AEE ANA ASS SD Miva . HEH ral Vi i eae i a NDN ern ; i Ae Bane iene a CORNELL UNIVERSITY MEDICAL LIBRARY ITHACA DIVISION. FROM. SIMON HENRY GAGE, CLASS OF 1877. pe a ee ye IMuy ~ quill EAS MEDIGAL LIBRARY, § 3 baa 3 (O nen en ene EY Figure 3. “16 ‘ / 26 1 ’ i i r fe Figure 4. A HANDBOOK OF VERTEBRATE DISSECTION. BY H. NEWELL MARTIN, D.Sc., M.D., M.A., PROFESSOR IN THE JOHNS HOPKINS UNIVERSITY, AND WILLIAM A. MOALE, M.D. . PART I. HOW TO DISSECT A CHELONIAN. Nt UNI lERSP MEDICAL LIBRARY, we MACMILLAN AND CO. 1881. Gin Bla MBS + | / Med.ryoo CopyrIGNT, 1881, BY MACMILLAN & CO. Trow’s PRINTING AND BookBINDING COMPANY 201-213 East 12th Street NEW YORK PREFACE, Tue following pages, which contain directions for the practical study of the anatomy of a Chelonian, are the first instalment of a series which has had its origin in my own needs as a teacher, and which, when com- pleted, will form a Handbook of Vertebrate Dissection. Some years ago Professor Huxley published a little book called ‘Practical Biology,” in the preparation of which it was my good fortune to assist him. That book was designed to give students commencing the study of biology a good knowledge, based on their own ob- servations, of the structure and life-history of a number of typical plants and animals, with the object of laying a firm foundation for the further study of animal or vegetable morphology or physiology : it was, so far as I know, the first important educational step taken in recognition of the fact that there is a science of living beings, as such, quite apart from any division of them into animals and plants ; and that the accurate observa- tion of the phenomena presented by living forms of matter of all varieties forms the basis of one single science. This truth had, of course, been recognized long before, and was accepted by nearly all scientific iv PREFACE. naturalists, but no really important step toward organ- izing the teaching of biology in accordance with it had previously been taken. In the past five years, during which I have been responsible for the direction of biological studies in the Johns Hopkins University, I have endeavored to arrange the curriculum so as to ensure that each stu- dent, before taking up any one branch of biology for special study, shall have acquired a fairly good knowl- edge of what may be called general biology. No un- dergraduate is permitted to devote his time to the study of botany, or animal morphology or physiology, until he has spent at least one year in learning some- thing about animals and plants in general. Such a course is indisputably far better than one more specially botanical or zodlogical for those who merely desire some knowledge of biological science as a part of general education ; and I have been yearly more firmly convinced that it affords also the best beginning for the student who desires to become ultimately a botanist, zoologist, or physiologist. While the general structure of all plants can be fairly well understood after the careful examination of a small number of selected types, this is not the case with ani- mals; and I have accordingly found it necessary to include in the annual course several types, especially vertebrate, not described in the ‘“ Practical Biology.” Of these a Chelonian is much the most difficult to dis- PREFACE. Vv sect ; and, partly for this reason, partly because the great persistence of vitality in its various organs after general death of the animal makes it extremely promising for physiological experiment, it was the one for whose dissection I first drew up laboratory directions for the use of my students. Finding them of great value in saving time to teacher and pupil, and also in prevent- ing the waste of material which is apt to occur when a student sits down without specific directions to dissect an animal whose structure is almost entirely unknown to him, I thought they might be of use in other labora- tories. I accordingly asked my friend and former pu- pil, Dr. William A. Moale, to assist me in preparing for publication detailed directions for the dissection of a number of vertebrate animals. The present pamphlet will shortly be followed by two others, containing direc- tions for the dissection of a pigeon and a rat, both of which are well on the way toward completion. We in- tend ultimately to include in the series a bony and a cartilaginous fish, a lizard, and one of the large-tailed amphibia which form such a characteristic feature of the American Fauna. . In the present instalment of our work, Pseudemys ru- gosa, though far from being the most widely distributed of American Chelonia, is the species selected for de- scription, mainly because it is sold in the markets here during the winter months, and was, therefore, readily obtainable by us. The fact that in many places this vi PREFACE, particular species may not be found is of no import- ance, as the end in view is not to provide a monograph on any one species, but to show a student “‘ How to dis- sect a Chelonian.” The members of the order are so similar in all important points that the best method of examining the structure of one species is the best also for almost any other. I am not sure, in fact, that it is not better in all cases to provide students with species slightly different from the one described ; their atten- tion is kept more alert when they find they cannot alto- gether rely on the description in the book, but have to look at everything carefully for themselves. These directions for dissection are of course not meant to be used by themselves, but to accompany lectures on the class and order of the type described, or the reading of a good text-book. Some knowledge of human osteology, which affords the best starting-point for every student of vertebrate morphology, is also assumed, H. NEWELL MARTIN, BALTIMORE, July 1, 1881. CONTENTS. ZOOLOGICAL POSITION OF THE RED-BELLIED SLIDER TER- RAPIN, . + Ra cee oe OH ee oe ne THE ANATOMY OF THE RED-BELLIED SLIDER TERRAPIN, . INDEX, . . . . . . . . . . . PAGE 89 DESCRIPTION OF THE FIGURES. Fic. 1, represents the skull viewed from the base ; Fic. 2, as seen from the left side and partly from the front; Fic. 3, represents the roof of the skull; and Fic. 4, the inner side of the right half. The references in the different figures are as follows: 1, the premaxilla; 2, the maxilla; 3, the palate bone; 4, the vomer; 5, the pterygoid; 6, the basi-sphenoid ; 7, the basi- occipital; 8, the exoccipital; 9, the opisthotic; 10, the squamosal ; 11, the quadrate; 12, the quadrato-jugal; 13, the jugal; 14, the post-frontal; 15, the columella auris: a thin plate of cartilage, which covered the inner division of the tympanum, has been removed to expose part of the columella ; 16, the parietal ; 18, foramen for exit of external carotid artery ; 19, the posterior nares; 20, part of the opisthotic ; 21, occi- pital condyle ; 22, orbito-temporal fossa ; 23, articular surface for mandible; 25, anterior nares ; 26, supra-occipital bone ; 27, frontal bone; 28, naso-prefrontal bone; 29, prodtic ; 30, epiotic, anchylosed to the supra-occipital ; 31, canal for entry of carotid artery; 32, alisphenoid bone; 33, cartilaginous inner wall of labyrinth ; 34, foramen for exit of internal carotid artery. ZOOLOGICAL POSITION OF THE RED- BELLIED SLIDER TERRAPIN. Suskincpom, Vertebrata. Division, Sauropsida, Cvass, Reptilia. Onrprer, Chelonia, Famitry, Emydoide, Genus, Pseudemys, Species, rugosa, Characters of the Sauropsida.* 1. Almost always an epidermic skeleton, in the form of scales or feathers. 2. The vertebral centra are ossified, but have no ter- minal epiphyses. 3. The skull has a completely ossified occipital seg- ment and a large basi-sphenoid. There is no separate para-sphenoid in the adult. The protic is always ossi- fied, and either remains distinct from the opisthotic and epiotic during life, or unites with them only after they have anchylosed with adjacent bones. 4, There is always a single convex occipital condyle, into which the ossified ex-occipitals and basi-occipital enter in various proportions. 5. A mandible is always present, and each ramus consists of an articular ossification and several mem- brane-bones. The articular is connected with the rest of the skull by an ossified quadrate. 6. The apparent ankle-joint lies between the proxi- mal and distal divisions of the tarsus. * The characters given are taken, with slight modification, from Huxley. I ee 2 ANATOMY OF A CHELONIAN. 7. The alimentary canal terminates in a cloaca. 8, The heart is trilocular or quadrilocular ; some of the blood-corpuscles are red, oval, and nucleated. 9, The aortic arches may be two or more ; when only one persists in the adult it is on the right side. 10. Respiration is never performed by branchiz ; and after birth always by lungs, in which the bronchi do not branch dichotomously. ll. A thoracic diaphragm may exist, but never forms a complete partition between the thoracic and abdomi- nal viscera. 12. The cerebral hemispheres are never united by a corpus callosum. 13, The reproductive organs open into the cloaca, The oviduct is a Fallopian tube with a posterior uter- ine dilatation. 14, There are no mammary glands. 15, All are oviparous or ovo-viviparous. 16. The Wolffian bodies are replaced functionally by permanent kidneys. 17. The embryo has an amnion and a large respira- tory allantois ; and develops at the expense of a large mass of food stored up in the egg. Characters of the Reptilia, as distinguished from Aves, the remaining class included in the division Sau- topsida. 1. Exoskeleton composed of horny plates (epidermic), or bony plates (dermic), or both. The epidermic scales never develop into feathers. 2. The vertebral centra may be amphi- or pro- or CHARACTERS OF REPTILIA, 3 opistho-ccelous, or have flat faces ; but their ends are never cylindroidal. , . 8. When a sacrum is present its vertebrz have large expanded ribs, with the ends of which the ilia articu- late. 4. The sternum, when present, is rhomboidal ; and, when many ribs are connected with it, the hindermost are attached to a single or double backward median prolongation. The sternum may be converted into cartilage-bone, but is never replaced by membrane- bone, and does not ossify from two or more definite centres. 5. When an interclavicle exists it remains distinct from the clavicles. 6. The manus contains more than three digits ; and, at fewest, the three radial digits have claws. 7. The ilia are prolonged farther behind the ace- tabula than in front of them, and the inner wall of the acetabulum is wholly or almost wholly ossified. The pubes are directed ventrally and forward, and, like the ischia, meet in a ventral symphysis. 8. The digits of the pes are not fewer than three ; the metatarsals are not anchylosed together or with the distal tarsal bones. 9. Not fewer than two aortic arches persist. Two arterial trunks are given off from the right ventricle, or the part of the single ventricle that answers to it. The venous and arterial currents are connected in the heart, or at the origins of the aortic arches. 10, The blood varies in temperature with the sur- rounding medium. There are usually two semilunar valves at the origin of the aortic and pulmonary trunks. 4 ANATOMY OF A CHELONIAN. ll, The corpora bigemina lie on the dorsal aspect of the brain. The spinal cord presents no sinus rhom- boidalis. 12, The caudal vertebrz often form a series equal in length to the rest of the body. 18, Teeth are frequently present. Characters of the Chelonia. 1. None of the vertebrae have transverse processes, and the dorsal vertebre are not movable on one another ; nor are the ribs movable upon the vertebrze. Most of the dorsal vertebrz.and ribs are restrained from motion by the union of superficial bony plates, into which they pass, to form a carapace. 2. All but the soft tortoises (Zrzonyx) have part of the epidermis modified to form horny: plates, which constitute the tortoise-shell. These plates are arranged in definite series on the carapace and plastron. 8: The presacral vertebrz are few. A. No sternal ribs, and no trace of a true sternum. The ventral surface is protected by a number (usu- ally nine) of dermal membrane bones, forming the plastron. 5. The sacrum consists of only two vertebrz ; the sacral ribs are not anchylosed to their vertebrz. 6. The anterior caudal vertebrze have no transverse processes, but some have ribs. . In the skull, all the bones but the mandible and hyoidean arch are immovably united together: the epiotic anchyloses to the supra-occipital ; the prodtic and opisthotic remain as distinct bones. The alisphe- CHARACTERS OF CHELONIA. 5 noid is unossified or small, a downward prolongation of the parietal taking its place. There is no bony pre- sphenoid or orbito-sphenoid. The mesethmoid carti- lage largely persists. The orbito-temporal fossa is covered by a bony arch. The dentary pieces of the mandible are anchylosed together. 8. The pectoral arch is ossified in such a way that scapula and precoracoid form one bone, but the cora- coid remains distinct. 9. The heart has a single ventricle. 10. There are no teeth, but the jaws are provided with horny cutting-plates. THE ANATOMY OF THE RED-BELLIED SLIDER TERRAPIN (Pseudemys rugosa).* 1. General External Appearance.—Note the hard case in which most of the animal is enclosed, and which va- ries in tint considerably in different specimens; on the whole it is dark brown above, and orange-red and yel- low beneath. The case consists of a convex dorsal plate, the cara- pace, and a ventral flat plate, the plastron, united at the sides by bony bridges, but separate anteriorly and posteriorly, leaving large open spaces, in which can.be seen certain soft parts covered by wrinkled, scaly skin, and protected by the projecting edges of the carapace and plastron. Most of the skin is dark, with bright yellow stripes ; but in the hollows which receive the hind limbs when withdrawn, and often also in the corresponding hol- lows for the fore limbs, it is almost white. 2. Insert a tenaculum into the soft parts beneath the head and draw out the latter; force open the mouth and direct a pipette, containing about a teaspoonful of chloroform, into the opening of the glottis, which will be found in an elevation at the base of the tongue; then blow the chloroform into the lungs. This will very soon kill the animal. Meanwhile, note the long, * Ptychemys rugosa (Ag.). mys rubriventris (Holbr.). EXTERNAL CHARACTERS. 7 flexible neck, the folds of skin about the shoulders, and, after the tenaculum is removed, the way the head is withdrawn between these folds, so that only the tip of the snout is visible. So soon as the animal is dead and flaccid, you can readily stretch out the neck and proceed with your examination. &. External Characters of Head and Neck. Qa. Observe the form of the head: flattened from above down ; wide posteriorly, where it is very distinctly differentiated from the neck; and narrowing toward the snout. On the ventral aspect of the head and neck the Ayoidean apparatus can be felt through the skin of the throat; and farther back the wind- pipe. The very large mouth opening, provided with notched horny plates instead of teeth along the margins of the jaws; note the marked projection on each side of the median notch of the upper jaw. 2 On the extremity of the snout the openings of the anterior nares ; a pair of round apertures placed close together. The eyes, around which can be felt the ante- rior margins of the bony ordits; the thick, opaque upper eye/id, and the larger, more mov- able lower one; the xictitating membrane, or third eyelid, may be found covering the eye- ball or withdrawn to the anterior corner of the eye opening ; in the latter case seize its mar- gin with forceps and draw it back over the eye so as to see it well; it is much more I ANATOMY OF A CHELONIAN. movable and less opaque than the eyelids proper. Just behind the angle of the gape, the tym- panic membrane will be seen as a circular slightly depressed area of skin, around the margin of which a. hard supporting ring can be felt. A, The Interior of the Mouth Cavity. a, Open the mouth and observe that the horny plates covering the jaws extend in for some way over both floor and roof of the buccal cavity ; also that each has a second notched ridge within the one forming its outer boun- dary. Into the groove between the two up- per ridges the external lower ridge fits, and similarly the inner ridge of the upper jaw fits between the two ridges of the lower. On the roof of the mouth, note that the horny plate is succeeded by diverging folds of mu- cous membrane, between which are seen the openings of the Zosterior nares with the back edge of the septum narium between them. Note also that the eyeballs do not cause projections on the roof of the mouth, as in the frog, but are completely separated from it by a hard partition. On the floor of the mouth is seen the short, con- ical, pointed, and but slightly movable tongue. At the base of the tongue is a considerable elevation, in which is the longitudinal slit of the aditus laryngis, unprotected by an epi- glottis. EXTERNAL CHARACTERS, 9 @. On each side of the mouth cavity, behind the elevation caused by the mass of muscles passing down to the lower jaw, is the small opening of a Eustachian tube. It will be found more easily later (177, 8). 5. The Limbs, a. Note the manner in which the limbs, when not in use, are packed away between the projecting edges of carapace and plastron, in hollows at the sides of the neck and pelvis. b. The fore limbs are flattened, clumsy, and pad- dle-like. When extended they curve back over the front edges of the bridges which unite carapace and plastron. The division into Jra- chium, antebrachium, and manus is not obvious to the eye, but may readily be felt. The limb ends in five digits, connected by a web, and each armed with a large claw. ¢ The hind limbs show more plainly the division into femur, crus, and pes. Each terminates in five digits united by a web, and possessing claws, except the fifth. d. Seizing the pelvic region between finger and thumb, note that it has a considerable range of lateral sway. This movement takes place at the articulation between the last dorsal and the first sacral vertebra, and to some extént compensates for the rigidity of the whole dor- sal region of the animal. 6. The tail, short, conical, and pointed ; usually bent to one side, so as to be protected by the overlapping edge of the carapace. 1* IO ANATOMY Of A CHELONIAN. On its under surface is the cloacal opening ; a trans- verse slit, with puckered edges, Tl, The Epidermic Exoskeleton mainly consists of horny plates (tortoise-shell), of definite number and very con- stant arrangement, found covering carapace and plas- tron. a On the plastron are sixteen pieces, twelve ar- ranged in pairs on the sides of the middle line, and the remaining four covering the margins of the bony bridges uniting carapace and plas- tron. On the carapace, in the middle line in front, is asmall zuchal plate ; and, meeting in the mid- dle line behind, over the base of the tail, are a pair of pygal plates. Running along the middle of the back, from nuchal to pygal plates, are five unpaired central plates. On each side of the latter are four centro-lateral plates; and, external to these, eleven marginal plates on each side, ex- tending along the edge of the carapace from the nuchal to the pygal plates, and, like them, curving around the edge so as to cover in the projecting margin of the carapace on its ventral side. The claws, the horny coverings of the jaws, and the scales (which are especially developed on the paddles and the dorsal side of the tail) are also parts of the epidermic exoskeleton. 8. Make drawings showing the arrangement and form of the epidermic plates on carapace and plastron. Then immerse the animal in boiling water for about two min- THE CARAPACE, II utes, giving first another dase of chloroform (2) should there be the least sign of sensibility remaining ; the tor- toise-shell can then be peeled off. When it is removed, note that though the bones beneath present surface- markings corresponding to the edges of the epidermic plates, their actual number and arrangement are quite different. 9. The Bony and Cartilaginous Skeleton.—For the sat- _isfactory study of the skeleton, the student should have beside him a prepared articulated skeleton for reference, and should disarticulate and examine another skeleton for himself. For this purpose boil the animal thor- oughly ; the plastron can usually then be separated from the carapace by seizing each and pulling them forcibly apart; if this prove impracticable, divide the uniting bridges by a saw, then cut through the soft parts at- tached to the dorsal aspect of the plastron and remove the latter; clean all the bones carefully, but for the pre- sent do not separate from one another.the pieces of the plastron, carapace, skull, manus, and pes. In the cleaning take great care not to injure the cartilaginous portions of the skeleton. 10, The Carapace is composed partly of dermic exo- skeletal bony plates, and partly of true endoskeletal elements. The dermic bones are printed below in small capitals. ' a, On the exterior of the carapace, note a median row of bones succeeding one another, from be- fore back, in the following order: the NucuauL Pate, rhomboidal in shape ; eight neural plates, formed by the expanded spines of the dorsal 12 ANATOMY OF A CHELONIAN. vertebrz from the second to the ninth, inclu- sive; the PycaL PuareE. On each side of the above middle row are eight costal plates, formed by expanded ribs attached to the dorsal vertebrze from the second to the ninth. In all except old full-grown specimens the outer ends of the costal plates are not fully ossified ; and, accordingly, spaces filled only by cartilage are then left between each one and its successor. The Marcinat Puates, eleven on each side, ex- tend from the nuchal to the pygal. From the second to the fifth, inclusive, they reach ven- trally to articulate with the plastron. U1. On the inner (ventral) aspect of the carapace, note the projecting centra of the Dorsal Vertebre. The most anterior is attached dorsally to the nuchal plate ; the eight succeeding ones bear, dorsally, the expanded neu- ral spines already seen on the exterior of the carapace as the neural plates. a, The first dorsal vertebra is comparatively short and thick, and bears anteriorly a pair of large stout prezygapophyses (anterior articular processes), which slope downward and forward. The centra of the succeeding dorsal vertebrz, back to the eighth, are considerably elongated in the antero-posterior axis, and compressed from side to side. Each has flattened ends, and between each pair lies a thick plate of cartilage, except in quite old specimens in which the intervening cartilage is much thinner. The whole set of dorsal vertebral centra, with these THE CARAPACE, 13 plates, thus forms a continuous osseo-cartila- ginous rod. 12. Examine the Ribs,—Attached opposite the inter- spaces between the vertebral bodies from the first to the fourth dorsal, and articulating either only with the inter- posed cartilage, or also with the posterior end of one centrum and the anterior end of the next, are the heads (capitula) of the second, third, and fourth ribs. @, From the capitula, thin bony bars, which may conveniently be called the zecks of the ribs, run outward and dorsally for a.short distance, and then fuse with the ventral aspect of the costal plates already mentioned (10, 4). 4. The costal plates by their inner ends articulate with the neural plates of the two vertebrz be- tween which the head of the corresponding rib lies. 18. The arrangement of the fifth, sixth, seventh, and eighth ribs is like that described above (12), except that each articulates with the centrum of only one dor- sal vertebra (that which corresponds in number with the rib); and the costal plate of the ninth rib articu- lates only with the neural plate of its own vertebra. In old specimens, also, the sides of the centra of the posterior dorsal vertebrz bear distinct capztular pro- cesses, to the ends of which the heads of the ribs are attached. 14, The ribs of the first pair are very small; they run backward and outward from the sides of the cen- trum of the first dorsal vertebra, and ‘fuse at their outer 14 ANATOMY OF A CHELONIAN, ends with the costal plates of the second dorsal verte- bra, the first vertebra having no costal plates of its own. 15. The tenth dorsal vertebra is comparatively wide and short, and carries a pair of small ribs which have no costal plates of their own, but anchylose with the eighth pair of costal plates (ze, those of the ninth dorsal vertebra). On the ventral aspect of each of these last costal plates is to be seen a small elevation, over which the sacral ribs (16) glide in lateral move- ments of the pelvis. 16. The two Sacral Vertebrea may be found still at- tached to the carapace, or one or both may have come away with the tail in preparing the specimen. Each has a pair of short ribs, which run outward and end in cartilages—which, in the articulated specimen, will be seen to articulate with the iliac bones (71, a). That end of each rib next the vertebral centrum is also car- tilaginous. The anterior rib is much stouter than the other. 17. Take the carapace to bits, piece by piece, noting meanwhile the finely dentated sutures by which most of the bones articulate. As you separate the pieces, note also that— a. The neural arch of the first dorsal vertebra is much shorter than the centrum, which is overlapped in front by the posterior end of the nuchal plate, and behind by the neural plate of the succeeding vertebra, the spine of the first dorsal vertebra not expanding to make THE CARAPACE, 15 any neural plate. This vertebra also has not a persistent neuro-central suture, the neural arch being firmly grown into continuity with the centrum. Its remarkable prezygapophyses, which articulate with the postzygapophyses (pos- terior articular processes) of the last cervical ver- tebra, have already been mentioned (11, 2). 4. The centrum of the second dorsal vertebra is covered on the dorsal side, for its anterior two- thirds, by its own neural arch, the two uniting by a persistent xeuro-central suture; the pos- terior third of the centrum is overlapped by, and articulates with, the neural arch of the vertebra behind. Its neural spine expands to form the first neural plate of the carapace. ce. The arrangement of the parts of the dorsal vertebrz from the third to the eighth, inclu- sive, is pretty much like that found in the second; but in each the neural plate reaches as far back as the posterior margin of the cen- trum, although the /amineg of the neural arch of the ninth vertebra overlap the posterior part of the centrum of the eighth. @ The neural plate of the ninth dorsal vertebra reaches back and overlaps the tenth vertebra, which has no neural plate of its own. 18. Examine carefully a Costal Plate—the third, for example. Note the dentated sutures on each of its margins ; the continuity of the neck of a rib with its ventral surface; the process which extends from its outer end to be inserted into a pit in the corresponding marginal plate, In partly grown specimens this process 16 ANATOMY OF A CHELONIAN. is long and conspicuous, the portions of costal plate in front of and posterior to it in that region being not yet ossified: (10, 8). ' Also, examine more carefully the marginal plates now that they are separated ; and note their relations to the various costal plates. 19. The Plastron is composed entirely of dermic bones. It consists of nine pieces: one median un- paired bone toward its anterior end, called the ENTO- PLASTRON ; and eight bones arranged in pairs on each side of the median line; those on each side, from be- fore back, are named successively, EPIPLASTRON (? clav- icle), HYOPLASTRON, HYPOPLASTRON, and XIPHIPLASTRON. The outward ends of the hyo- and hypo-plastron curve dorsally, and make up most of the bony bridges uniting carapace and plastron. 20. The Cervical Vertebre are eight in number and freely movable, except the first and second. In gen- eral, each consists of a centrum and neural arch, with pre- and post-zygapophyses ; and the articular surfaces of the prezygapophyses look dorsally, and those of the postzygapophyses ventrally; there are no trans- verse processes, but the arches present more or less of a median dorsal ridge, representing a rudimen- tary spinous process. The posterior end of the body is produced backward and ventrally some distance be- yond the neural arch; and the intervertebral foramina are arched over by the articular processes. The centra bear a slight median ridge on the ventral aspect, and are thick and cylindrical near the anterior end, but flattened dorso-ventrally at the posterior. THE CERVICAL VERTEBRA. 17 21, In individual cervical vertebrz, note the follow- ing peculiarities : a The jirst (a¢/as) is a ring-like mass, composed of three’ pieces: a ventral and two dorso-lateral, united by cartilages. Its anterior end presents, where the three pieces meet, a deep pit, in which the occipital condyle (25, 2) plays ; pos- teriorly is a similar pit for the odontoid pro- cess of the axis (21, 4). The second cervical vertebra (axis) has a large odontoid process, attached by cartilage to the anterior end of its centrum. The postzygapophyses of the seventh and eighth cervical vertebre are remarkably large and stout, and those of the eighth arch backward to ar- ticulate with the prezygapophyses of the first dorsal vertebra (11, @). These two vertebrz are also peculiar in their neural spines, which consist of a pair of ridges which meet ante- riorly, but diverge behind to run out over the postzygapophyses. The variety in the surfaces by which the cen- tra of the cervical vertebrz articulate with one another. The second and third vertdbrz are opistho-celous ; the fourth has a convexity on each end of its centrum; the fifth is con- cave anteriorly, and has a pair of convexities behind. The sixth has two concavities in front, and two convexities behind. The sev- enth has two concavities in front, and two behind. The eighth has two convexities in front and two behind. 18 ANATOMY OF A CHELONIAN, 22. The Caudal Vertebre are freely riowable, and in the anterior part of the tail proceelous. From the fifth to the tenth, inclusive, they have well-marked rudimen- tary ribs attached to them. None have transverse pro- cesses. Becoming smaller and smaller toward the tip of the tail, they are finally reduced to minute subcy- lindrical masses, without any processes, but each still possessing a centrum and a neural arch enclosing a neural canal. 23. The Skull.—A fter boiling the skull, clean away the soft parts, taking care to leave, in so doing, as much of its cartilaginous parts as possible—the thin plate between the nostrils is especially apt to be removed. When cleaned, make outline drawings of the skull, as seen from behind, from the base, and antero-laterally. 24. The skull is flattened from above down, and wide from side to side, Note that the brain-case proper is much narrower than the skull, which is expanded posteriorly, to form a pair of large post-auditory processes, from which two bony arches proceed forward on each side: one below the orbit to the upper jaw, and the other behind the orbit to the brain-case proper. The temporal fossa is covered in by this arch on each side, and is continuous with the orbital cavity, so that the two form one orbito-temporal fossa. 25, On the Posterior Aspect of the Skull, note: a. The foramen magnum, and below it the single occipital condyle, 4, On each side of the condyle are two small foramina; through the more mesial of these, | the Aypoglossal nerve (180, 7) passes out. e. THE SKULL. 19 External to these is the larger foramen lacerum postertus, which gives exit to the pneumogas- tric and spinal accessory nerves (180, #). Still farther out is seen the conical post-auditory process, covered over by the sguamosal bone. Above the foramen magnum the bony spine of the supra-occipital bone projects backward ; on eath side of this the roof of the skull is con- cave, and in the bottom of the hollow is a large foramen, through which the external caro- tid artery passes out to supply the exterior of the head. 26. On the Base of the Skull, note: a. The ventrally projecting guadrate bone, with its terminal facet for articulation with the mandi- ble. Farther forward, and near the middle line the posterior nares, and somewhat behind and to the outside of these, the aperture on each side for the transmission of a branch of the fifth cranial nerve. In front of the quadrate a large aperture leads up into the orbito-temporal fossa; through it the main muscles of mastication formerly passed to the lower jaw from their origins on the sides of the brain-case. Behind the quadrate is a plate of cartilage, ossified in some specimens, which is often re- moved in cleaning the skull; if this has not happened remove it now on one side. This will lay open part of the labyrinth and the inner section of the tympanic cavity, which will be 20 a ANATOMY OF A CHELONIAN, seen to communicate with an outer division by means of a narrow passage, through which the columella auris (now exposed 7x situ) passes from the tympanic membrane on its way to the fenestra ovalis. Just outside the cartilaginous plate referred to above and close behind the quadrate is a fora- men for the entry of the carotid artery, which, within the bone, divides into an z#fernal carotid, which enters the skull cavity, and an external carotid, which emerges by the foramen on the roof of the skull mentioned above (25, ¢). In front of the cartilage, and nearer its outer than its inner side, is a small aperture which leads into a canal which passes forward some way in the bone forming the base of the skull. Into it one division of the anterior extremity of the sympathetic nerve will subsequently (199) be found to pass. External to the aperture of the sympathetic channel, and in front of the aperture of the carotid canal, is the small foramen of exit for the seventh cranial nerve (200). 27. On the Side of the Skull, note: a. The large ear-opening leading into the external division of the tympanum, which reaches back into the post-auditory process. Close to the outer side of the proximal end of the quadrate bone is the narrow passage through which the columella passes on to the inner expansion of the tympanic cavity. Farther forward is the temporal fossa covered THE SKULL, 21 over by the arches already mentioned (24). In it, just above the inner side of the proximal end of the quadrate bone, is the large foramen through which the superior and inferior maxil- lary divistons of the fifth cranial nerve leave the skull (190, 191). 28. Note that the anterior end of the brain-case proper is not inclosed by bone, but opens widely be- tween the orbits ; also, that between the orbits there is no bony partition, the ¢xter-orbital sepium being nearly entirely membranous, and usually removed in cleaning the skull. In the middle line between the orbits and close to the bone bounding them below, will, however, be found the xaso-ethmoidal cartilage, passing out from the interior of the skull-chamber and there flattened dorso-ventrally ; between the orbits it becomes cylin- drical, and then, farther forward, expands into a verti- cal plate (mesethmoid), which enters the nose and forms most of the partition between the nostrils. 29. The floor of the orbit is not completely bony, but presents a considerable fontanelle, closed in the recent state by membrane: through this a branch of the su- perior maxillary nerve will subsequently (190) be found to pass. 30. On the posterior boundary of the nares, note a round aperture above the mesethmoid cartilage, and close to the roof of the nose. Into it, in the recent state, reached an anterior prolongation of the brain, en- veloped in dura mater (169), which passed out of the large anterior opening of the proper brain-case above 22 ANATOMY OF A CHELONIAN, noted (28), and, thence, forward between the eyeballs and close to the bones on the roof of this part of the skull. 81, If necessary, now boil the skull again until its bones are readily separable. Then, working with the articulated specimen beside you for reference, remove the bones, one by one, in the order in which they are described below ; as each is removed, and its boundaries thoroughly ascertained, sketch it in on your outline drawings (23). 32. The jost-frontal is an irregular, squarish bone which forms most of the posterior margin of the orbit; , it articulates with the frontal and parietal above, and Jugal and guadrato-jugal below. A long process reaches back from its postero-inferior margin. 33. Below the post-frontal and forming the posterior margin of the orbit, is the juga/, squarish as seen from the exterior, but sending inward a process which forms part of the floor of the orbit and reaches internally to the pterygoid. It is overlapped by the maxilla in front. The jugal overlaps behind the bone next described. 34. The guadratojugal bounds the anterior margin of the tympanic cavity. It sends downward and back- ward a slender process, which turns around the margin of the ear-opening for a variable extent. Posteriorly it joins the quadrate below and the squamosal above. 35. Behind the tympanum is a conical cap of bone, the sguamosal, which covers a similarly shaped semi- THE SKULL, 23 cartilaginous cap, whose hollow is continuous with the tympanic cavity. In front, the squamosal articulates with the quadrato-jugal and the quadrate ; and, behind, it overlaps and conceals parts of the quadrate and opis- thotic bones. 36. The guadrate forms a large, irregular, bony mass, in which lies much of.the tympanic cavity. It is pro- duced ventrally to articulate with the mandible. It articulates at its upper end, on the inner side, with the proétic and opisthotic bones. In removing the quad- rate, take care not to displace the columella auris. 37. The ofisthotic, which protects the posterior part of the inner ear, may now be removed and examined ; it forms the posterior boundary of the fenestra ovalis (26, @). Behind, it articulates with the exoccipital ; above, with the supra-occipital ; and in front with the proétic. It also articulates with the quadrate, which conceals a great portion of it in the natural positions of the parts. 38. In front of the opisthotic is the prodtic, bound- ing the fenestra ovalis in front. It articulates with the last bone ; also in the base of the skull with the basi- sphenoid and pterygoid; and above with the parietal and epiotic. 89. The ¢fiotic lies above the prodtic and opisthotic, with both of which it articulates. In adults it is not separable from the supra-occipital. 40. The supra-occipital bone bounds the foramen mag- num above; in front it is overlapped by the parietals ; 24 ANATOMY OF A CHELONIAN. below it articulates with the exoccipitals and anchy- loses with the epiotic. 41. The exoccipital bones form the lateral boundaries of the foramen magnum, and, together with the basi- occipital, form the occipital condyle. 42. The dasi-occifital articulates on its sides with the exoccipitals, and anteriorly with the basi-sphenoid. 43. On the base of the skull, in front of the basi- occipital, is seen the Jdasi-sphenotd. It articulates with the pterygoids in front, and the prodtics on its sides; when removed, observe that its upper or inner surface presents anteriorly a concavity (sed/a turcica) bounded by ridges, which rise up in front as a pair of thin bony plates, the anterior clinoid processes. Posteriorly its up- per surface presents a median ridge, continuous with a similar one on the corresponding surface of the basi- occipital. 44, In front of the basi-sphenoid, and partly covering its ventral surface, are the prerygoid bones. 45. The parietal bones form a large part of the roof of the cranium. Posteriorly they overlap the supra- occipitals ; in front they unite with the frontals; in the middle line they meet one another; laterally, they reach down and cover in much of the sides of the brain- case proper, meeting the pterygoids, palate bones, and prodtics. , 46. The great downward extension of the parietals is a marked feature of the Chelonian skull, causing THE SKULL, 25 them to cover in a region which, in. most cases, is pro- tected by the alisphenoid. This bone is small and closely attached to the middle third of the ventral margin of the parietal in the skull of the Slider. 41. The palate bones lie in front of the pterygoids. They partly bound the posterior nares above, and also form a small part of the roof of the mouth on the sides of the recess in which the posterior naresopen. Above they meet the pterygoids, and externally the superior maxilla. Between them lies— 48. The vomer, a slender bone having on its anterior extremity a knob which appears on the roof of the mouth. With the palate bones it completes the roof of the posterior nares. 49. Meeting in the middle line at the front of the skull are the small premaxilla, which bear part of the horny cutting-ridges of the upper jaw. 50. The maxil/e lie on the outer sides of the pre- maxillz, and form the greater part of the roof of the mouth and of the upper boundary of the gape; they also form a large part of the floors of the orbits. 51. The xaso-prefrontal bones roof in the front part of the nose chamber. In front they join the maxillz, and help to complete the orbital boundary. Behind they join— 52..The frontal bones, which meet in the middle line above the orbits. Behind, these articulate with the parietal and post-frontal bones, and in front with the naso-prefrontal bones. 2 26 ANATOMY OF A CHELONIAN. 53. The Mandible is a V-shaped mass, composed of several bones, and presents an anterior dorso-ventrally compressed Jody, and two lateral ram, one at the poste- rior end of each half of the body, and compressed later- ally. On the upper border, on each side, is a prominent coronoid process where ramus and body meet; and on the free end of the ramus is an oblique surface, with a cen- tral elevation, which articulates with the ventral end of the quadrate (36), which has a corresponding groove into which the ridge fits, so that a firm hinge-joint is formed between them. On the upper surface of the body are ridges, which bear the horny cutting plates of the lower jaw (4, a). On the upper edge of the ra- mus is a fissure leading into the mandible ; a branch of the inferior maxillary netve (191) enters there. On the inner side of the ramus are two foramina; through the lower a branch of the above nerve passes out into the floor of the mouth. 54. The following parts enter into the composition of the mandible ; to separate them needs some patience, as the bones adhere very tightly and the lines of artic- ulation are not very visible. a. On the posterior aspect of the bony body of the mandible is a groove, filled in the recent skeleton by a cartilaginous rod (Meckel’s cartilage), which will subsequently be found to extend back through the rami. 6. Take hold of the articular end of one ramus, and work it to and fro until it is loose. Then carefully detach it, disturbing the remaining bones as little as possible. It will bring with it Meckel’s cartilage, which will be found to THE SKULL. 27 join its fellow in the middle line in front; di- vide the cartilage at this point, and remove the whole loosened piece; it consists of four bones, which are to be separated and exam- ined. One of these pieces, placed to the outside, and forming the outer boundary of the fissure above mentioned (53), is a thin bone, lying in the vertical plane; it is the surangular. In the natural position of the parts it is largely over- lapped by the dentary (54, /). Forming the inner boundary of the fissure, and reaching back to form part of the surface which articulates with the quadrate, is another thin, flat bone, placed vertically : it is the splenial, and forms nearly all the inner surface of the ramus of the mandible. Wedged in between the lower edges of the splenial and surangular is a narrow bony bar, the os angulare. When the above pieces are removed, Meckel’s cartilage will be left, with a small polygonal bone continuous with its posterior end. This bone is the os articulare. It forms most of the articular facet of the mandible, and is the only part of it ossified in cartilage. The part of the mandible left when the above loosened portion (54, 4) was removed, contains two bones: one is the coronoid, which forms the process of that name (53), and articulates in front with— ; The dentary, which is anchylosed to its fellow in the middle line in front, and also sends back 28 ANATOMY OF A CHELONIAN. a process on the outside of the ramus, overlap- ping the surangular. ; 55. The bones of the skull, seen in their natural rela- tive positions from the interior of the cranial cavity, may be studied either on one-half of a prepared median dorso-ventral section of the cranium, or, better, on a recent specimen prepared by the student; as the carti- laginous parts, which are important, are apt to be re- moved unless special care has been taken in preparing the specimen. 56. On the Interior of the Skull, as viewed from one side, note: a. The dast-occipital bone, divided by the saw in the median line behind. 6, External to the basi-occipital, the exoccipital. having in it the foramen (25, 4) for the twelfth cranial nerve; between it and the basi-occi- pital another foramen ; and between it and the opisthotic the foramen of exit for the vagus and spinal accessory nerves (25, ¢). ce. Above the exoccipital the large supra-occipital, with its spine. d, On the base of the skull, and in front of the basi-occipital, the divided dast-sphenotd, with its median ridge and one of the clinoid processes described above (43); and in front of the cli- noid process a hollow from which some mus- cles jof the eyeball (184) arise. e. External and dorsal to the outer edge of the posterior portion of the basi-sphenoid is a car- tilaginous plate (already removed if care has THE SKULL. 29 not been taken in preparing the skull), which separates the cranial cavity from the internal ear. The extent of this plate varies very much, being less in older specimens. The corner of the supra-occipital which bounds it above, rep- resents the epiotic bone (39). : Behind the cartilage is the opisthotic bone, and in front of it the prodtic. In front of the supra-occipital and prodtic, and also reaching back so as to cover in a part of the supra-occipital, is the parietal bone, and be- tween it and the prodtic, the large foramen ( foramen ovale) for the exit of the main di- visions of the trigeminal nerve. External to the anterior clinoid process of the basi-sphenoid, and in the prodtic bone, is seen the opening of the canal through which the internal carotid artery enters the cranial cav- ity. - Pass a probe back through the canal to the point where the common carotid artery enters the skull cavity (26, ¢). In front of the basi-sphenoid is seen the Azery- goid bone, forming that part of the base of the skull. External to the pterygoid, below the parietal, and in front of the prodtic, is the small a/z- Sphenoid bone. In front of the descending plate of the parietal (45) is the large aperture left by the removal of the membranous interorbital septum in prepar- ing the skull. Bounding it behind is the parie- tal; above, the frontal and the naso-prefrontal bones; in front, the naso-prefrontal; below, the 30 ANATOMY OF A CHELONIAN. palate bone and the vomer, and, lying on these, the naso-ethmoid cartilaginous rod (28). In front of the naso-prefrontal bone is seen the nostril cavity, bounded below by the maxilla and the premaxilla ; externally by the maxilla and the naso-prefrontal bone; and above, by the latter bone. 57. The Hyoidean Apparatus is largely cartilaginous, except in old specimens. It presents— a A median piece, or Jody, with a concavity on its dorsal side into which the larynx and the anterior end of the trachea fit. The ventral surface of the body of the hyoid is convex, and its most prominent median part is com- posed of a connective-tissue membrane. From its anterior end arises a small median pointed process, which, in the recent state, enters the tongue. To each antero-lateral angle a small cartilaginous nodule is attached by a fibrous membrane. Attached to the sides of the body of the hyoid, about half way between its anterior and pos- terior ends, are the curved anterior cornua, which ossify earlier than the rest of the hyoid- ean apparatus. They run back, in their nor- mal position, parallel with and close to the posterior border of the mandible. The postero-lateral angles of the body of the hyoid form diverging processes to which the posterior cornua are attached ; they are shorter and stouter than the anterior cornua, and are curved in the opposite direction, THE FORELIMB. 3! 58. The Pectoral Arch consists on each side of two pieces. On the articulated skeleton note its general position with respect to carapace and plastron, and the attachment of the forelimbs to its outer angles. 59. One of the pieces of the pectoral arch on each side (the scapulo-precoracoid) is V-shaped, with the angle of the V turned outward. Its dorsal limb (scapula) is longer than the other and attached to the ventral as- pect of the first costal plate, opposite the first dorsal vertebra. 60. The grecoracoid, which forms the shorter and ven- tral limb of the V, nearly meets its fellow in the middle line opposite the entoplastron (19) ; in the recent state, stout ligaments attach it to the plastron. 61. The remaining bony piece of the pectoral arch on each side is the coracoid bone ; it is somewhat flat- tened dorso-ventrally, and passes back in a nearly hori- zontal plane from its articulation with the scapulo- precoracoid where the two limbs of the V formed by the latter meet. Its posterior end is expanded. 62. Note the deep glenoid fossa where the elements of the pectoral arch meet. 63. When you open another terrapin (77) observe the stout ligament joining the distal ends of coracoid and precoracoid ; it represents the epicoracoid, found as a distinct bone in some reptilia. 64. The Forelimb is short and stout. Note in the ar- ticulated skeleton that it lies in a nearly horizontal 32 ANATOMY OF A CHELONIAN. plane, and, in its position of rest, with the humerus di- rected forward and the forearm and manus backward ; also that the two bones of the forearm lie in a dorso- ventral plane, the ulna being dorsal. If the forelimb were stretched out so that its axis was perpendicular to the median antero-posterior dorso-ventral plane of the trunk the thumb side would be ventral. 65. The humerus has a short, thick shaft with expanded articular extremities. The proximal extremity, set on to the shaft nearly at a right angle, has two very large tuberosities, and articulates with the glenoid fossa. On the distal end is the articular surface for radius and ulna. 66. Zhe bones of the forearm (radius and ulna) are sep- arate and flattened, and somewhat constricted in their median portions. The ulna is thicker and larger than the radius, and reaches beyond it at the elbow; at the wrist, the reverse is the case. 67. The carpus is composed of eight bones. Three lie at the distal end of the ulna; of them, that on the ulnar side, considerably smaller than the others (and often removed in preparing the skeleton), is the pzs¢form ; next it is the cuneiform (os ulnare) which articulates on its proximal side with the ulna; the third bone of the proximal row is the semilunar (os intermedium), which articulates above with the ulna, and on its radial side with the side of the projecting end of the radius. 68. The distal end of the radius articulates with the proximal end of the largest bone in the carpus, which PELVIC GIRDLE. 33 probably represents the scaphoid (os radiale) and os cen- trale combined. 69. The four remaining bones of the carpus (carpalia) lie in a row at the bases of the digits ; those correspond- ing to the first, second, and third metacarpal bones (trapezium, trapezoid, and os magnum respectively) are separate ; the carpalia of the fourth and fifth digits, on the other hand, are united to form a single bone (uaei- form) which, however, presents a deep groove; this indicates its primitive doubleness, and will lead to the belief that it is made up of two distinct pieces, unless careful examination be made. 70. Each of the five digits consists of a metacarpal bone and three phalanges, except the first (pol/ex) and the fifth (sinimum), which each have but two phalanges. The terminal phalanx on each is long, curved, pointed, and claw-like. Tl. The Pelvic Girdle is composed of the iliac, the ischial, and the pubic bone on each side. a. The zlium is attached to the sacral ribs, as de- scribed above (16); from there the bone runs ventro-mesially and joins the ischium and os pubis at the acetabulum. b. The pubic bones are flat plates, which meet ven- trally in a mesial pubic symphysis, from which a cartilaginous plate proceeds forward in the abdominal wall. External to this each bone has a large, pointed process, directed forward. ¢. The ischial bones meet also in a median ven- tral symphysis, and are much like the pubics 2* 34 ANATOMY OF A CHELONIAN. in form, though smaller. Each reaches for- ward so as to meet a process sent back from the pubic bone on the same side, and enclose a large obturator foramen. 72. The Hind Lim), larger and somewhat stouter than the anterior, resembles it closely in general form and in its position with reference to the axial skeleton (64). 13. The femur is larger than the humerus, but re- markably like it in shape. 74. In the crus the “bia and fibula are distinct, and each enters into the knee- and ankle-joints. The tibia is larger than the fibula, and placed on its ventral side. 15. The tarsus has two bones in its proximal row. The larger of these (astraga/us), placed on the tibial side, is made up of a coalesced ¢#biale and intermedium.. The other bone in this row is the os fibulare (calcaneum). . The distal row of the tarsus presents five bones (¢arsa- Zia), of which that on the fibular side is much larger than the others, and is regarded by some morphologists as a metatarsal bone. If this be so, the proper tarsalia are four in number : one each for the first, second, and third digits, corresponding to the internal, middle, and external cuneiform bones of human osteology; while for the fourth and fifth digits there will be a single tarsal bone, corresponding to the cuboid. 76. Each digit of the foot has a metatarsal bone; but, accepting the above view as to the homology of the fifth bone in the distal row of the tarsus, the fifth metatarsal is very different in form from the rest. The great toe DISSECTION OF THE VISCERAL CAVITY. 35 (hallux), has two phalanges ; the second, third, and fourth toes three each, the terminal bone on each being long and claw-like. The fifth digit has, according to the homology accepted for the bone on the fibular side of the distal row of the tarsus, either three or two pha- langes ; the terminal one, in correspondence with the absence of a claw on it (5, ¢), is rudimentary. TT. General Dissection of the Pleuro-peritoneal Cavity. Kill a terrapin with chloroform in the manner above described (2); saw through the bony bridges uniting carapace and plastron, and, with scissors, divide the skin in front and behind, close to the plastron, and then placing the animal on its dorsum, gradually raise the plastron from before back. Dissect away, witha scalpel, the soft parts attached to its inner surface ; cut close to the bone, so as to avoid, as far as possible, all injury to the soft parts. As you separate the plastron, note the stout ligaments passing to it from the precoracoids. When the plastron is removed note the fibrous perios- teum covering it on its dorsal side, and the attachments of muscles to it. 718. On the ventral aspect of the animal, as exposed by removing the plastron, observe : a. The semi-transparent pericardium, and, seen through it, the heart, which may still be beat- ing. 6. Anteriorly, the muscles on the pectoral arch, and the bones of the latter which can be felt through them; posteriorly, the pelvic arch, which can be likewise felt through the muscles over it. 36 ANATOMY OF A CHELONIAN. The great pectoral muscle on each side ; flat, and made up of two portions—an anterior, which will be seen to have arisen from the plastron opposite the pectoral arch, and a posterior larger portion, which arose from the plastron considerably farther back. Both parts con- verge to their insertion on one of the tuberos- ities of the humerus (65). On the pelvis, a fan-shaped muscle, the origin of which from the plastron has been divided in removing the latter; the anterior fibres (attra- hens pelvis) ran backward, the posterior (7e- trahens pelvis) forward, to be attached to the large process on the antero-lateral margin of the pubis. This muscle is the homologue of the pyramidalis of human myology. On either side of the pectoral muscles, and between them, portions of jeritoneum are seen, covered here and there (as is also the ventral surface of the pericardium) with more or less yellow fat; in front of the pelvis the antertor abdominal veins are very conspicuous, lying on the peritoneum. 79. Dissect away carefully the great pectoral muscles and the pyramidales, noting the nerves which enter their deep surfaces. Take care to avoid the branches entering the anterior abdominal veins in front and be- hind, and note: a. Through the pericardium and peritoneum, the large quantities of lymph contained in the cavities they enclose. On the peritoneum, the two Anterior Abdominal THE RENI-PORTAL VEIN, 37 Veins, turning dorsally a short distance behind the heart, and entering the peritoneal cavity. Joining each, just at this point, is a vein from the pectoral region, and uniting them in front of the pelvis, and also behind the heart, are cross-branches ; that behind the heart will be seen to receive small pericardiac branches. c. Posteriorly, note the formation of each an- terior abdominal vein by the union of a small branch, running from the ventral aspect of the pelvis, with a larger vessel appearing at its outer side ; the former results from the division of a single larger median vein, which, when traced back, is seen to be formed by the union of two lateral trunks with a median one ; these all carry back some blood from the tail, and from the ventral regions of the pelvic girdle. d. Trace back the outer branch entering into the anterior abdominal trunk; on the muscles covering the ilium it is joined by a large vein from the hind limb ; this, the femoral vein,here divides into the trunk just described which enters the anterior abdominal, and another, the reni-portal vein, which turns dorsally. 80. If proper care has been taken in the previous dis- section the veins will be filled with blood and easily traced ; if they are empty they collapse, and are hard to follow, and their relative sizes are also impossible to appreciate. If this be so, cut a hole in one of the smaller branches ; take a fine blow-pipe, and direct a current of air on the vessel till it strikes the aperture and distends it, so that it is readily seen; then put in 38 ANATOMY OF A CHELONIAN. the tip of the blow-pipe, and inflate the veins with air. By repeating this procedure from time to time, as re- quired, the dissection of the venous system is greatly facilitated. 81. Trace the reni-portal division of the femoral vein on one side till it penetrates the muscles lying in the groin-hollow. Then, turning the leg and tail over to the opposite side, divide the skin between them and the carapace, and search in the hollow between leg and thigh for the large caudal vein; trace this up till it joins the reni-portal. 82. Beginning a short way behind the heart, divide the peritoneum in the middle line from before back ; a short distance in front of the pelvis it turns away toward the dorsal side, so that the peritoneal cavity does not extend to the posterior end of the trunk, nor does the peritoneal membrane line the pelvis, being merely re- flected over the anterior end of the urzzary bladder, which will be seen projecting forward from the pelvic cavity. 83. Remove the ventral portions of the peritoneum and pericardium, cutting the former away carefully from around the anterior abdominal veins and the branches entering them, so as to leave the vessels intact. Note the dladder veins, which enter the cross branch uniting the two anterior abdominal trunks near the pelvis, (79, 4). 84. Putting your thumbs under the coracoid bones, turn both halves of the pectoral arch forward, tearing the ligamentous attachment of the scapula to the cara- pace. ABDOMINAL VISCERA, 39 If necessary, gently run some water among the viscera to replace the abundant lymph normally pres- ent and float the organs into their normal positions ; if the lungs are collapsed inflate them moderately, by means of a blow-pipe inserted into the glottis; then sketch the parts as they lie. 85. The following points may be observed before disturbing the viscera : a. Anterior to the heart, and disappearing to its dorsal side, part of the trachea is seen. Note, that when the neck is retracted it makes a loop to the left, which is straightened out when the neck is extended. The heart, with its transversely elongated ven- tricle, and right and deft auricles; these, together, almost conceal the venous sinus, which, how- ever, projects slightly beyond the outer anterior corner of each auricle. Springing from the base of the ventricle are several large arteries. On each side of the heart the right and J/eft liver lobes, with the gall-bladder appearing from beneath the posterior border of the right lobe. Partly covered by the left lobe of the liver, but seen beyond its edge, is the U-shaped stom- ach, ending in the ylorus just behind the heart. The duodenum, starting at the pyloric end of the stomach, passes to the right, and then dips away to the dorsal surface. Farther back are seen some coils of the other portions of the intestine, especially on the right side of the abdominal cavity. 40 ANATOMY OF A CHELONIAN. f. On each side of the intestinal convolutions are seen the posterior ends of the lungs. g. Partly covered by the pubis is the bilobed urinary bladder, generally much distended. If collapsed, inflate it by means of a blowpipe inserted through the cloaca. 4. Immediately posterior to the gall-bladder, a portion of the Jazcreas will be seen lying along the duodenum. z Note the entry of each anterior abdominal vein into the liver-lobe on its own side. 86. Next raise the right liver-lobe, and after observ- ing the gall-bladder more closely, push the heart up, and gently separate the left liver-lobe from the stomach ; the great transverse Portal Vein will then be exposed, running across the liver from side to side ; opposite the heart it gets a large vein from the pancreas, and where it lies against the stomach many small veins enter it from that organ. Note, also, the bridge of hepatic tissue uniting the two main liver-lobes across the middle line, behind the heart ; and the deep fissure on the left lobe into which the right side of the stom- ach fits, and where many small gastric veins directly enter the liver. 87. Without cutting the mesentery, gently uncoil the Small Intestine, and trace it until it joins the Large Intes- tine; a small Cecum projects beyond the point of com- munication. Raising the gut, note the Mesentery which slings it, and in this the numerous arches formed by branches of the mesenteric artery, from which smaller twigs pass to the intestine; also the accompanying mesenteric veins. THE HEART, 4I 88, In connection with the first coil of the intestine, note the elongated yellowish Pancreas, doubled on it- self; and, somewhat farther back, lying in the mesentery near where the small and large intestines join, the dark-red, soft, rounded Spleen. Near this organ, the breaking up of the mesenteric artery to form its nu- merous primary branches will be found, and the union of the mesenteric veins to form the main radicle of the portal trunk. 89. Trace the Cystic Duct, which may readily be seen on squeezing some of the green bile into it from the bladder, from the gall-bladder to the duodenum. It opens into the duodenum obliquely after running close along it for some distance. The Pancreatic Duct opens into the duodenum about an inch nearer the stomach than the bile-duct ; it may easily be found on gently separating the pancreas from the intestine. 90. Trace the Large Intestine to the pelvis ; note the dilated Rectum, which forms its terminal portion. 91. Examine the Heart more carefully. Its two auri- cles about equal in size, and the larger ventricle, usually paralyzed by the chloroform and greatly dilated. Di- vide the ligament passing from the posterior border of the ventricle to the pericardium, and raise the former so as’ to see the transversely elongated venous sinus behind it. 92. Continuous with the right end of the venous sinus, is the right superior cava. Trace it for about an inch from the heart, where a small vein will be seen to enter its posterior side ; make an incision in this and 42 ANATOMY OF A CHELONIAN. inflate with a blow-pipe, so as to distend the heart and vessels connected with it. When the organ is blown up the relative size and the form of its parts can be much better seen than ‘was possible previously. 93. Follow now the superior cava on each side, shad- ing insensibly into the venous sinus, and formed a short way from the heart by the union of three large trunks (118). Entering the posterior border of the venous sinus, toward the left, is the left hepatic vein; at the corresponding point on the right side opens a much larger trunk, formed by the junction within the right liver-lobe of the zzferzor cava and the right. hepatic vein. 94. Clear away carefully the Zymph sinuses and loose areolar tissue surrounding the great vessels springing from the base of the heart, and carefully clean and separate these vessels down to their origin. Extend the neck and remove the skin and connective tissue cover- ing its ventral surface and sides. Three vessels spring from the ventricle. That most to the left is the pulmonary artery; that apparently next is the left aorta; the remaining one is the right aorta, which latter is, however, covered close to the heart by the innominate trunk, which it gives off. On tracing the aortz carefully to the ventricle it will be found that the attachment of the left aorta is rather more to the right than that of its fellow, the two cross- ing close to the heart. 95. The innominate artery divides almost immediately into the right and Jeft subclavian, and right and deft caro- tid arteries. Dissect these out. THE ARTERIAL SYSTEM. 43 96. The subclavians lic, at first, ventral to the carotids, and, diverging, embrace in the angle between them the reddish thyroid body; on being traced, each will be found to give off: Qa b A minute thyroid artery, distributed to the or- gan of that name. The ascending cervical, which is distributed on the ventral surface of the neck and throat. Farther on, the subclavian passing forward and outward gives off a short trunk, which soon divides into branches distributed to mus- cles about the shoulder and pectoral arch. Then turning dorsally, the subclavian gives off the supertor cervical, which runs to the side of the neck near its base, and there breaks up. Next, a branch, which runs to the side of the vertebral column, and there passes in between the first costal plate and the first rib. Then it gives off the axillary artery, which, crossing dorsal to the large cords of the bra- chial plexus, turns round the subscapularis muscle, and becomes the brachial artery, which is distributed to the forelimb. The remainder of the subclavian continues as the internal mammary artery, which runs out- ward to the edge of the carapace, and runs back along it, in the hollow of the marginal plate, to anastomose with the epigastric, which passes forward from the posterior portion of the dorsal aorta (110, ¢). 97. The carotid arteries, first dorsal and then external to the subclavians, cross dorsal to the latter and reach 44 ANATOMY OF A CHELONIAN. their inner sides ; they then run along the neck to the head. About half way up the neck they come into re- lation with the sympathetic and pneumogastric nerves, and the internal jugular vein. Trace each carotid, taking great care of the nerves near its upper end, until it en- ters the skull by a foramen (26, ¢), just in front of the auditory capsule.. 98. As each carotid is dissected, the thymus gland will be found—a loosely aggregated, yellowish mass, near the base of the neck on each side, and internal to the artery. , 99. It will be best to trace back the pneumogastric nerves now, as their terminal branches are apt to be injured in dissecting the aortic arches. Just behind the hyoidean apparatus, the carotid artery has the vagus on its outer, and the cervical sympathetic on its inner side. For the present follow the nerves from the skull, be- ginning about an inch and a half behind the cranium. A short way from the head, the sympathetic comes into close relation with the vagus, so that care is needed to separate them ; finally, about opposite the fifth cervical vertebra, the nerves separate, the sympathetic passing out toward the axilla. 100. Follow the left pneumogastric till it crosses the left aorta; at this point it gives off the recurrent laryn- geal nerve, which, turning round the aorta, runs up the neck alongside the gullet. After giving off this branch, the vagus stem breaks up into a leash of branches, some of which run mesially toward the heart, while others may readily be traced along the bronchus to the lung, and to the ventral side of the stomach near the cardia. THE ARTERIAL SYSTEM. 45 101. The right pneumogastric has a similar distribu- tion ; its terminal gastric branches are very long, and cross behind the heart to the dorsal-side of the stomach. 102. Divide the fibrous bands which pass between the right lung and the right lobe of the liver, taking great care not to prick the lung. Next push the right liver-lobe over to the left side, and carefully separate the lung from the muscles lying on the vertebral col- umn. Then trace the right aorta; it will be seen to arch over the pulmonary vessels and the right bron- chus, and to receive a communicating branch from the left aorta, near the dorsal side of the visceral cavity and opposite the fourth dorsal vertebra. From the point of union, the dorsal aorta will be seen passing backward. 103. Carefully divide, on the left side, the connective tissue uniting the lung to the cardiac end of the stomach, and the lung to the muscles on the dorsal ver- tebrze, and trace the left aorta. Passing round the left bronchus and pulmonary vessels to the dorsal side, it ends by dividing into three main trunks, which are to be traced successively by spreading out the mesentery and pushing aside the viscera. 104. The external division of the left aorta gives off : a. The gastric artery, which runs a short way on the dorsal aspect of the stomach and then bi- furcates to form the right gastro-epiploic artery, which runs along the great curvature of the stomach ; and the coronary artery of the stomach, which runs along the small curvature of that organ, 46. ANATOMY OF A CHELONIAN. 5. The remainder of this division runs on as the communicating artery to join the right aorta. 105. The middle division is the superior mesenteric; it breaks up in the mesentery (87) to supply most of the gut, and also gives a branch to the spleen. 106. The third division (the gastro-duodenal artery) di- vides into two main stems, the superior and inferior pan- creatico-duodenal arteries, the former running to the left, and the latter to the right end of the pancreas. Each then courses between duodenum and pancreas to anas- tomose with the other, giving off branches to the gut and gland on the way. , The superior pancreatico-duodenal gives off a branch, the left gastro-epiploic artery, which runs along the great cur- vature of the stomach, and inosculates with the right gastro-epiploic. 107. Now divide the intestine close to the stomach, and again in its rectal portion about two inches in front of the pelvis. Remove the portion of the gut be- tween the two incisions by cutting through the mesen- tery close to it; while so doing note the large fold, with its concavity to the left, made by the colon as it pro- ceeds from the junction with the small intestine, and before turning directly back to the cloaca as the rectum. 108. Spread out the removed portion of the gut; note that the small intestine is from five to six times longer than the carapace, and the large about one-fourth the length of the small. Then open the small intestine along its whole length, and note its thick muscular coat THE ARTERIAL SYSTEM, 47 and the longitudinal folding of its mucous membrane. Pass bristles in from the pancreatic and cystic ducts, and observe that each passes obliquely through the in- testinal wall. 109. Open the ccecum and colon along their free borders; note the absence of an ileo-colic valve, and the muscular and mucous coats of the tube. 110. The dorsal aorta may now be followed back from its point of formation (102). Passing between the kid- neys, it ends behind them by dividing into the vzgA¢ and the left common iliacs, In dissecting its branches, which is a matter of some difficulty, disturb the renal and re- productive organs as little as possible. With care the following branches will be found : a, Several small twigs to the kidneys and genital glands. &.