A COURSE OF INSTRUCTION . ZOOTOMY., (VERTEBRA TA.) hJL^ T. JEFFERY PARKER, B.Sc. LOND. PROFESSOR OF BIOLOGY IN THE UNIVERSITY OF OTAGO. NEW ZEALAND. WITH SEVENTY-FOUR ILLUSTRATIONS. MACMILLAN AND CO. 1884. The Right of Translation and Reproduction is reser-jed. 7*3 GIOLOGY " G LONDON : R. CI.AV, SONS, AND TAYLOR, BREAD STREET HILL. E C. TO MY FRIEND AND CRITIC, C. E. R. P., 280089 PREFACE. THE directions for the dissection of certain vertebrate animals of which the present book consists were begun many years ago when I was privileged to act as demon- strator to Professor Huxley, at the Royal School of Mines, South Kensington. They are drawn up on much the same plan as the " Laboratory Work," in Professors Huxley and Martin's Elementary Biology, and aim at being a continuation of the zoological part of that work, in much the same way as the Practical Physiology of Dr. Foster and Mr. Langley may be said to continue it on the physiological side. It must be borne in mind that the book is merely a " Course of Instruction," in the dissection of Vertebrates, and that it makes no pretence whatever at giving a complete account of the anatomy of the types selected. The time at the disposal of the average student of Comparative Anatomy is so short, that for him to examine half a dozen vertebrate animals — to say nothing of Invertebrates — in the same detail as the student of Human Anatomy examines his single type, would be quite out of the question even if it were necessary. On the other hand, it is of the first importance that he should viii PREFACE. not only be made familiar with the essentials of -vertebrate organisation, but should be so drilled in details as to be capable of working out, with some degree of thoroughness, any ordinary vertebrate animal which may be set before him. The advantage of the study of Comparative over that of Human Anatomy lies in the fact that in the former the dry facts are, to borrow an expression of Dr. Michael Foster's, "salted with the salt of morphological ideas." But if the same thoroughness in practical work is not demanded of the student of Animal Morphology as of the medical student, if he is allowed to shirk the discipline of laborious dissection, and to be content with a " general notion " of the structure of the types he examines, he runs a very serious risk of getting uncommonly little meat to his salt, and of losing in depth what he gains in breadth. It was therefore necessary to decide how much might be left out without leading the student into a superficial way of working ; and in striving to " keep the mean between the two extremes of too much stiffness in refusing and of too much easiness in allowing" any omissions, I am only too well aware how largely the personal equation enters into questions of this sort, and how unsatisfactory the compromise I have decided upon may seem to other teachers. The subjects described are mostly such as can be readily obtained at any time of the year. The Skate is chosen in preference to the more typical Dogfish, partly because it is PREFACE. ix a regular .market commodity, partly because it is, to my mind, quite unrivalled for the study of the vertebrate nervous system. The Rabbit is chosen in preference to the Dog or Cat — either of which, and especially the former, would have been preferable for some reasons — because it can be more readily obtained in quantity; its size, moreover, makes it more suitable than tHe Rat. The Green Lizard and the Lamprey cannot always be depended on, but, as they can both be easily preserved whole in alcohol, this is of less consequence than in the other cases. It was not thought necessary to include an amphibian, since the Frog is fully described in the Elementary Biology. The labour of correcting the proofs and of superintending the drawing on wood and engraving of the illustrations has fallen upon my brother, Mr. W. N. Parker, F.Z.S., without whose help the publication would have been almost out of the question. Besides the editorial work, he has made out several points in the anatomy of the Cod and Lizard, which, owing to lack of material, I was unable to decide myself. Many important omissions and some actual errors have thus been avoided. I am indebted to Professor Huxley for having kindly read over such parts of the work as were written when I left England, and for valuable suggestions thereon. But beyond this, I shall always feel that any value the book may possess is very largely due to the example set me by Professor Huxley during all the years I had the good fortune to be associated with him. x PREFACE. My friend and former colleague, Mr. G. B. Howes, rendered me much assistance in preparing and correcting those parts of the directions which were drawn up in England, and has also given considerable aid to my brother in working out some doubtful points which arose while the work was passing through the press. I am further indebted to Mr. Howes for the drawing for Fig. 34, and to my brother for Fig. 32. Figs. 35, 36, and 37 are copied from my father's monograph on the Lizard's skull (Phil. Trans. 1879), and Fig. 38 from Herpetologia Europaa ; the remaining illustrations are from my own drawings. The whole of them have been drawn on the wood by Mr. Coombs, and engraved by Mr. Cooper : judging from the few proofs which have so far reached me, I have every reason to be grateful to those gentlemen for the care and skill with which their work has been done. T. J. P. OTAGO UNIVERSITY MUSEUM, DUNEDIN, N.Z. June, 1883. CONTENTS. PREFACE PAGE vii LIST OF WOODCUTS Y vii INTRODUCTION THE LAMPREY— A. The Skeleton ' - • ' • • l B. Directions for Dissection THE SKATE — A. The Skeleton 27 B. Directions for Dissection 4° C. Special Dissection of the Nervous System and Sense Organs 9 THE COD — A. The Skeleton 86 B. Directions for Dissection IO1 THE LIZARD — A. The Skeleton . . 130 B. Directions for Dissection *53 xii CONTENTS. THE PIGEON— PAGE A. The Skeleton 182 B. Directions for Dissection 209 THE RABBIT — A. The Skeleton .262 B. Directions for Dissection ....... 286 WORKS OF REFERENCE 381 INDEX . . LIST OF WOODCUTS. FIG. PAGE 1 . Petromyzon marinus. The skull, from the left side .... 3 2. The brain-case, from above 4 3. The nasal capsule 5 4. Dissection of the anterior part of the body, from the left side 9 5. The urinogenital sinus and adjacent parts II 6. Transverse section through the branchial region .... 12 7. Transverse section through the abdominal region ... 14 8. Transverse section through the caudal region .... 17 9. The brain, from above 24 10. Raja nasuta. The skeleton, from beneath 30 11. Part of the vertebral column 31 12. A trunk vertebra, from the front 32 13. Longitudinal section of trunk vertebra 33 14. A caudal vertebra, from the front 34 15. The gall-bladder and bile-ducts 49 A.6. The portal vein 51 17. The venous system 53 1 8. Raja batis. Urinogenital organs (male) 55 19. Urinogenital organs (female) 57 20. Raja nasuta. The arterial system 62 ^21. Diagram of the heart and chief blood-vessels 63 22. The nervous system, from above 71 23. Raja batis. The brain, from beneath . . ., 73 24. Longitudinal section of the brain 74 25. The brain, from the left side 74 26. Raja nasuta. Roots of the fifth, seventh, and eighth nerves 75 LIST OF WOODCUTS. PAGE FIG. 27. Raja nasuta. Principal branches of the fifth, seventh, and eighth nerves 75 28. Raja batis. The auditory organ 8 1 29. Gadus morrhud. Side view of a disarticulated skull ... 92 30. The superficial muscles and nerves 104 31. The alimentary canal 108 2. The vascular system 117 33. The auditory organ 123 34. The brain 125 35. Lacerta agilis. Longitudinal section of the skull 137 36. The columella auris 142 37. The chondrocranium, from above 144 ( Lacerta viridis. \ ^ .. _ , 38. \ Lacerta agilis. I Outh»e.of ^ bead « the three species, \Zootocavivipara.} Bowing the epidermic scales . . . . 155 39. Lacerta viridis. Muscles of the trunk, ventral aspect ... 157 Dissection from the ventral aspect, showing the alimen- tary canal and vascular system 160 41. Urinogenital organs (male) 166 42. Urinogenital organs (female) 167 43. The heart, dorsal aspect 172 44. The aortic arches 173 45. The brain 177 46. Columba livia. Sacrum of a young individual 187 47. Skull of a young individual 189 48. The columella auris 195 49. Manus of a young individual 203 50. Pelvis of a young individual 204 51. Tarso-metatarsus of an unhatched embryo 207 52. Urinogenital organs (male) 228 53. Urinogenital organs (female) 230 54. The circulatory system 232 55. The cloaca 236 56. The heart, from the dorsal aspect 241 57. The lungs and syrinx 245 58. The brain ' 255 59. Dissections of the brain 259 60. Lepus cuniculus. Part of the alimentary canal with the portal system and bile-ducts 301 61. The vascular system . . 309 62. Urinogenital organs (male and female), from the side . 317 LIST OF WOODCUTS. xv « FIG. PAGE 63. Lepus cuniatlus. Part of the female organs, ventral aspect . 322 64. Longitudinal section of the head 334 65. Muscles of the fore limb — A. From the outer side 340 B. From the ventral aspect 341 C. From the inner side 342 66. Muscles of the manus 347 67. Muscles of the hind limb, inner side '. . . 352 68. Muscles of the hind limb, outer side 355 69. Muscles of the pes 361 70. The brain, from beneath 367 71. Dissections of the brain, from above . . 371 72. Longitudinal section of the brain 378 INTRODUCTION. DISSECTION is best performed at a strong deal table, not less than three feet long by two feet wide : it should, if possible, be placed at a window, so that the operator faces the light, otherwise the more delicate work will be hindered by the shadows of the hands and instruments. In nearly every case the subject should be firmly fastened down during dissection, either to the table, or, better, to a soft deal board, about one foot and a half long by one foot wide, with a narrow bead tacked round the edge so as to convert it into a shallow tray : the advantages of this are that the subject may be turned in any direction without unfastening, and that the edge confines the mess caused by escape of blood, &c., to a limited area. The best fastenings are small awls fixed into wooden handles, about an inch long, and just thick enough to be conveniently grasped : these can be more easily driven into the wood than large pins, are not so liable to bend, and hold more firmly. Care must of course be taken to thrust them through some b xviii INTRODUCTION. part — e.g. skin — the slight injury to which will not interfere with the dissection. The more delicate dissections are best conducted under water. A convenient dissecting dish is made by fitting a piece of sheet cork weighted with one of sheet lead into the bottom of a common pie-dish : the sloping sides of this latter are admirably adapted for admitting the greatest possible amount of light. The subject, in this case, is fixed out with small pins. The most necessary dissecting instruments are : — Three or four .scalpels of various sizes. A large and a small pair of scissors. A large and a small pair of forceps. A pair of bone-forceps. A " seeker/' i.e. a blunt bent needle fixed in a handle. A German silver anatomical blowpipe.1 The ordinary pointed form of scalpel is the best, those with obliquely truncated ends are rarely suitable. The scissors should have sharp points, and should bite well to the very end : this is especially important with the small pair, which will otherwise be perfectly useless. The forceps, also, should meet accurately at the points, which should be roughened so as to insure a firm grip ; in the small pair the pin placed to prevent the points crossing when pressure is applied, should fit easily but not loosely in the hole for its 1 Boxes containing the above set of instruments are made by J. Weiss & Son, 62, Strand ; Hawkesley & Son, 300," Oxford Street ; C. Baker & Co., 244, High Holborn ; J. Swift, 8r, Tottenham Court Road ; and J. B. Medland, 12, Boro' High Street. INTRODUCTION. xix reception ; if the latter is too large the points will always be liable to cross. The bone-forceps should have straight blades, and the handle should be sufficiently wide apart to admit of their being conveniently worked without obstruction by the fingers. They are used for cutting through bones ; for instance, those of the skull in the removal of the brain. The seeker is useful both as a probe and for clearing away the connective tissue from blood-vessels, nerves, &c., without danger of cutting them. All the instruments should be of the best steel ; it is false economy to buy inferior ones, as they lose their edge very quickly and require constant sharpening. A useful addition to the above is a common butcher's knife for rough work, e.g. for cutting through the skin of the skate, the asperities of which completely spoil a scalpel. For fine dissection spring scissors are very useful, but are by no means indispensable. Directions for injecting blood-vessels are given on pp. 48, in, 162, 218, and 298: to these I may add that a very convenient fluid injection for fine vessels is made by straining through muslin a strong solution of gum-arabic in water coloured with precipitated Prussian blue or carmine : after injection the subject is placed in alcohol, which coagulates the gum. This has the double advantage over gelatine (p. 162) that it is used cold and that it keeps better in alcohol. Injecting syringes provided with brass cannulae of various xx INTRODUCTION. sizes are to be had from the instrument-makers. But a common brass ear-syringe holding about two ounces answers every purpose, using for cannulae glass tubes of the form shown on p. 48, adapted to the nozzle of the syringe with short pieces of caoutchouc tubing. " Bull-dog " forceps will be found very useful in injecting for clamping any vessels which may have been accidentally cut. In large classes where the time of the student is limited, it is usually inconvenient for each one to inject his subject : it is then desirable to have an injected preparation in the room which may be consulted when necessary. For this purpose, a rough dissection which the students are allowed to handle is far more useful than a more elaborate preparation mounted in a bottle. In fact, one may say that the only alcoholic preparations of real use to beginners are those which are simple enough to tell their own tale almost at a glance. The most important, in my opinion, are : — a. Preparations of the heart with the origins of the great vessels, either filled with solid injection, or distended with alcohol, the cavities, in the latter case, being cut open. b. Preparations of the entire brain with the origins of the nerves, and various dissections of the same organ. c. Preparations of the adult urinogenital organs, with the various accessory glands, ducts, apertures, £c., displayed. Many other very useful preparations might be mentioned, , but the above, as demonstrating important points about which the beginner is certain to experience considerable difficulty, may be considered as the most essential. INTRODUCTION. xxi As the hearts and brains of most of the subjects selected are small, similar preparations from larger types are very valuable for demonstration; for instance, the monitor or iguana, the goose or turkey, and the dog, sheep, or even horse. It will, of course, be all the better if some of these structures — especially a larger mammalian brain than the Rabbit's— can be dissected by the students themselves as supplementary subjects. Dissections of large hearts for demonstration may be prepared by the glycerine jelly process described on p. 2 j l the various structures are more readily pointed out on such preparations than on those kept in alcohol : they may be made still clearer by colouring the different parts. The larger brains are best prepared by Giacomini's method : the organ is placed in a saturated solution of zinc chloride, and then, after removal of the pia mater, in strong alcohol, which should be renewed at least once. When thoroughly hardened it is transferred to strong glycerine, and retained therein until thoroughly permeated : this is shown by its sinking in the fluid. The brain is then removed from the glycerine, drained thoroughly, and, after a time, sized and varnished. Any dissections which may be required are made before placing in glycerine. 1 Since writing that description I find that the objects should be well hardened in alcohol before being placed in the glycerine fluid ; that it is best to substitute 0*05 parts of a concentrated solution" of phenol for the corrosive sublimate ; and that the specimens are best finished by varnishing, after one or two coats of size, with common oak-varnish. xxii INTRODUCTION. During the dissection of any animal it is always advisable to have the skeleton at hand for reference, and at some time or other a systematic study should be made of it. It is for this reason that an account of the skeleton is prefixed to the directions for the dissection of each type. With slight variations the management of the work is the same for all the subjects selected. The external characters are first studied : then a rough dissection is made for the purpose of acquainting the student with the position and general relations of the chief organs ; at the conclusion of this stage the brain is removed and preserved for future examination ; finally, the various parts are studied more or less in detail. The student should try and arrange his work so as to get the brain removed on the first day. In the case of the Lamprey and the Lizard, which can be satisfactorily preserved whole in alcohol, it has not been thought necessary to remove the brain until it is wanted for dissection. The directions for each stage in the dissection are given in " indented " paragraphs numbered with Roman numerals ; the following ordinary paragraphs with Arabic numerals giving descriptions of the structures brought into view by such dissection. By this arrangement the work is divided into sections, many of which may be omitted without serious disadvantage, if time runs short. The paragraphs in small type may also be omitted by the beginner. When a dissection is prolonged over say two days, the subject should be placed, when not in use, in a preservative INTRODUCTION. xxiii fluid, such as methylated spirit, Wickersheimer's fluid,1 or boro-glycerine. I should strongly advise students to adopt the plan so much insisted upon, by Professors Huxley and Martin in their Elementary Biology, of making sketches of their dissections. Even a rough drawing, if the various parts are properly named, and especially if they are further distinguished by different colours, forms a far better memorandum of work done than any mere description. 1 This fluid is made as follows : dissolve 100 grams of alum, 25 of common salt, 12 of saltpetre, 60 of potassic carbonate, and 20 of arsenious acid in 3 litres of boiling water, and add I *2 litre of glycerine and 0*3 litre of methylated alcohol. ZOOTOMY. THE LAMPREY. THE SEA LAMPREY (Petromyzon marinus). THE FRESH-WATER LAMPREY, OR LAMPERN (P.fluviatilis}. A.— THE SKELETON. I. The preparation of the lamprey's skeleton is a very laborious process, owing to the extreme toughness of the connective tissue which invests it. Re- moval of the latter is assisted by maceration in nitric acid, 10 per cent., care being taken not to allow the acid to act too long, the result of pro- longed maceration being the entire separation of the cartilages of the skull proper, and the total destruction of the branchial basket. In preparing a skeleton for demonstration purposes, it is, how- ever, advantageous to allow the cartilages to se- parate, and then to articulate them with fine platinum wire. The branchial basket can then be shown by itself in a special dissection. The 2 ZOOTOMY. skeleton may be either kept in spirit or prepared as follows : — (a) Place for about three days in a solution composed of Glycerine . . . . 10 parts. Water . . . 10 „ Corrosive sublimate . . cri ,, Alum . . . . o'2 „ (b) Transfer to melted glycerine jelly made by dissolving 2 parts of gelatine, or "gelatine glue," in the above fluid : allow to remain for 2 to 4 days at a temperature just sufficient to keep the jelly fluid. (c) Place in a dry room, until the surface no longer feels damp or sticky; then varnish with a solution of white (bleached) shellac in rectified spirit. II. In the prepared skeleton make out the following points :— 1. The notochord (Fig. r, nc), a cylindrical rod, occupy- ing the position of the vertebral column in one of the higher animals ; at its anterior end it tapers to a point some- what suddenly ; at its posterior end the tapering is more gradual. It is composed of a strong sheath of cartilage, inclosing a gelatinous central substance (Figs. 4, 6, 7, 8, nc). 2. The neural processes (Fig. i and 6 n.p), small rods of cartilage, set in pairs at short intervals alongthe dorso-lateral regions of the notochord, and partly inclosing the neural canal (Figs. 4 and 6 — 8, n.ca), in which the spinal cord lies. Between the neural processes and completing the shutting-in of the neural canal both dorsally and laterally is a quantity of very tough pigmented fibrous tissue (Figs. 4, and 6—8, //). B 2 4 ZOOTOMY. 3. The fin-rays (Figs. 7 and 8,/>), delicate cartilaginous filaments, supporting the dorsal and caudal fins (§§ 29, 30). They are connected ventrally with the fibrous tissue cover- ing in the neural canal, and lie parallel to one another and inclined backwards. 4. The brain-case, or hindmost division of the skull. Posteriorly it consists of a basal or parachordal plate (Figs, i and 2, b.p, b.p'), surrounding the anterior end of the notochord, and divided by the latter into dorsal (b.p} and ventral (b.p') portions. The ventral portion forms a continuous plate beneath the anterior end of the notochord (Figs. 2 and 4, b.p') ; the dorsal portion consists of two FIG. 2. — Petromyzon marinus. The brain case, from above, the subocular arches supposed to be removed (nat, size : from a larger specimen than Fig. i). au, auditory capsules : b.p, dorsal, and b.p', ventral portion of basal or parachordal plate : h.p, hard palate : na.p, naso-palatine canal : oc, occipital arch : tr, trabecula : w, side wall : II, optic fora- men : V, trigeminal foramen. longitudinal plates, which do not unite over the notochord. Anteriorly the basal plate is continued forward into two flattened plates, the trabeculse (Fig. 2, tr), which unite with one another in front, forming the hard palate (h.p), and inclosing an oval space, the naso-palatine canal (na.p). Laterally, the trabeculae and hard palate send up plates of cartilage (w), which afford side walls to the brain- THE LAMPREY. 5 case, and unite with one another above the brain in a narrow band, the so-called occipital arch (o.c). The side walls are perforated with apertures for the exit of the optic (II), and of the fifth and seventh (V) nerves. 5. The auditory capsules (Figs, i and 2, au\ paired ovoidal masses of cartilage, fused with the basal plate and cranial walls, and each containing a cavity for the correspond- ing auditory sac (§ 95) ; their inner walls bound laterally the posterior part of the brain cavity, and are pierced with apertures for the auditory nerves. 6. The nasal capsule (Fig. i, na ; Fig. 3), a concavo- convex plate of cartilage, of irregularly oval form, lying with its concave side forwards, in the posterior wall of the nasal sac (§ 89), and forming the anterior boundary of the cerebral FIG. 3. — Petromyzon marinus. The nasal capsule, front view (nat. size). I, olfactory foramina. cavity (see Fig. 4 na.c). Near its centre it is perforated by two oval apertures (Fig. 3, i) for the passage of the olfactory nerves. 7. The subocular arches, each consisting of an anterior lateral process (Fig. i, a.lp\ springing from the anterior end of the hard palate, and of a posterior lateral process (/././>), arising from the basal plate just beneath the auditory capsule. Both processes pass down- wards, outwards, and forwards, and meet with one another at an acute angle. 8. The styliform processes (Fig. i, st.p\ cylindrical rods springing one from the posterior edge of each posterior lateral process, near its proximal end, and taking a directly downward course. 6 ZOOTOMY. 9. The cornual -cartilages (Fig. i, c.c\ small, irregular, horizontal pieces, connected by fibrous tissue to the distal ends of the styliform processes. 10. The posterior dorsal cartilage (Figs, i and 4, p.d\ an arched plate, bilobed anteriorly, and truncated posteriorly, where it enters into fibrous union with the anterior edge of the hard palate. 11. The anterior dorsal cartilage (Figs, i and 4, a.d ), situated in front of and partly overlapped by the fore- going ; it is strongly arched from side to side, ends in front in a thin rounded edge, and posteriorly is produced on each side into a downwardly directed process. 12. The anterior lateral cartilages (Fig. i, a.l), situated one on either side, just in front of the descending process of the anterior dorsal cartilage ; their form is some- what sigmoidal. 13. The posterior lateral cartilages (Fig. i, /./), flattened plates, situated one on either side beneath the pos- terior dorsal cartilage, and between the descending process of the anterior dorsal caitilage, and the anterior lateral process of the subocular arch. 14. The lingual cartilage (Figs, i and 4, §), a long median ventral piece, flattened from side to side, truncated in front, and tapering posteriorly ; by its anterior end it is united by fibrous tissue to a small cartilage (Ig') having the form of a semicircle, and set transversely : with the free, upwardly directed ends of this are connected two small irregular cartilages (§"). The lingual cartilage lies in the floor of the mouth ; the semicircular cartilage (Ig1) sup- ports the median portion of the tongue ; the small cartilages (//') lie in the lateral wings of the tongue (§ 23, Fig. 4, //)• 15. The median ventral cartilage (Figs, i and 4, THE LAMPREY. 7 m.v), a slender rod, having the form of a T with a very long stem, and situated in the middle line beneath the lingual cartilage, the anterior ends of the two being con- nected by fibrous tissue. 1 6. The annular cartilage (Figs, i and 4, an), a stout circular cartilage, supporting the oral funnel (§ 21), and giving attachment to the maxillary and mandibular teeth (§ M). 17. The styliform cartilages (Fig. i, j/), two elongated, tapering rods, attached by their thickened proxi- mal ends to the posterior edge of the annular cartilage, a little below its middle, and directed backwards and some- what downwards. 1 8. The branchial basket (Fig. i, d.c, v.c, a—k, pc), a cartilaginous framework supporting the gills. It consists essentially, on each side, of (i) a longitudinal rod or dorsal cartilage (d.c\ springing from the dorsal portion of the para- chordal (b.fi), and passing backwards along the side of the notochord ; (2) a second longitudinal rod or ventral cartilage (v.c}, lying close alongside, and partly fused with, its fellow of the opposite side, in the middle ventral line ; (3) irregular transverse arches (a — g, k) uniting the dorsal and ventral cartilages and passing between the outer gill- clefts ; (4) lateral longitudinal bars (/i, j) connecting the transverse arches immediately above and immediately below the gill-clefts; and (5) a cartilage (pc) supporting the posterior and lateral walls of the pericardium. Each of the transverse arches, except the first and the eighth or last, consists of seven well-marked portions; of these, the first or dorsalmost (a) and the seventh or ventralmost (g) are flattened plates, produced into longer or shorter anterior and posterior processes; the second (b) and sixth (f) are short curved rods ; the third (c) and fifth ( -3 iiliMif^ lUl««*« IP IJli« sS'8"?.? o ^ c ' «T ^ tjD O s H-^ to B <" l^ilflWIIt^i a 22SS!§4ri c^S" S r^-5 io ZOOTOMY. body above and at the sides, while below it is separated by a deep furrow (Fig. 4, gr). 22. The mouth (Fig. 4, ;//), situated at the bottom of the oral funnel, and of a somewhat crescentic form. 23. The tongue (Fig. 4, /), the end of which forms a well-marked protuberance bounding the mouth below, and produced on either side into an upwardly directed, wing-like process (t). 24. The yellow horny teeth, which beset the inner surface of the oral funnel and the tip of the tongue : one immediately above the opening of the mouth is large and bifid, and is distinguished as the maxillary tooth; those on the tongue are the lingual teeth ; and a transverse crescentic ridge, below the tongue, and produced into several cusps, is known as the mandibular tooth. In P. marinus the two cusps of the maxillary tooth are close together, and the lingual teeth consist of two pairs of lunate denticulate ridges, the two ventral united with one another in the middle line. In P. fluviatilis the cusps of the maxillary tooth are somewhat widely sepa- rated, the dorsal lingual teeth are absent, and the ventral are united to form a strong transverse ridge, with a prominent median cusp. 25. The nostril, a single median aperture on the upper surface of the head, a short distance from its anterior end. 26. The eyes, situated at the sides of the head, a little posterior to the nostril ; they are devoid of eyelids, but covered with transparent integument. 27. The external branchial apertures (Figs. 4 and 6, e.a), a row of seven small slits on each side of the head, the first a little behind the eye. 28. The urinogenital papilla (Fig. 5, u.g.p\ a small elevation, situated in the median ventral line, at about a quarter of the length of the body from the hinder end. It is pierced at its summit by a small opening — the urino- THE LAMPREY. n genital aperture (z), — and lies in an oval depression, in the anterior part of which, just in front of the base of the papilla, is another small aperture, the anus (a). 29. The two dorsal fins (Figs. 7 and 8), median longi- tudinal folds of the integument : the anterior end of the first is near the middle of the body, that of the second somewhat in front of a vertical line taken through the anus. 30. The caudal fin, continuous in front with the second dorsal, and continued round the end of the tail on to its ventral edge; it is diphycercal, that is, evenly distributed above and below the axis of the tail. FIG. 5. — Petromyzon marinus. The urinogenital sinus, with the rectum and part of the left kidney (nat. size). a, anus : int, intestine : k, left kidney : ?', rectum : u.g.p, urino- genital papilla : zt.g.s, urinogenital sinus : ur, left ureter, x, aper- ture of left, and x' aperture of right ureter into urinogenital sinus : y, bristle passed through right abdominal pore : 2,. bristle passed into urinogenital sinus through its external aperture. 31. The absence of paired fins, or fore and hind limbs. 32. The apertures of the sensory tubes, minute punctiform openings on the surface of the head. IV. Remove the skin from the anterior part of one side of the body, from the end of the mouth to a short distance behind the gill-slits, and from the middle dorsal to the middle ventral line : make out— 33. The body muscles, lying beneath the skin, and 12 ZOOTOMY. arranged in transverse segments, called myotomes or myocommas, separated from one another by strong plates of fibrous tissue. Each myotome takes a zigzag course ; starting from the middle dorsal line, it passes first sharply backwards, then more gently forwards, then backwards, , and finally sharply forwards. The plane of the myotomes is not at right angles to the long axis of the body, but is inclined from the surface, inwards and forwards. The muscular fibres of which they are composed are longitudinal, i.e. at right angles to the general direction of the myotomes themselves. d.an FIG. 6. — Petromyzon marinus. Transverse section through the branchial region, semi-diagrammatic (nat. size). The gill sacs are supposed to be rotated forwards, so as to bring the external in the same plane as the internal branchial apertures. br.m., branchial membrane : d.ao, dorsal aorta : d.c, dorsal carti- lage of branchial basket : d.m, dorsal body-muscles : e.a, external branchial aperture : f.t, fibrous tissue inclosing neural canal : h, i, lateral longitudinal cartilages of branchial basket : i.a, internal branchial aperture : i.ju, inferior jugular vein : /«, jugular vein : my, myelon : nc, notochord : n.ca, neural canal : n.p, neural processes : as, oeso- phagus : p.br, peri-branchial sinus : r.m.t, retractor muscle of tongue : r.t, respiratory tube : s, circum-cesophageal sinus : v.ao, ventral aorta ; v.c, ventral cartilage of branchial basket : v.m, ventral body-muscle. 34. The division of the myotomes, immediately behind the last gill-cleft, into two longitudinal masses, a dorsal and THE LAMPREY. 13 a ventral, which pass forwards, the one above, the other below the line of branchial apertures, leaving these latter uncovered. The dorsal muscle is inserted partly by a broad tendon to the posterior dorsal cartilage (§ 10), and partly into the fibrous posterior wall of the orbit ; the ventral muscle is inserted by a longish tendon into the annular cartilage (§ 16). 35. The great mass of radiating muscular fibre, which, now the skin is removed, forms the outer surface of the oral funnel. V. Make a median ventral incision through the skin and muscle forming the walls of the body, begin- ning about the middle of the body, and proceeding forwards to within about half an inch of the last gill-cleft, and backwards to within about an eighth of an inch of the anus. From the ends of this incision carry up vertical incisions on the left side and remove the long flap 'thus made, so as to expose the body- cavity from the left side. Great care must be taken not to injure the liver (§ 37), the left kidney (§40), or the rectum (§ 39). The following points can now be made out : — 36. The pigmented peritoneum lining the whole body- cavity. 37. The liver (Fig. 4, /r), at the anterior end of the cavity, deep red in the fresh condition in P. fluviatilis, greenish in P. marinus. It consists of a single lobe, convex on the ventral side, excavated dorsally for the genital gland (§ 38) and intestine (§ 39), hollowed out anteriorly for the pericardium (§ 44), which it partly covers, and ending in a blunt point posteriorly. 38. The single genital gland (testis or ovary), oc- cupying in the adult the greater part of the body cavity : I4 ZOOTOMY. the testis is a soft, greatly lobulated organ, closely resembling fat : the ovary (Fig. 4, 0v), is also multilobular, each lobe containing numerous eggs, each about the size of a pin's head. The genital gland is suspended to the dorsal wall of the abdomen by a sheet of peritoneum, called mesorchium in the case of the male, mesoarium in that of the female. In the breeding season, the body cavity is found to be quite full of liberated ova, and the ovary itself is much reduced. ts mt FIG. 7. — Petromyzon marinus. Transverse section through the abdominal region, including the first dorsal fin (nat. size). cd, cardinal veins : d.ao, dorsal aorta : f.r, fin rays :, f.f, fibrous tissue inclosing neural canal : int, intestine, the line pointing to the spiral valve : k, kidneys : ly, sub-vertebral lymph sinus : m, body- muscles : my, myelon : nc, notochord : n.ca, neural canal : ts, testis : ur, ureter. 39. The intestine (Figs. 4 and 7, /"«/), a straight, very slender tube, entering the body-cavity at its anterior end and on the dorsal side : it passes backwards between the liver and the genital gland, and then between the lobes of the latter, till it reaches the posterior end of the body-cavity, where it dilates into the rectum (Fig. 5, r), and ends by THE LAMPREY. 15 the anus (a). The intestine is quite free for the greater part of its length, but at its hinder end is attached to the dorsal wall of the body-cavity by several delicate mesen- teric bands, carrying blood-vessels, while in front it is firmly connected by fibre with the anterior half of the dorsal surface of the liver. 40. The kidneys (Figs. 5 and 7, /£), two elongated band-like organs, of a deep red colour, attached by peri- toneum one on each side to the dorsal wall of the body- cavity, and extending from about the middle of the latter to within a short distance of the anus. 41. The ureters (Figs. 5 and 7, #;•), delicate tubes as wide as, or wider than the intestine, and attached all along the free (outer or ventral) edge of the kidneys: passing backwards they become connected with 42. The urinogenital sinus (Fig. 5, ti.g.s), a small ovoidal sac, lying close behind the rectum, and becoming narrowed ventrally to form the urinogenital papilla (u.g.p). 43. The sub-vertebral lymph sinus (Fig. 7, /)/), a considerable cavity included between the layers of peritoneum supporting the kidneys and genital gland : it is divided into two by a median vertical partition. 44. Note also the pericardium (Fig. 4, pc), lying just in front of and partly covered by the liver : its almost hemispherical posterior wall, strengthened by cartilage (§ 1 8, Fig. \t pc) is all that can be seen at present. VI. Open the urinogenital sinus by carefully slitting up its left wall, first introducing a guarded bristle J by the external aperture : observe — 45. The apertures of the ureters (Fig. 5, x, x'), situated close together in the antero-dorsal region of the sinus. 1 That is, a bristle tipped with a small knob of sealing-wax. 16 ZOOTOMY. 46. The abdominal pores (Fig. 5, y), small apertures situated one in each lateral wall of the sinus (the left will probably have been destroyed in opening the latter), and establishing a communication between the sinus and the body-cavity, through which the generative products escape. VII. Open the intestine by a longitudinal incision along its whole length : note — 47. The spiral valve (Figs. 4 and 7, int), a longitudinal fold of mucous membrane, projecting into the cavity of the intestine, and having a slight spiral twist. 48. The aperture of the ossophagus (Fig. 4, y), a longitudinal valve or slit, a short distance from the anterior end of the gut, and on its right side : in front of this aperture, the intestine is produced for- wards into a short thick-walled, blind pouch, situated to the left of the posterior end of the gullet and of the sinus venosus (§ 71). This will probably be seen better at a later stage (§ 59). 49. In P. marinus, the aperture of the bile duct (Fig. 4, b.d), on the ventral wall of the gut, just at the point where the latter becomes free from its attachment to the liver. The bile duct is absent in the adult P. fluviatilis, and is not usually present in P. marinus,- though very dis- tinct in the specimen figured. The spiral valve begins just posterior to this point. VIII. Turn the animal to the supine position (ventral aspect uppermost), and see the relations of the chief organs from the new point of view. Then remove the ovary or testis, the kidneys, and all but the anterior inch or so of the intestine : make out now — 50. The cardinal veins (Figs. 4, 6, and 7, cd\ two large vessels, lying one on each side of the middle line in the dorsal wall of the body-cavity. 51. The dorsal aorta (Figs. 4, 6, and 7, d.ao\ a small vessel, lying in the middle line between the two cardinal veins. 52. Traced backwards, the cardinal veins are found at the posterior end of the body-cavity to unite into a single trunk, or rather to THE LAMPREY. 17 be formed by the bifurcation of a single trunk,, the caudal vein (Fig. 8, c.v), which may be traced to the end of the tail, lying to the ventral side of the caudal artery (Fig. 8, c.a), which is the direct continua- tion of the dorsal aorta. FIG. 8. — Petromyzon marinus. Transverse section through caudal region, including the second dorsal fin (nat. size). c.a, caudal artery : c.v, caudal vein : f.r, fin rays : /J, f.t', fibrous tissue enclosing neural canal : m, body-muscles : my, myelon : nc, notochord : n.ca, neural canal. IX. Place the fish once more with the left side up- wards ; dissect away the dorsal and ventral muscles of the branchial region (§ 34), and, if the skeleton has not been examined, make out the various cartilages of the branchial basket (§ 18) : then remove the latter, as well as the muscular and connective tissues obscuring the gill-sacs (§53): get the latter well cleaned, open one or two of them and note : — 53. The gill-sacs (Figs. 4 br^ and 6), seven in number, arranged obliquely, each being inclined, from its inner side, backwards and outwards. They are compressed from before backwards, separated from one another by strong fibrous and muscular partitions, and marked externally with parallel horizontal lines, which mark the position of — c i8 ZOOTOMY. 54. The branchial filaments, sub-parallel ridges of the mucous membrane, lining the gill-sacs, and encroaching largely upon the cavity of the sacs. The whole set of filamen's on each side of each sac constitutes a demibranch' or half-gill : the septum between any two sacs, together with the two contiguous demibranchs, answers to a single gill of one of the higher fishes. (See p. 46, § 84, and p. 103, § 89.) 55. The internal branchial apertures (Figs. 4 and 6, i.a), on the inner walls of the gill-sacs, leading into the respiratory tube presently to be seen (§ 58). 56. The peribranchial sinuses (Fig. 6, p.br}, considerable spaces included between the gill-sacs themselves and the partitions which separate them. X. Remove the gill-sacs, cutting them away close round the internal branchial apertures, but taking great care not to injure the respiratory tube (§ 58), gullet (§ 59), &c. : also dissect away enough of the dorsal body muscles to allow of the structures mentioned being brought clearly into view. Ob- serve the following : — 57. The retractor muscles of the tongue (Fig. 4, r.m.t), surrounding the lingual cartilage (§ 14, Figs, i and 4, Ig), and forming a prominent cylindrical fleshy mass, in the middle ventral line, separating the gill-sacs of opposite sides, and extending back as far as the pericardium. 58. The delicate membranous respiratory tube (Figs. 4 and 6, r.t), lying almost immediately above the retractor of the tongue ! : the seven internal branchial apertures of the left side are seen perforating its lateral wall. 59. The oesophagus (Figs. 4 and 6, as), lying imme- diately above the respiratory tube, and becoming continuous 1 The ventral aorta which is between the two will be mentioned subsequently (§ 72). THE LAMPREY. 19 posteriorly with the intestine in the antero-dorsal region of the body-cavity. Its diameter is not more than half that of the respiratory tube, and its walls are very delicate and easily torn. The best way to make it out without damage is to pass a guarded bristle into it from the already opened intestine. 60. The pericardium, a large chamber, lying immedi- ately behind the last pair of gill-sacs : its posterior wall, as already seen (§ 44), is strongly convex ; its anterior surface fits closely against the hinder or inner walls of the last pair of branchial sacs, and presents therefore a double concavity. In the present view, of course, only the left of these con- cavities is seen. 61. The circum-cesophageal sinus (Figs. 4 and 6, s), a consider- able longitudinal cavity, lying above and at the sides of the gullet, and imperfectly divided into two tubes by a perforated vertical partition which is related to the gullet li.^e a mesentery. Behind the posterior end of the respiratory tube, the sinus extends also below the gullet as far downwards as the ventral aorta (§ 72) and between the inner or posterior walls of the last pair of gill-sacs, this portion (Fig. 4, /) being also divided by a per- forated vertical partition. The cavity is related to the gullet in much the same way as the body -cavity to the intestine. XI. If the anterior (pre-branchial) portion of the ven- tral body-muscle (§ 34) is still left, remove it, and note 62. A great mass of muscle, forming a prominent pro- jection beneath the eye, and just in front of the gills : it forms the lateral boundary of the mouth-cavity and contains imbedded in it the subocular arch (§ 7), styliform process (§ 8), and cornual cartilage (§ 9). 63. The salivary sac, appearing as a dark patch on the ventro- lateral region of the above mass of muscle : when cut into, it is seen to be a cavity with glandular walls : it is said to open by a fine duct into the mouth. C 2 20 ZOOTOMY. XII. Remove the eye, and dissect away the muscles, cartilages, &c. (§ 62), which form the left side wall of the mouth-cavity, first passing a probe into the latter from the oral aperture to guard against cutting too deeply. Also open the oesopha- gus and the respiratory tube by a longitudinal incision along the left side of each. The following points can now be made out : — 64. The almost tubular oral cavity (Fig. 4, ;;/), com- municating with the oral funnel by the very narrow oral aperture. 65. The oral caecum, a blind pouch of the mucous membrane in about the middle of the mouth-cavity, on the dorsal side (Fig 4, m) ; it is continued posteriorly into a longitudinal groove. 66. The aperture of the oesophagus (Fig. 4, between m and ess), at the hinder end of the oral cavity, and im- mediately beneath it, that of the respiratory tube. Between the two apertures the mucous membrane forms a sort of horizontal shelf, produced into five finger-like pro- cesses in P. fluviatilis, and in P. marinus into two blunt processes supported by small cartilages. The entrance of the respiratory tube is also guarded by two lateral flaps of mucous membrane, the vela. (Fig. 4, vl}. 67. The spirally arranged ridges into which the mucous membrane of the gullet is produced. 68. The extent of the respiratory tube, and the internal branchial apertures of the right side. XIII. Open the pericardium by carefully removing the greater part of its left wall : note 69. The auricle (Fig. 4, au), occupying the whole of the left side of the pericardial chamber, and therefore the only part of the heart seen at first. It is strongly convex on its THE LAMPREY. 21 dorsal and left side where it comes in contact with the peri- cardium, while on the right it adapts itself to the form of the ventricle. 70. The ventricle (Fig. 4, v), seen by lifting up the auricle to lie towards the right side of the pericardium : it has a prismoidal form, and is of firmer texture than the auricle. 71. The sinus venosus (Fig. 4, s.v), a tubular chamber, passing almost vertically from the dorsal to the ventral wall of the pericardium, between the auricle and ventricle : it is attached to the posterior wall of the pericar- dium by a thin vertical sheet of connective tissue. 72. The ventral aorta (Fig. 4. v.ao\ springing from the anterior end of the ventricle, and passing through the wall of the pericardium, forwards and in the middle line, between the respiratory tube above and the retractor of the tongue below. Opposite the fourth gill-sac the ventral aorta bifurcates and is con- tinued forwards as two parallel trunks. From each of these are given off four afferent branchial arteries, the first supplying the first demi- branch (anterior wall of first gill-sac), the second, the second and third demibranchs (posterior wall of first and anterior wall of second sac), the third, the fourth and fifth demibranch, and so on. The azygous posterior portion of the ventral aorta also gives off four afferent arteries, of which the first three supply each two contiguous demibranchs (i.e. one entire gill), and the fourth goes to the fourteenth or last demibranch. Each afferent artery is thus primarily related to a gill (§ 54) and not to a gill-sac. 73. The inferior jugular vein (Fig. 4, i.ju) situated just below the retractor of the tongue and above the median ventral cartilage of the branchial basket. It brings the blood from the lower part of the head to the sinus venosus, and is best made out by making a small aperture in the latter and passing a probe forwards. 74. The dorsal aorta (Figs. 4 & 6, d.ao\ immediately 22 ZOOTOMY. beneath the notochord ; it receives the efferent branchial arteries from the gills. XIV. Remove the outer (left) wall of the auricle, and observe 75. The comparatively thin walls of the auricle, strengthened by a network of pectinate muscles. 76. The auriculo-ventricular valve (Fig. 4, see description), composed of two membranous flaps, and guarding the oval opening leading from the auricle to the ventricle. 77. The sinu-auricular valve (Fig. 4, x), also com- posed of two flaps, and guarding the large aperture which leads from the sinus venosus into the auricle. XV. Pass a guarded bristle through the sinu-auricular valve upwards along the sinus venosus as far as it will go : also make an aperture in the left cardinal vein, pass a probe forwards, and open the vein along it. 78. It will be found that the cavities of the two cardinals unite with one another by an oval aperture (Fig. 4, x) just above the dorsal end of the sinus venosus, and that, at the same place, they both communicate with the sinus. 79. The blood from the anterior part of the body, except that re- turned by the inferior jugular, is brought back by the jugular veins (Figs. 4 and 6, j'u), which lie one on either side of the notochord, and, uniting each with the corresponding cardinal, pour their blood into the sinus venosus. The jugular is best made out by passing a guarded bristle forwards from the cardinal and gradually dissecting down to it. 86. The hepatic vein (Fig. 4, h.v] may also be seen at this stage ; leaving the liver, it pierces the pericardium and enters the sinus venosus at the Fame point as the inferior jugular. XVI. Open the ventricle and note 8 1. The thick fleshy walls and small cavity. THE LAMPREY. 23 82. The two membranous semilunar aortic valves between the ventricle and the ventral aorta. XVII. Turn the fish with the dorsal side upwards ; dis- sect away the muscles on the top of the head for about an inch (P. fluviatilis) or two inches (P. marinus) behind the nasal aperture; proceed until the brain, the nasal sac (§ 89), and the audi- tory capsules (§5) are exposed ; remove the roof from the latter. Observe the following : — 83. The flat band-like spinal cord or myelon (Figs. 4, 6 — 8, my, and 9), lying loosely in the neural canal (n.ca)t and passing in front into the brain (Figs. 4 br, and 9), which nearly fills the small cranial cavity. 84. The medulla oblongata or myelencephalon (Fig. 9, m.o\ the hindmost division of the brain, passing insensibly into the spinal cord behind, and on its upper surface presenting an escutcheon-shaped cavity, covered only by pia mater, the fourth ventricle or myeloccele ("• 4)- 85. The thin ledge of nervous matter overhanging the anterior end of the fourth ventricle is all that represents the cerebellum or epencephalon (Fig. 9, cb\ 86. The mid-brain, or mesencephalon (Fig. 9, .4, fourth ventricle : I — X, cerebral nerves. 90. The olfactory nerves (Fig. 9, I), passing directly forwards from the rhinencephala to the nasal sac, through the apertures in the nasal capsule (§ 6). 91. The optic nerves (Fig. 9, II), springing from the ventral surface of the thalamencephalon and passing directly outwards through the optic foramina (§ 4) to the eyes. 92. The oculomotor (third) nerves (Fig. 9, III), springing from THE LAMPREY. 25 the under side of the mesencephalon, and passing outwards and slightly forwards to the orbit, where they supply most of the eye muscles. 93. The fourth pair of nerves (Fig. 9, IV), arising from the dorsal side of the anterior end of the medulla. They supply the superior oblique muscles of the eyes. 94. The large nerve cord formed by the united roots of the fifth and seventh nerves (Fig. 9, V, VII), leaving the brain just in front of the auditory capsule, and passing forwards and outwards. 95. The auditory sac (Fig. 9, v\ exposed by the removal of the dorsal wall of the auditory capsule ; it con- sists of an ovoidal membranous sac, the vestibule (z/), presenting on its upper surface, towards the outer side, two semicircular canals (a.s.c, p.s.c\ corresponding to the anterior and posterior canals of the higher vertebrata, the horizontal canal being absent. 96. The auditory nerve (Fig. 9, VIII), passing directly outwards from the medulla oblongata to the auditory sac. 97. The glossopharyngeal (ninth) and vagus (tenth) nerves (Fig. 9, IX, X), arising from the medulla oblongata, just posterior to the auditory nerve, and passing backwards and outwards. XVIII. With a guarded bristle find an aperture lying in the anterior ventral region of the nasal sac, close under the entrance of the external nasal canal (see Fig. 4) ; pass the bristle carefully into • the opening ; it will be found to take a course backwards and downwards. Without removing the bristle, turn the fish once more with its left side upwards, and dissect away the tissues between the anterior end of the notochord and the roof of the mouth, until the bristle is found. It will be found to have passed into 98. The nasal caecum (Fig. 4, na'), a considerable pouch, lying close under the anterior end of the notochord. opening anteriorly, as already seen, into the ventral side of 26 ZOOTOMY. the nasal sac, and behind ending blindly a little posterior to the first internal gill-cleft. XIX. If another specimen is available, make a series of transverse vertical sections through the entire animal previously hardened in alcohol or chromic acid (see Figs. 6 — 8). The sections should be about 2 to 3 mm. thick in P. fluviatilis, 8 to 10 mm. in P. marinus. Be careful not to dis- turb the order of the sections. Examine each one separately, both from its anterior and its posterior face, and observe the precise relations of the various structures already seen by dissection. 1 1 It is important not to omit this section unless time or material fail?, as it forms an excellent introduction to the art of interpreting sections. THE SKATE. THE SKATE (Raja bails). THE THORNBACK (R. clavata). THE HOMELYN RAY (R. maculatd). ! A.— THE SKELETON. I. THE skeleton of the skate is mainly cartilagi- nous, being hardened only by a superficial de- posit of calcific matter, and in the vertebral column by internal laminae of the same material. It is best prepared by immersing the fish, after removal of the viscera, for a few seconds in hot water a few degrees below the boiling-point. This process softens the muscles and ligaments, and allows of their being readily stripped off the cartilage without injury to the latter. When pre- pared in the cold, the toughness of the ligaments, especially in the region of the vertebral column, renders their removal a matter of great difficulty. 1 These are the three commonest species cf the genus Raja brought to the London market. For the distinguishing characters of the three species see pp. 41 and 42, §§ 54 and 60. Several of the figures are taken from the common New Zealand species, R. nasuta. 28 ZOOTOMY. As some parts of the skeleton are more delicate than others, it is advisable, after a very short immersion in hot water, to dissect off as much of the flesh as will readily come away, and then to remove the branchial arches (§§ 40 and 41) and to disarticulate the skull and pectoral fins from their attachments to the vertebral column. The latter can then, if necessary, be subjected to a second immersion in hot water. In cleaning the skeleton special care is required to avoid injury to the branchial arches (§ 41), the spiracular cartilage (§ 37), and the labial cartilages (§ 34). The skeleton must not be allowed to dry, but should be either kept in spirit or prepared by the glycerine jelly process described on p. 2, § I. In the latter case about three to five days' immersion in the glycerine fluid, and two to three days in glycerine jelly, is required. During the process of drying, it will be found advisable to fix out any parts which show a tendency to twist or warp with pieces of wood or strappings of paper or calico. II. In the skeleton as a whole, note 1. Its division into tf, vertebral column, including dorsal and caudal fins (§§ 3 — 16) ; b, skull, composed of the brain- case (§§ 17 — 33), and of a number of loosely-attached carti- lages, consisting chiefly of the jaws and of the gill-arches (§§ 34 — 41 ) ; c> shoulder-girdle and pectoral fins (§§ 42 — 49) ; d, hip-girdle and pelvic fins (§§ 50 — 53). 2. The superficial crust of ossification on nearly all parts of the skeleton, except some of the smaller cartilages, which are entirely uncalcified, and the centra of the vertebrae, which are calcified in a special manner (§ 5) : the THE SKATE. 29 ossifications are deposited in the form of minute polygonal plates, forming a mosaic over the whole surface. III. In the vertebral column, make out 3. The anterior part of the column, consisting of a large mass of cartilage — the anterior vertebral plate (Fig. 10, a.v.p^ — not divided into distinct vertebrae, except in its posterior ventral portion, where there are rudimentary centra. It presents an almost flat ventral surface, a strong median dorsal ridge, and two lateral ridges, which, at about the middle of the plate, are produced upwards, so as to be nearly as high as the median ridge. The neural canal, for the reception of the spinal cord, runs from end to end of the plate, the side walls of which are perforated by two rows of small apertures, for the passage of the dorsal and ventral roots respectively of the spinal nerves. The antero-inferior region of the vertebral plate is produced into a scoop-like odontoid process, which fits between the condyles of the skull (§ 19) : on either side of this, on the front boundary of the lateral ridge, is a smooth surface, with which one of the condyles themselves articulates. 4. The remainder of the vertebral column, consisting of distinct vertebrae, which are divided into two sets : the trunk vertebrae, extending from the posterior end of the vertebral plate to the root of the tail, and the caudal vertebrae, reaching to the end of that appendage. IV. Examine the trunk vertebrae ; some from the sur- face ; some by means of longitudinal and trans- verse sections; some by disarticulation from the rest ; and others by allowing to dry. Make out 5. The centra of. the vertebrae (Figs, n, 12, and 13, c), cylindrical bodies with deeply-concave anterior and pos- terior ends ; these ends are formed by concavo-convex plates of bone, which meet one another in the middle of the ZOOTOMY. 16 f FIG. 10. — Raja nasuta (female). The skeleton seen from the ventral aspect (one-fourth nat. size). On the left side (right in the figure) the pectoral and pelvic fins, and on the right the hyoid and branchial arches (with the exception of the fifth cerato-branchial) and labial cartilages are removed. In the remaining pectoral fin, only the proximal ends of most of the fin rays are shown, and the cartilaginous branchial rays are omitted for clearness sake. ac. I, ac. 2, anterior and posterior acetabular facets : ant, antorbital cartilage : au, auditory capsule : a.v.p, anterior vertebral plate : c.br. 3, c.br. 5, third and fifth cerato-branchiab : c.f, coracoid fontanelle : crt THE SKATE. 31 coracoid : e.hy, ceratohyal : e.br. 3, third epi-branchial : e.hy, _epi-hyal : gl. I, gl. 2, gl. 3, anterior, middle, and posterior glenoid facets : h.br. I, h.br. 3, h.br. 5, hypo-branchials of the first, third, and fifth branchial arches: h.hy, hypo-hyal: hm, hyomandibular : ha, commencement of haemal canal : il, iliac process : Ib. i, Ib. 2, Ib. 3, Ib. 4, labial cartilages : mck, Meckel's cartilage or lower jaw : ms.pt, mesopterygiuin : mt.pt, metapterygium : ol, olfactory capsule : p. pi, propterygium : p.pu, pre-pubic process : pt.qu, pterygo-quadrate cartilage, or upper ja-v : pu, pubic portion of hip girdle : r, rostrum : r.c, rostral cartilage : sc, scapula : s.c.f, scapulo- coracoid fontanelle : sp, spiracular cartilage : s.sc, supra-scapula. longitudinal axis of the centrum ; the cartilage intervening between them is further strengthened by four radiating plates of bone, which give rise to a cruciform figure in a FIG. II. — Raja nasuta. The last seven trunk vertebrae, and the first ten caudal vertebrae, viewed from the left side (nat. size). c, centra : cd. I, first caudal vertebra : d.r, dorsal root of spinal nerve : k.p, haemal process : h.s, haemal spine : /.», inter-neural plate : ji.p, neural process: n.s, neural spine: r, rib : t, trunk of spinal nerve : tr, transverse process : tr. 28, twenty-eighth (last) trunk vertebra : v.r, ventral root of spinal nerve. transverse section of the centrum. The centra are seen to continue backwards the ventral portion of the anterior vertebral plate. 6. The transverse processes (Figs, n and 12, //*), backwardly directed rods of cartilage, which proceed one from either side of the centrum, and continue backwards the lateral ridges of the vertebral plate. 32 ZOOTOMY. 7. The rudimentary ribs (Figs, n and 12, r), small pieces of cartilage attached to the ends of the transverse processes. FIG. 12. — Raja nasuta. A trunk vertebra, seen from the front (nat. size). f, centrum : t.n, inter-neural plate : n.p, neural process : n.s, neural spine : r, rib : tr, transverse process. 8. The neural processes (Figs, n, 12, and 13, n.p\ small triangular plates rising one from each side of the dorsal surface of the centrum : a small aperture in each of them transmits the ventral root of a spinal nerve (Fig. n, v.r). 9. The neural spines (Figs, n, 12, and 13, n.s), flat plates dividing below into two triangular processes directed outwards, so that the whole plate has, in transverse action, the form of an inverted Y. Each neural spine is . situated immediately above the vertebra of which it forms a part, but,. save in exceptional cases, is not directly united with the neural processes, so that the neural arch is, so far, incomplete. 10. The interneural (or intercrural) plates (Figs. ii, 12, and 13, /.«), six-sided plates of cartilage, which complete the neural arches laterally, filling up at the same time what would otherwise be the intervertebral foramina. Each transmits the dorsal root of a spinal nerve (Fig. n, d.r), the ventral root of which traverses the neural process next in front. THE SKATE. 33 11. The intervertebral substance, a gelatinous tissue filling up the biconvex spaces between contiguous vertebrae, and containing the remains of the embryonic notochord. V. Examine the caudal vertebrae in the same way: make out the following points; — 12. The centrum of each vertebra (Figs, n and 14, c) gives off, on each side, a downwardly-directed haemal process (h.p), which is seen, by examining the transition region between trunk and tail (Fig. n), to be homologous with the transverse process of a trunk vertebra : the haemal processes, uniting below, form the haemal arch, which FIG. 13. — Raja nasuta. Longitudinal vertical section of a trunk vertebra (nat. size). ct centrum: i.n., inter-neural plate: n.p, neural process: n.s, neural spine. transmits the caudal artery and vein (§§ 157 and 158): a median process, the haemal spine (ti.s), is given off at the junction of the haemal processes of most of the vertebrae, or may occur as a distinct cartilage (see Fig. n). 13. The absence of inter-neural plates and of ribs. 14. The gradual reduction in size and simplification in structure of the vertebrae, seen in passing from the anterior to the posterior end of the caudal region. 15. The skeleton of the two dorsal fins, attached to the posterior caudal vertebras : each consists of several radial cartilages or fin rays, attached to two basal cartilages, these latter being attached by fibrous tissue to 34 ZOOTOMY. several contiguous neural spines. Connected with the distal ends of the radial cartilages are numerous horny fila- ments, the dermal fin rays, which support the distal portion of the fins. 1 6. The skeleton of the caudal fin is rudimentary, con- sisting of a few very small radial cartilages attached to the posterior caudal vertebrae : the fin is supported almost entirely by dermal fin rays. VI. In the brain-case, note 17. The flat floor (basis cranii, Fig. 10) and roof (tegmen cranii). •1*3 FIG. 14 — Raja nasuta. A caudal vertebra, seen from the front (nat. size). c, centrum, h.p, haemal process : k.s, haemal spine : n.p, neural process : n.s, neural spine. 1 8. The foramen magnum, a large rounded aperture on its posterior wall,, placing the cranial cavity in communi- cation with the neural canal of the vertebral column. The cartilage surrounding the foramen magnum constitutes the occipital region of the skull. 19. The occipital condyles, rounded protuberances, one on either side of the foramen magnum, for articulation with the corresponding surfaces on the anterior vertebral plate : between them the base of the skull is scooped out for the reception of the odontoid process. 20. The auditory capsules (Fig. 10, au), large out- standing masses of cartilage, one on either side of the THE SKATE. 35 hinder or occipital region of the skull, and serving for the lodgment of the organ of hearing. 21. In front of the auditory capsules — the interorbital region — the cranium narrows considerably, but soon widens out again to form 22. The nasal capsules (Fig. 10, ol], large outwardly projecting masses of cartilage, containing a cavity for the lodgment of the nasal sacs, which cavity is closed above, but widely open below, and communicates with the cranial cavity by a large aperture through which the olfactory nerve (§ 179) Passes (see §32). 23. In front of the nasal capsules the skull narrows again to form the long projecting rostrum (Fig. 10, r), at the sides of which the two thin rostral cartilages (r.c) are attached. 24. In the postero-inferior region of the auditory capsule close to where it joins the occipital region, is an aperture leading by a canal excavated in the wall of the auditory capsule, into the cranial cavity, and serving for the transmis- sion of the pneumogastric or vagus nerve (§ 214). 25. A smaller aperture in the capsule external to the last : this gives exit to the glossopharyngeal nerve (§ 215). 26. Two considerable apertures in front of the auditory capsule, where it joins the side wall of the skull : the upper and larger of the two is for the transmission of the fifth or trigeminal nerve, the smaller of the two, situated below and somewhat behind the first, for the seventh nerve or portk> dura (§ 1 86). 27. On the upper surface of the auditory capsule, near the^middle line, is an aperture — that of the aqueductus vestibuli — leading directly into the cavity of the capsule (see § 213). 28. On the upper surface of the skull, between and in D 2 36 ZOOTOMY. front of the auditory capsules, is a large oval space closed by dense fibrous tissue • this is the posterior fontanelle. 29. Anterior to and between the nasal capsules is a similar space, freely open in the prepared skull, the anterior fontanelle. 30. In the side-wall of the skull, about midway between the olfactory and auditory capsules, is the large optic foramen for the transmission of the optic nerve (§ 183) : almost immediately above this are several very minute apertures through which the fourth nerve (§ 185) passes, while behind it is a small foramen for the passage of the third nerve (§ 184). 31. The nasal capsule is perforated by two canals just where it joins the skull, one through its upper part for the orbito-nasal nerve (§ 205), another through its lower part for the palato-nasal nerve (§ 209). 32. By making a longitudinal vertical section of the skull, or by removing its roof, the large olfactory foramen is seen, leading from the cranial cavity into that of the olfactory capsule, and giving exit to the olfactory nerve (§ 179). 33. In the same section of the skull is shown a large foramen — the internal auditory meatus — leading from the cranial cavity to that of the auditory capsule, and trans- mitting the auditory nerve (§ 186) : a little posterior to this is a small aperture by which the glossopharyngeal nerve enters the auditory capsule to leave it by the foramen already seen (§ 25, see also §§ 188 and 218): posterior to this again is the inner aperture of the canal for the vagus (§§24, 189, 219). VII. In the remaining loosely-attached portions of the skull make out 34. The labial cartilages (Fig. 10, lb. i — 4), of which THE SKATE. 37 there are altogether four, in connection with the ventral region of each olfactory capsule : the first (Ib. i) supports the corresponding flap of the fronto-nasal process (§ 64), the second (Ib. 2) lies in the fold of skin external to the naso- buccal groove (§ 64), the third (Ib. 3) bounds the nostril internally, and the fourth (Ib. 4) externally. 35. The antorbital (palatine) cartilage (Fig. 10, ant], a thick rod, attached to the outer face of the olfactory capsule, and curving outwards and backwards to join the anterior prolongation of the pectoral fin. 36. The hyomandibular (Fig. 10, h.m\ a club-shaped cartilage, articulating by its broad end with the infero- external region of the auditory capsule, and passing down- wards and forwards. 37. The spiracular cartilage (meta-pterygoid) (Fig. 10, JT/), a semi-lunar plate, attached by ligaments above to the auditory capsule and below to the inferior end of the hyomandibular. 38. The upper jaw (Fig. 10, pt.qu), formed by the fibrous union in the middle line of the two pterygo- quadrate cartilages, which together form a strong, curved, transverse bar, connected at its extremities by ligaments to the hyomandibular and spiracular cartilages. Each end presents a smooth convex facet for articulation with the lower jaw. 39. The lower jaw or mandible (Fig. 10, mcK), formed by the fibrous union in the middle line of the two Meckel's cartilages ; it closely resembles the upper jaw in shape, and is articulated to it at its extremities. Both upper and lower jaws are more strongly calcified than the rest of the skull. 40. The hyoid arch (Fig. 10, e.hy, c.hy, h.hy), a slender rod of cartilage, attached dorsally to the postero -superior 38 ZOOTOMY. angle of the hyomandibular by a band of fibrous tissue, the inter-hyal ligament, and made up of three segments, an epi-hyal (e.hy) above, cerato-hyal (c.hy) next, and hypo-hyal (h.hy) below. 41. The five branchial arches (Fig. io),each of which consists primarily of four segments, which are, counting from above downwards, pharyngo-branchial, epi-branchial (e.br), cerato-branchial (c.br), and hypo branchial (h.br}. The fourth and fifth pharyngo-branchials unite with one another and with the fifth epi-branchial to form a single cartilage: the first hypo-branchials (h.br.i) unite with one another in the middle line, forming a slender transverse bar of cartilage just posterior to the lower jaw : and the fifth hypo-branchials (Ji.br. 5) also unite with one another to form a large basi-branchial plate, produced anteriorly into two processes, and lying immediately dorsally to the heart and ventral aorta. VIII. In the shoulder girdle, note 42. The complete union of the two halves of the girdle in the middle line below, and the attachment of each half above to the median dorsal ridge of the anterior vertebral plate (Fig. 10). 43. The three convex articular surfaces or glenoid facets (Fig. 10, gL i — 3), situated on the external surface of each half of the shoulder girdle, and serving for the attachment of the three chief divisions of the fin (see §§ 46 — 48). The part of the girdle which lies to the dorsal side of the glenoid facets is the scapular region (sct s.sc\ — that on the ventral side the coracoid region (cr). 44. The three large apertures or fontanelles which perforate the shoulder girdle : the anterior of these is the scapulo-coracoid fontanelle (Fig. 10, s.c.f) : the postero superior, the scapular fontanelle, and the THE SKATE. 39 postero-inferior one, separated from the preceding by a bar of cartilage, the coracoid fontanelle (t.f). .45. The separation from the remainder of the girdle of that part which is immediately attached to the vertebral column : this is the supra-scapula (Fig. 10, s.sc), a flat quadrate plate, attached by fibrous tissue to the scapula proper. IX. In the pectoral fin, make out 46. The pro-pterygium (Fig. 10, /.//), along stout car- tilage, articulated proximally to the anterior glenoid facet, and passing forwards and slightly outwards : it is continued forwards by a series of similar cartilages, of progressively diminishing size, which extend in front of the olfactory capsule, and one of which becomes connected with the antorbital cartilage. 47. The meso-pterygium (Fig. 10, ms.pt\ a flat, com- paratively small cartilage forming the central portion of the attached part of the fin : it articulates with the middle glenoid facet. 48. The meta-pterygium (Fig. 10, mt.pt), a similar cartilage to the pro-pterygium, which articulates with the posterior glenoid facet, and passes backwards and outwards : it is continued backwards by a series of smaller cartilages, which extend a little posterior to the pelvic girdle. 49. The fin rays, long jointed rods of cartilage, attached at their proximal ends to the three chief divisions of the fore-limb, and becoming very slender at their distal extremi- ties : a few enter into direct connection with the shoulder girdle, between the meso- and meta- pterygium. X. In the pelvic girdle and fins, observe 50. The hip girdle, consisting of a stout ventral bar (Fig. 10, pu) which sends off on each side a forwardly directed pre-pubic process (p.pu) from the external 4o ZOOTOMY. extremity of its anterior edge, and an iliac process (if) directed upwards and backwards from the external extremity of its dorsal surface. 51. The acetabular facets (Fig. 10, ac. i, ac. 2), two projecting convex articular processes on the extremities of the hip girdle, the anterior being directed outwards, the posterior backwards. 52. The basale metapterygii, a stout backwardly- directed cartilage, articulating with the posterior acetabular facet : it is continued by smaller cartilages to the posterior point of the fin. In the male this series of cartilages is directly ' continued into the skeleton of the claspers (see § 57), which is composed of several more or less calcified cartilages, some of them produced into sharp processes of various forms. 53. The fin rays : the first four or five are attached to the pelvic girdle, pass almost directly outwards, and support the anterior lobe of the fin (§ 56) ; the first, or pre-axial ray, is many times thicker than any of the others, and articulates with the anterior acetabular facet : the remaining fin rays are connected with the basale metapterygii, pass outwards and backwards, and support the posterior lobe of the fin. B.— DIRECTIONS FOR DISSECTION. XI. Verify the following external characters : — 54. The extreme depression of the body from above downwards : its rhomboidal shape, the anterior angle of the rhomboid being formed by the snout, the lateral angles by the points of the pectoral fins, and the posterior angle by the root of the tail, which is slender, depressed like the body in its anterior part, but compressed from side to side posteriorly. THE SKATE. 41 In R. batis the angle of the extremity of the snout is acute, and the lateral or pectoral angle slightly so : in R. clavata and R. maculata the angle of the snout is obtuse and the pectoral angles nearly right angles. 55. The immense pectoral fins, of a triangular shape, the bases of the triangles extending from the anterior ex- tremity of the snout to within a short distance of the base of the tail, and their apices forming the lateral angles of the rhomboidal body. 56. The pelvic fins, each of which lies in the angle between the posterior end of the corresponding pectoral fin and the root of the tail, and consists of two lobes, an ante- rior outwardly-directed narrow one, and a posterior broader one, produced backwards, parallel with the tail. 57. In the male, the claspers, elongated organs, each presenting a groove along the outer edge, and strengthened by a cartilaginous skeleton which projects into the cavity of the organ in the form of sharp plates of various shapes. 58. The dorsal fins, two small median lobes near the posterior end of the tail. 59. The caudal fin, a still smaller lobe, quite at the extremity of the tail. 60. The characters of the integument : it is tough and strong ; greyish brown on the dorsal, white or grey on the ventral side : in certain parts it is quite smooth and devoid of scales, but in others is roughened by minute asperities or by well-marked spines, both being the exposed portions of the placoid scales, each of which consists of a button- like bony base imbedded in the derm, and of a thorn-like enamelled portion, which projects through the epiderm on to the surface of the body : these scales are best made out by dissecting out one of the larger ones. In R. batis the dorsal integument is dark olive-green or brown, the ventral integument dark grey, with minute black dots marking the 42 ZOOTOMY. apertures of the sensory tubes : the only large spines are on the tail : the greater part of the skin is smooth. In R. clavata, the skin is brown above, white below : the dorsal surface of the whole body is covered with asperities often produced into distinct spines : the latter are especially large near the eyes and in the middle line of the back and tail : in the female especially, large spines occur on both dorsal and ventral surfaces of the body. In R. maculata the dorsal surface is brown with darker brown or black spots, the ventral surface white : the skin is nearly smooth, except on the tail and in the region of the eyes : in the male there is a patch of large movable spines on each side of the head and on each pectoral fin, both on the dorsal surface. 6 1. The mouth, a wide, transverse aperture on the under surface of the head, supported by the strong upper and lower jaws, which can be felt through the skin. 62. The teeth, forming a close pavement of small en- amelled plates, produced in some cases into sharp spines. In R. clavata the teeth are pointed in the male, flat in the female. 63. The nostrils, moderate-sized apertures, one on either side of the under surface of the head, a little in front of the mouth. 64. The fronto- nasal process, an escutcheon-shaped fold of integument, extending from the posterior boundary of tl^ nostrils backwards towards the mouth, at either angle of which it forms a rounded lobe, beset with fimbriae. This lobe bounds internally, and converts into an incomplete canal, a groove— the naso-buccal groove — which ex- tends from the nostril to the angle of the mouth. 65. The branchial apertures, five valvular slits on the ventral surface of the body, behind the mouth, those of opposite sides approaching one another posteriorly.1 1 Behind the last pair of branchial apertures, on the skin covering the ventral portion of the shoulder girdle, is a pair of slit-like depressions, looking like an obliterated sixth pair of gill slits. THE SKATE. 43 66. The vent, or cloacal aperture, a large opening with tumid lips, near the root of the tail. 67. The abdominal pores (Figs. 18 and 19, pp. 55 and 57> a'P)t small slits, one on each side of the middle line, just posterior to the vent. 68. A strong bar — the ventral portion of the shoulder girdle (Fig. 10, cr)— can be felt a little behind the last pair of gill slits, and a similar bar — the pelvic girdle (pu) — a little in front of the cloaca. Between these lies the abdominal cavity, and in front of the shoulder girdle, between the branchial apertures, is the position of the pericardial cavity. • 69. The eyes, on the dorsal surface of the head, just over the mouth : they are greatly depressed from above downwards, and have no eyelids. 70. The spiracles, two considerable apertures, one behind each eye : they communicate with the cavity of the mouth. The front wall of the spiracle is covered with fine ridges, which constitute the pseudobranchia, the remains of an embryonic gill. This is supported by a plate of cartilage which may be easily felt, called the spiracular cartilage (§ 37). 71. The sensory tubes, seen best on the ventra^ sur- face, as delicate, transparent, winding lines, arranged -sym- metrically on opposite sides of the body, just beneath the skin, on the surface of which they open by minute apertures. XII. Make a median longitudinal incision, first through the skin, then through the underlying muscle, from the posterior edge of the shoulder girdle to the anterior edge of the hip girdle : make transverse incisions from both ends of this, and reflect the flaps of skin and muscle, so as to expose the abdominal cavity. Make out the following : — 44 ZOOTOMY. 72. The peritoneum, a shining pigmented membrane lining the abdominal cavity and investing the viscera : from it is secreted the larger or smaller quantity of peritoneal fluid contained in the cavity. 73. The large, soft, trilobed liver, attached by a broad base at the anterior part of the abdominal cavity, to the hinder boundary of which its lobes extend ; in colour it varies from light brown to dark olive green. 74. The stomach, largely concealed by the middle and left lobes of the liver, and passing towards the posterior side of the abdominal cavity, where it becomes narrowed and bent upon itself in a U shape. 75. The intestine, partly hidden by the right lobe of the liver ; it is wider than the stomach and marked externally with a spiral groove. 76. The cloaca (Figs. 18 and 19, d\ connected with the posterior end of the intestine and situated quite in the posterior part of the cavity : it is much larger in the female than in the male. To bring it clearly into view it is advis- able to remove carefully the median portion of the pelvic girdle. 77. The spleen, a dark red lobulated body, situated between the limbs of the U-shaped stomach. 78. The pancreas, a firm whitish gland, consisting of two lobes, a large dorsal lobe, closely applied to the left side of the intestine and connected by a bridge of gland substance with the small ventral lobe, which lies to the ventral side of the junction between stomach and intestine. 79. In adult specimens, more or less of the testes (Fig. 1 8, /) (in the male) or of the ovaries (Fig. 19, ov) and oviducts (od) (in the female) will be seen without dis- turbing the other organs, at the sides of the abdominal cavity, on the dorsal side of (beneath in their present THE SKATE. 45 position) the foregoing viscera : they should be brought into view by turning over the latter. 80. The kidneys (Figs. 18 and 19, k) are also seen when the other viscera are turned aside, as long, dark red bodies, lying one on either side of the middle dorsal line of the posterior end of the body cavity : they are often obscured by the thick pigmented peritoneum which covers them. XIII. Make a median longitudinal incision from the anterior boundary, of the shoulder girdle to about the level of the second gill cleft : take transverse incisions from both ends of this, and reflect the flaps made, so as to expose the pericardial cavity : note 8 1. The strong fibrous partition bounding the peri- cardium posteriorly, and separating it from the abdominal cavity. 82. The heart (Figs. 17, 20, and 21), consisting of a fleshy ventricle (v), from which is given off anteriorly, and somewhat to the right side, the fleshy tubular conus arteriosus (c.a) ; and to the dorsal side of these (beneath in this position) the large thin-walled sub-triangular auricle (au), and posterior to this, the transverse, tubular, transparent sinus venosus (s.v). XIV. Remove the skin to a distance of about an inch on either side of the heart, so as to expose the gill-sacs : remove the ventral walls of the latter, so as to expose their cavities. Make out 83. The five pairs of gill cavities, separated from one another by complete partitions, and opening externally by the apertures already seen. 84. The red branchial filaments attached to both anterior and posterior walls of all the cavities except the 46 ZOOTOMY. last, the posterior face of which is devoid of them. Each set of filaments is a demibranch or half-gill : each partition with its pair of demibranchs constitutes a gill. It will be seen that there are four complete gills, and one odd half-gill forming the first of the series. XV. Make an incision through the skin of the head, about an inch in front of the eyes, i.e. in the region of the anterior fontanelle : lifting up the edge of the incision, so as to see what you are about, cut away the roof of the skull and the overlying skin, until the brain and the anterior part of the spinal cord are exposed. If no other specimen is to be dissected, go over §§ 169 — 189 ; then remove the brain by cutting through the nerves and place it in strong methylated spirit. If a special dissection of the nervous system is to, be made, remove to spirit at once,1 first noting 85. The dura mater, or membrane lining the cerebro- spinal cavity, in which the brain and spinal cord lie. 86. The pia mater, a delicate membrane investing the brain and cord and containing numerous blood- vessels. 87. The arachnoid fluid contained in the cerebro- spinal cavity. 88. A mass of gelatinous tissue filling up the anterior part of the cerebral cavity. 1 For the satisfactory dissection of the brain, it is necessary for it to be placed in spirit while fresh : it is therefore advisable for the student to reach this stage of the dissection by the end of the first day's work. For a permanent preparation, the brabi should be placed for 24 hours in a saturated solution of zinc chloride, and then, after removal of the pia mater, into strong alcohol, which should be changed at least once (Giacomini's method) : the brain, either separate or in situ, may then be prepared by the glycerine jelly process (p. 2, § i). THE SKATE. 47 XVI. Place the animal with the ventral side upwards, turn the lobes of the liver forwards so as to expose the remaining abdominal viscera, and without cutting or tearing anything, make out the following points : — 89. The relations of the various parts of the alimentary canal : the oesophagus or gullet enters the abdominal cavity through its anterior wall, to the dorsal side of the liver, and almost immediately dilates slightly to form the stomach : this passes to the posterior boundary of the abdomen, becomes narrowed, turns upon itself, and passes forward to about the middle of the cavity, where it forms a thickening — the pylorus — and becomes continuous with the intestine : this is, in its anterior or proximal portion, devoid of the spiral groove mentioned in § 75, and loses it again in its posterior or distal part, shortly before it passes into the dilated cloaca: the anterior smooth portion of the intestine may be called the duodenum, the middle, dilated, spirally-marked portion the colon, and the posterior smooth portion the rectum : to the latter is attached, dorsally, a small conical red body, the rectal gland. 90. The mode of attachment of the alimentary canal. The posterior part of the oesophagus and anterior part of the stomach are suspended to the dorsal wall of the abdo- minal cavity by a fold of peritoneum, the mesogaster : the rectum is similarly suspended by a second fold, the mesorectum. The greater part of the intestine, on the other hand, is entirely unsuspended, so that there is no mesentery proper. 91. The fold of peritoneum — gastro-hepatic omen- tum — which passes between the liver and stomach, and is joined near the latter by a similar but much longer fold, the 48 ZOOTOMY. duodeno-hepatic omentum — from the duodenum. In these folds are contained the various vessels passing to the liver (§ 93). 92. The attachment of the spleen to the dorsal wall of the stomach by a broad sheet of peritoneum, the gastro splenic omentum. 93. The vessels l contained in the duodeno-hepatic omentum, to see which the membrane should be put somewhat upon the stretch. These are the bile duct (Fig. 15, c.b.d) to the animal's right side, the duodenal 1 For the satisfactory dissection of the blood-vessels the fish should be injected : if not, they may be made out by inflating with air by means of an anatomical blowpipe. I find the following the most convenient method for injection. Have ready four of the movable cannulse usually provided with injecting syringes, or if these are not at hand, four glass tubes drawn out to the form shown in the annexed cut : the end a is for insertion in the vessel, the constriction b for the purpose of preventing any slipping of the ligature, over the end c a short piece of india-rubber tubing is placed, and into this the nozzle of the syringe is pushed. Make a small incision into the conus arteriosus, place one cannula in it, directed forwards, and tie it firmly in its place : tie the second, directed outwards, into the sinus venosus : the third, directed forwards (i.e. towards the dorsal aorta), into the duodenal artery : the fourth, also directed forwards, into the duodenal vein. Fill an ordinary tumbler half full of fine plaster of Paris, coloured with a little of the common " French blue " or ultramarine of the oil shops : fill up the tumbler with water, stir well and immediately strain the liquid through coarse muslin into a second tumbler. Fill the syringe, and inject through all four cannulas suc- cessively. This must be done very rapidly or the plaster will set. On removing the syringe from a cannula, the india-rubber tube should be plugged with a small piece of wood to prevent escape. All the chief vessels are injected in this way : the ventral aorta and its branches from the conus, the systemic veins from the sinus venosus, the dorsal aorta and its branches from the duodenal artery, and the portal vein form the duodenal vein. The caudal and renal portal veins have to be THE SKATE. 49 and superior mesenteric arteries (Fig. 20, */, s.m) towards the left, and the wide thin-walled portal vein (Fig. 16, f) between them. Running parallel with these vessels is also a transparent thin- walled lymphatic vessel, from which many of the chief lymphatics can be injected. 94. The gall bladder (Fig. 15, g.b\ a greenish or yellowish transparent sac, partly imbedded in the liver between its right and middle lobes. c.b.d FIG. 15. — Raja nasuta. The gall bladder and bile ducts (half nat. size). c.b.d, common bUe duct : c.d, cystic duct : g.b, gall bladder : l.h.d, left hepatic duct : r.h.d, right hepatic duct. XVII. Carefully dissect away the peritoneum from the bile duct : make a small aperture in its wall, in- troduce a blowpipe and inflate : the gall bladder will be distended : trace the duct in both directions and make out done separately : the femoral and ilio-hsemorrhoidal veins also often escape being filled. In a preparation for demonstrating purposes it is advisable to colour the plaster of Paris used for injecting the dorsal aorta with vermilion or carmine instead of French blue. E 50 ZOOTOMY. 95. Its passage anteriorly into the gall bladder, by the short cystic duct (Fig. 15, c.d). 96. Its entrance posteriorly into the duodenum, im- mediately behind the pylorus on the dorsal side. A bristle should be passed into the duodenum through the cut end of the duct. 97. The junction with it of the two hepatic ducts, one (Fig. 15, l.h.d} from the middle and left lobes, the other (r.h.d) from the right lobe of the liver : the latter enterf the common bile duct close to its junction with the liver, so that the cystic duct (c.d) is very short. XVIII. Dissect away the peritoneum from the pancreas, and make out 98. The pancreatic duct, passing from the ventral lobe of the gland to open into the ventral wall of the duodenum, almost exactly opposite the entrance of the bile duct. XIX. Dissect away the peritoneum from the blood vessels mentioned in § 93, and trace them in both directions, turning the stomach over to the left to see the origins 'of the arteries. Note 99. The portal vein (Fig. 16, /), passing towards the middle lobe of the liver, and sending off branches to all three lobes. It is constituted distally by a gastric vein (^), which receives the blood from the stomach, and by a mesenteric vein (du, spl, pn, z), \\hich receives the blood from the intestine, spleen, and pancreas. 100. The coeliac artery (Fig. 20, cx\ entering the abdominal cavity on the dorsal side of the oesophagus and dividing into two trunks, one of which, the gastro-hepatic artery, sends off a hepatic artery (//) to the liver and a gastric artery (g) to the stomach, while the second or duodenal artery (j) passes down the duodeno-hepatic omentum, and supplies the greater part of the duodenum and the pylorus. THE SKATE. 51 10 1. The superior mesenteric artery (Fig. 20, s.m) entering the abdominal cavity parallel with, and a little posterior to the cceliac. It divides into two main branches, one of which supplies the intestine (/), the other the pancreas (pn) and spleen (spl). The rectum is mainly supplied by the small inferior mesenteric artery (§ 157, Fig. 20, i.m], which passes directly from the aorta to the rectal gland. FIG. 1 6. — Raja nasuta. The portal vein (one-third nat. size). dut duodenal vein : g, gastric vein : z, intestinal vein : p, main trunk of portal vein : /«, pancreatic veins : j//, splenic vein. 102. The ramifications of the gastric branch of the pneumogastric nerve on the walls of the stomach (see § 214). XX. Turn the liver into its natural position again, and remove just sufficient of the shoulder girdle to bring into view 103. The hepatic sinus (Fig. 17, h.s), a large transverse vessel, lying across the ventral surface of the oesophagus, immediately in front of the anterior border of the liver : it receives the hepatic veins by which the blood is returned from the liver. 104. The anterior extremities of the oviducts (Fig. 19, fl.f} in the female, or the rudimentary pronephric ducts E 2 52 ZOOTOMY. in the male (Fig. 18, /«.W, see §§ 117 and 118.) The former are attached to the dorsal (under, in the present position,) surfaces of the shoulder girdle by a distinct ligament. XXL Remove the liver, taking care not to injure the hepatic sinus or oviducts : cut through . the stomach just beyond its junction with the oeso- phagus : cut through the rectum just anteriorly to the rectal gland : remove the alimentary canal between these two points. Wash out the contents of the alimentary canal by directing a stream of water through it, then fill with a 0*5 per cent, solution of chromic acid, by tying one end, pouring in the acid through a small funnel or injecting it with a syringe, and when full, tying the other extremity : place in a vessel of the same solution for a few days : when sufficiently hardened, cut windows in various parts and make out 105. The pyloric valve, a fold of mucous membrane extending between the stomach and intestine, and opening towards the latter. 106. The spiral valve, commencing in the duodenum as a simple inwardly-directed fold of the mucous membrane, and in the colon becoming a spiral inclined plane which finally terminates at the com- mencement of the rectum. The development of the spiral valve varies almost indefinitely : its width may be either less than, equal to, or greater than the semi-diameter of the gut : the plane of any part of it may be either at right angles to the long axis of the intestine, or in- clined to it in either direction. There is also much variation in the number of turns of the spiral and in the character of the mucous membrane. 107. The irregularly longitudinal ridges or rugae of the stomach. 108. The network of fine ridges, covering the interior of the intestine and the spiral valve. XXII. If the fish is not injected, make a small aperture in the sinus venosus, introduce a blowpipe directed outwards, and inflate. 109. If nothing has been cut, a large inflated sac will be seen in the middle of the abdominal cavity, between the genital glands : this is the great cardinal sinus (Fig. 17, cd.s), formed by the union in the middle line of the two posterior cardinal veins (cd), by which the blood FIG. 17. — Raja nasuta. ^The venous system, ventral aspect (one- third nat. size). The portal vein is not shown ; the renal portal vein (r.p} is supposed to be removed on the right side (left in the figure), and the femoral (ftri), ilio-hsemorrhoidal (il.h), &c., veins as well as part of the car- dinal (cd) on the left. The right precaval sinus (pc.s) is cut open, so as to show the apertures in its walls. The outlines of those portions of the auricle (au) and sinus venosus (s.v) which lie behind (dorsal to) the ventricle (z/), are dotted. ab, veins from abdominal walls : au, auricle : b.a, bulbus anteriosus : br, brachial vein : c, caudal vein : c.a, conus arteriosus : cd, cardinal vein : cd.', posterior anastomosis of cardinal veins : cd.s, cardinal sinus : epg, epigastric vein : fm, femoral vein : h.s, hepatic sinus : hce, hsemor- rhoidal veins : il.h, ilio-hsemorrhoidal vein : i.ju, inferior jugular vein : ju, jugular vein : ly, opening of lymphatic trunk into precaval sinus : pc.s, precaval sinus : r.p, renal portal vein : r.p', factors of renal portal vein from pelvic and lumbar regions : r.p", branches of renal portal veins entering kidney : sp.s, spermatic sinus : s.v, sinus venosus : v, ventricle. 54 ZOOTOMY. is brought back from the tail, kidneys, genital organs, cloaca, rectum, pelvic fins, &c. These veins run along the inner side of the kidneys (see § 130), and enter the sinus at about the anterior extremity of those glands : leaving the sinus, the cardinal veins are continued forwards and curve round the gullet to join the precaval sinus (pc.s) : they are best seen at a future stage. XXIII. The following organs are also best observed at this stage : — no. In the male, the testes (Fig. 18, /), irregularly oval bodies, closely • connected with the venous sinus, one on either side. In the adult they have a flat ventral and a rounded dorsal surface : the former has a granular appear- ance, the latter is beset with small rounded elevations. In the young condition the whole surface is quite soft and granular. At its anterior end, even in the adult, the testis is soft and thin, and passes into the upper end of the epididymis (see § 114) by which its secretion is carried off. in. In the female the ovaries (Fig. 19, ov] : these in the young condition are indistinguishable from testes, but in the adult state are covered with elevations varying from the size of the yolk of a hen's egg downwards — the Graafian follicles. Note the absence of any duct in direct con- nection with the ovary, the ova having to pass into the peritoneal cavity before reaching the aperture of the ovi- ducts. 112. The fold of peritoneum called mesorchium in the male, mesoarium in the female, by which the genital glands are supported. XXIV. Remove the genital glands and the venous sinus, and very carefully dissect away the perito- neum from the organs still left in the abdominal cavity, noting 113. The kidneys (Figs. 18 and 19, k), flat, reddish THE SKATE. 55 7/y.s FIG. 18. — Raja batis. The urinogenital organs of the male (one- third nat. size). The organs are supposed to be removed from the body along with a small portion of the oesophagus (ces), and viewed from the ventral aspect : the right testis (t) is removed, along with the corresponding epididyniis (epd) and all but the posterior extremity of the vas deferens (v.d), which, with the sperm sac (s.s) is turned outwards to display the ureters (ur) : the cloaca (cl), the urinogenital sinus (ug.s), and the right vesicula seminalis (v.s) and sperm sac (s.s) are laid open. a.p, abdominal pore : cl, cloaca : epd, epididyniis : i.r, inter-renal body : k, kidney : ces, oesophagus : pn.d, pronephric duct : s.s, sperm sac : s.s', its opening into the urinogenital sinus : t, testis : ug.p, urino- genital papilla: ug.s, urinogenital sinus: ur, ureter: ur1, its opening into the urinogenital sinus: v.d, vas deferens: v.s, vesicula seminalis : z/./, its opening into the sperm sac. 56 ZOOTOMY. brown, lobulated bodies, lying close to the dorsal wall of the abdominal cavity, and covered, on their ventral surfaces only, by peritoneum. In the male. 114. The epididymes (Fig. 18, epd\ long flat, whitish bodies overlapping the anterior part of the kidneys, and con- tinued forwards to the front boundary of the abdominal cavity. The greater part of the epididymis (mesonephros or paror- chis) has a granular appearance, and its actual tubular structure is only seen in microscopical examination, but on its ventral surface it is very evidently made up of a greatly convoluted tube, which becomes more distinct and less con- voluted near the posterior boundary of the parorchis, where it passes into 115. The vas deferens (Fig. 18, v.d), mesonephric duct, or duct of the testis, a convoluted tube passing back- wards from the hinder end of the epididymis, towards the posterior boundary of the abdominal cavity, where it becomes dilated. 116. The sperm sacs (Fig. 18, s.s\ large whitish ovoidal bodies, in the posterior region of the abdominal cavity, and immediately external to the posterior dilated portion of the vasa deferentia, from which they are separated externally by so slight a groove as not to be readily distinguishable from them. They are seen to advantage only in fully adult specimens. 117. The coalesced remnants of the Miillerian or pronephric ducts (Fig. 18, pn.d}, consisting of a fine thin-walled tube, situated on the ventral wall of the hepatic sinus, where it dies away at each side, and opens in the middle line by a small aperture homo- logous with the peritoneal opening of the oviducts in the female (see§ 118). In the female. 118. The oviducts (Fig. 19, /./, ut\ each of which consists of two parts : a posterior, wide, thick-walled uterine THE SKATE. 57 portion («/), opening into the cloaca, and an anterior, slender, thin-walled portion, or Fallopian tube (/./) which unites with its fellow of the opposite side on the f* FIG. 19. — Raja batis. The urinogenital organs of the female (one- third nat. size)* The organs are removed from the body along with a small portion of the oesophagus (