MEMCAL John Marshall Williamson Mwnofial QUAIN'S ANATOMY. QUAIN'S ELEMENTS OF ANATOMY EDITED BY WILLIAM SHARPEY, M.D, F.E.S. PROFESSOR OF ANATOMY AND PHYSIOLOGY IN UNIVERSITY COLLEGE, LONDON ALLEN THOMSON, M.D., F.R.S. PROFESSOR OF ANATOMY IN THE UNIVERSITY OF GLASGOW AND JOHN CLELAND, M.D. PROFESSOR OF ANATOMY IN QUEEN'S COLLEGE, GALWAY IN TWO VOLUMES ILLUSTRATED BY UPWARDS OF 800 ENGRAVINGS ON WOOD. VOL. II. LONDON JAMES WALTON BOOKSELLER AND PUBLISHER TO UNIVERSITY COLLEGE 137, GOWKR STREET. 1867. LONDON : BRADBURY, EVANS, AND CO., PRINTERS, WHITEFRTARS. 5 •.•*•••" •.!.***•••• CONTENTS OF THE SECOND VOLUME. DIVISION L— SYSTEMATIC AND DESCRIPTIVE ANATOMY (CONTINUED). PAGE SECTION V.— NEUROLOGY . 501 I. THE CEREBRO-SPINAL Axis . 501 A. THE SPINAL CORD . . . 502 Its description . . . 5°2 Internal structure . . . 507 Central Canal . . . 5°8 Minute structure of the Cord . 509 Origin of the Spinal Nerves . 511 B. THE ENCEPHALON . . . 513 The Medulla Oblongata . . 514 Course of fibres through the Medulla . . . . 518 Grey matter of the Medulla 5 19 The Pons Varolii and Cerebel- lum 521 Pons Varolii . . .521 The Cerebellum . . . 522 Its internal structure . 526 The Cerebrum . . . . 529 Exterior of the Cerebrum . 529 Cerebral Convolutions . 531 Base of the Cerebrum . . 53^ Internal parts of the Cere- brum . . . . 54° Lateral Ventricles . . 543 Third Ventricle . • • 55° Internal Structure of the Cerebrum . . . 554 "White matter . . . 555 Grey matter . . , 559 Membranes of the Brain and Spinal Cord . . . 562 Dura Mater . . .562 Pia Mater . . . . 564 Arachnoid Membrane . . 565 Blood-vessels of the Brain and x Spinal Cord . . .567 Size and Weight of the Ence- phalon .... 568 Weight of the several parts of the Encephalon . . . 571 Weight of the Spinal Cord . 572 Specific Gravity of the Ence- phalon . . . .572 Development of the Cerebro- Spinal Axis . . . of the Spinal Cord of the Encephalon . . . of the membranes of the En- cephalon. II. THE CEREBRO-SPINAL NERVES A. CRANIAL NERVES Connections of the Cranial Nerves with the Encephalon Distribution of the Cranial Nerves . ... Olfactory Nerve Optic Nerve . . . . Third Pair of Nerves . Fourth Pair of Nerves . . Fifth Pair of Nerves Ophthalmic Nerve . . . Lachrymal Branch . Frontal Branch . . . Nasal Branch . Ophthalmic Ganglion . . Superior Maxillary Nerve . Orbital branch Posterior Dental Branches Anterior Dental Branch . Infraorbital Branches Spheno - palatine Gang- lion . . . . Inferior Maxillary Nerve . Deep Temporal, Masse- teric, Buccal, and Ptery- goid Branches . . Auriculo-temporal Nerve Gustatory Nerve . . Inferior Dental Nerve Otic Ganglion Submaxillary Ganglion . Sixth Pair of Nerves Seventh Pair of Nerves . . Facial Nerve Connecting Branches . . ChordaTyinpani and Nerve to the Stapedius . Posterior Auricular Branch PAGE 573 574 575 581 582 582 583 587 592 592 593 594 595 597 597 59 5 599 600 600 60 1 60 1 602 603 605 605 606 606 608 608 609 610 610 610 611 611 612 VI CONTENTS. PAGE Digastric and Stylo-hyoid Branches . . .613 Temporo-facial Division . 613 Cervico-facial Division . 613 Auditory Nerve . . .615 Eighth Pair of Nerves . . 615 Glosso-pharyngeal Nerve . 615 Connecting Branches and Tympanic Branch . 616 Branches distributed in the Neck . . . 617 Pneumo-gastric Nerve . 618 Connecting Branches and Auricular Branch . 621 Pharyugeal Branch . .621 Superior Laryngeal Branch 621 Recurrent Laryngeal Branch . . .622 Cardiac Branches . . 623 Pulmonary Branches . 623 (Esophageal Branches . 623 Gastric Branches . . 623 Spinal Accessory Nerve . . 625 Ninth Pair of Nerves . . 626 Connecting Branches . . 626 Muscular and Lingual Branches . . . 626 B. SPINAL NERVES . . . . 628 Roots of the Spinal Nerves . 630 Posterior Primary Divisions of the Spinal Nerves . . 632 Suboccipital Nerve . . 632 Cervical Nerves . . . 633 Dorsal Nerves . . . 634 Lumbar Nerve . . . 634 Sacral Nerves . . .635 Coccygeal Nerve . . . 635 Anterior Primary Divisions of the Spinal Nerves . . 635 Cervical Nerves . . . 636 Suboccipital Nerve . . 636 Second Cervical Nerve . 636 Cervical Plexus . . . 636 1. Superficial Ascending Branches . . 638 Superficial Cervical Nerve . . .638 Great Auricular Nerve 638 Small Occipital Nerve 638 2. Superficial Descending Branches . . 639 Supraclavicular Nerves 639 3. Deep Branches : Inner Series . . 640 Muscular Branches 640 Phrenic Nerve . 640 4. Deep Branches : Exter nal Series . 641 Brachial Plexus . . 641 Branches above the Cla vicle . . . 643 Posterior Thoracic Nerve 644 Suprascapular Nerve . 644 Branches below the Clavicle 644 PAGE Anterior Thoracic Nerve 645 Subscapular Nerve . 645 Circumflex Nerves . 645 Internal Cutaneous Nerve . . . . 646 Small Internal Cuta- neous Nerve . . 646 Musculo- cutaneous Nerve . . . 648 Ulnar Nerve . . 648 Median Nerve . . 649 Musculo-spiral Nerve 652 Radial Nerve . . 653 Posterior Interosseous Nerve . .^ . . 654 Anterior Primary Divisions of the Dorsal Nerves . -655 First Dorsal Nerve . . 655 Upper or Pectoral Intercostal Nerves . -655 Lower or Abdominal Inter- costal Nerves . . . 657 Last Dorsal Nerve . . 658 Anterior Primary Divisions of the Lumbar Nerves . 658 Lumbar Plexus . . . 658 Ilio-hypogastric and Ilio- inguinal Nerves . . 660 Genito- crural Nerve . . 660 External Cutaneous Nerves 662 Obturator Nerve . . 662 Accessory Obturator Nerve 663 Anterior Crural Nerve . 664 Muscular Branches . . 665 Middle Cutaneous Nerve 665 Internal Cutaneous Nerve . . . 665 Internal Saphenous Nerve . . . 666 Fifth Lumbar Nerve . . 667 Superior Gluteal Nerve . 667 Anterior Primary Divisions of the Sacral and Coccygeal Nerves .... 668 The Sacral Nerves . . . 668 Fourth Sacral Nerve . . 668 Fifth Sacral Nerve . . 668 Coccygeal Nerve . . 668 Sacral Plexus . . . 669 Muscular Branches . .670 Pudic Branches . . . 670 Small Sciatic Nerve . 673 Great Sciatic Nerve . . 675 Internal Popliteal Nerve 676 External or Short Saphe- nous Nerve . . 677 Posterior Tibial Nerve 677 Internal Plantar Nerve 677 External Plantar Nerve 679 External Popliteal or Peroneal Nerve . 679 Musculo -cutaneous Nerve . . . . 680 Anterior Tibial Nerve . 68 1 CONTEXTS. Vll Synopsis of the Cutaneous Dis- tribution of the Cerebro- spinal Nerves . . . 682 Synopsis of the Muscular Dis- tribution of the Cerebro- spinal Nerves . . . 684 Muscles of the Head and Fore Part of the Neck . 684 Muscles belonging exclu- sively to the Trunk, and Muscles ascending to the Skull 684 Muscles attaching the Upper Limb to the Trunk . . 685 Muscles of the Upper Limb 685 Muscles of the Lower Limb 686 III. SYMPATHETIC NERVES . . 686 A. GANGLIATED CORDS . . 688 Cervical Part . . . . 688 Upper Cervical Ganglion . 688 Ascending Branch and Cranial Plexuses . . 688 Pharyngeal Nerves and Plexus . . . . 690 Upper Cardiac Nerve . 690 Branches to Blood-vessels 692 Middle Cervical Ganglion . 692 Lower Cervical Ganglion . 693 Thoracic Part . . . 693 Branches of the Ganglia . 693 Great Splanchnic Nerve . 695 Small Splanchnic Nerve . 696 Smallest Splanchnic Nerve . 696 Lumbar Part . . . 696 Sacral Part . . . . 696 Coccygeal Gland . .697 B. GREAT PLEXUSES OF THE SYM- PATHETIC . . . 698 Cardiac Plexus . . . 698 Superficial . . . . 698 Deep 698 Solar or Epigastric Plexus . 699 Aortic Plexus . . . 702 Hypogastric Plexus . . . 702 Pelvic Plexus . . .703 IV. ORGANS OF THE SENSES . . 705 THE EYE 705 Appendages of the Eye . . 705 Eyelids and Conjunctiva . 705 Lachrymal Apparatus . . 709 Globe of the Eye . . .710 External Coat of the Eyeball . 711 Sclerotic Coat . . .711 Cornea . . ... 714 Middle Tunic of the Eyeball . 716 Choroid Coat . . .716 Iris 718 Ciliary Muscle, Ligamentum Pectinatum, and Circular Sinus . . . .721 Vessels and Nerves of the Middle Tunic of the Eye . 721 Retina or Nervous Tunic . 725 Structure of the Retina . 726 PAGE Vitreous Body . . . . 731 The Lens and its Capsule . 733 Lens 733 Suspensory Ligament of the Lens, and Canal of Petit 736 Aqueous Humour and its Chamber . . . 736 Development of the Eye . 736 THE EAR 740 External Ear .... 740 Pinna 740 External Auditory Canal . 743 Middle Ear or Tympanum . 744 Small Bones of the Ear . 748 Ligaments and Muscles of Tympanum . . . 749 Lining Membrane of Tym- panum . . . • 751 Vessels and Nerves of Tym- panum . . . . 752 Internal Ear or Labyrinth . 753 Osseous Labyrinth . . 753 Membranous Labyrinth . 757 Vestibule . . . • 757 Semicircular Canals . . 75& Cochlea 760 Blood-vessels of Labyrinth . 767 Development of the Ear . 768 NOSE 771 Cartilages of Nose . . .771 Nasal Fossae . . . . 773 Mucous Membrane . . 774 Development of the Nose . . 778 SECTION VI. — SPLANCHNO- LOGY 779 ORGANS OF DIGESTION . . 779 Mouth 779 Teeth 780 Structure . ... 784 Development of Teeth . 792 Tongue 805 Mucous Membrane . . 805 Muscular substance . . 809 Palate 813 Tonsils 813 Salivary Glands . . .815 Parotid Gland . . . 815 Submaxillary Gland . . 816 Sublingual Gland . . . 817 Pharynx .... 819 (Esophagus . . . . 821 Abdominal Digestive Organs . 823 Abdomen ..... 823 Parts situated in each Re- gion of the Abdomen . 826 The Peritoneum . . . 826 Stomach .... 830 Structure of coats . . 832 Small Intestine . . .838 Structure of Small Intes- tine . . . . 841 Large Intestine . . . 851 Caecum . ... 852 viii CONTENTS. PAGE Colon .... 853 Rectum . . . . 856 Anus and its Muscles . 859 Development of the Alimentary Canal and Peritoneal Cavity 859 Liver ..... 862 Structure of Liver . . . 869 The Bile . . . .878 Development and Foetal Peculiarities of Liver . 879 Pancreas . . . . . 88 1 Spleen 883 ORGANS OF RESPIRATION . . 888 Trachea and Bronchi . . 888 Structure of the Trachea . 890 Pleurae 892 Lungs .... 894 Root of Lung . . . 897 Structure of Lungs . . 898 Development of Lungs and Trachea .... 904 Larynx or Organ of Voice . . 905 Cartilages of Larynx . . 905 Muscles of Larynx . . . 914 Vessels and Nerves of Larynx 919 Development and Growth of Larynx . . . -919 DUCTLESS GLANDS ON THE LARYNX AND TRACHEA . 920 Thyroid Body . . . 920 Thymus Gland . . . 923 URINARY ORGANS . . . 926 Kidneys .... 926 Suprarenal Bodies . . . 939 PAGE 944 952 952 952 952 955 956 958 959 963 963 Ureters .... Urinary Bladder . . . Urethra .... ORGANS OF GENERATION . . MALE ORGANS Prostate Gland . . . Penis .... Corpora Cavernosa . . Corpus Spongiosum Urethra of the Male . . Testes and Excretory Appa- ratus .... Coverings of Testis and Cord .... Vessels and Nerves of the Coverings of the Testis and Cord . . . 967 Testes . . . . 967 Vas Deferens . . . 971 Seminal Vesicles and Ejaculatory Ducts . . 973 Vessels and Nerves of Testis. . . .975 FEMALE ORGANS . . . 977 Vulva .... 977 Female Urethra . . . 980 Vagina .... 980 Uterus . ... 982 Ovaries and Fallopian Tubes 988 Development of the Urinary Organs .... 992 Development of the Organs of Generation . . . 995 MAMMARY GLANDS . . 1002 DIVISION II.— SURGICAL ANATOMY. SURGICAL ANATOMY OF THE ARTERIES Common Carotid Artery Subclaviau Artery Brachial Artery . Common Iliac Arteries Internal Iliac Artery . External Iliac Artery Femoral Artery . SURGICAL ANATOMY OF THE PARTS 1005 1005 ,1007 1010 1012 1014 1014 IOI5 CONCERNED IN CERTAIN ABDO- MINAL HERNLE . . . 1018 The Parts concerned in Inguinal Hernia ..... 1018 Inguinal Hernise . . . . 1025 The Parts concerned in Femoral Hernia 1031 Femoral Hernia . . . . 1034 THE PERINEUM AND ISCHIO-RECTAL REGION 1037 Lateral Operation of Lithotomy 1043 DIVISION III.— DISSECTIONS. GENERAL MANAGEMENT OF THE DISSECTIONS .... 1047 SPECIAL DIRECTIONS FOR THE DIS- SECTION OF EACH PART Head and Neck 1048 1048 Upper Limbs or Superior Extre- mities . . . . . 1059 Thorax 1066 Abdomen and Pelvis . . . 1069 Lower Limbs or Inferior Extre- mities 1078 NEUROLOGY.— CEREBRO-SPINAL AXIS. 501 SECTION V.— NEUROLOGY. UNDER the name of Neurology, it is intended to include the descriptive anatomy of the various organs forming parts of the nervous system. The nervous system consists of two sets of parts, one of which is eentral, the other peripheral. To the first set belong the brain and spinal cord, forming together the cerebro-spinal axis, and the ganglia : to the second set belong all the nerves distributed throughout the body ; and along with these may be included the organs of the senses, or those organs which contain the terminations of the several nerves of special sensation, in con- nection with certain apparatus or modifications of structure related to the reception of impressions by each of these nerves. Among the peripheral nerves it is necessary also to distinguish the cere- bro-spinal and the sympathetic or ganglionic, which, though intimately connected with each other at some places, are yet so different in their structure and mode of distribution as to require separate description. The description of these several parts of the nervous system will be brought under the following four subsections, viz. 1. The cerebro-spinal axis ; 2. The cerebro-spinal nerves and the ganglia connected with them ; 3. The sympathetic nerves and their ganglia ; 4. The organs of the senses. I.— THE CEREBRO-SPINAL AXIS. The cerebro-spinal axis is contained partly within the cavity of the cra- nium, and partly within the vertebral canal ; it is symmetrical in its form and structure throughout, consisting of a right and a left half, separated to a certain extent by longitudinal fissures, and presenting in their plane of union various portions of white and grey nervous substance which cross from one side to another, and form the commissures of the brain and spinal cord. Enclosed within the skull and the vertebral canal, the cerebro-spinal axis is protected by the bony walls of those tw6 cavities ; it is also surrounded by three membranes, which afford it additional protection and support, and are subservient to its nutrition. These envelopes, which will be described hereafter, are, 1st, a dense fibrous membrane named the dura mater, which is placed most superficially ; 2nd, a serous membrane called the arach- noid ; and, 3rd, deepest of all, a highly vascular membrane named the pia mater. The cerebro-spinal axis is divided by anatomists into the encephalon or enlarged upper mass placed within the cranium, and the spinal cord con- tained within the vertebral canal. These two parts have a relation, one to the other, very similar to that which subsists between the cranium and vertebral column : thus, they are continuous structures ; at the time of their first formation in the foetus they are nearly similar ; the earliest developed distinction consists in the enlarge- ment of the encephalon ; and, moreover, the spinal cord, like the vertebral column, continues to present a structure nearly uniform throughout its extent, while the encephalon becomes gradually more and more complicated, 502 THE SPINAL COED. till at last it is difficult to trace the serial relation of its constituent parts, or any correspondence with the structure of the cord. Fig. 339. — VIEW OP THE CEREBRO- SPINAL AXIS OF THE NERVOUS SYSTEM (after Bourgery). -g- The right half of the cranium and trunk of the body has been removed by a vertical section ; the membranes of the brain and spinal marrow have also been removed, and the roots and first part of the fifth and ninth cranial, and of all the spinal nerves of the right side, have been dissected out and laid separately on the wall of the skull and on the several vertebrae opposite to the place of their natural exit from the cranio-spinal cavity. F, T, 0, lateral surface of the cerebrum ; C, cerebellum ; P, pons Varolii ; m o, medulla oblongata ; m s, upper and lower extremities of the spinal marrow ; c e, on the last lumbar ver- tebra, marks the cauda equina ; v, the three principal branches of the nervus trigeminus or fifth pair ; C I, the sub- occipital or first cervical nerve ; above this is the ninth pair ; C vm, the eighth or lowest cervical nerve ; D I, the first dorsal nerve ; D xii, the last or twelfth ; L i, the first lumbar nerve ; L v, the last or fifth ; S I, the first sacral nerve ; S v, the fifth ; Coi, the coccygeal nerve ; st the left sacral plexus. A.— THE SPINAL CORD. The spinal cord, or spinal marrow (medulla spinalis), is that part of the cerebro- spinal axis which is situated within the vertebral canal. It extends from the margin of the foramen magimm of the occipital bone to about the lower part of the body of the first lumbar vertebra. It is continued into the medulla oblongata above, and ends below in a slender filament, the filum terminale or central ligament of the spinal cord. Invested closely by a proper membrane (the pia mater), the cord is enclosed within a sheath (theca) considerably longer and larger than itself, which is formed by the dura mater, and which is separated from the walls of the THE SPINAL CORD. 503 canal by numerous vascular plexuses, and much loose areolar tissue. The interval between the investing membrane and the sheath of the cord is occupied by a serous membrane (the arachnoid), and the space between the latter membrane and the pia mater is occupied by a fluid called the cerebro-spinal fluid. Within this space the cord is kept in position by proper ligaments, which fix it at different points to its sheath, and by the roots of the spinal nerves, — an anterior and a pos- terior root belonging to each, — which pass across the space from the surface of the cord towards the intervertebral fora- mina. From its lower part, where they are closely crowded together, the roots of the lumbar and sacral nerves descend nearly vertically to reach the lumbar intervertebral and the sacral foramina, and form a large bundle or lash of nervous cords named the cauda equina, which occupies the vertebral canal below the termination of the cord. A Fig. 340. -7 C 10 Fig. 340. — ANTERIOR AND POSTERIOR VIEWS OP THE MEDULLA OBLONGATA AND SPINAL CORD WITH SECTIONS. ^ The cord has been divested of its membranes and the roots of the nerves. A, presents an anterior, B, a posterior view, showing the upper or brachial, and the lower or crural enlargements. In these figures the filiform prolongation, repre- sented separately in B', has been removed ; C, shows a transverse section through the middle of the medulla oblongata ; D, a section through the middle of the cervical enlargement of the spinal cord ; E, through the upper region of the dorsal part ; F, through its lower ; Gr, through the middle of the lumbar enlargement ; and H, near the lower end of its tapering extremity. 1, anterior pyramids ; 1', their decussation ; 2, olivary bodies ; 3, restiform bodies ; 4, pos- terior surface of the medulla oblongata ; 4', cala- mus scriptorius ; 5, posterior pyramids ; 6, pos- terior lateral columns passing up into the restiform bodies ; 7, 7, anterior median fissure extending through the whole length of the spinal cord ; 8, 8, anterior lateral groove ; 9, 9, posterior median fissure; 10, 10, posterior lateral groove; x, lower end of the tapering extremity of the cord ; x , x , in B', the filiform prolongation of the cord and its pia-matral covering. Although the cord usually ends near the lower border of the body of the first lumbar vertebra, it sometimes terminates a little above or below that point, as opposite to the last 10- 504 THE SPINAL COED. dorsal or to the second lumbar vertebra. The position of the lower end of the cord also varies according to the state of curvature of the vertebral column, in the flexion forwards of which, as in the stooping posture, the end of the cord is slightly raised. In the foetus, at an early period, the cord occupies the whole length of the vertebral canal ; but, after the third month, the canal and the roots of the lumbar and sacral nerves begin to grow more rapidly than the cord itself, so that at birth the lower end reaches only to the third lumbar vertebra. Fig. 341. — POSTERIOR VIEW OP THE MEDULLA OBLONGATA AND OP THE SPINAL CORD WITH ITS COVERINGS AND THE ROOTS OF THE NERVES (from Sappey). 4 The theca or dura-matral sheath has been opened by a median incision along the whole length, and is stretched out to each side. On the left side, in the upper and middle parts (A and B), the posterior roots of the nerves have been removed so as to expose the liga- mentum denticulatum ; and along the right side the roots are shown passing out through the dura mater. The roman numbers indicate the different nerves in the cervical, dorsal, lumbar, and sacral regions : 9, several of the pointed processes of the ligamentum den- ticulatum ; 10, origin of several posterior roots ; 11, posterior median fissure ; 12, ganglia of the spinal nerves ; 13, part of the anterior roots seen on the left side ; 14, the united nerve ; 15, tapering lower end of the spinal cord; 16, filum terminale; 17, cauda equina. The length of the spinal cord is from fifteen to eighteen inches ; and it varies in diameter in different situations. Its general form is cylindrical, somewhat flattened before and behind. It presents two enlargements — an upper or cervical, and a lower or lumbar. The cervical enlargement is of greater size and extent than the lower. It reaches from the third cervical to the first dorsal vertebra ; its greatest diameter is from side to side. FORM AXD POSITION OF THE COED. 505 The lower or lumbar enlargement is situated nearly opposite the last dorsal vertebra ; its antero-posterior diameter is nearly equal to the transverse. Below this enlargement, the cord tapers in the form of a cone, from the apex of which Fig. 342. the small filiform prolongation is continued downwards for some distance within the sheath. Fig. 342. — LOWER PART OP THE SPINAL CORD WITH THE CAUDA EO.UINA AND SHEATH, SEEN FROM BE- HIND. £ The sheath has been opened from behind and stretched towards the sides ; on the left side all the roots of the nerves are entire ; on the right side both roots of the first aud second lumbar nerves are entire, while the rest have been divided close to the place of their passage through the sheath. The bones of the coccyx are sketched in their natural relative position to show the place of the filum terminale and the lowest nerves. a, placed on the posterior median fissure at the middle of the lumbar enlargement of the cord ; b, £, the terminal filament, drawn slightly aside by a hook at its middle, aud descending within the dura-matral sheath ; b', b', its prolongation beyond the sheath and upon the back of the coccygeal bones ; c, the dura-matral sheath ; d, double foramina for the separate passage of the anterior and posterior roots of each of the nerves ; e, pointed ends of several pro- cesses of the ligamentum denticulatum ; Dx, and DXII, the tenth and twelfth dorsal nerves ; Li, and Lv, the first and fifth lumbar nerves; Sr, and Sv, the first and fifth sacral nerves; Ci, the coccygeal nerve. The cervical and lumbar enlargements have an evident relation to the large size of the nerves which supply the upper and lower limbs, and which are connected with those regions of the cord, — in accordance with the general fact observed in the animal kingdom, that, near the origin of large nerves, the central nervous substance is accumulated in larger proportion. At the commencement of its development in the embryo the spinal cord is des- titute of these enlargements, which, in their first appearance and subsequent progress, correspond with the growth of the limbs. Sometimes the cord presents one or two bulbs or swellings towards its lower end. According to Foville, the lumbar enlargement is chiefly due to an increase in bulk of the anterior region of the cord. (Trait6 compl. de 1'Anat., &c., du Syst. Nerv. Cerebro-Spinal. Paris, 1844. Part I., p. 138.) "DXD Li St The terminal filament (filum terminale, cen- tral ligament) descends in the middle line amongst the nerves composing the cauda equina, and, becoming blended with the lower end of the sheath opposite to the first or second sacral vertebra, passes on to be fixed to the lower end of L L 606 THE SPINAL COED. the sacral canal, or to the base of the coccyx. Internally, it is a prolongation for about half its length of some of the nervous elements of the cord ; externally, it consists of a tube of the pia mater or innermost membrane, which, being attached at its lower end to the dura mater and vertebral canal, keeps pace with the latter in its growth, whilst the cord relatively shortens. It is distinguished by its silvery hue from the nerves amid which it lies. Small blood-vessels may sometimes be seen upon it. Fissures. — When removed from the vertebral canal, and divested of its membranes, the spinal cord is seen to be marked by longitudinal fissures. Of these, two, which are the most obvious, run along the middle line, one in front and the other behind, and are named the anterior and pos- terior median fissures. The anterior median fissure is more distinct than the posterior, and pene- trates about one-third of the thickness of the cord, its depth increasing towards the lower end. It contains a fold or lamelliform process of the pia mater, and also many blood-vessels, which are thus conducted to the centre of the cord. At the bottom of this fissure is seen the transverse connecting portion of white substance named the anterior white commissure. The posterior median fissure is less marked in the greater part of its extent than the anterior, but becomes more evident towards the upper part of the cord. In a certain sense it is no real fissure, except at the lumbar enlargement and in the cervical region, in both of which places a superficial fissure is distinctly visible ; for, although the lateral halves of the posterior part of the cord are quite separate, there is no distinct reflection of the pia mater between them, but rather a septum of connective tissue and blood- vessels which passes in nearly to the centre of the cord, as far as the posterior grey commissure. Besides these two median fissures, two lateral furrows or fissures have been described on each side of the cord, corresponding with the lines of attachment of the anterior and posterior roots of the spinal nerves. The posterior lateral fissure is a superficial depression along the line of attachment of the posterior roots, and is at the edge of the plane in which these roots pass inwards to the grey matter of the cord. The anterior lateral fissure, which is often described in the line of the origin of the anterior roots of the nerves, has no real existence as a groove. The fibres of these roots in fact, unlike the posterior, do not dip into the spinal cord in one narrow line, but spread over a space of some breadth. The grey substance of the cord, however, approaches the surface somewhat in the vicinity of the place where the anterior roots enter : and this, together with a slight depression, produces the appearance which has been described as a groove. Thus, each lateral half of the cord is divided by the posterior lateral fissure into a posterior and an antero-lateral column ; and although we cannot trace an anterior lateral fissure, this antero-lateral portion of the cord may, for the convenience of description, be considered as subdivided into an anterior and a lateral column by the internal grey matter. On the posterior surface of the cord, and most evidently in the upper part, there are two slightly marked longitudinal furrows situated one on each side, close to the posterior median fissure, and marking off, at least in the cervical region, a slender tract, named the posterior median column.. Between the anterior and posterior roots of the spinal nerves, on each side, the cord is convex, and sometimes presents a longitudinal mark correspond- ing with the line of attachment of the ligamentum denticulatum. Foville states, that in a new-born child there is a narrow accessory bundle of white INTERNAL STRUCTURE OF THE CORD. 507 matter, which runs along the surface of the lateral column, and is separated from it by a streak of greyish substance. According to the same authority, this narrow tract enlarges above, and may be traced upwards along the side ot the medulla oblongata into the cerebellum. (Op. cit. p. 285.) Fig. 343. Fig. 343. — DIFFERENT VIEWS OF A PORTION OF THE SPINAL CORD FROM THE CERVICAL REGION WITH THE ROOTS OP THE NERVES. Slightly enlarged. In A, the anterior sur- face of the specimen is shown, the anterior nerve - root of the right side being divided ; in E, a view of the right side is given ; in C, the upper surface is shown ; in D, the nerve-roots and gan- glion are shown from below. 1, the anterior median fissure ; 2, pos- terior median fissure ; 3, anterior lateral depres- sion, over which the ante- rior nerve-roots are seen to spread ; 4, posterior lateral groove, into which the posterior roots are seen to sink ; 5, anterior roots passing the ganglion ; 5', in A, the anterior root divided; 6, the posterior roots, the fibres of which pass into the ganglion, 6' ; 7, the united or compound nerve ; 7', the posterior primary branch seen in A and D, to be derived in part from the anterior and in part from the posterior root. Internal structure of the spinal cord. — The spinal cord consists of white aiid grey nervous substance. The white matter, forming by far the larger portion of the cord, is situated externally, whilst the grey matter is dis- posed in the interior. The grey matter, as seen in a transverse section of any part of the cord, presents two crescent-shaped masses, placed one in each lateral half, with their convexities towards one another, and joined across the middle by a transverse portion, the grey or posterior commissure of the cord. Each of these grey crescents has an anterior and a posterior cornu or horn. The posterior, generally longer and narrower, approaches the posterior lateral fissure : the anterior, shorter and thicker, extends towards the place of attachment of the anterior roots of the nerves. In front of it a layer of white substance separates it from the bottom of the anterior median fissure, this is named the anterior white commissure. Another white layer, very thin and indistinct, was formerly described as lying behind the grey commissure; but in the present state of our knowledge it seems sufficient to describe one white commissure, and one grey commissure behind it. At the back part or tip of the posterior horn, which is somewhat en- larged, the grey matter has a peculiar semitransparent aspect, whence it was named by Rolando substantia cinerea gelatinosa : the remaining and L L 2 508 THE SPINAL CORD. greater part of the grey matter, which resembles that most generally preva- lent, was named by Rolando the substantia spongiosa. The grey cornua vary in form in different parts of the cord : thus they are long and slender in the cervical portion, still more slender in the dor- sal, and shorter and wider in the lumbar region. The grey matter appears in a series of sections to be, relatively to the white, more abundant in the lumbar region of the cord, less so in the cervical region, and least so in the dorsal. The actual amount, however, of white matter is greatest in the neck. Towards the lower end of the cord, the double crescentic form gradually disappears, and the grey matter is collected into a central mass, which is indented at the sides. At its extreme point, according to Remak and Valentin, the cord consists of grey matter only. Fig. 344. Fig. 344. — SECTIONS OF THE SPINAL CORD IN DIFFERENT PARTS. These views are taken partly from Stilling's plates and partly from nature. A, is a section through the middle of the cervical enlargement, at the root of the sixth cervical nerve; B, through the mid- dle of the dorsal cylindrical portion ; C, through the middle of the lumbar enlarge- ment ; D, in the conical diminishing part of the cord ; E, farther down at the origin of the fifth sacral nerve ; F, at that of the coccygeal nerve ; Gf, is a sec- tion of the part where the conus medul- laris begins to pass into the filum termi- nale ; and H, at the lower part of this or in the commencement of the filum terminale. A, B, and C, are fully twice the natural size ; D, E, and F, about three times ; and Gr and H, about six times. In A, and C, a, marks the .interior root- fibres of the nerves ; and p, the posterior root- fibres as they enter the spinal cord. In D, E, and F, the great diminution of the white substance in proportion to the grey is seen ; in G-, the peculiar form of the central canal and medullary substance covering it ; and in H, the open con- dition of the central canal posteriorly. In all the figures the position is the same, viz., the anterior part placed down- wards. Central canal. — Extending through the whole length of the spinal cord, in the substance of the grey commissure, there is a minute central canal which in prepared transverse sections of the cord is barely visible, as a speck, with the naked eye. Superiorly, it is continued into and opens out at the calamus scriptorius of the fourth ventricle ; and inferiorly, it is prolonged into the filum terminale. It is lined with a layer of cylindrical ciliated cells or epithelium. This canal, though minute, is an object of considerable interest as a typical part of the structure of the cord, it being the permanent remains of the cavity of the cylinder formed by the spinal cord at the earliest period of its development. It is more distinctly seen MINUTE STRUCTURE OF THE CORD. 509 iu fishes, reptiles, and birds than in mammals. In the young human subject it is always present, but, according to the observation of Lock hart Clarke and Kolliker, it sometimes disappears in the adult. Minute Structure of the Spinal Cord. — The substance of the spinal cord consists of a large proportion of nervous substance, supported in a delicate framework of connective tissue and numerous minute blood-vessels. The white matter presents nerve-fibres, but is destitute of nerve-cells • the grey matter contains both elements. The fibres of the white substance are in greatest part longitudinal; the principal exceptions being those contained in the commissure, and in the roots of the nerves. The longi- tudinal fibres are finer in the posterior columns and posterior parts of the lateral columns than in other parts, and the deepest fibres are smaller than those placed more superficially. (Kolliker.) The fibres of the grey substance are for the most part not more than one half the diameter of their continuations in the white substance, and in the nerve-roots, but among them there are a few of larger size. They are very various in their direction, and, in great part at least, are connected with the roots of the nerves. Fig. 345.— TRANSVERSE Fig. 345. SECTION OP HALF THE SPINAL MARROW IN THE LUMBAR EN- LARGEMENT, f This is a semidia- grammatic representa- tion taken from a pre- pared specimen, and founded in part on the statements of Lockhart Clarke and of Kolliker. 1, anterior median fissure ; 2, posterior median fissure ; 3, cen- tral canal lined with epithelium ; 4, posterior commissure ; 5, anterior commissure ; 6, posterior column ; 7, lateral co- lumn ; 8, anterior co- lumn ; (at each of these places and throughout the white substance the trabecular prolongations of the pia mater are shown ; ) 9, posterior roots of the spinal nerve entering in one principal bundle; 10, anterior roots entering in four spreading bundles of fibres ; a, a, caput cornu posterioris with large and small cells, and above them the gelatinous substance ; b, in the cervix cornu, decus- sating fibres from the nerve roots and posterior commissure ; c, posterior vesicular columns (of Clarke) ; d, fibres running transversely from the posterior commissure into the lateral columns : near d, the lateral group of cells ; e, e, fibres of the anterior roots entering the anterior cornu, and passing through among the radiating cells, but not joining their processes; e', fibres from the anterior roots which decussate in the anterior column ; e", external fibres from the roots running round the outside of the anterior grey cornu towards the lateral columns ; f, fibres from the posterior commissure and from the posterior cornu running towards the anterior. Three groups of cells are seen in the anterior column ; of these the anterior are external and internal, the posterior are chiefly external or lateral. 510 THE SPIXAL CORD. The nerve-cells of the grey matter are of two kinds. Firstly, there are very large branched cells, from ^ to ^ of an inch in size, containing nuclei and pigment ; secondly, there are smaller cells, ranging from ^^ to ^ of an inch, but the majority are from -^^ to ~ of an inch in size. The smaller cells occur scattered throughout the whole of the grey matter ; the larger cells, on the contrary, are collected into groups. In the posterior cornua the large cells are almost entirely collected into a compact group, the posterior vesicular column of Clarke (the core of Stilling), which occupies the inner half of the cervix of the posterior cornu. This vesicular column is in intimate connection with the posterior roots of the nerves ; it may be traced continuously from near the lower extremity of the spinal cord to the middle of the cervical enlargement, where it terminates ; and it increases in size in both the lumbar and cervical enlargements. In the anterior cornu the large cells occur in greater number than in the posterior cornu, and are of somewhat greater size ; and they are principally placed at its forepart, and arranged in an inner and an outer group. There is likewise described by Clarke a small group of cells, collected in a tractus intermedio-lateralis, and forming a projection of the grey matter opposite the junction of the anterior and posterior cornua. This lateral vesicular column extends from the upper part of the lumbar to the lower part of the cervical enlargement ; and it may be said to reappear at the upper extremity of the cord, where it is traversed by the roots of the spinal accessory nerve, and is continued up into the medulla oblongata. Fig. 346. Fig. 346. — A SMALL PORTION OF A TRANSVERSE SECTION OP THE HUMAN SPINAL CORD NEAR THE SURFACE AT THE ENTRANCE OP A BUNDLE OF THE ANTERIOR ROOTS. ^ This figure, which is somewhat diagrammatic, is intended to show the relation to the nervous substance of the pia-matral sheath of the cord and the processes of connective tissue prolonged from it between the longitudinal and other nerve fibres, a, a, the primitive filaments of a bundle of the anterior roots, the medullary sheaths not repre- sented ; b, b, transverse sections of part of the anterior columns of the cord in which the dark points are the primitive filaments, and the circles represent the neurilemmal tube enclosing the medullary substance : in these parts the connective tissue is not represented, and many of the smallest nerve-fibres have also, for the sake of clearness, been omitted ; c, the pia-matral covering of the cord ; d, one of the compartments of the anterior column enclosed by septa of connective tissue prolonged from the pia mater, and exhibit- ing the fine frame-work of connective tissue extending through among the nerve-fibres, which last have been omitted : there are also indicated among the trabeculse minute nuclei of connective tissue. Connective tissue takes part in the structure of the cord to a very considerable extent. It forms a complete covering surrounding the white substance. In the inner margin also of the posterior columns, one on each side of the posterior fissure, two wedge-shaped bands (the bands of Goll) have been distinguished, in which the MINUTE STRUCTURE OF THE CORD. 511 connective tissue is remarkably abundant, and the nerve-fibres particularly small. The connective tissue forms also a reticulum (processus reticularis), in which the longitudinal nerve-fibres are imbedded. In the grey matter the connective tissue is still more abundant, more especially in the immediate neighbourhood of the central canal. Much discussion has taken place as to whether the smallest cells already described are really nervous or belong to the connective tissue. In the present imperfect state of knowledge of the development of nervous elements, it might be rash to express a decided opinion on this point ; but it may be stated that, independently of these, nuclei are figured by Kolliker in the reticulum, and also cells containing numerous and dividing nuclei in the neighbourhood of the central canal. Origin of the spinal nerves. — The anterior and posterior roots of the spinal nerves are attached along the sides of the cord in or near the anterior and posterior lateral grooves, and opposite to the corresponding cornua of the grey matter ; the posterior roots in a straight line, and the anterior roots scattered somewhat irregularly upon the surface (Fig. 345). The fibres of the anterior roots may be traced into and through the anterior cornua. They then diverge in different directions. The innermost fibres, after passing through among the cells in the inner group of the anterior cornu, cross in the white commissure to the anterior column of the opposite side. Many fibres pass backwards in the substance of the anterior cornu, where some of them would appear to form connection with fibres proceeding from other parts of the cord, and others to spread obliquely upwards and downwards ; while those which are most external passing through the outer group of cells, reach the lateral column. Fig. 347. — A SMALL FOR- Fig. 347. TION OF A TRANSVERSE SECTION OP THE SPINAL CORD AT THE PLACE WHERE TWO BUNDLES OP THE FIBRES OF THE ANTERIOR ROOTS PASS INTO THE GREY SUB- STANCE. ^P This figure may be looked upon as representing the inner ends of the anterior roots of the nerves, of which the outer part is shown in fig. 346. a, a, the two bundles of fibres of the anterior root passing between the compartments of longitudinal fibres of the cord ; b, b, these fibres running backwards through the grey substance towards the posterior cornua ; c, c', those spreading in the anterior cornua on the one side towards the anterior commissure, and on the other round the outer side of the anterior cornu ; d, d, portions of three com- partments of the anterior columns in which the longitudinal fibres of the cord are shown in transverse section ; e, e, large radiated and nucleated cells in the grey substance of the anterior cornu — some with three, others with a greater number of processes emanating from them : no direct communication is shown between these processes and the nerve fibres of the roots. The fibres of the posterior roots on reaching the posterior cornu diverge from each other in a curved manner, so as to form in great part the substantia gelatinosa. In front of this there may be seen, cut across in transverse sections, a group of these fibres which turn longitudinally upwards and downwards, and afterwards pass forwards, in part at least, to the anterior cornu, and in part to reach by the posterior commissure the posterior and lateral columns of the opposite side. Other fibres of the posterior roots pass forwards at once through the grey substance to the anterior 512 THE SPINAL CORD. and lateral columns. Another set of fibres slant principally upwards, but some downwards, in the posterior columns, and, interlacing with each other, most probably enter the grey matter at different heights. Some are lost to view in the posterior white columns, and it is uncertain whether or not they immediately ascend through these columns to the brain. Much discussion has taken place as to the course of the fibres in the cord, and their ultimate destination. It is easily understood that, by the examination of sections difficult to prepare, limited in extent, liable to undergo changes in the preparation, and giving views confined each to little more than a thin lamina, it is scarcely to be expected that the full history of many tortuous fibres can be accurately ascertained. Thus it remains still undecided whether any of the fibres of the nerve-roots pass up all the way to the brain. Volkmann concluded that none of them reached the brain, arguing from measurements of the size of the cord in different regions, that the cord could not contain in its upper regions all those nerve-fibres which were traceable to it in the lower. Kolliker pointed out the fallacy of this conclusion, in so far as Volkmann had not made proper allowance for the diminished size of the fibres as they ascend in the cord ; but although Volkmann's argument was thereby invalidated, it appears impossible to prove by microscopic observations that fibres of nerve-roots traced into the grey matter, and observed to emerge into the white matter, do not again re-enter the grey and terminate there. (Lockhart Clarke, Phil. Trans., 1851,1853, 1859; Stilling, Neue Unters. u. d. Bau des Ruckenmarks, 1856, 1857; Lenhossec, Neue Unters. u. d. Bau d. cent. Nervensystems, Vienna, 1855 ; F. Goll, Beitrage z. feineren Bau d. Ruckenmarks, Zurich, 1860. For a full account of the whole subject, see Kolliker's Handbucb der Gewebelehre des Menschen, 4th ed., 1863). It is also undetermined in what relation the nerve-fibres and branched or multipolar cells of the cord stand to each other. Most are inclined to believe that the radiating prolongations of the cells are in actual con tinuity with the axial filaments of nerve-fibres, whether proceeding from nerve-roots or from different parts of the cord itself; and the direct observation of such continuity has been affirmed by some, as by Schroeder Van der Kolk. But it is still considered by observers who have given most careful attention to this investigation that, although such continuity may be regarded as of the greatest probability, and, although it may be considered as proved in some other parts of the nervous system, especially in the lower animals, the actual passage of nerve-fibres into the processes of nerve-cells has not been proved as the result of actual observation in the spinal cord of man or of mammals. Results of Experiments. — Seeing the imperfect nature of the knowledge of the minute structure of the spinal cord as obtained from microscopic observations, it may be proper to give here a short account of the more important results of physiological experiments as to the course of the transmission of sensory impressions and motor influences through it, although it is at present difficult to reconcile them with the results of anatomical research. For the most important information upon this subject, derived from vivisection, science is indebted to the researches of Brown- Se"quard and Schiff. When the superior or dorsal * half of the cord is divided in animals, sensation still continues in the hind limbs. Sensation likewise continues after division of the inferior half of the cord, and even after the superior and inferior parts of the cord have been divided at different levels in such a manner that the hinder extremity of the cord may be supposed to communicate with the brain by means of the central grey matter only. But sensation is abolished by piercing the interior of the cord with an instrument, and so moving it as to divide as much as possible the grey matter without injuring the white matter. Moreover, section of the cord and irritation of the cut surfaces produce no pain, provided that the plane of section be sufficiently removed from the origins of nerves, as may be accomplished in the cervical region ; but in the neighbourhood of nerve-roots there is great sensibility. From all these circumstances it appears probable that the sensory fibres, viz., those of the posterior roots, pass quickly into the grey substance, and that the grey substance conducts sensory impressions upwards. Moreover, the circumstance that the posterior as well as the anterior surfaces of transverse sections made near the nerve-roots are sensitive seems * The student is reminded that "superior" applied to animals corresponds to " posterior" applied to the human subject. THE ENCEPHALON. 513 to be accounted for by the curving of the nerve-roots both toward and away from the brain. By similar experiments it is made probable that motor impressions likewise travel chiefly in the grey matter of the cord. Section of one lateral half of the cord is followed by loss of sensation in the opposite hind limb, and of motion in the limb of the side operated on : and a prolonged mesial incision produces loss of sensation in both hind limbs, without paralysis of motion. But in the medulla oblongata, above the decussation of the anterior pyramids, section of one side produces loss of both sensation and motion on the opposite side. From these circumstances it appears probable that the sensory fibres, viz., those of the posterior roots, decussate in the commissure ot the spinal cord, while the motor fibres, those derived from the anterior roots, cross chiefly at the decussation of the anterior pyramids of the medulla oblongata. (For further details, see Brown-Sequard, " Central Nervous System," 1860; also for a succinct account of the subject and for bibliography, J. Be"clard, " Physiologic Humaine," 4th ed., 1862 ; " Carpenter's Human Physiology/' 6th edit., 1865.) B.— THE ENCEPHALON. The encephalon admits of being conveniently divided into the medulla oblougata, the cerebellum with the pons Varolii, and the cerebrum. Fig. 348. Fig. 348. — PLAN IN OUTLINE OF THE ENCEPHA.LON, AS SEEN FROM THE RIGHT SIDE. J The parts are represented as separated from one another somewhat more than natural so as to show their connections. A, cerebrum ; /, g, h, its anterior middle and posterior lobes; e, fissure of Sylvius; B, cerebellum; C, pons Varolii; D, medulla oblongata; a, peduncles of the cerebrum ; b, c, d, superior middle, and inferior peduncles of the cerebellum ; the parts marked a, b, c, C, form the isthmus encephali. The medulla ollongata is the part continuous with the spinal cord : it rests on the basilar process of the occipital bone, and on its superior or dorsal surface presents a groove continuous with the central canal of the spinal cord. The cerebellum occupies the posterior fossa of the cranium. By the mesial part of its anterior and inferior surface, it forms the roof of a space, 5H THE MEDULLA OBLONGATA. the floor of which is the grooved posterior surface of the medulla oblongata, and which is named the fourth ventricle of the brain. Oil each side of this, the cerebellum is connected with the medulla oblongata and cerebrum, and also receives the fibres of the pons Parolii, which is a commissure passing beneath and between the fibres which extend upwards from the medulla oblongata, so as to unite the two lobes of the cerebellum. The cerebrum includes all the remaining and much the largest part of the encephalon. It is united with the parts below by a comparatively narrow and constricted portion or isthmus, part of which, forming the crura cerebri, descends into the pons Varolii, and through it is continued into the me- dulla oblongata, whilst another part joins the cerebellum. Situated on the fibres which extend up from the constricted part, are a series of eminences, named, from behind forwards, the corpora quadrigemina, optic thalami, and corpora striata ; and springing from the front and outer side of the corpora striata are the large convoluted cerebral hemispheres, which expand from this place in all directions, concealing the eminences named, and occupying the vault of the cranium, the anterior and middle cranial fossse, and the superior fossse of the occipital bone. The cerebral hemispheres are united together by commissures ; by means of which there is enclosed a cavity, which is subdivided into various ventricles, viz., the two lateral, the third, and the fifth. THE MEDULLA OBLONGATA. The medulla ollongata is bounded above by the lower border of the pons Varolii, whilst it is continuous below with the spinal cord, on a level with the upper border of the atlas, at a point which corresponds with the lower extremity of the anterior pyramids, to be presently described. It inclines obliquely downwards and backwards ; its anterior surface rests in the basilar groove, whilst its posterior surface is received into the fossa named the vallecula, between the hemispheres of the cerebellum, and there forms the floor of the fourth ventricle. To its sides several large nerves are attached. The term medulla oblongata, as employed by Willis, by Yieussens, and by those who directly followed them, included the crura cerebri and pons Varolii, as well as that part between the pons and the foramen magnum, to which, by Haller first, and by most subsequent writers, this term has been restricted. It is of a pyramidal form, having its broad extremity directed upwards : it is expanded laterally at its upper part : its length from the pons to the lower extremity of the pyramids is about an inch and a quarter ; its greatest breadth is nearly an inch ; and its thickness, from before back- wards, is about three-quarters of an inch. The anterior and posterior mesial fissures which partially divide the spinal cord are continued up into the medulla oblongata. The anterior fissure terminates immediately below the pons in a recess, the foramen ccecum of Vicq d'Azyr ; the posterior fissure is continued upwards into the floor of the fourth ventricle, where it opens and expands in a superficial furrow, and is gradually lost. In other respects an entirely different arrangement of the parts prevails from that in the cord. The surface of each half of the medulla presents four eminences or columns, which are met with in the following order, from before backwards, viz. : the anterior pyramids, the olivary bodies, the restiform bodies, and the posterior pyramids. COLUMNS OF THE MEDULLA OBLOXGATA. 515 The anterior pyramids are two bundles of white substance, placed one on either side of the anterior fissure, and marked off from the olivary body externally by a slight depression. They become broader and more pro- minent as they ascend towards the pons Varolii. At their upper end they are constricted, and thus enter the substance of the pons, through which their fibres may be traced into the peduncles of the brain. Fig. 349. Fig. 349. — VIEW OP THE ANTERIOR SURFACE OF THE PONS VAROLII AND MEDULLA OBLONGATA. a, a, anterior pyramids ; 6, their decussation ; c, c, olivary bodies ; d, d, restiforra bodies ; e, arciform fibres ; /, fibres described by Solly as passing from the anterior column of the cord to the cerebellum ; gt anterior column of the spinal cord ; h, lateral column; p, pons Varolii; i, its upper fibres ; 5, 5, roots of the fifth pair of nerves. In the lower part, a portion of each pyramid, arranged in several bundles, which interlace with the corresponding bundles of the other pyramid, passes downwards across the fissure to the oppo- site side. This decussation of the pyra- mids is not complete, but affects much the greater part of the innermost fibres. When traced from below, it is found that the whole or a great part of the decussating fibres come forward from the deep portion of the lateral columns of the cord, and advance to the surface between the diverging anterior columns, which are thus thrown aside. (Rosenthal, " Beitrag zur Encephalotomie," 1815.) The outer smaller portion of each pyramid does not decussate ; it consists of fibres, derived from the anterior column of the cord : these ascend, and are joined by the decussating portion from the opposite side. Together they form a prismatic bundle or column of white fibres, which extends deeply into the substance of the medulla, and is triangular in a cross section. The anterior pyramids contain no grey matter. The olivary bodies are two prominent oval masses placed to the outer sida of the pyramids, and sunk to a considerable depth in the substance of the medulla oblongata, appearing on its surface like two smooth oval eminences. They do not reach the pons Yarolii above, being separated from it by a deep depression ; nor do they extend so far in a downward direction as the pyramids, being considerably shorter than those bodies. The olivary bodies consist externally of white substance, of which the fibres chiefly run longitudinally ; and internally of a grey nucleus, named corpus dentatum or ciliare, or olivary nucleus. The olivary nucleus appears, on making a section, whether horizontal or vertical, through the middle, to present the form of a zig-zag line of a light yellowish colour, circumscribing a whitish substance within, and interrupted towards the centre of the medulla. It is arranged in the form of a capsule, which is open at its upper and inner part, and has its sides corrugated or 516 THE MEDULLA OBLOXGATA. plicated, so as to give the indented appearance to a section. This capsule is, moreover, surrounded with white matter externally, and through its open part white fibres pass into or issue from its interior, and connect it with other parts of the brain. The external fibres of the anterior columns of the cord, which at the decussation of the pyramids are thrown outwards, are con- tinued upwards, on the surface of the medulla oblongata, and then pass partly on the outside of and partly beneath the olivary bodies — being joined in their further progress by the fibres issuing from the olivary nucleus. To these fibres the term olivary fasciculus has been applied. The restiform bodies, placed behind and to the outer side of the olivary bodies, are two lateral rounded eminences or columns directly continuous with the posterior, and with part of the antero-lateral columns of the cord ; they diverge slightly as they ascend, and thus occasion the greater width of the Fig. 350. Fig. 350. — VIEW OF THE POSTERIOR SURFACE OF THE PONS VAROLII, CORPORA QUADRIGEMINA, AND MEDULLA OBLONGATA. The peduncles of tbe cerebellum are cut short at the side, a, a, the upper pair of corpora quadri- gemina ; 6, b, the inferior ;/,/, superior peduncles of the cerebellum ; c, eminence connected with the nucleus of the hypoglossal nerve; e, that of the glosso-pharyngeal nerve ; i, that of the vagus nerve ; d, d, restiform bodies ; p, p, posterior pyramids ; v, v, groove in the middle of the fourth ventricle ; v, calamus scriptorius, and eminence connected with the spinal accessory nerve ; 7, 7, roots of the auditory nerves. (See also Fig. 357, at p. 525.) medulla at its upper part. Each of them passes into the corresponding hemisphere of the cerebellum, and constitutes its inferior peduncle. At first they are in contact with the small tracts of the medulla, named the posterior pyramids ; but higher up they become free and pro- minent, and assist in forming the lateral boundaries of the fourth ventricle. There is a considerable portion of grey matter in their interior. By far the larger portion of the white substance of the restiform body consists of longitudinal fibres, which include all those belonging to the posterior column of the cord except the fasciculus gracilis, some derived from the lateral column, and also a small band from the anterior column. This last-named band runs obliquely below the olivary body, and, as was shown by Solly, connects the anterior column with the cerebellum. The part of the posterior column of the cord which belongs to the resti- form body of the medulla, is named fasciculus cuneatus. The posterior pyramids (fasciculi graciles) of the medulla oblongata, the smallest of the four pairs of columns into which it is divided, are situated one on each side of the posterior median fissure. They consist entirely of white fibres, and are continuous with the posterior slender tracts of the cord. They increase in size as they ascend till they reach the point where the medulla opens out to form the floor of the fourth ventricle ; and there, diverging from one another, they have the appearance of tapering and become closely applied to the restiform bodies. Their fibres quit these bodies, however, and pass up to the cerebrum. STEUCTUHE OF THE MEDULLA OBLONGATA. 517 The floor of the fourth ventricle, or space between the medulla and cere- bellum, is formed by that portion of the back of the medulla oblongata which is situated above the divergence of the posterior pyramids. Upon it, the central grey matter of the medulla oblongata, is, as it were, opened out to view. It is marked by a median furrow, ending inferiorly in the calamus scri2Jtorius, and at its lower end is a tubular recess, passing down the centre of the medulla for a few lines. This, which has been sometimes named the ventricle of Arantius, is the upper expanded portion of the central canal of the spinal cord. In the upper part of the floor of the fourth ventricle are two longitudinal eminences, one on each side of the middle furrow, greyish below, but appearing white higher up. These are formed by two bundles of white fibres, mixed with much grey matter, the fasciculi teretes of some authors, les faisceaux innomines of Cruveilhier. They seem to be derived from part of the lateral columns of the cord ; Cruveilhier believes, however, that they arise from the grey matter at the lower end of the medulla oblongata. Surmounting the free inner margin of the restiform body and posterior pyramid is a thin lamina, the lifjula (smaller pous of Meckel) occupying the angle between the cerebellum and the restiform body, and stretching towards its fellow of the opposite side. It derives a certain interest from indicating how the cylinder, which is closed in the spinal cord, might be completed in this region of the medulla oblongata by the union of the opposite margins. Crossing the grey matter in the floor of the fourth ventricle several transverse white lines, or stride, are usually observed, passing outwards from the median fissure, and round the sides of the restiform bodies. Some of these white strise form part of the roots of the auditory nerves, a few run slantingly upwards and outwards on the floor of the ventricle, whilst others again embrace the corresponding half of the medulla oblongata. These transverse lines are sometimes wanting, in which case the white fibres on which they depend probably exist at some depth below the surface. Santorini, and subsequently Kolando, described a set of superficial white fibres on the fore part and sides of the medulla oblongata, crossing over it below the olivary bodies, fibrce vel processus arciformes. They belong to a system of white fibres which pass transversely or horizontally outwards, and are probably continuous with the septal fibres about to be noticed. Sometimes the greater part of the pyramidal and olivary bodies is covered by a thin stratum of these transverse fibres, which appear to issue from the anterior median fissure ; but, most commonly, these superficial fibres are found only at the lower extremity of the olive, as the arciform fibres already mentioned. Besides the superficial transverse fibres now referred to, the medulla oblongata presents other horizontal fibres in its interior, some of them disposed in a mesial raphe or septum, and numerous others proceeding from that septum transversely outwards. Of these last, the majority, passing through the olivary bodies, and in part the pyramids, enter the corpus dentatum and form the whole of its white substance ; and these fibres, then passing radiately through the grey capsule, turn backwards to the fasciculus cuneatus and lateralis, those of them which pierce the anterior wall of the capsule arching round it to reach their destination. Other fibres pass behind the olivary into the restiform bodies, and seem to terminate in the grey substance of the floor of the fourth ventricle. (See Kolliker's Handbuch der Gewebelehre, 1863, p. 316.) A small band of fibres is represented by Eeichert as passing obliquely downwards and backwards from the side of the pons Varolii, descending between the auditory and facial nerves, and crossing over the upper end of the posterior pyramids. He names it the ala pontis. It probably is part of the ligula. (Keichert, Bau des Menschl. Gehirns, part 1st, plate I., 1859.) 518 THE MEDULLA OBLONGATA. Course of fibres from the spinal cord upwards through the medulla oblongata. — Assuming, for convenience of description, the existence of three white columns of the cord, these are disposed as follows. 1. The posterior column, with the exception of the fasciculus gracilis, is distinguished by the name of processus cuneatus and enters into the forma- tion of the restifonn body, which ascends to the cerebellum. The fasciculus gracilis ascends to the cerebrum. 2. The lateral column ascends towards the base of the olivary body, and is disposed of in three ways ; (1,) some of its fibres from the surface and deep part join the restiform body and proceed with it to the cerebellum ; (2,) a larger number, passing obliquely inwards, then come forwards between the anterior columns, and crossing the median plane appear as the fibres of decussation, and form the chief part of the opposite anterior pyramid ; (3,) the remaining fibres pass up to the cerebrum, as the fasciculi teretes Fig. 351. Fig. 351. — DIAGRAMMATIC REPRESENTA- TION OP THE PASSAGE OF THE COLUMNS OP THE MEDULLA OBLONGATA UPWARDS AND DOWNWARDS. A, the specimen, which, is seen from before, includes the medulla oblongata and the pons Varolii, with a small portion of the spinal marrow. The left lateral column (that to the reader's right) has been lifted out of its place to the side, and the ante- rior and posterior columns of that side remain undisturbed : the right anterior and posterior columns have been removed, and the lateral column remains in its place. The upper part of the right pyramid is removed. The transverse fibres of the pons Varolii have been divided in circumscribed portions to different depths corresponding with the several places of passage of the columns of the medulla. P, pons Varolii, part of the anterior sur- face, where it has been left entire ; p, the right and left pyramids, the upper part of the right has been cut away ; p', the fibres of the left pyramid as they ascend through the poris exposed by the removal of the superficial transverse fibres ; p'', placed on the deeper transverse fibres of the pons on the right side, close below the divided fibres of the pyramid ; a, left anterior column of the cord, passing upwards into the undecus- sated part of the anterior pyramid, and into a', the olivary column ; 0, olivary body ; o', the continuation of the olivary column ascending deeply through the pons, and exposed by the removal of a small portion of the deeper transverse fibres; o", the same fibres divided by a deeper incision on the right side ; I, the right lateral column, passing upwards into the following parts, viz., x, the deeper part passing by decussation into the left pyramid ; r, the part passing into the restiform body ; ft, the part ascending in the back of the fourth ventricle as fasciculus teres ; to the outer side of this are seen the ascending fibres of the posterior pyramid ; I', the left lateral column drawn aside from its place in the spinal cord ; the fasciculus teres, ft, and the part to the restiform body, r, cut short ; x , the deeper part passing by decussation into the right pyramid ; r', the part of the restiform body derived from the anterior column of the spinal cord ; pc, the posterior column of the left side exposed by the removal of the lateral column, and shown ascending to the restiform body as fasciculus cuneatus, fc : on the right side the posterior column being removed, fc, points to this fasciculus cuneatus cut short below. B, explanatory outline of the section of the spinal cord, a, anterior columns ; p, posterior; I, lateral. MINUTE STRUCTURE OF THE MEDULLA OBLOXGATA. 519 (faisceaux innomine's), appearing on the back of the pons Varolii, in the upper part of the floor of the fourth ventricle. 3. The anterior columns having reached the apex of the anterior pyramids, are thrust aside from their median position by the decussating fibres derived from the lateral columns, and are then distributed in three divisions. (1,) A very small division, ascends obliquely backwards beneath the olive, and joins the restiform body (Solly). (2,) Another division passes directly upwards, its fibres embracing the olivary nucleus, above which they are again collected together, and are joined by other fibres arising from the nucleus, so as to form the olivary fasciculus ; this ascends through the pons and at the side of the cerebral peduncle under the name of the fillet, and reaches the corpora quadrigemina and the cerebral hemispheres. (3,) The remaining division of the anterior column ascends into the anterior pyramid, forming its outer part. The anterior pyramids therefore are composed of fibres from the lateral and anterior columns, and are continued up through the pons into the peduncles of the cerebrum. It is to be remembered, however, that the separation between these different tracts of white fibres cannot be clearly followed out through the whole structure of the medulla oblongata, but that they are more or less blended with one another. Grey matter of the medulla oblongata followed upwards from the cord. — The central canal of the spinal cord, together with the grey matter which surrounds it, approaches nearer and nearer to the back of the medulla oblongata as it ascends, until it terminates in the calamus scriptorius. The anterior pyramids are free from grey matter in their interior, and are separated from the rest of the medulla by strong septa of connective tissue, and from one another by a raplie, which extends back to the grey matter surrounding the central canal, and which contains mesial horizontal fibres, named septal. The posterior cornua of grey matter in the lower part of the medulla oblongata extend transversely outwards from the central canal, and higher up stretch outwards and forwards to the surface. The substantia gelatinosa is swollen out into a mass which appears circular in a transverse section, and is named the grey tubercle of Rolando. The anterior cornua, together with the intermedio-lateral tract, which had re-appeared at the upper end of the cord, vanish in the form of elongated radiating streaks ; and between them and the anterior pyramids appear the olivary nuclei, unconnected with the system of grey matter prolonged from the spinal cord. Behind the posterior cornua two new cornua make their appearance — one extending into the processus cuneatus and the other into the posterior pyramid, and both of them increasing in size as the posterior pyramids increase. In the neighbourhood from which these and the posterior cornua spring there is seen in transverse sections a limited bundle of white fibres, the round fascicle of Stilling. In the upper part of the medulla oblongata the grey matter is principally spread out on the floor of the fourth ventricle. (Reichert, op. cit., part 2nd, plates I. and II.) According to the observations of Stilling, part of the grey matter at the back of the medulla forms special deposits or nuclei, which are connected with the roots of the spinal accessory vagus, glosso-pharyngeal, and hypoglossal nerves. Of these nuclei, the first or lowest is concealed in the substance of the medulla; whilst those which are situated higher up gradually appear in the floor of the fourth ventricle as small angular eminences pointing downwards, near the apex of the calamus scriptorius. The first nucleus proceeding from below is that for the spinal accessory nerve. It reaches some way down in the cord, and is there lost in the intermedio- lateral tract. Above this nucleus, and close to the middle of the medulla, is another, the second, commencing higher up, and connected with the hypoglossal nerve, the roots of which, coming forward between the anterior pyramid and the olivary body, appear at the surface in the depression between those parts. Continuing to ascend, these two nuclei reach the back of the medulla, and then make their appearance in the floor of the fourth ventricle. Higher up, the nucleus for the spinal accessory 520 THE MEDULLA OBLONGATA. Fig. 352. nerve is succeeded by a third in the same line, which is connected with the nervus vagus, and is also placed to the outer side of that for the hypoglossus. Further out, a fourth nucleus begins to be observed, belonging to the glosso-pharyngeal nerve. The last change in the arrangement of these small grey masses consists in the gradual narrowing of the nucleus of the par va- gum, and the approximation of those for the hypoglossal and glosso-pharyngeal nerves which were previously separated by it. Fig. 352. — MAGNIFIED VIEWS OF TRANS- VERSE SECTIONS OF THE MEDULLA OB- LONGATA (after Lockhart Clarke, and Reichert). f These figures are to be looked upon as in part diagrammatic, no attempt having been made to represent the natural difference of colour in the parts. For the most part, however, the grey substance is'indicated by the smoother dark shading, and the white substance by distinct lines. A, represents a section made at the lower part of the decussation of the pyra- mids; B, one immediately below the olivary bodies ; C, one a very short dis- tance below the calamus scriptorius ; and D, a section in the lower part of the fourth ventricle. The references are the following in all the four figures : — p, anterior pyramids ; p', their decussa- tion ; 0, olivary bodies ; 0', the radiating fibres proceeding from their interior; r, restiform bodies and their nucleus ; pp, posterior pyramids ; R, raphe ; c, central canal and substance surrounding it ; tr, grey tubercle of Rolando ; /, anterior median fissure ; fpt posterior median fissure ; a, arciform fibres ; I, lateral column ; Z', larger cells and vesicular tract of the lateral column ; CI a, anterior roots of the first cervical nerve ; CI p, posterior roots ; XII, hypoglossal nerve-roots issuing at the side of the pyramid ; XII', its nucleus ; XI, XI', spinal accessory nerve and its nucleus ; VIII', nucleus of the auditory nerve according to Reichert. In A and B, the decussation of the pyra- mids is represented ; in A, the anterior and posterior cornua of the grey matter still exist as in the spinal cord ; in B, the anterior cornua are much diminished in size, the posterior have begun to pass outwards, and to be converted into the grey tubercles, and the intermediate nuclei to make their appearance between them ; in C, the central canal is wider and ap- proaches the posterior aspect, and the olivary body appears between the anterior pyramid and the lateral column ; in D, the canal is opened up in the fourth ventricle, and the various grey nuclei are for the most part in the vicinity of its floor. C. a- Langenbeck and Forg maintain that the pail regarded by Stilling as the nucleus TEE PONS VAROLII. 521 for the glosso-pharyngeal nerve is really the place of origin of the greater root of the fifth or trigeminal nerve. Fig. 353. — TRANSVERSE SECTION Fig. 353. OF THE MEDULLA OBLONGATA (after Stilling). ± The section is made at the level of the middle of the olivary bodies]; the effect produced by transmitted light is brought out on the left- hand side of the figure, the half to the right being only sketched, a, anterior, and p, posterior fissure ; b, anterior pyramid ; c, olivary body with its corpus dentatum shown internally ; d, grey tubercle of Rolando in the lateral column ; e, the restiform body and its nucleus ; /, nucleus of the roots of the glosso-pharyn- geal nerve ; g, nucleus of the pneumo-gastric nerve ; h, that of the hypoglossal nerve ; z, the septum or raphe ; 8, roots of the pneumo-gastric nerve emerging ; 9, roots of the hypoglossal nerve. THE PONS VAROLII AND CEREBELLUM. THE PONS VAROLII or tuber annulare (mesocephalon of Chaussier, nodus encepliali of B-au and Sommerring), forms an eminence of transverse fibres above and in front of the medulla oblongata, below and behind the crura cerebri, and between the lateral lobes of the cerebellum. Its margins are arched ; the superior much more so than the inferior : thus, at the sides its transverse fibres are much more gathered together, and form at the place where it passes into the cerebellum a narrower bundle, which is named the middle cms of the cerebellum. In the middle line the pons presents a shallow groove in which the basilar artery lies, and is perforated by small branches of that artery. Although the superficial fibres are transverse in their general direction, they are not all parallel to each other. The middle fibres pass directly across, the lower set ascend slightly, whilst the superior fibres, which are the most curved, descend obliquely to reach the crura cerebelli on each side ; and there are also one or more superficial bands of the superior fibres which cross obliquely downwards over the middle and lower fibres, and completely conceal them at the sides. In its internal structure the pons consists of the longitudinal or peduncular fibres prolonged upwards from the medulla oblongata, of its own transverse or conimissural fibres, through which the longitudinal fibres pass, and of a large intermixture of grey matter. Behind the superficial transverse fibres are seen the prolonged fibres of the anterior pyramids, which, as they ascend through the pons, are widely separated into smaller bundles, intersected by other transverse white fibres, which, with those upon the surface, are all continued into the cerebellum. The alternation of transverse and longitudinal fibres just described extends to a considerable depth in the pons, the quantity of transverse fibres greatly preponderating ; posteriorly there succeeds a third layer, consisting entirely of longitudinal fibres, and comprehending the olivary fasciculi, and the fasciculi teretes. The median septum or raphe, which exists in the medulla oblongata, is M M 522 THE CEREBELLUM. prolonged throughout the whole height of the pons in its back part, but becomes indistinct in approaching the front or basilar surface, except towards its upper and lower edge, where the superficial fibres of the pons are mani- festly continuous in the median line with these septal fibres. Bundles of white fibres, belonging to the same system, encircle the crura cerebri at their emergence from the upper border of the pons. According to Foville, a few fibres from each of the three principal longitudinal elements of the medulla turn forwards and become continuous with the transverse fibres of the pons ; and, in like manner, one or more small bundles from each of the crura cerebri take a similar transverse course. (Foville, op. cit., pi. II., figs. 2 and 3 ; pi. III., figs. 5 and 6.) THE CEREBELLUM, hinder brain, consists of a body and of three pairs of crura or peduncles, by which it is connected with the rest of the eucephalon. These crura are named superior, middle, and inferior. Fig. 354. Fig. 354. — OUTLINE OP THE UPPER SURFACE OF THE CEREBELLUM. £ At the upper part of the figure, the crura cerebri and parts behind them have been cut through and left in con- nection with the cerebellum. Ill, the third pair of nerves lying upon the crura cerebri ; c r, white matter or crust of the crura cerebri ; In, locus niger ; t, tegmentum contain- ing grey matter in the upper part of the crura ; a s, aqueduct of Sylvius ; q, corpora quadrigemina, the upper elevations divided ; s v, superior ver- miform process or central folia of the middle lobe of the cerebellum ; I q, lobulus quadratus ; p s, posterior supe- rior lobe; fh, horizontal fissure ; pi, posterior inferior lobe; n, the notch between the hemispheres. The superior peduncles, crura ad cerebrum or processus ad testes, together with the valve of Vieusseus, a lamina stretched between them, connect the cerebellum with the cerebrum. The inferior peduncles, crura ad medullam, are the upper extremities of the restiform bodies. The middle peduncles, or crura ad pontem, much the largest, are the lateral extremities of the transverse fibres of the pons Varolii. They connect together the two halves of the cerebellum inferiorly. All these peduncles consist of white fibres only ; and they pass into the interior of the cerebellum at its fore part. The cerebellum is covered with grey cortical substance, rather darker than that of the cerebrum. Its greatest diameter is transverse, and extends to about three and a half or four inches : its width from before backwards is about two or two and a half inches ; and its greatest depth is about two inches, but it is much thinner round its outer border. It consists of two lateral hemispheres joined together by a median portion called the vermiform process, which in the human subject is distinguishable only as a small though well-marked part below, named the inferior vermiform process, and a mere elevation above, called the superior vermiform process. In birds, and in animals lower in the scale, this middle part of the cerebellum FORM OF THE CEREBELLUM. 523 alone exists ; and in most mammals it forms a central lobe very distinct from the lateral portions. The hemispheres are separated behind by a deep notch. Superiorly, the median portion or upper vermiform process, though slightly elevated, is not marked off from the hemispheres, so that the general surface of the organ, which is here inclined and flattened on each side, is uninterrupted. Below, the hemispheres are convex, and are separated by a deep fossa, named the vallecula, which is continuous with the notch behind, and in which the inferior vermiform process lies concealed in a great measure by the sur- rounding parts. Into this hollow the medulla oblongata is received in front, and the falx cerebelli behind. Fig. 355. — INFERIOR SURFACE OF THE CEREBELLUM WITH THE PONS VAROLII AND MEDULLA OBLONQATA (from Sappey after Hirschfeld and Leveille.) f 1, placed in the notch between the cerebellar hemispheres, is below the inferior vermiform process ; 2, 2, median depression or vallecula ; 3, 3, 3, the biventral, slender, and posterior inferior lobules of the hemisphere ; 4, the amygdala ; 5, flocculus or sub- peduncular lobule ; 6, pons Varolii ; 7, its median groove ; 8, middle peduncle of the cerebellum ; 9, medulla oblongata ; 10, 11, anterior part of the great horizontal fissure ; 12, 13, smaller and greater roots of the fifth pair of nerves; 14, sixth pair; 15, facial nerve; 16, pars intermedia; 17, auditory nerve; 18, glosso-pharyngeal ; 19, pneuino- gastric ; 20, spinal accessory; 21, hypoglossal nerve. The cerebellum, at the surface and for some depth, consists of numerous nearly parallel laminse or folia, which are composed of grey and white matter, and might be compared with the gyri of the cerebrum, but are smaller and without convolution. These laminae are separated by slightly - curved grooves or sulci of different depths. One principal fissure, or sulcus, named the great horizontal fissure, divides the cerebellum into an upper and a lower portion. It begins in front at the entrance of the middle peduncles, and passes horizontally backwards round the outer border of the hemispheres. From this primary fissure, numerous others proceed on both the upper and under surfaces, forming nearly parallel curves, having their concavities turned forwards, and separating the folia from each other. All these furrows do not go entirely round the hemisphere, for many of them coalesce with one another ; and some of the smaller furrows have even an oblique course between the others. Moreover, on opening the M M 2 624 THE CEREBELLUM. larger fissures, many of the folia are seen to lie concealed within them, and do not reach the surface of the cerebellum. Certain fissures, which are deeper than the rest, and constant in their position, have been described as separating the cerebellum into lobes, which are named as follows. The central lobe, situated on the upper surface, consists of about eight folia, immediately adjoining the anterior concave border. The superior and anterior lobe, sometimes called quadrate, and the superior and posterior lobe, are placed between the central lobe and the great horizontal fissure. On the under surface are seen successively the inferior posterior lobe, the slender lobe, the biventral lobe, the amygdala, and the subpeduncular lobe or flocculus. This last-named lobule, lobule of the pneumo-gastric nerve (Vicq-d'Azyr), subpeduncular lobe (Gordon), or flocculus, projects behind and below the middle peduncle of the cerebellum. It is connected by a slender pedicle of white fibres to the rest of the hemisphere ; but its exposed surface is grey, and is subdivided into five or six small laminae. Fig. 356. Fig. 356. — INFERIOR SURFACE OP THE CEREBELLUM WITH THE POSTERIOR MEDULLARY VELUM (after Reil and Reichert, and from nature). f The medulla oblongata has been in great part removed by a cut passing through it near the pons Varolii ; the two amygdaloid lobules have also been removed, and the medulla and pons Varolii pulled downwards in order to bring into view the posterior medullary velum. p s, posterior superior lobe of the cerebellum ; fh, horizontal fissure ; p i, posterior inferior lobe ; g, lobulus gracilis ; b i, biventral lobe ; c, placed on the folia which pass across between the hemispheres of opposite sides ; p, pyramid ; u, uvula ; n, placed in the fourth ventricle immediately below the nodule ; p v, on each side, placed on the cut surface where the amygdalae have been removed, points by a line to the posterior medullary velum ; v, v, cavity of the fourth ventricle within the borders of the velum and behind the inferior cerebellar peduncles; the cavity extends on each side into the pedicle of the flocculus, /; m, section of the medulla oblongata, in which the posterior opening of the olivary capsules of grey matter is shown ; VI, sixth nerves ; V, roots of the fifth nerves, and above them, the facial and auditory roots. Within the vallecula, or on its borders, the following parts are seen. Commencing from behind, a conical and laminated projection named the pyramid, is first met with. In front of that is another smaller projection, called the uvula, which is placed between the two rounded lobes at the sides of the vallecula, named the amygdala ; these terms having been suggested by a comparison with the parts so named in the throat. Between the uvula and amygdalse on each side, but concealed from view, is extended a ridge CENTRAL LOBE.— FOURTH VENTRICLE. 525 of grey matter' indented on the surface, and named the furrowed band. Still further forward is the anterior pointed termination of the inferior vermiform process, named the nodule, which projects into the fourth ven- tricle, and has been named the laminated tubercle (Malacarne). On each side of the nodule is a thin white lamella of a semilunar form, which is attached by its posterior convex border, and is free and concave in front. The outer ends of these lamellss are attached to the flocculi, and the inner ends to the nodule, and to each other in front of that projection. The two lamellae together constitute the posterior medullary velum, which has been compared with the valve of Vieussens, — the one being attached to the superior extremity and the other to the inferior extremity of the middle or vermiform portion of the cerebellum. This posterior velum is covered in and concealed by the amygdalae, and cannot be properly seen until those lobules have been turned aside or removed. The fourth ventricle. — The space left between the medulla oblongata in front and the cerebellum behind, is named the fourth ventricle, or ventricle of the cerebellum. Fig. 357.— VIEW OP THE Fig. 357. FLOOR OP THE FOURTH VEN- TRICLE WITH THE POSTERIOR SURFACE OF THE MEDULLA OBLONGATA AND NEIGH- BOURING PARTS (from Sappey after Hirschfeld and Le- veille). On the left side the three cerebellar peduncles have been cut short ; on the right side the white substance of the cerebellum has been preserved in connection with the supe- rior and inferior peduncles, while the middle one has been cut short. 1, median groove of the fourth ventricle with the fas- ciculi teretes, one on each side; 2, the same groove at the place where the white striae of the acoustic nerve emerge from it to cross the floor of the ventricle ; 3, inferior peduncle or restiform body ; 4, posterior pyramid ; above this the calamus scriptoriua ; 5, superior peduncle or processus a cerebello ad cerebrum ; on the right side the dissection shows the superior and inferior peduncles crossing each other as they pass into the white stem of the cerebellum j 6, fillet to the side of the crura cerebri ; 7, lateral grooves of the crura cerebri ; 8, corpora quadri- gemina. The cavity of this ventricle is of a flat rhomboidal shape, being contracted above and below, and widest across its middle part. The anterior extremity of the inferior vermiform process projects into it from behind, and higher up it is covered by the Vieussenian valve. It is bounded laterally by the superior peduncles, and by the line of union of the medulla oblongata and the cerebellum. The upper end of the ventricle is continuous with the Sylvian aqueduct or passage (iter) leading up to the third ventricle. The anterior surface or floor of the fourth ventricle is formed by the back of the medulla oblongata and pons Varolii. It is shaped like a lozenge, 526 THE CEREBELLUM. truncated at its upper part. Below, it is bounded by the diverging posterior pyramids and restiform bodies surmounted by the ligula. It has already been sufficiently described in connection with the medulla oblongata. The lining membrane of the ventricle is continuous with that of the ventricles in the interior of the cerebrum, through the aqueduct of Sylvius, in which situation it is marked by delicate rugse, oblique or longitudinal in direction. At the sides it is reflected from the medulla to the cerebellum, and extends for a considerable distance outwards between the flocculus and the seventh and eighth nerves. At the lower end of the ventricle, there is, as was ascertained by Magendie, a narrow orifice in the membrane by which the cavity communicates with the subarachnoid space. Projecting into the fourth ventricle at each side, and passing from the point of the inferior vermiform process outwards and upwards to the outer border of the restiform bodies, are two small vascular processes, which have been named the choroid plexuses of the fourth ventricle. Fig. 358. Fig. 358. — OUTLINE SKETCH OP A VER- TICAL SECTION OF THE CEREBELLUM TO SHOW THE CORPUS DENTATUM IN ITS MEDULLARY STEM. § The section has been carried through the left lateral part of the pons so as to divide the superior peduncle and pass nearly through the middle of the left cerebellar hemisphere. The olivary body has also been divided longitudinally so as to expose in section its corpus dentatum. cr, crus cerebri ; /, fillet ; q, corpora quadrigemina ; sp, superior peduncle of the cerebellum divided; m p, middle peduncle or lateral part of the pons Varolii, with fibres passing from it into the white stem ; av, continuation of the white stem radiating towards the arbor vitse of the folia ; cd, corpus dentatum ; o, olivary body with its corpus dentatum; p, anterior pyramid. Internal structure of the cerebellum. — The central part is composed of white matter, which sends out spreading and gradually thinning layers into the interior of all the laminse, larger and smaller, of the grey substance which form a continuous covering on the surface. In consequence of this arrangement of the white and grey substances, sections of the cerebellum crossing the laminae, and dividing the grey and white substance together, present a beautifully foliated or arborescent appearance, named arbor vitce. This appearance is seen in any vertical section, but it is most perfect in that which passes through the median plane, where the relative quantity of the central white matter is small. The foliations are arranged somewhat pin- nately, the section of each primary lamina having those of secondary laminse clustered round it like leaflets 011 a stalk. In the lateral hemispheres, where the peduncles enter, the white matter is more abundant ; and, if a section be made through either hemisphere half way between its centre and the middle of the vermiform process, it will display a nucleus of grey matter, which is named the corpus dentatum of the cerebellum. This structure, very similar to that already described in the olivary body of the medulla oblongata, presents the appearance of a waved line of compact yellowish brown matter, surrounded by white sub- stance and containing whitish matter within. This line is interrupted at INTERNAL STRUCTURE OF CEREBELLUM. 527 its upper and inner part. In whatever direction the section is carried through the corpus dentatum, this waved line is seen, so that the dentate body may be described as consisting of a plicated pouch or capsule of grey substance open at one part and inclosing white matter in its interior, like the corpus dentatum of the olivary body. White fibres may be traced from it to the superior peduncles of the cerebellum and to the valve of Vieussens. Fig. 359. — VIEW OF A DISSECTION OF THE FIBRES OF THE MEDULLA OB LONG AT A AND PoNS VAROLII (from Arnold). £ 6, the anterior pyramid ; &', its fibres traced upwards through, the pons Varolii ; c, olivary column ; d, olivary body ; m, superficial trans- verse fibres of the pons on its left side ; m', the deeper transverse fibres of the right side; m", the prolongation of these fibres as mid- dle peduncle of the cerebellum ; p, q, their continuation into the laminse and folia of the cerebellum ; n, inferior peduncle; x, the decus- sating part of the left lateral column crossing to the right ante- rior pyramid. The fibres in the primary lamelke can be traced continuously from the peduncles of the cerebellum. Upon these central plates are laid other collateral lamellae, which are not connected with the fibres proceeding from the middle of the cerebellum, but merely pass from one folium to another. The grey matter is not uniform throughout its whole thickness, but is composed of two or more layers differing in colour and other characters ; — resembling, in this respect, the cortical substance of the posterior convolutions of the cerebrum. The fibres composing the peduncles of the cerebellum are arranged in its interior in the following manner. The middle peduncles, which are the most superficial, enter the lateral parts of the cerebellum ; they may be traced into the folia of those parts, and form a large share of each hemisphere. The inferior peduncles pass upwards into the middle part of the cerebellum, in the folia of which they are distributed, especially in those of the upper surface. The superior peduncles, which are placed nearest to the middle line, are principally connected with the folia of the inferior vermiform process ; but a considerable number of them pass into or issue from the grey capsule of the corpus dentatum which has been already described. A very different account from, that which has generally been received of the course and relations of the tracts of nervous substance of the cerebellum has recently been put forward by Luys, and deserves mention in this place. According to the statement of this author, all the fibres of the cerebellar peduncles arise from the interior of the corpora dentata ; the cells of those centres receive externally fibres from the laminated periphery of the cerebellum, and internally give origin to the peduncular fibres ; the fibres of the inferior peduncles of opposite sides cross the middle line and terminate in the interior of the olivary nuclei ; and the fibres of the superior peduncles, likewise decussating in the mesial plane before quitting the cerebellum, terminate in a grey centre in the interior of the tegmentum of the crus cerebri, named by Luys the superior olivary body. He further alleges that different fibres pass in all directions from the superior and inferior olivary bodies, and that thus the fibres of the cerebellum form a separate system indirectly connected Avith the fibres of the rest of the cerebro- spinal axis. Only a short notice, however, of these views having as yet been published, it will be necessary that the observations on which they are founded be made known and fully corroborated, before statements of so startling a nature can be generally accepted. (Luys, in Journ. de 1'Anat. et de Physiol., 1864, p. 225.) 528 THE CEREBELLUM. Microscopic Structure. — The cortical grey matter which covers the foliated surface of the cerebellum is made up of the following elements, viz. : 1. Pellucid cells of considerable size. 2. Cells, for the most part of large size, and caudate, having the usual granular contents. These cells are embedded in a finely granular matrix ; the greater number of those of the caudate kind have a pyriform shape, and are prolonged Fig. 360. Fig. 360. — THE COLUMNS OP THE MEDULLA OBLONGATA TRACED UPWARDS INTO THE CEREBELLUM AND CEREBRUM (from Arnold). | a, part of the anterior column which ascends in the olivary column ; 6, decussating portion of the lateral column forming the pyramid and turned down ; c, olivary fasciculus ascending deeply through the pons ; d, olivary body ; e, restiform body; /, g, corpora quadrigemina ; c, h, i, the fillet ; h, the part which asoends to the cerebral peduncle ; i, the part passing up to the corpora quadrigemina ; m, m,', the trans- verse fibres of the pons divided ; n, inferior peduncle of the cerebellum ; o, septal fibres of the medulla oblongata ; q, fibres of the inferior peduncle continued into the laminse of the cerebellum ; ?•, r, superior peduncle ; t, fasciculus teres ; ut thalamus ; v, corpus albicans. Fig. 361. Fig. 361. — MINUTE STRUC- TURE OP THE SUBSTANCE OP THE CEREBELLUM (from Kolliker). A, large cells from the grey cortical substance of the human cerebellum. ~ a, three large cells exhibit- ing granular contents and a nucleus ; 6, the internal pro- cesses seen in two of the cells ; c, d, two external pro- cesses running towards the surface from two of the cells, in the third cell one large process only is seen; c', d', ramified finer parts of these processes. B, course of the nerve- tubes at the surface of the cerebellum, magnified with a low power. a, nerve of the medullary substance ; 6, nervus plexus of the substantia ferruginea ; c, border of that substance ; d, fine fibres running out from the dark -bordered tubes into the superficial grey sub- stance. at their small end into a simple or branched appendage, and this process, as first remarked by Purkinje, is in most of them directed towards the surface of the cerebellum. 3. Small bodies, like cell-nuclei densely aggregated without any inter- vening substance. These lie at some depth from the surface; according to Todd, MINUTE STRUCTURE OF CEREBELLUM.— THE CEREBRUM. 529 they form a thin light-coloured lamina, intermediate between two darker strata of grey matter which contain the nerve-cells ; one of these grey strata being the deepest and next the white matter of the cerebellum, while the other, which is the darker coloured of the two, is in contact with the pia mater. 4. Fibres. Tubular nerve- fibres pass from the white into the grey matter, and extend through it nearly as far as the surface. The mode of their termination, which is difficult to trace, has been investigated by various anatomists. According to Valentin, they form loops and return upon their course, but this statement has not been confirmed by other observers. Gerlach has recently described a very remarkable arrangement of the fibres of the cerebellum. According to him, these fibres, on approaching the grey matter, split up into extremely fine divisions, which form a network, while the granules, which he considers as small cells with ramifying processes, are placed at the angles of the meshes, and branching processes of the large nerve-cells also terminate in the network. According to Kb'lliker, networks of tubular fibres exist within the grey matter and communicate with the nerve-cells, while the granules belong to the reticulum of connective tissue. Luys, like Gerlach, describes lateral processes as being given oft' by the nerve-fibres to connect them with the granules, at the same time that they terminate likewise directly, although much attenuated, in the large nerve-cells. (Gerlach, "Microscopische Studien," pi. I., fig. 3; copied in Yirchow's "Cellular Pathology/' by Chance, p. 269.) THE CEREBRUM. The cerebrum, or brain proper, constitutes the highest and much the largest portion of the encephalon. It consists of the following parts, viz., the peduncular masses of the crura cerebri and processus a cerebello ad cerebrum ; the series of eminences or cerebral centres or ganglia concealed from view, named corpora quadrigemiua, optic thalami and corpora striata ; the cerebral hemispheres, which are by far the most bulky part of the cere- brum and of the whole encephalon, and form nearly the whole superficial part ; various commissural structures including the corpus callosum and fornix; and lastly some smaller structures, viz., the pineal and the pituitary bodies, and the olfactory bulbs. EXTERIOR OF THE CEREBRUM. The cerebral hemispheres together form an ovoid mass, flattened on its under side, and placed in the cranium with its smaller end forwards, its greatest width being opposite to the parietal eminences. They are separated in the greater part of their extent by the great longitudinal fissure. Each cerebral hemisphere has an outer or convex surface, which is in contact with the vault of the cranium ; an inner or flat surface, of a crescent shape, which forms one side of the longitudinal fissure ; and an irregular under surface, which rests on the base of the skull, and on the tentorium cerebelli. Three lobes, or large divisions, projecting in three different directions, have usually been distinguished in each hemisphere, under the names of anterior, middle, and posterior lobes. The division between the anterior and middle lobes is very clearly denned below and on the sides by a deep cleft, named the Sylvian fissure. There is no similar demarcation between the middle and posterior lobes ; but anatomists have generally considered as the pos- terior lobe that part of the hemisphere which lies over the cerebellum. The under surface of the anterior lobe is triangular and excavated to adapt it to the roof of the orbit on which it rests. The middle lobe is rounded 530 THE CEREBRUM. and prominent, and occupies the middle fossa of the skull — the edge of the lesser wing of the sphenoid bone corresponding with the Sylvian fissure. Fig. 362. — UPPER SUR- FACE OF THE BRAIN SHOWING THE CONVO- LUTIONS (from R. Wag- ner). 4 This view was taken from the brain of a famous mathematician, Professor C. F. Gauss, who died in 1854, aged 78. It is selected as an example of a well- formed brain of the usual size with fully developed convolutions. a, superior or first frontal convolution ; a', second or middle frontal ; «", third or inferior frontal ; A, A, anterior ascending parietal con- volution ; B, B, pos- terior ascending parietal convolution ; b, first or upper parietal convolu- tion ; b', second or mid- dle ; b", third or in- ferior ; c, first or upper tempoi'al convolution ; d, first or upper occipi- tal convolution ; d', second or middle ; d", third or lower ; I, I, the superior longitudinal fis- sure ; r, the fissure of Rolando ; p, the external perpendicular fissure. The posterior lobe is smooth and slightly concave on its under surface, where it rests on the arch of the tentorium. It is right to remark that some anatomical writers have admitted only two lobes, reckoning the middle and posterior lobes as one, under the name of the posterior lobe ; while others more recently have divided the middle lobe into two, an upper and lower, and have added that of the island of Reil, so as to make five principal lobes in all. These have been named respectively the frontal, parietal, temporal, occipital, and central lobes. The great longitudinal fissure, seen upon the upper surface of the brain, extends from before backwards throughout its whole length in the median plane, and thus separates the cerebrum, as already stated, into a right and left hemisphere. On opening this fissure, it is seen, both before and behind, to pass quite through to the base of the cerebrum : but in the middle it is interrupted by a large transverse mass of white substance, named the corpus callosum, which connects the two hemispheres together. While the brain is in its natural situation, this fissure is occupied by a vertical process of the dura mater — the falx cerebri — which dips down between the two hemispheres, not quite reaching to the corpus callosum. The Sylvian fissure, which separates the anterior and middle lobes, passes at first upwards and backwards in the outer part of the hemisphere, and FORM AND DIVISIONS OF THE CEREBRUM. 531 divides into two branches, anterior and posterior. It lodges the trunk and primary divisions of the middle cerebral artery, and at its commencement presents a spot pierced by numerous small arterial branches, and thence named the locus perforatus anticus. The surface of the hemispheres is composed of grey matter, and is moulded into numerous smooth and tortuous eminences, named convolutions, or gyri, which are marked off from each other by deep furrows, called sulci, or anfractuosities. Fig. 3G3. Fig. 363.— LATERAL VIEW OF THE RIGHT CEREBRAL HEMISPHERE (from Sappey after Foville). £ 1, fissure of Rolando ; 2, anterior ascending parietal convolution ; 3, frontal convolu- tions connected posteriorly with the anterior ascending parietal ; 4, union of two frontal convolutions ; 5, posterior ascending parietal convolution ; 6, another parietal convolution similarly Connected with those on the inner surface ; 7, 7, anterior part of the convolu- tion of the fissure of Sylvius; 8, 8, horizontal part of the same convolution; 9, 9, posterior part ; 10, 11, 12, anterior, middle, and posterior principal convolutions of the island of Reil or central lobe ; 13, supraorbital convolution ; 14, part of the temporal lobe ; 15, occipital lobe. CEREBRAL CONVOLUTIONS. — The convolutions are covered closely through- out by the vascular investing membrane, the pia mater, which sends pro- cesses down to the bottom of the sulci between them, while the serous covering, the arachnoid membrane, passes from one convolution to another, over their summits and without dipping between them. The sulci are generally from half an inch to an inch in depth ; but in this respect there is much variety in different brains, and in different parts of the same brain ; those upon the outer convex surface of the hemisphere being the deepest. In general, the depth of a convolution exceeds its thickness ; and its thick- ness, near the summit, is somewhat greater than through its base. Since the external grey or cortical substance is continuous over the whole surface of the cerebral hemispheres, being found alike within the sulci and upon the gyri, a far greater extent of grey matter is thus exposed to the vascular surface of the pia mater with a given size of the brain, than could have been the case had the hemispheres been plain and destitute of convolutions. The general arrangement of the convolutions has been made the subject 532 THE CEREBRUM. of study by various anatomists in earlier and recent times, but still re- quires farther elucidation. An attempt to describe minutely all the indi- vidual gyri would be difficult and useless, owing to their irregularity in different cases, and their want of symmetry in the same brain. .Nevertheless, there are some sufficiently constant in presence, and characteristic in situa- tion and form, to admit of being specially described ; and it seems probable that, by a sufficiently careful comparison of the convolutions in different animals, and the observation of their development in the foetus, certain general facts may be ascertained regarding them, tending to throw light upon their disposition in man. Fig. 364. Fig. 364. — OUTLINE OP THE CHREBRUM AS SEEN FROM THE LEFT SIDE, SHOWING THE CONVOLUTIONS AS DISTINGUISHED BI GRATIOLET. f F, frontal lobe ; P, parietal lobe ; T, temporal lobe ; 0, occipital lobe ; R, R, fissure of Rolando ; s, s. fissure of Sylvius, posterior division : s', s', its anterior division ; C, at the junction of the two, marks the place of the central lobe or convolutions of the island of Reil ; p, the place of the vertical or occipital fissure ; «, a', a", superior, middle and inferior frontal convolutions ; a*, supraorbital convolutions ; A, anterior transverse or ascending parietal convolution ; B, posterior transverse or ascending parietal convolution ; &, &', b", upper, middle and lower parietal convolutions ; c, c', c", upper, middle and lower temporal convolutions; d, d', d", upper, middle and lower occipital convolutions ; between b, b', b", and d, d'} d", are seen the connecting convolutions ; between c and c', the parallel fissure. The island of Reil constitutes the set of convolutions (gyri operti) which appear earliest both in the fostus and in the animal series, It is a triangular eminence, broken externally into short radiating convolutions, which forms a delta between the anterior and posterior division of the fissure of Sylvius, and is limited externally by a deep sulcus. This mass, constituting the central lobe of recent authors, derives additional interest from being the centre round which the principal convolutions of the cere- brum are arranged. It is only brought into view by laying open the fissure of Sylvius. (See Figs. 368 and 377.) The convolution of the Sylvian fissure is a very large convolution, which is also early in its appearance in animals. Commencing in front of the inner end of the Sylvian fissure, it takes a tortuous and much folded course all round that fissure, giving off numerous secondary gyri, and terminates behind the fissure opposite the point where it began. The gyrus fornicatus, convolution of the corpus callosum, or internal con- CEREBRAL CONVOLUTIONS. 633 volution, is one of the most distinct and symmetrical convolutions in the whole brain. Commencing on the under surface of the brain, immediately before the anterior perforated space, it ascends a short distance in front of the anterior recurved extremity of the corpus callosum, and then runs back- wards immediately above that body, as far as its posterior extremity : there it turns downwards and forwards, embracing the cerebral peduncle, to reach the entrance of the Sylvian fissure. This long convolution, therefore, describes a sort of arch or ring, open or interrupted opposite the Sylvian fissure, and embracing the corpus callosum above, and the cerebral peduncle below. It thus, as was pointed out by Foville, forms a sort of rim or border to the grey matter ; whence it is named by him convolution d'ourlet. The surface of this convolution, especially towards its inferior termination, is covered by a very thin cribriform layer of white substance, which, with the grey matter beneath, gives the surface a mottled aspect. This has been called the reti- culated white substance. The marginal convolution of the longitudinal fissure is a large convolution which may be traced, more or less indented or interrupted however in its course, along the line of junction between the convex and flat surfaces of the hemisphere, forming the lip of the great longitudinal fissure. Ifc com- mences on the under surface of the brain, in common with the gyrus fornicatus, and, passing forwards, forms the inner border of the triangular orbital surface of the anterior lobe. In this part it is cleft longitudinally by a deep sulcus, into which the olfactory bulb is received, and which, it may be mentioned, is developed at an earlier period than the convolution itself. On the front and upper surface of the cerebrum, this convolution may generally be traced for some distance along the margin of the longitudinal fissure, but soon becomes marked by deep sulci ; and, thus interrupted, may be followed round the posterior extremity, and along the under surface of the hemisphere forwards as far as the point of the middle lobe, running parallel for some space with the under portion of the gyrus fornicatus. Two of the sulci which interrupt the marginal convolution are very constant, viz., the vertical fissure with the fissure of the hippocampi, and the fissure of Rolando. The fissure of the hippocampi has a deep origin in the inner margin of the middle lobe of the brain between the fascia dentata and the gyrus fornicatus, and, passing backwards, crosses that gyrus on the under surface of the brain, behind the corpus callosum, and proceeds in a nearly horizontal course along the inner face of the hemisphere. This fissure is important as forming the reverse of the elevations of the hippocampi in the interior of the brain, and as being (according to Reichert) produced at an early period in connection with the general development of the hemispheres, and being comparable therefore rather to the fissure of Sylvius than to a mere sulcus. The part of the gyrus fornicatus beneath this fissure is distinguished as the gyrus hippocampi. The fissure of Rolando, starting from behind the vertex, runs outwards and forwards from the longitudinal fissure, so that the right and left grooves form a V-shaped line open in front. It derives its importance from being characteristic of the form of the brain of man and the quadrumana, and separating two considerable convolutions, which extend from the superior longitudinal fissure to the fissure of Sylvius. These convolutions, peculiar to the greater number of simise and attaining their fullest development in man, constitute the anterior and posterior transverse or anterior and posterior ascending parietal convolutions. 634 THE CEREBRUM. The vertical fissure of recent authors crosses the marginal convolution in the posterior part of the cerebrum, extending slightly outwards upon its upper surface and more deeply on its internal aspect, so as to form a separation between the so-called parietal and occipital lobes. According to Foville the convolutions may be arranged in four principal orders, founded in a great measure on their relative connections with the anterior perforated space, which, in his estimation, is a part of the highest importance. The first order issues from the perforated space, and consists of two portions. One, large and vertical, is the gyrus fornicatus, without its ascending secondary gyri ; the other, short and horizontal, is the slightly elevated ridge which bounds the perforated space in front and on the outer side. Fig. 365. — RIGHT HALF OE THE BRAIN DIVIDED BY A VERTICAL ANTERO -POSTERIOR SECTION (from various sources and from nature), i 1, great superior or marginal convolution ; 2, convolution of the corpus callosum ; 3, secondary convolutions running between this and the preceding ; within the numbers 2, 2, 2, the corpus callosum ; 4, the fifth ventricle ; 5, the third ventricle (see Fig. 377 for a larger view of these parts) ; 5', pituitary body; 6, immediately behind the corpora quadrigemina and pineal gland; +, the fourth ventricle; 7, pons Varolii ; 8, medulla oblongata ; 9, cerebellum ; the middle lobe showing the section of the arbor vitse ; I, the olfactory bulb ; II, the right optic nerve ; the commissure cut through ; III, the right nerve of the third pair. The second order, also consisting of two portions, commences from the horizontal portion of the first order on the limits of the perforated space. One part corresponds with the marginal convolution of the longitudinal fissure, as already described, except that part of it on the orbital surface of the anterior lobe which lies to the outer side of the olfactory sulcus ; the other part is the convolution of the Sylvian fissure. The third order consists of two sets, of which one occupies the inner surface of the hemisphere, and connects the gyrus fornicatus in its whole length with the marginal convolution of the longitudinal fissure ; the other set lies in the Sylvian fissure, forms the island of Reil, and connects the short horizontal portion of the first order with the convolution surrounding that fissure. The convolutions of the fourth order, the largest, deepest, and least symmetrical of all, are quite detached from the perforated space, and have no relation to the first order of convolutions. They connect the two convolutions of the second order CEREKRAL CONVOLUTIONS. 635 together, viz., the marginal convolution of the median fissure and that of the Sylvian fissure, and occupy the outer or convex surface of the cerebral hemisphere. Leuret, by an extended comparison of the brains of different animals, was led to divide mammals into fourteen groups, according to the disposition of the convolutions. In the lowest or simplest group, including the bat, mole, and rat, the Sylvian fissure is the only division of the surface present, or along with it a few very slight sulci. In a higher group, containing the fox and dog, and presenting in a marked form the t}rpical mode of division, Leuret recognises as fundamental six convolutions — four external, including the superior marginal and that of the fissure of Sylvius, and two internal, viz., the supraorbital and gyrus fornicatus. In other groups, together with various other modifications of form by subdivision or by union through supplemental ones, the number of the fundamental convolutions is frequently reduced to five or to four. In the brain of the elephant, on the other hand, placed by Leuret in the thirteenth group, he recognises the superior transverse convolutions; and in the last group, comprehending the quadrumana, these transverse convolutions are two in number, and are separated by the groove, named by Leuret fissure of Rolando. These trans- verse or ascending parietal convolutions are a constant and well-marked feature of the human bi'ain, in which they attain their highest development. Fi-. 366. Fig. 366. — OUTLINE OP THE INNER SURFACE OP THE EIGHT HALF OP THE BRAIN, SHOWING THE PRINCIPAL LOBES AND CONVOLUTIONS ACCORDING TO GrRATIOLET. F, frontal lobe ; P, parietal ; 0, occipital ; T, temporal ; r, fissure of Rolando ; /, fronto-parietal fissure ; p', inner perpendicular or occipito -parietal fissure ; h, the calca- rine fissure of Huxley, and with the line continued forwards between g and h', the hippo- campal fissure ; ti, convolution of the hippocampus ; g, gyrus fornicatus or convolution of the corpus callosum ; s, Sylvian fissure ; I, olfactory bulb ; II, optic nerve ; III, third nerve; C, cerebellum. More recently, Gratiolet has arranged the convolutions with great detail, according to their most distinguishing common features in man and the simiae. On the external surface of the hemisphere he distinguishes five lobes, viz., the frontal and parietal above the fissure of Sylvius ; the temporo-splienoidal below that fissure ; the occipital behind it, and the island of Reil, or central lobe, within the fissure. The frontal lobe he divides into an orbital and a frontal portion, and in the frontal portion 536 THE CEREBRUM. he distinguishes a superior, middle, and inferior tier of convolutions. In the parietal lobe are the anterior and posterior ascending convolutions (convolution of Rolando) surrounding the fissure of Rolando, and behind these a curved lobe. In the temporo- sphenoidal lobe are described a superior, middle, and inferior convolutions, lying parallel to the fissure of Sylvius. The occipital lobe presents also three tiers, but less distinct than those of the frontal, and besides these are four convolutions uniting the occipital and parietal lobes, named by Gratiolet plis de passage, or the connecting convolutions. The internal surface^ of the hemisphere Gratiolet divides into the fronto-parietal lobe, corresponding in extent to the frontal and parietal lobes of the external surface, and limited behind by the internal perpendicular fissure, the occipital lobe between that fissure and the fissure of the hippocampi; and the occipito-temporal lobe, including the tentorial surface, and extending outwards to the sphenoido-temporal lobe. It is to be remarked, however, that the divisions and nomenclature of Gratiolet, however useful they may be for the purpose of explicit comparison of the convolu- tions of the human brain with those of the quadrumana, the study in which the inventor has made use of them, are yet of a somewhat artificial description, and may not be applicable to a more extended comparison of the disposition of the convolu- tions among animals. From Reichert's plates it is apparent that the internal perpendicular fissure (occi- pito-parietal of Huxley) is the upper of two branches into which the fissure of the hippocampi divides posteriorly in its first development, and which together with that fissure constitutes his fissura occipitalis. The inferior branch, the posterior part of the fissure of the hippocampi, is the calcarine fissure of Huxley. Not only the comparison of the brain of man with those of other animals, but like- wise the comparison of human brains one with another, establishes the existence of a relation between mental development and the complication, size, and depth of the cerebral convolutions, and the extent of the grey matter contained in them. On the subject of the cerebral convolutions the reader may consult, in addition to the works of Arnold, Tiedemann, Foville and Reichert, that of Leuret and Gratiolet "Anat. Comp. du Systeme Nerveux, 1839-57;" Gratiolet, "Mem. sur les Plis C6re"braux de 1'Homme et des Primates, 1854 ; " R. Wagner, " Tiber die typischen Verschiedenh. der Windungen der Hemispharen," &c., Getting. 1860-62 ; Huschke, " Schadel, Hirn und Seele," 1854 ; Huxley, " Brain of Ateles paniscus," Proc. of Zool. Soc., June, 1861 ; J. Marshall, (( On the Brain of a Bush-woman, and on the Brains of Two Idiots, &c.," Trans. Roy. Soc. 1863. BASE or THE CEREBRUM. — When the brain is turned with its base upper- most, and the parts of which it is composed are allowed to fall slightly asunder by their own weight, two considerable masses, consisting of white substance externally, are seen emerging together from the fore part of the poiis Yarolii, and, separating from each other as they proceed forwards and outwards, to enter the inner and under part of the right and left cerebral hemispheres. These white masses, which are marked on the surface with longitudinal striae, and have somewhat the appearance of large bundles of fibres, are the peduncles or crura of the cerebrum. Immediately before entering the corresponding hemisphere, each is crossed by a flattened white cord, named the optic tract, which, adhering by its upper border to the peduncle, is directed forwards and inwards, and meets in front with its fellow of the opposite side to form the optic commissure, from the fore part of which the optic nerves proceed. Limited behind by these diverging peduncles, and in front by the con- verging optic tracts, is a lozenge-shaped interval, called the interpeduncular space, in which are found, in series from behind forwards, the posterior per- forated space, the corpora albicantia, and the tuber cinereum, from which is prolonged the infundibulum attached to the pituitary body. The posterior perforated space (locus perforatus posterior) is a deep fossa PARTS IX THE IXTERPEDUXCULAR SPACE. 537 situated between the peduncles, the bottom of which is composed of greyish matter, connecting the diverging crura together, and named pons Tarini. It is perforated by numerous small openings for the passage of blood-vessels ; and some horizontal white striae usually pass out of the grey matter and turn round the peduncles immediately above the pons. Fig. 367. Fig. 367. — BASE OP THE BRAIN WITH THE ORIGINS OP THE CEREBRAL NERVES. ^ This figure is taken from an adult male brain which had been hardened in alcohol. 1, superior longitudinal fissure ; 2, fissure of the olfactory tract and lower part of the superior convolution ; 2', orbital convolutions; 2", external or inferior frontal convolu- tion ; 3, inner part of the fissure of Sylvius, near the anterior perforated spot ; 3, 3, outer part; 4, inner convolution of the temporal lobe; 4', middle convolution; 4", outer con- volution; 5, 5', occipital lobe; 6, on the right pyramidal body of the medulla oblongata above the decussation ; 7, amygdaloid lobe of the cerebellum ; 8, biventral lobe ; 9, lobulus gracilis ; 10, posterior inferior lobe ; +, the inferior vermiform process; I, olfactory bulb ; I', the tract divided on the left side, showing the three white striai by which it is connected with the brain ; II, in the anterior perforated spot, marks the right optic nerve; the left has been cut short; III, on. the right crus cerebri, denotes the third pair ; IV, on the inner convolution of the middle lobe, the fourth pair ; V, the trige- minus; VI, on the pons Varolii, the sixth ; VII, also on the pons Varolii, the seventh ; VIII, on the left lobe of the cerebellum below the horizontal fissure and the flocculus, denotes the eighth pair; IX, on the upper part of the right amygdaloid lobe, denotes the ninth pair ; X, on the same, the suboccipital nerve. The corpora albicantia or mammillaria are two round white eminences in front of this fossa, each about the size of a small pea, surrounded by grey matter, and connected together across the middle line. The corpora albicantia are formed, as will hereafter be explained, by the anterior extremities of the fornix ; hence they have also been named bulbs of thefornix. In 538 THE CEREBRUM. the foetus they are at first blended together, and they become separated about the beginning of the seventh month. In most vertebrate animals there is but one white eminence or corpus albicans in their place. Fig. S68. Fig. 368.— VIEW FROM BEFORE OF THE ME- DULLA OBLONGATA, PONS VAROLII, CRURA CEREBRI, AND OTHER CFNTRAL PORTIONS OF THE ENCEPHALON. On the right side the convolutions of the cen- tral lobe or island of Eeil have been left, together with a small part of the anterior cerebral convolu- tions : on the left side these have been removed by an incision carried betweon the thalamus opticus and the cerebral hemisphere. I', the olfactory tract cut short and lying in its groove between two con- volutions ; II, the left optic nerve in front of the commissure^; II', the right optic tract ; Th, the cut surface of the left thalamus opticus ; C, the central lobe or island of Reil ; Sy, fissure of Sylvius ; x x , locus pevforatus anterior ; e, the external, and i, the internal corpus genicu- latum ; h, the hypophysis cerebri or pituitary body ; tc, tuber cinereum with the infundibulum ; a, one of the corpora albicantia ; P, the cerebral peduncle or crus ; /, the fillet ; III, close to the left oculo-motor neive ; x, the locus perforates pos- ticus; PV, pons Varolii ; V, the greater root of the fifth nerve ; +, the lesser or motor root ; on the right side this + is placed on the Gasserian ganglion, arid points to the lesser root, where it proceeds to join the inferior maxillary nerve ; 1, ophthalmic division of the fifth nerve ; 2, superior maxillary division ; 3, inferior maxillary division ; VI, the sixth nerve ; VII a, the facial ; VII b, the auditory nerve; VIII, the pneumo-gastric nerve ; Villa, the glosso- pharyngeal ; VIII b, the spinal accessory nerve ; IX, the hypoglossal nerve ; fl, the floc- culus ; fh, the horizontal fissure of the cerebellum (Ce) ; am, the amygdala; pa, the anterior pyramid ; 0, the olivary body ; r, the restiform body ; d, the anterior median fissure of the spinal cord, above which the decussation of the pyramids is represented ; ca, the anterior column ; cl, the lateral column of the spinal cord ; C I, the suboccipital or first cervical nerve. The tuber cinereum is a lamina of grey matter extending forwards from the corpora albicantia to the optic commissure, to which it is attached, and forming, as afterwards described, part of the floor of the third ventricle. ca PARTS SEEX IX THE BASE OF THE CEREBRUM. 539 In the middle it is prolonged into a hollow conical process, the infundi- bulum, to the extremity of which is fixed the pituitary body. The pituitary body or hypophysis cerebri, formerly called pituitary gland, from its being erroneously supposed to discharge pituita ii,to the nostrils, is a small reddish grey mass, of a somewhat flattened oval shape, widest in the transverse direction, and occupying the sella turcica of the sphenoid bone. It consists of two lobes, of which the anterior is larger, and concave behind, where it embraces the smaller posterior lobe. Its weight is from five to ten grains. In the adult it is solid, and of a firm consistence. The anterior lobe consists of two kinds of matter, one hard and grey, the other, situated within, softer and of a yellowish white colour. The posterior lobe is darker and redder than the anterior. Both are very vascular. The pituitary body appears to approach in structure to the vascular or duct" less glands, such as the thyroid and suprarenal bodies, &c. According to Sharpey's observations, with which those of subsequent writers agree, it differs greatly in structure, at least in its anterior and larger lobe, from any other part of the ence- phalon. The substance of the anterior lobe appears to be constituted by a mem- branous tissue forming little round cavities or loculi, which are packed full of nucleated cells. The loculi are formed of transparent, simple membrane, with a few fibres and corpuscles resembling elongated cell-nuclei disposed round their walls. The cells contained in the cavities are of various sizes and shapes, and not unlike nerve-cells or ganglion-globules ; they are collected into round clusters, filling the cavities, and are mixed with a semi-fluid granular substance. This thin granular matter, together with the cells and little specks of a clear glairy substance like mucus, can be squeezed from the cut surface, in the form of a thick, white, cream-like fluid. In the foetus, the pituitary body is proportionally large, and contains a cavity which communicates, through that of the infundibulum, with the third ventricle. This body is constantly present, and has the same connection with the brain in all vertebrate animals. In the middle line of the base of the brain, in front of the optic commis- sure, is the anterior portion of the great longitudinal fissure, which passes down between the hemispheres. At a short distance in front of the com- missure, this fissure is crossed transversely by a white mass, which is the anterior recurved extremity of the corpus callosum. On gently turning back the optic commissure, a thin connecting layer of grey substance, the lamina cinerea, is seen occupying the space between the corpus callosum and the commissure, and continuous above the commissure with the tuber cinereum. It is connected at the sides with the grey substance of the anterior perforated space, and forms part of the anterior boundary of the third ventricle : it is somewhat liable to be torn in removing the brain from the skull ; and, in that case, an aperture would be made into the fore part of the third ventricle. At a short distance outwards from the lamina cinerea is the anterior per- forated spot (locus perforatus anticus), a depression near the entrance of the Sylvian fissure, floored with grey matter, and pierced with a multitude of small holes for the passage of blood-vessels, most of which are destined for the corpus striatum, — the deeper portion of the brain beneath which it lies. The grey surface of each perforated space is crossed by a broad white band, which may be traced from the middle of the under surface of the corpus callosum in front, backwards and outwards along the side of the lamina cinerea towards the entrance of the Sylvian fissure. These bands of the two sides are named the peduncles of the corpus callosum. When the entire encephalon is viewed from below, the back part of the 540 THE CEKEBRUM. tinder surface of the cerebrum is concealed by the cerebellum and the pons Varolii. If, however, these parts be removed, it will be seen that the tw o hemispheres of the cerebrum are separated behind as they are in front, by the descent of the great longitudinal fissure between them, and that this fissure is arrested by a cross mass of white substance, forming the posterior extremity of the corpus callosum. This posterior part of the great longi- tudinal fissure is longer than the anterior portion. INTERNAL PARTS OF THE CEREBRUM. The anatomy of the interior of the cerebrum is most conveniently studied by removing, after the manner of Vieussens and Vicq-d'Azyr, successive portions of the hemispheres by horizontal sections, beginning from above. Fig. Ik Fig. 369. — VIEW OP THE CORPUS CALLOSUM FROM ABOVE (from Sappey after Foville). ^ The upper surface of the corpus callosum has been fully exposed by separating the cerebral hemispheres and throwing them to the side; the gyrus fornicatus has "been detached, and the transverse fibres of the corpus callosum traced for some distance into the cerebral medullary substance. 1, the upper surface of the corpus callosum ; 2, median furrow or raphe ; 3, longi- tudinal strise bounding the furrow ; 4, swelling formed by the transverse bands as they pass into the cerebrum ; 5, anterior extremity or knee of the corpus callosum ; 6, pos- terior extremity ; 7, anterior, and 8, posterior part of the mass of fibres proceeding from the corpus callosum ; 9, margin of the swelling ; 10, anterior part of the convolution of the corpus callosum; 11, hem or band of union of this convolution; 12, internal con- volutions of the parietal lobe; 13, upper surface of the cerebellum. The first horizontal section, to be made about half an inch above the corpus callosum, displays the internal white matter of each hemisphere, speckled with red spots where its blood-vessels have been divided, and sur- THE CORP (IS CALLOSUM. 541 rounded on all sides by the grey matter which is seen to follow closely the convoluted surface, and to be of nearly equal thickness at all points. This white central mass in each hemisphere was named by Vicq-d'Azyr centrum ovale minus. On separating the remaining portions of the two hemispheres from each other, two sulci are seen to exist between the corpus callosurn and the gyri immediately in contact with it, viz., the gyrus fornicatus of each side. These sulci were distinguished by the older anatomists as ventricles of the coitus callosum. Another section being made at the level of the corpus callosum, the white substance of that part is seen to be continuous with the internal medullary matter of both hemispheres : and the large white medullary mass thus displayed, surrounded by the border of cortical substance, constitutes what is generally described as the centrum ovale, of Vieussens. The corpus callosum or great commissure (trabs cerebri) is a white struc- ture, with a length not quite half of that of the brain, and approaching about two-fifths nearer to the front than the back of the hemispheres. It Fig. 370. Fig. 370. — HORIZONTAL SECTION OP THE BRAIN SHOWING THE LATERAL VENTRICLES AND THE FIFTH VENTRICLE OPENED (from Sappey after Vicq-d'Azyr). ^ 1, the fifth, ventricle ; 2, the two laminse of the septum lucidum meeting in front of it ; 3, lesser hippocampus of the posterior cornu ; 4, horizontal section of the posterior swelling of the corpus callosum; 5, middle part of the fornix, where it has been separated from the corpus callosum ; 6, posterior pillar of the fornix ; 7, hippocampus major descending in the middle cornu ; 8, eminentia collateralis ; 9, lateral parts of the fornix ; 10, choroid plexus ; 11, tsenia semicircularis ; 12, corpus striatum. is about an inch in width behind, and somewhat narrower in front. Its thickness is greater at the ends than in the middle, and is greatest behind, 542 THE CEREBRUM. •where it is nearly half an inch. It is arched from before backwards. Its upper surface is distinctly marked by transverse furrows, which indicate the direction of the greater number of its fibres. It is also marked in the middle by a slight longitudinal groove, the raphe, which is bounded laterally by two white tracts, placed close to each other, named striae longitudinales, or nerves of Lancisi. On each side, near the margin, are seen other longitudinal lines (striae longituclinales laterales) occasioned by a few scanty white fibres. In front, the corpus callosum is reflected downwards and backwards, between the anterior lobes, forming a bend named the genu. The inferior or reflected portion, which is named the rostrum, becomes gradually nar- rower as it descends, and is connected by means of the lamina cinerea with the optic commissure. It also gives off the two bands of white substance, already noticed as the peduncles of the corpus callosum, which, diverging from one another, run backwards across the anterior perforated space on each side to the entrance of the Sylvian fissure. Fig. 371. semicircularis ; y, enrinentia collaterals. Fig. 371. —THE LATERAL VENTRICLES OPENED BY A HORIZONTAL SECTION, AND THE MIDDLE CORNU EXPOSED ON THE RIGHT SIDE. £ a, b, anterior and pos- terior parts of the great longitudinal fissure ; c, section of the anterior part of the corpus callosum ; d, posterior part of the same ; e, the left choroid plexus ; /, the fornix ; g, the an- terior; 7t, the posterior, and q, the descending cornu of the lateral ven- tricle; k, Jc, corpora striata ; I, I, optic tha- larai ; n, n, right and left hippocampus minor ; o, posterior pillar of the for- nix ; v, the corpus fimbri- atura into which it passes; IS umber ot brains at each weight observed by 1 1 Number of brains at each weight observed ty 1 Classification 5 ' s^ -r- VMiiao&uva b&uu £ -^ into three eS '"" -s "£ . into three si a c groups fi 'S to show the *1 * , It S'S groups, to show the gl bo 1 1 § g ^ prevailing weight. | 1 I * 1— 1 prevailing ictight. 1 a « a 1 s 1 53 o 1 0 C/j a "§ •3 i^ 0 i H M H 6 a H tf p1 34 _ 1 1 >> 31 i 1 1 ^ 37 2 2 32 i 1 a 38 1 1 rH 35 2 oj / from ~i g 39 40 41 42 2 3 2 3 4 - 1 1 2 4 3 5 8 S r from ^ o X 1 1 o ji 3\r hi » I 45 oz. J jg 36 39 i 4 ! — 3 j 1 3 1 2 2 4 6 2 6 Si 31 oz. f c >• ! 45 46 47 48 6 2 2 4 8 10 6 8 2 1 8 10 11 >C O 00 >O r-H CM rH 04 * § r from ^ g 42 43 44 45 3 6 5 4 6 4 9 1 3 7 13 7 19 20 « f from -\ ^ 3 ' 41 oz. F § *!l to ii <3 v. 47 oz. J «> 49 3 2 2 12 19 c« J 46 OZ. f S 46 2 9 2 12 25 4 4 5 13 26 ° i *° I 0 47 2 5 7 14 J s 5! 3 3 2 19 27 S I. 53 oz. J ta 48 2 2 2 6 ^ 52 — 5 4 6 15 p 49 1 2 7 10 00 53 54 II 4 3 2 2 4 1 2 1 10 5 4 6 20 11 50 52 53 1 1 1 2 4 4 7 6 9 ( from "i § ,SJ 4802. F| § J to f C Si 56oz. Js§ 57 58 1 4 o 2 7 1C ?ro^ II 54 — 56 i — 2 1 — — 2 — 1 x P 59 60 61 - 1 2 2 3 1 1 ; m -vr j-| J hg (. 65 oz. J j§ Tot. 30 + 72+12 + 77=191 62 — — T i S 63 — — 1 i 1 6q — — 1 ~ i ; Tot. 35 + 78 + 39 + 126 = 278. According to this table, the maximum weight of the adult male brain, in a series of 278 cases, was 65 oz., and the minimum weight 34 oz. In a series of 191 cases, the maximum weight of the adult female brain was 56 oz., and the minimum 31 oz. ; the difference between the extreme weights in the male subject being no less than 31 oz., and in the female 25 oz. By grouping the cases together in the manner indicated by brackets, it is shown that in a very large proportion the weight of the male brain TABLE OF THE WEIGHT OF THE BRAIN. 569 ranges between 46 oz. and 53 oz., and that of the female brain between 41 oz. and 47 oz. The prevailing weights of the adult male and female brain may therefore be said to range between those terms ; and, by taking the mean, an average weight is deduced of 49| oz. for the male, and of 44 oz. for the female brain,— results which correspond closely with the statements generally received. Although many female brains exceed in weight particular male brains, the general fact is sufficiently shown, that the adult male encephalon is heavier than that of the female, — the average difference being from 5 to 6 oz. This general superiority in absolute weight of the male over the female brain has been ascertained to exist at every period of life. In new-born infants the brain was found by Tiedemann to weigh on an average from 14| oz. to 15| oz. in the male, and from 10 oz. to 131 oz. in the female : — a fact of considerable interest in practical midwifery, for it has been shown that difficult labours occur in by far the largest number in the birth of male children . (Simpson, London and Edinburgh Monthly Journal of Medical Science, 1845.) With the above results the observations of Peacock, published in the " Monthly Journ. of Med. Science " for 1847, and further observations by the same author in the " Journ. of the Pathol. Soc." in 1860, in the main agree. The elaborate table compiled by Rudolph Wagner, and published in his " Yorstudien zu einer Wissensch. Morphol. und Physiol. des Menschl. Gehirns," 1860, containing 964 recorded cases in which the weight of the brain had been ascertained, may also be referred to as another recent useful contribution to the knowledge of this subject. In illustration of the variation in the average weight of the brain at different ages the following table is given, deduced from the elaborate researches of Dr. Robert Boyd, in the examination of the brains of 2,086 sane persons of both sexes dying in the St. Marylebone Infirmary, and published in the Philos. Trans, for 1860. The weights are stated in oz. avoird. and decimal fractions of them. Table of the Weight of the Brain of Males and Females at different Ages. PERIODS OF LIFE. MALES. FEMALES. Number weighed. Maximum. EJ 1 Average. Average. 9 | Number weighed. 1 Children prematurely still- born 25 43 42 16 15 46 34 29 27 22 19 59 no J37 119 127 104 24 13.1 22. 15.37 32.75 30.75 36.13 41.25 50.5 49.5 57.25 58.5 57. 60.75 60. 59. 59.5 55.25 53.75 1.31 9.37 6. 10.5 1'>.75 17.75 23.25 30.5 24.5 39.25 36.5 39.25 33.75 33.75 30.5 36.25 37.75 41. 5.6 13.87 11.65 17.42 21.29 27.42 33.25 38.71 40.23 45.96 48.54 47.9 48.2 47.75 47.44 46.4 45.5 45.34 4.62 12.25 10. 15.94 19.76 25.7 29.8 34.97 40.11 40.78 43.94 43.7 43.09 42.81 43.12 42.69 41.27 39.77 1.29 8. 1.75 11 13. 16.37 18. 27.75 34.75 34. 37.5 35.75 33.25 27.5 36.25 32.5 29.25 33.25 9.13 15.12 16. 32.5 34.75 39.13 37. 44.5 £25 • 55.25 53. 52.5 52.5 54. 49.5 48. 18 3i 39 20 25 40 33 29 19 18 16 72 89 106 103 149 148 77 2 Children still-born at full period 4 Under 3 months 5 From 3 to 6 months 6 From 6 to 12 months 7 From 1 to 2 years 8 From 2 to 4 years 9 From 4 to 7 years 10 From 7 to 14 years 11 From 14 to 20 years .. 12 From 20 to 30 years 13 From 30 to 40 years 14 From 40 to 50 years 15 From 50 to 60 years 16 From 60 to 70 years 17 From 70 to 80 years 18 Upwards of 80 years be 1 Persons above 14 years ^.5 > ~ I Persons from 14 to 70 years . . < ) 699 57i 58. 59.12 36.1 35. 47.1 47.7 42.5 43.15 33.1 33.8 52.1 53.15 760 535 Anatomists have differed considerably in their statements as to the period at which the brain attains its full size, and also as to the effect of old age in diminishing the weight of this organ. Soemmerring held that the brain reached its full size as early P P 570 SIZE AND WEIGHT OF THE BRAIN. as the third year ; the Wenzels and Sir W. Hamilton fixed the period about the seventh , and Tiedemann between the seventh and eighth years. Gall and Spurzheim were of opinion that the brain continued to grow until the fortieth year. The observations of Sims, Tiedemann, and Eeid, appear to show that in both sexes the weight of the brain in general increases rapidly up to the seventh year, then more slowly to between sixteen and twenty, and again more slowly to between thirty-one and forty, at which time it reaches its maximum point. Beyond that period there appears a slow but progressive diminution in weight of about 1 oz. during each subsequent decennial period ; thus confirming the opinion that the brain diminishes in advanced life. According to Peacock, the maximum weight of the brain is attained between the ages of twenty and thirty years. The table of Boyd inserted above would appear to show a somewhat earlier period as that at which the maximum is reached in both sexes, and that the period of decline scarcely begins before sixty years. With this result the observations of Huschke, made upon the brains of 359 men and 245 women, in general agree. (" Schadel, Him, und Seele des Menschen und der Thiere, &c.," 1854.) All other circumstances being alike, the size of the brain appears to bear a general relation to the mental power of the individual, — although many instances occur in which this rule is not applicable. The brain of Cuvier weighed upwards of 64 oz., and there are other recorded examples of brains belonging to men of great talent which nearly equalled it in weight. (Emille Rousseau, " Maladie et autopsie de M. G. Cuvier," Lancette Fran§aise, Mai 26, 1832.) On the other hand, the brain in idiots is remark- ably small. In three idiots, whose ages were sixteen, forty, and fifty years, Tiedemann found the weight of their respective brains to be 19| oz., 25f oz., and 22^ oz; and Dr. Sims records the case of a female idiot twelve years old, whose brain weighed 27 oz. Allen Thomson has found the brain of a dwarfish idiot girl seventeen years of age to weigh 18^ oz. after preservation in alcohol. The human brain is found to be absolutely heavier than that of all the lower animals except the elephant and whale. The brain of the elephant, according to Perrault, Moulins, and Sir A. Cooper, weighs between 8 and 10 Ibs. ; whilst that of the whale was found by Rudolphi, in a specimen 75 feet long, to weigh upwards of 5 Ibs. The relative weight of the encephalon to the body is liable to great variation; nevertheless, the facts to be gathered from the tables of Clendinning, Tiedemann, and Reid, furnish this interesting general result. In a series of 81 males, the average proportion between the weight of the brain and that of the body at the ages of twenty years and upwards, was found to be as 1 to 36*5 ; and in a series of 82 females, to be as 1 to 36 '46. In these cases, the deaths were the result of more or less prolonged disease; but in six previously healthy males, who died suddenly from disease or accident, the average proportion was 1 to 40 -8. The proportionate weight of the brain to that of the body is much greater at birth than at any other period of life, being, according to Tiedemann, about 1 to 5'85 in the male, and about 1 to 6 '5 in the female. From the observations already referred to, it further appears that the proportion diminishes gradually up to the tenth year, being then about 1 to 14. From the tenth to the twentieth year, the relative increase of the body is most striking, the ratio of the two being at the end of that period about Ito30. After the twentieth year, the general average of 1 to 36'5 prevails, with a further trifling decrease in advanced life. Viewed in relation to the weight of his body, the brain of man may be stated generally to be heavier than the brains of the lower animals ; but there are some exceptions to the rule, as in the case of certain species of small birds, in the smaller apes, and in some small rodent animals. The attempts hitherto made to measure or estimate the relative proportions of the different convoluted parts of the cerebrum to each other and to the degree of intelli- gence, either more directly or by the cranioscopic methods, have as yet been attended with little success. The more recent researches of Rudolph Wagner, which have been farther prosecuted by his son, hold out some promise when fully carried out to afford more definite results. These researches had for their object to institute an accurate comparison between the brains of certain persons of known intelligence, cultivation, and mental power, and those of persons of an ordinary or lower grade. As examples of brains of men of MEASUREMENT OF THE CONVOLUTIONS. 571 superior intellect, he selected those of Professor Gauss, a well-known mathematician of eminence, and Professor Fuchs, a clinical teacher ; and as examples of brains of ordinary persons, those of a woman of 29 and a workman named Krebs, all of which he examined and measured with scrupulous care. The general result of R. Wagner's researches upon these and other brains may be stated to be as follows. 1st. Although the greatest number of brains belonging to men of superior intellect are found to be heaviest or largest, yet there are so many instances in which the brains of such persons have not surpassed, or have even fallen below the average size of the brains of ordinary persons, that superiority of size cannot in the present state of our knowledge be regarded as a constant accompaniment of superiority of intellect, even when due regard has been paid to the comparative stature and other circumstances of the individuals. 2nd. It would appear that, in the brains of certain persons of superior intellect, the cerebral convolutions have been found more numerous and more deeply divided than in those of persons of ordinary mental endowments and without culti- vation. But numerous exceptional instances are also found of paucity of convolutions coincident with superior intellect, which make it impossible at present to deduce any certain conclusion with respect to the relation between the number or extent of the convolutions and the intellectual manifestations in different persons. The careful measurement of all the convolutions and the intervening grooves in the four brains above mentioned has been carried out by the younger Wagner, and the tables and results of these measurements published by him as an appendix to his father's treatise. (Hermann Wagner, " Maasbestimmuugen der Oberflache des Grossen Gehirns," &c., Cassel und Gb'ttingen, 1864.) The following short table extracted from Hermann Wagner's memoir, and simplified by the omission of small fractions and by the reduction of the measurements from square millimetres to English square inches, may give the reader some idea of the nature of the inquiry. Comparative measurement of the extent of surface of the Convolutions of the Cerebrum and its lobes. Surface of each lobe separately. Free and deep surfaces of Cerebrum. Whole surface of 3 1 1 'a §1 S|| Cerebrum. 2 8 11 •la P, H , mark the depressions in the cranial wall which contain respectively the cerebral hemispheres, the thalarai, the corpora quadrigemina, the cerebellum, an,l the medulla oblongata; in 1, at o, the depression of the eye, and at o', the optic nerve is seen ; in 5, at a u, the primary auditory vesicle ; p, process from the phai'ynx, supposed by llathke to be con- nected with the formation of the pituitary body or hypophysis cerebri ; t, t, middle cranial septum or teutorium. These three vesicles, at first arranged in a straight line, one before the other, soon 576 DEVELOPMENT OF THE CEREBRO-SPINAL AXIS. alter their position, in correspondence with the curving downwards of the cephalic end of the embryo. Thus, at the seventh week there is an angular bend forwards between the hindmost vesicle and the rudimentary spinal cord, the projecting angle (backwards) being named the cervical tuberosity. Another bend, but in the opposite direction, exists between that part of the third vesicle which forms the medulla oblongata, and that which gives rise to the cerebellum. Lastly, a third angle is pro- duced by a bend forwards and downwards in the region of the middle vesicle, from which the corpora quadrigemina are developed, and which forms, at this period, the highest part of the encephalon ; whilst the anterior, or first vesicle, is bent nearly at a right angle downwards. Fig. 391. Fig. 391. — SKETCHES OF THE EARLY FORM OF THE PARTS OF THE CEREBRO- SPINAL Axis IN THE HUMAN EMBRYO (after Tiede- mann). A, at the seventh week, lateral view ; 1, spinal cord ; 2, medulla oblongata ; 3, cerebellum ; 4, mid- dle vesicle or corpora quadrigemina; 5, 6, 7, first vesicle. B, at the ninth week, posterior view ; 1, medulla oblongata ; 2, cerebellum ; 3, corpora quadrigemina ; 4, 5, tha- lami optici and cerebral hemispheres. C and D, lateral and posterior views of the brain of the human embryo at twelve weeks, a, cerebrum ; b, corpora quadrigemina ; c, cere- bellum ; d, medulla oblongata ; the thalami are now covered by the enlarged hemispheres. E, posterior view of the same brain dissected to show the deeper parts. 1, medulla oblongata ; 2, cerebellum ; 3, cor- pora quadrigemina ; 4, thalami optici ; 5, the hemisphere turned aside ; 6, the corpus striatum em- bedded in the hemisphere ; 7, the commencement of the corpus cal- losum. F, the inner side of the right half of the same brain sepa- rated by a vertical median section, showing the central or ventricular cavity. 1, 2, the spinal cord and medulla oblongata, still hollow ; 3, bend at which the pons Varolii is formed ; 4, cerebellum ; 5, lamina (superior cerebellar peduncles) passing up to the corpora quadrigemina ; 6, crura cerebri ; 7, corpora quadrigemina, still hollow ; 8, third ventricle ; 9, infundibulum ; 10, thata- mus, now solid ; 11, optic nerve ; 12, cleft leading into the lateral ventricle ; 13, com- mencing corpus callosum. F At an early period of the development of the brain, the anterior primary vesicle „ undergoes a peculiar change, by which two sets of parts are originated, the first of which corresponds to the cerebral hemispheres, the second to the thalami optici ; the middle vesicle, remaining single, gives rise to the corpora quadrigemina ; and the posterior vesicle, like the first, but at a somewhat later period, serves as the basis of the rudiments of two parts, viz., the cerebellum and the medulla oblongata. Thus, out of the three primary vesicles five fundamental parts of the encephalon are formed. The following tabular statement may serve as a synoptical view of the relation PARTS DERIVED FROM PRIMARY CEREBRAL VESICLES. 577 subsisting between the primary encephalic vesicles, the five fundamental parts, and the principal permanent structures of the brain : — • ( Cerebral Hemispheres, Corpus Callosum, /•I. Prosencephalon. * I Corpora Striata, Fornix, Lateral Yen- I. Anterior primary Vesicle J ' tricles' Olfa'tory nerve. U Diencephalon. II. Middle primary Vesicle, 3. Mesencephalon. . ,-, , , ( Cerebellum, Pons Varolii, anterior part of f 4- Epencephalon. J th(J Fom^ Ventricle> III. Posterior primary Vesicle, •< I , ,, . , . ( Medulla Oblongata, Fourth Ventricle, Au- lo. Metencephalon. { ditory nerve * At a later period of development, the anterior part of the first vesicle, which, as stated above, represents the cerebral hemispheres, increases greatly in size upwards and backwards, and gradually covers the parts situated behind it ; first the thalami, then the corpora quadrigemina, and lastly the cerebellum. On laying open the rudimentary encephalon, two tracts of nervous matter are seen to be prolonged upwards from the spinal cord upon the floor of the cephalic vesicles ; these tracts, which are doubtless connected with the anterior and lateral parts of the cord, are the rudiments of the crura cerebri and corresponding columns of the medulla oblongata. FARTHER DEVELOPMENT OF THE PRIMARY VESICLES.— The third vesicle. — The poste- rior portion of this vesicle, corresponding with the medulla oblongata, is never closed above by nervous matter. The open part of the medullary tube constitutes the'floor of. the fourth ventricle, which communicates below with the canal of the spinal cord, at the place where the calamus scriptorius is eventually formed. The three constituent parts of the medulla oblongata begin to be distinguished about the third month ; first the restiform bodies, which are connected with the commencing cerebellum, and afterwards the anterior pyramids and olives. The anterior pyramids become prominent on the surface and distinctly denned in the fifth month ; and by this time also their decussation is evident. The olivary fasciculi are early distin- guishable, but the proper olivary body, or tubercle, does not appear till about the sixth month. The fasciolae, cinerece of the fourth ventricle can be seen at the fourth or fifth month, but the white strice not until after birth. The anterior part of the third vesicle is soon closed above by nervous substance, and forms the commencing cerebellum. This part exists about the end of the second month, as a delicate medullary lamina, forming an arch behind the corpora quadri- gemina across the widely open primitive medullary tube. According to Bischoff, the cerebellum does not commence, as was previously sup- posed, by two lateral plates which grow up and meet each other in the middle line ; but a continuous deposit of nervous substance takes place across this part of the medullary tube, and closes it in at once. This layer of nervous matter, which is soon connected with the corpora restiformia, or inferior peduncles, increases gradually up to the fourth month, at which time there may be seen on its under surface the commencing corpus dentatum. In the fifth month a division into five lobes has taken place ; at the sixth, these lobes send out folia, which are at first simple, but afterwards become subdivided. Moreover, the hemispheres of the cerebellum are now relatively larger than its median portion, or worm. In the seventh month the organ is more complete, and the flocculus and posterior velum, with the other parts of the inferior vermiform process, are now distinguishable, except the amygdala, which are later in their appearance. Of the peduncles of the cerebellum, the inferior pair (corpora restiformia) are the first seen — viz., about the third month ; the middle peduncles are perceptible in the fourth month ; and at the fifth, the superior peduncles and the Vieussenian valve. * This and the four following terms are adopted as applicable to the principal secondary divisions of the primordial medullary tube, and as corresponding to the commonly received names of the German embryologists, viz., Vorderhirn, Zwischenhirn, Mittelhirn, Hinter- hirn, and Nachhirn ; or their less used English translations, viz., forebrain, interbrain, midbrain, hindbrain, and afterbrain. 578 DEVELOPMENT OF THE CEREBRO-SPINAL AXIS. The pons Varolii is formed, as it were, by the fibres from the hemispheres of the cerebellum embracing the pyramidal and olivary fasciculi of the medulla oblongata. According to Baer, the bend which takes place at this part of the encephalon thrusts down a mass of nervous substance before any fibres can be seen ; and in this substance transverse fibres, continuous with those of the cerebellum, are after- wards developed. From its relation to the cerebellar hemispheres the pon.s keeps pace with them in its growth ; and, in conformity with this relation, its transverse fibres are few, or entirely wanting, in those animals in which there is a corresponding deficiency or absence of the lateral parts of the cerebellum. Fig. 392. Fig. 392 A. — BRAIN AND SPINAL CORD EXPOSED FROM BEHIND IN ^ A FOSTUS OF THREE MONTHS (from Kolliker). h, the hemispheres ; m, the mesencephalic vesicle or corpora quadrigemina ; c, the cerebellum ; below this are the medulla oblongata, mo, and fourth ventricle, with remains of the membrana obturatoria. The spinal cord, s, extends to the lower end of the sacral canal and presents the brachial and crural enlargements. Fig. 392 B. — UPPER VIEW OF THE BRAIN OF A THREE MONTHS' FffiTUS, IN WHICH THE HEMISPHERES HAVE BEEN DIVIDED AND TURNED ASIDE, AND THE VESICLE OF THE MESENCEPHALON (CoR- PORA QDABRIGEMINA) OPENED (from Kolliker). /, anterior part of the great arch of the hemispheres over the cerebral fissure ; f, posterior part descending into the cornu am- monis ; cs, corpus striatum ; th, thalaraus opticus ; m, in the floor of the opened vesicle of the mesencephalon, which is still hollow. The second, or middle vesicle. — The corpora quadrigemina are formed in the upper part of the middle cephalic vesicle ; the hollow in the interior of which communicates with those of the first and third vesicles. The corpora quadrigemina, in the early condition of the human embryo, are of great propor- tionate volume, in harmony with what is seen in the lower vertebrata : but subsequently they do not grow so fast as the anterior parts of the encephalon, and are therefore soon overlaid by the cerebral hemispheres, which at the sixth month cover them in completely. Moreover, they become gradually solid by the deposition of matter within them ; and as, in the meantime, the cerebral peduncles are increasing rapidly in size in the floor of this middle cephalic vesicle, the cavity in its interior is quickly filled up, with the exception of the narrow passage named the Sylvian aqueduct. The fillet is distinguish- able in the fourth month. The corpora quadrigemina of the two sides are not marked off from each other by a vertical median groove until about the sixth month ; and the trans- verse depression separating the anterior and posterior pairs' is first seen about the seventh month of intra-uterine life. The first, or anterior vesicle. — This vesicle, very soon after its formation, exhibits two lateral outgrowths— the optic vesicles, — destined to form the fundamental parts of the organs of vision. Each of these soon becomes separated from the parent vesicle by a constricted part, which forms the optic nerve and tract. The first vesicle has usually been described as dividing into two portions — viz., a posterior, which is developed into the optic thalami and third ventricle, and an anterior, which forms the principal mass of the cerebral hemispheres, including the corpora striata. Reichert, however, has pointed out that the hemispheres and corpora striata are developed from the sides of the fore part of the vesicle, and become distinguished from it by a constriction similarly as the optic vesicles had previously been, and that there is left between the hemisphere-vesicles of opposite sides a wedge-shaped interval, which forms the third ventricle. He points out that the terminal extremity of the cerebro-spinal tube is at the tip of this wedge, and is placed immediately in front of the optic commissure, at the lamina cinerea ; and that therefore the infundibulum is not that PINEAL GLAND.— OPTIC TEAL AMI. 579 Fig. 393. extremity, as had been previously supposed by Baer, but is an expansion of the vesicle downwards, in similar fashion as there is an expansion of it upwards in the region of the pineal body. The pituitary body was asserted by Rathke to be derived from a prolongation upwards of the mucous membrane of the pharynx into the base of the skull between the trabeculse. It appears, however, from the researches of Reichert and Bidder, that the base of the skull is never imperfect in this region. Reichert suggested that the pituitary body might be derived from the extremity of the chorda dorsalis, but is now rather inclined to think that it is a development of the pia mater. Fig. 393. — BRAIN AND SPINAL CORD OP A FOSTUS OF POUR MONTHS, SEEN FROM BEHIND (from Kolliker). k, hemispheres of the cerebrum ; m, corpora quadrigemina or mesencephalon ; c, cerebellum ; m o, medulla oblongata, the fourth ventricle being overlapped by the cerebellum j s, s, the spiual cord with its brachial and crural enlargements. The pineal gland, according to Baer, is developed from the back part of the thalami, where those bodies continue joined together ; but it is suggested by Bischoff that its development may be rather connected with the pia mater. It was not seen by Tiedemann until the fourth month ; sub- sequently its growth is very slow ; and it at first contains no gritty deposit : this, however, was found by Sb'mmerring at birth. The two optic thalami, formed from the posterior part of the anterior vesicle, consist at first of a single hollow sac of nervous matter, the cavity of which communicates in front with the interior of the commencing cerebral hemispheres, and behind with that of the middle cephalic vesicle (corpora quadrigemina). Soon, however, by means of a deposit taking place in their interior Fig. 394. Fig. 394.— SEMIDIAGRAMMATIC VIEWS OP THE INNER SURFACE OP THE RIGHT CEREBRAL HEMISPHERE OP THE FCETAL BKAIN AT VARIOUS STAGES OP DEVELOPMENT (from Schmidt). 1, 2, and 3, are from foetuses of the respective ages of eight, ten, and sixteen weeks ; 4, from a foetus of six months, a, lamina terminalis or part of the first primary vesicle which adheres to the sella turcica ; 6, section of the cerebral peduncle as it passes into the thalamus and corpus striatum ; the arched line which surrounds this bounds the great cerebral fissure ; c, anterior part of the fornix and the septum lucidum ; d, inner part of the arch of the cerebrum, afterwards the hippocampus major and posterior part of the fornix ; e, corpus callosum, very short in 3, elongated backwards in 4 ; in 4, /, the superior marginal convolution; /', fronto-parietal fissure ; g, gyrus fornicatus ; p', the internal vertical fissure descending to meet the fissure of the hippocampus ; I, olfactory bulb ; F, P, 0, T, frontal, parietal, occipital and temporal lobes. 580 DEVELOPMENT OF THE CEREBRO-SPINAL AXIS. behind, below, and at the sides, the thalami become solid, and at the same time a cleft or fissure appears between them above, and penetrates down to the internal cavity, which continues open at the back part opposite the entrance of the Sylvian aqueduct. This cleft or fissure is the third ventricle. Behind, the two thalami continue united by the posterior commissure, which is distinguishable about the end of the third month, and also by the peduncles of the pineal gland. The soft commissure could not be detected by Tiedemann until the ninth month ; but its apparent absence at earlier dates may perhaps be attributed to the effects of laceration. At an early period the optic tracts may be recognised as hollow prolongations from the outer part of the wall of the thalami while they are still vesicular. At the fourth month these tracts are distinctly formed. The hemisphere-vesicle becomes divisible into two parts : one of these is the part which from the interior appears as the corpus striatum, and from the exterior as the island of Reil, or central lobe; the other forms the expanded or covering portion of the hemisphere, and is designated by Reichert the mantle. The aperture existing at the constricted neck of the hemisphere vesicle, Schmidt and Reichert have recognised as the foramen of Monro. The corpora striata, it will be observed, have a very different origin from the optic thalami ; for, while the optic thalami are formed by thickening of the circumferential wall of a part of the first cerebral vesicle, and thus correspond in their origin with all the parts of the encephalon behind them, which are likewise derived from portions of the cerebro-spinal tube, the corpora striata appear as thickenings of the floor of the hemisphere-vesicles, which are lateral offshoots from the original cerebro- spinal tube. On this account, Reichert considers the brain primarily divisible into the stem, which comprises the whole encephalon forwards to the tsenia semicircularis, and the hemisphere-vesicles, which include the corpora striata and hemispheres. The cerebral hemispheres enlarging, and having their walls increased in thickness form, during the fourth month (Tiedemann), two smooth shell-like lamellee, which include the cavities afterwards named the lateral ventricles, and the parts contained within them. Following out the subsequent changes affecting the exterior of the cerebral hemispheres, it is found that about the fourth month the first traces of some of the convolutions appear, the intermediate sulci commencing only as very slight Fig. 395. — THE SURFACE OF THE F', inter- nal vertical fissure ; Ti, hippo- campal fissure ; g, gyrus forni- catus ; c, c, corpus callosum ; s, septum lucidum ; f, placed between the middle commissure and the foramen of Monro ; v, in the upper part of the third ventricle immediately below the velum interpositum and for- nix : v', in the back part of the third ventricle below the pineal gland, and pointing by a line to the aqueduct of Sylvius ; v", in the lower part of the third ventricle above the infundibulum ; r, recessus pinealis passing backwards from the tela choroidea; p v, pons Varolii; Ce, cerebellum. MEMBRANES OF THE ENCEPHALON. It is remarked by Bischoff, that the pia mater and arachnoid are formed by the separation of the outer layer of the primitive cephalic mass ; and thus that the pia mater does not send inwards processes into the fissures or sulci, nor into the ventri- cular cavities ; but that every part of this vascular membrane, including the choroid plexuses and velum interpositum, is formed in its proper position in connection Avith the nervous matter. The dura mater, on the other hand, is developed from the inner surface of the dorsal plates. 582 THE CRANIAL NERVES. The pia mater and dura mater have both been detected about the seventh or eighth week, at which period the tentorium cerebelli exists. At the third month the falx cerebri, with the longitudinal and lateral sinuses, are perceptible; and the choroid plexuses of both the lateral and fourth ventricles are distinguishable. No trace of arachnoid, however, can be seen until the fifth month. II. THE CEREBRO-SPINAL NERVES. The nerves directly connected with the great cerebro-spinal centre constitute a series of symmetrical pairs, the number of which has been variously estimated from forty to forty- three. Of these nerves, when esti- mated at the smaller number, nine issue from the cranium through different foramina or apertures in its base, and are thence strictly named cranial. The teuth nerve passes out between the occipital bone and the first vertebra, and the remaining thirty nerves all issue below the corresponding vertebral pieces of the spine. To the whole series of thirty-one nerves the name of spinal is usually given. A.— CRANIAL NERVES. The cranial nerve?, besides being named numerically, according to the relative position of the apertures for their exit from the cranium, have likewise been distinguished by other names, according to the place or mode of their distribution, and according to their functions or other circum- stances. The number of the cranial nerves has been variously stated as nine or as twelve by different anatomists ; the difference consisting mainly in this, that, under one system, the nerves which enter the internal auditory meatus, and those which pass through the jugular foramen, are in each case considered a single pair (seventh and eighth) divisible into parts ; while under another system each of the nerves is held to constitute a distinct pair. The following table presents a synoptical view of the cranial nerves under these two modes of enumeration, as in the respective systems of Willis and of Sommerring. Olfactory nerves. Optic. Oculo-motor. Pathetic or trochlear. Trifacial or trigeminal. Abducent ocular. Facial motor. Auditory. Glosso-pharyngeal. Pneumo-gastric. Spinal accessory. Hypoglossal or lingual motor. The arrangement of Sommerring is the preferable one, as being the simplest and most natural ; for each of the parts included in the seventh and eighth pairs of Willis is really a distinct nerve. But as the plan of Willis is still in more general use, it will most conveniently be followed here. The cranial nerves will therefore, when not otherwise designated, be referred to as consisting of nine pairs. * Willis described the glosso-pharyngeal nerve as a branch of the vagus, and included the suboccipital nerve as a tenth among the cranial nerves. WILLIS* SCEMMERIUNQ. First pair of nerves First pair of nerves Second „ Second } , Third Third 1 • Fourth Fourth > • Fifth „ Fifth Sixth „ Sixth i • ( nervusdurus Seventh 1 • Seventh w | n< mollis . Eighth > . in. vagus ( Ninth , . \ Tenth t . accessorius. Eleventh , . Ninth „ Twelfth > • ORIGIN OF THE "CRANIAL NERVES. £83 CONNECTIONS OF THE CRANIAL NERVES WITH THE ENCEPHALON. The roots of the cranial nerves may be traced for some depth into the substance of the encephalon, a circumstance which has led to the distinction of the deep or real origin, and the superficial or apparent origin, by which latter is understood the place at which the nerve appears to be attached to the surface of the encephalon. The superficial origin of these nerves is quite obvious, but their deeper connection is, in most cases, still a matter of some uncertainty. Fig. 397.— VIEW FROM BELOW OF THE CONNEC- TION OF THE PRINCIPAL NERVES WITH THE BRAIN. The full description of this figure will be found at p. 538. The following references apply to the roots of the nerves : I', the right olfactory tract divided near its middle ; II, the left optic nerve springing from the com- missure which is con- cealed by the pituitary body ; II', the right optic tract; the left tract is seen passing back into i and e, the internal and external corpora genicu- lata ; III, the left oculo- motor nerve ; IV, the trochlear ; V, V, the large roots of the tri- facial nerves ; + + , the lesser roots, the -r of the right side is placed on the Grasserian ganglion ; 1, the ophthalmic ; 2, the superior maxillary, and 3, the inferior maxillary nerves ; VI, the left ab- ducent nerve ; VII, a, &, the facial and auditory nerves ; a, VIII, 6, the glosso-pharyngeal, pneu- mo -gastric, and spinal ac- cessory nerves ; IX, the right hypoglossal nerve ; at o, on the left side, the rootlets are seen cut- short ; C I, the left sub- occipital or first cervical nerve. Fig. 397. Ci cL ca 1. The first or olfactory nerve, as it is usually described, small in man in comparison with animals, lies on the under surface of the anterior lobe of the cerebrum to the outer side of the longitudinal median fissure, lodged in a sulcus between two straight convolutions. Unlike other nerves, it consists of a large proportion of grey matter mixed with white fibres, and indeed 584 THE CRANIAL NERVES. agrees closely in structure with the cerebral substance. It swells into an oval enlargement, the olfactory bulb, in front, which also contains much grey matter, and from this part small soft nerves descend through the cribriform plate into the nose. When traced backwards, it is found to be spread out and attached behind to the under surface of the anterior lobe by means of three roots, named external, middle, and internal, which pass in different directions. The bulbous part is therefore rather to be regarded as an olfactory lobe of the cerebrum than as a part of a true nerve, while the white part prolonged backwards into the brain, together with its so-called roots, may be termed the olfactory tract. The external or long root consists of a band of medullary fibres, which passes, in the form of a white streak, outwards and backwards along the anterior margin of the perforated space, towards the posterior border of the Sylvian fissure, where it may be followed into the substance of the cere- brum. Its further connections are doubtful, but it has been stated that its fibres have been traced to the following parts, viz., the convolutions of the island of Reil, the anterior commissure, and the superficial layer of the optic thalamus (Valentin). The middle or grey root is of a pyramidal shape, and consists of grey matter on the surface, which is prolonged from the adjacent part of the anterior lobe and perforated space. Within it there are white fibres, which have been traced to the corpus striatum. The internal root (short root, Scarpa), which cannot always be demon- strated, is composed of white fibres which may be traced from the inner and posterior part of the anterior lobe, where they are said by Foville to be connected with the longitudinal fibres of the gyrus fornicatus. The question whether the olfactory bulbs ought to be considered as nerves or as cerebral lobes is, if tested by reference to the history of development, not so simple as might at first appear. It is in favour of their being regarded as lobes, that in the lower vertebrate animals the olfactory bulbs are generally recognised by com- parative anatomists as additional encephalic lobes, and that in most mammals they are much larger proportionally than in man, and frequently contain a cavity or ventricle in their interior, and further that in their minute structure they nearly agree with the cerebrum ; but, as it is known that in the first development of the eye the peripheral part or retina, as well as the rest of the optic nerve, is originally formed by the extension of a hollow vesicle from the first foetal encephalic compart- ment, so in the case of the olfactory nerve, although the peripheral or distributed part is of separate origin from the olfactory bulb, the latter part is comparable in its origin with the optic vesicle. 2. The second pair or optic nerves of the two sides meet each other at the optic commissure (chiasma), where they partially decussate. From this point they may be traced backwards round the crura cerebri, under the name of the optic tracts. Each optic tract aiises from the optic thalamus, the corpora quadri- gemina, and the corpora geniculata. As it leaves the under part of the thalamus, it makes a sudden bend forwards and then runs obliquely across the under surface of the cerebral peduncle, in the form of a flattened band, which is attached by its anterior surface to the peduncle ; after this, becoming more nearly cylindrical, it adheres to the tuber cinereum, from which and, as stated by Yicq-d'Azyr, from the lamina cinerea it is said to receive an accession of fibres, and thus reaches the optic commissure. In the commissure the nerve-fibres of the two sides undergo a partial de- cussation. The outer fibres of each tract continue onwards to the eye of the ROOTS OF THE CEAXIAL NERVES.— OPTIC. 585 same side : the inner fibres cross over to the opposite side ; and fibres have been described as running from one optic tract to the other along the posterior part of the commissure, while others pass between the two optic nerves in its anterior part (Mayo). In front of the commissure, the nerve enters the foramen opticum, receiving a sheath from the dura mater and acquiring greater firmness. Fig. 398. Fig. 398. — LATERAL VIEW OF THE CONNECTION OP THE PRINCIPAL NERVES WITH THE BRAIN. The full description of this figure will be found at p. 553. The following references apply to the roots of the nerves ; I, the right olfactory tract cut near its middle ; II, the optic nerves immediately in front of the commissure ; the right optic tract is seen passing back to the thalamus (Th\ corpora geniculata (i, e,), and corpora quadrigemina (5) ; III, the right oculo-motor nerve ; IV, the trochlear nerve rising at v, from near the valve of Vieussens ; V, the trifacial nerve ; VI, the abducent ocular ; a, VII, &, the facial and auditory nerves, and between them the pars intermedia ; a, VIII, b, the roots of the glosso-pharyngeal, pneu mo-gastric, and spinal accessory nerves ; IX, the hypoglossal nerve ; C I, the separate anterior and posterior roots of the suboccipital or first cervical The fibres of origin of the optic tract from the thalamus are derived partly from the superficial stratum and partly from the interior of that body. According to Foville, this tract is also connected with the tsenia semicircularis, and with the termination of the gyrus fornicatus ; and he states further, that where the optic tract turns round the back of the thalamus and the cerebral peduncle it receives other delicate fibres, which descend from the grey matter of those parts. — (Op. cit. p. 514.) Q Q 586 THE CRANIAL NERVES. 3. The third pair of nerves (motores oculorum) have their apparent or superficial origin from the inner surface of the crura cerebri in the inter- peduncular space, immediately in front of the pons. Each nerve consists of a number of funiculi which arise in an oblique line from the surface. The deeper fibres of origin, when followed into the cms, are found to diverge in its substance, some being traced to the locus niger, others running down- wards in the pons among its longitudinal fibres, and others turning upwards to be connected with the corpora quadrigemina and Vieussenian valve. According to Stilling, with whom Kolliker agrees, the major part of the fibres arise from a grey nucleus in the floor of the Sylvian aqueduct, close to the origin of some fibres of the fourth nerve. 4. The fourth pair, pathetic or trochlear nerves, the smallest of those which are derived from the brain, are seen at the outer side of the crura cerebri immediately before the pons. Each nerve may be traced backwards round the peduncle to a place below the corpora quadrigemina, where it arises from the upper part of the valve of Vieussens. Kolliker states that, under the corpora quadrigemina, the fibres of origin are divided into two bundles ; the anterior being traceable through the lateral wall of the aqueduct of Sylvius to its floor, where it arises from a grey nucleus close to the middle line ; the posterior bundle being derived from a grey nucleus in the floor of the fourth ventricle, close to the origin of the fifth nerve. The roots of the nerves of opposite sides are connected together across the middle line in the form of a white band or commissure in the substance of the velum. 5. The fifth pair of nerves, par trigeminum, trifacial nerves, take their superficial origin from the side of the pons Varolii, where the transverse fibres of the latter are prolonged into the middle crus cerebelli, considerably nearer to the upper than to the lower border of the pons. The fifth nerve consists of a larger or sensory, and a smaller or motor root. The smaller root is at first concealed by the larger, and is placed a little higher up, there being often two or three cross fibres of the pons between them. On separating the two roots, the lesser one is seen to consist of a very few funiculi. In the larger root the funiculi are numerous, amounting sometimes to nearly a hundred. Deep origin. — The greater root runs behind the transverse fibres of the pons towards the lateral part of the medulla oblongata at the back of the olivary body. Several anatomists trace it into the floor of the fourth ventricle, between the fasciculi teretes and the restiform bodies. By some it is considered to be continuous with the fasci- culi teretes and lateral columns of the cord, whilst others connect it with the grey mass which is regarded by Stilling as the nucleus of the glosso-pharyngeal nerve. The motor root was supposed by Bell to descend to the pyramidal body, and Retzius believes that he has confirmed that opinion by dissection : but it would appear that the deep connection of this root is not yet known with certainty. According to Stilling the fibres pass through the pons to the floor of the fourth ventricle, and have their origin in its grey matter. According to Foville, some of the fibres of the sensory root of the fifth nerve are connected with transverse fibres in the pons, whilst others spread out on the surface of the middle peduncle of the cerebellum, and enter that part of the encephalon beneath the folia.— (Op. cit. p. 506.) 6. The sixth nerve (abducens), motor oculi externus, takes its apparent origin from between the pyramidal body and the pons Varolii by means of a larger and a smaller bundle. It is connected with the pyramid, and to a small extent with the pons also. Philipeaux and Vulpian, with whom ROOTS OF THE CRANIAL NERVES. 687 Kolliker concurs, state that the fibres may be traced more deeply to the floor of the fourth ventricle. 7. The seventh pair of nerves appear on each side at the posterior margin of the pons, between the middle and inferior peduncles of the cerebellum, and nearly in a line with the place of attachment of the fifth nerve. Deep origins. — The portio dura or facial nerve, placed a little nearer to the middle line than the portio mollis, may be traced to the medulla oblongata between the resti- form and olivary fasciculi, with both of which it is said to be connected. Some of its fibres are derived from the pons. Philipeaux and Vulpian affirm that the fibres arise from the outer wall of the fourth ventricle, and that many of them decussate in its floor. Connected with the portio dura, and intermediate between it and the portio mollis, is a smaller white funiculus, first described by Wrisberg (portio inter duram et mollein). The roots of this accessory or intermediate portion are connected deeply with the lateral column of the cord. The portio mollis, or auditory nerve, rises from the floor of the fourth ventricle, at the back of the medulla oblongata, in which situation, as already described, trans- verse white striae are seen, which form the commencement of the nerve. These roots are connected with the grey matter, and some appear to come out of the median fissure. The nerve then turns round the restiform body, and becomes applied to the lower border of the pons, receiving accessions from the former of those parts, and according to some authors from the latter also. Eoville says that the roots of the portio mollis are also connected by a thin layer on the under surface of the middle peduncle with the cortical substance of the cere- bellum ; also, with the small lobule named the flocculus ; and with the grey matter at the borders of the calamus scriptorius. 8. The eighth nerve consists of three distinct portions. The uppermost portion is the glosso-pharyngeal nerve ; next to this, and lower down, is the par vagum or pneumo-gastric nerve consisting of a larger number of cords. The roots of both these nerves are attached superficially to the fore part of the restiform. body. Still lower, is the spinal accessory nerve, which, ascending from the side of the spinal cord, enters the skull by the foramen magnum, and is associated with the pneumo-gastric nerve as it passes out through the foramen lacerum. The accessory nerve arises within the spinal canal from the lateral column of the cord behind its middle, by a series of slender roots, which commence as low down as the fifth or sixth cervical nerve. The nerve passes upwards between the posterior roots of the cervical nerves and the ligamentum deiiticulatuin, — the several funiculi of origin successively joining it as it ascends. On entering the skull, it receives funiculi from the side of the medulla oblongata. These three portions of the eighth pair are connected deeply with grey nuclei within the cord and medulla oblongata, as already described (see p. 521 ). 9. The ninth nerve (hypoglossal) arises, in a line continuous with that of the anterior roots of the spinal nerves, by scattered funiculi from the furrow between the olivary body and the anterior pyramid. The roots of the ninth nerve are traced by Stilling to one of the grey nuclei already described in the medulla oblongata, and they are said by Kolliker to undergo partial decussation in the floor of the fourth ventricle. DISTRIBUTION OF THE CRANIAL NERVES. Mode of exit from the cranium. — Each of the cranial nerves issues at first from the cranial cavity through a foramen or tubular prolongation of the dura mater : some of these nerves or their main divisions are contained Q Q 2 588 THE CRANIAL NERVES. in distinct foramina of the cranium, others are grouped together in one foramen. The numerous small olfactory nerves descend into the nose through the cribriform plate of the ethmoid bone ; the optic nerve pierces the root of the lesser wing of the sphenoid bone ; the third, fourth, and sixth nerves, with the ophthalmic division of the fifth nerve, pass through the Fig. 399. Fig. 399. — INTERNAL VIEW OF THE B/SE OF THE SKULL, SHOWING THE PLACES OF EXIT OF THE CKANIAL NERVES. The dura mater is left in great part within the base of the skull ; the tentoriuin is removed and the venous sinuses are opened. Ou the left side a small portion of the roof of the orbit has been removed to show the relation of certain nerves at the cavernous sinus and in the sphenoidal fissure. The roots of the several cranial nerves have been divided at a short distance inside the foramina of the dura mater through which they respectively pass. I, the bulb of the olfactory nerve lying over the cribriform plate of the ethmoid bone ; II, the optic nerves, that of the left side cut short ; III, placed on the pituitary body, indicates the common oculo-motor nerve ; IV, the trochlear nerve ; V, is placed on the left side opposite to the middle of the three divisions of the trigeminus, which, together with the ganglion and greater root, have been exposed by opening up the dura mater ; on the right side the greater root is seen ; VI, placed below the foramen of exit of the abducent ocular ; VII, placed on the upper part of the petrous bone oppo- site the entrance of the facial and auditory nerves into the meatus auditorius internus ; VIII, placed on the petrous bone outside the jugular foramen opposite the place of exit of the three divisions of the eighth pair of nerves ; IX, placed upon the basilar part of the occipital bone in front of the hypoglossal nerve as it passes through the anterior condyloid foramen. On the left side at the cavernous sinus, the third, fourth, and ophthalmic division of the fifth nerves are seen keeping towards the outer side, while the sixth nerve is deeper and close to the internal carotid artery. The explanation of the remaining references in this figure will be found at p. 461. GENERAL DISTRIBUTION. 589 sphenoidal fissure ; the superior maxillary and inferior maxillary divisions of the fifth pass respectively through the foramen rotundum and foramen ovale of the great wing ; the facial and auditory nerves pierce the petrous bone ; the three parts of the eighth pair descend in separate canals of the dura mater through the anterior part of the jugular foramen between the petrous and occipital bones ; and the hypoglossal nerve passes through the anterior condyloid foramen of the occipital bone. General distribution. — The greater number of the cranial nerves are en- tirely confined in their distribution within the limits of the head ; as in the case of the first six pairs and the auditory nerve. Of these, the olfactory, optic, and auditory are restricted to their respective organs of sense ; while the third, fourth, and sixth are exclusively motor nerves in connection with the external and internal muscles of the eyeball and that of the upper eye- lid. In the remaining nerve, the fifth or trifacial, all the fibres derived from the greater root, and connected with the Gasseriau ganglion, are en- tirely sensory in their function, and constitute the whole of the first and second and the greater part of the third division of the nerve : but the last of these divisions has associated with it the fibres of the lesser root, so as to become in some degree a compound nerve. As a nerve of sensa- tion the trifacial occupies in its distribution the greater part of the head superficially and deeply, excepting the interior of the cranium and that part of the scalp which is situated in the region behind a perpendicular line passing through the external auditory meatus. The muscular distribution of the inferior division of the fifth nerve is chiefly to the muscles of masti- cation. Of the remaining nerves, the facial and hypoglossal, both exclusively motor in function, are almost entirely cephalic in their distribution ; the facial nerve giving fibres to all the superficial and a few of the deeper muscles of the head and face ; and the ninth or hypoglossal supplying the muscles of the tongue. Of the facial, however, a small branch joins one of the cervical nerves in the platysma myoides ; and of the ninth, the descending branch supplies in part the muscles of the neck which depress the hyoid bone and larynx. Of the three parts of the eighth pair, ranked as cranial nerves in conse- quence of their passing through one of the foramina of the cranium, two have only a very limited distribution in the head, and furnish nerves in much greater proportion to organs situated in the neck and thorax. One of these, the pneurno-gastric, after giving a small branch to the ear-passages, and sup- plying nerves to the larynx and pharynx, the trachea, gullet, the lungs and heart, extends into the abdominal cavity as the principal nerve of the stomach. The other, the spinal accessory, which is partially united with the gloss o-pharyngeal and pneumo-gastric near their origin and thus furnishes some of their motor fibres, is entirely a motor nerve, and is distributed in the steruo-mastoid and trapezius muscles. The glosso-pharyngeal nerve is more strictly confined to the head, supplying branches to the tongue, pharynx, and part of the ear-passages. On the following two pages, Fig. 400 is introduced in illustration of the general view of the distribution above given. In this figure the cranium and orbit have been opened up to the depth of the several foramina through which the nerves pass. The greater part of the lower jaw has also been removed on the left side, and the tongue, pharynx, and larynx are partially in view. The occipital bone has been divided by an incision passing down from the occipital tuberosity and through the condyle to the left of the foramen magnum. The cervical vertebrae have been divided to the left of 590 THE CRANIAL NERVES. the middle, and the sheath of the spinal cord opened so as to expose the roots of the cervical nerves. Fig. 400, A. Fig. 400.— A. SEMIDIAGRAMMATIC VIEW OF A DEEP DISSECTION OP THE CRANIAL NERVES ON THE LEFT SIDE OF THE HEAD (from various authors and from nature). B. EXPLANA- TORY OUTLINE OF THE SAME. ± The roinan numerals from I to IX indicate the roots of the several cranial nerves as they lie in or near their foramina of exit. V, is upon the great root of the fifth with the ganglion in front ; a and b, in connection with VII, indicate respectively the facial and auditory nerves ; a, b, and c, in connection with VIII, point respectively to the glosso- pharyngeal, pneumo -gas trie, and spinal accessory nerves ; C I, the suboccipital or first cervical nerve ; C VIII, the eighth. The branches or distributed parts of the nerves are marked as follows, viz. : — I, frontal branch of the fifth ; 2, lachrymal passing into the gland; 3, nasal passing towards the internal orbitary foramen and giving the long twig to the ciliary ganglion (4') ; 3', external branch of the internal nasal nerve ; 4, lower branch of the third or oculo-motor nerve ; 5, the superior maxillary division of the fifth passing into the infra- orbital canal ; 5', its issue at the infraorbital foramen and distribution as inferior palpebral, lateral nasal, and superior labial nerves (5") ; 6, ganglion of Meckel and Vidian nerve passing back from it ; 6', palatine and other nerves descending from it ; 6", superior petrosal nerve ; 7, posterior superior dental nerves ; 7', placed in the antrum maxillare, which has been opened, points to the anterior superior dental nerves ; 8, inferior maxillary division of the fifth immediately below the foramen ovale ; 8', some of the muscular branches coming from it ; 8 x , the anterior auricular branch cut short, and above it the small pstrosal nerve to join the facial nerve ; 9, buccal and internal ptery- GENERAL DISTRIBUTION. 591 gold ; 10, gustatory nerve ; 10', its distribution to the. side and front of the tongue and to the sublingual glands ; 10", the submaxillavy ganglion connected with the gustatory Fig. 400, B. nerve ; below 10, the chorda tympani passing back from the gustatory to join the facial nerve above 12 ; 11, inferior dental nerve ; 11', the same nerve and part of its dental distri- bution exposed by removal of the jaw ; 11", termination of the same as mental and inferior labial nerves ; 12, the twigs of the facial nerve to the posterior belly of the digastric and to the stylo-byoid muscle immediately after its exit from the stylo-mastoid foramen ; 12', the temporo-facial division of the facial; 12'', the cervico-facial division; 13, the trunk of the glosso-pharyngeal passing round the stylo- pharyngeus muscle after giving pharyngeal and muscular branches; 13', its distribution on the side and back part of the tongue ; 14, the spinal accessory nerve, at the place where it crosses the ninth and gives a com- municating branch to the pneumo-gastric and glosso-pharyngeal nerves ; 14', the same nerve after having passed through the sterno-mastoid muscle uniting with branches from the cervical nerves; 15, ninth nerve; 15', its twig to the thyro-hyoid muscle; 15", its distribution in the muscles of the tongue; 16, descendens noni nerve giving a direct branch to the upper belly of the omo-hyoid muscle, and receiving the com- municating branches 16 x from the cervical nerve; 17, pneumo-gastric nerve; 17', its superior laryngeal branch; 17", external laryngeal twig ; 18, superior cervical ganglion of the sympathetic nerve, uniting with the upper cervical nerves, and giving at 18' the superficial cardiac nerve ; 19, the trunk of the sympathetic ; 19', the middle cervical ganglion, uniting with some of the cervical nerves, and giving 19", the large middle cardiac nerve ; 20, continuation of the sympathetic nerve down the neck ; 21, great occipital nerve ; 22, third occipital. THE CRANIAL XEHVES. OLFACTORY NERVE. The olfactory or first cranial nerve, the special nerve of the sense of smell, is distributed exclusively to the nasal fossae. From the under surface of the olfactory bulb about twenty branches proceed through the holes in the cribriform plate of the ethmoid bone, each invested by tubular prolongations of the membranes of the brain. These tubes of membrane vary in the extent to which they are continued on the branches : the offsets of the dura mater sheathe the filaments, and join the periosteum lining the nose ; those of the pia mater become blended with the neurilemma of the nerves ; and those of the arachnoid re-ascend to the serous lining of the skull. Fig. 401. XII Fig. 401. — DISTRIBUTION OP THE OLFACTORY NKRVES ON THE SEPTUM OF THE NOSE (from Sappey after Hirschfeld and Leveille). § The septum is exposed and the anterior palatine canal opened on the right side. I, placed above, points to the olfactory bulb, and the remaining roman numbers to the roots of the several cranial nerves ; 1, the small olfactory nerves as they pass through the cribriform plate ; 2, internal or septal twig of the nasal branch of the ophthalmic nerve ; 3, naso-palatine nerves. (See Fig. 408 for a view of the distribution of the olfactory nerves on the outer wall of the nasal fossa.) The branches are arranged in three sets. Those of the inner set, lodged for some distance in grooves on the surface of the bone, ramify in the pituitary membrane of the septum ; the outer set extend to the upper two spongy bones and the plane surface of the ethmoid bone in front of these ; and the middle set, which are very short, are confined to the roof of the nose. The distri- bution of the olfactory > nerve is confined to the upper part of the nasal fossa ; none of the branches reach the lower spongy bone. — (See Anatomy of the Nose.) OPTIC NERVE. The optic or second cranial nerve, the nerve of vision, extending from the optic commissure, becomes more cylindrical and firm as it diverges from its fellow and enters the orbit by the optic foramen. Within the orbit it forms a cylindrical trunk, thick and strong, with a uniform surface. On dis- OPTIC NERVE.— THIRD PAIR. •593 section it is seen to consist of a number of separate bundles of nerve fibres, imbedded in tough fibrous tissue prolonged from the dura mater, and per- forated in the centre by the small arteria centralis retinae, which passes into it soon after it enters the orbit. It is surrounded by the recti muscles, and, entering the eyeball posteriorly a little to the inside of its middle, it pierces the sclerotic and choroid coats, and expands in the retina. — (See the Anatomy of the Eye.) It may be mentioned that in many fishes the optic nerves do not unite in a com- missure, but merely cross each to the side opposite to that of its origin ; and that in a number of the same animals, as was first pointed out by Malphighi, the nerve consists of a lamina thrown into complicated longitudinal plications, and surrounded by a sheath. THIRD PAIR OF NERVES. This nerve, the common motor nerve of the eyeball (motorius oculi), gives branches to five of the seven muscles of the orbit, — viz., to the Fig. 402. — VIEW FROM ABOVE Fig. 402. OF THE UPPERMOST NERVES OF THE ORBIT, THE GAS- SERIAN GANGLION, &c. (from Sappey after Hirschfeld and Leveille). | I, the olfactory tract passing forwards into the bulb ; II, the commissure of the optic nerves ; IN, the oculo-motor ; IV, the trochlear nerve; V, the greater root of the fifth nerve, a small portion of the lesser root is seen below it ; VI, the sixth nerve ; VII, facial ; VIII, audi- tory ; IX, glosso-pharyngeal ; X, pneumo-gastric ; XI, spinal accessory ; XII, hypoglossal ; 1, the Gasserian ganglion; 2, ophthalmic nerve ; 3, lachrymal branch ; 4, frontal ; 5, external frontal or supraorbital ; 6, internal frontal ; 7, supra- trochlear branch ; 8, nasal nerve ; 9, infratrochlear branch ; ] 0, internal nasal passing through the internal orbital foramen; 11, anterior deep temporal proceeding from the buccal nerve ; 12, middle deep temporal ; 13, posterior deep temporal arising from the masseteric ; 14, origin of the temporo-auricular ; 15, great superficial petrosal nerve. superior, internal and inferior straight muscles, to the levator palpebrse, and to the inferior oblique muscle. Cylindrical and firm, like the other motor nerves, the third nerve, quitting the investment of the arachnoid membrane, pierces the inner layer of the dura mater close to the posterior clinoid process, and proceeds towards the sphenoidal fissure, lying in the external fibrous boundary of the cavernous sinus. 594 THE CRANIAL NERVES. After receiving one or two delicate filaments from the cavernous plexus of the sympathetic, the third nerve divides near the orbit into two parts, which are continued into that cavity between the heads of the external rectus muscle, and separated one from the other by the nasal branch of the ophthalmic nerve. The upper, the smaller part, is directed inwards over the optic nerve to the superior rectus muscle of the eye and the elevator of the eyelid, to both which muscles it furnishes branches. The lower and larger portion of the nerve separates into three branches ; of these one reaches the inner rectus ; another the lower rectus ; and the third, the longest of the three, runs onwards between the lower and the outer rectus, and terminates below the ball of the eye in the inferior oblique muscle. The last-mentioned branch is connected with the lower part of the lenticular ganglion by a short thick cord, and gives two filaments to the lower rectus muscle. The several branches of the third nerve enter the muscles to which they are distributed on the surface which in each looks towards the eyeball POSITION OP CERTAIN NERVES at the cavernous sinus, and as they enter the orbit. — There are several nerves, besides the third, placed close together at the cavernous sinus, and entering the orbit through the sphenoidal fissure. To avoid repetition hereafter, the relative positions of these nerves may now be described. The nerves thus associated are the third, the fourth, the ophthalmic division of the fifth, and the sixth. At the cavernous sinus. — In the dura mater which bounds the cavernous sinus on the outer side, the third and fourth nerves and the ophthalmic division of the fifth are placed, as regards one another, in their numerical order both from above downwards and from within outwards. The sixth nerve is placed separately from the others close to the carotid artery, on the floor of the sinus and internally to the fifth nerve. Near the sphe- noidal fissure, through which they enter the orbit, the relative position of the nerves is changed, the sixth nerve being here close to the rest, and their number is augmented by the division of the third and the ophthalmic nerves — the former into two, the latter into three parts. In the sphenoidal fissure. — The fourth and the frontal and lachrymal branches of the fifth, which are here higher than the rest, lie on the same level, the fourth being the nearest to the inner side, and enter the orbit above the muscles. The remaining nerves pass between the heads of the outer rectus muscle, in the following relative position to each other ; the upper division of the third highest, the nasal branch of the fifth next, the lower division of the third beneath these, and the sixth lowest of all. FOURTH PAIR OF NERVES. The fourth (nervus trochlearis, n. patheticus) is the smallest of the cranial nerves, and is distributed entirely to the upper oblique muscle of the orbit. From the remoteness of its place of origin, the part of this nerve within the skull is longer than that of any other cranial nerve. It enters an aperture in the free border of the tentorium, outside that for the third nerve, and near the posterior clinoid process. Continuing onwards through the outer wall of the cavernous sinus, the fourth nerve enters the orbit by the sphenoidal fissure, and above the muscles. Its position with reference to other nerves in this part of its course has been already described. FOURTH PAIE. 595 In the orbit, the fourth nerve inclines inwards above the muscles, and enters finally the upper oblique muscle at its orbital surface. While in its fibrous canal in the outer wall of the sinus, the fourth nerve is joined by filaments of the sympathetic, and not unfrequently is blended with the ophthalmic Fig. 403. — VIEW FROM ABOVE OP THE MOTOR NERVES OF THE EYEBALL AND ITS MUSCLES (after Hirsch- feld and Leveille, altered). Fig. 403. The ophthalmic division of the fifth pair has been cut short ; the attachment of the muscles round the optic nerve has been opened up, and the three upper muscles turned towards the inner side, their anterior parts being removed ; a part of the optic nerve is cut away to show the inferior rectus ; and a part of the sclerotic coat and cornea is dissected off showing the iris, zona ciliaris, and choroid coat, with the ciliary nerves. «, the upper part of the internal carotid artery emerging from the cavernous sinus ; 6, the superior oblique muscle ; &', its anterior part passing through the pulley ; c, the levator palpebrse superioris ; d, the superior rectus ; e, the internal rectus ; /, the external rectus; /', its upper tendon turned down ; gr, the inferior rectus j h, insertion of the inferior oblique muscle. II, the commissure of the optic nerve ; II', part of the optic nerve entering the eyeball ; III, the common oculo-motor ; IV, the fourth or trochlear nerve ; V, the greater root of the trigeminus ; V, the smaller or motor root ; VI, the abducent nerve ; 1, the upper division of the third nerve separating from the lower and giving twigs to the levator palpe- brse and superior rectus ; 2, the branches of the lower division supplying the internal and inferior recti muscles ; 3, the long branch of the same nerve proceeding forward to the inferior oblique muscle, and close to the number 3, the short thick branch to the ciliary ganglion : this ganglion is also shown, receiving from behind the slender twig from the nasal nerve, which has been cut short, and giving forwards some of its ciliary nerves, which pierce the sclerotic coat ; 3', marks the termination of some of these nerves in the ciliary muscle and iris after having passed between the sclerotic and choroid coats ; 4, the distribution of the trochlear nerve to the upper surface of the superior oblique muscle ; 6, the abducent nerve passing into the external rectus. division of the fifth. Bidder states that three or more small filaments of this nerve extend in the tentorium as far as the lateral sinus ; and has figured one as joining the sympathetic on the carotid artery. (Neurologische Beobachtungen, Von F. H. Bidder. Dorpat, 1836.) FIFTH PAIR OF NERVES. The fifth, or trifacial nerve (nerv. trigeminus), the largest cranial nerve, is analogous to the spinal nerves, in respect that it consists of a motor and a sensory part, and that the sensory fibres pass through a ganglion while the motor do not. Its sensory division, which is much the larger, imparts common sensibility to the face and the fore part of the head, as well as to the eye, the nose, the ear, and the mouth ; and endows the fore part of the tongue with the powers of both touch and taste. The motor root supplies chiefly the muscles of mastication. 596 THE CRANIAL NERVES. The roots of the fifth nerve, after emerging from the surface of the encephalon, are directed forwards, side by side, to the middle fossa of the skull, through a recess in the dura mater on the summit of the petrous part of the temporal bone. Here the larger root alters in appearance : its Fig- 404. Fig. 404.— GENERAL PLAN OP THE BRANCHES OF THE FIFTH PAIR (after a sketch by Charles Bell), i 1, lesser root of the fifth pair ; 2, greater root passing forwards into the Gasserian gang- lion ; 3, placed on the bone above the ophthal- mic nerve, which is seen dividing into the supra- orbital, lachrymal, and nasal branches, the latter connected with the oph- thalmic ganglion ; 4, placed on the bone close to the foramen rotundum, marks the superior max- illary division, which is connected below with the spheno-palatine ganglion, and passes forwards to the infraorbital foramen ; 5, placed on the bone over the foramen ovale, marks the submaxillary nerve, giving off the anterior auri- cular and muscular bran- ches, and continued by the inferior dental to the lower jaw, and by the gustatory to the tongue ; a, the submaxillary gland, the submaxillary ganglion placed above it in connection with the gustatory nerve ; 6, the chorda tympaui ; 7, the facial nerve issuing from the stylo-rnastoid foramen. fibres diverge a little, become reticulated, and enter the Gasserian ganglion. The smaller root passes inside and beneath the ganglion, without its nerve- fibres being incorporated in any way with it, and joins outside the skull the lowest of the three trunks which issue from the ganglion. The ganglion of the fifth nerve or Gasserian ganglion (ganglion semilunare), occupies a depression on the upper part of the petrous portion of the temporal bone, near the point, and is somewhat crescentic in form, the convexity being turned forwards. On its inner side the ganglion is joined by filaments from the carotid plexus of the sympathetic nerve, and, accord- ing to some anatomists, it furnishes from its back part filaments to the dura mater. From the fore part, or convex border of the Gasserian ganglion, proceed the three large divisions of the nerve. The highest (first or ophthalmic trunk) enters the orbit ; the second, the upper maxillary nerve, is continued forwards to the face, below the orbit ; and the third, the lower maxillary nerve, is distributed chiefly to the external ear, the tongue, the lower teeth, and the muscles of mastication. The first two trunks proceed exclusively from the FIFTH PAIR.-OPHTHALMIC NERVE. 597 ganglion and are entirely sensory, while the third or inferior maxillary trunk, receiving a considerable part from the ganglion, has associated with it also the whole of the fibres of the motor root, and thus distributes both motor and sensory branches. OPHTHALMIC NERVE. The ophthalmic nerve, or first division of the fifth nerve, the smallest of the three offsets from the Gasserian ganglion, is somewhat flattened, about an inch in length, and is directed forwards and upwards to the spheuoidal fissure, where it ends in branches which pass through the orbit to the sur- face of the head and to the nasal fossse. In the skull it is contained in the process of the dura mater bounding externally the cavernous sinus, and is joined by filaments from the cavernous plexus of the sympathetic : according to Arnold, it gives recurrent branches to the tentorium cerebelli. It also frequently communicates by a considerable branch with the fourth nerve. Near the orbit the ophthalmic nerve furnishes from its inner side the nasal branch, and then divides into the frontal and lachrymal branches. These branches are transmitted separately through the sphenoidal fissure, and are continued through the orbit (after supplying some filaments to the eye and the lachrymal gland) to their final distribution in the nose, the eyelids, and the muscles and integument of the forehead. LACHRYMAL BRANCH. The lachrymal branch is external to the frontal at its origin, and is con- tained in a separate tube of dura mater. In the orbit it passes along the outer part, above the muscles, to the outer and upper angle of the cavity. Near the lachrymal gland, the nerve has a connecting filament with the orbital branch of the superior maxillary nerve ; and when in close apposition with the gland, it gives many filaments to that body and to the conjunctiva. Finally, the lachrymal nerve penetrates the palpebral ligament externally, and ends in the upper eyelid, the terminal ramifications being joined by twigs from the facial nerve. In consequence of the junction which occurs between the ophthalmic trunk of the fifth and the fourth nerve, the lachrymal branch sometimes appears to be derived from both these nerves. Swan considers this the usual condition of the lachrymal nerve. (" A Demonstration of the Nerves of the Human Body," page 36. London, 1834.) FRONTAL BRANCH. The frontal branch, the largest division of the ophthalmic, lies, like the preceding nerve, above the muscles in the orbit, being situated between the elevator of the upper eyelid and the periosteum. About midway forwards in the orbit, the nerve divides into two branches, supratrochlear and supra- orbital. a. The supratrochlear branch (internal frontal) is prolonged to the inner angle of the orbit, close to the point at which the pulley of the upper oblique muscle is fixed to the orbit. Here it gives downwards a filament to connect it with the infratrochlear branch of the nasal nerve, and issues from the cavity between the orbicular muscle of the lids and the bone. In this position filaments are distributed to the upper eyelid. The nerve next pierces the 598 THE CRANIAL NERVES. orbicularis palpebrarum and occipito-frontalis muscles, furnishing twigs to these muscles and the corrugator supercilii, and, after ascending on the fore- head, ramifies in the integument. 6. The supraorbital branch (external frontal) passes through the supra- orbital notch to the forehead, and ends in muscular, cutaneous, and peri- cranial branches ; while in the notch it distributes palpebral filaments to the upper eyelid. The muscular branches referred to are comparatively small, and supply the corrugator of the eyebrow, the occipito-frontalis, and the orbicular muscle of the eyelids, joining the facial nerve in the last muscle. The cutaneous branches, among which two (outer and inner) may be noticed as the principal, are placed at first beneath the occipito- frontalis. The outer one, the larger, perforates the tendinous expansion of the muscle, and ramifies in the scalp as far back as the lambdoidal suture. The inner branch reaches the surface sooner than the preceding nerve, and ends in the integument over the parietal bone. The pericranial branches arise from the cutaneous nerve beneath the muscle, and end in the pericranium covering the frontal and parietal bones. Fig. 405. Fig. 405.— NERVES OP THE OR- BIT FKOM THE OUTER SlDE t "&- "$?ifrli (from Sappey after Hirschfeld and Leveilld). f The external rectus muscle has been divided and turned down: 1, the optic nerve; 2, thetrunkof the third nerve; 3, its upper divisioa pasing into the levator palpebrae and superior rectus ; 4, its long lower branch to the inferior oblique muscle ; 5, the sixth or abducent nerve joined by twigs from the sympathetic ; 6, the Gasserian 8 7 10 " -A ganglion ; 7, ophthalmic nerve ; 8, its nasal branch ; 9, the ophthal- mic ganglion ; 10, its short or motor root ; 11, long sensory root from the nasal nerve; 12, sympathetic twig from the carotid plexus ; 13, ciliary nerves passing into the eyeball ; 14, frontal branch of the ophthalmic nerve. NASAL BRANCH. The nasal branch (oculo-nasalis), separating from its parent trunk in the wall of the cavernous sinus, enters the orbit between the heads of the outer rectus. It then inclines inwards over the optic nerve, beneath the elevator of the upper eyelid and the superior rectus muscle, to the inner wall of the orbit, through which it passes by the anterior internal orbital foramen. In this oblique course across the orbit it furnishes a single filament to the ophthalmic ganglion, two or three (long ciliary) directly to the eyeball ; and, at the inner side of the cavity, a considerable branch (infratrochlear), which issues from the orbit at the fore part. On leaving the orbit the nasal nerve is directed transversely inwards to the upper surface of the cribriform plate of the ethmoid bone, and, passing forwards in a groove at its outer edge, within the cranium, descends by a special aperture close to the crista galli at the fore part of the plate to the roof of the nasal fossa, where it divides into two branches, one of which (external or superficial nasal) reaches the integument of the side of the nose, and the other (rainus septi) ramifies in the pituitary membrane. NASAL NERVE.— OPHTHALMIC GANGLION. 599 a. The branch to the ophthalmic ganglion (radix longa ganglii ciliaris), very slender, and about half an inch long, arises generally between the heads of the external rectus ; it lies on the outer side of the optic nerve, and enters the upper and back part of the ophthalmic ganglion, constituting its long root. This small branch is sometimes joined by a filament from the cavernous plexus of the sympathetic, or from the upper branch of the third nerve. b. The long ciliary nerves, two or three in number, are situated on the inner side of the optic nerve ; they join one or more of the nerves from the ophthalmic ganglion (short ciliary), and after perforating the sclerotic coat of the eye, are continued between it and the choroid to the ciliary muscle, the cornea, and the iris. c. The infratrochlear branch runs forwards along the inner side of the orbit below the superior oblique muscle, and receives near the pulley of that muscle a filament of connection from the supratrochlear nerve. The branch is then continued below the pulley to the inner angle of the eye, and ends in filaments which supply the orbicular muscle of the lids, the caruncula, and the lachrymal sac, as well as the integument of the eyelids and side of the nose. In the cavity of the nose the nasal nerve ends by dividing into the following branches. d. The branch to the nasal septum extends to the lower part of the partition between the nasal fossae, supplying the pituitary membrane near the fore part of the septum. e. The superficial branch (externus seu lateralis), descends in a groove on the inner surface of the nasal bone ; and after leaving the nasal cavity between that bone and the lateral cartilage of the nose, it is directed downwards to the tip of the nose, beneath the compressor naris muscle. While within the nasal fossa, this branch gives two or three filaments to the fore part of its outer wall, which extend as far as the lower spongy bone. The cutaneous part is joined by a filament of the facial nerve. Summary. — The first division of the fifth nerve is altogether sensory in function. It furnishes branches to the ball of the eye and the lachrymal gland ; to the mucous membrane of the nose and eyelids ; to the integument of the nose, the upper eyelid, the forehead, and the upper part of the hairy scalp ; and to the muscles a'bove the middle of the circumference of the orbit. Some of the cutaneous and muscular filaments join branches of the facial nerve, and the nerve itself communicates with the sympathetic. OPHTHALMIC GANGLION. There are four small ganglia connected with the divisions of the fifth nerve : the ophthalmic ganglion with the first, Meckel's ganglion with the second, and the otic and submaxillary ganglia with the third. These ganglia, besides receiving branches from the sensory part of the fifth, are each connected with a motor nerve from the third, the fifth, or the facial, and with twigs from the sympathetic ; and the nerves thus joining the ganglia are named their roots. The ophthalmic or lenticular ganglion (gang, semilunare, vel ciliare) serves as a centre for the supply of nerves — motor, sensory, and sympathetic — to the eyeball. It is a small reddish body, situated at the back of the orbit, between the outer rectus muscle and the optic nerve, and generally in contact with the ophthalmic artery ; it is joined behind by branches from the fifth, the third, and the sympathetic nerves ; while from its fore part proceed the ciliary nerves to the eyeball. Union of the ganglion with nerves : its roots. — The posterior border of the ganglion receives three nerves. One of these, the long root, a slender filament from the nasal branch of the ophthalmic trunk, joins the upper part of this border. Another branch, the short rooty much thicker and shorter than the preceding, and sometimes divided into parts, is derived 600 THE CRANIAL NERVES. from the branch of the third nerve to the inferior oblique muscle, and is connected with the lower part of the ganglion. The third root is a very small nerve which emanates from the cavernous plexus of the sympathetic, and reaches the ganglion with the long upper root : these two nerves are sometimes conjoined before reaching the ganglion. Other roots have been assigned to the ganglion. (Valentin, in Miiller's Archiv. for 1840.) Brandies of the ganglion. — From the fore part of the ganglion arise ten or twelve delicate filaments — the short ciliary nerves. These nerves are disposed in two fasciculi, arising from the upper and lower angles of the ganglion, and they run forwards, one set above, the other below the optic nerve, the latter being the more numerous. They are accompanied by fila- ments from the nasal nerve (long ciliary), with which some are joined. Having entered the eyeball by apertures in the back part of the sclerotic coat, the nerves are lodged in grooves on its inner surface ; and at the ciliary muscle, which they pierce (some filaments supplying it and the cornea), they turn inwards and ramify in the iris. SUPERIOR MAXILLARY NERVE. The superior maxillary nerve, or second division of the fifth cranial nerve, is intermediate in size between the ophthalmic and the inferior maxillary trunks. It commences at the middle of the Gasserian ganglion, and, passing hori- zontally forwards, soon leaves the skull by the foramen rotuudum of the sphenoid bone. The nerve then crosses the spheno-maxillary fossa, and enters the infraorbital canal of the upper maxilla, by which it is conducted to the face. After emerging from the infraorbital foramen, it terminates beneath the elevator of the upper lip in branches which spread out to the side of the nose, the eyelid, and the upper lip. Branches. — In the spheno-maxillary fossa a temporo-malar branch ascends from the superior maxillary nerve to the orbit, and two spheno- palatine branches descend to join Meckel's ganglion. Whilst the nerve is in contact with the upper maxilla, it furnishes two posterior dental branches on the tuberosity of the bone, and an anterior dental branch at the fore part. On the ace are the terminal branches already indicated. ORBITAL BRANCH. The orbital or temporo-malar branch, a small cutaneous nerve, enters the orbit by the spheno-maxillary fissure, and divides into two branches (temporal and malar), which pierce the malar bone, and are distributed to the temple and the prominent part of the cheek. a. The temporal branch is contained in an osseous groove or canal in the outer wall of the orbit, and leaves this cavity by a foramen in the malar bone. When about to traverse the bone, it is joined by a communicating filament (in some cases, two filaments) from the lachrymal nerve. The nerve is then inclined upwards in the temporal fossa between the bone and the temporal muscle, perforates the aponeurosis over the muscle an inch above the zygoma, and ends in cutaneous filaments over the temple. The cutaneous ramifications are united with the facial nerve, and sometimes with the superficial temporal nerve of the third division of the fifth. 6. The malar branch lies at first in the loose fat in the lower angle of the orbit, and is continued to the face through a foramen in the fore part of SUPERIOR MAXILLARY NERVE. 601 the malar bone, where it is frequently divided into two filaments. In the prominent part of the cheek this nerve communicates with the facial nerve. Fig. 406. Fig. 406. — SUPERIOR MAXILLARY NERVE AND SOME OF THE ORBITAL NERVES (from Sappey after Hirschfeld and Leveille). 3 1, the Gasserian ganglion ; 2, lachrymal branch of the ophthalmic nerve; 3, trunk of the superior maxillary nerve ; 4, its orbital branch, joining at 5, the palpebral twig of the lachrymal ; 6, origin of its malar twig ; 7, its temporal twig ; 8, spheno-palatine ganglion ; 9, Vidian nerve ; 10, its upper branch or great superficial petrosal nerve proceeding to join the facial nerve (11) ; 12, union of the lower branch of the Vidian nerve with the carotid branch of the sympathetic ; 13, 14, posterior dental nerves ; 15, terminal branches of the infrnorbital nerves ramifying on the side of the nose and upper lip ; 16, a branch of the facial uniting with some of the twigs of the infraorbital. POSTERIOR DENTAL BRANCHES. The posterior dental branches, two in number, are directed downwards and outwards over the back part and tuberosity of the maxillary bone. One of the branches enters a canal in the bone by which it is conducted to the teeth, and gives forwards a communicating filament to the anterior dental nerve. It ends in filaments to the molar teeth and the lining mem- brane of the maxillary sinus, and near the teeth joins a second time with the anterior dental nerve. The anterior of the two branches, lying on the surface of the bone, is distributed to the gums of the upper jaw and to the buccinator muscle. ANTERIOR DENTAL BRANCH. The anterior dental branch, leaving the trunk of the nerve at a varying distance behind its exit from the infraorbital foramen, enters a special canal in front of the antrum of Highmore. In this canal it receives the com- municating filament from the posterior dental nerve, and divides into two branches, which furnish offsets for the front teeth. (a) The inner branch supplies the incisor and canine teeth. Filaments from this nerve enter the lower meatus of the nose, and end in the membrane covering the lower spongy bone. Also above the root of the canine tooth, it unites with a branch of the posterior nasal nerve from Meckel's ganglion, and forms with it a small thickening, 602 THE CRAXIAL NERVES. the ganglion of Bochdalcl, from which branches are described as descending to the alveolar process and gums of the incisor and canine teeth. (See Hyrtl's Lehrbuch, p. 804.) (b) The outer branch gives filaments to the bicuspid teeth, and is connected with the posterior dental nerve. TNFRAORBTTAL BRANCHES. The infraorbital branches, large and numerous, spring from the end of the superior maxillary nerve beneath the elevator muscle of the upper lip, and are divisible into palpebral, nasal, and labial sets. Fig. 407. Fig. 407. — DEEP VIEW OP THE SpnENo-PALATiNE GANGLION, AND ITS CONNECTIONS WITH OTHEK NEKVES, &c. (from Sappey after Hirschfeld and Leveille). f 1, superior maxillary nerve ; 2, posterior superior dental ; 3, second posterior dental branch ; 4, anterior dental ; 5, union of these nerves ; 6, spheno-palatine ganglion ; 7, Vidian nerve ; 8, its great superficial petrosal t ranch ; 9, its carotid branch ; 10, a part of the sixth nerve, receiving twigs from the carotid plexus of the sympathetic ; 11, superior cervical sympathetic ganglion ; 12, its carotid branch ; 13, trunk of the facial nerve near the knee or bend at the hiatus Fallopii : 14, glosso-pharyngeal nerve ; 15, anastomosing branch of Jacobson ; 16, twig uniting it to the sympathetic : 17, filament to the fenestra rotunda ; 18, filament to the Eustachian tube ; 19, filament to the fenestra ovalis ; 20, external deep petrosal nerve uniting with the lesser superficial petrosal ; 21, internal deep petrosal twig uniting with the great superficial petrosal. a. The palpebral branch (there are sometimes two branches) turns upwards to the lower eyelid in a groove or canal of the bone, and supplies the orbicular muscle ; it ends in filaments which are distributed to the eyelid in its entire breadth. At the outer angle of the eyelids this nerve is connected with the facial nerve. b. The nasal branches, directed inwards to the muscles and integument of the side of the nose, communicate with the cutaneous branch of the nasal nerve. c. The labial, the largest of the terminal branches of the upper maxillary nerve, and three or four in number, are continued downwards beneath the proper elevator of the upper lip. Eamifying as they descend, these nerves are distributed to the integument, the mucous membrane of the mouth, the labial glands, and the muscles of the upper lip. Near the orbit the infraorbital branches of the superior maxill try nerve are joined by considerable branches of the facial nerve, the union between the two being named infraorbital plexus. SPHENO-PALAT1NE GANGLION. 603 SPHENO-PALATINE GANGLION". The splieno-palatine ganglion, frequently named Meckel's ganglion, is deeply placed in the spheno-maxillary fossa, close to the spheno-palatine foramen. It receives the two spheno-palatine branches, which descend together from the superior maxillary nerve as it crosses the top of the fossa. It is of a greyish colour, triangular in form, and convex on the outer surface. The grey or ganglionic substance does not involve all the fibres of the spheno-palatiue branches of the upper maxillary nerve, but is placed at the back part, at the point of junction of the sympathetic or deep branch of the Vidian, so that the spheuo-palatine nerves proceeding to the nose snd palate pass to their destination without being incorporated with the gangliouic mass. Branches proceed from the ganglion upwards to the orbit, downwards to the palate, inwards to the nose, and backwards through the Vidian and pterygo-palatine canals. ASCENDING BRANCHES. — There are three or more very small twigs, which reach the orbit by the spheno-maxillary fissure, and are distributed to the periosteum. Bock describes a branch ascending from the ganglion to the sixth nerve; Tiede- mann, one to the lower angle of the ophthalmic ganglion. The filaments described by Hirzel as ascending to the optic nerve, most probably join the ciliary twigs which surround that nerve. DESCENDING BRANCHES. — These are three in number, — the large, the small, and the external palatine nerves, and are continued chiefly from the spheno-palatine branches of the superior maxillary. They are distri- buted to the tonsil, the hard and soft palate, the gums, and the mucous membrane of the nose. a. The larger or anterior palatine nerve descends in the palato-maxillary canal, and divides in the roof of the mouth into branches, which are received into grooves in the hard palate, and extend forwards nearly to the incisor teeth. In the mouth it, supplies the gums, the glandular structure and the mucous membrane of the hard palate, and joins in front with the naso-palatine nerve. When entering its canal, this palatine nerve gives a nasal branch which ramifies on the middle and lower spongy bones ; and a little before leaving the canal, another branch is supplied to the membrane covering the lower spongy bone : these are inferior nasal branches. Opposite the lower spongy bone springs a small branch, which is continued to the soft palate in a separate canal behind the trunk of the nerve. 1). The smaller or posterior palatine branch, arising near the preceding nerve, enters with a small artery the lesser palatine canal, and is conducted to the soft palate, the tonsil, and the uvula. According to Meckel, it supplies the levator palati muscle. c. The external palatine nerve, the smallest of the series, courses between the upper maxilla and the external pterygoid muscle, and enters the external palatine canal between the maxillary bone and the pterygoid process of the palate bone. At its exit from the canal it gives inwards a branch to the uvula, and outwards another to the tonsil and palate. Occasionally, this nerve is altogether wanting. INTERNAL BRANCHES. — These consist of the naso-palatine, and the upper and anterior nasal, which ramify iii the lining membrane of the nasal fossae and adjoining sinuses. The upper nasal are very small branches, and enter the back part of the nasal fossa by the spheno-palatine foramen. Some are prolonged to the upper and posterior part of the septum, and the remainder ramify in the membrane covering it R 2 604 THE CRANIAL NERVES. the upper two spongy bones, and in that lining the posterior ethmoid cells. A branch, as has been already stated, forms a connection in the wall of the maxillary sinus, above the eye-tooth, with the anterior dental nerve. The naso-palatine nerve, nerve of Cotunnius (Scarpa), long and slender, leaves the inner side of the ganglion with the preceding branches, and after crossing the roof of the nasal fossa is directed downwards and forwards on the septum nasi, towards the anterior palatine canal, situated between the periosteum and the pituitary membrane. The nerves of opposite sides descend to the palate through the mesial subdivisions of the canal, called the foramina of Scarpa, the nerve of the right side usually behind that of the left. In the lower common foramen the two naso-palatine nerves are connected with each other ; and they end in several filaments, which are distributed to the papilla behind the incisor teeth, and communicate with the great palatine nerve. In its course along the septum, small filaments are furnished from the naso- palatine nerve to the pituitary membrane. (See Fig 402. This nerve was discovered independently by John Hunter and Cotunnius ; see Hunter's " Observations on certain parts of the Animal Economy;" and Scarpa, "Annotationes Anatomicse," lib. ii.) Fig. 408. Fig. 408. — NEIIVKS OP THE NOSE AND OF THE SPHENO-PALATINE GANGLION FROM THR INNER SIDE (from Sappey after Hirschftld and Leveille). f 1, network of the branches of the olfactory nerve descending upon the membrane covering the superior and middle turbinated bones ; 2, external twig of the ethinoidal branch of the nasal nerve ; 3, spheno-palatine ganglion ; 4, ramification of the anterior division of the palatine nerves ; 5, posterior, and 6, middle divisions of the palatine nerves; 7, branch to the membrane on the lower turbinated bone ; 8, branch to the superior and middle turbinated bones ; 9, naso-palatine branch to the septum cut short ; 10, Vidian nerve ; 11, its great superficial petrosal branch; 12, its carotid branch; 13, the sympa- thetic nerves ascending on the internal carotid artery. POSTERIOR BRANCHES. — The brandies directed backwards from the splieno- palatine ganglion are the Vidian aud pharyngeal nerves. The Vidian nerve arises from the back part of the ganglion, which seems to be pro- longed into it, passes backwards through the Vidian canal, and after emerging from this divides in the substance of the fibro-cartilage filling the foramen lacerum medium, into two branches : one of these, the superficial petrosal, joins the facial nerve, while the other, the carotid branch, communicates with the sympathetic. Whilst the Vidian nerve is in its canal, it gives inwards some small nasal branches, which supply the membrane of the back part of the roof of the nose and septum, as well as the membrane covering the end of the Eustachian. tube. INFERIOR MAXILLARY NERVE. 605 The large superficial petrosal branch of the Vidian nerve, entering the cranium on the outer side of the carotid artery and beneath the Gasserian ganglion, is directed backwards in a groove on the petrous portion of the temporal bone to the hiatus Fallopii, and is thus conducted to the aqueductus Fallopii, where it joins the gangli- form enlargement of the facial nerve. The carotid or sympathetic portion of the Vidian nerve, shorter than the other, is of a reddish colour and softer texture : it is directed backwards, and on the outer side of the carotid artery ends in the filaments of the sympathetic surrounding that vessel. In accordance with the view taken of the ganglia connected with the fifth nerve (p. 599), the superficial petrosal and carotid parts of the Vidian nerve may be regarded as the motor and sympathetic roots respectively of the spheno-palatine ganglion; the spheno-palatiue being its sensory root. The pharyngeal nerve is inconsiderable in size, and, instead of emanating directly from the ganglion, is frequently derived altogether from the Vidian. This branch, when a separate nerve, springs from the back of the ganglion, enters the ptery go-palatine canal with an artery, and is lost in the lining membrane of the pharynx behind the Eustachian tube. Summary. — The superior maxillary nerve, with Meckel's ganglion, supplies the integument above the zygomatic arch, and that of the lower eyelid, the side of the nose, and the upper lip ; the upper teeth, the lining mem- brane of the nose ; the membrane of the upper part of the pharynx, of the antrum of Highmore, and of the posterior ethmoid cells ; the soft palate, tonsil, and uvula ; and the glandular and mucous structures of the roof of the mouth. INFERIOR MAXILLARY NERVE. The lower maxillary nerve, the third and largest division of the fifth nerve, is made up of two portions, unequal in size, the larger being derived from the Gasserian ganglion, aud the smaller being the slender motor root of the fifth nerve. These two parts leave the skull by the foramen ovale in the sphenoid bone, and unite immediately after their exit. A few lines beneath the base of the skull, and under cover of the external pterygoid muscle, the nerve separates into two primary divisions, one of which is higher in position and smaller than the other. The small, anterior or upper portion, purely motor, terminates in branches to the temporal, masseter, buccinator, and pterygoid muscles. The larger or lower portion, chiefly sensory, divides into the auriculo-temporal, gustatory, and inferior dental branches : it likewise supplies the mylohyoid muscle, and the anterior belly of the digastric. The branch to the in- ternal pterygoid muscle, with which also are connected those proceeding from the otic ganglion to the tensors of the palate and tympanum, is sometimes counted as a part of the larger division, but is more correctly regarded as arising from the undivided trunk. DEEP TEMPORAL, MASSETERIC, BUCCAL, AND PTERYGOID BRANCHES. The deep temporal branches, two in number, anterior and posteriory pass outwards above the external pterygoid muscle, close to the bone, and run upwards, one near the front, and the other near the back of the tem- poral fossa, beneath the temporal muscle in the substance of which they are distributed. (See fig. 403.) The anterior branch is frequently joined with the buccal nerve, and sometimes with the other deep temporal branch. The masseteric branch likewise passes above the external pterygoid 606 THE CRANIAL NERVES. muscle, and is directed nearly horizontally outwards through the sigmoid notch of the lower jaw to the posterior border of the masseteric muscle, which it enters on the deep surface. It gives a filament or two to the articulation of the jaw, and occasionally furnishes a branch to the tem- poral muscle. The buccal branch pierces the substance of the external pterygoid muscle, and courses downwards and forwards to the face, in close contact with the deep surface of the temporal muscle at its insertion. It furnishes a branch to the external pterygoid muscle as it pierces it, and on emerging gives two or three ascending branches to the temporal muscle. It divides into two principal branches, an upper and a lower, which communicate with the facial nerve in a plexus round the facial vein, and are distributed to the integument, the buccinator muscle, and the mucous membrane. The external pterygoid branch, is most frequently derived from the buccal nerve. It is sometimes a separate offset from the smaller portion of the lower maxillary nerve. The nerve of the internal pterygoid muscle is closely connected at its origin with the otic ganglion, and enters the inner or deep surface of the muscle. AURICFLO-TEMPORAL NERVE. The auriculo-temporal nerve takes its origin close to the foramen ovale. It often commences by two roots, Between which may be placed the middle meningeal artery. It is directed at first backwards, beneath the external pterygoid muscle, to the inner side of the articulation of the jaw ; then changing its course, it turns upwards betwt ea the ear and the joint, covered by the parotid gland ; and emerging from this place, it finally divides iuto two temporal branches which ascend towards the top of the head. (a) Communicating branches. — There are commonly two branches which pass forward round the external carotid artery, and join the facial nerve. Filaments to the otic ganglion arise near the beginning of the nerve. (b) Parotid branches are given from the nerve while it is covered by the gland. (c) Auricular branches. — These are two in number. The lower of the two, arising behind the articulation of the jaw, distributes branches to the ear below the external meatus; and sends other filaments round the internal maxillary artery to join the sympathetic nerve ; the upper branch, leaving the nerve in front of the ear, is dis- tributed in the integument covering the tragus and the pinna above the external auditory meatus. Both are confined to the outer surface of the ear. (d) Branches to the meatus auditorius. — These, two in number, spring from the point of connection of the facial and auriculo-temporal nerves, and enter the interior of the auditory meatus between the osseous and cartilaginous parts. One of them sends a branch to the membrana tympani. (e) Articular branch. — The nerve to the temporo-maxillary articulation comes from one of the preceding branches, or directly from the auriculo-temporal nerve. (/) Temporal branches.— One of these, the smaller and posterior of the two, distributes filaments to the anterior muscle of the auricle, the upper part of the pinna and the integument above it. The anterior temporal branch extends with the superficial temporal artery to the top of the head, and ends in the integument. It is often united with the temporal branch of the upper maxillary nerve. Meckel mentions a communication between this branch and the occipital nerve. GUSTATORY NERVE. The gustatory nerve, or lingual branch of the fifth, descends under cover of the external pterygoid muscle, lying to the inner side and in GUSTATORY XERVE. 607 front of the dental nerve, and sometimes united to it by a cord which crosses over the internal maxillary artery. It is there joined at an acute angle by the chorda tympani, a small branch connected with the facial nerye, which descends from the inner end of the Glasserian. fissure. It then passes between the internal pterygoid muscle and the lower maxilla, and is inclined obliquely inwards to the side of the tongue, over the upper constrictor of the pharynx, (where this muscle is attached to the maxillary bone,) and above the deep portion of the submaxiliary gland. Lastly, the nerve crosses Wharton's duct, and is continued along the si con- 612 THE CRANIAL NEKVES. ducted towards the tongue. It enters the back part of the tympanic cavity through a short canal emerging below the level of the pyramid, close to the ring of bone giving attachment to the membrane of the tympanum ; and being invested by the mucous lining of the cavity, it is directed forwards across the membrana tympani and the handle of the malleus, to an aperture at the inner end of the Glaserian fissure. It then passes downwards and forwards, under cover of the external pterygoid muscle, and uniting with the gustatory nerve at an acute angle, descends in close contact with it, and is partly distributed to the submaxillary ganglion and partly blended with the gustatory nerve in its distribution to the tongue. As this nerve crosses the tympanum, it is said to supply a twig to the laxator tympaui muscle. Fig. 412. Fig. 412. — GENICULATE GANGLION OP THE FACIAL NERVE AND ITS CONNEC- TIONS FROM ABOVE (from Bidder). The dissection is made iu the middle fossa of the skull ou the right side; the temporal bone being removed so as to open the meatus iuteruus, hiatus Fal- lopii, and a part of the caual of the facial nerve, together with the cavity of the tympanum, a, the external ear ; b, middle fossa of the skull with the meningeal artery ramifying in it ; 1 , facial and auditory nerves in the meatus auditorius internus ; 2, large super- ficial petrosal nerve ; 3, small super- ficial petrosal nerve lying over the ten- sor tyrapani muscle ; 4, the external superficial petrosal joining sympathetic twigs on the meningeal artery ; 5, facial and chorda tympani ; b', nerves of the eighth pair. The chorda tympani is regarded by some anatomists as a continuation of the great superficial petro.sal nerve. According to Owen, in the horse and calf, the portio dura being less dense in structure, the Yidian branch of the fifth may be distinctly seen crossing the nerve after penetrating its sheath, and separating into many filaments, with which filaments of the seventh nerve are blended, Avhile a ganglion is formed by the superaddition of grey matter ; and the chorda tympani is continued partly from this ganglion, partly from the portio dura. (Hunter's Collected Works, vol. iv. p. 194, note.) The nerve to the stapedius muscle arises from the trunk of the facial opposite the pyramid, and passes obliquely inwards t j the fleshy belly of the muscle. POSTERIOR AURICULAR BRANCH. This branch arises close to the stylo-mastoid foramen. In front of the mastoid process, it divides into an auricular and an occipital portion, aud is connected with the great auricular nerve of the cervical plexus. It is said to be joined by the auricular branch of the pneumo-gastric nerve. a. The auricular division supplies filaments to the retrahent muscle of the ear, and ends in the integument on the posterior aspect of the auricle. 6. The occipital branch is directed backwards beneath the small occipital nerve (from the cervical plexus) to the posterior part of the occipito- TEMPORO-FACIAL DIVISION OF THE FACIAL. 613 frontalis muscle ; it lies close to the bone, and, besides supplying the muscle, gives upwards filaments to the integument. DIGASTRIC AND STYLO-HYOID BRANCHES. The digastric branch arises in common with that for the stylo -hyoid muscle, and is divided into numerous filaments, which enter the digastric muscle : one of these sometimes perforates the digastric, and joins the glospo-pharyngeal nerve near the base of the skull. The stylo-hyoid branch, long and slender, is directed inwards from the digastric branch .to the muscle from which it is named. This nerve is connected with the plexus of the sympathetic on the external carotid artery. TEMPORO-FACIAL DIVISION. The temporo-facial, the larger of the two primary divisions into which the main trunk of the facial nerve separates, is directed forwards through the parotid gland. Its ramifications and connections with other nerves form a network over the side of the face, extending as high as the temple and as low as the mouth. Its branches are arranged in temporal, malar, and infraorbital sets. (a) The temporal branches ascend over the zygoma to the side of the head. Some end in the anterior muscle of the auricle and the integument of the temple, and communicate with the temporal branch of the upper maxillary nerve near the ear, as well as with (according to Meckel) the auriculo-temporal branch of the lower maxil- lary nerve. Other branches enter the occipito-frontalis, the orbicularis palpebrarum, and the corrugator supercilii muscles, and join offsets from the supraorbital branch of the ophthalmic nerve. (b) The malar bran' lies cross the malar bone to reach the outer side of the orbit, and supply the orbicular muscle. Some filaments are distributed to both the upper and lower eyelids : those in the upper eyelid join filaments from the lachrymal and, supraorbital nerves ; and those in the lower lid are connected with filaments from the upper maxillary nerve. Filaments from this part of the facial nerve communicate with the malar branch of the upper maxillary nerve. (c) The infraorbital brandies, of larger size than the other branches, are almost horizontal in direction, and are distributed between the orbit and mouth. They supply the buccinator and orbicularis oris muscles, the elevators of the upper lip and angle of the mouth, and likewise the integument. Numerous communications take place with the fifth nerve. Beneath the elevator of the upper lip these nerves are united in a plexus with the branches of the upper maxillary nerve ; on the side of the nose they communicate with the nasal, and at the inner angle of the orbit with the infratrochlear nerve. The lower branches of this set are connected with those of the cervico-facial division. Near its commencement the temporo-facial division of the facial is connected with the auriculo-temporal nerve of the fifth, by one or two branches of considerable size which turn round the external carotid artery; and it gives some filaments to the tragus of the outer ear. CERVICO-FACIAL DIVISION. This division of the facial nerve is directed obliquely through the parotid gland towards the angle of the lower jaw, and gives branches to the face, below those of the preceding division, and to the upper part of the neck. The branches are named buccal, supramaxillary, and inframaxillary. In the gland, this division of the facial nerve is joined by filaments of the great auricular nerve of the cervical plexus, and offsets from it penetrate the sub- stance of the gland. 614 THE CRANIAL NERVES. (a) The buccal branches are directed across the masseter muscle to the angle of the mouth ; supplying the muscles, they communicate with the temporo-facial divi- sion, and on the buccinator muscle join with filaments of the buccal branch of the lower maxillary nerve. Fig. 413. Fig. 413. — SUPERFICIAL DISTRIBUTION OP THE FACIAL, TRIGEMINAL, AND OTHER NKRVES OF THE HEAD (from Sappey after Hirschfeld and Leveille). f a, References to the Facial Nerve. — 1, trunk of the facial nerve after its exit from the stylo-mastoid foramen ; 2, posterior auricular branch ; 3, filament of the great auricular nerve uniting with the foregoing ; 4, twig to the occipitalis muscle ; 5, twig to the posterior auricular muscle ; 6, twig to the superior auricular muscle ; 7, branch to the digastric; 8, that to the stylo-hyoid muscle ; 9, superior or temporo-facial division of the pes anseririus ; 10, temporal branches; 11, frontal ; 12, palpebral or orbital ; 13, nasal or infraorbital ; 14, buccal ; 15, inferior or cervico-facial division of the nerve ; 16, labial and mental branches ; 17, cervical branches. by References to the Fifth Nerve. — 18, temporo-auricular nerve (of the inferior maxillaiy nerve) uniting with tin- facial, giving anterior auricular and parotid branches, and ascend- ing to the temporal region ; 19, external frontal or supra-orbital nerve ; 20, internal frontal ; 21, palpebral twigs of the lachrymal ; 22, terminal branches of the infra- trochlear ; 23, malar twig of the orbito-malar ; 24, external nasal twig of the ethmoidal ; 25, infraorbital nerve ; 26, buccal nerve uniting with branches of the facial ; 27, labial and mental branches of the inferior dental nerve. c, Cervical Nerves. — 28, great occipital nerve from the second cervical ; 29, great auricular nerve from the cervical plexus ; 30, lesser occipital ; 31, another branch with a similar distribution ; 32, superficial cervical, uniting by several twigs with the facial. AUDITORY NERVE.— EIGHTH PAIR. 615 (b) The supramaxiUary branch, sometimes double, gives an offset over the side of the maxilla to the angle of the mouth, and is then directed inwards, beneath the depressor of the angle of the mouth, to the muscles and integument between the lip and chin ; it joins with the labial branch of the lower dental nerve. (c) The inframaxillary branches (r. subcutanei colli), perforate the deep cervical fascia, and, placed beneath the platysma muscle, form arches across the side of the neck as low as the hyoid bone. Some branches join the superficial cervical nerve beneath the platysma, others enter that muscle, and a few perforate it to end in the integument. Summary. — The facial nerve is the motor nerve of the face. It is distributed to most of the muscles of the ear, and to the muscles of the scalp ; to those of the mouth, nose, and eyelids ; aud to the cutaneous muscle of the neck (platysma). It likewise supplies branches to the integu- ment of the ear, to that of the side and back of the head, as well as to that of the face and the upper part of the neck. This nerve is connected freely with the three divisions of the fifth nerve, and with the submaxillary and spheno-palatine ganglia ; with the glosso- pharyngeal and pneuino-gastric nerves : with the auditory, and with parts of the sympathetic and the spinal nerves. AUDITORY NERVE. The auditory nerve, or portio mollis of the seventh pair, is the special nerve of the organ of hearing, and is distributed exclusively to the internal ear. As the auditory nerve is inclined outwards from its connection with the medulla oblongata to gain the internal auditory meatus, it is in contact with the facial nerve, being only separated from it in part by a small artery destined for the internal ear. Within the meatus the two nerves are con- nected to each other by one or two small filaments. Finally the auditory nerve bifurcates in the meatus : one division, piercing the anterior part of the cribriform lamina, is distiibuted to the cochlea ; the other, piercing the posterior half of the lamina, enters the vestibule of the internal ear. The distribution of these branches will be described with the ear. EIGHTH PAIR OF NERVES. The eighth pair is composed of three distinct nerves — the glosso-pharyn- geal, pneumo-gastric, and spinal accessory, which leave the skull through the anterior and inner division of the foramen lacerum posticum, to the inner side and in front of the internal jugular vein. Two of these nerves, the glosso-pharyngeal and pneumo-gastric, are attached to the medulla oblongata in the same line, and resemble one another somewhat in their distribution, for both are distributed to the first part of the alimentary canal. The other, the spinal accessory, takes its origin chiefly from the spinal cord, and is mainly distributed to muscles ; but it gives fibres to the first two nerves by its communicating branch. GLOSSO-PHARYNGEAL NERVE. The glosso-pharyngeal nerve is destined, as the name implies, for the tongue and pharynx. Directed outwards from its place of origin over the flocculus to the foramen jngulare, it leaves the skull with the pneumo-gastric and spinal- accessory nerves, but in a separate tube of dura mater. In passing through the foramen, somewhat in front of the others, this nerve is contained in a groove, or in a canal in the lower border of the petrous 616 THE CRANIAL NERVES. portion of the temporal bone, and presents, successively, two ganglionic enlargements, — the jugular ganglion, and the petrous ganglion. After leaving the skull, the glosso-pharyngeal nerve appears between the internal carotid artery and the jugular vein, and is directed downwards over the carotid artery and beneath the styloid process and the muscles con- nected with it, to the lower border of the stylo-pharyngeus muscle. Here, changing its direction, the nerve curves inwards to the tongue, on the stylo-pharyngeus and the middle constrictor muscle of the pharynx, above the upper laryngeal nerve ; and, passing beneath the hyo-glossus muscle, ends in branches for the pharynx, the tonsil, and the tongue. Fig. 414. Fig. 414. — DIAGRAMMATIC! SKETCH PROM BEHIND OF THE ROOTS OF THE NERVES OF THE EIGHTH PAIR, WITH THEIR GANGLIA AND COMMUNICA- TIONS (from Beudz). A, part of the cerebellum above the fourth ventricle ; B, medulla oMon- gata; C, posterior columns of the spinal cord ; 1, root of the glosso-pharyngeal nerve ; 2, roots of the pneumo-gastric ; 3, 3, 3, roots of the spinal accessory, the uppermost number indicating the filaments intermediate between the spinal accessory and pneumo-gastric ; 4, jugular ganglion of the glosso-pha- ryngeal ; 5, petrous ganglion ; 6, tympanic branch ; 7, ganglion of the root of the pneurao-gastric ; 8, auri- cular branch ; 9, long ganglion on the trunk of the pneumo-gastric; 10, branch from the upper ganglion to the petrous ganglion of the glosso-pharyn- geal ; 11, inner portion of the spinal accessory ; 12, outer portion ; 13, pharyngeal branch of the pneumo- gastric ; 14, superior laryngeal branch ; 15, twigs connected with the sympathetic ; 16, fasciculus of the spinal accessory prolonged with the pneumo-gastric. The jugular ganglion, the smaller of the two ganglia of the glosso- pharyngeal nerve, is situated at the upper part of the osseous groove in which the nerve is laid during its passage through the jugular foramen. Its length is from half a line to a line, and the breadth from half to three fourths of a line. It is placed on the outer side of the trunk of the nerve, and involves only a part of the fibres, — a small fasciculus passing over the ganglion, and joining the nerve below it. The petrous ganglion is contained in a hollow in the lower border of the petrous part of the temporal bone (receptaculuin ganglioli petrosi), and measures about three lines in length. This ganglion includes all the fila- ments of the nerve, and resembles the gangliform enlargement of the facial nerve. From, it arise the small branches by which the glosso-pharyngeal is connected with other nerves at the base of the skull : these are the tympanic nerve, and the branches which join the pneumo-gastric and sympathetic. CONNECTING BEANCHES, AND TYMPANIC BRANCH. From the petrous ganglion spring three small connecting filaments. One passes to the auricular branch of the pneumo-gastric, one to the upper ganglion of the sym- GLOSSO-PHARYXGEAL NERVE. 617 pathetic or vice versd, and a third to the ganglion of the root of the pneumo -gastric nerve. The last is not constant. There is sometimes likewise a filament from the digastric branch of the facial nerve, which, piercing the digastric muscle, joins the glosso-pharyngeal nerve below the petrous ganglion. The tympanic branch (nerve of Jacobson), arises from the petrous ganglion, and is conducted to the tympanum by a special canal, the orifice of which is in the ridge of bone between the jugular fossa and the carotid foramen. On the inner wall of the tympanum the nerve joins with a twig from the sympathetic in a plexus (tym- panic), and distributes filaments to the membrane lining the tympanum and the Eustachian tube, as well as one to the fenestra rotunda, and another to the fenestra ovalis. Fig. 415 Fig. 415. — SKETCH OP THE TYMPANIC BRANCH OF THE GLOSSO-PHARYN- GEAL NERVE, AND ITS CONNECTIONS (from Breschet). A, squamous part of the left tem- poral bone ; B, petrous part ; C, in- ferior maxillary nerve ; D, internal carotid artery ; a, tensor tympani muscle ; 1, carotid plexus ; 2, otic ganglion ; 3, glosso-pharyngeal nerve ; 4, tympanic nerve ; 5, twigs to the carotid plexus ; 6, twig to fenestra rotunda ; 7, twig to fenestra ovalis ; 8, junction with the large superficial petrosal nerve ; 9, small superficial petrosal ; 10, twig to the tensor tym- pani muscle; 11, facial nerve; 12, chorda tyrapani ; 13, petrous ganglion of the glosso-pharyngeal ; 14, twig to the membrane of the Eustachian tube. From the tympanic nerve are given three connecting branches, by which it communicates with other nerves; and which occupy channels given off from the osseous canal through which the nerve enters the tympanum. One branch enters the carotid canal and joins with the (sympathetic on the carotid artery. A second is united to the large superficial petrosal nerve, as this lies in the hiatus Fallopii. And the third is directed upwards, beneath the canal for the tensor tympani muscle, towards the surface of the petrous portion of the temporal bone, where it becomes the small petrosal nerve; and under this name it is continued to the exterior of the skull through a small aperture in the sphenoid and temporal bones, to end in the otic ganglion. As this petrosal nerve passes the gangliform enlargement of the facial, it has a connecting filament with that enlargement, which is by some considered its principal posterior termination. Jacobson described an anterior or internal branch from the tympanic nerve to the spheno-palatine ganglion. BRANCHES DISTRIBUTED IN THE NECK. The carotid branches course along the internal carotid artery, and unite with the pharyngeal branch of the pneumo-gastric, and with branches of the sympathetic. The pharyngeal branches, three or four in number, unite opposite the middle con- strictor of the pharynx with branches of the pneumo-gastric and sympathetic to form the pharyngeal plexus. Nerves to the mucous membrane of the pharynx perforate the muscles, and extend upwards to the base of the tongue and the epiglottis, and downwards nearly to the hyoid bone. 618 THE CRANIAL NERVES. The muscular branches are given to the stylo-pharyngeus and constrictor muscles. Tonsilitic brandies. — When the glosso-pharyngeal nerve is near the tonsil, some branches are distributed on that body in a kind of plexus (circulus tonsillaris). From these nerves offsets are sent to the soft palate and the isthmus of the fauces. Lingual branches. — The glosso-pharyngeal nerve divides into two parts at the border of the tongue. One turns to the upper surface of the tongue, supplying the mucous membrane at its base ; the other perforates the muscular structure, and ends in the mucous membrane on the lateral part of the tongue. Some filaments enter the circumvallate papillae. Summary. — The glosso-pharyngeal nerve distributes branches to the mucous membrane of the tongue, pharynx, tympanum, and Eustachian tube. The muscles supplied by it are some of those of the pharynx and base of the tongue. It is connected with the following nerves, viz., the lower maxillary division of the fifth, the facial, the pneumo-gastric (the trunk and branches of this nerve), and the sympathetic. PNEUMO-GASTRIC NERVE. The pneumo-gastric nerve (nervus vagus, par vagum) has the longest course of any of the cranial nerves. It extends through the neck and the cavity of the chest to the upper part of the abdomen ; and it supplies nerves to the organs of voice and respiration, to the alimentary canal as far as the stomach, and to the heart. The filaments by which this nerve springs from the medulla oblongata are arranged in a flat fasciculus, immediately beneath the glosso-pharyngeal nerve, and directed outwards with that nerve, across the flocculus to the jugular foramen. In passing through the opening at the base of the skull the pneumo- gastric nerve is contained in the same sheath of dura mater, and surrounded by the same tube of arachnoid membrane as the spinal-accessory nerve ; but it is separated from the glosso-pharyngeal nerve by a process of membrane. In the foramen the filaments of the nerve become aggregated together ; and it here presents a ganglionic enlargement, distinguished as the ganglion of the root of the pneumo-gastric. After its passage through the foramen, it is joined by the accessory part of the spinal accessory nerve, and a second ganglion is formed upon it, the ganglion of the trunk of the nerve. Several communications are at the same time established with the surrounding nerves. The upper ganglion, or ganglion of the root of the pneumo-gastric nerve, situated in the foramen jugulare, is of a greyish colour, nearly spherical, and about two lines in diameter ; it has filaments connecting it with other nerve*, viz., with the facial, the petrous ganglion of the glosso-pharyngeal, the spinal accessory, and the sympathetic. The lower ganglion, or ganglion of the trunk or the pneumo-gastric nerve, is about half an inch below the preceding. Occupying the trunk of the nerve outside the skull, it is of a flattened cylindrical form and reddish colour, and measures about ten lines in length and two in breadth. The ganglion does not include all the fibres of the nerve; the fasciculus, which is sent from the spinal accessory to join the vagus, is the part not in- volved in the ganglionic substance. It communicates with the hypoglossal, the spinal, and the sympathetic nerves. The pneumo-gastric nerve descends in the neck, between and concealed PXEUMO-GASTRIC NERVE. 619 by the internal jugular vein and the internal carotid artery, and afterwards similarly between that vein and the common carotid artery, being enclosed along with them in the sheath of the vessels. As they enter the thorax, the nerves of the right and left side present some points of difference. Fig 416. — DIAGRAM OF THE ROOTS Fig. 416. AND ANASTOMOSING BRANCHES OF THE NERVES OF THE EIGHTH PAIR AND NEIGHBOURING NERVES (from Sappey after Hirschfeld and Le- veille). 1, facial nerve ; 2, glosso-pharyn- geal with the petrous ganglion repre- sented ; 2', connection of the digastric branch of the facial neive with the glosso-pharyngeal nerve ; 3, pneu- mo-gastric, with both its ganglia re- presented ; 4, spinal access ry ; 5, hypoglossal ; 6, superior cervical ganglion of the sympathetic ; 7, loop of union between the two first cervical nerves ; 8, carotid branch of the sym- pathetic ; 9, nerve of Jacobson (tym- panic), given off from the petrous ganglion ; 10, its filaments to the sympathetic; 11, twig to the Eusta- chian tube ; 12, twig to the fenestra ovalis; 13, twig to the fenestra ro- tun'la ; 14, twig of union with the small superficial petrosal ; 15, twig of union with the large superficial petro- s tl ; 16, otic ganglion ; 17, branch of the jugular fossa, giving a filament to the petrous ganglion ; 18, union of the spinal accessory with the pneu- mo-gastric ; 19, union of the hypo- glossal with the first cervical nerve ; 20, union between the sterno-mastoid branch of the spinal accessory and that of the second cervical nerve ; 21, pharyngeal plexus ; 22, superior laryngeal nerve ; 23, external laryngeal ; 24, middle cervical ganglion of the sympathetic. On the rirjht side the nerve crosses over the first part of the right sub- clavian artery, at the root of the neck, and its recurrent laryngeal branch turns backwards and upwards round that vessel. The n rve then enters the thorax behind the right innominate vein, and descends on the side of the trachea to the back of the root of the lung, where it spreads out in the pos- terior pulmonary plexus. It emerges from this plexus in the form of two cords, which are directed to the resophagus. and uniting and subdividing form, with similar branches of the nerve of the left side, the oesophageal plexus. Near the lower part of the oesophagus the branches, which have thus interchanged fibres with the nerve of the left side, are gathered again into a single trunk, which, descending on the back of the oesophagus, is spread out on the posterior or inferior surface of the stomach. On the left side the pueumo-gastric nerve, entering the thorax between the left carotid and subclavian arteries and behind the left innominate vein, lies further forwards than the right nerve, and crosses over the arch of the aorta, while its recurrent laryngeal branch turns up behind the arch. It s s 2 620 THE CRANIAL NERVES. then passes behind the root of the left lung, and, emerging from the posterior pulmonary plexus, is distributed like its fellow to the oesophagus. Fig. 417. Fig. 417.— VIEW OP THE NERVES OP THE EIGHTH PAIR, THEIR DISTRIBUTION AND CONNECTIONS ON THE LEFT SIDE (from Sappey after Hirschfeld and Leveilld). 3 1, pneumo-gastric nerve in the neck ; 2, ganglion of its trunk ; 3, its union with the spinal accessory ; 4, its union with the hypoglossal ; 5, pharyngeal branch ; 6, superior laryngeal nerve ; 7, external laryngeal ; 8, laryngeal plexus ; 9, inferior or recur- rent laryngeal ; 10, superior cardiac branch; 11, middle cardiac; 12, plexiform part of the nerve in the thorax; 13, posterior pulmonary plexus ; 14, lingual or gustatory nerve of the inferior maxillary ; 15, hypoglossal, passing into the muscles of the tongue, giving its thyro-hyoid branch, and uniting with twigs of the lingual ; 16, glosso-pharyngeal nerve; 17, spinal accessory nerve, uniting by its inner branch with the pneumo-gastric, and by its outer, passing into the sterno-mastoid muscle ; 18, second cervical nerve ; 19, third; 20, fourth; 21, origin of the phrenic nerve; 22, 23, fifth, sixth, seventh, and eighth cervical nerves, forming with the first dorsal the brachial plexus ; 24, superior cervical ganglion of the sympathetic ; 25, middle cervical ganglion ; 26, inferior cervical ganglion united with the first dorsal ganglion; 27, 28, 29, 30, second, third, fourth, and fifth dorsal ganglia. PNEUMO-GASTR1C XERVE. 621 Inferiorly, it forms a single trunk in front of the oesophagus, and is spread out on the anterior or superior surface of the stomach. There are various circumstances in the distribution of the pneumo-gastric nerves which at first sight appear anomalous, but which are explained by reference to the process of development. The recurrent direction of the inferior laryngeal branches in all probability arises from the extreme shortness or rather absence of the neck in the embryo at first, and from the branchial arterial arches having originally occupied a position at a higher level than the parts in which those branches are ultimately distributed, and having dragged them down as it were in the descent of the heart from the neck to the thorax. The recurrent direction may therefore be accepted as evidence of the development of those nerves before the occurrence of that descent. The circumstance that one recurrent laryngeal nerve passes round the subclavian artery, and the other round the aorta, is seen to arise from an originally symmetrical disposition, when it is remembered that the innominate artery and the arch of the aorta are derived from corresponding arches of the right and left sides. The supply of the back of the stomach by the right pneumo-gastric nerve, and of the front by the left nerve, is connected with the originally symmetrical condition of the alimentary canal, and the turning over of the stomach on its right side in its sub- sequent growth. BRANCHES OF THE PNEUMO-GASTRIC NERVE. Some of its branches serve to connect the pneumo-gastric with other nerves, and others are distributed to the muscular substance or the mucous lining of the organs which the nerve supplies. The principal con- necting branches of this nerve are derived from the ganglia. In the different stages of its course branches are supplied to various organs aa follows. In the jugular foramen, a branch is given to the ear ; in the neck, branches are furnished successively to the pharynx, the larynx, and the heart ; and in the thorax, additional branches are distributed to the heart, as well as to the lungs and the oesophagus. Terminal branches in the abdomen are distributed to the stomach, liver, and other organs. CONNECTING BRANCHES AND AURICULAR BRANCH. Connections between the upper ganglion of the vagus nerve and the spinal accessory, glosso-pharyngeal, and sympathetic nerves. — The connection with the spinal accessory is effected by one or two filaments. The filament to the petrous ganglion of the glosso-pharyngeal is directed transversely ; it is not always present. The communi- cation with the sympathetic is established by means of the ascending branch of the upper cervical ganglion. The auricular branch is continued to the outer ear. Arising from the ganglion of the root, this branch is joined by a filament from the glosso-pharyngeal nerve, and then turns backwards along the outer boundary of the jugular foramen to an opening near the styloid process. Next, it traverses the substance of the temporal bone, crossing the aqueduct of Fallopius, about two lines from the lower end, and, reaching the surface between the mastoid process and the external auditory meatus, is distri- buted to the integument of the back of the ear. On the surface it joins with a twig from the posterior auricular branch of the facial nerve. Connections of the second ganglion with the hypoglossal, sympathetic, and spinal nerves. — This ganglion is connected by filaments with the trunk of the hypoglossal, with the upper cervical ganglion of the sympathetic, and with the loop formed between the first two cervical nerves. PHARYNGEAL BRANCH. The pharyngeal branch arises from the upper part of the ganglion of the trunk of the nerve. In its progress inwards to the pharynx this nerve crosses in some cases over, in others under the internal carotid artery ; and 622 THE CRANIAL NERVES. it divides into branches, which, conjointly with others derived from the glosso-pharyngeal, the superior laryngeal, and the sympathetic nerves, form a plexus (pharyngeal) behind the middle constrictor of the pharynx. From the plexus branches are given to the muscular structure, and to the mucous membrane of the pharynx. As the pharyngeal nerve crosses the carotid artery, it joins filaments which the glosso-pharyngeal distributes on the same vessel. — There is sometimes a second pharyngeal branch. SUPERIOR PHARYNGEAL BRANCH. This nerve springs from the middle of the ganglion of the trunk of the pneumo-gastric nerve. It is directed inwards to the larynx beneath the internal carotid artery, and divides beneath that vessel into two branches, distinguished as external and internal laryngeal, both of which ramify in the structures of the larynx. The external laryngeal branch, the smaller of the two divisions, gives backwards, at the side of the pharynx, filaments to the pharyugeal plexus and the lower constrictor muscle ; and it is finally prolonged beneath the muscles on the side of the larynx to the crico thyroid muscle in which it ends. In the neck this branch joins the upper cardiac nerve of the sympathetic. The internal laryngeal branch is continued to the interval between the hyoid bone and the thyroid cartilage, where it perforates the thyro-hyoid membrane with the laryngeal branch of the superior thyroid artery, and dis- tributes filaments to the mucous membrane : some of these are directed up- wards in the aryteno-epiglottidean fold of mucous membrane to the base of the tongue, the epiglottis, and the epiglottidean glands; while others are reflected downwards in the lining membrane of the larnyx, extending to the corda vocalis, on the inner side of the laryngeal pouch. A slender communicating branch to the recurrent laryngeal nerve descends beneath the lateral part of the thyroid cartilage. A branch enters the arytenoid muscle, some fila- ments of which seem to end in the muscle, while others proceed through it to the mucous membrane. RECURRENT LARYNGEAL BRANCH. The recurrent or inferior laryngeal branch of the vagus nerve, as the name expresses, has a reflex course to the larnyx. The nerve on the right side arises at the top of the thorax, winds round the subclavian artery, and passes beneath the common carotid and inferior thyroid arteries in its course towards the trachea. On the left side the re- current nerve is bent round, below and behind the arch of the aorta, imme- diately beyond the point where the obliterated ductus arteriosus is con- nected with the arch, and is thence continued upwards to the trachea. Each nerve in its course to the larynx is placed between the trachea and oesophagus, supplying branches to both tubes ; and each, while making its turn round the artery, gives nerves to the deep cardiac plexus. At the lower part of the cricoid cartilage the recurrent nerve distributes branches to supply all the special muscles of the larynx, except the crico-thyroid muscle, which is supplied from the upper laryngeal nerve. It likewise gives a few offsets to the mucous membrane, and a single communicating filament which joins the long branch of the upper laryngeal nerve beneath the side of the thyroid cartilage. BRANCHES OF PNEUMO-GASTRIC NERVE. 623 CARDIAC BRANCHES. Branches to the heart are given off by the pneumo-gastric nerve both in the neck and in the thorax. The cervical cardiac branches arise at both the upper and the lower part of the neck. The upper branches are small, and join the cardiac nerves of the sympathetic. The loiver, a single branch, arises as the pneumo-gastric nerve is about to enter the chest. On the right side this branch lies by the side of the innominate artery, and joins one of the cardiac nerves destined for the deep cardiac plexus ; it gives some filaments to the coats of the aorta. The branch of the left side crosses the arch of the aorta, and ends in the superficial cardiac plexus. The thoracic cardiac branches of the right side leave the trunk of the pneumo-gastric as this nerve lies by the side of the trachea, and some are also derived from the first part of the recurrent branch : they pass inwards on the air- tube, and end in • the deep cardiac plexus. The corresponding branches of the left side come from the left recurrent laryngeal nerve. PULMONARY BRANCHES. Two sets of pulmonary branches are distributed from the pneumo-gastric nerve to the lung ; and they reach the root of the lung, one on its fore part, the other on its posterior aspect. The anterior pulmonary nerves, two or three in number, are of small size. They join with filaments of the sympathetic ramified on the pulmonary artery, and with these nerves constitute the anterior pulmonary plexus. Behind the root of the lung the pneumo-gastric nerve becomes flattened, and gives several branches of much larger size than the anterior branches, which, with filaments derived from the second, third, and fourth thoracic ganglia of the sympathetic, form the posterior pulmonary plexus. Offsets from this plexus extend along the rami- fications of the air-tube through the substance of the lung. CESOPHAGEAL BRANCHES. The oesophagus within the thorax receives branches from the pneumo- gastric nerves, both above and below the pulmonary branches. The lower branches are the larger, and are derived from the cesophageal plexus, formed by connecting cords between the nerves of the right and left sides, while they lie in contact with the oesophagus. GASTRIC BRANCHES. The branches distributed to the stomach (gastric nerves) are the terminal branches of bath pneumo-gastric nerves. The nerve of the left side, on arriving in front of the oesophagus, opposite the cardiac orifice of the stomach, divides into many branches : the largest of these extend over the fore part of the stomach ; others lie along its small curvature, and unite with branches of the right nerve and the sympathetic ; and some filaments are continued between the layers of the small omentum to the hepatic plexus. The right pneumo-gastric nerve descends to the stomach on the back of the gullet and distributes branches to the posterior surface of the organ : a part of this nerve is continued from the stomach to the left side of the coeliac plexus, and to the splenic plexus of the sympathetic. Summary. — The pneumo-gastric nerves supply branches to the upper part of the alimentary canal, viz., the pharynx, oesophagus, and stomach with the liver and spleen ; and t6 the respiratory passages, namely, the larynx, Fig. 418. 40 23 24 26 0 . PXEUMO-GASTRIC.-SPINAL ACCESSORY NERVE. 625 Fig. 418. — VIEW OF THE DISTRIBUTION AND CONNECTIONS OP THE PNEUMO-GASTRIO AND SYMPATHETIC NERVES ON THE RIGHT SIDE (from Hirschfeld and Leveille). f a, lachrymal gland ; b, sublingual gland ; c, submaxillary gland and facial artery ; d, thyroid gland, pulled forwards by a hook ; e, trachea, below which is the right bronchus cut across; /, the gullet; g, the stomach, divided near the pylorus ; i, trans- verse colon, with some folds of intestine below. A, heart, slightly turned aside to show the cardiac plexus, &c. ; B, aortic arch, drawn forward by a hook ; C, innominate artery ; D, subclavian artery, of which a portion has been removed to show the sympathetic ganglia ; E, inferior thyroid artery ; F, a divided part of the external carotid artery, upon which runs a nervous plexus ; Q-, internal carotid, emerging from its canal superiorly; H, thoracic aorta; K, intercostal vein; L, pulmonary trunk, the right branch cut ; M, superior vena cava ; 0, intercostal artery. 1, ciliary nerves of the eyeball ; 2, branch of the oculo-motor to the inferior oblique muscle, connected with the ophthalmic ganglion ; 3, 3, 3, the three principal divisions of the trifacial nerve ; 4, ophthalmic ganglion ; 5, spheno-palatine ; 6. otic ; 7, submaxillary ; 8, sublingual ; 9, sixth nerve ; 10, facial in its canal, uniting with the spheno-palatine and otic ganglia; 11, glosso-pharyngeal; 12, right pneumo-gastric ; 13, left pneumo- gastric spreading on the anterior surface of the stomach ; 14, spinal accessory ; 35, hypo- glossal ; 16, lower nerve of the cervical plexus; 17, middle nerve of the brachial plexus ; 18, intercostal nerves ; 21, superior cervical ganglion of the sympathetic, con- nected with, 22, tympanic nerve of Jacobson ; 23, carotid branch of the Vidian nerve ; 24, cavernous plexus; 25, ophthalmic twig; 26, filament to the pituitary gland; 27, union with the upper cervical nerves ; 28, points to the pneurao-gastric nerve, close to the pharyngeal and carotid branches : 29, points to the superior laryngeal nerve, close to the pharyngeal and inter-carotid plexuses ; 30, laryngeal branch joining the laryngeal plexus ; 31, great sympathetic nerve ; 32, superior cardiac nerve ; 33, middle cervical ganglion ; 34, twig connecting the ganglion with, 35, the recurrent ; 36, middle cardiac nerve ; 37, great sympathetic nerve ; 38, inferior cervical ganglion ; below 37, branches from the ganglion, passing round the subclavian and vertebral arteries ; 39, the line from this number crosses the nerves proceeding from the brachial plexus ; 40, sympathetic twigs surrounding the axillary artery ; 41, branch of union with the first intercostal nerve ; the line from the letter e, pointing to the trachea, crosses the superior, middle, and inferior cardiac nerves ; 42, cardiac plexus and ganglion ; 43, 44, right aud left coro- nary plexuses ; 45, 46, thoracic portion of the great sympathetic nerve and ganglia, showing their connections with the intercostal nerves ; 47, great splanchnic nerve; 48, semilunar ganglion ; 49, lesser splanchnic ; 50, solar plexus ; 51, union with the pneumo-gastric nerve ; 52, diaphragmatic plexus and ganglion ; 53, coronary plexus ; 54, hepatic ; 55, splenic ; 56, superior mesenteric ; 57, renal plexus. trachea, and its divisions in the lungs. These nerves give branches likewise to the heart and great vessels by means of their communication with the cardiac plexus. Each pneumo-gastric nerve is connected with the following cranial nerves — the spinal accessory, glosso-pharyngeal, facial, and hypo- glossal ; also, with some spinal nerves ; and with the sympathetic in the neck, thorax, and abdomen. SPINAL ACCESSORY NERVE. The spinal nerve accessory to the vagus, or, as it is shortly named, the spinal accessory nerve, consists of two parts : one (accessory) joins the trunk of the pneumo-gastric ; the other (spinal) ends in branches to the stern o-mastoid and trapezius muscles. The internal or accessory part, the smaller of the two, joins in the foramen of exit the ganglion on the root of the pneumo-gastric, by two or three filaments ; and having passed from the skull, blends with the trunk of the pneumo-gastric beyond its second ganglion, as already said. It is stated by Bendz that a filament is given from the spinal accessory to the pha- ryngeal nerve above the place of junction with the pneumo-gastric, and that fibrils of the same nerve have been traced into each of the muscular offsets of the pneumo- gastric nerve. (Bendz, " Tract, de connexu inter nerv. vag. et acces." 1836.) The external portion of the nerve communicates with the accessory part 626 THE CRANIAL NERVES. in the foramen j ugulare. After issuing from the foramen, the nerve is directed backwards across the internal jugular vein, in some cases over, in others under it, and perforates the sterno-mastoid muscle, supplying this with branches, and joining amongst the fleshy fibres with branches of the cervical plexus. Descending in the next place across the neck behind the sterno-mastoid, the nerve passes beneath the trapezius muscle. Here it forms a kind of plexus with branches of the third and fourth cervical nerves, and distributes fila- ments to the trapezius, which extend nearly to the lower edge of the muscle. NINTH PAIR OF NERVES. The hypoglossal or ninth cranial nerve is the motor nerve of the tongue, and in part of some muscles of the neck. The filaments by which this nerve arises from the medulla oblongata are collected into two bundles, which converge to the anterior condyloid foramen of the occipital bone. Each bundle of filaments perforates the dura mater separately within the foramen, and the two are joined after they have passed through it. After leaving the cranium, this nerve descends almost vertically to the lower border of the digastric muscle, whera, changing its course, it is directed forwards above the hyoid bone to the under part of the tongue, It lies at first very deeply with the vagus nerve, to which it is connected ; but passing between the internal carotid artery and the jugular vein, it curves forward round the occipital artery, and then crosses over the external carotid below the digastric muscle. Above the hyoid bone it is crossed by the lower part of the stylo-hyoid muscle and posterior belly of the digastric, and rests on the hyo-glossus muscle. At the anterior border of the hyo- glossus it is connected with the gustatory nerve, and is continued in the fibres of the genio-hyo-glossus muscle beneath the tongue to the tip, distributing branches upwards to the muscular substance. The principal branches of this nerve are distributed to the muscles ascending to the larynx and hyoid bone, and to those of the tongue ; a few serve to connect it with some of the neighbouring nerves. In animals the ninth nerve not unfrequently possesses a posterior root furnished with a ganglion, in the same manner as that of a spinal nerve. CONNECTING BRANCHES. Connection with the pneumo-gastric. — Close to the skull the hypoglossal nerve is connected with the second ganglion of the pneumo-gastric by separate filaments, or in some instances the two nerves are united so as to form one mass. Union with the sympathetic and first two spinal nerves. — Opposite the first cervical vertebra the nerve communicates by several twigs with the upper cervical ganglion of the sympathetic, and with the loop uniting the first two spinal nerves in front of the atlas. MUSCULAR AND LINGUAL BRANCHES. Descending branch of the ninth nerve. — This branch (r. descendens noni), leaves the ninth nerve where this turns round the occipital artery, or, some- times, higher up. It passes downwards on the surface of the sheath of the carotid vessels, gradually crossing from the outer to the inner side, gives a branch to the anterior belly of the omo hyoid muscle, and joins about the middle of the neck in a loop with one or two branches from the second and third cervical nerves, forming the ansa hypoylossi. The concavity of this loop is turned upwards ; and the connection between the nerves is effected by means of two or more interlacing filaments, which HYPOGLOSSAL NERVE. 627 enclose an irregularly shiped space. From this interlacement of the nerves, filaments are continued backwards to the posterior belly of the omo-hyoid, and downwards to the sterno-hyoid and stern o- thyroid muscles. Occasionally a filament is continued to the chest, where it joins the cardiac and phrenic nerves. Fig 419 Fig. 419. — VIEW OF THE DISTRIBUTION OP THK SPINAL ACCESSORY AND HrpoaiossAi, NERVES (from Sappey after Hirschfeld and Leveille). ^ 1, lingual nerve ; 2, pneumo-gasiric nerve ; 3, superior laryngeal (represented too large) ; 4, external laryngeal branch ; 5, spinal accessory ; 6, second cervical ; 7, third ; 8, fourth ; 9, origin of the phrenic nerve; 10, origin of the branch to the subclavius muscle ; 11, anterior thoracic nerves ; 12, hypoglossal nerve ; 13, its descending branch ; 14, com- municating branch from the cervical nerves; 15, 16, 18, 19, descending branches from the plexiform union of these nerves to the sterno-hyoid, sterno-thyroid, and omo-hyoid muscles ; 17, branch from the descendens noni to the upper belly of the omo-hyoid muscle ; 20, branch from the hypoglossal nerve to the tbyro-hyoid muscle ; 21, communi- cating twigs from the hypoglossal to the lingual nerve ; 22, terminal distribution of the hypoglossal to the muscles of the tongue. It is not uncommon to find the descending branch of the ninth nerve within the sheath of the large cervical vessels, and in such cases it is placed either over or under the vein. This nerve in some cases appears to be derived either altogether from the pneumo-gastric, or from both the pneumo-gastric and hypoglossal nerves. There is every reason, however, to believe that these varieties in origin are only apparent, arising from the temporary adhesion of the filaments of this branch to those of the 628 THE CRANIAL NERVES. pneumo-gastric. It is probable, moreover, that the descendens noni has little if any real origin from the hypoglossal nerve : Luschka states it as the result of numerous researches on the human subject that the descendens noni usually contains no fila- ments from the hypoglossal, but is a branch from the first and second cervical, tem- porarily associated with the ninth nerve ; and this quite agrees with the circumstance that in the domestic animals the branches supplied to those muscles to which the descendens noni of the human subject is distributed come from the cervical plexus. Branches to muscles and the tongue. — The branch to the thyro-hyoid muscle is a separate twig given off from the hypoglossal nerve as it approaches the hyoid bone. The nerve supplies branches to the stylo -hyoid, hyo-glossus, genio-byoid, and genio-hyo-gloasus muscles as it becomes contiguous to each, and, when arrived close to the middle of the tongue with the ranine artery, gives off several long slender branches, which pass upwards into the substance of the organ. Some filaments join with others proceeding from the gustatory nerve. A branch is described as uniting with its fellow of the opposite side, in the sub- stance of the genio-hyoid muscle, or between it and the genio-glossus. This loop, as also the ansa hypoglossi, is recommended by Hyrtl as a particularly favourable example for the observation of nerve-fibres returning to the nervous centres without distribution, to which he gives the name of " nerves without ends." (" Nat. Hist. Review," Jan. 1862.) That in the ansa hypoglossi an interchange of fibres takes place, so that a filament of the spinal nerve is directed upwards along the branch of the hypoglossal, and vice versa, was noticed by Cruveilhier. Summary. — The hypoglossal nerve supplies, either alone or in union with branches of the spinal nerves, all the muscles connected with the os hyoides, including those of the tongue, with the exception of the digastric and stylo-hyoid, the mylo-hyoid, and the middle constrictor of the pharynx. It also supplies the sterno -thyroid muscle. It is connected with the following nerves, viz., pneumo-gastrie, gustatory, three upper cervical nerves, and the sympathetic. B. SPINAL NERVES. The spinal nerves are characterised by their origin from the spinal cord, and their direct transmission outwards from the spinal canal in the intervals between the vertebrae. Taken together, these nerves consist of thirty-one pairs ; and, according to the region in which they issue from the spinal canal, they are named cervical, dorsal, lumbar, sacral, and coccygeal. By universal usage each pair of nerves in the dorsal, lumbar, and sacral regions is named in correspondence with the vertebra beneath which it emerges. There are thus left eight pairs of nerves between the cranium and the first dorsal nerve, the first being placed above the atlas and the eighth below the seventh cervical vertebra, which are reckoned by the majority of writers as eight cervical nerves. The nerves of the thirty-first pair emerge from the lower end of the sacral canal, below the first vertebra of the coccyx, and are named coccygeal. Although the plan of counting eight cervical nerves is continued in this work for the sake of convenience, it being that which is most frequently followed, it is by no means intended to represent this method as scientifically correct. The plan of \Villis, who reckoned the suboccipital as a cranial nerve, had at least the advantage that it made the numbers of the remaining seven cervical nerves correspond each with the vertebra beneath which it emerged, as do the dorsal, lumbar and sacral nerves; and if the suboccipital nerve, while recognised as the first spinal nerve, be TEE SPINAL NERVES.— ROOTS. kept distinct from the seven which succeed, as is taught in some schools, a nomenclature is arrived at much less objectionable than that which is most prevalent. A reference, however, to development (p. 17) will remind the reader that in the primordial vertebrae each spinal nerve is originally situated above the rib and transverse process belonging to the same seg- ment; and it will become apparent that the scientifically accurate nomenclature of nerves might be rather to name each in accordance with the number of the vertebra below it. Thus the eighth cervical nerve would be called first dorsal, and so on. Fig. 420. — DIAGRAMMATIC OUTLINE OF THE ROOTS AND FIRST PART OF THE SPINAL NERVES, TOGETHER WI1H THE SYMPATHETIC CORD OF ONE SIDE. ^ The view is taken from before. In the upper part of the figure the pons Varolii and medulla oblongata are represented, and from V, to IX, the roots of the several cranial nerves from the trifacial to the hypoglossal are indicated. On the left side C 1, is placed opposite the first cer- vical or suboccipital nerve ; and the numbers 2 to 8 following below indicate the corresponding cer- vical nerves; Br, indicates the brachial plexus ; D 1, is placed opposite the intercostal part of the first dorsal nerve, and the numbers 2 to 12 follow- ing mark the corresponding dorsal nerves ; S 1, the first lumbar nerve, and the numbers 2 to 5 following the remaining lumbar nerves; Cr, the anterior crural, and o, the obturator nerve ; SI, the first sacral, and the following numbers 2 to 5, the remaining sacral nerves ; 6, the coccygeal nerve; Sc, the great sciatic nerve; +, +, the filum terrainale of the cord. On the right side of the figure the following letters indicate parts of the sympathetic nerves ; viz., a, the superior cervical ganglion, com- municating with the upper cervical spinal nerves and continued below in the great sympathetic cord ; b, the middle cervical ganglion ; c, d, the lower cervical ganglion united with the first dorsal ; d', the eleventh dorsal ganglion ; from the fifth to the ninth dorsal ganglia the origins of the great splanchnic nerve are shown ; I, the lowest dorsal or upper lumbar ganglion ; ss, the upper sacral ganglion. In the whole extent of the sympathetic cord, the twigs of union with the spinal nerves are shown. Br Sometimes an additional coccygeal nerve exists. Among seven cases which appear to have been examined with great care, Professor Schlemm (" Observat. Neurolagicee,'' Berolini, 1834) found two coccygeal nerves on each side in one instance, and on one side in another case. In all the rest there was only a single coccygeal nerve on each side. Icr Sc 630 THE SPINAL NERVES. THE ROOTS OF THE SPINAL NERVES. Each spinal nerve springs from the spinal cord by two roots which approach one another, and, as they quit the spinal canal, join in the corresponding intervertebral foramen into a single cord ; and each cord so formed separates immediately into two divisions one of which is destined for parts in front of the spine, the other for parts behind it. The posterior roots of the nerves are distinguished from the anterior roots by their greater size, as well as by the greater thickness of the fasciculi of which they are composed. Each spinal nerve is furnished with a ganglion ; but the first cervical or sub-occipital nerve is in some cases without one. The size of the ganglia is in proportion to that of the nerves on which they are formed. The ganglia are in general placed in the intervertebral foramina, imme- diately beyond the points at which the roots perforate the dura mater lining the spinal canal. The first and second cervical nerves, however, which leave the spinal canal, over the laminae of the vertebrae, have their ganglia opposite those parts. The ganglia of the sacral nerves are contained in the spinal canal, that of the last nerve being occasionally at some distance from the point at which the nerve issues. The ganglion of the coccygeal nerve is placed within the canal in the sac of dura mater, and at a variable dis- tance from the origin of the nerve. Fig. 421. Fig. 421.— DIFFERKS-T VIEWS OF A PORTION OP THE SPINAL CORD FROM THK CERVICAL REGION WITH THE ROOTS OF THE NERVES. Slightly enlarged. In A, the anterior sur- face of the specimen is shown, the anterior nerve- root of the right side being divided ; in I>, a view of the right side is given ; in C, tho upper surface is shown ; in D, the nerve-roots and gan- glion are shown from below. 1, the anterior median fissure ; 2, pos- terior median fissure ; 3, anterior lateral depres- sion, over which thu ante- rior nerve-roots are seen to spread ; 4, posterior lateral groove, into which the posterior roots are seen to sink ; 5, anterior roots passing the ganglion ; 5', in A, the anterior root divided ; 6, the posterior roots, the fibres of which enter the ganglion, 6' ; 7, the uciled or compound nerve ; 7', the posterior primary branch seen in A and D, to be derived in part from the anterior and in part from the posterior root. « The fibres of the po: terior root of the nerve divide into two bundles as they approach the ganglion, and the inner extremity of the oval-shaped ganglion is sometimes bilobate, the lobes corresponding to the two bundles of fibres. SIZE AND STRUCTURE.— MODE OF DIVISION. 631 These fibres in man and the mammalia appear to pass through the ganglion with- out union with its cells. The cells are both unipolar and bipolar, but the fibres con- nected with them all pass to the periphery (Kolliker), so that beyond the ganglion the posterior root of the nerve has received an additional set of fibres besides those which it contains before reaching the ganglion. In fishes, on the contrary, all the fibres of the posterior root are connected with the opposite extremities of the bipolar cells of the ganglion. The anterior roots of the spinal nerves are, as will be inferred from what has been already stated, the smaller of the two ; they are devoid of ganglioiiic enlargement, and their fibres are collected into two bundles near the intervertebral ganglion, as in the posterior root. Size, — The roots of the upper cervical nerves are smaller than those of the lower nerves, the first being much the smallest. The posterior roots of these nerves exceed the anterior in size more than in the other spinal nerves, and they are likewise composed of fasciculi which are considerably larger than those of the anterior roots. The roots of the dorsal nerves, exception being made of the first, which resembles the lowest cervical nerves and is associated with the in in a part of its distribution, are of small size, and vary but slightly, or not at all, from the second to the last. The fasciculi of both roots are thinly strewed over the spinal cord, and are slender, those of the posterior exceeding in thickness tho^e of the anterior root in only a small degree. The roots of the lower lumbar, and of the upper sacral nerves, are the largest of all the spinal nerves ; those of the lowest sacral and the coccygeal nerve are, on the other hand, the slenderest. All these nerves are crowded together round the lower end of the corJ. Of these nerves the anterior roots are the smaller, but the disproportion between the anterior and pos- terior roots is not so great as in the cervical nerves. Length of the nerves in the spinal canal. — The place at which the roots of the upper cervical nerves are connected with the spinal cord being nearly opposite the foramina by which they respectively leave the canal, these roots are comparatively short. But the distance between the two points referred to is gradually augmented from nerve to nerve downwards, so that the place of origin of the lower cervical nerves is the breadth of at least one vertebra, and that of the lower dorsal nerves about the breadth of two vertebrae above the foramina by which they respectively emerge from the canal. Moreover, as the spinal cord extends no farther than the first lumbar vertebra, the length of the roots of the lumbar, sacral, and coccygeal nerves increases rapidly from nerve to nerve, ami in each case may be estimated by the distance of the foramen of exit from the extremity of the cord. Owing to their length, and the appearance they present in connection with the spinal cord, the aggregation of the roots of the nerves last referred to has been named the " cauda equina." The direction the roots take within the canal requires brief notice. The first cervical nerve is directed horizontally outwards. The roots of the lower cervical and dorsal nerves at first descend over the spinal cord, held in contact with it by the arachnoid, till they arrive opposite the several iutervertebral foramina, where they are directed horizontally outwards. The nerves of the cauda equina run in the direction of the spinal canal. Division of the nerves. — The two roots of each of the spinal nerves unite immediately beyond the ginglion, and the trunk thus formed separates, as already mentioned, into two divisions, an anterior and a posterior, which are called primary branches or divisions. In the detailed description of the spinal nerves which follows, we shall 632 THE SPINAL NERVES. begin with their posterior primary divisions, calling attention first to certain characters common to the whole of them, and afterwards stating separately the arrangement peculiar to each group of nerves (cervical, dorsal, &c.) POSTERIOR PRIMARY DIVISIONS OF THE SPINAL NERVES. The posterior divisions of the spinal nerves are, with few exceptions, smaller than those given to the fore part of the body. Springing from the trunk which results from the union of the roots of the nerve in the inter- vertebral foramen, or frequently by separate fasciculi from each of the roots, each turns backwards at once, and soon divides into two parts, distin- guished as external and internal, distributed to the muscles and the integu- ment behind the spine. The first cervical, the fourth aud fifth sacral and the coccygeal nerve are the only nerves the posterior divisions of which do not separate into external and internal branches. THE SUBOCCIPITAL NERVE. — The posterior division of the suboccipital nerve, which is the larger of the two primary divisions, emerging over the arch of the atlas, between this and the vertebral artery, enters the space bounded by the larger rectus and the two oblique muscles, and divides into branches for the surrounding muscles. a. One branch descends to the lower oblique muscle and gives a filament, through or over the fibres of that muscle, to join the second cervical nerve. 6. Another ascends over the larger rectus muscle, supplying it and the smaller rectus. c. A third enters the upper oblique muscle. d. A fourth sinks into the complexus, where that muscle covers the nerve and its branches. A cutaneous branch is occasionally given to the back of the head ; it accompanies the occipital artery, and is connected beneath the integument with the great and small occipital nerves. Fig. 422. — SUPERFICIAL AND DEEP DISTRIBUTION OP THE POSTERIOR PRIMARY DIVISIONS OF THE SPINAL NERVES (from Hirschfeld and Leveille). £ On the left side the cutaneous branches are represented as lying upon the superficial layer of muscles ; on the right side, the superficial muscles having been removed, the splenius and complexus have been divided in the neck, and the erector spinae separated and partially removed in the back, so as to expose the deep issue of the nerves. «, a, lesser occipital nerve from the cervical plexus ; 1, external muscular branches of the first cervical nerve and union by a loop with the second ; 2, placed on the rectus capitis posticus major, marks the great occipital nerve passing round the short muscles and piercing the complexus : the external branch is seen to the outside ; 2', cranial dis- tribution of the great occipital ; 3, external branch of the posterior primary division of the third nerve ; 3', its internal branch, or third occipital nerve ; 4', 5', 6', 7', 8', internal branches of the several corresponding nerves on the left side : the external branches of these nerves proceeding to muscles are displayed on the right side : dl, io d 6, and thence to c? 12, external muscular branches of the posterior primary divisions of the twelve dorsal nerves on the right side ; d 1', to d 6', the internal cutaneous branches of the six upper dorsal nerves on the left side ; d 7', to d 12', cutaneous branches of the six lower dorsal nerves from the external branches ; Z, I, external branches of the pos- terior primary branches of several lumbar nerves on the right side piercing the muscles, the lower descending over the gluteai region ; I', l\ the same more superficially on the left side ; s, s, on the right side, the issue and union by loops of the posterior primary divisions of four sacral nerves ; s't s', some of these distributed to the skin on the left side. POSTERIOR PRIMARY DIVISIONS. 633 Fig. 422. CERVICAL NERVES, with the exception of the saboccipital. — The external branches give only muscular offsets, and are distributed to the splenius and the blender muscles prolonged to the neck from the erector spinse, viz., the 634 THE SPINAL NERVES. cervicalis ascendens, and the trans versa! is colli with the trachelo-mastoid. That of the second nerve is the largest of the series of external branches, and is often united to the corresponding branch of the third ; it supplies the complexus muscle which covers it, and ends in the splenius and trachelo- inastoid muscles. The internal branches, larger than the external, are differently disposed at the upper and the lower parts of the neck. That of the second cervical nerve is named, from its size and destination, the great occipital, and requires separate notice. The rest are directed inwards to the spinous pro- cesses of the vertebrae. Those derived from the third, fourth, and fifth nerves pass over the semispinalis and beneath the complexus muscle, and, having reached the spines of the vertebrae, turn transversely outwards and are distributed in the integument over the trapezius muscle. From the cutaneous branch of the third nerve a branch passes upwards to the integu- ment on the lower part of the occiput, lying at the inner side of the great occipital nerve, and is sometimes called third occipital nerve. Between the inner branches of the first three cervical nerves, beneath the complexus, there are frequently communicating fasciculi ; and this communication Cruveilhier has designated as " the posterior cervical plexus." The internal branches from the lowest three cervical nerves are placed beneath the semispinalis muscle, and end in the muscular structure, without furnishing (except occasionally the sixth) any offset to the skin. These three nerves are the smallest of the series. The great occipital nerve is directed upwards on the lower oblique muscle, and is transmitted to the surface through the complexus and trapezius muscles, giving twigs to the complexus. Ascending with the occipital artery, it divides into branches, which radiate over the occipital part of the occipito-frontalis muscle, some appearing to enter the muscle, and others joining the smaller occipital nerve. An auricular branch is sometimes supplied to the back of the ear by the great occipital nerve. DORSAL NERVES. — The external branches increase in size from above downwards. They are directed through or beneath the longissiinus dorsi to the space between that muscle and the ilio-costalis and accessory ; they supply both those muscles, together with the small muscles continued upwards from the erector spinse to the neck, and also the levatores costarum. The lower five or six nerves give cutaneous twigs, which are transmitted to the integu- ment in a line with the angles of the ribs. The internal branches of the upper six dorsal nerves appear in the interval between the multifidus spinee and the semispinalis dorsi ; they supply those muscles, and become cutaneous by the side of the spinous processes of the vertebras. The cutaneous branch from the second nerve, and sometimes others, reach as far as the scapula. The internal branches of the lower six dorsal nerves are placed between the multifidus spinso and longissimus dorsi, and end in the multifidus without giving branches to the integument. Where cutaneous nerves are supplied by the internal branches, there are none from the external branches of the same nerve, and vice versa. LUMBAR NERVES. — The external branches enter the erector spinse, and give filaments to the intertrans verse muscles. From the upper three, cutaneous nerves are supplied ; and from the last, a fasciculus descends to the corresponding branch of the first sacral nerve. The cutaneous nerves given from the external branches of the first three lumbar nerves, pierce the ANTERIOR PRIMARY DIVISIONS. 635 fleshy part of the ilio-costalis, and the apcmeurosis of the latissimus dorsi ; they cross the iliac crest near the edge of the erector spinse, and terminate in the integument of the gluteal region. One or more of the filaments may be traced as far as the great trochanter of the femur. The internal branches wind backwards in grooves close to the articular processes of the vertebrae, and sink into the mukifidus spinse muscle. SACRAL NERVES. — The posterior divisions of the nerves, except the last, issue from the sacrum through its posterior foramina. The first three are covered at their exit from the bone by the multifidus spinre muscle, and bifurcate like the posterior trunks of the other spinal nerves ; but the remaining two, which continue below that muscle, have a peculiar arrangement, and require separate examination. The internal branches of the Jirst three sacral nerves are small, and are lost in the multifidus spinse muscle. The external branches of the same nerves are united with one another, and with the last lumbar and fourth sacral nerves, so as to form a series of anastomotic loops on the upper part of the sacrum. These branches are then directed outwards to the cutaneous or posterior surface of the great sacro-sciatic ligament, where, covered by the gluteus maximus muscle, they form a second series of loops, and end in cutaneous nerves. These pierce the great gluteus muscle in the direction of a line from the posterior iliac spine to the tip of the coccyx. They are commonly three in number — one is near the innominate bone, another opposite the extremity of the sacrum, and the third about midway between the other two. All are directed out- wards over the great gluteal muscle. In six dissections by Ellis tliis arrangement was found to be the most frequent. The variations to which it is liable are these : — the first nerve may not take part in the second series of loops, and the fourth may be associated with them. The posterior divisions of the last two sacral nerves are smaller than those above them, and are not divided into external and internal branches. They are connected with each other by a loop on the back of the sacrum, and the lowest is joined in a similar manner with the coccygeal nerve ; one or two small filaments from these sacral nerves are distributed behind the coccyx. COCCYGEAL NERVE. — The posterior division of the coccygeal nerve is very small, and separates from the anterior primary portion of the nerve in the sacral canal. It is joined by a communicating filament from the last sacral nerve, and ends in the fibrous structure covering the posterior surface of the coccyx. ANTERIOR PRIMARY DIVISIONS OP THE SPINAL NERVES. The anterior primary divisions of the spinal nerves are distributed to the parts of the body situated in front of the vertebral column, including the limbs. They are, for the most part, ponsiderably larger than the posterior divisions. The anterior division of each spinal nerve is connected by one or two slender filaments with the sympathetic. Those of the cervical, lumbar, and sacral nerves form plexuses of various forms ; but those of the dorsal nerves remain for the most part separate one from another. T T 2 636 THE CERVICAL NERVES AND PLEXUS. CERVICAL NERVES. The anterior divisions of the four upper cervical nerves form the cervical plexus. They appear at the side of the neck between the scalenus medius and rectus anticus major muscles. They are each connected by a commu- nicating filament with the first cervical ganglion of the sympathetic nerve, or with the cord connecting that ganglion with the second. The anterior divisions of the four lower cervical nerves, larger than those of the upper four, appear between the scaleni muscles, and, together with that of the first dorsal, go to form the brachial plexus. They are each connected by a filament with one of the two lower cervical ganglia of the sympathetic, or with the plexus on the vertebral artery. The anterior divisions of the first and second nerves require a notice separately from the description of the nerves of the cervical plexus. SUBOCCIPITAL NERVE. The anterior primary division of the first nerve runs forwards in a groove on the atlas, and bends downwards in front of the transverse process of that vertebra to join the second nerve. In this course forwards it lies beneath the vertebral artery, and at the inner side of the rectus lateralis muscle, to which it gives a branch. As it crosses the foramen in the transverse process of the atlas, the nerve is joined by a filament from the sympathetic ; and from the arch, or loop of the atlas, which it makes in front of the transverse process, branches are supplied to the two anterior recti muscles. Short filaments connect this part of the nerve with the pneumo-gastric, the hypo- glossal, and the sympathetic nerves. Valentin notices filaments distributed to the articulation of the occipital bone with the atlas, and to the mastoid process of the temporal bone. , SECOND CERVICAL NERVE. The anterior division of the second cervical nerve, beginning between the arches of the first two vertebrae, is directed forwards between their trans- verse processes, being placed outside the vertebral artery, and beneath the iutertransverse and other muscles fixed to those processes. In front of the intertransverse muscles the nerve divides into an ascending part, which joins the first cervical nerve, and a descending part to the third. •V . CERVICAL PLEXUS. The cervical plexus is formed by the anterior divisions of the first four cervical nerves, and distributes branches to some of the muscles of the neck, and to a portion of the integument of the head and neck. It is placed opposite the first four vertebras, beneath the sterno-mastoid muscle, and rests against the middle scalenus muscle and the levator auguli scapuhe. The disposition of the nerves in the plexus is easily recognised. Each nerve except the first, branches into au ascending and a descending part : and these are united in communicating loojps with the contiguous nerves. From the union of the second and third nerves, superficial branches are supplied to the head and neck ; and from the junction of the third with the fourth, arise the cutaneous nerves of the shoulder and chest. Muscular and com- municating branches spring from the same nerves. The branches of the plexus may be separated into two sets — a superficial THE CERVICAL PLEXUS. 637 and deep ; the superficial consisting of those which ramify over the cervical fascia, supplying the integument and some also the platysma ; the deep comprising branches which are distributed for the most part to the muscles. The superficial nerves may be subdivided into ascending and descending ; the deep nerves into an internal and external series. Fig. 423. — DIAGRAMMATIC Fig 423. OUTLINE OP THE FIRST PARTS OP THE CERVICAL AND UPPER DORSAL NERVES, SHOWING THE CERVICAL AND BRACHIAL PLEXUSES. J The nerves are separated from tlie spinal cord at their origin and are sup- posed to be viewed from before. Cl, is placed op- posite the roots of the first cervical or suboccipital nerve, and the roman num- bers in succession from IF, to VIII, opposite the roots of the corresponding cer- vical nerves ; DI, is placed opposite to the roots of the first dorsal nerve, and II, and IK, opposite the second and third nerves ; the origin of the posterior primary branch is shown in all the nerves; of these p 2, indi- cates the great occipital from the second, and ^;3, the smallest occipital nerve from the third. In con- nection with the cervical plexus the following indica- tions are given ; 1, anterior primary branch of the first cervical nerve and loop of union with the second nerve ; 2, lesser occipital nerve proceeding in this case from the second cervi- cal nerve, more frequently from the second and third ; 3, great auricular nerve from the second and third ; 3', superficial cervical nerve from the third; 3 n, communicating branches to the descen- dens noni from the second and third ; 3 s, communicating to the spinal-accessory from the second, third, and fourth ; 4, supraclavicular and supraacromial descending nerves : the loops or arches of communication between the four upper cervical nerves, and between the fourth and fifth are shown ; 4', the phrenic nerve springing from the fourth and fifth nerves. In connection with the nerves of the brachial plexus and the remaining nerves the following indications are given — V, to VIII7, and D', the five roots of the brachial plexus ; 5, the rhomboid nerve ; 5', suprascapular ; 5", posterior thoracic ; 6, nerve to the subclavius muscle; 7, 7, inner and outer anterior thoracic nerves; 8, 8', 8", upper and lower subscapular nerves. In the larger nerves proceeding to the shoulder and arm from the plexus, those of the anterior division are represented of a lighter shade, those belonging to the posterior division darker ; ec, external cutaneous or musculo-cutaneous ; ?/i, median; M, ulnar, ic, internal cutaneous ; w, nerve of Wrisberg ; r, musculo -spiral ; c, circum- flex ; i, intercostal nerves ; i', lateral branch of the same ; ih, intercosto-humeral nerves. Ill 038 THE CERVICAL NERVES AND PLEXUS. I. SUPERFICIAL ASCENDING BRANCHES. SUPERFICIAL CERVICAL NERVE. This nerve takes origin from the second and third cervical nerves, turns forward over the sterno-mastoid about the middle, and, after perforating the cervical fascia, divides beneath the platysma myoides into two branches, which are distributed to the anterior and lateral parts of the neck. a. The upper branch gives an ascending twig which accompanies the external jugular vein, and communicates freely with the facial nerve (cervico-facial division) ; it is then transmitted through the platysma to the surface, supplying that muscle, and ramifies in the integument of the upper half of the neck on the fore part, filaments reaching as high as the lower maxilla. b. The lower branch likewise pierces the platysma, and is distributed below the preceding, its filaments extending in front as low as the sternum. The superficial cervical nerve may arise from the plexus in the form of two or more distinct branches. Thus Valentin describes three superficial cervical nerves, which he names superior, middle, and inferior. (" Sommerring v. Bau," &c.) While the superficial cervical nerve ramifies over the platysma myoides, the facial nerve is beneath the muscle. According to Valentin many anastomotic arches are formed on the side of the neck between those two nerves, as well as between the branches of the former, one with another. GREAT AURICULAR NERVE. This nerve winds round the outer border of the sterno-mastoid, and is directed obliquely upwards beneath the platysma myoides, between the muscle and the deep fascia of the neck, to the lobe of the ear. Here the nerve gives a few small branches to the face, and ends in the auricular and mastoid branches. a. The auricular branches are directed to the back of the external ear, on which they ramify, and are connected with twigs derived from the facial nerve. One of these branches reaches the outer surface of the ear by a fissure between the antihelix and the concha. A few filaments are supplied likewise to the outer part of the lobule. b. The mastoid branch is united to the posterior auricular branch of the facial nerve, and ascends over the mastoid process to the integument behind the ear. c. The facial branches of the great auricular nerve, which extend to the integu- ments of the face, are distributed over the parotid gland. Some slender filaments penetrate deeply through the substance of the gland, and communicate with the facial nerve. SMALL OCCIPITAL NERVE. The smaller occipital nerve varies in size, and is sometimes double. It springs from the second cervical nerve, and is directed almost vertically to the head along the posterior border of the sterno-mastoid muscle. Having perforated the deep fascia near the cranium, the small occipital nerve is continued upwards between the ear and the great occipital nerve, and ends in cutaneous filaments which extend upwards in the scalp ; it communicates with branches from the larger occipital nerve, as well as with the posterior auricular branch of the facial. It appears to supply sometimes the occipito- frontalis muscle. The auricular branch (ram. auricularis superior posterior) is distributed to the upper part of the ear on the posterior aspect, and to the elevator muscle of the auricle. This auricular branch is an offset from the great occipital nerve, when the small occipital is of less size than usual. STJPRACLAVICULAR NERVES. 639 II. SUPERFICIAL DESCENDING BRANCHES. SUPRACLAVICULAR NERVES. The descending series of the superficial nerves are thus named. There Fig. 424. Fig. 424. — VIEW OP THE SUPERFICIAL DISTRIBUTION OF THE NERVES PROCEEDING FROM TEE CERVICAL PLEXUS (from Sappey after Hirschfeld and Leveille). £ 1, superficial cervical nerve; 2,2, descending branches of the same; 3, ascending branches ; 4, twigs uniting with the facial ; 5, great auricular nerve ; 6, its parotid branch ; 7, its external auricular branch ; 8, twig of the same which pierces the auricle to pass to its outer surface ; 9, branch to the deep surface of the pinna ; 10, its union with the posterior auricular of the facial nerve ; 11, small occipital nerve ; 12, its branch which unites with the great occipital nerve ; 13, a mastoid branch or second small occipital ; 14, twigs from this to the back of the neck ; 15, 16, supraclavicular nerves; 17, 18, supraacromial nerves ; 19, branch of the cervical nerves passing into the trapezius muscle ; 20, spinal accessory distributed to the same and receiving a uniting branch from the cervical nerves ; 21, branch to the levator scapuli ; 22, trunk of the facial nerve ; 23, its posterior auricular branch passing into the occipital and posterior and superior auricular muscles ; 24, its cervico- facial branches. 640 THE CERVICAL NERVES AND PLEXUS. are two of these nerves, or, in some cases, a greater number. They arise from the third and fourth cervical nerves, and descend in the interval between the sterno-mastoid and the trapezius muscles. As they approach the clavicle, the nerves are augmented to three or more iii number, and are recognised as internal, middle, and posterior. a. The internal (sternal) branch, which is much smaller than the rest, ramifies over the inner half of the clavicle, and terminates near the sternum. b. The middle branch, lying opposite the interval between the pectoral and deltoid muscles, distributes some twigs over the fore part of the deltoid, and others over the pectoral muscle. The latter join the small cutaneous branches of the intercostal nerves. c. The external or posterior branch (acromial) is directed outwards over the acro- mion, and the clavicular attachment of the trapezius muscle, and ends in the integu- ment of the outer and back part of the shoulder. III. DEEP BRANCHES : INNER SERIES. CONNECTING BRANCHES. The cervical plexus is connected near the base of the skull with the trunks of the pneumo-gastric, hypoglossal, and sympathetic nerves, by means of filaments intervening between those nerves and the loop formed by the first two cervical nerves in front of the atlas (p. 637). MUSCULAR BRANCHES. Branches to the anterior recti muscles proceed from the cervical nerves close to the vertebrae, including the loop between the first two of these nerves. Two branches to the ansa hypoglossi, one from the second, the other from the third cervical nerve, descend over or under the internal jugular vein, to form a loop of communication with the rarnus descendens noni, and aid in the supply of the muscles below the hyoid bone (p. 6 20). PHRENIC NERVE. The diaphragmatic or phrenic nerve passes down through the lower part of the neck and the thorax to its destination. It commences from the fourth cervical nerve, and receives usually a fasci- culus from the fifth. As it descends in the neck, the nerve is inclined inwards over the anterior scalenus muscle ; and near the chest it is joined by a filament of the sympathetic, and sometimes also by another filament derived from the fifth and sixth cervical nerves. As it enters the thorax each phrenic nerve is placed between the sub- clavian artery and vein, and crosses over the internal mammary artery near the root. It then takes nearly a straight direction, in front of the root of the lung on each side, and along the side of the pericardium, — between this and the mediastinal part of the pleura. Near the diaphragm it divides into branches, which separately penetrate the fibres of that muscle, and then diverging from each other, are distributed on the under surface. The right nerve is placed more deeply than the left, and is at first directed along the outer side of the right innominate vein, and the descending vena cava. DEEP CERVICAL NERVES.- BRACIIIAL PLEXUS. 641 The nerve of the left side is a little longer than that of the right, in conse- quence of the oblique position of the pericardium round which it winds, and also because of the diaphragm beiug lower on this than on the opposite side. This nerve crosses in front of the arch of the aorta and the pul- monary artery before reaching the pericardium. Besides the terminal branches supplied to the diaphragm, each phrenic nerve gives filaments to the pleura and pericardium ; and receives sometimes an offset from the union of the descendens noni with the cervical nerves. Swan notices this union as occurring only on the left side. Luschka describes twigs from the lower part of the nerve to the peritoneum, the inferior cava, and the right auricle of the heart. One or two filaments of the nerve of the right side join in a small ganglion with branches to the diaphragm which are derived from the solar plexus of the sympa- thetic ; and from the ganglion twigs are given to the suprarenal capsule, the hepatic plexus, and the lower vena cava. On the left side there is a junction between the phrenic and the sympathetic nerves near the oesophageal and aortic openings in the diaphragm, but without the appearance of a ganglion. IV. DEEP BRANCHES : EXTERNAL SERIES. Muscular branches. — The sterno-mastoid receives a branch from the second cervical nerve. Two branches proceed from the third nerve to the levator anguli scapulas ; and from the third and fourth cervical nerves, as they leave the spinal canal, branches are given to the middle scalenus muscle. Further, the trapezius has branches prolonged to it ; and thus, like the sterno-mastoid, this muscle receives nerves from both the spinal accessory and the cervical plexus. Connection with the spinal accessory nerve. — In the substance of the sterno- mastoid muscle, this nerve is connected with the branches of the cervical plexus furnished to that muscle. It is also connected with the* branches distributed to the trapezius — the union between the nerves being beneath the muscle, and having the appearance of a plexus ; and with another branch of the cervical plexus in the interval between the two muscles. Summary of the cervical plexus. — From the cervical plexus are distributed cutaneous nerves to the ba?k of the head, to part of the ear and face, to the anterior half of the neck, and to the upper part of the trunk. The muscles supplied with nerves from the plexus are the sterno-mastoid, the platysma, and the lower hyoid muscles in part ; the anterior recti, the levator anguli scapulse, the trapezius, the scalenus medius, and the diaphragm. By means of its branches the plexus communicates with the pneumo-gastric, spinal accessory, hypoglossal, and sympathetic nerves. BRACHIAL PLEXUS. This large plexus, from which the nerves of the upper limb are supplied, is formed by the union of the anterior trunks of the four lower cervical and first dorsal nerves ; and it further receives a fasciculus from the lowest of the nerves (fourth), which goes to form the cervical plexus. The plexus extends from the lower part of the neck to the axillary space, and termi- nates opposite the coracoid process of the scapula in large nerves for the supply of the limb. The manner in which the nerves are disposed in the plexus is liable to some variation, but the following may be regarded as the arrangement most frequently met with. The fifth and sixth cervical are joined at the outer border of the scalenus, and a little farther out receive the seventh nerve, 642 THE BEACHIAL PLEXUS. — the three nerves giving rise to one large upper cord. The eighth cervical and first dorsal nerves are united in another lower cord whilst they are Fig. 425. Fig. 425. — DEEP DISSECTION OF THE AXILLA, SHOWING THE BRACHIAL PLEXUS AND NEIOHBOUKING NERVES (from Sappey after Hirschfeld and Leveille). £ The clavicle has been sawn through near its sternal end, and is turned aside with the muscles attached to it ; the subclavius, and the greater and lesser pectoral muscles have been removed from the front of the axilla. 1, loop of union between the descendens noni and a branch of the cervical plexus ; 2, pneumo-gastric ; 3, phrenic passing down to the inner side of the scalenus anticus muscle ; 4, anterior primary division of the fifth cervical nerve ; 5, the same of the sixth ; 6, 7, the same of the seventh and eighth cervical nerves ; 8, the same of the first dorsal nerve ; 9, 9, branch from the plexus to the subclavius muscle, communicating with the phrenic nerve; 10, posterior thoracic nerve distributed to the serratus magnus ; 11, upper anterior thoracic nerve passing into the great pectoral muscle ; 13, lower anterior thoracic distributed to the lesser pectoral ; 14, twig of com- munication between these two nerves ; 12, suprascapular nerve passing through the supra- scapular notch ; 15, lower of the two subscapular nerves ; 16, nerve of the teres major ; 17, long subscapular, or nerve of the latissimus dorsi ; 18, accessory of the internal cutaneous nerve ; 19, union of the accessory cutaneous with the second and third inter- costal nerves ; 20, lateral branch of the secoud intercostal ; 21, second internal cutaneous or nerve of Wrisberg ; 22, internal cutaneous nerve ; 23, the ulnar nerve to the inside of the axillary artery, passing behind the vein, and having, in this case, a union with the upper division of the plexus ; 24, the median nerve immediately below the place where its two roots embrace the artery, which is divided above this place; 25, the musculo-cutaneous nerve passing into the coraco-brachialis muscle; 26, the musculo-spiral nerve passing behind the divided brachial artery. BRANCHES OF THE BRACHIAL PLEXUS. 643 between the scaleni muscles. The two cords thus formed lie side by side in the fore part of the plexus, and external to the first part of the axillary vessels.. At the same place, or lower down, a third intermediate or posterior cord is produced by the union of fasciculi from each of the other two cords, or separately from the nerves forming them. The three cords of which the plexus now consists, are placed, one on the outer side of the axillary artery, one on the inner side, and one behind that vessel, and are continued into the principal nerves for the arm. The two fasciculi which unite to form the intermediate of the three trunks are generally separated at a higher level than the formation of the two other trunks, but they are also frequently given off as low as the clavicle, or even farther down ; this gives rise to some varieties, more apparent than real. The seventh nerve also may give a branch to the cord below it. The branches proceeding from the plexus are numerous, and may be conveniently divided into two classes — viz., those that arise above the clavicle, and those that take origin below the bone. BRANCHES ABOVE THE CLAVICLE. Above the clavicle there arise from the trunks of the brachial plexus, the posterior thoracic and supra scapular nerves, a nerve for the rhomboid muscles, another for the subclavius, irregular branches for the scaleni and longus colli, and a branch to join the phrenic nerve. The branches for the scaleni and longus colli muscles spring in an irregular manner from the lower cervical nerves close to their place of emergence from the vertebral foramina. The branch for the rhomboid muscles arises from the fifth nerve, and is directed backwards to the base of the scapula through the fibres of the middle scalenus and beneath the levator anguli scapulae. It is distributed to the deep surface of the rhomboid muscles, and gives sometimes a branch to the levator scapulae. Fig. 426. — DISTRIBUTION OP TOE SUPRASCAPULAR AND CIRCUMFLEX NERVES (from HirschfeldandLeveille). | Fig. 426. 1' a, the scalenus medius and posticus muscles ; b, levator anguli scapulae ; c, acromion ; d. deltoid muscle, of which the back part has been de- tached from the scapula and in part removed ; e, rhomboid muscle ; /, teres major ; g, la- tissimus dorsi ; 1 , the brachial plexus of nerves as seen from behind ; 1', the nerve of the levator scapulae and rhomboid muscles ; 2, placed on the clavicle, marks the supra- scapular nerve ; 3, its branch to the supraspinatus muscle ; 4, branch to the infraspinatus ; 5, placed on the back of the humerus below the insertion of the teres minor, marks the circumflex nerve passing out of the quadrangular interval ; 6, its branch to the teres minor muscle ; 7, branches to the deep surface of the deltoid ; 8, cutaneous branch to the back of the shoulder. 644 THE BRACHIAL PLEXUS. The nerve of the subdavius muscle, of small size, arises from the front of the cord which results from the union of the fifth and sixth cervical nerves. It is directed over the outer part of the subclavian artery to the deep surface of the subclavius muscle. This small nerve is commonly connected with the phrenic nerve in the neck or in the che-st, by means of a slender filament. Branch to join the phrenic nerve.— This small and short branch is an offset from the fifth cervical nerve ; it joins the phrenic nerve on the anterior scalenus muscle. POSTERIOR THORACIC NERVE. The posterior thoracic nerve (nerve of the serratus magnus, external respiratory of Bell) is formed in the substance of the middle scalenus muscle by two roots, one from, the fifth and another from the sixth nerve, and reaches the surface of the scalenus lower than the nerve of the rhomboid muscles, with which it is often connected. It descends behind the brachial plexus on the outer surface of the serratus magnus, nearly to the lower border of that muscle, supplying it with numerous branches. SUPRASCAPULAR NERVE. The suprascapular nerve arises from the back of the cord formed by the union of the fifth and sixth nerves, and bends beneath the trapezius to the upper border of the scapula, where it passes between the muscles and the bone. Entering the supraspinous fossa of the scapula, through, the supra- scapular notch (beneath the ligament which crosses the notch), the supra- scapular nerve supplies two branches to the supraspinatus, one near the upper, the other near the lower part of the muscle ; and it then descends through the great scapular notch into the lower fossa, where it ends in the infraspinatus muscle. In the upper fossa of the scapula, a slender articular filament is given to the shoulder-joint, and in the lower fossa other twigs of the nerve enter the same joint and the substance of the scapula. BRANCHES BELOW THE CLAVICLE. Origin of nerves from the plexus. — The several nerves now to be described are derived from the three great cords of the plexus in the following order. From the upper or outer cord, — the external of the two anterior thoracic nerves, the musculo-cutaneous, and the outer root of the median. From the lower or inner cord, — the inner of the two anterior thoracic, the nerve of Wrisberg, the internal cutaneous, the ulnar, and the inner root of the median. From the posterior cord, — the subscapular nerves, the circumflex, and the musculo-spiral. The nerves traced to the spinal nerves. — If the fasciculi of which the principal nerves are composed be followed through the plexus, they may be traced to those of the spinal nerves which in the subjoined table are named along with each trunk. The higher numbers refer to the cervical nerves, the unit to the dorsal nerve : — 5.6.7.8. Subscapular from Circumflex . • Musculo-spiral . External cutaneous . Median 5.6.7.8.1. 1. or 7.8.1. Ulnar Internal cutaneous . ) Small internal cutaneous ) outer 5.6.7 inner 8.1. Anterior thoracic The outline in Fig. 423, taken from a dissection, represents one of the most common arrangements. ANTERIOR THORACIC.— SUBSCAPULAR NERVES. 645 Some differences will be found in the statements of anatomists who have investigated the subject— for instance, Scarpa (" Annotations Anatom.")and Kronen- berg (" Plex. nervor. Structura et Virtutes ") — with respect to the nerves to which the branches are assigned. This difference is mainly owing to the variation which actually exists in different cases. ANTERIOR THORACIC NERVES. The anterior thoracic nerves, two in number, supply the pectoral muscles. The external, or more superficial branch, arising from the outer cord, crosses inwards over the axillary artery, and terminates in the great pectoral muscle. The internal, or deeper branch, springing from the inner cord, comes forwards between the axillary artery and vein to the small pectoral muscle, and is joined by a branch from the exterual. This nerve presents a plexi- form division beneath the small pectoral muscle, and supplies branches to it and the larger pectoral muscle. The two nerves are connected by a tila- ment which forms a loop over the artery at the inner side. SUBSCAPULAR NERVES. These nerves, three in number, take origin from the posterior cord of the plexus. The upper nerve, the smallest of the sub- scapular nerves, penetrates the upper part of the subscapular muscle. The lower nerve gives a branch to the subscapularis at its axillary border, and ends in the teres major muscle. There is sometimes a distinct nerve for the last-named muscle. The long subscapular nerve, the largest of the three, runs along the lower border of the sub- scapular muscle to the lutissinius dorsi, to which it is distributed. Fig. 427. — DISTRIBUTION OF THE POSTKRIOR CUTANEOUS NERVES OP THE SHOULDER AND ARM (from Hirschfeld and Leveille). I 1, supra-acromial branches of the cervical nerves de- scending on the deltoid muscle ; 2, ascending or reflected, and 2', descending cutaneous branches of the circumflex nerve ; 3, inferior external cutaneous of the musculo-spiral nerve ; 4, external and posterior cutaneous branches of the niusculo-cutaneous nerve to the forearm ; 5, internal cutaneous of the musculo-spiral ; 6, intercosto-humeral branches ; 7, twigs of the nerve of Wrisberg ; 8, upper posterior branch of the internal cutaneous nerve ; 9, lower branch of the same. CIRCUMFLEX NERVE. The circumflex or axillary nerve gives both muscular and cutaneous nerves to the shoulder. Springing from the posterior cord, this nerve is at first placed behind the axillary artery, but at the lower border of the subscapular muscle it is inclined backwards with the posterior circumflex artery, in the space between the scapula and tere& 646 THE BRACHIAL PLEXUS. major muscle above the long head of the triceps, and separates into an upper and a lower branch, which are distributed to the deltoid and teres minor muscles, the integument of the shoulder, and the shoulder-joint. a. The upper portion winds round the upper part of the humerus, extending to the anterior border of the deltoid muscle, to which it is distributed. One or two cutaneous filaments, penetrating between the muscular fibres, are bent downwards and supply the integument over the lower part of the muscle. b. The lower branch supplies offsets to the back part of the deltoid, and furnishes the nerve to the teres minor, which is remarkable in presenting a gangliform enlarge- ment. It then turns round the posterior border of the deltoid below the middle, and ramifies in the integument over the lower two-thirds of that muscle, one branch extending to the integument over the long end of the triceps muscle. c. An articular filament for the shoulder-joint arises near the commencement of the nerve, and enters the capsular ligament below the subscapular muscle. INTERNAL CUTANEOUS NERVE. At its origin from the inner cord of the brachial plexus, this nerve is placed on the inner side of the axillary artery. It becomes cutaneous about the middle of the arm, and after perforating the fascia, or, in some cases, before doing so, is divided into two parts ; one destined for the anterior, the other for the posterior surface of the forearm. a. The anterior branch crosses at the bend of the elbow behind (in some cases over) the median basilic vein, and distributes filaments in front of the forearm, as far as the wrist; one of these is, in some instances, joined with a cutaneous branch of the ulnar nerve. b. The posterior branch inclines obliquely downwards at the inner side of the basilic vein, and winding to the back of the forearm, over the prominence of the internal condyle of the humerus, extends somewhat below the middle of the forearm. Above the elbow this branch is connected with the smaller internal cutaneous nerve (nerve of Wrisberg), and afterwards communicates with the outer portion of the internal cutaneous, and, according to Swan, with the dorsal branch of the ulnar nerve. c. A branch to the integument of the arm pierces the fascia near the axilla, and reaches to, or nearly to the elbow, distributing filaments outwards over the biceps muscle. This branch is often connected with the intercosto -humeral nerve. SMALL INTERNAL CUTANEOUS NERVE. The smaller internal cutaneous nerve, or nerve of Wrisberg, destined for the supply of the integument of the lower balf of the upper arm on the inner and posterior aspect, commonly arises from the inner cord of the brachial plexus in union with the larger internal cutaneous and uluar nerves. In the axilla it lies close to the axillary vein, but it soon appears on the inner side of that vessel, and communicates with the intercosto- humeral nerve. It then descends along the inner side of the brachial vessels to about the middle of the arm, where it pierces the fascia, and its filaments are thence continued to the interval between the internal condyle of the humerus and the olecranon. Branches. — In the lower third of the arm, branches of this small nerve are directed almost horizontally to the integument on the posterior aspect ; and the nerve ends at the elbow by dividing into several filaments some of which are directed forwards over the inner condole of the humerus, while others are prolonged downwards behind the olecranon. Connection with the intercosto-humeral nerve. — This connection presents much variety in different cases : — in some, there are two or more intercommunications, form- ing a kind of plexus on the posterior boundary of the axillary space ; in others, the NERVES OF THE UPPER LIMB. 647 intercosto-humeral nerve is of larger size than usual, and takes the place of the nerve of Wrisberg, only receiving in the axilla a small filament from the brachial plexus ; Fig. 429. Fig. 428. — ANTERIOR CUTANEOUS NERYES OF THE SHOULDER AND ARM (from Sappey after Hirschfeld and Leveilld). I 1, 1, snpraclavicular and supraacromial nerves from the cervical plexus ; 2, 2, 2, cutaneous branches of the circumflex nerve ; 3, 4, upper branches of the internal cuta- neous nerve ; 5, superior external cutaneous branch of the musculo- spiral ; 6, internal cutaneous nerve piercing the deep fascia ; 7, posterior branch ; 8, communicating twig with one of the anterior branches ; 9, 10, anterior branches of this nerve, some turning round the median basilic and ulnar veins ; 11, musculo-cutaneous nerve descending over the median cephalic vein ; 12, inferior cutaneous branch of the musculo-spiral nerve. Fig. 429. — ANTERIOR CUTANEOUS NERVES OP THE FOREARM AND HAND (from Sappey after Hirschfeld and Leveille). fe 9, 10, 13, distribution of the anterior branches of the internal cutaneous nerve; 14, union of one of these with a twig of the ulnar nerve ; 12, inferior cutaneous branch of the musculo-spiral nerve; 11, 15, distribution of the external cutaneous nerve; 16, union of one of its branches with 17, the terminal branch of the radial nerve ; 18, palmar cutaneous branch of the median nerve; 19, 20, internal and external collateral branches to the thumb from the median nerve ; 21, external collateral to the index finger ; 22, 23, collateral branches to the index, middle and fourth fingers ; 24, 25, collateral branches from the ulnar nerve to the fourth and fifth fingers ; the network of communicating twigs formed by the terminal branches of these cutaneous nerves is repre- sented at the extremities of the fingers. 648 NER\ES OF THE UPPER LIMB. and this small communicating filament represents in such cases the nerve of Wrisberg. MUSCULO-CUTANEOUS NERVE. The musculo-cutaneous or external cutaneous nerve (perforans Casserii) in deeply placed between the muscles as far as the elbow, and below that point is immediately under the integument. Arising from the brachial plexus opposite the small pectoral muscle, it perforates the coraco-brachialis muscle, and, passing obliquely across the arm between the biceps and brachialis anticus muscles, reaches the outer side of the biceps a little above the elbow. Here it perforates the fascia, and nearly opposite the elbow-joint it passes behind the median-cephalic vein, and, inclining outwards, divides into two branches which supply the integument on the outer side of the forearm, one on the anterior, the other on the posterior aspect. A. Branches in the arm : — a. A branch to the coraco-brachialis and short head of the biceps is given off before the nerve pierces the former muscle ; and other filaments are furnished to the coraco- brachialis, while the nerve lies among its fibres. b. Branches to the biceps and brachialis anticus are given off while the nerve is between those muscles. c. Small filaments are given to the humerus and elbow-joint. B. Branches in the forearm : — a. The anterior branch descends near the radial border of the forearm. It is placed in front of the radial artery near the wrist, and distributes some filaments over the ball of the thumb. Piercing the fascia, it accompanies the artery to the back part of the carpus. This part of the nerve is connected at the wrist with a branch of the radial nerve. b. The posterior branch is directed outwards to the back of the forearm, and ramifies in the integument of the lower third, extending as far as the wrist. It com- municates with a branch of the radial nerve, and with the external cutaneous branch of the musculo-spiral nerve. Summary. — The musculo-cutaneous nerve supplies the coraco-brachialis, biceps, and brachialis anticus muscles, and the integument on the outer side of the forearm. Communications are established between it and the radial and the external cutaneous branch of the musculo-spiral. Varieties. — In some cases it does not perforate the coraco-brachialis muscle. It is frequently found to communicate by a cross branch with or to be an offset of the median nerve ; and in the latter case, the coraco-brachialis muscle receives a separate branch from the brachial ploxus, which may be explained thus, — that the main part of the musculo-cutaneous nerve, instead of piercing the coraco-brachialis muscle, remains adherent to the outer root and trunk of the median. ULNAR NERVE. The ulnar nerve, the largest branch of the inner cord of the brachial plexus, descends on the inner side of the artery of the limb as far as the middle of the arm, then turns backwards through the internal intermuscular septum with the inferior profunda artery, to reach the interval between the olecranon and the inner condyle of the humerus. From the axilla to this place it is covered only by the fascia, and it may be felt through the integu- ment a little above the elbow. It here passes between the two heads of the flexor carpi ulnaris, and it remains concealed by that muscle as far as the middle of the forearm ; it thence extends in a straight course along the' outer margin of the muscle, between it and the uluar artery, to the outer ULXAR AXD MEDIAN XEEVES. 649 side of the pisiform bone. Above the wrist it gives off a large dorsal branch to the hand, and continuing onwards it enters the palm on the surface of the annular ligament, and divides into muscular and cutaneous branches. The ulnar nerve gives off no branches in the upper arm. A. Branches in the forearm : — a. Articular filaments are given to the elbow-joint as the nerve passes behind it. Some filaments are also given to the wrist-joint. b. Muscular branches. — One branch enters the upper part of the flexor carpi ulnaris, and another supplies the two inner divisions of the deep flexor of the fingers.* c. Cutaneous branches to the forearm. — These two small nerves arise about the middle of the forearm by a common trunk. One pierces the fascia, and turning downwards, joins a branch of the internal cutaneous nerve. This branch is often absent. The second, a palmar branch, lies on the ulnar artery, which it accompanies to the hand. This little nerve gives filaments around the vessel, and ramifies in the integument of the hand, joining in some cases with other cutaneous offsets of the ulnar or median nerve. d. Dorsal branch to the hand.— This, large offset, leaving the trunk of the ulnar nerve two or three inches above the wrist, winds backwards beneath the flexor carpi ulnaris and divides into branches ; one of these ramifies on the inner side of the little finger, another divides to supply the contiguous sides of that finger and the ring finger, while a third joins on the back of the metacarpus with the branch of the radial nerve which supplies the contiguous sides of the ring and middle finger. The several posterior digital nerves, now described, are united with twigs directed back- wards from the anterior digital nerves of the same fingers. B. Palmar branches: — a. The deep branch separates from the trunk beyond the annular ligament, and, dipping down through the muscles of the little finger in company with the deep branch of the ulnar artery, it follows the course of the deep palmar arch across the hand. It supplies the short muscles of the little finger as it pierces them ; and as it lies across the metacarpal bones, it distributes two branches to each interosseous space — one for the palmar, the other for the dorsal interosseous muscle, and supplies filaments to the two innermost lumbricales muscles. Opposite the space between the thumb and the index finger the nerve ends in branches to the adductor pollicis, and the inner head of the flexor brevis pollicis. b. The remaining part of the nerve supplies a branch to the palmaris brevis muscle and small twigs to the integument, and divides into two digital branches. Digital nerves. — One of these belongs to the ulnar side of the little finger. The other is connected in the palm of the hand with a digital branch of the median nerve, and at the cleft between the little and ring fingers, divides into the collateral nerves for these fingers. The terminal disposition of the digital branches on the fingers is the same as that of the median nerve, to be presently described. Summary. — The ulnar nerve gives cutaneous filaments to the lower part of the forearm (to a small extent), and to the hand on its palmar and dorsal aspects. It supplies the following muscles, viz., the ulnar flexor of the carpus, the deep flexor of the fingers (its inner half), the short muscles of the little finger with the palmaris brevis, the interosseous muscles of the hand, the two internal lumbricales, the adductor pollicis and the inner half of the flexor brevis pollicis. Lastly, it contributes to the nervous supply of the elbow and wrist joints. MEDIAN NERVE. The median nerve arises by two roots, one from the outer, the other from the inner cord of the brachial plexus. Commencing by the union of these * A case has been recorded in which tlie ulnar nerve supplied also two branches to the flexor sublimis digitorum (Turner, " Kat. Hist. Review," 1864). u u 650 NERVES OF THE UPPER LIMB. Fig. 430. Fig. 431. 10 Fig. 430. — DEEP VIEW OP THE ANTERIOR NERVES OP THE SHOULDER AND ARM (from Sappey aiter Hirschfeld and Leveille). | 1, musculo-cutaneous nerve ; 2, its twig to the coraco-brachialis muscle ; 3, its branch to the biceps; 4, its branch to the brachialis anticus ; 5, twig of union with the median nerve (a variety) ; 6, continuation of the nerve in its cutaneous distribution ; 7, musculo- spiral nerve in the interval between the brachialis anticus and supinator longus ; 8, inferior external cutaneous branch of the musculo-spiral ; 9, the internal cutaneous and small internal cutaneous nerves divided ; 10, anterior branch of the internal cutaneous; 11, median nerve ; to the inside the ulnar nerve is crossed by the line from 11. Fig. 431.— DEEP VIEW OP THE ANTERIOR NERVES OF THE FOREARM AND HAND (from Sappey after Hirschfeld and Leveille). £ 12, the median nerve ; 13, its branches to the pronator teres ; 14, branch to the super- ficial flexor muscles, which have been removed ; 15, branch to the flexor digitorum pro- fund us ; 16, branch to the flexor longus pollicis ; 17, anterior interosseous branch; 18, cutaneous palmar branch cut short; 19, branches to the short muscles of the thumb ; 20, 21, collateral branches to the thumb; 22, 23, 24, collateral branches to the second, third, and fourth fingers ; 25, branch given by the ulnar nerve to the flexor carpi ulnaris ; 26, branch to the flexor digitorum profundus ; 27, cutaneous communicating twig ; 28, dorsal branch of the ulnar ; 29, superficial palmar branch ; 30, 31, collateral branches to the fourth and fifth fingers ; 32, deep palmar branch ; 33, its branch to the short muscles of the little finger ; 34, 35, 36, twigs given by the deep branch of the ulnar to the third and fouith lurnbricales, all the interossei, and the adductor pollicis. BRANCHES OF THE MEDIAN NERVE. 651 roots in front or on the outer side of the axillary artery, the nerve descends in contact with the brachial artery, gradually passing inwards over it, and near the elbow is at the inner side of the vessel. Crossing the bend of the arm it passes beneath the pronator radii teres, separated by the deep slip of that muscle from the ulnar artery, and continues straight down the front of the forearm, between the flexor sublimis digitorum and flexor profundus. Arrived near the wrist it lies b.neath the fascia, between the tendons of the flexor sublimis and that of the flexor carpi radialis. It then enters the palm behind the annular ligament, and rests on the flexor tendons. Some- what enlarged, and of a slightly reddish colour, it here separates into two parts of nearly equal size. One of these (the external) supplies some of the short muscles of the thumb, and gives digital branches to the thumb and the index finger ; the second portion supplies the middle finger, and. in part the index and ring fingers. The median nerve gives no branch to the upper arm. A. Branches in the forearm : — In the forearm the median nerve supplies muscular branches, and, near the wrist, a single cutaneous filament. All the muscles on the front of the f jrearm (pronators and flexors), except the flexor carpi ulnaris and part of the deep flexor of the fingers, are supplied from this nerve. a. The branches for the superficial muscles are separate twigs given off from the nerve below or near the elbow-joint, but the branch furnished to the pronator teres often arises above the joint. b. Anterior interosseous nerve. — This is the longest branch of the median nerve, and it supplies the deeper muscles of the forearm. Commencing at the upper part of the forearm, beneath the superficial flexor of the fingers, it passes downwards with the anterior interosseous artery on the interosseous membrane, and between the long flexor of the thumb and the deep flexor of the fingers, to the pronator quadratus muscle, in which it ends. c. The cutaneous palmar branch pierces the fascia of the forearm close to the annular ligament, and, descending over that ligament, ends in the integument of the palm about the middle : being connected by a twig with the cutaneous palmar branch of the ulnar nerve. It distributes some filaments over the ball of the thumb, which communicate with twigs of the radial or the external cutaneous nerve. B. Branches in the hand : — a. Branch to muscles of the thumb.— This short nerve subdivides into branches for the abductor, the opponens, and the outer head of the flexor brevis pollicis muscle. b. Digital nerves. — These are five in number, and belong to the thumb, and the fingers as far as the outer side of the ring-finger. As they approach the clefts between the fingers, they are close to the integument in the intervals between the longitudinal divisions of the palmar fascia. The first and second nerves lie along the sides of the thumb ; and the former (the outer one) is connected with the radial nerve upon the ball of the thumb. The third, destined for the radial side of the index finger, gives a muscular branch to the first or most external lumbrical muscle. The fourth supplies the second lumbricalis, and divides into branches for the adjacent sides of the index and middle fingers. The fifth, the most internal of the digital nerves, is connected by a crossing-twig with the ulnar nerve, and divides to furnish branches to the adjacent sides of the ring and middle fingers. Each digital nerve divides at the end of the finger into two branches, one of which supplies the ball on the fore part of the finger ; the other ramifies in the pulp beneath the nail. Branches pass from each nerve forwards and backwards to the integument of the finger; and one larger than the rest u u 2 652 NERVES OF THE UPPER LIMB. inclines backwards by the side of the first phalanx of the finger, and, after joining the dorsal digital nerve, ends in the integument over the last phalanx. Fig 432 Fi" 432. — DISTIUBUTION OP THE DIGITAL NERVES (from Hirschfeld and Leveille). 4 1, palmar collateral nerve ; 2, its final palmar distribution ; 3, its dorsal or ungual distribution, and between these numbers the network of terminal filaments ; 4, collateral dorsal nerve ; 5, uniting twigs passing between the dorsal and palmar digital nerves. Summary. — The median nerve gives cutaneous branches to the palm, and to several fingers. It supplies the proiiator muscles, the flexors of the carpus and the long flexors of the fingers (except the ulnar flexor of the carpus, and part of the deep flexor of the fingers), likewise the outer set of the short muscles of the thumb, and two lumbricales. Some similarity will be observed between the course and distribution of the median and ulnar nerves. Neither gives any offset in the arm. Together they supply all the muscles in front of the forearm and in the hand, and together they supply the skin of the palmar surface of the hand, and impart tactile sensibility to all tho fingers. MUSCULO-SPIRAL NERVE. The musculo-spiral nerve, the largest offset of the brachial plexus, occupies chiefly the back part of the limb, and supplies nerves to the ex- tensor muscles, as well as to the skin. Arising behind the axillary vessels from the posterior cord of the brachial plexus, of which it is the principal continuation and the only one prolonged into the arm, it soon turns backwards into the musculo-spiral groove, and, accompanied by the superior profunda artery, proceeds along that groove, Vet ween the humerus and the triceps muscle, to the outer side of the limb. It then pierces the external intermuscular septum, and descends in the interval between the supinator longus and the braohialis anticus muscle to the level of the outer condyle of the humerus, where it ends by dividing into the radial and posterior interosseous nerves. Of these, the radial is altogether a cuta- neous nerve, and the posterior interosseous is the muscular nerve of the back of tho forearm. The branches of the musculo-spiral nerve may be classified according as they arise on the inner side of the humerus, behind that bone, or on the outer side. A. Internal branches : — (a) Muscular branches for the inner and middle heads of the triceps. That for the inner portion of the muscle is long and slender; it lies by the side of the ulnar nerve, and reaches as far as the lower third of the upper arm. One branch, previously noticed by authors, but more particularly described by Krause, is named by him the ulnar collateral branch.. It arises opposite the outer border of the latissimus dorsi tendon, and descends within the sheath of the ulnar nerve, through the internal intermuscular septum, and is distributed to the short inferior fibres of the triceps (Reichert and Du Bois Reymond's Archiv. 1864). (b) The internal cutaneous branch of the musculo-spiral nerve, commonly united in origin with the preceding, winds backwards beneath the intercosto-humeral nerve, and after supplying filaments to the skin, ends about two inches from the olecranon ; MUSCULO-SPIRAL,- RADIAL XERVE. 653 in some instances extending as far as the olecranon. This nerve is accompanied by a small cutaneous artery. .B. Posterior branches : — These consist of a fasciculus of muscular branches which supply the outer head of the triceps muscle and the anconeus. The branch of the anconeus is slender, and remark- able for its length; it descends in the substance of the triceps to reach its destination. C. External branches : — (a) The muscular branches supply the supinator longus, extensor carpi radialis longior, (the extensor carpi radialis brevior receiving its nerve from the posterior interosseous,) and occasionally give a small branch to the brachialis anticus. (6) The external cutaneous branches, two in number, arise where the nerve pierces the external intermuscular septum. The upper branch, the smaller of the two, is directed downwards to the fore part of the elbow, along the cephalic vein, and distributes filaments to the lower half of the upper arm on the anterior aspect. The lower branch extends as far as the wrist, distributing offsets to the lower half of the arm, and to the forearm, on their pos- terior aspect, and is connected near the wrist with a branch of the external cutaneous Fig. 433. — DORSAL CUTANEOUS NERVES OP THE HAND. J The distribution delineated in this figure is not the most common, there being a larger than usual branch of the ulnar nerve : 1, the radial nerve descending beside the principal radial cutaneous vein ; 2, and 3, dorsal branches to the two sides of the thumb ; 4, branch to the radial side of the forefinger ; 5, branch to the fore finger and middle finger, communi- cating with one from the ulnar nerve; 6, the posterior branch of the ulnar nerve ; 7, communicating twig ; 8, collateral branch to the middle and ring fingers ; 9, collateral branch to the ring and little fingers ; 10, branch to the inner side of the hand and little finger. RADIAL NERVE. The radial nerve, continuing straight down from the musculo- spiral, is concealed by the long supinator muscle, and lies a little to the outer side of the radial artery. This position beneath the supinator is retained to about three inches from the lower end of the radius, where the nerve turns back- wards beneath the tendon of the muscle, -and becomes subcutaneous. It then separates into two branches, which ramify in the integument on the dorsal aspect of the thumb and the next two fingers in the following manner. 654 NERVES OF THE TIPPER LIMB. (a) The external branch extends to the radial side of the thumb, and is joined by an offset of the external cutaneous nerve. It distributes filaments over the ball of the thumb. (b) The internal portion communicates with a branch of the external cutaneous nerve on the back of the forearm, and divides into digital branches ; one running along the ulnar side of the thumb, a second on the radial side of the index finger, a third dividing to supply the adjacent sides of the index and middle fingers, while a fourth joins with an offset from the dorsal branch of the ulnar, and along with it forms a branch for the supply of the contiguous sides of the middle and ring fingers. These branches communicate on the sides of the fingers with the palmar digital nerves. Sometimes the interspace between the middle and ring fingers is entirely supplied by the radial, and at other times entirely by the ulnar nerve. POSTERIOR INTEROSSEOUS NERVE. This nerve, the larger of the two divisions of the musculo-spiral nerve, •winds to the back of the forearm through the fibres of the supinator brevis Fig. 434. Fig. 434. — VIEW OP THE RADIAL SIDE OP THE FORE-ARM, SHOWING THE FINAL DISTRIBUTION OF THE MuSCULO- SPIRAL NERVE (from Hirschfeld and Leveille). 5 The supinator longus, andextensores carpi radiales longior and brevior have been divided, and their upper parts re- moved ; the extensor communis digitorurn is pulled back- wards by a hook, and the supinator brevis has been par- tially dissected to show the posterior interosseous nerve passing through it. 1, placed upon the tendon of the biceps muscle, points to the musculo-cutaneous nerve ; 1', near the wrist, the lower part of this nerve and its plexus of union with the radial nerve ; 2, trunk of the musculo-spiral nerve emerg- ing from between the brachialis anticus, on which the number is placed, and the supinator longus muscle ; 2', its muscular twigs to the long supinator and long radial extensor of the carpus ; 2", the posterior interosseous nerve passing through the substance of the supinator brevis : 3, placed upon the cut lower portion of the supinator longus, the radial nerve ; 4, the external collateral nerve of the thumb ; 5, the common collateral of the fore-finger and thumb ; 6, the common collateral of the fore-finger and middle finger ; 7, the twig of union with the dorsal branch of the ulnar nerve ; 8, placed upon the common extensor of the fingers, the muscular branches of the posterior inter- osseous nerve to the long extensor muscles ; 9, upon the extensor secundi internodii pollicis, the branches to the short extensor muscles. muscle, and is prolonged between the deep and superficial layers of the extensor muscles to the interosseous membrane, which it approaches about the middle of the forearm. Much diminished in size by the separation of numerous branches for the muscles, the nerve lies at the lower part of the forearm beneath the extensor of the last phalanx of the thumb and the tendons of the common extensor of the fingers, and terminates on the back of the carpus in a gangliform enlargement, from which filaments are given to the adjoining ligaments and articulations. ANTERIOR DIVISIONS OF THE DORSAL NERVES. 655 The branches of the interosseous nerve enter the surrounding muscles, viz., the extensor carpi radialis brevior and supinator brevis, the superficial layer of the extensor muscles except the anconeus, and the deep layer of the same muscles : — that is to say, the nerve supplies the supinators, and the extensors of the carpus and fingers, with the exception of the supiuator longus and the extensor carpi radialis longior. Summary of the Musculo-spiral Nerve. The trunk of the nerve distributes its branches to the extensor muscles of the elbow-joint exclusively, with the exception of a filament to the brachialis anticus, which however receives its principal nerves from another source. Before separating into its two larga divisions, the nerve gives branches to two muscles of the forearm, viz., the long supiuator, and the long radial extensor of the carpus. The posterior iuterosseous division distri- butes nerves to the remaining muscles on the outer and back part of the forearm, except the anconeus (previously supplied), viz. , to the short supinator and the extensors. Cutaneous nerves are distributed, from the trunk of the nerve and its radial division, to the lower part of the upper arm, to the forearm, and to the hand — on the posterior and outer aspect of each. ANTERIOR PRIMARY DIVISIONS OF THE DORSAL NERVES. These nerves are twelve in number, and, with the exception of the larger part of the first of them, which joins the brachial plexus, they are dis- tributed to the walls of the thorax and abdomen. Eleven of the nerves so distributed are termed intercostal, and the twelfth is situated below the last rib. The cords connecting them with the sympathetic nerve, placed close to the vertebrae, are very short. The anterior divisions of these nerves pas3 separately to their destination, without forming any plexus by the connection or interlacement of their fibres, and in this respect they differ from those of the other spinal nerves. From the iutervertebral foramina they are directed transversely across the trunk, and nearly parallel one to another. The upper six nerves, with the exception of the first, are confined to the parietes of the thorax ; while the lower six nerves are continued from the intercostal spaces to the muscles and integument of the anterior wall of the abdomen. FIRST DORSAL NERVE. The greater part of the anterior division of this nerve ascends over the neck of the first rib and the first intercostal artery to enter into the brachial plexus. The remaining portion of the nerve is continued as the first inter- costal, a small branch which courses along the first intercostal space, in the manner of the other intercostal nerves, but has usually no lateral cutaneous branch, and may also want the anterior cutaneous. UPPER, OR PECTORAL INTERCOSTAL NERVES. In their course to the fore part of the chest, these nerves accompany the intercostal blood-vessels. After a short space they pass between the internal and external intercostal muscles, supplying them with twigs, and, about midway between the vertebrae and the sternum, give off the lateral cutaneous branches. The nerves, greatly diminished, are now continued forwards amid the fibres of the internal intercostal muscles as far as the costal cartilages, where they come into contact with the pleura. In approaching 656 THE DORSAL NERVES. F;c. 4C5. Fig. 435. — VIEW OF THE ANTERIOR DIVISIONS OP THE DORSAL AND SOME OF THE OTIIEK SPINAL NERVES PROM BEFORE (from Hirscbfeld and LeveiHe"). £ The pectoralis major and minor muscles have been removed ; on the right side the rectus abdominis and internal oblique muscles are shown, on the left side the anterior part of the rectus is cut away, and the transversalis is exposed. 1, The median and other nerves of the brachial plexus ; 2, the internal cutaneous ; 3, INTERCOSTAL NERVES. 657 the nerve of Wrisberg; 4, the intercostal nerves continued forwards to 4', their anteiior cutaneous twigs ; 5, the lateral cutaneous branches of these nerves ; 6, cutaneous branch of the last dorsal spinal nerve ; 7, the iliac twig of the ilio-hypogastric branch of the first lumbar nerve ; 8, termination of the ilio-hypogastric ; 9, the ilio-iuguinal ; 10, the middle cutaneous of the thigh. the sternum, they cross the internal mammary artery and the fibres of the triangularis sterni muscle. Finally, these nerves pierce the internal inter- costal muscle and the greater pectoral, and end in the integument of the breast, receiving the name of the anterior cutaneous nerves of the thorax. At the anterior part of the chest some of the muscular twigs cross the cartilages of the ribs, passing from one intercostal space to another. (a) The lateral cutaneous nerves of the thorax pierce the external intercostal and serratus magnus muscles, in a line a little behind the pectoral border of the axilla. The first intercostal usually gives no lateral branch or only a slender twig to the axilla, but, when that of the second nerve is unusually small, it is supplemented by that of the first. The branch from the .second intercostal is named intercosto-humeral, and requires separate description. Each of the remaining lateral cutaneous nerves divides into two branches, which reach the integument at a short distance from each other, and are named anterior and posterior. The anterior branches are continued forwards over the border of the great pectoral muscle. Several reach the mammary gland and the nipple; and from the lower nerves twigs are supplied to the digitations of the external oblique muscle of the abdomen. The posterior branches turn backwards to the integument over the scapula and the latissimus dorsi muscle. The branch from the third nerve ramifies in the axilla, and a few filaments reach the arm. The intercosto-humeral nerve, the lateral cutaneous branch of the second inter- costal nerve, corresponds with the posterior of the two divisions of the succeeding lateral cutaneous branches, the anterior being commonly wanting. It crosses the axillary space to reach the arm, and is connected in the axilla with an offset of the nerve of Wrisberg. Penetrating the fascia, it becomes subcutaneous, and ramifies in the integument of the upper half of the arm, on the inner and posterior aspect ; a few filaments reach the integument over the scapula. The branches of this nerve cross over the internal cutaneous offset of the musculo-spiral, and a communication is established between the two nerves. The size of the intercosto-lmmeral nerve, and the extent of its distribution, are in the inverse proportion to the size of the other cutaneous nerves of the upper arm, especially the nerve of Wrisberg. (b] The anterior cutaneous nerves of the thorax, which are the terminal twigs of the intercostal nerves, are reflected outwards in the integument over the great pectoral muscle. The branch from the second nerve is connected with the supraclavicular and the lateral cutaneous nerves; those from the third and fourth nerves are distri- buted to the mammary gland. LOWER, OR ABDOMINAL INTERCOSTAL NERVES. The lower intercostal nerves are continued from the anterior ends of the intercostal spaces, between the internal oblique and the transverse muscle of the abdomen, to the outer edge of the rectus. Perforating the sheath, they enter the substance of that muscle, and afterwards terminate in small cutaneous branches (anterior cutaneous). (a) The lateral cutaneous nerves of the abdomen pass to the integument through the external intercostal and external oblique muscles, in a line with the correspond- ing nerves on the thorax, and divide in the same manner into anterior and posterior branches. The anterior branches are the larger, and are directed inwards in the superficial fascia, with small cutaneous arteries, nearly to the edge of the rectus muscle. The posterior branches bend backwards over the latissimus dorsi muscle. (b) The anterior cutaneous nerves of the abdomen become subcutaneous near the 658 THE LUMBAR PLEXUS. linea alba, accompanying the small perforating arteries. Their number and position are very uncertain. They are directed outwards towards the lateral cutaneous nerves. A second set is described by Cruveilhier as existing at the outer edge of the rectus muscle. LAST DORSAL NERVE. The anterior primary division of this nerve is below the last rib, and is contained altogether in the abdominal wall. The nerve has the general course and distribution of the others between the internal oblique and transversalis, but, before taking its place between those muscles, it passes in front of the upper part of the quadratus lumborum, and pierces the posterior aponeurosis of the transverse muscle. This nerve is connected by offsets with the nerve above, and occasionally with the ilio-hypogastric branch of the lumbar plexus. Near the spine it sometimes communicates with the first lumbar nerve by means of a small cord in the substance of the quad- ratus lumborum. The lateral cutaneous branch of the last dorsal nerve^ passing through both oblique muscles, is directed downwards over the iliac crest to the integument, covering the fore part of the gluteal region and the upper and outer part of the thigh, some filaments reaching as far as the great trochanter of the femur. ANTERIOR PRIMARY DIVISIONS OF THE LUMBAR NERVES. The anterior divisions of the lumbar nerves increase in size from the first to the fifth ; and all, except the fifth, which passes down to join the sacral nerves, are connected together by communicating loops, so as to form the lumbar plexus. On leaving the inter vertebral foramina these nerves are connected by filaments with the sympathetic nerve, these filaments being longer than those connected with other spinal nerves, in consequence of the position of the lumbar sympathetic ganglia on the fore part of the bodies of the vertebrse. In the same situation are furnished small twigs to the psoas and quadratus lumborum muscles. LUMBAR PLEXUS. The lumbar plexus is formed by the communications between the anterior primary divisions of the four upper lumbar nerves. It is placed in the substance of the psoas muscle, in front of the transverse processes of the corresponding vertebrae. Above, the plexus is narrow, and is sometimes connected with the last dorsal nerve by a small offset from that nerve, named dorsi-lumbar ; below it is wider, and is joined to the sacral plexus by means of a branch given by the fourth lumbar nerve to the fifth. The arrangement of the plexus may be thus stated. The first nerve gives off the ilio-hypogastric and ilio-inguinal nerves, and sends downwards a communicating branch to the second nerve. The second furnishes the greater part of the geuito-crural and external cutaneous nerves, and gives a connecting branch to the third, from which some of the fibres of the anterior crural and obturator nerves are derived. From the third nerve, besides the descending branch to the fourth, two branches proceed : one of these, the larger, forms part of the anterior crural nerve ; the other, a part of the obturator nerve. The fourth nerve gives two branches, which serve to complete the obturator and anterior crural nerves, and a connecting branch to the fifth nerve. THE LUMBAR PLEXUS AND NEKVES. 659 The branches of this plexus form two sets, which are distributed, one to the lower part of the wall of the abdomen, the other to the fore part and inner side of the lower liinb. In the former set are the ilio-hypogastric and Fig. 436. — DIAGRAMMATIC OUTLINE OF THE LUMBAR AND SACRAL PLEXUSES WITH THE PRINCIPAL NERVES ARISING FROM THEM. 4 Fig. 436. DXIT DXII, placed opposite the divided roots of the last dorsal nerve ; LI to V, opposite the roots of the five lumbar nerves : the loops uniting the anterior primary divisions of these nerves together, and the first with the twelfth dorsal are shown; SI to V, and CI, the same in the sacral and coccy- geal nerves ; p, placed on some of the nerves marks the pos- terior primary divisions cut short ; p' p, the plexus formed by the union of the posterior branches of the third, fourth, and fifth sacral and the coccy- geal nerves ; d, the abdominal continuation of the last dorsal nerve, from which d' the iliac cutaneous branch arises; 1, 1', the ilio-hypogastric and ilio- inguinal branches of the first lumbar nerve ; 2, the genito- crural rising by a loop from the first and second lumbar; 2', external cutaneous of the thigh rising by a loop from the second and third ; ps, branches to the psoas muscle along the lumbar plexus ; cr, anterior crural nerve from the second, third, and fourth lumbar; il, branches to the iliacus ; ob, obturator nerve from the se- cond, third and fourth lumbar nerves ; ob', accessory obtura- tor; IV, V, loop from the fourth and fifth lumbar, form- ing the lumbo- sacral cord ; 3, superior gluteal nerve ; sc, sacral plexus ending in the great sciatic nerve ; 4, lesser sciatic nerve rising from the plexus posteriorly; 4', inferior gluteal branches ; 5, inferior puden- dal ; 5', posterior cutaneous of the thigh and leg ; 6, 6, branches to the obturator in- ternus and gemellus superior ; 6', 6', branches to the gemellus inferior, quadratus and hip-joint ; 7, twigs to the pyriformis ; 8, 8, pudic nerve from the first, second, third, and fourth sacral ; 9, visceral branches ; 9', twig to the levator ani ; 10, cutaneous from the fourth, which passes round the lower border of the gluteus maximus ; 11, coccygeal branches. IV V CI 660 THE LUMBAR PLEXUS. ilio-inguinal nerves, and part of the genito-crural ; and to the latter belong the remaining part of the genito-crural nerve, the external cutaneous, the obturator, and the anterior crural nerves. ILIO-HYPOGASTRIC AND ILIO- INGUINAL NERVES. These nerves are the upper two branches from the lumbar plexus ; they are both derived from the first lumbar nerve, and have a nearly similar distribution. They become subcutaneous by passing between the broad muscles of the abdomen, and through the outer one, and end in the integu- ment of the groin and scrotum in the male, and the labia pudendi in the female, as well as in the integument covering the gluteal muscles. The extent of distribution of the one is inversely proportional to that of the other. The ilio-hypogastric nerve, emerging from the upper part of the psoas muscle at the outer border, runs obliquely over the quadratus lumborum to the iliac crest, and there perforating the transverse muscle of the abdomen, gets between that muscle and the internal oblique, and divides into an iliac and hypogastric branch. (a) The iliac branch pierces the attachment of both oblique muscles, immediately above the iliac crest, and is lost in the integument over the gluteal muscles, behind the distribution of the lateral cutaneous branch of the last dorsal nerve. (b) The hypogastric or abdominal branch passes on between the transverse and internal oblique muscles, and is connected with the ilio-inguinal nerve near the iliac crest. It then perforates the internal oblique muscle, and, piercing the aponeurosis of the external oblique, a little above the superficial inguinal opening, is distributed to the skin of the abdomen above the pubes. The size of the iliac branch of this nerve varies inversely with that of the lateral cutaneous branch of the twelfth dorsal. The hypogastric branch is not unfrequently joined with the last dorsal nerve between the muscles, near the crest of the innominate bone. The ilio-inguinal nerve, smaller than the preceding, supplies the integu- ment of the groin. Descending obliquely outwards over the quadratus lumborum, it crosses the fibres of the iliacus muscle, being placed lower down than the ilio-hypogastric : it then perforates the transverse muscle further forwards than the ilio-hypogastric ; communicating with that nerve between the abdominal muscles. Then piercing the internal oblique muscle, it descends in the inguinal canal, and emerging at the superficial inguinal ring, is distributed to the skin upon the groin, as well as to that upon the scrotum and penis ia the male, or the labium pudendi in the female, com- municating with the inferior pudendal nerve. Tn its progress this nerve furnishes branches to the internal oblique muscle. The ilio-inguinal nerve occasionally arises from the loop connecting the first and second lumbar nerves. It is sometimes small, and ends near the iliac crest by joining the ilio-hypogastric nerve ; in that case the last nerve gives off" an inguinal branch having a similar course and distribution to the ilio-inguinal nerve, the place of which it supplies. GENITO-CRURAL NERVE. The genito-crural nerve belongs partly to the external genital organs and partly to the thigh. It is derived chiefly from the second lumbar nerve, but receives also a few fibres from the connecting cord between that and the first nerve. The nerve descends obliquely through the psoas muscle, and afterwards on its fore part, towards Poupart's ligament, dividing at a variable height into an internal or genital, and an external or crural branch. GENITO-CRURAL NERVE. 661 It often bifurcates close to its origin from the plexus, in which case its two branches perforate the psoas muscle in different places. (a) The genital branch (external spermatic, Schmidt), lies upon or near the external iliac artery, and sends filaments along that vessel ; then perforating the transversalis fascia, it passes through the inguinal canal with the spermatic cord, and is lost upon Fig. 437. — VIEW FROM BEFORE OP TUE ANTERIOR BRANCHES OP THE LUMBAR AND SACRAL NERVES WITH THE PLEXUSES (from Sappey, after Hirschfeld and Leveille). | 1, lumbar cord of the great sympathetic nerve ; 2, 2', anterior primary divisiun of the twelfth dorsal nerve ; 3, first lumbar ; 4, 4', ilio-inguinal branch of this nerve ; 5, 5', ilio-hypogastric branch ; 6, second lumbar nerve ; 7, 7', genito-crural nerve rising from the first and second lumbar ; 8, 8', external cutaneous nerve of the thigh ; 9, third lumbar nerve; 10, fourth ; 11, fifth ; 12, lumbo-sacral trunk ; 13, iliac branch of the ilio-inguinal; 1 4, its abdominal branch; 15, its genital branch; 16, external cutaneous nerve of the right side passing out of the pelvis under Poupart's ligament ; 17, 17, 17, cutaneous ramifications of this nerve ; 17', the same nerve exposed on the left side ; 18, 18', genital branch of the genito-crural ; 19, its crural branch on the right side becoming cutaneous ; 19', the same on the left side exposed as it descends in front of the femoral artery ; 20, anterior crural nerve ; 21, 21', obturator nerve ; 22, left sciatic plexus ; 23, aortic plexus of the sympathetic nerve connected superiorly with the other pre-aorti'c plexuses and the lumbar ganglia, and inferiorly with the hypogastric plexus. 662 THE LUMBAR PLEXUS. the cremaster muscle. In the female it accompanies the round ligament of the uterus. (b) The crural branch (lumbo-inguinal nerve, Schmidt), descends upon the psoas muscle beneath Poupart's ligament into the thigh. Immediately below that liga- ment, and at the outer side of the femoral artery, it pierces the fascia lata, and supplies the skin on the upper part of the thigh, communicating with the middle cutaneous branch of the anterior crural nerve. Whilst it is passing beneath Pou- part's ligament, some filaments are prolonged from this nerve on the femoral artery. It is stated by Schmidt, that when the crural branch of the genito-crural nerve is large, and commences near the plexus, he has observed it to give a muscular branch to the lower border of the internal oblique and transversalis muscles. EXTERNAL CUTANEOUS NERVES. This nerve, commencing from the loop formed between the second and third lumbar nerves, on emerging from the outer border of the psoas muscle, crosses the iliacus muscle below the ilio-inguiual nerve, and passing beneath Poupart's ligament, reaches the thigh beneath the anterior superior iliac spine, where it divides into an anterior and a posterior branch distributed to the integument of the outer side of the hip and thigh. (a) The posterior branch perforates the fascia lata, and subdivides into two or three others, which turn backwards and supply the skin upon the outer surface of the limb, from the upper border of the hip-bone nearly to the middle of the thigh. The highest among them are crossed by the cutaneous branches from the last dorsal nerve. (b) An anterior branch, the continuation of the nerve, is at first contained in a sheath or canal formed in the substance of the fascia lata ; but, about four inches below Poupart's ligament, it enters the subcutaneous fatty tissue, and is distributed along the outer part of the front of the thigh, ending near the knee. The principal offsets spring from its outer side. In some cases, this branch reaches quite down to the knee, and communicates there with the internal saphenous nerve. OBTURATOR NERVE. The obturator nerve (internal crural) is distributed to the adductor muscles of the thigh, and to the hip and knee-joints. It arises from the lumbar plexus by two roots, one from the third and the other from the fourth lumbar nerve. Having emerged from the inner border of the psoas muscle, opposite to the brim of the pelvis, it runs along the side of the pelvic cavity, above the obturator vessels, as far as the opening in the upper part of the thyroid foramen, through which it escapes from the pelvis into the thigh. Here it immediately divides into an anterior and a posterior branch, which are separated from one another by the short adductor muscle. A. — The anterior portion communicates with the accessory obturator nerve, when that nerve is present, and descends in front of the adductor brevis and behind the pectineus and adductor longus muscles. It gives branches as follows. (a) An articular branch to the hip-joint arises near the thyroid membrane. (b) Muscular branches are given to the gracilis and adductor longus muscles, and occasionally also others to the adductor brevis and pectineus. (c) The terminal twig turns outwards upon the femoral artery, and surrounds that vessel with small filaments. (d) An offset at the lower border of the adductor longus communicates beneath the fascia with the internal cutaneous branch of the anterior crural nerve, and with a branch of the internal saphenous nerve, forming a sort of plexus. Occasional cutaneous neroe. — In some instances the communicating branch described OBTURATOR NERVE.— ACCESSORY. 663 is larger than usual, and descends along the posterior border of the sartorius to the inner side of the knee, where it perforates the fascia, communicates with the internal saphenous nerve, and extends down the inner side of the limb, supplying the skin as low as the middle of the leg. Fig. 438. Fig. 438. — THE LUMBAR PLEXUS FROM BEFORE, WITH THE DISTRIBUTION OP SOME OF ITS NI-.RVES (slightly altered from Schmidt). | cr, the last rib ; J, quadratus lura- boruni muscle ; c, oblique and traus- verse muscles cut near the crest of the ilium and turned down ; dt pubes ; e, adductor brevis muscle ; /, pectineus dhided and turned outwards ; g, adduc- tor lougus; 1, ilio-hypogastric nerve ; 2, ilio-inguinal ; 3, external cutaneous; 4, anterior crural ; 5, accessory obtu- rator ; 6, obturator united with the ac- cessory by a loop round the pubes; 7, geuito-crural in two branches cut short near their origin ; 8, 8, lumbar portion of the gangliated sympathetic cord. When this cutaneous branch of the obturator nerve is present, the internal cutaneous branch of the anterior crural nerve is small, the size of the two nerves bearing an inverse proportion to each other. B. — The posterior or deep part of the obturator nerve, having passed through some fibres of the external obturator muscle, crosses behind the short adductor to the fore part of the adductor mag- DUS, where it divides into many branches, all of which enter those muscles, excepting one which is prolonged downwards to the knee-joint. (a) The muscular branches supply the external obturator and the great adductor muscle, with the short adductor also when this muscle receives no branch from the anterior division of the nerve. (b) The articular branch for the knee rests at first on the adductor magnus, but perforates the lower fibres of that muscle, and thus reaches the upper part of the popliteal space. Supported by the popliteal artery, and sending filaments around that vessel, the nerve then descends to the back of the knee-joint, and enters the articulation through the posterior ligament. (Thomson, " London Med. and Surg. Journal," No. xcv.) ACCESSORY OBTURATOR NERVE. The accespory obturator nerve, a small and inconstant nerve, arising from the obturator nerve near its upper end, or separately from the same nerves of the plexus, descends along the inner border of the psoas muscle, over the pubic bone, and, passing behind the pectineus muscle, ends by dividing into several branches. Of these one joins the anterior branch of the obturator nerve ; another penetrates the pectineus on the under surface ; whilst a third enters the hip-joint with the articular 'artery. 664 THE LUMBAR PLEXUS. This nerve is sometimes smaller than usual, and ends in filaments which perforate the capsule of the hip-joint. When it is altogether wanting, the hip-joint receives branches from the obturator nerve. Summary. — The obturator nerve and accessory obturator give branches to the hip and knee joint?, also to the adductor muscles of the thigh, and, in some cases, to the pecfcineus. Occasionally a cutaneous branch descends to the inner side of the thigh, and to the inner and upper part of the leg. Fir. 439. ANTERIOR CRURAL NERVE. This nerve is the largest branch of the lumbar plexus, and is derived piincipally from the third and fourth lumbar nervea, but in part also from the second. Emerging from the outer border of the psoas muscle, near its lower part, it descends into the thigh in the groove between that muscle and the iliacus, and, therefore, to the outside of the femoral blood-vessels. It now becomes flattened out and divides into two parts, one of which is cutaneous, while the other is dis- tributed to muscles. Fig. 439. — DEEP NERVES OP THE ANTERIOR AND INNER PART OF THE THIGH (from Sappey after Hirschfeld and Leveille). ± 1, anterior crural nerve ; 2, branches given to the iliacus muscle ; 3, branch to the lower pa't of the psoas ; 4, large musculo-cutaneous branches, divided to show the deeper nerves ; 5 and 6, mus- cular filaments from the small musculo-cutaneous ; 7. origin of the cutaneous branches ; 8, communi- cating filament of the internal cutaneous nerves ; 9, branches to the rectus ; 10, branches to the vustus externus ; 11, branches to the vastus inter- ims ; 12, internal saphenous nerve ; 13, its patellar branch; 14, its continuation down the leg ; 15, obturator nerve ; 16, branch from the obturator nerve to the adductor longus ; 17, branch to the adductor brevis ; 1 8, branch to the gracilis ; from this a filament is prolonged downwards, to unite with the plexus formed by the union of branches from the internal cutaneous and internal saphenous nerves ; 19, deep branch of the obturator nerve to the adductor magnus ; 20, lumbo- sacral trunk ; 21, its union with the first sacral nerve ; 22, 22, lum- bar and sacral part of the sympathetic nerve ; 23, external cutaneous nerve from the lumbar plexus. Branches of the trunk. — The branches given from the anterior crural nerve within the abdomen are few and of small size. (a) The iliacus receives three or four small branches, which are directed outwards from the nerve to the fore part of the muscle. (b) The nerve of the femoral artery is a small branch which divides into numerous filaments upon the upper part of that vessel. It sometimes arises lower down than i' ;nal in the thigh. It may, on the other hand, be found to take origin above the ordinary position ; and in this case it proceeds from the middle cutaneous nerve, ANTERIOR CRURAL NERVE. 660 when that branch springs from or near the lumbar plexus. In either case, its ulti- mate distribution is the same as that already described. Terminal branches. — From the principal or terminal divisions of the nerve the remaining branches take their rise as follows. From the SUPERFICIAL DIVISION cutaneous branches are given to the fore part of the thigh, and to the inner side of the leg. They are the middle and internal cutaneous nerves, and the internal saphenous nerve. One of the muscles, the sartorius, receives its nerves from this group. The DEEP BRANCHES supply the muscles on the fore part of the thigh, and also the pectineus muscle. The branch to the pectineus, however, some- times arises from the superficial part of the trunk. A. MUSCULAR BRANCHES. The branch to the pectineus muscle crosses inwards behind the femoral vessels, and enters the muscle on the anterior aspect. The sartorius muscle receives three or four twigs, which arise in common with the cutaneous nerves, and reach mostly the upper part of the muscle. The rectus muscle receives a distinct branch on its under surface. The nerve for the vastus externus, of considerable size, descends with the branches of the external circumflex artery towards the lower part of the muscle. It gives oft a long slender articular filament, which reaches the knee and penetrates the fibrous capsule of the joint. Another large nerve divides into two sets of branches, which enter the vastus internus and the crureus about the middle of those muscles. The nerve of the vastus internus, before penetrating the muscular fasciculi, gives a small branch to the knee- joint. This articular nerve passes along the internal intermuscular septum with a branch of the anastomotic artery, as far as the inner side of the joint, where it per- forates the capsular ligament, and is directed outwards on the synovial membrane beneath the ligamentum patellae. B. MIDDLE CUTANEOUS NERVE. The middle cutaneous nerve either pierces the fascia lata divided into two branches about four inches below Po apart' s ligament, or as one trunk which soon separates into two branches. These branches descend side by side on the fore part of the thigh to the inner side and front of the patella. After or before the nerve has become subcutaneous, it communicates with the crural branch of the genito-crural nerve, and also with the internal cutaneous. This nerve sometimes arises from the anterior crural, high up within the abdomen. C. INTERNAL CUTANEOUS NERVE. The internal cutaneous nerve gives branches to the skin on the inner side of the thigh, and the upper part of the leg ; but the extent to which it reaches varies with the presence or absence of the " occasional cutaneous" branch of the obturator nerve. Lying beneath the fascia lata, this nerve descends obliquely over the upper part of the femoral artery. It divides either in front of that vessel, or at the inner side, into two branches (one anterior, the other internal), which pierce the fascia separately. These two branches sometimes arise as distinct offsets from the superficial part of the anterior crural nerve. The distribution of the internal cutaneous nerve is as follows. (a) Branches previous to division. — Before dividing into its two ultimate branches, this nerve gives off two or three cutaneous twigs, which accompany the upper part of the long saphenous vein. The highest of these perforates the fascia 666 THE LUMBAR PLEXUS. near the saphenous opening, and reaches down to the middle of the thigh. The others appear beneath the skin lower down by the side of the vein ; one, larger than the rest, passes through the fascia about the middle of the thigh, and extends to the knee. In some instances, these small branches spring directly from the anterior crural nerve, and they often communicate with each other. Fig. 440. Fig. 440. — CUTANEOUS NERVES OP THE ANTERIOR AND INNER PART OF THE THIGH (from Sappey after Hirschfeld and Leveille). | 1, external cutaneous nerve ; 2, 2, middle cuta- neous branch of the anterior crural passing through the sartorius muscle and the fascia ; 3, 3, anterior division of the internal cutaneous ; 4, filament to the sartorius ; 5, inner or posterior division of the internal cutaneous ; 6, its superficial branch to the inside of the knee after perforating the fascia ; 7, deep or communicating branch ; 8, superficial branch of the musculo-cutaneous of the crural ; 9, patellar branch of the internal saphenous nerve ; 10, continuation of the saphenous down the leg. (b) The anterior branch, descending in a straight line to the knee, perforates the fascia lata in the lower part of the thigh ; it after- wards runs down near the intermuscular septum, giving off filaments on each side to the skin, and is finally directed over the patella to the outer side of the knee. It communicates above the joint with a branch of the long saphenous nerve ; and sometimes it takes the place of the branch usually given by the latter to the inte- gument over the patella. This branch of the internal cutaneous nerve sometimes lies above the fascia in its whole length. It occasionally gives off a cutaneous filament, which accompanies the long saphenous vein, and in some cases it communicates with the branch to be next described. The inner branch of the internal cutaneous nerve, descending along the posterior border of the sartorius muscle, perforates the fascia lata at the inner side of the knee, and communicates by a small branch with the internal saphenous nerve, which here descends in front of it. It gives some cutaneous filaments to the lower part of the thigh on the inner side, and is dis- tributed to the skin upon the inner side of the leg. Whilst beneath the fascia, this branch of the internal cutaneous nerve joins in an interlacement with offsets of the obturator nerve below the middle of the thigh, and with the branch of the saphenous nerve nearer the knee. D. INTERNAL SAPHEXOUS NERVE. The internal or long saphenous nerve is the largest of the cutaneous branches of the anterior crural nerve. In some cases it arises in connection with one of the deep or muscular brandies. This nerve is deeply placed as far as the knee, and is subcutaneous in the rest of its course. In the thigh it accompanies the femoral vessels, lying at first somewhat to their outer side, but lower down approaching close to ANTERIOR CRURAL.— FIFTH LUMBAR NERVE. 667 them, and passing beneath the same aponeurosis. When the vessels pass through the opening in the adductor muscle into the popliteal space, the saphenous nerve separates from them, and is continued downwards beneath the sartorius muscle to the ianer side of the knee ; where, having first given off, as it lies near the inner condyle of the femur, a branch which is distributed over the front of the patella, it becomes subcutaneous by piercing the fascia between the tendons of the sartorius and gracilis muscles. The nerve then accompanies the sapheuous vein along the inner side of the leg, and passing in front of the ankle is distributed to the inner side of the foot. In the leg it is connected with the internal cutaneous nerve. The distribution of the branches is as follows. (a) A communicating branch is given off about the middle of the thigh to join in the interlacement formed beneath the fascia lata by this nerve and branches of the obturator and internal cutaneous nerves. After it has left the aponeurotic covering of the femoral vessels, the internal saphenous nerve has, in some cases, a further connection with one or other of the nerves just referred to. (b) The branch to the integument in front of the patella perforates the sartorius muscle and the fascia lata ; and, having received a communicating offset from the internal cutaneous nerve, spreads out upon the fore part of the knee ; and, by uniting with branches of the middle and external cutaneous nerves, forms a plexus — plexus patellae. (c) A branch to the inner ankle is given off in the lower third of the leg, and descends along the margin of the tibia. (d) Filaments from this nerve enter the tarsal ligaments. Summary. — The anterior crural nerve is distributed to the skin upon the fore part and inner side of the thigh, commencing below the termination of the ilio-inguinal and genito-crural nerves. It furnishes also a cutaneous nerve to the inner side of the leg and foot. All the muscles on the front and outer side of the thigh receive their nerves from the anterior crural, and the pec- tineus is also in part supplied by this nerve, and in part by the obturator. The tensor muscle of the fascia lata is supplied from a different source, viz., the superior gluteal nerve. Lastly, two branches are given from the anterior crural nerve to the knee-joint. FIFTH LUMBAR NERVE. The anterior branch of the fifth lumbar nerve, having received a fasciculus from the nerve next above it, descends to join the first sacral nerve, and form part of the sacral plexus. The cord resulting from the union of the fifth with a part of the fourth nerve, is named the lumbo-sacral nerve. SUPERIOR GLUTEAL NERVE. Before joining the first sacral nerve the lumbo-sacral cord gives off from behind the superior gluteal nerve ; this offset leaves the pelvis through the large sacro-sciatic foramen, above the pyriformis muscle, and divides like the gluteal artery into two branches, which are distributed chiefly to the smaller gluteal muscles and tensor of the fascia lata. (a) The upper branch runs with the gluteal artery along the origin of the gluteus minimus, and is lost in it and in the gluteus medius. (b) The lower branch crosses over the middle of the gluteus minimus, between this and the gluteus medius, and supplying filaments to both those muscles, is con- tinued forwards, and terminates in the tensor muscle of the fascia lata. x x 2 668 THE SACRAL NERVES. ANTERIOR PRIMARY DIVISIONS OF THE SACRAL AND COCCYGEAL NERVES. THE SACRAL NERVES. The anterior divisions of the first four sacral nerves emerge from the spinal canal by the anterior sacral foramina, and the fifth passes out between the sacrum and coccyx. The first two sacral nerves are large, and of nearly equal size ; the others diminish rapidly, and the fifth is exceedingly slender. Like the anterior divisions of the other spinal nerves, those of the sacral nerves communicate with the sympathetic : the communicating cords are very short, as the sympathetic ganglia are close to the inner margin of the foramina of the sacrum. The first three nerves and part of the fourth contribute to form the sacral plexus. The fifth has no share in the plexus, — it ends on the back of the coccyx. As the description of the fourth and fifth sacral nerves and of the coccygeal will occupy only a short space, these three nerves may be noticed first, before the other nerves and the numerous branches to which they give rise are described. THE FOURTH SACRAL NERVE. Only one part of the anterior division of this nerve joins the sacral plexus ; the remainder, which is nearly half the nerve, supplies branches to the viscera and muscles of the pelvis, and sends downwards a connecting filament to the fifth nerve. (a) The visceral [branches of the fourth sacral nerve are directed forwards to the lower part of the bladder, and communicate freely with branches from the sympa- thetic nerve. Offsets are distributed to the neighbouring viscera, according to the sex. They will be described with the pelvic portion of the sympathetic nerve. The foregoing branches are, in some instances, furnished by the third sacral nerve instead of the fourth, and not unfrequently from both of these nerves. (b) Of the muscular branches, one supplies the levator ani, piercing that muscle on the pelvic surface ; another enters the coccygeus, whilst a third ends in the external sphincter muscle of the rectum. The last branch, after passing either through the coccygeus, or between it and the levator ani, reaches the perinaeum, and is distributed likewise to the integuments between the anus and the coccyx. THE FIFTH SACRAL NERVE. The anterior branch of this, the lowest sacral nerve, comes forwards through the coccygeus muscle opposite the junction of the sacrum with the first coccygeal vertebra ; it then descends upon the coccygeus nearly to the tip of the coccyx, where it turns backwards through the fibres of that muscle, and ends in the integument upon the posterior and lateral aspect of the bone. As soon as this nerve appears in front of the bone (in the pelvis) it is joined by the descending filament from the fourth nerve, and lower down by the small anterior division of the coccygeal nerve. It supplies small filaments to the coccygeus muscle. THE COCCYGEAL NERVE. The anterior branch of the coccygeal, or, as it is sometimes named, the sixth sacral nerve, is a very small filament. It escapes from the spinal THE SACRAL PLEXUS. 669 canal by the terminal opening, pierces the sacro-sciatic ligament and the coccygeus muscle, and, being joined upon the side of the coccyx with the fifth sacral nerve, partakes in the distribution of that nerve. THE SACRAL PLEXUS. The lumbo-sacral cord (resulting as before described from the junction of Fig. 441. Fig. 441. — DIAGRAMMATIC OUTLINE OP THE LUMBAR AND SACRAL PLEXUSES WITH THE PRINCIPAL NERYKS ARISING FROM THEM. ^ The references to the nerves of the lumbar plexus will be found at p. 659. DXII, roots of the last dorsal nerve ; LI to V, roots of the five lumbar nerves ; SI to V, and CI, roots of the five sacral and the coccygeal nerves ; IV, V, loop from the an- terior primary branches of the fourth and fifth lumbar nerves, forming the lumbo- sacral cord ; 3, superior glu- teal nerve ; SO, sacral plexus ending in the great sciatic nerve ; 4, lesser sciatic nerve, rising from the plexus pos- teriorly ; 4', inferior gluteal branches ; 5, inferior puden- dal ; 5', posterior cutaneous of the thigh and leg ; 6, 6, branches to the obturator in- ternus and gemellus superior ; 6', 6', branches to the ge- inellus inferior, quadratus and hip-joint ; 7, twigs to the pyriformis ; 8, 8, pudic from the first, second, third, and fourth sacral ; 9, visceral branches ; 9', twig to the levator ani ; 10, cutaneous from the fourth, which passes round the lower border of the gluteus maximus; 11, coccy- geal branches. the fifth and part of the fourth lumbar nerves), the anterior divisions of the first three sacral nerves, and part of the fourth, unite to form this plexus. Its con- struction differs from that of the other spi- nal nervous plexuses in this respest, that the several constituent nerves entering into it ci 670 THE SACRAL PLEXUS. unite into one broad flat cord. To the place of union the nerves proceed in different directions, that of the upper ones being obliquely downwards, while that of the lower is nearly horizontal ; and, as a consequence of this difference, they diminish in length from the first to the last. The sacral plexus rests on the anterior surface of the pyriform muscle, opposite the side of the sacrum, and escaping through the great sacro-sciatic foramen, ends in the great sciatic nerve. Branches. — The sacral plexus gives rise to the great sciatic nerve, and to various smaller branches ; viz., the pudic nerve, the small sciatic nerve, and branches to the obturator internus, pyriformis, gemelli, and quadratus femoris muscles. MUSCULAR BRANCHES. a. To the pyriformis muscle, one or more branches are given, either from the plexus or from the upper sacral nerves before they reach the plexus. b. The nerve of the internal obturator muscle arises from the part of the plexus formed by the union of the lumbo-sacral and the first sacral nerves. It turns over the ischial spine of the hip-bone with the pudic vessels, and is then directed forwards through the small sacro-sciatic foramen to reach the inner surface of the obturator muscle. c. To the levator ani one or more twigs proceed from the lower part of the plexus. d. The superior gemellus receives a small branch, which arises from the lower part of the plexus. e. The small nerve which supplies the lower gemellus and quadratus femoris muscles springs from the lower part of the plexus. Concealed at first by the great sciatic nerve, it passes beneath the gemelli and the tendon of the internal obturator, — between those muscles and the capsule of the hip-joint, — and reaches the deep (anterior) surface of the quadratus. It furnishes a small articular filament to the back part of the hip-joint. THE PUDIC NERVE. This nerve, arising from the lower part of the sacral plexus, turns over the spine of the ischium, and then passes forwards through the small sacro- sciatic foramen, where it usually gives off the inferior hsemorrhoidal branch. It is next directed along the outer part of the ischio-rectal fossa, in a sheath of the obturator fascia, along with the pudic vessels, and divides into two terminal branches, the perinseal nerve and the dorsal nerve of the penis. A. — The perinceal nerve, the lower and much the larger of the two divisions of the pudic nerve, lies below the pudic artery, and is expended in superficial and muscular branches. a. The superficial perinceal branches are two in number, anterior and posterior. The posterior branch, which first separates from the perinseal nerve, reaching the back part of the ischio-rectal fossa, gives filaments inwards to the skin in front of the anus, and turns forwards in company with the anterior branch to reach the scrotum. The anterior branch descends to the fore part of the ischio-rectal fossa ; and, passing forwaids with the superficial perinaeal artery, ramifies in the skin on the fore part of the scrotum and on the penis. This branch sends small twigs to the levator ani muscle. The superficial perinseal nerves are accompanied to the scrotum by the inferior pudendal branch of the small sciatic nerve. The three branches are some- times named long ncrotal nerves. In the female, both the superficial perinaeal branches terminate in the external labium pudendi. b. The muscular branches generally arise by a single trunk, which is directed inwards under cover of the transversalis perinaei muscle, and divides into offsets which PUDIC XEEYE. 671 are distributed to the tranversalis perinaei, erector penis, accelerator urinae, and compressor urethras. c. Slender filaments are sent inwards to the corpus spongiosum urethras ; some of these, before penetrating the erectile tissue, run a considerable distance over its surface. Fig. 442.— RIGHT SIPE OF THE Fig. 442. INTERIOR OP THE MALE PELVIS, WITH THE PRINCIPAL NERVKS DISPLAYED (from Hirschfeld and Leveille). £ The left wall has been removed as far as the sacrum behind and the sympbysis pubis in front; the viscera and the lower part of the levator ani have been removed ; a, the lower part of the aorta ; a', placed on the fifth lumbar ver- tebra, between the two common iliac arteries, of which the left is cut short ; b, the right external iliac artery and vein ; c, the sym- physis pubis ; d, the divided py- riformis muscle, close to the left auricular surface of the sacrum ; e, bulb of the urethra covered by the accelerator urinas muscle ; the membranous part of the urethra cut short is seen passing into it ; 1, placed on the crest of the ilium, points to the external cutaneous nerve of the thigh passing over the iliacus muscle ; 2, placed on the psoas muscle, points to the genito-crural nerve ; 3, obturator nerve ; 4, 4, placed on the lumbo-sacral cords ; that of the right side points to the gluteal artery cut short ; 4', the superior gluteal nerve ; 5, placed on the inside of the right sacral plexus, points by four lines to the anterior divisions of the four upper sacral nerves, which, with the lumbo-sacral cord, unite in the plexus ; 5', placed on the fifth piece of the sacrum, points to the fifth sacral nerves ; 5", the visceral branches proceeding from the third and fourth sacral nerves ; 6, placed on the lower part of the coccyx, below the coccygeal nerves ; 7, placed on the line of division of the pelvic fascia, points to the nerve of the levator ani muscle ; 8, placed at the lower border of the great sacro-sciatic ligament, points to the cutaneous nerves of the anus ; 9, nerve of the obturator internus ; 10, the pudic nerve; 10', is placed above the muscular branches of the perineal nerve ; 10", the anterior and posterior superficial perineal nerves, and on the scrotum the distribution of these nerves and the inferior pudendal nerve ; 11, the right dorsal nerve of the penis; IT, the nerve on the left crus penis which is cut short ; 12, the continuation of the lesser sciatic nerve on the back of the thigh ; 12', the inferior pudendal branch ; 13, placed on the transverse process of the fifth lumbar ver- tebra, marks the lowest lumbar sympathetic ganglion ; 14, placed on the body of the first piece of the sacrum, points to the upper sacral sympathetic ganglia ; between 14 and 6, are seen the remaining ganglia and sympathetic nervous cords, as well as their union with the sacral and coccygeal nerves, and at 6, the lowest ganglion or ganglion impar. B. — The dorsal nerve of the penis, the upper division of the pudic nerve, accompanies the pudic artery in its course between the layers of the deep perinseal or subptibic fascia, and afterwards through the suspensory ligament, to reach the dorsum of the penis, along which it passes as far as the glands, where it divides into filaments for the supply of that part. On 672 THE SACRAL PLEXUS. the penis, this nerve is joined by branches of the sympathetic system, and it sends outwards numerous offsets to the integument on the upper surface and sides of the organ, including the prepuce. One large branch penetrates the corpus cavernosum penis. In the female, the dorsal nerve of the clitoris is much smaller than the corresponding branch in the male ; it is similarly distributed. C. — The inferior hcemorrhoidal nerve arises from the pudic nerve at the back of the pelvis, or it may come directly from the sacral plexus, and be transmitted through the small sacro-sciatic foramen to its distribution in the lower end of the rectum. Fig. 443. Fig. 443. — DISSECTION OF THE PERINEUM OP THE MALE TO SHOW THE DISTRIBUTION OP THE PUDIO AND OTHER NERVES (from Hirschfeld and Leveille). ^ On the right side a part of the glutens maximus muscle and the great sacro-sciatic liga- ment have been removed to show the descent of the nerves from the great sacro-sciatic foramen. 1, great sciatic nerve of the right side ; 2, lesser sciatic nerve ; 2', its muscular branches to the gluteus maximus (right side) ; 2", cutaneous branches to the buttock (left side) ; 3, continuation of the nerve as posterior middle cutaneous of the thigh ; 3, internal and external cutaneous branches ; 4, 4, inferior pudendal branch ; 4', network of this and the perineal nerves on the scrotum ; 5, right pudic nerve ; 6, superior branch or nerve to the penis ; 7, the external superficial perineal branch ; 7', the internal superficial perineal branch ; 8, musculo-bulbal branches ; 9, hemorrhoidal or cutaneous anal branches ; 1.0, cutaneous branch of the fourth sacral nerve. Some of the branches of this nerve end in the external sphincter and in the adjacent skin of the anus ; others reach the skin in front of that part, and communicate with the inferior pudendal branch of the small sciatic nerve, and with the superficial perineal nerves. Summary. — The pudic nerve supplies the perinsBiim, the penis, and part of the scrotum, also the urethral and anal muscles in the male ; and the SMALL SCIATIC NERYE. 673 clitoris, labia, and other corresponding parts in the female. It communicates with the inferior pudendal branch of the small sciatic nerve. SMALL SCIATIC NERVE. The small sciatic nerve (tiervus ischiadicus minor) is chiefly a cutaneous nerve, supplying the integument of the lower part of the buttock, the back of the thigh, and upper part of the calf of the leg; it furnishes also branches to one muscle — the gluteus maximus. This nerve is formed by the union of two or more nervous cords, derived from the lower and back part of the sacral plexus. Arising below the pyriform muscle, it descends beneath the gluteus maximus, and at the lower border of that muscle comes into contact with the fascia lata. Continuing its course downwards along the back of the limb, it perforates the fascia a little below the knee. Fig. 444.— DEEP NERVES IN THE GLUTEAL AND INFERIOR PUDENDAL REGIONS (from Hirschfeld and Le- veille). \ Fig. 441. «, back part of the great trochanter ; b, tensor vaginae feraoris muscle ; ct tendon of the obturator internus muscle near its insertion ; d, upper part of the vastus externus ; e, coccyx ; ft gracilis muscle ; between /"and cl, the adductor magnus, semitendinosus, and biceps muscles ; * placed at the meeting of the crura penis above the urethia ; 1, placed upon the ilium close above the sacro-sciatic notch, marks the superior gluteal nerve, and on the divided parts of the gluteus meclius muscle, the supe- rior branch of the nerve ; 1', on the surface of the gluteus minimus muscle, the inferior branch of the nerve ; 1", branch of the nerve to the tensor vaginae fernoris ; 2, sacral plexus and great sciatic nerve ; 2', muscular twig from the plexus to the pyriformis ; 2", mus- cular branches to the geraellus superior and obturator internus ; 3, lesser sciatic nerve ; 3', placed on the upper and lower parts of the divided gluteus maximus, the inferior gluteal muscular branches of the lesser sciatic nerve ; 3", the cutaneous branches of the same nerve winding round the lower border of the gluteus maximus ; 4, the continuation of the lesser sciatic nerve as posterior cutaneous nerve of the thigh ; 4', inferior pudendal branch of the lesser sciatic ; 5, placed on the lower part of the sacral plexus, points to the origin of the pudic nerve ; 6, its perineal division with, its muscular branches ; b', anterior or superior superficial perineal branch ; 6", posterior or inferior superficial perineal ; + + , distribution of these nerves and the inferior puden- dal on the scrotum ; 7, dorsal nerve of the penis. The branches of tho small sciatic nerve are as follows. A. The inferior gluteal branches, given off under the gluteus maximus, supply the lower part of that muscle. — A distinct gluteal branch commonly proceeds from the sacral plexus to the upper part of the muscle. B. The cutaneous branches of the nerve principally emerge from beneath the lower border of the gluteus maximus, arranged iu an external and an internal set. Others appear lower down. 674 NERVES OF THE LOWER LIMB. a. The internal are mostly distributed to the skin of the inner side of the thigh at the upper part. One branch, however, which is much larger than the rest, is distinguished as the inferior pudendal. Fig. 445. Fig. 445. — POSTERIOR CUTANEOUS NERVES OF THE HIP AND THIGH (from Hirschfeld and Leveille). £ F a, gluteus maxinms muscle partially uncovered by the removal of a part of the fascia lata, and divided at its inferior part to show the lesser sciatic nerve ; b, fascia lata over the glutei muscles and the outer part of the hip ; c, d, part of the semitendinosus, biceps, and semimembranosus muscles exposed by the removal of the fascia ; e, gastrocnemius ; /, coccyx ; g, internal branches of the saphena vein ; 1, iliac cutaneous branches of the ilio-inguinal and ilio-hypogastric nerves ; 2, cutaneous iliac branches of the last inter- costal ; 3, posterior twigs of the external cutaneous nerve of the thigh ; 4, lesser sciatic nerve issuing from below the gluteus maximus muscle ; 4', its muscular branches ; 4", its cutaneous gluteal branches ; 5, posterior middle cutaneous continued from the lesser sciatic ; 5', 5', its inner and outer branches spreading on the fascia of the thigh ; 6, 6, its terminal branches descending on the calf of the leg ; 7, posterior tibial and fibular nerves separating in the popliteal space ; 8, lower posterior divisions of the sacral and coccygeal nerves ; 9, inferior pudendal nerve. Fig. 446. — DEEP POSTERIOR NERVES OF THE HIP AND THIGH (from Hirschfeld and Leveilie). | «, gluteus medius muscle ; I, gluteus maximus ; c, pyriformis ; d, placed on the GREAT SCIATIC NERVE. 675 trochanter major, points to the tendon of the obturator internus ; e, upper part of the femoral head of the biceps; f, semitendinosus ; g, semimembranosus ; h, gastrocnemins ; i, popliteal artery; 1, placed on the gluteus minimus muscle, points to the superior gluteal nerves ; 2, inferior gluteal branches of the lesser sciatic; 3, placed on the greater sacro- sciatic ligament, points to the pudic nerve ; 3', its farther course ; 4, inferior pudendal ; 5, placed on the upper divided part of the semitendinosus and biceps, points to the posterior middle cutaneous nerve of the thigh ; 6, great sciatic nerve, 6', 6', some of its muscular branches to the flexors ; 7, internal popliteal or posterior tibial nerve ; 7', its muscular or sural branches ; 8, external popliteal or peroneal nerve ; 8', its external cutaneous branch ; 9, communicating tibial ; &', communicating peroneal branch to the external saphenous nerve. The inferior pudendal branch turns forwards below the ischial tuberosity to reach the perinseum. Its filaments then extend forwards to the front and outer part of the scrotum, and communicate with one of the superficial perineal nerves. In the female, the inferior pudendal branch is distributed to the external labium pudendi. b. The external cutaneous branches, two or three in number, turn upwards in a retrograde course to the skin over the lower and outer part of the great gluteal muscle. In some instances one takes a different course, descending and ramifying in the integuments on the outer side of the thigh nearly to the middle. c. Of the lower branches some small cutaneous filaments pierce the fascia of the thigh above the popliteal space. One of these, arising somewhat above t'he knee-joint, is prolonged over the popliteal region to the upper part of the leg. Of the terminal twigs, perforating the fascia lata opposite the lower part of the popliteal space, one accompanies the short saphenous vein beyond the middle of the leg, and others pass into the integument covering the inner and outer heads of the gastrocnemius muscle. Its terminal cutaneous branches communicate with the short saphenous nerve. GREAT SCIATIC NERVE. The great sciatic nerve (nervus ischiadicus), the largest nerve in the body, supplies the muscles at the back of the thigh, and by its branches of con- tinuation gives nerves to all the muscles below the knee and to the greater part of the integument of the leg and foot. The several joints of the lower limb receive filaments from it and its branches. This large nerve is continued from the lower end of the sacral plexus. It escapes from the pelvis through the great sacro-sciatic foramen, below the pyri- formis muscle, and reaches down below the middle of the thigh, where it separates into two large divisions, named the internal and external popliteal nerves. At first it lies in the hollow between the great trochauter and the ischial tuberosity, covered by the gluteus maximus and resting on the gemelli, obturator internus and quadratus femoria muscles, in company with the small sciatic nerve and the sciatic artery, and receiving from that artery a branch which runs for some distance in its substance. Lower down it rests on the adductor magnus, and is covered behind by the long head of the biceps muscle. The bifurcation of the sciatic nerve may take place at any point intermediate between the sacral plexus and the lower part of the thigh ; and, occasionally, it is found to occur even within the pelvis, a portion of the pyriformis muscle being inter- posed between the two great divisions of the nerve. Branches of the trunk. — In its course downwards, the great sciatic nerve supplies offsets to some contiguous parts, viz., to the hip-joint, and to the muscles at the back of the thigh. a. The articular branches are derived from the upper end of the nerve, and enter the capsular ligament of the hip-joint, on the posterior aspect. They sometimes arise from the sacral plexus. 676 XERVES OF THE LOWER LIMB. 6. The muscular branches are given off under cover of the biceps muscle ; they supply the flexors of the leg, viz., the biceps, semitendinosug, and semimembranosus. A branch is likewise given to the adductor magnus. t TNTERNAL POPLITEAL NERVE. The internal popliteal nerve, the larger of the two divisions of the great sciatic nerve, following the same direction as the parent trunk, continues along the middle of the popliteal space to the lower border of the popliteus muscle, beneath which point the continuation of the trunk receives the name of posterior tibial. The interior popliteal nerve lies at first at a considerable distance from the popliteal artery, Fig. 447. at the outer side and nearer to the surface ; but, from the knee-joint downwards, the nerve, continuing a straight course, is close behind the artery, and then crosses it rather to the inner side. Fig. 447. — POSTERIOR CUTANEOUS NERVES OF THE LEG (from Sappey after Hirschfeld and Leveille). £ 1, internal popliteal division of the great seiatic nerve ; 2, branch to the internal part of the gastrocnemius muscle ; 3, 4, branches to the external part and plan- taris ; 5, communicating branch to the external saphe- neous nerve ; 6, external popliteal nerve ; 7, cutaneous branch ; 8, communicating branch descending to unite with that from the internal popliteal in, 9, the external saphenous nerve ; 10, calcaneal branch from this nerve ; 11, calcaneal and plantar cutaneous branches from the posterior tibial nerve; 12, internal saphenous nerve; 13, posterior branches of this nerve. The inner division of the sciatic nerve, from its commencement to its partition at the foot, is often described in anatomical works under the same appel- lation throughout ; the name varying, however, with different writers, as for example, " cruralis internus," or " popliteus internus," — Winslow : " tibialis pos- terior,"—Haller : " tibialis vel tibieus," — Fischer, &c. Branches. — The internal popliteal nerve sup- plies branches to the knee-joint and to the muscles of the calf of the leg, and also part of a cutaneous branch, the external or short sa- phenous nerve. ARTICULAR SERVES. — The articular branches are generally three in number ; two of these accompany the upper and lower articular arteries of the inner side of the knee-joint, the third follows the middle or azygos artery. These nerves pierce the ligamentous tissue of the joint. — The upper one is often wanting. MUSCULAR BRANCHES. — The muscular branches of the internal popliteal nerve arise behind the knee-joint, while the nerve is between the heads of the gastrocnemius muscle. a. The nerves to the gastrocnemius consist of two branches, which separate, one to supply each part of the muscle. POSTERIOR TIBIAL NERVE. 677 b. The small nerve of the idantaris muscle is derived from the outer of the branches just described, or directly from the main trunk (internal popliteal). c. The soleus receives a branch of considerable size, which enters the muscle on the posterior aspect after descending to it in front of the gastrocnemius. d. The nerve of the popliteus muscle lies deeper than the preceding branches, and arises somewhat below the joint ; it descends along the outer side of the popliteal vessels, and, after turning beneath the lower border of the muscle, enters the deep or anterior surface. EXTERNAL OE SHORT SAPHENOUS NERVE. The cutaneous branch of the internal popliteal nerve (ramus communicans tibialia) descends along the leg beneath the fascia, resting on the gastro- cnemius, in the furrow between the heads of the muscle, to about midway between the knee and the foot. Here it perforates the fascia, and a little lower down is usually joined by a branch from the external popliteal nerve (communicans peronei). After receiving this communicating branch, the external saphenous nerve descends beneath the integument near the outer side of the tendo Achillis in company with the short saphenous vein, and turns forwards beneath the outer malleolus to end in the skin at the side of the foot and on the little toe. On the dorsum of the. foot this nerve com- municates with the musculo- cutaneous nerve. In many cases, the external saphenous nerve supplies the outer side of the fourth toe, as well as the little toe. The union between the saphenous nerve and the branch cf the external popliteal nerve occurs in some cases higher than usual, occasionally even at or close to the popliteal space. It sometimes happens that the communication between the nerves is altogether wanting ; in which case the cutaneous nerve to the foot is generally continued from the branch of the internal popliteal nerve. POSTERIOR TIBIAL NERVE. The internal popliteal nerve receives the name of posterior tibial at the lower margin of the popliteus muscle. It passes down the leg with the pos- terior tibial artery, lying for a short distance at the inner side of the vessel, and afterwards at the outer side ; the artery inclining inwards from its origin while the nerve continues its straight course. In the interval between the inner malleolus and the heel, it divides into the two plantar nerves (internal and external). The posterior tibial nerve, like the accompanying vessels, is covered at first by the muscles of the calf of the leg, afterwards only by the integument and fascia, and it rests upon the deep-seated muscles. Lateral branches. — The deep muscles on the back of the leg and the integument of the sole of the foot receive branches from the posterior tibial nerve in its course along the leg. a. The muscular branches emanate from the upper part of the nerve, either sepa- rately or by a common trunk ; and one is distributed to each of the deep muscles, viz., the tibialis posticus, the long flexor of the toes, and the long flexor of the great toe. The branch which supplies the last-named muscle runs along the peroneal artery before penetrating the muscle. b. A calcaneo-plantar cutaneous branch is furnished from the posterior tibial nerve ; the plantar part perforates the internal annular ligament, and ramifies in the integu- ment at the inner side of the sole of the foot, and beneath the heel. INTERNAL PLANTAR NERVE. The internal plantar, the larger of the two nerves to the sole of the foot, into which the posterior tibial divides, accompanies the internal or smaller plantar artery, and supplies nerves to both sides of the three inner toes, and to one side of the fourth. From the point at which it separates from the 678 NERVES OF THE LOWER LIMB. posterior tibial nerve, it is directed forwards under cover of the first part of the abductor of the great toe, and, passing between that muscle and the short flexor of the toes, it gives off the internal cutaneous branch for the great toe, and divides opposite the middle of the foot into three digital branches. The outermost of these branches communicates with the external plantar nerve. Brandies. — a. Small muscular branches are supplied to the abductor pollicis and flexor brevis digitorum. b. Small plantar cutaneous branches perforate the plantar fascia to ramify in the integument of the sole of the foot. c. The digital branches are named numerically from within outwards : the three outer pass from under cover of the plantar fascia near the clefts between the toes. The first or innermost branch continues single, but the other three bifurcate to supply the adjacent sides of two toes. These branches require separate notice. The first digital branch is that destined for the inner side of the great toe ; it becomes subcutaneous farther back than the others, and sends off a branch to the flexor brevis pollicis. Fi?. 448. Fig. 448. — SUPERFICIAL AND DEEP DISTRIBUTION OP THE PLANTAR NERVES (from Hirschf'eld and Le- veille, slightly modified). J The flexor communis brevis, the abductor pollicis and abductor minimi digiti, a part of the tendons of the flexor communis longus, together with the lum- bricales muscles, have been removed so as to bring into view the trans versus and interossei in the middle of the foot. a, upon the posterior extremity of the flexor com- munis brevis, near which, descending over the heel, are seen ramifications of the calcaneal branch of the posterior tibial nerve ; b, abductor pollicis ; c, tendon of the flexor communis longus divided close to the place where it is joined by the flexor accessorius ; d, abductor minimi digiti ; e, tendon of the flexor longus pollicis between the two portions of the flexor brevis pollicis ; 1, internal plantar nerve giving some twigs to the abductor pollicis, and 1', a branch to the flexor communis brevis, cut as it lies on the acces- sorius ; 2, inner branch of the internal plantar nerve giving branches to the abductor pollicis, flexor brevis pollicis, and forming, 2', the internal cutaneous of the great toe ; 3, continuation of the internal plantar nerve, dividing subsequently into three branches, which form, 3', 3', 3', the collateral plantar cutaneous nerves of the first and second, second and third, and third and fourth toes ; 4, the external plantar nerve ; 4', its branch to the abductor minimi digiti ; 5, twig of union between the plantar nerves ; 6, superficial branch of the external plantar nerve ; subsequently dividing into 6', 6', the collateral cutaneous nerves of the fourth and fifth toes and the external nerve of the fifth ; 7, deep branch of the external plantar nerve giving twigs to the adductor pollicis, the interossei, the trans- versalis, and to the third and fourth lumbricales muscles. The second branch having reached the interval between the first and second meta- tarsal bones, furnishes a small twig to the first lumbricalis muscle, and bifurcates behind the cleft between the great toe and the second to supply their contiguous The third digital branch, corresponding with the second interosseous space, gives a slender filament to the second lumbricalis muscle, and divides in a manner similar PLANTAR NERVES.— PEROKEAL NERVE. 679 to that of the second branch into two offsets for the sides of the second and third toes. The fourth digital branch distributed to the adjacent sides of the third and fourth toes, receives a communicating branch from the external plantar nerve. Along the sides of the toes, cutaneous and articular filaments are given from these digital nerves ; and, opposite the ungual phalanx, each sends a dorsal branch to the pulp beneath the nail, and then runs onto the ball of the toe, where it is distributed like the nerves of the fingers. EXTERNAL PLANTAR NERVE. The external plantar nerve completes the supply of digital nerves to the toes, furnishing branches to the little toe and half the fourth : it also gives a deep branch of considerable size, which is distributed to several of the short muscles in the sole of the foot. There is thus a great resemblance between the distribution of this nerve in the foot and that of the ulnar nerve in the hand. The external plantar nerve runs obliquely forwards towards the outer side of the foot, along with the external plantar artery, between the flexor brevis digitorum and the flexor accessorius, as far as the interval between the former muscle and the abductor of the little toe. Here it divides into a superficial and a deep branch, having previously furnished offsets to the flexor accessorius and the abductor minimi diyiti. a. The superficial portion separates into two digital branches, which have the same general arrangement as the digital branches of the internal plantar nerve. They are distributed thus. Digital branches. — One of the digital branches continues undivided, and runs along the outer side of the little toe : it is smaller than the other, and pierces the plantar fascia further back. The short flexor muscle of the little toe, and occa- sionally one or two interosseous muscles of the fourth metatarsal space receive branches from this nerve. The larger digital branch communicates with an offset from the internal plantar nerve, and bifurcates near the cleft between the fourth and fifth toes to supply one side of each. &. The deep or muscular branch of the external plantar nerve dips into the sole of the foot with the external plantar artery, under cover of the tendons of the flexor muscles and the adductor pollicis, and terminates in numerous branches for the fol- lowing muscles : — all the interossei (dorsal and plantar) except occasionally one or both of those in the fourth space, the two outer lumbricales, the adductor pollicis, and the transversalis pedis. Summary of the internal popliteal nerve. — This nerve supplies all the muscles of the back of the leg and sole of the foot, and the integument of the plantar aspect of the toes, the sole of the foot, and in part that of the leg. EXTERNAL POPLITEAL OR PERONEAL NERVE. This nerve descends obliquely along the outer side of the popliteal space, lying close to the biceps muscle. Continuing downwards over the outer part of the gastrocnemius muscle (between it and the biceps) below the head of the fibula, the nerve turns round that bone, passing between it and the peroneus longus muscle, and then divides into the anterior tibial and the musculo- cutaneous nerves. Lateral branches. — Some articular and cutaneous branches are derived from the external popliteal nerve before its final division. ARTICULAR NERVES. — The articular branches are conducted to the outer side of the capsular ligament of the knee-joint by the upper and lower 680 NERVES OF THE LOWER LIMB. articular arteries of that side. They sometimes arise together, and the upper one occasionally springs from the great sciatic nerve before the bifur- cation. From the place of division of the external popliteal nerve, a recurrent articular nerve ascends through the tibialis anticus muscle with the recur- rent artery to reach the fore part of the knee-joint. Fig. 449. Fig. 449. — CUTANEOUS NERVES OF THE OUTER SIDE OF THE LEG AND FOOT (from Sappey after Hirschfeld and Leveille*). £ 1, external popliteal nerve ; 2, its external cutaneous branch ; 3, communi- cating branch which unites with 4, that form the internal popliteal in 5, the ex- ternal saphenous nerve ; 6, calcaneal branch of the external saphenous; 7, external dorsal digital branch to the fifth toe ; 8, collateral dorsal digital branch of the fourth and fifth toes ; 9, musculo- cutaneous nerve ; 10, its cutaneous branches ; 11, loop of union with the external saphenous; 12, union between its outer and inner branches ; 13, an- terior tibial nerve, shown by the removal of a part of the muscles, and giving muscular branches superiorly ; 14, its terminal branch emerging in the space between the first and second toes, where it gives the collateral dorsal digital branches to their adjacent sides ; 15, branches to the peronei muscles. CUTANEOUS NERVES. — The cuta- neous branches, two or three in number, supply the skin on the back part and outer side of the leg. The peroneal communicating branch (r. communicans fibularis), which joins the short sapheuous nerve below the middle of the back of the leg, is the largest of these nerves. In some instances, it continues a separate branch and its cutaneous filaments reach down to the heel or on to the outside of the foot. Another cutaneous branch extends along the outer side of the leg to the middle or lower part, sending offsets both backwards and forwards. MUSCULO-CUTANEOUS NERVE. The musculo-cutaneous (peroneal) nerve descends between the peronei muscles and the long extensor of the toes, and reaches the surface by per- forating the fascia in the lower part of the leg on the anterior aspect. It then divides into two branches, distinguished as external and internal, which proceed to the toes. The two branches sometimes perforate the fascia at a different height. PERONEAL NERVE. 681 (a) Muscular branches are given to the peroneus longus and peroneus brevis. (b) Cutaneous branches given off before the final division are distributed to the lower part of the leg. (c) The internal branch of the musculo-cutaneous nerve, passing forwards along the dorsum of the foot, furnishes one branch to the inner side of the great toe, and others to the contiguous sides of the second and third toes. It gives other offsets, which extend over the inner ankle and side of the foot. This nerve communicates •with the long saphenous nerve on the inner side of the foot, and with the anterior tibial nerve between the first and second toes. Fig. 450. Fig. 450. — VIEW OF THE DISTRIBUTION OP THE BRANCHES OP THE EXTERNAL POPLITEAL NERVE IN THE FRONT OP THE LEG AND DORSUM OF THE FOOT (from Hirschfeld and Leveille'). The upper part of the peroneus longus muscle has been removed, the tibialis anticus, the long extensor of the great toe and the peroneus longus have been drawn separate in the leg by hooks marked a, 6, and c, and the tendons of the extensor muscles have been removed in the dorsum of the foot, to show the deeper seated nerves ; 1, the external popliteal or peroneal nerve •winding round the other part of the fibula ; 1', its recurrent articular branches exposed by the dissection of the upper part of the tibialis anticus muscle ; 2, 2, the musculo-cutaneous nerve ; 2', 2', twigs to the long and short peroneal muscles ; 3, internal branch of the musculo-cutaneous nerve ; 3', 3', its dorsal digital branches to the inside of the great toe, and to the adjacent sides of the second and third toes ; 4, the external branch ; 4', 4', its dorsal digital branches to the adjacent sides of the third and fourth toes, and in part to the space between the fourth and fifth toes ; 5, the external saphenous nerve descending on the outer border of the foot, and uniting at two places with the outer branch of the musculo-cutaneous ; 5', its branch to the outer side of the fifth toe ; 6, placed on the upper part of the extensor communis digitorura, marks the anterior tibial nerve passing beneath the muscles ; 6, placed farther down on the tendon of the tibialis anticus, points to the nerve as it crosses to the inside of the anterior tibial artery ; 6', its muscular branches in the leg ; 6", on the tendon of the extensor longus pollicis points to the anterior tibial nerve after it has passed into the foot behind that tendon ; 7, its inner branch uniting with a twig of the musculo- cutaneous, and giving the dorsal digital nerves to the adjacent sides of the first and second toes; 8, distri- bution of its outer branch to the extensor brevis dlgi- torum and tarsal articulations. (d) The external branch, larger than the internal one, descends over the foot towards the fourth toe, which, together with the contiguous borders of the third and fifth toes, it supplies with branches. Cutaneous nerves, derived from this branch, spread over the outer ankle and the outer side of the foot, where they are connected with the short saphenous nerve. The dorsal digital nerves are continued on to the last phalanges of the toes. The number of toes supplied by each of the two divisions of the musculo-cuta- neous nerve is liable to vary ; together these nerves commonly supply all the toes on the dorsal aspect, excepting the outer side of the little toe, which receives a branch from the short saphenous nerve, and the adjacent sides of the gre.it toe and the second toe, to which the anterior tibial nerve is distributed : with this latter branch, how- ever, it generally communicates. Y Y 682 SYNOPSIS OF CUTANEOUS NERVES. ANTERIOR TIBIAL NERVE. The anterior tibial (interosseous nerve), commencimg between the fibula and the ]:eroneus longus, inclines obliquely beneath the long extensor of the toes to the fore part of the interosseous membrane, and there comes into contact with the anterior tibial vessels, and with those vessels it descends to the front of the ankle-joint, where it divides into an external and an internal branch. The nerve first reaches the outer side of the anterior tibial artery, above the middle of the leg ; and, after crossing in front of that vessel once or oftener, lies to the inner side of it at the bend of the ankle. (a) Muscular branches. — In its course along the leg, the anterior tibial nerve gives slender filaments to the muscles between which it is placed, namely, the tibialis anticus, the long extensor of the toes, and the special extensor of the great toe. (b) The external branch of the anterior tibial nerve turns outwards over the tarsus beneath the short extensor of the toes ; and, having become enlarged (like the pos- terior interosseous nerve on the wrist) terminates in branches which supply the short extensor muscle, and likewise the articulations of the foot. (c) The internal branch, continuing onwards in the direction of the anterior tibial nerve, accompanies the dorsal artery of the foot to the first interosseous space, and ends in two branches, which supply the integument on the neighbouring sides of the great toe and the second toe on their dorsal aspect. It communicates with the inter- nal division of the musculo-cutaneous nerve. Summary of the external popliteal nerve. — This nerve supplies, besides articular branches to the knee, ankle, and foot, the peronei muscles, extensor muscles of the foot, also the integument of the front of the leg and dorsum of the foot. It gives the ramus communicans fibularis to the short saphenous branch of the internal popliteal nerve, and communicates with the long saphenous nerve. SYNOPSIS OF THE CUTANEOUS DISTRIBUTION OF THE CEREBRO-SPiNAL NERVES. HEAD. — The face and head in front of the ear are supplied with sensory nerves from the fifth cranial nerve. The ophthalmic division supplies branches to the forehead, upper eyelid, and dorsum of the nose. The superior maxillary division supplies the cheek, ala of the nose, upper lip, lower eyelid, and the region behind the eye, over the temporal fascia. The inferior maxillary division supplies the chin and lower lip, the pinna of the ear on its outer side, and the integument in front of the ear and upwards to the vertex of the head. The head, behind the ear, is mainly supplied by the great occipital branch of the posterior division of the second spinal nerve, but above the occipital protuberance there is also distributed the branch from the posterior division of the third spinal nerve ; and, rn front of the area of the great occipital nerve, is a space supplied by anterior divisions of spinal nerves, viz., the back of the pinna of the ear, together with the integument behind and that in front over the parotid gland, which are supplied by the great auricular nerve ; while between the area of that nerve and the great occipital the small occipital nerve intervenes. The auricular branch of the pneumo-gastric nerve also is distributed on the back of the ear. TRUNK. — The posterior divisions of the spinal nerves supply an area, extending on the back from the vertex of the skull to the buttock. This area is narrow in the neck ; it is spread out over the back of the scapula ; SYNOPSIS OF CUTANEOUS NERYES. 683 and on the buttock the distribution of the lumbar nerves extends to the trochanters. The area supplied by the cervical plexus, besides extending upwards, as already mentioned, on the lateral part of the skull, stretches over the front and sides of the neck, and the upper part of the shoulder and breast. The area of the anterior divisions of the dorsal and Jirst lumbar nerves meets superiorly with that of the cervical plexus, and posteriorly with that of the posterior divisions of dorsal and lumbar nerves. It passes down over the haunch and along by the outer part of Pou part's ligament, and includes part of the scrotum and a small portion of the integument of the thigh internal to the saphenous opening. The perinceum and penis are supplied by the pudic nerve ; the scrotum by branches of the pudic, inferior pudendal, and ilio- inguinal nerves. UPPER LIMB. — The shoulder, supplied superiorly by the cervical plexus, receives its cutaneous nerves iuferiorly as far as the insertion of the deltoid from the circumflex nerve. The arm internally is supplied by the intercosto-humeral nerve and the nerve of Wrisberg. The iuner and anterior part is supplied by the internal cutaneous nerve ; and the posterior and outer part by the internal and external branches of the musculo-spiral nerve. The forearm, anteriorly and on the outer side, is supplied by the external cutaneous ; on its outer and posterior aspect, superiorly by the external cutaneous branches of the musculo-spiral, and inferiorly by the radial branch of the same nerve. On the inner side, both in front and behind, is the internal cutaneous nerve, and inferiorly are branches of the ulnar. On the back of the hand are the radial and uluar nerves, the radial supplying about three fingers and a half or less, and the uluar one and a half or more. On the front of the hand, the median nerve supplies three fingers and a half, and the ulnar one and a half. In the palm is a branch of the median given off above the wrist. On the ball of the thumb are branches of the mu- culo-cutaneous, median, and radial nerves. LOWER LIMB. — The buttock is supplied from above by the cutaneous branches of the posterior divisions of the lumbar nerves, with the ilio-hypo- gastric and lateral branches of the last dorsal nerves ; internally by the posterior divisions of the sacral nerves ; externally by the posterior branch of the external cutaneous nerve proceeding from the front ; and inferiorly by branches of the small sciatic nerve proceeding from below. The thigh is supplied externally by the external cutaneous nerve ; posteriorly, and in the upper half of its ii.ner aspect, by the small sciatic ; anteriorly, and in the lower half of the inner aspect, by the middle and internal cutaneous. The leg is supplied posteriorly by the small sciatic and short saphenous nerves ; internally by the long saphenous and branches of the internal cutaneous of the thigh ; and outside and in front by cutaneous branches of the external popliteal nerve, and by its musculo- cutaneous branch. On the dorsum of the foot are the branches of the mu^culo-cutaneous, supplying all the toes with the exception of the adjacent sides of the first and second, which are supplied by the anterior tibial, and the outer side of the little toe, which, with the outer side of the foot, is supplied by the short saphenous nerve. The long saphenous is the cutaneous nerve on the inner side of the foot. Y Y 2 684 SYNOPSIS OF MUSCULAR NERVES. The sole of the foot is supplied by the plantar nerves. The internal plantar nerve gives branches to three toes and a half ; the external to the remaining one toe and a half. SYNOPSIS OF THE MUSCULAR DISTRIBUTION OF THE CEREBRO-SPINAL NERVES. MUSCLES OF THE HEAD AND FORE PART OF THE NECK. The muscles of the orbit are mostly supplied by the third cranial nerve — the superior division of that nerve being distributed to the levator palpebrzo and the superior rectus muscles ; and the inferior division to the inferior and internal recti and the inferior oblique. The superior oblique muscle is supplied by the fourth nerve, the external rectus by the sixth ; while the tensor tarsi has no special nerve apart from those of the orbicularis palpebrarum, which are derived from the facial. The superficial muscles of the face and scalp, which are associated in their action as a group of muscles of expression, are supplied by the portio dura of the seventh cranial nerve ; the retrahens auriculam arid occipitalis muscles being supplied by the posterior auricular branch. The deep muscles of the face, employed in mastication, viz., the temporal, masseler, buccinator, and two pterygoid muscles, are supplied by the inferior maxillary division of the fifth cranial nerve. Muscles above the hyoid bone. — The mylo-hyoid muscle and anterior belly of the digastric are supplied by a special biauch of the inferior maxillary division of the fifth cranial nerve ; the posterior belly of the digastric muscle, and the stylo-hyoid, are supplied by branches of the portio dura. The genio-hyoid and the muscles of the tongue receive their nervous supply from the hypoglossal nerve. The muscles ascending to the hyoid bone and laiynx, viz., the sterno-hyoid, omo-hyoid, and sterno-thyroid, are supplied from the ramns descendens noni and its loop with the cervical plexus, while the thyro-hyoid muscle receives a separate twig from the ninth nerve. The larynx, pharynx, and soft palate. — The crico- thyroid muscle is sup- plied by the external laryngeal branch of the pneumo-gastric nerve, and the other intrinsic muscles of the larynx by the recurrent laryngeal. The muscles of the pharynx are supplied principally by the pharyngeal branch of the pneumo -gastric ; the stylo-pharyngeus, however, is supplied by the glosso-pharyngeal nerve. Of the muscles of the soft palate unconnected with the tongue or pharynx, the tensor palati receives its nerve from the otic ganglion (which also supplies the tensor tympani); the levator palati gets a twig (Meckel) from the posterior palatine branch of the spheno-palatiue ganglion, and the azygos uvulee is probably supplied from the same source. MUSCLES BELONGING EXCLUSIVELY TO THE TRUNK, AND MUSCLES ASCENDING TO THE SKULL. All those muscles of the back which are unconnected with the upper limb, viz., the posterior serrati, the splenius, complexus, erector spiuse, and the muscles more deeply placed, receive their supply from the posterior divisions of the spinal nerves. The sterno-mastoid is supplied by the spinal accessory nerve and a twig of the cervical plexus coming from the second cervical nerve. SYNOPSIS OF MUSCULAR NERVES. 6?5 The rectus capitis anticus major ar,d minor are supplied by twigs from the upper cervical nerves ; the longus colli and scaleni muscles by twigs from the lower cervical nerves. The muscles of the chest, viz , the intercostals, subcostals, levatores cos- tarum, arid triangularis sterni, are supplied by the intercostal nerves. The obliqui, transversus, and rectus of the abdomen are supplied by the lower intercostal nerves ; and the oblique and transverse muscles also get branches from the ilio-inguiual and ilio hypogastric nerves. The cremaster muscle is supplied by the genital branch of the genito-crural nerve. The quadratus lumborum (like the psoas) receives small branches from the lumbar nerves before they form the plexus. The diaphragm receives the phrenic nerves from the fourth and fifth cer- vical nerves, and likewise sympathetic filaments from the plexuses round the phrenic arteries. The muscles of the urethra and penis are supplied by the pudic nerve ; the levator and sphincter ani by the pudic an.l by the fourth and fifth S'icrai and the coccygeal nerves ; and the coccyyeus muscle by the three last named nerves. MUSCLES ATTACHING THE UPPER LIMB TO THE TRUNK. The trapezius and the sterno-cleido-mastoid receive the distribution of the spinal accessory nerve, and, in union with it, filaments from the cervical plexus. The latissimus dorsi receives the long subscapular nerve. The rhomboidei are supplied by a special branch from the anterior division of the fifth cervical nerve. The levator anguli scapulae is supplied by branches from the anterior division of the third cervical nerve, and sometimes partly also by the branch to the rhomboid muscles. The serratus majnus has a special nerve, the posterior thoracic, derived from the fifth and sixth cervical nerves. The subclavius receives a special branch from the place of union of the fifth and sixth cervical nerves. The pectorales are supplied by the anterior thoracic branches of the brachial plexus, the larger muscle receiviug filaments from both these nerves, and the smaller from the inner only. MUSCLES OF THE UPPER LIMB. Muscles of the shoulder. — The supraspinatus and infraspinatus are sup- plied by the suprascapular nerve ; the subsoapularis by the two smaller subscapular nerves ; the teres major by the second subscapular, and the deltoid and teres minor by the circumflex nerve. Posterior muscles of the arm and forearm. — The triceps, anconeus, supi- nator longus, and extensor carpi radialis Lmgior are supplied by direct branches of the musculo-spiral nerve ; while the extensor carpi radialis brevior and the other extensor muscles iti the forearm receive their branches from the pos- terior iuterosseous division of that nerve. Anterior muscles of the arm and forearm. — The coraco-brachialis, biceps, and brachialis anticus are supplied by the musculo- cutaneous nerve : the brachialis anticus likewise generally receives a twig from the musculo- spiral nerve. The muscles in front of the forearm are supplied by the median nerve, with the exception of the flexor carpi uluaris and the ulnar half of the flexor profuudus digitorum, which are supplied by the G86 THE SYMPATHETIC NERVES. ulnar nerve, and the supinator longus, which is supplied by the musculo- spiral. Muscles of the hand. — The abductor and opponens pollicis, the outer half of the flexor brevis pollicis, and the two outer lumbricales muscles, are supplied by the median nerve : all the other muscles receive their nerves from the ulnar. MUSCLES OF THE LOWER LIMB. Posterior muscles of the hip and thigh. — The gluteus maximus is mainly supplied by the small sciatic nerve, and receives at its upper part a separate branch from the sacral plexus. The gluteus medius and minimus, together with the tensor vaginse femoris, are supplied by the gluteal nerve. The pyri- formis, gemelli, obturator iiiternus, and quadratus femoris receive special branches from the sacral plexus. The hamstring muscles are supplied by branches from the great sciatic nerve. Anterior and internal muscles of the thigh. — The psoas muscle is supplied by separate twigs from the lumbar nerves. The iliacus, quadriceps extensor femoris, and sartorius are supplied by the anterior crural nerve. The adductor muscles, the obturator externus and the pectineus, are supplied by the obturator nerve, but the adductor maguus likewise receives a branch from the great sciatic, and the pectineus sometimes has a branch from the anterior crural. Anterior muscles of the leg and foot. — The muscles in front of the leg, together with the extensor brevis digitorum, are supplied by the anterior tibia! nerve. The peroneus longus and brevis are supplied by the musculo-cutaneous nerve. Posterior muscles of the leg. — The gastrocnemius, plantaris, soleus, and popliteus are supplied by branches from the internal popliteal nerve ; the deep muscles, viz., the flexor longus digitorum, flexor longus pollicis, and tibialis posticus, derive their nerves from the posterior tibial. Plantar muscles. — The flexor brevis digitorum, the abductor and flexor brevis pollicis, and the two inner lumbricales, are supplied by the internal plantar nerve ; all the others, including the flexor accessorius and iuterossei, are supplied by the external plantar nerve. III. SYMPATHETIC NERVES. The nerves of the sympathetic system (nervus intercostalis ; nerves of organic life — Bichat) are distributed in general to all the internal viscera, but some organs receive their nerves also from the cerebro spinal system, as the lungs, the heart, and the upper and lower parts of the alimentary canal. It appears from physiological researches to be also the special province of the sympathetic system to supply nerves to the coats of the blood-vessels. This division of the nervous system consists of a somewhat complicated collection of ganglia, cords and plexuses, the parts of which may, for con- venience, be classified in three groups, viz., the principal gangliated cords, the great prevertebral plexuses with the nerves proceeding from them, and the ganglia of union with cranial nerves. The gangliated cords consist of two series, in each of which the ganglia are connected by intervening cords. These cords are placed symmetrically in. GAXGLIATED SYMPATHETIC COEDS. 687 front of the vertebral column, and extend from the base of the skull to the coccyx. Superiorly they are connected with plex- uses which enter the cranial cavity, while iuferiorly they converge on the sacrum, and terminate in a single ganglion on the coccyx. The several portions of the cords are distinguished as cervical, dorsal, lum- bar, and sacral, and iu each of these parts the ganglia are equal in number, or nearly so, to the vertebrae on which they lie, except in the neck, where there are only three. Fig. 451. — DIAGRAMMATIC OUTLINE OF THE SYM- PATHETIC CORD OF ONE SIDE IN CONNECTION WITH THE SPINAL NERVES. The full description of this figure will be found at p. 629. On the right side the following letters in- dicate parts of the sympathetic nerves ; viz. a, the superior cervical ganglion, communi- cating with the upper cervical spinal nerves and continued below into the great sympathetic cord ; 6, the middle cervical ganglion ; c, d, the lower cervical ganglion united with the first dorsal ; d', the eleventh dorsal ganglion ; from the fifth to the ninth dorsal ganglia the origins of the great splanchnic nerve are shown ; I, the lowest dorsal or upper lumbar ganglion ; ss, the upper sacral ganglion. In the whole extent of the sympathetic cord, the twigs of union with the spinal nerves are shown. Connection of the ganyliated cords with the c&rebro-spinal system. — The ganglia are severally connected with the spinal nerves in their neighbourhood by means of short cords ; each connecting cord consisting of a white and a grey portion, the former of which may be considered as proceeding from the spinal nerve to the ganglion, the latter from the ganglion to the spinal nerve. At its upper end the gangliated cord communicates likewise with certain cranial nerves. The main cords interven- ing between the ganglia, like the smaller ones connecting the ganglia with the spinal nerves, are composed of a grey and a white part, the white being continuous with the fibres of the spinal nerves prolonged to the ganglia. The great prevertebral plexuses comprise three large aggregations of nerves, or nerves and ganglia situated in front of the spine, and occupying respectively the thorax, the abdomen, and the pelvis, They are single and median, and are Fig. 451. Br 688 THE SYMPATHETIC NERVES. named respectively the cardiac, the solar, and the hypogastric plexus. These plexuses receive branches from both the gangliated cords above noticed, and they constitute centres from which the viscera are supplied with nerves. The cranial ganglia of the sympathetic are the ophthalmic, spheno-pala- tine, subrn axillary, and otic, which, being intimately united with the fifth cranial nerve, have already been described along with that nerve. They nre also more or less directly connected with the upper end of the sympa- thetic gangliated cords ; but it will be unnecessary to give any special description of them in this place. A. THE GANGLIATED COEDS. THE CERVICAL PART. In the neck, each gangliated cord is deeply placed behind the sheath of the great cervical blood-vessels, and in contact with the muscles which immediately cover the fore part of the vertebral column. It comprises three ganglia, the first of which is placed near the base of the skull, the second in the lower part of the neck, and the third immediately above the head of the first rib. THE UPPER CERVICAL GANGLION. This is the largest ganglion of the great sympathetic cord. It is continued p.uperiorly into an ascending branch, and tapers below into the connecting cord, so as to present usually a fusiform shape ; but there is considerable variety in this respect in different cases, the ganglion being occasionally broader than usual, and sometimes constricted at intervals. It has the reddish-grey colour characteristic of the ganglia of the sympathetic system. It is placed on the larger rectus muscle, opposite the second and third cervical vertebrae, and behind the internal carotid artery. Connection with spinal nerves. — At its outer side the superior cervical ganglion is connected with the first four spinal nerves, by means of slender cords, which have the structure pointed out in the general description as being common to the series. The circumstance of this ganglion being connected with so many as four spinal nerves, together with its occasionally constricted appearance, is favourable to the view that it may be regarded as consisting of several ganglia which have coalesced. Connection irith cranial nerves. — Small twigs connect the ganglion or its cranial cord with the second ganglion of the pneumo-gastric, and with the ninth cranial nerve, near the base of the skull ; and another branch, which is directed upwards from the ganglion, divides at the base of the skull into two filaments, one of which ends in the second (petrosal) ganglion of the glosso-pharyngeal nerve ; while the other, entering the jugular foramen, joins the ganglion of the root of the pneumo-gastric. Besides the branches connecting it with cranial and spinal nerves, the first cervical ganglion gives off also the ascending branch, the upper cardiac nerve, pharyngeal nerves, and branches to blood-vessels. 1. ASCENDING BRANCH AND CRANIAL PLEXUSES. The ascending branch of the first cervical ganglion is soft in texture and of CAROTID BRANCH AND PLEXUS. 689 a reddish tint, seeming to be in some degree a prolongation of the ganglion itself. In its course to the skull, it is concealed by the internal carotid artery, with which it enters the carotid canal in the temporal bone, and it is then divided into two parts, which are placed one on the outer, the other on the inner side of the vessel. Fig. 452 Fig. 452. — CONNECTIONS OP THE SYMPATHETIC NERVE THROUGH ITS CAROTID BRANCH WITH SOME OP THE CRANIAL NERVES. The full description of this figure will be found at p. 602. The following numbers refer to sympathetic nerves and their connections : — 6, spheno-palatine ganglion ; 7, Vidian nerve ; 9, its carotid branch ; 10, a part of the sixth nerve, receiving twigs from the carotid plexus of the sympathetic; 11, superior cervical sympathetic ganglion; 12, its prolongation in the carotid branch ; 15, anastomosing nerve of Jacobson ; 16, twig uniting it to the sympathetic. The external division distributes filaments to the internal carotid artery, and, after communicating by means of other filaments with the internal division of the cord, forms the carotid plexus. The inner division, rather the smaller of the two, supplies filaments to the carotid artery, and goes to form the cavernous plexus. The terminal parts of these divisions of the cranial cord are prolonged on the trunk of the internal carotid, and extend to the cerebral and ophthalmic arteries, around which they form secondary plexuses, those on the cerebral artery ascending to the pia mater. One minute plexus enters the eye-ball with the central artery of the retina. It was stated by Ribes (Mem. de la Socie"te Med. d'Emulation, torn. viii. p. 606,) that the cranial prolongations of the sympathetic nerve from the two sides coalesce with one another on the anterior communicating artery, — a small ganglion or a plexus being formed at the point of junction; but this connection has not been satis- factorily made out by other observers. CAROTID PLEXUS. — The carotid plexus, situated on the outer side of the internal carotid artery at its second bend (reckoning from below), or between the second and third bends, joins the fifth and sixth cranial nerves, and gives many filaments to the vessel on which it lies. Branches. — (a) The connection with the sixth nerve is established by means of one or two filaments of considerable size, which are supplied to that nerve where it lies by the side of the internal carotid artery. 690 THE SYMPATHETIC NERVES. (6) The filaments connected with the Gasserian ganglion of the fifth nerve pro- ceed sometimes from the carotid plexus, at others from the cavernous. (c) The deep branch of the Vidian nerve passes backwards to the carotid plexus, and after leaving the Vidian canal, lies in the cartilaginous substance which closes the foramen lacerum medium. Valentin describes nerves as furnished to the dura mater from the carotid plexus. CAVERNOUS PLEXUS. — The cavernous plexus, named from its position in the sinus of the same name, is placed below and rather to the inner side of the highest turn of the internal carotid artery. Besides giving branches on the artery, it communicates with the third, the fourth and the ophthalmic of the fifth cranial nerves. Blanches. — (a) The filament which joins the third nerve comes into connection with it close to the point of division of that nerve. (b) The branch to the fourth nerve, which may be derived from either the caver- nous or the carotid plexus, joins the nerve where it lies in the wall of the cavernous sinus. (c) The filaments connected with the ophthalmic trunk of the///* nerve are supplied to its inner surface. One of them is continued forwards to the lenticular ganglion, either in connection with or distinct from the nasal nerve. 2. PHARYNGEAL NERVES AND PLEXUS. These nerves arise from the inner part of the ganglion, and are directed obliquely inwards to the side of the pharynx. Opposite the middle con- strictor muscle they unite with branches of the pneumo-gastric and glosso- pharyngeal nerves ; and by their union with those nerves the pliaryngeal plexus is formed. Branches emanating from the plexus are distributed to the muscles and mucous membrane of the pharynx. 3. UPPER CARDIAC NERVE. Each of the cervical ganglia of the sympathetic furnishes a cardiac branch, the three being named respectively the upper, middle and lower cardiac nerves. These branches are continued singly, or in connection, to the large prevertebral centre (cardiac plexus) of the thorax. Their size varies con- siderably, and where one branch is smaller than common, another will be found to be increased in size, as if to compensate for the defect. There are some differences in the disposition of the nerves of the right and left sides. The upper cardiac nerve (n. cardiacus superficialis) of the right side proceeds from two or more branches of the ganglion, with, in some instances, an offset from the cord connecting the first two ganglia. In its course down the neck the nerve lies behind the carotid sheath, in contact with the longus colli muscle ; and it is placed in front of the lower thyroid artery and the recurrent laryngeal nerve. Entering the thorax, it passes in some cases before, in others behind the subclavian artery, and is directed along the innominate artery to the back part of the arch of the aorta, where it ends in the deep cardiac plexus, a few small filaments continuing also to the front of the great vessel. Some branches distributed to the thyroid body accompany the inferior thyroid artery. In its course downwards the cardiac nerve is repeatedly connected with] other branches of the sympathetic, and with the pneumo-gastric nerve. Thus about the middle of the neck it is joined by some filaments from the external laryngeal UPPER CARDIAC XERVE. 691 nerve; and, rather lower down, by one or more filaments from the trunk of the pneumo-gastric nerve ; lastly, on entering the chest, it joins with the recurrent laryngeal. Fig. 453. Fig. 453. — CONNECTIONS OF THE CERVICAL AND UPPER DORSAL SYMPATHETIC GANGLIA AND NERVES ON THE LEFT SIDE. The full description of this figure will be found at p. 620. The following numbers refer to the sympathetic ganglia and nerves, and those immediately connected with them : — 3, pharyngeal plexus ; 8, laryngeal plexus ; 13, pulmonary plexus ; and to the reader's left, above the pulmonary artery, a part of the cardiac plexus ; 24, superior cervical ganglion of the sympathetic ; 25, middle cervical ganglion ; 26, inferior cervical ganglion united with the first dorsal ganglion ; 27, 28, 29, 30, second, third, fourth, and fifth dorsal ganglia. Variety. — Instead of passing to the thorax in the manner described, the superior cardiac nerve may join the cardiac branch furnished from one of the other cer- vical ganglia. Scarpa describes this as the common disposition of the nerve ; but Cruveilhier (Anat. Descript., t. iv.) states that he has not in any case found the cardiac nerves to correspond exactly ^ith the figures of the " Tabula* Xeurologicae." 692 THE SYMPATHETIC NERVES. The superficial cardiac nerve of the left side has, while in the neck, the same course and connections as that of the right side. But within the chest it follows the left carotid artery to the arch of the aorta, and ends in some instances in the superficial cardiac plexus, while in others it joins the deep plexus ; and accordingly it passes either in front of or behind the arch of the aorta. 4. BRANCHES TO BLOOD-VESSELS. The nerves which ramify on the arteries (nervi molles) spring from the front of the ganglion, and twine round the trunk of the carotid artery. They are prolonged on each branch of the external carotid, and form slender plexuses upon them. Communications with other nerves. — From the plexus on the facial artery is derived the filament which joins the submaxillary ganglion ; and, from that on the middle meningeal artery, twigs have been described as extending to the otic ganglion, as well as to the gangliform enlargement of the facial nerve. Lastly, a communication is established between the plexus on the carotid artery, and the digastric branch of the facial nerve. Small ganglia are occasionally found on some of the vascular plexuses, close to the origin of the vessels with which they are associated. Thus lingual, temporal, and pharyngeal ganglia have been described ; and besides these there is a larger body, the ganglion intercaroticum, placed on the inner side of the angle of division of the common carotid artery. This body, long known to anatomists as a ganglion, has been stated by Luschka to have a structure very different from the nervous ganglia in general, and has been named by him the "glandula intercarotica. " The ganglion intercaroticum was described by Luschka as presenting principally a follicular structure, and regarded by him as being of a nature similar to the glan- dula coccygea, which he had previously discovered. It appears, however, from the researches of Julius Arnold, that the follicular appearances observed by Luschka, both in this instance and in the coccygeal gland, were produced by arterial glomeruli seen in section; and that the ganglion intercaroticum consists of numbers of those glome- ruli gathered into several larger masses, and of dense plexuses of nerves surrounding respectively the glomeruli, the masses, and the whole structure. Within those plex- uses nerve-cells are scattered, but not in very great number. The ganglion is usually about one-fourth of an inch long ; but, according to Luschka, may be divided into small separate masses, and thus escape attention, or be supposed to be absent. — (Luschka, Anat. d. Menschen, vol. i. 1862 ; and Julius Arnold, in Virchow's Archiv., June, 1865.) MIDDLE CERVICAL GANGLION. The middle ganglion (ganglion thyroideum), much the smallest of the cervical ganglia, is placed on or near the inferior thyroid artery. It is usually connected with the fifth and sixth spinal nerves, but in a somewhat variable manner. It gives off thyroid branches and the middle cardiac nerve. THYROID BRANCHES. — From the inner side of the ganglion some twigs proceed along the inferior thyroid artery to the thyroid body, where they join the recurrent laryngeal and the external laryngeal nerves. Whilst on the artery, these branches communicate with the upper cardiac nerve. THE MIDDLE CARDIAC NERVE (nervus cardiacus profundus v. magnus) of the right side is prolonged to the chest behind the sheath of the common carotid artery, and either in front of or behind the subclavian artery. In the LOWER CEHVICAL GANGLION. 693 chest it lies on the trachea, where it is joined by filaments of the recurrent laryngeal nerve, and it ends in the right side of the deep cardiac plexus. While in the neck, the nerve communicates with the upper cardiac nerve and the recurrent branch of the pueumo-gastric. On the left side, the middle cardiac nerve enters the chest between the left carotid and subclavian arteries, and joins the left side of the deep cardiac plexus. AVhen the middle cervical ganglion is small, the middle cardiac nerve may be found to be an offset of the inter-ganglionic cord. LOWER CERVICAL GANGLION". The lower or third cervical ganglion is irregular in shape, usually some- what flattened and round or semiluuar, and is frequently united in part to the first thoracic ganglion. Placed in a hollow between the transverse process of the last cervical vertebra and the neck of the first rib, it is con- cealed by the vertebral artery. It is connected by short communicating cords with the two lowest cervical nerves. Numerous branches are given oif from it, among which the largest is the lower cardiac nerve. THE LOWER CARDIAC NERVE, issuing from the third cervical ganglion or from the first thoracic, inclines inwards on the right side, behind the sub- clavian artery, and terminates in the cardiac plexus behind the arch of the aorta. It communicates with the middle cardiac and recurrent laryngeal nerves behind the subclavian artery. On the left side, the lower cardiac often becomes blended with the middle cardiac nerve, and the cord resulting from their union terminates in the deep cardiac plexus. BRANCHES TO BLOOD-VESSELS. — From the lowest cervical and first dorsal ganglia a few slender branches ascend along the vertebral artery in its osseous canal, forming a plexus round the vessel by their inter-communica- tions, and supplying it with offsets. This plexus is connected with the cervical spinal nerves as far upwards as the fourth. One or two branches frequently pass from the lower cervical ganglion to the first dorsal ganglion in front of the subclavian artery, forming loops round the vessel (ansse Vieussenii), and supplying it with small offsets. THORACIC PART OF THE GANGLIATED CORD. In the thorax the gangliated cord is placed towards the side of the spinal column, in a line passing over the heads of the ribs. It is covered by the pleura, and crosses the intercostal blood-vessels. Opposite the head of each rib the cord usually presents a ganglion, so that there are commonly twelve of these ; but, from, the occasional coalescence of two, the number varies slightly. The first ganglion when distinct is larger than the rest, and is of an elongated form ; but it is often blended with the lower cervical ganglion. The rest are small, generally oval, but very various in form. Connection with the spinal nerves. — The branches of connection between the spinal nerves and the ganglia of the sympathetic are usually two in number for each ganglion ; one of these generally resembling the spinal nerve in structure, the other more similar to the sympathetic nerve. BRANCHES OF THE GANGLIA. The branches furnished by the first fivt or six ganglia are small, and are 946 THE SYMPATHETIC NERVES. Fig. 451 THORACIC GAXGLIA. 695 Fig. 451.— DIAGRAMMATIC VIEW OP THE SYMPATHETIC CORD OP THE RIGHT SIDT-, SHOWING ITS CONNECTIONS WITH THE PRINCIPAL CEREBRO-SPINAL NERVES AND THE MAIN PREAORTIC PLEXUSES. £ Cerebro-spinal Nerves. — VI, a portion of the sixth cranial nerve as it passes through the cavernous sinus, receiving two twigs from the carotid plexus of the sympathetic nerve; 0, ophthalmic ganglion connected by a twig with the carotid plexus ; M, connection of the spheno-palatine ganglion by the Vidian nerve with the carotid plexns ; C, cervical plexus; Br, brachial plexus ; D 6, sixth intercostal nerve ; D 12, twelfth ; L 3, third lumbar nerve; S 1, first sacral nerve ; S 3, third ; S 5, fifth ; Cr, anterior crural nerve ; Cr', great sciatic ; pn, pneumo-gastric nerve in the lower part of the neck ; r, recurrent nerve winding round the subclaviau artery. Sympathetic Cord. — c, superior cervical ganglion ; S AND CONJUNCTIVA. The eyelids (palpebrse) are moveable folds of integument, strengthened toward their margins by a thin lamina of cartilage. The mucous membrane, which lines their inner surface, and which is reflected thence in the form of a pellucid covering on the surface of the eyeball, is named membrana con- junctiva. The upper lid is larger and more moveable than the lower : the trans- parent part of the globe is covered by it when the eye is closed ; and the eye is opened chiefly by the elevation of this lid by a muscle (levator palpebrse) devoted exclusively to this purpose. The eyelids are joined at the outer and inner angles (canthi) of the eye. The interval between the angles, fissura palpebrarum; varies in length in different persons, and, according to its extent, the size of the globe being nearly the same, gives the appearance of a larger or a smaller eye. The greater part of the edge of each eyelid is flat- tened, but towards the inner angle it is rounded off for a short space, at the same time that it somewhat changes its direction ; and, where the two differ- ently formed parts join, there exists on each lid a slight conical elevation — papitta lachrymalis, the apex of which is pierced by the aperture or punctum of the corresponding lachrymal canalicule. In the greater part of their extent the lids are applied to the surface of the eyeball ; but at the inner canthus, opposite the puncta lachrymalia, there intervenes a vertical fold of conjunctiva, the plica semilunaris, resting on the eyeball ; while, occupying the recess of the angle internal to the border of this fold, is a spongy-looking reddish elevation, formed by a group of 3 A 706 THE EYE. glandular follicles, and named the caruncula lachrymalis. The plica semilunaris is the rudiment of the third eyelid (rneinbrana nictitans) found in some animals. Structure of the lids. — The skiu covering the eyelids is thin and delicate; and at the line of the eyelashes, altered in its character, it joins the conjunc- tival mucous membrane which lines the inner surface of the lids. Beneath the skin, and between it and the conjunctiva, the following structures are successively met with, viz. : — The fibres of the orbicularis muscle ; loose connective tissue ; the tarsal cartilages, together with a thin fibrous mem- brane, the palpebral ligament, which attaches them to the margin of the orbit ; and, finally, the Meibomian glands. In the upper eyelid there is, in addition, the insertion of the levator palpebrse superioris, in the form of a fibrous expansion fixed, to the anterior surface of the tarsal cartilage. Fig. 456. Fig. 456. — VERTICAL SECTION OF THE LEFT ORBIT AND ITS CONTENTS. The section has been carried through the middle of the optic foramen and optic nerve obliquely as far as the back of the eyeball, and thence forward through the eyeball, eyelids, &c., in an antero-posterior direction, a, the frontal bone; 6, the superior maxillary bone; c, the eyebrow with the orbicularis palpebrarum, integument, &c. , divided ; d, the upper, and d, the lower eyelid, partially open, showing the section of the tarsal cartilages and other component parts, the eyelashes, &c. ; e, e, the reflection of the conjunctiva from the upper and lower eyelids to the surface of the eyeball ; /, the levator palpebraa superioris muscle; n between the skin and the conjunctival mucous membrane. The lashes of the upper lid, more numerous and longer than the lower, have the convexity of their curve directed downwards and forwards ; whilst those of the lower lid are arched in the opposite direction. Near the inner canthus these hairs are weaker and more scattered. 3 A 2 708 THE EYE. Structure of the conjunctiva. — The conjunctiva consists of the palpebral part, along with which may be grouped the plica semilunaris and caruncula lachrymalis, and of the ocular part or conjunctiva bulbi, in which may be distinguished the sclerotic and corneal portions : each of these several parts presents peculiar and distinctive characters. The epithelium is stratified and thick ; the cells of the superficial strata scaly, delicate, and each with a distinct nucleus. The palpebral portion of the conjunctiva is opaque and red, is thicker and more vascular than auy other part of the membrane, and presents numerous fine papillae freely supplied with nerves. At the margins of the lids the palpebral conjunctiva enters the ducts of the Meibomian glands ; through the pun eta lachrymalia it passes into the canaliculi, and is con- tinuous with the lining membrane of the lachrymal sac ; and it is prolonged into the orifices of the ducts of the lachrymal gland. The sclerotic portion of the conjunctiva, changing its character at the line of reflection from the eyelids, becomes thinner, and loses its papillary structure : it is loosely connected to the eyeball by submucous tissue. It is also transparent and nearly colourless, but a few scattered branches of blood- vessels are generally visible on it in the healthy condition, and under the influence of inflammatory congestion a copious network of vessels very irre- gularly disposed comes into view. This network is derived from the palpebral and lachrymal arteries. It may be easily made to glide loosely on the sur- face of the eyeball by pressing the eyelid against it. But another set of vessels likewise exists on the surface of the sclerotic, and may be brought into view by congestion. The position of this set is entirely sub-conjunc- tival, adherent to the sclerotic coat ; they are less tortuous than the conjunc- tival set, and are derived from the muscular and anterior ciliary branches of the ophthalmic artery : they remain immoveable on pressure of the eyelid. They dip into the sclerotic near the cornea, and appear to unite with a more deeply connected minute network disposed in closely set straight lines, radiating from the margin of the cornea, and the gorged condition of which is well known to ophthalmic surgeons as characteristic of sclerotitis. The corneal conjunctiva consists almost entirely of epithelium, any under- lying membrane being extremely thin, transparent, and adherent to the anterior elastic layer of the cornea, in connection with which it will be again referred to. Vessels lie between it and the cornea, and form a circle of anastomotic capillary loops around the circumference. This plexus of vessels extends farther inwards in the foetus. A well developed network of lymphatics exists throughout the sclerotic and palpebral portions of the conjunctiva ; but at the margin of the cornea a sudden diminution takes place in the size of the meshes and diameter of the vessels. Of the network referred to, only a narrow circle ~th of an inch in diameter exists on the corneal conjunctiva, and this circle has a well defined inner margin within which no lym- phatics exist (Teichmann). The nerves in the membrane, as far as the cornea, seem to have the same arrange- ment as in the skin in general. In the submucous tissue of the eyelids there are small follicular glands spread over the whole surface of the conjunctiva palpebrarum, and in the vicinity of the reflection of the conjunctiva upon the eyeball a set of larger more complex glands of a racemose structure, somewhat similar to that of the lachrymal gland (Sappey, C. aud W. Krause). Closed follicles have also been observed in the conjunctiva by Bruch, and, after him, by other observers. LACHRYMAL GLANDS AND CANALS. 709 THE LACHRYMAL APPARATUS. The parts which constitute the lachrymal apparatus are the following, viz. : — The gland by \\hich the tears are secreted, situated at the upper and outer side of the orbit, together with its excretory ducts ; the two canals into which the fluid is received near the inner angle ; and the sac wuh the nasal duct continued from it, through which the teard pass into the inferior meat us of the nose. The lachrymal gland, an oblong flattened body, about the size of a small almond, is placed in the upper and outer part of the orbit, a little behind the anterior margin. The upper surface of the gland, convex, is lodged in a slight depression in the orbital plate of the frontal bone, to the periosteum of which it adheres by fibrous bands ; the lower surface is adapted to the convexity of the eyeball, and is in contact with the upper and the outer recti muscles. The fore part of the gland, separated from the rest by a slight depression, and sometimes described as a second lobe, or as a distinct gland, is closely adherent to the back of the upper eyelid, and is covered on the ocular surface only by a reflection of the conjunctiva. The glandular ducts, usually from six to eight in number, are very small, and emerge from the thinner portion of the gland. After running obliquely under the mucous membrane, and separating at the same time from each other, they open in a row by separate orifices, the greater number in the fold above the outer cauthus, and two of them (Hyrtl) in the fold below. Fig. 458.— FRONT OP THE LEFT EYELIDS, p. .„_ WITH THE LACHRYMAL CANALS AND NA- *>' SAL DUCT EXPOSED. 1,1, upper and lower lachrymal canals, showing towards the eyelids the narrow bent portions and the puncta lachrymal ia ; 2, lachrymal sac ; 3, the lower parjb of the uasal duct ; 4, plica semilunaris ; 5, ca- runcula lachrymalis. Lachrymal canals. — On the mar- gin of each lid, near the inuer angle, and in front of the fold of membrane called plica semilunaris, is a small elevation (papilla lachry- malis), already described. Each papilla is perforated by a small aperture, punctum lachrymale ; and at these apertures commence two small canals, canaliculi, which convey the tears from the eye to the lachrymal sac. The upper canal is rather the smaller and longer of the two : it first ascends from the punctum ; then makes a sudden bend, and is directed inwards and downwards to join the lachrymal sac. The lower canal descends from the corresponding punctum ; and soon changing its direction like the upper one, takes a nearly horizontal course inwards. Both canals are dilated where they are bent. In some cases they unite near the end to form a short common trunk ; more commonly they open separately, but close together, into the sac. The lachrymal sac and nasal duct constitute together the passage by which the tears are conveyed from the lachrymal canals to the cavity of the nose. 710 THE EYE. The lachrymal sac, the upper dilated portion of the passage, is situated at the side of the nose, near the inner canthus of the eye, and lies embedded in a deep groove in the lachrymal and upper maxillary bones. It is of an oval form ; the upper end closed and rounded, and the lower end gradually narrowiug somewhat into the nasal duct. On the outer side, and a little in front, it receives the lachrymal canals ; and here it is covered by the tendo palpebrarum, and by some of the inner fibres of the orbicular muscle of the lids; while on its inner or posterior. surface the tensor tarsi muscle is placed. The sac is composed of fibrous and elastic tissues, adhering closely to the bones above mentioned, and strengthened by fibrous processes sent from the tendo palpebrarum, which crosses a little above its middle. The inner sur- face is lined by a reddish mucous membrane, which is continuous through the canaliculi with the conjunctiva, and through the nasal duct with the mucous membrane of the nose. The nasal duct (ductus ad nasum), about six or seven lines in length, grooving the upper maxillary bone, descends to the fore part of the lower meatus of the nose, the osseous canal being completed by the ungual and lower turbiuated bones. A tube of fibrous membrane, continuous with the lachrymal sac, adheres to the parietes of this canal, and is lined by mucous membrane, which, at the opening into the nose, is often arranged in the form of an imperfect valve. The nasal duct is rather narrower in the middle than at either end ; its direction is not quite vertical, but inclined slightly outwards and backwards. The mucous membrane in the canaliculi possesses a laminar epithelium, but in the nasal sac and duct a ciliated epithelium as in the nose. Various valves have been described in connection with the lachrymal sac and canals. One, the valve of Hasner, is formed by the mucous membrane of the nose overhanging the inferior orifice of the nasal duct, and has had imputed to it the function of pre- venting entrance of foreign matters in violent expiratory movements; but the disposition of the mucous membrane at this orifice appears to be subject to some variation. Another fold, the valve of Huschke, placed at the deep orifice of the canali- culi, is supposed by some to prevent the return of the tears from the sac into those tubes, but by others, it is declared to be inconstant, and insufficient, even when found, to close the orifice. A third fold, the valve of Foltz, is described as forming a projection inwards on one side of the vertical part of each canaliculus, near the punctual lachrymale, and as being sufficient to close the tube when it is flattened by the pressure of the fibres of the orbicularis and tensor tarsi muscles as in winking. The experiments of Foltz on rabbits go to prove that the punctum lachrymale having been turned backwards towards the eye in winking, and the canaliculus being compressed by the muscles, as soon as the pressure is removed the canaliculus resumes its open form, and so sucks in tears which by the next compression in winking are forced onwards into the lachrymal sac ; and also, that when the muscles are paralysed, the canaliculi cease to carry away the tears. See review of Foltz 's paper in Dublin Quarterly Journal, Feby. 1863; also, Hyrtl, Topogr. Anatomic. THE GLOBE OF THE EYE. The globe or ball of the eye is a composite structure of an irregularly spheroidal form, placed in the fore part of the orbital cavity, and receiving the thick stem of the optic nerve behind. The recti and obliqui muscles closely surround the greater part of the eyeball, and are capable of changing its position within certain limits : the lids, with the plica semilunaris and caruncle, are in contact with its covering of conjunctiva in front ; and behind it is supported by a quantity of loose fat and connective tissue. THE EYEBALL. THE SCLEFxOTIC COAT. 711 The eyeball, when viewed in profile, is found to be composed of segments of two spheres, of which the anterior is the smaller and more prominent : the segment of the larger posterior opaque sphere corresponds with the limit of the sclerotic coat, and the translucent portion of the smaller sphere with that of the cornea. From before backwards the ball measures about nine-tenths of an inch, and its transverse diameter exceeds this measurement by about a line. Except when directed towards near objects, the axes of the eyes are nearly parallel ; the optic nerves, on the contrary, diverge considerably from one another, and each nerve enters the corresponding eye about a tenth of an inch to the inner or nasal side of the axis of the globe. The eyeball is composed of several investing membranes, concentrically arranged, and of certain fluid and solid paits contained within them. The membranes are three in number, with the following designations and general structure : — An external fibrous covering, named sclerotic and cornea ; a middle vascular, pigmentary, and in part also muscular membrane, the choroid and the iris ; and an iuternal nervous stratum, the retina. The enclosed refracting media, three in number, are the aqueous humour, the vitreous body, and the lens with its capsule. Around the eyeball there is an adventitious tunic of fascia, tunica vaginalis oculij or capsule of Tenon, which is perforated by the tendons of the recti and obliqui muscles, and connected with the sclerotic by merely the most delicate connective tissue. This capsule separates the eye-ball from the orbital fat, and enables it to glide freely in its movements. (See, for details, Richet, Traite d'Anatomie Medico-Chirurgicale ; and O'Ferrall, in Dublin Quart. Journ. Med. Science, July, 1841.) EXTERNAL COAT OF THE EYEBALL. The external investing membrane, which forms a complete covering for the ball, consists of two parts of different appearance and structure. Of these the hinder part, much the largest, is opaque and densely fibrous, and is named the sclerotic coat, while the anterior smaller segment is transparent, and is named the cornea. THE SCLEROTIC COAT. The sclerotic (cornea opaca), the tunic of the eye on which the mainte- nance of the form of the greater part of the organ chiefly depends, is a strong, opaque, unyielding, fibrous structure. The membrane covers about five-sixths of the eye-ball, and is pierced behind by the optic nerve. The outer surface is white and smooth, except where the tendons of the recti and obliqui muscles are inserted into it. The inner surface is of a light brown colour, and rough from the presence of a delicate connective tissue (membrana fusca), through which branches of the ciliary vessels and nerves cross obliquely. The sclerotic is thickest at the back part of the eye, and thinnest at about a quarter of an inch from the cornea : at the junction with the cornea, it is again somewhat thickened. The optic nerve pierces this coat about one-tenth of an inch internal to the axis of the ball, and the opening is somewhat smaller at the inner than at the outer surface of the coat. The fibrous sheath of the nerve, together with the membranous processes which separate the funiculi of its fibres, blend with the sclerotic at the margin of the aperture : in consequence of this arrangement, when the neive is cut off 712 THE EYE. close to the eye-ball, the funiculi are seen to enter by a group of pores ; and to the part of the sclerotic thus perforated the name of lamina cribtosa is sometimes given. Around this cribrous opening are smaller apertures for vessels and nerves. Fig. 459. Fig. 459. — VIEW OP THE LOWER HALF OP THE RIGHT ADULT HUMAN EYE, DIVIDED HORIZONTALLY THROUGH THE MIDDLE. ± The specimen from which this outline is taken was obtained by dividing the eye of a man of about forty years of age in the frozen state. It was carefully compared with other specimens obtained in a similar manner ; and in the drawing averages have been given in any particulars in which differences among them presented themselves. 1, the cornea ; 1', its conjunctival layer ; 2, the sclerotic ; 2', sheath of the optic nerve passing into the sclerotic ; 3, external or vascular layer of the choroid ; 3', its internal pigmental layer ; 4, ciliary muscle, its radiating portion ; 4', cut fibres of the circular portion ; 5, ciliary fold or process ; 6, placed in the posterior division of the aqueous chamber, in front of the suspensory ligament of the lens ; 7, the iris (outer side) ; 7', the smaller inner side ; 8, placed on the divided optic nerve, points to the arteria centralis retinae ; 8', colliculus or eminence at the passage of the optic nerve into the THE SCLEROTIC COAT. 713 retina ; 8", fovea centralis retinae ; r, the nervous layer of the retina ; /, the bacillar layer; 9, ora serrata at the commencement of the ciliary part of the retina ; 10, canal of Petit; 11, anterior division of the aqueous chamber in front of the pupil; 12, the crystalline lens, within its capsule ; 13, the vitreous humour ; a, a, a, parts of a dotted line in the axis of the eye; b, b, b, b, a line in the transverse diameter. It will be observed that from the pupil being placed nearer the inner side the axis of the eye-ball a, a, does not pass exactly through the centre of the pupil, and that this line falls a little to the inner side of the fovea centralis. The following letters indicate the centres of the curvatures of the different surfaces ; assuming them to be nearly spherical, viz. : c a, anterior surface of the cornea ; c p, posterior surface ; I a, anterior surface of the lens ; I p, posterior surface ; s c p, posterior surface of the sclerotic ; r a, anterior surface of the retina. In connection with this figure the following average dimensions of the parts of the adult eye in fractions of an English inch may be stated : — Transverse diameter of the eyeball . . . . . . . 1* Vertical diameter (Krause) ......... 0*96 Antero-posterior diameter . . . . . . . . . 0'96 Diameter of the optic nerve with its sheath . . . . . . 0'16 Diameter of the nervous part at its passage through the choroid membrane 0*09 Greatest thickness of the sclerotic, choroid, and retina together . . 0'08 Greatest thickness of the sclerotic posteriorly 0'05 Smallest thickness at the sides and in front ...... 0'025 Greatest thickness of the cornea 0'055 Distance from the middle of the posterior surface of the cornea to the front of the lens 0'07 Antero-posterior diameter of the lens . . . . . . . 0'19 Transverse ditto 0'35 Greatest thickness of the ciliary muscle and ciliary processes together . . 0'06 Greatest thickness of the ciliary muscle ...... 0'035 Thickness of the iris 0'015 Length of the radius of curvature of the anterior surface of the cornea (regarding it approximately as spherical) .0 '305 Radius of the posterior surface 0'275 Radius of curvature of the anterior surface of the lens . . . . 0'36 Radius of the posterior surface . . . . . . . . 0'21 Approximate length of the radius of curvature of the outer surface in the posterior half of the retina . . (H85 Approximate radius of curvature of the external surface of the posterior part of the sclerotic coat ......... 0*5 Distance of the middle of the posterior surface of the lens from the middle of the retina 0'575 Distance between the centre of the spot of entrance of the optic nerve and the middle of the fovea centralis retinae 0*14 Diameter of the base of the cornea ....... 0'48 Diameter of the base of the iris transversely . . . . . . 0'45 Diameter of the base of the iris vertically ...... 0*43 Diameter of the pupil . . . . 0'14 STRUCTURE. — The sclerotic coat is formed of connective tissue, and yields gelatine on boiling. Its fibres are combined with fine elastic tissue, and with fusiform and stellate nucleated cells, and are aggregated into bundles, which are disposed in layers both longitudinally and transversely, the longi- tudinal arrangement being most marked at the surfaces. These layers com- municate at intervals, and the sclerotic presents a ramified and laminar appearance on a vertical section. A few blood-vessels permeate the fibrous texture in the form of a net- work of the smallest capillaries with very wide meshes ; and in the neighbourhood of the cornea a ring of greater vascularity exists, which has been already noticed in the description of the sclerotic conjunctiva. The existence of nerves in the sclerotic has not yet been allowed by all anatomists. 714 THE EYE. THE CORNEA. The cornea (cornea pellucida), the transparent fore parb of the external coat, admits light into the interior of the ball. It is neaily circular in shape, and its arc extends to about one-sixth of the circumference of the whole globe ; it is occasionally widest in the transverse direction. Being of a curvature of a smaller radius than the sclerotic, it projects forwards beyond the general surface of curvature of that membrane, somewhat like the glass of a watch : the degree of its curve varies, however, in different persons, and at different periods of life in the same person, being more prominent in youth and flattened in advanced age. Its thickness is in general nearly the same throughout, viz., from ~ to ^ of an inch, except- ing towards the outer margin, where it becomes somewhat thinner. The posterior concave surface exceeds slightly in extent the anterior or convex, in consequence of the latter being encroached on by the opacity of the sclerotic. Fig. 460. A Fig. 461. Fig. 460.— STRUCTURES OF THE CORNEA (after Bowman). A 5p, B & C, 30° A, small portion of a vertical section of the cornea in the adult ; a, conjunctival epithelium ; 6, anterior elastic lamina ; c to d, fibrous laminae with nuclear bodies inter- spersed between them ; c, fibres shooting through some of these layers from the external elastic lamina ; d, posterior elastic lamina ; e, internal epithelium. B, epithelium of the membrane of Demours, as seen looking towards its surface. C, the same seen in section. Fig. 461. — SMALL PORTIONS OP A VERTICAL SECTION OF THE CORNEA AT BIRTH (from Kolliker). 3fJ The preparation has been treated with acetic acid. A, the anterior p.irt ; a, anterior elastic lamina ; b, layer of closely set granules (probably small cells) placed under the anterior elastic layer, with little fibrous structure ; c, developed fibrous tissue, with united connective-tissue corpuscles ; B, posterior part of the cornea ; c, as before ; d, posterior elastic layer. THE CORXEA. 715 At its circumference the cornea joins the sclerotic part by continuity of tissue, but always so as to be overlapped by the opacity of that structure like a watch glass by the edge of the groove into which it is received. STRUCTURE. — The cornea consists of a central thick fibrous part, the cornea proper, covered in front by the conjunctival epithelium and the ante- rior elastic lamina, and behind by the posterior elastic lamina or membrane of Demours. The cornea proper is a stratified structure, the constituent fibres of which, continuous externally with those of the opaque sclerotic, are soft and com- paratively indistinct, and between the strata of which are numerous delicate anastomosing nucleated cells, of fusiform appearance as seen in vertical sec- tions, but expanded in the direction of the laminae, and presenting in sections parallel to the surface a stellate appearance. The strata, about sixty in number, at a given spot (Bowman),* maintain frequent communications with contiguous layers, so that they can be detached only for a very short dis- tance : in consequence of this stratified composition the cornea may be penetrated or torn most readily in the direction of the supposed laminse. The transparency of the cornea is impaired by derangement of the relative position, or by approximation of the strata to each other. The cornea proper is permeable to fluid, and affords chondrin, not gelatine, on boiling (J. Miiller). There have been observed by v. Recklinghausen in the cornea of the frog, when examined in a chamber of liquid connected with the microscope, not only a rich net- work of anastomosing cells, but other cells also which change both their form and position by means of processes thrown out from and disappearing again into their sub- stance, like the pseudopods of amoebae. (Virchow's Archiv, Vol. 28, p. 157). According to Henle, the anastomosing cells of the cornea are mere spaces devoid of any walls distinct from the surrounding matrix, and are the only interlaminar spaces naturally existing. (Systematise-he Anatomic, Vol. ii. p. 599). The membranes investing the fibrous part of the cornea before and behind are both of them structureless, with epithelium on their free surface. The anterior elastic lamina (Bowman) is a transparent glassy stratum with- out recognised texture, from ^^^th to -y^^th of an inch thick, and not rendered opaque by acids. From the surface resting on the fibrous strata of the cornea, a few fine threads are prolonged in a slanting direction, and are lost among the more superficial of those strata : their action is supposed to be to keep the membrane tied down smoothly to the cornea. The epithelium on the front of this lamina is stratified, the superficial cells being flat, and the main thickness formed of three or four layers of rounded cells, the deepest of which are vertically elongated, so as to be nearly twice as long as broad. It is right to mention that this epithelium in the horse, the ox, and the sheep, has a much more remarkable appearance than in man, and one not to be accounted for by the ordinarily presumed mode of growth of stratified epithelia ; for the deepest cells are greatly elongated and larger than those which are immediately superimposed, and have precisely the appearance of true columnar epithelium, the flat ends resting on the subjacent elastic lamina, and the pointed extremities directed forwards. The membrane of Demours or Descemet (posterior elastic lamina, Bowman), not very closely united with the fibrous part of the cornea, is transparent and glassy in appearance, firm and structureless, but very brittle and elastic ; and * Lectures on the parts concerned in the operations on the eye, and on the structure of the retina. London, 1849. 716 THE EYE. when shreds are removed they curl up always with the attached surface innermost. Its transparency is not impaired by acids, by boiliug in water, or by maceration in alkalies. In thickness it varies between 3-oVo*k an(l "2oVo~*k of an inch. At its circumference the membrane breaks up into bundles of fine threads, which are partly continued into the front of the iris, forming the " pillars of the iris," and partly into the fore part of the choroid and sclerotic coats. It is lined with an epithelial covering, which resembles that on serous membranes, consisting of a single layer of flat poly- gonal transparent cells with distinct nuclei. Blood-vessels and nerves. — In a state of health the cornea is not provided with blood-vessels, except at the circumference, where they form very fine capillary loops and accompany the nerves. The existence of lymphatics has not been satisfactorily ascertained. The nerves of the cornea are very numerous, according to Schlemm.* Derived from the ciliary nerves they enter the fore part of the sclerotic, and are from twenty-four to thirty-six in number. Continued into the fibrous part of the cornea, they retain their dark outline for ith to ith of an inch, and then becoming trans- parent, ramify and form a network through the laminated structure. MIDDLE TUNIC OF THE EYEBALL. This coat consists of two parts, one a large posterior segment — the choroid, reaching as far as the cornea, and formed chiefly of blood-vessels and pig- mentary material ; the other, a small anterior muscular part — the irh. Between these and connected with both is situated the white ring of the ciliary muscle. Fig. 462. Fig. 462. — CHOROID MEM- BRANE AND IRIS EXPOSED BY THE REMOVAL OP THE SCLEROTIC AND CORNEA (after Zinn). f a, one of the segments of the sclerotic thrown back ; &, ciliary muscle and liga- ment ; c, iris ; e, one of the ciliary nerves ; /, one of the vasa vorticosa or choroidal veins. THE CHOROID COAT. The choroid coat of the eye (tunica choro- idea s. vasculosa) is a dark brown membrane lying between the scle- rotic and the retina. It reaches forwards to the ciliary ligament, or nearly to the cornea, where it ends by a series of plaits or folds named ciliary processes, disposed in a circle projecting inwards at the back of the circumferential portion of the iris. Afc the hinder part, where the tunic is thickest, the optic nerve is transmitted through a circular opening. The outer surface is rough, and is connected to the sclerotic by loose connective tissue (lamina fusca of * Berl. Encycl. Wort. art. Augapfel, Vol. iv. p. 22. THE CHOROID COAT. 717 authors), and by vessels and nerves. The inner surface, which is smooth, is lined by a continuous layer of pigmentary cells. The ciliary processes, about eighty-five in number, are arranged radiately in a circle. They consist of larger and smaller folds, without regular alter- nation, and the small folds number about one-third of the large. Each of the larger folds, measuring aboub -j^th of an inch in length and 4^th in depth, forms a rounded projection at its inner end, which is free from the Fig. 463. — CILIA.RY PROCESSES AS SEEN Fig. 463. FROM BEHIND. f 1, posterior surface of the iris, with the sphincter muscle of the pupil ; 2, anterior part of the choroid coat ; 3, one of the ciliary processes, of which about seventy are represented. pigment which invests the rest of the structure ; but externally they become gradually narrower, and disappear in the choroid coat : the smaller pro- cesses are only half as deep as the others. At and near their internal or anterior extremities the processes are connected by lateral loop-like projec- tions, and are separated from the iris by pigment. The plications of the ciliary processes fit into corresponding plications of the suspensory ligament of the lens. STRUCTURE. — From a difference in the fineness of its constituent blood- vessels, the choroidal coat resolves itself into two strata, inner and outer; — the latter containing the larger branches, and the former the capillary ramifications. In the outer part of the coat are situated the branches of the vessels. The arteries are large, and are directed forwards before they bend down- wards to end on the inner surface ; whilst the veins (vasa vorticosa) are disposed in curves as they converge to four of five principal trunks issuing from the eyeball. In the intervals between those vessels are lodged elongated and star-shaped pigment cells with very fine offsets, which intercommunicate and form a network or stroma. Towards the inner part of the tunic, this network passes gradually into a web without pigment : it resembles elastic tissue in its chemical and physical properties. The inner part of the choroid coat (tunica Ruyschiana s. chorio-capillaris) is formed by the capillaries of the choroklal vessels. From the ends of the large arteries the capillaries radiate in a star-like manner, and form meshes which are more delicate and smaller than in any other texture, and are finer at the back than the front of the ball. This fine network reaches as far forwards as about |th of an inch from the cornea, or opposite to the ending of the expansion of the optic nerve, where its meshes become larger, and join those of the ciliary processes. On the inner surface of the tunica Ruyschiana may be detected, according to various authors, a structureless transparent membrane, the membrane of Bruch, underlying the pigmentary layer. The ciliary processes have the same structure as the choroid, of which they are a part ; but the capillary plexus of the vessels, less fine, has meehes 718 THE EYE. with chiefly a longitudinal direction ; and tbe ramified cells, fewer in number, are devoid of pigment towards the free extremities of the folds. The pigmentary layer (choroidal epithelium, membrane of the black pig- ment) forms a thin dark lining to the whole inner surface of the choroid and Fig. 464. — PIGMENT CELLS OP THE MIDDLE COAT (after Kolliker). A, small portion of the chorcid with the stellate or ramified cells which form its stroma. B, pigment cells, which cover the inner surface of the choroid ; a, these cells seen from the surface, of hexagonal form, and showing nuclei in their interior ; b, three of the same cells viewed edgeways ; c, molecular pigment, which fills the cells. the iris. As far forwards as the ciliary pro- cesses it consists of only a single layer of flat six-sided cells, applied edge to edge liko mosaic work. Each cell contains a nucleus and more or less dense molecular contents, accumulated in greatest abundance towards the circumference of the cell, and parrly obscuring the nucleus. On the ciliary pro- cesses and the iris the pigment is several lay- ers deep, and the cells, smaller and rounded, are so filled with dark pigment as to cover up the nucleus. In the eye of the albino, pigment is absent both from the hexagonal cells and the ramified corpuscles of the choroidal tunic. It may be mentioned that in fishes, and in many mammals, including the ox and the sheep, the eyes of which are often selected for dissection, the choroid, instead of being uniformly lined with dark pigment, presents on a greater or less extent of its back part a silvery layer named tapetum. The tapetum in ruminants consists of tendinous fibres, and in carnivora and fishes of cells, filled, in the carnivora, with granular matter (Leidig), in fishes with slender rods. On its inner surface is the tunic of Ruysch, as well as the layer of hexagonal cells, which, however, is here destitute of pigment. THE IRIS. The iris is the contractile and coloured membrane which is seen behind the transparent cornea, and gives the tint to the eye. In its centre it is perforated by an aperture — the pupil. By its circumferential border, which is nearly circular, the iris is connected with the choroid, the cornea, and the ciliary ligament and muscles : the free inner edge is the boundary of the pupil, and is constantly altering its dimen- sions during life. The iris measures J an inch across, and, in a state of rest, from the circumference to the pupil about ^-th of an inch. Its surfaces look forwards and backwards. The anterior, variously coloured in different eyes, is marked by waving lines converging towards the pupil, near which they join in a series of irregular elevations ; and, internal to these, other finer lines pass to the pupil. The posterior surface is covered with dark pigment ; and this being removed, there is seen at the margin of the pupil a narrow circular band of fibres (sphincter muscle of the pupil), with which lines radiating inwards are blended. THE IRIS. 719 The pupil is nearly circular in form, and is placed a little to the inner side of the centre of the iris. It varies in size according to the contraction or relaxation of the muscular fibres, and this variation ranges from -g^th to ^rd of an inch. The movements of the iris regulate the quantity of light admitted to the eyeball, and are associated with convergence of the optic axes, and with the focal adjustment of the eye. STRUCTURE. — Fibrous and muscular tissues form the framework of the iris, and pigment is scattered through the texture. In front and behind is placed a distinct layer of pigment cells. It is still matter of discussion whether or not in the adult a delicate epithelium is continued from the margin of the cornea over the front of the iris : it is admitted to exist in childhood. The fibrous stroma consists of fibres of connective tissue directed radiat- ingly towards the pupil, and circularly at the circumference ; these, inter- weaving with one another, form a net-like web which is less open towards the surfaces. The muscular fibre is of the non-striated kind, and is disposed as a ring (sphincter) around the pupil, and as rays (dilatator) from the centre to the circumference. Fig. 465. Fig. 465. — A SMALL PART OF THE IRIS, SHOWING THE MUSCULAR STRUCTURE (from Kolliker). ass The specimen is from the albino- rabbit, and has been treated with acetic acid : a, the sphincter muscle at the margin of the pupil ; 6, fas- ciculi of the dilatator muscle ; c, connective tissue with nuclear cells rendered clear by the acid. The sphincter is the flat narrow band on the posterior surface of the iris, close to the pupil, and w about ^th of &n inch wide. At the edge of the pupil the fibres are close together, but at the peripheral border they are separated, and form less com- plete rings. The dilatator, less apparent than the sphincter, begins at the ciliary or outer margin of the iris, and its fibres, collected into bundles, are directed inwards between the vessels and nerves, converging towards the pupil, and forming a net-work by their intercommunications. At the pupil they blend with the sphincter, some reaching near to its inner margin. Pigmentary elements. — In the substance of the iris anteriorly and through- out its thickness are variously- shaped and ramified pigment cells like those in the choroid membrane. The pigment contained in them is yellow, or of lighter or darker shades of brown, according to the colour of the eye. On the fore part of the iris is a thin stratum of rather oval or rounded cells with granular ramified offsets (an epithelial layer — Kolliker). At the posterior surface is a covering of dark pigment — the uvea of authors ; this is con- 720 THE EYE. tinuous with the pigmentary layer lining the choroid and the ciliary pro- cesses, and consists of several strata of small roundish cells filled with dark pigment. The colour of the iris depends on the pigment ; in the different shades of blue eye it arises from the black pigment of the posterior surface appearing more or less through the texture, which is only slightly coloured or is colourless ; and in the black, brown, and grey eye, the colour is due to the pigment scattered through the iris substance. Fig. 466. Fig. 466.— SECTIONAL VIEW OP THE CONNECTIONS OF THE CORNEA, SCLEROTIC, IRIS, CILIARY MUSCLE, CILIARY PROCESSES, HYALOID MEMBRANE AND LENS, f The specimen extends from the middle of the lens to the ora serrata on the inner side of the right eye. C, the laminated cornea; cc, conjunctiva corneae ; cs, conjunctiva scleroticse ; ce, epithelium of the conjunctiva ; ela, anterior elastic layer of the cornea passing outwards in part into the conjunctiva; elp, posterior elastic layer; U, liga- mentum pectinatum iridis, elastic ligament, spreading into the base of the iris, the sclerotic, and the attachment of the radiated ciliary muscle ; S, the sclerotic at its thinnest part ; A, the anterior aqueous chamber ; ap, the recess forming the posterior division of the aqueous chamber ; sv, placed at the junction of the cornea and sclerotic, points to the circular venous sinus or canal of Schlemin ; ea, epithelium behind the cornea indicated by a dotted line ; ei, epithelium in front of the iris similarly indicated ; ir, radiating muscle of the iris ; io, divided fibres of the orbicular muscle ; u, pigment layer or uvea ; In, centre of the crystalline lens ; Ic, capsule of the lens ; Ice, layer of cells in front of the lens ; cir, radiating ciliary muscle or tensor choroidese ; do, divided orbicular fibres ; dp, ciliary process, along the inner border of which a layer of pigment is continued from the choroid to the uvea, excepting at the end of the process ; Ch, choroid membrane ; R, the retina close to the ora serrata ; re, the ciliary part of the retina, the structure of which is imperfectly represented ; V, the vitreous humour ; k, the hyaloid membrane ; P, canal of Petit ; k', the hyaloid membrane continued behind the canal to the capsule of the lens ; Z, zonule of Zinn, and II, suspensory ligament of the lens proceeding from the hyaloid covering the ciliary process to the front of the capsule of the lens. CILIARY MUSCLE AND LIGAMENT. 721 The vessels and nerves have a radiating arrangement through the stroma; the former giving rise to rings, one at the circumference, the other near the pupil ; and the latter forming a network. (See the description of the vessels and nerves of the vascular coat.) Pupillary membrane (membrana pupillaris). — In foetal life a delicate transparent membrane thus named closes the pupil, and completes the curtain of the iris. The pupillary membrane contains minute vessels, continuous with those of the iris and of the capsule of the crystalline lens; they are arranged in loops, which converge towards each other, but do not quite meet at the centre of the pupil. At about the seventh or eighth month of foatal life these vessels gradually disappear; and, in proportion as the vascularity diminishes, the membrane itself is absorbed from near the centre towards the circumference. At the period of birth, often a few shreds, sometimes a larger portion, and occasionally the whole membrane is found persistent. (See also the account of the development of the eye.) CILIARY MUSCLE, LIG AMENTUM PECTINATUM, AND CIRCULAR SINUS. When the outer coat of the eyeball is separated from the choroid, a circular groove is seen passing round on the inner surface of the sclerotic, at its corneal margin. This groove is the outer wall of a venous canal, the sinus circularis iridis or canal of Schlemm. On the middle coat a corresponding groove, which completes the canal, is seen, — and this is bounded in front by a torn membranous edge bounding the anterior surface of the iris, the ligameutum pectinatum, while the thickest part of the white ring of the ciliary muscle is behind it. This canal communicates with other venous spaces which give an erectile appearance to the tissue at the base of the ciliary processes. The ligamentum pectinatum consists of slight festoon-like processes of the fibres of the iris, lying in a transparent elastic fibrous tissue continuous with the posterior elastic layer of the cornea. It is a more developed structure in the eyes of the sheep and ox than in the human eye, and in them the festooned processes are prominent, giving a milled appearance like that of the edge of a coin. The ciliary muscle (Bowman) forms a ring of unstriped muscular tissue about T^th of an inch broad on the fore part of the choroid. Its fibres, yellowish-white in colour, and longitudinal in direction, are attached in front to the inner surface of the sclerotic coat ; and are also connected with the terminal fibres of the posterior elastic layer of the cornea. From that origin the fibres are directed inwards and backwards in a manner which in a section appears radiated, and end by joining the choroid coat opposite and beyond the ciliary processes. The muscle is soft, and ramified pigment-cells are scattered through its substance. Concealed by the longitudinal or radiated fibres is a ring of fibres taking a circular direction, and which were still described as the ciliary ligament after the radiated fibres had been admitted to be muscular. This set consti- tutes the circular muscle of H. Miiller. The ciliary muscle appears to be in some way effective in producing the change in the form of the lens which takes place in accommodation of the eye to near vision (see Allen Thomson in " Glasgow Medical Journal" for 1857). VESSELS AND NERVES OF THE MIDDLE TUNIC OF THE EYE. The arteries of the choroid and the ciliary processes are derived from the posterior and anterior ciliary vessels. The posterior consist of two sets, distin- guished as the short and the long. The short (posterior) ciliary branches of the 3 B 722 THE EYE. ophthalmic artery pierce the sclerotic close to the optic nerve, and divide into branches which pass forward in meridional directions in the choroid membrane. Communicating freely they diminish in size, and entering the choroid form a close network of fine capillaries (tunica Euyschiana) already described. Fig. 467. Fig. 468. Fig. 467. — LATERAL VIEW OP THE ARTERIES OF THE CHO- ROID AND IRIS (from Ar- nold), f a, optic nerve ; &, part of the sclerotic left behind, the greater part and the cornea having been removed ante- riorly ; c, ciliary muscle ; d, iris ; 1, posterior ciliary ar- teries piercing the sclerotic and passing along the choroid ; 2, one of the long posterior ciliary arteries ; 3, several of the short or anterior ciliary arteries. The veins of the choroid coat constitute an outer layer, partially separable from the arterial network, and easily recognised by the direction of the larger vessels. These converge to four nearly equidistant trunks, which pass through the sclerotic about half way between the margin Fig. 468. — LATERAL VIEW OF THE VEINS OF THE CHOROID (from Arnold). The preparation is similar to that represented in the pre- vious figure. 1, 1, two trunks of the vense vorticosse at the place where they leave the choroid and pierce the sclerotic coat. of the cornea and the entrance of the optic nerve, and pour their contents into the ophthalmic vein. From their whorl-like arrangement they are known as the vasa vorticosa. The blood-vessels of the ciliary processes are very numerous, and are derived from the anterior ciliary, and from those of the fore part of the choroidal membrane. Several small arterial branches enter the outer part of each ciliary process, at first running parallel to each other and communicating sparingly. As they enter the prominent folded portion, the vessels become tortuous, sub- divide minutely, and inosculate frequently by cross branches. Finally they form short arches or loops, and turn backwards to pour their contents into the radicles of the veins. On the free border of the fold, one artery, larger than the rest, extends BLOOD-VESSELS OF THE IRIS. 723 the whole length of each ciliary process, and communicates through inter- veuing vessels with a long venous trunk which runs a similar course on the attached surface. Fig. 469. Fig. 469.— INJECTED BLOOD-VESSELS OF THE CHOROID COAT (from Sappey). & 1, one of the larger veins ; 2, small communicating vessels ; 3, branches dividing into the smallest vorticose vessels. Arteries of the iris. — The special arteries of the iris are the long ciliary and the anterior ciliary. The long (posterior) ciliary arteries, two in number, and derived from the ophthal- mic, pierce the sclerotic a little before, and one on each side of, the optic nerve. Having gained the interval between the sclerotic and choroid coats, they extend horizontally forwards through the loose connective tissue (membrana fusca) to the ciliary muscle. In this course they lie nearly in the horizontal plane of the axis of the eye-ball, the outer vessel being however a little above, and the inner one a little below the level of that line. A short space behind the fixed margin of the iris each vessel divides into an upper and a lower branch, and these, anastomosing with the corre- sponding vessels on the opposite side and with the anterior ciliary, form a vascular ring (circulus major) in the ciliary muscle. From this circle smaller branches arise to supply the muscle; whilst others converge towards the pupil, and there, freely com- municating by transverse offsets from one to another, form a second circle of anasto- mosis (circulus minor], and end in small veins. The anterior ciliary arteries, five or six in number, but smaller than the vessels just described, are supplied from the muscular and lachrymal branches of the ophthal- mic artery, and pierce the sclerotic about a line behind the margin of the cornea ; finally, they divide into branches which supply the ciliary processes, and join the circulus major. Besides these special arteries, numerous minute vessels enter the iris from the ciliary processes. The veins of the iris follow closely the arrangement of the arteries just described. The circular sinus communicates with this system of vessels. 3 B 2 724 THE EYE. The nerves for the supply of the iris are named ciliary : they are nume- rous and large ; and, before entering the iris, divide in the substance of the ciliary muscle. Fig. 470. Fig. 471. Fig. 470. — VESSELS OP THE CHOROID, CILIARY PROCESSES AND IRIS OF A CHILD (from Kolliker after Arnold). >-<> a, capillary network of the posterior segment of the choroid ending at £, the ora serrata ; c, arteries of the corona ciliaris, supplying the ciliary processes d, and passing into the iris e ; f, the capillary network close to the pupillary margin of the iris. Fig. 471. — FRONT VIEW OF THE BLOODVESSELS OF THE CHOROID COAT AND IRIS FROM BEFORE (from Arnold). !_• A, interior part of the choroid : B, iris ; C, ciliary muscle, &c. ; 1, 1, long posterior ciliary arteries ; 2, five of the anterior ciliary arteries ramifying towards the outer margin of the iris ; 3, loop of communication between one of the anterior and one of the long posterior ciliary arteries ; 4, internal circle and network of the vessels of the iris ; 5, external radial network of vessels. Fig. 472. Fig. 472. — LATERAL VIEW OF THE CILIARY NERVES (from Arnold). a, optic nerve ; b, hack part of the sclerotic ; c, ciliary muscle, &c. ; d, iris ; e, outer surface of the choroid coat; 1, five of the ciliary nerves passing along the sheath of the optic nerve, piercing the sclerotic posteriorly, and thence passing forward on the choroid membrane to the ciliary muscle and iris. The nerves are represented too large. The ciliary nerves, about fifteen in num- ber, and derived from the lenticular ganglion and the nasal branch of the ophthalmic division of the fifth nerve, pierce the sclerotic near the entrance of the optic nerve, and come immediately into contact with RETINA OR XERYOUS TUXIC. 725 the choroid. They are somewhat flattened in form, are partly embedded in grooves on the inner surface of the sclerotic, and communicate occasionally with each other before supplying the cornea and entering the ciliary muscle. AY hen the sclerotic is Fig. 473. Fig. 473. — DISTRIBUTION OP NERVES IN THE IRIS (from Kolliker). 5JL The preparation was taken from the eye of an albino rabbit, and Avas treated with soda, a, smaller branches of the ciliary nerves ad- vancing from the choroid ; 6, loops of union between them at the mar- gin of the iris ; c, arches of union in the iris ; f the pinna. — The posterior auricular artery, a branch from the external carotid, is distributed chiefly on the posterior or inner surface, but sends small branches • round and through the cartilage to ramify on the outer surface of the pinna. Besides this artery, the auricle receives others, the anterior auricular from the temporal in front, and a small artery from the occipital behind. The vei)is correspond much in their course with the arteries. They join the tem- poral vein, and their blood is returned therefore through the external jugular. Nerves of the pinna. — The great auricular nerve (p. 638), from the cervical plexus, sup- plies the greater part of the back of the auricle, and sends small filaments with the pos- terior auricular artery to the outer surface of the lobule and the part of the ear above it. The posterior auricular nerve, derived from the facial (p. 612), after communicating with the auricular branch of the pneumogastric, ramifies on the back of the ear and supplies the retrahent muscle. The upper muscles of the auricle receive their supply from the temporal branches of the same nerve. The auriculo-temporal branch of the third division of the fifth nerve (p. 606) gives filaments chiefly to the outer and anterior surface of the pinna. THE EXTERNAL AUDITORY CANAL. The external auditory canal (meatus auditorius externus) extends from the bottom of the concha to the membrane of the tympanum, and serves to convey to the middle chamber of the ear the vibrations of sound collected by the auricle. The canal is about one inch and a quarter in length. In Fig. 499. — VIEW OP THE LOWER HALF OF THE Fig. 499. AURICLE AND MEATUS IN THE LEFT EAR DIVIDED BY A HORIZONTAL SECTION (after Sommerring). 1 and 2, cut surfaces of the bony part of the meatus ; 3, cut surface of the cartilage of the pinna ; 4, external meatus with the openings of numerous ceruininous glands indicated ; 5, lobule ; 6, membrane of the tympanum j 7, dura mater lining the skull. its inward course it is inclined somewhat forwards ; and it presents likewise a dis- tinct vertical curve, being directed at fir^t somewhat upwards, and afterwards turning somewhat abruptly over a convexity of the osseous part of its floor, and dipping downwards to its termination, — a change of direction which must be borne in mind by the surgeon in introducing specula into the ear. The 7-H THE EAR. calibre of the passage is smallest about the middle. The outer opening is largest from above downwards, but the tympanic end of the tube is slightly widest in the transverse direction. At the inner extremity the tube is terminated by the membrana tympani, which is placed obliquely, with the inferior margin inclined towards the mesial plane, and thus the floor of the meatus is longer than its roof. The meatus is composed of a tube partly cartilaginous and partly osseous, and is lined by a prolongation of the skin of the pinna. The cartilaginous part of the meatus forms somewhat less than half the length of the passage. It is formed by the deep part of the cartilage of the pinna, which has been already described. The osseous portion of the meatus is a little longer and rather narrower than the cartilaginous part. At its inner end it presents a narrow groove, which extends round the sides and floor of the meatus, but is deficient above ; into this the margin of the membrana tympani is inserted. The skin of the meatus is continuous with that covering the pinna, but is very thin, aod becomes gradually thinner towards the bottom of the pas- sage. In the osseous part of the canal it adheres very closely to the periosteum ; and at the bottom of the tube this lining is stretched over the surface of the membrana tympani, forming the outer layer of that struc- ture. After maceration in water, or when decomposition is advanced, the epidermic lining of the passage may be separated and drawn out entire, and then ib appears as a small tube closed at one end somewhat like the finger of a glove. Towards the outer part the skin possesses flue hairs and seba- ceous glands ; and in the thick subdermic tissue over the cartilage are many small oval glands of a brownish-yellow colour, agreeing in form and struc- ture with the sweat glands. The cerumen or ear-wax is secreted by these glands, glandulce ceruminosce, and their numerous openings may be seen to perforate the skin of the meatus. These accessory parts are absent over the bony part of the tube. Vessels and nerves. — The external auditory meatus is supplied with arteries from the posterior auricular, internal maxillary and temporal arteries; and with nerves chiefly from the temporo-auricular branch of the fifth nerve. State in the infant. — The auditory passage is in a very rudimentary state in the infant, for the osseous part begins to grow out of the tympanic bone only at the period of birth (p. 68), and thus the internal and middle parts of the ear are brought much closer to the surface than in the adult. THE MIDDLE EAR OR TYMPANUM. The tympanum or drum, the middle chamber of the ear, is a narrow irregular cavity in the substance of the temporal bone, placed between the inner end of the external auditory canal and the labyrinth. It receives the atmospheric air from the pharynx through the Eustachiau tube, and con- tains a chain of small bones, by means of which the vibrations communicated from without to the membrana tympani are in part conveyed across the cavity to the sentient part of the internal ear, and by which also pressure is maintained on the contents of the internal ear, varying in amount accord- ing to the tension of the membrana tympani. The tympanum contains likewise minute muscles and ligaments, which belong to the bones referred to, as well as some nerves which end within this cavity, or pass through it to other parts. The cavity of the tympanum may be considered as presenting for con- CAVITY AND MEMBRANE OF THE TYMPANUM. 745 sideration a roof and a floor, an outer and an inner wall, and an anterior and a posterior boundary. The roof of the tympanum is formed by a thin plate of bone, which may be easily broken through so as to obtain a view of the tympanic cavity from above ; it is situated on the upper surface of the petrous portion of the temporal bone, near the angle of union with the squamous portion, from which in its development it is derived. The floor is narrow, in consequence of the outer and inner boundaries being inclined towards each other. The outer wall is mainly formed by a thin semitransparent membrane — mernbrana tympani, which closes the inner end of the external auditory meatus ; and, to a small extent, by bone. Immediately in front of the ring of bone into which the membrana tympani is inserted, is the inner extremity of the fissure of G laser, which gives passage to the laxator tympani muscle, and attachment to the processus gracilis of the malleus. Close to the back of this fissure is the opening of a small canal (named by Cruveilhier the canal of Huguier), through which the chorda tympani nerve usually escapes from the cavity of the tympanum and the skull. Fig. 500.— MEMBRANA TYMPANI Ficr 500 AS SEEN FROM THE OUTER AND INNER SIDE. A, the outer surface ; B, the inner ; in the latter the small bones are seen adherent to the membrane and adjacent parts of the temporal bone ; in A,- the shaded part indicates the small bones as partially seen through the membrane ; 1, membrana tympani ; 2, malleus ; 3, stapes ; 4, incus. The membrana tympani is a nearly circular disc, slightly concave on its outer surface. It is inserted into the groove already noticed at the end of the meatus externus, and so obliquely that the membrane inclines towards the anterior and lower part of the canal at an angle of about 45°. The handle of the malleus, one of the small bones of the tympanum, descends between the middle and inner layers of the membrana tympani to a little below the centre, where it is firmly fixed ; and, as the direction of this process of the bone is slightly inwards, the outer surface of the mem- brane is thereby rendered concave, being held inwards in the shape of a shallow cone. Though very thin, the membrana tympani is composed of three distinct structures. A prolongation of the skin of the external meatus forms the outer layer ; the mucous membrane lining the cavity of the tympanum furnishes an inner layer ; and between those two is the proper substance of the membrane, made up of fine fibrous and elastic tissues with vessels and nerves. The greater number of the fibres radiate from near the centre at the attachment of the handle of the malleus ; but close to the circumfer- ence are some circular fibres, which form a dense, almost ligamentous ring. The inner watt of the tympanum, which separates it from the internal ear, is very uneven, presenting several elevations and foramina. Near its upper part is an ovoid, or nearly kidney-shaped opening — fenestra ovalis, which leads into the cavity of the vestibule. This opening, the long diameter of 746 THE EAR. which is from before backwards, with a slight inclination downwards in front, is occupied in the recent state by the base of the stapes, and the annular ligament connected with that process of bone. Above the fenestra ovalis, and between it and the roof of the tympanum, a ridge indicates the position of the aqueduct of Fallopius, as it passes backwards, contain- ing the portio dura of the seventh nerve. Below it is a larger and more rounded elevation, caused by the projection outwards of the first turn of the cochlea, and named the promontory, or tuber cochleae ; it is marked by grooves, in which lie the nerves of the tympanic plexus. Fig. 501. Fig. 501. — INNER WALL OP THE OSSEOUS TYMPANUM AS EXPOSED BY A LONGITUDINAL SECTION OP THE PETROUS AND MASTOID BONE (from Gordon). 1, opening of the tympanum into the inastoid cells ; 2, fenestra ovalis ; 3, fenestra rotunda ; 4, promontory ; 5, aqueduct of Fallopius, or canal of the facial nerve ; 6, junction of the canal for the chorda tympani with the aqueduct ; 7, processus cochleari- formis ; 8, groove above it for the tensor tympani muscle ; 9, Eustachian tube j 10, anterior orifice of the carotid canal. Below and behind the promontory, and somewhat hidden by it, is a slightly oval aperture named fenestra rotunda) which lies within a funnel- shaped depression. In the macerated and dried bone the feuestra rotunda opens into the scala tympani of the cochlea ; but, in the recent state it is closed by a thin membrane. The membrane closing the fenestra rotunda — the secondary membrane of the tympanum (Scarpa) — is rather concave towards the tympanic cavity, and is composed of three strata like the membrana tympani ; the middle layer being fibrous, and the outer and inner derived from the membranes lining the cavities between which it is interposed, viz., the tympanum and the cochlea. The posterior wall of the tympanum presents at its upper part one larger, and several smaller openings, which lead into irregular cavities, the mastoid cells, in the substance of the mastoid process of the temporal bone. These cells communicate freely with one another, and are lined by mucous mem- brane continuous with that which clothes the tympanum. Behind the fenestra ovalis, and directed forwards, is a small conical eminence, called the pyramid, or eminentia papillaris. Its apex is pierced by a foramen, through which the tendon of the stapedius muscle emerges from a canal which turns downwards in the posterior wall of the tympanum, and joins obliquely the descending part of the aqueduct of Faliopius. THE EUSTACHIAN TUBE. 747 The anterior extremity of the tympanum is narrowed by the gradual descent of the roof, and is continued into the Eustachiau orifice. The lower compartment of this orifice, lined with mucous membrane, forms the commencement of the Eustachian tube ; the upper compartment, about half an inch long, lodges the tensor tympaui muscle, and opens into the tympanum immediately in front of the feuestra ovalis, surrounded by the expanded and everted end of the cochleariforrn process, which separates it from the lower compartment. Fig. 502. Fig. 502. — ANTERO-POSTEKIOR SECTION OP THK TEMPORAL BONE, SHOWING THE INNER WALL OF THE TYMPANUM, wna THE EUSTACHIAN TUBE AND SMALL BONES IN THE RECENT STATE (from Arnold). 1, styloid process ; 2, mastoid process ; 3, tipper part of the petrous bone ; 4, pharyn- geal end of the Eustachian tube ; 5, its cartilage ; 6, its mucous surface ; 7, carotid caual ; 8, fenestra rotunda; 9, malleus; 10, incus; 11, stapes; 12, pyramid and stapedius muscle ; above 9, and behind 10, the suspensory ligaments of the malleus a ;d incus are also seen. The Eustachian tube is a canal, formed partly of bone, partly of cartilage and membrane, which leads from the cavity of the tympanum to the upper part of the pharynx. From the tympanum it is directed forwards and inwards, with a little inclination downwards ; and its entire length is about an inch and a half. The osseous division of the Eustachian tube, already described in the Osteology, is placed in the angle of junction of the petrous portion of the temporal bone with the squamous portion. The anterior part of the tube is formed of a triangular piece of cartilage, the edges of which are slightly curled round towards each other, leaving an interval at the under side, in which the canal is completed by dense but pliable fibrous membrane. Narrow behind, the tube gradually expands till it becomes wide and trumpet-shaped in front ; and the anterior part is compressed from side to side, and is fixed to the inner pterygoid process of the sphenoid bone. The anterior opening is oval in form, and is placed obliquely at the side and upper part of the pharynx, into which its prominent margin projects behind the lower meatus of the nose, and above the level of the hard palate. Through this aperture the mucous membrane of the pharynx is continuous with that which lines the tympanum, and under certain, conditions air passes into and out of that cavity. 748 THE EAB. SMALL BONES OF THE EAR. Three small bones (ossicula auditus) are contained in the uppr-r part of the tympanum : of these, the outermost (malleus) is attached to the mein- brana tympani j the innermost (stapes) is fixed in the fenestra oveilis ; and Fig. 503. Fig. 503. — BONES OP THE TYMPANUM OF THE RIGHT SIDE (from Arnold), f A, malleus; 1, its head; 2, the handle ; 3, long or slender process ; 4, short process ; B, incus ; 1, its body ; 2, the long process with the orbicular process ; 3, short or posterior process ; 4, articular surface receiving the head of the malleus; C, stapes; 1, hea4 ; 2, posterior crus ; 3, anterior crus ; 4, base ; C*, base of the stapes ; D, the three bones in their natural con- nection as seen from the outside ; a, malleus ; b, incus ; c, stapes. the third (incus), placed between the other two, is connected to both by articular surfaces. The malleus and incus are placed in nearly a vertical, the stapes in a horizontal direction. They form together an angular and jointed connecting rod between the membrana tympani and the membrane which closes the fenestra ovalis. The malleus, or hammer bone, consists of a central thicker portion, with processes of different lengths. At the upper end of the bone is a rounded head (capitulum), which presents internally and posteriorly an irregularly oval surface covered with cartilage, for articulation with the incus. Below the head is a constricted neck (cervix); and beneath this another slight enlargement of the bone, to which the processes are attached. The handle (manubrium) of the malleus is a tapering and slightly twisted process, com- pressed from before backwards to near its point, where it is flattened in the opposite direction : it descencre with a slight inclination forwards and in- wards, and is received between the middle and inner layers of the membrana tympani, to which it is closely attached. The long process (processus gra- cilis) is a very slender spiculum of bone, which in the adult is usually broken off in its removal from the tympanum, in consequence of its union with the temporal bone ; it projects at nearly a right angle from the front of the neck of the malleus, and extends thence obliquely downwards and forwards to the Glasserian fissure. Its end is flattened and expanded, and is con- nected by ligamentous fibres and by bone to the sides of the fissure. The short process (processus brevis vel obtusus) is a low canical eminence spring- ing from the root of the mauubrium, beneath the cervix, and projecting outwards towards the upper part of the membrana tympani. The incus has been compared to an anvil in form ; but it resembles per- haps more nearly a tooth with two fangs widely separated. It consists of a body and two processes. The body presents in front a concavo-convex articular surface, which is directed upwards and forwards, and receives the head of the malleus. The surfaces of the joint thus formed are tipped with articular cartilage and enclosed by a synovial membrane. The shorter of THE SMALL BOXES AND THEIR MUSCLES. 749 the two processes (crus breve) of the incus projects nearly horizontally backwards from the upper part of the body of the bone, and is connected by ligainentous fibres with the posterior wall of the tympanum near the entrance of the rnastoid cells. The long process (crus longum) tapers rather more gradually, and descends nearly vertically behind the handle of the malleus : at its extremity it is bent inwards, and is suddenly narrowed into a short neck ; and upon this is set a flattened rounded tubercle (pro- cessus lenticularis), tipped with cartilage. This tubercle, which articulates with the head of the stapes, was formerly, under the name of os orbiculare sen lenticulare, described as a separate bone, which indeed it originally is in childhood. The stapes, the third and innermost bone of the ear, is in shape remark- ably like a stirrup, and is composed of a head, a base, and two crura. The head is directed outwards, and has on its end a slight depression, covered with cartilage, which articulates with the lenticular process of the incus. The base is a plate of bone placed in the fenestra ovalis, to the margin of which it is fixed by ligameutous fibres. The form of the base is irregularly oral, the upper margin being curved, while the lower is nearly straight. The crura of the stapes diverge from a constricted part (neck) of the bone, situated close to the head, and are attached to the outer surface of the base near its extremities. The anterior cms is the shorter and straighter of the two. The crura, with the base of the stapes, enclose a small triangular or arched space, which in the recent state is occupied by a thin membrane stretched across. A shallow groove runs round the opposed surfaces of the bone, and into this the membrane is received. LIGAMENTS AND MUSCLES OF THE TYMPANUM. Ligaments. — In the articulations of the small bones of the ear with each other, the connection is strengthened ly ligainentous fibres which cover the synovial membranes. The attachment of the bones of the ear to tho walls of the tympanum is effected partly by the reflections of the mucous membrane lining that cavity, but chiefly by muscles and by the following ligaments. The suspensory ligament of the malleus consists of a small bundle of fibres, which descends perpendicularly from the roof of the tympanum to the head of the malleus. / The incus is likewise suspended by a small ligament (the posterior liga- ment of the incus), which extends from near the point of the short crus directly backwards towards the posterior wall of the tympanum, where it is attached near the entrance to the mastoid cells. • Arnold describes an upper ligament which attaches the incus, near its articulation with the malleus, to the roof of the tympanum. It lies close behind the suspensory ligament of the malleus. The annular or orbicular ligament of the stapes connects the base of the bone to the margin of the fenestra ovalis, in which it is lodged. Muscles. — There are three well-determined muscles of the tympanum. Sornmerring describes four, and some authors a larger number ; but the descriptions of these last muscles are not confirmed by later research. Of the three muscles generally recognised, two are attached to the malleus, and one to the stapes. The tensor tympani (musculus internus mallei) is the largest of these muscles. It consists of a tapering fleshy part, about half an inch in length, and a slender tendon. The muscular fibres arise from the cartilaginous 750 THE EAR. end of the Eustacliian tube and the adjoining surface of the sphenoid bone, and from the sides of the upper compartment of the Eustachian orifice. In Fig. 504. Fig. 504. — VIEW OF THE CAVITY OF THE EIGHT TYMPANUM FROM ABOVE. The cavity of the tympanum and some parts of the labyrinth have been exposed by a horizontal section removing the upper part of the temporal bone. 1, posterior semicircular canal opened ; 2, the cavity of the cochlea opened ; 3, osseous part of the Eustachian tube ; 4, head of the malleus ; 5, incus ; 6, stapes, with its base set in the fenestra ovalis ; 7, tensor tympani muscle ; 8, stapedius. this canal the muscle is con- ducted nearly horizontally backwards to the cavity of the tympanum. Immediately in front of the fenestra ovalis the tendon of the muscle bends at nearly a right angle over the end of the processus cochleariformis as through a pulley, and, contained in a fibrous sheath, passes out- wards to be inserted into the inner part of the handle of the malleus, near its root. The laxator tympani (laxator tympani major of Sommerring) is generally believed to be distinctly muscular, but being partly concealed by a band of fibrous tissue, doubts are still entertained by some observers as to whether the structure known under this name is of a muscular or ligamentous nature. Arising from the spinous process of the sphenoid bone, and slightly from the cartilaginous part of the Eustachiau tube, it is directed backwards, passes through the Glaserian fissure, and is inserted into the neck of the malleus, just above the root of the processus gracilis. The laxator tympani minor of Sommerring (posterior ligament of the malleus, Lincke) is made up of reddish fibres, which are fixed at one end to the upper and back part of the external auditory meatus, pass forwards and inwards between the middle and inner layers of the membrana tympani, and are inserted into the outer border of the handle of the malleus, and the short process near it. Sommerring. Icones Organi Auditus Humani, 1801. The stapedius is a very distinct muscle, but is hid within the bone, being lodged in the descending part of the aqueductus Fallopii and in the hollow of the pyramid. The tendon issues from the aperture at the apex of that little elevation, and passing forwards, surrounded by a fibrous sheath, is inserted into the neck of the stapes posteriorly, close to the articulation of that bone with the lenticular process of the incus. A very slender spine of bone has been found occasionally in the tendon of the stapedius in man : and a similar piece of bone, though of a rounder shape, exists con- ACTION OF THE MUSCLES.— LINING MEMBRANE. 751 stantly in the horse, the ox, and other animals. This circumstance is the more inte- resting when it is remembered that cartilage occupies the position of the stapedius before the muscle is developed. (P. 66 and fig. 528.) Actions. — The malleus and incus move together round an axis extending backwards from the attachment of the processus gracilis of the malleus in the Glasserian fissure to the attachment of the short process of the incus posteriorly. The tendon of the tensor tympani muscle passing from within to be inserted below that line, pulls the handle of the malleus inwards, while the laxator tympani inserted above that line, by pulling the head of the bone inwards, moves the handle outwards. The incus, moving along with the malleus, pushes the stapes inwards towards the internal ear when the membrana tympani is made tight, and withdraws that bone from the fenestra ovalis, when the membrana tympaui is relaxed. But the cavity of the inner ear is full of Fig. 505. — OUTLINE OF THE THREE SMALL BONES OF THE LEFT EAR AS SEEN FROM BEFORE. f This figure is designed to illustrate the effect of the action of the tensor and laxator muscles of the tympanic membrane in connection with their relation to the axis of rotation of the malleus, a, a', the malleus ; 6, the incus seen behind it ; c, the stapes ; m, mf, the inner part of the meatus externus closevl by the tympanic membrane, of which the posterior half is represented ; the axis of rotation of the malleus being supposed to pass through a point at the root of the processus gracilis, g ; the line t, indi- cates the direction and position of the tendon of the tensor tympani pulling the lower part of the malleus inwards, the line /, that of the laxator tympani pulling inwards the upper half of the malleus. liquid ; and its walls are unyielding, except at the fenestra rotunda ; when, there- fore, the stapes is pushed inwards the secondary membrane of the tympanum, which blocks up the fenestra rotunda, must be made tense by pressure from within. The attachment of the handle of the malleus, however, to the membrana tympani allows greater freedom of movement to that process than is allowed to the stapes by the ligament of its base, and when the movement of the stapes ceases, it is plain that the malleus in any movement must rotate on the head of the incus; and hence, probably, the necessity of a moveable articulation between tho*e bones. The action of the stapedius muscle is obviously to draw the head of the stapes backwards, in doing which the hinder end of the base of that bone will be pressed against the margin of the fenestra ovalis, while the fore part will be withdrawn from the fenestra. The object gained by this movement of the stapes is not sufficiently ascertained; but it is at least evident that, if the stapes be pressed inwards by the incus in the action of the tensor tympani, the stapedius muscle, if then contracted, will modify the pressure on the internal ear. It is conceivable that the stapedius may thus protect the sensitive part of the ear to a certain extent from excessive stimulation of the auditory nerve. THE LINING MEMBRANE OF THE TYMPANUM. The raucous membrane of the tympanum is continuous with that of the pharynx through the Eustachian tube, and is further prolonged from the tympanum backwards into the mastoid cells. Two folds which cross the breadth of the cavity descend from the part of the membrane which lines the roof. The anterior fold descends to turn round the tendon of the tensor tympani muscle ; the posterior fold passes round the stapes. The malleus and incus are invested by the lining of the outer wall of the cavity. The mucous membrane which lines the cartilaginous part of the Eustachian tube resembles much the membrane of the pharynx, with which it is immediately continuous ; it is thick and vascular, and is covered by several layers of laminar epithelium with vibratile cilia, and is provided with many simple mucous glands which pour out a thick secretion : in the osseous part of the 752 THE EAR. tube, however, this membrane becomes gradually thinner. In the tympa- num and the mastoid cells it is paler, thinner and less vascular, and secretes a less viscid, but yellowish fluid. The epithelium in the tympanic cavity is also ciliated. The cilia, however, are usually absent from the part which lines the meinbrana tympani (Kolliker, Handbuch, p. 691). THE VESSELS AND NERVES OF THE TYMPANUM. The arteries of the tympanum, though xery small, are numerous, and are derived from several branches of the external, and from the internal carotid. The fore part of the cavity is supplied chiefly by the tympanic branch of the internal maxillary (p. 356), which enters by the fissure of Glaser. The back part of the cavity, including the mastoid cells, receives its arteries from the stylo-mastoid branch of the posterior auricular aitery (p. 353), which is conducted to the tympanum by the aqueduct of Fallopius. These two arteries form by their anastomosis a vascular circle round the margin of the membrana tympani. The smaller arteries of tlie tympanum are, the petrosal branch of the middle meningeal, which enters through the hiatus Fallopii ; branches through the bone from the internal carotid artery, furnished from that vessel whilst in the carotid canal; and occasionally a twig along the Eustacliian tube from the ascending pharyngeal artery. The veins of the tympanum pour their.contents through the middle meningeal and pharyngeal veins, and through a plexus near the articulation of the lower jaw, into the internal jugular vein. Nerves. — The tympanum contains numerous nerves; for, besides those which supply the parts of the middle ear, there are several which serve merely to connect nerves of different origin. The lining membrane of the tympanum is supplied by filaments from the plexus (tympanic plexus), which occupies the shallow grooves on the inner wall of the cavity, particularly on the surface of the promontory. The tympanic plexus is formed by the communications between, 1st, the tympanic branch (nerve of Jacobson) from the petrous ganglion of the glosso- pharyugeal ; 2nd, & filament from the carotid plexus of the sympathetic ; 3rd, a branch which joins the great superficial petrosal nerve, from the Vidian ; 4th and lastly, the small superficial petrosal nerve, from the otic ganglion. FiS- 506- Fig. 506.— VIEW OP THE TYAIPANIO PLEXUS OP NERVES (after Hirschfeld and Leveille). 6, spheno-palatine ganglion ; 7, Vidian nerve ; 8, great superficial petrosal n?rve ; 9, carotid branch of the Vidian nerve ; 10, part of the sixth nerve con- nected by twigs with the sympathetic ; 11, superior cervical ganglion of the sympathetic ; 12, carotid branch ; 13, facial nerve ; 14, glosso-pharyngeal nerve ; 15, nerve of Jacobsou ; 16, its twig to the sympathetic ; 17, filament to the fenestra rotunda ; 18, filament to the Eustachian tube ; 19, filament to the fenestra ovalis ; 20, union of external deep petrosal nerve with the lesser superficial petrosal ; 21, internal deep petrosal twig uniting with the great superficial petrosal. The nerve of Jacobson enters the tympanum by a small foramen near its floor, which forms the upper end of a short canal in the petrous portion of the temporal bone, beginning at the base of the skull between the carotid foramen and the jugular THE INTERNAL EAR. OSSEOUS LABYRINTH. 753 fossa. The nerve from the carotid plexus is above and in front of this, and passes through the bone directly from the carotid canal. The branch to the great superficial petrosal nerve is lodged in a canal which opens on the inner wall of the tympanum in front of the fenestra ovalis. The small superficial petrosal nerve also enters at the fore part of the cavity beneath the canal for the tensor tympani. Nerves to Muscles. — The tensor tympani muscle obtains its nerve from, the otic ganglion (see fig. 410) ; the laxator tympani is said to be supplied by the chorda tympani: and the stapedius is figured by Sommerriug as receiving a filament from the facial nerve. The chorda tympani is invested by a tubular reflection of the lining mem- brane of the tympanum ; its course across the cavity has already been described (p. 611). THE INTERNAL EAR, OR LABYRINTH. The inner, or sensory part of the organ of hearing, is contained in the petrous portion of the temporal bone. It consists of a cavity — the osseous labyrinth — hollowed out of the bone, and of the membranous labyrinth con- tained within the osseous walls. Fig. 507. Fig. 507. — RIGHT BONY LABYRINTH, VIEWED FROM THE OUTER SIDE (after Sb'mmer- ring). ^ The specimen here represented is pre- pared by separating piecemeal the looser substance of the petrous bone from the dense walls which immediately enclose the laby- rinth. 1, the vestibule ; 2, fenestra ovalis ; 3, superior semicircular canal ; 4, horizontal or external canal ; 5, posterior canal ; *, am- pullae of the semicircular canals ; 6, first turn of the cochlea ; 7, second turn ; 8, apex ; 9, fenestra rotunda. The smaller figure in outline below shows the natural size. The osseous labyrinth is incompletely divided into three parts, named the vestibule, the semicircular canals, and the cochlea. They are lined throughout by a thin membrane, within which there is a clear fluid named perilymph. The membranous labyrinth is contained within the bony labyrinth, and, being smaller than it, leaves a space between the two, occupied by the peri- lymph just referred to. The membranous structure supports numerous minute ramifications of the auditory nerve, and encloses a fluid named the endolymph. THE OSSEOUS LABYRINTH. The vestibule forms a central chamber of the labyrinth, which communi- cates in front with the cochlea, behind with the semicircular canals, on the outer side with the cavity of the tympanum, and on the inner side with the roeatus auditorius interims. The vestibule is irregularly ovoidal in ^hape from before backwards, and is slightly flattened or compressed from without 3 D 751 THE EAR. inwards : except in the last-mentioned direction, in which it is somewhat smaller, it measures about -^th of an inch in diameter. The outer wall which separates it from the cavity of the tympanum, is perforated by the fenestra ovalis, which in the recent state is closed by the base of the stapes and its annular ligament. At the fore part of the inner wall is a small round pit, the fovea hemi- spherica, pierced with many small holes, which serve to transmit branches of the auditory nerve from the internal auditory meatus. This fossa is limited behind by a vertical ridge named crista vestibuli or eminentia pyramidalis. Behind the crest is the small oblique opening of a canal, the aqueduct of the vestibule, which extends to the posterior surface of the bone, and transmits a small vein in a tubular prolongation of membrane. In the roof is an oval depression, placed somewhat transversely, fovea hemi-elliptica, whose inner part is separated by the crest from the hemi- spherical fossa. At the back part of the vestibule are five round apertures, leading into the semicircular canals : and at the lower and fore part of the cavity is a larger opening, which communicates with the scala vestibuli of the cochlea — apertura scalm vestibuli. The semicircular canals are three bony tubes, situate above and behind the vestibule, into which they open by five apertures, the contiguous ends of Fig. 508. Fig. 508. — VIEW OF THE INTERIOR OF THE LEFT LABYRINTH (from Sommerring). ?i The bony wall of the labyriuth is removed superiorly and externally. 1, fovea hemi- elliptica ; 2, fovea hemispherica ; 3, common opening of the superior and posterior semi- circular canals ; 4, opening of the aqueduct of the vestibule ; 5, the superior, 6, the posterior, and 7, the external semicircular canals; 8, spiral tube of the cochlea (scala tyropani) ; 9, opening of the aqueduct of the cochlea ; 10, placed on the lamina spiralis in the scala vestibuli. two of the canals being joined. They are unequal in length, but each tube is bent so as to form about two-thirds of a circle ; and each presents, at one end, a slightly dilated part, called the ampulla. The canals are compressed laterally, and measure across about ^th of an inch ; but in the ampulla each has a diameter of -j^-th of an inch. The canals differ from one another in position with regard to the vestibule, in direction, and in length. The superior semicircular canal is vertical and transverse ; and, rising above any other part of the labyrinth, its place is indicated by a smooth arched projection on the upper surface of the bone. The ampullary end of this canal is the anterior, and opens by a distinct orifice iuto the upper part of the vestibule ; whilst the oppo- site extremity joins the non-dilated end of the posterior semicircular canal, and opens by a common aperture with it into the back part of the vestibule. The posterior semicircular canal, vertical and longitudinal in direction, is the longest of the three tubes: its ampullary end is placed at the lower and back part of the vestibule ; and the opposite end joins in the common canal above described. The external semi- THE OSSEOUS COCHLEA, 755 circular canal arches horizontally outwards, and opens by two distinct orifices into the upper and back part of the vestibule. This canal is shorter than either of the other two : its ampulla is at the outer end, just above the fenestra ovalis. Fig. 509. Fig. 509. — VIEWS OF A CAST OP THE INTERIOR OP THE LABYRINTH (from Henle). f Such casts may easily be marie in fusible metal, and give a very correct view of the form of the different parts of the labyrmthic cavity. A, view of the left labyrinth from the outer side ; B, the right labyrinth from the inner side ; C, the left labyrinth from above ; s, the superior, p, the posterior, and e, the external semicircular canals ; a, their several ampullae ; re, fovea hemi-elliptica of the vestibule ; rs, fovea hemispherica ; av, aqueduct of the vestibule ; fo, fenestra ovalis ; fr, fenestra rotunda ; c, the coiled tube of the cochlea ; c', the first part of the tube towards the base with the tractus forami- nosus spiralis. The cochlea is the most anterior division of the internal ear. When the dense bony substance, in which it lies embedded, is picked away, the cochlea presents the form of a blunt cone, the base of which is turned towards the internal auditory meatus, whilst the apex is directed outwards, with an inclination forwards and downwards, and is close to the canal for the tensor tympani muscle. It measures about a quarter of an inch in length, and the same in breadth at the base. The osseous part of the cochlea con- sists of a gradually tapering spiral tube, the inner wall of which is formed by the central column, or modiolus, round which it winds, and which is partially divided along its whole extent by a spiral lamina, projecting into it from the modiolus. From this osseous spiral lamina membranous structures are stretched across to the outer wall of the tube, and thus are completely separated two passages or scalee, oce on each side of the spiral lamina, which communicate one with the other by only a small open- ing, named helicotrema, placed at the apex of the cochlea. Fig. 510.— OSSEOUS LABYRINTH OF THE BARN-OWL (SiRix FLAMMEA) (from Breschet). * Fig. 510. 1, semicircular canals ; 2, vestibule ; of a short straight tube. cochlea in the form That the cochlea is justly to be considered as an elongated tube, coiled srirally on the modiolus, is illustrated by the simple pouch-like form of the rudimentary cochlea of birds. The spiral canal of the cochlea is about an inch and a half long, and about the tenth of an inch in diameter in its widest part at the commence- 3 D 2 756 THE EAR. ment. From this point the canal makes two turns and a half round the central pillar (from left to right in the right ear, and in the opposite direction in the left ear), and ends by an arched and closed extremity called the cupola, which forms the apex of the cochlea. The first coil, being much the widest in its curve and composed of the largest portion of the tube, nearly hides the second turn from view ; and bulging somewhat into the tympanum, forms the round elevation on the inner wall of that cavity called the promontory. Fig. 511. Fig. 511. — DIAGRAMMATIC VIEW OF THE CANAL OF THE COCHLEA LAID OPEN, f 1, modiolus or central pillar; 2, placed on three turns of the lamina spiralis ; 3, scala tympani ; 4, scala vestibuli. Fig. 512. — VIEW OF THE OSSEOUS COCHLEA DIVIDED THROUGH THE MIDDLE (from Arnold), f . 1, central canal of the modiolus ; 2, lamina spiralis ossea ; 3, scala tympani ; 4, scala vestibuli ; 5, porous substance of the modiolus near one of the sections of the canalis spiralis modioli. The modiolus (columella cochleae) forms the central pillar or axis round which turn the spiral tube and the spiral lamina. It is much thickest within the first turn of the cochlea, and rapidly diminishes in size in the succeeding parts. The outer surface is dense, being, iu fact, composed of the walls of the spiral tube ; but the centre is soft and spongy as far as the last half coil, and is pierced by many small canals, for the passage of the nerves and vessels to the lamina spiralis : one of these canals, larger than the rest (canalis centralis modioli), runs from the base through the centre of the modiolus. The lamina spiralis ossea is a thin, flat plate, growing from and winding round the modiolus, and projecting into the spiral tube, so as to divide it partly into two. Its free margin, which gives attachment in the recent state to the membranous septum, or zone, does not reach farther than about half of the distance between the modiolus and the outer wall of the spiral tube. The osseous lamina terminates close to the apex of the cochlea in a hook-like process (hamulus), which partly bounds the helicotrema. The lamina is thin and dense towards its free margin ; but near the modiolus it is composed of two dense outer plates enclosing a more open and spongy structure, in which are numerous small canals, continuous, but running at right angles with the canals in the centre of the modiolus. In these the nerves and vessels are lodged : they terminate on the inferior or tympanic aspect of the lamina, and the line of their orifices forms the tractus foraminosus spiralis. Winding round the modiolus, close to the lamina spiralis, is a small canal, named by Rosenthal the canalis spiralis modioli. The scalce in the osseous cochlea are two in number, distinguished as the scala tympani and scala vestibuli. THE MEMBRANOUS LABYRINTH. 757 The scala tympani, the portion of the tube on the basal side of the lamina spiralis, commences at the fenestra rotunda, where in the recent state it is separated from the tympanum by the secondary metnbrana tympani. Near its commencement is the orifice of a small canal aqueductus cochleae,, which extends downwards and inwards through the snbstance of the petrous part of the temporal bone to near the jugular fossa, and transmits a small vein . The surface of the spiral lamina which looks towards this scala is marked with numerous transverse striae. The scala vestibuli is rather narrower than the scala tympaui in the first turn of the cochlea ; it commences from the cavity of the vestibule, and communicates, as already described, with the scala tympani at the apex of the modiolus. TJie lining membrane of the osseous labyrinth. — This is a thin membrane (periosteum ?), which closely adheres to the whole inner surface of the several parts of the labyrinthic cavity just described. It has no con- tinuity with the lining membrane of the tympanum, being stretched across the openings of the round and oval fenestrse. It is composed of fibres of connective tissue. Its outer surface is rough, and adheres closely, like periosteum, to the bone : the inner surface is pale and smooth, is covered with a single layer of epithelium, like that of the arachnoid, and secretes a thin, slightly albuminous or serous fluid. This secretion, known as the liquor Cotunnii, or perilymph, separates the membranous from the osseous labyrinth in the vestibule and semicircular canals, occupies the cavities of the scala tympani and scala vestibuli in the cochlea, and is continued into the aqueducts as far as the membrane lining these passages remains pervious. THE MEMBRANOUS LABYRINTH. Within the osseous labyrinth, and separated from its lining membrane by the perilymph, membranous structures exist in which the ultimate ramifi- cations of the auditory nerve are spread. In the vestibule and semicircular canals these structures have a general resemblance in form to the com- plicated cavity in which they are contained. In the cochlea they complete the septum between the scalse already mentioned, and enclose a third spiral passage, the canalis membranacea, the existence of which has only been discovered of late years. The liquid contained within the membranous labyrinth is distinguished as endolymph. VESTIBULE. — The membranous vestibule consists of two closely connected sacs, and the parts by which they are united to the membranous semi- circular canals and canal of the cochlea. The larger of the two sacs, the common sinus or utricle, is of an oblong form and slightly flattened from without inwards. It is lodged in tho upper and back part of the osseous vestibule, occupying the fovea hemi- elliptica. Opposite the crista vestibuli several small branches of the audi- tory nerve enter from the foramina in the bone ; and here the walls of the common sinus are thicker and more opaque than elsewhere. The extre- mities of the membranous semicircular canals terminate in the cavity of the common sinus. A small mass of calcareous particles, otoliths or oto* conia, is lodged in the wall of the sac. These otoliths are crystals of carbonate of lime, and are described as six-sided, and pointed at their extre- mities. They are connected with the wall of the sac in a way not yet clearly determined. The smaller vestibular vesicle, the saccule, is more nearly spherical than the common sinus, but, like it, is somewhat flattened. The saccule is situated 758 THE EAE. in the lower and fore part of the cavity of the osseous vestibule, close to the opening from the scala vestibuli of the cochlea, and is received into the hollow of the fovea hemispherica, from the bottom of which many branches of nerve enter. The sacculus appears to have a cavity distinct from that of the utricle, but is filled with the like thin and clear fluid, endolymph, and contains similar otoconia in its wall. It is prolonged below into a short narrow duct, canalis reuniens, which opens abruptly into the membranous canal of the cochlea. Fig. 513. A. B. Fig. 513. — VIEWS OF THE INTERIOR OF THE RIGHT LABYRINTH WITH ITS MEMBRANOUS PARTS AND NERVES (from Breschet). f A, the outer wall of the osseous labyrinth in part removed so as to display the mem- branous parts within. 1, commencement of the spiral tube of the cochlea ; 2, posterior semicircular canal partially opened, showing its membranous canal and ampulla; 3, external or horizontal canal entirely opened ; 4, superior canal ; 5, utriculus or common sinus with its group of otoliths ; 6, saccule with its otoliths ; 7, placed on the lamina spiralis in the commencement of the scala vestibuli ; 7', scala tyrapani ; 8, membranous ampulla of the superior semicircular canal ; 9, ampulla of the horizontal, and 10, that of the posterior semicircular canal. B, membranous labyrinth and nervous twigs detached ; 1, facial nerve in the meatus auditorius internus ; 2, anterior division of the auditory nerve giving branches to 5, 8, and 9, the utricle and the ampullae of the superior and external canals ; 3, posterior division of the auditory nerve, giving branches to the saccule ; 6, posterior ampulla, 10, and cochlea, 4 ; 7, the united part of the superior and posterior canals ; 11, the posterior extremity of the external canal. SEMICIRCULAR CANALS. — The membranous semicircular canals are about one third the diameter of the osseous tubes in which they are lodged, and are dilated into ampullae within the ampullary enlargements of those tubes. At the ampullae they are thicker and less translucent than in the rest of their extent, and nearly fill their bony cases. That part of each ampulla which is towards the concavity of the semicircle of the canal is free ; whilst the opposite portion is flattened, receives branches of nerves and blood- vessels, and presents on its inner surface a transverse projection, septum transversum, which partly divides the cavity into two. The ampullae like- wise contain otoliths in their epithelial lib ing. Auditory nerve: vestibular division. — At the bottom of the meatus audi- torius internus the auditory nerve divides into an anterior and a posterior branch, which, broken up into minute filaments, pass through the perfora- tions of the cribriform plate which separates the meatus from the internal ear, and are distributed respectively to the cochlea and vestibule. In both branches, as well as in the trunk, there are numerous nerve-cells, appa- rently both with and without poles. The vestibular nerve divides into five branches, which proceed respectively to the utricle, the saccule, and the three ampullse of the semicircular canals : those for the utricle and the MINUTE STRUCTURE OF MEMBRANOUS LABYRINTH. 759 superior and external semicircular canals enter the cavity in a group along the crista vestibuli ; the fibrils for the sacculus enter the vestibule by a smaller group of foramina, which are situated below those just described, and open at the bottom of the fovea hemispherica ; the branch for the pos- terior semicircular canal is long and slender, and traverses a small passage Fig. 515. Fig. 514. •r '" Fig. 514. — TRANSVERSE SECTION OF ONE OP THE MEMBRANOUS SEMICIRCULAR CANALS (from Kolliker). ^ This specimen is from the ear of the calf : a, external fibrous layer with interspersed nuclei ; 6, homogeneous layer ; c, epithelial lining. Fig. 515.— AMPULLA OF THE SUPERIOR AND EXTERNAL SEMICIRCULAR CANALS AND PART OF THE COMMON SINUS SHOWING THE ARRANGEMENT OF THE NERVES (from Steifen- sand) . %£- 1, membranous ampulla of the superior canal ; 2, that of the external canal ; 3, part of the common sinus ; 4 and 5, fork-like swellings of the nerves at their ampullar dis- tribution ; 6, twig of the auditory nerve spreading in the common sinus. in the bone behind the foramina for the nerve of the sacculus. The nerves of the ampullae enter the flattened or least prominent side of the ampullaa, where they each form a forked swelling, which corresponds with the trans- verse septum already described, in the interior of the dilatation. No filaments have been fuund extending to any other parts of the semicircular canals. Microscopic structure. — The walls of the common sinus, sacculus and membranous semicircular canals are in general semitransparent ; but they are thicker and more opaque where nerves and vessels enter. On the outer surface is a layer of minutely ramified blood-vessels and loose tissue, which contains irregular pigment- cells : within this is a transparent layer, faiutly fibrillated, and presenting elongated nuclei when acetic acid is added ; lining the interior is an epithelial layer of polygonal nucleated cells. The mode of ending of the nerves in the membranous substance of the vestibule and semicircular canals is difficult to investigate, on account of the minuteness and delicacy of the parts ; for this reason also observers have had recourse in great measure to the examination of the vestibule 760 THE EAR. and semicircular canals in fishes, in which they are of large size. The subject still requires further research, but it appears to be pretty certain from the observations of Reich, the successive papers of M. and F. E. Schultze, and the corroborating observations of Kolliker, that the nerve fibres break up in the transparent layer into minute ramifications, which enter the epithelium and form between the epithelial cells spindle-shaped nucleated bodies with elongated extremities. There have also been ob- served long hair-like processes, fila acustica, projecting into the cavity, beyond the epithelial surface of the ridge of the ampullse, and likewise in the sacs ; and the actual continuity of these hairs with the nerve- terminations has been in one instance observed by F. E. Schultze. According to Lang the hairs are only the altered remains of a delicate cap of tissue on the surface of the epithelium. — (Kolliker's Gewebelehre, 4th ed., p. 694.) Fig. 516. Fig. 517. Fig. 516.— LEFT COCHLEA OP A CHILD SOME WEEKS OLD, opened (from Reichert). a The drawing was taken from a specimen which had been preserved in alcohol, and was afterwards dried ; the section is made so as to show the lamina spiralis, scalas, and cochlear canal in each of the three coils : the membranous spiral lamina is preserved, but the appearances connected with the organ of Corti, &c., have been lost from drying. / r, fenestra rotunda with its membrane ; s t, scala tympani ; s v, scala vestibuli ; I s, lamina spiralis ; ht hamulus ; c c, canalis cochleae ; d, opening of the aqueductus cochleae Fig. 517. — VERTICAL SECTION OF THE COCHLEA OF A FOETAL CALF (from Kolliker). f In this specimen the external wall was ossified, but the modiolus and spiral lamina were still cartilaginous ; the section shows in each part of the cochlear tube the two scalaa with the intermediate canalis cochleae and lamina spiralis ; the radiating lines in the modiolus indicate the passage of the auditory nerves towards the spiral lamina. COCHLEA. — The membranous cochlea has the form of a three-sided tube, the canalis membranacea, interposed between the scala vestibuli and the scala tympani. The peripheral wall of this canal is formed by part of the osseous cochlea, and on its other sides it is bounded by the basilar membrane and membrane of Reissner respectively, while at its inner angle is a structure named limbus laminae spiralis, and in its interior resting on the basilar membrane, is the organ of Corti with the membrana tectoria covering it. Each of these parts requires description. The membrana basilaris, or lamina spiralis membranacea, is stretched across from the free margin (labium tympanicum) of the osseous lamina to MINUTE STRUCTURE OF THE COCHLEA. 761 the outer part of the spiral canal, lying in the same plane as the osseous lamina, and attached peripherally through the medium of a thick structure, the spiral ligament. It increases in breadth from the base to the apex of the cochlea, while the osseous spiral lamina diminishes in breadth. Thus in the first turn of the cochlea this membrane forms about half of the breadth of the septum made by it and the osseous lamina ; but towards the apex of the cochlea the proportion between the two parts is gradually reversed, until, near the helicotrema, the membranous part is left almost unsupported by any plate of bone. Fig. 518.— SECTION THROUGH ONE Fig. 513. OP THE COILS OP THE COCHLEA (altered from Henle). ^ A, the section is made in a specimen softened by immersion in hydrochloric acid ; S T, scala tym- pani ; S V, scala vestibuli ; C C, canalis cochleae ; R, membrane of Reissner forming its vestibular /Jt wall ; I so, lamina spiralis ossea ; 1 1 s to I s p, lamina spiralis mem- branacea ; I Is, limbus laminae spiralis ; s s, sulcus spiralis ; n c, twigs of cochlear nerve ; g s, gang- lion spirale ; t, membrana tectoria; 6, membrana basilaris ; Co, organ of Corti ; Isp, ligameutum spirale. The limbus lamincz spiralis (denticulate lamina of Todd and Bowman) is a thick periosteal development near the edge of the osseous spiral lamina on the side which looks towards the vestibular scala. It makes a some- what convex elevation, presenting externally a sharp margin which over- hangs that to which the basilar membrane is attached, being separated from it by a groove. The groove is termed sulcus spiralis, and the margins labium vestibulare and labium tympanicum respectively. The membrane of Reissner (membrana vestibularis) arises from the inner part of the limbus, and extends outwards at a considerable angle with the osseous spiral lamina. The membrana tectoria (Claudius), or membrane of Corti (Kolliker), has been variously described, but, according to the most recent researches, is an elastic membrane attached on its one border close to the membrane of .Reissner, and on the other by an extremely delicate portion to the peri- pheral wall of the cochlea, a little above the membrana basilaris (Claudius and Henle). It thus divides the canalis membrauacea into two parts : the large part placed between it and the membrane of Reissner, and con- taining endolymph ; the other, a narrow interval dividing it from the membrana basilaris, and occupied by various cellular and rod-like structures of a highly complicated description, which together are designated as the organ of Corti. The canalis membranacea, or ductus cochlearis, bounded in the manner already described, presents a blind pointed extremity at the apex and another at the base. That at the apex extends beyond the hamulus, fixed to the wall of the cupola, and partly bounding the helicotrema ; that at the base fits into the angle at the commencement of the osseous spiral lamina in front of the floor of the vestibule. Near to this blind extremity the canalis membranacea receives a small duct, canalis reuniens (Hensen), 762 THE EAK. which is continued downwards from the saccule of the vestibule like the neck of a flask, and enters the membranous canal abruptly nearly at a right angle to it. Thus the cavity of the canalis membranacea is rendered con- tinuous with that of the saccule. Fig. 519. — THE LEFT LABYRINTH OF A CHILD AT BIRTH, PARTIALLY OPENED ON ITS OUTER SIDE TO SHOW THE COMMENCEMENT OF THE MEM- BRANOUS CANAL OF THE COCHLEA (slightly altered after Reich ert). f The external or horizontal canal has been removed; cs, superior canal; cp, posterior canal ; a s, membranous am- pulla and tube of the superior canal cut short ; a 7i, that of the external or horizontal canal ; h, undilated end of the horizontal canal in front of the common opening of the superior and posterior canals ; p s, united superior and posterior canals ; u, utriculus ; s, eacculus ; c c, vestibular part or commencement of the membranous canal of the cochlea ; c r canalis reuniens connecting it with the sacculus ; c, cochlea. It is necessary to explain that, although the canalis membranacea was described by Reissner so long ago as in 1851, yet, owing to some confusion having arisen between the membrane of .Reissner and the membrana tectoria described by Corti, whose work appeared at the same time, the nature of this canal has until comparatively Fig. 520. — DISTRIBUTION OF THE COCHLEAR NERVES IN THE LAMINA SPIRALIS (after Henle). A, part of the modiolus and spiral lamina showing the cochlear nerves form- ing a network, viewed from the base ; 1, the twigs of the nerve issuing frem the tractus spiralis foramino- sus ; 2, the branches of the nerve entering by the central canal of the modi- olus ; 3, wide plexus in the bony lamina spiralis ; 4, close plexus at its border ; 1 1, labium tym- pauicum; zi, zona interna ; z e, zona externa ; 1 8 p, ligamentum spirale. 13, part of the nerves ex- tracted and more highly magnified ; 2, twigs of the nerve from the modiolus close to the lamina spiralis ossea ; y s, spiral gangli- form enlargement of the nerve (habenaria gan- glionaris) ; f s, nerve-fibres running spirally along the gangliforra swelling (Henle) ; 3, wide plexus ; 4, close plexus of nerve -fibres as in A. MIXUTE STRUCTURE OF THE COCHLEA. 763 recently been generally misconceived. The history of the discovery and subsequent appreciation of the nature of the canalis membranacea is fully given by Reichert. (Abhandl. d. Konigl. Akad. d. Wissensch., Berlin, 1864.) Cochlear division of the auditory nerve. — The nerve of the cochlea is shorter, flatter, and broader than any of the other nerves of the internal ear, and perforates the bone by a number of foramina at the bottom of the internal rneatus, below the opening of the Fallopian aqueduct. These foramina are arranged in a shallow spiral groove (tractus spiralis fora- minulentus) in the centre of the base of the cochlea ; and they lead into small bony canals, which follow first the direction of the axis of the cochlea, through the modiolus, and then radiate outwards, between the plates of the bony lamina spiralis. In the centre of the spiral groove is a larger foramen which leads to the canalis centralis modiolL Through the central foramen and straight canal the filaments for the last half-turn of the lamina spiralis are conducted ; whilst the first two turns are supplied by filaments which occupy the smaller foramina and bent canals. In the bone the nerves have dark outlines, and near the edge of the spiral lamina they form a plexus which contains ganglion-cells, and may be considered as a spiral ganglion contained in an osseous canal, canalis spiralis modioli, already mentioned. From the outer side of this ganglion the fibres, still possessing the dark outline, pass onwards with a plexiform arrangement, and, emerging from the bone beneath the labium tympanicum of the limbus, are collected into bundles, which, opposite a line of perforations situated at the junction with the membrana basilaris and named habenula perforata, present the appearance of conical extremities entering those perforations. Beyond this they have not yet been traced with certainty, although it seems probable, as suggested by Kolliker, that the nerves are in continuity with spindle-shaped cells in the organ of Corti. Microscopic structure. — The limlus lamina spiralis is a thick structure continuous with the periosteum of the vestibular surface of the osseous lamina. Its free surface is thrown into a number of fungiform elevations narrower at the base than at their extremities. Towards the inner part of the limbus these elevations are short and vertical, but those which are placed further out are more and more oblique and longer, and the labium vestibulare is formed by the outermost of them, which are lengthened into rib-like processes with flat extremities placed edge to edge, overhanging the sulcus spiralis like teeth. In the spaces between the elevations numer- ous small bodies like nuclei are disposed. In the floor of the sulcus spiralis where the labium tympanicum is continued into the membrana basilaris a series of elevations (apparent teeth of Corti) are directed into the membrane, and between their outer extremities are the oblique perfora- tions occupied by the conical extremities of the nerve-bundlea. This part is the habenula perforata of Kolliker : it is described by him along with the membrana basilaris, and by Henle along with the limbus. Henle considers the appearance of elevations as caused merely by the nerve-bundles grooving the under surface and leaving thicker structure between. The membrana basilaris is divisible into an inner and an outer zone. The inner zone (habenula tecta vel arcuata) is covered over by the rods of Corti ; the outer zone (zona pectinata) is attached peripherally to the walls of the canal through the medium of the cochlear ligament. The inner zone, together with the apparatus on its surface, continues, according to Henle, of an uniform breadth of about -aj-oth of an inch, both in the dif- ferent parts of the same cochlea, and likewise in different animals : so that 764 THE EAR. Fig. 521. Fig. 521. —UPPER OR YESTIBULAR SURFACE OF A NARROW STRIP OF THE LAMINA SPIRALIS MEMBRANACEA (from Kolliker after Corti). 2-p The drawing is defective as regards the organ of Corti, but explains the nomenclature of the parts introduced by that author, and more or less adhered to by subsequent writers, although variously departed from in some of its details. The nomenclature adopted in the text has been selected from various writers, and it will be observed difiers considerably from the following : a, periosteum of the zona spiralis ossea ; d w, lamina spiralis mem- branacea ; d w', zona denticulata ; d f, habenula sulcata ; d, place where the perios- teum thickens ; e, granules in the areolse of the habenula sulcata ; fg, teeth of the first series; fffh, sulcus vel semicanalis spiralis; A, its lower wall ; h w, habenula denticu- lata; Jim, apparent teeth ; nt, teeth of the second series ; np, inner segments of the same; o, swellings with nuclei ; pq and qz, articulating pieces of the same : f, anterior segments of the second series ; s s s, three cylindrical cells placed on them ; w, epithelial cells placed under the membrane of Corti ; w' w, zona pectinata ; a a, band-like elevations of the habenula sulcata ; #, placed where a tooth of the first series takes its origin ; 7, holes between the apparent teeth ; 5, fore part of one of the teeth of the second series thrown back ; e, one of them in its place without its epithelial cells ; £ one with only the lowest epithelial cell ; i\, one with the two lowest cells ; 8, striae or slight elevations of the zona pectinata ; /c, periosteum attaching the lamina spiralis, with A, apertures between the bundles. the increasing breadth of the membrane from base to apex of the cochlea is due to broadening of the zona pectinata. According to the same observer the membrane is mainly homogeneous, and in the outer zone is thicker than in the inner, and somewhat tuberculated ; but on the surface towards the membranous canal it is transversely striated by a layer of extremely delicate fibres ; and on the other surface is a less perfect layer of fibres with spindle-shaped corpuscles, which are placed longitudinally, and in young subjects are arranged so as to cover the inner zone and the attachment to the spiral ligament, leaving the outer zone free. A single layer of epithelium lies on the surface. The ligamentum spirale (musculus cochlearis of Todd and Bowman) is triangular in section, receiving at its inner angle the basilar membrane, and spreading out rapidly to be attached by a broad base to the wall of the cochlea. Its fibres are directed outwards from the membrane to the bone, and it exhibits nuclei, like the ciliary muscle, whence Todd and Bowman conceived it to be muscular. Hensen represents it as composed of branch- ing nucleated cells. The organ of Corti. — Under this name may be comprised the whole of the structures intervening between the membrana basilaris and meinbrana tectoria. The most prominent part of it is formed by an outer and an inner series of rods, which, attached respectively to the inner and outer margins of the inner zone of the basilar membrane, meet together like the beams of a roof, and cover in a three-sided space, of which the inner zone of the basilar membrane is the floor. These structures, the fibres or rods of Corti, are closely adherent by their lower extremities to the basilar membrane. They are placed with the regularity of piano keys, and have been likened in con- THE ORGAN OF CORTI. Fig. 522. 765 Fig. 522. — DIAGRAMMATIC OUTLINE OP A RADIAL SECTION THROUGH THE LAMINA SPIRALIS MEMBRANACEA, ORGAN OF CORTI, &c. (after Kolliker, Heule, and other*). --^ This figure may be regarded as a more enlarged and explanatory view of the part of fig. 518 representing the organ of Corti : S V, part of the scala vestibuli ; C C, canalis cochleae ; S T, scala tympani ; R, membrane of Reissner, forming the partition between the scala vestibuli and the canalis cochleae ; I s o, a small part of the lamina spiralis ossea cut in the direction of one of the canals transmitting the cochlear nerves, nc; p, perios- teum lining the scala tympani ; Us, limbus laminae spiralis, presenting a great thickening of the periosteum, in which over the extremity of the osseous spiral lamina is found the sulcus spiralis s s, and upon the upper surface of which are the toothed projections ; I v, labium vestibulare ; 1 1, labium tympanicum of the sulcus spiralis ; Ivtolsp, the lamina spiralis meinbranacea with its contained parts ; mt, membrana tectoria passing from the limbus laminae spiralis to the outer wall of the cochlear tube ; mb, membrana basilaris, stretched from the labium tympanicum to the outer wall of the cochlear tube, where it expands in the ligamentum spirale, I sp ; the part marked by the letters m b, between two short dotted lines, forms the zona tecta or z. arcuata ; the part indicated by m b' and between the adjacent dotted lines is the zona pectinata ; C, the organ of Corti ; i, the internal rods ; e, the external rods ; these are set by their lower flattened ends on the basilar membrane, and are articulated together at their upper parts, a, the inner overlapping the outer ; a nucleus is seen close to the base of each of the rods close on the basilar membrane ; m r, membrana reticularis, stretched to the outer wall of the cochlea, pc; below mr, the cells of Corti lying obliquely on the outer rods, and between them the cells of Deiters, and between these and the outer wall of the cochlea epithelial cells ; between a and mr, are indicated the perforations through which the hair-like terminations of the cells of Corti project : the sulcus spiralis is seen filled with cylindrical and other epithelium. sistency to cartilage. The inner rods are more closely set and more nume- rous than the outer, and appear generally to be of a uniform breadth, flattened, and with a nucleiform body placed subjacent to the lower extremity. The outer rods are narrow and cylindrical in their shafts, and expanded at the lower extremity, which has a nucleiform body subjacent to it, as in the case of the inner rods. At their upper ends where they meet together, both sets of rods are thickened, and the parts which are in con- tact (coins articulaires externes et internes of Corti) have the appearance of quadrilateral plates directed outwards so that those of tUe inner row lie over those of the outer row, and those of the outer row are bent backwards from the direction in which the rods to which they belong are placed. From the junction line of the rods there extends outwards an extremely delicate network, the lamina reticularis of Kolliker (i. velamentosa, Deiters), which, it may be gathered from different accounts, is mainly constructed of a layer of squamous cells so disposed as to leave at least three rows of large perforations between them, and which are cemented together by a net- work of intervening substance which is sometimes detected when the cells are not. At its inner margin this lamina is united by flat plates to the inner 766 THE EAE. series of rods, and by narrow bodies with flattened extremities to the outer series : at its outer margin it has not yet been demonstrated that it is attached to the wall of the cochlea, although it has been supposed that its function might be to give fixity to the rods of Corti. Besides the rods and the lamina reticularis the organ of Corti presents various cellular elements. Of these the most important are an outer and inner series of cells with stiff Fig. 523. A. Fig. 523 A. — VIEW FROM ABOVE OP THE ORGAN OP CORTI AND LAMINA RETICULARIS IN THE Ox (from Kolliker). ^ a, inner rods or fibres of Corti ; 6, inner ends of the same with the deeper attached nuclei ; c, articulating part of the same ; d, clear plates appended, which with others from the outer rods form the commencement of the membrana reticularis ; e, outer rods or fibres of Covti ; /, their articulating portions ; g, their terminations at the membrana basilaris ; h, plates of the outer rods belonging to the membrana reticularis ; i i, apparent extension of the ends of the fibres of Corti in the stride of the zona pectinata of the basilar membrane ; I, their inner connecting plates ; I', their outer connecting plates ; m, %, o, first, second, and third series of perforations ; p, rectangular terminal part of the lamina ; q, prolongation of this in the form of fibres upon the large epithelial cells of the organ of Corti. Fig. 523 B.— THE ORGAN OP CORTI OF THE CAT (from Kolliker). 5-f 1, the organ of Corti from above ; c, the articulated part of the inner fibres or rods ; d, connected plates which form the commencement of the membrana reticularis ; f, articulating portions of the outer rods ; /', one of these connected with a filamentous process, and presenting granular or punctated contents ; ra, n, o, first, second, and third row of perforations, in which the cilia of Corti's cells are represented as dark arched lines ; a, inner ciliated cells with ($) their cilia, forming the outermost part of the thick epithelium of the sulcus spiralis (7), and which covers the inner fibres (rods) of Corti as far as their articulating pails ; 5, outer part of the network of the lamina reticularis ; 2, a cell of Corti with its hairs, but no visible filamentous appendage ; 3, lateral view of the lamina reticularis with the bundles of cilia of the cells of Corti. BLOOD-VESSELS OF THE LABYKIXTH. 767 cilia projecting from their upper extremities. The inner ciliated cells form a single row resting on the articulating ends of the inner rods : the outer ciliated cells (pedunculated cells of Corti) are placed in three rows external to the outer rods, aud are described as attached by pointed extremities to the membrana basilaris, and with their ciliated ends opposite the three rows of openings in the lamina reticularis ; so that sometimes when the lamina is detached the ends of the cells are detached with it. Alternating with the outer ciliated cells are the cells of Deiters, which are fusiform and prolonged into a thread at each extremity, one passing up to the lamina reticularis, and the other down to the outer zone of the membrana hasilaris. The upper surface of the remaining part of the basilar membrane is covered with hexagonal epithelium-cells. The sulcus spiralis is likewise filled with large epithelial cells, which, according to Kolliker, project in a swelling distinct from the proper organ of Corti. The mode of termination of the nerves, as has been already said, is uncer- tain, but minute fibres, consisting of axis-cylinders only, have been traced by Deiters into the organ of Corti, and his statements receive some support from Kolliker and Henle. These fibres are said to divide into a radiating set distributed both above and beneath the rods, and into a spiral set which are continued in the longitudinal direction of the canal. The membrana tectoria is described by Henle as presenting three zones. The inner of these is delicate and presents large openings corresponding to elevations of the limbus ; the middle or generally recognised part is formed of layers of fibres directed outwards, but yet crossing each other ; and the outer part, unrecognised by most observers, is extremely delicate, forming a network, the openings in which are elongated in the direction of the canal. The membrane of Heissner is an extremely easily torn membrane, on both sides of which epithelium has been described. On the microscopic anatomy of the cochlea may be consulted Henle's Systematische Anatomic ; Kolliker's Gewebelehre, 4th edition ; also the papers of Corti, Claudius, Deiters, and Hensen, in Vols., III. VII., X., and XIII. of Siebold and Kolliker's Zeitsch. f. Wissensch. Zoologie; and Deiters Untersuchungen liber die Lamina Spiralis Membranacea. BLOOD-VESSELS OF THE LABYRINTH. Arteries. — The internal auditory artery, a branch from the basilar, enters the internal meatus of the ear with the auditory and facial nerves, and at the bottom of that shallow canal divides into vestibular and cochlear branches. The vestibular branches are distributed to the common sinus, sacculus, and semicircular canals, with the branches of nerve which they accompany through the bony foramina. At first they ramify on the exterior of the membranous labyrinth, and end in capillaries both on the outer surface and in the substance of the special glassy layer. The plexus is best marked internally near the ending of the nerves. The cochlear branches, twelve or fourteen in number, traverse the many small canals in the modiolus and bony lamina spiralis, and form in the latter a capillary plexus that joins at intervals the vas spirale, to be pre- sently described. From this plexus offsets are distributed in the form of a fine network on the periosteum, but the vessels do not anastomose across the membrana basilaris. The vas spirale is a single, sometimes branched vessel which runs along the under surface of the membranous zone, near the bone : it is like a capillary in texture,, but larger in size, and is pro- 768 THE EAR. bably venous. On the outer wall of the membranous canal there is a specially vascular strip which has received the name of stria vascularis. Besides the foregoing vessel, which is the chief artery of the internal ear, the stylo-mast oid branch of the posterior auricular, and occasionally the occi- pital artery (Jones), send twigs to the vestibule and the posterior semicircular canal. Veins. — The veins of the cochlea issue from the grooves of the cochlear axis and join the veins of the vestibule and semicircular canals : these accom- pany the arterial branches, and, uniting with those of the cochlea at the base of the modiolus, pour their contents into the superior petrosal sinus. DEVELOPMENT OF THE EAR. In the very young embryo the first rudiment of the ear is seen in the form of a small vesicle — the primary auditory vesicle lying at the side of the third primary cerebral vesicle. It has to a certain extent an appearance similar to that of the primary optic vesicle situated further forwards, and was long very naturally supposed to be formed like it by a protrusion of the wall of the primary medullary cavity of the brain ; but it has latterly been established by various observers that it is pro- duced solely by invagination of the integument, and has no original connection with the brain. During the third day of incubation it can be seen in the chick, still open to the outside, above and behind the second branchial lappet. It soon becomes completely closed, and is afterwards developed into the membranous labyrinth. The first complication which the vesicle exhibits is by the extension of a process upwards and backwards, which remains permanent in the lower vertebrata, but in mammals is obliterated, its vestiges remaining in the aqueduct of the vestibule. The semicircular canals next appear as elongated elevations of the surface of the primary vesicle : the middle portion of each elevation becomes separated from the rest of the Fig. 524.— OUTLINES SHOWING THE FORMATION OP THE EXTERNAL EAR IN THE FCETUS. A, head and upper part of the body of a human foetus of about four weeks (from nature). ^ Four branchial plates (the first, forming the lower jaw, is marked 1), and four clefts are shown ; the auditory vesicle (a), though closed, is visible from the tran- sparency of the parts, and is placed behind the second branchial plate. B, the same parts in a human foetus of about six weeks (from Kcker). f The third and fourth plates have nearly disappeared, and the third and fourth clefts are closed ; the second is nearly closed ; but the first (!') is somewhat widened posteriorly in con- nection with the formation of the mealus externus. C, human foetus of about nine weeks (from nature), f The first branchial cleft is more dilated, and has altered its form along with the integument behind it in connection with the formation of the meatus externus and the auricle. DEVELOPMENT OF THE EAR. 769 vesicle by bending in of its walls under it, and thus the elevation is converted into a tube open at each end, which subsequently becomes elongated and presents an ampullar dilatation. The cartilage which forms the osseous labyrinth is continuous with that of the rest of the primordial cranium. The cartilaginous walls of the cavity are united by connective tissue to the vesicle : this connective tissue, according to Kolliker, becomes divided into three layers, of which the outer forms the lining periosteum, the inner forms the external walls of the membranous labyrinth, while the intervening layer swells up into gelatinous tissue, the meshes of which become wider and wider, till at last the space is left which ultimately is found containing perilymph. Fig. 525. Fig. 525. — LABYRINTH OF THE HUMAN FCETUS OP FOUR WEEKS, MAGNIFIED (from Kolliker). A, from behind ; B, from before; v, the vestibule ; r v, recessus vestibuli, giving rise later to the aqueduct ; c s, commencement of the semicircular canals ; a, upper dilatation, belonging perhaps to another semi- circular canal ; c, cochlea. The cochlea appears at first as a prolongation downwards from the auditory vesicle, but afterwards become tilted forwards. This prolongation of the auditory vesicle is the rudimentary canalis mem- branacea. Close to it is placed the cochlear nerve, with a gangliform extremity. The canal becomes elongated in a spiral direction, and the ganglion, which is elongated with it, becomes the ganglion spirale. Between the canal and the cartilaginous wall which afterwards surrounds it a large amount of con- nective tissue intervenes, and in this the cavities of the scala vestibuli and scala tym- pani appear at a later period, precisely as does the space for the perilymph in the Fig. 526. Fig. 526. — TRANSVERSE SECTION OF THE COCHLEA IN A FCETAL CALF, MAGNIFIED (from Kolliker). C, the wall of the cochlea, still carti- laginous ; c c, canalis cochleae ; I s, placed in the tissue occupying the place of the scala vestibuli indicates the lamina spiralis ; n, the central cochlear nerve ; g, the place of the spiral ganglion ; S, the body of the sphenoid ; c k, chorda dorsalis. vestibule. The modiolus and spiral lamina, according to Kolliker, are ossified without intervention of car- tilage. Within the canalis mem- branacea Kolliker finds in the em- bryo a continuous epithelial lining, thin on the membrane of Reissner and on the outer wall, but forming a thick eleva- tion in the position of the rods of Corti, and a larger elevation more internally, filling up the sulcus spiralis. On the surface of this latter elevation he observes a transpa- rent body, the membrane of Corti. With regard to the middle and external ear, it has been already explained at pages 65 and 66 that the external aperture, the tympanic cavity, and the Eustachian tube, are formed in the posterior or upper part of the first branchial cleft, which remains open except at the place where the passage is interrupted by the formation of the membrana tympani ; and also that the incus and malleus are formed in the first branchial lappet from the proximal part of Meckel's cartilage, and the stapes and stapedius muscle and the styloid process in the second lappet. It is pointed out by 3 E 770 THE EAR. Kolliker that during the whole period of foetal life the tympanic cavity is occupied by connective tissue, in which the ossicles are imbedded ; and that only after the breathing process is commenced this tissue recedes before an expansion of the mucous membrane. The pinna is gradually developed on the posterior margin of the first branchial cleft. It is deserving of notice that congenital malformation of the external ear, with occlusion of the meatus and greater or less imperfection of the tympanic Fig. 527. Fig. 527. — VIEWS OF THE CARTILAGE OP MECKEL AND PARTS CONNECTED WITH THE FIRST AND SECOND BRANCHIAL PLATES. A (after Kolliker), head of a foetus of about eigh- teen weeks, showing the cartilage of Meckel in con- nection with the malleus, &c. M, the cartilage of Meckel of the right side. B (from nature). An enlarged sketch explana- tory of the above view; z, the zygomatic arch ; ma, the mastoid process ; mi, portions of the lower jaw of which the parts near the angle and the sym- physis have been removed ; M, the cartilage of Meckel of the right side; M', a small part of that of the leftside, joiningthe left car- tilage at s, the symphysis ; T, the tympanic ring ; m, the malleus ; i, the incus; s, the stapes ; sta, the stapedius muscle ; st, the styloid process ; p, h, g, the stylo -pharyngeus, stylo- hyoid and stylo -glossus muscles, st-l, stylo-hyoid ligament attached to the lesser cornu of the hyoid bone ; hy, the hyoid bone ; tk, thyroid cartilage. In A, the head being turned somewhat upwards, the same parts are shown, to- gether with the surround- ing muscles, the carotid artery, jugular vein, &c. apparatus, are observed in connection with abnormal development of the deeper parts of the first and second branchial lappets and the intermediate cleft ; while cases have been observed of the persistence in the neck of the adult of one or more of the branchial clefts situated behind the first. (Allen Thomson, Proceed. Roy. Soc. of Edin. 1844, and Edin. Journ. of Med. Sc. 1847.) THE XOSE. CARTILAGES. 771 THE NOSE. The nose is the special organ of the sense of smell. It has also other functions to fulfil ; — for, communicating freely with the cavities of the mouth and lungs, it is concerned in respiration, voice, and taste ; and by means of muscles on its exterior, which are closely connected with the muscles of the face, it assists in the expression of the different passions and feelings of the mind. Fig. 528. — LATERAL VIEW OF THE CARTILAGES OP Fig. 528. THE NOSE (from Arnold), f a, rigbt nasal bone ; b, nasal process of the superior maxillary bone ; 1, upper lateral cartilage or wing-like expansion of the septal cartilage ; 2, lower lateral cartilage (outer part) ; 2*, inner part of the same ; 3, sesamoid cartilages. This organ consists of, first, the anterior prominent part, composed of bone and car- tilages, with muscles already described, which slightly move the cartilages, and two orifices, anterior nares, opening downwards ; and, secondly, of the two nasal fossae, in which the olfactory nerves are expanded. The nasal fossae are separated from each other by a partition, septum nasi, formed of bone and cartilage : they communicate at the outer side with hollows in the neigh- bouring bones (ethmoid, sphenoid, frontal, and superior maxillary); and they open backwards into the pharynx through the posterior nares. The skin of the nose is studded, particularly in the grooves of the alse or outer walls of the nostrils, with numerous small openings, which lead to sebaceous follicles. Within the margin of the nostrils there is a number of short, stiff, and slightly curved hairs — mbrissce, which grow from the inner surface of the alse and septum nasi, as far as the place where the skin is continuous with the mucous membrane lining the cavity of the nose. CARTILAGES OF THE NOSE. These are the chief support of the outer part of the organ. They occupy the triangular opening seen in front of the nasal cavity in the dried skull, and assist in forming the septum between the nasal fossoe. There are usually reckoned two larger and three smaller cartilages on each side, and one central piece or cartilage of the septum. The upper lateral cartilages (cartilagines laterales nasi) are situated in the upper part of the projecting portion of the nose, immediately below the free margin of the nasal bones. Each cartilage is flattened and triangular in shape, and presents one surface outwards, and the other inwards towards 3 E 2 772 THE NOSE. Fig. 529. Fig. 530. the nasal cavity. The anterior margin, thicker than the posterior one, meets the lateral cartilage of the opposite side above, but is closely united with the edge of the cartilage of the septum below ; so closely indeed, that by some, as Henle, the upper lateral are regarded as reflected wings of the median cartilage. The inferior margin is connected by fibrous mem- brane with the lower lateral cartilage ; and the posterior edge is inserted into the ascending process of the upper maxilla and the free margin of the nasal bone. Fig. 529. — FROKT VIEW OF THE CARTILAGES OF THE NOSE (from Arnold), f a, a', nasal bones ; 1, 1', upper lateral cartilages or wing-like ex- pansions of the septal cartilage ; 2, 2', lower lateral cartilages. Fig. 530. — VIEW OF THE CARTI- LAGES OF THE NOSE FROM BE- LOW (from Arnold), f 2, 2', outer part of the lower lateral cartilages ; 2*, 2*, inner part of the same ; 4, lower edge of the cartilage of the septum. The lower lateral cartilages (cartilagines alarum nasi) are thinner than the preceding, below which they are placed, and are chiefly characterised by their peculiar curved form. Each cartilage consists of an elongated plate, so bent upon itself as to pass in front and on each side of the nostril to which it belongs, and by this arrangement serves to keep it open. The outer portion is somewhat oval and flattened, or irregularly convex externally. Behind, it is attached to the margin of the ascending process of the upper maxilla, by tough fibrous membrane, in which are two or three cartilaginous nodules (cartilag. minores vel sesamoidese) ; above, it is fixed, also by fibrous membrane, to the upper lateral cartilage, and to the lower and fore part of the cartilage of the septum. Towards the middle line it is curved back- wards, bounding a deep mesial groove, at the bottom of which it meets with its fellow of the opposite side, and continues to pass backwards, forming a small part of the columna nasi, below the level of the cartilage of the septum. This inner part of the cartilage of the ala is thick and narrow, curls outwards, and ends in a free rounded margin which projects out- wards towards the nostril. The lower and most prominent portion of the ala of the nose, like the lobule of the ear, is formed of thickened skin with subjacent tissue, and is unsupported by cartilage. The cartilage of the septum has a somewhat triangular outline, and is thicker at the edges than near the centre. It is placed nearly vertically in the middle line of the nose, and completes, at the fore part, the separation between the nasal fossae. The anterior margin of the cartilage, thickest above, is firmly attached to the back of the nasal bones near their line of junction; and below this it lies successively between the upper and the lower lateral cartilages, united firmly with the former and loosely with the latter. The posterior margin is fixed to the lower and fore part of the central plate of the ethmoid bone ; and the lower margin is received into NASAL FOSSAE. 773 the groove of the vomer, as well as into the median ridge between the superior maxillae. Fig. 531. — OSSEOUS AND CARTILAGI- NOUS SEPTUM OP THE NOSE, SEEN FROM THE LEFT SIDE (from Ar- nold). § «, right nasal bone ; 5, superior maxillary bone ; c, sphenoidal sinus ; d, perpendicular plate of the ethmoid bone; e, vomer; 2*, inner part of the right lower lateral cartilage ; 4, carti- lage of the septum. This cartilage is the persistent anterior extremity of the primor- dial cranium. In young subjects it is prolonged back to the body of the presphenoid bone; and in many adults an irregular thin baud remains between the vomer and the central plate of the ethmoid. Fig. 531. NASAL FOSSAE. The nasal fossae, and the various openings into them, with the posterior nares, have been previously described as they exist in the skeleton, and the Fig. 532. Fig. 532. — TRANSVERSE VERTICAL SECTION OF TUB NASAL FOSS.E SEEN FROM BEHIND (from Arnold). ^ 1, part of the frontal bone ; 2, crista galli ; 3, perpendicular plate of the ethmoid ; be- tween 4 and 4, the ethmoid cells ; 5, right middle spongy bone ; 6, left lower spongy bone; 7, vomer ; 8, malar bone ; 9, maxillary sinus ; 10, its opening into the middle meatus. greater part of that description is also applicable generally to the nose in a recent state ; but it is proper to mention certain differences in the form and 774 THE NOSE. dimension of parts, which depend on the arrangement of the lining mem- brane, viz. — Throughout the whole of the nasal fossae it is to be observed that — First, owing to the thickness of the membrane in question, (which not only lines the walls of the fossae, but covers the spongy bones on both sides,) the nasal cavity is much narrower in the recent state. Second, in consequence of the prolongations of membrane on their free margins, the turbinate bones, and more particularly the lower pair, appear in the recent state to be both more prominent, and longer in the direction from before backwards, than in the dried skull. Third, by the arrange- ment of the mucous membrane round and over the orifices which open into the nasal fossae, some of the foramina in the bones are narrowed, and others completely closed. In the individual parts of the nasal fossae the following particulars are to be noticed. In the upper meatus, the small orifice which leads into the posterior ethmoidal cells is lined by a prolongation of the thin mucous membrane which continues into those cavities ; but the spheno-palatine foramen is covered over by the Schneiderian membrane, so that no such opening exists in the recent nasal fossa. In the middle meatus the aperture of the infundibulum is nearly hidden by an overhanging fold of membrane ; it leads directly into the anterior ethmoidal cells, and through them into the frontal sinus. Below and behind this, the passage into the antrum of Highmore is surrounded by a circular fold of the pituitary membrane, (sometimes prominent and even slightly valvular,) which leaves a circular aperture much smaller than the foramen in the bony meatus. In the lower meatus, the inferior orifice of the nasal duct is defended by one or two folds of membrane; and when there are two, the folds are often adapted so accurately together as to prevent even air from passing back from the cavity of the nose to the lachrymal sac. In the roof the apertures in the cribriform plate of the ethmoid bone are closed by the membrane, but the openings into the sphenoidal sinuses receive a prolonga- tion from it. In the Jloor the incisor foramen is in the recent state generally closed. Some- times, however, a narrow funnel-shaped tube of the mucous membrane descends for a short distance into the canal, but is closed before it reaches the roof of the palate. Vesalius, Stenson, and Santorini, believed that this tube of membrane opened generally into the roof of the mouth by a small aperture close behind the interval between the central incisor teeth. Haller, Scarpa, and, more recently, Jacob- son, find that in man it is usually closed, and often difficult of detection. (See Cuvier's Report on a paper by Jacobson, " Annales du Museum d'Hist. Naturelle ; " Paris, 1811 ; vol. xviii. p. 412.) MUCOUS MEMBRANE. The pituitary or Schneiderian membrane, which lines the cavities of the nose, is a highly vascular mucous membrane, inseparably united, like that investing the cavity of the tympanum, with the periosteum and peri- chondrium over which it lies. It is continuous with the skin through the nostrils ; with the mucous membrane of the pharynx through the pos- terior apertures of the nasal fossae ; with the conjunctiva through the nasal duct and lachrymal canaliculi ; and with the lining membrane of the several sinuses which communicate with the nasal fossae. The pituitary membrane, however, varies much in thickness, vascularity, and general appearance in these different parts. It is thickest and most vascular over the turbiuato bones (particularly the inferior), from the most dependent parts of which it forms projections in front and behind, thereby increasing the surface to some extent. On the septum nasi the pituitary membrane is still very thick and spongy ; but in the intervals between the turbinate bones, and over the floor of the nasal fossae, it is considerably thinner. In the maxillary, frontal, MUCOUS MEMBEAKB OF THE XOSE. 775 and sahenoidal sinuses, and in the ethmoidal cells, the mucous lining mem- brane, being very thin and pale, contrasts strongly with that which occupies the nasal fossae. Fig. 533. — OUTER WALL OF THE LEFT NASAL FOSSA, COVERED BY TUB PITUITARY MEMBRANE (from Arnold), f 1, frontal bone ; 2, left nasal bone ; 3, superior maxillary ; 4, body of the sphenoid with the sphenoidal sinus ; 5, projection of the membrane covering the upper spongy bone ; 6, that of the middle ; 7, that of the lower ; the upper, middle, and lower meatuses are seen below the corresponding spongy bones; 8, opening of the Eustachian tube ; 9, depression of the lining membrane of the nose in the anterior palatine canal. In respect of the characters of the mucous membrane, three regions of the nasal fossae may be distinguished. Thus, the region of the nostrils, including all the part which is roofed by the nasal cartilages, is lined with stratified squamous epithelium ; the remainder of the fossae is divisible into two parts, viz. , the olfactory region in which the epithelium is non-ci- Fig. 534. Fig. 534. — VERTICAL SECTION OF A SMALL PORTION op THE MEMBRANE OF THE NOSE FROM THE OLFACTORY HKGION (from Ecker), ^ a, coloured part of the epithelium ; a', nuclei ; 5, deeper part containing the olfactory cells and fila- ments ; c, connective tissue of the mucous membrane ; d, one of the mucous glands : d', its duct; e, twig of the olfactory nerve ; c', small twig passing to the surface. liated and columnar, and the respiratory region in which it is ciliated and columnar. The membrane in the respiratory part, con- sisting of the inferior turbinated and all the lower portions of the fossae, is studded with nu- merous mucous glands, which are of branched acinated appearance, and open by apparent orifices on the surface. These are most numerous about the middle and hinder parts of the nasal fossae, and are largest at the back of the septum near the floor of the nasal cavity. They are much smaller and 776 THE NOSE. leps numerous in the meuVbraue lining the several cavities which communi- cate with the nasal fossse. The olfactory region or that in which the olfactory nerve is distributed, includes the upper and middle turbinated parts, and the upper portion of the septum. Its mucous membrane is thicker and more delicate in consistence than that of the ciliated region, being soft and pulpy. The columnar cells on its surface are prolonged at their deep extremities into threads, which have been observed to communicate with stellate cells of ihe connective tissue. Beneath the columnar cells is a considerable thick- ness of densely nucleated tissue, compared by Henle to the cortical brain- substance. The glands of this region are numerous ; but are of a more simple structure than those in the lower part of the fossae. Fig. 535. — CELLS AND TERMINAL NERVE-FIBRES OP THE OLFACTORY REGION (from Frey after Schultze). 1, from the frog ; 2, from man ; a, epithelial cell, extending deeply into a ramified process; b, olfactory cells ; c, their peripheral rods ; e, their extremities, seen in 1 to be prolonged into ciliary hairs ; d, their central filaments ; 3, olfactory nerve-fibres from the dog ; a, the division into fine fibrillse. Olfactory Cells. — Intermixed with the columnar epithelial cells of the olfactory region, and so numerous as to surround each of them, are certain peculiar bodies, each consisting of a spindle - shaped nucleated cell, from which proceed a superficial and a deep process. The superficial process is a cylindrical or slightly tapering thread passing directly /7 ^BIKflflMi^! 'mt'm *° ^ne sur^ace) and terminating abruptly f IfMO at the same level as the epithelial cells I '*Wwf^ ^t between which it lies : the deep process A I3P1 *s more slender and passes vertically invrards. Both processes frequently pre- sent a beaded appearance similar to that observed in fine nerve - filaments, and considered to be of a similar accidental origin. It was suggested by Max Schultze, the discoverer of the olfactory cells, and is highly probable, that the deep processes are directly continuous with the filaments of the olfactory nerve, but the continuity does not appear to have been actually observed. The superficial process of the olfactory cell was observed by Schultze to be sur- mounted by a short stiff hair-like process, and has been so described by others ; but both the discoverer and others are now agreed that this appearance results from the coagulation of albumen escaped from the interior of the process. Long and fine hair- like processes do, however, exist on the olfactory membranes of amphibia, reptiles, and birds, and had been previously pointed out by Schultze. Olfactory Nerve. — The filaments of this nerve, lodged at first in grooves on the surface of the bone, enter obliquely the substance of the Schneiderian membrane, and pass to their distribution between its mucous and fibrous layers. The nerves of the septum are rather larger than those of the outer wall of the nasal fossse ; they extend over the upper third of the septum, OLFACTORY KERVE. 777 and as they descend become very indistinct. The nerves of the outer wall are divided into two groups — the posterior branches being distributed over the surface of the upper spongy bone, and the anterior branches descending ever the plain surface of the ethmoid and the middle spongy bone. Fig. 530. XT I Fig. 536. — NERVES OF THE SKPTUJI NASI, SEEN FROM THE RIOHT SIDE (from Sappey after Hirscbfeld and Leveille). f I, the olfactory bulb ; 1, the olfactory nerves passing through the foramina of the cribriform plate, and descending to be distributed on the septum ; 2, the internal or septal twig of the nasal branch of the ophthalmic nerve ; 3, naso-palatine nerves. The olfactory nerves as they descend ramify and unite in a plexiform manner, and the filaments join in brush-like and flattened tufts, which, spreading out laterally and communicating freely with similar offsets on Fig.' 537. Fig. 537. — NERVES OF THE OUTER WALLOP THE NASAL FOSSJE (from Sappey after Hirschfel.l and Leveille). § 1, network of the branches of the olfac- tory nerve, descending upon the region of the superior and middle turbinated bones ; 2, external twig of the ethmoiclal branch of the nasal nerve ; 3, spheno-palatine ganglion ; 4, ramification of the anterior palatine nerves ; 5, posterior, and 6, middle divi- sions of the palatine nerves ; 7, branch to the region of the inferior turbinated bone ; 8, branch to the region of the superior and middle turbinated bones ; 9, naso-palatine branch to the septum cut short. each side, form a fine net-work with elongated and narrow intervals between the points of junction ; but it is impossible to trace by dissection the termination of the nerves in the membrane, in consequence of the difficulty of recognising the filaments, destitute of dark outline, as they lie among the other nucleated tissues. In their nature the olfactory filaments differ much from the fibres of the cerebral and spinal nerves : they contain no white substance of Schwann, 778 THE NOSE. are pale, and finely granular in texture, firmly adherent one to anothef, and have oval corpuscles on their surface. The greater part of the mucous membrane of the nasal fossse is provided with nerves of common sensibility, derived from branches of the fifth pair : these have already been described at pp. 599, 603 and 604. Blood-vessels. — The arteries and veins of the nose are derived from nume- rous sources : those of the interior form rich plexuses of capillaries in the lining membrane. The description of the arteries will be found at pp. 350, 356, 361 and 362 ; that of the veins at pp. 456 and 464. DEVELOPMENT OP THE NOSE. The organ of smell, as was first pointed out by V. Baer, owes its origin, like the primary auditory vesicle and the crystalline lens of the eye, to a depression of the integument. This depression, the primary olfactory groove, is at first encircled by a uniform wall, and is unconnected with the mouth. This stage has been observed by Kolliker in the human embryo of four weeks. Soon, hoAvever, by the unequal growth of the surrounding parts, a groove is formed, descending from the pit and passing into the mouth. Thus the middle frontal process is isolated between the grooves of opposite sides, while the lateral frontal process separates the nostril from the eye (p. 65). The maxillary lobes, growing forwards from behind the eyes, complete the boundaries of the nostrils, which then open into the fore part of the mouth. Kolliker observes this stage in the latter half of the second month. The palate subsequently grows inwards to the middle line, as has been elsewhere stated, and separates the nasal from the buccal cavity ; leaving only the extremely minute communication of the incisor foramen. Meanwhile, with the growth of the face, the nasal fossae deepen, and the turbinated bones make their appearance as processes from their walls. Observations are still wanting to determine whether the olfactory nerves are developed from the bulbs, and have thus a cerebral origin, or are separately formed from peripheral blastema like all other nerves, with the exception of the optic. Fig. 537.* ABC Fig. 537.* VIEWS OP THE HEAD OP HUMAN EMBRTOES, ILLUSTRATING: THE DEVELOPMENT OP THE NOSE. A, Head of an embryo of three weeks (from Ecker). ]f 1, anterior cerebral vesicle ; 2, middle vesicle ; 3, nasal or middle frontal process ; 4, superior maxillary process ; 5, eye ; 6, inferior maxillary process or first visceral plate, and below it the first cleft j 7, 8, and 9, second, third, and fourth plates and clefts. B, Head of an embryo of about five weeks (from Ecker). ^ 1, 2, 3, and 5, the same parts as in A ; 4, the external nasal or lateral frontal process, inside which is the nasal groove ; 6, the superior maxillary process ; 7, the inferior maxilla ; x , the tongue seen within the mouth ; 8, the first branchial cleft which becomes the outer part of the meatus auditorius externus. C, View of the head of an embryo of eight weeks seen from below, the lower jaw having been removed (from Kolliker). | ?i, the external nasal apertures ; i, intermaxillary or incisor process, and to the outer side of this the internal nasal aperture ; m, one of the palatal processes of the upper jaw, which advancing inwards from the sides form the partition between the mouth and nose ; p, common cavity of the nose, mouth, and pharynx. OKGANS OF DIGESTIOX. THE MOUTH. 779 SECTION VI.— SPLANCEDTOLOGY. UNDER the division Splanchnology will be described those organs of the body which have not found a place in any of the foregoing parts of the work. These consist of the organs of digestion, the organs of respiration, the urinary organs, and the organs of generation. ORGANS OF DIGESTION. The digestive apparatus includes that portion of the organs of assimilation within which the food is received and partially converted into chyle, and from which, after the chyle has been absorbed, the residue or excrement is expelled. It consists mainly of a tubular part, — the alimentary canal, to- gether with various glands of which it receives the secretions. The alimentary canal is a long membranous tube commencing at the mouth and terminating at the anus, composed of certain tunics or coats, and lined by a continuous mucous membrane from one end to the other. Its average length is about thirty feet, being about five or six times the length of the body. Its upper extremity is placed beneath the base of the skull, the succeeding portion traverses the thorax, and by far the greater part is contained within the cavities of the abdomen and pelvis. The part situated above the diaphragm consists of the organs of mastica- tion, insalivation, and deglutition, and comprises the mouthy with the teeth and salivary glands, the pharynx, and the oesophagus or gullet. The remainder includes that part of the canal which is more immediately en- gaged in the digestive process, in absorption, and in defecation, as the stomach and the small and large intestine. The glands which are most intimately connected with digestion consist of those very numerous smaller glandular organs which are situated in the mucous membrane of the alimen- tary canal, and the larger glands, such as the pancreas and liver, whose ducts open within the canal. THE MOUTH. The mouth, or, more definitely, the buccal cavity, is the space included between the lips and the throat. Bounded by the lips, cheeks, tongue, and the hard and soft palate, it communicates behind with the pharynx through an opening called the fauces (isthmus faucium). The cavity of the mouth is lined throughout by a mucous membrane, which is of a pink rosy hue during life, but pale grey after death, and which presents peculiarities of surface and structure to be noticed hereafter. The lips and cheeks are composed of an external layer of skin, and of a a internal layer of mucous membrane, together with muscles, vessels, and nerves already fully described in other parts of this work, some areolar tissue, fat, and numerous small glands. The free border of the lips is pro- tected by a dry mucous membrane, which becomes continuous with the skin, is covered with numerous minute papillae, and is highly sensitive. On the inner surface of each lip, the mucous membrane forms a fold in the middle line, connecting the lip with the gums of the corresponding jaw. These are the frcena or frcenula of the lips : that of the upper lip is much the larger. Numerous small glands, called labial glands, are found beneath the 780 ORGANS OF DIGESTION. mucous membrane of the lips, around the opening of the mouth. They are situated between the mucous membrane and the orbicularis oris muscle. They are compound glands of a rounded form, the largest of them not ex- cseding the size of a split pea ; and they open into the mouth by distinct orifices. Between the buccinator muscle and the mucous membrane of the cheek, by which it is lined in its whole extent, are the buccal glands, similar to the labial glands, but smaller. Two or three glands, larger than the rest, found between the masseter and buccinator muscles, and opening by separate ducts near the last molar tooth, are called the molar glands. The duct of the parotid gland also opens upon the inner surface of the cheek, opposite to the second upper molar tooth. Immediately within the lips and cheek, are the dental arches, consisting of the teeth, gums, and maxillse. The jaw-bones, the articulation and move- ments of the lower maxilla, and the muscles used in mastication, are else- where described. The gums (gingivse) are composed of a dense fibrous tissue, connected very closely with the periosteum of the alveolar processes, and covered by a red and highly vascular but not very sensitive mucous membrane, which is smooth in its general surface, but is beset with fine papillae in the immediate vicinity of the teeth. THE TEETH. In the human subject, as in mammalia generally, two sets of teeth make their appearance in the course of life, of which the first constitutes the tem- porary, deciduous, or milk teeth, whilst the second is named the permanent set. The temporary teeth are twenty in number, ten in each jaw, and the permanent set consists of thirty two, sixteen above and sixteen below. Deficiencies in the number of the teeth sometimes occur, and the number is frequently increased by one or more supernumerary teeth. These are usually small, and pro- vided with only a single fang ; and, though generally distinct, they are sometimes attached to other teeth : they occur more frequently near the front than the hinder teeth, and are more often met with in the upper than in the lower jaw. General Characters of the Teeth. — Every tooth consists of three portions, viz., one which projects above the gums and is named the body or crovin, — another which is lodged in the alveolus or socket, and constitutes the root or fang, — and a third, intermediate between the other two, and, from being more or less constricted, named the cervix or neck. The size and form of each of these parts vary in the different kinds of teeth. The roots of all the teeth are accurately fitted to the alveoli of the jaws, in which they are implanted. Each alveolus is lined by the periosteum, which also invests the contained fang as high as the cervix. This dental perios- teum, sometimes named the periodontal membrane, is blended with the dense and slightly sensitive tissue of the gums, which closely surrounds the neck of the tooth. The roots of all the teeth taper from the cervix to the point, and this form, together with the accurate adjustment to the alveolus, has the effect of distributing the pressure during use over the whole socket, and of preventing its undue action on the apex of the fang through which the blood-vessels and nerves enter. The thirty-two permanent teeth consist of four incisors, two canines, four bicuspids, and six molars in each jaw. The twenty temporary teeth are four incisors, two canines, and four molars above and below. There are FORM OF PERMANENT TEETH. INCISORS. 781 no bicuspids among the temporary teeth, but the eight deciduous molars are succeeded by the eight bicuspids of the permanent set. The relative posi- tion and arrangement of the different kinds of teeth in the jaws may be expressed by the following formula, which also exhibits the relation between the two sets in these respects : — Temporary teeth Permanent teeth ( Upper Lower MO. CA. IN. CA. MO. 21412 =10 . ^^_____ = 20 21412 =10 MO. BI. CA. IN. CA. BI. MO. Upper 321412 3 = 16 = 32 (Lower 321412 3 = 16 Special Characters of the Permanent Teeth. — The incisors, eight in number, are the four front teeth in each jaw, and are so named from being adapted for cutting or dividing the soft substances used as food. Their crowns are chisel-shaped, and have a si arp horizontal cutting edge, which by continued use is bevelled off behind in the upper teeth, but in the lower teeth is worn down in front, where it comes into contact with the overlapping edges of the upper teeth. Before being subjected to wear, the horizontal edge of each incisor tooth is serrated or marked by three small prominent points. The Fig. 538. Fig. 538. — INCISOR TEETH OP THE UPPER AND LOWER JAWS. «, front view of the upper and lower middle incisors ; 6, front view of the upper and lower lateral incisors ; c, lateral view of the upper and lower middle incisors, showing the chisel shape of the crown ; a groove is seen marking slightly the fang of the lower tooth ; d, the upper and lower middle incisor teeth before they have been worn, showing the three pointed pro- jections of the cutting edge. anterior surface of the crown is slightly convex, and the posterior concave. The fang is long, single, conical, and compressed at the sides, where it sometimes though rarely presents a slight longitudinal furrow. The lower incisor teeth are placed vertically in the jaw, but the corre- sponding upper teeth are directed obliquely forwards. The upper incisors are, on the whole, larger than the lower ones. In the upper jaw the central incisors are larger than the lateral ; the reverse is the case in the lower jaw, the central incisors being there the smaller, and being, moreover, the smallest of all the incisor teeth. The canine teeth (cuspid ati), four in number, are placed one on each side, above and below, next to the lateral incisors. They are larger and stronger than the incisor teeth. The crown is thick and conical, convex in front and hollowed behind, and may be compared to that of a large incisor 782 ORGANS OF DIGESTION. tooth the angles of which have been removed, so as to leave a single central point or cusp, whence the name cuspidate applied to these teeth. this, as thrown Fig. 539. Fig. 539. —CANINE TOOTH OP THE UPPER JAW. a, front view ; &, lateral view, showing the long fang grooved on the side. The point always becomes worn down by use. The fang of the canine teeth is single conical, and com- pressed at the sides : it is longer than the faDgs of any of the other teeth, and is so thick as to cause a corresponding prominence of the alveolar arch : on the sides it is marked by a groove, an indication, as it were, of the cleft or division which appears in the teeth next following. a The upper canines, popularly called the eye-teeth, are larger than the lower, and in consequence of well as of the greater width of the upper range of incisors, they are a little farther outwards than the lower canine teeth. In the dog- Fig. 540. Fig. 541. Fig. 540. — FIRST BICUSPID TOOTH OF THE UPPER AND LOWER, JAWS. a, front view; 5, lateral view, showing the lateral groove of the fang, and the tendency in the upper to division. Fig. 541. — FIRST MOLAR TOOTH OF THE UPPER AND LOWER, JAWS. They are viewed from the outer aspect. tribe, and in the carnivora gene- rally, these teeth acquire a great size, and are fitted for seizing and killing prey, and for gnawing and tearing it when used as food. The bicuspids (bicuspidati), also called premolars, are four in each jaw ; they are shorter and smaller than the canines, next to which they are placed, two on each side. The crown is compressed before and behind, its greater diameter being across the jaw. It is convex, not only on its outer or labial surface, like the preceding teeth, but on its inner surface also, which rises vertically from the gum : its free extremity is broader than that of an incisor or canine tooth, and is surmounted by two pointed tubercles or cusps, of which the external one is larger and higher than the other. The fang is also flattened, and is deeply grooved in all cases, showing a tendency to become double. The apex of the fang is generally bifid, and in the first upper bicuspid the root is often cleft fora considerable distance; but the bicuspid teeth are very variable in this respect, and may be, all four, free from any trace of bifidity of the root. The upper bicuspids are larger than the lower ones, and their cups are more deeply divided. Sometimes the first lower bicuspid has only FORM OF PERMANENT TEETH. MOLARS. 783 one tubercle distinctly marked, i. e., the external, and in that case approaches in figure to a canine tooth. The molar teeth, true or large molars, or multicuspid teeth, are twelve in number, and are arranged behind the bicuspid teeth, three on each side, above and below. They are distinguished by the large size of the crown, and by the great width of its grinding surface. The first molar is the largest, and the third is the smallest, in each range, so as to pro- duce a gradation of size in these teeth. The last molar in each range, owing to its late appearance through the gums, is called the wisdom- toothy dens sapientise. The crowns of the molar teeth are low and cuboid in their general form. Their outer and inner surfaces are convex, but the crowns are rather flattened before and behind. The grinding surface it nearly square in the lower teeth, and rhomboid al in the upper, the corners being rounded off : it is not smooth, but is provided with four or five trihedral tubercles or cusps (whence the name of multicuspidati), sepa- rated from each other by a crucial depression. The upper molars have four cusps situated at the angles of the masticating surface ; of these the internal and anterior cusp is the largest, and is frequently connected with the posterior external cusp by a low oblique ridge. In the upper wisdom- teeth, the two internal tubercles are usually blended together. The crowns of the lower molars, which are larger than those of the upper, have five cusps, the additional one being placed between the two posterior cusps, and rather to the outer side : this is especially evident in the lower wisdom- teeth, in which the crown is smaller and rounder than in the others. The fangs of all the molar teeth are multiple. In the two anterior molars of the upper jaw, they are three in number, viz. two placed externally, which are short, divergent, and turned towards the antrum of the superior max- illa ; and a third or internal fang, which is larger and longer, and is directed towards the palate, the posterior border of which extends as far back as that of the posterior external fang. This third fang is often slightly grooved, especially when the two internal cusps are very distinct, and sometimes it is divided into two smaller fangs. The two anterior molars of the lower jaw have each two fangs, one anterior, the other posterior, which are broad, compressed, and grooved on the faces that are turned towards each other, as if each consisted of two fangs fused together : they have an inclination or curve backwards in the jaw, and are slightly divergent, or sometimes parallel, or even nearly in contact with each other : more rarely one or both of them is divided into two smaller fangs. In the wisdom-teeth of both jaws the fangs are often collected into a single irregular conical mass, which is either directed backwards in the substance of the jaw, or curved irregu- larly : this composite fang sometimes shows traces of subdivision, and there are occasionally two fangs in the lower tooth and three in the upper. The bicuspid and the molar teeth, from the breadth and uneven form of their crowns, are fitted for bruising, crushing, and grinding the food in mastication. The range of teeth in each jaw forms a nearly uniform curve, which is not broken by any intervals, as is the case in the dental apparatus of many animals, even in the Quadrumana. The upper dental arch is rather wider than the lower one, so that the teeth of the upper jaw slightly overhang those of the lower. This is owing principally to the fact that the lower teeth are placed either vertically, as in front, or are inclined somewhat inwards, as is seen behind and at the sides, while the corresponding teeth of the upper jaw have an inclination forwards in front, and outwards 784 ORGANS OF DIGESTION. behind. While there is a slight diminution in the height of the exposed parts of the teeth from the incisors backwards to the wisdom-teeth, there is in man a general uniformity in the amount of projection of the crowns throughout the whole series. In consequence of the large proportionate breadth of the upper central incisors, the other teeth of the upper jaw are thrown somewhat outwards, so that in closure of the jaws the canine and bicuspid teeth come into contact partly with the corresponding lower teeth and partly with those next following ; and in the case of the molar teeth, each cusp of the upper lies behind the corresponding cusp of the lower teeth. Since, however, the upper wisdom-teeth are smaller than those below, the dental ranges terminate behind nearly at the same point in both jaws. The Milk-teeth. — The temporary incisor and canine teeth resemble those of the permanent set in their general form ; but they are of smaller dimen- sions. The temporary molar teeth present some peculiarities. The hinder of the two is much the larger ; it is the largest of all the milk-teeth, and is larger even than the second permanent bicuspid, by which it is afterwards replaced. The crown of the first upper milk molar has only three cusps, Fig. 542. Fig. 542.— MILK TEETH OP THE RIGHT SIDE OF THE UPPER AND LOWER JAWS. a, the incisors ; 6, the canines ; c, the molar teeth. two external and one internal ; that of the second has four distinct cusps. The first lower temporary molar has four cusps, and the second five, of which in the latter case three are external. The fangs of the temporary molars resemble those of the permanent set, but they are smaller, and are more divergent from the neck of the tooth. Structure. — On making a section of a tooth, the hard substance of which it is composed is found to be hollow in the centre. The form of the cavity bears a general resemblance to that of the tooth itself : it occupies the interior of the crown, is widest opposite to or a little above the neck, and ex- tends down each fang, at the point of which it opens by a small orifice. In the crown of the incisor teeth the cavity is prolonged into two fine linear canals, which proceed one to each corner of the crown ; in the bicuspid and molar teeth it advances a short distance into each cusp. In the case of a root formed by the blending of two or more fangs, as occurs occasionally in the wisdom-teeth, each division has a separate canal prolonged down to its apex. STRUCTURE OF THE DENTINE. 785 The central cavity of a tooth is called the pulp-cavity, because it is occupied and accurately filled by a soft, highly vascular, and sensitive substance, Fig. 543. Fig. 543. — SECTIONS OP AN INCISOR AND MOLAR TOOTH. The longitudinal sections show the whole of the pulp-cavity in the incisor and molar teeth, its extension upwards within the crown and its prolongation downwards into the fangs with the small aperture at the point of each ; these and the cross section show the relation of the dentine and enamel. called the dental pulp. This pulp con- sists of areolar filaments, amongst which numerous nuclei and cells are rendered visible by the action of acetic acid. It is well supplied with vessels and nerves, which are derived from Fig. 544. — MAGNIFIED LONGITUDINAL SECTION OF A Fig. 544. BICUSPID TOOTH (after Ketzius). 1, the ivory or dentine, showing the direction and pri- mary curves of the dental tubuli ; 2, the pulp-cavity with the small apertures of the tubuli into it ; 3, the cement or crusta petrosa covering the fang as high as the border of the enamel at the neck, exhibiting lacunae ; 4, the enamel resting on the dentine ; this has been worn away by use from the upper part. the internal maxillary artery and the fifth pair, and which enter the cavity through the small aperture at the point of each fang. The solid portion of the tooth is composed of three distinct substances, viz. the proper dental substance, ivory or dentine, the enamel, and the cement or crusta petrosa. The dentine constitutes by far the larger part of the hard substance of a tooth ; the enamel is found only upon the exposed part or crown ; and the cement covers with a thin layer the surface of the implanted portion or fang. A fourth variety of tissue, osteodentine, is formed within the dentine, at the expense of the pulp, as age advances. A. The dentine, (Owen,) forming the principal mass or foundation of the body and root of a tooth, gives to both of these parts their general form, and immediately encloses the central cavity. It resembles very compact bone in its general aspect and chemical relations, but is not identical with it in structure, or in the exact proportions of its earthy and animal constituents. According to the analyses of Berzelius and Bibra, the dentine of human teeth consists of 28 parts per cent, of animal, aud 72 of earthy matter. The former is resolvable into gelatin by boiling. The composition of the latter, according to Bibra, is as follows, viz. , phosphate of lime 66 '7 per cent., carbonate of lime 3 '3, phosphate of magnesia and other salts, including a trace of fluoride of calcium, !• 8. Berzelius found 5 *3 carbonate of lime. 3 F 786 THE TEETH. Examined under the micro- scope, dentine is seen to consist of an immense number of very fine tubes, imbedded closely together in a hard intertubular matrix, and having the appear- ance of possessing distinct parie- tes. These dental tubules open at their inner ends into the pulp- cavity, the wall of which pre- sents very numerous minute ori- fices over the whole of its inner surface. Fruin thence they pass in a radiated manner Fig. 545. — SECTIONS OP DENTINE (from Kolliker). A, highly magnified cross sections of the tubuli of dentine. ±f-. a, from a part in which the tubuli are very closely set ; b, from a part where they are widely set. B, longitudinal section of the root. 2fQ a, the dental tubes near the inner surface of the dentine with few tubuli ; 6, subdivision of tubuli ; c, looped disposition of the tubuli ; d, granular layer consisting of small dental glo- bules at the margin of the dentine ; e, lacunas of the cement, one of them connected by tubuli with those of the dentine. through every part of the ivory towards its periphery. In the upper portion of the crown they have a vertical direction ; but towards the sides, and in the neck and root, they become gradually oblique, then hori- zontal, and are finally even in- clined downwards towards the point of the fang. The course of the tubules is not straight, but each describes, in passing from the central to the peri- pheral part of the dentine, two or three gentle curves' (primary curvatures, Owen), and is be- sides bent throughout its whole length into numerous fine undu- lations, which follow closely one upon another ; these are the secondary curvatures. The cur- vatures of adjacent tubules so THE DENTAL TUBULES. 787 far correspond, that the tubes are on the whole nearly parallel, being only slightly divergent as they pass towards the surface ; and as they divide several times dichotomously, and at first without being much diminished in size, they continue to occupy the substance of the dentine with nearly equi- distant tubes, and thus produce, when seen in fine sections of the tooth made parallel to their course, a striated appearance, as if the dentine were made up of fine parallel fibres. The concurrence of many of these parallel curvatures of the dental tubuli produces, by the manner in which they reflect the light, an appearance of concentric undulations in the dentine, which may be well seen with a low magnifying power. This, however, is not to be confounded with another set of curved marks called contour lines, which depend on conditions of the matrix, and will be afterwards described. The average diameter of each tubule near its inner and larger end is -j^^th of an inch, and the distance between adjacent tubules is about two or three times their width. (Retzius.) From their sides numerous immeasurably fine branches are given off, which penetrate the hard iutertubular substance, where they either anastomose or terminate blindly. These lateral ramuscles are said to be more abundant in the fang. Near the periphery of the ivory they are very numerous, and, together with the main tubules themselves, which there, by rapid division and subdivision, also become very fine, ter- minate by joining together in loops, or end in little dilatations, or in the cells of the granular layer to be described. The dental tubules, when highly magnified, appear like dark lines against transmitted light, but are white when seen upon a black ground. Their tubular character is proved by the fact that ink, or other coloured fluids, together with minute bells of air, can be made to pass along them, in sec- tions of dry teeth. Their walls, in transverse sections, may often appear thicker than they are in reality, owing to a certain length of the tubes being seen in the section : but if the orifice of the canal be brought exactly into focus, the wall appears as only a very thin, yellowish border ; and, indeed, Kolliker denies the existence of any wall distinct from the matrix. From the researches of Nasmyth, Tomes, and Kolliker, it appears that in the recent state the tubules are filled with substance (dental fibres), continuous with the pulp of the tooth : and it is suggested by Tomes that this is not only subservient to the nutrition of the dentine, but probably also confers on it a certain degree of sensibility. It has been noticed, indeed, that the dentine is more sensitive near the surface than deeper in its substance, — a fact not easily intelligible on the supposition that the sentient tissue is confined to the pulp-cavity. In the temporary, and sometimes even in the permanent teeth, the tubules are constricted at short intervals, so as to present a moniliform character. The terminal branches of tubules are occasionally seen to pass on into the cement which covers the fang, and to communicate with the small ramified canals of the characteristic lacunas found in that osseous layer. Tubules have likewise been observed by Tomes passing on into the enamel, more especially in the teeth of marsupial animals, but in a less marked degree in human teeth. The intertubular substance is translucent. The animal matter which remains in it, after the earthy matter has been removed by an acid, exhibits a tendency to tear in the direction of the tubules, but is in reality a homogeneous substance, deposited in a laminated manner. This was shown by Sharpey, who observed that in the softened teeth of the cachalot or sperm-whale the animal substance was readily torn into fine lamellae, disposed parallelly with the internal surface of the pulp-cavity, and there- * 3 F 2 788 THE TEETH. fore across the direction of the tubules. In these lamellse the sections of the tubules appeared as round or oval apertures, the lamellae having the same relation to the tubules as those of true bone to the canaliculi. The same tendency to lamination may be exhibited by boiling a longitudinal section of tooth with caustic potash, after which it presents closely set, short, and regular fissures, lying at right angles to the tubules, throughout the extent of the dentine. (Cleland.) Fu. 546. ~e Fig. 546. — VERTICAL SECTION OP THE UPPER PART OF AN INCISOR TOOTH (from Kol- liker). f a, the pulp-cavity ; b, dentine or tubular substance ; c, arched contour lines with inter- globular spaces ; d, cement ; e, cuamel with an indication of the direction of the columns ; /, coloured lines of the enamel. Fig. 547. — A SMALL PORTION OP THE DENTINE WITH INTEHGLOBULAR SPACES (from K61- liker). 3f 6, the tubules ; c, the interglobular spaces filled with air. A laminated structure of a more distinct description has been observed in the dentine of the crown, giving rise to the appearances in longitudinal sections termed contour lines. Czermak states that transverse sections of the tooth present concentric lines resembling the year-rings of wood : and Salter has shown that decalcified specimens readily break up in these lines ; the crowns of the teeth consisting of a series of superimposed hollow cones : the intervals between their strata, in longitudinal sections, appearing as contour markings, in transverse sections as annular lines ; in both cases corresponding with the surface of the pulp, as it existed during the forma- tion of the tooth. The contour markings, when examined with the micro- scope, are seen to be caused by irregularities of the intertubular tissue, which, opposite these marks, presents the appearance of spaces or clefts bounded by globular masses of the ordinary tubular and dense substance. These globules vary in size from -^oth to TQ^TTO^ °f an *ncn 5 tne largest being in the crown, the smallest in the fang. The tubuli pass through these globules, and appear to be continuous in direction across the interspaces from one globule to another. STRUCTURE OF THE EXAMEL, 789 Another kind of irregularity in the structure of the dentine gives rise to the granular layer of Purkinje ; the peculiarity of which consists in the presence of a number of minute cell-like cavities, which break up the uniformity of the matrix, and by branches anastomose one with another and receive terminations of dental tubuli. They are found principally in a layer beneath the cement, and also beneath the enamel. The circum- stance of their forming connections with the tubules points to a difference in nature between these cavities and the much larger iuterglobular spaces. The surface of the dentine where it is in con- tact with the enamel is marked by undulating grooves and ridges, and also by numerous minute hexagonal depressions, to which the microscopic fibres of the enamel are accurately adapted. B. The enamel is that hard white covering which encrusts and protects the exposed portion or crown of a tooth. It is the hardest of all the dental tissues, but it is gradually worn down by protracted use. It is thickest on the grinding surface and cutting edges of the teeth, and be- comes gradually thinner towards the neck, where it ceases. Its extent and thickness are readily Fig. 548. — THIN SECTION OF THE ENAMEL AND A PART OF THE DENTINE (from Kb'lliker). rf° a, cuticular pellicle of the enamel ; 6, enamel-fibres or columns with fissures between them and cross striae ; c, larger cavities in the enamel communicating with the extremities of some of the tubuli (d). seen on charring the tooth, by which the dentine becomes blackened, whilst the enamel, owing to the very small quantity of animal matter in its composition, remains white. According to Bibra it contains of earthy constituents 96 '5 per cent., viz. phosphate of lime with traces of fluoride of calcium 89 '8, carbonate of lime 4 -4, phosphate of magnesia and other salts 1'3 ; and has only 3-5 per cent, of animal matter. Berzelius, however, gives the proportion of carbonate of lime as 8, and of animal matter as only 2 per cent. The enamel is made up entirely of very hard and dense microscopic fibres or prisms, composed almost wholly of earthy matter, arranged closely to- gether, side by side, and set by one extremity upon the subjacent surface of the dentine. On the summit of the coronal portion of the tooth these enamel fibres are directed vertically, but on the sides they are nearly hori- zontal. As seen in a section they are disposed in gently waving lines, parallel with each other, but not so regular as the curvatures of the tubuli of the dentine, with which they have no agreement. The concurrence of these parallel curvatures produces, as in the case of the dentine, an appear- ance of concentric undulations in the enamel, which may be seen with a lens of low power. A series of concentric lines is likewise to be seen crossing the enamel fibres, as the contour lines cross the dentine : these are termed coloured lines from their brown appearance, but they seem rather to depend on lamination than on pigmentary deposit. Minute fissures not unfrequently exist in the deep part of the enamel, which run between 790 THE TEETH. clusters of the fibres down to the surface of the dentine ; and other much larger and more evident fissures are often observed leading down from the depressions or crevices between the cusps of the molar and premolar teeth. The surface of the enamel, especially in the milk-teeth, is marked by transverse ridges, which may be distinguished with a common magnifying glass. Fig. 549. Fig. 549.— ENAMEL FIBRES (from Kolliker). sf° A, fragments and single fibres of the enamel, isolated by the action of hydrochloric acid. B, surface of a small fragment of enamel, showing the hexagonal ends of the fibres. The enamel-fibres have the form of solid hexagonal prisms. Their dia- meter varies slightly, and is ordinarily about j^o^th of an inch. They are marked at small intervals by dark transverse lines. According to Tomes, the fibre is not in all cases solid, but has occasionally an extremely minute cavity in part or in the whole of its length, which is best seen in newly- developed enamel, but is also visible in adult teeth. The inner ends of the prisms are implanted, as it were, into the minute hexagonal depressions found on the surface of the dentine, whilst the outer ends, somewhat larger in diameter, are free, and present, when examined with a high magnifying power, a tesselated appearance. When submitted to the action of dilute acids, the enamel is almost entirely dissolved, and leaves scarcely any discernible traces of animal matter. Near the deep surface this is rather more abundant, according to the observations of Retains, who conceived that it there aided in fixing the enamel fibres. By the action of an acid, the enamel of newly formed or still growing teeth may be broken up, and its structural elements more easily distinguished. The prisms are then found to have interposed between them a delicate membranous structure, forming sheaths in which the cal- careous matter is deposited. As this latter accumulates, the membranous structure becomes almost or entirely obliterated, and the now earthy prisms are inseparably consolidated. Each membranous sheath, according to Tomes, contains a line of granular cells or masses, arranged in single series like the sarcous elements in muscular fibres, and thus occasioning the transverse markings. STRUCTURE OF THE CEMENT. 791 It is also found, on treatment with acid, that a very thin membrane called by Kolliker "cuticle of the enamel," — and by Busk and Huxley " Nasmyth's membrane, " (after its discoverer), entirely covers the enamel upon its outer surface. This membrane, which is calcined in the natural state, forms a protective covering to the enamel. Berzelius and Retzius say that a similar membrane also exists between the enamel and the dentine, but Kolliker has been unable to find any in that situation. c. The crusta petrosa or cement is the third substance which enters into the formation of the teeth. This is a layer of true bone, slightly modified in structure, and investing that part of the dentine which is not protected by the enamel. It covers the whole fang, towards the lower end of which it becomes gradually thicker, and is especially developed at the apex, and along the grooves of the compound fangs. Besides this, the calcified mem- brane or cuticle on the surface of the enamel has been regarded by various writers as a coating of cement iu that situation, the representative of the coronal cement on the compound teeth of many herbivorous animals. As life advances, the cement generally becomes thicker, especially near the apex of the fang, where it sometimes blocks up the orifice leading into the pulp-cavity. The crusta petrosa contains cells and canaliculi resembling those of bone ; they are placed lengthwise around the fang, and give off minute radiated ramifications, which are often found to proceed from one side only of a cell, towards the periodontal surface (Tomes). In the deeper layers of the cement the fine canaliculi sometimes anastomose with some of the terminal tubules of the subjacent dentine. Where the cement is very thick it may contain vascular canals, analogous to the Haversian canals of bone. On the deciduous teeth the cement is thinner, and contains fewer cells. It has been shown by Sharpey that perforating fibres, similar to those of ordinary bone, run abundantly through the cement. In chemical composition it resembles bone, and contains 30 per cent, of animal matter. The cement is, according to some, extremely sensitive at the neck of the tooth, if it be exposed by Fig. 550. — SECTION OP A PORTION OP THE DENTINE AND CKMENT FROM THE MIDDLE OF THE ROOT OP AN INCISOR TOOTH (from Kolliker). 3f° a, dental tubuli ramifying and terminating, some of them in the interglobular spaces (b and c), which resemble somewhat bone-laeunse ; d, inner layer of the cement witl\ numerous closely set canaliculi ; e, outer layer of cement; /, lacunce ; y, canaliculi. 792 THE TEETH. retraction of the gum. By its connection with the surrounding mem- branous structures it contributes to fix the tooth in the socket. It is the seat of the bony growths or exostoses sometimes found upon the teeth. D. Osteodentine (Owen), secondary dentine (Tomes), or the horny substance of Blumenbach, is a hard substance which begins to be deposited on the inner surface of the dentine after the age of twenty years or later, so that the central cavity of a tooth becomes gradually diminished in size, whilst the pulp slowly shrinks or disappears. This additional substance, formerly regarded as an extension of the cement into the interior of the tooth, has been shown to have a distinct structure, in part resembling dentine, and in part bone. It is traversed by canals, which contain blood-vessels, and are surrounded by concentric lamellae, like the Haversian canals of bone. From these canals, numerous tubules radiate in all directions, larger than the canaliculi of bone, resembling, in this respect, and also in their mode of ramification, the tubes of the dentine. This newly added structure may or may not coalesce with the previously formed dentine ; it appears to be pro- duced by a slow conversion of the dental pulp. Among special works on the teeth may be noticed, Retzius, in Muller's Archiv, 1837; Nasmytk, Researches on the Teeth, 1839; Owen, Odontography, 1840-45; Tomes, Lectures on Dental Physiology and Surgery, 1848, also in the Phil. Transactions, 1849 and 1850, and in Quart. Journ. of Micr. Science, 1856; Salter, in Quarterly Journal of Microscopic Science, 1853, in Guy's Hospital Reports, third series, vol. i. ; and in Trans. Path. Soc., 1854 and 1855 ; Czermak in Zeitschrift fur wissensch. Zoologie, 1850; Huxley in Quarterly Journal of Microscopic Science, 1853. DEVELOPMENT OP THE TEETH. Although the general phenomena of the growth and succession of the teeth had received considerable attention from various anatomists, the ob- servations of Arnold and Goodsir, made independently of each other, more especially the latter, were the first to give precision to our knowledge concerning their origin and the earlier stages of their formation. More recent researches have, it is true, shown that their account of the primor- dial condition of the dental germs may require some modification ; but nevertheless these authors were the first to establish the primordial con- nection of the teeth with the mucous membrane covering the edges of the maxillary arches, and Goodsir was the first to give a consistent view of the earlier steps of the formative process in the temporary and permanent series of teeth. (Arnold in Salzbtirger Med. Zeitung, 1831 ; Goodsir in Edin. Med. and Surg. Journal, 1839.) The changes which take place in the bones of the jaws relate only to the formation of the sockets of the teeth. In their earliest condition these bones present no appearance of alveoli, but, concurrently with certain changes in the mucous membrane, to be immediately described, a wide groove is developed aloi.'g the edge of the jaw, which gradually becomes deeper, and is at length divided across by thin bony partitions, so as to form a series of four-sided cells. These bony septa are not distinctly formed until near the fifth month of foetal life. By the subsequent growth of the bone, these cavities or loculi are gradually closed round, except where they remain open at the edge of the jaw. By the end of the sixth month they are distinctly formed, but continue afterwards, in proportion to the growth of the teeth, to increase in size and depth, by the addition of new matter which widens and deepens the jaw. The first stages in the development of the teeth, as observed by Arnold and Goodsir, consist of certain changes in the mucous membrane cover- DEVELOPMENT OF THE TEETH. 793 ing the borders of the maxilloe. About the sixth week of embryonic life, a depression or groove, having the form of a horse- shoe, appears along the edge of the jaw, in the mucous membrane of the gum ; this is the primitive dental groove (Goodsir), From the floor of this groove (supposed to be represented in a transverse section, in the diagrammatic figure 551,1) Fig. 551. /IS1 Fig. 551. — DIAGRAMMATIC OUTLINES OP SECTIONS THROUGH THE DENTAL GERMS AND SACS, AT DIFFERENT STAGES OF DEVELOPMENT (from Goodsir). 1, the primitive dental groove of the gum cut across in a foetus of about six weeks; 2, a papilla rising within the dental groove ; 3, 4, and 5, represent the follicular stage in which the papilla (or future tooth-pulp) is seen sunk within the follicle, and the lips of the follicle or opercula advancing towards each other gradually meet and close in the ful- licle; 5, may be looked upon as representing the section indicated by the line a b, in fig. 559, through the sac of an incisor tooth, in which a lunated depression (c) is left behind; in 6, the lips of the groove are seen to come together ; in 7, the union of the lips being complete, the follicle becomes a closed sac s, containing the dental pulp p, and having behind it the lunated depression c, now also enclosed, and forming the cavity of reserve for the germ of the corresponding permanent tooth ; in the remaining outlines, 8 to 12, are shown the commencement of the cap of dentine on the pulp, the subsequent steps in the formation of the milk tooth, and its eruption through the gum (11); also the gradual changes in the cavity of reserve, the appearance of its laminae and papilla, its closure to form the sac of the permanent tooth, its descent into the jaw, behind and below the milk tooth, and the long pedicle (12) formed by its upper obliterated portion. a series of ten papillae, as at 2, arise in succession in each jaw, and consti- tute the germs or rudimentary pulps of the milk-teeth. These pulps or papillae are processes of the mucous membrane itself, and not mere eleva- tions of its epithelium. The order in which they appear is very regular. The earliest is that for the first milk molar tooth : it is seen at the seventh week, as soon as the dental groove is formed ; at the eighth week that for the canine tooth appears ; the two incisor papillae follow next, at about the ninth week, the central one before the lateral ; lastly, the second molar papilla is visible at the tenth week, at which period this, the papillary stage of the rudiments of the teeth is completed. The papillae in the upper jaw appear a little earlier than those in the lower jaw. — In the next place, the margins of the dental groove become thickened and prominent, especially the inner one ; and membranous septa or prolongations of the mucous mem- brane pass across between the papillae from one margin to the other, so as to convert the bottom of the groove into a series of follicles, each containing one of the papillae. These changes constitute the follicular stage ; they take place in the same order as that in which the papillae make their appearance, and are completed about the fourteenth week. During the early part of this 794 THE TEETH. period the papillce grow rapidly, they begin to show peculiarities of form, and project from the mouths of the follicles. Soon, however, the follicles become deeper, so as to hide the papillae, which now assume a shape corresponding with that of the crowns of the future teeth. Small laminae or opercula of membrane are then developed from the sides of each follicle, their number and position being regulated, it is said, by the form of the cutting edges and tubercles of the coming teeth : the incisor follicles having two laminae, one external and one internal ; the canine, three, of which two are internal ; and the molars, four or five each. — The lips of the dental groove, as well as the opercula, now begin to cohere over the follicles from behind forwards, the posterior lip being very much thickened ; the groove itself ia thus Fig. 552. Fig. 552.— ENLARGED VIEW OP THE UPPER AND LOWER DENT\L ARCHES OP A FCETUS OP ABOUT FOURTEEN WEEKS. This specimen shows the follicular stage of develop- ment of all the milk teeth as described by Goodsir ; in each follicle the papilla is seen projecting ; but this exposure of the papillae and the cavity of the follicles probably arises from the accidental loss of the epithe- lial covering. gradually obliterated, the follicles are con- verted into close sacs, and the saccular stage of the milk-teeth is thus completed about the end of the fifteenth week. Certain lunated depressions, which are formed one behind each of the milk -follicles about the fourteenth week, escape the general adhesion of the lips of the groove. From these depressions, as will b'e afterwards described, the sacs of the ten anterior permanent teeth are subsequently developed. The first stages in the development of the teeth here described, the superficial origin and open condition of the dental sacs, and the free papillary commencement of the pulps, have been denied in recent years by Guillot, and by Robin and Magitot, who assert that the sacs with their contents make their first appearance in the submucous tissue, and are from the first closed sacs (Guillot in Annales des Sciences Naturelles, vol. ix., 1859; Robin and Magitot in Journal de la Physiologic, 1860, vol. iii., pp. 130 and 663). The observations of Kolliker, however, seem to furnish a clue to the explanation of what has been seen by these authors, at the same time that they con- firm, in its most important features, Goodsir's mode of viewing the phenomena. In the foetal lamb and calf, the first step in the formation of the tooth-germ, observed by Kolliker, consists in a depression of a part of the deepest layer of the epithelium into the subjacent mucous membrane. This depression, which, in common with Huxley, he regards as the commencement of the foetal structure known as the enamel organ, to be afterwards described, widens subsequently, so as to become flask-shaped, remaining connected with the deep surface of the epithelium by a narrow neck. In the next stage the dental papilla rising from the surface of the mucous membrane, projects into, or indents the deepest side of the epithelial process or future enamel organ, and the dental sac is formed at a somewhat later period in the surrounding substance of the mucous membrane. In these animals, therefore, the epithelium of the edge of the jaw covers in completely the enamel-germ or primary tooth-follicle. In man, Kolliker was unable to discover a similar arrangement, but found matters very much, in the disposition described by Goodsir; that is, the follicles open, situated in a dental groove of the jaw, and containing at their deepest part the dental papilke developed from the mucous membrane. But he conceives it not improbable that in Goodsir's specimens, as well aa in his own, the whole of the epithelium had been abraded, and that the follicles and papillae were thus unnaturally opened to the surface. ORIGIN OF THE DENTAL GERMS. 795 Fig. 553. — DIAGRAMS OF THE MODE OP ORIGIN OF THR DENTAL GEKM IN THE RUMINANT (after Kolliker). The three figures represent trans- Terse sections of the gum and a part of the jaw at or shortly after the period of the formation of the germ, and are designed chiefly to show the relation of the germ to the epithelium. A, represents the state in a very early condition, when the primitive deutal follicle of a milk or temporary tooth has been formed by a depression from the deep layer of the epithe- lium. B, represents a later stage, when the tooth-papilla has risen from the surface of the mucous membrane, and has inflected the primitive dental follicle. C, represents a more advanced stage in which the dental sac has begun to be formed. c, the superficial thick epithelium of the gum only sketched in outline ; c', the deep layer of cylindrical cells ; /, the primitive tooth -follicle ; /', its cel- lular or granular contents and cavity ; p, the dental papilla, and afterwards tooth-pulp ; e, the inner inflected layer of the wall of the primitive follicle forming the inner part of the enamel organ ; e', the outer wall of the same with the epithelial sprouts shooting into the tissue above ; s, the commencement of the dental sac ; fp, the follicle of the corresponding permanent tooth. Waldeyer has shown by more recent observations, that in the human embryo the teeth arise in a manner essentially the same as that described by Kolliker in the rumi- nant. (Waldeyer, lib. die Entwick.