"berkeieyN OF €ARTH aCIENCES IJBRARY ^V^ r r J/^. STRANGEWAYS' Veterinary Anatomy FOURTH EDITION REVISED AND EDITED BY I. VAUGHAN, F.L.S., F.Z.S., J-ELLOW OF, AND EXAMINER ON COMPARATIVE ANATOMY TO, THE ROYAL COLLEGE OF VETERINARY SURGEONS, LATE LECTURER ON ANATOMY AND ZOOLOGY AT THE NEW VETERINARY COLLEGE, EDINBURGH. NEW YORK WILLIAM R. JENKINS VETERINARY PUBLISHER AND BOOKSELLER 851 AND 853 Sixth Avenue 1904 8ClENCfi!9 LIBRARY ftu^ Ra.. U- supj X C^.<-\^^^>^ r^A^ TO ENGLISH-SPEAKIICC VETEKINARY STUDENTS, THIS, THE FOURTH EDITION STRANGEWAYS* ANATOHT IS DEDICATED NT IHB ESITOS. ivi'?749Sl r PREFACE TO FOURTH EDITION. The Third Edition of Strangeways* being exhausted, it is deemed advisable to issue a Fourth. The work has been very carefully read and considered, with the result that little or no material alteration has been made. The diction has occasionally been improved, and a few alterations and additions made in the nomenclature where such appeared necessary. Histology has become such a distinct branch of science, that the portions touching on that subject must, in a work like this, be somewhat brief and insufficient; but they have been modified and allowed to remain, as they may not prove altogether worthless. I trust that this Edition of the work will maintain the reputation acquired by its immediate predecessors. I. VAUGHiJN. JilDlNBURGH 29th April, 1892. PREFACE TO THE FIRST EDITION. On tho death of Professor Strangeways, there was a very genera! feeling chat his anatomical lectures should be given to the world. Working daily with him during my furlough, and being presex^ at his death-bed, I was solicited to take the matter in hand. His friend. Dr. Call, and I accordingly undertook to re-write and arrange the lectures. The late Professor Goodsir*s detached manuscript on the Myology of the Horse was, after an effectual search, discovered, and considerately placed in my hands by his brother, the Rev» Joseph Taylor Goodsir, F.R.S.E. It is believed this will enhance the value of the work, more especially os Strangeways was not oidy an ardent admirer of the great anatomist, but he informed me lis principal lectures had been perused and approved of by Professor Goodsir. Strangeways* lectures, although generally very complete and excellent, demanded an entire recasting. In doing so, I adopted Leyh's arrangement, which, with due regard to French and English veterinary anatomy, I selected as the best. Dr. Call, notwithstanding his many professional engagements^ has re-written the Osteology and the Anatomy of the Nervous System, the Eye, and the Ear. The Comparative Osteology, the Ligaments, Muscles, Digestive, Urinary, Sexual, and Respiratory Organs, and the Organs of Circulation, Lymphatics, Skin, and Hoof, have fallen to my lot. X PREFACE. Tt has been our object to produce what is greatly desiderated — a thorough-going Manual of Anatomy for the veterinary student. The photo-lithographs, with few exceptions, are selections from Leyh and Lecoq's classic?! works. To Dr. Morrison "Watson, Assistant Demonstrator of Anatomy in Edinburgh University, my thauks are due for his assistance in arranging them during my absence on the Continent. The Editors cordially thank Mr. Thomas H. Douglas, Photo- grapher, Chamberlain Road, for his handsome gift of the Vignette of his friend, which will be appreciated by all the Professor's former students. Messrs. Maclachlan & Stewart, the Publishers, deserve every praise for the generous manner in which they have undertaken the publication ; and Messrs. Waterston, Hanover Street, for the style of the photo-lithographs. To Professor Turner of Edinburgh University, and Mr. Joseph Johnston of Montrose, I am indebted for many valuable sug- gestions. The work owes no small measure of its completeness to the Kindly helping-hand of Dr. John Gray M'Kendrick, Assistant to the Professor of Physiology in the University of Edinburgh, who not only has been of immense service to me in the tedious work of proof correcting, but to whom the Editors are indebted for the complete Index and Gloissary which accompanies the work. The Appendices s|ieafc for themselves. The work would have been incomplete witfeoul^ a " dissection haanual," and a translation was accordingly' mads 'oif'Cliauveau's! directions, adopted because they are superior to^ny I am acquainted with. The Editors confidently commend the work to the veterinar*' studctit, farmer, stockbreeder, and to any and every one interested in dblnestic animals, inasmuch las the true pathological site of' ' disease is incidentally pointed out au courant With, the anatomical description. The Dentition Plates of the Horse, Cow, Sheep, and Dog afford a coup deceit which will be a reminder to the r PREFACE. XI adept, and a useful guide to the veriest tyro in the difficult subject of dentition as an index of age. It has been our effort to produce the work at the lowest remunerative rate commensurate with the interests of the deceased's family, to whom all benefit directly passes. Assured that the student will find in these pages a good quid pro quo investment, we leave it with him, ^along with Seneca's advice and the sententious rule given by Sir William Hamilton in an autograph letter — " Non multa sed multum." " Be more anxious to read attentively a* few than to read many works." J. WILSON JOHNSTON. KiNNABEB House, Uth September, 1869. PREFACE TO THE SECOND EDITION, The proprietor of Strange ways' Anatomy having resolved on issuing a new and revised edition of the work, placed the matter in my hands, with a carte blanche to do what I thought most advisable. This I have striTen to the best of my ability to do; whether successfully or not, the dictum of future students alone will decide, since for them the work is designed. Books on Anatomy seem naturally to divide themselves inta three classes — the exhaustive work for reference, the practical dissecting manual, and the current text-book. In the veterinaiy department of Anatomy, the first of these classes is represente 16 6. Skeleton of Horse, .| 18 7. Transverse vertebral segment. i 1 22 8. Cervical vertebrae articulated. 24 9. Cervical vertebra . . 25 . 10. Skull seen from above, 37 11. Inferior aspect of skull. 39 12. Lateral view of the skull. 41 13, Longitudinal section of the skull. 43 14. Inferior maxilla. 62 , 15. Bones of the hyoid series, 64 16. Bones of the carpus, .... 72 17. Bones of the carpus, metacarpus, and digit, . 73 18. Development of foot, . . , , 77 19. Phalanges disarticulated, 79 20. Lateral aspect of pelvis, 86 21. Posterior aspect of femur, 89 22. Bones of tarsus, . . . 94 23. Bones of tarsus, metatarsus, and digit, 1 96 23 XXIV TABLE OP ILLUSTRATIONS. no. 24. Posterior aspect of metatarsup, 25. Skeleton of Ox, 26. Skull of Ox, . . . 27. Cardiac bone of Ox, . 28. Skull of Boar, 29. Skeleton of Hog, 30. Section of Hog's skull, 31. Skeleton of Dog, 32. Bones of Digits compared, 33. Clavicle of Dog, 34. Clavicle of Cat, 35. Os penis of Dog, 36.' Skeleton of Bird, 37. Sternum of Bird, 38. Skull of Fowl, 39. Pectoral arch of Bird, 4a Pelvis of Bird, 41. Hyaline cartilage, 42. White fibrous tissue, . 43. Yellow elastic tissue, . 44. Adipose tissue, 45. Diarthrodial joint— diagram, 40. Odontoid and superior cor^mon ligaments, 47. Costo-vertebral articulation — lateral aspect, 48. Costo-vertebral articulation — superior aspect, 49. Temporo-maxillary articulation, 60. Hyoid articulations, . 51. Ligaments of elbow joint, 62. Ligaments of carpus — anterior, 53. Deep ligaments of carpus — external, 54. Deep ligaments of carpus — postero-intemal, 65. Superficial ligaments of carpus — posterior, 66. Sesamoidean and digital ligaments, . 57. Deep sesamoidean ligaments, 68. Navicular ligaments, . 69. Sacral and pelvic ligaments, . 60. Sacral and pelvic ligaments — inferior view, herical projection, supported by a roughened and constricted 'vix or neck. An ovoid convexity is called a condyle; and ften condyles are found in pairs, the articular surfaces of which may be continuous or separated. A trochlea is an^ articular surface presenting a pulley-like appearance. ^^^ Articular depressions. — A glenoid cavity is shallow, and may be cup-like, vt^hile a cavity is called cotyloid when it is deeper. The term facet is often applied to articular surfaces, which may be large, but are not well marked either as elevations or depressions. The rough irregularities of surface are more distinctly marked in the bones of the horse than in those of most other animals; their size is always proportionally greater in well-bred animals ; in heavy, coarsely-bred horses, which possess great strength but little activity, they are smaller in proportion to the absolute size of the bones. DEVELOPMENT OF BONE. Although the bones of the foal, calf, and young of many other large quadrupeds, possess greater solidity at birth than those of the human infant, yet they all pass through certain progressive stages of development before arriving at that degree of density which they ultimately possess. The tracing of future bone is recognised, about the seventh week of fcetal development, in local collections of soft, granular, gelatinous pulp, which becomes gradually flooded with nucleated cells, held together by an opaque, intercellular basis or matrix, which, with the cells equally dis- tributed through it, forms temporary cartilage — a material closely resembling in its properties ordinary gristle. The process of ossification, or conversion of cartilage into bone, begins at certain fixed points, and gradually spreads ; these points are called ossific centres, or points of ossification. When this conversion commeAces, that part of the cartilage about to become . ossified is permeated by large channels for the passage of the blood-vessels which convey the bone-earth ; and the cells, instead of being equally distributed throughout the matrix, become arranged in parallel groups, and increase in number, those nearest . the point of ossification enlarging. Matter, in the form of very minute granules, is now deposited in this column of intercellular or hyaline substance, as well as between each cell. Ossification of the cell walls ensues, which is followed by the absorption of the osseous matter between the cells, converting what was a row of closed cells into a tube, which is a rudiment- 16 OSTEOLOGY. ary Haversian canal, no trace being left of the nucleus of the original cartilage corpuscle ; but there are numerous very minute reddish' gi^anules, which almost fill the cavity, and are concerned in the form^-tion of blood-vessels, which now begin to appear. The oSsific . parietes of the cartilage cells lining the tube, at first thin, enlarge and thicken by successive layers of dense osseous matter, and thus produce the concentric lamellae, the lamella last formed pushing out the older one, until what was the lining of the tube becomes the external lamella of an Haversian system, while the ossific matter which was deposited in the column of intercellular material, becomes the connecting lamellae between the Haversian cylinders. In long bones this ossific process commences in the centre of Fia. 5. Section of ossifying cartilage magnified. On the left the ceils are becoming arranged in rows ; while to the rights between the rows, the earthy material is being deposited. the shaft, gradually spreading to the extremities, in which there are separate points of ossification ; there are generally three such points, one for the shaft, and one for euch extremity, the develop- ing shaft being called the diaphysis, the extremities the epiphyses. When any process is supera'dded, as the trochanter of the femur, \ which possesses a distinct point of ossification, it may be termed \&IL apophysis. As ossification commences in the shaft, there are ibr some time after birth, intervening portions of unossified ■ cartilage, marked by a deep ring in the dried long bones of young animals ; they disappear at variable periods, the portions of bone hitherto imperfectly united becoming consolidated into one firm mass. The bone increases in length by growth of the unossified ring, uniting the shaft and epiphysis, until the ring fills up, when growth is completed. Should an epiphysis unite with the diaphysis prematurely, by acceleration of the process of ossifi- cation through disease, growth being thus arrested, the bone will be shorter than its fellow. The shaft of a long bone increases in SKELETON OF THE HORSE. 17 circumference by deposits of new bone on its external surface, derived not from Cartilage, but from membrane — the. inner layer of the periosteum, which has been termed the osteogenic mcm- hrane. . In the periosteum there are two layers or strata — an outer, strong and fibrous ; an inner, soft^ and containing osteo- hlastic cells, which, after undergoing certain changes, produce layers of new bone ; the process is termed intramembranous,. as opposed to iutracartilaginous ossification. This goes on. till the bone has reached its full development, when Haversian systems cease to be formed, and then, as a climax, the peri- pheral lamellae, are formed, and the medullary canal enlarges by internal absorption. In flat bones, ossification usually radiates from a centre, and is directed by tlie membrane investing each surface of the bone; some of them possess numerous apophyses. Ossification is completed in some bones much earlier than in others, and at birth those which are required for support and progression are farthest advanced. The bones of the cranial vault are developed, not from carti- lage, but from membrane. In early foetal life the brain is covered by two membranes, closely united — viz., the pericranium and dura mater ; between these, bone becomes developed from radiating ossific centres. The Skeleton. The internal framework on which the animal body is built is termed the Endoskeleton, while the outer casing which deter- mines the shape and appearance of the animal is the ExosKELE- TON ; in som.e of the lower animals the latter assumes the form of a calcareous case, in others it is scaly, in others again, bony. The exoskeleton of the higher animals consists of the skin and its appended modifications, which will be described in a future sec- tion of the work. By the term skeleton is generally understood the endockeleton, or bones of an animal, held in their relative positions, or articulatecl by wires or screws, in which case all the soft tissues are first removed, and the preparation is termed an artificial skeleton : but if those soft structures, irhich, in the living animal, join the bones together, are allowed to remain, dried, and preserved, then the preparation is a natural skeleton. As the skeleton has two sides or halves, the "majority of the bones exist in pairs. There is, however, a central chain of single bones, formed by the back bonea or vertebras and the median c 18 OSTEOLOGY. Fig. 6. SKELETON OF THE HOESE (Soudungula). AilAL S;iEI,ETON. THE SKULL. Cranial Bones.— a. Occipital. 1; 6, Wormian, 1; c, Parietal, 2; d, Frontal, 2; c. Temporal, 2; Sphenoid. 1 ; Ethmoid. 1 ; Auditory ossicles.. 8. Faciei Bones.— h, Nasal, 2: g. Lachrymal. 2 ; /, Malar, 2 : i, Superior maxilla, 2; Ti, Prcmaxilla, 2 ; Palatine, 2 ; Pterygoid. 2 : Vomer. 1 ; Turbinals. 4 : I, Inferior maxilla.. 1 ; Hyoid (segments), 6. Teeth :— m. Incisors, 12 ; n. Canines, 4 ; o. Molars, 24. The Trunk.— p-v, Cervical vertebrse. 7: w. Dorsal vertebrae. 18; x, Lumbar vertebrae, 6; y. Sacrum, 1 ; r, Coccygeal vertebrae (variable), 18 ; a'a'. Ribs, 36 ; " Sternum (6-7 Stemebrae), 1 ; S Costal cartilages Appendioulab Skeleton. rECTOUAl LIMB. ', Iliam, 2 ; d'. Ischium, 2 ; (f. Pubis, 2. The Liinb.—jf, Femur, 2 ; 5*, Patella. 2 ; a". Tibia, 2 ; 6'', Fibula, 2. Tarsus :— «^, Calcaneum, 2 : except in the cervical region, where they project from the inferior central line of th-e bodies. The centra or bodies of the vertebrae, placed in natural apposition, thus form a central bony column, to v/hich the arches and processes are attached ; the arches, with their connecting ligaments, form superiorly a cavity, the spinal or neural canal. 'c^a^ Fig. 7. Diagramatic transverse sec- tion from the skeleton of a mammalian thocax, showins the chief features of a perfect vertebral segment. 1, Neural spine. 2,Lamina(neurapophy- Bis); 3, Pedicle; 4, Neural arch; 5. centrum; 6, Icferior Spine (hypapophysis) : 7 7, Haemal arch ; 8, Rib (pleurapophysis); 9, Costal cartilage (hsma. pophysis) ; 10, Stemebra , 11, Haemal spine. CERVICAL YERTEBB^. S# ^hich extends from the head to the tail, and contains the spinal- cord, with its membranes and blood-vessels; the articular pro- cesses strengthen the connections of the vertebrae, while the spinous afld transverse processes are levers to which muscles are attached, their development having great influence on' the physical conformation and capabilities of the animal The ribs may be regarded as continuations of the dorsal transverse processes ; they form the inferior or hasmal arch of their own region. FALSE VERTEBRiE. The false veriehrcB are found in the sacrum, which con- sists of vertebral segments united by the ossification of their connecting material, and in the coccyx, the skeleton of which consists of rudimentary or imperfectly-developed vertebne. The sacral segments in the early stages of life are separable, and they present all the characteristics of true vertebrae. CERVICAL VERTEBRA. General Features. (Fia. 8.) There are seven cervical vertebrce in all the Mammalia, with the exception of the Three-toed Sloth, which has nine, and one of the Sea-cows, which has six. They are numbered in order from the head, the first receiving the special name of atlas, and the second that of axis or vertebra dentata ; these, with the sixth and seventh, differ from the rest, which are essentially alike. The centra or bodies of the cervical vertebrae are larger and longer than those of any other true vertebrae, and frequently measure upwards of four inches in length ; they are quadrangular in shape, their anterior extremity or head being convex and some- what heart-shaped, with the apex downwards, while the posterior extremity presents a corresponding cup-like cavity. The flexi- bility of the neck is partly due to these convexities and cavities, which are more pronounced in the cervical region than in other parts of the column. The superior surface is flattened, and pre- sents, close to the pedicle on each side, a distinct furrow, which contains the spinal vein; these lateral furrows are united by 24 OSTEOLOGY. means of a central transverse furrow, and partly covered by a thin bony plate, to which the superior common ligament is attached. The inferior surface presents a longitudinal process or ridge, the inferior, spinous process, which increases in size as it approaches the posterior end of the bone, where it terminates in a projecting tuberosity, which gives attachment to the longus colli muscle. The lateral surfaces of the body, above the inferior spine, are flattened, and somewhat excavated. r CERVICAL VERTEBE^. 25 The superior spinous processes or neural spines are mostly rudiinentaxy, and rise from the centre of the quadrilateral space between the oblique processes. They are '^ bifid posteriorly, the ligamentum nuchse and spinalis colli muscle being attached in the bifurcation. The transverse processes, broad, short, strong, and irregular in shape, p^^ g pass directly outwards, and ^ divide ^^^^ ,^,^^^ ^^^ ^, ^ ^^^ ^^^ into two parts one projecting an- bra of a Horse, l, JCireural spine ; 2, An- . - . , , , , terior oblique processes; 3, Posterior terO-mienorly, and the Otner pOSterO- obUqueprocesses;5,Convexanteriorend, inferiorlv. TheV increase in size as and 9, concave posterior end of the cen. •' •' trum; 6,. Anterior ends of transverse pro- they extend backwards, and all of cesses; and 7, Posterior end of right one; ^j^ ihem, except the seventh, are 8, inferior process, or hypapophysls. ^ ' pierced by tho vertebral foramen, through which pass the verte- bral artery and vein. These processes give attachment to the serratus magnus, splenius, Ipngus colli, intransversalis colli, levator Jiumeri, and other muscles acting upon the head and neck. The articular processes, larger than in any other region, have flattened oval articular surfaces ; the anterior t^o look upwards and inwards, while the posterior look downwards and outwards. The articular processes of the posterior five cervical vertebrae give attachment to the complexus major, trachelo mastoideus, and spinalis colli muscles. The arches, stronger than in any other region, enclose the spinal canal, which progressively increases in size in the direction of the dorsal vertebrse, its vertical diameter being the greater. The notches of the three posterior cervical vertebras are also larger than the rest. Viewed in situ, it is seen that the transverse processes of the three central cervical vertebrae are largest and strongest, with the exception of that of the first, and they can be detected under the investing muscles in the living animal ; also that the bodies progressively diminish in length, and increase in breadth and depth from the second backwards. The first, second, sixth, and seventh cervical vertebrae havingj features peculiar to themselves, require special notice. iSi6 OSTEOLOGY. SPECIAL CERVICAL VERTEBRiE. The Atlas. The First cervical vertebra is called the Atlas, because in. iiuman anatomy it supports the head ; in quadrupeds the head k suspended from it. It presents no well-defined body, but consists of a strong ring of bone, the superior surface of which is convex, with a slight longitudinal elevation in the median line, from which the alee or wings slope downwards and backwards. The wings are large, flat transverse processes, wider than those of any other true vertebra, and they terminate in rough convex margins, which may be plainly felt through the skin in the living animal ; they give insertion to portions of the levator humeri, splenius, trachelo mastoideus, and obliquus capitis posticus muscles, and are always largely developed in the carnivora. Superiorly, each ala exhibits three foramina ; the posterior is the largest, and corresponds to the vertebral foramen, giving passage to the anastomotic branch of the occipital artery. The two anterior foramina are joined by a short, deep depression, the alar gutter ; the external foramen gives passage to the occipital artery, vein, and nerve, while the internal passes through the ring into the neural canal, representing the intervertebral foramen, and through it pass the cerebro-spinal artery, and the first spinal nerve. The inferior surface of the atlas is convex centrally, and presents posteriorly a short, obtuse eminence, which represents the inferior spine, this is the tubercle of the atlas to v^hich the tendon of the longus colli muscle is attached. On each side of the central convexity we find a large concave space limited exter- nally by the ala. The anterior surface presents two notches and two articular depressions. The notches are of great size, and , contain the superior and inferior suspensory ligaments — one being above, and the other below, the spinal canal. The arti- cular glenoid cavities receive tha condyles of the occipital bone, and are each constructed of a superior and an inferior continuous surface ; the inferior, r^resenting the convex head of other vertebrae, is concave ; while the superior, nearly flat, represents the oblique processes. A prominent bony ridge, to which is inserted the investing or capsiilar ligament, surrounds the anterior border of the bone. The posterior surface presents a somewhat THE DENTATA. 27 triangular outline ; its inferior margin is excavated to receive the odontoid process of the second vertebra, while the superior is thin, and roughened for ligamentous insertion, and, on each side, a broad slightly convex articular surface represents the posterior oblique processes. This surface is bounded externally by a i:idge, which gives insertion to the capsular ligament; and internally it is separated by a similar ridge from the spinal canal. The spinal foramen of the atlas is very large, in order that the spinal cord may be preserved from injury during the extensive potions which take place between the head and neck. Its floor is divided by a transverse ridge into two portions, the anterior of which is roughened for the attachment of ligaments, the posterior being smooth for the articulation of the odontoid process. Its roof is smooth, and penetrated by two foramina for the passage of an artery and nerves, and its sides have each an excavation in which a venous sinus is lodged ; a foramen from this excavation opens on the inferior surface of the ala, and transmits a vein from the sinus. The atlas has three articular processes, — two for the occipital condyles, and one for the axis, — all of which form true joints, the atlas being the only vertebra possessing none but true articulations. The Dentata, The Second vertebra is called also the axiSj because the head rotates upon it, also the vertebra dentata^ from a process which, in the corresponding human bone, somewhat resembles a tooth in shape, and is called the odontoid process ; it is situated on the anterior end of the centrum, projecting forwards into the ring of the atlas, and abound it the head and atlas rotate. In the horse the under surface of this process is smooth and rounded, and the upper roughened and excavated, for the attachment of the odontgidjigaments ; laterally, it terminates in a broad, oval, somewhat convex surface, which represents the oblique processes, and articulates with the posterior surface of the atlas ; these articular shoulders being bounded by a ridge, to which the capsular ligament is attached. The neural spine of the axis springs from a very strong arch, and is nearly as long as the body, which is longer than that of any other true vertebra ; this spine is convex, and consists of lateral halves, united anteriorly into a strong rough crest,. 28 OSTEOLOGY. but bifurcating posteriorly into ridges, which terminate m the oblique processes. The inferior spine arises from a notch in the inferior part of the odontoid process ; it is broad and rough anteriorly, but contracts into a sharp spine, which terminates in a roughened tubercle posteriorly. The transverse 'processes, the smallest in the cervical region, are single, and project outwards and backwards ; they are pierced by very small vertebral foramina. The spinal canal is somewhat narrow, and instead of notches, there are two oval foramina anteriorly for the passage of the spinal nerves. The posterior parts of the body and arch do not materially differ from those of the other cervical vertebrae. In the horse the atlas and axis do not approximate above the" spinal canal, and there is a considerable space between them, the atlo-axoid space, which is covered by soft structures only .; and here the operation of " pithipg" is, easily performed. The Two Last Segments. The Sixth vertebra has a much shorter body than those anterior to it, and is destitute of an inferior spine. Its trans- verse processes consist of three lateral divisions, and its vertebral foramina, notches and spinal canal are of great size. The Seventh vertebra, or Vertebra prominens, the shortest of the series, is very strong, and has an elevated neural spine, point- ing upwards and forwards, but scarcely the trace of an inferior one. Its oblique processes resemble the four preceding; its transverse processes are small, and have usually no vertebral fora- mina, while its notches and spinal canal are larger than in any other of the last six cervical vertebrae. On each side of its body, posteriorly, it presents a depression which, with a corre- sponding depression on the first dorsal centrum, forms a cup for the articulation of the first rib. Altogether it closely resembles in character the first dorsal vertebra, DORSAL VERTEBRA. (Pl. I. F.) These vertebrae, of which there are eighteen or rarely nineteen, always correspond in number with the pairs of ribs, and in the horse form the weight-bearing portion of the column, extending oyer the whole length of the chest. Their bodies, the smallest of the true vertebrsB, are short, thick, and somewhat semicircular DORSAL VERTEBRAE. 29 ia form, each presenting a middle ridge along its under surface, to which the inferior common ligament is attached. The superior surface of the body, which forms the floor of the spinal canal, is flattened and quadrilateral, presenting longitudinal furrows for the spinal vessels, and often a central transverse one, partially covered by a "bony plate. The anterior extremity presents a slightly convex head, on the superior and lateral aspect of which is a semicircular depression corresponding with another on the posterior extremity uf the vertebra in front, so that together they form a cup-shaped cavity for the articulation of a rib, each articu- lating with one-half of the head of the rib. The posterior extremity is concave, to articulate with the contiguous bone, and has on each side an articular depression similar to those on the anterior extremity. The transverse processes, rising from the sides of the arches, are small ; superiorly and anteriorly they are roughened for muscular attachment, and at its posterior inferior part, each presents a flat, smooth facet which articulates with the tubercle of the next anterior rib. The neural spines, larger than in any other region, vary much in size, shape, • and direction, the first twelve being directed backwards, the next three nearly upright, and the last tLree forwards ; their length gradually increases to the fifth, which is usually the longest, and then decreases to the fourteenth, which is generally somewhat shorter than those behind it ; the first is small and sharp, and the second, which is abruptly bent back- wards, is -^ery strong ; the summits of the next six or seven are flattened, roughened, and expanded laterally, assuming a bifid appearance, giving greater surface for the attachment of muscles and the great suspensory ligament of the head and neck, the ligamentum nwchce. The lateral surfaces are convex and slightly roughened, the anterior borders being thin and serrated, while the posterior, of the higher spines especially, are broad and concave, becoming cleft as they approach the oblique processes. The oblique processes are small, and their facets are more horizontal than in the cervical region, and closer together. The pedicles are short and strong, and, with the exception of the anterior four or five, possess notches on their posterior edges only ; backwards, we find these notches become more and more closed in, until posteriorly there are foramina in lieu of notches. The arch, and consequently the spinal canal, are small, the laminae passing almost directly inwards from the pedicles. I u'SO OSTEOLOGY. An ordinary dorsal vertebra has twelve articnlar surfaces — viz., three anterior and three posterior, as in the cervical, and three at each side ; of the latter, two are for the heads of two ribs, «ind the third for the tubercle of the anterior rib. The depres- sions for the heads of the ribs are deepest between the anterior vertebrae, and gradually grow shallower, in the two last becoming continuous with the facet on the transverse process. The eighteenth segment, being attached to but one rib on each side, has eight articulating surfaces only. Viewing the dorsal vertebrae in connection, it is seen that the spines diminish from the fifth backwards, and the vertebrae themselves grow narrower. The first exhibits some of the characters of a cervical vertebra, and the second has a short body, with transverse and anterior oblique processes formed on the same bony projection, and a neural spine, short, convex anteriorly, and more bent than any other in the vertebral chain. The first thirteen form the skeleton of the withers, and, when well developed, the height of their spines increases the surface for muscular attachment, and also affords greater leverage. ^^^ LUMBAR VERTEBRAE. L ^ ^^ (PL. LG.) ^-^ KrO"^^ These form the skeleton of the loins, and are shorter in the horse in proportion to his size, than! in other animals. Their number is six usually, sometimes five, in the horse, siz in the mule, generally five in the ass, and also, it is said in the Arab horse. Their bodies, intermediate in length between the cervical and the dorsal, are thick and strong, the three anterior being flattened superiorly and laterally, and possessing a strongly- developed median ridge ; the three posterior ones are convex laterally, and flattened above and below. More motion being required in the loins than in the back, the anterior extremities of the centra of the lumbar vertebrae are more convex, and the posterior extremities more concave than those in the dorsal region. The arches enclose a large semicircular spinal canal, and with one or two exceptions possess both anterior and posterior notches. The neural spines are strong, broad, and flattened laterally ; they incline slightly forwards, are about the same length as the posterior dorsal spine, and have sharp anterior and posterior THE SACRUM. SI edges, with rough expanded extremities ; they increase slightly in height, and diminish in strength backwards. The transverse processes, longer than the corresponding pro- cesses in any other region, are broad and flat with rounded extremities, and extend nearly horizontally from the bodies ; the central are tEe largest, the two first inclining a little back- wards, and the three last slightly forward. The last two of these processes articulate with each other by means of facets, and, in advanced age sometimes become united by ossification, the sixth articulating in a similar-, manner with the sacrum. The obliqice processes project farther from the arch than those of the dorsal region ; the articular facets of the anterior ones are concave and directed inwards, while those of the posterior are convex and directed outwards. The first four lumbar vertebras have six, the typical number of articular curfaces, the fifth haviog in addition one on each posterior border of its transverse processes, and the sixth one on each border, anterior and posterior, of these processes, or ten in all. False Vertebra. THE SACRUM. J t (PL. LH.) This, the bone of the croup, is a single, somewhat triangular- shaped bone, consisting of five false vertebrae united, in the young animal by articulation, and in the adult by ossification ; it con- tains the continuation of the spinal canal, forms the roof of .the pelvis, and has articular surfaces by which the pelvic arches are attached, and in the horse these are the only articular connec- tions between the axial and appendicular skeletons. Its direction varies somewhat according to the breeding of the animal ; in lightly-made, highly-bred, and well-formed animals its long axis is usually placed in a nearly horizontal line, while in horses of coarser breed its coccygeal extremity is often considerably lower than the other, thus giving a drooping appearance to the contour of the croup. It presents for consideration superior and inferior surfaces, two lateral borders, and anterior and posterior extremities. The superior surface is irregularly convex, with the flat-topped spines of its vertebral segments running along its centre, decreas- ing in height, but increasing in breadth as they extend backwards^ 32 OSTEOLOGY. In a groove at their base, opposite the interspinous spaces, are the four superior sacral foramina, which give exit to the superior branches of the sacral nerves. An irregularly-elevated ridge, external to the grooves, marks the division between the superior and inferior surfaces of the bone. ' The inferior or pelvic surface is smooth and rather concave ; at its anterior end is a trans- verse elevation, the sacral promontory, not very pronounced in the horse, and crossing the bone transversely are four slightly- elevated lines, which show the connectionG between the original cegments. between these lines, and clcso to the borders on each side are the four large foramina throiigh v/hich pass the inferior branches of the sacral nerves, and at the anterior end two notches, which correspond with similar notches in the last lumbar vertebra, and form the foramina through which the first sacral nerves find their exit. The anterior extremity or base is almost entirely articular ; the central part, oval and convex, articulates with the last lumbar vertebra, and above it is the spinal canal surmounted by the articular processes. The lateral parts are the thick expanded transverse processes which terminate in sharpened extremities, and contain two broad facets for articulation with those on the last lumbar transverse processes. The posterior extremity or apex presents the diminished spinal canal in its centre, with the last spinous process above it, and below the fiat surface which articulates with the first bone of the coccyx, while the notches and the sacral cornua are on its sides. The lateral hordero, anteriorly, are roughened for attachment to the iliac bones under which they lie, and v/ith which they form the sacro-iliac joint ; posteriorly, they are roughened for the attachment of the sacro-sciatic ligaments, and terminate in small transverse processes — the sacral cornua. The sacrum has five articular surfaces on its base, one on each side, and one pn its apex. Its spinal canal is somewhat triangular in shape, and decreases much in size posteriorly. ^ THE COCCYX. \ -" -^ (PL. I. I.) The coccygeal or caudal vertehrcBi&re false vertebrae, varying in number from thirteen to twenty. ^-In form, they are the most rudimentary of all the vertebral segments; their centra are r THE RIBS. 35 oblong, mostly constricted in the centre, and expanded wher© they articulate with one another: the four or five anterior one3 are slightly flattened above, hollowed longitudinally below, and they possess generally incomplete arches and imperfectly-developed processes. The remaining segments consist merely of centra, which diminish in size posteriorly. There is, therefore, no complete neural canal in the caudal region, only the first two or three vertebrae being sometimes found with their neural arches complete. THE THOBAX. The dorsal vertebra superiorly, the ribs and their cartilages laterally, and the sternum or breast-bone inferiorly, form the skeleton of a large cavity called the Thorax. THE EIBS. (PL. I. T. T.) In the horse the ribs usually number eighteen on each side. They extend in a series of arches of varying curvature from the dorsal vertebra above, towards the sternum and sides of the abdomen below. Their shape, in a great measure, determines the conformation of the thorax ; they protect its contents, and materially aid in its contraction and expansion. To the distal end of each rib an elongated piece of cartilage is attached, and eight of these connect the eight anterior, termed sternal or true ribs, with the sternum ; the ten posterior ribs. having only an indirect sternal attachment are known as asternal or false ribs. The ribs pass first outwards and backwards, and then in an arched direction downwards, their cartilages inclining inwards and forwards. They gradually lengthen from the first to the ninth, after which they progressively shorten ; their curvature increases from the first, which is nearly straight, to the last, which forms a large segment of a comparatively small circle. The greatest breadth is attained in the fifth, sixth, seventh, and eighth, which, in their middle portions, exhibit the more especial characters of flat bones. Each rib presents for consideration superior and inferior extremities, and a shaft or body having anterior and posterior borders and external and internal surfaces. D S4i OSTEOLOGY. The supeHor or proximal extremity consists of a head, a neck^ and a tubercle. The head, which rests in a cavity in the verte- brae, is separated by a vertical furrow, in which the interarticular ligament is attached, into two convex articular surfaces — one of which is directed forwards and inwards, and the other backwards and inwards. The neck is the constricted portion supporting the head ; it is strong and roughened for ligamentous attachment, and has a groove for the intercostal nerves and blood-vessels running across it in front. The tubercle is the prominent emi- nence at the posterior part of the neck ; it has a flat, smooth facet, which articulates posteriorly with the transverse process of a vertebra. External to the tubercle is another eminence, the angle, where the rib is suddenly bent downwards ; the distance between the angle and the head of the rib gradually increases from the third to the last, the first two scarcely possessing angles. In the third and fourth ribs the angles and the 'tuber- cles are from one to two inches apart, which distance increases, in a well-formed horse, to nearly five inches in the last. In horses possessing well-rounded chests the costal angles are plainly marked ^nd separated from the vertebrae, so as to form large costal grooves for the dorsal muscles ; in flat-sided animals they are indistinct and close to the spinal column, the grooves being consequently narrower. The inferior or distal extremity is expanded and constructed of more elastic bone than the proximal extremity ; it is quite porous, and joined firmly to its cartilage. The anterior ho^'der is rough, and excavated along its upper third to give attachment to the intercostal muscles. The posterior border is grooved along, its upper third for the intercostal muscles, nerves, and blood- vessels; in both borders the distal portion is thinner in the anterior than in the posterior ribs. The external surface is convex in every direction ; between the head and the angle it is roughened for muscular attachment, and below this point smooth, excepting in a few places, the chief of which, a short distance below the angle, give attachment to muscles. The internal quo face, concave from above downwards, and convex from side to side, is smooth, and for the greater part covered by the pleura, the membrane lining the thorax. With the exception of the last, and sometimes the last two on each side, each rib has its cartilage. These cartilages, which contain a large quantity of earthy or bony material, pass obliquely STERNUM. ZS forwards and inwards ; they diminish in thickness from before^ backwards, but increase in length to fhe eleventh or twelfth, after which they again grow shorter. Those attached to th& true ribs are smallest at their proximal ends, becoming expanded' before they articulate with the sternum ; those of the false ribs are largest at their proximal ends, and, gradually tapering to fine- points below, they pass forwards and downwards, so that, having no inferior articulations, each is overlapped by the succeeding one. The special ribs are the two first and the last four or five. The first is shorter and straighter than the others, with rough: surfaces, rounded borders, and no well-defined posterior groove ; its head is irregular in shape, and exceeded in size by the tubercle, and its distal end is flattened and expanded laterally, joining; the short thick cartilage, which contains much ossific matter. The second possesses the above-named characters of the first in a less degree. The last four or five are slender ; the articular surfaces of their tubercles and the posterior divisions of their heads are usually continuous ; their curvature is great ; they are broadest immediately behind the tubercle, and their cartilages are remarkably slender and elongated. Each true rib has four articular surfaces, two on the head, one on the tubercle, and one at the distal end. STERNUM. The sternum or breast-bone, a comparatively small and short bone in- the horse, is single in the adult, and placed in the inferior longitudinal line of the body at the antero-inferior part of the thorax. The anterior portion somewhat resembles the keel and cut-water of a boat ; it is elongated and concave above, convex below, with its anterior part flattened laterally, and its posterior part flattened above and below. It is constructed of six, rarely seven, irregularly-formed segments or sternehrce, united by cartilage in the young animal, and by partial ossifica- tion • in the adult ; complete ossification seldom or never takes place in this bone. Its anterior end is surmounted by the carini- form- cartilage, and its posterior extremity prolonged by the ensiform or xiphoid cartilage. Its superior surface is triangular in outline and concave, the superior sternal ligaments traversing its lateral borders. Its 36 OSTEOLOGY. inferior surface is narrow anteriorly and convex, the centre pre- senting a prominent ridge coated with cartilage, materially increasing the lateixd surfaces, which give origin to the pectoral muscles ; the sides are flat and irregular, and present between the segments depressions, in which the cartilages of the true ribs articulate, another depression being entirely formed in the first, a^d an eighth in the last segment. These depressions are oval in shape, and are nearer to each other as they proceed backwards. The Gariniforiiit, or heel-shaped cartilage presents a convex border looking forwards and upwards, and elevated so as to sur- mount the articular depressions for the first pair of costal cartilages, to which it is attached by ligaments ; laterally it is flattened to increase the surface for muscular attachment ; and its inferior border, prolonged over the first segments of the sternum, terminates in the cartilaginous ridge. The prominent convexity which this cartilage forms may often be plainly distiuguished in the living animal. The Xiphoid or Ensiform cartilage is somewhat heart-shaped, the apex being directed downwards and backwards. Its superior surface, broad and cup-shaped, occupies a space bounded by the cartilages of the false ribs, and supports -part of the abdominal viscera. Its inferior surface is convex, and roughened for muscular attachment, and its free borders are thin. It affords attachment for muscles, and for a fibrous cord called the linea alba. The bony framework of the thoracic cavity bears some resem- blance to a truncated cone, with its apex or anterior extremity compressed laterally. The anterior aperture is a triangular space, having its apex directed downwards and slightly forwards, formed by the sternum, the first pair of ribs, and the first dorsal vertebra; it gives passage to the ossophagus, trachea, and various important nerves and blood-vessels. The base or posterior aperture is oval in outline, and slopes obliquely downwards and forwards from the vertebraB ; it is formed by the last dorsal vertebra, the last pair of ribs, the cartilages of the false ribs, and the Xiphoid cartilage, and its boundary gives attachment td the diaphragm, a large muscular curtain which separates the thorax from the abdomen. GENERAL VIEW OF THE SKULL. 37 The Skull. GENERAL VIEW. The skull, or skeletoQ of the head, the most anterior part of the horse's skeleton, articulates with the first cervical vertebra, from which it is suspended by its posterior extremity, its anterior extremity being free. Its position varies with the attitude of the animal ; but in our descriptions we shall allude to it as if it were placed in a horizontal position, as in Fig. 12. In the young animal the skull is composed of a number of bones, all of which, with the exception of the lower jaw, the teeth, the bones of the tongue, and ossicles of the ear, become united by ossification in the adult ; excluding tlie teeth and the internal bones of the ear, there are thirty -eight bones in the skull — six single ones, and the rest pairs. The skull is divisible into two parts — viz., the cranium or calvarium, and the face. The former is a cavity situ- ated in the supero-posterior region of the skull, and continuous with the spinal canal; it contains the brain and its appendages, and in the horse is comparatively a small cavity, occupying about one-fifth of the skull. The re- maining bones of the skull collectively form the face, hence the whole struc- ture is composed of cranial and facial bones. We shall first endeavour to give a general idea of the articulated skull, and afterwards describe separately the bones v/hich com- pose it. The bones of the head are in early life united to each other by means of sutures, or interposed layers of fibrous material, and after union by ossification, a well-marked line usually indicates Fig. 10. Skull of the Horse seen from above I. Occipital bone ; II. Parietal bone ; III. Squamosal bone ; IV. Frontal bone ; V. Nasal bone ; VI. Lachrymal bone ; VII. Malar bone ; VIII. Sup- erior Maxilla ; IX. Premaxilla. a. Occipital crest ; b, Parietal crest ; c. Orbital process ; d. Supraorbital for- amen. ^8 OSTEOLOGY. the position of the late suture. One of the principal sutures of the skull is the longitudinal, which extends in the median line from the poll to the nasal peak, and marks the division of the skull into two lateral halves. In shape the skull resembles a quadranguhr pyramid, and contains various cavities or chambers. Supposing it to be placed in the horizontal position resting on the lower jaw, we can more easily give a general description of the most important external features if we divide it into the following regions : — Superior, Inferior, Lateral, Anterior, and Posterior." The Superior region is a surface formed by three pairs of bones, called the parietal, frontal, and nasal, each bone being joined to its -fellow by a ^B,vt orWiTo'S^^SmW'mtme. The parietal bones are the hindermost of the three, and are convex, forming part of the roof of the cranium or brain cavity, while- the frontal or middle pair are flatter, and very broad above the level of ihe orbits, the region of the forehead. The nasal bones together form a semi-cylinder, and gradually diminish in breadth anteriorly, finally forming the projecting nasal peak. The prominent trans- verse ridge botinding this region posteriorly is,.the occipital crest. The Inferior region presents a very irregular surface, bounded below by the inferior maxilla or lower jaw, a bone whose two segments are S'raTly' iuTited anteriorly, but diverge backwards somewhat in the form of a letter V, each terminating superiorly in a convex articiilar surface, th^ maxillary condyle, before which is the prominent coronoid process",'^ We "lever ^ of the lower jaw. The diverging parts or rami of the jaw include a space, appro- priately called the maxiUary space. We find in the united or anterior portion of this bone the inferior incisor and, in the male, the canine teeth, and in the rami the inferior molars or grinders ; the space between the molar and front teeth is called the diastema or interdental space, and is always large in herbivorous animals. If we remove the inferior maxilla, we notice the following objects : — Anteriorly the premaxilla, bearing the upper incisor and partly the canine teeth, and just behind the incisors, in the median line, a small round aperture, the foramen incisivum, while the interdental space and molar teeth are similar to those in the lower jaw. The flattened surface extending from the incisors backwards between the molars is the bony palate, formed chiefly by the superior maxilla, and bounded posteriorly by the palatine , GENERAL VIEW OF THE SKULL. 39 archy which is semi-elliptical in form, aud marks the entrance to a large cavity above called the nasal chamber ; this cavity is in the fresh state, divided into right and left compartments or fossae by a cartilaginous septum. Between the posterior molars and the palatine arch are the two palatine foramina. Behind, and bounded by the palatine arch, are the entr:?.nc£3 to the nasr.l chamber, right The whole articular surface is surrounded by a prominent ridge for the capsular ligament. The anterior part of this extremity is irregular, and has two deep vertical grooves for the tendons of the extensor muscles, and a shallow, oblique one, in which the tendon of the extensor metacarpi obliquus muscle plays. Laterally, two prominent processes, the internal being the largest, give attachment to the lateral ligaments ; the external of these processes is grooved for the passage of the extensor suffraginis tendon. ULNA. (Pl. I. L'.) The ulna is an irregular bone, in form triaiigular, with the base uppermost, and is placed on the supero-posterior part of the radius. This bone, which grows but little after birth, is larger in the young animal, proportionately to its ultimate size, than any other bone. It possesses a body and two extremities. The hody is triangular, and has three surfaces and three borders. The anterior surface is the counterpart of the posterior surface of the radius against which it is applied, having superiorly tvv^o convex facets to articulate with the concave ones 0:^1 the head of the radius ; below these is a rough portion for the attachment of the interosseous lio-aments, and still lower, a shallow transverse groove v/hich assists in the formation of the radio-ulnar arch, inferior to which is a roughened curface for the attachment of the ligaments, in which ossification takes place in the adult animal. The external surface is flattened and covered by the flexor metacarpi externus muscle, and the excavated inteimal face gives attachment to the ulnaris accessorius, and is covered by the flexor pedis muscles. The lateral borders are thin, and have 72 OSTEOLOGY. ike arciform ligaments attached, and the posffvior hordeVj concave- and round gives attachment to muscles. The distal extremity is pointed, and extends a little below the middle of the radius, though sometimes, in the ass and mule par- ticularly, it reaches the inferior extremity of that bone. The proximal extremity comprises that, considerable portion of the bone, corres- ponding to the elbow of man, which projects upwards and backwards from the articular surface of the radius, and is known as the olecranon process. It presents two sur- faces, two borders, and a summit. The external surface is slightly convex, and roughened for muscular attachment ; the internal surface is hollowed and smooth ; the posterior ^border, concave, thin, and smooth ; and the anterior border, thin superiorly, is hollowed into a crescent- shaped surface, which articulates with, or rather behind and between, the condyles of the humerus, the prominent portion being known as the beak of the olecranon. The summit is tho broad roughened protuberance which gives insertion to the tendon of the triceps extensor brachii muscle, the olecranon being the lever on which that muscle acts. It is important to note that the develcpment of the ulna is directly proportional to the number of fingers or digits, hence the horse, being a monodactyle, has a very short ulna; compare this bone in the on and dog. Fio. 16. Front aspect of the right «arpu8 of a Horse. 1, Cunei- form ; 2, Lunar ; 3, Scaphoid ; 4, Trapezium ; 5, Unciform ; 6, Magnum ; 7, Trapezoid ; * *, Small metacarpals, the large one lying between and f^before them. The uppermost bone is the dietal end of the i ndius. CARPUS, The carpus, wrist, or Jcnee, as it is incorrectly termed in quadrupeds, is coriiposed of seven and often of eight small, irregular bones, arranged in two rovrs of three each, one above the other, the severith being at the back of the three in tho upper row, and the eighth, when present, in a similar position ■with respect to the lower row. The joints between them pass completely through from front to back, and are so arranged that SCAPHOID. 73 those of one row do not correspond to those of the other. (Sed Fig. 16.) It may be noted that, virtually, continuous articular surfaces are formed by the bones, by which the upper row articulates with the ra- dius, the lower with the metacarpus, and the two rows with each other. Each bone also has facets, which are often deep-seated, for articulation with contiguous bones, and rough- ened depressions between the facets for the attachment of ligaments. The true carpal joint, or principal seat of motion, is between the radius and the upper row ; there is less motion between the rows, and still less between the lower one and the metacarpus. The lesion, termed ' " broken knees," usually occurs where there is the most extensive motion Naming from within outwards, the bones of the upper row are the scaphoid, lunar, and cuneiform, and the trapezium behind the latter; those of the lower row are the trape- zoid, OS magnum, and unciform and the pisiform behind the trapezoid. SCAPHOID. (Fig. ig. 3.) The scaphoid, the innermost and largest of the bones of the upper row, presents siz surfaces, the anterior and external being continuous, convex, and roughened for ligamentous attachment; the posterior is rough and irregular ; and the internal, excavated and roughened, has three projections, bear- ing facets which articulate with the lunar bone. The superior surface is Fia. 17. External view of bones of right car- pus, metacarpus, and digit of a Horso.. 1, Distal end of radius ; 2, Grooves for extensor tendons ; 3, Scaphoid ; 4, Lunar ; 5, Cuneiform : 6, Trapezium ; 7, Magnum ; 8, Unciform ; 9, Great Metacarpal ; 10, External small meta- carpal (splint) ; 11, Sesamoids ; 12, Proximal phalanx (os suffraginis) ; 13, Median phalanx (os coronse); 14, Third sesamoid (os naviculare) ; 15, Distal phalanx (os pedis); 16, Basilar pro- cess. smooth, concavo-convex. 74 OSTEOLOGY. and articulates with the internal part of the distal end of the radius ; the inferior surface is also smooth and articular, con- sisting of an anterior portion, slightly convex, for the os mag- num below, and a posterior concave or cup-shaped one for the trapezoid. The scaphoid articulates with four bones — viz., the radius above, the lunar internally, and the os magnum and trapezoid below. LUNAR BONE. (Fig. 16.2.) >■ The lunar bone (os lunare), the middle bone of the upper row, both in size and position, is somewhat wedge-shaped, and has four surfaces, a base, and an apex. The superior surface is all articular, triangular in . shape, with a concavity posteriorly ; it articulates with the middle part of the distal end of the radius. 5!he inferior surface is articular, and divided by a ridge into an oblong, concavo-convex portion, occupying about five-sixths of the surface, and articulating with the os magnum ; and another small, oblong, and flat part, situated at the antero- exteriial border, and articulating with the unciform bone. The internal surface is excavated and roughened, and possesses three articular projections, which correspond with those on the scaphoid, the external surface having two for the cuneiform bone. The base is rough, somewhat trapezium-shaped, and is placed anteriorly, the apex, rough and tuberous, being directed backwards. The lunar articulates with five bones — viz., the radius above, the scaphoid internally, the cuneiform externally, and the 06 mag- num and unciform below. CUNEIFORM BONE. (Fig. 16. 1.) This is the smallest and most external of the bones of the upper row, and has five surfaces; the superior, which is cup-shaped, articulates with the radius, and the inferior, somewhat concave^ with the unciform bone. The external surface is convex and rough, and gives attachment to ligaments, while the internal has two facets which articulate with the lunar; the posterior: r TRAPEZOID. 75 surfacey which slopes downwards and backwards, presents on its inferior half a cup-shaped articular facet for the trapezium. The cuneiform articulates with four bones — viz., the radius above, the lunar internally, the unciform below, and the trape- zium behind. TRAPEZIUM.* (Fig. 16. 4.) Placed immediately behind the cuneiform bone, the trapezium is broad and flattened, and presents two surfaces and a cir- cumference. Both its surfaces are rough, the internal being concave and the exienud convex, the latter having a deep groove for the passage of one of the tendons of the flexor meta- carpi externus muscle. The circumference is roughened, the superior part receiving the insertion of the tendon of the flexor metacarpi medius, with the second tendon of the externus muscles, while the remaining portion is rough for ligamentous attach- ment. Anteriorly there are two small facets, an upper concave one to articulate with the radius, and a lower convex one articu- lating with the cuneiform bone. As the trapezium is the lever bone of the carpal joint, its development and position are points of very great importance. TRAPEZOID (Fig. 16. 7.) This, the smallest of all the bones of the carpus, excepting the pisiform, is placed on the lower row on the inside ; it presents four surfaces, a base, and an apex. The superior surface, smooth and rounded from before backwards, articulates with the scaphoid. The inferior surface is smooth, with two united facets, one of which, largo, flat, and semicircular, articulates v/ith the inner metacarpal bone, and the other, small, cquare, and bevelled, v/ith the great metacarpci bone. The internal, surface is convex and rough, and the external rough, with the exception of three pro- jecting facets, which aLrticulate with the os magnum. The apex is placed forwards, and the base backwtirds, both being roughened ; a very small, cup-shaped articulation for the pisiform bone is often found on the posterior part of the base. The trapezoid articulates with five bones — viz., the scaphoid * See note on page 77. 76 OSTEOLOGY. above, the magnum internally, the large and inner metacarpals below, and the pisiform postero-externally. OS MAGNUM. (Fig. 16. 6.) The OS magnum, the largest bone in the carpus, and the xjentral one in the lower rovr. is somewhat triangular in shape, and presents four surfaces, a base, and an apex. The superior surface is divided into two portions by a ridge, the concave inner part articulating with the scaphoid, and the external, v>rhich is oblong and concavo-convex, with the lunar bone. The inferior surface y smooth and flat, rests on, and articulates with the large metacarpal bone, having also a very small bevelled portion near its inner surface, which articulates with the 7nner metacarpal bone. The internal surface is rough and irregular, and has three facets which articulate with the trapezoid ; the external Bwrface joins the unciform, having two facets. The hase is placed anteriorly, it and the apex both being roughened for ligamentous attachments. The OS magnum articulates with six bones — viz., the scaphoid and lunar above, the large and inner small metacarpals below, the trapezoid internally, and the unciform externally. UNCIFORM BONE. (Fig. 16. 5.) This, the external bone of the lower row, is very iiTegular in form, and somewhat resembles the trapezoid ; it has four surfaces, a base, and an apex. The superior surface y convex from side to side, and sloping externally, articulates with the lunar and cuneiform bones. The inferior swrface articulates by two facets with the large, and one with the small metacarpal bone. The internal surface presents two facets, which articulate with the OS magnum. The external surface is narrow ; the base is situated anteriorly, the apex being the prominent unciform pro- cess, and t?ll the three parts are roughened for ligamentous attachment. The unciform articulates with five bones — viz., the lunar and cuneiform above, the magnum internally, and the large and external metacarpals below. OS METACARPI MAGNUM. 77 PISIFORM BONE.* The pisiform is a very small, pea-shaped bone, situated, when present, 'at the postero-intemal part of the knee, in some cases articulating with the trapezoid, and in others being imbedded in the internal lateral ligament. It is generally, perhaps always, present in old subjects, but often overlooked owing to its small size. METACARPUS. The metacarpus, that part of the skeleton which lies between the carpus and the finger, consists, in the horse, of three bones. The principal one, the great metacarp?i bone, situated between the others, which are called the inner and outer small meta- carpals, is the only perfect one of the three ; the others are not D C B A Generic development of the Horse's foot. A. Foot of Eohippus ; B, That of Orchippus ; C, That of Hipparion ; D, That of Horse. The digits are numbered, when present, I. to V. only small, but they have no distal articular surface, frequently all three bones become united by ossification. Very OS METACARPI MAGNUM. (Fig. 17. 9.) The large metacarpal, or cannon bone, is a long, straight bone, placed in i* vertical direction. This bone, one of the most compact in the skeleton, is flattened in its shaft, from before back- wards, especially towards its distal end, the anterior surface being •convex and smooth, and the posterior broad, flattened, and pierced * [Some authorities call this bone the Trapezium, and our Trapezium the Pisiform. Either view may be admissible, as the nomenclature will depend upon whether we compare these bones analogously or homologously with those ■of the human carpus. — Ed,, Second Edition.] 78 OSTEOLOGY. at about one-third from the top by the medullary or nutrient foramen. On each side of this surface is a vertical ridge, to which the small metacarpals are attached. The proximal extremity presents a smooth surface, formed by three continuous articular facets, one large and flat, on which the OS magnum rests ; the second, very small, on -the postero- internal border, articulates with a portion of the trapezoid ; and the third, which articulates with the unciform, and occupies the whole external border, is bevelled off from within outwards, and divided by a deep furrow into two portions. In front of the large articulation, towards the intero-anterior portion of the head, is a roughened prominence for the insertion of the extensor metacarpi magnus tendon: and at the posterior part of the head a roughened surface, from which the suspensory and check ligaments originate, and on each side two facets, divided by furrows, articulate with the small metacarpal bones. The distal extreT/iity, widest from side to side, and convex from before backwards, presents an articular surface, consisting of two condyles joined by a prominent semicircular ridge, the whole of which articulates with the os suffraginis below, and the two sesamoid bones behind. Each of the condyles, the internal being slightly the larger of the two. presents a depression on ■ its side for the insertion of the lateral ligament. Thus the large metacarpal bone articulates superiorly with the trapezoid, magnum, and unciform, laterally with the small metacarpals, and infer iorly with the os suffraginis and the two sesamoid bones. OSSA METACARPI PARVA. (Fig. 17. 10.) The small metacarpal, or splint bones, tuberous in form at the carpus and tapering distally, are attached to the large bone, one on each side of its posterior surface, by ligaments in the young animal, and by ossification in most grown up, and in all old animals. They vary somewhat in length in different animals, but are usually about two-thirds of the length of the cannon, the internal being generally the largest. The base, or head, of each bone is turned upwards, its superior surface being articulatory, and assisting to form the carpal-joint. The internal one possesses two articular facets, one large and flat, on which the trapezoid rests, and the other small and bevelled DIGIT. 79 towards its anterior surface, to articul?.te witli a portion of the OG mpognum, while the external splint has but one carpal facet, which gives support to the unciform bone. Below the articular surface, externally, the heads are rough- ened for the insertion of the tendon of the flexor metacarpi intern us to the inner, and that of the flexor metacarpi externus to the outer. The head of each of these bones presents two articular facets, which correspond to those on the sides of the head of the cannon bone. The middle part or body tapers grad- ually downwards from the head, and is firmly attached to the large metacarpal bone by its anterior surface. The apex, terminates in a small knob, which never, except in disease, becomes attached to the parent bone. These knobs are very prominent in well-bred horses, and are sometimes mistaken foT splints, which are exotoses between the large and small metacarpal bones. DIGIT. The digit or finger is composed of three bones placed one immediately below the other, and having three supplemen- tary or sesamoid bones placed behind. The three principal bones are homolog- ous with the three phalanges of the human finger, the os suffraginis representing the first or proximal, the os coronae the second or median, and the os pedis the third or distal phalanx. The joint which the large metacarpal bene forms with the os sufFraginis and its two sesamoids is the fetlock-joint, that between the os suffraginis and the os coronae is the pastern joint, and that between the os corona and the os pedis, with its sesamoid or navicular bone, is the coflSn joint. Fig. 19. Posterior view of phalanges of a Horse disarticulated. A, Os suffraginis ; B, Os coronsa ; C, Os pedis ; D, Os naviculare, or third sesamoid ; 1 1, Glenoid cavities, joinedby ths groove, 2 ; 3, Eough surface f orV-shapedsssamoidean ligament ; 4 4, Condyles articu- lating with cavities, 5 5 ; 6 6, Con- dyles of corcnaB articiJating with glenoid cavities of pedal bone, 7 7 ; 8 8, Pyramidal process ; 9 9, Basilar processes ; 10 iO, Ketros- sal processes ; 11 11, Articular surfaces between navicular and pedal bones; 12, Surface con- tinuous with glenoid cavities, 77; 13, Posterior edge ; and 14 14, Extremities for lateralligaments of navicular bone. 80 OSTEOLOGY. PROXIMAL PHALANX. (Fio. 19. A.) The first phalanx, also called the os suffraginis, or large pastern bone, passes obliquely downwards and forwards, and articulates with the cannon bone above, and the median phalanx below. It belongs to the class of long bones. n - The shaft, which is very short and slightly flattened from before backwards, has an anterior surface convex and smooth, and a posterior surface somewhat flattened, the latter presenting two roughened ridges, in the form of a triangle, with its base upwards, to which certain of the sesamoid ean ligaments are attached. The proximal extremity, the larger of the two, presents a semilunar-shaped articular surface, convex in front, and consisting of two glenoid cavities for the condyles of the cannon bone, and a deep connecting groove for the eminence between them ; behind, on each side, is a roughened tuberosity for the attachment of the crucial sesamoidean ligaments. The distal extremity, much smaller than the proximal, presents two condyles connected by a shallow groove, continuous with which, posteriorly, is a pit or depression into which fits a prominent lip on the posterior part of the median phalanx, and in the centre of the front there is a slight eminence, to which a slip of the tendon of the extensor pedis muscle is attached. On each side is a roughened depression for the insertion of the lateral ligaments. GREAT SESAMOID BONES. (Fig. 17. 11.) These bones, two in number, are placed side by side at the post ero- inferior part of the metacarpus and postero-superior part of the OS suffraginis ; they are irregular or polyhedral in shape, having smooth and concave anterior surfaces, the internal bevelled edges of which* form a groove into which the ridge at the distal extremity of the cannon bone is received, the concave portions articulating with the condyles of that bone. The posterior surfaces when in situ form a channel, which is covered with fibro-cartilage, for the passage of the flexor tendons of the digit. The superior extremity or apex of each bone is roughened, as are also their lateral borders, which are grooved for DISTAL PHALANX. ST the reception of the suspensory ligament. The inferior surface or base is also roughened, to afford attachment to the ligaments by which these bones are attached to the phalanges below. MEDIAN PHALANX. (Fig. 19. B.) The second phalanx, os coronae, or small pastern bone, has no medullary canal, and belongs to , the class of irregular bones. It is inclined, like the os suffraginis, obliquely downwards and forwDTds, and is partly covered by the hoof The supenor surface is smooth, and divided by an eminence into two glenoid cavities fcr the condyles of the os suffraginis, and having in the centre two slight eminences, one in front and one behind, which, by limiting its motion, make the joint more secure ; a portion of the tendon of ihe extensor pedis muscle is attached to the anterior, and a ligament to the posterior of these eminences. The inferior surface of the bone is smooth and convex, and divided by a central depression into two condyles, which articulate with the os pedis and os naviculare. The (interior surface is convex, very rough, and widest superiorly; it affords attachment to part of the tendon of the extensor pedis muscle. The posterior surface, slightly excavated and not very rough, has on its upper part a prominent eminence covered by ■fibro-cartilage, over which plays the tendon cf the fiexor perforans, while on either side of this eminence is inserted part of the- i tend on of the flexor perforatus muscle. [ DISTAL PHALANX. (Fig. 19. C.) The third, or ungual phalanx, os pedis, or coffin bone, is an irregular bone situated within the hoof, and, when in a healthy state, corresponding somewhat to it in shape, being semilunar in form, with the convexity to the front. It is a very hard but porous bone, having many excavations and foramina for the transmission of arteries and veins. In this bone we notice the wall, the sole, the tendinous surface, the articular surface, and the alse or wings. The wall, or anterior surface, is the semicircular part in front G «2 OSTEOLOGY. which presents numerous depressions and foramina, the latter being for the passage of blood-vessels and nerves, and the former for the attachment of soft structures. Anteriorly it is surmounted by the coronal or pyramidal process, which gives insertion to the tendon of the extensor pedis muscle, and prevents the os coronse from slipping too far forwards ; a ligament is inserted in an excavation on each side of this process. The inferior edge of the wall is serrated or notched, the notches opening into various foramina ; and its declivity increases in degree, but decreases in extent as it proceeds backwards. At each side is the preplantar (/voovr, which terminates posteriorly in the large foramen of the same name, and along which the lateral laminal artery passes. The sole, or inferior surface, which lies on the sensitive or vascular sole, is slightly excavated and half-moon shaped, and, excepting the articular surface, is the smoothest part of the bone ; it is bounded externally by the inferior edge of the wall, and at its postero-internal part by an uneven semicircular ridge, the semilunar ridge, which separates it from the tendinous surface. The tendinous surface is the roughened portion placed imme- diately behind the sole ; it presents a triangular roughened depression on its middle and anterior part, where the tendon of the flexor pedis perforans muscle becomes inserted, and on each side a groove, the plantar groove, which terminates in the large plantar foramen along which passes the artery and nerve pro- ceeding to the interior of the bone. The posterior part of this surface is roughened for the attachment of the inferior navicular ligament. The articular surface presents two glenoid cavities, separated by a slight eminence which terminates in the coronal process; this part of the surface articulates with the inferior extremity of the os coronse. Behind the cavities, a flattened, narrow triangular surface articulates with the os naviculare. The alee, or xvings, are the irregular protuberances on the posterior part of the wall; they are bifid, being divided by a- fissure or notch, the preplantar fissure, which in old animals is converted into the preplantar foramen, through which the lateral laminal artery passes to gain the groove on the wall. The inferior and posterior portion of the ala, the more bulky of the two, is the retrossal process ; and the superior portion, thin, and giving attachment to the lateral cartilage, is the basilar process r PELVIC ARCH. 83 OS NAVICULARE. (Fig. 19. D.) The navicular, third sesamoid, or shuttle bone, is an irreg- ular bone, situated with its long axis transversely, behind and below the os coronae, and behind the os pedis, with both of which it articulates, the articulation of the three forming the so-called coffin joint. The superior svjrface is smooth, with two concavities and a centrd eminence, which complete the articular surface for the condyles of the os corona ; the inferior surface is rather rough, and also has two concavities and a central projection, which are covered with fibro-cartilage, and together form a kind of pulley over which plays the tendon of the flexor perforans muscle. The anterior border is divided into two portions, a superior, smooth and triangular, which articulates with the os pedis, and an inferior, elongated, rough, and porous, and attached to the same bone by the inferior navicular ligament. The posterior border is triangular, rough, and porous, and gives insertion to the superior ligament; the extremities are pointed, and attached to the alee of the os pedis by lateral ligaments. Pelvic Arch. The posterior extremity is united to the trunk by the direcV articulation of the pelvic arch with the femur and sacral vertebrae. The three bones which form the arch become early united by ossification, and the entire arch is called the os innominatum. The two ossa innominata articulate with each other in the inferior median line, and at a later period this union becomes also ossified; the complete structure is called the pelvis, and the space which it helps to enclose is the pelvic cavity. On examining the pelvis in situ, we find that the anterior portion bounds superiorly a ;^space which has no bony floor; this portion has been termed the Palse Pelvis, the True Pelvis being the posterior part which, by union of its right and left segments, forms the floor of the cavity. Each side of the floor is pierced by a very large opening, the obturator foramen, or foramen ovale. The pelvic cavity therefore is, in the skeleton, included between the sacrum, part of the coccyx, and the two ossa innominata. "The pelvis is always much smaller proportionally in the lower 84 OSTEOLOGY. animals than in man. where, especially in the female, it is large and well developed, possessing that peculiar basin-like form identified with an erect posture of body. We have already described the sacrum and coccyx, and have now to describe the ossa innominata. or right and left segments of the pelvis. OSSA INNOMINATA. The ossa innominata are flat, but somewhat irregularly-shaped bones, which form the sides, floor, and part of the roof of the pelvic cavity. Above they are connected with the sacrum, and below united to each other in the adult by ossification. In the young animal, as above stated, and especially in the foetus, each OS innominatum consists of three parts, which retain their names of ilium, ischium, and pubis, even after union by ossification. They all three meet in Jie acetabulum, or articular cavity tor the femur. ILIUM. (PL. L U.) The ilium, the largest and most symmetrical bone of the three^ and situated partly upon the sacrum with which it articulates, is flat and irregularly-triangular in shape, its extreme outer angle being one of the most prominent points of the animal, forming the projection commonly called the " point of the hip." It presents for consideration two surfaces, three borders, and three angles or processes. The external surface is concave at its upper part, and marked by elevated lines for the attachment of the gluteus maximus muscle ; lower down it becomes convex and narrow, forming the upper part of the shaft of the ilium, which is three-sided. As it approaches the acetabulum the shaft again siig'ntly expcmds, and becomes roughened for the attachment of the gluteus internus and outer head of the rectus femoris muscles. This surface terminates in an obtuse angle, the outer side of which forms a strong anterior margin for the acetabulum ; and the inner side, surmounting this cavity, marks the line of junction between the ilium and the ischium. The internal or "uenter surface is slightly convex, its upper portion consisting of two parts — an outer smooth one, correspond- ing to the iliac fossa in man ; and an inner, which rests on the ILIUM. 85 sacrum, and gives attachment to the inferior sacro-iliac ligament. The iliacus muscle is attached to the venter surface. On the lower portion is a line or ridge continuous with the anterior edge or brim of the pubis ; together these form the ilio-peetineal line, which inferiorly separates the true pelvis from the false. On the inferior border of the shaft is the nutrient foramen, and in front of the acetabulum a second depression for the inner head of the rectus femoris muscle. Below this depression is the ilio-pectineal eminence, which marks the junction of the ilium and the pubis, and gives attachment to the psoas parvus muscle. The inner part is smooth, concave, and grooved backwards and downwards for the obturator vessels Fio. 20. Left postero-lateral view of a Horse's pelvis. 1, Anterior iliac spine ; 2, Posterior iliac spine. The iliac crest is the border joining 1 and 2 ; 3, Uiac shaft; 4, The acetabulum, the large rough ridge above is the sciatic spine ; 6, Inferior ischiatic spine, posterior to which is the tuberosity. The anterior border, or crest of the ilium, lies above the sacral transverse process. It is concave above, convex below, thin in its middle, and roughened for the attachment of the longissimus dorsi and other muscles. Internally it terminates in a rounded eminence, the posterior iliac spine, which rises above the last lumbar and first sacral spines, and forms the highest part of the croup. Externally and anteriorly it terminates in the anterior iliac spin£, which consists of four eminences, two superior and two inferior, supported on a thick, strong, projecting bony plate ; these eminences give attachment to the oblique and transverse I 86 OSTEOLOGY. ■ abdominal and other muscles ; they are more developed in some horses than in others, and occasionally project so far as to form, what are termed ** ragged hips." The superior or internal horaer extends' from the posterior spine to the ischium. It is sharp and thin above, and becomes thicker posteriorly, presenting above the acetabulum a roughened ridge, the sciatic or superior ischiatic spine, the posterior por- tion of which is formed by the ischium, and to which a large part of the sacro-sciatic ligament is attached. ISCHIUM. (PL. I. 14.) The ischium, intermediate in size between the ilium and the pubis, is a flat, irregularly quadrilateral bone, which extends from the acetabulum, and forms the posterior part of the pelvis ; it presents a body, a shaft, and a ramus. The shaft, which forms part of the sciatic spine, also joins the ilium in the acetabulum ; it is rounded, and below the spine has a smooth surface over which the obturator intemus and pyri- formis tendons pass. It forms the external boundary of the obturator foramen. The body, which is nearly horizontal, is flat and smooth, and forms the posterior boundary of the obturator foramen. Inter- nally, it is roughened, and joins its fellow of the opposite side, forming the symphysis ischii ; posteriorly it is roughened for the attachment of muscles, and possesses on its external part a prominent projection, the tuberosity of the ischium, to which several muscles are attached. The ridge or" spin^ below, running forwards from the tuberosity, is the inferior ischiatic spine, 'While the posterior border of the bone is formed by a thick ridge running frona the tuberosity to the symphysis, forming with its fellow the ischial arch, which, in the male, supports the crura of the penis. The ramus, not well developed in the horse, is the small branch which joins the pubis, and forms part of the inter- nal boundary of the obdurator foramen, the nuion between the bones being usually marked by a transverse ridge. PUBIS. The pubis, which is the smallest division of the os innomin-. Xbtum, is likewise irregular in shape, and forms with its fellow the PELVIC APERTURES. 87 ■antero-inferior part of the pelvis ; it consists of a body and a ramus. The body reaches from the acetabulum to the median sym- physis ; its superior surface is concave to receive the urinary bladder, and its inferior surface is convex, and transversely crossed by a deep groove from the acetabulum, which contains the pubic-femoral ligament. The crest is the roughened anterior border, which terminates at the symphysis. The posterior border extends to the ramus, and forms the anterior margin of the obturator foramen; at its junction v/ith the ilium it is crossed by a groove for the obturator vessels. The outer extremity, which joins the ilium and the ischium in the acetabulum, is excavated to form the cotyloid notch. The raynus is the flattened portion which projects posteriorly, joins the ramus of the ischium, forming part of the boundary of the obturator foramen, and with its fellow the symphysis pubis internally. ACETABULUM. (Fig. 20. 4.) The cotyloid cavity or acetahuluw, is situated on the extero- lateral aspect of the pelvis, where the three segments of the os innominatum unite. It receives the head of the thigh-bone, and is one of the deepest articular depressions in the body, though relatively it is much less capacious in -the horse and in quadru- peds generally than in man. It is circular in cutiine, and, except at its inferior median part, is surrounded* by a prominent lip of bone, which becomes thin and slightly roughened at its free' surface for muscular and ligamentous attachment; its inferior border presents a large notch, the cotyloid notch, continued half-way across the articulation as the fundus acetabvZi, to give attachment to the round ligament (ligamentum teres), which mainly occupies it. Although the cotyloid cavity is formed by the three segments of the os innominatum, the ilium and the ischium are generally the only parts which form its aiticalar surface, the pubis in most cases merely helping to form ths roughened notch and fundus. PELVIC APERTURES. The obturator or thyroid foramen, or foramen ovale, the largest foranaen in the body, exists in each os innominatum, and 88 ' OSTEOLOGY. is oval in outline, its long diameter being directed downwards, backwards, and inwards. It is formed entirely by the pubis and ischium, and possesses smooth margins, and thick, except where they are formed by the pubis. The inlet, or brim of the pplvis, is bounded superiorly by the sacral promontory, laterally by the ilio-pectineal line, and inferiorly by the crest and symphysis of the pubis. The aper- ture thus defined inclines downwards and backwards, being somewhat ovoid in form. The diameters of the inlet vary according to the age and sex of the animal ; in the adult male, the verticle or sacro-pubic diameter is a little less than the transverse. The outlpt, or posterior aperture ^ is somewhat triangular in form, and is bounded above, at its apex, by the first coccygeal bone, laterally by the sacro-sciatic ligaments, and inferiorly, by the ischia and ischiatic spines. Its vertical diameter, from the last sacral or first coccygeal segment, to the ischiatic symphysis, is less than the transverse, taken between the ischiatic spines. The length, taken from the middle of the lateral part of the inlet to the ischiatic tuberosity, is usually about equal to the transverse diameter of the inlet. FEMALE PELVIS. The size and proportions of the pelvis differ considerably with the sex of the animal. Bearing in mind that we have referred hitherto to the pelvis of the adult male, the differences in that of the female may be thus summarised : — 'The whole structure is larger. The transverse diameters above named, in fact, the transverse measurements generally, are very large, the former exceeding the vertical diameters by a mr.i;h larger difference than is found in the male. The internal border of the ilium is more hollowed out, and smoother. The ischial arch is large, and it presents a concave border, tending but slightly to form an angle at the symphysis. The cptyloid cavities are v/ider apart than in the male, while the obturator foramina are larger and more circular in form. PELYIO LIMB. The bones of the pelvic or hind extremity are the femur, patella, tibia, and fibula ; the bones of the tarsus — viz., the astragalus, os calcis, cuboid and three cuneiform bones; one large and two small metatarsals; three phalanges and three sesamoids. See p. 65. FEMUB. $9 FEMUTt. (Fig. 21.) The OS feinoris, femur, or thigh bone, the largest, thickest, and strongest bone in the body, belongs to the class of long or cylindrical bones, and is placed in a direction obliquely down- wr.rds and forwards, articulating with the cotyloid cavity of the os innominatura, and also with the tibia and patella. The shaft is irregularly cylindrical, and has two surfaces and two borders. The anterior surface is smooth, prominent, and marked by a few muscular imprints. The 'posterior surface is flattened and expanded at its upper part, and presents, towards the external part of its upper third, a circular roughened surface for the insertion of part of the triceps abductor muscle; internal to which a slight ridge runs obliquely up- wards and inwards to join the internal trochanter, to this the ischio-femoralis muscle is inserted. About its middle third is a roughened surface, for the attachment of the adductor brevis and part of the adductor longus muscles. The external border ^ which separates the anterior from the posterior surface, presents a prominent ridge, on the upper third of which is a sharp, flat pro- tuberance, the trocho.nter Tninor, curved forwards, and affording attachment to the gluteus extern us and vastus externus muscles. At the lower third of this border is a deep, oval, roughened pit, the supra-condyloid fossa, Irom which the flpxor pf^rforatus supra-condyioid fossa. muscle arises ; and about level with this, towards the inner side, is an aggregation of tubercles forming the supra-condyloid crest, where arises one portion of the gastro- cnemius muscle. The internal border, dividing the anterior from the posterior surface internally, presents near its upper third Fig. 21. Posterior view of left femur of a Horse. 1, Head ; 2, Tro- chanter major ; 3, Trochanter minor ; 4, Trochanter in temus: 5, Notch for the round liga- ment ; 6, Trochanteric fossa ; 7, 8, Places of attachment for the lateral ligaments ; 11, The condyles, separated by the intercondyloid groove ; 10, 90 OSTEOLOGY. a blunt roughened prominence, the trochanter internus, from which a ridge extends upwards to the head, and to which the psoas magnus, iliacus. and vastus internus muscles are attached. From this trochanter another ridge, to which the pectineus muscle is inserted, runs downwards, the nutrient foramen being in its lower part. The proximal extremity terminates in the head and the trochanter major. The head is the smooth articular portion directed upwards and inwards, and is received in the cotyloid cavity ; it is separated from the body by a constricted portion, the neck, not well marked in solipedes, and between the head and neck there is a- ridge for the attachment of the capsular ligament. The deep notch at the inner part of the head is for the attachment of the pubio-femoral and round ligaments. The trochanter major is a very large eminence, which projects out- wards and upwards, and presents posteriorly a prominent part termed the summit, which stands a little higher than the arti- cular head, and gives attachment to one portion of the gluteus maximus muscle, and anteriorly the convexity, which is rounded and covered externally by cartilage, over which plays another tendon of the gluteus maximus, and becomes inserted to the ridge just below. Behind the trochanter, and between it and the head, is the trochanteric or digital fossa, around and in which several small muscles are inserted; bounding this fossa externally is the trochanteric ridge, continuous with the posterior part of the summit of the trochanter. The distal extremity presents posteriorly two condyles, and anteriorly a trochlea ; the condyles, which articulate with the head of the tibia, are placed side by side, being separated by a deep intercondyloid groove, from which the interosseous crucial ligaments of the articulation spring, and into which the spine of the tibia projects. The external condyle has two fossae on the outside, one for the origin of the popliteus, and one for the external lateral ligament ; the internal condyle has a roughened prominence on its lateral surface, for the attachment of the internal lateral ligament, the adductor magnus, and part of the adductor longus muscles. The trochlea is the pulley-shaped part to the front of the condyles, which articulates with the patella ; it consists of two prominences divided by a groove, and it is in a line with the intercondyloid fossa. The internal prominence is the thickest TIBIA. 91 and most pronounced, and on the side of the bone, between the external prominence and the external condyle, is a depression, in which the tendons of origin of the extensor pedis and flexor metatarsi muscles are attached. PATELLA. (PL. L X.) This, the knee-pan or stifle boue, is placed in front of the trochlea of the femur. It is very compact. *its anterior surface being irregularly convex and very much roughened, for liga- mentous attachment, and its posterior surface smooth to articu- late with the trochlea of the femur, presenting two concavities divided by a ridge, the innermost being the larger, and in the fresh state enlarged still more by a projecting fibro-cartilaginous lip, or process. The superior surface of this bone is broad, uneven, and roughened, giving insertion to the group of muscles called the triceps (or quadriceps) cruralis; the inferior surface is rough and pointed, and gives attachment to the middle straight ligament of the patella, while the lateral borders and angles have the externa] and internal straight ligaments attached. The patella is the lever bone of the stifle joint, or it may be regarded as a sesamoid bone, developed in the tendons of the attached muscles, so as to increase their power, enabling them to act at an advantageous angle. It is liable to fracture by muscular contraction, and to luxation ; in the latter case the internal lateral ligament is injured, or may by ruptured. TIBIA. (PL. I. Y.) The tibia, or leg bone, is a long bone, larger at its proximal than its distal end, situated between the femur and the astra- galus, slanting downwards and backwards. The shaft is three-sided, possessing outer, inner, and posterior surfaces, all of which are wider above than below. The outer surface, concave superiorly and convex inferiorly, is smooth, and lodges the extensor pedis muscle ; the inner surface, slightly convex from side to side, is smooth, excepting at its superior part, where it gives attachment to one tendon of the biceps rotator tibialis, the sartorius and gracilis muscles, and is covered chiefly by skia, fascia, and a strong periosteum. The posterior surface 92 OSTEOLOGY. the broadest of the three, presents on its superior third a triangular and rather smooth portion, to which the popliteus muscle is attached, the remaining two-thirds being strongly marked by a number of longitudinal ridges, and giving attach- ment to the deep flexor muscles of the foot ; the nutrient foramen is in the upper third of this surface. The anterior border is rounded, and indistinctly marked, except in its upper third, where we find the prominent tibial ridge, which is purved outwards, and joins the anterior tuberosity of the proximal extremity. The external border is thick and concave above, so that with the fibula it forms the tibial arch. The internal border is also thick, and at its upper part has a small tubercle, to which the popliteus muscle is attached. The proximal extremity is- much more • expanded than the distal, and presents two large, smooth, somewhat . undulated, articular surfaces, divided by a roughened conical process, the tibial spine, on the outer side of which is an irregular excava- tion for the insertion of one of the crucial ligaments. The semi- lunar cartilages are interposed between these surfaces and the condyles of the femur. Anteriorly a tuberosity, concave exter- nally and convex internally, joins the tibial ridge, and presents a vertical notch in front for the middle straight ligament of the patella. At the sides are two processes, to which the lateral ligaments are attached, the external being the largest, and presenting also an articular facet for the head of the iibnla. Betv/een this process and the anterior tuberosity is a deep groove, for the passage of the tendinous part of the flexor metatarsi muscle. The distal extre'mity, much smaller than the prozimalj and flattened transversely, presents two smooth, deep articular grooves, which run obliquely backwards and inwards, the internal being the deepest, and the external the widest ; also three pro- jections, the middle one forming a division between the groves, being articular and continuous with them, while the others, which form the lateral processes or TnaMsoli, are roughened outside for the reception of ligaments. The articular surface corresponds to the trochlea of the astragalus articulating with it. The internal malleolus is the most prominent, and the external the widest, being grooved for the passage of the tendon of the peroneus muscle. ASTRAGALUS. 93 FIBULA. (PL. L //.) This is a long slender bone, little developed in the horse, and ia an appendage to the tibia, being attached to the outer side of that bone, and extending from its head to its lower third, to Tvbich it is affixed by a ligement ; the space between the two bones is called the tibial arch. The head, or siiperio^ part, is nodular, somewhat flattened, and roughened externally for the attachment of the external lateral ligarnent of the joint above ; internally it articulates with the external lateral part of the head of the tibia. I)istally the bone becomes slender, and tapers to a point, from which a liga- ment is sometimes continued the whole length of the tibia. The peroneus muscle arises chiefly from the fibula. TARSUS. The tarsus, or hock, corresponding to the ankle-joint of a man, is composed of six irregular, compact bones, placed between the distal eiul of the tibia and the proximal end of the meta- tarsus ; they are arranged in two series ; one. consisting of the cuboid and three cuneiform bones, the magnum, medium, and parvum, corresponds to the lov/er row of carpal bones ; the other, or upper series, consists of the astragalus and calcaneum the first, forming with the bone above the mobile portion of the joint, may be said to correspond to the upper row of carpal bones, while the latter, being the lever bone, corresponds to the trapezium. These bones, like those of the carpus, are thickly covered on their articular surfaces by cartilage, which acts as a protection against concussion." ASTRAGALUS. (Fia. 22. 2.) This, otherwise termed the os tali or ankle bone, is a pulley^ like bone, placed immediately below the tibia, with which it articulates. A very large proportion of the surface of this bone is articular. The superior or supero-anterior surface presents an articular 94 OSTEOLOGY. trochlea consisting of two oblique prominences, separated by a. deep groove, directed downw'ards &nd outwards, which corres- pond to the articular surface on the distal end of the tibia. The inferior surface is concavo-convex, and excepting a small oval external portion, which rests on part of the cuboid bone, and a roughened, excavated posterior portion, in which the great inter- osseous ligament is attached, the whole of it articulates with the superior surface of the cuneiforme magnum. The posterior surface is very irregular, and has four facets, which articulate with the calcaneum, the intervening portion being excavated and roughened. The lateral surfaces^ the internal of which pre- sents a tubercle inferiorly, are roughened for the insertion of ligaments. The astra- galus articulates with the tibia and calcan- eum, the cuboid, and great cuneiform bones. CALCANEUM. (Fig. 22. 1.) The OS calcis or calcaneum, which forms the prominent part, termed the point of the hock, and corresponds to the heel-bone of man, is situated immediately behind the astragalus, and consists of a body and a tuberosity. The body is the inferior por- tion, which is flattened laterally, slightly convex externally, and unevenly concave internally, both surfaces being roughened. Anteriorly it has four articular facets, which correspond to those on the astragalus, the interspaces being rough for ligamentous attachment ; posteriorly it is grooved and smooth, for the passage of the deep flexor pedis tendon ; infer- iorly it has two facets to articulate with the cuboid bone. The tuberosity is oblong, and flattened laterally, its external surface being rough ; internally it is smooth, and forms the tarsal arch, a groove covered with fibro-cartilage, in which lies the above- named flexor pedis tendon. Both borders are roughened, the posterior one being straight, and giving attachment to the calcaneo-cuboid ligament, while the anterior and shorter one is curved The superior extremity is expanded and roughened ; posteriorly it is covered with fibro-cartilage, over which tha Fig. 22. Bones of left tarsus of a Horse, seen from the front and outside. 1, CalMneum ; 2, Astragalus ; 3, CQBEtn^ne magnum : 4, Cuneiforme med- ium : 5, Cuboid. OS CUNEIFORME MAGNUM. 95- tendon of the flexor perforatus muscle plays ; and anteriorly is a smaller portion, also covered with cartilage, for the gastrocne- mius tendon to play over ; and, finally, a roughened depression between the two smooth portions for the insertion of the last named tendon. The calcaneum articulates with the astragalus and cuboid bones. OS CUBOIDES. (Fig. 22. 5.) The cuboid bone is a small irregularly-shaped bone, which occupies the outer part of the hock between the os calcis and the large and outer small metatarsal bones; it presents four surfaces. The external surface is convex, very rough and irregular, and gives attachment to ligaments ; the internal surface has four articular facets, the two superior of which articulate with the cuneiforme magnum, and the two inferior with the cuneiforme medium ; between the upper and lower facets a large foramen is formed by these three bones, giving passage to the perforating pedal artery. The superior surface is smooth, and possesses two continuous articular facets, one large, to articulate with the OS calcis, and the other small, to articulate with the astragalus ; the inferior surface, also smooth, has two continuous articular facets, separated by a ridge, one flat, to articulate with the large metatarsal, and the other bevelled, to articulate with the outer small metatarsal bone. The cuboid articulates Nvith six bones — viz., the calcaneum and astragalus above, the cuneiforme magnum and medium internally, and the large and external small metatarsal bones below. OS CUNEIFORME MAGNUM. (Fig. 22. 3.) The large cuneiform, called also the scaphoid, and sometimes the navicular bone, is the bone on which the astragalus chiefly rests ; it is somewhat flattened and thin, and presents two sur- faces and a circumferent border. The superior surface is concave and entirely articulatory, with the exception of a groove which runs from its outer surface to its middle, and gives attachment to a. ligament ; this surface articulates with the astragalus. The 96 OSTEOLOGY. inferior surface is slightly convex, and presents three aroicular facets, two of them, separated by a rough excavation, articulating with the cuneiforme medium, while the third is small, and articulates with the cuneiforme parvum behind. The anterior and internal lateral borders are rough, for ligamentous attach- ment; the external lateral border has two facets, which articulate with the cuboid, the intervening portion being roughened. The posterior border, the smallest, is irregular, and gives attachment to ligaments. The large cunei- form bone articulates with the astragalus, the cuboid, medium and small cuneiform bones. OS CUNEIFORME MEDIUM. Fig. 2S. External view of bones of left tarsus, meta- tarsus, and digit of a Horse. 1, Distal end of tibia ; 2, Calcaneum ; 3, Astragalus ; 4, Cuboid ; 5, Cuneiforme magnum ; 6, Cunei- forme medium ; 7, Great metatarsal : 8, Exter- nal small metatarsal (splint); 9, Proximal phalanx (os suffraginis); 10, Sesamoids; 11, Median phclanx (os coronse); 12, Distal phalanx (os pedis); 14, Third Sesamoid (os naviculare) ; 15, Basilar process. -«ion between ; the internal (Fig. 22. 4.) The median cuneiform bone is somewhat flattened and tri- angular in shape, and a little smaller than the magnum, under- neath which it is placed. The superior surface is con- cave, and presents two articular surfaces for the magnum, with a roughened transverse space between. The inferior surface is convex, and rests on, and articulates with, the large meta- tarsal bone. The anterior border is rough, for ligaments ; the external lateral border has two facets for articulation with the cuboid, with a roughened depres- lateral border has one very small n' OS METATARSI MAGNUM. 97 facet, which articulates with the cuneiforme parvum, the remain- ing portion being excavated and roughened. The middle cuneiform articulates with the large and small cuneiform, the cuboid, and the large metatarsal bones. OS CUNEIFORME PARVUM. The small cuneiform is a very irregular bone, and the smallest in the hock, at the postero- internal part of which it is situated. It is sometimes divided into two parts, and presents four surfaces and two estremities. Its superior Burface is smooth and concave, to articulate with the magnum ; and its inferior surface has usually two small facets, one articulating with the inner small metatarsal, the other with both the inner and large metatarsal bones. The anterior extremity presents a very small facet for the cuneiforme medium, the remainder of tbe bone being very irregular, and roughened for ligaments. The small cuneiform articulates with the large and middle cuneiforms, and the large and inner small metatarsal bones. Metatarsus. Posterior view of left metatarsus of a Horse. 1, Large me- tatarsal bone ; 2, In- ternal, and 3, exter- nal, small metatarsal bones ; 4, Partial origin of suspensoiy and check-Ligaments: 5, Nutrient foramen: 6, Articular ridge joining the condyles. OS METATARSI MAGNUM. (Em. 24.) This bone presents the same general appear- ance as the large metacarpal bone, from which it dififers principally in being about one-sixth longer, flattened laterally, and rounded and more pro- minent anteriorly. It has three articular facets on its superior surface, a large one in the middle for the middle cuneiform, one on the inner side for the small cuneiform, and one on the outer side for the cuboid bones ; this surface also presents a deep, rough fossa of insertion in its centre. The deep groove which passes obliquely backwards and downwards, on the external side of this bone, is for the passage of the great meta- tarsal artery. The inferior extremity is larger and thicker than the superior. 98 COMPARATIVE OSTEOLOGY. OSSA METATARSI PARVA. (Fig. 24. 2, 3.) These also present the same general form ha^j tl»e small meta- carpal bones ; the external is the longest and l^.rgest, and has the largest head, with two facets which articulate with the cuboid bone ; the internal one has also three articular facets, two for the small, and one for the middle cuneiform bones. The two lateral facets on each head articulate with corresponding ones on the large metatarsal bone. The remaining bones of the hind extremity — viz., the three phalanges, with their three small accessory bones, so closely resemble the corresponding bones of the fore extremity, that it seems at first sight difficult to distinguish the one from the other ; the chief differences being, that the first phalanx of the hind extremity is longer, its proximal end larger, and its distal end smaller, than in the fore extremity. The second phalanx is longer, but not so broad transversely, and the third is more pointed, or semi-eliptical, in front, and more concave on its under surface, air these differences being more or less marked in degree. The three sesamoid bones are almost identical COMPAKATIVE OSTEOLOGY. In this section of the subject we shall endeavour to point out where the skele- tons of the domesticated animals, other than the horse, differ from the typical skeleton of the latter in any important particular. The following description* are therefore in all cases comparisons, where comparison is possible, between the typical skeleton and the skeleton in question. RUMINANTIA. In this class we take the Ox as the animal which represent? best for out purpose, the family Cavicornia or Bovldas. AxiAii Skeleton. THE SKULL. In the cranium of the ox an important feature is the development of the^ frontal bone, which extends from below the eyes to the back of the skull, forming the entire forehead and crest, in the middle of which is the frontal tuberosity, which is very large in hornless animals. Springing from the sides of the crest are two processes, varying in size and curvature, but corresponding r RUMINANT SKELETON. 99 Fig. 25. SKELETON OF THE OX (Euminantia). Axial Skeleton. the skull. Cranial Bow«s.— Occipital, 1 ; 6, Parietal, 2 ; a. Frontal, 2 ; c. Temporal, 2 ; Sphenoid, 1 ; JSthmoid, 1 ; Auditory ossiclas, 8. Facial Bones.— h, Nasal, 2 ; e, Lachrymal, 2 ; d, Malar, 2 ; /, Maxilla, 2 ; g, Premaxilla, 2 j i. Inferior maxilla,! 2; Palatine, 2; Pterygoid, 2 ; Vomer, 1; Turbinals, 4; Hyoid (segments), 7. Teeth :— Incisors, 6 ; Canines, 2 ; Molars, 24. The Trunk.— Tc, Cervical Vertebrae, 7; I, Dorsal verfebrse, 13; m, Lumbar verteb-ss, 6; n, Sacmm cation. The superior groove is narrow and uneven, and the superior foramina j not 80 regular; the under surface is more. concave, the promontory being; r. RUMENANTIA PECTORAL LIMB, 10$ T)etter marked, and the inlerior foramina larger. The sacral coraua are large,? and expanded for ligamentous attachment ; the spinal canal is oval, and the <;onvex articular portion of the body large, the articular processes being widelyj separated by a triangular opening leading into the canal. The transverse processes are short, thick, and nou -articular anteriorly ; their external extremist ties are bounded by a vertical border, the inferior angle of which is directed -downwards, giving a deeper surface for articulation with the ilium. The coccyrjeal bones, from 15 to 20 in number, are strong and tuberous., Articular processes exist in the anterior ones. THORAX. Very generally the ruminants have 13 pairs of rihs, of which 8 are criia and 5 false. They are straight, broad, long, and more uniform than tho^.e 'of ihe horse; the superior extremity is large and smooth, the necks of 'ihe anterior ones short and thick, and the tubercles large ; the necks of the- posterior ones are long and thin, and smaller than in the horse. The angles are not well marked ; the distal extremities are expanded to articulate with' their cartilages by means of true joints. The sternum is large and flattened, consisting of seven pieces, which, the» anterior one excepted, unite by ossification ; and between the first segment oiV| manubrium apd the second there is, in the larger ruminant, a true joint. The> superior surface is concave, forming the floor of the chest, the inferior convex,^ but slightly concave from side to side. The borders present between each two* segments articular depressions for the costal cartilages. The cariniform:] caitilaqe is small and conical, the ensi form large and circular. PECTORAL LIMB. The scapula is large and very triangular. The spine does not, as Tn the; horse, terminate gradually in the neck, but by an abrupt angle, prolonged to, ■a point, the acromion process. The neck is more distinct, and the coracoid! process and glenoid cavity are both small, and placed close together. In the humerus (Fig. 25. u), the bicipital groove is single ; the external trochanter, is very large, with its summit curved over the bicipital groove. The head is large, the tuberosities small, and the shaft less twisted, th-an in the horse. The ■radius is short ; the ulna, longer and larger than in the horse, extends to tha ' -distal end of the radius, and articulates with the cuneiform bone. Tiiere are two radio-ulnar arches, connected by a deep fissure. It is important to note here the fact that the development of the ulna, and to some extent its freedom,J -are directly proportional to the number of digits possessed by the animal. The carpus consists of 6 bones, 4 above and 2 .helow. The upper are the l^caphoid and lunar, which articulate with the radius ; the cuneiform, artlciJat-' fing with the radius and ulna ; and the trapezium, which is small, tuberoas in shape, and does not articulate with the radius. The lower are the os magnu'Ti md unciform, which articulate with the large metacarpal bone, the trapezoid rand pisiform bones being wanting ; the former, perhaps, is part of the os ["tnagnum. The large metacarpal bone presents a vertical groove down irs ayi?:sr-:,r iiddle, which marks the original division of the bone into two. The interior kjxtremity is divided by a deep fissure into two articulations, each resembling J04r COMPARATIVE OSTEOLOGY.. the single one of the horse, the external one being always the smaller ; a nidi-; irentary metacarpal is placed postero-externally. The phalanges' and sesamoids in either limb are double, one complete set forming each digit.; they are small imd narrow^ the coffin bone resembling half of that of the horse, mesially divided. Posterior to the fetlock joint are two rudimentary digits, each con- taining two undeveloped, phalanges, the median and the distal., PELVIS.. The OS innominatum is larger, but presents the same general appearance as in the horse. The ilium is thick, and possesses a prominent line running from the anterior spine to the superior ischiatic ridge. The internal surface is very convex, the ridge between the part resting on and that without the sacrum being well marked. The ilio-pectineal eminence is prominent, and the crest and spines very strong. The ischium equals the ilium in size ; the anterior extremity has a thick projecting external portion, which forms part of the cotyloid cavity, and is surmounted by the large superior ischiatic spine, whence a slight ridge is continued backward!? over the thick concave body to the tuber- osity. The inferior ischiatic spine is conical, pointing outwards and down- wards. The ischial symphysis presents inferiorly a ridge and tubercle, absent in the horse. The pubis is large and concave, and the symphysis is never completely ossified. The acetabulum is deep, and the cotyloid notch is naj-row and deep, being n«ar the large foramen ovale. The inlet of the pelvic cavity is oval ; its sacro-pubic diameter is greater than the transverse one> while the sacro- ischiatic diameter of the outlet is less than the transverse. PELVIC LIMB. The femur (Fig. 25. /') is distinguished from that oi the horse by the I trochanter minor being wanting. The trochanter internus is a round tubercle near the posterior surface ; the head is small, but prominent, the trochanteric fossa deep, but small ; the trochanter major has only one eminence, not very prominent, and is united to the internal trochanter by a ridge. The condyles and trochlea are somewhat small, and the supracondyloid fossa is shallow.. The patella is narrow^ and somewhat conical in shape. The tibia (Fig. 25. n') has no vertical fossa on the anterior tuberosity, and no articular facet for the fibula ; the distal extremity has its external malleolus detached, forming a small bone called the malleolar bone, which articulates with the tibia, calcaneum, and astragalus, and represents the distal end of the fibula, the remainder of which bone, small when present, is usually replaced by a long ligament stretching the whole length of the tibia. The tarsus consists of 5 bones. The astragalus is deep, but narrow, having a pulley-shaped surface inferiorly as well as superiorly. The calcaneum is lcr.»g and square ; the cuneiforme magnum and cuboid are united, forming the cubo-cuneiform bone ; the cuneiforme medium is like that of the horse, while the parvum is very small. The large metatarsal bone has its inferior extremity divided into two equal parts by a deep fissure, with a groove superiorly. The small metatarsal bones, •when present, are rudimentary and single. The digits correspond to those ol the pectoral limb... OMNIVORA THE SXULI* 105^ Visceral Skeleton. In the adult Ruminant, two bones are -commonly found in the heart, and may be termed the cardiac bones (ossa cordis). They are found related with the auriculo- ventric- ular rings. Jn shape they present three angles, three borders, and two surfaces. The left bone is considerably smaller than the right. ■ Fig. 27., OMNIVORA. Right cardiac bone of au Ox— natural size, a, Anterior angle ; b b, Posterior The Omnivora are represented in Veterin- % angles; c, Superior border; d. Anterior ary Anatomy only by the Hog. border: siiriciC6-. e. Posterior border ; /, Right Axial Skeleton.; the skull. In the skull of this animal the following points are noteworthy. The siqwa^^ occipital bone forms a very prominent crest ; the occipital condyles and the foramen magnum are small ; the styloid processes very long, inclining back- wards. The parietal bones are early anchylosed, the superior surface being contracted in the middle, with a sharp ridge on each side, limiting the temporal fossa. The orbital process of the frontal bone is short, the frontal arch being <;ompleted by a ligament ; in the centre of the bone, about a third from its anterior border, is the supraorbital foramen, and from it a groove passes forwards and outwaids. The frontal bone articulates with the superior . maxilla. The temporal is a smgle bone on -each side ; the ])etrous portion is small, and the zygomatic process large, bearing a promi- nent spine. A ridge connects the external auditory meatus, placed very high up, with the mastoid protuberance, which is very large, the styloid process being short] The maxillary articulation is not supported behind by a well-marked process,' and is smallest transversely.. The sphenoid is short, with large, flat pterygoid processes; the wings do not project, but are nearly perpendicular; the sella turcifc"a is deep, and the olivary and clmoid processes lar<::e. The nasal bones are long, straight, and strong, firnjly connected with X\iq frontal and superior maxillary, but c\o not articulate with the lachrymal bones; the nasal peak projects nearly to the level of the incisors. The lachrymals are small, with lachrymal fossoe on the supero-cxtemal part of the bone instead of in the or!)it, as in the horse and ox ; they are pierced by two conduit^ which' afterwards form one. The malar bone is very strong, and the jygvmatic' process large, awl terminating in two branches, between which rwsu the zygomatic process of the temporal bone ; the anterior branch is short, and not united to the orbital arch of the frontal bone. The superior meing absent.- The metacarpal hones are 4 in number. The miflclle pair are large, the side pair small ; the large ones articulate with each other, and with their relative small ones superiorly. Each terminates distally, as the single one of the horse, but the middle pair are the sole weight-carriers, for the lateral ones do not rest upon the ground. In each of the four digits there are three phalanges, with their accessory sesamoid and uavicular bones. PELVIS AND PELVIC LIMB. The OS innominatum presents the same general characters as that of the' ruminant ; it is, however, distinguished by the foim of the ilium, which is very convex on its anterior border and crest, and by the absence of the protuberance on the inferior symphysis. The femur differs tittle from that of the ox, except in its more contracted neck, which is about on a level with the trochanter major; the trochanter minor is wanting. The tihia resembles that of the ruminant ; its anterior tuberosity is notched, and the external malleolus is supplied by the distal end of the fibula. Tki jUnda extends the whole lengtli of the tibia, articulating with it at both extremities, and distally with the astragalus and calcaneum. The tarsus presents no important deviation from the typical joint, except that the cuneiforme medium is divided, hence there are in the lower row the ecto, meso, and endo-cuneiform bones ; the distal articular surface of the astragalus articulates partly with the cuboid bonej The metatarsus and phalanges closely resemble those of the anterior limb. There is a very rudimentary fifth metatarsal bone on the inside, a rsstige probably of the hallux or great toe. CARNIVORA. In this order our descriptions allude mostly to the Dog, that animal being an excellent type of the order,, and one easily obtained. Axial Skeleton. the skull. The occipital bone of the Dog is very strong, and triangular behind, termina-^ ting in a sharp pointed crest. The tuberosity is not well marked ; the styloid processes are short, and the condyles large. The foramen lacerum basis cranit is divided into two portions by the auditory bulla, which is large and rounded ; the basilar process is long and thick. The Wormian bone is united to th^, occipital ; the ossific tentorium is large. The parietal bones are very convex, in 5*v>me breeds meeting in a sharp ridge, continuous with the occipital crest. Th^ frontal bones are triangular, and present along their middle a hollow, more or less markecL The orbital process is simply a peak, the arch being completed by a ligament ; there is no supraorbital foramen ; the frontal bone articulates with the superior maxilla. The temporals are not divisible into distinct pieces, as in the horse ; the zygomatic processes are large, and "project very much, forming Capacious temporal fossce, and having glenoid cavities, ■which are elongated transversely, for the condyles of the inferior maxilla. 110 COMPARATIVE OSTEOLOGY. Fio. 3L SKELETON OP THE DOG (Carnivoka). Axial Skeleton, the skull. Cranial Bones.— a. Occipital. 1 : 6, Parietal, 2 ; c. Frontal, 2 ; fc. Temporal. 2 ;. Sphenoid, 1 ; Ethmoid. 2 ; Auditory ossicles, 8. Facial Bones.— f, Nasal, 2 ; e, Lachrymal, 2 ; d, Malar. 2 ; h. Maxilla. 2 ; g, Premaxilla, 2 ; i, Inferior Maxilla. 2; Palatine. 2; Pterygoid, 2; Vomer,!; Turbinals, 4; Hynoid series, 9. Teeth :— Incisors, 12 : Canines, 4 ; Molars, 26. T/te Trunk.— I I, Cervical vertebraj, 7 ; m m, Dorsal vertebrae. 13 ; n n. Lumbar vertebree, 7 ; o. Sacrum (three segments), 1 ; p p, Coccygeal vertebrae (variable), 20 ; t t. Ribs, 26 ; * Sternum (eight stemebrse), 1 ; SS Costal cartilages. Appendicular Skeleton. pectoral limb. ft «, Scapula, 2 ; v, Humenis, 2 ; to, Radius, 2 -, x, Ujlna. Carpus :—y, Trapezium, 2 ; z, Cunei- form, 2 ; a'. Scaphoid, 2 ; 5', Unciform, 2 ; c', Magnum. 2 ; d'. Trapezoid, 2 ; e', Pisiform, 2 ; Meta^ carpal bones, 10 ; h'. Anterior sesamoids, 10 ; g'. Posterior sesamoids, 20. Digit :— i'. Proximal phalanges, 10 ; //, Median phalanges, 8 ; V, Distal phalanges, 10 ; Small sesamoids wanting. PELVIC LIMB. Pelvis.— Os Innominatnm :—q. Ilium, 2 ; r. Pubis, 2 ; », Ischium. 2. The Limb.—m' Femur, 2 ; o', Fabellae, 4 ; n', Patella, 2 ; q'. Tibia, 2 ; p', Tibial sesamoid, 2 ; r*, Fibula, 2. Tarsus :— s', Calcaneum, 2 ; tf, Astragalus, 2 ; u'. Cuboid, 2 ; t/, Superior cuneiform, 2 ; «/) Ecto-cuneiforme, 2 ; a;', Meso-cuneiforme, 2 ; j/', Endo-cuneiforme, 2. Metatarsus :— Large bones, 8 ; /, Small bones, 2 ; Anterior sesamoid, 8 ; Posterior sesamoids, 16. Digit :— Proximal phalanges, . 8; Median phalanges, 8 ; Distal phalanges, 8 ; Small sesamoids wanting. Visceral Skeleton. Ot Penis, 1 ; Budimentary .clavicle (inconstant), 2. The bonei of the Carnivora Skeleton, thus considered, are 345. CARNIVORA VERTEBB2E. IH The external auditory meatus and auditory bulla are larjje, the sense of hearing in carnivora being very acute ; there are only diminutive liyoid, and styloid; processes. . There are t\yo canals, of which there exists no trace in other domestic animals — viz., the carotid, which traverses the mastoid portion to ioin the venous canal between the basilar process and temporal i and another which pierces the petrous portion at the upper part of the carotid canal, and gives passage to the fifth pair of nerves. The sphenoid bone reseml^ies that of man ; its posterior part is :jhort, and presents two large wings, which mount to the temporal fossae, the anterior part being straight, and prolonged by small wings. The pterygoid processes are very short, the pituitary fossa limited by the clinoid processes. The ethmoid bone presents very deep fossae and well- developed volutes. The nasal bones are small, narrow, but wi^er in front, presenting a semi- circular concavity, instead of a peak. The superior maxilla is short, but strong, diflering, as all the facial bones do, with the Breed; it articulates by a long process with the frontal, forms partly the socket for the canine tooth, and is spineless. The j;?emaxz?/a is short, and presents a small foramen incisivum, which is often wanting in the cat, alveoli for the incisors, and an oval incisive opening. Tlie lachrymal is small, and in the cat confined to the orl)ital cavity. The ma ^ar bone articulates in the usual manner, while its zygomatic process is large, and curved outwards, and its summit bifid, the arches being formed very similarly to those in the omnivora. The palatine bones form about a third of the palate ; they do not assist in the formation of the sphenoidal, but furnish a small portion of the maxillary sinuses. The pterygoids are strong and quadrilateral The turhinals extend to the anterior nares ; they are remark- able for the number of their convolutions, but do not assist in the formation of the frontal and maxillary sinuses. The inferior maxilla is strong, its rami broad and large, presenting a deep depression on the posteuo-external aspect, in which is inserted the raasseter muscle. The condyles are ovoid transversely, and the coronoid processes long and broad, the sigmoid notch very deep, the labial foramen double or triple, and there are no interdental spaces. There is a tubercle at the angle for the insertion of the stylo-maxillaris muscle. The symphysis rarely becomes ossified. The hyoid bone is triple— i.g., its three elements do not unite. It has two cornua and four cornicula, the cornua being united to the temporal bones by elastic ligaments. VEBTEBRiG. The true vertebral column consists of 27 segments — 7 cervical, 13 dorsal, and 7 lumbar. The cervical vertebrcs in carnivora are proportionally as large AS those of the horse. The atlas possesses large and expanded alas ; a groove or notch takes the place of the anterior foramen, and the posterior foramen is present ; the posterior articulation, instead of being flat, has glenoid cavities, the surface inside the ring, for the odontoid process, being continuous v/ith them. The axis is long, its neural spine single and prominent, overlapping and sometimes articulating with the atlas, thereby completely occluding the atlo-axoid space ; the odontoid process is long, convex on all its surfaces, pointed anteriorly, and more nearly resembles that of man than does that of any other- domestic animal ; it serves as a pivot, on which the head and atlas freely 112 • COMPARATIVE OSTEOLOGy.j relate ; laterally are the condyles articulating with the glenoid cavities of the atJas. The remaining cervical vertebrae diminish as they proceed backwards, and in most cases have large neural spines, which gradually increase from the third backwards. The dorsal vertebrce, 13 in number, vary with the breed ; the pedicles contain large posterior notches in place of foramina. The spinous processes are strong ; the four or five anterior ones are equal in height, while the succeeding ones decrease, and incline backwards. There are 7, sometimes 6, strong lumbar vertcbrce; the bodies are compressed from above downwards, the posterior notches are large, and the neural spines inclmed forwards. The transverse processes slope downwards and forwards ; the anterior articular processes expand laterally, receiving between them the posterior ones of the contiguous vertebra. These vertebrae possess anapophyses diminishing backwards. The sacrum usually consists of 3 segiHents, and is frequently as broad behind as in front ; the first segment resembles the last lumbar. The sacral spine is thin, and serrated superiorly ; the transverse processes are bifid, consisting of upper and lower portions, the upper resembling those of the lumbar region. The coccygeal bones vary from 16 to 21, the anterior ones having the characters of true vertebras. There are usually 13 j)airs of ribs, 9 true and 4 false ; their size and curvature vary much, but they are usually somewhat thick and straight. The sternum consists of 8 elongated cylindrical sternebrse, which resemble somewhat in form the terminal coccygeal bones of the horse. Appendicular Skeleton, pectoral limb The scapula is very large, the spine being almost central, and terminating 'inferiorly in an acromion process, which descends close to the glenoid cavity, I where it curves. backwards. The cartilage of prolongation is wanting. The humerus is long, slender, considerably curved, but not much twisted; the external trochanter is well developed, the internal almost wanting; the bicipital groove is single. The condyles are large, and the coronoid and intercondyloid fossre united, but not always, by a canal which penetrates the bone. In the :Felid£e there is a supracondyloid foramen, situated above the internal condyle, between the humeral shaft and an outer plate of bone. The radius -and ulna are about equal in volume, the ulna, if anything, being the larger ; these bones articulate with each other solely by their extremities, above, by an articular concave facet on the ulna, and a convex one on the radius ; below, by a concave facet on the radius and a convex one on the ulna ; the two, as it were, cross each other, the upper extremity of the ulna articulating behind and to the inner side, the lower extremity to the outer side. ! The bones of the carpus are 7. The upper are the scaphoid and lunar united^ the cuneiform, and trapezium ; the remainder correspond, mostly with those of the hog. There are 5 metacarpal bones, 4 large and 1 small., The digits of the former, homologues of the four fingers of man, have three phalanges each, and two sesamoids, th6 third sesamoid bone being replaced by a ridge on the third phalanx. The fifth and most internal digit has only two phalaiiges, the median CARNIVORA' — PELVTS AKD PELVIC LIMB. 113 phalanx being wanting ; it co Tesponds to the human poUex or thumb. Between each metacarpal bone and its proximal phalanx we have anteriorhj a very small sesamoid bone. T ELVIS AND PELVIC LIMB. The pelvic cavity is generally long and narrow, but the oasa, innominata are very strong ; the iliac spines and crest present a continuous thick rounded ridge. The ischium is also thick and stron.ur, the ischiatic spine and tuberosity becoming one tubercle. The otyloid cavity is surrounded by a prominent border, slightly notched within. The/emwr is straight and long,,presenting a proiainent neck, and a muscular line posteriorly, equivalent to the linea aspe.ra oi man. The supracondyloid fossa is represented by a small tubercle. Above 6ach condyle is a small facet, articulating with a sesamoid bone ; these two bones are called the fabellce^ or gastrocnemic sesamoids. The tibia and Jihda are long, and united in tha inferior half of their middle by ligaments, at either extremity by articulation ; the fibula also articilates- with the astragalus, thus supplying the external malleolus to the tibia. There is a small sesamoid bone at the external part of the head of the tibia. •JIt IV JU ?v Fig 32„ A. Hand or Anterior Foot of the Dog ; B, That of the Hog ; C, That of the Elk ; D, That of the Ox.. I.. Pollex ^^^ \l> Index; III. Mediixs;; .TV. Annulus: V. Minimus. The tarsus consists of 7 bones, as in the hog — viz., ihccalcaneum, astragalus,, cuboid, and four cuneiforms, a superior one corresponding to the magnum of the horse, and three in a row below it, the ecto, meso, and ■ endo-cuneiforms. The astralagus presents distally a distinct head, separated by a neck, which articulates with the cuneiforme magnum. The mdatarsal bones are ' large and 1 rudimentary, the large ones each^ teiminating in three phalanges, with their accessory sesamoids, as in thai anterior limb ; the fifth, or small rudimentary metatarsal, homologous with the, I 114 COMPARATIVE OSTEOLOGY. "hallux of man, is very generally only a ligamentous cord, ULWliicli is found a short bone, which represents a phalanx. Fig. 33. Fio. 84. Clavicle of a Dog— enlarged one-half. Clavicle of a Cat— natural size. VISCERAL SKELETON. In carnivora, generally speaking, there is & davicle^ but it is incomplete, and is found embedded in the soft structures between the sternum and shoulder. In the dog it is often represented by a piece of ligamentous tissue, and when it does exist as a bone, it is very small and somewhat triangular in shape. | The Felidse or cat tribe possess a clavicle which, to a certain extent, j:esembles in shape that of the human subject, being elongated, rounded, and slightly curved. Occasionally this bone in the cat is continued by ligaments, which unite it both to the sternum and to the acromion process. Os Penis. This is a single bone very generally found in the penis of the carnivora, and alVvays in the dog ; in the cat it is said to be less persistent, and when present much smaller. It is a thin piece of bone hollowed to form a longitudinal Fig. 35. Os Penis of a Dog, half the size of that of a large animal. a a. Inferior groove ; 6, Anterior end . c, Posterior end. groove, in which the uretha lies; the groove ceases anteriorly, and at' this extremity the bone becomes flat and pointed. Both extremities are prolonged by cartilages. RODENTIA. This large order we have already mentioned as bfeing characterised by its peculiar dentition. One representative of the order is the common Rabbit,' which belongs to the family Leporidse. Axial Skeleton. There are 12 dorsal, 7 lumbar, and 4 sacral vertebrae. The wing of the . Costal process; 33I.0, Pleurostson ; c. Carina; m.x. Middle Xiphoid, process^ AVES. 117 bone presenting a very large central process posteriorly, the central xipIiQid process (lophosteon)^ outside which is a large bifurcated process (metosteon^ the two projections of which are called the median and external xiphoid processes, and antero-laterally is the ridge (pleurosteon)^ which gives attachment to the ribs. The inferior edge of the central ridge is called the carina/ often a small median spine exists anteriorly, the rostrum or presternum. The following Table shows the nlimber of vertebral segments usually found in domesticated birds :— Cervical. ; 12 ^ 14 . 15 ; 18 Rasores, . Natatores, 5 Pigeon, . (Fowl, . j Duck, . ( Goose, . Dorsal. "t^umbo-Sacral. Coccygeal, i ' \ 14 The costal cartilages are ossified, and thus birds are said to possess sternal and vertebral ribs. Some of the lumbar and coccygeal vertebra9 become anchylosed, and assist in forming the sacrum; it is not indeed easy to define the exact points of demarcation betv,^een the lumbar, sacral, and coccygeal regions. The coccygeal bones terminate in an expanded segment, termed the Fig; 38. Skull of a fowl. A, Inferior aspect, the mandible being removed ; B, Lateral aspect ; px, Premaxiila ; True, Superior maxilla ; p. Palatine bone ; v, Vomer ; j, Jagal bone ; qj, Quactrato-jugal bone; I, Lachrymal; me. Median, ethnpoid ;/, I'rontal ; ^j/, Poat-frontal process ;p, Parietal ; pt. Pterygoid ; q, Os quadratum ; sj, SquamcsrJ ; eu. Process before the Eustachian aperture ; 6o, Basi-oocipital, and so, Supra-occipital bones ; ar, Articular, a, Surangular, and d, Dentary portion of the Mandible. ploughshare bone. In the skull we have to note chiefiy the absence of teeth, the existence of only one occipital condyle, and the articulation of the man- dible or lower jaw, which does not articulate directly with the skull above, but there is interposed the quadrate bene, which, when the lower jaw is depressed, acts on a process, the quadrato-jugal bone, connecting it with the maxilla, and so simultaneously raises the upper jaw, there being usually elight vertical motion between the latter and the cranium.. 118 COMPARATIVE OSTEOLOGY. The pectoral arch consists of three parts — the scapula, clavicle, and coracoi(? bone. The scapula is sword -shaped, and placed nearly horizontally; the coracoid bone, the strongest of tlie three, is almost perpendicular, and firmly attached to the sternum below, affording a strong basis for the bones of the , wing to move upon ; it helps to form the glenoid cavity for the humerus. The' clavicles project downwards and slightly forwards, arching inwards, and generally becoming united below to form a flattened plate, the hypocleideum ; ; the united clavicles are termed the /urcaZwm, familiarly known as the " meiTv^j thought." The hypocleideum is^ usually joined by a ligament to the sternum below ; in some classes of birds it is absent ; in some the clavicles are not united ; in some, again they are united by ossification to the sternum. The ulna is larger and stronger than the radius; the carpus consists of two bones, the metabarpus' of three, one of which 30 a rudimentary pollex. There are two digits, one of which has one, the other two or three phalanges. The pelvis is expanded and shield- like, -and consists of the ilium, ischium, and pubis ; but there is no inferior symphysis, and, therefore, no true pelvic cavity. The pubis is styliform, and directed backwards and inwards ; in the ostrich alone it articu- lates with its fellow.^ The femur is short, the tibia long, and anchylo&ed with Fio. 39. r Pectoral arch of a Bird, sc. Scapula : co, cora. coid bone ; /, Clavicles, terminating below in the hypocleidemn ; gl, Glenoid cavity. fio. 40. pelvis of a Bird A, Superior : B, Lateral aspect : «m. Sacrum ; U, Warn: Is, Ischir ^'^ /▲cetabnlam. iLVES. IW "the fibula, which is small.^ The tarsus is early fused with the metatarsus, th© latter consisting generally of one long bone. The digits vary in number ; the, domesticated birds usually have three anteriorly and the hallux postero-inter«i nally ; the outermost has five phalanges, the next four, the next three, while the hallux has only two. The spwr, a horny projection from the metatarsus, is sometimes counted as a digit. The bone tissue of birds is exceedingly compact and hard, and white in colour; and some of the bones are pneumaticj or contain air instead of marrow; notably these are the bones of the skull, the sternum, and the proximal bonea of the limbs. There is great variety in the amount of pneumaticity possesse4f by the skeleton in 'different species, but it is not necessarHy guided by thai Jlying power of the animal ^^ I CHAPTER II. AETHROLOGY. The several bones which form the skeleton are united by means of certain soft structures, forming a series of articulations or joints, the study of which is termed Arthrology or Syndesmology. Before considering the different forms of joints, it will be advis- able to describe briefly the various tissues, other than bone, which enter into and contribute to'^ards their formation. These are chiefly cartilage, connective and elastic tissues, and fat. In health, one bone never comes directly in contact with another, cartilage or fibrous tissue being always interposed ; an exception to this exists in the adult skull, most of the bones of which become firmly united by ossification of the interposed soft material. CARTILAGE. Cartilage, known also by the familiar name of gristle, is a firm, bluish-white, elastic animal substance, somewhat translucent, resilient, and flexible, possessing great cohesive power. That which forms the original basis of the bony framework is termed temporary, and that which persists in the adult, permanent cartilage; the former disappears as it is replaced by bone, but the latter, of which alone we have to treat here, never under normal circumstances becomes ossified. Cartilage consists of corpuscles or cells, usually imbedded in an intercellular substance or matrix. The cells, which are contained in lacunae in the matrix, are oval, round or fusiform, and nucleated, the nuclei, which appear under the microscope as small spots, containing still smaller objects called nucleoli. Cartilage when boiled yields chondrine, a substance varying slightly from gelatine. There are three varieties of the permanent kind — hyaline, fihro, and cellular cartilage. In the first, the matrix is homogen- eous, or void of definite structure, appearing slightly granular under 120 r CARTILAGE. 121 the microscope. Fibro-cartilage is ctaracterised by a matrix of fibrous tissue ; while the cellular variety consists of an aggrega- tion of cells without a matriz. Hyaline cartilage is distinguished by the following names, according to the purpose it serves : — Articvlar, when it encrusts the articular surfaces of bones, helping to form joints by supplying a smooth elastic cushion, which diminishes both concussion and friction ; Costal, when it supplies elastic prolongations (hsemapo- pbyses) to the ribs, connecting them distally with the sternum ; Membraniform, when it appears as thin plates, forming per- manently open tubes, — the trachea or wind-pipe is composed of this kind of cartilage. In articular or encrusting cartilage the matrix is abundant, and the cells vary in form, those near the surface being flatter and more numerous. It is always thickest in the young, becoming thinner as the sub- jacent ossification proceeds. It is thickest in the centre of convexities, thinnest in the centre of cavities. In the adult it is non- vascular, being nour- ished by a vascular zone in the synovial membrane, called the circulus articuli vasculosus, from which the nutritive ma- terial is conveyed. The blood- vessels of the bone underneath the cartilage also assist iw supplying nourishment to the latter. All hyaline cartilage,' except the articular kind, is covered by a membrane called the> perichondrium. Fibro-cartilage consists of cartilage cells and fibrous tissue,) which may be white or yellow, the former being tough and strong,! the latter highly elastic. White fibro-cartilage is much the more plentiful, and presents the following varieties : — It .is called Inter- articular when it appears as a pad interposed between the two articular cartilages which form a joint ; such a pad is termed a TYieniscus, and the temporo-maxillary and femoro-tibial joints are! furnished with such. Circumferential, where it surrounds andl deepens an articular cavity, as the acetabulum. Connecting,] when it is interposed between bones and firmly connects them, asl Fia. 41. Section of hyaline cartilage, a, Four separatin^^ cells ; b, Two cells in apposition ; c c. Nuclei ; 1 d. Cavity in the matrix containing three cells. 122 AKTHROLOGY. between the vertebral ceutra. SiraPlform or InvesHvg, wl'.e'i) it clothes the parts of hopes over which the tendons of muscles play, sometimes existing in the tendons themselves. This tissue is dullish white, opaque, and. for the mofit part. devoid of perichondrium | it is vascular, but its blood -vefisels are few, and confined to the fibrous tissue, which exists as interwoven bundles of fibres, with cartilage cells interspersed amongst them. In the variety connecting vertebras, it consists of concentric rings of fibrous tissue, enclosing a soft elastic centre, partty mude up of cartilixge cells, and often regarded as the remnant of the itotochord. In fishes this portion is soft and pulpy, filling the opposing con- cavities of the vertebral centra. Its power of cohesit>n is very great, surpassing even that uf bone. Yellow eladic fihro-cartilage is found in the epiglottis or vaive which closes the principal air-tube ; it forms part of the frame- work of the ear. and of the Eustachian tubes which convey air to the tympanum. The fibres forming the matrix aro similar to those of yellow elastic tissue. Cellular or ret'lcular cartilage is found in the v;ar of some small rodents, and in the bat. It consists of cells devisaly packed, and apparently without a matrix : the walls of tKe cells thus coming into contact, give it a net- like appearance, hence the name reticular cartilage. CONNECTIVE TISSUE. In one form or other this tissue is found in t-W }>arts of the body. The chief varieties are the areolar and the fibrous ; the former serving as a connecting medium, and support to the various organs, and to the structures of which they are formed. It appears as a loose translucent mesh, its interwoven bundles form- ing spaces termed the areolae or cells, hence its name Gellular or Areolar Tissue. It consists of minute lamina and filaments mixed with small fibres of elastic tissue, while cells, or their remains, nuclei and walls, are also present, the whole embedded in a perfectly transparent basis. Other slightly varyiug forms are termed Betiform,, Gelatinous, &c., while the coniiecti^'e tissue of the brain and retina has received the name of Neuroglia. White fibrous tissue has a similar structure to the above, but is dense, strong, and practically non-elastic. Tb& filaments which form it are mostly parallel and wavy in their arrangement. It ADIPOSE TISSUE. 12a Fro. 42. "White fibrous tissue from a ligament. 65 diamrs. appears in two forms — the sheeted or aponeurotic, which is found in investing ligaments, membranes, periosteum, &c. ; and the cordi- form, in which the fibres are col- lected in strong bundles ; this is the chief constituent of the binding ligaments, which hold articulating bones together and limit their mo- tion. The tendons of muscles are also made up mostly of this kind of tissue, but both in them and in ligaments yellow elastic fibres are also found. Connective tissue contains nerves and blood-vessels, for the supply of neighbouring structures as well as for its own nourishment, and also tendon cells, the latter lying in the spaces between the smaller bundles. When healthy this tissue is little sensitive to pain. YELLOW ELASTIC TISSUE. This difiers from the white tissue in being yellow, elastic, and not so tough or strong. Its fibres are sometimes as large in dia- meter as ^^QQ in.; but when mixed with white tissue in tendons the diameter may not be more than one-sixth of this. The fibres branch and join each other, and their ends curl up when cut or broken. Acetic acid has no effect on the yellow tissue, while it causes fibres of the white to swell greatly and become quite transparent ; again, when white tissue is boUed gelatine is obtained, which is net the result of boil- ing the yellow fibres. Yellow elastic tissue is found nearly pure in the ligamentum luchas, the tunica abdominis, the coats of the largest arteries, and elsewhere. The lungs contain a large quantity of this tissue. AriPOSE TISSUE., Fat or adipose tissue consists of cells containing an oily material, and arranged in isolated groups, or slightly separated by meshes Fig. va. Yellow elastic tissue, magnified, from the liga- mentum nuchas of a calf. 65 diamrs. 124 ANTHROLOGY. Fig. 44. Adipose tissue magnified. « o, Fat cells — these on the right in mass ; those on the left spread amongst the con- nective tissue fibres b b. of areolar tissue and capillary blood-vessels. It is found in many parts of the body, and varies greatly in quantity ; in joints it occurs between the ligaments, and serves the purpose of a packing material, while in the form of medulla or marrow it occupies the cavities of bones. In fat cells a nucleus is rarely visible, without special preparation. LIGAMENTS. Ligaments are dense, fibrous, connecting structures. They exist in most articula- tions, and are made up principally of white fibrous tissue. There are two kinds — capsular or bursal, and funicular or binding ligaments. Capsular ligaments are membranous structures, generally, but not always, en- closing true joints. They consist of a dense interlacement of fibres attached to bones, round the edges of the articular cartil- ages, partially or wholly surrounding the joint ; some regard them as a continuation of the periosteum. They are never closely applied, their use being to form cavities round the joints, enclosing and protecting the synovial or lubricating apparatus inside. Funicular or binding ligaments consist of rounded or flattened cords, or bands of fibrous tissue, passing from one bone to another, firmly attached to roughened portions of their surfaces. They hold the bones in their places, at the same time allowing ths requisite amount of motion in the joints. Ligaments which are situated between bones are often termed interossscus. Annular ligaments are those v/hich bind down and protect the tendons of muscles in certain joints, converting grooves in the bonos into channels or tubes which are lined with synovial membrane, and through which the tendons play. Some ligaments are composed almost entirely of yellow elastic tissue, such as the ligamentum nuchse and the ligaments con- necting the vertebral arches. SYNOVIAL MEMBRANES. These are thin membranes lining the capsular or binding ligaments of true joints, or they are interposed elsewhere r CLASSES OF JOINTS. 125 between structures which move one upon another, and which would otherwise be injured by the friction. They resemble what are termed serous membranes, in lining closed cavities, and in containing a layer of endothelial cells which secrete a a lubricating fluid, called synovia or joint-oil ; the foundation of these membranes is a layer of connective tissue, which varies considerably both in density and thickness. The synovial membrane terminates at the border of the articu- lar cartilage, which in the adult it never covers ; in the foetus it is said by some authorities that it . covers the cartilage also. Near the borders of articular cartilages the membrane is generally found as a projecting fold, the projection being due to a small pad of fat, interposed between the membrane and the capsular ligament* These projections were once erroneously termed synovial glands, but their use is probably to assist in forcing the synovia between the opposing surfaces of cartilage. Under the cellular layer blood-vessels are found, and near the articular cartilage there is formed a vascular zone, the circuliis articuli vascvlosus, in which the capillaries terminate by dilated loops ; articular cartilage derives its nourishment partly from this source (see page 121). There are three forms of these membranes : — the capsular, which line the capsular ligaments of all true joints ; bursal mem- branes, found where one structure moves upon another, as when a tendon plays over a bone, and known as synovial bursa;; or, when they exist in the subcutaneous tissue, between tLe skin and certain prominent parts of the skeleton, they are known as bursoi mucoscE. The third form, i/aginal membranes or sheaths, exist where one tendon forms a sheath for another, or in other canals through which tendons glide. Syvovia^ or joint oil, is a viscid, transparent fluid, colourless, or pale yellow, physically resembling oil, but it contains very little fatty material, consisting chiefly of albumen, salts, and water ; it is secreted by the cells on the inner surface of the membrane. When an animal is in active exertion, there is a greater demand for joint oil than when at rest, consequently there is an increased secretion of it. CLASSES OF JOINTS. Joints may be divided into three classes — Immovable or Synarthrodial, Movable or Diarthrodial, and Mixed or Amphi- -arthrodial. 126 ARTEP.CLOGY. SYNARTHROSIS. In an immovable joint there is only a thin layer of fibrous or cartilaginous material interposed between the bones, the fibrous layer of the periosteum of both bones uniting to cover and become attached to the connecting material, thus serving as a ligament. If the connection is fibrous, the joint is- generally called a suture ; if cartilaginous, a synchondrosis. These joints are found chiefly, but by no means solely, in the skull : and they tend to become obliterated, in the adult, by ossification of the connecting material. The varieties of synarthrosis are the sutura. synchondrosis, schindylesis, and gomjphosis. Sutures are true or false. In the sviura vera or true suture. the contiguous margins are united by a series of interlocking processes and indentations, a thin fibrous layer being interposed, connected externally with the periosteum. Variety of shape has led to the following nomenclature : — sutura dentata, where the processes are large and tooth-like, aa in the interparietal ; sutura aerratu, where they are small and fine, like the teeth of a saw, as in the interfrontal ; and sutura limhosa, where the xjontiguous parts are dentated and also bevelled, as in the parieto-occipital — the sutura lamhdoidalis of the human subject. In the false sutures, or sutura notha, the bones are joined by plain rough surfaces, of which there are two forms — sutura squamosa, where the adjacent borders are bevelled, the edge of one bone resting on and overlapping the other, as in the parieto- temporal ; and sutura harmonia, v/here the articulating surfaces of two bones present no marked irregularity, as the nasal and premaxilla. Synchondrosis, as already stated, resembles a suture, but the connecting medium is cartilage instead of fibrous tissue ; examples are found in the joints between the basi-occipital and basi-sphenoid bones, and between the latter and the pre-sphenoid. Schindylesis is that form of immovable articulation, where a ridge or plate of one bone is received into a slit or fissure in another, as the orbito-sphenoid into the incisura sphenoidaJis of the frontal bone. Gomphosis is the form where one bone is inserted in a cavity or socket in another, as the teeth in the alveoli. AMPHIAETHHOSiS. 127 DIARTHROSIS. In movable or true joints the articular surface of eacli bone is cohered by cartilage of encrustation; the bones are held together by ligaments, the capsular one closing the cavity of the joint, ^hich is lined by synovial membrane. In some joints there is ^ pad of fibro-cartilage interposed between the two articular '^jartilages. Such a pad is called a Tneniscus, and it adds to the elasticity and freedom of the joint. Movable joliitB form the most numerous iclass; they are found in the limbs and else- ^zhere. The chiaf varieties are the arthrodia, nnarthrosis, and the ginglymus. In Arth'f'odia the motion is slight and glid- ing, the bony surfaces being flat or slightly undulating, and the motion limited by ligaments or processes of bone, as in the small bones of the carpus and tarsus. Enarthrosis, the ball- -and-socket joint, is capable of moving in any direction ; the extremity of one bone is globular, and fits into a cup-shaped concavity in another bone ; the hip and shoulder joints are examples. The Ginglymus, or hinge joint, although it may allow extensive motion, limits it to one . plane, backwards and forwards, as in the elbow. A Rotatory joint (diarthrosis rotatorius), where the motion is limited to rotation, is formed by a pivot on one bone fitting into a ring on another, as the atlo-axoid joint. Fig. 45. Diagram of a diar- throdial joint, a a. Articulating bones ; c c c, Synovial mem- brane. The shaded portions represent the articular carti- lages, which are said by some to be covered in early foetal life by the inflected con- tinuations (6 6) of the synovial mem- brane. AMPHIARTHROSIS. There is but one kind of amphiarthrosis or mixed joint ; the variations are too slight to warrant separation into classes. The term mixed is used with reference, not to the motion in such joints, but to their structure, which partakes of the nature of both the movable and immovable, the bones being firmly joined together by a strong interposed pad of fibro- cartilage, which is likewise adherent to the ligaments of the joint. There are no capsular ligaments ; the cartilaginous pad or disc is softer towards the centre, where occasionally 128 ARTHROLOGY. there may be one, or even two, narrow cavities, and authorities diflfer as to whether such cavities are lined by synovial mem- brane or not. Since there are really no frictional surfaces in such a joint, motion depends upon the flexibility of the disc. The joints between the vertebral centra afford the best illustra- tion of the mixed class. The classification of the joints is here tabulated for reference. Synarthrosis (Immovable). r Dentata. "^era. J Serrata. Sutiira. / ' Limbosa. Notha. / Squamosa. I Harmonia. Synchondrosis. Schindylesis. Gomphosis. Diarthrosis (Movable). Arthrodia. Enarthrosis. Ginglymus. Diarthrosis rotatorius. Amphiarthrosis (Mixed). MOTION IN JOINTS. The following- terms express tne various movements^ allowed by joints : — extension tends to bring two bones as nearly into a straight line as the structure of the joint will permit ; flexion is the reverse of this, and diminishes the angle that extension increases ; abduction expresses the. outward movement of a limb or bone from the central plane of the body ; adduction is the reverse action ; rotation signifies the partial revolution of a bone or number of bones, as it were, on their own axis ; circumduc- tion implies the movement of the distal end of a bone or limb, when it describes a curve, as the arc of a circle, ellipse, &c. The term gliding explains itself, and is peculiar to diarthroses, other joints having no frictional surfaces. common ligaments. 129 Articulations of the Axial Skeleton. COMMON VERTEBEAL ARTICULATIONS. With the exception of the atlas and dentata, which form special joints, the true Vertebras present great uniformity in their mode of union, articulating with each other by an amphi- arthrosis, which unites their centra, and by a pair of true joints formed by the oblique processes. These connections are com- pleted or strengthened by ligaments, some of which are common, others special, the former are continuous, passing over and uniting many vertebraB, while the latter exist separately between the contiguous segments. The bodies are united by intervertebral discs of fibro-cartilage, convex in front, and concave behind, firmly fixed to the articular surfaces of the centra. The discs consist of laminss arranged concentrically, with fibres crossing among themselves, and passing from one articular surface to the other. The central portion is yellowish, presenting more the character of true cartilage, and towards the circumference the laminae become denser. The discs do not exist between the first and second cervical joints ; they are thick in the neck, and thinner in the dorsal region, where they assist in forming sockets for the heads of the ribs. The lumbo-sacral disc is very thick. Common Ligaments, These are the Superior and Inferior Common, and the Supra- spinous ligaments, the latter in the cervical region being termed the Ligamentum Nuchse. The superior common ligament is ribbon-like in form, extend- ing in the spinal canal from the sacrum to the axis, placed upon the superior part of the bodies of the vertebrae, to which, as well as to the intervertebral substances, it is attached, becoming broader at each of the latter attachments. The inferior common ligament, situated below the vertebral bodies, stretches from the sacrum only to the sixth dorsal vertebra, anterior to which its place is taken by a. muscle called the longus colli. It is strongest in the posterior part of the dorsal and in the lumbar regions, and broadest ofi the interverte bral substances. K 130 ARTHROLOGY. Posteriorly the supraspinous ligament is a white fibrous cord, extending from the spine of the sacrum, along the upper margin of the neural spines to the first dorsal vertebrss, where its character becomes so greatly changed that the cervical portion may be, and often is, described as a separate structure — the ligamentum michcz or ligamentum colli (PI. I. / f) ; it is formed of yellow elastic tissue, and remarkable for its strength, elasticity, and insensibility to pain. It consists of a funicular and a lamellar portion ; the former, called also the cord of the ligament, is double, and extends from the first, second, and third dorsal spines to the occipital tuberosity, continuous posteriorly with the. white supraspinous ligament, in which elastic tissue may be traced to some distance. The right and left ligaments meet in the mesian line, and from the postero-inferior aspect springs the lamellar portion, which is flat and triangular, separating the muscles of the neck into right and left. It consists of two plates, joined by cellular tissue ; the lamellae or bands descending from the cord and spinous processes usually of the first three dorsal vertebrae, run obliquely forwards, to be inserted to the superior spines of the six posterior cervical vertebrge, blending with the interspinous ligaments. The lamellae although widely separate, are connected by smaller branches, and also by connective tissue. This ligament being highly elastic, is not a binding ligament, but acts as a passive support to the head and neck, diminishing the muscular tension in the superior cervical region. Special Ligaments. The special ligaments of a common vertebral articulation are the interspinous J the lig amenta suhflava, the intertransverse, and the capsular. The interspinous ligaments connect the neural spines, and are continuous with the supraspinous ligament above ; they are composed of yellow elastic tissue in the cervical region, elsewhere of white fibrous tissue. The ligamenta suhflava, or ligaments of the arches, connect the laminae of the articulaticg vertebrae ; they may be regarded as bifurcations of the inter- spinous ligaments, and their regional structure varies like that of the latter. The intertransverse ligaments are found between the transverse processes, and are strongest in the lumbar region ; these ligaments are well marked only in the solipede (Fig. 60. a). The capsular ligaments invest the articulations of the oblique, processes, forming true synovial joints. SPECIAL VERTEBRAL ARTICULATIONS. 131 5PECIAL VERTEBRAL ARTICULATIONS. Occlpito-atloid Articulation. — This joint is formed by the occipital condyles and the glenoid cavities of the atlas, and possesses five ligaments — one capsular, two lateral or styloid, superior suspensory, inferior suspensory. This joint is a true one, having two synovial membranes — one for each condyle. The .styloid ligaments pass from the base of the occipital styloid prc3esses to the sides of the atlas. The superior suspensory or occipito-atloid is very broad, and consists of fibres, which cross each other, e3^,tending from the superior margin of the foramen magnum to the notch on the anterior border of the atlas. The inferior siispensory ov occijpito-atloid stretches from a notch on Fia. 46. Neural canal of first three cervical vertebrae, opened from above to show the internal ligaments. The occiput and foramen mag- Qum are seen to the right, b, The odontoid ligament; a, The occipito-atioid portion (long odontoid) ; c, Superior common ligament ; d, Posterior articular cavity of a vertebral centrum. the anteiv-inferior part of the atlas to the inferior margin of the foramen magnum; it is thin and membranous. The capsular ligament passing completely round the joint, becomes blended with the other ligaments. The latter are sometimes considered as mer--^ enlargements or strengthenings of the capsular ligament, which, this view being taken, would then become the only liga- ment of the joint. This joint allows of flexion, extension, circumduction, and lateral motion. Atlo-axoid Articulation. — This joint is formed by the oppo- sing articular f^urfaces of the atlas and axis, and is also a true joint. The atlo-axoid ligaments are the capsular, the superior, the inferior, and the odontoid. The capsular is very broad superiorly, where it closes the atlo-axoid space. The superior ligament passes from the supero-posterior part of the ring of the atlas to the neural spine of the dentata. The inferior joins the inferior spines of the two bones. The odontoid springs 132 ARTHROLOGY. from the superior part of the odontoid process, inside the ring of the atlas and may be regarded as a continuation of the superior common ligament ; it divides into two strong bands, which become attached on either side to roughened surfaces inside the neural canal of the atlas. This portion is sometimes called the short odontoid, while the loTig odontoid consists of smaller bands which pass forwards and are attached inside the foramen magnum of the occipital bone ; the latter ligament is also called the occipito- axoid. The motion of this joint is purely rotatory, being in fact the rotatory joint of the head ; or, in other words, when the head rotates the atlas moves with it. Sacro'lumhar Artimlation, — This is formed by the last lumbar and first sacral vertebrse. There are the usual typical articulations between the centra and zygapophyses, and in addition a pair of diarthroses formed by the facets on the trans- verse processes, which exist and form joints also between the fifth and sixth lumbar vertebras (Fig. 60). The usual vertebral ligaments are found, with the addition of a pair of capsular ones for the transverse joints. Coccygeal Articulations. — These are of the typical form, but become more and more rudimentary as the bones lose more and more the true vertebral character, the discs are formed, but the ligaments become gradually blended, finally enveloping the bones. in a fibrous sheath. Thoracic Articulations. The thoracic skeleton contains the articulations which unite the dorsal vertebras to one another and to the ribs, those which connect the ribs and costal cartilages, those joining the latter to the sternum, and finally, those which connect the sternal segments. We have already described the vertebral joints. OostO'Vertehral Articulation. — A' diarthrodial connection is here formed by the head and tubercle of a rib, the juxtaposed facets on the bodies of two dorsal vertebrae, and the transverse process of the posterior one. The ligaments are as follows : — The stellate or radiating ligament is situated inferiorly, and consists of strong fibres, divided into three fasciculi, uniting the head of the rib, one to the vertebra in front, a second to the intervertebral disc, while the third passes to the posterior vertebra ; the interarticular or round ligament passes from the THORACIC ARTICULATIONS. 133 ridge on the head of one rib through the articulation, giving a slip to the intervertebral disc, and is attached to the fellow rib on the opposite side; the head of the rib is thus divided into tWo distinct articulations, with capsular liga- ments and synovial sacs. Super- iorly the anterior costo-transverse unites the neck of the rib to the infero-anterior part of the vertebral transverse process, while the pos- terior costo-transverse passes from the supero-posterior part of the tubercle to the lateral part of' the transverse" process. One capsular ligament unites the tubercle and transverse process, enclosing a syno- vial sac. Fig. 47. Costo-vertebral articulation, right lateral aspect, a. Anterior, and h. Posterior costo-transverse ligaments ; c, Ligamen- tum subflavum ; d, Interepinous, and e, Suprarspinoua ligaments. Fig. 48. Costo-vertebral articulation. Neural canal opened from above, and superior common ligament removed, a, Inter- articular ligament ; & &, Branches joining the disc. Ghondro- costal AHiculation. — This is a fixed joint between the rib and its cartilage ; each rib is cupped on its lower extremity, the convexity of the cartilage resting in it, and the joint, a gomphosis, is clothed around with strong fibrous tissue. Gosto-sternal Articulation. — This joint is formed by two sternal segments and a true costal cartilage. The first cartilage, however, articulates with the presternum only, and the last only with the last sternal segment. The ligaments are the capsular and the superior and inferior costo-stemal^ which stretch from the costal cartilages to the sternum above and below, blending with the capsular ligament. The asternal or false cartilages are united, each free extremity becoming attached to the cartilage in front by a small elastic ligament. The first asternal cartilage is very firmly attached to the last sternal one ; a small ligament, the chondro-xiphoid, is also described, which connects the xiphoid and first asternal cartilages. 134 * ARTHROLOGY. The first pair of costo-sternal joints -which are close together usually have a common capsular ligament. Sternal Articulations. — These bind together the sternal seg- ments. The ligaments in the horse are the superior sternal^ extending along the upper surface of the bones, and the intervening fibro-cartilages which eventually ossify. The cartilaginous appendages of the sternum are the cariniform aid xiphoid cartilages. In the horse the former appears 2:3 a sharp ridge running from above and before the presternum, dov/n the lower mesian line* of the anterior sternal segments. Its shapo bears a marked resem_blance to the keel and cut-water of a boat, hence its name. The xiphoid is a flat ovoid plate of cartilage attached to the posterior segment of the meso-sternum ; unlike the cariniform, its sharp edge is placed transversely. It is alsa called the ensiform cartilage. Articulations of the Skull. These- are all synarthrodial, excepting the temporo-maxillary joints and those between the hybid bone and its appendages. Collectively, the remaining joints are called the sutures of the skull, and some of these have received special names. SUTURES. The straight median suture extending from the occipital crest to the nasal peak is the longitudinal one, subdivided into the nasal portion, which is open at the apex, the frontal, and the saggital, the latter situated between the parietal bones, while joining the nasal and lachrymal bones to the frontal is the trans- verse suture. The coronal suture extends obliquely upwards and backwards from the temporal fossa, between the frontal and parietal bones, while the sutura limbosa runs upwards between the parietal and occipital bones, reaching from the tempora.l bene to the saggital suture. For structure of sutures see page 126. TEMPORO-MAXILLARY JOINT. This articulation is a diarthrosis, and it is furnished with capsular, external lateral, and posterior ligaments, and also with a meniscus or interarticular disc of cartilage. The joint r ARTICULATIONS OF THE HYOID SERIES. 135 IS formed by the condyle of the inferior maxilla, and the condyle and glenoid cavity of the temporal bone. The meniscus ia irregular and flattened from above downwards, the superior surface being concavo-convex to correspond with the condyle and glenoid cavity above ; its inferior surface being con- cave for the reception of the maxillary condyle. The capsular ligament is at- tached to the circumference of the meniscus, so forming two synovial cavities. The posteriorligsiment runs from the mastoid process, and the external lateral one from the zygomatic arch of the temporal bone, both going to the neck of the maxilla ; both are mere thickenings of the capsular ligament. This joint admits of lateral motion, extension, flexion, and in the herbivora elevation and depression. Fig. 49. Eight temporo-maxillary articulation— external view. a, The meniscus ; b, External lateral, and c. Posterior ligaments. ARTICULATIONS OF THE HYOID SERIES. The Eyoid articulations are as follows. The temporo^ hyoid articulation is amphiarthrodial, the superior angle of Fig. 50. '^ Hyoid articulations, a, Point going to form the tem- poro-hyoid articulation; b, Eudimentary second comi- culum ; c. Proximal, and d, Distal interhyoid articulations. the comu articulating with the hyoia process of the petrosal 136 ARTHROLOGY. bone by a piece of fibro-cartilage. The proximal interhyoid articulation is also amphiarthrodial, a similar cartilage joining the comu and corniculum ; tKe latter articulates with the hyoid bone by a true synovial joint, the distal interhyoid. In the proximal interhyoid cartilage a small ossicle may be found, which in ruminants appears as a second corniculum. The motion in the two first-named joints is considerable. "We may mention here that the heel processes are attached at their ends to the thyroid cartilage of the larynx by the lateral hyo-thyroid ligaments, between which is found the middle ligament {see ** Laryngeal Ligaments "). Articulations of the Appendicular Skeleton. pectoral limb. the shoulder joint. The Scapulo-humeral articulation is formed by the glenoid cavity of the scapula, and the articular head of the humerus. It is a ball-and-socket joint, with one strong capsular ligament. The bones are held in position by the follow- ing muscles which pass from the shoulder- blade to the arm, and play the part of active ligaments ; — The antea spinatus, postea spinatus, postea spinatus minor, sub- scapularis, and flexor brachii. The motion ^■■■■^^^■^ of the joint is angular, lateral, and circum- ductive, THE ELBOW JOINT. The Humero-radio-ulnxir is a ginglymus formed by the radius, ulna, and humerus. It has capsular and lateral ligaments. The capsular is strongest in front, where it stretches from the distal end of the humerus to the head of the radius ; posteriorly it encloses the articulation of the ulna with the humerus, and it also surrounds the double articulation between the head of the ulna and the radius. Anteriorly it u attached to the tendon of the flexor brachii, posteriorly to that of the anconeus FlO. 61. Lijfaments of the ' elbow Joint — posterior view, a, External lateral ligament ; ht Internal lateral ligament ; c, External, and d. Internal ardform ligaments. SPECIAL LIGAMENTS. isr muscle. The internal lateral ligament is crucial, longer but less, strong than the external ; it stretches from a small tubero- sity on the inner side of the internal condyle of the humerus to the head of the radius. The external lateral ligament, crucial,' ishort and thick, passes from a ridge on the epitrochlea, and a cavity on its outside, to a tuberosity outside the h6ad of the radius. The joint possesses flexion and extension only. EADIO-ULNAR JOINT. This articulation, small and very firm, is formed by the articular surfaces of the radius and ulna, and consists of two true and two mixed joints. The arciform or superior radia- ting ligaments are attached on both sides to the superior part of the ulna and radius. They are curved, and blend with the lateral liga- ments of the elbow. Below the radio-ulnar arch are a few fibres, which constitute the inferior radiating ligament. The surfaces above and beneath the radio-ulnar arch are joined by the interosseous ligaments, which ossify early in life. The motion is practically nil. THE CARPUS. v^ The ligaments of this, joint or rather group of joints, are special and common. The articulations between the bones of the upper row may be termed the superior carpal; those between the bones of the lower row the inferior carpal; between the radius and the upper row we have the radio-cajyal ; between the upper and lower rows ih.Q inter-carpal ; and between, the lower row and the metacarpus the carpo-metacarpaL Fig. 62. Lisjaments of the car* pus— anterior aspect. a» Internal lateral ligaments b. External lateral liga- ment; c c, Anterior car- pal ligaments ; d tf. Anterior carpo-metacar- pal ligaments. Special Ligaments, Superior Carpal Ligaments. — The four bones of the upper row are held together . by three anterior and three interosseous ligaments. The anterior are flat bands placed one between each pair of bones; and the two inner ones are covered by and 1S8 AP.THP.OLOGY. attached to the capsular ligament ; the third, the median trapezial, is covered by the external lateral ligament. The interossei are attached to the roughened grooves between the .articular facets on the lateral surfaces of the scaphoid, lunar, and cuneiform bones. The two inner are blended with the anterior, while the external one is covered by the posterior common ligament. Inferior Carpal. — The bones of the lower row are held together by four ligaments, two anterior and two interos- seous. The anterior are covered, the internal one by the internal lateral, the other by the capsular ligament. The interossei are two ; the one joining the mag- num to the trapezoid is blended with the anterior ligament, but the other is separated from the corresponding anterior one by an articular facet. Radio-carpal. — The special ligaments join- ing the radius to the upper row are three in number. The oblique one stretching obliquely from the lower extremity of the radius, under the posterior common ligament, to the scaphoid bone. A second small one, the superior tra- pezial, stretches from the external side of thfe inferior extremity of the radius to the superior border of the trapezium, partly covered by the external lateral ligament. A third, the smallest of all, is buried under the former, and stretches from the inferior part of the radius to the os lunare. Intercarpal. — There are three special liga- ments ; two are short, and situated under the posterior common ligaments. The first runs vertically from the scaphoid to the magnum and trapezoid, the second passes obliquely from the cuneiform to the magnum ; while the third, the inferior trapezial, by far the strongest, stretches from the trapezium to the unciform and head of the external splint bone, blending externally with the lateral, internally with the posterior common ligaments. Garpo -metacarpal, — This joint has the following special ligaments : — two anterior, two posterior, and two interosseous. The first anterior consists of two bundles uniting the os magnum to the large metacarpal bone. The aenond anterior Flo. 53. Deep ligaaenta of tha carpus — external view, a and fc, Deep portions Of the external lateral ligament , c, Superior, d. Median and e, Inferior trapezial ligaments. COMMON CABPAL LIGAMENTS. 139 binds the unciform posterior bind the extemal splint bone. The two and trapezoid to the large and interossei unite the heads of of the lower to the magnum inner metacarpal bones. The , , , the splint bones to the large metacarpal and bones row. Common Ligaments, The Common Ligaments are the extei^nal and internal lateral, and the anterior and posterior common, or capsular. The internal lateral ligament, stronger than the extemal one, is slightly crucial, consisting of two bundles of fibres which cross each other; both spring from the internal side of the inferior extremity of the radius; the superficial bundle goes to the OS magnum and large metacarpal, and the deep set to the scaphoid, trape- zoid, and inner splint bones. A part of this ligament, deep-seated also, joins the scaphoid and small metacarpal bones. The extemal lateral ligament also con- sists of two fasciculi, springing from the extemal side of the distal end of the radius ; the superficial fibres are attached to the extemal splint, the deep to the same, and also to the cuneiform and unciform bones. The anterior common or capsular ligament is membranous, covering the ^Snterior portion of the carpus. This ligament is attached to the radius, the head of the large metacarpal bone, the lateral ligaments, and to the carpal bones and their anterior ligaments. The annular ligaments are thickenings of this structure, which bind down the extensor tendons. The inner surface is smooth, and* lined by synovial membrane. The posterior common ligament is one of the strongest in the body, and covers the posterior surface of the carpus, filling up the depres- sions. It passes firom the distal end of the radius to the head of the large metacarpal bone, adhering to the internal lateral, median. Fig. Bi. Ligaments of the carpus — postero-intemal view, a b, Deep portions of internal lateral liga- ment ; c, Oblique ligament ; d. Interosseous metacarpal liga- ment ; e. External interosseous - ligament of the upper row. ^ 140 ARTHROLOGY. and inferior trapezial ligaments. Its anterior surface is attached to the two rows of bones, while its posterior is smooth, for the passage of the great flexor tendons ; the inferior carpal or cheek ligament is continuous with it. A ligamentous structure passes obliquely downwards from the posterior border of the trapezium to the large and inner metacarpal bones, completing the carpal groove or sheath for the flexor tendons; this is the posterior or investing annular liga- ment. The carpal or check ligaments, superior and inferior, will be alluded to in describing the muscles of this region. The synovial capsules are /our, perhaps five — tvjo small and three large. Of the latter, one is for the radius and the upper row, extending betv^'een the bones as far as the interossei; another is situated between the upper and lov/er rows, and a third between the lower row and metacarpus, dipping be- tween its large and small bones. There is usually a separate synovial capsule between the trapezium and cuneiform T3one, and perhaps ODO foj the pisiform, when present. Motion in the carpus takes place chiefly in the radio- carpal portion, to a far less degree in the intercarpal, and very slightly in the carpo-metacarpal ; the movements are flexion and extension ; very slight lateral and circumductive movements are possible. Fig. 65. Superficial ligaments of the carpus— posterior view, a, Posterior annu- lar ligament ; 6 fc, Pos- terior common ligament. METACARPAL ARTICULATION. This consists of diarthrodial and synarthrodial joints. The latter are furnished with interosseous ligaments, which very generally become ossified ; the articular surfaces of the former are held together partly by those carpal ligaments v/hich sur- round them, and partly by the interosseous ligaments just named. METACARPO-PHALANGEAL ARTICULATION. This, whi'^h is popularly termed the fetlock joint, is formed by the large metacarpal bone, the proximal phalanx, and a pair r METACARPO-PHALANGEAL ARTICULATION. 14.1 of sesamcids. The ligaments may be divided into those proper to the joint and the accessory. The former consist of a capsular and two lateral ones. The capsular ligament passes from the lower end of the large metacarpal bone to the head of the os suffraginis, and is attached t'o the lateral liga- ments, which stretch from the infero-lateral aspect of the metacarpus to the supero-lateral surface of the os suffraginis. The accessory ligaments are those imme- diately connected with the sesainoid bones. The superior sesamoidean or sus'pensory ligament is a long, strong band, arising posteriorly from the lower bones of the carpus and the head of the metacarpus, occupying the space between the splints. It bifurcates, and becomes attached to the summits of the sesamoids, whence the parts pass downwards and forwards, reuniting as the broad ligarrient, and joining the extensor pedis tendon at the antero-inferior part of the os suffraginis. Theinferior sesamoidean liga- ments are named the external or riG. 56. Sccamoidean and digi- tal ligaments— posterior acpect. a, Suspensory ligament; bbb. External and middle inferior sesa- moidean ligaments. The central bundle is the Y, the two lateral ones forming the V ligament; c, Annular sesamoidean ligament; dd, Posterior ligaments of the pastern joint ; e e, Lateral, and /, Inferior, navicular ligaments. Fig. 57. Deep sesamoid- ean ligaments, a, Inter-sesamoidean long, the middle or short, and ligament ;&, cm- X liga- cial or ment. the internal or crucial. The external one is Y-shaped, and runs from the base of the sesamoids to the supero-posterior part of the os coronaB. The middle one is V-shaped, arising from the base of the sesamoids, and it passes down to a ridge on the back of the os suffraginis. The internal one, crucial or X-shaped, likewise passes from the base of the sesamoids to the supero-posterior part of the os suffraginis, its fibres intercrossino-. The lateral sesamoidean ligaments, external and internal^ are two thin layers, passing from the external surfaces of the sesa- moids to the tubercles on the head of the os suffraginis. Pos- teriorly, the sesamoid bones are connected by the interosseous 142 ARTHRCLOGY, or intersesamoidean ligament, and covered by a pad of fibro- cartilage, which forms a smooth groove for the passage of the flexor tendons, and is converted into a canal by the annular ligament, a strong fibrous band which forms an arch posteriorly from one sesamoid bone to the other. The joint is capable of flexion and extension, with very slight lateral motion. The synovial membrane of this joint is continued upwards posteriorly, in the bifurcation of the suspensory ligament, where it forms a large cul-de-sac. "Wind-galls" are projections of this sac when it is abnormally full. PASTERN JOINT. The Proximal interphalangeal articulation, or pastern joint, is formed by the proximal and mesian phalanges, joined by the capsular, lateral, and two posterior ligaments. The capsular ligament extends from the articular margin of one bone to that of the other, and is adherent in front to the extensor tendon. The lateral ligaments are large and very strong, springing from the distal end of the os suffiraginis and passing obliquely downwards to the postero-lateral aspect of the os coronss. The two posterior ligaments run each from three points on the sides of the os suffraginis to a piece of fibro-cartilage, described as the glenoid cartilage, and attached to the postero- superior edge of the os coronae ; between them is the insertion of the external inferior sesamoidean or Y-shaped ligament. The synovial membrane of this joint lines the glenoid cartilage and a portion of the extensor tendon, and sends upwards a sac v/hicK lies between the postero-inferior part of the first phalanx and the cartilage. The movements are flexion and extension, and, during flexion, some slight lateral motion. COFFIN JOINT. The Distal interphalangeal articulation, or coffin joint, is formed by the mesian and distal phalanges and the navicular bone. Its ligaments are the capsular, antero and postero- lateral, and the broad, lateral, and inferior navicular. The capsular ligament includes the articulation formed by the three bones, and is attached to the extensor tendon in front and the flexor behind. The antero-lateral, which are strong and thick,. THE PELVIS. 143 spring from the imprints on the lateral aspect of the os coronae, and are inserted into two depressions at the superior border of the OS pedis, partly covered by the lateral cartilages. The postero-lateral ar3 continuations of the lateral ligaments of the pastern joint, which, after reaching the os coronse, form an elastic fibrous cord, attached to the upper border of the navicular bone, the two uniting to form the superior or hroad ligament. They give off short lateral bundles to the retrossal pro- cesses and inner surfaces of the lateral carti- lages. The lateral navicular ligaments con- sist of strong w^hite fibres, which join the angles of the navicular bone to the inner aspect of the lateral cartilages, and the wings of the os pedis. Tho inferior ligament is an inter- osseous one, which is attached to a roughened groove on the anterior border of 'the navicular bone and to the semilunar ridge of the os pedis. The synovial laemhrane lines the cavity of the joint, and sends upwards a very large sac along the posterior surface of the median phalanx. Smaller projections are found bet7/een the anterior and posterior lateral ligaments. The motion of the joint is that of flexion and extension. Fig. 58. Navicular ligaments. a a, Superior, or broad ; 6, Inferior ; andc c, Late- ral ligaments. Articulations of the Pelvic Limb. THE PELVIS. Sacro-iliac Articulation. — This is the articular connection between the axial skeleton and the pelvic limb ; it is described both as a diarthrosis and an amphiarthrosis ; it is capable of little motion, and the synovia is small in quantity, if present at all ; the joint is formed by the venter of the ilium, and the supero-lateral surface of the sacrum, which articular surfaces are clothed with cartilage, and the union completed by the three sacro-iliac liga- ments, inferior, lateral and superior. The inferior consists of strong bundles of fibres, v^hich envelop the articulation like a strong and irregular capsular ligament, and are attached below to the transverse process of the sacrum, and above to the venter iln. The superior sacro-iliac, short and strong, stretches from: 144 AETHROLOGY. the spines of the sacrum to the posterior spine of the ilium. The lateral sacro-iliac is triangular, the fibres running obliquely Fig. 59. Sacral and pelvic ligaments— left lateral aspect, o, Superior sacro-iliac liga- ment : b, Sacral ligament ; c, Lateral sacra-iliac ligament ; d, Sacro-sciatic ligament. backwards, and it is attached above to the posterior spine and border of the ilium, below to the lateral border of the sacrum. Sacro-sciatic Ligament — This is a broad membranous expan- Fia. 60. Sacral and pelvic ligaments— inferior aspect, a, Intertransverse lumbar ligament ; b and c. Capsular ligaments of lumbar and sacro- lumbar transverse articulations ; d, Inferior sacro-iliac ligament : e. Obturator ligament ; //, Ligament of tlie ischio-pubic symphysis. sion situated at the side of the pelvis, helping to form tho pelvic cavity. It is attached superiorly to the lateral borders of the transverse processes of the sacrum and first two or three coccygeal HIP JOINT. 145 rertebrse ; inferiorly, to the superior ischiatic spine and tuberosity of the ischium. Between this ligament and the iliac shaft is a space, the great sciatic notch ; and a second, the lesser sciatic notch, exists between the ligament and the ischial shaft. The former gives passage to the great sciatic nerve and gluteal blood- vessels, the latter to the tendons of the obturator internus and pyriformis muscles. Some lateral bands are found joining the sacral spines to the transverse processes ; .these are termed the sacral ligaments » Pelvic or Ischio-puhlc Symphysis. — This articulation is formed by the respective surfaces of the ischium and pubis, and joins the right and left ossa innominata ; in the young it consists of fibro- cartilage and white fibrous tissue, which ossify with age. The OhtuTidor ligaments are thin membranes, almost closing up the obturator foramina, a small passage being left for the transit of blood-vessels. HIP JOINT. The FemoTc-pelvic is a ball-and-socket or enarthrodial joint, and is formed by the acetabulum of the os innominatum and the ^r^icuiar head of the femur. It has the following ligaments : Fig. 61. Ligaments of the hip joint— infero-internal view. a. Cotyloid ligament ; b, Hound ligament ; c, Pubio- femoral, crossed by the transverse ligament. The capsular, which grasps the brim of the acetabulum and roughened edge of the head of the femur ; the cotyloid^ which, surrounds and deepens the acetabulum; and the transverse, which stretches over the cotyloid notch, completing the circum- L 146 ABTHROLOGY. ference of the cavity, but leaving a space for the passage of the pubio-femoral ligament. The binding ligaments of the joint are two — the round or ligamentwm teres, very short and strong, v/hich arises from the notch in the head of the femur, and is inserted in the fundus acetabuli; the second is the pwhio-femoral lig;ament, which arises from the head of the femur, close by the round ligament ; bound down by the transverse ligament, it passes through the cotyloid notch and along the groove on the under side of the pubis, meeting and crossing its fellow at the symphysis, and becoming con- tinuous with the abdominal fascia of the opposite side ; thus the head of the right femur is partially supported in position by tbe muscles of the ^ left side, and vice versd. As it passes over the pubis, a synovial bursa is inter- posed. This ligament is peculiar to the Equidse. The motion of the joint is flexion, extension, abduction, adduc- tion, rotation, and circumduction. STIFLE JOINT. Fio. 62. -^-■ Ligaments of the stifle j6i&t — antero-internal aspect, a. Internal lateral femoro-tibial ligament ; b, In- ternal lateral patellar ligament; c, Internal, d, Middle, and e, External straight patellar ligaments. The Femoro-tihial articulation, a Compound ginglymus, is formed by the trochlea and condyles of the femur, the tibia, and patella. The ligaments con- sist of two groups, the femoro-tlhlal and the patellar. Patellar Group. — The capsular ligament, which is attached round the trochlea of the femur, and thp articular surface of the patella, is capacious, allowing considerable motion in the joint. The lateral ligaments, internal and external, arise from the lateral aspects of the femur, just abo /e the condyles, and are inserted to the corresponding surfaces of the patella, the ex- ternal being the larger; they may be regarded as thickened portions of the capsular ligament. The three straight ligaments, external, Tniddle, and internal, arise from the antero-inferior surface of the patella, and are inserted to the" anterior aspect of the tuberosity of the tibia, the middle one occupying the small fossa. STIFLE JOINT. 147 At its patellar attachment, the internal straight ligament becomes enlarged, and fibro-cartilaginous in structure, projecting over the edge of the femoral trochlea, and thus enlarging the articular surface of the patella. FemorO'tlhlal Group. — There are two crescentic fibro-carti- laginouG discs, the semilunar cartilages or oiieniscl, interposed between the condyles of the femur and the head of the tibia, the internal one being the larger and thinner. Their internal borders are sharp and con- cave, embracing the tibial spine, while the external are thick and convex. Their super- ior surfaces are hollowed for the reception of the femoral condyles, while the inferior are smooth and flat, resting on the tibia. Their extremities terminate in the coronary ligaments, which attach them to the bones; these are five in number, tivo for the inter - vial disc, an anterior one attaching it to an excavation in front of, while the posterior one is fixed to a furrow behind, the tibial spine. The external disc has threCy one fixed in front of the tibial spine, and two behind it, of which the superior one is longer and stronger, being inserted in the intercondyloid notch of the femur, while the inferior is thin and flat, and fixed to the head of the tibia. Crucial or hderosseus Ligaments. — These, anterior and 2^osterlor, are very strong, and are situated between the con- dyles of the femur. The anterior or exter- nal stretches obliquely forwards, and is attached in the intercondyloid notch inside the extarnal condyle of the femur, and to a depression on the summit of the tibial spine. The posterior or internal, the longer, . arising anteriorly inside the internal condyle, crosses the anterior ligament, and is attached posteriorly to a small eminence behind the inner articu- lar surface of the head of the tibia. Lateral Ligaments. — The external one, the shorter and stronger Fia. 63. Ligaments of the stifle joint — posterior aspect, a, Exter- nal lateral patellar ligament ; 6, £xtemal lateral femoro- tibial ligament; c. Posterior crucial ligament ; d, External meniscus ; e, Internal menis- cus ; f, Femoral coronary liga- ment ; g, Posterior external coronary ligament ; \ Fibulo- tibial ligament. 14^ ARTHROLOGY. arises from the external condyle of the femur, and. passes over the head of the tibia to the fibula; a synovial bursa lies between it and the tibia. It is separated from the capsular ligament by the tendon of origin of the popliteus. The internal lateral arises from the internal condyle of the femur, and is attached to the intero-lateral aspect of the head of the tibia. Capsular Ligament. — This name is usually applied to a mem- braiious ligament enclosing the joint posteriorly, and attached to the femur, tibia, lateral ligaments, and menisci. It is hj some called tho posterior ligament. Anterior to this there is a pair of membranes enclosing the joint antero- laterally. These are generally described as the synovial membranes; bat as they are considerably strengthened, and help to play the part of a capsular lig-ament, it may be convenient to describe them as such. There is therefore a complete capsular ligament investing the joint, thickened posteriorly. The synovial apparatus is double, each side having its own membrane, and. between the two are the crucial ligaments of the joint.' Anteriorly, the synovial membranes contact that of the- femoro-patellar joint, and it is found that sometimes the synovial cavities are continuous with that of the latter. A large quantity of fat fills up the space between the capsules and the straight ligaments of the patella. The motions of this joint are flexion and extension, and a certain amount of rotation, permitted by the presence of the disss. TIBIO-FIBULAR ARTICULATION. This small articulation is formed by the facets on the adjacent surfaces of the tibia and fibula, and is a diarthrodial joint. The ligaments are a strong capsular one and the interossei, which divide into superior and Inferior ; the former being a small bundle at the upper third of the fibula ; the latter consists of a membranous expansion, extending from the middle to the distal extremity of the fibula. Between the two interosseous parts pass the chief artery and vein of the region, the anterior tibial. A ligamentous cord extends downwards from the fibula to the external malleolus of the tibia, " where this cord bifurcates and unites witli the two exter-iuil Literal ligaments of the tarsal joint" (Bigot). Motion in tliis joint can hardly be said to exist. r COMMON LIGAMENTS. 149 THE TARSUS. Similar to the carpus, this, the hock joint, consists of a true or tihio-tarsal portion, together with the upper arid lower tarsal, the intertarsal, and the tarso-metatarsal accessory articulations. The ligaments are common and special. Common Ligaments. These are the external and internal lateral and the capsular The internal lateral is formed of three fasciculi of fibres, superficial, middle, and deep. The superficial, the longest and strongest, connects the internal malleolus of the tibia with the astragalus, two cuneiform, and the large and inner meta- tarsal bones. The middle fasciculus, con- sisting of two cords, likewise arises from the internal malleolus of the tibia, one division being attached to the astragalus, the other to the calcaneum. The deep fasciculus is very small; it passes from the internal malleolus to the astragalus. The external lateral ligament consists of two crucial fasciculi, superficial and deep. The superficial is strong and flat, joining the external malleolus of the tibia to the astragalus, calcaneum, cuboid, large and external metatarsal bonej. The deep fasiculus is short ; it passes obliquely backwards, arising from the external malleolus of the tibia, to the astragalus and calcaneum. The capsular ligament is ^ery strong, and attached superiorly round the distal articular surface of the tibia, to the inferior border of the astragalus, to the cuneiforme mag- num and medium, and to the lateral and oblique ligaments ; posteriorly it is attached to ^the calcaneum and astragalus, and there is a fibro-cartilaginous disc in its centre, over which glides the flexor tendon, furnished with a synovial membrane. The capsular ligament is often described as double, and named the anterior and posterior, the lateral ligaments with which it blends being the lines' of division. Fia. 64. Ligaments -of the tarsus— pos- tero-internal view, a, Internal lateral ligament ; b. Calcaneo- cuboid ligament. 1^0 AKTHROLOGY. Special Ligaments. Superior Tarsal. — These ligaments occur between the astra- galus and calcaneum, and consist of one superior, two lateral^ and one interosseous. The superior stretches from the upper border of the pulley of the astragalus to the calcaneum ; the lateral are very thin, and covered by the lateral common liga- ments ; the interosseous one is strong, occupying the greater part of the rough excavation between the articular facets of the bones. Inferior Tarsal — The ligaments of the lower row are five, two anterior, which con- nect the cuboid to the great and middle cuneiform bones, and three interosseous ones, two of which correspond to the anterior ligaments ; the third interosseous ligament unites the three cuneiform bones. Some of these ligaments bound the tarsal foramen, which gives passage to the perforating pedal artery. Intertarsal. — The four ligaments in this group are of greater importance than those of the two last groups. The calcaneo-cuhoid or calcaneo-metatarsal ligament stretches from the posterior border of the calcaneum to the posterior part of the cuboid, termina- ting on the head of the external metatarsal bone ; externally it reaches the lateral, in- ternally the tarso-metatarsal ligament. This ligament becomes implicated in the lesion known as curb. The Oblique, or Astragalo-metatarsal ligament, arising from the antero-internal side of the astragalus, becomes attached to the cuneiforme magnum and medium, the large riietatarsal bone, and the capsular ligament, the fibres radiating from above, and running downwards and outwards. This ligament covers thu seat of bone-spavin. The Tarso-Tnetatarsal is a single strong ligament, which covers the tarsal groove and unites posteriorly all the bones of the joint to the three metatarsal bones. It is smooth, for the passage of the flexor tendon, and is the analogue of the posterior Fia. 65. Ligaments of the tarsus— anterior-external view, a External lateral, and h Oblique ligament. I^UMINANTIA:^ AXIAL SKELETON. 151 carpal ligameDt. It is pierced by the perforating pedal artery and vein, and inferiorly may be continuous with the check ligament. The great interosseous ligament unites the calcaneum and astragalus to the cuboid and cuneiforme magnum, occupying the internal space fonned by these bones. Annular Ligaments. — The posterior of these closes in the tarsal groove, completing the sheath for the deep flexor tendon ; hence it passes from the tuberosity and posterior border of the calcaneum to the internal ridge of the same bone, and is reflected as far down as the inner metatarsal bone. It is strengthened by a strong band which arises almost with the calcaneo- cuboid ligament. The anterior annular ligament presents three well- marked portions ; they are strong and more or less flattened bands, an inferior one passing across from the proximal end of the outer to that of the inner metatarsal bone, a middle one attached to the cuboid bone and flexor metatarsi tendon, and a superior crossing the distal end of the tibia obliquely outwards and down- ^vards. The three portions of this ligament bind down the terdons playing over the tarsus anteriorly. There are at least three synovial membranes, one between the astragalus and tibia, another between the rows of bones, and one also between the lower row and the metatarsus, which sends a branch upwards between the calcaneum and astragalus. The motion in the tarsal joint is in effect limited to flexion and extension, and the joint may therefore be regarded as a ginglymus. The tarsal check ligament will be described with the muscles. The metatarsal, metatarso-phalangeal, and interphalangeal joints are like those of the anterior limb. COMPAKATIYE APiTHROLOGT. RUMINANTIA. AXIAL SKELETON. • In the ox, the dorso-lmnbar supraspinous ligament is composed of yellow elastic tissue, and anteriorly is expanded, and attached to the sides rather than to the summits of the neural spines. The inferior common ligament is very strong, and the intervertebral discs thicker than those of the horse ; the ligaTnen- turn nnchce is also stronger, as the vreight it has to bear is greater. The sternal ribs articulate with their cartilages by means of true diarthroses, and are supplied with synovial membranes. The sternum is furnished with an inferior rommon ligament, and the presternum or manubrium articulates with tte meso- 152 ' COMPARATIVE ARTHROLOGY. sternum by a diarthrosis of limited motion. The transverse lumbo-sacral and interlumbar articulations, being peculiar to the horse, are entirely wanting here. PECTORAL LIMB. In the eUtow joint the internal lateral ligament is shorter than the external. The carpus, being articulated on the same general plan as that of the horse, calls for no special description. The metacarpo -phalangeal joint is double, each digit articulating in a manner very like the single one of the horse, ani^ach having two lateral ligaments. The suspensory ligament divides into several parts inferiorly, four of which go to the sesamoid bones, one to each, either of the two external ones giving off a band which winds round to the front, and joins the tendon of the extensor proprius of the digit, while two other bands pasa directly from the ligament through the interarticular notch of the metacarpus, separate and likewise join the above-named extensor tendons from the inside ; two slips pass down, unite and become attached to the small rudimentary digits or claws, afterwards separating to become united postero-superiorly to the distal phalanges ; finally, two deep branches go to the tendon of the flexor perforatus and form two rings through which passes the divided tendon of the flexor perforans. The inferior sesamoid ligaments are small, and consist of two lateral bands, which attach the sesamoid bones to the head of the proximal phalanx, and between them a very small X ligament. The intersesamoidcan ligaments are three in number ; there i^ one between each pair of bones, and one joining the two internal ones. A common annular ligament is found about the region of the fetlocks, and two smaller special annular ligaments lower down. (Fig. 87, f g g'.) The superior irUerdigital ligament is crucial, and situated between the two proximal -phalanges, in small ruminants it is very rudimentary. There are only two fibrous bands which attach the glenoid cartilage to the first phalanx. The inferior interdigital ligament joins the distal phalanges and navicular bones together, and in the ox is connected with the tendon of the flexor perforans. The superior navicular ligament, coming from the mesian phalanx, is formed of elastic tissue. Pelvic Limb. The pubio-femoral^lig&ment is wanting in all the domesticated animals other than the horse ; the absence of this ligament enables the larger ruminants to deliver those sweeping circular blows with the foot, which are known by the familiar name of "cow-kicks." There is only one straight ligament of the patella in the smaller ruminants. With respect to the tarsus, we may remark, that there is more motion in that joint in the ruminant, due to the greater mobility of the astragalus, which possesses gliding motion upon the calcaneum, the cubo-cuneiform bone, the tibia, and the malleolar bone, all of which assist in forming the mobile portion of the joint. In the elephant there is no round ligament ; and the femur instead of being, when at rest, inclined downwards and forwards, maintains an almost perpen- dicular position ; this accounts for the peculiar contour of the haunch in that animal. "' ' r CARNIVORA. 153 OMNIVOEA. AXIAL SKELETON. In tlie hog the ligamentum nuchm can scarcely be said to exist ; a fibrous cord from the dorsal spines to the occiput represents it. There is only one s3Tiovial capsule in the occipito-atloid joint, and there is a transverse odontoid ligament which passes over the odontoid process, and keeps it down on the floor of the atloid ring. The sternal ribs articulate distally like those of the ox, and the remarks on the sternal articulations of that animal also apply to the hog. HhQ temporo-maxillary iomi possesses great motion anteriorly and posteriorly, resembling in its structure that of the rabbit, the anterior mastoid process being small, and the temporal articular sui-face large.' The ligaments" between the hyoid cornua and cornicula are elastic. APPENDICULAR SKELETON. ■ The syno\'ial membrane of the shoulder joint is continued into the bicipital groove. In the elbow joint the internal lateral ligament is shorter than the external one. The radius and ulna have been described as anchylosed and also as closely connected by fibrous tissue. Whichever be the more common mode of union, there is no motion between these bones. The four bones, of the metacarpus are joined by prolongations of the great carpal liga- ments above, and below by interarticular ligaments. Each metacarpo- phalangeal joint is supplied with an intersesamoid, two lateral, a crucial inferior sesamoid, and an anterior capsular ligament, also with a synovial membrane, and lateral ligaments for the joint itself. The suspensory liga- ment is replaced by the interosseous palmar muscles, and there are small superior interdigital ligaments between the proximal phalanges. A very small osseous nodule is usually foimd on each of the anterior capsular ligaments of these joints. The external lateral navicular ligaments resemble those of the horse ; the internal ones are wanting. An elastic ncivicular ligament like that of the ox is found in the large digits. There is no pubio-femoral and onlv one straiaht loaidlar ligament. The tibio- fibular articulation consists of an amphiarthrosis superiorly, a diarthrosis iaferiorly, and between these an interosseous ligament, stronger below than above. The tarsal articulation resembles iu the main that of the ruminant CARNIVOKA. AXIAL SKELETON. The ligamentum nuchce is represented by a fibrous band which is larger in the dog than in the cat ; in the cervical vertebrse of the former, and in the vertebrae generally of the latter, there are interspinous muscles instead of liga- ments. The occipito-atloid and odontoid ligaments are similar to those of the hog. In the temporo-maxillary }amt there is merely ginglymoid motion, an(?- the meniscus is very thin, ^, v- .-. . *" - v^ . \ 154 COMPARATIVE ARTHROIiOQY. , , APPENDICULAR SKELETON. la the camivora the synovial membrane of shoulder joint is similar to that of the hog in its arranagement. The lateral ligaments of the elhovo joint, together with the annular ligament, form a kind of ring in which the head of the radius slightly revolves, as there is a certain amount of motion between it and the ulna. The radioulnar articulation consists of a superior and an inferior lotatory diarthrcsis, and an interosseous ligament ; the rotatory movements' "between these bones are termed pronation and supination^ the prone being the normal position of the extremity. The metacarpus is formed similarly to that of the hog, but it is more mobile, and the rest of the articulations of the limb lesemble those of that animal, with the exception of the distal interphalangeal, "where we find anteriorly an elastic ligament which acts as the retractor of the claw, and is stronger and much more active in the cat than in the dog, the claw of the former being much more retractile. Posteriorly a piece of fibro- cartilage is the analogue of the navicular bone, which is wanting. The patella has one straight ligament, and the menisci are united. In the tibio-fibular articulation, there is superiorly a diarthrosis, otherwise it is formed on the same plan as that of the hog, as is the tarsal joint, excepting that the astragalus has an inferior head instead of a trochlea. CHAPTER III. MYOLOGY. The branch of anatomy which treats of the muscular system is called Myology. The muscles are the active organs of motion, or '>f locomotion, the bones and ligaments being passive organs of Mie same. Before studying the muscles individually it is necessary to take a brief view of their anatomical and histological structure. They contain the specific contractile substance termed muscular tissue, together with areolar and fibrous tissue, and a certain amount of fatty material ; they are also furnished with nerves, blood-vessels, and absorbents. MUSCULAR TISSUE. Muscular tissue is the name applied to contractile fibres, which are either collected into bundles connected at their extremities, and forming distinct organs termed muscles, to which the familiar name flesh is applied; or they are found helping to form the walls of the hollow viscera, as the bladder, stomach, &g. In the first variety the fibre presents, when magnified, a striped appearance, the stripes being placed transversely ; it is therefore known as striped or striated fibre, and as with little exception its contraction and relaxation are controlled by the will of the animal, it is also termed voluntary fibre or muscle. The second variety differs from the first in not being striped, and also in its action being beyond the control of the will ; hence it is named noTh-striated or involuntary fibre. The chief exceptions to this general distinction occur in the heart and in the upper part of the oesophagus, which contain t-nvoluntary striated tissue. Both varieties are red in colour, but +he hue of the striated kind is far deeper. We therefore describe two kinds of muscular tissue, the striated and the non-striated. 156 MYOLOGY. STRIA.TED MUSCULAll TISSUE. Voluntary or striated muscular tissue forms tlie mass of the so-called muscles, which terminate at either extremity in fibrous structures termed the tendons, by means of which they are attached to the bones ; the intermediate fleshy portion is often called the belly of the muscle. A muscle is composed of bundles, or fasciculi of fibres, which are the integral parts of the structure. The microscope shows these fibres to consist of fine filaments termed fihrilloe, which run parallel to each other, maintaining an undivided course throughout. Each fibre is enclosed in a delicate tubular sheath called the sarcolemma or myolemma, composed of a transparent and ap- parently homogeneous membrane, tough and elastic, which isolates each fibre, and frequently remains intact after rupture of its contents. The fibres, about 5^-J-oth of an inch in diameter, are gathered into prismatic or polyhedral fasciculi, and invested with a sheath of connective tissue, which is inflected between the fibres, and called the perimysium internum ; the entire muscle has likewise an investing sheath of connective tissue, the jperi- mysium externum, continuous with the above. This connective Fiu. 68. Fasciculus of l^striated muscu- lar fibres. Trans- verse sti'isB seen at a ; 6, U nion of fibres with the tendon. Fig. 67. A single striated muscular fibre, showing its com- ponent fibrillae. tissue is membranous in structure, its use being to connect the bundles and fibres, and to serve as a matrix for the ramification of blood-vessels, nerves, and absorbents. A muscular fibre, examined under a power of 300 diameters or less, will display . the transverse waving strioi or lines, from which the name " striated " is derived. Longitudinal markings r NON-STRIATED MUSCULAR TISSUE. 157 or lines are also often apparent, but are less regular than the striae. The component fibrillae of a muscular fibre may be demon- strated by macerating the tissue in strong alcohol, and pressing the prepared object, when each fibrilla will be seen to consist of a row of alternately light and dark spots. By other means, such as treatment with hydrochloric acid, or by a smart blow, a muscular fibre may be separated into transverse discs correspond- ing to its striated appearance. These two separations of a fibre have been termed the longitudinal and transverse cleavages. Could both these operations be* performed on the same fibre, the result would be a crucial cleav- age of it into a number of objects which would appear under a high power as dark spots, with light spaces round them, both being rectang- ular in form ; they are known as the* sarcous elements of Bowman^ and in them rests the inherent *power of contractility. Thus a trans- verse row of sarcous elements forms a disc ; ' a longitudinal row a fibrilla. When seen through the medium of the sarcolemma the dark spots appear transversely as a continuous line, hence the striated appearance of the fibre. The fibres cleave more readily into fibrillae than xnto discs. Modern observation modifies the above, the fibre being gener- tillj regarded as a series of alternate light and dark discs, the latter having on each transverse surface a number of darker granules, connected by fine longitudinal and transverse lines. The former with their nodular extremities are ternied 7miscl€-rods, A number of oval objects, related with the sarcolemma, appear on treating a fibre with acetic acid; these are the muscle corpuscles, and they are nucleated. Striated fibres are for the most part isolated, but those of the heart, which, as already stated, are involuntary, divide into branches, and the branches of different fibres frequently join, or, as it is termed, anastomose, (Fig. 152.) NON-STRIATED MUSCULAR TISSUE. Involuntary or non-striated muscular tissue is pale in colour, and consists of fibres, bound into fasciculi by a fine perunysium of areolar tissue. The fibres never terminate in tendons, and are not invested in s, sarcolemma ; they are cylindrical in - shape, and composed of Fig. 68. striated muscular fibres from the Horse. 158 MYOLOGY. fusiform or elongated cells, which become appareut after macer- ation of the tissue in dilute hydrochloric acid or other reagents,. or it may be without any such preparation. These cells are the contractile cells of Kolliker, and in them an elongated nucleus may be visible. The fasciculi vary very greatly in size in dif- ferent situations, and often crossing each other, they give the tissue in some parts a mesh-like appearance. The non-striped tissue is very abundant, being found in the walls of the ali- mentary canal and hollow viscera, in gland dncts, in the coats of blood-vessels, in the skin, and elsewhere. Both varieties of muscular tissue are plentifully supplied with blood, and in stri- ated tissue the capillaries or minute blood- vessels are arranged longitudinally with transverse connecting branches, but they do not penetrate the sarcolemma, they and the larger vessels alike being found in the perimysium or interstitial connective tissue. The striated tissue is supplied with nerves from the cerebro-spinal system, but the non- striated tissue receives its supply from the sympathetic system, and the vital stimulus conveyed by either of these causes the contraction of the fibres. The description of the arrangement of involuntary tissue forms no part of the present section of our subject ; the tissue is described here chiefly in order that its structure may be com- pared with that of the voluntary kind. TENDONS. The tendons in which voluntary muscles terminate at either end are structures resembling ligaments in their composition, being formed of white fibrous tissue mixed with yellow fibres. Like ligaments, they are practically non-elastic, and while they attach the muscles to the bones, they Inerely transmit the action of the former to the latter, and are therefore passive instruments of motion. The extremity of a muscle which has the most fixed attachment is called its origin ; the other extremity attached to the more movable structure, its insertion. The tendon of insertion is often longer than that of origin, which is frequently rudimentary. In some cases both extremities are equally movable. Fio. 69. A, Non-striated muscular fibres; a a, The component fusiform cells; 6, 6, The nuclei. B and C, Single cells more hlghl7 magnlfled; C having been treated with acetic acid. r FASCIA. 1 59 The strongest part of a muscle is its point of union with the tendon, but the manner in which that union is effected is not satisfactorily explained. According to some authorities, the muscular fibres are prolonged into the connective tissue of the tendon; or, "the contractile fibre terminates in a rounded ex- tremity which is buried in a corresponding depression in the tendon" (Chauveau), The sarcolemma and the areolar tissue, both of the fibre and tendon, are no doubt instrumental in effecting the union. Tendons often send processes into the substance of the muscle, which may extend throughout its length ; such pro- cesses are described as tendinous intersections ; they also appear to send small fibres into the substance of the bones to which they are attached. Tendons vary in form, size, and density, but all are either rounded or flattened. The former are funicular ^ the latter aponeurotic tendons ; in either form their use is the same. They become attached to bones through the medium of the periosteum, sometimes expanding to strengthen its outer layer. FASCIA. Each group of muscles is invested and bound down by a strong membranous expansion of white fibrous tissue, called fascia, which is firmly connected with the bone. This tern;i is however applied to other membranous expansions, differing very materially in strength, texture, and relations. For example, below the skin and panniculus there is a membranous expansion, which forms a continuous covering over the whole body, composed of connective tissue more or less condensed. Hence fasciae have been divided into superficial, and deep or aponeurotic. Superficial fascia consists of cellular and elastic tissue, varying in thickness in different regions of the body. Where the skin is loose it is most distinct; and sometimes it is inseparable from the muscles and skin, as in the eyelids and lips. Its meshes may be filled with adipose cells, or condensed so as to form a fibro-cellular membrane destitute of fat. Its use is to connect and protect the various structures it contacts, and to furnish a matrix for blood-vessels ; the fat in the subcutaneous fascia helps to conserve the animal heat, fat being a bad conductor. Aponeurotic fascia not only covers, supports, and binds down the groups of muscles, but affords processes between them, and becomes united to, and blended with, the periosteum. Some o£. 160 i jSYOLOGY. these fasciae have distinct muscles for rendering them tense, as the tensor fasciae latae. Fasciae are also found in connection with the walls of cavities, as in the pelvis. In the limhs, where the muscular bellies form lengthy masses, with long tendons attached at considerable distances, there would be considerable displacement during motion, were it not that ia these parts the fascia is very strong, enclosing the body of each muscle in a sheath, as also eaih group of muscles. MUSCULAR NOMENCLATURE. Muscular nomenclature • is unsatisfactory and confused, some muscles being named from their form, as Tra-pezium, Rhomboideus, Scalenus ; others from their use, as Flexor, Extensor, Adductor, Abductor, &c. ; some from their direction, as Rectus, Transversus, Obliquus ; others from their sitiiation, as Temporalis, Peroneus, Subscapularis ; some again from their attachments, .as Stemo- maxillaris, Coraco-radialis, and Stylo-hyoideus ; and some from their homologues in the human subject. A muscle may have a physiological name expressing, its use, and an anatomical one alluding to some feature in its morphology ; but perhaps the most satisfactory system of nomenclature is that which names muscles from their attachments. Muscles vary so much in shape that no classification of them can be based on that feature. Some of them, however, present such marked features that certain terms are used to describe their form. Thus, biceps and triceps express a two or three-headed muscle ; a diagastric muscle has two bellies, joined by a mesian tendon ; a radiating- muscle consists of bundles diverging from a point of attachment ; k penniform muscle resembles a feather in shape, and a semipenniform one the lateral half of the same, the tendon corresponding to the axis or scapus of the feather. In the descriptions of muscles which follow, the names printed in small capitals are those most commonly in use in Great Britain, whereas the names below, and in italics, are almost uniformly anatomical, expressing in most cases the places of attachment of the muscles, — a nomenclature more valuable though less current than the one in use. CLASSIFICATION OF MUSCLES. Either an Anatomical or Physiological mode of classification can be applied to the muscular system, but the former is of course the one adopted here. Again, muscles may be classed r r r EXPLiVNATION OF PLATE IL Muscles of the Horse. Superficial Layer. The panniculus and tunica ahdominalis are removed. 1. Abduceas. 33. Extensor metacarpi maguua. 2. Retrahentes muscles. 34 Humeralis obliquus. 2'. Attollens maximus. 35. Extensor pedis. 2". Attollens anticus. 36. Flexor metacarpi externus an«l 3. Temporalis. medius. 4. Nasalis longus. 37. Flexor metacarpi intemus. 5. Orbicularis palpebrarum. 46. Cervical) ^^ T^ 1 J- serratus magnus. 47. Dorsal j ^ 6. Levator labii superioris alaeque nasi. 48. Rhomboideus longus. 7. Dilatator naris lateralis. 49. Superficialis costarum. 8. Orbicularis oris. 50. Splenius. 9. Zygomaticus. 52. Intercostales. 9'. Buccinator. 54. Tensor fascia latos. 10. Depressor labii inferioris. 55. Triceps abductor femoris. 11. Masseter. 56. Gluteus externus. 12. Levator humeri 61. Biceps rotator tibialis. 13. Trapezius cervical is. 62. Rectus femoris. 14. Trapezius dorsalis. 63, Vastus externus. 15. Latissimus dorsi. 65. Gastrocnemius 18. Pectoralis parvus. 68. Flexor pedis perforans. 19. Pectoralis magnus. 69. Peroneus. 20. Sterno-maxillaris. 70. Extensor pedis. 23. Subscapulo-hyoideus. 71. Flexor metatarsi. 24. Antea-spinatus. 72. Flexor pedis accessorius. 25. Teres extemus. 74. Obliquus abdominis and two lateral groups j the latter lying on each side of the central division formed by the vertebrae and the ligamentum nuchse, and the former being situated underneath the vertebrae. Inferior Cervical Group. The following muscles, eight in number, may be placed in this group: INFERIOR CERVICAL GROUP. 179 Stemo-maxillaris. Stemo-thyro-hyoideus. Subscapulo-h yoideus. Bectus capitus anticus major. Eectus capitis anticus minor. Rectus capitus lateralis." Scalenus. Longus colli. STERNO-MAXILLARIS. (PL. 11. 20.) Placed along the lower border of the levator humeri, this muscle is long, narrow, and flat, its fibres extending forwards and upwards ; it is fleshy, terminating in a flat tendon. Origin. — From the anterior portion of the cariniform cartilage; it is united to its fellow along its inferior third. Insertion. — To the angle of the lower jaw. Relation. — Externally with the panniculus and the parotid gland ; internally with the sterno-thyro-hyoideus and subscapulo- hyoideus, the trachea and carotid artery; the jugular vein runs along its superior border. Action. — Acting with its fellow, it flexes the head downwards, or singly, it turns the head to one side. STERNO-THYRO-HYOIDEUS. (Stemo-thyroideus and Sterno-hyoideus.) (PL. ni. 3.) This is a slender muscle situated in front of the trachea ; it is narrow, ribbon-shaped, and .divided into two parts. Fleshy at its origin, it divides half way up the neck into two portions, each having a tendon of insertion. About their middle the stemo- thyxo-hyodei have tendinous intersections, which render them more or less digastric. Origin. — ^From the superior part of the cariniform cartilage, intimately blended with its fellow. Insertion. — By one tendon, to the postero-inferior part of the thyroid cartilage, and by the other to the spur process of the os iyoides. Relation. — Inferiprly with the sterno-maxillaris ; superiorly with the trachea. Action. — It depresses the hyoid bone, and with it the larynx -and base of the tongue. 180 MYOLOGY. SlTBSCAPULO-HYOIDEtTS. (Pl. n. 28.) ^ More laterally situated than the last, this muscle is broad^ thin, and elongated, its fibres extending forwards and upwards. 'Aponeurotic at its origin, it is followed by a long, flat, fleshy telly, ending; in a flat tendon, which joins that of the stemo- hyoideus. Origin. — From the fascia covering the subscapularis muscle. Insertion. — To the inferior border of the spur process of the OS hyoides. Relation. — Externally with the subscapularis, pectoralis parvus, and sterno-m axillaris, blending also with the levator humeri; internally with the muscles on the inner aspect of the shoulder, the scalenus and rectus capitis anticus major, the trachea and the carotid sheath. Action. — It depresses the hyoid apparatus. RECTUS CAPITIS ANTICUS MAJOR. ( Trachelo-suhoccipitalis. ) (PL. III. 2.) This is the long flexor of the head, and is situated along the anterior half of the region. It is long, and has a flattened, fleshy belly, converging from two or three slips of origin, and terminat- ing anteriorly in a conical tendon. Origin. — Posteriorly, from the transverse processes of the third, fourth, and fifth cervical vertebrse. Insertion. — To the basilar process of the occipital and body of the sphenoid bone. Relation. — Externally with the levator humeri, and subscapulo- hyoideus ; internally with its fellow and the longus colli ; anteriorly with the gutteral pouch and carotid artery, and superiorly with the occipito-atloid joint, and rectus capitis, anticus minor. Action. — With its fellow it flexes the head downwards ; when acting singly, it flexes it laterally. . r INFERIOR CERVICAL GROUP. 181 RECTUS CAPITIS ANTICUS MINOR". (Atloido-suhoccipitalis. ) (Fia. 75. €.) This, the short flexor of the head, is situated on the inner and upper side of the preceding muscle, and is short, slender, and almost entirely fleshy. Origm. — Posteriorly, from the lower part of the body of the atlas. Insertion. — To the basilar process of the occipital, and body of the sphenoid bone, by the preceding muscle. Relation. — Infero-externally with the rectus major ; supe- riorly with the capsular ligament of the occipito-atloid articu- lation. Action, — It assists in flexing the head. RECTUS CAPITIS LATERALIS. {Atloido-styloideus.) (Fig. 75. 6.) This muscle, still smaller than the last and like it in structure, is placed rather more externally. Origin. — From the inferior part of the ring of" the atlas, on the outer side of the rectus minor. Insertion. — To the styloid process of the occipital bone. Relation. — Inferiorly with the rectus major ; superiorly with the capsular ligament of the occipito-atloid articulation ; exter- nally with the parotid gland. Action. — It assists the preceding muscles. SCALENUS. (Costo-cervicalis.) (Pl. IIL 6.) Situated at the postero-inferior part of the region, at the side of the anterior aperture of the thoracic cavity, the scalenus is triangular in shape, and divided into a superior or posterior, and Iau inferior or anterior portion ; the fibres run forwards and upwards, and form several fleshy masses, with strong tendinous 1^2 MYOLOGY. intersections. The anterior portion is the larger, flat from side to side, and thin in front. Origin of the Anterior Portion. — From the transverse pro- cesses of the last four cervical vertebrae by short fleshy fasciculi. Insertion. — The anterior and outer border of the first rib. Origin of the Posterior Portion. — From the transverse pro- cesses of the last three or four cervical vertebrae. Insertion. — To the superior part of the first rib. Relation. — Superiorly with the intertransversalis colli; inferiorly with the stemo-maxillaris ; externally with the levator humeri, pectoralis parvus, and subscapulo-hyoideus ; internally with the trachea and carotid artery, and on the left side with the oesopha- gus. Across its inferior border runs the jugular vein, and between its anterior and posterior portions pass the nerves of the brachial plexus. Action, — When the first rib is fixed, together these muscles extend the neck ; acting singly, each turns it to one side. When the neck is fixed, by drawing the first rib forward and supporting it, it acts as an inspiratory muscle. LONGUS COLLI. (Sabdorso-atloidevs.) (Fig. 75. a.) In the horse this is a single muscle, situated under the centra of the cervical and anterior dorsal vertebrae. The dorsal portion is fleshy, the cervical being made up of smaller fasciculi, con- voluted and intersected by tendinous fibres. The fasciculi run inwards and forwards. Origin. — From the inferior surface of the centra of the first six dorsal, and the inferior spines and transverse processes of the six posterior cervical vertebrae. Insertion. — By a strong tendon to the inferior spine or tubercle of the atlas ; it is also strongly attached to the second cervical segment. Relation. — Externally and anteriorly with the rectus capitis anticus major ; externally and posteriorly with the scalenus ; inferiorly with the trachea, oesophagus, blood-vessels, and nerves ; superiorly with the vertebrae. The dorsal portion is related with the pleura and sympathetic nerves. LATERAL CESVICAL GROUP. 183 Action.— It flexes the neck downwards, and moves one vertebra on another. Lateral Cervical Group. This is a numerous group, but one difficult of satisfactory suo- di vision. The following Table enumerates the muscles in the order in which they may be conveniently demonstrated : — Levator humeri. Trapezius cervicalis. Rhomboideus longus. Serratus magnus (a portion). Splenius Trachelo-mastoideus. Complexus major. Complexus minor. Rectus capitis posticus major. Rectus capitis posticus minor. Obliquus capitis anticus. Obliquus capitis posticus. Spinalis colU. Litertransversalis colli. LEVATOR HUMERI. (Maatoido-humeralis.) (Pl. XL 12.) Occupying the infero-lateral part of the neck, this muscle is large, flat, and elongated, extending downwards from, the back of the head to the arm. Its fleshy portion is divisible into deep and superficial parts, the first being placed anteriorly. Attachments. — Anteriorly, by one tendon to the crest of the occiput and the mastoid process of the temporal bone ; by the other to the wing of the atlas, this tendon being also common to the splenius and trachelo-mastoideus ; to the transverse processes of the second, third, and fourth cervical vertebrae, and the fascia of the neck. Covering the shoulder joint, it is attached to a line extending downwards from the deltoid ridge ; and to the fascia of the muscles of the shoulder and arm, joining the scapular fascia by an aponeurotic expansion continuous also with the fascia Of the cervical trapezius.. Relation. — Externally with the panniculus ; inferiorly with the carotid artery, jugular vein, and stemo-maxillaris ; internally with the splenius, trachelo-mastoideus, rectus capitis anticus major, scalenus, serratus magnus, and other muscles ; anteriorly with the parotid gland. It is connected with the ligamentum nuchse by the aponeurosis of the panniculus, and infero-laterally becomes 184 MYOLOGY. blended with that muscle ; hence it may be said to have an indirect sternal attachment. Action, — "When the head is fixed, it advances the entire limb; if the limbs are fixed, it aids in turning the head and neck ta one side, or with its fellow in depressing them. TRAPEZIUS CERVICALIS. (Cervico-acfomialis.) (PL. IL 13.) Situated supero-posteriorly, this, the cervical portion of the trapezius muscle, is thin, flat, and triangular, its fibres converging downwards and backwards. It is aponeurotic above, and poste- riorly, where it joins the dorsal portion. Origin. — ^From the funicular portion of the ligamentum nuchas. Insertion.— Wi\h the dorsal trapezius to the spine of the scapula, at its tubercle, and to the scapular fascia. Relation. — Externally with fascia from the levator humeri and panniculus ; internally with the splenius, serratus magnus, rhom- boideus longus, pectoralis parvus, and antea spinatus. Action. — It elevates, and draws the shoulder forwards. RHOMBOIDEUS LONGUS. (Cervico-subscapulcms.) (PL.IIL9.) It is placed on the supero-lateral part of the neck, just below the cordiform portion of the ligamentum nuchas. It appears as a tapering triangle, widest posteriorly, and very fleshy in its structure. Origin. — From the funicular portion of the ligamentum nuchas, as high as the second cervical vertebra. Insertion. — To the inner surface of the anterior angle of the scapula, and to its cartilage of prolongation, just above the serratuB magnus. Relation. — Externally with the cervical trapezius ; inferiorly with the splenius ; posteriorly with the rhomboideus brevis, with which it blends ; internally with the ligamentum nuchse. Action. — To elevate and draw the scapula forwards. LATERAL CERVICAL GROUP. 185 SERRATUS MAGNUS. (PL. HL 10.) The cervical portion of the serratus magnus will be described with the costal portion. (See costal region.) SPLENIUS. {Cervico-mastoideus.) (PL. in. 7.) This is a large muscle included between the funicular part of the ligament um nuchae, and the vertebrae below. It is broad. Lateral cervical muscles — deep layer. cccc, Intertransversalis eollL Fig. 73. a, Complexus major; h, Trachelo-mastoideus ; Hut, and triangular ; aponeurotic only at its periphery, its belly is made up of large fleshy bundles, which are directed obliquely forwards and upwards to the head and first cervical vertebra Attachments. — To the funicular portion of the ligamentum nuchas, the transverse processes of the third, fourth, and fifth cervical, and the spines of the first four or five dorsal vertebrae ; to the crest and mastoid ridge, in union with the tendon of the trachelo-mastoideus, and to the wiug of the atlas, along with the common tendon of the trachelo-mastoideus and the levator humeri. 186 MYOLOGY. Relation, — Externally with the levator humeri, cervical trape- zius, serratus magnus, and rhomboideus muscles ; internally with the complexus major, trachelo-magtoideus, and obliquus capitis tnuscles. Action. — With its fellow it elevates the head; alone it draws the head to one side. TRA.CHELO-MASTOIDEUS.* {Dorso-mastoideus.) (Fig. 73.6.) Situated under and along tbe inferior border of the splenius,, it is elongated and fleshy, its fibres passing forwards and upwards; the belly is divided into two portions, which run parallel, each terminating by a tendon anteriorly. Origin. — From the transverse processes of the first two dorsal and the oblique processes of the last five cervical vertebrae. Insertion. — By two tendons; one to the wing of the atlas, common also to the splenius and levator humeri; the other, continuous with that of the splenius, to the mastoid ridge. Relation. — Externally with the splenius ; internally with the spinalis colli ; posteriorly with the longissimus and spinalis dorsi. Action. — With its fellow to erect the head ; acting alone, it draws it to one side. COMPLEXUS MAJOR. (Dorso-occipitalis.) (Fig. 73. a.) Situated on tbe inside of the splenius, this muscle resembles an elongated triangle, with the base backwards .; it is fleshy, with tendinous intersections. The posterior part is aponeurotic at its origin, the anterior terminating in a single tendon. Origin. — From the transverse and spinous processes of the first five dorsal, and the oblique processes of all the cervical vertebrae. Insertion. — To the side of the occipital tuberosity. Relation. — Externally with the splenius and trachelo- mastoideus; internally with the complexus minor, ligamentum nuchae, and oblique muscles ; posteriorly with the longissimus * This is the complexus minor of M. Chauveau. LATERAL .CERVICAL GROUP. 187 and spinalis dorsi. The superior cervical artery passes through its divisions posteriorly. Action. — It extends the head. COMPLEXUS MINOR. (Axoido-occipitalis Longus.) (Fig. 74. c.) Situated on the poll, it is fusiform, slender, and fleshy, being tendinous at its insertion. Origin. — From the neural spine of the dentata. Insertion. — With the tendon of the complexus major. Relation. — Externally with the complexus major; inferiorly with the rectus capitis posticus major; internally with the liga- mentum nuchas. Action. — To assist the complexus major. RECTUS CAPITIS POSTICUS MAJOR. {Axoido-occipitalis Brevis.) (Fig. 74. d.) Situated below the complexus minor, it is long, slender, and fusiform. Origin. — From the neural spine of the dentata. Insertion. — To a roughened depression on the occiput below its tubercle. Relation. — Externally with the complexus major ; inferiorly with the rectus capitis posticus minor. Action. — To extend the head. RECTUS CAPITIS POSTICUS MINOR. (Atloido-occipitalis Brevis.) (Fig. 74. e.) Situated below the preceding, this muscle is small, flat, and somewhat triangular. Origin. — From the supero-anterior part of the atlas. Insertion. — Below that of the preceding muscle. Relation. — Superiorly with the major ; inferiorly with the capsular ligament ; externally with the obliquus capitis anticus ; internally with the ligamentum nuchse. Action. — It assists the preceding muscle. laa MYOLOGY. OBLIQUUS CAPITIS ANTICUS. {Atloido-mastoideus.) (Fig. 74. h.) Situated on the side of the poll, it is flat, nearly square, and fleshy, with tendinous intersections. Origin, — ^From the supero-anterior portion of the roughened edge of the wing of the atlas. Insertion, — To the mastoid crest and styloid process of the occiput. Fiu. 74. Occlpito-atlo-azoid muscles— lateral view, a, Obliquus capitis posticus ; 6, Obliqaus capitis anticus; c, Complexus minor ; d, £ecvus capitis posticus major; e, Eectus capitis posticus minor. Relation, — Externally with the tendon of the splenius ; internally with the caosular ligament and rectus capitis posticus muscles. Action. — Together, to extend the head slightly; singly, to bend it laterally on the atlas. OBLIQUUS CAPITIS POSTICUS. {Axoido-atloideus.) (Fig. 74. a.) Situated between and upon the atlas and axis, it is broad, flat, thick, and fleshy. r LATERAL CERVICAL GROUP. 189 Origin. — From the lateral surface and superior spine of tbe dentata, and the capsular ligament. Insertion. — To the upper surface of the wing and body of the atlas. Relation. — Externally with the splenius, trachelo-mastoideus, and complexus major ; internally with the atlas, axis, and the atlo- axoid capsular ligament ; superiorly with the rectus posticus, and inferiorly with the rectus anticus major muscles. Action. — It is the rotator muscle of the head. SPINALIS COLLL [Dor SO- spinalis.) Deep-seated on the side of .the neck, it consists of six short fleshy bundles, intersected by tendons, whose fibres extend obliquely upwards and inwards. Origin. — Posteriorly, from the oblique processes of the first dorsal and the last five cervical vertebrae. • Insertion. — To the neural spines of all the cervical vertebrae but the first. Relation. — ^Externally with the complexus major ajid trachelo- mastoideus ; internally with the ligamentum nuchse and the vertebrae. Action. — To extend and curve the neck. Intehtransversalis Colli. (Intercervicalis.) (Fig. 73, c c c c.) Placed along the lateral part of the cervical vertebrae, it •consists of six distinct bundles with strong tendinous intersections, the fibres passing obliquely outwards and upwards. Origin. — The obhque process of one vertebra. Insertion. — The transverse process of the vertebra in front, filling up the interspaces of all, excepting those of the first and Relation. — With several deep-seated muscles of tbe neck, the Vertebrae, the vertebral artery, and vein. Action. — To assist in flexing the neck laterally. 190 MYOLOGY. Costal Region. The muscles of this region are those which cover the lateral aspect of the thoracic cavity ; some of them are attached to the anterior limb, three of which we describe the first, as it is necessary in dissection to cut through them, -and remove or deflect the limb in order to expose fully the deeper-seated muscles. The following are the muscles of the region : — Trapezius dorsaJis. Bhomboideus brevis. Lafcissimus dorsi. Serratus magnus. Superficialis costarum. Trans versalis costarum. Levatores costarum. Tntercostales. TRAPEZIUS DORSALIS. {Dorso-acromialis.) (Pl. n. 14.) Situated on the side of the withers, this muscle is flat and triangular, being almost the reversed counterpart of the cervical trapezius. The two form the trapezius rauscle. It is aponeu- rotic at its superior border, while its belly is fleshy, terminating in a flat tendon. Origin. — Superiorly, from the supraspinous ligament, and from the third dorsal spine back to the tenth or eleventh. The fibres converge downwards and forwards, over the superior costa of the scapula, and join the cervical portion. Insertion. — The tubercle on the spine of the scapula. Relation. — Externally with the skin and panniculus; internally with the rhomboideus brevis, postea-spinatus, and latissimus dorsi. Action. — To draw upwards and retract the scapula. rhomboideus BREVIS. (Dorsosuhscapularis. ) (PL. IIL 12.) Deep-seated, on the side of the withers above the scapula, it is flat and square ; the fibres extend downwards, and are entirely fleshy. r COSTAL REGION. 191 Origin. — From the neural spines of the first four or five dorsal vertebrae, and from their supraspinous ligament. Insertion. — To the inner surface of the superior costa of the scapula, and to its cartilage of prolongation. Relation. — Externally with the cartilage of the scapula, and the dorsal trapezius, and separated from the anterior portion of the superficialis costarum by a thin layer of elastic tissue; anteriorly with the rhomboideus longus ; posteriorly with the latissimus dorsi ; internally with the splenius. Action. — To draw the scapula upwards. LATISSIMUS DORSI ( Dorso-humeralis. ) (PL. IL 15.) This muscle is situated on the supero-lateral part of the chest and the loins; it is very large, flat, thick, and triangular, its fibres extending obliquely downwards and forwards ; it is aponeur rotic above, fleshy below, with a tendinous and aponeurotic insertion. Origin. — By a broad aponeurosis, from the supraspinous liga- ment and spinous processes of the vertebrae, commencing about the highest point of the withers, and stretching as far as the last lumbar. The fleshy portion becomes thick just behind the scapula, then it contracts, termiuating in a flat tendon, which passes under the latter. . It fits in a notch at the dorsal scapular angle, formed by the projection of the cartilage of prolongation, which it overlaps. Insertion. — The internal tuberosity of the humerus, along with the teres internus, and between the two insertions of the coraco-humeraiis. Before passing under the scapula, it gives off a strong aponeurosis, which passes over the supero-posterior part, of the scapula, and becomes continuous with its fascia. Relation. — Externally with the panniculus carnosus, skin, triceps extensor brachii, and dorsal trapezius; superiorly with the rhomboideus brevis and dorsal angle of the scapula ; inter- nally with the ribs, serratus magnus, superficialis costarum, and gluteus maximus. Action. — To elevate the humerus, and thus flex the shoulder- joint; it is likewise an expiratory muscle, when the limb is, fixed. li% MYOLOGY SERRATtJS MAGNUS. ( Costo-auhscapvlcms. ) (Pl. III. 10. 15.) Situated between the shoulder and chest, and on the side of the neck, this is a large fan-shaped muscle ; it may be divided into a cervical and a costal portion, and consists of several bundles with many tendinous intersections, converging upwards to the common point of insertion. Origin. — Anteriorly, from the transverse processes of the five posterior cervical vertebrae ; postero-inferiorly, from the external surfaces of the eight true ribs, from about their middles to their cartilages. Insertion, — Superiorly to the venter surface of the scapula, between the origin of the subscapularis and the insertion of the rhomboidei. Relation. — Anteriorly with the splenius; superiorly with the rhomboidei ; supero-posteriorly with the longissimus dorsi ; poste- riorly with the great oblique muscle of the abdomen, with which it interdigitates ; inferiorly with the pectorals ; internally with the ribs, longissimus dorsi, splenius, cervical vertebrae, and intercostals ; externally with the subscapular and triceps extensor muscles. Action. — It depresses the scapula ; when the limbs are fixed, it elevates the neck, and is also a subservient muscle of inspiration ; but it chiefly serves with its fellow as a muscular sling, in which the body is suspended between the anterior limbs. SUPERFICIALIS COSTARUM. , (Dorso-costalis.) (Pl. II. 49.) Placed on the supero-lateral part of the back, this muscle is broad, thin, and digitated, and consists of an anterior and a posterior portion. Origin. — Anteriorly, from the supraspinous ligament, and dorsal spines from the second to the thirteenth inclusive; posteriorly from the spines of the last eight dorsal and anterior lumbar vertebrae. Insertion. — The anterior part to the nine ribs behind the fourth, just below their angles, and to their anterior borders > the posterior part to the posterior borders of the last nine ribs. i r EXPLANATION OF PLATE IIL Muscles of the Horse. Deep Layer. 1. Temporalis. 22. Humeralis obliquus. 1 . Stylo-maxillaris. 22'. Caput parvum (of triceps extensor 2. Rectus capitis anticus major. brachii). S. Sterno-thyro-liyoideus. 23. Extensor suffraginis. 4. Stern o-maxillaris. 24.Extensormetacarpimagnusdivided. 5. The Trachea. 25. Extensor metacarpi obliquus 6. Scalenus. 25'. Its tendon. 7. Splenius. 26, 28. Flexor pedis perforans and per- 8. Funicular part of ligamentum foi-atus. nuchae. 29. Obliquus alxlominia intemus. 9. Rhomboideus longus. 30. Gluteus maximus.. 10. Cervical -1 \ serratus ma2;uu3. 15. Costal J 31. Erector coccygis. 32. Curvator coccygis. 11. Cartilage of prolongation. 33. Depressor coccygis. 12. Rhomboideus brevis. 34. Rectus femoris. 13. Trans versalis costarum. 35. Vastus extemus. 14. Longissimus dorsi. 36. Part covered by triceps abductor. 15. Serratus Magnus. 37. Biceps rotator tibialis. IS. External intercostfJs. 38. Gastrocnemius extemus. 17. Internal intercostals. 39. Plantaris. 18. Rectus abdominis. 40. Flexor pedis perforans. 19 19. Pectoralis magnus. 41. Peroneus. 20. Postea-spinatus minor. 42. Flexor metatarsL 21. Flexor brachii. 43. Extensor pedis (cut across). COSTAL EEGION. 19^ Relation. — Internally with the ribs, trans versalis cos tar um, and longissimus dorsi ; externally with the rhomboideus, serratus magnus, and latissimus dorsL Action. — Respiratory; the anterior portion drawing the ribs outwards and forwards, acts as an inspiratory, the posterior, by drawing them backwards and upwards, as an expiratory muscle. TRANSVERSALIS COST ARUM. (Trachelo-costalis.) (PL. ni. 13.) Situated on the supero-lateral part of the thorax, it is long, thin, and semipenniform, the fibres passing downwards, outwards, and forwards, its numerous muscular bundles each terminating in a flat tendon. Origin. — From the transverse processes of the first lumbar vertebrae, and the ribs near their tubercles. Insertion. — To the external surface of all the ribs, a tendon to each, and one to the last cervical vetebra. Relation. — Externally with the preceding muscle ; internally with the ribs ; superiorly with the longissimus dorsi. Action, — It compresses the "ribs, assisting in expiration. LEVATORES COSTARUM. {Transverso-costalis.) Situated deeply on the back, these muscles are small, flat, and triangular, extending obliquely downwards and backwards. They are fleshy and tendinous. Origin. — Superiorly, from the transverse processes of the dorsal vertebrae, just above the tubercles of the ribs. Insertion. — Inferiorly to the external faces of the ribs, just above their angles. Relation. — Externally with the longissimus dorsi ; internally with the external intercostals, with which posteriorly they are much blended. Action. — To raise and draw the ribs forwards, thus acting as inspiratory muscles. 194 MYOLOGY. INTERCOSTALES. (Externi and Interni). (PL. III. 16, 17). These fill up the spaces between the ribs, are external and internal, and usually seventeen in number, consisting of flat bands, included in, and intersected by, many broad aponeurotic slips. The external ones are thickest above, the internal below, the former terminating at the costal cartilages, between which the latter extend. Origin. — From the posterior border of each rib. Insertion. — The anterior border of each succeeding rib, the fibres of the external ones extending downwards and backwards, those of the internal ones downwards and forwards. The external terminate at the costal cartilages, while the internal do not extend above the angles. Relation, — Externally with the serratus magnus, supcrficialis and transversalis costarum, and latissimus dorsi ; internally with the pleura. Action. — They are inspiratory muscles, drawing the ribs for- ward, the first rib being rendered a fixed point by the contraction of the scalenus. They thus aid the diaphragm in its action. Pectoral Kegion. In this region we describe two groups of muscles, the pectoral and the sternal^ the latter being deep-seated. Pectoral Group. This group consists of four pairs of muscles, w^hich are largely developed in the horse, and all of which arise from the external surface of the sternum and its appendages, and become attached to the pectoral limb, upon which they, as a group, assist in sus- pending the body, also in moving the limb, and in respiration. They are differently described by different authorities ; Percival and Leyh describe three pairs, Chauveau two, but as the latter divides each of them into two parts, his consideration ultimately agrees with the one adopted here. We describe four pairs of pectoral muscles : — Pectoralis transversus. Pectoralis magnus. Pectoralis anticus. Pectoralis parvus. PECTORAL GROUP. 195 PECTORALIS TRANSVERSUS. (Stemo-aponeuroticus. ) (Fig, 75. d.) Situated on the latero-inferior part of the thorax, this muscle is quadrilateral, the fibres extending outwards and- downwards. Fto. 75. Pectoral mtwcles, and inferior deep muscles of the neck, a, Longus colli ; 6, Rectus capitis lateralis ; c, Rectus capitis anticus minor ; d, Pectoralis transversus ; e, Pectoralis anticus ; //, Pectoralis magnus ; g, Pectoralis panrus. On the left side the pectoralis transversus and anticus have been removed. Near its origin it is fleshy, mixed with tendon, but. afterwards becomes aponeurotic. Origin. — By fleshy fibres usually from the first four bones of the sternum, meeting its fellow at a white central line. Insertion, — To the olecranon, by fascia covering the inner side of the arm, and to the anterior part of the humerus. Relation. — Externally with the skin ; anteriorly with • the pectoralis anticus ; superiorly with the pectoralis magnus. Action. — To adduct the arm, and especially to tense the brachial fascia. 196 MYOLOGY. PECTORALIS MAGNUS. (Sterno-trochineus.) (PL. III. 19, 19. Fig. 75.//.) This muscle is situated on the infero-lateral part of the thorax^ and is large, irregularly four-sided, flat, and thick, the fibres extending forwards and outwards. Slightly aponeurotic ante- riorly, elsewhere it is fleshy. Origin. — ^From the inferior border of the last three or four bones of the sternum, the ensiform cartilage, and its fellow of the opposite side; externally from the cartilages of the false ribs, fascia of the external oblique muscle of the abdomen, and tha abdominal tunic. Insertion. — To the fascia on the inside of the arm, and to the inner trochanter of the humerus, under the tendon of the coraco- humeralis, and by fascia over the bicipital groove, to the external trochanter. Relations. — Externally with the panniculus, skin, and pectoralis transversus ; internally with the fascia of the external oblique, and the ribs ; anteriorly with the pectoralis parvus. Action. — To draw the shoulder back and adduct the arm ; in difficult respiration it acts as an inspiratory muscle. PEGTORALIS ANTICUS. {Sterno-humeraUs. ) (Fig. 75. e.) Situated on the anterior part of the breast, it foims the fleshy prominence seen in front. Short, thick, and fusiform, its fibres extend outwards ; it is tendinous at its attachments, with a fleshy belly. Origin. — From the cariniform cartilage and first bone of the sternum. It is directed somewhat backwards, outwards, and downwards. Insertic%\ — To a ridge on the anterior part of the shaft of the humerus by fleshy fibres, and an aponeurotic tendon common also to the levator humeri, and pectoralis transversus. Relations, — Externally with the skin ; anteriorly with the levator humeri and panniculus ; posteriorly with the pectoralis magnus and transversus ; internally with the parvus. Action. — Its chief action is to adduct the arm. STERNAL GROUP. 197 PECTORALTS PARVUS. {Sterno-prescapularis.) (Fig. 75.(7.) In front of the magnus, on the antero-inferior part of the thorax, elongated and prismatic in form, its fibres extend out- wards, forwards, and upwards ; it is tendinous at its origin, fleshy elsewhere. Origin. — From the three oi four anterior sternal segments, cartilages, ribs, and carinifonqfi cartilage. Insertion. — ^To the fascia in front of the shoulder-joint, and the anterior costa of the scapula, nearly as high up as the origin of the antea-spinatus. Relation. — Externally with the magnus and transversus ; inferiorly with the transversus and anticus ; internally with the first costal cartilages, intercostales, and transversalis costarum ; anteriorly with the levator humeri. Action. — To draw the shoulder- joint backwards and down- wards, assist the .magnus, and tense the scapular fascia. Sternal Group. The muscles of this unimportant group are two in number — Lateralis stern i. Triangularis stemi. LATERALIS STERNL (CostO'Sternalis.) Placed along the inferior border of the serratus magnus, its fibres extend downwards and backwards. It is flat, thin, and aponeurotic at its extremities. Origin. — From the outer surface of the first rib, passing over the next two or three ribs, and becoming attached to the ster- num at about the fourth segment. Relation. — Externally with the pectorals ; superiorly with the serratus magnus ; posteriorly with the rectus abdominis ; inter- nally with the ribs and intercostals. Action. — An auxiliary muscle of expiration. 1^8 MYOLOGY. TEIANGULARIS STERNL {Sterno-costalis.) Situated in the thorax and upon the sternum, it is triangular, tendinous, and dentated on its outer border. Origin. — From the superior sternal ligament and segments. Insertion. — To the cartilages, and inner surfaces of the distal ends of the true ribs, excepting the first. Action. — To assist in expiration. DORSO-LUMBAR KeGION. The muscles of this region, a single group, are closely related with the superior aspect of the vertebral column, and we describe them as consisting of four — Longissimus dorsi. I Semispinalis dorsi et lumborum. Spinalis dorsi. | Intertransversales lumborum. LONGISSIMUS DORSI. (Ilio-spinalis.) (Pl. IIL 14.) Situated on the superior part of the back and loins, this, the longest and most powerful muscle in the body, occupies the space between the costal angles and the dorso-lumbar spines ; broad and fleshy at its origin in the loins, it becomes deeper and narrower as it proceeds forwards. Towards the withers it diverges, presenting three distinct portions, two of which proceed in an oblique direction to the neck, and terminate by several tendons (the deeper portion is described as the spinalis dorsi) ; the third portion is adherent to the sides of the anterior dorsal spines. The belly of this muscle is intersected by several tendons, and is invested posteriorly by a very strong, tendinous aponeurosis. Attachments. — The crest, inner surface, and supero-anterior spine of the ilium; the spinous and transverse processes of the first two bones of the sacrum ; the spinous, transverse, and oblique processes of all the lumbar vertebrae ; the spinous and transverse processes of all the dorsal vertebrae; the external surface of the last fifteen or sixteen ribs just above the trans- versalis costarum, and the spinous and transverse processes of the last three or four cervical vertebrae. r DOBSO-LUMBAR REGION. 199 Relation. — Externally with the superficialis costarum, and gluteus maximus which overlaps it in the lumbar region; in- feriorly with the transversalis costarum ; internally with the ribs, vertebrae, and semispinalis dorsi et lumborum ; anteriorly with the spinalis dorsL Action. — It is brought powerfully into play in kicking anri rearing, by elevating the fore or hind quarters, according to whether the fore or hind limbs are fixed. Acting singly, the result is lateral flexion of the back and loins. It may assist also in expiration. SPINALIS DORSI.'"' Situated deeply on the withers, it is pyramidal in form, aponeurotic at its origin, with a fleshy belly; it is with difficulty separated from the longissimus dojsi. Origin, — By aponeurosis from the supraspinous ligament, as far back as the twelfth, and from the posterior borders of the spinous processes of the six anterior dorsal vertebrae. Insertion. — To the superior spinous processes of the last three or four cervical vertebrae. Relation. — Externally with the trapezius and rhomboideua brevis ; anteriorly with the complexus major and splenius ; infe- riorly with the longissimus dorsi ; internally with its fellow, the ligamentum nuchas, the anterior dorsal vertebrae, and semispinalis dorsi. Action. — To assist in elevating the neck. SEMISPINALIS DORSI ET LUMBORUM. (Spinalis Transversus.) In contact with the dorsal and lumbar spines, this muscle con- jts of a number of fasciculi, whose fibres are directed upwards ind forwards. Origin. — From the sacrum, the oblique processes of all liie lumbar, and transverse processes of all the dorsal vertebrae. Insertion. — The spinous processes of the vertebrae, the sciculi each passing over two or three spines before being iserted; it becomes continuous with the spinalis colli at the jventh cervical. * [This muscle may be regarded as part of the longissimus dorsi— Ed.] 200 >rroLOGY. Relation. — Externally with the longissimus dorsi ; internally with the vertebrae. Action, — ^To assist in extending the spine. INTERTRANSVERSALES LUMBORUM. These are small muscular slips, invested by strong tendinous fasciae, running from the transverse process of one lumbar vertebra to the one adjacent. Relation, — "With the longissimus dorsi and intertransverse ligaments. Action. — To assist in flexing the spine laterally, by bringing these processes nearer to each other. Abdominal Region. The infero-lateral walls of the abdomen are formed by a large musculo-aponeurotic envelope, consisting of four pairs of muscles, covered externally by the abdominal tunic, the muscles on the right being separated from those on the left by the linea alba, a white fibrous cord extending from the sternum to the pubis. These muscles, the rectus excepted, consist each of a fleshy and an aponeurotic portion, and the general line of demarcation between the aponeurotic and the fleshy region is known as the linea semUwnOjris, We have to describe the following structures : — Tunica abdominalis. Linea alba. Obliquus abdominis extemus. I Rectus abdominis. Obliquus abdominis internus. | Transversalis abdorainis. TUNICA ABDOMINALIS. (Tunica Elastica)» The abdominal tunic is an immense expansion, composed of yellow elastic tissue, which covers the external oblique muscles. It is thickest at the pubis, and on each side of the linea alba, thinning as it approaches the sternum, and disappearing at the posterior attachment of the pectoralis magnas muscle. It blonds with the external oblique, anteriorly reaching the digitations oi ABDOMINAL REGION. 201 the serratus magnus ; posteriorly it furnishes a few fibres, which, detached from the surface of the common abdominal tendon (prepubian), pass between tne thighs, and become lost in the muscles of that region. Relation. — Externally by cellular tissue to the panniculus and skin. It is continuous with the suspensory ligament of the sheath and dartos in the male, and the elastic envelope of the mamma in the female, in whom it is always thickest. Use. — To afford a mechanical support to the abdominal viscera, and conserve muscular action by substituting elasticity for it. On the application of distensile force it yields con- siderably. LINEA ALBA. The linea alba is a white fibrous cord situated between the inner borders of the two recti-abdominales, to which it gives attachment, as to the other abdominal muscles. Anteriorly it is attached to the inferior surface of the xiphoid cartilage, and posteriorly it becomes cenfounded with a large tendon, common to the abdominal muscles, the prepubian tendon, which is attached to the anterior border of the pubis, and assists in the formation of the internal commissure of the* inguinal canals. Between its posterior and middle third the linea alba is enlarged, and forms a lozenge-shaped space, in the centre of which is the remnant of the umbilicus. The fact of this structure joining the sternum to the pubic symphysis, together with certain co-related features, has induced anatomists to regard the linea alba as representing a rudimentary abdominal sternum. OBLIQUUS ABDOMINIS EXTEENUS. {Costo-ahdominalis,) (Pl. II. 74.) The largest and most external muscle of the group, situated on. the infero-lateral aspect of the abdomen, and consisting of a fleshy and an aponeurotic portion. It is quadrilateral, its fibres run- ning downwards and backwards. Its aponeurosis commences at a line called the linea semilunaris, and is continued to the linea alba, where it bends with that of the internal oblique. Attachments. — By fleshy fibres, anteriorly to the outer surface of the last thirteen or fourteen ribs, just below their middle ; the I 202 MYOLOGY. four anterior digitations are received between the corresponding ones of the serratus maguus ; to the fascia of the latissimus dorsi,. and superiorly to the lumbar fascia : to the anterior iliac spine and crest ; to the pubis and prepubian tendon, and inferiorly to the linea alba throughout its whole extent. Relatiov. — Externally with the abdominal tunic ; antero- externally with the pectoralis magnus; internally with the ribs, cartilages, and intercostals, the internal oblique . and the rectus ; anteriorly with the serratus magnus. Action. — To support and compress the abdominal viscera, and assist in defecation, urination, and parturition. It is also a flexor of the vertebral column, and a muscle of expiration. APONEUEOSIS OF THE OBLIQUUS EXTERNUS. The distribution of this aponeurosis being very singular and important, it merits separate consideration. It stretches from the anterior spine of. the ilium to the pubis, answers to the fold of the groin, and marks the division between the trunk and hind extremity. Posteriorly it splits into two layers ; one descends internally over the thigh, forming the crural aponeurosis; the other is reflected upward, and enters the abdominal cavity, this fold receiving the name of the crural arch or P^uparfs ligament Near the prepubian tendon, and immediately in front of its division, the aponeurosis is pierced by a large oval aperture, the external ahdomiv al ring, which is the external opening of the inguinal canal. Crural Aponeurosis. This descends over the fold of the groin to the patella, and internal surface of the thigh, blending outwardly with the fascia lata, and internally becoming less dense in structure : it covers the sartorius. part of the gracilis, vastus internus, and the crural vessels as they leave the abdomen. > Poupart*8 Ligament The Crural Arch or Pouparfs Ligament is a ribbon-shaped reflected portion of the aponeurosis of the external oblique, and is attached by its extremities to the anterior spine of the ilium, and anterior border of the pubis. Anteriorly it forms the posterior ABDOMINAL REGION. 203 pillar of the inguinal canal, and externally gives attachment to the posterior fibres of the internal oblique. Posteriorly it contacts the sartorius and pectineus muscles, and the crural vessels, embracing those parts in a sort of arch, hence its name. Its superior border at its external half is attached to the lumbo-iliac aponeurosis; while its middle is confounded with the external surface of the sartorius and iliacus. Inside the attachments of the pectineus and psoas parvus, it forms, with the anterior border of the pubis, the iliacus and sartorius, a triangular open- ing called the crural ring, through which the crural vessels pass out of the abdomen. The inferior border is continuous with the femoral and great oblique aponeuroses. Inguinal Canal. The Inguinal Canal is infundibuliform and compressed laterally ; through it pass the spermatic cord and external pudic artery of the male, and mammary vessels of the female. It is situated obliquely between -the crural arch, which is its posterior, and the internal oblique muscle, which forms its anterior wall. The external orifice is called the external abdominal ring, and is larger than the internal, being oval in fornv and directed backwards and inwards. It presents two pillars and two extremities or comfimissures. "The pillars, anterior and posterior, are merely the edges or lips of the aperture, and are formed by the arciform fibres of the aponeurosis of the external oblique muscle, the posterior one being assisted by Poupart's ligament. The commissures, external and internal, are formed by the union of the. pillars, the latter being limited by the prepubian tendon. The peritoneal or internal abdominal ring, the internal orifice of the canal, is situated in front of the crural ring. It is a mere dilatable cleft between the crural arch and the internal oblique, and but indifferently marked at its extremities. OBLIQUUS ABDOMINIS INTERNUS. {Ilio-dbdominalis.) (PL. III. 29.) Situated under the externus, on the postero-lateral and inferior aspects of the abdomen, its fibres expanding downwards, it is, like the externus, fleshy and aponeurotic ; the fleshy portion is I 204 MYOLOGF. thick, and occupies the flank ; the aponeurosis commences at the linea semilunaris, its fibres blending with those .of the external oblique. Attachments. — Supero-posteriorly, to the anterior spine of the ilium, whence its fleshy fibres radiate ; a portion is attaqhed to the transverse processes of two or three of the first lumbar vertebrae, and passes to the posterior border of the last rib (this portion is described by 'the German anatomists as a retractor costce) ; and to the fascia of the latissimus dorsi ; to the cartil- ages of the false ribs ; postero-inferiorly to the symphysis pubis, by the prepubian tendon, aiding in the formation of the internal abdominal ring ; inferiorly to the linea alba throughout it^ whole extent. Relations. — Externally with the external oblique ; internally with the transversalis and rectus abdominis. Action. — It assists the externus in compressing the abdomen in the act of respiration, and in flexing the spine. It also draws the last rib backwards. RECTUS ABDOMINIS. (Sterno-puhialis.) (Pl. III. 18,) Situated along the inferior and middle part of the abdomen, it is long, flat, polygastric, and broadest in the middle. Tendmous at its attachments, its belly consists of numerous flat muscular fasciculi, with transverse tendinous intersections, to which the aponeuroses of the oblique muscles are adherent ; ihtz2 intersec- tions are called the lineoe transversce (inscriptiones tendinccs), and may be regarded as the abdominal representatives of the ribs. The posterior part of the muscle assists in the formation of the internal abdominal ring. Attachments. — Anteriorly to the inferior surface of the xiphoid cartilage and sternum ; to the cartilages of the last four true and first two false ribs ; posteriorly to the crest of the pubis, through the medium of the prepubian tendon, which is directly continuous with it ; internally to the linea alba. Relations. — Inferiorly with the aponeurosis of the internal oblique muscle ; anteriorly with the pectoralis magnus ; superiorly with the transversalis, and the cartilages of nearly all the ribs ; internally with its fellow at the linea alba. SUBLUMBAR BEGION. 205 Action. — To support and compress the abdominal viscera and assist in respiration. It is the chief flexor of the spinal column. TRANSVERSALIS ABDOMINIS. (Lumho-dbdominalis.) Placed on the infero-lateral aspect of the abdomen, imme- ttately outside the peritoneum, this muscle is broad, flat, and [uadrilateral, its fibres extending downwards. It is fleshy rom its origin to the linea semilunaris, where it becomes Iponeurotic. Attachments. — To the transverse processes of the lumbar rertebrse, and the inner surface of the cartilages of the false ribs, iterdigitating with the attachments of the diaphragm, and by aponeurosis to the xiphoid cartilage and linea alba, becoming idimentary posteriorly. Relations. — Anteriorly with the diaphragm ; externally with bhe cartilages of the false ribs, the obliquus internus and rectus ; iternally with a thin layer of fascia (the fascia transversalis) rhich connects it with the peritoneum. Action. — To assist the oblique muscles, and raise the viscera. SUBLUMBAR REGION. The muscles of this region, a single group, connect the lumbar md last dorsal vertebrae with the pelvis or the posterior limb. They ire covered by the iliac fascia, and this by the peritoneum, a jerous membrane lining the abdominal cavity. In this group we >lace four muscles : — Psoas magnus. I Iliacus. Psoas parvus. | Quadratus lumborum^ PSOAS MAGNUS. (Suhlumho-trochantineus.) (Fig. 76. c.) Situated below the transverse processes of the lumbar vertebrae, it is elongated and fusiform, flattened anteriorly, conical posteriorly, its - fibres extending downwards and backwards ; it is almost entirely fleshy, except at its insertion. Origin. — From the inferior surfaces of the last two ribs, the 206 MYOLOGY. 'bodies of the last two dorsal, and all the lumbar vertebrss except the last, and to the lumbar transverse processes, passing between the two parts of the iliac us. Insertion. — By a tendon, common to it and the iliacus, to the internal trochanter of the femur. Belation.— Posteriorly with the iliacus ; internally with the psoas parvus and the bodies of the vertebrae; above with the Fia. 76. Muscles of the sublumbar and internal deep femoral regions— seen from below, a, a. Quadratus \ lumborum ; b, Psoas parvus ; c, Psoas magnus ; d. e, Iliacus ; /, Pectineus ; g, Adductor brevis ; ' h, Adductor longus ; i, Adductor magnus ; k. Vastus internus : I, Rectus femoris. quadratus lumborum, and below with the kidney and iliac fascia, the diaphragm, and, in the thoracic cavity, with the pleura. Action. — To flex and rotate the thigh, or, the latter being fixed, to flex the loins ; the latter action tends to ** roach " the back. PSOAS PAEVUS. (Suhlumho-puhialis.) (Fig. 76. h.) Situated on the inner side of the psoas magnus, it is long, thin, and semipenniform, the fibres extending backwards and outwards. r SUBLUMBAR REGION. 207 Fleshy above, it has posteriorly a strong flat tendon passing along the lower surface to its insertion. Origin. — From the bodies of the last three or four dorsal, and all the lumbar vertebrae. Insertion. — To the ilio-pectineal eminence on the brim of the pubis, midway between the symphysis and the acetabulum, and to the iliac fascia. Relation. — Inferiorly with the diaphragm, pleura, posterior aorta and vena cava ; externally with the psoas magnus. Action. — To flex the pelvis on the ppine, when the loins are fixed ; when the pelvis is fixed, to arch the back. It is also the tensor of the iliac fascia. ILIACUS. (Ilio-trochantineus.) (Fig. 76. d, e.)- Situated under the false pelvis, this muscle is strong, thick, and pyramidal, the base being forwards, and the fibres extending downwards, backwards, and inwards. The belly is incompletely divided by a fissure into two unequaL portions, the external being the larger ; through this fissure passes the tendon of the psoas magnus, which its own tendon joins. Origin. — From the ilio-pectineal ridge, nearly all the venter surface of the ilium, and the inferior sacro-iliac ligament. Insertion. — To the internal trochanter of the femur, along with the psoas magnus. Relation. — Superiorly with the ilium ; inferiorly with the iliac fascia and sartorius ; externally with the tensor fasciae latas and rectus femoris, from which it is separated by a layer of fat ; internally with the crural vessels. It passes between the vastus internus and the pectineus. Action. — To flex the femur, and rotate it outwards. QUADRATUS LUMBORUM. (Sacro-lumbalis. ) (Fig. 76. a.) Placed below and' between the lumbar transverse processes, this is a flat, thin muscle, consisting of several bundles, with strong ^tendinous intersections. The principal bundle is situated exter- 208 MYOLOGY. nally and longitudinally, the lesser ones diverging from it inwards and forwards. OHgin. — The chief bundle arises from the inferior sacro-iliac ligament at tjie angle of the sacrum, passing directly forwards. Insertion.—l^' the posterior border of the last rib, becoming attached in its bourse to the free extremities of the transverse processes of the lumbar vertebrae. The other bundles leave the- internal border of the first, and are attached to most of the trans- verse processes of the lumbar vertebrae, and inner surfaces of the last two or three ribs. Relation. — Superiorly with the vertebrse, and intertransversales lamborum ; inferiorly with the psoas magnus. Action. — To assist in lateral flection of the lumbar vertebrae, and to draw the last ribs backwards. DiAPHKAGMATIC REGION. This region contains only one muscle, from which it takes it« name. DIAPHRAGM. {Diaphragma.) (Fig. 77. A.) The diaphragm, or midrif, is the muscular partition which separates the thorax from the abdomen ; it slopes obliquely down- wards and forwards, and is in form elliptical, or somewhat heart- shaped, being widest superiorly. The thoracic surface is convex and covered with pleura, the abdominal concave and covered with peritoneum. It is divided into a body or septum, and two crura or appendices; the body, or greater muscle, is made up of a fleshy periphery and tendinous phrenic centre (Speculuvo Helmontii). Attachments. — The fleshy portion is attached to the inner surface of the distal ends of the last twelve ribs, or to their cartilages, and to the superior surface of the ensiform cartilage, the fibres converging towards the tendinous centre. The crura or pillars, two in number, lie below the vertebrae in the sublumbar region. The right is the longer and larger, and arises from the inferior surface of the bodies of all the lumbar vertebrae but the last, by strong tendinous fibres which blend with the inferior common ligament. The left differs from the right in arising from only one or two anterior lumbar vertebrae. The crura pass DIAPHRAGMATIC REGION. 20^ down the central line of the tendinous portion, and gradually blend with its fibres. Near the centre- of the diaphragm, and a little to the right, is a large opening, the foramen dextruTn, through which passes the posterior vena cava. Between the pillars superiorly is a second opening, the hiatus aorticus, through which pass the posterior aorta, vena azygos, and thoracic duct. Below this,^the right crus forms towards the left a third opening, the foramen sinistrum, for the passage of the oesophagus and pneumogastric nerves, accompanied by the pleural artery. There Fig. 77. The diaphragm, and superficial muscles of the internal femoral region— viewed from below.' A, The diaphragm ; a a, The tendinous centre; a' a'. The fleshy periphery; a" a", The crura; a"', The hiatus aorticus ; a"". The foramen sinistrum ; a""', Tlie foramen dextrum ; ft, The sar- torius ; c, The gracilis. are thus three openings — the hiatus aorticus above, the foramen sinistrum in the middle, and the foramen dextrum below. Certain of the sublumbar muscles originate partly in the thorax, and the diaphragm forms arches which allow their passage, and that of the sympathetic and splanchnic nerves ; these arches are bounded by ligaments, the ligamenta arcuata ; outside the arches the diaphragm is attached to the last rib by a broad fold of elastic tissue. Relation. — Anteriorly with the pleura, which covers both it! p "210 MYOLOGY. and the lungs ; posteriorly, covered by peritoneum, it contacts the liver, stomach, spleen, and the large colon. Action. — Essentially a muscle of inspiration. When it eon- tracts it becomes flattened, forces the abdominal viscera back- wards, and so enlarges the thoracic cavity. This action is antagonistic to one of the actions of the abdominal muscles. It also assists in the expulsive eflbrts of defecation and parturition. Coccygeal Region. The muscles of this region, that of the tail; are enclosed in strong fascia, which may be said to be continuous with the approximate pelvic ligaments. We find one group containing four muscles : — Erector coccygis. Depressor coccygis. Curvator coccygis. Compressor coccygis. ERECTOR COCCYGIS. (Sacro-coccygeus Superior.) (PL. IIL31.) Situated on the supero-lateral part of the tail, it consists of bundles of fibres, intersected by tendons, which gradually diminish in size from before backwards, each terminating in a short tendon. Origin. — The tuberous summits and lateral aspect of the posterior sacral spines, and superior surface of the coccyx. Insertion. — To the coccygeal bones. Relation. — -Internally with its fellow, and the coccygeal verte- brse ; externally with the skin and fascia. Action. — When acting together to elevate the tail; singly, to draw it upwards and outwards. DEPRESSOR COCCYGIS. (Sacro-coccygeus Inferior.) (PL. XXL 33.) Situated on the infero -lateral aspect of the tail, and similar to the erector, but thicker. Origin. — Within the pelvis, from the inferior surface of the sacrum, the inner surface of the sacro-sciatic ligament, and the coccygeal vertebrae. MUSCLES OF THE LIMBS. 211 Inserticra. — By tendons to the inferior surface of all the coccygeal vertebras successively. Relation. — Superiorly with the sacrum, coccyx, and curvator; irferiorly with the rectum ; externally with the curvator and sacro-sciatic ligament ; internally with its fellow. Action, — To bend the tail downwards ; singly, to draw it downwards and to one side. CURVATOR COCCYGIS. (Sacro-coccygeus Lateralis.) (Pl. IIL 32.) Situated on the side of the tail, and similar in structure to the preceding, it is merely a continuation of the semispinals lumborum. Origin. — From the spines of the last lumbar, and lateral aspect of the sacral and coccygeal vertebrae. InseHion. — The side of the coccyx, between the erector and depressor. Relation. — Superiorly with the erector and sacral ligament; inferiorly with the depressor ; externally with the compressor. Action. — To curve the tail, drawing it sideways over the quarter. CO>IPRESSOR COCCYGIS. (Ischio-coccygeus.) Situated at the side of the pelvis, it is a large, thin, and tri- angular muscle. Origin. — By aponeurosis, from the superior ischiatic spine and the inner surface of the sacro-sciatic ligament, running upwards and backwards. Insertion. — By fleshy fibres, to the side of the terminal sacral and first two coccygeal vertebrae. Relation. — Externally with the sacro-sciatic ligament ; inter- nally with the curvator and rectum. Action. — To depress the entire tail. Muscles of the Limbs. The muscles of this class are those which are specially related to the limbs, for the most part acting upon them alone ; they arc intrinsic and extrinsic, according to their origin. These muscles 212 MYOLOGY. are either flexors^ extensors, abductors, adductors, or rotators, but in the horse the last are comparatively few, limited in their action, and nearly all extrinsic, the joints of the horse's limbs below the shoulder and hip allowing very slight rotatory motion. Muscles of the Pectoral Limb, These may be conveniently divided Scapular . Brachial . Antibrachial Metacarpal nto the following regions; The shoulqler. The arm. The fore-arm. The foot (hand). Scapular Region. Externally the region is covered by the strong scapular fascia, and comprises an external group of four and an internal of three muscles. External Scapular Group. Teres externus. f Postea-spinatus. Antea-spinatus. ' Postea-spinatus minor. TERES EXTERNUS. (ScOipido-humeralis Magnus.) (Fig. 78. c.) This is the long abductor of the arm, which corresponds to the deltoid of man. Situated on the outer and posterior part of the shoulder, it consists of two portions, anterior and posterior. The posterior or larger portion is triangular in form, and very fleshy, the fibres extending obliquely downwards and forwards ; it is lodged in a depression in the caput magnum. The anterior or superior portion is thin, and aponeurotic above, extending over the postea-spinatus muscle, to which it is adherent. Attachonents. — The posterior section arises from the dorsal angle and posterior costa of the scapula ; the anterior by strong fascia from a tubercle on the spine of the scapula, and the scapular fascia. They unite inferiorly, and by tendinous and fleshy fibres are inserted to the deltoid ridge of tte humerus below the insertion of the postea-spinatus minor. • r EXTERNAL SCAPULAR GROUP. 213 Helat Ion. — Anteriorly with the caput magnum, caput medium,andpostea- spinatus ; externally with the scapular fascia. A ction . — To abduct the humerus, and rotate it outwards; when acting with the teres internus io flex the shoulder joint. with the postea-spinatus ; internally. ANTEA-SPINATUS. (Superacro?7iio-trochiterius.) (Fig. 78, a.) Occupying the antea- spinatus fossa of the scapula, this muscle is ppamidal in shape, with the base downwards. Its •fleshy fibres extend ob- liquely forwards; then be- coming tendinous infer- iorly, it is bifurcated for the passage of the flexor brachii tendon, the divi- sions being connected by aponeurosis. Origin . — From the anterior fossa, anterior costa, and cervical angle of the scapula, and the anterior surface of its spine. Insertion. — By two parts, one external, to the summit of the exter- nal trochanter, and one internal, to the summit of the internal trochanter, of the humerus. Fig. 78. Muscles of the anterior limb— external view, o, Antea- spinatus ; b, Fostea-spinatas ; c, Teres extemus ; d, Caput magnum ; e, Caput medium ; /, Flexor brachii ; g, Extensor metacarpi magnus ; ^, Extensor metacarpiobliquus;i,Flexor metacarpi extemus ; k, Extensor pedis ; kf. Its tendon ; fc" Fibrous band from the suspensory ligament ; I, Extensor suffraginis ; V, Its tendon. 214 MYOLOGY. Bdation. — Externally with the scapular fascia; anterioriy with the pectoralis parvus ; posteriorly with the scapular spine and the anterior border of the postea-spinatus ; internally with the bone ; antero-inferiorly with the levator humeri and the tendon of the flexor brachii. Action. — To extend the humerus on the scapula, and tense the fascia covering the flexor brachii. It serves, like the other scapular muscles, as an active ligament of the shoulder joint. POSTEA-SPINATUS. {SuhacromiO'trochiterius. ) (Fig. 78. h.) Lodged in the postea-spinatus fossa, it is broad, flat, and triangular, with the apex below, to which its fibres converge ; it is fleshy, with strong tendinous intersections. Origin. — From the posterior costa and fossa of the scapula, the posterior border of its spine, and the cartilage of prolongation Insertion. — By two divisions, one of which goes to the inner side of the convexity of the external humeral trochanter ; the other, a strong tendon, passes over the trochanter, and is inserted to, a roughened ridge below. Between the tendon and convexity is a synovial bursa. Relation. — Externally with the aponeurosis of the teres ex- ternus and with the scapular fascia ; anteriorly with the antea- spinatus and the scapular spine ; posteriorly with the teres extemus; internally with the scapula, its cartilage, and the postea-spinatus minor ; inferiorly it contacts the capsular ligament of the shoulder joint. Action. — To abduct the humerus, and rotate it outwards. POSTEA-SHNATUS MINOB. (ScapulO'humeralis Parvus.) (Fig. 80. o a.) Situated on the inside of the teres extemus, below the postea- spinatus, and along the posterior border of the scapula, it is long and prismatic inferiorly, fleshy, and intersected by tendon, and is easily divided into a large and small portion. Origin. — From the posterior border of the scapula, and by INTERNAL SCAPULAR GROUP. 215 tendinous slips from the posterior fossa, and a small tubercle on the external side of the rim of the glenoid cavity. Insertion. — To the deltoid ridge. Relation. — Externally with the teres externus and postea- spinatus ; internally with the caput magnum, caput medium, and capsular ligament. Action. — Like the last, to abduct, and rotate the humerus •outwards. Internal Scapular Group. Subscapularis. Teres internus. Scapulo-humeralis posticus. subscapularis. {Suhscapulo-trochineus. ) (Fig. 79. a.) Situated on the inner side of the shoulder blade, occupying the subscapular fossa, it is fan-shaped, forming three points superiorly, its fibres converging downwa^rds. It is covered by strong fascia, from which arises the subscapulo-hyoideus. Origin. — From the whole of the subscapular fossa. Insertion. — To the internal humeral trochanter, by a strong ten- don passing over its summit, where there is a small synovial bursa. Relation. — Externally with the scapula; internally with the serratus magnus ; anteriorly with the antea-spinatus, with which it blends, the two forming a space through which passes the pre- scapular artery ; posteriorly with the teres internus. Action. — To adduct the arm, and perhaps to rotate it slightly inwards. TERES INTERNUS. (Teres Major — Suhscapulo-hurmralis. ) (Fig. 79. 6.) This, an adductor of the arm, is situated just behind the sub- scapularis, at the posterior border of the scapula ; it runs obliquely downwards, corresponding to the terres externus. It is elongated, wide in the middle, tapering at the extremities, its posterior edge being thin. Origin. — From the dorsal angle and posterior costa of the scapula. 216 MYOLOGY. Insertion, — By a flat tendon, which joins that of the latissi- mus dorsi, to the internal tuberosity of the humerus, between the tendons of in- sertion of the coraco-humeralis. Relation. — Postero - externally with the fascia of the latissimus dorsi and scapulo-ulnaris ; anteriorly with the sub- scapularis; internally with the serratus magniis; inferiorly with the coraco- ■ humeralis and humeralis obliquus. Action. — To adduct, and rotate the humerus inwards ; acting with the teres externus the result is flexion. SCAPULO-HUMERALIS POSTICUS. (Scapulo-kumeralis Gracilis — Grele. ) Situated behind the shoulder joint, between the caput magnum and the cap- sular ligament, it is very small, slender-, and fusiform, with a pale, delicate, fleshy belly, and tendinous extremities. Origin. — From the postero-inferior part of the scapula, just above the glenoid cavity, and the capsular ligament of the shoulder joint. Insertion. — Between the fibres of the humeralis obliquus, to the posterior part of the humerus, just below its head. Action. — To render tense the capsular ligament of the joint, and thus prevent its being crushed during flexion ; this action was ascribed to it by Bigot, who was the first to describe it. It is believed to be peculiar to the solidun- gula. Fio. 79. Mascles of the anterior limb- internal view, a, Subscapolaris; b, Teres intemus ; c, Coraco- humeralis; d, Scapulo-ulnaris; e. Flexor metacarpi intemus; /, Plexor metacarpi medius; g, «Capat parvum. Brachial Region. I This region clothed by the brachial fascia, includes the muscles Tvhich cover the humerus and its vicinity j they consist of an r ANTERIOR BRACHIAL GROUP. 21? anterior and a posterior group, the fonner being mostly anterior or lateral to the bone, the latter situated behind it, In either ^roup we find three muscles. Anterior Brachial Group. Flexor brachii. Coraco-humeralis. Humeralis obliquus. FLEXOR BRACHIL (Coraco-radialis.) . (Fig. 78./.) The analogue of the biceps in man, this muscle is situated in front of the humerus : it is long and cylindrical, passing down- wards and backwards. The tendon of origin contains fibro-cartilage, and the belly is intersected by tendinous fibres. Origin. — From the base of the coracoid process of the scapula, by a strong tendon, which passes over the bicipital groove where there is a synovial bursa. Insertion. — By a short tendon to the bicipital tuberosity on the antero-intemal part of the head of the radius, and to the capsular ligament of the elbow joint ; a part of it passes under the internal-lateral ligament of the elbow joint. A strong fibrous band is given off inferiorly which' joins and expands over the extensor metacarpi magnus, and becomes blended with the anti- brachial fascia. Relation. — Anteriorly with fascia, covered by the levator humeri ; internally with the coraco-humeralis ; posteriorly with the humerus; superiorly its tendon passes between the two insertions of the antea-spinatus, where a strong fascia envelopes it and is tensed by the last-named muscle. Action, — To flex the radius on the humerus, extend the latter on the scapula, and to tense the antibrachial fascia. A band of unyielding tendinous material runs through this musde, enabling it to act as a ligament, and passively support the shoulder joint, when the animal is at rest ; the band joining the extensor metacarpi also relieves muscular tension. 218 MYOLOGY. CORACO-HUMERALIS. Omo-brachialis. (Fig. 79. c.) Situated on the inner side of the humerus, this muscle is ten- dinous, long, and fusiform, its fibres passing obliquely downwards. Attachments. — From the beak of the coracoid process of the scapula. Passing between the subscapularis and the antea- spinatus, the tendon is succeeded by two fleshy bellies, a super- ficial and a deep one. The latter, thin and short, is inserted to the shaft of the humerus just above its internal tuberosity ; the former, by far the larger, is inserted to a rough surface on the same bone, lower down, and more anteriorly. Relation. — Anteriorly with the flexor brachii j superiorly with the antea-spinatus and subscapularis ; internally with the pector- alis magnus; posteriorly with the latissimus dorsi and terea internus, whose tendons pass between its two bellies. Action. — To extend, adduct, and rotate the arm inwards. HUMERALIS OBLIQUUS. (Humero-radialis — Brachialis Anticus.) (Fig. 80, d.) OccupyiDg the musculo-spiral groove, it is flat, oblong, wide superiorly, and almost entirely fleshy; it covers successively portions of the posterior, external, and anterior surfaces of the humerus, terminating on the inner aspect of the radius. Origin. — From the postero-superior part of the shaft of the humerus, just below the articular head, winding round the bone under the external tuberosity. Insertion. — To a ridge on the inner part of the head of the radius, after passing through a transverse groove just below, and within the insertion of the flexor brachii ; also to the ulna, passing imder the internal-lateral ligament of the joint, and blending with the arciform ligament. Relation. — Externally with the caput magnum and caput medium ; internally with the humerus ; anteriorly with the flexor brachii. Action. — Solely to flex the elbow joint. f-OSTEEIOR BRACHIAL GROUP. 219 Posterior Brachial Group Scapulo-ulnaris. Triceps extensor brachii. Anconeus. SCAPULO-ULNARIS. [Scapulo-olecranius Longus.) (Fig. 79. d.) Situated on the postero-internal aspect of the region, adhering to the caput magnum, this is a broad and flat muscle, aponeurotic at its origin, with a fleshy belly, and divisible into an anterior and posterior portion. Origin. — Aponeurotic, from the dorsal angle and posterior costa of the scapula. Insertion. — To the inner part of the apex of the olecranon, and to the antibrachial fascia. Relation. — Externally with the caput magnum; anteriorly with the caput medium ; internally with the pectoralis magnus ; superiorly with the latissimus dorsi. Action. — To flex the shoulder joint, extend the elbow joint, and tense the antibrachial fascia. TRICEPS EXTENSOR BRACHU. {Triceps Brachii.) (Fig. .78. d, e.) A very large and powerful muscle, occupying the space between the posterior border of the scapula, the humerus, and the olecranon. It consists of three parts, which have different origins, but a common insertion to the olecranon process. We describe them as if they were separate muscles, under their respective names : — Caput magnum. Caput medium. Caput parvum. 220 MYOLOGY. CAPUT MAGNUM. (Scapnlo-olecranius Magnus.) (Fig. 78. d.) This, the great extensor of the fore-arm, is situated on the posterior aspect of the shoulder. It is thick and triangular, extending obliquely downwards and backwards, and consists of several bundles, with tendinous intersections. Origiv. — From the dorsal angle and posterior, costa of the scapula. Insertion. — By a strong tendon to the inner and upper part of the olecranon, a synovial bursa being interposed between it and the apex. It receives many fibres from the caput medium. Relation. — -Externally with the fascia, the panniculus carnosus, and the teres externus, which occupies a depression in it ; inter- nally with the latissimus dorsi, scapulo-ulnaris, and teres intemus; inferiorly with the caput medium and caput parvum. Action. — To flex the shoulder joint, and extend the fore-arm. CAPUT MEDIUM. {Humero-olecranius Externus.) (Fig. 78. e.) Placed between the preceding niuscle and the humerus, it is thick, short, and fleshy, extending obliquely backwards and down- wards. Origin. — Aponeurotic, from a ridge on the supero-posterior part of the shaft, of the humerus, running from the deltoid ridge to the neck. Insertion. — The supero-posterior part of the olecranon; or it may join the tendon of the caput magnum. Relation. — Superiorly with the caput magnum; externally with the teres externus ; inferiorly with the humeralis obliquus and extensor metacarpi magnus; internally with the caput parvum. Action. — To extend the fore-arm. r ANTIBRACHIAL EEGION. 221 CAPUT PARVUM. {Burner o-olecranius Internus.) (Fig. 81. a.) Placed on the inner and mesian portion of the shaft of the humerus, along the inferior border of the caput magnum, this muscle is slender and triangular, with a fleshy origin. The fibres pass obliquely backwards and downwards, terminating in two flat tendons. Origin. — From the postero-internal part of the middle third of the humerus, extending from the inner tubercle. Insertion. — To the inner part of the apex of the olecranon, one tendon passing over a small groove before its insertion, which is situated below the other one. Relation. — Superiorly with the caput magnum; externally with the humerus, humeralis obliquus, and caput medium ; in- ternally with the insertion of the coraco-humeralis, with the teres internus, latissimus dorsi, and scapulo-ulnaris. Action.-^To extend the fcre-arm. ANCONEUS. (Humero-olecranius Parvus.) (Fig. 80. e.) Situated at the back of the elbow joint, it is small, thick, and almost entirely fleshy, filling up the space between the condyles of the humerus, or the olecranon fossa. Origin. — From the borders of the fossa, chiefly the epi trochlea, and the capsular ligament of the elbow joint. Insertion. — The antero-extemal part of the olecranon. Relation. — Posteriorly with the caput medium muscle ; ante- riorly with the elbow joint and humerus. Action. — To tense the capsular ligament, and prevent it from being crushed during extreme extension. ANTIBRACHIAL REGION. The muscles of this region, the fore-arm, cover the ulna and radius, except on the inner aspect of the latter, where there is little interposed between the skin and the bone ; they are divided into 222 MYOLOGY. two distinct groups, the anterior and posterior, the first of which are all extensors, the second all flexors. All these muscles are inserted below the radius, and therefore act upon the carpus or on the joints below. The region is enclosed in the antibrachial fascia, an exceedingly strong covering, which is firmly attached to the radius and ulna. Anterior Antibrachial Group, extensors. The extensor group includes four muscles : — Extensor metacarpi magnus. Extensor metacarpi obliquus. Extensor pedis. Extensor suffraginis. EXTENSOR METACARPI MAGNUS, {Epicondylo-premeiacarpeus.) (Fig. 78. g.) Situated in front of the radius, and in figure pyramidal, extend- ing downwards, it consists of a fleshy belly, and a long flat tendon, which commences at about the lower third of the radius, and passes over the carpus, terminating at the head of the metacarpus. Origin. — From the epitrochlea, or ridge above the external condyle of the humerus, from the capsular ligament of the elbow joint anteriorly, and the surface just above. It receives a strong tendinous band from the flexor brachii. The tendon passes through a groove or theca in the anterior part of the distal end of the radius, where there is a synovial sheath or bursa, then over the knee through a second synovial apparatus. Two synovial sheaths are thus interposed betv/een the bones and the tendon, the latter being bound down by the anterior annular ligaments, and by the tendon of the extensor metacarpi obliquus, which crosses it in an oblique manner just above the carpus. Insertion. — To a tuberosity on the anterior part of the head of the great metacarpal bone, towards its inner side. Relation. — Anteriorly with the fascia ; posteriorly with the radius ; externally with the extensor pedis ; supero-internally with the humeralis obliquus and flexor brachii ; inferiorly with the extensor obliquus. Action, — To extend the carpus. r- ANTERIOR ANTIBRACHIAL GROUP. 22S EXTENSOR METACARPI OBLIQUUS. (Eadio-premetacarpeus. ) (Fig. 78. h.) This muscle is situated on the infero- anterior part of the radius, and is tri- angular and penniform ; aponeurotic above, it terminates in a small tendon, which crosses obliquely the inferior extremity of the anterior surface of the radius, under the extensor pedis, and over the extensor metacarpi magnus tendon. Origin. — From the external border of the radius. Its tendon passes through the oblique groove on the antero-intemal part of the distal end of the radius, where there is a synovial sheath. Insertion. — The head of the inner metacarpal bone. Relation. — Anteriorly with the ex- tensor pedis and the fascia ; posterior- ly with the extensor metacarpi magnus and the bone. Action. — To extend the metacar- pus, and rotate it slightly, carrying the inner aspect forwards. EXTENSOR PEDIS. (Epitrochleo-prephalangeus. ) (Fig. 78. fc; Fig. 80./.) Placed on the antero-external part of the fore-arm, it is long and pyra- midal, extending downwards ; fleshy above, its belly is bifid inferiorly, and ^terminates in a long tendon, which is louble, and commences about the ferior third of the radius. Fig. 80. External view of the muscles of the anterior limb— showing the deeper ones of the upper region, a a, Postea- spinatus minor ; 6, Deep portioji of postea-spinatus ; c, flexor brachii divided, and the upper part raised ; c'. Its tendon, which fits the bicipital groove ; d, Humeralis obliquus ; c. An- coneus ; /, Extensor pedis ; g, Thier- nesse's muscle; h, Phillips' muscle;. h\ Its tendon. 224 MTOLOGT. Origin^ — The fleshy part arises from the base of the epitrochlea, ^ and t^e anterior border of the external lateral ligament of the : elbow joint, the front of the distal extremity of the humerus, and J the outer part of the head of the radius. The tendon, which is double, pisses through a synovial theca in the external groove on the distal ^nd of the radius, under the anterior annular ligament. Below, the knee it sends, a small tendon to join that of the extensor suffraginis ; then expanding, it passes over the front of the fetlock joint, being attached to the capsular Jigament, and having a small synovial bursa interposed; below 'tjie-jfetlock it :feceives on either side a strong slip from the suspensorjjjligament, and it becomes attached to the anterior part of the- first and second phalanges. , Insertion. — To the pyramidal process of the os pedis. •Relibiion. — Anteriorly and externally it is covered by the fascia ; 'posteriorly related with the extensor suffraginis, the radius; carpus, metacarpus, and phalanges ; internally with the extensor metacarpi magnus. Action. — To extend the phalanges on each other, and assist in extending the carpus. If the tendon which joins that of the extensor suffraginis be carefully traced upwards, it will be found to be continuous with a long thin muscle separable from the extensor pedis, and placed along its postero-extemal aspect; it arises from the external lateral ligament of the elbow joint and the corresponding tuber- osity pf the radius, and has received the name of Phillips' muscle (Fig. 80. h). Somewhat anteriorly to the above a still smaller muscle may be found arising from the external arciform ligament, and terminating in a small tendon, which joins that of the extensor pedis a short distance above the carpus ; this has been called Thiernesse's muscle (Fig. 80. g). These two muscles are not generally described, but are regarded as forming a part of the extensor pedis. EXTENSOR SUFFRAGINIS. (Radio-prephalangeus.) (Fig. 78. i) Situated on the external part of the fore-arm, between the extensor pedis and the flexor metacarpi externus, this muscle is semipenniform, consisting of a flattened fleshy belly, enveloped ia POSTERIOR ANTIBRACHtAL GROUP 225 a strong aponeurotic sheath, and having its edge turned outwards. The belly ends in a round tendon", which passes through a theca in the vertical groove on the external side of the distal end of the radius, and down the external aspect of the carpus, reaching the anterior surface of the large metacarpal bone. Origin. — From the external part of the head of the radius, the external lateral ligament of the elbow joint, the shaft of the radius, and the lateral aspect of the ulna. iTisertion. — To the head of the os suffraginis, related also with the capsular ligament of the fetlock joint. Below the knee it is joined by two tendinous slips, one from the tendon of the extensor pedis, the other, a species of check ligament, from the trapezium. Relation. — Anteriorly with the extensor pedis ; posteriorly with the flexor pedis perforatus, the perforans, and flexor meta- carpi externus ; externally with the fascia. Action. — To extend the digit, and assist the extensor pedis. Posterior Antibrachial Group. FLEXORS. This, the flexor group, consists of seven muscles, three flexors of the carpus, and four fliexors of the digit : — Flexor pedis perforatus. Flexor pedis perforans Flexor metacarpi externus Flexor metacarpi medius. Flexor metacarpi intern us Ulnaris accessorius. Radialis accessorius. FLEXOR METACARPI EXTERNUS. (Epitrochleo-carpeus.) (Fig. 78. i.) Situated on the postero-externai aspect of the fore-arm, this muscle is elongated and flattened, the fleshy belly being inter- sected by strong, tendon. Origin. — By a very short strong tendon from the summit of the epitrochlea of the humerus, terminating in two tendons ; the anterior, longer, and more delicate, passes through a synovial theca, in a groove on the external surface of the trapezium. Inaertion. — The anterior tendon goes to the head of the outer splint bone ; the posterior, short and flat, becomes inserted to the Q 226 MYOLOGY. superior part of the trapezium,, blending with the flexor meta- carpi medius. Relation. — Externally with the fascia ; internally with the flexor pedis muscles and the flexor medius ; anteriorly with the extensor suffraginis. Action. — To flex the carpus. FLEXOR METACARPI MEDIUS. (Flexor M. Ohliquics — Epicondylo-carpeus.) (Fig. 79. /.) Similar in structure to the preceding muscle, it is situated on the postero-internal part of the radius, extending downwards and outwards. It is long, flat, and bifid above ; one head is smaU, the other large and fleshy. Origin. — The large head arises from the epicondyle, the small head from the posterior surface of the olecranon ; they unite at a short distance down the radius. Insertion. — 3y one tendon to the supero-posterior and inter- nal part of the trapezium, blending with the extemus. Relation. — Externally with the fascia; internally with the flexors bf the foot ; anteriorly vdih. the flexor intemus ; posteriorly with the flexor externus. Action. — To assist the preceding muscle in flexing the carpus. FLEXOR METACARPI INTERNUS. {Epicondylo-metacarpeus.) (Fig. 79. e.) Situated on the internal aspect of the fore-arm, it resembles the two preceding muscles in its structure, being long and flattened, with a fleshy belly, but having a long tendon of insertion. Origin. — By tendinous fibres from the base of the epicondyle just by the medius. Insertion. — To the head of the inner splint bone, the long round tendon passing through a synovial theca on the inner side of the carpus. Relation. — Externally with the fascia ; internally with the chief radial vessels and nerves, and the flexors of the foot ; anteriorly with the radius ; posteriorly with the medius. Action. — Like the preceding, to flex the carpus. POSTERIOR AXTIBRACHIAL GROUP. 227 c- FLEXOR PEDIS PERFORATUS. {Flexor Subliniis — Bpicondylo-pTialangeus. ) (Fig. 81. b.) Situated in the posterior region of the Ibre-arm, under the flexors of the carpus, this muscle is -long, thin, and prismatic, its belly being fleshy, with tendinous intersections, and extending almost to the carpus, where it is succeeded by a long tendon, which passes through a synovial sheath behind the joint, closed in by the posterior annular ligament. Above the carpus, the tendon is joined by a broad band of fibrous tissue, called the superior carpal or superior *' check " ligament, which spriogs from the infero-posterior surface of the radius, being also attached to the antibrachial fascia, and usually to the perforans muscle ; below the knee, the tendon assists in the formation of a synovial sheath for the tendon of the flexor perforans. At the fetlock it ex- pands and forms a ring or sheath, through which passes the perforans tendon, hence the names perforans and perforatus; below the pastern joint the tendon divides into two. Origin. — From the summit of the epi- condyle, by a tendon common to it and the perforans. Insertion. — To the projecting lateral parts of the os coronse. Relation. — Posteriorly with the flexor metacarpi extemus and medius ; anteri- orly with the perforans. Two important synovial sheaths or canals are related with this and the perforans tendon, the carpal and the metacarpb-phalangeal. The first, to which is attached the antibrachial fascia, is formed by the posterior Fio. 81. Internal view of the deep muscles of the anterior limb, a, Caput par- vum of triceps extensor brachii ; i, Flexor pedis perforatus ; h', Ita tendon ; h" b'", Slips to the phal- anges ; c c, Flexor pedis perforans ; c', Eadialis accessorius ; c", Ulnaris accessorius ; c'", Inferior check liga- ment ; d, Perforans tendon leaving the sheath of oerforatus tendon. 228 MYOLOGY. carpal and annular ligaments ; the second is formed by the car- tilaginous pad clothing the great sesamoid bones, the posterior face of their' inferior, and their annular ligaments, the latter being very .adherent to the perforatus tiendon, which it covers, and is continued both upwards and downwards, being attached to the phalanges by three fibrous bands on each side. The synovial membranes lining these sheaths, and reflected on the tendons, are very large, and project considerably above and below, each forming an upper and a lower cul-de-sac ; the lower one of the sesamoidean sheath reaching that formed by the mem- brane of the coffin joint, and also the superior one of the navicular sheath. Action. — To flex the pastern and fetlock joints, and assist in flexing the carpus. The superior check ligament enables it to act as an unyielding brace to the joints below during rest. FLEXOR PEDIS PERFORANS. {Flexor-Profundiis — Epicondylo-phalangeus. ) (¥iG. 81. c c.) This muscle is situated between the preceding one and the radius ; it is long, tendinous at its origin, with a round fleshy belly, much larger than that of the perforatus, and ending, above the carpus, in a funicular tendon. This tendon passes through the posterior carpal sheath, then through a sheath partly formed by the perforatus tendon below; it is joined by the tendons of the accessory flexors, and half-way down the metacarpus by the inferior carpal or check ligament, a strong fibrous band whicli is continuous 'with the posterior carpal ligament. The tendon then passes through the sesamoidean sheath anteriorly to the per- foratus tendon, and then between the terminal slips of the latter, over the supero-posterior part of the os coronge, when it expands, the expanded part being termed the plantar aponeurosis; it passes thence over the navicular bone, and its synovial capsule, to the solar aspect of the pedal bone. Origin. — In common with the perforatus from the epicondyle. InseHion. — To the semilunar ridge on the solar aspect of the OS pedis. Relation, — Posteriorly with the perforatus; anteriorly with the radialis accessorius and the radius. Connected with the terminal portion of the tendon, we may remark that the synovial r POSTERIOR ANTIBRACHIAL GROUP. 2^9 capsule of the navicular bone, termed the navicular sheath, forms two cul-de-f^acs, one stretching upwards almost to the inferior cul-de-sac of the sesamoid sheath, the other being situated under the inferior navicular ligament. A broad strengthening sheath of fibrous tissue covers the plantar aponeurosis and blends with it inferiorly, being attached above by two bands to the sides of the first phalanx. Action,— It flexes the joints below the carpus, and assists in flexing the latter. Fig. 82. Longitudinal section through the digit of a Horse. 1, The skin ; 2, Extensor pedis tendon ; 3, Synovial cap- sule of pastern joint ; 4, Metacarpus ; 5, Perforatus tendon ; 6 (omitted in cut), Perforans tendon ; 7, Synovial sheath ; 8, Projecting synovial cul-de-sac; 9, Inner aspect of sesamoid bone ; 10, Tlie fetlock ; 11, The Y-ligament ; 12, The v-ligameut ; 13, Proximal phalanx ; 14, Terminal portion of extensor tendon ; 15, Mesian phalanx ; 16, Third sesamoid or navicular bone ; 17, The sensitive frog ; 18, Distal phalanx ; 19, The hoof ; 20, Sensitive laminae. ULNARIS ACCESSORIUS. {Flexor Accessorius Suhlimis.) (Fig. 81. c".) Situated on the posterior part of the fore-arm, between the external and middle flexors of the metacarpus, it is triangular. 230 MYOLOGY. passing obliquely downwards and inwards ; it has a short, thick, fleshy belly, ending in a long, slender, flat tendon. OHgin. — From the posterior border and summit of the ole^ cranon. Insertion. — It blends with, and helps to form the tendon of the perforans near the carpus. Relation. — Superiorly with the fascia ; internally with the flexor metacarpi intemus ; externally with the medius. Action. — It assists the flexor perforans. RADIALIS ACCESSORIUS. (Flexor Accessor iua Profundus.) (Fig. 81. c'.) A small muscle situated on the postero- inferior part of the radius. Somewhat radiating, flat, and elongated, passing down- wards and slightly inwards, it ends above the knee in a slender tendon. OHgin.— Yiom. the posterior part of the shaft of the radius. Insertion. — It joins the tendon of the perforans. Relation. — Anteriorly- with the radius ; posteriorly with the perforatus and perforans. Action. — To assist the flexor perforans. Metacarpal Region. Below the carpus we find only two pairs of exceedingly small muscles : — Interossei metacarpei. Lumbricales. INTEROSSEI METACARPEI. {Interossei Palmares, Human.) Situated on the inside of the small metacarpal bones, these muscles each consist of a thin, fleshy belly, and a long, slender tendon, which sometimes joins the band extending from the suspensory ligament to the extensor tendon, or may join the tendon itself. These muscles belong to the rudimentary small metacarpal bones, and hence are themselves rudimentary ; the interosseus of the middle bone is usually considered as being represented by the suspensory ligament GLUTEAL KEGION. 231 LUMBRICALES. (Lvmihrici.) These small muscles originate on either side of the perforans, and the sesamoidean ring of the perforatus tendons ; they termi- nate in their tendons, which become lost in the coverings of the fetlock joint. Muscles of the Pelyic Limb. The movements caused by these muscles resemble those of the anterior limb. It should, however, be borne in mind that the stifle joint allows more extensive and varied motion than the elbow, while the motion in the tarsus is less free than that in the carpus, the former being in effect purely ginglymoid ; also that the posterior is capable of more extensive abduction at the hip joint than is the anterior limb at the shoulder, although the former is more bound by ligaments. The muscles of the limb in question may be divided into those associated with the follow- ing regions : — Gluteal The hip. Femoral The thigh. Tibial The leg. Metatarsal . . . . . The foot. Gluteal Kegion. The muscles of this region, called also the hip or the croup, arise externally or internally from the pelvis, the sacrum, and the sacro-sciatic ligament, and are all attached to the femur near its proximal end, being related with the hip joint. Collectively the muscles from which this region is- named form in the horse an enormous fleshy mass, apparent in the living animal as a rounded prominence, behind and above the anterior iliac spine, to which, and to the sacral spine, the strong gluteal fascia which invests them is firmly attached ; a thin layer of fat is generally found covering the region superiorly. In this region we have one group containing nine muscles, named as follows : — 232 MYOLOGY. Gluteus externus. Gluteus maxim us. Gluteus internus. Rectus parvus. Obturator externus. Obturator internus. Pyriformis. Gemellus anticus. Gemellus posticus. GLUTEUS EXTERNUS. {Ilio-trochanterius Medius.) (Pl. IL 56 ; Fig. 84. 6.) This is a V-shaped muscle situated on the external part of the croup, its fibres converging downwards. It consists of a muscular and an aponeurotic portion ; the former is double, the parts con- verging and ending in a flat tendon ; the aponeurotic joins the fleshy portion posteriorly, and is hidden under the triceps abduc- tor femoris. Origin. — The anterior portion arises from the anterior spine of the ilium, the posterior from the second and third sacral spines ; also from the gluteal fascia. Insertion. — To the trochanter minor ; the aponeurotic portion JTcaches the tuberosity of the ischium and the sacro-sciatic liga- ment. lielation. — Externally with the gluteal fascia ; anteriorly with the fascia lata ; posteriorly with the triceps abductor ; internally with the maximus. Action. — It abducts the thigh. GLUTEUS MAXIMUS. {Ilio-trochanterius Magnus.) (PL. IIL 30 ; Fig. 84. c.) This is a very large muscle occupying the iliac dorsum, and stretching forwards over the lumbar region ; it is fleshy and thick in its centre, terminating in two tendons. Origin. — From the iliac shaft, crest, dorsum, and spines, anterior and posterior, the side of the sacrum, the sacral and part of the sacro-sciatic ligaments, and the tendinous envelope of the longissimus dorsi as far forward as the last rib. Insertion. — By two tendons, one to the summit of the tro- chanter major, the other anteriorly to the crest below the con- r GLUTEAL REGIONS. 233 Texity, over which it passes, with an interposed synovial bursa ; a small fleshy insertion is often found posteriorly. Relation. — Externally with the extemus and the fascia; internally with the internus, sacro-sciatio ligament, and the ilium ; anteriorly with the fascia lata and the longissimus dorsi; posteriorly with the triceps abductor femoris. The inner and anterior portion which terminates in the anterior tendon has been rather unnecessarily described as a separate muscle ; this possible separation is shown in Fig. 83. a. Action. — To extend the femur on the pelvis, and when the posterior limbs are fixed, to assist in rearing. Fig. 83. Deep-seated muscles of the gluteal region, a. Deep anterior portion of gluteus maximus ; b. Gluteus internus ; c. Common tendon of obturator internus and pyrifonnis ; d d, Gemellus anticus and posticus ; e, Ischio- femoralis. GLUTEUS INTERNUS. (lUo-trochanterius Parvu&.) (Fig. 83. 6.) Situated underneath the maximus and above the hip joint, this is a short and fan-shaped muscle, the fibres converging outwards. OHgin.— From the shaft of the ilium, the ischiatic spme, and the capsular ligament of the hip joint. .234 MYOLOGY. iTisertion. — By a tendon to a roughened space inside the con- vexity of the trochanter major of the femur. Relation. — Externally with the maximus ; internally with the femur and hip joint. Action. — To abduct the thigh, and rotate it inwards. RECTUS PARVUS. (Ilio-femoralis Parvus — Grele.) Situated in front of the hip joint, this is a very small, pale^ and fusiform muscle, with a fleshy belly, and tendinous ex- tremities. Origin. — From the brim of the acetabulum, towards the out- side ; or it may be by two origins, an outer one, and one from between the tendons of origin of the rectus fern oris, and the capsular ligament of the hip joint. Insertion. — To the anterior and upper part of the femur, just below the hip joint, by aponeurotic slips. Relation. — Externally and internally with the rectus femoris ; posteriorly with the capsular ligament. Action.-^To tense the capsular ligament of the hip joint during flexion of the femur. OBTURATOR EXTERNUS. (Suhp uhio-trochan terius- Externus. ) Placed on the inferior surface of the os. innominatum, below the obturator foramen, which it covers, this muscle is flat, thick, and triangular, its belly consisting of delicate fasciculi, which pass outwards. Origin. — From the surface of the pubis and ischium, attached to the obturator ligament. Insertion. — In the trochanteric fossa. Relation. — Inferiorly with the pectineus and adductors ; supe- riorly with the capsular ligament of the hip joint and obturator ligament ; posteriorly with the tricepS abductor and' iscli^o- femoralis. Action. — To rotate the femur outwards, and adduct it. GLUTEAL REGION. ^35 OBTURATOR INTERNUS. {Suhpuhio-trocJianteriivs Internus.) (Fio. 83. c.) Situated on the floor of the pelvic cavity, covering the obturator foramen, and corresponding to the extemus; it is fan-shaped, with a delicate, fleshy belly, terminating in a flat tendon. Origin. — From the border of the obturator foramen and its ligament ; it passes through the lesser sciatic notch, behind the acetabulum, where its tendon joins that of the pyriformis. Insertion. — In the trochanteric fossa. Relation. — Superiorly with the pelvic fascia ; inferiorly with the obturator ligament, ischium, and pubis ; outside the pelvis, with the sciatic nerve above, and the externus below. Action. — To rotate the femur outwards, and perhaps to abduct it slightly. PYRIFORMIS. (Sacro-trochanterius.) (Fig. 83. c.) Situated laterally in the pelvic cavity, this is a flat, elongated, semipenniform muscle, with a small tendon of insertion. Origin. — From the transverse processes of the sacral vertebrae, and the inner surface of the iliac shaft ; lying along the inner side of the sacro- sciatic ligament, it passes through the lesser sciatic notch to join the tendon of the obturator internus. Insertion. — In the trochanteric fossa. Relation. — With the pelvic • fascia internally ; externally with the OS innominatum; outside the pelvis it is crossed by the sciatic nerves ; the obturator vessels and nerves pass along its lower border. Action. — To rotate the femur outwards. GEMELLUS ANTICUS AND POSTICUS. (Gemini — Ischio-trochanterii.) (Fig. 83. d d.) A pair of very delicate muscles, variable in form, and usually situated one above and before, the other below and behind the obturator internus tendon, with fleshy bellies and tendinous insertions. 236 MYOLOGY. Origin. — From the shaft of the ischium ou either side of the conjoined tendon of the pyriformis and obturator internus, their fibres blending with it and passing outwards. There may be another flat and somewhat large muscle situated between the above and the obturator externus, originating also from the ischial ramus. Insertion. — In the trochanteric fossa. Relation. — Posteriorly with the sciatic nerves ; anteriorly with the capsular ligament of the hip joint, and the obturator externus. Action. — Like the preceding, to rotate the femur outwards. Femoral Region. The muscles of this regiou cover more or less the shaft of the femur, some of them reaching as far as, or below the stifle joint ; the majority of them have a pelvic origin. These muscles may be conveniently divided into the four following groups : — Internal. External. Anterior. Posterior. Internal Femoral Group, adductors. These form the large fleshy mass situated between the inferior pelvic surface and the stifle joint ; they are six in number : — Sartorius. Gracilis. Pectineus. Adductor brevis. "j Adductor longus. r Triceps adductor femoris. Adductor maguus J SARTORIUS. {Sublu7nbo-tibialis.) (Fig. 77. I.) Situated in the abdominal cavity at the pelvic inlet, and along the inner aspect of the thigh, it is long, thin, fleshy, and pyra- midal, extending obliquely downwards, forwards, and outwards. INTERN AX FEMORAL GROUP. 237 Origin. — From the brim of the pelvis, and from the iliac fascia, near the tendon of the psoas parvus. Insertion. — lu common with the gracilis, by fascia to the internal straight ligament of the patella Relation. — Anteriorly with the crural arch and fascia ; inter- nally with the psoas magnus and. iliacus; posteriorly with the o^racQis, pectineus, and vastus internus. Its posterior border is related with the femoral artery, which, with the vein and internal saphenic nerve, passes through a space included between this muscle, the iliacus, and the pectineus, termed the femoral space. Action, — To adduct and flex the femur. GRACILIS. (S^cbpuhio-tib talis.) (Fio. 77. c.) Situated on the internal pai-t of the thigh, this is a broad, thin, quadrilateral muscle, directed downwards and outwards. It has a flat fleshy belly, terminating in a broad aponeurosis. O'ngin. — From the inferior surface of the ischio-pubic sym- physis, where it meets its fellow. Insertion. — With the sartorius, to the internal straight liga- ment of the patella, and also to the supero-internal part of the tibia ; posteriorly its fascia blends with that of the biceps rotator tibialis, the two forming the fascia of the region. Relation. — Anteriorly with the sartorius; internally with the adductor muscles of the thigh ; posteriorly with the biceps rotator tibialis ; externally with the crural aponeurosis and saphenic vein. Action, — To adduct the limb, and tense, the fascia of the leg. PECTINEUS. (Super-puhio-femoralis. ) (Fig. 76./.) Situated on the inner side of the preceding, this muscle is conical, the fibres extending outwards and backwards. It is tendinous, with a fleshy belly, bifid superiorly for the passage of the pubio-femoral ligament. 238 • MYOLOGY. Origin. — From the brim and inferior surface of the pubis ; it ; is also attached to the pubio-femoral ligament, which passes through its tendons of origin. Insertion. — To a roughened surface' on the inner side of th^? femur, below the internal trochanter, and near the nutrient fora- men. Relation. — ^Anteriorly with the sartorius, part of the ps magnus, iliacus, and vastus intemus ; posteriorly with the adductor] brevis and gracilis ; superiorly with the obturator extemus. The femoral vessels cross it. Action^ — To adduct and flex the thigh, and to rotate it in- wards. TRICEPS ADDUCTOR FEMORIS. This name has been applied to a group of three muscles, situ- ated on the inner surface of the thigh, and covered by the gracilis, which act the part of adductors. They have also been described as consisting of a biceps and a single muscle ; we describe them as three distinct muscles, and name them, from before backwards, the hrevis, the longus, and the magnus. ADDUCTOR BREVIS. (Suhpubio-jemoralia.) (Fig. 76. g.) Situated on the dnher aspect of the thigh, behind the pec- tineus, this muscle is pyramidal, with the base upwards, its fibres converging downwards and outwards. Fleshy, with tendinous insertions inferiorly, it is often somewhat blended with the longus. Origin. — Superiorly from the inferior surface of the pubis. iTisertion. — To a square, roughened surface on the posterior part of the shaft of the femur, about the middle, together with a portion of the long adductor. Relation. — Anteriorly with the pectineus ; posteriorly with the longus ; externally with the gracilis ; internally with the obturator externus. Action. — To flex, adduct, and rotate the femur outwards. r- EXTERNAL FEMORAL REGION. 239 ADDUCTOR LONGUS. (Subpubio-femoralis Posterior.) (Fig. 76. A.) Situated on the inner aspect of the thigh, covered by the gracilis, this muscle is long, flat, and prismatic, extending outwards and downwards. Origin. — From the inferior surface of the posterior part of the pubis. Insertion. — By two divisions, one attached by the insertion of the brevis, the other, with the magnus, above the internal condyle of the femur at the attachment of the lateral ligament. Relation. — Anteriorly with the brevis and obturator externus ; posterioisly with the magnus ; externally with the gracilis ; inter- nally with the ischio-femoralis and sciatic nerves. The femoral vessels pass between its two divisions. Action. — To adduct the femur, and rotate it outwards. ADDUCTOR MAGNUS. (Semimembranosus — Ischio-tibialis. ) (Fig. 76. i.) Placed behind the preceding, on the postero-intemal part of the thigh, this muscle is thin at its extremities and posterior border, thick and fleshy elsewhere, terminating in a short tendon. Origin. — Chiefly from the inferior surface and tuberosity of the ischium by tendinous fibres, and by a slender band from the coccygeal fascia. Insertion. — To a small roughened surface on the inner side of the internal condyle of the femur Relation. — Anteriorly with the longus, to which it is very adherent ; externally wi uii the gracilis ; posteriorly with the biceps rotator tibialis ; internally with the triceps abductor. Action. — To adduct and extend the thigh. If the limb be fixed, it assists in raising the anterior parts of the trurk in "rearing." External Femoral Region, abductors. This region contains only one muscle, which is situated laterally with respect to the haunch, but more posteriorly with regard to the femur. 240 MYOLOGY. TRICEPS ABDUCTOR FEMORIS. (Ischio-tibialis Extermcs.) (Pl. II. 55; Fig. 8L d d d.) Situated on the external part of the haunch, behind and below ifie great gluteal muscles, this is a very large and fleshy muscle. Fxa. 84. Muscles of the thigh and haunch— left side ; the external fascia being removed, a, Tensor fasciae latse ; b, Gluteus extemus ; c, Gluteus maximus ', d d d^ TricAps abductor femorls ; e e. Biceps rotator tibialis ; /, Part of adductor magnus. made up of two prismatic portions, with tv/o origins and three insertions. The anterior portion is much the longer. The fibres pas3 downwards in a somewhat curved manner, the larger con- vexity being to the rear. r ANTERIOR FEMORAL REGION. 241 Origin. — The aaiterior portion arises from the spine of the sacrum, the coccygeal fascia, and the sacro-sciatic ligament ; also from the ischial tuberosity ; the posterior portion is attached to the crest of the ischial tuberosity. Insertion. — Anteriorly to the external side of the patella and its external ligament, a synovial bursa lying between it and the bone ; posteriorly by a strong aponeurosis to the tibial fascia, which it helps to form, and by it to the tibial crest. It sends a strong slip which is attached near the insertion of the ischio- f em oralis. Relation. — Externally and superiorly with the gluteal fascia, to which it adheres above ; internally with the fascia of the gluteus externus, which separates it from the maximus and the femoral trochanter ; with the sciatic nerves, the adductor muscles, and biceps rotator, excepting at the upper portion, where it is related posteriorly with the latter muscle. Action. — The anterior portion extends the femur and abducts the limb ; the posterior portion flexes the stifle joint and tenses tlie tibial fascia. It assists the abductor magnus when the limb is fixed. (Vide Abductor Magnus.) Anterior Femoral Region. The muscles of this region lie in the space between the iliac spine above, the patella below, and the femur and hip joint posteriorly. They are as follows : — Tensor fasciae latse. Rectus femoris. Yastus externus. v m • i • !• ■^T -^ • ^ r Triceps or quadriceps crura lis. V astus mtemus. ^ r -i r Crureus. ( tensor fascia LATiE. {Tensor Vagince Femoris — Ilio-aponeuroticus.) (Pl. n. 54 ; Fig. 84. a.) Situated in front of the gluteus externus, and on the outside of the vastus externus, this muscle is flat and triangular, radiat- ing downwards and backwards. Attachments. — The fleshy portion arises from the anterior iliac r 242 MYOLOGY. spine, and from it springs the aponeurotic expansion termed the fascia lata. (See Fasciae of the Posterior Limb, p. 255.) Relation. — Internally with the iliacua, rectus femoris, and vastus .extemus ; externally with the skin ; posteriorly with the gluteus maximus and externus; anteriorly with the precrural lymphatic glands. Action. — It assists in flexing the femur, raising the limb ; and it tenses the fascia lata. CRURAL MUSCLES. The remaining muscles of this region, being all of them inserted to the patella, may be described as a single muscle, the triceps or quadriceps cruralis ; or the rectus may be regarded as a single muscle, and the other three described together as the triceps cruralis; or, again, they may be considered as separate muscles. The above names being borne in mind, the last is perhaps the simplest method, and is the one adopted here. These muscles are considerably blended, and cannot well be perfectly separated without cutting muscular fibre. RECTUS FEMORIS. {Ilio-rotvlms.) (PL. IIL34J Fig. 76. Z.) Situated on the anterior part of the thigh, between the two vasci, it is thick, elongated, and fusiform, consisting of two short, flat tendons of origin, and a fleshy intersected belly, terminating in a conical aponeurotic envelope. It is directed downwards and forwards. Origin. — ^From two depressions, one on each side of the iliac shaft, just before the acetabulum. Insertion. — To the upper part of the patella. Relation. — It lies between the vasti, and above the crureus, and superiorly between the iliacus and the tensor fascias latae, with which it is related anteriorly. A pad of fat occupies the space between its tendons of origin and the capsular ligament of the hip joint. Action. — To flex the femur, and extend the leg. r ANTERIOR FEMORAL REGION. 243 VASTUS EXTERNUS. (Femoro-Totuleus Extemus.) (PL. III. 35.) Situated on the outer side of the rectus femoris, this muscle 't broad, thick, flattened laterally, and semi-ovoid, extending do\TTi wards and forwards; it is fleshy, with strong tendinous intersections. Origin. — From the external and part of the anterior aspects of the shaft of the femur, and from the base of the trochanter major downwards. Insertion. — To the upper and outer part of the patella; or it may join the rectus femoris. Relation. — Externally with the tensor fascise latas, and gluteus extemus ; internally with the rectus, crureus, and vastus intemus, with which inferiorly it is intimately blended ; posteriorly with the triceps abductor femoris and the femur. Action. — To extend the leg. VASTUS INTERNUS. (Femoro-rotideus Intemus.) (Fig. 76. h) Corresponding to the extemus, this muscle is situated on the inner side of the rectus femoris, the two forming a channel in which are lodged the rectus and crureus. It is semi-ovoid, and fleshy, becoming tendinous at its insertion. Origin. — From the neck of the femur, its an tero- internal surface, and the trochanter internus. Insertion. — To the upper and inner side of the patella. Relation. — Externally with the rectus; internally with the sartorius, pectineus, psoas magnus, iliacus, adductor magnus, and crural fascia. Action. — To extend the leg. CRUREUS. (Femoro-rotuleus Medius.) Situated below the rectus, and between the two vasti, this muscle is small, cylindrical, fleshy, and tendinous at its extremi- ties ; it is separated from the vasti with difiSculty. 244 MYOLOGY. Origin. — From about the lower third of the anterior surface of the femur. Insertion. — To the upper surface of the patella, and the capsular ligament of the joint. Relation. — Anteriorly with the rectus ; posteriorly with the femur ; laterally with the vasti. Action. — To assist the vasti, and tense the capsular ligament. Posterior Femoral Region. This region contains two muscles, a large superficial one, and a small one deeply situated; they are as follows :— Biceps rotator tibialis. Ischio-fem oralis. BICEPS ROTATOR TIBIALIS. {Semitendinosus — Ischio-tihialis Posticus. ) (PL. XL 61 ; Fig. 84. e. e.) Situated behind the triceps abductor, and curved like it, with the CQUvexity behind, this muscle is long, cylindrical, and bifid above, consisting of pale, fleshy fibres, divided by a strong aponeurosis. Origin. — By one head, from the spine of the sacrum, and the sacro-sciatic ligament, in common with the triceps abductor; the other, which is considerably shorter, comes from the ischial tuberosity. Insertion. — To the supero-internal part and anterior crest of the tibia, its aponeurosis blending with the tibial fascia and the periosteum. Relation. — Superiorly and posteriorly it is covered by the gluteal fascia, and its sacral portion partly covers the triceps abductor, being related with it and the sciatic nerves anteriorly ; externally with the abductor magnus. Action. — To extend the femur, flex and rotate the leg out- wards, and tense the tibial fascia. ISCHIO-FEMORALIS. (Quadraiua Femoris.) (Fig. 83. ortioa8 of the annular ligament. A ttachments, — r The tendinou s portion arises from the depression between the trochlea and condyle of the femur, and lies in the superior tibial groove, clothed above by a reflection of one of the synovial membranes of the stifle joint ; below this point it gives attachment to fibres of the fleshy portion and of the extensor pedis ; in front of the astragalus it forms a ring, through which the tendon of the fleshy por- tion passes ; at the tarsus it bifur- cates, 3, very strong slip being at- tached to the large metatarsal bone, and a small one, which inclines Out- wards, to the cuboid bone. The fleshy portion arises from the head of the tibia, and its groove, also from the tendinous part, receiv- ing slips from the latter; its tendon of insertion, after passing through the above-named ring, bifurcates, and is inserted by a broad portion to the front of the great metatarsal bone, and by a smaller slip, which winds inwards, to the small cunei- form bone. Relation. — Anteriorly with the extensor pedis; posteriorly with the external aspect of the tibia, and the anterior tibial artery. Action. — It flexes the tarsal joint. The tendinous portion may be re- garded as a strong fibrous com- munication between the femur and the metatarsus, which, when the stifle joint is flexed, becomes tensed, and mechanically repeats the action upon the joint below. ANTERIOE TIBIAL . GROUP. 247- EXTENSOR PEDIS. {FemoTO-pi'ephalangeus. ) (Tig. 86. h.) Situated on the anterior surface of the tibia and bones below, this is a long^ fusiform muscle, extending downwards and back- wards. A little a.bove the tarsus, the belly terminates in a long, flat tendon, which, bound down by the three bands of the annular ligament, passes down the front of the tarsus and metatarsus, near the middle of which it receives the extensor brevis, and the tendon of the peroneus ; tha united tendon now passes down, and is arranged like that of the anterior limb. Origin. — From the fossa between the trochlea and external condyle of the femur, by the tendon of the flexor metatarsi, common to it. Insertion. — To the capsular ligament of the fetlock joint, the anterior surface of the two first phalanges, and the pyramidal process of the os pedis. Relation. — Anteriorly with the fascia ; internally with the flexor metatarsi ; posteriorly with the peroneus. Action. — To extend the entire digit, and flex the tarsal joint. PERONEUS. (Peroneo-preplialangeus.) (Fig. 85. c.) Situated on the external side of the leg, this is a long and somewhat penniform muscle, consisting of a prismatic, fleshy belly, which originates by a short, and terminates by a long tendon ; the latter passes through a theca on the external side of the tarsus, joining the tendon of the extensor pedis below the joint. Origin. — From the external lateral ligament of the stifle joint, and the entire length of the fibula. Insertion. — It joins the tendon of the extensor pedis. Relation. — Externally with the fascia; anteriorly with the extensor pedis ; posteriorly with the flexor pedis perforans. Action. — It assists the extensor pedis. 2^8 MYOLOGY. Posterior Tibial Group. For convenience of description, we subdivide the muscles of this group, but the subdivision is a somewhat artificial one, as some^ of the muscles have two actions, flexing one joint and extending another. Extensors, Gastrocnemius. Plantaris. Flexors, f Flexor pedis perforatus. Flexor pedis perforans. Flexor pedis accessorius. Popliteus. GASTROCNEMIUS. {Bifemero-cricaneus.) (PL. III. 38.) Situated at the back of the leg, this muscle is somewhat heart- shaped, ending in a flattened tendon ; the fleshy belly is divisible into two portions, and intersected superiorly by strong tendons. Origin. — By two heads ; one from a ridge extending upwards from the external condyle in front of the supracondyloid fossa ; the other from the posterior surface of the femur, just above the intercondyloid fossa, and from the internal condyle. Insertion, — To the posterior part of the summit of the calcaneum, a synovial bursa being interposed between it and the anterior part, over which it passes. Relation, — Anteriorly with the flexor perforatus, popliteus, popliteal vessels and nerves, and the vastus externus above ; posteriorly with the triceps abductor femoris ; internally with biceps rotator tibialis ; superficially with the tibial fascia ; inferiorly the tendon is covered by that of the flexor perforatus, the two forming the Tendo-Acliillis. Action. — To extend the tarsal joint. r POSTERIOR TIBIAL GROUP. 249 PLANTABIS. {Soleus — Peroneo-calcaneus.) (Pii. III.39.) Situated on the postero-external part of the leg, to the out- side of the gastrocnemius, this muscle is, in the horse, slender and rudimentary, with a small, delicate tendon of insertion. Origin. — From the external part of the he^d of th6 fibula. . /wser/zoT^.— Together with, the tendon of tlje gastrocnemius to ■ the point of the calcaneum. \ Belqtion. — Externally with the fascia ; intey-n^lly with the gastrocnemius.. . Action.— It assists very slightly ihe gastrocnemius. FI/EXOK PEDIS PEKFORATUSL* (Femoro-phalangeus.) ^ (Fig. 86 6) ' , Situated immediately underneath the gastrocnemius, this muscle is in shape funicular, consisting of a strong fibrous cord, with a slightly fleshy portion above, and arising from the supra- condyloid fossa ; the belly is succeeded by a strong tendon, united to fascia, which is fixed to the inner surface and ridge of the tibia and the summit of the calcaneum, being continuous with the tibial fascia, and enclosing the entire tendo-Achillis. The tendon, at first under that of the gastrocnemius, winds round its inner side, and then surmounts it ; on reaching the point of the calcaneum it forms a cap, giving slips of insertion to the sides of that bone ; a large synovial bursa exists here, which is one of the seats of the lesion termed capped hock. It now descends posteriorly, and is disposed as is the corresponding tendon in the anterior extremity, forming a synovial sheath and ring for the perforans tendon, and finally bifurcating to become attached to the sides of the os coronse. Relation. — Posteriorly with the gastrocnemius ; anteriorly with the tibia, the popliteus, perforans, and accessorius muscles. * This muscle was formerly described under the name of ' gastrocnemius intemus. The more appropiiate one now in use is adopted here. 250 MYOLOGY. Action. — To flex the fetlock and pastern joints, and assist ia extending the tarsus ; when the animal is. stationary, it serves mechanically, a» a fibrous band, to prevent flexion of the tarsal joint. FLEXOR PEDIS PEBFORANS. ( Tibio-phalangeus. ) (Fig. 86. c.) Situated on the posterior aspect of the leg, extending from the head of the tibia to the distal phalanx, this muscle is thick and prismatic, consist- ing of a fleshy, intersected belly and long tendon of insertion. The belly is partially bifid, the internal portion being the larger. The tendon com- mences a little above the hock, passes through the groove on the inner side of the calcaneum, first crossing the posterior capsular ligament of the tarsus, where it is bound down by fibrous tissue, in a synovial sheath, the usual seat of Thorov^h-pin, It then descends behind the metatarsal bone ; about half-way down, it is joined by the check ligament, which springs from the lower bones of the tarsus and head of the metatarsal bone, and is similar to, but considerably less than, that of the fore extremity. It is joined above by the tendon of the flexor accessorius, and is otherwise disposed exactly as the perforans tendon of the anterior extremity. Origin. — From the roughened pos- terior aspect, and head of the tibia, the fibula, and fibulo-tibial ligament. Insertion. — To the semilunar ridge on the solar surface of the os pedis. Via. 86. Posterior tibial group of muscles ©f the right limb— postero-internal "View. The gastrocnemius ia removed. a, Popliteus; 6, Flexor pedio per- foratus; &', Its tendon; 6", Expansion of its tendon forming the cap of the hock; c, Flexor pedis perforans; c', Its tendon ; d, Floxor accessorius, d'. Union of its tendon with that of the perforans. r POSTERIOR TIBIAL GROUP. ■ 251 Belation. — Posteriorly with the gastrocnemius and flexor perforatus ; anteriorly with the tibia ; internally with the flexor pedis accessorius ; exterually with the peroneus. Action.— To flex the phalanges, and assist in extending the tarsal joint. FLEXOR PEDIS ACCESSORIUS. (Flexor Obliquus — Peroneo-phalangeus.) (Fig. 86. d.) Tbis muscle is situated on the posterior part of the leg, between the popliteus and flexor pedis perforans. It is fleshy, with numerous fibrous intersections, and inferiorly a terminal tendon. Origin. — From the external tuberosity of the tibia, and some- times slightly from the fibula ; the tendon commences just above the tarsal joint, and passes through a theca on its internal aspect. Insertion. — It joins the tendon of the flexor perforans at about a third from its commencement. Rtlation, — Posteriorly with the gastrocnemius and flexor perforatus ; anteriorly with the perforans, the popliteus, and the posterior tibial artery. Action. — To assist the flexor pedis perforans. POPLITEUS. (Feinoro-tibialis Obliquus.) (Fig. 86. o.) Situated at the back of the tibia, just below the stifle joint, this muscle is triangular and fleshy, the fibres passing obliquely downwards and inwards. Origin. — By a tendon from a fossa outside the external con- dyle of the femur ; it is attached to the capsular ligament of the stifle joint. Insertion. — The triangular surface on the supero-posterior part of tlie tibia, and the upper portion of its internal border. Relation. — Posteriorly with the gastrocnemius and flexor perforatus ; anteriorly with the tibia, the capsular ligament, and the tibial vessels ; externally with the flexor pedis perforans and accessorius; internally with the biceps rotator, and tibial fascia. Action. — It flexes the leg, rotates it inwards, and tenses the capsular ligament of the stifle joint. 262 MYOLOGY. Metatarsal Region. In this region we have the lumbricales and interossei as in the anterior extremity, and also the extensor pedis brevis. EXTENSOR PEDIS BREVIS. {Extensor Pedis Accessorius.) (Fig. 85. d.) Situated in front of, and below the tarsal joint, it is small and triangular in form, filling up the space between the converging tendons of the extensor pedis and peroneus. Origin. — From the infero-anterior part of the astragalus ; it is also attached to the cuneiform bones. Insertion. — It joins the tendons of the extensor pedis and peroneus. Relation. — Underneath this muscle passes the anterior tibial artery, giving off the perforafeg pedal branch. Action. — It assists slightly the extensors of the foot. Arrangement of the Fascia. We have already seen that the muscular system is invested by an areolo-fibrous covering, which has been named the superficial fascia. This covering varies very much in density in different regions, and in some becomes blended with the srponeurosis of the panniculus ; and generally where the muscles are braced by the fleshy portion of the latter, the investing f&rrcia is more or less rudimentary, as in the head and neck ; it is with difficulty demonstrable as a separate structure in the latter. The tunica abdominalis has been considered as an elastic development of the investing abdominal fascia. DEEP FASCIA. The following may convey a general idea of the arrangement of the deep or aponeurotic fasciae. Each muscle is more or less completely covered by a fold of fascia, which forms a sheath round it and its tendon ; it then passes to and covers another r ARRANGEMENT OF THE FASCIA. 253 muscle, and so on until it finally gives off an expansion which covers the entire group or region, becoming firmly attached to the skeleton, and usually at its salient points. Hence we may regard an aponeurotic fascia as a compound sheath, which con- tains in its compartments muscles and their concomitant struc- tures, and aids the former in their action by passive support ; the support thus afforded is not always wholly passive, since, as we have seen, some fasciae are regulated as to their tension by special muscles, the fasciae of the limbs affording good examples of this arrangement. Some of the deep fasciae merit special attention, and we shall consider them in the order generally observed in dealing with other widely-diffused structures — ?'.6., as apertaining to the Head, the Trunk, and the Limbs. FASCLffi OF THE HEAD. In this region there is little that is noteworthy in the disposi- tion of the fascia. It is, however, much stronger in the posterior than in the anterior portion, the muscles of the former being, separated merely by folds which closely resemble ordinary con- nective tissue. The temporal fascia is the name given to a strong fold vvhich covers the temporal fossa, being attached to the parietal ridge and to the zygoma, and corresponding to the temporalis and attollentes muscles. FASCIA OF THE TRUNK. These are the cervical, dorso-lumbar, abdominal, and thoracic fascise. The deep fascia of the cervical region is better marked than the superficial, and it invests the muscles in the typical manner above described, becoming attached to the vertebrae. In the dorso-liombar region it is variable, being thin in some situations, but thick and strong in others ; that covering the postero- superior part of the longissimus dorsi is actually tendinous in structure, giving origin to part of the gluteus maximus. The dorso-lumbar fascia becomes continuous posteriorly with that of the gluteal region, and anteriorly- with that of the external scapular region. The deep abdominal fascia chiefly includes the following 264 MYOLOGY. portions : — The transverse^ the iliac, the pelvic, the inguinal, and the perineal. The transverse (fascia transversalis) is inter- posed between the transversalis abdominis and the peritoneum, and is in the horse a very thin structure ; in the human subject, and in some other animals, it is thickened posteriorly, and attached to the crural arch. The iliac fascia (fascia iliaca) covers the muscles of the sublumbar region, especially the psoas magnus and iliacus, which it enfolds and accompanies to their insertion. It is attached internally along the tendon of the psoas parvus muscle, by which it is tensed, externally to the anterior iliac spine ; anteriorly it becomes very rudimentary, although it may sometimes be traced as far as the arcuate ligament of the diaphragm. The sartorius and cremaster muscles arise partly from this fascia. The pelvic fascia (fascia pelvica) is a strong layer lining the pelvic cavity, and covered anteriorly by the peritoneum ; inferiorly, it splits into two folds, the external of which lines the sides and floor of the cavity, and is named the obturator fascia, since it covers the internal muscles of that name ; it also furnishes a sheath for the internal pudic vessels. The other fold, the recto- vesical fascia, is reflected inwards and posteriorly gives off bands, ene of which separates the bladder from the rectum, another investing the latter, while two others serve as ligaments of the bladder. The inguinal and perineal fasciae will be more appro- priately described in a future section of the work. The thoracic fascia stretches across the anterior opening of the thorMX, and is its anterior boundary, surrounding and bracing the vmious structures which pass through, and helping to keep them in their relative positions. FASCIA OF THE ANTERIOR LIMB. These correspond to the various regions of the limb. The external scapular fascia is very strong superiorly, and it covers the external scapular muscles, giving off folds which enclose them. It is attached to the cartilage and spine of the scapula, and is continuous with the dorso-lumbar fascia behind, the subscapular fascia round the edge of the antea-spinatus^ and below with tho brachial fascia. It is tensed by the pectoralis parvus and teres extemus muscles. The brachial fascia is comparatively thin ; it covers and invests the humeral and triceps extensor muscles^ r ABRANGEMENT OF THE FASCI-E. 255 mid is continued below by the antibrachial fascia, 'which is exceedingly thick and strong, firmly bracing the muscles of * the fore-arm ; it is attached to the inner side of the radius, to its distal end both externally and internally, and likewise to the olecranon. On the inner aspect of the limb it is separable into layers, the external of which is tensed by the pectoralis transversus, while the internal gives off folds which pass between the muscles and form sheaths for them, and is attached supe- riorly to the flexor brachii and scapulo-ulnaris muscles, which are its tensors. Inferiorly, this fascia becomes continuous witk the annular ligaments of the carpus, thus helping to form sheatha for the passage of the tendons. FASCIA OF THE POSTEBIOR LIMB. The gluteal fascia covers the region of the same name, and is thick, strong, and somewhat elastic, usually containing more or less fatty matter. It is continuous anteriorly with the fascia of the dorso-lumbar region, posteriorly and extenmlly with the crural fascia, and is firmly attached to the anterior iliac and the sacral spines. Its internal surface gives attachment to portions of the gluteus maximus and externus. The femoral or crural fascia surrounds the muscles of the thigh. The anterior and external portions are known as the fascia lata ; the internal portpn anteriorly is derived from the aponeurosis of the obliquus abdominis externus; passing backwards, it becomes rudimentary, and is replaced posteriorly by connective tissue. The fascia lata encloses the triceps cruralis, and exter- nally divides into two folds, internal and external ; the former passes between the vastus • externus and triceps abductor, and accompanies the tendon of the gluteus externus to its insertion at the trochanter minor ; the external fold covers the triceps abduc- tor muscle, becoming continuous above with the gluteal fascia. The fascia lata is attached inferiorly to the patella, and below is continuous with the aponeurotic insertion of the triceps abductor, and so with the tibial fascia ; it is tensed by its own muscle, the tensor fasciae latse. The tibial fascia, like the antibrachial, to which it corresponds, is very strong and thick, and covers the tibial group of muscles, sending in folds to form sheaths for them. It gives attachment to the triceps abductor, biceps, rotator, and gracilis muscles, which ^56 MYOLOGY. ^presumably act as its tensors. It is attached to the crest arid inner aspect of the tibia, and also to the calcaneum, and it blends unth the annular ligaments of the tarsal joint, assisting in form- ing sheaths for the tendons. This fascia is continued over the tarsus and metatarsus; becoming somewhat thinner inferiorly; "between the tendo-Achillis and the flexor muscles of the foot it i^^x^ery strong, giving powerful bands to the former, and, near the <;a;lidaneum, helping to form a sheath for the gastrocmius tendon, ^31:6^ and before the tendo-Achillis it divides into two folds, T^hich assist externally and internally in the formation of the tarsal sheath, for the perforans tendon ;' between these folds are the posterior vessels and nerves of the'region. TABLE OF MUSGULAR ATTACHMENTS. In the following Table we enumerate the principal bones of the liorse, tabulating the names of the most important muscles which are attached to each :- THE HEAD. Cranial Bones, occipital. Xevator humeri Splenius. CoiD plexus, major and minor. Jlectus capitis anticus, major, minor, and lateralis. Hectus capitis posticus, major and minor. Obliquus c^^itis anticus. jStylo-hyoideus. Stylo-maxillaris. Digastricus. PARIETAL. Temporalis. FRONTAL. liCvator labii superioris alaeque nasi. TEMPORAL, "irachelo-m astoide us. Levator humeri Temporalis. Mastoido-auricularis. SPHENOID. Rectus capitis anticus, major and minor. Pterygoideus, extemus and in- ternus. Facial Bones. superior maxilla Panniculus carnosus. Masseter. Buccinator. Nasal is longus. Dilatator naris lateralis. PREMAXILLA. Dilatator naris inferioris. Depressor labii superioris. r MUSCULAB ATTACHMENTS. 25T NASAL. Dilatator naris suDerioris. LACHRYMAL. Orbicularis palpebrarum. Lachrymalis. MALAR. Nasalis longus. PALATINE. Pterygoideus internus. INFERIOR MAXILLA. Masseter. Temporalis. Pterygoideus, externus and interixus. Sterno-maxillaris. Stylo-maxillaris. Buccinator. Levator labii inferioris. Depressor labii inferioris. Mylo-hyoideus. Genio-hyoideus. Digastricus. HYOID SERIES. Stemo-thyro-hyoideus. , Subscapulo-liyoideus. Myo-hyoideus. Genio-hyoideus. Hyoideus magnus. Hyoideus parvus. Hyoideus transversus. Stylo-hyoideus. Certain muscles of the tongue^, pharynx, larynx, and soft palate are not enumerated here. THiS TRUNK. Cervical Vertebs^. ATLAS. Levator humeri. Splenius. Trachelo-mastoideus. Obliquus capitis, antixus major. Longissimus dorsi (4th to 7th), DORSAL VERTEBRA. Splenius ) Complexus major f ^ ^ ^• Trachelo-mastoideus (first 2). Trapezius dorsalis (3rd to 11th).. Latissimus dorsi (last 15). Superficialis costarum (last 17). Rhomboideus brevis (2nd to 7th),.. Longissimus dorsi. 258 MYOLOGY. Semispinalis dorsi. Leva tores costarum. Longus colli. Psoas parvus (last 3). Psoas magnus (last 2). LUMBAR VERTEBRiE. Latissimus dorsi. Superficialis costarum (first 3), Longissimus dorsi. Semispinalis lumborum* Psoas magnus. Psoas parvus. Quadratus lumborum. Intertransversalis lumborum. Transversal is abdominis. Crura diaphragmatica. SACRUM. Longissimus dorsi. Semispinalis lumborum. Gluteus externus. Gluteus maximus. Triceps abductor femoris. Bicejts rotator tibialis. Pyriformis. All the coccygeal muscles. COCCYX. All the coccygeal muscles. The Compressor coccygis first 2 segments. RIBS AND COSTAL CARTILAGES. Scalenus (1st). Superficialis costarum (last 14). Longissimus dorsi (last 16). Transversalis costarum. Serratus magnus (first 8). Lateralis sterni (1st). Triangularis sterni (2nd to 8th), Intercostales. Levatores costarum. Obliquus abdominis externus (last 14). Transversalis abdominis (last 10). Obliquus abdominis \ internus. ^ (cartilages). Rectus abdominis. ) Diaphragm (last 12). Psoas magnus (last 2). Quadratus lumborum (last 3). SCAPULA. Trapezius. Levator humeri. Antea-spinatus. Postea-spi nat u s. Postea-spiuatus minor. Teres externus. Rhomboideus, longus and brevis. Serratus magnus. Subscapularis. STERNUM. Pannicnlus carnosus. S terno-maxill aris. Sterno-thyro-hyoideus. The four Pectorales. Lateralis sterni. Triangularis sterni. Rectus abdominis, to the Transversalis abdominis. Diaphragm. PECTORAL LIMB. Pectoralis parvus. Scapulo-ulnaris. Caput magnum. Scapulo-humeralis posticus. Teres internus. Coraco-humeralis. Flexor brachii. HUMERUS. Antea-spinatus. Postea-spinatu;e. MUSCULAR ATTACHMENTS. 259 Postca-spinatus minor. Subscapularis. Scapulo-humeralis posticus. Pechoralis, magnus and anticus. Piinniculus carnosus. Teras, externum and intern us. C oraco-humeralis. Humeralis obliquus. Caput medium and parvum. Anconeus. T^atissimus dorsi. Levator humeri. Extensor metacarpi magnus. Extensor pedis. Three Flexores metacarpi. Flexor, perforans and perforatus. RADIUS. Tlexor brachii. Humeralis obliquus. Extensor metacarpi, magnus and obliquus. Extensor pedis. Extensor suffraginis. Hadialis accessorius. UINA. Triceps extensor brachii. Scapulo-ulnaris. Anconeus. j Flexor metacarpi medius. ^ Ulnaris accessorius. Humeralis obliquus. Extensor suffraginis. TRAPEZIUM. Flexor metacarpi, extemus and medius. METACARPUS. LARGE BONE. Extensor metacarpi magnus. EXTERNAL BONE. Flexor metacarpi extemus. INTERNAL BONE. Extensor metacarpi obliquus. Flexor metacarpi intemus. DIGIT. Extensor pedis (three phalanges). Extensor suffraginis (1st phalanx). Flexor perforatus (2nd phalanx). Flexor perforans (3rd phalanx). PELVIC LIMB. OS INNOMINATUM. Xongissimus dorsi. ■Compressor coccygis. Four Abdominales. Three Glutei. Tensor fasciae lataB. Rectus fern oris. Rectus parvus. Obturator, extemus and intemus. Pyriformis. Two Gemelli. Iliacus. Psoas parvus. Quadratus lumborum. Oracilis. Sartorius. Pectineus. ' Triceps adductor femoris. Triceps abductor femoris. Biceps rotator tibialis. Isehio-femoralis. FEMUR. Psoas magnus. Iliacus. Three Glutei. Obturator, extemus and intemus, Pyriformis. Two Gemelli. Tensor fascise latse. Vastus, extemus and intemus. 260 COMPAEATIVE MYOLOGY. Rectus parvus. Crureus. Pectin eus. Triceps adductor femoris. Triceps abductor femoris* • Ischio-femoralis. Gastrocnemius. Flexor perforatus. Extensor pedis. Flexor metatarsi. Popliteus. TIBIA. Sartorius. Gracilis. Triceps abductor femoris. Biceps rotator tibialis. Flexor metatarsi. Plantaris. Popliteus. Flexor perforans. Flexor accessorius. FIBULA. Peroneus. Flexor perforans. PATELLA. Tensor fasciae latse. Quadriceps cruralis. Triceps abductor femoris. TARSUS. CALCANEUM, Gastrocnemius. CUBOID AND SMALL CUNEIFORM. Flexor metatarsi. METATARSUS. LARGE BONE. Flexor metatarsi. DIGIT. Extensor pedis (three phalanges). Flexor perforatus (2nd phalanx). Flexor perforans (3rd phalanx). COMPARATIVE MYOLOGY. An extensive section devoted to this subject -would be somewhat out of place in an ordinary class-book;' therefore for fuller descriptions and details the student must have recourse to exhaustive works of reference, or, what is still better, to his own dissections and observations, bearing in mind the typical branch of the subject. We shall endeavour to point out where the more important muscles of the domesticated animals present features which, for our purpose, are worthy of comparison with those of the selected type ; and in this attempt we observe very generally the same sequence as to regions and groups that we have adopted in describing the muscles of the horse. KUMINANTIA. Subcutan:eous Region. The panniculus carnosus in the cervical region is mostly aponeurotic ; a muscle which resembles the eteriio-maxillaris of the horse is sometimes regarded as constituting its inferior tieshy portion. In the head it resembles that of the horse, but there is a fleshy expansion in the frontal region — the so-called frontalis muscle — which is apparently a part of the panniculus. In the trunk there is no very important deviation from the arrangement already^ described. RUMINANTIA THE TRUNK. 261 The Head. In the ruiiiinaiit the palatine ridges being closer together, the pterygoid muscles originate nearer to the median line of the head, and thus produce more lateral motion in the lower jaw than there is in that of the horse. There is no digastric muscle in the domesticated animals other than the horse, the muscle representing it having only one belly ; in the ox it is joined to its fellow on the other side by a small, square, transverse muscle. The massetcr and temporalis are both less strong. Passing from the root of the horn core to the upper edge of the orbital fossa is a fiat thin muscle, the frontzlis^ V7h:cli blends with the external levator of the cvelid ; it is, perhaps, a portion of the panniculus. The levator lahii superioris alceqne nasi is not present in the smaller ruminants, and in the ox it differs in that the anterior, instead of the posterior division, covers the dilatator naris lateralis, and that it covers the nasalis longus as well. Two accessory muscles arise in common with the last named, and go to the upper lip. The delators of the nostril, except the lateral hy are wanting. The zygomaticus has a long tendon of origin reaching up to the zygoma. The long tendon of insertion of the depressor lahii inferioris is wanting. The hycidzus magnus has a long tendon of origin, and it forms no sheath, there being no median digastric tendon. Tlie lachrymalis is closely blended above with the anterior border of the orbicularis palpebrarum, and is moi-e developed and thicker than in the horse. The Trunk. The muscle which would appear to correspond to the sterno-maxillaris of the horse, is considered by Chauveau as representing the inferior fleshy band of the panniculus camosus ; it is attached superiorly, not to the angle of the maxilla, but to the fascia of the masseter muscle, and sometimes it may be traced to the zygoma. This view being taken, the sterno-maxillaris finds its representative in the stemo-siiboccipitalis, a muscle which becomes inserted to the basi-occipital bone in company with a tendon of the levator humeri. The stemo-thyro-Jiyoideus is larger than in the horse, and not digastric. The rectus capitis ardicus major is covered by the trachelo-atloideuSj a fiat muscle joining the atlas inferiorly to some of the succeeding vertebrae. The levator humeri is attached anteriorly to the mastoid process, to the posterior surface of the occipital bone and the ligamentum nuchse, to the basi- occipital bone together with the stemo-suboccipitalis, and to the wing of the atlas by a tendon serparate from that of the splenius and' trachelo-mastoideus. In ruminants the splenius is very^mall ; in the camel it is stated by Cuvier to be non-existent, or at least so small as to escape ob; Nucleated cells ; 6. Cilia. of columnar cells, provided at their free extremities with delicate hair-like processes or cilia, which wave to and fro in a marked manner. The motion is apparently independent of the direct influence of the nervous system, since it is observable for some time after the death of 272 SPLANCHNOLOGY. the animal. This tissue is found in the mucous membrane of the air-passages, where its cilia tend by their motion to expel particles of foreign matter which are inhaled with the breath ; it is found also in the ventricles of the brain, in the canal of the spinal cord, and in the mucous membrane lining the uterus and Fallopian tubes of the female, and part of that lining the vas deferens of the male ; and in the convoluted uriniferous tubes. MUCOUS MEMBRANES. These structures are widely diffused, lining the canals of the four systems now under consideration, and becoming continuous with the skin at each of their orifices. A mucous membrane con- sists of one or more layers of epithelial cells placed upon a sub- epithelial layer or corium, the latter consisting of a modified form of connective tissue, and serving as a matrix in which are situated the nerves and vessels of the membrane, together with numerous glands. Some authorities have described a membrane separating the cellular from the vascular layer, and it has received the name of the basement membrane. By others it is regarded as a mere condensation of the corium. The secretion of the glands proper to the mucous membranes is mucus, a viscid fluid which lubri- cates their free surfaces. The surface of a mucous membrane may be smooth, as in the air-passages, or it may be papillated — i.e., furnished with small projections, papillae, as in the tongue ; it may be rugeous, or thrown into folds or rugae, as in the oeso- phagus and stomach ; in the small intestine it presents finger-like projections termed villi, and is then said to be villous, and in the same situation the membrane presents valve-like folds, and may be termed valvular. The mucous membrane which lines the digestive canal becomes continuous in the pharynx with that lining the respiratory canal, the pharynx being a cavity common to the two systems ; hence the entire membrane may be termed the gastro-pulmonat^ mucous membrane, which is also produced so as to line the Eustachian tube and tympanic cavity of the ear, and is, in some animals, continuous by means of the lachrymal duct with the conjunctiva of the eye. At the lips and anus it is directly con- tinuous with the skin. In a similar manner, the mucous mem- brane of the urinary canal becomes continuous with that of the* r SEROUS MEMBRANES. 27^ genital canal in the vagina in the female, in the urethra in the male; the membrane so formed is termed the uriTW-genital mucous membrane, and it becomes continuous with the skin at the orifices of these organs. Mucous membrane also lines the ducts of the mammary glands; and in fact the ducts of all glands which open on the skin or mucous membranes. SEROUS MEMBRANES. The closed cavities of the body are lined by membranous structures of this class. By a closed cavity we understand a receptacle impervious, under normal circumstances, to the atmo- spheric air. A serous membrane consists of an endothelial and a subendothelial portion, the cells of the former being arranged in a single layer. Synovial membranes may- be regarded as a variety of serous membranes, dififering chiefly in the nature of their secre- tion ; they have already been described (see p 125). Since a serous membrane is so arranged as to line a closed cavity, and at the same time to cover its contents, it follows that the entire membrane must form a closed sac, the endothelial layer being on the inside ; such a sac is called a serous sac or cavity. The fold of the membrane which lines a cavity is called the parietal, that which covers its contents the visceral portion; the two surfaces contacting, and gliding readily upon each other, are lubricated by a fluid secretion contained in the sac ; hence one use of these membranes is to prevent friction between the walls of cavities and the organs contained therein. The following are the serous membranes and their position in the body : — The arachnoid membranes form closed sacs, situated, one between the two coverings of the brain, the other between those of the spinal cord. The peritoneum lines the abdominal cavity and covers its viscera ; the pleurae, right and left, each covers the lung, and lines the half of the thoracic cavity of its own side. The peri- cardium lines * the fibrous sac which contains and supports the heart, and also covers the latter. The cavities of the heart are also lined by a membrane of a serous nature — the endocardium — which is continued through the veins and arteries; as the chief Ijnnphatic vess»3ls c^iimunicate with the venous system, the endothelial lining of tba former becomes continuous with that of the latter. Lymphatic vessels open into the serous sacs by very small- apertures, or stomata, so that these sacs are now con- T 274 SPLANCHNOLOGY. sidered as beiag depositories of lymph ; and " thus a continuity of surface is established between the serous membranes and the lining membrane of the blood-vascular system through the- lymphatics" {Turner), GLANDS. Without attempting an exhaustive definition of the glands, it may suffice to state here that for the most part they are organs in which is carried on the process of secretion, or separation from the blood of certain matters, which may be required to assist in the various vital functions, or may be destined to be speedily cast off as effete or poisonous material. Most glands in their typical structure resemble a mucous membrane, consisting of epithelial, subepithelial, vascular, and nervous portions ; the first of these portions usually rests upon a condensed layer of the second, which is known as the memhrana propria, or basement mem- brane. The vessels supply the gland with blood, from which the secretion peculiar to the gland is separated by the vital power of the cells, which power is stimulated by the nerves, the latter also regulating the blood supply. Lymphatic vessels are present, but their use in these organs is obscure. The sub- epithelial tissue supports the other component structures of the gland, at the same time determining its anatomical form. Tho secretions of glands are, as a rule, discharged on the free surfaces of the body — i.e., on the mucous membranes or skin — by means of tubes known as the gland-ducts ; hence such glands may be conveniently regarded as depressions in the mucous membrane or in the skin. When a gland appears as a tube-like depression in the mucous membrane it is termed a follicle, crypt, or simple tubular gland ; if the cavity is dilated, it is known as a sac, or saccular follicle ; and if either of these forms be provided with secondary recesses, it is said to be Qiiultilocular. A tubular gland may be coiled upon itself; or it may branch, in which case it becomes a compound tubular gland. A tubular depression ending in a number of vesicular recesses constitutes a simple racemose gland ; a compound racemose or conglomerate gland consists of a number of simple ones with a common duct. The ductless glands form a group which difiers from any of the above in the absence of a duct, the secretion usually being r EXPLANATION OF PLATE IV. Digestive Apparatus of the Horse. 1. Mouth. 2. Pharynx. 3. (Esophagus. 4. Diaphragm. - . 6. Spleen. 6. Stomach (left sac). 7. Duodenum. 8. Liver (upper extremity). 9. Great colon. 10. Caecum. 11. Small intestine. 12. Floating colon. 13. Rectum. 14 Anus. 15. Left kidney and uiteter. 16. Bladder. 17.' Urethra. A. Hard palate. B. Tongue. C. Soft palate. D. Trachea. E. Pulmonary artery (divided). F. Heart. G. Posterior aorta. r ■t^^ »0 t 4 I u oi O X THE AUMENTAEY CANAL. 275 carried away by rupture of the glandular sac, or by absorption into the neighbouring lymphatics. The liver has been termed a reticular gland, because its ducts fonn a network at their origin. Digestive System. The* digestive organs comprise the alimentary canal and its accessories, by which the alimentary matter is received and sub- jected to specific actions, which adapt it for purposes of nutri- tion. Digestion therefore embraces the collective operations and changes which the food undergoes in the alimentary canal. The functional processes of digestion are — Prehension, the taking up of food, which is performed in the horse by the lips ; Mastication, chewing, grinding ; and, simultaneously with this, Insalivation, or mixing the ingesta with the fluid secretion of the salivary glands ; Deglutition, or swallowing the prepared food by means of the tongue, pharynx, and ossophagus; Chymifica- 'Hon, or conversion of food in the stomach into a pultaceous chyme, by maceration and the action of the gastric juice ; Chylification, or conversion of the chyme into chyle, a change which takes place in the duodenum, presumably 'by the agency of the biliary and pancreatic secretions; Absorption of the nutrient material into the circulation ; and finally, Defecation or excretion, the expulsion of residual inert matter. the alimentary canal. The alimentary canal is a musculo-membranous tube extend- ing from the lips to the anus ; its walls are composed of muscular tissue, for the most part of the non-striated kind, . and lined throughout by mucous membrane. It consists of a continuous series of tubes and cavities, the chief of which are the Mouth, Pharynx, (Esophagus, Stomach, and the Intestines. It may be divided into three portions — the preparatory, or ingestive, embracing the mouth, pharynx, and oesophagus, in which the food is prepared ; the essential, or digestive, including the stomach and most of the intestines, where the food passes through various changes, and is deprived of its nutritive por- tions; and the egestive, or expulsive portion, by which the residue is expelled from the system. Each division is provided 276 SPLANCHNOLOGY. with accessories, the preparatory with teeth and salivary glands, and the essential organs with the liver, pancreas, spleen, &c. We will describe the parts of the alimentary canal in the order above given — the order in which the food traverses them. THE MOUTH. The mouth is an irregularly oval cavity at the commencement of the alimentary canal, containing the organs of taste and the instruments of mastication ; it is situated between the jaws, its long diameter following that of the head. It is pierced by two openings ; the anterior for the introduction of food, and the posterior, through which the latter passes into the pharynx. It is bounded in front by the lips and their aperture, the Jissura oris, and laterally by the cheeks ; the roof is formed by the hard palate ; its floor is occupied by the tongue, while the posterior boundary is the velum pendulum palati, or soft palate, a mem- branous partition separating it from the pharynx. The mucous Tiiemhrane is pale, roseate, continuous with the skin at the lips, and covering the whole free surface of the mouth and its contents, excepting the teeth. THE LIPS. The labia, or lips, superior and inferior, are movable fleshy curtains surrounding the anterior opening, and united laterally by a commissure. They consist of skin and mucous membrane, which enclose muscles, vessels, nerves, areolar tissue,, fat, and certain labial glands situated between the mucous membrane and muscle. Tbe mucous surface of each lip is bridled mesially to the gum by a doubling of the membrane, constituting the frcBTium labii superioris and inferioris. The arterie". and veins of the lips are the palato-labials and the superior and inferior coronaries. The nerves come from the fifth and seventh cranial pair, the first supplying the sensory, or nerves of feeling, which are well developed in the lips of the horse, since these are organs of touch as well as of prehension. THE CHEEKS. The buccce, or cheeks, are two musculo-membranous walls, which close the mouth laterally ; they are continuous with the TSk SOFT PALATE. 277 lips, and consist of an external cuticular, a central muscular, and an internal mucous coat ; the latter is termed the buccal mem- brane, and . is provided with numerous small buccal glands, similar to the labial ones, which open on its surface by straight projecting pointlets ; a few larger ones are known as the molar glands. On the buccal membrane of each side, near the third upper molar tooth, is a papilla, in which is the opening of the duct of the parotid gland. The gingivae, or gums, are reflections of the buccal membrane, and contain dense fibrous tissue, con- tinuous with the periosteum of the alveolar processes, with an epithelial covering ; they embrace, without being attached to, the necks of the teeth, and are reflected into the alveoli. The chief arteries and veins of the cheek are the facial and the coronaries. The nerves come from the same source as those of the lips. The cheeks by their muscles serve during mastication to support the food, and press it between the molars. THE HARD PALATE. The hard palate, or mouth-roof, is bounded anteriorly by the incisor teeth, posteriorly by the soft palate. It is firmly attached to the bony palate, formed by the palatine bones and palatine processes of the superior and premaxillse. It consists of a dense layer of mucous membrane, with a thick subjacent layer of fibrous tissue. It is equally divided by a longitudinal groove corresponding to the palatine suture, which originates anteriorly at the base of a small tubercle. From this raphe spring trans- verse ridges, which divide the palate into a number of arches with their concavities backwards ; they become smaller posteri- orly, and are from seventeen to twenty in number. The palate is supplied with blood from the palatine arteries, returned in a venous plexus, which forms a kind of erectile tissue in the submucous layer. The sensory nerves come from the superior maxillary division of the fifth pair. The hard palate furnishes a fixed surface, against which the tongue can mani- pulate the food. THE SOFT PALATE. The soft palate, or velum pendulum palati, is the valvular curtain suspended between the mouth and the pharynx, and it consists of a double fold of mucous membrane, enclosing muscles, glands, vessels, and nerves. It presents two surfaces and four 278 SPLANCHNOLOGY. . borders. Its superior border is attached to the palatine arch, and is continuous with the hard palate, whence the velum passes downwards and backwards. The lateral borders are united to the line of demarcation between the cavity of the mouth and th?.t of the pharynx. The inferior border is concave and free, resting upon, and closely embracing the base of the epiglottis. From the extremities of this border, two very thin prolongations n\n along the lateral walls of the pharynx as far as the beginning cf the oesophagus; these are the posterior pillars of the fauces. Between the free border of the velum pendulum palati and base of the epiglottis is the posterior opening of the mouth, called the isthmus faucium, which in the horse, from the extreme development of the soft palate, is constantly shut, except during the passage of food or water. It is owing to the great size of the velum that a horce is unable to breathe through his mouth. The anterior surface of the velum forms the posterior boundary of the mouth, is marked by longitudinal folds and transverse lines, and studded v/ith the mouthlets of numerous submucous glands. This surface is united laterally to the base of the tongue by large mucous columns, the posterior pillars of the tongue, or anterior pillars of the fauces. Behind these are two lateral triangular spaces, the tonsilar spaces, v/hich take the place of the tonsils or amygdalcB, these being absent in the horse ; numerous gland ducts open in these spaces. The posterior surface of the soft palate is convex, and forms the anterior wall of the pharynx ; it presents three very small longitudinal ridges. MUSCLES OF THE SOFT PALATE. A strong layer of aponeurosis or fibrous tissue, the staphyline aponeurosis, forms as it were the foundation of the soft palate, being attached above to the palatine arch. The following muscles control the soft palate : — Teusor palati. I Pharyngo-staphylinns. Levator palati. | Palato-staphylinus. Pd2,to-glossu3. ( T2NS0R PALATL ' {Pcriztaphylinus Extc7nu2.) (Fig. 00. i.) A long slender muscle with tendinous extremities, running longitudinally between the levator palati and the pterygoideL It MUSCLES OF THE SOFT PALATE. 279 arises from the petrosal styloid process ; its tendon of insertion, playing over the staphyline groove, expands and becomes lost in the fibrous layer of the velum, of which it is a tensor and depressor. LEVATOR PALATL (Peristaphjjjinus Internus.) (¥iG. 90. h.) A slender muscle which arises with the last-named one, and lies between it and the Eustachian tube. It passes directly to the soft palate expanding between the Pharyngo-staphylinus and the Palato-staphylinus, and finally joins its fellow of the opposite side. It raises the velum Fig 90. Right infero-lateral view of the mnscles of the maxillary space ; the ramus and hyoid cornu are cut away, o, Lingualis : & 6, Hyo-glossus longus ; c, Hyo-glossus brevis ; d, Genio-hyo-glossus ; f, Genio-hyoideus : /, Stylo-hyoideus : g, Hyoideus magnus ; h. Levator palati ; i, Tensor palati ; k, PharjTigo-staphylinus : I, Pterygo-pharyngeus ; m. Kerato-pharyngeus; m, Hyc-pharyngeus ; o, Thyro-pharyngeus ; p, Crico-pharyngeus : q, (Esophagus. PHARYNGO-STAPHYLINUS. (Staphylinus Communis.) (Fig. 90. X:.) This is a broad, thin muscle, occuppng the inferior half of the velum, and meeting its fellow in the median line ; they are sometimes described as a single muscle. The fibres run back- wards and outwards, and a portion, after following the free border of the velum, is continued under the pharyngeal mucous mem- 230 SPLANCHNOLOGY. brane and attached to the thyroid cartilage ; this portion helps to form the posterior pillar of its own side. This muscle is chiefly a tensor of the velum. PALATO-STAPHTLINUS. {Azygos Uvulce — Human.) This is a small cylindrical muscle contacting its fellow of the opposite side, and arising by a small tendon from the palatine arch and staphyline aponeurosis, to become attached to the free border of the velum at its middle ; the pair of muscles thus indicate the right and left halves of the structure. The action of this muscle is to raise and draw forwards the velum, thus helping to dilate the isthmus. PALATO-GLOSSUS. If this muscle exists in the horse, it will be found under the mucus membrane of the anterior pillar. Trhich it helps to form, thus joining the soft palate and the tongue. The soft palate is supplied with blood by the staphyline and pharyngeal arteries. Its nerves come from the second division of the fifth pair, and from Meckel's ganglion. It acts as a valve between the mouth and pharynx, opening to allow the passage of alimentary materials during deglutition, but completely prevent- ing the return of such from the pharynx to the mouth ; hence in case of vomition in the horse the material is voided through the nasal chambers. Respiration is likewise effected in the solipede only through the nose. THE TONGUE. The tongue is a movable, musculo-membranous organ, situated on the floor of the mouth, between the rami of the lower jaw ; the space it occupies is termed the lingual canal. It is the special organ of taste, and at the same time materially assists in mastication and deglutition. In the ox it is prehensile, and the carnivora lap or prebend water with it. The tongue consists of muscles, glands, vessels, and nerves, having its free surface enveloped by mucous membrane, which varies in thickness, r LINGUAL MUSCLES. 2§l being smooth and pellucid infero-laterally, where the ranine vein can be traced. Irregularly pyramidal in shape, it has a root or base, a body, and an apex or tip. The base, the widest and thickest part, is muscularly attached to the OS hyoides and inferior maxilla; to the epiglottis by a fold of mucous membrane, the glosso-epiglottic ligament ; and to the velum pendulum palati by the anterior pillars of the fauces. The apec^, or tip, is free, and broa'd in the horse, being directed forwards against the inner surfaces of the lower incisors. Tha under surface of the tongue is attached anteriorly to the lower jaw by the genio-hyo-glossi muscles, and laterally by the reflec- tion of the mucous membrane, over the sublingual glands, to the inner surface of the inferior gums. Antero-mesially, the mucous membrane folds into a frcenum linguce, or anterior pillar, in front of which is a small papilla, containing the openings of the submaxillary glands; and on either side, between the tongue and maxilla, are the ducts of the sublingual glands. The dorsum^ or upper surface, is convex, and marked along its middle by a raphe, or groove, which indicates the division of the organ into two lateral halves. The raphe terminates near the base in a cavity known as i\iQ foramen ccecum, or foramen of Morgagni, in which numerous mucous follicles open. Posteriorly the tongue is divided by fibrous tissue, which forms a partial longitudinal septem, commencing near the hyoid bone, and losing itself in the muscles. According to Briihl, a piece of fibro-cartilage exists here, pecuhar to the solipede, and it has been named the lingual cartilage. LINGUAL MUSCLES. The substance of the tongue is composed chiefly of muscular layers running in different directions, between which adipose tissue is interposed. The muscles are divided into extrinsic and intrinsic. The extrinsic muscles of the tongue are as follows : — Hyo-glossus longus. Genio-hyo-glossus. ». Hyo-glossus brevis. Pharyngo-glossus. \' Hyo-glossus parvus. Palato-glossus. ^ 282 SPLANCHNOLOGY. EYO-GLOSSUS LONGUS. (Stylo-glossus.) (Fia. 90, 6 &.) Situated along the border of tlie tongue, this muscle is long^ and fiat. OHgin. — From the external surface of the comu of the os hyoides. Insertion. — To the substance of the tongue expanding towards the tip. Relation. — Externally with the mylo-hyoideus and sublingual gland, sublingual nerve, and canal of Wharton ; internally with the genio-hyo-glossus and hyo-glossus brevis. Action. — With its fellow, to retract the tongue within the- mouth ; singly, to draw it to one side. HYO-GLOSSUS BREVIS. (Basio-g lossus. ) (Fig. 90. c.) Situated on the inner surface of the hyo-glossus longus, it is a broad, flat, and somewhat radiating muscle, the fibres passing obliquely forwards and upwards. Origin. — From the side of the body and spur process of the os hyoides and the inferior part of the cornu. Insertion. — The side of the tongue, passing inwards to form the "transverse fibres." Relation. — Externally with the mylo-hyoideus and hyo-glossus longus, the hypoglossal nerve, Wharton's canal, and the mucous membrane of the tongue ; internally with the hyoideus parvus and the corniculum, genio-hyo-glossus, the lingual artery, and the glosso-pharyngeal nerve. Action, — To draw the base of the tongue downwards and back- wards, on one side, or both if acting with its fellow. HYO-GLOSSUS PARVUS. Situated immediately under the mucous membrane, intimately blended with the last named, this is a small radiating muscle. Attachments. — It arises from the inner aspect of the corniculum and hyoid bone, crosses the hyoideus transversus, its fibres then running forwards. It expands over the dorsum and sides of the tongue, its fibres crossing those of the hyo-glossus brevis. r LINGUAL MUSCLES. 283 GENIO-HYO-GLOSSUS {Genio-glossus.) (Fio. 90. d.) Situated in the vertical median plane of the tongue, this is a broad, thin, and fan- shaped muscle, its fibres radiating upwards. Attachments. — Its basis may be said to stretch from the hyoid bone to near the maxillary symphysis, the radiating fibres passing upwards and some backwards, some forwards, buried in the sub- stance of the tongue. Relation,. — Internally with its fellow ; inferiorly with the genio- hyoideus ; externally with the hyo-glossus longus and brevis, the sublingual gland, and the lingual artery. The anterior borders of this pair of muscles help to form the frsenum linguae. Poste- riorly a certain amount of fat constantly occurs between them. Action. — This varies. It may protrude the tongue by depress- ing the dorsum, or help to retract it ; or it may depress the entire organ, according to the part of the muscle which acts, and to co-operation of the other muscles. PHARYNGO-GLOSSUS. This name has been applied to a few fibres which unite the tongue to the lateral wall of the pharynx, passing between the fibres of the genio-hyo-glossus and hyo-glossus parvus, and blend- ing with them. PALATO-GLOSSUS. (See muscles of the soft palate.) The intrinsic muscles are collectively described under the name LINGUALIS. (Fig. 90. a.) This muscle is arranged in two layers of longitudinal, with an intervening set of transverse, fibres. The lingualis superficialis lies on the upper surface of the tongue just below the mucous membrane, running longitudinally from the apex nearly to the OS hyoides. The lingualis inferior, also longitudinal in direc- 284 SPLANCHNOLOGY. tion, is arranged in a rounded band, which extends in the inferior region of the tongue from base to apex, a few fibres reaching the hyoid bone. The lingualia tranaversua lies between the super- ficial and deep layers, intersecting the extrinsic muscles ; its fibres are always intermixed with a quantity of adipose tissue, and form the bulk of the organ. These layers alter the form of the tongue, the superficial tilting the tip upwards ; the inferior curves it down- wards; while the transverse protracts or elongates it. The fibres of the intrinsic muscles are regarded by Chauveau. and others as prolongations of the' extrinsic muscular fibres. The mucous membrane is plentifully supplied with glands^ simple and compound. The simple are mere follicles, secreting mucus. The compound glands, and certain closed follicles, are. found chiefly at the base of the tongue, about the foramen caecum, posterior pillars, and papiilse circumvallatse, into which many of their ducts open. LINGUAL PAPILLJ3. The mucous membrane covering the under part of the free surface of the tongue is smooth, but as it passes over the borders it assumes a papillary character, and on the dorsum it is covered with papillae, which roughen and give it a velvety appearance. The papillae comprise three varieties : — papiilse maximas, calici- form, or circumvallate ; mediae, or fungiform; and minimae, or filiform. The papillcB circiimvallatce, three to five in number, are situated at the back part of the dorsum. They are arranged triangularly, the single one being posteriorly and mesially placed, corresponding to the foramen caecum. These papillae rest in cup- like depressions of mucous membrane, and are inversely conical, with the apex below ; several such papillae may be enclosed in the same calyx. The fungiform papilloe are more numerous, and scattered irregularly over the dorsum, being most numerous on the posterior third ; they are attached by a narrow neck, the base being round, free, and often furnished with filiform papillae. The filiform papillcs cover the greater part, but especially the anterior two-thirds of the dorsum, vanishing towards the base. They are simple or compound, the former having one free pro- cess, the latter more than one. Papillae are processes of the corium of the mucous membrane, containing terminal nerve filaments, numerous in the larger, but difficult to trace in tht; pa:iotid gland. 28$ smaller, papiliss. Like the mucous membrane, they are covered by a thick layer of squamous epithelium, which is sometimes imbricated. It is generally believed that the caliciform papillae are subservient to the special sense of taste; that the fungiform variety possesses common sensibility ; while the filiform papills3 serve a mechanical purpose during the action of the tongue on the foocL The blood-supply of the tongue comes from the lingual and sublingual branches of the glosso-facial artery, and the blood is returned by the lingual or ranine, and sublingual veins. The principal nerves are — the. lingual, or gustatory branch of the fifth ; the lingual branch of the glosso-pharyngeal ; and the hypoglossal or twelfth pair. Fxa. 91. Parotid and molar glands of tlie left side, a a. Parotid gland ; h b, Steno'a duct; c, Superior, and d. Inferior molar glands. SALIVARY GLANDS. The salivary glands are accessories of the mouth. They secrete the saliva, v/hich is discharged into the mouth, and saturates the food, during mastication. There are three primary pairs — viz. the Parotid, the Submaxillary, and the Sublingual. PAROTID GLAND. This, the largest of the salivary glands, is long and flat, and is situated in the cpace bounded bj the posterior border of the 286 SPLANCZ::C10GY. inferior maxilla and the anterior border of tlie wing of the atlas ^ it lies immediately below the ear, v/hich it partly surrounds, and is covered by the deprimens aurem. It 13 related internally with the guttural pouch, and inferiorly it occupies the angular spacs formed by the jugular and glosso-facial veins. It io greyish, and, like all salivary glands, conglomerate, consisting of c number of' lobes held together by dense areolar tissue, these again consic'^- ing of lobules, each of which is formed by minute vesicles, originating in the dilatation of the branched origins of th:^* ducts. The latter unite to form larger ones, and terminate in Steno's dvbcty which commences at the antero-inferior surface. Fio. 92. Eight infero-lateral view of tlie liead ; tlie maxillary ramus, cheek, parotid gland, and upper lip being removed, a, Submaxillary gland ; 6, Wharton's duct ; c, Sublingual gland ; d. Its excretory orifices; e e, Labial glands ; /, Their excretory orifices; g. Papilla, with orifice of Steno's duct : h. Orifices of the superior, and, i, those of the inferior molar glands ; fc. The hard palate ; I, The soft palate ; m, The tongue, with its papillae ; n, Pillars of the tongue and soft palate ; o, Frcaum- lingusQ. near the insertion of the stemo-maxillaris, passes* along the posterior aspect of the digastricus, round' the ramus of the lower jaw, in company with, and posterior to, the glosso-facial artery and vein ; it thus runs along the anterior border of the masseter, and enters the mouth at about the level of the third upper molar tooth, the orifice of the duct being marked by a papilla on the buccal membrane. In some animals there is a small detached gland connected with it, the glandula soda paro- tidis, which opens into the parotid duct as it crosses the masseten The duct consists of an internal mucous and an external con- tractile coat. r MINOR SALIVARY GLANDS. 287 The parotid gland is supplied with blood by numerous small arteries given off from larger vessels in the immediate neighbour- hood. The nerves come from the carotid plexus, also from the fifth and seventh pairs. SUBMAXILLARY GLAND. ' This gland, smaller than the parotid, is long, thin, and cres- centic, with the concavity directed forwards and upwards. It lies in the maxillary space, below and behind the parotid, and on the outer side of the pharynx, extending from the wing of the atlas to the body of the hyoid bone, where it terminates in Wharton* s duct, which passes between the mylo-hyoid and hyo-glossus brevis, and is continued along the side of the jaw between the hyo-glossus longus and the sublingual gland, open- ing into the mouth rather in front of the frsenum lingua6, where it is protected by a thick papilla on the mucous membrane, commonly called the harh. In structure it is similar to the parotid, but its lobes are larger, its attachments looser, and its duct- coats thinner. Like the parotid, this gland receives many small arteries ; they come mostly from the external carotid and glosso-facial. The nerves are chiefly from the carotid plexus. SUBLINGUAL GLAND. This gland is smaller than the last-named, long, flat, and delicate. Situated under the tongue, it is placed longitudinally, with its edges vertical, and included between the mylo-hyoideus, hyo-glossus longus, and genio-hyo-glossus muscles ; its superior border reaches the mucous membrane of the floor of the mouth ; anteriorly it extends to the maxillary symphysis, posteriorly to the hyoidean spur process. In the horse it opens by from fifteen to twenty small ducts, the ducts of Rivinus, which are arranged along the floor of the mouth, on what has been termed the sub- lingual crest, each duct being marked at its opening by a papilla. Unlike the salivary glands hitherto described, the sublingual gland has a special artery of supply, the sublingual artery ; its nerves come from the gustatory nerve and carotid plexus. MINOR SALIVARY GLANDS. Other presumably salivary glands are the Molar, the Labial, the Lingual, and the Staph yline. The Molar glands, so called. 288; SPLANCHNOLOGY. because they are parallel to the rows of molar alveoli, are two in number, superior and inferior ; they are situated in the cheek, along the upper and lower borders of the buccinator. They dis- charge by numerous orifices in the buccal membrane. The Labial glands are placed under the mucous membrane of the lips, especially of the upper one. The Lingual glands are found at the base of the tongue, and partly along its sides. The Staphyline are situated in the soft palate, and between its anterior and posterior pillars, discharging into the mouth or isthmus faucium. SALIVA. Saliva, the fluid secreted by these glands, is clear, viscid, colourless, and slightly saline in taste, with a specific gravity of 1-005. Alkaline in reaction, it consists of water with about one-half per cent, of solids, including fat, albumen, and a special nitrogenous principle, ptyalin, or " animal diastase," which helps to convert starchy material into grape sugar. Saliva also con- tains alkaline and earthy salts, with a trace of sulphocyanide of potassium. The secretion of the different glands varies ; that of the parotid is most watery, while that of the submaxillary and sublingual is viscid. The parotid secretes most abundantly during mastication, and always in direct ratio to the dryness of the food ; the others secrete equally, whether the aliment be dry or moist, but appear to be influenced by its taste. The sight or thought of food will frequently induce a secretion from the submaxillary and sublingual glands. The food thus becomes saturated in the mouth with two fluids, mucus and saliva, both assisting in mastication and deglutition, the latter in addition acting upon the starchy constituents of the food. TEETH. Teeth are objects implanted in and protruding from the maxil- lary alveoli. They are characterised by the hardness and density of their specific tissues. Like bone, these tissues consist of earthy salts, with a basis of organic animal matter. They are harder than bone, which contains about 67, while teeth contain 76 J, per cent, of earthy salts. One material physical difl'erence between a bone and a tooth is that the free portion of the latter bears exposure and friction with impunity, while tlie former can r TEETH. 28^ endure neither without becoming diseased. Teeth vary with the class of animal in number, size, form, structure, position, and attachment, but in all cases they are in correlation with the food and generic habits of the animal. Thus, in herbivora, where grinding the food is necessary, the contacting surfaces of the molars are rough and flat. In carnivora, where tearing and crushing are requisite, the molars are sharp, pointed, and serrate ; in cmnivora, where the food is general, the teeth are mixed ia their character. The form of the teeth thus depends upon the natural food of the animal, and there is always a certain harmony between their disposition and the conformation of correlated organs. They are not found in all animals. Birds have none, while the typical number of mammalian teeth as viewed by Pro- fessor Owen is forty-four. Three hard structures enter into the formation of the teeth — Dentine, or Ivory ; Enamel ; and Cementum, or Crusta petrosa. DENTINE. Uentine constitutes the major part of the tooth, and is a hard, yellowish substance, consisting of very minute tubuli em- bedded in a dense, granular, intertubular jnatrix, which contains the bulk of the earthy matter, the latter being about thirty per cent, of the whole. The tubuli commence at the pulp cavity, and radiate to the superficies of the dentine, where they anastomose "and their branches terminate in minute cavities, the dentinal cells, which perhaps are analogous to the lacunse of bone. The tubuli are about the 4o\)xr of ^^ i'^ch in diameter, and, Fig. 93. pblique section of dentine, show« ing the tubuli and coalescence of the calcified nodules. in the fresh state, they contain processes from the pulp. During the development of a tooth the calcification of the dentine proceeds from centres, around which tte calcific material becomes deposited. Thus nodules are formed, which, by expanding, finally coalesce and form the solid matrix. 290 SPLANCHNOLOGY. ENAMEL. In appearance enamel is distinguished by its peculiar white- ness. It is the hardest animal texture, containing about OG per cent, of earthy salts. It consists of hexagonal prisms, which are arranged side by side, with one extremity resting on the surface of the dentine, Vv^hence they are disposed in gently wav- ing lines towards the surface of the tooth. They vary somewhat in diameter, but average t-oVo ^^ ^^ i^^^- No nutrient vessels ornerves have been traced into ena- mel, and v/hen destroyed ii is not reproduced. This tissue is protective, sometimes covering the entire exposed surface of the tooth, as in the human subject and the dog, and it also furnishes the rough projections and cutting edges found in the teeth of some classos of animals, the herbivora affording the best example of this. Fio. 94. A, Transverse section of enamel, shcn'ing the cut ends of its hexagonal prisms ; B, Prisms separated. CRUSTA PETROSA. Crusta Petrosa, or cementum, the third constituent, completely covers the imbedded portion of the tooth, and occupies the cavities on the free portion, where such exist. It is thickest towards the roots, most abundant on the molar teeth, and is distinguished by its brownish-yellow colour. It is the softest dental texture, closely resembling true bone in structure, having tubuli and cells resembling the canaliculi and lacunae, and w^here it is thick it may be traversed by vascular tubes analogous to the Haversian canals. The proportion of earthy matter, the same as in bone, is about 67 per cent. ARRANGEMENT AND KINDS OF TEETH. Teeth may be simple or compound. Simple as in the dog, where the entire exposed surface is covered by a solid cap of enamel, which alone is in wear ; compound or complex, as in the horse, where various tissues are in wear. A tooth consists of r INCISOR TEETH. 291 the following anatomical parts ; the body, or crown, which is free of the gum, the grinding or cutting surface of which is the table ; ths cervix, or neck, the part invested by the gum ; and the fang, or root, which is inserted into the socket or alveolus. The ulvtoli are more porous, spongy, and vascular than other bone ; they appear and grow with the teeth, and when these decay, become absorbed. They are lined by periosteum, which, reflected from the gum, at the base of the socket, covers the fang, communicating with the pulp cavity, which runs up the fang centre, and contains a highly vascular and nervous organ,- WiQ pulp, whence the dentine of the tooth grows. This pulp is enclosed in a vascular membrane, the dentine tubuli radiating from it. In the aged tooth this membrane becomes ossified, forming the secondary or osteo-dentiyie. The sensory nerve of the pulp comes from the fifth pair; and it is owing to its extreme sensibility that toothache is so severe w^ien the pulp is exposed. Teeth are arranged alongside of each other, so as to form the dental arches : these are interrupted at each side, leaving the interdental spaces, or dlcistemce. Teeth are of three kinds ; the; Incisors, or cutting teetb, situated in front of the arches; Canine teeth, or tushes, in the interdental spaces; and Molars, or grinders, behind. The horse, like many other animdls, has two sets ; the temporary or milk teeth, and the permanent or horse tefeth, the former numbering 24, the latter 40. In the mare there are usually. 36 permanent teeth, the tushes being wanting or rudi- mentary. INCISOR TEETH. The incisor or front teeth in the horse are 12 in number, 6 in each jaw ; the upper ones are the longer, their surfaces meet- ing those of the lower ones ; in rare cases the former overlap, constituting a '' parrot mouth." The central pair are the largest, the adjacent ones are called the middle, or lateral, while the outer ones, which are the smallest, are termed the corner incisors. The row of incisors forms a curve, which is part of the so- called dental arch; the younger the tooth the greater the curvature, which gradually decreases with age. The anterior surface of a young incisor tooth presents a triangular shape, with th« base at the table. Viewed laterally it is still triangular, but ^92 SPLANCEITOLOGT. Fig. 95. Incisor and canine teeth of f ftorse. A, Front, B B, Lateral and C C, Corner incisors Canine teetb. D J). its apex is at the table. The table is therefore oblong, its long axis following the line of the dental arch. As it wears, it narrows laterally, but its short axis Widens, until in old age it is nearly round, what was the fang being in wear. The free surface of an incisor tooth, excepting the table, is covered by a layer of enamel; the fang, which is a single process, being covered by crusta petrosa. Towards the centre of the .table, in a young tooth, a second ring of enamel is visible, which is the mouth of a funnel- shaped cavity called the infundibwlum. This cavity in the young animal is ovoid, its long axis following that of the table ; it is lined by crusta petrosa, which, be- coming stained by the food, constitutes the so-called " mark." The space be- tween the two tubes of enamel is filled up with dentine ; hence the table is a comDound one — i.e., all three of the dental tissues are in wear on it l^ ^ The infundibulum, or mark, being conical in shape, wears with the tooth, becomes smaller, and ultimately vanishes. For example, the permanent central incisors are up at three years; in the lower jaw the infundibulum wears av/ay about one-third in each year; the animal will probably, therefore, be six years of age when the mark is gone from the central incisors. Sometimes the cavity is absent, its place being occupied by crusta petrosa ; still, in the centre of the tooth there is the inner ring of enamel Thus, in the transverse sec- tion of a young tooth, we notice an outer and an inner ring of enamel, the interspace being filled by a mass of dentine, and the inner ring lined by crusta petrosa (see Fig. 96). In the centre, the table in front of the infundibulum is broader than that behind it, and as the tooth wears it still broadens. In this space sometimes a spot is apparent which differs from the rest cf the dentine ; it is the ostco-dentine covering the pulp cavity ; this Fig Incisor tooth of a .Horse — posterior view. a. Outer layer of enamel; 6, Inner layer of enamel round the infundibulum; c. Dental star; d. The dcntint". MOLAR TEETH. 2^3 object has been termed the dental star. The corner teeth may have no posterior tables, constituting shell teeth ; rarely they are absent in every tooth whea we have a shell mouth. The incisor milJc teeth are whiter than the permanent ones, and have distinct necks, the necks of the latter being imaginary. They are convex and grooved posteriorly, and have their dentine stained. Almost perpendicular to the axis of the head, in the young animal, the incisors become more and more horizontal as the animal ages. Permanent incisors are convex anteriorly, the lower incisors having one, the superior two grooves down the centre of the body 3 these are filled with cementum, but are absent in old teeth. The incisor teeth attain their greatest development in the elephant, in which animal they project from the mouth as tusks, it may be to an enormous extent. CANINE TEETH. The tushes, tuslcs, or canine teeth, well developed in dogs and other carnivora, are simple teeth, four in number, a pair above and belov/. They rest in the interdental spaces, the lower being nearer the incisors than the upper ones ; they are permanent oh initio, and appear between the fourth and fifth year, sometimes a yeair in advance. The crown is somewhat conical^ the base being at the gums. The external surface is convex, and marked by several fine longitudinal lines ; the internal surface presents on either side a sharp ridge which separates it from the external. The crown terminates in a conical eminence, somewhat hollowed internally during growth, and bounded by a sharp ridge. When a tusk has been long in wear, the ridge disappears, and the internal surface becomes nearly smooth ; and as the apex of the tooth becomes worn away, often a small mark appears, but no second ring of .enamel. These teeth have no constricted neck, and the fang is single. In the horse tribe, as a rule, canine teeth are developed only in the male ; if they exist in the female they are rudimentary. MOLAR TEETH. The Molars, or grinders, are 12 in the temporary setj 3 on either side of each jaw; 24 in the permanent set, 6 on each side above and below ; they are numbered from before backwards, and, like the incisors, those of the upper jaw are the larger. A molar tooth is constructed on the same general plan as au 294 SPLANCHNOLOGY. incisor, but the contour of the various parts is much more irregular. There are generally two infundibula containing a large quantity of cementnm, a layer of which also covers the greater part of the external enamel. The crown of the upper molars is somewhat cubic ; their external surface presents two grooves running from table to root, the anterior being the deeper. The crown of the lower molars is narrower, but longer than that of the upper ones, and has only one groove. The inner surface of the upper molars is not so deep as the outer, while the inner surface of the lower ones is the deeper ; the two lower rows diverge towards the back of the mouth, while the two upper rows are rather convex externally. The molar grinding sur- AA, External crustapetrosa;B, Exter- face is verv irresfular, owin2f to the nal enamel; CO, The dentine; D D, • i i -i j i? • Internal enamel surrounding the infun- VanablQ hardneSS 01 itS Components. fhr/^nmbui?'''*^'^™'*°''''^^^ -^ ^^^^® ^^y ^^^® supplementary molars, or wolf teeth ; these are small, and placed one on each side of the jaw, anterior to the first molars ; they are usually shed with the milk teeth. The teeth which replace the deciduous or milk molars are situated anteriorly, and are termed in general zootomy premolars. A Fig. 97. Transverse section of a molar tooth. DENTAL FORMULA. A dental formula expresses in a concise manner the number and position of the teeth possessed by. an animal. The numbers are written somewhat in the form of fractions, and prefixed are the initial letters of the names of the various teeth. Thus, i\ stands for incisors, c. for canines, p.m. for premolars, and m, for molars. For example, the molax teeth of the dog are thus 2 - 2 . represented : — m. ^— ^ ; this means that there are two molars on each side in the upper jaw, and three on each side in the lower jaw upper, and three on each side in the lower jaw. The full dental formulae of the horse are as follows : — In the ox the incisors are ^. 5— „, or none whatever in the DEVELOPMENT OF THE TEETH. 295 Deciduous or milk teeth. . 3^ 0-0 3-3_12 ^- 3-3' ^* 0~0' ^* 3^~12~^** Permanent teeth. I .3-3 1-1 3-3 3-3 20 ,^ '• 3-:: 3' '' r--r ^''^' 3-^> ^'- 3^3 = 20 = ^^• DEVELOPMENT OF THi: TEETH. The devslopment of the teeth, as demonstrated by the late Professor Goodsir, consists of three distinct stages — papillary, follicular, and saccular. About the sixth wesk of foetal life a depress- sion is formed in the mucous membrane of the gum, which is the primitive dental groove, from the floor of which arise papillae or processes corresponding numerically to, and constituting the germ^ of, the milk teeth ; this is the papillary stage. About the tenth week the groove deepens, the papillae enlarge, the margins of the grooves thicken and become prominent ; prolongations or septa pass from one side of the groove to the other, enclosing each papilla in an open follicle or sac ; this constitutes the follicular stage ; it terminates about the fourteenth week. Somewhat later, the papillae begin to assume the shape of the crowns of the future teeth. Small membranous processes or opercula are now developed from the sides of the follicle, which correspond in number and shape with the table surfaces of the teeth; thus, for the incisors, there is one on either side, the tushes have three, and the molars four or five, according to their size and situation. The lips of the follicles, as well as the opercula, close and cohere, and the grooves becoming obliterated, what were open follicles are con- verted into closed sacs, thus completing the saccular stage. Shortly before the closing of the follicles of the milk teeth, a lunated depression is noticed behind, and to the inner aspect of each follicle; these become converted into cavities of reserve, which ultimately form sacs for the development of the permanent incisors, as well as the three anterior permanent molars. The dental sac, as well as the enclosed papilla, continues to enlarge, the papilla becoming converted into the pulp, and acquiring the semblance of the dental crown. The contents of the sac now consist of the vascular pulp, covered by its membrane — an internal vascular layer, lining the sac, called the periodontal membrane ; and a fluid lying between the two membranes, the outer or 296 SPLANCHNOLOGY. enamel pulp. The process of calcification now commences. A thin lamina or cap of dentine is first developed on the outer and most prominent part of the pulp, from its covering membrane ; this continues to be formed by the substance of the pulp, which gradually decreases as the dentine increases, the enamel being, at the same time, deposited in crystals from its own peculiar or outer pulp. The cementum also forms pari passu, from the calcification of the periodontal membrane lining the sac. When calcification of the dental textures is sufficiently advanced, the tooth makes its way through the gum, which is absorbed^ as the crowns are forced upwards by the growth of their fangs. The septa or divisions between the dental sacs now ossify, and con- Btitute the alveoli. As growth continues, the base of the pulp contracts and forms the neck. The dental sac now elongates, and gradually becomes less, owing to the formation of dehtine on its outer surface, until only a small cavity is left in the centre, in which rests the pulp and its vessels. In the molars, every point on the crown has a separate cap of calcification. These enlarge, and finally meet. In the formation of the molar fangs the pulp divides, ossification in each section proceeding as in a single-fanged tooth. The permanent teeth are developed like the temporary ones. As the permanent tooth continues to grow, it gradually presses on the milk tooth, and ensures absorption of its roots, until the entire fang becoming removed, the crown of the milk tooth falls out, and the permanent tooth appears above the gum. The remaining permanent teeth, the three posterior molars in each side of either jaw, are developed thus : — ^Behind the third molars there is a portion of the dental groove unobliterated, which forms a cavity,- called the posterior cavity of reserve, in which a papilla appears, and undergoes the same change as that of the temporary teeth, forming the rudiment of the fourth molar. From this cavity is developed a second follicle for the fifth, and from this the follicle of the sixth or last molar. PHARYNX. The pharynx is a musculo-membranous cavity common to the digestive and respiratory canals. Somewhat cylindrical in the horse, it extends obliquely downwards and backwards, and lies behind the velum palati, which separates it from the mouth, an(J forms its anterior wall. It is attached superiorly to the base of PHARYNGEAL MUSCLES. 297 the cranium by muscles and aponeurosis, infero-laterally to the larynx, and infero-posteriorly it is continuous with the oesophagus. It communicates with other cavities by seven openings — viz., the two posterior nares superiorly ; posteriorly, on either side, with the slit-like openings of the Eizstachian tubes, which lead to the guttural pouches, and are guarded by a cartilaginous valve ; anteriorly, below the posterior nares, is the isthmus of the fauces, leading into the mouth, and, excepting during deglutition, closed by the velum palati ; inferiorly, behind the root of the tongue, is the opening of the larynx, and behind this the oesophagus. The walls of the pharynx consist of a muscular layer, with a lining of mucous membrane. PHARYNGEAL MUSCLES. The muscular layer of the pharynx is separable into seven pairs of muscles. These are best seen posteriorly, where they appear as a series of flattened, fleshy bands, the superior of which meet their fellows of the opposite side at a mesian vertical line or raphe. The names of the muscles are as follows, and, excepting the first and last, they are named in order from above downwards : — Pharyngo-staphylinus. Pterygo-pharyngeus. Kerato-pharyngeus.. Hyo-pharyngeus. Thyro-pharyngeus. Crico-pharyngeus. Aryteno-pharyngeus. PHARYNGO-STAPHYLINUS. (See Muscles of the soft palate.) PTERYGO-PHARYNGEUS. (Fig. 90. I) This is a thin, broad band of muscle arising^ from the pterygoid process. Its fibres are directed backwards and downwards. It terminates by meeting its fellow at the posterior median line of the pharynx, of which cavity it is a constrictor. KERATO-PHARYNGEUS. (Fig. 90. m.) Arising from the inner aspect of the hyoid comu, this muscle, A small, narrow band, runs inwards and downwards to the wall of the pharynx, becoming blended with the pterygo-pharyngeus. It is a levator, and by some considered a dilator of the pharynx. 298 SPLANCHNOLOGY. HYO-PHARTNGEUS. (Fig. 90. n.) This is a flat muscle arising from the heel process of the hyoid bone, and slightly from the thyoid cartilage of, the larynx. It* fibres passing upwards and backwards, it reaches its fellow of the opposite side at the posterior median line. It is a constrictor. THYRO-PHARYNGEUS. (Fig. 90. 0.) Placed immediately below the muscle last described, this muscle joins its fellow in a similar manner, arising from th© thyroid cartilage. It also is a constrictor. CRICO-PHARYNGEUS. (Fig. 90. p.) Situated below the thyro-pharyngeus, this muscle arises from the lateral aspect of the cricoid cartilage. Its fibres run back- wards, converging slightly upwards, and it terminates similarly to the two muscles last described, its action resembling theirs. ARYTENO-PHARYNGEUS. This is a small band stretching from the posterior aspect of the arytenoid cartilage to the muscular wall of the oesophagus, its action being to raise the latter. The pharynx is supplied with blood by the pharyngeal and thyro-iaryngeal arteries. Its nerves are derived from the ninth and tenth pairs, and from the sympathetic. Its respiratory function is purely a passive one, while what may be termed its alimentary function is an active one, to assist in deglutition. (ESOPHAGUS. The oesophagus, or gullet, is a long musculo-membranous cylindrical canal, passing from the pharynx to the stgmach, through which the food reaches the latter. Originating at the lower part of the pharynx, immediately beliiiul th^ aperture of the lirynx, it descends the iipck, at lirst b.hind the tnu-liea, then incliues to the. left of it, the two entiiiiig the tboiax together; it (ESOPHAGUS. 299 then passes lo tlio upper bide of the trachea, over the base of the heart, through the posterior mediastinum, and through the diaphragm by the foramen sinistrum; it thus gains the abdom- inal cavity, and terminates in the cardiac orifice of the stomach. It is narrowest at its origin behind the larynx, then of uniform size until it reaches the diaphragm", where it again constricts. The oesophagus may be said to consist of a cervical, a thoracic, and an abdominal portion, the latter being very short. It con- sists of two tunics, an internal mucous and an external muscular, which are very loosely united by areolar tissue. The mucous coat is continuous with that of the pharynx and stomach, but is pale in colour, and clothed with dense stratified epithelium ; it presents numerous longitudinal folds, which allow of considerable dilatation, and a number of racemose glands. The muscular coat consists of an external longitudinal, and an internal circular layer of fibres. The cervical and anterior thoracic muscular coat :! striated, the remainder non-striated, but both are involuntary. The longitudinal layer commences by three fasciculi, one in front and one on either side, which unite to form a continuous layer. The circular fibres originate at the inferior constrictors of the pharynx. Posteriorly, both sets of fibres pass to the muscular coats of the stomach. The oesophagus is supplied with blood anteriorly by twigs from the carotid, and the broncho-cesophageal arteries posteriorly; its nerves come from the pneumogastric. The oesophagus has no other use than for the conveyance of aliment from the pharynx to the stomach. Its most noteworthy features in the horse are, — first, the abrupt manner in which it enters the stomach, hardly dilating at all before doing so ; secondly, the enormous proportionate size of its mucous membrane posteriorly ; this is so large, that near the stomach its folds completely fill the tube when empty, thus acting as a valve, and preventing regurgitation of the food. The process of deglutition, or swallowing the food, is performed in the following manner : — The masticated food gathers as a bolus at the root of the tongue, which by retracting forces the pellet through the isthmus faucium into the pharynx ; the velum pendulum palati recedes backwards and upwards, while the food forces down the epiglottis, effectually closing the larynx; finally, the pharynx, by its constrictor muscles, grasps the bolus, a-nd presses it downwards into the oesophagus. » The passage of food 300 SPLANCHNOLOGY. into the pharynx is purely voluntary ; but as soon as it enters the oesophagus, the act of deglutition is entirely involuntary, the food travelling by a vermicular or peristaltic motion, caused by the circular muscular fibres of the oesophagus contracting with successive regularity. ABDOMEN. The ultimate organs of digestion are contained in the abdomen, or belly, v^hich is a large and somewhat ovoid cavity, bounded superiorly by the muscles of the sublumbar region ; inferiorly and laterally by the abdominal muscles ; and anteriorly by the dia- phragm ; posteriorly it is continuous with the pelvic cavity. It contains chiefly the stomach, intestines, and hidneys, with their acccf^sories. It is lined by the peritonei'^m, a serous membrane^ which is reflected over the viscera. For convenience of description, the abdomen 12 divided into nine regions, indicated by imaginary lines drawn as follows : — • Two transverse lines divide it into three primary regions. The first line is drawn from the cartilage of the last false rib on one side, to that of the other ; the second unites the right and left anterior iliac spines. These divide the cavity into the anterior or epigastric, middle or umbilical, and posterior or hypogastric regions. These regions are each subdivided into three secondary, or right, left, and central regions, by two longitudinal lines, extending from either side of the ensiform cartilage to about the ilio-pectineal eminences, completing the division, which may he tabulated as follows : — Right. Centbal. Left. Anterior. Middle. Posterior. Ptight Hypochon- driac. Right Lumbar. Right iliac. Epigastric. Umbilical. Hypogastric. Left hypochon- driac. Left Inmoar. Left iliac. The portion of the alimentary canal contained in the abdomen comprises the stomach and intestines. I STOMACH. 301 STOMACH. The stomach is a dilatation of the alimentary canal, continuous with the oesophagus and small intestine, where the food is con- verted into chyme, by maceration and the action of the gastric juice. In the horse it is small in proportion to the size of the animal, and rests in the left hypochondriac region, stretching when full into the epigastric ; when distended, it resembles a bent tube with two lateral dilatations, divided by a central constriction into a left, or cardiac, and a right, or pyloric portion. The former is Fig. 98. Posterior view of the stomach of a Horse, a, Left cul-de-sac; 6, Right eul-de-sac ; c. Greater curvature ; d. Lesser curvature ; e, (Esophagus ; /, Duodenum. the larger, and called the greater cul-de-cac, or fundus; the right portion, is the lesser cul-de-sac, or antrum pylori. It has one opening on the left, leading into the cesophagus, through which the food enters; this is the cardiac orifice; and another on the right, which communicates with the first portion of the intestine called the duodenum ; this is the pyloric orifice. At the pyloric orifice there is a constriction called the pyloric ring. Between the two openings the upper and lower borders are termed the curvatures, the superior or lesser being concave, the inferior or greater convex. The curvatures indicate the division of the surface of the stomach into two portions, an anterior and posterior. The 302 SELANCH2TCL0aY. anterior is related with the diaphragm and liver, the posterior with the diaphragmatic flexure of the colon. The spleen lies along the inferior and external part of the greater cul-de-sac, its base being directed backwards and somewhat upwards ; the pyloric extremity, which is placed lower than the cardiac, is related with the right lobe of the liver and the intestines. The walls of the stomach are composed of three coats — an external serous, a middle muscular, and an internal mucous coat. The serous coat, a reflection of the peritoneum, is smooth and elastic, adhering intimately to the muscular, except at the lesser curvature, where, strengthened by addition of yello^w elastic tissue, it forms a ligament, which appears to support the two extremities of the stomach ; forming around the cardiac orifice a circular fold, which surrounds the oesophagus and passes to the dia- phragm ; this is the gastro-phrenic, or coronary ligament The peritoneum also passes in a double fold from the greater curvature to the spleen, as the gastro-splenic, to the colon as the gastro-colic, or great omentum ; and from the lesser curvature to the liver, as the gastro-hepatcc omentum. In the muscular coat are three sets of fibres — an external longitudinal, a middle circular, and an internal oblique layer. The longitudinal are continuous with those of the oesophagus, and radiate from the cardiac orifice ; they are thickest at the curvatures, and are thinly scattered over the surfaces ; towards the pyloric end they again converge, and form a uniform layer, which is continuous with that of the duodenum. The middle layer consists of circular fibres, which cover the entire organ ; near the pylorus they thicken into a circular ring, which projects into the orifice, and forms with a doubling of the mucous mem- brane, a sphincter, called the pyloric valve, which by contraction prevents crude food from passing into the intestine. The inner layer, is composed of oblique fibres, continuous with the circular oesophageal ones ; they are confined to the cardiac portion, descend obliquely over either surface, and disappear towards the central constriction. All these layers are composed of pale or involuntary tissue; the longitudinal layer, by contracting, enables the stomach to dilate ; the circular produces vermicular motion, while the obliqa.3 layer tends to force the food from the left into the right cavity ; thus there is produced a kind of churning motion, which macerates the food and brings each portion of it into contact with thp; rnucoiis curfrxe. STOMACH. 303 The internal, or Tnucous coat, is divided into right and left portions. The latter is the cuticular portion, continuous with the mucous membrane of the oesophagus, which it resembles in structure and appearance; it is covered by a thick layer of stratified epithelium. The line of demarcation between the two portions is abrupt and dentated. The right portion, the villoTis, or true digestive coat, is reddish in colour, soft, very vascular, and velvety-looking. When examined with a lens, it appears honey-combed, or covered by small shallow polygonal depressions or alveoli, separated from each other by projecting intervals. Fig. 99. Internal aspect of Horse's stomach, opened ifrom below, a a, Cuticular mucous membrane ; bb. Villous mucous membrane ; c c c, Line of demarcation between the two portions ; d, Cardiac orifice ; «, Pyloric orifice and valve. Into these alveoli the gastric follicles open ; the latter lie in the subepithelial tissue, perpendicular to the surface of the mem- brane ; at the pyloric end some of these foUiqles terminate in dilated sacs, or divide into two or more tubes. They consist of a basement membrane, lined by columnar epithelium ; some of them secrete gastric juice, others mucus ; the latter are lined throughout with epithelium, while the gastric juice follicles have their lower part filled with nucleated cells and granules. The villous coat is also covered with numerous simple or lenticular follicles. The mucous membrane, when the organ is empty, is thrown into folds, or inigce, which are very well seen in the villous por- 304 SPLAl^CHNOLOGT. tion, where they do not entirely disappear on inflation. The cardiac orifice is closed by the mucous membrane of the oeso- phagus ; its numerous folds completely filling that tube at its termination when empty ; the valve thus formed is air-tight. The arteriei^ of the stomach arise from all the branches of the coeliac axis ; they are the gastric, the left gas tro- epiploic from the splenic, and the right gastro-epiploic from the hepatic ; the blood is returned by satellite veins which join the vena porta. The nerves are from the pneumogastric, and solar plexus of the sympathetic. The use of the stomach is to macerate the food by the action of its muscular walls, and also to saturate it v/ith mucus and gastric juice, the latter containing a principle called pepsine, which acts chemically on albuminous matters. The entire operation is called chymiflcaiion, and the food thus prepared the chyme. ; ' THE INTESTINES. These are divided into the large and small ; the two however form a continuous musculo-membranous tube, the small intestine being likewise continuous with the stomach at. its pyloric orifice. These organs are tortuous in their course, and in herbivorous animals are long and capacious. SMALL INTESTINE. The small intestine commences at the pylorus, and terminates, in the caecum. It consists of a cylindrical convoluted tube, rather more than an inch in diameter, and about seventy-two feet in length. It presents two curvatures, the greater one, convex and free, the lesser concave and attached to the mesentery, by which it is suspended from the roof of the abdomen, occupying the central region, and partly surrounded by the large intestine. It is arbitrarily divided into the Duodenum, the Jejunum, and the Ileum. The duodenum, continuous with the pylorus, is the only fixed portion of the small intestine. In the horse it is short, present- ing a dilatation at its origin resembling a miniature stomach, with its curvatures disposed inversely to those of the stomach itself. On leaving the pylorus it runs forwards, then backwards, forming an abrupt curve. It now crosses from right to left, and r SMALL I2TTEST1NE. 305^ becomes the jejunum at tlie level of the anterior mesenteric artery. The first portion iz more free than the latter. At from four to five inches from the pylorus is the opening by which the ducts of the liver and the pancreas enter the intestine. The. jejunum succeeds the duodenum, and includes about two-fifths of the remainder of the small intestine, the ileum constituting the rest ; both are floating — i.e., they are attached to the free edge of the mesentery. The ileum terminates, in the right iliac region, in the large intestine. Fig. 100. The two mesenteries; the great colon being removed, a, Anterior mesenterj* : h ft. Mesenteric glands ; ccc. Loops of the small intestine ; d, Colic mesentery ; e e e. Loops of the floating colon : /, Sphincter ani— internal layer ; g, Levator ani. The walls of the small intestine, in common with all- hollow viscera of the abdomen, consist of an external serous, a middle muscular, and an internal mucous coat. The two latter are joined by areolar tissue, which is sometimes regarded as a submucous coat. The serous coat envelops the intestine, except- ing just at its attached border, where the two folds join and form the mesentery. The muscular coat consists of two layers of fibres, an outer longitudinal, which is very thin, especially at the attached border, and an inner circular one, which is thicker ; both are pale, and involuntary. The mucous coat is soft, spongy, reddish, and vascular, covered X 306 SPLANCHNOLOGY. by numerous minute villi and follicular openings, the whole being clothed by columnar epithelium. It is thrown into folds when empty, which usually disappear when it is dilated ; these •are known as valvulce conniventes. INTESTINAL GLANDS. The mucous membrane of the small intestine is furnished with glands and absorbents. Besides the mucous follicles, we note the following glands :■. — Glands of Brunner. I Payer's patches, Crypts of Lieberkiihn. | Solitary glands. The glands of Brunner j which are small glands, resembling the acini of the salivary glands, are found in the duodenum. The crypts J or follicles of Lieherkilhn, are very small, and are found throughout the intestines, between the villi and around the larger glands. The glands or patches of Ftyer, are oval or circular groups of solitary glands, forming agminated glands, and are found in the jejunum and ileum ; they are most numerous near the termination of the ileum. Each gland is a simple vesi- cular ductless sac, containing a lym- phoid material. Single sacs, similar to those forming Beyer's patches, called solitary glands, are scattered throughout the intestines, and sur- rounded by Lieberkuhn's crypts, which form round each gland a ring known as the corona tubulorum. The absorbents originate in the villi, which are small, finger-like, vascular processes, thickly distri- buted over the mucous surface ; they consist of loops of the lacteal or chyle vessels, surrounded by a net-work of capillaries, fine muscular fibres, and small gran- ular corpuscles, with a mucous layer covered by columnar epithelium. The small intestines are supplied with blood by the anterior mesenteric and duodenal branch of the hepatic arteries, the blood being returned by the satellite veins to i'lo. 101. Section of mucous membrane of the small intestine. Ou the left a villus is seen in section, a, The epithelial covering ; c, The blood-vessels ; d, The basement membrane, or subepithelial layer; e, Spaces for re- ception of the chyle ;/, Origin of a lacteal vessel. On the right- is a follicular depres- sion in the mucous membrane, with b. The cells lining it ; and c. The subepithelial layer. r CJE.CTJU. 3a7 the portal system. The lymphatic vessels of the small intes- tine are distinctively known as the lacteal vessels, and they convey away the chyle absorbed by the medium of the villi. The nerves are from the solar plexus. The vessels and nerves gain or l3ave the small intestine by passing between the two folds of peritoneum which form the mesentery. In the duodenum the chyme becomes saturated with the bile and pancreatic juice, the change thus induced being termed chyliUcation or conversion of the chyme into chyle. In the rest of the intestine we note the absorption of the chyle by the lacteals, th3 final preparation of the food by the various gland secretions, and the reabsorption of the bile by the blood-vessels. Chyle is a milky-looking fluid, its turbidity being due to the presence of an immense number of minute granules. It contains also the chyle A.^«3:.^ Fl3. 102. A, Microscopic appearance of a drop of chyle from the thoracic duct; c, Granular base; 6, Fatty particles; c, Chyle corpuscles ; 3, Isolated corpuscles showing the cell- membrane ia its developing stages, ah c d. corpuscles, which are nucleated sacs resembling those of the lymph, or the colourless corpuscles of the blood. LARGE INTESTINE. The large intestine extends from the termination of the ileum to the anus, and may be regarded as consisting of four parts, which will be described in order : the Caecum, the Great colon, the Floating colon, and the Rectum. C^CUM. The caecum, blind intestine, or caput ccecum coli, is a large cul-de-sac, commencing in the right iliac region, passing obliquely downwards and forwards, and terminating in the left hypochon- driac region by a pointed, blind extremity ; thus it crosses 308 SPLANCHNOLOGY. obliquely the middle line of the abdominal floor. It measures about thirty-six inches in length, and its capacity may average six gallons. It is somewhat conical in shape, and curved at its supero- posterior extremity, presenting on its outer surface a number of circular constrictions, and certain longitudinal muscular bands, of which there are four about the middle. The superior extremity is called the base or arch, and presents a convex curvature directed backward, and a concave one forwards. In the concave curvature the ileum terminates, and there also the large colon originates. The middle part of the caecum is related with the small intes- tines, the apex being free, and prolonged to the sternum. It is fixed to the abdominal wall posteriorly by cellular tissue, and to the origin of the colon by a double fold of peritoneum, called the meso-csecum. The interior of the caecum presents a number of transverse ridges, corresponding to the external transverse constrictions. Two orifices, placed one above the other, are found in its concave curvature; the inferior one marks the termination of the ileum, and is guarded by the ileo-ccecal valve, which is formed by a doubling of the mucous membrane, within which is a band of muscular fibres. The superior opening communicates with the colon. The caecum has three coats, serous, muscular, and mucous, the latter being thicker than that of the small intestines, and having neither Brunner's glands nor Peyer's patches. The folli- cles of Lieberkiihn, solitary glands, and a few scattered villi are however present. GREAT COLON. The great or double colon originates from the caecum, and ter- minates near its origin, in an abrupt contraction, whence arises the floating colon. Taken out of the abdomen, it appears as a voluminous tube, with successive dilated and constricted portions; like the caecum, it is marked throughout by longitudinal bands and transverse furrows. It measures, on an average, from nine to eleven feet in length, and sometimes has the capacity of eighteen gallons. It is doubled on itself, forming two branches of equal | length, placed one on the other, and so disposed that the terminal end is near the origin. When in situ, the doubled portion forms a curve whose convexity is directed forwards, and corre- spondc to the walls of the abdomen, thus forming four divisions, a right and left being above, and a right and left below, with r GREAT COLON. 309 threo Jlezuvea or c^.n^ls. Iq treeing its courcs, these four divisions present themsshes tbus. Leaving the arch of the csecum in the right lumbar region, it passes obliquely forwards to the posterior surface of the diaphragm in the epigastric region, v/here it turns round to the left, forming the first or sternal fiexure. Here the second division originates, and in contact with the inferior ab- Fia. 103. Caecum and Great Colon of a Ilor;3. a,5C3ecum ; h, c, Its muscular bands ; d. Termination of the' ilcura ; e. First, e', Second, /, Third, and /', Fourth division of colon ; g, Pelvic flexure ; ft, Origin of Floating Colon. The arrows indicalcj the course of the food through the colon. the posterior surface, which they cover, meeting at thef posterior fissure to form the gastro-hepatic or lesser omentum, which proceeds from the liver to the lesser curvature of the stomach. The two layers now cover the stomach, form the coronary ligament round the oesophagus, and again meet at the greater curvature, forming on the left the gastro-splenic omentum, and passing to the hilus of the spleen, which is covered by them. On the right the two layers form the gastro-colic or great omentum ; these cover the colon and advanco upward towards the vertebrae, forming the meso-colon and meso-caecum. RESPIRATORY SYSTEM.'- ' 32S The two layers now separ^^te ; the superior passes forwards along the roof of the abdomen, and again returns to the posterior part of the diaphragm. The inferior layer descends to and envelops the small intestines, and returns to the abdominal roof, the douMe layer constituting the mesentery. It now passes back- T^ards to the iliac region, where it again descends to suspend the floating colon and the rectum, forming the colic mesentery and meso-rectum by returning upwards. In the pelvis it forms the recto- vesical ligament, between the bladder and rectum, finally returning along the inferior parietes of the abdomen to the diaphragm. In the female, ' the peritoneum, after leaving the rectum, passes to the anterior surface of the vagina and uterus, forming the broad ligaments. On the abdominal floor, stretching forwards in the median line from the umbilicus to the quadrate lobe of the liver, is the broad ligament of the latter, and in a similar manner, passing backwards to the fundus of the bladder, we find also a broad ligament. Neither of the latter structures are well marked in the adult, especially the last. Respiratory System. By the action of these organs certain chemical and physical changes take place in the blood, the chief of these consisting in absorption of oxygen from, and giving off carbonic acid to, the atmospheric air, the former change being necessary for the elaboration of the fluid, the latter for the elimination of a sub- stance which, if retained, would prove prejudicial. The organs of respiration are invariably adapted to the wants of the animal iind the medium in which it lives. Thus, insects breathe by air- tabes, opening on the surface of the body; in the oyster breath- ing is performed by fringes ; in fishes by gills ; in the mammalia by means of elastic air-receptacles, called lungs, which are enclosed in special cavities, and communicate with the atmos- phere by means of an air-tube. In the horse, who breathes only through his nose, the organs of respiration are the Nostrils, Nasal Chambers, Pharynx, Larynx, Trachea, and in the thoracic cavity the Bronchi, Bronchial tubes, and Lungs. THE NOSTRILS. The nasal openings, or nostrils, are two, right and left, oblong openings, situated in the anterior part of the face at the 324 ^LANCHNOLOGY. extremity of the nasal chambers, and disposed obliquely from above downwards, and without inwards, being slightly curved so as to present their concavities externally. The nostrils consist of an incomplete cartilaginous skeleton covered by muscles, and lined internally by mucous membrane. They are bounded by movable wings, or alee, which are covered within and without by a thin delicate skin, clothed with fine soft hairs. The external wing is concave on its free border, the internal being convex, the commissures of the alse are a superior and an inferior. The finger introduced into the superior commissure does not enter the nasal cavity, but a conical cul-de- sac, the false nostril, a diverticulum of the nose. This cavity is formed by the skin, and lies in the * space between the nasal peak and the external process of the premaxillary bone. The false nostrils communi- cate freely with the nasal chambers ; their precise use is unknown, but they probably enlarge the nasal openings during respiratory exertion. The inferior commissure is large and round, presenting, at a short distance within, an opening, some- times double, which is the inferior orifice of the lachrymal conduit. In the ass and mule this opening is situated on the deep surface of the external ala near to the superior Fio. 110. Cartilaginous framework of the nostril — seen fronr^abOTe. a a. Right alar carti- lage ; a' a'. Left alar cartilage ; b. Termi- nal portion of the septum nasi. commissure. Each of the alar cartilages resembles an incomplete ring, the incomplete portion being directed outwards. They are loosely attached to the anterior extremity of the septum nasi and to each other, and they serve to keep the nostrils open, permit dilatation, and protect the nasal peak. They are divided into a superior and inferior part. The former is large and flat, and situated within the substance of the internal ala, being covered by the dilatator haris transversalis. The inferior part is prolonged by a blunt point to the external ala, to which the orbicularis oris, dilatator naris lateralis, and levator labii superioris alaeque nasi are attached. The skin which covers the NASAL CHAMBERS. 325 nostrils is very thin, containing a quantity of pigment, or colouring material. It is continuous with the mucous membrane of the interior, and adheres to the muscles by dense fibro-cellular tissue. The blood-vessels are the superior coronary, nasal, and palato- labial arteries and veins. The nerves are derived from the fifth and seventh pairs. In the horse the power of dilating the nostril attains its maximum. The use of the nostril is to give passage to the air in inspiration and expiration. NASAL CHAMBERS. These are cavities extending from the cribriform plates of the ethmoid bone to the nostrils, in a direction parallel to the long axis of the face, and are separated from each other by the cartila- ginous septum nasi, which in age undergoes partial ossification, and is attached postero-inferiorly to the groove of the vomer. Being continuous with the perpendicular plate of the ethmoitl, superiorly it rests in a groove formed by the union of the nasal bones, thus preventing any communication between the chambers. Anteriorly, it is expanded and attached to the alar cartilages of the nostrils. The interval wall of the chambers is smooth, and formed by the septum nasi ; the external, which is irregular, is chiefly formed by the superior maxilla. The roof is formed by the nasal and part of the frontal bones. The floor, broader and shorter than the roof, is completed by the palatine process of the superior maxilla and the palatine bones, and is concave from wall to wall. The anterior extremity contains the nasal openings. The posterior is occupied above by the cells of the ethmoid ; below is the oval opening common to the 'postemor nares, which communicate with the pharynx. Each chamber is divided by the turbinated bones into three passages, or meati ; the superior lies between nasal and frontal bones above, and the superior turbinated bone below; the middle between the two turbinated bones, reaching to the cribriform plates of the ethmoid bone ; while the inferior is between the inferior turbinated bone and the floor of the chamber. The nasal chambers are lined by a delicate, pale rose-coloured mucous membrane, the pituitary or Schneiderian membrane, which is continuous with the skin at the nostrils, the mucous 326 ; SPLAKCHNOLOGY. membrane of the pharynx, and with that lining the sinuses of the head , and, in some animals, with the conjunctiva, by the lach- rymal duct. It is attached, and sometimes inseparably, to the perichondrium of the septum and the periosteum of the bones. The pituitary membrane is sensitive, varying in vascularity and thickness, being most vascular on the septum and turbinated bones, and thinnest in the sinuses; its free surface is smootb, and covered by epithelium. Near the external opening the epithelium is scaly, the remainder ciliated. It is studded with numerous follicles or crypts, which secrete mucus to keep the surface moist, preserve its sensitiveness, and defend it from noxious vapours. The blood-vessels come from the lateral nasal Fig. 111. Longitudinal section of the head, showing the pharynx and nasal chamber— the septum rasi being removed, a, Superior turbinal ; 6, Inferior turbinal ; c, Superior, d, Middle, and e. Inferior nazal meatus ; /, Cavity of the piarynx ; g, Opening of Eustachian tube ; h, Isthmus faucium ; i, Posterior naris ; k, Opening of the larynx ; I, Opening of the oesophagus. and spheno-palatine arteries. The nerves are the first or olfac- tory pair, or nerves of the special sense of smell, and certain branches of the fifth. The canal of Jacobson in the horse is a blind canal, with its orifice on the floor of the nasal chamber about the incisive opening; it runs backv/ard for about four inches, being related with the septum nasi. Its use is unknown. Each nasal chamber communicates with four distinct sinuses — Frontal, Maxillary, Ethmoid, and Sphenoid. The maxillary sinus is divided into two ; the anterior cavity, often called the inferior maxillary sinus, is generally isolated from the rest. (See p. 44.) The sinuses are lined with mucous membrane, and contain air. The uacal chambers give passage to the respir'^d LARYNGEAL CARTILAGES. 327 air, and are at the same time concerned in the special sense of smell. The pharynx has been described with the digestive organs. (See p. 296.) LARYNX. This is a complex musculo-cartilaginous valve, situated at the anterior extremity of the windpipe. It gives passage to air, and at the same time is the organ of voice. The anterior extremity opens into the pharynx ; the posterior is continuous with the trachea. It lies at the posterior part of the maxillary space, is directed obliquely from above downwards and backwards, being suspended below the os hyoides, and united by one of its cartilages to the extremity of the heel process on either &ide. It is attached to the pharynx by muscles, and partly supported by the trachea. LARYNGEAL CARTILAGES. The cartilages which form the larynx are seven in number, three single ones, and two pairs. The former are the Cricoid, Th3Toid, and Epiglottis ; the latter, the Arytenoid and Cuneiform cartilages. The cricoid, or ring-like cartilage, is situated at the base of the larynx, surrounding the air passage. It is narrow and convex infero-anteriorly ; deep and broad postero-superiorly. It presents two surfaces and two borders. The internal surface is smooth, and covered by mucous membrane; the external one postero- superiorly presents in the medi;ui line a longitudinal ridge, to which are attached a few longitudinal fibres of the oesophagus. On either side of the ridge is a broad concavity, in which rests the crico-arytenoideus posticus ; while on each side of the con- cavities is a small protuberance for articulation with the posterior cornu of the thyroid cartilage. The superior border bounding the oval orifice is directed obliquely upwards and backwards, and comprised between the two branches of the thyroid. On either side of this border is a smooth, convex surface for articulating with the arytenoid cartilages. The inferior border is level, and encircles the upper part of the first ring of the trachea, to "which it is attached. The thyroid, or shield-like cartilage, is tlie largest in the 328 SPLANCHNOLOGY. Iar3'nx. It consists of two lateral expansions or alae, which meet and unite antero- superiorly at a rather acute angle, forming a projection called the body of the thyroid, equivalent to the pomum Adami in man. Its inferior surface is smooth, giving attachment to a tendon of the sterno-thyro-hyoideus. On the superior surface is a blunt, irregular protuberance, with which the epiglottis articulates. The alaB are quadrilateral, slightly convex externally, and clothed by the attachments of the hyo- thyroid and thyro-pharyngeal muscles. They are slightly concave internally, and covered postero-superiorly by mucous membrane. From the angle of the wings anteriorly and internally spring the thyro-arytenoideus muscles, the thyro-arytenoidean ligaments or vocal cords, and the tbyro-epiglottidean ligament ; to the inferior border the crico-thyroid ligament is attached, to the superior the hyo- thyroid ligaments. Posteriorly, each wing terminates in two cornua. The superior inclines upw^ard,. and is attached by fibro- cartilage to the extremity of the heel process of the os hyoides ; the inferior, the larger and more prominent, articulates with the small protuberance on the posterior surface of the cricoid cartilage. The arytenoid, or ewer-shaped cartilages, a pair, lie upon the cricoid, and bound supero-posteriorly the entrance of the larynx. They are irregularly pyramidal, each presenting two surfaces, four borders, and an apex. The internal surface is smooth, and covered by mucous membrane ; the external is divided by a ridge into two portions; a superior which is covered by the arytenoid muscle, and an inferior which receives the attachment of the crico- arytcuoideus lateralis and thyro-arytenoideus. The inner border unites with its fellow; the posterior one, forming the base, is turned backwards, and receives the attachment of the crico-arytenoideus posticus the outer angles articulating with convexities on the side of the superior border of the cricoid cartilage. The anterior border is thick, and covered by mucous membrane, while the inferior border receives the insertion of the vocal cords. The apex formed in front by the junction of the two arytenoids is prolonged by two pieces of fibro-cartilage, t'.e corniciila laryngis, which pass outwards and backwards, forming a spout or lip, in which rests the epiglottis, when the larynx is closed. The epiglottis is a soft, leaf-like cartilage, flexible, and situated in front of the opening of the larynx, which it completely closea during the passage of .food through the pharynx into the oeso« LARYNGEAL LIGAMENTS. S29 phagus. Ics anterior surface, somewhat convex, is attached to the tongue, by the glosso-epiglottidean ligaments, and to the hyoid bone by the hyo-epiglottidean muscle. The posterior surface is rough, and studded with numerous mucous glands. The base articulates with the posterior part of the body of the thyroid. The apex is free, and somewhat curved forwards. From the base of the epiglottis, two lateral processes extend backwards : these are the cunieforni cartilages, and they are situated in the folds of mucous membranfe which stretch from the epi- glottis to the arytenoid cartilages, being attached to the latter by elastic ligaments, together forming the false vocal cords. Fia. ir:. ~ Posterior view of tlie epiglottis. a, Base ; 6 &, Cuneiform cartilages; c. Summit ; d d. Lateral borders. LARYNGEAL LIGAMENTS. The liganients connected with the larynx are extrinsic and intrinsic. The extrinsic ones are as follows : — Lateral Hyo-thyroid. Middle Hyo-thyroid. Hyo-epiglottidean. Crico-trachealis., The, lateral-hyo- thyroid pass from the superior border of the thyroid cartilage to the heel process of the os hyoides. The ^middle hyo-thyroid ligament is a broad membrane, filling up the space between the anterior border of the thyroid cartilage and the heels and body of the os hyoides. The hyo-epiglottidean ligament is a band of yellow elastic tissue, running -between the base of the epiglottis and body of the os hyoides, covered by the hyo-epiglotti- dean muscle. The crico-trachealis }om?i the cricoid cartilage to the trachea. The intrinsic ligaments are : — Thyro-epiglottidean. Arytenoidean. Crico-arytenoidean. Crico-thyroidean. Thyro-ary tenoidean . The thyro-epiglottidean ligament binds the base of the epi- glottis to the superior border of the thyroid cartilage. The arytenoidean ligament joins the two arytenoid cartilages together. 330 SPLANCHNOLOGY. The crico-arytenoidean ligaments connect the outer angles of the arytenoid with the superior border of the cricoid cartilages. The crico-thyroidean ligaments, three in number, connect the cricoid and thyroid cartilages ; they consist of an anterior or broad one, and two lateral ones attached to the posterior extremities of the thyroid wings. The thyro-arytenoidean ligaments are likewise known as the ^?n/.e voccd cords, and they stretch from the inner aspect of the angle of the thyroid cartilage to the base of the arytenoid carti- lages. The superior aper- ture of the larynx, which, when open communicates with the pharynx, is some- what oval, and bounded anteriorly by the epiglottis, posteriorly by the arytenoids and cornicula laryngis, later- ally by the false vocal cords. Inside itbecomes constricted, leaving a narrow triangular fissure running antero-pos- teriorly, and bounded later- ally by folds of mucous membrane, in which lie the thyro - arytenoid ligaments or true vocal cords. The narrow opening of the lar- ynx between the right and left vocal cords is called the rUna gloitidifi, or ylottis, and is wider posteriorly from tlie divergence of the cords. Between the true and false vocal cords, on either side, is a deep ovoid fossa, the lateral sinus or ventricle of the larynx ; at the base of the epiglottis is a third, small, blind depression, the middle ventricle. The inferior opening of the larynx which communicates with the trachea is nearly circular. Fia. 113. ' Larynx, hyoid bone, and commencement of trachea— posterior view. 1, Epiglottis ; 2, Left ary- tenoid ; 3, Posterior ridge of cricoid cartilage. Liga- ments— /-t, Hyo-epiglotti- dean ; b, Thyro-epiglotti- rtean ; c, Arytenoidean ; d d, Crico-arytennidean ; « e. Lateral crico-thyroi- dean — the epiglottis is fastened down. Fig. 114. Larynx, hyoid bone,, and commencement of trachea— anterior view. 1, Thyroid, 2, Cricoid car- tilages. Ligaments— a, Hyo-thyroid ; a', Lateral portion of the same ; h, Crico-thyroidean ; c, Crico-trachcalis. LARYNGEAL MUSCLES. 351 LARYNGEAL MUSCLES. The muscles of the laryax are extrinsic, or those' arising from neighbouring parts, and intrinsic, or those acting between the diflferent cartilages. The extrinsic muscles are three in number : — Sterno-thyro-hyoideus. | Hyo-thyroideus. Hy o-epigl ottideus. STERNO-THYRO-HYOIDEUS. (See page 179.) HYO-THYROIDEUS. ^FiG. li5. 0.) This is a triangular muscle, its fibres running backwards and downwards. Origin. — The inferior border of the heel process of the os hyoides. Insertion. — To a line on the external side of the wing of the thyroid cartilage. Action. — To depress the os hyoides, or elevate the larynx. HYO-EPIGLOTTIDEUS. (Fig. 115. a.) Single and fusiform, this muscle is usually enveloped in adipose tissue. Origin. — The middle of the body of the os hyoides. Insertion. — The inferior part of the anterior surface of the epiglottis, covered by the mucous membrane. Action. — To draw the epiglottis forward, and thus open the larynx. The intrinsic muscles consist of four pairs and one single muscle, as follows : — Crico-thyroideus. Crico-arytenoideus lateralis Crico-arytenoideus posticus. Thyro-arytenoideus. Arytenoideus. 332 SPLANCHNOLOGY. CRICO-THYKOIDEUS. (Fig. 115. e.) This is a small muscle whose fibres run upwards and backwards. Origin. — The external surface of the cricoid cartilage. Insertion. — To the posterior border of the thyroid cartilage. Action. — To shorten the larynx by drawing the two cartilages together. CRICO-ARYTENOIDEUS POSTICUS. (Fro. 116. 6.) The most powerful of the intrinsic muscles, this is situated on the infero- posterior aspect. Origin. — The cavity on the poste- rior surface of the cricoid cartilage, whence its fibres converge upwards and outwards. Insertion. — To the posterior tuber- cle of the arytenoid cartilage, covered by the oesophagus and crico-pharyngeus muscle. Action. — To dilate the entrance of the larynx, and also the glottis by separating the vocal cords. Fxa 115. Muscles of tbe larynx— left lateral view, a, Hyo-epiglottideua ; b, Hyo- thyroideus ; c, Crico-tbyroideus. CFIICO-ARYTENOIDEUS LATERALIS. (Fig. 116. c.) This muscle is triangular in shape, and lies between the wing of the thyroid and the arytenoid cartilage. Origin. — The side of the anterior border of the cricoid cartil- age, passing upwards. Insertion. — To the outer tubercle at the base of the arytenoid cartilage outside the posticus. Action. — To contract the opening of the larynx, and thus antagonise the posticus. LARYNGEAL MUSCLES. S33 THYRO-ARYTENOIDEUS. (Fig. 116. d.) Situated on the inner side of the wing of the thyroid cartilage, it consists of two bundles, separated by the ventricle of the glottis. Origin. — From the inner surface of the angle of the thyroid cartilage, outside of the vocal cord. Insertion. — To the middle line at the junction of the arytenoid cartilages. (Action. — To constrict the glottis. By its relation with the vocal cord this muscle powerfully influences the tension of the same, and consequently the voice. ARYTENOIDEUS. (Fig. 116. a.) This muscle, the smallest of the group, is single; and situated upon the arj^tenoid cartilages, stretching from one cartilage to the other, the fibres intercrossing in the median line. Action. — To approximate the cartilages, and thus constrict the glottis. Fig. 116. Muscles of the larynx — left lateral view— the thyriid wing being removed. a, Arytanoideus ; h, Crico-aiy- tenoideus posticus ; c, Crico- arytenoideus lateralis ; d. Thyro-arytenoideus. The mucous membrane is continuous with that of the tongue and pharynx, forming, from the tongue to the epiglottis, the glosso- epiglottidean folds. It is reflected over the posterior face of the epiglottis to the anterior part of the arytenoids, covering the lateral boundary of the laryngeal opening. In these folds lie the cuneiform cartilages. It thus passes over the false vocal cords, lining the ventricles, and returning over the true vocal cords ; it clothes the inner surface of the cricoid cartilage and middle of the crico-thjrroid ligament, and so is prolonged into the trachea. It is very thin, and exqui- sitely sensibive, especially about the glottis ; it is covered with ciliated epithelium, and studded with mucous glands, which moisten it and preserve its sensitiveness. The glands are h $34 SPLANCHNOLOGY. Fio. 117. Cviitj of the larfnz— opened posteriorly, a a. Lateral ventricles of the larynx ; b, Middle Tentrlde ; c c, True vocal cords. numerous on the posterior as- pect of the epiglottis, in front of the arytenoids, and in the laryngeal ventricles. The larynx is supplied with blood from the laryngeal arteries. The nerves are from the superior and inferior laryngeal branches of the vagus ; twigs also come from the sympathetic. The larynx gives passage to the air of respiration, prevents the intrusion of food into the air-tubes by closure of its lid, the epiglottis ; and it contains the organ of voice, the latter being produced by vibration of the true vocal cords. TRACHEA. The trachea, or windpipe, is a nearly cylindrical, and flexible tube, consisting of a series of incomplete cartilaginous rings. It succeeds the larynx, runs down the neck, enters the thorax, and terminates at the base of the heart, where it divides into the right and left bronchi. Like the neck, it varies in length, and consists of forty or fifty rings, the ends of which overlap pos- teriorly, forming a perfect expansile tube. It presents a number of transverse furrows, which correspond to the interspaces between the rings. The latter vary in depth, averaging half-an-inch, and they are completed and united by strong elastic ligaments. The first is attached to the cricoid cartilage by a band called the crico-trachealis ligament The ligaments contain involuntary muscular fasciculi, and they are attached by their extremities to th© inner and posterior surface of the .rings, and to their ends, so completing each ring. The entire trachea is lined by mucous membrane, which is continuous with, but not so sensitive as that of the larynx ; it is clothed with ciliated epithelium, and studded with glands. The trachea is related with the oesophagus and carotid arteries, the latter running along its sides. The arteries supplying the r BRONCHI BRONCHIAL TUBES. 335 anterior and middle parts, consist of twigs from the carotid ; posteriorly the supply comes from the broncho-cesophageal ; the nerves are derived from the recurrent and sympathetic. THYROID AND THYMUS GLANDS. About the two first tracheal rings is the brownish-red, th3rroiLl body, consisting of two lobes, right and left, joined by a narrow- band, the isthmus. Each lobe is ovoid, and consists of minute vesicles surrounded by a plexus of capillaries, and connected by areolar tissue. The gland is ductless, but copiously supplied with blood by branches of the carotid, and secretes an albumin- ous fluid, which is perhaps absorbed by the lymphatics, and conveyed into the blood. It is very large in foetal life, but its use is unknown. The thymus is another ductless gland, situated on the inferior aspect of the trachea, and above the sternum. It consists of" two halves united by areolar tissue, and is composed of lobules disposed round a central canal, having no external opening. Within are vesicles similar to those of the thyroid body ; in the foetus it is attached to the thyroid, and is large at birth,, gradually disappearing. BRONCHI — BRONCHIAL TUBES. The terminal branches of the trachea are the right and left bronchi, which enter the lungs and subdivide dichotomously into branches termed bronchial tubes, the latter becoming gradualljr smaller, and finally terminating in the air-cells. The entire ramification when isolated has the appearance of a tree, the trachea being the main trunk, the bronchi and bronchial tubes the branches, and the air-cells the leaves. These structures are accompanied throughout by the arteries, veins, and nerv^es, which. Lave the same arborescent distribution. The right bronchus is the larger, the left the longer, since it passes under the aorta before reaching the lung. The bronchi and bronchial tubes are made up of cartilaginous rings, differing only from those of the trachea in being made up of several pieces, which overlap and are united by cellular tissue on their inner surface. As the tubes diminish in size, the num- ber of these pieces is diminished, and ultimately they disappear^ -336 SPLANCHNOLOGY. The small bronchial tubes, after ramifying in the longs, terminate in cellular recesses or air-cells, which consist only of the lining membrane of the tubes. The muscular bands of the trachea are continued along the inner face of the rings of the bronchi and larger bronchial tubes, also gradually disappearing. These tubes are lined by mucous membrane, which is continuous with, but more sensitive than that of the trachea. Blood is supplied by the bronchial arteries. At the root of each lung there are a number of absorbent bronchial glands. The principal ones are closely adherent to the bifurcations of the bronchi Fig. 118. General view of the respiratory organs, a, Septum nasi ; 6, Posterior naris ; c, Larynx; d, Trachea ; e, Thyroid gland ; //, Anterior mediastinum ; g g, Posterior mediastinum ; h, Left lung ; h', Its apex ; h" Its base ; h'". Its superior, and h"". Its inferior borders. THORAX, The thorax, or thoracic cavity, is formed by the ribs, sternum, and bodies of the dorsal vertebrae, the intercostal muscles, thoracic fascia, and diaphragm ; it contains the liings, the heart and its adjuncts, the trachea, oesophagus, and a quantity of nerves ; it resembles a hollow horizontal cone, flattened from side to side. Its base, formed by the diaphragm, slopes obliquely downwards and forwards. r LUNGS. 33r PLEUILE. The thorax is lined by two serous membranes, the right and left pleurae, which consist of parietal and visceral portions, and forpa distinct sacs. Each pleura lines one side of the thorax and half of the diaphragm ; the pleura costalis is the portion lining the ribs and intercostal spaces, the pleura diaphragmatica is that covering the diaphragm ; in the median longitudinal plane it forms with the opposite pleura the mediastinum, whence each is reflected over one of the lungs, forming the pleura pulmoTialis. The mediastinum is therefore a longitudinal passage through the thorax, bounded on each side by a pleural fold ; it is divided into three portions — the anterior mediastinum lies in front of the heart, the middle contains it, while the posterior Hes behind it. The mediastina are occupied by the trachea, oesophagus, heart, vessels, •and nerves, and the anterior one in the foetus by the thymus gland. In tracing the course of a pleura, if wo commence on the lateral aspect of the bodies of the dorsal vertebrae, we find that it extends downwards over the inner surfaces of all the ribs and intercostal spaces, forming the pleura costalis ; posteriorly it passes to the anterior convex surface of the diaphragm, constituting the pleura diaphragmatica^ At the centre of the sternum it is reflected upwards between the lungs, enclosing the pericardial sac. Gaining the root of the lung, the parietal portion passes on to it, forming the visceral portion or pleura pulmonalis. clothes the free surface of the lung, and again on the lung root it is reflected up to the vertebra, returning to its place of origin. The pleura is thick and loosely attached over the ribs, attenuated over the diaphragm and pericardium, and extremely so on the lungs ; its surface is smooth and glistening, emitting a vapoury fluid, which lubricates the contacting surfaces and facilitates motion. The posterior mediastinum is cribrated inferiorly, several open- ings leading from one pleural sac to the other. This arrange- ment is peculiar to solipedes, and explains the fact that in these animals there cannot be pleural effusion confined to one side of the chest. LUNGS. The lungs, the essential organs of respiration, are spongy gans of a conical shape, situated in the thoracic cavity, right 338 — SPLANCHNOLOGY. and left, the former being a little the larger ; they are separated "by the mediastinum, heart, pericardium, and large blood-vessels. During life, they occupy the major part of the cavity, resting on the inner surface of the walls, and adapting themselves to its varying capacity. They are light, porous, and highly elastic, possessing considerable strength. Healthy lungs float m water, their buoyancy being due to the air they always contain ; when air is admitted into the thorax, they collapse considerably. In the adult, they are of a rosy flesh colour, marked by an irregular marbling or mottling. The lung is attached midway by the root, Xvhich consicts of the bronchus, vessels, and nerves, enveloped by the pleura. Each lung presents two surfaces, external and internal, a base, an apex, and three borders. The external costal surface is convex, cerre- cponding to the thoracic wall. The internal, or mediastinal surface, forms a vertical plane in contact with the mediactinum, and presents an anterior division, which rests against the anterior mediastinum, in front of an excavation in which the heart 13 .lodged ; above and behind this is the root of the lung. Two Jissuree present themselves on the superior aspect, an anterior and posterior. The former crosses towards the superior border, and receives the posterior aorta ; the latter, lower down, shallower, and more distinct in the left lung, is destined for the passage of the oesophagus. On the inner aspect of the right lung there is a small lobule, wanting on the left lung, formed by a deep fissure, through which the posterior vena cava passes ; it is lined by a fold of pleura. The concave base is sloped downwards and forwards, fitting the convex surface of the diaphragm, where the fissure above noted originates. The summit or apex lies behind the first rib, and presents a partially detached appendage, the anterior lobe. The superior border is round, thick, and convex, and is lodged in the channel between the ribs and bodies of the vertebrse. The inferior border is thinner and shorter, deeply cleft near the heart, and more so on the left than on the right side. The posterior border is elliptical, surrounding the base, which it separates from the costal and mediastinal surfaces. Structurally, the lungs consist of an external serous coat, a subserous layer, and the long tissue proper, or parenchyma. The serous coat is the pleura pulmonalis. The subserous layer is com- posed of cellular tissue, intermixed with yellow elastic fibres; it clothes the entire lung surface, and is continuous with the inter- LUNGS. SSd lobular cellular tissue. The parenchyma is divided into many- polyhedral lobules of various sizes, united by connective tissue ; ther.e are again made up of smaller ones, which are composed of a small bronchial tube and its terminal air-cells, in the walls of whi:h lie the capillary vessels uniting the pulmonary arteries with 'he pulmonary veins. The air-cells are vesicular cavities, arranged as it were in bunches at the end of the tube ; they consist of a thin membrane of connective and elastic tissue, with a layer of pavemental epithelium. Each lobule is provided v/ith its own bronchial tube and air-cells, functional and nutritive vessels, lymphatics, nerves, and interstitial cellular tissue, and is enveloped by the interlobular tissue. The interlobular cellular tissue is very fine, and continuous with the subserous layer. The lobular division is constant in all mammiferous animals ; in the horse it is less distinct than in ruminants, where there is a much larger amount of interlobular cell- ular tissue. The pneurncnic functional vessels are the pulmonary artery and veins. The artery conveys venous blood from the heart to the lungs. At the lung-root it divides into right and left branches, which are distributed to their respective lungs, in company with the ramifying bronchial tubes, terminating in a capillary network around the terminal air-cells, whence arise the radicles of the pulmonary veins, which return the purified blood from the lungs to the heart. The nutrient vessels are the bronchial arteries and .veins. These arteries proceed from the posterior aorta; their branches are smaller than the pulmonary, and also accompany the air- tubes. The pulmonary lymphatics are numerous, and divided into superficial and deep. The former are situated in the subserous layer, forming a network, the latter in the interlobular tissue. Both communicate at the lung-roots, and pass through the bronchial glands. The nerves are from the pulmonary plexus, formed by the vagus and sjnnpathetic. Fig. 119. Arrangement of capillaries round the air-cells of the lung. 340 *'- ' SPLANCHNOLOGY. Urinary System. , The organs of this system secrete tbe urine from the blood,* and excrete or expel it from the body. These organs are chiefly the Kidneys, Ureters, Bladder, and Urethra. The urine, livhich is a watery fluid, is secreted by the kidneys, and carried off by their ducts, the ureters, to a special reservoir, the bladder, where it accumulates, and from which it is finally expelled at intervals through the urethra. KIDNEYS. The kidneys are two compound tubular glands, situated on the right and left of tlie vertebral column, in the sublumbar Fio. 120. Horizontal section of the right kidney, n, Fibrous capsule detached ; b h b, Cortical layer ; n c, Medullary layer : d d d, Cut ends of large blood-vessols : f. Pelvis of the kidney • /, Ureter. region of the abdomen, in contact with the crura of the diaphragm and psoe muscle?. They are supported by perito- neum and cellular tissue, in which is deposited a quantity of fat ; less perhaps in the horse than in other herbivorous animals. The kidneys are also supported by their vessels as well as by the pressure of the digestive organs ; the right one is in advance of the left, lying just behind and baneath the last pair of ribs, whereas the left one lies about two inches farther back. They somewhat resemble in shape the heart on playing cards, the left r KIDNEYS. 341 ouo beiDg longer and narrower than tho right. From perverted > ture ; e. Greater curvature ; /, (Esophagus ; g, Pyloxio orifice. .3-3 **3:^' ^ 1-1 ^^ 3-3 ^ 4-4 _ ., The incisors differ from each other in a remarkable degree ; the central and lateral ones in the upper jaw resemble the corresponding ones in the horse, having cavities in their tables, while the upper comer incisors are isolated, and small in proportion to the other four. The central and lateral incisors of the lower jaw are long, nearly straight, projecting forwards, and somewhat resem- bling the incisors of the rodent ; the lower corner incisors are also isolated, but smaller than those of the upper jaw. The canine teeth are well developed. 878 Comparative splanchkologt. especially in the male, having the character of tusks ; the lower ones are the largest, and curve outwards and upwards ; the upper pass outwards and down- wards. The tusks continue to grow during the life of the animaL The molars also vary in shape, gradually increasing from the first to the last, which is large and strong ; they are intermediate between herbivorous and carnivorous, -and somewhat resemble the human teeth. The first, which is small, and corresponds to the v/olf- tooth of the horse, is a permanent or true molar, the next three are the premolars, and the remaining three, true molars. The stomach is simple and somewhat capacious ; it consists, as m the horse, of two divisions, cardiac and pyloric, the latter being the smaller, but the division externally is marked by a much more distinct constriction. At the upper and left portion of the cardiac half is a small diverticulum or cul-de-sac. The oesophagus is infundibuliform at its termination. The mucous membrane, for Fig. 140. Caecum and colon of a Hog— inflated, a, Ileum ; 6 h, Csacum :ccc, Colon ; d, Bectum. the most part villous in its structure, forms two folds which extend from the cardiac towards the pyloric orifice, representing undeveloped (Esophageal pillars and canal. In the general sense the intestines resemble those of the ruminant, but only the posted cr part of the colon lies between the folds of the mesentery. A Peyer's patch of enormous size occurs at the terminal portion of the small intestine. The ccecum recembles that of the horse in having longitudinal muscular bands, three in number, and transverse constrictions, and that of the ruminant in its shape, and the direct continuity of its canal with that of the colon ; the latter is coiled in a similar manner to that of the ruminant. OMNIVORA — URINO-GENITAL SYSTEM. S79 •The liver of the hog consists of four chief lobes ; a right and left external, and a right and left internal ; a small quadrate and a Spigelian lobe exist, the Fig. 141. Liver of a Hog— posterior view, a, Eight external lobe ; &, Bight internal lobe ; c. Left external lobe ; d, Left internal lobe ; e, Spigelian lobe ; /, Posterior cava ; gr. Quadrate lobe : h, Gall bladder ; i. Cystic duct : k, Ductus Choledocus. latter being cleft by a fissure for the posterior vena cava. There is a gall bladder, and the biliary and pancreatic ducts enter the intestine singly. RESPIRATORY SYSTEM. The anterior extremity of the nose is the snout, which is flat anteriorly, and presents on either side the small, round nasal opening. Like the muzzle of the ruminant, it is always damp in health. At the anterior, extremity of the septum nasi is the small snout bone, os rostri, covered by cartilJage which extends round the nasal openings. The nasal fossae are long and ' narrow. The frontal sinuses extend back- wards to the parietal bone. The larynx is loose and mobile, being attached to the hyhoid heel processes by the epiglottis rather than by the thyroid C£urti- lage. The epiglottis is very large ; the lateral ventricles are large but shallow. Thetracheasmd lungs resemble those of the ruminant, and, as in that animal, there is a third bronchus ; the pleural sacs are separated completely. Urino-genital System. The kidney is large, simple in form, and like that of the horse externally. The urini- ferous tubes discharge by papillae and calices. The ureters enter the bladder very near together jecting considerably into the abdomen. e Fio. 142. Horizontal section of the kidney of a Hog. a. Cortical substance ; h. Medullary substance ; c. Renal papillaa ; d, Inf undibulum ; e. Ureter cct across. the bladder itself is large, pro- 380 COMPARATIVE SPLANCHNOLOGY. The testicle is large and spherical, being situated in the perineal region, and closely covered by the scrotum. The bulbous portion of the vas deferens is less marked, but the vesiculce seminales are large and very glandular in structure, like those of the ruminant, and diverticular internally. There are two prostate glands^ an anterior and posterior. The latter may be alluded to by Leyh, when he describes Cowper's glands as being very large in this animal. The yenis also resembles that of the ruminant ; it is long, thin, and pro- vided with a preputial sac, which secretes a peculiar fluid. The sheath has no muscles. In the female the ovary is- irregularly lobulated, owing to the Graafian vesicle? being prominent. The body of the uterus is short, but the cornua are extremely long, depending among the intestinal convolutions. In the vulva we find the canals of Gariner as in the ruminant, which apparently originate in the parovarium. The mamma} usually number five or six on each side, arranged in a longi- tudinal row ; each gland has its own teat, which is pierced by several lactifer- (ous canals, but there are no sinuses. CARNIVORA. DIGESTIVE SYSTEM". Tlie lips of carnivora are thin and mobile, but are not organs of prehension ; ithe upper one is mesially fissured, and projects more or less over the lower ; the latter is deutated posteriorly. The upper lip of the felidae is provided with long, straight, stiff hairs. The hard palate is like that of the small ruminant ; the soft palate is very short ; the tonsils are well marked. The buccal membrane often contains much pigmentary matter, giving rise to large patches of a black colour. The tongue is thin and very mobile. In cats, the papillae on the anterior part are numerous and horny, their points being directed backwards, giving the organ a rough surface ; in dogs the papillae are neither prominent nor hard. The parotid gland is small, its duct crossing the masseter externally. The submaxillary gland is larger than the parotid, and has a small accessory gland anteriorly. The sublingual gland is very small in the cat, and wanting in the dog ; in the latter is the orbital gland, which is placed under the zygoma, and in the inferior part of the orbit ; its canals unite to form the duct of Nuckius, which opens into the mouth about the last molar looth. The dog has forty-two teeth^ formulated thus : — . 3-3 ^ 1-1 ^^ 4-4 ^ 2-2_,„ In the carnivora the crowns of all the teeth are completely covered with enamel. The upper incisors are the strongest ; the corner ones are the largest, the central the smallest. They, in common with the other teeth, are remark- able for their brilliant whiteness, and present, when not worn on their tables, three tubercles, a large central and two small lateral ones, the tooth somewhat resembling a trefoil or fieur-de-lix. As the animal ages, these projections wear CAENIVORA DIGESTIVE SYSTEM; 381 away. The canines, temporary and permanent, are very large, strong, conical, and curved outwards and backwards ; the upper ones are the largest, and have a space between them and the incisors, which lodges the lower canines when the mouth is shut. The molars, twelve in the upper, and fourteen in the lower jaw, terminate in sharp projections ; the last upper premolar and the first lower true molar are the largest, and being furnished with cutting edgss, they have been termed the sectorial teeth, dens sectorius ("dent carnassiere" of Cuvier). The other molars are slightly sectorial, and also tuberculate — i.e., provided with pro- cesses for crushing the food. The cat has only fourteen molars, eight above and six l?elow ; the other teeth are like those of the dog, making up a total of thirty. The formula probably is ;- Fio. 143. Teeth of a Lion (CarnivoraX . 3-3 ^ 1-1 ^^ 3-3 I. . c. — , p.m. , 3-3' 1-1 -^ 2-2 1-1 1-1 = 30. The last upper premolar, and all the lower molar and premolar teeth may be said to be sectorial in this animal. The oesophagus is very dilatable, and presents a well-marked infundibuli- iorm union with the stomach. Fig. 144. Ctomach of a Dog -inflated, a, Cardiac por- tion : b, Pyloric portion ; c, (Esophageal orifice ; d. Duodenum. Fig. 145. CsBCtun and colon of a Dog— inflated. a, neum ; b, Caecum ; c, Colon. The stomach is simple and only slightly curved ; it is commonly described as pear-shaped, resembling that of the horse, but with a very small and narrow pyloric portion, terminating in a constricted valve. The mucous membrane is all villous, the natural food of these animals requiring but little preparation. The intestines are short and small. The small intestine is suspended by a mesentery ; its walls are thick. The colon is somewhat larger than the small intestines, and divided, as in man, into ascending, transverse, and descending portions ; the csecum is only a small, spiral appendix ; there is no floating 882 COMPARATIVE SPLANCHNOLOGY. colon. Near the anus, the rectum presents on either side the openings of twc- glandular pouches, where is secreted a strong foetid matter. Accessory Organs of Digestion. The liver is large, and deeply cleft into five lobes, a gall bladder being lodged in the middle lobe. The biliary duct unites with a small duct from the pancreas before entering the duodenum. The pancreas is elongated, running along the concave curvature of the duo^ denum ; its anterior end reaches the lesser curvature of the stomach. There are two ducts, a large one entering the duodenum alone, and a smaller, which joins the bile duct. The spleen is long and irregularly club-shaped. It is suspended in the great om,entum, near the left sac of the stomach. Its thick, blunt extremity is placed anteriorly. Fig. 146. Stomach, Liver, Pancreas, and Duodenum of a Pog. a a, Liver; 6, Gall-bladder ; c c, Biliary Canals ; d. Cystic Duct ; e, Ductus Chole- docus ; /, Pancreas ; g, Pancreatic Ducts. RESPIRATORY SYSTEM. The septum nasi is prolonged on either side, thus taking the place of the alar cartilages, and being continuous with the cartilaginous prolongations of the inferior turbinals. There is only cJtie maxillary sinus on each side. The thoracic cavity is usually very large in carnivora. The lungs are divided, the left into three, the right into four lobes, by clefts which reach almost to. the root of the organ. The heart is completely surrounded by the lungs, not embedded in depressions in them. The pulmonary tissue is very compact, the lobules being small, while the air-cells are well developed. URINARY AND GENITAL SYSTEMS. The kidney is ovoid, but shorter than in the hog ; in the cat it is still shorter, being almost round. The pelvis is simple, presenting a single large elongated papilla. The bladder is furnished with a very strong muscular coat. RODENTIA- 383 The testicles are situated in the perineal region, below the anus. The vesiculce seminales are wanting, but the prostate is large, forming a con- spicuous bulb around the origin of the urethra. Cowper's glands are wanting in the dog, and are small in the cat The penis of the dog is long, and termi- nates in a point. In common with the camivora generally, a bone is found in the penis ; its anterior extremity is fixed in the glans, while the posterior is attached to the corpus cavernosum, occupying all that portion of the organ which is lodged in the sheath. The os penis is long and curved, presenting an inferior gutter, in which the urethra is placed, continuous with the groove of the corpus cavernosum ; it favours the introduction of the penis into the vulva. In the dog, the corpus spongiosum forming the glans undergoes a very remark- able degree of tumefaction, which retains the two sexes in coitw for a con- siderable time. The differences in the female organs are imimportant. In the cat, the penal bone is not so well developed, and the penis, when relaxed, is turned backwards ; when erect, it assumes the same position as in other car- nivora. In the female, a small bone exists in the clitx)ris. The mammse are arranged as in the 89W. RODENTIA* The front teeth form one of the leading characteristics of the rabbit. The dental formula is — . 2-2 0-0 3-3 3-3 „„ *• rrr ^' 0^' ^'"^' 2^2' '^ 3^ = 28. The upper incisors consist of a large, curved, chisel-shaped pair, which grow from permanent pulps ; they are covered with enamel only on their anterior surface, which, wearing more slowly than the rest, gives rise to the chisel- like edge. The second pair of upper incisors are situated immediately behind the first, and are remarkably small. The lower incisors resemble in most respects the large upper • . ^ Lateral half of Mandible of a Rabbit, opened to There is an enormous diastema. show the arrangement of Eodent Teeth. The Qjiolar and premolar teeth have compound transversely ridged tables, and grow from permanent pulps.^ The large papillsD of the tongue appear as two well-marked oval spaces, the papillcB foliatcB, one on each side posteriorly, not upon the dorsum. These contain the minute organs of taste, which occur in the larger papillee of the horse's tongue. The stoTTiach is simple in structure. The ccecum is long, being slender and glandular at its termination. The liver and pancreas are both large, and the pancreatic duct enters the intestine far behind the biliary duct. The testicle is large, ovoid, sometimes scrotal, sometimes abdomii^al in situa- tion ; in the latter case it is fixed by the gubernuculum testis. The vai deferens is so separated ' from the blood-vessels that the spermatic cord is. reaUy double. The vasa discharge into the urethra on each side of the duct of a large uterus masculinus, described by some authorities as a single, median vesicula seminalis. ^84 COMPARATIVE SPLANCHNOLOGY. Is the possession of two uteri, each uterus opening into the vagina by a distinct orifice ; the two are near together posteriorly, and anterially they diverge. The vulva has both major and minor labia, and the clitoris is large and very prominent. ** The following principal forms of uterus are found in the mammalia : — The simple uterus (uterus simplex), in woman and the monkey ; the tivo-horned tiierus (uterus bicornis), in the mare and ruminant; the bifurcated uterus (uterus divisus), in the sow and carnivora ; and the double uterus (uterus duplex), in the rodent." — France. Tor many reasons, this part of the subject is interesting, but very little space can be given here to its discussion. Birds have no teeth, the maxillse being covered anteriorly, on the outside, "by a homy modification of the integument, the Whole constituting the rostrum or beak. The tongue is horny in structure, and apparently an organ of prehension, not of taste. The oesophagus is v6ry long, and its longi- tudinal muscular coat, is internal, the circular extemaL In seed-eatina "birds, the oesophagus expands in the cervical region into the ingluvics^ or crop,— a large sac which rests upon the fascia connecting the clavicles, and in "which maceration of the food is carried on. The oesophagus is then con- tinued and expanded into the first cavity of the stomach, i)iQ proventriculus^ a Tery vascular and glandular cavity, where a fluid analogous to the gastric juice is secreted. To this portion succeeds the second or muscular cavity, the gizzard, which is oval and flattened in shape, but with a structure vary- ing according to the nature of the animal's food. In granivorous or seed- eating birds, the muscular coat possesses extraordinary thickness and strength, while the lining membrane exhibits a dense, horny, epithelial structure. In the upper portion are two orifices, a large one opening into the proven- triculus, and just to the right of this a smaller pyloric orifice opening into the duodenum. All the domesticated birds possess a gizzard similar to this, but in those birds which feed naturally on flesh, the wails of the' gizzard are mem- "branous in their thinness, the development of the organ being usually correlated with the size of the ingluvies. Granivorous birds always s\7allow a quantity of stones or sand, which is deposited in the gizzard, and with the action of the muscular wall and horny lining, assists in grinding the ingesta to a pulp. Thus the gizzard may be viewed as an organ of mastication. The intestines are very much shorter than in the mammalia, the layers of muscular fibre being inversely arranged, as in the ORsophagus. There are two separate cwca, long and narrow, with their blind ends directed forwards. The duodenum forms a loop or bend near its origin, embracing the pancreas ; the Test of the small intestine is suspended by a mesentery. The large intestine is very 'ihort, running straight from the cssca to the termination of the canal ; it is commonly termed the rectum, and it opens into a cavity called the cloaca^ an excretory recess, common to the alimentary, urinary, and genital organs. The pancreas usually consists of two distinct pieces, and its ducts are two in number, opening separately into the duodenal loop. The liver is very large, and as the diaphragm is rudimentary, it can hardly be regarded as a pure AVES. ,35 abdominal organ. It consists of two lobes, between wbich, anteriorly is the apex of the heart, and posteriorly a double fold of peritoneum, analogous to the broad ligament of the mammal. There are two hepatic ducts, one pro- ceeding direct to the duodenum, the other passing from the right lobe to the gall bladder, a cystic duct proceeding from the latter to the intestine. The ColumbidsB or pigeon class, as also some classes of the order Scansores, have no gall bladder. The vena porta, in addition to its fundamental radicals, is joined by branches from the femoral and sacral veins. The organs of respiration in birds are interesting. The nasal openings are very smalt, and placed on each side of the beak, or at its base, surrounded by naked skin, a few feathers, or even scales, which form alae or wings; the nasal cavities open into the pharynx by two dis- tinct apertures, which lie close to- gether. The air-passages consist of a superior larynx, trachea, inferior larynx, bronchi, bronchial tubes, and air-sacs. The superior larynx is situated just behind the root of the tongue, opening by a longitu- dinal slit. It consists of several bony or cartilaginous pieces, varying In number, joined by membranes and moved by muscles. There is no epiglottiSf the sides of the rima closing the orifice during the passage of food. The trachea winds down the neck as a single tube, composed of complete bony or cartilaginous rings, not overlapping, as in mam- malia. They are round or com- pressed, varying in diameter. The syrinx, or inferior larynx, is the organ of sound, and is best devel- oped in song-birds, varying in form and structure in different species. At its origin is a membranous tongue, composed of a doubling of lining membrane ; the free portion is directed upwards, and its vibration produces sound. Below, the tube divides into a pair of bronchi, which lead to the lungSL < They consist of incomplete segments of bone or cartilage, completed by mem- brane. The lungs are spongy, bright red, long, flat, oval, and applied against the sides of the vertebrae and ribs, to which they are attached by cellular 2c Flo. 148. Alimentary canal of a Bird, a, Ingluvies ; &,^ Proventriculus : c. Pancreas ; d, Duodenum ; e. Liver ; /, Biliary cyst and duct ; g, Pancreatic duct ; h. Intestine ; i. The two caeca ; k, Itectum^ I, Kight ureter ; m, Oviduct ; n, Its aperture in cloaca ; o. Opening of cloaca. 386 COMPARATIVE SPLANCHNOLOGY. tissue. They present Beveral openings on their surfaces, which communicate with air -sacs hollowed out in the cellular tissue of the body. These sacs are continuous with the interior of certain hones, which thus receive a constant supply of air (sse p. 119). There are usually nine sacs — viz., one inter- clavicular, and the cervical, anterior and lateral thoracic, and abdominal, which are pairs. By means of these, air penetrates nearly every region of the body. The kidney is very irregular in shape, con- sisting of several portions which occupy the osseous irregularities in the sublumbar and anterior pelvic regions. The ureters open into the cloaca, a diverticulum of which is regarded as the analogue of the urinary bladder ; the latter organ is distinctly possessed by only one member of the class, the ostrich. The testicle is. abdominal, occupying almost the position of the mammalian kidney, which it resembles somewhat in shape, being ovoid. There is scarcely any epididymis ; the vas deferens is tortuous, and it terminates in the cloaca at the side of a papilla, which is the organ of copulation. In the natatores this papilla is very large, spirally elongated, and retractile. In the bird there is only one ovaryj the right one being undeveloped. It resembles a bunch of grapes in form, consisting of ova in various stages of development ; the more advanced ones are large, and yellow in colour. The representative of the Fallopian tube is called the oviduct) which is large, flexuous, and very dilatable, leading to the cloaca. It is not merely the duct of the ovary, since ifc also assists in forming the ovum ; while the latter is passing through it, the outer casing of calcareous material known as the shell, and the inner layer of albumen or "white of the egg" become developed. The coats of the duct are serous, muscular, and mucous, arranged in the typical manner. Fio. 149. Urino-genital organs, &c., of a male bird (fowl). 1, Heart; 2, (Eso- phagus cut across ; 3, Aorta ; 4, Pos- terior cava ; 5 5, Psoe muscles ; a a, Testicles ; b b, Vasa deferentia ; b' b', their oriflcea ; c c, Suprarenal capsules; dd, Kidneys; ec.Ureters; e* tf. Their openings into the cloaca. CHAPTER V. ANGIOLOGY. Under this heading we describe the organs of circulation, by the action of which certain fluids are propelled through the body It is customary to divide this branch of the subject into two sections, considering respectively the Blood- Vascular and Lym- phatic Systems. Blood-Vascular System. This involves the consideration of the Blood, a fluid which supplies nutriment to the tissues, and receives eifete material from them ; the Heart, a muscular organ which, by its contrac- tion, initiates the motion of the blood ; the Arteries, a series of tubes which convey the blood from the heart ta all parts of the body ; the Veins, tubes which return that fluid to the heart ; and the Capillaries, minute tubes joining the smaller arteries and veins. BLOOD. Blood is a fluid tissue, which nourishes all living structures, being the medium by which nutritive material is conveyed to, and effete or waste material conveyed away from, the solid tissues. It is an opaque, thickish, clammy fluid, with a peculiar odour, sickly saline taste, and alkaline reaction. Its colour varies in different parts of the same animal, that in the arteries being bright red or scarlet, while the blood in the veins is of a dark purplish hue. When examined microscopically, the blood is found to consist of minute corpuscles, and a clear, transparent, yellow fluid, the liq'wor sanguinis, or plasma, in which the corpuscles float. The corpuscles are of two kinds, the red, and the white or colourless ; the former, by far the more numerous, exist in vary- 387 38d ANGIOLOGY. ing proportions. Red corpuscles vary in shape, but in all mammals are more or less discoid, the camelidae excepted, where they are oval ; in birds, reptiles, and fishes, they are oval, and also nucleated. Their average diameter in the horse, ox, or sheep is about ^j^j^-^ih. part of an inch, their average thickness being about one-fourth of this. Each surface is depressed towards its centre, hence the corpuscle is appropriately described as a bi-concave disc. The ivliite corpuscles are larger than the red, round in shape, and nucleated. Occurring also in lymph they are sometimes termed lymph-corpuscles. The liquor sanguinis is pale and clear, and consists of water, fibrin, albumen, fatty compounds, extracts, odoriferous and saline matters. The serum is a thin, transparent liquid, of a pale- straw or yellow colour, consisting of the liquor sanguinis deprived of fibrin. -It contains nearly 90 per cent, of water, is always slightly alkaline, and coagulates when heated, owing to the large quantity of albumen it contains. Fibrin is a white, stringy, elastic substance, which, when the blood is in circulation, is in solution, and cannot be distinguished from the other constituents of the plasma. HEART. The heart is a hollow, ipvoluntary muscular organ, situated between the layers of the middle mediastinum, and in the peri- cardial sac, to a reflection of which it owes its external smooth, glistening aspect. Its form is that of a blunt cone, slightl}^ flattened from side to side, and it presents a base and an apex. The foraier is turned upwu^ds, a^i to\.ards the dorsal veivebrte, from which the heart is suspended by the blood-vessels that spring from it; the apex points downwards, backwards, and to the left side, lying at about the level of the last bone of the sternum ; the organ extends from about the third to the sixth rib inclusive. The average weight of the horse's heart is about six pounds and a-half, its length from base to apex about eight inches, its antero-posterior diameter rather less, and its lateral diameter less still. The heart is divided by a longitudinal septum into a right and left, or anterior and posterior side. Each of these is again subdivided by a transverse septum into two compartments, which commimicate. Thus there are four cardiac cavities, the superior ones, whose free extremities somewhat resemble the ears of a EIGHT AURICLE. 389 dog, being called the auricles, the inferior the ventricles. These divisions are marked externally by deep grooves, in which the cardiac blood-vessels run, and which are generally filled with fat. Two of these grooves extend from the base of the ventricles to the apex of the heart, and correspond to the internal septum ; they are called the anterior and posterior longitudinal furrows. Around the base of the ventricles is a deep transverse auriculo- ventricular furrow, which marks the division of the heart into an upper or auricular, and a lower or ventricular portion. The right side of the heart is sometimes called the venous, the left the arterial side, named from the kind of blood which passes through them. We will describe first the cavities of the right side, and then those of the left. RIGHT AURICLE. The right auricle is the larger, and forms the right and anterior portion of the base. It consists of two portions ; the sinus venosus, or principal cavity, is somewhat quadrangular ; its walls are thin, and connected inferiorly with the right ventricle ; internally, with the left auricle ; anteriorly, they are prolonged to form the appendix. The appendix auriculce, or proper auricle, is a small conical pouch, which projects forwards from the sinus ; its walls are thick, and its edges, more particularly the outer one, serrated. On laying open the interior of the auricle (which is best done by an incision from the appendix to the mouth of the posterior vena cava, then opening the anterior cava, and connecting the incisions), the smooth transparent Endocardium or lining membrane, anterior and posterior Venae cavae. Coronary sinus. Foramina Thebesii, and right Auriculo- ventricular opening are displayed. The anterior vena cava returns the blood from the. anterior part of the body, and opens into the supero-posterior part of the sinus venosus. The posterior cava, which returns the blood from the posterior region of the body, opens into the infero- posterior part of the external wall of the sinus, near the inter- auricular, or superior part of the longitudinal septum. The coronary sinus, the dilated termination of the larger coronary or cardiac veins, is situated below the opening of the posterior cava, between it and auriculo- ventricular opening ; and through it the blood is returned from the substance of the heart. The coronxjbry 890 ANGIOLOGT. valve or valve of Thehesius, is a fold of the endocardium which covers the coronary sinus, preventing regurgitation of blood during the contraction of the auricle. The foramina Thebesii are minute openings on the inner surface of the auricle ; some of them are mere depressions, whilst others are the openings of minute veins, vencB cordis minimce, which return blood directly from the substance of the walls. The right auriculo-ventricular opening is a large oval aperture, occupying the floor of the auricle ; it communicates with the right ventricle. The tuber- culum Lowerii is a slight projection situated between the openings of the cavse, and is supposed to direct the blood from the anterior cava into the auriculo-ventricular open- ing. In man the remains of a foetal structure, called the Eustachian valve are situ- ated at the anterior margin of the posterior cava, stretch- ing from it to the left side of the annulus ovalis. It is a doubling of the lining membrane, largest in the foetus, and serves to direct the blood from the vein to the foramen ovale; in quad- rupeds, this structure, if present at all, is extremely rudimentary. The fossa ovalis is an oval depression in the interauricular septum, being an obliter- ated foramep, which in the foetus joins the right and left auricles. At birth this opening is closed. Its lower border is indistinct ; its upper thick and projecting, forming the annulus ovalis or isthmus Vieusseni. The musculi pecti- nati are columns of muscular fibres situated chiefly in the appendix; they are called pectinati, from their resemblance in arrangement to the teeth of a comb. Smaller bundles cross the large ones, giving the whole a reticulated appearamce, between which are depressions, some of which are the foramina Thebesii Fio. 150. Right side of the heart— laid open. 1, Eight ven- tricle ; a a, Its external wall ; b b, Carneae columnse ; c, Great moderator band ; d, Origin of pulmonary artery ; e e e, Sigmoid valves ; 2, Eight auricle ; a a, Foramina Thebesii and mijsculi pectinati ; b, Opening •of anterior, and c, of posterior vena cava. EIGHT VENTRICLE. 391 RIGHT VENTRICLE. The blood leaves the right auricle through the auriculo-ven- tricular opening, and enters the right ventricle, which occupies the antero-inferior part of the right side of the heart. It is some- what conical in shape, with its base uppermost, and extends from the auriculo-ventricular septum to near the apex. Its outer walls, although thicker than those of the auricle, are much thinner than those of the left ventricle. The inner wall is convex, and formed by the interventricular septum ; on laying the cavity open (by an incision along the side of the anterior longitudinal furrow, and a second one below and parallel to the transverse septum, joining the first), two openings present themselves. The auriculo'Ventricular is the large oval opening, situated at the base of the ventricle, surrounded by the fibrous auriculo-ven- tricular ring; it communicates with the auricle, and is guarded by the tricuspid valve, which is formed by a redoublicature of the endocardium, strengthened by an intermediate layer of fibrous tissue. It consists of three triangular cusps or segments, which, connected at their bases, surround the auricular opening. The cusps are attached to each other above for a short distance, but their apices freely project into the cavity of the ventricle ; the largest is placed between the auriculo-ventricular opening and the opening of the pulmonary artery ; a second rests against the septum of the ventricles, the third between the other two. The free edges of the cusps are thickened, and to their ventricular surfaces and free margins are attached a number of delicate tendinous cords, or chordce tendinece, which spring from the inner surface of the ventricle. The majority of these arise from the free blunt extremities of the muscvli papillares, which are a variety of carnece columnce, the remainder from the walls of the ventricle, diverging towards the valve ; some terminate in the free margins and apices of the cusps, others in the central thick portion ; while a few reach the attached borders, and become continuous with the auriculo-ventricular ring. This valve pre- vents the regurgitation of blood into the auricle when the ventricle contracts. The second opening in the right ventricle is the origin of the pulmoTiary artery. It is situated above and to the left of the auriculo-ventricular opening, is circular, and arises from the summit of a conical prolongation called the conus arteriosus, or 392 ANGIOLOGY. infundihulum, whose smooth inner surface is destitute of carne^ columnae. The entrance of the pulmonary artery is guarded by three semilunar or sigmoid valves, which consist of semicircular folds of the lining membrane ; they are almost transparent, and attached by their convex margins to the tendinous ring which surrounds the origin of the artery. Their free edges are almost straight, and thinner than the attached ones, each presenting a mesian fibre- cartilaginous nodule, the corpus Arantii. When blood passes from the ventricle to the pulmonary artery, the valves are laid against the sides of the vessel; when the current is checked, a portion of it falls back towards the ventricle^ and the valves are now thrown inwards ; they become distended, overlap, and completely close the tube. When the valves are shut, the surfaces next the vessel are concave, the ventricular ones convex. The corpora Arantii are said to fill up the small space that' would otherwise be left in the axis of the canal by the meeting of the circular valves ; but these bodies are frequently indistinct in the pulmonary artery, and rarely project beyond the free margins of the valves. Behind the valves, at the commencement of the artery, are three dilations or pouches, bounded below by the valves themselves, and called the sinuses of Valsalva. From the inner surface of the ventricular walls project the fleshy columns, or carnece columnce. They are of three kinds, attached by their external surface and extremities, their internal surfaces being free, forming prominent ridges, sometimes dividing and subdividing. One variety, three or four in number, terminate in short blunt processes, and constitute the musculi papillares, whence the chordae tendineae spring. These carneae columnae form an intricate network on the inner surface of the ventricle, occasionally crossing the cavity, and forming what are called the moderator bands. A very well developed one crosses the middle of the cavity from the interventricular septum to the outer wall ; this is termed the great moderator hand, and is said to be especially well marked in .*' running " animals. LEFT AURICLE. The blood, after being purified in the lungs, re-enters the heart at the left auricle, which is smaller than the right, but its walls are thicker. It is situated at the left postero-superior pait LEFT VENTRICLE. 393 of the heart, and consists of two parts, a sinus and auricular appendix. The sinus is separated from the right one by the interauricular septum. The appendix is longer, narrower, more serrated than the right one, and constricted at its junction with the sinus. It runs along the left side of the origin of the pulmonary artery, which helps to separate it from the right auricle. On laying open the cavity, we find the openings of the pul- monary veins, usually two pairs, one pair on the right, the other on the left of the sinus ; they are not guarded by valves. The remaining opening in the left auricle is the auriculo-ventricular, which occupies the floor, and with the left upper margin communicates ventricle, its being surrounded by a white tendinous ring. The obliter- ated foramen ovale on the septum is indistinct. The inner surface of this auricle is smoother than that of the other, the musculi pectinati fewer, and confined to the appendix. The appendix communicates with the sinus through a round constricted opening. Fig. 151. Left side of the heart— laid open. 1, Left ven- tricle ; a a, External wall ; b, Cameae columnse ; c, Moderator band ; d d d. Mitral valve ; d' d'. Chordae tendinese ; 2, Left auricle ; a a, Musculi pectinati ; i, Openings of pulmonary veins. LEFT VENTRICLE. The blood leaving the left auricle enters the left ventricle, which is conical, and occupies the posterior left region of the heart. It is larger, rounder, and more prominent than the right, extending from the auricle to the apex, which it occupies, projecting lower than the right ventricle. The external wall is much thickep than that of the right side, being thickest in the centre. After death the walls of this cavity remain apart, those of the right collapsing; on laying open the cavity (by an incision close upon the anterior furrow, from the apex to near the origin of the aorta, and another upon the posterior furrow, the two lijeeting at the apex), two openings present themselves, the left auriculo- ventricular and the aortic. . The left auriculo-triLtricular open- 394 ANGIOLOGY. ing resembles the right in structure, and is guarded by a valve^ with two cusps, the bicuspid or mitral valve. The cusps consist of doublings of the lining membrane, strengthened with fibrous tissue, and, it has been said, by muscular fibre. One cusp rests between the auriculo-ventricular and aortic openings; the other, larger and freer, is opposite. They surround the opening, their sides being attached for a short distance, their apices separate. The musculi papillares of the left side are two, corresponding to the valve segments ; they are large and prominent, one anterior,. the other posterior. The chordae tendineae are few, longer, and more powerful than those of the right side ; they are attached to the flaps in a similar manner, and spring from the musculi papillares. The aortic opening 'i^ deeply situated in the supero-anterior part of the ventricle, a little to the right of the auriculo-ventricular opening, from which it is separated by one of the segments of the mitral valve. It is guarded by three semilunar valves, which are similar in shape and appearance to, but thicker and stronger than, those of the right side ; the corpora Arantii are larger and better developed, the sinuses of Valsalva deeper. From two of the latter spring the coronary arteries, which supply the substance of the heart with blood. The septum of the ventricles is triangular in shape, and extends to the apex of the heart. It is thick at the base^ thinner at the apex; convex in the right ventricle, concave ia the left. STRUCTUEE OF THE HEART. The heart consists of a fibrous framework, muscular and con- nective tissue, vessels, and nerves, the Vhole being covered by one, and the cavities lined by another, serous membrane. The fibrous frameworh consists of fibro-cartilaginous rings placed around the auriculo-ventricular and arterial openings, extending within ^ the doubling of lining membrane which forms the valves and chordae teydineae ; they are strongly developed on the left side. The auriculo-ventricular rings divide the heart into two distinct parts, an auricular and ventricular; they are thicker on their lower edge, whence spring the muscular fibres of the ventricles, the mitral and tricuspid valves, while from the upper edge arise the muscular fibres of the auricles. The right margin of the left fturiculo-ventricular ring is connected with the ring surrounding STilUCTURE OF THE HEART. '3^5 the aortic opening. Between the aortic ring and auriculo-ven- tricular opening is a fibro-cartilaginous mass, connected with the several rings, to which muscular fibres are attached, and which in the Ruminant is replaced by a triangular bone or os cordis. A second bone is sometimes found between the pulmonic and auiiculo- ventricular rings. The arterial rings gird the arterial openings, and serve for the attachment of the vessels, semilunar valves, and some of the ventricular muscular fibres. They seem to consist of three semilunar portions united, which gives them a festooned border, to which is attached the middle coat of the artery. The other edge is straight, atfording attachment to the muscular fasciculi of the ventricles. The mass of the heart is composed of muscular fibres, con- nected by filamentous areolar tissue. These fibres are involuntary, and of a deep-red colour, difiering from other involuntary muscles, the oesophagus excepted, in being transversely and longitudinally striated. They are smaller than voluntary fibres, and are anasto- matic. The muscular fibres of the auHcles are separable into super- ficial and deep ; the former common to both auricles, the latter proper to each. The superficial, common, or transverse fibres surround the base of the auricles, and are most abundant on their anterior part. They cross from one auricle to the other, diverging to enclose the appen- dices and the openings of the large veins. They are also prolonged into the inter- auricular septum, to assist in forming the circular band which surrounds the fossa ^^°- ^^2. T tTM. J m X -L Muscular fibres from the heart ovahs. The deep fibres proper to each ^f the Horse. Magnified 310 auricle consist of two sets, looped diamrs. and annular, which are superficial where the external circular fibres are deficient. The looped fibres are attached by their extremities to the auriculo- ventricular tendinous rings ; passing over, they embrace each auricle, forming right and left loops. The annular fibres are arranged in rings, forming a continuous layer. They abound most in the appendices, and around the coronary sinus and pulmonary veins, extending .some distance along the course of the latter, and of the cavse. Like the muscular fibres of the auricles, those of the ventricles. S96' \ .' ANGIOLOGT.^ '- are arranged in two sets, one common to both, and another proper to each ventricle, thus forming as it were two muscular sacs enclosed in a third. The fibres, whether common or proper, are attached directly or indirectly by both extremities to the tendin- ous-rings. The common fibres are arranged in successive layers, arising from the auriculo-ventricular ring. They extend spirally from above downwards, on the anterior surface from right to left, on the posterior from left to right. They are thin and broad at the upper part of the ventricles, becoming thick and narrow as they reach the apex, where they eocoil, forming a whorl, then penetrate beneath the layers, and pass up internally, forming the walls and septum, terminating on the auriculo-ventricular ring. The common fibres thus form a superficial layer, passing down- jwards, and a deep layer reflected upwards, between which are enclosed the layers special to each ventricle. The special fibres form circular or curved bands, inserted by both extremities to the tendinous rings. The heart is supplied with blood by the coronary arteries, which arise from the sinuses of Valsalva. The blood is returned by the coronary veins which pass to the coronary sinus, and the venae cordis minimse, which terminate in the foramina Thebesii. The nerves of the heart come chiefly from the cardiac plexus, formed by the sympathetic and the vagus. The lymphatics follow the course of the blood-vessels, and terminate in glands at the base of the heart. ENDOCARDIUM. The cavities of the heart are all lined by the serous endocar- dium, which is continuous with the lining membrane of the blood- vessels. It is thin, smooth, and glistening, giving a polished appearance to the inside of the heart, to which it adheres by cellular tissue. It enters into the formation of the valves, being strengthened by fibrous and muscular tissue between its folds. It is rather red in colour on the right side. So far as the heart itself is concerned, since, in the adult, the right side is separate from the left, there are two Endocardia, but as the lining membrane of the arteries is continuous through the capillaries with that of the veins, the two membranes ultimately form a continuous structure. COURSE OF THE CIRCULATION. 397 PERICARDIUM. The pericardium is a fibro-serous sac, which encloses and is reflected over the heart, and origins of the large blood-vessels. It consists of a parietal and visceral portion, and is composed of two membranous layers ; one external, dense, and fibrous, the other internal and serous. * The outer fibrous layer enters into the formation of the sac, or free portion only of the pericardium, having no direct attachment to the heart itself. It is made up of fibres, which interlace with each other and form a sac, whose apex embraces the origins of the larger blood-vessels, as tubular prolongations. The basal fibres of the membrane sometimes blend with the dia- phragm, and are also attached to the last hones of the sternum and ensiiorm cartilage. The parietal layer is covered by the pleural folds which form the middle mediastinum. The serous layer is much larger than the fibrous, which it lines, and is reflected over the origin of the blood-vessels, and external surface of the heart, thus forming a closed sac. The reflected portion is often called the ppicardium. Between the parietal and visceral layers is secreted a pale, lubrica- ting serous fluid, the liquor pericardii. The pericardium supports the heart, and is-^lates it fi'oiii the other thoracic viscera. Fig. 153. nUESE OF THE CIRCULATION. Diagram of the circulation in Mammalia and Aves. a, Boundary of the heart, con- taining four cavities ; h. Vena cava (represented as single- here) ; c, Eight auricle ; d. Right ventricle ; e. Pulmon- ary artery ; /, Capillaries of the lungs ; g. Left auricle, receiving the purified blood from the pulmonary vein (only one shown here) ; A, Left ventricle; i. Aorta; j. Somatic capillaries convey- ing the blood again to the veins. We have seen that the heart is divided into a right or venous, and a left or arterial portion. In tracing the circulation it matters little where we commence, since wherever it be we come back to the .same point. Briefly, the following is the course of the blood : — The venous blood is carried into the right auricle by the anterior and posterior venaB cavae. It then passes through the right auriculo- ventricular opening into the right ventricle ; thence through the pulmonary artery to the lungs. It returns by the pulmonary veins to the left auricle ; thence to the left ventricle, which propels it through the aorta and its branches 398 ANGIOLOGY. into the system- generally ; the veins returning it again to tho heart, The circulation is, therefore, double — the Pulmonary or lesser being performed by the right, and the Somatic or greater circulation by the left side. Some writers speak of the portal and chylo-poietic or visceral circulation as forming a third system, but with respect to the heart it is not so, since they are merely a branch of the somatic circulation. Arteries. These are tubes conveying the blood from the heart, a series belonging to each circulation. The somatic and pulmonary arteries leave th^ heart each by a single trunk, which subdivides and terminates in capillaries, whence the venous radicles originate. The volume of the secondary arteries exceeds that of the primi- tive trunk, and similar relations exist, as far as the ultimate 'divisions of the artery, their inclusive Capacity increasing towards their termination. Arterial branches arise at variable, angles, and the originating angle exerts a decided influence on the velocity of the blood current. Blood passing froixi a primary into a secondary vessel which arises from it at a right angle, as in some branches from the aorta, must have its speed slackened ; on the contrary, the velocity is little modified in vessels which kave the paient trunk at a very acute angle, as do many of the arteries of the limbs. The large arteries are usually deep-seated, occupying the cavi- ties of the trunk and the inner surfaces of the limbs, where they are less exposed to injury. When they pass over an articulation, they are generally found on the flexor side. In general, the direction of the larger arteries is straight, but in some parts they are tortuous, as in the stomach, intestines, bladder; tongue, and lips; in fact, wherever the circulation might be impeded by sudden functional change in the form or volume- of the organ. Sometimes this tortuosity is apparently for the purpose of moder- ating the energy with which the fluid is propelled into delicate structures, such as the brain and testicle ; small arteries which run amongst loose structures generally become tortuous during the contraction of the left ventricle. Arteries freely communicate with each other, forming what are termed anaatomoaes ; by convergence, where two branches join at an angle to constitute a single trunk, as the cerebro-spinal STRUCTURE OF ARTERIES. 399^ "branches to form the basilar ; by inosculation, where two vessels of nearly equal size become continuous and form an arch, from t7hich may spring smaller vessels, as in the arteries of the intestines ; by transverse branches^ where two collateral arteries are joined by a small communicating branch, as between the umbilicals as they approach the placenta. In the smaller arteries anastomoses are frequent, forming a network which pervades almost every tissue of the^ body. This is a point of great importance, since the circulation can be thus carried on after the main artery of the region has been obliterated, blood being conveyed from neighbouring sources by the anastomosing arteries, and it is proved that under such circumstances the smaller arteries of the part increase in size. STRUCTURE OF ARTERIES. Arteries are dense and elastic, possessing great power of resist- ance. When empty, they are of a pale buff colour, and preserve their cylindrical form. Their walls consist of three tunics — an internal, middle, and external. The internal, serous, or tunica intima, is the thinnest, and continuous with the lining membrane of the heart. It is made up of two layers ; an inner, consisting of a layer of epithelial scales ; and an outer, transparent, whitish, highly elastic, and perforated, being known as the fenestrated membrane of Henle. When the artery is empty, it is thrown into folds, longitudinal in the large, transverse in the. small arteries ; and when distended, it is smooth and glistening. The tunica media, or contractile middle coat, is elastic, dense, and of a yellow colour, consisting of non-stria,ted muscular, and elastic fibres ; thickest in the larger arteries, it becomes thinner in the smaller. In the largest arteries this coat is composed chiefly of elastic tissue ; in the smallest vessels it is almost entirely muscular. The tunica extima, or external coat, is made up of areolar tissue and elastic fibres, very thin in the large, as thick as the middle coat in the smaller, while in the smallest arteries it is rudimentary or wanting. The external surface is loose, and connected by laminae with the sheath. The arterial sheaths consist of cellular tissue, intimately con- nected with the surrounding textures. The artery has only a loose attachment to the sheath, so as to allow of free gliding on its inner surface. An artery is usually accompanied by a vein. 400 ANGIOLOGY. sometimes by two veins, and generally by a nerve, all of which may lie in the same sheath, the veins being usually more super- ficial. The coats of arteries are supplied with nutrient blood- vessels, the vasa vasorum, which come from neighbouring vessels, and ramify in the external tunic ; they can occasionally be traced into the middle tunic. Arteries are also provided with absorbents, which are only visible on the larger trunks ; and plentifully supplied with nerves, chiefly by the sympathetic, which form plexuses on the larger vessels. The external coat is very tough, ■while the middb and internal are elastic and brittle. On ligaturing an artery, the internal and middle coats give way, while the external one is left unbroken. From the power of resistance possessed by the external coat, we are enabled to stop haemorrhage by torsion ; the middle and internal coats giving way, the external, which remains unbroken, forms a spiral ligature round the others, so tight that it cannot be unravelled by twisting in an opposite direction. CAPILLARIEa The smaller arteries terminate in a system of minute vessels — the capillaries — which are interposed between the termination of the arteries and the commencement of the veins, forming plexuses which vary much in arrangement. Their average diameter is about 75^oVcr^^ ^^ ^^ inch, varying in different textures, smallest in the- brain and mucous membrane of the intestines, largest in the skin, in glands, and the interior of bones. All arteries do not terminate in capillaries, an exception being in erectile tissue, ^here the arteries end in cells or cavities placed at the origin of the veins. PULMONARY ARTERY. (Fig. 154. /.) The pulmonary artery springs from the conus arteriosus of the right ventricle, its origin being guarded by the sigmoid valves ; it curves upwards and. backwards until it reaches the upper part of the left auricle, where it divides into right and left branches, which penetrate the substance of their respective lungs, along with the bronchi, ramifying in the substance along with the bronchial tubes, and terminating by capillary branches, which form a dense network on the walls of the air-cells; the branchesj EXPLANATION OF PLATE V. Blood- Vascular System of the Horse. 1. Heart, right ventricle 2. Heart, left ventricle. 3. Heart, left auricle. 4. Pulmonary artery. 6. Pulmonary veins. 6. Anterior aorta. 7. Carotid artery. 8 8. Glosso-facial artery. 9. Left brachial artery. 10. Dorsal artery. 11. Superior cervical artery. 12. Vertebral artery. 12'. Internal thoracic artery. 13. Humeral artery. 14. Radial artery. 14'. Cubital artery. 15. Great metacarpal artery. 16. Ungual branches. 17. Posterior aorta. 18. Coeliac axis. 19. Mesenteric arteries. 20. Renal artery (left). 21. Small testicular artery* 22. Posterior vena cava. 23. Portal vein. 23'. Hepatic circulation. 24. External iliac artery. 25. Internal iliac artery. 26. Lateral sacral artery. 27. Femoral artery. ?8. Posterior tibial artery. 28'. Anterior tibial artery. 28".Femoro-popliteal artery. 29. Metatarsal vessels. 30. Venous plexus of the foot, 31. Internal saphenic vein. 32. Cephalic vein. 33. Jugular vein. COEONART ARTERIES. 401 belonging to different lobules do not anastomose ; from these capillaries spring the radiclei of the pulmonary veins. The pulmonary artery at its origin is joined by its right side to tho aorta, round which it winds, both .vessels being enclosed in a serous tube, formed by a continuation of the visceral layer of the pericardium ; above this is attached the fibrous layer of the same membrane, which is carried onwards for a short distance as a tubular sheath. About its centre, this artery is united to the posterior aorta by a short, dense, fibrous cord, the remains of the foetal ductus arteriosus ; its walls are thinner than those of the aorta. The pulmonary is the only artery in the adult that conveys venous blood. COMMON AORTA. (Fig. 154. e.) The common or primitive aorta is the main trunk of the arterial system. It arises from the antero-superior part of the left ventricle, being attached to the aortic fibrous ring, and guarded by the sigmoid valves ; it passes upwards and forwards for nearly two inches, then divides into two, the anterior and posterior aortce, the former supplying the fore extremity, neck, and head, the latter the rest of the body, and limbs. The aorta has on its right side the right auricle, and on its left the pulmonary artery, to which it is joined by cellular tissue, the two lying in one sheath. The trunk is traversed by the cardiac nerves. CORONARY ARTERIES. (Fig. 154. d.) In addition to its terminal divisions, the aorta gives off the right and left coronary, or cardiac arteries, each of which arises from one of the sinuses of Valsalva ; thence the right one passes to the right of the pulmonary artery, under the right auricle, and along the auriculor ventricular furrow ; oi. reaching the right longi- tudinal furrow, it divides into vertical and transverse branches. The vertical descends the right longitudinal furrow, yielding branches to the ventricular walls, rounds the apex, and anasto- moses by convergence with, the corresponding left branch ; the small transverse branch passes along the transverse furrow, anasto- mosing with its fellow. The left coronary artery arises as the 2d 402 ANGIOLOGY. Tight, passing out behind and between the pulmonary artery, and the apex of the left auricular appendix, and immediately divides into vertical and transverse branche?, with a distribution similar to that of the right one. We will first consider the Posterior, afterwards the Anterior Aorta POSTERIOR AORTA. ^PlateV. 17.) The posterior aorta is larger and longer than the anterior. It ' Fig. 164. Thorax opened on the left side — showing the heart and large vessels in aitu. a a, Piericardial sac*; 6, Left ventricle ; c, Eight ventricle ; d, Left coronary artery : e, Primitive or common aorta ; «', Anterior aorta ; c", Posterior aorta ; /, Pulmonary artery, divided and ligatured ; g, Anterior vena cava ; h. Posterior vena cava ; i, Eight bracial, or brachio-cephalic artery ; k, Left brachial artery ; I, Left dorsal artery, giving off the subcostal posteriorly ; m. Left superior cervical artery ; n, Left vertebral artery ; o, Left inferior cervical artery ; p, Left external ; and q. Internal thoracic arteries. commences at about the level of the fourth dorsal vertebra, passes upwards and backwards, forming the aortic arch, and reach- ing the left side of the spine at the sixth or seventh dorsal ver- tebra. It passes straight backwards to the hiatus aoi'ticus, entering the abdomen between the pillars of the diaphragm, and terminat- PARIETAL BRANCHES. 403 ing in the posterior part of the sublumbar region by breaking up into the external and internal iliacs. It is divided into thoracic and abdominal portions. The arch of the thoracio portion is crossed on the right by the trachea and oesophagus, having the puLnonary artery on the left ; along the spine it lies in the pos- t-.'ior mediastinum, related on the right with the vena azygos and the thoracic duct. The ahdoTninal portion is embraced by tv/igs of the sympathetic nerve, and related with the reservoir of Pecquet above, and the posterior vena cava on its right. The posterior aorta furnishes parietal and visceral branches, which we tabulate as follows : — PARIETAL BRANCHES. Aortic intercostal.. j Phrenic. Lumbar. I Middle sacral. The Intercostal arteries are doublets, seventeen in number, the last thirteen of which, the aortic ivJerccctals, arise directly from the posterior aorta ; while the first arises from the superior cervical, the next three from the dorsal artery. The aortic inter- costals leave the superior part of the trunk at right angles, skirt the dorsal vertebra, and at the upper margin of the intercostal spaces divide into inferior or intercostal, and superior or dorso- f pinal. The intercostal branch is the larger, and travels along the grooved posterior border of the rib down the side of the thorax, associated with the vein and nerve. These arteries anastomose with the asternal, and anterior abdominal branches of the internal thoracic ; while the last four traverse the abdominal muscles, and anastomose with the abdominal and circumflex ilii. The intercostal branch supplies the pleura, intercostal, and thoracic muscles. The dorso-spinal branch is distributed to the dorsal muscles and integument, supplying the spinal cord and its coverings through the intervertebral foramen. The Lumbar arteries, five or six pairs, originate like the inter- costals, dividing in the intertransverse spaces into superior or lumho-spinal, the larger, which are distributed to the muscles and integument of the loins, furnishing spinal branches to the cord and its membranes ; and inferior , which pass to the psoe, transyersalis abdominis, and internal oblique muscles, and there anastomose wHth the circumflex ilii. The last lumbar may arise from the internal iliac artery (Fig. 158. 1, 1), The Phrenic or Diaphragmatic arteries are usually two or. 404 ANGIOLOGY. three small vessels which arise at thd hiatus aorticus ; one goes to the left, the other to the right diaphragmatic crus, terminat- ing on the phrenic centre. The right gives twigs to the pleura and right lung. The Middle Sacral artery is a single mesian continuation of the posterior aorta. Large in some animals, when present in the horse it is extremely rudimentary, and it is often absent. VISCERAL BRANCHES. Broncho-oesophageal. — Thoracic Coeliac axis. Great mesenteric. Small mesenteric. i » , , . , _, , >Abaommal. Renal. Spermatic. Small testicular. The BrOncho-cesophageal arises close to and sometimes with the first pair of aortic intercostals, breaking up into bronchial and oesophageal branches. The bronchial arteries pass between the aortic arch and the oesophagus, to the bifurcation of the trachea, dividing into right and left, which enter the lungs with the bronchi, ramifying with the air-tubes, and terminating in the pulmonary capillaries. The oesophageal artery proceeds back- wards to the posterior mediastinum ; reaching the oesophagus, it divides into two. The large superior one is distributed to the upper, the inferior to the tinder surface, Anastomosing with the pleural branch of the gastric, and supplying the posterior mediastinum. CCELIAC AXIS. (Fig. 155. 1.) This is a short trunk arising from the lower surface of the aorta as it enters the abdomen. About an inch in length, it divides into the gastric, splenic, and hepatic arteries. The Gastric, the central and smallest division, passes the cardiac orifice of the stomach, and divides into right or anterior, left or posterior, and pleural ; the latter enters the thorax by the foramen sinistrum, bifurcates and anastomoses with the oesophageal and superior branches of the thoracic artery. The right gastric passes to the oesophagus over the lesser curvature of the stomach. CCBLUC AXIS. 405 and is distributed to the anterror a^p^et of the greater cvl-de-saG ; the left gastric gains the posterior aspect, and ramifies over the right cul-de-sac ; both are tortTiou?, and anastomose with each other and with the splenic artery. The Splenic artery, the largest coeliac division, passes to the left, over the fundus of the stomach, and enters the hilus of the l.O. 155. Abdominal branches of the posterior aorta- ^che left abdominal wall and diaphragm, small intes- tine and great colon being removed. I, Aorta ; II, Liver ; III, Sto&ach ; IV, Spleen ; V, Left kidney ; VI, Floating colon ; 1, Coeliac axis ; a, Gastric artery ; a'. Its anterior, and a". Its posterior branch; a'", Pleural artery; b b. Hepatic artery ;. 6' 6', Pyloric artery; 6", Duodenal artery ; 5"', Right gastro-epiploic artery ; c, Splenic artery ; lciniar arteries. Each clings to its relative side of the deep flexor tendon, and at the level of the upper end of the suspensory ligament, both anasto- mose with the perforating pedal artery, forming a second or inferior anastomotic, arch. From this^ arch are given off two small vessels which ramify over the flexor tendons, and au external and internal interosseous 'plantar- artery ; the latter is the larger, and appears to be the continua- Fig. 160. Arteries of the right posterior limb — external view. 1, Popliteal; 2 2, Poste- rior tibial; 3 3, Anterior tibial; a, Per- oneal ; h. Muscular branches ; 4, Perfor- ating pedal ; 5, Great metatarsal. 416 . . ANGIOLOGf. lion of the perforating artery, running down the inner border of the suspensory ligament ; the external one, very small, passes down the outer border. At the fetlock joint these vessels unite with the great metatarsal artery to form the sesamoidean arch. ANTERIOR TIBIAL ARTERY. (Fig. 160. 3, 3.) This is part of the main trunk, being really the continuation of the popliteaJ ; it winds forwards between the tibia and fibula to the fore part of the leg, gaining it midway between the stifle and hock. It lies between the deep face of the flexor metatarsi muscle and the tibia. At the hock it passes obliquely outwards, crossing the joint, and becomes the, great metatarsal artery at the proximal end of the metatarsus. It gives off twigs to the adjacent muscles, which anastomose with the popliteal, and the j>eroneal branch, which supplies and runs under the peroneus, and it finally divides about the tarsus into the great ^metatarsal and perforating pedal arteries. The ArterIa pedis perforans, or Perforating pedal artery passes through the tarsal joint, in a canal between the cuboid and cuneiformes magnum and medium, down the back of the metatarsus, to the arterial arch formed by the plantar branches of the posterior tibial artery. GREAT METATARSAL ARTERY. (Fig. 160. 5.) The great metatarsal artery originates at the proximal and external aspect of the large metatarsal bono ; lying in the groove between it and the small metatarsal bone, it insinuates itself between them, passing under the osseous nodule of the latter; it gains the back of the large bone, passing through the bifurca- tion of the suspensory ligament, and finally anastomoses with the internal and sometimes the external interosseous plantar branches of the posterior tibial ; thus forming the sesamoidean arch, whence spring the external and internal digital arteries, which gain the sides of the fetlock. DIGITAL ARTERIES. 417 DIGITAL ARTERIES. The digital arteries, v/hich are alike in the fore and hind limbsy originate at an acute angle below the bifurcation of the suGpensciy ligament, in front of the flexor tendons, passing over tho inDGi" and outer sides of the fetlock joint, accompanied by satellite veins and nerves ; the artery being central, and the n^rve posterior. Each runs down the side of the digit, inside the lateral cartilage, to the superior border of the ala of the 03 pedis, thence they reach the tendinous surface of the bone, terminating at the plantar foramina on either side of the insertion of the flexor pedis perforans. They supply numerous tvags to the flexor and extensor tendons, fetlock pad and joint, and give off the following branches, which are usually regarded as tbe arteries of the foot — Artery of the Frog. Perpendicular. Transverse. Preplantar ungual. Plantar ungual. The Perpendicular artery, which arises at right angles, below the middle of the os suffraginis, descends on the side of the digit, inclining forvv^ards, and terminates above the coronary ligament by anastomosing with its fellow, their union forming the superficial coronary arch, whence spring about twenty branchlets, which descend to the coronary substance. The Transverse artery, given off under the lateral cartilage, passes forward between the front of the bone and the extensor tendon, and inosculates with its fellow, forming a second arch — - the deep coronary arch (superior coronary circle), from which spring several branches to the neighbouring parts, some passing on to the superficial CDronary arch; a second branch inosculates with its fellow posteriorly just above the navicular bone. The Artery of the Frog arises behind the pastern joint at the superior part of the lateral cartilage, entering the sensitive frog. It divides into anterior and posterior ; the latter also assists in supplying the lateral cartilage. The Preplantar ungual, or Lateral laminal, given off at the posterior aspect of the ala of the distal phalanx, passes through the notch and foramen between the retrossal and basilar processes, and along the preplantar groove in the wall of the bone, at the anterior extremity of which it terminates by several branches, which enter the pedal bone, and anastomose with the 2 E AiS ANGIOLOGT. circnlus arteriosus. At its origin, a retrograde branch passes to the bulb of the frog ; and after traversing the preplanter groove, it gives off a second retrograde, which supplies the external part of the lateral cartilage, one twig inosculating below with the circumflex artery. It supplies numerous ascending and descending branches which ramify in the sensitive laminae, anastomosing with those of the coronary arch and circumflex artery. The Plantar unoual is the terminal branch of the digital ; it passes through the plantar foramen on the tendinous surface of the OS pedis, and enters the bone, within which it inosculates with its fellow, forming the circulus arteriosus, or plantar circle, from which spring ascending and descending branches. The former are the anterior laminals, which leave the bone through numerous apertures on its wall, and ramify among the sensitive laminae ; the latter are the inferior communicating arteries, which average fourteen in number ; they pass through the foramina situated just above the edge of the os pedis, and unite outside to form the circumflex artery, which runs round the toe, giving o^ ascending branches to the sensitive laminse, and about fourteen descending ones, the solar arteries, which supply the sensitive sole, uniting posteriorly to constitute the inferior circumflex artery. Anterior Aorta. (Fig. 154. e.) The anterior aorta is rather more than one inch in length, arul passes obliquely upwards and forwards, between the layers of the anterior mediastinum, over the right auricle, under the trachea, and to the left of the anterior vena cava ; after furnishing a few insignificant twigs to the pericardium and mediastinum, it divides into the right and left -arteria innominata, or brachial arteries. brachial arteries. (Fig. 154. i, h) The brachial arteries separate at an acute angle, the left being uppermost, and pursue -a diverging course towards the anterior aperture of the thorax, whence they proceed to the pectoral limbs, winding round the first ribs, and below the scalenus muscles; the right one gives off the common carotid trunk ^ hence it is distinctively known as the brachio-cephalic arteQi:pf.nd. is larger BRACHIAL ARTERIES. 41^ than the left. Both pass forward between the layers of the anterior mediastinum, the rip;ht below, the left to the side of the trachea, and partly under the oesophagus. The following are the arteries given off alike by both brachials. The first four arise within the thorax, the next two at its entrance, ''vhile the last two arise externally. Dorsal. Superior cervical. Vertebral. Internal thoracic. External thoracic. Inferior cervical. Prescapular. Subscapular. Fio. 161. Arteries of the neck expojsed on the left side, a, Anterior aorta; a'. Left brachial; a'^. Bight ■ brachial, or brachio-cephalic ; 6, Left dorsal ; e c, Superior cervical ; d, Vetebral ; e. Inferior cervical ; /, Cephalic or common carotid ; /', Left, and /", Eight carotid ; g g, (Esophageal twigs ; h h. Tracheal twigs ; i i, Muscular twigs ; fc, Thyroid : I, Thyro-laryngeal ; m. Branch to Parotid gland. The Dorsal artery runs on the outer side of the trachea, oesophagus, sympathetic nerve, and longus colli muscle, through the second intercostal sjpace, reaching* the withers ; it supplies the muscles of that region. The anterior branch goes to the splenius and complexus major, anastomosing with the terminal twigs of the cervical. Within the thorax, the dorsal gives off a few twigs to the mediastinum, and a large subcostal branch 420 ANGIOLOGY. which furnishes usually from the second to the fourth anterior intercostal arteries. The Superior cervical artery arises anterior to the dorsal, sometimes along with it, having the same relations until it passes through the first intercostal space. It then runs upwards along the ligamentum nuchas, covered by the complexus major, as far as the vertebra dentata, distributing branches to the muscles of the neck, and anastomosing with the dorsal and vertebral arteries. Within the thorax, it gives off the first intercostal artery, and a twig to the mediastinum. The Vertebral artery arises opposite the first rib, gains the outer side of the trachea and cesophagus, and leaves the thorax, passing under the transverse process of the seventh, and through the foramina in the transverse processes of the sixth to the second cervical vertebrae," covered by the intertransversalis colli. On reaching the atlas it anastomoses with the retrograde branch of the occipital artery, or ramus anastomoticus, which comes through the posterior foramen on the wing of the atlas. Here it is covered by the obliquus capitis posticus muscle. It supplies branches to the muscles of the neck, also to the spinal cord and its membranes, through- the intervertebral foramina. The Internal thoracic. Pectoral, or Mammary artery, ori- ginates at the first rib, opposite the vertebral. It descends to the second bone of the sternum, passing over the costal cartilages to the ensiform, where it splits into anterior abdominal, and asternal branches, after giving twigs to the pericardium and mediastinum ; and intercostal branches, which are distributed to the pectoral muscles, anastomosing with the external thoracic and first seven intercostal arteries. In the young it supplies the thymus gland. The anterior abdominal leaves the thorax at the ensiform. cartilage, penetrates the rectus abdominis, and anastomoses with the epigastric artery. The asternal artery winds round the cartilages of the false ribs, crossing the digit ations of the trans- versalis abdominis, and terminating in the thirteenth intercostal space, by anastomosing with the intercostal artery ; it supplies the diaphragm and transversalis muscles. The Inferior cervical- artery is given off as the brachial leaves the thorax, passing between the jugular confluent and the pectoralis parvus, and dividing into ascending and descending branches. The former runs between the levator humeri and sub- scapulo-hyoideus, supplying the lymphatic glands and adjacent BRACHIAL ARTERIES. 421 muscles; the latter lies between the pectoralis anticus and levator humeri, terminating in the pectoral muscles. The External thoracic or mam- mary artery arises close to the inferior cervical, turns round the anterior border of the first rib, and passes along the internal aspect of the pec- toralis magnus and parvus, a small branch accompanying the spur vein, and ramifying in the panniculus. The Prescapular artery arises from the brachial, in front of the tendon of the subscapularis, passing between it and the antea-spinatus,; it is accompanied by a vein and nerve to the dorsum scapulse, supply- ing the shoulder joint, pectoralis parvus, scapular muscles, and flexor brachii tendon. The Subscapular artery arises at right angles from the brachial, just before it becomes the humeral, near the interstice separating the subscapu- laris and teres internus muscles. It passes up the inner side of the caput magnum, and terminates at the dorsal angle of the scapula, supplying branches to the latissimus dorsi, scapu- lar, and lateral thoracic muscles ; also the nutrient scapular y and the soapulo-humeral, or posterior cir- cumflex artery, which passes outwards behind the shoulder joint, under the caput magnum and postea-spinatus, terminating in the external muscles of the region. When the brachial artery reaches ithe humerus it assumes the name of the humeral artery, just as the exter- nal iliac becomes the femoral -as it Fig. 162. Arteries of the anterior limb— viewed from inside. 1, Brachial ; 2, Humeral ; 3, Anterior radial ; 4, Posterior radial; 5, Becnrrent radial ; 6, Badio-palmar ; 7, Large metacarpal ; a, Prescapular ; h. Subscapular ; Vy Branch to latissi- mus dorsi ; &", Posterior drcumflez ; V", Scapular nutrient and muscular branch; 6"", Main branch supplying the muscles ; c. Anterior circumflex ; d, Humeralis profunda : e. Cubital : e', Nutrient artery of humerus ; ef'. Branch to inferior brachial glands ; d". Descending branch forming supe- rior carpal arch ; e"". Anterior sub- cutaneous ; /, Interosseous ; /, Branch to the carpus ; g^ Muscular branches. passes the pelvic brim. 42 S ANGIOLOGY. , ■.•>.> • - • ■ ■ - - HUMERAL ARTERY. (Fig. 162. 2.) . The humeral artery, the continuation of the brachial, descends obliquely backwards, along the inner side of the humerus ; just above the elbow joint i^ divides into anterior and posterior radial arteries, or more correctly speaking it gives off the former, and is continued by the latter. Its principal branches are as follows : — Anterior circumflex. Humeralis profunda. Cubital. Coraco-radial. Anterior radial. The PREHUMERAL or Anterior circumflex artery passes between the two heads of the coraco-humeralis, reaches the front of the humerus, and terminates in the levator humeri, giving twigs to the flexor brachii, coraco-humeralis, and the shoulder joint, anastomosing with the posterior circumflex. The Arteria humeralis profunda arises near the conjoined tendon of the latissimus dorsi and teres intemus, is divided into two chief branches, which are distributed to the caput magnum and medium, the anconeus, humeralis obliquus, and extensor metacarpi magnus, anastomosing by one branch with the anterior radial artery. The Cubital or Ulnar artery passes backwards beneath the scapulo-ulnaris, along the lower border of the middle head of the triceps extensor, down the forearm, between the external and middle flexors of the metacarpus, with the cubital nerve and vein, inosculating at the knee with the recurrent branch of the posterior radial artery, so forming the superior cdrpal arch. It gives off branches, to the caput medium, scapulo-ulnaris, pectoralis trans- versus, brachial fascia, and flexors of the leg; also a nutrient artery to the humerus, and twigs to the elbow joint, with a small anterior subcutaneous branch. The Coraco-radial artery, given off nearly opposite to the last, passes forwards to the flexor brachii muscle, dividing into ascending and descending branches. The Spiral or Anterior radial artery is given off at an acute angle, just above the condyle of the humerus. It descends over the anterior surface of the elbow joint, and beneath the flexor muscles of the fore-arm and origin of the extensor meta- <^arpi, where it meets the radial nerve. They travel together in POSTERIOR RADIAL ARTERY 42 S front of the radius, and approach the knee below the extensor pedis. It divides into numerous branches, which are distributed to the capsular ligament of the carpus and extensor muscles, anastomosing with the interosseous branch of the posterior radial artery. POSTERIOR RADIAL ARTERY. (Fig. 162. 4.) The posterior radial is the continuation of the humeral artery.* It passes down the inner side of the fore-arm, with a vein and nerve, inclining backwards beneath the flexor metacarpi internus,' and is sometimes described as dividing at the distal end of the radius into large and small metacarpals ; it can be felt just behind the insertion of the flexor brachii. It supplies twigs to the elbow joint, which anastomose with those of the ulnar, and muscular branches to the posterior region of the arm, with the following :named branches : — Interosseous. | Badio-palmar. Recurrent radial. The Interosseus artery of the fore-arm comes off near the radio-ulnar arch, through which it passes outwards, crossing the posterior surface of the radius below the perforans. It then descends in the radio-ulnar groove, covered by the extensor sufifraginis, and inosculates with the anterior radial, forming a plexus above the carpus ; it yields branches to the elbow joint and flexor muscles, also the nutrient radial, to supply the radius. The Recurrent radial artery is a small branch given off just above the carpus; passing outwards and downwards, under the flexor metacarpi medius, it inosculates with the cubital and forms the superior carpal arch, from which a branch descends in the thickness of the annular ligament, to inosculate with the radio-palmar, below the carpus, and form the inferior carpal arch. The Radio-palmar or Small metacarpal artery is given off at an acute angle. It passes the inner and posterior aspect of the carpus, external to the posterior annular ligament, which separates it from the large artery. About the head of the meta- carpus it crosses from the inner to the outer side at the back of the leg; inosculating with a descending branch from the superior carpal arch, and so forming the inferior carpal arch, whence 424 ANGIOLOGY. originate two anterior arid two posterior interosseous palmars. The antet*ior ones pass round the heads of the small metacarpal bones, and along the grooves between them and the large bone, anastomosing with the spiral above, and a branch of the large metacarpal artery below. The posterior interossei descend on either side of the suspensory ligament, inosculating near the distal end of the metacarpus with branches from the large meta- carpal artery. One of them gives off the nutrient artery of the great metacarpal bone. LARGE METACARPAL ARTERY. (Fig. 162. 7.) This is the continuation of the posterior radial artery. It runs beneath the posterior annular ligament in company with the flexor tendons, afterwards descending to their inner side, along with the internal metacarpal nerve and vein. Above the fetlock it passes between the tendons and suspensory ligament, dividing into the external and internal digital arteries. At its bifurca- tion it gives off a recurrent branch, which divides and ascends, one branch on the inner, another on the outer lateral aspect of the suspensory ligament, anastomosing with the posterior inter- ossei. From the sesamoidean arch, thus formed by union of all the posterior arteries of the region, the digital arteries may be said to arise, and likewise small transverse branches, which encircle the fetlock joint. The metacarpal artery gives off. branchlets to the tendons and ligaments during its course. The circulation of the digit is the same as in the pelvic limb. t Cephalic and Carotid Arteries. (Fig. 161.//'/".) The right brachial artery, besides supplying branches corre- sponding to those of the left, gives off the common carotid or cephalic artery, which is detached at an acute angle, and directed forwards under the trachea and above the anterior vena cava. On reaching the anterior opening of the thorax, ifc bifurcates, forming the Left and Right carotids, which pass up the side of the neck, diverging as they ascend, at first belov/, afterwards on the sides of the trachea, to which they are attached by areolar tissue. At the middle of the neck, they reach the posterior OCCIPITAL AKTERY. 425 tracheal aspect, and are continued to the level of the larynx^ where they break up. Throughout their course, they are accom- panied by the par vagum, cervical portion of the sympathetic, and inferiorly by the recurrent nerves, all being enclosed in the same sheath. The arteries are covered at the lower part of the neck by the scalenus and levator humeri; in the middle by the sub- scapulo-hyoideus, w^hich separates them from the jugular vein ; and they are related with the rectus capitus anticus major, and longus colli superiorly. The carotid and jugular are usually separated by slips of the subscapulo-hyoideus, but at the entrance of the thorax they contact, the artery lying superiorly. The carotids give off several small branches to the muscles of the neck, twigs to the trachea and oesophagus, and near their termination, the thyroid and thyro-laryngeal arteries. The thyroid artery enters the inferior part of the thyroid gland, to which it is distributed. The thyro-laryngeal arises just above the latter, opposite the upper tracheal ring, winds round the trachea, and divides into branches, supplying the thyroid body, pharynx, and larynx. The carotid artery terminates by a trifurcation, forming the following important arteries : — Occipital. I Internal carotid. External carotid. OCCIPITAL ARTERY. (Fig. 163. 1.) The occipital artery comes off at the carotid trifurcation. At first it accompanies the internal carotid, then crosses it, and reaches the under -surface of the wing of the atlas, at the back of the guttural pouch, passing between the submaxillary gland and anterior straight muscles of the head, through the external anterior foramen of the atlas, and at the upper surface of the latter it divides into the cerebrospinal and musculo-occipital. It is crossed by the par vagum and spinal accessory nerves and the cervical portion of the sympathetic chain, and accompanied by divisions of the inferior branch of the spinal nerves. Its branches are these : — Prevertebral. Ramus anastoraoticus. Mastoid. Musculo-oecipital. Cerebro-spinal. ^'23 ANGIOLOGY. The PiiEVERTEBRAL artery comes off as it crosses the internal carotid, and divides into muscular and meningeal branches, the muscular going to the anterior straight muscles of the head and occipito-atloidean articulation. The meningeal are small superior and inferior branches, which are distributed to the dura mater through the foramen lacerum basis cranii,and the condyloid foramen. The Mastoid artery leaves the trunk opposite the pre- vertebral, is directed to the mastoid foramen of the temporal bone, passing over the styloid process of the occipital, under the obliquus capitis anticus. It gains the parieto-temporal conduit, and inosculates with the meningeal branch of the internal maxillary artery. It supplies the temporal nauscle, and the dura mater. The Ramus Anastomotic us'"' is detached at the under surface of the wing of the atlas ; it passes backwards through the posterior foramen under the obliquus capitis posticus, land inosculates, with the vertebral artery. It supplies numerous muscular twigs, and furnishes a direct communication between the carotid and vertebral arteries. The MUSCULO-OCCIPITAL artery arises from the occipital, in the alar gutter; covered by the obliquus capitis posticus, it passes transversely outwards to the posterior straight muscles, and divides into ascending muscular and cuticular branches for the occipital region, and descending y which anastomose with the superior cervical artery. The Cerebro-spinal artery springs from the occipital in the alar gutter, and enters the neural canal through the internal atloid foramen, traverses the spinal dura mater, dividing on the inferior surface of the cord into an anterior branch, which passes forwards, anastomosing by convergence with its fellow from the opposite side, to form the basilar trunk; and a iwsterior branch, which, after a short backward course, likewise anastomoses with its fellow from the opposite side, constituting- the middle spinal artery. INTERNAL CAROTID ARTERY. (Fig. 163. 2,) This, the second terminal of the coilimon carotid, is directed upwards towards the base of the skull, to the outer side of the ♦ [This artery Is described as inconstant and variable ; doubtless it is the latter, but hitherto I do not recollect ever to have sought for it in vain, — Ed.] EXTERNAL CAROTID ARTERY. 427 anterior straight muscles, accompanied in the first part of its. course by the occipital artery, the carotid being more posterior. At the origin of the prevertebral and mastoid branches, it is in- flected forwards, crossing the occipital behind the comu of the os hyoides; it passes to the foramen lacerum basis cranii, at first lying in a fold of the guttural pouch, along with the superior cervical ganglion and a branch of the sympathetic which enters the cranium ; it is crossed by the nerves which form the guttural plexus. Passing through the foramen lacerum, it enters the cranial tavity to assist in supplying the brain. For description of the cranial portion of this artery, see the description of the brain itself. EXTERNAL CAROTID ARTERY. (Fig. 163. 3.) The external carotid artery is the continuation of the carotid itself, being deeply buried between the guttural pouch and parotid gland. It passes forwards and upwards, until it reaches the comu of the os hyoides, passing between it and the hyoideus magnus, and curves upwards towards the neck of the condyle of the lower jaw, where it divides into superficial temporal and internal maxillary arteries, the latter being its continuation. In the first part of its course it has the guttural pouch, glosso- pharyngeal, and superior laryngeal nerves on its inner, and the superior belly of the digastricus and the hypo-glossal nerve on its outer aspect. From it spring the four following branches : — Glosso-facial. I Posterior auricular. Maxillo-muscular. j Superficial temporal. The Glosso-facial or Submaxillary artery arises before the carotid passes between the hyoid cornu and the hyoideus magnus. It passes the anterior extremity of the submaxillary gland, runs along the upper border of the digastricus, crosses the outside of Wharton's canrl, reaches the ramus of the lower jaw within the mazillary space, and winds round it subcutaneously, reaching the cheek, where it ascends in front of the masse ter muscle, and at the maxillary spine terminates in ascending and descending branches ; the latter, or lateral nasal, passes forwards; the former divides into dorsal nasal, which goes inwards, and angulcir artery of the eye, which passes backwards to supply the orbicularis palpebrarum, inosculating with branches from the superior dental artery. In 428 ANGIOLOGY. addition to twigs supplied to the submaxillary gland and facial muscles, five branches are given off, the pharyngeal, lingual, sub- lingual, and inferior and superior labial or coronary arteries. The pharyngeal, or ascending pharyngeal, is given off near the origin of the glosso-facial, passing obliquely upwards between the comu of the os hyoides and the hyo-pharjmgeal muscle. It takes a flexuous course towards the pterygoid process, terminating in the velum palati, and giving off ascending and descending branches to the walls of the pharynx. Fio. 163. Arteries cf the head— the left maxillary ramus being removed. 1, Occipital ; 2, Internal carotid : 3, External carotid ; a, Branch to submaxillary gland ; b, Prevertebral ; c, Mastoid ; c/ Ine ; 4, CwcTjm • 5, Great colon ; 6, Floating c<»lon and tectum ; 7, Pancreas; 8; Liver; a a, Portal vein ; h, Anterior mesenteric vein ; 2/ V, Veins of small intestine ; V, Ileo-caacal; &"', Colie vein ; c c, Posterior mesenteric vein ; d, Gaslro-splenio ; d'. Posterior gastric vein ; d", Splenic vein ; d"\ Its Afjistric brandies, They join tlie upper surface of the vena cava. The anterior ones often terminate in the vena azygos. COMMON ILIAC VEINS, (Fia 165, ttj 6.) These are two large, short ve.^sels, formed by the union ofthe^ external and internal iliacs, the former collecting the blood iroila. VEINS OF THE FOOT. 439 the posterior extremity, the latter from the hinder part of the trunk. They are lodged in the angles of separation comprised between the external and internal iliac arteries, the right one, the shorter, passing above the external iliac artery to meet the left at the origin of the posterior vena cava. The left one before it joins its fellow passes between the body of the last lumbar vertebra and terminal extremity of the posterior aorta. EXTERNAL ILIAC VEIN. (Fig. 166. b'.) In studying the branches of the external iliac vein, it is advis- able to commence at the foot. The venous plexuses of the foot unite to form two digital veins, and these are succeeded by three Tnetatarsais, the common origin of the four veins of the thigh, which are distinguished as subcutaneous and deep. The deep are continued as the popliteal and femoral, the latter being conr tinned hy the external iliac vein. VEINS OF THE FOOT. The veins of the foot are very numerous, and arranged in a superficial and interosseous network. They are valveless, allowing the blood to flow in either direction during sudden emergency. The external or superficial plexuses are the solar, laminal, and cm^onary. The SOLAK PLEXUS is remarkable for the equality of the dia- meter of its veins throughout the extent of the plantar surface of the foot, as well as for the paucity of anastomoses of them with the deep-seated veins. They chiefly terminate in the large cir- cwmjkx vein which accompanies the artery of the same name, and receives also descending twigs from the laminal plexus, as it passes back to the wing of the bone, and thence into the coronary plexus. The remaining branches of the solar plexus reach the small central vein, situated around the semilunar ridge, on the solar surface, and terminate also in the coronary plexus. The Laminal plexus rests on the sensitive wall of the foot The branches, uniform in the sensitive laminae, gradually increase in size as they approach the coronet, where the majority terminate in the coroTiart/ plexus ; the remainder pass down to the circum- ^ex vein. 440 ANGIOLOGY. The Coronary plexus surrounds the os coronse and upper part of the OS pedis. Extending backwards below the lateral cartilages, the plexus consists of an anterior or middle, and two lateral por- tions.- The middle coronary lies in front of the foot, and receives the anterior ascending branches of the laminal plexus. The lateral coronary plexus consists of a superficial and a deep portion, the former situated upon, the latter under, the lateral cartilage, and formed by the posterior branches of the laminal, the deep one being joined by veins from the coronet, and from the ligaments and tendons of the region. The veins of the frog extend over the external surface of the sensitive frog, ascend the sides of the lateral cartilages, and unite to form a large vein, which, with branches from the superficial and deep coronary plexuses, runs up the lateral aspect of the os coronse, all uniting near its head to form the digital vein. The internal or interosseous veins of the foot form a system of satellites to the circulus arteriosus and its branches. Tliey pass out of the bone through the plantar foramina, at each side of the tendinous surface ; thence up the inner side of the lateral cartilages, finally uniting with the branches of the deep coronary plexus. DIGITAL VEINS. The digital veins, formed by the union of the deep and supei-ficial coronaries, and veins from the frog, ascend the digit in company with the arteries and nerves, and terminate a little above the fetlock, by uniting to forni an arch between the flexor tendons and suspensory ligament. From this arch, the sesamoid dearly spring the three metatarsal veins. The digitals receive branches corresponding to the perpendicular and transverse divi-^ sions of the arteries, as well as twigs from surrounding structures* METATARSAL VEINS. The metatarsal veins are three in number, internal, external, and deep, originating in the sesamoidean arch. The internal is the largest, and appears to be a continuation of the internal digital. It passes up the cannon bone, internal to, and a little in front of, the flexor tendons, accompanied by the internal metatarsal nerve. Nearing the hock, it crosses obliquely to the anterior surface of the joint, where it communicates hy a large. SUPERFICIAL VEINS. 441 transverse branch with the origin of the anterior tibial vein, and then passes along the inner surface of the leg, forming the anterior root of the internal saphenic vein. The external metatarsal vein occupies a position on the outer side of the flexor tendons, analogous to that of the internal. Towards the superior extremity of the cannon, it anastomos'es with the deep vein, then continues its course upwards, accompanied by the plantar arteries, gains the hollow- above the tarsus, passing along the femoro-popliteal nerve, and forms the posterior root of the internal sphenic vein. The deep metatarsal vein originates below the flexor tendons, and passes up underneath the suspensory ligament, to the inner side of the chief interosseous plantar artery. Below the hock, it receives the large anastomotic branch from the external vein, passes through the canal formed between the cuboid and cuneiform bones, finally forming the principal branch of the anterior tibial vein. Above the hock there are four large veins — a deep-seated pair, the anterior and posterior tibial, and a superficial pair, the. internal and external saphenic veins. DEEP VEINS. The Anterior tibial vein is a satellite of the corresponding artery. It is frequently double, arising on the anterior surface of the hock by several branches, the chief one being the deep metatarsal vein. Accompanying the artery, between the tibia and fibula, it joins the posterior tibial to form the popliteal vein. The Posterior tibial vein commences in the hollow in front of and inside the calcaneum, by branches furnished principally by the two saphenic veins. It passes up the leg, with the posterior tibial artery, and under the popliteus muscle unites with the anterior tibial vein. SUPERFICIAL veins. The superficial or subcutaneous veins are the internal and external saphenics. The Internal or Vena saphena major originates by two large roots at the inner part of the hock. The anterior root is a continuation of the internal, the posterior of the external metatarsal veins; these converge, and form one large vessel on 442- ANGIOLOGY, the internal surface of the leg. It ascends, and terminating near the groin, may either pass through the interstice between the gracilis and sartorius muscles, entering the femoral vein; or it may end, near the origin of the gracilis, by joining the external pudic veins. The External saphena or Vena saphena minor, originates at the front of the os calcis, anastomosing with the posterior root of the internal saphenic, with which, above the hock and in front of the calcaneum, it forms a large plexus of veins. It also anas- tomoses with the posterior tibial vein, by a large branch which passes between the tibia and flexor pedis perforans ; and it runs along the tendon of tke. gastrocnemius, in company with a nerve, terminating near the stifle joint in the popliteal vein. The Popliteal vein, formed by the union of the anterior and posterior tibials, is a satellite of the popliteal artery, and receives branches corresponding to those given off from the latter. The principal one is the femoro-jpopliteal, which enters with the external saphenic vein. The Femoral vein, a satellite of the artery, is the continuation of the popliteal. Its branches are similar to those of the femoral artery, with the addition of the internal saphena, which joins about its middle third. The femoral terminates in the extenial iliac vein. The External iliac is thus the continuation of the femoral vein ; and is the larger of the two branches which form the common iliac. In its course, this vein, which commences at the pubis, receives no important collateral branches, excepting the circumflex vein of the ilium, a satellite of the corresponding artery. INTERNAL ILIAC VEIN. (Fia. 165. 6'.) The internal iliac vein, which, with the external, forms the common iliac trunk, is very short, and formed by the union of satellites, corresponding to the branches given off from the inter- nal iliac artery. ANTERIOR VENA CAVA. (Fig. 167. 1, 1.) The anterior vena cava is the venous trunk, which returns the blood chiefly from the head, neck, fore extremities, and part of ANTERIOR VENA CAVA. 443 the thorax. Thia large but short vessel is cituated at the anterior part of the thorax, between the layers of the anterior mediastinum, below the trachea, and to the right of the anterior aorta, to which it corresponds. It is formed between the first pair of ribs, by the union of the two jugular and two brachial veins, receiving the internal thoracic, vertebral, superior cervical, dorsal, and the great vena azygos. The Internal thoracic, Vertebral, and Superior cervical veins, are satellites of, and counterparts in distribution to, their corresponding arteries. Fjo. 2C7. Thorax opened on the right side to show the hc&rt aad veins. A, Heart, with left coronary vein ; 1 1, Aaterior cava ; 2, Posteficr cava ,» a, Lsft brachial ; 6, Eight brachial cut ; c, Left jugular ; d. Internal thoracic ; d! , A mediastntJ vela ; t, Bight vertebral ; /, Dorsal and superior cervical ■veins discharging together ; /, Bight suTierlor cervical ; /", Eight dorsal ; g. Vena azygos ; g', CEso- phageal ; g". Bronchial ; (/"' £/'", Intercostals. The Dorsal vein follows the same course as the dorsal artery, receiving also several intercostaJ branches, the right one returning the blood from the second to the fifth intercostal spaces ; the left, sometimes called the lesser vena azygos^ is prolonged as far back as the eleventh or twelfth intercostal space, receiving blood from the intercostal veins of all the spaces it crosses. On the right side the vertebral, superior cervical, and dorsal veins may reach the vena cava separately, whereas those on the -left enter by a common truiik. 44.4 ANGIOLOGY. The Vena azygos is a long single branch, whose radicles originate near the first lumbar vertobra. It passes forwards on the right side of the posterior aorta, below the bodies of the dorsal vertebras, reaching the sixth, where it becomes inclined downwards, and terminates in the anterior vena cava. It receives branches from the spinal and psoe muscles, the posterior thirteen right, and usually the posterior five or six left intercostal, and also the oesophageal veins. J BRACHIAL VEIN. ^Fio. 167. a, b.) The brachial vein, the largest trunk which enters into the formation of the anterior vena cava, receives the greater part of the blood from the anterior extremity, as well as extrinsic branches corresponding to those of the artery, and the sub- cutaneous thoracic or spur vein. The Pedal plexuses and digital veins are identical with those of the posterior limb. The Metacarpal veins are the external, internal, and inter- osseous. The internal vein, by far the largest, passes up the limb to the side of the flexor tendons, in company with the artery and nerve, the vein being in front, the artery in the centre ; passing the knee in companj^ with the radio-palmar artery it is continued as the internal subcutaneous vein. It forms a free anastomosis with other metacarpal veins, receiving also branches from the joint. The external metacarpal is situated on the external side of the flexor tendons, accompanied hj the corre- sponding nerve, and it also receives branches from the skin and adjacent structures. On reaching the upper part of the trapezium, it divides into numerous branches, which either anas- tomose with those of the internal, or go to form the posterior radial and cubital veins. . The deep or interosseous vein is very irreg\ilar and flexuous, and may be double ; it passes up the limb between the posterior surface of the cannon bone and the suspensory liga- ment. At the head of the metacarpus, it splits up to unite with branches of the external and internal veins, and sends one or two small branches, through the carpal sheath, which help to form the posterior radial vein. The Posterior radial vein is a continuation of the meta- carpals, terminating at the lower end of the humerus in the DEEP VEINS. 445 humeral. The artery is always accompanied, and in a great measure enveloped, by three or four venous branches, that freely anastomose, and result from the terminals of the metacarpals. The Anterior radial follows a course similar to the anterior radial artery, receiving satellite branches equivalent to those of the latter. The Ulnar or cubital accompanies the ulnar artery, receiving muscular and cutaneous branches, terminating at the inferior extremity of the .humeral. It is sometimes double in the latter part of its course. SUPERFICIAL VEINS. The superficial veins of the arm and chest are the external and internal subcutaneous , which are slightly separated from the skin and fascia of the arm; and the subcutaneous thoracic. The Internal subcutaneous vein ascends the limb on the mner side of the fore-arm, at the superior extremity of which it passes obliquely forwards, and terminates by two large branches • — the basilic and the cephalic. The basilic vein crosses the pectoralis transversus, and terminates in the humeral. The cephalic vein passes over the flexor brachii to the interstice between the pectoralis anticus and levator humeri, emptying itself into the jugular vein. The External subcutaneous vein is much smaller than the internal, and ascends the leg on the anterior surface of the fore- arm, terminating at the superior extremity by uniting either with the internal, or more commonly, the cephalic vein. The Subcutaneous thoracic or Spur vein commences by numerous branches in the flank, which unite in one common trunk. Posteriorly it lies near the external surface of the pan- niculus, being directed along the superior border of the pectoralis magnus ; it then dips into the caput muscles, terminating in the humeral, sometimes in the brachial vein. deep veins. The Humeral vein is a satellite of the corresponding artery, and lies behind it, commencing above the elbow by the union of the radial and articular branches. It terminates in the brachial vein. The Brachial vein commences at the scapulo-bumeral articula- 446 ANGIOLOGY. tion, being the continuation of the humeral ; in company with the artery, it winds round the first rib, below the lower insertion of the scalenus muscle, enters the thorax, uniting with its fellow and the jugular confluent to form the anterior vena cava. JUGULAR VEIN. (Fig. 168. 2, 4.) The jugular vein, the great vein of the head, and satellite of the carotid, commences by two branches, the superficial temporal and internal maxillary, just behind and below the temporo- raaxillary articulation, its origin thus corresponding to the break- ing up of the external carotid artery. Lodged at first in the posterior part of the parotid gland, in the neck it is superficially placed, occupying the jugular gutter, a canal formed by the levator humeri and sterno-maxillaris muscles; it enters the thorax, joining its fellow, between the first ribs, and under the trachea, to form the jugular confluent^ into which the brachial veins discharge, the whole forming the anterior cava. The veins joining the jugular correspond for the most part to their respect- ive arteries. SUPERFICIAL TEMPORAL VEIN. (Fig. 168. i.) The superficial temporal, one of the radicals of the jugular vein, and a satellite of the corresponding artery, is situated behind the posterior border of the jaw, near the temporo- maxillary articulation, and buried in and* under the parotid gland. It results from the union of the anterior auricular and subzygomatic veins. The large anterior auricular receives the superior cerebral vein, which leaves the cranium by the parieto- temporal conduit, just behind the articulation of the lower jaw. The superficial temporal vein passes through the temporalis muscle, receiving branches from it and from the external part of the ear. The subzygomatic vein is divided into two branches, the trans- verse, a satellite of the equivalent artery, and the masseter, which anastomoses with the maxillo-muscular infer iorly, and with a large vein from the temporalis which comes through the sigmoid notch, and receives the deep temporal branches of the internal maxillary 3cein superiorly. BRANCHES OF THE JUGULAR VEIN. 447 INTERNAL MAXILLARY VEIN. This, the other radical of the jugular, is a large vessel situated between the pterygoid muscles and the maxillary bone ; it runs obliquely upwards and backwards, to the inner aspect of the maxil- lary articulation, just below the condyle of the lower jaw, where, after turning slightly downwards, it joins the superficial temporal ; it originates in the hvbccal vein, near the superior extremity of the buccinator. Its branches are the lingual, the inferior dental, deep temporals, pterygoids, and other satellites of the branches of the internal maxillary artery. The arrangement of the buccal vein is worthy of note. It proceeds from the facial vein at the anterior edge of the masseter muscle, and passes upwards and backwards under that muscle, presenting an enormous dilatation or pouch. Towards the superior end of the buccinator it becomes the internal maxillary vein. BRANCHES OF THE JUGULAR VEIN. CFiG. 168.) The chief branches entering the jugular are the maxillo- muscular, posterior auricular, occipital, glosso-facial, thyroid, and cephalic. The maxillo-muscular veins are two in number, and correspond to the branches of the artery. The posterior awricnlar, which commences under the ear, descends over the parotid gland, where it receives numerous branches, and enters the jugular just below, and on the opposite side of the preceding. The occipital vein, the satellite of the artery, receives blood from the brain, spinal cord, and muscles about the poll. The glosso-facial, external or submaxillary vein, also a satellite, commences by two branches : the posterior or angular comes from the angle of the eye ; the anterior or dorsalis nasi, from the upper part of the nose. It descends along the anterior border of masseter, and winds round the lower jaw, between the artery and Steno's duct. Below the pterygoideus, at the antero-inferior border of the submaxillary gland, it leaves the artery, and enters the jugular at an acute angle. The chief branches of the glosso- facial, in addition to a small lateral nasal vein near its origin, are the alveolar, superior and inferior coronary, buccal, and sub- lingual veins. The alveolar vein, or vena varicosa, is peculiar in form and disposition, being buried under the masseter, between the zygoma 448 ANGIOLOGY. and the alveoli of the upper molars ; its anterior extremity opens into the facial vein ; posteriorly it crosnes the alveolar tuberosity, and passes through the optic fossa, receiving the superior dental, spheno-palatine palatine, and staph yline veins ; in the ocular sheath, it receives the veins from the eye. By the side of the ophthalmic nerve, it enters the cranium by the foramen lacerum orbitale, and communicates with the cavernous sinus at the base of the brain. Before this vein winds round the alveolar tuber- no. 168. Veins of the face and neck. 1, Glosso-facial ; A, Its facial portion ; 2, Jugular ; 3, Occipital ^, Cervical portion of jugular ; o, Superior coronary ; b, Small labial branch , c, Inferior coronary a', Common coronary trunk; d. Angular vein of the eye; e, Dorsal nasal; e', Lateral nasal J, Alveolar; g, Buccal; h, Posterior auricular; i. Superficial temporal ; fc, Anterior auricular I, Subzygomatic ; m, Superior cerebrcl — cut ; n, Maiillo muscular ; o o o. Muscular, oesophageal and tracheal twigs. osity, it forms a large venous reservoir, which diminishes before entering the ocular sheath. The use of this reservoir is apparently to prevent congestion in the cavernous sinuses. The superior and inferior coronary veins are the next branches, and sometimes they unite to form a common trunk. The superior gives off a small labial branch. LYMPHATIC VESSELS. 44jJ5 The buccal or inferior communicating vein resembles the vena varicosa, and is a satellite of the buccal artery ; being the radical of the internal maxillary vein, we have described it with that vessel. The suhlin/gual vein is large, consisting of two branches, whic^ unite and pierce the mylo-hyoideus muscle. The thyroid vein, a large vessel formed by the laryngeal and thyroid veins, gains the jugular near the termination of the glosso-facial. . The cephalic vein enters at the inferior extremity of the jugular, coming from the internal superficial vein of the arm ; it is a satellite of the pectoral branch of the inferior cervical artery, and is found in the interstice between the levator humeri and pectdralis aotlcus muscles. The minor branches of the jugular are several nameless ones, •^vhich return blood from the parotid gland and cervical muscles. Lymphatic System. The lymphatic or absorbent system is connected with the blood- vascular system, and consists of a series of tubes, which absorb and convey to the blood certain fluids ; a number of glandular bodies through which the tubes frequently pass ; and the fluids themselves, which are lymph and chyle. LYMPHATIC VESSELS. These are called lymphatic vessels, because the)- convey a clear limpid fluid ; or absorbent vessels, because they absorb aliment- ary ^laMter. The absorbents of the chyle are called lacteal, or ciyliferous vessels, but do not differ from the rest in character or anatomical structure. The lymphatics unite to form two large trunks, the thoracic duct, and the right lymphatic vein, both of which enter the venous system near the heart Delicate in structure, and transparent, they are present in nearly every tissue ; and although mote numerous than the blood-vessels, their collective capacity is probably not greater. They are placed superficially and deeply with respect to the more solid organs. The walls of the larger vessels consist of three coats ; the external is composed of a network of interlacing areolar tissue, mixed with fibres of elastic and smooth muscular tissue , this coat connects the vessel with its surroundings. The middle coat is 26 450 ANGIOLOGT. thin and bighly clastic, consisting of smooth muscular fibres interlaced with areolar and elastic tissue. The internal coat is merely a basement membrane of elastic tissue, covered by a simple layer of endothelium. The coat of the small vessels, lymph capillaries, consists of membranous and cellular layers. The lymphatic vessels are beaded in appearance, due to the presence of valves in their interior, which aid the onward flow of their contents. These generally consist of two semilunar flaps, with an attached convex and a free concave border ; they are most numerous in the proximity of the glands, and are always found where the lymphatic trunks enter the blood-vessels. Lymphatic vessels may pass through two or more glands, or ^ they may enter a central y . trunk without approach- ing any gland. LYMPHATIC GLANDS. The lymphatic glands are small, round, or oval in shnpe, varying in size from a hemp seed to a kidney bean; in colour they vary much, but are generally some modifica- tion of pale red, reddish brown, or groy. They consist of a cortical sub- stance covered externally by a fibrous capsule which sends trabecu- lae within the gland, dividing it into numerous polygonal cavities, callfed loculi or alveoli, which are filled with a whitish pulp containing cells and nuclei, identical in character with lymph corpuscles ; the deeper part of the gland is called the medullary substance ; it also contains loculi and lymphoid tissue. The loculi are lined by very delicate processes given cff from the trabeculae, which divide them into very minute cavities com- municating with each other, forming a spongy texture enclosing the lymphoid tissue. The vessels, just before reaching the glands, divide into the afferent vessels, or vaaa afferentia, which enter the gland ; these subdivide into intricate plexuses, which open into the spongy cavities, whence originate vessels which lead to those Fia. 109. "•".•■ Section of a Lymphatic Gland, a a, Capsule ; 6 6, Trabe- culae of cortical portioa ; c, TrabectOsa of medullary por- tion : d e, Lymphoid contents of loculi; //, Afferent vessels ; ; g. Their confluence, leading to h, the efferent vessel. THORACIC DUCT. 451 emanating from and leaving the gland, the vasa efferentia, or efferent vessels. The efferent, fewer but larger than the afferent, after a short course unite to form larger vessels. Sometimes a depression on the surface of a gland, the hilus, marks the spot where the efferent vessels leave it The closed glands of the stomach, intestines, tongue, &c., con- sist of a material resembling that of the lymphatic glands, and which has been termed lymphoid or adenoid tissue ; it consists mainly of retiform connective tissue and colourless corpuscles. LYMPH AND CHYLE. Lymph is a colourless fluid, containing a number of objects v^hich resemble almost perfectly the white corpuscles of the blood ; these are the lymph corpuscles, and they are believed to be formed in lymphoid tissue, but notably in the lymphatic glands, and conveyed thence by the efferent vessels. Chyle is a milky fluid found in the lacteals or lymphatic vessels of the intestines during digestion ; it contains corpuscles similar to those of the lymph. Since both tl^e lacteal and pos- terior lymphatic vessels lead to the great lymphatic trunk, or thoracic duct, it follows that the lymph and the chyle become mixed. THORACIC DUCT. (Fig. 170.) This, the largest and longest lymphatic vessel, receives all the others, except those of the right anterior extremity, and right side of the head, neck, and thorax ; it originates in the lambar region between the posterior aorta and vena cava, by a very irregular dilatation called the receptcLCvZum chyli, or reservoir of Pecquet, into which flow the contents of the neighbouring vessels. From the anterior aspect of this reservoir, the duct proceeds for- wards on the right side of the vertebral column, enters the thoracic cavity through the aortic hiatus of the diaphragm, passing along the vertebrae until it reaches about the sixth dorsal, where it curves downwards to the left side, over the base of the heart, and towards the beginning of the anterior vena cava, in most cases terminating in the jugular confluent about the anterior border of the first rib. Its orifice is dilated and guarded by a valve, ^hich prevents the influx of blood ; it may be double, when we 4^^ ANGIOLOGY. liave a right and left, or double at its origin only ; or it may be single at its origin, then bifid for a short distance, again forming a single trunk ; it contains a few valves. The lymphatics, which form the afHuents of the thoracic duct, may be divided into five groups, comprised within the following divisions of the body : — Posterior rescion. | Thoracic viscera. Digestive viscera. Thoracic walls. Anterior region. Fio. 170. Thorax laid open on tho right side— the lungs being removed. 1, Part of posterior aorta ; 2, Trachea divided ; a a, Eight and left branches of origin of thoracic duct (double posteriorly in this instance) ; 6, Point of union of the branches ; c c, Loops leaving and rejoining the duct ; (i, Point of discharge of the duct ; e, Cervical lymphatic vessel ; e'. Its termination in the duct. POSTERIOR REGION. This embraces the lymphatics of the posterior extremity, pelvis, abdominal walls, and organs of the pelvic region. They all converge to a large group of glands, the sublumbar, presenting, however, at dififerent parts of their passage,. other groups. We note th6 following*! — Sublumbar. Popliteal. Beep inguinal. Iliac. Superficial inguinal. Precrural The sublumbar glands occupy the sublumbar region, resting in the angles formed by the bifurcation of the ix)sterior aorta. POSTERIOR REGION. 453 extending as far forward as the posterior mesenteric and sper- matic arteries. This group receives the lymphatics of the pelvis, the efferent branches from the deep inguinal, and iliac glands, branches from the rectum, double colon, and spermatic cord. The numerous different branches of the sublumbar glands, after forming ohe or more trunks, terminate in the receptaculum chyli. The deep inguinal glands are formed by a considerable num- ber of lobes lodged under the crural aponeurosis and arch, in the interstices between the adductor muscles of the thigh, along with, and' to the inner aspect of, the crural vessels. The group is elongated, and superficial exteriorly, reaching almost to the anterior pubic border. The colour of the lobes varies from grey to brown, or almost black. The afferent vessels are formed by the superficial lymphatics, which accompany the internal saphenie vein, and by satellites of the deep blood-vessels. The efferent branches of this group pass into the sublumbar glands, entering the abdomen in company with the external iliac vessels. The superficial inguinal glands are placed in front of the inguinal ring, at the side of the sheath. They are oblong, and consist of ten or twelve lobes. The afferent vessels are numerous, and receive the lymph from the internal part of the thigh, the sheath, scrotum, and inferior abdominal walls. The efferents, larger, but less numerous, pass up the inguinal canal in company with the external pudic artery, and terminate in the deep inguinal glands. The small popliteal glands consist of from three to five lobes, situated' just behind the great sciatic nerve and gastrocnemius muscle, and between the adductor magnus and biceps rotator tibialis, near the femoro-popliteal artery. They receive the lymph- atics from the posterior part of the haunch and from the neigh- bourhood of the hock. The efferents join the deep inguinal glands, passing through the muscular interstices of the thigh. The iliac glands consist of five or six lobes, which form a soft yellow group, situated in the triangular space between the two branches of the circumflex ilii artery. They receivd the efferents from the precrural glands, and numerous deep lymphatics from the abdominal walls. The five or six efferent vessels follow the circumflex artery, and terminate in the sublumbar glands. The precrural glands rest on the inner side of the anterior border of the tensor fascia lata, upon the circumflex artery, and constitute a small elongated mass, composed of about twelve iobes. It receives the lymphatics from the anterior and internal 454l ANGIOLOGY. part of the thigh. Its three or four efferents are very large ;- passing up the internal face of the fascia lata muscle, they enter the abdominal cavity towards the angle of the haunch, and join the iliac glands. ABDOMINAL VISCERA. The lymphatics of the rectum and floating colon. There are two or three lobes at the base of the tail on each side of the sphincter, a series of glands along the small curve of the viscera, and the mesenteric glands, comprised between the layers of the mesentery, receiving the radical vessels which arise in the mucous and fleshy coats of the intestine generally. Their efferent vessels frequently traverse the glands placed on the passage of the blood-vessels, and reassemble towards the origin of the posterior mesenteric artery by numerous large branches, which join the divisions of the sublumbar lymphatics, or those of the double colon. The lymphatics of the large colon. — Upon this viscus a double chain of glands accompanies the colic arteries. Numerous small lobes, at short distances from the principal glands, are dis- seminated over the lateral branches of the blood-vessels. Tbo lymphatics emanating from the coat of this intestine pass for the most part into these small lobes, afterwards joining the principal glands, whence they emerge ^ numerous large satellites of the colic blood-vessels. These, and the lymphatics of the small intestine, unite to form the two great mesenteric trunks, which, with the efferent branches of the sublumbar glands, form the reservoir of Pecquet. The lymphatics of the ccecum. — The glands of this organ are found along the passage of the caecal arteries, constituting a series not so close as those of the great colon, into which are received the lymphatic vessels of the membranes of the caecum. These, on leaving the glands, form larger branches, which are satellites of the blood-vessels, and enter the same trunk as those of the small intestine. The lymphatics of the small intestine. — The lymphatic glands, which receive the lacteals of this intestine, are about thirty iu number, of a groj colour, large, fusiform, very compact, and often bifurcated at their superior extremity. They are lodged in the mesentery, cear the origin of the anterior mesenteric artery. THORACIC VISCERA. 455 Besides these larger glands, there are about fifteen smaller lobes dispersed along the course of the ilio-csecal artery. The lymphatic vessels form a large network, converging from the visceral walls to the mesenteric glands, which they enter at the superior extremity of the mesentery. The efferent branches, usually two or three from each gland, unite to form larger ones, which finally join the intestinal branch of the receptaculum chyli. The lymphatics of the stomach. — The glands of the stomach are divided into two classes; a large series, situated in the lesser, and a chain of smaller ones, distributed along the greater curva- ture, and attached to the gastro-colic omentum. The deep and superficial lymphatics of the stomach enter these glands, and collecting on the blood-vessels, pass up towards tlie greater cuU de-sac near the coeliac axis, where they anastomose with branches from the spleen and liver, forming' large flexuous trunks, some of ^hich enter the thoracic duct, while others pass backwards to the trunks of the intestinal lymphatics. The lymphatics of the spleen. — Those of the spleen are deep and superficial ; the former occurring in the parenchyma, the latter on the surface. They all pass to the branches of the vessels in the hilus, enter numerous groups of glands, and are dispersed along the blood-vessels, anastomosing with the lymphatics of the stomach and liver. The lyw^phatics of the liver consist of a deep series in the parenchyma of the gland, and a network of superficial ones on -the capsule. They assemble towards the posterior fissure, and, entering a group of small glands, pass into a much larger group situated between the trunk of the vena porta and the pancreas.' Their efferents anastomose with those of the stomach and spleenJ THORACIC VISCERA. . In the thorax there are three groups of lymphatic glands ; a^ series of small ones in the posterior mediastinum, which receive the lymphatic vessels of the posterior part of the oesophagus; the bronchial glands, -w^hich a.re situated at the angle of bifurcation of the trachea, stretching a short distance into the . parenchyma of the lungs, and receiving their lymphatic vessels ; two series of glands, extending along the infero-lateral face of the trachea from the base of the heart to the first rib, receiving the lymphatics , from the pericardium and heart, and portions of the trachea and 456 ANGIOLOGY. oesophagus. The efferent vessels unite to form two or three^ trunks which enter the thoracic duct in different places. THORACIC WALLS. In this group there are also three sets ; a double chain of small round glajids, situated on each side of the dorsal vertebrae above the intercostal spaces, and under the costal pleura ; a large gland- ular mass, resting on the xiphoid cartilage, just behind the heart and in front of the inferior part of the diaphragm; and a group of rudimentary glands, which accompany the internal thoracic arteries. The lymphatics of the diaphragm, after receiving, it is said,, those from the convex face of the liver, enter the glands at the base of the diaphragm, leaving them by numerous branches which accompany the internal thoracic arteries, and either join the anterior extremity of the thoracic duct or the great lymphatic- vein, usually after passing through the prepectoral glands. They receive the lymphatics from the inferior part of the intercostal spaces. The other lymphatic vessels of the thoracic walls run upwards in the intercostal spaces, and enter the chain of glands along the sides of the dorsal vertebrae, forming two canals, which, pass forwards to enter the anterior portion of the thoracic duct. ANTERIOR REGION. The lymphatics of the head, neck, and anterior extremity are directed to the entrance of the tho^rax, where there is a group of glands termed the prepectoral, which may be regarded as the lymphatic centre of the whole anterior, as the sublumbar is of the posterior part of the body. Before the vessels reach this, point of convergence, they are intercepted by one or more of four other glandular groups. We have in this region the following groups of glands : — Prepectoral. | Submaxillary. Guttural. ] Prescapular, Brachial. The prepectoral glands are found on each side of the ter- minal extremity of the jugular veins, inside the inferior border of the scalenus ; they are massive, passing into the chest under the brachial vessels, and along the internal aspect of the first pair of ANTERIOR REGION. 467 ribs. Entering these glands are the emerging lymphatic branches of the prescapular and brachial glands, those from the guttural glandsj which descend the trachea with the carotid artery, as well as most of those which accompany the internal thoracic vessels. They afford numerous short and voluminous branches, those of the right side forming the lymphatic vein ; those of the left joining the thoracic duct, at times reaching the anterior cava by a separate trunk. The guttural glands are numerous, and attached slightly to each other. They are disposed in an elongated mass which occupies the lateral wall of the pharynx, below the guttural pouch, reaching almost to the thyroid gland. They receive all the lymphatics of the head, some directly from the base of the tongue, soft palate, walls of the larynx and pharynx ; others are efferents from the submaxillary glands, and from a lobe lodged in the substance of the parotid gland. The efferents form four or ^YQ large branches, which descend the trachea singly, or united into a bundle which follows the carotid; numerous elongated glands receive the radical lymphatics from the cervical portion of Ihe trachea and oesophagus. On arriving at the entrance of the thorax, the efferents enter the prepectoral glands; branches sometimes pass directly to the thoracic duct on the left, or the lymphatic vein on the right side. The submaxillary glands are a fusiform mass situated at the base of the tongue, between the digastric and mylo-hyoid muscles, and a little above the glosso-fascial artery ; they receive the lymphatic vessels from the tongue, cheeks, lips, nose, and nasal cavities, the efferent vessels going* to the guttural glands. The presca'pidar glands form by their union a chain running in the course of the ascending branch of the inferior cervical artery, lender the internal face of the levator humeri, and descending almost to tlio attachment of the sterno-maxillaris. The cervical hm/rJiaUcSj superficial and deep, mostly enter this glandular chain, as well as those from the breast, and a part of those from the shoulder ; their efferents, short and voluminous, pass to the prepectoral glands. The brachial glands, situated under the shoulder, consist of two groups ; one is situated near the elbow to the inside of the inferior extremity of the humerus, receiving the lymphatic vessels of the foot and fore-arm, which accompany the superficial veins, or pass up the interstices of the muscles with the deep vessels ; 458 COMPARATIVE ANGIOLOGY. the other is disposed in-ja mass behind the /brachial vessels, near the common insertion of the latissimus dorsi and teres internus ; it receives nine or ten lymphatic branches from the shoulder and arm.. The efFerents accompany the brachial vessels, and enter the prepectoral glands. LYMPHATIC VEIN. The second principal trunk is the lymphatic vein, or ductus lymphaticus dexter, a vessel measuring in length from three- quarters to one inch, situated near the junction of the jugular veins, and terminating in their confluent ; it is also guarded by a valve, and receives the lymphatic vessels from the right anterior extremity, and the right side of the head, neck, and thorax. ; COMPAHATIYE ANGIOLOGY. RUMINANTIA In the heart of the ruminant, the most prominent feature ""s the presence of the cardiac bones (see ^. 105), which, appear in adult life. They are two in number, and lie between the auriculo-ventricular rings and the common aorta on the left, the pulmonary artery on the right side. There is a third longi- tudinal furrow running down the wall of the left ventricle posteriorly. The furrows contain more fat as a rule than those of the horse's heart. There are usually nine aortic intercostals, and three anterior ones, or twelve in all. The ccdiac axis reaches the rumen just behind the oesophagus-. On the left is, given off the artery of the reticulum, which passes to the left of the 03Sophagus, and divides into a superior and an inferior branch. Just posterior to this the splenic artery arises, and still farther back the hepatic, which supplies the live? and gall-bladder, giving olf the duodenal branch, which anastomoses with the superior artery of the abomasum, and the anterior mesenteric. The terirdnal branch of the coeliac axis divides and forms a superior and an inferior arti^ry of the psalterium and abomasum, which pass along the surfaces of these, cavities, the former anastomosing vrith the duodenal. The superior and iafericr arteries of the rumen are placed in the longitudinal groove, the former Visually arises fium the splenic, running backwards ; the latter is generally given oil by the artery of the reticulum, and runs forwards and bet'^-een the anterior sacs, to gain the inferior surface, where it passes backwards and reaches the groove between the conical sac?, anastomosing with the superior vessel. * The anterior mesenteric artery divides into two branches, an anterior for the email, and a posterior for tlie large intestine. The former resembles that of the horse in its distribution ; the latter instead of following the flexures of the colon gives *off branches which cross them^ The posterior vatsciteric artery is small. The middle sacral artery is very large, giving off the aiteries of the tail ; it may be regarded a3 the continuation of the posterior aorta, the lateral saerah being somewhat rudimentary, and their terminal branches RUMINANTIA. 459 wanting. In the smaller ruminants, branches from the deep femoral take the place of the obturator and iliaco-femoral arteries -which are wanting ; in the ox they are rudimentary. The uterine artery is very large, arising from a trunk common also to the umbilical. The arteries of the pelvic limb offer no deviation from those in tjie typical animal, of sufficient importance to merit description in an elementary work, until we descend to the tarsal joint, below which the arteries, like the other appendicular structures, present certain comparative features worthy of notice. The great metatarsal artery, with two veins, occupies the median groove on the front of the metatarsus, passes through the notch between the distal articular surfaces, and gains the back of the digit as the common digital artery. Above the distal ends of the ossa suffraginis it divides into external and internal ungual arteries, each of which gains the inner aspect of its respective digit, and enters the distal phalanx, where it behaves similarly to the plantar ungual of the horse. The lateral digital arteries pass down the outer sides of the digits, that of the external digit being formed by the interosseous plantar and a transverse communicating branch, while that of the internal digit is given off by the great metatarsal artery. The anterior aorta, it has been stated, is wanting ; if it is present it is remarkably short. If it be absent, we must describe the brachials as arising from the common aorta. The dorsal and vertebral arteries arise by a common trunk, the former fulmishing a branch which takes the place of the superior cervical artery, which is wanting. The vertebral artery is large, and does not inosculate with the occipital, but terminates in muscular branches. The humeral artery is small, as are most of its branches ; the chief artery supplying the muscles of the posterior brachial region is the scapulo-humeral branch, of the subscapular artery. The radio-palmar artery forms an inferior arch, as in the horse, from which are given off three interosseous palmars and one dorsal; of the former the internal is the largest and most constant ; the dorsal or interior interosseous artery gains the front of the limb, anastomosing superiorly with the anterior radial artery, while inferiorly it occupies the vertical groove in the metacarpus, and inosculates with a recurrent branch of the great meta- carpal artery, which passes between the articulations at the distal end of the bone. The arteries of the digit resemble in the main those in the pelvic limb. The carotid arteries arise, as in the horse, by a primitive trunk from the brachio-cephalic artery ; they break up at the head, forming the external carotid, and a small occipital artery ; the internal carotid is wanting, its function being performed by the encephalic artery. The occipital artery enters the cranium by the condyloid foramen, passes backwards and inosculates with the lateral artery of the spinal cord, at about the level of the internal foramen of the atlas ; a branch given off from this union passes out through the fora- men to supply the muscles of the poll. The lingual artery is given off by the external carotid, and the former gives off the sublingual branch. The mastoid artery of the horse is represented by a branch of the posterior auricular. In the smaller ruminants the coronary arteries of the lips are formed by the bifur- cation of the transverse facial, a branch of the superficial temporal artery. The internal maxillary artery has no pterygoid foramen to pass through in 460 COMPARATIVE ANGIOLOGY. uny of the domesticated riiinmaiits ; some of its branches, however, lead to the formation of structoren interesting to the anatomist ; these are the arterial plexuses, or retia mirabilia, the largest of which is formed inside the cranium by branches from the internal maxillary artery. One of these branches, the spheno-spinaly en^-srs the cranium by the foramen ovale, and, as a rule, two arteries of the rete enter by the anterior common foramen ; the first of these inclines forwards, the two latter backwards. The three arteries anastomose by forming a small and intricate plexus known as the cranial rete mirahilej it ia 8itua%:-d at the side of the sella' turcica of the sphenoid bone, communicating with its fellow posteriorly, and giving off superiorly the encephalic artery, a branch considered by Chauveau to be "completely analogous to the intra/- craniftl portiou. of the internal corotid in the solipede." From this artery are given off the cerebral branches, anterior, middle, and posterior ; the last passing backwards, forms a convergent anastomosis with its fellow, thus constituting the basilar trunk leading to the mldrlle spinal artery. Another arterial plexus is found on . the ophthalmic artery just where the arteries of the eye are given off. The glosso-facial artery is found only in the larger ruminants. Veins.. The suheutaneous abdominal vein is very large in the ox, the subcutaneous thoracic being proportionally small. The saphenic veins differ from those of the horse, the external one being larger than the internal. The jugular vein is large, and there is a small accessory jugular which varies much in size, originating in the occipital vein, and joining the great jugular near its termi- nation. The angular vein of the eye is very prominent in sma'll ruminants. The digital veins of the posterior limb are three in number, an anterior or common one between the digits, formed by twigs from the solar plexuses of both, and two lateral ones placed on the outer sides of the digits. There are usually five metatarsal veins ; two anterior deep ones which accompany the great metatarsal artery ; an anterior superficial one, which forms one root of the external saphenic ; an internal and external posterior vein, which pass upwards over the tarsus, and assist i^ forming the saphenic veins. In the anterior limb there is a fourth or posterior digital vein, which accompanies the common digital and internal metacarpal arteries. Ths Lymphatics. In the large ruminants the thoracic duct not only exhibits great complexity of form, but it is also extremjely variable, being sometimes double throughout its extent. Some compleintj generally exists near its anterior termination. It is more deeply seated than that of the horse, lying between the right upper part of the aorta and the vertebral column, buried in a quantity^ of fat. It does not pass through the aortic hiatus, but has an opening in the diaphragm for itsel£ OMNIVORA. In the hog the branches of the posterior £S)rta call for no remark, since they resemble those of the horse, excepting the mesenteric arteries, which are distri- buted somewhat like those of the ruminant. Alter giving off the gluteal and OMNIVORA GARNIVORA. 461 umbilical branches, the internal iliac artery is apparently continued by the internal pudic, which gives off the hsemorrhoidai artery to supply the urinary and genital organs of the region, and the rectum posteriorly, and finally the cavernous arteries. The external iliac artery resembles in its distribution that of the ruminant. The anterior aorta is wanting, the brachial trunks arising from the common aorta. The vertebral, dorsal, and subcostal arteries of the right side are given off by a branch which itself appears to represent the superior cervical artery. A branch from the subscapular artery is the analogue of the deep humeral in the horse ; the rest of the circulation of the anterior limb is mostly like that of the ruminant. The carotid arteries arise singly from the brachio-cephalic trunk ; they break up like those of the horse. There is no cerebrospinal branch of the occipital artery. The internal carotid enters the cranium by the foramen lacerum posti- cum, and forms a rete mirabile, assisted by the ophthalmic. The basilar artery is formed as in the ruminant. The external carotid extends to the maxillary hiatus, where it breaks up — i.e., the internal maxillary artery is in this animal con- sidered as part of the carotid. The lingual artery is separate from the facial. The veins call for little remark. What we have said of the jugular and saphenic veins of the ruminant is also applicable here. The superficial veins in the hog^re for the most part buried in an exceedingly thick layer of fat. The thoracic duct usually opens into the left jugular vein, near its termina- tion. It sometimes divides anteriorly a*nd reunites, forming a cavity which receives the terminal lymph vessels. CARNIYORA. The heart in camivora is extensively related with the sternum, the apex being directed backwards. In shape the organ is very bluntly ovoid. There are no well-defined feroncAiaZ arteries, but several oesophageals proceeding direct from the aorta, in the posterior mediastinum ; some of these give off bronchial branches. The cceliac axis divides into the three typical branches, but there is no dis- tinct right and left division of the gastric artery. There is given off a pancre- atico-duodenal branch from the hepatic which anastomoses with the great mesenteric artery. Near the latter a vessel arises which divides, supplying the diaphragm anteriorly and thesublumbar region posteriorly. The internal iliac arteries are somewhat separated from the external ones, the umbilicals being given off from their common trunk. They divide into two chief branches, which may be considered representatives of the internal pudic and gluteal arteries of the horse ; the first of these calls for no special comment, the second passes through the great sciatic notch with the great sciatic nerve, and becomes lost in the gluteal and femoral muscles, first giving off spinal branches ; the coccyx is supplied by branches of the middle sacral artery. The branches of the external iliac artery present few deviations of importance. The circumjlex ilii comes direct from the aorta. The posterior tibial artery is radimentary, while the anterior one gives off a large tarsal branch, and descends in the third intermetatarsal space, inclining backwards, and forming a plantar arch underneath the flexor tendons ; from this arch are given off three digital 462 COMPARATIVE ANGIOLOGY. or plantar arteries, which are distributed like those of the superficial palmar arch in the anterior limb. The brachial arteries iu the main resemble those of the hog. The vertebral inosculates with the ramus anastomoticus ; it supplies many cervical branches,. the superior cervical artery being both small and short. The humeral artery gives off branches resembling those described in the typical animal, but it terminates by dividing into radial and cubital arteries, the presence of the anterior radial being merely indicated. The cubital artery gives off the inter- osscows,' which divides under the pronator quadratus, into anterior and posterior branches ; the former passes between the radius and the ulna, forms a carpal plexus, and supplies the digits anteriorly ; the latter is the larger, and in the region of the carpus divides into a superficial and a deep branch ; the first assists with the cubital in forming the superficial palmar arch, which is chiefly formed by the inosculation of the cubital and radio-palmar arteries ; the deep branch helps with the radial to form the deep palmar arch, underneath the flexor tendons. From the latter arch are given off eight interosseous branches, four palmares and four dorsales, the latter passing through the intermetacarpal spaces and anastomosing with branches of the anterior interosseous artery. All these vessels pass down the digits, and join ultimately the collateral palmarsy which emanate from the superficial palmar arch. Thus there ara three sets of digital vessels, an anterior, and a superficial and deep posterior. The carotic? arteries arise singly from the brachio-cephalic trunk, but other- wise resemble those of the horse ; in their breaking up and in the disposition of the occipital artery and ramus anastomotious there is no important deviation. The internal carotid enters the carotid canal, passes forwards, and vends a pro- jecting loop out through the carotid foramen, receiving a small branch of the external carotid ; it joins the spheno-spinal and recurrent ophthalmic brancheSt forming a kind of rudimentary rete mirabile. The glasso-facial artery is represented by separate facial and lingual branches. The mt£mal maxillary artery resembles that of the horse ; the superior denfct^l is usually regarded as its continuation. It gives off an alveolar artery which fchiefly supplies the orbital gland. The receptaculum chyli in camivora is very large, extending forwards as far as the thorax. The thoracic duct usually bears a marked resemblance to that of the hog. KODENTIA. Even were the subject of importance, there is little space for its consideration here. It is, however, interesting to note that the heart presents external indica- tions of division, the apax being in some cases slightly cleft. The external jugular vein is very much larger than the internal, and there are two separate anterior venae cavae. AVES. The heart in birds is divided into four cavities as in mammals ; its apex is situated between the lobes of the liver, as there is no absoluie separation be- tween the thoracic and abdominal ccvities. CIRCULATION IN LOWER ANIMALS. 463 The right auricle is much larger than the left, and a single triangular valve takes the place of the tricuspid. The common aorta di"\'ides into three branches, a single descending or posterior, aorta, and a right and left trunk, termed by Chauveau the brachio- cephalic arteries, the first supplying chiefly the viscera ; the latter the wing, head, neck, ai d anterior parietes of the body ; these lateral trunks are regarded by some authorities as representing the mammalian thoracic arteries, giving off the carotid and subclavian branches. A large number of retia mirabilia are found among the arteries of the head and viscera. There is only one terminal pulimonary vein and two superior cavce. The jugular veins have a large transverse anastomotic branch just below the cranium. The portul vein receives branches from the veins of the posterior extremities,^, notably the coccygeo-mesenteric vein, which is con- a nected with the femoral by the renal-portal vein. Thus is constituted the renal-portal system, whose existence in the bird is a disputed point, even amongst high authorities. The blood of birds is higher in temperature than that of any other vertebrate class. The corpuscles are large, elliptical in shape, and nucleated. The lymphatics consist of glands and vessels. There are two thoracic ducts, each discharging into the cava of its own side. They originate in a kind of receptaculum chyli, near the coeliac axis. The glands are said to be confined to the cervical region, CIRCULATION IN LOWER ANIMALS. Fia. 171. Diagram of the Circu- lation in a Reptile, a, Pulmonic, a.nd h, Soma- tic circulation ; c, Heart, showing the three cavi- ties. The arrows indicate the course of the blood current. ft may be not oat of place here to explain very briefly how the circulatory apparatus, in animals placed lower than the class Aves, differs in the general plan from the type we have hitherto con- sidered. It will be seen that in none of the mammals or birds we have attempted to describe, is there any important difference in the general plan of the heart, course of the blood, or function of the vessels. In that class placed next below the Aves, the Beptilia, or reptiles, we find the following interesting features (see Fig. 171). The heart is less complex, having only three cavities, two auricles, and one common ventricle. As the general disposition of the vessels is the same as in the heart of four cavities, it follows that both the purified blood from the lungs, and the venous blood from the ca^ae, are passed through their respective auricles to the ventricle, where they become mixed. This mixed blood is driven into the aorta and pulmonary artery, both of which arise from the common ventricle. Hence, though the circulation in these animals is double, the blood supplied to the tissues is impure or mixed. In a still lower class of animals, that of the Pisces, or fishes, we find that the ♦64 COMPARATIVE ANGIOLOGY. heart is still more rudimentary, consisting of but two cavities, an auricle vA s, ventricle, but still the tissues are supplied with pure artenal blood ; the course of the blood being as follows : — The venous blood is conveyed by the cava to the auricle, thence into the ventricle, and then by the branchial arUry to the BranchicB or gills, structures which are analogous to the lungs of higher animals, and in which, consequently, the blood becomes arterialised. The blood thus purified, is sent from the gills throughout the body to supply the various tissues, and is finally returned by the cava to the heart. Hdnce the circulation in these animals is single^ the purified blood not being returned to the heart, but driven all through the body. The impulse of the heart is there- fore branchial. In the higher orders of the Crustacea, a still lower class of animals (Inverte. Fio. 172. Diagram of the Circulation in a Fisli. a, Branchial circulation ; 6, Somatic circulation ; c, Heart ; d, Auricle ; e, Ventricle ; /, Arte- rial trunk. Fio. 173. Diagram of the Circulation in a Crustacean, a, Bran- chial ; h, Somatic circulation. On the right is the heart with its single cavity, and on the left the venous lacunae. brate), we find that the cavities of the heart are reduced to one, which is however contained in a kind of sac, very incorrectly called the pericardium. Although these animals are supplied with gills, the impulse of the heart is systemic, not branchial ; andj as in the fishes, the circulation is single. The blood is driven by the heart through the body, and then collected into certain venous dilatations or lacunae, whence it is conveyed to the branchia9 for purification. The branchial vessels then pour it into the so-called pericardium, and it finally re-enters the heart by a number of valvular orifices. The blood thus supplied to the tissues is, however, not pure ; for it is ascer- tained that certain veins, instead of leading to the lacunae, or branchiae, pass to the pericardium, in which cavity the blood thus becomes mixed. CHAPTER YL NEUROLOGY. The subject of this chapter, the nervous system, includes those organs which may be regarded as receiving and interpreting impressions ; stimulating and regulating the vital functions. The nervous system in the broad sense consists of three sets of organs, peripheral, central, and communicating, the function of the latter being to establish a communication between the other two ; that of the first to receive and deliver impressions ; and that of the second to generate the nervous force. In other v/ords, the system comprises peripheral end-organs, nerves, and nerve centres ; it is with the two latter that we have more immediately to deal. The nervous system is divided into two minor systems — the Cerebro- spinal, which is to a considerable extent influenced by the ;iw^^ of the animal; and the Sympathetic, or ganglionic system, which comprises the nerves of organic life, which are not directly influ- enced by the will. Each of these has its own central and peripheral organs. In the first, the centre is made up of two portions — one large and expanded, the brain or encephalon, which occupies the cranial cavity ; thej other, the spinal cord, is elongated and continuous with the brain, being lodged in the canal of the vertebral column. The communicating portion of this system consists of the cerebro- spinal nerves, which leave the axis in symmetrical pairs, and are distributed to the voluntary muscles, and the organs of common sensation, and special sense. In the second, the central organ consists of a chain of ganglia connected by a nerve cord, which extends from the head to the coccyx, on each side of the spine. The nerves of this system are distributed to the involuntary muscles, mucous membranes, viscera, and blood-vessels. The two systems have free intercommunica- tion, ganglia being placed at the junctions. 465 2 H -466 NEUROLOGY, ^ NERVOUS TISSUE. Two substances, distinguishable by their colour, enter into the formation of nervous tissue — viz., the white and the grey matter. Botb are soft, fragile, and easily injured, in consequence of which the principal nervous centres are always well protected by the skeleton. When examined under the microscope, two distinct structures, fibres and cells, are found; the fibres being of two kinds, the white or meduUated, and grey or non-medullated, the former being more abundant. The white fibres, which form the white matter of the brain, spinal cord, and the nerves, and are also sparingly met with in the ganglia and nerves of the sympathetic system, have three distinct components — Is^, An exter- nal envelope, the neurilemma^ which is fine, transparent, and nearly homogeneous; 2nd, A layer of white, fatty matter, the medullary sheath, or ivhite suhstaTice of Schwann ; and 3rcZ, the cylinder axis, or ^primitive hand of Remak, in the centre of all. The diameter of these fibres varies • between xTtnrth and -jTrWth of an inch, though some are very much less. . The grey or non-m^dullated fibres constitute the chief nerves of the gang- lionic system, and are also present in the cerebro-spinal nerves. They are smaller than the white fibres, . resembling their cylinder axis, measuring from ToWth to a 0^0 th of an inch in diameter, and are apparently almost homogeneous in their structure. The nerve cells, or ganglionic corpuscles, are found in the nerve centres, and in the peripheral end organs of some of the nen^es. In shape they are spheroidal, caudate, or stellate. Each cell is composed of a transparent membrane, filled with a homogeneous, colourless matrix, in which is a number of diffused minute granular bodies, and an, internal vesicular nucleus, presenting one or more minute, but distinct nucleoli. The processes of the cells become continuous with the cylinder axes of nerve fibres, vrhile the medullary sheath appears to be prolonged over the cell ; hence these cells have been described Fio. 174. • Nerre tissue — *bi-polar cells and fibres. NERVES. 467 as nucleated enlargements of the axial cylinders." The cells are termed unipolar, bipolar, and multipolar, according to the number of processes they possess. The ganglia are composed of nerve cells and gelatinous fibres, invested by a thin envelope, continuous with the neurilemma of the nerves, which sends minute processes inwards. NEKVES. A nerve consists of a bundle of tubular fibres, held together by areolar tissue, enclosed in a membranous sheath, and divided into a number of fasciculi, each being invested by an inflectioa of the sheath ; they have also an external <}overing of cellular tissue, known as the Tagina cellulosa or cellular sheath. During their course, the nerves have frequent intercommunication, either by con- necting branches or in a , more intimate and complex manner in what is termed a, plexus. When the nerves divide into branches, there is never any splitting of the ultimate fibres, nor yet is there ever any coalescing of them — they retain their individuality from their source to their termination.' Nerves may be traced from the surface of the brain and spinal cord into the substance of these organs, the place where they leave the surface being termed the apparent, and the ultimate origin the deep origin or root of the nerve. In some cases the root is single, but in others the fibres spring from different parts of the nerve centre ; such nerves are said to have two or more roots. These roots may have different functions, as in the spinal nerves, where the superior root is sensory and the inferior motor. Whenever this admixture of functionally distinct fibres is found, a ganglion is, placed at or near the apparent root of the nerve. Nerves terminate in a variety of ways — by loops, as in the voluntary muscles, and in some of the soft structures, as the dental pulp ; by terminal plexuses, and bulbs in mucous membranes. In many of the sensory nerves, there are small, oval masses, the Pacinian bodies, at or near their peripheral terminations ; these Fig. 175. Pacinian bodj from the mesentery of a cat. o. Stem of the body ; b. Layer of connective tissue; c. Cavity of the body : d. Nerve 'fibre. 468 NEUROLOGY. are plentiful in the spinal nerves. Some nerve fibres have no termination, but form a loop by joining with others in the same bundle, and so return to the axis ; while others, as the auditory and optic nerves, have end organs of great complexity. Nerves which convey impressions to the centres are termed centripetal or afferent ; those which transmit stimuli from the centres to the various organs, centrifugal or efferent; while those which pass from one centre to another are called inter- central. Centrifugal nerves are called motor when they stimulate mus- cular contraction, and if this contraction be in the coats of vessels, the nerves are then vaso-motor ; when they stimulate the secre- tion of glands, they are called secretory, and when they have the power of diminishing function, inhibitory ; some nerves are believed to control the process of niftrition in the parts they supply, and have been named trophic. Centripetal nerves which convey ordinary feeling are termed sensory ; when they convey impressions peculiar to an organ, as- the nerves of sight and hearing, they are' known as nerves of special sense. Nerves conveying impressions which lead to the stimulation of motor nerves are termed excito-motor ; if to that of secretory nerves, excito -secretory ; and if to that of inhibitory nerves excito-inhihitory. This reflection of nervous impulse from. one nerve to another is known as reflex action. CEREBRO-SPINAL SYSTEM. The centre of this system is the cerebrospinal axis; consisting of the brain and spinal cord, which like their coverings or meninges, are continuous with each other. The cerebro-spinal axis is invested by three distinct membranes — rviz., the dura mater externally, the arachnoid in the. middle,. and the pia mater internally. MENINGES OF THE SPINAL CORD. The dura mater of the cord is a strong, inelastic membrane,, composed of intersecting bands and laminae of white fibrous tissue. It extends from the foramen magnum, to which it is attached, and where it is continuous with the dura mater of the braiii, to the posterior extremity of the neural canal, where, as a slender cordj MENINGES OF THE BRAIN. 4>6d it blends with the periosteum in the first bones of the coccyx. Excepting near the posterior part, where they are attached by fibrous slips, the dura mater is separated from the periosteum of the canal by areolar tissue and a plexus of veins, so that it forms a loose sheath round the cord. Its inner surface is smooth, and lined by the arachnoid membrane ; opposite each intervertebral foramen it is pierced for the passage of the spinal nerves, which it accompanies, as a tubular sheath, through the foramen. The arachnoid (so called from its extreme tenuity, resembling- somewhat a spider's web) is a delicate serous membrane, and, like other, serous membranes, is a shut sac. Its visceral layer loosely envelops the pia mater of the cord, leaving between them an interval, the snh-arachnoideaTi space, continuous with an opening at the posterior border of the brain, which contains the limpid cerebro-spinal fluid. The parietal layer is a continuation of the visceral, the latter surrounding the nerves as they leave the cord until they pierce the dura mater, when it is reflected on to the inner surface of that membrane. The pia mater, the inner envelope of the cord, is a thin vascular membrane, composed of areolar tissue, containing blood-vessels. It is less vascular, but thicker, denser, and more fibrous than the corresponding membrane of the brain, of which it is a coatinua^ tion. It closely invests th» whole surface of the cord, sends pro- cesses into its longitudinal fissures, and forms a sheath for the spinal nerves. When the cord terminates, the pia mater is pro- longed as a slender filament (Jilum ternriinale) through the centre of the mass of nerves forming the caiwZa equina, .2J[idi blends with the terminal cord of the dura mater. The ligamentum denticulatum is a narrow fibrous band, which runs between the superior and inferior roots of the spinal nerves, from the foramen magnum backwards, so as to form a support for the cord. Its inner border is continuous with the pia mater ; the denticulations of its outer edge being attached to the dura neater in the intervals between the roots of the nerves. MENINGES OF THE BRAIN. The Dura mater is the thick, white, fibrous membrane which lines the cavity of the cranium, acting as the internal periosteum of the bones. It is continuous with the spinal dura mater at the foramen magnum, and is also prolonged as a sheath for the nerves. 470 NEUROLOGY. In some places its layers separate to form irregular channels, the ainuaea of the dura mater, which are lined by a continuation of the inner coat of the veins, for the reception of the venous blood. On its external surface, the branches of the meningeal arteries can be traced ; and from the inner surface, which h smooth and lined, by the arachnoid membrane, processes are directed inwards for the support and protection of the different parts of the brain. These membranous processes, regarded as duplicatures of the inner layer of the' dura mater, are three in number — viz., the falx cerebri, tentorium cerehelli, and falx cerehelli. The falx cerebri, so named in the human subject from its being sickle-shaped, is an arched process, which descends in the longitudinal fissure between the hemispheres of the cerebrum. Anteriorly it is attached to the crista galli process, and posteriorly to the upper part of the ossific tentorium. Its convex upper border, along which runs the superior longitudinal sinus, is attached along the longitudinal suture joining the pairs of parietal and frontal bones ; its under border is free. The tentorium, cerebelli is a transverse partition, formed by lateral inflections of the dura mater, between the cerebellum and the hemispheres of the cerebrum. Each lamina presents an outer convex adherent border, attached to the lateral ridges of the ossific tentorium, and enclosing a lateral sinus ; an inferior concave, free border, turned outwards and a little forward ; a superior extremity attached to the ossific tentorium ; and an inferior extremity, which reaches the upper part of the Gasserian ganglion, and contains the petrosal sinus. The falx cerebelli is a short double process, proceeding from the ossific tentorium towards the foramen magnum, between the lobes of the cerebellum. The occipital sinus is found within its folds. The Arachnoid membrane, like that of the cord, is a closed sac, the parietal layer of which is firmly adherent to the dura mater, and is reflected over the several processes. The visceral layer is thin and transparent on the upper surface of the brain, to which it is loosely attached by the subarachnoidean cellular tissue ; at the base, where the subarachnoidean spaces are found, it is thicker and more opaque. These spaces, three in number (anterior, middle, and posterior), contain the cerebro-spinal fluid ; they communicate freely with each other, and with the 'spinal SPINAL COED. 471 subarachnoidean space. The anterior space is situated between the lobes of the cerebrum, immediately in front of the optic commissure ; the middle, between the pituitary body and the pons Varolii ; and the posterior, between the medulla oblongata and the posterior part of the cerebellum. Yellow and white fibres, intimately blended, enter into the composition of the arachnoid, the free surface being lined with scaly epithelium. It surrounds the nerves at their apparent origin, and ?ccompanies them to their exit from the cranial cavity, when the layers become continuous. The PiA ^lATER (tunica vasculosa) is closely adherent to the entire surface of the brain, dipping into every fissure or depres- sion, into the sulci between the convolutions, and passing into the interior in several places. It is thinner, but much more vascular, than the pia mater of the cord, its vascularity being greatest on the surface of the hemispheres, where it is little more than a ramification of minute vessels, part of which can be traced some distance into the brain substance. SPHTAL COED. The spinal cord, medulla spinalis, or myelon, is a large, white, irregularly cylindrical cord, flattened from above downwards, which extends from the foramen magnum to the sacral portion of the neural canal, where it terminates in a slender filament. In order to allow considerable motion of the vertebral column with- out risk of injury to the cord, it is loosely suspended in the canaJ, the other contents being the meninges and subarachnoidean fluid, with numerous arterial and venous plexuses. In its course, the cord varies in size, being dilated at its origin, where it joins the medulla oblongata, and having a considerable enlargement between the fifth cervical and second dorsal vertebrae, where the large nerves which -form the brachial plexus are given off; and again at and posterior to the third lumbar vertebra, where the lumbar and sacral nerves which constitute the lumbo-sacral plexus arise. Towards its termination the cord gradually tapers to a point, to which portion the name conus medullaris has been applied ; and here is given off an indefinite number of filaments to supply the coccyx and neighbouring structures, forming a bundle of nerves termed the cauda equina. The roots of the spinal nerves have their origin opposite to the intervertebral foramina. 472 NEUROLOGY. The terminal filament of the cord, which is constructed 'of white fibrous tissue externally, and nervous matter internally, passes through the centre of the cauda equina backwards to the second coccygeal bone. When denuded of its coverings, the spinal cord is found to be divided into two lateral symmetrical columns by longitudinal fissures, one on the upper surface, narrower but deeper, the superior median fissure; the other, on the under surface, broader, but shallower, the inferior median fissure. A layer of white matter at the bottom of the latter fissure unites the lateral columns, constituting the inferior white commissure, above which a band of grey matter, the grey commissure^ extends the whole length of the cord. Fio. 17e, , ' Transverse Section through Spinal Cord, showing roots of nerve. o, Inferior median fissure ; 6, Superior median fissure ; c, Central canal ; d. Inferior, and e, Superior cornu of grey matter ; g. Inferior fc, middle, i, superior columns (?) ; k, White commissure ; I, Grey com- missure ; m, Motor root, and n. Sensory root of spinal nerve ; n'. Ganglion on sensory root. (This cut is lettered upside-dovm.) Each lateral column is again divided conventionally into three parts by lateral fissures, a superior (best marked), corresponding with the sensory, and an inferior, corresponding with the motor roots of the spinal nerves. A transverse section of the cord shows the white matter exter- nally, in the form of two semi-cylinders , and the grey matter in the centre of each. The grey substance varies in size in different parts of the cord, but always presents the same general appear- ance of two crescentic-shaped masses united in the middle by the grey commissure. Each crescent presents two cornua or horns ; the superior, long and thin, traversing the whole thickness of the cord, and prolonged outwards and upwards to the superior lateral fissure ; the inferior^ thicker and more irreo-idar, is directed towards. MEDULLA OBLONGATA- 473 the inferior roots of the nerves. The connective tissue of the cord is a reticular variety, very delicate and gelatinous in its structure ; it is termed the neuroglia. In the middle of the grey commis- sure the central spinal canal runs the whole length of the cord, being continuous anteriorly with the fourth ventricle of the brain. The fibres of the cord are not all continuous with those of the encephalon, some being proper to the cord itself; while of those which proceed to the brain, some decussate with each other before doing so. The proportionate size of the brain and spinal cord varies in different animals, according to the position which they occupy in the scale of intelligence ; the higher that position the larger and heavier proportionately is the brain, and the smaller and lighter the cord relatively. Thus in man, the most intelligent of the animal creation, the brain averages 50 oz.,'and the spinal cord about IJ oz. — a proportionate weight of 1 to 33. In the horse the brain averages about 23 oz., and the spinal cord 10 J oz., or a propor- tionate weight of 1 to 2 '19. THE ENCEPHALON, The encephalon or brain is that portion of the cerebro-spinal axis situated within the cranium. In form it is a slightly flattened and elongated ovoid body, which may be considered as consisting of four parts — the onedvlla oblongata, the pons Varolii^ the ccTeheUurriy and the cerebrum. MEDULLA OBLONGATA. This is the prolongation of the spinal cord, extending to the pons Varolii, from which it is separated by a shallow fissure. This portion of the brain is very large in the domesticated animals, and wherever the spinal cord is largely developed It is pyramidal in shape, the narrowest part being continuous with the cord. The inferior surface is convex, and rests upon the basilar process, and the superior surface is received between the hemispheres of the cerebellum, where it forms the floor of the fourth ventricle. Two median fissures, continuous with the supe- rior and inferior longitudinal fissures of the cord, divide the medulla into symmetrical halves. The superior, deep and narrow, expands 474 NEUROLOGY. into the posterior part of the fourth ventricle, while the inferior terminates in a small depression, the foramen ccecuni, at the pos- terior part of the pons Varolii. On each half of the medulla the following objects can be distinguished — viz., the inferior pyra- Tnids, the olivary bodies, the restiform bodies, the intermediate fasciculi, and the superior pyramids. The inferior pyramids are bundles of white fibres, placed on each side of the inferior median fissure, and continuous with por- tions of both the inferior and lateral columns of the cord. They are constructed of three sets of fibres, the innermost of which decussate with those of the oppo- site pyramid ; the second pass in a direct manner from the cord ; and the third, the arciform fibres, form a series of curves which wind round the olivary body, to join the restiform body. The corpora olivaria, Yerj rudimentary, are two elongated, oval-shaped bodies, on the outside of the inferior pyramids. They are separated from the pons Varolii by a slight depression, and are partly covered by the arciform fibres. A section shows the corpus olivarium to be a mass of white matter, in which is a hollow indented capsule of grey matter {corpus dentaium). This capsule has an anterior opening, and contains a nucleus of white matter, from which a bundle of fibres springs. These fibres pass through the opening, and, joining the fibres from the inferior pyramids, constitute the olivary coluoit.ns, which become con- tinuous with the thalami optici and corpora quadrigemina. The restiform. bodies constitute the lateral, and greater part of the supeiior- portion of the medulla, and form the connecting link between the cord and cerebellum. They are composed chiefly of white longitudinal fibres, derived from the superior and lateral columns of the cord, and the arciform fibres, and they increase in thickness as they pass forwards and upwards to ^orm Fia. 177. ^' Base of the brain, a a. Crura cerebri ; b. Corpus albicans ; c, Infundibulum ; d. Pituitary body ; e, Mammillary eminence ; /, Tuber cinereum.; g. Pons Varolii ; g' g". Middle peduncles of the cerebellum ; h. Medulla oblongata ; i i, Inferior pyra- mids ; k k. Olivary bodies ; I I, Restiform bodies. CEREBELLUM. 475 the posterior peduncles of the oerebellum The lateral walls of the fourth ventricle are formed by the divergence of the restiform bodies. The swperioT pyramids are small bands of fibrous matter between the superior mesian fissure and restiform bodies on each side. They are a continuation of the superior columns of the cord, passing to the crura of the cerebrum. The intermediate fasciculi are bundles of fibres, which pass from the' lateral columns to the crura cerebri, between the resti- form bodies and olivary fasciculi. PONS VAEOLII. The pons Varolii is the transverse projection on the base of the brain, between the medulla oblongata and the crura of the cere- brum; it is lodged in the anterior depression on the basilar process of the occipital bone, and has a groove for the basilar artery along its middle line. It consists of a semicircular band of white fibres, which stretch as a bridge from one side of the cerebellum to the other, each extremity being curved upwards, to form the thick processes, which constitute the middle peduncles of the cerebellum. CEREBELLUM. The cerebellum, or lesser brain, is lodged in the posterior part of the cranial cavity, immediately above the medulla oblongata, and, in the domestic animals, behind the cerebrum, from which it is separated by the tentorium cerebelli. It is globular or elliptical in shape, the transverse diameter being the greater, and it consists of a body and three pairs of peduncles, the anterior of which con- nect it Y*'ith the corpora quadrigemina, the middle wdth the pons Varolii, and the posterior with the restiform bodies of the med ilia oblongata. The body of the- cerebellum is composed of grey matter exter- nally, and white in the centre. Its surface presents numerous fissures, the two deepest of which run in a longitudinal manner, so as to divide it into a middle and two lateral lobes. The mi