into the bottom of the internal acoustic meatus, if into the more lateral, it will pass through the facial canal, and, provided the channel be clear, will appear on the inferior surface of the bone at the stylo-mastoid foramen. Leading forwards and medially from the hiatus towards the anterior border is a groove ; in this lies the greater superficial petrosal nerve, which passes out of the hiatus. A smaU branch of the middle meningeal artery also enters the bone here. A little lateral to the hiatus is another small opening (apertura superior canalis tympanici), often difficult to see ; from this a groove runs forwards which channels the upper surface of the roof of the canal for the tensor tympani muscle. Through this foramen and along this groove passes the lesser superficial petrosal nerve. Behind this, and in front of the arcuate eminence, the bone is usually thin (as may be seen by holding it up to the light falling tlirough the external acoustic meatus), roofing in the cavity THE TEMPOKAL BONES. 131 within tlie boue called the tympanum and forming the tegmen tympani. Liiterally the line of fusion of the petrous with the squamous part is ol'teii indicated by a faint and irregular jjetro-squamous fissure. Posterior Surface. — Tiie most conspicuous object on the posterior surface of the petrous part of the bone istlu^ meatus acusticus intemus (internal acoustic meatus), about 8 mm. deep in the adult. Tliis has an oblique oval aperture, and leads laterally and slightly downwards into the substance of the bone, giving passage to the acoustic and facial nerves, together with the nervus intermedius and the auditory branch of the basilar artery. The canal appears to end blindly ; but if it is large, or still l>etter, if part of it is cut away, its fundus will be seen to be crossed by a horizontal ridge, the falciform crest, which divides it into two tbssie, the floors of which (laminae cribrosae) are pierced by numerous small foramina for the branches of the acoustic nerve and the vessels passing to the membranous labyrinth, whilst in the anterior and upper part of the higher fossa the orifice of the canalis facialis, through which the facial nerve passes, is seen leading in the direction of the hiatus canalis facialis (vide supra). I^ateral to the internal acoustic meatus and above it, close to the superior border, an irregular depression, often faintly marked, with one or two small foramina opening into it, is to be noticed. This is the fossa subarcuata, best seen in young bones (see Fig. 143 C), where it forms a distinct recess, which is bounded above by the bulging caused by the superior semicircular canal, within the concavity of which it is placed ; it lodges a process of the dura mater. Below and lateral to this, separated from it by a smooth, elevated curved ridge, is the opening of the apertura externa aquaeductus vestibuli (aqueduct of the vestibule), often concealed in a narrow curved fissure overhung by a sharp scale of bone. In this is lodged the saccus endolymphaticus, developed as an evagi nation from the otocyst, together with a small vein. The ridge above it corresponds to the upper half of the posterior semicircular canal. External acoustic meatus Osseous part of the aiulitory tube Internal acoustic meatus Vestibule Canalis facialis Fenestra vestibuli cut across Fenestra cochleip cut across Superior opening of the canal for the tympanic branch of glosso-pharyngeal Fig. 140.— Vertical Transverse Section through the Left Temporal Bonb (Anterior Half of Section). - Tlie teiiipoial witli the zygomatic, Connexions bonearticulat sphenoid, parietal, and occipital bones, and by a movable joint witli the mandibla Occasionally the temporal articulates with the frontal, as happens normallv in the anthropoid apes ; although the region of the pterion is characterised by an X-like form, in the lower races of man there is no evidence that the occurrence of a fron to -squamosal suture IS more frequent in the lower than the higher races, its occurrence being due to the manner of fusion of the so-called epipteric ossicles with the surrounding bones. Ossification. — The temporal boue of man represents the fused periotic, squamosa], and tympanic elements ; the two latter are membrane or investing bones, whilst the former is developed in cartilage around the auditory capsule. The cartilages of the I. and II. visceral arches are also intimately associated with its development, as will be elsewhere explained (Appendix E). The human temporal bone is characterised by the large proportionate size of the squamosal, the comparatively small size of the tympanic, tlie absence of an auditory bulla, and the exceptional development of the mastoid process. Ossification commences in the ear capsule in the fifth mouth, and proceeds so rapidly that by the end of the sixth month the individual centres are more or less fused. Of these, one, the Pro-otic (Huxley), which appears in the vicinity of the emiueutia arcuata, is the most definite in position and form ; from this a lamina of bone of spiral form is developed, which covers in the medial limb of the superior semicircular canal, and forms the roof of the internal acoustic meatus, together with the commencement of the 9 a 132 OSTEOLOGY. Lateral semicircular canal Superior semicircular canal Vestibule into openings of semicircular canals Internal acoustic meatus Fenestra vesti- buli cut across Fenestra coclikte cut across Opening leading into tympanic antrum Canalis facialis Canalis stapeclii Tympanum External acoustic meatus Fig. 141. — Vertical Transverse Section through the Left Temporal Bone (Posterior Half of Section). facial canal. Reaching forwards, it extends to the apex of the petrous part; whilst laterally it forms part of the medial wall of the tympanum, surrounds the fenestra vesti- buli, and encloses within its substance portions of the cochlea, vestibule, and superior semicircular canal. Another centre, the Opisthotic, appears in the vicinity of the promontory on the medial wall of the tympanum, surrounds the fenestra cochleae, forms the floor of the vestibule, and extends medially to complete the floor of the internal acoustic meatus. Surrounding the cochlea inferiorly and laterally, it completes the floor of the tympanum, and ultimately blends with the anterior and inferior part of the tympanic ring. The carotid canal at first grooves it, and is then subsequently suiTOunded by it. According to Lambertz the lamina spiralis of the cochlea ossifies in membrane. The roof of the tympanum is formed from a separate centre, the Pterotic, which extends backwards to- wards the superior semicircular canal, and encloses the tympanic part of the facial canal ; later- ally this centre unites by suture with the squamosal, and sends down a thin process, which ap- peal's between the lips of the petro - tympanic fissure, and forms the lateral wall of the auditory tube. Nuclei, either single or multiple, Epiotic, appear in the base of the petrous part, and envelop the posterior and lateral semi- f^' circular canals. It is by ex- tension from this part that the mastoid process is ulti- mately developed. The styloid process, an inde- pendent development from the upper end of the carti- lage of the second visceral arch, is ossified from two centres. The upper or basal appears before birth, and rapidly unites with the petro- mastoid, the tympanic plate encircling it in front. This represents the tympanohyal of comparative anatomy. At birth, or subsequent to it, another centre appears in the cartilage below the above : this is the stylohyal. Anky- losis usually occurs in adult life between the tympanohyal and stylohyal, the union of the two constituting the so-- called styloid process of human anatomy. The centre from which the squamo- zygomatic develops appears in membrane about the end of the second month. Situated near the root of the zygoma, it extends forwards and laterally into that process, medially to form the floor of the infra-temporal fossa, and upwards into the squamosal. From this latter there is a downward and backward exten- Osseous part of tbe auditory tube Styloid process broken off Mandibular fossa Groove for membraua tympani External acoustic meatus Mastoid air-cells Carotid canal Tympanum Cochlea Internal acoustic meatus Vestibule, fenestra vestibuli cut across Superior semicircular canal Canalis facialis Lateral semicircular canal Fia. 142. — Horizontal Section through the Left Temporal Bone (Lower Half of Section). THE SPHEXOID BONE. 133 sion, which forms the post-auditory process ; this ultimately blends with the posterior limb of the tympanic ring, bein<,' separated from it in the adult by the petro-inastoid fissure. It forms the lateral wall of the tympanic antrum, and constitutes the anterior and upper part of the mastoid process in the adult. About the third mouth a centre appears in the outer membranous wall of the tympanum : from this the tsrmpanic ring is developed. Incom- plete above, it displays two free extremities. (Jf these, the anterior is somewhat enlarged, and unites in front with the mandibular portion of the squamo-zygomatic, being separated from it by the petrotympanic fissure and the downgrowth from the tegmen tympani ; the posterior joins the post-auditory process of the squamo-zygomatic above mentioned. Below, it blends medially with the portion of the petro-mastoid which forms the floor of the tympanum and ensheathes the tympanohyal behind. From the medial surface of the ring below there is an extension medially and forwards which forms the floor of the osseous part of the auditory tube, as well as the lateral wall and half the floor of the carotid canal. From the lateral side of the lower part of this ring two tubercles arise ; d » b a __^^^_^ 9 f A B C The squaino-zygoiiiatic part is coloured blue ; the petro-mastoid red. The tyuipauic ring is left uncoloured. Fig. 143. — a. The Parietal Sdhface of the Right Temporal Boxe at Birth. B. The same with the Squamo-zygomatic Portion removed. (The lettering is the same in both A and B.) a, Tympanic ring, h. Medial wall oftyoipanum. c, Fenestra cochlea;, rf. Fenestra vestibuli. e, Tympanic antrum. /, Mastoid process, g. Masto- squamosal suture, ■with foramen for transmission of vessels, h, Squamo-zygomatic, removed in tigure B to show how its descending process forms the lateral wall of the tympanic antrum. C. Cerebral Surface of the Right Temporal Bose at Birth. a, Squamo - zygomatic. 6, Petro- squamosal suture and foramen (just above the end of the lead line). c, Subarcuate fossa, d, Aquaeductua vestibuli. e, Aquaeductus cochleae. /, Internal acoustic meatus. g. Upper end of carotid canal. these grow laterally, and so form the floor of the external acoustic meatus. The interval between them remains unossified till about the age of five or six, after which closure takes place. This deficiency may, however, persist even in adult life (see Appendix B, Temporal). At birth the temporal bone can usually be separated into its component parts. The lateral surface of the petrous part not only forms the medial wall of the tympanum, but is hollowed out behind and above to form the inner side of the tympanic antrum, the outer wall of which is completed by the post-auditory process of the squamo-zygomatic. As yet the mastoid process is undeveloped. It only assumes its nipple-like form about the second year. Towards puberty its spongy substance becomes permeated with air spaces, which are in communication with and extensions from the tympanic antrum. Occasionally this pneumatic condition is met with in early childhood. The external acoustic meatiis is unossified in front and below, the outgrowth from the tympanic ring occurring subsequent to birth. The mandibular fossa is shallow and everted ; the jugular fossa is ill-marked ; whilst the subarcuate fossa is represented by a deep pit, the so-called floccular fossa of comparative anatomy. The hiatus of the facial canal is an open groove, displaying at either end the openings of the medial and lateral portions of the facial canal. Os Sphenoidale. The sphenoid bone lies in front of the basilar part of the occipital medially, and the temporals on either side. It enters into the formation of the cranial, orbital, and nasal cavities, as well as the temporal, infra-temporal, and pterygn- 9& 134 OSTEOLOGY. palatine foss?e. It consists of a body with three pairs of expanded processes, the great wings, the small wings, and the pterygoid processes. The corpus (body), more or less cubical in form, is hollow, and contains within it the two large sphenoidal air sinuses. These are separated by a partition, which Groove for the abducent nerve Foramen rotundum Groove for auditory tube Petrosal proceb-^ Pterygoid canal Lateral lamina of the _ pterygoid proces'- Medial lamina of the pterygoid process. Superior orbital Pteiygoid fossa Pterygoid notch Hamulus of medial pterygoid lamina Fig. 144. — The Sphenoid seen from behind. is usually deflected to one or other side of the median plane. Each sinus extends laterally for a short distance into the root of the great wing, and downwards and laterally towards the base of the pterygoid process of the same side. They com- Infra-teuiporal , ,^ surface toramen rotundum Orbital surface Infra temporal crest Angular spine Splieno-maxillary surface Lateral pterygoid lamina Pterygoid notch Fig. 145. — Thk Sphenoid seen fuom the front. Hamulus of medial pterygoid lamina municate by apertures with the upper and posterior })art of the nasal cavities. In the adult the posterior aspect of the body displays a sawn surface due to its separation from the basi-occipital, with which in the adult it is firmly ankylosed. The superior surface, from the anterior angles of which the small wings arise, displays an appear- ance comparable to that of an oriental saddle (sella turcica). Over its middle there is a deep depression, the fossa hypophyseos, in which is lodged the hypophysis (O.T. pituitary body). Behind, this is overhung by a sloping ridge, the dorsum sellae, the posterior surface of which is inclined upwards, and is in continuation with THE SPHENOID BONE. 135 the basilar groove of the occipital bone, supporting the pons and the basilar artery. Anteriorly and laterally Ihe angles of this ridge project over the fossa hypophyst'os in tlie form of ])r()niinent tubercles, called tlie processus clinoidei posteriores (posterior clinoid processes). To tlieso are attached the tentorium cerebelli and interclinoid ligaments. In front of the fossa hyjtopliyscos there is a transverse eltnation, the tuberculum sellae, towards the lateral extremities of whicli, and somewhat behind, there are oitentimes little spurs of bone, the processus clinoidei medii (middle clinoid processes). In front of the tuberculum selhc is tlie sulcus chiasmatis, which passes laterally on either side to become continuous, between the roots of the small wings, with the optic foramina. This groove is liable to considerable variations, and apparently does not always serve fur tlie lodgment of the optic chiasina. (Lawrence, " Proc. Soc. Anat.," Journ. Anat. and Physiol. vol. xxviii. p. 18.) In front of the sulcus chiasmatis, from which it is often separated by a thin sharp edge, the superior surface continues forwards on the same plane as the upper surfaces of the small wings, and terminates anteriorly in a ragged edge, which articulates with the lamina cribrosa of the ethmoid, and has often projecting from it, in the median plane, a pointed process, the sphenoidal spine. The lateral aspects of the body are fused with the great wings, and in part also with the roots of the pterygoid processes. Curving along tlie side of the body, above its attachment to the great wing, is an jT-shaped groove, the sulcus caroticus (carotid groove), which marks the position and course of the internal carotid artery. Posteriorly, the hinder margin of this groove, formed by the salient lateral edge of the posterior surface of the body, articulates with the apex of the petrous portion of the temporal bone, and is hence called the petrosal process ; just above this, on the lateral border of the dorsum sellae, there is often a groove for the abducent nerve. The anterior siuface of the body displays a vertical, median crista sphenoidalis (sphenoidal crest), continuous above with the sphenoidal spine, and below with the pointed projection called the sphenoidal rostrum. This crest articulates in front with the perpendicular plate of the ethmoid. On each side of the median plane are seen the irregular openings leading into the sphenoidal air sinuses, the thin anterior walls of which are in part formed by the absorption of the sphenoidal conchie (O.T. turbinated bones) with which in early life they are in contact. With exception of a broad groove leading downwards from the apertures above mentioned, which enters into the formation of the roof of the nasal cavity of the corre- sponding side, the lateral aspects of this surface of the bone are elsewhere in articulation with the labyrinths of the ethmoid and the orbital processes of the palate bones. The sphenoidal rostrum is continued backwards for some distance along the inferior surface of the body, where it forms a prominent keel which fits into the recess formed by the alse of the vomer. The edges of the alae serve to separate the rostrum from the incurved vaginal processes at the roots of the medial plates of the pterygoid processes. Posteriorly, the inferior surface of the body of the sphenoid is rougher, and covered by the mucous membrane of the roof of the pharynx ; here, occasionally, a median depression may be seen which marks the position of the inferior extremity of a foetal channel, called the canalis craniopharyngeus. Alae Parvae. — The small wings are two tiattened triangular plates of bone which project forwards and laterally from the anterior and upper part of the body of the bone, with which they are united by two roots which enclose between them the optic foramina for the transmission of the optic nerves and ophthalmic arteries. Of these roots, the posterior springs from the body just wide of the tuberculum selhc, separating the carotid groove behind from the optic foramen in front ; laterally this root is confluent with the recurved posterior angle of the small wing, forming the projection known as the processus clinoideus anterior (anterior clinoid process), which overhangs the anterior part of the body of the bone and affords an attachment to the tentorium cerebelli and interclinoid liga- ments. The anterior root, broad and compressed, unites the upper surface of the small wing with the anterior and upper part of the body. Laterally, the lateral 136 OSTEOLOGY. angle terminates in a pointed process which reaches the region of the pterion and there articulates with the frontal, and may come in contact with the great wing. The superior aspect is smooth, and forms, in part, the floor of the anterior cranial fossa. The inferior surface constitutes part of the posterior portion of the upper wall of the orbit, and also serves to roof in the superior orbital fissure (O.T. sphenoidal fissure), which separates the small wing from the great wing below. The anterior edge is ragged and irregular, and articulates with the orbital parts of the frontal. The posterior margin, sharp and sickle-shaped, separates the anterior from the middle cranial fossa, and corresponds to the position of the stem of the lateral cerebral Assure on the inferior surface of the cerebrum. Alae Magnae. — The great wings, as seen from above, are of a somewhat crescentic shape and form a considerable portion of the floor of the middle cranial fossa. If the medial convex edge of the crescent be divided into fifths, the posterior fifth extends backwards and laterally beyond the body of the bone, presenting a free posterior edge, which forms the anterior boundary of the foramen lacerum. This border ends behind in the horn of the crescent, from which a pointed process projects downwards, called the spina angularis ; this is wedged into the angle between the petrous and squamous parts of the temporal bone. The medial surface of the posterior border and spine is furrowed for the cartilaginous part of the auditory tube (sulcus tubae), whilst on the medial side of the spine the course of the chorda tympani nerve is indicated by a groove (Lucas). The second fifth of the convex border of the crescent is fused to the side of the body and united below with the root of the pterygoid process. The angle formed by the union of the great wing with the side of the body posteriorly corresponds to the posterior end of the carotid groove, the lateral lip of which is formed by a projecting lamina called the lingula. The remaining three-fifths of the convex border is divisible into two nearly equal parts ; the medial is a free, curved, sharp margin, which forms the inferior margin of the superior orbital fissure, the cleft which separates the great wing from the small wing, and which establishes a wide channel of communication between the middle cranial fossa and the cavity of the orbit, transmitting the oculomotor, trochlear , ophthalmic divisiaa---Qf_the trigeminal, and the a bduc ent nerves, together with the ophthalmic veins. Wide of the superior orbital fissure this edge luecomes Inroad and serrated,' articulating with the frontal bone medially, and at the part corresponding to the anterior horn of the crescent, by a surface of variable width, it unites with the sphenoidal angle of the parietal bone. The lateral border corresponds to the concave side of the crescent, and is serrated for articulation with the squamous part of the temporal, being thin and bevelled at the expense of its parietal surface above and laterally, and broad and thick behind as it passes towards the angular spine. The internal or cerebral surface is concave from behind forwards, and, in its anterior part, from side to side also ; it forms a considerable part of the floor of the middle cranial fossa, and bears the impress of the gyri of the extremity of the temporal lobe of the cerebrum, which rests upon it ; towards its lateral- side it is grooved obliquely by an anterior branch of the middle meningeal artery. The following foramina pierce the great wing : Close to and in front of the alar spine is the foramen spinosum, for the transmission of the middle meningeal artery and its companion vein, together with the nervus spinosus from the man- dibular division of the trigeminal nerve. In front of and medial to this, and close to the posterior free border, is the foramen ovale, of large size and elongated form. This gives passage to the motor root and mandibular division of the trigeminal nerve, and admits the accessory meningeal branch ^ of the middle meningeal artery ; a small emissary vein from the cavernous sinus usually passes through this foramen, and occasionally also the lesser superficial petrosal nerve. Near the anterior part of the root of the great wing, and just below the sphenoidal fissure, is the foramen rotundum, of smaller size and circular form. Through this the maxillary division of the trigeminal nerve escapes from the cranium. Occasion- ally there is a small canal — the foramen of Vesalius — which pierces the root of the great wing to the medial side of the foramen ovale. This opens below into the scaphoid fossa at the base of the medial pterygoid lamina, and transmits a THE SPHENOID BONE. 137 small vein. Occasionally there is a small foramen {canaliculus innominatus) to the medial side of the foramen spinosum for the transmission of the small superficial petrosal nerve. The external surface of the great wing enters into the formation of the walls of the orbital, temporal, infni-temporal, and pterygo-palatine fossae by three well- defined areuH ; of these the upper two, i.e. the orbital and the temjjoral, are separated by an oblique jagged ridge, the margo zygomaticus (zygomatic border), for articula- tion with the fronto-sphenoidul process of the zygomatic bone. Occasionally the lower part of this ridge articulates with the zygomatic process of the maxilla. The fades orbitalis (orbital surface) lies to the medial side of this crest and is directed forwards and a little medially ; of quadrilateral shape, it forms the posterior and lateral wall of the orbit ; plane and smooth, it is bounded posteriorly by the sharp inferior free margin of the superior orl)ital li.ssure, towards the medial extremity of which a pointed spine (spina recti lateralis), for the attachment of the inferior common ligament of origin of the ocular muscles, can usually be seen. It is limited superiorly by the edge of a rough triangular area which articulates with the frontal bone ; anteriorly by the zygomatic border ; whilst inferiorly a free, well-defined oblique margin constitutes the posterior and lateral boundary of the fissura orbitalis inferior (inferior orbital fissure), which separates this part of the bone from the orbital surface of the maxilla. Below this border there is a grooved surface which leads medially toward the orifice of the foramen rotundum. In the articulated skull this forms part of the posterior wall of the pterygo-palatine fossa. To the lateral side of the zygomatic border, which bounds it in front, is the facias temporalis (temporal area), concavo-convex from before backwards. It slopes medially below, where it is separated from the spheno-maxillary area by a well- marked muscular ridge, the crista infratemporalis (infra-temporal crest). Behind, the temporal surface is bounded by the margin of the great wing which articulates with the squamous part of the temporal (margo squamosus), and above by the edge which unites it with the sphenoidal angle of the parietal and with the frontal bone. The temporal surface enters into the formation of the floor of the fossa of the same name, and affords an extensive attachment to the fibres of origin of the temporal muscle. The facies sphenomaxillaris (spheno-maxillary surface), the third of the areas above referred to, is situated below the infra-temporal crest, and corre- sponds to the under surface of the posterior half of the great wing ; it extends as far back as the angular spine and posterior border. Opening on it are seen the orifices of the foramen spinosum and ovale. It is slightly concave from side to side, and is confluent medially with the lateral surface of the lateral pterygoid plate. In front, it is bounded by a ridge which curves upwards and laterally from the anterior part of the lateral pterygoid plate to join the infra-temporal crest. In the articulated skull this ridge forms the posterior boundary of the pterygo- maxillary fissure. The spheno-maxillary surface overhangs the infra-temporal fossa, and affords an origin for the superior head of the external pterygoid muscle. The processus pterygoidei (pterygoid processes) spring from the inferior surface of each lateral aspect of the body as well as from the under side of the roots of the great wings, and pass vertically downwards. Each consists of two laminae, the lateral and medial laminae of the pterygoid process, fused together anteriorly, and enclosing between them posteriorly the pterygoid fossa. The lateral pterygoid plate, thin and expanded, is directed obliquely back- wards and laterally, its lower part being often somewhat everted. Its posterior edge is sharp, and often has projecting from it one or two spines, to one of which (processus pterygospinosus) the pterygo-spinous ligament, which stretches towards the angular spine, is attached. Laterally it furnishes an origin for the inferior head of the external pterygoid muscle, and on its medial side, where it forms the lateral wall of the pterygoid fossa, it supplies an attachment for the internal pterygoid muscle. The medial pterygoid plate is narrower and somewhat stouter. By its medial aspect it forms the posterior part of the lateral wall of the nasal cavity ; laterally it is directed towards the pterygoid fossa. Its posterior edge ends 138 OSTEOLOGY. below in the hamulus pterygoideus (pterygoid hooklet), which, reaching a lower level than the lateral plate, curves backwards and laterally, furnishing a groove on its lower surface in which the tendon of the tensor veli palatini muscle glides ; superiorly, the sharp posterior margin of the medial plate bifurcates, so as to enclose the shallow scaphoid fossa from which the tensor veli palatini muscle arises, and wherein may occasionally be seen the inferior aperture of the foramen VesaHi. To the medial edge of this fossa, as well as to the posterior border of the medial pterygoid plate, the pharyngo-hasilar fascia is attached. Here, too, the cartilage of the auditory tube is supported on a slight projection, and the pharyngo-palatinus muscle receives an origin, whilst the superior constrictor of the pharynx arises from the inferior third of the same border and from the pterygoid hamulus. Superiorly and medially the medial plate forms an incurved lamina of bone, the processus vaginalis (vaginal process), which is applied to the inferior surface of the lateral aspect of the body, reaching medially towards the root of the rostrum, from which, however, it is separated by a groove, in which, in the articulated skull, the ala of the vomer is lodged. The angle formed by the vaginal process and the medial edge of the scaphoid fossa forms a projection called the pterygoid tubercle, immediately above which is the posterior aperture of the pterygoid canal, through which the nerve and artery of the canal (O.T. Vidian) are transmitted. On its inferior surface the vaginal process displays a groove (sulcus pterygopalatinus), which in the articulated skull is converted into the pharyngeal canal by its union with the palate bone. In front, at its root, the pterygoid process displays a broad smooth surface (facies sphenomaxillaris), which is confluent above with the root of the great wing around the foramen rotundum, and forms the posterior wall of the pterygo- palatine fossa. Here, to the medial side of the foramen rotundum, is seen the anterior opening of the pterygoid canal. Below, the pterygoid laminae are separated by an angular cleft, the pterygoid fissure ; in this is lodged the pyramidal process of the palate bone, the margins of which articulate with the serrated edges of the fissure. Connexions. — The sphenoid articulates with the occipital, temporal, parietal, frontal, ethmoid, sphenoidal conchae, vomer, palate and zygomatic bones, and occasionally with the maxillse. Ossification. — The sphenoid of man is formed by the fusion of two parts, the pre- sphenoid and the post-sphenoid, each associated with certain processes. In most mammals the orbito-sphenoids or small wings fuse with the pre-sphenoid, whilst the alisphenoids or great wings, together with the medial pterygoid lamina, ankylose with the post-sphenoid. The ossification of these several parts takes place in cartilage, with the exception of the medial pterygoid lamina, which is developed from an independent centre in the connective tissue of the side wall of the oral cavity (Hertwig). At the end of the second month a centre appears in the root of the great wing between the foramen ovale and foramen rotundum; from this the ossification spreads laterally and g ij f, b r. backwards and also downwards into the lateral pterygoid lamina. According to Fawcett the pterygoid laminae or the common root of the two laminae in the adult is practically the only part of the ala temporalis preformed in cartilage ; the whole of the lateral pterygoid lamina and that part of the alisphenoid pro- jected into the orbital and temporal fossae are ossified in membrane ; so too are the foramen ovale and foramen spinosum. Meanwhile two centres appear about the same time in the basi-sphenoid in relation to the floor of the fossa hypophyseos and on either side of the cranio-pharyngeal canal, around which tliey ossify, ultimately leading to the obliteration of that channel. Somewhat later a sphenotic centre appears on each side, from which the lateral aspect of the body and the lingula are developed. Fusion between these four centres is usually complete by the sixth month. In the pre-sphenoid a pair of lateral nuclei make their appearance about the middle of the third month, just lateral to the optic foramina; from each of these the orbito- FiG. 146. d e d -OSSIKICATION OF THE SPHENOID. a, Pre-.spheiioid ; b, Orbito-sphenoids ; c, Alisphenoids ; d, Medial pterygoid laniinte ; e, Basi-sphenoid. THE ETHMOID BONE. 139 sphenoids (small wings) and their roots are developed. About the same time another pair of centres, placed medial to the optic foramina, constitute the body of the pre- sphenoid. At first the superior surface of the body of the pre-sphenoid is exposed in the interval between the orbito-sphenoid.s, but by the ultimate coaleijcence of the medial borders of the orbito-sphenoids to form the jugum sphenoidale the body of the pre-sphenoid is almost completely covered over superiorly. By the coalescence of these in front, and their ultimate union with the basi-sphenoid behind, a cartilaginous interval is enclosed, of triangular shape, which, however, becomes gradually reduced in size by the ingrowth of its margins so as to form two medially placed foramina, as may be frequently observed in young bones — one opening on the surface of the tuberculum sellee, the other being placed anteriorly. (Lawrence, " Proc. Soc. Anat.," Joum. Anat. and Physiol, vol. xxviii. p. 19.) As has been seen, the medial pterygoid laminae are developed in membrane and are the first parts of the sphenoid to ossify. (Fawcett, An f^. readily be distinguished by the presence Q^^^^,^ on either side of an everted lip or ala, for septal slopcs from behind upwards and forwards, and articulates with the inferior surface of the body of the sphenoid,- the pointed rostrum of which is received into the groove bounded by the projecting alse. Laterally these alae are wedged in between the sphenoidal processes of the palate bones in front, and the vaginal processes at the root of the medial laminae of the pterygoid processes behind. The posterior border, which slopes from behind down- wards and forwards, is free, and forms a sharp, slightly curved edge ; this con- stitutes the posterior margin of the nasal septum, and serves to separate the openings of the choanse (O.T. posterior nares). The inferior border, more or less horizontal in direction, articulates with the nasal crest formed by the maxillae and palate bones. The anterior edge is the longest ; it slopes obliquely from above downwards and forwards. In its upper half it is ankylosed to the perpendicular plate of the ethmoid ; in its lower half this margin is grooved for the reception of the septal cartilage of the nose. The anterior extremity of the bone forms a trun- cated angle, which articulates with the posterior border of the incisor crest of the maxillae, and sends downwards a pointed process which passes between the incisor foramina. The right and left surfaces of the bone are smooth and covered by mucous membrane. It is not uncommon to find them deflected to one or other side. A few vascular grooves may be noticed scattered over these surfaces, and one, usually more distinct than the others, running obliquely down- wards and forwards, indicates the course of the naso-palatine nerve. Connexions.— The vomer articulates with the sphenoid, the ethmoid, the palates, and the maxillai. In front it supports the septal cartilage. Ossification. — The vomer commences to ossify in membrane at the end of the second month. A nucleus appears on each side of the middle line, below the nasal septum, medial to the plane of the anterior paraseptal cartilages and posterior to them. During the third month the nuclei, which have increased in height and length. Fig. 155. Vomer at Birth, displaying its forma- tion by two Osseous Laminae united inferiorly. The figure to the right exhibits the appearance of the bone, in vertical section, at the point marked -x- iu tlie left figure. THE NASAL BONES. 145 fuse at their lower edges, and by forward growth invade the posterior end of each anterior paraseptul cartihige, thus forming a deep groove in whicli the septal cartilage is lodged (Fawcett). As growth goes on the groove becomes reduced by the further fusion of the lateral plates and the absorption of the cartilage, initil the age of puberty, by which time the lateral laminjc have united to form a median plate, the primitively divided condition of which is now only represented by the eversion of the also and the grooving along the anterior border. According to Fawcett, the ossification of the Jacobsonian cartilage produces a hitherto undescribed clement in the formation of the osseous nasal septum. Ossa Nasal ia. The nasal bones, two in number, lio in the interval between the frontal processes of the maxillae, there forming the bridge of tlie nose. Each bone is of elongated quadrangular form, having two surfaces — an inner and ^^a^ b^"^^' outer — and four borders. The outer /^^i^iii /r3^ surface, somewhat constricted about = its middle, is convex from side to | side, and slightly concavo-convex from a above downwards. Near its centre M 3 there is usually the opening of a | nutrient canal. '" The inner surface is not so ex- tensive as the outer, as the superior and anterior articular borders encroach somewhat upon it above. Concave ,^ -.r^ „, t. xt ^ r. -1 ^ ^-1 J 1 r. 1 Fig. 156.— The Right Nasal Bone. from side to side, and also from above A, Lateral side ; B, Me.lial side. downwards, it is covered, in the recent condition, by the mucous membrane of the nose. Eunning downwards along this surface is a narrow groove (sulcus ethmoidalis) which transmits the anterior ethmoidal nerve. The anterior or medial border, thin below, is thick above, and, in conjunction with its fellow at the opposite side, with which it articulates, forms a median crest posteriorly, which is united to the spine of the frontal, the perpendicular plate of the ethmoid, and the septal cartilage of the nose, in that order from above downwards. The posterior or lateral border, usually the longest, is serrated and bevelled to fit on to the anterior edge of the frontal process of the maxilla. The superior border forms a wide toothed surface, which articulates with the medial part of the nasal notch of the frontal bone anteriorly ; whilst, posteriorly, it rests in contact with the root of the nasal process of the same bone. The inferior border is thin and sharp, and is connected below with the lateral cartilage of the nose, and is usually deeply notched near its medial extremity. Connexions. — The nasal bone articulates with its fellow of tlie opposite side, with the frontal above, posteriorly with the perpendicular plate of the ethmoid and with the frontal process of the maxilla. It is also imited to the septal and lateral cartilages of the nose. Ossification. — The nasal bones are each developed from a single centre, which makes its appearance, about the end of the second month, in the membrane covering the anterior part of the cartilaginous nasal capsule. Subsequent to birth the underlying cartilaginous stratum disappears, persisting, however, below in the form of the lateral nasal cartilage, and behind as the septal cartilage of the nose. Ossa Suturarum (O.T. Wormian). Along the line of the cranial sutures and in the region of the fontanelles, isolated bones of irregular form and variable size are occasionally met with. These are the once so- called Wormian bones, nan\ed after the Danish anatomist Wormius. They are now called ossa suturarum (sutural bones). Their presence depends on the fact that they are either developed from distinct ossific nuclei, or it may be from a division of the primary ossific deposit. Their occurrence may also be associated with certain pathological conditions 10 146 OSTEOLOGY. which modify the development of the bone. They usually include the whole thickness of the cranial wall, or they may only involve the outer or inner tables of the cranial bones. They are most frequent in the region of the lambda and the lambdoid suture. They occur commonly about the pterion, and in this situation are called epipteric hones (Flower). By their fusion with one or other of the adjacent bones they here lead to the occurrence of a fronto-squamosal suture. Their presence has also been noted along the line of the sagittal suture, and sometimes in metopic skulls in the inter-frontal suture. They are occasionally met with at the asterion and more rarely at the obelion. They appear less frequently in the face, but their presence has been noted around the lacrimal bone, and also at the exti-emity of the inferior orbital fissure, where they may form an independent nodule wedged in between the great wing of the sphenoid, the zygomatic, and the maxillary bones. OSSA FACIEI. The bones of the face, seven in number, comprise two maxillse, two palates, two zygomatics, with the mandible or lower jaw. The lYIaxillaB. 'Frontal process Lacrimal groove The maxillae, of which there are two, unite to form the upper jaw. Each consists of a body, with which are connected four projections, named respectively the zygomatic, frontal, alveolar, and palatine processes. The body (corpus) is of pyramidal form, and contains within it a hollow called the maxillary sinus. It has four surfaces — a facial or antero-lateral, an infra- temporal or postero-lateral, an orbital or supero-lateral, and a nasal or medial — and four processes — the malar, frontal, alveolar, and palatine. Surfaces. — The fades anterior (antero-lateral surface) is confluent below with the alveolar process. Above, it is separated from the orbital aspect by the margo infraorbitalis (infra- orbital margin), whilst medially it is limited by the free margin of the nasal notch, which ends below in the pointed spina nasalis anterior (anterior nasal spine). Posteriorly it is separated from the infra-temporal surface by the inferior border of the zygomatic process. The facial aspect of the bone is ridged by the sockets of the teeth (juga alveolaria). The ridge corresponding to the root of the canine tooth is usually the most pronounced; med- ial to this, and over- lying the roots of the incisor teeth, is the shallow incisive fossa, whilst placed laterally, on a higher level, is the deeper canine fossa, the floor of which is formed in part by the projecting zygomatic process. Above this, and near the infra- orbital margin, is the infra - orbital foramen, the external opening of the infra-orbital canal, which transmits the infra-orbital nerve and artery. Infra-orbital foramen Tuberosity Fig. l.'i?.— The Uiuht Mami.i.a (l.aterul \'icw). THE MAXILLARY BONES. 147 or postero - lateral surface is separated abfjvu I'rom ruiuided I'reo edi^e, vvliicli forms the anterior uiarfriu Front ril lirorr-^s Kidge for middle conulia Middle meatus' Kidge for inferior concha Incisor crest Anterior nasal spine Palatine jirocess Alveolar I)roce88 Nasal crest Fig. 158. — The Right Maxilla (Medial Aspect). The infra - temporal the orbital aspect by a of the inferior orbital fissure in the articulated skull. luferiorlyand an- teriorly it is separated from the auterior surface by the zygomatic process and its free lower border. Medially it is limited by a sharp, irregular margin with which the palate bone articulates.. This surface is more or less convex, and is directed towards the infra-tem- poral and pterygo-pala- tine fossii}. It is pierced in a downward direction by the apertures of the alveolar canals (foramina alveolaria), two or more in number, which trans- mit the corresponding nerves and vessels to the molar teeth. Its lower part, slightly more pro- minent wiiere it over- hangs the root of the third molar, is often called the tuber maxillare (maxillary tuberosity). The planum orbitale (orbital surface), smooth and plane, is triangular in shape and forms part of the floor of the orbit. Its anterior edge corresponds to the infra-orbital margin ; its posterior border coincides with the anterior boundary of the inferior orbital fissure. Its thin medial edge, which may be regarded as the base of the triangle, is notched in front to form the sulcus lacrimalis (lacrimal groove), behind which it articulates with the lacrimal bone for a short distance, then for a greater length with the lamina papyracea of the ethmoid, and terminates posteriorly in a surface for articulation with the orbital process of the palate bone. Its lateral angle corresponds to the base of the zygomatic process. Traversing its substance is the infra-orbital canal, the anterior opening of which has been already noticed on the anterior aspect of the body. Behind, however, owing to deficiency of its roof, the canal forms a groove which lips the edge of the bone which constitutes the anterior boundary of the inferior orbital fissure. If this canal be laid open, the orifices of the middle and anterior alveolar canals will be seen, wliich transmit the corresponding vessels and nerves to the premolar, canine and incisor teeth. The fades nasalis (nasal surface) of the body is directed medially towards the nasal cavity. Below, it is confluent with the superior surface of the palatine process ; anteriorly it is limited by the sharp edge of the nasal notch ; above and anteriorly it is continuous with the medial surface of the frontal process ; behind this it is deeply channelled by the lacrimal groove, which is converted into a canal by articulation with the lacrimal and inferior conchal bones. The channel so formed conveys the naso-lacrimal duct from the orbital cavity above to the inferior nasal meatus below. Behind this groove the upper edge of this area corresponds to the medial margin of the orbital surface, and articulates from before backwards with the lacrimal, lamina papyracea of the ethmoid, and the orbital process of the palate bone. The posterior border, rough for articulation with the palate bone, is traversed obliquely from above downwards and slightly medially by a groove, which, by articulation with the palate bone, is converted into the pterygo-palatine canal, which transmits 10 a 148 OSTEOLOGY. the greater palatine arterj and anterior palatine nerve. Towards its upper and posterior part the nasal surface of the body displays the irregular, more or less triangular, opening of the maxillary sinus. This aperture which, in the articulated skull opens into the middle meatus of the nose, is much reduced in size by articula- tion with the lacrimal, ethmoid, palate, and inferior conchal bones. In front of the lacrimal groove the nasal surface is ridged horizontally by the crista conchalis (inferior conchal crest), to which the inferior conchal bone is attached. Below this the bone forms the lateral wall of the inferior nasal meatus, receiving the termina- tion of the lacrimal groove. Above, and for some little distance also on the medial side of the frontal process, it constitutes the smooth lateral wall of the atrium of the middle meatus. Processes. — The processus zygomaticus (zygomatic process), which is placed on the antero-lateral surface of the body, is confluent anteriorly with the facial surface of the body ; posteriorly, where it is concave from side to side, with the infra-temporal surface ; whilst superiorly, where it is rough and articular, it forms the apex of the triangular orbital surface, and supports the zygomatic bone. Inferiorly, its anterior and posterior surfaces meet to form an arched border, which fuses with the alveolar process opposite the root of the first molar tooth, and serves to separate the anterior from the infra-temporal surfaces of the body. The processus frontalis (frontal process) arises from the upper and anterior part of the body. It has two surfaces — one lateral, the other medial. The lateral is divided into two by a vertical ridge (crista lacrimalis anterior), which is the upward extension of the infra-orbital margin. The narrow strip of bone behind this ridge is hollowed out, and leads into the lacrimal groove below. Posteriorly the edge of the frontal process here articulates with the lacrimal, and so forms the fossa for the lodgment of the lacrimal sac (fossa sacci lacrimalis). In front of the vertical crest, to which the medial palpebral ligament is attached, the lateral surface is confluent below with the facial surface of the body, and forms the side of the root of the nose. Here may often be seen a vascular groove entering the bonei. Its anterior edge is rough, or grooved, for articulation with the nasal bone. Superiorly the summit of the process is serrated for articulation with the nasal notch of the frontal bone. The medial surface of the frontal process is directed towards the nasal cavity. It is crossed obliquely from below upwards and backwards by a ridge — the agger nasi or ethmoidal crest which is considered to be a vestige of the naso- turbinal which is met with in some mammals. Below this the bone is smooth and forms the upper part of the atrium of the middle meatus, whilst the ridge itself articulates posteriorly with the anterior part of the middle conchal bone, formed by the inferior concha of the ethmoid bone. The processus alveolaris (alveolar process) projects from the inferior surface of the body of the bone below the level of the palatal process. Of curved form, it completes, with its fellow of the opposite side, the alveolar arch, in which are embedded, in sockets or alveoli, the roots of the teeth of the maxilla ; ordinarily in the adult, when dentition is complete, each alveolar process supports eight teeth. Piercing the medial surface of the alveolar border behind the incisor teeth two small vascular foramina are usually visible. When any or all the teeth are shed the alveoli become absorbed, and the process may under these circumstances be reduced to the level of the plane of the palatine process. Posteriorly the alveolar process ends below the maxillary tuberosity of the body ; anteriorly it shares in the formation of the intermaxillary suture. The processus palatinus (palatine process), of the form of a quadrant, lies in the horizontal plane; it has two surfaces — superior and inferior — and three borders, a straight medial, a more or less straight 'posterior, and a curved lateral, by which latter it is attached to the medial side of the body and alveolar process as far back as the interval between the second and third molar teeth. Its inferior surface, together with that of its fellow, forms the anterior three-fourths of the vaulted hard palate ; it is rough and x>itted for the glands of the mucous membrane of the roof of the mouth, and is grooved, near the alveolar margin, by one or two channels which pass forward from the pterygo - palatine canal and transmit the THE MAXILLARY BONES. 149 anterior palatine nerve and greater palatine artery. Its superior surface, smooth and concave from side to side, forms the Hoor of the corresponding nasal cavity. Its medial border, Ijroud and serrated, rises in a ridgi; superiorly, so as to form with its i'ellow of the opposite side the nasal crest, whicli is grooved superiorly to rt^ceive the inferior border of the vomer. In front of its articulation with the vomer this ridge rises somewhat higher, being named the incisor crest, anterior to which it projects beyond the free border of the nasal notch, and together with its fellow forms the pointed projection called the anterior nasal spine. These parts support the septal cartilage of the nose. Immediately to the lateral side of the incisor crest the superior surface of the palatine process is pierced by a foramen which leads downwards, forwards, and a little medially, to open into a broad groove on the medial border of the bone immediately behind the central incisor tooth. When the two maxillae are articulated, the two grooves form the oval foramen incisivum, into which the two afore-mentioned foramina open like the limbs of a Y ; these are called the foramina of Stensen, and represent the channels ))y which in lower animals the organs of Jacobson open into the mouth. In man they afford a means of establishing an anastomosis between the vessels of the mouth and nose. In front and behind these, and lying within the fossa and in the line of the suture, are the smaller foramina of Scarpa, which transmit the naso-palatine nerves, the right nerve usually passing through the posterior foramen, the left through the anterior. The posterior border of the palatine process, which is sharp and thin, falls in line with the interval between the second and third molar, and articulates with the horizontal part of the palate bone. Sinus Maxillaris. The maxillary sinus lies within the body of the bone, and is of corresponding pyramidal form, its base being directed towards the nasal cavity, with the middle meatus of which it communicates, its summit extending laterally into the root of the zygomatic process. It is closed in anteriorly, posteriorly, and above by the thin walls which form the anterior, infra -temporal, and orbital surfaces of the body. Inferiorly it overlies the alveolar process in which the molar teeth are implanted, more particularly the first and second, the sockets of which are separated from it by a thin layer of bone. The angles and corners of this cavity are frequently groined by narrow ridges of bone, one superiorly corresponds to the relief formed by the infra-orbital canal. A vascular and nervous groove is often exposed, curving along the floor of the maxillary sinus just above the alveoli of the teeth. The interior of the cavity is lined by an extension from the mucous membrane of the nose. Connexions. — The maxilla articulates with the nasal, frontal, lacrimal, and ethmoid bones al)ove,, laterally with the zygomatic, and occasionally with the .sphenoid, posteriorly and medially with the palate, whilst on its medial side it unites with its fellow of the opposite side, and also supports the inferior concha and the vomer. Ossification. — The maxillae (proper) are developed in the connective tissue around the oral aperture of the embryo. Ossification commences in membrane from one centre in the neii^hbourhood of the canine tooth <,'erm. From this centre growth takes place rapidly in several directions, viz., upwards on the lateral side of the nasal capsule to form the posterior part of the frontal process, backwards to form the zygomatic process, downwards to form the lateral wall of the alveolar process, and medially to form the palatine process. From the latter a process descends downwards on the medial side of the teeth to form the medial wall of the alveolar process. At first a large gap intervenes between the greater part of the palatine process and the zygomatic process, but bridges of bone ultimately connect the two, separating the various tooth germs, and so forming the tooth sockets. About the fourth month the maxilla invades a small lateral cartilaginous process of the nasal capside (Mihalkovics), and incorporates it within itself. The infra-orbital nerve is at fii-st placed considerably above the orbital surface of the maxilla, and only comes in contact with it in the second month when a groove is formed on the bone, which by the uprising of its lateral wall and its folding over medialwards finally encloses the nerve and forms the infra-orbital canal and fora- men. This account of the ossification of the maxilla, which differs considerably from that given in previous editions, is based on the work of Mall and F'awcett. In the early stages of the development of the bone the alveolar groove, in which the teeth are 10 5 150 OSTEOLOGY. A ^ B developed, lies close below the infra-orbital groove, and it is not till later that they become separated by the growth of the maxillary sinus, which first makes its appearance as a shallow fossa to the medial side of the orbito-nasal element about the fourth month. In the adult bone the course of the infra-orbital canal and foramen indicates the line of fusion of the orbito-nasal and zygomatic elements, whilst the position of the anterior palatine canal serves to determine the line of union of the incisive with the palatine elements. In addition to the foregoing centres, Rambaud and Renault describe another, the infra -vomerine, which, together with its fellow, is wedged in between the incisive and the palatine elements beneath the vomer, thus explaining the Y-shaped arrangement of the foramina of Stensen, which open into the incisive foramen. The premaxillse, which in most vertebrates are in- dependent bones lying in front of the maxillse, constitute in man and apes the portions of the maxilla which lie in front of the incisive foramen, and support the superior incisor teeth. Each premaxilla is developed from two centres : a facial, which ultimately contains the incisor and canine teeth, and forms the anterior part of the hard palate, as well as the anterior half of the frontal process of the complete maxilla (Fawcett) ; and a palatine centre (infra vomerine of Rambaud and Renault) which forms the medial wall of the correspond- ing canal of Stensen. The former develops very early, either before or after the maxilla (Mall), and fuses almost ,._-,,.,.,. p at once with the maxilla along the alveolar margin ; the A, Jj3;tGrftl side J x5. iViediQii sme ^ Oj n , , ijjiiTnii i t p Under side, a Nasal process • 6 latter appears about the twelfth week, and soon fuses Orbital plate ; c, Anterior nasal spine ; with the facial centre. The line of fusion of the pre- c^, Infra-orbital groove ; e, Infra-orbital maxillse with the maxillae proper can be readily seen foramen; /, Anterior palatine groove ; -^ ^^^^^ ^^^ occasionally also in the adult. It g, Palatine process; /i, Premaxillary ^^j^ ^j„ 4.„ „ „„4. „u;„t, „. „ j-i,„ ^^^-^ C Fig. 159. — Ossification of the Maxilla. suture ; i, Alveolar process. corresponds to a suture which passes on the palate obliquely laterally and forwards, from the incisive foramen to the interval between the lateral incisor and the canine tooth. In cases of alveolar cleft palate the adjacent bones fail to unite along the line of the suture. In some instances, however, the cleft passes outwai'ds between the central and lateral incisor teeth, and this condition suggests the explanation that the premaxillary element is derived from two centres — a lateral and a medial. The researches of Albrecht and Warinski support this view. The latter anatomist further observes that the lateral cleavage may lead to a division of the dental germ of the lateral incisor tooth, and so explain the occurrence of the supernumerary incisor which is occasionally met with. In this way the different varieties of cleft palate are readily explained ; median cleft palate being due to failure of union between the two premaxillary bones. Lateral cleft palate may be of two types : the cleft in one case passing forwards between the central and lateral incisor, and being due to the non-union of the two elements from which the premaxilla is primarily developed ; the other, in which the cleft passes between the lateral incisor and the canine, or between the lateral incisor and a supernumerary in- cisor, owing to the imperfect fusion of the premaxilla laterally with the maxilla. Ossa Palatina. Tlic palate bone, of irregular shape, assists in the formation of the lateral wall of the posterior part of the nasal cavity, the posterior portion of the hard palate, the orbit, the pterygo-palatine, the infra-temporal, and the pterygoid fossce. It consists of horizontal and vertical parts, united to each other like the limbs of the letter L. At tlieir point of union there is an irregular outstanding process, called the pyramidal process, wliilst capping the summit of the vertical part and separated by a deep cleft are two irregular pieces of bone, called the sphenoidal and orbital processes. THE PALATE liONES. 151 The pars horizontalis (horizontal part) has two Hurf'aces aud four borders. As its uaiiie iiiiplie.s, it is hori/outal in position, and forms the posterior third of the hard palate. Its superior surface, which is smooth, is slightly concave from side to side, and forms the floor of the posterior part of the nasal cavity. Its inferior surface, rougher, is directed towards the mouth, and, near its posterior edge, often displays a transverse ridge for tiie attachment of a part of the aponeurosis of the tensor veli palatini muscle. The anterior border articulates Vjy means of an irregular suture with the posterior edge of the palatini; process of the ma.xilla. The posterior margin is free aud concave from side to side; Ijy its sharp edge it furnishes attachment to the aponeurosis of the soft palate. The medial border is upturned, and wlien it articulates with its fellow of the opposite side it forms superiorly a central crest continuous in front with the nasal crest of the maxilla ; it supports the posterior part of the inferior border of the vomer, and projecting beyond the line of the posterior border forms the posterior nasal spine. The lateral border fuses with the vertical part, forming with it a right angle. The posterior extremity of this edge is grooved by the foramen palatinum majus. Sphenoid Orbital process , Ethmoid Orbital surface For maxilla Orbital process Pterygo- palatiue fossa Sphenoidal process Spheno-imlatine notch For medial pteiy|{oii Masseteric border Orbital j-roccss Ti'iiiix)ral process Infra- temporal surface Fig. 162. — The Right Zygomatic Bone. A, Lateral Side ; B, Medial Side. (processus frontosplienoidalis), the marginal or pointed extremity of the maxillary border, and the temporal (processus temporalis). The most elevated part of the convex malar surface (facias malaris) forms the malar tuberosity. The temporal process ends posteriorly in an oblique edge, which articulates with the extremity of the zygomatic process of the temporal bone. The fronto- sphenoidal process, the most prominent of the three, is united superiorly to the zygomatic process of the frontal bone. The edge between the frontal and temporal processes is thin and sharp ; it affords attachment to the temporal fascia, and near its upper end there is usually a pronounced angle (processus marginalis), formed by a sudden change in the direction of the border of the bone. It is just below this point that the zygomatico-temporal branch of the zygomatic nerve becomes cutaneous. The inferior margin of the temporal process is somewhat thicker and rounded ; it extends downwards and forwards towards the inferior angle, where the bone articulates with the maxiUa, and is there confluent with the ridge which separates the facial from the infra- temporal aspect of the maxilla. This edge of the bone is sometimes called the masseteric border, since it aftbrds attachment to the fibres of origin of the masseter muscle. Sweeping downwards, in front of the fronto-sphenoidal process, is a curved edge which terminates inferiorly in a pointed process. This border forms the lateral and, in part, the inferior margin of the orbital cavity. Between the anterior extremity of the masseteric edge and the pointed anterior angle there is an irregular suture by which the bone is joined to the maxilla. The opening of the foramen zygomaticofaciale (zygomatico- 154 OSTEOLOGY. facial foramen) is seen on the lateral surface of the bone ; its size and position are very variable. The medial aspect of the bone is distinguished by a curved elevated crest, called the orbital process, which extends medially and backwards, and is confluent laterally with the orbital margin. This process has two surfaces — one anterior, which forms a part of the lateral and lower wall of the orbit, and one posterior, which is directed towards the temporal fossa above and the infra- temporal fossa below. The free edge of the orbital process is thin and serrated ; a little below its middle it is usually interrupted by a non-articular notch, which corresponds to the anterior extremity of the inferior orbital fissure. The part above this articulates with the great wing of the sphenoid, the portion below with the orbital surface of the maxilla. Behind the orbital process the medial surface of the bone is concave from side to side, and extends backwards along the medial aspect of the temporal process and upwards over the posterior half of the medial side of the frontal process, thus entering into the formation of the infra-temporal and temporal fossae respectively. The orbital surface of the orbital process usually displays the openings of two canals (foramina zygomatico-orbitalia) — one which traverses the bone below the orbital margin and appears on the front of the bone as already described, the other which passes obliquely upwards and laterally through the orbital process and appears in the temporal fossa, to the medial side of the frontal process (foramen zygomaticotemporale). The former transmits the zygomatico-facial branch, the latter the zygomatico- temporal branch of the zygomatic nerve. Just under the orbital margin and a short distance below the zygomatico- frontal sutures there is usually a small tubercle serving for the attachment of the lateral palpebral raphe. (Whitnall, Journ. Anat. Club-shaped process ^^^^ Phvsiol VOl xlv ) ''%\'o„;7.rB™frB™. '■"= Bflo" the orbital process there is a rough tri- angular area, bounded laterally by the maxillary border. This articulates with the zygomatic process of the maxilla, and occasionally forms the lateral wall of the maxillary sinus. Connexions. — The zygomatic bone articulates with the frontal, sphenoid, maxilla, and temporal bones. Ossification. — The zygomatic ossifies in membrane. Its basis appears about the tenth week as a thin ossifying lamina which corresponds to the orbital margin, attached to which there is a backward expansion corresponding to the body of the bone ; from this posteriorly there extends the element of the temporal process. On the medial side, and lying within the angle formed by the orbital and temporal elements, there appears a secondary thickening, which develops into a cup-shaped layer which fits into the recess and ultimately forms the surface of the bone directed to the temporal fossa. Below the orbital margin on the medial side, and extending backwards towards the temporal process, is another secondary thickening, which forms a club-shaped nodule, the thick end of which is directed forwards, whilst posteriorly it forms, in part, the lower margin of the body and temporal process. The overlap of these several parts leads to the formation of grooves which may persist in the adult as sutures. (Karl Toldt, junr., Sitzshr. ties Akad. des Wiss., Wien, July 1902.) Regarding the ossification of this bone there are great differences of opinion ; not a few anatomists describe it as developed from a single centre. Support, howevef, is given to its origin from multiple centres owing to the frequency with which in the adult it is met with in a divided condition. IVIandibuIa. The mandible or lower jaw, of horse-shoe shape, with the extremities up- turned, is the only movable bone of the face. Stout and strong, it supports the teeth of the lower dental arch, and articulates with the base of the cranium, by the joints, on either side, between its condyles and the mandibular fosste of the THE MANDIBLE. 155 temporal bones. Tfie iinterior or liorizontal part, which contains the teeth, is called the corpus mandibulae (body) ; the posterior or vertical portions constitute the rami mandibulae. 'i'he body (lisplay.s in the median plane, in front, a faint vertical ridge, the symphysis, which indicates the line of fusion of the two symmetrical lialves from wliich llie hone is primarily developed. In- teriorly this ridge divides so as to enclose, in well-marked s])ecimens, a triangular area — the protuberantia mentalis (mental protuberance), the centre of which is somewhat depressed, thus emphasising the inferior angles, which are known as the tubera mentalia (mental tubercles). The lateral surface is crossed l»y a faint, elevated ridge, the linea obliqua (oblique line), which runs upwards and backwards from the mental tubercle to the lower part of the anterior border of the ramus, with which it is conflu- ent. From this ridge arise the m. quadratuslabiiin- feriorisand the tri- angular muscle. A little above this, midway between the upper and lower borders of the mandible, and in line with the root of the second premolar tooth, the bone is pierced by the mental fora- men ; this is the anterior opening of the inferior alveolar canal, which traverses the body of the bone. Through this aperture the mental vessels and nerves reach the surface. The upper border supports the sixteen teeth of the mandible. It is thick behind and thinner in front, in correspondence with the size of the roots of the teeth. Anteriorly the sockets of the incisor and canine teeth produce a series of vertical elevations (juga alveolaria), of which that corresponding to the canine tooth is the most prominent. When this is outstanding it gives rise to a hollowing of the surface between it and the symphysis, often referred to as the incisor fossa ; frequently, however, this is only faintly marked. Below the oblique line the bone is full and rounded, and ends below in the basis mandibulae (inferior border). This slopes laterally at the sides, and forwards in front, where it is thick and hollowed out on either side of the symphysis to form the digastric fossae, to which the anterior bellies of the digastric muscles are attached ; narrowing somewhat behind this, the base again expands opposite the molar teeth, and finally becoming reduced in width, terminates posteriorly at the angle formed between it and the posterior border of the ramus. The medial surface of the body is crossed by the mylo - hyoid line. This slants from above downwards and forwards towards the lower part of the symphysis. It serves for the origin of the mylo - hyoid muscle, and also, just behind the last molar tooth, furnishes an attachment to the superior constrictor of the pharynx. Below the posterior part of this ridge the surface is hollowed to form a fossa for the lodgment of the submaxillary gland. Above the anterior part of the mylo-hyoid line the bone is smooth and usually convex. Here the sublingual gland lies in relation to it. In the angle formed by the convergence of the two mylo-hyoid lines, and in Fio. 164. — The Mandible as seen from the Left Side. 1. Mental tubercle. 2. Mental protuberance. 3. Symphysis. 4. Coronoifl processes. 5. Condyloid processes. 6. Neck. 7. Angle. 8. Oblique line. 9. Mental foran)en. 156 OSTEOLOGY. The Medial Side of the Right Half of the Mandible. 10. Fossa for submaxillary correspondeuce with the back of the lower part of the symphysis, there is a raised tubercle surmounted by two laterally placed spines, the mental spines. Occasionally these are again subdivided into an e upper and lower pair, or it may be that the lower pair may fuse to form a rough median ridge. To the upper pair of spines the genio-glossi muscles are attached, whilst the lower pair serve for the origin of the genio-hyoid muscles. Immediately above the tubercle there is a median foramen for the transmission of a nutrient vessel, and close to the alveolar border opposite the intervals be- tween the central and lateral incisors, there are two little vascular canals. The ramus mandibulse passes upwards from the posterior part of the body, form- ing by the junc- tion of its pos- terior border with the base of the body the angulus mandibulae (angle), which is usually rounded and more or less everted. The lateral sur- face of the ramus affords attach- ment to the mas- seter muscle, and when that muscle is powerfully de- veloped the bone is usually marked by a series of oblique curved ridges, best seen towards the angle. About the middle of the deep or medial surface is the large opening (foramen mandibulare) of the inferior alveolar canal, which runs downwards and forwards to reach the body, and transmits the inferior alveolar vessels and nerve. This aperture is overhung in front by a pointed scale of bone, the lingula mandibulse, to the edges of which the spheno-mandibular ligament is attached. Behind the lingula and leading downwards and forwards for an inch or so from the opening of the inferior alveolar canal is the sulcus mylohyoideus (mylo-hyoid groove), along which the mylo-hyoid artery and nerve pass. Behind and below this groove the medial surface of the angle is rough for the attachment of the internal pterygoid muscle. Superiorly the ramus supports the coronoid process in front, and the condyloid process behind, the two being separated by the wide incisura mandibulae (mandibular notch), over which there pass in the recent condition the vessels and nerve to the masseter muscle. The coronoid process, of variable length and beak-shaped, is limited behind by a thin curved margin, which forms the anterior boundary of the mandibular notch. In front its anterior edge is convex from above downwards and forwards, and becomes confluent below with the anterior border of the ramus arid the oblique line. To the medial side of this edge there is a grooved elongated triangular surface, the medial margin of which, commencing above near the summit of the coronoid process, leads downwards along the medial side of the root of the last molar tooth towards the mylo-hyoid line. Behind this ridge the thickness of the ramus is mucli reduced. The temporal muscle is inserted into the margins and medial surface of the coronoid process. The posterior border of the ramus is continued upwards to support the capitulum mandibulae (condyle), below which it is some- what constricted to form the coUum mandibulse (neck), which is compressed from 12 Fig. 165.- Mental spines. Surface in relation to the sublingual gland. Alveolar border. Lingula. 5. Coronoid process. 6. Condyloid process. 7. Mandibular foramen. 8. Mylo-hyoid groove. 9. Angle. 11. 12. gland. Mylo-hyoid line. Digastric fossa. THE MANDIBLE. 157 before backwards, and bounds the mandibular notch posteriorly. To the medial side of the neck, immediately below the condyle, there is a little depression (fovea ptery- goidea) for the insertion of the external pterygoid muscle. The convex surface of the condyle is transversely elongated, and so disposed that its long axis is in- clined nearly horizontally medio - laterally and a little forwards. The con- vexity of the condyle is more marked in its antero- posterior than in its trans- verse diameter, and tends slightly to overhang the mandibular notch. The medial and lateral ends of tlie condyle terminate in tubercles which serve for the attachment of part of the articular capsule of the joint. Fio. 166. — Development of the Mandible. As seen from tlie medial side ; B, from the lateral side ; C, showing accessory (metaplastic) cartilages (blue). (lu A aud B Meckel's cartilage is coloured blue.) Ossification. — Its de- velopment is intimately as- sociated with Meckel's carti- lage, the cartilaginous bar of the first visceral or man- dibular arch. Meckel's car- tilages, of which there are two, are connected proxi- nmlly with the periotic capsule and cranial base. These distal ends meet, but do^ not fuse, in the region of the symphysis. Ossification takes place chiefly from membrane, in part from primordial cartilage (Meckel's cartilage), and also in part from accessory (metaplastic) cartilages, which have no connexion with Meckel's cartilage, but arise in the membrane fi-om which the greater part of the bone is formed. Before ossifica- tion commences three structures are seen lying side by side in the mandibular arch of the embryo. These are, from medial to lateral side, Meckel's cartilage, the inferior alveolar nerve, which anteriorly divides into its two terminal branches, viz., the incisor and mental nerves, and a dense connective tissue which stretches from before backwards from close to the mid-line anteriorly to near the acoustic region posteriorly. Ossification in membrane commences about the fortieth to forty-fifth day in the angle between the incisor and mental nerves ; it extends rapidly backwards under the mental nerve, which grooves its upper surface, and is ultimately enclosed within the mental foramen. At the same time the outer alveolar wall is formed by the extension of this ossifying membrane bone, from which later, about the third month, is developed by backward growth the angle and ramus, the latter surmounted by a well-defined coronoid process. About the forty-fifth day the inner alveolar wall, the so-called splenial element, is formed by an ingrowth from the anterior part of the floor of the mental groove. This passes below the incisor nerve and passes up between it and Meckel's cartilage, which it subsequently overlaps, extending rapidly forwards and backwards to end posteriorly in the lingula anterior to the point of origin of the mylo-hyoid nerve. The mandible, in point of time, is the second bone to ossify, being preceded only by the clavicle. Ossification in Meckel's cartilage. — This commences a little later than the first formation of the coronoid process, opposite the first and second incisor tooth germs, not by independent ossification, but by invasion of osteoblasts from the neighbouring membrane bone. The cartilage becomes surrounded by shelves of bone projected medially both above and below it from the main membrane bone. A bony tube is thus formed which extends from near the mid-line anteriorly to the second milk tooth posteriorly. Within these limits Meckel's cartilage becomes incorporated within the mandible. The extreme anterior end of the cartilage does not, however, undergo ossification, and the posterior end, save that part concerned in the formation of the malleus and incus, degenerates and ultimately disappears. Ossification in accessory cartilages. — These appear at the following sites : one, 158 OSTEOLOGY. a carrot-like mass, at the condyle ; the large end forms the condyle ; the tapering end is wedged into the ossifying ramus under the root of the coronoid process. This cartilage appears about the eleventh week. About the thirteenth week a strip of cai'tilage appears along the anterior border of the coronoid process. Along the anterior end of the alveolar walls close to the middle line, and turning down the symphysial surface of the mandible to end below in the region of the future digastric impression, another mass of cartilage appears about the fourteenth week. All the above cartilages are ossified by invasion from the surrounding membrane bone and are not therefore independent centres. It is possible that the symphysial cartilages may be occasionally independently ossified and thus give rise to the ossa mentalia when they exist. From what has been stated it thus appears that under normal conditions each half of the mandible ossifies from one centre only. The above account is based on the researches of Low ^ and Fawcett.^ In a third or fourth month foetus the cartilage can be traced from the under surface of the anterior part of the tympanic ring downwards and forwards to reach the jaw, to which it is attached at the opening of the mandibular canal ; from this it may be traced forwards as a narrow strip applied to the medial surface of the mandible, which it sensibly grooves. The proximal end of this furrow remains permanently as the mylo-hyoid groove. The part of the cartilage between the tympanic ring and the mandible dis- appears, and its sheath becomes converted into fibrous tissue, and persists in the adult as the spheno-mandibular ligament, its proximal end being continuous, through the petro-tympanic fissure, with the slender process of the malleus, with the development of which bone it is intimately associated. I. Chaine {Comptes Rendus, Biologie, 1903) takes exception to this view and regards the spheno-mandibular ligament as the remnant of a muscular slip. At birth the mandible consists of two halves united at the sj'^mphysis by fibrous tissue ; towards the end of the first, or during the second year, osseous union between the two halves is complete. In infancy the mandible is shallow and the rami proportionately small ; further, owing to the obliquity of the ramus, the angle is large, averaging about 150°. The mental foramen lies near the lower border of the bone. Coincident with the eruption of the teeth and the use of the mandible in mastication, the rami rapidly increases in size, and the angle becomes more acute. After the completion of the permanent dentition it approaches more nearly a right angle varying from 110° to 120°. The body of the bone is stout and deep, and the mental foramen usually lies midway between the upper and lower borders. As age advances, owing to the loss of the teeth and the consequent shrinkage and absorption of the alveolar border of the bone, the body becomes narrow and attenuated, and the mental foramen now lies close to the upper border. At the same time the angle opens out again (130° to 140°), in this respect resembling the infantile condition. In old age the coronoid process and the condyle form a more open angle with each other than in the young adult. Os Hyoidcum. The hyoid bone, though placed in the neck, is developmentally connected with the skull. It lies between the mandible above and the larynx below, and is connected with the root of the tongue. Of U-shaped form, as its name implies (Greek v and e?5os, like), it consists in the adult of a central part, or body, with which are united two long pro- cesses extending backwards — the greater cornua — one on each side. At the point where these are ossified with the body, the lesser cornua, which project upwards and backwards, are placed. The body is arched from side to side and compressed from before backwards, so that its surfaces slope downwards and forwards. Its Pig. Ifi/. — I HE Wyoid Bone as seen .. _cti ^• -Ui. j- -j FKOM THE Fkont antcnor surface displays a slight median ridge, on either side of which the bone is marked by the attachment of the mylo-hyoid muscles. Its posterior surface, deeply hollowed, is concave from side to side and from above downwards. Herein lie a quantity of ^ J(/u,rrwX of A'tmlvrtiy and Physiology, vol. xHv. p. 82. ^ Graduation Tliesis, Edinburgh, 1906. THE SKULL AS A WHOLE. 159 fat and a bursa, which separates this aspect from the tliyreo-hyoid membrane. The upper border, usually described witii the anterior surface, is broad ; it is separated from the anterior aspect by a transverse ridge, behind which are the impressions for the attachment of the genio-hyoid muscles. Its posterior edge is thin and sluirp ; to this, above, are attached the genio-glossi, whilst behind and Vjelow the thyreo-hyoid membrane is connected with it. The inferior border is well defined and narrow ; it serves for the attachment of the omo-hyoid, sterno-hyoid, thyreo- hyoid, and stylo-hyoid muscles. The greater cornua are connected on either side with the lateral parts of the body. At first, union is effected by synchondroses, which, however, ultimately ossify. These cornua curve backwards, as well as upwards, and terminate in more or less rounded and expanded extremities. Compressed laterally, they serve for the attachments laterally of the thyreo-hyoid and hyo-glossi muscles, and the middle constrictor of the pharynx from below upwards, whilst medially they are con- nected with the lateral expansions of the thyreo-hyoid membrane, the free edges of which are somewhat thickened, and connect the extremities of the greater cornua witli the ends of the superior cornua of the thyreoid cartilage below. The lesser cornua, frequently cartilaginous in part, are about the size of grains of wheat. They rest upon the upper surface of the bone at the junctions of the greater cornua with the body. In youth they are separated from, but in advanced life become ossified with, the rest of the bone, from which they are directed upwards, backwards, and a little laterally. Their summits are connected with the stylo- hyoid ligaments ; they also serve for the attachment of muscles. Connexions. — The hyoid is shuig from the styloid processes of the temporal bones by the stylo-liyoid ligaments. Inferiorly it is connected with the thyreoid cartilage of the larynx by the thyreo-hyoid ligaments and membrane. Posteriorly it is intimately associated with the epiglottis. Ossification.— In considering the development of the hyoid bone it is necessary to refer to the arrangement and disposition of the cartilaginous bars of the second and third visceral arches. That of the second visceral arch, the hyoid bar — or Reichert's cartilage, as it is sometimes called— is united above to the petrous part of the temporal, whilst ventrally it is joined to its fellow of the opposite side by an independent median cartilage. Choudrifica- tion of the third visceral arch only occurs towards its ventral extremity, forming what is known as the thyreo-hyoid bar. This also unites with the median cartilage above mentioned. In these cartilaginous processes ossific centres appear in certain definite situations. Towards the end of foetal life a single centre (by some authorities regarded as primarily double) appears in the median cartilage, and forms the body of the bone (basihyal). About the same time ossification begins in the lower ends of the thyreo-hyoid bars, and from these the greater cornua are developed (thyreo-hyals). During the first year the lower ends of the hyoid bars begin to ossify and form the lesser cornua (cerato-hyals). The cephalic ends of the same cartilages meanwhile ossify to form the styloid process (stylohyal) on either side and one of the auditory ossicles called the stapes, whilst the intervening portions of cartilage undergo resorption and become converted into the fibrous tissue of the stylo-hyoid ligaments, which in the adult connect the lesser cornua witli the styloid processes of the temporal bone. The greater cornua fuse with the body in middle life ; the lesser cornua only at a more advanced period. Variations in the course of development lead to interesting anomalies of the hyoid apparatus. The lesser cornua may be unduly long or the stylo-hyoid ligament may be bony ; in this case the cartilage has not undergone resorption, but has passed on to the further stage of ossifica- tion, tluis forming an epihyal element comparable to that in the dog. The ossified stylohyoid ligament, as felt through the pharyngeal wall, may be mistaken for a foreign' body. (Farmer, G. W. S., Brit. Med. Journ.\^00, vol. i. p. 1405.) THE SKULL AS A WHOLE. The skull as a whole may be studied as seen from the front (norma frontalis) from the side (norma lateralis), from the back (norma occipitalis), from above (norma verticalis), and from below (norma basalis). 160 OSTEOLOGY. The Skull from the Front (Norma Frontalis). lu front, the smooth convexity of the frontal bone limits this region above, whilst inferiorly, when the lower jaw is disarticulated, the teeth of the maxillse form its lower boundary. The large openings of the orbits are seen on either side ; whilst placed centrally, and at a somewhat lower level, is the apertura piriformis (anterior nasal aperture) leading into the nasal cavity. The frontal region, convex from above downwards and from side to side, is limited laterally by two ridges, which are the anterior extremities of the temporal lines. Superiorly the fulness of the bone blends with the convexity of the vertex. Inferiorly the frontal bone forms on each side the arched superior border of the orbit (margo supraorbitalis). The space between these borders corresponds to the root of the nose, and here are seen the sutures which unite the frontal with the nasal bones medially, and with the frontal process of the maxilla on each side, called the naso-frontal and fronto -maxillary sutures, respectively. The supra-orbital margin is thin and sharp laterally, but becomes thick and more rounded towards its medial end, where it forms the medial angular process and unites with the frontal process of the maxilla and the lacrimal bone in the medial wall of the orbit. This arched border is interrupted towards the medial side by a notch (incisura supraorbitalis), sometimes converted into a foramen, for the transmission of the supra-orbital nerve and artery. In the median plane, just above the naso-frontal suture, there is often the remains of a median suture (sutura frontalis), which marks the fusion of the two halves from which the bone is primarily ossified. Here also a prominence, of variable extent — the glabella — is met with; from this there passes out on each side above and over the orbital margin a projection called the superciliary arch. The orbital fossae, of more or less conical form, display a tendency to assume the shape of four-sided pyramids by the flattening of the superior, inferior, and lateral walls. The base, which is directed forwards and a little laterally, corresponds to the orbital aperture. The shape of this is liable to individual and racial variations, being nearly circular in the Mongoloid type, whilst it displays a more or less quadrangular form in Australoid skulls. The superior margin, as has been already stated, is formed by the frontal bone between the zygomatic and medial angular processes. The lateral and about half the inferior margins are formed by the sharp curved edge between the facial and orbital surfaces of the zygomatic bone. The medial border and the remainder of the inferior margin are determined by the lateral surface of the frontal process of the maxilla, and the sharp edge separating the facial from the orbital surface of the same bone. Three sutures interrupt the continuity of the orbital margin — zygomatico-frontal laterally, the fronto -maxillary medially, both lying about the same level, and the zygomatico-maxillary inferiorly. The apex of the space is directed backwards and medially, so that the medial walls of the two orbits lie nearly parallel to each other, whilst the lateral walls are so disposed as to form almost a right angle with each other. The depth of the orbit measures, on an average, about two inches (5 cm.). At the apex there are two openings ; the larger, known as the superior orbital fissure (O.T. sphenoidal), passes from the apex of the space laterally and a little upwards for the distance of three-quarters of an inch or so, between the roof and lateral wall of the orbit. The medial third of this fissure is broad and of circular form. Laterally it is considerably reduced in width. Through this the oculomotor, trochlear, ophthalmic division of the trigeminal, and the abducent nerves enter the orbit, whilst the ophthalmic veins pass backwards through it. Above and medial to the medial end of the sphenoidal fissure there is a smaller circular opening, the optic foramen, for the transmission of the optic nerve and ophthalmic artery. The roof of the orbit, wliich is very thin and brittle towards its centre, is formed in front by the orbital part of the frontal bone, ;i.nd behind by a small triangular piece of theZsmall wing of the sphenoid, which surrounds the optic foramen and forms tlie upper border of the superior orbital fissure. Laterally THE FKONT OF THE SKULL. 161 this surface is 8e})arat('d from the lateral wall by the superior orbital fissure Fig. 168. — The Front of thk Skui.l. The nasal bones, lamina papyracea of the ethmoid, vomer, inferior conclue, zygomatic, and parietal bones are coloured red. The splienoid, lacrimal, perpendicular part and middle conchae of the ethmoid, and mandible are coloured blue. The maxilhe are coloured yellow. The frontal and temporal bones are left uncoloured. 1. Mental protuberance. 2. Body of mandible. 3. Ramus of mandible. 4. Anterior nasal spine. 5. Canine fossa. 6. Infra-orbital foramen. 7. Zygomatico-facial foramen. 8. Orbital surface of maxilla. 9. Temporal fossa. 10. Lamina papyracea of ethmoid. 11. Superior orbital fissure. 12. Lacrimal bone and groove. 13. Optic foramen. 14. Ethmoidal foramina. 15. Temporal line. 16. Supra-orbital notch. 17. Glabella. 18. Frontal tuberosity. 19. Superciliary arch. 20. Parietal bone. 21. Naso-frontal suture. 22. Rerion. 23. Great wing of sphenoid. 24. Orbital surface of great wing of sphenoid. 25. Squamous part of the temporal. 26. Left nasal bone. 27. Zygomatic bone. 28. Inferior orbital fissure. 29. Zygomatic arch. 30. Apertura piriformis, displaying nasal septum and inferior and middle concha>. 31. Mastoid process. 32. Incisor fossa. 33. Angle of jaw. 34. Mental foramen. 35. Symphysis nieuti. posteriorly, anteriorly by an irregular suture between the orbital part of the 11 162 OSTEOLOGY. frontal and the upper margin of the orbital surface of the great wing of the sphenoid, lateral to which the zygomatic process of the frontal articulates with the zygomatic bone, often forming a ridge which limits the fossa for the lodgment of the lacrimal gland inferiorly (Whitnall). Medially the roof is marked off from the medial wall by a suture, more or less horizontal in direction, between the orbital plate of the frontal and the following bones, in order from before backwards, viz., the frontal process of the maxilla, the lacrimal bone, and the lamina papyracea of the ethmoid. In the suture between the last-mentioned bone and the frontal there are two foramina, the anterior and posterior etlimoidal foramina ; both trans- mit ethmoidal vessels and the ethmoidal branches of the naso-ciliary nerve as well. The roof is concave from side to side, and to some extent also from before backwards. About midway between the fronto-maxillary suture and the supra- orbital notch or foramen, but within the margin of the orbit, there is a small depression, occasionally associated with a spine (fovea vel spina trochlearis), for the attachment of the cartilaginous pulley of the superior oblique muscle of the eyeball. Under cover of the zygomatic process the roof is more deeply exca- vated, forming a shallow fossa for the lodgment of the lacrimal gland (fossa glandulae lacrimalis). In front, the roof separates the orbit from the frontal sinus, and along its medial border it is in relation with the ethmoidal air-cells. The relation to these air spaces is variable, depending on the development and size of the sinuses. The rest of the roof, which is very thin, forms by its upper surface part of the floor of the anterior cranial fossa, in which are lodged the frontal lobes of the cerebrum. The floor of the orbit is formed by the orbital surface of the maxilla, together with part of the orbital surface of the zygomatic bone, and a small triangular piece of bone, the orbital process of the palate, which is wedged in posteriorly. Laterally, for three-quarters of its length posteriorly, it is separated from the lateral wall, which is here formed by the great wing of the sphenoid, by a cleft called the inferior orbital fissure. Through this there pass the maxillary division of the trigeminal nerve on its way to the infra-orbital canal, the zygomatic branch of the maxillary nerve, the infra-orbital vessels, a branch connecting the inferior ophthalmic vein with the pterygoid plexus, and some twigs from the spheno- palatine ganglion. By means of this fissure the orbit communicates with the pterygo- palatine fossa behind, and the infra -temporal fossa to the lateral side, though in the recent condition the fissure is bridged over by the involuntary orbitalis muscle of Mliller. Medially the floor is limited from behind forwards by the suture between the following bones, viz., the orbital process of the palate below with the body of the sphenoid above and behind, and the lamina papyracea of the ethmoid above and in front — ^anterior to which the orbital surface of the maxilla below articulates with the lamina papyracea of the ethmoid and the lacrimal above and in front. At the anterior extremity of this Hne of sutures the medial edge of the orbital plate of the maxilla is notched and free between the point where it articulates with the lacrimal posteriorly and the part from which its frontal process arises. Here it forms the lateral edge of a canal, down which the membranous naso-lacrimal duct passes to the nose. The floor of the orbit is thin behind and at the sides, but thicker in front, where it blends with the orbital margin. Passing in a sagittal direction through its substance is the infra-orbital canal, the roof of which is usually deficient behind, where it becomes continuous with a broad, shallow groove, which leads forwards from the anterior margin of the inferior orbital -fissure. This canal (canalis infraorbitalis) opens on the anterior surface of the maxilla immediately below the orbital margin (foramen infraorbitale) and transmits the maxillary division of the trigeminal nerve, together with the infra-orbital vessels. The floor forms a thin partition which separates the orbit from the maxillary sinus, which lies beneath it. Medially it completes the lower ethmoidal air-cells, and separates the orbit from the middle meatus of the nasal cavity. The lateral wall of the orbit, which is the strongest, is formed by the orbital surface of the great wing of the sphenoid and the superior part of the orbital surface of the zygomatic bone. Above it, behind, is the superior orbital fissure, whilst below. THE FKONT OF THE SKULL. 163 and exteudinj^ much farther forward, is the inferior orbital fissure. Tlie posterior portion of tliis wall, formed ]>}' the' great wing of the sphenoid, serv^'S as a partition betwe(;n the orbit and the anterior extremity of the middle cranial fossa, in which is lodged the pole of the temporal lobe of the cerebrum. In front of this, and behind the line of the spheno-zygomatic suture, this wall is strengthened on its outer aspect by its confluence with the cranial wall. Still more anteriorly, the lateral wall separates the orbit from IIk; temporal fossa. I'he anterior margin of the lateral wall is stout and formed by the zygomatic bone, behind which, formed in part by the orbital process of the zygomatic bone and the zygomatic edge of the great wing of the sphenoid, it forms a fairly thick partition between the orbit in front and the temporal fossa behind. Crossing this surface from above downwards, close to the anterior extremity of the inferior orbital fissure, is the suture between the zygomatic bone and the great wing of the sphenoid (sutura sphenozygomatica). This wall is pierced in front by one or two small canals (foramina zygomatico-orbitalia), which traverse the zygomatic bone and allow the transmission of the zygomatico- temporal and zygomatico-facial branches of the zygomatic portion of the maxillary division of the trigeminal nerve. A small tubercle, which can be more readily felt than seen, is situated just within the orbital margin near the middle of the anterior part of this wall, and indicates the site of attachment of the lateral palpebral raphe (Whitnall). The medial wall of the orbit is formed from before backwards by a small part of the frontal process of the maxilla, by the lacrimal, and by the lamina papjrracea of the ethmoid, posterior to which is a small part of the lateral aspect of the body of the sphenoid in front of the optic foramen. Above, the orbital part of the frontal bone forms a continuous suture from before backwards with the bones just enumerated ; whilst below, the lacrimal and the lamina papyracea of the ethmoid articulate with the orbital plate of the maxilla ; posteriorly the posterior extremity of the lamina papyracea and the anterior part of the body of the sphenoid articulate with the orbital process of the palate. The orbital surface of the lacrimal bone is divided into two by a vertical ridge — the lacrimal crest (crista lacrimalis posterior) — which forms in front the posterior half of a hollow, the fossa sacci lacrimalis, the anterior part of which is completed by the channelled posterior border of the frontal process of the maxilla. In the fossa is lodged the lacrimal sac, whilst passing from it and occupying the canal, of which the upper opening is at present seen, is the membranous naso- lacrimal duct. The lower part of the fossa separates the orbit from the anterior part of the middle meatus of the nasal cavity. To the medial side of the upper part of the fossa for the lacrimal sac lie the anterior ethmoidal cells, the passage leading from the nose to the frontal sinus (infundibulum ethmoidale), and the part of the bone behind the lacrimal crest forms the thin partition between the orbit and the ethmoidal cells. Behind, where the body of the sphenoid forms part of the medial wall of the orbit, the sphenoidal air sinus is in relation to the apex of that space, though here the partition wall lietween the two cavities is much thicker. The skeleton of the face on its anterior surface is formed by the two maxillae, the frontal processes of which have been already seen to pass up to articulate with the medial angular processes of the frontal bone, thus forming the lower halves of the medial margins of the orbits. Joined to the maxillte laterally are the zygomatic bones, which are supported by their union with the temporal bones posteriorly through the medium of the zygomatic arches. The suture which separates the zygomatic from the maxilla (sutura zygomaticomaxillaris) commences above about the centre of the inferior orbital margin and passes obliquely downward and laterally, its inferior end lying in vertical line with the lateral orbital margin. The two maxilke are separated by the nasal cavities, which here open anteriorly. Above, the two nasal bones are wedged in between the frontal processes of the maxillcB ; whilst below the apertura piriformis, the maxilke themselves are united in the middle line by the intermaxillary suture (sutura intermaxillaris). The apertura piriformis (piriform aperture) (O.T. nasal aperture or anterior nares), which lies below and in part between the orbits, is of variable 11a 164 OSTEOLOGY. shape and size — usually piriform, it tends to be long and narrow in Europeans, as contrasted with the shorter and wider form met with in the negroid races. Its edges are formed below and on either side by the free curved margin of the body and the frontal process of the maxilla ; and above, and partly at the sides, by the free border of the nasal bones. In the median plane, inferiorly, corresponding to the upper end of the intermaxillary suture there is an outstanding process — the anterior nasal spine, formed by the coalescence of spicules from both maxillae ; arising from this, and passing backwards and upwards, is a thin bony partition — the osseous septum of the nose. Often deflected to one or other side, it divides the cavity of the nose (cavum nasi) into a right and a left half. Projecting into these chambers from their lateral walls can be seen the medial surfaces and free borders of the middle and inferior conchse, the spaces below and between which form the inferior and middle meatuses of the nose, respectively. Below the orbit, and to the lateral side of the piriform aperture, the interior or facial surface of the body of the maxilla is seen ; this is continuous inferiorly with the lateral surface of the alveolar process, in which are embedded the roots of the upper teeth. A horizontal line drawn round the maxillse on the level of a point midway between the lower border of the piriform aperture and the alveolar edge corre- sponds to the plane of the hard palate. Below that the alveolar process separates the cavity of the mouth from the front of the face ; whilst above, the large air space, the maxillary sinus, lies within the body of the maxilla. The zygomatic bone forms the lower half of the lateral and lateral half of the lower border of the orbit. Its lateral aspect corresponds to the point of greatest width of the face, the modelling of which depends on the flatness or projection of this bone. When the mandible or lower jaw is in position, and the teeth in both jaws are complete, the lower dental arch will be seen to be smaller in all its diameters than the upper, so that when the jaws are closed the upper teeth slightly overlap the lower both in front and at the sides. Exceptionally, a departure from this arrange- ment is met with. Lateral Aspect of the Skull (Norma Lateralis). Viewing the lateral aspect of the skull, in the first instance without the mandible, it is seen to be formed in part by the bones of the cranium, and in part by the bones of the face. A line drawn from the fronto-nasal suture to the tip of the mastoid process serves to define roughly the boundary between these portions of the skull. Of ovoid shape, the cranium is formed above by the frontal, -parietal, and occipital bones from before backwards ; whilst below, included within these are the sphenoid and temporal bones. The sutures between these several bones are arranged as follows : Commencing at the zygomatic process of the frontal, the suture between that bone and the zygomatic bone is first seen ; tracing this backwards and a little upwards, the lower edge of the frontal next articulates with the upper margin of the great wing of the sphenoid for a distance varying from three-quarters of an inch to one inch. Here the posterior border of the frontal turns upwards and slightly back- wards, forming with the parietal the sutura coronalis (coronal suture). The lower border of the parietal bone, which is placed immediately behind the frontal, articulates anteriorly with the posterior part of the superior border of the great wing of the sphenoid. The extent of this suture (sutura sphenoparietalis) is liable to very great individual variation — at times being broad, in other instances being pointed and narrow, whilst occasionally the parietal does not articulate with the sphenoid at all. Behind the spheno-parietal suture the parietal articulates with the squamous part of the temporal (sutura squamosa), the posterior extremity of which is about one inch behind the external acoustic meatus. Here the suture alters its character and direction, and in place of being scaly, becomes toothed and irregular, uniting, for the space of an inch or so, the mastoid angle of the parietal with the mastoid process of the temporal bone. This suture (sutura parietomastoidea) is more or less horizontal in direction, and lies in line and on a level with the superior border of the zygomatic arch. At a point about two inches behind the external acoustic LATERAL ASPECT OF THE SKULL. 165 meatus tlie posterior l)order of the parietal Uoiie turns obliquely upwards and backwards, and foinis with the s(|u;i,ni<)us part of the occipital bone the strongly denticulated sutura lambdoidea (lambdoid suture). Inferiorly this suture is con- tinued obliquely downwards between the occipital bone and the posterior border of the mastoid portion of the tem])oral, where it forms the sutura occipitomastoidea Fig. 169. — Norma Lateralis of the Skull. The occipital, sphenoid, and lacrimal bones and the mandible are coloured lilue. The parietal, zygomatic, ;iud nasal bones are coloured red. The temporal, frontal, ethmoid, and maxillary bones are left nncoloured. 1. Mental foramen. 2. Bodv of the nianvhich lies in direct continuation anteriorly with the line of the sagittal suture. The frontal suture is, as a rule, more or less completely fused by the sixth year. The size of the infant's skull at birth varies considerably, and is to a large extent dependent on the bulk and development of the child. The size of the skull in female infants is absolutely smaller than in the case of male children, though not necessarily proportionately smaller, since the weight of female children at birth is on the average absolutely less than male foetuses at full term. 196 OSTEOLOGY. In viewing the skeleton of the face the observer is struck with the large proportionate size of the orbital and nasal apertures. The former are circular in outline, with sharp crisp margins. Under cover of the zygomatic process of the frontal bone the roof and lateral wall of the orbit is deeply recessed. The fossa sacci lacrimalis is oftentimes directed more towards the facial aspect than towards the orbital cavity. The superior and inferior orbital fissures are proportionately large, and the latter, in the macerated skull, forms a wide channel of communication with the fossa infratemporahs. The nasal aperture, apertura piriformis, is cordate in form, and exhibits a greater proportionate width than is met with in the adult ; its inferior margin is not far beneath the level of the inferior orbital margins. The vertical depth of the maxillse is small, and as yet the processus alveolaris is imperfectly developed, its inferior edge lying but little below the level of the inferior border of the arcus zygomaticus. Sunk in the alveolar border at this Position of fonticulus frontalis Tuber parietale Cartilaginous nasal septum Position of -fonticulus occipitalis Suture between ' terparietal and supra-occipital parts of occipital bone Fonticulus mastoideus Fig. 183.— Lateral Aspect of the Skull at Birth. stage may be seen the relatively large hollows in which the dental sacs are lodged. Within the body of the maxilla the maxillary sinus is represented by a shallow groove, disposed in relation to. the middle meatus of the nose. For this reason the space separating the orbital floor from the palatine surface of the bone is small, but is later increased to its adult proportions by the enlargement of the maxillary sinus and the consequent expansion of the body of the maxilla. Viewed from the inferior surface, the hard palate is shallow, owing to the poor development of the alveolar border. The sutures between the ossa incisiva and the processus palatini of the maxillse are readily recognisable, and the vertical height of the choanae is seen to be relatively small, owing to the perpendicular parts of the palate bones not having reached their adult proportions. The mandible consists of two parts united, in the median plane in front, by fiVjrous tissue to forui the symphysis. The alveolar l)order is deeply grooved for the recex^tion of the dental sacs, whilst the remaining substance of the body of the bone is but slightly developed. The foramen mentale pierces the bone about midway between its superior and inferior borders. THE CLAVICLE. 197 The ramus is proportionately \yide, ami forms with the body an angle whicli is very obtuse. The coronoid process rises considerably above the level of the capitulum, and comes into close relationship with the crista infratemporalis. The capitulmn, which is proportionately more expanded than in the adult, occupies the somewhat laterally directed shuUuw mandibular fossa of the temjjoral bone. On viewing the lateral aspect of the skull, the meatus acusticus externiis, as such, is not seen ; it is replaced by the slender annulus tympanicus, which supports the tympanic membrane. This ring of bone, incomplete above, is united by its extremities superiorly to the inferior surface and lateral aspect of the S(iuamo- zygomatie part of the temporal bone. The ring itself is disposed so that it slopes downwards, forwards, and medially ; as yet it fails to enter into the formation of the posterior wall of the /oss« mandihularis, and only at a later stage does it grow laterally to form the floor of the external acoustic meatus. Through the ring the labyrinthic wall of the cavum tympani is seen ; exposed on this surface are the promontory, the fenestra vestibuli, and the fenestra cochlea3. Posterior to the tympanic ring the sutura squamosomastoidea, still open, is seen separating the pars mastoidea from the squama temporalis of the temporal bone. On turning the skull over so that its inferior surface is exposed, the partes late rales of the occipital bone are seen separated in front from the pars basilaris by a suture, which runs through the occipital condyle on either side. Posteriorly an open suture, which curves backward and laterally on each side of the posterior margin of the foramen ovale, separates them from that part of the squama occipitalis which is developed in cartilage. The squama occipitalis at this stage exhibits a lateral cleft on each side, passing backwards from the fonticulus mastoideus, whicli serves to indicate the line of union of the parts which are developed in cartilage and membrane respectively. The latter, the superior, sometimes separate, constitutes the os interparietale. DIFFERENCES DUE TO AGE. At birth the face is proportionately small as compared with the cranium, constituting about one-eighth of the bulk of the latter. In the adult the face equals at least half the cranium. About the age of puberty the development and expansion of some of the air- sinuses, more particularly the frontal sinus, lead to characteristic differences in form in both the head and face. The eruption of the teeth in early life and adolescence enables us to determine the age with fair accuracy. After the completion of the permanent dentition, the wear of the teeth may assist us in hazarding an approximate estimate. The condition of the sutures, too, may guide us, synostosis of the coronal and sagittal sutures not as a rule taking place till late in life. Complete obliteration of the synchondrosis between the occipital bone and sphenoid may be regarded as an indication of maturity. In old age the skull usually becomes lighter and the cranial bones thinner. The alveolar borders of the maxilla) and mandibles become absoi-bed owing to the loss of the teeth. This gives rise to a flattening of the vault of the hard palate and an alteration in the form of the mandible, whereby the mandibular angle becomes more obtuse. THE BONES OF THE SUPERIOR EXTREIYIITY. Clavicula. The clavicle, or collar bone, one of the elements in the formation of the shoulder girdle, consists of a curved shaft, the extremities of which are enlarged. The medial end, since it articulates with the sternum, is called the sternal extremity ; the lateral extremity, from its union with the acromion of the scapula, is known as the acromial end. The extremitas sternalis (sternal end) is enlarged, and rests upon the disc 198 OSTEOLOGY. of fibro-cartilage which is interposed between it and the clavicular facet on the upper and lateral angle of the manubrium sterni. It is also supported by a small part of the medial end of the cartilage of the first rib. Its articular surface, usually broader from above downwards than from side to side, displays an antero-posterior convexity, whilst tending to be shghtly concave in a vertical direction. The edge around the articular area, which serves for the attachment of the capsule of the Sternal articular SURFACE Acromial articular surface Tuberositas coracoidea Fig. 184.^ — The Right Clavicle seen prom above. sterno-clavicular articulation, is sharp and well defined, except below, where it is rounded. The body exhibits a double curve, being bent forwards in the medial two- thirds of its extent, whilst in its lateral third it displays a backward curve. Of rounded or prismatic form towards its sternal end, it becomes compressed and flattened at its acromial extremity. It may be described as possessing two surfaces, a superior and an inferior, separated by anterior and posterior borders, which are well defined towards the lateral extremity of the bone, but become wider and less well marked medially where they conform more to the cylindrical shape of the bone. The superior surface, which is smooth and subcutaneous throughout its whole length, is directed upwards and for- wards. The anterior border, which separates the superior from the inferior surface in front, is rough and tubercular towards its medial end for the attachment of the clavicu lar fibres of thejjgctoralis major, whilst laterally, where it becomes continuous with the anterior margin of theacromial end, it is better defined, and bears the imprint of the origin of the fibyes of the^jj^ltoid jim§ cle ; h ere, not uncommonly, a projecting spur of bone, called the deltoid tubercle, may be seen. The 'posterior larder is broad medially, FtNO-HYOID T B A f Fig. 185. — The Upper Surface of the Right Clavicle WITH Muscle Attachments. Sternal articular surface where it i^ppcd superiorly to furnish an attachiSpWHTthe clavicular fibres of the sterno-ma1»jL muscle ; behind and below this the sterno-hyoid and sterno- thyreoid muscles arepSbched to the bone. Laterally, the post^or border /becomes more rounded, ancMponfluent with the posterior edge of the^ acromial end at a point where there JF a marked outgrowth of bone from its inferior surface, the tuberositas coracoidea. Into the lateral third of this border are inserted the THE CLAVICLE. 199 in- by Trapezoid ligament Costo-clavicular ligament Fig. 187. — Tin: L'.ndeh Surface of the Right Clavicle with thk Attachments of the Muscles mapped out. upper and anterior fibres of tlie trapezius muscle. The inferior surface, clined downwards and backwards, is marked close to the sternal end an irregular elongated impression (tuberositas costalis), often deeply pitted, for tlie attach- ment of the co.sto- clavicuhirliLrament,which unites it to the cartilage of the first rib. Lateral to this the shaft is channelled by a groove which terminates close to the coracoid impression ; into this groove the subclavius muscle is inserted. The acromial end of the bone is Hattened and compressed from above down- wards, and expanded from before backwards ; its anterior edge is sharp and well defined, and gives attachment to the deltoid muscle, which also spreads over part of its upper surface. Its posterior margin is rougher and more tubercular, and provides a surface for the insertion of the trapezius. The area of the superior surface between these two muscular attachments is smooth and subcutaneous. The lateral edge of this forward-turned part of the bone is provided with an oval facet (facies articularis acromialis) for articulation with the acromion of the scapula ; the margins around this articular area serve for the attachment of the capsule of the joint. The inferior surface of the acromial end of the bone is traversed obliquely from behind forwards and laterally by a rough ridge or line called the trapezoid ridge. The posterior extremity of this ridge, as it abuts on the posterior border of the bone, forms a prominent process, the tuberositas coracoidea; to these, respectively, are attached the trapezoid and conoid portions of the coraco-clavicular ligament. The morphology of the clavicle is of special interest. Its presence is associated with the freer use and greater range of movement of the fore-limb, such as are necessary for its employment for more specialised actions than those of mere progression. In conse- quence of these requirements, the limb, and with it the scapula, become further removed from the trunk, and so the support which the lilade bone received through the union of its coracoid element with the sternum, as in birds and reptiles, and to some extent in the lowest mammals, is withdrawn. Some substitute, however, is necessary to meet the altered conditions, and in consequence a new element is introduced in the form of a clavicle. The origin of this bone appears to be intimately associated with the precoracoid element met with in amphibia or reptiles, but whereas the precoracoid is always laid down in cartilage, which, however, not infrequently disappears, the clavicle develops in the membrane overlying the precoracoid cartilage. In the course of its development it may become intimately associated with the remains of that cartilage. Thus, it is probable that the articular discs at the sterno-clavicular and acromio-clavicular joints, as well as the sternal articular end of the clavicle, represent persistent portions of the primitive cartilage, whilst it is possible that the supra-sternal ossicles occasionally present may be also derived from it. In this way, in its most specialised form, a secondary support is established between the sternum and scapula, which serves as a movable fulcrum, and greatly enhances the range of movement of the shoulder girdle. Nutrient Foramina. — The foramina for the larger nutrient vessels, offsets of the transverse scapular artery, of which there may be one or two directed laterally, are usually found about the middle of the posterior border, or, it may be^ opening into the floor of the groove for the subclavius muscle. Ossification. — The clavicle in man is remarkable in commencing to ossify before any other bone in the body ; this occurs as early as the fifth or sixth week of fa?tal life. The shaft is ossified from two primitive centres (Mall). These are preceded by a curved rod of connective tissue on the interior of which are developed two masses of a peculiar precartilagiuous nature, one, the stenial, placed medially, lies above and overlaps in front the acromial mass, which is placed laterally. In each of these near their approxi- mated ends a centre of ossification appears. These, subsequent to the fusion of the 200 OSTEOLOGY. two independent precartilaginous masses, coalesce and form a bridge of bone uniting the two primary ossitic centres. At a later stage cartilage cells appear in the medial extremity of the sternal pre- Sternal epiphysis ossifles about Primary centres appear about cartilaginous mass and Still 20th year ; fuses about 25th year 5th or bth week of fatal hfe ? , i t , i i ^ later m the lateral end of the acromial mass. By the growth and subsequent ossifi- cation of the cartilage so formed the clavicle increases in length (Fawcett). A secondary centre ap- pears at the sternal end about the age of twenty or later, and fusion rapidly occurring between it and the shaft, ossification is completed at the age of twenty-five or thereabouts. The Scapula. The scapula, or shoulder blade, is of triangular shape and flattened form. It has two surfaces, costal or ventral, and dorsal. From the latter there springs a triano-ular process called the spine, which ends laterally in the acromion; Fig. 188. — Ossification of the Clavicle. Claviculak articular surface p CORACOID PROCESS Medial angle StTPIlA-SPINOUS FOSSA Vertebral margin [nfka-spinods fossa Arterial foramen 'JROMIAL angle Head. AND glenoid cavity Neck Great scapular notch Groove for circumflex scapular artery Axillary margin Inferior anglf. Fig. 189. — The Dorsal Surface of the Right Scapula. whilst from its superior margin there arises a beak-like projection called the coracoid process. The bone overlies the postero -lateral aspect of the thoracic framework, reaching from the second to the seventh rib. THE SCAPULA. 201 Long head OF TRICEPa Groove for circum- flex SCAPULAR ARTERV The body of the bone, which is thin and translucent; except along its margins and where the spine s])rings from it, has three margins and three angles. Of these margins the vertebral (margo vertebralis) is the longest ; it stretches from the medial angle above to the inferior angle below. Of curved or somewhat irregular outline, it affords a narrow surface for the insertion of the levator scapuke, rhom- buideus minor, and rhoml)oideus major muscles. The superior margin, which is thin and sliarp, is the shortest of the tiiree. It runs from the medial angle towards the root of the coracoid process, before reacliing which, however, it is interrupted by the scapular notch, which lies very close to the medial side of the base of that process. This notch, which is converted into a foramen by a ligament, or occasioually by a spicule of bone, transmits the supra- scapular nerve, whilst the transverse scapular artery runs above it. Attached to the superior margin, close to the notch, is the posterior belly of tlie omo-hyoid. The axillary margin, so called from its rela- tion to the hollow of the axilla (armpit), is much stouter than either of the others ; it ex- tends from the lateral angle above to the inferior angle below. The upper inch or so of this border, which lies im- mediately below the glenoid articular cavity, is rough and tubercular (tuberositas infra- glenoidalis), and affords at- tachment to the long head of the triceps. Below this it is usually crossed by a groove which marks the position of the circumflex scapular artery. The medial angle is sharp and more or less rectangular ; the inferior angle is blunter and more acute ; whilst the lateral angle corresponds to that part of the bone which is sometimes called the head, and which supports the glenoid cavity and the coracoid process. The glenoid cavity is a piriform articular area, slightly concave from above down- wards and from side to side ; its border is but slightly raised above the general surface and affords attachment in the recent condition to the labrum glenoidale, which helps to deepen the socket in which the head of the humerus rests. Below, the margin of the glenoid cavity is confluent with the infra-glenoidal tuberosity, whilst, above, it blends with a tubercle (tuberositas supraglenoidalis), to which the long head of the biceps muscle is attached. Springing from the upper part of the head, in line with the superior margin, is the processus coracoideus (coracoid process). The base of this is limited laterally by the glenoid edge, whilst medially it is separated from the superior margin by the scapular notch. Eising upwards for a short space, it bends on itself at nearly a right angle, and ends in a process which is directed laterally and slightly forwards, overhanging the glenoid cavity above and in front. Compressed from above downwards, it has attached to its upper surface near its angle the conoid ligament, lateral to which there is a rough area for the trapezoid ligament. Attached to its dorsal border is the coraco- SCAPULAR SLIP OK LATISSIMUS DORSI Fig. 190. — The Dorsal Surface of the Right Scapula WITH the Attachments of the Muscles mapped out. 202 OSTEOLOGY. acromial ligament, whilst at acromion clavicular articular • . , • , -t , ^ . CORACOID PROCESS its extremity and towards the front of its ventral border, is the combined origin of the biceps and coracobrachialis, together with the insertion of the pectoralis minor. The col- luin scapulae (neck) is that somewhat constricted part of the bone which supports the head ; it corresponds in front and behind to a line drawn from the scapular notch to the infra-srlenoidal tuberosity. The body of the bone has two surfaces, a dorsal (fades dorsalis) and a costal (fades costalis). The former is divided into two fossse by an outstanding process of triangular form, called the spina scapulae. The at- tached border of this crosses the dorsal surface of the body obliquely in a direction Coracobrachialis and short head op BICEPS Pectoralis minor Omo-hyoid Medial angle Long head OF triceps Subscapular fossa Axillary border Inferior angle Fio. 192. -Costal SnRKACE ok the Right Scapula with the Attachments of Mdscles mapped out. Fig. 191. — The Right Scapula SEEN from the FRONT. ' laterally and slightly upwards, extending from the vertebral border, near the lower limit of its upper fourth, towards the centre of the posterior glenoid edge, from which, however, it is separ- ated by the great scapular notch, which here corresponds to the dorsal aspect of the neck. Within this notch the transverse scapu- lar vessels and the supra-scapular nerve pass to the infra-spinous fossa. The surfaces of the spine, which are directed upwards and downwards, are concave, the upper entering into the formation of the supra -spinous fossa, which lies above it, the lower forming the upper wall of the infra-spinous fossa, which lies below it. The two fossae are in communication THE SCAPULA. 203 with each other round the free lateral concave border of the spine, where that curves over the great scapular notch. The dorsal free border of the spine is subcutaneous throughout its entire length. Its upper and lower edges are strongly lipped, and serve — the superior, for the insertion of the trapezius ; the inferior, for the origin of the deltoid. The intervening surface varies in width — l)road and triangular wliere it becomes confluent with the vertebral border, it displays a smooth surface, over which the tendinous fibres of the trapezius play ; narrowing rapidly, it forms a surface of varying width which blends laterally with a flattened process, the two forming a compressed plate of bone which arches across the great scapular notch above and behind, and then curves, upwards, forwards, and laterally to overhang the glenoid cavity. The medial border of this process is con- tinuous with the upper margin of the si)ine, and is gently curved. The lateral border, more curvt?d than the medial, with which it is united in front, is confluent with the inferior edge of the spine, with which it forms an abrupt bend, termed the acromial angle. The bone included between these two borders is called the acromion. Of compressed form, it much resembles the acromial end of the clavicle, with which it articulates by means of a surface (facias articularls acromii) which is placed on its medial border near its anterior extremity. The superior surface of the acromion, which is broad and expanded, is subcutaneous, and is directed upwards and dorsally, and in the normal position of the bone laterally as well. Its medial edge, where not in contact with the clavicle, has attached to it the fibres of the trapezius, whilst its lateral margin affords origin to the central part of the deltoid. At its anterior extremity it is connected with the coracoid process by means of the coraco- acromial ligament. Its inferior surface is smooth and overhangs the shoulder-joint. The supra-spinous fossa, of much less extent than the infra-spinous, is placed above the spine, the upper surface of which assists in forming its curved floor ; in it is lodged the supraspinatus muscle. The scapular notch opens into it above, whilst below and laterally it communicates with the infra-spinous fossa by the great scapular notch, through which the transverse scapular artery and supra- scapular nerve pass to reach the infra-spinous fossa. The infra-spinous fossa, overhung by the spine above, is of triangular form. The axillary margin of the bone limits it in front, whilst the vertebral margin bounds it behind ; the greater part of this surface affords origin to the infraspinatus muscle, excepting a well-defined area which skirts the axillary margin and inferior angle of the bone, and which affords an attachment to the fibres of origin of the teres minor. This muscle extends along the dorsal surface of the axillary margin in its superior two-thirds, reaching nearly as high as the glenoid edge ; whilst a cresceutic surface, whicli occupies the inferior third of the axillary border and curves backward round the dorsal aspect of the inferior angle, furnishes an origin for the teres major muscle. Here also, near the inferior angle, are occasionally attached some of the fibres of the latissimus dorsi muscle. The facies costalis (costal aspect) of the body is hollow from above downwards and from side to side, the greatest depth being in correspondence with the spring of the spine from the dorsal surface. Its medial boundary, which is formed by the anterior lipped edge of the vertebral margin, affords attachment to the fibres of insertion of the serratus anterior along the greater part of its extent. The area of insertion of this muscle is, however, considerably increased over the ventral aspects of the medial and inferior angles respectively. Running down from the head and neck above to the inferior angle below, there is a stout rounded ridge of bone, which imparts a fulness to the costal aspect of the axillary margin and increases the. depth of the costal hollow ; to this, as well as to the floor of the fossa, the sub- scapularis muscle is attached. The tendinous intersections of this muscle leave their imprint on this surface of the bone in a series of three or four rough lines which converge towards the neck. The scapula of man is characterised by the greater proportionate length of its base or vertebral margin as compared with lower forms. This proportion is expressed by what is termed the scapular index (Appendix D). The greater size of the acromion is also a distinctive feature. The double ossification of the coracoid occurs only in mammals. It is probable that the centre for the upper and anterior part of the 204 OSTEOLOGY. Primarj' centre appears about 2nd m. foetal life, coracoid process represents the epicoracoid or precoracoid of lower forms, whilst the subcoracoid centre (metacoracoid) which assists in the formation of the glenoid cavity is the rednced and vestigial remains of the stout coracoid element met with in Ornithorhynchus, which articulates with the sternum. Nutrient Foramina. — Foramina for the passage of nutrient vessels are seen in different parts of the bone ; the most constant in position is one wliicli opens into the infra-spinous fossa, about an inch or so from the scapular notch. Others are met with on the upper and under surfaces of the spine, on the costal aspect near its deepest part, and also around the glenoid margin. Connexions. — The scapula is not directly connected with the trunk, but articulates with the lateral end of the clavicle, in union with which it forms the shoulder girdle, supporting the humerus on its glenoid surface. Placed on the upper and back part of the thorax, it covers the ribs from the second to the seventh inclusive. Possessed of a wide range of movement, it alters its position according to the attitude of the limb, rising or falling, being drawn medially or laterally, or being rotated upon itself according as the arm is moved in various directions. These changes in position can easily be determined by recognising the altered relations of the subcutaneous and bony prominences, more especially the former, which include the spine, the acromion, and the inferior half of the vertebi'al border. Ossification. — Ossification begins in the body of the cartilaginous scapula about the end of the second month of foetal life. At birth the head, neck, body, spine, and base of the coracoid process are well defined ; the vertebral margin, inferior angle, glenoid cavity, acromion, and coracoid process, are still cartilaginous. The centre for the upper and anterior part of the coracoid appears in the first year, and fusion, along an oblique line leading from the upper edge of the glenoid cavity to the conoid tubercle, is complete about the fifteenth year. A separate centre (subcoracoid), which ultimately includes the superior part of the glenoid cavity and lateral part of the coracoid process, makes its appearance about the tenth year, and fuses with the surrounding bone about sixteen or seventeen. Up till the age of puberty the ac- romion remains cartilaginous ; centres, two or more in num- ber, then make their appear- ance, which coalesce and ulti- mately unite with the spine about the twenty-fifth year. Failure of union may, however, persist throughout life (see Appendix B — Variations). Ossification commences in the cartilage in the inferior angle about puberty, and in- dependently and a little later, along the vertebral margin, fusion with the body occurring at from twenty to twenty-five years. Small scale-like epiphyses make their appeai'ance on the superior surface and at the extremity of the coracoid, and are completed about the twentieth year. A thin epiphysial plate develops over the inferior part of the glenoid cavity about sixteen or seventeen, fusion being complete about eighteen or twenty years of age. Acromial centres appear 15-16 yrs. ; fuse about 25 yrs. "y- Secondary centre for coracoid appears about end 1st yr. ; fuses about 18 yrs. \ Appears about 16-17 yrs. ; fuses about 20 yrs. Subcoracoid centre appears 10 yrs. ; fuses / 16-17 yrs. Appears about 17 yrs. ; fuses about 20 yrs. Appears about 16 or 17 yrs. ; fuses 18-20 yrs. Appears 16-17 yrs. fuses 20-25 yrs. Scapula at end of First Year. Scapula about the Age of Puberty. Fig. 193. — Ossification of the Scapula. The Humerus. The humerus, or bone of the arm, articulates proximally with the scapula and distally with the bones of the forearm, namely, the radius and ulna. Its proximal end comprises the head and greater and lesser tubercles ; its body, which is longer than any of the other bones of the upper extremity, is cylindrical proximally and flattened distally. At the distal extremity, which is expanded to form the epicondyles on either side, it supports the trochlear and capitular articular surfaces for the ulna and radius respectively. THE HUMERUS. 205 Tlie proximal extremity is the thickest and stoutest part of the bone. The caput humeri (head), which forms about one-third of a spheroid and is covered with articular cartilaj^'o, is directed proxim- ally, medially, and slightly dorsally, and rests in the glenoid cavity of the scapula; the convexity of its surface is most pro- nounced in its jjosterior half. Separating the head from the tubercles laterally is a shallow groove, which fades away on the surface of the Ijone which supports the articular part inferiorly. This is named the coUum ' anatomicum (anato- mical neck) and serves for the attachment of the capsule of the shoulder-joint. The Supra- Subscapularis Latissimusidobsi Pectoralis major Tkres major Medial epicondylic RIDGE (medial margin) CORONOID FOSSA Medial epicondyle Trochlea - Deltoid Coracobrachialis Brachioradialis Extensor carpi radialis lokocs Extensors Pronator teres and flexors Fig. 194. — Antekior Vikw ok thk Right Humerus. Fig. 195. — The Anterior Surfaces OF THE Humerus with Muscular Attachments mapped out. articular edge of the groove opposite the lesser tubercle is usually notched for the attachment of the superior gleno-humeral ligament. The tuberculum majus (greater 206 OSTEOLOGY. Head Anatomical NECK Deltoid tukeeosity tubercle) abuts on the lateral side of the head and becomes continuous with the body distally. Its proximal surface forms a quadrant, which is subdivided into three more or less smooth areas of un- equal size. Of these the upper and an- terior is for the insertion of the supra- spinatus luuscle, the middle for the infra- spinatus, whilst the most distal and posterior serves for the insertion of the teres minor muscle. The lateral surface of this tubercle, which bulges beyond the line of the shaft, is rough and pierced by numerous vascular foramina. Anteriorly the greater tubercle is separated from the tuberculum minus (lesser tubercle) by a well-defined furrow, called the sulcus intertubercularis (intertubercular groove) (O.T. bicipital groove). The transverse humeral ligament stretches across the groove between the two tubercles, thus converting the groove into a canal in which the tendon of the long head of the biceps and the ascending articular branch of the anterior circumflex artery of the humerus are lodged. The lesser tubercle lies in front of the lateral half of the head ; it forms a pronounced eleva- tion, which fades into the shaft distally. The surface of this tubercle is faceted above and in front for the insertion of the subscapularis muscle, whilst laterally it forms the prominent medial lip of the inter-tubercular groove. Distal to the head and tubercles the shaft of the bone rapidly contracts, and is here named the coUum cbirurgicum (surgical neck) owing to its liability to fracture at this spot. The corpus humeri (body, or shaft) is cylindrical in its proximal half. On it the inter- tubercular groove may be traced distally and slightly medially, along its anterior surface. The edges of the groove, which are termed its lips, are confluent proximally with the greater and lesser tubercles, respectively. Here they are prominent, and form the cristae tuberculi majoris et minoris (crests of the greater and lesser tubercles). Distally the lips of the intertubercular groove gradually fade away, the medial more rapidly than the lateral, which latter may usually be traced distally to a rough elevation placed on the lateral anterior surface of the shaft about its middle, called the deltoid tuberosity. Into the lateral lip of the intertubercular groove are in- serted the fibres of the pectoralis major tendon ; hence it is sometimes described as the pectoral ridge. To the floor of the groove the latissimus dorsi is attached ; whilst the teres major muscle is inserted into the medial lip. Media I, EPICONDYLE Groove Koii UL.VAR. nekve Groove ior radial nerve Olecranon KOSSA Lateral ei'icondyle Trochlea Fio. 19G. — PcsTERiOR Surface ok the Right Humerus. THE HUMEKUS. 207 Tekrh minor Triceps (lateral The tuberositas deltoidea (deltoid tuberosity), to which the powerful deltoid muscle is attached, is a rough, sliglitly elevated V-shaped surface, placed on the lateral anterior surface of the body about its middle. The anterior limb of the V is parallel to the axis of the l»ody, and is continuous proximally with the lateral lip of the intertubercular groove, whilst the posterior limb of the V winds obliquely round the lateral anterior surface of the bone towards the posterior surface, where it becomes continuous with a slightly elevated and occasionally rough ridge which leads proximally along the ]»osterior aspect of the bone towards the greater tubercle ; from this latter ridge the lateral head of the triceps muscle arises. The medial anterior surface of the body about its middle inclines to form a rounded border, on which there is often a rough linear impression mark- ing the insertion of the coracobrachialis muscle. Distal to this the body becomes compressed Irom before backwards and expanded from side to side, ending distally on each side in an epicondyle. Its surfaces are now anterior and posterior, being separated from each other by two clearly defined borders, the medial and lateral margins, or epi- condylic ridges. Of these, the medial is the more curved and less prominent, and is continuous proxi- mally with the surface to which the coracobrachialis is attached, whilst distally it ends by blending with the medial epicondyle. The lateral is straighter and more projecting ; its edge is usually distinctly lipped. Confluent with the lateral epicondyle dis- tally, it may be traced proximally to near the deltoid tuberosity, where it turns backwards more or less parallel to the posterior oblique border of that im- pression, to be lost on the posterior surface of the body. The interval between this border and the deltoid eminence is thus converted into a shallow oblique furrow, which winds round the lateral surface of the bone just distal to its middle ; this constitutes the groove for the radial nerve along which the radial (O.T. musculo - spinal) nerve, together with the profunda brachii artery, passes from the back to reach the front of the arm. To the epicondylic ridges are attached the inter- muscular septa, whilst the lateral in its proximal two-thirds furnishes a surface for the origin of the brachioradialis muscle, and in its distal third for the extensor carpi radialis longus muscle. The anterior surface of the distal half of the body is of elongated triangular form, the base corre- sponding to the distal extremity of the bone. Kunning down the centre of this is a broad, rounded, elevated ridge, most pronounced proximally, where it joins the deltoid tuberosity, and sloping on either side towards the epicondylic ridges ; it is into the lateral of these slopes that the groove for the radial nerve passes. Distally the elevated surface spreads out, and becomes confluent with the epicondyles. The epicondylus medialis (medial epicondyle) is the more prominent of the two, and furnishes a surface for the origin of the pronator teres, and the superficial flexor muscles of the forearm. The epicondylus lateralis (lateral epicondyle), stunted and but Uttle projecting, serves for the attachment of the common tendon of origin of the extensor muscles. The brachialis muscle has an extensive origin from the anterior surface of the distal half of the body, including between its proximal sHps the insertion of the deltoid. Origin of extknsors of forearm ONiEUS Fig. 197. — Posterior Surface ok the Right Humerus with Attachments OF Muscles mapped out. 208 OSTEOLOGY. Head .. Inter tubercular / GROOVE Medial _j EPI-— ( CONDYLE " Lateral epicondyle Capitulum Olecranon fossa Groove for ulnar nerve Fig. 199. — Distal Aspect of the Distal Ex- tremity OF THE Eight Humerus. The posterior surface of the distal half of the body is smooth and rounded from side to side ; somewhat flattened Lesser tubercle j-j.ii t, j_r, t. t t_ i distally, where the whole body tends to incline forwards, it be- comes continuous on either side with the posterior surfaces of the epicondyles, the medial of which is grooved for the passage of the ulnar nerve, whilst the lateral supplies an origin for the an- conseus muscle. The medial head of the triceps muscle has an exten- sive attachment from the posterior Fig. 198. — Proximal Aspect of the Head of the Right surface of the distal two-thirds of Humerus (with the outline of the distal extremity in relation fj^g bodv medial to and distal to thereto shown in dotted line). • , , n J_^ t ^ the groove lor the radial nerve. The distal extremity of the humerus is furnished with two articvilar surfaces (the condyles proper), the lateral of which, called the capitulum, for articulation with the proximal surface of the head of the radius, is a rounded eminence, placed on the anterior surface and distal border, but not extending on to the posterior surface of the distal end of the bone. Proximal to it, in front, there is a shallow depression (fossa radialis), into which the margin of the head of the radius sinks when the elbow is strongly flexed. A shallow groove separ- ates the capitulum medially from the trochlea, which is a grooved articular surface, with prominent edges winding spirally round the distal extremity of the body. The spiral curves from behind forwards and medially, and its axis is slightly oblique to the long axis of the shaft. The medial hp is the more salient of the two, and forms a sharp and well-defined margin to the articular area ; its cartilage-covered surface is slightly convex. Thelateral lip, much less prominent, is rounded off into the articular groove which separates it from the capitulum, posterior to which, however, it is carried up as a more or less definite crest. It is by means of the trochlea that the humerus articulates with the semilunar notch of the ulna. On the anterior surface of the bone, imme- diately proximal to the trochlea, is a depression — the fossa coronoidea (coronoid fossa) — into which the coronoid process of the ulna slips in flexion of the joint, whilst in a corresponding position on the posterior aspect of the distal end of the body there is a hollow, called the fossa olecrani (olecranon fossa), just proximal to the trochlea posteriorly. Into this the olecranon process sinks when the elbow is extended. The two fossae are separated by a thin translucent layer of bone which may be deficient, thus leading to the formation of a The Distal End of the foramen between the two hollows in the macerated SEEN from the ]^q^q Thc autcrlor part of thc capsulc of thc clbow- joint is attached to the proximal margins of the radial and coronoid fossae in front, whilst the posterior ligament is connected with the proximal border and lateral edges of the olecranon fossa behind. The strong Lateral epicondylic RIDGE (lateral margin) Lateral epicondyle Capitulum Radial collateral ligament Trochlea Fig. 200. Right Humerus Lateral Sidi THE HUMEKUS. 209 ulnar and radial collateral ligaments of the elbow joint are attached proximally to the medial and lateral epicondyles respectively. The proportionate length of the humerus to the Ixxly height is as 1 is to 4-93-5*25. Nutrient foramina are usually to be seen, one at or near the surface for the insertion of the coraco-lirachialis, the other usually close to the jiosterior border of the deltoid tuberosity ; both have a distnl direction. Numerous vascular foramina are scattered along the line oi the anatomical neck, the larger ones being situated near the ])roximal end of the inter-tubercular groove. The vascidarity of the bone is here intimately associated with the activity of its growth in this situation. Connexions. — The humerus articulates proximally with the scapula, and distally with the radius and ulna. Embedded, as the humerus is, in the substance of the arm, its body and head are surrounded on all sides. It is only at its distal ])art that it comes into direct relation with the surface, the medial epicondyle forming a characteristic projection on the medial side of the elbow ; whilst the lateral epicondyle, less prominent, and the lateral epicondylic ridge can best be recognised when the elbow is bent. At birth. About 5 years. About 12 years. Fig. 201. — Ossification of the Humerus. About 16 years. 8. Centre for lesser tubercle fuses with otlier centres about 7 years. 9. Appears about 11 or 12 years. 10. Distal epiphysis fuses with shaft about 16 to 17 years. 11. Proximal epiphysis fuses with shaft about 25 years. 12. Fuses with shaft about 17 to 18 years. 1. Appears early in 2iul month of fcetal life. 2. For jjieater tubercle, appears 2 to 3 years. 3. For lieaj, appears within first 6 months after birth. 4. For medial epicondyle, apjie^rs about 5 years. 5. For capituluin, appears 2 to 3 years. 6. Appears about 12 years. 7. Centres for head and ^'reater tubercle coalesce about years. Sexual differences. — Dwight (American Journ. of Anat. vol. iv. 1904) has shown that the head of the humerus in the female is proportionately smaller than that of the male. Ossification. — At birth the body of the humerus is usually the only part of the bone ossified, if we except the occasional presence (22 per cent.) of an ossific centre in the head. (H. R. Spencer, Journ. Anat. and Physiol, vol. xxv. p. 552.) The centre for the body makes its appearance early in the second month of intra-uterine life. Within the first six months after birth a centre usually appears for the head ; this is succeeded by one for the greater tubercle during the second or third year. These soon coalesce ; and a third centre for the lesser tubercle begins to appear about the end of the third year, or may be delayed till the fourth or fifth year. These three centres are all blended by the seventh year, and form an epiphysis, which ultimately unites with the body about the age of twenty-five. It may be noticed that the proximal end of the diaphysis is conical and pointed in the centre, over which the epiphysis fits as a cap, an arrangement which thus tends to prevent its displacement before union has occurred. The first centre to appear in the distal extremity is that for the capitulum about the second or third year. This extends medially, and forms the lateral half of the troclilear surface, the centre for the medial half not making its appearance till the eleventh or twelfth year. 14 210 OSTEOLOGY. Olecranon Separate centres are developed in connexion with the epicondyles ; that for the lateral appears about the twelfth year, and, rapidly coalescing with the centres for the capitulum and trochlea, forms an epiphysis, which unites with the body about the sixteenth or seventeenth year. The centre for the medial epicondyle appears about the fifth year ; it forms a separate epi- physis, which unites with the body about eighteen or nineteen. These two epiphyses at the distal end of the bone are separated by a down-growth of the shaft, which lies between the medial epicondyle and the trochlea, and forms part of the base and medial side of the latter j)rocess. The epicondylic process when present is developed from the diaphysis, and has been observed to be already well ossified by the third year. (" Proc. Anat. Soc." Journ. Anat. and Physiol. 1898.) Tuberosity Incisura semilunaris CORONOID process Bicipital hollow The Ulna. Posterior border -Interosseous border Of the two bones of the forearm, the ulna, which is placed medially, is the longer. It con- sists of a large proximal extremity supporting the olecranon and the coronoid process ; a body or shaft tapering distally; and a small rounded distal end called the head. Proximal Extremity. — The olecranon lies in line with the body. Its dorsal surface, more or less triangular in form, is smooth and subcutane- ous and covered by a bursa. Its proximal aspect, which forms with the posterior surface a nearly rectangular projection — the tip of the elbow — furnishes a surface for the insertion of the tendon of the triceps brachii muscle, together with a smooth area which is overlain by the same tendon, but separated from it by a bursal sac. To the volar (anterior) crescentic border of this process are attached the jfibres of the posterior part of the capsule and a portion of the ulnar collateral ligament of the elbow-joint. The volar (anterior) surface is articular, and enters into the formation of the semilunar notch. The processus coronoideus (coronoid process) is a bracket-Hke process, which juts forwards from the volar and proximal part of the shaft, and is fused with the olecranon proximally. By its proximal surface it enters into the formation of the semilunar notch, whilst its volar aspect, which is separated from its proximal side by a sharp irregular margin, slopes distally and dorsally to become confluent with the volar /); , W surface of the body. Of triangular shape, this "^ Tj..., area, which is rough' and tubercular, terminates inferiorly in an oval elevated tubercle (tuberositas ulnae), into which the tendon of the brachialis muscle is inserted. Of the lateral margins of the coronoid process, the medial is^ usually the better defined. Proximally, where it joins the proximal border, there is generally a salient tubercle, to which one of the heads of origin of the flexor digi- torum sublimis muscle is attached, whilst distal to this point the medial border furnishes origins for the pronator teres, and occasionally for the flexor pollicis Articular circum- ference FOR radius Groove for ext. carpi ulnaris Styloid process Fig. 202. — The Right Ulna as viewed FROM THE Lateral Side. THE ULNA. 211 Olkcranon INCISUBA SEiirLUNARIS CORONOID PROCESS HeAD' Interosseous (REST longus muscles, from above downwards. The smooth medial surface of the coroaoid process merges with the olecranon dorsally, and with the medial surface of the body distally. The incisura semilunaris (O.T. greater sigmoid cavity), for articulation with the trochlea of the luimerus, is a semicircular notch, the proximal part of which is formed by the volar surface of the olecranon, whilst distally it is com- pleted by the proximal surface of the coronoid process. Constricted towards its deepest part by the notching of its borders, the articular surface is occasionally crossed by a narrow im- pression which serves to define the ole- cranon proximally from the coronoid distally. The articular area is divided into a medial portion, slightly con- cave transversely, and a lateral part, transversely convex to a slight degree, by a longitudinal smooth ridge which extends from the most prominent part of the border of the olecranon proxim- ally to the most outstanding point of the coronoid process distally. The margins of the semilunar notch are sharp and well defined, and serve, with the exception of the area occupied by the radial notch, for the attachment of the capsule of the elbow-joint. The radial notch(O.T. lesser sigmoid cavity), placed on the radial side of the coronoid process, is an oblong articular surface for the reception of the head of the radius. It encroaches on the distal and lateral part of the semilunar notch, so as to narrow it considerably. Separated from it by a rectangular curved edge, it displays a surface which is plane proximo- distally, and concave from before backwards. Its volar extremity is narrower and more pointed than its dorsal, and becomes coniiuent with the anterior edge of the coronoid pro- cess, at which point the annular liga- ment, which retains the head of the radius in position, is attached in front. Its dorsal border, wider and more out- standing, lies in line, and is continuous with the interosseous margin of the shaft. Dorsal to this border, the annu- lar ligament is attached posteriorly. The body of the ulna (corpus ulnae), which is nearly straight, or but slightly curved, is stout and thick proximally, gradually tapering towards its distal extremity. It may be divided into tliree surfaces, a volar (O.T. anterior), a dorsal or posterior, and a medial, by three well-defined borders, an interosseous crest, a dorsal margin, which latter is Tuberosity Bicipital hollow Interosseous BORDER OR CREST Fig. 203. Styloid ■process -The Right Radius and Ulna seen FROM THE Volar Aspect. 212 OSTEOLOGY. Flexor DiGiTORDMSuBLiMis ^'^mmK Pronator teres \^\ ^^" Brachialis "v '\ Flexor pollicis longus ~\ Biceps subcutaneous throughout its whole length, and a volar margin (O.T. anterior border). The crista interossea (interosseous crest) is crisp and sharp in the proximal three-fourths of the body, but becomes faint and ill-defined in the distal fourth. To this, with the exception only of the part which forms the dorsal boundary of the hollow in which the tuberosity of the radius is disposed when the two bones are articulated, is attached the interosseous membrane which connects the two bones of the forearm. The dorsal margin^ of sinuous out- line, curving laterally above, and shghtly medially below, is continuous proxim- ally with the triangular subcutaneous area on the back of the olecranon, being formed by the confluence of the borders which bound that sur- face ; well marked above, it becomes faint and more rounded below, but may he traced distally to the dorsal surface of the base of the styloid process. To this border is attached an aponeurosis common to the flexor carpi ulnaris, extensor carpi ulnaris, and flexor digitorum profundus muscles. A nateworthy feature in connexion with this part of the body is the fact that it is subcutaneous, and can easily be felt beneath the skin throughout its whole length. The volar or anterior surface corresponds to the front and medial side of the body. It is described as consisting of two surfaces, a volar and a medial, which are separated by a rounded volar margin, which extends from the tuber- osity proximally towards the styloid process distally. The prominence of this ridge varies in different bones, being well marked in bones of a pronounced type, but corresponding merely to the rounding of the surfaces in poorly developed specimens. The volar aspect of the bone affords an extensive origin to the flexor digitorum profundus muscle, which clothes ' its volar and medial surfaces in its proximal three- fourths, reaching as far hack as the dorsal border, and extending proximally as high as the medial side of the olecranon process. Immediately distal to the radial notch there is a hollow triangular area, limited dorsally by the proximal part of the inter- osseous crest, and defined in front by an obhque line which extends distally and backwards from the lateral margin of the coronoid process. In this hollow the tuberosity of the radius rests when the forearm is in the prone position, and to its floor are attached the fibres of origin of the supinator muscle. The distal fourth of the Fio. 204.— Volar Aspect of Bones of body is crossed by the fibres of the pronator quad- THE Right Foreakm with Muscular j^tus muscle, which derives its ori^dn from a Attachments MAPPED OUT. i n i c j i. i,- i, „• j„ more or less well- denned crest, which wmds spirally distally and backwards towards the volar surface of the root of the styloid process, and is continuous proximally with the volar margin. The dorsal surface of the body lies between the dorsal margin and the in- terosseous crest. At its proximal part it is jjlaced behind the semilunar and radial notches, extending on to the lateral side of the olecranon* Here an area corresponding to the proximal third of the length of the bone is marked off dis- tally by an oblique ridge which leaves the interosseous crest about an inch or more distal to the dorsal edge of the radial notch. Into this somewhat triangular surface the fibres of the auconseus are inserted. Distal to this the THE ULNA. 213 posterior surface is Hubdivided by a I'aint longitudiiiid ridge, the boue betwee vvhicli and the interosseous crest furnishes origins for the abductor pollicis longus, extensor pollicis longus, and extensor indicis jaoprius muscles, in order proximo- distuUy. The surface of bone between the dorsal margin and the afore-mentioned longitudinal line is smooth and overlain by the extensor carpi ulnaris muscle, which, however, does not arise from it. The distal extremity of the ulna presents a rounded head (capitulum ulnae), from which, on its medial and dorsal aspect, there projects distally a cylindrical pointed process called the styloid process. To the extremity of this latter is attached the ulnar collateral ligament of the carpus, whilst on the volar aspect it has connected with it the antero-meilial portion of the capsule of the wrist-joint. The antero-lateral half of the circumference of the head is furnished with a smooth narrow convex articular surface, which fits into the ulnar notch of the radius. Its distal surface. Hat and semilunar in shape, and separated from the root of the styloid process by a well-marked groove, rests on the upper surface of the triangular articular disc of the wrist, the ajiex of which is attached to the groove just mentioned. The margins of the head, to the volar side and dorsal to the radial articular surface, have attached to them the volar and dorsal distal radio- ulnar ligaments. The dorsal and medial surface of the styloid process is channelled by a groove which separates it from the dorsal surface of the head, and extends proximally some little way upon the dorsal surface of the distal end of the body. In this is lodged the tendon of the extensor carpi ulnaris muscle. The pro- portionate length of the ulna to the body height is as 1 is to 6'26-6-66. Nutrient Foramina. — A foramen, having a proximal direction, for the nutrient artery of the body opens on tlie volar surface of the bone from two to three inches distal to the tuberosity. Vascular canals of large size are seen i^roximal and dorsal to the radial notch, just dorsal to the notched lateral bortler of the semilunar notch. At the distal end of the bone similar openings are seen in the groove between the styloid process and the distal articular surface of the head. Connexions. — The ulna articulates proximally with the trochlea of the humerus. On the lateral side it is in contact with tlie radius at bolli proximal and distal ends, the proximal radio- ulnar articulation being formed by the head of the radius and the radial notch of the idna, the distal radio-ulnar joint comprising the head of the ulna, which tits into the ulnar notch of the radius. Between these two joints the bodies of the bones are united by the interosseous membrane. The distal surface of the head of the ulna does not articulate witli the carpus, but rests on the j)roximal surface of the interposed articular disc. The ulna is superficial throughout its entire extent. Proximally the olecranon process can be readily recognised, particularly when the elbow is bent, as in this position the olecranon is withdrawn from tlie olecranon fossa of the humerus in which it rests when the joint is extended. Distal to this the subcutane- ous triangular area on the back of the olecranon can be easily determined, and from it the posterior border of the bone can readily be traced along the line of the " ulnar furrow " to the styloid process. With the hand supine this latter process can be felt to the <^ medial side and slightly behind the wrist. When the hand is 2)ronated, the distal end of the radius rolls round the distal extremity of the ulna, and the antero-lateral surface of the head of the latter bone now forms a well- marked projection on the dorsum of the wrist in line with the cleft between the little and ring fingers. Ossification. — The ulna is ossified from one primary and two or more secondary centi'es. The centre for the body appears early in the second month of fa!tal life. At birth the body and a considerable part of the proximal extremity, including the coronoid process, are ossified, as well as part of the distal extremity. The olecranon and the distal surface of the head and the styloid process are cartilaginous. About ten years of age a secondary centre appears in the cartilage at the proximal end of the bone, and Fuses with shaft about 16 years Appears about 10 years Appears about C years Fuses with shaft 20-23 years \t Birth. About 12 years. About 16 years. Fio. 205. — The Ossification of the Ulna. 214 OSTEOLOGY. Subcutaneous SURFACE Neck Interosseous CREST forms an epiphysis which unites with the body about sixteen. In this connexion Fawcett (Proc. Anat. Soc. Great Britain and Ireland, 1904, p. xxvii) has described the occurrence Olecranon of two ossific Centres in the olecranon. One, the more volar, the "beak centre," enters into the formation of the proximal end of the articu- lar surface of the semilunar notch, the other centre, not in any way forming it. A scale-like centre appears in the cartilage of the head about the sixth year, from which the distal surface of that part of the bone is developed, and by the extension of which the Tuberosity , i • i ■ ^ ■ r^ ^ styloid process is also ossined ; this epiphysis does not unite with the shaft till the twen- tieth or twenty -third year. Independent centres for the styloid process and for the extreme edge of the olecranon have also been described. The student may here be warned that the epiphysial line be- PosTERioR tween the shaft and proximal OBLIQUE LINE Or olecrauou epiphysis does not correspond to the con- stricted part of the semilunar notch, but lies considerably proximal to it. The Radius. The radius, or lateral bone of the forearm, is shorter than the ulna, with which it is united on the medial side. Proximally it articulates with the hum- erus, and distallyit supports the carpus. It consists of a head, a neck, a tuberosity, a body, and ■ an expanded distal extremity. The body is narrow proximally, but in- creases in all its diameters distally. Proximal Extremity. — The capitulum (head) is disc-shaped and provided with a shallow concave sur- face (fovea capituli radii) proximally for articulation with the capitulum of the humerus. The circumfer- ence of the head (circum- ferentia articularis) is smooth and is embraced by the annular ligament. On the medial side it is usually much broader, and displays an articular surface, plane in the proximo-distal direction. Heai) .STYI.Oro PROCRKS Ext. poll, brevis Ext. carpi rad. longus Ext. carpi rad. brevis Ext. poll, long. Styloid process Groove for ext. Ext. dig. commiin. carpi ulnaris and ext. indicia proprius Fio. 206. — The Right Radius and Ulna sekn from the Dorsal Aspect THE RADIUS. 215 TllKEI-S which rolls within the mdial notch of the ulna in the movements of pronation and supination. The character of the lateral half of the circumference differs from the medial, in bein^ narrower, and rounded proximo-distally. The coUum radii (neck) is the constricted part of the body which supports the head, the overhang of the latter being greatest towards the lateral and dorsal side. Distal to the neck, on the medial side, there is an outstanding oval prominence, the tuberositas radii (radial tuberosity). The dorsal part of this is rough for the insertion of the biceps tendon, whilst the volar half is smooth anil covered by a bursa which inter- venes between it and the tendon. The body (corpus radii), which has a lateral curve and is narrow proximally and broad distally, is wedge-shaped on section. The edge of the wedge forms the sliarp medial interos.seous crest of the bone (crista interossea), whilst its base corresponds to the thick and rounded lateral border over which the volar or anterior surface becomes confluent with the dorsal or posterior surface. The interosseous crest, faint proximally where it lies in line with the dorsal margin of the tuber- osity, becomes sharp and prominent in the middle third of the bone. Distal to this it splits into two faint lines, which lead to either side of the ulnar notch on the distal end of the bone, thus includ- ing between them a narrow triangular area into which the deeper fibres of the pronator quadratus muscle are inserted. To this crest, as well as to the dorsal of the two divergent Hnes, the interosseous membrane is attached. The' lateral surface (once described as the lateral border) is thick and rounded proximally, but becomes thinner and more prominent distally, where it merges with the base of the styloid process. About its middle the anterior and posterior oblique lines become confluent with it, and here, placed between them, is a rough elongated impres- sion which marks the insertion of the pronator teres muscle. Proximal to this, and on the Radial EXTENSORS lateral surface of the neck, the supinator muscle is inserted, whilst distally this surfadfe is overlain by the tendons of the brachio-radiahs and the extensor carpi radialis.longus and brevis muscles. The volar or anterior surface (facias volaris) is crossed obliquely by a line which runs from the tuberosity distally and laterally towards the middle of the lateral surface of the body. This, often called the anterior oblique line, serves for the attach- ment of the radial head of origin of the flexor digitorum sublimis muscle. Proximal o o to it, the volar aspect of the bone has the fibres of the su pina tor muscle inserted into it, whilst distal and medial to it, extending as far as the distal limit of the middle third of the bone, is an extensive surface for the origin of the flexor poUicisJongus muscle. In the distal fourth of the bone, where the volar aspect of tlie body is broad and flat, there is a surface for the insertion of the pronator quadratus muscle, which also extends dorsally to the interosseous ridge. The dorsal or posterior surface (facies dorsalis) is also crossed by an oblique line, less distinct than the anterior. This serves to define the proximal ABDrCTOR POLLICIS IX)NGUS AND EXTENSOR POLLICIS BREVIS Extensor digitorcm commcnsi AND extensor INDICIS PROPRIUS ^ Extensor pollicis lonous Fig. 207. — Dorsal Aspect of Bones of Right Fore- arm WITH Attachments of Muscles mapped out. 216 OSTEOLOGY. limit of the origin of the abductor pollicis longus muscle. Proximal to this, the dorsal aspect of the neck and proximal part of the body is overlain by the fibres of the supinator muscle which become attached to this surface of the bone in its lateral half. Distal to the posterior oblique line the dorsal surface in the proximal . part of its medial half gives origin to the abductor pollicis longus and the extensor pollicis brevis muscles, in that order proximo-distally. The distal extremity, which tends to be turned slightly forwards, has a somewhat triangular form. Its distal carpal articular surface, concave from before backwards, and slightly so from side to side, is divided into two facets by a slight antero- posterior ridge, best marked at its extremities where the volar and dorsal margins are notched ; the lateral of these areas, of triangular shape, is for articulation with the navicular, whilst the medial, quadrilateral in form, is for the os lunatum. The volar border, prominent and turned forwards, is rough at its edge, where it serves for the attachment of the volar part of the capsule of the wrist-joint. The dorsal border is rough, rounded, and tubercular, and is grooved by many tendons ; of these grooves the best marked is one which passes obliquely across its dorsal surface. This is for the tendon of the extensor pollicis longus muscle. The lateral lip of this groove is often very prominent, and forms an outstanding tubercle. To the medial side of this oblique groove there is a broad shallow furrow in which the tendons of the extensor digitorum communis and extensor indicis proprius muscles are lodged, whilst to its lateral side, and between it and the styloid process, there is another broad groove, subdivided by a faint ridge into two, for the passage of the tendons of the extensor carpi radialis brevis medially and the extensor carpi radialis longus laterally. The styloid process lies to the lateral side of the distal extremity; broad at its ^ base, it becomes narrow and pointed distally where by its medial cartilage -covered surface it forms the summit of the distal triangular articular area. The lateral surface of this process is crossed obliquely distally and forwards .by a shallow groove, the volar lip of which is sharp and well marked, and serves to separate it from the volar surface of the bone, whilst the dorsal lip is often emphasised by a small tubercle above. The tendon of the brachio-radialis muscle is inserted into the proximal parts of both lips, and also spreads out on to the floor of the groove, whilst the tendons of the abductor pollicis longus and the extensor pollicis brevis muscles lie within the groove. To the tip of the styloid process is attached the radial collateral ligament of the wrist. On the medial side of the distal extremity is placed the incisura ulnaris (ulnar notch) for the reception of the head of the ulna. Concave from before backwards, and plane proximo-distally, it forms by its inferior margin a rectangular edge which separates it from the distal carpal surface. To this edge the base of the articular disc is attached, a structure which serves to separate the distal articular surface of the head of the ulna from tl«e carpus. The volar and dorsal edges of the ulnar notch, more or less prominent, serve for the attachment of ligaments. The proportionate length of the radius to the body height is as 1 is to 6"70-7'll. Nutrient Foramina. — The openings of several small nutrient canals may be seen in the region of the neck. That for the body, which has a proximal direction, is usually placed on the volar .surface of the bone, medial to the anterior oblique line, and from an inch and a half to two inches distal to the tuberosity. The dorsal surface of the distal extremity of the bone is pierced by many small vascular foramina. Connexions. — The radius articulates with the capitulum of the humerus in the flexed position of the elbow, with the ulna to its medial side by the proximal and distal radio-ulnar joints, and with the navicular and lunate bones of the carpus distally. Proximally, the head of the bone can be felt in the intermuscular depression on the lateral side of the back of the elbow ; here the bone is only covered Vjy the skin, superficial fascia, and the thin common tendinous origin of the exten.sor muscles, as well as the ligaments which support it. Its position can best be ascer- tained Vjy pronating and supinating the bones of the forearm, when the head will be felt rotating beneath the finger. The distal end of the bone is overlain on the volar and dorsal aspects by the flexor and extensor tendons, but its general form can be readily made out. The styloid process lying to the lateral side of the wrist in line with the extended thumb can easily be recognised ; note that it reaches a more distal level than the corresponding process of the ulna. The lateral border of the lower third of the body can be distinctly felt, as here the bone is only overlain by tendons. Ossification. — The centre for the body makes its appearance early in the second THE CARPUS. 217 Z 2 Appears ■^ o about -5-7 li years Fuses witli shaft 18-20 yearsi Appears about 2-3 years Unites with shaa 20-25 years At Birth. About 12 years. About 16 years, Fig. 20S. — The Ossification of the Radios. epiphysis capping the summit of the tuberosity has been described ; this ap- pears about the fourteenth or fifteenth year, and rapidly fuses with that process. I. Metacarpal month of intru-uterine Hfe. At birtli the body is well formed; its proximal and distal extremities are capped with cartilage, and the tuberosity is beginning to appear. A secondary centrd appears in the cartilage of the distal extremity about the second or third year ; this does not unite with the body until the twentieth or twenty-fifth, year, somewhat earlier in the female. From this the carpal and ulnar articular surfaces are formed. The centre for the head appears from the fifth to the seventh year, and fuses with the neck about the age of eighteen or twenty. It forms the capitular articular surface and combines with the neck to form the area for articulation with the radial notch of the ulna. A scale-like Os HAMATUM Os TRICJUETRDM PiSIKORM THE BONES OF THE HAND. Sesamoid bones . — V. Metacarpal The bones of the hand, twenty -seven in number, may be conveniently divided into three groups : — (1) The bones of the wrist or carpus — eight in number. (2) The bones of the palm or metacarpus — -Jive in number. (3) The bones of the fingers and thumb or phalanges — -fo^ir- teen in number. The Carpus. The ossa carpi (carpal bones) are arranged in two rows : the first, or proximal row, comprises from radial to ulnar side, the navi- cular (O.T. scaphoid), os lunatum (O.T. semi-lunar), os triquetrum (O.T. cimeiform), and os pisifonne or pisiform ; the second or distal row includes the greater mult- angular (O.T. trapeziimi), lesser multangular [O.T. trapezoid), os capitatum (O.T. os magnum), and Fig. 209. -The Bones of the Right Wrist and Hand seen from the volar aspect. 218 OSTEOLOGY. Os CAPITATUM Lesser multangular Navicular Abductok pollicis brevis / Greater multangular (\ry- Opponexs pollicis V Abductor pollicis long us Flexor carpi radialis M.I. Adductor/ Oblique head pollicis \ Transverse head Os lunatum Os HAMATUM Os TRIQUETRUM Flexor carpi ulnaris Pisiform Abductor dioiti quinti Flexor digiti quinti brevis Flexor carpi ulnaris Opponens digiti quinti Volar interossei Fro. 210.— Volar Aspect op Bones of the Right Carpus AND Metacarpus with Muscular Attachments mapped out. OS hamatuin (O.T. unciform). Irregularly six-sided, each of these bones possesses non-articular volar and dorsal surfaces. In addition, the marginal bones are non- articular along their ulnar and radial aspects according as they form the medial or lateral members of the fjeries. Os Navicuiare(O.T. Scaphoid). — The navicular is the largest and the most lateral bone of the first rovr. Its volar surface, rough for the attach- ment of ligaments, is irregularly triangu- lar. The distal angle on the lateral side forms a projec- tion called the tuber- osity; this can be felt at the base of the root of the thumb. Its ;proximal surface is convex from side to side and before backvv^ards for articula- tion v^ith the radius. This area extends considerably over the dorsal surface of the bone. Its distal surface is convex from before backwards, and ex- tends on to the dorsal aspect of the bone, slightly convex from side to side ; it is divisible into two areas, the lateral for articulation with the greater multangular, the medial for the lesser multangular. The lateral surface is narrow and rounded and forms a non-articular border, which extends from the radial articular surface proximally to the tuberosity distally. The medial surface is hollowed out in front for articulation with the head of the capitate bone. Proximal to this it displays a small semilunar- shaped facet for the os lunatum. The dorsal non - articular surface lies between the lateral articular surface proxi- mally and the surface for Extensor carpi 4.U i. 11 ulnaris the greater and lesser multangular bones dis- tally. It is obUquely grooved for the attach- ment of the dorsal liga- ments of the wrist. The navicular articulates with five bones — the radius, the os lunatum, the capitate, the lesser multangular, and the greater multangular. Os Lunatum (O.T. Semilunar Bone). — So called from its deeply excavated form, the os lunatum lies between the navicular on the lateral side and the OS triquetrum on the medial. Its volar surface, of rhombic form and consider- able size, is rough for the attachment of ligaments ; its 'proximal surface, convex from side to side and from before backwards, articulates with the radius and in part with the distal surface of the articular disc of the wrist. Its distal aspect, deeply Os triquetrum Pisiform Os lunatum Os capitatum Navicular Os HAMATUM E\TENSOR carpi RADIALIS BREVIS ll sser multangular Greater multangular Extensor carpi radialis longus Abductor pollicis longus Fig. 211. — Dorsal Aspect of Bones of the Right Carpus and Metacarpus with Muscular Attachments mapped out. THE CARPUS. 219 Os CAPITATUM Os LUNATUM Os TKIQUETRUM Pisiform Metacarpal hollowed from before backwards,- is divided into two articular areas, of which the lateral is the larger ; tliis is for the head of the capitate bone ; the medial, narrow from side to side, articulates with the os hamatum. Its lateral surface, crescentic in shape, serves for articulation with the navicular, and also for the attachment of the interosseous ligaments whicli connect it with that bone. Its medial surface, of quadrilateral form, is cartilage-covered for articulation with the 08 triquetrum, and the edge which separates this from the proximal surface has attached to it the interosseous ligament which unites these two bones. The rough dorsal non-articular surface is much smaller than the volar; by this means the volar and dorsal sur- faces of the bone can readily be determined. The os lunatum articulates with live bones — the navicular, the radius, the os triquetrum, the os hamatum, and the capitate bone. Os Triquetrum (O.T.Cunei- form). — This bone may be recognised by the small oval or circular facet on its volar surface for the pisiform. This is placed towards the distal part of the volar surface, which is elsewhere rough for liga- ments. The bone is placed obliquely, so that its surfaces cannot be accurately described as distal, proximal, etc. ; but for convenience of description, the method already adopted is ad- hered to. The 'proximal surface has a convex rhombic area for articulation with the distal surface of the articular disc in adduction of the hand, though ordinarily it does not appear to be in contact with that structure. To the medial side of this it is rough for liga- ments. The distal surface is elongated and concavo-convex from radial to ulnar side ; here the bone articulates with the os hamatum. The lateral surface, broader in front than behind, articulates with the os lunatum. The medial swr/«cf, rounded and rough, is confluent proximally and dorsally with the proximal and dorsal aspects of the bone. The dorsal surface, rounded and smooth laterally, is ridged and grooved medially for the attachment of ligaments. The os triquetrum' articulates with three bones, viz., the pisiform, the os hamatum, and the os lunatum. Os Pisiforme. — About the size and shape of a large pea, the pisiform bone rests on the volar surface of the os triquetrum, with which it articulates by an oval or circular facet on its dorsal aspect. The rounded mass of the rest of the bone is non-articular, and inclines distally and laterally so as to overhang the articular facet in front and laterally. The mass of the bone is usually separated from the articular surface by a small but distinct groove. Into the summit of the bone the tendon of the flexor carpi ulnaris^muscle is inserted, and Third OR VXOUAL PHALANX Fig. 212.- -The Bones of the Right Wkist and Hand sekn from the dorsal asi'ect. 220 OSTEOLOGY. Radius Os lunatum Fig. 213. — The Right Navicular Bone. Note. — The bone is represented in the centre of the figure in the position which it occupies in the right hand viewed from the volar aspect. The views on either side, and above aud below, represent respectively the corresponding surfaces of the bone turned towards the reader. here also the transverse carpal ligament is attached. The ulnar artery and nerve are in immediate relation with the lateral side of the bone. Os Multangulum Majus (O.T. Trapezium). — The greater mult- Capitiite^JHd %\ ^ _ angular is the most lateral bone of the distal row of the carpus. It may be readily recognised by the oval saddle-shaped facet on its distal surface for articulation with the metacarpal bone of the thumb. From its volar aspect there rises a prominent ridge, medial to which is a groove along which the tendon of the flexor carpi radialis muscle passes. The ridge furnishes an attachment for the transverse carpal ligament, as well as for some of the short muscles of the thumb. The proximal surface has a half- oval facet for the navicular, lateral to which it is rough, and becomes continuous with the non-articular lateral aspect, which serves for the attachment of ligaments. On its medial surface there are two facets ; the proximal is a half-oval, concave proximo-distally, and very slightly convex from volar to dorsal side, and is for articulation with the lesser multangular ; the distal, small and circular, and not always present, is for articulation with the lateral side of the base of the second metacarpal bone. The dorsal surface, of irregular outline, is rough for the attach- ment of ligaments. The greater multangular articulates with four bones, the navicular, lesser multangular, and the first and second metacarpal bones. Os Multangulum Minus (O.T. Trapezoid Bone).— With the exception of the pisiform, the lesser multangular is the smallest of the carpal bones. Its rough volar surface is small and pentagonal in outline. By a small oblong area on its proximal surface it articulates with the navicular. Distally, by a somewhat saddle-shaped surface, it articulates with the base of the second metacarpal. Separated from this by a rough note.— The bone is represented in the centre of the figure in the V-shaped impression prolonged position which it occupies in the right hand viewed from the from its volar aSDCCt is the volar aspect. The views on either side, and above and below, . , , , y \ '' „ represent respectively the corresponding surfaces of the bone area on the lateral surface for turned towards the reader. articulation with the greater multangular ; this is obliquely grooved from before backwards and distally. The medial facet, for articulation with the capitate, is narrow proximo-distally, and deeply curved from before backwards. The dorsal surface of the bone, which is rough and non-articular, is much larger than the volar aspect. The mass of the bone, Os hamatuui Os triquetrum Os haniatum Capitate Os hamatuni Radius Navicular Fig. 214. — The Right Os Lunatum. THE CARPUS. 221 The lesser multantjular Us hamaturn On luiiatuni dorsally, is directed distally and tojvards the medial side, articulates with four bones — the greater multangular, navicular, and capitate bones, and the second metacarpal. Os Capitatum 'O.T. Os Magnum . — This is tiie largest of the carpal bonus. Its volar surface is rough and rounded. The j)^'oximal portion of the bone forms the head, and is furnished with convex articular facets which tit into the hollows on the medial surface of the navicular and distal surface of the os lunatum ; that for the latter is medial to and separated by a slight ridge from the navicular artic- ular area. The distal surface, narrow to- wards its volar border and broad dorsally, is subdivided usually into three facets by two ridges — that towards the lateral side is for the base of the second metacarpal ; the inter- mediate facet is for the third metacarpal ; whilst the medial facet of the three, NoTK.— The figure to the left repre- not always present, very small and placed near the dorsal Fig. 216. Os triquetruiii -Thb Right Pisiform BOSB. Articular disc" of wrist Fig. 215.— The Right Os Triqcetrum. Note. — The bone is represented in the centre of the figure in the position which it occupies in the right hand viewed from the volar aspect. Tlie views on either side, and above and below, represent respectively the corresponding surfaces of the bone turned towards the reader. sents the bone ; that dorsal \iew. rt' t\T'lht Se ^''^^.^^ ^^® ^^^^' is for the fourth metacarpal. The lateral to the right the surface of the body has an articular area for the lesser multangular, not infrequently separated from the navic- ular surface on the head by a rough line, to which the interosseous ligament connecting it with the navicular is at- tached. The medial surface of the body has an elongated articular area, usu- ally deeply notched in front ; or it may be divided anteriorly into a small cir- cular area near the dorsal edge, and a larger posterior part. This latter articulates either singly or doubly with the OS hamatum, the interosseous liga- ment which unites the two bones being attached either to the notch or to the surface separating the two articu- lar facets. The dorsal surface is rough for ligaments; it is somewhat constricted below the head, the articular surface of which sweeps round its proximal border. The capitate bone articulates with seven bones — the os hamatum, the os lunatum, the na\dcular, the lesser mult- ^ ^ angular, and the second, third, and r»iOTE. — The bone is represented in the centre of the figure r i.v. i. i i, • n in the position which it occupies in the right hand fourth metacarpal bones ; occasionally viewed from the volar aspect. The \iews on either the fourth metacarpal doCS nOt ar- side, and above and below, represent respectively ticulate with the capitate. the corresponding surfaces of the bone turned /\ tt x //-v rr tt_ -c^ towards the reader. Os Hamatum (O.T. Unciform Bone). — The os hamatum can be readily distinguished by the hook-like process (hamulus) which projects from the distal and XaNicular Fig. 217. — The Right Greater Miltangilar Bone. 222 OSTEOLOGY. Capitate bone II. Metacarpal Navicular Greater multangular III. Metacarpal medial aspect of its volar surface. To this is attached the transverse carpal ligament as well as some of the fibres of origin of the short muscles of the little finger. The medial side of the hamulus is sometimes grooved by the deep branch of the ulnar nerve. ( Anderson, W., " Proc. Anat. Soc." Journ. Anat. and P%sio/. vol. xxviii. p. 11.) ThQvolar surface, rough for ligaments, is somewhat triangular in shape Froximally and towards \i\iQmedial side there is an elongated articular surface for the os triquetrum, convex proximally and concave distally. The lateral aspect of the bone is provided with a plane elon- gated facet, occasionally divided into two for articulation with the capitate bone (see above). Where „ ^, „ ^ „ ^ ,, „ the proximal and lateral surfaces Fig. 218. — The Right Lesskr Multangular Bone. f i • t.i . j i „ ■ , , o .. n • meet, the angle is blunt, and has Note. — The bone is represented m the centre of the iigure in <• i. i • t. i.- i i. the position which it occupies in the right hand viewed a narrow lacet which articulates from the volar aspect. The views on either, side, and with the OS lunatum. Distally above and below, represent respectively the corresponding ^J^epg ^^g tWO articukr facetS surfaces of the bone turned towards the reader. . j i • o ^i, separated by a ridge ; these are slightly concave from before backwards, and are for articulation, the lateral with the fourth, and the medial with the fifth metacarpal bone. The dorsal surface, more or less triangular in shape, is rough for liga- ments. The OS hamatum articu- lates with five bones — viz., the capitate, os lunatum, os triquetrum, and the fourth and fifth metacarpals. The Carpus as a Whole. When the carpal bones are articulated together they form a bony mass, the dorsal surface of which is convex from side to side. Anteriorly they present a grooved appearance, con- cave from side to side. This arrangement is further emphasised by the forward projection, onthe medial side, of the pisiform and hamulus of the OS hamatum, whilst laterally the tuberosity of the navicular and the ridge of the greater multangular help to deepen the furrow 'by their elevation. To these IV. Metacarpal II. Metacarpal III. Metacarpal Navicular Fig. 219. — The Right Capitate Bone. Note. — The bone is represented in the centre of the Iigure in the position which it occupies in the right hand viewed from the volar aspect. The views on either side, and above and below, represent respectively the corresponding surfaces of the bone turned towards the reader. THE METACAEPUS. 223 four points the transverse carpal ligament is attached, which stretches across from side to side, and thus converts the furrow into a canal through which the flexor tendons pass to reach IV. Metacarpal the fin'^ers. V. Metacarpal /Capitate bone FlQ. Os lunatum 221. — Radiograph of the Hand at Birth. Fig. 220. — The Right Os Hamatum. It will be noticed that whilst the primary centres for the metacarpus and phalanges are well ossified, the Note. — The bone is represented in the centre of the figure in the position carpus is still entirely cartilaginous. which it occupies in the right hand viewed from the volar aspect. Compare this with the tarsus at The views on either side, and above and below, represent respectively birth, in which the tarsus is shown the corresponding surfaces of the bone turned towards the reader. in part already ossified. Ossification. — At birth the carpus is entirely cartilaginous. An exceptional case is figured by Lambertz, in which the centres for the capitate and triquetral bones were already present. The same authority states that it is not uncommon to meet with these centres in the second month after birth. According to Debierre {Journ. de I'Anat. et de la Physiol, vol. xxii. 1886, p. 285), ossification takes place approximately as follows: — Capitate bone . Os hamatum Os triquetrum . Os lunatum Greater multangular Navicular Lesser multangular Pisiform . 11 to 12 months. 12 to H months. 3 years. 5 to 6 years. 6 years. 6 years. 6 to 7 years. 10 to 12 years. The same observer failed to note the appearance of a separate centre for the hamulus of the os hamatum, and records the occurrence of two centres for the pisiform. The Metacarpus. The metacarpal bones form the skeleton of the palm, articulating proximally with the carpus, wliilst by their distal extremities or heads they support the bones of the digits. Five in number, one for each digit, they lie side by side and slightly divergent from each other, being separated by intervals, termed interosseous spaces. Distinguished numerically from the lateral to the medial side, they all display certain common characters ; each possesses a body or shaft, a base or carpal extremity, and a head or phalangeal end. The bodies, which are slightly curved towards the volar aspect, are narrowest towards their middle. The dorsal surface of each is marked by'two divergent lines which pass distally from the dorsum of the base to tubercles on either side of the 224 OSTEOLOGY. Head ;iiaft Fig. 222.— First Right Metacarpal Bone. Tubercle head. The surface included between the two lines is smooth and of elongated triangular form. On either side of these lines two broad shallow grooves wind spirally on to the volar surface, where they are separated by a sharp ridge which is continuous with a somewhat triangular surface which corresponds to the volar aspect of the base. The grooved surfaces on either side of the shaft furnish origins for the interossei muscles. Close to the volar crest is the opening of the nutrient canal, which is directed towards the proximal extremity, except in the case of the first metacarpal bone. The capitulura (head) is provided with a surface for articulation with the proximal phalanx. This area curves farther over its volar than its dorsal aspect. Convex from before backwards and from side to side, it is wider anteriorly than posteriorly ; notched on its volar aspect, its edges form two prominent tubercles, which are sometimes grooved for the small sesamoid bones which may occasionally be found on the volar surface of the joint. On either side of the head of the bone there is a deep pit, behind which is a prominent tubercle ; to these are attached the collateral hgaments of the metacarpo-phalangeal joints. The bases, all more or less w^edge-shaped in form, articulate with the carpus ; they differ in size and shape according to their articulation. Of the five metacarpal bones, the first, viz., that of the thumb, is the shortest and stoutest, the second is the longest, whilst the tMrd, fourth, and fifth display a gradual reduction in length. The medial four bones articulate by their bases with each other, and are united at their distal ex- tremities by ligaments. They are so arranged as to conform to the tiollow of the palm, being concave from side to side anteriorly, and convex posteriorly. The first metacarpal differs from the others in being free at its distal extremity, whilst its proximal end possesses only a carpal articular facet. The first metacarpal bone is the shortest and stoutest of the series. Its body is comjiressed from Note before backwards. Its head, of large size, is but slightly convex from side to side, and is grooved on its volar aspect for the sesamoid bones. The base is provided with a saddle-shaped surface for articulation with the greater multangular, and has no facets on its sides. Laterally there is a slight tubercle to which the abductor pollicis Capitate bone Lesser multangular Fig. 223. — Second Right Metacarpal Bone. The bone is represented in the centre of the figure in the position which it occupies in the right hand viewed from the volar aspect. The views on either side, and below, represent respectively the corresponding surfaces of the bone turned towards the reader. THE METACARPUS. 225 longus muscle is attached. The : canal lor the nutrient artery is directed towards the head of the bone. The second metacarpal bone is recognised by its lengtii and its broad and deeply notched base for articulation with the K-sser multangular. It has a small half-oval facet for the grciater mult- angular on the lateral side of its base, whilst on its medial aspect it presents a narrow vertical strip for the capitate, in front of which there are two half-oval surfaces for the third metacarpal. To the dorsal aspect of the base is attached the tendon of the extensor carpi radialis longus muscle, whilst the Hexor carpi radialis is inserted into the volar surface. The third metacarpal bone can usually be re- cognised by the pointed styloid process which springs from the dorsum of its base, towards the radial styloid process Capitate bone Metacariml rroxinial Fig. 224. — Third Right Metacarpal Bone. Note. — The bone is represented in the centre of the figure in the position which it occupies in the right hand viewed from the volar aspect. The views ou either side, and below, represent respectively the corre- sponding surfaces of the bone turned towards the reader. Capitate bone III. Metacarpa C'apitatf bone IV. Metacarpal riuxiiual Fig. 225. — Fourth Kight Metacarpal Boxe. Fig. 226. — Fifth Ki<;ht Metacarpal Bone. Note. — The bone in each figure is represented in the centre of the figure in the position which it occupies in the right hand viewed from the volar aspect. The views on either side, and below, represent respectively the corresponding surfaces of the bone turned towards the reader. side. On the proximal surface of the base there is a facet for the capitate. On the lateral side there are two half-oval facets for the second metacarpal. On the medial side there are usually two small oval or nearly circular facets for the 15 226 OSTEOLOGY. fourth metacarpal. The extensor carpi radialis brevis muscle is inserted into the dorsum of the base. The fourth metacarpal bone may be recognised by a method of exclusion. It is unlike either the first, second, or third, and differs from the fifth, which it resembles in size, by having articular surfaces on both sides of its base. Proximally there is a quadrilateral surface on its base for articulation with the os hamatum. On its lateral side there are usually two small oval facets for the third metacarpal. Of these facets the dorsal one not infrequently has a narrow surface for articula- tion with the capitate. On the medial side there is a narrow articular strip for the base of the fifth metacarpal. The fifth metacarpal bone can be recognised by its size and the fact that it has an articular facet only on one side of its base, namely, that on its lateral side for the fourth metacarpal. The carpal articular surface is saddle-shaped, and there is a tubercle on the medial side of the base for the insertion of the extensor carpi ulnaris muscle. As has been ah-eady pointed out, the oi)enings of the arterial canals are usually seen on the volar surfaces of the metacariials, those of the medial four bones being directed proximally towards the base or carpal end, differing in this respect from that of the first metacarpal, which is directed distaUy towards the head or phalangeal extremity. The opening of the latter canal usually lies to the medial side of the volar aspect of the body. Ossification. — The metacarpal bones are developed from primary and secondary centres ; but there is a remarkable difference between the mode of growth of the first and the remaining four metacarpals, for whilst the body and head of the first metacarpal are developed from the primary ossific centre, and its base from a secondary centre, in the case of the second, third, fourth, and fifth metacarpals the bodies and bases are de- veloped from the primary centres, the heads in these instances being derived from the secondary centres. In this respect, therefore, as will be seen hereaftei', the metacarpal bone of the thumb resembles the phalanges in the manner of its growth, a circumstance which has given rise to considerable discussion as to whether the thumb is to be regarded as possessing three phalanges and no metacarpal, or one metacarpal and two phalanges. Broom {Anat. Anz. vol. 28), by a reference to reptilian forms, offers an explanation in regard to the difference in the mode of ossification of the first metacarpal on the ground that the most movable joint is that between the first metacarpal and the carpus, whereas on the other digits the most movable joints are those between the metacai'pals and phalanges. In consequence those ends of the bones which enter into the formation of the joints where movement is most free are the ends where the epiphyses will appear. This is in accordance with the law to be suggested in connexion with the fibula. The primary centres for the bodies and bases of the second, third, fourth, and fifth metacarpals appear in that order during the ninth or tenth week of intra-uterine life, some little time after the terminal phalanges have begun to ossify ; that for the body and head of the metacarpal bone of the thumb a little later. At birth the bodies of the bones are well formed. The secondary centres from which the heads of the second, third, fourth, and fifth metacarpals and the base of the first are developed, appear about the third year, and usually completely fuse with the shafts about the age of twenty. There may be an independent centi*e for the styloid process of the third metacarpal, and there is usually a scale-like epiphysis on the head of the first metacarpal which makes its appearance about eight or ten, and rapidly unites with the head. The occurrence of a basal epiphysis in the second metacarpal bone has been noticed. Phalanges Digitorum IVIanus. The phalanges or finger bones are fourteen in numljer— -three for each finger, and two for the thumb; and they are named numerically in order from the proximal toward the distal ends of the fingers. Phalanx Prima. — The first phalanx, the longest and stoutest of the three, has a semi-cylindrical body which is curved slightly forwards. The volar surface is flat, and bounded on either side by two sharp borders to which the fibrous sheath of the flexor tendons is attached. The dorsal surface, convex from side to side, is overlain by the extensor tendons. The proximal end, considerably enlarged, has a simple oval concave surface, which rests on the head of its corresponding metacarpal bone. On either side of this the bone displays a tubercular form, and affords attachment to THE PHALANGES. 227 III. I'halaiix, iiiiKMal or tt'riiiliial II. I'lial.'i the collateral ligaments of the metacarpo-phalangeal joint, and also to the interossei muscles. The distal end is much smaller than the proximal ; the convex articular surface is divided into two condyles by a central groove. Phalanx Secunda. — The second phalanx resembles the first in general form, but is of smaller size. It differs, however, in the form of its proximal articular surface, which is not a simple oval concavity, but is an oval area divided into two small, nearly circular con- cavities by a central ridge passing from volar to dorsal edge; these articulate with the condylic surfaces of the proximal phalanx. Into the margins of its volar surface near the proximal end ..are inserted the split portions of the tendon of the Hexor digitorum sublimis, whilst on the dorsal aspect of the proximal end the central slip of the extensor digitorum communis muscle is attached. Phalanx Tertia. — The third or terminal or ungual phalanx is the smallest of the three ; it is easily recognised by the spatula-shaped surface on its distal extremity which supports the nail. The articular surface on its proximal end resembles that on the proximal end of the second phalanx, but is smaller. On the volar aspect of this end of the bone there is a rough surface for the insertion of the tendon of the flexor digitorum profundus muscle. The dorsal surface of the same extremity has attached to it the terminal portions of the tendon of the extensor digitorum communis muscle. The phalanges of the thumb resemble in the arrangement of their parts the first and third phalanges of the fingers. The arterial canals, usually two in number, placed on either side of the volar aspect and nearer the distal than the proximal ^°^ metacarpal end of the bone, are directed towards the finger-tips. Fig. 227. — The Phalanges of . THE Fingers (Volar Aspect). Ossification. — The phalanges are ossified from primary and secondary centres. From the former, which appear as early as the ninth week of I. riialanx Head Shaft ■ f 1^ Fui. 228. — Radiographs of Fcetal Hands. 1. About ten weeks. Here the ossific nuclei of the terminal phalanges and the medial four metacarpal bones are seen. 2. A little later. The centre for the metacarpal for the thumb is now present, as al.so the centre.s for the proximal row of phalanges. The centres of the medial row of phalanges have appeared in the ca.se of the middle and ring fingers. 3. During the third month. All the primary centres for the metacarpal bones and phalanges are now developed. 4. About the fourth to fifth month. 5. About the sixth to seventh month. fcetal life, the body and distal extremities are developed ; whilst the latter, which begin to appear about the third year, form the proximal epiphyses which unite with the bodies 15 a 228 OSTEOLOGY. from eighteen to twenty. Dixey {Froc. Roy. Soc. xxx. and xxxi.) has pointed out that the primary centre in the distal phalanges commences to ossify in the distal part of the bone rather than towards the centre of the body. This observation has been confirmed by Lambertz, who further demonstrates the fact that ossification commences earlier in the distal phalanges than in any of the other bones of the hand. Of the other phalanges, those of the first row, beginning with that of the third finger, next ossify, subsequent to the appearance of ossific centres in the shafts of the metacarpal bones, w^hilst the second or middle row of the phalanges is the last to ossify about the end of the third month. Sewell has recorded a case in which the proximal phalanx had a distal as well as a proximal epiphysis. Ossa Sesamoidea. Two little oval nodules (sesamoid bones), which play in grooves on the volar aspect of the articular surface of the head of the first metacarpal bone, are constantly met with in the tendons and ligaments of that metacarpo-phalangeal articulation. Similar nodules, though of smaller size, are sometimes formed in the corresponding joints of the other digits, more particularly the index and little finger ; as Thilenius has pointed out (Morph. Arheiten, vol. v.), these are but the persistence of cartilaginous elements which have a phylogenetic interest. THE BONES OF THE INFERIOR EXTREMITY. THE PELVIC GIRDLE AND THE PELVIS. The pelvic girdle is formed by the articulation of the two hip bones with the sacrum dorsally, and their union with each other ventrally, at the joint called the symphysis pubis. Os Coxae. The hip bone (os coxae) (O.T. innominate) is the largest of the " flat " bones of the skeleton. It consists of three parts— the os ilium, the os ischium, and the os pubis — primarily distinct, but fused together in the process of growth to form one large irregular bone. The coalescence of these elements takes place in and around the acetabulum, a large circular articular hollow which is placed on the lateral side of the bone. The expanded wing-like part above this is the os ilium ; the stout V-shaped portion below and behind it constitutes the os ischium ; while the <;-shaped part to the medial side, and in front and below, forms the os pubis. The two latter portions of the bone enclose between them a large aperture of irregular outline called the foramen obturatum (obturator foramen), which is placed in front and below, and to the medial side of the acetabulum. The ilium, almost a quadrant in form, consists of an expanded plate of bone, having a curved superior border, the crista iliaca (iliac crest). Viewed from the side, this forms a curve corresponding to the circumference of the circle of which the bone is the quadrant ; viewed from above, however, it will be seen to display a double bend — convex anteriorly and laterally, and concave posteriorly and laterally. The iliac crest is stout and thick, and for descriptive purposes is divided into a labium externum (external Kp), a labium internum (internal lip), and an intermediate surface (linea intermedia), which is broad behind, narrowest about its middle, and wider again in front. About 2^ inches from the anterior extremity of the crest the external lip is usually markedly prominent and forms a projecting tubercle, which can readily be felt in the living. Attached to these surfaces and lips anteriorly are the muscles of the flank, whilst from them posteriorly the latissimus dorsi, quadratus lumborum, and sacro-spinalis muscles derive origins. The crest ends in front in a pointed process, the spina iliaca anterior superior (anterior superior iliac spine). To this the lateral extremity of Poupart's inguinal ligament is attached, as well as the sartorius muscle, which also arises from the edge of bone immediately below it, whilst from the same process and from the THE HIP BONE. 229 anterior end of the external lip of the iliac crest the tensor fasciae latie muscle takes origin. The anterior border of the ilium stretches from the anterior superior iliac spine to the margin of the acetabulum below. Above, it is thin ; liut below, it forms a thick blunt i)rocess, the spina iliaca anterior inferior (anterior inferior iliac spine). From this tlie rectus fenutris muscle arises, whilst the sloul fil>rfs "f the CltKST i>K THE II.IIM .■\NTKRK1U OI.I'TK.M. LINK Posterior gluteal link 'Anterior inferior SPINE Posterior superior SPINK Posterior inferior spinf AcETAlilLAR NOTCH Groove for obturator externus *, N TF.RIOR ,1 HF.RIOR SPISE Inferior outeal LINK Acetabulum lio-pectineal eminence Lesser sciatic notch Sciatic tuberosity SUPFRIi'R RAMI S -OF PUBlr BONE PlJBlC tubercle Crest of pdbic BONE Body of pubii BONE Infkhior ramus of riBic bone Inferior ramus of ischium Fig. 229. — The Right Hip Bonk seen from the lateral side. ilio-femoral ligament of the hip-joint are attached to it immediately above the aceta})ular margin. Posteriorly, the crest terminates in the spina iliaca posterior superior (posterior superior iliac spine). Below this, the posterior border of the bone is sharp and irregularly notched, and descends to a prominent angle, the spina iliaca posterior inferior (posterior inferior iliac spine). In front of the posterior inferior iliac spine the edge of the bone becomes thick and rounded, and swet'\>s forwards and downwards, round a wide notch called the incisura ischiadica major (greater sciatic notch), to join the posterior border of the ischium behind the acetabulum. 15 & 230 OSTEOLOGY. LiTissiurs ARTORIUS Tessor FaSCUS. LAT-E Keflected head Of RECTUS FEMORIS Straight head of rectus femoris The ilium has two surfaces, medial and lateral The lateral surface is divided into two parts, viz., a lower, acetabular, aud an upper, gluteal part. The lower forms a little less than the upper two-fifths of the acetabular hollow, and is separated from the larger gluteal surface above by the upper prominent margin of the arti- cular cavity. The gluteal surface, broad and expanded, is concavo-convex from behind forwards. It is traversed by three rough gluteal (O.T. curved) lines, well seen in strongly developed bones, but often faint and indistinct in feebly marked speci- mens. Of these the linea glutaea inferior (inferior gluteal line) curves backwards from a point immediately above the anterior inferior spine towards the greater sciatic notch posteriorly ; the bone between this and. the acetabular margin is marked by a rough shallow groove, from which the reflected head of the rectus femoris muscle arises. The linea glutsea anterior (anterior gluteal line) commences at the crest of the ilium, about one inch and a half behind the anterior superior iliac spine, and sweeps backwards and do^vn wards towards the upper and posterior part of the greater sciatic notch. The sur- face between this line and the preceding furnishes an extensive origin for t he glutg eus minimusjuuscle. The linea glutsea posterior (posterior gluteal line) leaves the iliac crest about two and a half inches in front of the posterior superior iliac spine, and bends down- wards and sHghtly for- wards in a direction anterior to the posterior inferior spine. The area between this and the anterior gluteal line is for the origin of the glutseus medius muscle, whilst the rough surface immediately above and l^hind it is for some of the fibres of origin of the glutseus maximus muscle. The medial surface of the ilium is divided into two areas which present very characteristic differences. The posterior or sacral part, which is rough, displays, in front, a somewhat smooth, auricular surface (facies auricularis) which is cartilage- coated in the recent condition, and articulates with the sacrum. This area is said to be proportiouately smaller in tlie female, wliilst curving rouud in front of its anterior margin theie is often a groove, for the attachment of the fibre.s of the anterior sacro-iliac ligaments, called the pre-auricular sulcus. Accoitiing to Derry this groove is better marked in the female, and may be regarded as chai-acteristic of that sex. Above and behind this there is an elevated irregular area, the tuberosity (tuber- ositaa iliaca), which is here and there deeply pitted for the attachment of the strong interosseous and posterior sacro-iliac ligaments. Above this the bone becomes con- fluent with the inner hp of the iliac crest, and here it affords an origin ^QJihe_sacro- .spinalis and multifidus muscles, and some of the fibres of the quadratus laimborum. The anterior part of the medial aspect of the bone is smooth and extensive; it Gemellus sitpeeiob Sejomembeasoeu Biceps axd SEinTEXDISOSrS Quadratus femoris Fig. Fyramidalis Rectus abdominis Adductor loxgds Gracilis Adductor brevis 230. — Latebal Aspect of the Right Hip Bose with the Attachments of the Muscles mapped out. THE HIP BONE. 231 is subdivided by au oblique ridge, called the ilio- pectineal line (linea arcuata), which passes forwards and downwards, from the most prominent point of the auricular surface towards the medial side of the ilio- pectineal eminence, which is placed just above and in front of the acetabulum and marks the fusion of the Crest or the ii.ii m ILIUM Tlberositv FOR SACRO-ILIAC LIGAMENTS Anterior superior SPINE Lesser sciatic notch ISCHIUM Tuber ischiadiccm (ischial TUBEROSinr) InJERIOR RAMUS OF OS PUBIS RaMUS OF ISCHIUM Fig. 231.— The Right Hip Bone (Medial Aspect). ilium with the os pubis. Above this the bone forms the shallow Uiac fossa, from the floor of which the iliacus muscle arises, whilst leading from the fossa, below and in front, there is a shallow furrow, passing over the superior acetabular margin, between the anterior inferior iliac spine on the lateral side and the ilio-pectineal eminence medially, for the lodgment of the tendinous and fleshy part of the ilio-psoas muscle. If held up to the light the floor of the deepest part 15 232 OSTEOLOaY. of the iliac fossa will be seen to be formed of but a thin layer of bone. A nutrient foramen of large size is seen piercing the bone towards the posterior part of the fossa. Below and behind the ilio- pectineal line the medial surface of the ilium forms a small portion of the wall of the pelvis minor ; the bone here is smooth, and rounded off posteriorly into the greater sciatic notch, where it becomes confluent with the medial aspect of the ischium. This part of the bone is proportionately longer in the female than in the male, and forms with the ischium a more open angle. Just anterior to the greater sciatic notch there are usually the openings of one or two large vascular foramina. From this surface arise some of the posterior fibres of the obturqjtQ^_internus muscle. The ischium constitutes the lower and posterior part of the hip bone. Superiorly its body (corpus) forms somewhat more than the inferior two-fifths of the acetabulum together with the bone supporting it behind and medially. Below this, the superior ramus passes downwards and backwards as a stout three-sided piece of bone, from the inferior extremity of which a compressed bar of bone, called the inferior ramus, extends forwards at an acute angle. This latter unites in front and above with the inferior ramus of the pubis, and encloses the aperture called the obturator foramen. Superiorly, and on the lateral aspect of the ischium, the acetabular surface is separated from the bone below by a sharp and prominent margin, which is, however, deficient in front, where it corresponds to the acetabular notch (O.T. cotyloid notch) leading into the articular hollow; the floor of this notch is entirely formed by the ischium. Below the prominent acetabular margin there is a well-marked groove in which the obturator externus lies. Beneath this the antero-lateral surface of the superior and inferior rami furnishes surfaces for the attachments of the obturator externus, quadratus femoris, and adductor magnus muscles. The postero-lateral surface of the ischium forms the convex surface on the back of the acetabulum. The medial border of this is sharp and well defined, and is confluent above with the border of the ilium, which sweeps round the greater sciatic notch. From this border, on a level with the lower edge of the acetabulum, there springs a pointed process, the spina ischiadica (ischial spine), to which are attached the sacro - spinous ligament and the superior gemellus muscle. Inferior to this, the postero-lateral surface narrows rapidly, its medial border just below the spine being hollowed out to form the incisura ischiadica minor (lesser sciatic notch). The lower part of this surface and the angle formed by the twp rami are capped by an irregularly rough piriform mass called the tuber ischiadicum (ischial tuberosity). This is divided by an oblique ridge into two areas, the upper and lateral for the tendon of origin of the semimembranosus muscle, the lower and medial for the conjoined heads of the biceps and semitendinosus muscles. Its prominent medial lip serves for the attachment of the sacro-tuberous ligament, whilst its lateral edge furnishes an origin for the quadratus femoris muscle ; in front and below, the adductor magnus muscle is attached to it. The medial surface of the body and superior ramus of the ischium form in part the wall of the pelvis minor. Smooth and slightly concave from before backwards, and nearly plane from above downwards, it is widest opposite the level of the ischial spine. Below this, its posterior edge is rounded and forms a groove leading to the lesser sciatic notch, along and over which the tendon of the obturator internus passes. To part of this surface the fibres of the obturator internus are attached, whilst the medial aspect of the spine supplies points of origin for the coccygeus and levator ani muscles, as well as furnishing an attachment to the " white line " of the pelvic fascia. The medial surface of the inferior ramus of the ischium is smooth, and so rounded that its inferior ecjge tends to be everted. To this, as well as to its margin, is attached the crus penis, together with the ischio-cavernosus, obturator internus, transversus perinei, and sphincter muscle of the membranous urethra. In the female, structures in correspondence with these are found. The anterior part of the hip bone is formed by the os pubis ; it is by means of the union of this bone with its fellow of the opposite side that the pelvic girdle is completed in front. The pubis (os pubis) consists of two rami — a superior (ramus superior ossis THE HIP BONE. 233 pubis) and an inferior (ramus inferior ossis pubis). The broad part of the bone formed by the fusion of these two rami is the body. Tiie body of the os pubis has two surfaces. Of these the posterior or postero- superior is smot^th, aud forms the anterior part of the wall of the pelvis minor ; hereto are attaclied the levator ani muscle and pul)0- prostatic ligaments, and on it rests the bladder. The anterior or antero-inferior surface is rougher, and furnishes origins for the gracilis, adductor longus, adductor brevis, and some of the fibres of the obturator externus muscles. The medial border is provided with an elongated oval cartilage-covered surface (facies symphyseos) by means of which it is united to its fellow of the opposite side, the joint being called the symphysis pubis. The superior border, thick and rounded, projects somewhat, so as to over- hang the anterior surface. It is called the crest. Medially this forms with the medial border or symphysis the angle, whilst laterally it terminates in a pointed process, the pubic tubercle (O.T. pubic spine). From the crest arise the rectus Rectus kemoris (straight head of origin) Ukctus femokis (reflected head of origin) Attachment of ILIO-FE.MORAI. LKiAMENT ADDUCTOR LONGUS (origin) Pyramidalis abdominis (origin) Rectus abdominis (origin) Semimembran- X"^ ^ "'l*nft ^ ,^ /^ U \ Gracilis (origin) osus (origin) i» . QuADRATUs (I" '%„/ lB)s ^ ^ ^^ '«. J^ Adductor brevis (origin) FEMOKis (origin) Biceps and semitendinosus- (origin) Fia. 232. — MuscLB Attachments to the Lateral Suuface of the Os Pdbis and Ischium. abdominis and pyramidalis muscles, and to the tubercle is attached the medial end of the inguinal ligament. Passing upwards and laterally from the lateral side of the body towards the acetabulum, of which it foirms about the anterior fifth, is the superior ramus. This has three surfaces: an an tero - superior, an antero-inferior, and an internal or posterior. The antero- superior surface is triangular in form. Its apex corresponds to the pubic tubercle ; its anterior inferior border to the crista obturatoria (obturator crest), leading from the pubic tubercle to the upper border of the acetabular notch ; whilst its sharp postero- superior border trends upwards and laterally from the tubercle, and is continuous with the iliac portion of the ilio-pectineal line just medial to the iHo-pectineal eminence, forming as it passes along the superior ramus the pubic portion of that same line (pecten ossis pubis). On this line, just medial to the ilio-pectineal eminence, there is often a short sharp crest which marks the insertion of the psoas minor. The base of the triangle corresponds to the ilio-pectineal eminence above and the upper margin of the acetabular notch below. Slightly hollow from side to side, and convex from before backwards, this surface provides an origin for, and is in part overlain by, the pectineus muscle. The posterior or postero-superior surface of the superior ramus is smooth, concave from side to side, and slightly rounded from above downwards ; by its sharp inferior curved border it completes the obturator foramen, as seen from behin(i The antero- 234 OSTEOLOGY. inferior surface forms the roof of the broad sulcus obturatorius (obturator groove) which passes obliquely downwards and forwards between the lower margin of the antero-superior surface in front and the inferior sharp border of the posterior or internal surface behind. The inferior ramus of the os pubis passes downwards and laterally from the lower part of the body. Flattened and compressed, it unites with the inferior ramus of the ischium, and thus encloses the obturator foramen, whilst in correspondence with its fellow of the opposite side it completes the formation of the pubic arch. Anteriorly it furnishes origins for the gracilis, adductor brevis, and adductor magnus muscles, as well as some of the fibres of the obturator externus muscle. Its medial surface is smooth, whilst its lower border, rounded or more or less everted, has attached to it the anterior part of the crus penis and the arcuate (O.T. subpubic) ligament. The acetabulum is the nearly circular hollow in which the head of the thigh bone fits. As has been already stated, it is formed by the fusion of the ilium and ischium and pubis in the following proportions : the ilium a little less than two-fifths, the ischium somewhat more than two -fifths, the pubis constituting the remaining one-fifth. It is so placed as to be directed downwards, laterally, and forwards, and is surrounded by a prominent margin, to which the capsule and labrum glenoidale of the hip-joint are attached. Opposite the obturator foramen this margin is interrupted by the incisura acetabuli (acetabular notch) ; immediately lateral to the ilio- pectineal eminence the margin is slightly hollowed, whilst occasionally there is a feeble notching of the border above and behind. These irregularities in the outline of the margin correspond to the lines of fusion of the ilium and pubis and the ilium and ischium respectively. The floor of the ace- tabulum is furnished with a horseshoe-shaped articular surface, which hnes the circumference of the hollow, except in front, where it is interrupted by the ace- tabular notch. It is broad above; narrower in front and below. Enclosed by articular surface there is a more or less circular rough area (fossa acetabuli) continuous in front and below with the floor of the acetabular notch. This, some- what depressed below the surface of the articular area, lodges a quantity of fat, and provides accommodation for the intra-articular Ligament of the joint (ligamentum teres). As may be seen by holding the bone up to the Hght, the floor of this part of the acetabulum is usually thin. The major part of the non- articular area is formed by the ischium, which also forms the floor of the acetabular notch. The foramen obturatum (obturator foramen) lies in front of, below, and medial to the acetabulum. The margins of this opening, which are formed in front and above by the os pubis, and behind and below by the ischium, are sharp and thin, except above, where the antero-inferior surface of the superior ramus of the pubis is channelled by the obturator groove. Below, and on either side of this groove, two tubercles can usually be seen. The one, situated on the edge of the ischium, just in front of the acetabular notch, is named the posterior obturator tubercle ; the other, placed on the lower border of the posterior surface of the superior ramus of the os pubis, is called the anterior obturator tubercle. Between these two tubercles there passes a ligamentous band, which converts the groove into a canal along which the obturator vessels and nerve pass. Elsewhere in the fresh condition the obturator membrane stretches across the opening from margin to margin. The form of the foramen varies much, being oval in some specimens, in others more nearly triangular; its relative width in the female is greater than in the male. Nutrient foramina for the ilium are seen on the floor of the iliac fossa, just in front of the auricular surface ; on the pelvic aspect of the bone, close to the greater sciatic notch ; and on the gluteal surface laterally, near the centre of the anterior gluteal line. For the ischium, on its pelvic surface, and also laterally on the groove below the acetabulum. For the pubis, on the surface of the body, and deeply also from the acetabular fossa. Connexions.— The hip bone articulates with the sacrum behind, with the femur to the lateral side and below, and with its fellow of the opposite side medially and in front. Each of its three parts comes into direct relation with the surface. Above, the iliac crest assists in forming the iliac furrow, which serves to separate the region of the flank from that of the buttock. In front, the anterior superior iliac spine forms a definite landmark ; whilst behind, the posterior superior iliac spines will be found to correspond with dimples situated on either side of the median plane of the root of the back. The symphysis, the crest, and tubercle of THE PELVIS. 235 Appeuis about later enil of "iiid 111. of f(etal life AppearR about 15 yars : fuses 22-25 llie j)iibis can all he distinguished in front, tlioiigh overlain by a considerable quantity of fat, whilst the position of the tubero.sities' of the i.schia, when uncovered by the great gluteal Miiiscles in tlie flexed jjosition of the thigh, can readily be a.scertained. In the perineal region the outline of the pubic and ii^chial rami can easily be determined by digital e.xamination. Ossification commences in the ilium about the ninth week of intra-uterine life ; about the fourth month a centre appears below the acetabulum for the ischium, the os pubis bein<^ developed from a centre which appears in front of the acetabulum about the Hfth or si.xtli month. At birth tlie form of the ilium is well defined ; the body and i)art of the tuberosity of tiie ischium are ossified, as well as the superior ramus and ])art of the body of the os pubis. All three parts enter into the formation of the sides of the acetabulum, and by the third yearhave conver}j;ed to form the bottom of that hollow, being sopaoited from each otlier by a tri- radiate piece of cartilage, in which, about the twelfth year, independent ossific centres make their appearance, which may or may not become fused with the adjacent bones. In the latter case they unite to form an inde- pendent ossicle, the os acelabuli, which subse- quently fuses with and forms the acetabular part of the OS pubis. By the age of si.xteen the ossifica- tion of the acetabulum is usually completed, whilst the rami of tlie ischivim and OS pubis conmionly unite about the tenth year. Secondary centres, seven in number, make their appearance about the age of puberty, and are found in the following situations : one for the anterior inferior iliac spine ; one for the ventral two-thirds of the iliac crest and the anterior superior iliac spine which grows backwards, one for the posterior superior iliac spine and dorsal third of the iliac crest which grows forwards — these two unite about the twentieth year ; a scale-like epiphysis over the tuberosity of the ischium ; a separate epiphysis for the spine of the ischium ; (?) a point for the tubercle and another foi* the angle of the os pubis. Fusion between these and the primary centres is usually complete between the twentj'-second and twenty-fifth years. Le Damany states that the proportionate depth of the acetabular cavity at the sixth month of fa^tal life is greater than at birth. In the third year a rapid increase in its depth again takes place correlated with the assumption of the erect position. Parsons (Journ. A7iat. and Physiol, vol. xxxvii. p. 315)regai-ds the ischial epiphysis as the homologue of the hypo-ischium in reptiles, and suggests that the epiphysis over the angle of the pubis may represent the epipubic bone of marsupials. Appears about 4th 111. of foetal life Appears about 18 years Appears about 18 years bout 10 years At Birth. Fig. '2-33.- AljuuL 12 or lo ) e;ir.s. -Ossification of the Hip Bone. The Pelvis. The pelvis is tbriued by the uuion of the hip bones witli each other in front, and witli the sacrum behind. In man the dwarfed caudal vertebrie (coccygeal) are curved forwards and so encroach upon the limits of the pelvic cavity interiorly. The pelvis is divided into two parts by the ilio-pectiueal lines, which curve forwards from the upper part of the lateral parts of the sacrum behind to the roots of the pubic tubercles in front. The part above is called the pelvis major, and serves by the expanded iliac fossa? to support the abdominal contents ; the part below, the pelvis minor contains the pelvic %'iscera, and in the female forms the bony canal through which at full term the foetus is expelled. 236 OSTEOLOGY. The pelvis minor is bouuded in front by the symphysis pubis in the median plane, and by the body and rami of the os pubis on each side, laterally by the smooth medial surfaces of the ischia and ischial rami, together with a small part of the ilium below the iliac portion of the ilio-pectineal line. Springing from the posterior margin of the ischium are the inturned ischial spines. Behind, the broad curved Fig. 234. — The Male Pelvis seen from the front. anterior surface of the sacrum, and below it, the small and ■ irregular coccyx, form its posterior wall. Between the sides of the sacrum behind, and. the ischium and. ilium in front and above, there is a wide interval, called the greater sciatic notch, which is, however, bridged across in the recent condition by the sacro-tuberous and sacro-spinous ligaments, which thus convert it into two foramina — the larger above Fig. 23.'. — Thk Female Pelvis seen from the front. the spine of the ischium, the greater sciatic foramen ; the lower and. smaller below the spine, called the lesser sciatic foramen. Apertura Pelvis Superior. — The upper opening of the pelvis minor is bounded in front by the symphysis pubis, with the crest of the pubis on each side ; laterally by the ilio-pectineal lines ; and behind by the sacral promontory. The circum- ference of this aperture is often called the brim of the pelvis ; in the male it is THE PELVIS. 237 heart-shaped, in the female more oval. The antero-posterior or conjugate diameter is measured from the sacro-vertebral angle to the symphysis pubis ; the oblique diameter from the aicro-iliac joint of one side to the ilio-pectiueal eminence of the other ; whilst the transverse diameter is taken across the greatest width of the pelvic u[)erture. Apertura Pelvis Inferior. — The lower opening is bounded anteriorly by the arcus pubis (pubic arch), formed in front and above by the bodies of the ossa pubis, with the sympliysis between them, and the inferior pubic rami below and on either side. These latter are continuous with the ischial rami, which pass backwards and laterally to the ischial tuberosities, which are placed on either side of this aperture. In the median plane behind, the tip of the coccyx projects forward ; and in the recent condition the interval between this and the ischial tuberosities is bridged across by the sacro-tuberous ligament, tlie inferior edge of which necessarily assists in determining the shape of the outlet. As the anterior wall of the cavity, formed by the symphysis pubis, measures from li to 2 inches, whilst the posterior wall, made up of the sacrum and coccyx, is from 5 to 6 inches in length, it follows that the planes of the inlet and outlet are not parallel, but placed at an angle to each other. The term axis of the pelvis is given to lines drawn at right angles to the centres of these planes. Thus, with the pelvis in its true position, when the figure is erect, the axis of the upper opening corresponds to a line drawn downwards and backwards from the umbilicus towards the tip of the coccyx below, whilst the axis of the lower opening is directed down- wards and slightly backwards, or downwards and a little forwards, varying according to the length of the coccyx. Between these two planes the axis of the cavity, as it passes through planes of varying degrees of obliquity, describes a curve repeating fairly closely the curve of the sacrum and coccyx. Position of the Pelvis. — The position of the pelvis in the living, when the figure is erect, may be approximately represented by placing it so that the anterior superior iliac spines and the symphysis pubis lie in the same vertical plane. Under these conditions the plane of the upper opening is oblique, and forms with a horizontal line an angle of from 50° to 60°. The position of the pelvis depends upon the length of the ilio-femoral ligaments of the hip-joint, being more oblique when these are short, as usually happens in women in whom the anterior superior iliac spines tend to lie in a plane slightly in advance of that occupied by the symphysis pubis. In cases where the ilio-femoral ligament is long a greater amount of extension of the hip-joint is permitted, and this leads to a lessening of the obliquity of the pelvis. This condition, which is more typical of men, results in the anterior superior iliac spines lying in a plane slightly posterior to the plane of the sym- physis, whilst the angle formed by the plane of the inlet and the horizontal is thereby reduced. Bearing in mind the oblique position of the pelvis, it will now be seen that the front of the sacrum is directed downwards more than forwards, and that the sacral pro- montory is raised as much as from ^\ to 4 inches above the upper border of the symphysis pubis, lying higher than the level of a line connecting the two anterior superior iliac spines. From the manner in which the sacrum articulates with the ilia, it will be noticed that the weight of the trunk is transmitted downwards through the thickest and strongest part of the bone (see Architecture, Appendix A) to the upper part of the acetabula, where these rest on the heads of the femora. Sexual Differences. — The female pelvis is lighter in its construction than that of the male ; its surfaces are smoother, and the indications of muscuhxr attachments less marked. Its height is less and the splay of its walls not so pronounced as in the male, so that the female pelvis has been well described as a short segment of a long cone as contrasted with the male pelvis, which is a long segment of a short cone. The cavity of the pelvis minor in the female is more roomy, and the ischial spines not so much intumed. The pubic arch is wide and rounded, and will usually admit a right-angled set-square being placed within, so that the summit touches the inferior surface of the symphysis pubis, whilst the sides lie in contact with the ischial rami. In the male the arch is narrow and angular, forming an angle of from 65° to 70°. The greater sciatic notch in the female is wide and shallow. The distance from the posterior edge of the body of the ischium to the posterior inferior iliac spine is longer, measuring on an average 50 mm. (2 inches) in the female, as contrasted with 40 mm. (1| inches) in the male. The angle formed by the ischial and iliac borders is more contracted and acute in the male as compared with the 238 OSTEOLOGY. female, in whom it is wider and more open. In the female the acetabulum is proportion- ately smaller than in the male. The upper opening in the female is large and oval or reniform, as compared with the cribbed and heart-shaped aperture in the male. The sacro-vertebral angle is more pro- nounced in the female, and the obliquity of the upper opening greater. The sacrum is shorter and wider. The posterior superior iliac spines lie wider apart ; the pubic crests are lont^er ; and the pubic tubercles are separated by a greater interval than in man. The outlet is larger : the tuberosities of the ischia are farther apart ; and the coccyx does not project forward so much. The curve of the sacrum is liable to very great individual variation. As a rule the curve is more uniform in the male, whilst in the female it tends to be flatter above and more accentuated below. There is a greater proportionate width between the acetabular hollows in the female than in the male. Of much importance from the standpoint of the obstetrician are the various diameters of the pelvis minor. In regard to this it is worthy of note that the plane of "greatest pelvic expansion" extends from the union between the second and third sacral vertebrae behind, to the middle of the symphysis pubis in front, its lateral boundaries on either side correspond- ing with the mid-point of the medial surface of the acetabulum ; whilst the plane of "least pelvic diameter" lies somewhat lower, and is defined bylines passing through the sacro-coccygeal articulation, the ischial spines, and the lower third of the symphysis pubis (Norris). Subjoined is a table showing the principal average measurements in the two sexes : — PELVIS MAJOE. Maximum distance between the iliac crests Distance between the anterior superior iliac spines Distance between the last lumbar spine and the front of the symphysis pubis Males. 11| in., or 282 mm. 9^ in., or 240 mm. 7 in., or 176 mm. Females. lOf in., or 273 mm. 9f in., or 250 mm. 7^ in., or 180 mm. PELVIS MINOB. Males. Antero-posterior (conju- gate) diameter ObUque diameter . Transverse diameter Upper Opening. 4 in., or 101 mm. 4| in., or 120 mm. 5 in., or 127 mm. Females. Lower Opening. Upper Opening. Cavity. Greatest. 3| in., or 95 mm. 3i in., or 88 mm. 3^ in., or 88 mm. 4§ in., or 110 mm. 5 in., or 125 mm. ; 5j in., or 1 135 mm. 5 in., or 127 mm. 4 J in., or 125 mm. Least. 4§ in., or 110 mm. 4§ in., or 110 mm. Lower Opening, 4^ m., or 115 mm. 4| in., or 115 mm. 4§ in., or 110 mm. Growth of the Pelvis.— From the close association of the pelvic girdle with the lower limb we find that its growth takes place concurrently with the development of that member. At birth the lower limbs measure but a fourth of the entire body length ; consequently at that time the pelvis, as compared with the head and trunk, is relatively small. At this period of life the bladder in both sexes is in greater part an abdominal organ, whilst in the female the uterus has not yet sunk into the small pelvic cavity, and the ovaries and uterine tubes rest in the iliac fossai. The sacro-vertebral angle, though readily recognised, is as yet but faintly marked. Coincident with the remarkable growth of the lower limbs and the assumption of the erect position when the child begins to walk, striking changes take place in the form and size of the pelvis. These consist in a greater expansion of the iliac bones, necessarily associated with the growth of the muscles which control the movements of the hip, together with a marked increase in the sacro-vertebral angle due to the development of a forward lumbar curve ; at the same time, the weight of the trunk being thrown on the sacrum causes the elements of that bone to sink to a lower level between the hip bones. The cavity of the pelvis minor increases in size proportionally, and the viscera afore-mentioned now begin to sink down and have assumed a position within the pelvis by the fifth or sixth year. The extension of the thighs in the upright position nece.ssarily brings about a more pronounced pelvic obliquity, whilst the stoutness and thickness of the ilium over the upper part of the acetabulum is much increased to withstand the pressure to which it is obviously subjected. Coincident with this is the gradual development THE FEMUR 239 of the iliac portiou of the ilio-pectiueal line, which serves in the adult to .separate sharply the pelvis m:ijor from the pelvis minor. This part of the bone is reniaikalily strong, as will be shown (see Architecture, Aj>penilix A), and serves to transmit the body weight lV(»m the sacrum to the thigh bone. The sexual differences of the jielvis, .so far as they refer to the general con- tiguration of this part of the .skeleton, are as jironounced at the third or fourth month of fcctal life as they are in the adult. (Fehling, Ztschr. f. Geburtsh. u. Gynaek. Bd. ix. and x. ; A. Thomson, Journ. Anat. and Physiol, vol. xxxiii. p. 359.) The rougher ajjpearance of the male type is correlated with the more powerful muscular development. Oreatkk trochanteh TrBEBCI.E Intertko- chanteric LIXK Lesser trochanter Lateral epicondvle — The Femur. The femur or thigh boue is remark- able for its leiii/th, being the longest 'Obturator internus Piriformis Vast IS medialis Ilio-psoas Lateral condyle Fig. 'J26. — The Right Fkmur seen kuom the Fuont medially, and slightly forwards. Fig. 237. — Anteuiuu Aspect of Piioximal Por- tion OF the Right Femik with Attach.ments OF Muscles mapi-ed out. bone in the body. Proximally the femora are separated by the width of the pelvis. Distally they articulate with the tibiw and patellae. In the military position of attention, with the knees close to- gether, the bodies of the thigh bones occupy an oblique position. For descriptive purposes the bone is divided into a proximal extremity, com- prising the head, neck, and two trochanters ; a body ; and a distal ex- tremity, forming the ex- pansions known as the condyles. The caput femoris (head) is the hemi- spherical articular sur- face which fits into the acetabulum. Its pole is directed upwards, A little below the summit, and usually somewhat Adductor tubercle Medial El'ICONDYLE 240 OSTEOLOGY. Neck Greater trochanter Tubercle of quadratns Intertrochan- teric CREST — Gluteal tuberosity Arterial foramen behind it, is a hollow, oval pit (fovea capitis femoris) for the attachment of the ligamentum teres. Piercing the floor of this depression are seen several foramina through which - vessels Trochanteric fossa paSS tO Supply tllC head Pit FOR Lio. TERES — / 1^^ \ of the bone ; the proximal epiphysis thus having a double blood supply, viz., from the neck distally,and through the medium of the ligamentum teres proxi- mally. The circumfer- ence of the head forms a lip with a wavy outline, more prominent above and behind than in front. The head is supported by a stout compressed bar of bone, the coUuni femoris (neck), which forms with the proxi- mal end of the body an angle of about 125 degrees, and is directed proximally, medially, and a little forwards. Its vertical width exceeds its antero-posterior thickness. Constricted about its middle, it expands medi- ally to support the head, whilst laterally, where it joins the shaft, its vertical diameter is much in- creased. Anteriorly it is clearly defined from the shaft by a rough ridge which commences above on a prominence, some- times called the tubercle of the femur, and passes obliquely downwards and medially. This constitutes the upper part of the linea intertrochanterica (intertrochanteric line), and serves for the attachment of the ilio- femoral liga- ment of the hip -joint. Posteriorly, where the neck unites with the body, there is a full rounded ridge passing from the trochanter major proxi- mally to the trochanter minor distally ; this is the crista intertrochan- terica (intertrochanteric crest). A little proximal to the middle of this ridge there is usually a fulness which serves to indicate the proximal limit of attachment of the quadratus femoris muscle, and is called the tubercle for the quadratus. Laterally the Adductor tubercle Medial epicondyle Medial CONDYLE Surface for attachment of posterior cruciate ligament Fia. Media L EPICONDYLIC LINE Lateral epicondylic line Popliteal plane IjATEKAL epicondyle .Surface for attaclinient of ant. cruciate ligament Lateral condyle Intercondyloid fossa 2.38.— The Right Femur seen from behind. THE FEMUE. 241 neck is embedded in the medial suid'ace of the tro- chanter major, Ity which, at its up})er aud dorsal part, it is tc» some extent tnerhunif. Here is situ- ated the trochanteric fossa, into which the tendon of the oliturator externus is inserted. Passing nearly horizontally across the l)ack of the neck there is a faint groove leading into this depression ; in this the tendon of the obturator externus muscle lies. Distally the neck becomes continent with the tro- chanter minor behind, and is continuous with the medial surface of the boely in front. The neck is pierced by many vascular canals, most numerous at the proximal and dorsal part. Some are directed proximally towards the head, whilst others pass in the direction of the trochanter major. The trochanter major (greater trochanter) is a lar^e quadrangular process which caps the proxi- mal and lateral part of the body, and overhangs the root of the neck above and behind. Its lateral surface, of rounded irregular form, slopes up- wards and medially, and is separated from the lateral surface of the liody distally by a more or less horizontal ridge. Crossing it obliquely from the posterior superior to the anterior inferior angle is a rough line which serves for the insertion of the )liTtRATOR E-XTERKUS OBTfRATOB INTBRNUg Pit fOR /yi. I.!'- Tl.-1-V> Neck Trochanteric kossa Intertrochahteric crest Lesser trochanter Greater trochanter Spiral line Pectineal line Gluteal Tl herositv Arterial foramen LiNEA ASI'ERA Fig. 240. — Dorsal View of the Proximal P.\rt ok THE Right Femdr. Fig. 239. — Dor.sal Aspect ok ihk Proximal Portion of the Right Femcb with the Attachments ok Muscles mapped oit. glutseus medius muscle ; both proximal and distal to this the surface of the bone is smoother and is overlain by bursiij. The ventral surface, somewhat oblong in shape, and inclined obliquely from below upwards and medi- ally, is elevated from the general aspect of the body, from which it is separated in front by an oblique line leading upwards and medially to the tubercle at the upper end of the superior part of the intertrochanteric line. This surface .serves for the insertion of the glutceus mini- mus. The superior border is curved and elevated ; into it ate inserted the tendons of the obturator iuternus and gemelli muscles medially and in front, and the piriformis muscle above and behind. The dorsal border is thick and rounded, and forms the upper part of the inter- trochanteric crest. The angle formed by the superior and dorsal borders is sharp and pointed, and forms the tip of the ti:ochanter overhanging the trochanteric fossti, which lies immediately below and medial vto its medial surface. 16 242 OSTEOLOGY. The lesser trochanter (trochanter minor) is an elevated pyramidal process situated at the dorsal side of the medial and proximal part of the body, where that becomes continuous with the distal and dorsal part of the neck. Confluent above with the intertrochanteric crest, it gradually fades away into the dorsal aspect of the body below. The combined tendon of the ilio-psoas is inserted into this process and into the bone immediately below it. The body (corpus femoris), which is characterised by its great length, is cylin- drical in form. As viewed from the front, it is straight or but slightly curved ; as seen in profile, it is bent forwards, the curve being most pronounced in its proximal part. The body is thinnest at some little distance proximal to its middle ; distal to this it gradually increases in width to support the condyles ; its antero- posterior diameter, however, is not much increased distally. Its surfaces are generally smooth and rounded, except behind, where, running longitudinally along the centre of its curved dorsal aspect, there is a rough-lipped ridge, the linea aspera. Most salient towards the middle of the body, the linea aspera consists of a medial lip and a lateral lip, with a narrow intervening rough surface. Proximally, about 2 to 2h inches from the trochanter minor, the linea aspera is formed by the convergence of three hnes. Of these the lateral is a rough, somewhat elevated ridge, called the gluteal tuberosity which commences proxim- ally, on the back of the body, lateral to and on a level with the trochanter minor, and becomes continuous distally with the lateral lip of the linea aspera. This serves for the bony insertion of the glutseus maximus, and is occasionally de- veloped into an outstanding process called the trochanter tertius. The medial lip of the linea aspera is confluent proximally with a line which winds round the body proximally and forwards, in front of the trochanter minor, to become continuous with the intertrochanteric line (see p. 240). The whole consti- tutes what is known as the spiral line, and extends from the anterior part of the trochanter major proximally to the linea aspera distally. Intermediate in position between the spiral line in front and medially, and the gluteal ridge laterally, there is a third line, the pectineal line, which passes distally from the trochanter minor and fades away into the surface between the two lips of the linea aspera. Into this the pectineus muscle is inserted. About the junction of the middle with the distal third of the body the two lips of the linea aspera separate from one another, each passing in the direction of the epicondyle of the corresponding side. The lines so formed are called the medial and lateral epi- condylic lines, respectively, and enclose between them a smooth triangular area corresponding to the* back of the. distal third of the body ; this, called the planum popliteum (popliteal surface), forms the floor of the proximal part of the popliteal fossa. The continuity of the proximal part of the medial epicondylic hne is but faintly marked, being interrupted by a wide and faint groove along which the popliteal artery passes to enter the fossa of that name. Distally, where the line ends on the proxi- mal and medial surface of the medial epicondyle, there is a little spur of bone called the adductor tubercle, to which the tendon of the adductor magnus is attached, and Ijehind which the medial head of the gastrocnemius muscle takes origin. The linea aspera affords extensive linear attachments to many of the muscles of the thigh. The vastus medialis arises from the spiral line pi'oximally and the medial lip of the linea aspera distally. This muscle overlies but does not take origin from the medial as])ect of the body. The adductor longus is inserted into the medial lip about the middle thii-d of the length of the body. The adductor magnus is inserted into the intermediate jjart of the line, extending to the level of the trochanter minor, where it lies medial to the insertion of the glutseus maximus. Distally, its insertion passes on to the medial epicondylic ridge, reaching as far as the adductor tubercle. The adductor brevis muscle is inserted into the linea aspera proximally, between the pectineus and adductor longus muscles medially and the adductor magnus laterally. Distal to the insertion of the glutaeus maximus the short head of the biceps arises from the lateral lip as well as from the lateral epicondylic line ; in front these also serve for the Origin of the vastus lateralis muscle. There is frequently a small tubercle which marks the distal attachment of the lateral intermuscular septum on the lateral condylic line, aljout two inches from the condyle. Immediately proximal to this there is often a groove for a large muscular artery which jiierces the septum at this point (Frazer). The canals for the nutrient arteries of the body, which have a proximal direction, are usually two in number, and are placed on or near the linea aspera — the proximal one about the level of the Junction of the middle and proximal third of the bone, the distal some three or four inches distal THE FEMUE. 243 Addictor MAONfS to this — usually on the medial side of the bmly, iniincdiately in fronl ut tiie medial lip of the linea aspera. The anterior tiud lateral aspects of the body are covered by, and furnish surfaces for, the origins of the vastus lateralis and vastus intermedins. The medial asjtect is covered by the vastus medialis. The distal extremity of the femur comprises the two condyles and epicon- dyles. The condyles are two recurved processes of bone, each provided with an articular surface, and separated behind by a deep intercondyloid fossa. United in front, where their combined articular surfaces form an area on which the patella rests, the two condyles differ from each other in the following respects : If the body of the bone is held vertically, the medial condyle is seen to reach a more distal level than thu lateral ; but, as the femur lies obliquely in the thigh, the con- dyles are so placed that their distal surfaces lie in the same horizontal plane. Viewed on their distal aspect, the medial condyle is seen to ])e the narrower and shorter of the two. The lateral condyle is broader, and advances farther forward and to a more proximal level on the anterior sur- face of the shaft. The intercondyloid fossa reaches Medial head ok ga TROCNEMir I.ATERAI. HEAD OF OAS- TR0CNBMIU8 Posterior cruciate Anterior criciate lioament ligament Fig. '241. — Fusteriok Aspect ok Distal Portion ok the Right Femur with forwards as far as a transverse line drawn through ATTACHMENTS OK Mi'scLEs MAPPED ^^^ ^^^^^^ ^^ ^^^ ^^^^^^^ condylc. Its sidcs are OUT. . *' formed by the medial and lateral surfaces of the lateral and medial condyles respectively, the latter being more deeply excavated, and displaying an oval surface near its distal and anterior part for the attachment of the posterior cruciate ligament of the knee-joint. On the posterior and proximal part of the medial surface of the lateral condyle there is a corresponding surfjice for the attachment of the anterior cruciate ligament. The floor of the notch, which is pierced by numerous vascular canals, slopes proximally and tlorsally towards the popliteal surface on the back of the body, from wiiich it is separated by a slight ridge (linea inter- condyloidea) to which the posterior part of the capsule of the knee-jniut is attached. Epicondyles. — The cutaneous aspect of each condyle (i.e. the lateral surface of the lateral condyle and the medial surface of the medial condyle) presents an elevated rough surface called the epicondyle, the medial (epicondylus medialis) projecting more prominently from tlu: line of the body ; capped }»roximally by the adductor tubercle, it affords attachment near its most prominent point to the fibres of the tibial collateral ligament of the knee-joint. The epicondylus lateralis (lateral epicondyle), less pronounced and lying more in line with the lateral surface of the body, is channelled behind by a curved groove, the distal rounded lip of which serves to separate it from the distal articular surface. This groove ends in front in a pit which is placed just distal to the most salient point of the tuberosity ; hereto is attached the tendon of the popliteus muscle, which, in the extended position o^ the joint, overlies the distal lip of the groove, which is often indented for it, but slips into and occupies the groove when the joint is flexed. Dorsal to the most prominent part of the lateral epicondyle, and just proximal to the pit for the attachment of the popliteus, the fibular collateral ligament of the knee-joint is attached, whilst proximal to that there is a circumscriljed area f<»r the origin of the tendinous part of the lateral head of the gastrocnemius muscle. Surface for the attacliiiieut of. tlie libular col- lateral ligament Groove for tendon of popliteus Fig. 242.- -DisTAi. End ok thk Jiiiiiir FEMiit (Lateral Side). 244 OSTEOLOGY. The articular surface on the distal extremity is divisible into three parts — that which corresponds to the distal surface of the body and is formed by the coalescence of the two condyles in front ; and those which overlie the distal and posterior aspects of each of those processes. The former is separated from the latter by two shallow oblique grooves which traverse the articular surface from before backwards, on either side, in the direction of the anterior part of the intercondyloid fossa. These furrows are the impressions in which fit the anterior parts of the medial and lateral menisci of the knee-joint, respectively, when the knee-joint is extended. The anterior articular area or patellar surface is adapted for articulation with the patella. Convex proximo-distally, it displays a broad and shallow central groove, bounded on either side by two slightly convex surfaces. Of the two sides, the lateral is the wider and more prominent, and rises on the front of the bone to a more proximal level than the medial, thus tending to prevent lateral dislocation of the patella. The condylar or tibial surfaces are convex from side to side, and convex from before backwards. Sweeping round the distal surface and posterior extremities of the condyles, they describe a spiral curve more open in front than behind. The medial condylar articular surface is narrower than the lateral, and when its distal aspect is viewed it is seen to de- scribe a curve around a vertical axis. Along the lateral edge of this, and in front, where it bounds the intercondyloid fossa, is a semilunar articular area, best seen when the bone coated with cartilage. Patellar surface POPLITEAI GROOVI; Impression of medial meniscus Semilunar facet for medial edge of patella in extreme flexion Medial tibial surface IS Lateral TIBIAL SCEFACE Lateral condyle Iktercondyloid fossa Medial condyle Surface of attachment of posterior cruciate ligament Fig. 243. — Distal Aspect ok Distal End of the Right Femcr. This articulates with the medial edge of the patella in extreme flexion of the joint. The articular sur- face of the lateral con- dyle is inclined obliquely from before backwards and slightly laterally. The surfaces of the condyles proximal to the articular area posteriorly are continuous with the popliteal surface of the shaft. The area from which the medial head of the muscle springs is often elevated in the form of a tubercle placed on the distal part of the popliteal surface of the body, just proximal to the medial condyle. The proportionate length of the femur to the body height is as 1 is to 3 -5 3-3 '9 2. Arterial Foramina. — Numerous vascular canals are seen in the region of the neck, at the bottom of the trochanteric fossa, in the fossa for the ligaraentitm teres, on the inter- trochanteric crest, and on the lateral surface of the greater trochanter. The nutrient arteries for the body pierce the bone in a proximal direction on or near the linea aspera. Both the back and the front of the distal end of the liody display the openings of numerous vascular canals, and the floor of the intercondyloid fossa is also similarly pierced. Connexions.— The femur articulates with tbe hip bone proximally and the tibia and patella distally. The lateral surface of the greater trochanter determines the point of greatest hip width in the male, being covered only by the .skin and superficial fascia and the aponeurotic insertion of the gluteeus maximus. In the erect position the tip of the trochanter corresponds to the level of the centre of the hip-joint. When the thigh is flexed the trochanter major sinks under cover of the anterior fibres of the glutseus maximus. In women the hip width is usually greatest at some little distance distal to the trochanter, due to the accumulation of fat in this region. The body of the bone is surrounded on all sides by muscles. Its forward curve, however, is account- able to some extent for the fulne.S3 of the front of tlie thigh. T}i,e exposed surfaces of the condyles determine to a large extent the form of the knee. In flexion the articular edges can easily be recognised on either side of and distal to the patella. Sexual Differences.— According to Dwight, the head of the femur in the female is propor- tionately smaller than that of the male. Ossification. — The body begins to ossify early in the second month of foetal life, and at birth displays enlargements at both ends, which are capped with cartilage. If at birth the distal cartilaginous end be sliced away, a small ossific nucleus for the distal epiphysis will usually be seen. This, as a rule, makes its appearance towards the latter end of the ninth THE PATELLA. 245 Appears about parly part of tlrst year Fuses with slittfl about 18-ly years month of foetal life, and is of service fifem a niedico-legal standpoint in detonniniiig tlie a"e of the fa'tns. Accordinjj; to Hartman, it is absent in about 12 per cent, of children at term, and may appear as early as the eighth month of foetal life in about 7 per cent. The proximal extremity, entirely cartilaginous at birth, com- prises the head, neck, and ti'ochanter major. A centre appears for the head during the early part of the first year. It is worthy of note § that this epiphysis has a g double blood -supply — one through the neck, the other through the ligaftientum teres. That for the tro- chanter major begins to ossify about the second or third year, whilst the neck is developed as a proximal extension of the body, which is, however, not confined to the neck alone, but forms the distal circmuference of the articular head, as may be seen in bones up to the age of twelve or sixteen ; after that, the separate epi- physis of the head begins to overlap it so as to cover it entirely when fusion is com- plete at the age of eighteen or twenty. The epiphysis of the greater trochanter unites with the body and neck about eighteen or nineteen, whilst the epiphysis for the trochanter minor, which usually makes its appearance about the twelfth op- thirteenth year, is usually completely fused with the body about the age of eighteen. The epiphysis for the distal end, although the first to ossify, is not completely united to the body until from about the twentieth to the twenty-second vear. It is worthy of note that the line of fusion of the body and distal epiphysis passes through the adductor tubercle, a point which can easily be determined in the livino'. The distal end is the so-called "growing end of the bone." Usually appears i the 0th month of foetal life At birth. Fuses with shaft abotr About 12 years. About 16 years. Fig. 244. — Ossification of the Femuk. The Patella. The patella, the largest of the sesamoid bones, overlies the front of the knee- joint in the tendon of the quadriceps extensor. Of compressed form and somewhat triangular shape, its distal angle forms a peak, called the apex patellae, whilst its proximal edge, or base (basis patellae), broad, thick, and sloping forwards and a little distally, is divided into two areas by a transverse line or groove ; the anterior area so defined serves for the attachment of the common tendon of the quadriceps extensor muscle, whilst the posterior, of com- pressed triangular shape, is covered with synovial membrane. The medial and lateral borders, of curved outline, receive the insertions of the vastus medialis and lateralis muscles, respectively, the attachment of the vastus medialis being more extensive than that of the vastus lateralis. The anterior siirface of the bone, slightlv convex in both diameters, has a fibrous appearance, due to its longitudinal striation, and is pierced here and there by the openings of vascular canals. Oftentimes at the superior lateral angle there is a well-defined area for the tendinous insertion of the vastus lateralis. The posterior or artictdar swrface is di^dded into two unequal parts (of which the lateral is the wider) by a vertical elevation which glides in the furrow of the patellar surface of the femur, and in extreme flexion passes to occupy the intercondyloid fossa. The lateral of the two femoral surfaces is slightly concave in both its diameters; the medial, though slightly concave proximo -distally, is 246 OSTEOLOaY. Fig. 245, A. Anterior Surface. Surface for the ligainentum patellse -The Right Patella. B. Posterior Surface. usually plane, or somewhat convex transversely. Occasionally, in the macerated bone, indications of a third vertical area are to be noted along the medial edge of the posterior aspect. This defines the part of the articular surface which rests on the lateral border of Lateral articular facet ^|^g medial COudylc in - extreme flexion. In the recent condition, when the femoral sur- face is coated with cartilage, a more com- plex arrangement of facets may be in some cases displayed (as in- dicated in Fig. 244). Lamont (Journal of Anat. and Physiol., 1910, vol. xliv. p. 149) has shown that these areas undergo con- siderable variation in their arrangement in races who habitually adopt the squatting posture. Distal to the femoral articular area the posterior surface of the apex is rough and irregular ; the greater part of this is covered with synovial membrane, the liga- mentum patellae being attached to its summit and margins, reaching some little distance round the borders on to the anterior aspect of this part of the bone. . Ossification. — The patella is laid down in cartilage about the third month of foetal life. At birth it is cartilaginous, and the tendon of the quadriceps is continuous. with the ligamentum patellae over its anterior surface, and can easily be dissected off. About the third year an ossific centre appears in it and spreads more particularly over its deeper surface. Two centres, vertically disposed, have also been described. Ossification is usually com- pleted by the age of puberty. The Tibia. The tibia is the niedial, bone of the leg. It is much stouter and stronger than its neighbour the fibula, with which it is united proximally and distally. By its proximal expanded ex- t-rpnn't-v ii- Qin-,r>nvfa f>ia Surface for attachment of antciior Tuberosity (O.T. Tubercle) Cremity it SUppOltS tne extremity of n.pdial mon.scus condyles of the femur, Anterior c ruciate ligament while distally it shares EMiNENTra- ^, „ '' . „ , INTERCONDYLOIDPA^ m the tormation oi the ankle-joint, articulat- ing with the proximal surface and medial side of the talus. The proximal ex- tremity comprises the medial and lateral con- dyles (O.T. tuberosities), the intercondyloid emi- nence (O.T. spine), and the tuberosity. Each condyle is provided on its ]3i't)ximal aspect with an articular surface (facies articularis superior), which supports the corresponding femoral condyle, as well as the interposed meniscus. Of these two condylic surfaces the medial is the larger. Of oval shape, its long axis is placed antero-posteriorly ; slightly concave from before backwards and from side to side, its circumference rises in the form of a sharp and well-defined edge. The lateral condylic surface is smaller and rounder. Slightly concave from side to side, and gently convex from before backwards, its circumfer- Surf. for attachment of ant. extremity of lateral meniscus Synovial coveui SURFACE Surface for attach, of post. extrem. of medial iiKiiiiscus I'll.STERlOB inter- condyloid FOSSA .Post, cruciate lie face for attach, of post, extremity of lateral meniscus Fig. 246. -Thk Proximal Suhkace ok the Proximal Extremity OK thk Right Tibia. THE TIBIA. 247 eiufe is well detiued iu t'ruut, but iS; the convexity of its posterior part. Between the two condylic surfaces the bone is raised in the centre to form the intercondyloid eminence whicli consists of two intercondyloid tubercles separated by an oblique groove, in the anterior part of whicli lies the anterior cruciate ligament. The metlial tubercle (tuberculum intercondyloideum mediale), the higher, i.s |irolonged backwards and laterally by an oblique ridge to which part of the posterior cornu of the lateral meniscus is attached. The lateral tubercle (tuberculum intercondyloideum laterale) is more pointed and notsoelevated. In front of and behind the intercondyloid eminence tlie articular areas are separated by two irregular V-shaped surfaces, the intercondyloid fossae. The anterior intercondyloid fossa, the larger and wider, furnishes areas for the attachment of the menisci on either side, and for the anterior cruciate ligament immediately in front of the intercondyloid emin- ence. The floor of this space is pierced by many nutrient foramina. The posterior intercondyloid fossa is concave from side to side, and slopes downwards and backwards. The lateral meniscus is attached near its apex to a surface which rises uu to the back of the inter- condyloid eminence ; the medial meniscus is flxed to a groove which runs along its medial edge^ and the posterior cruciate ligament derives an attachment from the smooth posterior rounded surface. The lateral condyle is tlie smaller of the two. It overhangs the Vtody to a greater extent than the medial, though this is obscured in the living by its articulation with the fibula. The facet for the fibula, often small and indistinct, is placed postero- laterally on the distal surface of its most projecting part. Antero-lateraUy the imprint caused by the attachment of the trachis iliotibialis (O.T. ilio-tibial band) is often quite distinct. Curv- ing distally and forwards from the fibular facet there is often a definite ridge for the attachment of the expansion of the biceps tendon ; rounded off behind, thus markedly increasing Tntctus ilidtlbialjr, iNTKRfONDYI.OID KMINKNc K I.ATEKAI. V J \ ^W^^^ ■OSUYI.K JlLi\i , ■HiTiTiBIl Intkrosseous CREST" Posterior part of medial. Sl'RFAi-K Anterior part ok MEDIAL Sl'RFACE .■>UBCUTANEOVs SURFACE Fio. 247. — The Rnmi Tibia and Fibula as seen FROM THE FRONT. The anterior part of the medial .snrf.-tce of the fibula is coloured blue. The posterior part of the medial surface of the fibula is coloured red. The lateral or peroneal surface of the fibula is left uncoloured. 248 OSTEOLOGY. Fibular collateral ligament of knee Sartorius Gracilis distal to this the areas for the origins of the perouteus longiis and extensor digitorum longus are often crisply defined. The circumference of the medial condyle is grooved postero-medially for the insertion of the tendon of the semi-membranosus. In front of the condyles, and about an inch distal to the level of the condylic sur- faces, there is an oval elevation called the tuljerosity of the tibia. The proximal half of this is smooth and covered by a bursa, while the distal part is rough and serves for the attachment of the hgamentum patellae. Considered in its entirety, the proximal extremity of the tibia is broader transversely than antero-posteriorly, and is inclined backwards so as to overhang the shaft posteriorly. The corpus tibiae (body) is irregularly three-sided, possessing a medial, a lateral, and a posterior surface, separated by an anterior crest, a medial margin, and a lateral or interosseous crest. It is narrowest about the junction of its middle and distal thirds, and expands proximally and distally to support the extremities. Eunning along the front of the bone there is a gently-curved, prominent margin, the crista anterior, confluent proximally with the tuberosity, but fading away distally on the anterior surface of the distal third of the bone, where it may be traced in the direc- tion of the anterior border of the medial malleolus. This is the anterior crest or shin, which is subcutaneous throughout its entire length. To the medial side of this is a smooth, slightly convex semitendinosus surface, which reaches the medial condyle proximally, and distally becomes con- tinuous with the medial sur- face of the medial malleolus. This is the medial or sub- cutaneous surface of the body, which is covered only by skin and superficial fascia, except in its proximal fourth, where the tendons of the sartorius, gracilis, and semitendinosus muscles overlie it, as they pass towards their insertions. This surface is limited posteriorly by the medial margin, which passes from the medial and distal surface of the medial condyle proximally to the posterior border of the medial malleolus distally. This margin is rounded and indefinite proximally and distally, being usually best marked about its middle third. To the lateral side of the anterior crest is the lateral surface of the bone ; it is limited behind by a straight vertical ridge, the crista interossea (interosseous crest), to which the interosseous membrane, which occupies the interval between the tibia and the fibula, is attached. This ridge commences near the middle of the lateral and distal surface of the lateral condyle, and terminates about two inches from the distal extremity by dividing into two linesi, which separate and enclose between them the surface for articulation with the distal end of the fibula, and the area of attachment of the interosseous ligament, which here unites the two bones. ^ In its proximal two-thirds the lateral surface provides an extensive origin for the tibialis anterior. Distally, where the anterior crest is no longer well defined, the lateral surface turns forwards on to the front of the body, and is limited by the anterior margin of the distal articular surface. Over this the tendon of the tibialis anterior, and the combined fleshy and tendinous parts of the extensor hallucis proprius and extensor digitorum longus muscles pass obliquely distally. The posterior surface of the body lies between the interosseous crest laterally and the medial margin on the medial side. Its contours are liable to considerable variation according to the degree of side to side compression of the bone. It is usually full Fig. 248. — Anteukjr aspect of the Proximal Portions of the Bones of the Right Leg with Attachments of Muscles MAPPED out. THE TIBIA. 249 and rounded proxiinally, and flat distally. Proxinially it is crossed by the linea poplitea. (popliteal line), which runs distally and medially, from the fibular facet to the medial border on a level with the junction of the middle with the proximal third of the body. To this line tlie deep transverse fascia is attached, whilst distal to it, as well as from the medial border of the bone distally, the soleus muscle takes origin. Into the bulk of the triangular area proximal to it the popliteus muscle is inserted. Arising from tlie middle of the popliteal line there is a vertical ridge, which passes distally and divides the posterior aspect of the body into two surfaces — a lateral for the tibial origin of the tibialis posterior muscle, and a medial for the flexor digitorum longus muscle. The distal third of this surface of the body is free from muscular attachments, but is overlain by the tendons of the aljove muscles, together with that of the flexor hallucis longus. A large nutrient canal, having a distal direction, opens on the posterior surface of the l)0(ly a little distal to the popliteal line and just lateral to the vertical ridge which springs from it. The distal extremity of the tibia displays an expanded quadrangular form. It is furnished with a saddle-shaped articular surface on its distal surface (fades articularis inferior), which is concave from before backwards and slightly convex from side to side. This rests upon the upper articular surface of the body of the talus, and is bounded in front and behind by well-defined borders. The anterior border is the rounder and thicker, and is oftentimes channelled by a groove for the attachment of the anterior ligamen t of the joint ; further, it is occa- sionally provided with a pressure facet caused by the locking of the bone against the neck of the talus in extreme flexion. Laterally the edge of the articular area corresponds to the base of the triangle formed by the splitting of the interosseous ridge into two parts. Where these two lines join it, both in front and behind, the bone is elevated into the form of tubercles, in the hollow between which (incisura fibularis) the^ distal end of the fibula is lodged, being held in position by powerful ligaments. The cartilage-covered surface occasionally extends for some little distance proximal to the base of the triangle. Medially there is a process projecting distally, and called the medial malleolus, the medial aspect of which is subcutaneous and forms the projection of the medial ankle. Its lateral surface is furnished with a piriform facet (fades articularis malleolaris), confluent with the cartilage- covered area on the tarsal surface of the distal extremity ; this articulates with a corresponding area on the medial surface of the body of the talus. Distally the malleolus is pointed in front, but notched behind for the attachment of the deltoid or tibial collateral ligament of the ankle. Running obliquely along the posterior surface of the malleolus there is a broad groove (sulcus malleolaris) in which the tendons of the tibialis posterior and flexor digitorum longus muscles are lodged ; whilst a little to the fibular side of this, and running distally over the posterior surface of the distal extremity of the bone, there is another groove, often faintly marked, for the lodgment of the tendon of the flexor hallucis longus muscle. The proportionate length of the tibia to the body height is as 1 is to 4'32-4-80. Arterial Foramina. — Nutrient canals are seen piercing the proximal extremity of the bone around its circunit'erence and proximal to the tuberosity. The floors of the intercondyloid fossae are also similarly pierced, and there is usually a canal of large size opening on the summit of the intercondyloid eminence. Two or three foramina of fair size are seen running pruximally into the substance of the bone a little distal to and to the medial side of the tuberosity, while the principal vessel for the Viody passes distally into the bone on its posterior surface, about the level of the junction of the proximal and middle thirds. The medial surface of the medial malleolus, as well as the anterior and posterior borders of the distal extremity, are likewise pitted by the orifices of small vascular channels. Connexions. — Proximally the tibia supports the condyles of the femur, and is connected in front with the patella by means of the patellar ligament. Articulating laterally with the fibula proximally and distally, it is united to that bone tTiroughout nearly its entire length by the inter- osseous membrane. The anterior crest and medial surface can be readily examined, as they are subcutaneous, except proximally, where the medial surface is overlain by the thin tendinous aponeuroses of the muscles passing over the medial side of the knee. The form of the distal part of the knee in front is determined by the condyles on eitlier side crossed centrally by the Hga- mentum patellae. Distally the medial malleolus forms the projection of the medial ankle, which is wider, not so low, less pointed, and extends further forwards than the projection of the lateral 250 OSTEOLOGY. ankle. The front and back of the distal end of" the bone are crossed by tendons, which mask to a certain extent its form. Ossification. — The body begins to ossify early in the second month of intra-uterine life. At birth it is well formed, and capped proximally and distally by pieces of cartilage, in the proximal of which the centre Fuses with shaft about 20-24 years May appear Appears independently before birth about 11 a ears Appears about li years Fuses about ISth yeai At birth. About 12 years. About 16 year.' Fig. 249. — Ossification of the Tibia. for the proximal epiphysis has al- ready usually made its appearance. From this the condyles and tuber- osity are developed, though some- times an independent centre for the latter appears about the eleventh or twelfth years, rapidly joining with the already well-developed mass of the rest of the epiphysis. Complete fusion between the proximal epi- physis and the body does not take place until the twentieth or the twenty-fourth year. The centre for the distal articular surface and the medial malleolus makes its appear- ance about the end of the second year, and union with the shaft is usually complete by the age of eighteen. Lambertz notes the occa- sional presence of an accessory nucleus in the malleolus. The prox- imal end is the so-called "growing end of the bone." The Fibula. The jBbula is a slender bone with two enlarged ends. It lies to the lateral side of the tibia, with which it is firmly united by ligaments, and nearly equals that bone in length. The first difficulty which the student has to overcome is to determine which is the proximal and which the distal extremity of the bone. This can easily be done by recognising the fact that there is a deep pit on the medial aspect of the distal extremity immediately behind the triangular articular surface. Holding the bone vertically with the distal extremity downwards and so turned that the triangular articular area lies in front of the notch already spoken of, the subcutaneous non-articular aspect of the distal extremity will point to the side to which the bone belongs The proximal extremity or head of the fibula (capitulum fibulae), of irregular rounded form, is bevelled on its medial surface so as to adapt it to the form of the distal surface of the lateral condyle of the tibia. At the border where this surface becomes confluent with the lateral aspect of the head there is a pointed upstanding eminence called the apex capituli fibulae ; to this the short fibular collateral ligament is attached, as well as a piece of the tendon of the biceps, which is inserted into its anterior part. Immediately to the medial side of this, and occupying the summit of the medial sloping surface, there is an articular area (facies articularis capituli), of variable size and more or less triangular shape. This area articulates with the lateral condyle of the tibia. The long fibular collateral ligament, together with the remainder of the tendon of the biceps muscle which surrounds it, is attached to the lateral and proximal side of the head in front of the apex capituli. On the front and the back of the head there are usually prominent tubercles. The anterior of these is associated with the origin of the peronjBus longus muscle ; the posterior furnishes an origin for the proximal fibres of the soleus, and serves to deepen the groove, behind the proximal tibio-fibular joint, in which the tendon and fleshy part of the popliteus muscle play. The constricted portion of the body distal to the head is often referred to as the neck ; around the lateral side of this the common peroneal nerve winds. THE FIBULA 251 IDSUYLK Sl'RFAC'H Intkuconpyi.oih KmIN'ICNCK i.atkhal condylk Sl'UKAl Popliteal NOTCH Apkx oi- •riiK hkai> 'J'he body of the fibula (corpus : fibulae) presents many varieties in the details of its shape and form, being ridged and channelled in such a way as greatly to increase the difficulties of the student in recognising the various surfaces described. It is described as possessing three surfaces, named the lateral, the inedial, and the l>OHterior. The surfaces are separ- ated from one another by three borders or crests, named medial, lateriil, and anterior; and, in addition, the medial surface is traversed longitudinally by a ridge called the Interosaeoun credit, which divides it into an anterior and a posterior part. The most important point is first to de- termine the position of the rorLITEAI. I. INK Lai KRAI- CREST INTEROSSEOI'S CREST MrniAI. BORDER Posterior surface o J ° g < z S u 2 ^ a 5: f- ? o c 2 f. c 3 - .Mediai MALLEOLrs' Lateral SURFACE W Tali.s ^'^WlJ FOR/ ^^Kh ^ — iROOVE FOR i:ndons OF KROX.tUS >)N01S AND REVIS Groove for^ flexor halluci8 LONG US Fig. 250.— The Right Tibia and Fibdla sekn krom BEHIND. The Posterior surface of the fibula is coloured red hitoral surface is left uncol^ured. Lateral malleolus the SEM IM KM BRAMOSUS Tibialis posterior Flexor hallucis lonhus Pkron.eis i.ongus and brevis Fifi. 251. — Posterior aspect of the Bones of the Leg with Attach- ments OF Muscles mapped out. 252 OSTEOLOGY. Apex capituli FArET FOR TIBIA- Head- Neck- IXTEROSSEOUS CREST Nutrient foramen (in tliis case directed proximally) ixterosseous_ ceest" . Roi;gb surface FOR inter- osseous" ligament Facet for tai.us_ £ <« o -S - tj) =5 • Latkbal' malleolus Fig. 252. — Right Fibdla as seen from the medial side. The anterior part of tlie medial surface is coloured blue ; the posterior part of the medial surface is coloured red. anterior crest. If the bone is held in the position which it normally occupies in the leg, it will be noticed that the lateral surface of the distal extremity is limited in front and behind by two lines, which converge and enclose between them a triangular subcutaneous area which lies immediately proximal to the lateral malleolus. From the summit of the triangle so formed a well- defined ridge may be traced along the front of the body to reach the anterior aspect of the head. This is the anterior crest. The interosseous crest, so named because the inter- osseous membrane is attached to it, is the ridge which lies just medial to the anterior crest, or towards the tibial side on the anterior aspect of the bone. It is not so prominent as the anterior crest, and it extends from the neck of the bone to the apex of a rough triangular impression that lies proximal to the articular surface on the medial aspect of the distal end. The interval between the anterior and interosseous crests is the anterior part of the medial surface. This interval is, as a rule, of considerable width in the distal half of the bone, but the two crests tend to run much closer together proximally ; indeed, it is not uncommon to find that they coalesce to form a single crest. The posterior part of the medial surface is the elongated area behind the proximal three-fourths or four-fifths of the interosseous crest. It is limited posteriorly by the medial crest, a sharp, salient ridge, which commences at the medial margin of the posterior aspect of the head, but does not reach the distal end of the bone ; for the distal end of the medial crest curves forwards and joins the interosseous crest about three or four inches from the distal extremity of the body ; therefore, the posterior part of the medial surface is not represented in the distal part of the body. On the proximal third of this surface there is frequently found an oblique ridge which begins near the interosseous crest at the level of the neck and extends distally and backwards to join the medial crest. When the proximal part of the medial crest is indistinct this ridge may be mistaken for it. The lateral surface, which is separated from the medial surface by the anterior crest, is often hollowed out in its middle part, and it is twisted, so that its proximal part is directed somewhat forwards, while its distal part turns backwards and becomes continuous distally with the broad, shallow groove which occupies the posterior surface of the lateral malleolus. The lateral surface is limited posteriorly and separated from the posterior surface of the body by the lateral crest, which is usually sharp and well defined except at its extremities, where it tends to become smooth and rounded. Its proximal end joins the head distal to and in front of the apex capituli, and terminates distally at a point just proximal to the pit on the medial surface of the distal extremity. In its proximal third or fourth the lateral crest is often rough where fibres of the soleus muscle arise from it. The posterior surface forms the remainder of the THE FIBULA. 253 boily. It is tlie district bduiided laterally by tlu'. lateral crest aud medially by the medial crest and the distal fourth or fifth of the interosseous crest. It is twisted in the Humede^'ree as the lateral surface ; and, therei'ore, while its proximal part is directed backwards, its distal part is directed medially and is in line with the medial surface of the malleolus. The Jiutrient foramen is situated on the posterior surface, at or near tlie middle of th(^ body near the medial crest, and is directed towards the distal end of the bone. The anterior crest gives attachment to the anterior intermuscular septum, and, at its distal end, to the ligamentum traiisversum cruris, while the posterior inter- muscular septum is attached to the lateral crest. These septa »Miclose the peroneus lougus and brevis muscles, which arise iiom the lateral or peroneal anrface, and separate them iiom the muscles on the front and the })ack of the leg. 'J"he inter- osseous membrane is attached to the whole length of the interosseous crest. The anterior part of the medial surface provides origin for the extensor halluciis, the extensor digitorum longus and the peroneus tertius; while the tibialis posterior arises from tlie jwsterior part of the medial surface. The medial crest is the fibular attachment of a strong sheet of fascia which covers the tibialis posterior, and separates it from the flexors of the toes. The soleus nmscle arises from the }>roximal third of the j^osterior surface, while the flexor hallucis longus takes origin from its distal two-thirds. The distal extremity of the fibula, or lateral malleolus, is of pyramidal form. Its medial surface is furnished with a triangular articular area (fades axticularis malleoli), plane from before backwards, and slightly convex proximo- distally, which articulates with a corresponding surface on the lateral side of the body of the talus. Behind this there is a deep pit, to which the posterior talo-fibular ligament is attached. Proximal to the articular facet there is a rough triangular area, from the summit of which the interosseous crest arises ; to this are attached the strong fibres of the distal interosseous ligament which binds together the opposed surfaces of the tibia and fibula. The lateral surface of the distal extremity forms the elevation of the lateral malleolus which determines the shape of the projection of the lateral ankle. Rounded from side to side and proximo- distally, it terminates in a pointed process, which reaches a more distal level than the corresponding process of the tibia, from which it also differs in being narrower and more pointed and being placed in a plane nearer the heel. Proximally, this surface, which is subcutaneous, is continuous with the triangular subcutaneous area so clearly defined by the convergence of the lines which unite to form the anterior crest. The anterior border and tip of the lateral malleolus furnish attachments to the anterior talo-fibular and calcaneo - fibular ligaments. The posterior surface of the lateral malleolus, broad proximally, where it is confluent with the lateral or peroneal surface, is reduced in width distally by the presence of the pit which lies to its medial side. This aspect of the bone is grooved (sulcus malleolaris) by the tendons of the peronseus longus and brevis muscles, which curve round the posterior and distal aspects of the malleolus. The proportionate length of the fibula to the body height is as 1 is to 4-37-4"82. Arterial Foramina. — Numerous minute vascular canals are seen piercing the lateral surface of the head, and one or two of larger size are seen on the medial surface immediately anterior to the Sro.xinial articular facet. The canal for the nutrient artery of the body, which has a distal irection, is .situated on the posterior surface of the bone about its middle. The lateral surface of the lateral malleolus displays the openings of many small canals, and one or two larger openings are to be noted at the bottom of the pit behind the distal articular surface. Connexions. — The head and lateral malleolus, and part of the Ixxly immediately proximal to the latter, are subcutaneous. The remainder of the l)ody is covered on all sides by the muscles which surround it. Proximally the l)one plays no part in the formation of the knee-joint, but distally it assists materially in strengthening the ankle-joint by its union with the tibia and its articulation with the talus. In position the bone is not parallel to the axis of the tibia, but oblique to it, its proximal extremity lying posterior and lateral to a vertical line passing through the lateral malleolu.-5. Ossification. — The body begins to ossify about the middle of the second month of foetal life. At the end of the third month there is but little difference in size between it and the tibia, aud at birth the fibula is much larger in proportion to the size of the 254 OSTEOLOGY. tibia than in the adult. Its extremities are cartilaginous, the distal extremity not being as long as the medial malleolar cartilage of the tibia. It is in this, however, that an ossific centre first appears about the end of the second year, which increases rapidly in size, and unites with the body in about nineteen years. The centre for the proximal epiphysis begins to ossify about the third or fourth year, and union with the body is not complete until a period somewhat later than that for the distal epiphysis. The mode of ossification of the distal extremity is an Appears about xS^sv Fuses with shaft ,. ,,1. 1 ij.ij.-i_ 3-4 years /^?^f^ about 20-24 years exception to the general rule that epiphyses which are the first to ossify are the last to unite with the body. This may possibly be accounted for by the fact that the distal end is functionally more important than the rudimentary proximal end, since in man alone, of all vertebrates, does the lateral malleolus reach beyond the level of the medial malleolus. Its early union with the body is doubtless required to ensure the stability of the ankle-joint necessitated by the assumption of the erect position. In its earlier stages of development it has been stated, on the authority of Leboucq, Gegenbaur, and others, that the fibula as well as the tibia is in contact with the femur. This is, however, denied by Grimbaum (" Proc. Anat. Soc," Journ. Anat. and Physiol, vol. xxvi. p. 22), who states that after the sixth week the fibula is not in contact with the femur, and that prior to that date it is impossible to dift'erentiate the tissue which is to form femur from that which forms fibula. Appears about 2nd year At birth. Fuses with shaft about 19 years About About 12 years. 16 years. BONES OF THE FOOT. Fig. 253. — Ossification of Fibula. The bones of the foot, twenty -six in number, are arranged in three groups : the tarsal, seven in number ; the meta- tarsal, five in number ; the phalanges, fourteen in number. Comparing the foot with the hand, the student will be struck with the great j^'oportionate size of the tarsus as compared with the car j) us, and the reduction in size of the bones of the toes as compared with the fingers. The size of the meta- tarsal segment more nearly equals that of the metacarijus. The Tarsus. The tarsus consists of seven bones (ossa tarsi) — the talus or astragalus, calcaneus, navicular or scaphoid, three cuneiforms, and the cuboid. Of irregular form and varying size, they may be described as roughly cubical, presenting for examination dorsal and plantar surfaces, as well as anterior, posterior, medial, and lateral aspects. The Talus. The talus (O.T. astragalus) is the bone through which the body weight is tran.smitted from the leg to the foot. Proximally the tibia rests upon it, whilst on either side it articulates witli the medial and lateral malleolar processes of the tibia and fibula respectively ; inferiorly it overlies the calcaneus, and anteriorly it articulates with the navicular. For descriptive purposes the bone is divisible into three j)arts — the corpus tali (body) blended in front with the collum tali (neck), which supports the caput tali (head). The dorsal surface of the body is provided with a saddle-shaped articular surface (trochlea tali), broader in front than behind, for articulation with the distal surface of the tibia. The medial edge of the trochlea is straight ; whilst the lateral border, which is sharp in front and more rounded behind, is curved medially pos- teriorly, where it is f)evelled to form a narrow, elongated, triangular facet, which is in contact with the transverse or distal tibio-fibular ligament during flexion of the ankle. (Fawcett, 7iVZ. Med. Journ., 1895.) Over the lateral border the cartilage- covered surface is continuous laterally with an extensive area of the form of a quadrant. This is concave from above downwards, and articulates with the medial THE TALUS. 255 surface of the lateral malleolus. The distal augle of this area is ]»roiiiinent and somewhat everted, and sometimes referred to as the processus lateralis tali (lateral process). The medial aspect of the body has a comma- shaped facet, confluent with the dorsal articular surface, over the medial edge of the trochlea ; this Surface of talus for articulation with tlbula Cuboid Surface of talus lor iticulation witli tibia Navicular V. Metatarsal Third "j Second v Cuneiforms First I — I. Metatarsal ' J— Sesamoid bone Third or terminal phalanx Fxo. 254. — DoHSAL Sukface ok the Boxes of the Right Foot. articulates with the lateral surface of the medial malleolus. Below this facet the bone is rough and pitted by numerous small openings, and just below the tail of the comma there is a circular impression for the attachment of the deep fibres of the deltoid ligament (talo-tibial fibres). On the plantar surface of the body- there is a deep concave facet, called the posterior calcanean facet (facies calcanea 256 OSTEOLOGY. articularis posterior), which is of more or less oval or oblong form and is placed obliquely from behind forwards and laterally ; this rests upon a corre- sponding surface on the dorsal aspect of the calcaneus. In front of this, and crossing the bone from the medial side laterally and forwards, is a deep furrow (sulcus tali), Calcaneus SCISTEKTACULUM TALI Surface of talus blue rests on the plauta calcaneo-navicula ligamen Navicular First cuneiform I. Metatarsal Sesamoid bone First or Proxi- mal phalanx Cl BOID Second cuneiform Third cuneiform V. Metatarsal Seconi PHALANX' Third or terminal phalanx Fig. 25.'). — Plantar Surkace of the Bones of the Right Foot. the floor of which is pierced by numerous large canals. It serves for the attach- ment of the strong interosseous ligament which unites the talus with the calcaneus, and separates the facet already described from a smaller oval articwlar area having a slightly convex surface, which lies immediately in front of it. This is called the middle calcanean facet (facies articularis calcanea media), and articulates with THE TALUS. 25^ the dorsal surface of the sustentaculum tali of the calcaneus. Tosteriorly the body is provided with two tu})ercles, sejiarated by a groove; tbe lateral of these (processus posterior tali) is usually the larger, and is occasionally a separate ossicle (OS trigonum). To it is attached the posterior talo-fibular ligament of the ankle- joint. The groove, which winds obliquely from above downwards and medially over the posterior surface of the bone, lodges the tendon of the flexor hallucis longus muscle. The head, of oval form, is directed forwards and medially. Its anterior surface Abductor ili^;iU iniinti (ori;,'in) Qu.iilratus plantae (origin) Loiif; ;iiilantar ( liKiinii'iits 1 Tibialis posterior (])art ot insertion) Peronanis brevis (insertion) Flexor digiti quint i brevis (origin) Oblique head of abi(M the edges of which are striated. I»to this surface the tendo calcaneus is inserted. The lowest surface is rough and striated, and is conHuent below with the medial and lateral processes; this is overlain by the dense layer of tissue which forms the pad of the heel. Os Navicularc Pedis. The navicular bone (U.T. scaphoid), of compressed piriform shape, is placed on the medial side of the foot, between the head of the talus posteriorly and the three cuneiform bones anteriorly. The bone derives its name from the oval or boat-shaped hollow on its posterior surface, which rests upon the head of the talus. Its anterior aspect is furnished with a semilunar articular area, which is sub- divided by two faint ridges into three wedge-shaped facets for articulation, niedio-laterally, with the first, second, and third cuneiform bones. The dorsal surface of the bone, convex from side to side, is rough for the attachment of the liga- ments on the dorsal aspect of the foot. On its plantar aspect the bone is irregularly con- cave ; projecting down- wards and backwards from its lateral side there is often a pro- minent spur of bone, the plantar process, to which is attached the plantar calcaneo-navicular ligament. The lateral surface is narrow from before backwards, and rounded from above downwards. In 70 per cent, of cases (Manners Smith) it is provided with a facet which rests upon a corresponding area on the cuboid. Behind this, in rare instances, there is a facet for the calcaneus. The medial surface of the bone projects beyond the general line of the medial border of the foot, so as to form a thick rounded tuberosity (tuberositas ossis navicularis), the position of which can be easily determined in the living. To the medial and plantar suriace of this process an extensive portion of the tendo n of the ti bialis po sterior mus cle is inserted. Ti'BKKOsiTY For head ok Pl.ANTAK I'UOI'KSS TALU.S Plantar Proiess TlBEROSITY Fio. 261. — The Right Navicular Bone. A. Seen from behind. B. Seen from the front. The Cuneiform Bones. The cuneiform bones, three in number, are placed between the navicular posteriorly and the bases of the first, second, and third metatarsal bones anteriorly, for which reason they are now named the first, second, and third cuneiforms (O.T. internal, middle, and external). More or less wedge-shaped, as their name implies, the first is the largest, whilst the second is the smallest of the group. Combined, they form a compact mass, the posterior surface of which, fairly regular in outline, rests on the anterior surface of the navicular; whilst anteriorly they form a base of support for the medial three metatarsals, the outline of which is irregular, owing to the base of the second metatarsal bone being recessed between the first and third cuneiforms, as it articulates with the anterior surface of the shorter second cuneiform. The first cuneiform bone, the largest of the three, lies on the medial border of the foot between the l)ase of the metatarsal bone of the great toe anteriorly, and the medial part of the anterior surface of the navicular jiosteriorly. In form the bone is less characteristically wedge-shaped than its fellows of the same name and differs from them in this respect, that whilst the second and third cuneiforms are so disposed that the bases of their wedges are directed upwards towards the dorsum of the foot, the first cuneiform is so placed that its base is 262 OSTEOLOGY. II. Metatarsal /' III. Met^tars\l IT. Metatarsal Second cuneiform directed towards the plantar aspect ; further, the vertical diameter of the bone is not the same throughout, but is much increased at its anterior or metatarsal end. The dorsal and medial surfaces are confluent, and I. Metatarsal form a convexitj from above downwards, which is most pronounced inferiorly, where it is turned round the plantar side of the foot to become con- tinuous with the plantar or inferior aspect, which is rough and irregular. On the anterior part of the medial aspect of the bone there is usually a distinct oval impression, which indicates the surface of insertion of a portion of the tendon of the tibialis anterior muscle. Elsewhere this surface is rough for ligamentous attachments. The lateral surface of the bone, quadrilateral in Fig. 262.— Anterior Sorfaces^op the shape, is directed towards the second cunei- THREE Cuneiform Bones of the form ; but as it exceeds it in length, it also Right Foot. comes in contact with the medial side of the base of the second metatarsal bone. Eunning along the posterior and dorsal edges of this area is an r"-shaped articular surface, the anterior and dorsal part of which is for the base of the second metatarsal bone, the remainder articulating with the medial side of the second cuneiform. The non-articular part 'of this aspect of the bone is rough for the attachment of the strong inter- osseous ligaments which bind it to impression the second cunei- form and second metatarsal bones. The posterior sur- face of the bone is provided with a piriform facet which fits on the most medial articular area of the navicular.- Here the wedge-shaped form of the bone is best displayed. Anteriorly the vertical diameter of the bone is much increased, and the facet for the base of the metatarsal bone of the great Thirl. CUNEIFORM ^^^ -^ consequently much larger than that for the navicular. This metatarsal facet is usually of semilunar form, but not infrequently is more reniform in shape, and may in some cases display complete separation into two oval portions. The second cuneiform is of a typical wedge shape, the base of the wedge being II. Metatarsal (ji^ected towards the dorsum of the foot ; Fig. 266.— The Right shorter than the others, it lies between (^Lateral skS^"'"'''' ^^®"'' articulating with the base of the second metatarsal in front, and the middle facet on the anterior surface. of the navicular behind. Its dorsal surface, which corresponds to the base of the wedge, conforms to the round- ness of the instep, and is slightly convex from side to side, affording attachments for the dorsal ligaments. Its plantar aspect is narrow and rough, forming the edge of the wedge ; with this the plantar ligaments are connected. The medial surface, quadrilateral in outline, is furnished with an r-shaped articular area along its posterior and dorsal borders in correspondence with the similar area on the lateral side of the first cuneiform. The rest of this aspect is rough for ligaments. I. Meta- tarsai FOR TENDON OF tibialis ANTERIOR Fig. 263.— The Right First Cuneiform (Medial Side). Fig. 264. — The Right First Cuneiform (Lateral Side). II. First Metatarsal cuneiform Fia. 265.— The Right Second Cuneiform (Medial Side). THE CUBOID BONE. 263 The lateral surface displays a facet arranged along its posterior border, and usually somewhat constricted in the middle ; this is for the third cuneiform. In front of this tlie bone is rough for the interosseous ligaments which bind the two bones together. The posterior surface is provided with a triangular facet sliglitly concave from above downwards ; this rests on the intermediate articular surface on the anterior aspect of the navicular. In front the bone articulates by means of a wed^'B-shaped facet with the y_„„ „ ,,„„ . ,„ „ o , i Skcond cuNEiroKM Cuboid IV. Mktataksai, base ot the metatarsal bone of the second toe. The third cuneiform, intermediate in size between the tirst and second, is also of a fairly typical wedge shape ; though its antero- posterior axis is not straight butl)ent, so that the anterior ^ „^, ,, 1 f. 4.1 K 4- ^^^- 267.— Right Thikd Fig. 268.— Right Third end ot tne Done turns Cdneiform (Medial Side). Cuneiform (Lateral Side), slightly medially. Its dorsal surface, which corresponds to the base of the wedge, is slightly convex from side to side, and provides attachments for the dorsal ligaments. Its inferior or plantar aspect forms a rough blunt edge, and serves for the attachment of the plantar ligaments. Its medial surface, of quadrilateral form, displays two narrow- articular strips, placed along its anterior and posterior borders respectively, each somewliat constricted in the middle. The anterior facet articulates with the lateral surface of the base of the second metatarsal bone, the posterior with the lateral surface of the second cuneiform. The rough non-articular surface, which separates the two elongated facets, serves for the attachment of ligaments. The lateral aspect of the bone is characterised by a large circular or oval facet, placed near its posterior border, for articulation with the cuboid ; in front of this the anterior border is lipped above by a small semi-oval facet for articulation with the medial side of the base of the fourth metatarsal. The rest of the bone around and between these facets is rough for ligaments. Posteriorly the bone is furnished with a blunt, wedge-shaped facet for articulation with the corresponding area on the anterior surface of the navicular. Below this the surface is narrow and rough for the attachment of ligaments. The anterior surface of the bone articulates with the base of the third metatarsal by an area of triangular shape Os Cuboideum. The cuboid lies on the lateral side of the foot, about its middle, articulating with the calcaneus posteriorly and the fourth and fifth metatarsal bones anteriorly. Its dorsal surface, plane in an antero-posterior direction, is slightly rounded from side to side, and provides attachment for ligaments. Its plantar aspect is tra- versed obliquely from the lateral side medially and forwards by a thick and prominent ridge, the lateral extremity of which, at the point where it is confluent with the lateral surface, forms a prominent tubercle (tuberositas ossis cuboidei), the anterior and lateral surface of which is smooth and facetted to allow of the play of a sesamoid bone which is frequently developed in the tendon of the peronaeus longus muscle. Anterior to this ridge there is a groove (sulcus peronsei) in which the tendon of the peronaeus longus muscle is lodged as it passes across the plantar surface of the bone. Behind the ridge the bone is rough, and serves for the attachment of the plantar calcaneo-cuboid ligament, the superficial fibres of which pass forwards and are attached to the summit of the ridge. The lateral aspect of the bone is short and rouuded, and is formed by the confluence of the dorsal and plantar surfaces : it is more or less notched by the peroneal groove which turns round its plantar edge. The medial surface of the bone is the most extensive ; it is easily recognisable on accowat - of. the presence of a rounded or oval facet situated near 264 OSTEOLOGY. Na^ icular Third tiNEifORM (uccasional) Tuberosity Groove for peron^us LONOUS A Groove for 'Tuberosity peron^us lonous its middle and close to its dorsal border. This is for articulation with the lateral side of the third cuneiform ; anterior and posterior to this the surface is rough for ligaments. Not infrequently, behind the facet for the third cuneiform, there is a small articular surface for the navicular, as is the case normally in the gorilla, whilst posteriorly and on the plantar aspect the projecting in- ferior angle is sometimes pro- vided with a facet on which the head of the talus rests. (Sutton, " Proc. Anat. Soc," Journ. Anat. and Physiol, vol. xxvi. p. 18.) The anterior surface is oval or conical in outline ; sloping obliquely from the medial side laterally and backwards, it is divided about its ndddle by a slight vertical ridge into two parts, the medial of which articulates with the base of the fourth metatarsal bone, the lateral with that of the fifth. The posterior surface, also articular, has a semilunar outline, the convex margin of which corresponds to the dorsal roundness of the bone. The inferior lateral angle corresponds to the tubercle on the lateral border of the bone, whilst the inferior medial angle forms a pointed projection which is sometimes called the calcanean process. This surface articulates with the calcaneus by means of a saddle-shaped facet, which is convex from side to side, and concave from dorsal to plantar margins. The tarsus as a whole may be conveniently described as arranged in two Fig. 269.- Lateral Side. -The Right Cuboid Bone. B. Medial Side. Fig. 270. — Radiographs of the F(etal Foot. 1. About fifth month. No ossification in the tarsus visiltle. 2. About sixth month. Appearance of a nucleus for the calcaneus. 3. Aljout seventh month. Nucleus for calcaneus well developed. 4 and 5. About eighth month. Centre for talus, as well as for calcaneus, is now seen. 6. About birth. Centres for the talus and calcaneus are well developed ; there is also a considerable centre for the cuboid, and the appearance of a centre for the third cuneiform is now displayed. columns ; the medial, corresponding to the medial border of the foot, comprising the talus, navicular, and three cuneiforms, and forming a base for the support of the medial three metatarsal bones and their phalanges. The lateral column, formed by the calcaneus and cuboid, supports the fourth and fifth metatarsal bones, together with their phalanges. The dorsal surface of the anterior portion of the THE METATARSUS. 265 tarsus determines the side-to-side roundness of the instep, whilst its plantar surface forms arches in both a transverse and a longitudinal direction, in which the softer tissues of the sole are lodged, and so protected from injury. Ossification. — I'nlike the carpus, the tarsus is at birtli partially ossified. At this period tliere is a well-marked osseous nucleus within the body and neck of the talus, and the calcaneus is extensively ossified. In the latter the deposition of earthy matter appears as early as the sixth mouth of fcetal life, whilst in the talus the ossific centre makes its appearance in the later weeks of gestation. Shortly before or after birth the Fig. 271. — Kadiogbaph ok the Hand AT Birth. It will be noticed that whilst the primary centres for the metacarpus and phalanges are well ossified, the carpus is still entirely cartilaginous. Fig. 272. -Radiograph of the Foot at Birth. The centres of ossification for the calcaneus and talus are well developed, the nucleus for the cuboid is quite distinct, and in this instance the tliird cuneiform is already commencing to ossify. cuboid begins to ossify, succeeded early in the first year by the third cuneiform, followed in order by the second cuneiform, first cuneiform, and navicular. The ossific centre of the latter appears at the third year or somewhat later. An epiphysis, which forms a cap over the extremity of the tuberosity of the calcaneus, appears from the seventh to the ninth year, and fusion is completed between the ages of sixteen and twenty. To emphasize the different conditions which obtain in the wrist and ankle, at, and for some time after birth, drawings of radiographs of both are given. The Metatarsus. The metatarsal bones, five in number, in their general configuration resemble the metacarpal bones. They are, however, slightly longer, their bases are proportionately larger, their bodies are more slender and are compressed from side to side, and their heads are proportionately smaller. They are named numerically the first, second, third, fourth, and fifth metatarsal bones, in order from the tibial to the fibular side. The first can be readily recognised on account of its stoutness ; it is also the shortest of the series. The second is the longest of the five, and the fifth can easily be distinguished by the projecting tubercle at its base. 266 OSTEOLOGY. Grooves for sesamoid bones Shaft The first metatarsal, or metatarsal bone of the great toe, the shortest of the series, is remarkable for its stoutness. Its proximal end or base, where the bone is provided with' a reniform facet for articula- tion with the first cuneiform, is wider from the dorsal to the plantar aspect than from side to side. The concavity of the kidney -shaped arti- cular area is directed to the fibular side. As a rule the lateral aspects of the base are non-arti- cular, though occasionally on its lateral side there is a "pressure" facet for the base of the second metatarsal bone. The plantar basal angle pro- jects proximally and laterally, and forms a pro- minent tubercle which is pitted for the insertion of the tendon of the peronseus longus muscle, whilst its tibial margin is lipped by a surface for the attachment of part of the tendon of the tibialis anterior. The body, short, thick, and pris- matic on section, tapers rapidly towards the head, the distal and plantar surfaces of which are articular. The former is convex in both directions, and supports the proximal or first phalanx. It is con- fluent with the plantar articular surface, which is divided by a median ridge into two shallow grooves. Fig. 273. — The First Metatarsal of which the tibial is the wider. In these grooves Bone OP the Right Foot (Plantar ^^^ lodged the two sesamoid bones of the metatarso- ^^^° phalangeal joint. On either side of the head, the bone is pitted for the strong collateral ligaments of the joint. The second metatarsal, the longest of the series, has a base of wedge-shaped Tl'berositv Tibialis anterior I. Metatarsal (pressure facet) II. METATARSAL First cuneiform III. Metatarsal III. METATARSAL IV. Metatarsal IV. METATARSAL Third cuneiform III. Metatarsal A. Medial sides. V. Metatarsal B. Lateial sides. Fig. 274. — View ok thk Bases and Shafts of the Second, Third, and Fourth Metatarsal Bones of the Right Foot. form, the proximal aspect of which articulates with the second cuneiform. On its tibial aspect, near its dorsal edge there is a small circular facet for the first THE PHALANGES. 267 cuneiform; distal to this and near the plantar surface there is sometimes a tubercle with a " pressure " facet on it, where the bone comes in contact with the base of the first metatarsal. On the fibular side of the base there is one, more usually two small facets, each divided into two parts, a proximal for articulation with the third cuneiform, and a distal for the base of the third metatarsal. The bodies of this and the succeeding three bones are slender and compressed from side to side. The heads are small and narrow, and display a pronounced side-to-side and vertical convexity. The third metatarsal bone also possesses a base of wedge-shaped form, the proximal surfactj of which articulates with the third cuneiform. On its tibial side it is provided with one, more usually two, small facets, for articu- lation with the base of the second metatarsal. Laterally the base has a larger facet for articulatipn with the base of the fourth metatarsal, more or less conical in outline, and having its plantar edge sharply defined by a narrow groove which underlies it. The fourth metatarsal possesses a base more cubical in shape. Its proximal aspect articulates with the cuboid, whilst medially an elongated oval facet, divided by a slight vertical ridge, provides sur- faces for articulation with the third metatarsal distally and the lateral side of the first cuneiform proximally. On the lateral side there is a denii-oval facet, bearing a slightly saddle- shaped surface, for articulation with the tibial side of the base of the fifth metatarsal. The fifth metatarsal can be readily recognised by the peculiar shape of its base, from the lateral side of which there projects proximally and laterally a pro- minent tuberosity (tuberositas ossis metacarpi quinti). To the posterior extremity of this is attached the tendon of the peronseus brevis muscle. Into its dorsal surface the tendon of the peronseus tertius is inserted, whilst its plantar surface provides an origin for the flexor digiti quinti brevis muscle. The medial surface of the base is provided with a demi-oval, slightly concave facet, for the lateral side of the base of the fourth metatarsal, whilst proximally it articulates with the cuboid by means of a semicircular facet. Vascular Foramina. — The canals for the nutrient vessels open, as a rule, on tlie plantar aspects of the middle of the bodies. Those of the lateral four metatarsals are directed towards the bases of the bones, whilst that for the metatarsal of the great toe passes towards its head. Ossification. — In correspondence with the mode of ossification which obtains in the metacarpus, the primary centres for the metatarsus appear as early as the third month of foetal life. In the case of the second, third, fourth, and fifth, these centres furnish the bases and bodies of the bones, the heads being developed from secondary centres which appear from two to four years after birth, fusion with the body being usually completed about the eighteenth year. In striking contrast to this is the mode of ossification of the first metatarsal. From its primary centre the head and body is developed ; the secondary centre appears at its base about the second or third year, and fuses with the body about eighteen. In this respect, therefore, the metatarsal bone of the great toe resembles the phalanges in its mode of development. Mayet, however {Bull. Soc. Anat. Paris, 1895), describes the occurrence of two ossific centres in the proximal epiphysis. These fuse early, and he considers that the one represents the metatarsal element, whilst the other may be regarded as phalangeal in its origin. CVBO Ppron*us bre\ns Fig. 275. — Fifth Right Metatarsal Boxe (Dorsal Aspect). Phalanges Digitorum Pedis. The phalanges of the toes differ from those of the fingers in the striking reduction of their size, and in the case of the bones of the first row, in the compression of their bodies from side to side. Each toe is provided normally with three phalanges, except the great toe, which has only two. In their general 268 OSTEOLOGY. III. Ungual, OR TERMINAL PHALANX 11. Phalanx coafiguration and in the arrangement of their articular facets they resemble. the phalanges of the fingers, though owing to the reduction in their size, the bodies, particularly those of the second row, are often so compressed longitudin- ally as to reduce the bone to a mere nodule. The proximal end of each of the bones of the first row is pro- portionately large, and is provided with a simple hollow in which the head of the metatarsal bone rests; the distal ends are furnished with condyloid surfaces. The proximal extremities of the second row are each provided with two small concavities, separated by a slight ridge, for articulation with the condyles of the first row. The joint between the second and third row displays the same arrangement — the third, or ungual phalanx, being easily distinguished by the spatula-shaped surface at its extremity, on which the bed of the nail is supported. The phalanges of the great toe, two in number, differ from the others in their size and length. Into the base of the first phalanx are inserted the short muscles of the great toe, whilst the second phalanx receives on its plantar aspect the insertion of the fiexor hallucis longus muscle, the tendon of the extensor hallucis longus being inserted into the dorsal aspect. Ossification. — Each phalanx is developed from two centres — one primary for the body and distal extremity, the other for the epiphysis on the proximal end. The primary centres for the ungual phalanges are the first to appear, commencing to ossify from the eleventh to the twelfth week of foetal life. The centre for the ungual phalanx of the great toe makes its appearance before that of its corresponding metatarsal bone. The primary centres for the phalanges of the first row appear from the fourteenth to the sixteenth week. The primary centres for the middle phalanges of the second and I. Phalanx Metatarsal Fig. 276. — The Phalanges OF THE Toes (Plantar Aspect). I r Fig. 277. A. About the enil of tlie third month. The primary centres of all the metatarsals are shown as well as the centres for the phalanges of the great toe and the terminal phalanx of the third toe. B.' A little later. The centres for the terminal phalanges of the medial four toes are seen, as well as the centres for the first phalanges of the great and second toe. C. About the fourth month. The centres for all the terminal phalanges as well as those of the first row are well ossified. D. About the fifth month. In this the centre for the second plialanx of the second toe has already made its appearance. 1 This specimen displays the ocoiirrence of anomalous centres within the tarsus the signilicaiice of which is not apparent. The appearance is not due to any defect in the plate, but recurred in repeated radiographs. third toes begin to ossify about the sixth month, those for the fourth and fifth toes not till later — the body of the middle phalanx of the fourth toe being frequently cartilaginous at birth, the normal condition in the case of the fifth toe (Lambertz). The proximal epiphyses do not begin to ossify until about the fourth year, and are usually fused with the diaphyses about the age of sixteen or eighteen. Union between the bodies and epiphyses of the first row precedes that of the second and third rows. SESAMOID BONES. 269 * Ossa iScsamoidca. As in the hand, small independent nodnles of bone, culled sesamoid bones, are met with in the lij^aments and tendons of the foot. The most constant of tlie.se are found in connexion with the metatarso-phalangeal articulation of the great toe, where they lie in grooves on the plantar surface of the head of the metatarsal bone in connexion with the tendons of the short muscles of the great toe. Small osseous nodules occupying a corresponding position are occasionally met with in the other toes, and in^stances liave been recorded of like ossicles occurring on the jjlantar aspect of the interphalangeal joint of the great toe. An osseous nodule is not infrequently met with in the tendon of the peronseus longus as it turns round the lateral border of the foot to lie in the groove on the under surface of the cuboid. APPENDICES TO THE SECTION ON OSTEOLOGY. A. Architecture of the Bones of the Skeleton. B. Variations in the Skeleton. C. Serial Homologies of the Vertebrse. D. Measurements and Indices employed in Physical Anthropology. E. Development of the Choudro-Cranium and Morphology of the Skull. F. Morphology of the Limbs. APPENDIX A. ARCHITECTURE OF THE BONES OF THE SKELETON. The Vertebrae. — The vertebra are formed of spongy bone confined witbin a thin and dense envelope. In the bodies the arrangement of the spongy tissue, which is traversed by venous channels, is such as to display a vertical striation with lamellse arranged horizontally. The lateral, superior, and inferior walls are very thin — that directed to the vertebral canal being usually thicker and denser than the others. In the roots of the vertebral arches and roots of the transverse processes the spongy tissue is much more open. The outer envelope is much thicker where it bounds the vertebral canal, and where it forms the bottom of the superior and inferior intervertebral notches. In the laminae the spongy tissue is confined between two compact layers, of which that directed to the vertebral canal is the thicker. In the spinous processes the upper edge is always the more compact. The Sternum consists of large-celled spongy bone, which is highly vascular, and is contained between two layers of thin compact tissue. The Ribs. — Each rib consists of a curved and compressed bar of bone, the interior of which consists of highly vascular spongy tissue with an external envelope of compact bone. The inner table is much the stronger, attaining its maximum thickness opposite the angle — in front and behind which it becomes gradually reduced. The outer table, much thinner, is stoutest opposite the angle ; on the posterior surface of the tubercle and neck it forms but a thin layer. The compact layers forming the upper and lower borders are not so thick as those forming the inner and outer surfaces. The spongy tissue, loose and open in the body, is most compact in the region of the head and towards the anterior extremity. The Frontal Bone. — The frontal bone is composed, like the other bones of the cranial vault, of two layers of compact tissue, enclosing between them a layer of spongy cancellous texture — the diploe. In certain definite situations, owing to the absorption of this intermediate layer, the bone is hollow, forming the frontal air-sinuses. The position and extent of these is to some extent indicated by the degree of projection of the superciliary ridges, though this must not be taken as an absolutely reliable guide, for cases are recorded where the ridges were low and the sinuses large, and vice versa. Of much surgical importance, these air-spaces only attain their full development after the age of puberty, being of larger size in the male than in the female, a circumstance which accounts for the more vertical appearance of the forehead in woman as con- trasted with man. Usually two in number, they are placed one on either side of the median plane, and communicate by means of the infundibulum with the nasal cavity of the same side. It is exceptional to find the sinuses of opposite sides in communication with each other, as they are generally separated by a complete partition which, however, is occasionally much deflected to one or other side. Logan Turner (" On the Illumination of the Air Sinuses of the Skull, with some OKservations upon the Surgical Anatomy of the Frontal Sinus," Edin. Med. Journ., May 1898) gives the average dimensions of these sinuses as follows : — Height, 31 mm., i.e. from the fronto- nasal aperture upwards ; breadth, 30 mm., i.e. from the septum horizontally in a lateral direction; depth, 17 mm., from the anterior wall at the level of fronto-nasal suture backwards along the orbital roof Exceptionally large sinuses are sometimes met with extending backwards over the orbit so as to form a double roof to that space. There is a specimen in tne Oxford collection in which the sinus is so large, and extends so far back, that the optic nerve is transmitted through it in a Vjony tube. Another point of some practical importance is that the sinuses are hardly ever symmetricaL It is rare to meet with cases of their complete absence, although sometimes the sinus on one or other side may be wanting. The zygomatic process, from the arrangement of its surfaces and the density of its structure, is particularly well adapted to resist the pressure to which it is subjected when the jaws are firmly closed. The Parietal Bone.— Thin towards its lower part, where it enters into the formation of the temporal fossa, it is thickest along the superior border and in the neighbourhood of the posterior superior angle. The Occipital Bone. — The squamous part displays thickenings in the position of the various ridge and crests, the stoutest part corresponcling to the internal and external occipital protuberances, 270 ARCHITECTUKE OF THE BONES OF THE SKELETON. 271 though it should be noted that the two protuberances do not necessarily coincide, the internal being, as a rule, placed at a higher level tiian the external. If the bone be held up to the light it will be at once apj)arent that it is much thinner where it forms the floor of the inferior fo.s.sui than in the upper j>art. The basilar portion consists of a spongy core surrounded by a more compact outer envelope, thickest on its lower surface. In the condyles the spongy ti.ssue is arranged radially to their convex articular surfaces, the hypoglossal canal being surrounded by )>articularlv dense and compact bone, which assists in strengthening this naturally weak part of the bone. The Temporal Bone. — The temporal bone is remarkable for the hardness and density of its petrous part, wherein is hxiged the osseous labyrinth, which contains the delicate organs a-ssociated with the senses of hearing and eiiuilibration. The middle ear or tjrmpanum is a cavity which contains the small auditory ossicles, and is separated from the external acoustic meatus by the membrana tympani. In front it communicates with the pharynx by the auditory tube ; behind, it opens into the tympanic antrum and ma.stoid air-cells by the aditus ad antrum. Superiorly, it is separated from the middle cranial fos.sa by a thin plate of bone called the tegmen tympani. Tnferiorlu, its floor is Jbrmed in part by the roof of the jugiilar fo.s.sa and the carotid canal. Medialli^, it is related to the structures which form the inner ear, notably the cochlea and vestibule, in front of which it is separated by a thin plate of bone from the carotid canal. Owing to the disposition of the intenial and external acoustic meatus the weakest part of the bone corresponds to a line connecting these two channels, the only parts intervening being the cochlea and tympanum. It is usually in this position that fracture of the bone occurs. Curving over the cavity of the tympanum is the oanalis facialis, tlie thin walls of which are occasionally deficient. These details, together with an account of the tympanic ossicles, will be further dealt with in the section devoted to the Organs of Sense. The Sphenoid Bone. — In the adult the body of the bone is hollow and encloses the sphenoidal air-sinuses, usually two in number, separated by a septum. The arrangement and extent of these air-sinuses vary ; sometimes they are multilocular, at other times simple, while occasionally they extend backwards into the basi-occipital and laterallv and downwards into the roots of the great wings and pterygoid processes. Cases are on record, in which in the adult the body of the bone was not pneumatic The Lacrimal Bone. — The bone consists of a thin papery translucent lamina, somewhat strengthened by the addition of the vertical crest. The Vomer. — The bone is composed of two compact layers fused below, but separated above by the groove for the lodgment of the rostrum of the sphenoid behind, and the septal cartilage in front. The lamellfe are also separated from each other by a canal which runs horizontally from be- hind forwards in the substance of the bone, and which transmits the nutrient vessel of the bone. The Nasal Bone. — Formed of dense and compact bone ; the strength of the nasal bones is increased I'V their mode of union and the formation of a median crest posteriorly. The Maxilla. — The disposition of the maxillary sinus within the body of the bone has been already referred to. In union with its fellow, the vaulted arrangement of the hard jialate is well displayed, and the arched outline of the alveolar processes is obvious. It is in these latter processes around the sockets for the reception of the teeth that the spongy tissue of the buue is seen ; elsewhere its walls are formed by thin and dense bone. The Zygomatic Bone. — In structure the bone is compact, with little spongy tissue. Together with the zygomatic process of the temporal bone it forms the buttress which supports the maxilla and the lateral wall of the orbit. Additional strength is imparted to the bone by the angular mode of union of its orbital and facial parts. The Mandible. — The mandible is remarkable for the density and thickness of its medial and lateral walls. Where these coalesce below at the base of the body, the bone is particularly stout. Superiorly, where they form the walls of the alveoli, they gradually thin, being thicker, however, on the medial than the lateral side, except in the region of the last molar tooth, where the medial wall is the thinner. The spongy substance is open-meshed below, finer and more condensed where it surrounds the alveoli. The mandibular canal is large and has no very definite wall ; it is prolonged beyond the mental foramen to reach the incisor teeth. From it numerous channels pass upwards to the sockets of the teeth, and it com- municates freely with the surrounding spongy tissue. Above the canal the substance of the bone is broken up by the alveoli for the reception of the roots of the teeth. In the substance of the condyle the spongy tissue is more compact, with a general striation vertical to the articular surface. The mental protuberance is an essentially human characteristic ; by some it is associated with the development of speech in man, others regard it as due to the reduction in the size of the teeth. The Clavicle. — The body consists of an outer layer of compact bone, thickest towards the middle of the shaft, but graclually thinning towards the extremities, the investing envelope of which consists merely of a thin sliell. Within the l>ody the spongy tissue displays a longitudinal striation, which internally assumes a more cellular appearance. At the acromial end the general arrangement of the fibres resembles the appearance of the sides of a Gothic arch. The curves of the bone impart an elasticity to it, which is of much service in reducing the effects of the shocks to which it is so frequently subjected. The Scapula. — For so light and thin a bone, the scapula possesses a remarkable rigidity. This is owing to the arrangement of its part*. Stout and thick where it supports the glenoid cavity 272 OSTEOLOGY. and coracoid process, tlie rest of the bone is thin, except along the axillary margin ; but strength is imparted to the body by the manner in which the spine is fused at right angles to its dorsal surface. The Humerus. — The body consists of a layer of compact bone surrounding a long medullary cavity. The outer shell, thickest in the distal third of the bone, gradually thins until it reaches the proximal epiphysial line, where it forms a layer no thicker than stout paper. Distally the external shell is thicker and stouter than it is proximally, until it reaches the epicondyles, distal to which the articular surfaces are formed of a layer of compact spongy bone. The proximal end of the medullary cavity is surrounded by loose spongy tissue, the fibres of which arch inwards from the inner surface of the compact outer layer, whilst at the distal end the spongy tissue which springs from the outer shell sweeps distally in a radiating fashion on either side of the olecranon fossa towards the epicondyles. Proximal to the olecranon fossa there is a number of laminae of dense bone which arch across from one side to the other, the con- vexity of the arches being directed distally. The j^roximal epiphysis, formed of spongy bone, is united to the l^ody by a wavy line, concave laterally and convex medially, leading from the base of the greater tuberosity on the lateral side to the distal articular edge on the medial side. The mass above this includes the head and the tM^o tubercles. The spongy tissue of the head is fine, and is arranged generally in lines radial to its surface ; that of the greater tubercle is more open, and often displays large spaces towards its interior, which in old bones communi- cate freely with the medullary cavity of the body. The general direction ot the fibres is parallel to the lateral surface of the tuberosity. The distal articular end is formed of fine spongy tissue, more compact towards the surface, and arranged in lines more or less at right angles to its articular planes. In the adult the principal nutrient canal, viz., that which opens on the surface near the insertion of the coraco-brachialis, traverses the outer compact wall of the body obliquely distally for a distance of two and a quarter inches before it opens into the medullary cavity. The Ulna. — The weakest parts of the bone are the constricted portion of the semilunar notch, and the body in its distal third, the bone being most liable to fracture at these points. On section the medullary cavity is seen to extend proximally as high as the base of the coronoid process ; distally it reaches the proximal end of the distal fifth of the bone. The walls of the body, which are formed of dense bone, are much thicker on the dorsal surface than on the volar. Proximally they are continuous with the volar suii'ace of the coronoid process and the dorsal surface of the olecranon, where they are composed of layers of looser texture, which, however, gradually become thinner as the points of these processes are reached. Distallj^ they gradually taper until the head and styloid process are reached, round which they form a thin shell, con- siderably thickened, however, in the region of the groove for the extensor carpi ulnaris muscle. The bulk of the proximal extremity is formed of loose spongy bone, arranged in a series of arcades, stretching from the interior to the dorsal wall over the proximal end of the medullary canal. Proximal to the constricted part of the semilunar notch the bone displays a dift'erent structure ; here it is formed of spongy bone, of closer texture, arranged generally in lines radiating from the articular surface. At the point of constriction of the semilunar notch the layer immediately subjacent is much denser and more compact. The distal fifth of the bone is formed of loose spongy bone, the fibres of which have a general longitudinal arrangement ; towards its extremity the meshes become smaller. The Radius. — The neck is the narrowest part of the bone; here fracture may occur, though not commonly. The point at which the bone is usually broken is about one inch proximal to the distal extremity. This is accounted for by the fact that the radius supports the hand at the radio-carpal articulation, and the shocks to which the latter is subjected, as in endeavouring to save oneself from falling, are naturally transmitted to the radius. On section, the medullary cavity is seen to extend to the neck ; distally, it reaches to the level of the distal fifth of the bone. Its walls are thick as compared with the diameters of the bone, particularly along the interosseous border, thus imparting rigidity to the curve of the body ; these walls thin out proximally and distally. Proximally, the surface of the tuberosity is formed of a thin shell of bone, which, however, thickens again where it passes on to the neck. The proximal extremity is formed of spongy bone arranged in the form of arcades, reaching distal to the level of the tuberosity mecfially, but not extending distal to the level of the neck laterally. Beneath the capitular articular surface there is a dense layer, thickest in the centre, and thinning towards the circumference ; this is overlain by a very thin layer of less compact bone. The distal fifth of the body and distal extremity are formed of loose spongy bone arranged more or less longitudinally. Immediately subjacent to the carpal articular surface the tissue is more comj^act, and displays a striation parallel to the articular plane. The nutrient canal of the shaft pierces the volar wall of the proximal part of the medullary cavity obliquely, running proximally for half an inch. The Carpus. — The bones are formed of fairly compact spongy tissue, surrounded by a thin shell of denser bone. They are very vascular, and their non-articular surfaces are pierced by many foramina. The Metacarpus. — Similar in arrangement to that of long bones generally, though it may be noted that tlie compact walls of the body are thicker in proportion to the length of the bone than in the other long bones of the upper extremity. The Phalanges. — Each phalanx has a medullary cavity, the walls of the body being formed of dense compact bone, especially thick along the dorsal aspect. The extremities are made up of spongy bone within a thin dense shell. ARCHITECTUKE 0¥ THE 150NES OF THE SKELETON. 273 rHOCIIANTKHIC KOSS The Hip Bone. — As a flat bone the'os coxiie consists of sjumgy tissue between two coni- j)act external layers. These latter vary much in thickness, being exceptionally stout along the ilio-pectineal line and the floor of the iliac fossa iniuiediately al)ove it. The gluteal as])ect of tlie ilium is also formed l)y a layer of considerable thickness. The si)ongy tissue is loose and cellular in the thick i)art of the ilium and in tlie body of tlie ischium ; absent where tlie floor of the iliac fossa is formed by the coalescence of tlie thin dense confining layers ; fine grained and more com])act in the tuberosity of the ischium, the iliac crest, and the floor of the acetabulum, in which latter situation it is striated by fibres which are directed radi- ally to the surface again beingr crossed at Posterior surface OF NECK which are arranged circumferentially. This spongy tissue forms a more compact layer over the surface of the ujiper and jiosterior portion of the acetabular articular area. The bottom of the floor of the acetab- ulum varies in thickness ; in most cases it is thin, and in exceptional instances the bone is here deficient. The same condition has been met with in the iliac (iREATKR IROCHAMTER Interior of tro- cliaiitf^r m.'i.jor uoiitaiiiiiiK loose ponny lissiK! (scrajied away) (iiiiliact tissue — Willi ilc'iiso core loriiiiiiv! tlie calcar foinorale Space containing loose spongy tissue (scraped away) between the calcar and the base of the tro- chanter minor of that hollow, right angles by Fig. 278. — Dissection showing the Calcar Femokale. A slice of bone has been removed from the pos- terior aspect of the proximal part of the shaft of the femur, passing through the trochanter major superiorly and the trochanter minor iuferiorly and to the medial side. The loose spongy tissue has been scrajied away, leaving the more compact tissue with the dense core forming the calcar feniorale. By a similar dissection from the front the an- terior surface of the calcar may Vie exposed. Posterior ^^^'^''^^^'-Xm^^^^^i^tM^iY anterior fossa, where absorption of the thin bony plate or ^KCK-^m^mmMK^.ll,^^,^,^ has taken place. "' \ OF NECK The Femur. — The body has a medullary cavity which reaches the root of the lesser trochanter proximally. Distally it extends to within 3i inches of the distal articular surface. In the proximal half the outer compact wall is very thick, but distal to the middle of the body it gradually thins until it reaches the condyles, over which it passes as a thin, hardly definable external layer. Proximally, it is especially thick along the line of the linea aspera, and here the large nutrient canal may be seen pass- ing obliquely towards the proximal end in the substance of the dense bone for the space of two inches. In the proximal end of the body the osseous lamellae springing from the sides of the medullary cavity arch inwards towards the centre, intersecting each other in a manner comparable to the tracery of a Gothic window. The lower wall of the neck is thick distally, near the trochanter minor, but thins rapidly before it reaches the head. From this aspect of the neck there spring a series of oblique lamelljE which pass proximally and upwards, spreading in fan-shaped manner into the under surface of the head. These are intersected above by lamellae which arch medially from the lateral side of the 18 Calcar femorai.k Trochanter MINOR Fig. 279. — Section through Head and Neck ok Femur to show Calcar Femorale. 274 OSTEOLOGY. shaft distal to the greater trochanter, as well as from the inner surface of the thin but compact outer shell of the upper surface of the neck, the whole forming a bracket-like arrangement which assists materially in adding to the strength of the neck. Further supjjort is afforded by the addition of a vertical layer of more compact bone within the spongy tissue of the neck. Distally, as may be seen in Fig. 278, this is continuous with the dense posterior wall of the body below ; whilst proximally it sweeps up beneath the lesser trochanter, from which it is separated by a quantity of loose spongy tissue, to fuse proximally with the posterior dense wall of the neck above and medial to the intertrochanteric crest. It may be regarded as a continuation proximally of the posterior wall of the body beneath the trochanteric epiphysis. When studied in section (see Fig. 279), the central dense core of this partition exhibits a spur -like appearance : hence the name calcar femorale applied to it. It is of surgical importance in cases of fracture of the neck of the femur. {R. Thompson, Journ. Anat. and Physiol, vol. xlii. p. 60.) From it, stout lamellae having a vertical direction arise. The spongy tissue of the head and greater trochanter is finely reticulated, that of the distal part of the neck and proximal part of the shaft being more open in its texture. Passing vertically through this tissue there is a vascular canal, the orifice of which opens externally on the floor of the trochanteric fossa. The sjDongy tissue of the distal part of the body is more delicate and uniform in its .arrangement, displaying a more or less parallel striation in a longitudinal direction. Subjacent to the articular surface the tissue is rendered more compact by the addition of lamellae disposed in curves in harmony with the external aspect of the bone. The Patella. — The bone consists of a thick dense layer anteriorly, which thins towards the edges on either side and distally ; proximally, it corresponds to the area of insertion of the quadriceps. The femoral articular surface is composed of a layer of compact bone, thickest in correspondence with the vertical elevation. Sandwiched between these two layers is a varying thickness of spongy tissue of fairly close grain, the striation of which on cross section runs in jaarallel lines from back to front ; on vertical section the tissue appears to be arranged in lines passing radially from the deep surface of the femoral area to the more extensive anterior dense plate. Tlie Tibia. — The body of the bone is remarkable for the thickness and density of the osseous tissue which underlies the anterior crest. The posterior wall is stout, but the medial and lateral walls are thinner. The several walls are thickest opposite the middle of the body, and thin out proximally and distally where the body unites with the epiphyses. The medullary cavity, narrow and circular in the middle of the bone, increases in all its diameters proximally and distally, and reaches to within 2^ to 3 inches of either extremity. Proximally the arrangement of the lamellae of the spongy tissue resembles a series of arches springing from the dense outer walls. These form a platform on which the proximal epiphysis rests, the spongy tissue of which displays a more or less vertical striation. This is much more compact under the condylic surfaces, the superficial aspect of which is formed by a thin layer of dense bone. The intercon- dyloid eminence and the tuberosity are also formed of compact tissue, whilst the circumference of the condyles is covered by a thinner and less dense wall. In the distal end of the body the spongy tissue, of a loose and cellular character, is arranged in vertical fibres, blending with the closer tissue of the distal epiphysis, the articular surface of which is covered by a thin but dense layer. In the adult bone the nutrient canal for the body is embedded in the dense posterior wall for the space of two inches. The Fibula. — A medullary cavity runs throughout the length of the body, reaching the neck proximally, and extending to a point about 2i inches from the distal extremity of the lateral malleolus. The lateral wall of the body is usually considerably thicker than the medial. The head is formed of loose spongy bone, enclosed within a very thin dense envelope. The spongy tissue of the distal extremity is moi-e compact, and acquires considerable density on the surfaces underlying the articular area and the pit behind it. The canal for the nutrient artery of the body opens into the medullary cavity about an inch distal to its external aperture. The Bones of the Foot. — A longitudinal section through the articulated bones of the foot reveals the fact that the structure of the spongy substance of each individual bone is determined by the stress to which it is habitually subjected. In this connexion it is necessary to refer to the arched arrangement of the bones of the foot, a subject which is also treated in the section which deals with the Joints. The summit of the arch is formed by the talus, on which rests the tibia. Subjected as the talus is to a crushing strain, it is obvious that this load must be distributed throughout the arch, of which the calcaneus is the posterior pillar, whilst the heads of the meta- tarsal bones constitute the anterior pillar. It is found, consequently, that the lamellae of the spongy tissue of the talus are arranged in two directions, wliich intercross and terminate below the dor.sal articular surface. Of these fibres, some sweep backwards and downwards towards the posterior calcanean facet, beyond wliich they are carried in the substance of the cal- caneus in a curved and wavy manner in the direction of the heel, where they terminate ; whilst others, curving downwards and forwards from the trochlea of the talus, pass througli the neck to reach the articular surface of the head, through which in like manner they may be regarded as passing onwards through the several Vjones which constitute the anterior part of the arch, thus accounting for the longitudinal striation as displayed in the structure of tlie navi- cular, cuneiform, and metatarsal bones. In tlie calcaneus, in addition to the foregoing arrange- ment, another set of curving fibres sweep from back to front of the bone beneath the more com- pact tissue which forms its under shell. These are obviously of advantage to prevent the spread of the bone when subjected to the crushing strain. In the su.-itentaculum tali a bracket-like VAKIATIONS IN THE SKELETON. 275 arrangoiueut of fibres is evident, aiul tlui jilantar surface of the neck of the talus is further strengthened by lamtdUe arranged vertically. In the separate bone.s tlie investing envelope is tliin, though under the articular surfaces there is a greater density, due to the accession of lamelhe lying parallel to the articular planes. Tlie stoutest bony tissue in the talus is met with in tlie region of the plantar surface of the neck, wliilst in the calcaneus the greatest density occurs along the floor of the sinus tarsi. The Metatarsus.— In structure and the arrangement of their lamelUe the metatarsal bones agree with the metacarpus. The Phalanges.— In their general structure tliey resemble the bones of the fuiger.s. APPENDIX P.. VARIATIONS IN THE SKELETON. Cervical Vertebrae. — Szawlowski records the presence of an independent rib element in the transverse process of the fourth cervical vertebra. {Anat. Anz. Jena, vol. xx. p. 306.) Atlas. — The foramen transversarium is often deficient in front. Imperfect ossification occa- sionally leads to the anterior arch, and more frequently the posterior arch, being incomplete. The superior articular surfaces are occasionally partially or completely divided into anterior and ])osterior portions. In some instances the extremity of the transverse process has two tubercles. The transvei-se process may, in rare cases, articulate with a projecting process (paroccipital or paramastoid) from the under surface of the jugular process of the occipital bone (see p. 278). An upward extension from the medial part of the anterior arch, due probably to an ossification of the anterior occipito-atlantal ligament, may articulate with the anterior surface of the summit of the dens of the epistropheus. Allen has noticed the articulation of the superior border of the posterior arch with the posterior border of the foramen magnum. Cases of partial or complete fusion of the atlas with the occipital bone are not uncommon (see p. 278). Epistropheus. — In some instances the summit of the dens articulates with a piominent tubercle on the anterior border of the foramen magnum (third occipital condyle, see p. 278). Bennett {Trans. Path. Soc. Dublin, vol. vii.) records a case in which the dens was double, due to the persistence of the primitive condition in which it is developed from two centres, Occasionally the dens fails to be united with the body of the epistropheus, forming an os odontoideam comparable to that met with in the crocodilia. (Giacomini, Romiti, and Turner.) The foramen transversarium is not infrequently incomplete, owing to the imperfect ossification of the posterior root of the transverse process. Elliot Smith, has recorded a case in which there was fusion between the atlas and epistropheus without any evidence of disease. Seventh Cervical Vertebra. — The foramen transversarium may be absent on one or other side. Thoracic Vertebrae. — Barclay Smith {Joiim. Anat. and Physiol. Loud. 1902, p. 372) records five cases in which the superior articular processes of the twelfth thoracic vertebra displayed thoracic and lumbar characteristics on opposite sides. Duckworth (Journ. of Anat. and Physiol. vol. xlv. p. 65) has described a first thoracic vertebra, in which a bony process, arising from the front of the root of the transverse process, curves forwards and medially .so as almost to enclo.'^e a foramen like that of the cervical vertebra?. The ventral surface of this process articulates with the neck of tlie first rib. Lumbar Vertebrae. — The mamillary and accessory processes are sometimes unduly de- veloped. The vertebral arch of the fifth lumbar vertebra is occasionally interrupted on either side by a s}Tichondrosis which runs between the upper and lower articular j^rocesses. In macerated specimens the two parts of the bone are thus separate and independent. The anterior includes the body, together with the roots of the vertebral arches and the transveree and superior articular processes ; the posterior comprises the inferior articular processes, the lamin;?, and the spine. (Turner, Challenger Reports, vol. xvi.) Fawcett has seen the same con- dition in the fourth lumbar vertebra. Szawlowski and Dwight record instances of the occurrence of a foramen in the transverse process of the fifth lumbar vertebra (Anat. Anz. Jena, vol. xx.), and Ramsay Smith describes a case in which the right transverse process of the fourth lumbar vertebra of an Australian sprang from the side of the body in front of the root of the vertebral arch, being unconnected either with the arch or articular process. Sacrum. — The number of sacral segments may be increased to six or reduced to four (see p. 276). Transition forms are occasionally met with in which the first sacral segment displays on one side purely sacral characters, i.e. it articulates with the hip bone, whilst on the opposite side it may present aU the features of a lumbar vertebra. Through deficiency in the development of the laminae, the sacral canal may be exposed throughout its entire length, or to a greater extent than is normally the case. (Paterson, Roy. Dublin Soc. Scientific Trans. vol. V. Series II.) Szawlowski and Barclay Smith record the occurrence of a foramen in the lateral part of the first sacral vertebra. (Journ. of Anat. and Physiol. Lond. vol. xxxvi. p. 372.) Vertebral Column as a Whole. — Increase in the number of vertebral segments is usually 276 OSTEOLOGY. due to differences in the number of the coccygeal vertebrae ; these may vary from four — which may be regarded as the normal number — to six. The number of presacral or movable vertebrae is normally 24 (7 C, 12 Th, and 5 L) ; in which case the 25tli vertebra forms the fii-st sacral segment (vertebra, fulcralis of Welcker). The number of presacral vertebrte may be increased by the intercalation of a segment either in the thoracic or lumbar region without any alteration in the number of the sacral or coccygeal elements : thus we may have 7 C, 13 Th, and 5 L, or 7 C, 12 Th, and 6 L, or it may be reduced by the disajjpearance of a vertebral segment — thus, 7 C, 12 Th, and 4 L. Such an arrangement presupposes developmental errors either of excess or default in the segmentation of the column. On the other hand, the total number of vertebral segments remaining the same (24 or 25), we may have variations in the number of those assigned to different regions due to the addition of a vertebral segment to one, and its consequent subtraction from another region. Thus, in the 24 presacral vertebrae, in cases of the occurrence of cervical ribs the formula is rearranged thus — 6 C, 13 Th, and 5 L, or, in the case of a lumbar rib being present, the formula would be 7 C, 13 Th, 4 L, as happens normally in the gorilla and chimpanzee. Similarly, the number of the presacral vertebrae (24) may be increased by the withdrawal of a segment from the sacral region — 7 C, 12 Th, 6 L, and 4 S — or diminished by an increase in the number of the sacral vertebrae, as in the formula 7 C, 12 Th, 4 L, and 6 S. In- crease in the number of sacral segments may be due to fusion with a lumbar vertebra, or by the addition of a coccygeal element : the latter is more frequently the case. This variability in the constitution of the sacrum is necessarily correlated with a shifting tailwards and headwards of the pelvic girdle along the vertebral column. Rosenburg considers that the 26th, 27th, and 28th vertebrae are the primitive sacral segments, and that the sacral characters of the 25th vertebrae (the first sacral segment in the normal adult column) are only secondarily acquired. He thus supposes that during development there is a head ward shifting of the sacrum and pelvic girdle, with a consequent reduction in the length of the presacral portion of the column. This view is opposed by Paterson {Roy. Dublin Soc. Scientific Trans, vol. v. Ser. II.), who found that ossification took place in the alae of the 25th vertebra (first adult sacral segment) before it made its appear- ance in the.alfe of the 26th vertebra. He thus assumes that the alae of the 25th vertebra may be regarded as the main and primary attachment with the ilium. His conclusions, based on a large number of observations, are at variance with Rosenburg's views, for, according to his opinion, liberation of the first sacral segment is more common than assimilation with the fifth lumbar vertebra, and assimilation of the first coccygeal vertebra with the sacrum is more common than liberation of the fifth sacral, thus leading to the inference that the sacrum tends to shift tail- wards more often than headwards. Dwight (Anctt. Anz. Jena, vol. xxviii. p. 33), after a study of this question, whilst admitting that some of these variations may be reversive, denies that there is any evidence that they are progressive, and further states that after the occurrence of the original error in development, there is a tendency for the vertebral column to assume as nearly as possible its normal disposition and proportions. Sternum. — The sternum is liable to considerable individual variations affecting its length and directioiL The majority of bones are asymmetrical, displaying irregularities in the levels of the clavicular facets. The higher costal facets may be closer together on one, usually the right side, than the other, whilst the synchondrosis sternalis is often oblique, sloping somewhat to the right. According to Birmingham, these are the result of the strain thrown on the shoulder by pressure either directly applied or through the pull of a weight carried in the hand. Sometimes the sternum articulates with eight rib cartilages. This may happen on one or both sides, but when unilateral, much more frequently on the right side — a condition by some associated with right-handedness. It is, however, more probably a persistence of the primitive condition of the cartilaginous sternum, in which each half is connected with the anterior extremities of the first eight costal arches. In some rare cases only six pairs of ribs articulate by means of their costal cartilages with the sternum. Recently Lickley has brought forward evidence to show that the seventh rib is undergoing regressive changes. {Anat. Anz. vol. xxiv. p. 326.) Occasionally the presternum supports the, first three ribs ; in other words, the manubrium has absorbed the highest segment of the body. Keith has pointed out that this is the condition most commonly met with in the gibbon, and regards its occurrence in man as a reversion to the simian type. As far as is at present known, its occurrence seems more common in the lower races. Through errors of development the sternum may be fissured throughout, due to failure of fusion of the cartilaginoas hemisterna. The two ossified halves are usually widely separated above, but united together below by an arthrodial joint. The heart and pericardium are thus uncovered Vjy the bone. Occasionally this condition is associated with ectopia cordis, under which circumstances life is rendered impossible. Through defects in ossification tlie body of the sternum may be pierced by a hole, usually in its lower part, or through failure of fusion of the collateral centres one or more of the segments of the body may be divided longitudinally. Sometimes small ossicles are found in the ligaments of the sterno-clavicular articulation. These are the so-called epistemal bones, 'the morphological significance of which, however, has not yet been satisfactorily determined. They are by some regarded as the homologues of the interclavicle or epistemal bone of monotremata, whilst by others they are considered to represent persistent and detached portions of the pre-coracoids. Bibs. — The number of ribs may be increased or diminished. Increase may occur by the addition of a cervical rilj due to tlie indejiendent development of the costal element in the transverse process of the seventh cervical vertebra. This may happen on one or both sides. The range of development of these cervical ribs varies ; they may unite in front with tlie sternum, or they may VARIATIONS IN THE SKELETON. 277 be fused ariterioily with tlio cartilage of. tin: first rib, or the CL-rvical rib may be free. It may in some iiistancea be represented mainly by a ligamentous band, or its vertebi-al and steruul ends may be alone developed, the intermediate part being fibrou.s. At times the vertebral end only may be formed, and may be fused with the first rib, thus leading to the formation of a bicipital rib such as occui-s in many cetaceans. (For a det;iiled account of this anomaly see Wingate Tod's paper in the Joum. of A nut. and Pliysiol. vol. xlvi. jjp. 244-288.) Increase in thenumber of ribs may also be due to the ossification of the costal element whicli is normally present in the embryo in conne.xion with the tii-st lumliar vertebra. (Rosenljerg, Murph. Jahrb. i.) Reduction in the number of ribs is less common. The twelfth rib rarely aborts ; in some cases the fii'st rib is rudimentary. Cases of congenital absence of some of the ribs have been recorded by Hutchin.son, Murray, antl Ludeke. Fusion of adjacent ribs may occur. (Lane, Guy's Hosp. liejiorls, 1883.) In this way, too, the occurrence of a bicipital rib is explained. This anomaly occurs most usually in conne.xion with the first rib, which either fu.ses with a cervical rib above or with the second rib below. Variations in form may be in great part due to the occupation of the individual and the con- stricting inlluencc of eorsets. Independently of these influences, the ventral part of the body is sometimes cleft so as to appear double ; at other times the cleft may be incomj»lete so as to form a j)erfoi'ation. Occasionally adjacent ribs are united towards their posterior part by processes having an intermediate ossicle between (Meckel), thus recalling the condition normally met with in birds ; more usually, however, the bony projections are not in contact. The number of true or vertebro-sternal ribs may be reduced to six, or increased to eight {vide ante, p. 276). Dwight (Journ. of Anat. and Physiol, vol. xlv. p. 438) describes a series of cases in which the interval between the transverse process of the first thoracic vertebra and the neck of the first ril) is bridged across or converted into a linear cleft by a dorsal exten.sion from the neck of the rib. Costal Cartilages. — Occasionally a costal cartilage is unduly broad, and may be pierced by a foramen. The number of costal cartilages connected with the sternum may be reduced to six or increased to eight (see j). 276). In advanced life there is a tendency towards ossification in the layers underlying the perichondrium, more particularly in the case of the first rib cartilage, in which it may be regarded as a more or less normal occurrence. Frontal Bone. — The variation most frequently met with is a persistence of the suture which unites the two halves of the bone in the infantile condition : skulls displaying this peculiarity are termed metopic. The researches of various observers — Broca, Ranke, Gruber, Manouvrier, Anoutchine, and Papillault (Rev. mens, de I'ecole d'Anthropol. de Paris, annde 6, n. 3) — point to the more frequent occurrence of this metopic .sutxire in the higher than in the lower races of man ; and Calmette asserts its greater frequence in the brachycephalic than the dolichocephalic type. Separate ossicles (ossa suturarum) may occur in the region of the anterior fontanelle. The fusion of these with one or other half of the frontal explains how the metopic suture is not always in line with the sagittal suture (Stieda, Anat. Anz. 1897, p. 227) ; they occasionally persist, however, and form by their coalescence a bregmatic bone. (G. Zoja, Bull. Scientifico, xvii. p. 76, Pavia.) Turner {Challenger Reports, part xxix.) recoi-ds an instance of direct articulation of the frontal with the frontal process of the maxilla in a Bush skull, and other examples of the same anomaly, which obtains normally in the skulls of the chimpanzee and gorilla, have been observed. {Journ. Anat. and Physiol, vol. xxiv. p. 349.) There is sometimes a small arterial groove just medial to the supra-orbital notch or foramen, and occasionally the latter is double, the lateral aperture piercing the orbital margin wide of its middle point. Frequently the bone corresponding to the floor of the lacrimal fossa displays a cribriform appearance. Schwalbe (1901) records the presence of small independent ossicles (supra-nasal bones) in the anterior part of the metopic suture. The same anatomist has also directed attention {Zeit. f. Morph. und Anthr. vol. iii. p. 93) to the existence of the metopic fontanelle, first described by Geifly, and the occurrence of metopic ossicles (ossa interfrontalia) and canals. Parietal.— A number of cases have been recorded in which the parietal is divided into an upjier and lower part by an antero-posterior suture parallel to the sagittal suture. Coraini (Atti d. XI. Conyr. Med. Internaz. Roma, 1894, vol. v.) records a case in which the parietal was in- completely divided into an anterior and posterior part by a vertical suture. A tripartite condition of the bone has also been observed (Frasetto). The parietal foramina vary greatly in size, and to some extent in position. They are sometimes absent on one or other side, or both. They correspond in position to the sagittal fontanelle. Sometimes the ossification of this fontanelle is incomplete and a small transverse fissure remains. The jjarietal foramen represents the patent lateral extremity of this fissure after its edges have coalesced. Occasionally in the region pf the anterior fontanelle an ossicle of variable size may be met with. This is the so-called pre-interparietal bone. According to its fusion with adjacent bones it may disturb the direction of the sagittal suture. Occipital. — The torus occipitalis transversus is the term applied to an occasional eleva- tion of the bone which includes the external occipital protuberance and extends laterally along the superior curved line. Occasionally an emissary vein pierces the bone opposite the occipital protuberance. In about 15 per cent, of cases the hypoglossal canal is double. Much rarer three or even four foramina may be met with. The most striking of the many variations to which this bone is subject is the separation of the upper part of the squamous part of the occipital to form an independent bone — the interparietal bone, called also, from the frequency 18a 278 OSTEOLOGY. of its occurrence in Peruvian skulls, the os Incce. By a reference to the account of the ossi- fication of the bone, the occurrence of this anomaly is explained developmentally. In place of forming a single bone the interparietal is occasionally met with in two symmetrical halves, and instances have been recorded of its occurrence in three or even four pieces. In the latter cases the two anterior parts form the pre-interparietals. Not imcommonly the internal occipital crest is split and furrowed close to the foramen magnum for the lodgment of the vermis of the cerebellum, and is hence called the vermiform fossa. Instances are recorded of the presence of a sepai'ate epiphysis between the basi-occipital and the sphenoid, the OS basiotwum (Albrecht) or the as pre-hasi-occipitale. An oval pit, the fovea bursae or pharyngeal fossa, is sometimes seen in front of the tuberculum pharyngeum. This marks the site of the bursa pharyngea. Occasionally the basilar part is pierced by a small venous canal. The articular surface of the condyles is sometimes divided into an anterior and posterior part. The so-called third occipital condyle is an outstanding process arising from the anterior border of the foramen magnum, the extremity of which articulates with the dens of the epistropheus. Guerri has recorded a case, in which in a foetal skull, there were two projecting tubercles in the position of the third occipital condyle, independent of the basi-occipital portions of the condyles. (Anat. Anz. vol. xix. p. 42.) This appears to confirm the view of Macalister that there are two different structures included under this name — one a medial ossification in the sheath of the notochord, and the second, a lateral, usually paired process, caused by the deficiency of the medial part of the hypochordal element of the hindmost occipital vertebra, with thickenings of the lateral parts of the arch. Springing from the under surface of the extremity of the jugular process, a rough or smooth elevated surface, or else a projecting jjrocess, the extremity of which may articulate with the transverse process of the atlas, is sometimes met with. This is the paroccipital or paramastoid process. The size and shape of the foramen magnum varies much in different individuals and races, as also the disposition of its plane. Elliot Smith has called attention to the asymmetry of the cerebral fossae, which is correlated with asymmetrj' of the occipital poles of the cerebral hemispheres. Numerous instances of fusion of the atlas with the occipital bone have been recorded. Many are, no doubt, pathological in their origin ; others are associated with errors in development. Interesting anomalies are those in which there is evidence of the intercalation of a new vertebral element between the atlas and occipital, constituting what is termed a pro-atlas. Temporal Bone. — The occurrence of a deficiency in the floor of the external acoustic meatus is not uncommon in the adult. It is met with commonly in the' child till about the age of five, and is due to incomplete ossification of the tympanic plate. The line of the petro-squamosal suture is occasionally grooved for the lodgment of a sinus (petro-squamosal) ; sometimes the posterior end of this is continuous with a canal which pierces the superior border of the bone and opens into the transverse sinus. Anteriorly the groove may pass into a canal which pierces the root of the zygoma and ajapears externally above the lateral extremity of the petro-tympanic fissure. These are the remains of channels through which the blood passed in the foetal condition (see ante). Kazzander has recorded a case in which the squamous part of the temporal was pneumatic, the sinus reaching as high as the parietal and the squamoso - sphenoidal suture. Symington has described a case in which the squamous part was distinct and separate from the rest of the temporal bone in an adult ; whilst Hyrtl has observed the division of the squamous part of the temporal into two by a transverse suture. The zygomatic process has been observed separated from the rest of the bone by a suture close to its root (Adacni). P. P. Laidlaw (Journ. Anat. and Physiol, vol. xxxvii. p. 364) describes a temporal bone in which there was absence of the internal acoustic meatus and of the stylo-mastoid foramen. The jugular fossa also was absent, and there was partial absence of the groove for the transverse sinus, associated with the presence of a large mastoid foramen. An instance of a rudimentary condition of the carotid i;anal is also referred to in the same volume by G. H. K. Macalister. G. Caribbe {Anat. Anz. vol. xx. p. 81) notes the occurrence in idiots and imbeciles of a more I)ronounced form of post-glenoid tubercle, and associates it with regressive changes in the develop- ment of the temporal bone. Sphenoid. — Through imperfect ossification the foramen spinosum and foramen ovale are sometimes incomplete posteriorly. Le Double (Bull, et mim. de la Soc. d'Anth. de Paris, 5« sdr. vol. iii. p. 550) records a case in which the foramen rotundum and the superior orbital fissure were united so as to form a single cleft. Through deficiency of its lateral wall, the optic foramen, in rare instances, communicates with the superior orbital fissure. Duplication of the optic foramen is also recorded as a rare occurrence, the artery passing through one canal, the nerve through the otliei-. Persistence of the cranio -pharyngeal canal is also occasionally met with. Owing to the ossification of fibrous bands whicn frequently connect the several bony points, anomalous foramina are frequently met with. Of such are the carotico-clinoid formed by the union of the anterior and middle clinoid processes, the jjterygo-spinous foramen enclosed by the ossification of the ligament con- necting the angular spine with the lateral pterygoid lamina, and the porus crotaphitico- buccinatorius similarly developed by the o.ssification of ligament immediately below and lateral to the inferior aperture of the foramen ovale. Ethmoid. — Tlie size of the lamina papyracea is liable to considerable variations. In the lower races it tends to be narrower from above downwards than in the higher, in tliis respect resem- bling the condition met with in the anthropoids. The lamina papyracea may fail to articulate with the lacrimal owing to the union of the frontal with the frontal process of the maxilla VAKIATIONS IN THE SKELETON. 279 in front of it. (Orltito-niaxillary-fiontal suture. A. Thoni.s(jn, Junrn. Anut. and J'hysiul. vol. xxiv. J). 349.) Divihiun of the l.uiiina pajiyiiicca ]>y a vertical suture into an anteritjr and posterior part ha.s been freepiently recoixled. The number of the conchui may be increased from two to four, or may be reduct-d to one. (Report of Committee of Collect. Invest., Journ. Anal, and Physiol, vol. xxviii. j). 74.) Maxillse. — Not infrec[uently there is a Buture loimiing vertically through the bar of bone wliich -separates the infra-orbital foramen from the infra-orbital margin. Through imperfections in ossification, the infra-orljital canal nuay form an open groove along the floor of the orbit. Duckworth records four instances of a spinous process ])rojectiug inwards into the apertura piriformis from the lower part of the na.sal notch. A case has Ijeen described (Fischel) in which there was complete absence of the premaxilUe, together with the incisor teeth. A not uncommon anomaly is the occurrence of a rounded elongated ridge extending along the interpalatal or intermaxillaiy sutures on the under surface of the hard palate. This is called the torus palatiniis, and is of interest because its pre.seuce has given rise to the assumption that it was due to a pathological growth. (See Stieda, Virchow's Festschrift, vol. i. p. 147.) The sulcus lacrim.ilis may be constricted towai-ds its centre. A part of the maxillaiy sinus may be constricted off anteriorly and, owing to its relation to the naso-lacriuud duct, is called the recessus LicrinialLs. UudeiAvood {Journ. Anat. and Physiol, vol. xliv. p. 359) records the occurrence of all but complete .septa dividing the cavity of the maxillary sinus. Zygomatic Bone. — Cases of division of the zygomatic bone by a horizontal suture have been recorded, as well as instances of its separation into two parts by a vertical suture. Owing to the supposed more frequent occurrence of this divided condition in Asiatics the zygomatic has been named the os Japonicuni. Barclay Smith (" Proc. Anat. Soc," Journ. Anat. and Physiol., Apiil 1898, p. 40) describes a case in which the zygomatic Ijone was divided into two parts, an ujjper and lower, by a backward extension of the maxilla, which articulated with the zygomatic process of the temporal, thus forming a temporo-maxillary arch. Varieties of a like kind have also been described by Gruber and others. Cases have been noted wliere, owing to deficiency in the develop- ment of the zygomatic, the continuity of the zygomatic arch has been incomplete. Nasal Bones. — The size and configuration of the nasal bones vary greatly in different mces, being, as a rule, large and prominent in the white races, and flat and reduced in size, as well as depressed, in the Mongolian and Negro stock. Complete absence of the nasal bones lias been recorded, and their division into two or more parts has also been noted. Obliteration of the internasal suture is unusual ; it is stated to occur more frequently in negroes, and is the recognised condition in adult apes. Duckworth has recorded a case {Journ. Anat. and Physiol, vol. xxxvi. p. 257) of undue extension downwards of the nasal bone, which may be perhaps accounted for on the supposition that the lower part is a persistent portion of the premaxiUa. Lacrimal. — The lacrimal is occasionally absent. In some cases it is divided into two parts ; in others replaced by a number of smaller ossicles. In rare instances the hamulus may extend forwards to reach the orbital margin, and so bear a share in the formation of the face, as in lenjurs (Gegenbauer). In other instances the hamulus is much reduced in size. Occasionally the lacrimal is separated from the lamina papyracea of the ethmoid by a down-growth from the frontal, which articulates with the frontal process of the maxilla, as is the normal disposition in the gorilla and chimpanzee. (Turner, Challenger Reports, "Zoology," vol. x. Part IV. Plate I. ; and A. Thomson, Journ. Anat. and Physiol, London, vol. xxiv. p. 349.) Inferior Concha. — A case in which the inferior concha; were absent has been recorded by Hyrtl. Vomer. — Owing to imperfect ossification there may be a deficiency in the bone, filled up during life l)y cartilage. Tne separation of the two lamellae along the anterior border varies considerably, and instances are recorded where they were separated by a considerable cavity within the substance of the bone. Instances of an extension forwards of the sphenoidal air sinus into and separating the lamime of the bone have also been described. The spheno-vomerine canal is a minute opening behind the rostrum of the sphenoid, and between it and the ala; of the vomer, by which the nutrient artery enters the bone. Palate Bones. — The occurrence of a torus palatinus may be noted (see Variations of Maxilla). Mandible. — Considerable differences are met with in the height of the coronoid process : usually its summit reaches the same level as the condyle, or slightly above it ; occasionally, how- ever, it rises to a much higher level ; in other cases it is much reduced. These differences naturally react on the form of the mandilnilar notch. The projection of the mental protuberance is also liable to vary. Occasionally the mental foramen is double, and sometimes the mylo-hyoid groove is for a short distance Converted into a canaL There is often a marked eversion of the angle of the mandible, which Dieulafe homologises with the angular apophysis met with in lemurs and caruivora. Clavicle. — The clavicles of women are more slender, less curved, and shorter than those of men. In the latter the bone is so inclined that its acromial end lies slightly higher or on the same level with the sternal end. In women the bone usually .slopes a little downwanl and laterally. The more pronounced curves of some bones are probably associated with a more powerful develo])ment of the jjcctoral and deltoid mu.scle.s, a circumstance which also affords an explana- tion of the differences usually seen between the right and left bones, the habitual use of the right 18 b 280 OSTEOLOGY. upper limb reacting on the form of the bone of that side. Tlie influence of muscular action, however, does not wholly account for the jiroduction of the curves of the bone, since the bone has been shown to display its characteristic features in cases where there has been defective de- velopment or absence of the upper limb (Reynault). Partial or complete absence of the clavicle has been recorded. W. S. Taylor exhibited an interesting case of this kind at the Clinical Society of London, October 25, 1901. Sometimes there is a small canal through the anterior border of the bone near its middle for the transmission of one of the supra-clavicular nerves. Scapula. — The most common variation met with is a separated acromion. In these cases there has been failure in the ossific union between the spine and acromion, the junction between the two being effected by a layer of cartilage or by an articulation possessing a joint cavity. The condition is usually symmetrical on both sides, though instances are recorded where this arrangement is unilateral Very much rarer is the condition in which the coracoid 2)rocess is separable from the rest of the bone. The size and form of the scapular notch differs. In certain cases the superior border of the bone describes a uniform curve reaching the base of the coracoid without any indication of a notch. In some scapulae, more particularly in those of very old people, the floor of the subscapular fossa is deficient owing to the absorption of the thin bone, the periosteal layers alone filling up the gap. At birth the vertical length of the bone is less in proportion to its width than in the adult. Humerus, — As has been stated in the description of the bone, the olecranon and coro- noid fossae may communicate with each other in the macerated bone. The resulting supra- trochlear foramen is most commonly met with in the lower races of man, as well as in the anthropoid apes, and in some other mammals. The occurrence of a hook -like spine, called the epicondijlic process, which projects in front of the medial epicondylic ridge, is not uncommon. Its extremity is connected with the medial epicondyle by means of a fibrous band, underneath which the median nerve, accompanied by the brachial artery, or one of its large branches, may pass, or in some instances, the nerve alone, or the artery unaccompanied by the nerve. This arrangement is the homologue in a rudimentary form of a canal present in many animals, notably in the camivora and marsupials. In addition to the broad radial groove already described, and which is no doubt produced by the twisting or torsion of the body, there is occasionally a distinct narrow groove posterior to it, which marks precisely the course of the radial nerve as it turns round the lateral side of the body of the bone. Ulna. — Cases of partial or complete absence of the ulna through congenital defect have been recorded. Rosenmiiller has described a case in which the olecranon was separated from the proximal end of the bone, resembling thus in some respects the patella. In powerfully developed bones there is a tendency to the formation of a sharp projecting crest corresponding to the inser- tion of the triceps. Eadius. — Cases of congenital absence of the radius are recorded ; in these the thumb is not infrequently wanting as welL Carpus. — Increase in the number of the carpal elements is occasionally met with, and these have been ascribed to division of the navicular, os lunatum, os triquetrum, capitate, lesser multangular, and os hamatum. Of these the most interesting is the os centrale, first described by Rosenberg, and subsequently investigated by Henke, Leboucq, and others. This is met with almost invariably as an independent cartilaginous element during the earlier months of foetal life, and occasionally becomes developed into a distinct ossicle placed on the back of the carpus between the navicular and capitate bones and the lesser multangular. Its significance depends on the fact that it is an important component of the carpus in most mammals, and is met with normally in the orang and most monkeys. Ordinarily in man, as was pointed out l^y Leboucq, it becomes fused with the navicular, where its presence is often indicated by a small tubercle, a condition which obtains in the chimpanzee, the gorilla, and the gibbons. Dwight has described a case in which there was an OS subcapitulum in both hands. The ossicle lay between the base of the middle metacarpal bone and the capitate bone, with the lesser multangular to its radial side. {Anat. Anz. vol. xxiv.) Further addition to the number of the carpal elements may be due to the separation of the styloid process of the third metacarpal bone and its persistence as a separate ossicle. Reduction in the number of the carpus has been met with, biit this is probably due to pathological cau.ses. Morestin {Bull. Soc. Anat. de Paris, tome 71, p. 651), who has investigated the subject, finds that ankylosis occurs most frequently between the bases of the second and third metacarpal bones and the carpus, seldom or never between the carpus and the first meta- carpal, or between the pisiform and os triquetrum. Instances of complete fusion of the os lunatum and triquetral bones, without any apparent pathological change, have been recorded in Europeans, Negroes, and an Australian. Metacarpal Bones. — As previously stated above, the styloid process of the third metacarpal bone appeara as a separate ossicle in about 1-8 per cent, of cases examined. (" Fourth Annual Report of the Committee of Collect. Invest. Anat. Soc. Gt. Brit, and Ireland," Journ. Anal, and Physiol, vol. xxviii. p. 64) In place of being united to the third metacarpal, the styloid process may be fused with either the capitate bone or the lesser multangular, under which conditions the ba.se of the third metacarpal bone is without this characteristic apophysis. Phalanges. — Several in.stances have been recorded of cases in which there were three phalanges in the thuml>. Bifurcation of the terminal phalanges has occasionally been met with, and examples of suppression of a phalangeal segment or its absorption by another phalanx have also been de- scribed. (Ha.sselwander, Zeits. f'tir Morph. u. Anthr. vol. vi. 1903.) VARIATIONS IN THE SKELETON. 281 Hip Bone. — Suiue of tlio auomalics liiet with in the liip Ixjiie aiu due to ossiBcatiou of the li^'iuiRiits coum-clL-il witli it; in otherwises llicy (h'lmiid on errora of develojuueiit. Failure of union between tlie jmbic and ischial rami has also Ijeen recorded. Cases have occurred where tlie oliturutor groove has l)een l)ri(iged across hy hone, and one case is noted of absence of the acetabular notcii on the acetal)ular margin. In rare cases the os acetabuli (see Ossification) remains as a separate bone. Derry (Jinirti. Aiiat. and I'ltyniol. vol. xlv. p. 202) lias drawn attention to the occurrence of a small accessf)ry articular facet, situated on the rough non-articular area im- mediately liehiml the auricul.ir surface of the ilium, which articulates witli a depressed facet on the posterior surface of the .sacrum to the lateral side of the first posterior sacral foramen, in the neigh- Ijourhood of the transverse j)rocess of the .second sacral segment. Tliis he liomelogises with liie normal articulation l)etweenthe ilium and sacral transverse ])rocesses found in many lower animals. Femur. — Ab.sence of the fovea on the head of the femur for the attaclnnent of the liga- mentum teres has been recorded. This corresponds with the condition met with in the orang. Not infrequently there is an extension of the articular surface of the head on to the anterior and ui)per a.spect of the nock ; this is a "pressure facet" cau.sed by the contact of the iliac portion of the acetabular margin with the neck of the bone, when the limb is maintained for long jjcriods in the Hexed position, as in tailors, and also in those races who habitually squat (Lane, Joum. Anat. and Physiol, vol. xxii. p. 606). The occurrence of a trochanter tertius has been already referred to. Its presence is not confinetl to individuals of })owerful physique, but may occur in those of slender build, so far suggesting that it is not to be regarded merely as an indication of excessive muscular develop- ment. The observations of Dixon (Joum. Anat. and Physiol, vol. xxx. p. 502), who noted the occurrence of a separate epij)hysis in three cases in connexion with it, seem to point to its possessing some morphological significance. Occasionally the gluteal tuberosity may be replaced l)y a hollow, the fossa hypotrochanterica, or in some cases the two may co-exist. The angle of the neck is more ojjcn in the child than in the adult, and tends to be less when the femoral length is short and the pelvic width great — conditions which jjarticularly appertain to the female. There is no evidence to show that after growth is comjjleted any alteration takes place in the angle with advancing vears (Humphry). The curvature of the body may undergo considerable variations, and the ai)pearance of the j)osterior surface of the bone may be modified by an absence of the linea asjjera, a condition resembling that seen in apes ; or by an unusual elevation of the bone which supports the ridge (fSmur a jnlastre), produced, as Manouvrier has suggested, by the excessive development of the muscles here attached. Under the term " platyinerie," Manouvrier describes an antero-posterior compression of the l)roximal part of the body, frequently met with in the femora of prehistoric races. Patella. — Cases of congenital absence of the patella have been recorded. F. C. Keni})3on {Joum. Anat. and Physiol, vol. xxxvi.) has recently drawn attention to the condition described as emargination of the patella. In specimens displaying this appearance the margin of the bones is concave from a point about half an inch to the lateral side of the middle line, to a point half-way down the lateral margin of the bone; here there is usually a pointed spine directed proximally and laterally. The condition appears to be associated with the insertion of the tendon of the vastus lateralis. G. Joachimstal (Archiv u. Atlas der normalen und patholo- yischen Anatomie in typischen Rdntyenhildern, Bd. 8) figures a case in which on both sides the ])atella was double in an adult, the distal and much the smaller portion was embedded in the ligamentum patelkt. Tibia. — The tibia is often unduly compressed from side to side, leading to an increase in its antero-jjosterior diameter as compared with its transverse width. This condition is more commonly met with in the bones of prehistoric and savage races than in modern Europeans. Attention was first directed to this particular form by Busk, wdio named the condition platyknemia. The general appearance of such tibiae resembles that seen in the apes, and de])ends on an exceptional development of the tibialis posterior muscle, though, as Manouvrier has pointed out, in apes this is associated with the direct action of the muscle on the foot, as in climbing, whereas in man, as a consequence of the bipedal mode of progression, the muscle is employed in an inverse sense, viz., by steadying the tibia on the foot, and thus ])roviding a fixed base on which the femur can move. This explanation, however, is disputed by Derry {Joum. Anat. and Phys. vol. xli. p. 123). Such platyknemic tibiie are occasionally met with in the more highly civilised races, and are, according to Manouvrier, associated with habits of great activity among the inhabitants of rough and mountainous districts. Another interesting condition is one in which the proximal extremity is more strongly recurved than is usual. This retroversion of the head of the tibia was at one time supjiosed to represent an intermediate condition in which the knee could not be fully extended so as to bring the axis of the leg in line with the thigh ; but such opinion has now been upset by the researches of Manouvrier, who claims that it is the outcome of a habit not uncommon amongst peasants and countrymen, viz., that of walking habitually with the knees slightly bent. Habitual posture also leaves its impress on the form of the tibia, and in races in which the use of the chair is unknown, the extreme degree of flexion of the knee and ankle necessitated by the adoption of the squatting position as an attitude of habitual rest is associated with an increase in the convexity of the lateral cond^dic surface, and the appearance, not infrequently, of a pressure facet on the anterior border of the distal extremity, which rests in that position on the neck of the talus. Cases of congenital absence of the tibia have been frequently described, amongst the most recent being those recorded by Clutton, Joachimsthal, Bland-Sutton, and Waitz. 282 OSTEOLOGY. Fibula. — The fibiila may be ridged and grooved in a remarkable manner, as is the case in many bones of prehistoric races. This is probably associated with a greater development and perhaps with more active use of the muscles attached to it. The proximal articular facet varies much in size. Bennett {Dublin Joum. Med. Sc, Aug. 1891) records a case in wliich it was double, and also notes the occurrence of specimens in which it was absent and in which the head of the bone did not reach the lateral condyle of the tibia. Many instances of partial or complete absence of the bone have been published. (Lefebre, Contribution a Vitude de Vabsence congenitale die peron^, Lille, 1895.) Talus. — The anterior calcanean facet is sometimes separated from the middle by a non- articular furrow. The posterior process, often largely developed, is occasionally (2-6 per cent.) a separate ossicle forming what is known as the os trigonum (Bardeleben) ; or it may be united to the body of the talus by a distinct synchondrosis. A smooth articular surface may occasionally be found on the medial side of the proximal surface of the neck. This is a pressure facet dependent on the frequent use of the ankle-joint in a condition of extreme flexion, and is caused by the opposition of the bone against the anterior edge of the distal end of the tibia. The form of the bone at birth differs from that of the adult in that the medial splay of the neck on the body is more pronounced, forming on an average an angle of 35° as compared with a mean of 12° in the adult ; moreover, the articular surface for the medial malleolus extends forwards along the medial side of the neck, and to some extent overruns its superior surface. This is doubtless a consequence of the inverted position of the foot maintained by the foetus , during intra-uterine life. In these respects the foetal bone conforms to the anthropoid type. For a detailed study of the varieties of this bone, see R. B. S. Sewell. (Joum. Anat. and Physiol. voL xxxviii.) Calcaneus. — The trochlear process is occasionally unduly prominent, constituting the sub- malleolar apophysis of Hyrtl, and cases are recorded of the calcaneus articulating with the navicular. (Morestin, H., Bull, de la Soc. Anat. de Paris, 1894, 5^ sir. t. 8, n. 24, p. 798 ; and Petrini, Atti del XL Gongr. Med. Internaz. Roma, 1894, voL ii., "Anat." p. 71.) Pfitzner {Morplio- logische Arbeiten, vol. vi. p. 245) also records the separation of the sustentaculum tali to form an OS sustentacula (See also P. P. Laidlaw, Joum. Anat. and Physiol, vol. xxxviii. p. 133.) Navicular. — According to Manners Smith this bone displays more variety of form than any other of the tarsal bones. He accounts for this both on morphological and mechanical grounds. He regards the tuberosity as probably of threefold origin, an apophysial, an epij)hysial, and a sesamoid element, the latter being the so-called sesamoid bone in the tendon of the tibialis posterior. Cases are recorded where the tuberosity has formed an independent ossicle. Cuneiform Bones. — Numerous cases of division of the first cuneiform bone into dorsal and plantar parts have been recorded ; the frequent division of its metatarsal articular facet is no doubt correlated with this anomalous condition. T. Dwight has described {Anat. Anz. voL xx. p. 465) in two instances the occurrence of an os intercuneiforme. The ossicle so named lies on the dorsum of the foot at the posterior end of the line of articulation between the first and second cuneiform bones. Cuboid. — Blandin has recorded a case of division of the cuboid. Occasionally there is a facet on the lateral surface of the bone for articulation with the tuberosity of the fifth metatarsal (Manners Smith). Tarsus as a Whole. — Increase in the number of the tarsal elements may be due to the occurrence of division of either the first cuneiform or the cuboid bone, or to the occasional presence of an os trigonum. Cases of separation of the tuberosity of the navicular bone have been recorded, and instances of supernumerary ossicles l^etween the first cuneiform and second metatarsal bone have been noted. Stieda mentions the occurrence of a small ossicle in connexion with the articular surface on the anterior and upper part of the calcaneus, and Pfitzner notes the occurrence of an os sustentaculi. For further information on the variations of the skeleton of the foot, see Pfitzner. {Morphologische Arbeiten, vol vi. p. 245.) The possibility of an injury having been the cause of the occurrence of some of these so-called supernumerary ossicles must not be overlooked. The use of the Rontgen rays has proved that accidents of this kind are much more frequent than was at first sujDposed. The reduction in the number of the tarsus is due to the osseous union of adjacent bones. In many instances this is undoubtedly pathological, but cases have been noticed (Leboucq) of fusion of the cartilaginous elements of the calcaneus and talus, and the calcaneus and^ navicular in fcjctuses of the third month. Metatarsal Bones. — Several instances of separation of the tuberosity of the fifth metatarsal (o3 Vesaleanuni) have been recorded, whilst numerous examples of an os intermetatarsum between the bases of the first and second metatarsal bones have been recorded by Gruber and others. The tubercle on the base of the first metatarsal for the attachment of the peronaeus longus tendon is occasionally met with as a separate ossicle. An epiphysis over the spot where the tuberosity of tlie fifth metatarsal rests on the ground has been described. (Kirchner, Archiv klin. Chir. B 80.) Phalanges.— It is not uncommon to meet with fusion of the second and third phalanges, j)articularly in the fiftli, less frequently in the fourth, and occasionally in the second and third toe.s. The union of the phalangeal elements has been observed in the foetus as well as the adult (Pfitzner). The proportionate length of the phalanges varies much ; in some cases the imgual phalanges are of fair size, the bones of the second row being mere nodules, whilst in other instances the reduction in size of the terminal phalanges is most marked. SEEIAL HOMOLOGIES OF THE VERTEBRAE. 283 APPENDIX C. SERIAL HOMOLOGIES OF THE VERTEBRAE. CERVICAL True tbansvkrsk I'ROCKSS Foramen trans- VF.RSAHM \! Costal proi i ~- Nevro-cestral I TrANSVER: I HIE TBANS- VKRSK PROCESS Costal pRoct:ss THORACIC Foramen transversariim Xeubo-cestral synchondrosis AlCESSOKV TCBERl I I Transverse PROCESS UlB LUMBAR Accessory pp.ocess It is a self-evident fact that the vertebral coluiim consists of a number of segments or verte- bne all possessing some charactere in common. These vertebrte or segments undergo modifications according to the region they oc- cupy and the functions they are called upon to serve, so that their correspondence and identity is thereby obscured. Tliere is no diflSculty in recognising the homo- logy of the bodies and veitel)ral arches throughout the column. According to some anatomists the vertebral arch is the more primi- tive element in the formation of a vertebra, whilst others hold that the bodies are the foundation of the column- Be that as it may, we find that in the higher vertebrates, at least, the bodies are the parts which most persist. They are, however, subject to modifications dependent on their fusion with one another. This occurs in the cervical part of the column where the body of the first cervical or atlas has for functional reasons become fused with the body of the second or epistropheus to form the dens of that segment. For similar reasons, and in association with the union of the girdle of the hind-limb with the column, the bodies of the vertebrte which correspond to the sacral segment become fused together to form a solid mass. In tlie terminal por- tion of the caudal region the bodies alone represent the vertebral seg- ments. As i-egards the vertebral arch, this in man becomes deficient in the lower sacral region, and absent altogether in the lower coccygeal segments. The spinous processes are absent in the case of the first cervical, lower sacral, and all the coc- cygeal vertebrte, and display characteristic dift'erences in the cervi- cal, thoracic, and lum- bar regions, which have been already described. The articular processes (zygajtophyses) are secondary develop- ments, and display great divei-sity of form, deter- mined by their func- tional requirements. It is noteworthy that, in the case of the upper two cervical vertebrae, they are so disposed as to lie in front of the foramina of exit of the upper two spinal nerves, and by this arrangement the weight of the head is transmitted to the solid column formed by the vertebral bodies, and not on to the series of vertebral arches. It is in regard to the homology of the transvei-se processes, so called, that most difficulty arises. In the Costal ki Occasional foramen TBAN.SVERSARirM XeIRO-CENTRAL SVNCHONDROSl Tr ansversk , -^ >\^ PH.. I --r Costal element (rib) SACRAL Costal Ei.hM OCCASU)N \I. KOKAMEX TRANSVERSARIIM NeI BO-CEXTRAI SVNCHONDROSI'J Transverse ^^ processes Costal elements A B Fig. 280.— Diagram to illustrate the Homologous Parts of the Vkrtebk.*:. The bodies are coloured purple ; the vertebral arch aud its processes, red ; the costal elements, blue. A, from above. B, from the side. 284 OSTEOLOGY. thoracic region they can best be studied in their siniialest form ; here the ribs — which Gegenbauer regards as a differentiation from the inferior or haemal arches, in opposition to the view advanced by others that they are a secondary development from the fibrous intermuscular septa — articulate with the transverse processes and bodies of the thoracic vertebrae through the agency of the tubercular (diapophyses ) and capitular (parapophyses) processes respectively, the latter being placed, strictly speaking, on the vertebral arch behind the line.of the neuro-central synchondrosis. An interval is thus left between the neck of the rib and the front of the transverse process ; this forms an arterial passage which corresponds to the foramen transversarium in the transverse processes of the cervical vertebrte, the anterior bar of which is homologous with the head and tubercle of the thoracic rib, whilst the posterior part lies in series with the thoracic transverse process. These homologies are further emiDhasised by the fact that in the case of the seventh cervical vertebra the anterior limb of the so-called transverse process is developed from an independent ossific centre, which occasionally persists in an independent form as a cervical rib. In the lumbar region the lateral or transverse process is serially homologous with the thoracic ribs, though here, owing to the coalescence of the contiguous parts, there is no arterial channel between the rib element and the true transverse process, which is represented by the accessory processes (anapophyses), placed posteriorly at the root of the so-called transverse process of human anatomy. Support is given to this view by the presence of a distinct costal element in connexion with the transverse process of the first lumbar vertebra, which accounts for the occasional formation of a supernumerary rib in this region. The cases of foramina in the transverse processes of the lumbar vertebrae (see p. 275) are also noteworthy as supporting this view. In the sacrum the lateral part of the bone is made up of combined transverse and costal elements, with only very exceptionally an intervening arterial channel. In the case of the upper three sacral segments the costal elements are largely developed and assist in support- ing the ilia, and they are called the true sacral vertebrte ; whilst the lower sacral segments, which are not in contact with the ilia, are referred to as the pseudo-sacral vertebrae. The anterior arch of the atlas vertebra is, according to Froriep, developed from a hypochordal strip of cartilage (hypochordal spange). APPENDIX D. MEASUREMENTS AND INDICES EMPLOYED IN PHYSICAL ANTHROPOLOGY. (1) Craniometry. The various groups of mankind display in their physical attributes certain features which are more or less characteristic of the stock to which they belong. Craniology deals with these differences so far as they affect the skull. The method whereby these differences are recorded involves the accurate measurement of the skull in most of its details. Such procedure is included under the term craniometry. Here only the outlines of the subject are briefly referred to ; for such as desire fuller information on the subject, the works of Broca, Topinard, Flower, and Turner may be consulted. The races of man display great variations in regard to the size of the skull. Apart altogether from individual differences and the proportion of head-size to body -height, it may be generally assumed that the size of the skull in the more highly civilised races is much in excess of that displayed in lower types. The size of the head is intimately correlated with the develop- ment of the brain. By measuring the capacity of that part of the skull occupied by the encephalon, we are enabled to form some estimate of the size of the brain. The cranial capacity is determined by filling the cranial cavity with some suitable material and then taking the cubage of its contents. Various methods are employed, each of which has its advantage. The use of fluids, which of course would be the most accurate, is rendered impracticable, without special precautions, owing to the fact that the macerated skull is pierced by so many foramina. As a matter of practice, it is found that leaden shot, glass beads, or seeds of various sorts are the most serviceable. The results obtained display a considerable range of variation. For purposes of classification and comparison, skulls are grouped according to their cranial capacity into the following varieties : — Microcephalic skulls are those with a capacity below 1350 c.c, and include such well-known races as Andamanese, Veddahs, Australians, Bushmen, Tasmaniaiis, etc. Mesocephalic skulls range from 1350 c.c. to 1450 c.c, and embrace examples of the following varieties : American Indians, Chinese, some African Negroes. Megacephalic skulls are those with a capacity over 1450 c.c, and are most commonly met with in the more highly civilised races : Mixed Europeans, Japanese, etc. Apart from its size, the form of the cranium has been regarded as an important factor in the classification of skulls ; though whether these differences in shape liave not been unduly emphasised in the past is open to question. The relation of the breadth to the length of the skull is expressed by means of the cephalic index which records the proportion of the maximum breadth to the maximum length of the skull, assuming the latter equal 100, or — Max. breadth x 100 -, , , . . , ,, , , = Cephalic index. Max. length MEASUREMENTS AND INDICES. 285 The results are classified into three gr9up3 : — 1. Dolichocephalic, with an index below 75 : Australians, KatFirs, Zulus, Eskimo, Fijians. 2. Mesaticephalic, ranging from 75 to 80 : Europeans (mixed), Chinese, Polynesians (mixed). 3. Brachycephalic, with an index over 80 : Malays, Burmese, American Indians, Anda- manese. In order to provide for uniformity in the results of different ol)servere, some system is neces- sary by which the various points from which the measurements are taken must correspond. Whilst there is much difference in the value of the measurements insi.sted on by individual anatomists, all af'ree in endeavouring to select such points on the skull as may be readily deter- mined, and which have a fairly fixed anatomical position. The more important of these " fixed points " are included in the subjoined table : — Stephanion Obklion Maximum occiriTAi, POINT Inion jugal point Akanthion Prosthion (alTSSIar point) POGOJJION Nasion. — The middle of the naso-frontal suture. G-labella. — A jjoint midway between the two superciliary ridges. Opliryon. — The central point of the narrowest transverse diameter of the forehead, measured from one temporal line to the other. Inion. — Tlie external occipital protuberance. Maximum Occipital Point. — The point on the squamous part of the occipital in the sagittal plane most distant from the glabella. Opisthion. — The middle of the posterior margin of the foramen magnum. Basion. — The middle of the anterior margin of the foramen magnum. Bregma. — The point of junction of the coronal and sagittal sutures. Rhinion. — The most prominent point at which the nasal bones touch one another. Alveolar Point or Prosthion. — The centre of the anterior margin of the upper alveolar margin. Subnasal Point. — The middle of the inferior border of the piriform (anterior nasal) aper- ture at the centre of the anterior nasal spine. Akanthion.— The most prominent point on the nasal spine. Vertex. — The summit of the cranial vault. Obelion. — A point over the sagittal suture, on a line with the parietal foramina. Lambda. — The meeting-point of the sagittal and lambdoid sutures. Pterion.— The region of the antero-lateral fontanelle where the angles of the frontal, parietal, squamous part of the temporal, and great wing of sphenoid lie in relation to one another. As a rule, the sutures are arranged like the letter Hj the parietal and great wing of sphenoid separating the frontal from the squamous temporal. In other cases the form of the suture is like an X ; whilst in a third variety the frontal and squamous part of the temporal articulate with each other, thus separating the great wing from the parietal. Asterion is the region of the postero-lateral fontanelle where the lambdoid, parieto-mastoid, and occipito-mastoid sutures meet. Stephanion.— The point where the coronal suture crosses the temporal line. Dacryon. — The point where the vertical lacrimo-maxillary suture meets the fronto-nasal suture at the inner angle of the orbit. 286 OSTEOLOGY. Jugal Point. — Corresponds to the angle between the vei-tical border and the margin of the temporal process of the zygomatic bone. Supra-auricular Point. — A point immediately above the middle of the orifice of the external acoustic meatus close to the edge of the posterior root of the zygoma. Gonion. — The lateral side of the angle of the mandible. Pogonion. — The most prominent point of the chin as represented on the mandible. The measurements of the length of the skull may be taken between a variety of points — the nasion, glabella, or ophryon in front, and the inion or maximum occipital point behind. Or the maximum length alone may be taken without reference to any fixed points. In all cases it is better to state precisely where the measurement is taken. The maximum breadth of the head is very variable as regards its jJosition ; it is advisable to note whether it occurs above or below the parieto-squamosal suture. The inter-relation of these measurements as expressed by the cephalic index has been already referred to. The width of the head may also be measured from one asterion to tlie other, biasterionic width, or by taking the bistephanic diameter. The height of the cranium is usually ascertained by measuring the distance from the basion to the bregma. The relation of the height to the length may be expressed by the height or vertical index, thus— Height X 100 „ .. ... — s — = Vertical index. Length Skulls are classified in accordance with the relations of length and height as follows : — Tapeinocephalic index below 72. Chamsecephalic index up to 70. Metriocephalic index between 72 and 77. Orthocephalic index from 70-1 to 75. Akrocephalic index above 77 (Turner). °^ Hypsicephalic index 75-1 and upwards (Kollmann, Ranke, and Virchow). The horizontal circumference of the cranium, which ranges from 450 mm. to 550 mm., is measured around a plane cutting the glabella or ophryon anteriorly, and the maximum occipital point posteriorly. The longitudinal arc is measured from the nasion in front to the opisthion behind ; if to this be added the basi-nasal length and the distance between the basion and the opisthion, we have a record of the vertico-median circumference of the cranium. This may further be divided by measuring the lengths of the frontal, parietal, and occipital jDortions of the superior longitudinal arc. In this way the relative proportions of these bones' may be expressed. The measurements of the skeleton of the face are more complex, but, on the whole, of greater value than the measurements of the cranium. It is in the face that the characteristic features of race are best observed, and it is here that osseous structure most accurately records the form and proportions of the living. The form of the face varies, like that of the cranium, in the relative proportions of its length and breadth. Generally speaking, a dolichocephalic cranium is associated with a long face, whilst the brachycephalic type of head is correlated with a rounder and shorter face. This rule, how- ever, is not universal, and there are many exceptions to it. The determination of the facial index varies according to whether the measurements are made with or without the., mandible in position. In the former case the length is measured from the ophryon or nasion above to the mental tubercle below, and compared with the maximum bizygomatic width. This is referred to as the total facial index, and is obtained by the formula — Ophryo-mental leng^hxlOO^^^^^^ ^^^.^^ .^^^^ Bizygomatic width More usually, however, owing to the loss of the mandible, the proportions of the face are expressed by the superior facial index. This is determined by comparing the ophryo-alveolar or naso-alveolar length with the bizygomatic width, thu.s — Ophryo-alveolar length x 100 _ . o . , . j -^ — ttt. ^-r-. ?,-., = Superior facial index. Bizygomatic width The terms dolichofacial or leptoprosope and brachyfacial or chamoeprosope have been employed to express the differences thus recorded. Uniformity in these measurements, however, is far from complete since many anthropologists compare the width with the length = 100. The proi)ortion of the face-width to the width of the calvaria is roughly expressed by the use of the terms cryptozygous and phsenozygous as applied to the skull. In the former case the zygomatic arches ai'e concealed, when tlie skull is viewed from above, by the overhanging and projection of tlie sides of the cranial l)Ox ; in the latter in.stance, owing to the narrowness of the calvaria, tlie zygomatic arches are clearly visible. The projection of the face, so characteristic of certain races (Negroes for example), may be estimated on the living by measuring the angle formed by two straight lines, the one passing from the middle of the external acoustic meatus to the lower margin of the septum of the nose ; the other drawn from the mo.st prominent part of the forehead above to touch the incisor teeth below. The angle formed by the intersection of these two lines is called the facial angle (Camper), and ranges from 62° to 85°. The smaller angle is characteristic of a muzzle-like MEASUREMENTS AND INDICES. 287 projection of tlie lower part of the face. -Tlie larj^'er an<,'le is the concomitant of a more vertical l>rotile. The degree of i)r()jection of the maxilla in llie macerated cranium i.s most commonly expressed by employing the gnathic or alveolar index of Flower. This records the relative ])roportions of tne basi-alveolar and basi-na-sal lengths, the latter being regarded a8=100, thus — Basi-alveolar length X 100 „ ^,- ■ ■, - ,. . , , .1 = Gnathic index, iia-si-nasal length The results are conveniently grouped into three classes : — Orthognathous, index below 98 : including mixed Europeans, ancient Egyptians, etc. Mesognathous, index from 98 to 103 : Chinese, Japanese, Eskimo, Polynesians (mixed). Prognathous, index above 103 : Tasmanians, Australians, Melanesians, various African Negroes. Unfortunately, hovyever, little reliance can be i)laced on the results obtained by this method, since it takes no account of the proportion of the third or facial side of the gnathic triangle. P'or a further discu.ssion of this matter see Thom.son and Maclver, Races of the Tliehaid (Oxford : Clarendon Press, 1905). The form of the piriform aperture in the macerated skull is of much value from an ethnic stand])oint, as it is so intimately associated with the shape of the nose in the living. The greatest width of the aperture is compared with the nasal height (measured fi-om the nasion to the lower bonier of the aperture) and the nasal index is thus determined : — Nasal width x 100 „ , • j - ... — .,- . , ^ =Nasal index. Nasal height Skulls are — Leptorhine, with a nasal index below 48 : as in mixed Europeans, ancient Egyptians, American Indian.s, etc. Mesorhine, witli an index ranging from 48 to 53 : as in Chinese, Japanese, Malays, etc. Platyrhine, with an index above 53 : as in Australians, Negroes, Kaffirs, Zulus, etc. The form of the orbit varies considerably in different races, but is of much less value from the standpoint of classification. The orbital index expresses the proportion of the orbital height to the orbital width, and is obtained by the following formula : — Orbital height x 100 ,»,..,. , — ^ ... 1 -i.T, — = Orbital index. Orbital width The orbital height is the distance between the upper and lower margins of the orbit at the middle ; whilst the orl)ital width is measured from a i)oint where the ridge which forms the posterior boundary of the lacrimal groove meets the fronto- lacrimal suture (Flower), or from the dacryon (Broca) to the most distant point from these on the anterior edge of the lateral border of the orbit. The form of the orbital aperture is referred to as — Megaseme, if the index be over 89 ; Mesoseme, if the index be between 89 and 84 ; Microseme, if the index be below 84. The variations met with in the form of the palate and dentary arcade may be expressed by the palato-maxillary index of Flower. The length is measured from the alveolar point to a line drawn across the posterior borders of the niaxilke, whilst the width is taken between the outer borders of the alveolar arch immediately above the middle of the second molar tooth. To obtain the index, the following formula is emjjloyed : — Palato-maxillary width x 100 _ i x n • j — T, , ^ TY j r\ — = Palato-maxillary index. Palato-maxillary length For purposes of classification Turner has introduced the following terms : — Dolichuranic, index below 110. Mesuranic, index between 110 and 115. Brachyuranic, index above 115. As is elsewhere stated the size of the teeth has an imjjortant inlluence on the architecture of the skull. Considered from a racial standpoint, the relative size of the teeth to the length of the cranio-facial axis has been found by Flower to be a character of much value. The dental length is taken by measuring the distance between tlie anterior surface of the first premolar and tlie posterior surface of the third molar of the upper jaw. To obtain the dental index the following formula is used : — Dental length x 100 _ . , . , ts • TT T^= Dental index. Basi-nasal length 288 OSTEOLOGY. Following the convenient method of division adopted with other indices, the dental indices may be divided into three series, called respectively — Microdont, index below 42 : including the so-called Caucasian or white races. Mesodont, index between 42 and 44 : including the Mongolian or yellow races, Megadont, index above 44 : comprising the black races, including the Australians. ^lany complicated instruments have been devised to take the various measurements required, but for all practical purposes the calipers designed by Flower or the covipas glissilre of Broca are sufficient. As an aid to calculating the indices, the tables published in the Osteological Catalogue of the Royal College of Surgeons of England, Part I., Man ; Index- Tabellen zum anthropometrischen Gebrauche, C. M. Furst, Jena, 1902 ; or the index calculator invented by Waterston will be found of much service in saving time. (2) Indices and Measurements of other Parts of the Skeleton. In addition to the indices employed to exjaress the proportions of the cranial measurements, there are others similarly made use of to convey an idea of the proportions of different parts of the skeleton. Of these the following may be mentioned as those in most common use : — Scapula. — At birth the form of the human scapula more closely resembles the mammalian tj^e in that its breadth, measured from the glenoid cavity to the vertebral border, is greater in comparison with its length than in the adult. This proportion is expressed as follows : — Breadth from glenoid cavity to vertebral border x 100 „ , • j ^ 7^^-? ,. T ^ — ■ „ . :, = Scapular index, Lengtli from medial to mierior angle The index ranges from 87 in African pygmies, which therefore have proportionately broader scapulae, to 61 in Eskimos. The average European index is about 65. Hip Bone. — The relation of the breadth of this bone to its height is computed as follows : — Iliac breadth x 100 _ . , . , T 1 ■ — ^. — ^ — ^-j-; = Innominate index. Ischio-iliac height Man as compared with the apes is distinguished by possessing proportionately broader and shorter hip bones. The index in man ranges from 74 to 90. Pelvis. — The form of the human pelvis is characterised by an increased proportionate width and a reduced proportionate height or length. The relation of these diameters is expressed by the formula : — Ischio-iliac height X 100 _p i • u ^+i, v, • hf ' A Greatest breadth between the outer lips of the iliac crests "" The average index for white races is 73. Pelvic Cavity. — The measurements usually taken are those of the superior aperture. In man there is a proportionate increase in the transverse diameter as compared with lower forms : — Antero-j)osterior diameter (conjugate) from mid -point of sacral promontory to the posterior margin of pubic symphysis X 100 _-p i • y, ■ -a Greatest transverse width between ilio-pectineal lines Turner has classified the indices into three groups : — Dolichopellic, index above 95 : Australians, Bushmen, Kaffirs. Mesatipellic, index between 90-95 : Negroes, Tasmanians, New Caledonians. Platypellic, index below 90 : Europeans and Mongolians generally. Vertebral Column. — A characteristic feature of man's vertebral column is the pronounced lumbar curve associated with the erect posture in the living. Apart from the consideration of the interposition of the intervertebral fibro-cartilage between the segments, the bodies of the lumbar vertebrie influence and react on the curve by exhibiting differences in their anterior and posterior vertical diameters. Advantage has been taken of this to endeavour to reconstruct the lumbar curve from the dried and macerated bones, but it must be borne in mind that habitual po.sture or increased range of movements may yield results which are possibly misleading. Thus there is reason for believing that the squatting position, when habitually adopted, may give rise to a compression of tlie anterior parts of the bodies of the vertebrae which it might be a.SHumed was associated with an absence of or flattening of tlie lumljar curve, which in fact did not exist during life. The quality of the curve is estimated from the macerated bones by an index which is com- puted as follows : — Sum of posterior vertical diameters of the bodies of five lumbar vertebrae x 100 _ „ , , , . , Sum of anterior vertical diameters of the liodies of five lumbar vertebrte MEASUREMENTS AND INDICES. 289 The results are classified as follows :-;- Kurtorachic, index below 98, displaying a forward convexity : includes Europeans gi^nerally, Chinese. Orthorachic, index bcdween 98 and 102, column practically straight : includes examples of Kskiino and Maori. Koilorachic, index above 102, displaying a backward convexity : includes Australians, Negroes, Bushmen, and Andamanese. Sacrum. — Man's sacrum is characterised by its great breadth in proportion to its length. These relations are exjiressed as follows : — Greatest breadth of ba.se of sacrum x 100 _ , . , Length from middle of promontory to middle of anterior inferior border of fifth sacral vertebrae The diverse forms are grouped as follows : — Dolichohieric, index below 100, .sacra longer than broad : includes Australians, Tasmanians, Bushmen, Hottentots, Kaffirs, and Andamanese. Platyhieric, index above 100, sacra broader than long : includes Europeans, Negroes, Hindoos, North and South American Indians. Limb Bones. — The proportionate length of the limb bones to each other and to the body height is of jiractical interest. It is a matter of common knowledge that the forearms of Negroes are proportionately longer than those of Europeans. Great differences, too, are met with in the absolute and proportioiiate length of the lower limbs, nor must the relation of these to body height be overlooked. An enumeration of the more important of these indices, and the manner of their computation, will suffice. The proportion of the length of the radius to the length of the humerus is expressed as follows : — Length of radius x 100 t, .-. i • j -~^- — = — 5-T = Eadio-humeral index. Length of humerus Sub-divided into three groups : — Brachykerkic, index less than 75 : includes Europeans, Lapps, Eskimo. Mesatikerkic, index between 75-80 : Chinese, Australians, Polynesians, Negroes. Dolichokerkic, index above 80 : Andamanese, Negritoes and Fuegians, Bonindae in general. The proportion of the length of the tibia to the femur is computed by the formula — Length of tibia from surface of condyle to articular surface for talus x 100 „., . . ... 2 ^ — J-^ — = Tibio -femoral index. Oblique length oi lemur Sub-divided into two groups : — Brachyknemic, index 82 and under : includes Europeans and Mongolians generally. Dolichoknemic, index 83 and over : includes Australians, Negroes, Negritoes, American- Indians. The proportion of the length of the upper limb to that of the lower limb is obtained thus : — Lengths of humerus -I- radius x 100 _ . > i • j ^ -. 5-» -TY-. = Intermembral index. Lengths oi lemur + tibia A comparison between the relative lengths of the upper segments of the limbs is obtained by the following formula : — Length of humerus x 100 „ . i • j - -T — 1 i. I- = Humero-femoral index. Length ot lemur Platymeria (see p. 281). — The amount of compression of the femur is estimated as follows : — Sagittal diameter of shaft immedi ately distal to lesser trochanter x 100 _ pi o+^meric index Transverse diameter of shaft immediately distal to lesser trochanter Platyknemia (see p. 281) — The degree of compression of the tibia is estimated by the formula — Transverse diameter of shaft at level of nutrient foramen x 100 „, . , „•.. • j„„ ^-,— 7i 5 ^ — e ■ r =Platyknemic index. Antero-posterior diameter of shaft at level oi nutrient loramen The index ranges from 60 in a Maori tibia to 80 to 108 in modem French tibiae. For further and more detailed information relating to the various measurements and indices employed by the physical anthropologist, the reader is referred to Topinard's Elements d'Anthro- pologie ; Sir W. Turner's Challenger Memoirs, Part 47, vol. xvi. ; and Duckworth's Morphology and Anthropology. 19 290 OSTEOLOGY. APPENDIX E. DEVELOPMENT OF THE CHONDRO-ORANIUM AND MORPHOLOGY OF THE SKULL. As has been already stated, tlie chorda dorsalis or notochord extends headwards to a point immediately beneath the anterior end of the mid-brain. In front of this the head takes a bend so that the large fore-brain overlaps the anterior extremity of the notochord. At this stage of development the cerebral vesicles are enclosed in a membranous covering derived from the mesen- Pars ethmoidalis Orbito-splienoid Superior orbital fissure r j Alisphenoid y"T Carotid canal Meatus acusticus internus Subarcuate fossa Jugular foramen — ^| Canalis hypoglossi Foramen magnum Lamina cribrosa Orbital portion of orbito-sphenoid I '-^^^ i Optic foramen Tuberculum sellse \ (Olivary process) Sella turcica ~~/ \ — \\~ Dorsum sella^ \\\ Pars petrosa Superior semicircular canal Pars mastoidea isupra-occipital Occipital fontanelle Fio. 282. — View ok the Chondro- Cranium of a Human Foetus 5 cm. in length from Vertex to Coccyx (about the middle of the third month) ; the cartilage is coloured blue. The line to the right of the drawing shows the actual size. chyme surrounding the notochord ; this differentiated mesodermal layer is called the primordial membranous cranium. From it the meninges which invest the brain are derived. In lower vertebrates this membranous capsule becomes converted into a thick -walled cartilaginous envelope, the primordial cartilaginous cranium. In mammals, however, only the basal part of this capsule becomes chondrified, the roof and jaart of the sides remaining membranous. In considering the chondrification of the skull in mammals, it must be noted that part only of the base is traversed by the notochord, viz., that jjortion which extends from the foramen magnum to the dorsum sellae of the sphenoid. It is, therefore, conveniently divided into two jiarts — one posterior, surrounding the notochord, and hence called chordal, and one in front, into which the notochord does not extend, and hence termed prechordal. These correspond respectively to the vertebral and evertebral regions of Gegenbaucr. In the generalised type, a pair of elongated cartilages called the para- chordal cartilages appear on either side of tlie chorda in the chordal region, similarly in the prechordal region two curved strips of cartilage named the prechordal cartilages, or the trabeculae cranii of Rathke, develop on either side of the cranio-pharyngeal canaL In the human embryo, however, this symmetrical arrangement has not hitherto been observed. In man, chondrification of the cranial base commences early in the second month and attains its maximum development about the end of the third month, at which time the chordal part of the chondrocraniuiu consists of a ring of cartilage, the ventral part of which is formed by the fusion of two parachordal cartilages, so forming around the chorda dorsalis, a central axial part, MORPHOLOGY OY THE SKULL. 291 which comprises the basilar portion of tlie occipital bone. From this there pass e.xtensious which form the lateral parts of the occfj)ital bone, and serve to unite the occipifcil plate, as this part of the cartilaL'inous base is sometimes called, to the cartilaginous auflitory capsules on either side. These latter are formed by the chondrification of the cochlear and canalicular parts of the hibyrinth, which do not develop at the same rate, so that the part around the semi- circular canals is c()mplet<'d nuuh .sooner than the cochlear jKjrtion ; in consequence, at the end of the second month, the facial nerve and tin; genicular ganglion lie in a groove, to be subse- quently converted into a canal, on the vestibular part of the capsule. The doi"sal part of the ring consists of a thin cartilaginous jdate, the tectum posterius, from which is developed the oidy part (i.e. the inferior part of the occijntal squama) of the cranial vault preformed in cartilage. In the membranous tissue from which this plate is developed chondritica- tion at fu-st begins, on either side, liy an extension from the posterioi' aspect of the pars lateralis of the occipital; growing rapidly forwards this ultimately unites with the posterior and doi-sal bordei-s of the cartilaginous auditory capsule, from which it is for some time sei)arated by a narrow membranous interval. At a later sfcige the cartilages of either side unite, dorsal to the foramen magnum, tojorm the tectuvi posterius or the tectum synoticum (Keibel and Mall). To the axial part of this portion of the chondrified base the chorda dorsal is has the following Basi-sphenoid centrps [ Pre-spliPiioifl centre Frontal . S(|uaniou.s part r temporal .Si)lienotic centre Fig. 283. — Ossification on Bask and Latkhai. Walls of Skull of four and a half Months' FcETfs (Schultze's method). Cartilage, blue ; cartilage-bone, black ; membrane-bone, red. relations : in front of the foramen magnum it runs for a short distance in a groove on the dorsal surface of the occipital plate, then pierces the cartilage so as to lie ventral to it in the retro- pharyngeal tissue, again enters the chondro - cranium by passing dorsalwards in the suture between the occipital plate and sphenoidal cartilage and ends dorsal to the latter cartilage. The prechordal portion of the cartilaginous liasis cranii in man displays the following features : at the thirtl month it is irregularly diamond-shaped in outline, its posterior angle is wedged in between the two auditory capsules and is related to the anterior jiart of the axial portion of the occipital plate. The anterior angle forms the ventral end of the nasal capsule, whilst the lateral angles extend over the orbital cavities and correspond to the tips of the alae orbitales of the sphenoid. Within this area chondrification takes place as follows (Bai-deen). In the region of the posterior angle, above referred to, a cartilaginous nodule appears anterior and ventral to the end of the chorda doi-salis ; from this arises the cartilaginous body of the sphenoid, the further development of which is associated with its union witli the anterior end of the median portion of the occipital plate and the formation there, by the appearance of an independent transverse strip of cartilage, of the dorsum sellse of the sphenoid ; whilst from its anterior and superior surface on either side there extend forwards strips of cartilage which surround the hypophyseal pocket, and unite in front of it to form the anterior part of the body of the sphenoid, thereby enclosing the hypophyseal canal, which, at tii-st wide, is gradually closed by the chondrification of its -walls. It may, however, remain open. 19 a / 292 OSTEOLOGY. Tlie region occupied by tlie ala temporalis is slow to cliondrily. According to Fawcett, the only part of it which is preformed in cai'tilage is that which corresponds to the root of the two pterygoid laminas in the adult : this is, perforated by the maxillary division of the trigeminal nerve. According to the same authority, the whole of the lateral pterygoid lamina and that part of the ala temporalis projected into the orbital and temporal fossa; are ossified in membrane. So, too, are the foramen ovale and foramen spinosum. The ala orbitalis, at first much larger than the ala temporalis, is described as chondrifying in the foDowing way. The process begins by the appearance of cartilage posterior to the position of the optic foramen ; medially this fuses with the lateral aspect of the anterior part of the body of the sphenoid, laterally it extends into the orbital plate, with the independent cartilaginous centre of which it unites. Tlie foramen opticum is completed by the extension of the cartilage from the side of the anterior extremity of the body of the sphenoid, in front of the nerve, to reach the orbital plate. These three centres fuse to form a single piece of cartilage during the third month. Anterior to the orbito-sphenoids, the base of the skull is intimately associated with the nasal capsule, and is the last part of the chondro-cranium to become cartilaginous, this change not being effected till the third month. The roof of the capsule is formed by the coalescence of cartilaginous elements appearing, first in the nasal septum by an extension of the cartilage from the ventral surface of the body of the sphenoid and secondly by an independent centre in each lateral wall of the capsule. At first the nasal capsule is open dorsally on either side of the nasal septum in correspondence with the olfactorj'- bulbs, but during the third month the wall of the capsule corresponding to the cribriform plate commences to chondrify around the perforating ■ nerve-fibres, and so the lamina cribrosa is preformed in cartilage. Laterally strips of cartilage (cartilage ethmosphenoidalis) pass backwards from the lateral edges of the cribriform plate to , unite it with the anterior edges of the alae orbitales of the sphenoid. By the third month the nasal capsule has become cartilaginous. As has been stated above, the nasal septum chondrifies by an extension forwards of the ventral part of the body of the cartilaginous sphenoid. On either side of the ventral margin of this septum anteriorly are developed the paraseptal cartilages, which in man persist tiU after birth. These are cojmected posteriorly by means of a connective tissue bridge with small pieces of cartilage — the posterior I^araseptal cartilages, which are in turn associated with the paranasal cartilages posteriorly, and there in part form the floor of the recessus terminalis or cupola of the cartilaginous nasal capsule (Fawcett). In man, owing to the deficiency of the lamina transversalis anterior, the fenestra narina and the fenestra basalis which pierce the floor of the nasal capsule, on either i^ide of the septum, become confluent and form the fissura rostroventralis of Gaupp. Meanwhile the lateral w^alls of the nasal capsule are chondrifying independently, forming the paranasal cartilages. These become subsequently united anteriorly with the nasal septum to form the tectum nasi or roof of the nose. At first this is open posterionly where it is in relation with the olfactory bulb, but later, as has been already described, the tissue around the nerve filaments chondrifies to form the cartilaginous lamina cribrosa. The inferior concha is derived from the cartilage of the lower and lateral part of the nasal capsule, from which, however, it becomes isolated about the seventh month. Above and behind this the middle and superior conchae, the ethmoidal turbinals, become chondrified, as well as the cartilaginous rudiments which subsequently form the agger nasi, the bulla ethmoidalis, and the concha sphenoidale or ossiculum Bertini. Throughout life certain parts of the cartilaginous nasal capsule persist as the cartilaginous nasal septum and the cartilages of the alae of the nose, whilst other parts are absorbed and are replaced by surrounding bones of membranous origin. The various foramina met with in the cranial base are formed either as clefts in the line of union of the several caitilaginous elements, or through inclusion by means of bridging processes derived from these same elements. From the ventral surface of this cartilaginous platform — formed, as described, by the union of the trabeculse, parachordal cartilages, and cartilaginous auditory capsules — is suspended the cartilaginous framework of the visceral arches, which play so important a part in the develop- ment of the face, an account of which is elsewhere given. A consideration of the facts of comparative anatomy and embryology appears to justify the assumption that the mammalian skull is of twofold origin — that, in fact, it is composed of two envelopes, an outer and an inner, primarily distinct, but which in the process of evolution have become intimately fused together. The inner, called the primordial skull, is that which has just been describecl, and consists of the chondro-cranium and the branchial skeleton. The outer, which is of dermic origin, includes the bones of the cranial vault and face which are developed in membrane. This secondary skull, which first appears in higher fishes as ossified dermal plates overlying the primary skull, acquires a great importance in the mammalia, as owing to the expan.sion of the brain and the progressive reduction of the chondro-cranium, these dermal bones become engrafted on and incorporated with the primordial skull, and act as covering bones to the cavities of the cranium ana face ; for it may be well to point out that these dermal or membrane bones are not necessarily external in position, as over the cranial vault, but also develop in the ti-ssues underlying the mucous membrane of the cavities of the face. Advantage is taken of tliis difference in the mode of development of the bones of the skull to classify them according to their origin into cartilage or primordial bones, and membrane or secondary bones. These differences in the growth of the bone must not be too much insisted on in determining the homologies of the bones of the skull, as it is now generally recognised that MOKPHOLOGY OF THE LIMBS. 293 all bone is of membranous origin, and. that wliilst in some cases cartilage may become calcified, it never undergoes conversion into triie bone, but is replaced by ossific deposit derived from a membranous source. In the subseciuent growth of the skull, parts of the cartilaginous cranium persist as the septal and alar cartiLiges of the nose, whilst for a considcralde period the basi- sphenoid and basi-occipital are still united by cartilage. The cartilage al.so wnich blocks the foramen lacerum may be rt'ganled as a remnant of the chondro-craniuru. Whilst in many instanci-s tlie primordial and .secondary bones remain distinct in the fully- develojKid condition, they sometimes fuse to form complex bones, such as the temporal and sphenoid. Various theories have been advanced to account for the mode of formation of the skull. The earliest of these was called the vertebrate theory, which assumed that the cranium was built up of a serius of mwiitied vertebrae, the bodies of which corresponded to the basi-cranial axis, whilst the vertebral arches were represented by the covering bones of the cranium. In view of the more recent researches regarding the composite origin of the skull above referred to, this theory was neces-sarily abandoned. It gave way to the suggestion of Gegenbauer that the primordial cranium has arisen, by the fusion ot several segments equivalent to vertebrae, the number of whicli he determined by noting the metameric arrangement of the cerebral nerves, of wliich he concluded there were nine pairs, arranged much like spinal nerves, both as to their origin and distribution. The olfactory and optic nerves, though frequently referred to as cerebral nerves, are excluded, since from the nature of their development they are to be regarded as meta- morpho.sed parts of the brain itself. Gegenbauer therefore assumed that that portion of the cranial base which is traversed by the nine pairs of segmentally arranged cerebral nerves must be formed by the fusion of nine vertebral segments ; and as the region where the nerves escape corresponds to the part of the chondro-cranium traversed by the notochord, he calls it the vertebral portion of the cranial base, in contradistinction to the trabecular or non-vertebral part which lies in front. This latter he regards as a new formation adapted to receive the greatly- developed brain and afford protection to the organs of sight and smelL As has been pointed out by Hertwig, there is an essential difference between the development of the axial cartilaginous skeleton of the trunk and head. The former becomes segmented into distinct vertebrae alternating with intervertebral ligaments ; whilst the latter, in order to attain the rigidity necessary in this part of the skeleton, is never so divided. It follows from this that the original segmentation of the head is only expressed in three ways, viz., in the appearance of several primitive segments (myotomes), in the arrangement of the cerebral nerves, and in the fundament of the visceral skeleton (visceral arches). According to Froriep, the mammalian occipital corresponds to the fusion of four vertebrae, and there is some reason for supposing that in some classes of vertebrates the occipital region of the primordial cranium is increased by fusion with the higher cervical segments. The form of skull characteristic of man is dependent on the large proportionate development of the cranial part, which contains the brain, and the reduction in size of the visceral part (face), which protects the organs of special sense. This leads to a decrease in the mass and projection of the jaws, as well as a reduction in the size of the teeth. Associated with the smaller mandible there is a feebler musculature, with a reduced area of attachment to the sides of the skull. In this way the disappearance of the muscidar crests and fossae, so characteristic of lower forms, is accounted for. At the same time the fact that the skull is poised on the summit of a vertical column, leads to important modifications in its structure. The disposition of parts is such that the occipito-vertebral articulation is so placed that the fore and hind parts of the head nearly balance each other, thus obviating the necessity for a powerful muscular and ligamentous mechanism to hold the head erect. Another noticeable feature in connexion with man's skeleton is the prolonged period during which growth may occur before maturity is reached ; this is associated with a more complete consolidation of the skull, since bones, which in lower forms remain throughout life distinct, are in man fused with each other, as exemplified in the case of the presphenoid and postsphenoid, the occipital and the interparietal, to mention one or two instances amont many. It is noteworthy, however, that (Turing ontogeny the morphological significance of' these bones is clearly demonstrated by their independent ossification. The points of exit of the various cerebral nerves remain remarkably constant, and in their primitive condition serve to suggest the segmental ariangement of the cartilaginous chondro- cranium already referred to. Owing to the very great modifications which the mammalian skull has undergone in the process of its evolution, it may be pointed out that the pa.ssage of the nerves through the dura mater — a derivative, the readers may be reminded, of the primordial membranous cranium (see ante) —alone represents the primitive disposition of the nerves. Their subsequent escape through the bony base is a later and secondary development. In some cases the two, membranous or primary and the osseous or secondary foramina, correspond. In other instances the exit of the nerves through the dura mater does not coincide with the passage through the lx)ne. Of interest in this connexion it may be pointed out that the foramina and canals which traverse the skull are either situated in the line of suture between adjacent bones or in the line of fusion of the constituent parts of which the bone pierced is made up. For example, the superior orbital fissure is situated between the orbito and alisphenoids ; the hj'poglossal canal between the basi and exoccipitals ; the jugular between the petrous, basi, and exoccipital ; the optic between the orbito-sphenoid and the presphenoid ; the pterygoid between the alisphenoid, medial pterygoid lamina, and the lingula. 19 & 294 OSTEOLOGY. APPEN"DIX F. MORPHOLOGY OF THE LIMBS. Development and Morphology of the Appendicular Skeleton, The paired limbs first appear in the human embryo about the third week as small buds on either side of the cephalic and caudal ends of the trunk. That these outgro^yths are derived from a large number of trunk segments is assumed on the ground that they are supplied by a corresponding number of segmental nerves, and the circum- stance that they are more particularly associated with the ventral offsets of these nerves would point to the conclusion that they belong rather to the ventral than the dorsal surface of the body. At first the surfaces of these limb buds are so disposed as to be directed ventrally and dorsally, the ventral aspect correspond- ing to the future flexor surface of the limb, the dorsal to the extensor side. At the same time, the borders are directed head- wards (pre-axial), and tailwards (post-axial). As the limbs grow, they soon display evidence of division into segments corre- sponding to the hand and foot, forearm and leg, upper arm and thigh. Coincident with this (about the second month) the cartil- aginous framework of the limb is being differentiated. The disposition of these cartilages furnishes a clue to their homo- logies. In the fore-limb the radius and thumb lie along the pre-axial borders, and correspond to the tibia and great toe, which are similarly disposed in the hind-limb ; whilst the ulna and fifth finger are homo- logous with the fibula and fifth toe, which are in like manner arranged in relation to the posterior (post-axial) border of their respective limbs. Up to this time the limbs are directed obliquely ventralwards. During the third month a change in the position of the limbs takes place, associated with the assumption of the foetal position. Owing to the elongation of the limbs, they loecome necessarily bent at the elbow and knee, the upper arm inclining down- ward along the thoracic wall, whilst the thigh is directed upwards in contact with the abdominal parietes. At the same time a rotation of each of these segments of the limb takes place in an inverse direction, so that the pre-axial border of the humerus is turned laterally, whilst the pre-axial border of the femur is turned medially. Assuming that these borders are homologous, it results from this, that the lateral condyle of the humerus corresponds to the medial corldyle of the femur. This torsion of the limb is in part effected at the shoulder and hip joints, and to some extent also in the shafts of the bones. Some anatomists hold that this rotation is not confined to the limb, but involves the dorsal part of the limb girdles. Others maintain that there is no evidence that such takes place. In the upper limb, owing to a certain amount of pronation, the Fia. 284. — DiAGKAM TO ILr.USTUATE THE HOMOLOGIES OF THE Bones of the Limbs. The two limb buds of an embryo prior to Hexion and rotation. The anterior or pre-axial border is coloured red ; the posterior or post-axial border, blue. B. After the assumption of the fcetal position. Flexion and rotation have now taken place. The red and blue lines indicate the altered position of the pre-axial and post-axial borders. C. The fully developed limbs with the flexor aspects directed towards the reader. The coloured lines indicate the effect of the torsion of the upper segment of the limb through quarters of a circle. I MOKPHOLOGY OF THE LIMBS. 295 pre-axial (radial) side of the forearm is now directed forwards and somewhat laterally, whilfit in the hind limb the pre-axial (tibial) side of the leg is turned backwards and laterally, the pre-axial boulers of the hand with thumb, and foot with gi-eat toe being in correspondence. In consequence of these changes in the position of the limbs, amounting in all in the upper segments to a rotation through an angh; of 90', the extensor surface of the fore limb is directed Imckwarde, whilst that of the hind limb is directed forwards. In order to homologise the arrangement of the bones in the extended limb, it is necessary to place them so that their flexor or extensor surfaces are similarly disposed. It will then be observed (see diagram) that the medial or tibial side of the leg and foot (primitively pre-axial) corresponds to the lateral or radial side of the forearm and hand (primitively pre-axial), whilst the fibula and lateral border of the foot homologise with the ulnar or medial border of the forearm and hand (primitively post-axial), the result, as previously explained, of the torsion or twisting in opposite directions through an angle of 90' of the upper seguient of the limb. In accordance with this view, it will be evident that in the fore limb there is nothing homologous with the patella, whilst in the hind limb there is no part to rejiresent the olecranon. In the axial mesoderm of each member, differentiation into cartilaginous segments begins about the second month ; each of these cartilages becomes invested by a perichondrial layer which stretches from segment to segment, and ultimately forms the ligaments surrounding the joints, which are subsequently developed between the segments. Chondrification first begins in the ba^al part of the limb, and extends towards the digits. The homodynamy of the carpal and tarsal elements may be tabularly expressed, and compared with the more generalised types from which they are evolved. Type. Hand. Foot. Radiale (Tibiale) = Navicular (body) = Talus. Intermedium =0s lunatum = Absent, or Os trigonum (1). Ulnare (Fibulare) =0s triquetrum = Calcaneus. Centrale = Absent, or fused with Navicular = Navicular, less its tuberosity. Carpale (Tarsale), i. =0s multangulum majus = First Cuneiform. Carpale (Tarsale), ii. =0s multangulum minus = Second Cuneiform. Carpale (Tarsale), iii. = Capitate = Third Cuneiform. Carpale (Tarsale), iv.^ _p, , . = Cuboid, plus the peroneal Carpale (Tarsale), v. / "^^ namatum sesamoid. The pisiform is omitted from the above table, since it is now generally regarded as being a vestige of an additional digit placed post-axial to the little finger (digitus post-minimus). Its homologue in the foot is by some considered as fused with the calcaneus. The tuberosity of the navicular, formed, as has been stated, of three elements, of which the sesamoid bone in the tendon of the tibialis posterior may be one, is to be regarded as the homologue of the pre-axial sesamoid in the hand, which probably fuses with the navicular to form its tuberosity. The peroneal sesamoid probably corresponds to the hamulus (sometimes an independent ossicle) of the OS hamatum. Similarly, on the pre-axial border of the hand and foot, vestiges of a suppressed digit (prepollex and prehallux) may occasionally be met with. The frequent occur- rence of an increase in the number of digits seems to indicate that phylogenetically the number of digits was greater than at present, and included a prepollex or prehallux, and a digitus post- minimus. The correspondence of tlie metacarpus with the metatarsus and the phalanges of the fingers with those of the toes is so obvious that it is sufficient merely to mention it. The differences in size, form, and disposition of the skeletal elements of the hand and foot is easily accounted for by a reference to the functions they subserve. In the hand, strength is sacrificed to mobility, thus leading to a reduction in the size of the carpal elements, and a marked increase in the length of the phalanges. The freedom of move- ment of the thumb, and its opposability to the other digits, greatly enhances the value of the hand as a grasping organ. In the foot, where stability is the main requirement, the tarsus is of much greater proportionate size, whilst the phalanges are correspondingly reduced. Since the foot no longer serves as a grasping organ, the great toe is not free and opposable like the thumb. Limb Girdles. — The free limbs are linked to the axial skeleton by a chain of bones which constitute their girdles. The fimdamental form of these limb girdles consists each of a pair of curved cartilages placed at right angles to the axis of the trunk on either side, and embedded within its musculature. Each cartilage has an articular surface laterally, about the middle, for the reception of the cartilage of the first segment of the free limb. In this way each pectoral and pelvic cartilage is divided into an upper or dorsal half and a lower or ventral half. The dorsal halves constitute the scapula and ilium of the pectoral and pelvic girdles respectively. With regard to the ventral halves there is more difficulty in establishing their homologies. The original condition is best displayed in the pelvic girdle ; here the ventral segment divides into two branches — one anterior, which represents the pubis, the other posterior, which ultimately forms the ischium. Ventrally, the extremities of these cartilages unite to enclose the obturator foramen. In the pectoral girdle the disposition of the ventral cartilages is not so clear, consisting primitively of an anterior branch or precoracoid, and a posterior portion or coracoid ; these, in higher forms, have undergone great modifications in adaptation to the requirements of the fore limbs. The posterior or coracoid element, the homologue of the ischial cartilage in the pelvic girdle, is but feebly represented in man by the coracoid process and the coraco-clavicular ligament. 296 OSTEOLOGY. With regard to the homologue of the pubic element in the pectoial girdle, there is much difference of opinion ; in reptiles and amphibia it corresponds most closely to the precoracoid, but it is doubtful what represents it in mammals. According to Goette and Hoffman, the clavicle is a primordial bone, and not, as suggested by Gegenbaur, of secondary or dermic origin. If this be so, it corresponds to the ventral anterior segment of the pectoral girdle, and is therefore homo- logous with the ventral anterior (pubic) segment of the pelvic girdle. On the other hand, if Gegenbaur's view be accepted, the clavicle has no representative in the pelvic girdle. It must, however, be borne in mind that during its ossification it is intimately associated with cartilage, and that that cartilage may represent the precoracoid bar ; nor must too great stress be laid upon the fact that the clavicle begins to ossify before it is preformed in cartilage, since that may be merely a modification in its histogenetic development. According to another view (Sabatier), the subcoracoid centre (see Ossification of Scapula) is derived fi'om the posterior ventral segment, and corresponds to the ischium, whilst the coracoid process is the remains of the anterior ventral segment (precoracoid), and is homodynamous with the pubis. In no part of the skeleton does fimction react so much on structure as in the arrangement of the constituent parts of the pectoral or pelvic girdles. In man, owing to the assumption of the erect position and the bipedal mode of progression, the pelvic girdle acquires those characteristics which are essentially human, viz., its great relative breadth and the expansion of its iliac portions, which serve as a support to the abdominal viscera, and also furnish an extensive origin for the powerful muscles which control the movements of the hip-joint. The stability of the 'Vertebral or internal surface\ ^Vertebral or internal surfac^' B AC Fig. 285. — Diagram to illustrate the Homologous Parts of the Scapula and Ilium ACCORDING to FlOWER. A, ideal type ; three-sided rod. B, scapula rotated forward through quarter of a circle (90°), so that the primitive medial or vertebral surface is now directed anteriorly. C, ilium rotated backwards through quarter of a circle so that the primitive medial surface is now turned posteriorly. In the diagram the primitive medial or vertebral surface of each figure is coloured black, the pre-axial surfaces red, and the post-axial surfaces blue. pelvic girdle is insured by the nature of its union with the axial skeleton, as well as by the osseous fusion of its several parts, and their union in front at the symphysis pubis. Various attempts have been made to homologise the several parts of the ilium and scapula. All are open to objection ; that by Flower is perhaps the most generally accepted. Assuming that the primitive type is represented by a prismatic rod, of which the dorsal end represents either the epiphysial border of the vertebral edge of the scapula or the iliac crest, whilst the ventral end corresponds to the glenoid or acetabular articular areas respectively, the surfaces of the three-sided rod are disposed so that one is vertebral or medial, another pre-axial, and the third post-axial. These surfaces are separated by borders, of which one is lateral, separating the pre-axial and post-axial surfaces, whilst the antero - medial and postero- medial margins separate the pre-axial and post-axial surfaces respectively from the vertebral or medial asjDCct. It is a necessity of Flower's theory that this part of the girdle undergoes a rotation along with the rest of the limb. Thus in the fore limb the surfaces of the primitive type are turned so that the vertebral surface looks forward, whilst in the case of the hind limb the vertebral surface is turned backward. A study of the accompanying diagram will enable the reader to realise how the ventral surface of the scapula is thus rendered homologous with the gluteal surface of the ilium, for by reference to the type, both these surfaces will be seen to correspond to the post- axial areas of the primitive condition. In accordance with this view the surfaces and borders of the scapula are homologised by Flower, as shewn in the subjoined table : — Scapula. Supra-spinous fossa Infra-spinous fossa Subscapular fo-ssa Surfaces Ideal. 1. Vertebral 2. Pre-axial 3. Post-axial Pelvis. I Medial surface of ilium behind linea ar- cuata interna, including the articular surface for the sacrum and the portion of the bone above and below this Iliac fossa Gluteal surface of ilium MOKPHOLOGY OF THE LIMBS. 297 Borders Axillary border, posterior on most animals (attachment of triceps muscle) Si)ine continued into acromion Superior Itonler, anterior in most animals, with scapulo- coracoid notch 1. Lateral 2. Antero-medial 3. Postero-medial Anterior border (attachment of rectus muscle) Linea arcuata interna continued into pubis Posterior border with greater sciatic notch Flower's views of this matter were strenuously opposed by Humphry, who maintained that there is strong presumptive evidence against any rotation of the superior parts of the girdles, since it is difficult to suppose that the scapula and ilium can undergo a rotation which is not participated in by the coracoid and ischium. According to this anatomist the homologous parts of the two boTies are as- stated below : — Scapula. Pre-spinal ridge forming the floor of the pre- spinal fossa Spine and acromion Post-spinal part of scapula forming the floor of the post-spinal fossa Posterior angle Posterior border Medial or ventral surface Ilium. LineA ilio-pectinea Fore part of the blade and crest of the ilium, with its anterior spine or angle Hinder part of blade and crest of ilium Posterior spine or angle Posterior or sciatic border of ilium Inner or true pelvic surface of ilium, including the surface for the articulation of the sacrum Fig. 286. — Diagkam to illustrate the Homologous Parts of the Scapula and Ilium, ACCORDING to HUMPHRY. A, primitive rod-like ilium of kangaroo, prismatic on section. B; scapula. C, iliiun. The corresponding surfaces are similarly coloured. The difficulty arising in this scheme of attempting to homologise thie attachments of the triceps and rectus femoris, Humphry explains by pointing out that the former muscle also arises from the lateral surface of the scapula, whilst the rectus overruns the lateral surface of the ilium above the acetabulum, so that there is a correspondence in the origins of both these muscles from the lateral surface of their respective bones ; but in consequence of the rotation of the extensor surfaces of the limbs in opposite directions the triceps has been turned backwards on to the posterior border of the scapula, whilst the rectus has been turned forwards on to the anterior border of the iliuni. Sufficient has been said to enable the reader to recognise that all attempts to determine in detail the homologies of these parts are beset with difficulty. It is wiser, therefore, in our present state of knowledge to be content with establishing a general correspondence, and so avoid the error of endeavouring to establish a closer homological relationship than actually exists. In man, since the erection of the figure no longer necessitates the use of the fore limb as a means of support, the shoulder girdle has become modified along lines which enhance its mobility and determine its utility in association with a prehensile limb. Some of its parts remain independent (clavicle and scapula), and are imitea by diarthrodial joints, whilst others have 298 OSTEOLOGY. become much reduced in size or suppressed (coracoid, precoracoid, see ante). The dorsal part of the girdle (scapula) is not directly united with the axial skeleton as is the ilium, but is only indirectly joined to it through the medium of the clavicle, which is linked in front with the presternum. The same underlying principles determine the differences in mobility and strength between the shoulder, elbow, and wrist, and the hip, knee, and ankle joints of the fore and hind limbs respectively, whilst the utility of the hand is further enhanced by the movements of pronation and supination which occur between the bones of the forearm. In the leg such movements are absent, as they would interfere with the stability of the limb. ^» THE ARTICULATIONS OR JOINTS. SYNDESMOLOGY. By David Hepburn. Syndesmology is that branch of human anatomy which treats of the articulations or joints. A junctura o.ssium (articulation or joint) constitutes a mode of union or con- nexion subsisting between any two separate segments or parts of the skeleton, whether osseous or cartilaginous. It has for its primary object either the preservation of a more or less rigid continuity of the parts joined together, or else the permission of a variable degree of mobility, su])ject to the restraints of the uniting media. Classification of Joints. — In attempting to frame a classification of the numerous joints in the body, several considerations must be taken into account, viz., the manner and sequence of their appearance in the embryo ; the nature of the uniting media in the adult, and also the degree and kind of movement permitted in those joints where movement is possible. In this way we obtain two main subdivisions of joints : — (1) Those in which the uniting medium is co-extensive with the opposed sur- faces of the bones entering into the articulation, and in which a direct union of these surfaces is thereby effected (2) Those in which the uniting medium has undergone more or less of interrup- tion in its structural continuity, and in which a cavity of greater or less extent is thus formed in the interior of the joint. To the first group belong all the immovable joints, many of which are only of temporary duration ; to the second group belong aU joints which possess, as their outstanding features, mobility and permanence. Intervening membrane SYNARTHROSES. The general characteristics of this group are partly positive and partly nega- tive. Thus, there is uninterrupted union between the opposed surfaces of the bones joined together at the plane of the articulation, i.e. there is no trace of a joint cavity, and further, there is an entire absence of movement. DevelopmentaUy, these joints result from the approxi- mation of ossitic processes which have commenced from separate centres of ossification, and therefore the nature of the uniting medium varies accordincr as the bones thus joined together have originally ossified in membrane or in cartilage. In the former case union is effected by an interposed fibrous membrane continuous with, and corresponding to, the periosteum. To such articulations the term sutura (Fig. 287) is applied. In the latter case the uniting medium is a plate of hyaline cartilage. Such articulations are called synchondroses (Fig. 288). In all the synchondroses, and in many of the sutures, the uniting medium tends to disappear in the procuress of 299 Fig. 287. — Vertical Section through a scture. 300 THE AKTICULATIONS OE JOINTS. ossification, and thus the plane of articulation becomes obliterated, so that direct structural continuity between the osseous segments takes place. The primary features common to all synarthroses are — (a) continuous and direct union of the opposing surfaces; (&) no joint ca\dty ; (c) no movement. Sutura. — This form of synarthrosis is found only in connexion with the bones of the skull. In a large number of cases the bones which articulate by suture present irregular interlocking margins, between which there is the interposed fibrous membrane to which refer- ence has ah'eady been made. When these interlocking margins present well-defined projections they are said to form a sutura vera (true suture) ; on the other hand, when Fig. 288. — Section through the opposed surfaces present ill-defined projections, or THE OcciPiTo-spHENoiD Syn- evcu flat arcas, they are described as sutura notha cHONDRosis. (false suture). In each of these subdivisions the particular characters of the articulating margins are utilised in framing additional descriptive terms. Thus true sutures may possess interlocking margins whose projections are tooth-like (sutura dentata), e.g. in the interparietal suture ; saw-like (sutura serrata) (Fi"''^"'*' number of minor sections, in order to emphasise the occurrence of certain well- cartiia-o/ marked structural features, or because of the articuiaris particular nature of the movement by which they are characterised. Although in all ^'''^- -^'^• diarthroses there is a certain amount of gliding movement between the opposed surfaces of the bones which enter into their formation, yet, when this gliding movement becomes their prominent feature, as in most of the joints of the carpus and tarsus, they are termed artlirodia. But bones may be articulated together so as to permit of movement in one, two, or more fixed axes of movement, or in modifications of these axes. Thus in uniaxial joints the axis of movement may lie in the longitudinal axis of the joint, in which case the trochoid rotatory form of joint results, as in the proximal and distal radio-ulnar articulations ; or it may correspond with the transverse axis of the articulation, as in the elbow-joint and knee-joint, when the ginglymus or Mnge variety results. If movement takes place about two principal axes situated at right angles to each other, as in the radio-carpal joint, the terms ellipsoid (biaxial or condyloid) are applied. Movements occurring about three principal axes placed at right angles to each other, or in modifications of these positions, constitute multiaxial joints, in which the associated structural peculiarities provide the alternative terms of enarthrosis or ball-and-socket joints. STRUCTURES WHICH ENTER INTO THE FORMATION OF JOINTS. The structures which enter into the formation of joints vary with the nature of the articulation. In every instance there are two or more skeletal elements, whether bones or cartilages, and in addition there are the uniting media, which are either simple or elaborate according to the provision made for rendering the joint more or less rigid, or capable of movement. We have already seen that the uniting medium in sjmarthrodial joints is a remnant of the common matrix, whether fibro- vascular membrane or hyaline cartilage, in which ossification has extended from separate centres. Among the ampMarthroses there is still extensive union between the opposing surfaces of the articulating bones, but the character of the uniting medium has advanced from the primitive embryonic tissue to fibrous and fibro- cartilaginous material, as well as hyaline cartilage. These, with very few exceptions, are permanent non-ossifying substances, such as may be seen between the opposing osseous surfaces of two vertebral bodies. The joint cavity, more or less rudimentary, is confined to the centre of the fibro-cartilaginous plate, and may result from the softening or imperfect cleavage of the central tissue. It may also present rudiments of a synovial membrane. In the diarthrodial group the extensive cavity has produced great interruption in the continuity of the uniting structures which originally existed between the 302 THE AETICULATIONS OR JOINTS. bones forming such a joint. Ligaments have therefore additional importance in this group, for not only do they constitute the uniting media which bind the articulating bones together, but, to a large extent, they form the peripheral boundary of the joint cavity, although not equally developed in all positions. Thus, every diarthrodial joint possesses a fibrous or ligamentous envelope con- stituting the Jibrous stratum of the articular capsule, which is attached to the ad- jacent ends of the articulating bones. For special purposes, particular parts of the fibrous stratum may undergo enlargement and thickening, and so constitute strong ligamentous bands, although still forming continuous constituents of the envelope. The fibrous stratum is lined by a stratum synoviale (O.T. synovial membrane), the two strata constituting the capsula articularis. The synovial stratum is con- tinued from the inner surface of the fibrous stratum to the surface of the intra- articular portion of each articulating bone. The part of the bone included within the joint consists of a " non-articular " portion covered by the synovial layer and an " articular " portion covered by encrusting hyaline cartilage. The latter provides the surface which comes into apposition with the corresponding area of another bone. In its general disposition the synovial layer may be likened to a cylindrical tube open at each end. This layer is richly supplied by a close network of vessels and nerves. Certain diarthroses present intracapsular structures which may be distinguished as interarticular ligaments and articular discs and menisci (O.T. interarticular fibro-cartilages). Ligamenta Interarticularia. — Interarticular ligaments extend between, and are attached to, non-articular areas of the intracapsular portions of the articulating bones. They usually occupy the long axis of the joint, and occasionally they widen sufficiently to form partitions which divide the joint-cavity into two com- partments, e.g. the articulation of the heads of the ribs with the vertebral column, and certain of the costo-sternal joints. Articular discs and menisci (O.T. interarticular fibro-cartilages) (Fig. 291) are more or less complete partitions situated between and separating opposing articular surfaces, and when complete they divide the joint cavity into two distinct compartments. By its periphery, a disc is rather to be associated with the articular capsule than with the articulating bones, although its attachments may extend to non - articular areas on the latter. Those found in the knee-joint are called menisci ; those found in other joints are called articular discs. Both interarticular ligaments and articu- lar discs and menisci have their free surfaces covered by the synovial stratum. Adipose tissue, forming pads of varying size, is usually found in certain localities within the joint, between the synovial stratum and the surfaces which it covers. These pads are soft and pliable, and act as packing material, filling up gaps or intervals in the joint. During movement they adapt themselves to the changing conditions of the articulation. In addition to merely binding together two or more articulating bones, ligaments perform very important functions in connexion with the different movements taking place at a joint. They do not appreciably lengthen under strains, and thus ligaments may act as inhibitory structures, and by becoming tense may restrain or check movement in certain directions. Synovial strata, in the form of closed sacs termed mucous or synovial bursse, are frequently found in other situations besides the interior of joints. Such bursas are developed for the purpose of reducing the friction, (a) between the integument and certain prominent subcutaneous bony projections, as, for instance, the point of the elbow, or the anterior surface of the patella stratum synoviale Fig. 291. — Diagram of a Diahthrodial Joint WITH Abticdlar Disc dividing the Joint- Cavity INTO TWO Compartments. THE DIFFERENT KINDS OF MOVEMENT AT JOINTS. 303 (subcutaneous mucous bursae) ; (h) hetwi'tin a Iciidoii and .-ioim* siuract-, Ijony or cartilaj,'inoiis, over wliicli it plays (subtendinous mucous bursae) ; (c) l>cl\vccii a tciidun or a ^m-oiij) of IcikIcjii.s and tin- walls of osteo-fascial tinuK Is, in which they play (vaginae mucosae tendinum oi' mucous sheaths of tendons). Siil)toiulinous mucous bursiu are often placed in the neighliourhood of joints, and in such cases it not iiifre(pieutly happens that there is a direct continuity between the Ijui-sa and the synovial stratum which lines tht^ cavity of the j(jint through an ajierture in the articular capsule. THE DIFFERENT KINDS OF MOVEMENT AT JOINTS. Reference has already been made to the existence of fixed axes of movement as a l)asis for the classification of certain forms of diarthrodial joints. Hence it is evident that tlie movements which are possible at any particular joint depend to a large extent upon the shape of its articular surfaces as well as upon the nature of its various ligaments. Therefore the technical terms descriptive of movements either indicate the directions in which they occur, or else the character of the com- pleted movement. In the great majority of articulations between short bones, the amount of move- ment is so restricted, and the displacement of the opposing articular surfaces so shght, that the term gliding sufficiently expresses its character. A gliding movement of an extensive kind, for example that of the patella upon the femur, in which the movement largely resembles that of the tyre of a wheel revolving in contact with the ground so that different parts are successively adapted to each other, is called co-aptation. Articulations between long bones, on the other hand, are usually associated with a much freer range of movement, with a corresponding variety in its character. Rotation is a movement around an axis which is longitudinal. Sometimes it is the only form of movement which a joint possesses ; at other times it is merely one of a series of movements capable of execution at the same joint. Flexion or bending is a movement in which the formation of an angle between two parts of the body is an essential feature. As it is possible to perform this movement in relation to two axes, viz., a transverse and an antero-posterior axis, it is necessary to introduce qualifying terms. Thus, when two anterior or ventral surfaces are approximated, as at the hip-, elbow-, or wrist-joints, the movement is called ventral, anterior, or palmar flexion ; but if posterior or dorsal surfaces are approximated by the process of bending, then the flexion becomes posterior or dorsi-flexion, as at the knee- or wrist- joints. Further, at the wrist-joint, the formation of an angle between the ulnar border of the hand and the corresponding aspect of the forearm, produces ulnar flexion, and similarly the bending of the hand towards the radial border of the forearm is radial flexion. Extension or straightening consists in obliterating the angle which resulted from flexion. In the case of certain joints, therefore, such as the elbow, wrist, and knee, the segments of the limb occupy a straight line as regards each other when extended. At the ankle-joint the natural attitude of the foot to the leg is flexion at a right angle. The diminution of this angle by approximating the dorsum of the foot towards the anterior aspect of the h^g constitutes flexion ; while any effort at placing the foot and leg in a straight line, i.e. obliteration of the angle, as in pointing the toes towards the ground and raising the heel, constitutes extension. Abduction is a term which either expresses movement of an entire limb in a direction away from the median plane of the body, or of a digit, away from the plane of the middle finger in the hand, or the plane of the second toe in the case of tlie foot. Adduction is the reverse of abduction, and signifies movement towards the median plane of the body, or towards the planes indicated for the digits of the hand and foot. Circumduction is a movement peculiarly characteristic of multiaxial or ball- and-socket joints. It consists in combining such angular movements as flexion, extension, abduction, and adduction, so as to continue the one into the other, whereby the joint forms the apex of a cone of movement, and the free end of the limb travels through a circle which describes the base of this cone. 304 THE AETICULATIONS OE JOINTS. THE DEVELOPMENT OF JOINTS. Just as the question of structure determines to a large extent the presence or absence of movement in joints, so in tracing their development it will be found that the manner of their appearance forecasts their ultimate destination as immovable or mov- able articulations. All joints arise in mesodermic tissue which has undergone more or less differentiation. When this differentiation has produced a continuous membranous layer, in which ossific centres representing separate skeletal segments make their appearance, we get the primitive form of suture. The plane of the articulation merely indicates the limit of the ossific process extending from different directions. If, again, the differentiation of the mesoderm has resulted in the formation of a continuous cartilaginous layer, in which ossification commences at separate centres, the plane of the articulation is marked out by the unossified cartilage — in other words, the articulation is a synchondrosis. Ulti- mately this disappears through the extension of the process of ossification. To some extent sutures also disappear, although their complete obliteration is not usual even in aged people. Developmentally, therefore, synarthroses or immovable joints do not present any special structural element, and, speaking generally, they have only a temporary existence. The development of all movable joints is in marked contrast to that of synar- throses. Not only are they permanent arrangements so far as concerns normal conditions, but they never arise merely as planes which indicate the temporary phase of an ossific process. From the outset they present distinct skeletal units, from which the special structures of the joint are derived. The primitive movable joint is first recognised as a mass of undifferentiated meso- dermic cells situated between two masses, which have differentiated into primitive cartilage. The cell-mass which constitutes the joint-unit presents the appearance of a thick cellular disc, the proximal and distal surfaces of which are in accurate apposition with the primitive cartilages, while its circumference is defined from the surrounding mesoderm by a somewhat closer aggregation of the cells of which the disc is composed. From this cellular disc or joint-unit all the structures characteristic of amphiarthrodial and diar- throdial joints are ultimately developed. Thus, by the transformation of the circumferential cells into fibrous tissue the invest- ing ligaments are produced. Within the substance of the disc itself a transverse cleft, more or less well-defined and complete, makes its appearance. In this manner the disc is divided into proximal and distal segments, separated from each other by an interval which is the primitive articular cavity. This cleft, however, never extends so far as to interrupt the continuity of the circumferential part of the disc which develops into the fibrous tissue of the investing ligaments. From the proximal and distal segments of the articular disc the various structures, distinctive of movable joints, are developed. Thus, in amphiarthrodial joints the cellular articular disc or primitive joint-unit gives origin to the following structures : — From its circumference, investing ligaments ; from its interior, the fibro cartilaginous plate in which an imperfect articular cavity with corresponding imperfect synovial stratum may be found. In the case of a diarthrodial joint the changes take place on a more extended scale. The articular cavity becomes a prominent feature, in relation to which the surrounding fibrous structures form an investing capsule, lined wdth a synovial stratum. When a single cleft arises, but does not extend completely across the longitudinal axis of the articular disc, the undivided portion develops into fibrous interarticular ligaments. On the other hand, when two transverse clefts are formed, that portion of the cellular disc which remains between them becomes transformed into a fibro-cartilaginous disc (or in the case of the knee-joint, menisci), which in its turn may either be complete or incomplete, and thus we may obtain two distinct synovial joint cavities belonging to one articulation.^ In considering the development of the synovial layer, and the surfaces on which it is found in the interior of a joint, it is necessary to keep clearly in mind that a synovial layer is a special structure, whose function it is to produce a lubricating fluid or synovia, and that, therefore, its position is determined by the essential necessity of proximity to a direct blood-supply. In other words, this condition is provided by all parts of ' From a series of oVjservations upon the development of diarthrodial joints, the writer considers that there is evidence to show that the " cellular articular disc " is directly responsible for the production of the epiphyses which adjoin the completed articular cavity, and that, among such amphiarthroses as exist between the bodies of vertebrae, not only the intervertebral fibro-cartilage, but the proximal and distal epiphyses which ultimately unite with the vertebral bodies have a common origin in the joint-unit. LIGAMENTS OF THE VERTEBKAL COLUMN. 305 the iiiterioi' of an articular cavity except the articular encrusting cartilage. Conse- quently the synovial stratum is absent only from the free surface of articular cartilage, altiiough it forms a thicker layer ujjou the inner surface of the articular capsule than upon the free surfaces of interarticular ligaments, discs, and menisci. It is not necessary to suppose that the synovial stratum has disappeareil from these articular cartilages as the result uf friction, becau.se, notwitiistanding constant friction, such parts as the interior of articular capsules or the menisci of the knee-joint have not been denuded of their synovial covering. As the epiphyses adjoining articular cavities are produced in the joint-units, the attachments of the capsule should bo found upon, and restricted to, the non-articular surfaces of the articular epiphyses. While this is the case in their earliest stages, yet, as development advances, considerable variations arise, until, in the adult condition, the capsule of the larger articulations, more particularly of the extremities, is not always restricted to the epiphyses for its attachments. The student will readily perceive and appreciate these variations by comparing the accounts and illustrations of the epiphyses with those of the articulations, and he should note that in some cases the epiphysial line is extrd-capsidar, i.e. the capsular attachment is restricted to the epiphysis ; in some the line is intra-capsu/(ir ; and in some the epiphysial line is partly intra-capsular and partly e.\tra-capsular. MORPHOLOGY OF LIGAMENTS. From what has been said in connexion with the development of joints, it will be evident that ligaments are essentially products derived from the cellular articular disc. Nevertheless, in relation to the fully formed joint, many structures are described as ligaments which do not take origin in the manner just indicated. Some of these ligamentous structures remain fairly distinct from the articular capsules with which they are immediately associated ; others become thoroughly incorporated with the articular capsules and cannot be separated therefrom, while yet others may be found situated within the capsule of a joint, and thus play the pai't of interarticular ligaments. instances oi each of these forms of adventitious ligaments may be readily given. For exami)le, we may instance the expansion of the tendon of the semimembranosus muscle to the oblique ligament of the knee-joint, and the offshoots from the tendon of the tibialis posterior muscle to the plantar asjiects of various tarsal bones, as illustrations of structures which play an important jjart as ligaments, but are not indelibly incorporated with the joint capsule. Of structures which have become indelibly incorporated Avith the primitive capsule, we may instance the broad tendinous expansions of the quadriceps extensor muscle around the knee-joint. The tibial collateral ligament of the same joint is regarded as a detached portion of the tendon belonging to that part of the adductor magnus muscle which takes origin from the ischium, while the fibular collateral ligament of the knee is considered by some to be the jjrimi- tive femoral origin of the perona3US longus muscle. Another illustration of the same condition is found in the coraco-humeral ligament, which is regarded by some as representing a detached portion of the pectoralis minor muscle. Two illustrations may be given of structures playing the part of ligaments within the capsule of a joint, although in the first instance they are not cleveloped as ligaments. It is questionable if the ligamentum teres of the hip-joint is an interarticular ligament in the true sense of the term ; it has been regarded as the isolated and displaced tendon of the ambiens muscle found in hinh. In the shoulder-joint, many observers look upon the superior gleno-hunaeral ligament as representative of the ligannrntum teres. Such sti'uctures as the stylo-hyoid ligament and the spheno-mandibular ligament, although described as ligaments, are in reality skeletal jjarts which have not attained their complete ossific development. Again, certain portions of the deep or muscular fascia of the body which become specialised into restraining and sujjporting bands {e.g. the ilio-tibial tract of the fascia lata ; the stylo-mandi- bular ligament ; the transverse cari)al and dorsal carpal ligaments of the wrist-joint ; the transverse crural ligament, and lig. laciniatum of the ankle-joint), although called ligaments, have no direct developmental association with articular ligaments. Lastly, the inguinal ligament of Poupart and the lacimar ligament of Gimbernat, being special developments in connexion with an exjjanded tendon or aponeurosis, are still further removed from association with an articulation. LIGAMENTA COLUMN^E VERTEBRALIS ET GRANIL Ligaments of the Vertebral Column and Skull. — All vertebra?, with the exception of those which deviate from the coininon vertebral type, present two sets of articulations whose various parts are arranged upon a uniform pattern. Thus, every pair of typical vertebrae presents an articulation between the bodies and a pair of articulations between the vertebral arches. With the latter there 20 306 THE AKTICULATIONS OE JOINTS. are associated various important accessory ligaments which bind together laminse, spinous processes, and transverse processes. Articulations between Bodies of Vertebrae. — These are amphiarthrodial joints. Singly, they present only a slight degree of mobility, but when this amount of move- ment is added to that of the whole series, the ranee of movement of the vertebral Vertebral body Intervertebral fibro- cartilage Nucleus pulposus Ligamentnm flavum Spinous process Fig. 292. — Median Section through a Portion of the Lumbar Part of the Vertebral Column. column becomes considerable. The articular surfaces are the flattened surfaces of adjacent vertebral bodies. They are bound together by the following structures : — Fibrocartilagines Intervertebrales (Fig. 292). — Each intervertebral fibro- cartilage accommodates itself to the space it occupies between the two vertebral bodies, to both of which it is firmly adherent. The fibro-carbilages, from different \Hterior longitudinal ligament Rib Three slips of the radiate ligament of the head of the ri Anterior costo- transverse ligament 4wii'f'ii iiil^^p^^^ Fig. 293. — Anterior Longitudinal Ligament of the Vertebral Column, and the Costo-vertebral Joints as seen from the front. parts of the vertebral column, vary in vertical thickness, being thinnest from the third to the seventh thoracic vertebra, and thickest in the lumbar region. In the cervical and lumbar regions each fibro- cartilage is thicker anteriorly than posteriorly, thereby assisting in the production of the anterior convexity which characterises the vertebral column in these two regions. In the thoracic region LIGAMENTS OF THE VEETEBRAL COLUMN. 307 the fibro-cartilages are thinnest on their anterior aspects in correspondence with the anterior concavity of this section of the vertebral cohimn. Each tihro-cartilage consists of a circumforential ])orLi()n,annulus fibrosus, formed for the most part of obUque parallel fibres running from one vertebra to the other; horizontal librcs are also found. The axial or central part of the tibro- cartilage, tlie nucleus pulposus, is clastic, soft, and pulpy. The superior and inferior surfaces of the fibro-cartilage are closely adherent to the adjoining epiphyseal plates of the vertebral bodies, and as ossification advances, the distinction between epiphyseal plates and vertebral Ijody disappears. As a rule the transverse diameter of the fil^ro-cartilage corresponds to that of the vertebral bodies which it joins together; but in the cervical region, where the inferior margin of the super-imposed vertebra is overlapped on each side by the one which bears it, the fibro-cartilage does not extend to the extreme lateral margin, and in this position a small diarthrosis may be seen at each lateral margin of tlie liliro-cartilage. Lig. Longitudinale Anterius. — The anterior longitudinal ligament (O.T. anterior common ligament) (Fig. 293) consists of a wide stratum of longitudinal fibres which extends from the front of the epistropheus vertebra to the front of the superior segment of the sacrum, and becomes gradually wider from above downwards. It Hes on the anterior surfaces of the intervertebral fibro-cartilages, to which it is firmly attached as it passes from one vertebra to the other. Its fibres vary in length. Some are attached to contiguous margins of two adjoining vertebne ; others pass in front of one vertebra to be attached to the next below, and yet others find their lower attachment three or four verteljrte Ijelow the one from which they started. None of the fibres are attached to the transverse depression on the anterior surface of a vertebral body. Lig. Longitudinale Posterius. — The posterior longitudinal ligament (O.T. posterior common ligament) (Fig. 294) is found within the verteltral canal upon the posterior aspect of the vertebral bodies. It consists of longitudinal fibres, and it extends from the sacrum to the epistropheus vertebra, superior to which it is continued to the skull as the membrana tectoria. Opposite each interverte- bral fibro-cartilage it is attached to the entire width of the adjacent margins of the two vertebral bodies, its fibres being continued over the posterior surface of the fibro-cartilage. In the lumbar and thoracic regions the width of the ligament is con- siderably reduced opposite the back of each vertebral body, and thus it forms a series of dentate pro- jections along both of its margins ; but in the cervical region the width of the ligament is more uniform. One or two large thin -walled veins escape from the body of each vertebra under cover of this ligament. Articulations between Vertebral Arches. — The vertebral arch of each typical vertebra carries two pairs of articular processes, by means of which it articulates with adjacent vertebral arches. The articulations between these processes are true diarthroses of the arthrodial variety. The distinctive characters of these articidar surfaces, as regards their shape and direction in the different groups of vertebrae, have been referred to in the section on osteology. All these articulations are provided with complete but very thin-walled cap- sulae articulares, which are thinnest and loosest in the cervical region, where also the movements are freest. Each capsule is lined with a stratum synoviale. Associated with these joints between vertebral arches are certain ligaments' which are accessory to the articulations, although they are quite distinct from the capsule. Root of ver- tebral arch divided i'lli, 294. — PoSTEKlOR LONtilTDDINAL Ligament of the Vertebral Column- 308 THE AETICULATIONS OR JOINTS. Root of vertebral arch divided The laininiE of adjoining vertebrae are bound together by the ligamenta flava (O.T. subflava) (Fig. 295), which consist of j^ellow elastic fibres. The ligamenta flava close the vertebral canal in the intervals between the laminse. Each ligament is attached superiorly to the anterior aspect of one lamina at a short distance above its inferior border, and inferiorly it is attached to the posterior aspect of the subjacent lamina. In the thoracic region, where the imbrication of adjoining laminse is a prominent feature, these ligaments are not so distinctly visible from behind as they are in the regions where imbrication of the laminse is not so marked. Laterally they extend as far as the articular capsules, while medially the margins of the ligaments of opposite sides meet under cover of the root of the spinous process. Contiguous spinous processes are also attached to each other by ligamenta interspinalia (interspinous ligaments) (Fig. 292). These are strongest in the lumbar, and weakest in the thoracic region. Each consists of layers of obliquely inter- lacing fibres which spring from near the tips of the two adjacent spinous process and radiate to their op- posing margins. In the antero - posterior direc- tion they extend from the base to the tip of the spinous process. The ligamenta supra- spinalia (supra-spinous ligaments) (Fig. 292) consist of longitudinal bands of fibres of varying lengths. They extend from spine to spine, being attached to their tips, and are situated superficial to, although in continuity "with, the ligamenta interspinalia. Transverse In the ccrvical rcgiou piocess ^^^^ series of ligaments is extensively developed, where they project back- wards from the spinous processes between the muscles of the two sides of the neck in the form of an elastic partition called the ligamentum nuchse. The antero-posterior extent of the ligamentum nuchas increases as it approaches the occiput, where it is attached to the external occipital crest from the external occipital protuberance to the posterior border of the foramen magnum. Its posterior margin is free, and extends from the external occipital protuberance to the spine of the vertebra prominens. Between the transverse processes there are ligamenta intertransversaria, which consist of vertical fibres extending from the postero-inferior aspect of one transverse process to the superior margin of that next below. These ligaments are generally absent from the cervical and upper thoracic regions. Sacro-coccygeal Symphysis. — The last piece of the sacrum is joined to the first piece of the coccyx by an intervertebral fibro-cartilage, and the junction is rendered more secure by the presence of certain strong ligaments. A lig. sacro- coccygeum anterius, continuous with the lig. longitudinale anterius, is placed in front. A lig. sacrococcygeum posterius, which stretches downwards from the sharp border of the lower opening of the sacral canal, strengthens the joint behind. A Fig. 295. — Ligamenta Flava as seen from the front after Re- moval OF the Bodies of the Vertebr/e by sawing through the Roots of the Vertebral Arches. ARTICULATION OF ATLAS WITH AXIS. 509 lig. sacrococcygeum laterale supporta the joint on each side, whilst strong Vmuds pass between the cornua of tlie two bones and constitute the interarticular ligaments. Intercoccygeal Joints. — So long as they remain separate, the dillerent pieces of the coccyx are joincnl by intervertebral fibro-cartilages and by anterior and posteridr ligaments. Movements of the Vertebral Column. — Althougli the amount of movement permissible between any two vertebiie is txtivnuly limited, yet tlie total range of movement capal)le of being attained by tlie entire vertt'l)ral column is very con.siderable. Flexion may occur lK)th forwai-ds and l)ackwai-ds at the articulations of vertebral bodies, but more freely in the lumV)ar and cervical region.s than in the thoracic region, where the limited amount of intervertebral tibro-cartilage and the imbrication of the laminae and spines restrict the movement. Backward flexion is most pronounced in the cervical region, and forwai-d Hexion in the lumbar region. Between the articular surfaces of the articulations lietween vertebral arches a variety of movements are permitted, dependent upon the directions of the.se surfaces. Thus lateral flexion ~is permitttd in the lumbar, but not in the cervical or dorsal region-s. Again, in tlic lumlmr region rotation does not occur, owing to the shape of the articular processes, wliile it is possible in the thoracic region. In the cervical region the shape and position of the aiticular surfaces prevent the occurrence both of lateral flexion and of rotation as isolated movements, Init a combination of these two movements may take j^lace, whereby rotatory move- ment in an oblique median axis results. Finally, in the lumbar region, Ijy combining the four forms of flexion, viz., forward, backward, and lateral, a certain amount of circumduction is possible. Articulatio Atlantoepistkophica. Between the atlas and epistropheus vertebrae three diarthroses occur. Two of them are situated laterally, iu relation to the articular processes, and are called Membrana tectoria Basilar part of occipital bone Anterior atlaiito-oecipital ligament Ligamentum apicis dentis Synovial cavity Anterior arch of atlas ^T^^f/f/.^i^.'^ii-l i Transverse ligament of atlas Inferior crns of cruciate ligament ~'~ir"'rf^''ZT'"'^r* 'j ' i \ t Rudimentary intervertebral I: [r "?.'>^'''*V-'r ■: ;/ libro-cartilage Superior crus of cniciate ligament of the atlas Synovial cavity Posterior atlanto-occipital membranes ^•^^ Occipital bone Posterior longitudinal ligament Posterior arch of atlas Root of spine of epistropheus Fic;. 296. — Median Section through the Atla.\to-occipital and Atlaxto-kpistropheal Joints. arthrodial diarthroses, because of the flattened nature of the articulating surfaces. The third articulation is median in position. It is found between the smooth anterior surface of the dens of the epistropheus and the articular facet on the posterior aspect of the anterior arch of the atlas. This joint is a rotatory diarthrosis. Ligamenta. — Each of the joints is furnished with a capsula articularis, whereby the articular cavity is circumscribed. In the case of the lateral articulations, each articular capsule presents a distinct band, named the accessory ligament, which is situated within the vertebral canal (Fig. 297),and passes downwards and medially from the lateral mass of the atlas to the superior aspect of the body of the epistropheu.s. The following additional ligaments constitute the leading bonds of union : — Lig. Obturatorium Atlantoepistrophica Anterior. — The anterior covering atlanto-epistropheal ligament (O.T. anterior atlo-axoid ligament) (Fig. 296) is a mem- branous structure which is thin laterally, but strong in the median plane, where it is thickened by a prolongation of the lig. longitudinale anterius. It extends from the anterior arch of the atlas to the front of the body of the epistropheus. 310 THE AKTICULATIONS OE JOINTS. Lig. Obturatorium Atlantoepistrophica Posterior. — The posterior covering atlanto-epistroplieal ligament (O.T. posterior atlo-axoid ligament) (Fig. 296) occupies the position which is elsewhere taken by the ligamenta flava. It extends from the posterior arch of the atlas to the upper border of the vertebral arch of the epistropheus. Lig. Transversum Atlantis. — The transverse ligament of the atlas (Figs. 296 and 297) is a strong band, placed tra.nsversely, which arches backwards behind the neck of the dens of the epistropheus. By its extremities it is attached to the tubercle on the medial aspect of each lateral mass of the atlas. A thin plate of fibro-cartilage is developed in its central part. A stratum synoviale (synovial membrane) lines each of the three articular capsules, and in addition a synovial sac is developed between the dens and the lig. transversum atlantis. This is more extensive than the synovial cavity between the dens and the atlas. Articulatio Atlanto-occipitalis. There are two articulations between the atlas and the occipital bone. Each is a diarthrosis in which movement takes place in relation to two axes, viz. the Membiana teotona Cius supeims Occipital bo Lateral mass of atlas Atlanto-epistropl Body c 'Liganientum apicis dentis Ligameutum alare Crus superius Ligameutum crucia- tum atlantis Accessory atlanto- epistroplieal ligament Cius inferius Membiana tectoria Fig. 297. — Dissection from behind of the Ligaments connecting the Occipital Bone, the Atlas, AND the Epistropheus with each other. transverse and the antero-posterior. The condyle of the occipital bone is bi- convex, and fits into the bi-concave superior articular surface of the atlas, while the long axes of the two joints are directed horizontally forwards and medially. Ligamenta.— Each articulation is provided with a capsula articularis which is thin but complete. It is attached to the rough non-articular surfaces surrounding the articular areas on the atlas and occipital bone. The following supplementary ligaments are the chief structures which bind the atlas to the occipital bone : — The membrana atlanto-occipitalis anterior (anterior occipito-atloid membrane) (Fig. 296) is a strong although thin membrane, attached inferiorly to the anterior arch of the atlas, and superiorly to the anterior half of the circumference of the foramen magnum. Laterally it is in continuity with the articular capsules, while in the median plane, where it extends from the anterior tubercle of the atlas to the basilar x>art of the occipital bone, it presents a specially well-defined thickened band which might be regarded as a separate accessory ligament or as the beginning of the anterior longitudinal ligament of the vertebrce. The membrana atlanto-occipitalis posterior (posterior occipito-atloid membrane) (Fig. 296) is another distinct but still thin membrane which is attached superiorly to the posterior half of the circumference of the foramen magnum, and inferiorly to the upper border of the posterior arch of the atlas. Laterally it also is continuous with the articular capsules. On each side of the median plane its inferior border ARTICULATION OF SPINE WITH CRANIUM. 311 is arched in relation to the vertebral groove, and is therefore to some extent free, in order to permit the passage of the posterior ramus of the first cervical nerve and the vertebral artery. Not infrequently this arched border becomes ossified, thus converting the groove on the bone into a foramen. A synovial stratum lines each of the articular capsules. There is no direct articulation between the epistropheus and the occipital bone, but union l)etwecn theiu is effected by means of the folloNving accessory ligaments : — The membrana tectoria (Fig. 296) is situated within the vertebral canal, and is usually regarded as the upward continuation of the posterior longitudinal ligament of the vertebral bodies. It extends from the posterior surface of the body of the epistropheus to the basilar groove on the superior surface of the basilar part of the occipital bone, spreading laterally on the circumference of the foramen magnum. Some of its deepest fibres are attached to the atlas iriimediately above the atlanto- epistroi)heal articulation. Subjacent to the membrana tectoria there is the ligamentum cruciatum atlantis (Fig. 297), a structure which is very closely associated with the lig. transversum atlantis. It consists of a cms transversum, formed by the superficial fibres of the transverse ligament of the atlas ; a ci'us inferius, consisting of median longi- tudinal fibres wliich are attached below to the posterior surface of the body of the epistropheus, and above to the crus transversum ; and a cms superius, also median and longitudinal, whose fibres extend from the crus transversum upwards to the posterior surface of the basilar part of occipital bone, immediately subjacent to the membrana tectoria. Ligamenta Alaria. — The alar ligaments (O.T. check ligaments) (Fig. 297) are two very powerful, short, and somewhat rounded bands. They are attached medially to the sides of the summit of the dens, and laterally to the tubercle on the medial aspect of the condylar portions of the occipital bone. Ligamentum Apicis Dentis. — The ligament of the apex of the dens (O.T. middle odontoid) (Fig. 297) consists of fibres running vertically upwards from the apex of the dens to the median part of the anterior margin of the foramen magnum. This ligament to some extent represents an intervertebral fibro-cartilage, in the centre of which remains of the notochord may be regarded as present. Even in advanced life a small lenticular mass of cartil- age, completely surrounded by bone, persists in the plane of fusion between the dens and the body of the epistropheus. Movements at these Joints. — At tlie joints between occipital bone and atlas the movements are very simple, and consist essentially of movements whereby the head is elevated and depressed upon the vertebral column (nodding move- ments). In addition a certain amoimt of oblique movement is possible, during which great stabil- ity is attained by resting the anterior and posterior parts of opposite condyles upon correspond- ing parts of the atlas. The head and the atlas rotate together upon the epistropheus, the pivot of rotation being the dens, and the amount of rotation is limited by the ligamenta alaria. No rota- tion can occur between the occiput and atlas, and stability between atlas and epistropheus is best attained after a slight amount of rotation, similar to the oblique movement between occipital bone and atlas. Teniporo-mandibular ligament (anterior and posterior parts) Styloid process Stylo-niandibular ligament Fig. 298. — Mandibular Joixt. 312 THE AETICULATIONS OE JOINTS. ARTICULATIO MANDIBULARIS. i. > o a 'C " Tuberculum articulare Fig. 299.- -Section through the Mandibular Joint. The mandibular joint (O.T. temporo-mandibular) is an arthrodial diarthrosis. It occurs between the mandibular fossa of the temporal bone and the condyle of the mandible. These two articular surfaces are markedly dissimilar both in size and shape. In its general outline the articular surface of the head of the mandible is cjlindricai, having its long axis directed from the medial side laterally and forwards. On the other hand, the mandibular fossa is concavo-convex from behind forwards. Its articular surface includes the tuberculum articulare — the eminence at the base of the anterior root of the zygoma. The articular surfaces of the bones are clothed with hyaline en- crusting cartilage, whilst the articular cavity is divided into a superior and inferior part by a disc of fibro-cartilage. Ligaments. — The joint is invested by an articular capsule which is quite com- plete, but is very thin on the medial, side. The lateral part of the fibrous stratum of the capsule — the temporo-mandibular liga- ment (O.T. external lateral) (Fig. 298) — is divisible into anterior and posterior portions which are attached superiorly to the root tubercle and inferior border of the zygomatic process of the temporal bone, and inferiorly to the lateral side and posterior border of the neck of the mandible. The direction of its fibres is downwards and backwards. Within the capsule there is a disc of fibro-cartilage, the discus articularis (Fio-. 299), which is moulded upon the condyle of the mandible below, and on the articular surface of the temporal bone above. It thus compensates for the incongruity between the articular surfaces of the two bones. The disc is attached circumferentially to the capsule. It is widest in the trans- verse direction, thicker posteriorly than anteriorly, and thinnest towards the centre, where it may be perforated. Its anterior margin is intimately associated with the insertion of the external pterygoid muscle. A synovial stratum lines each of the compartments into which the joint cavity is divided by the disc. As a rule these membranes are separate from each other, but they become continuous when the disc is perforated. The superior synovial stratum is larger and more loosely disposed than the lower. Situated on the medial aspect of the joint, but at a short distance from it, and quite distinct from the ca^jsule, there is an accessory band called the lig. spheno- mandibulare (Fig. .300). Superiorly the spheno-mandibular ligament (O.T. internal lateral; is attached to the angular spine of the sphenoid Ijone, and inferiorly to the inferior as well as the anterior border or lingula of the inferior alveolar foramen. It is not an articular ligament in the true sense ; for, instead of being connected with the joint, it is developed in the tissue surrounding part of Meckel's cartilage. Splieno-mandibular ligament mandibular ainent Fig. 300. — Spheno-Mandibular Ligament of the Mandibular .Joint. THE JOINTS OF THE THORAX. 313 Portions of the following structures afe found in the interval between the spheno-niandihular ligament and the ramus of the mandible — viz., the external j^terygoid muscle; internal maxillary vessels ; inferior alveolar vessels and nerve ; middle meningeal vessels ; auriculo- temporal iicrvf ; and sonu'tiuu's a ileep portion of the parotid gland. Movements of the Mandible. — The nature of the movements which the mandible can perform is tletermined partly Ijy llie character of the articular surfaces of the mandibular joint, and partly by the fact that, while the two joints always act simultaneously, they may al.su, to some extent, perform the same movement alternately. When movement takes place through the long or transverse horizontal axis of each joint, the mandible may be elevated, as in clenching the teeth, or it may be depressed, as in gaping. In the latter movement the condyle leaves the mandibular fos.sa, and, along with the disc, it moves forwards until they rest upon the tuberculum articulare. Meantime the chin de.scribes the arc of a circle, of which the centre or point of least movement corresponds to the position of the inferior alveolar foramen, and thus the structures which enter at that foramen are protected against stretching. Coincidently with the forward movement of the condyle, it glides in a revolving manner upqn the inferior aspect of the di.sc. At any stage in the movement of depressing the chin the mandible may be protruded, so that the inferior incisor teeth are projected in front of the upper .set, a movement which results from the condyles of the mandible being drawn forwards upon the articular tubercles. A similar relation of the condyle to the articular tubercle occurs during the exaggerated depression of the mandible Avhich results from yawTiing, in M'liich position the articulation is liable to be dislocated. When the two joints perform the same movement alternately, a certain amount of lateral motion results, from the fact that the long axis of each joint presents a slight obliquity to the transverse axis of the skull, and consequently a grinding or oblique movement in the horizontal ]ilane is produced. Excessive depression, with the risk of dislocation, is resi.sted by the fibres of the temporo-mandibular ligament, which becomes tense. In all movements of the mandible the disc conforms closely to the position of the condyle, and they move forwards and backwards together, but at the same time the disc does not restrict the movements of the condyle. Thus while the disc, along with the condyle, is gliding upon the temporal aspect of the joint, the condyle itself revolves upon the inferior surface of the disc. Cranial Ligaments not directly associated with Articulations. Lig. Stylomandibulare. — The stylo-mandibular ligament (Figs. 298 aud 300) is a specialist'd portion of the deep cervical fascia which extends from the anterior aspect of the tip of the styloid process of the temporal bone to the posterior border of the angle of the mandible, between the insertions of the masseter and internal pterygoid muscles. Lig. Pterygospinosum. — The pterygo-spinous ligament is a membrane extending from the upper part of the posterior free margin of the lateral pterygoid lamina, posteriorly and slightly laterally, to the angular spine of the sphenoid. An interval is left between its upper border and the floor of the skull for the outward passage of those branches of the inferior maxillary nerve which supply the external pterygoid, temporal, and masseter muscles. This ligament has a tendency to ossify either wholly or partially. Lig. Stylohyoideum. — The stylo-hyoid ligament may be regarded as the down- ward continuation of the styloid process of the temporal bone. Inferiorly it is attached to the lesser cornu of the hyoid bone. It is not infrequently ossified, in which case it constitutes the epihyal bone found in many animals. THE JOINTS OF THE THORAX. Articulationes Costovertebrales (Costo - vertebral Articulations). — The typical rib articulates with the vertebral column both by its head and by its tubercle. Thus, two sets of articulations, with their associated ligaments, exist between the ribs and the vertebrae, but each set is constructed upon a common plan, with the exception of certain joints situated at the upper and lower ends of the series, where the ribs themselves deviate from the typical form. Articulationes Capitulorum. The articulations of the heads of the ribs with the bodies of the vertebne (Fig. 293) are all diarthroses, which, from their somewhat hinge-like action, may be classed as ginglymoid. 31-i THE AKTICULATIONS OK JOINTS. The head of eveiy typical rib is wedge-shaped, and presents two articular facets, an upper and a lower, separated from each other by an antero-posterior ridge which abuts against an intervertebral fibro-cartilage, while the articular facets articulate with similar surfaces on the contiguous margins of the two vertebrae adjoining the fibro-cartilage. These surfaces form a wedge-shaped depression or cup, the bottom of which is more elastic than the sides, and thus an arrangement is provided which tends to reduce the shock of blows upon the walls of the chest. Each of these articulations is provided with an articular capsule which surrounds and encloses the joint, and is attached to contiguous non-articular margins on the head of the rib and the two vertebral bodies. On its anterior or ventral aspect the capsule presents three radiating fasciculi which collectively form the lig. capituli costse radiatum (radiate ligament of tlie head of the rib (O.T. stellate)) (Fig. 293). These fasciculi radiate from a centre on the anterior surface of the head of the rib, so that the middle fasciculus becomes attached to the intervertebral fibro-cartilage while the upper and lower fasciculi proceed to the adjacent margins of the two vertebrae between which the fibro-cartilage is situated, and with which the rib articulates. To a slight extent these radiating fasciculi pass under cover of the lateral margin of the anterior longitudinal ligament of the vertebral bodies. In those joints in which the head of the rib does not articulate with an inter- vertebral fibro-cartilage the central fasciculus of the radiate ligament is wanting, but the other two retain the same general arrangement. Lig. Capituli Costae Interarticulare. — The interarticular ligament of the head of the rib consists of short transverse fibres within the capsule. These are attached, on the one hand, to the ridge which intervenes between the two facets on the head of the rib, and on the other to the lateral aspect of the intervertebral fibro-cartilage. This ligament is not a disc or meniscus, but merely an interarticular ligament, of width sufficient to divide the joint cavity into an upper and a lower compartment. It is absent from those joints which do not articulate with an intervertebral fibro- cartilage, i.e. from those ribs which articulate with the body of only one vertebra. The interarticular ligament is supposed to represent the lateral end of a ligament which, under the name of the lig. conjugale costarum, connects the heads of the ribs of certain mammals across the posterior aspect of the intervertebral fibro-cartilage, and, in the hiiman subject, until the seventh month of foetal life, connects the posterior aspects of the necks of a pair of ribs with each other across the median plane. A stratum synoviale lines each joint cavity, and therefore, in all cases where the joint is divided into two compartments, each one has its own synovial lining. Aeticulationes Costotransveksaki^. In the costo-transverse joints the tubercle of each typical rib articulates with the transverse process of the lower of the two thoracic vertebrse with which the head of the rib is associated. Near the tip of the transverse process there is an articular facet, on its anterior aspect, for articulation with the corresponding facet on the medial articular part of the rib tubercle. The joint so formed is an arthrodial diarthrosis. The joint cavity is surrounded by a comparatively feeble capsula articularis, which is attached immediately beyond the margins of the articular facets, and in which no special bands can be distinguished. A simple stratum synoviale lines the capsule in all cases where the latter is present. The following accessory ligaments, in connexion with this joint, strengthen and support the articulation : — Ligamentum Costotransversarium Anterius. — The anterior costo-transverse ligament (O.T. superior) (Fig. 293) consists of strong bands of fibres which are attached to the superior border of the neck of the rib, extending from the head laterally to the non-articular part of the tubercle. All these fibres may be traced upwards. Those situated nearest to the head of the rib proceed obUquely upwards and laterally, to be attached to the transverse process immediately above, but with STERNO-COSTAL JOINTS. 315 extensions to the adjoining rib ami its costo-transverse articular capsule. Others proceed almost vertically upwards to the adjoining transverse process, while those which ascend from the upper surface of the tubercle pass obliquely upwards and inwards to reach the postero-inferior aspect of the adjoining transverse process. Some posterior fibres connected with the transverse })rocess at its junction with the lamina are called the posterior costo-transverse ligament. Lig. Tuberculi Costse. — The ligament of the tubercle of the rib is a band of transver.se tibres applied to the postero-lateral aspect of tiie capsule. By one end these fibres are attached to the tip of the transverse process behind its articular tacet, and by the other to the external rough surface of the tubercle of tlie rib. Lig. Colli Costae. — The ligament of the neck of the rib (O.T. middle costo- transverse ligament) consists of short filjres which stretch from the posterior aspect of the neck of the rib, backwards and medially, to the anterior aspect of the transverse process, but, in addition, a proportion of the fibres passes to the posterior aspect of the inferior articular process of the upper of the two vertebrae with which the head of the rib articulates. The following exceptions to the general plan of rib-articulation indicated above must be noted : — 1. There is no articulation between the eleventh and twelfth ribs and the transverse processes of the corresponding vertebrae. 2. The anterior costo-transverse ligament is wanting from the first rib, and is either rudimentary or wanting in the case of the twelfth rib. 3. The lig. colli costa3 is rudimentary in the eleventh and twelfth ribs. The ligamentum lumbocostale extends from the superior surface of the base of the transverse process of the first lumbar vertebra to the inferior surface of the neck of the twelfth rib, as well as to the inferior surface of the transverse process of the twelfth thoracic vertebra. Articulationes Costochondrales. Each rib possesses an unossified portion, termed its costal cartilage. As age advances, this cartilage may undergo a certain amount of superficial ossification, but it never becomes entirely transformed. The line of demarcation between bone and cartilage is clear and abrupt, and usually the bone forms an oval cup, in which the end of the cartilage is retained by means of the continuity which exists between the periosteum and the perichondrium. There is no articulation in the proper sense between the rib and its cartilage, although a synovial cavity has occasionally been found between the first rib and its cartilage. Articulationes Interchondrales. Interchondral joints are arthrodial diarthroses, and they are found between adjoining margins of certain of the costal cartilages, viz., from the fifth to the eighth or ninth. The cartilages which thus articulate develop flattened, somewhat conical, prolongations of their substance, and thereby the intercostal spaces are interrupted where these flat articular facets abut against each other. Each joint is closed by a surrounding articular capsule, the superficial and thoracic aspects of which are specially strengthened by external and internal interchondral ligaments. These bands extend obliquely between adjacent cartilages. A stratum synoviale lines each joint capsule. Articulationes Sternocostales. The upper seven pairs of costal cartilages, as a rule, extend to the lateral margins of the sternum to form sterno-costal joints. Of these, the /ii'st pair is implanted directly upon the manubrium sterni. The ossific process ends abruptly in connexion with the rib, and also ceases as suddenly in connexion with the sternum, and hence the cartilage does not normally present an articulation at either end. From the second to the seventh pairs of ribs inclusive, the sterno-costal joints are constructed upon the type of arthrodial diarthroses, although, in the case 316 THE AETICULATIONS OE JOINTS. of the sixth and seventh cartilages, the joint ca%dty is always small, and is frequently obliterated. The sternal end of each of these costal cartilages presents a slight antero-pos- terior ridge which fits into a shallow V-shaped depression upon the lateral margin of the sternum. With the exception of the sixth cartilage, they articulate opposite the lines of union between the primary segments of the sternum ; the sixth articu- lates upon the side of the lowest segment of the body of the sternum. Each joint is enclosed by a capsula articularis, the fibrous stratum of which is attached to the adjacent borders of the articulating elements. Specially strong fibres distinguish the superficial and deep aspects of the capsule. The lig. sternocostale radiatum (O.T. anterior costo-sternal ligament) (Fig. 301) is composed of strong fibres which radiate from the anterior surface of the costal cartilage, near its sternal end, to the front of the sternum. The ligaments of opposite sides interlace with each other, and so cover the front of the sternum with a felted membrane — the membrana stemi. Joint capsule Joint cavity Interarticular ligament Joint cavitj ■ — ^^ ' "i VvV Costo-claWcnlar ligament Anterior stemo-clavicular ligament sterno-costale radiatum Fig. 301. — Sterno-clavicular and Sterno-costal Joints. The lig. sternocostale posterius (posterior costo-sternal ligament) — also a part of the capsule — has attachments similar to the foregoing, but the arrangement of its fibres is not so powerful. The ligamentum costoxiphoideum passes from the front of the upper part of the xiphoid process, obliquely upwards and laterally to the front of the seventh, and sometimes to the front of the sixth costal cartilage. Within the capsules of these joints ligamenta sternocostalia interarticularia (inter- articular ligaments) (Fig. 301) may be found. Their disposition is somewhat uncertain, for whereas, in the case of the second pair of cartilages, they invariably di\dde the joint cavity into two distinct compartments — an upper and a lower — such an arrangement is very uncertain in the other joints, and they occasionally, especially in the cases of the sixth and seventh cartilages, entirely obliterate the joint cavity. These ligaments extend horizontally between the ends of the costal cartilages and the side of tlie sternum. The stratum s3moviale is found wherever a joint cavity is developed, and there- fore there may be one or two synovial strata, according to the presence or absence of a proper interarticular ligament. When the joint cavity is obliterated by the fibrous structure which represents the interarticular ligament, a synovial stratum is also absent. AKTICULATIONS OF THE CLAVICLE. 317 Artio=ulationes Steuni. rrimiirily the steruuin consists of an elongated plate of hyaline cartilage, which becomes subdivided into segments by the process ol' ossification. The lour segments of which the body of the sternum is originally composed unite with eacli other after tlu^ manner of typical synchondroses. Similarly the xiphoid process and the body ultimately liecome united. It is not usual to find the joint between the manultrium and the body obliterated by the ossification of the two bony segments. Even in advanced life it remains open, and the joint, which is named the synchondrosis stemalis, partakes of the nature of an ampliiarthrosis (Fig. 301), although a joint cavity is not found under any circum- stances in the plate of fibro-cartilage whicii intervenes between the manubrium anil the body of tlie sternum. The membrana stemi, to which reference has already been made, assists in strengthening the union between the different segments of the sternum. Movements of the Ribs and Sternum. — These movements may be considered either independently of, or as associated with, resi)iration. In the fornuT concUtion the ribs move in cxmnexion with flexion and extension of the vertelu'al cohunn, Ijeing more or less depressed and approximated in tlie former, and elevated or pulled apart in tlie latter case. Considered in connexion with respiration, it is necessary to observe that, to all intents and purposes, the vertebral colunm and the sternum are rigid structures. Next, we must remember that the heads of all the ribs occupy fixed positions, and similarly the anterior ends of seven pairs of cartilages are fixed to the lateral margins of the sternum. The ribs thus form arches, presenting a lai'ge amount of obliquity from behind forwards. Tliere- fore, during inspiration, when the rib is elevated, the arch becomes more horizontal, and the transverse diameter of the chest is increased. At the same time, the anterior ends of the sternal ribs tend to thrust the sternum forwards and upwards ; but the nature of the attachment of the first pair of ribs to the sternum, as well as the attachment of the diaphragm to the xiphoid process, prevents this movement from becoming excessive, and hence the sternum becomes a line of resistance to the forward thrust of the rib.s. As a consequence, the ribs rotate upon themselves about an oblique axis which passes downwards, laterally, and i)osteriorly through the capitular joint and the neck of the ril) anterior to the costo-transverse joint. In this way increase, both of the antero-posterior and transverse diameters of the thorax, is provided for, although the amount of increase is not equally pronounced in all planes. Thus at the level of the first rib very little eversion is possible, because the axis of rotation is nearly transverse, and therefore any increase in the transverse or antero-posterior thoracic diameters at this level may be disregarded, although a certain amount of elevation of the manubrium sterni and anterior end of the first rib is evident. Below the level of the sixth rib elevation and rotation of the rib during inspiration are usually said to be complicated by a certain amount of backward movement, due to the character of the costo-transverse joint, until, in the case of the last two ribs, which are destitute of costo- transverse joints, a movement backwards is almost entirely substituted for elevation. It is probable, however, that the movements of the asternal ribs exactly correspond to those of the sternal series, and that by the contraction of the costal digitations of the diaphragm the anterior ends of the false ribs are provided with fixed positions comparable to those sujiiilied by the sternum to the ribs of the sternal series. We may therefore say that during inspiration the ribs move upwards and laterally between their fixed ends, while as a whole the rib rotates, and its anterior end is thrust slightly forwai-ds. During expiration these movements are simply reversed. THE ARTICULATIONS OF THE SUPERIOR EXTREMITY. The bony arch formed by the clavicle and scapula articulates directly with the axial skeleton only at one point, viz., the sterno-clavicular joint. ARTICULATIONS OF THE CLAVICLE. Articulatio Sternoclavicularis. The sterno-clavicular joint is an example of an arthrodial diarthrosis. The articular surfaces concerned in its formation present the following appearances : — 1. The sternal end of the clavicle is somewhat triangular in outline, having its most prominent angle directed inferiorly and posteriorly. The anterior and 318 THE AKTICULATIONS OE JOINTS. posterior sides of the triangle are slightly roughened for the attachment of ligaments, while the base or inferior side is smooth and rounded, owing to the prolongation of the articular surface to the inferior aspect of the bone. In the antero-posterior direction the articular surface tends to be concave, while vertically it is slightly convex. 2. An articular facet, situated on the superior lateral angle of the manubrium sterni, but in a plane slightly behind the supra-sternal notch, articulates with the clavicle. This facet is considerably smaller than the clavicular facet with which it articulates. 3. The superior surface of the first costal cartilage close to the sternum also participates to a small extent in the articulation. It should be noted that the articular surfaces of the clavicle and sternum are covered mainly by fibro-cajtilage. A capsula articularis is well marked on all sides except inferiorly, where it is very thin. The epiphyseal line of the clavicle is intra-capsnlar. Lig". Sternoclaviculare Anterius. — The anterior stemo-clavicular ligament (Fig. 301) forms part of the fibrous stratum of the articular capsule, and consists of short fibres which extend obliquely inferiorly and medially from the anterior aspect of the sternal end of the clavicle to the adjoining anterior surface of the sternum and the anterior border of the first costal cartilage. Lig. Sternoclaviculare Posterius. — The posterior stemo-clavicular ligament also forms part of the fibrous stratum of the capsule, and consists of similarly disposed, but not so strong as the anterior ligament, oblique fibres situated on the posterior aspect of the articulation. Discus Articularis. — A fibro-cartilaginous articular disc (Fig. 301) divides the joint cavity into two compartments. It is nearly circular in shape, and adapts itself to the articular surfaces between which it lies. It is thickest at the circum- ference and thinnest at the centre, where it occasionally presents a perforation, thereby permitting the two synovial cavities to inter-communicate. By its circum- ference it is in contact with, and adherent to, the surrounding capsule, but its superior margin is attached to the apex of the articular surface of the clavicle, while by its inferior margin it is fixed to the sternal end of the first costal cartilage. Two accessory ligaments are associated with this joint, viz., the intercla\dcular and the costo-clavicular. Lig. Interclaviculare. — The interclavicular ligament (Fig. 301) is a structure of considerable strength, forming a broad band of fibrous tissue which is attached to the superior rounded angle or apex of the sternal end of the clavicle as well as to the adjacent margins of the articular surface. Its fibres pass across the interclavicular notch to become attached to corresponding parts of the opposite clavicle, but in their course they dip down into the supra-sternal notch, in which many of them are fixed to the sternum. In this way their presence neither bridges nor obliterates the notch between the two clavicles, and the ligament really becomes a superior sterno- clavicular ligament for each joint. Lig. Costoclaviculare. — The costo-clavicular ligament (Fig. 301) consists of short, strong fibres which are attached inferiorly to the superior surface of the first costal cartilage. They pass obhquely upwards, laterally and posteriorly, to a rough impression situated on the inferior aspect of the sternal end of the clavicle, and are distinct from the articular capsule. Occasionally a bursa is found in the interior of this ligament. As a rule there is a synovial stratum hning each of the two joint cavities (Fig. 301), separated from each other by the articular disc. Sometimes, however, the two membranes establish continuity through a perforation in the disc. Aeticulatio Acromioclavicularis. The acromio-clavicular joint is another instance of an arthrodial diarthrosis. It is situated between the acromial end of the clavicle and the medial aspect of the acromion. Each articular surface is an oval, flattened facet, covered with flbro-cartilage. ACEOMIO-CLAVICULAR JOINT. 319 The ligaments vvliich surround this suiall joint form a complete articular capsule, of which the superior and inferior parts are specially strong, and are there- fore named the superior and inferior acromio-clavicular ligaments (Fi<^. 303). These consist of short til)n's passing Ijotvveen the udjuceiiL rough margins of the two bones in the ])ositioiis iiulii'ated by tlieir names. An articular disc, which is nearly always incomplete, and may occasionally be wanting, is usually found within the joint cavity, where it lies obliquely, with its superior margin farther from the median plane than its inferior margin, and having its borders attached to the surrounding capsule. Frequently the disc is wedge- shaped, with its base directed upwards and its apex free. A synovial stratum is found forming eitlier a single or a double sac, according to the condition of tlic disc. Complete division of the joint cavity, however, is rare. Ligamentum Ooracoclaviculare. — Accessory to this articulation there is the strong coraco-clavicular ligament which binds the acromial end of the clavicle to the coracoid process of the scapula. It is readily divisible into two parts, viz., lig. conoideum and tlie lig. trapezoideuni. The conoid ligament (Fig. 303) is situated medial to and slightly posterior to the trapezoid. It is narrow and pointed at its inferior end, by which it is attached to the superior aspect of the coracoid process, in close proximity to the scapular notch. Its superior end widens out in the manner expressed by its name, and is attached to the coracoid tuberosity of the clavicle. The trapezoid ligament (Fig. 303) is attached inferiorly to the superior surface of the posterior half of the coracoid process, lateral and anterior to the attachment of the conoid Ligament. Superiorly it is attached to the ridge on the inferior surface of the acromial end of the clavicle. Its lateral and medial borders are free. Its anterior surface is principally directed upwards, and its posterior surface, to a similar extent, looks downwards. A mucous or synovial bursa usually occupies the re-entrant angle betw'een these two ligaments. Movements at the Clavicular Joints.— The movements of the medial end of the clavicle at tlie sterno-clavicular joint are limited in their range, owing to the tension of the ligaments. When the shoiUder is raised or depressed the acromial end of the clavicle moves upwards and downwards, whilst its sternal end glides upon the surface of the articidar disc ; when, on the other hand, the shoulder is carried forwards or backwards, the sternal end of the clavicle along with the articular disc moves upon the sternal facet. In addition to these movements of elevation, depression, forward movement and backward movement of the clavicle, there is also allowed at the sterno-clavicular joint a certain amount of circumduction of the clavicle. The part which is played by certain of the ligaments in restraining movement requires careful consideration. The costo-clavicular ligament checks excessive elevation of the clavicle, and restrains within certain limits both backward and forward movement of the clavicle. When the clavicle is depressed, as in cases where a heavy weight, such as a bucket of water, is carried in the hand, it rei'eives support by resting upon the first rib, and the tendency for the medial end of the bone to start uj) out of ita sternal socket is obviated by the tension of the articular disc, the interclavicular ligament, and the anterior and posterior sterno-clavicular ligaments. The articular disc not only acts as a cushion which lessens the shock of blows received upon the shoulder, but it also acts as a most important bond of union, and prevents the medial end of the clavicle from being driven upwards upon the top of the sternum when force is applied . to its lateral end. The movements at the acromio-clavicular joint are of such a kind as to allow the inferior angle, and to some extent the vertebral border of the scapula, to remain more or les^s closely applied to the chest-wall during the various movements of the shoulder. The strong connexion between the coracoid process and the acromial end of the clavicle, by means of the conoid and trapezoid ligaments, renders it necessary that the scapula should follow the clavicle in its various excursions. The presence of the acromio-clavicular joint, however, enables the scapula to change its position somewhat with reference to the clavicle as the shoulder is moved. Thus, when the shoulder is raised and depressed, a marked difference takes place in the angle between the two bones ; again, when the shoulder is thrown forwai-ds or backwards, these movements can be performed without altering in a material degree the direction of the glenoid cavity of the scapula, or in other words, the socket of the shoulder-joint. The conoid and trapezoid ligaments set a limit upon the movements of the scapula at the acromio-clavicular joint. They both, but more particularly the trapezoid ligament, prevent the acromion from being carried medially below the lateral end of the clavicle when blows fall upon the lateral aspect of the shoulder. 320 THE AKTICULATIONS OE JOINTS. Ligaments of the Scapula. These ligaments are not directly connected with any articulation. lAg. Ooracoacromiale. — The coraco-acromial ligament (Fig. 302) completes the arch between the coracoid process and the acromion, and thus provides a secondary socket for the greater protection and security of the shoulder-joint. It is a flat triangular structure stretched tightly between its attachments. By its base it is fixed to a varying amount of the postero-lateral border of the coracoid process, and by its narrower apical end to the tip of the acromion, immediately lateral to the acromio-clavicular joint. Its surfaces look upwards and downwards, and its free borders laterally and medially. It is thinnest in the centre, where it is sometimes perforated by a prolongation of the tendon of the pectoralis minor muscle. Lig. Transversum Scapulae Superius. — The superior transverse scapular ligament (O.T. suprascapular ligament) is a distinct but short flat band which bridges the scapular notch. It may be continuous with the conoid ligament, and it is frequently ossified. As a rule the foramen completed by this ligament transmits the supra- scapular nerve, while the transverse scapular vessels pass superior to the ligament to reach the supraspinous fossa. A small duplicate of this ligament may often be found bridging the foramen on its costal aspect, subjacent to which smaU branches of the transverse scapular artery return from the supraspinous to the subscapular fossa. Lig. Transversum Scapulae Inferius.— The inferior transverse scapular ligament (O.T. spino-glenoid ligament) consists of another set of bridging fibres which are situated on the posterior aspect of the neck of the scapula. By one end they are attached to the lateral border of the scapular spine, and by the other to the adjacent part of the posterior aspect of the head of the scapula. The suprascapular nerve and the transverse scapular vessels pass subjacent to this ligament. ARTICULATIO HUMERI. The shoulder-joint is one of the largest as well as the most important of the joints of the upper limb. It is an example of the enarthrodial, i.e. ball-and-socket, variety of a diarihrosis, and, at the cost of a certain amount of security, it has obtained an extended range of movement. The bones which enter into its formation are the glenoid cavity of the scapula and the head of the humerus. The glenoid cavity is a shallow piriform articular surface, having its narrow end directed upwards and slightly forwards. The superior half of the anterior margin of the fossa is characterised by a shallow notch which accommodates the narrow part of the subscapularis muscle as it runs laterally to its insertion. At the apex of the cavity there is a flat area for the attachment of the long tendon of the biceps brachii muscle. The head of the humerus is hemispherical and articular, while, lateral to its articular margin, there is a slight constriction (the anatomical or true neck of the humerus), which is most strongly marked in relation to the .greater and lesser tubercles of the humerus. Under ordinary conditions the two articular surfaces are maintained in apposition by muscular action, aided by atmospheric pressure, and thus, when the muscles are removed, the bones fall asunder to the full extent of the restraining ligaments. Only a small part of the head of the humerus is in contact with the glenoid cavity at any particular moment, because the humeral head is much larger than the cavity, but, by reason of the shallow character of the cavity, all parts of the two articular surfaces may successively be brought into contact with each other. In the position of rest, as the limb hangs parallel to the vertical axis of the trunk, the inferior aspect of the neck of the humerus is brought into close relation with the inferior part of the glenoid cavity. Labrum Glenoidale. — The labrum glenoidale (O.T. glenoid ligament) (Fig. 303) deepens the glenoid cavity, and thus extends the articular surface. It is situated within the fibrous stratum of the articular capsule, and to some slight extent increases the security of the articulation. It consists of a strong ring of dense fibrous THE SHOULDER-JOINT. 321 tissue attached to the margin of: the glenoid cavity. Many of its fibres are short, and pass obliquely from the inner to the outer aspect of the ridge, so that its attached base is broader than its free edge, and therefore in cross section it appears somewhat triangular. The long tendon of tl)e biceps, which arises from the apex of the glenoid cavity, becomes to a considerable extent in- corporated with the labrum glenoidale. Capsula Articularis. — The fibrous stratum (O.T. capsular ligament) (Fig. 302) of the articular capsule presents the general shape wliicii is characteristic of tlie corresponding part in otiier ball-and-socket joints, viz., a hollow cylinder. By its proximal end the fibrous stratum is attached to the circumference of the glenoid cavity, external to the labrum glenoidale, and also, to a considerable extent, to the labrum glenoidale itself. By its distal ejid it is attached to the neck of the humerus, and therefore beyond the articular area of the head. The fibrous stratum is strongest on its superior aspect, while inferiorly, where the neck of the bone is least defined, it Coraco-iicioinial litjaiiieiit Coraro-limiieral !i''aiii<.'iit Subscapularis imisr.le Coininunication between subscapular bursa ami joint cavity -Vitieulai- capsule Fig. 302. — Capsule ok the Shoulder-Joint and Coraco-acuomiai. Ligament. extends distally for a short distance upon the humeral shaft. Its fibres for the most part run longitudinally, but a certain number of them pursue a circular direction. The greater part of the epiphyseal line of the proximal end of the humerus is extra-capsular, but it is intra-capsular on the medial side of the bone. A prolongation of the fibrous stratum, the transverse himieral ligament presenting both longitudinal and transverse fibres, bridges that part of the iutertubercular groove which is situated between the tubercles of the humerus. At this point an interruption in the fibrous stratum, beneath the transverse humeral ligament, permits the long tendon of the biceps to escape from its interior. In addition to the opening just referred to, there is another very constant deficiency in the superior and anterior part of the fibrous stratum, where the narrowing tendon of the subscapularis muscle is brought into contact with a bursa formed by a protrusion of the synovial stratum. This defect in the fibrous stratum has its long axis in the direction of the longitudinal fibres. Occasionally there is a sinular but smaller opening under cover of the tendon of the infraspinatus muscle. Through the two latter openings the joint cavity communicates with bursse situated between the capsule and the muscles referred to. The tendons of the subscapularis, supraspinatus, and infraspinatus muscles fuse with, and so strengthen, the articular capsule as they approach their respective insertions. On the superior aspect of the articulation the capsule is augmented by an 21 322 THE AETICULATIONS OE JOINTS. accessory structure, the ligamentum coracohumerale (Fig. 302). By its proximal end, which is situated immediately above the glenoid cavity, but subjacent to the coraco-acromial ligament, it is attached to the lateral border of the root of the coracoid process, while its distal end is attached to the humeral neck close to the greater tubercle. This hgament forms a flattened band, having its posterior and inferior border fused with the articular capsule, but its anterior and superior margin presents a free edge, slightly raised above the level of the capsule. This structure is believed to represent that portion of the pectorahs minor to which reference has already been made in connexion with the coraco-acromial ligament (p. 320). The coraco-glenoid ligament is another accessory structure, wliich is not always present. It springs from the coracoid process along with the former ligament, and extends to the superior and posterior margin of the head of the scapula. Gleno-humeral Ligaments (Fig. 303). — If the articular capsule is opened from behind, and the head of the humerus removed, it will be seen that the longitudinal fibres of the anterior part of the fibrous stratum are specially developed in the form of thick flattened bands which extend from the anterior border of the glenoid cavity to the anterior aspect of the neck of the humerus. These gleno-humeral ligaments are three in number, and occupy the following positions : the Coraco- "» Conoid clavicular > Trapezoid ligament J Coraco-acromial ligament — Coracoid process Acromio- cla\-icular ligament Superior gleno- liumeral ligament Bursal perforation in articular capsule Inferior gleno- humeral ligament Glenoid cavity Capsule of shoulder-joint Labrum glenoidale Fig. .303.— Capsular Ligament of Shoulder- Joint cut across and Humerus removed. superior is placed above the aperture in the front of the capsule ; the middle and inferior on the antero-inferior aspect of the capsule, and below the aperture mentioned. The superior gleno-humeral ligament, which some believe to represent the ligamentum teres of the hip-joint, springs, along with the middle gleno-humeral band, from the superior part of the cavity. The inferior ligament is the strongest of the three, and springs from the inferior part of the anterior margin of the glenoid. Intra-capsular Structures.— 1. The labrum glenoidale, already described. 2. The long tendon of the biceps passes laterally from its attachment to the apex of the glenoid cavity and the adjoining part of the labrum glenoidale, above the head and neck of the humerus, to escape from the interior of the capsule by the opening between the tubercles of the humerus, subjacent to the transverse humeral ligament. A synovial stratum (Fig. 304) lines the fibrous stratum of the capsule, and ex- tends from the margin of the glenoid cavity to the humeral attachments of the fibrous stratum, where it is reflected towards the margin of the articular cartilage. It is therefore important to note that the inferior aspect of the humeral neck has the most extensive clothing of the synovial stratum. Further, the synovial stratum envelops the intra-capsular part of the tendon of the biceps, and although this tubular sheath is prolonged upon the tendon into the proximal part of the THE ELI^OW-JOINT. 323 Long head la Fu;. 304. — Vertical Section thuough the Shoulder-Joint. intertill »ercular sulcus, yet the closQci character of the synovial cavity is maintained. Thus, while the tendon is within the capsule, it is not within the synovial cavity. The synovial stratum is continuous with those bursie which communicate with the joint cavity through openings in tlio fibrous stratum of the capsule. Bursae (a) Communicating unth the Joint Cavity. — Practically there i.« only one bursa which is constant in its position, vi/., tJie subscapular, Wlween tlie cap-sule and the teudou of the subscapiilaris muscle. It varies considerably in its dimensions, but its lining mem- brane is always continuous with the synovial stratum of the capsule (Figs. 301 and 302), and therefore it may be "regarded merely as a prolongation of the articular synovial stratum. Occasionally a similar but smaller bursa occui-s between the capsule and the tendon of the infraspinatus muscle. (b) Not cotnm unicating with the Joint Cavity. — The sub- deltoid or sub-acromial bursa is situated between the muscles on the superior aspect of the shoulder-joint on the one hand and the deltoid muscle on the other. 1 1 is an extensive bursa, and is prolonged subjacent to the acromion and the coraco- acromial ligament It does not communicate with the shoulder -joint, but it greatly facilitates the movements of the proximal end of the humerus against the inferior surface of the coraco-acromial arch. Movements at the Shoulder-Joint. — A ball-and-socket joint permits of a great variety of movements, practically in all directions ; but if these movements are analysed, it will be seen that they resolve themselves into movements around three primary axes at right angles to each other, or around axes which are the possible combinations of the primary ones. Til us, around a transverse axis, the limb may move forwards (flexion) or backwards (extension). Arounil an antero-posterior axis it may move laterally, i.e. away from the median plane of the trunk (abduction), or medially, i.e. towards, and to some extent up to, the median plane (adduction). Around a vertical axis, the humerus may rotate upon its axis in a medial or lateral direction to the extent of a quarter of a circle. Since these axes all pass through the shoulder -joint, and since each may present varying degrees of obliquity, it follows that very elaborate combinations are possible until tlie movement of circumduction is evolved. In this movement the head of the humerus acts as the apex of a cone of movement with the distal end of the humerus, describing the base of the cone. The range of the shoulder-joint movements is still further increased owing to the mobility of the scapula as a whole, and owing to its association with the movements of the clavicle already described. ARTICULATIO CUBITI. The elbow-joint ^ provides an instance of a diarthrosis capable of performing the movements of flexion and extension around a single axis placed transversely, i.e. a typical ginglymus diarthrosis or hinge-joint. The bones which enter into its formation are the humerus, ulna, and radius. The trochlea of the humerus articulates with the semilunar notch of the ulna (articulatio himieroulnaris) ; the capitulum of the humerus articulates with the shallow depression or cup on the proximal aspect of the head of the radius (articu- latio hmneroradialis). The articular cartilage clothing the trochlea of the humerus terminates in a sinuous or concave margin both anteriorly and posteriorly, so that it does not line either the coronoid or the olecranon fossa. Medially, it merely rounds off the medial margin of the trochlea, but laterally it is continuous with the encrust- ^ The articulatio cubiti or elbow-joint incliuk-s the humero-radial, huniero-ulnar, and the proximal radio-ulnar joints ; but, for convenience, the description given here is limited to the humero-radial and huniero-ulnar joints. 524 THE AETICULATIONS OE JOINTS. liar collateral ligament ing cartilage covering the capitulum, to the margin of which the cartilage extends in all directions, and thus it presents a convex edge in relation to the radial fossa. The cartilage which lines the semilunar notch of the ulna presents a transverse in- terruption, considerably wider on its medial as compared with its lateral aspect. Thereby the coronoid and olecranon segments of the notch are separated from each other. The cartilage which clothes the coronoid segment is continuous with that which clothes the radial notch of the ulna. The shallow cup-shaped depression on the head of the radius is covered with cartilage which rounds off the margin, and is prolonged without interruption upon the vertical aspect of the head, extending to its most distal level on that part opposed to the radial notch of the ulna. CapsulaArticularis. — Taken as a whole, the liga- ments form a complete fibrous stratum of the articular capsule, which is not defective at any point, although it is not of equal thickness throughout, and certain bands of fibres stand out distinctly because of their greater strength. The common epiphyseal line for the trochlea, capit- ulum, and the lateral epi- condyle of the humerus, is partly intra -capsular and partly extra-capsular ; that for the medial epicondyle is extra-capsular. The epiphyseal line of the ole- cranon is intra -capsular only anteriorly, and it may be altogether extra-cap- sular. Lig. Anterius. — The anterior ligament (Fig. 305) consists of a layer whose fibres run in several direc- tions — obliquely, trans- versely, and longitudinally — and of these the vertical fibres are of most import- ance. It is attached proxi- mally to the proximal margins of the coronoid and radial fossse ; distally, to the margins of the coronoid process and to the annular ligament of the proximal radio-ulnar joint, but some loosely arranged fibres reach as far as the neck of the radius. The marginal portions of this ligament, which are situated in front of the capitulum and the medial margin of the trochlea respectively, are much thinner and weaker than the central part. Fibres of origin of the brachialis muscle are attached to the front of this ligament. Lig. Posterius.— The posterior ligament is an extremely thin, almost redundant layer. Proximally it is attached, in relation to the margin of the olecranon fossa, at a varying distance from the trochlear articular surface, and distally to the summit and sides of the lip of the olecranon. Laterally some of its fibres pass from the posterior aspect of the capitulum to the posterior border of the radial notch of the ulna. This ligament derives material sujjport from, and participates in the movements of, the triceps brachii muscle, since they are closely adherent to each other in the region of the olecranon. Lig. CoUaterale Ulnare. — The ulnar collateral ligament (O.T. internal lateral) insertion of biceps mii&ole Oblique chord liadius Fig. 305. — Antekiok View of Elbow-Joint. THE ELBOW-JOINT. 325 (Figs. 305 and 306j is a fan-shapeci structure of unequal thickness, but its margins, which are its strongest bands, are continuous with the adjoining parts of the anterior and posterior ligaments. By its proximal end it is attached to the anterior, distal, and posterior aspects of the medial epicondyle of the humerus. By its broad distal end it is attacheil to the medial margin of the semilunar notch, so that thf anterior band is associated principally with the medial margin of the coronoid process, and the posterior hand with the medial margin of the olecranon, while the intermediate weaker portion sends its fibres downwards to join a trans- verse hand, sometimes very strong, which bridges the notch between the adjoining medial margins of tho coronoid process and the olecranon. Lig. Collaterale Radiale. — The radial collateral ligament ((J.T. external lateral) (Fig. 305) is a strong flattened band attached proximally to the distal and HuniiTUs Interosseous meiiibraim Radius Coronoid process Obliiine chord Tendon of biceps \ I Mwlial epicondyle Anterior part of ulnar •y collateral ligament Posterior jiart of ulnar collateral ligament Olecranon Ulna Transverse jiart of ulnar collateral ligament Fig. 306. — Elbow- Joint (Medial Aspect). posterior aspects of the lateral epicondyle of the humerus. It completes the con- tinuity of the articular capsule on the lateral side, and blends distally with the lig. annulare radii, on the surface of which its fibres may be traced both to the anterior and posterior ends of the radial notch of the ulna. Both of tlie collateral ligaments are intimately associated with the muscles which take origin from the medial and lateral epicondyles of the humerus. Synovial Pads of Fat (Fig. 307).— Internal to the hbrous stratum of the articular capsule, there are several pads of fat situated between it and the synovial stratum. Small pads are so placed as to lie immediately in front of the coronoid and radial fossie, but a larger one projects towards the olecranon fossa. A stratum synoviale (Fig. 307) lines the entire fibrous stratum and clothes the pad.'^ of tat referred to above, as well as those portions of l^one enclosed within the capsule which are not covered by articular cartilage. By its disposition the elbow and the proximal radio-ulnar joints pos.sess a common joint cavity. It should be specially noted that the proximal part of the neck of the radius is surrounded by this synovial layer. Movements at the Elbow-Joint. — Thi" inoveiiK-nts of tin- lailius and ulna njion the huniei-us have already been referred to as those characterii^ing a uniaxial joint constructed on the plan of a hinge. In this case the axis of the joint is obliquely transverse, so that in the extended position the humerus and ulna form an obtuse angle open towards the radius, whereas in the 326 THE ARTICULATIONS OR JOINTS. flexed position the hand is carried medially in the direction of the mouth. Extreme flexion is checked by the soft parts in front of the arm and of the forearm coming into contact, and extreme 'extension by the restraining eft'ect of the ligaments and muscles. In each case the movement is checked before either the coronoid process or the olecranon come into contact with the humerus. The anterior and pos- terior bands of the ulnar collateral liga- ment are important factors in these re- sults. Lateral move- ment of the ulna is not a characteristic movement, although it may occur to a slight extent, owing to a want of complete adaj)tation between the trochlear surface of the humerus and the semilunar notch of the iilna. This incongruence is note- worthy since the medial lip of the trochlea is prominent in front, and the lateral lip is promi- nent behind. Conse- quently, this latter part is associated with a surface on the lateral side of the olecranon which is only utilised in com- plete extension. The capitulum and the opposing surface ujjon the head of the radius are always in varying degrees of contact. The head of the radius participates in the movements of flexion and extension, and is most closely and completely in contact with the humerus during the position of semi-flexion and semi-pronation. In complete extension a very considerable part of the capitulum is uncovered by the radius. Olecranon pad of fat Trochlea ■Olecianon Fig. 307. -Vertical Section through the Humero-ulnar Part of the Elbow-Joint. The radio-ulnar joints. These articulations, which are two in number, are situated at the proximal and distal ends of the radius and ulna. They provide an adaptation whereby the radius rotates around a longitudinal axis in the movements of pronation and supination, and hence this form of uniaxial diarthrosis is termed lateral ginglymus. Articulatio Radioulnaris Proximalis. — The proximal radio-ulnar joint forms a part of the articulatio cubiti or elbow-joint. The articular surfaces which enter into its formation are the radial notch of the ulna and the lateral aspect of the head of the radius. In each case the articular cartilage is continuous with an articular surface entering into the formation of the humero-radial and humero- ulnar joints, consequently the joint cavity is continuous with the cavities of those joints,' and therefore, in a sense, it lies within the cover of the articular capsule of the elbow-joint ; but its special feature is the annular ligament of the radius. Lig. Annulare Radii. — The annular ligament of the radius (O.T. orbicular ligament) (Figs. 305 and 308) has been mentioned above as the distal line of attachment of the radial collateral ligament and the ligaments on the front and back of the elbow-joint. It is a strong, well-defined structure, attached by its extremities to the volar and dorsal margins of the radial notch of the ulna, and thus it forms nearly four-fifths of an osseo-tendinous circle or ring. The circle is somewhat wider at the proximal than at the distal margin of the annular ligament of the radius, which, by encircling the proximal part of the neck of the radius, tends to prevent THE EADIO-ULNAE JOINTS. 527 Transverse portion of ulnar <'oUat>-ial liL'aiiifiit Semilunar notcli displacement of the head of that, bone in a distal direction. The distal margin of this ligament is not directly attached to the radius. The synovial stratum is continuous with that which lines the elbow-joint. It closes the joint cavity at the distal unattached margin of the annular ligament, where it is somewhat loosely arranged in its reliexion from the ligament to the neck of the radius. 1'iie c]ii])hysoaI line at tlie pro.ximal end of the radius is intra-capsular. Articulatio Radioulnaris Distalis. — Tlie distal radio ulnar joint is situ- ated betwecMi the lateral aspect of the head of the ulna and the ulnar notch on the medial side of tiie distal end of the radius. In addition, it includes the distal surface of the head of the ulna, which articulates with the pro.ximal surface of a tri- angular articular disc l)y means of which the joint is excluded from the radio-carpal articulation. Discus Articularis. — The tri- angular articular disc (Figs. 309 and 311), besides presenting articular surfaces to two separate joints, is an important ligament concerned in binding together the distal ends of the radius and ulna. It is attached by its apex to the depression at the lateral side of the root of the styloid process of the ulna, and by its base to the sharp line of demarcation between the ulnar notch and the carpal articular surface of the radius. Capsula Articularis. — The fibrous stratum is very imperfect, and consists of scattered fibres, termed the anterior and posterior radio-ulnar ligaments (Fig. 310). These ligaments pass transversely between adjoining non-articular surfaces on the radius and ulna, and are of sufficient length to permit of the movements of the radius in pronation and supination. The synovial stratum completes the closure of the joint cavity. It forms a loose bulging projection (recessus sacciformis), passing proximally between the distal ends of the shafts of the radius and ulna, and it also clothes the proximal surface of the articular disc (Fig. 311). The cavity of this joint is quite distinct from that of the radio-carpal articulation, except when the articular disc presents a perforation. Between the proximal and distal radio-ulnar articulations there are two accessory ligaments, viz., the chorda obliqua and the interosseous membrane, which connect together the shafts of the radius and ulna. Chorda Obliqua. — The oblique chord (Fig. 306) is a slender fibrous band of very varying strength which springs from the lateral part of the coronoid process of the ulna, and stretches obliquely distally and laterally to the radius where it is attached immediately distal to the tuberosity of the radius. Membrana Interossea Antibrachii. — The interosseous membrane of the fore- arm(Fig. 306)is a strong Annular lii^'anient of tho raflius Coronoifl process Fig. 308. — Annular Ligament of the Radius. Ilfad of ulna Surface f' navicular boi Groove for tendoii of extensor Ionf;Ms pollicis Styloid process of ulna fibrousmembrane which stretches across the interval between the radius and ulna, and is firmly attached to the interosseous crest of each. Distally it extends to the distal limit of the space be- tween the bones, whilst proximally it only reaches a point about one inch distal to the tuberosity of the radius. A gap, called the hiatus interosseus, is thus left between its proximal margin and the chorda obliqua, and through this the dorsal interosseous vessels pass back- Apex of articular disc Articular disc Surface for lunate bone Fig. 309. — Carpal Articular Surface of the Radius, AND Articular Disc of the Wri.st. 328 . THE AETICULATIONS OE JOINTS. wards bet\Yeen the bones to reach the dorsal aspect of the forearm. The fibres which compose the interosseous membrane run for the most part distally and medially from the radius to the ulna, although on its dorsal aspect several bands may be observed stretching in an opposite direction. The interosseous membrane augments the surface available for the origin of the muscles of the forearm ; it braces the radius and ulna together ; and when shocks are communicated from the hand to the radius, owing to the direction of its fibres, the interosseous membrane transmits them, to a large extent, to the ulna. Movements of the Radius on tlie Ulna. — The axis around wliicli the radius moves is a longitudinal one, having one end passing through the centre of the head of the radius and the other through the styloid process of the ulna and the line of the ring-finger. In this axis the head of the radius is so secured that it can only rotate ujaon the radial notch of the ulna within the annular ligament of the radius, and consequently the radial head remains upon the same j^lane as the ulna ; but the distal end of the radius being merely restrained by the articular disc, is able to describe nearly a half-circle, of which the apex of this ligament is the centre. In this movement the radius carries the hand from a position in which the palm is directed forwards, and in which the radius and ulna lie parallel to each other (supination), to one in which the palm is directed backwards, and the radius lies diagonally across the front of the ulna (pronation). The ulna is unable to rotate upon a long axis, but while the radius is travelling through the arc of a circle from lateral to medial side in front of the ulna, it will usually be seen that the ulna appears to move through the arc of a smaller circle in the reverse direction, viz., from medial to lateral side. If the humerus is prevented from moving at the shoulder -joint, a very large proportion, if not the entire amount, of this apparent movement of the ulna will disappear. At the same time some observers maintain that it really occurs at the elbow -joint, associated with lateral movement during slight degrees of flexion and extension at that joint. ARTICULATIO RADIOCARPEA. The radio-carpal joint is a bi-axial diarthrosis, frequently called a condyloid joint. The articular elements which enter into its formation are : on its proximal side, the carpal surface of the distal end of the radius, together with the distal surface of the discus articularis ; on its distal side, the proximal articular surfaces of the navicular, lunate, and triquetral bones, and the interosseous ligaments between them. The articular surface of the radius is concave both in its antero-posterior and transverse diameters, in order to adapt itself to the opposing surfaces of the navicular and lunate, which are convex in the two axes named. In the ordinary straight position of the hand the articular disc is in contact with the lunate bone, and the proximal articular surface of the triquetral bone is in contact with the capsule of the joint. When, however, the hand is bent towards the ulna the triquetral bone is carried laterally as well as the lunate and navicular and the articular disc comes into contact with the triquetral. The articular surface of the radius is subdivided by an antero-posterior, slightly elevated ridge, into a lateral triangular facet which usually articulates with the navicular, and a medial quadrilateral facet for articulation with a portion of the lunate bone. In the intervals between the navicular, lunate, and triquetral bones, the con- tinuity of the distal articular surface is maintained by the presence of interosseous ligaments which are situated upon the same level as the articular cartilage. Capsula Articularis. — An articular capsule completely surrounds the joint. It is somewliat loosely arranged, and its fibrous stratum permits of subdivision into the following four portions : — Lig. Radiocarpeum Laterale. — ^The lateral radio-carpal ligament (0. T. external lateral j TFig. .310) is a well-defined band which is attached by one end to the tip of the styloid process of the radius, and by the other to a rough area at the base of the tuberosity of the navicular bone, i.e. lateral to its radial articular surface. Lig". Ulnocarpeum Mediale. — The medial ulno-carpal ligament (O.T. internal lateral; (Fig. :jlO; is also a distinct rounded structure, having one end attached to the tip of the styloid process of the ulna, and the other to the rough non-articular border of the triquetral bone, some of its fibres being prolonged to the pisiform bone. Lig". Radiocarpeum Volare. — The volar radio-carpal ligament (O.T. anterior ligament) (Fig. .310) is attached proximally to the volar margin of the distal end CARPAL JOINTS. 329 AntiTiiir riulin- ilial iiliKi-carpat ligament Pisiform Capilaboboiie ligaments Fiii. 310.— Ligaments on Volak Aspect uk Radio-cakpal, Carpal, and Carpo-metacarpal Joints. of the radius, as well as slightly tp the base of the styloid i^roce.ss of the ulua. Some transverse fil)res may be seeu, but the greater num- ber pass obliquely dis- tally and medially to the volar mtn-artic- ular surfaces of the navicular, lunate, and triquetral bones, while some of them may even be continued as far as the capitate Ijone. Those fibres from the ulna run obliquely laterally. On its deeper aspect this ligament is closely adherent to the volar 1 )order of the articular disc of the distal radio- ulnar articulation. Lig". Radiocar- peum Dorsale. — The dorsal radio-carpal ligament (O.T. poster- ior ligament) extends from tl le dorsal margin of the distal end of the radius, in an oblique direction distally and medially, to the dorsal non-articular areas on the proximal row of the carpal bones. The slip to the latteT assists in forming the fibrous sheath tlirough which the tendon of the ex- tensor carpi ulnaris muscle travels to its insertion. The principal bundle of fibres is connected with the triquetral bone. The stratum synoviale (Fig. 311) is simple, and is confined to the articulation, except in tho.se cases in which the articular disc is perforated, or in which one of the interosseous ligaments between the carpal bones of the first row is absent. The epiphyseal lines at the distal ends of radius and ulna are cxtra-capsular. Movements at the Radio-carpal Joint— The radio-carpal joint affords an excellent example of a l)i-axial articulation, in which a long transverse axis of movement is situated more or less at right angles to a short axis placed in the antero-posterior direction. The nature of the move- ments whi. Movement in a Horizontal Plane. Elevation. | Depression. Forwards. Backwards. Trapezius (superior I Trapezius (inferior fibres) fibres) Levator scapulae Subclavius Rhomboidei Pectoralis minor Sterno-mastoid Latissimus dorsi Omo-hyoid Pectoralis major (lower fibres) Serratus anterior Trapezius \ Pectoralis major Rhomboidei Pectoralis minor 1 Latissimus dorsi c. Rotation — a combination of these muscles. 1 B. Acromio- Clavicular Joint.— Movements at this joint are associated with rotation of the scapula. By the combined action of such muscles or the trapezius and serratus anterior (inferior fibres), the inferior angle of the scapula is drawn or thrust forwards, the body of the scapula is rotated, and the glenoid cavity is tilted upwards, so facilitating the upward movement of the arm above the horizontal level In forced inspiration, the sterno-mastoid, trapezius, levator scapulae, rhomboidei, sub- clavius, omo-hyoid, serratus anterior, pectoral muscles, and latissimus dorsi, acting together, raise and fix the sKoulder girdle ; while those of them which have costal attachments — subclavius, pectoral muscles, serratus anterior, and latissimus dorsi — simultaneously elevate the ribs and expand the thorax. Lateral flexion and rotation of the vertebral column in the neck is effected partly by the action of the trapezius, levator scapulae, and rhomboid muscles (with the shoulder fixed). The latissimus dorsi and pectoralis major act in climbing in a similar way, raising up the trunk towards the shoulder. Action on the Upper Limb. — By reason of their insertion into the humerus the pectoralis major and latissimus dorsi muscles assist the movements of the upper limb. Acting together, the two muscles depress the shoulder, and draw the arm to the side of the body, at the same time rotating the humerus medially. The two parts of the pectoralis major have slightly different actions on the humerus. The clavicular part of the muscle {portio attollens) draws the arm medially and upwards ; the sterno-costal part of the muscle {portio deprimens) draws it medially and downwards. The latissimus doi-si acting alone, besides rotating the limb, draws it medially and backwards, as in the act of swimming. FASCI>E AND lYIUSCLES OF THE SHOULDER. The deep fascia covering the scapular muscles presents no feature of special importance. Attached to the clavicle, acromion, and scapular spine, it is thin over the deltoid muscle. Below the deltoid it is thicker ; it encases and gives origin to the infraspinatus muscle, and is continuous with the fasciae of the axilla and the back. lYIuscIes. The muscles proper to the shoulder comprise the deltoid, supraspinatus, infra- spinatus, teres minor, teres major, and subscapularis. M. Deltoideus. — The deltoid, a coarsely fasciculated multipennate muscle, has an extensive origin from (1) the front of the clavicle in its lateral third (Figs. 327, p. 366, and 331, p. 371) ; (2) the lateral border of the acromion ; (3) the inlerior edge of the free border of the spine of the scapula (Figs. 329, p. 368, and 333, p. 372) ; and (4) from the deep fascia covering the infraspinatus muscle. Its origin embraces the insertion of the trapezius. The fibres of the muscle converge to the lateral aspect of the body of the 374 THE MUSCULAK SYSTEM. Levator scapul/e Rhomboideus minor Spine of scapula .. Infra SPINATli humerus, to be inserted into a well-marked V-shaped impression above the radial groove (Fig. 336, p. 376). The insertion is partly united with the tendon of the pectoralis major. The most anterior part of the deltoid muscle is formed of parallel fibres, not uncommonly separ- ate from the rest of the muscle at their origin from the cla- ^^^^^^^ ^^^^^„^^^ vicle. These fibres supRASPiN-ATus-;^^^^^^'^^^^^^^^^ jjj^y ]3g continuous with the trapezius over the clavicle. The most posterior part arises by a fascial origin from the spine of the scapula and the fascia over the in- fraspinatus muscle. These portions are attached respect- ively to the front and back of the main tendon of in- sertion. The inter- mediate fibres are multi-pennate, attached above and below to three or four septal tendons, which extend for a variable distance downwards and upwards from the origin and insertion of the muscle. The deltoid is superficial in its whole extent, and forms the pro- minence of the shoulder. Its an- terior border is separated from the pectoralis major by a narrow in- terval, in which the cephalic vein and deltoid branch of the thoraco- acromial artery are placed. The deep surface of the muscle, separated from the capsule of the shoulder-joint by a large bursa, is related to (1) the cor acoid process, associated with which are the coraco-acromial liga- ment, and the attachments of the pectoralis minor, the coracobrachi- alis, and the short head of the biceps brachii ; (2) the capsule of the shoulder-joint covering the head of the humerus, associated with which are the long head of the biceps, and the attachments of the subscapularis, supraspinatus, infra- spinatus, and teres minor ; and (3) the proximal part of the lateral surface of the hod;/ of the humerus, associated with which are the posterior circumflex vessels of the humerus and the axillary nerve. Nerve-Supply.— The deltoir] muscle is supplied by the terminal branches of the axillary (O.T. circumHex) nerve from the fifth and sixth cervical nerves. Action.— The main action of the deltoid is to abduct the arm, and bring the humerus mto Triceps brachii (tendon of insertion) KXTENSOR CARPI I'.AI.IALIS BKEVIS Fio. 3.34.— Left Scapular Muscles and Triceps. MUSCLES OF THE SHOULDER. 375 , Skiuiatih anterior St;im(AlMi.ARl« •IIAHI'INATUS I'KCTORAI.IH INOK Coracoid prOCPHH Triceps brachii oiiK head) the horizontal position. In this movement it is aided by the supraspinatus and infraspinatus. The anterior (clavicular) portion of thfe muscle assists the pectoralis major in drawinf,' the arm forwards, while the posterior portion draws it backwards. M. Supraspinatus. — The supraspinatus arises by fleshy fibres ironi the supra- spinous t'o.ssa (except near the neck of the bone) and from the deep fascia over it (Fig. 329, p. 368). It is directed laterally under the trapezius muscle, the acromion and coraco- acromial ligament, to be inserted by a broad thick tendon into tfie most proximal facet on the larger tul^ercle of the humerus, and into the capsule of the shoulder- joint (Fig. 336, p. 376). Nerve-Supply. — The muscle is supplied by the supra-scapular nerve (C. 5. 6.). Action. — The supraspin- atus assists the deltoid in ab- ducting the arm from the side. Skr RATUrf ANTERIOR LaTISSIMI'S DORSI TkRES MAJOR CoRACOBRACHtALlS Biceps (short head) Teres major M. Infraspinatus. — The infraspin- atus arises from the infra-spinous fossa of the scapula (excepting near the neck of the bone and the flat surface along the axillary margin) and from the thick fascia over it (Fig. 337, p. 376). The fibres of the muscle converge to the neck of the scapula ; and are inserted by tendon into the middle facet on the larger tubercle of the humerus, and into the capsule of the shoulder-joint (Fig. 336, p. 376). A bursa separates the muscle from the neck of the scapula, and in a minority of cases communicates with the synovial cavity of the shoulder-joint. The supraspinatus and the upper part of the infraspinatus muscles are concealed by the trapezius, acromion, and deltoid. They cover the neck of the scapula, the transverse scapular artery, and supra- scapular nerve, and the capsule of the shoulder-joint. Nerve-Supply. — Supra-scapular nerve. Action. -The muscle assists the deltoid in abducting and drawing back the arm at the- shoulder-joint. M. Teres Minor. — The teres minor is a small muscle, arising by fleshy fibres from the proximal two-thirds of the flat surface on the dorsal aspect of the axillary margin of the scapula, and from fascial septa separating it from the infra- spinatus and teres major muscles (Fig. 337, p. 376). Lying alongside the lateral border of the infraspinatus, it is inserted, under cover of the deltoid, by a thick flat tendon, into the most distal of the three facets on the Biceps ten Brachioradia Ki.EXOR c\ RADIA Pronator teres Fig. 33.^. — Muscles ok Postekior Wai i Lekt Axilla and Front of Arm. 376 THE MUSCULAR SYSTEM. larger tubercle of the humerus and into the capsule of the shoulder-joint, and, by fleshy fibres, into the posterior aspect of the surgical neck and body of the humerus distal to the tubercle for about an inch (Fig. 341, p. 380). It is separated from the teres major by the long or scapular head of the triceps brachii, and by the posterior circumflex vessels of the humerus and the axillary nerve. Its origin is pierced by the circumflex scapular artery. The muscle is invested by the deep fascia enclosing the infraspinatus, and is diiserfion)'*"'' somctimcs inseparable from that muscle. Nerve-Supply. — The teres minor is supplied by a branch of the axillary nerve (C. 5. 6.). The nerve has a pseudo- ganglion, a fibrous swelling on it in its course to the muscle. Action. — The muscle is a lateral rotator of the humerus. Supraspiiiatus (iusertion) Pectoialis major ' (insertion) Latissinius dorsi (insertion) M. Teres Major. — The teres major is much larger than the preceding muscle. It arises by fleshy fibres from the lower third of the flat surface on the dorsum of the scapula along its axillary Coracobrachialis (insertion) Bracliialis (origiiO Bracliioradialis (origin)^ Extensor carpi radialis longiis , (origin) Common tendon for origin of Ijronator teres and Hexor muscles of forearm Common tendon for origin of extensor muscles of forearm Fio. 336. — Muscle - Attachments to THE Anterior Aspect of the Ricjht Humerus. Teres minor (origin) with gap for circumflex scapular artery Teres major (origin) Latissimus dorsi (origin) Fio. 337. — Muscle- Attachments to the Right Scapula (Dorsal Surface). margin (except for a small area at the inferior angle), and from fascial septa, which separate it on the one side from the subscapularis, and on the other from the infraspinatus and teres minor (Fig. 337). The muscle is directed along the axillary margin of the scapula to the front of the body of the humerus, where it is inserted, by a broad flat tendon, into the medial border of the sulcus intertubercularis medial to the latissimus dorsi muscle (Fig. 337). Just before its insertion it is closely adherent to the tendon of the latissimus dorsi. The teres major lies below the subscapularis muscle in the posterior wall of MUSCLES OF THE SPIOULDER. 377 the axilla. The latissimus dorsi; muscle, sweeping round from the back, covers its axillary surface on its way to its insertion. The muscle forms the inferior boundary of a triangular space in the posterior wall of the axilla, of which the other boundaries are, above, the borders of the subscapularis and teres minor muscles, and laterally the surgical neck of the humerus. This space is subdivided by the long head of the triceps brachii, which passes behind the teres major muscle, into (a) a quadrilateral space above, for the passage of the axillary nerve and posterior circumtle.\ artery of the humerus ; and (6) a smaller triangular space below, for the circumflex scapulae artery. Nerve-Supply. — The teres major is supplied, along with part of the subscapularis muscle, hy the lower subscapular nerve (C. 5. 6.), Action. — A medial rotator of the humerus. M. Subscapularis. — The subscapularis is a large triangular muscle which covers the costal surface of the scapula. It arises by fleshy fibres from the whole of the subscapular fossa and the groove along the axillary margin, excepting the surfaces at the angles of the bone (Fig. 333, p. 372). Springing from several ridges in the fossa are fibrous septa projecting into the substance of the muscle, which increase the extent of its attachment. Converging to the head of the humerus, the muscular fibres are inserted by a broad, thick tendon into the smaller tubercle of the humerus and into the capsule of the shoulder-joint, and by fleshy fibres into the surgical neck and the body of the humerus distal to the tubercle for about an inch, under cover of the coraco- brachialis and short head of the biceps (Fig. 336, p. 376). This muscle forms the greater part of the posterior wall of the axilla. Its medial or anterior surface is in contact with the serratus anterior and the axillary vessels and nerves. It is separated from the neck of the scapula by a bursa, which is in direct communication with the synovial cavity of the shoulder-joint. The subscapularis minor is an occasional muscle situated below the capsule of the shoulder- joini. It arises from the axillary border of the scapula below the subscapularis, and is inserted into the caj)sule of the joint or the proximal part of the body of the humerus. Nerve-Supply. — There are two and often three nerves supplying the subscapularis, viz., the short subscapular (C. 5. 6.), which is often double ; and the lower subscapular (C. 5. 6.), which, after supplying its lateral (lower) portion, ends in the teres major. Actions. ^ — The muscle aids in drawing the arm forward and medially rotating the humerus. The principal action of the above group of muscles is on the shoulder-joint, secondary actions in relation to movements of the trunk and limbs. 1. Movements at the Shoulder -Joint. They have also a. Abduction. Adduction. b. Flexion (Forwards). Extension (Backwards). Deltoid Supraspinatus Teres major Teres minor Pectoralis majctr Latissimus dorsi Coracobrachialis Biceps (short head) Triceps brachii (long head) Weight of limb Deltoid (anterior fibres) Subscapularis Pectoralis major Coracobrachialis Biceps brachii Deltoid (posterior fibres) Teres major Infraspinatus Latissimus dorsi Triceps brachii c. Rotation Laterally. Deltoid (posterior fibres) Infraspinatus Teres minor Rotation Medially. Deltoid (anterior fibres) Teres major Pectoralis major Latissimus doi-si d. Circumduction — combination of previous muscles. The various movements at the shoulder-joint are greatly aided by the muscles acting on the shoulder girdle. In raising the arm above the head, for instance, the humerus is brought to the horizontal position by the deltoid and supraspinatus, and the movement is continued by the 378 THE MUSCULAE SYSTEM. elevators of the shoiilder girdle. Again, in forward and backward movements at the shoulder- joint, great assistance is derived from muscles acting directly on the shoulder girdle — pectoralis minor and serratus anterior ; trapezius and rhomboidei. 2. In relation to the trunk and limbs, the shoulder muscles, by fixing the humerus, have auxiliary power on the one hand in movements of the trunk, such as forced inspiration ; on the other hand, acting along with muscles fixing the elbow-joint, they stiffen the limb so as to permit of the more refined movements of the wrist and fingers. FASCIyE AND IVIUSCLES OF THE ARIVI. FASCIJE. The superficial fascia presents no features of iinportance. There is a bursa beneath it over the olecranon, and occasionally another over the medial epicondyle of the humerus. The deep fascia forms a strong tubular investment for the muscles on the anterior and posterior aspects of the humerus. It is continuous above with the deep fascia of the shoulder and axilla, and is further strengthened by fibres derived from the insertions of the pectoralis major, latissimus dorsi, and deltoid muscles. At the elbow it becomes continuous with the deep fascia of the forearm, and gains attachment to the epicondyles of the humerus and the olecranon of the ulna ; it is strengthened also by important bands associated with the insertions of the biceps anteriorly and the triceps posteriorly, to which reference will be made in the account of these muscles. About the middle of the arm on the medial side, the deep fascia is per- forated for the passage of the basilic vein and the medial cutaneous nerve of the forearm. The intermusctilar septa are processes of the deep fascia attached to the epicondylic ridges of the humerus. The medial and stronger septum is placed between the brachialis muscle anteriorly and the medial head of the triceps posteriorly, and gives origin to both. It extends proximally to the insertion of the coracobrachialis (which is often continued into it), and the ulnar nerve and superior ulnar collateral vessels pass distally over its medial edge. The lateral septum is thinner. It separates the brachialis muscle and brachioradialis in front from the medial and lateral heads of the triceps behind, and gives origin to those muscles. It extends proximally to the insertion of the deltoid, and is pierced by the radial nerve and profunda brachii vessels. , MUSCLES OF THE ARM. The muscles of the arm comprise the biceps, coracobrachialis, and brachialis on the anterior aspect, and the triceps brachii on the posterior aspect of the humerus. Except at its extremities, the biceps brachii is superficial, and forms a rounded fleshy mass on the anterior aspect of the arm. The coracobrachialis is visible on its medial side in the proximal half of the arm, particularly when the arm is raised. The brachialis is concealed by the biceps. The triceps brachii forms the thick mass of muscle covering the posterior surface of the humerus. M. Coracobrachialis. — The coracobrachialis is a rudimentary muscle. It arises under cover of the deltoid from the tip of the coracoid process, by fleshy fibres, in common with the short head of the biceps, and also frequently from the tendon of insertion of the pectoralis mi^or muscle. The fleshy belly is pierced by the musculo-cutaneous nerve, and ends in a flat tendon which is inserted into a faint linear impression about an inch in length on the middle of the medial border of the Viody of the humerus (Fig. 336, p. 376). It is often continued into the medial intermuscular septum. The coracobrachialis is the remains of a threefold muscle, of which only two elements are usually present in man, but of which in anomalous cases all the parts may be more or less fully developed. The passage of the musculo-cutaneous nerve through the muscle is an indication of ita natural separation into two parts, which represent the persistent middle and distal elements. MUSCLES OF THE ARM. 379 The commonest variety is one in which the more superficial (distal) part of the muscle extends more distfilly than usual, so as to be inserted into the medial intermuscular septum, or even into the medial epicondyle of the humerus. A third slip (coracobrachialis superior or brevis, ISSKRTl OK FKlTl AI.IS MAJ COKACDBRACin U I- Short hkaii >n Long head ok BICEPS Brachiai.is Triceps (medial head) Mnsculo-cutaiieons nerve Radial tierve Brachiorapialis Extensor carpi radialis lon(3ds Radial artery (cut) Abductor poi.licis LONOUS Radial artery (cut) Transverse carpal lij^ament Insehtios ok pectoralih MINOR -Axillary artery MUDCUlO- "cutaneous nerve Median nerve ^(lateral head) ^ Median nerve (medial heud) Ulnar nerve Trapezius I.acertus tibrosus Pronator teres Deep fascia of forearm Flexor carpi radialis Palmaris loxous Flexor carpi ulnaris Flexor digitorum siiblimis Flexor pollicis lonous Pronator quadratus Ulnar artery Ulnar nerve Fig. 338. — Superficial Miscles on the Anteriok Aspect of THE Right Arm and Forear.m. I.ATl.SSIMVB DO RSI EXTK.V.SOR ( ARPI RADIALIS LONi;l S Extensor carpi radialis bbevis Deep fascia of forearm Extensor dioitorum commtnis Extensor carpi ii.naris ABDrcTOR pollicis LONT.I « Extensor pollicis brkv js Extensor dioiti qcisti propriis TeNDO.NS of RADIAL EXTENSO OK CARPI'S Dorsal carpal lij^ment Extensor ihjllicis longcs Extensor indicis proprius Fio. 339.— The Musclf^ on the Posterior Sir of the Left Arm, Forearm, and Hand. rotator humeri) may more rarely be present, forming a short muscle arising from the root of the coracoid process, and inserted into the medial side of the humerus just distal to the capsule of the shoulder-joint 380 THE MUSCULAR SYSTEM. Subscapularis [(insertion) Pectoralis major (insertion) Latissimus dorsi (insertion) Teres major '(insertion) Triceps : lateral head (origin) Coracobracliialis (insertion) Deltoid (insertion) Nerve-Supply. — The nerve to the coracobrachialis comes from the 7th or 6th and 7th cervical nerves. Incorporated with the musculo-cutaneous, the nerve sejjarates to supply the muscle l)efore the latter nerve pierces it. Action. — The muscle assists the biceps to raise the arm and draw it medially. M. Biceps Brachii. — The biceps brachii arises by two tendinous heads. (1) The short head (caput breve) is attached in common with the coracobrachialis to supraspinatus the tip of the cora- (insertion) Coid prOCCSS of the scapula (Fig. 333, p. 372). Concealed by the deltoid and tendinous at first, this head forms a separate fleshy belly, which is united to the long head by an invest- ment of the deep fascia. (2) The long head (caput longum) arises by a round tendon from the supra- glenoidal tuberos- ity at the root of the coracoid pro- cess and from the labrum glenoidale on each side. Its tendon passes through the cavity of the shoulder - joint, and, emerg- ing from the cap- sule beneath the transverse humeral ligament (invested by a prolongation of the synovial membrane), it occupies the inter- tubercular groove of the humerus -extensormuscles ^yhgrC it )S COVCTCd of forearm Ancona;ns by a fascial pro- (origin) longation of the tendon of the pec- FiG. 341.— Muscle- Attachments to toralis major. In THE POSTEUIOR SURFACE OF THE ^^^ ^^.^ ^^ f^^^^^ g^ PaOHT HUMERUS. ^^^^^ ^^^j^ ^^.^.^^ to that derived from the short head by an envelope of deep fascia. The insertion of the muscle is likewise twofold. (1) The two bellies become connected to a strong tendon, attached deeply in the hollow of the elbow to the rough dorsal x^ortion of the tubercle of the radius (Figs. 335, p. 375, and 348, p. 389). A bursa separates the tendon from the volar portion of the tuberosity. (2) From the medial and anterior part of the tendon, and partly in continuity with the fleshy fibres of the muscle, a strong membranous hand (the lacertus fibrosus) extends, distally and medially, over the hollow of the elbow to join the deep fascia covering the origins of the flexor and pronator muscles Bracliioradialis "(origin) Extensor carpi - radialis longus (origin) Common tendon for origin of . ])ronator teres and flexor muscles of forearm Ckimmon tendon for origin of extensor musclee of forearm Fio, 340. — Muscle - Attachments to THE Anterior Aspect of the Right Humerus. Common tendon U)T origin of MUSCLES OF THE AEM. 381 of the forearm. Its proximal psft-t is thickened and can be felt subcutaneously as a crescentic border. In the arm the biceps conceals the brachialis muscle and the musculo-cutaneous nerve. Its medial border is the guide to the position of the brachial artery and median nerve. The biceps is an extremely varialtle muscle. Its chief .anomalies are due to an increase or diminution in the number of origins. A third head of origin is common (10 per cent), and usually arises from the humerus, between the insertions of the deltoid and coracobrachialis. Two or even three additional heads may be present at the same time. The long head of the muscle may be absent, or may take origin from the intertubercular groove. The muscle may have an additional insertion into the medial epicondyle of the humerus, or into the fascia of the forearm. Nerve-Supply. — The biceps is supplied by the musculo-cutaneous nerve (C. 5. 6.). Actions. — The"action8 of the biceps are complex, in that they affect three articulations — the shoulder, huniero-radial, and radio-ulnar joint. The muscle raises and draws forward the humerus at the shoulder-joint, it flexe.s the elbow-joint, and it supinates the forearm. The combination of these actions results in a simple movement like that of raising the hand to the mouth. M. Brachialis. — The brachialis (O.T. brachialis anticus) is a large muscle arising from the distal two-thirds of the anterior aspect of the body of the humerus and from the intermuscular septum on each side (Figs. 340 and 341, p. 380). Clasping the insertion of the deltoid proximally, it ends distally in a strong tendon, which is inserted, deep in the hollow of the elbow, into the anterior ligament of the elbow-joint, the distal surface of the coronoid process, and slightly into the immediately adjacent part of the volar surface of the body of the ulna (Fig. 348, p. 389). The lateral part of the muscle arising from the lateral epicondylic ridge and lateral intermuscular septum forms a slip more or less separate, which may be partially fused with the brachioradialis muscle. It is concealed for the most part by the biceps muscle in the arm. It forms the floor of the cubital fossa, and covers the anterior aspect of the elbow-joint. Nerve-Supply. — It is supplied by the musculo-cutaneous nerve (C. 5. 6.) ; and also (in most instances) at its lateral border by a fine branch of the radial nerve (C. (5.) 6.). Action. — This muscle is a flexor of the elbow-joint. M. Triceps Brachii. — The triceps brachii is the only muscle on the posterior aspect of the arm. It arises by three heads : a lateral and a medial head, from the humerus, and a long or middle head, from the scapula. (1) The long head (caput longum) begins as a strong tendon attached to a rough triangular surface on the axillary border of the scapula just below the glenoid cavity (infra-glenoidal tuberosity) (Figs. 333, p. 372, and 337, p. 376). This gives rise to a fleshy belly which, after passing between the teres major and teres minor muscles, occupies the middle of the back of the arm. (2) The lateral head is attached by fibres, partly tendinous and partly fleshy, to the curved lateral border of the humerus from the insertion of the teres minor proximally to the radial groove distally, and receives additional fibres from the posterior surface of the lateral intermuscular septum (Fig. 341, p. 380). Its fibres are directed distally and medially over the radial groove, concealing the radial (musculo-spiral) nerve, the profunda brachii artery, and the medial head of the muscle, to the tendon of insertion. (3) The medial head arises by fleshy fibres from an elongated triangular area on the posterior surface of the humerus, extending proximally to the level of the insertion of the teres major, and distally nearly to the margin of the olecranon fossa (Fig. 341, p. 380). It also arises, on each side, from the intermuscular septum, — from the whole length of the medial septum, and from the part of the lateral septum which is below the passage of the radial nerve. The three heads of origin are inserted, by a broad and membranous common tendon, into an impression occupying the posterior part of the proximal end of the olecranon of the ulna (Fig. 355, p. 397), and into the deep fascia of the forearm on each side of it. The long and lateral heads join the borders of the tendon of insertion, and the medial head is attached to its deep surface. A small 382 THE MUSCULAE SYSTEM. thick-walled bursa separates the tendon of the triceps from the posterior ligament of the elbow-joint and the proximal end of the olecranon. The muscle is superficial in almost its whole extent. The long (scapular) head is concealed at its origin by its relation to the teres muscles, between which it passes. The subanconaeus is a small muscle occasionally present. It consists of scattered fibres arising from the distal end of the posterior surface of the humerus, deep to the triceps, and it is inserted into the posterior ligament of the elbow -joint. Nerve-Supply. — The several heads of the muscle are supplied separately by branches of the radial nerve. Tlie lateral head receives fibres from C. (6.) 7. 8. ; the long and medial head from C. 7. 8. The medial head has a double supply. One nerve enters its proximal part, another (ulnar collateral nerve of Krause) enters the distal part of the muscle. Actions. — The triceps is the extensor muscle of the elbow -joint. The long head also acts as an adductor of the humerus at the shoulder-joint. The chief action of these muscles (excepting the coracobrachialis) is on the elbow -joint, producing along with other muscles flexion and extension. The flexor muscles are much more powerful than the extensors. Table of Muscles acting on tlie Elbow-Joint. Flexors. Extensors. Biceps brachii Brachialis Brachioradialis Pronator teres Flexors of wrist and fingers Extensors of wrist (in pronation) Triceps brachii Anconseus Extensors of wrist and fingers (in supination) FASCIAE AND MUSCLES OF THE FOREARIVI AND HAND. Fasciae. The superficial fascia in the forearm presents no exceptional features. On the dorsum of the hand it is loose and thin ; in the palm it is generally well furnished with fat, forming pads for the protection of the vessels and nerves. It is closely adherent to the palmar aponeurosis and to the skin, especially along the lines of flexure. M. Palmaris Brevis. — The palmaris brevis is a quadrilateral subcutaneous muscle which lies in the medial side of the hand, under the superficial fascia. It arises from the medial border of the thick central portion of the palmar aponeurosis and from the volar surface of the transverse carpal ligament of the wrist, and is inserted into the skin of the medial border of the hand for a variable distance. It covers the ulnar artery and nerve, branches of which supply it. Its action is to wrinkle the skin of the medial border of the hand, and by raising up the skin and superficial fascia, to deepen the hollow of the hand. The deep fascia of the forearm and hand is continuous above with the deep fascia of the arm. In the proximal part of the forearm it is strengthened by additional fibres around the elbow ; in front, by fibres from the lacertus fibrosus (semilunar fascia) of the biceps ; behind, by the fascial insertions of the triceps ; and laterally, by fibres derived from the humeral epicondyles in relation to the common tendons of origin of the flexor and extensor muscles of the forearm which in part take their origin from them. It is attached to the dorsal margin of the ulna, and affords increased attachment to the flexor and extensor carpi ulnaris and the flexor digitorum profundus muscles. Above the wrist the volar part of the fascia is pierced by the tendon of the palmaris longus, and by the ulnar artery and nerve. At the wrist it gains attachment to the bones of the forearm and carpus, is greatly strengthened by addition of transverse fibres, and constitutes the transverse carpal and dorsal carpal ligaments. Ligamentum Carpi Transversum. — The transverse carpal ligament (O.T. anterior annular ligament) is a band about an inch and a half in depth, continuous, proximally and distally, with the deep fascia of the forearm and the palm of the FASCIA AND MUSCLES OF THE FOREAEM AND HAND. 383 hand. It is attached laterally ta the navicular and large multangular; medially to the pisiform and os hamatum; and it forms a membranous arch binding down, in the hollow of the carpus, the flexor tendons of the fingers, and the median nerve. It is divided into hvo compartments, the larger accommodiiting the tendons of the flexors of tlie digits and the median m-rve, the smaller (placed laterally) containing the tendon of the flexor carpi radialis. There are three synovial membranes in these compartments: one for the flexor carpi radialis tendon, and two others, which often communicate together, enveloping the tendon of the flexor pollicis longus and the flexor tendons of the fingers respectively. The surface of the liga- ment is crossed by the palmar branches of the median and ulnar nerves ; by the tendon of the palmaris longus muscle, whicli is attached to its sur- face; and by the ulnar artery and nerve, which are again bridged over and pro- tected by a band of fibrous tissue, called the volar carpal liga- ment, which passes from the pisiform bone and the super- ficial fascia to the surface of the trans- verse carpal ligament. To the distal border of the ligament are attached the palmar aponeurosis in the centre, and the super- ficial muscles of the thumb and the mus- cles of the little finger on each side. Ligament um Carpi Dorsale. — The dorsal carpal ligament (O.T. pos- terior annular liga- ment) is placed at a . „ more proximal level than the transverse carpal ligament. It consists ot an oblique band of fibres about an inch broad, continuous proximally and distally with the deep fascia of the forearm and hand. It is attached laterally to the lateral side of the distal end of the radius, and medially to the distal end of the ulna (styloid process), the carpus, and the ulnar collateral ligament of the wrist. It is crossed by veins, by the superficial ramus of the radial nerve, and by the dorsal branch of the ulnar nerve. Six compartments are formed deep to it by the attachment of septal bands to the distal ends of the radius and ulna. Each compartment is provided with a mucous sheath, and they serve to transmit the extensor tendons of the wrist and fingers in the following order from lateral to medial side : — , . _ . (1) Abductor pollicis longus and extensor pollicis brevis, (2) Extensores carpi Palmar aponeurosis Thenar eminence Hypotlienar . eminence Palmaris brevis Transverse carpal ligament Abductor pollicis longus Flkxor oarpi radialis ._ Palmaris lonoos - Flexor dioitoru SUBLI Flexor carpi ulnaris- FiG. 342. — The Palmak ApoNEruosis. 384 THE MUSCULAR SYSTEM. "Flexor carpi ulnaris -Flexor digitorum sublimis — 'Flexor carpi radialis Palmaris longus — Pisiform bone — Abductor pollicls longus Transverse carpal Abductor diciti quinti Abductor pollicis brevis Flexor digiti QUINTI brevis __Flexor pollicis "brevis . Adductor pollicis Flexor pollicis ous radiales, longus and brevis, (3) Extensor pollicis longus, (4) Extensor digitorum communis and extensor indicis proprius, (5) Extensor digiti quinti proprius, (6) Extensor carpi ulnaris. The thin deep fascia of the dorsum of the hand is lost over the expansions of the extensor tendons on the fingers. Between the metacarpal bones a strong layer of fascia covers and gives attachment to the interossei muscles. Aponeurosis Palmaris. — The palmar aponeurosis is of considerable import- ance. In the centre of the palm it forms a thick triangular membrane, the apex of which joins the distal edge of the trans- verse carpal ligament, and, more superfici- ally, receives the insertion of the tendon of the palmaris longus muscle. The fascia separates below into four slips, one for each finger. The slips are con- nected together by transverse fibres, which form, beneath the webs of the fingers, the superficial trans- verse metacarpal ligament (fasci- culi transversi). More distally each slip separ- ates into two parts, to be con- nected to the sides of the metacarpo- phalangeal joints and the first phalanx of the medial four -Superficial Muscles and Tendons in the Palm of the Left Hand, digits. In the cleft between the two halves of each slip the digital sheath is attached and extends distally on to the finger. The lateral borders of this triangular central portion of the palmar aponeurosis are continuous with thin layers of deep fascia, which cover and envelop the muscles of the thenar and hypothenar eminences. The medial border gives origin to the palmaris brevis muscle (p. 382). The digital sheaths (vaginse mucosae) are tubular envelopes extending along the palmar aspect of the digits and enclosing the flexor tendons. Each consists of a fibrous sheath attached to the lateral borders of the phalanges and inter-phalan- geal joints, and continuous proximally with the palmar aponeurosis. Opposite each inter- phalangeal articulation the digital sheath is loose and thin ; opposite the first two phalanges (the first only in the case of the thumb) it becomes extremely thick, and gives rise to the ligamenta vaginalia, which serve to keep the tendons closely LuWBRICAL MUSCLES ^ Tendons of plexor digitorum ^^^sublimis t'LEXOR digitorum SUBLIMIS ""Flexor digitorum profundus Fig. 343.- MUSCLES ON ANTERIOR AND MEDIAL ASPECTS OF FOREARM. 385 applied to the bones during flexion of the fingers. Within each digital sheath are the flexor tendons, enveloped in a mucous sheath which envelops the tendon and lines the interior of the sheath. The mucous liniuL,^8 of the digital sheaths extend a short distance proximally in the palm, and in some cases com- municate with the large mucous sheaths enclosing the flexor tendons beneath the transverse carpal ligament. There may be a separate distinct raucous sheath for each digit; but most commonly only the sheaths for the three middle digits are separate ; those of the flexor pollicis longus and the flexor tendons of the little finger usiuiUy communicate with the mucous sheaths placed beneath the transverse carpal ligament. THE MUSCLES ON THE ANTERIOR AND MEDIAL ASPECTS OF THE FOREARM. The muscles on the anterior and medial aspects of the forearm comprise the pronators and the flexors of the wrist and fingers. In the forearm they are arranged in three strata: (1) a superficial layer consisting of four muscles which radiate from the medial epicondyle of the humerus, from which they take origin by a common tendon. They are named, from radial to ulnar side, pronator teres, flexor carpi radialis, palmaris longus, and flexor carpi ulnaris. These muscles conceal the muscle which by itself constitutes (2) the intermediate stratum — the flexor digitorum sublimis, and this again conceals, for the most part, (3) the deep layer of muscles, including the flexor digitorum profundus covering the ulna, the flexor pollicis longus on the radius, and the pronator quadratus, which is more deeply placed than the previous muscles, and stretches across the forearm between the distal portions of the radius and ulna. I. Superficial lYIuscIes. M. Pronator Teres. — The pronator teres is the shortest muscle of this group. It has a double origin: (1) a sujyerjicial head (caput humerale), the main origin, partly fleshy, partly tendinous, from the most distal part of the medial epicondylic ridge of the humerus and from the medial intermuscular septum, from the medial epi- condyle of the humerus, from the fascia over it, and from an intermuscular septum between it and the flexor carpi radialis (Fig. 346, p. 387) ; (2) a deep head (caput ulnare), a slender tendinous slip from the medial side of the coronoid process of the ulna, which joins the superficial origin of the muscle on its deep surface (Fig. 348, p. 389). The median nerve separates the two heads from one another. The muscle passes distally and laterally to be inserted by tendon into an oval impression on the middle of the lateral surface of the body of the radius (Figs. 346, p. 387, and 348, p. 389). The fibres of the muscle are twisted on them- selves, so that the most proximal humeral fibres form the most distal fibres of the tendon of insertion, and the most distal humeral fibres and those arising from the coronoid process are most proximal at the insertion. The pronator teres forms the medial boundary of the hollow of the elbow. It is superficially placed, except near its insertion, where it is covered by the brachio- radialis muscle and by the radial vessels and superficial branch of the radial nerve. Nerve-Supply.— Median nerve (C. 6.). Action. — The muscle is a flexor of the elbow-joint and a pronator of the forearm. M. Flexor Carpi Radialis. — The flexor carpi radialis muscle takes its origin from the common tendon from the medial epicondyle of the humerus, from the fascia over it, and from the intermuscular septa on either side. Its fleshy belly gives pLice, in the distal half of the forearm, to a strong round tendon which, at the wrist, enters the hand in a special compartment under cover of the transverse carpal ligament, and after occupying the groove on the large mult- angular bone, is inserted into the proximal ends of the second and third metacarpal 26 386 THE MUSCULAR SYSTEM. bones on their volar surfaces (Fig. 351, p. 392). The chief tendon is that to the second metacarpal bone. The muscle is superficial except near its insertion. Its tendon, in the distal half of the forearm, is an important guide to the radial vessels, which are placed to its radial side. After passing beneath the transverse carpal ligament the tendon is concealed by the origins of the short muscles of the thumb, and is crossed, from medial to lateral side, by the tendon of the flexor pollicis longus. Besides the mucous sheath enveloping the tendon beneath the ligament, a mucous bursa is placed beneath the insertion of the tendon. Nerve-Supply. — Median nerve (C. 6.). Actions. — Tliis muscle lias a threefold action. It is mainly a flexor of the elbow and wrist, but it abo acts as an accessory pronator of the forearm. M. Palmaris Longus. — The palmaris longus arises also from the common flexor tendon from the medial epicondyle of the humerus, from the fascia over it, and from intermuscular septa on each side. It forms a short fusiform muscle, which ends, in the middle of the forearm, in a long flat tendon. This pierces the deep fascia, near the wrist, and passing over the trans- verse carpal ligament, is in- serted (1) into the surface of the transverse carpal ligament, and (2) into the apex of the thick central portion of the palmar aponeurosis. A ten- dinous slip is frequently sent to the short muscles of the thumb and the fascia covering them. The palmaris longus is the smallest muscle of the forearm. In the distal third of the H G Pig. 344. — Distal Surface of a Section across the Right Forearm in the Middle Third. A, Pkokator teres (insertion) ; B, Flexor carpi radialis ; C, Flexor DiGiTORUM scBLiMis ; D, Palmaris LONGUS ; E, Flexor carpi ulnaris ; F, FLE.XOR DIOITORUM PROFUNDUS ; G, ExTENSOR CARPI ULNARIS ; H, Extensor poLLipis longus ; I, Extensor dioitorum communis and forearm itS tCndon is placed EXTENSOR digiti quinti proprius ; J, Abductor pollicis longus ; K, rji v-gofly gvcr the median Extensor carpi radialis brevis; L, Extensor CARPI radialis longus; J j • i i. M, Brachioradialis. a, Radius ; 6, Interosseous membrane ; c, Ulna, ncrve, alOng the radial border 1, Superficial ramus of radial nerve ; 2, Radial artery ; 3, Volar Inter- q^ ^]-^g tcndonS of the flcXOr osseous artery; 4, Volar interosseous nerve (underneath flexor pollicis -,• ., ViTm' longus); 5, Median nerve; 6, Ulnar artery; 7, Ulnar nerve; 8, Dorsal UlglUOrum SUDiimiS. interosseous artery ; 9, Dorsal interosseous nerve. mi i The palmaris longus is the most variable muscle in the body, and is often absent (10 per cent). Nerve-Supply.— Median nerve (C. 6.). Actions. — The muscle assists in flexion of the elbow and wrist. It also by tightening the palmar aponeurosis deepens the hollow of the hand and helps to flex the fingers. M. Flexor Carpi Ulnaris. — The flexor carpi ulnaris muscle has a double origin, from the humerus and from the ulna. (1) It arises from the common tendon attached to the medial fepicondyle of the humerus, from the fascia over it, and from a lateral intermuscular septum. (2) By means of the deep fascia of the forearm it olDtains an attachment to the medial border of the olecranon and the dorsal margin of the ulna in its proximal three-fifths. The fleshy fibres join a tendon which lies on the anterior border of the muscle and is inserted into the pisiform bone, and in the form of two ligamentous bands (piso-hamate and piso-metacarpal) into the hamulus of the os hamatum, and the proximal end of the fifth metacarpal bone (Fig. 351, p. 392). The muscle is superficially placed along the medial border of the forearm. It conceals the flexor digitorum profundus muscle, the ulnar nerve (which enters MUSCLES ON ANTERIOR AND MEDIAL ASPECTS OF FOREARM. 387 the forearm between the two heads of origin of the muscle), and the ulnar artery. The tendon serves as a guide to the artery in the distal half of the forearm. BlCKI'S BKA'IIII . Medial istkr- m'SClLAR SKITIM Mkdial kpicosdvle Lacerti rlBROSl Supinator >il'si i Pronator terk P'lexor carpi ' kadialis Palmaris LONGUS' Flexor carpi VLXARla Extensor CARPI. RADIALIn LftNUl'S Brachio- radialis' Flexor diui- torcm subumis Flexor pollicis, Loxors Brachioradialis (tendon) Flexor carpi radiali^ (tenilon) Palmaris LONOrs (temioii ) Flexor cap.pi clsaris (ti-niioii) PisitMriiL d'Hi Abdcctor pollicis Losors Palmar apoxecrosis Biceps bkaiiiii Media I. intermusculai 8EPTI \i Lacertus pibroscs Biceps tendo Pronator teres (I'l'tnerHl orijjin) Pronator TERES. (ulnar origin) Ki.EXOR carpi r\dialis supinator musc Brachioradialis Pronator teres (insertion) Flexor digitorcm suBLiMis (radial . origin) Flexor carpi ulnaris Flexor DioiTORUM^- SUBLIMIS "-^ Brachioradialis TENDON •- .4. Flexor pollicis longv Pronator quadrati Flexor »igitori-m prokindi's Pisiform bone-- Flexor carpi radiams Abductor pollicis loxgus Fig. 345. — The Sipekkicial Muscles of THE Left Forearm. Fig. 346. — Deeper Muscles ok THE Left Forearm. Nerve-Supply.- Ulnar nerve (C. 8. T. 1.). Actions.— The tii-xor carpi ulnaris is a flexor and adductor of the wrist, and an accessory flexor of the elbow -joint. 26 rt 388 THE MUSCULAR SYSTEM. 2. Intermediate Layer. M. Flexor Digitorum Sublimis. — The flexor digitorum sublimis occupies a deeper plane than the four previous muscles. It has a threefold origin, from the humerus, radius, and ulna. (1) The chief or humeral head of origin is from the medial epicondyle of the humerus by the common tendon, from the ulnar collateral ligament of the elbow, and from adjacent intermuscular septa. (2) The ulnar head of origin is by a slender fasciculus from the medial border of the coronoid process of the ulna, proximal and medial to the origin of the pronator teres (Fig. 348, p. 389). (3) The radial head of origin is from the proximal two-thirds of the volar margin of the radius by a thin fibro- muscular attachment (Fig. 348, p. 389). The muscle divides in the distal third of the forearm into four parts, each provided with a separate tendon which goes beneath the transverse car- >YExiiansion of extensor tendon ^^i ligament, passes through the palm I^^FLEXOR DICTORLM ^J ^^^ ^^^^^ ^^^ ^^^^^^ ^^^ COrrCSpOUd- ing digital sheath of a finger. At the wrist the four tendons are arranged in pairs, those for the middle and ring fingers in front, and those for the fore and little fingers behind, and are sur- rounded by a mucous sheath, along with the tendons of the flexor digi- torum profundus, beneath the trans- verse carpal ligament. In the palm of the hand the tendons separate, and conceal the deep flexor tendons and lumbrical muscles. Within the digital sheath each tendon is split into two parts by the tendon of the flexor digitorum pro- fundus ; after surrounding that tendon the two parts are partially re-united on its deep surface, and are inserted, after partial decussation, in two portions into the sides of the second phalanx. The vincula tendinum form additional insertions of the muscle. They consist of delicate bands of connective tissue enveloped in folds of the mucous sheath, and are known as the vincula longa and brevia. The vinculum breve is a triangular band of fibres containing yellow elastic tissue (ligamentum subflavum), occupying the interval between the tendon and the digit for a short distance close to the insertion. It is attached to the front of the inter -j^halangeal articulation and the head of the first phalanx. The .ligamentum longum is a long narrow band extending from the back of the tendon to the proximal part of the palmar surface of the first phalanx. Nerve-Supply.— Median nerve (C. 6.). Actions. — The muscle is a flexor of the ellww, wrist, metacariJO-phalangeal and first (proximal) interphalangeal joints. Ainculuni breve Flexor DiorroRL^M si'blimis PROFUNDUS First lumbrical muscle First dorsal inter- osseous MUSCLE Extensor indicis proprius tendon Extensor digitorum COMMUNIS tendon Fig. 347. -The Tendons attached to the Index Finger. 3. Deep Layer. M. Flexor Digitorum Profundus.— The flexor digitorum profundus is a large muscle arising from the ulna, the interosseous membrane, and the deep fascia of the forearm, under cover of the flexor digitorum sublimis and the flexor carpi ulnaris. Its ulnar origin is from the volar and medial surfaces of the bone in its proximal two-thirds, extending y^roximally so as to include the medial side of the olecranon, and to embrace the insertion of the brachialis muscle into the coronoid. MUSCLES ON ANTERIOE AND MEDIAL ASPECTS OF FOREARM. 389 Brachialis muscle (insertion) Supinator intisclo (ulnar origin) Kloxordigitoruin sub- limis (ulnar origin) Pronator teres (ulnar origin) Klexor pr>llicislongns (occasional origin) Biceps brachii (insertion) Flexor digi- torum sublimis (radial origin) Pronator teres (insert,ion) Flexor pollicis longus (origin) Flexor digitorum profundus (origin) process. It arises laterally from -the medial half of the interosseous membrane in its middle third (Figs. 348, p. 389, and 349, p. 390), and medially from the deep fascia of the forearm dorsal to the origin of the flexor carpi ulnaris. The muscle forms a broad thick tendon which passes beneath the transverse carpal ligament, covered by the tendons of the flexor digitorum sublimis, and enveloped in the same mucous sheath, and divides, in the palm, into four tendons for insertion into the terminal phalanges of the fingers. The tendon associated with the forefinger is usually separate from the rest of the tendons in its whole length. Each tendon enters the digital sheath of the finger deep to the tendon of the flexor digitorum sublimis, which it pierces opposite the first phalanx, and is finally inserted into the base of the terminal phalanx. Like the tendons of the flexor sublimis, those of the deep flexor are provided with vincula, viz., vincula brevia attached to the capsule of the second inter- phalangeal articulation, and vincula longa, which are in this case connected to the tendons of the subjacent flexor digitorum sublimis. Mm. Lumbricales. — The lumbricales are four small cylindrical muscles associated with the tendons of the flexor digitorum profundus in the palm of the hand. The two lateral muscles arise, each by a single head, from the radial sides of the tendons of the flexor digitorum profundus destined respectively for the fore and middle fingers. The two medial muscles arise, each by two heads, from the adjacent sides of the second and third, and third and fourth tendons. From their origins the mus- cles are directed distally to the lateral side of each of the metacarpo- phalangeal joints, to be inserted into the capsules of these articulations, the lateral border of the first phalanx, and chiefly into the lateral side of the extensor tendon on the dorsum of the phalanx. The lumbricales vary considerably in number, and may be increased to six or diminished to two. Nerve-Supply. — Tlie flexor digitorum profundus is supplied in its lateral part by the volar interosseous branch of the median nerve (C. 7. 8. T. 1.) ; and in its medial part by the ulnar nerve (C. 8. T. 1.). The lateral two lumbricales are supplied by the median nerve (C. 6. 7.), and the medial two muscles by the ulnar nerve (C. 8. (T. 1.)). Actions. — The flexor digitorum profundus is a powerful flexor of the wrist. It also flexes the fingers at the metacarpo-phalangeal joint, ancf acts in a similar way at both the inter- phalangeal joints. The lumbrical muscles act as flexors of the fingers at the metacarpo-phalangeal joints, and Pronator quad- ratus (insertion) Brachioradialis (insertion) Pronator quadratus (origin) Fkj. MS. -Muscle-Attachments to the Right Radius AND Ulna (Volar Aspects). 390 THE MUSCULAE SYSTEM. Biceps bhaoiii Lacertcs fibrosus (by tlieir attacliment to the extensor tendons) as extensors of the fingers, acting on both inter- phalangeal joints. M. Flexor Pollicis Longus. — The flexor pollicis longus arises, beneath the tlexor digitorum siiblimis, by fleshy fibres, from the volar surface of the body of the radius in its middle two- fourths, and from a corresponding portion of the interosseous mem- brane. It has an additional origin, occasionally, from the medial border of the coronoid process of the ulna (Fig. 348, p. 389). Its radial origin is limited proximally by the oblique proximal part of the volar margin of the radius and the origin of the flexor digitorum sublimis, and distally by the insertion of the pronator quadratus muscle. The muscle ends, proximal to the wrist, in a tendon, which passes over the pronator quadratus into ' the hand beneath the transverse carpal ligament, and is enveloped in a special mucous sheath. In the palm the tendon is directed distally along the medial side of the thenar eminence, be- tween the flexor brevis and ad- ductor muscles of the thumb, to be inserted into the base of the terminal phalanx of the thumb on its volar surface. The muscle is placed deeply in the forearm, being concealed by the superficial layer of muscles and by the flexor digitorum sublimis. Nerve - Supply. — Volar interosseous branch of the median (C. 7. 8. T. 1.). Actions. — The muscle is a flexor of the wrist and thumb, acting in the latter movement on the metacarpal bone and both phalanges. M. Pronator Quadratus. — The pronator quadratus is a quadri- lateral fleshy muscle, occupying the distal fourth of the forearm. It is placed beneath the deep flexor tendons, and arises from the distal fourth of the volar margin and surface of the ulna (Fig. 348, p. 389). It is directed transversely later- ally to be inserted into the distal fourth of the volar surface of the radius, and into the narrow tri- angular area on its medial side, in front of the attachment of the interosseous membrane (Fig. 348, p. 389). The pronator quadratus is subject to considerable variations. It may even be absent ; or it may have an origin from radius or ulna, or from both bones, and an insertion into the carpus. Flexor digitorum profundus Flexor digitorum PROFUNDUS (for- iiidex linger) Flexor pollicis longus Brachioradiali Pronator quadratus Flexor digitorum sublimis Pisiform bone- Flexor carpi radialis,. Abductor pollicis L0NOU8 Fig. 349. —The Deepest Muscles on thi; Volar Aspect OF THE Left Foreakm. SHORT MUSCLES OF THE HAND. 391 The muscle is placed deeply in the distal part of the forearm, and is wholly concealed by the teudons of the nniscles which desceml, under cover of the transverse carpal ligament, to the wrist and fingers. The ratlial artery and its accompanying veins pass over it at its insertion into the radius. ABDUCTpB rOI.LICIS UlNlU'S „.. Extensor pollicis brevis -f Abductdr pollicis bre\ is Opponens pollicis Flexor pollicis brevis ^. ^ (siiperticial part) Adductor pollicis (obli'iiu' heaU)-^.^ Addcctor pollicis (trans- , vorse head) A norcTOR I'OLLICIS BREVIS ^^^^. Pronator yrADRATUs Kl.KXOR CARPI L'LNARIS PlSIKOKM BONE Hook of os hamatum ABDICTOR DIOITI QUINTI (CUt) Fi KXfiR digiti qdinti brevis (cut) Third volar interosseous mvscle -- Fourth dorsal interosseous musclk Second volar interosseous muscle Third dorsal interosseous muscle Flexor digiti quisti HKEvis and Abductor Ii|i;lTl QUINTI INSERTION Tendons of third and FOURTH LUMBBICALS Flexor digitorum sublimls tendon Digital sheath Flexor digitorum profu tendon Flexor digitorum profundi's insertion" Fig. 350.— The Palmar Muscles (Right Side). Nerve-Supply.— Volar interosseous branch of the median nerve (C. 7. 8. T. 1.). Action.— The muscle acts along with the pronator teres in producing pronation of the forearm. SHORT MUSCLES OF THE HAND. The short muscles belonging to the hand, in addition to the palmaris brevis and the lumbrical muscles, ab-eady described, include the six muscles of the 392 THE MUSCULAE SYSTEM. thumb which produce the thenar eminence, the three muscles of the little finger, which form the hypothenar eminence, and the interossei muscles, which are deeply placed between the metacarpal bones. Muscles of the Thumb. The short muscles of the thumb are the abductor, opponens, and flexor brevis (with its deep portion, interosseus jprimus volaris), and the adductor muscle, sub- divided into two heads — oblique and transverse. M. Abductor Pollicis Brevis. — The abductor poUicis brevis (O.T. abductor pollicis) arises by fleshy fibres from the tubercle of the navicular, the ridge of the greater multangular, the volar surface of the transverse carpal ligament, and from Capitate bone NaMcular bone Abductor pollicis brevib (origin) Opponens pollicis (origin) Greater multangular bone J Abductor pollicis longus (insertion) Lesser inultangulai bone Opponens pollicis (inseition) Flexor carpi radialis (insertion) Adductor pollicis (origin of oblique head) Os lunatum Os liamatuni quetrum Pisifoiia bone First dorsal interosseous muscle (one origin) First volar interosseous muscle (origin) Abductor digiti qiiinti (origin) Flexor carpi ulnaris (insertion) Plexor brevis digiti quinti (origin) Flexor carpi ulnaris (insertion) Opponens digiti quinti (origin and insertion) Third volar inter- osseous muscle (origin) Fourth dorsal interosseous inubcle (one origin) Second volar interosseous muscle (origin) Second dorsal interosseous muscle (one origin) Adductor pollicis (origin of transverse head) Third dorsal interosseous muscle (one origin) Fig. 3.51. — Muscle-Attachments to the Volar Aspect of the Carpus and Metacarpus, tendinous slips derived from the insertions of the palmaris longus and abductor pollicis longus muscles (Fig. 350, p. 391). Strap-like in form, and superficial in position, it is inserted by a short tendon into the radial side of the first phalanx of the thumb at its proximal end, and into the capsule of the metacarpo-phalangeal joint. Nerve-Supply. — Median nerve (C. 6. 7.). Actions. The muscle acts on the thumb at both the carpo-metacarpal and metacarpo- phalangeal joints. It abducts and draws forward the thumb. M. Opponens Pollicis. — The opponens pollicis arises by fleshy and tendinous fibres from tlie volar surface of the transverse carpal ligament and from the ridge on the greater multangular bone. It is partially concealed by the preceding muscle. Extending distally and laterally it is inserted into the whole length of the lateral border and the radial half of the volar surface of the first metacarpal bone (Fig. 351, p. 392). SHOKT MUSCLES OF THE HAND. 393 Nerve-Supply. —Median nerve (C. 6. 7.). Action. It acts solely on the fii-st metacarpal bone, in the movement of opposition of the tluimb. M. Flexor Pollicis Brevis. — The flexor pollicis brevis consists of two parts. a. The sicperjicial part of the muscle, partly concealed by the abductor pollicis brevis, arises, by fleshy aud tendinous fibres, from the distal border of the transverse carpal ligament, and sometimes from the ridge of the greater multangular. It is inserted into the radial side of the base of the first phalanx of the thumb, a sesamoid bone being present in the tendon of insertion. b. 'The deep part of the muscle (interosseus primus volaris) arises from the medial side of the base of the first metacarpal bone. It is inserted into the medial side of the base of the first phalanx of the thumb along with the adductor pollicis. This little muscle is deeply situated in the first interosseous space, in the interval between the adductor poUicis obliquus and the first dorsal interosseous muscle. It may be regarded as homologous with the volar interossei muscles, with which it is in series. Nerve-Supply. - Median nerve (C. 6. 7.). Actions. — It is a flexoi- of the thumb and assists also in the movement of opposition of the thumb to the linger.-. M. Adductor Pollicis. — The adductor pollicis is .separated into two parts by the radial artery. (1) The oblique head lies deeply in the palm, covered by the tendons of the long flexors of the thumb and fingers. It arises by fleshy fibres from the volar surfaces of the greater and lesser multangular and capitate bones, from the sheath of the tendon of the flexor carpi radialis, from the volar surfaces of the bases of the second, third, and fourth metacarpal bones, and from the volar ligaments con- necting the.se bones together (Fig. 351, p. 392). It is inserted by a tendon, in which a sesamoid bone is developed, into the medial side of the base of the first phalanx of the thumb. At its lateral border a slender slip separates from the rest of the muscle, and passing obliquely, deep to the tendon of the flexor pollicis longus, is inserted into the lateral side of the base of the first phalanx along with the superficial part of the flexor pollicis brevis. (2) The transverse head, lying deeply in the palm beneath the flexor tendons, arises by fleshy fibres from the medial ridge on the volar aspect of the body of the third metacarpal bone, in its distal two-thirds (Fig. 351, p. 392), and from the fa.scia covering the interosseous muscles in the second and third spaces. Triangular in form, it is directed laterally, over the interossei muscles of the first two spaces, to be inserted by tendon into the medial side of the base of the first phalanx of the thumb along with the oblique head. Nerve-Supply. —Deep branch of the ulnar nerve (C. 8. (T. 1.)). Actions. — Adduction aud opposition of the thumb. IVIuscIes of the Little Finger. The short muscles of the little finger are t^he adductor, opponens, and flexor brevis digiti quinti. M. Abductor Digiti Quinti. — The abductor digiti quinti is most superficial. It arises from the pisiform bone and from the tendon of the flexor carpi uluaris and its ligamentous continuations (Fig. 351, p. 392). It is inserted by tendon into the medial side of the base of the first phalanx of the little finger. Nerve-Supply.— Deep branch of the ulnar nerve (C. 8. (T. 1.)). Actions. — Till- muscle separates the little finger from the ring finger, and assists in flexion of the finger at the metacarpo-phalangeal joint. M. Opponens Digiti Quinti. — The opponens digiti quinti arises under cover 394 THE MUSCULAE SYSTEM. of the preceding muscle, by tendinous fibres, from the transverse carpal ligament and from the hamulus of the os hamatum. It is inserted into the medial margin and medial half of the volar surface of the fifth metacarpal bone in its distal three-fourths (Fig. 351, p. 392). Nerve -Supply. — Deep branch of the ulnar nerve (C. 8. (T. 1.)). Action. — The muscle acts only on the metacarpal bone, drawing it forward, so as to deepen the hollow of the hand. M. Flexor Digiti Quinti Br e vis. — The flexor digiti quinti brevis may be absent or incorporated with either the opponens or abductor digiti quinti. It arises, by tendinous fibres, from the transverse carpal ligament and from the hamulus of the os hamatum (Fig. 351, p. 392). It is inserted along with the ab- ductor into the medial side of the first phalanx of the little finger. Nerve -Supply. — The deep branch of the ulnar nerve (C. 8. (T. 1.)). Actions. — Flexion of the little finger at the carpo-metacarpal and metacarpo- phalangeal joints. Fig. 352. — The Volar Interosseous Muscles (Right Side). V^, first ; V-, second ; and V^, third volar interosseous muscles. The Interosseous IVIuscIes. The interosseous muscles of the hand occupy the spaces between the metacarpal bone.s. They are arranged in two sets, volar and dorsal. Mm. Interossei Volares. — The volar (O.T. palmar) interossei are three in Extensor carpi ulnaris (insertion) Fourth dorsal interosseous muscle (origin) Third dorsal inter- osseous muscle (origin) Extensor carpi radialis brevis (insertion) Extensor carpi radialis ,/longus (insertion) First dorsal inter- osseous muscle (origin) Second dorsal interosseous muscle (origin) Fig. 353. — Muscle-Attachments to the Dorsal Aspect ok the Right Metacarpus. number, occupying the medial three interosseous spaces. Each arises by a single head ; t\\Q first from the medial side of the body of the second metacarpal bone ; the second and third from the lateral sides of the bodies of the fourth and fifth metacarpal MUSCLES ON THE DORSAL SURFACE OF THE FOREARM. 395 boues respectively (Fig. 352, p. 394). Each ends in a tendon which is directed distally behind the deep transverse metacarpal ligament, to be inserted into the dorsal expansion of the extensor tendon, the capsule of the metacarpo- phalangeal articulation, and the side of the first phalanx' of the finger ; the first is inserted into the medial side of the second linger ; the second and tJdrd into the lateral sides of the fourth and tifth fingers. The deep part of the flexor pollicis brevis {inter- osseus i-)rimus volaris) is to be regarded as the homologous muscle of the first interosseous space. Mm. Interossei Dorsales. — The dorsal interossei are four in number. Each arises by two lieads from the sides of tiie metacarpal bones })Ounding each in- terosseous space (Figs. 353, p. 394, and 354, p. 395). Each forms a Heshy mass, ending in a membranous tendon which, passing distally, behind the deep transverse metacarpal ligament, is inserted exactly like the volar muscles into the dorsal aspect of each of the four fingers. The insertion of the first dorsal interosseous muscle is into the lateral side of the index finger ; the second muscle is attached to the lateral side of the middle finger; the third Insektion of flexor carpi ulnaris ORIfilKS OF volar inter- osseous muscles Insertion of opponens digit! gUINTI Insertion of - abductor DIC.ITI QUINTI Abductor pollicis urevis : origin (cut)— Insertion of flexor carpi radialis Insertion of opponens pollicis Lateral head of First dorsa interosseous crossed interosseos primus volaris Abductor pollicis urevis : Insertion (cut) Adductor pollicis obliquus (insertion) Adductor pollicis transversus- (insertion) First dorsal interosseous muscle Second dorsal interosseous muscle Third dorsal interosseous muscle Fourth dorsal interosseous muscle Fig. 354. — Dorsal Interosseous Muscles of the Hand (seen from the Volar Aspect). muscle to the medial side of the same finger; and the fourth muscle to the medial side of the ring finger. The interosseous muscles of the hand in some cases have a disposition similar to that of the corresponding muscles of the foot (p. 435). Nerve-Supply. — The deej) brancli of the ulnar nerve (C. 8. (T. 1.)). Actions. — The interossei muscles act in a similar way to, and along with, the lumbricales, flexing the fingers at the metacarpo-phalangeal joints, and extending them at the inter- phalangeal joints. In addition, the dorsal interossei serve to abduct the fingers into which they are inserted (fore, middle, and ring fingers) from the middle line of the middle finger ; the volar muscles on the other hand are adductors of the fingers into which they are inserted (fore, ring, and little finger) towards the middle line of the middle finger. THE MUSCLES ON THE DORSAL SURFACE OF THE FOREARM. The group of muscles occupying the lateral side of the elbow and the dorsal surface of the forearm and hand include the supinator muscles of the forearm and the extensors of the wrist and digits. They are divisible into a superficial and a deep layer. The superficial layer comprises seven muscles, which are in order, from the radial to the ulnar side of the forearm, the brachioradialis, the two radial extensors of the carpus, the extensor digitorum communis and extensor digiti quinti proprius, the extensor carpi ulnaris, and the anconoeus. 396 THE MUSCULAE SYSTEM. The deep muscles are five in number : one, the supinator, extends between the proximal parts of the ulna and radius ; the others are the special extensors of the thumb and forefinger, viz., the abductor pollicis longus, extensor poUicis longus and extensor pollicis brevis, and extensor indicis proprius. They cover the dorsal surface of the bones of the forearm and the interosseous membrane, and are almost wholly concealed by the superficial muscles. Only the abductor pollicis longus and the extensor pollicis brevis become superficial in the distal part of the forearm, where they emerge between the radial extensors of the carpus and the extensor digitorum communis. Superficial Muscles. M. Brachioradialis. — The brachioradialis arises, by fleshy fibres, from the anterior aspect of the proximal two-thirds of the lateral epicondylic ridge of the humerus, and from the anterior surface of the lateral intermuscular septum (Fig. 340, p. 380). The muscle lies in the lateral side of the hollow of the elbow, passes distally along the lateral border of the forearm, and ends about the middle of the forearm in a narrow, flat tendon which is inserted, under cover of the tendons of the abductor pollicis longus and extensor pollicis brevis, by a transverse linear attachment, into the proximal limit of the groove for the above-named muscles on the lateral side of the distal extremity of the radius. Some of its fibres gain an attachment to the ridge on the volar margin of the groove, and others spread over the surface of the groove for a variable distance (Figs. 355, p. 397, and 348, p. 389). Nerve-Supply. — The muscle is supplied by a branch of the radial nerve (C 5. 6.) in the hollow of the elbow. Actions. — The muscle is primarily a flexor of the elbow -joint. It is also a semi-pronator and semi-supinator of the forearm, bringing the limb from the supine or prone position, into a position in which the radius is uppermost. It thus assists both the pronator and supinator muscles. M. Extensor Carpi Radialis Long-us. — The extensor carpi radialis longus arises, by fleshy fibres, from the anterior aspect of the distal third of the lateral epicondylic ridge of the humerus, from the anterior surface of the lateral inter- muscular septum, and from the common tendon of origin of succeeding muscles, attached to the lateral epicondyle (Figs. 356 and 357, p. 399). In the distal half of the forearm, it ends in a tendon which passes beneath the dorsal carpal, ligament, to. be inserted into the dorsal surface of the base of the second metacarpal bone on its radial side (Fig. 353, p. 394). The muscle is concealed in its proximal part by the brachioradialis, and its tendon, in the distal half of the forearm, is crossed, obliquely, by the abductor pollicis and by the extensor pollicis brevis. Nerve-Supply.— The muscle is supplied by a branch of the radial nerve in the hollow of the elbow (C. (r,.) 6. 7. 8.). Actions. — The muscle is an extensor of the wrist, and also an accessory flexor of the elbow- joint. M. Extensor Carpi Radialis Brevis. — The extensor carpi radialis brevis arises from the common tendon, from the radiaL-aoUaieral ligament of the elbow, from the fascia over it, and from inte rmus cular septa on either side. It passes distally, in the dorsal surface~of the forearm and under the dorsal carpal ligament, in close relation, to the previous muscle, to be inserted, by a tendon, into the bases of the second and third metacarj)al bones (Fig. 353, p. 394). A bursa ia placed beneath the two radial extensor tendons close to their insertion. It is practically concealed, in the forearm, by the extensor carpi radialis longus, and in the distal half is crossed obliquely by the abductor pollicis longus and the extensor pollicis brevis. The tendons of the two muscles are crossed, on the dorsum of the wrist, by the tendon of the extensor pollicis longus. Nerve-Supply.— -The deep branch of the radial nerve (C. (5.) 6. 7. (8.)). Actions.— Like the long extensor, this muscle extends the hand at the wrist; and is a sub.sidiary flexor of the elbow -joint. MUSCLES ON THE DORSAL SUEFACE OF THE FOREARM. 397 Imi (iiiseiUon) Biceps bracliii (insertion) •Supinator muscle (insertion) Abductoi- poUicis longus (origin) Pronator teres (insertion) M. Extensor Digitorum Communis. — The extensor digitorum communis arises from the common tendon, from the lateral epicondyle of the hiunerus, from the fascia over it, and from intermuscular septa on either side. Extending along the dorsum of the forearm it ends, proximal to the wrist, in four tendons, of which the most lateral often has a separate Heshy belly. After passing under the dorsal carpal ligament, in a compartment along with the extensor indicia proprius, the tendons separate on the dorsum of the hand, where the three most medial tendons are joined together by two obliquely placed bands. One passes distally and laterally, and connects to- gether the third'and second ten- dons ; the other is a broader and shorter band, which passes also distally and laterally, and joins the fourth to the third tendon. In some cases a third band is present which passes distally and medially from the first to the second tendon ; and, frequently, the tendon for the little finger is joined to the tendon for the ring finger, and separates from it only a short distance above the distal end of the metacarpal bone. The tendons are inserted in the following manner: — On the finger each tendon spreads out so as to form a membranous expan- sion over the knuckle and on the dorsum of the first phalanx. The border of the tendon is indefinite over the metacarpo - phalangeal articulation, of which it replaces the dorsal ligament. On the dorsum of the first phalanx the tendon receives at its sides the insertions of the interosseous and lumbrical muscles. At t^e distal end of the first phalanx it splits into ill-de- fined median and collateral slips, which pass over the dorsum of the first inter-phalangeal articulation, where they replace the dorsal ligament. The median slip, is inserted into the dorsum of the base of the second phalanx, while the two lateral pieces become united to form a membranous tendon on the dorsum of the second phalanx, which, after passing over the second inter-phalangeal articula- tion, is inserted into the base of the terminal phalanx. The muscle is placed superficially in the forearm, between the extensors of the carpus and the proper extensor of the little finger. Nerve-Supply. — The doi-sal interosseous nerve (C. (5.) 6. 7. 8.). Actions. The muscle extends the elbow, wrist, and fingers. On account of the attachment together of the tendons to the third, fourth, and fifth fingers by accessory bands in the dorsum of the hand, these three fingei-s can only be fully extended together, while extension of the fii-st finger Extensor poUicis (origin) brevis Fig. 355. Hi-achioradialis (insertion) Groove for tendons of radial extensors of carpus Groove for extensor pollicis longus Groove for extensor digitorum com- munis and extensor indicis i)roprius -Mdscle-Attachments to the Right R.\Dirs AKD Ulna (Dorsal Aspect). 398 THE MUSCULAR SYSTEM. can take place separately. In extension of the inter-plialangeal joints, the muscle is aided by the interossei and lumbrical muscles. M. Extensor Digiti Quinti Proprius. — The extensor digiti quinti proprius has an origin, similar to and closely connected with that of the preceding muscle, from tlie common tendon, the fascia over it, and from intermuscular septa. It passes along the dorsum of the forearm, as a narrow fleshy slip, between the extensor digitoriim communis and the extensor carpi ulnaris, and ends in a tendon, which occupies a groove between the radius and ulna in a special compartment of the dorsal carpal ligament. On the dorsum of the hand the tendon, usually split into two parts, lies on the medial side of the tendons of the extensor digitorubi communis, and is finally inserted into the expansion of the extensor tendon on the dorsum of the first phalanx of the little finger. Nerve-Supply. — The dorsal interosseous nerve (C. (5.) 6. 7. 8.). Actions. — The muscle extends the elbow, wrist, and little finger. M. Extensor Carpi Ulnaris. — The extensor carpi ulnaris has a double origin : (1) from the common tendon from the lateral epicondyle of the humerus, from the fascia over it, ami from the intermuscular septa ; "^nd (2), through the medium of the deep fascia, from the dorsal nwginof the uln a in it s^jnjddle two,- fourths. Lying in the forearm upon tKedorsal surface -of the ulna, it ends in a tendon which occupies a groove on the dorsal surface of the ulna in a special compartment of the dorsal carpal ligament, and is inserted into the medial side of the base of the fifth metacarpal bone (Fig. 353, p. 394). Nerve-Supply. — The dorsal interosseous nerve (C. (5.) 6. 7. S.^^JP Actions. — The muscle is an extensor of the wrist, and at flJP^me time, acting with the flexor carpi ulnaris it is a jiowerful adductor of the wrist. Its hiifheral attachment makes it also a subordinate extensor of the elbow-joint. H^. M. Anconseus. — The anconseus is a small trianguls^ muscle. It arises, by a separate tendon, from the distal part of the dorsal surface of the lateral epicondyle of the humerus (Fig. 341, p. 380), and from the dorsal part of the capsule of >. the elbow-joint. \ It covers part of the dorsal surface of the elbow-joint and proximal part of the ulna, and is inserted, by fleshy fibres, into a triangular surface on the lateral aspect of the olecranon and dorsal surface of the ulna, as far distally as the oblique line (Fig. 355, p. 397). It is ^Iso inserted into the fascia which covers it. The epitrochleoanconaeus is an occasional small muscle which arises from the dorsal surface of the medial epicondyle of the humerus, and is inserted into the medial side of the olecranon., It covers the ulnar nerve in its passage to the forearm. Nerve-Supply. — The muscle is supplied by the terminal branch of the nerve to the medial head of the triceps muscle from the radial (C. 7. 8.). Actions. — The anconeeus is an extensor of the elbow. Deep Muscles. M. Supinator. — The supinator muscle (O.T. supinator radii brevis) is the most proximal of the deeper muscles. It is almost wholly concealed by the superficial muscles, and has a complex origin, — (1) from the lateral epicondyle of the humerus ; (2) from the radial collateral, and annular ligaments of the elbow-joint ; (3) from the triangular surface on the shaft of the ulna just distal to the radial notch ; and (4) from the fascia over it. From this origin the muscle spreads laterally and distally, enveloping the proximal part of the radius, and is inserted into the volar and lateral surfaces of the bone, as far forwards as the tubercle of the radius, as far proximally as the neck, and as far distally as the oblique line and the insertion of the pronator teres (Figs. 348, p. 389, and 355, p. 397). The muscle is divisible into superficial and deep imrts with humeral and ulnar origins, between which the deep branch of the radial nerve passes in its course to the dorsal part of the forearm. MUSCLES ON THE DOESAL SUKFACE OF THE FOKEARM. 399 Nerve-Supply. -The supinator is shpplied by a branch from the deet) brancli of the radial nerve, which arises from the nerve before the main trunk enters tin; muscle (C. 5. 6.). Action. — The muscle is an extensor of the elbow, and the main supinator of tlie forearm. In the latter action it is assisted by the biceps. Triceps BRACK 1 1 ^— - TEKDON Brachio- RAtllALIR Lateral epicondyi.e Deep fascia of the foreami AXCON.€fS Extensor carpi radialis LONG I' S Dorsal niar^iu of ulna Extensor carpi radialis BREVia Extensor dioitorum communis Extensor dioiti quinti proprivs Extensor carpi ULNARIS Flexor carpi dlnaris Abductor polucis LONGOS Extensor inpicis proprics Extensor pollicis BREVIS Extensor pollicis lonocs Dorsal carpal ligament - Extensor carpi \ radiahs lonous ( Extensor carpi \ RADIALIS BREVIS f Extensor carpi iOR CARPI \ . ILNARIS / Triceps braciiii TENDON Brachiu- radialis ObKIIN I)F Sl'PERKICIAL EXTENSOR MI'HCLBS Annular lioa- MENT OK radios' Anconeus Extensor carpi radialis lonoi'.s Dorsal niari,'iii • of ulna Extensor carpi radialis brevis Supinator... MUSCLE Fig. 356. -Sci'ERFUiAL Muscles on the Dorsum OF THE Left Foreakm. Abductor pollicis LONOUS Dorsal marciin of ulna--— Extensor pollicis LONG US' Extensor indicis proprh Extensor pollicis brevis... Dorsal carpal ligament Extensor carpi \ RADIALIS LONGI'S f "-- Extensor carpi \ ,. radialis brevis / Extensor carpi \ .. ULNARIS / Extensor dioiti \ yUINTl PROPRIUS / Extensor — pollicis lonous Extensor indicis proprius ''" Fig. 357. — Deep Muscles on the Dorsum OF THE Left Forearm. M. Abductor Pollicis Longus. — The abductor pollicis longus (O.T. extensor ossis metacarpi pollicis) arises by fleshy fibres, distal to the supinator muscle, from the most proximal of the narrow impressions on the lateral half of the dorsal surface of the ulna; from the middle third of the dorsal surface of 400 THE MUSCULAE SYSTEM. the radius ; and from the intervening portion of the interosseous membrane (Fig. 355, p. 397). Becoming superficial in the distal part of the forearm, along with the extensor pollicis brevis, between the extensors of the wrist and the common extensor of the fingers, its tendon passes, with the latter muscle, under cover of the dorsal carpal ligament, to be inserted into the lateral side of the base of the first metacarpal bone (Fig. 356, p. 399). From the tendon, close to its insertion, a tendinous slip passes to the abductor pollicis brevis and the fascia over the thenar eminence, and another is frequently attached to the greater multangular bone. Nerve-Supply. — The dorsal interosseous nerve (C. (5.) 6. 7. 8.). Actions. — The muscle abducts the metacarpal bone of the thumb, and assists in abduction and extension of the wrist M. Extensor Pollicis Brevis. — The extensor pollicis brevis (O.T. extensor primi internodii pollicis), an essentially human muscle, is a specialised portion of the previous muscle. It arises from a rhomboid impression on the dorsal surface of the radius, and from the interosseous membrane, distal to the abductor pollicis longus (Fig. 355, p. 397). It is closely adherent to that muscle, and accompanies it deep to the dorsal carpal ligament and over the radial artery to the thumb. Its tendon is then continued along the dorsal surface of the first metacarpal bone, to be inserted into the dorsal surface of the base of the first phalanx of the thumb. Before reaching its insertion the tendon helps to form the capsule of the metacarpo-phalangeal joint. Nerve-Supply. — The dorsal interosseous nerve (C. (5.) 6. 7. 8.). Actions. — The muscle extends the wrist and thumb (or the metacarpo-phalangeal joint), and assists in abduction of the wrist and thumb. M. Extensor Pollicis Longus. — The extensor pollicis longus (O.T. extensor secundi internodii pollicis) arises from the lateral part of the dorsal surface of the ulna, in its middle third, and from the interosseous membrane, distal to the abductor pollicis longus (Fig. 355, p. 397). Its tendon grooves the dorsal surface of the radius, and occupies a special compartment under cover of the dorsal carpal ligament. Extending obliquely across the dorsal surface of the hand, the tendon crosses the radial artery, helps to form the capsule of the first metacarpo-phalangeal articulation, and is inserted into the dorsal surface of the base of the second phalanx of the thumb. At the wrist the tendons of the muscles of the thumb, the abductor pollicis longus and extensor pollicis brevis laterally, and the extensor pollicis longus medially, bound a hollow (the " anatomical snuff-box ") best seen in extension and abduction of the thumb, which corresponds to the position of the radial artery as it winds round the wrist to reach the palm of the hand. Nerve-Supply. — The dorsal interosseous nerve (C. (5.) 6. 7. 8.). Actions. — This muscle is an extensor and an abductor of the thumb, and of the wrist. > M. Extensor Indicis Proprius. — The extensor indicis proprius (O.T. extensor indicis) arises, distal to the extensor pollicis longus, from the most distal impression on the dorsal surface of the ulna, extending distally from the middle of the body to within two inches of its distal end, and sometimes also from the interosseous membrane (Fig. 355, p. 397). Its tendon passes through a compartment of the dorsal carpal ligament along with the tendons of the extensor digitorum communis. On the dorsum of the hand the tendon lies on the medial side of the tendon of the common extensor destined for tlie forefinger, and is inserted into the forefinger, joining the membranous expansion of the tendon of the extensor digitorum communis on the dorsum of the first phalanx. Nerve-Supply. — The dorsal interosseous nerve (C. (5.) 6. 7. 8.). Actions. — The muscle is an extensor of the wrist and forefinger. MUSCLES ON THE DORSAL SURFACE OF THE FOREARM. 401 Actions of the Muscles of the Forearm and Hand. These muscles are concerned in tlie movements of the elbow, wviat, and digits. In tlie majority of cases the muscles act upon more than one joint. 1. Action on the Elbow- Joint. — It lias been shown already tliat tlcxion and extension of the ilbuw are as5;isti=olely by the long extensor muscles. Separate extension of the index finger only is possible ; the three inner fingers can only be flexed and extended together, on account of the connecting bands joining the extensor tendons together on the back of tne hand. 5. Movements of the Thumb. — The movements of which the thumb is capable are flexion 27 402 THE MUSCULAK SYSTEM. and extension (occurring at the carpo-metacarpal, metacarpo-phalangeal, and inter-phalangeal joints) ; abduction and adduction, together with circumduction (occurring at the carpo-metacarpal joint). The muscles and their respective actions are given in the following table : — Flexion. Extension. Opponens poUicis { (^^0^^--^^^-?-! Flexor brevis 1 (carpo-metacarpal and Adductor ,- metacarpo-phalangeal Abductor brevis J joint) Flexor pollicis longus (all joints) Abductor pollicis J (carpo-metacarpal ' longus I joint) Extensor poiiicis/(<^^^P°:"^^t^'-^^^I'f ^^^"^ brevis 1 metacarpo-phalan- , I geal joint) Extensor pollicis longus (all joints) Adduction. Abduction. Adductor of the thumb Flexor pollicis brevis Opponens pollicis First dorsal interosseous Abductor pollicis brevis Extensors of the thumb Circumduction — a combination of the above muscles. The characteristic features of the movements of the upper limb are their range and refinement. The hand, in addition to its intrinsic powers, can be moved through a wide range and in several planes by the muscles acting on the wrist and radio-ulnar joints ; this range is increased by the fore and aft movements at the elbow-joint, and the extensive movements of which the shoulder and clavicular joints are capable. The result is that the hand can be brought into a position to cover and guard any portion of the body. The precision and refinement of movement is made possible by the co- ordinate movements of the various muscles acting upon the several joints, so that actions can be performed (as raising the food to the mouth) in which all the articulations of the limb are brought into play ; while others (such as writing) are possible by movements at the joints of the wrist and fingers along with fixation of the elbow-joint. THE LOWEK LIMB. FASCIit AND MUSCLES OF THE THIGH AND BUTTOCK. FASCI-a:. The superficial fascia of the thigh and buttock is continuous above with the fascia of the abdomen and back, medially with that of the perineum, and distally with that of the leg. It presents noticeable features in the buttock and groin. In the buttock the superficial fascia is of considerable thickness, and is usually loaded with fat, whereby it assists in forming the contour of the buttock and the fold of the nates. In the groin it is divisible into two layers : a superficial fatty layer, continuous with a .similar layer on the anterior surface of the abdominal wall above, and over the perineum medially, and a deeper membranous layer, which is attached above to the medial half of the inguinal ligament, and to the deep fascia of the thigh just distal to the lateral half of that ligament. Medially it is attached to the pubic arch, and below the level of the femoral triangle it blends inseparably with the superficial fatty layer. The separation of these two layers of the superficial fascia is occasioned by the presence between them of the inguinal and superficial subinguinal lymph glands, the great saphenous vein and its tributaries, and some small arteries. The attachment of the deeper layer of the fascia to the pubic arch and the. inguinal ligament cuts off the superficial tissues of the thigh from the perineum and the abdominal wall, and prevents the passage into the thigh of fluid collected in the perineum or beneath the fascia of the abdominal wall. FASCIA AND MUSCLES OF THE THIGH AND BUTTOCK. 403 The deep fascia or fascia lata forms a tubular investment for the muscles and vessels of the thigh and buttock. It is firmly attached above to the iliac crest, the sacro-tuterous ligament, the ischium, the pubic arch, the pubic symphysis and crest, and the inguinal ligament. In the distal part of the thigh it forms the inter- muscular septa ; and in relation to the knee, it is continuous with the deep fascia of the leg, gains attachment to the patella, the condyles of the tibia and tlie head of the tilnila, and forms the collateral ligaments of the patella. On the front of the thigh the deep fascia is thick and strong. It is pierced by numerous openings for vessels and nerves, the most important of which is the fossa ovalis (O.T. saphenous opening) for the passage of the great saphenous vein. A femoral Linea alba - Lig. fundiforme penis Spermatic funiculus Internal spermatic fascia Dorsal vein of penis OBLIQL-I'S ABDOMINIS EXTERSUS Anterior xnperior iliac spine External oblique aponeurosis Superficial circum- Hex iliac artery Intercrural fibres ( Attachment of mem- ■< branous layer of ( superficial fascia Pouparfs inguinal ligament Superficial epigastric artery Superficial external puilendal artery Superficial sub- inj;uinal lymph gland Great saphenous vein Fig. 35S. — Siterficial Anatomy ok ihe Lkft Groin. hernia passes through this opening to reach the groin and anterior abdominal waLL It is an oval opening, of variable size, situated just distal to the medial half of the inguinal ligament, and immediately anterior to the femoi'al vessels. It is covered by the superficial fascia, and by a special layer of fascia, the fascia cribrosa, a thin perforated lamina attached to the margins of the opening. The lateral edge of the opening (margo falciformis) is formed by the margin of the iliac ■portion of the fascia lata, which is attached above to the iliac crest and the inguinal ligament ; the medial edge is formed by the fascia pectinea which is continued proximally, behind the femoral sheath, over the adductor longus and pectineus muscles to the ilio-pectineal line and the capsule of the hip-joint. These two layers of the fascia lata are continuous at the distal concave margin of the fossa ovalis, forming its inferior comu. As they pass proximally towards the pelvis they occupy different 27 a 404 THE MUSCULAE SYSTEM. planes, the iliac portion being in front of the sheath of the femoral vessels, while the pectineal fascia is behind it. The superior cornu of the fossa ovalis, placed in front of the sheath, is derived solely from the iliac portion of the fascia lata. It forms a strong triangular band of fascia known as the falciform margin, attached above to the medial half of the inguinal ligament. It has an important share in directing the course of a femoral hernia upwards on to the abdominal wall. On the medial side of the thigh the fascia lata is thin where it covers the adductor muscles. At the knee it is associated with the tendons of the vasti muscles, and forms the collateral ligaments of the patella, attached to the borders of the patella and to the condyles of the tibia. On the lateral side of the thigh it Obliquus abdominis EXTERNUS (reflected) Spermatic funiculus -i- Intercolumtiar fascia Obliquus abdominis externus Obliquus abdominis internus Superior anterior iliac spine Trans VERSUS abdominis Obliquus abdominis INTERNUS (reflected) Aponeurosis of obliquus externus (reflected) Abdominal inguinal ring Spermatic funiculus and infundibuliforna fascia Fascia transversalis Inguinal aponeurotic falx -Fossa ovalis Great saphenous vein Fig. .359. — The Dissectjon of the Left Inguinal Canal. forms the tractus iliotibialis — a broad thick layer of fascia which is attached above to the iliac crest, and receives the insertions of the tensor fasciae lata3, and part of the glutseus maximus muscles ; its distal attachment is to the capsule of the knee- joint and the lateral condyle of the tibia. A strong band of fascia continued proximally from the ilio-tibial tract, beneath the tensor fasciae latae muscle, joins the tendon of origin of the rectus femoris and the capsule of the hip-joint. On either side of the thigh above the knee an intermuscular septum is formed. The lateral intermuscular septum extends medially from the ilio-tibial tract to the lateral epicondylic line and linea aspera of the femur, and gives attachment to the vastus lateralis and vastus intermedins anteriorly, and the short head of the biceps posteriorly. The medial intermuscular septum in the distal third of the thigh is associated with, and to a large extent represented by, the tendon of insertion of the adductor magnus muscle. It is also related to the fascia which envelops the MUSCLES ON THE ANTERIOR ASPECT OF THE THIGH. 405 adductor muscles, and forms the sheaths for the sartorius .ind gracilis muscles. In the middle third of the thigh the fascia under the sartorius is greatly thickened by transverse fibres and binds together the vastus medialis and adductor longus and adductor magnus muscles. This layer of fascia roofs over the femoral vessels in their course through adductor camd (Hunter's). Tlie fascia lata of the buttock is tiiick anteriorly where it covers and gives origin to the glutaius medius, thinner posteriorly over the glutseus maximus, at the upper border of which it splits to enclose the muscle. It is thickened over the greater trochanter, where it forms the insertion of the greater part of the latter muscle. On the posterior surface of the thigh and over the popliteal fossa the fascia is strengthened by transverse fibres derived from the hamstring muscles. The popliteal fascia forming the roof of the popliteal fossa is specially thick, and is usually pierced by the small saphenous vein. Femoral Sheath. — This is a conical membranous investment, derived from the fascial lining of the al)dominal cavity, the fascia transversalis in front and the fascia iliaca behind, prolonged along the femoral vessels in their passage behind the inguinal ligament into the femoral triangle. The sheath is about an inch and a half in length, and is divided into three compartments — a lateral space for the artery, an intermediate space for the vein, and a medial channel containing lymph vessels and fat, and named the femoral canal. This canal is the passage through which a femoral hernia enters the thigh. Its proximal limit is the femoral ring, bounded anteriorly by the inguinal ligament, posteriorly by the origin of the pectineus muscle from the pu])is, medially hy the ligamentum lacunare (Gimbernati), and laterally by the femoral vein. In front of it the fascia transversalis forming the sheath is thickened to form the deep femoral arch. The part of the inguinal ligament in front of the ring is called the superficial femoral arch. The inferior epigastric artery separates the ring from the abdominal inguinal ring. The canal ordinarily contains fat which is continuous above with the extra -peritoneal tissue. The ring is filled by a plug of fat or a lymph gland, constituting the femoral septum. The femoral canal ends behind the fossa ovalis, covered by the fascia cribrosa, while the falciform margin crosses over it and conceals its proximal portion. The course of a femoral hernia is determined by this band. The hernia descends through the femoral ring, pushing the femoral septum before it ; after passing through the femoral canal, it is directed forwards through the fossa ovalis. The anterior part of the hernia being pressed upon and retarded by the femoral arches, and by the falciform margin, the posterior part pushes onwards, hooks round the falciform margin, and is directed upwards over the inguinal ligament. The coverings of a femoral hernia, in addition to peritoneum and extra-peritoneal tissue (femoral septum), are femoral sheath, fascia cribrosa, superficial fascia, and skin. MUSCLES OF THE THIGH AND BUTTOCK. The muscles of the thigh and buttock are divisible into four main groups by their situation, action, and nerve-supply. On the anterior surface of the thigh are the quadriceps femoris, the sartorius, ilio-psoas, and pectineus muscles ; on the medial side of the thigh are the adductor muscles ; in the region of the buttock are the glutsei and rotators of the hip-joint ; and on the posterior aspect of the thigh are the hamstring muscles. THE MUSCLES ON THE ANTERIOR ASPECT OF THE THIGH. The chief muscle on the anterior aspect of the thigh is the quadriceps femoris, which occupies the space between the tensor fascite latoe and ilio-tibial tract laterally, and the sartorius medially. The sartorius crosses the thigh obliquely ; it separates the quadriceps femoris from the adductor muscles ; it forms in the proximal third of the thigh the lateral boundary of the femoral triangle, and in 27 & 406 THE MUSCULAE SYSTEM. Psoas majok Tensor fasci.b LAT^ •— Ilio-tibial tract __ Gracilis the middle third of the thigh, the roof of adductor canal (Hunter's). The ilio-psoas, passing into the thigh beneath the inguinal liga- ment, assists, along with the pectineus and adductor muscles, in forming the floor of the femoral triangle. M. Sartorius. — The sartor- ius, a long strap-like muscle, arises from the superior anterior spine of the ilium and half of the margin of the notch below it (Fig. 360). It passes distally in the thigh, across the medial side of the knee, and is inserted, by aponeurotic fibres, into the medial surface of the body of the tibia just distal to the medial condyle, and by its borders into fascial expansions which join the capsule and the tibial collateral ligament of the knee-joint, and the fascia lata of the leg (Fig. 363, p. 408). The sartorius is superficial in its whole extent. Its proximal third forms the lateral boundary of the femoral triangle ; its middle third forms the roof of the ad- ductor canal ; and its distal third, in contact with the medial side of the knee, is separated from the tendon of the gracilis muscle by the saphenous nerve and the saphenous branch of the arteria genu suprema. A bursa lies be- neath the tendon at its insertion. Nerve -Supply. — The sartorius is supplied by two sets of nerves associated with the two intermediate cutaneous branches of the femoral nerve (L. 2. 3.). Actions. — The sartorius, " the tailor's muscle," is a flexor of the hip and knee joints. It also everts the thigh and assists in medial rotation of the tibia. M. Quadriceps Femoris. — The quadriceps femoris is com- posed of four muscles — the rectus femoris, vastus lateralis, vastus intermedius, and vastus medialis. The rectus femoris is super- ficial except at its origin, which is covered by the glutsei, sartorius, and tensor fasciae latte muscles. The vasti lie on either side of the rectus muscle, the vastus lateralis being partially concealed by the tensor fasciae latee and ilio-tibial tract, the vastus medialis by the sartorius Rectus femoris Vastus medialis Tendon ok RECTUS femoris Fig. 360.- LlOAMENTUM PATELL/K -The Muscles of the Anteuior Aspect of THE Right Thigh. ririfoftiiis (iiiHertiuti) MUSCLES ON THE ANTElilOK ASPECT OF THE THIGH. 407 muscle. The vastus intermedius envelops tlie femur, and is concealed by the other muscles. M. Rectus Femoris. — The rectus femoris has a double tendinous origin. (1^ The straight head arises from the inferior anterior spine of the ilium (Fig. 366, p. 412) ; (2) the reflected head springs from a rough groove on the dorsum ilii just above the highest part of the acetabulum (Fig. 306, p. 412;. A bursa lies beneath this head of origin. The two heads, bound together and connected to the capsule of the hip-joint by a band of fascia derived from the deep surface of the tensor fascise latre (ilio-tibial tract), give rise to a single tendon which extends, for some distance, on tlie anterior surface of the muscle, and from which the muscular fibres arise. The muscular fibres springing from this tendon, and also from a median septal tendon, present a bipennate arrangement, and end below in a broad tendon whicli passes proximally, for some distance, along the posterior surface of the muscle. This tendon gradually narrows towards the knee, and spreading out again, is inserted into the proximal border of the patella. It receives laterally and medially J^'k- 361 parts of the insertions of the lateral and medial vasti muscles, and on its deep surface is joined by the insertion of the vastus intermedius, A bursa, which communi- cates with the synovial membrane of the knee-joint, lies between the tendon and the front of the distal end of the shaft of the femur. Muscle-Attachments to the An- terior Surface ok the i'koximal part ok the Left Fe.muh. Va.STUS MEDIAl.IS Saphenous nerv(!.. y^, Frtiiioral vessel Adductor longus — i Adductor macinu.s Gracilis SE.MIMKMBRANOSIS Rectus kemoris Vastus lateralis Vastus intermedius Fpiiinr liic Ei's Femoris (short head) BiiEPS Fkmorls (long head) Semitendinosus Sciatic nerve Fio. 362.— Transverse Section of the Thigh (Hunter's Adductor Canal). 1V[. Vastus Lateralis. — The vastus lateralis has an origin, partly fleshy, partly -membranous, from (1) the capsule of the hip-joint, (2) the tubercle of the femur, (3) a concave area on the anterior surface of the shaft of the bone medial to the 27 c 408 THE MUSCULAE SYSTEM. Semi-membranosus (insertion) Ligamentum patellae (insertion) Popliteus (insertion) Attachment of tibial col- lateral ligament of the knee Gracilis (insertion) greater trochanter, (4) the distal border of the greater trochanter, (5) the lateral margin of the gluteal tuberosity of the femur and the tendon of the glutseus maximus, (6) the proximal half of the linea aspera, and (7) the fascia lata and . lateral intermuscular septum (Fig. 360, p. 406). It forms a thick, broad muscle directed distally and forwards, and is inserted by a broad membranous tendon into (1) the lateral border of the tendon of the rectus femoris, (2) the proximal and lateral border of the patella, and (3) the capsule of the knee-joint and the fibular collateral ligament of the patella. A bursa intervenes between it and the membranous insertion of the glutaius maximus. M. Vastus Medialis. — The vastus medialis is larger than the vastus lateralis and has a more extensive origin, from (1) the distal two-thirds or more of the spiral line, the linea aspera, and the proximal two -thirds of the line leading from the linea aspera to the medial condyle of the femur ; (2) the membranous ex- pansion of the fascia lata which lies beneath the sartorius and forms the roof of the adductor canal ; and (3) the medial intermuscular septum and the tendon of the adductor magnus (Figs. 359, p. 404, and 365, p. 410). From its origin the muscle is directed distally and laterally towards the knee ; it is inserted by a strong aponeurotic tendon into (1) the medial border of the rectus tendon ; (2) into the proximal and medial border of semi-tendinosus (insertion) the patella; and (3) the capsule of the knee-joint and the collateral liga- ment of the patella. The muscle con- ceals the medial side of the body of the femur and the vastus intermedius, with which it is closely incorporated in its distal two-thirds. M. Vastus Intermedius. — The vastus intermedius muscle (O.T. crureus) arises by fleshy fibres from (1) the proximal two-thirds of the body of the femur on the anterior and lateral Fig. 363.— Muscle- Attachments TO THE Medial Side surfaces — but not the medial surface; OF THE PROX.MAL PART OF THE RiGHT TiBIA. ^3) the distal half of thC ktcral ]ip of the linea aspera and the proximal part of the line leading therefrom to the lateral condyle ; and (3) a corresponding portion of the lateral intermuscular septum (Fig. 359, p. 404). For the most part deeply placed, the muscle is directed distally to an insertion into the deep surface of the tendons of the rectus and vasti muscles by means of fibres which join a membranous expansion on its surface. It is closely adherent to the vastus lateralis muscle in the middle third of the thigh ; it is inseparable from the vastus medialis below the proximal third. In the distal third of the thigh it conceals the articularis genu muscle, a bursa, and the proximal prolongation of the synovial membrane of the knee-joint. M. Articularis Genu. — The articularis genu (O.T. subcrureus) muscle consists of a number of separate bundles of muscular fibres arising deep to the vastus intermedius from the distal fourth of the anterior surface of the femur, and inserted into the synovial membrane of the knee-joint. The four elements composing the quadriceps femoris muscle have been traced in their convergence to the patella. Their ultimate insertion is into the tubercle of the tibia (Fig. 363), by means of the ligamentum patellae, and the vasti MUSCLES ON THE ANTERIOR ASPECT OF THE THIGH. 409 muscles are in addition connected with the collateral ligaments of the patella. The patella, indeed, is in one sense a sesamoid bone formed in the tendon of the muscle, the lig'amentu'm patellse being the real tendon of insertion, and the collateral ligume^nts fascial expansions from its borders. The insertion of the nmscle forms the anterior part of the capsule of the knee-joint. Midillf arcuate ligament Vena caval opening Aortic opening ^^ ^ (Esophageal opening in diaphragm Anterior ranni.s of twelftli tlioracic ner\e QuadKitus liiniboruiii Ilio-liypOKastric. nerve Uio-inguinal- Lateral cutaneous nerver of thigh Femoral ner\ CJenito-femoral nerve Obturator ner\e-r-T Descentiiiig branch of fourth lumbar' nerve Anterior ramus. of fifth lumbar nerve Medial au^l . lateral liimb")- Vcostal arches Ant. ramus of twelfth "ilioracic nerve ..Quadratus lumboiuiii -Ilio-liypoga.stric nerve nio-inguinal ^soas nijyor Genito-femoral nerve Lateral .cutaneous nerve of thigh -Jliacus Lumbo-sacral trunk Femoral nerve Obturator neno Fiu. 364.— The Vessels and Nervbs on the Posterior Abdominal Wall. Nerve-Supply.— The parts of the quadriceps extensor are supplied by separate branches of the femoral nerve (L. 3. 4.). Actions. — The quadriceps muscle is the great extensor of the leg at the knee-joint. The articuliiris genu draws proximally the synovial sheath of the joint during this movement. The rectus femoris is in addition a flexor of the hip-joint. The straight head acts when the movement begins ; the reflected head is tightened when the thigh becomes bent. The ilio-psoas muscle is a compound muscle, consisting of two elements,-— psoas (major and minor), connecting the femur and pelvic girdle to the axial 410 THE MUSCULAE SYSTEM. Piriformis (insertion) Glutieus mepex of the lesser trochanter of the femur (Fig. 365). A bursa, which may be continuous with the synovial cavity of the hip- joint, separates the tendon from the pubis and the capsule of the hip-joint. M. Psoas Minor. — The psoas minor (O.T. parvus) is often absent (40 per cent). It arises from the intervertebral fibro-car- tilage between the last thoracic and first lumbar vertebrae, and from the contiguous margins of those vertebrae. The muscle is closely apposed to the anterior surface of the psoas major. It forms a slender fleshy belly, and is inserted, by a narrow tendon, into the middle of the linea terminalis and the ilio-pectineal eminence, its margins blending with the fascia covering the psoas major. M. Iliacus. — The iliacus muscle arises in the pelvis major by fleshy fibres, mainly from a horseshoe-shaped origin around the margin of the iliac fossa ; it has additional origins also from the ala of the sacrum, the anterior sacro-iliac, lumbo-sacral, and ilio-lumbar ligaments, and outside the pelvis, from the proximal part of the capsule of the hip-joint (ilio-femoral ligament). It is a fan-shaped muscle, and its fibres pass distally over the hip-joint towards the lesser trochanter of the femur. Lying lateral to the psoas muscle, it passes through the femoral triangle, and is inserted by fleshy fibres (1) into the lateral side of the tendon of the psoas major ; (2) into the concave anterior and upper surfaces of the lesser trochanter ; and (3) into the body of the femur distal to the lesser trochanter for about an inch (Fig. 365) ; and (4) by its most lateral fibres into the capsule of the hip-joint. These fibres are often separate, forming the iliacus minor, or iliocapsularis. Glutap.us maxim us (insertion) Adductor magnus (insertion) Adductor brevis (insertion) Pectinens (insertion) Vastus medial is (origin) Fig. 365. — Muscle- Attachments to the Posterior Aspect OF THE PROXIMAL PART OK THE LEFT FeMUR. Nerve-Supply.- The psoas major is supplied directly by branches from the anterior rami of the second and third lumbar nerves with additional branches in some cases from the first and fourth. THE MUSCLES. ON THE MEDIAL SIDE OF THE THIGH. 411 The psoas minor receives a nerve from tlie Orst or second lumbar nerve. The iliacUB is supplied bv branches from the femoral nerve (L. 2. 3. 4.) within the abdomen. Actions. -The psoas minor assists the j)soas major in Hexing forwards and laterally the vertebral column. Besides this action the psoas major acts with the iliacus muscle as a flexor of the hip-joint. Witli the thighs fixed the two muscles can draw the trunk downwards. M. Pectineus. — The pectineus muscle arises by fleshy fibres from, (1) the sharp anterior portion of the linea terminalis' of the pubis, and the triangular surface of the pubic bone in front of the linea terminalis (Fig. 3G6, p. 412), (2) the femoral surface of the ligamentum lacunare, and (3) the pectineal portion of the fascia lata which covers it. Forming a l)road muscular band, which lies in the floor of the femoral triangle, medial to the ilio-psoas, it is inserted by a thin flat tendon, about two inches in length, into the proximal half of the pectineal line, leading from the back of the lesser trochanter of the femur towards the linea aspera ; its distal attachment being placed in front of the insertion of the adductor brevis muscle (Fig. 365, p. 410). The muscle may be occasionally divided into medial and lateral parts, the former innervated by the obturator, the latter by the femoral nerve, i Nerve-Supply. — The pectineus is always supplied by a branch of the femoral nerve (L, 2. 3.; which passis medially behind the femoral vessels to enter its lateral border. It receives in some instances an additional nerve from the obturator, or when that is present, the accessory obturator nerve. Actions. — The muscle is mainly an adductor of the hip-joint. It is also a flexor of the hip. THE MUSCLES ON THE MEDIAL SIDE OF THE THIGH. The muscles on the medial side of the thigh include the adductors of the femur — the adductor longus, adductor brevis, and adductor magnus ; the gracilis, and the obturator externus. The gracilis is superficially placed along the medial side of the thigh. The adductor muscles are placed in the medial part of the thigh between the hip bone and the femur, and in different vertical planes. The adductor longus is in the same plane as the pectineus and lies superficially in the femoral triangle ; the adductor brevis, on a more posterior plane, is in contact with the obturator externus, and along with it is largely concealed by the pectineus and adductor longus ; the adductor magnus, the largest apd most posterior of these muscles, is in contact with the other adductors and the sartorius anteriorly, while its posterior surface is in relation to the hamstring muscles on the back of the thigh. M. Gracilis. — The gracilis muscle is a long flat band placed on the medial side of the thigh and knee. It arises by a tendon from the lower half of the edge of the symphysis pubis, and for a similar distance along the border of the pubic arch (Fig. 366, p. 412). Its flattened belly passes distally, on the medial side of the thigh to the knee, to end in a tendon, placed between the sartorius and semitendinosus, which expands to be inserted into the medial surface of the body of the tibia just distal to the medial condyle, behind the sartorius, and proximal to and in front of the semitendinosus (Fig. 376, p. 420). It is separated from the sartorius tendon by a bursa, and deep to its tendon is another bursa, common to it and the semi- tendinosus. It is superficial in its whole extent. Nerve-Supply. — Obturator nerve (L. 2. 3.). Actions. — The gracilis has a threefold action. It adducts the thigh, and it flexes and rotates medially the tibia. M. Adductor Longus. — The adductor longus is a triangular muscle which lies in the floor of the femoral triangle and the floor of adductor canal (Hunter's). It arises from the anterior surface of the body of the pubis in the angle between the crest and symphysis (Fig. 366, p. 412). It extends distally and laterally, it is inserted into the middle two-fourths of the medial lip of the linea aspera in front of the adductor magnus. 412 THE MUSCULAR SYSTEM. Nerve-Supply. — Obturator nerve (L. 2. 3.). Actions. — The muscle adducts and assists in flexing the thigh. M. Adductor Brevis. — The adductor brevis is a large muscle which arises from an elongated oval surface on the front of the body and upper part of the inferior ramus of the pubic bone, surrounded by the other muscles of this group (Fig. 366). Directed distally and laterally the muscle expands, to be inserted, by a short aponeurotic tendon, behind the insertion of the pectineus, into the distal two- thirds of the line leading from the lesser trochanter of the femur to the linea aspera, and to the proximal fourth of the linea aspera itself (Fig. 365, p. 410). Nerve-Supply. — Obturator nerve (L. 2. 3. 4.). Actions. — The muscle adducts and flexes the thigh. Rectus feiuoris (straight head of origin) . Rectus femoris (reflected head of origin) . Attachment of ilio-feiuoral ligament Pyramidalis abdominis (origin) Rectus abdominis (origin) racilis (origin) Adductor brevis (origin) Semimembranosu: ^__ (origin) U m ^ Quadratus femoris "'' "' (origin) Biceps and semitendin- osus (origin) Fig. 36(5. — MuscLE-ATXACHMENXti to the Outer Suuface of the Right Pubis and Ischium. M. Adductor Magnus.— The adductor magnus, the largest of the adductor group, is a roughly triangular muscle. It arises, mainly by fleshy fibres, by a curved origin from the lower part of the lateral border and a large portion of the adjoin- ing inferior surface of the sciatic tuberosity, from the edge of the inferior ramus of the ischium, and from the anterior surface of the inferior ramus of the pubic bone, its most anterior fibres arising between the obturator externus and adductor brevis (Fig. 366). Its upper fibres are directed horizontally and laterally from the pubic bone towards the proximal part of the femur; the lowest fibres are directed distally from the sciatic tuberosity to the medial condyle of the femur ; while the intermediate fibres radiate obliquely laterally and distally. The muscle is inserted by tendinous fibres (1) into the space distal to the insertion of the quadratus femoris, proximal to the linea aspera; (2) into the THE MUSCLES ON THE MEDIAL SIDE OF THE THIGH. 413 whole length of the linea aspera ; (3) into the medial epicondylic line of the femur ; (4) into the adductor tubercle on the medial condyle of the femur : and (5) into the medial intermuscular septum (Fig. 365, p. 410). The part of the muscle attached to the space proximal to the linea aspera is often separated from the rest as the adductor minimus. The attachment of the muscle to the epicondylic ridge is interrupted for the passage of the femoral vessels into the popliteal fossa. The attachment to the medial condyle is by means of a strong tendon which receives the fibres arising from the ischium (the part of the muscle associated with the hamstring group). This tendon is closely connected with the tibial collateral ligament of the knee-joint. The muscle is covered, anteriorly, by the other adductors and by the sartorius muscle. The profunda femoris artery separates it from the adductor longus muscle. Obturator nerv Pubi Psoas majoi Branch to hip-joint Deep brancli Superficial branch Descending muscular branches Pectineus Ascending branch to obturator extern us Medial circumflex artery Adductor long us Adductor brevis Cutaneous branch Sacrum Piriformis GLUT^:rs maximus Pelvic fascia Obturator internus Obturator externus Ischium Deep branch of medial circum- flex artery of femur QUADRATUS FEMORIS Superflcial branch of medial circumflex artery Descending uiuscular branches Adductor maonus Branch to knee-joint Branch to femoral artery Gracii. Fig. 367.— Scheme of the Course and Distribution of the Right Obturator Ner\t!;. while the femoral artery is in contact with the muscle as it pursues its course through the adductor canal. The posterior surface of the muscle is in relation with the hamstring muscles. Nerve-Supply.— The adductor niagnus is a double muscle, and has a double nerve-supply. The medial part of the mupcle •■xtending between the tuber ischiadicum and the medial condyle of the femur, associated with the hamstring group of muscles, derives its nerve from the nerve to the hamstring muscles, from the tibial nerve (L. 4. 5. S. 1.). This enters the muscle on its posterior surface. i i. j v v. r The adductor portion of the muscle is supplied on its anterior surface by the deep branch of the obturator nerve (L, 3. 4.). Actions. — The adductor magnus is an adductor and extensor of the thigh. M. Obturator Externus.— The obturator externus is placed deeply, under cover of the previous muscles. It is a fan-shaped muscle lying horizontally in the angle between the hip bone and the neck of the femur. It arises from the surfaces of the pubic bone and ischium, which form the inferior half of the margin of the obturator foramen, and from the corresponding 414 THE MUSCULAE SYSTEM. portion of the superficial surface of the obturator membrane (Eigs. 366, p. 412 and 367, p. 413). Its fibres converge towards the greater trochanter, and end in a stout tendon which, after passing distal to and posterior to the hip-joint, Sacro-tuber- is inserted into the trochan- ment^^' tcric fossa of the greater tro- glutjeus chanter of the femur fEigs. MAXIMUS £~k n ^ A u- V O Obturator 365, p. 410, and 373, p. 417). INTERNUS Biceps AND Nsrve-Supply.— Tlie deep part of the obturator nerve (L. 3. 4.). Actions. — This muscle is mainly a lateral rotator of the thigh ; it also flexes and adducts it. Fascia lata , SBMITENDIN- osus _Semimem- ""branosus quadratus "■"FBMORIS Adductor MAGNUS Trigonum Femorale. — The femoral triangle (O.T. Scarpa's triangle) is a large triangular space on the front of the thigh in its proximal third, which contains the femoral vessels in the proximal part of their course and the femoral nerve. It is bounded above by the inguinal liga- ment, laterally by the sartorius, and medially by the medial border of the adductor longus muscle. Its floor is formed laterally by the ilio-psoas, and medially by the pectineus, adductor longus, and a small part of the adductor brevis. Canalis Adductorius Hunteri. — The adductor canal (O.T. Hunter's Biceps caual) lics in the middle third of the (short head) j^^edial sidc of the thigh, and contains the femoral vessels in the distal part of their course. It is bounded superficially by the sartorius, under which is a dense fascia derived from the fascia lata, binding to- gether the vastus medialis, which forms the lateral wall of the canal, and the adductors, longus and raagnus, which form the medial wall or floor of the canal. Be- sides the femoral vessels and their sheath, the canal contains the saphenous nerve. ■Gracilis Biceps (long head) Semimem- branosus THE MUSCLES OF THE BUTTOCK. This group includes the three glutsei muscles, the tensor fascise latae, piriformis, obturator internus and gemelli, and quad- ratus femoris. The glutseus maximus and tensor fasciae lat£e muscles are in the same plane, invested by envelopes of the fascia lata. The glutteus medius, partially covered by the glutseus maximus, conceals the glutseus minimus ; while the piriformis, obturator internus, gemelli, and quadratus femoris intervene between the glutseus maximus and the posterior surface of the hip-joint. Fio. 368. — Deep Muscles on the Postehior Aspect of the Right Thigh. THE MUSCLES OF THE BUTTOCK. 415 M. Glutaeus Maximus. — The glutaeus maximus is a large quadrilateral muscle, with a cresceutic origin. It arises from, (1) a portion of the area on the dorsum ilii above the posterior gluteal line (Fig. 369); (2) the tendon of the sacro- spinalis muscle; (3) the dorsal surface of the sacrum and coccyx (Fig. 395, p. 443) ; and (4) the posterior surface of the sacro-tuberous ligament. The fibres which form its su})erior and lattsral border take origin directly from the fascia lata which envelops the muscle. The muscle forms a large fleshy mass, whose fibres are directed obliquely over the buttock, invested by the fascia lata, and are inserted, by short tendinous fibres, partly into the f^iscia lata over the greater trochanter of the femur (joining the ilio-tibial tract), and partly into the gluteal tuberosity (Fig. 370, p. 416). The fascia lata receives the insertion of the whole of the superficial fibres of the muscle and the superior. half of the deep fibres. The inferior half of the deep portion of ()blir(iiu8 extenius abdominis (insertion) Gluteus maximus (origin) Tensor fasciie lata; (origin) Sartorius (origin) Rectus femoris (reflected;.hea(l of origin) Gemellus superior (origin) Gemellus inferior (origin) Semimembranosus (origin) Biceps and semitendinosus (origin) Quadi-atus femoris (origin) Obturator externus (origin) Adductor magnus (origin) Adductor magnus (origin) Fio. 369. — Muscle- Attachments to the Right Dorsum Ilii and Tuber Ischiadicum. the muscle is inserted, for the most part, into the gluteal tuberosity ; but the most inferior fibres of all are inserted into fascia lata, and are thereby connected with the lateral intermuscular septum and the origin of the short head of the biceps. The glutaeus maximus is the coarsest and heaviest muscle in the body. By its weight it helps to form the fold of the nates. It is superficial in its whole extent. The glut?eiis medius is visible at its superior border, covered by the fascia lata ; at its lower border the hamstring muscles and sciatic nerve appear on their way to the thigh. Three burste are deep to it : one (not always present) over the sciatic tuberosity, a second over the lateral side of the greater trochanter, and a third over the vastus lateralis. The fibres of the glutieus maximus arising from the coccyx may form a separate muscle (agitator caudae). Nerve-Supply. — Inferior gluteal nerve, from the sacral plexus (L. 5. S. 1. 2.). Actions. —The glutteiis maximus is mainly an extensor of the thigh, and has a powerful action in straightening the lower limlj, as in climbing or running. Its lower fibres also adduct the thigh and rotate it laterally. M. Tensor Fasciae Latse. — The tensor fasciae latse arises from the iliac crest 416 THE MUSCULAR SYSTEM. Piriformis (insertion) Glutseus mediiis (insertion Obturator internus and ;emelli (insertion) Obturator externus (insertion) Quadratus femoris (insertion) Ilio-psoas (insertion) Gluteus maximus (insertion) Adductor magnus (insertion) Adductor brevis (insertion) Pectineus (insertion) Vastus medialis (origui) and the dorsum ilii just lateral to the superior anterior spine, and from the fascia covering its lateral surface (Fig. 369, p. 415). Invested, like the glutaeus maximus, by the fascia lata, it is inserted, distal to the level of the greater trochanter of the femur, into the fascia, which forms the ilio- tibial tract (p. 404). The muscle is placed along the an- terior borders of the glutseus medius and glutseus minimus. Nerve - Supply. — The superior gluteal nerve from tlie sacral plexus (L. 4. 5. S. 1.) ends in tliis muscle after passing between the glutoeus medius and glutaius minimus. Actions. — It assists in the abduction and rotation of the thigh ; and along with the glutseus maximus, by its in- sertion into the ilio-tibial tract, it helps to support the knee-joint in the extended position. M. Glutaeus Medius. — The glutseus medius arises from (1) the dorsum ilii, be- tween the iliac crest and posterior gluteal line above and the anterior gluteal line below (Fig. 369, p. 415), and (2) the strong fascia lata covering its surface anteriorly. It is a fan-shaped muscle, its fibres oon- FiG. .370. — Muscle -Attachments to the Posterior Aspect of the proximal part of the Left Femur. verging to the greater tro chanter, to be inserted by a dorsai'iasc'ia strong, short tendon into the postero-superior angle of the greater trochanter, and into a well-marked diagonal line on its lateral surface (Fig. 3V0, and Fig. 372, p. 417). A bursa is placed deep to the tendon at its insertion. The muscle is partly super- ficial, partly concealed by the glutseus maximus. It covers the glutseus minimus, and the superior gluteal nerve and the deep branches of the superior gluteal artery. Nerve -Supply. —The superior gluteal nerve from the sacral plexus (L. 4. 5. S. 1.). Actions. — This muscle is a powerful abductor and medial rotator of the thigh. M. Glutseus Minimus. — The glutseus minimus arises, under cover of the glutseus Lumbo- — ^m The lumbar triangle OF Petit Fascia lata Glut-4:us maximus- Gracilis Abductor maonus Semimembranosus Semitendinosus Ficj.'371. — The Iticiir (ii.rr.Ki .s Maximus Muscle. THE MUSCLES OF THE BUTTOCK. 417 medius, by fleshy fibres, from the dorsum ilii between gluteal hues (Fig. 369, p. 415). This muscle is tan-shaped and its fibres converge to of the greater tro- chanter, to be inserted into tlie anterior sur- face of the trochanter, and sometimes also into the front part of the superior border (Figs. 361, p. 407, and 373). It is also inserted into the cap- sule of the hip-joint. A bursa is placed deep to the tendon in front of the greater p^ervetobiuX trochanter. ititemus Nerve-Supply.— The superior gluteal nerve from the sacral plexus (L. 4. 5. S. 1.). Actions. — The mus- cle is 2>riiuarily an ab- ductor of the thigh. Its anterior fibres in addition produce medial rotation and its posterior fibres lateral rotation of the limb. the anterior and inferior the antero-superior angle Gracilis Adductor maonus Hamstrino muscles (biceps) Superior gluteal nervrt Glut/Eus medics (cut) Inferior gluteal nerve Piriformis Obturator intkksus AND fiEMELLI Obturator exter.vus quadratvs kemoris Sciatic nerve (and subdivisions) Posterior cutaneous nerve of thigh GLUT.eUS MAXIMUS (insertion) \I>DlTTOR MAONUS Fig. 372.— The Muscles and Nerves of the Right Buttock. The ghiteeuR niaximiis is reflected ; and the glutoeus medius is cut, in part, to show the glutaeus minimus. Glutit'us minimus (insertion) Piriformis (insertion) M. Piriformis. — The piriformis is one of the few mus- cles connecting the lower limb to the axial skeleton. It arises (1) within the pelvis from the roots of the vertebral arches of the second, third, and fourth sacral vertebrae, and from the adjacent part of the bone lateral to the anterior sacral foramina. Passing out through the greater sciatic foramen, it receives an origin from (2) the upper margin of the greater sciatic notch Obturator intemus and gemelli (insertion) ^^^^^H^^^^^ of the ilium, and (3) the pelvic surface of the sacro-tuberous ligament. In the buttock it forms a rounded ten- don, which is inserted into a facet on the superior border and medial aspect of the greater trochanter of the femur (Figs. 370, p. 416, and 373). The piriformis, at its origin, covers part of the inner surface of the posterior wall of the pelvis minor. In the buttock it is covered by the gluteus maximus, and lies behind the capsule of the hip-joint, between the gluteus medius and superior gemellus. Nerve-Supply. — Branches direct from the anterior rami of the first and second sacral uerve.s. 28 (insertion) Fig. 373. — MusclEtAttachments to the Proximal Aspect of the Greater Trochanter of the Left Femur. 418 THE MUSCULAR SYSTEM. Actions. — Tlie muscle is an abductor and lateral rotator of the liij). M. Obturator Internus. — The obturator internus arises on the pelvic aspect of the hip bone, from (1) the whole of the margin of the obturator foramen (except the obturator notch) ; (2) the surface of the obturator membrane ; (3) the whole of the pelvic surface of the hip bone behind and above the obturator foramen ; and (4) the parietal pelvic fascia covering it. medially. It is a fan-shaped muscle. Its fibres converge to the lesser sciatic foramen, and end in several tendons, united together, which hook round the margin of the foramen (a bursa intervening), and after passing over the posterior surface of the hip-joint, are inserted into a facet on the medial surface of the greater trochanter of the femur above the trochanteric fossa (Figs. 370, p. 416, and 373, p. 417). In the pelvis minor the muscle occupies the side wall, covered by the parietal pelvic fascia, which separates it from the pelvic cavity above and the ischio-rectal fossa below. In the buttock the tendon is embraced by the gemelli muscles which are attached to its superior and inferior margins. The gemelli muscles form accessory portions of the obturator internus. M. Gemellus Superior. — The superior gemellus arises from the gluteal surface of the ischial spine (Fig. 369, p. 415). It is inserted into the upper margin and superficial surface of the tendon of the obturator internus muscle. M. Gemellus Inferior. — The gemellus inferior arises from the superior part of the gluteal surface of the ischial tuberosity (Fig. 369, p. 415). It is inserted into the inferior margin and superficial aspect of the tendon of the obturator internus. Nerve-Supply. — The obturator internus and superior gemellus receive branches from a special nerve, the nerve to the obturator internus from the anterior aspect of the sacral plexus (S. 1. 2. 3.). The inferior gemellus is supplied by the nerve to the quadratus femoris, a branch derived also from the anterior aspect of the sacral plexus (L. 4. 5. S. 1.). Actions. — The obturator internus and gemelli are abductors and lateral rotators of the hip. M. Quadratus Femoris. — The quadratus femoris arises from the lateral margin of the tuber ischiadicum (Figs. 366, p. 412, and 369, p. 415). It is inserted into the quadrate tubercle and quadrate line of the femur (Fig. 370, p. 416). The muscle is concealed by the glutseus maximus and the hamstring muscles. Its anterior surface is in contact with the obturator externus muscle and the lesser trochanter of the femur, a bursa intervening. The muscle is not infrequently fused with the adductor magnus. Nerve-Supply. — A special nerve from the sacral plexus (L. 4. 5. S. 1.) which enters its deep (anterior) surface. Actions. — The muscle is an adductor and lateral rotator of the thigh. THE MUSCLES ON THE POSTERIOR ASPECT OF THE THIGH. The Hamstring Muscles. The muscles comprised in this series include the biceps, semitendinosus, and semimembranosus. A part of the adductor magnus, already described, also belongs, morphologically, to this group. They lie in the buttock and posterior aspect of the thigh, and diverge at the knee to bound the popliteal fossa. The origins of thi muscles are concealed by the glutseus maximus. In the back of the thigh, enveloped by the fascia lata, they are placed behind the adductor magnus — the semitendinosus and semimembranosus medially, the biceps laterally. The former two muscles help to form the medial boundary of the popliteal fossa, of which the biceps is a lateral boundary. M. Biceps Femoris. — The biceps femoris has a double origin. (1) Its long head arises, by means of a tendon, in common with the semitendinosus, from the inferior and medial facet upon the sciatic tuberosity (Figs. 366, p. 412, and 369, p. 415) and from the sacro-tuberous ligament. This head, united for a THE MUSCLES ON THE POSTERIOR ASPECT OF THE THIGH. 419 distauce of two or three inches with the semiteudinosus, forms a separate Heshy mass, which exteuds to the distal third of the thigh, to end in a tendon joined by the short head of the muscle. (2) The short head arises separately from, (1) the whole length of the lateral lip of the linea aspera and the proximal two-thirds of the lateral epicondylic line of the femur, and (2) the lateral intermuscular septum. The proximal limit of its origin is sometimes blended with the insertion of the lowest fibres of the glutieus maximus. Tiie fibres of the short head, directed distally, join the tendon of the long head, and the muscle is inserted (1) into the head of the fibula by a strong tendon, which is split into two parts by the filular collateral ligament of the knee-joint ; (2) by a slip attached to the lateral condyle of the tibia ; and (3) along its posterior border by a fascial expansion which connects the tendon with the popliteal fascia. Obliquus externus alxloininis (insprtion) Tensor fasciae latae Glutiuusmaxiinii.s (origin) Rectus feinoris (retlected head of origin) Gemellus suiierior (origin) Gemellus inferior (origin) Semimembranosus (origin) Biceps and seinitendinosus (origin) Quadratus femoris (origin) Obturator extemus (origin) Adductor magnus (origin) Ailductor magnus (origin) ' Fig. 374. — Muscle-Attachments to the Right Dohsc.m lui and Tl'ber Ischiadiccm. There is a bursa between the tendon and the fibular collateral ligament of the knee-joint. The short head may be absent : there may be an additional origin from the ischium or femur ; and the long head may send a slip to the gastrocnemius or teiido calcaneus (Acliillis) (tensor fasciae suralis). M. Semitendinosus. — The semitendinosus arises, in common with the long head of the biceps, from the inferior and medial facet upon the ischial tuberosity (Fig. 374, p. 419). Separating from the common tendon, two or three inches from its origin, the muscle forms a long, narrow band which becomes tendinous in the middle third of the thigh. Passing over the medial side of the knee it spreads out and becomes membranous, and is inserted (1) into the medial side of the body of the tibia just distal to the medial condyle, distal to the gracilis and behind the sartorius (Fig. 376, p. 420), and (2) into the deep fascia of the leg. A bursa separates it from the sartorius superficially, and another, conimon to it and the gracilis, lies deep to its insertion. The belly of the muscle is marked by an oblique septal tendinous intersection about its middle. 420 THE MUSCULAE SYSTEM. Obturator INTERN us ANDGEMELLI Nerve-Supply. — The semitendinosus is supplied by two branches from the nerve to the hamstring muscles (L. 5. S. 1. 2.) Actions. — A flexor of the knee, a medial rotator of the tibia, and an extensor of the hip. M. Semimembranosus.— The semimembranosus arises by a tendon from the superior and lateral facet on the ischial tuberosity (Figs. 366, p. 412, and 374, p. 419). In the proximal tlMrd of the thigh the tendon gives place to a rounded fleshy belly, which lies an- terior to the ischial portions of the biceps and semitendinosus muscles. Becoming tendinous, at the back of the knee, it is inserted into the horizontal groove on the postero- medial aspect of the medial condyle of the tibia (Eigs. 376, below, and 384, p. 428). A bursa lies deep to the tendon at its insertion. It has three additional membranous inser- tions : (1) a fascial band extends distally and medially to join the posterior border of the tihial collateral ligament of the knee-joint; (2) an- other fascial band extends distally Adductor magnus Semitendinosus Semimembranosi's 8artoriu.s tendon Tibial nerve Biceps tendon (with common peroneal nerve) Plantaris Semimembran- osus (insertion) Ligamentum patellse (insertion) Popliteus (insertion) Attaclinient of tibial collateral ligament Gracilis (insertion) Gastro- cnemius Semitendinosus (insertion) Fig. 375. — The Muscles on the Postkrioh Aspect of the Right Thigh. Fig. 376. — Muscle- Attachments to the Medial surkace of the proximal part of the Right Tibia. and laterally, forms the fascia covering the popliteus muscle {popliteus fascia), and is attached to the oblique line of the tibia ; and (3) a third strong band extends proximally and laterally to the back of the lateral condyle of the femur, forming the oblique popliteal ligament of the knee-joint. THE MUSCLES ON THE POSTERIOR ASPECT OF THE THIGH. 421 The membrauous origin of the muscle is concealed by the proximal parts of the semitendinosus aud loug liead of the biceps. The insertion covers the origin of the inner head of the gastrocnemius. Nerve-Supply. — It is innervated by the nerve to the hamstring muscles (L. 5. S. 1. 2.). Actions. A flexor of the knee, a medial rotator of the tibia, and an extensor of the hip. • Actions of the Muscles of the Thigh and Buttock. Most of the above muscles act on the pelvis and on the hij)- and knee-joints. The psoas major muscle in addition assists in the movements of the vertebral column (p. 411). 1. Movements at the Hip- Joint. — The movements of the thigh at the liip-joint are flexion and extension, adduction and abduction, medial and lateral rotation. The following table gives the muscles~producing these movements :■ — u. Flexion and Extension. Sartorius Qlutaeus maximus Iliacus „ medius Psoas majot „ minimus Rectus femoris Bicejjs femoris Pectineus Semitendinosus Adductor longus Semimembranosus Gracilis Adductor magnus Obturator externus b. Adduction and Abduction. Pectineus Tensor fascise latae Adductor longus Glutaeus medius „ brevis „ minimus ,, magnus Obturator externus Gracilis Piriformis ^ Quadratus femoris Obturator internus Glutaeus maximus Gemelli during (lower fibres) Sartorius Glutaeus maximus flexion (upper fibres) 1 c. Medifil Rotation and Lateral Rotation. Tensor fasciae latae Glutaeus medius (anterior fibres) „ minimus „ „ Obturator externus ' Glutaeus maximus (lower fibres) Quadratus femoris Glutajus medius \ (posterior „ minimus j fibres) Piriformis "i^^,^^ Obturator internus [^^^^^^^^^ Gemelli J Sartorius liio-psoas Pectineus Adductor longus „ brevis „ magnus Biceps femoris 2. Movements of the Pelvis on the Thigh.— It is to be noted that the several movements tabulated above refer to the movements of the femur at the hip-joint. The contraction of the same groups of muscles produces similar movements of the pelvis on the femur, exemplified in the various changes in the attitude of the pelvis in relation to the thigh and the vertebral column, which occur in locomotion. 3. Movements at the Knee-Joint. — The movements at the knee-joint are mainly flexion and extension. Flexion is much more powerful than extension. There is also a limited amount of rotation of the tibia. The movements are produced by certain of the muscles described above, associated with certain of the' muscles of the leg. 422 THE MUSCULAR SYSTEM. a. Flexion an d Extension. b. Rotation medially and Rotation laterally. Sartorius Quadriceps femoris Sartorius Biceps femoris Gracilis Gracilis Semitendinosus S emitendinosus Semimembranosus Semimembranosus Biceps femoris Popliteus Gastrocnemius Plantaris 1 ! Popliteus i THE FASCIA AND IVIUSCLES OF THE LEG AND FOOT. FASCIiE. The superficial fascia of the leg and foot presents no special features except in the sole, where it is greatly thickened by pads of fat, particularly under the tuberosity of the calcaneus, and under the balls of the toes. The deep fascia has numerous important attachments about the knee. Posteriorly it forms the popliteal fascia, and is joined by expansions from the tendons of the sartorius, gracilis, semitendinosus, and biceps femoris muscles. In front of the knee it is attached to the patella, the Ugamentum patellae, and the tubercle of the tibia ; medially and laterally it is connected to the condyles of the tibia and the head of the fibula, and helps to form the collateral patellar ligaments — broad fascial bands which pass obliquely from the sides of the patella to the condyles of the tibia, and are joined by fibres of the vasti muscles. Passing into the leg, the fascia blends, over the medial surface of the tibia, with the periosteum of the bone. It extends round the lateral side of the leg from the anterior crest to the medial border of the tibia, binding together and giving origin to the muscles, and gaining an attachment to the distal part of the body of the fibula. Two septa pass from its deep surface ; one septum (anterior peroneal septum), attached to the anterior crest of the fibula, encloses the superficial peroneal nerve, and separates the extensor from the peroncei muscles. The other septum (posterior peroneal septum) is attached to the lateral crest of the fibula, and separates the peronsei from the flexor muscles. From the last-named septum another extends across the back of the leg ; it forms a partition between the superficial and deep flexor muscles, and encloses the posterior tibial vessels and the tibial nerve. It gives rise to subordinate septa attached to the vertical line of the tibia and the medial crest of the fibula, which separate the tibialis posterior from the flexors of the toes on either side. At the ankle the deep fascia is strengthened by additional transverse fibres, which give rise to thickened bands named the ligamentum laciniatum, lig. trans- versum cruris, lig. cruciatum cruris and the retinaculum of the peroneal muscles. They were formerly known as the annular ligaments. The ligamentum laciniatum (O.T. internal annular ligament) stretches between the medial malleolus and the tuberosity of the calcaneus. While it is continuous, at its proximal border, with the general investment of the deep fascia, it is chiefly formed by the septal layer covering the deep muscles on the back of the leg. It sometimes gives insertion to the plantaris muscle. It is continuous, distally, with the plantar aponeurosis, and gives origin to the abductor hallucis muscle. It is pierced by the calcanean vessels and nerve. Along with the posterior tibial vessels and the tibial nerve, the tendons of the tibiahs posterior, flexor digitorum longus, and flexor hallucis longus, pass beneath it, each enclosed in a separate mucous sheath. The superior peroneal retinaculum (O.T. external annular ligament) is a thickened band of the deep fascia stretching between the lateral malleolus and the calcaneus. It binds down the tendons of the peronsei, which occupy a space beneath the ligament, lined by a single mucous sheath ; while the inferior THE FASCIA AND MUSCLES OF THE LEG AND FOOT. 423 EXTKNSOK HALLUCIS LONOUS Deep peroneal nerve an dorsalis pedis arter Extensor dioitorum lonous PER0N,*:U3 TERTir Fibula Interosseous talc- calcaneal ligament Calcaneus PEBON.fiUS BREVIS Peroneal retinaculum PER0N,«U3 LONOUS Abductor digiti quinti Plantar aponeurosis — Lig. transversum cruris. Tibialis anterior Talus Tibialis posterior peroneal retinaculum liiuds them down separately on the lateral surfaces of the calcaneus. Tlie ligamentum transversum cruris (O.T. anterior annular ligament, upper band), l)roa(l and umlelined at its proximal and distal borders, stretches across the front of tlie ankle between the two malleoli. This band binds down, to the distal end of the tibia, the tendons of the tibialis anterior and extensor muscles of the toes. One mucous sheath is found deep to it, surrounding the tendon of the tibialis anterior. Ligamentum Cruciatum Cruris. — On the dorsum ol" the foot, where the general covering of deep fascia is much thinner, a special well-defined band, named the ligamentum cruciatum cruris (O.T. anterior annular ligament, lower band), stretches over the extensor tendons. It has an attachment laterally to the lateral border of the dorsal surface of the calcaneus. It divides into two bands as it passes medially over the dorsum of the foot — a proximal -part, which joins the lig. transversum cruris and is attached to the medial malleolus, and a distal part, which passes across the dorsum of the foot, and joins the fascia of the sole at its medial border. Deep to this liga- ment are three special compart- ments with separ- ate mucous sheaths, one for the tibialis anterior tendon, a second for that of the extensor hal- lucis longus, and a third for the ex- tensor digitorum longus and per- onseus tertius ten- dons. There are occasionally other additional bands of the deep fascia passing, like the straps of a sandal, across the dorsum of the foot. The plantar aponeurosis is of great importance. In the centre of the sole it forms a thick triangular band, attached posteriorly to the tuberosity of the calcaneus. It spreads out anteriorly and separates into Jive slips, which are directed forwards to the bases of the toes. These slips as they separate are joined together by ill-defined bands of transverse fibres, which constitute the superficial transverse metatarsal ligament (fasciculi transversi aponeurosis plantae). The slip for each toe joins the tissue of the web of the toe and is continuous with the digital sheath. It splits to form a band of fibres directed forwards on each side of the toe to be attached to the sides of the metatarso-phalangeal articulation and the base of the first phalanx. This central portion of the plantar aponeurosis assists in preserving the arch of the foot, by drawing the toes and the calcaneus together. On each side it is continuous with a much thinner layer, which covers the lateral and medial muscles of the sole and joins the fascia of the dorsum of the foot at each border. It also gives rise to intermuscular septa, which pass deeply on each side of the flexor digitorum brevis, enclosing that muscle in a separate sheath, and giving investments on either side to the abductor muscles of the great and little toes. At the lateral border of the foot the calcaneo-metatarsal ligament, a thickened band of the fascia, connects the tuberosity of the calcaneus with the base of the fifth metatarsal bone. Ligamentum laciniatum Flexor dioitorum plantar artery ial plantar nerve KXOB HALLUCIS LONOUS AliDUCTOR HALLUCIS Lateral plantar nerve ^\Lateral plantar artery ^VFlEXOR dioitorum BRKVIS Fig. 377. — Frontal Section through the Left Ankle-Joint, Talcs, AND Calcaneus. 424 THE MUSCULAE SYSTEM. The digital sheaths, though smaller, are the same in arrangement as those of the lingers (p. 389). Vaginal ligaments are present in relation to the first and second phalanges. THE MUSCLES OF THE LEG AND FOOT. The muscles of the leg and foot are divisible into three series : (1) the extensor muscles on the front of the leg and dorsum of the foot ; (2) the peronaei on the lateral aspect of the leg ; and (3) the flexor muscles on the back of the leg and in the sole of the foot. The Muscles on the Front of the Leg and Dorsum of the Foot. The muscles on the front of the leg and dorsum of the foot include two groups: (1) on the front of the leg, the tibialis anterior, long extensors of the toes and peronseus tertius ; and (2) on the dorsum of the foot, the extensor digitorum brevis, and ex- tensor hallucis brevis. On the front of the leg the tibialis anterior and the extensor digitorum longus and peronseus tertius are superficially placed, and conceal the extensor hallucis longus muscle. On the dorsum of the foot the extensor digitorum brevis muscle lies beneath the tendons of the long extensor of the toes. M. Tibialis Anterior. — The tibialis anterior arises from the lateral condyle and the proximal two -thirds of the lateral surface of the body of the tibia, from the inter- osseous membrane from the fascia over it, and from an intermuscular septum laterally. The muscle ends in a strong tendon which passes over the dorsum of the foot, to be inserted into a facet on the medial surface of the first cuneiform and the medial side of the base of the first metatarsal bone (Fig. 379, p. 425). Its tendon occupies special compartments beneath both liga- mentuni transversum and lig. cruciatum cruris, enclosed in a separate, single, mucous sheath. Tlie tibio-fascialis anterior is a separated jjortion of the muscle occasionally present, inserted into tlie fa-scia on the dorsum of the foot. Nerve-Supply.— Deep ])eroneal nerve (L. 4. 5. S. 1.). - 'Actions.— The muscle is a dorsi-fiexor of the ankle, and (in combination witli tlie tibialis posterior) it invests the foot. Calcaneo- meta tarsal band Fig. 378. — The Lekt Plantau Fascia. THE MUSCLES OF THE LEG AND FOOT. 425 M. Extensor Digitorum Longus. — The extensor digitorum longus arises, by flesliy fibres, from the lateral side of the lateral condyle of the tibia, from the proximal two-thirds or more of the anterior part of the medial surface of tlie body of tlie fibula, from the fascia over it, and from intermuscular septa on either side. It gives rise to a tendon which passes deep to the ligamentum transversum and cruciatum, and in front of the ankle subdivides into four tendons, inserted into the four lateral toes, exactly in the same way as the corresponding tendons in the hand (see p. 397). They form membranous expansions on the dorsum of the first phalanx, joined by the tendons of the extensor digitorum brevis, lumbricales, Abductor dfgiti quinti (origin) Quadratus plantae (origin) Long plantar ligament Plantar ealcaneo-cuboid ligament Tibialis posterior (part of insertion) ¥ Peronaeus brevis (insertion) Flexor digiti quinti brevis (origin) Adductor hallucis (origin of oblique head) Flexor digitorum brevis (origin) Abductor liallucis (origin) Allaclinieiits of plantar calcaneo- navicular ligament Flexor hallucis brevis (origin) Tibialis posterior (main part of insertion) Peronaius longus (insertion) Tibialis anterior (insertion) Fk;. 379. — Muscle- Attachments to Lkft Tarsus and Metatarsus (Plantar Aspect). and interossei, each of which separates into one central and two collateral slips, attached respectively to the middle and terminal phalanges. The tendon occupies a separate compartment, along with the peronaeus tertius, deep to the ligamentum cruciatum cruris, invested by a special mucous sheath. Nerve-Supply. —Deep peroneal nerve (L. 4. 5. S. 1.). Actions. — A dorsi-flexor of the ankle and an extensor of tlie four lateral toes. M. Peronseus Tertius. — The peronaeus tertius is a separated portion of the extensor digitorum longus. It is an essentially human muscle. It arises (insepar- ably from the extensor digitorum longus) from the anterior part of the medial surface of the fibula, and from the inter-muscular septum lateral to it. 426 THE MUSCULAE SYSTEM. The tendon of the muscle is inserted into the dorsal aspect of the base of the fifth metatarsal bone. Nerve-Supply, — Deep peroneal nerve (L. 4. 5. S. 1.). Actions. — The muscle dorsi-flexes the ankle and raises the lateral border of the foot (as in skating or dancing). M. Extensor Hallucis Longus. — The extensor hallucis longus arises from the anterior part of the medial surface of the fibula in its middle three -fifths, medial to the origin of the 'extensor digitorum longus, and for a corresponding extent from the interosseous membrane. Its tendon passes over the dorsum of the foot, to be inserted into the base of the terminal phalanx of the great toe. The extensor primi internodii longus and extensor ossis metatarsi hallucis are occasional separate slips of this muscle inserted into the proximal phalanx and the metatarsal bone. Nerve-Supply. — Deep peroneal nerve (L.4. 5. S. 1.). Actions, — This muscle dorsi-flexes the ankle, and extends the great toe. ; M. Extensor Digitorum Brevis. — The extensor digitorum brevis arises, on the dorsum of the foot, from a special impression on the dorsal surface of the calcaneus, and from the deep surface of the ligamentum cruciatum cruris. It usually gives rise to four fleshy bellies, from which narrow tendons are directed for- wards and medially, to be inserted into the four medial toes. The three lateral tendons join those of the long extensor muscle to form the membranous expansions on the dorsum of the toes. The most medial tendon (ex- tensor hallucis brevis) is inserted separately into the base of the first phalanx of the great toe. Nerve -Supply, — Deep peroneal nerve (L. 4, 5. S, 1.). Actions, — Extension of the four medial toes. SOLEUS Extensor digitorum LOKOUS PERON.E0S LONGUS Peron/Eus brevis Ligamentum cruci- atum cruris Tendon of peron.«us TEKTIUS Most medial slip of extensor digitorum BREVIS (extensor hallucis brevis) The Muscles on the Lateral Side of the Leg. These muscles comprise the peronsei, — longus and brevis. They are placed on the lateral side of the leg between the extensor digitorum longus in front, and the soleus and flexor hallucis longus behind, enclosed in a special compartment of the deep fascia. M. Peronseus Longus. — The peronaeus longus arises from the head and the proximal two-thirds of the lateral surface of the body of the fibula, from intermuscular septa on either side, and from the fascia over it. It forms a stout tendon, which lies superficial to the peronteus brevis, hooks round the lateral malleolus deep to the peroneal retinaculum, crosses the lateral side of the calcaneus, and, passing through a groove on the cuboid bone, is directed across the sole of the foot to be inserted into the lateral sides of the first cuneiform and the Fig. 380. — Muscles of the Fuont ok the Right Leg and Dorsu,m of the Right Foot THE MUSCLES ON THE LATERAL SIDE OF THE LEG. 427 base of the first metatarsal bones (Fig. 379, p. 425). As it enters the sole of the foot a jihro -cartilage is formed in the tendon, which plays over a smootli tubercle on the cuboid bone, a burs;i intervening. In its passage across the foot the tendon is enclosed in a sheath derived from the long plantar (long calcaneo-cuboid) ligaments and the tibialis posterior tendon. i.ONia's I'KRON^US IKKVIS Nerve - Supply. - Superficial peroneal uervo (L. 4. 5. S. 1.). Actions. — An extensor of the ankle; this muscle also everts the foot. It strengthens the arch of the foot' by its passage across the sole to its insertion. Semimkmbkanosls TESDON (cut) Tibial nerve and popliteal vessels Plantauis tkndok (cut) Fig. 381. — The Insertions of the Tibialis POSTKlilOR AND PERONJiDS LONGUS IN THE SOLE OF THE Left Foot. M. Peronaeus Brevis. — The peronaeus brevis arises by fleshy fibres t'roui the distal two- thirds of the lateral surface of the body of the fibula, and from an intermuscular septum along its anterior border. Its tendon grooves the back of the lateral malleolus and the lateral side of the calcaneus, invested by a mucous sheatli common to it and the perouccus longus, and is inserted into the tuberosity and dorsal surface of the base of the fifth metatarsal bone. The peronieus longus and brevis may be fused together, or additional slips may be present, as peronseus accessorius, peronaeus digiti quinti, peronaocalcaneus externus, and peronseocuboideus. TENDO CALCANEI.-S Li;,'ani('ntuiii laciniatuiu PF.UOX.ffS LONOt'S Suiierior it-tina- culuiii of peroneal muscles Nerve - Supply. — Superficial peroneal nerve (L. 4. b. S. 1.). Actions. — An extensor of the ankle and an evertor of the foot Fig. 382. — The I^ight Soleus Mosclk. 428 THE MUSCULAR SYSTEM. Medial head of gastrocnemius Plantaris Lateral head or i^g OASTROCNEMIl'S Semimem- branosus Popliteus ' (insertion) Soleus (origin)' Tibialis -posterior (origin) The IVIuscIes on the Posterior Aspect of the Leg. The muscles on the back of the leg are divisible into two groups, superficial and deep. The superficial group comprises the gastrocnemius and soleus (constituting to- gether the triceps surae) and the plantaris. They form the prominence of the calf of the leg. The gastrocnemius is superficial except at origin, where the two bellies, forming the boundaries of the pop- liteal fossa, are over- lapped by the tendons of the hamstring mus- cles. The soleus muscle is partially concealed by the gastrocnemius and plantaris, and be- comes superficial in the distal part of the leg on each side of the common tendon (tendo calcaneus). M. Gastrocnemius. —The gastrocnemius arises by hvo heads, medial and lateral, by means of strong ten- dons which are pro- longed over the surface of the muscle. The lateral head arises from an impression on the proximal and posterior part of the lateral sur- face of the lateral con- dyle of the femur, and from the distal end of the lateral epicondylic line ; while the medial head arises from a prominent rough mark on the popliteal surface of the femur, proximal to the medial epicondyle and posterior to the adductor tubercle. Each head has an ad- ditional origin from the back of the capsule of the knee-joint. A bursa lies deej) to each ^'i« tendon of origin. Each fleshy belly of the muscle is inserted, separately, into a broad membranous tendon, prolonged proximally on its deep surface for some distance. The medial head is the larger. The tendo calcaneus is formed by the union of the two membranous insertions Plexor hallucis LONG OS PeRON/KUS brevis Plexor fligitonim longus (origin) Liganientiini laoini- atuin Tendo calcaneus Peroneal rBtinaculiim Fig. .383. — The Dbep Muscles on- Back OF THE Right Leg. 384. — Muscle - Attach- ments TO THE Posterior Surface of the Right Tibia. THE MUSCLES ON THE POSTERIOR ASPECT OF THE LEG. 429 of tlie bellies of the gastrocuemius. Prolonged proximal ly beneath the separate bellies, the tendon forms a broad membranous band connecting together the distal parts of the two bellies. Narrowing gradually, and becoming thicker in the distal half of the leg, the tendon is finally inserted into the posterior aspect of the calcaneus. A bursa lies deep to the ttiudou at its insertion. The tendo calcaneus also affords insertion to the soleus and (sometimes) the plantaris muscles. Nerve-Supply. Each head of tlio muscle is innervated by a branch from the tibial nerve (S. 1. ±). Actions. - Tiie muscle is a poweriul flexor of the knee and extensor ot the ankle. M. Plantaris, — The plantaris arises by fleshy fibres from the lateral epicondylic line of the femur for about an inch at its distal end, from the adjacent part of the popliteal surface of the femur, and from the oblique ligament of the knee-joint. It forms a narrow fleshy slip which ends in a tendon that extends distally in the back of the leg, to be inserted into, the medial side of the tuberosity of the cal- caneus, or the tendo calcaneus, or the ligamentum laciniatum. The tendon of the muscle is capable of considerable lateral extension. The plantaris lies between the lateral head of the gastrocnemius and the soleus. In the distal half of the leg its tendon lies along the medial border of the tendo calcaneus. The muscle is not always present. Nerve-Supply.— Tibial nerve (L. 4. 5. S. 1.). Actions. — Tlie muscle is an accessory flexor of the knee and extensor of the ankle. M. Soleus. — The soleus has a triple origin from (1) the posterior surfaces of the head and the proximal third of the body of the fibula ; (2) a fibrous arch (arcus tendineus m. solei) stretching, over the popliteal vessels and tibial nerve, between the tibia and fibula ; and (3) the oblique line, and the middle third of the medial border of the tibia (Fig. 384, p. 428). From their origin the proximal muscular fibres are directed distally to join a tendon, placed on the superficial aspect of the muscle, which is inserted into the tendo calcaneus ; the more distal fibres are inserted directly into the tendo calcaneus to within one or two inches of the calcaneus. Nerve-Supply. — Two nerves supply this muscle. One from the tibial nerve in the popliteal space enters its superficial surface (S. 1. 2.) ; the other from the tibial nerve in the back of the leg supplies the deep surface of the muscle (L. 5. S. 1. 2.). Actions. — The soleus is a powerful extensor of the ankle. The deep muscles of the back of the leg comprise the popliteus, flexor digitorum longus, flexor hallucis longus, and tibialis posterior. The popliteus muscle is deeply placed behind the knee-joint, in the floor of the popliteal fossa, and is covered by the popliteal vessels and tibial nerve. The flexor digitorum longus lies behind the tibia, the flexor hallucis longus behind the fibula, and the tibialis posterior, lying between them, is related to the interosseous mem- brane and both bones of the leg. All these muscles are concealed by the superficial group, and are bound down to the bones of the leg by layers of the deep fascia. M. Popliteus. — The popliteus arises, by a stout tendon, from a rough impression in front of a groove on the lateral aspect of the lateral epicondyle of the femur. The tendon passes between the lateral meniscus and the capsule of the knee-joint, and pierces the posterior ligament, from which it takes an additional fleshy origin. A bursa is placed on the medial side of the tendon, and it usually communicates with the synovial cavity of the knee-joint. The muscle is inserted, by fleshy fibres, (1) into a triangular surface on the back of the tibia above the oblique hne (Fig. 384, p. 428), and (2) into the fascia over it (the popliteus fascia, derived from the. tendon of the semimembranosus muscle). The popliteus minor is a small occasional muscle attached to the popliteal surface of the femur and the posterior ligament of the knee-joint. Nerve-Supply. — Tlie popliteus is supplied by a branch of the tibial nerve (L. 4. 5. S. 1.), which winds round the distal border of the muscle and enters it in its deep surface. Actions. — A medial rotator of the tibia and flexor of the knee. 430 THE MUSCULAK SYSTEM. M. Flexor Digitorum Longus. — The flexor digitorum longus lies in both the back of the leg aud the sole of the foot. Its origin is, by fleshy fibres, from the posterior surface of the Ijody of the tibia in its middle three-fifths, distal to the oblique line, and medial to the vertical line and the origin of the tibialis posterior . from the fascia over it, and from an intermuscular septum on each side / (Fig. 384, p. 428). Its tendon, after crossing obliquely over the tendon of the tibialis posterior, passes deep to the ligamentum laciniatum, in- vested in a special mucous sheath, and enters the sole of the foot. There it crosses superficially the tendon of the flexor hallucis longus, and finally divides into four sub- ordinate tendons, which are inserted into the four lateral toes in pre- cisely the same manner as the flexor digitorum profundus is in- serted in the hand (p. 389). Each tendon enters the digital sheath of the toe, perforates the tendon of the flexor digitorum brevis, and is inserted into the base of the ter- minal phalanx. Vincula accessoria (longa and brevia) are present as in the hand. The tendon of the flexor haUucis longus sends a fibrous band to the tendon of the flexor digitorum longus as it crosses it in the «ole of the foot ; the band usually passes to the tendons destined for the second and third toes. Associated with this muscle in the sole of the foot are the lumbricales and quad- ratus plautaj muscles. Mm. Lumbricales. — The lum- bricales are four small muscles which arise in association with the tendons of the flexor digitorum longus in the sole. The ^rs^ 7nuscle arises by a single origin from the tibial side of the tendon of the flexor digitorum longus for the second toe ; each of the other three arises by two heads from the ad- jacent sides of two tendons. Each muscle is inserted into the dorsal expansion of the extensor Fig. 385. —The Muscles OF THB Right Foot (Secoml Layer), tendon, the metatarso- phalangeal capsule, and the base of the first phalanx, ^Jrecisely as in the case of the lumbrical muscles of the hand. Each muscle passes forwards on the tibial side of the corresponding toe, superficial to the transverse metatarsal ligament. Nerve-Supply. — The flexor digitorum longus is supplied by the tibial nerve (L. 5. S. 1.). The first lumbrical is supplied by the medial plantar nerve (L. 4. 5. S. 1.) ; the other three, by the lateral plantar nerve (S. 1. 2.). ■ Actions. — The flexor digitorum longus extends the ankles and flexes the four lateral toes. LUMBRICALS Flexor hallucis BREVIS Flexor digitorcm LON'GUS Flexor digiti quinti beevis quadeatus PLANTS Abductor hallucis Abductor digiti QUIKTI PEROX.EUS LONGUS Flexor digitorum LONGUS Flexor hallucis LONGUS Long plantar ligament THE MUSCLES ON THE POSTERIOK ASPECT OF THE LEG. 431 The lumbrical muscles liave a similar action to those of tlie hand ; they flex the metatarso- ])halangeal, and extend tlie interphalangeal joints of the four lateral toes. M.Quadratus Plantae. — The quadratus plantse (O.T.accessorius) arises by two heads: (1) tlie lateral tendinous head springs from the lateral border of the plantar surface of the calcaneus and from the lateral border of the long plantar ligament ; (2) the medial head, which is fleshy, arises from the concave medial surface of the calcaneus in its whole extent, and from the medial border of the long plantar ligament (Fig. 379, p. 425). The long plantar ligament separates the two origins. The two heads unite to form a flattened band, which is inserted into the dorsal aspects of the tendons of the flexor digitorum longus, and usually into those destined for the second, third, and fourth toes. In the sole of ^he foot the tendons of the flexor digitorum longus, along with the luml)ricales and quadratus plantse, and the flexor hallucis longus muscles, constitute the second layer of muscles, lying between the abductors of the great and little toes and the flexor digitorum brevis superficially, and the flexor brevis and adductor of the great toe more deeply. Nerve-Supply. — Lateral plantar nerve (S. 1. 2.). Actions. — The muscle is an accessory flexor of the toes, assisting the long flexor of the toes. It tends to draw the tendons into which it is inserted into the middle of the sole of the foot. M. Flexor Hallucis Longus. — The flexor hallucis longus arises, on the back of the leg, between the tibialis posterior and the peromei muscles, from the distal two-thirds of the posterior surface of the Ijody of the fibula, from the fascia over it, and from intermuscular septa on either side. Its tendon passes deep to the ligamentum laciniatum, enclosed in a special mucous sheath, and after grooving the posterior surface of the distal end of the tibia, the talus, and the plantar surface of the sustentaculum tali of the calcaneus, it is directed forwards in the sole of the foot, to be inserted into the base of the terminal phalanx of the great toe. In the foot it crosses over the deep aspect of the tendon of the flexor digitorum longus, and gives to it a strong fibrous slip, which is prolonged into the tendons for the second and third toes. Nerve-Supply.— Tibial nerve (L. 5. S. 1. 2.). Actions. — The muscle is one of the most important in the leg and foot. It is an extensor of the ankle and a flexor of the great toe. By its position in relation to the tarsus and inferior calcaneo-navicular ligament, it has an important share in maintaining and supporting the arch of the foot. M. Tibialis Posterior. — The tibialis posterior has a fourfold fleshy origin in the leg. It arises (1) from the proximal four-tifths of the medial surface of the body of the fibula between the medial crest and the interosseous crest ; (2) from the distal part of the lateral condyle, and from the proximal two-thirds of the liody of the tibia, distal to the oblique line and between the vertical line and the interosseous border (Fig. 384, p. 428) ; (3) from the interosseous membrane ; and (4) from the fascia over it and the septa on either side. The muscle gives rise to a strong tendon which passes deep to the ligamentum laciniatum, invested by a special mucous sheath, and grooves the back of the medial malleolus, on its way to the medial border of the foot. After crossing over the plantar calcaneo-navicular ligament between the sustentaculum tali and the navicular bone, the tendon spreads out and is inserted by three bands into (1) the tubercle of the navicular bone and the plantar surfaces of the first and second cuneiform bones, (2) the plantar aspects of the bases of the second, third, fourth, and sometimes the fifth metatarsal bones, the second and third cuneiform bones, and the groove on the cuboid, and (3) into the medial border of the sustentaculum tali of the calcaneus (Fig. 379, p. 425). Tlie peronaeo-calcaneus muscle, when present, arises from the fibula, and is inserted into the calcaneus;. Nerve-Supply.— Tibial nerve (L. 5. S. 1.). Actions. — The muscle extends the ankle and inverts the foot. 432 THE MUSCULAK SYSTEM. The IVIuscIcs in the Sole of the Foot. The muscles in the sole of the foot are divisible into four layers placed deep to the plantar aponeurosis. The first layer includes the abductor hallucis, flexor digitorum brevis, and abductor digiti quinti. The second layer consists of the lumbricales and quadratus plantae, together with the tendons of the flexor hallucis longus and flexor digitorum longus. The third layer comprises the flexor hallucis brevis, adductor hallucis, and Abductor digiti quinti (origin) Quadratus plantse (origin/ Long plantar ligament Planter calcaneo-cuboKi ligament Tibialis posterior (part o( insertion^! Peronseus brevis (insertion) Flexor digiti quinti brevis (origin) Adductor halb.icis (origin of oblique. head) Flexor digitorum brevis (origin) xlbductor hallucis (origin) Attachments of plantar calcaneo- navicular ligament Flexor hallucisbrevis (origin) Tibialis posterior ^main partof insertion) Peronseus longus (insertion) Tibialis anterior (insertion) Fig. .386. — Muscle-Attachments to Left Tarsus and Mi;tatausus (Plantar Aspect). flexor digiti quinti brevis. T\iQ fourth layer consists of the interossei (plantar and dorsal), placed between the metatarsal bones : and the tendons of insertion ot the tibialis posterior and peronseus longus. FIRST LAYER. M. Abductor Hallucis.— The abductor hallucis has a double origin: (1) by a short tendon from the medial side of the medial process of the tuberosity of the calcaneus (Fig. 386), and (2) by fleshy fibres from the ligamentum laciniatum, the plantar aponeurosis which covers it, and the intermuscular septum between it and the flexor digitorum brevis. The muscle lies superficially, along the medial border of the sole ; its tendon is THE MUSCLES IN THE SOLE OF THE FOOT. 433 PlaiiUr aponeurosis inserted, along with part of the flexor hallucis brevis into the medial side of the base of the tirst phalanx of the great toe. Nerve-Supply. — Medial plantar nerve (L. 4. 5. S. 1.). Actions. A flexor and abductor of the great toe. M. Flexor Digitorum Brevis. — Tlie flexor digitorum brevis has likewise a double origin: (1) from the an- terior part of the medial process of the tuberosity of the calcanens (Fig. 386, p. 432), and (2) from the tliick central part of the plantar aponeurosis which covers it, and from the intermuscular septa on either side. It passes forwards, and gives rise to four slender tendons, which are inserted into the second phalanges of the four lateral toes, after having been perforated by the long flexor tendons, just as in the case of the tendons of the flexor digitorum sublimis of the hand (p. 389). Nerve-Supply. — Medial plantar nerve (L. 4. 5. S. 1.). Actions. — The muscle is a flexor of the toes, acting on the metatarso- phalangeal and first inter-phalangeal articulations of the four lateral toes. M. Abductor Digiti Quinti. — The abductor digiti quinti also has a double origin: (1) by fleshy and tendinous fibres from the anterior part of both pro- cesses of the tuberosity of the calcaneus, partly concealed by the flexor digitorum brevis (Fig. 386, p. 432), and (2) by fleshy fibres from the lateral portion of the plantar aponeurosis and the cal- caneo- metatarsal ligament, and from the intermuscular septum between it and the flexor digi- torum brevis. Its tendon lies along the fifth metatarsal bone, and is inserted into the lateral side of the pos- terior end of the first phalanx of the little toe. The most lateral fibres usually obtain an ad- ditional insertion into the lateral side of the plantar surface of the fifth metatarsal bone. Fourth lumbrical Third lumbrical Second..., lumbrical First lumbrical Flexor hallucis longus Fia. 387. — Superficial Muscles of the Right Foot. Nerve-Supply, — Lateral plantar nerve (S. 1. 2.). Actions. — Flexion and abduction of the little toe. SECOND LAYER. The tendons of the long flexors of the toes, the lumbricales and quadratus planta muscles, constituting the second layer of muscles, have already been described 29 434 THE MUSCULAR SYSTEM. Long plantar ligament Flexor hal- lucis lonous Flexor digi- torum lonous quadratus , PLANTS < (origins) '■ Peron^us LONG us (p. 430). They lie deep to the abductor hallucis and the flexor digitorum brevis, and occupy the hollow of the tarsus and the space between the first and tifth metatarsal bones; their deep surfaces are in contact with the adductor of the great toe and the interossei muscles. THIRD LAYER. M. Flexor Hallucis Brevis. — The flexor hallucis brevis arises by tendinous fibres from (1) the medial part of the plantar surface of the cuboid bone (Fig. 386, p. 432), and (2) the tendon of the tibialis posterior. Directed forwards, over the first metatarsal bone, the muscle separates into two parts, between which is the tendon of the flexor hallucis longus. Each portion gives rise to a tendon which is inserted into the corresponding side of the base of the first phalanx of the great toe ; in each tendon, under the metatarso- phalangeal articulation, a sesamoid bone is developed. The medial tendon is united with the insertion of the abductor, the lateral tendon with the insertions of the adductor muscle of the great toe. Nerve - Supply. — Medial plantar nerve (L. 4. 5. S. 1.). Actions. — A jflexor of the metatarso- phalangeal joint of the great toe. M. Adductor Hallucis. — The adductor hallucis consists of two parts. The oblique head of the muscle arises (1) from the sheath of the peronseus longus, and (2) from the plantar surfaces of the bases of the second, third, and fourth metatarsal bones (Eig. 386, p. 432). It lies in the hollow of the foot, on a deeper plane than the long flexor tendons and lum- bricales, and on the lateral side of the flexor hallucis brevis, and it runs obliquely medially and forwards, to be inserted on the lateral side of the base of the first phalanx of the great toe between and along with the flexor brevis Flexor digiti — quinti brevis Flexor hal- — lucis brevis interosseous" MUSCLES Adductor hallucis"" (oblique head) Adductor hallucis (transverse head) Fig. .388. — Deep Muscles of the Sole of the Foot. and the transverse head of the adductor hallucis. The transverse head arises from (1) the capsules of the lateral four metatarso- phalangeal articulations and (2) the transverse metatarsal hgament. It runs transversely medially under cover of the flexor tendons and lumbricales, the muscle is inserted, along with the oblique head, into the lateral side of the base of the first phalanx of the great toe. Nerve-Supply.— Lateral plantar nerve (S. 1. 2.). Actions.— Flexion and adduction of the great toe towards the middle line of the foot. THE MUSCLES IN THE SOLE OF THE FOOT. 435 M. Flexor Digiti Quinti Brevis. — The flexor digiti quinti brevis arises from (1) the sheath of the peronaeus longus and (2) the base of the fifth metatarsal bone (Fig. 380, p. 432). Partially concealed by the abductor digit! quinti, the muscle passes along the fifth metatarsal bone, to be inserted, in common with that muscle, into the lateral side of the base of the first phalanx of the little toe. Nerve-Supply. — Lateral plantar nerve (S. 1. 2.). Actions. — Flexion of the little toe. Fig. 389. — Interosseous Muscles ok the Right Foot. FOURTH LAYER. Mm. Interossei. — The interossei muscles of the foot resemble those of the hand except in one respect. In the hand the line of action of the muscles is the middle line of the middle finger. In the foot the second toe is the digit round which the muscles are grouped, and their attachments and their actions diHer accordingly. There are four dorsal and three plantar muscles, which occupy to- gether the four in- terosseous spaces, and project into the hollow of the foot. The four dorsal muscles, one in each interosseous space, arise by two heads each from the shafts of adjacent metatarsal bones. Each gives rise to a tendon, which, after passing dorsal to the transverse metatarsal ligament, is inserted on the dorsum of the foot, into the side of the first phalanx, the metatarso-phalangeal capsule, and the dorsal expansion of the extensor tendon. The first and second muscles are inserted respectively into the medial and lateral sides of the proximal end of the first phalanx of the second toe. The third and fourth muscles are inserted into the lateral sides of the third and fourth toes. The three plantar muscles occupy the three lateral interosseous spaces. Each arises, by a single head, from the medial side of the third, fourth, and fifth metatarsal bones respectively. Each ends in a tendon which passes dorsal to the transverse metatarsal ligament, and is inserted, in the same manner as the dorsal muscles, into the medial sides of the third, fourth, and fifth toes. Nerve-Supply. — Lateral plantar nerve (S. 1. 2.). Actions.— The muscles are flexors of the metatarso-phalangeal joints, and extensors of the inter-phalangeal joints of the four lateral toes. The dorsal interossei abduct the toes into which they are inserted from the middle line of the second toe. The plantar interossei adduct the three lateral toes towards the second toe. Actions of the Muscles of the Leg and Foot. The muscles of the leg and foot act chiefly in the movements of the ankle-joint (assisted by movements of the intertareal joints) ; of the metatarso-phalangeal joints (assisted by movements of the tarso-metatai-sal and inter-metatarsal joints) ; and of the inter-phalangeal joints. I. Tibio-Fibular Articulations. — The proximal tibio-fibiilar articulation is only capable of 436 THE MUSCULAK SYSTEM. slight gliding movement, occasioned by tlie action of tbe biceps and popliteus and the muscles arising from the fibula. II. Movements at the Ankle-Joint.— The movements at the ankle-joint are movements of flexion and extension of the foot on the leg, along with inversion and eversion (only during extension). These movements are produced at the ankle, aided by movements in the intertarsal joints, and are occasioned by the following muscles : — a. Flexion. Extension. b. Inversion. Eversion. Tibialis anterior Gastrocnemius Tibialis anterior Peronseus tertius Extensor digitorum longus Plantaris Peronseus longus Extensor hallucis longus SoleuR Tibialis posterior Peronseus brevis Peronseus tertius Tibialis posterior Peroneeus longus Peronseus brevis Flexor digitorum longus Flexor haUucis longus III. Movements of the Toes.— ^. At the'Metatarso-Phalangeal Joints (assisted by move- ments at the tarso-metatarsal and inter- metatarsal joints). — These movements are flexion and extension, abduction and adduction (in a line corresponding to the axis of the second toe). a. Flexion. Extension. Flexor digitorum longus Quadratus plantse Lumbricales Flexor hallucis longus Flexor hallucis brevis Flexor digitorum brevis Flexor digiti quinti brevis Interossei Extensor digitorum longus Extensor digitorum brevis Extensor haUucis longus Extensor hallucis brevis b. Abduction. Adduction. {From and to the middle line of the second toe.) Abductor hallucis Dorsal interossei Abductor digiti quinti Adductor hallucis Plantar interossei B. At the inter-phalangeal joints the movements are Kmited to flexion and extension. Flexion. Extension. Flexor digitorum brevis {acting on the first joint) Flexor digitorum longus {acting on both joints) Flexor hallucis longus {acting on the hallux) Extensor digitorum longus ^ Extensor digitorum brevis Interossei Lumbricales J Extensor hallucis longus 1 {acting on both joints) Movements of the Lower Limb generally. The characteristic features of the lower limb are stability and strength, and its muscles and joints are both subservient to the functions of transmission of weight and of locomotion. In the standing position the centre of gravity of the trunk falls between the heads of the femora, and is located about the middle of the body of the last lumbar vertebra. It is transmitted from the sacrum through the posterior sacro-iliac ligaments to the hip bone, and through the bones of the lower limb to the arch of the foot, where the talus distributes it backwards through the calcaneus to the heel, and forwards through the tarsus and metatarsus to the balls of the toes. Locomotion. — The three chief means of progression are walking, runniug, and leaping. In walking, the body and its centre of gravity are inclined forwards, the trunk oscillates from side to side as it is supported alternately by each foot, the arms swing alternately with the corresponding leg, and one foot is always on the ground. The act of progression is performed by the leg, aided in two ways by gravity. The movements of the leg occur in the following way. At the beginning of a step, one leg, so to speak, " shoves off" ; the heel is raised and the limb is extended. By the action of the muscles flexing the hip and knee-joints, and extending the ankle-joint and toes, this limb is raised from the ground sufficiently to clear it, and passes forwards by the action of gravity, aided by the force given to the movement by the extensor muscles. After passing the AXIAL MUSCLES. 437 line of the centre of gravity the flexion of the joints ceases, the muscles relax, and tlie limb gradually returns to the ground. The other limb then passes tlirough the same cycle, the weight of tlie body now resting on the limb which is in contact with the ground. As the focjt reaches the ground it, as it were, rolls over it; the heel touches it first, then the sole, and lastly, as the foot leaves the ground again, only the toes. In running, tlie previous events are all exaggerated. The time of the event is diminished, while the force and distance are increased. Both feet are off the ground at one time ; the action of flexors and extensors alternately is much more powerful, so that on the one hand the knees are drawn upwaids to a greatei- extent in the forward movement, and not the wliolo foot, but only the toes reach the ground in the extension of the limb. The attempt is made to bring the foot to the ground in front of the line of the centre of gravity. At the same time tlie trunk is sloped forwards much more than in w.alking. In leaping, tlie actions of the limbs are still more exaggerated. The movements of flexion of the limb are still more marked, and the foot reaches the ground still farther in front of the line of the centre of gravity. AXIAL MUSCLES. THE FASCI>E AND IVIUSCLES OF THE BACK. OBLIQUUS EXTERNl'S ABDOMINIiS Obliqiius INTKRNUS abdominis Tran.sversus abdominis Fascia tran.sversalis Peritoneum Colon THE FASCIiE OF THE BACK. The general fascial investments of the back have been described along with the superficial muscles associated with the shoulder -girdle (p. 365). The latissimus dorsi muscle has been described as arising in large part from the posterior layer of the lumbo-dorsal fascia. This is a strong fibrous lamina which conceals the sacro- spinalis muscle. T , , . ., Rectus ABDOMINIS In the loin it extends from the spines of the lumbar vertebrae, laterally, to the interval between the last rib and the iliac crest, where it joins the middle layer. Below the loin the posterior layer of the lumbo- dorsal fascia is attached to the iliac crest, and more medially blends with the subjacent tendin- ous origin of the sacrospiualis. The layer can be followed upwards over the sacro- spinalis in the region of the thorax, where it is attached later- ally to the ribs and is continuous with the intercostal aponeuroses. In the lower part of the thorax it is replaced by the muscular slips of the serratus posterior inferior ; in the upper part of the thorax it passes beneath the serratus posterior superior and blends with the deep cervical fascia. Fascia Lumbodorsalis. — The lumbo-dorsal fascia consists of three fascial strata, called respectively the posterior layer, just described; the middle, and the anterior layers. They unite at the lateral margin of the sacrospiualis muscle to 29 a Extraperiton«.al tissue Kiilney Lumbo-dorsal fascia Latissimus dorsi quadratrs lumborum Psoas fascia Second lumbar vertebra — Psoas major Anterior layer of lumbar fascia MULTIFIDCS Semispinalis dorsi Middle layer of lumbar fascia Iliocostalis Vertebral aponeurosis LONOISSIMUS DORSI Fig. 390. — Transverse Section through the Abdomen, opposite the Second Lumbab Vertebra. 438 THE MUSCULAR SYSTEM, form a narrow ligamentous band which connects the last rib to the iliac crest between the muscles of the back on the one hand and those of the abdominal wall on the other. The middle layer is a fascia which stretches laterally from the ends of the transverse processes of the lumbar vertebrae, between the sacrospinalis behind and the quadratus lumborum muscle in front. The anterior layer is attached to the lumbar vertebrae near the bases of their transverse processes. It covers the anterior surface of the quadratus lumborum muscle, and separates it from the psoas major. The psoas fascia is continuous at the lateral border of the psoas major muscle with the anterior layer of the lumbo-dorsal fascia. At the lateral borders of the quadratus lumborum and sacrospinalis muscles the three layers blend together, and give partial origin to the obliquus internus and transversus abdominis muscles. LOJfGISSIMUS CAPITIS LONCISSIMUS CERVICIS Iliocostalis DOR.SI [LIOCOSTALIS LUMBORLM LONGISSIMUS DORSI Iliocostalis. cervicis THE MUSCLES OF THE BACK. The muscles of the back are ar- ranged in four series according to their attachments : (1) vertebro - scapular and vertebro -humeral, (2) vertebro- costal, (3) vertebro -cranial, and (4) vertebral. They are in irregular strata, the most superficial muscles having the most widely spread attach- ments. The first series of muscles of the back, connecting the axial skeleton to the upper limb, have already been described. They are arranged in two layers : (1) trapezius and latissimus^ dorsi superficially ;. (2) levator scapulae, and rhomboidei, deep to the trapezius (p. 368). The remaining muscles are almost entirely axial, and may be divided into four groups : (1) serrati posteriores,' superior and inferior ; splenius capitis and splenius cervicis ; (2) sacrospinalis and semispinahs capitis ; (3) semi- spinaHs dorsi and cervicis (transverso- spinales) ; and (4) the small deep muscles (rotatores, interspinales, inter- transversarii, and suboccipital mus- cles). They extend from the sacrum to the head, forming a cylindrical column in the loin, filling up the vertebral groove in the thorax, and giving rise to the muscular mass at the back of the neck. First Group. M. Serratus Posterior Superior.— The serratus posterior superior has a membranous origin from the ligamentum nuchse and the spines of the last cervical Fig. 391. — Schematic Representation of the Parts OF the Left Sacrospinalis Muscle. THE MUSCLES OF THE BACK. 439 and upper three or four thoracic vertebrae. It is directed obliquely downwards and laterally, to be inserted, by separate slips, into the second, third, fourth, and fifth ribs. The muscle is concealed by the vertebro-scapular muscles, and crosses obliquely over the s])leuius, sacrospinalis and semispinalis capitis. It lies super- ficial to the lumbo-dorsal fascia. Nerve-Supply. —Posterior rami of upper thoracic nerves. Actions. — It is an accessoiy muscle of inspiration and an extensor of the vertebi-al column. Acting on tlie verti-bral colunin, from the costal attachment, it a.ssist.s in lateral movement of the column. M. Serratus Posterior Inferior. — The serratus posterior inferior has a meml»ranous origin, through the medium of the luml»o-dorsal fascia, from the last two thoracic and first two lumbar spinous processes. It forms four muscular bands which pass almost horizontally to an insertion into the last four ribs. The muscular slips overlap one another from below upwards. The muscle is on the same plane as the posterior layer of the lunibo- dorsal fascia, and is concealed by the latissimus dorsi. Nerve-Supply. - Posterior rami of the lower thoracic nerve.-;. Actions. Tilt! muscle is an extensor of the vertebral column and an accessory nuiscle of inspiralitin, raising, everting, and fixing tiie lower four ribs. M. Splenius. — The splenius muscle is a broad, flattened baud which occupies the back of the neck and the upper part of the thoracic region. It arises from the ligamentum nucha? (from the level of the fourth cervical vertebra downwards) and from the spinous processes of the last cervical and higher (four to six) thoracic vertebra?. Its fibres extend upwards and laterally into the neck, separating in their course into an upper and a lower part. The upper part forms the splenius capitis, which is inserted into the mastoid portion of the temporal bone and the lateral part of the superior nuchal line of the occipital bone (Fig. 396, p. 444). The lower part forms the splenius cervicis, which is inserted into the posterior tubercles of the transverse processes of the upper three or four cervical vertebrae, behind the origin of the levator scapulse. Tiie muscle is partially concealed by the trapezius and sterno-mastoid, and appears between them in the floor of the posterior triangle of the neck (splenius capitis). It is covered by the rhomboid muscles, levator scapulse, and serratus posterior superior. Nerve-Supply. — Posterior rami of cervical and upper thoracic nerves. Actions. — The splenius cervicis extends the spine, and assists in lateral movement and rotiition. The splenius capitis helps in the movements of raising the head, and also of lateral flexion and rotation. Second Croup. M. Sacrospinalis.— The sacrospinalis (O.T. erector spinae) possesses vertebral, vertebro-cranial, and vertebro-costal attachments. It consists of an elongated mass composed of separated slips extending from the sacrum to the skull. Simple at its origin, it becomes more and more complex as it is traced upwards towards the head. It arises (1) by fleshy fibres from the iliac crest; (2) from the posterior sacro- iliac ligament ; and (3) by tendinous fibres continuous with the former from the diac crest, the dorsum of the sacrum, and the spines of the upper sacral and all the lumbar vertebrse. Its fibres extend upwards through the loin, enclosed between the posterior and middle layers of the lumbo-dorsal fascia, and separate into two columns — a lateral portion derived from the lateral fleshy origin, the iliocostalis, and a medial portion comprising the remaining larger part of the muscle, the longissimus. M. Iliocostalis. — The iliocostalis Ivunborum is inserted by six slender slips into the lower six ribs. Medial to the insertion of each of these slips is the origin of the iliocostalis dorsi (O.T. accessorius), which, arising from the lower six ribs medial to the 29 b 440 THE MUSCULAE SYSTEM. iliocostalis lumborum, is inserted iu line with it by similar slips into the upper six ribs. The iliocostalis cervicis (O.T. cervicalis ascendens) arises in the same way by six slips from the upper six ribs, medial to the insertions of the previous muscle. It forms a narrow band, which, extending into the neck, is inserted into the posterior tubercles of the transverse processes of the fourth, fifth, and sixth cervical vertebrse, behind the scalenus posterior. Tlie iliocostales, lumhorum, dorsi, and cervicis form together a continuous muscular column, and constitute tlie most lateral growp of the component elements of the sacrospinalis. M. Longissimus.— The longissimus is the largest element in the sacrospinalis muscle. The longissimus dorsi forms the middle column of the muscle. It is continued up into the neck as the longissimus cervicis and longissimus capitis. Mostly tendinous, on the surface, at its origin, it becomes fleshy in the upper part of the loin. It is thickest in the loin, and becomes thinner as it passes upwards in Posterior tubercles of transverse processes Articular! Xjrocesses" scalencs medius Levator scapula Splexius cervicis scalexl's posterior- Iliocostalis cervicis Longissimus cervicis Longissimus capitis SEMI3P1NALIS capitis — Semispinalis cervicis' multifidus' I ONOus capitis Anterior tubercles of 'transverse jirocesses LciNGUS COLLI J Fig. 392. — Scheme ok Muscular-Attachments to the Trans%'erse and Articular Processes of the Cervical Vertebk^e. the back between the column formed by the iliocostalis and its upward continua- tions laterally, and the spinalis dorsi medially. It is inserted by two series of slips, medial and lateral, laterally into nearly all the ribs, and medially into the transverse processes of the thoracic and the accessory processes of the upper lumbar vertebrae. It is prolonged upwards into the neck by its association with the common origin of the longissimus cervicis and the longissimus capitis. The longissimus cervicis (transversalis cervicis) has an origin from the transverse processes of the upper six thoracic vertebriB, medial to the insertions of the longissimus dorsi. Extending upwards into the neck, it is inserted into the posterior tubercles of the transverse processes of the second, third, fourth, fifth, and sixth cervical vertebrae. It is concealed in the neck by the iliocostalis cervicis and splenius cervicis muscles. The longissimus capitis (trachelo-mastoid) arises, partly by an origin common to it and the previous muscle, from the transverse processes of the upper six thoracic vertebrae, and partly by an additional origin from the articular processes of the lower four cervical vertebrae. Separating from the longissimus cervicis, the muscle ascends through the neck as a narrow band which is inserted into the mastoid portion of the temporal bone, THE MUSCLES OF THE BACK. 441 KEITI'S CAPITIS POSTERIOR MISoK RkiTIS CAPITIS POSTERIOR M\JOK .^ \ J^ OBLIQOUS CAPITIS SrPEK Obliquus capitis iskerior- .SPI.EXH'S IM i . ; Splesius cervicis Sterno-cleido-mastoid Semispinalis cerv lo.noissimus cervicis I.lOAMENTl'M NC( M.K SeMISPIXALIS CAPITI! L11SOI88IMU8 CAPITIS PLKXIIS CAPITIS ET CERVICIS Levator scapll* Ii.IOCOrTALIS CERVICIS LONOISSIM' -- I I nvins Iliocostalis dorsi Semispi.valis dorsi Levatores costarum QCADRATCS I.UMBORUM . Spinalis dorsi LosGissiiius dorsi OCOSTALIS LCMBORl'M Sacrospixalis Fig, 393. — The Deep Muscles of the Back. 442 THE MUSCULAE SYSTEM. deep to the splenius capitis muscle. In the neck the muscle is placed between the splenius capitis and semispinalis capitis. M. Spinalis Dorsi. — The spinalis dorsi forms the medial column of the sacro- spinalis. It lies in the thoracic region, and arises by tendinous fibres from the lower two thoracic and upper two lumbar spinous processes, and also directly from the tendon of the longissimus dorsi. It is a narrow muscle which, lying close to the thoracic spinous processes medial to the longissimus dorsi, and it is inserted into the upper (four to eight) thoracic spines. It is not prolonged into the neck. The sesiiBpinalis capitis (O.T. complexus) closely resembles in position and attachments the longissimus capitis. It takes origin from the transverse processes of the upper six thoracic and the articular processes of the lower four cervical vertebrae, medial to the longissimus cervicis and longissimus capitis. It has an additional origin also from the spinous process of the last cervical vertebra. It forms a broad muscular sheet which extends upwards in the neck, to be inserted into the medial impression between the superior and inferior nuchal lines of the occipital bone (Fig. 396, p. 444). The medial portion of the muscle is separate, and forms the biventer cervicis, consisting of two fleshy bellies with an intervening tendon, placed vertically in contact with the ligamentum nuchas. The muscle is covered mainly by the splenius and longissimus capitis muscles. It conceals the semispinalis cervicis and the muscles of the suboccipital triangle. Nerve-Supply. — Posterior rami of spinal nerves. Actions. — The several parts of the sacrospinalis muscle have a complex action, on the vertebral column, head, ribs, and pelvis. The muscle serves as an extensor of the vertebral column, and assists in lateral movement and rotation. The longissimus capitis and semispinalis capitis assist in extension, lateral movement and rotation of the head. The iliocostales and longissimus are accessory muscles of inspiration. The whole muscle helps in extension and lateral movement of the pelvis in the act of walking. Third Group. This group comprises the semispinales (dorsi and cervicis) and multifidus. They occupy the vertebral furrow, under cover of the sacrospinalis and semispinalis capitis muscles. They are only incompletely separate from one another. The semispinales, dorsi and cervicis, form a superficial stratum, the multifidus being more deeply placed. The more superficial muscles have the longer fibres ; the fibres of the multifidus pass over fewer vertebrae. Both muscles extend obliquely upwards from transverse to spinous processes. M. Semispinalis. — The semispinalis muscle extends from the loin to the second cervical vertebra. Its fibres are artificially separated into an inferior part, the semispinalis dorsi, and a superior part, the semispinalis cervicis. The semispinalis dorsi arises from the transverse processes of the lower six thoracic vertebrae. It is inserted into the spinous processes of the last two cervical and first four thoracic vertebrae. The semispinalis cervicis arises from the transverse processes of the upper six thoracic, and the articular processes of the lower four cervical vertebrae. It is inserted into the spines of the cervical vertebrae from the second to the fifth. M. Multifidus. — The multifidus (O.T. multifidus spinse) differs from the previous muscle in extending from the sacrum to the second cervical vertebra, and in the shortness of its fasciculi, which pass over fewer vertebrae to reach their insertion. It arises from the sacrum, from, the posterior sacro-iliac ligament (Fig. 395, p. 443), from the mamillary processes of the lumbar vertebrae, from the transverse processes of the thoracic vertebrae, and from the articular processes of the lower four cervical vertebrae. It is inserted into the spines of the vertebrae up to and including the second cervical. THE MUSCLES OF THE BACK. 443 Insertion of sterno- MASTOID SPLENIUS CAPIT13 LONOISSIMUS CAPITIS Semispinai.is capitis (thrown laterally) TliirU occipital nerve Splenius capitis LONOISSIMUS CAPITIS Trapezius Semispinalis capitis p'ater occipital nerve OBI.IyUt'8 capitis SCPKRIOP. Uectus capitis posterior major Recti's oapiti.h posterior minor Vertebral artery Suboccipital nerve Posterior arch of atlas Obliquus capitis inferior Posterior ramus of second cervical nerve Posterior ramus of third cervical nerve _ Deep cervical artery — Posterior ramus of fourth cervical nerve Semispinalis cervicis »;''^ Fio. 394. — The Suboccipital Triangle of the Left Side. Lying in contact with the vertebral laminae, the muscle is covered in the neck and back by the semispinalis, and in the loin by the sacrospinalis muscle. Attachment of interosseous sacro-iliac ligaments Multifirtus (origin) Gluteus maxiinus (origin) Flo. 395. — Muscle- Attaci TO the Sacbum (Dorsal Aspect). 444 THE MUSCULAR SYSTEM. Nerve-Supply. — Posterior rami of the spinal nerves. Actions. — Tliese muscles are concerned in extension, lateral movement and rotation of tlie spine. Fourth Group. This group includes several sets of small muscles, which are vertebro-cranial or intervertebral in their attachments. The muscles bounding the suboccipital triangle are four in number — obliqui capitis, inferior and superior, and recti capitis posteriores, major and minor. These muscles are concealed by the semispinalis capitis and splenius capitis ; they enclose a triangular space (the suboccipital triangle) in which the vertebral artery, the posterior ramus of the suboccipital nerve, and the posterior arch of the atlas are contained. Semispinalis capitis (insertion) Rectus capitis posterior minor (insertion) Rectus capitis posterior major (insertion) Trapezius (origin) Sterno-cleido-mastoid (insertion) Splenius capitis S^(insertion) Obliquus capitis superior (insertion) Rectus capitis lateralis (insertion) Rectus capitis anterior (insertion) Superior constrictor of pharynx (insertion) Longus capitis (insertion) Fig. 396. — Muscle- Attachments to the Occipital Bone. The obliquus capitis inferior arises from the spine of the epistropheus, and is inserted into the transverse process of the atlas. Nerve- Supply. — Posterior ramus of the first cervical (suboccipital) nerve. Actions. — Extension, lateral flexion and rotation of the atlas in the axis. M. Obliquus Capitis Superior. — The obliquus capitis superior arises from the transverse process of the atlas, and is inserted into the occipital bone deep and lateral to the semispinalis capitis and above the inferior nuchal line (Eig. 396). Nerve-Supply. — Posterior ramus of the first cervical (suboccipital) nerve. Actions. — Elevation, lateral movement and rotation of the head on the atlas. M. Rectus Capitis Posterior Major. — The rectus capitis posterior major arises from the spine of the second cervical vertebra, and is inserted into the occipital bone deep to the obliquus capitis superior and semispinalis capitis and below the inferior nuchal line (Eig. 396). Nerve-Supply. — Posterior ramus of the first cervical (suboccipital) nerve. Actions. — Elevation, lateral movement and rotation of the liead. M. Rectus Capitis Posterior Minor. — The rectus capitis posterior minor arises deep to the preceding muscle from the posterior tubercle of the atlas, and is THE MUSCLES OF THE BACK. 445 inserted into the occipital bone below the inferior nuchal line medial to and beneath the rectus capitis posterior major (Fig. 396, p. 444). Nerve-Supply. — PosU-rior ramus of the fwst cervical (suboccipital) nerve. Actions. Elevation, lateral UKivenient and rotation of the head. Mm. Rotatores. — The rotatores are eleven pairs of small muscles occupying the vertebral groove in the thoracic region, deep to the semispinalis dorsi, of which they form the deepest fibres. Each consists of a small slip arising from the transverse process and inserted into the lamina of the vertebra directly above. Nerve-Supply. Pasterior rami of the thoracic nerves. Actions. K.xtension and rotation of the vertebral column. Mm. Interspinales. — The interspinales are bands of muscular fibres connect- ing together the spinous processes of the vertebrse. Nerve-Supply. — Posterior rami of the spinal nerves. Action. Extension of the vertebral column. Mm. Intertransversarii. — The intertransversarii are slender slips extending between the transverse processes. They are double in the neck, the anterior branches of the spinal nerves passing between them. In the loin the inter- transverse muscles are usually double, but they are often absent, or are replaced by membrane. Nerve-Supply.-^ Anterior rami of the spinal nerves. Actions. — Lateral movement and rotation of the vertebral column. Mm. Rectus Capitis Lateralis. — The rectus capitis lateralis, extending from the transverse process of the atlas to the jugular process of the occipital bone (Fig. 396, p. 444), is homologous with the posterior of the two inter-transverse muscles. Nerve- Supply. — Anterior ramus of the first cervical (suboccipital) nerve. Action. — Lateral movement and rotation of the head. The action of these muscles is extremely complex. Not only do they act on the vertebral column, ribs, head, and pehds, in conjunction with other muscles, but some of them act also in relation to the movements of the limbs as well. In this section will be given an analysis of their movements in relation to the vertebral column, head, and pelvis. The movements of the limbs and of the ribs (respiration) are dealt with in other sections. The chief muscles are engaged in preserving the erect position, and in the movements of the trunk they are assisted in large measure by muscles whose chief actions are referred to elsewhere. 1. Movements of the Vertebral Column. — The movements of the vertebral column are flexion, extension, and lateral movement or rotation. These movements occur in all regions — neck, thorax, and loin ; flexion and extension and lateral movement are most limited in the region of the thorax ; while rotation is most limited in the region of the loin. a. Flexion. Extension. 1 Longus colli Serrati posteriores 1 Longus capitis Splenius capitis Scaleni anteriores (together) Splenius cervicis Psoas major and minor Sacrospinalis Levator ani Semispinalis dorsi Coccygeus Semispinalis cervicis Semispinalis capitis Sphincter ani extemus Multitidus Rectus abdominis Interspinales Pyramidalis Obliquus abdominis extemus Intercostal muscles Obliquus „ internus Diaphragm Tramjversus „ Transversus thoracis b. Lateral Movement (Rotation). Levator scapuliB Longus capitis 1 1 Serrati posteriores Scaleni, anterior, medius, posterior Splenius cervicis Psoas (major and minor) 1 Sacrospinalis Quadratus lumborum Semispinalis capitis Obliquus abdominis externus 1 Semispinalis (dorsi and cervicis) Obliquus „ internus 1 Multifidus Transversus „ Rotatores Rectus „ Intertransversarii Pyramidalis „ Longus coUi 1 446 THE MUSCULAR SYSTEM. 2. Movements of the Head. — The movements of the head are flexion and extension, at the occipito-atlantoid articulation ; lateral movement and rotation at the atlanto-epistropheal joint. a. FlexioiL \ Extension. Digastric Sterno-mastoid Stylo-hyoid Splenius capitis Stylo-pharyngeus Mylo-hvoid Longissimus capitis Semispinalis capitis Hyo-glossus Obliquus capitis inferior Sterno-liyoid Recti capitis posteriores (major and minor) Sterno-thyreoid Omo-hyoid Longus capitis Rectus capitis anterior {the muscles of both sides acting together) b. Lateral Movement. c. Rotation. Sterno-mastoid Splenius capitis Longissimus capitis Semispinalis capitis Obliquus capitis superior Rectus capitis lateralis Sterno-mastoid Splenius capitis Longissimus capitis Semispinalis capitis Obliquus capitis inferior „ „ superior Recti capitis posteriores (major and minor) Movements of the Pelvis. — The movements of the pelvis (as in locomotion) are partly caused by certain of the muscles of the back. Those muscles, which are attached to the vertebral column or the ribs on the one hand, and to the hip bone on the other, produce the movements (flexion, extension, and lateral movement) of the whole pelvis. In addition, the muscles passing between the hip bone and femur, in certain positions of the lower limb, assist in these movements. a. Extension. Flexion. Latissimus dorsi Psoas major and minor Sacrospinalis Rectus abdominis Multifidus (acting on both sides) Pyra'midalis abdominis Obliqu.us abdominis externus Obliquus „ internus Transversus abdominis (acting on both sides) Piriformis Glutaei Obturator (externus and internus) Sartorius Tensor fasciae latae Iliacus Rectus femoris Adductors (in the erect position) b. Lateral Movement. Flexors and extensors of one side only Quadratus lumborum THE FASCIiC AND MUSCLES OF THE AND NECK. FASCIiE. HEAD The superficial fascia of the head and ueck possesses certain features of special interest. Over the scalp it is closely adherent to the skin and subjacent galea aponeurotica and contains the superficial vessels and nerves. Beneath the skin of the eyelids it is loose and thin and contains no fat. Over the face and at the side of the neck it is separated from the deep fascia by the facial muscles and the platysma. Between the buccinator and the masseter it is continuous with a pad of fat {corpus adiposum buccce) occupying the interval between those muscles. FASCIJi: AND MUSCLES OF THE HEAD AND NECK. 447 The deep fascia of the head' and neck presents many reraiirkable characters. Over the scalp it is represented by the galea aponeurotica (O.T. epicranial aponeurosis), the tendon of the epicnineus muscle. This is a tough nieuibraiie, tightly stretched over the calvaria, from which it is separated by loose areolar tissue. It is attached posteriorly, partly through the agency of the occipitalis muscle, to the superior nuchal line of the occipital bone ; anteriorly it joins the frontalis muscle and the orbicularis oculi, and has no bony attachment ; laterally it is attached to the temporal line and the mastoid process. Below the temporal line it is continuous with the temporal fascia, a stout layer of fascia attached to the temporal line and zygomatic arch, which covers and gives origin to the temporal muscle. This fascia separates into two layers above the zygomatic arch, to en- close a quautity of fat along with branches of the temporal and zygo- matico- orbital arteries. On the face the fascia is practically non-existent anteriorly in relation to the facial muscles. Pos- teriorly it forms the thin parotideo - masseteric fascia, and is much thicker in relation to the parotid gland, for which it forms a capsule. In the neck the deep fascia invests the mus- cles, and forms fascial coverings for the Fig. 397. — Transverse Section in the Cervical Reoion (between the fourth and fifth cervical vertebrse). 1. CRICO-ARYTyENOIDEUS POSTERIOR MUSCLE. 2. Inferior constrictor mcscle. 3. Pharynx. 4. Cricoifl cartilage. •i. Vocal fold. 26. Vertebral vein. 27. Scalenus medius. 28. Posterior triangle. 29. Scalenus posterior. 30. Levator scapula. 31. Acce.ssory nerve. muscles. 7. Thyreoid cartilage. 8. Rinia Glottidis. 9. Layers of deep cervical fascia, i ~ . 1 _ 10. Sterno-hyoid muscle. pharynx, trachea, oeso- n. omohyoid muscle. 12. Sterno-thyrf.oid muscle. 13. Cervical fascia. 14. Thyreoid gland. 1.'). Coniiiion carotid artery. 16. Uescendens hypoglossi nerve. 17. Sterno-mastoid muscle. 18. Internal jugular vein. 19. Vagus nerve. 20. Sympathetic trunk. 21. Carotid sheath. 22. Phrenic nerve. 23. LoNous colli muscle. 24. LoNOUs capitis. 25. Scalenus anterior. VOCALIS AND ThYREOARYT^NOIDEUS 32. SPLENIU.S CERVICIS. 33. LONOISSIMUS CERVICIS. 34. LONHISSIMUS CAPITIS. 35. Fifth cervical nerve. 36. Vertebral artery. 37. Profunda cervicis vein. 38. Profunda cervicis arterj'. 39. MuLTiriDus 40. Semispinalis cervicis. 41. Semispinalis capitis 42. Splenivs capitis. 43. Trapezius. 44. Liganientuni nucha". 45. Spine of fourth cervical vertebra. 46. I.,ainina of fifth cer\'ical vertebra. 47. Dura mater. 48. Spinal medulla. 49. Transverse process. 50. Fibro -cartilage between fourth and fifth cervical vertebrae. phagus, glands, and large vessels. It encloses the sterno - mastoid muscle, and can be traced back- wards over the posterior triangle to the trapezius and deeper muscl.es, which it surrounds ; it can be traced forwards over the anterior triangle to the median plane of the neck, where it forms a continu- ous membrane. Above the stermim the fascia, after enclosing the sterno-mastoid muscles, is attached in the form of two layers to the front and back of the jugular notch. The layer enclosing the infra-hyoid muscles passes across the median plane of the neck anterior to the trachea, and is attached above to the hyoid bone, below to the sternum, clavicle, and first rib. A third layer of fascia passes medially anterior to the trachea, enclosing the thyreoid gland. Deep to the sterno-mastoid the fascia helps to form the carotid sheath, which is completed by septal processes stretching medially across the neck in relation to the infra-hyoid muscles, trachea. 448 THE MUSCULAE SYSTEM. cesophagus, and pharynx, and the praevertebral muscles. The trachea, oesophagus, and pharynx are Ukewise encapsuled in cervical fascia, a septal layer passing across the median plane of the neck between the trachea and oesophagus. Lastly, a strong praevertebral fascia passes across the neck anterior to the praevertebral muscles, and posterior to the oesophagus and pharynx. The cervical fascia is attached above to the bones of the skull : superficially to the superior nuchal line of the occipital bone, the mastoid process, the zygoma (over the parotid gland), and the inferior border of the mandible ; more deeply to the styloid and vaginal processes of the temporal bone, the great wing of the sphenoid and the basikr part of the occipital bone. This deeper attachment (jprcBvertehral fascia) is posterior to the parotid gland and pharynx, and is associated with the formation of three ligaments : stylo-mandibular ligament, spheno- mandibular ligament, and pterygo- spinous ligament. The fascia is attached below, through its muscular connexions, to the sternum, first rib, clavicle, and scapula. By means of its connexion with the trachea and the common carotid artery it is carried down behind the first rib into the superior mediastinum, and so becomes continuous with the pericardium. By means of its connexion with the subclavian vessels and brachial nerves it is carried down to the axilla, as the axillary sheath, which becomes connected with the costo-coracoid membrane. THE MUSCLES OF THE HEAD. The muscles of the head are divisible into three separate groups : the super- ficial muscles, muscles of the orbit, and muscles of mastication. Superficial Muscles. The superficial muscles comprise a large group, including the muscles of the scalp and face, and the platysma in the neck. The platysma is a thin quadrilateral sheet extending from chest to face over the side of the neck, between the superficial and deep fasciae. It arises from the deep fascia of the pectoral region. It is directed upwards and forwards, and is partly inserted (by its intermediate fibres) into the inferior border of the mandible, becoming connected with the quadratus labii inferioris and triangularis muscles (Fig. 398, p. 449). The more anterior fibres pass across the median plane of the neck and decussate for a variable distance below the chin with those of the opposite side. The posterior fibres sweep over the angle of the jaw and become continuous with the risorius muscle. The platysma is the rudiment of the cervical portion of the panniculus carnosus of lower animals, in which it has a much more intimate connexion with the muscles of the face than is usually the case in man. Nerve-Supply. — Cervical branch of the facial nerve. Actions. — It depresses the mandible and laterally flexes the head. It also throws into folds the skin of the side of the neck. The IVIuscIes of the Scalp. The muscles of the scalp comprise the epicranius muscle and the muscles of the auricle. M. Epicranius. — The epicranius (O.T. occipitofrontalis) is a muscle with four bellies, two posterior and two anterior, and an intervening tendon (the galea aponeurotica) which stretches uninterruptedly across the median plane of the cranium. Each posterior belly (occipitalis) arises as a broad flat band from the lateral two-thirds of the superior nuchal hne of the occipital bone. Each anterior belly (frontalis) has no bony attachments ; arising from the galea aponeurotica about the level of the coronal suture, it passes downwards to the supra-orbital arch, where it blends with the orbicularis oculi and corrugator supercilii muscles. It extends across the full width of the forehead, and blends in the median plane with the muscle of the opposite side. THE MUSCLES OF THE SCALP. 449 The galea aponeurotica (O.T. epicranial aponeurosis), extending between the two anterior and the two posterior Heshy bellies, is a continuous membrane which glides over the calvaria, and has attachments laterally to the temporal ridge, and behind, between the posterior bellies, to the superior nuchal lines of the occipital bone. It has no osseous attachment anteriorly. Nerve-Supply.— The occipitalis is supplied by the posterior auricular branch of the facial nerve. The frontalis is supplied by the temporal branche,s of the same nerve. Actions. —The epicraneus is usually rudimentary. By the contraction of the fibres of the frontalis muscle the skin of the forehead is thrown into horizontal parallel folds. Galea ajirinpurotica — r^, Frontalis Orbicularis oci'li M. PROCERl'S Caput anoularb - m. nasa lis Caput anoulare Caput inkraorbitalk put zygomaticum CaNINL'S zvoomaticus Orbicularis oris BufXINATOR 'J m. triangularis ^^^^ ^^^^^^ -- m. quadratus labil inferiorisl Masseter Platysma Fig. 398. — Tbk Mtscles of the Face and Scalp (Muscles of Expression). The extrinsic muscles of the ear are three in number : posterior, superior, and anterior. They are rudimentary and usually I'uuctionless. The m. auricularis posterior (O.T. retrahens aurem) is a narrow fleshy slip which arises from the surface of the mastoid process and is inserted into the cranial surface of the auricle. It bridges across the groove between the mastoid process and the auricle, and conceals the posterior auricular vessels and nerve. The m. auricularis superior (O.T. attoUens aurem) is a small fan-shaped muscle which arises from the temporal fascia, and descends to be inserted into the top of the root of the auricle. The m. auricularis anterior (O.T. attrahens aurem) is a similar small muscle, placed in front of the auricularis superior, and stretching obUquely between the temporal fascia and the top of the root of the auricle. 30 450 THE MUSCULAE SYSTEM. The Muscles of the Face. The facial muscles are divided into three groups, associated with the several apertures of the eye, nose, and mouth. 1. The muscles of the eyelids include four muscles : the levator palpebrse superioris (described with the orbital muscles (p. 452)), orbicularis oculi, lacrimal part of the orbicularis, and corrugator supercilii. M. Orbicularis Oculi. — The orbicularis oculi is a transversely oval sphincter muscle surrounding and occupying the eyelids. It is divisible into an orbital 'portion (jpars orbitalis) composed of coarse fibres, spreading on to the forehead, temple, and cheek, and a palpebral portion (pars palpebralis), composed of finer fibres, situated beneath the skin of the eyelids. At the medial commissure of the eye the muscle (by its palpebral fibres) gains an attachment to the medial palpebral lio-ament and the borders of the naso- lacrimal groove. Its fibres enclose the lacrimal sac and the canaliculi. The posterior fibres, extending between the posterior edge of the naso-lacrimal groove and the tarsal ligaments behind the lacrimal sac, constitute the pars lacrimalis (O.T. tensor tarsi muscle). The fibres of the muscle which extend along the margins of the lids constitute a separate ciliary bimdle. Laterally the orbicularis oculi has no bony attachment ; so that when it contracts and closes the eyelids, both lids at the same time tend to be drawn towards the medial commissure of the eye. M. Corrugator Supercilii. — The corrugator supercilii arises from the medial part of the superciliary arch, and passing horizontally laterally, blends with the upper fibres of the orbicularis oculi on its deep surface. The contraction of this muscle throws the skin of the forehead into vertical folds, while at the same time drawing the medial half of the eyebrow upwards, it produces concentric curved folds on each side of the median plane of the forehead. 2. The muscles of the nose comprise five small muscles proper to the nose, and one common to the nose and upper lip : the m. procerus, nasahs, dilatores naris (anterior and posterior), depressor alee nasi, and angular head of the quadratus labii superioris. They are all small and feeble muscles. The m. procerus (O.T. pyramidalis nasi) arises from the epicranius muscle and the skin over the glabella ; it is inserted into a membrane stretching over the nose, which gives attachment to the musculus nasalis also. The m. nasalis (O.T. compressor naris) arises by a narrow origin from the maxilla, under cover of the quadratus. It passes forwards over the bridge of the nose, and ends in a membranous insertion common to it and the preceding muscle. The mm. dilatores naris are feeble muscular slips placed on the lateral surface of the margin of the nostril, one anteriorly, the other posteriorly. The m. depressor alse nasi is a small muscle arising from the upper part of the incisor fossa of the maxilla ; it divides into two parts as it passes upwards and mediiUy, and is inserted into the ala and the septum of the nose (depressor septi). The caput angulare (O.T. levator labii superioris alseque nasi) is a portion of the quadrate muscle of the upper lip, and is a narrow band arising from the root of the frontal process of the maxilla. It descends alongside the nose, and is inserted, partly into the ala of the nose and partly into the orbicularis oris muscle. 3. The muscles of the mouth comprise a number of muscles, of which all but one, the orbicularis oris, are bilaterally placed. The muscles are : (1) quadratus labii superioris, which includes the angular head just described, the infra-orbital head, and the zygomatic head; (2) the canine muscle; (3) zygomaticus; (4) risorius; (5) orbicularis oris; (6) triangularis; (7) quadratus labii inferioris ; (8) mentalis ; and (9) buccinator. M. Orbicularis Oris. — The orbicularis oris is the sphincter muscle surround- ing the lips. It is continuous with the other muscles converging to the mouth. It lies between the skin and mucous membrane of the mouth, and is limited superiorly by the nose, inferiorly by the junction of the lower hp and chin. Its medial fibres are attached above to the septum of the nose (naso-labial band) and THE MUSCLES OF THE FACE. 451 to the incisor fossa (mperior incisive bundle) ; below they are attached to the mandible on each side of the symphysis (inferior incisive bundle). 1'hese bundles radiate laterally to join the rest of the muscle, which is joined at its margin by the elevators and depressors of the lower lip and angle of the mouth, and by the buccinator muscle. The lower fibres of the muscle are continued laterally into the buccinator and canine muscles ; its vpper fibres are continued into the buccinator and triangularis muscles. M. Quadratus Labii Superioris. — The quadratus labii superioris comprises three muscles. (1) The caput angulare (O.T. levator labii superioris aleeque nasij lias already been described. (2) The caput infra-orbitale (O.T. levator labii superioris) arises from the maxilla just above the infra-orbital foramen. It passes almost vertically down- wards to join the orbicularis oris and the skin of the upper lip between the attachments of the caput angulare and the caninus. It conceals the infra-orbital vessels and nerve. (3) Tlie caput zygomaticum (O.T. zygomaticus minor) arises from the zygomatic bone, and is often continuous with the most peripheral fibres of the orbicularis oculi. It is directed obliquely downwards and forwards over the caninus, to be inserted along with the caput infra-orbitale into the margin of the orbicularis oris. M. Caninus. — The caninus (O.T. levator anguli oris) arises from the canine fossa of the maxilla below the infra -orbital I'oramen and under cover of the caput zygomaticum. It is directed laterally and downwards, to be inserted into the orbicularis oris and the skin at the angle of the mouth. M. Zygomaticus. — The zygomaticus (O.T. zygomaticus major) is a narrow muscular band which arises from the zygomatic portion of the zygomatic arch. It passes to the angle of the mouth, to be inserted partly into the skin, partly into the orl>icularis oris. M. Risorius. — The risorius is a thin flat muscle which forms in part a con- tinuation of the platysma on the face, in part a separate muscle, with an origin from the parotideo - masseteric fascia. It passes transversely forwards, to be inserted at the angle of the mouth into the orbicularis oris and skin. M. Triangularis. — The triangularis (O.T. depressor anguli oris) arises from the oblique line of the mandible and is continuous with the platysma (Fig. 398, p. 449). It is triangular in form, its fibres converging to the angle of the mouth, where they are inserted into the orbicularis oris and the skin. Some of the fibres reach the upper lip through the orbicularis muscle. M. Quadratus Labii Inferioris. — The quadratus labii inferioris (O.T. de- pressor labii inferioris) arises from the lateral surface of the mandible deep and medial to the preceding muscle (Fig. 398, p. 449). It is quadrilateral in form, and is directed upwards, to be inserted into the orbicularis oris and the skin of the lower lip. Its lateral fibres are overlapped by the triangularis. Its medial fibres join with those of the opposite muscle. M. Mentalis. — The mentalis (O.T. levator menti) is a small muscle which arises from the incisor fossa of the mandible and is inserted into the skin of the chin. M. Buccinator. — The buccinator muscle forms the lateral wall of the mouth, and is in series posteriorly with the constrictor muscles of the pharynx. It arises (1) from the alveolar arches of the maxillae and mandible (Fig. 407, p. 457), and between these attachments ; (2) from the pterygo-mandibular raphe. Its fibres are directed forwards to the angle of the mouth, where they blend with the corresponding (upper and lower) portions of the orbicularis oris muscle. The middle fibres of the muscle decussate at the angle of the mouth, so as to pass, the lower set to the upper lip, the upper set to the lower lip. The liDuccinator is covered on its deep surface by the mucous membrane of the mouth. Superficially it is concealed by the muscles above mentioned, which converge to the angle of the mouth ; it is separated from the masseter by the corpus adi- posum bticccr ; it is pierced by the duct of the parotid gland, and by branches of the buccinator nerve. 30 a 452 THE MUSCULAE SYSTEM. Nerve-Supply. — The facial and scalp muscles are all innervated by the facial nerve. The posterioi- auricular branch supplies the posterior auricular muscle and occipitalis; the branches into which it breaks up in the parotid gland supply the frontalis, superior and anterior auricular muscles, the several muscles associated with the apertures of the eye, nose, and mouth (including the buccinator), and the platysma. Actions. — The almost infinite variety of facial expression is produced partly by the action of these muscles, partly by their inactivity, or by the action of antagonising muscles (antithesis). On the one hand joy, for exam^sle, is betrayed by the action of one set of muscles, while grief is accompanied by the contraction of another (opposing) set. Determination or eagerness is accom- panied by a fixed expression due to a combination of muscles acting together ; despair, on the other hand, is exj^ressed by a relaxation of muscular action. For a philosophical account of the action of the facial muscles, the student should consult Darwin's Expression of the Emotions in Man and Animals, and Duchenne's Mecanisme de la Physiologie humaine. The platysma retracts and depresses the angle of the mouth, and depresses the mandible. Tlie epicranius, by its anterior belly, raises the eyebrows ; both bellies acting together tighten the skin of the scalp ; acting along with the orbicularis oculi, it shifts the scalp back- wards and forwards. Tlie corrugator supercilii draws the eyebrow medially and wrinkles the skin of the forehead vertically. The procerus draws downwards the skin between the eyebrows, as in frowning. The upper eyelid is raised by the levator palpebrae superioris. The closure of the lids is effected by the orbicularis oculi, whose fibres also assist in the lowering of the eyebrows, in the j)rotection of the eyeball, and, by pressure on the lacrimal gland, in the secretion of tears. The tarsal part, acting along with the orbicularis oculi, compresses the lacrimal sac and aids in the passage of its contents into the naso-lacrimal duct. The muscles of the ear and nose have quite rudimentary actions. Of the muscles of the mouth, the orbicularis oris has a complex action, depending on the degree of contraction of its component jjarts. It causes compression and closure of the lips in various ways, tightening the lips over the teeth, contracting them as in osculation, or causing pouting or protrusion of one or the other. The accessory muscles of the lips draw them upwards (zygomaticus, quadratus labii superioris), laterally (zygomaticus, risorius, platysma, triangularis, buccinator), and downwards (triangularis, quadratus labii inferioris, platysma). The mentalis muscle elevates the skin of the chin and protrudes the lower lip. The buccinator retracts the angles of the mouth, flattens the cheeks, and brings them in contact with the teeth. I E\ MOR I \LlLim 1 '^l 1 1 IllORIS pnaoR ( rUS MEDIALIS Rectus lateralis Obliquus inferior Rectus inferior The Fasciae and lYIuscIes of the Orbit. The eyeball, with its muscles, vessels, and nerves, is lodged in a mass of soft and pelding fat which entirely fills up the cavity of the orbit. Surrounding the posterior part of the eyeball is the fascia bulbi (O.T. cap- sule of Tenon), which con- stitutes a large lymph space or synovial bursa in relation to the posterior part of the eyeball. Anteriorly the cap- sule is in contact with the conjunctiva, and intervenes between the latter and the eyeball ; posteriorly it is pierced by and prolonged along the optic nerve. It is a smooth membrane connected to the globe of the eye by loose areolar tissue. It is pierced by the tendons of the ocular muscles, along which it sends prolongations continuous with the muscular sheaths. The muscles of the orbit are seven in number : one, the levator palpebrae superioris, belongs to the upper eyelid ; the other six are muscles of the eyeball. M. Levator Palpebrae Superioris. — The levator palpebrae superioris lies immediately beneath the orbital periosteum and covers the superior rectus muscle. It has a narrow origin above that muscle from the margin of the optic foramen. It expands as it passes forwards, to end, in relation to the upper lid, in a membranous expansion which is inserted in a fourfold manner : (1) into the orbicularis oculi and skin of the upper lid, (2) mainly into the superior border of the superior tarsus, (3) into the conjunctiva, and (4) by its edges into the upper border of the margin of the orbital opening. Fig. 399. — Transverse Vertical Section through the Left Orbit BEHIND the Eyeball to show the Arrangement of Muscles. THE FASCIA AND MUSCLES OF THE OPiBIT. 453 Nerve-Supply. — The muscle is srtpplied by the superior division of the oculo-inotor nerve. Actions. — 1 1 elevates the upper eyelid and antagonises the action of the orbicularis ociili muscle. -superior, inferior, medial, < )ui;l< ri.AKis Rectus superior Levator palpebr^e superioris Fig. 400. — Mdscles of the Right Orbit (from above). Mm. Recti. — The recti muscles are tuur in imml»er- and lateral. They all arise rioia a meiubraiiou.s ring surrounding the optic foramen, which is separable into two parts — a superior common tendon, giving origin to the superior and medial recti and the superior head of the lateral rectus ; and an inferior common tendon^ giving origin to the medial and inferior recti and the in- ferior head of the lateral rectus. The two origins of the lateral rectus muscle are separated by the passage into the orbit of the oculo- motor, naso-ciliary, and abducent nerves. Forming flat- tened bands which lie in the fat of the orbit around the optic nerve and eye- ball, the four muscles end in tendons which pierce the fascia bulbi, and are inserted into the sclera about eitfht millimetres (three to four lines) behind the margin of the cornea. The superior and inferior recti are inserted in the vertical plane slightly medial to the axis of the eyeball ; the lateral and medial recti in the trans- verse plane of the eyeball ; and all are attached in front of the equator of the eyeball. M. Obliquus Superior. — The obliquus superior arises from the margin of the optic foramen between the rectus superior and rectus medialis. It passes forwards, as a narrow muscular band, medial to the rectus superior, and at the anterior margin of the orbit forms a narrow ten- don which passes through a special fibrous pulley (trochlea) attached to the roof of the orbit. Its direction is then altered, and passing laterally, between the tendon of the superior rectus and the eye- ball, it is inserted into the sclera be- tween the superior and lateral recti, midway between the margin of the cornea and the entrance of the optic nerve. M. Obliquus Inferior. — The obliquus inferior arises from the medial side of the floor of the orbit just behind its anterior margin, and lateral to the naso- lacrimal groove. It forms a slender rounded slip, which curls round the inferior rectus tendon. 30 & Obliquus superior Levator palpebR/G superioris (cut) Rectus superior Rectus lateralis Octilo-inotor nerve Xaso-ciliary nerve Abducent nerve Obliquus inferior Rectus inferior Fig. 401. — Muscles of the Left Orbit (from lateral aspect). 454 THE MUSCULAR SYSTEM. and passes between the lateral rectus and the eyeball, to be inserted into the sclera between the superior and lateral recti, and farther back than the superior oblique muscle. M. Orbitalis (O.T. Miiller's muscle) is a rudimentary bundle of non-striated muscular fibres bridging across the inferior orbital fissure and infra-orbital groove. It is supplied by fibres from the sympathetic, and may have a slight influence in the protrusion of the eyeball. Lacrimal gland Frontal nerve Supra-orbital nerve Lacrimal nerve Nerves to rectus superior and levator palpebrje superioris, from oculo-motor nerve Trochlear nerv Rectus lateralis Abducent nerve Oculo-motor nerve (inferior, division) Ciliary ganglion Nen'e to rectus inferior, from oculo-motor nerve Nerve to obliquus inferior, from oculo-motor nerve Supra-troclilear nerve Levator palpebr^e superioris Rectus superior Obliquus superior Anterior ethmoidal branch of naso-ciliary nerve Infra-trochlear branch Rectus medialis Nerve to rectus medialis, from oculo-motor Ophthalmic artery Optic nerve Long ciliary nerves Rectus inferior Fig. 402.- Obliquus inferior -Schematic Kepresentation of the Nerves which traverse the Cavity of the Right Orbit. Nerve-Supply.— The muscles of the eyeball are supplied by the third, fourth, and sixth cerebral nerves. The trochlear (fourth nerve) supplies the obliquus, superior ; the abducent (sixth.) supplies the rectus lateralis ; the oculo-motor (third nerve) supplies the others — recti, superior, inferior, and medialis, and obliquus inferior. Actions. — The six muscles inserted into the eyeball serve to move the longitudinal axis of the eyeball ujnvards, downwards, medially, and laterally, besides causing a rotation, of the eyeball on its own axis. The following table expresses the action of individual muscles. It must be remembered that, while similar movements occur simultaneously in the two eyebaUs, the horizontal movements may, by adduction of the muscles of both sides, cause convergence of the axes of the two eyebaUs for the jjurposes of near vision. a. Adduction. Abduction. Rectus medialis Rectus superior Rectus inferior Rectus lateralis Obliquus svi-peviov\{correctmg Obliquus inferior J adductors) b. Elevation. Depression. Rectus superior Obliquus inferior Rectus inferior Obliquus superior c. Rotation laterally. Rotation medially. Obliquus superior Rectus superior \,. ^j t- \ Rectus inferior 1^*^^'^^^^**"'^) Obliquus inferior IVluscIes of lYIastication. The muscles of mastication comprise the masseter, temporal, external and internal pterygoids, and buccinator (described above). M. Masseter. — The masseter is the most superficial. Covered by the parotid gland on the side of the face, it has an origin which is partly tendinous and partly fleshy. It arises in two parts : (1) superficially from the inferior border of the zygomatic arch in its anterior two-thirds, and (2) more deeply from the deep surface of the zygomatic arch in its whole length. The superficial fibres are MUSCLES OF MASTICATION. 455 directed downwards and backwkrds towards the angle of the mandible ; the deeper fibres are directed vertically downwards. The muscle is inserted by fleshy and tendinous fibres into the lateral surface of the ramus and angle of tlie mandible and the coronoid process (Fig. 403). The deepest fibres blend with the fibres of the sub- jacent temporal muscle. The partially Exteri Tfiinporal (part of insprtioii) Masseter (insertion) Buccinator (itart of origin) M. triangularU / I f '// M^ J^^ (origin) Hji M. quaiiratu.s r\J* \^^\ iT^^^^^^ W^^ "T labii inferioris \ \ \^ ^ -r~«*=s=s=i (origin) J \ ^ ^ M. nientalis r\ \ (origiiO'W' \ C^' Platysma*. ^Sft3 (insertion)W. >^^fcZ Fig. 403. — Musclb-Attachment.s to the L.meral Aspect of the Mandible. External ptery- goid (in.sertion) muscle is concealed on the face by the parotid gland", ac- cessory parotid gland, and parotid duct ; by the ex- ternal maxillary artery ; the branches of the facial nerve ; and by the zygo- matic and platysma muscles. It conceals the ramus of the mandible, and, at its anterior border, is separated from the buccinator muscle by the corpus adiposum buccce. M. Temporalis. — The temporal muscle is a fan-shaped muscle arising from the whole area of the temporal fossa, as well as from the temporal fascia which covers it. Its converging fibres pass medial to the zygomatic arch. The muscle is in- serted into the deep surface and apex of the coronoid process, and into the anterior border of the ramus of the mandible (Figs. 403 and 404). The origin of the muscle is concealed by the temporal fascia. As it passes to its in- sertion the muscle is concealed by the zygo- matic arch, the masseter muscle, and the coronoid process of the mandible. It is separated from the external pterygoid in a majority of cases by the internal maxillary artery. The masseteric nerve and vessels appear at its posterior border ; the buccinator nerve and vessels at its anterior liorder. M. Pterygoideus Externus. — The external pterygoid muscle is deeply placed under cover of the temporal muscle, in the infra-temporal fossa. It arises by two heads, superior and inferior. The superior head is attached to the infra-temporal surface of the great wing of the sphenoid ; the inferior head takes origin from the lateral surface of the lateral pterygoid lamina of the pterygoid process. The muscle is directed laterally and backwards, to be inserted into (1) the 30 c Genio-hyoid Fig. -104.- -Mlocle-Attachments on the Medial Side of the Maxdible. 456 THE MUSCULAE SYSTEM. Galea aponeurotica Temporal fascia Temporal fascia (deep layer) Occipitalis musclk — {4-L- ^.^l' Temporal muscle— "-^—J'^'^' Aiiriculo-temporal nerve Superficial temporal artery Masseter (deep fibres)- Parotid gland (drawn backwards and downwards) Orbicularis ocoli Caput zygomaticum of quadratus labii superioris Masseter (superficial fibres) Parotid duct Buccinator Triangularis muscle External maxillary artery Fig. 405. — Muscles of Mastication (superficial xiew). Temporal muscle --Buccinator Fio. 406. — The Riqht Temporal Mdscle. (The Zygomatic Arch and the Masseter Muscle have been removed.) MUSCLES OF MASTICATION. 457 fovea pterygoidea on the anterior a.spect of the neck of the mandihle (Figs. 403 and 404, p. 455), and (2) the articular disc and capside of the mandibular articulation. This muscle is covered Ity the insertion of the temporal muscle and the coronoid process of the mandible, and is usually crossed y>y the internal maxillary artery. It conceals the mandibular Iiranch of the trigeminal nerve, and the pterygoid origin of the internal jtterygoid muscle. M. Pterygoideus Internus. — The internal pterygoid muscle, placed beneath tiie external pterygoid m\isele and the ramus of the niaiidil)le, has likewise a double origin — (1) from the medial surface of the lateral pterygoid lamina and the pyramidal process of the palate bone, and (2) by a stout tendon from the tuberosity Temporal mi'scle (rettectpH) e.xtern.il pterygoid Internal pteryooid Pterygo-niaiidibular raphe Buccinator Fig. 407. — The Pterygoid Muscles of the Kight Side. of the. maxilla. Its two heads of origin embrace the inferior fibres of the external pterygoid muscle. 'It is quadrilateral in form, and is directed downwards, laterally, and backwards lateral to the auditory tube and the tensor and levator muscles of the palate, to be inserted into a triangular impression on the medial surface of the mandible, between the mylo-hyoid groove and the angle of the bone (Fig. 404, p. 455). This muscle is covered by the ramus of the mandible and temporal muscle, and partially by the external pterygoid muscle. In contact with its superficial surface are the spheno-mandibular ligament, and the inferior alveolar and lingual nerves and their accompanying vessels. The muscle conceals the tensor veli palatini and the wall of the pharynx (superior constrictor). Nerve-Supply.— The mandibular division of the trigeminal nerve supplies all the muscles of luastication except the buccinator, wliich is supplied by the facial nerve. The internal pterygoid muscle is supplied by the nerve before its division into anterior and posterior parts ; the other muscles are innervated by the anterior trunk. Actions.— The above muscles, assisted by others in the neck, produce the various move- ments of the mandible as follows : — 458 THE MUSCULAR SYSTEM. a. Opening of the Mouth. Weight of the mandible Digastric Mylo-hyoid Genio-hyoid Genioglossus Infra-hyoid muscles h. Protrusion of the Mandible. External pterygoid Internal pterygoid Temporal {anterior fibres) Closure of the Mouth. Masseter | Temporal Internal pterygoid Retraction of the Mandible. Temporal {posterior fibres) c. Lateral Movement of the Mandible. frnT/^'^T'iw »»-■*) THE MUSCLES OF THE NECK. In addition to those included among the muscles of the back (p. 438), the following series of muscles occur in the neck : (1) sterno-cleido-mastoid; (2) the muscles of the hyoid bone (supra-hyoid and infra-hyoid) ; (3) the muscles of the tongue (extrinsic and intrinsic) ; (4) the muscles of the pharynx and soft palate ; and (5) the prte vertebral muscles. M. Sternocleidomastoideus. — The sterno-mastoid muscle is the prominent muscle projecting on the side of the neck, and separating the anterior from the posterior triangle. It arises by two heads — (1) a narrow, tendinous, sternal head, from the anterior surface of the manubrium sterni (Fig. 330, p. 370), and (2) a broader clavicular origin, partly tendinous, partly fleshy, from the superior surface of the clavicle in its medial third (Fig. 327, p. 366). The muscle is inserted into the lateral surface of the mastoid portion of the temporal bone and into the superior nuchal line of the occipital bone (Fig. 396, p. 444). The muscle passes obliquely over the side of the neck, separating the anterior from the posterior triangle. It is almost superficial in its whole extent, but is overlapped superiorly by the parotid gland and is covered in its inferior part by the platysma. It is crossed by the external jugular vein, and by superficial branches of the cer\ical plexus. Its deep surface is in contact with: {a) in its lower third, the infra-hyoid muscles, which separate it from the common carotid artery, and the subclavian artery and the internal jugular vein ; (&) in its middle third, with the cervical nerves which emerge between the transverse processes of the cervical vertebrse to form the cervical plexus ; and (c) in its superior third, with the splenius capitis muscle, and the accessory nerve, which there pierces the deep surface of the muscle. Near its insertion the muscle is related to the splenius capitis, longissimus capitis, the posterior belly of the digastric, and the occipital artery. The stemo-cleido-mastoid muscle is properly divisible into three parts : (l) sterno-mastoid, placed superficially, and passing obliquely from the sternum to the mastoid process ; (2) cleido- mastoid, placed more deeply, and directed vertically upwards from the clavicle to tlie mastoid proce.ss ; and (3) cleido-occipitalis, passing obliquely upwards and backwards behind the cleido- mastoid to the sujjerior nuchal line of the occipital bone. Nerve-Supply. — The sterno-mastoid muscle is innervated by the accessory nerve, joined by a branch from the cervical plexus (C. 2.). Actions. — When one muscle acts alone, it flexes the head laterally, and rotates it to the opposite side. The two muscles acting together (1) flex the head in a forward direction, and (2) act as extraordinary muscles of inspiration, by raising tke sternum and clavicles. The Muscles of the Hyoid Bone. The muscles attached to the hyoid bone are in three series : (1) infra-hyoid muscles, connecting the hyoid bone to the scapula, the wall of the thorax, and THE MUSCLES OF THE HYOID BONE. 459 thyreoid cartilage : (2) supra-hyoid muscles, connecting it to the mandible, cranium, and tongue ; and (3) the middle constrictor muscle of the pharynx (p. 464). The infra-hyoid muscles comprise the omo-hyoid, sterno-hyoid, sterno-thyreoid, and thyreo-hyoid muscles. M. Omohyoideus. — The omo-hyoid is a muscle with two bellies, anterior and posterior. The posterior belly arises from the superior margin of the scapula and the superior trausvei-se scapular ligament (Fig. 333, p. 372). It forms a narrow muscular band, which passes obliquely forwards and upwards, and ends in an intermediate tendon beneath the sterno-mastoid muscle. From this tendon the anterior belly proceeds upwards, to be inserted into the lateral part of the inferior border of the body of the hyoid bone. The posterior belly of the muscle separates the posterior triangle into occipital and subclavian parts ; the anterior belly crosses the common carotid artery at the STVLOOLOSSIs - Htcki Losses -Gr.NIO-HTOID ■^ :5TERJ!0-TH VBEOID _Sterno-hyoid Fig. 4v-. — iMh n iHE TuNtiUE A>D Hyoiu Bone iright side). level of the cricoid cartilage, and in the anterior triangle forms the boundary between the muscular and carotid triangles. A process of the deep cervical fascia binds down the tendon and the posterior belly to the cla\dcle and the first rib. M. Sternohyoideus. — The sterno-hyoid muscle arises from the posterior surface of the manubrium, from the back of the first costal cartilage, and from the clavicle (Fig. 327, p. 366). It passes vertically upwards in the neck, medial to the omo-hyoid and anterior to the sterno-thyreoid muscle, to be inserted into the medial part of the body of the hyoid bone. ' Except near its origin, whicli is covered by the sternum, clavicle, and sternal head of the sterno-mastoid, the muscle is superficially placed. M. Sternothyreoideus. — The sterno-thyreoid muscle arises beneath the sterno-hyoid from the back of the manubrium and first costal cartilage. Broader than the preceding muscle, it passes upwards, and sHghtly in a lateral direction in the neck, in front of the trachea and thyreoid gland, and deep to the sterno-mastoid, omo-hyoid, and sterno-hyoid muscles. It is inserted into the oblique 460 THE MUSCULAE SYSTEM. line of the thyreoid cartilage. The muscle is marked by an oblique tendinous intersection in the middle of its length. M. Thyreohyoideus. — The thyreo-hyoid muscle continues the line of the preceding muscle to the hyoid bone. Short and quadrilateral, it arises from the oblique line of the thyreoid cartilage. Passing over the thyreo-hyoid membrane, deep to the omo-hyoid and sterno- hyoid, it is inserted into the body and great cornu of the hyoid bone. The levator glandulse thyreoideae is an occasional slip stretching between the hyoid bone and the isthmus or pyramid of the thyreoid gland. Mylo-hyoid Digastric Hyoolossus Stylo-hyoid Middle constrictor Thykeo-hyoid Inferior constrictor Omo-hyoid Inferior constrictor Sterno-hyoid Sterno-thyreoid Fig. 409. — The Muscles op the Side of the Neck (anterior and posterior triangles). Nerve-Supply.— The sterno-hyoid, sterno-thyreoid, and omo-hyoid are supplied by the ansa hypofjlossi ; the thyreo-hyoid, by a special branch from the hypoglossal nerve. Through the ansa hypoglossi the muscles are innervated by nerves which are ultimately derived from the first three cervical nerves. The descendens hypoglossi is derived from the first two cervical nerves, the descendens cervicis by the second and third ; and these two trunks combine to form the ansa. The thyreo-hyoid muscle is innervated (through the hypoglossal) from the loop between the first and second cervical nerves. Actions.— The sterno-hyoid, sterno-thyreoid, and omo-hyoid are depressors of the hyoid bone. The two f(jrmer muscles are also accessoiy muscles of inspiration. The omo-hyoid is a feeble elevator of the scapula. The thyreo-hyoid is, on the one hand, an elevator of the thyreoid cartilage, and acting with the pr(;vious muscles, on the other hand, it is a depressor of the hyoid bone. The supra-hyoid muscles comprise the digastric, stylo-hyoid, mylo-hyoid, and THE MUSCLES OF THE HYOID BONE. 461 genio-hyoid muscles; and also two muscles, the genioglossus aud hyoglossus, which will be described along with the extrinsic muscles ot" the tongue. M. Digastricus. — The digastric muscle, as its name implies, possesses two bellies — anterior and posterior. The podevior belly arises, under cover of the sterno-mastoid muscle, from the mastoid notch medial to the mastoid process. It is directed forwards aud down- wards, in company with the stylo-hyoid muscle, to end in an intermediate tendon, which is connected by a pulley-like band of cervical fascia to the body of the hyoid bone. The anterior belly of the muscle is directed iorvvards aud upwards, over the mylo-hyoid muscle, to the chin, aud is inserted into the oval digastric fossa on the inferior border of the mandible close to the symphysis (Fig. 410). The muscle forms the inferior boundary of the submaxillary division of the anterior triangle, containing the submaxillary gland. The posterior belly in company with the stylo-hyoid crosses the carotid arteries and internal jugular vein. The occipital arterv ex- . 1 ^ ^ . , " , External ptery- tends posteriorly along Koid (insertion) its inferior margin, and the parotid gland covers its superior border. The hypoglossal nerve emertjes from under ^ ^ , , , Superior con- COVer ot the muscle. stricter (origin) The anterior l)elly, as it passes to its insertion, lies upon the mylo- hyoid muscle.' Nerve - Supply. — The posterior belly is supplied by the facial nerve ; the anterior belly by the nerve to the mylo-hyoid, a branch of the inferior alveolar Fig. 410. -Muscle-Attachments on the Medial Side ok the Mandible. M. Stylohyoideus. — The stylo-hyoid muscle arises from the posterior border of the styloid process of the temporal bone. Crossing the anterior triangle obliquely, along with the posterior belly of the digastric muscle, it is inserted into the body of the hyoid bone, by two slips which enclose the tendon of the digastric muscle. Nerve-Supply. — Facial nerve. M. Mylohyoideus. — The mylo-hyoid muscle forms with its fellow a diaphragm in the floor of the mouth. It arises from the inferior three-fourths of the mylo-hyoid ridge of the mandible (Fig. 410). It is directed downwards and medially, to be inserted into (1) the superior border of the body of the hyoid bone, and more anteriorly (along with the opposite muscle) into (2) a median raphe extending from the hyoid bone nearly to the chin. The muscle is in contact, on its superficial or lateral surface, with the digastric muscle and the submaxillary gland. Its deep or medial surface is partially covered by the mucous membrane of the floor of the mouth, and is separated from the muscles of the tongue by the deep part of the submaxillary gland, the sub- lingual gland, the submaxillary duct, and the lingual and hypoglossal nerves. Nerve-Supply, — The muscle is supplied by the nerve to the mylo-hyoid, a branch of the inferior alveolar nerve. M. Geniohyoideus. — The genio-hyoid muscle arises from the inferior of the two mental spines on the posterior surface of the symphysis of the mandible (Fig. 410). 462 THE MUSCULAE SYSTEM. It is directed downwards and somewhat posteriorly, along the inferior border of the genioglossus, to be inserted into the anterior surface of the body of the hyoid bone. The muscles of opposite sides are often fused together. The muscle is placed deeper than the anterior belly of the digastric muscle and the mylo-hyoid, and is in contact with the inferior border of the genioglossus muscle. Nerve-Supply. — It is supplied by the hypoglossal nerve, but its nerve can be traced back to an origin from the communication between that nerve and the first and second cervical nerves. Actions.— The digastric, stylo-hyoid, mylo-hyoid, and genio-hyoid muscles are all elevators of tlie hyoid bone. The posterior belly of the digastric and stylo-hyoid also retract, while the anterior belly of the digastric and the genio-hyoid protract it. The anterior belly of the digastric, mylo-hyoid, and genio-hyoid also assist in opening the mouth. M. ^■erticali.s linguae Profunda linguw artery Septum B linyua M. longitudinalis inferior The IVIuscIcs of the Tongue. The muscular substance of the tongue consists of two symmetrical series of muscles placed on either side of a membranous raphe in the median plane. The series comprise (1) extrinsic M. transversus M. verticaiis '" ";;;^"prTnr ~ "" linrcm* musclcs arisiug from the soft palate, styloid process, hyoid bone and mandible, and (2) intrinsic muscles proper to the tongue itself. Each set consists of four series of muscles. A. The extrinsic mus- cles are four in number : (1) genioglossus, (2) hyo- glossus, (3) styloglossus, and (4) glossopalatinus. M. Genioglossus. — The genioglossus muscle (O.T. geniohyoglossus) M. transversus (Fig. 408, p. 459) is an ex- trinsic muscle of the tongue as well as a supra -hyoid muscle. It is a fan-shaped muscle arising by its apex from the superior of the- two mental spines, behind the symphysis of the mandible (Fig. 410, p. 461). From that origin the muscular fibres diverge ; the lowest fibres are directed downwards and backwards, to be inserted into the body of the hyoid bone ; the highest fibres curve forwards, to be attached to the tip of the tongue ; the inter- mediate fibres are attached to the substance of the tongue in its whole length between the base and tip. The muscles of opposite sides are separated by the median raphe of the tongue. On the lateral aspect, of each, are the hyoglossus and mylo-hyoid muscles. M. Hyoglossus. — The hyoglossus muscle is also an extrinsic muscle of the tongue as well as a supra-hyoid muscle. It arises from the body and great cornu of the hyoid bone. It is directed upwards and forwards, to be inserted into the side of the tongue, its fibres interlacing with the fibres of the styloglossus. The muscle is quadrilateral, and lies between the genioglossus and mylo-hyoid muscles, separated from the latter by the mucous membrane of the floor of the mouth, the sublingual and part of the submaxillary glands, the lingual and hypo- glossal nerves, and the submaxillary duct. The chondroglossus is a small separated slij) of the hyoglossus, not always present. Fig. 411. — A, Transverse, and B, Longitudinal Vertical Sections through the Tongue (Krause). THE MUSCLES OF THE TONGUE. 463 M. Styloglossus. — The styloglossus muscle arises from the anterior border of the styloid process near its tip, and from the stylo-hyoid ligament. It sweeps forwards and medially, and is inserted into the side and inferior surface of the tongue, its fibres spreading out to decussate with those of the glossopalatinus and hyoglossus muscles beneath the subma.xillary gland and the mucous membrane of the tongue. M. Glossopalatinus. — The glossopalatinus (O.T. palatoglossus) is a thin sheet of muscular fibres arising from the inferior surface of the soft palate, where it is continuous with fibres of the opposite nmscle. It passes downwards, in the glosso-palatiue arch, and spreads out, to be inserted into the sides of the tongue, blending with the styloglossus and the deep transverse fibres of the tongue. The muscle is placed directly beneath the mucous membrane of the soft palate and tongue. B. Intrinsic Muscles of the Tongue. — Besides receiving the fibres of insertion of the extrinsic muscles, the substance of the tongue is composed of four intrinsic muscles on either side — two in the sagittal plane, the superior and inferior longi- tudinal muscles ; two in the frontal plane, the transverse and vertical muscles. M. Longitudinalis Superior. — The superior longitudinal muscle extends from base to tip of the tongue. It is placed on its dorsum immediately under the mucous membrane, into which many of its fibres are inserted. M. Longitudinalis Inferior. — The inferior longitudinal muscle is a cylindrical band of muscular fibres occupying the inferior part of the organ on each side, in the interval between the genioglossus and the hyoglossus muscles. Posteriorly some of its fibres extend to the hyoid bone. M. Transversus Linguae. — The transversus linguae (O.T. transverse fibres) arises from the median raphe, and radiates outwards to the dorsum and sides of the tongue, intermingling with the extrinsic muscles and the fibres of the vertical muscle. It occupies the substance of the tongue between the superior and inferior longitudinal muscles. M. Verticalis Linguae. — The verticalis linguae (O.T. vertical fibres) arises from the dorsal surface of the tongue, and sweeps downwards and laterally to its sides, intermingled with the fibres of the preceding muscle and the insertions of the extrinsic umscles. The transverse and vertical muscles form a very considerable part of the total muscular substance of the organ. Nerve-Supply. — All these muscles except the glossopalatinus are supplied by the hypo- glossal nerve. The glossopalatinus is supplied by the accessory nerve through the pharyngeal plexus. Actions. — The genioglossus and the hyoglossus are both elevators of the hyoid bone besides having actions in relation to the tongue. The tongue is protruded by the action of the posterior fibres of the genioglossus, retracted by the anterior fibres aided by the styloglossus. The styloglossus and glossopalatinus are elevators, while the genioglossus and hyoglossus are depressors of the tongue. Actions of the Infra -hyoid and Supra -hyoid Muscles, and the Muscles of the Tongue. — These muscles have a complexity of action, owing to their numerous attachments to more or less movable points. The movements for which they are responsible in whole or part are : (1) movements of the hyoid bone in mastication and deglutition, (2) movements of the thyreoid cartilage, (3) movements of the tongue, (4) movements of the head, (5) movements of the shoulder, and (6) respiration. (1) Movements of the Hyoid Bone. — The hyoid bone is elevated or depressed, and moved for- wards or backwards along with the mandible and tongue, in speech, mastication, and swallowing. a. Elevation. Digastric Stylo-hyoid Mylo-hyoid Genio-hyoid Genioglossus Hyoglossus Muscles closing mouth the Depression. Thyreo-hyoid Sterno-hyoid Omo-liyoid Stemo-thyreoid b. Protraction. Genio-hyoid Genioglossus Retraction. Stylo-hyoid Middle constrictor 464 THE MUSCULAR SYSTEM. (2) Movements of the Thyreoid Cartilage. — The thyreoid cartilage is raised and lowered during speech and deglutition. Elevation. Depression. Thyreo-hyoid StylopharjTigeus Pharyngopalatinus Elevators of hyoid bone Muscles closing mouth Sterno-thyreoid Crico-thyreoid Depressors of hyoid bone (3) Movements of the Tongue. — The chief movements of the tongue in speech and de- glutition are elevation and depression, protrusion and retraction, and lateral movements. a. Elevation. 1 Depression. Styloglossus (base) Glossopalatinus Muscles elevating hyoid bone Muscles closing mouth Genioglossus Hyoglossus Chondroglossus Muscles depressing the hyoid bone 6. Protrusion. Retraction. Genioglossus {posterior fibres) Genioglossus {anterior fibres) Styloglossus c. Lateral Movements. — The muscles of one side only. (4) Movements of the Head. — The stemo-mastoid muscles, acting together, flex the head on the vertebral column, assisted by the supra-hyoid and infra-hyoid muscles. The stemo-mastoid muscle of one side, acting alone, bends the head to the same side, and simultaneously rotates it to the opposite side, as seen in torticollis (wryneck). (5) Movements of the Shoulder Girdle. — The omo-hyoid and stemo-mastoid muscles have already been included among the elevators of the shoulder girdle. (6) Respiration. — The muscles in the front of the neck are auxiliary muscles in extraordinary or difficult inspiration. The masseter and temporal muscles fix the mandible ; the hyoid bone is raised and fixed by the supra-hyoid muscles ; and the sternum is raised by the stemo-mastoid and infra-hyoid muscles. The lYIuscIes of the Pharynx. The muscular envelope of the pharynx is composed of two strata. The external or circular layer consists of the three fan-shaped constrictor muscles ; the internal or longitudinal layer consists of the fibres of the stylopharyngeus and pharyngo- palatinus muscles. M. Constrictor Pharyngis Superior. — The superior constrictor muscle arises successively from the inferior half of the posterior border of the medial lamina of the pteryg9id process (pterygopharyngeus), from the pterygo- mandibular raphe (buccopharyngeus), from the mylo-hyoid line of the mandible (mylopharyngeus) (Fig. 410, ix 461), and from the mucous membrane of the fioor of the mouth (glossopharyngeus). The muscular fibres radiate backwards, and are inserted, for the most part, into a raphe extending down the posterior wall of the pharynx in the median plane. The highest fibres are attached to the pharyngeal tubercle of the occipital bone (Fig. 396, p. 444), and the lowest fibres are overlapped by the middle constrictor. A crescentic interval occurs above the muscle, below the base of the skull, in which the auditory tube and the levator and tensor veli palatini muscles appear. Its lower border is separated from the middle constrictor by the stylopharyngeus muscle. M. Constrictor Pharyngis Medius. — The middle constrictor muscle arises from the stylo -hyoid ligament and from both cornua of the hyoid bone (chondro- pharyngeus, ceratopharyngeus). From its origin the mu.scular fibres radiate backwards, to be inserted into the median raphe on the posterior aspect of the pharynx. THE MUSCLES OF THE PHARYNX. 465 the Pharyngo-basilar fascia The superior fibres overlap -the inferior part of the superior constrictor; the inferior fibres are concealed from view by the inferior constrictor muscle. In the interval between the middle and inferior constrictors are found the superior laryngeal artery and internal laryngeal nerve. M. Constrictor Pharyngis Inferior. — The inferior constrictor muscle arises from the obli(|ue line of the thyreoid cartilage (thyreopharyngeus), and from the side of the cricoid cartilage (cricopharyngeus). Its fibres radiate backwards, to be inserted into the median raphe on the posterior wall of the pharynx, the superior fibres overlapping the inferior part of the middle constrictor, the inferior fibres blending with the muscular fibres of the oesophagus. Below the inferior border of the muscle the inferior laryngeal artery and nerve enter into relation with the larynx. Nerve-Supply. — The constrictors of the pharynx receive their nerve-supply through pharyngeal i)lexiis from the accessory nerve. The inferior constrictor is supplied also by the external laryngeal and recurrent branches of the vagus nerve. The deeper longitudinal stratum of muscles in the pharyngeal wall is composed of the insertions of the stylopharyngeus and pharyngopala- tinus muscles. M. Stylopharyngeus. — The stylo- pharyngeus arises from the root of the styloid process on its medial side, and passes downwards between the external and internal carotid arteries. It enters the wall of the pharynx in the interval between the superior and middle constrictor muscles. Spreading out beneath the middle constrictor muscle, it is inserted into the superior and posterior borders of the thyreoid cartilage and into the wall of the pharynx itself, becoming continuous posteriorly with the palato- pharyngeus. In the neck the glosso- pharyngeal nerve winds round it on its way to the tongue. Nerve-Supply. —Glossopharyngeal nerve. oesophagus (with posterior ends of traclieal rings showing at the sides) Auditory tube Levator veli palatini Ml'SCLE (cut) Tensor veli palatini Superior constrictor bcccinator Pterygo- mandi- bular raphe Stvlo- pharvnoeus Middle constrictor Greater cornu of hyoid bone Inferior constrictor Fig. 412. — Posterior View of the Pharynx and Constrictor Mdsclks. M. Pharyngopalatinus. — The pharyngopalatinus (O.T. palato- pharyngeus) occupies the soft palate and the pharyngeal wall. In the substance of the soft palate it consists of two layers, a postero-superior layer, thin, and continuous across the median plane with the corresponding layer on the opposite side, and an antero-inferior layer, which is thicker, and is attached to the posterior border of the hard palate. The levator veli palatini and the musculus uvulae are enclosed between the two layers, which unite at the posterior edge of the palate, receiving at the same time additional fibres arising from the auditory tube (salpingopharyngeus). The muscle descends to the pharynx in the pharyngo-palatine arch. Its fibres spread out in the form of a thin sheet in the wall of the pharynx, in continuity anteriorly with the stylopharyngeus, and are inserted into the posterior border of the thyreoid cartilage, and behind that into the aponeurosis of the pharynx, reaching down as far as the inferior border of the inferior constrictor. The muscle is placed beneath the middle and inferior constrictors, and the fibres 31 466 THE MUSCULAE SYSTEM. of the muscles of opposite sides decussate in the median plane, in the inferior part of the pharyngeal wall. Nerve-Supply. — The muscle is innervated througli tlie pliaiyngeal plexus, by the accessory nerve. The IVIusclcs of the Soft Palate. The soft palate and uvula form a muscular fold, covered on each surface by mucous membrane, projecting backwards into the pharynx, and forming the posterior parts of the floor of the nasal cavities and the roof of the mouth. The muscular fold is composed of five pairs of muscles — the pharyngopalatinus, m. uvulae, levator veli palatini, tensor veli palatini, and glossopalatinus. The pharyngopalatinus muscle has been already described (p. 465). The m. uvulae (O.T. azygos uvulae) consists of two narrow bundles enclosed, along with the insertion of the levator veli pala- tini, between the layers of the pharyngopala- tinus. The slips arise from the posterior nasal spine and the aponeurosis of the soft palate, and unite as they pro- ceed backwards to end in the uvula. M. Levator Veli Palatini. — The levator veli palatini has a double origin : (1) from the inferior surface of the apex of the petrous por- tion of the tem- BUCCINATOR Mylo-hyoid Hyoolossus Digastric Stylo-hyoid Omo-hyoid Sterno-hyoid Thyreo-hyoid Crico-thyreoid- — Tensor veli palatini MUSCLE Auditory tube Levator veli palatini ■Pteiygo-inandibular raphe Superior constrictor Stylopharyngeus -Styloglossus Glosso-pliaryiigeal nerve Stylo -liyoid ligament Hypo-glossal nerve Middle constrictor Digastric Superior laryngeal iierve Inferior constrictor External laryngeal nerve (Esophagus Recunent nerve Fig. 413.— Latekal View of the Wall of the Pharynx. poral bone and (2) from the inferior part of the cartilaginous part of the auditory tube. It passes obliquely downwards and medially, across the superior border of the superior constrictor muscle, and enters the soft palate between the two layers of the pharyngopalatinus muscle. t^ ■. nr It is inserted into the aponeurosis of the soft palate, and some ot its fibres become continuous with those of the opposite muscle. It is separated from the tensor veli palatini muscle by the auditory tube and the deeper layer of the pharyngopalatinus muscle. M. Tensor Veli Palatini.— The tensor veli palatini arises (1) from the scaphoid fossa and the angular spine of the sphenoid bone, and (2) from the lateral side of the cartilaginous part of the auditory tube. LATEEAL AND PE^:VERTEBEAL MUSCLES OF THE NECK. 467 It descends, between the internal pterygoid muscle and the medial pterygoid lamina, and ends in a tendon which hooks round the pterygoid lianiulus. The tendon is inserted, beneath the levator veli palatini, into the ])Osteri(jr border of the hard palate, and into the aponeurosis of the soft palate. M. Glossopalatinus. — The glossopalatinus (O.T. palatoglossus), occupying the inferior surface of the soft palate and the glosso-palatinc arch, has already been described with the muscles of the tongue (p. 463). Nerve-Supply, — The nnisclcs of the soft jjalate (except the tenaor veli palatini, which is innervated throiif,'h the otic ganglion by the trigeminal nerVe) are supplied througli the j)haryu- geal pli'.\.us l>y tlu; accessory nervi-. Actions of the Muscles of the Pharynx and Soft Palate. -Tlie muscles of the i)liarynx and soft palate are chiefly brouglit into action in the act of swallowing. This act is divided into a voluntary stage, in which the bolus lies anterior to tlie arches of th(! fauces, and an involuntary stage, during which the food passes from the moutli througli the pharynx. The movements occurring during the passage of food through the mouth are as follows : the cheeks are compressed by the action of the buccinator nuiscles ; the t(jngue, hyoid bone, and thyreoid cartilage are successively raised upwards by the action of the muscles which close the mouth and elevate the hyoid bone. By those means the food is puslied Ijackwards between the palatine arches. At the same time, by the contraction of the gloss(j-j)alatinus and pharyngo-palatinus, the palatine arches of the fauces are nai'rowed, while the muscles of the soft palate, contracting, tighten the soft palate, and by bringing it in contact with the posterior wall of the pharynx, shut off the nasal portion of the cavity. The elevation of the tongue, hyoid bone, and larynx simultaneously causes the elevation of the epiglottis and the superior aperture of the larynx, which is closed by the approximation of the arytajnoid cartilages and the combined action of laryngeal nuiscles (ai'ytieuoideus, thyreoarytrenoideus, and thyreoepiglotticus). The food thus slij)s over the anterior surface of the epiglottis and the closed superior aperture of the larynx, and between the palatine arches on either side, into the pharynx. It is now clasped by the constrictor nuiscles, which, by their contractions, force it down into the oesophagus. The contraction of the constrictor muscles results in a flattening of the pharynx and elevation of its anterior attachments. During the act of swallowing, it is generally thought that the auditory tube is opened by the contraction of the tensor veli palatini muscle, which arises from it. It has been held, on the other hand, that the auditory tube is closed during swallowing by the compression of its wall by the contraction of the levator veli palatini. Deep Lateral and PraBvertebral Muscles of the Neck. Three series of muscles are comprised in this group : (1) vertebro-costal (scaleni, anterior, medius, and posterior), (2) vertebro- cranial (longus capitis and rectus capitis anterior, and lateralis), and (3) vertebral (longus colli). They clothe the anterior surface of the cervical portion of the vertebral column for the most part, and are in relation anteriorly with the pharynx and oesophagus, and the large vessels and nerves of the neck. M. Scalenus Anterior. — The scalenus anterior (O.T. anticus) arises from the anterior tubercles of the transverse processes of the third, fourth, fifth, and sixth cervical vertebrae. It descends, posterior to the carotid sheath and subclavian vein, to be inserted into the scalene tubercle and ridge on the first rib (Fig. 414, p. 468). It is separated posteriorly from the scalenus medius by the roots of the brachial plexus, the subclavian artery, and the pleura, and it is concealed by the sterno- mastoid muscle. M. Scalenus Medius. — The scalenus medius arises from the posterior tubercles of the transverse processes of the cervical vertebrse, from the second to the sixth inclusive. It descends in the posterior triangle, behind the subclavian artery and the roots of the brachial plexus, to be inserted into the rough impression on the first rib behind the subclavian groove (Fig. 414, p. 468). The muscle is pierced by the dorsal scapular and long thoracic nerves. It is separated from the scalenus anterior by the subclavian artery and the roots of the bracliial plexus. M. Scalenus Posterior. — The scalenus posterior arises, behind the scalenus medius, from the posterior tubercles of the fourth, fifth, and sixth cervical transverse processes. It is inserted into an impression on the outer side of the second rib. 468 THE MUSCULAE SYSTEM. Serratus posterior superior (insertion) Serratus anterior (origin) Pectoralis minor (occasional origin) Fig. 414. — Muscle-Attachments to First Rib, and the External (Right Side). . „. ' A, First rib : Nerve-Supply.— The mus- cle receives nerves directly from the anterior rami of the first four cervical nerves. Action. — Flexion of the head and cervical vertebrae. M. Rectus Capitis Anterior. — The rectus capitis anterior (O.T. rectus capitis anticus minor) arises, under cover of the preceding muscle, from the lateral mass of the atlas. It is inserted into the basilar part of occipital bone between the preceding muscle and the occipital condyle (Fig. 417, p. 469). Nerve -Supply. — The mus- cle is innervated by the loop between the first two cervical nerves (anterior rami). Action. — Flexion of the head on the vertebral column. M. Longus Colli. — The longus colli is a flattened muscular band extending from the third thoracic vertebra to the atlas. It Nerve -Supply. — The scalene muscles are supplied by branches which arise directly from the anterior rami of the lowest four or five cervical nerves. Actions. — The actions of those muscles are twofold. They are lateral flexors of the vertebral column, and are also important scalenus medius (insertion) ^^^^^^^^ ^f respiration, as elevators of the first and second ribs. M. Long-US Capitis. — The longus capitis (O.T. rectus capitis anticus major) arises from the an- terior tubercles of the trans- verse processes of the third, fourth, fifth, and sixth cervi- cal vertebrae. It forms a flat triangular muscle, which is directed up- wards, alongside the longus colli muscle and behind the carotid sheath, to be inserted into an impression on the inferior surface of the basilar the Superior Surface of the part of the occipital bone, Surface of the Second Rib anterior and lateral to the B, Second rib. pharyngeal tubercle (Fig. 417, p. 469). Rectus capitis lateralis Rectus capitis anterior Longus capitis Longus colli Fig. 415. — The PuiF^VERTEBRAL Muscles of the Neck. LATEEAL AND PK^VERTEBKAL MUSCLES OE THE NECK. 469 is divisible into three portions — a vertical, an inferior oblique, and a su[>erior oblique portion. Atlachi'il to IHistcrior tubercles (ifv transverse Iiroi'essus SlAI.ENHS MKllIUij Lkvatou scatula; Sri.KNIUfJ CEKVICIS fJcALE.NUS POSTKKIOB Iliocostalis CKRVICIS LONOISSIML'S CEUVIflS f LONOISSIM AUacheil to Semisi'INai artic-tilar-: processes Semispi LONOISSIMIS <'AI'ITI8 IS CAPITIS NALIS CERVICIS MULTIKIUUS LoNfiUS CAPITIS ' 4 LONCUS CXJLLI ^ Attaclitxl to anterior tubercles of transverse jirocesscs Fu;. 416. — Scheme of Muscular Attachments to Cekvical Vkhtebum. The vertical portion of the muscle arises from the bodies of the first three thoracic and the last three cervical vertebrie. Passing vertically upwards, it is inserted into the bodies of tiie second, third, and fourth cervical vertebrne. Scmispinalis capitis (insertion) Rectus capitis posterior minor (insertion) \ Rectus capitis posterior iiuijor (insertion) Trapezius (origin) Sterno-cleido-iiiastoid (insertion) Splenius capitis (insertion) Obliiinus capitis superior (insertion) Rectus capitis lateralis (insertion) Rectus capitis anterior (insertion) )erior constrictor of pharj-nx (insertion) Longus capitis (insertion) Fig. 417. — Muscle-Attachments to the Occipital Bone. The inferior oblique portion arises from tlie bodies of the first three thoracic vertebra\ It is inserted into the anterior tubercles of the fifth and sixth cervical vertebrae. 31a 470 THE MUSCULAR SYSTEM. The superior oblique portion arises from the anterior tubercles of the transverse processes of the third, fourth, and tifth cervical vertebrae. It is directed upwards, to be inserted into the anterior tubercle of the atlas. Nerve-Supply. — It is supplied by nerves from the anterior rami of the second, third, and fourth cervical nerves. Action. — A Hexor of the vertebral column. M. Rectus Capitis Lateralis. — The rectus capitis lateralis, in series with the posterior inter- transverse muscles in the neck, arises from the transverse process of the atlas. It is inserted into the inferior surface of the jugular process of the occipital bone. It is placed alongside the rectus capitis anterior, separated from it by the anterior ramus of the first cervical nerve. Nerve-Supply. — The loop between the anterior rami of the first two cervical nerves. Actions. — A lateral flexor of the head and vertebral column. The movements produced by these muscles are considered along with those of other muscles acting on the head, vertebral column, and thorax (pp. 445, 446). THE MUSCLES OF THE THORAX. Muscles of Respiration. The muscles which complete the boundaries of the thorax are the diaphragm and intercostal muscles (external and internal), along with three series of smaller muscles — the transversus thoracis, the levatores costarum, and the subcostal muscles. Mm. Intercostales. — The intercostal muscles are arranged in eleven pairs, which occupy the intercostal spaces. Each external muscle arises from the sharp lower border of a rib, and is directed inferiorlj and anteriorly, to be inserted into the external edge of the superior border of the rib below. It extends from the tubercle of the rib posteriorly nearly to the costal cartilage anteriorly. The anterior intercostal aponeurosis is continuous with it anteriorly, and extends forwards to the side of the sternum. Each internal muscle arises from the costal cartilage and the internal or superior edge of the costal groove, and is directed inferiorly and posteriorly, to be inserted into the internal edge of the superior border of the rib and costal cartilage below. It extends from the side of the sternum anteriorly to the angle of the rib posteriorly, where it is replaced by the posterior intercostal aponeurosis extending to the tubercle of the rib. The superficial surface of the external muscle is covered by the muscles of the chest, axilla, abdomen, and back. The deep surface of the internal muscle is in contact with the pleura. Mm. Levatores Costarum. — The levatores costarum are in series with the external intercostal muscles. They are twelve small slips arising from the trans- verse processes of the seventh cervical and upper eleven thoracic vertebrae. Each spreads out in a fan-like manner as it descends to the lateral surface of the rib immediately below where it is inserted jjosterior to the angle. Mm. Subcostales. — The subcostal muscles are slips of muscles found on the internal surface of the lower ribs near their angles. They are in series with the internal intercostal muscles, but yjass over the deep surface of several ribs. M. Transversus Thoracis. — The transversus thoracis (O.T. triangularis sterni) occupies the posterior aspect of the anterior thoracic wall, and is separated from the costal cartilages by the internal mammary vessels. It arises from the posterior surface of the xiphoid process and body of the sternum as high as the level of the third costal cartilage. From that origin its fibres radiate laterally, the lower horizontally, the upper fibres obliquely upwards, to be inserted into the second, third, fourth, fifth, and sixth costal cartilages. Tlie muscle is continuous below with the transversus abdominis. THE MUSCLES OF THE THORAX. 471 Diaphragma. — The diaphragm is the great membranous and muscular parti- tion separating the cavities of the thorax and abdomen. It forms a thin lamella arching over the abdominal cavity, and clothed on that surface, for the most part, by peritoneum. It is related, on its inferior concave surface, to the liver, stomach, and spleen, the kidneys and suprarenal glands, and the duodenum and pancreas. Its superior convex surface projects into the thoracic cavity, rising higher on the right than on the left side, and is related to the pericardium and pleurte, and along its margin to the chest wall. The oesophagus and thoracic aorta are iu contact with it posteriorly. It possesses a peripheral origin from the sternum, ribs, and verteVjral column. EXTKRNAL INTERCOSTAL MUSCI F Obliquds EXTERKT ABDOMINIS (reflected) Anterior intercostal membrane removed, exposing the internal intercostal muscle Internal inter- fOsTAL MUSCLE TCS ABDOMINIS -i-rtion) Sheath of the rectus abdominis Fig. 418. — The Muscleo ok the Right Side of the Thoracic Wall. and an insertion iuto a central tendon. It arises (1) anteriorly (pars stemalis) from the posterior surface of the xiphoid process by two slender fleshy slips, directed backwards ; (2) laterally (pars costalis), from the deep surface of the lower six costal cartilages on each side by fleshy bands which interdigitate w^ith those of the trans- versus abdominis; (3) posteriorly (pars lumbalis), from the lumbar vertebrae, by the crura, and the medial and lateral lumbo-costal arches. The crura are two elongated fibro-muscular bundles which arise, on each side of the aorta, from the anterior surface of the bodies of the lumbar vertebrae, on the right side from the first three, on the left side from the first two lumbar vertebrae. They are directed upwards and decussate across the median plane in front of the aorta, the fibres of the right crus passing anterior to those of the left crus. The fibres then encircle the cesophagus, forming an elliptical opening for its passage, and finally join the central tendon, after a second decussation anterior to the gullet. 316 472 THE MUSCULAR SYSTEM. The medial part of each eras is wholly tendinous and is sometimes called the crus mediate ; it is connected with its fellow of the opposite side by a tendinous band called the middle arcuate ligament, which arches between them, in front of the aorta, and gives origin to fibres which join the crura as they decussate to encircle the gullet. The most outlying part of the crus is sometimes called the crus laterale ; its infero-lateral margin is continuous with the medial lumbo-costal arch. The intermediate part of the crus is the crus intermedium ; the splanchnic nerves pierce the diaj^hragm between it and the medial crus. The sympathetic trunk sometimes jjierces the diaphragm between the intermediate and lateral crura. The arcus lumbocostalis medialis (O.T. internal arcuate ligament) is a thickening formed by the attachment of the psoas fascia to the body of the first lumbar vertebra medially and its transverse process laterally. Stretching across the superior end of the psoas muscle, the ligament gives origin to muscular fibres which join the fibres of the crus. The arcus lumbocostalis lateralis (O.T. external arcuate ligament) is the thickened superior border of the fascia over the quadratus lumborum muscle CEsophagus and its opening Foramen quadratuni (for inferior vena ca\a) y,''' Middle arcuate ligament (in front of aortic opening) al lumbo-co.stal ateral lumbo-costal QADRATUS LUMBORUM MUSCLE ^!!v Right crus of diaphragm Fig. 419. — The Diaphragm (from below). and is attached medially to the transverse process of the first lumbar vertebra, and laterally to the last rib. It gives origin to a broad band of muscular fibres, separated by an interval from the fibres arising from the medial lumbo- costal arch which sweep upwards to the central tendon. From this extensive origin the muscular fibres of the diaphragm converge to an insertion into a large trilobed central tendon called the centrum tendineum. Of its lobe.s the right one is the largest, the middle or anterior is intermediate in size, and the left is the smallest. It does not occupy the centre of the muscle, being placed nearer the front than the back. The fibres of the crara are con- sequently the longest ; those from the xiphoid process are the shortest. The diaphragm is pierced by numerous structures. The superior epigastric artery enters the sheath of the rectus abdominis })etween its sternal and costal origins ; the musculo-phrenic artery passes between its attachments to the seventh and eighth ribs. The sympathetic trunk and the splanchnic nerves pierce, or pass posterior to the diaphragm ; the last thoracic nerve passes behind the lateral lumbo-costal arch ; and the aorta, the azygos vein, and thoracic duct pass between the crura, underneath the middle arcuate ligament {hiahcs aorticus or aortic opening). The special foramina are two in number. The foramen vence cavce (O.T. foramen THE MUSCLES OF THE THORAX. 473 quadratum) in the right lobe 'of the central tendon transmits the inferior vena cava, and small branches of the right phrenic nerve. The hiatus oesophageus {oesophageal opening) is in the muscular substance of the diapliragm, posterior to the central tendon, and is surrounded by a sphincter- like arrangement of the crural filtres. Besides the cesophagus, this opening transmits the two vagi nerves. Mi. Ml" :u.-iiMt,. li 'airi.'til Vena caval niieiiiiig lEsophageaL opening in diaphragm Aortic opening Anterior ramus of twelfth thoracic nerve Quadratns Uimboruni lio-hypogastric nervfi Ilio-inguiiial nerve Lateral iilaneous nerve of tliigh b\'inoral nerve Ceinto-femoral A nerve -/y— Ubliirator nerve J — \ ' V Anterior ramus . / I if fourth lumbar ^ nerve Viiterior ramus t (ifth lumbar nerve ( Medial and -, lateral lumbo- l costal arches Ant. ramus of twelfth thoracic nerve Quadratus lumborum lllo-hypogastric nerve Ilio-inguinal nene Psoas major Genito-femoral nerve Lateral —^ cutaneous ner\-e j of thigh I^umbo-sacral trunk Femoral nerve Obturator nerve ^ J FiQ. 420. — The Diai-hka(;.m and Posteriok Abdominal Wall. The diaphragm is found as a complete septum between the thorax and abdomen only in mammals. It is occasionally deficient in the human subject, producing hernia of the diaphragm, either into the pericardial cavity through the central tendon, or into the pleural cavity through tlie lateral portions of the muscle. A rare condition is congenital deficiency of a part of the lateral half of the muscle, generally placed posteriorly, and on the left side. This produces, by continuity of the pleural and peritoneal cavities behina the diaphragm, a co«(/eni7ai diaphragmatic hernia. 474 THE MUSCULAK SYSTEM. Nerve-Supply.— The intercostal muscles, levatores costariun, subcostal muscles, and trans- versus thoracis, are all supplied by the anterior rami of the thoracic nerves. The diaphragm receives its chief, if not its entire, motor supply from the phrenic nerves (C. 3. 4. 5.). It is innervated also by the diaphragmatic plexus of the sympathetic, and is sometimes said to receive fibres from the lower thoracic nerves. Actions,— The act of respiration consists of two opposite movements— inspiration and ex- piration. / X 1 ■ T. 1. The movement of expiration is performed by (1) the elasticity of the lungs, (2) the weight of the chest walls, (3) the elevation of the diaphragm, (4) the action of muscles— trans versus thoracis and muscles of the abdominal walL It is sometimes stated that the interosseous fibres of the internal intercostal muscles are depressors of the ribs. 2. The movement of inspiration resiUts in the enlargement of the thoracic cavity m aU its diametei-s. Its antero-posterior and transverse diameters are increased by the elevation and forward movement of the sternum, and by the elevation and eversion of the ribs, while its vertical diameter is increased by the descent of the diaphragm. The muscles of inspiration are divided into two series— ordinary and accessory. a. Ordinary Muscles. h. Extraordinary and Accessory Muscles. Diaphragm Intercostals Scaleni Serrati posteriores Levatores costaruni Subcostales Quadratus lumborum Pectorales Serratus anterior Sterno-mastoid Latissimus dorsi Infra-hyoid muscles Extensors of the vertebral column Of the ordinary muscles the diaphragm is the most important. Its action is twofold — centrifugal, elevating the ribs and increasing the transverse and antero-posterior diameters of the thorax, and centripetal, drawing downwards the central tendon and increasing the vertical diameter of the thorax. Of the two movements the former is the more important. There has been considerable diversity of opinion regarding the action of the intercostal muscles. It is generally agreed that the external muscles elevate the ribs ; it is probable that the whole of each internal muscle acts in the same way, although it has been stated by different observers that the whole internal muscle is a depressor ; or that the interosseous part is a depressor, the inter- chondral portion of the muscle an elevator of the ribs. FASCIit AND lYIUSCLES OF THE ABDOIVIINAL WALL. The space between the base of the bony thorax and the pelvis is filled up by a series of muscular sheets, covered externally and internally by fascise. FASCIJE. The fascise of the abdominal wall are — externally, the superficial and deep fascise ; internalhj, the fascia transversalis, which clothes the interior of the abdominal cavity, and is continuous with the diaphragmatic, lumbo-dorsal, psoas, iliac, and pelvic fascise, and is lined within by the subserous coat of extra-peritoneal tissue. The superficial fascia of the abdomen is liable to contain a large quantity of fat. In the groin it is separated into two layers : a superficial fatty layer con- tinuous over the inguinal ligament with the fascia of the anterior surface of the thif^h (p. 402), and a deeyjer membranous layer attached to the medial half of the inguinal ligament, and more laterally to the fascia lata of the thigh distal to the inguinal ligament. The two layers are separated by the lymph glands and the superficial vessels of the groin. Higher up in the abdominal wall the two layers blend together. As they jjass downwards over the spermatic funiculus, they unite to form 'the fascia and dartos muscle of the scrotum. The attachment of the fascia to the groin prevents the passage into the thigh of fluid extravasated in the abdominal wall. The deep fascia of the abdominal wall resembles similar fascise in other situa- tions. It forms an investment for the obliquus externus muscle, and becomes thin and almost imperceptible in relation to the aponeurosis of that muscle. FASCIiE AND MUSCLES OF ABDOMINAL WALL. 475 Fascia Transversalis. — The fascial lining of the abdomiual cavity (fascia transversalis) consists of a coutiiiuous layer of lueiubraiK^ wiiich rt;ceives dilfereiit names in dillereut })art.s of its extent. It covers the deep surface of the trausversus muscle, and is continuous medially with the fasciie of the quadratus lumborum and the psoas muscles. It is continuous above with the diaphragmatic fascia, and below the iliac crest and the inguinal ligament with the fascia iliaca. Along with the last-named fascia it forms the femoral sheath, enclosing the femoral vessels and the femoral canal in their passage to tlie thigh behind the medial part of the inguinal ligament (p. 405). It is pierced by the spermatic funiculus or Linea al Lif". suspensoriii Sj)enu;ilic fiiniuulu External spermatic _ fascia Dorsal vein of penis - (JnMQtJUS EXTKIINUS AUDOMINIS Anterior snperior iliac spine Aponeurosis of obliipius cxternus Supcrlieial eircmii- fli'x iliac artery -liilercrural libres C Attaeliincnt of niem- - 'I branous layer of _ ( superficial fascia "Poupart's inguinal ligament ..Siiperlicial epigastric artery External piiiiential arteiy Siiperlicial sub-inguinal 'lymph gland (ireat saphenous vein Fig. 421. — Supehkicial Anatomy of the Guoin. round ligament of the uterus at the abdominal inguinal ring, and its prolongation into the inguinal canal around the funiculus forms the internal spermatic or in- fundibuliform fascia. It is lined internally by the peritoneum, I'roui which it is separated by a layer of extraperitoneal tissue. The subserous coat or extraperitoneal tissue is usually loaded witli fat ; it envelops the kidneys, ureters, suprarenal glands, abdominal aorta and inferior vena cava and their branches, and forms sheaths for the vessels and ducts (ureter, ductus deferens, etc.). It is continued upwards into the posterior mediastinum of the thorax through the aortic opening in the diaphragm, and below is in continuity with the extraperitoneal tissue in the pelvis. It not only completely invests the kidneys and suprarenal glands, but it also becomes interpolated between the layers of peritoneum upholding and enveloping the intestines. This tissue is absent in relation to the diaphragm, on the under surface of which there is no fat. 476 THE MUSOULAK SYSTEM. THE MUSCLES OF THE ABDOMINAL WALL. The muscles of the abdominal wall are in three series — lateral, anterior, and posterior. The lateral muscles of the abdominal wall comprise the obliquus externiis abdominis, obliquus internus abdominis, and transversus abdominis. M. Obliquus Externus Abdominis. — The obliquus externus abdominis is a broad thin sheet of muscle, with an origin from the lateral surfaces of the lower eight ribs, by slips which interdigitate with the serratus anterior and latissimus Obliquus extern us abdominis' (reflected) Obmquus externus abdominis Obliquus internus abdominis Anterior superior iliac spine Transversus abdominis Obliquus internus ABDOMINIS (reflected) Aponeurosis of obliquus externus (reflected) . Abdominal ini;uinal rinj; Spermatic funiculus and infundibuliform fascia Fascia transversalis Palx aponeurotica in- guinalis Fossa ovalis (O.T. saphen- ous opening) Great saphenous vein Fia. 422. — The Dissection of the Inguinal Canajl. dorsi muscles. The muscular fibres radiate downwards and forwards, the lowest fibres passing vertically downwards. The muscle fibres of the lower and posterior part of the muscle are inserted, directly, into the external lip of the iliac crest in its anterior half or two-thirds (Fig. 369, p. 415). The rest of the muscle fibres are inserted into an extensive triangular aponeurosis which loriiis part of the anterior abdominal wall. This aponeurosis is broader 'below than above ; it is united with part of the aponeurosis of the obliquus internus in the superior three-fourths of its extent, to form the anterior layer of the sheath of the rectus muscle. It thus gains an attachment, above to the xiphoid process, below to the symphysis pubis, and by its intermediate fibres to the linea alba. The linea alba is a band of interlacing fibres, about half an inch in width at its widest part. It occupies the median plane of the anterior abdominal wall in its whole extent, is |>ierced by the umbilicus (annulus umbilicalis), and forms the greater part of the ultimate insertion of all the lateral abdominal muscles. THE MUSCLES OF THE ABDOMINAL WALL. 477 Obliqdcs externus ObLIQUUS INTERNVS Tkansversus abdominis Fascia transversalis Peritoneum Colon The superior part of the aponeurosis covers the insertion of the rectus abdominis muscle on the chest wall, and gives origin to lihres of the pectoralis major. In- feriorly, in the groin, the lower part of the aponeurosis gives rise to the inguinal ligament, the ligamentum lacuuare, the two crura of the subcutaneous inguinal ring, the external spermatic fascia and the intercrural fibres, and the ligamentum inijuiuale reHexum of Colles. Lig. Inguinale [Pouparti]. — The inguinal ligamentum (O.T. Poupart's ligament) is an aponeurulic l)aud which extends from the anterior superior iliac spine to the tubercle of the pubis, arching over the iliacus, psoas, and pectineus muscles. It repre- sents the inferior margin of the aponeurosis of the obliquus externus abdominis, and it gives attachment below to the iliac portion of the fascia lata of the thigh. Its lateral part affords partial origin, to the obliquus internus and transversus nmscles, and receives the -attachment of the fascia transversalis and fascia iliaca ; the medial part forms the gutter-like floor of the inguinal canal. At its medial end a triangular band of fibres is reHected horizon- rectos abdom.ms tally backwards to the ilio- pectineal line, forming the lig. lacunars [Gim- bernati] (O.T. Gim- bemat's ligament), the lateral edge of which forms the medial bound- ary of the femoral ring. The femoral vessels, enclosed in the femoral sheath, enter the posterior to the incTuinal lifjament, on the anterior Postenoraponeurosis surface of the psoas major muscle, and the term super- ficial femoral arch is given to the part of the liga- ment which covers the vessels. Annulus In- guinalis Subcu- taneus. — Tlie subcutaneus inguinal ring (O.T. external abdominal ring), the place of exit of an inguinal hernia, is a split in the aponeurosis of the obliquus externus, just above the tubercle of the pubis. It transmits the spermatic funiculus, or (in the female) the round ligament of the uterus, covered by the cremaster muscle or cremasteric fascia. The opening is of considerable extent, and its edges are drawn together by a thin fascia, strengthened superficially by a number of arched and horizontal fibres, called the intercrural fibres, which arise from the inguinal ligament and sweep medially across the cleft in the aponeurosis. The margins of the ring constitute its crura. The inferior cms is narrow, and is formed from that part of the aponeurosis which joins the pubic tubercle, and is continuous with the medial end of the inguinal ligament. The superior crus is the part of the aponeurosis medial to the ring which is attached to the crest and symphysis of the pubis. It is flat and broad. The intercrural fibres and the crura of the subcutaneous inguinal ring are continuous with a thin tubular sheath, the intercolumnar or external spermatic fascia, which is attached to the margins of the " ring," and forms an envelope for the fhicVl Extraperitoneal ^ "^ tissue Kidney of transversus Latissimus dorsi quadratus lumboium Middle layer of luinbo-dorsal fascia Iliocostalis Posterior layer of lumbo-dorsal fascia Psoas fascia Second lumbar vertebra Psoas major Anterior layer of lumbo -dorsal fascia MULTIFIDUS Semispisai.is DORSI LONOISSIMUS nORSI Fig. 423. — Transverse Section through the Abdomen, opposite the Second Lumbar Vertebra. 478 THE MUSCULAE SYSTEM. spermatic funiculus or round ligament after they have passed beyond the abdominal wall. Lig. Inguinale Reflexum Collesi. — The reflexed inguinal ligament of CoUes (O.T. triangidar fascia), is a triangular band of fibres placed behind the medial superior cms of the subcutaneous inguinal ring. It consists of fibres from the Anterior superior iliac spine The inguinal ligament Subcutaneous inguinal , Ting a- Suspensory ligament ■ of penis Spermatic funiculus Fig. 421.— The Left Obliquus Externus Abdominis opposite external oblique aponeurosis, which, having traversed the linea alba, to gain an insertion into the crest and tubercle of the pubis. The obliquus externus muscle is superficial in almost its whole extent. It is overlapped posteriorly by the latissimus dorsi muscle, but may be separated from it just above the iliac crest by an angular interval (trigonum lumbale or triangle of Petit). M. Obliquus Internus Abdominis. — The obliquus internus abdominis is a broad thin sheet of muscle which lies between the obliquus externus and the THE MUSCLES OF THE ABDOMINAL WALL. 479 transversus. It arises from, (1) the lumbo-dorsal fascia, (2) the anterior two- thirds of tlie ihac crest, and (3) the lateral half of the inguinal ligament. It runs for the most i)art, upwards and forwards, and its liighest fibres are inserted directly into the last three ribs. Tlie rest of the fibres end in an extensive aponeurosis, broader above than below, which splits along the linea semilunaris, to form, along with the aponeuroses of the obliquus externus and transversus muscles, OBLIQUUS INTERNUS ABDOMINIS Aponeurosis ok obmquus exteknus (reflected) Aponeurosis of obliquus internus r Aponeurosis i '} 11 (reflected) iijuC v? CREMASrER MUSCLE Suspensory ligament____ of penis" Spermatic funiculus'- • ------- - Fig. 425. — The Right Obliquus Internus Abdominis. the sheath of the rectus abdominis, and is inserted into the seventh, eighth, and ninth costal cartilages, and into the linea alba from the xiphoid process to the symphysis pubis. The fibres arising from the inguinal ligament join with those of the transversus muscle having a similar origin to form the falx aponeiurotica inguinalis (O.T. conjoined tendon), which passes altogether anterior to the rectus muscle, to be attached to the pubic crest and tubercle, and to the ilio-pectineal line. The obliquus internus is limited above by the inferior margin of the thorax 480 THE MUSCULAE SYSTEM. Its lower fibres, arching over the spermatic funiculus, assist in forming, laterally, the anterior wall of the inguinal canal ; medially, by means of the falx inguinalis, it helps to form the posterior wall of the canal. Its lowest fibres are continued into the cremaster muscle, which is prolonged along the spermatic cord through the inguinal canal. M. Cremaster. — The cremaster muscle forms an investment for the testis and sper- matic funicukis deep to the external spermatic fascia. In the female it is more largely represented by fascia than muscular fibres, and constitutes the cremasteric fascia. It may be said to have an origin from the inferior edge of the obliquus internus and the Aponeurosis of obliquus externus" (reflected) Linea alba Subcutaneous inguinal riu.; Lig. reflexum inguinal i- Inferior crus ut riii^ Pubic fascia aii'l suspensory liga-- ment of penis Obliquus externus abdominis Anterior superior iliac spine Obliquus internus abdominis Aponeurosis of .obliquus externus (reflected) -—Spermatic funiculus Inguinal canal Falx aponeurotica inguinalis Lig. reflexum inguinale Inferior crus of sub- cutaneous inguinal ring (the inguinal ligament) Spermatic funiculus (cut) Fig. 426. — The Left Inguinal Canal. Structures seen on reflection op the Obliquus Externus. adjacent part of the inguinal ligament. Its fibres form loops over the spermatic funiculus and testis, the highest fibres getting an insertion into the pubic tubercle. M. Transversus Abdominis. — The transversus abdominis muscle arises (1) from the deep surface of the costal cartilages of the lower six ribs, interdigitating with the origins of the diaphragm ; (2) from the lumbo-dorsal fascia ; (3) from the anterior half of the medial lip of the iliac crest ; and (4) from the lateral third of the inguinal ligament. The muscular fibres run, for the most part, horizontally forwards, and end in an aponeurosis which has a twofold insertion. (I) After forming (along with the aponeurosis of the obliquus internus) the posterior layer of the sheath of the rectus, the aponeurosis is attached to the xiphoid process and linea alba. (2) The inferior fibres of the muscle arising from the inguinal ligament are joined by the inferior part of the obliquus internus to form the larger part of the falx THE MUSCLES OF THE ABDOMINAL WALL. 481 aponeiirotica inguinalis (O.T. conjoined tendon), which passes anterior to the inferior part of the rectus muscle, to l)e inserted into the crest and tultercle of the puhis and the iho-pectineal Hue. The transversus muscle is separated by the lower intercostal nerves from the obliquus internus muscle, and is lined on its deep surface by the fascia transversalis. Its inferior border forms a concave edge, separated from the inguinal ligament by a lunular interval in which the fascia transversalis appears, and through which the spermatic funiculus emerges at the abdominal inguinal ring, under cover of the obliquus internus muscle and the aponeurosis of the obliquus externus. Obliqi'Us extern i-s ABDOMINIS* (reflected) Spermatic funiculus- External spermatic fascia' „ Obliquus rxterntjs abdominis Obmquus internus AHLiOMINIS Anterior superior iliac spine Transversus abdominis ,Obi.iquus internus ABDOMINIS (reflected) Aponeurosis of obliquus ■externus (reflected) ■Abdominal inguinal ring ,Si)eimatic funiculus and iiifundibulifonn fascia ■Fascia transversalis ,Kalx aponeurotica in- guinalis .Fossa ovalis(O.T. saphen- ous opening) Great saphenous vein Fig. 427. — The J)i.s>ei tion hf the Inouinai. Canal. The anterior muscles of the abdominal wall include the pyramidalis and rectus abdominis, enveloped by the sheath of the rectus, on either side of the linea alba. M. Pyramidalis Abdominis. — The pyramidalis abdominis is a small triangular muscle arising from the pubic crest, anterior to the rectus muscle (Fig. 428, p. 482). It is directed obliquely upwards, to be inserted, for a variable distance, into the linea alba. The muscle is often absi'nt. M. Rectus Abdominis. — The rectus abdominis muscle is broad and strap- like, and arises, by a medial and a lateral head, from tlie symphysis and crest of the pubis (Fig. 428, p. 482). The muscle expands as it passes upwards, and is inserted, from medial to lateral side, into the anterior surface of the xiphoid process (Fig. 428, p. 482), and into the superficial surface of the seventh, sixth, and fifth costal cartilages. On its anterior 32 482 THE MUSCULAR SYSTEM. surface, but not extending through the entire substance of the muscle, are three or more transverse tendinous intersections (inscriptiones tendineae).. adherent to the sheath of the muscle ; the lowest opposite the umbilicus, and the highest about the level of the xiphoid process. The medial border of the muscle lies alongside the linea alba ; its lateral border is convex, and corresponds to the linea semilunaris. The muscle is pierced by the terminal branches of the lower thoracic nerves. Aponeurosis ot obliquiis externus abdominis (rertected) Rectus abdominis Anterior lamella of sheath of rectus Linea alba Obliqous ex- ternus ABDOMINIS Obliquus in- ternus abdominis Aponeurosis of obliquus externus Inguinal ligament Aponeurosis ol obliquus exteriiu-: (reflected; Crkmaster MUSCLI Spermatic funiculus Obliquus externus abdominis Rectus abdominis (cut) Posterior lamella of rectal sheath Anterior lamella of sheath of rectus Aponeurosis of obliquus externus Obliquus internus abdominis Transversus abdominis Linea semicircularis of Douglas Fascia transversalis Rectus abdominis (cut) Inguinal ligament Obliquus externus aponeurosis (reflected) 1?yramidalis abdominis Suspensory ligameni of penis Fig. 428. — Deep Dissection of the Abdominal Wall. The Rectus Muscle and its Sheath. Vagina M. Recti Abdominis.— The sheath of the rectus muscle is derived from the aponeuroses of the lateral muscles of the abdominal wall, which, after enclosing the muscle, give rise, in the median plane, to the linea alba. At the linea semilunaris along the lateral border of the rectus muscle, the aponeurosis of the obliquus internus splits into anterior and posterior layers. The anterior layer, joined by the aponeurosis of the obliquus externus, passes in front of the rectus, and constitutes the anterior lamina of the sheath. The posterior layer, joined by THE MUSCLES OF THE ABDOMINAL WALL. 483 the aponeurosis of the transversus muscle, passes behind the rectus, and constitutes the posterior lamina of its sheath. This arrangement obtains in the superior three- fourths of the abdominal wall. lielow the level of the iliac crest the sheath of the muscle is deticieut posteriorly, and a crescentic border, the linea semicircularis (semilunar fold of Douglas), marks the inferior limit of the posterior lamina. In conscHjueuce, the rectus in the lower fourth of the abdominal wall rests directly upon the fascia transversalis. Close examination, however, usually reveals a thin layer behind the muscle in continuity with the fold of Douglas, and merging below with the fascia transversalis. In this region the rectus is covered anteriorly by the fal.K aponeurotica inguinalis of the obliquus internus and transversus, and by the aponeurosis of the obliquus externus, which gradually separates from the subjacent aponeurosis. The superior part of the rectus, lying on the chest wall, is only covered anteriorly by a single layer of aponeurosis derived from the obliquus externus, which in this situation is giving origin to the pectoralis major muscle. Canalis Inguinalis. — Inguinal canal. — The spermatic funiculus in the male, and the round ligament in the female, in their passage through the inferior part of the abdominal wall, pass through the inguinal canal, which is bounded by these abdominal mus- cles. The canal begins at the a&f?omtnaZ d inguinal ring, placed half an inch above the inguinal ligament, and midway between the anterior superior iliac spine and the symphysis pubis. It ends at the subcutaneous inguinal ring, placed above the tubercle and crest of the pubis. The anterior wall of the canal is formed by the aponeurosis of the obliquus externus, and in its lateral part by the muscular fibres of the obliquus internus ; the posterior toall ,^ . ^ , of the oanal is formed bv the fasoia ^ ' ^^ thoracic wall; (II.) In the superior three- 01 tne canal is lormea Oy tne laSCia quarters of the abdominal wall ; (in.) in the inferior transversalis, and m its medial part by fourth of the abdominal wall. the falx aponeurotica inguinalis ; while -^' Pectus muscle ; S, Obliquus externus ; c, DiA the /oor of the canal is formed by the HTZLu^.^^'^'r^T^ '"'T''''' v'^' 'F^'^TT *'. . •' SLS ABDOMINIS. «, Anterior layer of rectus sheath : inguinal ligament, and in its medial b, Fifth costal cartilage : c. Sixth costal cartilage ; part by the lacunar ligament. The '^' ^iP^O'tl process; c. Posterior layer of rectus o,^^^,>->r.fi^ A, »,;«„!,, o •^4«„^;^™ <-U^ 4- „ sheath; /, Fascia transversalis ; g, Peritoneum; h, spermatic funiculus, piercing the trans- Linea alba, l, inferior epigastric artery versabs fascia, enters the inguinal canal at the abdominal inguinal ring, and is there invested by its first envelope, the infundibuliform or internal spermatic fascia, a sheath of fascia derived from the margins of the ring and continuous with the fascia transversalis. It then passes obliquely medially, downw^ards, and forwards, and escapes below the inferior border of the obliquus internus muscle, from which it carries off a second investment, partly fascial, partly muscular, — the cremaster muscle or cremasteric fascia. Con- tinuing its course, in front of the falx inguinalis, it emerges through the sub- cutaneous inguinal ring, from the edges of which the intercolumnar fascia is derived, the th ird or external investment for the funiculus. Hesselbach's triangle, bounded below by the line of the inguinal ligament, medially by the rectus abdominis muscle, and laterally by the inferior epipfastric artery, coursing upwards and medially beneath the fascia transversalis on the medial side of the abdominal inguinal ring, is the site of one form of inguinal hernia. 32 « Fio. 429. -The Sheath of the Rectus Abdomtnis Muscle. 484 THE MUSCULAE SYSTEM. The spermatic funiculus passes over the base of the triangle, covered over by the aponeurosis of the obliquus externus. Behind the funiculus, and forming the floor of the triangle, is the fascia transversalis partially covered, in the medial portion of the triangle, by the falx inguinalis of the obliquus internus and transversus muscles. Middle arcuate ligament Vena caval openin Aortic opening,' ^ V Esophageal opening in diaphragm Anterior ramus of twelt'tli. thoracic nerve Quadratus lumboruni" Ilio-hypogastric_ nerve Ilio-inguinal- Lateral cutaneoua nerve- of thigh Femoral ner\e- Genito-femoral nerve-y 1 Obturator ner^»;- Descending branch Vjj of fourtli lumbar nervi- Anterior ramus of fifth lumbar nerve Ll Medial and lateral lumbo- costal arches Ant. ramus gf twelfth "thoracic nerve ..Quadratus lumborum -Uio-hypogastric nerve -nio-inguinal -Psoas major Genito-femoral nerve Lateral cutaneous nerve of thigh ,— Hiacus Lvinibo-sacral trunk Femoral nerve -Obturator nerva Fig. 430. — The I)iai'HRA(;m and Postkiuor Ardominal Wall. Inguinal Hernia. — For an account of the anatomical relations of the inguinal canal to the various forms of inguinal hernia, see the section on " Applied Anatomy." Nerve-Supply. — The nerve-supply of the majority of the foregoing muscles is derived from the anterior rami of the lower six thoracic nerves. Tlie pyramidalis muscle is innervated by the last thoracic nerve. The cremaster muscle receives its supply from the genito-femoral nerve (L. 1. 2.). Actions.— (1) The chief action of these muscles is to retract the abdominal walls. By compres.sing the contents of the abdomen, they are powerful agents in vomiting, defsecation, FASCIA OF THE PEKINEUM. 485 micturition, parturition, and laboured expiration. (2) They are also flexors of the vertebral column and pelvis — the muscles of both sides acting together ; the vertebral column and pelvis are laterally Hexed, when one set of muscles acts alone. The posterior muscles of the abdominal wall and pelvis major include the psoas (major and minor) and iliacus, described already (p. 410), and the quadratus lumborum. M. Quadratus Lumborum. — The quadratus lumborum lies in the posterior wall of the abdomeu, lateral to the psoas, and extends Ijetween the iliac crest and the last rib. It arises from the posterior part of the iliac crest, from the ilio- lumbar ligament, and from the transverse processes of the lower lumbar vertebrae. It is inserted, above, into the medial part of the inferior border of the last rib and tlie transverse processes of the lumbar vertebrse. Its lateral border is directed obliquely upwards and medially. It is enclosed between the anterior and middle layers of the lumbo-dorsal aponeurosis (p. 437), between the psoas major muscle, in front, and the sacro- spinalis behind. Nerve-Supply. — The quadratus lumborum is supplied directly by branches from the anterior rami of tlu; tirst three or four lumbar nerves. Actions. — Tlie muscle is a lateral flexor of the vertebral column, an extensor of the column and a mu.scle of inspiration. FASCliC AND IVIUSCLES OF THE PERINEUM AND PELVIS. FASCIA OF THE PERINEUM. The superficial fascia of the perineum possesses certain special features. It is continuous with the superficial fascia of the abdominal wall, thigh, and buttock, and is prolonged on to the penis and scrotum. In the penis, it is devoid of fat and consists only of areolar tissue. In the scrotum, it is intermingled with in- voluntary muscular fibres, and constitutes the dartos muscle, which assists in suspending the testes and corrugating the skin of the scrotum. This fascia also forms the septum of the scrotum, which, extending upwards, incompletely separates the two testes and their coverings. In the female the superficial fascia, in which there is a considerable quantity of fat, takes a large share in the formation of the mons Veneris and labia majora pudendi. The fascia over the 'posterior part of the perineuin tills up the ischio-rectal fossae, in the form of two pads of adipose tissue, on either side of the rectum and anal canal. Over the tuberosities of the ischium the fat is intermingled with bands of fibrous tissue closely adherent to the subjacent deep fascia. The fascia in the anterior part of the perineum closely resembles the same fascia in the groin. It is divisible into a superficial fatty and a deeper membranous layer ; the former continuous with the same layer in the thigh, and with the fat of the ischio-rectal fossa posteriorly. The deeper membranous layer is attached laterally to the pubic arch, posteriorly to the base of the fascia . inferior of the urogenital diaphragm and in the median plane to the root of the penis (bulb and corpus cavernosum urethra) by a median raphe continuous, farther forwards, with the septum of the scrotum mentioned above. Anteriorly the fascia is continued over the spermatic funiculi to the anterior abdominal wall. The importance of this fascia lies in relation to the extravasation of urine from a rupture of the urethra in the perineum. By the fascial attachments the fluid is prevented from passing posteriorly into the ischio-rectal fossa, or laterally into the thigh. It is directed forwards into relation with the scrotum and penis, and along the spermatic funiculus to the anterior abdominal wall. The septum of the scrotum being incomplete, fluid extravasated on one side can pass across the median plane to the opposite half of the perineum and scrotum. The deep fascia of the perineum exists only in the form of the delicate fasciae of the muscles. 486 THE MUSCULAK SYSTEM. THE MUSCLES OF THE PERINEUM. The perineal muscles are naturally separated into a superficial and a deep set by the fascia inferior of the urogenital diaphragm. Superficial to it are the sphincter ani externus; transversus perinei superficialis, bulbocavernosus, and ischiocavernosus ; deep to it are the sphincter muscle of the membranous urethra and the transversus perinei profundus. M. Sphincter Ani Externus. — This muscle is fusiform in outline, flattened, and obliquely placed around the anus and anal canal. It can be separated into three layers, — subcutaneous, superficial, and deep. (1) The most superficial lamina Posterior scrotal / nerves I - Perineal branch of posterior cutaneous nerve of tliigh Superficial branch of perineal nerve Deep branch of perineal nerve Nervus perinei Inferior lisemorrhoidal branches Dorsal nerve of penis (displaced) Nerve to corpus cavernosum penis [vX Nerve to corpus WL cavernosum urethrie ^' %- Superflciallj;^^-,, -¥- ^''^P j nerve '~\' Perineal nerve Pudendal nerve Inferior hsemorrhoidal branches Pudendal nerve Fig. 431. — The Muscles and Is'kkves of the Male Pekineum. consists of subcutaneous fibres decussating posterior and anterior to the anus, but without bony attachments. (2) The sphincter ani superficialis constitutes the main portion of the muscle. It is attached posteriorly to the coccyx, and, anterior to the anus, it reaches the central point of the perineum. (3) The deep fibres of the muscle form, for the most part, a complete sphincter for the anal canal. They are continuous with the fibres of the levator ani ; they encircle the anal canal, and blend anteriorly with the central point of the perineum and the transversus perinei supf;rficialia miiRcle. M. Corrugator Cutis Ani. — The corrugator cutis ani consists of bundles of unstriped muscular fibres which radiate from the margin of the anal opening superficial to the external sphincter. THE MUSCLES OF THE PERINEUM. 487 Nerve-Supply. -Tlie external spliincter is supplied by tlie inferior liuiiuorrlioidal branch of the pudendal nerve (S. 3. 4.), by the pi-rineal branch of the fourth sacral nerve, and by the deep perineal lirancli of the pudendal nerve (S. 3. 4.). Actions. — The muscle closes the anal aperture. It is a voluntary niusclr. M. Transversus Perinei Superficialis. — The transversus perinei superficialis is not always prcjsunt. It consists of a more or less I'eeble bundle of lihres, wliicli arises from the interior ramus of the ischium and the fascia over it, and from the base of the fascia inferior of the urogenital diaphragm. It passes obliquely over the base of the fascia inferior to be inserted into the central point of the perineum. Nerve-Supply,— Deep perineal branch of pudendal nerve (S. 3. 4.). Action. Tiie_ two muscles acting together draw backwards and fix the central i>oint of the pciineuni. M. Bulbocavernosus.— The bulbocavernosus (O.T. ejaculator urinae;, in the male, surrounds the bulb, corpus cavernosum urethrae, and root of the penis. It is sometimes separ- ated into two parts — posterior (compressor bulbi), and anterior (compressor radicis penis). It arises from the central point of the perineum, and from a median raphe on the under surface of the bulb and corpus cav- ernosum urethrie. The muscular fibres pass laterally and forwards and have a triple insertion : from behind forwards, (1) into the inferior sur- face of the fascia in- ferior of the urogenital diaphragm ; (2) into the dorsal aspect of the corpus cavernosum urethras ; and (3), after encircling the corpora cavernosa penis, into the fascia covering the dorsum of the penis. The ischiobulbo- SUS, not always pi'eseut, arises from the ischium, and passes obliquely medially and forwards over the bulbocavernosus, to be inserted into the raphe superficial to that muscle. It belongs to the same stratum as the transvei-sus perinei superficiaHs and ischiocavernosus. The compressor hemispheriorum bulbi is frequently absent. It consists of a thin cap-like layer of muscular fibres surrounding the extremity of the bulb under cover of the bulbocavernosus. M. Bulbocavernosus. — The bulbocavernosus, in the female ((_).T. sphincter vaginae), is separated into lateral halves by the vaginal and urethral openings. It forms two thin lateral layers covering the bulb of the vestibule, and arises behind the vaginal orifice from the central point of the perineum. Anteriorly it is inserted into the root of the clitoris, some of its fibres em- bracing the corpora cavernosa clitoridis so as to reach the dorsum of the clitoris. Ischio- cavernosus Bulbo- cavernosus Ischio- cavernosus Transversus I'KRINEI SUPER- FICIALIS Levator ani Sphincter ani externus FiQ. 432. — The Muscles of the Female Perineum (after Peter Thompson). 488 THE MUSCULAE SYSTEM. Nerve-Supply. — Deep branch of tlie perineal nerve (pudendal, S. 3. 4). Actions. — In tlie male. — The bulbocavernosus contracts the urethra in the emission of urine and semen, and is an accessory muscle in erection of the penis. In the Female. — The muscle contracts the vaginal orifice, and compresses the bulb of the vestibule of the vagina. M. Ischiocavernosus.— The ischiocavernosus (O.T. erector penis), in the male, covers the crus penis. It arises from the ischial tuberosity and the sacro- tuberous ligament. Passing forwards, it is inserted by a fascial attachment into the inferior surface of the crus penis, and into the lateral and dorsal aspects of the corpus caver- nosum penis. The ischiocavernosus (O.T. erector clitoridis), in the female, h&s a similar dis- position, but is of much smaller size than in the male. The pubocavernosus is an occasional slip arising from the pubic ramus, and inserted into the dorsum of the penis. It corresponds to the levator penis of lower animals. Nerve-Supply. — Deep branch of the perineal nerve (pudendal, S. 3. 4). Action. — The muscle assists in erection of the penis (or clitoris). Corpus cavernosum penis (cut) Nerve to corpus cavernosum penis Nerve to dorsum of penis Sphincter urethrjE membranacea; Nerve to bulb Fascia superior of uro- genital luophragm Pudendal nerve Bulb of penis Fascia inferior of urogenital diaphragm Crus penis Levator ani Fig. 433. — The Fasci>e of the Urogenital Diaphragm of the Perineum, AND the Termination of the Pudendal Nerve. Diaphragma Urogenitale. — The sphincter urethrse membranace£e and the transversus perinei jjrofundus constitute the deeper muscular stratum of the perineum and form the urogenital diaphragm. They lie between two layers of fascia called the fascia inferior, and fascia superior of the urogenital diaphragm (O.T. superficial and deep layers of the triangular ligament). M. Sphincter Urethrse Membranaceae. — The sphincter of the membranous urethrte (O.T. compressor urethrte) arises from the inferior part of the pubic ramus, and is directed medially, its fibres radiating so as to enclose the membranous urethra. It is inserted into a median raphe, partly anterior to the urethra, but for the most part posterior to it. The fibres most intimately related to the urethra form a muscular sheath for the canal, and have no bony attachments. M. Transversus Perinei Profundus. — The transversus perinei profundus consists of a bundle of fibres on each side whicli arises from the inferior ramus of the ischium just below the sphincter urethrte membranacece. It is inserted into a median raphe continuous with that of the sphincter urethrge membranacese. The muscle, in fact, constitutes a separate bundle below and behind the sphincter. The ischiopubicus is a term applied to a feeble bundle of fibres which, when present, lies above and in front of the sphincter urethrse membranaceae. It arises from PELVIC FASCIA. 489 the pubic ramus, and is inserted into a median raphe on the dorsum of the membranous urethra. This muscle is homologous with the compressor venae dorsalis penis of lower animals. The sphincter urethrse in the female is smaller than in the male. Its insertion is modified by the relations of the urethra to the vagina. The anterior fibres are continuous with those of the opposite side above the urethra ; the intermediate fibres pass between the urethra and vagina, and the posterior fibres are attached, along with the transversus perinei profundus (transversus vaginae), into the side of the vagina. Nerve-Supply. — Deep branch of the perineal nerve (pudendal, S. 3. 4.). Action. — It is a feeble comijressor of the membranous urethra, and by no means a sphincter. In tlie female it has an acce.ssory influence in constricting the vagina. THE FASCIA OF THE PELVIS. The extra-peritoneal tissue in the pelvic cavity is of great importance. The hypogastric vessels and their branches, the visceral nerves and plexuses, the ureters, and ductus deferentes, take their course in this tissue outside the peri- toneum. It forms in relation to the rectum a thick sheath, for the most part devoid of fat, which encloses the lower part of the rectum completely, down to its termination in the anal canal. It forms a kind of packing for the parts of the bladder uncovered by peritoneum, and is present under the organ in relation to the symphysis pubis and pubo-prostatic ligaments. In the female it forms, in addition, the basis or matrix of the broad ligament, and also occurs as a layer devoid of fat, which loosely connects the anterior surface of the cervix uteri with the base of the bladder. FASCIA PELVINA The cavity of the pelvis minor, in the erect position, resembles a basin tilted forward, with its margin formed by the superior aperture of the pelvis, with a cylindrical wall, and a concave floor, formed by bones, ligaments, and muscles. The deficiencies in the bony walls of the cavity are filled up laterally by the obturator membrane and the sacro- tuberous and sacro- spinous ligaments. In- feriorly and anteriorly, behind the symphysis pubis, the fascia diaphragmatis urogenitalis inferior fills up the pubic arch, and separates the anterior pari of the pelvic ca\'ity from the perineum. The inner surface of this osseo- ligamentous chamber is lined by a series of muscles ; the piriformis and coccygeus posteriorly, the obturator internus on each side, and the sphincter urethrae membranacecC and transversus perinei profundus, inferiorly and anteriorly, on the pelvic surface of the inferior fascia of the urogenital diaphragm. The pelvic fascia, continuous above with the fascial lining of the abdominal cavity, forms a continuous cylindrical investment for these muscles. On the pelvic surface of the pubis, where muscles are absent, it is merged with the periosteum. It gains an attachment to the spine of the ischium as that projects between the piriformis and obturator internus muscles. Perforations occur in it for the trans- mission of the obturator nerve and the parietal branches of the hypogastric artery. At the inferior aperture of the pehis, it is attached to the posterior border or base of the fascia inferior of the urogenital diaphragm, to the ischial ramus and tuberosity, and to the lower edge of the sacro-tuberous ligament. Different names are applied to the fascia in relation to the several muscles which it covers. Posteriorly it constitutes the piriformis fascia : laterally it is the obturator fascia, while that part of the sheet of fascia which covers the pelvic surface of the sphincter urethras membranacese and transversus perinei profundus is known as the fascia diaphragmatis urogenitalis superior. The disposition of the pelvic fascia is complicated by its relations to (1) the structures which constitute the pelvic floor, and (2) the genito-urinary passages and the rectum. 4:90 THE MUSCULAR SYSTEM. The pehdc floor, tense in its anterior part and flexible posteriorly, is formed behind the symphysis pubis by, successively, (1) the fasciee of the urogenital diaphragm and the transversus perinei profundus and sphincter muscle of the membranous urethra between them, the latter enclosing the urethra; and the vagina in the female. (2) The perineal body. (3) The levator ani and external sphincter of the anus on each side of the anal canal; (4) the ano-coccygeal body, between the anal canal and the coccyx, containing the main insertions of the levatores ani and external sphincter. Vesicula seminalis Rectal channel Recto-vesical layer of pelvic fascia 1 Ductus deferens Anal canal Obturator forainen Suspensory ligament of prostate Lateral pubo-prostatic ligament Tendinous arch of pelvic fascia Prostate Median pubo-prostatic ligament Cavum Retzii Fig. 4.34. Urethra Relations of the Pelvic Fascia to the Rectum and Prostate. The levator ani muscle completes the concave floor of the pelvic cavity, sweeping downwards and backwards from its lateral wall, so as to form a muscular diayjhragm, with an intra-pelvic and a perineal surface. Its superior concave pelvic surface occupies the lateral part of the pelvic floor. Its inferior convex surface forms the oblique medial wall of the ischio-rectal fossathe, lateral wall of which is formed by the obturator fascia covering the pelvic surface of the obturator internus. In this wall is a fascial sheath containing the pudendal vessels and nerve. The levator ani is covered on both surfaces by pelvic fascia. The anal fascia clothing its perineal surface is thin and unimportant. The fascia covering its intra-pelvic surface is thick and strong. At the origin PELVIC FASCIA. 491 of the muscle it is continuous with the general fascial lining of the pelvic cavity, and gives rise to a conspicuous thickening, the tendinous arch (arcus tendineus) of the pelvic fascia, which stretches like a bow-string from the back of the symphysis pubis to the ischial spine. This band is related not so much to the origin of the levator ani muscle, which often extends higher uj) external to the pelvic fascia, as to the attachments of the fascial investments of the genito-urinarv passages, to be described below. There are sometimes additional thickenings of the fascia, branching upwards from the tendinous arch towards the superior aperture of the pelvis. At the insertion of the levator ani, the fascia clothing its pelvic surface is attached to the perineal body, the margin of the anal canal, and the ano-coccygeal body, over which it passes to be continuous, above the raphe of in- sertion of the leyatores ani, with the layer of the opposite side. At the antero- posterior (recto-vesical) layer Superior layer : lateral true ligament of the bladder , Suspensory ligament of the prostate gland Rectal channel Sphincter urethr.« membranace^: mtsclf Anal canal Sheath of the prostate gland FiQ. 435.— Relations of Pelvic Fascia to the Rectum and Prostate (Median Section of the Pelvis). inferior border of the muscle the fascioe enclosing it become continuous with the superior fascia of the urogenital diaphragm ; at its postero-superior border they join the fascia enclo.sing the coccygeus muscle. Within the pelvic basin, the walls and floor of which are thus continuously invested by the pelvic fascia, are contained the rectum and bladder, and in the female the uterus, suspended and maintained in position by the peritoneum, extra-peritoneal tissue, and the pelvic vessels and nerves. They are essentially free to distend or collapse, and are not bound down by the pelvic fascia. The rectum in both sexes extends down to the floor of the pelvis, where the anal canal takes its origin. It is invested by the peritoneum and extra-peritoneal tissue, and occupies a special rectal channel ; this is lined by pelvic fascia, which gains an attachment to the floor of the pelvis at the margin of the anal canal. The arrangement of the fascia in relation to the genito-urinary passages is essentially different. Just as from the perineal aspect the inferior aperture of the pelvis is divisible into two different parts,— a posterior or dorsal part, comprising the ischio-rectal 492 THE MUSCULAE SYSTEM. fossse for the passage of the anal canal, and characterised by looseness and dis- tensibility ; and an anterior or ventral part, — the urethral triangle for the genito- urinary passages, and characterised by firm fixation to the pubic bones ; so also from the abdominal aspect it is found that, while in the posterior part of the pelvis a rectal channel exists, in which the rectum is free to collapse and distend, in the ventral part of the basin the genito-urinary passages are firmly fixed by means of Psoas major muscle Suspensory ligament of \ / the vagina and urethra V . ^'^^ Obturator foramen Arcus tendineus Kecto- vaginal layer Lateral pubo-prostatic ligament Urethro-vaginal layer Lig. pnboprostati- cum medium Cavum Retzii Pubo-urethral fascia (pubo-vesical ' ',■;', ligament) ; ' ; ; Urethral layer of pelvic fascia ; : ; ; Urethra .' ! ; Vagina • 1 Bulb of the vagina ; BULBOCAVERNOSUS Sciatic spine Rectal channel External sphincter ani • \ \ Levator ani \ Internal sphincter ani 'i Anal canal Junction of rectum and anal canal Internal sphincter ani External sphincter ani Fig. 436.— Relations of the Pelvic Fascia to the Rectitm, Urethra, and Vagina (Median Section). the pelvic fascia, which gives rise to a special suspensory ligament for the prostate gland and the prostatic urethra in the male, and for the urethra and vagina in the lemale. A crescentic fold of pelvic fascia (suspensory ligament) arises in the neighbour- hood of the sciatic spine from the general fascia covering the pelvic wall. It has a posterior free edge, through which the ductus deferens, vesical vessels, and nerves pass. Sweeping across the median plane, this border is continuous with the fold of the opposite side, the two together constituting the anterior limit of the rectal MUSCLES OF THE PELVIS. 493 channel. The fascial fold is composed of two layers, posterior and superior, between which is a large plexus of veins. They have separate attachments laterally to the general pelvic fascia. The posterior (recto-vesical) layer passes across the pelvis between the prostate gland and the rectum. Its inferior edge is attached to the perineal body between the base of the fascia of the urogenital diaphragm and the beginning of the anal canal. It forms a sheath for the vesicuke seminales and ductus deferentes. This is rather in the form of a septum than a complete sheath ; it eftectually separates the vesicuhe seminales and the bladder from the rectum, forming the anterior wall of the rectal channel, but it allows the vesiculae seminales to rest directly against the bladder. The superior layer extends forwards to the symphysis pubis. It has a lateral origin from the arcus tendineus in its whole length, and sweeping over the prostate gland, it is inserted along its line of junction with the bladder, and constitutes the so-called lig. puboprostaticmn laterale (lateral true ligament of the bladder). It contains numerous bundles of muscular fibres in its anterior part, and forms a sheath for the passage of the inferior vesical vein along the lateral surface of the prostate gland. In front the fascia stretches from the back of the symphysis pubis, the arcuate ligament of the pelvis, and the superior fascia of the uro- genital diaphragm to the neck of the bladder and the prostate gland, forming the lig. puboprostaticum medium. It is continuous across the median plane with the ligament of the opposite side. In the median line, where the two ligaments unite, a hollow occurs behind the symphysis pubis, known as the cavum Retzii. This ligament is composed of several layers separated by large veins (the pudendal plexus), which connect the inferior vesical vein with the dorsal vein of the penis and the hypogastric vein. The sheath of the prostate gland (fascia prostatas) is formed by (1) the superior fascia of the urogenital diaphragm on which it lies, (2) by the general pelvic fascia covering the intra-pelvic surfaces of the levatores ani on each side, and (3) it is completed above and behind by the two special layers of pelvic fascia just described. By these means the prostate gland and prostatic urethra are given a firm attachment to the anterior part of the pelvic walls and floor. In the female an essentially similar arrangement of the pelvic fascia occurs in relation to the vagina and urethra. A crescentic fold of the fascia springs from the pehic wall in the neighbourhood of the spina ischiadica, and sweeping medially to the lateral fornix of the vagina and in front of the rectum, separates into two layers, posterior and superior. Between the layers are numerous vessels, which, along with the visceral nerves, pierce its free edge. The posterior (recto-vaginal) layer passes medially behind the vagina, and gaining the median plane between the vagina and rectum, gives rise to the anterior wall of the rectal channel, and is attached below to the perineal body in the floor of the pelvis. The superior layer, taking origin from the arcus tendineus, is attached medially to the neck of the bladder, and constitutes the lateral pubo-vesical ligament. It is continuous in front with the anterior pubo-vesical ligament, which, as in the male, is divisible into several layers separated by veins. An intermediate (urethro-vaginal) layer of the fascia passes between and separates the urethra and vagina. The urethra and vagina are by means of these layers of fascia firmly bound to the pelvic walls and floor, while the uterus and bladder are free to distend in the pelvic cavity. MUSCLES OF THE PELVIS. Diaphragma Pelvis. — The pelvic diaphragm is formed by the levator ani and coccygeus muscles, which serve to uphold the pelvic floor, and are related to the rectum and the prostate gland or vagina. M. Levator Ani. — The levator ani arises from (1) the inferior part of the posterior surface of the body of the pubis, (2) the general pelvic fascia above or along the arcus tendineus, and (3) the pelvic surface of the spine of the ischium. Its fibres are directed downwards and backwards, to be inserted into (1) the central point of the perineum (perineal body), (2) the external sphincter around 494 THE MUSCULAR SYSTEM. the origin of the anal canal, (3) the ano-coccygeal raphe behind the anus, and (4) into the sides of the lower coccygeal vertebrae. The levator ani muscle fills up and completes the pelvic floor on each side of the median plane. Enclosed in a sheath derived from the general pelvic fascia along the arcus tendineus, the muscle presents an upper concave surface in relation to the pelvic cavity, prostate gland (or vagina), and rectum, and an The arcus tendineus of the pelvic fascia Pubic bone (cut) Bl-lbo- caversosus Fig. 437.- Transversus pennei ^ superiicialis Superior fascia of the urogenital diaphragm Sphincter crethr/E membranace.e Inferior fascia of the urogenital diaphragm -The Fascial and Muscular Wall of the Pelvis after Removal of Part of the Left Hip Bone. Sacro-tuberous ligament (cut) COCCYGEUS Spina ischia- dica (cut) ISCHIO- COCCYGEUS Ilio- COCCYGEDS \v PUBO- COCCY'GEUS J Sphincter ani externus inferior convex surface which appears in the perineum and forms the medial wall of the ischio-rectal fossa. The levator ani is divisible into four parts — puborectalis, pubococcygeus, ilio- coccygeus, and iliosacralis. The puborectalis (levator prostatse) is the part inserted into the central point of the perineum. The pubococcygeus is the part inserted into the anus and the ano-coccygeal rapthe, and the iliococcygeus and ischiococcygeus are represented by the fibres attached to the sacrum and coccyx. The first two are best developed ; the last two series of fibres are the most rudimentary. These several parts of the muscle represent the remains of the flexor caudse of tailed animals. Nerve-Supply. — The levator ani is supplied from two sources : by the perineal (muscular) branch of thf; pudendal nerve, and, on its pelvic surface, by special branches from the third and fourth sacral nerves. MORPHOLOGY OF THE SKELETAL MUSCLES. 495 Actions. — (1) The levator ani nuificle serves to uphold and slightly raise the pelvic floor. (2) It is likewi.se capable of producing slight fle.xiou of the coccy.x. (3) The anterior fil)re8 of the levator ani, in tlie female, sweeping round the vagina, conipres.s il.s walls laterally,. and along witli tlie .sphincter vagin;e, Iielp to voluntarily diminish tlie lumen of tlie tube. (4) The same j)art of the muscle in the male elevates the prostate gland (levator prostata.-). (5) The chief action of tlie levator ani is in defiecation. Along with the external sphincter it acts as a sphincter of the rectum, clo.sing tlu^ anal canal. During defiecation the muscle draws upwards the anus over tlie f;ecal mass, and so assists in its expulsion. (6) In parturition, in the same way, the muscle, contracting below the descending fcetal head, retaifis uelivery. Contracting on the fcetal head, it draws u]>wards the pelvic floor over the foetus, and .so assists delivery. M. Coccygeus. — The coccygeus is a rudimentary muscle overlapping Llie posterior border of the levator ani. It arises i'rom the ischial spine and the sacro- spinous ligament. It is inserted into the sides of the lower two sacral and upper two coccygeal vertebrje. The muscle is in contact by its anterior border with the levator ani. It is enclosed in pelvic fascia, assists in forming the pelvic Hoor, and is in contact laterally with the sacro-tuberous and sacro-spiuous ligaments. Nerve-Supply.— The coccygeus is supplied on its pelvic surface by the third and fourth sacral nerves. Actions. — The muscle is a feeble lateral flexor of the coccyx, and assists the levator ani to uj)hold tlie pelvic floor. THE DEVELOPMENT AND MORPHOLOGY OF THE SKELETAL MUSCLES. The mesoderm on either side of the embryonic medullary tube separates into three main parts— the myotome, nephrotome, and sclerotome or lateral plates (somatopleure and splanchnopleure). The myotomes are probably directly or indirectly the source of the striated muscles of the whole body. Each consists at first of a quadrilateral bilaminar mass, resting against the medullary tube and notochord on either side. The cleft between its two layers represents the remains of the coelomic cavity. In the early stages of embryonic life the growth of the myotome is rapid. On its medial side masses of cells arise, which grow medially and surround the medullary tube and notochord to form the foundation of the vertebral column. On its lateral side cells appear to be given off which participate in the formation of the cutis vera. At the same time the dorsal and ventral borders of the myotome continue to extend, and present extremities (growing points) with an epithelial structure for a considerable period. On the dorsal side it overlies the medullary tube, and gives rise to the muscles of the back ; while by its ventral extension, which traverses the somato-pleuric mesoderm in the body wall, it produces the lateral and ventral muscles of the trunk. By a medial extension it probably gives rise also to the hypaxial muscles of the neck and loin. The cells of the medial layer of the myotome are responsible for the formation of the muscle fibres. The cells elongate in a direction parallel to the long axis of the embryo, and give rise, by fusion with the cells of neighbouring myotomes, to the columns and sheets of muscles of the back and trunk. For the most part {e.g. back and abdomen) the originally segmental character of the muscular elements is lost by the more or less complete fusion of adjacent myotomes. The intercostal muscles, however, are the direct derivatives of individual myotomes. Muscles of the Limbs. — In fishes and (doubtfully) reptiles there is evidence that the myotomes are concerned in the formation of the limb-muscles by their extension into the limb-bud in a manner similar to that described for the trunk. In birds and mammals, however, in which the limb-bud arises as an undifterentiated, uusegmented mass of mesodermic tissue, partly from the mesoderm surrounding the notochord, and partly from the somato-pleuric mesoblast, the myotomes stop short at the root of each limb, and do not penetrate into its substance. Instead, the muscular elements of the limb take origin independently as double dmsal and ventral strata of fusiform cells on the dorsal and ventral surfaces of the limb-bud. These strata are unsef/mented ; they are grouped around the skeletal elements of the limb, and they gradually become differentiated into the muscle masses and individual muscles of the limb. Muscles of the Head. — Notwithstanding the obscurity and complexity of this 496 THE MUSCULAE SYSTEM. subject, it appears certain that at least two series of elementary structures are concerned in the formation of the muscles of the head and face — the cephalic myotomes and the muscular structure of the branchial arches. The number of myotomes originally existing in the region of the head is not known, although it is stated with some authority that nine is the complete number. Tlve first three are described as persisting in the form of the ocular muscles, the last three in relation to the muscles of the tongue, while the three intervening myotomes disappear. Fig. 4.38. — Scheme to illustrate the Disposition of the Myotomes in the Embryo in relation to THE Head, Trunk, and Limbs. A, B, C, First three cephalic myotomes ; N, 1, 2, 3, 4, Last persisting cephalic myotomes ; C, T., L., S., Co., The myotomes of the cervical, thoracic, lumbar, sacral, aiid caudal regions ; I., IL, III., IV., V., VI., VII., VIII., IX., X., XL, XII., refer to the cerebral nerves and the structures with which they may be embryologically associated. The following table shows the possible fate of the cephalic myotomes : — First, Superior, medial and inferior recti, obliquus inferior, levator palpebrse superioris. Second, OVjliqiius superior. Third, Rectus lateralis. Fourth, Fifth and Sixth, Absent. Seventh, \ Eighth, \ Muscles of the tongue. Ninth, I Muscles connecting the cranium and shoulder girdle. Tenth (first cervical) j The mesoblastic tissue of the branchial arches is j)robably concerned in the production of the following iiuisclcs of the; face and neck : — First (mandihidar) arch . . Muscles of mastication. (Platysma and facial nuiscles. Muscles of the soft palate. Stapedius, stylo-hyoid, and digastric. T}nrd{thyreo.hyoid)arch . . (Stylopharyugeus ^ " » / I Superior constrictor. /"Middle and inferior constrictors. Fourth and Fifth (branchial) arches I Muscles of the larynx. THE NERVOUS SYSTEM. I.— THE CENTRAL NERVOUS SYSTEM. Originally writtkn by D. J. Cunningham, F.R.S., Late Professor of Anatomy, University of Edinburgh ; Revised and partly rewritten by G. Elliot Smith, F.RS., Professor of Anatomy, University of Manchester. [In its original form this chapter represented perhaps the most characteristic work of the late Editor of this Text-book, which continues to bear his name, and is a lasting memorial of his personality and scientific attainments. By his lamented death the difficult task has fallen upon the reviser of making such considerable alterations as the rapid changes in the state of our knovAedge of the nervous system have rendered unavoidable, while endeavouring at the same time to preserve unaltered the general character of his friend's work.] — peripheral process nerve eel ELEMENTS OF THE CENTRAL NERVOUS SYSTEM. Every type of nervous system with which we are acquainted, from the simplest and most primitive, such as that of Hydra, to the most complex and highly elaborated mechanism found in man, is com- posed essentially of three categories of elements. These are (1) sensory cells, so situated and so special- ised in structure as to be capable of being a fleeted by changes in the animal's environ- ment, and of transmit- ting the effects of such stimulation, directly or indirectly, to (2) effer- ent nerve-cells, which intluence the muscles or other active tissues, so that the stimulation may find expression in some appropriate action ; and (3) intercalated nerve-cells, which regu- late such responsive be- haviour by bringing it under the influence of other sensory impressions and of the state and activities of the body as a whole. 497 33 intercalated nerve cells muscle KiG. 439. — A Diagram representing the Essential Features in the Arrangement ok the most pbimitite Type of Nervous System. 498 THE NEKVOUS SYSTEM. The study of a simple scheme representing the relationship that obtains between these three classes of elements in the extremely primitive animal, Hydra (Fig. 439), will make these fundamental facts plain. Changes in the animal's environment affect the extremities of the peripheral processes of the sensory cells (A, B, and O), which in Hydra are situated amongst the ordinary tegumentary cells : the effect is transmitted by the central processes of such cells {A, for example), either directly to the efferent cell, represented in the diagram by a motor nerve-cell, or more usually to an intercalated nerve-cell {a, b, or e). Into this (a) impulses stream from other intercalated cells (h and c), bringing the impulse from the sensory cell A under the influence of those coming from B and from more distant parts of the body through the intermediation of the intercalated cell c. The cells a, c, and d are connected with the motor nerve-cell. Thus, there is provided a mechanism whereby the conditions affecting other regions of the body, B and C, may influence the nature of the response which the stimulation of A evokes — either increasing or diminishing its effect or perhaps altering its character. In this way the intercalated nerve-cells form a great co-ordinating mechanism, linking together all parts of the body in such a way that the activity of any part of the organism may be influenced by the rest, and thus be enabled to act in the interest of the whole. Hence the nervous system becomes the chief means whereby the various parts of the body are brought into functional relationship one with the other, and co- ordinated into one harmonious whole. Throughout the whole course of its subsequent evolution the nervous system is formed of these three kinds of elements ; and the essential feature in its elaboration and increasing complexity is the multiplication of the intercalated cells, and their concentration, together with the motor nerve-cells, to form a definite organ, which we call the central nervous system. During this process of development of the more complex forms of nervous system, most of the sensory cells migrate from their primitive positions in the skin (Fig. 439) ; and, as the free extremity of the peripheral process retains its primitive relationship to the skin, such migration of the cell bodies necessitates a great elongation of their peripheral processes. Although these sensory cells thus move inwards into the deeper tissues of the body, the great majority of them do not become incorporated in the central nervous system, but become collected into groups, which form the ganglia of the sensory nerves. In addition to its primary functions of (a) providing the means whereby the organism can be brought under the influence of its surroundings, and (&) co- ordinating the activities of the whole body, the nervous system also comes to perform other functions of wider significance. In the course of its evolution the co-ordinating mechanism formed by the intercalated cells becomes so disposed in each animal that an appropriate stimulus applied to the sensory nerves can evoke a definite response, often of great com- plexity and apparent purposiveness. In other words, the nervous system becomes the repository of those inherited dispositions of its constituent parts which determine the instincts : and in the course of time it eventually provides also the apparatus by which individual experience and the effects of education can be brought to bear upon and modify such instinctive behaviour. In other words, from the nervous system is formed the instrument of intelhgence ; and the relatively great bulk and extreme complexity of that instrument — the brain — in man are in a sense the physical expression of human intellectual pre-eminence. In conformity with its jjrimary function of affording a means of communication with the outside world, almost the whole* nervous system in the human embryo, as in other animals, is developed from the ectoderm, as has already been explained in the chapter dealing with General Embryology (p. 30 et seq.). In the most primitive Metazoa the sensory cells remain in the ectoderm (Fig. 439), but other ectodermal cells become converted into motor nerve-cells and intercalated nerve-cells, which wander into the underlying tissues (Fig. 439). In the human embryo there is an analogous process of development, but with the important difference that the various nervous elements do not wander into the mesoderm individually. A ELEMENTS OF THE CENTRAL NERVOUS SYSTEM. 499 sKin sensory intercalated nerve cell median qroove )Tf-- ectoderm •JvJdU: - -endoderm definite patch of ectoderm is set apart to produce the greater part of the nervous tissues for the whole body ; and all except the margins of this area sinks into the body, en masse. In one area of ectoderm all the motor nerve-cells develop (Fig. 440, d), in another (c) only intercalated nerve-cells, in yet another (6) the sensory cells originate ; and the rest forms the epidermis of the skin (a). With ovir know- ledge of the fact that the sensory cells were originally distributed throughout the skin (Fig. 439), the idea naturally suggests itself that in man also the units of the sensory ganglia might be formed in sitit in the ectoderm, and that the collection of sensory cells in the ganglia might possibly be brought about by the migration of such sensory cells inwards, while their peripheral processes elongate to permit such migration of the cell bodies without disturbing their original endings in the skin. But there is no evidence to show, or even to suggest, that such a process takes place in the human embryo. The facts at our disposal seem to indicate that the sensory cells are derived from sharply circumscribed patches of ectoderm, and that the peripheral processes of these cells are distributed to the outlying area of ectoderm beyond them, from which the epidermis is eventually formed (Fig. 440). At the beginning of the second week the nervous system of the human embryo is represented by two thickened plates of ectoderm lying parallel the one to the Fk; mesoderm 440. — DiAGHAM REl'RESENTIXC; (iX BLACK) THE LeKT HaLF OF A Transverse Section ok a 2 mm. Human Embryo. Supejimposed upon it there is shown (in colours) the hypo- thetical primitive arrangement of the nervous elements derived from each part of the ectoderm. Yolk-sac, Neural groove _j Neurenteric canal __ Primitive streak Body stalk -..j^i^' Fk;. 441.- The Dorsal Aspect ok a Vekv Early Human Embryo (after von Spee). I other, alongside the median axis of the embryo (Fig. 441), which is occupied by a shallow furrow. Upon a diagram (Fig. 440), representing a transverse section through one-half of I such an embryo (the uncoloured part), colours corresponding to those employed in 500 THE NEEVOUS SYSTEM. Fig. 439 have been placed to indicate the nature of the elements that are known to develop in relation with each area of the ectoderm at a later period in the history of the embryo : b represents an area which later will form the crista neuralis, from . which the sensory cells will be developed. The peripheral processes of these cells will pass into the skin (a) and their central processes into the area cd, which will become part of the neural tube. In the area c intercalated cells will develop to receive the incoming sensory nerves ; and in the area d the motor nerve-cells (as well as other intercalated cells) will be formed. When it is recalled that all the elements of the primitive nervous system of Hydra are modified ectodermal cells, and, moreover, that when the intercalated and motor nerve-cells wander into the deeper tissues the protoplasm of the whole nervous network remains in uninterrupted continuity (Fig. 439), it is instructive to note that in the primitive human nervous system the rudiment of the epidermis of the skin is linked to the medullary plate by the patch of ectoderm from which the sensory ganglia will be formed. In the discussion of the inter-relationships of the various constituent elements of the nervous system, there will be occasion to refer to this matter again. But while we are studying Fig. 440 it is important to emphasise the fact that in accordance with the commonly accepted ideas it is taught that the area h becomes completely severed from a and c, and shortly afterwards fibres are budded off from the cells in the area h to form the sensory nerves linking a to c, thus re-establish- ing a connexion which existed a few days earlier. This suggests the possibihty that the connexions between these three series of elements may not have been completely sundered during the intermediate phase of development. Early in the second week in the human embryo the axial groove separating the two bands of thickened ectoderm (Fig. 441) that form the medullary plate becomes deepened by the tilting-up of the lateral margins of the two bands. This process becomes accentuated during the next day or two until a deep cleft is formed, the walls of which consist of the thickened ectoderm and the floor of the thinner ectoderm (floor-plate) joining them together. Before the end of the week the dorsal edges of these thickened plates become joined in the region which will develop into the neck ; and during the third week the sealing of the hps of the neural groove extends upwards (headwards) and downwards (tailwards), so that the neural tube becomes completely closed by the end of that week. The extreme anterior (head-) end and the dorsal aspect of the caudal extremity of the tube are the last parts to close, the latter being, as a rule, a httle later than the former. When the tube is in the stage of being patent only at its two ends, the openings are known as the neuroporus anterior and neuroporus posterior, respectively. In the process of closing, the extreme dorsal edge of the medullary plate becomes excluded, in the greater part of its extent, from participation in the constitution either of the neural tube or of the skin, and forms a column of cells lying between the two. This is the neural crest (Fig. 442, A, B, and C ; x and y represent the places where the apparent sundering occurs). It is commonly supposed that the neural crests do not extend the whole length of the neural tube. Nevertheless, peculiar ectodermal areas, which ultimately give origin to sensory nerves, are found at the junction of the medullary plate with the skin in those regions where the neural crest is supposed to be lacking. At the extreme anterior end of the neural tube the margins of the anterior neuropore become thickened to form crest-like patches ; but when the tube closes these areas do not separate from the skin (at x, Fig. 442, D), as the rest of the neural crest does. They remain part of the skin and become the olfactory areas, in which sensory cells, precisely like those found in Hydra (Fig. 439), develop. A little farther on the caudal side of the olfactory region a very large crest- like mass of ectoderm fails to separate from the medullary plate as it closes, and becomes a constituent part of the neural tube (Fig. 442, E). It develops into the optic diverticulum from which the cells of origin of the optic nerve are formed. In several other regions sensory nerves originate from cells of ectodermal, and possibly even entodermal, areas which do not form parts of the neural crest, as that term is usually understood. Tlie nerves of hearing and taste are developed ELEMENTS OF THE CENTEAL NERVOUS SYSTEM. 501 neural plate crista neuralis skin crista neuralis peripheral sensory nerve sensory nerve root qanqlii ^"SXN^ sensitivum in a way that seems at lirst sight utterly abnormal, until it is remembered that they afford examples of very primitive methods of nerve- formation. The essential part of the organ of hearing is an ecto- dermal sac (otic vesicle) that develops as a diverticulum on the side of the head, from a thickened patch of ectoderm, which in the lower vertebrates forms part of a more exten- sive area, known as the dorso- lateral placode. Some of the cells of this area seem to be- come transformed into nerve- cells, which migrate into the space between the otic vesicle and the neural tube (Fig. 443) and form the acoustic ganglion. At the upper margins of gan9iion the branchial clefts a series of °ifa-ctorium ectodermal (and possibly also entodermal) thickenings develop, which are known as the epi- branchial placodes. Com- parison with the process of development in fish embryos, which has been elucidated by Landacre {Journal of Compara- tive Neurology and Psycliology, 1910-1912), suggests that the nerve-cells may arise from these placodes, from which the nerves of taste originate vesicula optica Fl( • 442. — Diagrams of Tkaxsvehse Sections representing Three St.\ges (A, B, and C) in the development ok a Sensory Ganglion from the Neural Crest ; and Two Diagrams (D and E) sucsgesting a Possible Homology OF the Olfactory (D) and Visual (E) Epithelium with THE Neural Crest. Ganglion geniculi Xervus facialis Epibranchial placode of facial nerve Vesicula optica Ganglion acusticiim Vesicula otica . Ganglion petrosuni Epibranchial placode , of glosso-pharyngeal nerve Ganglion nodosum Epibranchial placode of vagus nerve Area olfactoi i Fig. 443. — Reconstruction of the Ganglia of the Fa( ial, Acoustic, Glosso-pharyngeal, and Vagus Nerves of a Human Embryo 5 Millimetres long (about three weeks old). The epithelium of three branchial clefts and the otic vesicle is represented diagramniatically ; and the supposed mode of origin of the gustatory nerve-cells (and their fibres) from the epibranchial placodes is indicated in blue, and of the acoustic nerve-cells from the otic vesicle in purple. 502 THE NERVOUS SYSTEM. Such fibres are constituent elements of the facial, glosso-pharyngeal, and in some animals also the vagus cerebral nerves (Fig. 443), in connexion with the ganglia of which these epibranchial placodes are formed (Froriep and Streeter). The observations of Professor J. P. Hill upon embryos of Echidna seem to suggest that in mammals these gustatory neuroblasts are derived from the entoderm. AVhen first formed, the neural tube is compressed from side to side and presents an elliptical outline in transverse section (Fig. 444). The two side walls are very thick, whilst the narrow dorsal and ventral portions of the wall are thin, and are termed the roof-plate and floor-plate respectively (Fig. 444). The cavity of the tube in transverse section appears as a narrow slit. The wall of the neural tube consists at first of low columnar epithelium arranged in a fairly regular series, but with a certain number of large spherical so-called germinal cells scattered between the columns. But this regular disposition as a single layer Funiculus posterior .,<<'vV«>-^Js '^ ' - w^ Commissure Sensory £j/K- ganglion-^^S Marginal layer Commissural fibre Anterior nerve root Fig. 444. — Diagram of Transvkkse Section of Eakly Neuual Tube. of cells does not last long. For even by the second week the rapid proliferation of the cells has led to a marked increase in the thickness of the side wall and a scattering of the more numerous nuclei, apparently irregularly, throughout its substance (Fig. 444). The latter consists of a network of protoplasm in which definite outlines of cells cannot be detected. As growth proceeds the innermost part of this nucleated protoplasmic syncytium becomes condensed to form a delicate membrane termed the internal limiting membrane, which lines the lumen of the tube, whilst its outermost part presents a similar relation to an external limiting membrane, which invests the outer surface of the tube. To- ward the end of the first month the side walls of the tube show signs of a differentiation into three layers. Next to the central canal there is an epithelial- like arrangement of the innermost cells of the syncytium, forming the ependyma. Then there is an intermediate layer crowded with nuclei, hence known as the nuclear or mantle layer. On the surface is a layer singularly free from nuclei, which is called the non-nuclear or marginal layer. The germinal cells are ELEMENTS OF THE CENTEAL NERVOUS SYSTEM. 503 placed in the ependymal layer between its radially arranged cells as they pass in towards the internal limiting membrane ; and the protoplasm of the germinal cells forms part of the syncytium. At one time it was ima^dn'/'d that the germinal cells were embryonic nerve-cells, the parent-cells of the real neuroblasts, and that the whole of the rest of the syncytium represented the supporting' tissues, which in the a(hdt form the neuroglia. l>ut it is now known that from the prolil'eration of tlie germinal cells, in which mitotic figures can usually be seen, some cells are formed which Ijccome ependymal epithelium, and others which migrate peripherally into the mantle layer. There, while forming ])art of the mantle syncytium, tliey undergo further proliferation and some of the resulting cells develop into spongioblasts, which constitute the supporting framework, the embryonic neuroglia; others become rudimentary nerve- cells or neuroblasts, and others again are known as indifferent cells. The latter are destined to undergo further subdivision and become the parents of more spongioblasts and neuroblasts. From this it is clear that the greater part — all except the germinal cells — of the syncytium, which is known as the myelospongium, is not merely supporting neuroglial tissue, as was once supposed, but is the rudiment of both neuroglia and true nervous tissues. The details of the process by which the neuroblasts become dissociated from the neuroglial network are quite unknown. It is commonly supposed that a spherical cell in the mantle layer that is to be transformed into a neuroldast frees itself from the syncytium, and remains for a time independent and wholly unatt iched amidst the meshes of the neuroglial network : it is supposed lurther that its true nature as a neuroblast becomes revealed when it takes on a pear- shape, and a protoplasmic process, the stalk of the pear, pushes its way into some other part of the nervous system, or out of it into the mesoderm to reach some musc"ular or glandular tissue, and becomes the axis cylinder process or axon of the nerve-cell. Such an interpretation of the appearances exhibited in the walls of the neural tube at the end of the first month is adduced in support of a view concerning the constitution of the nervous system known as the neurone theory. "Neurone" is the term applied to a nerve-cell and all its processes ; and the neurone doctrine assumes that there is no continuity whatever between the substance of one neurone and that of another, such as occurs in Hydra (Fig. 439), and that the functional connexions between them are brought about merely by the contact of the processes of one element with the processes, or the cell-body itself, of another element. In accord- ance with this conception the facts of embryology are supposed (by His) to demon- strate that when the axon grows out from a previously spherical and unattached cell it is able to push into the surrounding tissues, and, as it were guided by some instinct, eventually finds its way to that particular area of skin, muscle, gland, or other part of the body where nature intends it to go. This is the current teaching in regard to the neurone-theory ; and it is supposed to have been conclusively demonstrated by the facts revealed not only by embryo- logy and the study of the minute structure of the nervous system, but also by the phenomena of degeneration and regeneration. Harrison has shown that the out- growth of processes can be witnessed in the living nerve-cells of the frog. There are certain facts, however, which have always led some anatomists to refuse to believe in the validity of the neurone doctrine as a true expression of the real constitution of the nervous system. It has been clearly demonstrated by Graham Kerr that at a very early stage of development the neural syncytium of the spinal medulla (of the mud-fish Lepidosiren) is in free and uninterrupted continuity with the protoplasm of the muscle-plate, which lies in contact with the neural tube ; and no stage is known in which these connexions do not exist. When, in the course of the subsequent growth of the embryo, the muscle-plate becomes removed further and further away from tlie central nervous system the protoplasmic strand, which links them the one to the other, gradually becomes stretched and elongated. As the neuroblast matures its chemical constitution becomes modified ; it becomes specialised in structure to fit it for the peculiar functions it has to perform. These 504 THE NEKVOUS SYSTEM. changes manifest themselves first in the body of the nem-one itself and thence spread along its processes. With the knowledge that protoplasmic bridges exist long before the time His supposed the axon of his neuroblast to push its way outward, it seems not unreasonalile to suppose that it is the chemical modification of these existing bridges which has been revealed in stained specimens, as it spreads from the cell body outwards into its processes. It is now a well-recognised fact that soon after the neural tube becomes closed the outhnes of its constituent cells become blurred and then disappear, and a continuous protoplasmic network or syncytium is formed. No one has ever been able to detect the process of detachment of embryonic nerve-cells (neuroblasts) from this syncytium ; and it is at least a possibility that the free anastomosis of the protoplasmic processes of many of the cells is not destroyed in the way demanded by the neurone doctrine. The known facts might be interpreted, at least as reasonably, by supposing that when nerve currents begin to traverse the syncytium (Fig, 444) structural modifications occur around the nuclei of the cells affected, and gradually spread along their processes, so as to give the appearance (in sections stained by special methods) of processes growing out from each neurone. Impulses brought from the skin by fche sensory nerves, the nutrition of which is controlled by the cells in the sensory ganglion (Fig. 443), are carried into the wall of the neural tube, where they are received by processes of intercalated cells, which in turn transmit their efiects directly or indirectly to (a) motor nerve-cells (or other kind of efferent nerve-cells), which stimulate a muscle, a viscus, or other active tissue to perform some work, or (h) to intercalated cells, the axons of which proceed to some other part of the nervous system, perhaps above or below the place where the sensory nerve enters (Fig. 444, funicular cells). As the walls of the neural tube increase in size the various neurones gradually become drawn apart, and the protoplasmic links uniting them become stretched and extended to form processes of varying length. It is right to explain that most writers give an explanation of the process of development which is at variance with that just sketched. The neuroblast is supposed to originate as a free-lying spherical cell, which is stimulated by some unknown force, sometimes assumed to be of the nature of a chemical attraction (chemotaxis), to protrude a process, which gradually elongates and pushes its way through the tissues, perhaps to some particular patch of skin, muscle, gland, or some other nerve-cell. The difficulty involved in such a conception is not only that it is opposed to all that is known of the early stages in the evolution of the nervous system, but also that it is difficult to conceive that every one of the millions of nerve-cells, muscle-cells, visceral and cutaneous elements can each have some specific attractive power which leads every individual nerve fibril to its appropriate and predestined place in the body. The Efferent Nerves. — The efferent cells of the neural tube are distinguished by the fact that their axons leave the central nervous system and traverse the mesoderm for a longer or shorter distance to end in relation to some muscle, gland, or other tissue outside the nervous axis. At an early stage of development (Fig. 445) such efferent fibres pass not only to muscles but also to viscera and other kinds of tissues. In the course of the growth of the body these various structures supplied by efferent fibres become removed progressively further and further from the central nervous system ; and in this process a distinction can be detected in the behaviour of the efferent fibres proceeding (a) to the striped or voluntary muscles, (c) and the viscera and unstriped muscle, respectively. The efferent cells (a) which innervate voluntary muscles retain their positions in the central nervous system, their axis- cylinder processes (motor nerves) becoming elongated in proportion to the migration of the muscle from its original situation. But the cells (c) innervating non-striped muscles and viscera behave in a different manner. As the viscus or muscle migrates (Fig. 445, B), the nerve-cell (c) follows it more or less closely, being as it were dragged out of the wall of the neural tube by its axon into a peripheral position, where it Ijecomes a constituent element of one of the so-called sympathetic or autonomic ganglia.^ As these sympathetic cells migrate from the central nervous system, each of them appears to draw out with it the axon of an inter- ELEMENTS OF THE CENTEAL NERVOUS SYSTEM. 505 calated cell (rf) ; and it is cuatoiiiary to distinguish these latter elements (within the central nervous system) as splanchnic efferent cells. It is, however, a matter of fundamental imjKjrtaiice to recognise clearly that the real splanchnic efferent cells, the homo- logues of the ^ ^ '=' . . a, ^ ^^"-"T^ Roof Pic somatic efferent cells, are found in the sympathetic ganglia, and that the elements to which this term is usually applied are in reality inter- v -n^ ^ , . „ \ i a,*j. / c •' vC'V^"^^ ( motor cells \ / ^Wr -f - - SomaCic calated cells. X/ ./a ^ ' V I /a V- efferent nucleus Splanchnic efferent cell 445. — Diagram of a Transverse Section through the Left Half op the Neural Tube representing Two Stages in the Development of the Efferent Nerves, to suggest the Possiri.e Ohigin of the Cells of the Sympathetic Ganglia by mtguation from the Neural Tube. This accoiuit is at variance with the customary descrip- tion of tlie develop- ment of the sym- pathetic system, acconling to which the cells of the sym- pathetic ganglia are said to be wholly derived from tlie sen- sory ganglia ; but it offers a reasonable explanation of the facts (i.) that the cells Fig in the sympathetic ganglia are of the efferent, and not of the sensory, type, ,,. , . , • •. •. and (ii.) that the fibres from the central nervous system establisliing relations with them emerge along the motor nerves. Moreover, the information brought to light by recent research in embiyology (Froriep, Kuntz, and others) affords positive evidence in support of this view. Elliott, however, opposes this interpretation {Journal of Physiology, 1907, p. 438). Many, if not all, of the sympathetic cells are derived from the walls of the neural tube, and they migrate along the pathways formed by the motor, rather than the sensory, nerves, "in the case of the spinal medulla they pass out chiefly along the anterior roots, and from the brain along the motor nerves— the oculo- motor, and the motor divisions of the facial and vagus nerves. Nerve Components.— From the statements in the preceding paragraphs it must be evident that there are several varieties of afferent and efferent nerves respectively entering and leaving the central nervous system. The cells of origin of the efferent nerves are all placed in the ventral part of the side wall of the neural tube ; and for this reason this part of the wall becomes swollen at an early stage ot develop- ment (Figs. 445 and 446). It is called the basal lamina. Most of the cells that emit afferent fibres are situated in the sensory ganglia outside the central nervous system, so that their growth can have no direct influence upon the form of the neural tube; but their central processes become inserted into the dorsal part of the side wall of the tube, which is called the alar lamina; and groups of intercalated cells collect around the entering fibres to form receptive or terminal nuclei. Ihe growth of these terminal nuclei leads to an expansion of the alar lamina ^vhlch is analogous to, but much less extensive than, that seen in the basal lamina. I his unequal swelling of the dorsal and ventral parts of each side wall ot the neural tube leads to the development of a longitudinal groove, sulcus limitans, as a demarcation between the alar and basal lamime. The nuclei of origin of the efferent fibres, which are found m the basal laminae, may be divided into two (and, in some regions of the nervous axis, three) main groups. There is first the group of large multipolar nerve-cells which emit fibres to innervate the ordinary striped voluntary muscles. This is commonly called 506 THE NEEVOUS SYSTEM. the somatic efferent nucleus. Then there is a group of small multipolar cells, the axons of which pass out into sympathetic ganglia, and indirectly control the involuntary unstriped muscles and other active parts of viscera. These cells form the splanchnic efferent nucleus. In the upper cervical and lower cranial region a portion of the somatic efferent nucleus is set apart to innervate the striped muscles developed in the branchial arches. This is the lateral somatic or intermediate efferent nucleus. Many recent writers are of the opinion that this nucleus is splanchnic ; but its fibres directly innervate striped voluntary muscles, which are developed from the same material ROOF-PLATE Splanchnic Terminal Nucleus. '< Gustatory Nucleus. Acoustico-Laleral Terminal Nucleus. Somatic Terminal Nucleus. LAMI BASALI Somatic Efferent Nucleus Floor Plate --- Ear Vesicle. -Sensory Ganglion. Skin. Unstriped - Muscle Viscera Mucous Membrane Fig. 446. — DiACiu.^M of a Tran.sverse Section through the Eight Half of the Fcetal Ehomben- CEPHALON AND EPITHELIAL AREAS ASSOCIATED WITH IT TO ILLUSTRATE THE DIFFERENT CATEGORIES OF Nerve Components and their Central Nuclei. (myotomes) from which the other striped muscles are formed (Agar and Graham Kerr). The alar lamina also can be subdivided into a series of functional areas (Fig. 446). At the dorsal edge is the somatic afferent terminal nucleus, which receives im- pulses coming from the skin. In one region a part of this nucleus is specialised for the reception of impulses coming from the internal ear (acoustico- lateral terminal nucleus). Then there is a group of cells collected' around the incoming visceral sensory nerves-r-the splanchnic afferent terminal nucleus. A part of this is specialised to receive taste impressions — the gustatory nucleus — but this has not yet been clearly demarcated from the rest of the nucleus. This analysis of the various functional elements that may enter into the constitution of the various cerebral and spinal nerves is made use of in elaborating the theory of nerve components, which will help us to understand many features of the structure of the nervous system that otherwise would be unintelligible. Nerve-cells. — We have already noticed that there is a broad distinction between the nerve-cells which are found in the ganglia of sensory nerves and those NERVE-CELLS. 507 ••^t*. found in the rest of the nervous system. They differ not only in tlieir mode of origin and in their subsequent development, but also in the connexions of their nerve-fibre processes. Nerve-cells of the Brain and Spinal Medulla. — The cells in the cerebro- spinal axis are variable both in size and form. Some are relatively large, as, for example, certain of the pyramidal cells of the cerebral cortex and the motor cells in the spinal medulla, which almost come within the range of unaided vision ; others are exceedingly minute, and require a high power of the microscope to bring them into view. The cell consists of a protoplasmic nucleated body, from which the axon proceeds, and the protoplasmic processes of Deiters, or the dendrites (Fig. 447). Tlie axon presents a uniform diameter and a smooth and even outline. It gives off in its course fine collateral branches, but does not suffer thereby any marked diminution in its girth. The most important point to note in connexion with the axon, how- ever, is the fact that it becomes continu- ous with the axis- cylinder of a nerve- fibre. The axon then is simply a nerve-fibre, and in certain circum- stances it assumes one or two invest- ing sheaths, of which more will be said later. The axon may run its entire course within the substance of the brain or spinal medulla, either for a short or a long dis- tance (intercalated cells), or it may emerge from the brain or spinal medulla in one of the cerebral or spinal nerves as the essential part of an efferent nerve-fibre, and run a variable distance before it finally reaches the peripheral structure in relation to which it ends (efferent nerve-cells). The axon and the collaterals which spring from it appear to terminate either in small button-like swellings or knobs, or more frequently in terminal arborisations, the extremities of which seem to be furnished with ex- ceedingly small terminal varicosities. In those cases where the axon or its collaterals end within the brain or spinal medulla, some of the terminal arborisa- tions interlace with the dendrites of nerve-cells, whilst others are twined around the bodies of other cells. In the latter case the interlacement may be so close and complete that it almost presents the appearance of an enclosing basket-work. In cases where the axon emerges from the cerebro-spinal axis its terminal arborisa- tion ends in relation to a muscle-fibre or some other tissue in the manner described below. Fici. 447.- -Thuee Nerve-cells from the Anterior Coli'mn ok Gr.vt Matter of the Human Spinal Medclia. 508 THE NEEVOUS SYSTEM. Fig. 448. — Two Multipolar Nerve- cells (from a specimen prepared by the Golgi method). view, therefore, four forms of nerve-fibre recognised :— different may be Non-med ullated — 1. Naked axis-cylinders. 2. Axis -cylinders with primi- tive sheaths. Medullated — .3. Primitive sheath absent. 4. Primitive sheath present. Every nerve -fibre near its origin and as it approaches its termination is unprovided with sheaths of any kind, and is simply represented by a non- medullated, naked axis- cylinder. The fibres of the olfactory nerves afford us an example of non - medullated fibres furnished with a primi- tive sheath. Medullated fibres are present in greater quantity in the cerebro- spinal system than non -medullated fibres. Thus, all the nerves attached to the Nerve - fibres. — Nerve - fibres, ar- ranged in bundles of greater or less bulk, form the nerves which pervade every part of the body. They also constitute the greater part of the brain and spinal medulla. Nerve-fibres are the conduct- ing elements of the nervous system ; they serve to bring the nerve -cells into relation both with each other and with the various tissues of the body. There are different varieties of nerve- fibres, but in all the leading and essential constituent is a delicate thread-like axon. The most obvious difference between individual fibres depends upon the nature of the covering of the axon. When it is coated on the outside by a more or less thick sheath of a fatty substance, termed myelin, it is said to be a myelinated or medullated fibre. When the coating of myelin is absent, the fibre is termed a non-myelinated or a non -medullated fibre. A second sheath — thin, delicate, and membranous, and placed externally — may also be present in both cases. It is termed the primitive sheath or the neurolemma. From a structural point of Fig. 449. — Nerve-ckll from Cerebellum (Cell of Pcjrkikje) SHOWING the Branching of the Dendritic Processes (from a photograph by Professor Symington). NERVE-FIBRES. 509 Axis 'cylinder Myelin Pritnitivt slieath brain and spinal medulla, with the exception of the olfactorj' and optic, are formed of meduUated fibres provided with a primitive sheath ; whilst the entire mass of the white substance of the brain and spinal medulla, and also the optic nerves, are formed of medullated fibres devoid of a primitive sheath. It is important to note that the distinction between the medullated and non- medullated fibres is not one which exists throughout all stages of development. As will be presently pointed out, every fibre is tlie prolongation of a cell, and in the first instance it is not provided with a medullary sheath. Indeed, it is not until about the fifth month of fcetal life that those fibres which are to form the white substance of the cerebro- spinal axis begin to acquire their coating of myelin. Further, this coating appears in the fibres of different fasciculi or tracts at different periods, and a knowledge of this fact has enabled anatomists to follow out the connexions of the tracts of fibres which compose the white matter of the brain and spinal medulla. Every nerve-fibre is directly continuous by one extremity with a nerve-cell, whilst its opposite extremity breaks up into a number of ramifications, all of which end in relation to another nerve-cell, or in relation to certain tissues of the body, as, for example, muscle- fibres or the epithelial cells of the epidermis. The length of nerve- fibres, therefore, varies very greatly. Some fibres are short and merely bring two neighbouring nerve-cells into relation with each other ; others travel long distances. Thus, a fibre arising from one of the motor cells of the lower end of the spinal medulla may, after leaving the spinal medulla, extend to the most outlying muscle in the sole of the foot, before it reaches its destination. But even when a fibre does not leave the central axis, a great length may be attained, and cells situated in the uppermost part of the brain give origin to fibres which pass down to the lower end of the spinal medulla. It has already been explained that fibres which form the nerves may be FROM A Frog (after i -n i • . , , oc . '' -, V. Kiiiiiker). Classified into two sets, arterent and efferent. Afferent nerve -fibres conduct impressions from the peripheral organs into the central nervous system ; and as a change of consciousness, or, in other words, a sensation is a frequent result, these fibres are often called sensory. Efferent nerve -fibres carry impulses out from the brain and spinal medulla to peripheral organs. The majority of these fibres go to muscles and are termed motor ; others, however, go to glands and are called secretory ; whilst some are in- hibitory and serve to carry impulses which restrain or check movement or secretion. The dendrites, or protoplasmic processes of the nerve- cell, are thicker than the axon, and present a rough- edged irregular contour. They divide into numerous branches, and these gradually, as they pass from the cell-body, become more and more attenuated until finally they appear to end in free extremities. The branching of the dendritic processes sometimes attains a marvellous degree of complexity (Fig. 449), but it is commonly supposed that there is no anastomosis between the dendrites of neighbouring cells, or between the dendrites of the same cell. It is commonly believed that the neuroblast passes through stages analogous to those shown in the diagram (Fig. 451) ; that just as a seed gives off a root which strikes downward, and leaves which grow upward, so the neuroblast sprouts out an Fig. 450, Nerve-fibre Fic. 451. — Ramon y Cajal's In- TERl'RKTATION OK THE DEVELOP- MENTAL Stages exhibited by a PYRAMIDAL CELL OF THE BRAIN. ri, Neuroblast, with rudimentary axon, but no dendrites ; b and c, The dendrites beginning to sprout out ; (/ and e. Further develop- ment of the dendrites and appear- ance of collateral branches on the axon. 510 THE NEEVOUS SYSTEM. axon (a) and subsequently develops a bunch of dendritic processes (6), In the case of the axon reasons have already been given for not accepting this view as the whole explanation ; and in the case of the dendrites, although the appearance of microscopic sections seems to favour the view expressed in the diagrams, the fact that the neuroblasts are united into a continuous network or syncytium at an early stage of development (see p. 503) raises the possibility that the dendrites may be formed by the gradually drawing out of the existing bridges as the linked cell-bodies become moved apart. The Ganglia of the Sensory Nerves. — The cells found in the ganglia of the cerebral nerves and on the posterior or dorsal roots of the spinal nerves have a different origin, and present many points of contrast with neurones in the gray matter of the brain and spinal medulla. As already indicated, the ganglia in question are derived from the neural crest. The cells forming these ganglionic masses are some- what oval in form, and each extremity or pole becomes drawn out into a process, so that the neurones become bipolar. These processes are distinguished as central and peripheral, according to the direction which they take. The central processes penetrate the wall of the neural tube. In the region of the spinal medulla they form almost the whole of the fibres which enter into the composition of the posterior roots of the spinal nerves. In the substance of the cerebro- spinal axis they give off numerous collaterals, and after a course of varying ex- tent they end, after the manner of an axon, in terminal arborisations, which enter into relationships with certain nerve-cells in the cerebro-spinal axis. The peripheral processes proceed along the path of the particular nerve with which they are associated, and they finally reach the skin or other sensory surface. Thus, to take one example : the majority of the fibres which go to the skin break up into fine terminal filaments, w^hich end freely between the epithelial cells of the epidermis. The two processes of a ganglion cell, therefore, form the afferent fibres of the cerebro-spinal nerves, and con- stitute the path along which the influence of peripheral impressions is conducted to- wards the brain and spinal medulla. The body of the cell is, as it were, interposed in the path of such impulses. But the original bipolar character of these cells, with very few exceptions (ganglia in connexion with the acoustic nerve and the bipolar nerve-cells in the olfactory mucous membrane), gradually undergoes a change which ultimately leads to their transformation into unipolar cells. This is brought about by the tendency which the cell-body has to grow to one side, viz., the side towards the surface of the ganglion (v. Lenhossek). This unilateral growth leads to a gradual approxima- tion of the attached ends of the processes, and finally to a condition in which they appear to arise from the extremity of a short common stalk in a T-shaped manner (Fig. 452). It is interesting to note that in fishes the original bipolar condition of these cells is retained throughout life, without change. Both the central and peripheral processes of these ganglionic cells become the axis-cylinders of nerve-fibres, which, acquiring a medullary sheath, belong there- fore to the medullated variety. From this it might very naturally be thought that the ganglionic neurone, with its two axons and no typical dendrites, is a nervous unit very different from a neurone in the gray matter of the cerebro-spinal axis. It is believed by some, however (van Gehuchten and Cajal), that the peripheral process, in spite of its enclosure within a medullary sheath, and though presenting all the characters of a true axon, is in reality a dendrite If this is the case, the Fig. 452. — Three Stages in the Development OP A Cell in a Spinal Ganglion. NEUEOGLIA. •511 morphological dittereuce between a dendrite and an axon disappears, and van Grehuchten's functional distinction alone remains characteristic, viz., that the axon is cdlulifngal and conducts impulses away from the cell, whilst the dendrites are cellulipetal and conduct impulses towards the cell. It is, however, more in accordance with the facts to regard the sensory neurones as genetically quite distinct from the rest of the nervous system (see p. 498). Neuroglia.— The neuroglia is the supporting tissue of the cerebro-spinal axis. It may be considered to include two ditferent forms of tissue, viz., the Hning ependymal cells and the neuroglia ]jroY)er. We place these under the one heading, seeing that they have a common developmental origin. The ependymal cells are the columnar epithelial cells which line the central canal of the spinal medulla and the ventricles of the brain. In the embryonic con- dition a process from the deep extremity of each cell, traverses the entire thickness of the neural wall, and reaches the surface. It is not known whether this process exists in the adult. The neuroglia proper is present in both the white and the gray matter of the cerebro-spinal axis. It constitutes an all- pervading basis substance, in which the various nerve elements are embedded in such a way that they are all bound together into a consistent mass, and are yet all severally isolated from each other. Neuroglia consists of cells and fine filaments. The fibrils are present in enormous numbers, and by their interlacements they constitute what appears to be a fine feltwork. At the points where the fibrils intercross may be seen the flattened glial cells. Whilst the neuroglia is for the most part intimately intermixed with the nerve elements, there are, in both brain and spinal medulla, certain localities where it is spread out in more or less pure layers. Thus, upon the surface of the brain and of the spinal medulla there is such a layer ; likewise beneath the epithelial lining of the central canal and of the cavities of the brain there is a thin stratum of neuroglia. The ependymal cells are derived from the original neuro-epithelial cells of the early neural tube, and in all probability the neur- oglia proper has a similar origin. They both, therefore, are products of the ectoderm. Summary. — 1. The cerebro-spinal nervous system is composed of two parts, viz., (a) a central part, consisting of the brain and spinal medulla, with the efferent nerve- fibres which pass out from them ; (b) the ganglionic part, with the afferent nerve-fibres. 2. Each of these parts has a different origin, and is composed of neurones which possess characteristic features. 3. The ganglionic neurones are derived from the primitive cells of the neural crest, and have each one process, which divides into two. Of these the central division enters the cerebro-spinal axis, whilst the peripheral division becomes con- nected with a peripheral part. The central fibres from the ganglionic cells in the region of the spinal medulla form the dorsal or posterior roots of the spinal nerves. The cells of origin of these posterior roots are outside the spinal medulla, and carry impulses into its substance. 4. The cerebro-spinal neurones are derived from the neuroblasts in the wall of the early neural tube. Certain of these furnish efferent nerve-fibres, which issue from the spinal medulla in separate bundles termed the anterior or ventral roots of the spinal nerves. In the case of the cerebral nerves, however, with the exception of the trigeminal and facial nerves, the efferent fibres are not thus separated from the afferent fibres at their attachment to the brain. Fig. 453. — Section through the Centkal Canal of the Spinal Medulla of a Hitman Embryo, showing Ependymal and Neur- oglial Cells (after v. Lenhos.sek). A, Ependymal cell. B, Neuroglial cell. [Note tliiit the dorsal (posterior) aspect is hrloir.] 512 THE NEEVOUS SYSTEM. 5. The brain and spinal medulla, when studied by the naked eye, are seen to be composed of white matter and gray matter. The white matter forms very nearly two- thirds of the entire cerebro-spinal axis. It is composed of medullated nerve-fibres embedded in neuroglial tissue. The gray matter is composed of nerve-cells with their dendrites and axons. Some of the axons are in the form of naked axis cylinders, whilst others have a coating of myelin. Intimately intermixed with these parts is the neuroglia, which isolates them more or less completely from each other. THE NATUEE OF THE BEAIN. In the foregoing account it has been explained that the nervous system is composed of a series of afferent nerves bringing information from every part of the body into the central nervous system, from which efferent nerves pass out to the muscular and other active parts of the body, providing the means for translating such information into appropriate action. But it has been seen that the essential part of the central nervous system is the intercalated cells, which provide the means whereby the information brought in by any sensory nerve may be placed at the service of the whole body, and the response which it excites may be controlled and regulated by the condition of the rest of the body. The system of intercalated cells links together into one co-ordinated mechanism the whole nervous system, and, through it, every part of the body itself. In some very primitive and remote ancestor of man (and in fact of the vast majority of animals) the front end of the nervous system became enhanced in importance to form a brain, which assumed a dominant influence over the rest. This was brought about in the first place by the fact that in an elongated prone animal moving forwards, the front end would naturally come first into relation- ship with any change in environment ; and this earlier acquisition of information concerning the outside world would necessarily give the head end of the nervous system exceptional opportunities for influencing the rest of the nervous system. This predominance is further accentuated by the development in the head region of the organs of special sense, which provide mechanisms specially adapted to be influenced by light, sound, and such delicate chemical forms of stimulation as excite in ourselves sensations of smell and taste. As the information conveyed by these special senses, such as the scent of food or the visual impression of some enemy, must be able immediately to influence the movements of the whole body, it follows that a specially abundant system of intercalated elements link the central ends of these nerves of the special senses with the rest of the central nervous system. Moreover the predominant influence of the head end of the central nervous system implies that it must be provided with a specially large series of nerve- fibres, not only for the purpose of bringing this influence to bear upon the rest of the nervous system, but also of being itself brought into intimate relationship with the nervous system as a whole, seeing that sensory impulses are constantly pouring into every part of it. Thus the head end of the central nervous system becomes the brain, which is characterised by a series of large irregular swelhngs, due to (a) the develop- ment around the insertion of each special sensory nerve of a mass, or group of masses, of intercalated cells which will enable the effects of the visual, acoustic, olfactory, gustatory or other sensations to influence the whole nervous system, and (b) the evolution of complicated systems of intercalated cells, which receive, and in a sense blend, impressions coming from all parts of the nervous system, and emit fibres which pass, directly or indirectly, to the various groups of motor nerve-cells and control their activities and, through them, the behaviour of the animal. In the development of the human embryo this distinction between the head end and the rest of the central nervous system is indicated even before the medullary plate is completely folded up to form the neural tube. The widened THE NATURE OF THE BRAIN. 513 part represents the rudiment of the encephalon or hrain ; and the rest of the tube will become converted into the medulla spinalis. If the attempt is made to analyse the meaning of the early broadening of the brain rudiment it will be found to be due in great measure to the fact that there is added to the margius of the medullary plate (see Fig. 442, E, p. 501) the material from which the sensitive part of the eye and the optic nerve will be developed; Imt soon after the neural tube is closed irregular swellings will make their appearance around the attachments of the nerves of smell, vision, hearing, and taste (Fig. 454), Optic tract Tectum inesencephali r I Ked nucleus ' / Tecto-spin.il tract Rubro-spinal tract HetathalamuR Tlialannisv ^Brachium conjunctivum ^-- Lemniscus medialis (ij» --'Lemniscus lateralis Corpus striatum , rebral hemisphcn" /* rebro-spinal tract-' Olfactory iiei\ c . Olfactory epithelium < indicates the place where a tract crosses the median plane. Fio. 454. — Diagram representinq the connexions ok some important Sknsory and Motor Tracts IN THE Brain to which references are made in pages 513 to 517. Motor paths in red ; sensory in other colours. and also the great vagus nerve that is widely distributed to the viscera of the neck, thorax, and abdomen. lUit there are other factors besides these irregularities of growth of its walls which add complexity to the" form of the encephalon in the embryo. In the course of their growth both parts (encephalon and medulla spinalis) of the neural tube undergo great extensions in length, breadth, and thickness; but in the case of the spinal medulla it is the increase in length that is most distinctive, whereas in the encephalon, the irregular expansion in breadth and thickness is more obtrusive. Nevertheless, the brain elongates more rapidly than that part of its mesodermal capsule which ultimately becomes the brain-case or cranium ; and hence it becomes bent to permit of its being packed in the limited length of the cranial cavity. Hut if it is admitted that these mechanical considerations are in a measure responsible for the three bends which develop in the embryonic encephalon, their situation and the forms they assume are determined by the irregularities of growth inherent in the brain itself. 34 514 THE NEEVOUS SYSTEM. TELENCEPHALON PROSENCEPHALON Anterior neurophore kj^. HYPOTHALAMUS .jS^ :^'^' ^^^ Upper limit of -' '^rhombencephalon Recessus / ' infundibuli Recessus mamillaris' Cephalic flexure Even at a time, during the second week, when the anterior (oral) end of the neural tube is still open (neuroporus anterior), a right-angled bend has already developed in the rudiment of the brain (cerebral vesicle). Slightly less than half of the length of the vesicle had projected beyond the upper (anterior) end of the .,.,..,„ , , no tochord and became flexed Anterior limit of mesencephalon . ventrally round it (rig. /■ 455). / This bend is known as the cephalic flexure. The region of the brain vesicle in which it develops will later on become the mesen- cephalon or mid-brain; and even at the early stage of development now under consideration (Fig. 455) there is a slight narrowing of the tube (isthmus) that marks the boundary be- tween the mid-brain and the rhombencephalon or hind-brain. Just beyond the end of the notochord there is an even fainter trace of a constriction in- dicating the line of de- marcation between the mid-brain and the prosen- cephalon or xore-brain. Shortly after the appearance of the cephalic flexure a similar bending occurs in the region where the encephalon becomes continuous with the medulla spinalis (Fig. 456, A). This is the cervical flexure. But at this stage, or even earlier (Fig. 456), there has been developing a third bend which produces effects differing from those just mentioned. At the end of the second week a slight bulging can be detected on the ventral side of the hind- RHOMB- ENCEPHALON.?i Notochord - — Fig. Upper limit of " spinal medulla 455. — Left Lateral Aspect of an Early Human Embryo (after His's model, reversed). CEPHALIC FLl ^\0-8;^ CEREBRAL^ . HEMISPHERE \ OPTIC VE5ICUE A B Fig. 456. — Two Stages in the Development of the Human Brain (after His). A, Brain of an embryo of the third week. B, Brain of an embryo of five weeks. brain (Fig. 455) : during the next four weeks this steadily becomes accentuated and forms the pontine flexure. The convexity of the bend is directed ventrally, differing in this respect from both of the other flexures. This difference in direction has a profound influence upon the form which the hind-brain assumes. If a plastic tube is bent a strain is thrown upon the wall in the concavity THE NATUKE OF THE BRAIN. 515 of the flexure. If this wall is strong and resisting, like the floor-plate of the neural tube (in the cases of the cephalic and cervical flexures) the beuding does not affect the outline of the tube (in section) very materially. But when the strain is thrown upon the thin roof-plate during the development of the pontine flexure it is not strong enough to resist; it becomes stretched and allows the side walls of the neural tube to splay laterally in precisely the same manner as occurs wlien a rubber tube is bent towards a side which has Ijeen split (or weakened) longitudinally (Fig. 457). This mechanical factor determines the form assumed by the hiud-brain at the end of the first month ; and gives its cavity, the fourth ventricle, a lozenge or rhomboid form, when seen from its dorsal aspect through the thin translucent roof. For this reason the hind-brain is known as the rhombencephalon. The rhombencephalon forms at first more than half of the encephalon, and as it expands it appears to become marked off from the rest by a constriction (the isthmus rhombencephali). The development of the pontine flexure subdivides the rhomben- cephalon into two parts, one joined to tlie spinal medulla, the myelen- cephalon, and the other, joined to the rest of the brain, the metencephalon. In the myelencephalon develop the nuclei of the nerves that regulate the activities of the heart, lungs, and a considerable part of the aUmentary canal, and also the receptive nuclei of the nerves of taste. It is known as the medulla oblongata. The insertion of the uervus acusticus in the neighbourhood of the outsplayed lateral angle of the rhombencephalon leads to the pro- found transformation of the meten- cephalon. The nervus acusticus conveys into the hind-brain impulses which are stimulated by movements of fluid in the closed sac developed from the otic vesicle (Fig. 443, p. 501). The truly acoustic function of this apparatus is called into activity when the movements of this fluid are caused by waves of sound transmitted to it from the outside world. But it is obvious that motion may also be set up in this fluid by changes in position of the body itself; in other words, movements in the fluid of the otic vesicle may stimulate nerves to convey to the brain information concerning the position and movements of the body itself. A great mass of nerve-cells develops around the insertion of the uervus acusticus (that part of it, however, which is called vestibular and is not concerned with the function of hearing) to make use of this information for the regulation of the movements of the body in balancing or equilibration. To enable this terminal vestibular nucleus the better to perform this function of equilibration, depending as it does upon the co-operation and adjustment of the movements of vast numbers of widely separated muscles, nerve tracts coming from muscles and skin areas of all parts of the body make their way into this vestibular nucleus ; and it expands and forms a great excrescence which is known as the cerebellum. And as this cerebellum has to adjust the activities of all the muscles of the body it necessarily becomes the great organ of muscular co-ordination, and as such it is made use of by those parts of the brain which have to initiate and control complex actions such as skilled movements. It will be shown in the subsequent account how the 34 a Fig. 457. — Profile View of the Brain of a Human Embryo of Ten Weeks (His). The various cerebral nerves are indicated by numerals. A, Cerebral diverticulum of hypophysis cerebri. B, Buccal diverticulum of hypophysis cerebri. 515 THE NERVOUS SYSTEM. FORE CEREBRI, cerebellum becomes linked to the mesencephalon to co-ordinate the movements of the body which are excited by this part of the encephalon ; and later how it becomes associated with the prosencephalon, when the latter becomes respons- ible for the acquisition and control of the most highly skilled actions. For the latter purpose a great pathway of nerve -fibres is laid down to connect the fore-brain with the cerebellum : the terminal stage of this connexion is situated upon the ventral (anterior) aspect of the metencephalon in the form of a great mass of transverse fibres. At one time these strands of nerve-fibres were looked upon as a bridge between the two hemispheres of the cerebellum : hence the name pons was applied to them. This term is now apphed not only to the fibres themselves, but also to the upward prolongation of the medulla oblongata, to the surface of which they are applied. The subdivision of the |5 rest of the encephalon into mesencephalon and prosen- cephalon develops later and is less fundamental than the primary demarcation between them and the rhombencephalon. The visual apparatus is connected with both the mid -brain and the fore- brain, but at first more intimately with the former, to which nerve pathways are established to convey from the spinal medulla and medulla oblongata sen- sory impressions of touch and hearing. From the alar laminae of the mesen- cephalon there are developed four little hillocks (col- liculi) — corpora quadri- gemina — to receive these Fig. 458.— The Brain op a Human Embryo in the Fifth Week varied impressions and to (from His). enable them to influence A, Brain as seen in profile. B, Median section through the same brain, the actionS of the wliolc M, Mamillary eminence ; Tc Tuber cinereum ; Hp, Hypophysis ]yQ^j^ Special nervC paths (hypophyseal diverticulnm from buccal cavity) ; Opt, Optic stalk ; i • j j r i-x. TH, Thalamus ; Tg, Tegmental part of mesencephalon ; Ps, ^^^ ^^^^ QOWn trom tfie Hypothalamus ; Cs, Corpus striatum ; FM, Foramen inter- COrpOra quadrigemina (Fig. ventricnlare ; L Lamina terminalis ; RO, Recessus opticus; Ri, 454) to the Spinal medulla Kecessus mfundibuli. ^ '^ . , 1 -i n to enable the mid- brain to control the motor nuclei of the muscles of the trunk and hmbs. These are called the fasciculi tectospinales (tectum being a synonym for corpora quadrigemina). A group of intercalated cells known as the nucleus ruber develops upon each side of the mesencephalon for the purpose of establishing connexions between the cerebellum and the mid-brain. When an impulse passes out of the mid-brain by the tecto- spinal bundle to excite some movement of the body, the red nucleus provides the link by which the cerebellum can co-ordinate the actions of the muscles involved. By means of a fasciculus rubrospinalis it can bring its influence to bear directly upon the nuclei of motor nerves in the brain and spinal medulla (Fig. 454). The prosencephalon is at first, and in some of the lower fishes remains, the most insignificant of the three brain vesicles, but in the human brain (as also in that of most other vertebrates, though in varying degrees) a pair of enormous THE SPINAL MEDULLA. 517 excrescences — the cerebral hemispheres — are budded off from it ; and they become the dominant part of the nervous system (Fig. 458). Each hemisphere is formed, however, from a relatively small part of the side wall of the prosencephalon, the rest of which goes to form the optic diverticula, the thalamus, and the hypothalamus, among other structures. The cerebral hemisphere is at tirst pre-eminently olfactory in function, the nerves of smell being inserted directly into it. But impressions of the associated sense of taste make their way into the cerebral hemisphere in the most primitive vertebrates : the gustatory nerves are inserted into the medulla oblongata, but fibre-paths are laid down to establish connexions with the hypothalamus, which in turn emits fibres to the cerebral hemisphere (Fig. 454). The thalamus is a greatly swollen part of -the prosencephalic wall adjoining the mesencephalon. Its main part receives sensory impressions brought up from the spinal medulla and the terminal nuclei of the sensory cerebral ner^'es and transmits them to the cerebral hemisphere. Its caudal portion becomes specialised as a special receptive nucleus for visual and acoustic impressions for transmission to the cerebral hemisphere. It is called the metathalamus or corpora geniculata. Thus the cerebral hemi- sphere from being essentially a receptive organ for smell impressions ultimately becomes the terminus of all the sensory paths, and the structure that is concerned with the consciousness of all kinds of sensations. It also controls the voluntary movements of one-half of the body and emits a great strand of fibres — pedunculus cerebri — to establish relations with the cerebellum and all the motor nuclei on the other side of the encephalon and spinal medulla (Fig. 454, p. 513). MEDULLA SPINALIS. The spinal medulla is that part of the central nervous occupies the upper two-thirds of the vertebral canal. It is cylindrical structure, slightly flattened in front and behind, which extends from the margin of the foramen magnum to the level of the inferior border of the body of the first lumbar vertebra or to the superior border of the body of the second lumbar vertebra. Its average length in the male is 45 cm. and in the female 43 cm. Cervical swelling of the spinal medulla Lumbar swelling of the spinal medulla A considerable amount of variation within certain limits (viz., the mid-point of the body of the last thoracic vertebra and the superior border of the body of the third lumbar vertebra) is observed in diiferent individuals as to the precise level at which the spinal medulla ends inferiorly, and in the female there would appear to be a tendency for the medulla to reach a slightly lower point in the canal than in the male. Further, the relation presented by the spinal medulla to the vertebral column differs in a marked degree in the fojtus and infant at different periods of development. Up to the third month of intra-uterine life the spinal medulla occupies the entire length of the vertebral canal ; it extends downwards to the lowest limit of the vertebral canal. But from this time onwards, as growth proceeds, the vertebral column lengthens at a more rapid rate than the medulla. The spinal medulla, therefore, has the appearance of shrink- ing in an upward direction within its canal, and at birth its inferior end is usually found to be opposite the body of the third lumbar vertebra. The attitude assumed by the individual affects to a small degree the position of the inferior end of the spinal medulla. Thus, when the trunk is bent well forwards, the terminal part of the spinal medulla rises slightlv within its bony canal. 34 6 system which an elontjated Cerebral hemisphere Mesencephalon Cerebellum Fourth ventricle Medulla oblongata FlO. 4.=)9. — HfMAN KlKTDS IN THE THIRD Month of Dkvklofment, with thk Brain and Spinal Medui.i.a kxposed FKOM behind. 518 THE NERVOUS SYSTEM. At the margin of the foramen magnum the spinal medulla becomes continuous with the medulla oblongata of the brain, whilst below, it tapers rapidly to a point and forms a conical extremity termed the conus medullaris. From the end of the conus medullaris a slender glistening thread is prolonged downwards within the vertebral canal, and finally anchors the spinal medulla to the back of the coccyx. This prolongation receives the name of the filum terminale. The diameter of the spinal medulla is very much shorter than that of the vertebral canal within which it lies. A wide interval is left between its surface and the walls of its canal, and this excess of space is clearly a provision for allowing free movement of the vertebral column without producing any jarring contact between the delicate spinal medulla and the surrounding bones. Three protective membranes are wrapped around the spinal medulla. Erom within outwards these are termed (1) the pia mater, (2) the arachnoid, and (3) the ^ dura mater. The pia mater is a fibrous membrane which forms the immediate investment. It is closely applied to the spinal medulla, and from its deep Conus medullaris Posterior lateral srroove Anterior uerve-root Posterior nerve-root Fig. 460. — Thk Con0S Mkdullakis and the Filum Terminale exposed within the Vertebral Canal. Spinal ganglion Anterior ramus of spinal nerve Posterior ramus of spinal nerve Fig. 461. — The Roots of Origin of the Seventh Thoracic Nerve (semi-diagram- matic). surface numerous fine septa penetrate into the substance of the spinal medulla. The arachnoid is an exceedingly dehcate transparent membrane which is loosely wrapped around the spinal medulla so as to leave a considerable interval, between itself and the pia mater, termed the subarachnoid space, in which there is always a varying amount of cerebro-spinal fluid. Outside the arachnoid, the dura mater forms a wide, dense, fibrous, tubular sheath, which extends downwards within the vertebral canal for a considerable distance beyond the conical extremity of the spinal medulla. The spinal medulla is suspended within its sheath or theca of dura mater by two lateral wing- like ligaments, termed the ligamenta denticulata. These extend laterally from the sides of the spinal medulla and are attached by a series of pointed or tooth-like processes to the inner surface of the theca of dura mater. Between the wall of the vertebral canal and the dura mater there is a narrow interval, wliich is filled up by soft areolo- fatty tissue and numerous thin-walled veins arranged in a plexiform manner. Thirty-one pairs of spinal nerves arise from the sides of the spinal medulla. THE SPINAL MEDULLA. 519 These are classified into eight cervical, twelve thoracic, five lumbar, five sacral, and one coccygeal; and according to the attachments of these groups of nerves the spinal medulla is arbitrarily subdivided into cervical, thoracic, lumbar, and sacral regions. In employing these terms, therefore, for different districts of the spinal medulla, it must be understood that the regions are determined by the nerve attachments and not by any direct relationship between these parts of the spinal medulla and the sections of the vertebral column which liear the same names. Each spinal nerve is attached to the spinal medulla by an anterior or ventral and a posterior or dorsal root, and as these are traced to their central attachments they are seen to break up into a number of separate nerve fascicles or bundles, which spread out, in some cases very widely from each other, as they approach the side of the spinal medulla (Fig. 461). Each pair of nerves is therefore attached to a portion of spinal medulla of some length, and such a portion, with its pair of nerves, receives the name of a "segment of the spinal medulla." It must be clearly understood, how- ever, that, in so far as the surface of the spinal medulla is concerned, there is no means of marking off one segment from another except by the nerve attachments. In the cervical and huabar regions uf the spinal medulla the nerve-roots are somewhat crowded together, so that little or no interval is left between the adjoining root fila or fascicles of neigh- bouring nerves. In the thoracic region, however, distinct intervals may be observed, and the root fila are more loosely arranged. From this, it will be evident that the seg- ments in different parts of the spinal medulla are not of equal length. In the cervical region the segments measure about 12 mm. in length, in the thoracic region from 20 to 24 mm., and in the lumbar region about 10 mm. The number of fila which attach the different nerve-roots to the spinal medulla is very different in dif- ferent nerves, and is not necessarily the same in the same nerve-root in different individuals. Owing to the great difference which exists between the length of the spinal medulla and the length of the vertebral column, the farther we pass down the greater the dis- tance becomes between the attach- ment of the various nerve-roots to the spinal medulla and the intervertebral foramina through wluch the corresponding nerves leave the vertebral canal. The lower nerve-roots, therefore, have to traverse the vertebral canal for a considerable distance before they reach their apertures of emergence. It thus happens that the nerve-roots which spring from the lumbar and sacral regions of the spinal medulla attain a very great length and descend vertically in the lower part of the vertebral canal in a bunch or leash, in the midst of which lie the conns medullaris and the filum termiuale. This great bundle of nerve-roots receives the appropriate name of the cauda equina. Enlargements of the Spinal Medulla. — Throughout the greater part of the thoracic region, the spinal medulla presents a uniform girth and a very nearly circular outline when seen in transverse section. In the cervical and lumbar regions, however, it shows marked swellings. The intumescentia cervicalis or cervical enlargement is the more evident of the two. It begins very gradually at the upper end of the spinal medulla, attains its greatest breadth (12 to 14 mm.) opposite the fifth or sixth cervical vertebra, and finally subsides opposite the second thoracic vertebra. To this portion of the spinal medulla are attached the great nerves which supply the upper limbs. The intumescentia limibalis or lumbar enlargement begins at the level of the tenth thoracic vertebra, and acquires its maximum transverse diameter (11 to 13 mm.) opposite the last thoracic vertebra. Below, it rapidly tapers away into the conus medullaris. To the lumbar enlarge- ment are attached the great nerves of the lower limbs. 34 c Arachnoid Conus meduUarii^ Roots of first lumbar nerve Cauda equina Fig. 462. — Section thkougu thk Conus Meddllabis and THE Cauda Equina .vs they lie in the Vektebral Canal. 520 THE NEEVOUS SYSTEM. These enlargements of the spinal medulla are associated with the outgrowth of the limbs. In the earlier developmental stages of the spinal medulla they are not present, and they take form only as the limbs become developed. In different animals their size corresponds with the degree of development of the limbs. Thus, in the long-armed orang and gibbon the cervical swelling stands out with a remarkable degree of prominence. Development of the Spinal Medulla. — The early stages of the process by which the originally simple epithelial neural tube becomes converted into the central nervous system have already been considered. It remains to be explained how the features specially distinctive of the spinal medulla are produced. In the early stages of the development of the spinal medulla (Fig. 463), the neuroblasts are found to be scattered in the intermediate of the three bands of Posterior nerve roob Fig. 46.3. — Diagram of Transverse Section of the left half of Early Neural Tube. which the thick side wall of the neural tube is composed — the mantle layer. These primitive nerve-cells soon congregate in much larger numbers in the ventral part of the basal lamina (Fig. 464), so that the mantle layer expands there into a broad excrescence, which is the rudiment of the columna anterior or anterior cornu of gray matter. This anterior column contains the efferent or motor nerve- cells, the axons of which emerge as the anterior root of a spinal nerve. At this stage the rest of the mantle layer consists of a thin stratum of neuroblasts (Fig. 463), mainly intercalated cells, which receive the sensory impressions entering the spinal medulla through the radix posterior, and transmit impulses into axons passing (a) to the motor nuclei, (&) to the other side of the spinal medulla through the floor-plate (Fig. 463), or (c) into the superficial stratum (peripheral layer) of the spinal medulla where they bend upwards or downwards as constituent elements of the funiculi (or white columns). As development proceeds (Fig. 463) the substantia grisea (gray substance) formed of these intercalated cells becomes much more abundant and forms a broad blunt boss (Figs. 464, B and C), which is the rudiment of the columna posterior (O.T. posterior cornu). The surfaces of these gray columns become coated with a layer of white sub- THE SPINAL MEDULLA. 521 stance, composed at first mainly of the axons intercalated cells in the spinal medulla ; and as these funiculi increase in size they help to mould the form of the gray coluums. This is displayed best in the case of the posterior column (O/J'. posterior cornu). The major portion of the white substance, funiculus posterior, which accumulates behind (and after- warils lies on the medial side of) the posterior column, does not consist of libres springinj^ from intercalated cells, either of the spinal medulla or any other part of the central nervous system, but of the direct continua- tions of the central processes of the cells in the spinal ganglion on the posterior root (Figs. 463 and 464). A large proportion of the fibres of the posterior root do not enter the gray columns imniediately after their insertion into the alar lamina, but bifurcate to form two vertical nerve-fibres, one passing upwards, and the other downwards, in the funiculus posterior before they end in the gray column, some distance above or below the place where they gained admission to the medulla spinalis. As the spinal medulla grows, the originally blunt posterior column becomes drawn backwards into an increasingly attenuated process, and the funiculus posterior, which was placed originally upon its lateral surface (Fig. 464, A), and then upon its posterior surface (Fig. 464, B), gradually assumes a wedge-shaped form (Figs. 464, C, and 466), upon the medial side of the gray matter. Development of the Anterior Median Fissure, Posterior Median Septum, and of the Central Canal. — As the anterior columns of gray matter and the anterior funiculi of white matter increase in size, the anterior surface of the spinal medulla, on each side of the median plane, bulges forwards, and the fissura mediana anterior (Fig. 464, A, B, and C) is produced as the natural result. There has been considerable discussion as to the mode of formation of the posterior median septum ; but there is now no doubt as to the essential facts. Early in the third month the walls of the posterior three - fourths (of the sagittal extent) of the central canal of the spinal medulla become approximated (Fig. 464), and later they fuse to obliterate that part of the canal. But the part of the septum thus formed is only an insignificant portion of the whole. For most of the septum is produced by the gradual elongation of the epithelial cells lining the remnant of the central canal as the fibre- masses of the posterior funiculi expand and separate the posterior surface of the spinal medulla further and further from the situation of the canal (see Fig. 453, p. 511). Furrows of the Spinal Medulla. — When of cells in the root ganglia and Ki.ot-plal.! ^^^^tiv^ Alar l.iiiiiiia Eurly po.slerior fiiiiicui\iH Kiinicular Mid-ventral liiiiiiiia A Uaxal laijiiria Auti'rior iiervH-root Anterior funii-iilus Fasciculus gracilis Fasciculus cunoatus Postcriiir median septum Posterior iSx- column Ai.tt'iioi nerve-root Anterior funiculus Fasciculus irracilis Fasciculus cuneatus Posterior median septum I'usterior column l'(jsterior root Ependyma Anterior column Anterior mi'dian lissuri' .\nterior root .\nterior Timiculus Fi(!. 464. — Three Stages ix the Develop- ment OF the Spinal Medulla (His). cross- sections of the adult spinal 522 THE NEEVOUS SYSTEM. Posterior median septum Cervical swellin Sulcus intei medius posterio Posterior lateral sulcus -THVu medulla are made, it is seen to be a bilateral structure which is partially subdivided into a right and a left half by a median cleft (fissura mediana anterior) in front and a septum (septum niedianum posterius) behind. The anterior median fissure penetrates only for a distance corresponding to somewhat less than a third of the antero-posterior diameter of the spinal medulla. The pia mater dips down into it and forms a fold or reduplication within it. The posterior median septum in the cervical and thoracic regions penetrates into the spinal medulla until it reaches a point somewhat beyond its centre. It is extremely narrow, and consists of ependymal and neuroghal elements, and is intimately con- nected with the adjacent sides of the two halves of the spinal medulla, between which it intervenes. The pia mater, which invests the surface of the spinal medulla, passes continuously over the posterior median septum and sends no prolongation of any kind into it. In the lumbar region of the spinal medulla the septum becomes shallower, whilst the anterior median fissure deepens, and ultimately in the inferior part of the spinal medulla the fissure and septum present a very nearly equal depth. The two halves of the spinal medulla may show trifling differences in the arrangement of the parts which compose them ; but to all intents and purposes they are symmetrical. They are joined together by a more or less broad band or commissure, which intervenes between the median fissure and the septum. An inspection of the surface of each half of the spinal medulla brings into view a longitudinal groove or furrow, at some little distance from the posterior median septum, which extends along the whole length of the spinal medulla. Along the bottom of this groove the fila of the posterior nerve-roots enter the spinal medulla in accurate linear order. It is called the sulcus lateralis posterior. There is no corresponding furrow on the anterior part of each half of the spinal medulla in connexion with the emergence of the fila of the anterior nerve-roots. These fila emerge irregularly over a broad strip of the surface of the spinal medulla, which corresponds in its width to the thickness of the subjacent anterior surface of the anterior column of gray matter. The sulcus lateralis posterior subdivides each half of the spinal medulla into a small funiculus posterior and a much larger antero- lateral funiculus, and it is customary to map the latter arbitrarily off into a funiculus lateralis and a funiculus anterior by a line corresponding to the emergence of the most lateral of the fila or fascicles of the anterior nerve-roots. In the cervical region a distinct longitudinal groove may be observed on the surface of the posterior funiculus. It is placed rather nearer to the posterior median septum than to the posterior lateral sulcus, and as it is traced down into the thoracic region it gradually becomes in- distinct and finally disappears. This is called the sulcus intennedius posterior, and it marks on the surface the position of a septum of pia mater which dips into the spinal medulla and subdivides the posterior funiculus into a lateral part, termed the fasciculus cuneatus (O.T. column of Burdach), and a medial portion, which receives the name of the fasciculus gracilis (O.T. column of GoU). Lumbar swellinj; -THVx -THVxii Fig. 46.5. — Diagram of the Spinal Mbdulla as seen from behind. CVi shows the level of the 1st cervical vertebra ; CVv of the 5th cervical vertebra ; THVii iif the 2nd thoracic vertebra ; THVx of the 10th thoracic vertebra ; THVxii of the 12th llioracic vertebra ; LVii of the 2nd lumbar vertebra. THE SPINAL MEDULLA. 523 Fasciculus gracilis Posterior funiculus _ac^t=.^_ Fasciculus cuneatus Formatio reticularis Lateral funiculus Central canal Accessory root Origin of accessory nerve Internal Structure of the Spinal Medulla. The spinal medulla is composed of a central core of gray matter thickly coated on the outside by white matter. At only one spot does the gray matter come close to the surface, viz., at the bottom of the sulcus lateralis posterior. Gray Matter of the Spinal Medulla. — The gray matter in the interior of the spinal mt'duUa has the form of a Huled column, but it is customary to describe it as it appears in transverse sections. It then presents the appearance of the capital letter H. In each half of the spinal medulla there is a semilunar or crescentic mass, shaped somewhat like a comma, the concavity of whicli is directed laterally and the convexity medially. The two cresceuts of opposite sides are con- nected across the median plane by a transverse band, which receives the name of the commissura grisea (gray commissure). The posterior mediau septum extends forwards in the spinal medulla until it reaches the gray commissure. The bottom of the anterior median fissure, however, is separated from it by an intervening strip of white matter, which is termed the commissura anterior alba, or anterior white commissure. In the gray commissure may be seen the central canal of the spinal medulla (canalis centralis), which tunnels the entire length of the spinal medulla and is just visible to the naked eye as a minute speck. The por- tion of the gray commis- sure which lies behind the central canal is called the commissura posterior; whilst the portion in front receives the name of the commissura anterior grisea. Each crescentic mass of gray matter presents cer- tain well - defined parts. The projecting portions which extend behind and in front of the connecting transverse gray commissure are termed respectively the posterior and the anterior columns of gray matter (columnae griseae). These stand out in marked contrast to each other. In section the columna anterior is short, thick, and very blunt at its extremity. Further, its extremity falls considerably short of the surface of the spinal medulla and is separated from it by a moderately thick coating of white matter. Through this the fila of the anterior nerve-roots, as they emerge from the gray matter of the anterior column, pass on their way to the surface. Throughout the greater part of the spinal medulla the columna posterior (O.T. posterior comu) is elongated and narrow, and is drawn out to a fine point, which almost reaches the bottom of the posterior lateral sulcus. This pointed extremity receives the name of the apex columnae posterioris ; the slightly swollen part which succeeds it is the caput columnae ; whilst the slightly constricted part adjoining the gray commissure goes under the name of the cervix columnae posterioris. The apex or tip of the posterior column ditlers considerably in appearance from the general mass of the gray matter. It is composed of a material which presents a lighter hue and has a somewhat translucent look. It is called the substantia gelatinosa [Rolandi], and, when seen in transverse section, it exhibits a V-shaped outline and fits on the posterior column like a cap. A pointed and prominent triangular projection juts out from the lateral aspect of the gray matter nearly opposite the gray commissure. This is the columna lateralis (O.T. lateral comu), and it is best marked in the upper thoracic region (Fig. 467, B). Traced upwards it becomes absorbed in the greatly expanded anterior column of the cervical swelling, but it reappears again in the upper part of the spinal medulla, and is particularly noticeable in the second and third cervical Accessory nerve- root Anterior nerve-root Anterior funiculus Fig. 466. — Transverse Section through the Superior Part of the Cervical Region of the Spinal Medulla of an Orang. (From a .specuneu prepared by the Weigert-Pal method, by which the white matter is rendered dark whilst the gray matter is bleached.) 524 THE NEKVOUS SYSTEM. segments ; followed iu a downward direction it blends with the anterior column in the lumbar swelling and contributes to the thickening of that column. The gray matter is for the most part mapped off from the surrounding white matter with a considerable degree of sharpness ; but in the cervical region, on the lateral aspect of the crescentic mass and in the angle between the anterior and posterior columns, fine bands of gray matter penetrate the white matter, and, joining with each other, form a network, the meshes of which enclose small islands of white matter. This constitutes wliat is called the formatio reticularis. Although best marked in the cervical region, traces of the same reticular formation may be detected in lower segments of the spinal medulla: Characters presented by the Gray Matter in Different Regions of the Spinal Medulla. — The gray matter is not present in equal quantity nor does it exhibit the same form in all regions of the spinal medulla. Indeed, each segment presents its own special characters in both of these respects. It is not necessary, however, in the present instance, to enter into this matter with any degree of minute detail. It will be sufficient if the broad distinctions which are evident in the different regions are pointed out. It may be regarded as a general law that, wherever there is an increase in the size of the nerves attached to a particular part of the spinal medulla, a correspond- ing increase in the amount of gray matter will be observed. It follows from this that the regions where the gray matter bulks most largely are the lumbar and the cervical swellings. The great nerve-roots which go to form' the nerves of the large limb-plexuses enter and pass out from those portions of the spinal medulla. In the thoracic region there is a reduction in the quantity of gray matter in correspondence with the smaller size of the thoracic nerves. In the thoracic region (Fig. 467, B) both columns of gray matter are narrow, although the distinction between the anterior column and the still more attenuated posterior column is sufficiently manifest. In this region the lateral column of gray matter also is characteristic, and the substantia gelatinosa in transverse section is pointed and spear-shaped. In the upper three segments of the cervical region the anterior columns of gray matter are not large and they resemble the corresponding columns in the thoracic region. A lateral column also is present. But in these segments (and more especi- ally in the first and second) there is a marked attenuation of the neck of the posterior column; and the posterior commissure is very broad. In the cervical swelling the contrast between the two columns is most striking ; the anterior column is of great size and presents a very broad surface towards the anterior aspect of the spinal medulla, whilst the posterior column remains narrow. This great increase in the bulk of the anterior column is due to a marked addition of gray matter on the lateral side of the column, and seeing that this additional matter is traversed by a greater number of fibres, it stands out, in well-prepared specimens, more or less distinctly from the part of the column which lies to the medial side, and which may be considered to represent the entire anterior column in the thoracic and upper cervical segments. Within this lateral addition to the anterior column are placed those collections of ceUs which constitute the nuclei of origin of the motor nerves of the muscles of the upper limb. The characteristic thickening of the anterior column of gray matter is evident, therefore, in those segments of the spinal medulla to which the nerves which enter the brachial plexus are attached, viz., the lower five cervical segments and the first thoracic segment. In the lumbar swelling the anterior columns again broaden out, and for the same reason as in the case of the corresponding columns in the cervical swelling. The nuclear masses which contain the cells from which the motor fibres which supply the muscles of the lower limbs take origin are added to the lateral aspect of the columns and give them a very characteristic appearance. In this region of the spinal medulla, however, the posterior columns also are broad and are capped by substantia gelatinosa which in transverse section presents a semilunar outline. There is consequently no difficulty in distinguishing, from an inspection of the gray matter alone, between transverse sections of the spinal medulla taken from the cervical and lumbar swellings of the spinal medulla. THE SPINAL MEDULLA. 525 111 the lower part of the conus medullaris the gray matter in each half of the spinal medulla assumes the ioriii of an (jval mass joined to its fellow of the opposite side by a thick gray commissure. Here, almost the entire bulk of the spinal medulla consists of gray matter, seeing that the wliite matter is reduced to such an cxlnit that it furnis 'Hily a thin coating on the outside. White Matter of the Spinal Medulla. — In transverse sections of the spinal medulla the three funiculi into which the white matter is subdivided become very Posterior median septum Septum isterior lateral groove Posterior nerve-root SubstanI la gelatinosa Root-tlbri's I entering gray mattei Processus) reticularis Central /; canal ftjiterior net \ e root Anterior median fissure-^' PoKterior median 'spptuni Posterior lateral groove Posterior column Dorsal nucleus Lateral colunm Central canal Anterior column Anterior metlian lissure B. — Through the mid-thoracic region. A. — Cervical region — at the level of the fifth cervical nerve. (From a specimen prepared by Dr. A. Bruce.) Posterior nerve-root Posterior median septum Substantia gelatinosa Root-fibres enter- ing gray matter Central $^, canal -^ Anterior whitr ~_^ __ ^ n commissure ^ — Nuclei of origiii —- - — " i from which til' 7^- — ~~ ^'' ' v niotor-fibrr^ " ' \. ~\^ ' for uuiscles ■ i ~ ll ''^' i the lower limb arise Anterior neri-e root Anterior median fissure Posterior median septum Posterior nerve-root. Substantia '\ gelatinosa ^Posterior gray commissure f_ Anterior white commissure Anterior median Hssure -Through the lumbar region at the level of the fourth lumbar nerve. Fig. D. — Through the sacral region at the level of the third sacral nerve. (From a specimen pre- pared by Dr. A. Bruce.) 467. — Section through each ok the Four Regions ok the Medulla Spinalis. (From specimens prepared by the Weigert-Pal method ; therefore the white matter is rendered dark in colour whilst the gray matter is bleached.) apparent. The posterior fimiculus is wedge-shaped, and lies between the posterior median septum and the posterior column of gray matter. The lateral funiculus occupies the concavity of the gray crescent. Behind, it is bounded by the posterior column of gray matter and the sulcus lateralis posterior, whilst in front it extends as far as the most lateral fasciculi of the anterior nerve-roots as they pass out from the anterior column. The anterior funiculus includes the white matter between the ^.nterior median lissure and the anterior column of gray matter, and also the white 526 THE NERVOUS SYSTEM. matter which separates the broad extremity of the anterior column from the sur- face of the spinal medulla. This latter portion of the anterior funiculus is traversed by the emerging lila of the anterior nerve-roots. In cross-sections of the spinal medulla the partition of pia mater, which dips in at the sulcus intermedins posterior and divides the posterior funiculus into the medial fasciculus gracilis and the lateral fasciculus cuneatus, is very strongly marked in the cervical regions, but as it is traced downwards into the thoracic region it becomes shorter and fainter, and finally disappears altogether at the level of the eighth thoracic nerve. Below this point there is no visible demarcation of the posterior funiculus into two parts. The white matter is not present in equal quantity throughout the entire length of the spinal medulla. It increases steadily from below upwards, and this increase is most noticeable in the lateral and posterior funiculi. In the lower part of the conus medullaris the amount of gray matter is actually greater than that of the white matter : but very soon this state of affairs is changed, and in the lumbar region the proportion of gray to white matter is approximately as 1:21; in the thoracic region as 1 : 5 ; and in the cervical region as 1 : 5*1. When it is remembered how the gray matter expands in the lumbar and cervical regions, and how greatly it becomes reduced in the thoracic region, the significance of these figures will become more apparent. Canalis Centralis. — As previously, stated, the central canal is found in the gray commissure. It is a very minute tunnel, barely visible to the naked eye when seen in transverse section, and it traverses the entire length of the spinal medulla. Above, it passes into the medulla oblongata, and finally opens into the fourth ventricle of the brain ; below, it is continued for a variable distance into the filum terminale, and in this it ends blindly. Only in the lumbar region does the centra] canal occupy the centre of the spinal medulla. Above this level, in the thoracic and cervical regions, it lies much nearer the anterior than the posterior aspect of the spinal medulla; whilst below the lumbar region, as it is traced down into the conus medullaris, it inclines backwards and , approaches the posterior aspect of the spinal medulla. The calibre of the canal also varies somewhat in different parts of the spinal medulla. It is narrowest in the thoracic region ; and in the lower part of the conus medullaris it expands into a distinct fusiform dilatation (very nearly 1 mm. in transverse diameter), which is termed the ventriculus terminalis (Krause). The central canal is lined with a layer of ciliated columnar cells, the deep taper- ing ends of which are prolonged into slender processes which penetrate into the substance of the spinal medulla. These cells constitute the lining ependymal cells of the canal. The cilia of the epithelial cells are very early lost, and it is not un- common to find the canal blocked up by epithelial debris. The central canal is of interest because it represents in the adult the relatively wide lumen of the early ectodermal neural tube from which the spinal medulla is developed. Filum Terminale. — The delicate thread to which this name is applied is con- tinuous with the inferior tapered end of the conus medullaris. It is easily distin- guished, by its silvery and glistening appearance, from the numerous long nerve-roots (Cauda equina) amidst which it lies. It is about six inches long, and down to the level of the second sacral vertebra it is enclosed with the surrounding nerve-roots within the dura mater. Below this point the dura mater is applied directly to the surface of the filum terminale and is called filum durse matris spinalis. The filum terminale proceeds downwards in the sacral canal, and finally receives attachment to the periosteum on the posterior aspect of thecoccyx (Fig. 460, p. 518). It is customary to speak of the filum as consisting of two parts, viz., the filum terminale internum and the filum terminale externum, or the part inside and the part outside the tube of dura mater. The filum terminale externum is simply a fibrous thread, strengthened by the pro- longation it receives from the dura mater. The filum terminale internum is composed largely of pia mater; but in its superior half it encloses the terminal part of the central canal, and around this a variable amount of the gray substance of the spinal medulla is prolonged downwards into the filum. When transverse sections are made through THE GRAY MATTER OF THE SPINAL MEDULLA. 527 the superior part of the tilum terminale internum some bundles of medullated nerve-tibres are observed clinging to its sides, and with these are associated some nerve-cells identical with those in the spinal ganglia. These represent rudimentary or aborted caudal nerves (Rauber). Summary of the Chief Characters presented uy the Spinal Medulla IN ITS Different Regions. Cervical Region. In transverse section, out- line of spinal medulla transversely oval ; in the middle of the cervical swelling the transverse diameter being nearly one-third longer than the antero- posterior diameter. Fostero - median sep- tum very dee]*, extend- ing beyond the centre of the spinal medulla ; antero - median fis- sure shallow. Thoracic Region. In transverse sectitin, outline of spinal medulla more nearly circular ; but still the transverse diameter is greater than the antero -posterior dia- meter. Postero - median sep- tum very deep, extend- ing beyond centre of ■ the spinal medulla: antero - median fis- sure sliallow. Lumbar Region. In transverse section, outline of spinal medulla more nearly circular than in thoracic region. Postero - median sep- tum not nearly so deep as in regions above : antero - median fis- sure, on the other hand, much deeper. Sacral Re>;iun. In transverse section, outline of spinal medulla, nearly circu- lar, but still some- what conijjressed from before backwards. Postero - median sep- tum and antero- median fissure of equal depth. Gray matter greatly in- creased in quantity in the cervical swelling : anterior column thick and massive ; posterior column slender in comparison. Lateral column evident only above the level of the fourth cervical nerve. Processus reticularis strongly marked. White matter in great quantity, and especi- ally massed in the lateral and posterior funiculi. Sulcus intermedins posterior and corre- sponding sej)tum well markeil. Gray matter greatly reduced in quantity. Both columns slender. Lateral column well marked. Processus reticularis scarcely ap- parent. White matter less in quantity than in cervical region, but bulking largely in comparison with the quantity of gray matter. Gray matter greatly in- creased in the lumbar swelling. Both columns very thick and massive. Lateral column absorbed in anterior column. Pro- cessus reticularis ab- sent. Sulcus intermedins posterior absent ; but the corresponding sep- tum can be traced as low down as the eighth thoracic nerve. White matter small in quantity compared with higher regions, and verj- small in amount in relation to increased quantity of gray matter. No sulcus intermedius posterior or corre- sponding septum. Both columns of g^ay matter very thick and massive. Lateral column apparent. No processus reticularis. White matter very j small in quantity in comparison with the : gray matter. No sulcus intermedius posterior and no corresponding septum. Central canal consider- ably nearer the anterior surface than the pos- terior surface of the spinal medulla. Central canal consider- ably nearer the anterior surface than the pos- terior surface of the spinal medulla. Central canal in the Central canal iu the centre of the spinal centre of the spinal medulla. medulla. Component Parts of the Gray Matter of the Spinal Medulla. Neuroglia enters largely into the constitution of the gray matter of the spinal medulla. It forms a bed within which the nervous elements are distributed. These nervous elements consist of (1) nerve -cells and (2) nerve -fibres — both medullated and non- medullated. The nerve -cells lie in small spaces in the 528 THE NEKVOUS SYSTEM. neuroglia, whilst the nerve -fibres traverse tine passages the walls of which are formed of the same substance. The neuroglia is thus an all-pervading basis sub- stance which isolates the nervous elements one from the other more or less com- pletely, and at the same time binds them together into a consistent solid mass. In two situations the gray matter presents peculiar features, viz., the apex of the posterior column and the tissue surrounding the central canal. In both situations the gray matter stains more deeply with carmine and presents a more translucent appearance ; in other respects the substantia grisea centralis and the substantia gelatinosa are very different. The substantia grisea centralis forms a thick ring around the central canal. It is traversed by the fine processes which proceed from the deep ends of the ependymal cells which line the canal. It is composed almost entirely of neuroglia. In transverse sections of the spinal medulla the substantia gelatinosa, in the cervical and thoracic regions, presents the appearance of a V-shaped mass, embracing the extremity of the posterior column of gray matter ; in the lumbar region this cap assumes a semilunar outline. In the substantia gelatinosa the neuroglia is present in small quantity, and small nerve-cells are developed within it in considerable numbers. Nerve-Cells. — The nerve-cells are scattered plentifully throughout the gray matter, but perhaps not in such great numbers as might be expected when we note the enormous number of nerve-fibres with which they stand in relation. They are all, without exception, multipolar, and send off from their various aspects several branching protoplasmic processes or dendrites, and one axon, which becomes the axis-cylinder of a nerve-fibre. In size they vary considerably, and as a rule (to which, however, there are many exceptions) the bulk of a nerve-cell has a more or less definite relation to the length of the axis-cylinder which proceeds from it. When the nerve-celLs are studied in a series of transverse sections of the spinal medulla, it will be noticed that a large proportion of them are grouped in clusters in certain districts of the gray matter; and as these groups are seen in very much the same position in successive sections, it is clear that these cells are arranged in longi- tudinal columns of greater or less length. Thus we recognise — -(1) a ventral group or column of cells in the anterior column of gray matter; (2) an intermedio-lateral group or column in the lateral column of gray matter, where this exists ; and (3) a posterior vesicular column of cells (nucleus dorsalis), forming a most conspicuous group in the medial part of the neck of the posterior column in the thoracic region of the spiual medulla. Other cells, besides those forming these columns, are scattered somewhat irregu- larly throughout the gray matter of the posterior column and the part of the gray crescent which lies between the two columns ; and although these also in some measure may be classified into groups, the arrangement thus effected is not of so definite a character as to justify us in dwelling upon it in the present instance. Ventral Cell-Column and the Origin of the Fibres of the Anterior Nerve- roots. — The ventral cell-group occupies the anterior col imn of gray matter, and in it are found the largest and most conspicuous cells in the spinal medulla. It extends from one end of the spinal medulla to the other. These ventral nerve-cells have numerous wide-spreading dendritic processes, and it is to be noticed that certain of these dendrites do not confine their ramifications to the gray matter. Thus, some of the cells along the medial border of the anterior column of gray matter send dendrites across the median plane in the anterior commissure to end in the anterior gray column of the opposite side ; whilst others, lying along the lateral margin of the anterior column of gray matter, send dendrites in amongst the nerve- fibres of the adjoining white matter. The axons or axis-cylinder processes of a large proportion of the ventral cells con- verge together ; and, becoming medullated, they form bundles which pass out from the gray matter, and through the white matter which separates the thick end of the anterior column from the surface of the spinal medulla, to emerge finally as the fila of the anterior nerve-roots. These cells, then, are the sources from which the nerve- fibres of the anterior nerve-roots proceed, and in consequence they are frequently spoken of as the " motor cells " of the spinal medulla. Whilst this is THE GEAY MATTER OF THE SPINAL MEDULLA. 529 the arrangement of the axons of the great majority of the motor cells, it should be noted that a few cross the median plane in the anterior white commissure and emerge in the fila of origin of the opposite anterior nerve-root. The ventral cells are not scattered uniformly throughout the anterior cohunu of gray matter. They are aggregated more closely together in certain parts of the anterior column, and thus form sub-groups or columns more or less perfectly marked off from each other. Thus, one sub-group or column of ventral cells occupies the medial part of the anterior colunm of gray matter throughout almost its whole length. In only two segments of the medulla is it absent, viz., the fifth lumbar and the first sacral ; at this level in the spinal medulla alone is its continuity broken (Bruce). It is termed the anteromedian column or group of ventral cells. Behind this cell-column there is another classed with it to which the name of posterq^nedian column or group is given, but this column of cells is not con- tinuous throughout the entire length of the medulla. It is present in the thoracic region of the spinal medulla, where the motor nuclei for the muscles of the limbs are absent ; and it is seen also in two or three of the segments of the cervical region and in the first lumbar segment (Bruce) ; elsewhere it is not represented. In the cervical and lumbar swellings of the medulla, where the marked lateral out- Posterior lateral furrow "' ^^ Posterior column of gray matter Posterior median septum Gray comnii.ssure Postero-lateral motor cells Anterior median fissure Antero-median group of motor cells Aiitero-lateral group of motor cells Fig. 468. — Section through the Fifth Cervicai, Segment of the Spinal Medulla. (To a large exteut founded on Plates in Dr. Bruce's Atlas.) growth is added to the lateral side of the anterior column of gray matter, certain groups of large multipolar cells are visible. These are the nuclei of origin of the motor-fibres which supply the muscles of the limbs, and consequently they are not represented in the upper three cervical segments of the spinal medulla ; nor in any of the thoracic segments, with the exception of the first thoracic segment ; nor in the lowest two sacral segments. These lateral cells are arranged in several columns, which extend for varying distances in the superadded lateral parts of the anterior column of gray matter. The two main columns are an antero-lateral and a postero-lateral column ; in certain segments there is likewise a retro-postero-lateral column, and in a number of segments in the lumbar and sacral regions a central colmnii of cells (Bruce). There cannot be a doubt that the grouping of the motor cells in the anterior column of gray matter of the medulla stands in relation to the muscle groups to which their axis-cylinder processes are distributed ; but from what has been said it will be apparent that sharply defined cell-clusters associated with particular muscles do not exist. Still, much can be learned regarding the localisation of the motor nuclei in the anterior column of gray matter of the medulla from the study of the changes which occur in the cell-columns after atrophy of isolated muscles or groups of muscles, and after complete or partial amputa- tions of limbs. It has been pointed out that the long muscles of the trunk (as, for example, the different parts of the sacro-spinalis muscle) receive nerve-fibres from all the 35 530 THE NEKVOUS SYSTEM. Posterior column gray matter segments of the spinal medulla. Now, we have noted that there is only one cell-column, the ventro-median column, which pursues an almost uninterrupted course throughout the entire length of the medulla. Posterior lateral furrow It may be assumed, therefore, that the nerve-fibres which go to these long trunk -muscles take origin in these medial cells. Edinger states that in the anterior column of gray matter the nuclei of origin of the nerves which supply the proximal mus- cles are medially placed ; that those for the distal muscles are in general situated laterally. If this is the case, the cells connected with the shoulder muscles will lie nearer the middle of the anterior column of gray matter than those which are connected with the hand- muscles. In cases where the forearm and hand, or the leg and the foot, are amputated, it would appear that it is the pos- tero-lateral column of cells that shows changes in consequence of its separation from the muscles to which its fibres are distributed.^ Posterior median septum Nucleus dorsal is Gray commissure Anterior median fissure Antero-medial group of motor cells Intermedio-lateral column of cells Postero-medial group of motor cells Fig. 469. — Section through the Eighth Thoracic Segment of the Spinal Medulla. (To a large extent founded on Plates in Dr. Bruce's Atlas.) Posterior median septum Posterior lateral furrow Posterior column of matter Intermedio-lateral Cell-column. — The intermedio-lateral cells form a long slender column which extends throughout the entire thoracic region of the medulla in the lateral column of gray matter. It is also pro- longed downvi^ards into the first and second lum- bar segments, where it dis- appears. In transverse sec- tions through the spinal medulla this cell -group presents a very character- istic appearance, because the cells which compose it are small and are closely packed together. Al- though these cells, as a continuous column, are restricted to the region indicated, it should be noted that the same group of cells reappears above, in certain of the cervical segments, and also in the third and fourth sacral segments. From these cells very fine fibres arise and leave the spinal medulla, intermingled with the motor fibres of the anterior nerve-roots ; they pass into the sympathetic ganglia, of which they ' Those who seek further information regarding the grouping of the ventral cells of the medulla may with advantage study Dr. Alexander Bruce's Atlas of the Spiiml Cord. Anterior median fissure Postero-Iateral group Antero-medial group of cells Fig. 470. — Section through the Third Lumbar Segment of the Si'iNAL Medulla to show the oroui-ing of the Motor Cells, (To a large extent founded on Plates in Dr. Bruce's Atlas.) THE WHITE MATTEE OF THE SPINAL MEDULLA. 531 Posterior- median spiitnin Gray commis- sure Anterior median fissure Posterior-lateral furrow- Posterior column of gray matter Retro- ijostero- lateral group of cells constitute the white rami coinmunicantes. They represent the splanchnic efferent fibres of the medulla spinalis. Nucleus Dorsalis (O.T. Clarke's Column). — This occupies the posterior column of gray matter and is the most conspicuous of all the cell-groups in the medulla. It does not, however, extend along the whole length of the medulla ; indeed it is almost entirely confined to the " dorsal " region, which is the rea.son for the designation "nucleus dorsalis." (When, in the recent revision of nomenclature, the term "thoracic" was substituted for "dorsal" the revisers omitted to change the name of this structure to " thoracic "). Above, it begins opposite the seventh or eighth cervical nerve, whilst below, it may be traced to the level of the second lumbar nerve, where it disappears. In transverse section of the medulla it presents an oval outline, and is seen in the median part of the cervix of the posterior column of gray matter, immediately behind the gray commissure (Fig. 469, p. 530). On the lateral side it is circumscribed by niimerous curved fibres from the entering posterior nerve-root, and in the lower thoracic region of the spinal medulla (opposite the eleventh and twelfth thoracic nerves) it becomes so marked that it forms a bul^fing on the median aspect of the pos- terior gray column. The cellaof the nucleus dorsalis are large, and pos- sess several dendritic pro- cesses. The axons enter the lateral funiculus of white matter and there form a strand of fibres, which will be described later under the name of the fasciculus spino- cerebellaris (tvnmgly called " cerebellospinalis " in the B.KA.). Nerve -fibres in the Gray Matter of the Medulla Spinalis. — Nerve-fibres of both the medullated and the non- medullated variety per- vade every part of the gray matter. They are of three kinds, viz., (1) collaterals, (2) terminations of nerve- fibres, (3) axons given off by the cells. Many of the nerve-fibres which compose the funiculi of the medulla give off numerous fine collateral branches, which pass into the gray matter from all sides and finally end in relation with the nerve- cells. The majority of the nerve-fibres themselves, which thus give off collaterals, finally enter the gray matter, and end similarly. The axons of the majority of the cells leave the gray matter and emerge either for the purpose of entering a peripheral nerve or for the purpose of entering a strand of fibres in the white matter of the spinal medulla. The nerve-fibres thus derived are interwoven together in the gray matter in a dense inextricable interlacement. Postero-lateral group Central group of cells Antero-lateral group of cells Fig. 471. — Section through the First Sacral Segment of the Spinal Medulla to show the grouping ok the Motor Nerve- cells. (To a large exteut founded on Plates iu Dr. Bruce's Atlas.) Component Parts of the White Matter of the Spinal Medulla. The white matter of the spinal medulla is composed of medullated nerve-fibres, embedded in neuroglia. The fibres, for the most part, pursue a longitudinal course ; and, from the deep surface of the pia mater which surrounds the medulla, fibrous septa or partitions are carried in along vertical planes between the fibres so as 532 THE NEKVOUS SYSTEM. js<;>g^T'->^^ to form an irregular and very imperfect fibrous framework of support. The neuroglia is disposed in a layer of varying thickness around the medulla, subjacent to the pia mater, and is carried into the medulla so as to give a coating to both sides of the various pial septa. The neuroglia is disposed also around the various nerve- fibres, so that each of these may be said to lie in a canal or tunnel of this substance. The nerve-fibres are all medullated, but they are not provided with primitive sheaths. It is the medullary substance of the nerve-fibres which gives to the white matter its opaque, milky-white appearance. When a thin transverse section of the medulla is stained in carmine and examined under the microscope the white matter presents the appearance of a series of closely applied circles, each with a dot in the centre. The dot is the transversely divided axis-cylinder of a nerve-fibre, and the dark ring which forms the circumference of the circle represents the wall of the neuroglial canal which is occupied by the fibre. The medullary substance is very faintly seen. It presents a filmy or cloudy appearance between the axis-cylinder and the neuroglial ring. Arrangement of the Nerve -fibres of the White Matter in Fasciculi or Tracts. — When the white matter of a healthy adult spinal medulla is examined, the fibres which compose it are seen to vary consider- ably in point of size ; and although there are special places where large fibres — or it may be small fibres — are present in greater numbers than elsewhere, yet, as a rule, both great and small fibres are mixed up to- gether. No conclusive evidence can be obtained in such a spinal medulla, by any means at our disposal, of the fact that the longitudinally arranged fibres are grouped together in more or less definite tracts or fasciculi, the fibres of which run a definite course and present definite connexions. Yet this is known to be the case, and the existence of these separate tracts has been proved both by embryological investigation, as well as by the examination of the effects of injuries produced experimentally or accidentally on the nervous system in living beings. By the experimental method it has been shown that when a nerve-fibre is severed the part which is detached from the nerve-cell from which it is an oflfshoot degenerates, whilst the part which remains connected with the nerve-cell under- FiG. 472. Transverse Section goes little or no change. This is called the law of " Wallerian " THRODGH THE WHITE MATTER OF degeneration. Thus, if in a living animal one-half of the THE Medulla Spinalis, as seen spinal medulla is cut across, and after a few weeks the animal through the microscope. is killed and the medulla examined, it will be seen that there are degenerated tracts of fibres in the white matter, both above and below the plane of division ; but, still further, it will also be manifest that the tracts which are degenerated above the plane of division are not the same as those which are degenerated in the part of the medulla which lies below this level The interpretation of this is obvious. The nerve-tracts which have degenerated above the plane of section are the ofi'shoots of nerve-cells which lie in lower segments of the medulla or in spinal ganglia below the plane of section. Severed from these nerve-cells, they undergo what is called ascending degeneration. The nerve- tracts, on the other hand, which have degenerated in the portion of the medulla below the plane of division are the axons of cells which lie at a higher level than the plane of section, either in higlier segments of the spinal medulla or in the brain itself Cut off from the nerve-cells from which they proceed, they present an example of descending degeneration. Tlie embryological method was first employed by Flechsig, and it is often referred to as Flechsig's method. It is based upon the fact that nerve-fibres in the earliest stages of their development consist of naked axis-cylinders, and are not provided with medullary sheaths. Further, the nerve- fibres of dift'erent strands assume the medullary sheaths at different periods. If the foetal central nervous system is examined at different stages of its development, it is a comparatively easy matter to locate the dift'erent tracts of fibres by evidence of this kind. Speak- ing broadly, the tracts which myelinate first are those which bring the central nervous system into relation with the peripheral parts (skin, muscles, etc.) ; then those fibres which bind the various segments of the central nervous system together ; next, those which connect the spinal medulla with the cerebellum ; and, lastly, the tracts which connect the spinal medulla with the cerebral hemispheres. The nervous apparatus for the performance of automatic movements is fully THE WHITE MATTER OF THE SPINAL MEDULLA. 533 provided, therefore, before this is put under the control and direction of the higher centres. It by no means follows that in all tlie higher animals corresjionding strands myelinate at relatively corresponding j)eriods. Take the case of a young animal which from the time of its birth is able to move about and perform voluntary movements of various kinds in a more or less perfect manner, and compare it with the heljness new-born infant which is capable of exhibiting auto- matic movements only. In the former, tlie cerebro-spinal tracts, or motor tracts, which descend from the cerebrum into the spinal medulla, and which are the paths along which the mandates of the will travel, myelinate at an early period ; whilst in the infant the corresponding fibres do not obtain their medullary sheaths until after birth. The study of the dates, therefore, at which the various strands of nerve-tibres myelinate not oidy gives the anatomist a means of locating their position in the white matter of the central nervous system, but it also affords the physiologist most important information regaixling their functions, and also the periods at which these functions are called into play. It is a matter of interest to note that influences which either accelerate or retard the periods at whicli nerve-fibres are brought into functional activity have also an effect in determining the dates at which these fibres assume their sheaths of myelin. Thus, when a child is prematurely bom the whole process of myelinisalion is, as it were, hurried up ; and furtlier, when in new- born animals light is freely admitted to one eye whilst it is carefully excluded from the other, the fibres of the optic nerve of the former myelinate more rapidly than those of the opposite nerve. Study of the minute structure (Anatomical method) of the central nervous system, especially of material that has been stained by the metho