Cornell University Library The original of this book is in the Cornell University Library. There are no known copyright'restrictions in - the United States on the use of the text. htip:/www.archive.org/details/cu3192 ALBERT R. MANN LIBRARY New YorK STATE COLLEGES OF AGRICULTURE AND HomME ECONOMICS AT CORNELL UNIVERSITY ornell University Libra course of instruction in zootomy. (Ver A COURSE OF INSTRUCTION IN ZOOTOMY (VERTEBRATA.) A COURSE OF INSTRUCTION ZOOTOMY. (FTERTEBRATA.) BY T. JEFFERY PARKER, B.Sc. LonpD. x PROFESSOR OF BIOLOGY IN THE UNIVERSITY OF OTAGO, NEW ZEALAND. WITH SEVENTY-FOUR ILLUSTRATIONS. London : MACMILLAN AND CO. 1884. The Right of Translation and Reproduction is reserved. cs Ot F772 pas ofa, Ore R. Cray, Sons, anD TAYLOR, BREAD STREET AILL, © G. TO MY FRIEND AND CRITIC, C By Be Pe ¥ Dedicate this Book. PREPACE, 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 Llementary Biology, and aim at being a continuation of the zoological part of that work, in much the same way as the Practical Phystology 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 Zvementary 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 (P42. Trans. 1879), and Fig. 38 from Llerpetologia Europea ; 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. ne aes Oraco UNIVERSITY Museum, DuNEDIN, N.Z. Fune, 1883. CONTENTS. PAGE PREFACE . : vii List oF Woopcurs A xiii INTRODUCTION. . xvii THE LAMPREY— A. The Skeleton . I B. Directions for Dissection F 8 THE SKATE— A. The Skeleton . é 2 27 B. Directions for Dissection a o> oy ot 40 C. Special Dissection of the Nervous System and Sense Organs , . 69 THE Cop— A. The Skeleton . i ue 3 : . 86 B. Directions for Dissection 101 THE LizAaRD— A. The Skeleton oe s 4 + 130 B, Directions for Dissection . . : 4 153 xii CONTENTS. THE Picron—. PAGE A. The Skeleton . ; eo = TS2 B. Directions for Dissection 209 Tue RasBir— A, The Skeleton 262 B. Directions for Dissection 286 Works OF REFERENCE 381 INDEX . ee. ee. A Ow OG 384 Co ge Pep ns LIST OF WOODCUTS. Petromyzon marinus. The skull, from the left side... . The brain-case, from above ... ...,.. The nasalcapsule ....... 2.2.2, Dissection of the anterior part of the body, from ‘ihe leftsidé: 04 4 a8 ae Ra oe ae The urinogenital sinus and adjacent parts Transverse section through the branchial region. . Transverse section through the abdominal region . . Transverse section through the caudal region ‘The braim, from above « 4 + = « & » & x Raja nasuta. The skeleton, from beneath. . .. . Part of the vertebral column ste tea A trunk vertebra, from the front Longitudinal section of trunk vertebra A caudal vertebra, fromthe front. ....... The gall-bladder and bile-ducts .. «...... The portal vein ...... : The venous system... - +e - ee ee ee Raja batis. Urinogenital organs (male). » Urinogenital organs (female) . . Raja nasuta, The arterial system ...... — Diagram of the heart and chief blood-vessels . . . The nervous system, from above ee 5 Raja batis. The brain, from beneath... ..... Longitudinal section of the brain... The brain, from the leftside. .--- 1... - Raja nasuta. Roots of the fifth, seventh, and eighth nerves ‘ xiv LIST OF WOODCUTSs. FIG, PAGE 27. Raja nasuta. Principal branches of the fifth, seventh, and eighth nerves ... Reo oR Se ae, ANS: 28. Raya batis. The auditory agen ‘ ee 29. Gadus morrhua. Side view of a di: artioulned skull . 92 30. The superficial muscles and nerves : 104 Br. ‘The alimentary canal . 108 32. The vascular system. : . 17 33- The auditory organ... 123 34. ‘The brain « . 2 + « i ae : 125 35. Lacerta agilis. Longitudinal section of the skull ‘ 137 36. The columella auris . . 142 37. The chondrocranium, from abave . 144 Lacerta wees Outline of the head in the three species, i Weal showing the epidermic scales 155 Zootoca vivipara. 39. Lacerta viridis. Muscles of the trunk, ventral aspect . . . 157 40. Dissection from the ventral aspect, showing the alimen- tary canal and vascular system. . 1€0 4l. Urinogenital organs (male) . : . a 4% © N60 42. Urinogenital organs (female) . 167 43. The heart, dorsal aspect . a «172 44. The aortic arches. . s a 373 45- The brain . 3 : 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 sl. Tarso-metatarsus of an unhatched embryo 207 2 Urinogenital organs (male) 228 53- Urinogenital organs (female)... 230 54. The circulatory system bs 232 55. ‘The cloaca . 236 56. The heart, from the dorsal diet. 2 241 ve The lungs and syrinx - 245 58. The brain < 255 59. Dissections of the brain . - Pe 259 60. Lepus cuniculus. Part of the alimentary canal w ih the portal system and bile-ducts . 301 61. The vascular system do ox 309 62. Urinogenital organs (male aasil female), oni the side 317 LIST OF WOODCUTS. Lepus cuniculus. Part of the female organs, ventral aspect . Longitudinal section of the head Muscles of the fore limb— A. From the outer side B. From the ventral aspect C. From the inner side Muscles of the manus . . ho Muscles of the hind limb, inner side . Muscles of the hind limb, outer side . Muscles of the pes The brain, from beneath . Dissections of the brain, from above . Longitudinal section of the brain . XV PAGE 322 334 340 341 342 347 352 355 361 367 371 378 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,” ze. a blunt bent needle fixed in a handle. A German silver anatomical blowpipe.? 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 ; Cc. Baker & Co., 244, High Holborn; J. Swift, 81, 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, 111, 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 cannulz 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 cannula 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. ¢. 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;1 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,’ or boro-glycerine. I should strongly advise students to adopt the plan so much insisted upon by Professors Huxley and Martin in their Evementary 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 1°2 litre of glycerine and 0°3 litre of methylated alcohol. ZOOTOMY. THE LAMPREY. THE Sea Lamprey (Péetromyzon 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 fot 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 € B 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 . ro parts. Water LO <5 Corrosive sublimate . ; OE 45 Alum ‘ OFZ 45 (2) 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. Il. In the prepared skeleton make out the following points :-— 1. The notochord (Fig. 1, 7c), 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, 70). 2. The neural processes (Fig. 1 and 6 ~.p), smal! 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, z.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, 4). ‘sainpiade yertpueiq [eusayxa ‘L—z : uauivroy pearmadiy ‘A : uaureioy odo “TJ + asvo ureaq Jo [[eM apts ‘ar ryoyseq [eIqouwlq jo adepyqwo fesuaa “7-2 ; yore aepnooqns jo ssesoid muuytAls “Pye : aBepyswo wopyAys ys : yore qe[nvoqns jo ssavoid Jerayey rotsaysod ‘¢y"¢ : a8evyyswo Yerajye] Aoweysod ‘7-d : aBvpAVO pesiop A01Ia}sod ‘og : asenaes petpreotwad ‘9g : yore yeyidioo0 ‘vo : sassaooid yeimau ‘g'z% : psoypojou ‘9% : apnsdeo yeseu ‘yee 1 OBELIVS [VIJUSA UeIpauT ‘aw : sadwyavo penSury Arossaooe 4,57 (57 : aBvpyysvo yenSury ‘37 : Joyseq yerouesq jo adel Awd Jesiop ‘7p : adv[IIeo enus0d ‘9-9 : oSvpyjzeo [epsoyoured 10 peseq yo uosod peyuaa ‘¢'g pue ‘{usiop ‘¢'g ? amnsdvo Aroypne ‘vp : aSernzeo aejnuue ‘wn : yore rvndoqns jo ssado1d yesoye] AOVAIUE “¢'7-y +: aBepyIVO [eIDIe] Jolajue 7'p : edvpyIVS [sop roL1ayUe ‘p'y : YI § UoIdrIOsep 995 { Jayseq [eu dy} Jo sucKIod snorrea ‘y—v *(azIs *yeu) proysojou ayy Jo yxed soj19jue pue jayseq yerpouIg ay} YM aps Yar oq} Wo [[MYs oy], “snuwew uozhwoyeg—! ‘oy i as im, 4 ZOOTOMY. 3. The fin-rays (Figs. 7 and 8, /7), 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. 1 and 2, 3.f, 8.9’), surrounding the anterior end of the notochord, and divided by the latter into dorsal (.A) and ventral (4.f’) portions. The ventral portion forms a continuous plate beneath the anterior end of the notochord (Figs. 2 and 4, 4’); the dorsal portion consists of two Fic, 2,—Petromyzon marinus. The brain case, from above, the subocular arches supposed to be removed (nat. size: from a larger specimen than Fig. 1). au, auditory capsules: 4.2, dorsal, and 4.7’, ventral portion of basal or parachordal plate: 4.4, hard palate: a.p, naso-palatine canal: oc, occipital arch: ¢7, 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 trabecule (Fig. 2, 7), which unite with one another in front, forming the hard palate (4.9), and inclosing an oval space, the naso-palatine canal (na.p). laterally, the trabecule and hard palate send up plates of cartilage (z), 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 (0.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. 1 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. 1, za; 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 Fic. 3.—Petromyzon marinus. The nasal capsule, front view (nat. size). I, olfactory foramina. cavity (see Fig. 4 za.c). Near its centre it is perforated by two oval apertures (Fig. 3, 1) for the passage of the olfactory nerves. 7. The subocular arches, each consisting of an anterior lateral process (Fig. 1, a./), springing from the anterior end of the hard palate, and of a posterior lateral process (2.44), 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. 1, s¢.), 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. 1, ¢c), small, irregular, horizontal pieces, connected by fibrous tissue to the distal ends of the styliform processes. 10. The posterior dorsal cartilage (Figs. 1 and 4, p.@), 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. 1 and 4, a.@ ), 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. 1, a./), 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. 1, 2./), flattened plates, situated one on either side beneath the pos- terior dorsal cartilage, and between the descending process of the anterior dorsal cartilage, and the anterior lateral process of the subocular arch. 14. The lingual cartilage (Figs. 1 and 4, 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 (/e’) having the form of a semicircle, and set transversely: with the free, upwardly directed ends of this are connected two small irregular cartilages (/g"). The lingual cartilage lies in the floor of the mouth; the semicircular cartilage (/e’) sup- ports the median portion of the tongue ; the small cartilages (Zg") lie in the lateral wings of the tongue (§ 23, Fig. 4, 42’). 15. The median ventral cartilage (Figs. 1 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. 16. The annular cartilage (Figs. 1 and 4, az), a stout circular cartilage, supporting the oral funnel (§ 21), and giving attachment to the maxillary and mandibular teeth (§ 24). 17. The styliform cartilages (Fig. 1, s¢), 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. 18. The branchial basket (Fig. 1, dc, v.c, a—h, pc), a cartilaginous framework supporting the gills. It consists essentially, on each side, of (1) a longitudinal rod or dorsal cartilage (d¢.c), springing from the dorsal portion of the para- chordal (2.f), 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, &) uniting the dorsal and ventral cartilages and passing between the outer gill- clefts; (4) lateral longitudinal bars (4%, 7) connecting the transverse arches immediately above and immediately below the gill-clefts; and (5) a cartilage (gc) 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 (4) and sixth (/) are short curved rods; the third (c) and fifth (e) are flattened, and are produced into forwardly directed processes ; the fourth or middle portion (d) is a curved rod situated immediately 8 ZOOTOMY. behind the corresponding gill-cleft. The longitudinal connecting bars (2 and 2) are flattened, and unite with the third (c) and the fifth (e) segments of the transverse arches respectively. In front of the first gill- cleft the two longitudinal connecting bars run together and form a single rod, which becomes connected with the first transverse arch (é). This latter is free at its dorsal end, of tolerably regular cylindrical form, and united by a short rod of cartilage with the proximal end of the styliform process (s¢.9). The eighth transverse arch is also regularly cylindrical at its dorsal and ventral ends, but in the middle of its course becomes fused with the hinder ends of the longitudinal connect- ing bars and with the pericardial cartilage (fc). The latter has the form of a backwardly directed hemisphesical cup, supporting the posterior wall of the pericardium, and produced into dorsal, ventral, and lateral processes, of which the last enter into union with the bran- chial basket proper, as already described. The cartilages of the branchial basket lie, for the most part, immedi- ately beneath the dorsal and ventral muscles covering the gills (§ 34, Fig. 6, 2, 2), so that they are seen at once when those muscles are removed : but the pieces marked 4, d, and f, are curved inwards and are con- sequently not seen until the surrounding tissues are dissected away.1 B.—Directions for Dissection. III. Verify the following external characters :— 19. The elongated vermiform body, almost circular in section anteriorly, but becoming compressed from side to side posteriorly ; the head passes insensibly into the trunk, and the trunk into the tail. 20. The integument, smooth and slimy, and entirely devoid of scales: marbled with black in P. marinus, of a uniform bronze-green tint in P. fluviatilis. 24. The sucker-like oral funnel (Fig. 4, o,f) at the anterior end of the body, inclined obliquely downwards and forwards: its rim, which is beset with numerous vascular papilla, passes insensibly into the general surface of the ?This description of the branchial basket is taken from a single specimen of P, marinus—the only one at my disposal. *yor[US OJUL auTJsaqUT WO. passed apystiq ‘€ : sulsA [VUIPIYd OJ sNsoUAA sMUIS YSnoiq) spine wioy passed apstiq ‘x : apsnur Apoq [erjusa ‘wre : wnped ‘72 : Joyseq Terpouvsq Jo aSeTNAed jeQuaa 7-2 : saqroyaw [eIpoUKIq JUETEYe OY} YO SuqatS ‘eyrov [eayUaA ‘ov'a2 ; apoyaguaa ‘2 : aNSuo, Jo Burs Jessy] Su (7 : oNFuo} Jo aqoy werpaur % : snsousa snus ‘e's :uotsod rolsaysod syt ‘s : snurs peadeydosao-umosto ‘st aqny Aroyeatdsoa 4-4 :Uopuay SH {y*w4 1 ANBUo] JO JoywNar Yruw's : onFuo} Jo ajosnut soyoerjoid ‘z''¢ : a8epyseo yesiop so1ajsod ‘pg : wmipses -uiad ¢ : kreao ‘ao : yauuny vio So :sn3eydosao ‘sa : yore yeydiooo “o : Teuvo [Anau ‘y7'% > WI9A Ivpnsnf{ sy} MOYS O} JIU IJoeT St uorod v aay $72 ye ydaoxa uoIIaS [EUIPNITSUOT ur “psroqoojou “7 :ornsdvo peseu ‘2'ww : amyjsode yeseu {yz : wMowo [eseu “vu + 9Bs yeseu ‘vw : uojadur ‘Are : adeyy.ted yeryUSA uBIpeut ‘ewe : WNdHd [BIO 94} MOTE Ajayerpewunt peserd 199397 ay} ‘Ajawo YMow ‘zw + JaAT{ “4” : soSepiyzeo pendury ‘57 ‘57 : urea repnsnl “ef: aayea yerds ay} jo JuetaouauIUCD ay} 0} syutod our, ayy ‘aUIysazUT “Juz : UIOA Jensnl so1ayut ‘nfe :yuomnSayut @ : usa oneday ‘ey : ayeed preg ‘G-y + apis Teawuaa ay} UO JauUNY [eIO Surpunog eacoas “AF : [eULd [v.Mau SuTsopoua ansst} snoiqu ‘7f :9¥s [[tS WYYy jo omnjiode [eusayxo ‘v's :soposnu-Apoq [esiop ‘wp : sayieyre permouesq jusrayo aq} Surateser ‘vyov Tesiop ‘ov-p 1 UIA TeuIpres YoT ‘py? : swOU]Y [eu oT] MOYS 0} P2dotied [Ivar JOLIE SIT JO ITY Jaddn ay} ‘apis yey aq} jo oes TS way ‘S 4g + uresq ‘ug : ayeyd pesvq jo uotjsod pexuaa ‘,¢"9 : onp ayiq “p'g : aAoqe aayeA puv ornjody repMOLMe-nuIs By} PUL ‘OT DATeA pus oIn}iode AvfMotyUaA-oTNOTNe ay} Uses VIE YIM Ut ‘gpoume ‘zo :oSepyseo avpnuue ‘wy : aseyyAwo [esiop Jolieyue “pv “Sunjop Lq poysmBuysrp st aFepyzvo ayy, “(azis yeu) wuowoas [woIWOA PeUIPNITSUOT Ut Saced ysour aq} Joy ‘Bulaq samjonays snoriva oy} “opis Yet 94} Wory uoutoads apeway B Jo uOIaSSIg’ “snuyIeU uozZAWOI}Eg—'Y “OI ‘ula oma mba TO ZOOTOMY. body above and at the sides, while below it is separated by a deep furrow (Fig. 4, g7). 22. The mouth (Fig. 4, m), situated at the bottom of the oral funnel, and of a somewhat crescentic form. 23. The tongue (Fig. 4, 7), 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 (¢). 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, é.@), 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, ~g.f), 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. II 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. Fic. 5.—Petromyzon marinus, The urinogenital sinus, with the rectum and part of the left kidney (nat. size). @, anus: zvf, intestine: 2, left kidney: 7, rectum: w.9.f, urino- genital papilla: w.g.s, urinogenital sinus: wz, left ureter, «, aper- ture of left, and x’ aperture of right ureter into urinogenital sinus : y, bristle passed through right abdominal pore: z, 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 toa 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, 7.e, at right angles to the general direction of the myotomes themselves. Fic. 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. ér.m., branchial membrane: d.ao, dorsal aorta: d.c, dorsal carti- lage of branchial basket: d.m, dorsal body-muscles: ¢.a, external branchial aperture: f¢, fibrous tissue inclosing neural canal: 4, 2, lateral longitudinal cartilages of branchial basket : z.@, internal branchial aperture : z.7z, inferior jugular vein: /v, jugular vein : my, myelon : nc, notochord : z.ca, neural canal: 2.2, neural processes : @s, ceso- phagus : g.6r, peri-branchial sinus : 7.7.4, retractor muscle of tongue : r.t, respiratory tube : s, circum-cesophageal sinus : v.ao, ventral aorta ; v.c, ventral cartilage of branchial basket : v.#, 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, Zr), 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 cae 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 : 14 ZOOTOMY. the testis is a soft, greatly lobulated organ, closely resembling fat: the ovary (Fig. 4, 07), 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. Fic. 7.—Petromyzon marinus. Transverse section through the abdominal region, including the first dorsal fin (nat. size). cd, cardinal veins: d.ao, dorsal aorta : Jv, fin rays: f.4, fibrous tissue inclosing neural canal : 7#, intestine, the line pointing to the spiral valve: 4, kidneys: /y, sub-vertebral lymph sinus : m, body- muscles : zy, myelon : 2c, notochord : n.ca, neural canal: Zs, testis : ur, ureter, 39. The intestine (Figs. 4 and 7, i#), 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, 4), 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, m7), 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, ~g.s), a small ovoidal sac, lying close behind the rectum, and becoming narrowed ventrally to form the urinogenital papilla (w.¢.). 43. The sub-vertebral lymph sinus (Fig. 7, Zy), 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, Zc), lying just in front of and partly covered by the liver: its almost hemispherical posterior wall, strengthened by cartilage ($ 18, Fig. 1, fc) 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! by the external aperture : observe— 45. The apertures of the ureters (Fig. 5, x, 2’), 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, zz¢), a longitudinal fold of mucous membrane, projecting into the cavity of the intestine, and having a slight spiral twist. 48. The aperture of the cesophagus (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, 4.¢), 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, ca), 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, dao), 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, 7 be formed by the bifurcation of a single trunk, the caudal vein (Fig. 8, ¢.v), which may be traced to the end of the tail, lying to the ventral side of the caudal artery (Fig, 8, c.2), which is the direct continua- tion of the dorsal aorta. Fic. 8.—Petromyzon marinus, Transverse section through caudal region, including the second dorsal fin (nat. size). c.a, caudal artery : ¢.v, caudal vein: fir, fin rays: fit, £7’, fibrous tissue enclosing neural canal: m, bedy-muscles: my, myelon: xc, notochord : #.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 47, 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— € 18 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, 2c), on the inner walls of the gill-sacs, leading into the respiratory tube presently to be seen (§ 58). 56. The peribranchial sinuses (Fig. 6, #.67), 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. 1 and 4, 7), 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, 7.#), 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 cesophagus (Figs. 4 and 6, es), 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), 1s 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 likea 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, s’) being also divided by a per- forated vertical partition, The cavity is related to the gullet in much the same way as the Lody-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 cesopha- 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, 7), com- municating with the oral funnel by the very narrow oral aperture. 65. The oral czecum, a blind pouch of the mucous membrane in about the middle of the mouth-cavity, on the dorsal side (Fig 4, ™) ; it is continued posteriorly into a longitudinal groove. 66. The aperture of the cesophagus (Fig. 4, between m and @s), 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, v/). 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. XIJIL Open the pericardium by carefully removing the greater part of its left wall : note 69. The auricle (Fig. 4, aw), 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. 7°. 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.a0), 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 (2.z. 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, 7.7u) 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, 7w), 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. 80. The hepatic vein (Fig. 4, 4.v) may also be seen at this stage; leaving the liver, it pierces the pericardium and enters the sinus venosus at the sane point as the inferior jugular. XVI. Open the ventricle and note 81. 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 (x.ca), and passing in front into the brain (Figs. 4 47, and 9), which nearly fills the small cranial cavity. 84. The medulla oblongata or myelencephalon (Fig. 9, 2.0), 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 (v. 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, ). 86. The mid-brain, or mesencephalon (Fig. 9, o./). consisting on the upper surface of a pair of rounded eleva- tions, the optic lobes, immediately anterior to the me- dulla ; they contain a cavity, the aqueduct of Sylvius, or mesoccele (ag.s), open above, save for pia mater, and in communication behind with the fourth ventricle. 87. The thalamencephalon, or twixt-brain (Fig. 9, th), situated just in front of the mesencephalon ; it consists of two paired masses, the thalami optici, between which is a cavity, the third ventricle, or thalamoccele (z.3), continuous behind with the aqueduct of Sylvius. 24 ZOOTOMY. 88. Two paired, somewhat kidney-shaped masses, forming the anterior division of the brain, and having their convexi- ties towards the middle line ; they are divided by depressions on their outer sides into two parts, the smaller posterior part answering to cerebral hemispheres, or prosence- phala (Fig. 9, ¢/), the larger anterior part to olfactory lobes, or rhinencephala (o//). 89. The nasal sac (Fig. 4, za), a rounded chamber, opening by a short tubular prolongation in the single nasal aperture. On opening, it is seen to be lined with strongly pigmented epithelium, and to have its walls much plaited. Fic. 9.—Petromyzon marinus, The brain from the dorsal aspect, with the right auditory sac (* 3). ag.s, aqueduct of Sylvius : a.s.c, anterior semicircular canal: cd, cerebellum : ¢.4, cerebral hemispheres: ».0, medulla oblongata: 0./, optic lobes : off, olfactory lobes ; .5.c, posterior semicircular canal : ¢/, thalamencephalon: v, vestibule: v.3, third ventricle: 7.4, fourth ventricle : I—X, cerebral nerves, go. The olfactory nerves (Fig. 9, I), passing directly forwards from the rhinencephala to the nasal sac, through the apertures in the nasal capsule (§ 6). g1. 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, IIT), 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, 7), exposed by the removal of the dorsal wall of the auditory capsule; it con- sists of an ovoidal membranous sac, the vestibule (7), presenting on its upper surface, towards the outer side, two semicircular canals (a.s.c, .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 czecum (Fig. 4, za’), 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 te 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 3mm. thick in P. fluviatilis, 8 to ro 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 Itis important not to omit this section unless time or material fails, asit forms an excellent introduction to the art of interpreting sections, THE SKATE. THE SKATE (Layja batis). THE THORNBACK (2. clavata). THE Hometyn Ray (&. maculata).' A.—THE SKELETON. I. Tue 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 laminz 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 of the genus Raja brought to the London market. For the distinguishing characters of the three species see pp. 41 and 42, §§ 54and 60, Several of the figures are taken from the common New Zealand species, 2. asuta. 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, § 1. 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 a, vertebral column, including dorsal and caudal fins (§§ 3—16) ; 4, 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) ; ¢ shoulder-girdle and pectoral fins (§§ 42—49) ; d, hip-girdle and pelvic fins (§§ 50—5 3). 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 vertebree, 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 vertebre, 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 vertebree, extending from the posterior end of the vertebral plate to the root of the tail, and the caudal vertebrze, reaching to the end of that appendage. IV. Examine the trunk vertebre ; 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 vertebra (Figs. 11, 12, and 13, ¢), 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 30 ZOOTOMY, Fic. 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. Inthe remaining pectoral fin, only the proximal ends of most cf the fin rays are shown, and the cartilaginous branchial rays are omitted for clearness sake. ac. I, a¢, 2, anterior and posterior acetabular facets : az¢, antorbital cartilage : az, auditory capsule: a.v.g, anterior vertebral plate : c.d7. 3, ¢.ér, 5, third and fifth cerato-branchials: ¢f, coracoid fontanelle : «7, THE SKATE. 31 coracoid : czy, ceratohyal :@br, 3, third epi-branchial : ey, epi-hyal : gt. 1, gl. 2, gl. 3, anterior, middle, and posterior glenoid facets : h.br, 1, h.br. 3, h.br. §, hypo-branchials of the first, third, and fifth branchial arches: 4.4y, hypo-hyal: Am, hyomandibular: Aw commencement of hzemal canal: 7/, iliac process: /b. 1, 6. 2, 2b. 3, 4. 4, labial cartilages : mck, Meckel’s cartilage or lower jaw: ms. pr, mesopterygium: 2m.p/, metapterygium : o/, olfactory capsule : pp propterygium: f.f%, pre-pubic process: ft.gz, pterygo-quadrate cartilage, or upper jaw : fz, pubic portion of hip girdle : », rostrum : r.c, rostral cartilage : sc, scapula: s.c.f, scapulo-coraccid fontanelle : sf, 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 Fic. 11.—Raja nasuta. The last seven trunk vertebre, and the first ten caudal vertebrze, viewed from the left side (nat. size). ¢, centra: cd. 1, first caudal vertebra : d.r, dorsal root of spinal nerve: 4.f, hamal process : 4.5, heemal spine: 2.7, inter-neural plate : n.p, neural process: #.5, meural spine: r, rib: 4, trunk of spinal nerve: ¢r, transverse process: ¢. 28, twenty-eighth (last) trunk vertebra: v.7, 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. 11 and 12, tr), 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. 11 and 12, 7), small pieces of cartilage attached to the ends of the transverse processes. Fic. 12,—Raja nasuta, A trunk vertebra, seen from the front (nat. size), ¢, centrum : z., inter-neural plate: 7.2, neural process : #.s, neural spine: 7, rib: 7”, transverse process. 8. The neural processes (Figs. 11, 12, and 13, 7.), 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. II, U7). g. The neural spines (Figs. 11, 12, and 13, #5), 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. ro. The interneural (or intercrural) plates (Figs. 11, 12, and 13, z), 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. 11, @.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 vertebre, and containing the remains of the embryonic notochord. V. Examine the caudal vertebre in the same way: make out the following points :— 12. The centrum of each vertebra (Figs. 11 and 14, ¢) gives off, on each side, a downwardly-directed hemal process (4.p), which is seen, by examining the transition region between trunk and tail (Fig. 11), to be homologous with the transverse process of a trunk vertebra: the hemal processes, uniting below, form the heemal arch, which Fic. 13.—Raja nasuta, Longitudinal vertical section of a trunk vertebra (nat. size). ¢, centrum: 7.#., inter-neural plate: #.f, neural process: 2,5, neural spine, transmits the caudal artery and vein (§§ 157 and 158): a median process, the hamal spine (4.5), is given off at the junction of the hemal processes of most of the vertebree, or may occur as a distinct cartilage (see Fig. 11). 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 vertebree: each consists of several radial cartilages or fin rays, attached to two basal cartilages, these latter being attached by fibrous tissue to D 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. 16. The skeleton of the caudal fin is rudimentary, con- sisting of a few very small radial cartilages attached to the posterior caudal vertebre: 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). Fic. 14——Raja nasuta, A caudal vertebra, seen from the front (nat. size). ¢, centrum, 4.2, hemal process: 4.5, hemal spine: z.Z, neural process : #.s, neural spine. 18. 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. ro, aw), 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, o/), 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, 7), at the sides of which the two thin rostral cartilages (7c) 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 sgmewhat behind the first, for the seventh nerve or portio dura (§ 186). 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 D2 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). VIL. In the remaining loosely-attached portions of the skull make out 34. The labial cartilages (Fig. 10, 7s, 1—4), of which THE SKATE. 37 there are altogether four, in connection with the ventral region of each olfactory capsule: the first (Jd. 1) supports the corresponding flap of the fronto-nasal process (§ 64), the second (/d, 2) lies in the fold of skin external to the naso- buccal groove (§ 64), the third (2. 3) bounds the nostril internally, and the fourth (7, 4) externally. 35. The antorbital (palatine) cartilage (Fig. ro, 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, 4.7), 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, sf), 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, pg), 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, mcf), 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. , 4o. The hyoid arch (Fig. 10, ey, chy, 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.Ay) above, cerato-hyal (c¢./y’) next, and hypo-hyal (4.47) below. 41. The five branchial arches (Fig. to), each of which consists primarily of four segments, which are, counting from above downwards, pharyngo-branchial, epi-branchial (er), cerato-branchial (¢.é7), and hypo-branchial (4.6r). 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 (4.47.1) 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 (4.47.5) 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. ro). 43. The three convex articular surfaces or glenoid facets (Fig. 10, g/, 1—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 (sc, s.s¢), —that on the ventral side the coracoid region (¢7). 44. The three large apertures or fontanelles which perforate the shoulder girdle: the anterior of these is the scapulo-coracoid fontanelle (Fig. 10, s.cf): 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 (cf). 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. ro, 4.47), a long 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-pterygitim (Fig. 10, ms.f7), 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, m¢¢), 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, £z) which sends off on each side a forwardly directed pre-pubic process (fu) from the external 40 ZOOTOMY. extremity of its anterior edge, and an iliac process (i) directed upwards and backwards from the external extremity of its dorsal surface. st. The acetabular facets (Fig. 10, ac. 1, 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 thomboid 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. 4t 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. 61. 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 the nostrils backwards towards the mouth, at either angle of which it forms a rounded lobe, beset with fimbriz. 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. ? 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, @.~), 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. yo. 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 ventral 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. 7s. 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, ¢/), 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. 18, 4) (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, 4) 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 81. 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 (ca) ; and to the dorsal side of these (beneath in this position) the large thin-walled sub-triangular auricle (az), and posterior to this, the transverse, tubular, transparent sinus venosus (5.7). 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, Ze. 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,’ first noting 85. The dura mater, or membrane lining the cerebro- spinal cavity, in which the brain and spinal cord he. 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. Fora permanent preparation, the brain should be placed for 24 hours ina 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 77 stfu, may then be prepared by the glycerine jelly process (p. 2, § 1). 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 cesophagus 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. go. 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. gt. 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! 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, ¢0.@) 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 cannule 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 & for the purpose of preventing any slipping of the ligature, over the end ¢ 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 (ze. 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” cr 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 cannulz 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, d, s.m) towards the left, and the wide thin-walled portal vein (Fig. 16, 9) between them, Running parallel with these vessels is also 2 transparent thin-walled lymphatic vessel, from which many of the chief lymphatics can be injected. 94. The gall bladder (Fig. 15, 2.4), a greenish or yellowish transparent sac, partly imbedded in the liver between its right and middle lobes. Fic. 15.—Raja nasuta, The gall bladder and bile ducts (half nat. size), ae common bile duct: ¢.d, cystic duct: g.d, gall bladder: /.4.d, left hepatic duct : 7.4.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-hemorrhoidal veins also often escape being filled. Ina 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 5° ZOOTOMY. 95. Its passage anteriorly into the gall bladder, by the short cystic duct (Fig. 15, ¢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, 1.4,.d) from the middle and left lobes, the other (7.4.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 (¢.@) 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, 4), passing towards the middle lobe of the liver, and sending off branches to all three lobes. It is constituted distally by a gastric vein (g), which receives the blocd from the stomach, and by a mesenteric vein (du, sf/, pn, 7), which receives the blood from the intestine, spleen, and pancreas. 100. The ceeliac artery (Fig. 20, cz), entering the abdominal cavity on the dorsal side of the cesophagus and dividing into two trunks, one of which, the gastro-hepatic artery, sends off a hepatic artery (7) to the liver and a gastric artery (g) to the stomach, while the second or duodenal artery (d) passes down the duodeno-hepatic omentum, and supplies the greater part of the duodenum and the pylorus. THE SKATE. 51 ror. 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 (7), the other the pancreas (47) and spleen (s#/). The rectum is mainly supplied by the small inferior mesenteric artery (§ 157, Fig. 20, 7,m), which passes directly from the aorta to the rectal gland. Fic. 16,—Raja nasuta. The portal vein (one-third nat. size). du, duodenal vein: g, gastric vein: 2, intestinal vein: #, main trunk of portal vein : 4, pancreatic veins: sf/, splenic vein. 1oz. 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, 4.s),a large transverse vessel, lying across the ventral surface of the cesophagus, 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, jit) in the female, or the rudimentary pronephric ducts E 2 52 ZOOTOMY. in the male (Fig. 18, pv.d, 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. XXI. Remove the liver, taking care not to injure the hepatic sinus or oviducts: cut through the stomach just beyond its junction with the ceso- 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 ao’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. ‘Lhe irregularly longitudinal ridges or ruge 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 « 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, ca.s), formed by the union in the middle line of the two posterior cardinal veins (cd), by which the blood Fic. 17,—Raja nasuta. The venous system, ventral aspect (one- third nat. size). The portal vein is not shown ; the renal rortal vein (7A) is supposed to be removed on the right side (left in the figure), and the femoral (fm), ilio-hemorrhoidal (77.4), &c., veins as well as part of the car- dinal (cd) on the left. ‘The right precaval sinus (c.s) is cut open, so as to show the apertures in its walls, The cutlines of those portions of the auricle (az) and sinus venosus (s.v) which lie behind (dorsal to) the ventricle (v), are dotted. ab, veins from abdominal walls: az, auricle: 5.2, bulbus anteriosus : br, brachial vein: ¢, caudal vein: ¢.a, conus arteriosus: cd, cardinal vein : cd.’, posterior anastomosis of cardinal veins : ¢d.s, cardinal sinus : epg, epigastric vein: fm, femoral vein: 4.5, hepatic sinus : 42, heemor- rhoidal veins: 7.4, ilio-heemorrhoidal vein: 77x, inferior jugular vein : jz, jugular vein: /y, opening of lymphatic trunk into precaval sinus: #¢.s, precaval sinus: 7.g, renal portal vein: ».9’, factors of renal portal vein from pelvic and lumbar regions: 7p”, branches of renal portal veins entering kidney: sf.s, spermatic sinus: s.v, sinus venosus : v, ventricle. 54 ZOOTOMY. is brought back from the tail, kidneys, genital ergans, 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 (fc.s) : they are best seen at a future stage. XXIII. The following organs are also best observed at this stage :— t10. 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. 111. In the female the ovaries (Fig. 19, ov): these in the young condition are indistinguishable from testes, but in the adult state aré 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, 2), flat, reddish THE SKATE, 55 Fic. 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 cesophagus (¢s), and viewed from the ventral aspect : the right testis (¢) is removed, along with the corresponding epididymis (epd) and all but the posterior extremity of the vas deferens (v.¢), which, with the sperm sac (s.s) is turned outwards to display the ureters (ur): the cloaca (¢/), the urinogenital sinus (mg.s), and the right vesicula seminalis (v.s) and sperm sac (s,s) are laid open. a.p, abdominal pore: ci, cloaca. epd, epididymis: 7.7, inter-renal body: 4, kidney: @s, cesophagus: fx.d, pronephric duct: s.s, sperm sac: s.s’, its opening into the urinogenital sinus: 4, testis: wg.f, urino- genital papilla: ug.s, urinogenital sinus: wr, ureter: 27’, its opening into the urinogenital sinus: v.d, vas deferens: v.s, vesicula seminalis : v.#, 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. Ln the male. 114. The epididymes (Fig. 18, efd), 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.@), 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 te 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, #7.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). Ln the female. 118. The oviducts (Fig. 19, 7.4 wt), each of which consists of two parts : a posterior, wide, thick-walled uterine THE SKATE. 57 portion (ut), opening into the cloaca, and an anterior, slender, thin-walled portion, or Fallopian tube (/.4) which unites with its fellow of the opposite side on the Fic. 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 cesophagus (@s), and are viewed from the ventral aspect. The left ovary (ov) is removed as well as the greater part of the right oviduct ; the cloaca and the right horn of the urinary bladder are laid open. ap; abdominal pore: ¢/, cloaca: /7.¢, Fallopian tube, or anterior portion of oviduct : #,/’, common opening of the conjoined Fallopian tubes into the abdominal cavity: 4, kidney: mz.d, mesonephric duct : od.g, oviducal gland : @s, cesophagus: ov, ovary : w.4, urinary bladder: u.p, urinary papilla: wr, ureters: wé, uterine portion of oviduct : wt’, its opening into the cloaca.’ 58 ZOOTOMY. ventral surface of the gullet, where the two tubes have a common oval opening (77) into the peritoneal cavity. At the anterior end of the uterine portion of the oviduct is a large, solid, reniform body, of a whitish hue, imbedded in its walls: this is the oviducal gland (od.g), and secretes the horny “purse” in which the eggs are laid: it is not developed in very young specimens. — rig. The urinary bladder (Fig. 19, 1.4) a bilobed sac with thin membranous walls, situated between the posterior ends of the oviducts: it will be better seen after distension with air (see § 123). X XV. Open the cloaca by a median incision along its ventral wall, and note in it 120. The opening of the rectum. Ln the mate. 121. A small, thin-walled tube, the urinogenital papilla (Fig. 18, gf), projecting from the dorsal wall of the cloaca. By inserting a blowpipe into this and inflating, the sperm sacs and vasa deferentia will be dilated. in the female. 122. The large, thick-lipped apertures of the oviducts (Fig. 19, wz), one on each side of the anterior region of the cloaca. In young specimens each of these is closed by a fold of the mucous membrane, the hymen. 123. A small conical elevation, the urinary papilla (Fig. 19, w#.£), situated between the oviducal apertures and having at its apex a small opening ; by inserting a blowpipe into this and inflating, the urinary bladder will be distended. Ln the male. XXVIL_ Slit up the urinogenital papilla, cutting along a probe or 1 The following points (§ 124—127) can only be made out to advantage in fully adult specimens. THE SKATE. 59 blowpipe passed into it, and taking care not to go too far, The papilla will be found to lead into 124. The urinogenital sinus (Fig. 18, zg.s), a small cavity attached to the dorsal wall of the cloaca, into which it opens by the urinogenital papilla: at its anterior extremity will be seen two pairs of apertures, one pair (s.s’) ventrally situated, round, and opening into the sperm sacs, the other pair (z7“) dorsally situated with regard to the first, partly hidden by the projection into the sinus of the sperm sacs, of a somewhat crescentic form, and leading into the ureters (§ 128). XXVII. Remove all that is left of the rectum, and of that part of the cloaca anterior to the urinogenital sinus: slit open the sperm sacs along their ventral wall ; note 125. The greenish epithelium lining the sperm sacs, and the greenish viscid fluid which fills them, and which consists of semen mixed with the secretion of the sacs. 126, A crescentic, thick-lipped aperture (Fig. 18, v.s’), on the dorsal wall of each sperm sac, just within (anterior to) the opening of the sac into the urinogenital sinus : this aperture leads into the vas deferens. XXVIII. Open the lower part of the vas deferens and note 127. Its expansion posteriorly into « chamber—a sort of vesicula seminalis (Fig. 18, v.s), which has its walls produced into lamine, dividing its cavity into a number of compartments ; at its posterior end this dilatation of the vas deferens opens into the sperm sac by the crescentic aperture already noticed. XXIX. Carefully dissect one or both of the vasa deferentia from the surrounding parts, and either remove it entirely or turn it over to one side. Make out 128. The ureter (metanephric duct, Fig. 18, wr), a delicate, colourless tube, situated close to the inner edge of each kidney ; it is made up by lesser tubes proceeding from the several lobes of the kidney, and passes backwards to open into the urinogenital sinus by the slitlike aperture already noticed. 129. The inter-renal (Fig. 18, 27), a long, irregular body of a yellow colour, lying just to the inner side of the ureter. 60 ZOOTOMY. The true adrenals or supra-renal bodies are small yellow masses in connection with the sympathetic g ganglia. 130. The cardinal veins (Fig. 17, c@) lying to the ventral side of the ureters, receiving veins from the hidneys, uniting with one another posteriorly by a transverse anastomosis, and passing forwards to enter the cardinal sinus (§ 109). 131. The dorsal aorta (Fig. 20, d.ae), a delicate artery lying in the middle line between the kidneys, to which it sends branches. (See $157). XXX. Dissect away the skin from the ventral face of one of the pelvic fins, and make out 132. The gland of the clasper, consisting cf a large ovoidal sac with thick muscular walls, which leads by a widish passage at its posterior end into the cavity of the clasper, and which receives the secretion of the gland itself. This is seen by cutting away the ventral wall of the sac to consist of two lobes, with a longitudinal groove between them, in which are the numerous papilliform terminations of the efferent ducts. Ln the female. XXXI. Turn over one of the oviducts and the corre- sponding half of the cloaca to the opposite side of the body, so as to expose one of the kidneys: dissect out— 133. The ureters (Fig. 19 wv), delicate tubes proceeding from the inner edge of the kidney: those coming from the anterior part of the gland pass backwards, those from its posterior part forwards, towards the dorsal wall of the urinary bladder, which they enter. 134. A delicate thread proceeding forwards from each horn of the bilobed bladder, and presenting slight enlarge- ments at intervals: this is the parovarium (Fig. 19, m7.d) the rudiment of the anterior part of the Wolffian body or mesonephros of the embryo, and answering to the parorchis in the male. XXXII. Remove the ventral wall of the urinary bladder, and ncte THE SKATE, 61 135. The three or four minute apertures on each side of the dorsal wall of the bladder, by which the ureters open. 136. The adrenals, inter-renals, dorsal aorta, and cardinal veins, which have the same relations as in the male (§§ 129- 131). Ln both sexes. XXXIII. Carefully dissect away the muscular tissue immediately anterior to the heart and between the two sets of gills, and make out 137. The synangium or bulbus arteriosus (Figs. 20 and 21, 4.2), a white dilatation, connected with the anterior end of the conus arteriosus or pylangium (ca, § 82), and giving off three vessels, one anteriorly, the ventral aorta (v.a0), and one on each side, the posterior innominate arteries (f.77). The ventral aorta passes forwards to the level of the anterior gill cavity, and there divides into two vessels, the anterior innominate arteries (a./z) which are given off at right angles to the ventral aorta, one on either side. Each anterior innominate artery soon divides into two trunks, each posterior innominate into three ; these five vessels are 138. The afferent branchial vessels (Figs. 20 and 21, ' a.br, 1—5), each of which goes to one of the plates by which the gill cavities are separated from one another, passes from the ventral to the dorsal extremity of the plate, external to the branchial arch (see § 166), and gives off branches to the gill filaments. 139. The hypobranchial artery (Figs. 20 and 21, Ay.dr), running antero-posteriorly, just internal to the gills, and crossing the afferent branchial arteries : it springs from the brachial artery (§ 157), anastomoses with the efferent branchial arteries (§ 156), and, besides supplying the tissue ofthe gills, sends off an anterior coronary artery (Figs, 20 and 21, a@.co) to the conus arteriosus and ventricle, and a posterior coronary (.co), to the sinus venosus. 62 ZOOTOMY. Fic. 20,—Raja nasuta. The arterial system, seen from the ventral aspect (one-third nat. size). The heart and ventral aorta (v.ao) are slightly displaced towards the right side (left in the figure): the left afferent branchial arteries (2.7) are removed, and the right efferent branchials (¢.67): the lett efferent branchials are straightened out, so as to bring their ventral ends to the THE SKATE, 63 extreme right of the figure: the left hypobranchial artery is also displaced outwards ; that of the right side (left in the figure) (Ay.67) is drawn zz site, a.br, I, first, and adr. §, last afferent branchial artery: a.co, anterior coronary artery : a@.7#, anterior innominate artery: 4.a, bulbus arterio- sus: 67, brachial artery: ¢, caudal artery: c.a, conus arteriosus: ¢.¢, common carotid artery: ca, coeliac artery: d@, duodenal artery : dao, dorsal aorta: e¢.ér. 1, first, and er. 9, last efferent branchial artery : ¢.c, external carotid artery ; 7, artery to fronto-nasal process : g, gastric artery: , hepatic artery: Ay, hyoidean artery: hy.dr, hypobranchial artery: 2, intestinal artery : z.c, internal carotid artery: z/, iliac artery: 7., inferior mesenteric artery: mm, artery to man- dible: 7.67, nutrient arteries of the gills: od, oviducal arteries: f.co, posterior coronary artery: f.7, posterior innominate artery: pv, pancreatic arteries: 7, renal arteries: s, artery to snout: s.c/, sub- clavian artery: 5.72, superior mesenteric artery: s#/, splenic artery : spm, spermatic artery: v, ventricle: v.a0, ventral aorta: v7, vertebral artery. 140. The inferior jugular vein (Figs. 17 and 21, 7.7) situated in the dorsal wall of the pericardium, near its outer border: it brings blood from the floor of the mouth and pericardial walls, and enters the precaval sinus (§ 149, Figs. 17 and 21, fe.s). aco | hybr peo Fic. 21.—Raja nasuta. Diagram of the heart and chief blood- vessel, from the left side (half nat. size). : : a.br. 1, first, and a.ér. 5, last afferent branchial artery : @.co, anterior coronary artery: az, auricle: d7.a, brachial or subclavian artery : br.v, brachial vein: ¢.a, conus arterlosus : ed, cardinal vein: @.ao, dorsal aorta; ¢.6. I, first, and ¢47. 9, last efferent branchial artery : h.s, hepatic sinus : 2y, hyoidean artery: hy.6r, hypo-branchial artery : 2.ju, inferior jugular vein : 72, jugular vein: 7.dr, nutrient arteries o the gills: Z.co, posterior coronary artery: c.s, precaval sinus: 5.v, sinus venosus : v, ventricle : v.ao, ventral aorta. ‘ 64 ZOOTOMY. - 141. The thyroid gland, a flattened rounded body, of a deep red colour, situated immediately in front of the anterior end of the ventral aorta. XXXIV. Cut through the ventral aorta and posterior innominate arteries close to the bulbus arteriosus, and turn the heart backwards, so as to expose the pericardial cavity. Note 142, An aperture in the centre of the posterior dorsal region of the pericardium : by passing a probe into this it will be found to lead into a funnel-shaped cavity which soon divides into two membranous canals. ‘Ybese—the pericardio-peritoneal canals—pass backwards along the ventral wall of the gullet, and open each by a widish aperture, thus placing the pericardium in communication with the peritoneal cavity. XXXV. Remove the heart entirely, by cutting through both ends of the sinus venosus and the membrane by which it is united to the pericardium: make out carefully the relations of the various parts of the heart (§ 82), then cut open, first the auricle and sinus venosus from the dorsal side, and afterwards the ventricle and conus arteriosus from the ventral side. Make out 143. The thin, smooth walls of the sinus venosus. 144. The thin walls of the auricle, strengthened by a complicated network of muscular fibres, the musculi pectinati. 145. The large sinu-auricular aperture guarded by the two membranous flaps of the sinu-auricular valve. 146. The circular auriculo-ventricular aperture, guarded by the two long flaps of the auriculo-ventricular valve, which are attached round the margins of the aper- ture, and hang down into the ventricle. 147. The small, horseshoe-shaped cavity of the ventricle, and its immensely thick walls, strengthened internally by muscular ridges or columne carnez. 148. The three longitudinal rows of aortic valves in THE SKATE. 65 the conus arteriosus, each row containing five somewhat semilunar flaps, opening towards the synangium. XXXVI. Pass a probe, directed outwards and backwards, into either of the cut ends of the sinus venosus: carefully cut away the cartilage of the shoulder girdle and other tissues until the end of the probe is brought into view: it will be found to have passed into 149. A small chamber, the precaval sinus (Figs. 17 and 21, gc.s), situated in the antero-lateral angle of the abdominal cavity. In its wall are several apertures : one, situated antero-internally, is the opening of the jugular vein (7), by which the blood is returned from the head: another, postero-internal in position, is the opening of the cardinal vein (cd) already seen: a third, on the ventral wall of the sinus, puts it in communication with the hepatic sinus.(4.s) : a fourth, at its anterior end, leads into the sinus venosus (s.v) : a fifth, very small, just internal to the last, into the inferior jugular vein (2.ju) : a sixth, on the outer wall, into the brachial vein (47) and lastly, in the middle of the dorsal wall, is a transverse aperture, guarded by two valves, by which the contents of the chief lymphatic trunk (Fig. 17, dy) axe poured into the sinus. 150. A sympathetic ganglion (see § 220), a whitish elongated body about a quarter of an inch long, will be found immediately outside the inner wall of the sinus. XXXVII. Cut away the remainder of the ventral portion of the shoulder girdle, and cut through the floor of the mouth, by making an incision a little to one side of the median line so as not to injure the ventral aorta, through the cesophagus and basibranchial plates (see § 41), and through both jaws. Fasten back the two halves of the mouth-floor thus separated, so as to expose the whole oral cavity from beneath. Note 1st. The internal branchial clefts, five long vertical fissures, by which the gill pouches communicate with the cavity of the mouth. 152. The opening of the spiracle into the mouth, just in front of the first gill cleft. F 66 ZOOTOMY. 153. The curved hard bars which separate the gill clefts from one another: these are the branchial arches. 154. A similar hard bar of cartilage separating the spiracle from the first gill cleft: this isthe hyoid arch. 155. The relations of the branchial filaments to the bran- chial arches: there is a set of filaments on both the anterior and posterior walls of all the gill cavities except the last, the posterior wall of which is devoid of filaments. Thus there are nine sets of filaments or half-gills in all, one of which occurs on the posterior face of the hyoid arch, and one on each face of each of the first four branchial arches, the fifth branchial arch being without filaments. XXXVIIIL. Carefully dissect away the mucous mem- brane from the roof of the mouth; remove the dorsal ends of the gill arches or pharyngo-bran- chials ; and follow out 156. The efferent branchial arteries (Figs. 20 and 21, ¢.6r. 1—g), of which there are nine, one for each demi- branch: after leaving the dorsal ends of the gills they unite with one another in pairs, that from the hyoidean demi- branch uniting with that from the anterior demibranch of the first branchial arch, that from the posterior demibranch of the first with that from the anterior demibranch of the second branchial arch, and so on. Four trunks are thus formed, the last of which receives the vessel from the posterior demibranch of the fourth branchial arch, and the first two of which soon unite with one another, so that there are now three main efferent branchial trunks on each side. These takea direction inwards and backwards. The most anterior of the three pairs unite with one another in the middle line and form a short trunk: with this the next pair unite and produce a somewhat larger trunk, with which, finally, the third pair join. The longitudinal vessel thus THE SKATE. 67 formed by the union of the efferent branchial trunks is the dorsal aorta (§ 157). The efferent branchial arteries unite with one another in the way described at their ventral as well as at their dorsal ends, thus forming complete loops, the spaces enclosed by which correspond to the bran- chial clefts. The two arteries of each complete gill are united with one another by a cross branch at about the middle of their length: it is through this anastomotic branch of the last gill that the ninth efferent artery (e.d7. 9) pours its blood into the eighth. From the junction of the third and fourth and of the fifth and sixth arteries, short anastomotic branches go off to the hypobranchial artery (§ 139). 157. The dorsal aorta (Figs. 20 and 21, @ao), passing along the ventral face of the vertebral column: it gives off, just before being joined by the third pair of efferent branchial trunks, a large vessel from each side, which passes directly outwards to the pectoral fin: this is the brachial or sub- clavian artery (Fig, 20, s.c, Fig. 21, 67a). The aorta then passes backwards in close contact with the verte- bral column to the posterior extremity of the abdominal cavity, giving off at about the level of the shoulder girdle two large vessels, the coeliac (Fig. 20, cw), and superior mesenteric (s.m) arteries (§§ 100 and 107), then the arteries to the oviducts (ed) or epididymes, sper- matic arteries (sf) to the testes or ovaries, a single inferior mesenteric artery (¢.m), (§ 101), the numer- ous small renal arteries (7) to the kidneys, and vessels to the pelvic fins and the parietes of the body. At the end of the abdominal cavity the dorsal aorta becomes the caudal artery (c), which passes through the heemal arches of the caudal vertebree (Fig. 10, 2@) to the end of the tail. 158. The caudal vein (Fig. 17, ¢), running parallel and ventral to the caudal artery : on leaving the hzemal canal it divides into the two renal portal veins (72), which pass to and ramify in the corre- sponding kidneys (7f”) receiving numerous veins (77’) from the pelvic and lumbar regions. F 2 68 ZOOTOMY. 159. The femoral veins (Fig. 17, fm) bringing the blood from pelvic fins : each divides into two trunks: one, the ilio-haemorrhoidal vein (¢/.2), passes at first backwards and inwards, then forwards along the lateral surface of the rectum and cloaca, and opening finally into a posterior prolongation of the cardinal sinus : the second of the two veins into which the femoral divides is the epigastric vein (epg) ; it passes almost directly forward along the lateral wall of the abdominal cavity, receiving veins from the abdominal walls (24), and finally unites with the brachial vein (47). It will be seen from Fig. 17, that the brachial, epigastric and ilio- hzemorrhoidal veins really form one continuous trunk, opening anteriorly into the precaval, posteriorly into the cardinal sinus, and receiving veins from the pectoral and pelvic fins, the abdominal walls, and the rectum and cloaca. The anterior portion of the epigastric should probably be considered as representing the mammary vein of mammals, the two being continuous instead of merely anastomosing. 160. The common carotid artery (Fig. 20, ¢.c), a small vessel springing from the efferent branchial vessel of the hyoid arch: it first passes somewhat inwards, and then directly forwards near the outer edge of the base of the skull, sending a branch inwards—the internal carotid artery (¢.c)—which unites with its fellow of the opposite side to form an azygos trunk which perforates the base of the skull and is distributed to the brain, especially to the pituitary body and saccus vasculosus (§§ 176 and 177): the external carotid (ec) then passes forwards and slightly outwards, and sends branches to the jaws, snout, &c. 161. The vertebral artery (Fig. 20, vv), a small trunk arising from the first of the three efferent branchial trunks: it passes inwards and slightly forwards, perforates the base of the anterior vertebral plate (§ 3), and is distributed to the brain and spinal cord, on the ventral surface of which it forms, with its fellow, a plexus. 162, A small hyoidean artery (Fig. 20, Ay) given off from the first efferent branchial: it passes to the dorsal side of the hyomandi- bular and sends a branch to the pseudobranchia. XXXIX. Remove two of the gills and make out, in one by dissection, in the other by transverse sections 163. -The cartilaginous branchial arch which supports the inner edge of the gill. THE SKATE. 69 164. The fibrous partition continued from the outer face. of the branchial arch, and supported by the cartilaginous branchial rays. 165. The soft vascular branchial filaments covering , both sides of the partition, to which they are firmly connected along almost their whole length, their outer extremities only being free. 166. The afferent branchial artery, running along the outer face of the branchial arch, in the middle line: it is of considerable size at the ventral end of the gill, but gradually diminishes towards its dorsal end. 167. The efferent branchial arteries, two trunks smaller than the afferent vessel, and running along the lateral edges of the arch, at the bases of the rows of filaments. They are of considerable size at the dorsal end of the arch, and diminish somewhat towards its ventral end. 168. The thymus glands are exposed by the removal of the gills : each is a whitish body, about an inch long, lying immediately dorsal to the pharyngo-branchials, C.—SPECIAL DISSECTION OF THE NERVOUS SYSTEM AND SENSE ORGANS. XL. It is advisable to take a fresh skate for the nervous system, at least unless the subject used for the foregoing work has been well preserved in strong spirit. The viscera, with the exception of the kidneys and vasa deferentia, may be removed at once. Expose the brain and anterior part of the spinal cord, as directed in § XV., p. 46. Ifa preserved brain is not available, the verification of the description of the ventral surface must be left until the origins of the nerves have been made out (§§ 179—189) when the brain may be removed. Observe the following :— 70 ZOOTOMY. 169. The spinal cord (Fig. 22, my) lying in the neural canal of the vertebral column, and, at the junction of the latter with the skull, passing insensibly into the brain. It is divided into a pair of dorsal and a pair of ventral columns by deep dorsal and ventral fissures, and is traversed through its centre by the minute central canal. 170. The medulla oblongata or myelencephalon (Figs. 22—25, m.o), the hindmost division of the brain : passing forwards from its junction with the spinal cord, it undergoes a gradual increase in diameter, and is produced dorsally, on each side, into a greatly convoluted body, the corpus restiforme (Fig. 22, a7). Both dorsal and ventral surfaces of the medulla are marked with obscure inedian grooves, continuous respectively with the dorsal and ventral fissures of the spinal cord : the dorsal groove separates the dorsal pyramids, the ventral groove the ventral pyramids of the medulla. 171. The cerebellum (Figs. 22, 24, 25, cb), a median structure, situated to the dorsal side of the myelencephalon, and composed of two distinct lobes, a posterior, having the form of an isosceles triangle with the apex directed back- wards, situated between the restiform bodies, and a squarish anterior, partly overlapping the optic lobes (§ 173). Both lobes are marked on the surface by ridges (gyri) with inter- vening depressions (sulci). 172. A small transparent area behind the cerebellum (Fig. 22, 7 4), roofing over the fourth ventricle (§ 180). 173. The mesencephalon (Figs. 22—25, 0./, ¢.¢) con- sisting on the upper surface of the two optic lobes (0.2), ovoidal bodies, lying just in front of, and partly overlapped by the cerebellum. The under surface of the mesencephalon is formed by the crura cerebri (c.), THE SKATE, 71 Fic, 22.—Raja nasuta. Dorsal view of the brain and anterior part of the spinal cord, with the cerebral and anterior spinal nerves (half nat. size). On the left side the 2nd, 5th, and 7th—1oth cerebral nerves are removed, and on the right side the 3rd, 4th, and 6th. The spinal nerves are shown only on the left side: the distal end of the left olfactory lobe is not shown. Central Nervous System. my, spinal cord: mm.o, medulla oblongata: vw. 4, fourth ventricle: ¢.7, corpora restiformia: cd, cere- bellum: 0.4, optic lobes: ¢h, thalamencephalon : ¢.4, prosencephalon : olf; olfactory lobes. Nerves. /, olfactory: Z/, optic: /7Z, oculomotor: 2.7, branch of oculomotor to internal rectus: s.7, to superior rectus: 7¢.7, to in- ferior rectus: 7.0, to inferior oblique: /V, patheticus: V7, dorsal, 72 ZOOTOMY. and /'>, ventral ramus of V7? orbito-nasal nerve: V2, palato-nasal nerve: >, maxillary nerve: 773, mandibular nerve: V//?, palatine branch of portio dura: V/ZZ>, hyomandibular branch: ¢.ty, chorda tympani: VZ//, auditory nerve: ZX, glossopharyngeal nerve : X, vagus: Ay, branch of glossopharyngeal to hyoid arch: 67. 1, branches of glossopharyngeal and vagus to Ist branchial arch: 67. 2, dr. 3, 47. 4, branches of vagus to 2nd, 3rd, and 4th branchial arches: v, ventral (gastric and cardiac) branch of vagus: /, lateral branch of vagus: 67, brachial plexus, forward continuations of the ventral pyramids of the medulla oblongata. 174. The thalamencephalon (Figs. 22, 24, 25, ¢h), a small division of the brain just anterior to the optic lobes: it consists of two lateral masses of nervous matter, the thalami optici, between which is a space, covered only by pia mater, the thalamoccele or third ventricle (v. 3). 175. The lobi inferiores (Figs. 23—25, 22) paired ovoidal bodies on the under surface of the thalamencephalon. 176. The pituitary body or hypophysis cerebri (Figs. 23—25, f/), a rounded structure on the ventral surface of the brain, behind the lobi inferiores and attached to a backward prolongation of the thalamencephalon called the infundibulum; with it is connected anteriorly the median artery formed by the union of the two internal carotids (§ 160). 177. The saccus vasculosus (Figs. 23—25, 5.7, 5.0’). a thin-walled hollow body, consisting of three lobes, two large and paired, situated one on either side between the pituitary body and the lobi inferiores, and a median azygos lobe lying in the groove between the lobi inferiores. 173. The prosencephalon (Figs. 22—25, , dorsal or posterior root of the same: J’//, VZ’, roots of the portio dura: V/ZJ/, root of the auditory nerve. bodies. Each bundle is seen to consist of an anterior smaller and a posterior larger fasciculus. The former (Figs. 23, 26, and 27 V’*) goes to form the inferior ramus of the Fic, 27.—Raja nasuta. The principal branches of the 5th, 7th, and 8th cerebral nerves (nat. size). Va, ventral and ”», dorsal root of the fifth: 17, dorsal, and V™, ventral ramus of the orbito-nasal nerve: V8, palato-nasal nerve : Be, maxillary nerve: 173, mandibular nerve: pi.gu, nerve to upper jaw : ya, nerves to the region of the nostrils: V2/, portio dura: VIZ, auditory nerve. first division of the fifth nerve, and the main part of its third division, besides contributing fibres to the second 76 ZOOTOMY. division: the latter (V°, V7Z, V7/Z) contains the remainder of the fifth, the seventh, and the eighth nerves. The fifth, seventh, and eighth nerves arise altogether by seven roots. Two of these, a smaller dorsal (Fig. 26, Y’) and a larger ventral (V) go to form the anterior fasciculus already mentioned, both arising ventro- laterally from the medulla, The five roots forming the posterior fasci- culus divide naturally into an anterior and 2 posterior set. The anterior set consists of two roots, a dorsal (VZ/) and a ventral (7 7/’), together forming the seventh nerve: the posterior set consists of three roots, a dorsal (V'»), arising along with the dorsal root of the seventh, and two ventral, arising close together: the uppermost ventral root unites immediately with the dorsal root to form the remainder of the fifth nerve (>): the lowermost ventral root (VZ/Z) constitutes the eighth nerve. 187. The sixth pair (abducentes, Figs. 22 and 23, V7) arise from the under surface of the medulla oblongata, internal to the eighth. They are very fine nerves, and are easily detached with the pia mater. 188. The ninth pair (glossopharyngei, Figs. 22, 23, 25, JX), a small pair arising from the sides of the medulla oblongata, and passing outwards and forwards to enter the au- ditory capsule at about the centre of its inner surface (§ 33), 189. The tenth pair (vagi or pneumogastrici, Figs. 22, 23, 25, X ), arise by several roots from the lateral regions of the hinder part of the medulla oblongata, and pass out- wards and backwards to leave the cranial cavity by a foramen in the posterior part of the inner surface of the auditory capsule (§ 33). XLI. Remove the skin from the dorsal surface of the head, on both sides of the cranial cavity, and by carefully dissecting away the connective tissue from the eye and surrounding parts, make out 190. The dorsal ramus of the orbito-nasal nerve (first division of the fifth, Figs. 22 and 27, V%*) lying close THE SKATE, 77 against the outer side of the skull wall, and springing from the posterior dorsal root mentioned in § 186, 191. The superior oblique muscle of the eye, passing from its origin at the anterior part of the skull wall to its insertion in the antero-superior region of the eye-ball. 192. The superior rectus muscle, arising from the skull wall, a little in front of the auditory capsule, and passing to its insertion on the postero-superior region of the eye-ball. 193. The internal rectus, arising immediately in front of the superior rectus and passing to the front part of the eye-ball, beneath the superior oblique. 194. The external rectus, arising just behind the superior rectus and passing almost directly outwards to the posterior region of the eye-ball. 195. The fourth nerve (Fig. 22, ZV), leaving the skull by its numerous foramina, and spreading out in a fan-like manner on the dorsal surface of the superior oblique muscle. 196. The third nerve (Fig. 22, 77/7), which, after leav- ing the skull, sends branches to the superior (s.7) and internal (7) recti, and then curves round the posterior edge of the former: its further course will be seen at a later stage (§ 203). 197. The sixth nerve (Fig. 22, V7), leaving the skull along with the fifth and seventh, and being distributed to the external rectus muscle. XLII. Remove the superior oblique and the superior and external recti. Make out 198. The ventral ramus of the orbito-nasal nerve (Figs. 22 and 27, V?") springing from the anterior fasciculus mentioned in § 186: after leaving the skull by the trigeminal foramen, it passes over the external rectus, under the 78 ZOOTOMY. superior and internal recti, over the peduncle of the eye (§ 200) and the optic nerve (§ 199), under the superior oblique, and finally unites with the dorsal ramus as it perforates the nasal capsule (§ 205). 199. The optic nerve (Fig. 22, 77), which, after leaving the skull, passes almost directly outwards to the hinder region of the eye-ball. Its extra-cranial portion is invested with a strongly pigmented sheath. 200. The ophthalmic peduncle, an irregular stalk of cartilage, articulated at its proximal end with the skull wall behind the optic foramen, and at its distal end with a knob on the sclerotic coat of the eye. 201. The inferior oblique muscle of the eye, running parallel with the superior oblique, to the antero-inferior region of the eye. 202. The inferior rectus, arising with the other recti, and passing parallel with the superior rectus to its insertion on the inferior region of the sclerotic. 203. The remaining course of the third nerve (Fig. 22, Z/1): after curving round the superior rectus, it passes forwards and sends branches to the inferior rectus (¢#.7) and inferior oblique (2.0). XLIII. Remove successive slices from the nasal cap- sule, until the following structures are brought into view. 204. The strongly pigmented nasal sac, filling up the cavity of the nasal capsule. 205. The orbitc-nasal nerve (Fig. 22, ¥1) which, just before the junction of its two rami, enters the nasal capsule, and divides into two branches, a large one which passes along the outer edge of the rostrum, and a small one, which passes outwards and forwards over the roof of the nasal sac. THE SKATE. 79 206. The distal ends of the olfactory lobes (Fig. 22, olf), each forming a slightly convex white band on the dorsal surface of the corresponding nasal sac. XLIV. Remove one of the nasal sacs, and note 207. Its cup-like form, the cavity being open below. 208. The ridges into which its lining of mucous mem- brane is raised: they are arranged in two rows at night angles to a central ridge. XLV. Remove the eye with its remaining muscles, and set it aside for future examination.' Dissect out 209. The second division of the fifth nerve (Figs. 22 and 27, V?), arising mainly from the posterior fasciculus mentioned in § 186, but also receiving fibres from the anterior fascicu- lus: it passes forwards and slightly outwards, and divides into two chief branches, an internal, the palato-nasal nerve (/7*) and an external, the maxillary nerve (V») the former passing directly forwards alongside the cranial wall and beneath the eye muscles, and the latter passing outwards and forwards towards the antorbital cartilage ($ 35). 210. The third division of the fifth, or mandibular nerve (/73), arising mainly from the anterior, but receiving fibres from the posterior fasciculus: it runs parallel with the common trunk of the second division as far as the bifurcation of the latter, and then takes a course internal to and nearly parallel with the maxillary nerve. The three divisions of the fifth nerve supply between them all the anterior part of the head: the orbito-nasal goes to the dorsal region of the rostrum and nasal capsule, and to the gelatinous tissue in their neighbourhood : the palato-nasal to the ventral region of the same parts, as well as to the fronto-nasal process and the movie? it also sends 1 The eye must be dissected in the fresh condition : for directions see _ § LIL, p. 84. 80 ZOOTOMY, fibres to the upper jaw: the main part of the mandibular nerve goes to the sensory tubes in front of the antorbital cartilage: the mandibular goes to the lower jaw (outer side), but also sends a large branch to the upper jaw. There is, however, endless variation in the distribution of these nerves. XLVI. Carefully slice away the cartilage forming the roof of the auditory capsule, taking care not to injure the membranous labyrinth (§ 213); dissect away the connective tissue, &c., from the hyo- mandibular, and the muscles on the floor of the orbit, making out 211. The hyomandibular nerve, or posterior branch of the seventh (Fig. 22, /’//*): after leaving the cranial cavity it curves round the anterior border of the auditory capsule, and passes almost directly outwards, over the hyomandibular cartilage and behind the jaw muscles, break- ing up at last into a number of fibres which are distributed to the large sensory tubes situated in front of the gills. As the hyomandibular nerve passes the jaw muscles, it gives off two small branches (¢¢y), which represent the chorda tympani of the higher animals, and are distributed to the inner surface of the lower jaw. 212, The palatine nerve (Fig. 22, VZ/*), or anterior division of the seventh, which separates from the common root of the seventh soon after its exit from the skull, passes in front of the spiracle, and breaks up into a number of branches, some of which are distributed to the mucous membrane of the mouth and others to the pseudobranchia. 213. The membranous labyrinth (Fig, 28) or internal ear, a delicate apparatus enclosed within the auditory capsule, and consisting of a large sac or vestibule (2), and three semicircular canals, one of which is anterior and vertical (a.s.c), another posterior and vertical (#.s.¢), and the third horizontal (A.5.c). THE SKATE. 81 The vestibule is a rounded sac with two small diverticula, containing an otolithic mass which consists of minute calcareous particles bound together by gelatinous connective tissue: from its dorsal surface pro- ceeds a canal, the aqueductus vestibuli (¢7./), which passes through the roof of the auditory capsule, and dilates between the latter and the external integument into a small sac, lined with strongly pigmented epithelium ; this opens on the surface of the head bya minute aperture. The canals form nearly complete circles, the posterior being the largest of the three. Each is dilated at one part of its course into an ampulla (a). The posterior canal communicates with the vestibule in an unusual manner, namely by a short distinct tube (x). Fic, 28.—Raja batis. The right membranous labyrinth, seen from the outer side (nat. size). v, vestibule: ag.f, aqueductus vestibuli: @.s.c, anterior, f.s.¢, posterior, and 4.s.c, horizontal semicircular canals: @,a,a, ampulle : x, side tubulure by which the posterior canal communicates with the vestibule : 2,#,2, branches of auditory nerve. XLVII. Clear away the skin and muscles from the dorsal surface of the anterior vertebral plate and from that of the gills. Dissect out 214. The vagus or tenth nerve (Fig. 22, X ), which, after leaving the skull by the vagus foramen, passes directly back- wards between the inner boundaries of the gills and the lateral ridge of the anterior vertebral plate, giving off the branchial nerves as it goes, to the front edge of the pro- pterygium, where it divides into two chief branches, a ventral branch (X,z), to the stomach and heart, and a lateral branch (X,J), which passes between the peritoneum and dorsal G 82 ZOOTOMY. muscles, on the dorsal side of the spinal nerves (§ 222). The branchial nerves (dr. 2—5) are four in number, and are given off opposite the four posterior gill clefts. Each one, soon after leaving the vagus divides into two branches, one of which goes to the posterior face of the gill in front of the cleft to which it belongs, the other to the anterior face of the gill next behind. In this way all the gill filaments except those on the posterior face of the hyoid and those on the anterior face of the first branchial arch (first and second demibranchs) are supplied. 21s. The glossopharyngeal or ninth nerve (Fig. 22, 7X), seen emerging from its foramen, in front of the anterior branchial branch of the vagus: it divides above the first gill cleft and supplies the hyoid half-gill and the anterior half- gill of the first branchial arch (Ay, 47.1). 216, The brachial plexus (Fig. 22, 47), lying in the depression between the median and lateral ridges of the anterior vertebral plate, and formed by the convergence and subsequent union of the first sixteen or eighteen spinal nerves: the common trunk thus formed turns round the posterior edge of the lateral ridge, and passes outwards behind the propterygium to the pectoral fin. Each spinal nerve arises by two roots, a dorsal (Fig. 11, d.7) and a ventral (v.v), the former having a ganglionic enlargement : the two pass separately through the wall of the neural canal (see §§ 8, 10) and unite outside it in the trunk (¢7) of the nerve. XLVIII. Remove carefully the greater part of the membranous labyrinth, cut away the walls of the auditory capsule, and make out 217. The auditory or eighth nerve (Fig. 22, VZ/7), entering the capsule at its anterior end through the in- ternal auditory meatus, and passing backwards, sends off THE SKATE. 83 branches to the vestibule and ampullz of the semicircular canals (Fig. 28, 7). 218. The course of the ninth nerve through the capsule (Fig. 22, JX): it enters the latter by an aperture in about the middle of its anterior wall, passes backwards and out- wards nearly parallel with the eighth and leaves the capsule in its postero-external region by an aperture already noticed in the skull (§ 25). 219. The course of the vagus through the auditory capsule (Fig. 22, X): leaving the cranial cavity it passes through a canal excavated in the postero-internal wall of the capsule, the outer end of the canal being the vagus foramen (see §§ 24, 33). XLIX. Place the fish in the supine position, find the large sympathetic ganglion mentioned in § 150, and trace back 220. The sympathetic nerve, which consists of a longitudinal cord on each side of the vertebral column, presenting ganglia at intervals, and connected by rami communicantes to the spinal nerves. As already mentioned, the adrenals or supra-renal bodies are in intimate connection with the sympathetic ganglia, L. Dissect away the kidneys and the peritoneum from the dorsal wall of the abdominal cavity, and note 221, The spinal nerves, passing to the body walls and fins: many of them converge, and exhibit a tendency to the formation of plexuses. 222. The lateral branch of the pneumogastric (Fig. 22, X,/), a longitudinal nerve, lying to the dorsal side of the spinal nerves. LI. Make a longitudinal vertical section of a brain hardened in spirit, and note 223. The relations of the various divisions of the brain already seen, and of the cavities they contain (Fig. 24): the G2 84 ZOOTOMY. latter are seen to form a continuous series, from the myeloccele (v. 4), which is continued behind into the central canal of the spinal cord, through the mesoccele (ag.s) to the thalamoccele (v. 3). The latter is further seen to send a small prolongation forwards into the otherwise solid pros- encephalon, and another downwards and backwards into the infundibulum. LII. Make out the chief structures in the eye, first viewing from the outside,then removing successively the sclerotic (§ 224), choroid (§ 225) and retina (§ 227) from the flattened dorsal surface. 224. The cartilaginous sclerotic or outer covering of the eye-ball: externally it passes into the transparent fibrous cornea, which is the part exposed to view in the entire animal; internally, the sclerotic is pierced by a small aperture for the passage of the optic nerve, and is raised into a knob- like prominence for articulation with the ophthalmic peduncle (§ 200). 22s. The black choroid lining the sclerotic: at the junction of the latter with the cornea, it passes into the iris, the coloured (yellow and black) part of the eye, seen from the outside through the transparent cornea. The iris is pierced by a central aperture, the pupil, the upper margin of which is produced into a sort of curtain, divided at its free edge into several processes. Between the iris and the cornea is a space, the anterior chamber of the eye, filled with a watery fluid, the aqueous humour. 226. The crystalline lens, a nearly globular transparent body, situated immediately behind the iris. 227. The retina, a delicate, greyish-white membrane, lying immediately within the choroid, from which it is readily detached except at the place of entrance of the optic THE SKATE. 85 nerve. Externally (ze towards the cornea) it ends at the junction of the choroid and iris. 228, The vitreous humour, a gelatinous substance, fill» ing the whole posterior chamber of the eye, or space enclosed between the retina and the inner surface of the lens and iris. THE COD. Tue CoprisH (Gadus morrhua). Tue WHITING (G. merlangus). THE Happock (G. aglefinus).' A.—THE SKELETON. I. A cod’s skeleton is readily prepared by placing the fish, after removal of the viscera, into boiling water for a few minutes, and thus stripping off the flesh and other soft parts. By this process the bones are obtained separate from one another, with the exception of those forming the brain-case, the high temperature causing gelatinization of the connective tissue which unites them. The bones should be removed one by one and placed out in order, to dry, each being as far as possible identi- fied and its relations to surrounding bones deter- mined before removal. As this is a matter of considerable difficulty in the case of the bones of the head, it is advisable to prepare a second skull 1 These are the three commonest species of the genus Gadus brought to the English markets : the differences between them are comparatively unimportant (see §§ 8, 18, 19, 72, 80, 85). THE COD. 87 by carefully dissecting away the muscles, &c., while fresh, without either boiling or maceration, the bones being kept together in their natural position by their ligaments. Of this skull it is as well to make a longitudinal vertical section by sawing through the brain-case a little to one side of the middle line and cutting through the mandi- bular and hyoidean symphyses (§§ 51 and 52) : from the worst side, the jaw apparatus should be removed from the brain-case by disarticulating the palatine (§ 46, Fig. 29, 2) and the hyomandibular (§ 40, Fig. 29, 4m). In the first skull the bones of the brain-case may be separated from one another by boiling for a considerable time and then gently pulling them asunder. It is advisable to examine the second or entire skull before drying, so as to see its cartilaginous portions (§§ 47, 49, &c.).1 II. In the skeleton as a whole note the following regions :— 1. The vertebral column, consisting of (a) trunk vertebra, bearing movable ribs which do not unite 1 Owing to the small amount of cartilage left in the adult cod’s skull, the beginner will find some difficulty in seeing the relation between it and that of the skate. A useful intermediate type is furnished by the salmon or trout, in which there is a cartilaginous brain-case, quite readily comparable with that of the skate but containing the occipital and otic bones, basi- and pre-sphenoid, as endogenous ossifications : the remaining homologues of the bones of the cod’s brain-case (parietals, frontals, parasphenoid, vomer, &c.) are seen to be membrane-bones, easily detachable without injury to the cartilage (see Parker and Bettany, Morphology of the Skull, p. 66). The skull of the salmon or trout should be prepared like that of the cod, by b iling ; the brain- case, Meckel’s cartilages, &c., may be preserved by the glycerine jelly process, described on p. 2. 88 ZOOTOMY. below, and (4) caudal vertebree, with complete inferior arches. 2. The skull, consisting of (2) the brain-case, formed of a number of bones firmly united by suture; (2) a num- ber of more or less loosely attached bones, in relation with the brain-case, and constituting the skeleton of the upper and lower jaws and suspensorium, the hyoidean ap- paratus or tongue-bones, and the gill-covers; and (¢) the branchial arches or bony framework which supports the gills, 3. The bones of the median fins, namely, the three dorsal fins, the two anal fins, and the caudal fin (see § 94). 4. The bones of the pectoral fins, or fore-limbs, and of the shoulder girdle to which they are attached ($ 95). 5. The bones of the pelvic fins, or hind-limbs, and of the hip-girdle to which they are attached (§ 96). III. Examine a vertebra from about the middle of the trunk region, and make out 6. The centrum or body of the vertebra, a short bony cylinder with deeply concave anterior and posterior ends ; the bi-convex spaces between adjacent centra are filled in the recent state by a gelatinous substance, the remains of the embryonic notochord. 7. The neural processes, two plates arising vertically one from each side of the upper surface of the centrum, near its anterior end, and uniting with one another to form the neural arch, from the vertex of which the long slender neural spine springs and takes a direction upwards and slightly backwards. From the anterior edge of each neural process a somewhat triangular projection is continued forwards, and answers to the anterior zygapophysis of THE COD. 89 the higher vertebrata: there is no true posterior zygapophy- sis, but from the hinder end of the centrum arises on each side a small vertical process, which fits owés¢de the anterior zygapophysis of the vertebra next behind. 8. The transverse processes, large outstanding plates of bone, which spring one from each side of the centrum, and pass outwards, downwards, and backwards. The transverse processes are proportionally much larger in the Haddock than in either of the other species. IV. In the rest of the trunk region, the following are the chief points to be verified :— g. In the first vertebra or atlas the centrum is very short from before backwards, the neural spine is vertical, the transverse processes are absent, and the anterior zyga- pophyses are very large and come into relation with the posterior part of the skull (exoccipital bone, § 22); im- mediately beneath each zygapophysis is a small articular facet for articulation with a corresponding facet on the exoccipital. The union between the skull and the atlas is thus much more intimate than that between any two vertebree, and in consequence the atlas is, in preparation, often left attached to the skull. 10. In the next three or four vertebre a gradual transition is seen between the characters of the atlas and those of the typical trunk vertebra described in §§ 6—8. 11. The transverse processes in the anterior part of the trunk region look almost directly outwards; proceeding towards the caudal region, they gradually increase in size and come to look more and more downwards and back- : wards, until in the last trunk vertebra they nearly meet. 12, Between the ventral or proximal ends of contiguous: neural arches, spaces are left : these are the intervertebral | go ZOOTOMY. foramina ; they serve for the transmission of the spinal nerves. 13. The ribs, slender, flattened bones, articulated to the distal ends of the transverse processes and curving outwards and downwards. 14. The inter-muscular bones, shorter and slenderer than the ribs, but otherwise resembling them : they are articu- lated one to each transverse process on its dorsal side and a short distance from its distal end, and curve upwards and outwards. V. In the caudal vertebree note 15. The hemal arch, formed by the union in the middle ventral line of two heemal processes, springing one from each side of the ventral surface of the centrum near its anterior end ; from the point of union a hemal spine is given off and passes downwards and backwards. The heemal processes give rise to anterior zygapophyses like those on the neural arches, and similarly articulating with small processes from the centrum of the vertebra next in front. 16. In the anterior caudal region the hzemal are very much larger than the neural arches, but passing back the former diminish progressively until there is no difference of import- ance, either in the size of the arches or the length of the spines, between the neural and heemal aspects of the vertebrze. 17. Following the last undoubted caudal vertebra is the small fan-shaped hypural bone, which together with the somewhat flattened posterior neural and haemal spines supports the tail-fin. VI. In the median fins make out 18. The interspinous bones of the dorsal and anal fins, alternating with the neural and hemal spines respec- tively, and attached to them by fibrous tissue. THE COD. g1 In the Whiting the anterior anal fin extends in front of the caudal region, so that most of its interspinous bones are unconnected with the vertebrze and lie free amongst the muscles, 19. The fin-rays, attached, in the case of the dorsal and anal fins, at their proximal ends to the interspinous bones, and forming the actual skeleton of the fins; each is a deli- cate, rod-like bone, transversely jointed and flexible at its distal end (“soft fin-rays’’). In the caudal fin the fin-rays come into direct relation with the hypural bone and the posterior neural and hemal spines. In the Codfish there are 13 rays to the first dorsal fin, 16 to 19 to the second, 17—19 to the third, 18—19 to the first anal, and 17—18 to thesecond, The formula for the fin rays is therefore, D. 13 | 16—19 | 17—19.