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THE 
 
 ANATOMY OF VERTEBRATES. 
 
 VOL. I. 
 
JVorhs by the same Author. 
 
 LECTURES on the COMPARATHrE ANATOMY and 
 
 PHYSIOLOGY of the IKYERTESrvATE Al^IMALS, delivered at the 
 Koyal College of Surgeons. Second Edition (18-j.[;), illustrated by 
 numerous AYoodcuts 8vo. 21^. 
 
 On the CLASSIFICATION and GEOGRAPHICAL DIS- 
 TRIBUTION of MAHMALIA, being the Lecture on Sir R. Reade's 
 Foundation, delivered before the University of Cambridge, in the 
 Senate House, May 1859. To which is added an AppendLx: on the Gorilla, 
 and on the Extinction and Transmutation of Species. AYith 9 Figures 
 on AVood 8vo. 55. 
 
 INSTANCES of the POA¥ER of GOD as manifested in His 
 
 Animal Ci'eatjon : a Lecture delivered before the Young Men's Christian 
 Association, November 1863. With 11 Figures Crown 8vo. la. 
 
 London: LONGMANS, GEEEN, and CO. 
 
ON THE 
 
 ANATOMY OF VERTEBRATES. 
 
 VOL. I. 
 
 FISHES AND EEPTILES. 
 
 BY 
 
 KICHAPtD OWEN, F.R.S. 
 
 SUPEUlNTIiNDENT OF THE NATURAL HISTOKY DEPATlTilENTS OF THE ETITISH MUSEU■^r, 
 FOREIGN ASSOCIATE OF THE INSTITUTE OF FILVNTE, ETC. 
 
 LONDON : 
 LONGMANS, GEEEN, AND CO. 
 
 18G6. 
 
A 
 
 7..- 
 
 PRINTED BY SPOTTisWOODE AND CO. 
 XEIV-STREKT SQUARE 
 
PREFACE. 
 
 The present atork completes the outline of tlie Organisation 
 of the Animal Kingdom which was begun in that on the In\-erte- 
 brates.' They may be regarded as jiarts of a whole, having the 
 same general aim, and, together, form a condensed summary of 
 the subjects of my ' Lectures on Comparative Anatomy and 
 Physiology, according to the Classes of Animals,' delivered in the 
 Theatre of the Eoyal College of Surgeons of England in the 
 years 1852, 1853, and 1854. 
 
 In the choice of facts, as then and since acquired by science, 
 I have been guided by their authenticity and their applicability 
 to general priucijiles. 
 
 In the first, regard has been had to the agreement of several 
 observers, or to the nature of the fact as making it acceptable on 
 the testimony of a single expert. Appearances that require helps 
 to vision are those that call for multi2)lied concurring testimony, 
 and on such alone are offered the descrip)tions and illustrations of 
 the microscopical characters of ' tissues ' premised to most of the 
 chapters. 
 
 In the second ami, the parts and organs, severally the subjects 
 of these chapters, are exemplified by instances selected with a 
 view to guide or help to the power of apprehending the unity 
 which underlies the diversity of animal structures ; to show in 
 these structures the evidence of a predetermining Will, producing 
 
 ' Lecturps on the Comparatire Anatomy and Pliysiology of the Invfrteljratfi 
 Animals. 8vo, lS-13: 2n(i piI. Svo. ISoo. 
 
Ti PREFACE. 
 
 them in reference to a final purpose ; and to indicate the direction 
 and degrees in which organisation, in subserving such Will, rises 
 from the general to the particular. 
 
 Anatomy, or the ' Science of the Structure of Organised 
 Bodies,' is primarily divided into ' Phytotomy,' or that of plants, 
 and ' Zootomy,' or that of animals. When particular pro^-inces, 
 classes, or species of animals have monopohsed the time and skill 
 of anatomists, such special knovrledges have received particular 
 denominations : such as ' Malacotomy,' or anatomy of mollusca ; 
 ' Entomotomy,' or anatomy of insects ; ' Ichthyotomy,' or anatomy 
 of fishes ; ' Ornithotomy,' or anatomy of birds, &c. 
 
 An animal may be dissected in order to a knowledge of its 
 structure, absolutely, without reference to or comparison mth any 
 other, its species being regarded as standing alone in creation. 
 The knowledge so gained, from the very limitation of the field of 
 enquiry, may be most accurate and minute, most valuable in its 
 application to the repair of accident, the remedy of injury and 
 decay, and the cure of disease. Such, e.g., is ' Anthropotomy,' 
 or the anatomy of man, and ' Hippotomy,' or that of the horse. 
 Besides the numerous and excellent works on these special sub- 
 jects, I may cite the ' Traite Anatomique de la Chenille du Saule,' 
 4to., 1762, by Ltonnet ; the ' Anatome Testudinis Europa^te,' 
 foL, 1819, by Bojaxus; the ' Anatomie Descriptive du Melolon- 
 tha vul ff uris, '' 4to., 1828, and the 'Anatomic Descriptive du Chat,' 
 4to., 2 vols., by Sthaus-Dueckheim ; also, in application of the 
 science to art, ' The Camel, its Anatomy, Proportions, &c.,' fob, 
 1865, by Elijah Waltox ; as imsurpassed examples of this 
 monographical kind of anatomical science. As applied to Man it 
 is commonly called ' Human Anatomy,' and is, in strictness of 
 speech, one of the manifold ways of human work. 
 
 But the anatomist may apply himself to a particular organ 
 instead of a particular species, either exhaustively in one animal, 
 or by tracing such organ or system throughout the animal king- 
 dom. The ' Neurotomies' and ' Xeiu-ographies' to which Joseph 
 Swan, e.g., has devoted a laborious life, the ' Osteograiihie ' of 
 
PREFACK. vii 
 
 De Blainville, and my own ' Odontography,' are examples of 
 this way of anatomy. John Hunter assembled the evidences 
 of his labours, in the unique and grand department of his Museum 
 illustrative of anatomy properly so called, in series according to 
 the organ, beginning with the simplest form, fijUowed in succession 
 by the progressively more complex conditions of the same organ, 
 the series culminating, in most cases, mth that which exists in 
 the human frame. The mechanism of the organ is here ruifolded, 
 and its gradations were compared, to discover its mode of work- 
 ing ; and, as ' Physiology ' mainly consists in such determinations 
 of functions or final aim, this kind of investigation of organic 
 structures might be termed ' Physiological Anatomy.' ' 
 
 ' Homological Anatomy ' seeks in the characters of an organ 
 and part those, chiefly of relative position and connections, that 
 guide to a conclusion manifested by applying the same name to 
 such part or organ, so far as the determination of the namesakeism 
 or homology has been carried out in the animal kingdom. This 
 aim of anatomy concerns itself little, if at all, \^^th function, and 
 has led to generalisations of high import, beyond the reach of one 
 who rests on final causes. It has been termed, grandiloquently, 
 ' Transcendental ' and ' Philosophical ;' but every kind of anatomy 
 ought to be so pursued as to deserve the latter epithet. 
 
 A fourth way of anatomy is that which takes a p)articular 
 species in the course of individual development, from the impreg- 
 nated ovum, tracing each organ step by step in its evolution up 
 to the adult condition. It is called ' Embry?i)logy ' and ' Develop- 
 mental Anatomy.' 
 
 A fifth way of anatomy is that which investigates the structure 
 of an animal in its totality, with the view of learning how the 
 form or state of one part or organ is necessitated by its functional 
 connections ivith another, and how the co-ordination of organs is 
 adapted to the habits and sphere of life of the species ; but does 
 
 ' See ' Deseriptivo and Illustrated Catalogue of tlie Thj-siological Series of Com- 
 parative Anatomy in the Museum of the Royal College of Surgeons,' 4to. 5 vols. 
 1832-1840 ; 2nd od. vol. i. 1852. 
 
viii PEEFACE. 
 
 not stop here, having for its main end the comparison of these 
 associated modifications and interdependencies of organs in all the 
 species of animals. As their degrees of affinity and the characters 
 and circumscription of natural groups are hereby illustrated, this 
 way may be termed ' Zoological Anatomy.' 
 
 In the hands of the anatomist the microscope has been mainly 
 applied to the constituent parts of an organ, called ' tissues ;' and 
 the results of such research, combined with those of chemical 
 tests, constitute a sixth sort of anatomy called ' Histology.' It 
 has been termed ' Microscojjical Anatomy,' but this is essentially 
 only a more refined method of the scrutiny of organic parts. In 
 so far, however, as ' Histology ' treats of structure according to 
 the proximate tissues common to different organs, it corresponds 
 i^dth the branch of the science which Bichat, its founder, called, 
 loosely, ' Anatomic Generale.' ' 
 
 Finally, a seventh way in which the highest generalisations in 
 biological science may be aimed at is that which is taken when 
 we pursue investigations of form and structure beyond the animals 
 that are to those that have been. Here, however, the anatomist 
 is limited, as a rule, to such tissues and organs as are petrifiable, 
 e.g., corals, shells, crusts, scales, scutes, bones, and teeth ; but he 
 has been stimulated to a degree of minuteness and accuracy of 
 observation in this field of research to which few of the other 
 ivays and auns would have led him. lu applying the results of 
 such researches to the restoration of extinct species, physioloo-y 
 has benefited by the study of the relations of structure to function 
 requisite to obtain an insight into the food, habits, and sphere of 
 life of such species; and zoology has gained an immense accession 
 of subjects through such determinations, with improved svstems 
 of classification due to the expanded survey of organic nature 
 opened out by ' Pala;ontology.' 
 
 The word ' Anatomy ' is still commonly used to signify ' Anthro- 
 potomy,' or ' Human Anatomy.' Almost all begin the study of 
 the science, as medical students, with the dissection of the human 
 
 ' Aniitomie Gi'^m^ralp, iippliq.uV -i la riiysiolonio, &.■„ Svo. I81II. 
 
PREFACE. IX 
 
 body, and most end there ; but no special anatomy can be rightly 
 and fully understood save on the basis of the general science of 
 wliich it is an integral part. The reason lies in the diversities of 
 organic structure being subordinated to a principle of unity. Of 
 this principle, apprehended as an ' idea ' or truth of reason, the 
 understanding receives evidences in number and comprehen- 
 sibihty differing in different natural groups of the animal king- 
 dom. Illustrations of the ' idea ' will be found in the chapters on 
 the Articulate Province and other parts of the ' Lectures on In- 
 vertebrates,' and, in accordance with the present phase of ana- 
 tomical science, more abundantly in the present Work. True it is 
 that in the first steps to organisation we seem to see a tendency to 
 disintegration, to a reduction of the i)rimary whole to the sub- 
 ordinate characters of a part. The first centre of sarcode, or 
 undifferenced oi'ganic matter, however originated, yet with de- 
 finite tendencies to formal character and course of growth (as in a 
 Foraminifer, e.g.), buds forth a second centre of identical nature; 
 this a third, and so on, until a group of such exists as an assem- 
 blage of coherent homogeneous or like parts. These, if clothed by 
 a delicate crust of characteristic structure, constitute a chambered 
 shell, straight, bent, or spiral, each chamber occupied by the 
 same vital sarcode, outshooting filamentary food-getting processes 
 through the shell-pores ; in which seeming comjjlexity the inci- 
 pient unity or ' wdiole ' is reduced to the ' part ' called innermost 
 chamber, or is conceivable as a lesser whole in the larger one. 
 The Annelides offer a familiar example of such repetitions of a 
 pi'imal complexly organised whole, by successive buddings in a 
 linear direction ; the nerve-centre, the muscles, the skeleton-seg- 
 ment, perhaps heart and gills, being regularly repeated in each, 
 and thereby reducing the original whole to one of many parts of 
 a segmented unit}^ 
 
 Almost every organ in the pi'ogressively differenced organism 
 initiates itself under a similar cliaracter of irrelative rej^etition, 
 suggestive of operance akin to that of inorganic polar growths, as 
 in a groujj of crystals, wherein each exemplifies the characters 
 
I PREFACE. 
 
 of the mineral or crystalline species, but is subject, like vital 
 growths, to occasional malformation. 
 
 As this jmnciple of growth by multiplication of like parts is 
 manifested more commonly and extensively in plants, it is illus- 
 trated in the ' Invertebrate Volume ' ' under the term ' Vegetative 
 E-epetition.' In the vertebrate series it is exemplified by the 
 hundreds of similar teeth in the jaws of many of that low class 
 {Pisces) in which true dentinal teeth first appear in the animal 
 kingdom. The numei^ous and similar many-jointed terminal divi- 
 sions of the pectoral limbs of the fishes thence called ' Eays,' the 
 multiplied similar endoskeletal segments of the vertebral column of 
 these and other cartilaginous fishes, of murasnoids and serpents, are 
 likewise lingering exemjjlifications of the low irrelative j^rinciple 
 of development. 
 
 In the vertebral embryo the first aj)pearance of the parts of the 
 skeleton, in gristle or bone, is a segmental one ; in fishes the mus- 
 cular system shows much, and in all Vertebrates a little, of the 
 like segmental constitution of the trunk ; the same idea is suo-o-ested 
 by the symmetrical and parial origins of the nerves, and pjhy- 
 siologists have mentally recognised a corrcspondino- seo-mental 
 condition of the myelon or spinal chord, which is visibly exem- 
 jjlified in certain fishes. But these appearances are concealed bv 
 the general tegument ; not exposed, as in the Articulates, in which 
 the segmented skeleton is at the same time tegument. A Verte- 
 brate may be defined as a clothed sum of segments. But in this 
 highest i^rovince of the animal kingdom growth by repetition of 
 parts rapidly gives place to the higher mode of development by 
 their differentiation and correlation for definite acts and complex 
 functions. iSTevertheless, I am constrained liy evidence to affirm 
 that in the vertebrate as in the invertebrate series there is mani- 
 fested a principle of development through polar relations, work- 
 ing by repetition of act and by multiplication of like parts, con- 
 trolled Ijy an opposite tendency to diversify the construction and 
 enrich it with all possible forms, proportions, and modifications of 
 
 ' Op, cil, 211(1 rd. p. hW. 
 
riiEFACE. xi 
 
 parts, conducive to the fulfilment of a pre-ordained purpose and 
 a final aim : these opposite yet reciprocally complemental factors 
 co-operating to the ultimate result, i\'ith different degrees of dis- 
 turbance, yet without destruction, of the evidences of the typical 
 unity.' 
 
 Thus, the dentition of Vertebrates will be seen to pass from 
 irrelative sameness and multitude to the state in which the teeth 
 in the same jaw are classed according to diversities of form and 
 function, and where each tooth has its own character, bears its 
 own name and symbol. 
 
 In like maimer may be traced the gradations by which the 
 terminal divisions of the limb ascend from the multitude of many 
 jointed rays, swathed in a common sheath of integument, to indi- 
 vidual freedom, with reduction of number and of joints, and with 
 a special form and action ; according to which each digit in the 
 liiunan hand, e.g., has its sjiecial name and symbol, and can be 
 combined in action with any other digit for a particular purpose. 
 The same jirinciple, through reduction of number with differen- 
 cing of the parts, is exemplified by the lact that the competent 
 anthropotomist "wdll distinguish and name each of the four and 
 twenty 'true vertebra3' of the human skeleton. 
 
 In the Mammalian class there are four muscular pulsatile 
 cavities concerned in the propulsion of blood ; l3ut they difier from 
 those cavities in the Annelide, in each having its own special 
 structure and powers, and being in such relation with another 
 cavity that the whole can combine to effect two complete but 
 mutually related systems of circulation, the four pulsatile cavities 
 constituting one complex and perfect ' heart.' The ox has four 
 bags for the digestion of food ; but they differ from those cavities 
 of the Polygastriu, not only in their minor number and more de- 
 finite structure as bags, but l^y each performing a distinct part in 
 the process of digestion, and combining with the rest, in mutual 
 
 > This idea will be found more fully exemplified in my work, ' Trincipes d'Ostuolo- 
 gie Comparee,' 8vo. (Paris) 1855, p. 366, et .-eq. 
 
xii _ PREFACE. 
 
 subserviency, to the completion of the most perfect act of that 
 function, the conversion, namely, of grass into flesh. 
 
 Thus, in tracing through the animal series this course of parts 
 and organs, we pass from the many and the like to the few and 
 the diverse. 
 
 A ' homologue ' is a part or organ in one organism so answer- 
 ing to that in another as to require the same name. 
 
 Prior to 1843 the term had been in use, but vaguely or 
 wrongly.' 'Analogue' and 'analogy' were more commonly 
 current in anatomical works to signify what is now definitely 
 meant by ' homology.' But ' analogy ' strictly signifies the 
 resemblance of two things in their relation to a third ; it im- 
 plies a likeness of ratios. An ' analogue ' is a part or organ in 
 one animal which has the same function as a part or organ in 
 another animal. A ' homologue ' is the same part or organ in 
 difl^erent animals under every variety of form and function. 
 
 In the Draco volans (Vol. I. fig. 163) the fore-limbs are 
 ' homologous ' with the wings of the bird (Vol. II. fig. 1 ) ; the 
 parachute is ' analogous ' to them. 
 
 Relations of homology are of three kinds ; the first is that 
 above defined. When the ' basilar process of the occipital bone ' 
 in Man is shown to answer to the distinct bone called ' basioc- 
 cipital ' in the fish, the special homologij of that anthropotomical 
 process is determined ; as such homologies are multiplied, the 
 evidence grows that man and fish are constructed on a common 
 type. 
 
 A wider relation of homology is that in which a part or series 
 of parts stands to such general type. When the ' basilar process 
 of the occipital bone 'is determined to be the 'centrum' of the 
 last cranial vertebra, its general homologi/ is enunciated. 
 
 The archetype skeleton represents the idea of a scries of 
 essentially similar segments succeeding each other in the axis 
 
 ' ' Les orgaiK'S d.-s sens sont Iiomo/oqurs, ooiniiio s'exprimovait l;i philosopliip 
 alleman.lf ; c'cst-ii-dirp, qu'ils sont analogues clans lour nioclr do doroloppmuent.'— 
 (Tooffrny ,St. Hihiiro, A)niah'S des Sciences Nat., torn. xii. 182.">, p. ;U1, 
 
PREFACE. xiii 
 
 of the body ; such segments being composed of parts snnilar in 
 number and arrangement. Accordingly, a given part or appen- 
 dage in one segment is repeated in another, just as one bone is 
 represented in the skeletons of different Vertebrates; and this 
 representative relation in the segments of the same skeleton is 
 '' serial homology.' As, however, the parts can be namesakes 
 (inly in a general sense, as ' centrums,' ' ribs,' &c., and since they 
 must be distinguished by special names according to their special 
 modifications, as ' basioccipital,' '' mandible,' ' coracoid,' 'humerus,' 
 &c., I have called such serially related or repeated parts ' homo- 
 types.' The basioccipital is the homotype of the basisphenoid, 
 and the humerus is the homotype of the femur : when the basi- 
 occipital is shown to repeat in its ' vertebra ' the element which 
 the ' odontoid process ' represents in the succeeding vertebra, or 
 the basisphenoid in the preceding one, its ' serial homology ' is 
 indicated. 
 
 The extent to which serial homologies can be determined 
 shows the degree in which vegetative repetition prevails in the 
 oro-a]iisation of an animal. 
 
 o 
 
 The study of homologies is comparatively recent; much of this 
 field of research remains for future cultivators, especially in 
 regard to the muscular and nervous systems. 
 
 When engaged in the ' third way ' of anatomy, and in making 
 known the results of such labour as apjolied to the skeleton,' I 
 found a great impediment in the want of names of bones. For 
 these, when first studied, had been mostly described under phrases 
 suggested by forms, proportions, or likeness to some famihar 
 object, which they present in the human body. A reform of this 
 nomenclature was an essential first step, and it is gradually 
 making its way against the usual impediments. 
 
 The best workman uses the best tools. Terms are the tools of 
 the teacher ; and only an inferior hand persists in toiling with a 
 clumsy instrument when a better one lies within his reach. But 
 ' he has been used to the other.' No doubt ; and some extra 
 
 ' On the Archetype and Homologies of the Vertehrate Skeleton, 8vo. 1848; and 
 On the Nature of Limbs, 8vo. 1849. 
 
xiv PREFACE. 
 
 practice is necessary to acquire the knack of applying the new 
 tool. But in this acquisition a small capital of trouble will have 
 been invested with a sure return of large profits. A single sub- 
 stantive term is a better instrument of thought than a parajohrase.' 
 But the substitution of such terms for definitions is still more 
 advantageous when they are susceptible of becoming adjectives by 
 inflection. Thus the term ' notochord ' for ' chorda dorsalls ' or 
 ' dorsal chord ' enables one to predicate of species or groups of 
 vertebrates as being ' notochordal ; ' that single ejoithet imj^lying 
 that the embryonal body in question is^ in them, persistent. A 
 like advantage cleaves to ' myelon ' for ' chorda spinalis ' or 
 ' spinal chord ;' the Physiologist, e.g., can then speak of 'myelonal 
 functions,' and the Pathologist of 'myelonal' disease, with the cer- 
 tainty of being understood to signify properties and affections of 
 the ' spinal chord ;' not, as in ' spinal disease,' that of its case, or 
 ' spinal column.' In regard to the part so called and its con- 
 stituent ' vertebras,' their modifications are so many, so charac- 
 teristic, so imi^ortant, especially in the application of Anatomy to 
 Palaaontology, that I was early compelled in the latter kind of 
 labour to substitute single pliable terms for the jjhrases ' trans- 
 verse process,' ' obhque ' or ' articular process,' ' body of the 
 vertebra,' ' vertebral lamina,' ' vertebral rib,' ' sternal rib,' &c., 
 by which the parts of the ' vertebra ' were then designated. 
 
 But the single names of jjarts and constituents of the skeletal 
 segment called ' osteocomma ' or ' vertebra ' have not merely the 
 advantage above illustrated, as where the adjective ' neurapo- 
 physial ' can be applied to a ' ridge,' notch, or ' foramen,' in the 
 vertebral lamina (neurapojihysis) ; the vertebral terminology in 
 use in the present Work indicates a profound truth which is 
 hidden by the language of anthropotomy. The terms ' pleur- 
 apophysis' and ' ha3mapophysis' imjily parts of the segment corre- 
 
 ' ' Superoceipital,' e.g., for ' pars occipitalis sh-ictc sic dicta partis occipitalis ossis 
 spheno-occipitalis ' of the emiai'iit anthropotumist Soem5leeing. (See Table op 
 Synonyms, &c., appended to Vol. II.) Similarly, in the present Work, I use the word 
 ' Vertebrate ' as a suhstantive. We do not speak of a ' Confederate ' animal, and the 
 added word is as unnecessary in regard to the ' Vertebrate ' one. 
 
I'REFACE. XV 
 
 lative in independency of development and elemental grade with 
 the ' neiirapophysis,' — a fact of high generalisation not only 
 ignored but impliedly contradicted by the reckoning of the 
 ' vertebral rib ' and the ' sternal rib,' or ' rib-cartilage,' as bones 
 distinct from, and countable with, that which the anthropotomist 
 equally holds to be a single bone under the name ' vertebra.' 
 Furthermore, as each distinctly recognisable part or thing must 
 have its verbal sign, for the purposes of intelligible predication of 
 its nature and qualities, the course of knowledge of the vertebral 
 column would have enforced the origination of such signs irre- 
 spective of the abstract need of improving the mental tools oi' 
 anatomy. 
 
 When it came to be discovered that ' the transverse process 
 of a cervical vertebra ' Avas other, and more than, as well as 
 formally different from, the ' transverse jn-ocess of a dorsal ver- 
 tebra,' and that this process Avas a different thing from the 
 ' transverse process ' of a ' lumbar ' or ' sacral ' vertebra, the re- 
 sults of such analysis necessitated the creation of a correspondent 
 nomenclature. 
 
 ' Transverse processes,' as such, ai-e, as Johannes Mullek 
 first pointed out, of tAvo kinds ; they are, in relation to hori- 
 zontally disposed vertebrates, ' upper ' and ' lower ' — in our no- 
 menclature, ' diapophyses ' and ' parapophyses.' Both kinds exist 
 in the ' transverse processes ' of the neck from the crocodile 
 upwards ; and the seeming unity of the outstanding jiart in 
 birds and mammals is caused by the soldering thereto of a third 
 element — the ' cervical rib ' of the herpetotomist, the ' styloid 
 process' of the ornithotomist.' 
 
 Referring to the ' Introductory Chapter ' of the ' Archetype 
 of the Vertebrate Skeleton,'^ for further illustrations of the 
 advantage of single Avell-defined terms, I will here only show 
 hoAV such advantage may be affected by reason of an unsettled 
 definition. 
 
 The anatomical term ' organ ' has diverse significations. The 
 
 I Macartney, Art, 'Birds,' Ecfs' Cyclopwdia. ' Op. cit. 
 
xyi PllEFACE. 
 
 chief constituent idea is ' work for a special end :' thus, the heart 
 is the ' organ ' of circulation ; the lungs, the ' organ ' of respira- 
 tion ; the Hver, the ' organ' of bilification, &c. But also, incipient 
 stages in the development or formation of parts are called the 
 'organs' of such; e.g., the periosteum is the 'organ of bone,' 
 the pulp is the ' dentine organ ; ' other parts of the growing 
 complex tooth are the ' enamel oi'gan,' ' cement organ,' &c. The 
 parts in which independent cells, with special powers, originate, 
 are also called the ' organs ' of such ; as, e.g., the ovary is the 
 ' organ of ovvilation ;' the testis the ' organ of semination.' It 
 is obvious, however, that the part which the more or less con- 
 densed cellular basis, or ' stroma,' of the ovary or the testis may 
 take in the production of the germ-cells or sperm-cells and sf)erma- 
 tozoa is very different from that which the heart performs in the 
 motion of the blood, or the lungs in the mutation of the air 
 inspired. 
 
 Zoological anatomy is now an indispensable instrument to the 
 classifier, if not to the determiner, of the species of animals. The 
 anatomist properly so called, but commonly qualified as the 
 ' comparative ' one, makes known the results and appKcations of 
 his comparisons of structure in zoological as well as homologi- 
 cal or anatomical works. The ' Regne Animal ' and the ' Lepons 
 d' Anatomic Comparee ' of Cuvier exemplify these different appli- 
 cations and ways of exposition of his science. 
 
 As a zoologist or classifier, the anatomist avails himself of the 
 definite modification and full develojjment of a part or organ, in- 
 dicating, and predicating of such conditions by special terms, 
 for the required characters. The ' fin,' the ' hoof,' the ' paw,' the 
 ' foot,' the ' hand,' are to him so many kinds of limbs, the presence 
 or absence of which serve to differentiate his groups ; anthropo- 
 tomical terms of parts of the brain reaching their full and cha- 
 racteristic development in Mammals or in ]\Ian, e.g., 'fornix,' 
 ' corpus callosum,' ' hippocampus minor,' ' posterior cerebral lobe,' 
 &c., serve and are used, absolutely, for the same end ; so likewise 
 
PREFACE. XTii 
 
 with regard to special forms and proportions of teetli indicated by 
 tlie terms ' canine,' ' carnassial,' ' tusli,' &c. 
 
 The absolute way in which the things or characters so desig- 
 nated are affirmed or denied in zoological definitions is essential to 
 their purpose. 
 
 Amongst the characters by which CuviEii differentiated the 
 hoofed quadrupeds which he had restored from their frag- 
 mentary fossil remains in the building-stone of Paris, the most 
 unportant in his estimation was ' tlie presence of canines ' in 
 one i^Palceotheriian), their absence in the other ( Aiwplotlu' riuiyi y 
 Nevertheless, Homological Anatomy easily indicates in the series 
 of nine teeth in the ' morceau de conviction,'^ on which the 
 character was founded, the teeth answerable to those which, 
 because their pointed crowns projected beyond their neighbours 
 in the Palajothere, were called and characterised as ' canines.' 
 Now here was a temptation to an aspirant to scientific notoriety 
 ' to meet ' the great anatomist ' by a flat contradiction,' and 
 ' affirm that the Anoplotherium possessed canine teeth.' I allude 
 to such abuse because, of late, a practice has been cree[>ing 
 in, to the opprobrium of some of our English zootomists, of repre- 
 senting a zoological definition of a part which an anatomist may 
 have given in a classificatory work, as the exponent of his homo- 
 logical knowledge and descriptions of such part in its various 
 modifications and grades of development. 
 
 CuviEE, in his characters of the order Bimana, affirms that 
 Man is the only animal possessing ' hands ' and ' feet : ' — 
 ' L'homme est le seul animal vraiment biinane et bipede."^ The 
 Quadrumana are distinguished as having ' hands' instead of ' feet,' 
 a ' hand' being defined as having the thumb opposable — ' le pouce 
 libra et opposable aux autres doigts, qui sont longs et flexibles.' ' 
 
 The aim of the author in the zoological work above cited was 
 to impart obvious and easily apprehended diflferential characters 
 
 ' ' Le plus important fut celui cjui m'apprit que cette espece n'a point de dents 
 canines.' — Bechcrches si'r les Osseinens Fossilcs, 4to. 1822, torn. iii. p. 14. 
 
 2 Ibid. ' Eigne Anim.al, torn. i. p. 70. 1829. ' Ibid. p. »o. 
 
 VOL. I. a 
 
xviii PREFACE. 
 
 of the organ which observation had shown to define the groups. 
 The naturalist, thus enabled to place his subject in its proper 
 class or order, is not concerned, as such, in knowing the homo- 
 logical or transcendental relations of the part or character which 
 has afforded him the means of effecting what he wished to do. 
 
 LiNNiEDS, to whom mainly is due the discernment of the power- 
 ful instrument of well-defined terms in acquiring a systematic 
 Science of Nature, and to whom we owe our best knowledge of 
 its use, so named the guiding fiarts of plants and animals, for such 
 arbitrary or special ap23lication, in botany and zoology : to this 
 end he differentiates the ' bract,' the ' spath,' the ' sepal,' the 
 ' petal,' from the ' leaf,' as things distinct. 
 
 What would be thought of the botanical critic who, quoting the 
 definition of the flowers of Cyperaceous plants, as consisting, for 
 example, of ' glumes,' should meet the statement by affirming that 
 they were ' noticing but little bracts,' and who, then, with a show 
 of profounder research, should proceed to expound the 'bract' as 
 being the first step by which the common leaf is changed into a 
 floral organ ? The answer is obvious. But what next mio-ht be 
 said, if it were pointed out that the objector had obtained this 
 very notion from the ' Prolepsis Plantarum,' or other homological 
 writings of the author criticised, where such philosophical con- 
 siderations, foreign to the classificatory work, were the proper aim 
 and. object? So, with regard to the zoological definitions and 
 characters of CuviKE. Those which I have cited are open to the 
 opposite averment that, ' The " hind hands " of the Quadrumana 
 are nothing but " feet ; " ' and the contradictor might then proceed 
 to demonstrate, with much show of original research, the homoloo-y 
 of the ' astragalus,' ' calcaneum,' ' cuboides,' ' cuneifonn bones,' 
 &c., in order to establish his discovery that a hand and foot are 
 all one. 
 
 It IS true that if the homological descriptions in the ' Lerons 
 d' Anatomic Comparce ' had been quoted, as well as the zoological 
 definitions in the ' Regne Animal,' the immortal author of' the 
 latter work would be shown to have had previous possession of 
 the pretended discovery. Moreover, in the ' Cinquieme Lejon, 
 
TKEFACE. xix 
 
 Articles VII.-IX. " Des os du pied,"" the frame of tlie hind 
 feet of Man, Ape, Lion, Seal, Elephant, &c., is shown to consist 
 of homologous bones. Nevertheless the great zootomist, in his 
 labour aud character as zoologist, does not hesitate to define and 
 differentiate the ' foot,' the ' hand,' the ' paw,' the ' fin,' and the 
 ' hoof,' respectively : nor does he deem the demonstration of the 
 unity underlying the diversity to make the ' man ' an ' ele])hant ' 
 or a ' seal,' any more than it makes him a ' dog ' or an ' ape ' ! 
 
 The ' corpus callosum ' is defined as ' a horizontal mass of trans- 
 verse fibres covering the lateral ventricles, and exposed by divari- 
 cating the cerebral hemispheres.' If a group of manmials want 
 such commissural fibres, and another group possess them, the 
 classifier will avail himself of a well-defined term expressing such 
 difference, without prejudice to his recejition of any homological 
 determination of the parts, or their rudiments,^ in anatomical 
 works of the applier of the term. 
 
 Only by ignoring such indication of the ' rudlmental com- 
 mencement of the corpus callosum,' may a semblance of superior 
 knowledge be assumed by him who asserts, as an antagonistic 
 proposition to an affirmation of its absence as a zoological cha- 
 racter, that the Marsupialia, e.g., do possess the ' great com- 
 missure,' or ' corpus callosum.'^ 
 
 So likewise with other well-defined parts of the human brahi, 
 the homologues of which may not be traceable to the same extent 
 down the mammalian series. Kuhl, e.g., in Ateles Bdzehuth,^ 
 TiEDEMANN in the Macafjue'"^ and Orang," Van der Kolk and 
 VeOlik in the Chimpanzee,' and myself in the Gorilla,' had 
 
 ' Lemons d'Auat. Comparee, vol. i. 1799. 
 
 - As given in the "Philosophical Transactions' for 1837, p. 41. 
 
 = Proceedings of the Eoyal Society, No. 72, aud March 23, 1865. 
 
 ^ Beitrage zur Zoologie und vergleichenden Auatomie, 4to. 1820, zweite Ahtheihuig, 
 
 p. 70, Taf Tii. 
 
 5 Icones cerebri Simiarum, fol. 1821, p. 1-1, fig. iii. 2. 
 
 = TreTiranns, Zeitschrift fiir Physiologic, Bd. ii. ,S. 25, Taf iy. 
 
 ' Nieuwe VerhandUngen der erste Klasse ran liet Koningl. Nederlandsche lustituut. 
 Amsterdam, 1849. 
 
 » Fnllerian Lectures ou Physiology, Eoyal Institution (jidaroh 18, 1861); reported, 
 with copies of diagrams, in ' Athenpeum,' March 23rd, 1861, p. 395. 
 
XX PREFACE. 
 
 severally shown all the homologous parts of the human cerebral 
 organ to exist, under modified forms and grades of development, 
 in Quadrumaua. But because the presence or absence of the 
 ' ergot,' or ' pes hippocampi minor,' as defined by Tiedejiaxx 
 (see Vol. II. p. 273 of the present Work), had been used as a 
 zoological character, the anatomical world has been deluged, since 
 the date of the last under-cited work, -\\ith descriptions and figures 
 of the homologous part in the Orang and other Quadrumana, as a 
 new discovery mainly serviceable as a battery of contradictory 
 affirmations. 
 
 Nevertheless the distinctive characters of the human brain, iuch 
 as the manifold and complex convolutions of the cerebral hemi- 
 spheres, their extension in advance of tlie olfactory lobes and 
 farther back than the cerebellum, thereby defining a posterior 
 lobe, with the corresponding ' horn of the lateral ventricle ' and 
 ' hippocampus minor,' are as available to the zoologist in classifi- 
 cation as are the equally peculiar and distinctive characters of 
 the calcaneum, hallux, and other structures of the foot. 
 
 So much, in connection with the ' fifth way ' and application of 
 anatomy, I regret to find myself compelled to state, in order to 
 expose and stigmatise procedures which consist in representing 
 the homological knowledge and opinions of an author bv his de- 
 finitions in a purely zoological work, and in suppressing all re- 
 ference to the descriptions and statements in the anatomical 
 writings of the same author, where his actual knowledge and 
 opinions on the nature and homology of parts are given, and 
 where alone they can be expected to be found. 
 
 Somewhat analogous to the course of observation pursued 
 through the animal kingdom, from the lowest to the hicrhest 
 species, is that which traces each organ through the several 
 phases of its development in the same species. 
 
 The right use of sense, in both ways, stores the understanding, 
 empirically, with a series of facts, as the raw matei-ial for reasoning 
 up to their principles. But Embryology has this inferioritv, that 
 
PREFACE. x.\i 
 
 every species is such ah initio, and takes its own course to the full 
 manifestation of its specific characters, agreeably with the nature 
 originally impressed upon the germ. 
 
 A perch, a newt, a dog, a man, does not begin to be such only ^ 
 when the embryologist may discern the dawnings of their respect- ( 
 ive specific characters. The embryo derived its nature, and the j 
 potency of self-development according to the specific pattern, from , 
 the moment of the impregnation ; and each step of development 
 moves to that consummation as its end and aim. 
 
 This truth has been masked to some apprehensions by the 
 course of the developmental steps from the general to the par- 
 ticular ; the initial ones, more especially, otFering likenesses or 
 analogies to finished lower species exemplifying degrees of organi- 
 sation in the animal kingdom. Each step differs in degree of 
 dift'erence from the analogous grade at which a lower species rests, 
 and inversely as the advance of such species. Accordingly, the 
 less the degree of difference, and the wider the resemblance or 
 analogy spreads between the embryonal phase and the parallel 
 grade in the series of species. 
 
 The formation of the germ-mass ( Vol. I. figs. 1-4, 422,452) — 
 the first step after impregnation — is a general phenomenon in 
 animality (Vol. ' On Invertebrates,' figs. 48-5C, 73, 74, 80-84, 
 181, 209-212, 2,32) ; thereat and thereby the man resembles and 
 behaves like the monad.' But, the germ-mass completed, the 
 vertebrate at once circumscribes itself or withdraws into its 
 vertebrality. The proteine substance is the seat of a chemical 
 differencing, leading to excess of albumen along one tract, 
 balanced by excess of gelatine along a parallel tract. Thus are 
 laid down the bases of the myelencephalon and vertebral axis. 
 The ' notochord ' is soon followed by the protovertebral specks 
 in double parallel series (Vol I. fig. 5; Vol.11, fig. 133): the 
 embryonal trace is established, and it is one of a vertebrate. 
 
 The formation of neural and hasmal arches next follows ; and 
 
 ' Compare the above-cited figurer, with fig. 17, ' Lectures on Invertebrates,' 2nd 
 i-d. p. 29. 
 
xxn PREFACE. 
 
 the phenomenon of the appearance of the lattei', in which the 
 blastema! is accompanied by a vascular arcli, ■\'\'ith clefts inter- 
 vening between contiguous arches, especially at the fore part of 
 the embryo, has led to the idea that a reptile, bird, or mammal, 
 is a fish before it becomes what it is tending to. True it is, that 
 the embryos of these air-breathers float in fluid, and not any of 
 them breathe the air until birth or exclusion, or near to exclusion ; 
 but they do not breathe water : the oviparous air-breather has one 
 kind of temporary lung, the mammiferous embryo another kind, 
 each alike special to the class. From the vascular loops accom- 
 panying the hffimal arteries branchias are not developed ; one only 
 of the interhajmal fissures is deepened on each side, brought into 
 communication with the i}harynx, and straightway converted into 
 the ' eustachian tube,' according to the precocious rate of gro\vth 
 and development characteristic of the special organs of sense 
 and their appendages. No true branchial or piscine breathing 
 apparatus is at any time, or in any degree, manifested in the 
 embiyo of an air-breathing vertebrate. The deepening and open- 
 ing of several interhfemal fissures in the embryo of a perch, and 
 the subsequent course of development therewith of gill-arches and 
 "■ills, Avith their subservient mechanism of branchiostesal ravs and 
 the opercular lid or door, are as distinctive manifestations of the 
 original nature of the fish, as is the vascular lining of the egg that 
 of the bird, or the vascular arrangement for borrowing breath 
 from the mother that of the foetal mammal. 
 
 At the incipient stages of these provisional and deciduous 
 respiratory conditions the circulation in the embryo lizard, fowl, 
 beast, is like that of a fish in its simplicity ; but, as Teevieaxus' 
 rightly remarked, it is far from being identical ; there are, indeed, 
 characters of the circulating organs at this grade of simplicity, 
 which not only distinguish the embryo of the air-breather from 
 that of the water-breather, but also the embryo of the mammal 
 from that of the bird or reptile ; so soon is the course of deve- 
 lopment afl:ected by the specific taint ! 
 
 1 G. E. in 'Zeitschrift furPliysiologir,' vol. iy. ; ;iiul • Edinluirgii Ni-^v riiilosophical 
 Journal,' 1832, vol. xiii. p. 75-86. 
 
PREFACE. xxiii 
 
 Marked deviations from the archetype characterising existing 
 species are directly approached in the progress of development. 
 
 If, as, e.g., in a thoracic or jugular fish, the position of the 
 pelvic limbs departs from the typical one, these limbs bud out in 
 the embryo in that special and anomalous jilace. When a higher 
 species departs from type by a thoracic position of the scapular or 
 occipital limbs, they likewise bud out in such special position. In 
 both cases the ha;mal arch, sustaining such appendages, is libe- 
 rated from the rest of its segment for the special needs of the 
 species, and the embryo of such never shows it fixed. At most, 
 perhaps, the general character and typical connections may be 
 indicated by the closer contiguity of the detached scapular arch to 
 the rest of its proper occipital segment; as, e.g., in the embryo of 
 birds and lono'-necked ruminants, to be removed to a distance 
 determined by the later growth of the series of verteljra; inter- 
 vening between head and chest. 
 
 To infer from such developmental phenomena that the throat- 
 fins of the cod are not the displaced homologues of the hind legs 
 or pelvic limbs of air-breathers, and that the fore-legs of such are 
 not the homologues of the typically situated and connected scapu- 
 lar limbs of fishes, is an abuse or misuse of the empirical facts 
 ascertained by observation of embryonal phenomena. 
 
 In like manner the developmental phenomena of the skull of 
 an avian and mammalian species, succeeding those that broadly 
 and intelligibly mark out the four pairs of neurapophj-ses and 
 corresponding hremal arches, plainly indicating the segmental or 
 vertebral type of the skull, depart therefrom to attain the par- 
 ticular character of the face and mouth of the species. After 
 the first budding indications of the halves of the maxillary (fore- 
 most cranial hajmal) arch, the development of it, as upper jaw, 
 with that of the palate, pterygoid, and zygomatic appendages, 
 obeys the impress of impregnation, and proceeds directly to es- 
 tablish the specific characters of such jaw in the particular bird 
 or beast ; the points of ossification, their deposit in membrane or 
 o-ristle, and subsequent growth, having no other or deeper signifi- 
 
xxiT PREFACE. 
 
 cation. If a species be gifted with acute hearing, and the move- 
 ments of the ear-drum require several ossicles^ these, like the 
 labyrinth, grow to full size in the embryo, appropriating the 
 blastema of the contiguous hsemal arch, and projiortionally re- 
 ducing, by aiTesting the development of, the pleurapophysis of 
 such arch. The inherited tendency to a sj^ecial or specific form 
 which thus influences early developments and growth of parts has 
 misled some who ha^'e mistaken such for homological or archetypal 
 characters. But the determination of these characters is arrived 
 at by other routes of research ; and, so reached, such determination 
 serves to explain many of the jihenomena of development which 
 otherwise would remain as mere empirical facts. 
 
 Embryology, e.g., shows that in the human fcetus the sternum 
 is developed from a series of ossific centres (Vol. II. p. 55.5, fig. 
 SGi), whilst the co-articulated cla\dcle — as long a bone — is de- 
 veloped from a single ossific centre, and a contiguous rib, though 
 of greater length, is also hardened from a single ossific centre ; 
 but embryology affords no explanation of the reason of such dif- 
 ference. That is afforded by a knowledge of the archetype 
 skeleton, which teaches that the sternum — reckoned as a sino-le 
 bone in anthropotomy — consists of a series of vertebral elements, 
 but that the rib and the clavicle are single elements. 
 
 Embryology shows that the canon-bone of a ruminant, re- 
 garded as a single bone by the veterinarian, is developed from five 
 ossific centres ; two on the same transverse line near the middle, 
 one on the upper, and a pair which soon coalesce at the lower end. 
 But no clue is afforded to the signification of these several cen- 
 tres : embryology is no criterion of their homologies ; these are 
 determinable on other grounds or ' ways of anatomy.' 
 
 A knowledge of the ' Nature of Limbs,' derived from homolo- 
 gical studies leading to a recognition of the archetype, could alone 
 determine that two only out of those five centres represent dis- 
 tinct bones in the typical pcntadactyle foot of the mammal ; the 
 rest having no such signification, but serving to jierfcct the ulti- 
 mate growth as ' epiphyses.' So likewise with the collar-bone 
 
PREFACE. XXV 
 
 and rib. At a period long subsequent to the deposition of the 
 first centre of bone, a second appears at the sternal end of the 
 liuman clavicle, and two are added to complete the head and 
 tubercle of the rib, the shaft of which had been ossified by growth 
 from a single centre. 
 
 Recognition of the archetype skeleton elucidates the empirical 
 facts of embryology, and teaches us to distinguish laetween the 
 points of ossification of a bone in a higher vertebrate wliich sio-- 
 nify or ansAver to bones that retain their distinctness in lower 
 vertebrates, and the points of ossification which merely help out 
 the growth or have their final purjjose in the exigencies of the 
 young animal. A lamb or foal, e.g., can stand on its fore legs 
 shortly after it is born, and soon begins to run and bound. The 
 shock to the limbs themselves is broken at this tender age by the 
 cushions of cartilage at the ends of the shafts, and which continue 
 for some time to be interposed between the ' epij)h3-ses' and ' dia- 
 physis.' The jar that might affect the large and pulpy brain oi 
 the immature man is similarly dilfused and intercepted by the 
 ' epiphysial ' extremities of the vertebral centrums. 
 
 Such final purpose in the several centres of ossification of the 
 vertebral bodies and the long bones of the limbs of mammals does 
 not apply to those of reptiles ; and no epiphyses with interposed 
 cartilage attend the growth of the limb-bones of saurians and 
 tortoises. But, wdien tlie reptile moves by leaps, ossification of 
 the long limb-bones by distinct centres again prevails ; the ex- 
 tremities of the humeri and femora are ' epiphyses ' in the frog. 
 
 Embryology affords no criterion between the ossific centres that 
 have a ' homological ' and those that have a ' teleological ' signifi- 
 cation. A knowledge of the archetype skeleton is requisite to 
 teach how many and which of the separate centres that appear 
 and coalesce in the human, mammalian, or avian skeleton, re- 
 present and are to be reckoned as distinct bones, or elements of 
 the archetype vertebra. For the want of this guide great and 
 estimable anatomists have gone astray. Thus Cutiee, comment- 
 incr on the arbitrary enumeration of the single bones in the human 
 
xxvi PREFACE. 
 
 skeleton, affirmed tliat to learn their true number in any given 
 species we must go to the first osseous centres as these are 
 manifested in the fostus ; ' and Geoffroy St. Hilaire^ concurred 
 in this view. 
 
 In the cartilages called ' epiphysial,' that eke out the ends 
 and margins of bones, ossification begins later than does that of 
 the bone itself. The times of appearance of the osseous nucleus 
 in the coracoid process and acromion of the human scapula well 
 exemplify this difference; in the coracoid, e.g., at the first year, 
 in the acromion at the fifteenth year. Embryology teaches the 
 facts but affords not the reason. 
 
 Special homology shows that the coracoid is a distinct bone, the 
 acromion a mere jjrocess, in the vertebrate series. General ho- 
 mology gives the ground of the distinctness — the coracoid being 
 the hajmapophysis of the haemal arch of which the scapula proper 
 is the pleurapophysis. In most mammals this haemapophysis is 
 stunted and terminates freely, like that of the last (floating) rib. 
 In Monotremes it attains and articulates with its hsemal spine, as 
 in the ' true rib,' and keeps this normal extent and condition 
 through all the lower vertebrates. It is the typical state of the 
 coracoid, which is departed from in all vertebrates above Mono- 
 tremes : but such typical state is not passed through in the 
 covirse of their development. As in that of other modified hfemal 
 arches, the maxillary, e.g., so in the scapular arch, the special con- 
 dition of the aborted hajmapophysis is gained directly, not through 
 any intervening transitory manifestation of the general character. 
 So far is embryology from being a criterion of homology. 
 
 In regard to what I have reckoned a ' seventh way of ana- 
 
 ' ' Pour ayoir le veritable nonibre des os de chaquc esp^oe, il faut remonter jusqu'aux 
 premiers noyaux osseux tels qii'ils se montrent dans le fcetus.' — Lcfons (TAnatomk Cmn- 
 })ark, 8to. ed. 1835, torn. i. p. 120. 
 
 ■■^ ' Ayant imagine de compter antaut d'os qu'il y a de centres d'ossification distincts, 
 et ayant cssaye de suite eette manicre de faire, j'ai eu bieu d'apprecier la justesse de 
 cette lAte.'— Annates du Museum, torn. x. p. 344. See, however, the remarks on this 
 point in my ' Lectures on the Comparative Anatomy of the Vertebrate Animals,' Svo. 
 1846, p. 37, et seq. 
 
PREFACE. xxvii 
 
 tomy,' I would remark that the existing kinds of vertebrates 
 constitute part only, perhaps but a small proportion, of those 
 which have lived. Two large primary groups of fishes have 
 almost wholly passed away ; but the Polypterus, Lepidosteus, and 
 sturgeon yield the anatomist some insight into the structural 
 modifications of the Ganoidei of Agassiz ; whilst the shark, the 
 skate, and the cestracion give a fuller knowledge of those of the 
 Placoidei. 
 
 Present reptiles form a mere fragmentary remnant of the great 
 and varied class of cold-blooded air-breathing vei'tebrates which 
 prevailed in the mesozoic age. More than half of the ordinal 
 groups of the class, indicated by osteal and dental chai-acters, have 
 perished ; and it is only by petrified fffices or casts of the intestinal 
 canal, by casts of the brain-case, or by correlative deductions from 
 characters of the petrifiable remains, that we are enabled to gain 
 any glimpse of the anatomical conditions of the soft parts of such 
 extinct species : by such light some of the perishable structures of 
 these animals are indicated in the text. 
 
 As vertebrates rise in the scale and the adaptive principle pre- 
 dominates, the law of correlation, as enunciated by Cuvier,' be- 
 comes more operative. In the jaws of the lion, e.g., there are 
 large laniaries or canines, formed to pierce, lacerate, and retain its 
 prey. There are also compressed trenchant flesh-cutting teeth, which 
 play upon each other like scissor-blades in the movement of the 
 lower upon the upper jaw. The lower jaw is short and strong ; 
 it articulates to the skull by a transversely extended convexity or 
 condyle, received into a corresponding concavity, forming a close- 
 fittino- joint, which gives a firm attachment to the jaw, but almost 
 restricts it to the movements of opening and closing the mouth. 
 
 ' ' Tout etre organise forme un ensemble, un systeme unique et clos, dont les parties 
 se correspondent mutuellement, et concourent a la meme action definitive par une re- 
 action reciproque. Aueune de ces parties ne pent changer sans que les autres ehangent 
 aussi; et par consequent chacune d'elles, prise separement, indique et donne toutes les 
 
 autres.' Discours sur hs Eevolutions de la Sur/aie du Glube. 4to. 1826, p. 4-7. In 
 
 tliis definition Cuvier apprehended, exclusiTely, the operanee of the differencing and 
 adapting pole, and the law becomes limited in its application accordingly. 
 
ixviii PREFACP:. 
 
 The jaw of the Carnivore developes a plate of bone of breadth 
 and height adequate for the implantation of muscles, with power 
 to inflict a deadly bite. These muscles require a large extent of 
 surface for their origin from the cranium, with concomitant 
 strength and curvature of the zygomatic arch, and are associated 
 ■\vith a strong occipital crest and lofty dorsal spines for vigorous 
 uplifting and retraction of the head when the prey has been 
 griped. The limbs are armed with short claws, and endued with 
 the requisite power, extent, and freedom of motion, for the wield- 
 ing of these weapons. These and other structures of the highly- 
 organised Carnivore are so co-ordinated as to justify Cuvier in 
 asserting that ' the form of the tooth gives that of the condyle, of 
 the blade-bone, and of the claws, just as the equation of a curve 
 evolves all its properties ; and exactly as, in taking each j^roperty 
 by itself as the base of a particular equation, one discovers both 
 the ordinary equation and all its j^roperties, so the claw, the 
 l)lade-bone, the condyle, the femur, and all the other bones in- 
 dividually, give the teeth, or are given thereby reciprocally ; and 
 in commencing by any of these, Avhoever possesses rationally the 
 laws of the organic economy will be able to reconstruct the entire 
 animal.' ' 
 
 The law of correlation receives as striking illustrations from 
 the structure of the herbivorous mammal. A limb may termi- 
 nate in a thick horny hoof Such a foot serves chiefly, almost 
 exclusively, for locomotion. It may ' paw the ground,' it may 
 rub a part of the animal's hide, it may strike or kick ; but it 
 cannot grasp, seize, or tear another animal. The terminal uno-u- 
 late phalanx gives, as Cdvier declares, the modifications of all 
 tlie bones that relate to the absence of a rotation of the fore-leo-. 
 and those of the jaw and skull that relate to the mastication 
 offered by broad-crowned complex molars. 
 
 But there are certain associated structures for the coincidence 
 of which the physiological law is unknown. ' I doubt,' M-rites 
 
 ' Op. cit. p. 4 9. 
 
PREFACE. xxix 
 
 CuviER, ' whether I shovild have ever divined, if observation had 
 not taught it me, that the ruminant hoofed beasts slioukl all have 
 the cloven-foot, and be the only beasts with horns on the frontal 
 bone.' ' I may add that we know as little why horns should be in 
 one or two pairs in those ungulates only which have hoofs in one 
 or two pairs ; whilst in the horned ungidates with three hoofs 
 there should be either one horn, or two odd horns placed one be- 
 hind the other, in the middle line of the skull ; or why the ungu- 
 lates with one or three hoofs on the hind foot should have three 
 trochanters on the femur, whilst those with two or four hoofs on 
 the hind foot should have only two trochanters.^ 
 
 ' However,' continues Ccjvier, ' since these relations are con- 
 stant, they must have a sufficing cause ; but as we are ignorant 
 of it, we must supply the want of the theory by means of observa- 
 tion. This wll serve to establish empirical laws if adequately 
 pursued, as sure in their application as rational ones.' ^ 'That 
 there are secret reasons for all these relations oljservation may 
 convince us, independently of general philosophy.' ' The con- 
 stancy between such a form of such organ and such another fomr 
 of another organ is not merely specific, but one of class with a 
 corresponding gradation in the development of the two organs.' ^ 
 
 ' For examjjle, the dentary system of non-ruminant imgulates 
 is o-enerally more perfect than that of the bisulcates ; inasmuch 
 as the former have almost always both incisors and canines in the 
 upper as Avell as the lower jaw ; the structure of their feet is in 
 c-eneral more complex, inasmuch as they have more digits or hoofs 
 less completely enveloping the phalanges, or more bones distinct 
 
 1 Op. cit. 50. 2 Quarterlj' Journal of the Geological Societ)', p. 138. 1847- 
 
 ' ' Puisqiie ces rapports sont constants, il faut bien qu'ils aient une cause suiEsanto, 
 mais corame nous ne la connaissons pas, nous devous suppleer au defaut de la theorie 
 par le moj-en de robservatioii.' — Op. cit. p. 50. 
 
 ■' ' En effet, quand on forme un tableau de ces rapports, on y remarqne non seulement 
 une consistance specifique, si Ton peut s'exprimer ainsi, entre telle forme de tel organe 
 et telle autre forme d'uil organ different ; mais Ton apercjoit aussi une Constance 
 classique et une gradation correspondante dans le dereloppement de ces deux organes, 
 qui montrent, presque aussi bien qu'un raisonnement effectif, leur influence mutuelle.' — 
 Op. cit. p. 51. 
 
XXX PREFACE. 
 
 in the metacarpus and metatarsus, or more numerous tarsal bones ; 
 or a more distinct and better developed fibula ; or a concurrence 
 of all these modifications. It is imjiossible to assign a reason for 
 these relations ; but, in proof that it is not an affair of chance, 
 we find that whenever a bisulcate animal shows in its dentition 
 any tendency to approach the non-ruminant ungulates, it also 
 manifests a similar tendency in the conformation of its feet.' After 
 citino; similar instances of such constant relations, Cl'VIER a2;ain 
 declares that the palaeontologist ' must avail himself of the method 
 of observation' as a supplementary instrument when the reason or 
 law of such relations is undiscovered ; and that he is most suc- 
 cessful in the reconstruction of a whole from a jiart, who applies 
 to the task ' efficacious comparison,' guided by 'tact {adresse) in 
 discerning likeness.' ' 
 
 As we descend in the scale of life from the grade illustrative 
 of ' Cuvier's Law,' the method of empirical observation becomes 
 more and more essential, the tact with which it is applied beino-, 
 however, in the ratio of the discernment of the correlations of 
 structures. The results of the combined methods of interpreting 
 fossil remains are leading to views of life transcendino- the Grains 
 to zoology as a record of well-classed species, or to physiologv as 
 illustrative of final purpose. A progress from more generalised 
 to more specialised structures, analogous to that exemplified in 
 existing grades of animal life and in successive phases of individual 
 development, is appreciable in the series of species which have 
 succeeded one another upon our planet. 
 
 Certain structures which are transitory or rudimcntal in exist- 
 ing species are persistent and developed in extinct. 
 
 The caudal vertebras are laid down in a o-raduallv decreasino- 
 series of cartilaginous nuclei, in the embryo of modern bony fishes ; 
 but in the course of ossification they become massed and blended 
 together to form the base of a vertically extended symmetrical 
 tail-fin. In all palajozoic fislies the initial embryo-state persists, 
 and the tail-fin, througli the length of the upper lobe retainino- the 
 
 ' Op. cit. p. :>•!. 
 
PREFACE. xxxi 
 
 terminal series of vertebrje, is unsymmetrical. The process of 
 clifFerencing which leads to the ' homocercal ' type begins in the 
 mesozoic period and prevails in the neozoic. (See Table of 
 Strata, &c.,p. xxxviii.) 
 
 A corresponding modification of the caiidal vertebra3 prevails 
 in neozoic birds ; but the embryos of the existing species show 
 the terminal vertebras distinct, in a tapering series, before they 
 are massed into the ' ploughshare bone ;' and such, doubtless, was 
 the law of development in all the extinct species which have left 
 tertiary ornitholites. But the earliest and as yet sole evidence 
 of the fossil skeleton of a mesozoic bird shows the retention of 
 the embryo condition, with ordinary growth of the vertebroB.' 
 
 Modern ruminants are hornless when born, and have the me- 
 tapodials supporting the phalanges of the cloven foot distinct ; 
 at an earlier fatal period rudiments of upper fore-teeth start in 
 the gum but do not get bej^ond it. The eocene mammal that first 
 indicates the ruminant type retained the transitory, and developed 
 the aborted, characters of its successors. The metacarpals and 
 metatarsals never coalesced to form a ' canon-bone ;' the upper 
 canines and incisors were functional, but small and equal-sized ; 
 and, as horns never sprouted, Cuvieu called the extinct beast 
 ' weaponless' (^Ayioplotheriuin). In modern horses the digit on 
 each side the one supporting the hoof is luideveloped, and is 
 represented by a concealed rudiment of the metaiiodial called 
 ' splint-bone.' In the miocene horses these metapodials reached 
 their full length and supported hoofed digits, but of small size, 
 like the ' spurious hoofs ' of the ox. The eocene mammal initia- 
 ting the type had these hoofs so developed as to form a functional 
 tridactyle foot. Moreover, in the Palaotherium, certain teeth 
 (symbolised in the present Work as ;9 1 ) which are rudimental and 
 deciduous in the horse, were persistent and functional. The mesozoic 
 marsupials manifested a lower or less differenced state of dentition, 
 either by the degree of sameness of form (Phascolothere), or by the 
 superior number (Thylacothere) of the molar series of teeth. 
 
 ' Philosophical Transactions, 1863, pp. 33, 4.5, pis. I. and III. 
 
xxxii PREFACE. 
 
 The ' rudiments ' of parts and organs which are retained un- 
 developed, or do not acquire the state capable of acting, or ' per- 
 forming the function ' done Ijy them in other species, are of two 
 kinds : one exhibits the totality of the organ in miniature, as, 
 e.g., lacteal glands and nipples of the male mammal ; the other 
 is a pai't of an organ, as, e.g., the few concealed caudal vertebraj 
 in the sloth, to which other vertebras are added, with concomitant 
 growth, to make the organ perfect for its function, as in the tail 
 of the Megathere. Some rudiments show beginnings of parts 
 which rise to perfection in higher species of the existing series ; 
 others are remnants of organs that were fully developed and func- 
 tional in extinct species. Tiedejiann's ' scrobiculus parvus in 
 loco coruu posterioris ' in the brain of Macacus,' and the part 
 which Vrolik believed himself entitled to regard as an indication 
 of the 'hippocampus minor' in the brain of Troglodytes,- are 
 beginnings of structures which show their full development iu 
 the human brain, and merit the nomenclature assigned to them 
 in anthropotomy. 
 
 The filamentary limb of Protopterus (Vol. I. fig. 101, a), the 
 didactyle Umb in AmpJduma {lb. B), the tridactyle homologue in 
 Proteus, are beginnings of organs which attain full functional de- 
 velopment in higher vertebrates. The styliform metacarpals and 
 metatarsals in Eqmis, on the other hand, are remnants of parts 
 of digits which were entire in Hipparion, and were functionally 
 developed in Palceotherium. 
 
 Ruminants which habitually frequent heated arid plains or 
 deserts, as the giraffes and camels, e.g., have lost the digits (ii 
 and V, Vol. II. fig. 193, ox) that add to the resistance of the hoof 
 on swampy ground, as in the bison, elk, and reindeer {lb. fi"'. 
 .311). 
 
 The visual organ degenerates in species inliabiting dark caves 
 or XQWssQB,{Ambli/opsis (Vol. I. fig. 175), Heteropygii, Proteus, 
 
 ' loones oeivbi-i Simiarum, fol. ].. 11, flg. iii. 2. 
 
 ^ Versl. cii Medeilcel ilcr K.jii. AL:i.l., xiii. 18G2, p. 7. 
 
I'EEFACE. xxxiii 
 
 the craw-fisli of the ' jMammoth Cave,' and numerous insects and 
 arachnidans). 
 
 Lcpidojnis, Trichiurus, Stromateus, exemplify fishes which lose 
 the veuti-al fins entirely with age ; they are rudimental in Gon- 
 iryliis, Pscttus and Centronotiis ; Soleotalpa has only the right 
 ventral developed and the left rudimental ; the pectoral fins are 
 rudimental in many pleuronectoids, either on l)0th sides, as in 
 Buglossus and Ac/iirus, or on the blind side only, as in Monoclilr 
 and many species of Sijnapturu. The ' adipose fin ' of certaiji 
 Siluroid and Salmonoid fishes is a rudimental dorsal, sometimes , 
 showing traces of rays. 
 
 The prevalence of liirds in New Zealand without wings (Dhwr- 
 nis), or too feebly developed for the purpose of flight (^Apterijx, 
 Brachyptcryx, Notornis, &c.), is associated with the absence in . 
 those islands of any higher form of life exercising destructive / 
 mastery of organisation, until the immigration of the human race. 
 The wings of such birds, like the eyes of the cavern fishes and 
 crustaceans, would seem to have degenerated for want of use ; 
 their legs, by wdrich locomotion was exclusively exercised, to have 
 gained in size and strength. 
 
 Lamarck,' adverting to observed ranges of variation in certain 
 sjoecies, affirmed that sucii variations would proceed and keep pace 
 with the continued operation of the causes producing them ; that 
 such changes of form and structure would induce corresponding 
 changes in actions, and that a change of actions, when habitual, 
 became another cause of altered structure ; that the more frequent 
 employment of certain parts or organs leads to a proportional 
 increase of development of such parts, and that as the increased 
 exercise of one part is usually accompanied by a corresponding 
 disuse of another part, this very disuse, by inducing a proportional 
 degree of atrophy, becomes an added element in the progressi^'e 
 mutation of organic forms. 
 
 Concomitant changes of climate, and other conditions of a coun- 
 
 ' Pliilosopl.iie Zoologiipp, torn. i. chaps, iii. ti. "\'ii. 
 VOL. I. b 
 
xxxiv PREFACE. 
 
 try affecting the sustenance or well-being of its indigenous animals, 
 may lead not only to their modification but to their destruction. I 
 have, in another work, pointed out the characters in the animals 
 themselves calculated to render them most obnoxious to such ex- 
 tirpating influences ; and have applied the remarks to the expla- 
 nation of so many of the larger species of particular groups of 
 animals having become extinct, whilst smaller species of equal 
 antiquity have remained. 
 
 ' In proportion to its bulk is the difficulty of the contest which, 
 as a li\-ing organised whole, the individual of such species has to 
 maintain against the surrounding agencies that are ever tending 
 to dissolve the vital bond and subjugate the living matter to the 
 ordinary chemical and physical forces. Any changes, therefore, 
 in such external agencies as a species may have been originally 
 adapted to exist in, will militate against that existence in a degree 
 proportionate, perhaps in a geometrical ratio, to the bulk of the 
 species. If a dry season be gradually prolonged, the large mam- 
 mal will suffer from the drought sooner than the small one ; 
 if such alteration of climate affect the quantity of vegetable food, 
 the bulky Herbivore will first feel the effects of stinted nourish- 
 ment ; if new enemies are introduced, the lai'gc and conspicuous 
 quadruped or bird will fall a prey, whilst the smaller sjiecies con- 
 ceal themselves and escape. Smaller animals are usually, also, 
 more prolific than larger ones.' ' 
 
 The actual presence, therefore, of small species of animals in 
 countries where larger species of the same natural families for- 
 merly existed, is not the consequence of any gradual diminution 
 of the size of such species, but is the result of circumstances, 
 which may he illustrated by the faljle of the ' Oak and the Reed ; ' 
 the smaller and feebler animals have bent and accommodated 
 themselves to changes which have destroyed the larger species. 
 They have fared better in the ' battle of life.' 
 
 Accepting this explanation of the extirpation of species as true, 
 
 ' On the Grmis D'nwrnis (Part iv.), Zuul. Truns., Tol. ir. p. 15 (FcbriuuT 1S.50). 
 
s 
 
 PREFACE. XXXV 
 
 Mr. Wallace ' has applied it to tlio extirpation of varieties ; and 
 as these do arise in a wild species, he shows how such deviation 
 from type may either tend to the destruction of a variety, or to 
 adapt a variety to some changes in surrounding conditions, under 
 which it is better calculated to exist, than the type-form from 
 which it deviated. 
 
 No doubt the type-form of any species is that -which is best 
 adapted to the conditions under ^\'hich such species at the time 
 exists ; and as long as those conditions remain unchanged, so long 
 will the type remain ; all varieties departing therefrom being 
 in the same ratio less adapted to the en\droniug conditions of 
 existence. But if those conditions change, then the variety of the 
 species at an antecedent date and state of things may become 
 the type-form of the species at a later date, and in an altered 
 state of things. 
 
 In his work ' On the Origin of Species by Natural Selection,'^ 
 Mr. Darwin more fully exemplifies, conjecturally, the reciprocal 
 influence of external conditions and inherent tendencies to variety, 
 in carrying on, as he believes, the deviations from type to specific 
 and hiorher decrees of difierence. 
 
 All these, however, are conceptions of what may have, not 
 observations of Avhat have, originated a species. Applied to 
 the structures which differentiate Trocilodi/tes f'rf)m Homo} or 
 Chiromys from Lemur, "^ "^^^^J are powerless to explain them : and 
 the structural differences in these instances are greater than in 
 many other species maintaining their distinction by sexual in- 
 capacity to produce fertile hybrids. 
 
 An innate tendency or susceptilnlity in an offspring to differ 
 from a parent is a fact of observation : when carried beyond a 
 certain point the issue is called, from its rarity, a ' monster.' But 
 this tendency and its results are independent of internal volitions 
 and external influences. 
 
 ' Proceedings of the Linnean Societ)', August 1858, p. 57. - Svo. 1859. 
 
 = On the Classification and Geographical Distribution of the ^lammaha, Sro. 1859, 
 p. 92. * Transactions of the Zoological .Society, vol. v. p. 86. 
 
 h3 
 
xxxvi PREFACE. 
 
 Therefore, with every disjiosition to acquire information and 
 receive instruction as to how sjjecies become such, I am still com- 
 l)elled, as in 1849, to confess ignorance of the mode of oj)eration 
 of the natural law or secondary cause of their succession on the 
 earth. But that it is an ' orderly succession,' or according to 
 law,' and also 'progressive' or in the ascending course, is evident 
 from actual knowledge of extinct species. 
 
 The inductive basis of belief in the operation of natural law or 
 ' secondary cause ' in the succession and progression of organised 
 species, was laid by the demonstration of the unity of jjlan under- 
 lying the diversity of animal structures, as exemplified by the 
 determinations of special and general homology; by the discovery 
 of the law of ' Irrelative repetition ; ' by observation of the ana- 
 logies of transitory embryonal stages in a higher animal to the 
 matured forms of lower animals ; and by the evidence that in the 
 scale of existing nature, as in the development of the individual, 
 and in the succession of species in time, there is exemplified an 
 ascent from the general or lower to the particular or higher con- 
 dition of organism. 
 
 The most intelligiljle idea of homologous parts in such series 
 is that they are due to inlieritance. How inherited, or what may 
 be the manner of operanee of the secondary cause in the iiro- 
 duction of species, remains in the hypothetical state exemplified 
 by the guess-endeavours of Lajiarck, Daum'ix, Wallace, and 
 others. 
 
 In the lapse of ages, hypothetically invoked for the mutation 
 of specific disthrctions, I would remark that JMan is not likelvto 
 preserve his longer than contemporary species theirs. Seeing 
 the greater variety of influences to which he is subject, the 
 present characters of the human kind are likely to be sooner 
 clianged than those of lower existing species. And, with such 
 
 > Pjaiien PowEi.i,, quutijig from my Work ' On tlie Nature of Limbs,' 8to. 1849, \\ 
 8fi, wriirs:— ■ To what acluiil or socomlary cause' ('Essays on tlio Unity uf 'Worlds,' 
 18')5, p. -nil), insti-iid of, ' To wliat natural la-srs or sr-coudury cause the orderly suc- 
 cession and progrc'ssion of species may luire Lcen committed, ive are, as yet, ignorant.' 
 
PREFACE. xxxvii 
 
 change of specific character, especially if it should be in the 
 ascensive direction, there might be associated powers of pene- 
 trating the problems of zoology so far transcending those of our 
 present condition, as to be equivalent to a difierent and higher 
 phase of intellectual action, resulting in what might be termed 
 another species of zoological science. 
 
 With the present psychical and structural characteristics of the 
 human species, it may be reasonably concluded that those of other 
 existing species, especially of the distinctly marked vertebrate 
 classes, will be, at least, concurrent and co-enduring ; and, in that 
 sense, we may accept the dictum of the French zoologist: — ' La 
 stabilite des especes est une condition necessaire a I'existence de 
 la science d'Histoire Naturelle.' At the same time, indulging with 
 Lamarck in hypothetical views of transmutative and selective 
 influences during ajons transcending the periods allotted to the 
 existence of ourselves and our contemporaries, as we now are, we 
 may also say : — ' La nature n'offre que des individus qui se suc- 
 cedent Ics uns aux autres par voie de generation, et qui provien- 
 nent les uns des autres. Les especes parmi eux ne sont que 
 relatives, et ne le sont que temporairenient.' 
 
o 
 
 N 
 O 
 
 H 
 
 o 
 
 Pi 
 
 M 
 
 Eh 
 
 pq 
 
 Eh 
 
 Table of Strata mid Order of Ajjjiearance 
 V^®< An-^ I "/ Verteljrate Life upon the Earth. 
 
 Turbary. g MAU by Kemams. 
 
 Shell Marl. § 
 
 Glacial Drift, gs m \ by Weapons. 
 
 Brick Earth. ;§ 3 g 
 
 °'"'^"*^ I <o Mammals under present geographical 
 
 Eed r Crag. g distribution. 
 
 Coralline ■' ? v 
 
 w o^^ 
 
 0) I? 
 
 Faluns. g '^5' n 1 
 
 o Euminantia. c? Quadruraana. 
 
 Molasse. 3 »•' Proboseidia. ^'h' 
 ...^ |: ^^ 
 
 Gyps. S ^ Eodentia. ^.^^^ 
 
 London ) „, o .^^ , „ . ' 
 
 Plastic I '^^' H U^ngiilata. Carnivora. 
 
 Maestricht. m Cycloid. 1 Mosasaurus. 
 
 Upper Chalk. o jDtenoid. J ^^^^^"^^ Polyptychodon. 
 
 Lower Chalk. § Birds, by Bones. 
 
 Upper Greensand. <u Proccelian Crocodilia. 
 
 Lower Greensand. U Pterodactyles. 
 
 Weald Clay. g 
 
 Hastings Sand. 2 Iguanodon. 
 
 Purbeek Beds. ^ —Marsupials. — Chelonia by Bones. 
 
 Kimmeridgian. P Pliosaui-us. 
 
 Oxfordian. p Birds by Bones and Feathers. »■; 
 
 Kelloyian. :? 
 
 Forest Marble. .0 t? . ^ 
 
 Bath-Stone. ^ '% ^ ■^' '§' '^ 
 
 Stonesfield Slate. O jj j^j^^ # f' / o^ 
 
 Great Oolite. 4 ■?^# / # 
 
 Lias. Ichthyopterygia. V O «, /ij 
 
 Bone Bed MAMMALIA 
 
 U. New Eed Sandstone, g AVES, by Foot-prints. 
 
 MuschelkaUc. 'S Sauropterygia. 
 
 Bunter. ^ Labyrinthodontia. 
 
 Marl-Sand. , ^ 
 
 Magnesian Limestone. <".h Sauria. 
 
 L. New Eed Sandstone. " Chelonia, by Foot-prints. 
 
 Coal-Measures. I § EEPTILIA ganoeephala. 
 
 Mountain Limestone. 'S [5 
 Carboniferous Slate. O-i 
 
 U. Old Eed Sandstone. T ' ^> 
 
 Caithness Flags. >| /ganoid. ^cf' 
 
 L. Old Eed Sandstone, fi ^ placo-ganoid. jj!- 
 
 Ludlow.^ PISCES I P''tg°''l- ^ 
 
 Wenloek, . ^o' . . 
 
 Llandoilo g ^ WW^WVX'^' 
 
 Liugula Flags. xn > ^ <^ "^ C v 
 
 '^'^'^^"'^"- , Fuooids. Zoophytes. 
 
 O 
 
 M 
 
 o 
 o 
 
 m 
 
 u 
 o 
 
 < 
 
 o 
 o 
 
 02 
 
 O 
 
 M 
 
 o 
 
 tq 
 o 
 
 < 
 
 >H 
 H 
 
CONTENTS, OE SYSTEMATIC INDEX. 
 
 CHAPTER I. 
 
 CHAEACTERS OF TEKTEBBATES. 
 
 SECTION 
 
 1. Developmental character 
 
 2. Structural characters 
 
 3. Piscine modificatiou 
 
 4. Reptilian modification 
 
 5. Avian modification 
 
 6. Mammalian modification 
 
 7. Genetic and thermal distinctions 
 
 8. Sub-classes of Htematocrya, or Cold-blooded Vertebrate 
 
 9. Orders of Hseniatocrya 
 
 PAOK 
 
 1 
 3 
 
 4 
 5 
 6 
 6 
 6 
 7 
 9 
 
 CHAPTER II. 
 
 OSSEOUS SYSTEM OF IlyEMATOCEYA. 
 
 10. Composition of Bone 
 '' H. Development of Bone 
 
 12. Growth of Bone 
 
 13. Classes of Bone 
 
 14. Type-segment, or Vertebra 
 1.5. Archetype Skeleton 
 
 16. Development of Vertebras 
 
 17. Vertebral column of Fishes 
 
 18. Vertebral column of Batrachia 
 
 19. Vertebral column of Ichthyopterygia 
 
 20. Vertebral column of Sauropterygia 
 
 21. Vertebral column of Ophidia 
 
 22. Vertebral column of Lacertia 
 
 23. Vertebral column of Chelonia 
 
 24. Vertebral column of Crocodilia 
 
 25. Vertebral column of Pterosauria 
 
 26. Development of the SkuE 
 
 27. Skull of Plagiostomi 
 
 28. SkuU of Protopteri 
 
 19 
 21 
 23 
 26 
 
 27 
 
 29 
 
 3(1 
 
 34 
 
 46 
 
 60 
 
 51 
 
 S3 
 
 57 
 
 60 
 
 65 
 
 70 
 
 71 
 
 76 
 
 82 
 
xl 
 
 CONTENTS. 
 
 SECTION 
 
 29. Skull of Batrachia 
 
 30. Skull of Osseous Fishes .... 
 
 31. Skull of Chclouia 
 
 32. Skull of Crocodilia 
 
 33. Skull of Ophidia 
 
 3i. Skull of Lacertilia 
 
 35. Skull of Ichthyopterygia .... 
 
 36. Skull of Dicynodontia 
 
 37. Skull of Pterosauria 
 
 38. Scapular arch and appendages of Htematocrya 
 
 39. Pectoral limb of Fishes .... 
 
 40. Pectoral limb of Eeptiles .... 
 
 41. Pelvic arch and limb of Fishes 
 
 42. Pelvic arch and limb of Reptiles . 
 
 43. Dermoskeleton of Fishes .... 
 
 44. Dermoskeleton of Eeptiles .... 
 
 92 
 126 
 135 
 146 
 154 
 158 
 159 
 161 
 161 
 163 
 169 
 179 
 181 
 193 
 198 
 
 CHAPTEE III. 
 MUSCULAH SYSTEM OF H.EJIATOCRYA. 
 
 45. .Structure of Muscle 
 
 46. Myology of Fishes 
 47- Myology of Eeptiles 
 
 48. Locomotion of Irishes 
 
 49. Locomotion of Serpents 
 
 50. Locomotion of Limbed Eeptiles 
 
 200 
 202 
 215 
 243 
 2.59 
 262 
 
 CHAPTEE IV. 
 
 NERVOUS SYSTEM OF II^EMATOCKYA. 
 
 61. Nervous Tissues . 
 
 52. Myelcnceplialon of Fishes 
 
 53. Myelencepilialon of Eeptiles 
 64. Myelencephalic membranes in Htematocrya 
 
 55. Nerves of Fishes .... 
 
 56. Nerves of Eeptiles 
 
 67. Sympathetic nervous sy.stem . 
 
 68. Sympathetic nervous system of Fishes 
 
 69. Sympathetic nervous system of Eeptiles 
 
 60. Appendages of the Nervous System 
 
 61. Organ of Touch in Hasmatocrya 
 
 62. Organ of Taste in Eeptiles 
 
 63. Organ of Smell in Iliematocrya 
 
 64. Organ of Sight in Fishes 
 
 65. Organ of Sight in Eeptiles 
 06. Organ of Hearing in Fiyiies 
 
 67. Organ of Hearing in Ei'ptilcs 
 
 68. Electric Organs of Fishes 
 
 266 
 
 208 
 
 290 
 
 296 
 
 297 
 
 309 
 
 318 
 
 320 
 
 321 
 
 323 
 
 323 
 
 327 
 
 323 
 
 331 
 
 337 
 
 342 
 
 347 
 
 350 
 
CONTENTS. 
 
 
 
 
 
 
 xlj 
 
 CHAPTEE V. 
 
 DIGESTIVE SYSTEM OF IliEMATOCUYA. 
 
 SKC-nON p^„,j. 
 
 69. Duntal Tissues ;;59 
 
 70. Teeth of Fishes 
 
 
 
 
 
 
 368 
 
 71. Teeth of Reptiles .... 
 
 
 
 
 
 
 385 
 
 72. AUmentjiiy canal of Fislius . 
 
 
 
 
 
 
 -109 
 
 73. Liver of I'ishes 
 
 
 
 
 
 
 425 
 
 74. Pyl(3ric appendages and jianereas of Fishes 
 
 
 
 
 
 
 42S 
 
 7'>. Alinieutary canal of lirptiles 
 
 
 
 
 
 
 433 
 
 76. Lirer of Eeptiles .... 
 
 
 
 
 
 
 448 
 
 77. Pancreas of Reptiles .... 
 
 
 
 
 
 
 453 
 
 CHAPTER VI. 
 ADSOEBENT SYSTEM OF ILEMATOCKYA. 
 
 78. Connective tissue ; serosity 
 
 79. Absorbents of Fishes 
 
 80. Absorbents of Reptiles . 
 
 465 
 456 
 458 
 
 CHAPTER VII. 
 
 CIECDLATING AND EESriEATOKY SYSTEMS OF ILEMATOCEYA. 
 
 81. Blood of Fishes . 
 
 82. Veins of Fishes 
 
 83. Heart of Fishes 
 
 84. Gills of Fishes 
 
 85. Arteries of Fishes 
 
 86. Air-bladder of Fishes 
 
 87. Blood of Reptiles . 
 
 88. Veins of Reptiles . 
 
 89. Heart of Reptiles . 
 
 90. Gills of Batrachians 
 
 91. Arteries of Reptiles 
 
 92. Lungs of Reptiles 
 
 93. Laiynx of Reptiles 
 
 94. Respiratory actions of Reptiles 
 
 463 
 464 
 470 
 475 
 488 
 491 
 500 
 501 
 605 
 512 
 516 
 521 
 527 
 630 
 
 CHiiP'TER VIII. 
 UEINAEY SYSTEM OF HiEMATOCYEA. 
 
 95. Kidneys of Fishes 
 
 96. Kidneys of Reptiles 
 
 97. Adrenals of Htcmatocrya 
 
 VOL. I. 
 
 533 
 537 
 542 
 
xlii 
 
 CONTENTS. 
 
 CHAPTER IX. 
 TEGDMEflTAKY SYSTEM OF IlyEMATOCJtYA. 
 
 BECnON 
 
 98. Composition of Toglimtnt 
 
 99. Tegument.^ of Fi.slif<s 
 100. Teguments of Eeptik'S . 
 
 I-AGE 
 
 oi.5 
 .546 
 550 
 
 CHAPTER X. 
 PECITLIAE AXD DUCTLESS GLANDS AND liErRODUCIDLE PAUTS. 
 
 lOL Scuiit-glands of Reptiles 
 
 102. Poison-glands of Reptiles 
 
 103. Thyroid body or glsind of Hsematocrj-a 
 10-t. Thj-mus body or gland of Reptiles 
 105. Reproducible parts in Hsematocrya 
 
 562 
 563 
 564 
 565 
 566 
 
 CHAPTER XI. 
 GENERATIVE SYSTEM OF HiEMATOCia'A. 
 
 106. Male organs of Fishes . 
 
 107. Female organs of Fishes 
 
 108. Male organs of Batrachians . 
 
 109. Male organs of Reptiles 
 
 110. Female organs of Batrachians and Reptiles 
 
 .568 
 571 
 576 
 579 
 583 
 
 CHAPTER XII. 
 GENERATIVE PRODUCTS AND DEVELOPMENT OF ILEMATOCRYA. 
 
 111. Semination of Hfematoerya ......... ,589 
 
 112. Ovulation in osseous Fishes and Batrachians ..... 592 
 
 113. Ovulation in cartilaginous Fishes and scaled Reptiles .... 597 
 
 114. Fecundation in Fishes .......... 599 
 
 115. Development of Fishes .......... 601 
 
 116. Growth and nests of Fishes ......... (jn 
 
 117. Fecundation in Reptihs •■•...... 614' 
 
 lis. Ovi2:'Osition in Reptiles ......... 616 
 
 119. Development, of Batrachians . . . . . . . . (jjg 
 
 120. Dcvelopiment of Reptiles ......... 630 
 
 ERRATA. 
 
 Below Cats 13-1, 1 :).'">, 1:10, l:i7,/.j/- 'xx.xin.,* ?ce./ ' XNm " 
 Pago 331), eight lines from Lou, /or ' proma-xillrtry,' rc,(,! ' voniei-inc.' 
 „ I-IS, eighteen lines from top,/oc ' tunica],' rca.l ' tumiil.' 
 ,, 512, eleven lines from bottom, trtaixjiose ' fig. :!9n, u " u> lentil lino, alter ' 
 ,, 62.5, four lines from top,/o/- ' fig. .jy.-,,' j-^ad ' fig. 4'>-l, />/ 
 „ G30, five lines from bottom, /or ' bodies,' read ' borders.' 
 
THE 
 
 ANATOMY OF VERTEBRATES. 
 
 0)^.0 
 
 CHAPTER I. 
 
 CHARACTERS OF VERTEBRATES. 
 
 § 1. Developmental characters. — Vertebrates, like lower animals, 
 begin in a semifluid nitrogenous substance called ' plasma,' fig. 1 , A, 
 rt ; primarily differentiating into albumen, fibrine, lemma, ib. b, c^, 
 nuclei and cells ; in which lat- 
 ter form the individuality of 
 the new organism first dawns 
 as a nucleated ' germ-cell ' or 
 germinal vesicle, ib. d. 
 
 By the evolution of albumi- 
 nous granules and oil-particles 
 plasma becomes ' yolk,' fig. 1, 
 B, C ; the germinal vesicle may 
 be obscured by endogenous 
 multiplication of granul es, gra- 
 nular cells and oil-globules, 
 which combine with those of 
 the yolk to form its germinal 
 part : an outer layer of ' lem- 
 ma,' D, ch, completes the un- 
 impregnated vertebrate egg. 
 
 For further developement 
 another principle is needed, 
 
 VIZ. the hyahne nucleus or sta„pgo((,„y|,iopement.oftbeovarianegKofa\-ei-tebralc 
 
 product of the sperm-cell, fig. ™™'" (e<»*™»*"'^)- oi-xxvi. 
 
 2, called ' spermatozoon.' Its reception by the egg, as at a, b, fig. 
 
 3, is followed by the formation of a germ-mass. This mass is due 
 
 ' Gr. krnma, skin ; also called 'primary' or Miasemcnt' membrane ; distinguished, 
 through its relations, as ' iienrilemraa, sarcolcmraa, adcnolerauia' or the limitary 
 membrane of gland-follicles, &c. 
 
ANATOMY OF VERTEBRATES. 
 
 stages of dcveloperaent of the ovarian ctrfe' of a verto- 
 brate animal {continued), clxxvi. 
 
 to a series of self-si^littings of the impregnated centre, whicli 
 
 ' fissiparous' j)rogcny assimi- 
 late or incorporate more or 
 less of the yolk. In fig. 4, a, 
 d is the impregnated germ- 
 yolk ; e the fluid between it 
 and the zona, f; f is albumen 
 from which the chorion, cho, 
 arises. In b, fig. 4, is shown 
 the first division or segmen- 
 tation of the germ-yolk ; c 
 shows the second division; and 
 D, a later stage in which the 
 '■^z^'c^c'^^il:^^ properties of the impregnated 
 
 centre have been diffused 
 and distributed by fissiparous 
 midtiplication 'amongst the countless nucleated cells which form 
 the eerm-mass. 
 
 Thus far the vertebrate germ resembles in form, structure, and 
 2 behaviour, the infusorial monad and the germ- 
 
 stage of invertebrates. The next step impresses 
 upon the nascent being its ' vertebrate ' type. 
 Linear rows of the nucleated cells coalesce and 
 become converted into the nervous axis, which 
 under the form or appearance of a double chord, 
 fig. 5, cli, marks the dorsal or ' neural ' aspect 
 of the embryonal rudiment. The nutritive organs 
 grow from the opposite side. Along the inter- 
 space is laid the basis of the skeleton, as a 
 gelatinous cylinder, in a membranous sheath, called ' notochord,' ' 
 3 which de velopes a pair of jjlates ' neurad ' ^ 
 
 to enclose the nervous axis, and a pair of 
 plates ^ hfemad ' ' to enclose the vascular 
 axis and organs of vegetative life. Flesh 
 and skin coextend with the enclosing plates. 
 This formation of two distinct parallel 
 cavities — ' neural ' and ' hremal ' — under 
 symmetrical guidance in the vertical or 
 ' neuro-hannal' direction, with a repeti- 
 tion of parts on the right and left sides, 
 establishing transverse or 'bi-latcral' 
 
 Spcnii-cclJ, with tlireo 
 spei-matoa, and tinii- 
 nucleus tlie 'spLTmato- 
 zoon' (Cock). CLXivii. 
 
 ^Clt 1 
 
 The ' chunia dorsaiis' of cinbvyologists. - Bi)ck\varJ in man, ujnvmd in beasts. 
 
 " Foi\Viii'd ill man, dowi:\varJ in beasts. 
 
ANATOMY OF VERTEBRATES. 
 
 3 
 
 7; 
 . 6, 
 
 stages of Jovelopcmci't of a vcrttbratc S'^^'t^^ (Rabbit), cvii. 
 
 symmetry, constitutes the chief developmental characteristic of 
 the vertebrate animal. 
 
 The twofold symmetry is shown in the l^one-segment, fif 
 also in the flesh-segment surrounding the skeletal one in fi 
 in which the mid point 
 marks the ' noto- 
 chord ; ' with the neu- 
 ral canal above, the 
 hfemal canal below ; 
 both surrounded by 
 the two neural and 
 two hfcmal masses of muscles on each side. 
 
 The lancelet, Brancluostoma, fig. 2.3, superinduces its distinc- 
 tive characters upon this stage. Aponeurotic septa accompany the 
 pairs of nerves and divide the longitudinal muscular masses into 
 segments. At the next rise segmentation is shown by the develop- 
 ment of cartilage, forming pairs of plates, fig. 5, v, 
 commonly corresponding with the pairs of nerves — , 
 
 sent off from the neural axis, and with the i)airs 
 of vessels from the hicmal axis. As these plates 
 ossify, ossification commonly also begins at cor- 
 responding points of the notochord, dividing it 
 into as many central parts as there are peri- 
 pheral plates or arches, and constituting skeletal 
 segments or ' vertebras ; ' according, or reducible 
 to, the type, fig. 7. 
 
 § 2. Structural characters. — The series of ' vertebras, 
 their several modifications, as the neural or hfemal organs 
 may predominate, constitute the vertebral column. The 
 neural axis consists of ' encephalon' or Ijrain, and of 
 ' myelon' or sp)inal chord. The organs of the five senses 
 — touch, taste, smell, hearing, and sight — are usually 
 present. The blood-discs, fig. 8, speedily acquire the red 
 colour which, by thcu' numljer and minuteness, they 
 impart to the whole blood. The heart is a compact mus- 
 cular organ, of two or more cavities, propelling the blood, 
 throuo-h a closed system of arteries and veins, directly to 
 the breathing-organ, and, in most vertebrates, directly also to the 
 body. The breathing-organ communicates with the pharynx. The 
 alimentary canal has distinct receptive and expellent apertures, 
 usually at opposite ends of the trunk. Tlie mouth Is provided 
 with two jaws, placed one above or before the other, working 
 in the direction of the axis of the body. The muscles surround 
 
 E 2 
 
 Germ of a Rabbit (Barry) 
 
 under 
 
 Section of a 
 ' myoeomma ' 
 or flesli-f^eg- 
 mentitailofa 
 ilackerel.xxi. 
 
ANATOJiy OF VERTEBEATES. 
 
 zygapophy=;t9 
 diai)oplijsi3 
 
 parapopliT^is - 
 
 zygapopliysls 
 
 1 
 
 [neural Bplne 
 
 ipurapophysis 
 
 ■'ioCIS pleurapopliysis 
 
 the bony or gristly levers on which they act. The limbs do not 
 exceed two pairs. Tlie sexes are distinct, and tlie individual 
 is developed directly from an impregnated ovum. Under the 
 
 vertebrate plan of structure animals 
 grow to a greater size and live a 
 longer time, than under any of the 
 invertebrate plans. 
 
 § .3. Piscine modification. — All 
 vertebrates, during more or less of 
 their developmental life-period, float 
 in a liquid of similar specific gravity 
 to themselves. A large proportion, 
 constituting the lowest organised and 
 first developed forms of the pro- 
 vince, exist and breathe in water. 
 Of these a few retain the primitive 
 vermiform condition and develope no limbs : in the rest they are 
 ' fins,' of simple form, moving by one joint upon the body, rarely 
 adapted for any other function than the impulse or guidance 
 
 /, I hsmapopbyeis 
 
 I 
 
 [' lia;inal epino 
 Ideal typical vertetoa- OSLT. 
 
 and are called ' fishes.' 
 
 
 Blood-discs, eadi magnified 300 diameters linear. <u Man ; h, Jlnsk-decr : c. Goose ; d, Cr'Xodile ; 
 r, Frog ; /, Siren ; ;;, Cod-n=h ; 7/, Skate. CXLV. 
 
 of the body through the water. The shape of the body is usually 
 such as is adapted for moving with least resistance through a 
 liquid medium. Tlie surface of the body is either smooth and 
 Ivibricous, or is smoothly covered by ovcrlapyiing scales, is rarely 
 defended by bony plates or roughened by tubercles, still more 
 rarely armed with spines. 
 
 The neural axis presents but one local enlargement, at the fore 
 end, forming the ' encejihalon ; ' it is small, and consists of a suc- 
 cession of simple ganglionic masses, most of which are appro- 
 priated to the function of a nerve of s^jccial sense. Touch is 
 feebly exercised, and an organ for tliat sense rarely developed. 
 
AIJTATOMY OF VERTEBRATES. B 
 
 The tongue, as an organ of taste, is hardly conspicuous; the 
 framework supporting it relates chiefly to the mechanism of swal- 
 lowing and l^reathing, and is suspended to a pedicle common to it 
 and the mandiljle. Of the organ of hearing there is no outward 
 sign ; but the essential internal part or ' lal_)yrinth ' is pjresent, 
 and its semicircular canals are, in most fishes, largely developed. 
 The lahyrinth is devoid of a ' cochlea,' and is rarely provided with 
 a proper chamber, hut is lodged, in common with the brain, in 
 the cranial cavity. The eyes are usually large, seldom defended 
 by eyelids, and never served by a lacrymal apparatus. The ali- 
 mentary canal is commonly short and simjde, with the divisions 
 less clearly marked than in higher verteljrates ; the short and 
 wide gullet iDoing hardly distinguishable from the stomach. The 
 j)ancreatic function a}ipears to be performed by commonly more 
 or fewer ca;cal appendages to the duodenum. The heart consists 
 essentially of one aiu-icle receiving the venous blood, and one 
 ventricle propelling it to the gills, or organs submitting that blood 
 in a state of minute subdivision to the action of aerated water. 
 From the gills the arterial blood is carried over the entire body 
 by vessels, the cireidation being aided by the contraction of the 
 surrounding muscles. The blood is cold, or with a temperature 
 rarely above that of the surrounding medium. The coloured 
 chscs are, in some fishes, subcircular, fig. 8, r/ ; in others, 
 subelliptical, ib. /*, or elliptical ; comparatively large, but not 
 the largest amongst vertebrates. The primordial renal glands 
 (^corpora J-Folffianff) are persistent, and secrete the urine from 
 venous blood. Such are the leadino: anatomical characters of the 
 class Pisces — Fishes. 
 
 § 4. BeptiUan modification. — Llanjr fishes have a bladder of air 
 between the digestive canal and kidneys, which, in some, com- 
 municates by an air-duct with the gullet ; but its office is chiefly 
 hydrostatic. Wlien, in the rise of structure, this air-bladder 
 begins to assume the vascular and pharyngeal relations, with the 
 form and cellular structure of lungs, the limlDS acquire the 
 character of feet; at first, as in Lepidosiren, fig. 41, 99, thread- 
 like and many-jointed — then bifurcate, or two-fingered, with the 
 ordinary elbow and wrist-joints of land-limbs (Amphiiima), fig. 
 100, B, D, — next, three-fingered, as in Proteus, — or foiu'-fingered, 
 but reduced to the pectoral pair, as in Siren. From these gill- 
 retaining transitional forms, up to and including crocodiles, all 
 cold-blooded vertebrates, with lungs, breathing air directly, are 
 called Keptiles {Reptilia, Cuv.). The heart has two auricles; 
 the ventricle, in most, is imperfectly divided, and more or less of 
 
6 ANATOMY OF VERTEBRATES. 
 
 the venous blood is mixed with the arterial blood which circulates 
 over the body. The lungs retain the form of bags, with cellulo- 
 vascular walls, varying as to thickness, and are situated, with the 
 other organs of vegetative life, in a common thoracic-abdominal 
 cavity. 
 
 § 5. Avian modification. — When the lungs become spongy, and 
 the cavity of the air-bag is obliterated by the midtiplication of 
 vascular cellules, and when a four-chambered heart transmits the 
 venous blood to the lungs, and pure arterial blood to the body, 
 the temperature is raised, and is maintained at from 90° to 105° 
 Fahr., whatever may be that of the surrounding medium. Of 
 these hot-blooded vertebrates, one class has the lungs fixed, and 
 communicating with air-cells extending into the aljdomen, and 
 usually other parts of the body ; this class is oviparous, is clothed 
 with feathers, and has the pectoral limbs modified as wings ; it is 
 called Ares — Birds. 
 
 § 6. Mammalian modification. — In the other class of warm- 
 blooded animals, the spongy lungs are freely suspended and 
 confined to a thoracic cavity, defined by a midrift' from the 
 abdomen ; the class is hair-clad, vivijoarous, and suckles the 
 young, whence it is called Mammalia — Mammals. 
 
 § 7. Genetic and thermal distinctions. — The broad and well- 
 marked characters afixjrded by the respiratory system will probably 
 give permanence to the division, so convenient for most purjDoses, 
 of the verteljrate province into the four great classes above 
 defined, viz. Pisces, Reptilia, Aves, Mammalia. 
 
 But many important relations and affinities are thereby masked. 
 Although the last two classes agree, as ' hot-blooded vertebrates,' 
 in their higher cerebral developement, and in the more complex 
 heart and lungs, birds, by genetic and developmental characters, 
 as well as by the general plan of their organisation, are more 
 intimately and naturally allied to the oviparous saurians than to 
 the viviparous mammals. In their generation and development, 
 modern batrachians difter from other cold-blooded air-breathers, 
 and agree with fishes. Present knowledge of extinct forms more 
 clearly exposes the artificial nature of the primary groups of the 
 oviparous vertebrates. An important link, the Pterosauria, or 
 flying reptiles, witli wings and air-sacs, fig. 108, more closely 
 connecting birds with the actual remnant of the reptilian class, has 
 passed away. Other extinct orders {Ganocephala and Lalu/rintho- 
 dontia) have demonstrated the artificial nature of the distinction 
 between fishes and reptiles, and the close transitions that connect 
 together all the cold-blooded vertebrates. 
 
ANATOMY OF VERTEBRATES. 7 
 
 Thus vertebrates might be binarily divided into oviparous, i. 
 II. III., and viviparous, iv. ; into anallantoic or branchiate and 
 allantoic or abranchiate ; into HamatoUteniial,'^ having the four- 
 chambered heart, spongy lungs, hot blood, and Hmaatocryal,'^ 
 having less perfect breathing organs, less complex heart, with cold 
 blood ; and each of such divisions are artiticial and convenient. 
 It suits my present purpose to adopt the latter. 
 
 § 8. Snhclasses of Ilmmatocrya. — With the best insight — 
 peering into the dark vistas of the remote past — tliat one can 
 command into the nature of the strange forms which then 
 perished, and comljining with pala3ontological research the results 
 of anatomical and developmental scrutiny of existing vertebrates, 
 the following seem to be the best defined cold-blooded groups, 
 each with such characters in common as leads to their being called 
 ' natural,' and of a value which may be expressed l^y the term 
 ' sub-class.' 
 
 I. Deemopteei. III. Plagiostomi. 
 
 II. Teleostomi. IV. DirNoA. 
 
 V. MONOPNOA. 
 
 Subclass I. Deemopteei. — Body vermiform, limbless; endo- 
 skeleton membrano- cartilaginous and notocliordal,'^ ril^less ; skin 
 scaleless, lul)ricous ; a vertical fin-fold Ijordering the hind part of 
 the body, without fin-rays ; myelon opaline, ductile, elastic ; no 
 sympathetic nerve ; organ of smell single ; eyes wanting, or very 
 small ; ojDtic nerves not crossing each other ; auditory labyrinth 
 of one or two semicircular canals ; mouth jawless, or suctorial ; 
 alunentary canal straight, simple, without c;ecal appendages, 
 pancreas, or spleen. Branchial function independent of the mouth ; 
 heart, without ' bulbus arteriosus ; ' a pulsatile portal sinus ; no 
 swim-bladder ; testes and ovaria elongated plates without ducts ; 
 generative outlet peritoneal ; ova numerous, small, simultaneously 
 developed, and impregnated externally ; cleavage of yolk entire ; 
 no amnios or allantois ; a metamorjjhosis, as, e. g. from Ammo- 
 ccetes to Petronvjzon, after the third year from the egg. 
 
 Subclass II, Teleostomi.'' — Body piscifonn, with medial and 
 
 ' Gr. haima, blood ; thennos. Lot. 
 
 ^ Gr. haima, blood; cruos, cold. 
 
 ' Retaining the notoehord or primitiTe basis of the vertebral column. 
 
 ■* This word (from Gr. telos, end or completion ; stoma, mouth ;) refers to the com- 
 pletion of the mouth by opposing upper and lower jaws, and also to its terminal 
 position, opening at the fore end of the head. 
 
8 ANATOMY OP VERTEBRATES. 
 
 parial fins, supijorted by rays; endoskeleton in most, more or 
 less ossified ; hyoid arch attached to tympanic pedicle ; scapular 
 arch attached to the occiput ; no sternum : skin defended hy scales 
 or plates ; brain with predominant mesenceplialon ; myelon opake, 
 inelastic; a sympathetic nerve; organ of smell double ; eyes usually 
 large, with bony sclerotic ; auditory labyrinth with three semi- 
 circular canals, in the cranial cavity ; mouth formed by upj^er and 
 lower jaws, opening at the fore part of the head, and admitting the 
 resphatory currents ; intestine, in most, with pyloric appendages 
 and spleen ; anus in front of urethra ; air-bladder in most ; gills, 
 free ; branchial outlet single on each side, defended by a bran- 
 chiostegal flap, ^vith one or more rays ; testes (' milt ') and ovaries 
 ('roe') large, with continuous ducts in most; ova very numerous 
 and small, simultaneously developed, and uupregnated, usually, 
 externally ; no amnios or external allantois. 
 
 Subclass III. Plagiostomi. — Endoskeleton cartilaginous, or 
 ptartially ossified ; scapular arch detached from occiput ; exo- 
 skeleton as osseous granules or tubercles ; body with medial and 
 parial fins, the hinder pair pelvic in position ; caudal-fin with 
 produced upper lobe ; brain with the prosencephalon predominant ; 
 auditory laljyrinth in a special chaml>er ; mouth, in most, a wide 
 transverse slit, opening below tlie head ; intestine with a spiral 
 valve, pancreas, and spleen ; no air-bladder ; bulbus arteriosus 
 with numerous rows of valves ; gills, in most, fixed, and with 
 several branchial outlets on each side ; testes of moderate size, 
 with sperm-duct and copulatory apparatus ; ovaries with few and 
 large ova, successively developed and conveyed away by a 
 detached oviduct ; ova impregnated and, in some, developed in- 
 ternally ; embryo without amnios or allantois, and with deciduous 
 external gills. 
 
 Subclass IV. DiPNOA. — Endoskeleton more or less ossified; 
 ribs wanting, or short and free ; parial members as legs ; brain with 
 predominant prosencephalon ; optic nerves not decussatino- ; audi- 
 tory labyrinth in a special chaml)er, but with only the ' fenestra 
 vestibuli ; ' nostrils communicating with the mouth ; intestine, 
 with pancreas and spleen ; air-bladder as a pair of lungs, com- 
 municating by a duct and glottis with the hremal side of the 
 pharynx; heart, in most, with one ventricle and two auricles. 
 Testes of moderate size, with sperm-ducts, but no intromittent 
 organs or claspers ; ovaries with detached oviducts ; ova simulta- 
 neously developed, and, in most, impregnated externally. Embryo 
 without amnios or allantois, and with cxtcrual "-ills. 
 
ANATOMY OF VERTEBRATES. 9 
 
 Subclass V. MoNorNOA.—Endoskeleton ossified; exoskeleton 
 in most as horny scales, in some as bony scutes; one occipital 
 condyle ; vomer usually single ; trunk-ribs long and curved. Brain 
 with predominant prosencephalon. Labyrinth with both fenestra 
 vestilnili and fenestra rotunda ; a tympanum in most ; lungs ; 
 heart with two auricles, and with the ventricle more or less 
 completely divided. Testes with ducts and intromittent organ. 
 Ovaria with detached oviducts. Ova successively developed, 
 impregnated with copulation. An amnios and allantois. No 
 metamorphosis. 
 
 § 9. Orders of H^EMATOCKYA. 
 
 Subclass I. , Order I. CIREOSTOMI. 
 
 Body compressed ; mouth a longitudinal fissure with sub-rigid 
 cirri on each side. Pulsating vessels or sinuses in place of heart. 
 Blood pale ; free pharyngeal branchial filaments, and a branchial 
 dilatation of the cesophagus. 
 
 Gen. Brancldostoma. Ex. Lancelot. 
 
 Order II. CYCLOSTOML 
 
 Body cylindrical ; heart distinct ; branchial artery without 
 bulb ; brancliise sacciform, with external spiracles, six or seven on 
 each side, blood red. Mouth subcircular, suctorial, but longitu- 
 dinal when closed. Olfactory sac communicating with, or produced 
 into, a canal. 
 
 Gen. Myxhie. Ex. Hag-fish. 
 
 Pctrorinjzon. Ex. Lamprey. 
 
 Subclass II. ^ A. Arterial bulb with one pair of valves; optic 
 nerves decussating; vertebras biconcave. 
 
 Order III. MALACOPTEEI. '^ 
 
 Skin, in most with cycloid scales, in a few with ganoid plates ; 
 rarely naked. Fins supported by rays, all of which (save the first 
 in the dtjrsal and pectoral, in some) arc ' soft,' or many-jointed ; 
 a swim-bladder and air-duct ; peritoneal outlets in many. 
 
10 ANATOMY OF VERTEBRATES. 
 
 Suborder I. Apodes. 
 
 Fam. 1. SymbranchidcB. Ex. Cuchia. 
 
 2. MuranidcB. Ex. Eel. 
 
 3. Gymnotida. Ex. Gymnotus. 
 
 Suborder II. Aedominales. 
 
 Fam. 1. Heteropi/yii. Ex. Amblyopsis. 
 
 2. Clupeida;. Ex. Hening. 
 
 3. SalmonidcB. Ex. Salmon. 
 
 4. Scopelidce. Ex. Saurus. 
 
 5. Characinid(E. Ex. Myletes. 
 
 6. Galaxidce.. Ex. Galaxias. 
 
 7. Esocidce. Ex. Pike. 
 
 8. MormyridcB. Ex. Mormyrus. 
 
 9. Cyprinodontida:. Ex. Umber. 
 
 10. Cyprinida'. Ex. Carp. 
 
 11. Siluridce. Ex. Sheat-fish. 
 
 12. Alepisauridce. Ex. Marine Sheat-fish. 
 
 Suborder III. Phartngognathi. 
 Fam. 1. Scomher-esocidcE. Ex. Saury-Pike. 
 
 Order IV. ANACANTHINI. 
 
 Endoskeleton ossified ; exoskeleton in some as cycloid, in others 
 as ctenoid scales ; fins supported by flexible many-jointed rays ; 
 ventrals beneath or in advance of the pectorals, or wanting ; swim- 
 bladder, when present, Avithout a duct. 
 
 Fam. 1. OpJiidid(F. Ex. Ophidium. 
 
 2. GadidcB. Ex. Cod. 
 
 3. Eleiironcctidce. Ex. Plaice. 
 
 Order V. ACANTHOPTERI. (j 
 
 Endoskeleton ossified; exoskeleton, in most, as ctenoid scales; 
 fins with one or more of the first rays unjointed or inflexible 
 spines ; ventrals, in most, beneath or in advance of the pectorals ; 
 duct of swim-bladder obliterated. 
 
ANATOMY OF VERTEBRATES. 11 
 
 Suborder I. Pharyngognathi. 
 
 Fam. 1. ChronudcB. Ex. Chromis. 
 
 2. Ci/clo-lahridce. Ex. Wrasse. 
 
 3. Ctaw-labridm. Ex. Pomacentrus. 
 
 Suborder II. Acastthopteki veri. 
 
 Fam. 1. PercidcE. Ex. Perch. 
 
 2. Squammipennes. Ex. Cbffitodon. 
 
 3. Sparidce. Ex. Sea-bream, Gilthead. 
 
 4. SciamidcE. Ex. Malsre. 
 
 5. Ldhijrinthobranchii. Ex. Anabas or Tree-climber. 
 
 6. MnfiUida;. Ex. Mullet. 
 
 7. Afhejinidce. Ex. Sand-smelt. 
 
 8. Sphyrmiidce (cycloid). Ex. Barracuda. 
 
 9. Scomhmda (cycloid). Ex. Mackerel. 
 
 10. ScUrogenidce. Ex. Gurnard, Miller's thumb. 
 
 11. Tauioidei. Ex. Riljand-fish. 
 
 12. Teutla/ida. Ex. Lancet-fish, 
 
 13. Fistuhiridce. Ex. Pipe-mouth. 
 
 14. Gobiida. Ex. Goby. 
 
 15. BknnudxB (cycloid). Ex. Wolf-fish. 
 
 16. LopldidcE (skiu muricate or naked). Ex. Angler.' 
 
 Order VI. PLECTOGNATHI. 
 
 Endoskeleton partly ossified ; exoskeleton as ganoid scales, 
 jalates, or spines ; ventrals wanting in most ; maxillary and pre- 
 maxillary immoveably connected on each side of the jaw; swim- 
 bladder without air-duct. 
 
 Suborder Scleeodermi. 
 Fam. 1. Balistini. Ex. File-fish. 
 
 Suborder Apleuri (ribless). 
 
 Fam. 1. Ostraciontida. Ex. Trunk-fish. 
 2. Gymnodontida. Ex. Globe-fish. 
 
 ' This selection of the chief family-diversities of the vast acaiithopterous order is 
 designed, like the families cited under other orders, merely to exemplify it by familiar 
 fishes with vernacnlar names. For the characters and affinities of all the present 
 known acanthopterous families, see Dr. Giinther's excelleut work, clxxiv., 
 vol. iii. 
 
12 ANATOMY OF VEETEBEATES. 
 
 Order VII. LOPHOBRANCHII. 
 
 Endoskeleton partially ossified, witliout ribs ; exoskeleton ganoid ; 
 gills tufted ; opercular aperture small ; swim-bladder without air- 
 duct. Males marsupial. 
 
 Fam. 1. Hippocampidee. Ex. Sea-horse. 
 2. Symjnatldda. Ex. Pipe-fish. 
 
 B. Arterial bulb mviscular, M'ith more than one row of valves. 
 Optic nerves not decussating. 
 
 Order VIII. GANOIDEI. 
 
 Endoskeleton cartilaginous, partly bony, or ossified ; in a few 
 recent and in most palteozoic extinct forms, notochordal ; exo- 
 skeleton as ganoid scales or plates ; fins usually with the first 
 ray a strong spine ; caudal fin in most unsymmetrical ; a swim- 
 bladder, often cellular, and with an ah-duct ; intestine in many 
 with a spiral valve. 
 
 Suborder I. Lepidoganoidei. 
 
 Fam. 1. Salamandroidei. Ex. Lepidosteus, Polypterus. 
 
 2. Pijciwdontidce. Ex. Pj'cnodus. 
 
 3. Lepidoidei. Ex. Dapedius. 
 
 4. Leptolepldm. Ex. LejJtolejois. 
 
 5. Acanthodei. Ex. Acanthodes. 
 
 6. Dipteridw. Ex. Dipterus. 
 
 7. Ccelacaiitld. Ex. Coelacauthus. 
 
 8. HoloptijchidcE. Ex. Holoptychius. 
 
 Suborder II. Placogaxoidei. 
 
 Fam. 1. Sturionidce. Ex. Sturgeon. 
 
 2. Ostracostei. Ex. Pterichthys. 
 
 Subclass III. Order IX. HOLOCEPHALI. 
 
 Endoskeleton cartilaginous, subnotochordal ; cranial wall com- 
 plete ; tympanic pedicle confluent thcrewitli ; endoskeleton as 
 placoid granules. Anterior dorsal fin witli a strong spine; 
 mouth terminal, beak- shaped; dental plates and columns fused 
 with the jaws. 0]>tic nerves not decussating. Valves of bulbus 
 arteriosus multlserial. Gills laminar, with a small proportion of 
 
ANATOIiIY OE VEETEBRATES. 13 
 
 the border free ; a single external gill-aperture on each side ; 
 opercular and branchiostegal rays. 0^^parous ; ova few and large, 
 
 Fam. 1. CJiimccridce. Ex. Chimera, Callorhynchus. 
 
 2. Edapliodontida. Ex. Edaphodus, Ischiodus, Elasmodus. 
 
 Older X. PLAGIOSTOMI. 
 
 Endoskeleton cartilaginous or partially ossified ; verteljrfo 
 biconcave ; exoskeleton as placoid granules or tubercles, spiny in 
 some. Mouth transverse on the lower surface of the head. Optic 
 nerves commissurally united, not decussating. Valves of bulbus 
 arteriosus multiserial. Gills attached to the skin by the outer 
 margin, with intervening gill-apertures, five or more in number, 
 on each side ; no operculum. 
 
 Suljorder I. CESTEAniOKi.' 
 (Spine in front of each dorsal fin ; back teeth obtuse.) 
 
 Fam. 1. Hj/hodontidce. Ex. Hybodus. 
 
 2. CestraciontidcB. Ex. Cestracion. 
 
 Suborder II. Selachii. (Sharks, branchial apertures lateral.) 
 
 Fam. 1. Notidanid(E. Ex. Grey Shark. 
 
 2. Spinacida. Ex. Piked Dog-fish. 
 
 3. Scylliadm. Ex. Spotted Dog-fish. 
 
 4. Nictitantes. Ex. Tope. 
 
 5. Lamnidae. Ex. Porbeagle. 
 
 6. AlopecidcB. Ex. Fox Shark. 
 
 7. Scymniida. Ex. Greenland Shark. 
 
 8. Squatlnm. Ex. JMonk-fish. 
 
 9. ZygcEuidcB. Ex. Hammer-head Shark. 
 
 Suborder III. Batides. (Pays, branchial apertures inferior.) 
 
 Fam. 1. Pristidce. Ex. Saw-fish. 
 
 2. RJdnohutidce. Ex. Ehinobates. 
 
 3. TorpedinidcB. Ex. Electric ray. 
 
 4. EaiidcB. Ex. Skate. 
 
 5. TryyoiiidcE. Ex. Sting Pay. 
 
 6. MyliohatidcE. Ex. Eagle Pay. 
 
 7. CcplicdopteridcB. Ex. Cephalopterus. 
 
 ' Kentva, a weapon ; pliero, I bear. Many extinct species of this group are known 
 only by their fossil weapons, called ' Ichthyodorulites.' 
 
14 ANATOMY OF VEETEBKATES. 
 
 (Transitional) Order XI. PROTOPTEEI. 
 
 Endoskeleton notochordal, partly cartilaginous, partly osseous ; 
 no occipital condyle ; vomer undivided ; temporal fossas roofed 
 over by bone ; pleurapopliyses short, with free extremities ; exo- ■ 
 skeleton as subcuticular cycloid scales ; scapular arch attached to 
 occiput ; proximal ends of hyoidean and tympano-mandibular 
 arches distinct. Vertical fin a continuous border to the com- 
 pressed tail. Pectoral and ventral fins svibulate, many jointed ; the 
 former fringed beneath ; the latter pelvic in position ; the pelvis 
 unattached to the spine ; gills filamentous, free, in a branchial 
 chamber with a single vertical outlet ; branchial arches imcon- 
 nected with the hyoid ; air-bladder double, lung-like, with air-duct, 
 glottis, and pulmonary vein. Prosencephalon predominant in 
 brain; nasal sacs snblabial with two remote extra-buccal aper- 
 tures ; auditory labyrinth in a distinct chamber ; bulbus arteriosus 
 long, with two longitudinal valves ; intestine with a spiral valve, 
 vent anterior to urethra ; ovaria distinct from oviducts. 
 
 Fam. Sirenoidei. Ex. Lepidosiren. 
 
 Subclass IV. Order XII. GANOCEPHALA. (Extinct.) 
 
 Endoskeleton notochordal and osseous ; no occipital condyle ; 
 vomer divided ; temporal fossfe roofed over by Ixme ; hyoid arch 
 not connected with tymimnic pedicle ; branchial arches (?) un- 
 connected with hyoid ; exoskeleton as subganoid scales ; pleur- 
 apophyses short and free. Teeth with converging inflected 
 folds of cement at their basal half Pectoral and pelvic limbs 
 short, slender, three or four digitate ; natatory. 
 
 Genus Dendrcrpeton. 
 Archcgosaurus. 
 
 Order XIII. LABYRINTHODONTIA. {Extinct.) 
 
 Head defended, as in Ganocephala, by a continuous casque of 
 externally sculptured and unusually hard and polished osseous 
 plates, including the supplementary "post-orbital" and "super- 
 temporal " bones, but leaving a " foramen parictalc." Two occi- 
 pital condyles. Vomer divided and dcntigerous. Vertebral 
 bodies, as well as arches, ossified, biconcave. Pleurapophyses of 
 the trunk, long and bent. Exoskeleton, in some, as smaH'o-anoid 
 
ANATOMY OF VEUTEBRATES. 15 
 
 scales. Teeth rendered complex by undulation and side branches 
 of the converging folds of cement, whence the name of the order. 
 
 Genus Bhombojjhol/s. 
 Lahi/rinthodon. 
 
 Order XIV. BATEACIIIA. 
 
 Endoskeleton ossified ; two occipital condyles ; vomer divided, 
 in most dentigerous ; temporal fossas unroofed ; scajDular arch 
 detached from occiput ; riljs as processes, or short, straight and free ; 
 skin nude, often lubricous. Limits digitate, trisegmental. Intestine 
 without spiral valve, vent posterior to urethra. Embryonal gills, 
 in some retained, in most lost ; with a metamorphosis associating 
 a tail-less body with pulmonary respiration and a heart of two 
 auricles and one ventricle. 
 
 Suborder I. Opiiiomorpha. ' ;,'-'' *-'-''' 
 
 iU-J 
 
 Fam. CceciliadcB. Ex. Cascilia. 
 
 Suborder II. Iciitiiyomoepha. 
 
 Fam. Protekl(e. Ex. Siren, Proteus. i 
 
 Salamandndce. Ex. Newt, Salamander. 
 
 •7 < 
 
 Suborder III. Theeiomoepha. Anura. t-i- ' 
 
 Fam. 1. Aglossa. Ex. Pipa or Surinam Toad. 
 
 2. Ranida. Ex. Frog. 
 
 3. Ihjlidce. Ex. Tree-frog. 
 
 4. Bufonida. Ex. Toad. 
 
 Subclass V. Order XV. ICHTHYOPTERYGIA.' {Exti7ict.) 
 
 Body fish-like, without neck ; limbs natatory, with more than 
 five multiarticulate digits ; vertebraj many, short, biconcave ; no 
 sacrum ; anterior trunk-ribs with bifurcate heads ; an episternum 
 and claT,dcles ; post-orbital and supra-temporal bones ; a foramen 
 parietale ; maxillaries small ; premaxillaries long and large. 
 Teeth confined to maxillary, premaxillary, and premandibular 
 bones, implanted in a common alveolar groove, penetrated by 
 convero-ing folds of cement at the base ; nostrils two, small, near 
 
 ' Gr. ichthys, a fish ; ptenjx, a fin. 
 
16 ANATOMY OF VERTEBEATES. 
 
 the orbits ; orbits large ; a circle of sclerotic plates. Skin naked, 
 forming a vertical tail-fin (inferential). 
 
 Genus Ichthyosaurus. 
 
 Order XVI. SAUEOPTERYGIA. {Extinct.) 
 
 Body, in most, with a long neck ; limbs natatory, with not 
 more than five digits ; an epjisternum and clavicles ; vertebraj 
 with flattened, or slightly cupped, articular surfaces ; a sacrum 
 of one or two vertebras for the attaclunent of the pelvic arch, 
 in some ; ribs with simple heads ; no post-orbital and supra- 
 temporal bones ; large temporal and other vacuities between 
 certain cranial bones ; a foramen i:)arietale ; two antorbital nostrils ; 
 teeth simple, in distinct sockets of premaxlllary, maxillary, 
 and premandibular Ijones, rarely on the palatine or pterygoid 
 bones ; maxillaries larger than premaxillaries. 
 
 Genera Plesioscnirus, Pliosaurus, Nothosaurus, Placodus. 
 
 Order XVII. ANOMODONTIA. {Extinct.) 
 
 Teeth wanting, or limited to a single maxillary pair, having the 
 form and proportions of tusks ; a ' foramen parietale ; ' two ex- 
 ternal nostrils ; tympanic pedicle fixed ; vertebra; biconcave ; an- 
 terior trunk-ribs with a bifurcate head, ischiopubic symphysis 
 continuous. 
 
 Fam. Dicynodontia. 
 
 A long ever-growing tusk in each maxillary bone ; pre-maxil- 
 laries connate, forming with the lower jaw a beak-shaped moutli, 
 probably sheathed with horn. Sacrum of more than two verte- 
 bras. Limbs ambulatory. Ex. Dicynodou. 
 
 Fam. Cryptodontia. 
 Upper as well as lower jaw edentulous ; premaxillaries distinct 
 and produced. Ex. Ehynehosaurus. 
 
 Premaxillaries confluent, short. Ex. Oudenodon. 
 
 Order XVIII. CIIELONIA. 
 Trunk-ri))S broad, flat, suturally united, formino- ,vith their 
 
ANATOMY OP VEKTEBKATES. 17 
 
 vei'tebrre, the sternum, and dermal bones, an expanded 
 thoracic-abdominal case, into wliich the limbs, tail, and, usually, 
 tlie head, can be withdrawn ; sacrum of more than two A'crtcljra; ; 
 no teeth ; external nostril single, a cavum tympani ; body covered 
 1 ly horny scales in most ; ventricle of heart single. 
 
 Limbs natatory. Genus Chclone. (Turtles.) 
 
 T . 1 , ., . f Trionyx. (Mud turtles.) 
 
 Ijimbs amiilubious. \ r, "^ /m \ 
 
 ^ \ hniijs. (lerrapenes.) 
 
 Limbs terrestrial. Teshido. (Tortoises.) 
 
 Order XIX. LACERTILIA. 
 
 Vcrtel3ra3 prococlian, with a single transverse pu'occss on each 
 side, and Avith single-headed ril)s ; sacral vertebrae wanting, or 
 n(.)t exceeding two ; two external nostrils ; eyes with moveable 
 lids ; body covered by horny, sometimes bony, scales. 
 
 Limbs natatory, no sacrum. Ex. jMosasaurus. (Extinct.) 
 Limbs amljulatory, a sacrum. Ex. Lacerta, L. 
 Liniljs abortive, no sacrum. Ex. Anguis. 
 
 Order XX. OPHIDIA. 
 
 Vertebra; very numerous, procoelian, with single-headed hollow 
 ribs ; no sacrum ; no visible limbs ; two external nostrils ; no 
 ca^'um tympani ; eyeball covered by an immoveable transparent 
 lid. Body covered by horny scales. Teeth anchylosed to jaw. 
 
 Order XXI. CROCODILIA. 1'^- ' ' ' 
 
 Teeth in a single row, implanted in distinct sockets ; 
 external nostril single and terminal or sub-terminal. Anterior 
 trunk vertebra; Avitli par- and di-apophyses, and bifurcate ril^s ; 
 sacral vertebras two, each supporting its own neural arch; this 
 arcli usually articulated by suture. Tail long, vertically com- 
 pressed ; feet short, webbed. Skin protected by bony, usually 
 pitted, plates. Ventricle of heart double. 
 
 Suborder Aimpiiiccelia (vertebra; cupped at both ends). 
 Ex. Teleosaurus. 
 
 Suborder OriSTiiocfELiA (vertebra; convex in front, concave 
 behind). Ex. Streptospondylus. 
 
 Suborder Peoccelia (vertebra; concave in front, convex 
 
 behind). Ex. Crocodilus. 
 VOL. I. c 
 
18 ANATOMY OF VERTEBKATES. 
 
 Order XXII. DIXOSAUKIA. (Extinct.) 
 
 Cervical and anterior dorsal vertcbraj with par- and di-apo- 
 pliyses, articulating with bifurcate ribs ; a few anterior vertebrfe 
 more or less convex in front and cupped behind ; the rest 
 with flat or slightly concave articular ends ; dorsal vertebras with 
 a neural platform ; sacral vertebras exceeding two in numljer ; 
 body supported on four strong, ambulatory, unguiculate limbs. 
 Skin in some armed by bony scutes. Teeth confined to upper 
 and lower jaws ; implanted in sockets. Ventricle of heart double 
 (inferential). 
 
 Genera, Iguanodon, Scelidusaurus, Megalosaurus. 
 
 Order XXIII. PTEEOSAURIA. (Extinct.) 
 
 Pectoral members, by the elongation of the anti-brachium 
 and fifth digit, adapted for flight. Vertebrte prococlian ; those 
 of the neck veiy large, those of the pelvis small. Anterior 
 trunk-ribs with bifurcate heads. Most of the bones pneumatic. 
 Head large ; jaws long, and armed with teeth. Ventricle of 
 heart double (inferential). 
 
 Genera, Dimorplwdon, Ramplwrhynclius , Ptcrodacti/lus. 
 
ANATOMY OF VEETEBEATES. 19 
 
 CHAPTER II. 
 
 OSSEOUS SYSTEM OP HyEMATOCRYA. 
 
 § 10. Composition of bone. — The vertebrate organisation will 
 be first described as manifested in the great cold-blooded scries, 
 under the diverse modifications, and progressive stages, indicated 
 by the characters of the foregoing sulxlivisions of the class. 
 But lieflire entering upon the details of the osseous system, some 
 observations must be premised on the vertebrate skeleton in general. 
 
 The original substance of all animals consists of a fluid with 
 granules and cells. In the course of developement tubular tracts 
 are formed, some of which become filled with ' neurine ' or nervous 
 matter ; others with ' myonine ' or muscular matter ; other portions 
 are converted into vessels, glands, &c. ; but a great proportion 
 of suljstance, akin to primordial, remains as ' cellular tissue.' 
 This, as a rule, Ijccomes hardened in certain parts of the body of 
 vertebrates by earthy salts, chiefly phosphate of lime. Thus 
 the tissues called ' osteine ' or bone, and ' dentine ' or tooth, 
 are constituted ; between which the chief distinction lies in the 
 mode of arrangement of the earthy particles, in relation to the 
 maintenance of a more or less free circulation of the nutrient 
 juices through such hardened or calcified bodies. 
 
 Fishes have the smallest proportion, birds the largest propor- 
 tion, of the earthy matter in their Ijoncs. The animal or soft 
 part in all is chiefly a gelatinous substance. 
 
 PROPORTIONS OF EARTHY OR HARD,! AND OF ANIMAL OE SOFT, MATTER IN 
 THE BONES OF THE VERTEBRATE ANISIALS. 
 
 FISHES. 
 
 Salmon Carp Cod 
 
 Soft ... 60-62 40-40 34-30 
 
 Hard. . . . 39-38 69-60 05-70 
 
 100-00 10000 10000 
 
 1 This has been termed inorganic ; but that tlio combination of phosphorus and 
 calcium has ever taken place in nature save under the influences of a living organism, 
 remains to be proved. 
 
 c 2 
 
20 
 
 ANATOMY OF VERTEBRATES, 
 
 
 
 REPTILES. 
 
 
 
 Frog 
 
 Snake 
 
 Lizard 
 
 Soft . . 
 
 . . 35-50 
 
 31-04 
 
 46-67 
 
 Hard . . 
 
 . . 64-50 
 
 68-96 
 
 53-33 
 
 10000 
 
 100-00 
 
 100-00 
 
 
 
 MAMMALS. 
 
 
 
 
 Porpoise 
 
 Ox 
 
 Lion 
 
 Man 
 
 Soft . 
 
 . 35-90 
 
 31-00 
 
 27-70 
 
 31-03 
 
 Hard. 
 
 . 64-10 
 
 69-00 
 
 72-30 
 
 08-97 
 
 100-00 
 
 100-00 
 
 100-00 
 
 100-00 
 
 Soft . 
 Hard . 
 
 Goose 
 32-91 
 67-09 
 
 10000 
 
 Turkey 
 30-49 
 69-51 
 
 10000 
 
 Hawk 
 26-72 
 73-28 
 
 100-00 
 
 From the alDove taljle it will 1)6 seen that the l^ones of the 
 fresh-water fishes have more animal matter, and are, couse(|uently, 
 lighter than those of fishes from the denser element of sea- 
 water ; and that the marine mammal called Porpoise differs little 
 from the sea-fish in this respect. The batrachian Frog has more 
 animal matter in its bones than the ophidian or saurian reptiles, 
 and thereby, as in other respects, more resembles the fish. Ser- 
 pents almost equal birds in the great proportion of the osseous 
 salts, and hence the density and ivory-like whiteness of their 
 bones. 
 
 The chemical nature of the hardening particles, and of the soft 
 basis of bone, is exemplified in the sulijoined Table, including a 
 species of each of the four classes of Vertebrata : — 
 
 CHEJIICAL COMrOSITION OF BONES. 
 
 Phosphate of lime, -with trace of fluate 
 
 Hawk 
 
 JUan 
 
 Tortoise 
 
 Cod 
 
 
 
 
 
 of liinL' ...... 
 
 64-39 
 
 5903 
 
 52 60 
 
 57-29 
 
 Carbonate of lime .... 
 
 7-03 
 
 7-33 
 
 12-53 
 
 4-90 
 
 Phosphate ot magnesia 
 
 0-94 
 
 1-32 
 
 0-S2 
 
 2-40 
 
 Sulphate, carbonate, and chlorate of 
 
 
 
 
 
 soda ...... 
 
 0-92 
 
 0-09 
 
 0-9O 
 
 1-10 
 
 Gliitiii and cliondriii . 
 
 2.-)-73 
 
 29-70 
 
 31-75 
 
 32-31 
 
 Oil 
 
 0-99 
 
 1 -33 
 
 1-34 
 
 2-00 
 
 
 10000 
 
 1 00-00 
 
 100-00 
 
 I 00-00 
 
ANATOMY OF VERTEBRATES. 
 
 21 
 
 § 11. Dcvclopement of hone. — The primitive basis, or ' l)liis- 
 tema,' of bone is a sul)transparent glairy matter containing 
 numcrons minute corpuscles. It progressively 9 
 
 acquires increased firaniess; sometimes assuming 
 a membranous or ligamentous state, usually 
 a gristly consistence, before its conversion into 
 bone. The change into cartilage is noted b}^ 
 the a|)pcarance of minute nucleated cells ; which 
 increase in number and size, and are a<iiire<i-ated 
 in rows, with intercellular tracts, where the ossi- 
 fication is abovit to begin, as in fig. 9. These 
 rows, in the cartilaginous basis ol' long bones, 
 are vertical to its ends : in that of fiat bones 
 
 , -11 • mi Section of temponiry cai-tl- 
 
 they are vertical to the margm. The cells I'lsc, iviiicn bas umingono 
 
 ,-.",,, , f, •? ,• a , the last sl;igo towards ossl- 
 
 tin-tncst trom the seat ot ossifacation are flat- tkation. cl. 
 tened and in close contact; nearest that scat they become enlarged 
 and separated. In fig. 9, a is the intercellular or ' intercolumnar ' 
 tissue ; h the enlarged cell- wall ; e 
 the nucleus. The first appearance 
 of bone is that of minute granules 
 in tlie intercolmnnar and intercellu- 
 lar tissue, fig. 10, II. Canals are 
 next formed in the bone, liy absorp- 
 tion, which ultimately receive blood- 
 vessels, and become the ' vascular 
 canals.' The immediate nutrition of 
 Ijone is provided for by the produc- 
 tion of minute ' plasmatic canals ' 
 fi'om the vascular ones. 
 
 In most fishes the plasmatic canals are free from partial dilata- 
 tions, and appear as in the magnified section of bone, fig 11 ; where 
 a shows the area of the ' -vascular canal,' and b the orifices of the 
 ' jdasmatic canals,' exposed in a longitudinal section of a vascular 
 canal. In some fishes, e. g. the Garpike {Belone), partial dilatations 
 do occur in the plasmatic canals, of the form shown in fig. 12, d; and 
 in a Sea-l)ream ( Siirf/us) of that marked c ; in the Frog they are 
 wider and more defined, as in the two dilatations shown at a. In 
 serpents, e. g. the Pi/tlwn, they are commonly, where best defined, 
 of the elongate oval form shown in 1, 2, and 3, fig. 13 ; but in 
 transverse section they apjiear as in 5 and 6. In the bird, e. g. 
 the Goldfinch, they have the form shown in h, fig. 12. In human 
 bone they assume the forms represented in fig. 14. When so 
 defined they are termed ' lacunas ' or ' bone-cells ; ' and, in some 
 
 of temporary cartilage 
 of os.^iDcation. ci^. 
 
22 
 
 ANATOMY OF VERTEBRATES. 
 
 degree, characterise, by their shape and size, the osseous tissue of 
 the resi)ective vertebrate classes. ' In the concentric laminje sur- 
 
 11 
 
 Plasmatic canals in a fislt-bnnc. n transverse, b longitudinal, section 
 of vascular canal 1.T0MES, cl.) 
 
 rounding the vascular canal, fig. 15, a, a, tlie bone-cells are 
 
 arranged concentrically, between the lamina;, with the lono- axis 
 
 12 
 
 
 ^ 
 
 jS> 
 
 & 
 
 Forms of bone-cells in ^^n,on ami Boa Constrictor. Cb 
 
 in the direction of the circular line of tlie plate. Iklost of the 
 plasmatic tubes continued from the bone-cells pierce the plates at 
 
ANATOMY OF VERTEBRATES. 
 
 23 
 
 right angles in tliolr course to the vascular canal, with which they 
 communicate ; and tlicy form the U 
 
 essential vehicle of the material 
 for future trrowth. 
 
 H4f 
 
 § 12. Growth of hone. — In 
 fishes the l^oncs continue to grow 
 throughout life, and their peri- 
 phery, whether in the flat Irenes of 
 the head which overlap each other, 
 or in the thicker bones that inter- Thof<,ni 
 lock, is cartilaginous or membranous, 
 sive ossification. The long bones of most reptiles retain a layer 
 of ossifying cartihrge beneath the terminal articular cartilage ; 
 and growth continues at their extremities while life endures. 
 
 15 
 
 ^ usbiuuca l>y the boiic-cells 
 
 and the seat of 
 
 progres- 
 
 
 .' 1 
 
 
 _'. ^ 
 
 ..-■f<k\r..-t-~-. 
 
 
 
 -c* J 
 
 
 
 ■«i' 
 
 ctiou from the de!i?c portlDii ol tin 
 
 Some of the long bones in frogs, birds, and most of those in mam- 
 mals, have their ends distinct from the body or shaft of the grow- 
 ino- bone; these separately ossified ends are termed 'epiphyses': 
 the seat of the active growth of the sliaft is in a cartilaginous 
 crust at the ends supporting the epiphyses. When these coalesce 
 Avith tlie shaft, growth in the direction of the Ijone's axis comes to 
 
24 ANATOMY OF VERTEBRATES. 
 
 an end; but there is a slower growtli going on over the entire peri- 
 phery of the bone, which is covered by a membrane, called the 
 ' periosteum.' In this membrane, the vascular system of a l)one, 
 except the vessel supplying the marrow-cavity, imdergoes the 
 amount of subdivision which reduces its capillaries to dimensions 
 suited for penetrating the pores leading to the vascular canals, 
 figs. 11 and 15, a, a. 
 
 Thus bone is a living and vascular part, growing by in- 
 ternal molecular addition and change, and having the power of 
 repairing fracture or other injury. The shells and crusts of 
 molluscous and crustaceous animals are unvascular ; they grow 
 by the addition of layers to their circumference, may be east off 
 wlien too small for the growing body, and be reproduced of a 
 more eonformal)le size. AVhen fractured, the l^i'oken parts may 
 be cemented togctlicr by newly superadded shell-substance from 
 without ; but are not unitable by the action of the fractured sur- 
 faces from witliin. 
 
 Extension of parts, however, is not the sole process wliicli 
 takes place in the growth of bone ; to adajjt a bone to its destined 
 (jffice changes are wrought in it by the remo\al of parts pre- 
 viously formed. In fishes, indeed, we observe a simple unmodi- 
 fied increase. To whatever extent the bone is ossified, that jiart 
 remains, and conscfpiently most of tlic bones of fishes are solid or 
 spongy in their interior, except where tlie ossification has been 
 restricted to the surface of the primary gristly mould.' The bones 
 of the heavy and sluggish turtles and sloths, of tlie seals, and of 
 the whale-tribe, are solid. But in the acti\ e land quadrupeds, the 
 shaft of tlie long bones of the limbs is hollow, the first formed 
 osseous substance being absorbed, as new bone is licing deposited 
 from without. The strength and lightness of the limli-bones are 
 thus increased after the well-known principle of the hollow cohunn, 
 which Galileo, by means of a straw picked up from his ])rison 
 floor, exemplified, as an evidence of design, in refutation of a 
 charge of Atheism brought against him by the Inquisition. The 
 bones of birds, especially those of powerful flight, are remarkalde 
 for their lightness. The osseous tissue itself is, indeed, more 
 compact than in other animals; but its quantity in any given 
 bone is much less, the most admiralile economy being traceable 
 throughout the skeleton of ))irds in tlic advantageous arrange- 
 
 ' In this case, cxomplified in bones of the Lophiiis, Gi/roxiciis-, ami the lower 
 Batracliia, fossilisatioii, wliicli aflVcts only the ossilied ciust. lonves tlie a). pea ranee, 
 throngh the solution of the unossiiied cartilat;e, of a wide inedullarv cavity, wliieb 
 might mislead the raltcontologist in his inferences. 
 
ANATOMY OP VEKTEBRATES. 25 
 
 merit of tlic weighty material. Tims, in the long bones, the cavi- 
 ties analogous to those called 'medullary' in beasts, are more 
 capacious, and their walls are much thinner: a large aperture 
 called the ' pneumatic foramen,' near one end of the bone, com- 
 municates with its interior ; and an air-cell, or prolongation of tlie 
 lung, is continued into and lines the cavity of tlic bone, which is 
 thus filled with rarefied air instead of marrow. The extremities 
 of such air-bones present a light open net-work, slender columns 
 sliooting across iu different directions from wall to wall, and these 
 little columns are likewise hollow. 
 
 In the mammalian class, the air-cells of bone are confined to 
 the head, and are filled fronr the ca^'itics of the nose or ear, not 
 from the lungs. Such cells are called ' fr(jntal sinuses,' ' an- 
 trum,' ' sphenoidal,' and ' ethmoidal sinuses,' in man. The 
 frontal sinuses extend backward over the top of the skull in the 
 ruminant and some otlier quadrupeds, and penetrate the cores of 
 the horns in oxen, sheep, and certain antelopes. The most re- 
 markable developcmcnt of cranial air-cells is presented by the ele- 
 phant; the intellectual pltysiognomy of this huge quadruped being 
 caused, as in tlie owl, not by the actual capacity of the lirain case, 
 but by the vast extent of the pneumatic cellular structure between 
 the outer and iimer plates of the skull-wall. 
 
 In all these varied modifications of the osseous tissue, the cavi- 
 ties therein, whether mere cancelli, or small medullar}' cavities 
 as in the Crocodile, or large medullary cavities as in the Ox, or 
 pneumatic cavities and sinuses as in the Owl, are the result of 
 secondary changes by absorption, and not of the primiti'^'e consti- 
 tution of the bones. These are solid iu their commencement in 
 all classes, and the vacuities are estaldishcd by the removal of 
 osseous matter previously formed, wlulst increase proceeds by 
 fresh bone Ijcing added to the exterior siu-face. The thinnest- 
 walled and widest air-bone of the bird of flight was first solid, 
 next a marrow-bone, and finally became the case of an air-cell. 
 The solid bones of the Penguin, and the medullary bones of the 
 Apteryx, exemplify arrested stages of that course of developement 
 through which the pneumatic wing-bone of the soaring Eagle had 
 previously passed. 
 
 But these mechanical modifications do not exhaust all the 
 chano-es through which the parts of a skeleton, idtimately becom- 
 ino- Idouc, have passed ; they have been previously of a fibrous 
 or of a cartilaginous tissue, or both. Entire skeletons, and parts 
 of skeletons, of vertebrate animals exhiljit arrests of these early 
 stafi-es of developement ; and this quite irrespccti^'e of the grade of 
 
2G 
 
 ANATOMY OF VERTEBRATES. 
 
 the entire animal in the zoological scale. The capsule of the eye- 
 ball, for example, in man, is a fibrous membrane ; in the Turtle, it 
 is gristle ; in the Tunny, bone. The skeletal framework of tiie 
 Lancelot (Branchiostoma) docs not pass beyond the fibrous stage 
 of tissue-change. In the Sturgeon and Skate it stops at the gristly 
 stage, and hence these fishes are called ' cai-tilaginous.' Inmost 
 fishes, and all air-breatliing verteljrates, it proceeds to the bony 
 stage, with the sul:)sequent modifications and developements above 
 recited. 
 
 § 1.3. Classes of hone. — Bony matter is variously disposed in 
 the bodies of vertebrate animals. The Trunk-fish, fig. 16, dn, dp, 
 d.h, the Crocodile, and the Armadillo are instances of its accumu- 
 lation upon or near the surface of the body ; and hence tlie ball- 
 proof character of the skin of the largest of these mailed examples. 
 The most constant position of bone is around the central masses 
 of the nervous, ib. n, and vascular, ib. h, pi, systems, with rays 
 thence extending into the middle of the chief muscular masses, 
 forming the bases of the limbs. Portions of bone are also deve- 
 loped to protect and otherwise subserve the organs of the senses, 
 and in some species are found encasing mucus-ducts, and buried 
 in the substance of certain viscera — as, e. g. the heart in the 
 Bullock and some other large quadrupeds. Strong membranes, 
 called ' aponeurotic,' and certain tendons, become bony in some 
 animals; as, e. g. the 'tentorium' in the Cat, the temporal fascia 
 in the Turtle, the ' leaders' of the leg-muscles in the Turkey, the 
 nuchal ligament in the i\Iole, and certain tendons of the abdominal 
 muscles of the Kangaroo, which, so ossified, 
 are called the ' marsupial-bones.' The pri- 
 mary classification of the parts of the osseous 
 system is, therefore, according to their pre- 
 valent position, as in the cases abo^-e cited. 
 The superficial or skin-bones constitute the 
 ' dcrmo-skeleton' ; ' the deep-seated bones, in 
 relation to the nervous axis and locomotion, 
 form the ' neuro-skeleton' ;- the bones con- 
 s.cKums, ,,,,„,„,„„ iiected Avith the sense-organs and viscera 
 
 f)rm the ' splanehno-skeleton'; ' those de- 
 veloped in tendons, ligaments, and aponeuroses, the ' sclero- 
 skeleton.'' 
 
 
 Segment nf 
 
 ' Gr. ilcniKi, skin, and .v!ie!ii<m. 
 
 '' Gr. neuron, ruTvo, and .s/oc/c/on. 
 
 = Gr. .■:/,/, lycliiiim, visciis, or inward jiarl, and x/ufctvn. 
 
 ' Gr. xclcivs. Inu-d, and skdeion. 
 
ANATOMY OF VERTEBRATES. 27 
 
 In the arrangement of the parts of the clermo-, splanchno-, and 
 sclero-skeletons, no common pattern is recognisable. One can 
 but discern a purpose gained by such bony plates, cases, or rods, 
 in special relation to the halDits and well-being of the creatures 
 manifesting them ; but the diversity in the number, size, shape, 
 and relative position of dermal, tendinal, and visceral l^ones seems 
 interminable. The neuro-skeleton, which is the main part of the 
 osseous system, and might be termed the ' skeleton proper,' ex- 
 emplifies not only the principle of design and adaptation, but 
 that of unity of composition. Its parts are arranged in a series 
 of segments following and articulating with each other in the 
 direction of the axis of the body. 
 
 § 14. Tyjte scrpuent or vertebra. — Each complete segment, 
 called ' vertebra,' consists of a series of osseous pieces arranged 
 according to a type or general plan, exem- 17 
 
 plified in fig. 17 ; in which they form a 
 hoop or arch aljove, and another beneath, 
 a central piece. The upper hoop, encircling 
 a segment of the nervous axis, is called the 
 neural ' arch, n ; the lower hoop, encircling 
 a part of the vascular system, is called the 
 hremal ^ arch, 11 : their common centre is 
 termed the 'centrum.''^ The neural arch 
 is formed by a pair of bones, called ' neura- 
 pophyses,''' n, n, and by a bone sometimes 
 cleft or bifid, called the ' neural spine,' 
 ns : it also sometimes includes a pair of 
 bones, called 'diapophyses'" d, d. The hasmal arch is formed by 
 a pair of bones, called ' pleurapophyscs,'^ /;/; by a second pair, 
 called ' hajmapophyscs,'' A ; and by a bone, sometimes bifid, called 
 the 'hajmal spine,' hs. It also sometimes includes parts, or 
 bones, called ' parapojihyses.'^ Bones, moreover, may be developed 
 which diverge as rays from one or more of the above parts. 
 
 The parts of a vertel^ra which are developed from independent 
 centres of ossification are called ' autogenous ; ' those that grow 
 from prc^'iously ossified parts are called ' exogenous : ' the autoge- 
 nous parts of a vertel^ra are its ' elements,' the exogenous parts 
 are its ' processes.' ISTo part, however, is absolutely autogenous 
 
 ' Gr. neuron, ncrvo. ' Gr. dia, across, and apophusis. 
 
 ' Gr. haiina, blood. ^ Gr. pleuron, rib, and apophusis. 
 
 ' Gr. kentron, centre. ' Gr. for blood, and apoplnms. 
 
 * Gr. for norve, and apophusis, a pro- ° Gr. jmra, transverse, and apophusis. 
 jectina; part. 
 
28 
 
 ANATOMY OF VERTEBRATES. 
 
 18 
 
 Cranial sogmcii^or vertoljia 
 
 throughout the vertebrate series; and some parts, usually, exo- 
 genous, are autogenous in a few instances. 
 
 The vertebral elements are, the centrum 
 c, the neurapophyses n ; the neural spine 
 ns, the pleurapophyses pi, the Ivccmapo- 
 physes /(, and the haimal spine hs. The 
 exogenous parts are the diapophysis d, the 
 parapophysis;), the zygapophysis r,' the ana- 
 popliysis «,^ the metapophysis m,^ the hypa- 
 jiophysis, fig. 17, y,"* and the epapophysis, 
 fig. 17, e.^ Of the autogenous parts, the 
 neural spine is most commonly exogenous; 
 of the exogenous parts, the parajiophyses, 
 diapophyses, and hypapophyses, are sometimes autogenous. 
 
 Vertebra3 are suliject to many and great modifications — e. g. as 
 to the number of the elements retained in tlieir composition, as to 
 the form and pro2:)ortion of the elements, and e^'en as to the relative 
 position of the elements ; but the latter modification is never 
 carried to such a degree as to obscure the general pattern or 
 type of the bony segment. 
 
 Sometimes, as in the example, fig. 18, of the third segment of 
 the human skeleton, tlie neural arch, N, is much expanded, the 
 hcBmal one, ii, is contracted; and, in the expanded neural arch, 
 the autogenous diapophyses, d d, are wedged between the neura- 
 pophyses, n, and the enormously expanded neural spine, ns. IMore 
 19 commonly, as in the example from the thorax, fin-. 
 
 19, the ]ia3mal arch, /;.«, is much expanded, the neural 
 one n, contracted; and the parapophysis is re]>re- 
 sented somethnes by tlie exogenous growth from 
 the centrum, commonly by that, p, from the ril) pi. 
 Sometimes, again, as is exemplified in the neck of 
 the bird, fig. 20, and tlie tail of the Crocodile, both 
 neural and luvmal arches arc alike contracted, the 
 pleurapophyses, /)/, being excluded from the latter, 
 and standing out as continuations of the confluent 
 diapophyses and parapopliyses ; and the ha?mal arch 
 l)eing formed, either liy ha-majiopliyscs (Crocodile), fig. 7, or 
 hypapophyses (bird), fig. 20, /,//. Such vertebra deviate but 
 little from the ideal type, under its less developed condition, 
 as in fig. 7. The segments arc commonly simplified and made 
 
 ' Gr. j«f/,«, jmictioii, ,iu,l apvphiisis. • Qr. /,„/„,, l,,loiv, and „pophi,sis. 
 
 - Gr. ami, backwai-ds, ami ,v«7./,».v/.v. f Qr, cj,i, above, an.l „p,:ph„yis. 
 
 ^ Gr. iiict(/, bctwcon, iiiul ftpojiliusis. 
 
 ^xrlulira 
 
ANATOMY OE VERTEBRATES. 29 
 
 smuUcr as they apjiroach the end of the vertebral column ; one 
 clement or process after another is removed, until the vertebra 
 is reduced to its centrum, as in the suljjoined diagram, fig. 21, 
 of the archetype vertebrate skeleton. 
 
 § 15. Archeti/pe skeleton. — In this scheme, which gives a side 
 view of the series of segments or ' vertebraj ' of 20 
 
 which the skeleton is composed, the extreme 
 ones are the seat of those modifications, which, 
 according to their kind and degree, impress 
 class-characters upon the type. 
 
 The four anterior neurapophyses, 14, io, 
 n 6, 2, give issue to the nerves, the terminal 
 modifications of which constitute the organs 
 of special sense. That of smell, 4, 19, is 
 situated in advance of its proper (nasal) seg- 
 ment, which becomes variously modified to enclose and protect 
 it. The organ of sight, lodged in a cavity or 'orbit' l)e- 
 tween its own (the frontal) and the nasal segment, is here 
 drawn above that interspace. The nerve of taste perforates 
 the uenrapophj'sis of the third segment, 6, or passes by 
 a notch between this and the frontal segment, to expand in the 
 sense-organ, or ' tongue,' which is supported by the hannal spine, 
 41, 42, of its own (parietal) segment. The fourth is the organ 
 of hearing, 16, indicated above the interspace between the neura- 
 pophysis of its own (occipital) and that of the antecedent (parietal) 
 vertebra, in which it is always lodged ; the surrounding vertebral 
 elements being modified to form the cavity for its reception, which 
 is called ' otocrane.' 
 
 The jaws are the modified ha3mal arches of the first two seg- 
 ments. The month opens at the interspace between these liKinal 
 arches ; the position of the vent varies (in fishes), but always 
 opens behind the pelvic arch, s, 62, 63, p, when this is ossified. 
 
 Outlines of the chief developements of the dermoskeleton, in 
 difterent vei'tebrates, which are usually more or less ossified, are 
 added to the neuroskeletal archetype ; as, e. g. the median horn 
 supported by the nasal spine, 15, in the rhinoceros; the pair of 
 lateral horns developed from the frontal spine, 11, in most rumi- 
 nants ; the median folds, D 1, D u, above the neural spines, one or 
 more in number, constituting the ' dorsal ' fin or fins in fishes and 
 cetaceans, and the dorsal hump or humps in the bufialoes and 
 camels ; similar folds are sometimes developed at the end of the 
 tail, forming a ' caudal ' fin, C, and beneath the hromal spines, 
 constituting the ' anal ' fin or fins, A, of fishes. 
 
30 
 
 ANATOMY OF VERTEBRATES. 
 
 Ji^ 
 
 nil, 
 
 2 !5^ -J ct,X-«-* ^ 
 
 C)QB|aBllin3D| 
 
 The different elements of the pri- 
 mary segments are distinguished by- 
 peculiar markings : — 
 
 The neurapophyses by diago- 
 nal lines, thus — 
 
 The diapophyses by vertical 
 lines — 
 
 The parapophyses by horizon- 
 tal lines — 
 
 The centrum by decussating : 
 horizontal and vertical lines — ! 
 The pleurapophyses \>j diago- 
 nal lines — 
 
 The appendages by dots — '..'.'.'. 
 The neviral spines and haemal sinnes 
 are left blank. 
 
 In certain segments the elements 
 are also specified by the initials of 
 their names : — 
 
 ns is the neural spine. 
 n is the neurapophj'sis. 
 j)l is the pleurapophysis. 
 c is the centrum. 
 h is the ha3mapophysis, also indi- 
 cated by the numbers 21, 29, 
 
 44, 52, 58, 63, 64.' 
 
 lis is the hasmal spine. 
 a is the appendage. 
 
 The centrum is the most constant 
 vertebral element as to its existence, 
 but not as to its ossification. There 
 are some living fishes, and formerly 
 there were many, now extinct, in 
 which, whilst the peripheral elements 
 of the vertelira become ossified, the 
 central one remains unossificd ; and 
 here a few words are requisite as to 
 the developement of vcrtcbra\ 
 
 § 16. Di'vchpcmcnt of rerfebrcp. — 
 The central basis of the ncuroskcleton 
 is laid down in the embryo of every 
 vertebrate animal as a more or less 
 
 ' Sco 'Table or Synonyms, Spcciiil Homologies,' 
 indicated by numbers. 
 
 for the names of tlic bones 
 
ANATOMY OF VERTEBRATES. 
 
 31 
 
 ai.liposc wLiljytjTuce 
 
 liner ]:iyer 
 
 -a, 22 
 
 outer Inyer 
 of flbrous capsule 
 
 ueural caual 
 
 fll^rous liantl, 
 or basis of 
 latiuous chorda 
 
 cylindrical fibrous slieatli, filled with simple cells containing jelly. 
 The centrums, or ' bodies of the vertebra,' are developed in and 
 from the notochord. The leases of the other elements are laid 
 down in fibrous bands, diverging from the notochord, and giving 
 the first indication of the segmental character of the skeleton. 
 
 In Denitopteri the neu- 
 ral and h;\3mal canals are 
 formed by a separation of 
 the layers of the outer 
 division of the sheath of 
 
 ,1 ,1 If. .-^.-i A Transverse vertical sectiou of vertelintl column of JV/'/x/iie. XXI. 
 
 the notochord, fig. 22. A 
 
 transverse partition divides the larger portion of the neural canal, 
 lodging the myelon, from a smaller portion above containing 
 adipose tissue. In the Lancelet the substance of the noto- 
 chord, fig. 23, cli, consists of a number of circular discoid 
 or flattened vesicles, p)resscd one upon another within the 
 sheath, like a pile of coins in a purse ; the sheath is strength- 
 ened by a longitudinal filamentary ligament above and below. 
 Apjoneurotic septa jiass off, with each pair of nerves, to the 
 interspaces of the muscular segments, giving attachments to 
 the fibres. A median vertical membrane rises from the neural 
 
 riiagram of anatomy of tlic Lancelet, BranclnoUovia 
 
 sheath, and beyond the abdominal cavity descends from the hasmal 
 sheath, passing between the right and left series of myocommata. 
 The dermo-neural and dermo-hasmal spines are indicated by short 
 linear series of firmly adhering flattened cylindrical cells. The 
 next step in the skeletal tissues is shown in a pair of jointed 
 cartilaginous filaments, fig. 23, /*, which bound or strengthen the 
 borders of the longitudinal oral slit, each cartilage supporting on 
 conical prominences the oral cirri (ib. /, /): numerous carti- 
 lao-inous filaments strengthen the sides of the branchial cavity, ib. 
 a, with intervening fissures, not opening upon the skin. In the 
 Lamprey cartilaginous neurapophyses, fig. 24, n, n, strengthen the 
 sides of the neural canal. In the Sturgeon, fig. 25, the inner 
 
32 
 
 ANATOMY OF VERTEBRATES. 
 
 layer of the notochordal capsule has assumed the texture of tough 
 hyaline cartilage; and not only are firm opake cartilagmous 
 neurapophyses "present, but also parapophyses, pleurapophyses, 
 
 fibro-aiiliroso 
 CMual 
 
 neural canal 
 gclatlniius chorda 
 
 c=a( 
 
 inner l-iyei" I'f 
 niiruUH capsule as 
 hyaline cartilage 
 
 ncurapopnysis 
 internenral cartilage 
 
 plcurapopliysis 
 
 j>arainipliysis 
 iiiterliLeraal cartiiag 
 
 hanial canal 
 Abjonlina! vertebra, Sturgemi 
 
 Fore part ef skeleton. Lamprey trdwmiizon) 
 
 and neural spines. The part of the neurapophysis Ijounding the 
 true neural canal is usually distinct from that l^ounding the fat- 
 filled fissure aljove. The parapophyses are united by a con- 
 tinuous phvtc of cartilage forming an inverted arch beneath the 
 
 aorta, in the truidv, ana- 
 logous to that formed by 
 bone in the lower neck- 
 vertebra3 of birds, fig. 20. 
 In the Ch'uiKxra slen- 
 der subossified rinss 
 appear in the cartilagi- 
 nous sheath of the noto- 
 cliord, ■svhich are more 
 numerous than the neu- 
 ral arches. These, where unconfluent with each other, are 
 distinct also from the parajiophyses, which in the tail bend 
 down to form the hasmal arches. In the INIeditcrranean Grey 
 Shark (Nofiduniis cinerens) the vertebral centres arc still feebly 
 and irrelatively marked out by numerous slender rings of hard 
 cartilage in the notochordal capsule, the uumljer of vertebra? being 
 more definitely indicated by the neurapophyses and i^arapophyses ; 
 but these remain cartilaginous. 
 
 In the Lepidosiren the peripheral vertebral elements, fig. 41, n, 
 nx, p, hs, arc ossified, but the notochord, eh, with a thicker and 
 condensed capsule, remains. In the Piked Dog-fisli {Acaiitliiof:) 
 the vertebral centres coincide in number with tlic neural arches, 
 and are defined by a thin plate of bone, sliajicd like an hour- 
 glass, and fornnng the conical cavity at eacli end of the centrum : 
 the rest of whieli is cartilaginous external to the ' lionr-^Iass," and 
 sul)gelatinous within its terminal cavities. In the 8[iotted Dog- 
 fisli {Sri/Uiiiiii) the two thin bony cones of each centrum are con- 
 
ANATOMY OF VBRTEBKATES. 33 
 
 fluent at tlieir apices, which are perforated, and the notochord, 
 reduced to a beaded form, is continued through them : the 
 exterior of the bony cones is occupied Ijy 
 a clear cartilage. In the Porbeagle Shark 
 {Lamna cornubica) further ossification of 
 the conical plate has reduced the central 
 communication to a minute foramen. Os- 
 seous plates have also been developed in 
 the exterior clear cartilage : these plates 
 are triangular, parallel with the axis of the 
 vertebra, their apices converging towards 
 
 the centre: the interspaces are filled by v«,i™i t,,„,.^c,.. .cct.™ oj 
 cartilage. In the great Basking Shark cuufumof,sw«<7,»™<,a:.ma 
 CSelache maxima) fig. 26, the longitudinal bony lamina; are more 
 numerous and shorter than in Lamna, are peripheral in position, 
 and extend about one-third of the way towards the centre of the 
 interspace between the terminal cones, the rest being occupied by 
 a series of concentric cylinders of bone, interrupted by four 
 conical converging cavities, filled by cartilage ; of these, two, n, n, 
 are closed by the bases of the neurapophyses, and two, jh Jh hy 
 those of the parapophyses. There is a transition from the cylin- 
 drical to the longitudinally lamellar structure, the exterior and 
 largest of the cylinders sending out processes which join the in- 
 ternal margins of the conver<2;ino; lamclla3. In the Monk-fish 
 {Squatliui) the osseous jDart of the centrum between the termi- 
 nal cones is entirely in the form of concentric layers, few in numl^er, 
 and decreasing in breadth as they approach the centre. In the 
 Cestracion there are no concentric cylinders, but only longitudinal 
 lamellffi, radiating from the centre to the circumference, and giving 
 off short lateral plates as they diverge. 
 
 In the Topes ( Galeus), the Blue Sharks ( Carcharias), and in 
 most sharks which possess the nictitating eyelid, may be seen the 
 most advanced stage of ossification in the cartilaginous fishes : 
 the entire centrum, save at the four cavities closed by the neur- 
 and par-apophyses, is occupied by a coarse bone, more compact 
 where it forms the smooth exterior surface and that of the ter- 
 minal articular cavities. In osseous fishes (most Teleostomi) the 
 neur- and par-apophysial cavities are obliterated by bone, and 
 the neur- and par-apophyses are confluent, or suturally joined, 
 with the centrum ; but they retain a greater proportion, than in 
 higher classes, of the primitive gelatinous basis, which fills up the 
 deep cone or cup at each end of the centrum, fig. 27, c c. Only 
 in the ganoid Lepidosteus, among fishes, does ossification so extend 
 
 VOL. I. D 
 
34 
 
 Ai^ATOMY 05 VERTEBRATES. 
 
 Lfpidostcus 
 
 as to obliterate the front cavity, and protrude into the liind cavity 
 of the preceding vertebra, fig. 28 ; thus establishing a cup-and- 
 ball articulation on the ' opisthocoelian ' plan. 
 The cup-and-ball structure prevails throughout 
 the air-breatliing, land-seeking, or terrestrial, 
 Hamatocrya. So interlocked, the vertebra are 
 better fitted to support the body in air, and 
 transfer its weight to legs. Sometmies the cup 
 is behind, as in the land-salamander, the Surinam 
 marm, ^Q^d (Pipa), and some extinct crocodiles, thence 
 
 called Streptospondylus ; but, as a general rule, existing reptiles 
 have ' procoelian ' vertebras, or with the cup in front. In many 
 extinct reptiles {Sauropterygia, Dinosauria) ossi- 
 fication was so advanced as to leave no cavity 
 at either end of the centrum ; and these parts 
 were coarticulated by flattened or almost flat- 
 tened surfaces, as in mammals. Finally, both 
 extinct and recent Keptilia afibrd instances in 
 which the parts or elements of the vertebra have 
 coalesced into one bone. 
 
 The progressive stages in the developement of 
 a vcrteljra, which have been illustrated by the chief of those at 
 which it is arrested in the cold-blooded series, bear a close analogy 
 to those by which it reaches the coalesced condition as a siugle 
 bone in the warm-blooded classes. The principal secondary and 
 adaptive modifications will next be pointed out which mark with 
 special characters the collective trunk-vertebras in Hamatocrya. 
 
 § 17. Vertehrul column of Fishes. — In the Stiu-geon {Aci- 
 penser), fig. 29, the first five or six neural arches are confluent 
 with each other and with the parapophyses, forming a continuous 
 sheath of firm cartilage (fig. 62), inclosing the fore part of the 
 notochord, ib. a, and myelon, and perforated for the exit of 
 the nerves. The tapering end of the notochord is continued 
 forward into the fused basal elements of the cranial vertebras, 
 ib. ff, (f, and backward into the base and upper lobe of the 
 tail-fin, fig. 29, c. The vertebras are represented by their 
 peripheral elements, and ])rincipally by the neural and hasmal 
 arches. The pleurapo])liyses are limited to about twelve of 
 the anterior trunk-vertebras, are articulated by simple heads 
 to parapophyses, fig. 62, p, and rapidly shorten in the two or 
 three hinder pairs ; the large ones sometimes consist of two or 
 three pieces joined end on end, like the modified occipital rib, 
 called ' scapula.' Vegetative repetition of perivertebral parts 
 
ANATOMY OF VERTEBKATES. 
 
 35 
 
 not only manifests itself in the double pleur- 
 and neur-apophyses on each side, but in small 
 interneural and interha3mal cartilages, fig. 25. 
 These peripheral cartilages are more feebly 
 developed in Spatularia. 
 
 In the Chima3roids (Holocepliali) the iDases 
 of the neur- and par-apophyses of about ten 
 of the anterior trunk-vertebraj coalesce and 
 form a continuous accessary cartilaginous 
 covering of the fore part of the notochord ; 
 and the confluent neural spines here form a 
 broad and high compressed plate. Between 
 the neurapophyses are wedged accessory in- 
 terneural cartilages. 
 
 In Notidanus,Acantliias, Centrina,9iv\ Scjjm- 
 nus, the interneurals, fig. 30, i, resemble the 
 neurapophj^ses, ilj. n, inverted, and are in- 
 terposed, like wedges, between them, with 
 the apices reaching the centrum. In ScijlUum, 
 JMusteltis, Sphijrna, and Carcliarias, the in- 
 terneurals resemble the neurapophyses in size 
 and shape, but occupy a position above the 
 intervertebral joint. In Galeus the ' vegeta- 
 tive repetition ' is further exemplified by four 
 stellate points of ossification, one of which is 
 intervertebral ; and above these are rudiments 
 of neural spines. The spinal nerve directly 
 perforates the neurapophysis ; or, when the 
 two roots escape separately, one also per- 
 forates the interneural. The pleurai^opliy- 
 ses are short and simple cartilages, either 
 wedged into the interspaces of the parapo- 
 physes {Notidanus, Carcliarias, Scijmnus), 
 or attached to the ends of the parapophyses 
 ( Galeus) of, say, the twenty-six anterior verte- 
 brEB. In Acanthias there may be forty pairs 
 of such riblets, fig. 30, jA. 
 
 In the flat Plagiostomes (Skates, fig. 64, 
 Kays, Torpedos) vegetative repetition mani- 
 fests itself in the multiplication of verteljrre, 
 and especially of the central elements ; which, 
 as indicated by their rudimentary ossification ' 
 in Chimcera, are commonly more numerous 
 
 D 2 
 
 f/, 
 
 yM 
 
 Skeleton of Sturgeon, 
 iAcip(niser Sturio). CXTT. 
 
36 
 
 ANATOMY OF VERTEBRATES. 
 
 than the neural arches ; nor are interneural and interhasmal pieces 
 wanting. In Raia clavata these ' ossa intercalaria ' constitute the 
 
 chief part of the neural arch, at the 
 anterior part of the vertebral column ; 
 whilst the neurapophyses resume 
 their ordinary share in its formation 
 at the posterior part of the column. 
 In ZygcEJia there are interspinal 
 cartilages. In Rhinobatus a single 
 spine answers to two vertebral bodies, 
 and we may well suppose this mul- 
 tiplication of central pieces to have 
 been carried still farther in the pri- 
 meval fossil Ray { Spinachorhinus) 
 from the lower Lias. 
 
 In the anchylosed cervical verte- 
 l:)ra3 of the Skate the short centrums 
 are indicated by transverse bars along 
 the middle of the under j^art. In 
 the INIonk-fish (Srjuatina) the body 
 of tlie atlas is confluent with the 
 basioccipital, but the neural arch re- 
 mains distinct. 
 
 The parapophyses in most Eays 
 pass forward, and then backward, the 
 angle of one fitting, like an articular 
 process, into the notch of the para- 
 pophjrgis in advance : they do not 
 support pleurapophyses ; they gradu- 
 ally bend down behind the pelvic 
 arcli, and comjdete the hremal canal 
 about six vertebrm bevond it ; the 
 hffimal si>ines become flattened in the 
 tail of some Eavs. 
 In osseous fishes a trunk-vcrtelira consists of a biconcave body, 
 fig. 27, r, of a pair of neurapophyses, fig. 31, n, usually develop- 
 ing a spine, ib. iix, from their point of coalescence abo^'e the 
 neural canal ; and of a pair of parapophyses, ib. j' ; to which 
 are added in the alxlominal region in most fishes, and also in the 
 caudal region of some, a pair of pleurapophyses,/)/, figs. 31, 32. 
 Ossification usually couunences in the bases of the nenr- and 
 l)av-apophyscs, and iu tlie terminal cones of the centrum ; it 
 may proceed to blend the six jjoints into one bone, and fill 
 
 Forepart of skeleton, Piked Dog-fish 
 {AcaiUlitat<). XLiij. 
 
ANATOMY OF VERTEBRATES. 
 
 37 
 
 as indicated 
 in some, a 
 
 31 
 
 by the dotted 
 comnuinicatino'- 
 
 Abdominjil vertebrco (Mu.riU) 
 
 iiiiina] ve]'tebro3. 
 Pike {Bfii'X) 
 
 up the hollow outside the cones, 
 tract in the section, fig. 27. But. 
 aperture is left between the 
 terminal cones, as indicated 
 by the dotted line in fig. 31. 
 In many fishes the plates 
 by which the bone attains 
 the i)eriphery of the centrum 
 leave interspaces permanent- 
 ly occupied by cartilage, 
 forming cavities in the dried 
 or fossil bone, or giving a 
 reticulate surface to the sides 
 of the centrum. The bases of the neur- and par-apophyses 
 sometimes expand so as to wholly inclose the centrum before 
 coalescing therewith ; as, for example, in the Tunny, where 
 the line of demarcation may be seen at the border of the articu- 
 lar concavity. 
 
 In the Pike the neurapophyses seldom, in the Pohjptervji and 
 Aniia, never, coalesce with the centrum : the letter *■ shows the 
 neurapophysial suture in fig. 32. In the ScihiionidcB the neur- 
 apophyses remain distinct from both the centrum and from each 
 other, in the anterior vertebra; ; where each developes a long and 
 slender spine.' The parapophyses remain for some time distinct 
 from the l^ody of the vertebra, as well as from the ribs. In the 
 anterior vertebraa of the Carp the neurapophyses remain distinct, 
 as they do in the atlas of many other fishes, and a suture is ob- 
 servable between the parapophyses and centrum in embryo Cypri- 
 noids. In each vertebra the summits of the two neurapophyses 
 usually become anchylosed together, and to their spine ; but in the 
 Lepidosiren, fig. 41, the spine retains its character as a distinct 
 element, and is always attached by ligament to the top of the 
 neurapophysis, as it is in the Sturgeon, fig. 25. In the anterior 
 abdominal vertebraj of the Tetrodon, each of the neurapophyses, 
 though they coalesce in the interspace of the two spines to form 
 the roof of the neural canal, sends iip its own broad truncated 
 spine ; and these are not much-developed oblique processes, but 
 gradually apjjroximate and blend together, to form the single 
 normal sj^ine at the fifth abdominal vertebra.^ In the Barbel 
 the neural arches also support two spines, but one is placed 
 beliind the other. 
 
 xnv. vol. i. p. 16, No. 46. 
 
 lb. vol. i. p. 81. 
 
38 
 
 ANATOMY OF VERTEBRATES. 
 
 Terminal caudal vertebra?, Sword-flsti. xxill. 
 
 The interspaces of the neural arches -are occupied by a filjrous 
 aponeurosis— the remains of the primitive covering of the neural 
 
 axis : but in 
 most fishes the 
 arches are ad- 
 ditionally con- 
 nected toge- 
 ther by articu- 
 lar or oblique 
 process e s 
 {zyrj apophy- 
 ses ) : in the 
 Pike the ante- 
 rior one, fig. 
 
 32, z, is present, which barely touches the neural arch in advance ; 
 in Pohjpterus it overlaps that part. In the Perch a posterior 
 zygapophysis projects to receive the overlapping anterior one, 
 the relative positions being the reverse of those in most air- 
 breathing vertebrates. But, in some fishes, a second pair of 
 zygapophyses are developed, which resemljle the normal pair 
 in higher vertebrates in relative co-adaptation, but seem to 
 grow as exogenous processes, from the centrum itself, fig. 
 SI, z. It is also peculiar to fishes to have articular processes 
 developed from the parapophyses, as, e. g. in the abdominal region 
 of the Rays, and from the caudal vertebraj of the Sword-fish, fig. 
 
 33, z. In the Tunny these processes are branched, and form a 
 network about the h;cmal canal. ' In Loricaria peculiar accessory 
 processes are sent out from the neural arch of the seven anterior ver- 
 tebra wliich abut against the lateral shields of the dermo-skelcton. 
 The parapophyses are short in some fis\\cs,( Salmo, Clupcca, Atnia), 
 of moderate size in many, and longest in the Cod-trilDC, fig. 34, 
 p, where they expand in the abdominal region and sustain 
 the air-bladder which adheres to their under surface. In one species 
 of Gddus, the bladder sends processes into deeper cavities of the 
 parapophyses, foreshowing, as it were, the imeumatic bones of 
 birds. The parapophyses gradually bend lower down as they 
 approach the tail, where, in many fishes, they unite to form the 
 lifcmal canal. In Lcpidosteus the canal is formed by the pleura- 
 pophyses: whilst these, in Amia, Thi/ini its, ami some others, are 
 appended to the parapophysial inverted arclies, like luvnial spines. 
 In Lepidosireu the elements p, fig. 41, which in the abdomen 
 represent either iilcurapophyses or long parapophyses, bend down 
 in the tail to form the luumal arch. Not until we reach tlie 
 Ijatrachia in the ascciisi\e comparison do we find true ' luvma- 
 
ANATOMY OF VERTEBRATES. 39 
 
 pophyses,' fig. 43, /;, forming the htemal arch in the tail, and 
 coexisting there with par- and pleur-apophyses, ib. p, and pi. 
 
 The pleurapophyses of fishes correspond to what are termed in 
 Comparative Anatomy, ' vertebral ribs,' and in Human Anatomy 
 ' false or floating rilis : ' for, with few exceptions, of which the 
 Herring is one, fig. 37, their distal ends are not connected with 
 any bones analogous to sternal ribs or sternum ; i. e. the alDdomen 
 is unclosed below by the osseous parts completing the hajmal arch. 
 The true homologues of sternal ribs and sternum retain the primitive 
 aponeurotic texture, and may be well seen in the Bream, ex- 
 tending from the ends of the vertebral ribs. These elements, or 
 jdeurapophyses, figs. 31, 32, /;/, are usually appended to the 
 extremities of the parapophyses, p, the articulation frecpiently pre- 
 senting a reciprocal notch in each. But, in some bony fishes, as 
 Platax, the ribs articulate with the bodies of the vertebrae, in de- 
 pressions behind the parapo])hyscs ; and in PoJypterus beneath the 
 jiarapophyses, as in the cartilaginous Heptanchus, Carcharias, and 
 Alopias. 
 
 Between the floating ribs extends an aponeurosis, the remains 
 or homologue of the primitive fibrous investment of the abdomen 
 in the Lancelet and Lamprey. In the Salmon and Dory the ribs 
 continue to be attached to some of the parapophyses after they are 
 bent down, as in the Amia and Tunny, to form the hasmal canal 
 and sjiine in the tail. The costal apjjendages of the first vertebra of 
 the trunk are usually larger than the rest, and detached from the 
 centrum ; at least if we regard as such the styliform bones which 
 project from the inner side of the scapula?, and which have been 
 described as coracoids (Cuvier), and sometimes as displaced iliac 
 bones (Carus) : by the muscles attached to these styliform bones 
 the succeeding ribs are drawn forward and the abdomen expanded 
 in the Cyprinoids. Pleurapophyses are entirely absent in the 
 Sun-fish, Globe-fish (Diodon), the Tetrodon, the Pipe-fish {Fistu- 
 laria and Sijrupiathns), the Lump-fish and the Angler. Of all 
 osseous, or rather semi-osseous, fishes, Lophiits presents the simplest 
 vertebral column : the abdominal vcrtebraj are not only devoid of 
 ribs, but have the feeblest rudiments of parapophyses. The bodies 
 of the vertebras interlock at their lower and lateral parts by a short 
 angular process fitting into a notch in the next vertebra ; the lower 
 border of this notch represents the lower transverse process in 
 other fishes : it is obsolete in the anterior abdominal vertel^rm ; 
 begins to appear about the middle ones ; shows its true character 
 in the tenth ; and elongates, bending downward, backward, and 
 inward, to coalesce with its fellow, and form the ha;mal arcli at 
 the twelfth or thirteenth vertebra, from which the liamal spine is 
 
40 
 
 ANATOMY OF VERTEBRATES. 
 
 developed. The interlocking process of the anterior vertebra dis- 
 appears as the true inferior transverse process is increased. The 
 side of the neural arch is perforated for the nerve, and that of the 
 heemal arch for the blood-vessel. The anterior abdominal vertebrae 
 
 of the Tetrodon are 
 firmly clamped to- 
 gether by the para- 
 pophyses. 
 
 A vegetative same- 
 ness of form 2^revails 
 in fishes throughout 
 the vertebral column 
 of the trunk, fig. 34, 
 which is made up of 
 only two kinds of ver- 
 tebra;, characterised 
 by the direction of 
 the parapophyses, p : 
 these in the abdomi- 
 nal region are lateral, 
 iisually stand out and 
 support rilis : but in 
 the caudal region 
 bend down to form, 
 either by direct co- 
 alescence or by the 
 ribs that continue to 
 be attached to them 
 in a vertical position, 
 the hajmal arch. 
 
 The atlas is usu- 
 ally distinguished by 
 some modification of 
 the anterior articular 
 end of the centrum, 
 by the persistent 
 suture of the neural 
 arch, or by the ab- 
 sence or detachment 
 of its plcurapophy- 
 ses. Peculiar pro- 
 cesses are sometimes 
 sent ofi:' from the 
 
 Skeleton o£ the Haddoeli ^G^alas (vijUfinua) 
 
ANATOMY OF VERTEBRATES. 41 
 
 xmder part of the centrum, as, e. g. the two which articuhate with 
 the basioccipltal in the Arapaima gigas. As the centrum of the 
 athis retains its normal relations to the other elements, and the 
 ordinary mode of articulation with the body of the second verte- 
 bra, this shows no ' odontoid j^rocess ' in fishes. 
 
 The number of vertebrre varies greatly in the different osseous 
 fishes : the Plectognathi {Diodon, Tetrodon) have the fewest and 
 largest: the apodal fishes (Eels, Gymnotes) have the 35 
 most and smallest, in proportion to their size. It is not 
 easy to determine the precise number, on account of the 
 coalescence of some of the vertebras, or at least of their 
 central elements, in particular parts of the column. In- 
 stances of anchylosis of some of the anterior vertebra?, 
 analogous to that noticed in tire cartilaginous Sturgeons, 
 Chlma;ra3, Ehinobatcs, and some Sharks, occur also 
 amongst the osseous fishes, as in many Siiuroid and Cy- 
 prinoid species, in Loricaria and Dactglopterus. Fig. 35 
 represents the four singTilarly elongated anchylosed ante- 
 rior vertebraB in the Tobacco-pipe fish {Fistidaria tahac- 
 caria). A coalescence of several vertebrae is more con- 
 stant at the opposite end of the column in osseous fishes, 
 in order to form the base of the caudal fin, when this is 
 symmetrical in form, as in fig. 33, and in most existing 
 species of Teleostomi. But this modification is arrested 
 at difterent stages in the piscine class. In Cydostomi 
 the gristly parts of the vertebrre continue distinct, with 
 gradual reduction in size to the taper end of the long tail : AnoLjinsta 
 in Protopteri the bony representatives of the caudal ver- tcbnE,' Piue- 
 tebra3 behave in the same way: the notochord jDersists in (Fistuiaria) 
 both orders. In Muraidda, where it is changed into cen- 
 trums, these also gradually diminish in size, and remain distinct 
 to the tail-end. The continuous vertical fold of skin bordering 
 the compressed, long, and slender termination of the vertebral 
 column is not specialised as a caudal fin.' In Plagiostomi, Holo- 
 cepliali, Sturionida, and many Ganoidei, the caudal fin, fig. 
 29, c, is formed chiefly by the htemal spines and appendages, 
 developed to support a lower ' lobe ;' the vertebra? continue 
 distinct to the end of the tail, which bending upward, seems to 
 form an uj^per lobe longer than the lower : to this unsymme- 
 trical tail-fin the term ' heterocercal ' is applied. By decreased 
 
 ' This primitive embiyonal basis of the piscine tail-fin is not to be eonfonntled, 
 because it is symmetrical as to shape, with the extreme stage of derelopemental modi- 
 fication constituting the true ' honiocercal ' type of most existing fishes. 
 
42 ANATOMY OF VERTEBRATES. 
 
 number, with progressive confluence, of the caudal vertebras, the 
 ' upper lobe ' becomes gradually reduced in length, until the 
 symmetrical shape is attained. But this coexists in the Salmon, 
 Perch, and many extinct Ganoids with an unsymmetrical bend 
 of the coalesced caudal vertebras into the base of the upper lobe. 
 In true ' homocercals ' the terminal bodies of the caudal vertebrae 
 are not separately established in the primitive notochord, but are 
 continuously ossified to form a common, compressed, vertically 
 extended, and often bifurcated bony pjlate, fig. 3.3, rih' , from 
 which the neural and hasmal arches and their spines 
 radiate : from these elements alone can the number of 
 vertebras of such caudal fin be estimated ; normal de- 
 velopement proceeding here in the peripheral elements, 
 as throughout the vertebral column in Lepidosiren, whilst 
 it is arrested in the central parts of the vertebrje. In 
 the Sun-fish ( Orthagoriscus mala) it would seem as if a 
 row of rudimental vertebras had been blended together 
 mif ^^ right angles to the rest of the column, in order to 
 support the rays of the short, but very deep caudal 
 fin, which terminates the suddenly truncated body of 
 this oddly shaped fish. 
 is{; It is rare to find anchylosis save at the ends of the 
 
 vertebral series in fishes : sometimes, however, in the 
 Pleuronectidce, a kind of sacrum is formed by such bony 
 imion of the bodies, c, and hasmal spines, hs, of the 
 first two of the caudal series, as in fig. 36 ; ' in which 
 the broad and deep liamal spines are concave forwards, 
 and form a sort of pelvic posterior wall of the abdomen. 
 a In the Halibut {Hippor/lossus) the parapophyses of the 
 
 corresponding vertebras with those of the last abdominal 
 are similarly united, though the bodies remain distinct. 
 In Loricaria both the upper and lower arches of a con- 
 siderable part of the caudal region are blended together 
 into an inflexible sacrum ; but, as a general rule, there 
 exists no such impediment to the lateral inflections of 
 the tail in the present class. 
 
 Tlie number of trunk-vertebras is a useful specific 
 character in Iclitliyology ; and in counting them the 
 coalesced caudals are usually reckoned as ' one.' In tlic 
 Sun-fish (Orthiu/orisnis) I find but 8 abdominal and 8 
 caudal vertc1n-;T3 )iy distinct bodies. In a Globe-fish 
 ( Tetrodon) there are 7 abdominal and 10 caudal vertebrx : 
 
 ' Cslcol. CuUputiou, Mils Cull. Cliir. No. 188 ; xliv. /. p. 50. 
 
ANATOMY or VERTEBRATES. 
 
 43 
 
 m osseous 
 
 total, 17.' In the Conger there are 162 vertebra3 ; in the 
 Ophidium, 204; in the Gynmotus, 236; and even this number 
 is sui-passed in some Plagiostomes. 
 
 Although the vertebras maintain a considerable sameness of 
 form in tlie same fish, they vary much in different species. The 
 bodies are commonly subcylindrical ; as deep, but not so broad, 
 as they arc long ; more or less constricted in the middle, in some 
 to such a degree as to present an hour-glass figure. In Spina- 
 chorhinus they are extremely short; in Fistularia extremely 
 long ; in Tetrodon ^ they are much comjiressed ; in Platycephalus 
 they are more depressed ; in the tail of the Tunny the entire ver- 
 tebra is cubical,' with the ends hollowed as usual, but the four 
 other sides flat, the upper and lower ones being formed, in the 
 connected series, by the neural and ha3mal arches of the vertebra 
 in advance, flattened down and, as it were, pressed into cavities 
 on the upper and under surfaces, of the centrum of the next 
 vertebra ; so that the series is naturally locked together in the 
 dried skeleton ; and these arches cover not the neural and htemal 
 canals of their own, but of the succeeding, centrum. 
 
 The principle of vegetative repetition is manifested, 
 fishes, by the numerous centres of ossification, 
 from which shoot out bony rays affording ad- 
 ditional strength to many of the intermuscular 
 aponeuroses. In this system of bones may 
 be ranked those spines which arc attached to, 
 or near to, the heads of the ribs, and extend 
 upward, outward, and backward, between the 
 dorsal and lateral masses of muscles, fig. 32, i p, 
 fig. 21, pi, a. These 'scleral' spines are 
 termed, according to the vertel^ral element 
 they may adhere to, ' epineurals,' ' epicen- 
 trals,' and ' ei)ipleurals ' ; though each may 
 shift its place, rising or falling gradually along 
 the series of vertebra;. All three kinds are 
 present in the herring, fig. 37, in which n a 
 is the ' ei)ineural,' p a the ' epicentral,' jA a the epipleural spines. 
 The latter have been called ' upper ribs,' and in Polypterus are 
 stronn-er than the ('under') ribs themselves. In Esox and 
 Thymallus the epineural and epicentral spines are present : in 
 Cuprinus the epineural and epipleural ones : in Perca and Gadiis 
 the middle series only is found, passing gradually from the 
 
 Alulnmiiial verfehra, 
 IlL'rring (67"^«'«) 
 
 1 Ostcol. Collection, Mus. Coll. Chir. No. 357, p. SI. 
 "- lb. No. 357. " lb. No. 24-7. xxiv. i, p. 62. 
 
44 
 
 ANATOIIY OF VERTEBRATES. 
 
 par- to the pleur-ajiophyses : in Salmo only the upper series 
 exists, develoioed from the second to the antepenultimate abdo- 
 minal neurapoj)hysis, in <S'. Eriox} There are, however, gristly 
 representatives of epipleurals. In Glijphysodon the epipleurals 
 are anchylosed to the ribs, foreshowing their normal condition 
 in the bird's thorax. According to the seat of their develojie- 
 ment they belong to the ' scleroskeleton : ' by their attachments 
 to bone they are ' vertebral appendages.' 
 
 The vertical folds of skin from the middle line, constituting 
 the azygos fins, are the seat of ossifications in most fishes, develop- 
 ing a second row of spines, figs. 34, 38, dn, dn, above the neural, 
 n, and a corresponding row, dh, dh, below the hajmal, h, spines. 
 Some of these dermal bones, in certain fishes, project as hard 
 enamelled weapons from the surface of the l^ody. From the 
 bases of the dermal spines, other spines (fig 34, in, ill) usually 
 shoot downward into the intervals of the neural and hfemal spines. 
 In deep-bodied fishes they are broad and strong, as e. g. in the 
 Cock-fish, fig. 38 ; in the fiat-fishes they are doulale, figs. 39 and 
 40 ; and these modifications are usually repeated above and 
 below. Both interneural and interha?mal spines are commonly 
 shaped like daggers, plunged in the flesh to the hilt, which is re- 
 
 38 
 
 A rgii ?■(, iosns set ipi )iiii3 
 
 presented liy tlie jiart to wliich the fin-ray (dcrmoneural or 
 dermoliremal spine) is attached. In the ]ilaice tribe (P/oiro- 
 ncctidci'.) these superadded dermal ossifications are develojicd 
 above the cranial as well as the corporal vertebr* (fig. 39, dn). 
 
 xuv. /, p. IG. cuii. 
 
ANATOMY or VERTEBRATES. 
 
 45 
 
 and along the whole liEcmal region of the tnmk, from the head to 
 the tail. This want of correspondence with the number of the 
 true segments of the endoskeleton, and the seat of developement 
 of the inter- and dermo-neurals and inter- and dermo-hasmals, with 
 some minor considerations, led me, in 1845, to substitute for the 
 views and illustration of the typical vertebra; pro23osed by Geoffroy 
 St.-Hilairc, ' and then accepted and taught by Professor li. E. 
 Grant - in this country and by others abroad, the interpretation of 
 the supposed type-exemplar, which is contrasted with Geoftroy's in 
 fig. 40. The names applied by the French philosophical anatomist 
 to the several parts of the combined endo- and exo-skelctal segment 
 
 Plciu-oncctcs Solca. XLIII. 
 
 are opposite the left hand of the reader : those applied to them 
 in my ' Archetype of the Skeleton ' are opposite the right hand. 
 
 The small exogenous process standing out from the sides 
 of the centrum is a dismemberment of the parapojDhysis ; in 
 the first caudal vertebra it is given off' from the base of the 
 parapophysis, increases in length in the second caudal, rises upon 
 the side of the centrum in the third, and becomes distinct from 
 the parapophysis in the fourth : it diminishes and disajjpears in 
 the ninth and tenth caudal verteljric. In Polijptems and ]\Iura3- 
 noids a transverse process coexists, from the same cause, with the 
 parapophysis. This, in the twenty-fifth trunk-vertebra of 
 Murcena Helena,'^ bifurcates, and in the following vertebra} the 
 
 ' Memoires du Mus. 4to, ix. 1822, p. 119, pi. y. 
 ' Lectures on Conip. Anat. p. 58. ' xnv. p. 14. 
 
 No. 37. 
 
46 
 
 ANATOMY OF VERTEBRATES. 
 
 fissure deepens and tlic fork elongates, until at the seventy-third 
 
 the lower prong descends at a right angle to the upper one, and, 
 
 meeting its fellow, forms the hasmal arch. There are no true 
 
 40 hasmajDophyses in the tail of fishes : the elements there 
 
 composing the hajmal arch are parapophyses, pleura- 
 
 pophyses, or iDoth combined. In the abdomen only are 
 
 hasmapophyses represented by the supporting bones of 
 
 the ventral fins, fig. 41, e4. The slender ossicles 
 
 along its under part in the Hemng, fig. 37, dli, are 
 
 dermal bones, which, like the scutes of serjients, are 
 
 connected with the lower ends of the riljs, jjl- 
 
 In the subclass Protopteri the notochord, fig. 41, 
 ch, persists : the neural arches, n, ns, are ossified : 
 the hajmal arches in the abdomen are represented 
 by parial bones, p, attached to the notochordal sheath, 
 and curving outward, like the long parapophyses in 
 the Cod, and the short pleurapophyses in the Amia 
 and Salamander, with which they, more probably, 
 are homologous. These riblets bend down and 
 meet at the beginning of the tail, p, to form the 
 hasmal arch and support the hajmal spines, hs, along 
 that region. As in fishes, the Lepidosiren also de- 
 velopes in the continuous vertical fin-fold the acces- 
 sory ossicles marked m, ili, in the cut. 
 
 § 18. Vertehral column of Batrachia. — Xcither 
 inter- nor dcrmo-neurals are present in any gano- 
 cephalan or batrachian. In the former amphiljious 
 order the notochord persists, but with Ijeginnings of 
 the ossification of centrums : ' in Batrachia it is con- 
 verted into a series of separate centrums. These in 
 the Ichtliyomorphs are biconical, and deeply cupped 
 at Ijotli ends, through the same arrest of ossification 
 as in fishes : the developemeut of the vertebra goes 
 through tlie same piscine stage in the larvre of the 
 Theriomorphs, as indicated by the dotted lines d, fig. 
 42 ; in tlie mature quadrupedal stage of these Ba- 
 trachia, ossification converts one terminal cup into a 
 ball ; which may l)e the front one, as in Pipa, or the 
 hind one, as in Btitui, and most frogs and toads. In 
 the Land- Salamander, also, ossification goes to this 
 stage, with the ball in front. 
 
 I'liidd-iiTii] exii-ske- 
 Ictal L'k'iiieiits (il II 
 t'fiudal vt'rtflirii of 
 tliG riakc, II. 
 
 ' Loctuvcs OH Coiiip. Aunt. p. 191, I'ig. 81. 
 
ANATOMY OF VERTEBRATES. 
 
 47 
 
 The Siren lacertlna has betwe en eighty and ninety trunk-vertebrae. 
 They have many longitudinal ridges, the neural arch has coalesced 
 with the centrum, the neural spine forms the highest ridge and 
 bifurcates posteriorly to terminate upon the zygapophysis. A 
 
 41 
 
 skeleton of Lepidosircii anncctens. xxxiij. 
 
 hypapophysial ridge forms, by defect of ossification on each side, 
 the under part of the centrum. A parapophysial ridge extends 
 from a short anterior parapophysis to the longer parapophysial 
 part of the posterior transverse process. A diapophysial ridge 
 extends above, and nearly parallel with the former, from the 
 anterior zygajiophysis to the diapophysial part of the posterior 
 transverse jn'ocess. Thence a third short ridge is continued ti3 the 
 posterior zygapoj^hysis. The vacuities between these several ridges 
 resemble those in the vertebra of some fishes. The body of the 
 atlas extends forward like a short odontoid process : short par- 
 and di- apoiihysial plates are developed from each side of the atlas, 
 which has also the posterior zygapoi^hyses. In the second vertebra 
 the par- and di-apophysial plates have united to form a compound 
 
 42 
 
 Skeleton of Tadiiole of liLuia csoilenta 
 
 transverse process, which supports a short straight pjleurapophysis. 
 These elements are similarly developed from six or seven succes- 
 sive vertebrfe. In the tail the vertebra is compressed and vertically 
 extended by the bending down of the parapophysial plates to form 
 two vertical walls, intercepting a litemal canal. In the Proteus, 
 which has about sixty trunk-vertebra3, the third to the ninth in- 
 clusive support short ribs, attached to the lower (parapophysial) 
 
48 
 
 ANATOMY OF VERTEBRATES. 
 
 BkeU^toii of tlic Monopdmo 
 or rrotonopsia 
 
 half of the transverse process : they are wanting 
 in the twenty-one following vertebras, and re- 
 appear, well developed, in the thirty-first, where 
 they form with cartilaginous ha3inapophyses, a 
 pelvic arch. In the Menopome, fig. 4.3, the 
 second to the nineteenth vertebras support short 
 straight plevirapophyses, articulated to the ends 
 of transverse processes formed by par- and di- 
 apophyses, which intercept by their terminal 
 confluence an arterial canal. These processes, 
 t, are enlarged in the twentieth vertebra, s, and a 
 second rib-like piece, 62, the homotype of the 
 second part of the scapula in fishes, is articulated 
 to the short and thick rudimental rib, pi; the 
 inferior or ha3mal arch 63, 64, being cartilaginous. 
 The segment thus completed by tlie htemal arch, 
 represents a so-called ' sacral ' vertebra : the 
 second division of its rib answers to the ' ilium,' 
 6-2, and the hajmal cartilage to the ' ischium,' or 
 ' pubis.' Transverse processes t, progressively 
 decreasing in length are developed from the six 
 succeeding vertebras. Bony pleurapo})hyses pi, 
 are attached to the first of these, and cartila- 
 ginous rudiments of the same element to the 
 three following. Hasmal arches are anchvlosed 
 to the under part of the centrum of the second 
 to the twelfth caudal vertel^ra inclusive, and 
 these become more compressed to the cud of the 
 tail, for the support of a vertical fin. The ueiu-al 
 arches are broad, depressed, anchvlosed to the 
 centrum : they are complete to the fourteenth 
 caudal vertebra. The body of the atlas pre- 
 sents an odontoid process between the two arti- 
 cular surfaces for the occipital condvles ; it is 
 deeply cupped behind, as are the succeeding 
 vertebras at both ends. This vertebra has neither 
 di- nor pleur-apoiihyses. 
 
 The skeleton of the Newt ( Triton) resembles 
 that of the jNIenopome iu its general characters; the 
 neural and hannal s])ines are uiore produced in the 
 long tail, supporting there the chief swimming 
 organ of this aquatic batrachian. In one kind 
 the ribs arc more developed, occasioning the sub- 
 
ANATOMY OF VERTEBRATES. 
 
 49 
 
 genus called Pleurodeles. In the land Salamander the backbone 
 is strengthened by the ball-and-socket articulation of the trunk- 
 vertebra;. Cuvier notices a curious inconstancy in the place of 
 attachment of the jjclvic arch, sometimes to the fifteenth, some- 
 times to the sixteenth, 
 and in one instance sus- 
 l^ended by the right pier 
 to the sixteenth, by the 
 left to the seventeenth, 
 vertebra, in Salainun- 
 dra atra.^ 
 
 The oj)hiomorphous 
 batrachia are remark- 
 able for the multiplicity, 
 the theriomorphous for 
 the paucity, of distinct 
 vertebra; in the trunk ; 
 these latter have tlie 
 ball-and-socket articula- 
 tion. The frog, fig. 44, 
 A, has nine vertel^rin 
 and the coccygeal style 
 c ; but by coalescence of 
 this with the sacrum, 
 and of the atlas with the 
 second vertebra, in the 
 Surinam toad (^^pa), the 
 number of distinct triuik- 
 segments is in that 
 species reduced to seven. 
 
 In Rana boans the 
 atlas has no diapophy- 
 ses ; but they are present 
 
 and 01 great iengtn m skeleton of Iroe, a ; Tertelira B ana cru-pu3 c o£ toad. 
 
 the succeeding vertebras 
 
 to the sacrum inclusive, where they are thick and support by 
 their truncate ends two long rib-like bones, ib. A, 62, which 
 expand at their distal ends, and unite there to two partially 
 anchylosed bony plates, 64, which complete the haemal arch of the 
 ninth segment of the trunk. The superior developement of this 
 arch relates to the great size and strength of its appendages — 
 
 ' CLi. torn. V. pt. ii. p. 413. 
 E 
 
50 ANATOMY OF VERTEBRATES. 
 
 the hinder extremities — in the tailless order, especially the frogs. 
 In the seven vertebraj between the atlas and sacrum, two zyga- 
 pophyses loolcing upward are developed from the fore part, and 
 two looking downward from the back part of the neural arch ; 
 there is also a short spine. 
 
 In the Toad {Bufo vulgaris) the number of trunk-vertebra3, fig. 
 44, B, is the same as in the Frogs, iDut the diapophyses of the third 
 and fourth vertebra are relatively longer, those of the sacral 
 vertebra, s, relatively shorter, broader, and expanded so as to over- 
 lap the ilia, which are shorter' and more arched. In Cijstignathus 
 pachijpus the sacral diapophyses are subcylindrical. In Pipa the 
 diapophyses of the second and third vertebra3 are of unusual 
 length, and support semi-ossified, short, flattened pleurapophyses. 
 The diapophyses of the four succeeding vertebra; are short and 
 slender ; those of the sacrum are more expanded than in the toad, 
 and rest upon the anterior halves of the iliac Ijones. The coccy- 
 geal style shows, in most anourans, a simj^le anchylosed neural 
 canal, and also a hremal canal, as at h, d, fig. 44. 
 
 In the Ophiomorphs ( CcEcilice) the vertebra3, besides being very 
 numerous, are biconcave. 
 
 § 19. Vertebral column of Iclithyojiterygia. — In an extinct 
 order {lelttliifujiteri/f/ia) of Dipnoal Reptiles, modified for marine 
 life, but Ijreathing air, the trunk-vertebraj were very numerous, 
 very short, and Ijiconcave ; the centrums remained distinct from 
 the neural and hasmal arches, and were ligamentously, not sutur- 
 ally, united thereto. In the Ichthijosaiirus communis, fig. 105, 
 there are about 140 vertebra; ; in the anterior sixteen a short 
 parapophysis is developed from the side of the centrum, and 
 a diapophysis from the base of the neural arch ; but this soon 
 begins to project from the neurapophysial liorder of the centrum, 
 and then from the side of the centrum lielow that border. It 
 continues gradually to sink in position until, at about the fortieth 
 vertebra, it blends with the parapophysis, which alone continues 
 to rejiresent a transverse process, as far as at about the eightieth 
 vertebra,' where it disappears and the succeeding centrums Isecome 
 comjjressed, indicating the vertical position of the dermal tail-fin 
 which they supported. The atlas and axis centrums become 
 anchylosed by flat surfaces ; Init each supports its own neural 
 arch. Between the lower part of the atlas and the occipital 
 condyle is a wedge-shaped hypapo])]iysis, representing tlic part 
 called 'body of the atlas' in anthropotomy : a similar bone is 
 
 ' A dislocation or fracture commonly occurred at tliis part between the death and 
 final imbedding of the decomposing animal ; cr.xi. 
 
ANATOMY OF VEKTEBRATES. 51 
 
 wedged betweeu the atlas and axis, a third ))etween this and tlie 
 third vertebra ; all tending to strengthen and stiffen the part of 
 the vertebral column sustaining the skull, and adding to its power 
 of displacing the water in the agile movements of this ancient 
 predatory aquatic animal.' As in Fishes, also, the continuity of 
 the broad occiput with the trunk was uninterrupted by any cervical 
 constriction. The ribs commence at the second vertebra, but by 
 a Ijifurcate head ; and so continue, articulating with both par- and 
 di-a])ophyses until the confluence of those processes, when they 
 become single-headed. The ribs rapidly increase in length, which 
 is greatest at the middle of the thoracic-abdominal cavity, and 
 then gradually diminish to short and straight appendages, resem- 
 bling detached transverse processes, in the taiL The longer ribs 
 are grooved longitudinally ; their lower ends are united to ha;m- 
 apophyses, suljdivided into two or three overlapping slender 
 porti(jns, the lowest articidating ■with a median transverse style, 
 pointed at each end, representing the hajmal spine, and completing 
 the hicnial arch in the alxlomen. In the tail the hremapophyses 
 are simple, and attached by ligament, above to the centrum, and 
 below to one another. 
 
 § 20. Vertehral eolanm of Sai/ropten/f/ia. — In this extinct 
 order of aquatic Reptiles the vertebral bodies had their terminal 
 articidar surfaces either flat or slightly concave, or with the 
 middle of such cavity a little convex. In certain genera the 
 neck-vertebrfc were uncommonly numerous ; this was remarkably 
 so in the Plesiosaurus, fig. 45, in which those vertebra; consist of 
 centrum, neural arch, and pleurapophyses. The latter are wanting 
 in the first vertebra ; but both this and the second have the 
 hyjjapophyses. The cervical ribs are short, and expand at their 
 free end. They articulate by a simple head to a shallow pit, which 
 is rarely sujjported on a process, on the side of the centrum. 
 The body of the atlas articulates with a large hypapophysis 
 Ijelow, with the neurapophysis above, with the body of the axis 
 behind, and with part of the occipital condyle in front; and all 
 the articulations, save the last, may become oljliterated by 
 anchylosis. The hypapophysis forms the lower two-thirds, the 
 neurapophysis contributes the upper and lateral parts, and the 
 centrum forms the middle or bottom of the cup for the occipital 
 condyle. The second hypapophysis becomes confluent with the 
 inferior interspace between the bodies of the atlas and axis.^ As 
 the cervical vertebraj approach the dorsal, the costal pit gradually 
 
52 
 
 ANATOMY OF VERTEBRATES. 
 
 45 
 
 RlcoU'liiii of ricslosaums. OLXIII. 
 
 rises from the centrum to the 
 neurapophysis. This takes 
 
 i'place at the fortieth vertebra 
 in the Plesiosaurus liomalo- 
 spontlylus of the Whitby Lias, 
 but, in the PI. dolichodeirus, 
 fio-. 45, of the Dorsetsliire 
 Lias, at about the thirtietli, c. 
 The dorsal region is arbitrarily 
 commenced by the vertebra in 
 which the costal surface begins 
 to be supported on a diapo- 
 physis ; this progressively in- 
 creases in length in the second 
 and third dorsal, continues as 
 a transverse process to near 
 the end of the trunk, and on 
 the vertebra, S, between the 
 iliac bones, 62, it subsides to the 
 level of the neurapophysis. In 
 the caudal vertebrre the costal 
 surface gradually descends from 
 the neurapophysis upon the 
 side of the centrum ; it is 
 never divided by the longitu- 
 dinal groove wliich, in most 
 Ph'siosanri, indents that sur- 
 face in the cervical vertebra\ 
 The neural arches are com- 
 monly unanchylosed with the 
 centrum. The lono- and lara;e 
 spinous processes, in contact 
 along the trunk and base of the 
 neck, nuist have restricted the 
 bending movements chiefly to 
 the lateral directions. The 
 plcurapophyses gain in length, 
 and lose in terminal breadth, 
 in the hinder ecrvicals ; and 
 become long and slender ribs 
 m the dorsal region, curving 
 outward and downward so as 
 to encompass the upper two- 
 
ANATOMY OF VERTEBRATES. 53 
 
 tliii-ils of tlic thoracic-abdominal cavity. They decrease in lengtli 
 and curvature as they approach the tail, where they are reduced 
 to short straight pieces, as in the neck, l)ut are not terminally 
 expanded ; they cease to he developed near the end of the tail. 
 The hromapophyses in the abdominal region, are subdivided, 
 and with the hajmal spine or median piece, form a kind of 
 'plastron' of transversely extended, sliglitly bent, median and 
 lateral, overlapping bony bars, occupying the suljabdominal space 
 l)etween the scaprdar, 52, and pelvic, 64, arches. In the tail the 
 haimapophyses are short and straight, and remain, as in the 
 Iclithyosaurus, ununited l)oth above and below. One Sauro- 
 pterygian genus, Tiimjstrophai.s, had the centrum, in certain 
 "S'ertebrre, so long and hollow as to simulate a limb-bone. In 
 another genus, (^PUosaurus) they were as short, in the cervical 
 region, as in tlio Iclttlnjo.iaurus. In a third genus (NotJwsaurus) 
 two vertel)rffi are recognised as sacral hj their tliick, straight, and 
 convergent pleurapophyscs, of which the first overlaps the second. 
 In a fourth genus the wedge-shaped hypapophyses occur at the 
 lower interspaces of the dorsal and lumbar vertebrfc, whence its 
 name, Sjj/ienosaurus. 
 
 § 21. Vertebral column of Ojjhidia. — Amongst existing Keptiles, 
 the Serpents ( Oj/Jridict) surpass all others in the vast number of 
 their vertebra;, which, with incomplete hajmal arches, compose the 
 skeleton of the long, slender, limbless trunk, fig. 46. 
 
 In all these vertebra; the autogenous elements, except the 
 pleurapo])hyses, fig. 46, pi, coalesce with one another, and the 
 pleurapophyscs become ancliylosed to the diapophyses in the tail. 
 There is no trace of suture between the neural arch, fig. 47, 
 7is, z, and centrum, c. The outer substance of the vertebra is 
 compact, with a smooth or polished surface. The vertebra; are 
 ' procGjlian ; ' that is, they are articulated together l)y ball-and- 
 socket joints, the socket being on the fore jiart of the centrum, fig. 
 47 A, where it forms a deep cup with its run sharpl}^ defined ; 
 the cavity lof)king not directly forAvard, but a little downward, 
 from the greater prominence of the upper border : the well-turned 
 prominent ball terminates the back part of the centrum rather 
 more obliquely, its aspect being backward and upward, fig. 47, 
 c. The hypapophysis, A, is developed in different proportions 
 from different ^'ertcbraj, but throughout the greater part of the 
 trunk presents a considerable size in the cobra, 46, liy, and 
 crotalus, figs. 47, 47 A, It: it is shorter in the python and boa. 
 A vascular canal perforates the under surface of the centrum, and 
 there are sometimes two or even three smaller foramina. In the 
 
54 
 
 ANATOMY OF VERTEBRATES. 
 
 python a large, vertically oblong, but short diapophysis extends 
 from the fore part of the side of the centrum obliquely backward : 
 
 it is covered by the ar- 
 ticular surface for the 
 rib, is convex lengthwise 
 and convex vertically 
 at its upper half, but 
 slightly concave at its 
 lower half. In the 
 rattlesnake the diapo- 
 physis devclopes a small, 
 circumscribed, articular, 
 tubercle, ib. d, for the 
 ' vertebral rib ' or pleur- 
 ajjophysis, pi; a parapo- 
 physis,^', extends down- 
 ward and forward below 
 the level of the cen- 
 trum ; the anterior zy- 
 gapophysis, z, is sup- 
 ported by a process, 
 ib. d" , from the upper 
 end of the diapoijhysis. 
 The base of the neural 
 arch swells outward 
 from its confluence with 
 the centrum, and de- 
 vclopes from each angle 
 a transversely-elongated 
 zygapophysis ; that from 
 the anterior angle, z, 
 looking upward, that 
 from the posterior angle, 
 r', downward ; both sur- 
 faces being flat, and 
 almost horizontal, as in 
 the Batrachians. The 
 neural canal is narrow ; 
 the neural spine, na, is of 
 moderate height, about 
 equal to its antoro-pos- 
 terior extent; it is compressed and tnuicate. A wedge-shaped 
 process, ' zygosphcne,' zs, is developed from the fore part of the 
 
 skeleton of the colii'a {Naija tripihli,nis) 
 
ANATOMY OF VEKTEBRATES. 
 
 •55 
 
 47 
 
 ti-hr.v of tbe Rattlesuakc 
 tCmtillua) 
 
 base of the spine ; the lower apex of the wedge being, as it were, 
 cut off, and its sloping sides presenting two smootli, flat, articular 
 surfaces. This wedge is received into a cavity, the ' zygantruni,' 
 excavated in the posterior expansion of the neural arch, and 
 ha-^'ing two smooth articular surfaces to which the zygosphenal 
 surfaces arc adapted. Thus the vertcl^ras of serpents articulate 
 with each other by eight joints in addition to those of the cup and 
 ball on the centrum ; and interlock by parts reciprocally receiving 
 and entering one another, like the joints called tenon-and-mortice 
 in carpentry, fig. 47. In the caudal vertebra, tlie hypapophysis 
 is double, the transition being effected by 
 its 2^rogressive bifurcation in the posterior 
 abdominal vertebrfc. The diapophyses be- 
 come much longer in the caudal vertebra?, 
 and support in the anterior ones short ribs 
 which usually become anchylosed to their 
 extremities. 
 
 The pleurapophyses or vertebral riljs 
 have an oljlong articular surface, concave 
 above and almost flat below in the Pytlion, 
 with a tubercle developed from the upper 
 part, and a rough surface excavated on the fore part of the ex- 
 panded head for the insertion of the precostal ligament. They 
 have a large medullary cavity, with dense but thin walls, and a 
 fine cancellous structure at their articular ends. Their lower end 
 supports a short cartilaginous hajmapophysis, which is attached 
 to the broad and stiff abdominal scute. These scutes, alternately 
 raised and depressed by muscles attached 
 to the ribs and integument, aid in the glid- 
 ing movements of serpents ; and the ribs, 
 like the legs in the centipede, subserve 
 locomotion ; but they have also accessory 
 functions in relation to breathing and con- 
 striction. The anterior ribs in the colira, 
 fig. 4G, pi, are unusually long, and are 
 slightly bent ; they can be folded back one 
 upon another, and can be cbawn forward, 
 or erected, when they sustain a fold of 
 integument, peculiarly coloured in some 
 spectacled cobra — and which has the effect of making this 
 venomous snake more conspicuous at the moment when it is 
 about to inflict its deadly bite. The ribs commence in the 
 cobra, as in other serpents, at the third vertebra from the head. 
 
 4:7a 
 
 Frunt view of a. TevtclT.i, 
 itattlesnake 
 
 species — e.g., the 
 
56 ANATOMY OF VERTEBEATES. 
 
 The centrum of the first vertebra coalesces with that of the 
 second, and its place is taken by an autogenous hypapophysis : 
 this, in the python, is articulated by suture to the neurapojihyses ; 
 it also presents a concave articular surface anteriorly for the lower 
 part of the basioccipital tubercle, and a similar surface behind for 
 the detached central part of the body of the atlas, or ' odontoid 
 process of the axis.' The base of each neurapophysis has an 
 antero-internal articular surface for the exoccipital tubercle, the 
 middle one for the hypapojihysis, and a postero-internal surface 
 for the upjjer and lateral parts of the odontoid ; they thus rest on 
 both the separated parts of their proper centrum. The nenra- 
 pophyses expand and arch over the neural canal, but meet 
 without coalescing. There is no neural spine. Each neura- 
 pophysis developes from its upper and hinder border a short 
 zygapophysis, and from its side a still shorter diapophysis. In 
 the second vertebra, the odontoid j)i'esents a convex tubercle 
 anteriorly, which fills up the articular cavity in the atlas for the 
 occipital tubercle ; below this is the surface for the hyjiapophysial 
 part of the atlas, and above and behind it are the two surfaces 
 for the atlantal neurapophyses. The whole i)osterior surface of 
 the odontoid is anchylosed to the proper centrum of the axis, and 
 in part to its hyi)apophysis. The neural arch of the axis de- 
 velopes a short ribless diapophysis from each side of its base ; a 
 thick sub-bifid zygajjophysis from each side of the posterior 
 margin ; and a moderately long bent-back sirine from its ujiper 
 part. The centrum terminates in a ball behind, and below this 
 sends downward and backward a long hypajiophysis. 
 
 At the opposite extreme of the elongated body, two or three 
 much simplified vertel)ra3 are usually found blended together ; they 
 support the horny rings forming the warning rattle of the Cro- 
 talus. There is no sternum in true Ophidia. 
 
 The skeleton of the Python (P. tir/ris)^ has 291 vertebra'', of 
 which the 3rd to the 25 1st support moval)le ribs. The 74 
 anterior vertebraB develope hypapophyses. The skeleton of the 
 Hoa constrictor"^ has .305 vertebra3, a hypapophysis being developed 
 from the 60 anterior ones. In the skeleton of a Eattle-snake 
 {Crotalus horridusy with 194 vertebras, 168 support movable 
 ribs, and all these develope hypapophyses, fig. 47, h, as long as the 
 neural spines, ns. In the Naja, fig. 46, as many vertebra have 
 the lower process, but of less length. In the Kough Tree-snake 
 {DetrodoH scahcrY with 256 vertebra-, a hyi apophysis projects 
 
 ' XLIV. Yol. i. No. C02, p. 123. = Ih., No. 630, p. 132. 
 » lb., No. C40, p. 135. ' lb.. No. 638, p. 134. 
 
ANATOMY OF VERTEBRATES. 
 
 57 
 
 48 
 
 from the 32 anterior ones, directed backward in the first ten, and 
 forward in the hist ten, where tliey are nnusiialljr k)ng, and tipped 
 with a coat of hard dentine ; these perforate the oesophagus, and 
 serve as teeth. The jaws are merely roiigliened by rudiments of 
 teeth. The relation of this singular condition of the cervical 
 hypapophyses and the modification of the dental system to the 
 food of the Deirodon will be explained in the chapter on teeth. 
 
 § 22. Vertebral column of Lacertki. — The anguine or snake- 
 like reptiles, with fixed upper-jaws and a 
 scapular arch, pass gradually, by other forms 
 with rudiments of limbs (^Pseiidopus), to the 
 slender-bodied long-tailed lacertians. The dis- 
 tinction is effected through the establishment 
 of a costal arch in the trunk, completed by the 
 addition of a hajmal spine (sterniun) and hajma- 
 pophyscs (sternal ribs) to the pleurapciphyses 
 or vertebral ribs, which arc alone ossified in 
 Oph/d/a. 
 
 The A'ertebra; of the trunk have the same prococlian character, 
 i. e., with the cup anterior and the ball Ijchind, fig. 48 ; the latter, 
 c, being usually less prominent, more oblique, and more trans- 
 versely oval than in serpents. The vertebra; also are commonly 
 larger, and always fewer in number than in the typical Ophidia. 
 
 Those of the Iguanas retain the superadded articular surfaces 
 of the zygosphene, fig. 48, zs, and zygantrum ; but I have not 
 met with these superadded processes in other lacertians. In the 
 
 Trunk vertobni. Igiiium 
 
 49 
 
 Foi-c part o£ skeleton of a I^izard 
 
 Geckos the vertebraj are, exceptionally, liiconcave. ' The ribs do 
 not begin to he developed so near the head as in Ophidia. Not 
 only the atlas and dentata, but the third vertebra, fig. 49, and 
 sometimes, as in the Monitor ( Varcmus), the four following verte- 
 bra3, are devoid of pleurapophyses : when these first appear they 
 
 Sec those of the subgenus Hhynchocephalus, xliv. vol. i. No. 662, p. 142. 
 
58 
 
 ANATOMY OF VERTEBRATES. 
 
 are short, as at a ; but elongate in succeeding vertebra;, i to e ; 
 
 and usually at the eighth, 
 or ninth, fig. 49, /, 6, 
 {Lacerta), from the head 
 or tenth ( Varanus), they 
 are joined through the 
 medium of ossified ■ hasma- 
 pophyses to the ster- 
 num. Two( Varanus),\\\xt<i, 
 { Chameho, Ljuana), or four 
 ( Cyelodus), following ver- 
 tebra; are similarly com- 
 pleted; and then the ha3ma- 
 pophyses are either united 
 below without intervening 
 sternum ( Cliamdco), or two 
 or three of them are joined 
 by a common cartilage to 
 the cartilaginous end of 
 the sternmn. The ha?ma- 
 pophyses afterwards pro- 
 ject freely, and are reduced 
 to short appendages to 
 the pleurapophyses. These 
 also shorten, and sometimes 
 suddenly, as, e. g., after 
 the eighteenth vertebra iu 
 the Monitors ( Varanus), in 
 which they end at the 
 twenty-eighth vertebra, as 
 they began, viz., in the 
 form of short straight ap- 
 jiendages to the diapo- 
 physes. 
 
 The Draco volans, fig. 
 50, is so called on accoimt 
 of the wing-like expansions 
 from the sides of its body, 
 su])j)ortcd, like the hood of 
 the coln'a, by slender elon- 
 gated ribs. In this little 
 li/.ard there arc twenty 
 liieh commence apparently 
 
 ^crtebrtc supporting moNalilc rib; 
 
ANATOMY OF VERTEBRATES. 59 
 
 at the fifth. Those of the eighth vertebra first join the sternum, 
 as do those of the ninth and tenth ; the pleurapophyses of the 
 eleventh vertebra suddenly acquire extreme length ; those of the 
 four following vertebrte are also long and slender ; they extend 
 outward and Ijackward, and support the parachute formed by the 
 broad lateral fold of the abdominal integuments. The pleurapo- 
 j)hyses of the succeeding vertebral rapidly shorten. The sacrum 
 consists of two vertebras. There are about fifty caudal vertebra;. 
 
 The semi-ossified sternum in the Iguana has a median 
 groove and fissure, and readily separates into two lateral 
 moieties. The long stem of the episternum covers the outer 
 part of the groove, where it represents the ' keel ' of the sternum 
 in birds. 
 
 The two sacral vertebral retain, in most Lacertians, the cup- 
 and-ball joints ; and in the Scincks, where they coalesce, the 
 second presents a ball to the first caudal. Hremapophyses are 
 wanting in the first caudal, commence in the second, but are 
 displaced to the interval between this and the third ; they are 
 conflu.ent at their distal ends, and there produced into a sjiine : 
 these ' chevron bones ' are continued usually along two-thirds of 
 the tail. In most of the caudal vertebra; the anterior third of 
 the centrum is marked off by a line, just anterior to the dia- 
 pophyses, where the tail snaps off, when a lizard escapes, leaving 
 the part that has been seized in the hands of the bafHed pursuer. 
 The ossification of the centrum from two points, and their in- 
 comjjlete anchylosis has jDrospective relation to the liability of 
 lizards to be caught by their long tail, and lends itself to their 
 escape. The epiphysial line does not extend through the thin 
 and brittle neural arch, which readily snaps when the two parts 
 of the centrum to which it is anchylosed are separated. Lizards 
 reproduce the lost tail ; but the vertebral axis is never ossified in 
 the new-formed part. 
 
 In the slow- worm (Angxiis) there arc 111 vertebras, 61 of wliich, 
 beginning at the fourth, support free ribs. The transverse pro- 
 cesses of the tail are formed by short anchylosed 2:)lenrapophyses, 
 winch are bifurcate in the second and third caudals. The hypa- 
 pophyses are, also, anchylosed to the centrum ; but, instead of 
 remaining distinct, as in true Oplddla, they unite at their lower 
 ends and complete the htemal arch. The vertebral of the Amphis- 
 bcEna have no neural spine. 
 
 The lacertian modifications of the atlas and axis' agree in the 
 
 ' XLiv. vol. i, pp. 139 — 149. 
 
60 
 
 AIJATOMY OF VERTEBRATES. 
 
 main with those in the Python. In Istiurus the cervical hypa- 
 popliyses are compressed, distinct, and articulated to the inter- 
 sjjace between their own vertebra and the one in advance. The 
 caudal vertebraj are remarkable for the great length of their 
 neural spines. 
 
 In the Chameleon the ribs commence at the fourth vertebra, 
 and those of the sixth are articulated by semiossified cartilages to 
 the sternum, as are the tlu^ee following pairs ; in the next eight 
 or ten jiairs the long and slender cartilages meet and unite to- 
 gether at their extremities. There are two lumbar and three 
 sacral vertebra3 ; the tail is long and prehensile. In the 
 Iguana tuberculata twenty-one vertebra;, commencing with the 
 fifth, support free ribs, and those of the ninth first join the 
 sternum. 
 
 § 23. Vertebral column of Chelonia. — This column is most ex- 
 
 51 
 
 SkeU'tnii iir J^miis Eiiropd-a. xxxviil. 
 
 traordinary in those RepfiUa to wliich, in llie manifold modifica- 
 tions of tlie organic framework, has been given a portable abode, 
 in compensation for inferior powers of locomotion and the want 
 of dcfcnsl^•e weapons. 
 
ANATOMY OF VERTEBRATES. 
 
 61 
 
 The expanded tlioracic-abdominal case, fig. 51, K, K, into 
 wliicli, in most Clielonians, tlie head, the tail, and the four ex- 
 tremities can be withdrawn, and in some of the species be there 
 sliut np by mo^-alile doors closely fitting both the anterior 
 and posterior apertures — as, e.g., in the box-tortoises (Cino- 
 steriioii, Cistudo) — has been the subject of many investigations; 
 and not the least interesting residt has been the discovery 
 that this seemingly special and anomalous superaddition to the 
 ordinary vertebrate structure is due, in a great degree to the 
 modification of form and size, and, in a less degree, to a 
 change of relative position, of ordinary elements of the vertebrate 
 skeleton. 
 
 The natural dwelling-chamlaer of the Chdonia consists chiefly, 
 and in the marine species ( Cheluue) and soft-turtles ( Trionyx) 
 solely, of the floor and the roof: 
 side-walls of variable extent are 
 added in the fresh-water species 
 {Eiiu/s) and land-tortoises ( Tes- 
 tudo). The whole consists 
 chiefly of osseous ' plates ' with 
 superincumbent horny ' scutes,' 
 except in Trionyx and Spharyis, 
 in which these latter are 
 wanting. 
 
 The roof, or ' carapace,' fig. 
 52, consists of a ' median ' series 
 of symmetrical plates, ch, s i to 
 6-11, and of two 'lateral' series 
 forming a pair, -pi i to pi 8, the 
 whole being surrounded by a 
 circle of ' marginal ' pieces, m i 
 
 to py, completed anteriorly by c/*, the first of the median 
 series. Of the median series eight, s i to « 8, are attached to 
 the spines of eight subjacent vertebra; : the lateral or parial 
 plates, pd 1 to p)l 8, are attached to, and more or less blended 
 with, the ribs of the same vertebraj ; and the ends of these ribs 
 usually articulate by gomphosis with a corresponding nvnnber 
 of the marginal pieces, of which, however, there may be from 
 twenty-four to tAventy-six, including the two median and symme- 
 trical ones, di and py. That these marginal pieces are the least 
 essential parts of the carapace is shown, not only by their incon- 
 stant number, Isut by their partial or total absence in some of the 
 soft-turtles {Gymnopus, Sphargis). 
 
 m.7 
 
 Carapace oC tiio Lnggcrbond Tm-tlc iChdouG 
 caouaiiiui) 
 
62 ANATOMY OF VERTEBRATES. 
 
 The median pieces, « i to s n, are called the 'neural' plates; 
 the lateral pieces, pi i to pi 8, the ' costal ' plates ; the term 
 ' marginal ' is restricted to those peripheral pieces which form pairs, 
 m 1 to m 12 ; the anterior symmetrical piece, ch, constant in all 
 Chelonia, is called the ' nuchal ' plate ; the posterior symmetrical 
 piece, pij, which is wanting in all the Trionycida, is the ' pygal ' 
 plate. The neural arch, connate with the first neural plate, s j, is 
 supported partly by the centrum of the vertebra to which the first 
 pair of free riljs is articulated, and which, therefore, is reckoned 
 as the first dorsal vertebra : these ribs are small and slender, 
 attached at both their extremities, the outer end abutting against 
 the under part of the first pair of costal plates, wliich they help 
 to sustain. The second to the ninth dorsal vertebras inclusive, 
 being those which are more immediately connected with the neural 
 and costal plates, are the ' vertebrre of the carajjace : ' their 
 characters, though not less artificial than those which distinguish 
 the ' dorsal ' or ' lumbar ' vertebras of other rejitiles, are much 
 more marked and constant. The eighth vertel^ra of the cara- 
 l^ace is succeeded by one, which in some species (e. g. Chelone 
 caouanna) supports a pair of short ribs, in others ( Trionyx) none, 
 and which is therefore reckoned a ' lumbar ' vertebra ; this is 
 followed by two otlier vertebras, with short and thickened ribs, 
 abutting against the iliac bones and representing the ' sacrum,' 
 fig. 51, G : as these three vertebras are not innnediatelv united with 
 the ninth, tenth, and eleventh ' neural plates,' they have less claim 
 than the first dorsal vertebra to be regarded as euterino- into the 
 composition of the carapace. 
 
 The ' plastron,' fig. 53, or floor of the thoracic-abdominal 
 chamber, consists, in all recent Chelonia, of nine pieces. The 
 median and symmetrical piece, .?, is the ' entosternal ; ' the four 
 pairs, counted from liefore backward, are res])cctively, the 
 ' episternals ' (e.s), ' hyostcrnals ' {hs,) ' hyposternals ' {ps), and 
 ' xiphisternals ' {xs). 
 
 In all the Chclonians, save the coriaceous (Splitnyis) and soft 
 turtles ( Trioriyeidce), the outer surface of the carapace is impressed 
 by the horny scutes, commonly called ' tortoise-shell ; ' and these 
 epidermal productions have received definite names in Zoological 
 Treatises, their modifications being found of great use in charac- 
 terising species. In fig. 52, v i is placed on" the first ' vertebral 
 scute ' close to its union with the first and second ' costal scutes • ' 
 and v'2 io V r, indicate the succeedhig ^•crtebral scutes, the outer 
 angles of which are similarly wedged between (lie adj,.inino- pairs 
 of ' costal scutes : ' beyond the costal scutes arc a scries of'^' mar- 
 
ANATOMY OF VERTEBRATES. 
 
 (i3 
 
 ginal scutes,' suiiported by the marginal plates, and crossing their 
 sutures. 
 
 In the Trianijcida the exterior surfiice of the carapace and 
 plastron is remarkable ibr its rougli vermicular or piuictate 
 sculptiu'ing. 
 
 The median bony pieces of the carapace, fig. 52, ch, s i to .s ii, 
 have been regarded as lateral expansions of the summits of the 
 neural spines ; the medio-lateral pieces, ib. pi i to pi 8, as similar 
 devclopemcnts of the ril^s ; and the marginal pieces ib. m i to m 13, 
 as the homologues of the sternal ribs. But the developement of 
 the carapace sliows that ossification begins independently in a 
 fil)ro-cartilaginous matrix of the corium in the first, cli, and some 
 of tlie last, s 9 to « u, median plates, 
 and extends from tlie summits of the ^^ 
 
 neural spines into oidy eight of the in- 
 tervening plates, « 1 to .? 8 : ossification 
 also extends into the contiguous lateral 
 plates, j)l 1 to 2^1 8? in some Chelonia, 
 not from the corresponding part of the 
 sulijaeent ribs, but from points alter- 
 nately nearer and fartlier from their 
 heads,' showing that such extensitin of 
 ossification into the corium is not a 
 developement of the tubercle of the 
 rib, as has been supposed. Ossification 
 commences independently in the corium 
 for all the marginal jolates, m i to ptj ; these never coalesce witli the 
 bones uniting the sterniun with the vertebral ribs, are often more 
 numerous, sometimes less numerous, than those ribs, and in a few 
 species are wanting. Whence it is to be inferred that the ex- 
 ])anded bones of tlie carapace, whicli are supported aiad impressed 
 by the thick epidermal scutes called 'tortoise-shell,' are dermal 
 ossifications, homologous with those which support the nuchal and 
 dorsal epidermal scutes in the crocodile. Along the under surface 
 of the costal plate the slender or jorojoer portion of the rib may 
 be traced, of its ordinary breadth to near the head, which liberates 
 itself from the costal plate, as at I, fig. 51, to articulate to the in- 
 terspace of the two contiguous vertebra;, to the posterior of which 
 such rib jiroperly belongs. 
 
 In the 'plastron,' fig. 53, the entosternal, s, answers to the 
 sternum iu the crocodile : the parial pieces are ' ha3ma2Dophyses ' or 
 
 ri;istron of Clielonc caotumna 
 
 CLXII. p, 163, pi, xiii. fig. 1. 
 
64 ANATOMY OF VERTEBRATES. 
 
 sternal ribs, connate in a more or less complete degree with dermal 
 bony plates. There were five pairs in the extinct Pleurosternon. 
 
 In the marine Chelonians the dermal ossifications, fig. 52, pi i to 
 8, do not cover the whole of the intercostal spaces ; the slender 
 ribs project beyond them. In the fresh-water and land kinds 
 they extend to the marginal plates and complete the bony roof, as 
 in fig. 51. There is a similar diff'erence in the degree of ossification 
 of the ' plastron ' between the genus Chelone and the genera Emys 
 and Testudo. 
 
 In the Chelonia the true centrum of the atlas does not coalesce, 
 as an 'odontoid' process, with that of the axis, and usually supports 
 its own neural arch: the hypapophysis is proportionally reduced.' 
 All the eight cervical vertebras, fig. 51, E, are free, movable, and 
 ribless : the fourth of these vertebraj has a much elongated centrum, 
 wliich is convex at both ends : the eighth is short and broad, with 
 the anterior surface of the body di^-ided into two transversely 
 elongated convexities, and the posterior part of the body forming 
 a single convex surface divided into two lateral facets ; the under 
 part of the centrum is carinate ; the neural arch, wliich is 
 anchylosed to this centrum, is short, broad, obtuse, and overarched 
 by the broad expanded nuchal plate. The first dorsal vertebra 
 is also short and broad, with two short and tliick pleurapophyses, 
 articulated by one end to the expanded anterior part of the 
 centrum, and united by suture at the other end to the succeeding 
 pair of ribs. The head of each rib of the second pair is supported 
 upon a strong trihedral neck, and articulated to the interspace of 
 the first and second dorsal vertebra : it is connate, at the part 
 corresponding to the tuljcrclc, with the first broad costal plate, 
 which articulates by suture to the lateral margin of the first 
 neural plate, and to portions of the nuchal and third neural 
 plates : the connate rib, which is almost lost in the sul^stance of 
 the costal plate, is continued with it to the anterior and outer part 
 of the carapace, where it resumes its subcylindrical form, and 
 articulates with the second and third marginal pieces of the cara- 
 pace. The neural arch of the second dorsal vertebra is shifted 
 forwards to the interspace between its own centrum and that of 
 the first dorsal vertebra. A similar disposition of the neural 
 arch and of the ribs jircvails in the third to the ninth dorsal 
 vertebrre inclusive. The bony floor of the great abdominal box, 
 or ' plastron,' is formed by the h;«mapophyses and stermnn connate 
 with dermal osseous plates, forming, as in the turtle, nine pieces, 
 
 ' CLXVII. p. 435, pi. xiii. 
 
ANATOMY OF VERTEBRATES. 65 
 
 but tliey are more ossified, and the liyo- and hypo-sternals unite 
 suturally with the fourth, fifth, and sixth marginal phxtes, forming 
 the side-walls of the bony chamber cut through in fig. 51. Tlie 
 junction between the hyo- and hypo-sternals admits of some 
 yielding movement. The iliac bones abut against the pleurapo- 
 physes of the tenth, eleventh, and twelfth vertebra;, oomiting from 
 the first dorsal vertebra. These three vertebra form the sacrum : 
 their pleurapophyses are unanchylosed, converge, and unite at 
 their distal extremities to form the articular surface for the ilium. 
 Beyond these the caudal vertebric, ib. H, thirty-five in number in 
 Testudo elephantojJus, are free, with short, straight, and thick 
 pleurapophyses, articulated to the sides of the anterior expanded 
 portions of the centrums. They diminish to mere tubercles in the 
 tenth caudal vertebra, and disappear in the remainder. The )ieural 
 arches of the caudal vertebras are flat above, and without s])ines. 
 
 § 24. Vertchrul column of CrocodUia. — In this order free I 
 j^leurapophyses are developed from all the cervical vertebras ; that \ 
 of the atlas, fig. 54, a, is attached to the hypapophysis ; the neur- 
 apophyses rest, in jJart upon this element, in part upon the proper 
 centrum, which coalesces with that of the axis : the neural spine 
 of the atlas remains distinct, like that of the occiput, and is broad 
 and flat. The centrum of the axis is flat in front, and convex 
 behind : the neural arch, as in the succeeding verteljra, is com- 
 pleted by the connate spine. The pleurapophysis, ib. h, lias a 
 Ijifurcate head. With the exception of the two sacral vertebras, 
 wliich are flat at one end and concave at the other, and of tlie first 
 caudal vertebra, wliich is convex at both ends, the l>odies of 
 all the vertel:)ra3 Ijeyond the axis are conca^'e in front and con^'cx 
 behind. Tlie proccelian centrum of the third cervical is shorter 
 but broader than the second ; a parapojihysis is developed from 
 the side of the centrum, and a diapophysis from the base of the 
 neural arch ; the pleurapophysis is shorter, its fixed extremity is 
 bifid, articulating to the two above-named processes ; its free 
 extremity expands, and its anterior angle is directed forward to 
 abut against the inner surface of the extremity of the rib of both 
 the axis and atlas, whilst its posterior prolongation overlaps the rib 
 of the fourth vertebra. The same general characters and imbri- 
 cated coadaptation of the ribs, not given in the diagram, 54, 
 characterize the succeeding cervical vertebra; to the seventli 
 inclusive, fig. 57,;:^, the hypapophysis progressively though slightly 
 increasing in size. In the eighth cervical the rib, li, becomes 
 elongated and slender ; the anterior angle is almost or quite 
 suppressed, and the posterior one more developed and produced 
 
 VOL. I. F 
 
66 
 
 ANATOMY OF VERTEBRATES. 
 
 54 
 
 more downward, so as to form the body of the rib, which termi- 
 nates, however, in a free point. In the ninth cervical, the rib, i, 
 is increased in length, but is still what would be termed a ' false ' 
 or ' floating ril) ' in anthropotomy. 
 
 In the succeeding vertebra the pleurapojihysis, fig. 54, /.•, 
 articulates with a hjcmapophysis, and 
 the haemal arch is completed by a 
 hajmal spine; by which completion 
 of the typical segment we distinguish 
 tlie commencement of the series of 
 dorsal vertebri-c. With regard to the 
 so-called ' 2:)erforation of the transverse 
 process ' this equally exists in the pre- 
 sent vertebra, as in the cervicals ; on 
 the other hand, the cervical vcrtebraj 
 equally show surfaces for the articu- 
 latidu of ribs. The typical characters 
 of the segment, due to the completion 
 of both neural and liannal arclies, are 
 continued in some species of Crocodilia 
 to tlic sixteenth, in some { Crocodilus 
 acutns) to the eighteenth vertebra. In 
 the Crocodilus acutus and the Alligator 
 luciiis the hremapophysis of the eighth 
 dorsal rib (seventeenth segment from 
 the head) joins that of the antecedent 
 vertebra. The jdeurapophyses ]iroject 
 freely outward, and become * floating 
 riljs ' in the eighteenth, fig. 55, h, 
 nineteenth, ib. c, and twentieth, ib. d, 
 vertebra\, in which tliey liecome rapidly 
 shorter, and in the last appear as mere 
 appendages to the end of the long and 
 broad diapophyses : but the hwmapo- 
 ])hyscs by no means disappear after 
 the solution of their union with their 
 ])leuraj)ophyscs ; tliey are essentially 
 independent elements of the segment, and are according! v con- 
 tiniied, in ])airs, fig. 55, 3, 4, 5, f,, 7, and 56, along the ventral sur- 
 face of tlie abdomen of the Croeodilin, as far as their modified 
 liomoty])es the ynd.iic l)oncs,ib. 8. Tliey are more or less ossified, 
 and are generally divided inio two en- three iiieces. A sboi't carti- 
 laginous piece, an unossificd jiart of the iikMu-ajiopliysis, intervenes 
 
 r)i;icnviii) uf niilr 
 
ANATOMY OF VEETEBRATES. 
 
 67 
 
 between it and the litemapopliysis. A small cartilaginous appen- 
 dage is attached to some of the ribs. 
 
 The lumbar vertebnB are those in which the diapophyses cease 
 to support moveable pleurapophyses, although they are elongated 
 by the coalesced rudiments of such, ib. e,f,fj, h, which are distinct 
 in tlie young Crocodile. The length and j)ersistent individuality 
 of more or fewer of these rudimcntal ribs determines the numljcr 
 of tlic dorsal and lumljar vertel5ra3 respectively, and exemjilifics 
 the purely artificial character of the distinction. The numl:)er of 
 verteljr;T3 Ijctween the skull and the sacrum is twenty-four. In 
 the skeleton of a Gavial, I have seen thirteen dorsal and two 
 lumbar; in that of a Crocodihis cutuphractus twelve dorsal and 
 three luml^ar ; in those of a Crocodilus acutus and AlUr/otor lucius, 
 eleven dorsal and four lumbar, fig. 57, which is the most com- 
 mon number. Cuvier assigns five lumbar vertebras to Croc. 
 
 55 
 
 riia.^vani of postcrioi- trimlc-vcrtclira;, Crocodile, cc. 
 
 hiporcatus. But these varieties in the developement or coales- 
 cence of the stunted pleurapophysis are of no essential moment. 
 The coalescence of the rib with the diapophysis obliterates of 
 course the character of the ' costal articidar surfixce,' Avhicli we 
 have seen to be common to both dorsal and cervical ^-ertel^raj. 
 The lumbar zygapo2)hyses have their articular surfaces almost 
 horizontal, and the diapophyses, if not longer, have their antero- 
 posterior extent somewhat increased ; they are much depressed, 
 or flattened liorizontally. 
 
 The sacral vertebrfc, fig. 57, S, are very distinctly marked by 
 the flatness of the coadapted ends of their centrums ; there are 
 never more than two such vertebrfe in the Crocodilia, recent or 
 extinct : in the first the anterior surface of the centrum is concave, 
 in the second the posterior surface ; the zygapophyses are not 
 obliterated in either of these sacral vertebras, so that the aspects of 
 
 F 2 
 
68 
 
 ANATOMY OF VERTEBRATES. 
 
 66 
 
 their articular surface — upward in the anterior pair, downward 
 in the posterior pair — determines at once the corresponding ex- 
 tremity of a detached sacral verteljra. The thick and strong 
 transverse processes form another characteristic of these vertebrae ; 
 
 for a long j^eriod the suture 
 near their Isase remains to show 
 how large a proportion is formed 
 by the pleurapophysis. This 
 element, fig. 55, i, articulates 
 more with the centrum than 
 with the diapophysis developed 
 from the neural arch ; it ter- 
 minates by a rough, truncate, ex- 
 jaanded extremity, which almost 
 or quite joins that of the similarly 
 but more expanded rib, ib. k, 
 of the other sacral vertebra. 
 Against these extremities is ap- 
 plied a supplementary costal 
 piece, serially homologous with 
 the fibrous tract indicated by 
 the dotted lines between h and 
 r, [I and 6, fig. 55 ; but ossified, 
 expanded, and interposing it- 
 self between the pleurapophyses 
 and liEemajiophyses of both sacral 
 vertebra?, not of one only. 
 This intermediate pleura2)ophy- 
 sial part is called the ' ilium ' 
 fig. 57, 62: it is short, tliick, 
 very broad, and subtriangular, 
 the lower truncated apex form- 
 ing with the connected extrem- 
 ity of the htemapophysis an arti- 
 cular cavity for the diverging 
 ajuiendage, called the ' hind leg.' 
 The hremapophysis of the anterior sacral vertebra is called ' pubis,' 
 fig. 55, 8, fig. 56, 5 ; it is moderately long and slender, but cx]xinded 
 and flattened at its lower extremity, which is directed forward 
 toward that of its fellow, and joined to it through the intermedium 
 of abroad, cartilaginous, luvnial spine, ib. lo and ii, comjtleting the 
 htemal canal. The hremapopliysis of the second sacral, fig. 55, n, 
 fig. 50, 4, is broader, sulxloi)ressed, and subtriangular, expanding 
 
 Diagram of tbo lircmal arches nf tlic trunk, 
 viewed from above. Crucedile. ce. 
 
ANATOMY OF VERTEBRATES. 69 
 
 as it approaches its fellow to complete the second pelvic lifcmal 
 ai'cli. The size of these eleinents of the ha;mal arch, and their 
 distinctive shapes, have obtained for them, in anthropotomy, special 
 names : their divergino- appendage being developed into a potent 
 locomotive member. The crocodile yields a clear view of the serial 
 homologies of the hremal elements along the trunk. In fig. .56, 
 they are sketched as seen from the dorsal aspect. The hmmapo- 
 physcs extend from h i, 2, 3, to h 6, 5, 4 : the lu^mal spines, mostly 
 contlucnt, are co-extensive from lis to 10, where they expand as a 
 cartilage between c, and 5. The pair of ha^mapophyses, /( 1, are 
 called 'coracoids,' and bear the special number 52: the pair, 5, are 
 the ' pubic bones ' ; the pair, 4, the ' ischia.' The hremal spine, hs, 
 is called ' ej)isterni"im,' the succeeding more or less confluent spines, 
 9, form the ' sternum ' : in Man their abdominal continuation, not 
 quitting the fibrous tissue-state, is called ' linea alba ' ; it be- 
 comes cartilage in the Crocodilia, ib. 10, and partly bony in old 
 specimens. The abdominal hsemapophyses, represented by the 
 'iutcrsectiones tendineaj musciili recti abdominis' of anthrop<.>tomy, 
 are commonly ossified, each from two centres, in old Crocodilia. 
 
 The i^leurapophysis is reduced to a transverse process in the 
 first caudal vertebra, fig. 55, I; which, besides being biconvex, 
 has no articular surface for the ha;mapophyses : these elements 
 reappear in the succeeding segments, detached, as in the lumbar 
 series, from their pleurapophyses, but articulated to the centrum 
 directly, fig. 7, with a backward displacement, to the interspace 
 between their own and the succeeding vertebra, fig. 57, h. After 
 the fourteenth caridal vertebra the transverse processes disappear, 
 the centrum becomes compressed, and the neural and haemal 
 spines give adequate vertical extent to the long and strong nata- 
 tory tail, to near its pointed termination. 
 
 The characters of the trunk-vertebrai of existing Crocodilia, 
 especially their prococlian type, are those which their predecessors 
 presented throughout all the tertiary series of deposits,^ and by 
 some species from cretaceous beds.'^ But in all the secondary 
 series below the chalk, the Crocodilia present flattened or sub-con- 
 cave vertebral surfaces ; or, if the cup-and-ball structure be 
 jiresent, it shows reverse positions to the proccelian type, e. g. in 
 the anterior trunk-vertebra3 of the genus of oolitic Crocodilian, 
 thence termed ' Streptosporuhjlus.^ A similar ' opisthocoelian ' 
 modiflcation is presented by the cervical and anterior dorsal 
 vertebra; of the more gigantic Cetiosaurus ; and, in a minor degree, 
 
 ' CLXiii., part iii. p. 117, pis. 1 D, 3, .3 a. 
 - Crocodilus basijissus, CLXIV. p. 380. 
 
70 
 
 ANATOMY OF VERTEBRATES. 
 
 57 
 
 (XV^ 
 
 and vi. 
 
 by some of the great reptiles, with 
 limbs more adapted for terrestrial pro- 
 gression, called ' Dinosauria' ; favour- 
 ing in these the flexilnlity of the neck, 
 as the same ball-and-socket structure 
 does in the large herbivorous quadru- 
 peds of the present day. ' The neural 
 arch in the dorsal region of Dinosauria, 
 was enlarged and strengthened by a 
 Ijony platform, with supporting ridges : 
 the sacrum included from four to six 
 vertebra;, having the neural arch 
 shifted so as to rest upon two cen- 
 trums and bind them together. 
 
 § 25. Vertebral column of Ptero- 
 sauria. — In tracing the modifications 
 of the skeleton from the earliest forms 
 of extinct species, the procoelian type of 
 vertebra appears first in the extinct 
 group of Reptiles {Pterosauria) adap- 
 ted for flight ; the Pterodactyles of the 
 Lias show it, with a confluent neural 
 arch and a j^jueumatic foramen on each 
 side of the vertebra.^ The cervical ver- 
 tebras of Pterodactyles, fig. Ill, are the 
 largest, seven or eight in number, of 
 which the first two coalesce. The atlas 
 has a very short discoid centrum and 
 two slender neurapophyses. The dorsal 
 vertebrai become smaller to the pelvis ; 
 they may be fifteen in number, fol- 
 lowed by two lumbar, from three to 
 seven sacral, and a variable number 
 of caudal vertebra?. One family of 
 Pterodactyles had a long and stifi:" tail ; 
 the rest, as in fig. Ill, a short tail. 
 The anterior free ribs have Ijifurcate 
 heads ; and, as tliis structure is asso- 
 ciated in modern Ecptilitu with a 
 four-chambered heart, that organ had 
 probably readied the same stage of 
 perfection in tlic flying Reptiles, the 
 
 XXX. p. 285. = CLII. p. 101, pi. X. 
 
ANATOMY OF VERTEBRATES. 71 
 
 huge terrestrial Dinosaurs, and other extinct grouiis with the same 
 costal structure. The existing lieptiUa are but a remnant of a 
 once extensive and varied class of cold-blooded vertebrates, which, 
 since the mesozoic epoch has been on the wane.' 
 
 § 26. Developement of the skull. — In reviewing the modifications 
 of this part of the vertebral column in the Ilannatocrya, we 
 retrace our steps to the lowest water-!n-eathing forms, and 
 recommence with the Dermopterous subclass. 
 
 Passing from the trunk to the head, we find in the Lancelet 
 {-f>r(i)ichi.osto)na^, fig. 23, that the cranium is not indicated by 
 ditt'erence of size or structiu-e of the rudimental vertebral cohnnn, 
 but consists of the gradually contracting anterior termination of 
 tlie neural canal, which retains its primitive fibro-membranous wall, 
 ?!, ob, without any superaddition of parts, and is supported l)y the 
 tapering end of the iiotocliord, ib. eli. This part extends farther 
 forward than the cranial end of the neural canal, indicating the 
 non-developcment of the prosencephalon and corresponding part 
 of the cranial cavity. In fact, there is no ganglionic cerebral 
 exf)ansion whatever in this vermiform fish : tlie epencephalon or 
 medulla oblongata is indicated by the origin of the trigeminal 
 nerve, ib. oh, in advance of which the mesencejAahc segment sends 
 oft" the short optic nerve to the dark ocellus, op, and there terminates, 
 somewhat obtusely, beneath what Dr. KiJLLiKER^ has described 
 as a ciliated olfactory capsule, ib. ol. The cranium of the Lancelet, 
 therefore, may be said to be composed of the notochord aud its 
 mcmljranous capsule, without the superaddition of cartilaginous 
 or osseous co\'erings. But, as an appendage to the skidl, may be 
 described the jointed, cartilaginous, hremal arch, ib. h, which 
 extends from below the cranial end of the chorda dorsalis, down- 
 ward and backward on each side of the orifice of the pharynx ; 
 this represents the labial arch of higher INIyxinoids, and supports 
 several pairs of the jointed slender oral filaments. It is tlie sole 
 chondrified part of tlie skeleton in the Branchiostorna. 
 
 The cartilaginous tissue is superinduced upon the fibrous l^rain- 
 sac in osseous fishes, in the following manner. The notochord 
 advances as far as the pituitary sac, or ' hypophysis cerebri,' where 
 it terminates in a point ; cartilage is develojicd on each side, 
 forming a thick ' occipito-sphenoidal ' ^ mass, wliich extends out- 
 ward, and forms the earball or acoustic capsule. The cartilage 
 rises a little way upon the lateral walls of the cranium, and is 
 there insensibly lost in the primitive cranial membrane. At the 
 
 ' CLxxx. p. 320. - XXXII. p. 32. 
 
 ^ Plaque ntichale, Vogt ; Knucherne basis cranii, Miiller, xxi. 
 
72 ANATOMY OF VERTEBRATES. 
 
 end of tlie notocliord the basal cartilages, developed in continua- 
 tions of its capsule, diverge, surround the pituitary vesicle, and 
 meet in front of it, forming the ' sphenoidal arches,' ' which join, 
 or expand into the 'vomerine plate.' ^ 
 
 The immature Lamprey, called Sand-lance {Ammoccetes), retains 
 a like condition of the skull, fig. 58, to the second or third year. 
 The occipital cartilages extend from the sides of the pointed end 
 of the notochord, ib. ch, and expand into the acoustic 
 capsules, ilj. 16 : the sphenoidal arches, ib. 5, encom- 
 pass the pituitary or hypophysial space, hy, now closed 
 hj a membrano-cartilaginous plate, and unite anteriorly 
 to form a small vomerine plate, ib. 13, in front of 
 which is the single undivided nasal capsule, ib. 19. 
 The now expanded cerebral end of the neural canal, 
 fig. 59, n, is still defended by fibrous membrane only; 
 . , .. hut is divided from the vomerine plate, ib. 13, bv a 
 
 Ease of slnill, -t ' ^ J 
 
 Amnwcf.tc, backward extension of the nasal sac, ib. 19, to the 
 
 Jliiller . . . , 
 
 pituitary vesicle. 
 In the ]\Iyxiue the acoustic capsules are approximated at the 
 base of the skull ; the s})henoidal arches are longer, and unite with 
 the palatine plate and arches, from which are sent off the labial 
 cartilaginous processes supporting the buccal tentacles homologous 
 with those in the Lancelot. In the long hypophysial interspace of 
 the sphenoidal arches a more or less firm 
 „ _ cartilaginous plate is developed, from which 
 
 a slender median process is continued for- 
 ward to the vomerine or palatine plate, 
 which svipports the nasal capsule ; another 
 process extends backward to the occipital 
 cartilage. Other processes are also sent 
 off" from the sides, which form a complex system of peculiarly 
 Myxinoid cartilages.^ 
 
 In the mature Lamprey {Petromtjzon), fig. 60, the occipital 
 cartilage is continued backward, in the form of two slender 
 processes, c, upon the under part of the notochord, cli, into the 
 cervical region. The hypophysial space, hi/, in front of the 
 occipital cartilage, remains permanently open, Init has been con- 
 verted hito the posterior aperture of the naso-palatine canal. The 
 sphenoidal arches, 5, are very short, approximated towards the 
 middle line; and the vomerine cartilage, 13, is brought back 
 closer to the sphenoidal arches. Two cartilaginous ai-chcs, 24, 
 
 ' Aiiscx lalcrali'K, Vogt ; FIiiiH'l-fors<'ilz<: hisis crtniii, JliUler. 
 * I'liiijiicfficialc, Yogt; Gaiimciipliilli; filulkr. ■' xxi. 
 
 of ^kul], ADunocdc, 
 
 MllllLT 
 
ANATOMY or VERTEBRATES. 
 
 73 
 
 circumscribe elliptical spaces outside the Y)respheuoicl plate : these 
 appear to -represent the pterygoid arches, fig. 61, i, but, as in the 
 embryo of higher fishes, are uot sejiarated from the base of the skull 
 by distinct joints. The basal cartilages, after forming 
 the car-capsules, ib. g, exteud upon the sides of the cra- 
 nium, ib. h, arch over its back part, and leave only its 
 upper and middle part membranous, as in the human 
 embryo when ossification of the cranium commences. 
 The cranium is continued below the olfactory cajisrrle, 
 ib. /(, into the ' rostral plate,' /. Behind the pterygoid 
 arch, i, the process representing the stylo-hyal, ib. i' , 
 i" , passes down, and expands to give attachment to 
 the muscles of the tongue ; the ' basihyal ' supports, 
 by its forward ' glossohyal ' extension, the large den- 
 tigerous tongue, and by its laackward ' urohyal ' growth, .s, adds to 
 the surface of insertion of the muscles. The cartilage descending 
 from the side of the fore part of the cranium to join the pterygoid 
 arch, i, may represent a ' tympanic ' pedicle : it mainly supports, 
 as in the Sturgeon, fig. 62, ?8, and Shark, the membrane, fig. 61, x, 
 and cartilages, forming the roof and margin of the mouth ; in which 
 
 B;ise fif skul), 
 xxr. 
 
 01 
 
 SlaiU ul Sea Lami'i'c.v (Pdro, 
 
 n may be compared to the ' palatine,' and o to the maxillary, wlule 
 J) seems to be a special labial cartilage in this suctorial fish : q and r 
 are processes for the muscles working this peculiar apparatus ; 
 and in addition to these is the cartilaginous basket before de- 
 scribed, fig. 24, 45, which supports the modified and perforated 
 homologue of the large respiratory pharynx, fig. 23, a, in the 
 Branchiostome. 
 
 Thus, in the Dermopterous fishes, the developement of the skull 
 is arrested at more or less early embryonic stages ; whence it 
 
74 
 
 ANATOMY OF VEETEBRATES. 
 
 proceeds in a sjiecial direction, to stamp the species with its own 
 distinctive and peculiar character : in the Brancliiostoma by the 
 articulated cartilaginous labial arch and its numerous filaments ; 
 and in the proper Myxinoids and Lampreys by the formation of 
 the complex system of lateral and labial cartilages ; or by the 
 modification of the palatine, maxillary, and hyoid rudiments, in 
 relation to the suctorial function of the mouth. 
 
 In the Sturgeon (Adpenser) fig. 62, the growth of cartilage has 
 inclosed the whole of the brain-case, f, (j, and blended with its 
 walls the ear-capsules : in advance of this it developes protective 
 cavities for the now well-developed eyes and doul^le nasal sacs : the 
 orbit, i, being divided from the nostril, U, by tlie ridge, 2, and 
 Ijoth sup)ported by a ' \'fimerine ' basis, ff" : beyond which the 
 cranium is continued forward as a long pointed rostrum. The 
 cartilaginous pedicle susj^endlng the palato-maxiilary apparatus is 
 
 Fore part uf ciiaoskelcLuu, Sturgeon 
 
 divided into three piieces ; the epitympanic, ilx m, the mesotvm- 
 panic, ib. n, and the hypotympanic, ib. 26. The latter supports 
 the j)alatine vault, 20, with wliich the pterygoids, se, are confluent ; 
 the maxillary, 21, the premaxUlary ljone,'2"2, the lalnal cartilage^ 
 74, and the mandible, 32. All these parts of the edentulous 
 suctorial mouth are very small in proportion to the size of the 
 bead and entire fish; and they are the only ossified parts of 
 the end(3skeleton. The premaxillary is a subtriangular plate, 
 jomed by ligament to its fellow, trenchant anteriorly, and 
 extending in an arched form to the mandible. The mandible, 32, 
 articulates by a concavity to the ptervgoid and premaxillary, and 
 consists of a single piece, united to its fellow by a ligamentous 
 sym])liysis. 
 
 The mouth of the Sturgeon opens upon the under surface 
 of tlie head, and is protruded and retracted eliieflv by the move- 
 
ANATOMY OF VERTEBRATES. 75 
 
 ineiits of tlie tympanic pedicle, which swings, like a pendulum, 
 from its point of suspension to the post-orbital process, fig. 29, (/' . 
 The hyoid arch is also small and simple in the Sturgeon. The 
 epi-hyal is short, and attached to near the upper end of the hypo- 
 tympanic. The cerato-hyal, fig. G2, 4n, of thrice the length, is 
 expanded above, and is attached by ligament extending from that 
 part to near the joint of the lower jaw. Tlic Ijasi-hyal is a short 
 subcubical piece : it gives attaclunent anteriorly to cerato-hyals, 
 and posteriorly to the anterior basi-branchial and hypo-branchial 
 cartilages. 
 
 The tlu'co first branchial arches consist of hypo-branchials, 
 progressively decreasing in size, of ccrato-branchials, epi-bran- 
 cliials, and pharyngo-branchials : the fourth arch consists of 
 cerato-branchials and cpi-branchials : the fifth arch of cerato- 
 brancliials only. The Ijranchial cavity is closed by an ojiercidar 
 dermal scale, d, 35, supported by the expanded tympanic cartilage, 
 'III, fig. 62. 
 
 The cartilaginous representative of the par-occipital projects 
 backward from each angle of the occiput. A triangular supra- 
 scapular cartilage, fig. G2, 50, has the angles of its base slightly 
 produced, one being articulated to the end of the par-occipital, 
 the other to the ex-occipital region. To the apex is attached 
 the scapulo-eoracoid arch, ib. .51, 52. The coracoid cartilage 
 expands as it descends, sends inward and forward a broad 
 wedge-shaped plate, and presents a large perforation at its thick 
 posterior part, answering jjrobably to the perforated ulna of 
 osseous Fishes, here confluent with the arch. The pectoral fiji 
 is articulated to the under part of this perforated projection : the 
 coracoid terminates by a broad thin plate beneath the jiericardium, 
 where it is joined by strong aponeurosis to that of the opposite 
 coracoid. 
 
 Special developement proceeds further in the skull of the 
 singular Acij^enseroid, called ' j^f'^^^^lG-fish ' {Planirostra Sfcitula). 
 It is remarkable for the rostral jwolongation of the nasal and 
 vomerine bones, the rostrum being flattened horizontally and 
 expanded like the mandibles of a Spoonbill. The sides of the 
 rostrum are strengthened by a reticulate disposition of bony 
 matter in the form of stars, the rays of which anastomose. Tlie 
 upper part of the cranium is less perfectly chondrified than in 
 the Sturgeon. There is a long vacuity between the frontal, 
 parietal, jJostfrontal and mastoid bones : the tymjoanic pedicle is a 
 simple elongated piece of bone expanded at both ends. The 
 mandibular and hyoidean arches are suspended by a short cartilage 
 
76 ANATOMY OF VERTEBRATES. 
 
 to the end of tlie tympanic bone : the palatines are extremely small. 
 The T)remaxillary and maxillary bones seem to have coalesced ; 
 they expand as they extend backward to become attached to the 
 cartilage supporting the mandibular arch. The slightly ossified 
 pterygoids run parallel with them along the inner sides to the same 
 part. The articular and dentary pieces of the lower jaw have coa- 
 lesced, but there is a trace of a slender splenial piece on the inner 
 side of the mandible. All the liones of the mouth are edentulous, 
 but the membrane covering the extremities of the upper and 
 lower jaw is roughened by extremely minute denticles in the 
 recent fish. The ceratohyals are partially ossified : the rest of 
 the hyoidean arch is cartilaginous. A branchiostegal appendage 
 in the form of an irregular elongated flattened bone, resolved 
 posteriorly into osseous fibres, extends from each side of the 
 commencement of the hyoidean arch. A similar but larger oper- 
 cular appendage extends backward from the extremity of the 
 tympanic pedicle. 
 
 § 27. Skull of Plar/iostomi. — The more or less cartilaginous skull 
 of the Plagiostomous fishes might be histologically regarded as the 
 transitional step from the Cyclostomous to the Osseous fishes ; but, 
 morpliologically, it offers a difterent, apparently simpler type ; and 
 one which, through the progress of developement in the direct 
 vertebrate route, more nearly approximates to the cranial organi- 
 sation in the Batrachia. The Monk-fish {Squatina, — an interme- 
 diate form between the Sharks and Eays,) affords a good and typical 
 example of the essential characters of the plagiostomous skull. 
 The cranial end of the notochord and its capsule are converted 
 into firm granular cartilage ; extending forward so as to constitute 
 an ol)long flattened plate forming the whole basis cranii. The 
 posterior margin of this ' occipito-sphcnoidal ' plate supports two 
 convex condyles, for articulation with the body and parapophyses 
 of the axis. The body of the atlas has coalesced with the basi- 
 occipital, as is indicated by its slender but separate neural arch. 
 The lateral margins of the basal cartilage ha\-e two notches, the 
 intervening prominence representing the primitive sphenoidal 
 arch, here filled up and sending off a rudimental pterygoid process 
 outwards. Just anterior to the median ridge there is a small 
 fossa, (in the young Sqiiativji a foramen,) the last trace of the 
 pituitary canal : the basal cartilage tlien expands to form the 
 lower border of the groove which receives tlic palatine process or 
 ])oint of suspension of the palato-maxillary arcli, in front of wliich 
 it contracts to form the vomerine base of tlie cranium. The cra- 
 nial cavity is not moulded on the In-ain, but is of larger size ; it 
 
ANATOMY OF VERTEBRATES. 77 
 
 communicates by means of the nervous and vascular foramina 
 with the acoustic chamber in the tliick hiteral wall : this insulation 
 of the labyrinth is common to the Plagiostomes. The cranial 
 ca^'ity is closed by membrane anteriorly. The foramina for the 
 fifth pair of nerves mark the ' alisphenoidal ' portion of the cndo- 
 cartilage : those for the optic nerves the ' orbitosphcnoidal' part: 
 the ' prefrontal' portion is marked by the olfactory foramina, and 
 their articulation Avith the palatine part of the maxillary arch. 
 
 The exterior of the skull is variously and singularly modified in 
 different Sharks and Rays, the developemcnt proceeding from the 
 advanced cartilaginous stage just described, to establish peculiar 
 plagiostomous characters, and to adapt the individual to its special 
 sphere of existence. 
 
 The same general confluence of cartilage, which pervades the 
 protecting walls of the brain-case, characterises the appended 
 arches of the cranium. A single strong suspensory pedicle, fig. 
 30, c, articulated to the side of the skull beneath the posterior 
 angular (mastoid) process, has the hyoidean, and partly the man- 
 dibular,' arches attached to its lower end, the former, d, by a close 
 joint, the latter by two ligaments. The maxillary arch, in Squa- 
 tina, is suspended by a ligament from its ascending or palatal 
 process, to the notch between the vomerine and the anterior 
 supracranial cartilaginous plate. From this point the jaw is con- 
 tinued in one direction forward and inward, completing the arch, 
 ib. e, by meeting its fellow, to which it has a close ligamentous 
 junction ; and in the opposite direction, backward and outward, as 
 a coalesced diverging appendage to the outer side of the tympanic 
 jiedicle, where it forms the more immediate articulation for the 
 lower jaw, like the hypotympanic continuation of the upper 
 maxillary bone in the Batrachia, fig. 71, e. Each lateral half or 
 ramus of the mandible, fig. .30, d, consists of a single cartilage, 
 the two being united together at the symphysis by ligament. 
 
 Two slender labial cartilages, ib. f, are developed on each 
 side the maxillary, and one, g, on each side the mandiliular 
 arch ; which complete the sides of the mouth. These cartilages 
 Cuvier regarded as rudmicnts, respectively, of the maxillary 
 and dentary Ijones, the dentigerous maxillary arch as the palatine 
 bones, and the mandit)ular arch as the articular piece of the 
 lower jaw : but both palatines and articulars co-exist with 
 labial cartilages, like those of Squatina, in a Brazilian Torpedo 
 
 ' Throughout this work the term 'mandible' is applied to the lower jaw, and the 
 inverted cranial arch which that jaw completes is called ' mandibular ; ' the ai'ch 
 formed by the upper jaw is called 'maxillary.' 
 
78 
 
 ANATOMY OF VERTEBEATES. 
 
 03 
 
 {Narcine), and at the same time with distinct pterygoid 
 
 cartilages.' 
 
 Four or five short cartilaginovis rays diverge from the posterior 
 mamin of the tympanic pedicle, ib. c, and support a membrane 
 answerincr to the opercular flap in Osseous fislies ; in their ultimate 
 homology these rays are the skeleton of the diverging appendage 
 or limb of the tympano-mandibular arch. 
 
 The hyoid arch in Squatina, as in most other Plagiostomes, 
 consists of two long and strong cerato-hyals, and a median flat- 
 tened symmetrical piece, 
 the basi-hyal. Six short 
 cartilaginous rays extend 
 outwards from the back 
 part of the cornua, support- 
 ing the outer membranous 
 wall of the branchial sac : 
 these answer to the bran- 
 chiostegal raj's in osseous 
 fishes, and support the di- 
 verging appendage or limb 
 of the hyoidean arch. But 
 
 ^^Z'^'^^^Ib— r^-5^^5l?^^' ^^^'^ ^'^^^ '^^ integument in 
 
 ^ ■ '^ ^ ' — '"""^■'^ which they project is not 
 
 liberated, and is continuous 
 with that supported by the 
 opercular rays from the 
 tympanic pedicle. Five 
 branchial arches, fig. 30, 
 I, 2, 3, 4, 5, succeed the 
 hyoidean ; but are sus- 
 pended, as in the Lam- 
 prey, I'rom the sides of the 
 anterior vertebra3 of the 
 trunk. In the Sea-hound 
 [Sri/uniiis iicliia), fig. 63, the 
 ceratobranchials, _/', f, and 
 basiln-anchials, c, e, are 
 shown, with the frame- 
 work of the gills, 17, /. Be- 
 hind these arches is the sca- 
 
 ]iulo-coracoid arc, 52, united by cartilaginous confluence at the 
 
 mid-line, not by ligament as hi the Sturgeon. 
 
 ' xxi. I 8.')6, ])1. V. i\%%. 3 S: 4. It niay be questioned wliellief tlic ilctuclied pliite, 
 e.'i]k'(l |i:iliitii}c l)y J)r Ileiile, be not rather tile cntoiiteryjroul. 
 
 Pliiil] Willi liraiicliial and scnpiilar arcliop. .9cf/»i 
 
ANATOJIY OF VEETEBEATES. 79 
 
 The Cestracion, so interesting from its early introduction into 
 the seas of this planet, is not so far advanced in cranial dc- 
 vclopcment as is the more modern Squatina. In the existing 
 species of the Australian seas (^Cestracion Phillijn), the cartilagi- 
 nous basioccipital retains a deep conical excavation, adapted to a 
 corresponding one in the atlas, which cavity is consolidated by 
 cartilage in the Squatina ; the original place of the extended ante- 
 rior end of the chorda, along the middle of the posterior half of 
 the basicranial cartilage, continues membranous, and the pitui- 
 tary perforation is permanently closed by membrane only ; the 
 basal cartilage expands anterior to this, and comes into close 
 connection with the maxillary arch, and is thence continued 
 forward, contracting to a point ))etween the nasal capsules, which 
 meet at the middle line above the symphysis of the up])er jaw. 
 The proper cranial cartilage is thinner than in the Squatina ; 
 the anterior or pineal fontancUe forms an extended membranous 
 tract on the upper part of the cranium ; the vertical ridges, which 
 rise from the sides of this tract, extend forward and outward to 
 support the nasal sacs, and are continued laackward, interrupted 
 by a notch filled by membrane, to the posterior angular processes, 
 which overhang the joint of the maxillo-hyoidean pedicle. The 
 maxillary and mandibular arches are as simple as in Squatina, 
 but much stronger, since they sujiport a series of massive grinding 
 teeth, as well as pointed ones, or laniaries. The rami of the lower 
 jaw are confluent at the symphj^sis. 
 
 The Skates and Eays have the skull movably articulated, as in 
 Squatina, by tAVO basilar condyles and an intervening space, to 
 the axis. The skidl is flat and broad ; the upper wall mem- 
 branous for a greater or less extent, fig. 64, except in Narciii.e, 
 where it is closed by cartilage. The anterior or vomerine part 
 forms a long pyramidal rostrum, to which arc usually artieidatcd 
 cartilages connecting its extremities with the anterior angles of 
 the enormously developed pectoral fin, ib. 12 : in the space 
 between the skull and those fins, the Torpedo carries its electric 
 batteries. The tympanic pedicles, are short and thick ; the 
 maxillary and mandibular arches long and wide, stretching trans- 
 versely across the imder part of the head. 
 
 In the ordinary Sharks the forward prolongation of the cranial 
 cavity gives a quite anterior position, and almost vertical plane, 
 to the fontanelle : three columnar rostral cartilages are produced, 
 two from above, and one from between the nasal canities, which 
 processes converge and coalesce to form the framework of a kind (if 
 cut-water, at the fore-part of the skull. In the place of articular 
 
80 
 
 ANATOMY OF VEIiTEBEATES. 
 
 condyles, processes extend Ijackward from each side of the occi- 
 pital foramen and clasp, as it were, the bodies of three or four 
 anterior vertebras of the trunk. The pterygoidean arches extend 
 outward, in Carcliarias, from the base of the cranium, l^ut, as in 
 embryo osseous fishes, are confluent therewith at both ends. The 
 maxillary arch, suspended near its closed anterior extremity to 
 
 64 
 
 Skate tTfiiHi liaVii) 
 
 the vomerine part of the liase of the skull, is thence extended 
 l^ackward to tlie articulation of tlie lower jaw. A simple carti- 
 laginous pedicle forms tlie upper part (plcurapophysis) of the 
 mandiljular arch, which is completed below by tlie lower jaw. A 
 few cartilaginous rays di\crgc t)utward and l.iackward from the 
 pedicle, and support a small oiiercular flap or fin. The hyoid 
 
ANATOMY OF VERTEBRATES. 
 
 65 
 
 arch consists of a baslhyoid and two simple ceratohyoid carti- 
 lages ; the stylohyal is ligamentous, as in the Squatina. Short 
 cartilaginons rays diverge from the ceratohyal to support the 
 branchiostegal membrane, or hyoid fin. The scapular arch, 
 which we shall find normally articulated with the occiput in 
 osseous fishes, is attached thereto, at a little distance behind the 
 head, by ligament and muscles in the Sharks, fig. 30, 51 : from 
 this arch, also, cartilaginous rays, ib. h, I, immediately diverge for 
 the support of a radiated appendage or fin — the homotype of the 
 tympanic or opercular fin. 
 
 The capsules of the special organs of sense are all cartilaginous: 
 that of the ear is involved in the lateral 
 walls of the cranium ; that of the eye is 
 articulated by a cartilaginous pedicle with 
 the orbit ; and that of the nose, figs. 30 and 
 63, b, is overarched by the nasal processes 
 of the epicranial cartilage, ib. «, and is 
 completed below by membrane. At the 
 summit of the occiput in Carcharias and 
 some other sharks may be seen two closely 
 approximated oval ' fenestraj,' which lead 
 to the acoustic labyrinth, and are covered 
 by skin in the recent fish. 
 
 Amongst the stranger forms in which 
 special developement radiates, in diverging 
 Irom that stage of the common vertebrate 
 route attained by the Plagiostomes, may 
 be noticed the lateral transverse elonga- 
 tions of the orbital processes, supporting 
 the eyeballs at their extremity, and giv- 
 ing the peculiar form to the skull of 
 certain Sharks, thence called 'Hammer- 
 headed' (Zijrj(Bna). In the 'Saw-fish' 
 {Pristis), the rostrum, fig. &5, is produced 
 into a long, flat, plate, having a row of 
 tooth-like bodies implanted in sockets along 
 each margin. The walls of these sockets 
 and the mldpart of the rostrum are ossified. 
 The i^roper jaws and teeth a have the usual Inferior position in the 
 Sharks. • In the Eagle-ray {Myliobates) a cartilage is attached to 
 the anterior prolonged angle of the great pectoral fin, and con- 
 nects it with the fore part of the cranial (internasal) cartilage ; 
 it supports a number of branched and jointed cartilaginous rays, 
 
 VOL. I. G 
 
 -I. .1.1. .1 b-1. llj. 
 
 'rittis). 
 
82 AIJATOMY OF VERTEBRATES. 
 
 which project forward, and are connected at the middle line 
 with a like series from the opposite side of the head ; they may 
 be regarded as partial dismemberments of the great pectorals; 
 and in Rhinoptera Braziliensis their supporting cartilage is 
 directly continued from that of the pectoral fins, though it is 
 closely attached to the fore part of the head. These form what 
 Miiller has termed 'cranial fins;' but the parts more properly 
 meriting that name are the opercular and branchiostegal appen- 
 dages of the tympanic and hyoidean arches. 
 
 § 28. Skull of Protoptcri. — Thus far we have seen that the base 
 of the skull is first formed by the anterior prolongation of the 
 notochord and the expansion therefrom of its capsule ; and that the 
 cranial cavity results from the extension of the outer layer of that 
 membrane over the anterior end of the nervous axis. We saw 
 next the superaddition of special capsules for the organs of sense ; 
 and the cartilaginous tissue developed in the notochordal sheath 
 at the base and sides of the cranium, according to a pattern 
 common to the lowest and to the embryos of the higher -^-ertebrata. 
 We saw the cartilaginous tissue acquiring a firmer texture, hard- 
 ened by superficial osseous grains, or tesserro, mounting higher 
 upon the lateral and upper walls of the cranium, and at lengtli 
 entirely defending it : and we then also recognised the maxillary, 
 mandibular, and hyoidean arches, established in a firm cartilaginous 
 material, and on a recognisable ichthyic type. 
 
 AVe have now to trace the course and the forms under which 
 the osseous material is superadded to, or substituted for, the 
 primitive cartilaginous material of the skull ; and the remarkable 
 Lepidosiren, whose organisation was first made known as in the 
 generic form called Protopteriis,^ offers a transitional step, in the 
 shape and structure of its skidl, between the gristly and the bony 
 cold-l3looded vertebrates. 
 
 In the Lepidosiren, ossification of the cranial end of the noto- 
 chord extends along the under and lateral part of its sheath, 
 backward to beneath the atlas, fig. 41, i, the posterior slightly 
 expanded end of this ossified part supporting, as in Sqnatina, 
 the neurapophyses of the atlas, fig. 66, n, the bases of which 
 expand and meet above the notochord and below the spinal 
 canal. Ossification of the notochordal sheath commencing at 
 its under part, ib. h, ascends upon the sides of the notochord as 
 it advances forward, and encloses it above, where it supports the 
 medulla oblongata, and the lateral bony plates (neurapophyses) 
 
ANATOMY OF VERTEBRATES. 83 
 
 called exoccipitals, ib. 2 ; leaving behind a wide oblique conca- 
 vity lodging the anterior unossified end of the 
 notochord, which does not extend further upon the 
 basis cranii. The exoccipitals, ib. 2, 2, expand as 
 they ascend and converge to meet above the ' fora- 
 men magnum' which they complete. A small mass ^* 
 
 J, ., 1 • T • 1 1 Atlas and 
 
 ot cartilage connects their iipi)er ends with each occiritai vertebra, 
 other, and with the overhanging backwardly pro- 
 jecting point of the frontoccipital spine, ib. 3. This cartila- 
 ginous mass answers to the base of the superoccipital in better 
 ossified fishes : a similar cartilage connects the exoccipitals with 
 the occipital spine in the Tctrodon. 
 
 We clearly perceive in the Lepidosiren that ossification, ad- 
 vancing on the common cartilaginous mould of the piscine skull, 
 has marked out the neurapoph3^ses and centrum of the posterior 
 cranial vertebra. The occipital pleurapophyses, called ' scapidie,' 
 fig. 41, 51, appear as strong, bony, styliform appendages, articu- 
 lated by a synovial cajisule and joint, one on each side, to the ex- 
 aiid basi-occipitals. To the pleurapophyses are attached the upper 
 extremities of the ha3mapophyses (coracoids, fig. 41, 52) Avhich 
 unite together below, and thus complete the hajmal arch of the 
 occijiital vertebra, here unusually developed in relation to its 
 office of protecting the heart and pericardium. The coracoids 
 belong to the same category of vertebral elements as the sternal 
 ribs which protect the heart in higher Vertebrata. The lucmal 
 arch of the occipital vertebra of the Lepidosiren supports a filiform 
 appendage, ib. 57 ; it is the key to the homology of the anterior 
 or upper limbs of the higher Vertebrata. 
 
 In the second (parietal) and third (frontal) cranial vertcl3ra3, 
 ossification extends along the basal and along the spinal elements, 
 but not into the neurapophysial or lateral elements ; these remain 
 cartilaginous in continuation with the cartilage surrounding the 
 internal ear. The basal ossification, representing at its posterior 
 end the body of the atlas, then the basioccipital, expands as 
 it advances along; the base of the skull in the situation of the 
 sphenoids, constituting the floor of the cerebral chamber, sup- 
 porting the medulla oblongata, the hypophysis, the crura and 
 lobes of the cerebrum, and terminating a little in advance of the 
 olfactory lobes by a broad transverse margin, bounding a triangular 
 space left between it and the converging palatine arches, which 
 space is filled by the persistent ' vomerine ' cartilage. The sides 
 of the basicranial plate bend down to abut against the bases of 
 the pterygoid plates. In this expansion of the Ijasisphenoid the 
 
 G 2 
 
84 ANATOMY OF VERTEBRATES. 
 
 Lepidoslren resembles the Plagiostomes. Two ridges rise from the 
 upper surface of the basioccipito-sphenoidal plate, near its outer 
 margin, and support the cartilaginous lateral walls of the cranium. 
 The cranial cavity is defended above by a longitudinal bony roof, 
 fig. 67, 11, nearly coextensive with the bony floor beneath: the 
 roof commences behind by the sj^ine or point which overhangs the 
 exoccipltals, gradually expands as it advances, resting upon the 
 cartilaginous walls of the cranium, is then suddenly contracted, and 
 is united anteriorly by fibrous ligament to the ascending process of 
 the palato-maxillary arch, 20, and to the base of the naso-premax- 
 illary plate, 15. A strong sharjj crest or sp)ine rises from above the 
 whole of the middle line of the cranial roof-bone, which may be 
 regarded as representing the mid-frontal, the parietal, and super- 
 occipital l)ones, or, in more general terms, the neural spines of the 
 three cranial vertebrse : but this supracranial bone not only covers 
 the medulla oblongata, cerebellum, optic lobes, pineal sac, and 
 cerebral hemispheres, but also the olfactory lobes. The lateral 
 cartilaginous walls of the cranium are continued forward from the 
 acoustic capsule between the basal and superior osseous plates: 
 the part perforated by the fifth pair of nerves, and jjrotectino- 
 the side of the optic lobes, represents the 'alisphenoid': the 
 next portion in advance, protecting the sides of the cerebral 
 hemispheres and perforated by the optic nerve, answers to the 
 orlntosphenoid : and the cartilage terminates by a ' prefrontal' part 
 which is perforated hj the olfactory nerve, and which aljuts laterally 
 against the ascending or palatine process of the maxillary arch. 
 
 The extension of the lateral cartilages of the cranium forward 
 and downward to form the articulation for the lower jaw, is like 
 that in the Chimera and batrachian lar^'a, fig. 69a, e ; but ossifica- 
 tion has co-extended along two tracts, which con- 
 verge as they descend, one, fig. 41, 28, from above 
 and behind to the outer, the other, ilj. 2.3, from before 
 to the inner, side of the cartilaginous mandibular 
 Cranial spines and J*'™*'' wliicli thcse bouy platcs Strengthen and sup- 
 """'2:r» ''"''' port like the backs of a book. The posterior of these 
 IS the tympanic, the anterior one the pterygoid, 
 which is confluent with the palato-maxillary bone, the dentige'rous 
 part of which extends outward, downward," and backward, fi'g. 67, 
 21, but does not reach, as in the Sharks and Eays, the mandilxilar 
 joint. From the upper part of the palato-maxiilary a compressed 
 sharp process, ib. 20, ascends obliquely backward, and terminates 
 m a point : the inner side of this process is closely attaolied by 
 ligament to the fore and outer part of the frontal portion of the 
 
ANATOMY OF VERTEBRATES. 83 
 
 epicranial bone, ib. ii ; the outer side of the process is excavated 
 for the reception of the outer and anterior process of the super- 
 temporal bone. This bone, fig. 41, 12, in connection with the 
 ascending process of the maxillary, ib. 20, forms the ujjper part 
 of the orbit, and behind this connection it sends out the post- 
 orbital process, beyond which it extends Ijackward, freely over- 
 hanging the fronto-occipital, and gradually decreasing to a 2)oint, 
 and giving attachment to the anterior end of the great dorso-lateral 
 muscles of the trunk. This bone is flat above like a scale, and 
 from its superficial position might be classed with the dermal 
 skeleton : the strong temporal muscle is attached to the two 
 suri'aces, divided by the ridge on its inferior part : it is movable 
 up and down upon its anterior ligamentous union. It represents 
 the postorbital and supratemporal bones in Ganoccjihala. 
 
 Each ramus of the lower jaw is composed of an articular, ib. 29, 
 and a dentary, ib. 32, piece, the latter anchylosed together at the 
 symphysis, and completing the tympano-maudibular arch. The 
 articular piece is a simple slender jilate, strengthening the outer 
 part of the articular concavity of the jaw, and closing the outer 
 groove of the dentary, along which it is continued forward to near 
 the symphj^sis, where it ends in a point. The articular trochlea is 
 formed by the persistent cartilage. The dentary piece has the 
 notched and trenchant dentinal plate anchylosed to it, and sends 
 ujj a strong coronoid process. Serial homology guides in the 
 determination of the special one of the part of the upper jaw to 
 which the dentary is opposed. Behind the tympanic is the pre- 
 opcroular, fig. 41, 34. The ceratohyal, 40, is suspended to the 
 petrosal cartilage close l^ehind the tympanic pedicle ; it joins its 
 fellow below without the intervention of a basihyal : it supports a 
 branchiostegal ray, 37. 
 
 In the Ganocefhala the head was connected by ligament, as in 
 the Protopteri, to the vertebral column of the trunk, and chiefly 
 by the basioccipital part. The temporal vacuities were more 
 completely roofed over by bone, including the postorbital and 
 supertemporal ossifications. 
 
 § 29. Skull of Batracliia. — In modern members of this order 
 the ossification of the skull, like its chondrification in Plagiostomi, 
 is simplified, or so continuous as to indicate but obscurely its essen- 
 tially segmental character : and this condition will be noticed 
 before entering upon the description of the complex and instruc- 
 tive osteology of the head in the more specially developed and 
 divergent cold-blooded Vertebrates, called ' bony fishes.' 
 
 In Batracliia the plagiostomous articulation of the head to the 
 
8G ANATOMY OP VERTEBRATES. 
 
 trunk by a pair of condyles, fig. 72, e, e, is resumed. The chief steps 
 In the developement of the batrachlan skull will be premised before 
 entering upon the various modifications. In the larva of the frog, 
 fig. 42, the outer layer of the notochordal capsule expands at the 
 fore part of that vertebral basis to enclose the brain, and its appen- 
 dages, the sense-organs. The cartilage therein developed, fig. 68, 
 as the head expands, forms an occipito-petrosal mass, fig. 42, 
 16, including laterally the ear-cajisules ; it bifurcates anteriorly 
 into the ' sphenoidal arches,' wliich reunite in front of an oblong 
 hypophysial space to form a broad prefronto-vomerine mass. The 
 occipito-petrosal cartilage sends out on each side a tliick ' masto- 
 tympanic ' process, which bifurcates ; the division directed for- 
 ward and inward fig. 42, 26, is the ' pterygoid ; ' that passing 
 forward and downward is the ' hyjDotympanic' To the back part 
 is attached the hyoid cartilage, ib. 4o : to the end is attached the 
 'mandibular' cartilage, ib. so, fig. 69a, d, also called 'Meckel's 
 process.' The subsequent ossification begins partly iii the carti- 
 lage, partly in the piersistent notochordal membrane: the first 
 may be called ' chondrogenous,' the second ' sclerogenous ' bones : 
 some are disjwsed to regard the first only as ' endoskeletal,' the 
 latter as ' exoskeletal.' 
 
 To the first category belong the neurapophyses of the occijuit, 
 exoccipitals, figs. 43 and 68, 2 ; each of which developes a ' zygapo- 
 physis ' or condyle, fig. 73, e, for tlie atlas, fig, 43, a : 
 any petrosal ossification upon the ear-capsule is a 
 growth from the cxoccipital and from the alisplie- 
 nuid, ib. 6 : the expanded disc of the ' columella ' or 
 ' stapes ' is a distinct ossicle, between 2 and 25, 
 fig. 43 ; as is also the ' hypotjTiipanic ' articulation, 
 ib. 29, for the mandible, so, 32. The neurapophyses 
 of the third segment, ' orbitosphenoid,' fio-g. 42 and 
 orti, skull Lmi 43, 10, perforated by the oiitic nerves, are ossified 
 m the cartilaginous basis, as are those ot the 
 fourth segment (prefrontals), figs. 42, 44, 68, 14, perforated by 
 the olfactory nerves ; whilst tliose of the second segment, ' ali- 
 s]ilienoids,' ib. 6, perforated by the trigeminal, longer remain 
 gristly. All the chondrogenous elements are thick bones. 
 
 From tlie membranous basis of the skull are developed the 
 following bones, wliich are more or less lamclliform. The basi- 
 occipito-splicnoldal plate, fig. 73, w(, forms the base of the skull 
 from the condyles to tlie vonierino cartilage. The mastotym- 
 jianic, fig. 43, 25, fig. 44, 8, ■>:., fig. 68, 8," extends from "the 
 mastoid cartilage, where it is broadest, to the outside of the 
 
ANATOMY OP VERTEBRATES. 
 
 87 
 
 69 
 
 69a 
 
 Hyo-brancliijil Xranu', skull, Tiidiirile. oxxxix. 
 
 liypotympanic, fig. 43, 29. The parietals, ib., 44 and 68, 7, and 
 
 afterwards the frontals, ib. ib., u, progressively cover the 'fon- 
 
 tanelle ' above, as the basioccii^ito-sphenoid covers the hypophj^sial 
 
 vacuity below. An antorbltal plate, fig. 72, b, extends from the 
 
 frontal to the maxillary. The premaxillaries, at first beak-shaped, 
 
 figs. 42, 22, and 69a, ?«, expand transversely as the mouth widens 
 
 to form its fore-part, fig. 71, 
 
 n : external to the premaxillary 
 
 pedicles liegins the ossification of 
 
 the turbinals. The 'pterygoid 
 
 plate,' fig. 43, 24, extends to the 
 
 inner side of the hypotympanic, 
 
 29, and forward to the ' palatine ' 
 
 bone, and the bifid dentigerous 
 
 'vomerine' plate, fig. 73, I, I. 
 
 From the membrane covering 
 
 ' Meckel's cartilage,' figs. 69a and 70, d, are exclusively developed 
 
 the mandibular elements, the ' angular,' fig. 43, so, and ' dentary,' 
 
 ib. 32, being the chief; there is also a ' splenial,' which in some 
 
 perennibranchiate Batrachia supports teeth. As the mandible, 
 
 fig. 71, (/, lengthens, the tympanic, il). e, shortens and becomes 
 
 more vertical, and the hyoid arch, ib. a, shifts its attaclmient to 
 
 the i)etro3al, close Ijchind, but distinct from, the tympanic. 
 
 In the Lepidosiren the ali- and orbito-sphcnoids and the 
 tympanic remain cartilaginous ; 
 premaxillaries are represented 
 by their ascending or facial 
 parts coalesced into a single 
 l)late, sujiporting the two pre- 
 Iiensile teeth. The postorbito- 
 supcrtemporals, fig. 41, 12, are 
 ' dermal ' or scleral bones, over- 
 la2:)ping the fronto- parietals. 
 They are not present in modern Batrachia. 
 
 In the Axolotl [Axulotes marmoratus), the basioccipital is repre- 
 sented by the posterior part of the common broad and flat basi- 
 cranial bone. The exoccipitals are separated below by this process, 
 and above by a cartilaginous representative of the superoccipital. 
 Each exoccipital developes a small, almost flattened condyle, 
 anterior to which it is perforated by the eighth pair of nerves ; it 
 articulates above with the parietal and masto tympanic, and is 
 separated from the alisphenoid by the large cartilaginous petrosal, 
 to which a small discoid representative of the stapes is attached. 
 
 hypo- 
 
 Hyo-lir.tnchial fmiiic, slatll, older Tadpole, cxxxi 
 
88 ANATOMY OF VERTEBRATES. 
 
 closing the homologue of the ' fenestra ovalis.' The basi- 
 si)henoidal portion of the basicranial plate sends out an angular 
 process on each side, which supports the alisphenoid. The 
 surfaces of the alisphenoid are directed forward and backward, 
 instead of from side to side, and it constitutes chiefly the anterior 
 parietes of the otocrane ; the inner and anterior border is 
 notched by the great trigeminal nerve. The parietals are long 
 and broad, divided by the sagittal suture, and impressed at the 
 posterior and outer angle by the anterior attaclunent of the great 
 dorsal trunk-muscles. The masto-tympanic is articulated to this 
 part of the parietal and to the exoccipital ; it includes all the 
 divisions of the pedicle save the lowest, ' hypotympanic,' which 
 affords the articulation to the mandible. The orbitosphenoids 
 are divided by an unossified tract of some extent from the ali- 
 sphenoids, and articulate alcove with the extremity of the parietal, 
 the frontal and prefrontal bones. There are neither paroccipitals 
 nor ] lostfrontals. The vomerine portion of the basicranial plate 
 is chiefly cartilaginous. The turbinals are very small, and 
 separated from each other by the junction of the premaxillaries 
 with the frontals. The bone extending from the frontal to the 
 maxillary in front of the orbit may be termed ' antorbital ; ' the 
 ossification which extends therefrom, in higher Batrachians, takes 
 the situation of the facial plate of the prefrontal, of the nasal, and 
 of the lacrj-mal. The pedicles (' apophyse montante,' Cuvier,) 
 of the premaxillaries are long and narrow. The small maxillary is 
 attached to the antorbital, to the palatine, and to the premaxil- 
 lary; the end of the bone extends freely backward as in the 
 Menopome, fig. 43, 21. The alveolar border of both premaxillaries 
 and maxillaries supports a single row of small equal and sharp- 
 pointed denticles. Two bones attached to the anterior and outer 
 part of the basicranial bone, and which may be regarded either as 
 vomerine or palatal, support each a narrow rasp-like group of 
 minute denticles, which are continued backward upon the be- 
 ginning of the pterygoids ; the pterygoids continued from these 
 bones and from the sides of the basicranial bone expand as they 
 extend backward and apply themselves to the inner side of the 
 tympanic jjedicle. The nasal meatus has its posterior termination 
 between tlie beginning of the pterygoid and the end of the 
 maxillary bones. Besides the ordinary row of denticles upon the 
 dentary i)icce of the lower jaw, there is a second shorter series 
 upon the splenial piece. 
 
 In the]\lenol)rancli(i)/c//(//^m;;r//?/.v latcniUs) tlie occipital condyles 
 are trans^'erscly oblong, convex vertically, concave trausverscly, 
 
ANATOMY 03? VERTEBRATES. 
 
 89 
 
 developed from the cxoccipitals, which are separated above and 
 below, as in the Axolotl : each exoccipital forms the posterior half of 
 the otocraue, is perforated by the nervus vagus, and articulates 
 above with the parietal and masto-tympanic. The basisphenoid is 
 very broad and flat : the alisphenoids bound the fore part of the 
 otocraue, transmit the trigeminal nerve, and al^ut against the tym- 
 panic jiedicle in its course backward to the mastoid. The parietals 
 are divided by the sagittal suture and develope a small ridge there 
 posteriorly : each jiarietal sends down a process in front of the ali- 
 sphenoid which rests upon the pterygoid, representing the so-called 
 ' colmncUa' in Lizards. There are no maxillary bones. The alveolar 
 border of the prcmaxillaries, which support a single row of long 
 and slender teeth, ten in mnnber in each bone, terminates in a 
 jioint projecting freely outward and backward. The vomero-])ala- 
 tine bones unite together anteriorly, but diverge posteriorly, where 
 they give attachment liy their outer margin to the pterygoids. 
 
 The two foregoing are examples of the Ichthyomorphs which 
 retain the gills, and thence are termed ' perennilsranchiate.' Tlie 
 Meuopome, figs. 43, 72, and 73, represents a later phase of larval 
 
 72 
 
 Upiier vic-\\' of skull of the Moiiopoiiie. cxxxix. 
 
 UndLl MLV, of IbL bkull. 
 
 life, the gills being absorbed and only the branchial slits re- 
 maining. In fig. 72, e c are cxoccipitals, each developing a 
 condyle ; c, c, parietals ; ff, (j mastotympanics ; /t hypotympanic ; 
 «, a, frontals, h, b, antorbitals ; d, d, nasals ; n, orbitosphenoid ; 
 k, k, prcmaxillaries ; i, i, maxillaries ; /, /, pterygoids. In fig. 
 73, m is the basioccipito-sphenoidal ; e, e, cxoccipitals ; g, y, 
 mastotympanics ; h, h, hypotympanics ; /, /, pterygoids ; /, /, 
 vomers ; k, k, prcmaxillaries. 
 
 In the Frog [Rana) when the metamorphosis is comp)lete, the 
 
90 ANATOMY OF VERTEBRATES. 
 
 exoccipitals have coalesced with the superoccipital above, and with 
 the basiocci23ito-sphenoidaI plate below ; this latter, fig. 98 A, sends 
 out on each side a process to form the floor of the otocrane, and its 
 forward extension is long and narrow : the tympanic develop>es a 
 frame for the large ear-drum, fig. 44, N : the stapes, now colu- 
 melliform, stretches from that membrane to the foramen of the 
 labyrinth. 'Meckel's cartilage,' figs. 69 and 71, d, contributes 
 nothing to the bony conductor of sonorous vibrations which 
 becomes subdivided into a chain of ossicles in Mammalia. The 
 hypotympanic, fig. 44, 2s, sends forward a process to the end of 
 the maxillary, thus articulating, as in the Plagiostomes, with both 
 upper and lower jaws. The essential or neurapophysial parts of 
 the p)refrontals encompass the prosencephalon, and coalesce to 
 form a ring of bone, like the exoccipitals : it is the ' os en 
 ceinture ' of Cuvier,' part of which appears at the upper surface 
 of the cranium, fig. 44, u, between the frontals and antorbitals, 
 ib. 15, which here, and still more in the Toad, assume the 
 character of nasals connate with lacrymals. Between these and 
 the premaxillaries are the small bony parts of the olfactory sacs, 
 usually described as ' nasal bones.' The orbital and temjroral 
 fosssc form one wide common vacuity on each side the cranium : 
 it is divided from the nostril by the junction of the maxillary, 
 ib. 21, with the naso-lacrymal bone : the premaxillaries, ib. 22, 
 are small bones, with a well-marked facial and buccal portion. 
 The palatines, fig. 98, A, are transversely extended : the divided 
 vomer is dentigerous : the pterygoid, ib. 24, sends out three rays 
 for the splienoidal, tympanic, and palato-maxillarj^ connections re- 
 spectively. The mandible is edentulous. The hyoid arch with 
 its branchial appendages has clianged its connections as well as 
 shape. In the tadj)ole, with the fully-developed gills, the carti- 
 lage representing the stylo- and cerato-hyals, figs. 69 and 6 9 A, a, is 
 short and thick, and attached to the back of the tympanic pedicle, 
 ib. e, to the end of which is articulated the mandible, ib. d. The 
 ceratohyals are connected below to a median piece, ib. b, which may 
 represent both the basihyal and basibranchial: it directly supports 
 the hypobranchials c, c, to which the ceratobranchials, or branchial 
 arches are attached. As the gills wither, the stylo-ccratohyals, figs. 
 70 and 71, a, lengthen, attenuate, and acquire an independent 
 attachment to the petrosal ; the basi- and hypo-branchlals, fig. 
 74, c, c, coalesce into a single cartilaginous plate, with the 
 ' basihyal,' ib. b ; and the ceratobranchials arc reduced to a single 
 pair, which represent the so-called ' posterior cornua ' of the hyoid. 
 
 ' cxxxix. torn V. pt. 2, p. 389, pla. xxiv.— xxvii., well illustrate the osteology of 
 the Batrachia. 
 
Hyubrancbial frame, Uana puradoxa. cxxxjx. 
 
 ANATOMY OF VERTEBRATES. 91 
 
 The scapular arch, fig. 42, so, 51, retrogrades, like the hyoid, from 
 its primitive position in the larva. 
 
 Cuvier, at the conclusion of his description of the batrachian skull, 
 remarks, ' This skull does 
 not accord with the theory 
 of the three, four, or seven 
 vertebrae, or even of one 
 (cranial) vertebra, any more 
 tban it does with that of the 
 identity in the number of 
 bones ' (in different animals). ' 
 
 At the same time he de- 
 termines the special homo- 
 logy of the twenty-six bones, 
 exclusive of the mandible and hyoid apparatus, and assigns to them 
 the same names, — and as regards the majority, correctly, — which 
 those bones bear in the rest of the vertebrate province. We have 
 been led, therefore, to look for some higher law within which that 
 of the special conformity may be included. 
 
 In many instances of trunk-vertebraj, the neurapophyses meet 
 below, as well as above the neural axis, their bases being extended 
 towards each other so as to interjDOse between that axis and the 
 vertebral centrum. This condition is repeated hj the exoccipitals 
 which form the neural arch of the epencephalon, and encompass it, 
 in Batrachia, giving passage to its chief joair of nerves and de- 
 veloping articular processes for the succeeding vertebra. The two 
 pairs of neurapophyses in advance, retain the more ordinary rela- 
 tions of these elements, the more expanded mes- and pros-encephala 
 having their bony ring or arch completed by a centrum below and 
 a spine above. One neurajjophysis (alisphenoid) transmits the 
 trigeminal nerve, the other (orbitos2)henoid) the optic nerve : the 
 fourth or anterior neural arch (' os en ceinture ' and ' ethmoide ' 
 of Cuvier) encompasses the foremost segment of the brain 
 as the exoccipitals do the hindmost ; and they give passage 
 to the olfactory nerves. Ossification of this ring of bone begins 
 in its lateral halves : the essential relations and functions beino; 
 
 o 
 
 those which characterise the bones wluch in bony fishes will be 
 described as ' prefrontals.' Beneath, and supporting them, is a 
 pair of bones wliich may be regarded as a mesially divided 
 ' centrum ' (vomer) : and above is a pair of bones which may be 
 
 ' CXX3IX, ' Ce crane ne s'accorde pas plus avec la tlieorie des trois, dcs quatro, ou 
 dcs sept vertebrcs, meme avec celle d'uno vertebre, qu'avcc celle do I'idcutitc de 
 nombre des os,' vol. T. pt. ii. p. 391. 
 
92 ANATOMY OF VERTEBRATES. 
 
 regarded as a mesially divided neural spine (nasal). Thus may be 
 discerned four cranial segments having the essential characters and 
 relations of the neural arch of the tyjoe vertebra. The upper, 22, 
 and lower, 30, jaws, the hyoid, 40, and sca2oulocoracoid, 50-52, fig. 42, 
 constitute four inverted arches ; but their vertebral relations will 
 be better understood in the composition of the skull in bony fishes. 
 § 30. Skull of Osseous Fishes. — The head is larger in proportion 
 to the trunk in fishes than in other vertebrate classes ; it is usually 
 in forru of a cone, figs. 34, 38, whose base is vertical, directed back- 
 ward, and joined at once to the trunk, and whose sides are three in 
 number, one sujierior, and two lateral and inferior. The cone is 
 shorter or longer, more or less compressed or squeezed from side 
 to side, more or less depressed or flattened from above downward, 
 with a sharper or blunter aj)ex, in different species. The l^ase of 
 the skull is perforated by the hole, called ' foramen magnum,' for 
 the exit of the spinal marrow ; the apex is more or less widely and 
 deeply cleft transversely by the ajierture of the mouth ; the eye- 
 sockets or 'orbits,' ib. 17, are lateral, large, and usually with a 
 free and wide intercommvmication in the skeleton ; the two 
 vertical fissures behind are called ' gill-slits,' or branchial or oj^er- 
 cular apertures ; and there is a mechanism like a door, ib., 35, 36, 
 37, for opening and closing them. The mouth receives not only 
 the food, but also the streams of water for respiration, which 
 escape by the gill-slits. The head contains not only the brain and 
 organs of sense, but likewise the heart and breathing oro-ans. 
 The inferior or ' ha3mal ' arches are greatly developed accordingly, 
 and their diverging appendages support membranes that can act 
 upon the surrounding fluid, and are more or less emjjloyed in 
 locomotion : one pair of these appendages, ib. P, 50, 56, answers, 
 in fact, to the fore-limbs in higher animals ; and their sustainino- 
 arch, ib. 51, 52, in many fishes, also supports the homologues of 
 the liind-limbs, v, 70. Thus brain and sense-organs, jaws and 
 tongue, heart and gills, arms and legs, may all belong to the head ; 
 and the disproportionate size of the skull, and its firm attachment 
 to the trunk, required by these functions, are precisely the 
 conditions most favourable for facilitating the course of the fish 
 through its native element. 
 
 It may well be conceived, then, that more bones enter into the 
 formation of the skull in fishes than in any other animals ; and the 
 composition of this skull has been rightly deemed the most 
 diflicult problem in Comparative Anatomy. ' It is truly remark- 
 able,' writes the gifted Okcn, to whom we owe the first clue to its 
 solution, ' what it costs to solve any one problem in Philosopliieal 
 
ANATOMY OF VERTEBRATES. 
 
 93 
 
 Anatomy. Without knowing the ivhat, the hoiv, and the ichy, 
 one may stand, not for hom's or days, but weeks, before a fish's 
 skidl, and oiu- contemphxtion will be little more than a vacant 
 stare at its complex stalactitic form.' 
 
 To show what the bones are that enter into the composition of 
 the skull of the fish ; 11010, or according to wliat law, they are there 
 arranged ; and why, or to what end, they are modified, so as to 
 deviate from that law or archetype, will next be our aim. These 
 points, rightly understood, yield the key to the composition of the 
 skull in all verteV)rata, and they cannot be omitted without detri- 
 ment to the main end of the most elementary essay on the 
 skeletons of animals. The comprehension of the description will 
 be facilitated by reference to figs. 75 — 85; and still more if the 
 reader have at hand the skull of any large fish. 
 
 lu the Cod((?a(/M.s' morrhua,!^. fig. 75),e. g., it may be observed, 
 in the first place, that most of the bones are, more or less, like 
 
 SkuU o£ Cod {Morrhuafi/Jo^'i'i^), Cuv. 
 
 larce scales ; have what, in anatomy, is called the ' squamous ' cha- 
 racter and mode of union, being flattened, thinned off" at the edge, 
 and overlapping one another ; and one sees that, though the skull, 
 as a whole, has less freedom of movement on the trunk, more ot 
 the component bones enjoy independent movements. Before wc 
 proceed to pull apart the bones, it may be well to remark, that the 
 principal cavities, formed by their coadaptation, are the ' cranium,' 
 
94 
 
 ANATOMY OF VERTEBRATES. 
 
 76 
 
 lodging the brain and the organs of hearing; the 'orbital,' and ' nasal' 
 
 chambers ; the ' buccal ' and ' Ijranchial ' canals. Some of these 
 
 cavities are not well defined. The exterior of the skull is traversed 
 
 by five longitudinal crests, intercepting four channels which lodge 
 
 the beginnings of the great muscles of the upper half of the trunk. 
 
 - The median crest is developed from the sujieroccipital, figs. 75, 76, 3, 
 
 // and sometimes also from the frontal, fig. 75, ii : the lateral crest is 
 
 i.,^^ formed by the parietal, fig. 76, 7, and paroccipital, ib. 4: the 
 
 n external crest by the postfrontal, ib. 12, 
 (^, and mastoid, ib. 8. The lower border 
 of the orbit, fig. 75, ff, ff, projects freely 
 downward. The hind 1>order of the 
 operculum is produced into spines in 
 some species, fig. 82. 
 
 In the analysis of the fish's skull 
 it is best to begin at the back part ; 
 for the segments of the skeleton de- 
 viate most from the archetype as they 
 recede in position toward the two ex- 
 tremes of the body. After a little 
 practice one succeeds in detaching the 
 bones which form the back jiart or 
 l^ase of the conical skvill, and which 
 immediately precede and join those of 
 tlie trunk ; we thus ol)tain a ' segment ' 
 or ' vertebra ' of the skull. If we 
 next proceed to separate a little the 
 bones composing this segment, we 
 find those that were most closely in- 
 terlocked to be in number and ar- 
 -Two single and symmetrical bones, 
 and two pairs of unsymmetrical bones, forming a circle ; or, if 
 the lower symmetrical bone, which is the largest, be regarded as 
 the base, the other five form an arch supported by it, of which 
 the upper symmetrical bone is the key-stone, fig. 77. This 
 answers to the ' neural ' arch of the typical vertebra : the base- 
 bone is the ' centrvmi,' 1 ; the pair of bones, which articulated with 
 its upper surface and protected the hind division of the brain, 
 form the ' ncurapophyses,' 2; the smaller pair of bones, projcctiu"- 
 outward, like transverse processes, are the ' diapophyses,' 4 ; the 
 symmetrical bone completing tlie arch, and terminating above in a 
 long crest or spine, is the 'neural s])ine,' 3. It will be observed 
 that the centrum is concave at that surliicc which articulates with 
 
 Upper surface of enniura, Percb 
 i^I'trcafiurLatilL^) 
 
 rangement as follows ; 
 
ANATOMY OF VERTEBKATES. 95 
 
 the ceiitnim of the first vertebra of the trunk : the opposite 
 surface is also concave, but expanded and very irregular, in order 
 to effect a much firmer union with the centrum of the next cranial 
 segment in advance — great strength and 
 fixity being required in this part of the 
 skeleton, instead of the moljility and elas- 
 ticity which is needed in the vertebral 
 column of the trunk. It may be also 
 ol)served that the ' neurapophyses ' are per- 
 forated, like most of those in the trunk, 
 for the passage of nerves ; that the diapo- 
 physes give attachment to the bones which 
 form the great inferior or liromal arch ; and 
 that the neural spine retains much of the 
 shape of the parts so called in the trunk. 
 
 -.^■^^ /•! 1 Disarticulated epencephalie arclj, 
 
 JN evcrtheless, the elements ot the neural Tiowtatrombehiua: coa 
 arch 01 this Inndmost segment oi the skull 
 
 ha^'e undergone so much dcvclopement and modification of shape, 
 that they have received special names, and have been enmnerated 
 as so many distinct and particular bones. The centrum, i, is 
 called ' basioccipital ; ' the neurapophyses, 2, ' exoccipitals ; ' the 
 neural spine, 3, ' superoccipital ; ' the diapophyses, 4, ' parocci- 
 pitals.' In the Iiuman skeleton all those parts are blended together 
 into a mass, which is called the ' occipital bone.' In Philosophical 
 Anatomy it is the ' epenceplialic arch,' because it surroimds the 
 liindmost segment of the brain called ' epencephalon.' 
 
 The entire segment, here disarticulated, is called the ' occipital 
 vertebra,' and in it we have next to notice the widely-expanded 
 iirferior or ha3mal arch, fig. 81, 50, H. This consists of three 
 pairs of bones. (The first pair are bifurcate, and have two points 
 of attachment to the neural arch, the lower prong, answering to 
 what is called the ' head of the rib,' abutting upon the neura- 
 pophysis ; the uj)per prong, answering to the ' tubercle of the 
 rib,' articulating to the diapophysis. -, (The second pair of bones 
 are long and slender, and represent the body of the rib.' The 
 first and second piece together answer to the element called 
 ' pleurapophysis ; '(the third pair of bones are the ' hajmapophyses ; ' 
 these support diverging appendages consisting of many bones 
 and rays. ) The special names of the above elements of the 
 hjemal arch of the occipital vertebra are, from aliove downwards, 
 ' suprascapula,' so ; ' scapula,' 51 ; ' coracoid,' 52. The inverted arcli, 
 so formed, encompasses, supports, and protects the heart or centre 
 of the haemal system; it is called the 'scapular arch.' There 
 
96 ANx\TOMY OF VERTEBRATES. 
 
 are cold-blooded animals — the gymnothorax and slow- worm, 
 e. g. — in which this arch supports no appendage ; there are others 
 — Lepidosiren and Protopterus, fig. 41, 52 — in which it supports 
 an appendage in the form of a single many-jointed ray, ib. 57. 
 In other fishes, the number of rays progressively increase, until, 
 in those called ' rays ' pai' excellence, fig. 64, they exceed a hundred 
 in number, and are of great length, forming the chief and most 
 conspicuous parts of the fish. The more common condition of 
 the appendage in question is that exliibited in the Cod, fig. 34, 
 So developed, it is called in Ichthyology the ' pectoral fin,' ib. p : 
 otherwise and variously modified in higher animals, the same part 
 becomes a fore-leg, a wing, an arm and hand. 
 
 Proceeding to the next segment, in advance, in the Cod-fish's 
 skull, Ave find that the bone which articulated with the centrum 
 of the occipital segment is continued forward beneath a great pro- 
 portion of the skull. In quadrupeds, however, the corresponding 
 part of the base of the skull is occupied by two bones ; and if the 
 single long bone in the fish be sawn across at the part where the 
 natural suture exists in the beast, we have then little difficulty in 
 disarticulating and bringing away with it a series of bones shnilar 
 in number and arrangement to those of the occipital segment. 
 
 In the skeletons of most animals the centrums of two or more 
 segments become, in certain p)arts of the body, confluent, or they 
 may be connate ; they form, in fact, one l^one, like that, e. g., 
 which human anatomists call ' sacrum.' By the term ' confluent ' 
 is meant the cohesion or blending together of two bones which 
 were originally separate ; by ' connate,' that the ossification of 
 the common filirous or cartilaginous bases of two bones proceeds 
 from one point or centre, and so converts such bases into one 
 bone : this is the case, e. g., in the radius and ulna of the froo-, 
 and in its tibia and fibula. In both instances they are to the eye 
 a single bone ; but the mind, transcending the senses, recognises 
 such single bone as being essentially two. In like manner it 
 recognises the ' occipital bone ' of man as essentially four bones ; 
 but these have become ' confluent,' and Avere not ' connate.' The 
 centrums of the two middle segments of the fish's skull are con- 
 nate, and the little violence above recommended is requisite to 
 detach the penultimate segment of the skull. "When detached, 
 the bones of it are seen to be so arranged as to form a neural and 
 a hremal arch. In the neural arch, fig. T8, the centrum, ncura- 
 pophyses, diapophyses, and neural siiine arc distinct: moreover, 
 the neural spine in the Cod, and many other fishes, is bifid, or 
 split at the median line. Tlie centrum is called ' basiphenoid," 5 ; 
 
ANATOMY OF VERTEBRATES. 97 
 
 the neurapophysis, ' alisphenold,' 6 ; the neural spine, ' parietal,' 
 7 ; and the diapophysis, ' mastoid,' 8. The alisplienoids protect 
 the sides of the optic lobes, and the 
 rest of the penultimate segment of 
 the brain called ' mesencephalon ; ' 
 the mastoids project outward and 
 backward as strong transverse pro- 
 cesses, and giii'e attachment to the 
 piers of the great inverted haemal 
 arch. Before noticing its struc- 
 ture, I may remark that, in the 
 recent Cod-fish, the case, partly 
 
 gristly, l)artly bony, Avhicll contains Dlsartlcnlalcclmescncciilialicmcli.riewed 
 
 , • ^ •'-.,•'. . from litliilid ; Cod aionhua i-nbjaris) 
 
 the organ ol hearmg, is wedged 
 
 between the last and penultimate neural arches of the skull. 
 The extent to which tJie ear-case is ossified varies in different 
 fishes, but the bone is always developed in the outer-wall of tlie 
 case. In the Cod it is unusually large, and is called ' petrosal,' 
 fig. 81, 16; in the Perch, fig. 84, 16, and Carp, fig. 83, lo, it is 
 smaller : it forms iw part of the segmented neuroskeleton. In the 
 acoustic organ whicli it contributes to enclose, there is a body as 
 hard as shell, like half a split almond : it is the ' otolite,' fig. 
 81, 16. 
 
 The ha?mal arch consists of a pleurapopliysis and a ha;mapo- 
 physis on each side, and a hasmal spine ; the pleurapopliysis is in 
 two jjarts, the upper one called ' stylohj'al,' i)3. 38 ; the lower one 
 called ' epihyal," ib. 39 ; the hjemapophj-sis is called ' ceratohyal,' 
 ib. 40. The lia3mal spine is subdivided into four stumpy bones, 
 called collectively 'basihyal,' ib. 4i ; and wliich, in most fishes, 
 supj^ort a bone directed forward, entering the substance of the 
 tongue, called ' glossohyal,' ib. 42 ; and another bone directed 
 backward, called ' urohyal,' ib. 43. 
 
 The ceratohyal part of the hsemapophysis supports an appendage, 
 or rudimental limb, called ' branchiostegal,' fig. 81, 44, answering 
 to the pectoral fin diverging from the haimal arch, in the adjoining 
 occipital segment. 
 
 The penultimate segment of the skull above described is called 
 the ' parietal vertebra ; ' the neural arch is called ' mesencephalic ; ' 
 and the hajmal arch is called ' hyoidean ' in reference to its sup- 
 porting and subserving the movements of the tongue. 
 
 The next segment, or the second of the skull, counting back- 
 ward, can be detached from the foremost segment without dividing 
 any bone. It is then seen to consist, like the third and fourth 
 
 VOL. I. H 
 
98 
 
 ANATOMY OF VERTEBRATES. 
 
 Disarticulated prosL-in-ciilinlic ! 
 
 segments, of two arches and a common centre ; but tlie consti- 
 tuent bones have been subject to more extreme modifications. 
 The centrum, called ' presphenoid,' fig. 79, 9, is produced far 
 forward, slightly expanding ; tlie neurapophyses, called ' orbito- 
 
 sphenoids,' ib. lo, are small semi- 
 oval plates, protecting the sides of 
 the cerebrum; the neural spine, or 
 key-bone of the arch, called ' frontal,' 
 ib. 11, is enormously expanded, but 
 in the Cod is single ; the diapophyses, 
 called ' post-frontals,' ib. 12, jn-oject 
 outward from the hinder angles of 
 the frontal, and give attachment to 
 the piers of the inverted htcmal arch. 
 The first bone of this arch is com- 
 mon in Fishes to it and to that of the 
 last described vertebra, being the 
 bone called ' epitympanic,' fig. 81, 25 ; 
 this modification is called for by the 
 necessity of consentaneous move- 
 ments of the two inverted arches, in 
 connection with the deglutition and course of the streams of 
 water req^uired for the branchial respiration. The hremal arch 
 of the present segment — enormously developed — is plainly 
 divided primarily on each side into a pleurapophysis and hrema- 
 pophysis ; for these elements are joined together by a movable 
 articulation, whilst the bones into which they are subdivided 
 arc suturally interlocked together. The pleurapophysis is so 
 subdivided into four pieces ; the upper one, articulating Avith 
 the postfrontal and mastoid — the diapophyses of the two middle 
 segments of the skull — is called 'epitympanic,' ib. 25; the hind- 
 most of the two middle pieces is the 'mesotympanic,' \h. 26: the 
 foremost of the two middle pieces is the ' pretympanic," ib. 27 ; 
 the lower piece is the hypotympanic, \h. 2S ; this presents a joint- 
 surface, convex in one way, concave in the other, called a ' glngly- 
 moid condyle,' for the h;\»mapophysis, or lower division of the 
 arch. In most air-breathing vertebrates — the Serpent, fig. 97, 
 e.g. — the pleurapophysis resumes its normal simplicity, and is a 
 single bone, 28, which is called the '' tympanic ; ' in the ecl-tribo, as 
 in the Batrachia, figs. 4.3, 72, 7, h, it is in two pieces. The greater 
 sidjdivision, in more actively In-eathing Fishes, of the tvmpanic 
 pedicle, gives it additiimal elasticity, and by their overlappino-, 
 interlocking junction, greater resistance against fracture : aiul 
 
ANATOMY OF VEUTEBRATES. 99 
 
 these qualities seem to have been required in consequence of the 
 presence of a complex and largely developed diverging appendage, 
 which forms the framework of the principal flap or door, called 
 ' operculum,' figs. 81, 84, 34-37, that opens and closes the branchial 
 fissures on each side. The appendage in question consists of foru- 
 bones ; the one articulated to the tympanic pedicle is called ' pre- 
 opcrcular,' ib. 34 ; the other three are, counting downward, tlie 
 ' opercular,' ib. 35 ; the ' subopercular,' ib. 36 ; the interopercular,' 
 lb. 37. The hremapophysis is subdivided into two, three, or more 
 pieces, in different fishes, suturally interlocked together ; the most 
 common division is into two subequal parts, one presenting the 
 concavo-convex joint to the pleurapophysis, and called ' articular,' 
 ib. 29 ; the other, bifurcated behind to receive the point of 29, and 
 joining its fellow at tlie ojiposite end, to complete the Ixremal arch : 
 it supports a number of the hard bodies called ' teeth,' and hence 
 it has been termed the ' dentary,' il). 32. In the Cod there is a 
 small separate bone, below the j(_)int (jf the articular, forming an 
 angle there, and called the ' angular piece,' fig. 75, 30. 
 
 In consequence of this extreme modification, in relation to the 
 offices of seizing and acting upon the food, the pair of hrema- 
 jjophyses of the present segment of the skull have received the 
 name of 'lower jaw,' or 'mandi1)le' {mandihula). The ha}mal 
 arch is, hence, called ' mandiluilar : ' the neural arch ' prosen- 
 cephalic : ' the entire segment is called the ' frontal vertebra.' 
 
 TIic first segment, forming the anterior extremity of the neuro- 
 skeleton, like most 2:ieripheral jiarts, is that which has undergone 
 the most extreme modifications. The 
 obvious arrangement, nevertheless, of its 
 constituent bones, wlien viewed from be- 
 hind, after its detachment from the second 
 segment, affords one of the most conclu- 
 sive proofs of the principle of adlierence 
 to common type which governs all the 
 segments of the neuroskeleton, whatever 
 offices they may be modified to fulfil. Disaiticuintcd riimeucepbaiio .-uxii. 
 The neural arch, fig. 80, is pJamly mani- 
 fested, but is now reduced to its essential elements — viz., the 
 centrum, the neurapophyses, and the neural spine. The centrum 
 is expanded anteriorly, where it usually supports some teeth on 
 its under surface in fishes; it is called the 'vomer,' il). i3. The 
 neurapopliyses are notched (in the Cod), or perforated (in the 
 Sword-fish), by the crura or prolongations of the brain, which 
 expand into its anterior division, called rliinencephalon, or 
 
 H 2 
 
100 
 
 ANATOMY OF VERTEBRATES. 
 
 ' olfactory lobes' ; the special name of such neurapophysis is ' pre- 
 frontal,' ib. 14. The neural spine is usually single, sometimes 
 cleft along the middle; it is the 'nasal,' ib. 15. 
 
 The ha3mal arch, fig. 81, 20-i2, H, is drawn forward, so that its 
 apexi as well as its piers, are joined to the centrum (vomer), and 
 usually also to the neural spine (nasal), closing up anteriorly the 
 neural canal. The pleurapophyses are simple, short, sending 
 backward an expanded plate ; they are called ' palatines,' ib. and 
 fin-. 84, 20. The hasmapophyses are simple, and their essential 
 part, intervening between the pleurapophysis and hajmal spine, is 
 
 81 
 
 side view &f cranial vcrtelirie ami senf-e-capsules ; tlie biumai arelic?, H n, in outline, Cotl (^[ui^rJlua i-uJiroris) 
 
 short and thick ; Ijut they send a long ])rocess backward ; this 
 element is called 'maxillary,' ib. 21. The haemal spine, cleft 
 at the middle line, sends one process upward of varying length 
 in different fislies, and a second downward and backward, and 
 its under surface is beset with teeth in most fishes : it is called 
 ' premaxillary,' ib. 22. Each pleura[)ophysis supports a ' diverg- 
 ing appendage,' consisting commonly of two bones : the outer 
 oue, which fixes the present hajmal arch to the succeeding one, 
 is called 'pterygoid,' figs. 75, 81, 24; the inner one is the ' ento- 
 pterj'goid,' ib. 23. The entire segment is called the ' nasal vertebra ;' 
 its neural arch is the ' rliinencephalic ; ' its hremal arch, forming 
 what is termed the upper jaw (ma.riUa), is called the ' maxillary ' 
 arcli and appendages. 
 
 On reviewing the arrangement of the bones of the foregoing 
 segments, one cannot but be struck l)y the strength of the arches 
 which protect and encompass the brain, and by the efficiency of that 
 
ANATOMY OF VERTEBRATES. 
 
 101 
 
 arrangement which provides such an arch for each jtrimary divi- 
 sion of the l:irain ; and a sentiment of admiration naturally arises 
 on examininn- the firm interlockin"; of the extended sutural sur- 
 faces, and especially of those uniting the proper elements of the 
 arch with the buttresses wedged in between the piers and key- 
 stone, and to which buttresses (diajiophyses) the larger hasmal 
 arches are suspended. 
 
 In addition to the parts of the neuroskelcton, the bones of the 
 head include the ossified part of the ear-capsule, ' petrosal,' fig. 
 81, 16, already mentioned; an ossified part of the eye-capsule, 
 commonly in two pieces, ' sclerotals,' ib. 17 ; and an ossified part 
 of the capsule of the organ of smell, ' turbinal,' ib. 19. Another 
 assemblage of splanchnoskeletal bones support the gills, and are 
 in the form of slender bony hoops, called ' branchial arches,' 
 fig. 85, 48, 49. They are partly supported by the hyoidean arch. 
 Amongst the bones of the muco-dermal system, may be noticed 
 those that circumscribe the lower part of the orbit, fig. 75, g, f/ ; 
 of which the anterior, ib. 73, is pretty constant in the vertebrate 
 series, and is called ' lacrymal.' In fishes they are called ' subor- 
 bitals,' and are occasionally present in great )uimbers, as, e. g., in 
 the Tunny, or developed to enormous size as in the Gurnard, 
 fig. 82, and allied fishes, thence called ' mail-cheeked.' A similar 
 
 82 
 
 Fore part of tlie skeleton of tiic Giiriiai-d (Trlgla Lyr«) 
 
 series of bones called ' supertemporals ' sometimes overarches the 
 temporal fossa. 
 
 At the outset of the study of Osteology it is essential to know 
 well the numerous bones in the head of a fish, and to fix in the 
 memory their arrangement and names. The latter, as we have 
 
102 ANATOMY OF VERTEBRATES. 
 
 seen, are of two kinds, as regards the bones of the neuroskeleton : 
 the one kind is ' general,' indicative of the relation of the skull- 
 bones to the typical segment, and which names they bear in 
 common with the same elements in the segments of the trunk ; 
 the other kind is ' special,' and bestowed on account of the par- 
 ticular dcvelopement and shape of such elements, as they are 
 modified in the head for particular functions. A great proportion 
 of the bones in the head of a fish exist in a very similar state of 
 connection and arrangement in the heads of other vertebrates, up 
 to and includino- man himself jSTo method could be less con- 
 duci'\'e to a true and philosophical comprehension of the verteVjrate 
 skeleton than the beginning its study in man — the most modified 
 of all vertebrate forms, and that which recedes furthest from the 
 common pjattern. Through an inevitable ignorance of that pattern, 
 the bones in Anthropotomy are indicated only lij^ special names 
 more or less relating to the particidar fomis these l^ones happen 
 to bear in man ; such names, when applied to the tallying bones 
 in lower animals, losing that significance, and becoming arljitrary 
 signs. Owing to the frequent modification by confluence of the 
 hmnan l^ones, collections of them, so united, have received a 
 single name, as, e. g. ' occipital,' ' temporal,' &c. ; whilst their 
 constituents, which are usually distinct vertebral elements, have 
 received no names, or are defined as processes, c. g. ' condyloid 
 process of the occipital bone,' ' styloid process of the temporal 
 bone,' ' petrous portion of the temporal bone,' &c. The classifi- 
 cation, moreover, of the bones of the head in Pluman Anatomy, 
 viz. into those of the cranium and those of the face, is artificial or 
 special, and consequently defective. Many bones which essentially 
 belong to the skull are wholly omitted in such classification. 
 
 In regard to the archetype skeleton, fishes, Avliich were the first 
 forms of vertebrate life introduced into this planet, deviate the 
 least therefrom ; and according to the foregoing analysis of the 
 bones of the head, it follows that such bones arc primarily divisible 
 into those of — 
 
 The Neuroskeleton ; 
 The Splauchnoskeleton ; 
 The Dermoskcletou. 
 
 The neuroskelctal Ijones are arranged in four scn-mcnts, called 
 
 The Occii)ital vertebra ; 
 The Parietal vertebra ; 
 The Frontal vertebra ; 
 The Nasal vertebra. 
 
ANATOMY OF VERTEBEATES. 103 
 
 Each segment consists of a 'neural' and a 'liajmal' arch. 
 (Fig. 81, N, II.) The neural arches are — 
 
 N I. Epenceiihalio arch (bones Nos. i, 2, 3, 4); 
 
 N II. Mcsencei)halic arch (5, o), 7, s) ; 
 
 N HI. Prosenccphalic arch (0, 10, n, 12); 
 
 N IV. Ilhincncephalic arch (1.3, u, 15). 
 
 The hremal arclies are — 
 
 H I. Scapular arch (50-52) ; 
 
 IT II. Hyoidean arch (38-43) ; 
 
 H III. Mandibular arch (28-32) ; 
 
 H IV. Maxillary arch (20-22). 
 
 The diverging appendages of the hajmal arches are — 
 
 1. The Pectoral (54-57) ; 
 
 2. The Branchiostegal (44) ; 
 
 3. The Opercular (34-37); 
 
 4. The Pterygoid (23-24). 
 
 The bones or parts of the splanchnoskeletou which are inter- 
 calated Avitli or attached to the arches of the true vertebral 
 segments, are — 
 
 The Petrosal (le) or ear-capsule, with the otolite, ic"; 
 The Sclerotal(i7) or eye-capsule; 
 The Turhinal (i9) or nose-capside ; 
 The Branchial arches (45-49) ; 
 The Teeth. 
 
 The bones of the dermoskeleton are — 
 
 The Supratemporals (74) ; 
 The Postorbitals (72); 
 The Superorbitals ("i); 
 The Suborbitals (;3); 
 
 The Labials (75), and others which will be pointed out in 
 certain ganoid fislies. 
 
 Such appears to be the natural classification of the parts which 
 constitute the complex skull of Osseous Fishes, 
 
104 
 
 ANATOMY OF VERTEBRATES. 
 
 The term ' cranium ' might well be applied to the four neural 
 arches collectively, figs. 76, 83 ; but would exclude some bones 
 called ' cranial,' and include some called ' facial,' in Human 
 Anatomy. In a side view of the naturally connected bones of 
 those arches, such as is shown in the Carjj, fig. 83, the ujiper 
 part of the cranium is formed by the neural spines called sujoer- 
 occipital 3, parietal 7, frontal ii, and nasal 15; the lower part 
 by the centrums called basioccipital i, basisphenoid 5, presphe- 
 noid D, and vomer 1 3 : the side-walls by the neurapophyses called 
 exoccipital 2, alisphenoid 6, orbitosphenoid lO, and prefrontal 14. 
 Between 2 and 6 is intercalated the petrosal 16: between the 
 fore part of 9 and lO is the ' interoi'bital 18,' which is an inconstant 
 ossification in fishes. The outstanding or transverse processes 
 are the paroccipital 4, the mastoid 8, and the postfrontal 12. 
 
 Cranium of a Carp 
 
 In the Carp the parietals meet and unite upon the ^■ertex by a 
 ' sagittal ' suture : in most osseous fishes, as in the Cod and Perch, 
 figs. 76, 77, they are separated by the junction of the superocci- 
 pital, 3, with the very large frontals, n, ii. At the base of the 
 skull may be seen, in the Perch, fig. 84, the basioccipital i, the 
 articular processes of the exoccipitals 2, and the spine-shaped' end 
 of the superoccijntal 3. The paroccipital 4, is separated below 
 from the exoccipital by the petrosal 16. The basi-prcsphenoid, 5 
 and 9, carries forward the bodies of the vertebra^ to the vomer 13, 
 which is expanded and dentigcrous anteriorly, as the bodies of 
 the cervical vertebra; supjiort teeth in the DviVodon (p. 57) The 
 alisphenoids g, the orbitosplienoids lo, and the prefrontals u are 
 attached to the sides of tlic basal elements ; more externally are 
 seen the frontal ii, postfrontal 12, mastoid a, and paroccipital 4 
 On the left side are shown the palatine 20, the entopteryo-oid 
 
ANATOMY OF VERTEBRATES. 
 
 103 
 
 23, and external to it the pterygoid abutting upon the hypotym- 
 panic, 28 d: between this and the epitympanic, 28, are the 
 niesotymjianic, 38, and the pretympanic b. The preopercular, 34, 
 runs parallel with, strengthens, and connects together the divisions 
 
 84 
 
 Base of the skull with left side (if raanjihtilar arch and its opercular aiaicndage, Perch iFcrcafluviat'U.9') 
 
 of the tympanic pedicle : it supports the opercular, 35, the sub- 
 opercular, 36, and the interopercular, 37. In the mandibular 
 ramus the articular is marked 29, and the dentary 32. The free 
 end of the maxillary is seen at 21. 
 
 In fig. 85 the maxillary and mandibular arches and appendages 
 are removed, the stylohyal, 38, having been detached from the 
 epitympanic. It resumes its normal attachment to its segment 
 when the special branchial apparatus becomes abrogated, as in 
 the advanced batracluan, fig. 71, in which we saw the change of 
 position, as contrasted with the earlier piscine condition of the 
 larva, fig. 69 A. In the complex and ossified hyoidean arch of 
 
106 
 
 ANATOMY OF VERTEBRATES. 
 
 fishes we find, after the stj'lohyal 33, the epihyal 39, the cerato- 
 hyal 40, and basihyal 41 ; to which may be articulated a glosso- 
 hyal 42, and a urohyal 43 : this is a large compressed lamelli- 
 form bone in the Perch. Seven branchiostegal rays, 44, are 
 articulated to the epi- and cerato-hyals. Four branchial arches 
 are attached to the base of the cranium. The first consists of the 
 ceratobranchial, 47, and epll^ranchial, 48, elements : both of which 
 support a series of jirocesses, 63, directed towards the cavity of 
 the mouth and defending the entry to the branchial fissures. The 
 second and third arches are connected aljove by the pharyngo- 
 
 85 
 
 Hyobrancliial and scamilar avdios, rerch l^c)■c^J^m•iatiUs^ 
 
 branchial elements, 49, to the cranium; and these elements usually 
 support teeth. The gills arc attached to grooves on the outer 
 side of the ei>i- and cerato-ljranchials ; the' arches being closed 
 below by the ' basibrancluals ' which are attached to the hyoid. 
 The suprascapula, 50, is attached by its lower branch to the basi- 
 occipital, and by its upjjcr one 'to the iiaroecipital, 4. The 
 scapula, 51, supi)orts the eoracoid, 52, to which the clavicle, bs, is 
 attached, the relative j^osition ol' whicli to the eoracoid becomes 
 changed as the scapular arch is detached from its natural con- 
 
ANATOMY OF VERTEBRATES. 107 
 
 iiectlon and dlsiilaced backward. The humeral segment of the 
 fore limb is rarely developed in fishes ; the radius, 54, and ulna, 55, 
 are directly articulated with the eoracoid, and are commonly much 
 more broad than louf. 
 
 home of the special characters and modifications of the bones 
 of the head will next be briefly noticed. 
 
 The articular cup for the atlas varies from the deep conical 
 excavation seen, fig. 77, i, in the Cod, to the almost flat surface 
 in the Halibut ; it is rare to find, as in the Pipe-fish (Festular/a), 
 the basioccipital presenting a convex surface for articulation with 
 the body of the atlas ; or to find this centrum confluent with the 
 basioccipital, as in Poli/ptcrus. In many fishes the vmder part 
 of the basioccipital is expanded and excavated ; in the Carp, 
 the under part is produced into a broad triangular plate, fig. 83, i, 
 which supports the large upper pharyngeal grinding tooth ; in 
 the ganoid Lepidostcus, the basioccii)ital developes two plates 
 from its upper and outer angles, which complete the foramen 
 magnum and support the exoccipitals aljove. The exoccipitals, 
 fig. 77, 2, are perforated for the passage of the nervi vagi, some- 
 times for the first spinal or hypoglossal nerve ; the foramina being 
 unusually large in the Carp tribe, fig. 83, 2, where they relate 
 also to the connection of the air-bladder with the organ of hearing, 
 by means of the ossicles, a, h, c, d, and e. 
 
 In some fishes, e.g. Perca, fig. 84, 2, the exoccipitals send 
 liackward articular processes modified to allow a slight move- 
 ment upon the anterior articular processes of the atlas. Like 
 the neurapophyses of the trunk in some fishes (e.g. Lepidosiren, 
 Tliynnus, Xij)li-ias), the bases of the exoccipitals expand, and 
 meet upon the upper surface of the basioccipital, and immediately 
 sui^jiort the medulla oblongata. 
 
 The superoccipital, fig. 77, 3, usually sends upward and back- 
 ward a strong compressed spine from the whole extent of the 
 middle line, and a transverse ' superoccipital ' ridge outwards 
 from each side of the base of the spine, to the external angles of 
 the bone. In most fishes this bone advances forward and joins 
 the frontal, pushing aside, as it were, the parietals, as in fig. 76, 
 3 ; in Batistes the produced jjart of the superoccipital is even 
 Avedged into the hinder half of the frontal suture. In the Carp, 
 on the contrary, the anterior angle of the superoccipital is trun- 
 cated, forming the base of the triangle, and is articulated by a 
 lamboidal suture to the jjarietal bones, fig. 83, 7, which here meet 
 at the mid-line of the skidl, and the upper part of the occipital 
 spine is low and flattened. The superoccipital is also separated 
 
108 ANATOMY OF VERTEBRATES. 
 
 from the frontal by tlie parietals, in the Sahnonoid, Clupeoid, 
 Murrenoid, and most ganoid fishes ; and is itself divided, in Amia 
 and Lepidosteiis, by a median suture ; these modifications tell 
 strongly against extending the homology of the superoccipital with 
 the supermimerary 'interparietal' bone of Mammals, beyond the 
 anteriorly produced interparietal portion ; which, however, is not 
 developed from a separate centre in Fishes. 
 
 When the skull is much compressed the occipital spine is 
 usually very lofty, as in the Opah-fish and Argi/reiosus, fig. .38 : in 
 the Light-horseman fish {EpMppus) it expands above its origin into 
 a thick crest of bone, giving the skull the appearance of a helmet ; 
 but in low flattened skulls the spine is much reduced, projecting 
 merely backward, as in the Pike and Salmon, and being some- 
 times obsolete, as in the Remora. In a few instances, the broad 
 posterior part of the superoccipital articulates with the neural 
 arch and spine of the atlas, and sometimes, on the other hand, e.g. 
 in the Halibut, the entire bone is jiushed by the paroccipitals 
 upon the ujiper surface of the skull, where it manifests the loss of 
 S3'mmetry by the absence of the expanded plate on the left side of 
 the spine. 
 
 In broad and depressed skulls the paroccipital,' fig. 76, 4, forms 
 a strong crest, and exceeds the exoccipital in size ; in narrow and 
 deep skulls the proportions of these bones are commonly reversed, 
 and the parocciDitals sometimes disappear. In the Shad, the 
 paroccipitals unite with the mastoids almost as in the Chelonia ; 
 and in Pohjprion they are connate with the exoccipitals as in 
 Imtrachian and crocodilian Reptiles. In St/nodus, CalUchthi/s, 
 and Iletcrohranchus , the paroccipital is visil)le only at the back 
 part, not at the upper part, of the skull. The inner surface of 
 the paroccipital, like that of the exoccipital, is excavated for the 
 lodgment of part of the posterior and external semicircular canal 
 of the enormous internal organ of hearing in Fishes. The outer 
 projecting process supports the upper fork of the first piece of 
 the scapular arch ; sometimes, as in JEphlppus, by a distinct arti- 
 cular cavity. The neural parts of the occipital vcrtclira are those 
 which arc commonly in Fishes the most comjiletely ossified at the 
 expense of their primitive cartilaginous bases ; and, in Pohjpterus, 
 they become anchyloscd into one piece, like the occipital bone 
 of Anthropotomy, the superoccipital being as little developed as 
 in Protoptcnis. 
 
 ' The paroccipitals are not to bo confounded with tlic dermal bone called ' epiotic ' 
 by Professor Huxley, in his reproduction of Mailer's figure of the head of Pohipterus, 
 in the Government Publication, (clxviii.) p. 22, fig. 16. 
 
ANATOMY OP VERTEBRATES. 109 
 
 The hasisphenoid (figs. 78 and 84, s) is iTSually bifurcate poste- 
 riorly, and more or less expanded beneath the cranial cavity ; it 
 is then continued forward (sometimes after sending out a pair of 
 lateral processes, as in the Perch, more commonly without such 
 processes) along the base of the interorbital space to near the 
 ftire part of the roof of the mouth : its posterior extremity is 
 joined by a squamose suture, as in Diodo7i, to the basioccipital ; 
 or, more commonly, as in the Cod, is firmly wedged hj a kind of 
 double gomphosis into the basioccipital ; its expanded part sup- 
 |)orts the 2:>etrosals and alisphenoids : the presp)henoidal prolonga- 
 tion (figs. 8.3 and 84, 9) articulates with the orbitosphenoids and 
 the ethmoid, I8, when this is ossified; and it terminates forward 
 by a cavity receiving the pointed end of the vomer, fig. 84, 13. 
 It is this portion of the basi-prc-sphenoid which manifests the loss 
 of symmetry in the flat fishes {Pleuronecfida), being twisted up 
 to one side of the skidl. The basi-pre-sphenoid varies in form 
 with that of the head in general, being longest and narrowest in 
 long and narrow skulls, and the converse. The whole of its 
 upper surface is commonly rough for articidation with the petrosals 
 and alis})henoids ; rarely does any portion enter into the direct 
 fcn'mation of the cranial cavity, and then, e. g. in the Cod, a small 
 surface may support the pituitary sac. When it enters more 
 largely into the formation of the floor of the cranial canity, it 
 usually sends upward a little process on each side ; or, as in Fit;- 
 tidaria, a transverse ridge. The hasisphenoid is smooth below, 
 where it is usually flattened or convex, but sometimes is pro- 
 duced downward in the form of a median ridge, and sometimes is 
 2>erforated for the lodgment of certain muscles of the eyeball. 
 In the Polypterus both ali- and orbito-sphenoids are anchylosed t(_> 
 the basi-pre-sphenoid, and the result is a Ijone that answers to the 
 major part of the ' os sphenoides' of Anthropotomy. As two large 
 and important ha?.mal arches of the head are suspended from the 
 parapophyses of the second and third cranial vertebra), this seems 
 to be the condition of the fixation and coalescence of the bodies of 
 those vertebras in all Fishes. 
 
 In some, e. g. Perch and Carp, the base of each alisphenoid 
 rises above the hasisphenoid, and then sends inward a horizontal 
 jilate, which, meeting that of the opposite alisphenoid, forms the 
 innnediate support of the mesencephalon, and at the same time the 
 roof of a canal, excavated in the hasisphenoid, and wdiich 
 traverses the base of the skull, below the cranial cavity, from 
 before backwards, opening behind at the under part of the basi- 
 occipital ; this subcranial canal exists in the Salmonoids, Sparoids, 
 
no ANATOMY OF VERTEBRATES. 
 
 Scomberoitls, and is very remarkable in most fishes with lofty 
 comx^ressed skulls, as the EjMpptis. In them it resembles, but is 
 not homologous with, the posterior prolongation of the nasal pas- 
 sages in the Crocodiles, and it lodges some of the muscles of the 
 ej'xjball. The form of the alisphenoids is influenced by that of the 
 skull ; when this is low and flat, their antero-posterior exceeds their 
 vertical extent ; in deep and compressed skulls they are narrow and 
 high plates ; in ordinary shaped skulls they present either a sub- 
 circular form, and are perforated, as in the Carp, fig. 8.3, 6, or arc 
 reniform, the anterior border being deeply notched, as in the Cod, 
 fin-. 81, c; they form a more definite and fixed proportion of the 
 lateral parietes of the skull than do the petrosals, ib. 16, which 
 arc interposed between them and the exoccipitals ; and they have 
 their essential function in sustaining and protecting the sides of 
 the mesencephalon, and in affording exit to the second and third 
 divisions of the fifth pair of nerves. The alispheuoid articulates 
 in the Cod with the petrosal posteriorly, with the orbitosphenoid 
 anteriorly, and with the mastoid and postfrontal alcove. ^Fhere 
 the alisphenoids have a greater relative size, as in the Perch, and 
 where the less constant jietrosal decreases or disappears, their 
 connections arc more extensive ; they then reach the exoccipitals, 
 and sometimes even join a small part of the basioccijiital. In 
 the incompletely ossified skulls of some fishes, e. g. the Pike and 
 the Salmon tribe, the basal and lateral cranial bones are lined by 
 cartilage, which forms the medium of union between them, 
 especially the lateral ones : in better ossified fishes, e. g. the Cod, 
 the union of the alisphenoids is by suture, partly dentated, partly 
 squamous. In the Cod the second and third di^-isions of the tri- 
 geminal nerve pass out of the cranium by the anterior notch ; in 
 some other fishes they escape l_)y foramina in the alisphenoid : a 
 part of the vestibule and the anterior semicircular canal of the 
 acoustic labyrinth usually encroach upon its inner conca^ity, 
 whence some have deemed it to be the petrous bone. The chief 
 variety in the parietals, figs. 76 and 83 7, has been noted in con- 
 nection with the superoccipital, \h. 3. 
 
 In some fishes the parietal is perforated by the ' ncrvus 
 lateralis,' which supplies tlie vertical fins. The left parietal is 
 broader than the right in the Halibut and some other flat fishes 
 (^Plctironecfidce^. 
 
 Tlie process fiir tlie attachment of the great trunk-muscles is 
 developed from the outer uiargin of the mastoid, figs. 83, 8,5, s ; 
 the inner side of this bone is expanded, and enters'^ slightly into 
 the formation of the walls of the cranial, or rather of tlie acoustic 
 
ANATOMY 03? VERTEBRATES. Ill 
 
 cavity ; its inner, usnally cartilaghions, surface lodging part of 
 one of the semicircular canals. It is wedged into the interspace 
 of the ex- and par-occijntals, the petrosal, the alisphenoiil, the 
 parietal, the frontal, and postfrontal bones. The projecting pro- 
 cess lodges above the chief mucous canal of the head, and below 
 aft(.)rds attachment to the epitympanic, or upper j)iece of the 
 bony pedicle from which the maudiljidar, hyoid, and opercular 
 bones are sus2)ended. 
 
 The orb ito sphenoids, figs. 83, 85, lo, are osseous plates usually 
 of a square shape, sometimes semicircular or semlelliptic, as in 
 the Cod; larger in the Malacopteri, fig. 83, lo ; very small in 
 nvmt Acaiithopteri; and sometimes represented by a descending 
 plate of the frontal, as in the Garpike, or by unossified cartilage, 
 as in mail-cheeked fishes. In the Carp their bases meet, like those 
 of the alisphenoids, above the sphenoid : when osseous matter is 
 developed in the iuterorbital septimi the orbitosphenoids are 
 articulated by their under and anterior part to that bone or 
 bones, fig. 83, lO.' The olfactory nerves pass forward by the 
 superior interspace of the orbitosphenoids and the optic nerves 
 escape by their inferior interspace, or by a direct perforation ; and 
 the essential functions of the orbitosphenoids relate to the pro- 
 tection of the sides of the cerebrum or prosencephalon, and to 
 the transmission of the optic ner"S'es. The orbitosphenoids 
 frequently bound or complete the foramen ovale. 
 
 Although the fro7ital always enters into the formation of the 
 cranial cavity, its major jiart forms the roof of the orbits, which 
 accessory function is the chief condition of the great expanse of 
 this neural spine in fishes. Single, and sending up a median crest 
 in the Cod, the Eplripjius, and some other fishes, the frontal is 
 more commonly divided along the median line, the divisions 
 having the form of long and Inroad subtriangular plates, fig. 76, 
 11, 11 ; narrower in the lofty compressed skulls, smaller in those 
 with large orbits, and becoming greatly expanded in the fishes 
 with small and deep-set eyes. Each frontal sends up its own crest 
 in the Tunny,^ the interspace leading to a foramen, penetrating the 
 cranial cavity in front of the single occipital spine : a larger 
 fontanelle exists in the Cobitis and some Siluroids between the 
 frontal and parietal bones. In the Salamandroid fishes (e. g. 
 Poli/i)terus) each frontal sends down a vertical longitudinal plate, 
 
 ' The speciall)' developed iuterorbital septum, or 'cranial rethmoid' of Cuvier in 
 the Bream and Carp, misled Bojanus into tlie belief that it was the body of the 
 proscncephalic vertebra (vertebra optica). — /sis, 1818, p. 502. 
 
 - Reminding one of the double spine of the neural arch of the atlas in Totrodon. 
 
112 ANATOMY OF VERTEBRATES. 
 
 which rests directly upon the presphenoid, and intercepts a 
 canal along which the olfactory ' crura ' are continued forward 
 to the prefrontals : the lateral parietes of this canal thus form 
 not only a complete, but a douljle bony partition between the 
 orbits. In the Shad a corresponding descending plate takes 
 the place of the orbitosphenoid. In most Acanthopteri an olfac- 
 tory groove is formed by short vertical descending plates from 
 the under surface of the frontal. The niidfrontal is single in 
 the Pleuronectidce, but has undergone more modiiication than 
 any of the preceding bones in connection with the general distor- 
 tion and loss of symmetry of the head : in the Halibut the right 
 posterior angle is truncated, and the rest of that side scooped out, 
 as it were, to form the large orbit of the right side : the left side 
 of the bone retains its normal form : a median crest, a continuation 
 of that upon the sujjeroccipital, divides the two sides. 
 
 The postfrontah, figs. 75, 76, 83, 12, 12, obviously belong to the 
 same category of vertebral pieces as the mastoids, whose promi- 
 nent crest they partly underlie and com])lete, lending their aid in 
 the formation of the single (e. g. Cod, Salmon), or double, (e. g. 
 Pike) articular cavities for the tympanic pedicle: like the mastoids 
 they are ossified in and from the primitive cranial cartilage ; and 
 their inner surface is expanded, Ijut this less frequently enters 
 into the formation of the cranial cavity : they form the posterior 
 boundary of the orbit ; are articulated below to the orbitosphenoid 
 and alisphenoid, above to the frontal, and by their jiosterior and 
 upper ourfaces to the mastoid. 
 
 The vomer, figs. 83, 84, 13, is wedged into the under part of 
 the presphenoid ; its antcro-lateral angles are articulated to the 
 prefrontals; its upper surface supports the nasal bone, sometimes 
 immediately, sometimes by an intervening ethmoidal cartilage. 
 The palatine bones abut against the expanded anterior part of 
 the vomer, the under side of which commonly supports teeth. 
 The left ala of the anterior end of the vomer is eliietly developed 
 in the Halibut and other flat fishes. In the Lepidosteus, the 
 vomer is divided into two, rs in Batraclda, by a median cleft. 
 Although its postericn- end joins olilifpiely to the under part of 
 the presphenoid, it is not, therefore, less a continuation of the 
 basicranial series than is the postsphenoid, which joins in a 
 similar manner with the basioccipital. 
 
 The prefrontals defend and support the olfactory prolongations 
 of the cerebral axis, gi\'o jmssage to tliese so-called ' olfactory 
 nerves,' bound the orbits anteriorly, form the surface of attaclmieut 
 or suspension for the palatine bones, and through these for the 
 
ANATOMY OF VERTEBRATES. 113 
 
 palato-maxillary arch : they rest below iiiwn the presphenoiti and 
 vomer, support above the fore part of the frontal and the back 
 part of the nasal bones, and, by their outer or i'acial extension, 
 give attachment to the large antorbital or lacrymal bone. They 
 are ossified in and from pre-existing cranial cartilage. 
 
 Such are the essential characters of the bones which Cuvier has 
 called ' frontaux anterieures ' ' in Fishes, and to which I apply the 
 name of ' prefrontal ' in all classes of Vertebrate animals. In the 
 Cyprinoids, and most Halecoids, the jirefrontals form part of an 
 interorbital septum. When anchylosis begins to prevail in the 
 cranial bones of Fishes, the prefrontals manifest their essential 
 relationship to the vomerine and nasal bones by becoming confluent 
 with them : thus we recognise the prefrontals in the confluent 
 parts of the nasal vertebra of the Conger, by the external groove 
 conducting the olfactory nerves to the nasal capsules, and l^y the 
 inferior process from which the palatine bone is suspended.'^ In 
 the Murmia-, also, the prefrontals are plainly confluent with the 
 nasal, 15, bone, and form the well marked articular surfaces for the 
 palato-maxillary bone. In some fishes a process of the prefrontal 
 circumscribes the foramen by which the olfactory ' crus ' finally 
 emerges from the anterior prolongation of the cranio-vertebral 
 canal. In the Carp this j^art of the brain traverses a deep notch 
 on the inner side of the prefrontal, fig. 8.3, u. In the Cod the 
 palatine arch is chiefly but not wholly suspended to the prefron- 
 tals. The right prefrontal is the smallest in the unsymmetrical 
 skulls of the flat-fishes. 
 
 The nasal hone is usually single, and terminates forward in a 
 thick obtuse extremity. The anterior end of the nasal is deepest 
 in those Fishes which have a small maxillary arch susj)ended from 
 the cranial axis by vertical palatines, and which have a large 
 
 ' ' Deux frontaux anterieures, qui donnent passage aux nerfs olfactifs, ferment Ics 
 orbites en avant, s'appuyeiit sur le sphenoido et le vomer, et donnent atlaclic par une 
 facette de leur borde inferienre aux palatins.' — Zepjiis d' Anat. Comp,n. 1837, p. 606. 
 Compare this enuneiation of the essential characters of the anterior frontals with 
 Cuvicr's descriptions of the bones to which he applies that name in otlier classes, and 
 with the variable determinations of the same bones by other anatomists — le laerymat, 
 GeofFroy and Spix ; lamina cribrosa ossis ethmoidei of Bojanus ; seitliehe re'ichheine, 
 Meckel, Wagner. Without at present entering into the respective merits or demerits 
 of these determinations, I shall only state that the prefrontals, under whatever names 
 they are described, are essentially the neurapophyses of the nasal vertebra, and that 
 the failure in the attempt to determine the special homologies of these bones may, in 
 every case, be traced to the non-appreciation of their true general homology. 
 
 '■^ In the Conger, Cuvier ' recognises the prefrontals as persistent cartilages. 
 
 ' Op. cit. (.\nr,), ii. p. 235. 
 VOL. I. I 
 
114 Al^ATOMY OF VERTEBRATES. 
 
 basicranial canal. In some fishes, as the SalmonidcB, the nasal is 
 broad but not deep : in Istiophorus it is long and narrow : in the 
 Discoboles and Loplwhranchii it is a short vertical compressed 
 plate : it is altogether absent in the Lophius, or is represented 
 here, as in the Diodon, by a fibrous membrane, retaining the 
 primitive liistological condition of the skeleton. In the Flying 
 Gurnard the nasal has no immediate connection with the vomer ; 
 but this is a rare exception. In most fishes the nasal canity is 
 more completely divided by the nasal bone into two distinct lateral 
 fossa3 than in any other class of Vertebrates. 
 
 In Amia, Lepidosteus, Polypterus, and many extinct ganoid 
 Fishes the nasal is divided at the median line. The horn-like pro- 
 jection from the fore part of the skull of the Naseus unicornis is 
 formed chiefly by a process of the frontal bone, to the under part 
 of which a small nasal is articulated. 
 
 The turbinals, or osseous capsules of the nose, are situated at the 
 sides or above the nasal: the premaxillary and the maxillary 
 bones are usually attached to its extremity through the medium of 
 a symmetrical cartilage which is articulated with the fore part of 
 the nasal bone, and extends forward to the interspace of the upper 
 ends of the premaxillaries. This ' prenasal ' cartilage often forms 
 a septum between the two ' ossa turbinata : ' it is partially ossified 
 in the Carp. 
 
 The sense-capsules are so intercalated with the neural arches, 
 which are modified to form cavities for their reception, that the 
 demonstration of the skull will be best facilitated by describing 
 them before we proceed to the hajmal arches of the cranial verte- 
 brte. 
 
 Acoustic capsule, or petrosal, figs. 81, 83, 85, 16. 
 
 We have seen that the first developed cartilage upon the 
 primitive membranous wall of the skull forms a special protecting 
 envelope for the labyrinth, which alone constitutes the organ of 
 hearing in Fishes (Ammocetes, fig. 58, le). In the progressive 
 accumulation of cartilaginous tissue upon the base and sides of 
 the cranium, the ear-capsule loses its individuality, and becomes 
 bu^ried in the common thick basilateral parietes of the cranium. 
 It is blended with that persistent cartilaginous part of the skull in 
 the Lepidosircn ; but, in the better ossified Fishes, when the 
 osseous centres of tlie neurapophyscs of the cranial vertebra; 
 begin to be establislied in that cartilaginous basis, a distinct bone 
 is likewise, in most cases, developed for the more express defence 
 of the labyrinth. Since, however, fiuictious are less specialised, 
 less confined to the particular organ ultimately destined for their 
 
ANATOMY OF VERTEBRATES. 115 
 
 performance in the lower than In the higher classes, we find in 
 Fishes several bones taking part with the special acoustic capsule 
 in the lodgment of the labyrinth ; and it is only in the higher 
 Vertebrates that the capsule, under the name of the ' i)etrous 
 bone,' entirely and exclusively cnveloj^es the labyrinth. Its 
 ossification commences later than that of the cranial neurapo- 
 ])hyses, in the series of Osseous Fishes : there are sjoecies (c. g. 
 Pike) in which, after the exoccipitals, alisphenoids, and orljito- 
 sphenolds have received their destined amount of ossification, the 
 petrosal still remains in the cartilaginous state : it is small in the 
 Carp, fig. 83, 16, and Bream; in the Perch, figs. 84, 85, ic, it is 
 more developed ; it is somewhat larger in the flat-fish (e. g. 
 Halibut); and in the Cod, fig. 81, ic, attains an equal size with 
 the alisphenoid, ib. g, which it resembles in form, except that the 
 notched margin is posterior. Here it forms the posterior lateral 
 wall of the cranium ; articulates below with the basioccipital i, and 
 basisphenoid, above witli the mastoid 8, and paroccipital 4, behind 
 with the exoccipital 2, and before with the alisphenoid 6 : it sup- 
 ]x>rts the cochlear division of the labyrinth containing the ot(_>lites. 
 The cavity called ' otocrane ' lodging the jietrosal with the rest 
 of the ear-capsule, is formed, on each side, by the exoccipital, 
 paroccipital i, alisphenoid 6, mastoid 8, and postfrontal 4 : it is some- 
 times closed externally, but oj^ens widely into the cranial ca^•ity. 
 
 The optic capsule, or sclerotal, fig. 81, 17, like tlie acoustic caj)- 
 sule, is cartilaginous in Plagiostomes, and also in the semi-osseous 
 fishes, as in most Granoids, the Lepidosiren, the Lophius, the 
 Lo] )liobranchs and Plectognathes. In better ossified fishes it is 
 bony, and commonly consists of two hollow hemispheroid pieces, 
 each with two opposite emarginations ; the inner ones circum- 
 scribing the hole, (analogous to the meatus internus of the 
 petrosal), for the entry of the nerves and vessels to the essential 
 parts of the organ of vision ; and the outer or anterior emargina- 
 tions supporting the cornea. As this part of the skeleton of the 
 head retains its primitive fibro-membranous condition in J\Ian, it 
 is called ' the sclerotic coat of the eye ; ' and the osseous plates 
 developed in it in Birds, many Reptiles, and Fishes, are termed 
 ' sclerotic bones.' It bears, however, the same essential relation 
 to the vascular and nervous parts of the organ of sight, which the 
 petrous bone does to those parts of the organ of hearing, and 
 whicli the turbinal bones do to the organ of smell : the })er- 
 sistent independence of the eye-capsule, which has led to its being 
 commonly overlooked as part of the skeleton, relates to tlic 
 requisite mobility and free suspension of the organ of vision. In 
 
116 ANATOMY OF VEUTEBRATES. 
 
 the Cartilaginous Fishes, however, it is articulated by means of a 
 pedicle with the orbitosphenoid. The osseous cavity or ' orbit ' 
 lodging the eyeball is formed by the presphenoid, orbitosphenoid, 
 frontal ii, postfrontal 4, prefrontal 14, and palatine 20, bones: it 
 opens widely outwards, where it is, often, further circumscribed 
 by the chain of suborbital scale-bones below, and, but less fre- 
 quently, by a superorbital bone above. The bony orbits in most 
 fishes communicate freely together, or rather with that narrow 
 prolongation of the cranial cavity lodging the olfactory crura : 
 but, in many Malacopteri, e. g. the Shads and Erythrinus, the 
 Citharinus and Hijdrocyon, the Synhranchus , and the genus 
 Cyprinus, fig. 83, an osseous septum, 18, divides the orbits. In 
 the Amia, Lej)idosteus and Polypterus the orbits are divided 
 by a double septum, forming the proper walls of the olfactory 
 prolongation of the cranium, as is the case in the Batrachia. 
 
 The olfactory capsules, or turhinals, fig. 81, 19, are lodged in a 
 cavity called ' nasal,' bounded by a variable number of bones, of 
 which the vomer, ib. 13, the prefrontals, ib. u, and the nasals, ib. 
 15, are the most constant : in many bony fishes the nasal chamber 
 is closed behind by cartilage, which partly forms the interorbital 
 septum ; but in which, in some species, a slender symmetrical 
 bifurcate (Perch) or subquadrate ossicle is developed ; in the 
 Cyprinoid (fig. 83, is) and Siluroid Fishes, it articulates below to 
 the presjihenoid, behind and above to the orbitosphenoids, and 
 above and before to the frontals and prefrontals, forming the chief 
 jiart of the interorbital septum. The capsules of the terminal 
 pituitary expansion of the organ of smell are cartilaginous in the 
 Plagiostomes, Chima3roids, in most Ganoids, and in the Lepido- 
 siren. They form a single tube, with interrupted cartilaginous 
 parietes, like a trachea, in several of the Cyclostomes. The tur- 
 binals are developed for the more immediate support of each ol- 
 factory capsule, in osseous fishes ; they are generally thin, more or 
 less elongated, and coiled scales ; situated at the sides of the nasal 
 bone and of the ascending processes of the premaxillaries ; usually 
 free, but in the Gurnards articulated with the prefrontals and 
 nasal, and in the Cock-fish {Aryyreiosus) suspended above the nasal 
 bone, from the anterior prominence of the frontal spine. 
 
 The palato-maxillary arch, fig. 81, 20,21,22, 11, presents a simple 
 and intelligible condition in the Lepidosiren and Plagiostomous 
 fishes ; in all it is completed or closed at one point only, viz., where 
 the premaxillaries meet or coalesce, fig. 67, 22. The palatine bones 
 are the piers of this inverted arch, and their points of suspension 
 are their attachments to the prefrontals, tlie vomerine, and the 
 
ANATOMY OF VERTEBEATES. 117 
 
 nasal bones. The arch is completed by the maxillary and pre- 
 maxillary bones, the symphysis of the latter forming its apex ; 
 and it is inclined forward, nearly or quite parallel with the base 
 of the skull ; which, in most fishes, extends to the apex of the 
 arch, and in some far beyond it, being usvially more or less closely 
 attached to it. In air-breathing Vertebrates the arch is more de- 
 l^endent, circumscribing below the nasal or resjiiratory canal. The 
 ])terygoid bones project backward and outward as the appendages 
 of the palato-maxillary arch, ib. 23. Both maxillary and intermax- 
 illary bones tend by their peculiar developement and independent 
 movement in bony fishes to project freely outward, downward, and 
 backward. We find, at least, that the general form, position, and 
 attaclunents of the single and simi^le palato-maxillary arch, in the 
 Lepidosiren or Cestracion, are represented in most osseous fishes, 
 by their several detached bones, the names of which have been 
 just mentioned. 
 
 The palatine (pleurapophysis of nasal vertebra, figs. 81, 84, 2o) is 
 an inequilateral triangular bone, thick and strong at its upper 
 l>art, which sends off two processes : one is the essential point of 
 suspension of the palato-maxillary arch, and articulates with the 
 prefrontal and vomer at their point of union ; the other is convex, 
 and passes forward to be articulated to a concavity in the superior 
 maxillary, to which, in all Fishes, it affords a more or less moveable 
 joint. In the Parrot-fishes and Diodons the articulation is quite 
 analogous to that of the mandible below with the tympanic pedicle. 
 In the Lepidosteus, Amia, and most Ganoids, it is by a suture. In 
 the Shad the palatine articulates with the premaxillary as well as 
 the maxillary. In the Mormyrus the palatines meet, and unite 
 together at the median line. The posterior border is joined to 
 the entopterygoid, fig. 84, 23, and its outer angle to the pterygoid. 
 The palatine contributes to form the floor of the orbit and the 
 roof of the mouth ; in many fishes it supports teeth, but is eden- 
 tulous in the Cod. It varies much in form in difterent species ; is 
 slender and elongated in the wide-mouthed voracious fishes as 
 the Pike, and is short and broad in the broad-headed, small- 
 mouthed fishes. 
 
 The maxillary (hfemapophysis of nasal vertebra, fig. 81, 2i) is 
 usually a small edentulous bone,' concealed in a fold of the skin 
 between the palatine and premaxillary : it lies, in the Cod, fig. 
 75, 21, posterior to and parallel with the premaxillary, 22, which it 
 resembles in form, but is longer and thinner in most osseous fishes ; 
 
 ' The Os mystaceum of ichthyotomists, 
 
118 ANATOMY OF VERTEBRATES. 
 
 tlie upper, usually bifurcate, end of the maxillary, forms a socket 
 on wliicli the ascending or nasal process of the premaxillary 
 glides ; a posterior tubercle at this end is attached to the palatine, 
 and ligaments connect the same expanded end to the nasal, the 
 turbinal, the vomer, and the premaxillary : the lower and hinder 
 expanded end of the bone is attached by strong elastic ligament, 
 in which a labial gristle is commonly developed, to the lower jaw. 
 In the Salmon and Herring tribe, the Sudis, fig. 86, 21, Amia, 
 and most Ganoids, the maxillary supports teeth. In the Plecto- 
 gnathi (Globe-fish and File-fish), the 
 maxillaries coalesce wholly or in part 
 with the premaxillaries. In the Lepi- 
 dosteus the contrary condition prevails : 
 the jiremaxillary and maxillary Ijones 
 constitute, indeed, a single dentigcrous 
 arch or border of the upper jaw, as in 
 DisarticuMed bones of pai.hv fig- 86, but are Subdivided into many 
 maxillary arch (4™ya;mo(,/(7<«u jjouy pJeces, a coudition wliich sccms to 
 have prevailed in some of the ancient extinct ganoid fishes. In 
 the Polyptems the maxillary is large and undivided on each side ; 
 it supports teeth, and sends inward a palatine plate to join the 
 •N'omer and the palatine bone ; thvis acquiring a fixed position and 
 all the normal features of the bone in higher animals. The 
 maxillary bone is very diminuti\'e in the Siluroid fishes, and 
 appears, with the premaxillary, to be entirely wanting in certain 
 Eels (Muranidce). 
 
 The premnxillanj (hremal spine of nasal vertebra, figs. 75, 81, 22), 
 one of a symmetrical pair in the Cod and most other osseous fishes, 
 is moderately long and slender, slightly curved, expanded and 
 notched at both extremities : the anterior end is bent upward, 
 forming the nasal process, and is attached by lax ligaments to the 
 nasal bone and prenasal cartilage, to the palatine, and to the 
 anterior ends of the maxillary bones. The premaxillaries are 
 movably connected to each other by their anterior ends ; the nasal 
 processes are separated by the prenasal cartilage, the lower or 
 outer branches project freely downward and outward, fio-. 75, 22 : 
 the labial border of each premaxillary is beset Avith teeth, whilst 
 the maxillary bone is quite edentulous in most osseous fishes, as 
 in the Cod, ib. 21. In Diodon the ]n-cmaxillaries and their 
 lamellated dental apparatus coalesce and constitute a single svm- 
 metrical bcak-slia]>od bone: the premaxillary is also siuo-le in 
 l\forim/nis. The ccnifluent premaxillaries constitute the sword- 
 like anterior prolongation of the snout in Xiphias, and are firmlv 
 
ANATOMY OF VERTEBRATES. 119 
 
 and immovably articulated with tlie prenasal and maxillary bones, 
 in both the Sword-fish and the Garpike. The premaxillaries are 
 commonly more extended in the transverse than in the vertical 
 direction ; but there are many examples in Fishes where their de- 
 velopement is equal in both directions. The vertical extension, 
 which forms the nasal branch of the premaxillary, is of unusual 
 length in the fishes with protractile snouts, as, for example, in the 
 Picarels {Blenidce), the Dories (Zeus), and in certain Wrasses, as 
 Coricus, and especially the Epibulus, or Sparus insidiator of 
 Pallas, fig. 87, 22. In this fish the nasal branch of the inter- 
 maxillary, ib. 22', plays in a groove 
 
 on the upper surface of the skull, and /;,^^^. S7 
 
 reaches as far back as the occiput when 
 the mouth is retracted. The descend- 
 ing or maxillary branch is attached 
 by a ligament, ib. 22", longer than 
 itself, to the lower end of the maxil- 
 lary bone, ib. 21, and consequently 
 draws forward that bone, together with 
 the lower jaw, to which the same end Mtrinm mnf riotrictiomninetnction 
 01 the maxillary is attached by liga- 
 ment, when the long nasal branch of the premaxillary glides 
 forward out of the epicranial groove. The protractile action is 
 further favoured by a peculiar modification of the hypotympanic, 
 ib. 28, which, by its great length and movaljle articulation at 
 both ends, cooperates with the long premaxillary in the sudden 
 projection of the mouth, by which this fish seizes the small, agile, 
 aquatic insects that constitute its prey. In the Lopliius the nasal 
 2")rocesses of the premaxillaries enter a groove in the frontal : 
 in the Uranoscopus they also reach the frontal, playing upon the 
 small nasal bone and pressing it down, as it were, upon the 
 vomer. In the Dactylopterus they penetrate between the nasal 
 and the vomer, and play in the cavity of the rhinencephalic arch. 
 The diverging appendage of the palato-maxillary arch consists, 
 in Fishes, of the pterygoid and entopterygoid bones, which, as 
 they are the least important parts of the arch, so are they the 
 least constant : they are wanting, for examjjle, in the Synodon, 
 Platystacus, Hydrooyon, and Lopliius ; are connate with, or 
 indistinguishable from, the palatine in most Salmonoids and Eels ; 
 whilst in the Murtena a single bone, the pterygoid, exists, but is 
 disconnected with the maxillary arch. Most Fishes, however, 
 present, as in the Cod, the two bones above named. The ento- 
 pterygoid is edentulous in the Perch, fig. 84, 23, Cod, and most 
 
120 ANATOMY OF VEETEBRATES. 
 
 other fishes, but Is richly beset with teeth in the Arapaima gigas. 
 It princijoally constitutes the floor of the orbit, its breadth de- 
 pending much upon the depth of that cavity ; it sometimes is 
 joined by its median margin to the vomer and presphenoid, as in 
 the Cod-tribe, Carp-tribe, and Flat-fishes ; and to the basisphenoid 
 in Lepidosteus, Erythrinus, and Pohjpterus, and then divides the 
 orbit from the mouth ; but more commonly a vacuity here exists 
 in the bony skull, filled up only by mucous membrane in the 
 recent fish ; in Upeneus, Polyprion, and Cheilinis, for example, 
 the entopterygoid does not join the basisphenoid. 
 
 The pterygoid forms in the Cod, fig. 75, 24, an inequilateral 
 triangular plate, but more elongated than the palatine, with which 
 it is dovetailed anteriorly ; it becomes thicker towards its pos- 
 terior end, which is truncated and firmly ingrained with the 
 anterior border of the hypotympanic ; its lower border is smooth, 
 thickened, and concave ; edentulous in the Cod, but more fre- 
 quently supporting teeth, as in the Perch. The pterygoid and 
 jjalatine appear to form one bone in the great Sudis, (Arapaima 
 giijas, fig. 86, 20, 24): and they are confluent in the Eel tribe. 
 
 The ten bones of which the palato-maxillary arch is composed 
 in Osseous fishes are, in the Cod and most other species, so dis- 
 jtosed, in relation to the pecvdiar movements of the mouth, as to 
 appear like three parallel and independent arches, successivelv 
 attached behind one another, by their keystones, to the fore part 
 of the axis of the skull, and with their piers or crura suspended 
 freely downward and outward, fig. 75, 22, 21, except those of the 
 last or pterygo-palatine arch, ib. 23, 24, which abut against the 
 tympanic pedicles. The simplification or confluence of the two 
 first of these spurious arches is effected in the Salmonoid Fishes, 
 Sudis, fig. 86, &c., by the shortening of the premaxillarv, and by 
 the mode of its attachment to the maxillary, wliich now forms 
 the larger part of the border of the mouth and sujiports teeth : 
 the maxillaries are brought into close articulation with the pala- 
 tines in the Plectognathes, and the consolidation of the whole 
 series into its normal unity is effected in the Lepidosireu. The 
 palatines form the true bases of the inverted arch at their points 
 of attachment to the prefrontals ; the premaxillarics constitute the 
 true apex, at their mutual junction or symphysis ; the approxi- 
 mation of which to the anterior end of the axis of the skull is 
 rendered possible in fishes, by the absence of any air-passage or 
 nasal canal ; the pterygoids arc the dlA'crging appendages o? the 
 arcli ; but are attached posteriorly to slreugtheu the pedicle sup- 
 porting the lower jaw, and combine its movements with those of 
 
ANATOMY OF VERTEBRATES. 121 
 
 the upper jaw ; just as the bony appendages of one costal arch in 
 Birds associate its movements with those of the next. 
 
 Tympano-mancUbular arch, fig. 81, H, 25 — 32.— This presents 
 its true inverted or hasmal character ; its apex or key-stone formed 
 by the symphysial junction of the lower jaw hanging downwards 
 freely, below the vertebral axis of the skull. The piers, or points of 
 suspension, of the arch, are formed by the efitymf aides : each epi- 
 tympanlc is articulated to both the postfrontal, 12, and the mastoid, 
 8, and is divided artificially in fig. 81; its articular surface is formed 
 m the Cod by a single elongated condyle, fig. 75, 28 ; in many 
 other fishes by a double condyle, one for each of the above-named 
 cranial parapophyses, fig. 84, 28. In the Diodon the upper border 
 of the epltympanlc is articulated by a deeply indented suture to 
 the frontal, the postfrontal and mastoid bones : its posterior 
 margin supports, as in many other fishes, a circular articular sur- 
 face for the opercular bone, fig. 84, 35. Below the condyle, the 
 e})ltympanlc in the Cod, fig. 75, becomes compressed laterally, 
 but Is much expanded from before backward. The almost con- 
 stant bifurcation of both ends of the epltympanlc in osseous 
 fishes, for articulation with two cranial parapophyses above, and 
 suspending two Inverted arches below, make it appear like a 
 coalescence of the uppermost pieces of both those arches. In 
 most fishes the lower end is bifid, and supports both the man- 
 dibular and the hyoldean arches; the stylohyoid, fig. 81,38, being 
 attached near the junction of the epltympanlc with the meso- 
 tympanic. The contiguous ribs of the Chelonla are immovably 
 connected together to ensure fixity and strength to the carapace : 
 the bulky ajiparatus suspended from the parietal and frontal ver- 
 tebrae of osseous fishes demanded the additional strength in the 
 supporting axis which is gained by the confluence of their bodies, 
 and also by that of the proximal pieces of the pleurapophyses by 
 which the two haemal arches are suspended from those vertebras. 
 The anterior division of the epltympanlc piece articulates with 
 the preopercular, fig. 75, 34, the mesotympanic, fig. 81, 26, and 
 pretympanic, lb. 27 ; the posterior division is again bifurcate in 
 the Cod, supporting part of the preopercular and part of the 
 opercular bone. A strong crest projects from its outer surface in 
 tliis and many other fishes. The epltympanlc is simple at both 
 ends in the Carp tribe. 
 
 The inesotijinfanic, figs. 81, 26, 84, 38, is a slender, compressed, 
 slio'htly curved, elongated bone, articulated by its upper part or 
 base to the epitympanio and preopercular ; by its lower end to the 
 inner side of the hypotympanic, reaching almost to the mandibular 
 
122 ANATOMY OF VERTEBRATES. 
 
 trochlea; and by its anterior border to the pretympanic. ib. b. The 
 mesotympanic is confluent with the epitympanic in the Siluroid, the 
 MuriEnoid, and some other fishes ; but does not join the epitympanic 
 in the Lepidosteus, being in that fisli supported by the preopercular. 
 
 The pretympanic, figs. 81, 27, 84, b, is an oblong bony scale, 
 with the posterior margin thickened and grooved for the reception 
 of the fore part of the mesotymiianic and the upper and fore part 
 of the hypotympanic. It is confluent with the hypotymj^anlc in 
 the Conger and Murajna : it does not join either this or the meso- 
 tympanic in the Lepidosteus. 
 
 The hypotympanic, figs. 81, 28, 75 and 84, 28fZ, is a triangular 
 plate of bone, like the epitympanic reversed, bearing the articular 
 convex trochlea for the lower jaw upon its inferior apex and with 
 a straight base. The posterior margin of the hypotympanic is 
 grooved for the reception of piart of the preoj^ercular, ib. 34, 
 its inner side is excavated for the insertion of the jaointed end 
 of the mesotympanic, and the anterior angle is wedged between 
 the pretympanic and the pterygoid, 24, and is firmly united to 
 the latter ; the trochlea is slightly concave transversely, convex 
 in a greater degree from before backwards. The Sly-bream 
 {Epibuhis, Cuv.), presents the most remarkable modification of 
 the hypotymjianic, fig. 87, 28 ; it is much elongated and slender, 
 carrying the lower jaw at an unusual distance from the base of the 
 skull, and it is itself movably connected at its upper end with the 
 mesotympanic. Thus, in the extensive protractile and retractile 
 movements of the mouth, the under jaw swings backward and for- 
 ward on its long pedicle, as on a pendulum ; the lower jaw being- 
 further sujiported or steadied in those movements by a long ligament, 
 extending from the preoperculum to its angular piece, ib. /, so. 
 
 By the confluence of the meso- and epi-tympanics, and of the 
 pre- and hypo-tympanics, in the Eel tribe, the suspensory pedicle 
 of the lower jaw is reduced to two pieces, as in Batrachia. In 
 the LejDidosiren it is represented, as we have seen, by a single 
 osseous piece ; but this I regard as the homologue of only the 
 lower half of the pedicle in the Murmice, \\z. the confluent pre- 
 and hypo-tympanic pieces. This progressive simplification, or 
 diminution of the multiplied centres of ossification of the tympanic 
 pedicle of Fishes, even within the limits of the class, has mainly 
 weighed witli me in rejecting the Cuvicrian view of its special 
 homologies; according to which, not only the squamotcmporal 
 bone and the malar bone of higlier animals, but also the ' symplectic ' 
 — a peculiar ichthyic bone — are superadded to the '"tymi>anic' 
 or quadrate bone of Reptiles and Birds, in the formation of the 
 
ANATOMY OF VERTEBRATES. 123 
 
 suspensory pedicle of the under jaw of Fishes. Ascending to the 
 higher generalisations of homology, we see in the tympanic pedicle 
 a serial repetition of the palatine bone ; and, in both, the ribs or 
 plcurajjophyses of contiguous vertebra specially modified for the 
 masticatory functions of the arches they support. 
 
 The mandible, figs. 81, 84, 29, 32, is the lower portion of the 
 arch, being articulated to the hypotymjianics above, and closed by 
 a ligamentous union or bony symphysis with its fellow at its lower 
 end. The term ' ramus ' is applied in Anthropotomy to each half 
 C)f the mandible, and each ramus consists of two, three, or more 
 pieces in different fishes. Most commonly it consists of two 
 pieces, one (hasmapophysis proper, 29,) articulated to the suspensory 
 ])edicle, and edentvdous, analogous to the maxillary ; and the other 
 (liannal spine, 32,) completing the arch, and commonly supporting 
 teeth, like the [)remaxillary. In the Cod, and some other fishes, 
 a third small jnece is superadded, at the angle of the jiosterior 
 piece, fig. 75, 30. The dentary, 32, is deeply excavated, and 
 receives a cylindrical cartilage, the remnant of the embryonal 
 hxmal arch, fig. 69 A, d, and the vessels and nerves of the teeth. 
 The Sudis, fig. 88, the Polypterus, and Amia, have the splint- 
 like plate along the inner 
 surface of the ramus, called 
 ' splenial : ' it supports teeth 
 and developes a coronoid pro- 
 cess. In both Sudis and Lc- 
 pidosteus there is superadded a 
 small bony piece, ib, 29 a, answering to the surangular in Reptiles. 
 
 The Diverfjing Appendatje of the tympano-mandibular arch 
 consists of the bones which support the gill-cover, a kind of short 
 and broad fin, the movements of which regulate the passage of 
 the currents through the branchial cavity, opening and closing the 
 branchial aperture on each side of the head. The first of these 
 'opercular' bones is the preopercular, fig. 75, 34, which is usually 
 the longest in the vertical direction. In the Gurnards, or ' mailed- 
 cheeked ' Fishes, fig. 82, the preopercular is articulated with the 
 enormously developed suborbital scale bone, 73. 
 
 Three bones usually constitute the second series of this 
 appendage : the upper one is commonly the largest and of a 
 triano-ular form, thin and with radiated lines like a scale : it is 
 the opercular, figs. 75, 84, 35 : in the Cod it is principally connected 
 with the posterior margin of the preopercular, and below with the 
 subopercular, ib. 36 ; but it has usually, also, a partial attachment 
 to the outer angle of the epitympanic, fig. 84 ; and is some- 
 
124 ANATOMY OF VERTEBRATES. 
 
 times (Diodon, Lophius, Anguilla) exclusively suspended therefrom. 
 In the Lophius piscatorius the oi^ercular is a long and strong bone 
 suspended vertically from the convex epitympanic condyle, and 
 with a long and slender fin-ray proceeding from the back part of 
 that joint. The subopercular forms the chief part of the opercular 
 fin by its long backwardly produced lovi^er angle. The sub- 
 opercular bone in the Conger is soon reduced to a mere ray, 
 wliich curves backwards and upwards like one of the branchio- 
 stegals. The opercular itself, though shorter and retaining more 
 of its laminated form, also shows plainly, by its length and curva- 
 ture in the Eels, its essential nature as a metamorphosed ray of 
 the tympanic fin. We have seen that all the framework of this 
 fin had the form of rays in the Plagiostomes. In Murrena the 
 small opercular bones articulate only to the under half of the 
 tympanic pedicle. The subopercular is wanting in the Shad. 
 The lowermost bone, called the interopercular, figs. 75, 84, 37, is 
 articulated to the preopercular above, to the subopercular behind, 
 and usually to the back part of the mandible ; it is attached, also, 
 in the Cod, by ligament to the ceratohyoid in front. The inter- 
 opercular and preopercular are the parts of the appendage which 
 are most elongated in the peculiarly lengthened head of the 
 FistMlaria. 
 
 The third inverted archof the skull is the 'hyoidean,' fig. 81,38-41, 
 and is suspended, in Osseous Fishes, through the medium of the epi- 
 tympanic bone, 25, to the mastoid, 8 ; showing it to be the ha?mal arch 
 of the parietal vertebra. The first portion of the arch, stylohyal, fio-. 
 85, 38, is a slender styliform bone, which is attached at the upper 
 end by ligament to the inner side of the epitympanic, close to its 
 junction with the mesotympanic, and at the lower end to the 
 apex of a triangular plate of bone, which forms the upper portion 
 of the ' great cornu.' I apply to this second piece, which is pretty 
 constant in fishes, the name of epihyal, ib. 39 : the third longer 
 and stronger piece is the ceratohyal, il). 4o. The kevstoneor 
 body of the inverted hyoid arch is formed by two small subcubical 
 bones on each side, the basihyals, ib. i\. These complete tlie 
 bony arch in some fishes: in most others there is a median 
 styhform ossicle, extended forward from the basihyal symphysis 
 into the substance of the tongue, called the glosso-hyal, ib. 42 ; and 
 another symmetrical, but usually triangular, coinin-essed bone, 
 which expands as it extends backwards, in the middle line, from 
 the basihyals ; this is the urohyal, ib. and fig. 75, 43. It is connected 
 with the symphysis of the coracoids, which closes below the fourth 
 of the cranial inverted arches, and it thus forms the isthmus which 
 
ANATOMY OF VERTEBRATES. 125 
 
 separates below the two branchial apertures. In the Conger the 
 hyoidean arch is simplified by the persistent ligamentous state of 
 the stylohyal, and by the confluence of the basihyals with the 
 ceratohyals ; a long glossohyal is articulated to the upper part of 
 the ligamentous symphysis, and a long compressed urohyal to the 
 under part of the same junction of the liyoid arch. The glosso- 
 hyal is wanting in the Mnrcenopliis. 
 
 The Diverfjing Appendage of the hyoidean arch retains the form 
 of simple, elongated, slender, slightly curved rays, articulated to 
 depressions in the outer and posterior margins of the epi- and 
 cerato-hyals : they are called ' branchiostegals,' or gill-cover rays, 
 fig. 85, 44, because they support the membrane which closes 
 externally the branchial chamber. The number of these rays 
 varies, and their presence is not constant even in the bony Fishes : 
 there are but three broad and flat rays in the Carp ; whilst the 
 clupeoid Elops has more than thirty rays in each gill-cover : the 
 most common number is seven, as in the Cod, fig. 75, 44. They 
 are of enormous length in the Angler, and serve to support the 
 membrane which is developed to form a great receptacle on each 
 side of the head of that singular fish. 
 
 The fourth cranial inverted arch, fig. 81, 50 — 52, H, is that 
 which is attached to the paroccipital ; or to the paroccipital and 
 mastoid ; or, as in the Cod, to the paroccipital and petrosal ; or 
 as in the Perch, fig. 85, 50, and Shad, to the paroccipital and 
 basioccipital : thus either wholly or in part to the parapophysis 
 of the occipital vertebra, of which it is essentially the haimal 
 arch ; it is usually termed the ' scapular arch.' In the Eel tribe, 
 where it is very feebly developed, and sometimes devoid of any 
 diverging appendage, it is loosely suspended behind the skull ; 
 and in the Plagiostomes, fig. 30, 5i, 52, it is not directly 
 attached to its jiroper vertebra, the occiput, but is removed 
 further back, where we shall usually find it displaced in higher 
 Vertebrates, in order to allow of greater freedom to the move- 
 ments of the head. 
 
 The superior piece of the arch, 'supra-scapular,' figs. 81, 85, 
 50, is bifurcate in the Cod, or consists of two short columnar 
 bones, attached anteriorly, the one to the paroccipital, the other 
 and shorter piece to the petrosal, and coalescing posteriorly at an 
 acute angle, to form a slightly expanded disk, from which the 
 second piece of the arch is suspended vertically. This piece, 
 called 'scapula,' ib. 5i, is a slender, straight bone, terminating in 
 a point below, and mortised into a groove on the upper and outer 
 side of the lower and principal bone of the scapular arch. The 
 
126 ANATOMY OF VERTEBRATES. 
 
 sujDrascapula and scapula together represent tlie rib or pleur- 
 apojihysis of the occipital vertebra ; they are always confluent in 
 the Siluroids. The lower bone ' coracoid,' ib. 52, completes the 
 arch. In the Cod its pointed upper extremity projects behind 
 the scapvila ; the middle 2)art developes backward a broad jjlate 
 giving attachment to the radiated appendage of the arch : the 
 lower end bends inward and forward gradually decreasing to a 
 point, which is usually connected to that of the opposite coracoid 
 by ligament, and also to the urohyal. In the Siluridte the 
 coracoids expand below, and are united together by a dentated 
 suture. In all Fishes they sujjport and defend the heart, and form 
 the frame or ' sill ' against which the opercular and branchiostegal 
 doors shut in closing the branchial cavity : they also give attach- 
 ment to the aponeurotic diaphragm di'\'iding the pericardial from 
 the abdominal cavity. 
 
 The bones of the head being in completest number, de- 
 parting least from the vertebral pattern, and susceptible of the 
 most intelligible definitions in the class of Fishes, afford the best 
 basis for determining their homologies and fixing their nomencla- 
 ture in the higher vertebrate series. 
 
 § 31. Skull of Chelonia. If the back part of the skull of a 
 Turtle (Chclonc, fig. 89) be compared with 
 that of a Cod, fig. 77, it will be seen that the 
 lowest bone, i, offers an articular surface 
 for the centrum of the atlas, passes for- 
 ward, expanding, to articulate with the 
 basisphenoid, supports the 'medulla ob- 
 longata,' and is suturally articulated above 
 to the pair of bones, fig. 89, 2, 2, which j^ro- 
 tect the sides of the eponcephalon. These, 
 moreover, transmit the hypoglossal and 
 vagal nerves, develope each an articulation for the neurapophvses 
 of the atlas, and converge above to support the keystone of the 
 arch, 3. We have, thus, unmistakcable characters of the basi- 
 ex- and super-occipitals ; there is also a bone, 4, wedged between 
 the ex- 2, and super- 3, occipitals mesially, and joined laterally 
 to the mastoid, 8 : excavated on its inner surface by the postero- 
 external semicircular canal, and iiroduccd on its outer surface for 
 the insertion of the 'bi venter corvicis' and ' com[)lcxus' ; it is the 
 homologue of the paroccipital (' occipitale cxtcrne,' Cuvier), and 
 bears the same general relation to the liindmost vertebral segment 
 of the skull wliich the mastoid, s, docs to the next segnieiit in 
 advance. 
 
 Click view of crauiiim. Turtle 
 
ANATOMY OF VEUTEBRATES. 
 
 127 
 
 In fig. 90, the centrum i, neurapophyses 2, and neural spine 
 3, of the epencephalic arch, are seen from their inner or cranial 
 surfiice : -vvith the increasing bulk of the brain, the spine, 3, 
 begins to expand laterally, and take a greater share in roofing- 
 over the hinder part or epencephalon : the parapophysis, 4, is 
 excluded in this view. The gristly capsule of the ear-organ fills 
 up the otocrane formed by the bones, 2, 3, 5, and 6 ; and extends 
 outward and backward to enter the basal cavity of 4, the par- 
 
 90 
 
 Section of cranium. Turtle (Chelone mydas^ 
 
 occipital : were ossification to extend into the acoustic capsule, 
 either from an independent centre, like 16, figs. 81, 83, 84, or 
 by continuous growth from any of the otocranial bones, the true 
 homologue of the ' petrosal ' or ' petrous portion of the temporal 
 bone ' of Anthropotomy would be established. In some Emydians 
 there is a small autogenous bony plate in the acoustic cartilage, 
 close to the foramen caroticum. 
 
 The basisphenoid, 5, continues forward the series of cranial 
 centrums, expands beneath the cranial cavity, articulates on each 
 side with the alisphenoid, 6, and sends out from its under and 
 lateral surface a plate to articulate with the pterygoids, fig. 98 b, 24, 
 and, in the Emys, with the petrosal. The alisphenoid, 6, fig. 90, 
 protects the side of the mesencephalon (optic lolje), is widely 
 notched anteriorly by the emerging divisions (2ncl and 3rd) of the 
 trigeminal nerve, is perforated posteriorly by a filament of the 
 acoustic nerve, where it joins the cartilaginous petrosal ; it 
 articulates above with the mastoid, 8, and parietal, 7, and in 
 front with the orbitosphenoid, 11. The anterior semicircular 
 canal is partly lodged in the cavity of the otocraue contributed 
 
128 
 
 ANATOMY OF VERTEBRATES. 
 
 by the allsplienoid. Thus in the bone 6, we have all the characters 
 of that so numbered in figs. 81, 83, and 85, and called ' ali- 
 sphenoid ' in the fish. The chief modification is due to the greater 
 developement of 3, fig. 90, in Chelonia, which overlaps 6 as well 
 
 as 2. 
 
 The parietals, figs. 90, 91, are united, as in Cyprinoid and 
 Ganoid fishes, by the sagittal suture, and are much expanded both 
 transversely and longitudinally, overlapping, in the Turtle, the 
 
 91 
 
 Skull of Turtle {Chcloiw mydm) 
 
 superoccipital, fig. 90, 3, and articulated with it and the mastoids, 
 fig. 91, 8, behind; and with the frontals, ib. n, before. Each 
 parietal, also, sends down a long vertical plate, ?', fig. 90, which 
 unites with the alisphenoid, 6, and orbitosphenoid, lo, this ossifica- 
 tion taking the place and function of the latter neurapiiphj'ses in 
 fishes. 
 
 The bone, figs. 89, 91,8, which articulates with the paroccipital 
 4, parietal 7, and postfrontal 12, which aftbrds the surface of attach- 
 ment to the upper end of the tympanic 28, enters into the for- 
 mation of the acoustic chamber in some Emydians, and projects 
 outward and backward to give insertion to the latissimus colli 
 and trachelomastoideus, repeats the chief and essential characters 
 of tlie bone so numbered, and called 'mastoid' in Fishes, figs. 75, 
 76,83,85,8: and forms the transverse process of the parietal 
 vertebra. 
 
 The forward continuation of the vertebral bodies from 5 remains 
 cartilaginous : the lower half of the sides of the prosencephalon 
 
ANATOMY OF VEETEBRATES. 129 
 
 are defended partly by fibro-cartilagc, partly by the exogenous 
 descending lamellas, ?', of the parietals : there are no separate ossifi- 
 cations answering to 9 and lo in fishes.' The frontals, figs. 90, 91, 
 11, are supported like an arch between the parietals 7 and pre- 
 frontals, 14 : and each sends down a longitudinal lamella, bound- 
 ing the sides of the narrow anterior continuation of the brain- 
 chamber, as in Pohjpterus ; but continued l)y an unossified })late to 
 the cartilaginous presphenoid and vomer below. The postfrontal, 
 fig. 91, 12, extends from its connections with the frontal ii, and 
 parietal 7, downward and backward to unite with the mastoid, 8, 
 in the Turtle, and with the malar, 26, and squamosal, 27, in all 
 Cheloida. It forms the posterior boundary of the orbit, but does 
 not contribute any share to the proper cranial walls. 
 
 The median symmetrical bone, fig. 90, 13, which, like a hypa- 
 pophysis, is developed in the lower part or production of the 
 notochordal ca})sule, which underlaps the anterior end of the 
 basi-pre-sphenoid, 5, by its narrow hinder \)axi, — expanding as it 
 advances to articulate with the prefrontals, \a, — having the j)ala- 
 tine bones, ib. 20, abutting against the broad anterior part, and 
 entering by its under surface into the formation of the roof of the 
 mouth, fig. 98 B, n, repeats the essential characters of the bone so 
 nimibered and termed ' vomer ' in Fishes, figs. 81, 83, 84, 9'5, 13 ; 
 and, like it, represents the centrum of the foremost segment of the 
 vertebral series. The vomer is single in Chelonia, as in most fishes. 
 
 The bones, fig. 90, u, in neurapophysial relation with the vomer, 
 protecting the sides of the rhinencephalon or olfactory bulbs, 
 entering into the antero-superior boundary of the orbit, forming 
 part of the surface of attachment of the palatines, supporting 
 the fore part of the frontals, and connected, but more commonly 
 connate, with the nasals, ib. is, fig. 91, 14, repeat the essential 
 characters of the prefrontals of Fishes, figs. 83, 85, 14. Connate, as 
 in Chelonia they usually are, with the nasals, their outer expanded 
 plate unites with the maxillary, fig. 91, 21, and completes the 
 upper border of the nostril, 18. 
 
 The palatines, figs. 90, 98 B, 20, form the sides of the roof of the 
 mouth, articulating medially with the vomer, 13, n, and laterally 
 with the maxillary, 21, and pterygoid, 24. The maxillary, figs. 
 90, 91,21, presents a palatal, facial, and orbital plate. The palatal 
 plate, fig. 98 b, 21, developes a masticatory ridge parallel with the 
 sharp alveolar border. The facial plate, fig. 91, 21, shows the con- 
 nections with the prefronto-nasal, u, the premaxillary, 22, and the 
 malar, 26 ; the orbital plate is usually perforated by the lacrymal 
 
 ' xxxvm. ; Tab. xxi. fig. 89, 1, r. 
 VOL. I. K 
 
130 ANATOMY OF VERTEBRATES. 
 
 canal, the bone so called being ossified continuously, as a process, 
 from the maxillary. The premaxillaries, figs. 90, 91, 22, closing the 
 arch anteriorly, are very small in all Chelonia, and the sutures 
 marking them off from the maxillaries are wanting in some 
 Mud-turtles {Tetronyx lonfjicollis, Fitz. Trionyx Bihroni)-} the 
 premaxillary part of the facial profile is vertical in many Chelonia, 
 as in fig. 91 : but in Tetronyx it extends from the nostril down- 
 ward and backward — the reverse of prognathism. 
 
 The pterygoid, fig. 90, -M, diverges from the vomer and pala- 
 tine, or from the palatine and maxillary, fig. 98 B, backward and 
 outward: uniting, in Chelone, with its fellow below the l>asi- 
 sphenoid, fig. 90, 5, and diverging outward and backward to abut, 
 at a, against the tympanic, 28. In some Soft-turtles, e.g., Trionyx 
 ( Gymnopiis) indicus, the vomer is directly continued from the basi- 
 pre-si)henoid, and divides the pterygoids from each other. 
 
 A second outer bar of bone, fixing the maxillary arch to the 
 tympanic, is present in all Chelonia, and divided into two pieces. 
 The proximal piece, fig. 91, 26, is articulated with the maxillary, 
 21, enters into the lower and back part of the orbital border, unites 
 superiorly with the postfrontal, 1 2, and posteriorly with the second 
 piece, 27. To the bone, 26, the term ' malar ' is given ; to the 
 bone, 27, the name ' sqviamosal.' The latter, resembling a vertical 
 scale or plate, articulates above with the postfrontal, 12, and 
 mastoid, 8 ; and behind with the tympanic, 28. It completes the 
 arch called ' zygomatic,' bounding externally the temporal fossa, 
 which is roofed over by bone in the Turtles (figs. 89 and 91 ), and 
 a few Emyds ; but is widely open above in other Chelonia. 
 
 The tympanic pedicle is a single bone, fig. 91, as, expanded above, 
 with a more or less circular border for the insertion of the mem- 
 brana tymjiani ; excavated internally by the tympanic air-cells ; 
 notched behind for the reception of the columellar stapes, as in 
 the Turtles, fig. 91 ; with a narrower cleft in Tetronyx, and with 
 the borders uniting in the Tortoises and some other Chelonia, 
 reducing the stapedial passage to a foramen or canal, fig. 92, 28. 
 The lower end of the tympanic supj^orts a transversely extended 
 condyle with an undulated or nearly fiattcncd surface. The tym- 
 panic articulates above with the paroccipital, fig. 89, 4, in some 
 species with the alisphenoid, in others with the superoceipital, as 
 well as with the mastoid, ib. and fig. 91,8. 
 
 The mandible consists of an 'articular' clement, small, but dis- 
 tinct in the Turtle, fig. 91, ,;o ; connate in Emya with the ' suran- 
 
 ' XLiv. No. 954, p. 185. 
 
ANATOMY OF VERTEBRATES. 
 
 131 
 
 giilar,' fig. 92, 29 ; of an ' angular ' continued into a ' splenial,' ib. 30 ; 
 of a ' coronoid,' ib. 29' ; and of a ' dentary,' ib. 32. All Chelonia 
 are edentulou.s : the alveolar borders of both upper and lower 
 jaws are sbeatlied with horn : Init in a few species, especially the 
 soft turtles ( Triontjx, Tetronyx) these borders are notched or pro- 
 duced into tooth-like processes. The dentary elements coalesce 
 at the symphysis ; which, in the Snappers, especially Chehjdra 
 (^Chehnura) Temndnchii, is produced into a sharp hook. 
 
 Tlie liyoid arch consists of a basihyal, fig. 92, 41, a pair of short 
 
 
 Side view of cninial vcrtelu-a\ Enujs 
 
 processes, ib. e, giving attachment to the genio- and hyo-glossi 
 muscles : of a pair of long ceratohyals, 40, by which the arch is 
 suspended to the mastoids ; and of a pair of hyobranchials, 47. To 
 complete the series of skull-ljones homologous with those of the 
 fish, represented in fig. 81, it is necessary to bring forward the 
 scapular arch which had receded a short distance from its vertebra 
 in the Batrachia, fig. 42, 52, from a more remote position in the 
 Chelonia : we then find that 51, fig. 92, answers to the scapula, 
 fio-. 81, 51 ; and that 52, fig. 92, answers to the coracoid, fig. 81, 52 : 
 the diverging series of many-jointed rays in the fish, fig. 81, are 
 now developed into the fore-limb, fig. 92, 53 — 5S. 
 
 K 2 
 
132 ANATOMY OF VERTEBRATES. 
 
 lu this figure the several bones of the head of the European 
 Box-terrapene {Emys Europaa, Wgl.) are represented, disarti- 
 culated, in a side view of their vertebral relations. Beneath the 
 Koman figure, l, are the centrum, i. neurapophysis, 2, neural 
 spine, 3, and parapophysis 4, forming the neural (epencepihalic) 
 arch ; with the pleurapophysis, 5i, and hsemapophysis, 52, forming 
 the hfemal (scapular) arch, with its appendage, of the occipital 
 vertebra. Beneath ii are the centrum, 5, the neurapophysis, 
 6, the neural spine, 7, the parapophysis, 8, forming the neural 
 (mesencephalic) arch : from 8 is suspended by an unossified 
 pleurapojjhysis the hajmapophysis, 40, the hajmal spine, 4i, with 
 the appendage, 47, of the ha?mal (liyoidean) arch of the parietal 
 verteljra. Under iii are the neurapophysis, lO, neural spine, ii, 
 and parapophysis, 12, forming the neural (prosencephalic) arch; 
 with the pleurapophysis, 28, and composite hremapophysis, 29 — 32, 
 forming the hamal (mandibular) arch of the frontal vertel^ra, of 
 which the centrum is not an independent ossification. Beneath 
 IV are, the centrum, 1.3, the connate neurapophvses and neural 
 spines, 14, forming the neural (rhinencephalic) arch ; with the 
 pleurapo])]iysis, 20, hffimapophysis, 21, and haemal spine, 22, 
 forming the ha;mal (maxillary) arch of the nasal verteljra. The 
 diverging ap])endages, for the fixation of this hajmal arch are 
 more developed than in Fishes, where it retains more of its 
 typical mobility. Besides the appendage, 24, of the pleurapo- 
 physis, there is now another, extending in two successive 
 segments, 26 and 27, from the hiemapophysis. The splanchnic 
 ossicle, ic', is jwrt of the acoustic organ : the circle of liones, 17, 
 belong to the visual organ. Such are the ' general homologies ' 
 of the bones of the chelonian jiead, in reference to the vertebrate 
 archetype, fig. 21. Compared with bones of the piscine head, 
 fig. 81, previously named and characterised, those of fig. 92 are : — 
 
 1. Basioccipital. 
 
 2. Exoccipital. 
 
 3. Superoccipital. 
 
 4. Paroccipital. 
 
 5. Basisplienoid. 
 
 6. Alisphenoid. 
 
 7. Parietal. 
 
 8. Mastoid. 
 
 9. Presphcnoid (unossified). 
 
 10. Orbitosphenoid (in great part cartilan-inous). 
 
 11. Frontal. 
 
 12. Postfrontal. 
 
ANATOMY OF VERTEBRATES. 133 
 
 13. Vomer. 
 
 14. Prefrontal (with, 15, nasal, distinct in some Chdonia^. 
 
 16. (Petrosal, unossified from an independent centre); if/, a 
 superadded ossicle, ' stapes,' ' columella ' ; witli a gristly represen- 
 tative of ' malleus ; ' in special relation to an organ of hearing affected 
 by viln-ations of air : superadded to all the bones developed in and 
 from the cmlnyonic hiemal arch called ' Meckel's process.' 
 
 17. Sclerotals. 
 
 lit. Tur))inal (unossified). 
 
 20. Palatine. 
 
 21. Maxillary. 
 
 22. Premaxillary. 
 
 24. Pterygoid, with ossification extending into the seat of 23, 
 ento-pterygoid. 
 
 26. Malar (not answering to the bone so numbered in fig. 81). 
 
 27. Squamosal (ib. these bones do not exist in Fislics). 
 
 28. Tympanic (here a single bone ; its subdivisions are 25 — 28 
 in fig. 81). 
 
 29. Articular with )Surangular. 
 29'. Coronal. 
 
 30. Angidar with Splenial. 
 32. Dentary. 
 
 40. Ceratohyal. 
 
 41. Basihyal. 
 
 47. Cerato-branchial, (or ' thyrohyal ' in reference to the 
 larynx of air-breathers, a new developement upon the vestige 
 of the branchial apparatus of fishes). 
 
 50. Suprascapula (unossified). 
 
 51. Scapula. 
 
 52. Coracoid. 
 
 52'. Acromial process of scapula. 
 
 53. Humerus (rarely a separate ossification in Fishes). 
 
 54. Ulna. 
 
 55. Radius. 
 
 56. Carpus. 
 
 57. 53. Digital rays. 
 
 The chief difl:erences in regard to the presence and absence of 
 bones between the Tortoise and the Fish are seen in those 
 belonging to the category of ' diverging appendages : ' thus the 
 ' branchiostegals,' 43, and ' operculars,' 34 — 37, fig. 81, are sup- 
 pressed in the Reptile ; wMle the ' malar,' 26, and squamosal, 
 27, are not developed in the fish. Some minor, but interesting, 
 modifications of cranial structure present themselves within the 
 
134 ANATOMY OF VERTEBRATES. 
 
 limits of the Chelonian order. Figs. 90 and 91 exemplify that 
 which prevails in the marine species ( Chelone). In them the head 
 is proportionally larger ; and, being incapable of retraction witliin 
 the carapace, is additionally protected by extension of bone into 
 the fascia covering the temporal muscles, so as to form a complete 
 osseus vaulted roof over the temporal fosste, due to exogenous 
 growths from the postfrontals, fig. 91, 12, the parietals, 7, and the 
 mastoids, 8. 
 
 In the almost sole instance in which such accessory defence is 
 afforded to a non-marine species — the Brazilian Pipitu {Podo- 
 cneviis expansa) — the temporal roof is cliiefly formed by the 
 parietals, and is completed laterally by a larger proportion of the 
 squamosal than of the postfrontal, wliich does not exceed its 
 relative size in other Terrapenes. The present species further 
 differs from the marine Turtles in the non-ossification of the 
 vomer and the consequent absence of a septum in the posterior 
 nostrils ; in the greater breadth of the pterygoids, winch send 
 out a compressed rounded process into the temporal depressions : 
 tile orbits also are much smaller, and are bounded l^ehind by 
 orbital processes of the postfrontal and malar bones : the mastoids 
 and paroccipitals are more produced backward, and the entire 
 skull is more depressed than in the Turtles. In other freshwater 
 Tortoises (Emys, &c.), the parietal crista is continued into the 
 occijjital one without being extended over the temporal fossje ; 
 the fascia covering the muscular masses in these fossas underg-oinor 
 no ossification. The bony hoop for the membrana tympani is 
 incomplete behind, and the columelliform stapes passes through a 
 notch instead of a foramen to attain the tympanic membrane. 
 The mastoid is excavated to form a tympanic air-cell. 
 
 In the true Tortoises the temporal depressions are exposed, as in 
 the Terrapenes : the head is proportionally small and can be 
 Avithdrawn beneath the protective roof of the carapace. The skull 
 is rounder and less depressed than in the Terra])enes. The 
 tympanic hoop is notched l)ehind, but the columelliform stapes 
 passes through a small foramen. The palatine processes of the 
 maxillaries are on a j^lane much below that of the continuation of 
 the basis cranii formed by the vomer and palatines. 
 
 In the soft-turtles (Trionicidw), the skull is long, depressed, 
 triangular, tlic muzzle forming the obtuse apex, and tlie base 
 remarkable for its four liackAvard prolongations. The inferior of 
 these is the shortest, and terminates in the occii)ital condyle ; the 
 superior is the longest, and is Ibnned by the siipcroccipital spine : 
 the two lateral processes arc developed from the paroccipitals and 
 
ANATOMY OF VERTEBRATES. 
 
 135 
 
 mastoids. The pvemaxillary is either wanting, or it is very small, 
 and represented by its alveolar border only; the maxillaries 
 meeting above it. The alveolar borders of both upper and lower 
 jaws show a regular series of vascular pits or foramina, indica- 
 tive ol the primitive separate matrices, like those of teeth, which 
 laid the foundation in the young animal of the continuous horny 
 coverings of the jaws. 
 
 Temminck's Snapper ( Chelonura Temminckii) is remarkaljle for 
 the upper convexity and enormous expanse of the cranium, chiefly 
 due to the temporal fossaj, contrasted with the short and narrow 
 face. In a fossil chelonian from the Portland stone ( Ch. planiceps) 
 and in another from the Clialk ( Ch. pulchriceps) the nasals Avere 
 distinct from the prefrontals, wliich is a rare exce2)tion in existing 
 species. 
 
 93 
 
 Hro 
 
 Side view of cranial vcrtcbnTS and Eeusc-capsnles, Crocodile 
 
 § 32. Skull of Crocodilia. — Passing next to the skull of the 
 Crocodile, we find the first difference in the less complex condition 
 of the epencephahc arch, fig. 9.3, n i, which consists of four, instead 
 of, as in the Fish and Turtle, six bones. The basioccipital, figs. 93 
 and 94, i, presents, Hke the centrums of the trunk, a convexity at 
 its posterior articular surface ; but its anterior one, like the hind- 
 most centrum of the sacrum, unites with the next centrum in ad- 
 vance, ib. 5, by a flat rough sutural surface. Like most of the cen- 
 trums in the neck and beginning of the back, that of the occiput 
 developes a hypapophysis, but tliis descending process is longer and 
 laro-er. The exoccipitals, ib. 2, articulate suturally, like the neur- 
 apophyses of the trunk, with the upper and lateral parts of their 
 
136 ANATOMY OF VERTEBKATES. 
 
 centrum; are concave mesially, fig. 94, 2, towards the brain-segment 
 which they protect, meeting above it to support the neural spine, 3 ; 
 they develope a petrosal plate, which meets a corresponding one 
 from the alisphenoid ; they give exit to the vagal and hypo- 
 glossal nerves, and send outward a strong jirocess, fig. 93, 4, 
 which articulates with the mastoid and tympanic. The anterior 
 and inner part of the base of this process is excavated by part 
 of the acoustic cavity : its outer extremity is rough for the attach- 
 ment of muscles : it thus repeats the essential characters of the ' par- 
 occipital ' in the Fish and Turtle ; but it is ossified, as an exogenous 
 transverse process, from the neurapophysis (exoccipital, 2). The 
 superoccipital, figs. 93 and 94, 3, is Inroad and flat, like the 
 similarly detached neural sj)ine of the atlas ; it advances a little 
 forward, beyond its sustaining neurapophyses, to protect the upper 
 surface of the cerebellum ; it is traversed by tympanic air-cells, 
 and assists with the ex- and par-occipitals, 2, 4, in the formation of 
 the ear-chamber. 
 
 Proceeding with the neural arches of the Crocodile''s skull, if we 
 dislocate the segment in advance of the occiput, fig. 93, N" 2, we 
 bring away, in connection with the long base-ljone, 5, the bone, 9. 
 The two connate cranial centrums must be artificially divided, in 
 order to obtain the segments distinct to which they belong. The 
 hinder portion, 5, of the great base-bone, which is the centrum of 
 the parietal vertebra, is the basisphenoid. It supports that jiart 
 of the ' mesencephalon,' which is formed liy the lobe of the tliird 
 ventricle, and its upper surface is excavated for the pituitary 
 prolongation of that cavity. The basisphenoid developes from its 
 under surface a ' hypapophysis,' which is suturally united with the 
 fore part of that of the basioccipital,but extends further down, and is 
 similarly united in front to the ' pterygoids,' fig. 94, 24. These rough 
 sutural surfaces of the long descending process of the basisphenoid 
 are very characteristic of that centrum, when detached, in a fossil 
 state. The neurapophyses of the parietal vertebra, g, r, the ali- 
 sphenoids, protect the sides of the mesencephalon, and are notched 
 at tlieir anterior margin, for a conjugational foramen transmitting 
 the trigeminal nerve. As accessory functions they contribute, like 
 the corresponding bones in fishes, to the formation of the car- 
 chamber. They have, however, a little retrograded in position, 
 resting below in part upon the occipital centrum, and supporting 
 more of the spine of that segment, 3, than of tlieir own, 7. The 
 spine of the parietal vertebra (])arietal, figs. 93, 94, 95, r), is a single, 
 depressed bone, like that of the occipital vertebra ; it completes 
 the mesencephalic arch, as its crown or key-bone ; it is partially 
 
ANATOMY OF VERTEBEATES. 137 
 
 excavated by the tympanic air-cells, and overlaps the superocci])ital. 
 The bones, ib. s, 8, wedged between c and 7, are developed from 
 independent centres, and preserve their individuality, as in Fishes. 
 They form no part of the inner walls of the cranium, but are 
 partially exca-^-ated by the tympanic cavity, and send outAvard and 
 backward a strong transverse process for muscular attachment. 
 They afford a ligamentous attachment to the haimal (hyoid, fig. 
 93, II 2, 4o) arch of their own segment, and articulate largely with 
 the pleurapophyses, (tympanic, ib. 28), of the antecedent hremal 
 arch, whose more backward displacement, in comparison witli its 
 position in the fish's skull, is well illustrated in the metamorphosis 
 of the Frog, figs. 69 A and 71. 
 
 On removing the neural arch of the parietal vertebra, alter the 
 section of its confluent centrum, the elements of the corresponding 
 arch of the frontal vertebra, fig. 93, N ill, are seen to present the 
 same arrangement. The compressed produced centrum (presphe- 
 noid, ib. a) has its form modified like that of the vertebral centrums 
 at the opposite extreme of the body in many Ijirds. The neiirapo- 
 physes (orbitos2jhenoids, ib. lo) articulate with the upper j)art of 
 9 ; they are expanded, and smoothly excavated on their inner surface 
 to supjjort the sides of the large prosencephalon, showing more 
 plainly their archetypal character than in Chehmia ; they dismiss 
 the optic nerves by a notch. They show the same tendency to a 
 retrograde change of position as the neighbouring neurapophyses, 
 6 ; for though they support a greater proportion of their proper 
 spine, 11, they also support part of the parietal spine, 7, and rest, 
 in part, below upon the parietal centrum, 5. The neural spine, ii, 
 of the frontal vertebra retains its normal character as a single 
 symmetrical bone, like the parietal sjiine wliicli it partly overlaps ; 
 it also completes the neural arch of its own segment, but is remark- 
 ably extended forward, where it is much thickened, and assists in 
 forming the cavities for the eyeballs ; it is the 'frontal' bone. 
 
 In contemplating in the skull itself, or such side view as is 
 given in fig. 94, the relative position of the frontal, ii, to the 
 parietal, 7, and of this to the superoccipital, 3, which is overlapped 
 by the parietal, just as itself overlaps the flattened spine of the 
 atlas, we gain a conviction which cannot be shaken by any 
 difference in their mode of ossification, by their median bipartition, 
 or Ijy their extreme expansion in other animals, that the aljove-named 
 single, median, imbricated bones, each completing its neural arch, 
 and permanently distinct from the piers of such arch, must repeat 
 the same element in those successive arches — in other words, 
 must be ' homotypes,' or serially homologous. In like manner the 
 
138 ANATOMY OF VERTEBRATES. 
 
 serial homology of those piers, called ' neurapophyses,' viz., the 
 lamiua3 of the atlas, the exoccipitals, the alisphenoids, and the 
 orbitosphenoids, is equally unmistakable. Nor can we shut out of 
 view the same serial relationship of the paroccipitals, fig. 95, 4, as 
 coalesced diapophyses of the occipital vertebra, with the mastoids, ib. 
 8, and the postfrontals, 12, as par- or di-apophyses of their respective 
 vertebras. All stand out from the sides of the cranium, as tranverse 
 processes for muscular attachment ; all are alike autogenous in the 
 Turtles ; and all of them, in Fishes, offer articular surfaces for the 
 ribs of their respective vertebra3 ; and these characters are retained 
 in the postfrontals as well as in the mastoids of the Crocodiles. 
 
 The frontal diapophysis, figs. 93, 95, 12, is wedged between the 
 back part of the spine, 11, and the neurapophysis, 10 ; its out- 
 wardly projecting process extends backward, and joins that of 
 the succeeding diapophysis, 8 ; but, notwithstanding the retro- 
 gradation of the inferior arch, it still articulates with part of its 
 own pleurapoi)hysial element, 28, which forms the proximal element 
 of that arch. 
 
 There finally remain in the cranium of the Crocodile, after the 
 successive detachment of the foregoing arches, the bones termi- 
 nating the fore part of the skull, n 4, fig. 93 ; but, notwithstand- 
 ino- the extreme degree of modification to which their extreme 
 position subjects them, we can still trace in their arrangement 
 a correspondence with the vertebrate type. 
 
 A long and slender symmetrical grooved bone, fig. 93, 13, is con- 
 tinued forward from the coalesced pterygoids, 24, and stands in the 
 relation of a centrum to the vertical plates of bone, 14, which expand 
 as they rise into a broad, thick, triangular plate, with an exjiosed 
 horizontal superior surface. These bones, the prefrontals 14, stand 
 in the relation of neurapophyses to the rhinencephalic prolonga- 
 tions of the brain commonly called 'olfactory nerves;' and they 
 form the piers or haunches of a neural arch, which is completed 
 above by a pair of symmetrical bones, 15, called ' nasals,' which I 
 regard as a divided or bifid neural spine ; the independent basal 
 ossification, answering to the vomer in Fishes, figs. 81, 84, 13, and 
 Clielonians fig. 98 B, n, is in advance of its proper segment, and 
 divided in the middle line as in Ganoid Fishes and Batrachia. In 
 some Alligators {All. iiu/er) the divided vomer extends far for- 
 ward, expands anteriorly, and appears upon the bony palate. 
 
 Almost all the other bones of the head of the Crocodile are 
 adjusted so as to constitute four inverted arches. These are the 
 ha3mal arches of the four segments or vertebra\, of whioli the 
 neural arches have been just described. But they have been the 
 
ANATOMY OF VERTEBRATES. 
 
 139 
 
 seat- of much greater modifications, by which they arc made sul^- 
 servient to a variety of functions unknown in the hajmal arches of 
 the rest of the body. Thus the two anterior hromal arches of the 
 head perform the office of seizing and bruising the food; are 
 armed for that purpose with teeth : and, whilst one arch is firmly 
 fixed, the other W()rks upon it like the hammer upon the anvil. 
 The elements of the fixed arch, called ' maxillary arch,' fig. 93, H, 
 iv, have accordingly undergone the greatest amount of change, in 
 order to adapt that arch to its share in mastication, as well as for 
 forming part of the passage for the respiratory medium which 
 traverses it. Almost the whole of the upper surface of the max- 
 illary arch is firmly united to contiguous parts of the skull Jjy 
 rough or sutural surfaces, and its strength is increased l^y l^ony 
 
 94 
 
 Section of cranium, Crocodile 
 
 appendages, which diverge from it to abut against other parts of 
 the skull. Comparative Anatomy teaches that, of the numerous 
 places of attachment, the one which connects the maxillary arch by 
 its element, 'iO, with the centrum, 13, and with the descending plates 
 of the neurapophyses, u, of the nasal segment, is the normal or 
 the most constant point of its suspension ; the bone, 20, being the 
 pleurapophysial element of the maxillary arch : it is called the 
 ' palatine,' because the under surface forms a portion of the bony 
 roof of the mouth, called the ' palate,' as in fig. 98 C, 20. It is 
 articulated at its fore part with tlie l^one, 21, which is the hroma- 
 po|)hysial element of the arch. This bone is called the ' maxil- 
 lary,' and is greatly developed Ijoth in length and breadth, fig. 
 95, 21 : it is connected with 20, figs. 94, 98 C, behind and 
 with 22 in front, which are parts of the same arch, and with 
 the diverging appendages of the arch, viz., fig. 95, 26, the malar 
 bone, and fig. 98 c, 25, the ectopterygoid : the maxillary is also" 
 united with the nasals, 15, and the lacrymal, 73, as well as 
 with its fellow of the opposite side. The smooth, expanded 
 
140 ANATOMY OF VERTEBRATES. 
 
 horizontal plate, which effects the latter junction, is called 
 the palatal plate of the maxillary, fig. 98 C, 2i ; the thickened 
 external border, where this plate meets the external rough surface 
 of the bone, and which is perforated for the lodgment of the 
 teeth, is the ' alveolar border.' The haemal spine or key-bone of 
 the arch, 22, is bifid, and the arch is completed by the symphysial 
 junction of the two symmetrical halves ; these halves are called 
 ' premaxillary bones : ' these bones, like the maxillaries, have a 
 rough facial plate, fig. 95, 22, and a smooth palatal plate, fig. 98 c, 
 22, with the connecting alveolar border. The median symphysis 
 is perforated vertically through laoth plates ; the outer or upper 
 hole being the external nostril, fig. 95, 22, the under or palatal 
 one being the premaxillary aperture, fig. 98 C, p. 
 
 Both the palatine and the maxillary bones send outward and 
 backward j^arts or jjrocesses which diverge from the line of the 
 haemal arch, and give attachment to distinct bones, which form 
 the ' diverg-ing appendages ' of the arch, and serve to attach it, as 
 do the diverging appendages of the thoracic lia;mal arches in the 
 bird, to the succeeding arch. 
 
 Tlie appendage, 2j, called ' pterygoid,' efl^ects a more extensive 
 attacliment, and is peculiarly developed in the Crocodilia. As it 
 extends backward it exjjands, luiites with its fellow both below 
 and above the nasal canal, encom])assing it so as to form the hinder 
 or jialatal nostril, fig. 98 C, n ; the coalesced pterygoids articulate 
 anteriorly with the divided vomer, the palatines, and the basi- 
 pre-sphenoid : posteriorly each broad wing, extending outward, 
 gives attachment to a second bone, ib. 25, called ' cetopterygoid,' 
 Avhich is firmly connected with the maxillary, 21, the malar, 26, 
 and the postfrontal, 12. The second diverging ray of the maxil- 
 lary arch is of great strength ; it extends from the maxillar}', fig. 95, 
 21, to the tympanic, 28, and is divided into two pieces, the malar, 
 26, and the squamosal, 27 ; both of which begin to assume more 
 lengthened and slender proportions than in the Turtle (compare 
 fig. 95 with 91). Such are the chief Crocodilian modifications of 
 the hremal arch and appendages of the anterior or nasal vertebra 
 of the skull. 
 
 The hremal arch of the frontal vertebra, fig. 92, 11, iii, is 
 somewliat less raetamoriihoscd, and has no diverging appendage. 
 It is slightly displaced backward, and is articulated by only a 
 small proportion of its i)leurapophysis, 28, to the parapophysis, 12, 
 of its own segment ; llie major i^art of that short and strong rib 
 articulating with the parajjophysis, 8, of the succeeding segment. 
 TJie bone, fig. 95, 2s, called 'tympanic,' because it serves to support 
 
ANATOMY OF VEUTEBRATES. 141 
 
 the ' drmn of the ear ' in air-breathhig vertebrates, is short, strong, 
 and immovably wedged, in the Crocodilia, between the paroccipital, 
 4, mastoid, 8, postfrontal, 12, and squamosal, 27 ; and the conditions 
 ot this fixation of the pleurapophysis are exemplified in the great 
 developemcnt of the ha3mapophysis (mandible), which is here 
 unusually long, supports numerous teeth, and requires, therefore, 
 a firm ])oint of suspension, in the violent actions to which the jaws 
 arc put in retaining and overcoming the struggles of a powerful 
 living })rcy. The movable articulation l)ctween the tympanic, 28, 
 and the rest of the hremal arch is analogons to that which we find 
 between the thoracic pleurapophysis and h;emapopliysis in birds. 
 But the hfcmapophysis of the mandibular arch in the Crocodiles 
 is subdivided into several pieces, in order to combine the greatest 
 elasticity and strength with a not excessive weight of bone. The 
 diiferent pieces of this adaptively subdivided element have received 
 definite names. That numbered 29, fig. 9.3, which offers the articular 
 conca'S'ity to the convex condyle of the tympanic, 28, is called the 
 ' articular ' piece ; that beneath it, so, which developes the angle 
 of the jaw, when this projects, is the ' angular ' piece ; the piece 
 above, 29, and e, fig. 95, is the ' surangular ;' the thin, broad, flat 
 piece, 31, fig. 93, applied, like a splint, to the inner side of the 
 other parts of the mandible, is the ' splenial ; ' the small accessory 
 ossicle, 3i', is the 'coronoid,' because it develoj^es the process, so 
 called, in lizards ; the anterior piece, 32, which supports the teeth, 
 is called the ' dentary.' The purport of this subdivision of the 
 lower jaw-ljone has been well explained by Conybeare' and 
 Buckland,^ hj the analogy of its structure to that adopted in 
 binding together several parallel plates of elastic wood or steel to 
 make a crossbow, and also in setting together thin plates of steel 
 in the springs of carriages. Dr. Buckland adds — ' Those who 
 have witnessed the shock given to the head of a crocodile by the act 
 of snapping together its thin long jaws, must have seen how liable 
 to fracture the lower jaw would be, were it composed of one bone 
 only on each side.' The same reasoning applies to the composite 
 structure of the long tympanic pedicle in fishes. In each case the 
 splicing and bracing together of thin flat bones 'of unequal length 
 and of varying thickness, atfords compensation for the weakness 
 and risk of fracture that would otherwise have attended the 
 elongation of the jiarts. In the abdomen of the crocodile the 
 analoo-ous subdivision of the haBniapophyses, there called abdo- 
 minal ribs, allows of a slight change of their length, in the 
 expansion and contraction of the walls of that cavity ; and since 
 
 " ' Geol. Trans.' 1821, p. 565. ^ ' Bridgewater Treatise,' 1836, vol. i. p. 176. 
 
142 ANATOMY OF VERTEBRATES. 
 
 amphibious reiitiles, when on land, rest the whole weight of the 
 abdomen directly ujoon the ground, the necessity of the modifi- 
 cation diminishing lial^ility to fracture further appears. These 
 analogies are important, as demonstrating that the general homo- 
 logy of the elements of a natural segment of the skeleton is not 
 affected or obscured by their subdivision for a special end. 
 The purposive modification of the hajmapophyses of the frontal 
 vertebra is but a repetition of that which affects the same 
 elements in the abdominal vertebraj. 
 
 Passing next to the hromal arch of the parietal vertebra, fig. 
 93, H, ii, we are first struck by its small relative size. Its 
 restricted functions have not required it to grow in jjroportion 
 with the other arches, and it consequently retains much of its 
 embryonal dimensions. It consists of a ligamentous ' stylohyal,' 
 retaining the same primitive histological condition which obstructs 
 the ordinary recognition of the pleural element of the lumbar htemal 
 arches ; of a cartilaginous ' epihyal,' 39, intervening between this 
 and the ossified ha;mapophysis, or ceratohyal, 40 ; and of the ha;mal 
 spine, 41, which retains its cartilaginous state, like its homotypes, 
 in the aljdomen : there they get the special name of ' abdominal 
 sternum,' here of ' basihyal.' The liasdiyal has, however, coalesced 
 with the thyrohyals to form a broad cartilaginous plate, the anterior 
 border rising like a valve to close the fauces, and the posterior 
 angles extending beyond and sustaining the thyroid and other 
 parts of the larynx. The long bony ' ceratohyal ' and the com- 
 monly cartilaginous ' epihyal ' are suspended by the ligamentous 
 ' styloliyal ' to the back part of the tympanic at its junction ^vith 
 the paroccipital process ; the whole arch having, like the man- 
 dibular one, retrograded from the connection it presents in Fishes. 
 
 This retrogradation is still more considerable in the succoedino- 
 hnsmal arch, fig 92, h i ; fig. 57, 5i. In comparing the occipital 
 segment of the Crocodile's skeleton with that of the Fish, fig. 81, 
 the chief modification that distinguishes that segment in the Cro- 
 codile is the apparent absence of its hasmal arch. We recognise, 
 however, the sjiccial homologues of the constituents of that arch 
 of the Fish's skeleton, fig. 34, in the bones 5i and 5-j of the Cro- 
 codile's skeleton, fig. 57 ; but the ui)per or suprascapular piece, so, 
 fig. 92, retains, in connection with the loss of its proximal or cranial 
 articulations, its cartilaginous state: the scapula, 5i, is ossified, as 
 is likewise the coracoid, 5l>, the lower end of which is sejiarated 
 from its fellow by the interposition of a median, svmmetrical, 
 partially ossified ])iece called ' episternum.' Tlic power of recoo-- 
 nisiiig the special homologies of so, 5i, and 5-> in the Crocodile. 
 
ANATOMY OF VERTEBRATES. 143 
 
 with tlic similarly numbered constituents of the same arch in 
 Fishes — though masked, not only by modifications of form and 
 proportion, but even of very substance, as in the case of so — 
 depends upon the circumstance of these bones constituting the 
 same essential element of the archetyjial skeleton, viz. the fourth 
 hremal arch, numbered pi, 52, in fig. 17. For although in the pre- 
 sent instance there is superadded to the adaptive modifications 
 above cited the rarer one of altered connections, Cuvier does not 
 hesitate to give the same names, ' suprascapulaire' to 50, and 
 ' scapulaire' to 5i, in both Fish and Crocodile ; but he did not pcr- 
 cfAxe or admit that the narrower relations of special homology 
 were a result of, and necessarily included in, the Avider law of 
 general homology. According to the latter law, we discern in fig. 
 93, 50 and 5i, a compound ' pleurapophysis,' in 52 a 'hajmapophysis,' 
 and in hs, the ' ha3mal spine,' completing the haemal arch.' 
 
 The scapulo-coracoid arch, both elements, 6i, 52, of which 
 retain the form of strong and thick vertebral and sternal ribs in 
 the Crocodile, is applied in the skeleton of that animal over the 
 anterior thoracic hajmal arches. Viewed as a more robust hreraal 
 arch, it is obviously out of place in reference to the rest of its 
 vertebral segment. If we seek to determine that segment by the 
 mode in which we restore to their centrums the less displaced 
 neural arches of the antecedent vertebra? of tlie cranium or in the 
 sacrum of the bird,^ we proceed to examine the vertebra; before 
 and behind the dis2")laced arch, with the view to discoA-er the one 
 wdiich needs it, in order to be made typically complete. Finding 
 no centrum and neural arch without its pleurapophyses from the 
 
 ' The author of No. clxxi, in criticising this conclusion, omits consideration of 
 the cartilaginous element, fig. 93, 60 ; as it exists and required due attention, I 
 was led to regard it as tlie homologue of the ossified element, figs. 81, 85, 50, in 
 Eishes, and as being part, one might say, half, of the pleurapophysis. No anatomist has 
 impugned such determination of the special homology of the ' lame cartilagineuse 
 du bord spinal de I'omoplate ' of the Crocodile, with the ' partie spinal de I'omoplate ' 
 of the Frog, and with the ' os surscapulaire ' of the Fish. Now the latter is the 
 homotype of the proximal half of the compound pleurapophysis of the pelvic arch, 
 of which tlie part called ' ilium ' answers to the part called ' scapula.' There remains, 
 therefore, for Dr. Humphrey's consideration, the serial and general homologies of the 
 ' suprascapula ; ' in the omission of which lurlcs the fallacy of his criticism, clxxi, 
 pp. 27, 28. Tlie alleged difference of devclopement, at most one of direction of growth, 
 is futile. 
 
 A ' htemal arch ' having been defined as including the ' pleurapophysis ' as well as 
 'hajmapophysis,' by altering the meaning of the term and restricting the ' haemal parts 
 of the vertebra ' to the ' hajmapophyses and haamal spine,' Dr. Humphrey makes 
 ground for pronouncing the part of the haemal arch, 50 and .51, in figs. 81 and 92, 
 as being the hxm- not the pleur-apophysis. 
 
 ^ See 'On the Archetype and Homologies of tlie Vertebrate Skeleton,' pp. 117 
 and 159. 
 
144 ANATOMY OF VERTEBRATES. 
 
 scapula to the pelvis, we give up our search in that direction ; 
 and in the opposite direction we find no vertebra without its ribs, 
 until we reach the occiput ; there we have centrum and neural 
 arch, with connate parapophyses, but without the haamal arch, 
 which arch can only be supplied by a restoration of the bones 
 50-52 to the place which they naturally occuiDy in the skeleton of 
 the fish. And since the bones 50-52 in the Crocodile, fig. 57, are 
 specially homologous with those so numbered in the Fish, fig. .34, 
 we must conclude that they are likewise homologous in a 
 higher sense ; that in the Fish the scapula-coracoid arch is in its 
 natural or typical position, Avhereas in the Crocodile it has been 
 displaced for a special pur2)0se. Thus, agreeably with a general 
 principle, we perceive that, as the lower vertebrate animal illus- 
 trates the closer adhesion to the archetype' by the natural articu- 
 lation of the scapuLi-coracoid arch to the occiput, so the higher 
 vertebrate manifests the superior inflvience of the antagonizing 
 power of adaptive modification by the removal of that arch from 
 its proper segment. 
 
 The anthropotomist, by his mode of counting and defining the 
 dorsal vertel5ra3 and ribs, admits, unconsciously perhaps, the 
 important principle in general homolog)^ wliich is here exemplified ; 
 and which, pursued to its legitimate consequences, and further 
 applied, demonstrates that the suprascapula and scapula are the 
 modified rilj of that centrum and neural arch, which he calls the 
 ' occipital bone ; ' and that the cliange of place which chiefly masks 
 that relation (for a very elementary acquaintance with Compara- 
 tive Anatomy shows how little mere form and proportion affect 
 the homological characters of bones), differs only in extent, and 
 not in kind, from the modification which makes a minor amount 
 of comparative observation requisite, in order to determine the 
 relation of the shifted dorsal rib to its proper centrum in the 
 human skeleton. 
 
 With reference, therefore, to the occipital vertebra of the Cro- 
 codile, if the comparatively well-developed and permanently 
 distinct ribs of all the cervical vertebra^ prove the scapular arch 
 to belong to none of those segments,'^ and if that hajmal arch be 
 required to complete the occipital segment, which it actuallv does 
 complete in fishes, then the same conclusion nuist apply to the 
 same arch in other animals, up to man himself. 
 
 ' The term ' simple primary form ' appears to Dr. Ilumplirey, clxxi, p. 34, to 
 be more correet than the word ' arehctyiic.' 
 
 2 Close the eyes to the fact of the suprascapular element in the Crocodile, and you 
 then may, with Dr. Huni])hrcy, see its representative in one of the cervical pleur- 
 apophyscs. Comp. ib. p. 28, and note, p. 14+, of the present work. 
 
ANATOMY OP VERTEBRATES. 
 
 145 
 
 The locomotive extremity, fig. 92, 53-57, is the diverging aji- 
 pendagc of the arcli, under one of its nvmierous modes and grades 
 of developemcnt. 
 
 Coadjusted as the above-defined vertebral elements are in the 
 skull of the Crocodile, they compose such a whole as is represented 
 in fig. 95. Each temporal fijssa is circumscriljcd externally by 
 two horizontal bony arches ; the upper one formed l^y the post- 
 frontal, 12, and mastoid, 8; the lower one by the malar, 2G, and 
 squamosal, 27: the tympanic, 28, and mastoid, 8, bound the 
 fossa behind : the coarticulated processes from the postfrontal and 
 malar form a partial division between the fossa and the orbit in 
 
 95 
 
 Skull of Crocodile 
 
 front. The orbit is circumscribed by these bones, with the frontal, 
 11, prefrontal, 14, and lacrymal, h. A superorbital or palpebral 
 derm-ossicle strengthens the upper eyelid. The external nostril, 
 single and advanced in Crocodilia, is surrounded sometimes, as in 
 Gavials, by the premaxillaries, 22 ; sometimes, as in fig. 95, admit- 
 ting also the points of the nasals, 15. The internal nostril opens far 
 back, beneath the occiput, fig. 98 c, n, and is exclusively surrounded 
 by the pterygoids, 24 : its plane is horizontal in Gavials and some 
 Allir^ators ; but is more or less oblique, looking backward, in 
 Crocodiles. Behind and above it are the median and lateral 
 Eustachian bony outlets, from which the membranous continua- 
 tions of the tubes converge and unite in the single valvular aper- 
 ture on the soft palate.' The vast extent of the bony roof of the 
 
 ' CLXXU., pi. xii. fig. 5. This paper may be referred to for other evauial foramina, 
 and for the details of the complex bony structure of the median and lateral 
 VOL. I. L 
 
146 ANATOMY OF VERTEBRATES. 
 
 moutli is interrupted by the large ' pterygomaxillary ' vacuities, 
 ila. y, bounded externally by the maxillaries and ectopterygoids : 
 at the fore part is the small 'prepalatine' opening, ib. p. In the 
 Gavials each pterygoid expands at its outer and fore border into a 
 large oval bulla. The palatines and maxillaries are excavated by 
 sinuses commimicating with the nasal passages. The form of the 
 maxillo-premaxillary palatine suture helps by its variation to the 
 distinction of species.' The anterior expanded parts of the divided 
 vomer appear upon the laony palate in some Alligators.^ 
 
 The otic capsule remains in great part cartilaginous : towards 
 the cranial cavity it is defended by the thin otocranial plates of 
 the alisphenoid, supcroccipital and paroccipital, with occasionally a 
 small scale, represcnthig a rudimental petrosal. The eye-capsule 
 is not defended by bony plates, as in Cludonia. The turbinals 
 remain cartilaginous. 
 
 The cranial cavity is miserably small in these huge cold-blooded 
 Carnivora ; its main part, shown in section, fig. 94, 2, o, 10, may 
 be filled by a man's thumb in a skull of three feet in length. The 
 l)roper brain-chamber is, however, continued along the groove 
 beneath the interorbital platform to the second slight expansion 
 between the prefrontals, 14, where the rhinencephalic (olfactory) 
 lobes send forward the true olfactory uerves. 
 
 If the foregoing statement of the grounds for determining the 
 liomologies, general and special, of the skull-bones of the Crocodilia 
 may have seemed tedious or unnecessary, I excuse myself by the 
 importance attached to the subject by Guvier, who, in the last 
 lecture which he delivered, stated : ' If we were agreed as to the 
 Crocodile's head, we should be so as to that of other animals ; be- 
 cause the Crocodile is intermediate between mammals, Ifirds, and 
 fishes.' Admitting, with some latitude, the reason, a sense of the 
 importance of a determination of the Ijoues answerable to those 
 previously defined in Chelonia and Fishes, has influenced me in 
 the foregoing description of the skull of the Cr-ocodiUa. 
 
 § 33. Skull of Oplddia. — The skull in Lacertians and Ophi- 
 dians departs from the vertebral pattern by a greater deo-ree of 
 confluence and a minor extent of neurapophysial ossification, 
 than in Crocodilia : and that of Serpents manifests more strongly 
 the principle of adaptive devclopement. 
 
 Eiistr.cliinn cannls in Croco.liUa. Sec also the piepavations, xnv., Nos 706 7"7 7-\S 
 750,1111.154 — 164. ,.-i,'-^. 
 
 ■ lb. XLiv p. 163, wlic-o tliat clmractci-istic of CvcodiU,, rUombifa- is spccifioil. 
 ' 111. No 764, p. 166. ' ' 
 
ANATOMY OF VERTEBRATES. 
 
 147 
 
 In the Pytlion, figs. 96 and 97, the basloccipltal, i, Is subhex- 
 agonal, broadest anteriorly, smootli and concave above, suturally 
 rough on each side, with a recurved pointed hypapophysis : the 
 hinder facet forms the lower half of the occipital condyle, on eacl 
 
 96 
 
 Section ol tlio Skull of a Python 
 
 side of which is a small sharp process. The basioccipital unites 
 above with the exoccipital, 2, and alisphenoid, f, ; and in front 
 with the basisj)henoid, 5. The exoccipitals (2,2) are each pro- 
 duced backward into a peduncular process supporting a moiety 
 of the upper half of the occipital condyle : at the outer side of 
 the base of the peduncle is an obtuse process, forming the 
 upper part of the ridge continued upon the basioccipital. The 
 outer and fore part of the exoccipital expands, and is perforated 
 by a slit for the eighth pair f>f nerves, articulates l^elow with 
 the basioccipital, is excavated in front to lodge the petrosal 
 cartilage where it articulates with the alisphenoid, and unites 
 above with the superoccii)ital, 3. This is of a subrhomboidal 
 form, sends a spine from its upi)er and hinder surface, expands 
 laterally into oblong processes, is notched anteriorly and sends 
 down two thin plates from its under surface, bounding on the 
 mesial side the surface for the cerebellum, and by the outer 
 side forming the inner and upper parts of the acoustic cavities. 
 The superoccipital articulates below with the exoccipitals and 
 alisphenoids, and in front with the parietal, liy which it is over- 
 lapped in its whole extent. The occipital vertebra is as if it were 
 sheathed in the expanded posterior outlet of the parietal one, the 
 centrum resting on the oblique surface of that in front, and the 
 anterior l^ase of the neural spine entering a cavity in and being- 
 overlapped by that of the preceding neural spine : the analogy of 
 this kind of ' emboitement ' of the occipital in the parietal vertebra 
 with the firm interlocking of the ordinary vertebras of the trunk is 
 
]48 
 
 ANATOIMY OF VEETEBRATES. 
 
 very interesting: the end gained seems to be, in grovelling 
 reptiles liable to have the head bruised, an extra protection of 
 the epencephalon — the most important segment to life of all the 
 ]irimary divisions of the cerebrospinal axis. The thickness of 
 its immediately protecting walls (formed by the basi-, ex-, and 
 super-occipitals) is equal to that of the same vertebral elements 
 in the human skull ; but they are moreover composed of very 
 firm and dense tissue throughout, having no diploe : the epen- 
 cephalon also derives a further and equally thick bony covering 
 from the basisphenoid and the parietals, the latter being partly 
 overlapped by the mastoids, fig. 97, 8, which form here a third layer 
 of the cranial wall. 
 
 The basisi^henoid, fig. 96, 5, and presphenoid, 9, form a single 
 
 97 
 
 ^'^i'l^bkM^kkUI'Usi 
 
 SkiiU t,i a Pytlion 
 
 bone, and the chief keel of the cranial superstructure. The 
 posterior articular surface looks obliquely upward and backward, 
 and supjiorts that of the vertebral centrum behind, as the jJosterior 
 ball of the ordinary vertebra?, su]iports the oblique cup of the 
 succeeding one : here, however, all motion is al.trogatcd between 
 the two vertebra?, and the co-adapted surfaces arc rouiih and 
 sutural. The basisphenoid presents a smooth cerebral cliannel 
 above for the mesencephalon, in front of which a deep depression 
 (sella) sinks abruptly into the expanded part of tlie bone, and 
 tlicrc bifurcates, each fork forming a short cul-de-sac in the sub- 
 stance of the bone. The transverse processes from tlic under 
 and lateral surfaces are well marked, strong, but short, mucli 
 thicker in the Python tlum in tlie Boa. Tlic alisphcnoids, «, form 
 the anterior half of the fenestra ovalis, which is conqilcted by 
 tlic exoccipitals ; and in their two large perforations for the 
 ])cisterior divisions of the fifth pair of nerves, as well as in their 
 
ANATOMY OF VERTEBKATES. 14i) 
 
 relative size and position, tlie alisphenoids agree with those of the 
 Frog. Each alisphenoid is a thick suboval piece, with a tuber- 
 cular process on its under and lateral part : it rests upon the 
 basisphenoid and basioccipital, sup])orts the posterior part of the 
 parietal and a portion of the mastoid, 8, and unites anteriorly with 
 the descending lateral plate of the parietal bone. 
 
 riie parietal, 7, is a large and long, symmetrical roof-shaped 
 bone, with a median longitudinal crest along its up]ier surface, 
 wdiere the two originally distinct moieties have coalesced. It is 
 narrowest posteriorly, where it overlaps the superoccipital, and is 
 itself overlapped by the mastoid : it is convex at its middle part on 
 each side the sagittal spine, and is continued downward and in- 
 ward to rest immediately upon the basisjjhenoid, 5. This j^art of 
 the parietal seems to 1)6 formed hj an extension of ossification 
 along a membranous space, like that which permanently remains 
 so in the Frog, between the alisphenoid and orbitosphenoid : the 
 mesencephalon and the chief part of the cerebral lobes are protected 
 by this unusually developed spine of the mesencephalic vertebra. 
 The optic foramina are oonjugational ones, between the anterior 
 border of the lateral plate of the ])arietal and the posterior border 
 of the corresponding plate of the frontal. 
 
 The frontals, ii, rest by descending lateral plates, representing 
 connate orbitosphenoids, upon the presphenoidal prolongation of 
 the basisphenoid : the upper surface of each frontal is flat, sub- 
 quadrate, broader than long in the Boa, and the reverse in the 
 Python, where the roof of the orbit is continued outward by a 
 detached superorbital bone : there is a distinct, oval, articular sur- 
 face near the anterior median angle of each frontal to which the pre- 
 frontal; 1 4, is attached : the angle itself is slightly produced to form 
 the articular process for the nasal bones. The smooth orbitosphe- 
 noidal plate of the frontal joins the outer margin of the upper surface 
 of the frontal at an acute angle ; the inner side of each frontal is 
 deeply excavated for the prolongation of the cerebral lobes, and 
 the cavity is converted into a canal by a median vertical plate of 
 bone at the inner and anterior end of the frontal. The frontals join 
 the parietals and postfrontals behind, and, by the connate orbito- 
 sphenoid plates, the presphenoid below, the prefrontals and nasals 
 before, and the superorbitals at their lateral margins. The orbito- 
 sphenoidal plates have their bases extended inward, and meet below 
 the prosencephalon and above the presphenoid, as the neurapo- 
 ijhyses of the atlas meet each other above the centrum. The anterior 
 third part of such inwardly produced base is met by a downward 
 production of the mesial margin of the frontal, forming a septum 
 
150 ANATOMY OE VERTEBRATES. 
 
 Ijetween tlie olfactory prolongations of the brain, but is not con- 
 fluent with the frontal septum: the outer portion of the orbitosphe- 
 noidal jilate is smootli externally, and deeply notched posteriorly 
 for the optic foramen. 
 
 The post-frontal, fig. 97, 4, is a moderately long trihedral bone, 
 articulated by its exjianded cranial end to the frontal and parietal, 
 and l)ent down to rest upon the outer and fore angle of the ecto- 
 pterygoid, 25. It does not reach that l^one in the Boa, nor in 
 poisonous Ser2ients. In both the Boa and Python it receives the 
 anterior sharp angle of the parietal in a notch. 
 
 The natural segment which terminates the cranium anteriorly, 
 and is formed by the vomerine, prefrontal and nasal bones, is very 
 distinct in the Ophidians. 
 
 The vomer is divided, as in some ganoid Fishes and Batrachians, 
 but is edentulous : each half is a long, narrow plate, smooth and 
 convex below, concave above, with the inner margin slightly 
 raised : pointed anteriorly, and with two processes and an inter- 
 vening notch above the base of the pointed end. The prefrontals, 
 14, are connate with the lacrymals. The two bones which inter- 
 vene between the vomerine and nasal bones are the turbinals, fig. 
 96, d, they are Ijcnt longitudinally outwards in the form of a 
 semicylinder about tlic termination of tlie olfactory nerves. 
 
 The spine of the nasal vertebra is divided symmetrically as in 
 the Frog, forming the nasal bones, fig. 97, 15 ; they are elongated, 
 licnt plates, with the shorter upper part arching outward and 
 downward, completing the olfactory canal above ; and with a longer 
 median plate forming a vertical wall, aj)plied closely to its fellow, 
 exccjrt. in front, where the nasal process of the premaxillary is 
 received in the interspace of the nasals. 
 
 The acoustic capsule remains in great part cartilaginous : there 
 is no detached centre of ossification in it : to whatever extent this 
 capsule is ossified, it is by a continuous extension from the alisphe- 
 noid. The long stapes, fig. 97, 16, extends from the ' fenestra vesti- 
 buli ' to the subcutaneous ear-drum attached to the tympanic bone, 
 28. The sclerotic capsule of the eye is chiefly fibrous, witli a thin 
 inner layer of cartilage ; the olfactory capsule is in a great measure 
 ossified, as above described. 
 
 MaxiUary arch. — The palatine, fig. 96, 20, or first piece of this 
 arch is a strong, olilong bone, having the inner side of its obtuse 
 anterior end applii'd to the sides of the prefrontals and turbinals, 
 and, near its posterior end, sending a short, thick process upward 
 and inward for ligamentous attadunent to the lacrymal, and a 
 second similar process outward as the point of suspension of the 
 
ANATOMY OF VERTEBRATES. 151 
 
 maxillary bone : between these processes the palatine is perforated, 
 and behind them it terminates in a point. The chief part of the 
 maxillary bone, 21, is continued forward from its point of suspen- 
 sion, increasing in dci)th, and terminating oljtuscly : a shorter 
 process is also, as usual, continued l^ackward. The point of 
 suspension of the maxillary forms a short, narrow, palatine process : 
 the dental ))ranch of the supramaxillary nerve penetrates the 
 upper and fore part of this process, and its chief division escapes 
 by a foramen on the outer and fore part of the maxillary. A space 
 occupied by elastic ligament intervenes between the maxillary and 
 the jiremaxillary, 22, which is single and symmetrical, and firmly 
 wedged into the nasal interspace : the anterior expanded part of 
 this small triangular bone supports two teeth. Thus the bony 
 maxillary arch is interrupted by two ligamentous intervals at the 
 sides of the premaxillary key-bone, in functional relation to the 
 peculiar independent movements of the maxillary and palatine 
 bones required by Serpents du.ring the act of engulfing their 
 usually large prey. 
 
 Two bones extend backward as appendages to the maxillary 
 arch ; one is the ' pterygoid,' 24, from the palatine, the other the 
 ectopterygoid, 25, from the maxillary. The pterygoid is continued 
 from the posterior extremity of the jjalatine to aljut against the 
 end of the tympanic pedicle : the under part of its anterior half 
 is beset with teeth, fig. 96, 24. The ectopterygoid, 25, overlaps 
 the posterior end of the maxillary, and is articulated by its posterior 
 oljliquely cut end to the outer surface of the middle expanded part 
 of the pterygiiid. 
 
 Mandibidur arch. — The tymjianic bone, 28, is a strong, trihedral 
 pedicle, articidated by an oblique upper surface to the end of the 
 mastoid, 8, and expanded transversely below to form the antero- 
 posteriorly convex, transversely concave, condyle for the lower jaw. 
 This consists chiefly of an articular 31, and a dentary 32, with a 
 small coronoid and splenial piece. The articular piece, 31, including 
 the angular and surangular elements of the Crocodile, ends ob- 
 tusely, immediately behind the condyle : it is a little contracted in 
 front of it, and gradually expands to its middle jjart, sends up two 
 short processes, then suddenly contracts and terminates in a point 
 wedded into the posterior and outer notch of the dentary piece. The 
 articular is deeply grooved above, and produced into a ridge below. 
 The coronoid is a short compressed plate : the splenial is a longer 
 plate applied to the inner side of the articular and dentary. The 
 outer side of the dentary has a single perforation near its anterior 
 end : this is united to that of the opposite ramus by elastic ligament. 
 
152 ANATOMY 03? VERTEBRATES. 
 
 The skull of the Boa Constrictor differs from that of the 
 Python, not only in the greater breadth of the frontals, but in 
 that of the nasals ; in the absence of the superorbital, in the 
 more slender and cylindrical form of the ectopterygoid, and in 
 the larger and higher internal border of the coronoid. But the 
 mechanism of the jaws is the same. By the elastic matter join- 
 ing together the extremities of the maxillary and mandibular 
 bones, those on the right side can be drawn apart from those on 
 the left, and the mouth can be opened not only vertically, as in 
 other vertebrate animals, but also transversely, as in insects. 
 Viewing the bones of the mouth that support teeth in the great 
 constricting serpents, they offer the appearance of six jaws — four 
 above and two below ; the inner pair of jaws above are formed by 
 the palatine and pterygoid ])one3, fig. 96, 20-24, the outer pair by 
 the maxillarics, ib. 21, the under pair by the mandibles, or 'rami,' 
 as they are termed, of the lower jaw, fig. 97, 31-32. 
 
 Each of these six jaws, moreover, besides the movements ver- 
 tically and laterally, can be protruded and retracted, independently 
 of the otlier : by these movements the Boa is enabled to retain 
 and slowly engulf its prey, which may be much larger than its 
 own body. At the first seizure the head of the prey is held 
 firmly by the long and sharp recurved teeth of all the jaws, 
 whilst the body is crushed by the overlapping coils of the serpent ; 
 the death-struggles having ceased, the Constrictor slowly uncoils, 
 and the head of the prey is bedewed with an abundant slimy 
 mucus : one jaw is then unfixed, and its teeth withdrawn by 
 being pushed forward, when they are again infixed, further back 
 ujjon the prey ; the next jaw is then unfixed, protruded, and 
 reattached ; and so with the rest in succession — tins mo\'ement of 
 protraction being almost the only one of which they are susceptible 
 whilst stretched apart to the utmost by the bulk of the animal 
 encompassed by them : thus, liy their successive movements, the 
 prey is slowly and spirally introduced into the wide gullet. 
 
 In comparing the skull of a poisonous with that of a constrict- 
 ing Serpent, the differential characters consist, in the Eattlesnake 
 (^Crotalus) e.g., chiefly in the modification of form and attach- 
 ments of the maxillary, which is movably articulated to the 
 l)alatine, ectopterygoid, and lacrymal bones ; Ijut chiefly supported 
 by the latter, which presents the form of a short, strong, three- 
 sided i)edicle, extending fmm the anterior external angle of the 
 frontal to the anterior and upper part of the maxillary. The 
 articular surface of the maxillary is slightly conca\e, of an oval 
 shape : the surface articulating with the ectopterygoid on the poste- 
 
ANATOMY OF VERTEBRATES. 153 
 
 rior and upper part- of the maxillary is smaller and convex. Tlie 
 maxillary l)()ne is pushed h>rward and rotated upon the lacrymal 
 joint by the advance of the ectopterygoid, which is associated with 
 the movements of the tympanic pedicle of the lower jaw by means 
 of the true pterygoid bone. The premaxillary is edentulous. A 
 long, perforated poison-fang is anchylosed to the maxillary. The 
 palatine bone has four or five, and the pterygoid from eight to ten, 
 small, imperforate, pointed, and recurved teeth. The frontal bones 
 are broader than they are long : there are no superf)rbitals. A strong- 
 ridge is developed from the under surface of the basisphcnoid, and 
 a long and strong recurved spine from that of the l;)asioccipital ; 
 these give insertion to the powerful ' longi colli ' muscles, by which 
 the downward stroke of the head is performed in the inflicti(m of 
 the wound by the poison-fangs. 
 
 The skull of the ty])lcal Ophidian reptiles most resembles that 
 of Lizards, biit lacks the outer diverging appendage, formed by the 
 malar and squamosal, ut the maxillary arch. It differs from that 
 of Batrachians in the distinct basi- and superoccipitals ; in the 
 superoccipital forming part of the car-clianil5er ; in tlie liasioc- 
 cipital combining with the exoccipital to form a single articular 
 condyle for the atlas ; in the ossification of the membranous space 
 between the elongated parietals and the s]ilienoid; in the constant 
 coalescence of the parietals with one another ; in the connation of 
 the orbitosphenoids with the fVontals, and in the meeting of the 
 orbitosphenoids below the prosencephalon upon the upper sur- 
 face of the presphenoid ; in the presence of distinct postfrontals, 
 and the attachment thereto of the ectopterygoids, whereby they 
 form an anterior point of suspension of the lower jaw, through the 
 medium of the pterygoid and tympanic Ijones ; in the connation 
 of the prefrontal? and lacrymals. 
 
 In the Amj^liisbccna fulii/inosa coalescence still further simplifies 
 the cranial structure : the parts of the epencephalic arch con- 
 stitute a single occipital bone ; the superoccipital crest extends 
 forward into a sagittal one ; a small foramen marks the boundary : 
 the premaxillary is single, and, with the rest of the upper jaw, is 
 fixed ; the tympanic is short, compared with that of true Serpents, 
 and extends almost horizontally forward, in a line with the lower 
 jaw which it supports; the coronoid is more developed. The 
 nostrils, divided by the premaxillary, are terminal ; or even, as 
 in Lepldosternon, may open behind the fjre end of the skull : in 
 this Amphisba3nian the maxillaries overlap the nasals to join the 
 premaxillary. ^ 
 
 ' CLXXIII., pi. 15, figs. 8, 11. 
 
154 Alf ATOMY OF VERTEBRATES. 
 
 § 34. Skull of Lacertilia. — Lizards, like Serpents, have tLe cra- 
 nial bones, especially those of the ha;mal arches and appendages, 
 more elongated, slender, and liberated than in Crocodiles and Che- 
 lonians ; the temporal vacuities and orbits are large, and the external 
 nostrils are apart. Lizards retain the malo-squamosal bar connect- 
 ing the maxillary with the tympanic ; and some of them develoj^e, 
 as in the Crocodile, the uj^per zygomatic arch formed by the post- 
 frontal and mastoid. The neurapophysial walls of the parietal and 
 frontal seg-ments retain much of their filjro-cartilaginous tissue : and 
 the cranial roof is there sustained by a bony pillar on each side 
 (' columella ' of Cuvier), which has its base imi:)lanted in a fossa 
 of the pterygoid, and underprops the parietal near its outer border. 
 The homologies of the cranial bones of the Python, figs. 96 and 
 97, with those of the Crocodile, figs. 93, 94, and 95, being recog- 
 nised, those of any Lizard will be readily understood. 
 
 In a New Zealand Gecko {Rhynclwccphulus ') the occi23ital con- 
 dyle is unusually elongated transversely, and presents the form of 
 a crescentic, convex bar, bent iipward. The basisphenoid sends 
 down two short processes to abut against the pterygoids. The 
 parietal bone is perforated by a small median fontanelle close to 
 the sagittal suture : its upper surface presents two strong curved 
 and approximated temporal crests, divided by a median, angular, 
 longitudinal furrow : the crests are continued outward upon the 
 jiosterior bifurcated part of the parietal to be continuous with that 
 forming the upper border of the mastoid : the frontal is divided 
 by a median suture, as is the parietal in the common Gecko. 
 The posterior frontal supports a strong, obtuse ridge ftirming the 
 back part of the frame of the orbit, and unites below with the 
 malar and behind with the mastoid. The premaxillary bones are 
 divided by a median suture, and their dentigerous border projects 
 below the level of that of the maxillary bones. The vomer is 
 likewise divided by a median suture. Tlie palatal apertures of 
 the nostrils are bounded behind by the vomer and palatal plate of 
 the maxillary : tliis plate is of unusual breadth, as compared with 
 the Lizards generally, and presents the imusual peculiarltv of a 
 dentigerous ridge parallel with the posterior half of the alveolar 
 border. It is situated close to the inner side of this border, leav- 
 ing only space sufficient for the reception of the teeth of the 
 under jaw. The teeth are confluent with the summits of the 
 pro])er and accessory alveolar ridges. The palatine bones are 
 united together along the anterior hah-es. The rami of the lower 
 jaw are not anehylosed at the symphysis. The alveolar border is 
 
ANATOMY OF VERTEBRATES. 155 
 
 serrated by a single row of aiicliyloscd teetli. The coronoid piece 
 is triangular, rises into a point, and presents a smooth articular 
 surface on its inner side, adapted to the anterior lateral projection 
 of the pterygoid. 
 
 In the skull of the black Scink {Cijdodus nir/er), the frontal and 
 parietal bones are thick and expanded ; the parietal is bifurcated 
 behind, and articulated with the mastoids and paroccipitals. The 
 postlrontals are separated from the malars by the srpianiosals, 
 which extend between the malars and the mastoids to form the 
 strong lateral l)ony arch resting anteriorly upon the malar and the 
 inaxillary, and posteriorly on the parietal and tympanic. C'l.in- 
 comitantly with the strong osseous roof of the cranium, there is 
 an arrest of osseous developement in the fibro-mendjranous 
 neurapophysial walls of the cranium : two lateral processes 
 extend downward into these walls from the parietal and for- 
 ward from the exoccipitals ; but the protective office of the 
 alisplienoids is solely performed by the columnar ' columella},' 
 Avhioh extend from the interspaces of the processes above 
 mentioned, to rest upon the upper groove of the pterygoids. 
 The orbitosphenoids are represented by still more slender bony 
 styles, which circumscril)e the outlets for the optic nerves, and 
 form the anterior boundary of the prosenceplialic division of the 
 cranium. The lacrymal bones are large and divided on each side, 
 as in most Lizards. The premaxillaries are confluent, and their 
 nasal process separates the external nostrils from eacli otlier. 
 Each pterygoid presents a rougli surface towards tlie palate, Jjut 
 does not support teeth. There is a small ossicle between the 
 pterygoid processes of the sphenoid and the true pterygoid bones. 
 The eolumelliform stapes is extremely long and slender. 
 
 In the Iguana the jaarietal supports a single median crest : the 
 jiosterior margin of the frontal is notched l^y the fronto-parietal 
 fontanelle : both lacrymal and postfrontal are sul3di\'ided into two 
 pieces ; the lacrymal foramen is a ' conjugational ' one between the 
 two pieces. The iipper portion of the lacrymal represents the 
 facial part of the prefrontal ; it does not send down a neurapo- 
 physial plate to join the vomer or palatines, nor forms any part of 
 the lateral walls of the idiinencephalie cavity, or of the foramen 
 for the transmission of the olfactory nerves. The palatine nostrils, 
 firr. 98, D, 11, are very long, and notch the large palatines, 2o; the 
 pterygoids, 24, each support a row of small teeth. 
 
 In the skull of the IMonitor Lizard ( Varamis nihiiciis) the 
 basioccipital sends down a pair of short, olotuse Iiypapophyses : 
 those of the basisphenoid are larger and abut against the ptery- 
 
156 ANATOMY OF VERTEBRATES. 
 
 goids : these bones are applied to the back part of the tympanic, 
 and the slender ' columella ' rests upon the middle of their upper 
 surface. The parietal is perforated near its anterior border. 
 The postfrontal has a descending postorliital process. The pre- 
 frontal developes a partial post-lateral wall for the rhinencephalic 
 chamber ; externally It supports an antorbltal dermal bone : the 
 small perforated lacrymal is a distinct bone. The nasal and pre- 
 maxlllary are both single bones, as in most Lacertians. The 
 malar, wedged anteriorly between the maxillary, palatine, lacrymal 
 and ectopterygoid, curves backward as a slender style terminating 
 in a point, leaving the orbit uncircled by bone behind : the 
 squamosal, wedged behind between the mastoid and tympanic, 
 curves forward to a point beneath the postfrontal. 
 
 In the American Monitor {Tejus nigrnpunctatus) tlie nasals are 
 divided: the malar articulates behind with the postorbital — a dis- 
 memberment of the postfrontal, which continues the zygomatic 
 arch with the squamosal : there is no ' foramen parietale.' 
 
 In the Chameleon the teeth are short, and so confluent with the 
 jaws that these appear to have simply a serrated margin. The 
 external nostrils ])ci'forate the maxillary bone ; a long, compressed, 
 serrated crest arches upward and backward from the superocclpltal 
 and ])ariet:al bones, and joins the processes of bone continued from 
 the mastoids. In the Cliameleo bifurcus the anterior fork-like 
 productions are formed by the maxillary and prefrontal bones. 
 The premaxillary at the bottom of the cleft is -^'ery small. 
 
 In Draco volans there is merely the rudiment of a spine or 
 ridge from the superoccipital ; an arched transverse ridge separates 
 the occipital from the parietal region of the skull. The jjost- 
 frontal, mastoid, and paroccipital project successivelv from their 
 respective cranial segments, and well manifest their character as 
 the transverse processes of these. 
 
 The vacuities In the Ijon}^ palate are many, and show much 
 variety in the cold-blooded, especially the reptilian, series, in 
 regard to their numlier, kind, and relati\c size. The most con- 
 stant are those which are more or less circumscribed bv the max- 
 illary and pterygoid, and constitute a pair. They are present in 
 Polyj>terus and most Ganoids, l)Ounded outwardly bv the maxil- 
 lary, medially by the palatine, and behind by the pterygoid. 
 In the jMcnopome the vomer, fig. 73, /, forms the mediaV and 
 the pterygoid,/, the ]iostcrior lioundary. In the Frog, fig. OS, 
 A, the pterygo-maxillary vacuities, //, are divided from" each 
 other by the basisphenoid ; whilst the palatine forms the front 
 buundary and scjjaratcs them iVom the nasal apertures, n. In 
 
ANATOMY OF VERTEBRATES. 
 
 157 
 
 Lizards, ib. D, tlie ]ialatine 20, and pterygoid 24, form the median 
 boundary, the maxillary, 21, and ectoi)tcrygoid the outer one of?/. 
 In tlie Crocodiles, il). c, the palatine 20 forms the median, the 
 ectoptevygoid 25 the outer, the maxillary 21 the fore, and the ptery- 
 goid 24 with the ectoptcrygoid the hind, boundary. In the Che- 
 loiiia there is no ectopterygoid to divide the pterygo-maxillary 
 vacuity from the lower opening of the temporal fossa. The next 
 openings in point of constancy are the palatal, or posterior, 
 or internal nostrils — ' palatonares ; ' but they are variously formed 
 and situated. In the Menopome, fig. 73, there is no palatine bone 
 to divide them from the pterygo-maxillary vacuity ; in fig. 98 A, 
 the Frog, the transverse palatine forms the posterior boundary 
 of the palatonares, n, the vomer the inner, and the maxillary the 
 outer, lioundar}^; they are similarly encompassed in the Lizards, 
 
 98 
 
 Frog. 
 
 Tortoise. CrocodUo. 
 
 Palatal niierlurcs, B':ptiVni. 
 
 ib. T> n. In the Crocodiles, the palatonares, ib. C, 11, form a single 
 aperture surrounded ].)y the pterygoids, and situated far Ijack. 
 There is also a single premaxillary foramen, ib. C, p, at the fore 
 part of the bony palate. This is sometimes divided into two by the 
 premaxillary, like the external nostrils, as in the Iguana, Ih. D, p. 
 In most Lizards there is a more or less elongate ' interpterygoid' 
 vacuity, ib. T>, •?, bounded behind by the hypapophyses of the 
 basispiienoid, laterally l:iy the pterygoids, and usually extending 
 some way between the palatines. In the Blosasaurus the inter- 
 ptcryn-oid fissure does not extend far l3ack between the pterygoids, 
 but is" bounded in a greater proportion by the palatines. Some- 
 times there is a distinct small ' interpalatiue ' vacuity, ib. m, in 
 
158 ANATOMY OF VERTEBRATES. 
 
 advance of the interpterygoid ; and more rarely there occurs an 
 'intervomerine' vacuity still more in advance. 
 
 Thus there are definable and nameable, in the bony palate of 
 reptiles, the ' pterygo-maxillary,' ' palatonarial,' ' premaxillary,' 
 ' interpterygoid,' ' interpalatal,' and ' intervomerine ' vacuities or 
 foramina — more or less valuable as characters of recent and 
 extinct species. 
 
 § 35. Skull of Ichthyoptenjgia. — Amongst the illustrations of 
 extreme varieties in the reptilian skull which Palteontology has 
 brought to light, may be cited the Ichthyosaurus, the Dicynodon, 
 and the Pterodactylus. 
 
 That of the first combines in a peculiar manner some piscine 
 with reptilian characters. It differs from all existing Reptilia in 
 the great size of the premaxillary, fig. 105, 22, and small size of 
 the maxillary, 21 ; in the lateral aspects and antorbital jjosition of 
 the nostrils ; in the immense size of the orbits, and in the large and 
 numerous sclerotic plates, wliich latter structures give to the skull 
 of the Ichthyosaurus its most striking features. 
 
 The two supplemental bones of the skull, which have no homo- 
 logues in existing Crocodiliaus, are the postorbital and super- 
 squamosal ; both, however, are developed in Archeyosauriis and 
 the Labyrinthodonts. The postorbital is the homologue of the 
 inferior di'sdsion of the postfrontal in those Lacertians — e. g.. 
 Iguana, Tejus, Ophhaurus, Anguis, in which that bone is said to 
 be divided ; but in Ichthyosaurus it more resembles a dismember- 
 ment of the malar, 26. Its thin obtuse scale-like lower end over- 
 laps and joins by a squamous suture the hind end of the malar : 
 the postorbital expands as it ascends to the middle of the back of 
 the orbit, then gradually contracts to a point as it curves upward 
 and forward, articulating with the supersquamosal and post- 
 frontal, 12. The supersquamosal may be in like manner regarded 
 as a dismemberment of the squamosal, 27 ; were it confluent there- 
 with, the resemblance which the bone would present to the zygo- 
 matic and squamosal parts of the mammalian temporal bone would 
 be very close ; save that the squamous part would be removed 
 from the inner to the outer wall of the temporal fossa. The nostril 
 is bounded by the lacrymal, 73, nasal, 15, maxillary, 21, and pre- 
 maxillary, 22, bones. It is distant from the orbit about half its own 
 long diameter. Like the orbit, the plane of its outlet is vertical. 
 The pterygo-maxillary vacuities are very long and narrow, 
 broadest behind, where they are bounded, as in Lizards, by the 
 antei'ior concavities of the basispheniiid, and gradually narrowino- 
 to a point close to the palatine nostrils. These arc smaller than 
 
ANATOMY OF VERTEBRATES. 159 
 
 in most Lizards, and are circumscriljed by tlie palatines, ecto- 
 pterygoid, maxillary, and premaxillary. The pterygomalar fis- 
 sures are the lower outlets of the temporal fossse ; their sudden 
 posterior breadth, due to the emargination of the pterygoid, relates 
 to the passage of the muscles for attachment to the lower jaw. 
 The parietal foramen is bounded by Ijoth parietals and frontals, 
 11 ; its presence is a mark of labyrinthodont and lacertian affini- 
 ties ; its formation is like that in Ifjuana and Rhynchoeepluilus. 
 The occipitoparietal vacuities are larger than in Crocodilia, smaller 
 than in LdcertiUa ; they are bounded internally by the basi-, ex-, 
 and super-ocoipitals, externally by the parietal and mastoid. The 
 auditory apertures are boimded by the tympanic and squa- 
 mosal : the tympanic, 28, takes a greater share in the formation 
 of the ' meatus auditorius' in Lizards ; in Crocodiles the bone 28 
 is restricted to that which it takes in Ichtlujosaurus.^ 
 
 In comparing the jaws of the Ichthyosaurus tenuirostris with 
 those of the gangetic Gharrial, an equal degree of strength and 
 of alveolar border for teeth result from two very different propor- 
 tions in which the maxillary and premaxillary bones are comljined 
 together to form the upper jaw. The prolongation of the snout 
 is the same : the dilference of structure relates to the collective 
 tendency <if the affinities of the lehthyosaurus to an antecedent 
 ha;mat(5cryal type of structure still partly shown by Lizards. 
 The l)ackward or antorbital position of the nostrils, lilce that in 
 Avhales, is related to the marine existence of the Ichthyosaurs. 
 But in the Labyrinthodonts, in which the nostrils are nearer the 
 fore part of the head, their anterior boundaries are formed by 
 the premaxillaries, as in modern Lizards : it appears, therefore, 
 to be in conformity with these affinities that the premaxillaries 
 of the Ichthyosaur should enter into the same relation with the 
 nostrils, although this involves an extent of anterior develope- 
 ment proportionate to the length of the jaws, the forward pro- 
 duction of which sharp-toothed instruments fitted the Ichthyosaur, 
 like the mcjdern Dolphin for the prehension of agile fishes. 
 
 § 36. Shull of Dicynodontia. — The skull of the Dicynodon, 
 fig. 99, is articulated with the atlas by a single condyle, formed by 
 tlie liasi- and ex-occipitals in equal proportions : the latter have 
 coalesced, as in the Crocodiles, with the paroccipitals. The parie- 
 tals form one bone, perforated by a small ' foramen parietale ' close 
 to the coronal suture. The frontals, ii, contribute a share to the 
 superorbital border ; their median suture is distinct, as is that 
 
 ' CXLVII. p. 388. 
 
IGO 
 
 ANATOMY OF VERTEBRATES. 
 
 between the nasals, is. The prefrontal, 14, extends to the nostril, n. 
 Tlie lacrymal, 13, forms the rest of the fore part of the orbit, ex- 
 tending forward upon the face. The sides of the premaxillary, 22, 
 bend abruptly down in front of the nostrils, to join the maxillary, 
 20, 21 ; this forms the lower boundary of the nostril, n, and joins 
 above and behind with the prefrontal, lacrymal, and nasal bones : 
 the maxillary projects below the orljit, like a forward continuation 
 of the zygoma, becomes more prominent as it advances, and soon 
 forms the outer angle of the three-sided socket of the canine tusk, c. 
 There is a single but strong zygomatic arch formed by the malar, 
 26, and squamosal, 27, abutting against the upper end of the tym- 
 
 of Dicinwdon 
 
 panic pedicle, 28. The rami of the lower jaw aixgment in depth 
 from the angle to the symphysis, where they are confluent. The 
 angle 2)rojects a very little way beyond the articulation. The 
 articular surface is moderately concave, and looks oVdiquely up- 
 ward and backward. The elements of the posterior half of the 
 ramus answer to tlic articular, angular, 26, and surangular, 25. A 
 thin vertical splenial plate, on the inner side of the ramus, begins 
 about an inch in advance of the angle, and extends forward to the 
 symi»hysis, at the back part oi' which it appears to become con- 
 fluent with its fellow. The part answering to the angular diverges 
 from the surangular, and fornis the hind boundary of an oblong 
 vacuity at the middle of the side of the ranuis, the fore part of 
 which -^'acuity is foi-med l>y a bifurcation of the dentary element, 
 23. This is thickened and strcngtliencd by a ridge, sul)siding at 
 the vertical channel upon the side of the symphysis, receiving the 
 
ANATOMY OE VETITEBEATES. 101 
 
 tusk, s, wlien the month is closed. The symphysis of the man- 
 dible is peculiarly massive — broad, high, and thick. Anteriorly 
 it is convex in every direction ; it is bent or produced upward, 
 terminating in a broad trenchant margin, like the fore part of the 
 lower mandible of a macaw. The modification of the back part 
 of the cranium, especially the great expansion due exclusively to 
 the developement of ridges for augmenting the surface of attach- 
 ment of muscles (for the brain of the cold-blooded reptile would 
 need but a small spot of the centre of the occipital plates for its 
 protection), indicates the power that was brought to bear upon 
 the head as the framework in which were strongly fixed the two 
 large tusks. The strength or resistance of the cavities receiving 
 the deeply implanted bases of the tusks was increased by the 
 ridges developed from the outer part of their l^ony wall. 
 
 Only the Crocodiles now show a like extent of ossification of the 
 occiput, and only the Chelonians the trenchant toothless mandible ; 
 but in both the outer nostril is single and median : the Lizards 
 rep)eat the divided apertures for resjiiring air : in Mammals alone 
 do we find a developement of canine tusks like that in the 
 Dicynodonts. 
 
 § 37. Skull of Pterosauria. — The skull of the Pterodactyle, 
 fig. Ill, was as remarkable for its lisi'ht and delicate structure as 
 that of the Dicynodont for its comjjact massiveness. It had a 
 single occipital condyle : a post-fronto-mastoid arch and a malo- 
 squamosal arch on each side ; the latter abutting against the end 
 of the tympanic pedicle. The orbit was large, and the eyeball 
 defended by sclerotic plates. The external nostrils were di^dded, 
 and placed about midway between the orbits and the muzzle. 
 There was a large vacuity between the orbits, o, and nostrils, n. 
 The jaws varied much in length in different species. 
 
 § 38. Scapular arch and ajypendage. — Parts which project 
 from the body to act on the surrounding medium commence as 
 a bud or fold of skin, within which is formed the framework, in 
 texture and structure according to the work to be done. The 
 reaction of the medium, whether air, water, or earth, calls for the 
 due resistance usually afforded by junction of the projecting part 
 with a segment of the endoskeleton. Thus, in Fishes, the frame 
 of the opercular flap articulates with the tympano-mandibular 
 arch : that of the branchiostegal (gill-covering) flap with the 
 ha3mal arch of the parietal vertebra : that of the pectoral flap or 
 limb with the same arch of the occipital vertebra. The frame 
 of the caudal flap or fin is attached to the terminal vertebra; of 
 the body : those of the dorsal and anal fins are less firmly inter- 
 
 A'OL. I. M 
 
162 ANATOMY OF VERTEBRATES. 
 
 locked with the neural and hremal spines of more advanced 
 vertebrse. 
 
 All these various supports of flaps, fins, or limbs belong to the 
 same natural genetic group of skeletal parts : their peripheral rays 
 are not 'dermal bones;' they are developed between folds, not in 
 the substance, of the integument ; although in some instances 
 they press away the skin and become coated by a ganoid conver- 
 sion or calcification of its outer layer. 
 
 The most simple condition of the parial (pectoral and pelvic) 
 limbs is manifested by the Lepidosiren, fig. 100. A filamentary 
 appendage is sustained by a single many-jointed cartilaginous ray, 
 fig. 101 A, a. In one species there are attached at right angles 
 to the pectoral ray fine filaments sustaining the narrow fold 
 of membrane continued from its f)osterior side. A similar series 
 of finer rays supports the membrane continued from the dorsal 
 detached dermoncurals of Polyjitcrus. 
 
 Protopt,n-iis {LrpidosiyaL') anvcclc] 
 
 ^ The arch sustaining the pectoral Jimbs of Lepidosiren is also 
 simple, departing least from its archetypal condition. A long 
 straight cylindrical bone, fig. 101, a, 51,;?/, is attached by a shoi^ 
 ligamentous mass to the epencephalic arch, ib. n, of which it is 
 the rib, or ' iDlcurapophysis,' assuming in ulterior developements 
 the special name of ' scapula.' With each scapula is articulated a 
 larger and more flatteued bone, ib. 52 : the two converge and 
 meet at their lower ends, completing, as hiumapophvscs, a "widelv 
 expanded hannal arch. The entire segment, A, conforms to the 
 thoracic modification of the archetype vertebra, fig. 19 : and, simi- 
 hirly, IS expanded in order to encompass and protect tlie heart : but 
 it is simplified I)y the absence of the haemal spine in Protopterus, 
 as the neural spine is sometimes wanting in a neural arch. The 
 hicmapoi.hysis, h, in ascending the vertebrate scale, assumes special 
 forms, signified 1)y the term ' coracoid,' with the number 52. In 
 
ANATOMY OF VERTEBRATES. 103 
 
 Protoptcri, as in more piscine Hamatocrya, the coracoid ex- 
 clnsively sujiports the appendage or limb. 
 
 From the condition exemplified in fig. 101, A, the developement 
 
 101 
 
 Elementary limbs, .1. c, Lcpldc. siren ; n, d, Ami'iiiumn, r\r,. 
 
 of the pectoral member diverges in two directions : one by multi- 
 plication of many-jointed rays, the other by simplification as to 
 number of rays and joints, with special modification and differen- 
 tiation of the latter. 
 
 § 39. Pectoral limb of Fishes. — The first series of modifications 
 is now confined to Fishes : but, before describing the appendage, 
 a brief notice of the arch is requisite. 
 
 In most Osseous Fishes the pleura jjophy sis of the occipital, like 
 that of the two antecedent cranial vertebras, is in more than one 
 piece ; but the divisions do not exceed two. The U2:iper piece 
 (^suprascapula) is commonly bifurcate, as in the Cod, figs. 34, 75, 
 81, 50, the lower prong answering to the 'head,' the upper one to 
 the ' tubercle ' of the thoracic rib in the Crocodile : the latter 
 articulates with the transverse process {par occipital). The lower 
 piece {scapula), ib. 5i, is 'a slender straight bone, pointed below, 
 and mortised into a groove of the coracoid, ib. 52. The two parts 
 of the scapula are confluent in the Siluroid Fishes. In the 
 Murainoids the suprascajjula is ligamentous, and loosely appends 
 the scapular arch to the skull. In the Plagiostomi the arch is 
 detached from its vertebra, and has receded in position, to allow, 
 as it seems, for the great expanse of the appended fin. 
 
 The hffimapophysis, or ' coracoid,' figs. 34, 38, 39, 75, 85, 52, is 
 lono-er and usually broader than the scapula. In the Cod-tribe, 
 
164 ANATOMY OF VERTEBRATES. 
 
 its pointed upjier extremity j)i'ojects behind that bone and ahnost 
 touches the suprascapula ; a broad angular plate of the coracoid 
 projects backward and gives attachment to the radiated appendage, 
 below which it Ijends inward and forward, gradually decreasing 
 to a point, which is connected by ligament to its fellow, and to 
 the urohyal bone, fig. 43. The inner side of the coracoid is ex- 
 cavated, and its anterior margin folded inward and backward, 
 lodsfins the origin of the great lateral muscle of the trunk. 
 
 In most fishes the lower end of the arch is completed, as in the 
 Cod, by the ligamentous symphysis of the coracoids ; but in the 
 Siluri and Platycephali the coracoids expand below, and are firmly 
 joined together by a dentated suture. In all Fishes they support 
 and defend the heart, and form the frame, or sill, against which 
 the opercular and branchiostegal doors shut in closing the great 
 branchial cavity ; they also give attachment to the ajjoneurotic 
 diaphragm, dividing the pericardial from the abdominal cavity. 
 
 To the inner side of the upper end of the coracoid there is 
 attached, in the Cod and Carp, a bony appendage in the form of 
 a single styliform rib ; but in other Fishes this is more frequently 
 composed of two pieces, as in the Perch. This single or double 
 bone, figs. 34, 38, 85, 58, is slightly expanded at its upper end in 
 the Cod-tribe, where it is attached by ligament to the inner side 
 of the angular process of the coracoid : its slender pointed portion 
 extends downward and backward, and terminates freely in the 
 lateral mass of muscles. In the Batrachii.s its upper extremity 
 rises aljove the coracoid, and is directly attached to the spinous 
 process of the atlas. In some Fishes, as the Snipe-fish ( Centriscus 
 Scolopax), the Cock-fish {Argyrciosus Vomer), the Lancet-fish 
 (^Siganus), it is joined by the lower end to the corresponding- 
 bone of the opposite side, thus completing an independent in- 
 verted arch, behind the scapular one. There is some reason, 
 therefore, for viewing the bone 58 as representing the ha?mal 
 arch of the atlas, or its hiemapophysial portion. 
 
 The usually free lower extremities of these ha;mapophyses, to- 
 gether with their taking no share in the direct support of the pec- 
 toral fins, and their inconstant existence, o]>pose the view of their 
 special homology with the coracoids of higher Vertebrates. 
 To that with the ' clavicles' of higher classes it has been 
 objected that these bones are always situated in those classes in 
 advance of the coracoids ; but this inverted position may be a 
 consequence of the backward displacement of the scapula and 
 coracoid in the air-l)reathing Vertebrates. 
 
 Tlie appendage of the scapular arch, in most Osseous Fishes, 
 
ANATOMY OF VERTEBRATES. 1G5 
 
 is composed of three segments : the first, of two, rarely of three, 
 bones immediately articulated with the coracold ; the next, of a 
 series of from two to six smaller bones ; which, lastly, support a 
 series of spines or jointed rays. These rays serially repeat the 
 branehiostegal rays in the hyoidean appendage, and the opercular 
 rays in the tympanic appendage. The vegetative repetition of 
 digits and joints, and the vegetative sameness of form in those 
 mnltiplied peripheral parts of the fins of Fishes, accord with the 
 characters of all other oro-ans on their first introduction into the 
 animal series. The single row of fewer ossicles, figs. 34 and 
 81, 5(;, snpporting the rays, 57, obviously represents the double 
 car})al series in JNIammals ; and the bones of the brachium and 
 antiln-achium seem in like manner to be reduced to a single series, 
 54, 55. In the ventral fin, fig. .34, v, no segment is developed 
 between the arch, 6.3, and the digital rays, 70 : it is in this resi)ect 
 like the branehiostegal fin, 40, 44. 
 
 The pectoral fin is directed backward, and being api)lied, 
 prone, to the lateral snrlace of the trnnk, the ray or digit answer- 
 ing to the thumb is toward the ventral surface. The lowest of 
 the bones supporting the carpus should, therefore, be regarded as 
 the radius (figs. 34 and 81, 54), holding the position which that 
 lionc unquestionably does in the similarly disposed pectoral fin of 
 the Plesiosaur, fig. 45, 54, and Cetacea. The upper bone, which 
 commonly aftbrds support to a smaller proportion of the carj^al 
 row, may be compared to the ulna (ib. 55). As a third small 
 bone is articulated to the coracoid, in some Osseous Fishes, 
 at least in their immatiu-c state, the name of humerus may be 
 confined to that bone : but in these it is generally above and on 
 the inner side of the ulna, and seems to be rather a dismemlDcr- 
 ment of it. In the SulmoHidcE, it is more distinctly developed ; 
 it is articulated in the Bull-trout (S. erioxY to the middle of the 
 back part of the coracold I)y a transversely elongated extremity ; 
 and is expanded at its distal end, where it articulates by cartilage 
 with the radius and ulna. In the Cod, Haddock, and most other 
 Fishes there is no separate representative of the himierus : in 
 these the ulna is a short and broad plate of bone, deejily emargi- 
 natc anteriorly, attached by suture to the coracoid, and by the 
 onposite expanded end to the radius, and to one or two of the 
 carpal ossicles, and directly to the upper or ulnar ray of the fin. 
 
 In the Bull-head and Sea-scorpion (Cottus), the radius and 
 ulna are widely separated, and two of the large square carpal 
 
 ' XLiy. p. 18, No. 4 6. 
 
166 ANATOMY OF VERTEBRATES. 
 
 plates in tlieir interspace articulate directly with the coracoicl. A 
 similar arrangement obtains in the Gurnards and the Wolf-fish ; 
 Ijut the carpals in the interspace of the radius and ulna are sepa- 
 rated from the coracoids by a space occupied by clear cartilage ; 
 and in the Wolf-fish the intermediate carpals are almost divided 
 by two opposite notches. The ulna is perforated in all these 
 fishes. The radius is of enormous size in the Opah (Lampris), the 
 Cock-fish, fig. 38, and the Flying -fish ; it is anchylosed with the 
 coracoid in the Silurus, to give firmer support to the strong 
 serrated pectoral spine. Both radius and ulna are connate with 
 the coracoid in the Angler {Lophius, fig. 102, 54, 55). 
 
 The ossicles called carpals are usually four or five in number, 
 
 102 
 
 Coracoid anil lionce of pectoral fin, Angler {Lupliiu.^') 
 
 as in the Cod tribe, fig. 81,56; they progressively Increase in 
 length from the ulnar to the radial side of the carpus, especially 
 in the Parrot-fish {Scarus) and the INIullets {M/if/il). They are 
 three in number and elongated in the Polypterus, fig. 103, sfi, 
 but arc reduced to two in number, and more elongated in the 
 Lophius, fig. 102, 56) ; thus they retain in this species and in the 
 Sharks, fig. 104, their primitive form of 'rays ;' but change to broad 
 flat bones in the Wolf-fish, just as the rays of the opercular fin 
 exchange that form in the Plagiostomes for broad and flat plates 
 in ordinary Osseous Fishes. 
 
 The rays representing the metacarpal and pihalaiic/ial bones arc, 
 in the Cod, twenty in number, and all soft, jointed, and sometimes 
 bifurcate at the distal end. Tlieir proximal ends are slightly 
 expanded and overlap eacli otiier, but arc so articulated as to 
 ])ermit an oblicpie divarication of tlie rays to the extent permitted 
 by the uniting fin-membrane, the combined cftcct being a move- 
 ment of the fin, like that called the ' fealherintr of an oar.' Each 
 
ANATOMY OF VERTEBRATES. 167 
 
 soft and jointed ray splits easily into two halves as far as its base, 
 and appears to be essentially a conjoined pair. 
 
 In the series of Osseous Fishes the -rays of the pectoral and 
 ventral fins offer the same modifications as those of the median 
 fins, on M'hieh have been founded the division into ' Malacoptery- 
 ' gians' and ' Acanthopter3^o-ians :' in the former, the last or ulnar 
 fin-ray, is usually thiclvcr than the rest ; in the latter it is always 
 a hard, nnjointed spine : in some Fishes it forms a strong pointed 
 or serrated weapon ( Silnrus). In the Gurnards, fig. 82, the three 
 lowest rays arc detached and free, like true fingers ; and are soft, 
 multi-articulated, and larger than the rest ; they are su2)plied by 
 special nerves, which come from the peculiar ganglionic enlarge- 
 ments of the spinal chord, and are organs of exploration and of 
 suliaqueous reptation.' In all the Gurnards the natatory part of 
 the pectoral member is of large size; but in one species {Dacfylo- 
 pferus) it presents an unusual expanse, and is able by its strolce to 
 raise and sustain for a brief period the l^ody of the fish in the air. 
 The pectoral fins present a still greater developement in the true 
 Flying-fish ( ExoccBtus). 
 
 In some Malacopteri and Ganoidei a segment analogous to a 
 metacarpus may be distinguished by modification of structure 
 from the phalangeal portion of the fin rays : in the Polypterus 
 there are seventeen simple cylmdrical metacarpal bones, fig. 103, 
 5 7, the middle ones being the longest: they sustain thirty-five 
 digital rays, and are supported by jog 
 
 carpal bones, ib. 10.3, ne, of which 
 two are almost as remarkable for 
 their length as in tlie Lophins ; the 
 third, shorter and broader, is wedged 
 into the interspace of the two longer 
 ones, but does not directly join the B„ucsofrori,ir,ifln„fp„/,,;„cr„s 
 metacarpus. The carpus is supported by a small radius, 5 5, and 
 ulna, 54, which articulate directly with the coracoid. A further 
 approach to tlie higher conditions of the pectoral member is made 
 by the same Fish in the carpal portion projecting treely from the 
 side of the body, as in the Lophioid Fishes. In the Salmon, 
 where eleven such metacarpals support thirteen or fourteen fin- 
 rays, the carpus is short and consists of four bones. 
 
 In the Plagiostomes the scapular arch is detached from the oc- 
 ciput, the conditions of its displacement being the more varied and 
 vio-orous use, or the enormous expanse, of the pectoral fin ; per- 
 
 ' CLIX. p. 46. 
 
168 
 
 ANATOMY OF VERTEBRATES. 
 
 haps, also, the more posterior position of the heart in these Fishes. 
 In the Sharks and Chimsera3 the arch is loosely suspended by 
 ligaments from the vertebral column : in the Rays the point of re- 
 sistance of their enormous pectoral fins has a firmer, but somewhat 
 anomalous attachment, by the medium of the coalesced upper ends 
 of the suprascapular pieces to the summits of the spines of the 
 confluent anterior portion of the thoracic abdominal vertebras. In 
 the Sharks the scapular arch consists chiefly of the coracoid por- 
 tions, fig. 104, 52, which are confluent together beneath the peri- 
 cardium which they support and defend ; the scapular ends of the 
 arch, connected to the coracoids by ligament, project freely upward, 
 backward, and outward. To a posterior prominence of the cora- 
 coid cartilage corresponding with the anchylosed radius and ulna, 
 ib. 54, 55, in the Lophius, there are attached, in the Dog-fish and 
 most other Sharks, three sub-compressed, sub-elongated carpal 
 
 104 
 
 Cni-tilages of Llic pectoral fin and arch o£ the Dog-flsll (:S>Ml(T,r ncaiUliias) 
 
 cartilages, the uppermost, ib. 56, the smallest, and stylifurm ; it 
 supports the upper or outer phalangeal ray. Tlie next bone, ib. 56', 
 is the largest and triangular, attached by its apex to the arch, and 
 supporting by its base the majority of the phalanges. The third 
 carpal, ib. so", is a smaller but triangular cartilage, and supports 
 six of the lower or radial phalanges. Three joints (metacarpal 
 and digital) complete each cartilaginous ray or representative 
 of the finger, ib. 57 ; and into the outer surface of the last are 
 inserted the fine horny rays or filaments, ib. 57", the homologucs 
 of the claws and nails of higher A'^ertcbrata, but which on their first 
 appearance, in the present highly organised class of Fishes, mani- 
 
ANATOMY C»F VERTEBRATES. 160 
 
 fest, like other newly introduced organs, the principle of vegetative 
 repetition, there being three or four horny filaments to each carti- 
 laginous ungual phalanx. 
 
 On the fore part of the coracoid arch, near to the prominence 
 supporting the fin, there are developed a vertical series of small 
 bony cylindrical nuclei in the substance of the cartilage in most 
 Sharks. In the Rays the coraco-scapular arch forms an entire 
 circle or girdle attached to the dorsal spines : it consists of one 
 continuous cartilage in the Rhinobates, but in other Rays is divided 
 into coracoid, scapular, and suprascapular portions, the latter 
 united together by ligament. The scapula and coracoid expand 
 at their outer ends, whore they join each other by three points, to 
 each of which a cartilage is articulated homologous to the tln-ee 
 alcove described in the Shark, and which immediately sustain the 
 fin-rays. The posterior cartilage answering to the upper one in 
 the Shark curves backward and reaches the ventral fin : the an- 
 terior cartilage curves forward, and its extremity is joined by the 
 antorbital process as it proceeds to be attached to the end of the 
 rostral cartilage ; the middle proximal cartilage is comparatively 
 short and crescentic, and sustains about a sixth part of the fin-rays, 
 which are the longest, the rest being supported by the anterior 
 and posterior carpals, and gradually diminishing in length as they 
 approach the ends of those cartilages. 
 
 Developement by irrelative repetition of parts reaches a maximum 
 in the present plagiostomous group. In the common Ray, fig. 64, 
 there are upwards of a hundred many-jointed fingers in each pectoral 
 limb : but all are bound up in a common function of the simplest 
 kind. 
 
 § 40. Pectoral limb of Reptiles. — The other route of develope- 
 ment from the prototypal condition exemplified in fig. 101, A and 
 C leads to a differentiation of the several divisions and parts of the 
 limb, and their adaptation to particular functions or parts of com- 
 Ijined and varied mechanical actions. 
 
 The first step, as manifested in the Amphiume, ib. B, c, is the 
 formation of a long inflexible segment, as a lever of greater resist- 
 ance, 53 and 65 ; tliis is followed l)y a pair of similar, but shorter 
 cylindrical bones, each sustaining a ray of few joints. The 
 proximal bone assumes through ulterior developements the special 
 name ' humerus,' or arm-bone, with the symljol 53, in the fore 
 limb; and of 'femur,' or thigh-bone, with the symbol 65, in the hind 
 limb. The two bones of the next segment become, in the fore 
 limb 'radius,' 54, and ' ulna,' 55 — collectively, antibrachium or 
 ' fore-arm ; ' in the hind limb, tibia, 66, fibula, 67 — collectively. 
 
170 
 
 ANATOMY OF VERTEBRATES. 
 
 the cnemion or leg. The mass of fibro-cartilage, in which 
 more or fewer ossicles are subsequently developed, interposed 
 between the antibrachium and terminal 
 rays, is the ' carpjus, 56 : the corre- 
 .' , ''; spionding mass in the hind limb is the 
 
 tarsus, 68. The terminal rays are the 
 digits, called ' hand,' and ' fingers,' 69, 
 in the fore limb ; ' foot ' and ' toes ' in 
 the liind limb. The proximal joints of 
 these rays, being bound together in a 
 sheath of integument, are diiferentiated 
 as ' metacarpals ' in the hand, and ' meta- 
 tarsals ' in the foot. The other joints 
 are the ' phalanges,' ultimately distin- 
 guished as ' jiroximal,' ' middle,' ' distal ' 
 or ' ungual,' as usually supporting a claw 
 or nail. 
 
 In the extinct Ganocepluda, and in the 
 few surviving ichthyomorphous or per- 
 ennibranchiate Batrachia, the simple 
 type of limb, as in fig. 101, B, is re- 
 tained ; only that the digital rays in- 
 crease in ninnber from the ' two ' in 
 '^j/i Amphiuma, to ' tluree ' in Proteus, and 
 
 J^'i^l to 'four' in Menopoma, fig. 43, 57, and 
 
 Axolotes. 
 
 Inthe extinct Ichfhi/opferi/r/ia the digits 
 may be seven, eight, or nine in number, 
 and consist of numerous short joints — 
 a significant mark of piscine atfinitv : 
 they are bound together, but converge 
 towards a point : the joints are of a fiat- 
 tened angular form, and interlock with 
 those of the contiguous digit, the whole 
 forming a continuous, broad, slightly 
 flexible basis of support to the fin. The 
 essential distinction from the fin of the 
 fish is shown by the well developed 
 'humerus,' 5:1, and by the comjilcx sca- 
 pular arcli. The two autibrachial bones 
 retain the jiiscine shortness and breadth ; 
 and the metacarpal series is less distinctly 
 defined than in some fishes. 
 
 «// 
 
 1 i>[ TchnniaHiiiirii:<. willi 
 sj)ifiil JiitcijLiiic. UI-.XIII, 
 
ANATOMY OF VERTEBRATES. 171 
 
 Tlie scapula, 51, is sliort and straight, displaced ])ackward from 
 the occiput, and contributing to form the shoulder-joint, as in the 
 Batrdclua and higher air-breathers : hut it sliows a certain breadth 
 and flatness. The coracoid, 52, is still broader, not cartilaginous 
 as in most perennibranchs, but well ossified, and united below 
 with its fellow, and with a small ' episternum ' of a triradiate 
 form, one ray of which is wedged into the fore part of the 
 mtercoracoid fissure. There is also a pair of bones, 50, long and 
 slender, articulated with the fore border of the scapula and the 
 transverse rays of the episternum : they are the cla^'icles. A 
 supplementary flattened bone, the ' epicoracoid,' is wedged between 
 the scapula, clavicle, and coracoid. The above complex and 
 powerful scapular arch would enable the fore-paddles to act upon 
 the land with sufficient power to effect a shuffling forAvard move- 
 ment of the body, as in the Turtle {Cliehnu;) and Seal tribe: but 
 the main office of the fore-limb in the Ichthyosaur was that of a 
 pectoral fin. 
 
 In the Plesiosaurus, fig. 45, the limbs acquired a developcment 
 more closely accordant with that in Chdona. The scapula, r>i, 
 developes an acromial process representing the clavicle. The 
 coracoid, 52, is unusually extended in the trunk's axis, and is united 
 with its fellow by a long symiihysis interposed between the an- 
 terior abdominal rib and the episternum ; it articulates at its fore 
 part with the episternum and clavicular process, and, further back, 
 with the lower end of tlie scapida to form the humeral joint. 
 
 The humerus is proportionally longer than in IcMlujosaurus ; 
 the radius is better developed, and slightly expanded at both ends ; 
 the ulna retains a flattened reniform shape. The cardial scries is 
 distinct, in a double row of ossicles, the largest at the radial side 
 of the wrist, the opposite side retaining more imossified material. 
 The tligits are five in number, with the proximal and more elongated 
 joints representing a metacarpus. The jjhalanges are shorter, and 
 decrease in size to the tips of the digits, which converge. The 
 first or radial digit ha^ generally 3 j'halanges, the second from 5 
 to 7, the third 8 or 9, tJie fourth 8, the fifth 5 or 6 : all are flattened 
 and included in a common sheath of integument like those of the 
 Turtle ; but the paddle had no claws. 
 
 The scapular arch retains the same essential simplicity in the 
 Chelonian as in the Sauropterygian order, only the acromial or 
 clavicular process is relatively longer', more like a collar bone ; it 
 extends from irear the articular part of the scapula toward the 
 median line, in advance of the coracoid, fig. 51, o, with tl 
 
 ie 
 
 medial end ligameutously attached to the episternal. In the 
 
172 
 
 ANATOMY OF VERTEBRATES. 
 
 lOG 
 
 Tortoise ( Testudo) it is shorter, in Chelys, fig. 106, h, it is longer 
 than the scapuhi, a. This bone in all Chelonians is a strong, straight 
 cohimnar one, with the upper end connected by ligament with the 
 inner surface of the first costal jilate, fig. 5 1 , N ; it descends almost 
 vertically to the shoulder -joint, of which it forms, in common with 
 the coracoid, the 'glenoid' cavity, fig. 106, (j. The coracoid, 
 suturally united at that end with the scapula, passes inward and 
 backward, fig. 51, o, expanding and becoming flattened at its 
 median end, which does not meet its fellow nor articulate with 
 the sternvun. The coracoid is broad and short in the Tortoise ; 
 
 long and slender in Chelone and 
 Ermjs, fig. 51, O, of intermediate 
 proportions in Trionijx and Cliehjs, 
 fig. 106, c. The sca|)ular arch 
 and proximal part of the limb being 
 included in the thoracic abdominal 
 box, the humerus is peculiarly 
 bent and twisted in the terres- 
 trial species in order to emerge 
 from the front fissure, and plant 
 the foot on the ground, fig. 51, 
 p. In the Tortoise the ordinary 
 position of the fore-limb is that 
 of extreme pronation, with the 
 olecranon forward and outward, 
 and the radial side of the hand 
 downward. The capside of the 
 shoulder-joint includes a consider- 
 able part of the neck of the 
 humerus. The hemispheroid head projects unusually from the 
 back jjart of the bone, which looks upward : the tuberosities 
 are large and bent toward the palmar aspect : that which is 
 internal in most animals is here ' postero-superior ; ' that called 
 ' external ' is ' postero-internal ' in position ; from the former is 
 continued the ' deltoid crest.' The distal end is expanded and 
 rather flattened from ))efore backward. In the Turtle the humeral 
 shaft and its lower end is compressed laterally : and the bone 
 is almost straight in those marine species ; in all Chelonia it is 
 solid throughcnit. 1'hc ulna is shorter, and in the Turtle, fig. 
 107, h, the olecranon is less developed than in the Tortoise, fig. 108, 
 h, 55. The contrast l>ctween the marchers and the swhnniers is 
 most sti'iking in the proportions of the toes. In the Turtle, 
 fig. 107, the pollex, /, is short and has two phalanges after the 
 
 Scajntlar arcli, Clivhjs. QiA. 
 
ANATOMY OF VERTEBRATES. 
 
 173 
 
 107 
 
 metacarpal : the last phalanx supporting a claw. The three 
 nnddle digits, //, ///, in, have each tln-ce long phalanges, tlie 
 last heing flattened and without a claw ; the fifth has two pha- 
 langes. All these are connected together by a web. In the 
 Tortoise, fig. 108, all the toes are very short and subequal ; and 
 each lias one metacarpal and two phalanges, the last supporting a 
 claw ; the few species in which the fifth has but one yihalanx 
 and no claw form the genus Homopiis, Dum. and Bilj. In 
 JSnnjs curopa-a, fig. 51, T, u, the first and fifth digits have each a 
 metacarpal and two phalanges ; the others have three plialanges ; 
 the last bears a claw in each diffit. In the Soft or Mud-turtles, 
 the poUex has two phalanges, the 
 second with a claw ; the three middle 
 digits have each three j)halanges, 
 l)ut only the index and medius liave 
 the claw ; the fifth digit has two 
 2>halangcs and no claw, whence 
 the generic name Triovi/x, proposed 
 for these frequenters of the nuiddy 
 estuary. 
 
 In the Crocodilia the scai)ular arch 
 consists of a simple scapula, fig. 57, 
 51, and coracoid, ib. 52, and fig. 54, 
 8 : these compressed, narrow, mode- 
 rately long plates of Ijone, arc 
 thickest where they are united to- 
 gether to form the glenoid cavity 
 for the humerus. In each, the bone 
 contracts beyond the articular ex- 
 pansion, becomes sub-cylindrical, 
 but soon again flattens and expands 
 to its opposite end ; that of the sca- 
 pula is free, that of tlic coracoid 
 joins the lateral border of the ster- 
 num. TJiere is no trace of clavicle, 
 no acromial projection from the sca- 
 pula. 
 
 The humerus, fig. 51, 53, presents two curves : the articular liead 
 is a transversely elongated, sidj-oval convexity ; it is continued 
 up(3n the short, obtuse, angular prominence, answering to the inner 
 or ulnar tuberosity. The radial crest begins to project from the 
 sliaft at some distance from the head of the bone. There is a 
 longitudinal ridge on the anconal surface close to the radial border. 
 
 Bonos of rorc-arm and paGdle, Chclvnc. cli. 
 
174 
 
 ANATOMY OF VERTEBKATES. 
 
 108 
 
 I II III IV V 
 
 Lnud Ti>rtoi?c. CLI. 
 
 The distal end Is transversely extended and divided anteriorly 
 into two condyles. The shaft has a medullary 
 cavity smaller than in land lizards. The radius, 
 fig. 57, t, fig. 109, h, 54, has an oval head, an 
 almost cylindrical and straight shaft, with an 
 oblong and subcompressed distal end. The ulna, 
 fig. 57, .s, fig. 109, a, 55, articulates with the 
 outer condyle of the humerus by an oval facet, 
 the thick convex border of which swells out be- 
 hind like the beginning of an ' olecranon ; ' the 
 shaft of the ulna is compressed transversely and 
 curves slightly outward ; tlie distal end is less 
 than the proximal one, and articulates with the 
 second and third bones of the carpus. The first 
 metacarpal supports two phalanges, I, the second three, ii, the 
 third and fourth, each four, the fifth, v, three phalanges which 
 109 arc very slender ; but the proportions are shown 
 
 in the cut ; only the toes, I, ii, and ill, have the 
 claw. All are basally imitcd by a short web, 
 but the fore-foot is chiefly vised in movements 
 upon land. 
 
 In the Monitor ( Varanus niloticus) the supra- 
 scapula is a broad semiossified plate : the 
 scapula is short and broad, and appears to 
 have coalesced with the coracoid. This bone 
 is much expanded, and has two deep notches 
 anteriorly, and a perforation near the humeral 
 articulation. In some Lizards it sends for- 
 ward an acromial j^rocess. The coracoid is 
 shorter and broader than in the Crocodile, 
 abuts against the upper margin of the rhom- 
 boidal sternum, and sends off two processes 
 from its anterior border, the one next the sca- 
 pula al;)utting against the transverse branch of 
 the e])isternimi ; the other against the sub- 
 ossified epicoracoid : this element overlaps that 
 of the opposite side. In the Monitor, as in 
 most Ijizards, there arc distinct clavicles : usu- 
 ally long and slender liones, with more or less 
 expanded extremities, extending from tlie body 
 ' ■ """"'"'■• '■'■'■ c>f the ci)isternum and accomjianying the trans- 
 verse ))rancli to abut against the scapula; and sometimes also 
 )-ea,ching the outer process of the coracoid. In Lavcrta, Cuv. 
 
ANATOMY OF VERTEBRATES. 
 
 175 
 
 110 
 
 and Scincus, the ckyicle expands at its medial lialf, which has a 
 
 large vacuity or perforation occupied Ijy membrane. In the 
 
 Chameleon tlic scapular arch is 
 
 as simple as in tlic Crocodile, 
 
 Ijut the coracoid is shorter and 
 
 broader. 
 
 The humerus in Lacertians is 
 
 iisually larger and straighter, fig. 
 
 50, Driico volans, than in the 
 
 Crocodiles, with a more compact 
 
 wall and Avidcr mcdidlary cavity. 
 
 Tiie radius, ib. and fig. 110, h, 
 
 r34, is aluiost straight, and slender, 
 
 witli an oval proximal articular 
 
 concavity, and a distal surface 
 
 partly convex, partly concave. 
 
 The ulna, fig. 110, a, 55, shows 
 
 tlie olecranon better developed 
 
 than in the Crocodile : its dis- 
 tal articular surface is convex. 
 
 The digits are five in number, 
 
 the phalanges are 2, 3, 4, 5 and 3, 
 
 counting from the metacarpal of 
 
 the first to that of the fifth digit : 
 
 each has a claw supported on 
 
 a moderately long, compressed, 
 
 curved, and pointed phalanx. Tlie Cliameleon offers an exception 
 to the numerical rule, the phalanges Ijcing 2, 3, 4, 4, 3 ; and the 
 
 direction of the digits modified for the scansorial function in these 
 arboreal Lacertians : I, 11, and iii, enveloped by the skin as tiir 
 as the claws, are directed forward ; iv, and v, similarly sheathed, 
 are directed backward : and the joints are shorter and broader than 
 in Land-lizards. 
 
 The fore limbs in Draco volans accord with the usual lacertian 
 type, and take no share in the support of the parachute. But 
 in the extinct order of truly volant Reptiles {Pterosauria) they 
 were modified for the exclusive snjiport and service of the win^s. 
 The scapula, fig. Ill, 51, long, narrow, flattened, and slightly 
 expanded, lay more parallel with the spine tlian in land and sea 
 Reptiles. The coracoid, strong and straiglit, and coinl)ining, as 
 nsual, witli the scapula to form the glenoid cavity, articulated at 
 the opposite end with a groove at the fore-part of a discoid 
 sternum, which part is produced and keeled. The humerus, ilj. 
 
 BntHls nf rlJl■c■-,^nn Miia fuot, Cliniilrler)!]. CLI. 
 
170 
 
 ANATOMY OF VERTEBRATES. 
 
 53, is more expanded at its proximal end than in the Crocodile or 
 Lizard ; the inner (ulnar) tuberosity is more prominent, the radial 
 crest much more developed : with a base coextensive with one 
 fifth of the shaft of the bone, it extends in a greater proportion 
 from the shaft, affording a powerfid lever to the muscles inserted 
 into it. The articular head is reniform. The shaft is cylindrical : 
 
 
 Stuk-ton ol Ptirmlacliilus cm 
 
 (.s?/-(^\ A. Restonition of Pterod:icty!e. CLXXX. 
 
 the walls thin and compact, the cavity large, and was filled with 
 air as in birds of flight.' 
 
 The ' pneumatic foramen,' or that by which the air passed from 
 a contiguous air-cell into the bone, is situated on the fore (palmar) 
 side, a little below the radial end of the head of the bone. The 
 radius, ib. 54, and ulna, ib. 55, are very long, straight, and closely 
 connected together. The digits show the lacertian number of 
 
 > CXLix. p. 16. iLXTi. p. 451. This tliscovei-y breaks down the following 
 distinction : ' Au ruslc, on distingue tonjours riinmoi us d'un Kzaid do celui d'uii 
 oiscau, p.arcecpic le premier n'est pas crcnx ni perco dc trous pour rentrce de I'air 
 dans son interieur.' CLi. v. pt. 2, p. 296. 
 
ANATOMY OF VERTEBRATES. 177 
 
 phalanges from the first to the fourth, and shghtly increase in 
 length : each terminated by a deep compressed, curved and 
 pointed ungual phalanx. The modification converting the limb 
 into a wing is confined to and concentrated upon the fifth digit, ib. 
 5 : its metacarpal presents almost the thickness of an antibrachial 
 bone : the proximal phalanx, of equal thickness, has more than 
 twice the length, and at the proximal joint shows a process like 
 an olecranon. This is usually followed, as in Pterodactylus 
 crassirostris, by three similarly elongated phalanges, of which the 
 last gradually tapers to a point. The fore limb thus exceeds in 
 length the whole body, and is presumed to have supported a 
 membranous wing, as in the sketch A, fig. 111. 
 
 Such are the chief modifications by which the fore-limb, in the 
 Reptilian series of cold-blooded air-breathers is or has been 
 adapted for aquatic, amphiljious, terrestrial, arboreal, and aerial 
 life. Before, however, quitting this subject, it may facilitate the 
 comprehension of the homologies of the carpal series of ossicles, 
 by concluding with a separate and serial review of them in the 
 Reptilian group. 
 
 In the Toad {Bitfo) the carpus includes eight bones : the two 
 principal are the ' huiare,' fig. 44, C, I, and ' cuneiforme,' ib. c, 
 respectively articulating with the radial and ulnar divisions of the 
 antibrachial bone, ib. 54, 55 ; the scaphoid, c, s, presents its ' inter- 
 medial' position between the lunare and the four ossicles on the 
 radial side of the distal series : these consist of the trapezium t, 
 trapezoides tr, magnum m, and the divisions of the unciform u for 
 the fourth and fil\h digits ; that for the fifth being the largest 
 of the five bones. The thumb, i, is represented by its metacarpal 
 only; the index, fig. 44, A, ii, and medius, ill, have each a 
 metacarpal with two phalanges ; the digits iv and v have each 
 three phalanges. 
 
 In the Tortoise {Testudo, fig. 108), the antibrachium articulates 
 with three carpals forming the proximal row ; the first or radial 
 bone, ib. a, answers to the ' scaphoid ' with the ' intermedium ' e ; 
 the second ib. c, to the lunare ; the third, ib. d, to the cunei- 
 forme ; the lunare being interposed between the ends of the radius 
 and ulna. In the Emys, fig. 51, S, the carpus has a similar struc- 
 ture ; but in some species there is a distinct pisiforme. In the 
 Turtle ( Chelone), the scaphoid is reduced in size, and represents 
 only the intermedium, fig. 107, e; it is separated by the lunare 
 c, from the radius a, and is pushed into a position analogous to 
 that which its homotype the ' naviculare' holds in the mammalian 
 tarsus. Without the light from the testudinate modification, 
 
 VOL. I. N 
 
178 ANATOMY OF VERTEBRATES. 
 
 fig. 108, the bone c, fig. 107, might be taken for a connate 
 ' scapliolunar.' In both tortoise, terrapene, and turtle, the distal 
 row of carpals consists, as in the Toad, of five bones, one to each 
 of the five metacarpals. About their homology there is no diffi- 
 culty ; the bone, fig. 107, i, wliich supports the pollex, i, is the 
 traj-iezium ; the next 2, the trapczoides ; the third 3, the magnum ; 
 and the fourth and fifth are the two parts showing the type-state 
 of the connate bones, called ' unciform ' in mammals. A bone 
 analogous to a 'pisiform, y, fig. 107, is attached to the ulnar 
 division, 5, of the unciform, and, usually, also articulates witli tlie 
 cuneiform in the Turtle. In Chdys and Trwnyx, the bone 
 answering to a, e, fig. 108, is divided ; the part, e, answering to 
 the ' intermedium ; ' Trionyx has also a ' pisiform.' The carpus 
 in most Lacertians, e.g. in Varamis nihticus^, has the scaphoid 
 reduced, as in Clielmie, to the intermedial portion ; but the trape- 
 zium unites directly with the lunare, and this articulates exclu- 
 sively with the radius, simulating the scaphoid in position ; it 
 has, liowever, on its ulnar side, the ' cuneiform ' articulating with 
 the idna, and a ' i)isilbrm ' terminates the proximal row. The 
 distal row consists of five distinct bones ; the unciform beiu"' 
 divided, as in Chelouians. In the Chameleon, fig. 110, the 
 proximal carpal series consists of the bones c and d, answering to 
 the two respectively articulating with the radius and ulna in 
 Varaiuis, and with those marked c and d in figs. 107 and 108. 
 The second carpal row has received two interpretations. In one 
 they are represented by the five subelongate bones having the 
 distal joints of metacarpals ; in the other they have coalesced into 
 the single bone c, which otherwise would be merely an enlarged 
 ' intermedium.' 'NA^e shall afterwards see how the principle of 
 ' serial homology ' helps in the solution of such problems. The 
 five bones radiating from the bone c are metacarpals ; the first 
 supports two, the second three, the third four phalanges, as in other 
 Lacertians ; and the equality of length in the opposing pair of 
 digits, IV and v, is preserved by the deduction of a phalanx from 
 the lacertian number. 
 
 The correspondence of the Chameleon's scapular arch with that 
 of the Crocodile has been adverted to ; and, similarly, the distal 
 row of carpals is reduced to a single bone, fig. 109, f. in the 
 Crocodile, supi)orting the mcdius, ill, annularis, iv, and mininuis, 
 V, digits ; and answering to the magnum and unciformc connate. 
 The proximal row includes three bones answering to the lunare, 
 c, and CLUieiformc, d, in Clidoi,,', fig. 107, and Chamclco, fig. 110 ; 
 ' cr.i, I'l. xYTi, lig. -15. 
 
ANATOMf OF VERTEBRATES. 
 
 179 
 
 112 
 
 to which is added a pisiibmie, fig. 109, e, in the usual position. 
 The peculiarity of the hones c and d in CrocodiUa, is their unusual 
 length, sliowing a constricted sliaft ))etwcen tlie expanded ends, 
 tlms simulating metacarpals in shape, for which, wlicn found as 
 detached fossils, they have been mistahen. 
 
 Tlie digits in tlie class Reptilia are generally characterised by 
 a progressive increase in the number of their joints, from the first 
 or innermost to the third or fourth ; the Chelonia being the chief 
 exceptions. In Testudo, fig. 108, each digit has one metacarpal 
 and two pjhalanges ; in Test, tdhidata the fifth digit lias but one 
 phalanx.' 
 
 §41. Peloic arch and liinh of Fis/ie.i. — Some cold-blooded verte- 
 brates, e. g. Muraanoids and Opliidians, have neither fore nor hind 
 limbs. In a few, e. g. Anr/iuUidfe, Gyiintoti, 
 Xijdiias, Sirrn, the scapidar arcli and limlis 
 are present, but not the pelvic arch and limbs. 
 In most fishes the latter exist, but less deve- 
 loped than the pectoral ones, and less fixed in 
 position. 
 
 Only the hffimajiophysial portion of the 
 pelvic arch is developed in connection with 
 the diverging appendages, termed in Fishes the 
 ' ventral fins.' Their rays in osseous fishes, 
 fig. 1 12, 68, are directly supported by the bones, 
 r,s, which, uniting together, near the point of 
 attachment of the fins without an intervening 
 bone, resemble their homotypcs, the coracoids ; 
 by virtue of whicli ' serial homology,' Ave infer 
 their special one with the ischia of higher 
 animals. Each bone is a subtriangular plate, supporting the 
 fin by its expanded end; and, either suspended in the fiesh, 
 as in the Salmon and Sturgeon, fig. 29, v, or attached by the 
 narrower end to the coracoid, 52, as in the Cod, fig. 36, 63. The 
 representatives of tarsal, tibial, and femoral bones, are wanting in 
 all Fishes. In Acanthopterans one or more of the anterior rays 
 of the ventral fin may be hard unjointed spines, as in the other 
 fins ; in Malaeopterans all the A-entral rays are soft, multiarti- 
 culate, and bifurcate. 
 
 In no fish is this incomplete pelvic arch directly attached to the 
 vertebral column. If we may judge from the position in which 
 the ventral fin aj.ipears in the developement of the embryo fish, as 
 
 ' XLiv. p. 205, No. 1079 ; see also pp. 206, 207, Nos. 1079, 1083, 1087 
 1093 for further details of the bony structure of the fore foot in Chelonia. 
 
 I09I 
 
180 ANz\TOMY OF VERTEBRATES. 
 
 a little bud attached to the skin of the belly, and from the fact 
 that all the fishes in the geological formations anterior to the 
 chalk are abdominal, that is, have the ventral fins near the pos- 
 terior end of the alDdomen, as in the Sturgeon, fig. 29, v, we may 
 conclude that the supporting bones are, essentially, the hfemapo- 
 physes of the last rib-ljearing (or pelvic) abdominal vertebra. 
 Being suspended more or less freely from the under or ventral part 
 of the bodj^ these fins are subject to great diversity of position in 
 relation to the two extremes of the abdomen. On these difi^erences 
 Linnffius based his primary classification of Fishes ; he united 
 together, for example, those fishes which have the pelvic or 
 ventral fins near the anus, fig. 29, to form the order called 'Pisces 
 Abdominales ; ' those with the ventral fins beneath the pectorals, 
 fig. 38, into an order called ' Pisces Thoracic'. ; ' and those with 
 the ventrals in advance of the pectorals, fig. 34, v, into an order 
 called ' Pisces Jugulares;^ lastly, those fishes in which the ventral 
 fins were absent formed the order called ' Pisces Apodes,^ indicating 
 his recognition of the homology of such fins with the hinder or 
 lower limbs of higher animals. 
 
 In the Salmonidce (S. Eriox, fig. 112, c) the iscliia, 6.3, are 
 united by a cartilaginous symphysis at the medial line, and 
 underlie the last six abdominal vertebras. Each supports a 
 ventral fin of nine rays, 68. In the Angler {Lophius piscatorius) 
 the ischium is attached by one end to the coracoid, and expands 
 at the opposite end to join its fellow, and support the six rays of 
 the ventral. It also sends up a vertical process, simulating an 
 ilium. The ' thoracic ' character depends on the greater length of 
 the ischia, as compared with that in the 'jugular' fishes. In the 
 Lepidosiren, fig. 41, as in the Sturgeon, fig. 29, and other 
 ' ventral fishes,' the ischia, 64, are suspended beneath their proj^er 
 vertebra. They support in Lepidosiren a single-jointed ray, g6. 
 In Lepidopus, in the Blennies, the Forked Hake {Phi/cis), the 
 Forked Beard (Raiiiceps), and some other fishes, the ventral fins 
 are likewise mere filamentary feelers. In the Lvmip-suckers 
 ( Cyclopterus), the ventrals unite together, and combine with part 
 of the pectorals to form a sucking disc or organ of adhesion, 
 below the head, just as the opercular and branchiostcgal fins are 
 united together to form the gill-cover. The ventral fin is better 
 developed in the Plagiostomcs than in other fishes. The support- 
 ing arch consists indeed of the same simple elements, hajmapo- 
 pliysial, cartilaginous, confluent at the middle line, and loosely 
 suspended in the abdominal walls ; but they do not immediately 
 support the fin-rays. Two intermediate cartilages are articulated 
 to the expanded outer ends of the inverted arch ; the anterior is 
 
ANATOMY OF VERTEBRATES. ISl 
 
 the shortest in the Dog-fish, and supports three or four rays ; the 
 posterior one is much longer, and supports the remainder of the 
 rays, fifteen or sixteen in number. To the end of this cartilage 
 likewise is attached, in the male Plagiostomes, the peculiar ac- 
 cessory generative organ or clasper. In the Torpedo the arch 
 sends forward two processes, and these are of greater length in 
 the extinct Cyduhates oluiodaetijlus, XL. p. 22.5, pi.' 5. In the 
 Chimeroids the short narrow processes which extend above 
 the place of articulation of the ventral fins simulate iliac bones : 
 the expanded portions which meet below represent the iscliia ; 
 they are each of them perforated by a large round aperture, filled 
 by membrane. The cartilage, answering to the tibia, supports 
 the rays of the ventral fin and the clasper. 
 
 § 42. Pelvic arch and limb of Reptiles. — Passing from the 
 Protoptenis, fig. 101, c, to the Proteus, ib. D, we find the 
 pair of cartilages answering to the piscine ' ischia' aided by 
 a second pair, 62, called ' ilia,' in supporting the diverging 
 appendage ; and this pair is attached to the riblets of the last 
 abdominal or ' sacral ' vertel^ra. The appendage or ' limb ' now 
 consists of definable segments, which are specialised through sub- 
 sequent developements : the first, as the ' femur ;' the second — a 
 pair of shorter and smaller joints — respectively as ' tibia ' and 
 ' fibula ; ' these being followed, with the intervention of a cartila- 
 ginous ' tarsal ' mass, by a pair of many-jointed rays or ' digits.' 
 
 A closer correspondence, however, with the piscine type was, 
 in some respects, retained by the extinct Ichthyosauri, fig. 105. 
 
 Although the iliac element, 62, was joined with the ischial, 63, 
 in supporting the fin, such sustaining arch remained freely sus- 
 pended, as in the ' ventral fishes ' of Linnajus. A second ha^ma- 
 jjophysial arch, 64, was likewise present, in advance of the ischial 
 one, answering to the ' pubis ; ' this aiforded the extent of origin 
 required by the muscles of the better developed fin. The next step 
 in 23rogress is exemplified by the single long and inferiorly flattened 
 and expanded bone, 65, answering to the ' femur,' and through 
 which, as on a pedicle, the fin could be more freely rotated, and 
 moved to and fro. To the end of the femur were ligamentously 
 articulated the two short flattened bones representing the tibia 
 and fibula ; followed by the series of multiarticulate digits, joined 
 too'cther to form the common basis of the fin, which, like the 
 pectoral one, tapered to a point.' 
 
 With the increased length, and progressive difix?rentiation of the 
 several segments of the fin, as in Plesiosaurus, fig. 45, the pubic 
 
 ' No twist, real or imaginary, of hiimerna or femur obscures or is needed to 
 explain the homotjpcs in the pectoral and pelvic members, clx. 
 
182 ANATOJIY OF VERTEBRATES. 
 
 Ijasis, 64, for muscular attachments, became co-expanded ; the 
 ischia also, 63, assumed the form of flattened triangular plates ; 
 and the ilia, though still ' long bones,' were stronger, and attached 
 by ligament to the riblets of one or two vertebra3 ; and these, in 
 Nothosaurus, became expanded for more effective fixation of the 
 pelvic arch. A ' tarsus,' 68, and ' metatarsus,' are now definable ; 
 and the ' digits,' with fewer joints, do not exceed five in number. 
 All the bones are solid in both IclttJii/o- and Sauro-pterygia. 
 
 From the Sauropterygian type of pelvic arch and limb, the 
 transition is easiest to that in the marine Chelurda of the j^resent 
 day. But the course of developement from the Proteus will Jae 
 here resumed and traced to the saltatory grade which the hind- 
 limlj acquires in the Batrachian order. 
 
 Amplduma tridactylum, with proportionally shorter hind-limbs 
 than in Protevis (fig. 101, d), has them terminated by three toes. 
 Menohranchus shows four toes : and Menopoma five, which is the 
 numljcr usual in the hind-limbs of Newts and Salamanders. In 
 Mmopoina, fig. 43, the sacral vertebra, ,?, has a longer and 
 stronger transverse process, t, and riblet, pjh than the vertebras 
 before and behind ; and pi is united to the cartilaginous elements, 
 63 and 64, closing the inverted arch by the ri))-like continuation, 62. 
 To the lower end of this simple 'ilium' and conjoined part of the 
 ' ischio-pubic ' cartilage is ligamentously attached the short and 
 simple femur. To this succeeds a shorter tibia and fibula — the 
 latter reminding us of the plesiosaurian fibula, by its outward 
 curve. The tarsus is cartilaginous in Menopoma ; the metatarsals 
 support 1, 2, 3, 3, 2 phalanges, resj)ectively, from the innermost, I, 
 to the fifth, V. The toes are webbed to near the last joint. Every 
 joint in the limb is syndcsmotic, and the ossification of the bones is 
 limited to an outer crust, covering persistent solid cartilage. In 
 the dccomj^osing body this dissolves away ; and if the ossified 
 parts Ijccome petrified, the fossil lione appears to have had a large 
 medullary cavity. 
 
 In the Land-salamander the broad ischio-pubic plate, fig. 113, 
 , „ liecomes ossified at h, hwi remains cartila- 
 
 ginoiis at the angles c, and the symphysis ; 
 whence it extends forward, and bifurcates, 
 as at d, representing the last pair of abdo- 
 minal ribs in higher reptiles. There is a 
 vasevdar perforation in eacli pubic part of 
 tlio ])late. Tlie ilium, a, retains its siniiile 
 rih-like character. 
 Tlic Ta(li«ilc, fig. 42,afi['ords a significant example oi' the trans- 
 
ANATOMY OF VERTEBRATES. 
 
 183 
 
 imitation of a natatory to a saltatory type of hlnd-limlj, irre- 
 spective of efforts and exercises throuo-h successive o-cnerations 
 producing and accumulating small changes, and independently of 
 any selection liy nature of such generations as were enal)led, 
 through the accidental A'ariety of a slightly lengthened hind-limb, 
 to conquer in the battle of life, and to transmit the tendency 
 towards such dispro]iortion to their posterity. 
 
 It the law l)y which so much of the change of structure adapted 
 to terrestrial life takes place in the active independent aquatic 
 animal be a mystery, and seeming exception, it does not the less 
 impress the lielicver in the derivative origin of species with the idea 
 of unseen and undiscovered powers, that may operate in produc- 
 ing such residt, ' according to a natural Law or Secondary Cause.' ' 
 The hind-limb of the Frog (Rana) closely accords at first with 
 that of the Menopome ; a rib-like continuation, fig. 42, 62, of the 
 pleurapophysis, ^/, of the last abdominal vertebra, gives attachment 
 to a short femur, 65 ; ossification of the shorter tibia, 56, and fibula, 57, 
 S]icodily unites them proximally ; five subeqnal digits bud out of 
 the primitive fin-like i)rojection from the integument; and a simple 
 cartllaginouR tarsus, 08, at first intervenes between the toes and 
 the leg. The due length and power of the hind-limlj is produced 
 by elongation of all its elements, including tlie iliac parts of the 
 sustaining arch. In the Toad (Bufo) the sacral process, or anchy- 
 loscd riblets, transmitting thereby the weight 
 of the trunk upon the legs, are depressed and 
 expanded at their extremities ; in Pipo, 
 fig. 44, B, s, remarkably so, and resting upon 
 the anterior halves of the ilia. In the Toad 
 the femur is shorter than the ilium, and the 
 tiliia is shorter than the femur. In tlie Frog, 
 fig. 44, contrary proportions prevail. The im- 
 pulse of the hind-limbs is applied, in all tail- 
 less Batrachia, to the hindmost part of the 
 body, beyond the lengtJiencd coccygeal style, 
 fig. 114, A, f/, \)y the remarkable backward 
 production of the ilia, ib. A, 62, which expand 
 and unite, forming a symphysis, above the 
 acctabula ; thence they transmit the impulse 
 of the limbs to the short and strong trans- 
 verse processes of the sacrum, a. A pair 
 of commonly anchylosed semicircular bony 
 plates, ' ischia,' C3, unite with the iliac sym- 
 physis to form the lower half of the j(3ints for the femora, 65. 
 
 ' CXLI. p. 86. 
 
 IM 
 
184 ANATOMY OF VERTEBEATES. 
 
 The femur in the Frog, fig. 44, 65, is a long slender bone, with 
 a slight double bend ; the head is expanded, convex, and ter- 
 minal ; the back part of the upper fourth of the shaft shows a 
 longitudinal ridge ; the distal end is expanded and truncate. 
 Both ends of the femur are usually in the state of epiphyses. 
 The tibia and fibula are confluent longitudinally, but preserve 
 their respective medullary canals, and indicate their transcend- 
 ental distinction by an anterior and posterior longitudinal furrow 
 at the expanded ends of the seeming single bone ; usually, also, 
 by a perforation from before backward. A single epiphysis con- 
 stitutes each articular end. The astragalus a, and calcaneum cl, 
 are much elongated. The former is slightly bent. They com- 
 monly coalesce at their proximal and distal extremities ; at the 
 former, by means of an epiphysis ; at the latter, with the connate 
 representatives of the na'S'iculare, s, and cuboides, h. Two cunei- 
 form bones remain distinct and support the three inner toes, ^, ii, 
 in: a third expanded bone projects, like a supplemental digit, ci, 
 from the inner (tibial) side of the tarsus ; it may represent the 
 ' entocuneiform.' One (Rana) or two (Pipa) sesamoid bones are 
 developed in the extensor tendons behind the tibio-tarsal joint : 
 their function is that of the lever part of the calcaneum. The 
 first metatarsal supports two phalanges, i ; the second, two ; the 
 third, three ; the fourth, four ; and the fifth, three. 
 
 In Bufo agua I found a semiossified tubercle upon the proximal 
 end of each ilium. In Pijpa, the confluent calcaneum and cuboid 
 form a long three-sided bone with the angles sharp : the long- 
 astragalus presents a similar form. 
 
 To the student of Comparative Anatomy entering upon the 
 vast domain of that science with ideas of the bones derived from 
 those of the human skeleton, and associating the special shapes 
 and proportions they there present with the names that have been 
 learnt from Anthropotomy, few parts are more perplexing or de- 
 ceptive than the pelvis in the Chelonian reptiles. Viewing, for 
 example, that of the Trionyx, as it is represented in fig. 116, he 
 would conclude h to be the iliac bones, and i the pubic bones, 
 separated at the symphysis ; or as answering to the parts so called 
 in the single ' os innominatum ' of man. The rectification of the 
 error affords a valuable lesson of the unimportance of size and 
 shape in determining special homology, and of the necessity of 
 knowing the fatal as well as the adult conditions of the human 
 pelvis. He would learn, first, that the threefold nature of the 
 'innominate' bone, which is transitory in man, is permanent 
 in the reptile ; next, that the bone which is largest and 
 
AMATOMY OF VERTEBRATES. 185 
 
 broadest in tlie human foetal pelvis is the least and slenderest 
 in that of the Turtle. To comprehend the nature of the Chelo- 
 nian pelvis, the connections and relative positions of its bones 
 must be studied in the entire skeleton. 
 
 The two bones that articulate with the transverse processes 
 of vertcbrte and, extending ' haimad ' (downward or forward), 
 combine at the opposite end with the other bones forming the 
 acetabulum, arc those alone which show the essential characters 
 of the ilia in air-breathing vertebrates. In the figrire of the 
 pelvis of the Turtle viewed from below or from the hajmal aspect, 
 hg. 115, that surface of the sacrum is figured to illustrate the 
 
 115 
 
 Pelvis of Chtloiu. tfium below). CLX. 
 
 above character of connection. Two stunted pleurapophyses 
 convero'c from the two centrums, and afford a close ligamentous 
 attachment to the proximal or upper ends of the ilia, a, a. These 
 bones are also attached to the contiguous costal plates of the cara- 
 pace, which they support as stout strong pillars. They slightly 
 expand at their acetabular ends, where each unites with two other 
 bones. The bone c descends and meets its fellow at the mid 
 line, as does likewise the bone b : c c being posterior in position 
 answer to the ischia of the human foetus; b b to the pubics. 
 These are remarkably expanded, and, besides forming an exten- 
 sive symphysis between b, b, each developes a broad angular 
 process or tuberosity which is ligamentously attached to the 
 plastron forming the foundation for the support of the pillar, a, 
 that underprops the carapace. 
 
ISG ANATOMY OF VERTEBRATES. 
 
 A sllri-lit modification is presented by Trionyx, in which a view 
 of tlie pelvis is given from the dorsal aspect, the sacrum being 
 removed, in fig. 116: here i shows the end of the ilium, 62, which 
 was attached to that part of the vertebral column : a is the ex- 
 panded acetabular end of these short, straight, columnar bones. 
 
 no 
 
 The ischia, c, c, develope tuberosities/,/, and unite at the ischial 
 symphysis, 64, d. The pubics h, h, articulate by a broader tube- 
 rosity, /(, with the plastron, and have a greater transverse extent. 
 The ' outlet ' of the pelvis is not, as might be supposed, between e' 
 and 64, but between -; and/ The wider space answers to the ob- 
 turatorial one in Man ; and, were ossification to be extended from 
 the ischial, 64, to the pulwc, e , symphysis, it would be divided into 
 the two vacuities called ' foramina ovalia seu obturatoria " in the 
 human pelvis. Such division does actually take place in the 
 Tortoises {Tcstudo) and Terra] )eues, as shown at v, fig. 51, in 
 Emys Europa'a. 
 
 In the Tortoise ( Teatudi)) the iliac bones are vertical and 
 columnar, like the scapula, but are shorter and more compressed. 
 The pubis expands to join its fellow at the median symphysis and 
 the ischium posteriorly : it sends outward and downward a long- 
 thick obtuse process from its anterior margin. The ischia, in like 
 manner, expand where they unite together to prolong the sj-m- 
 physis backward. The ' foramen ovale seu thyroidcuni ' is nearly 
 circular on each side. In Hi/draqns the ilia articulate directly by 
 part of their under siu'face to the xiphistcrnals, and the pidiis 
 becomes confluent with the same ixirts of tlie })lastron liy the 
 tuberoiis process. 
 
 The femur is shorter than llie Inuncrus in the Turtles : the head 
 is round, surmounted by a broad, thick, short trochanter: the 
 
ANATOMY OF VEKTEBRATES. 
 
 187 
 
 shaft is almost straight, sliglitly expanded at the distal end, at the 
 back pai't of which the condyles are fceljly indicated. In Terra- 
 penes, fig. 51, w, and Tortoises, the femur equals or exceeds the 
 luimerus in length : its shaft is more bent : the trochanter is divided 
 into two processes, most distinct in Trionyx. In no Clielonian is 
 there a medullary cavity : ossification extends throughout the bone : 
 the two l)ones of the leg, ib. x, Y, are nearly straight ; the til)ia is the 
 largest, with the proximal end almost semi- 
 circular, and the distal one less expanded 
 and suljconcave, with a slightly-developed 
 malleolus in TesttuJo and Ennjs. Tlie fibula, 
 fig. 117, G7, is a little bent, enlarging the 
 interosseous space in Trionijx : it presents 
 a convexity to the tarsus. There is no bony 
 patella in any Chelonian. In Tuatudo 
 tdhnlata I found a synovial joint between 
 its fibrous representative and the femur, 
 distinct from the proper capsule of the knee- 
 joint. The piroximal row of the tarsus con- 
 sists of two bones, astragalus, a, and cal- 
 caneum, which in most Tortoises liccome 
 contluent. The distal row consists of five 
 bones, four of which support the four nor- 
 mal toes, and the fifth a rudiment of the 
 metatarsal of the fifth toe, v ; the fourth 
 and fifth of the second row of tarsals 
 answer to the os cidwides of higher ani- 
 mals ; the other three bones to the three 
 c>ssa cimeiformia. The astragalar part of 
 the single proximal bone includes also the naviculare. 
 
 In the Trionyx, fig. 117, the proximal row consists of a single 
 ])one, a, answering to the astragalus and naviculare : the distal 
 row consists of five l>ones, of wliich the three cuneiformia are very 
 small : the two divisions of the cuboides, h' , c, are very large ; 
 the first may include the articular part of the calcaneum ; the 
 outermost is dilated and angidar. In Clidonc and Chelys the 
 calcaneum is distinct from both the cuboid and the astragalo-navi- 
 cular bones. The digits are moderately long, rather flattened and 
 divaricated, supporting the hind weighed foot ; the metatarsal sup- 
 ports two jihalangcs in the first toe; in the other toes it supports 
 three, the last having a claw. 
 
 In Trionyx the fifth digit, fig. 117, v, has two small phalanges 
 and no claw. In Einys and Cistudo the digits decrease in strength 
 
 TliuVlJX. CLI. 
 
ANATOMY OF VERTEBRATES. 
 
 from the first to the fifth, and in length from the second to the 
 fifth. In the Land tortoises, the fifth toe is reduced to a metatarsal 
 rudiment : the others are short and thick, fig. 
 118, each with two phalanges, the second sup- 
 porting a claw, and adapted, like those of the fore 
 foot, for burrowing. The two extremes of modi- 
 fication of the hind foot in the chelonian series 
 are presented by the Turtle and Tortoise : the 
 great comparative weight and bulk of the body 
 to be supported on dry land involve a form of 
 limb and foot resembling that in the Elephant ; 
 whence the largest kind of Land-tortoise has been 
 termed ' Testudo elepliantopus.^ 
 
 The general homology of the pelvic bones of 
 the Crocodile has been jDreviously discussed, 
 pp. 67-69, and illustrated, figs. 55, 56, 57. The 
 serial homology of the two hffimapoph3'sial elements derives satis- 
 factory elucidation from their crocodilian condition. Of those of the 
 scapular arch, called clavicle' and 'coracoid,' in the vertebrates pos- 
 sessing both, the anterior very rarely enters into the formation of the 
 joint for the appendage ; whilst the posterior invariably does so. 
 
 119 
 
 Bones of lea: -iiitl 
 lout, Tcsiiulo 
 
 Left pclTic bouca Cr.....JJ^. 
 
 In the fcetal mammal, before the coalescence of the stunted cora- 
 coid, this relation may be seen. So in the Crocodile, the posterior 
 hffimapophysis, fig. 119, 63, combines with the ilium, 62, to the 
 exclusion of the pubis, 64, in the formation of the acetabulum, 
 repeating the articular characters of the coracoid ; whilst the 
 more slender pubis placed anterior to the joint, and abutting by its 
 mesial end against the abdominal sternum, figs. 5, 6, lo, repeats 
 
ANATOMY OF VERTEBRATES. 189 
 
 those characters of the clavicle of lizards. Accordingly in tlie 
 I)rogressive reduction of the pelvic arch to a single ha3mapophysial 
 element sustaining the appendage, as in Osseous Fishes, we may 
 discern the characters of the ' ischium ' in that element, rather 
 than of the puljis. 
 
 The ilium of the Crocodile is twice as broad as long, produced 
 beyond the two verteljras to which it is articulated : it descends 
 vertically to the acetabulum, of which it forms the upper half. 
 The anterior production or tuberosity, a, is the thickest, the pos- 
 terior IS the longest. The ischium developes a strong bent process 
 from the fore part of the acetabular end, to which the puljis is 
 articulated : as it descends and inclines inward, it becomes flat- 
 tened and expanded, b, and joins its fellow by a moderately 
 extended ischial symphysis. The pubis is directed more forward, 
 and though smaller and more slender, resembles the ischium by 
 the expanse of the medial end. As ossification is not extended 
 along the mid-line from the ischial symphysis to the pubis, no 
 ' obturator foramina ' are defined, but a wide vacuity intervenes, as 
 in Chelone and Trionyx. 
 
 The femur, fig. 57, w, is bent in curves opposite to those of the 
 humerus : the head is convex, subcompresscd laterally, flattened 
 externally : the chief process is from the inner side, at the upper 
 third of the shaft : there is a ridge external and above this process : 
 the distal end expands transversely, and developes backward two 
 condyles ; the outermost receives part of the head of the fibula. It 
 is longer than the humerus, but in a less degree in modern than in 
 mesozoic crocodiles. The tibia, figs. 57 and 120, 66, presents a 
 large triangular head to the femur, the division of the back part of 
 which into two condyles is feebly indicated : it offers a smaller 
 convex crescentic surface to the tarsus. The fibula, ib. 67, is 
 slender and subcyliudrical ; much compressed above, more ex- 
 panded and triangular below. Each of the foregoing long bones 
 has a medullary cavity. There is no patella ; but there is a fibro- 
 cartilaginous 'fabella,' with granular bone, in old crocodiles, 
 behind the outer condyle. 
 
 The principal tarsal bone, fig. 120, c, represents the astragalus, 
 naviculare, and entocuneiform, connate, of the human series; 
 articulatino- with the distal end of the tibia and a small part of the 
 fibula above, with the calcaneum and cuboid externally, and with 
 the first and second metatarsals and the ectocuneiform below. 
 The calcaneum, d, intervenes between the fibula and cuboid, and 
 has a short but thick posterior tuberosity, y, fig. 57. The cuboid, 
 fio'. 120, e, supports the fifth, u, fourth, iv, and part of the third. 
 
190 
 
 ANATOMY OF VERTEBRATES. 
 
 120 
 
 in, metatarsals. The ectocuneifcjrm, f, is ^vedged between the 
 bases of the second and thh-d metatarsals. These, by the oblique 
 overlapping arrangement of their expanded bases, resemble the 
 
 articulations of the ventral fin- 
 rays in most fishes. The fifth 
 is flattened and expanded to sup- 
 port the broad scale from the 
 outer side of the foot, but is 
 curtailed in length and supports 
 no toe. 
 
 The four normal metatarsals 
 are much larger than the corres- 
 ponding metacarpals. That of 
 the first toe, i, is the shortest 
 and strongest ; it supports two 
 phalanges : the other three are 
 of nearly equal length, l^ut lose 
 thickness from the second, ii, to 
 the fourth, in: the second sup- 
 p)orts three phalanges ; the third, 
 four ; the fourth, also four, tlie 
 claw and its phalanx being ab- 
 sent in this toe : ii, Hi, and iv, 
 are webbed in true Crocodiles, 
 but semipalmate in Alligators. 
 In most Lacertians two verte- 
 bra are modified for articulation 
 with the iliac bones, as in the ]Mo- 
 nitor ( Varamis, fig. 121, a) : but 
 in the Chameleon there are three 
 sacrals. In the great INIonitor 
 the ilium, I, extends backward 
 beyond the junction, terminat- 
 ing obtusely, and bends down 
 as it passes forward with a short 
 , , , . ,., process above the acetabulum. 
 
 Billies nl lr:A aiiil [iinl. l_nirudlli' J- 
 
 Both ischium and pubis com- 
 bine with the ilium in forming this cavity. The ischium, c, 
 is usually most expanded at its symphysial border, which is pro- 
 duced backward. Tlie pubis, f, appears as a more direct con- 
 tinuation of the ilium, and is perforated near its acetabular end, 
 anterior to wliich it devclopes a jirocess. The sym]ihysial car- 
 tilage is continued from tlie ischium to the pul)is, dividing the 
 
ANATOMY 01' VERTEBRATES. 191 
 
 intcrs})ace into the ' obturator foramina,' and becoming ossified in 
 
 old IMonitors. The femur resembles that of 
 
 the Crocodile, but with the imicr trochanter 
 
 better developed, with a larger medullary cavity, 
 
 and with a more marked depression on the outer 
 
 condyle lor the fibidar articulation. The division 
 
 ol' the back jiart of the head (jf the tibia is usually 
 
 more marked. The head of the hbula, fig. 122, 
 
 07, b, rises higher than in the Crocijdile. 
 
 In Varmms niloticuis,^ the elongated iliac ['tiviBnf uiosinnitor 
 bone alnits against the transverse processes of 
 the two sacral vertebra, the first on the right side and the second 
 on the left side being applied on a plane higher than the 
 opposite processes : that of the first caudal vertebra also abuts 
 against the ilium on the left side. The ilium sends off a tuber- 
 osity in front of the sacro-iliac syndesmosis, and it joins the puljis 
 and ischium Ijy a broad suture. The trochanter arises from the 
 inner and back part of the proximal end f»f the shaft of the 
 femur. There are two ossified patelhc in the tendon of the great 
 extensor of the leg. The tarsus differs from that of the Crocodile 
 chiefly in there being a ' mesocnneifonn ' supporting the second 
 metatarsal, fig. 122, ii: but this is wanting in many lacertians. 
 The bone ci is as composite as in the crocodile. The fifth meta- 
 tarsal is flattened, and articulated farther Ijack than the rest, 
 extending along the outer side of the cuboid, c, to the calca- 
 neum, U: it supports an imguiculate toe of fjur phalanges, 
 fig. 122, 7 1 : the number of jihalanges in the other toes progres- 
 sively increases from two in the first, i, to five in the fourth, io, 
 with proportionate increase of length. 
 
 The chief modification of the hiiid limb of Lacertians is fijund 
 in the Chameleon, fig. 123. The ilinm is a simple elongate, 
 subcomprcssed bo)ie descending vertically from the converging 
 ends of the sacral processes to the acetabulum. The fibula, 
 fio-. 123, b, 67, is bent outward. In the tarsus may be seen a 
 stunted homologue of the astragalo-uavicnlar bone, a', receiving 
 the end of the tibia ; and a larger calcaneum, b' , in like relation 
 with the fibula : these form a cavity for the spheroid ' cuneiform,' 
 d, by which the prehensile foot rotates on the leg ; and there is a 
 cuboid, c, exclusively supporting the fifth metatarsal, r. This 
 determination of the homologies of the tarsal bones with those of 
 the ambulatory lizards, shows the natiu-e of the five short but 
 metatarsially shaped bones supporting the toes, and settles the 
 
 ' xLiv. p. 149, No. 678. 
 
)9-2 
 
 ANATOMY OF VERTEBRATES. 
 
 122 
 
 homology of their homotypes in the fore-foot, fig. J 10. The first 
 metatarsal supports two phalanges, fig. 123, i ; the second, three ; 
 the third and fourth, each four phalanges ; and the fifth, three. The 
 
 first and second toes are opposed 
 to the other three in the hind foot, 
 contrariwise to the arrangement in 
 the fore foot. 
 
 In the Pterodactyle, fig. Ill, 
 the hind limb adhered closely to 
 the lacertian type ; the metatarsals 
 were distinct; the phalanges in- 
 creased in number from the first 
 to the fourth toe, but retained 
 more equality of length than in 
 lizards : all the five toes were 
 unguiculate, the claw phalanx com- 
 pressed and deep. Although in 
 some species there were four or 
 five sacral vertebra;, the hind- 
 limbs were too feeble to sustain 
 the body, as in Birds : they more 
 probably served to suspend it, as 
 in Bats, with a concomitant 
 strengthening of the claws. 
 
 The reptilian hind-limbs, with 
 their arch, acquired the most com- 
 plex structure in the great extinct 
 Dicynodont ' and Dinosaurian ^ 
 orders. In Dici/nodon tiffriceps 
 ossification extended over the 
 whole of the interspace between 
 the ischium and pubis, obliterat- 
 ins altogether the cbtviratorial 
 foramina: and both iliac and 
 ischial bones articulated, as in 
 edentate mammals with a long 
 sacrum. In the Iguanodon six 
 vertebras were modified with interlocking centrums and neural 
 arches, the latter resting on, and suturally joined , to, the 
 contiguous halves of two centrums. The femur exhibited an 
 upper and external ' great trochanter,' besides the inner tro- 
 
 Bcmes of leg and iool, ]\[oiiitor 
 
 cxLvi. (1811), pp. 11-1, 130. 
 
ANATOMY OF VEETEBRATES. 
 
 193 
 
 chanter better developed than in modern lizards: examples of 
 this bone fonr feet in length have been discovered. In the 
 almost equally colossal Sclelidosaur the toes 
 of the liind foot were reduced to four in num- 
 ber by suppression, as in the Crocodile, of 
 tlie fifth. In the Iguanodon they were re- 
 duced to three by the suppression also of the 
 first toe ; the retained toes were short and 
 broad, with phalanges in number respectively 
 three, four, and five ; but the latter so mucli 
 shorter as to reduce the outer to the same 
 length as the inner toe, and with the middle 
 one both lono-er and larger ; showint; in the 
 great ^lerliivorous Saurian an interesting ana- 
 logy to the hind limb of the Rhinoceros.' 
 
 § 43. permoskeh'ton of Fishes. — The scales 
 of fishes may be regarded, from their seat and 
 mode of developement, as parts of the dcrmo- 
 skeleto^' : and in the palteo- and meso-zoic 
 species they were ossified, in the form of 
 granules, tubercles, plates, or imbricated 
 scales. Bony fishes, with scales so soft and 
 soluble as to leave no trace in fossilization, 
 seem not to have existed before the creta- 
 ceous period : for even the exoskeleton of the 
 Leptolepidce of the louver and middle oolites 
 has iDeen preserved to us through the thin coating of petrifiable 
 ganoine with which their minute and delicate scales were covered. 
 Tubercular integument, like the ' shagreen ' of sharks and dog- 
 fishes, has come down to lis from a period as remote as the 
 Silurian. In skates and rays the skin is studded by bone in larger 
 masses; sometimes, as in the ' Thornback,' developing a small 
 bent spine. 
 
 The hard-rays in the fin of the Perch and other Acanthopteri, 
 the laro-er and fewer spear-like weapons of the Sticklebacks 
 (Gasterostn), Sheat-fishes {Siluridce), Trigger-fishes (i?ttZi«fe,s), and 
 some Snipe-fishes ( Centriscus), are all parts of the dermoskeleton. 
 
 In Balistes capriscus — a rare British fish — the anterior dorsal 
 is preceded by a strong erectile spine : its base is expanded and 
 perforated, and a bony bolt from the supporting plate passes freely 
 throui^h it : when the spine is raised, a hollow at the back part of 
 
 Bones of the leg and foot, 
 Ijharaeleoii. ci,i. 
 
 VOL. I. 
 
 CLIV. 
 
 
 
194 ANATOMY OF VERTEBRATES. 
 
 the base receives a prominence from the next bony ray, which 
 fixes the spine in the erect position, as the hammer of a gun-lock 
 acts at full cock ; and the spine cannot be forced down till the 
 small spine or ' hammer ' has been depressed, as by pulling the 
 trigger. This mechanism may also be compared to the fixing 
 and unfixing of a bayonet. When the spine is unfixed and bent 
 down it is received into a groove on the supporting plate, and 
 offers no impediment to the progress of the fish through the water. 
 The generic name (Balistes) and the common Italian name of the 
 fish (Pesce halestra), refer to this structure : the spine is rough- 
 ened by ganoid grains, whence our English name of ' File-fish.' 
 The hind border of the analogous weapon of the Centriscus 
 humerosus and of most Sheat-fish is denticulated, so that they 
 infiict a ragged wound. In all such weaponed osseous fishes, the 
 base of the spine is modified for articulation with another bone. 
 In gristly fishes so armed the base of the spine is simple, smooth, 
 hollow, implanted deeply in the flesh and attached to ligament 
 and muscle. 
 
 The great majority of such weapons found in a fossil state, 
 called ' ichthyodorulites,' show by their basal structure that the}^ 
 come from Plagiostomous fishes, and exemplify in a remarkable 
 manner the efficiency, beauty, and variety, of the ancient armoury 
 of that order. In some, the marginal serrations were themselves 
 denticulate (Edestes)} Certain Rays {Trygon) have si^ines with 
 both margins serrate.^ 
 
 The series of side-scales perforated by the mucous duct in the 
 modern soft-scaled fishes are usually more or less ossified. In the 
 Eel tribe the lateral mucous ossicles are tubular and concealed by 
 the cpiderm. In the Sole and Plaice the mucous scale bones of 
 the lateral line are quite superficial. There are many circular 
 radiated ossicles scattered over the dark or u]iper side of the skin 
 of the Turbot. A row of small chcvron-sliajied dermal bones 
 extends along the median line of the belly of the Herring, and the 
 extremity of each lateral process, fig. 37, dli, is connected with 
 that of the long and slender vertebral rib, completing the inferior 
 arch, like a sternum and sternal ribs. The Dory has two rows of 
 thick osseous plates along the under part of the abdomen ; but 
 their superficial position indicates their essentially dermal charac- 
 ter. Parts analogous to a sternum arc thus supjilicd from the 
 cxoskeleton as tliey arc from tlie splauchnoskelcton in the Lam- 
 prey, fig. 1 1 ; but the true honiologucs of the sternum arc first 
 
 ' CLXXX. 11. 121, fig. 38. - III. 123. 
 
ANATOMY OF VERTEBRATES. 
 
 195 
 
 seen in the endoskoleton of the Batracliia. In the Trunk-fishes 
 ( Ostracion), and Pipe-fishes ( Sipujnathm), the dermal scale bones 
 form a continuous coat of mail, like a tessellated quincuncial pave- 
 ment, over the entire body, as shown in the transverse section, 
 fift'. 16, d n, dp, d h, and the endoskeleton is but little ossified. 
 The like is seen in the Hippocamps. Thus, in Pegasus draco, 
 fig. 124, "with the exception of the small jiremaxillaries d, and 
 mandible e, all the visiljle hard parts of the head are due to the 
 dermoskeleton : such, e. g., as the rostrum, a; the plates in which 
 the eyes are placed, h ; the gill-covers, li ; the median plate, g, 
 
 124 
 
 Dermoskeleton ol tlie Plying Hippocainp (Pfgrisus) 
 
 supporting the hyobranchial arches ; the zone, i, sustaining the 
 large pectoral fins ; and the hard case of the incubating pouch. 
 
 in the Ganoidei, parts of the exoskeleton coalesce with endo- 
 skeletal bones of the skull, especially the sclerogenous ones, while 
 others overlie the true cranial bones. Thus, in the Sturgeon, 
 the ganoid plate, marked d z, fig. 125, simrdates a superocci- 
 pital ; ' but its homologue in Pohjpterus and Lepidosteus is subdi- 
 vided : and as the cartilaginous homologue of the epencephalic arch 
 
 ' CXLV. (1846) p. 134. 
 O 2 
 
196 
 
 ANATOMY OF VERTEBRATES. 
 
 underlies the plate d 3, in Acipenser Sturio, so also do the ossified 
 ex- and super-occipitals underlie in PoJypterus the three dermal 
 plates corresponding in position with d 3 in Ac. Sturio. The true par- 
 occipital is equally distinct from the plate marked d 8, in Ac. Sturio 
 and its representative subdivisions in Pohjpterus. The dermal 
 plates in advance of these coalesce with the true parietals, frontals, 
 postfrontals, and part of the mastoids. But the varieties in the 
 dermal plates within the limits of a genus, as exemplified by the 
 
 126 
 
 Furc rmtf of ciido- .'iiid exo-skeletiiii of Stu 
 
 sino-le intorfrontal in Acipenser Sturio, by the three interfrontals 
 in Ac. Scypha, by the divided superoccipital plate in Ac. brcviros- 
 tris, &c., sufficiently warn against the confusion arising from 
 applying to dermal plates the names of the true cranial bones in 
 recent and extinct ganoid and placoganoid fishes. The median 
 cranial ganoid plates in the Sturgeons are plainly a continuation 
 forward of the dermal plates, (ib. d s, fig. 125), of the mid-line of 
 
 the back ; and examples of a like re- 
 petition occur amongst the Osseous 
 Fishes in the dermal epicranial spines, 
 for example, of the Angler (Lophius), 
 which suppi5rt the long fishing-fila- 
 ments upon the liead, or in those 
 modified ones forming the sucking disk 
 on the head of the Remora. 
 
 In certain fishes of the Devonian or 
 Old Red Sandstone ]>eriod the head and part of the trunk were 
 encased by coarticulated ganoid bony jilates. Fig. 127 shows the 
 proportions in which the exo- and endo-skcleton entered into the 
 conservable framework of one of these ancient fishes, termed 
 Coccostei/s (Itdhhos berry, osteon bone), in reference to the tuber- 
 cular enamelling of tlic exterior of the combined helmet and 
 
ANATOMY OF VERTEBRATES, 
 
 107 
 
 cuirass. In the composition of tlii 
 sntures, not mncons grooves, may be 
 discerned the i'ollowing lAutesi : 5, 
 n/fdum ; 6, lateral ; 7, jjremedian ; 8, 
 jirelateral; 9, rostral; \2,dorsomedian; 
 14, ]>ostdorsoinediun ; is, suhlatcral; 20, 
 liostventrolateral; 22, preventrolateral ; 
 24, .sid)orhital. 
 
 Tlie blanli space l)etween the neu- 
 ral, v., and haBmal, A, spines of the 
 fossil endoskeleton indicates the posi- 
 tion of the soft ' notochord,' c, which 
 has l:)cen dissolved away. 
 
 In the Pterichtlnjs of the same geo- 
 logical formation, the helmet was 
 moveably articulated with the truidi- 
 buckler. 
 
 In Cephalaftpis the armour of the 
 head was shield-shaped, with the pos- 
 terior angles produced backward in a 
 pointed form. 
 
 The fishes with enamelled dermal 
 bones in the form of j^lates, whether 
 coarticulated, fig. 127, or detached as in 
 the Sheat-fishes and Sturgeons, fig. 125, 
 d J), d s, are called ' placoganoid : ' 
 those in which they have the size, 
 form, and overla2)ping arrangement of 
 scales, fig. 126, are called 'lepidoganoid.' 
 The genera Poh/ptcrns and Lcpidostcus 
 exceptionally exemplify the latter con- 
 dition of the dermoskeleton at the 
 ])resent day : it was the rule with the 
 fishes of the mesozoic period, and 
 with those of the pala30zoic wliich 
 were not ' placoid ' or 'placoganoid.' 
 
 In fig. 126, « indicates the outer 
 siu-face of parts of two series of the 
 rhomboidal ganoid scales of the extinct 
 Amhlfjpterus: and h \\\e inner surface 
 of two scales, showing the ridge pro- 
 duced at one end into a projecting 
 jieg, which fits into a notch of the next 
 
 s armour, as defined by 
 
 127 
 
 L 
 
 'N 
 
 '^:'S. 
 
 : *l 
 
 EiuTo-an(U\T -kelttoii, Coccr^s^jcs. clvt. 
 
198 ANATOMY OP VERTEBRATES. 
 
 scale, in the way that tiles are pegged together in the roof of a 
 house. 
 
 In the Porcupine-fishes (Diodon) the spines are supported by 
 triradiate interlocking dermal bones. 
 
 § 44. Dermoslieleton of Reptiles. — In the Scincoid family of the 
 Lacertians, the scales are more or less ossified ; least so in the 
 smooth-scaled genera(<S'cH«cM5, Tiliquci); but in Cyclodus resembling 
 scutes, and giving a knoliby character to the surface. In Cyclura, 
 Lophura, and Xiphosurus velifer, dermal bones in the form of 
 spines project or raise the skin above the dorsal or caudal vertel^raj. 
 The horizontal plates connate with the neural spines, and with 
 the ribs, are dermal ossifications, as are the neural plates and 
 marginal plates which remain distinct from the endoskeleton, 
 in the comjiosition of the carapace of the Chelonia. The plastron 
 is also formed by dermal plates, connate with the sternum and 
 sternal ribs. 
 
 In existing Crocodilia the upper surface of the trunk is de- 
 fended by bony scutes, usually quadrate in form, smooth on the 
 inner surface, sculptured and longitudinally ridged on the outer ; 
 arranged in transverse series, more or less apart, of twos or 
 fours, upon the neck ; but six or eight in a transverse line and 
 close set, so as to have a longitudinal as well as transverse 
 arrangement along the back. The numbers and patterns of these 
 scutes are noted in zoological comparisons and characters of 
 genera and species.' The Alligators are defended by a ventral 
 as well as dorsal cuirass, separated, as Natterer observed in 
 Champsa palpehrosa, Ch. trlgnnata, Ch. gibbiceps, only by a 
 narrow and soft longitudinal groove along the sides of the neck 
 and trunk.^ But the most remarkable anatomical modifications 
 are presented by the extinct and especially the mesozoic Cro- 
 codilia. 
 
 The presence of a ventral as well as a dorsal series of scutes 
 and their distinctive characters were first noted in the Teleosauri. 
 The dorsal scutes are in close-set sub-imbricate transverse rows, 
 the posterior margin overlapj^ing the anterior one of the next 
 row. I counted twenty such rows in a specimen of the A^Hritby 
 Teleosaur, of which sixteen covered the vertebra3 between the 
 last cervical and first caudal. In the ventral shield or plastron, 
 only the two scutes in each row arc on the same transverse parallel 
 which border the mid-line of the abdomen ; the others liave an 
 alternate interlocking arrangement. These ventral scutes are 
 
 ' CLi. torn. V. pp. 79, 80, pi. II. 2 n.vii. torn. ii. (lS-10) p. 320. 
 
ANATOMY OF VERTEBEATES. J 99 
 
 not carinate ; and such Is the case likewise with the dorsal scutes 
 of certain species' of Telcosaur. In a Wealden Crocodile (Gonio- 
 pholis), the angles of the oblong quadrilateral dorsal scutes are 
 well marked, and from one of them was continued a peg-like 
 process, which fitted a depression on the under surface of the con- 
 tiguous angle of the next scute, thus serving to hind together the 
 scutes in the way in which the enamelled scales were united in 
 many extinct ganoid fishes, fig. 125. The outer surface was 
 impressed by numerous deep, round, or oblong pits ; but a larger 
 proportion of the fore part of this surface was overlapped by the 
 antecedent scute than in Teleosaurus, and this part is smooth and 
 thinner than the rest of the scute. Associated with the quadrate 
 toothed scutes, ascribed to the l^ack of Goniojiholis, and irregu- 
 larly scattered in the matrix, I have observed others of a hexa- 
 gonal form, with a similarly pitted outer surface, l)ut without the 
 peg, and with thick sutural margins. They indicate a similar 
 alternate arrangement and interlocking of the ventral scutes, as 
 in Teleosaurus. 
 
 The dermal armour of Ilijlceosaurus and Seelidosaurus appears to 
 have consisted of series of detached scutes of an elliptical or circular 
 form, without sutural or smoothly overlapping margins : of great 
 thickness, with the outer surface, in most, pyramidal, or rising to 
 a longitudinal ridged summit. In Hylcensaurus certain scutes 
 situated above the dorsal spines were of a very long and narrow 
 triangular form with the base oblique ; and seem to have 
 formed a defensive fringe of strong spines along the back, as in 
 Xiphnsurus. In Seelidosaurus the surface was defended by several 
 longitudinal series of massive unconnected bones : those in the 
 middle of the dorsal surface being in jiairs upon the nape, and 
 single along the tail, where three are coextensive with from five 
 to seven subjacent vertebraj : a corresponding medial series of 
 rather smaller and less vertically developed scutes defended the 
 under surface of the tail ; and there were one or more lateral 
 series of a more depressed and fuller ovate form, in that region.^ 
 
 ' cxivi. p. 79. The volume of the Serial containing Nattercr's memoir, though 
 bearing the date 1840, had not readied this coimtry when I communicated the second 
 part of my ' Eeport on Fossil Eeptiles ' to the British Association. 
 
 ^ CXCIII. 
 
200 
 
 CHAPTER III. 
 
 MUSCULAR SYSTEM OF H^MATOCRYA. 
 
 § 45. Structure of Muscle. — Muscular tissue is fibrous, and resol- 
 vable into fine threads inclosed in a delicate sheath, called ' elemen- 
 tary fibres.' These, in Vertebrates, are of two kinds ; in one the 
 fibre is crossed by close parallel lines ; in the other it is smooth. 
 The transversely strijied character is too fine to be seen withovit the 
 aid of the microscope ; but may be indicated to the naked eye by 
 the iridescence of the surface in certain lights.' All the muscles 
 subject to the influence of the will, or cerebral action, have striped 
 fibres. Most of the involuntary muscles have unstriped fibres ; 
 those of the heart and gullet are among the exceptions ; and, on 
 the other hand, the muscles performing the rhythmical movements 
 of the gill-covers in fishes, like those of the thoracic walls in 
 
 higher air-breathers, ha^e the 
 striped fibre. But besides the close 
 cross parallel lines, longitudinal 
 ones, darker, wider ajiart, and of 
 varying extent, often present them- 
 selves on the elementary fibre of 
 voluntary muscle, as in fig. 128, 
 
 A fl.- 
 
 The fibre, though termed ' ele- 
 mentary ' may, by manipulation 
 and chemical agency, be resolved 
 into parts of different forms. ^ It 
 
 128 
 
 Portioi}R (if stri 110(1 elementary flbrea, eliowiiig 
 in opposil 
 300 diam. 
 
 a cleavage In opposite dlrertionE, luagnlfled SeemS mOSt prOnC tO Split lutO loU- 
 
 gitudinal tracts, which have been 
 termed 'fibrils,' fig. 128, a, b and c, and these have a show 
 of segments equalling in length the breadth of the transverse 
 stria;. Sometimes such segments appear by alternate dark and 
 light parts of a continuous rectilinear fibril, as in the upper por- 
 tion at c, fig. 128. Sometimes the segments are marked oft' by 
 
 ' XX. vol. i. p. 10. 
 
 CLxxxv. p. 508. 
 
 lb. 
 
STRUCTURE OF MUSCLE. 
 
 201 
 
 constrictions, giving a scolloped border and beaded character to 
 the fibril, as in the lower portion, at c. Sometimes the striped 
 fibre cleaves into transverse portions or discs, fig. 128, B, a, h, 
 corresponding in breadth to the cross-stripes, and to the seeming 
 segments of the fibrils. 
 
 The following is the average diameter of the striped filjre, of 
 different classes, in fractions of an inch : — 
 
 Fislies 
 Reptiles 
 Birds 
 Mammals 
 
 frc 
 
 to 
 
 _i_ 
 
 1 o U 
 
 1 
 
 110 
 
 65 
 1 
 
 " 10 
 
 _J 
 
 " 3 5 
 
 1 
 
 " 1 91! • 
 
 Thus, among vertebrates, fishes, and in fishes the Skates {Jxaia), 
 have the thickest elementary striped muscular fibre ; and its 
 elastic tunic, the ' sarcolemma,' can be best demonstrated in them. 
 When the fibre is broken across, as in fig. 129, the sarcolemma a 
 may remain, connecting the severed portions, h, b. 
 
 The characteristic vital property of muscular fibre is to alter, 
 
 129 
 
 I'crtious of a Iji'ola'ii ulcmciitar; ( 
 l>y the untnrn t\\isf(?d sarci 
 
 ■llilimn. Jt,lii: b.ili:,. ri.xxxv. 
 
 under stimulus. Its relative dimensions of length and breadth. 
 When It becomes shorter and thicker it is said ' to contract ; ' and 
 Ijy these contractions the movements of the body, and of its parts, 
 are produced. 
 
 In the contraction of a smooth elementary nniscular fibre It has 
 been seen to grow thicker at a part, and shorter, without filling 
 out of the straight llne.^ In the contraction of a striped elemen- 
 tary fibre it has been seen to grow thicker at successive parts, by 
 approximation of the cross stripes, as in fig. 1.30, at a, a, a, along- 
 one side; or engaging the whole thickness of the fibre, as at b,b,b; 
 and these successive partial thickenings, with concomitant shorten- 
 ing of the fibre, have Ijeen termed 'waves of contraction.'^ 
 
 On the cessation of the act, the fibre may fall into zig-zag folds 
 
 CLXXXV. p. 510. 
 
 xciv. Editor's note, p. 261. (1837). 
 
 CLXxxv. p. 525. 
 
•202 
 
 ANATOMY or VERTEBRATES. 
 
 130 
 
 on resuming its length ; but it is commonly drawn out straight, as 
 before the contraction, by ' antagonistic ' muscles, in the living 
 animal. The uncontracted state of mus- 
 cular fibre is sometimes termed ' relaxa- 
 tion,' but is more properly a state of 
 quiescence or equipollency. 
 
 Muscles consist of series or bundles of 
 the elementary fibres, with their vessels 
 and nerves, connected together by areolar 
 tissue : either in lengthened or flattened 
 masses, fixed at the two extremities, called 
 ' solid muscles ; ' or disposed around cavities 
 or canals, and called ' hollow muscles.' 
 
 The non-contractile fibrous parts by 
 which the ' solid muscles ' are attached to 
 the endo- sclero- and exo-skeletons, are 
 called ' tendons ' when long and slender, and 
 ' aponeuroses ' when broad and flat. 
 § 46. M)/ologij of Fishes. — The modification of the active organs 
 of motion, and their deviation from the fundamental vertebrate 
 type, proceed concomitantly with the metamorphosis of the passive 
 organs, as Vertebrates rise in the scale and gain higher and more 
 varied endowments : therefore, as the segments of the skeleton 
 
 stages of contraction seen m an 
 elementary fibre of tlie Skate. The 
 uppermost state is that previous io 
 the commencement of contraction. 
 
 CLXXXV. 
 
 131 
 
 Muscular f.ystem, P^yra Jliiriatnis 
 
 preserve the greatest amount of uniformity in the lowest class, so 
 does the principle of vegetative repetition most prevail in the 
 corresponding segments of the muscular system. 
 
 The chief masses of this system in ordinary Osseous Fishes are 
 disposed on each side of the trunk, in a series of vertical flakes or 
 
MYOLOGY OF FISHES. 203 
 
 segments, corresponding in number with the vertebra3. Each 
 lateral flake {myocomma, fig. 131, a, b, c) ' is attached by its inner 
 border to the osseous and fibrous parts of the corresponding 
 vertically extended segment of the endoskeleton, by its outer 
 border to the skin, and by its fore and hind surfaces to an aponeu- 
 rotic septum common to it and the contiguous myocommas. The 
 gelatinous tissue of these septa is dissolved by boiling, and the 
 muscular segments or flakes are then easily separated, as we find 
 m carving a fish at table. The vegetative similarity of the myo- 
 commas of the trunk has led to their being described as parts of 
 one ' great side-muscle,' extending from the occiput and scapular 
 arch to the bases of the caudal fin-rays. The modifications of the 
 cranial vertebra3 impress corresponding changes on their muscular 
 segments, and special names have been conveniently applied to 
 their constituent, and in fact often separated and independently 
 acting, fasciculi. 
 
 The fibres of each myocomma of the trunk run straight and 
 nearly horizontally from one septum to the next ; but they are 
 peculiarly grouped, so as usually to form semi-conical masses, of 
 which the upper, a, and lower, b, have their apices turned back- 
 ward ; whilst a middle cone, c, formed by the contiguous parts of 
 the preceding, has its apex directed forward ; this fits into the 
 interspace between the antecedent upper and lower cones, the 
 apices of which reciprocally enter the depressions in the succeed- 
 ing segment, whereby all the segments are firmly locked together, 
 their general direction being from without obliquely inward and 
 backward, and their peripheral borders describing the zig-zag- 
 course represented in fig. 131, in which one myocomma is repre- 
 sented partly detached, and others quite removed from the side of 
 the abdomen. Thus, guided by the fundamental segmental type 
 of the vertebrate structure, we come to recognise the ' grand 
 muscle laterale,' of Cuvier, as a group of essentially distinct 
 vertical masses or segments. A superficial view of these seg- 
 ments, or an artificial analysis, has led to their being regarded as 
 forming a series of horizontal muscles, extending lengthwise from 
 the head to the tail : the upper jDortions, a, of the myocommas 
 being grouped together, and described as a dorsal longitudinal 
 
 ' Professor Goodsir proposes (cLxxvin.) to alter this term to ' myotome,' and to 
 substitute for ' yertebra ' or ' ostcocomma ' (cxli, 1849, p. 88) the term ' sclerotome,' 
 &c.: but this form of compound has been pre-engaged, for their -special cutting 
 instruments, by the sclerotomists, neurotomists, lithotomists, and other classes of 
 operating surgeons and their instrument-mailers. If the itch of change be uncontrol- 
 lable, I would suggest 'osteomere,' ' scleromere,' ' neuromcre,' &c. (Gr. ftf'pos, pari 
 instead of K6fiiJ.a, segment. 
 
204 
 
 ANATOMY OF VERTEBRATES. 
 
 muscle, with tendinous intersections directed downward and back- 
 ward — the lower portions, h, as a ventral longitudinal muscle, 
 with tendinous intersections directed downward and forward, 
 whilst the margins of the middle portions of the myocommas, c, 
 being curved, and usually bisected by the lateral mucous line, have 
 been taken as indications of two intermediate longitudinal muscles. 
 In the Sharks, instead of a curve the margins of the middle 
 portions of the myocommas form an angle with the aj^ex turned 
 forward, fig. 132; and in the Rays the dorsal portions have 
 
 :Mii3i'les nf fore larr (il .Shark {Sqv'du.fi (ilaucii^). XT.ijr, 
 
 Caudal sertion 
 MackarL'l. 
 
 actually become insulated from the middle ones, and metamor- 
 phosed into a continuous longitudinal muscle, fig. 1.39, a, the 
 133 change being essentially the same with that which the 
 bony segments themsch'es undergo, when by anchy- 
 losis the sacral or cranial vertebra; are blended into a 
 continuous longitudinal piece. In many bony fishes 
 the middle fibres of the caudal myocommas are dis- 
 ]iosed in two cones ; a transverse section of the tail 
 as in fig. 133, shows the two concentric series of cut 
 segments of the sheathed cones, on each side of the 
 spine. The portions of the myocommas above the lateral line 
 become grouped, in fish-like Batrachia and in Ophidia, into three 
 longitudinal muscles, comparable respectively to the ' spinalis 
 dorsi,' ' longissimus dorsi,' and ' sacrolumbalis,' the portions below 
 the line responding to certain intcrcostals and the ' rectus abdo- 
 minis,' of higher vertebrates. 
 
 The myocommas of one side are se]iarated from those of the 
 opposite side of the body by the vcrtebruN liy the intcrneural 
 and interliwmal aponeuroses, and by the abdominal cavity and its 
 proper walls, fig. 131, li,j,. The ventral portions rc(X'de from each 
 other to give passage to the \eutral fins, v, as in fig. 135, a : and 
 
MYOLOGY OF FISHES. 
 
 205 
 
 the ventral and lateral tracts separate to give passage to the pec- 
 toral fins, as at a, h, fig. 134. 
 
 From tills part forward, portions of the niyocommas undergo 
 that change, analogdus to anchjdosis, which justifies their being 
 regarded as distinc't longitudinal muscles : here the separated 
 ventral tract, fig. 135, a, derives a firmer origin from the clavicle, 
 and, ill consec[uence of the forward curve of the coracoid, it is 
 not i->n]y expanded hut lengthened out, in order to be inserted 
 there. But the serial homology of this fasciculus with the more 
 normal ventral portions of the succeeding myocommas, the h;ema- 
 pophysial attachments of which have not risen abo\'e the aponeu- 
 rotic state, is unmistakeable. The lateral portion of the anterior 
 myocomma, fig. 134, h,(j, is attached to the upper end of the coracoid 
 and to the scapula; the dorsal ])ortion,_/j to the suprascapula, par- 
 occipital and sujieroccipital. We recognise the dorsal portion of 
 tlie posterior cranial myocomma in the lasciculus called ' protractor 
 scapvdas,' fig. 134, c, the middle portion in that which is ox})osed 
 by the renroval of the operculum, and which extends from the 
 scapxda to the mastoid, fig. 137, 2G; the ventral portions in the 
 fasciculi continued from the coracoid forward to the hyoid, c, c. 
 
 134 
 
 Ic inusr)cs Qi licail, Pcrcli. xxxrir. 
 
 fig. 135 : the corresponding portions of the more anterior cephalic 
 muscular segments may be recognised in d and 27, fig. 135. 
 
20C 
 
 ANATOMY OF VERTEBRATES. 
 
 Other dismemberments of the cranial myocommas are specialised 
 to act upon the branchiostegal appendages, the branchise, the 
 ujiper and lower jaws, &c. ; and the chief of these, under their 
 special denominations will next be noticed. 
 
 The upper and lower jaws are so connected together in Osseous 
 Fishes that one cannot be moved without affecting the other, and 
 both are alike moveable. Protrusion and retraction affect them 
 equally, and usually to a greater extent than divarication and ap- 
 proximation, or the opening and sliutting of the mouth : in a 
 minor degree, also, the two halves of both maxillary and mandibu- 
 lar arches have transverse movements, varying the angle at which 
 they severally meet at the premaxillary or premandibular symphysis. 
 The most important retractor, wliich tends in that action also to close 
 the mouth, is the large subquadrate muscle, retractor oris, fig. 134, 
 20, 20, which arises from the tympanic pedicle and anterior border 
 of the preoperculum, and is inserted by the upjDcr fasciculus into 
 the maxillary ; by a lower fasciculus into the mandible behind the 
 coronoid process ; and by an aponeurosis into the membrane uniting 
 the two jaws near the angle of the mouth. The muscle which 
 tends to open the mouth by depressing the mandible, on which it 
 
 135 
 
 Lriwoi- niii.'jrles of hmd jiiKl fins. Perch, xxxrii. 
 
 exclusively acts, is that marked 27 in fig. 135 ; it arises from the 
 ceratohyal, and is inserted into tlie back part of the dentary, near 
 the sympliysis. Cuvier deems it the homologue of the qrniohy- 
 oideus. Above tlie insertions of tlic geniohyoid pair is a muscle, 
 the interynandib'idaris, fig. 135, 21, wliich passes transversely from 
 one dentary to the other, approximating the halves of the man- 
 
MYOLOGY or FISHES. 
 
 207 
 
 dible aftei- they may have been divaricated. The latter movement 
 depends upon the drawing upward and outward of the tympanic 
 pedicle. This action is performed chiefly by the muscle, levator 
 tyrnpani, figs. 134 and 137, 24, which arises from the postfrontal 
 and expands to be inserted into the epi- and pre-tympanics and 
 into the ectopterygoid. In raising or drawing outward the tym- 
 panic pedicle and attached part of the pterygoid, this muscle tends 
 to dilate the Ijranchial cavity and the back part of the mouth. It 
 is antagonised by the muscle, depressor tyrnpani, fig. 136, 22, 22, 
 which arises from the basi- and ali-sphenoids, and expands with 
 diverging fibres to be inserted into the epi- and pre-tympanics and 
 into the entopterygoid. It depresses the tympanic, or approximates 
 it to the opposite pedicle, and contracts the branchial cavity. 
 
 The movements of the opercular appendage are like those of its 
 supporting arch, and ai-e performed by muscles placed behind 
 those of that arch. The levator operculi, figs. 134 and 136, 25, 
 arises from the mastoid crest, and is inserted into the vipper and 
 outer part of the opercular bone. The dejjressor operculi, fig. 136, 
 
 13G 
 
 JInscles "t liyoid and (jpei'CLiIuiii, Percli. XXXIIT. 
 
 26, arises from the alisphenoid and petrosal, and is inserted into 
 the inner i-idge of the opercular bone. The retractor hyoidei, 
 fig. 137, 1 d, fig. 135, c, c, extends from the coracoid to the uro- 
 and basi-hyals, but is chiefly implanted into the sides of the 
 
208 
 
 ANATOMY OF VERTEBRATES. 
 
 former, and becomes through the medium of 27, a retractor of the 
 mandible. When the retractor hyoidei relaxes and the mandible 
 is the fixed point, the genio-hyoidei, fig. 135, 27, become pro- 
 tractors of the hyoid arch. In some fishes a transverse muscle, 
 repeating the characters of 21, fig. 135, passes from one ceratohyal 
 to the other. The branchiostegal appendage has muscles for rais- 
 ino- and depressing, divaricating and approximating the rays. The 
 levator hranchiostegorum, figs. 135 and 136, 28, arises from the 
 inner surface of the hinder half of the opercular bone and from 
 a contiguous part of the subopercular, and is continued from ray 
 to ray to the lowest, being loosely attached to their inner surface. 
 It forms a kind of muscular capside of the branclual chamber. 
 The depressor hranchiostegorum, fig. 135, d, arises from the lower 
 end of the ceratohyal and passes obliquely backward, crossing 
 its fellow, to be inserted into the inferior branchiostegal ray. 
 These muscles regulate the capacity of the branchial chamber, 
 
 137 
 
 and mainly act njion the water it contains : they show accord- 
 ingly much diversity, especially 2s, in relation to the respiratory 
 characteristics and comiected peculiarities in different fishes. In 
 
MYOLOGY OF FISHES. 200 
 
 the Anglei- (Lophius) the levator is enormous, forming tlie wall 
 of the capacious reservoir on each side and behind the gills, and 
 uniting extensively with its fellow at and beyond the urohyal : 
 each long branchiostegal ray has, likewise, its peculiar muscles, 
 originating from the sui)porting arch. In the Aii/juilUdce the 
 isthmal vmion or raphe of the levatores reaches from the basi- 
 ancl uro-liyals to the coracoid. 
 
 The l^ranchial arches are supplied with muscles attaching them 
 to surrounding parts, or passing from one part to anotlier of the 
 arch itself. 
 
 The branehi-levatores, fig. 137, 3, arise from the allsphenoid and 
 divide into four fasciculi, respectively inserted into the epibran- 
 chlal of its own arch. The vMsto-hrancldulis, ib. 2fi, arises from 
 the extremity of the mastoid, and divides into two fasciculi, one 
 i7iserted into the foiu-th epibranchial, the other into the third 
 pharyngol^ ranch ial and the contiguous part of the pharynx. 
 
 The brauchl-retractorcs consist of two fasciculi, one superior, 
 fig. 137, 37, which arises from the upper half of the coracoid, 
 passing horizontally to its insertion : the other inferior, ib. 32, 
 passing from the lower part of the coracoid obli(j^uely upward : 
 they retract and partly depress the branchial arches. 
 
 The hrancld-dejjrcssor, fig. 137, 35, arises from the basihyal and 
 ascends obliquely backward to its insertion into the cerato- 
 branchials : it is the more direct antagonist of the levatores. 
 
 The protractor scapula;, fig. 1 34, e, arises from the back ] lart of 
 the masto-parietal ridge, and is inserted into the coarticulated 
 parts of the suprascapula and scapula. The middle portion of the 
 great lateral muscle, ib. g, li, serves, by its insertion, as a retractor 
 scapiilcE. The corresjionding insertion of the lower portion of the 
 great muscle into the coracoid retracts that part of the scapulo- 
 coracoid arch, and is so modified as to have received the name 
 syjjcoracoideus, ib. a, fig. 131,/'. 
 
 The muscles of the pectoral fiji form a pair, in two layers, on 
 both the outer and inner sides of its antibrachio-earpal base : and 
 the fibres of one layer run obliquely in a different direction from 
 those of the other layer in both pairs of muscles. The outer pair 
 abducts or protracts the fin, the inner pair adducts or retracts it, 
 sweeping it back into contact with the flank : the first movement 
 might be called 'extension,' the second, 'flexion.' The superficial 
 abductor, fig. 134, 14, arises from the upper and outer part of the 
 coracoid ; it tends to elevate as well as extend the pectoral : the 
 deep abductor, fig. 137, 15, comes from the outer border of the 
 lower part of the coracoid ; it depresses as well as extends the fin. 
 
 VOL. I. P 
 
210 ANATOMY 01? VERTEBRATES. 
 
 The lower portions of both muscles are shown in fig. 1.35, U, 15. 
 Of the inner pair of muscles, a portion of the deeper layer, dis- 
 posed so as to raise as well as addvict the pectoral fin, is shown at 
 iG.ficr. 1-37. Each muscle is inserted into the bases of the fin-ravs, 
 resolving itself into fasciculi and short tendons corresponding in 
 number with those rays : by diflFerent comljinations of action these 
 fasciculi di-sarioate or ajiproximatc tlie rays. 
 
 The ischial basis of the ventral fins in abdominal fishes may be 
 moved a little forward or backward liy the action of the ' infra- 
 carinales ' according as they lie in front or behind the pelvis. 
 The latter, ' retractor ischii," fig. 131, lo, pass backward to the 
 vent, inclose it, and are continued to the base of the anal fin. The 
 protractor ischii, fig. 135, IS, passes forward to be attached to the 
 lower end of tlie coracoid. The protractors are short in thoracic 
 fishes, e. g., the Perch, and less distinct from the lower parts of 
 the myocommas than in ventral fishes, e. g., the Salmon. In 
 fishes, e. g., the Lophius, where the ischia are wide apart, there 
 is a transverse muscle to draw them together, and antagonise 
 the portions of the side muscles that tend to draw them further 
 apart. The muscles which act upon the ^•entral rays, like those 
 of the pectoral ones, form a pair, or two layers of slightly decus- 
 sating fibres, on both the outer and inner sides of the base of the 
 fin. The outer or inferior muscles, fig. 135, IG, 17, depress or 
 extend the ventral fins ; the opposite muscles raise or flex them. 
 Tlie ]iortion of the deeper depressor shown at 17, fig. 135, serves 
 to exjiand or dilate the ventrals. 
 
 The movements of the rays of the median fins are effected 
 by three or four pairs of small muscles attached to each ray. 
 The superficial ones, fig. 131, .r, arising from the skin, are 
 inserted into the sides of the base of the dermoneural or dermo- 
 ha3mal spine. The deep ones, ib. y, arise from the interncural 
 or interhffimal spine, and are inserted into the base of the 
 dermoneural or dermoluxjmal spine : the anterior of these, fie 
 137, 3, erects the spine ; the posterior, ib. 4, depresses it. The 
 myocommas answering to the neural and hwmal spines of the 
 coalesced or suppressed centres of the terminal caudal vertebra\ 
 change their direction like those spines, slightly divero-ing from 
 the axis of the trunk to l)e inserted into them : these modified ter- 
 minal segments, liy their connection with the interlocked myo- 
 commas of the great lateral masses, concentrate the chief force 
 of those muscles upon the (\audal fin. The rays of this im- 
 portant fill are mo\'ed by three series ol' nniscles,' the one super- 
 ficial, the second deep-seated, tlie third interspinous. The 
 
]\[TOLOGY OF FISHES. 211 
 
 superficial mxisclc, arising" i'rom tlie temiinal aponeurosis of the 
 'lateral nuiscle,' cxpaiuls and separates i'an-wise, fig. 131, z, to its 
 insertion into the bases of the caudal rays. Tlie deeper-seated 
 lascicles are ex])osed l)y tlic removal of the foregoing and tlicir 
 ajioneurotic origin, and arise from the coalesced terminal centrums 
 oi the caudal vcrtehra;, to l)e inserted further from the basal joints 
 of tlie rays, and more advantageousiy ibr effecting tlie movements 
 wliich alter the spread of the tail-fin. Slender longitudinal mus- 
 cles, suj)ra-cariii,ulcs, extend along the mid-line of tlie Ijack from 
 the occiput to the first dorsal, and along the interspaces of the 
 dorsal fins in the Cod : similar muscles, fig. 1.31, u, extend from 
 the hist dorsal to the caudal fin in the Perch ; and infrn-cdri- 
 iialcs, ib. V, extend from the anal to the caudal along the keel of 
 the tail. In the Gymnotus the su])ra-carlnales form a single pair, 
 which extends from the occij)ut to the end of the tail. The modi- 
 fied cranio-dermal spines, which constitute the oval sucking-disc 
 of the Remora, \vx\e a complex series of minute muscles, which 
 raise or depress the transverse lattice-work ; and thus become tlve 
 means of giving the little feeble fish all the advantage of the i"apid 
 course of the whale or the ship to which it may have attached 
 itself. The muscular and membranous webs of the coalesced jjec- 
 torals and ventrals of the Lump-fish, form a sucker on the opjio- 
 site surtirce of the body, by which it may safely anchor itself to the 
 rock, in the midst of the turbident surf or storm-tossed breaker. 
 
 There are many modifications of the muscular system in the 
 orders at the two extremes of the class. 
 
 The segmental disposition of the muscular masses is most 
 simple, most distinct, most like the annulose type, in the Cijdo- 
 stomi : yet it is considerably specialised for the due working of 
 the suctorial apparatus. In the Lamprey, fig. 138, slips are con- 
 tinued or derived from the anterior part of the myocommas, for 
 drawing back, bending in different directions, and ex])anding the 
 mouth. Of these, the superior, e, is inserted into the cartilage, 
 fig. 24, 20 ; raises and fixes it, giving a fulcrum and favourable 
 direction tor the muscle, fig. 138, h, which directly retracts and 
 raises the sucker, a: the inferior slip,/, is inserted into the pro- 
 cess, fig. 24, (J, and into the lower border of the gristly l)ase of the 
 sucker, ib. 22 : it retracts and depresses the sucker. An interme- 
 diate lateral slip, inserted a little higher upon the margin oi' q, fig. 
 24, retracts and draws outward the sucker. All these retractors, 
 co-operating, serve to expand the sucker ; or, if duly antagonised 
 by the spli.iiicter oris, pull back the object seized by the sucker, or 
 draw tlie body of the fish towards it, according to the fixed jtoint. 
 
 P 2 
 
212 
 
 ANATOMY OF VERTEBRATES. 
 
 138 
 
 Shorter muscles arise, above, from the cranial cartilage, fig. 24, d, 
 and below, from the liyoid cartilage, to act upon parts of the sucker ; 
 the latter, (j, h, diverge to their insertions. Part of the deep- 
 seated longitudinal expansor oris, more directly antagonising the 
 circular sphincter oris, a, is seen at m, fig. 136. 
 
 Details of the myology of the Myxinoids with a comparison of 
 the muscular system of Fislies with that of liigher Vertebrates, will 
 be found in xxi. ])p. 179-249. 
 
 In the Trunk-fish ( Osfracioii) flexion of the trunk is abrogated 
 
 by the case of ganoid armour, fig. 1 6, 
 chi, dh, inclosing the Ijody, and which 
 leaves only the jaws and fins free. 
 The myocommas are accordingly re- 
 duced to a thin layer of longitudinal 
 fibres, modified posteriorly for inser- 
 tion into the moveable part of the 
 tail and its fin. 
 
 In another plectognath, the odd- 
 shaped Sun-fish ( Orthngoriscus^ the 
 muscles of the continuous vertical fins 
 take the place of the ordinary myocom- 
 mas : those of the lofty dorsal com- 
 mencing behind the occiput ; those of the deep anal liehind the 
 short abdomen : the dcrmoneurales arise from tlie integument, 
 especially the fibrous septum of the lateral line ; the deeper-seated 
 interneurales from the neural and interneiiral spines. Each series 
 is more or less blended together, conformably with the degree of 
 confluence of tlie interneurals, upon the e.\])anded ends of which 
 the spines of the dorsal fin move as one body, the anal fin having 
 a similar structure. Nevertheless, towards their insertion, the 
 fasciculi of the fin-rays become, like them, distinct ; each one 
 beliind being sheathed by the one in front, and their long tendons 
 passing through lubricated grocncs or sheaths to their insertions. 
 On the sides of the abdomen tlic muscles are reduced to two fas- 
 ciculi, expanding, the one from the clavicle, the other from the 
 coracoid, upon the ])eritoneum.' 
 
 Amongst tlie Fkujiostomi , the Sharks are the most active and 
 powerful, and in tbcm the muscular system is most developed, and 
 in certain parts most specialised. The more acute angles formed 
 by the bitermyoconnnal septa have already been noticed, fig. l.')2. 
 A fasciculus c(mtinued from the up])er portion is iuserlcd, by a 
 strong aponeunisis into the upper part of the cranium, ib. «, a. 
 
 Muscles of hfud ninl sui'ker; Lamprey, 
 
 XLIII, 
 
 y.\.\\. ;iinl cxrvii. 
 
MYOLOGY OF FISHES. 
 
 213 
 
 The muscles of the jaws are very powerful, as might be expected 
 ill these fierce and predatory fishes. One, analoti'oiis to the ' tem- 
 
 poral,' fig. 13i 
 
 III, arises 
 
 from the lateral and posterior ridge of 
 
 139 
 
 the cranium, and its fibres converge as they pass obliquely down- 
 ward and forward to their insertion into the mandible. They are 
 covered in great part l^y the stronger muscle ib. /, analogous to 
 the ' masseter,' which arises from the under part of the postfrontal 
 ridge, passes over the maxillo-mandibular joint, as over a pulley, 
 a.nd expands to its insertion in the lo"\ver side and ridge of the 
 hinder two-thirds of the mandible. Smaller muscles, ' inaxillo- 
 }iian(llhul(n-es,' ib. fj, pass from the upper to the lower jaw, and 
 directly close the mouth. Tlic openers are chiefly the mus- 
 cles, ji, which have their chief fulcrum in the coracoids, 
 and ex])and to be inserted into the .symphysis mandibular. 
 The gill-apertures arc contracted by the muscles, q, q, and di- 
 lated by others passing oljlitpicly from abo^e to their front boun- 
 daries. The muscular invest- 
 ment of the branchial chamber 
 of the Torpedo fig. 139, r, re- 
 ceives a fascicidus from the 
 scapula, and sends another, 
 \h. o, forwards to the cra- 
 nium, from which the con- 
 strictor of the electric bat- 
 tery, E, is continued. The 
 jrrntractor scapula: in the 
 Skate and Torpedo is of con- 
 siderable length, in conse- 
 quence of the backward dis- 
 placement of the scapular 
 arch, and is of great strength, 
 by reason of the enormous 
 pectoral appendage which 
 tlie arch sustains. The myo- 
 commas of the trunk are 
 fused into four great longitu- 
 dinal masses. The neuro- 
 medial mass, fig. 139, a, ^'"' 
 
 arises from the scapula, S, and by strong carneous fasciculi 
 I'rom the vertebrre behind the scapular attachment : above the 
 pelvis they divide into tendinous slips, which pass backward 
 in separate sheaths, to be successively inserted into each vertebra 
 as far as the end of the tail. The neuro-lnteral mass or muscle, 
 
'214 ANATOMY OF VERTEBRATES. 
 
 ib. c, arising from tlie outer j^iart of the scapula and from the 
 parapophyses of succeeding vertebras, is inserted by similarly 
 disposed, but more slender tendons. At their termination, each 
 tendon bifurcates, allowing that appropriated to the succeeding 
 vertebra to pass through it, so that all, save the last, are both 
 perforati and ■perforuntes. The protractor scapula, ib. i, be- 
 comes, when antagonised by the two foregoing muscles, the 
 chief elevator of the head. Of the two muscles of the ros- 
 trum in the Ray, the siiperior, levator rostri, arises from the 
 scapula by a short fleshy Ijelly ending in a slender round tendon 
 which runs above the branchia; in a synovial sheath to the rostral 
 cartilage, which it serves to raise : the inferior, dcprcHsor rostri, 
 arises from the lower part of the coalesced anterior vert el)ra3, runs 
 obliquely outward, and then curves inward to its insertion into the 
 lower ])art of the liase of the rostrum. The muscles of the jaws 
 in the Kays include, with 'inaxillo-mandilulares, those answering 
 to I and lit in the Shark, fig. 132. The depressor mandibuU is a 
 large oblong mass of parallel hmgitudinal filires, arising from the 
 lower (coracoid) part of the scapular cincture, and passing forward 
 to be inserted into the raid part of the mandilile. Two small mus- 
 cles, one on each side, contribute to depress the mandilile : they 
 are attaclied in front near the commissure of the lips, and, running- 
 inward, almost cross each other beneath the great depressor. A 
 third muscle has its fibres remarkably interlaced, but divisible into 
 three chief fascicles, two of which arc anterior and one posterior : 
 this is derived from the end of the upjter jaw and joins the hinder 
 margin of the second mass. The first portion is situated in front 
 and abo\e the maxilla, near its conmiissurc, and riuis obliquelv to 
 join the outer edge of the second fixscicle : all co-operate in firndy 
 closing the mouth. Tlie p>rotractor oris forms a pair of long and 
 slender muscles passing from the rostrum l:)etween the cranial base 
 and tlic palate to be inserted into the maxilla. The muscles of 
 tlie vast pectoral fins form two thick fleshy layers, covcrinn- its car- 
 tilages above, fig. 139, t, and below, and dividing into as many 
 fasciculi as there arc fin-rays, into which they arc inserted. A 
 similar arrangement obtains in the muscles of the ventral fins, ib. i\ 
 
 The muscles, in Fishes, of the eye-ball, the air-bladder, and of 
 some other special organs, will be described with tlie parts they 
 move. 
 
 The nuiscular tissue (rayonine) of fishes is usually colourless, 
 often opaline, or yellowish ; white when boiled : the muscles t>f 
 Ihe j)ectoral fins of the Sturgeon and Sliark are, however, dee]ier 
 coloured than the others ; and most of the nuisclcs of the Tunny 
 
MYOLOGY OF KEPTILES. 215 
 
 ure red, like tliose of tlie wnmi-ljloodcd classes. The want of 
 colour relates to the comparatively small proj)ortioii of red 1)lood 
 circulated through the muscular sj-stcm,' and the smaller propor- 
 tion c)t red-particles in the blood of fishes : the exceptions cited 
 seem to de])end on increased circulation with great energy of 
 action ; and, in the Bonito and Tunny, with a greater quantity of 
 Mood and a higher temperature- than in other fishes. The deep 
 orange colour of tlie fiesh of the Salmon and Char depends on a 
 ])ecidiar oil diffused thi'ough the cellular sheaths of the fibres. 
 The muscular fasciculi of Fishes are usually short and simple: 
 and very rarely converge to be inserted by tendinous chords.'^ The 
 projjortion of myonine is greater in Fishes than in other Verte- 
 brata; the irritability of its filtres is considerable, and is long re- 
 tained. Fishermen take ad^•antage of this property, and induce 
 rigid muscidar contraction, long after the usual signs of life haAO 
 disappeared, by transverse cuts ajid immersion of the muscles in 
 cold water : this operation, by which the firmness and specific 
 gravity of the muscular tissue are increased, is called ' crimping.' 
 
 § 47. JSIyology of Rtqit'des. — The my(jniiie of the air-breathing 
 lliematocrya is always pale in colour, and the fibres arc tenacious 
 of their irritability : the energy of the muscular contraction is in 
 some instances, and on some occasions, great ; but cannot he ex- 
 cited in frequent succession, such power being soon exhausted. 
 
 In the ichtliyomorphous Batrachia the recent myonine pi-esents 
 a pearly clearness, as in some fishes, and the chief bulk of the 
 tissue is arranged in transverse segments, of which, however, the 
 jirogress of massing into longitudinal groups is greater than in the 
 Sharks. In the Salamander, figs. 140, 141, the neural or U})per 
 halves of the myocommas, separated at the midlijie of the l^ack by 
 a furrow lodging cutaneous follicles, have a tendency to group 
 themselves into distinct longitudinal tracts, as they advance for- 
 ^s'ard : just as their liomologue — the common ' erector spina) ' in 
 man — srdidivides into the longitudinal masses called ' sacro-lum- 
 balis,' ' lougissimus dorsi,' and 'spinalis dorsi,' &c., in its corres- 
 ponding course. The median portion, fig. 140,5 «, in Salamandra, 
 i-epresenting the spinalis dorsi in the trimk, has its anterior 
 insertions in the neural arclics and spines of the cervical and occi~ 
 ])ital vertebras; and there answers to the ' spinaHs ' and ' seniisj)!- 
 nalis ' colli, and to the ' biventer cervicis ' and ' complexus.' The 
 lateral portion, answering to the longissinuis dorsi and sacro-lniii- 
 halis in the trunk, represents, by its insertions, the ' transversalis 
 colli' and trachelo-mastoideus, fig. 140, 5, in the neck. The hremal 
 
 ' XLvni. lip. 4, IG. ^ L. ' XLix. p. 3. 
 
140 
 
 216 ANATOMY OF VERTEBRATES. 
 
 I[ \ 01^ lower half of the myocommas in the 
 
 trunk, fig. 140, 6, has been held to represent 
 
 8 1^ iW - the ohUquus externus ahdominis ; but, as it 
 
 is segmented by aponeurotic prolongations of 
 the short jileurapophyses, both in the abdo- 
 minal and caudal regions, it is more like a 
 series of intercostals. The broad, thin, car- 
 ncotendinous sheets, called ' external ' and 
 ' internal oblique ' muscles in Mammals, hav- 
 ing their fibres running in opposite directions, 
 may, indeed, be referred to the same system 
 of segmental trunk-muscles ; but this grade 
 of dliferentiation is not reached in Fishes 
 and fish-like Batrachians. The medial parts 
 of the hremal myocommas are more distinct, 
 and show more of the character of a longi- 
 tudinal nmscle with tendinous intersections, 
 like the ' linear transversa3 ' of the human 
 ' rectus abdominis ;' and this muscle is one 
 of the determinable homologues of a recog- 
 nisable tract of the myocommas of the fish 
 and newt. In the Salamander, however, 
 the tract, fig. 141, ?, is as superficial as that 
 part of the sheath of the ' rectus abdominis ' 
 in Mammals ; and it forms a corresponding 
 ]iart of the sheath of a deeper-seated longi- 
 tudinal muscle, fig. 141, 7. Both 7 and 8 
 are specialisations of the lowest hcBnial por- 
 tions of the myocommas : thej' are anteriorly 
 resolved, or continued, as in Fishes, into 
 muscles acting upon the scapular, hyoidcan, 
 and mandibidar arches. The jiuholnjoidcus, 
 7, arises from the pubis and outer part of 
 the gristly ha>mapophysis, or Y-shaped 
 cartilage, fig. 113, d\ it runs forward 
 in a sheath, analogous to that formed 
 by the aponeurosis of the external and in- 
 ternal oblique muscles of jMaunnals, and is 
 inserted into the ceratohyal. The muscle, 
 s, called rertus ahdoiiiiiiis, by Funk,' has its 
 attacluncnt to the pubis througli the medium 
 <if the Y-slinpcd cartilage, wliich represents 
 llie marsupial bones and tendinous ' pillars 
 t»f the abdominal ring" in jNIannnals : it is 
 
MYOLOGY OF REPTILES. 217 
 
 attached anteriorly in part to the triangular short sternum, ex- 
 tending beyond it to the transverse part of the episternum, and 
 is thence continued (as in fig. 1.35, 27), to the symphysis mandi- 
 bnhtt, representing the fjeninlii/oideiis. A small fasciculus, fig. 141, 
 10, is also sent to the coraco-scapular joint. 
 
 The up])er jaw is fixed. The muscle which, hy its insertion 
 into the lower jaw, acts as a teniporalis, is divided into two 
 fasciculi ; one, fig. 140, 2, has the normal origin from the side of the 
 cranium; the other, il). 1, atlanto-mandihularh, acts with greater 
 force by deriving its origin from the neural arch and spine of the 
 atlas. The maxxfter, ib. 3, arises from the mastoid and ejiitym- 
 panic, and is inserted into the outer surface of tlie hinder half of 
 the mandil)le. The occipi.to-iiKmdihularis, or diijastricus, ib. 4, 
 arises fi'om the parocci])ital and Ijack part of the epitympanic, 
 and is inserted into the angular element behind the tymjiano- 
 mandibidar joint whereby it opens tlie mouth. In this action it 
 is aided by the strip, ib. 1:3, which ])asses from the angle of the 
 jaw upward to the skin. Some amovmt of lateral movement of 
 the mandible is effected by a ptcrijr/oid muscle. The retraction of 
 the mandible is provided by the nniscle, ib. 1.3, although it seems 
 lost in the skin, as it passes backward from the angular process. 
 A mi/hdiijoidens, fig. 141, n, passes from one ramus to the other, 
 external to the gcniohijoideiii!, ib. 8/, and to the following 
 muscles of the hyoid arch. The gviiio-ceratoldeas, ib. 14, arises 
 from near the symphysis mandibuhis, and is inserted into the cera- 
 toliyal. Tlie lu/obranchicdix, \h. 15, passes from the base of the 
 ceratohyal to the hyobranchial cornu. 
 
 Witli the growth and specialisation of the segments of the 
 limbs the muscles became larger, more numerous, and more dis- 
 tinct. The pectoralis,-&g. 141, I6<i, 16, has its origin extended from 
 the fore part of the coracoid and epistermun to the linea all;)a, or 
 aponeurotic continuation of the stcrmun, half an inch beyond the 
 coracoid ; the fibres converge to their insertion into the pectoral 
 ridge of the humerus ; but so that the coracoid portion is almost 
 a distinct muscle. This muscle suspends the fore part of the 
 trunk upon the fore-legs, and besides depressing the humerus, 
 rotates it in the plane of the body's axis as different portions of 
 the muscle come into action. 
 
 A muscle, fig. 140, 11, arising from scattered filires by a longi- 
 tudinal tract of the aponeurosis, covering the lonrjhsiinus and 
 spinalis dorsi, collects those fil^res and contracts as it descends 
 over the hijid part of the scapula to be inserted into the liack part 
 of the pectoral ridge. An anterior part, ib. 22, of the same 
 
218 
 
 ANATOMY OF VERTEBUATES. 
 
 Ill 
 
 system of converging fibres 
 takes its origin from the 
 scapula itself, and converges 
 to an insertion close to that 
 of the preceding. The entire 
 mass of the muscles 22 and 
 11 antagonise that, 16, ica, 
 below ; one raises, the other 
 ^ji depjrcsses, and both rotate, 
 '*'' the humerus to and fro. As 
 the fore-limb gains size and 
 power in higher air-breathers, 
 the muscle 11 seeks a more 
 extended origin, covers a 
 greater proportion of the seg- 
 mental system of trunk- 
 muscles, acquires the name 
 of latissiinns dorsi, and, in 
 Anthropotomy, is classed 
 amongst the ' first layer of 
 the muscles of the back.' The 
 muscle 22, becomes deve- 
 loped into ' supra- ' and ' in- 
 fra-spinafus,^ and, perhaps, 
 also deJ/o'idcs. The pro- 
 
 tractor scajiiihp, arising, as in 
 Fishes, from the paroccipital, 
 now also derives fi1)rcs from 
 the transverse processes of the 
 first and second truidv-verte- 
 bra;, and divides into two dis- 
 tinct liisciculi ; one, fig. 140, 
 
 19, is inserted into tlie base 
 of the scapula ; the other, ib. 
 
 20, into the humeral end of 
 that bone. A small strip, is, 
 which tends more directly 
 to raise the scapida, arises 
 from the transverse proces- 
 ses of the third vertebra : but 
 tlie muscle, i;i, is tliat wliich 
 l>est answers to the Irrtitor 
 scapuhc of Mammals. Two 
 
MYOLOGY or REPTILES. 219 
 
 strips Iroin the second and tliird cervical diapopliyses, inserted 
 into the under ])art of the scapula, indicate the commencement of 
 tlie serratiis vuii/nus aiif.iciis, fig. 141, 21. The mass of muscle, 
 fiji;s. 140, 141, 23, wliich protracts or 'flexes' the fore-arm, aris- 
 ing from the fore and inner part of the glenoid cavity and from 
 tlie fore part of tlie luimerus, represents the blcrps and hraclikdh 
 niterims. Tlie retractor or extensor mass, ib. 24, answers to 
 tlie divisions of the triceps. On the aiitibrachiam the flexor of 
 the wrist is divided into a 'radial,' fig. 141, 25, and ' idnar,' 
 fig. 140, 2G, i)ortion ; as is likewise the extensor, of which, 27, 
 fig. 141, represents the extensor c/irjri idnarh, and 28 the extensor 
 carpi. riid/'aUs : 29 is the flexor cliijitoram coinmunia, and 30 the 
 extensor diijitorum cornrnnrds. 
 
 The pectoreilis, fig. 141, lo, is represented in the pelvic limb 
 by the muscle, ib. 3C, wliicli arises from the ischiopubic syni- 
 }ihysis, and is inserted into the front and inner part of the 
 head of the tibia. This mass in higher reptiles becomes dif- 
 ferentiated into the pectineus, the adductors, and the i/racdis ; 
 it depresses and adducts the pelvic liml). Its chief antagonist 
 is marked 36 in fig. 140. It rises from the ilium, and is inserted 
 into the lower and outer part of the femur, and also into the 
 outer part of the head of the, tibia; it corresponds by its origin 
 with 22 in tlie fore limb, and becomes develo2)ed into gluteus 
 exteruus Mxd ' tensor fascice fenwris^ m Mammals. The fasciculi 
 wliich correspond with 11, in the fore-limb are 37 and 32, fig. 140; 
 tliey arise from fascia connected with tlie transverse processes of 
 the third and fijurth caudal vertebra^, and are inserted into the 
 middle and back part of the femur. The muscle, 31, which arises 
 from the fore part of the ilimri, and is inserted into the upper 
 third of the femur, rejieats the anterior filn-es of 22 in the scapular 
 limb. The chief difference is that the pnjtractors, 31, and retrac- 
 tors, 32 and 37, of the thigh are more distinct from the abductor 
 and levator, 36 ; and that this has a more ad^^antagcous insertion 
 fir its office Ijy being extended to the second segment of the 
 limb. The retractors, 32, 37, act like the latissiinus dorsi 11 : their 
 origin is in connection with the vertebral or axial system : they 
 l^ecome developed in the pelvic limb of liigher animals into parts 
 of the ' glutei ' and ' pyriformis.' 
 
 Tlie protractors or flexors of the thigh, 34, 3;j, which answer t(j 
 those of the arm, 23, arise from the fore and under part of the 
 ilium, and are inserted into the fore and upper end of the tibia. 
 The muscle, fig. 141, 35, which passes to the inner side of the head 
 of the tibia, answers best to the surtorius ; the larger mass on its 
 
220 ANATOMY OF VERTEBRATES. 
 
 outer side, S4, to the triceps extensor cruris, and more especially 
 to tlie rectus femoris, as Iiaving its chief origin from the ilium ; 
 whilst its tendon expands over the fore part of the knee joint, as 
 that of 23 passes over the fore part of the elljow joint ; and both 
 witliout having any sesamoid lever developed therein. 
 
 The retractors or extensors of the thigh and leg, ib. 33, answer- 
 ing to the retractors of the arm and fore-arm, 24, arise from the 
 hinder and outer part of tlie ilium, and are inserted partly into the 
 femur, partly into the outer part of the head of the tibia. A 
 muscle, fig. 141, 38 {sacro-plantdris^, forming part of this system, 
 has a special extent and disposition, favouring the effective ]:)ack- 
 "ward stroke of the foot in swimming : it arises from the sacral rib 
 and is inserted into the plantar fascia. It is a ' flexor ' of the leg, 
 like tlie ' biceps flexor crviris :' it is an ' extensor ' of the foot, like 
 the ' plantaris.' And here a few remarks may he offered on the 
 terms ' flexion ' and ' extension,' as applied to the ' fore-arm ' and 
 ' leo; ' in higher air-breathino- Vertebrates and in Islaxi. 
 
 The fore and hind limbs of the Salamander are figured extended 
 in corresponding positions, in fig. 140, as those of the Plesiosaurus 
 are represented in fig. 4.5. The ulna is external or posterior in the 
 arm, the fibula in the leg. If, in the dead newt, the fore-arm be 
 moA'ed upon the arm to and fro, in the direction of tlie trunk's axis, 
 it can be bent at an angle with the arm eitlier way ; and the like 
 would most probably be the case in the Plcsiosaur : there is 
 no bony configuration of the elbow-joint to prevent this in either 
 reptile ; only the ligaments favour the forward bend more 
 than the hinder one, in the batrachian. In the hind limb the leo- 
 can be bent at an angle with the thigh, both forward and back- 
 ward ; but the ligaments of the joint offer more resistance to the 
 forward than to the backward bend. As we ascend the verte- 
 brate scale in the comparison of limbs, a lione of the fore-arm 
 sends a process across the back part of the elbow-joint which 
 fits into a cavity in the bone above the joint when the two are 
 Ijrought into the same line ; and the fore-arm cannot be bent 
 Ijaclc at an angle with the arm without fracture of the inter- 
 locking bar or ' olecranon.' In the leg the contrary bend, at an 
 angle forward u]ion the tliigh, is prevented )iy configiu-ation of 
 the knee-joint, with intcrarticnlar cartilages and ligaments. 
 
 Thus tlie forward licnd is favoured in the fore-lind.i ; the l)ack- 
 ward bend in the liind lindi. 
 
 In quadrupeds tlie linil)s are haliitually retained with tlie first 
 and second segments more or less bent in the directions favoured 
 by tlie configuration of the elbow-joint and knee-joint respcc- 
 
MYOLOGY OF REPTILES. 221 
 
 tively, to which the muscles conform in relative size and posi- 
 tion. These opposite l^ends are sh(jwn in the skeleton of the 
 Crocodile, fig. 57. 
 
 When the leg, 66, is hrought forward (protracted), widening the 
 angle between it and the thigh, v, and when the fore-arm, 55, is 
 brought forward, contracting the angle between it and the arm, 
 53, the motions are the same, or homologous in both limbs. But 
 in one case such motion is called ' flexion :' in the other ' exten- 
 sion :' these terms relating not to the absolute line or direction of 
 motion of the lind), but to the resulting relative pjosition of one 
 segment of the liml:) to another. The protractor muscles draw- 
 ing forward the second segment of the limb to an angle ^vith 
 the first, are called 'flexors;' those drawing forward the second 
 segment y)7;i»( an angle with the first, are called ' extensors.' The 
 same distinction is made with the ' retractors,' according as, in 
 drawing back the second segment, they rotate it from an aiigle 
 to a straight line with the first segment, or from a straight line t(j 
 an angle. Thus the homologous movements are signified by dif- 
 ferent terms, and the homotypy of the muscles has been masked 
 by tlie same artificial verbal distinctions. The ' flexors ' of the 
 fore-arm answer to the ' extensors ' of the leg in serial homology. 
 The ' biceps flexor cubiti,' with the ' Ijrachialis anticus,' is the 
 homotype of the ' triceps extensor cruris,' not of the ' biceps flexor 
 cruris ;' while this muscle, with tlie semitendinosus, is the homotype 
 of the ' triceps extensor cubiti.' Much of the difficulty of com- 
 prehending the true serial homology of the parts of the fore and 
 hind limb has arisen from regarding tlie flexors in the one liml) to 
 )je the h(jmotypes of the flexors of the other, and vice versa. The 
 pertinacity with which the idea of the patella being the homotype 
 of the olecranon is maintained, depends in a great degree \\\)on the 
 error of sujiposing the ' triceps extensor cidjiti ' and tlie ' biceps 
 extensor cruris' to be homotypes or serial homologues.' 
 
 Returning to the Newts, we find the chief retractor or extensor, 
 fiw. 141, 39, of the foot answering to the retractors or flexors of 
 the carpus, 25 and 26. But, as regards the toes, since their joints 
 are so arranged as to allow them to l)e most easily and extensively 
 
 ' Some anatomists assuming this to be a matter determined and unquestionable, 
 make it the basis for impugning tlie opinion that the patella answers serially to the 
 tendon of the bieeps brachii, and especially to the sesamoid sometimes developed 
 therein. " Unless we are entirely to disregard the guidance of muscular relations 
 in determining homology, we must admit that the ossicle upon the olecranon is the 
 homotype of the patella," &c, clxxi. p. 21, and clx. passim. The muscular 
 concur with the osseous relations in showing that the ossicle upon the olecranon is 
 the homotype of that upon the pcronecranon, or produced head of the libula in 
 certain marsupial and other manunals. clxi. pi. 1, fig. 16. 
 
222 ANATOMY OF VERTEBRATES. 
 
 moved in tlie direction of ' retraction,' as the limbs hang in fig. 140, 
 tlie 'flexors ' of the fingers have their homotypes in the hind limb 
 called ' flexors of the toes,' and the mnscles effecting the opposite 
 movements of the digits are termed ' extensors ' in both fore and 
 hind limbs. The muscle, 40, arising from the fascia of the knee, 
 becomes by its insertion the extensor longus digitorum pedis. 
 The muscle, 41, is the flexor longus digitorum pedis. A short 
 extensor arises from the fore part of the tarsus ; its tendons 
 unite with those of the long extensor. A short flexor from the 
 opposite side of the tarsus divides, to be inserted by fleshy filjres 
 into the tendons of the flexor longus. The hallux has a special 
 extensor and aljductor : the fifth toe has also an abductor : these 
 combining in action, enlarge the breadth of the foot. 
 
 In the higher reptiles, of the order Crocodilia, chiefly affecting 
 the watery element, and with frame and limljs propcn-tioned 
 for natation, the ]irimitive segmental structure continues to 
 be shown by the vertical aponeuroses passing outward from each 
 successive vertelara, especially from the di- and plcur-ajiophyses ; 
 tlicy divide the mass of muscles answering to the caudal myo- 
 connnas of Fishes and fish-like Batrachia in the tail ; to the 
 spinalis dorsi, lone/issimus dorsi, and sacrolumhalis of higher Ver- 
 tel)rates in the back ; and to the cervicalis ascendens, spleniiis capitis, 
 and transversalis colli in the neck. The posterior attachment of 
 the sacrolurnixdis is to the fi)rc part of the ilium by a slender ten- 
 don : that of the longissimus dorsi is to the sacral ribs. External 
 to the lono'issimus dorsi is the tracltehimastoideus, oriirinatinsj 
 Ijchind from the diapophyses of the second or third dorsal vertebra, 
 passing forward between the di- and zyg-apophyses of the cer- 
 vical vertebras, deriving slips therefrom, and inserted into the 
 mastoid. The complexns rises from the sides of the neural spines 
 of the middle cervical vertebra, and is inserted into the parocci- 
 pital. The splenius capitis arises from the neiu'al spines of the 
 anterior dorsals, and is partly a continuation of the spinalis dorsi: 
 it is inserted into the superocci])ital, and shows traces of the seg- 
 mental structure. The powerful muscles of the tail are more 
 decidedly divided by aponeurotic septa into segments, correspond- 
 ing with the vertebra? ; but they are grouped together, by Cuvier, 
 into three pairs of longitudinal muscles. The first is neural in 
 position, and chiefly a liackward prolongation of the spinalis dorsi ; 
 the myocommal septa form an angle directed forward. The 
 second is lateral, and begins by a strong tendon from the upper and 
 back ])art of the ilium, and by a second tendon from the ischium : 
 It is also connected with fleshy flattened fasciculi from the pubis 
 
MYOLOGY OF REPTILES. 
 
 223 
 
 and abdominal ril)s : its inyoconnual ,se])ta describe an acute angle 
 directed backward. At tlie l^ase of the tail it descends to tlie 
 lower border, and covers part of the third muscular column. 
 This derives a tendinous origin from the inner trochanterian ridge 
 of the femur, and from a ligament thence extending to the femoro- 
 fibidar articidation : from those attachments the muscle passes 
 l^ackward to the haemal arches and spines related thereto by 
 alternating origins and insertions, and there assumes the myocom- 
 nial character of the lowest or hasmal tract in the tail of the Newt 
 and Fish. By its anterior attachments in the Crocodile, this series 
 of muscles — t\\efemoro-j]ero7ieo-(:occy(iiuii of Cuvier — closely asso- 
 ciates the pelvic limljs with the tail in the natatory actions and 
 evolntions of the amphibious carnivore. 
 
 The mandiljvdar muscles are strongly dc^•cloped m the Cro- 
 codile in comparison 
 
 with other Saurians ; 112 
 
 although they seem, 
 after a comparison with 
 those of carnivorous 
 mammals, small in pro- 
 portion to the length 
 and massiveness of the 
 jaws. The temporal 
 is represented by two 
 muscles, one of which, 
 the pretemjjoralis, fig. 
 
 142, e, has its origin extended forward into the orbit from 
 lieneath the })Ostfrontal, whence its fibres pass oljliquely l^ack- 
 ward : the larger temporalis, ib. f, is attached to the parietal, 
 the mastoid, and tympanic, and its fibres pass vertically external 
 to those of the pretemporal, to be inserted into the coronoid and 
 surangular. The pterj/goidei are larger muscles than the tem- 
 porales ; the one from the ectopterygoid, fig. 142, /«, receives 
 an accession of fibres from the long pterygoid bone, and, 
 passing obliquely backward, swells out into almost a hemi- 
 spheric prominence at its insertion into the outer side of the 
 angxdar elements at li. The apiertor oris, or dhjnatric, ib. r/, arising 
 from the back part of the prominent mastoid, descends obliquely 
 backward to the projecting angular process behind the tympano- 
 mandibular joint. When the mandible rests on the bank, as at 
 «, a, supporting the head of the crocodile, and makes its angles, 
 ib. 29, the fixed point, the digastrici, g, acting upon the lever of the 
 mastoid, 8, open the mouth l^y rotating the cranium and upper 
 
 JkiiidibiiLir muscles, GrocodiJe 
 
224 
 
 ANATOMY OP VERTEBRATES. 
 
 jaw from l> to c, ii]>on tlie tympano-mandibular joints, t. Obser- 
 vation of this action engendered tlie notion tliat the ii]:)i)er jaw 
 was moveal^le, and tliat this was a peculiarity of the Crocodile ; 
 but it moves only as part of the entire cranium. 
 
 As the muscles of the limbs reach their maximum of number 
 and variety in the Chelonia and saltatory Batrachia, they will be 
 specified in those groups ; and the myology of the trunk will be 
 resumed, as it is seen in the Opiudla. 
 
 In these reptiles, as might be expected from the functions of 
 the spinal column, specialisation of the muscles of the vertebra; 
 and ribs reaches its maximum. The coalescence of the upper or 
 neuromesial and neurolateral parts of the myocommas into longi- 
 tudinal tracts is more complete and distinct than in the fish-like 
 
 Batrachia, or the CroeodiUa ; 
 the primitive distinction or 
 segmentation being pre- 
 served only at the points of 
 attachment. 
 
 In the neuromesial tract, 
 fig. 143, A, those which 
 may be called ' origins ' are 
 in two series, one from the 
 bases of the neural spines, 
 the other by short tendons 
 from the diajiophyscs : the 
 flesliy fibres from each ori- 
 gin converge and coalesce 
 as they pass forward, and 
 terminate in a long slender 
 tendon : these tendons are 
 attached to the summits 
 of the neural spines. AA'c 
 have here the characters 
 ol scmispiiiaUs and sjiiiialis 
 dorsi. The column external 
 to the preceding answers to 
 the lo/ir/issiinuii dors/ ; it 
 arises by a series of fieshy 
 origins from the transverse 
 processes, and by tendons 
 MiisrU'8(.ruio vciuiiiiu;nMi rill,. I'j 1 h.n,, rxii. ivoiw tlic coutlguous ])arts 
 
 of the ribs ; the fleshy fibres 
 pass forward and outward partly to the fascia coveriiig the 
 
MYOLOGY OF REPTILES. 225 
 
 scmispinalis dorsi, and partly to its insertions into the neural 
 sjiines ; its I'uremost attachment is to tlie superoccipital. The 
 third (neurohiteral) tract derives fibres from the tendinous origins 
 of the longissimus dorsi, and detaches from its outer side tliin 
 slips, each inserted by a slender tendon into a rib ; it represents 
 the sacrohmihalh. A muscle deriving slij)s of origin from the 
 zygfipopliyses of four or six anterior vertebra; passes forward to be 
 inserted into the mastoid, fig. 145, r, and represents the trachelo- 
 mastoideus. On the under part of the vertebral centrum are a 
 series of oljlique fasciculi, extending and converging in pairs from 
 the diapophysis of one vertebra to the hypapophysis of the second 
 or third vertebra in advance. The lonrjus colli at the fore 
 or upper part of the spinal column in Mammals and Man is a 
 rei)etition of this series ; the greater extent and developement of 
 wluch in Ophidians is indicated by the numljcr and length of the 
 hypapophyses, //,//, figs. 46, 47 : and of the subdiapophyses, d' , 
 fig. 47 a ; and these are maximised in Crotalus and Naia ; tlie 
 co-related muscle, having its fjremost insertion into the occipital 
 hypapophysis, fig. 146, p, brings down the head in the blow 
 inflicted Ijy the venom-fangs with proportionate force. 
 
 On removing the semispinalis dorsi, muscles appear which pass 
 obliqiiely Ijetween the transverse and spinous processes, like the 
 series called midtifidus spinoi in Man. Beneath these are inter- 
 spinales and intertransversales. External to the multifidus spinas 
 is a series of levatores costarum hreviores, fig. 14.3, B, arising 
 from the chapophyscs, and respectively inserted into the rib of 
 the succeeding vertebra. At their insertion arise the pretra- 
 heiites costarum, ib. C, which run more obliquely l)ackward, 
 and terminate each in the eighth (Naia) rib beyond that 
 from which it arose ; being attached also to the intermediate 
 ribs and intercostal fasciaB. In Python they are continued on 
 to the tenth or twelfth rib, fig. 14.3, D, and these continua- 
 tions have been described as a distinct series. Beneath them 
 is a shorter series, the pretralientes hreviores, ib. E. The retra- 
 hentcs costarum, fig. 144, C, arise from the lower part of the 
 diapophysis, and pass obliquely forward and outward along the 
 internal surface of the ribs to be inserted into the fourth rib in 
 advance. Where these muscles terminate, the transversalis ahdo- 
 minis, ib. D, takes its serrated origin ; its fibres descend obliquely 
 forward and terminate, with those of the opposite side, in the 
 ra})he, or medial tendinous line ; which closely adheres to that 
 part of the inserted border of the ventral scutes. The retraJientes 
 inferiores, ib. B, interdigitate at their origins (in Python) with 
 
 VOL. I. Q 
 
226 
 
 ANATOMY OF VERTEBRATES. 
 
 those of the transoersalis ahdommis, and pass forward to be 
 inserted at the end of the bony part of the fourth rib in advance. 
 The muscle answering to the rectus abdominis, ib. A, has the 
 short rib-cartilages for its intersections, instead of the fibrous 
 ' linear transversa;,' as in Man. 
 
 The inter costales, fig. 143, F, have their usual position and 
 decussating arrangement in two planes. Tlie squamo- costales, 
 figs. 143, 144, I, I, arise from the ribs near the insertions of the 
 levatores costaruin, B : these origins have been detached and the 
 muscles reflected ; in the figures they pass obliquely backward, 
 
 and are inserted into 
 the skin near the outer 
 margins of the ventral 
 scutes, 
 
 The scuto-costales, fig. 
 143, II II, rise from the 
 fore part of the end of 
 the rib, and are inserted 
 into the edge of the 
 scute. 
 
 The inter scut ales, figs. 
 143, 144, F, G, K, are 
 in two layers, which 
 decussate each other, 
 and cooperate with the 
 scuto-costales in alter- 
 nately erecting and de- 
 pressing the scutes.' 
 The fixed point of one 
 series is the ' linea aH)a,' 
 ib. E ; of the other, the 
 line of Insertion of the 
 sqnamo-costales, ib. i. 
 The co-ordinate cftects 
 of the foreffoina: mus- 
 clcs of the ribs and 
 scutes produce deter- 
 minate movements, to 
 and fro, of the ribs, with alternate erection and depression of the 
 broad transverse ventral scutes. 
 
 The tympano-mandibular arch has unusual mobility in Ser- 
 
 Jliis.ks ,.r Uiu rlliBHi 
 
 XX. vol. i. pp. 69-72. 
 
MYOLOGY or REPTILES. 
 
 227 
 
 pents : the long tympanic bone, fig. 97, 28, is suspended by its 
 extremity ironi that of the outstanding mastoid ; and besides tlie 
 movements of swinging to and fro to the extent allowed by the 
 loose articulations of the upper jaw, it is affected by the muscles 
 tending to divaricate the mandibular rami, as Avell as by a 
 muscle directly drawing its lower end outward. This latter re- 
 peats the levator tympanici of Fishes, fig. 134, 24 : but, with the 
 retrograde course of the ophidian tympanic, its levator lias a 
 more posterior origin, viz. i'rom the end of the mastoid, and is 
 inserted into the lower, instead of tlie ujiper, end of the tympanic. 
 To counteract these movements, we find a muscle answering 
 to the ' depressor tympani' of Fishes, fig. 13G, 22, which arises 
 from the basi-occipito-sphenoid, fig. 146, m, and passes trans- 
 versely outward and l^ackward to the lower end of tlie tym- 
 panic and co-articulated end of the mandible : it depresses the 
 tympanic and draws it and the articular part of the mandible 
 inwards. 
 
 Of the muscles which close the mouth, one, like the muscle I, 
 fig. 132, of the Shark, bears analogy to the rnassrter; in the 
 aljsence of a zygoma, it arises from the postfrontal and contiguous 
 part of the ectopterygoid, fig. 145, e, passes backward, winding- 
 round the tympano-raandibular joint, and is inserted into the 
 surangular and angular, as far forward as the dentary. In 
 venomous snakes its fascial origin spreads over the poison-bag, 
 ib. a. The teinporalis, 
 ib. i, arises from tlie 
 side and spine of the 
 parietal, and descends 
 almost vertically, partly 
 covered by the mas- 
 seter, to be inserted into 
 the coronoid plate. The 
 post-temporalis, ib. f, 
 arises from the fore part 
 of the mastoid and con- 
 tiguous part of the pa- 
 rietal, and descending 
 in front of the tympa- 
 nic is inserted into the coronoid ridge nearer to the joint of the 
 lower jaw. 
 
 The ' tijmpano-nuindiJmlaris,' ib. g, which is analogous to the 
 din-astricus, or its hinder belly in Mammals, arises from the liack 
 part of the tympanic, and is inserted into that of the angular 
 
 Q 2 
 
 145 
 
 Muscles of the jaws, Crutalii.s. OXC'II. 
 
228 
 
 ANATOMY OF VERTEBRATES. 
 
 process of the mandil)le. From fascia attached to the neural 
 spines of some of the anterior vertebraj there extends a flattened 
 muscle, neuro-viandihularis, fig. 145, ^, which unites with a smaller 
 strip from fascia connected with the ribs of those vertebras, 
 costo-mandihulurk, figs. 145, 147, m, to be inserted into the lower 
 border of the mandible. These muscles depress and retract the 
 lower jaw. 
 
 A powerful muscle, ectupterycjoideus, fig. 146, h, which in its 
 mandibular relations resembles the external pterygoid, advances 
 
 146 
 
 '^^ 
 
 Muscles of the ptcrygo-imlntine apparatus of the Crcta\ns, 
 
 forward to the fore part of the ectopterygoid, and to the back part 
 of the maxillary in Fi/tho]i. In Crofahis it expands into a fascia, 
 spread over the pouch lodging the venom-fangs, preserving a 
 tract of tendinous strength tor insertion into the lower part of the 
 hinder process of the maxillary. It cooperates with the erector 
 of the fang in fixing the moveable maxilla during the blow, and 
 retracts the fang on the relaxation of the erector. When its fore 
 part is the fixed point, the ectopterygoideus spreading its man- 
 
MYOLOGY OF REPTILES. 
 
 229 
 
 dilnilar attachment over tlie articular capsule to the back part of 
 the angular process, protracts the lower jaw. 
 
 The entopteryfioideus, fig. 145, k, is attached anteriorly to the 
 pterygoid bone, ib. 4, whence its fibres pass outward and back- 
 ward to the inner surface of the angular and suranffular elements, 
 covered by the ectopterygoideus. It retracts and divaricates the 
 palato-pterygiiid jaws, protracts and approximates the back j)arts 
 of the mandibular rami. The fore parts of those bones whicli, 
 through their loose elastic symphysial connection, yield laterally to 
 the pressure of the prey when seized, are brought together, after 
 it is swallowed, by an in- 
 ter inandlhularis, answering ^*^ 
 to 21, fig. 137, in fishes: 
 it is shown in fig. 147, 
 passing from the end of 
 one ramus to that of the 
 other, at v, v, with a me- 
 dian raphe, as in the my- 
 lohyoideus ; and sending a 
 slip V from each attach- 
 ment, which expands upon 
 the intermandibular inte- 
 gument, restorino; and cor- 
 rugating it after its great 
 occasional stretching. In 
 this it Is aided Ijy a thin 
 layer of fibres internal to 
 and in close connection 
 with the insertion of the 
 costomandibularis expiosed 
 l)y the outward reflection 
 of that muscle at fig. 
 147, a. 
 
 In Fishes the fore part 
 of the levator tympani, fig. 
 136, 22, is inserted into the 
 pterygoid : in Serpents 
 the oris'in of the answer- 
 
 o 
 
 able part, presphenopteri/f/oiJeu.^, is advanced forward to the pre- 
 sphenoid, whence its fi)>res, fig. 146, /, pass outward and backward 
 to their insertion into the pterygoid, 4, and ectopterygoid, 3, at 
 their junction. In jirotracting the pterygoid it pushes forward 
 the maxillary, rotating it outward in the Constrictors ; but, by 
 
 ■It fit the l;atMcsuakf. iCmlahn:.) cxcil 
 
230 AiTATOMY OF VEKTEBRATES. 
 
 the modification of the bones peculiar to venomous serpents, as 
 shown at 3 and 2, fig. 146, the muscle rotates the short maxillary 
 vertically through the ectopterygoid, so as to bring the venom- 
 fang from the recumbent to the vertical position ready for the 
 blow. 
 
 The ■pres-phenoipalatine muscle arises from the side of the fore 
 part of the presphenoid and passes outward to its insertion along 
 the inner surface of the palatine. From the side of the pre- 
 sphenoid rises the small presplierw-vomerine muscle, fig. 146, v, 
 which sends forward a slender tendon to the half of the divided 
 vomer, and through that bone depresses and retracts the pre- 
 maxillary, ib. i, after the displacement of all the bones of the 
 mouth caused by the engulphing of the prey. 
 
 The hyoid arch is reduced to a pair of slender cartilaginous 
 ceratohyals, running forward, almost parallel, fig. 147, B, beneath 
 the sheath of the filamentary tongue, before their anterior mem- 
 branous union. Tlie raphe of the muscles v and ?<, fig. 147, is so 
 far attached to the hyoid and lingual sheath, that by their con- 
 traction they raise the tongue after it has been pushed down : the 
 fibres of the costomandibularis, u, attached to the foremost jiart of 
 the mandible, throvigh the same medial attachment protract the 
 lingual sheath ; the posterior part of the costomandibularis can 
 retract the lingual sheath, and these actions are analogous to those 
 of the 'sternohyoid' and 'geniohyoid' muscles in higher verte- 
 brates. On reflecting the costomandibularis from the raphe out- 
 ward, the genioglossi are exposed : their antero-median attachment, 
 fig. 147, z', z' , is to the raphe of the intermandibularis, v ; their 
 antero-lateral attachment, z", is to the fore end of the mandibular 
 ramus. The muscle formed by their union, r, extends backward 
 along the lingual sheath to its extremity : it is the chief pro- 
 truder of the tongue. The retractors, answering to hi/oqlossi, 
 ib. A, arise from the hinder ends of the ceratohyals, run forward, 
 enter the lingual sheath, and seem to coalesce in forming the 
 main substance of the cylindrical tongue ; but they again separate 
 to terminate in its forked extremit}'. The fore ]iart of the trachea 
 is closely connected witla the lingual sheath, and advances so fiir 
 forward to terminate in the mouth, as to be subject to the stretch- 
 ings and displacements of the elastic floor of that cavity. A 
 special muscle, r/c?riofrarheaKs, fig. 147, ;/, arises from the fore 
 end of the mandibular ramus, and passes inward and backward 
 to cxjiand upon the sides of the fore part of the trachea. The 
 pair draw forward the glottis ; its retraction is cflcctcd through 
 the medium of the lingual sheath and its muscles. 
 
MYOLOGY OF EEPTILES. 231 
 
 There are small modifications of the muscles of the long anterior 
 outstretched ribs of the Coljra, fig. 46, jil, which sustain the 
 peculiar folds of integument forming the conspicuous ' hood ' of 
 that poisonous snake. These ribs are protracted or raised by the 
 Icvatores breviores, and by two sets of pretrahentcs, one passing- 
 over two ribs to the third behind, Ihe others passing over one 
 rib to the second, and by the intercostales externi. The muscles 
 passing from the hood-ribs to the skin come off" about fijur lines 
 I'rom the head by a short tendon, the fleshy band extending 
 Ijctween one and two inches, outward and backward to its inser- 
 tion into the skin. 
 
 The muscular system of the trunk reaches, in Reptiles, its 
 maximum in Serpents ; it is reduced to a minimum in Tortoises : 
 yet, where it has to act on the only moveable part of the verte- 
 Ijral column of these slow and heavy house-l)earers, it is specially 
 and in some parts largely dcA'cloped. 
 
 Homology can seldom be determined or discerned, save in a 
 general way, in the fleshy parts of Clwlonia ; as, e. g., that the 
 muscles upon or about the triuik-vcrtebraj answer to those so situ- 
 ated in lower or higher Vertebrates ; and that the primitive seg- 
 mental character of such muscles is still indicated by distinct and 
 successive attachments to a consecutive series of bony segments, as 
 is shown, e. g., in fig. 148, 37, 39, fig. 149, 27. AVhere a more 
 special determination has been attem])tcd it has usually rested on 
 a similarity of attachment of one end of a muscle, with acknowledged 
 discrepancy at the other end; as when Cuvier' compares 27, fig. 
 148, to the sacrolumhalis and hmgissirnus dorsi ; and when Bojanus^ 
 gives the latter name to the portions of myocommas at the opposite 
 side of the back-bone, fig. 148, or calls the muscle, fig. 152, 9i, 
 which arises from the pubis, the iliacus internum. It will be 
 understood, therefore, that in applying to the muscles of the Box- 
 tortoise {Emys Eiiropa'a), the names assigned to thcni by the 
 author of the exemplary and beautifid monograph' from which 
 the illustrations, figs. 148 — 159, have been copied, they are to be 
 taken more or less in an ai'bitrary sense, and that the characters 
 of the muscles mainly exemplify the greater degree in which the 
 adaptive jirinciple prevails over the archetypal one in the soft than 
 in the hai'd parts of the frame. 
 
 On the dorsal aspect of the vertebra; of the back, the muscular 
 system is restricted to the ' xpmalls dorsi,' fig. 148, 39 ; it rises 
 from the neural and beginning of the costal plates, neural arch 
 
 ' XIII. i. p. 292. ^ xxxviii. '■' lb. 
 
232 
 
 ANATOMY OF VERTEBRATES. 
 
 148 
 
 and rib of the seventh to the third dorsal vertebra inclusive, 
 occupying the interspaces between those parts ; it is inserted 
 into the neural arch of the last cervical, and into the post- 
 zygapophysis of the next vertebra in advance. 
 
 The series of muscles called ' longus colli,' ib. 28, 28, com- 
 mences by the broad origin from the under part of the first and 
 second costal plates, and is continued by eight narrower slips 
 from the hypapophyses of the first dorsal, and seven antecedent 
 cervical vertebras. These fasciculi incline forward and inward, 
 
 overlapping each other, to 
 be inserted successively 
 into the parapophyses of 
 the eighth and lower part 
 of the centrum of the ante- 
 cedent cervicals, with in- 
 terposed sesamoids at the 
 sixth, fifth, and fourth ver- 
 tebra3 ; the foremost inser- 
 tion being into the basi- 
 oceipital. 
 
 Six or seven lateral por- 
 tions of cervical myocom- 
 mas, called hitertransver- 
 xfirii colli ; ib. 36, pass from 
 the diapopliyscs of the 
 eighth to the second cervi- 
 cals, and are inserted along 
 with the corresponding in- 
 sertions of the longus colli 
 from the sixth to the cen- 
 trum of the atlas, or odon- 
 toid. The intertransversnrii 
 iibliqni, figs. 148, 149, 37, 
 are four strips from the 
 diapophyses of the sixth, 
 fifth, fourth, and third vertcbr;\3, which pass fiirward and down- 
 ward to the parapophyses of the fourth, third, second, and first 
 cervicals respectively. There arc hitcrsji/iidh's between the 
 neui-al spines of the first three cervicals. 
 
 MiisclL'b <>i Lhc ilnrsiil, ocTviiMl, niKl (H'oiiiiLal vrrtclira 
 
 The trans 
 
 salt 
 
 S (■(TVICtS, 
 
 fig. 151, 33, arises from the post- 
 
 zygaiiophysis of the fifth, fourth, and third cervicals ; these blend 
 outwardly, and detach inwardly insertions to the i)ostzygapo- 
 physes of the fourth, third, and second ccr\icals, and into the 
 
MYOLOGY OF REPTILES. 
 
 233 
 
 (liapopliysis of the atlas : the tendon so inserted is shown at 33, 
 fig. 148. 
 
 The comjih-xus, fig. 148, 23, arises from tlie diapophyscs of the 
 first tliree cervicals, and is inserted into the paroccipital : in 
 fig. 150, the hindmost origin of tins mnscle is marked 25. 
 
 The rectus capitis anticus lonfjus, fig. 148, 29, arises from the 
 hypapophyses of the third and second cervicals, and is inserted 
 into the side of the basioccipital. The rectus capitis anticus 
 hrevis, fig. 152, 30, arises from the atlantal hypapophysis, and is 
 inserted into the basioccipital. The rectus cajritis piosticus major, 
 fig. 148, 31, arises from the neural spines of the axis and atlas, 
 and is inserted into the paroccii)ital. The rectus capitis posticus 
 vimor, ib. 31, arises from the neural arch and diapophysis of 
 the atlas, and is inserted into the base of the exoccipital. 
 
 The largest and most remarkable portions of muscular segments 
 of the trunk are those which are combined to effect the retraction 
 beneath the carapace of the head and neck. The retralwiis 
 
 149 
 
 Siilo A'k'w (if Uirjik-iiiupcles aii'l ilcciicr .sc;Ued linib-iiuisclcf?, ICtivjs Hni-oprra. xxx^'iii. 
 
 capitis collique, figs. 149, 150, 27, arises by six fleshy fasciculi 
 from the neural arches and spines of the eighth to the fifth 
 dorsals inclusive ; these pass forward, blending together, and then 
 detach four tendinous insertions : of these, the anterior and 
 longest, as well as strongest, is into the basioccipital fossa ; the 
 other three are into the diapopliyses of the fourth, fifth, and sixth 
 cervicals. It is not difficult to sever the part of the great re- 
 tractor connected with the cervical insertions, as a distinct muscle 
 from that inserted into the occiput. The hiventer cervicis, figs. 
 150, 151, 2-i, arises from the neural spines of the fifth, fourth, and 
 
234 
 
 ANATOJIY OF VERTEBRATES. 
 
 third cervicals, and is inserted into the same part of the occipital 
 vertebra. 
 
 The trachelomastoiclQUs, fig. 150, 26, arises from the hypapophyses 
 of the third and second cervicals, and ascends obliquely to be 
 inserted into the mastoid. 
 
 The scalenus, fig. 150, 34, arises from the inner border of the 
 lower three-fourths of the scapula ; its fibres emerge as it 
 advances, and deliver strips of insertion to the diapophyses of the 
 eiffhth to the second cervical inclusive. 
 
 150 
 
 Sido view of muscles of tlic trunk, head, nud liuilis, Einy^ Furopwa. XXXTITI. 
 
 The stcrnomostoideus, fig. 150, 22, arises from the middle of the 
 inner surface of the cntosteruum, and is inserted into the mastoid. 
 
 The dlaphragmaticus, figs. 148, 149, 150, 42, 42, arises by three 
 sheets from the bodies of the fifth and fourth dorsals, and from 
 the rib of the third dorsal ; the two posterior unite to apply them- 
 selves and adhere to the mesial surface of the lung ; the third 
 sweeps over to the outer surface, 42, fig. 150, and 42, fig. 151, and 
 is reflected from its lower border upon the peritoneum. 
 
 The transijersalis ahdomiii.is, figs. 150, 151, 4i, ai'iscs along a 
 curved line on the inner surface of the fourth, fifth, sixth, and 
 seventh costal plates, extending from the end of the fourth to the 
 beginning of the seventh; also by a separate f;\sciculus from the 
 eighth rill ; and by three slender tendons from near the cardinal 
 border of ihe hyposternal ; it is inserted liy a broad tendinous 
 sheet into the mesial border of the same plastral clement, which 
 is the homologue of tlie abdominal luemapophyscs and spine 
 receiving the same insertion. 
 
 The obliqi/us cxternus, fig. 151, 40, arises from the inner side 
 of the extremities of the last lour costal plates, and adherent 
 
MYOLOGY OF REPTILES. 
 
 235 
 
 marginal ones ; it is Inserted along a sigmoid line extending from 
 the postero-external angle of tlie liypostcrnal to the middle of the 
 xiphisternal and by a special fasciculus and tendon into the lateral 
 process of the pubis. 
 
 The lattsftimus colli, figa. 151, 152, 21, consists of two parts; 
 both arc attached, above, to aponeuroses connecting them with 
 the cervical diapojihj'ses ; the fibres of the posterior di-^'ision, 
 fig. 149, 21 a, pass down and rather backward, over the muscles of 
 the base of the neck, and are inserted into the midline of the 
 
 151 
 
 8iik' vk'W iif ^iipcillcial iiiuscK'S nT trunk. liOfiQ rinil linilt.^, /iyft/K Eiirop^irr. xxx\"ill. 
 
 epi- and ento-sternals : the fibres of the longer anterior portion 
 sweep transversely across the lateral and lower parts of the neck, 
 fig. 152, 21. 
 
 The extensor caudcB, fig. 151, 47, includes the neural jiortions of 
 the myocommas of this region from its base, where the foremost 
 has a sacral origin, to near the tip. The flexor caudce. lateralis, 
 ib. 48, consists of the lateral parts of the same muscular seg- 
 ments. The flexor caudce inferior is shown at ib. 49 : i\\e flexor 
 caudce, lumhalis in fig. 150, 50 : the flexor caudce ohturatorius in 
 figs. 151 and 156, 51. 
 
 The following are muscles of the tympano-mandibidar arch. 
 
 Tlie temporalis, figs. 151, 152, 1, arises from the parietal and 
 superoccipital spines, and is Inserted into the coromiid part of the 
 mandible. The pferT/f/oidexs, figs. 148, 149, 152, 4, arises from 
 the outer surface of the pterygoid, and is inserted into the internal 
 tuberosity of the articular element of the mandible. The apertor 
 oris, or digastricus, figs. 150, 15.3, 3, arises from the mastoid, and 
 is inserted into the angular process of the mandible. The dilatator 
 
236 
 
 ANATOMY OF VERTEBRATES. 
 
 tubcB, fi""S. 148, 149, 4, arises from the mastoid, and is inserted 
 into the postero-inferior angle of the tympanic and into the begin- 
 ning of the eustachian tube. 
 
 The following are muscles of the hyoidean arch and appen- 
 dages. The mylohyoideus, fig. 153, 13, extends transversely between 
 the mandibular rami, and is attached to the hyoid by its median 
 
 152 
 
 raphe. The iniio/ii/Didnis, llgs. 150, 152, 14, arises from the 
 coracoid, and is inserted into tlie basi-, cerato-, and thyro-hyals. 
 The r/eniohi/o/flcHs, fiis;^. 150, 15"2, iri, iB, arises from the back part 
 of the symphysis niaiidihuhe ; is united to its fellow as far back 
 as tlie basihyal, and there diverges to its insertion into the cera- 
 tohyal. The /n/oiiin.ii/hiris, fig. 150, 16, arises from the articular 
 clement and is inserted into the ceratohyal. The gi-iihylossus, 
 
MYOLOGY OF REPTILES. 
 
 237 
 
 fig. 152, 17, arises from the dentary and is inserted into tlie outer 
 angle of the basihyal and into its triangular ap])endage. The 
 hyoglossus, fig. 151, 18, passes from the basihyal and its appendage 
 to the ceratohyal, which it covers on the left side of fig. 152. 
 The proper muscles of the scapular arch are very few, by 
 
 153 
 
 Muscles of trunk and linihs, from below, _E//i//.5 Europaa. xxxvill. 
 
 reason of Its fixity, although it gives origin to many which act 
 upon other more moveable parts. 
 
 The subclavins, fig. 148, 59, arises from the nnder part of the 
 first costal plate, and is inserted into the suprascapula and con- 
 tiguous part of the scapula. The serratus magnus, fig. 152, 75, 
 
238 ANATOMY OF VERTEBRATES. 
 
 fig. 153, 57, arises from part of the outer margins of the first and 
 second costal plates and from the same margin of the cardinal 
 jirocess of the hyosternal and contiguous part of the hyposternal : 
 it is inserted into the upper surface of the coracoid. The latis- 
 simus dorsi, fig. 152, 5S, arises from the inner surface of the first 
 costal plate, and is inserted into the neck of the humerus. The 
 deltoides, fig. 15.3, 60, arises by three heads ; one, ib. 60 a, from the 
 inner surface of the ento- and epi-sternals ; another, ib. 60 h, from 
 the clavicular process of the scapula ; and the third from the 
 angle between that process and the body of the scapula : it is 
 inserted into the lesser tuberosity of the humerus. The clariculo- 
 hrachialis, fig. 152, 6i, arises from the clavicle, and is inserted into 
 the outer tuberosity of the humerus. The suhcoracoideus, fig. 153, 
 62, arises from the under surface of the coracoid, and is inserted 
 into the inner tuberosity of the humerus. The stipercoracoidms, 
 figs. 151, 152, 64, arises from the upper surface of the coracoid, 
 and is inserted into the outer tuberosity of the humerus. The 
 teres vihior, fig. 152, 65, arises from the posterior border of the 
 coracoid and is inserted into the pit between the humeral tuberosi- 
 ties, with an attachment to the capsule of the shoulder-joint. 
 The triceps bracldi, figs. 152, 153, 65 « c, arises from above the 
 glenoid margin of the scapula, 65 a, and from tlie humerus, 65 c : 
 it is inserted into the olecranon. The biceps brachii, fig. 153, 66, 
 arises from the back part of the coracoid, 66" : it is inserted, 
 with the brachialis internus, into the ulna, and by a slender tendon, 
 66 a, into the radius. The brachialis internus, fig. 152, 67, 
 arises from the inner tuberosity and concave surface of the 
 humerus and is inserted into the proximal ends of l)otli the radius 
 and idna. The palmaris, figs. 150, 153, 68, arises from the outer 
 condyle of the liumerus, and is inserted into the palmar aponeu- 
 rosis. Thejiexor sublimis, figs. 151, 153, 69, arises from the outer 
 condyle of tlie humerus and is inserted into the metacarjial of the 
 fifth digit and into the tendon of the ulnaris internus. The fle.ror 
 jrnifundus, figs. 150, 151, 70, arises from the concave side of the 
 ulna, and is inserted into an ajioneurosis sj)litting into five tendons 
 for the last phalanges of the five digits. The pronator teres arises 
 from the outer condyle of the humerus : its insertion, shown in 
 fig. 154, 71, is into the radial side of the carpus, with that of the 
 pronator quadratns, ib. 72. Tlie nlnaris internus, figs. 151, 153, 
 
 73, arises from the tubercle above the outer angle of the huincrus, 
 and is inserted into the ulnar side of the carpus and contiguous 
 end of the fifth metacarpal. The nlnaris e.rternns, figs. 151^ 152, 
 
 74, arises from the tubercle above the inner condyle of the 
 
MTOLOGY OF REPTILES. 
 
 239 
 
 154 
 
 humerus, and is inserted into tlic carpus near the uhia. The 
 radkdk intcrnus, fig. 154, 7o, arises from the tuberosity above the 
 outer condyle of the humerus, and is inserted into the distal end 
 o± the radius. The radialis cxternus longus, 
 fig. 152, 76, arises from the tuberosity above 
 the internal humeral condyle, and is inserted 
 into the radial margin of the carpus ; the 
 muscle converging towards 76, in the same 
 figure, is the radialis iiiteriius. The radialis 
 exterrms hrevis, fig. 150, 77, arises from the 
 tuberosity above the internal hrnneral condyle, 
 and is inserted into the back of the carpus. 
 The supinator longus, figs. 152, 15.3, 78, arises 
 above the internal humeral condyle, and is in- 
 serted into tlie radial side of the carpus and 
 the same border of the radius. The siijiinatur 
 hrevis, fig. 152, 79, arises from the tubercle 
 above the inner humeral condyle, and is in- 
 serted into the back of the radius. The extensor 
 communis digitorum, fig. 151, 80, arises fi'om tlie 
 tuberosity above tlie inner humeral condyle, and is inserted into 
 the five metacarpals. The extensor proprius poUicis, fig. 150, 81, 
 arises from the ulna, and is inserted into the metacarpal of the 
 pollex. The extensor projn'iiis digiti minimi, fig. 152, 82, arises 
 from the ulnar side of the carpus and is inserted into the meta- 
 carpal and first phalanx of the fifth digit. The extensores Ijreoes 
 digitorum, figs. 151, 153, 83, arise from the back of the carpus 
 
 f fi.rof.iot, Ewjia 
 LCit. ixwixi. 
 
 and metacarpus, and are inserted into the distal phalang 
 
 The 
 
 abductor pollicis, fig. 153, 84, arises from the 
 inner side of the carpus, and is inserted into 
 the first phalanx of the pollex. The flcxores 
 breves digitorum, fig. 153, 88, arise from the 
 palmar sesamoids and fascia, and are inserted 
 into the phalanges. There are also, iiiterossei, 
 both external and internal ; the latter are shown 
 at 90, figs. 154 and 155. The adductores digi- 
 torum, fig. 155, 86, are limited to the first, 
 second, and third fingers, to the metacarpals of 
 which the muscles incline, radiad, from the 
 second row of carpals. 
 
 Tlie following are the muscles of the pelvic 
 arch and limb : — 
 
 The uttraliens pelvhn, figs. 150, 153, 43, arises from contiguous 
 
 Miiwcles i>t fore-root, 
 Eiinj^ EurOiiKii. XXXVIII. 
 
240 
 
 ANATOMY OF VERTEBRATES. 
 
 156 
 
 parts of the hypo- and xiphi-sternals, and is inserted into the 
 outer process of tlic )nil)is. The retrahens pelvini, ib. 44, arises 
 from the posterior half of the xiphisternal, and has a similar in- 
 sertion. More direct retractors of 
 the pelvis are the muscle called 
 Jiexor cauda ohturatorius, which 
 arises from the caudal hajmapo- 
 physes, and is inserted into the 
 front border of the obturator 
 foramen ; and the Jiexor caudoi 
 ischiadicus, ib. 52, with a similar 
 origin, but inserted into the ischial 
 
 Muscles of pelvis, -E»iys i;7u-oi'«a. xxxvili. , . ,^, ,.,. 
 
 symphysis. x.he pectineus {\\ia.cu5 
 internus, i?o/.), figs. 150, 152, 153, 91, arises from the upper surface 
 and outer process of the pubis, and is inserted into the inner tro- 
 chanter of the femur. Its insertion receives also a small fasciculus 
 from the ninth dorsal centrum, and the tenth pleurajjophysis, which 
 may represent the psoas. A glutceus, figs. 150, 151, 93, arises from 
 the ninth and tenth pleurapophyses, and from the ilium. A second 
 (jlutoius, figs. 150, 151, 152, 94, arises from the sacral and anterior 
 caudal pleurapophyses. Both are inserted into the outer trochanter, 
 together with a fasciculus, representing an ohturatorius, from the 
 inner surface of the oljturator fascia, and from the ischial symphysis. 
 The triceps adductor, figs. 152, 153, 97, arises from the inferior sur- 
 face of the pubis, and is inserted into the inner trochanter, crossed 
 by the ischio-pubic ligament. The quadratus, fig. 152, 9S, arises 
 from the tuber ischii, and is inserted into the back interspace of 
 the trochanters. The rectus fenioris, fig. 151, 99, arises by a bifid 
 tendon from the upper end of the ilium, and is inserted, with the 
 vastus externus, fig. 150, lou, vastus internus, fig. 151, 101, cruraus, 
 fig. 152, 102, and sartorius, fig. 153, 106, into the fore-part of tlie 
 head of the tibia. The semitendinosus, figs. 150, 152, 104, has 
 three origins, one from the back part of the upper end of the 
 ilium and contiguous part of the sacrum, a second from the tuber 
 ischia, a third from the back part of the ischial symphysis ; they 
 join a common tendon which passes behind the knee-joint, and 
 then bifurcates to be inserted into the outer proximal tuberosity 
 of the tibia, and into the gastrocnemius, wib. The semimem- 
 branosus, fig. 153, 105, has two origins, one, 105 a, from the first 
 caudal vertebra; the other, 105 /;, from the tuber ischii and isehio- 
 pubio ligament. It is inserted into the upper part of the tibia. 
 The //mc?7/.«, fig. 153, 107, arises from the middle of ischiopubic 
 ligament, and is inserted into the upper and outer part of the 
 tibia. The extensor communis dii/itorum, fig. 151, los, arises from 
 
MYOLOGY OF REPTILES. 
 
 OA] 
 
 the ridge anterior to the outer femoral condyle, and is inserted 
 into the distal phalanx of the hallux and into tlie proximal phalanges 
 of the other toes. The tibialis unticus, figs. 150, 153, 109, arises 
 from the antero-internal margin of the tihia, and is inserted into 
 the til)ial side of the tarsus and first metatarsal. The peroneus, 
 fig. 151, 10, arises li-om the fore part of the fihnla, and is inserted 
 into the cuboid, and fourth and fifth metatarsals. The digit- 
 extensor es breves, figs. 149, 151, iii, arise from the dorsal aspect 
 of tiie second row of tarsals, metatarsals, and proximal phalanges, 
 and are inserted into the ungual phalanges. The extensor jiroyrius 
 hallucis, figs. 152, 15.3, 112, arises from the lower end of the 
 fibula, and is inserted Ijy a bifurcate tendon into the sides of the 
 first plialanx of the hallux. Tlie ahductor hallucis arises from the 
 tendon of the tihiulis unticus, and from the first metatarsal, and is 
 inserted into the base of the proximal phalanx of the hallux. 
 The gastrocnemius, figs. 151, 153, lu, has two heads, one, 114 «, 
 from the outer femoral condyle; the other, wih, from the outer 
 margin of the tiljia, and this receives also the tendon from the 
 semitendinosus : it is inserted into the calcaneum and ex])anded 
 metatarsal of the filth digit, and is continued into the plantar 
 fascia. The plantaris, fig. 153, 115, arises above the outer femoral 
 condyle, and coalesces with the se/leus, fig. 152, lie, and the digiti- 
 Jiexor longus, 117, to termhiate in a common aponeur(,>sis, attached 
 to both sides of the tarsus, and dividing, as in fig. 157, 117, to be 
 inserted into the ungual phalanges. The ddgitiflexores breves, 
 fig. 157, 118, are four in number, arise from the tarsus, and are 
 
 157 
 
 Musclos of liind-foot, Eiidj^ Europfru. XXXYIII. 
 
 inserted into the sides of the middle plialanx, and iDy a slender 
 tendon into the ungual phalanx, of the four outer toes. The 
 tibialis posticus, figs. 152, 158, 119, arises from the inner and back 
 part of the fibula, and expands into an aponeurosis, including a 
 sesamoid, which divides to be inserted into the second row of 
 tarsals, and the metatarsals of the hallux and fifth digits. The 
 
 VOL. I. K 
 
242 
 
 ANATOMY OP VERTEBRATES 
 
 interosseus cruris, fig. 158, 120, extends obliquely between the 
 opposite margins of the leg-bones. The mterossei digitorum 
 
 158 
 
 Musrlcs of liilld-foot, Emits Europ^ra. xxxvill. 
 
 dvrsah's, are shown at 122, and those of the plantar surface at 123, 
 fig. 158. 
 
 The highest faculty of terrestrial locomotion in the reptilian 
 class, is manifested by the saltatory batrachians. 
 
 In the hind limlj of the frog tliere is a muscle which extends 
 from the diapophysis of the third vertclira to the ilium, which it 
 tends to protract, and acting from which it may slightly Ijend the 
 back. Tlie ccUxjlutnis receives an accessory strip from the 
 coccygeal style. The mesot/hifeiis is a strong muscle. The entn- 
 (/luteus and iliacus are united. The ohturator e.rternus has a semi- 
 circular form. The quadratiis femoris is in two strata. There 
 are Uvo pcctinei and four addiictores femoris. Tlie extensor cruris 
 consists of a vdstus internus and a vastus e.rternus with a coalesced 
 crurcEtis; there is no rectus feumris. T\\e Jicror cruris has l.nit 
 one head or origin from the lower and back part of the ilium. 
 The semitcndinosus has two heads, one from the fore part, the 
 other from the back part of the ischio-pubic symph\-sis. The 
 seuiiniemhranosus and (p'acilis have the usual attaclnncnts. The 
 sartor/us resembles the rectus in its position and course in front of 
 the thigh: it is united to tlie feasor fa seiee lata-. The gastro- 
 cnemius is represented by its external moiety, which is so large as 
 to give the a])i)earancc of a ' calf " to tlie leg: its tendon glides 
 behind the tibio-larsal joint, and expands as it descends along 
 the tarsal segment into a plantar fascia. The tihialis autieus 
 arises by a strong tendon 1'rom the fonuir, and divides at the 
 middle of the tibia into a fascicle inserted into the astragalus, and 
 a second inserted into tlie calcanemu ; in both at tlie proximal 
 end. A eruro-tdiinHs rises from the lower end of the femur, and 
 
LOCOMOTION OF FISHES. 243 
 
 is inserted into the fore part of the lower three-fourtlis of the 
 tibia. The tibialis posticus, with the usual origin, is inserted into 
 the astragalus, fig. 44, a. A peroneus arises from the outer 
 femoral condyle, and from the outer side of the leg-bone ; its 
 tendon bifurcates, one part being attached to the outer malleolus, 
 the other to the base of the calcanemn, ib. d. An extensor hnu/us 
 di(/itorum arises from the outer malleolus, passes between the two 
 portions of the tibialis anticus, and, after sending an insertion to 
 the astragalus, is continued to the three middle toes. The 
 extensor brevis arises from the whole length of the calcancum, and 
 divides into six parts, an external to the metatarsal of the hallux, 
 an internal to that of the minimus, and the intermediate four to 
 the plialanges of the four outer toes ; these unite with the tendons 
 of interossei extend, to which mirdit be referred the extensor of the 
 hallux. Both this toe and the outermost have their abductors 
 for S2ireading the web. There is also an abductor of the ento 
 cunciform, fig. 44, ci, wliich resembles a small accessory digit. 
 The plantar aponeurosis, which receives a fleshy fascicle from the 
 tibio-tarsal capsule, gives oi-igin to a muscle inserted into the 
 w]H)le length of the astragalus, divides into six fascicles, whicli 
 form sheaths for the flexor tendons, two of which lielono- to the 
 foiu'th toe ; and, finally, is resolved into three tendons, of which 
 two go to the fifth toe, and one to the fourth. Thej?c'xo?- hmfjus 
 diijitorum arises from the tibio-tarsal capsule, and is ex})ended 
 u])on the three outer toes. The several insertions of the fore- 
 going digital flexors give one tendon for the ungual phalanx, a)Kl 
 two for the other phalanges. 
 
 § 48. Locomotion of Fishes. — Hitherto the osteology and myo- 
 logy of the cold-blooded Vertebrates have been considered chiefly 
 from a homological point of view. I have aimed at relie'S'ing the 
 dryness of descriptive detail, and at connecting the multifarious 
 particulars of this difficult part of Comj)arative Anatomy in 
 natural order, so as to lie easily retained in the memory, by 
 referring to the relations which the bones and muscles of Fishes 
 and Reptiles bear to the general plan of vertebrate organisation, 
 and by indicating their analogies to transitory states of structure 
 in the embryo of higher animals, and to those answerable con- 
 ditions of the mature skeleton wliich, in longer lapse of time, 
 have successively prevailed and ])assed away in the generations 
 of species that have left recognisable remains in the superimposed 
 strata of the earth's crust. 
 
 To determine the parts of the vertebrate structure which are 
 most constant — to trace their general, serial, and special lionio- 
 
 R 2 
 
244 ANATOMY OF VERTEBRATES. 
 
 logies, under all tlie various modifications by wliich they are 
 adapted to the several modes and spheres and grades of existence 
 of the different species — should be the great aim of anatomical 
 science ; as l^eing that which reduces its facts to the most natural 
 order, and their exposition to the simplest expressions. 
 
 It is impossible, in pursuing the requisite comparison upward 
 through the higher organised classes, not to recognise resemblances 
 between the idtimate states and forms of ichthyic organs, and the 
 transitory condition of the same parts, in the higher species. 
 But these resemblances have been sometimes overstated, or pre- 
 sented under unqualified metaphorical expressions, calculated to 
 mislead the student and to obstruct the attainment of complete 
 conceptions of their nature. We should lose most valuable fruits 
 of anatomical study were vfe to limit the application of its facts 
 to the elucidation of the unity of the verteljrate type of organi- 
 sation, or if wc were to rest satisfied with the detection of the 
 analogies between the embryos of higher and the adults of lower 
 species in the scale of being. We must go further, and in a 
 different direction, to gain a view of the fruitful jihysiological 
 principle of the relation of each adaptation to its appropriate 
 i'unction, if we would avoid the danger of resting in sjieculations 
 on the mode of operation of derivative secondary causes, and of 
 blinding the mental vision to the manifestations of Design which 
 the various forms of the Animal Creation oft'er to our contem- 
 plation. 
 
 To revert, then, to the skeleton of Fishes, with a view to the 
 teleological application of the facts determined by the studv of 
 this complex modification of the animal framework. Xo doubt 
 there is analogy between the cartilaginous state of the cndo- 
 skeleton of Cuvier's Chondropterygians, and that of the same 
 part in the emlnyos of air-lireathing Vertelirates ; Init why the 
 gristly skeleton should be, as it connnonly has been pronounced to 
 be, absolutely or teleologically inferior to the bouv one is not so 
 obvious. The ordinary course of age, decrepitude, aud decav of 
 the living body is associated witli a ])rogressivc accumulation of 
 earthy and inorganic ])articles, gradually ini])cding and stiffeniu"- 
 the movements, and finally stopping the i)lay of tlic vital machine. 
 And I know not why a flexible vascular animal substance should 
 be sujiposed to ))e raised in tlie histological scale because it has 
 become unpregnated, and as it were p^Hrificd, by tlie abundant 
 intus-susception of earthy salts in its areolar tissue." It is iierfcetly 
 intelligible that this accelerated progress to the inori;-anic state 
 may be re()uisile for some special otiice of sucli calcified parts in 
 
LOCOMOTION OF FISHES. 245 
 
 the individual economy ; but not, therefore, that it is an absolute 
 elcYation of such parts in tiie scries of animal tissues. 
 
 It has been deemed no mean result of Comparative Anatomy 
 to have pointed out the analogy between the shark's skeleton and 
 that of the himian emlnyo, in their histological conditions ; and 
 no doubt it is a very interesting one. But the perception of 
 such analogy is nf)t incompatible witb the endeavoiu- to gain 
 insight into the purpose of the Creator, in so arresting the ordi- 
 nary course of osteogeny in the highly organised fish. No law of 
 human intelligence condemns it to restrict its cognizance of the 
 pheuomenon, as solely those of an unfinished, incomplete stage of 
 an hypothetical serial dcvelopement of organic forms. 
 
 The predaceous Sharks arc tlie most active and vigorous of 
 fishes ; like birds of prey, they soar, as it were, iu the upper 
 regions of their atmosphere, and, without any aid from a modified 
 respiratory apparatus, devoid of an air-bladder, they habitually 
 maintain themselves near the surface of the sea, by the action of 
 their large and muscular fins. The gristly skeleton is in pro- 
 spective harmony with this moile and s])herc of life, and we shall 
 subsequently find as well-marked modifications of the digestive 
 and other systems of the shark, by Avhicli the body is rendered as 
 light, and the space which encroaches on the muscular system as 
 small, as might be compatible with those actions. Besides, light- 
 ness, toughness, and elasticity are the qualities of the slvcleton 
 m<jst essential to the shark : to yield to the contraction of the 
 lateral inflectors, and aid in the recoil, are the functions which tlie 
 spine is mainly required to fulfil iu the act of locomotion, and to 
 which its alternating elastic balls of fluid, and semi-ossified l)i- 
 concave vertebra;, so admirably adapt it. To have had their entire 
 skeleton consolidated and loaded with earthy matter would have 
 proved an encumbrance altogether at variance with the offices 
 which the Sharks are appointed to fulfil in the economy of the 
 great deep. 
 
 I suspect that those who see in a modification of the skeleton, 
 so beautifully adapted to the exigencies of the highest organised 
 of fishes, nothing more than a foreshowing of the cartilaginous 
 condition of the reptilian embryo in an enormous tadpole, arrested 
 at an incomplete stage of typical dcvelopement, liave been misled 
 by the common name given to the Plagiostomous fishes. The 
 animal basis of the shark's skeleton is not cartilage ; it is not that 
 consolidated jelly which forms the basis of the bones of higher 
 Vertebrates: it has more resemblance to mucus; it requires 1000 
 times its weight of boiling water for its solution, and is neither 
 
■246 ANATOMY OF VERTEBRATES. 
 
 precipitated by infusion of galls, nor yields any gelatine upon 
 evaporation. 
 
 In like manner the modifications of the dermal skeleton of 
 fishes have been viewed too exclusively in a retrospective relation 
 with the prevalent character of the skeleton of the Invertebrate 
 animals. Doul:)tless it is in the lowest class of Verteljrata that 
 the examples of great and exclusive developement of the exo- 
 skeleton are most numerous ; but some anatomists, in their zeal 
 to trace the serial progression of animal forms, seem to have lost 
 sight of all the vertebrate instances of the bony dermal skeleton, 
 except those presented by the ganoid and placoid fishes. He 
 nmst have sunk to the low conception that nature had been 
 limited to a certain allowance of the salts of lime in the formation 
 of each animal's skeleton, who could afiirm that in the higher 
 Verteln-ata ' the internal articulated skeleton takes all the earthy 
 matter for its consolidation,' ' forgetting that the Ijulky Glyptodon, 
 and its diminutive congeners the Armadillos, have their internal 
 skeleton as fully developed and as completely ossified as in any 
 other mammal. The organising energies which perfect and 
 strengthen the osseous internal skeleton do not destroy nor in 
 any degree diminish the tendency to calcareous depositions on the 
 surface, when the habits and s])here of life of the warm-blooded 
 quadruped require a strong defensive covering from that source. 
 Neither do wc find in the cold-lilooded series that the endo- 
 skcleton of the alligator or scelidosaur was consolidated by a 
 minor amount of earthy matter than that of the naked fro"- or 
 horn -scaled lizard. 
 
 The moment that the observations of tlie naturalist bring to 
 light the mode of life of any of tliose fishes which are said to 
 retain an unusual proportion of the external shell of the Inverte- 
 brata, we are in a condition to appreciate the adaptation of that 
 external defensive covering to such mode of life. The Sturgeons, 
 for example, were designed to be the scavengers of the great 
 rivers; they swim low, grovel along the Vinttom, feedino-, in 
 shoals, on the decomposing animal and vegetable substances 
 wliicli are hurried down with the debris of the continents drained 
 l\y those rapid currents ; thus they are c^-er Inisied reconverting 
 the substances, wliich otherwise would tend to corrupt the occaii, 
 into living organised matter. Tliese fishes are, therefore, duly 
 weighted liy a ballast of dense dermal osseous jilates, not scattered 
 at random over their surface, but regularly arrano-od, as the 
 seaman knows how ballast slundd be, in orderly series alou"- the 
 
 ' xxvii. p. S27. 
 
LOCOMOTION OF FISHES. 247 
 
 middle and at the sides of the )3ody. Tlie protection against the 
 water-loo-o-ed timber and stones hurried alon<T their I'ecdino- 
 grounds, whicli the sturgeons derive from their scale-armour, 
 renders needless the ossification of the cartilaginous case of the 
 brain or other parts of the endoskeleton ; and the weight of the 
 armour requires that endoskeleton to be kept as light as may be 
 compatible with its elastic property and other functions. The 
 sturgeons are further adjusted to their place in the licjidd element, 
 and endowed with the power of changing their position and rising 
 to the surface, by a large air-bladder. 
 
 These teleological interpretations of the dermal bony plates 
 may give some insight into the habits and conditions of existence 
 of those Ganoid and heavilj'-protccted Plaooid Fishes wMch so 
 predominated in the earlier periods of animal life in OTir planet, 
 which Ganoids and Placoids have hitherto been viewed almost 
 exclusively fiy the light of the analogy of an embrycjnic ' Age of 
 Fishes,' or explained as arrested stages in the ti'ansmutation of 
 Crustacea. I long ago demonstrated that both placoid plates and 
 ganoid scales, in the extinct {Lcjridotus^) as well as existing 
 (Lepidosteus) iishes, differed from the su})erficial shells of tlie 
 Invertebrata ^ in presenting the same organisation for growth and 
 repair, the same essential microscopic structure, as the ossified 
 parts of the endoskeleton which they serve to protect. 
 
 The Cocciistcus, fig. 127, of the Old Red Sandstone, like the 
 Piiiidodus of the Ganges, had a half suit of such organised 
 armour; and, as Hugh JNIiller' suggests, the habits of the modern 
 sheat-fish may have l)een foreshown in priine\'al times by the 
 placoganold, burying the undefended jiart of its body in the mud, 
 and exposing ovllj its helm and cuirass, to arrest, as they passed, 
 the smaller animals on which it preyed. 
 
 Nevertheless, the degree in which the exoskeleton jiredominates 
 <jver the endoskeleton as we penetrate into past time, descending 
 into the fossiliferous strata of the earth for evidence of ancient 
 life, is highly interesting and suggestive. 
 
 At the present day only two lepidoganoid genera of fishes are 
 known — the Lepidostens of North America, and the Pohjpterus of 
 vlfrica — both restricted to fresh waters. Other existing fishes of 
 cognate organisation (Am/a, S'lidi,':, e. g. ) have soluble and flexible 
 scales. As we descend to the older tertiary beds the number of 
 Lepidoganoids increases, their geographical relations expand, and 
 their sphere of life embraces the salt waters of the ocean. At 
 the present day the jjlacoganoid and placoid, or plagiostomous, 
 
 ' V. p. 14. '' xxvu. p. 337. ^ cxcvi. p. 288. 
 
248 ANATOMY OF VERTEBRATES. 
 
 fishes, form a small minoi'ity of the class. In the chalk forma- 
 tions the number of the species of Placoicls and Ganoids rapidly 
 increases, and soon preponderates ; in all the older fossiliferous 
 strata they exclusively represent the class of Fishes. The pre- 
 dominance of osseous matter deposited in the tegumentary system 
 in these ancient extinct Fishes is not unfrequently accompanied 
 by indications of a semi-cartilaginous state of the endoskeleton, 
 like that in the Lepidosiren of the present day ; the total absence 
 of any trace of vertebral centres, and the vacant tract, where they 
 should have been, between the bases of the neur- and hasm- 
 apophyses which ha^'C been little disturbed, as in fig. 127, show 
 jDlainly enough that the primitive gelatinous notochord has been 
 piersistent.' In not one of the extinct Fishes of the Devonian 
 and Silurian systems has a vertebral centrum been discovered ; 
 but the enamelled dermal osseous scales and plates are richly 
 developed, and most remarkable for their beautiful and varied 
 external sculpturing, and often for their great size. 
 
 In the mesozoic strata ganoid species exhibit a progressive 
 expanse and downward growth of the neurapophyses, converting 
 the notochordal capsule into distinct bony segments ; the terminal 
 cups of bone are subsequently added, and the centrum is completed. 
 
 At the present day the Lepidosiren repeats the notochordal con- 
 dition of the endoskeleton, but without the compensating ganoid or 
 placoid devclopements of the skin ; and the Sheat-fishes {S'iliirida') 
 combine the large tuberculated osseous dermal plates with a well 
 ossified internal skeleton. The existing sturgeons alone manifest 
 contrasted conditions of the endo- and exo-skelctons, like those in 
 the ancient placoganoids ; but what is now a rare and exceptional 
 instance of analogy to the testaceous and crustaceous Iiwerte- 
 brates was the rule in the first-born fislies of our globe. 
 Those fishes, which from the determination of the ossifying 
 energies to the endoskeleton have been termed Tcleosfei, consti- 
 tute the bulk of the tertiary and existing species of this class. 
 But gradations of cndoskelctal ossification are still indicated. 
 A great propf)rtion of the primitive cartilage is retained in the 
 skull of many of tlie Teleostci, the Salmon and Pike, for example; 
 and the greater proportion of the animal to tlie earthy matter in 
 all the bones, their coarse texture, tlie radiating fibres of the flat 
 cranial l>ones, and the general alisonce of don'tated sutures, are 
 characters in all Osseous Fishes, which remind the Authro])otouiist 
 of transitional ones in the human f,rtus ; but tlve light of teleo- 
 
 ' Sec also tlic beantifiil illnslvntion of tliis fact in tlic .V,-m.,/,K nir/m^iw-, No. 620 
 of thu lliuitcrian Scries of Fossil Fishes in (lie J[uscum of the Loiulon'coUo"e of 
 Surgeons; cxciii. p. 155. ° 
 
LOCOMOTION OF FISHES. 249 
 
 logy demonstrates the perfection of such conditions, in relation to 
 the atmosphere and movements of the Fish. It is generally in 
 Iresh-water abdominal Fishes that the semi-osseous condition of 
 the skull is found, and the diminution of the (|uantity of heavy 
 earthy particles may be connected with the less dense quality of 
 their medimn, as compared with sea-water, and with the usually 
 more posterior position of the ventral fins. 
 
 In the form of a fish, the head is disproportionate^ large, as it 
 is in the mammalian embryo. But the head of a fish must needs be 
 large to meet and overcome the resistance of the fluid, in the 
 mode most favoural:)le for rapid progression : it must therefore 
 grow with the growth of the fish. Hence the large cranial bones 
 always show the radiating osseous s})icidiB in their clear circum- 
 ference, which is the active seat fif growth ; hence the number of 
 overlapping squamous sutiu-es, which least ojipose the progressive 
 extension of the bones. The cranial cavity expands with the 
 expansion of the head : the absorbents remove from within as the 
 arteries build u]) from without; but the brain undergoes no cor- 
 responding increase ; it lies at the bottom of its capacious chamber, 
 which is principally occupied by a loose cellular tissue, situated, 
 like the arachnoid, between the pia mater and the dura mater, and 
 having its cells filled with an oily fluid, or sometimes, as in the 
 Sturgeon, Ijy a com})act fat.' Now, tins condition of the en- 
 veloi)cs of the brain is not only, like the filirous tissue and 
 squamous sutures of the ever-growing cranial bones, related to 
 tlie requisite proportions of the fore-part of the fish for facilita- 
 ting its progressive motion, luit it is one which no embryo of a 
 higher animal ever presents : it is as peculiarly piscine, as it is 
 expressly adapted to the exigencies of the fish. 
 
 It has been held that confluence of distinct bones is a consequence 
 of high circulating and respiratory energies ; yet the anchyloses 
 of the superocclpital, parietal, and frontal above the craniiuu, and 
 of the basi-ocoipital, basi-sphenoid, and pre-sphenoid below the 
 cranium, in Lepidosiren, and the constant confluence of the basi- 
 and pre-sphcnoids in all bony fishes, disprove the constancy of the 
 supposed relationship, and lead us to look for other explanations 
 of such coalescence of primitively or essentially distinct Ijoues. 
 We shall find a final cause for the rapid consolidation and union 
 of the elongated bodies of the two middle cranial -s'ertebra; of 
 Fishes in tlie necessity for strength in the basis of that part of 
 the skull, from the sides of which the large and heavy mandibular 
 and hyoid arches and their appendages are to be suspended, and 
 
 ' xxiu t. i. p. 309. 
 
250 ANATOMY OE VERTEBRATES. 
 
 to swing freely to and fro. The posterior and anterior sphenoids 
 continue distinct bones in all Mammals during a period of life at 
 which they form one continuous Ijone in Fishes. 
 
 The loose connections of most of the bones of the face may 
 likewise remind the homologist of their condition in the im- 
 perfectly developed skull of the embryos of higher animals ; but 
 this condition is especially subservient to the peculiar and ex- 
 tensive movements of the jaws, and of the bones connected with 
 the hyoid and branchial apparatus. 
 
 Not any of the limbs, j^roperly so called, of Fishes, are pre- 
 hensile ; the mouth may be propelled and guided by them to the 
 food, but the act of seizing must be performed by the jaws. 
 Hence in many fishes both upper and lower maxillary bones enjoy 
 movements of jirotraction and retraction, as well as of opening 
 and shutting. The firm connections of the upper jaw, and wedged 
 fixity of the bone suspending the under jaw, which characterise 
 the higher Reptiles and Mammals, woiild be imperfections in the 
 Fish ; in which, therefore, such characters are not only absent, 
 but special developement in the opposite direction not unfre- 
 qucntly goes so far as to produce the most admirable mechanical 
 adjustments of the maxillary apparatus, compensating for the 
 absence of hands and arms, like those which have been exemplified 
 in the instance of the Epihidiis ijisidiutor.^ AVe must guard our- 
 selves, howe^'cr, fi'om inferring absolute superiority of structure 
 from apparent complexity. The lower jaw of fishes might at first 
 view seem more complex than that of man, because it consists of 
 a greater numljer of pieces, each ramus being composed of two or 
 three, and sometimes more separate bones. But, by parity of 
 reasoning, the dental system of that jaw might be regarded as 
 more complex, because it supports often three times, or ten times, 
 perhaps fifty times, the number of teeth which are found in the 
 human jaw. We here perceive, however, only an illustration of 
 the law of vegetative repetition as the character of inferior organ- 
 isms ; and we may view in the same liglit the nmltiplication of 
 pieces of which the supporting jicdicle of the jaw is composed in 
 Fishes. But the great size and the doidile glenoid or trochlear 
 articulation of that jiedicle, are developements beyond, and in 
 advance of the condition of the Ijones sujipcniing tlie lower jaw 
 in Manunals, and relate l)oth to the increase of the ca]iacity of'the 
 mouth in Fishes tor the hulgment of the great hyoid and branchial 
 ap])aratus, and to the sujiport of tlie opercula, or doors whicli open 
 and close the branchial cliamliei-s. The di\ ision i>f the lono- 
 
 ' r- ii'j, fig. 87. 
 
LOCOMOTION OF FISHES. 251 
 
 tympanic pedicle of Osseous Fishes into several partly ovcrlap]>ing 
 ])ieccs adds to its streno-th^ and by permitting a slight elastic 
 Ijending of the whole diminishes the liahility to fracture. The 
 enormous size, moreover, of the tympano-mandibular arch, and of 
 its diverging appendages, contributes to ensure that proportion of 
 the head to the ti'unk which is best adapted for the progressive 
 motion of the fish through the water. But without the admission 
 and appreciation of these pre-ordained adaptations to special exi- 
 gencies in the skeleton of Fishes, the superior strength and 
 complex developement of the tympanic pedicle and its ajipendages 
 Avould be inexplicable and unintelligible in this lowest and first 
 created class of Vertebrate animals. 
 
 All writers on Animal Mechanics have shown how admirably 
 the whole form of the fish is adapted to the element in which it 
 Ha'cs and moves : the viscera are packed in a small comjiass, in a 
 canity brought forwards close to the head ; and whilst the conse- 
 quent abrogation of the neck gives the advantage of a more fixed 
 and resisting connection of the head to the tnmk, a greater pro- 
 portion of the trunk behind is left free for the developement and 
 allocation of the muscidar masses which are to move the tail. In 
 the caudal, which is usually the longest, portion of the trunk, 
 transverse processes cease to be developed, whilst dermal and 
 intercalary spines shoot out from the middle line above and below, 
 and give the A'crtically extended, compressed form, most efficient 
 lor the lateral strokes, by the rapid alternation of which the fish 
 is propelled forwards in the diagonal, Ijetwccn the direction of 
 those forces. The advantage of the bi-concave form of vertebra 
 with intervening elastic capsules of gelatinous fluid, in effecting a 
 combination of the resilient with the muscular j^iowcr, is still more 
 obvious in the Bony Fishes than in the Shark. 
 
 The normal character of Ichthyic myology shows itself in the 
 ■\-ast proportion of the vegetatively-repeated myocommas, corre- 
 sponding with the vertebral segments, as compared with the 
 su})eradded system of muscles subservient to the action of their 
 diverging appendages : but this condition, which, inasmuch as it 
 deviates so little from the fundamental type, throws so nnich light 
 upon the essential nature and homologies of the muscles of the 
 Vertelu-ata, is not less admirably and expressly adapted to the 
 habits and medium of existence of the Fish. Tlie interlocked 
 myocommas of the trrmk constitute, physiologically, two great 
 lateral muscular masses, adapted by their attachments, and 
 especially by those of the anterior and posterior ends, to bend 
 vio'orously from side to side, with the whole force of their alter- 
 
252 ANATOMY OF VERTEBRATES. 
 
 nating antagonistic contractions, the caudal moiety of the trunk, 
 producing that douljle lasli of the tail by which the fish darts 
 forwards with such velocity. When the lateral muscles are more 
 violently contracted, so as to bend the whole trunk, the recoil 
 may even raise and propel the fish some distance from its native 
 element : thus the salmon overleaps the roaring cataract which 
 opposes its migration to the shallow sources whither an irresistiljle 
 instinct impels it to the business of spawning ; and thus the 
 flying-fisli, in the extremity of danger, baffles its j^ursuer by 
 springing aloft, and prolongs its oblique course through the air 
 by the aid of its outspread pectorals. When the anterior por- 
 tions of the creat lateral masses act from the trunk as a fixed 
 point upon the head, they move it rapidly and forcibly from side 
 to side : in tliis way tlie Siluri deal severe blows with their out- 
 stretclied serrated pectoral spines ; thus the Percoid and Cottoid 
 Fishes strike with their opercular spines ; and so likewise may 
 the Saw-fish {Prlstis) and Sword-fisli (^X/phia.i) wield their for- 
 midal^Ie weapons, although their deadly cut or thrust is commonly 
 delivered with the whole impetus of the onward course, the head 
 being rigidly fixed upon the trunk. 
 
 The supracarlnales, combining with the dorsal jiortions of the 
 myocommata, give tension to the region of the back, slightly 
 raise the tail, and depress the dorsal fins. Tlie infracarinales, in 
 combination witli the retractores pubis, tend to compress the 
 abdomen, to constrict the anus, and to depress the tail. 
 
 The muscles of the pectoral fins, tliougli, compared with those 
 of the homologous members in higher Vertebrates, they are very 
 small, few, and simple, yet suffice for all tlie requisite movements 
 of the fins ; elevating, depressing, advancing, and aixain lavino- 
 them prone and flat, by an oblique stroke, upon tlie sides of the 
 body. The rays or digits of both pectorals and ventrals, as well 
 as those of the median fins, can be divaricated and approximated, 
 tlie intervening webs spread out or folded up, and the extent of 
 surface rer[ulred to react upon the ambient medium in each chano-e 
 and degree of motion, can be duly regulated at pleasure. 
 
 In the ordinary forward movement the tail first Itends from the 
 vertebral axis, whicli is tlie axis of motion, fig. 159, f] (/, to a. 
 During this action the centre of gravity, r, slightly recedes. 
 From a the tall Is next forcibly bent by the muscles on the 
 opposite side, in tlie direction of the line a i. The force of the 
 action u])on the water in /i i is translated to the body in / a, 
 causing the centre of gravity, c, to move obliquely forward, in 
 tlie direcllon of r h, parallel to i a. The tail, continulno- its 
 
LOCOMOTION OF FISHES. 
 
 253 
 
 nf h>ri>inotive act, 
 
 ^li. C-\XXJ. 
 
 flexion in e o, acts backward, in tlic direction of o e ; havinf; 
 reached the point o, it is again forciljly bent in the line o e 
 causing an impulse on the centre of gravity in c b, parallel to o e ; 
 if the tAvo forces c h and c h acted simul- 
 taneously, we should obtain the resultant 
 c f; but, as they do not, the point c will 
 not move exactly in the line c f, but in a 
 curved line, evenly between d ey"and a line 
 drawn parallel to it tln-ough /(. The fish 
 being in motion, the tail descril)es the arc 
 of an ellipse ; whereas, if it were station- 
 ary, it would describe the arc of a circle. 
 The power of varying the position and ex- 
 panse of the tail-fin during the side-strokes 
 complicates the ])roblem ; its plane may be 
 perpendicidar to the stroke's direction, and 
 its expansion greatest at the begiiniing of 
 the stroke, as in a i ; and it may be oblique 
 to the direction of the rest of the stroke, 
 as in e o, with contraction of the surface. It 
 must, further, be considered that the water 
 having been set in motion by flexion in one direction, produces, 
 when meeting the tail moving in the opposite direction, a resis- 
 tance proportional to the sum of the squares of the two velocities. 
 The shape of the caudal fin varies nuich in fishes, according 
 to the kind and degree of motion required : in the imprisoned 
 embryo, or newly-hatched fry, in the long and slender undulating 
 eel, in the sluggish Lepidosiren, the vertelDra; continue to the end 
 of the body in a straight line, distinct, and decreasing to a point ; 
 and the tail is bordered above and below by a vertical f(.)ld of 
 skin; terminating either in a point, as in fig. 100, or obtusely. 
 Such fold or fin is symmetrical, but not ' homocercal.' ' The 
 vertical folds deepen; at first, in some Plagiostomes, e. g., 
 equably, forming a terminal lobe ; then excessively, in the lower 
 or ha3mal fold, with the developement therein of rays, and with an 
 upward or neural inclination of the supporting vertebras. Shorter 
 rays are developed in the shalhjwer neural fold, which terminates 
 at the pointed end of the vertebral series. The anterior rays of 
 the ha?.mal fold, which are the longest, form a second point. The 
 tail-fin is thus bifurcate, but unsymmetrical ; and this stage of 
 
 ' By tliis latter terra M. Agassiz signifies a subscrnient grade of moilificatiDn and 
 developement, and a grave fallaey lurks in its misapplieation totheeonimon embryonal 
 condition of the tail-fin in Fishes, as by the Author of cxcvin. 
 
254 ANATOMY OF VERTEBRATES. 
 
 developement is termed the ' heteroccrcal ' one. It is shown by 
 the Sturgeon, fig. 29, and by the Chimteras and Sharks of the 
 jwesent day. It was the faslrion of tail (fig. 127) which prevailed 
 in Fishes throughout the paleozoic and triassic periods. 
 
 In some oolitic fishes first is observed such a lengthening of 
 the dermoneurals of the tail, with such a shortening and running 
 together of the terminal vertebraj, and such a jiroportion of the 
 dermoha3mals, as leads to an equal-lobed caudal fin, which has 
 been termed ' homocercal ; ' but as it is only symmetrical in 
 contour, and remains more or less unsymmetrical in its frame- 
 work, I term it 'homocercoid.' The ganoid fishes of the mesozoic 
 periods manifest several interesting gradations of this transitional 
 state from the hetero- to the true homo-cereal form, each step 
 being a permanent character of the extinct sjiecies presenting it. 
 The embryos and j'oung of Salmonida, of most Malacopteri, and 
 of many Acantlioytcri, go through closely analogous stages to 
 those which were jDcrmanent in extinct fishes ; and the slight 
 upward twist of the coalesced terminal caudals, and the inequality 
 of its up2)er and lower lobes, indicate the fact in the symmetrically- 
 shaped ' homocercoid ' tail-fin of the adults.' In the Anacanthini, 
 fig. 34, and Scomlieroids, fig. 33, the terminal tail-vertebras shrink 
 and coalesce in the line of the trunk's axis ; the dermoneural and 
 dermohajmal rays are equally developed, and a truly symmetrical 
 or ' homocercal ' caudal fin is the result ; and this is the latest 
 and greatest modification of the organ. The majority of existing 
 species of bony fishes indicate, in the course of their acquisition of 
 the symmetrical tail-fin, the heteroccrcal stages at which it is seve- 
 rally arrested in different older extinct species, doubtless in close 
 relation with the power and kind of swinnning required l_iy each. 
 
 The heteroccrcal tail helps the fish to vary its onward course. 
 The Shark wheels about in pursuit of prey, and rotates the trunk, 
 to bring the inferioi'ly-opening mouth to bear upon the victim. 
 Tlie Sturgeon maintains its body in the obli(iue position while 
 u})turning the muddy bottom of the strongly-running stream, and 
 avoids, by deftly bending to right or left, the drift bodies that are 
 hurried down the river. The homocercal tail is a more eftcctive 
 form for a straight forward rush. When it is truncate and tri- 
 angidar, tlic apex being the centre of motion, the centre of force 
 is three-fourths the distance of its base from the axis of oscillation, 
 and the muscles of the tail act at a corresponding disadvantage. 
 AVhen the tail is forked, as in fig. 33, the area is" in the inverse 
 
 ' See the persistent " trace of the emhvyonal hcteroecrcnl form of the tail " in the 
 Sea-perch {Centropnslis ghjax, Owen), No. 191, p. 51, xuv. 
 
LOCOMOTION OF TISHES. 255 
 
 ratio of the distance from the centre of gra-^'ity, and the centre of 
 force is one-half tlie distance from tlie centre of motion ; conse- 
 quently the fislies so endowed have the greatest velocity. It is 
 such in the Sword-fish as to enable it to drive its rostral weapon 
 through a ship's timliers with the force of a cannon ball — for 
 example, through fourteen inches of oak, after penetrating the 
 copper sheathing, four inches of deal, and a layer of felt.' 
 
 As most fishes require to sustain themselves above the bed or 
 bottom of their rivers, lakes, or seas, and as their specific gravity 
 is greater than that of water, they are couimonly provided with 
 an air-bladder, situated immediately under the spine, and above 
 the centre of gravity, and usually accompanied with powers of 
 renewing, expelling, compressing, and dilating its gaseous contents. 
 This hydrostatic apparatus thus becomes an important auxiliary 
 organ of locomotion. 
 
 The Diodons and Tetrodons fill an immense expansion of the 
 ccso])hagus by swallowing air ; and as this lies below the centre of 
 gravity, the body, so inflated, rolls over, and they are drifted, 
 passively, back downward, by the winds and currents. 
 
 The air-bladder is absent in Dermopteri, Plagiostomi, Ploii.ro- 
 nretidce ; and such fishes, unless endowed with compensating 
 powers and propiirtions of body and fins, as in the Sharks, 
 habitually grovel at the bottom, and exhibit flattened forms of 
 body, as in the Rays and Flounders. 
 
 With the exception of the above-described modifications of a 
 few terminal A'ertebraj, those of the trunk remain throughout life 
 distinct from one another in Fishes, as they originally are in the 
 embryos of all liigher Vertebrates. The confluence of vertebra 
 at the base of tlie tail would have been a hindrance to the 
 required movements of such part of the spijie in creatiu-es which 
 progress by alternate vigorous inflections of a muscular tail. A 
 sacrum is a consolidation of a greater or less proportion of the 
 vertebral axis for the transference of more or less of the weight 
 of the body upon limljs organised for its support on dry land ; 
 such a modification would have been viseless to the fish, and not 
 only useless, but a defect. 
 
 The pectoral fins — those curtailed prototypes of the fore-limbs 
 
 of other Vertebrata, with the last segment, or hand, alone jiro- 
 
 jccting freely from the trunk, and swathed in a common undivided 
 
 teo'umentarv sheath — present a condition analogous to that of 
 
 & . ... 
 
 the embryo buds of the homologous memljcrs in the higher Ver- 
 
 ' See the specimen in tiie Museum of the Roj'al College of Siir^^eons, London, 
 described in cxov. p. 5, 
 
25G ANATOMY OF VERTEBRATES. 
 
 tebrata. But what would have been the effect if both arm and 
 fore-arm had also extended freely from the side of the fish, and 
 dangled as a long flexible many-jointed appendage in the water ! 
 This higher developement, as it is termed, in relation to the pre- 
 liensile limb of the denizen of dry land, would have been an im- 
 perfection in the structure of the creature which is to cleave the 
 liquid element : in it, therefore, the fore liml) is reduced to the 
 smallest proportions consistent with its required functions : the 
 brachial and antibrachial segments are abrogated, or hidden in the 
 trunk : the hand alone projects and can be applied, when the fish 
 darts forward, prone and flat, by flexion of the wrist, to the side 
 of the trunk ; or it may be extended at right angles, with its flat 
 surfaces turned forward and backward, so as to check and arrest 
 more or less suddenly, according to its degree of extension, the 
 progress of the fish ; its breadth may also be diminished or 
 increased by approximating or divaricating the rays. In the act 
 of flexion, the fin slightly rotates and gives an obliqvie stroke 
 to the water. If one of the pectorals be extended, it will turn 
 the fish in a curve towards that side : if the other only, it 
 will turn it on the opposite side : they tluis act as a rudder. For 
 tliese functions, however, the hand requires as much extra 
 developement in breadth, as reduction in length and thickness ; 
 and this is gained by the addition of ten, twenty, or it may be 
 even a hundred digital rays, beyond the number to which the 
 fingers are restricted, in the hand of the liigher classes of Verte- 
 brata. We find, moreover, as numerous and striking modifi- 
 cations of the pectoral fins, in adjustment to the peculiar habits 
 of the species in Fishes, as we do of the fore limbs in any of the 
 higher classes. This fin may wield a formidable and sjtecial 
 weapon of offence, as in many Siluroid fishes. But the modified 
 hands have a more constant secondary office, that of touch, and 
 are applied to ascertain the nature of surrounding objects, and 
 j)articularly the character of the bottom of the water in which the 
 fish may live. The tactile action of the pecttu'al fins mav be 
 witnessed when gold fish are transferred to a strange acsscI ; they 
 com])ress their air-bladder, and allow themselves to sink near the 
 bottom, which they sweep as it were, by rajiid and delicate vibra- 
 tions of the pectoral fins, apparently ascertaining ihat no sharj) 
 stone or stick jirojects U])wards, which might injure them in their 
 rapid movements nnnid their jirison. If the pectorals are to 
 perform a siiccial office of exi)loration, certain digits are liberated 
 from the web, and are specially endowed with nervous power for 
 a finer sense of touch, as we see in the Gurnards, ivj:. 82; in 
 
LOCOMOTION OF FISHES. 257 
 
 which they also serve as limhs to creep along the bottom, when 
 the fish is exjiloring the sand Avitli its mailed mouth. 
 
 Some Gobioids (Periopthalmus) can use their mnsciilar pecto- 
 rals to shuffle along the shore, or hunt for insects in humid places.' 
 Certain Lophioids living on sand-banks that are left dry at low 
 water are enabled to hop after the retreating tide by a special 
 prolongation of the carpal joint of the pectoral fin, tig. 102; which 
 fin in these 'frog-fishes' projects like the limb of a terrestrial 
 quadruped, and presents two distinct segments clear of the trunk. - 
 
 The sharks, whose form of body and strength of tail enable 
 them to swim near the surface of the ocean, are further adapted 
 lor this sphere of activity and compensated for the absence of an 
 air-bladder by the large proportional size and strength of their 
 pectoral fins, figs. 30, 104, which take a greater share in their 
 active and varied evolutions than they can do in ordinary fishes. 
 
 The flat-bodied Hays, equally devoid of an air-bladder, and 
 with a long and slender tail, deprived of its ordinary propelling- 
 powers, grovel at the bottom ; but have a still greater develope- 
 ment of the hands, fig. 64, 12, 12, which surpass in breadth the 
 whole trunk, and react with greater force upon it in raising it 
 from tlie bottom, by virtue of a special modification of the scapular 
 arch, which is directly attached to the dorsal vertebraj. 
 
 Nor is the pectoral member restricted in length where its 
 office, in subserviency to the special exigencies of the fish, 
 demands a devclopement in that direction ; the fingers of the 
 Exoccetus and Dactijlopterus, arc as long, and the web which they 
 sustain as broad, as in the expanded wing of the flying mammal. 
 Everywhere, whatever resemblance or analogy we may perceive 
 in the iehthyie modifications of the Vertebrate skeleton to the 
 lower forms or the embryos of the higher classes, we shall find 
 such analogies to be the result of special adaptations for the \)\\v- 
 pose or function for which that part of the fish is designed. 
 
 The ventral fins or homologues of the hind-legs are still more 
 rudimental — still more embryonic, having in view the comparison 
 with the stages of devclopement in a land animal — than the ] ec- 
 toral fins ; and their small proportional size reminds the homologist 
 of the later appearance of the hind limbs, in the devclopement of 
 the land Vertebrate. But the hind limbs more immediately relate 
 to the support and progression of an animal on dry land than the 
 fore limbs : the legs are the sole terrestrial locomotive organs in 
 Birds, whose fore limbs are exclusively modified, as wings, for 
 motion in another element. The legs are the sole organ of sup- 
 
 ' ci.xxiv. viil. iii. p, 97. 
 VOL. I. ^> 
 
258 ANATOMY OF VERTEBRATES. 
 
 port find progression in Man, whose pectoral members or arms 
 are liberated from that office, and made entirely subservient to 
 the varied purposes to which an inventive facidty and an intel- 
 ligent will would apply them. To wliat purpose, then, encumber 
 a creature, always floating in a medium of nearly tlie same specific 
 gravity as itself, with hind limbs ? They could be of no use : 
 nay, to creatures that can only attain their prey, or escap>e their 
 enemy, by vigorous alternate strokes of the hind part of the 
 trunk, the attachment there of long flexiljle limbs would be a 
 grievous hindrance, a very monstrosity. So, therefore, we find 
 the developement and connections of the hind limbs of Fislies, 
 figs. 29, 34, .38, 64, v, restricted to the dimensions and form 
 which, whilst suited to the limited functions they are capable of 
 in tliis class, would prevent their interfering with the action of 
 more important parts of the locomotive machinery. 
 
 Tlie plane of each ventral fin Ijeing horizontal, at right angles 
 to that of the caudal fin, their action serves to balance the body, 
 to incline it on either side when one fin only acts, and to elevate 
 or depress the fish by their joint eftbrt. 
 
 In most fishes the ventral fins merely combine with the pectoral 
 fins in raising the body, and in preventing, as outriggers, the roll- 
 ing movement : but some interesting modifications in relation to 
 particular habits of certain species have previously been pointed 
 out (p. 180). In the long-ljodied and small-headed abdominal 
 fishes, the ventrals are situated near the anus, where they best 
 suliserve the office of accessory balancers ; in the large-headed 
 thoracic and jiigular fishes, the loose suspension of these fins, and 
 the alisence of any connection with a sacral part of the vcrteliral 
 column, permits their transference forward, to aid the pectoral 
 fins in raising the head. 
 
 The planes of the dorral, figs. 24, 39, D, and anal, ib. a, fins 
 are in that of the mesial longitudinal section, and their mo-\ements 
 are usually restricted to elevation and depression. They acciird- 
 ingly increase or diminish the lateral siirfaces of the fish, cor- 
 recting any tendency to oscillate laterally, or to turn ujisido 
 down, as the Ijody would do without some muscular effort, since 
 in the ordinary posture, back ujnvard, the centre of ixra\ ity lies 
 a1)ove the centre of figure. When the fins collapse and the nuis- 
 cular action ceases, as in death, the fish floats belly upward. 
 However, in some singular exceptions, e. g. the Sun-fish, the dorsal 
 and anal fins are unusually extended, and take a more direct share, 
 liy lateral undulating movements, in the locomotion of tlie fish. 
 
 In ordinary shaped Osseous Fishes, if the dorsal and ana! fins be 
 
LOCOMOTION OF SERPENTS. 2.59 
 
 cut off, the fish reels to the rij^ht and left. If the pectorals be cut 
 off in a Perch or otlier hig-headed fish, the head sinks ; if one 
 ]>ectoral be cut off", the fish leans to that side; if the ventral of 
 the same side be also renio\ed, the fish loses its equilibrium ; 
 if the tail be cut off, the loeoinotive power is abrogated. 
 
 § 49. Locomotion of Serpents. — The sole locomotive organs in 
 serpents are the vertebral column, with its muscles, and the large 
 stift' erectile epidermal scutes crossing the under siu-face of the body. 
 
 Although thc^'erteljrai have s3'iiovial cup-and-ball terminal joints, 
 their reciprocal movements are greatly restricted by the ' tenon- 
 and-niortice ' articulations of the double zj^gapophyses at each end, 
 of which tlie inferior have flat horizontal siu-faccs, the superior 
 slightly oblique planes. But as a single segment of the back- 
 bone may be Init -.jy^ part of the length of the body, the sum of 
 the small movements between two Acrteliraj becomes considerable 
 in a certain extent of the long trunk. 
 
 A serpent may, however, be seen to progress without any 
 inflections, gliding slowly, with a ghost-like movement, in a 
 straight line. If the observer have the nerve to lay his hand flat 
 in the reptile's course, he will feel, as the body glides over the 
 palm, the surface pressed, as it were, by the edges of a close-set 
 series of paper-knives, successively falling flat after such a])plica- 
 tion. The skin of the hand has Ijcen seized, so to speak, f)y the 
 edges of the stiff, short, but broad, transverse, horny, ventral 
 scutes, erected or made vertical for that pjurpose, and folding flat 
 upon the body when the effect of the resistance has been gained. 
 Each scute having secured a fulcrum in the plane of motion, the 
 libs connected with it rotate, and transmit the movement u}>on 
 the trimk ; it is, in fact, a step whose length de})ends on the arc 
 through which the pair of ribs may oscillate and on the distances of 
 the scutes from the axes of motion. As both these are small, and 
 the motion has to be transmitted by the succession of short scutal 
 steps through the whole length of the body, this first kind of 
 progression is slow and gliding. 
 
 A second and swifter mode of locomotion on land is by succes- 
 sively bending and straightening portions of the body. Extension 
 Avill carry the straightened part forward in the direction of least 
 resistance. If most resistance be made by the point of the 
 tail, fi"'. 160, e, or by the application to the ground of the edges 
 of the erect scutes, between d and e, the extension of a c will 
 carry the head to h, the smooth overlapping uuerected scutes 
 between a and d favouring the for\vard movement ; and this being 
 effected, and the ground gras])ed by the erection of the scutes 
 
260 ANATOMY OF VERTEBRATES. 
 
 between a and c, flexion of the rest of the body will draw forward 
 the tail, as from h to e. As the extent of the flexion of, say a 
 fourth part of the body, exceeds the space through which a single 
 scute is moved in erection, so does this mode of motion greatly 
 exceed in swiftness the preceding. And this swiftness is accele- 
 rated when the serpent raises the body, in arched curves, from the 
 ground, increasing their span, and progressing in a vertically, 
 instead of a horizontally, undulating course ; when, by augmented 
 vigour of the muscular actions, the whole trunk may be raised 
 into a single arc, and the movement acquire the character of a 
 leap. Thus the body being bent, whilst the neck-scutes fix the 
 head, as at h, the tail will advance from a to e, fig. 161 ; when, 
 being fixed there by the subcaudal scutes, extension will carry 
 the head forward to d, and the serpent will have advanced by the 
 two actions of flexion and extension through a space eqvial io a e 
 or h h. But, if the act of extension be vigorous and sudden, 
 and an equivalent fulcrum be afforded by the tail, the whole body 
 may be carried forward, as by a leaj], farther than its own length. 
 For the saltatory motion, however, the mechanism of a spiral 
 spring is commonly simulated ; the whole body is bent into a 
 series of close-set coils, the svidden extension of which, reacting 
 upon the point of earth against which the tail presses, throws the 
 serpent obliquely forward into the air. In all these movements 
 the curve is essentially lateral ; the amount of rotation between 
 the smaller vertebras, at the two extremes of the body, permits 
 the flexion of the intermediate joints to assume, as in fig. 161, the 
 vertical position. There is no natural undulation of the body 
 njjward and downward — it can take j^lace oidy from side to side. 
 So closely and compactly do the ten pairs of joints between each 
 of the two hundred or tliree hundred vertebr* fit together, that 
 even in the relaxed and dead state the body cannot be twisted. 
 If the attempt at rotation be made at the end of the tail on a 
 dead snake outstretched, the part grasped may be half-twisted ; 
 but the rest of the trunk will turn over, rigid, like a stick. 
 
 Serpents derive the same advantage from their lungs in water 
 as eels ironi their swim-bladder, the air-receptacles in both being- 
 much alike, and placed above the centre of gravity. They lu'o- 
 grcss by a similar scries of successive lateral undulations, gene- 
 rating a surplus force in the moving body equal to the difference 
 between the force of the locomotive organs and the resistance 
 of the medium. In Avatcr-snakes this resistance is made more 
 effective by the lateral flattening (u- compression of tlie tail, which 
 can be drawn forward edgewise, and flapped back breadthwise. 
 
LOCOMOTION OF SERPENTS. 261 
 
 Serpents climb trees by the same mechanism and actions as in 
 the first kind of locomotion ; the edges of the erected scutes 
 laying hold of the bark in succession, as the body glides spirally up 
 the bougli. The tail has a prehensile faculty, especially exercised 
 by the great Constrictors while waiting for their prey. ^^^ 
 
 They instinctively select a tree at the part of the 
 stream easiest of access to the thirsty mammals of 
 the forest, and suspend themselves, bke a jiarasitic 
 creeper, from an overhanging branch, the head and 
 fore-part of the body being floated by the bladder- 
 like lungs upon the stream. 
 
 Serjients are too commonly looked down upon as 
 animals degraded from a higher type ; but their 
 whole organisation, and especially their bony struc- 
 ture, demonstrate that their parts are as exquisitely 
 adjusted to the form of their whole, and to their ^ 
 
 habits and sphere of life, as is the organisation of 
 any animal which we call superior to them. It , 
 is true that the serpent has no limits, yet it can 
 outclimb the monkey, outswim the fish, outleap the 
 jerboa, and, suddenly loosing the close coils of its 
 crouching spiral, it can spring into the air and seize 
 the bird upon the wing : all these -creatures have 
 been observed to fall its prey. The serpent has 
 neither hands nor talons, yet it can outwrestle the 
 athlete, and crush the tiger in the emln-ace of its 
 ponderous overlapping folds. Instead of licking up 
 its food as it glides along, the serpent uplifts its 
 crushed prey, and presents it, grasped in the death- ?/,:'! ',""„"!; ti'S' 
 coil as in a hand, to its slimy gaping mouth. 
 
 It is truly wonderful to see the work of hands, feet, and 
 
 161 
 
 Jlotion of serpent by ar&l'hig the trunk . COTV. 
 
 fins, i)erformed by a modiflcation of the vertebral column — by 
 
2G2 ANATOMY OF VERTEBRATES. 
 
 a multiplication of its segments with mobility of its ribs But the 
 verteljrao are specially modified, to compensate, by the strength of 
 their numerous articulations, for the weakness of their manifold 
 repetition, and the consequent elongation of the slender column. 
 As serpents move chiefly on the surface of the earth, their danger 
 is greatest from pressure and l)lows from above ; all the joints are 
 fashioned accorchngly to resist yielding, and sustain pressure in a 
 vertical direction. 
 
 § .50. Locomotion of limbed Reptiles. — The fish-like Batrachia 
 move in water by means of the lateral inflections of the hinder- 
 half of the trunk, which is compressed and extended vertically 
 by a marginal tegumentary fin. The pjarial limbs are small and 
 feeble : they are limited, in the amphibious Siren, to the pectoral 
 region, and to the function of raising the head and fore-part of 
 the trunk upon the Ijank or shore. In the rest of the order 
 both pairs arc present : in the Amphiumc they are too feeble to 
 suggest any particular locomotive function ; hut they subserve, 
 when somewhat more developed, a slow and awkward reputation, 
 as in the Menopome and Newt. In the Land-Salamander, fig. 
 140, they acquire the due strength for terrestrial progression, and 
 the tail is shortened and rounded. In the Toads and Frogs the 
 tail is absorbed, and the legs lengthened and strengthened, espe- 
 cially the hinder pair ; but with an outward direction from the 
 body, and a position too horizontal to enable them to raise or 
 support it alaove the ground. 
 
 The Frog, in repose, assumes a sitting posture, the thighs 
 turned outward and forward, the legs bent backward, and the 
 lengthened tarsi and feet directed forward. The fore-part of 
 the trunk is propped up by the fore limbs, at an angle of 45^, 
 with the base between the hind limbs, which, in their state of 
 flexion, are ready on the least alarm to project the body forward 
 by their sudden extension. The shoulder-joints of the limbs 
 that receive the shock on alighting from the leap are strength- 
 ened by an interarticular ligament. The great Bull-Frog may 
 clear six feet at a leap, and repeat them so rapidly as to escape a 
 l)ursuer, unless chased at a great distance from the water. Both 
 fore and hind feet arc webbed for swimming, which is chicflv 
 effected by strokes of the strong hind liml)s. Tiie large Indian 
 frog {Rana tigrinci) is said to be able to run along the surface of 
 the water for a short distance. 
 
 Tlic Tree-Frogs (Tli/la) have a concave disc at the end of 
 each toe, for clhnljlug and adhering to the bark and lca\cs of 
 trees. 
 
LOCOMOTION OF LIMBED REPTILES. 
 
 263 
 
 102 
 
 Toads, with semipalmatc feet, have an awkward, l)ut not always 
 slow, progression on land by alternate movements of tiie limbs. 
 Some species are enabled, by peculiar tubercles or projections 
 from the palm or sole, to clamber up old walls. 
 
 But the most remarkable climbers in the reptilian class are 
 certain lizards, es])ecially those called ' Geckos.' Each foot has 
 five toes, which are spread wide apart, expanded at the ends, and 
 terminated by a slender sharp claw. The flattened under surface 
 of the toe-pad, fig. 162, is traversed by a series of 
 transverse folds, with deep interspaces ; the 
 margins of the folds, when applied to a smooth 
 surface, adhere thereto l)y atmos]iheric pressure, 
 through the vacuum caused by muscular erec- 
 tion of the folds, with concomitant exjiansion of 
 the interspaces ; thus the animal, alternately 
 applying and releasing its suckers, climbs a 
 vertical wall or plate of glass, or proceeds along 
 a ceiling with its back downward. 
 
 For climl^ing trees the adjustment of the toes 
 in opposition to each other, in equal or suIj- 
 equal groups, as already described in the Cha- 
 meleon, pp. 175, 193, figs. 119, 123, is an 
 eifective modification. In this reptile the limbs 
 are short and strong, and a prehensile tail is 
 added to the scansorial feet. 
 
 Ordinary lizards, by the great length of the trunk in proportion 
 to its breadth, and l^y the outward extension of the humerus and 
 femur, are under unfavourable mechanical conditions for rapid 
 course upon land. Yet such is the energy of the muscular con- 
 tractions in some species, under the stimulus of solar heat, that 
 they arc deservedly called ' agile,' and ' dart ' out of view in the 
 first rush from a pursuer. They have not, however, the power of 
 maintaining the exertion, and are soon overtaken, if they happen 
 to be far from their retreat. The swiftest runners, e. g. the Tachy- 
 dromi, have the fore and hind limbs least differing in length, and 
 consequently the vertebral column most parallel with the plane of 
 motion. 
 
 In the Crocodiles the fore limits are shorter than the hind ones, 
 in which the foot is longer and more expanded, so as to present a 
 larger surface for striking the water in swimming. But the chief 
 natatory organ in these large amphibious reptiles is the long, 
 compressed tail. In the act of swimming, the fore limbs are 
 applied flat to the sides of the body, and the hind ones chiefly 
 
 Toe of Gickn, inagn. 
 
2C4 
 
 ANATOMY OF VERTEBRATES. 
 
 used in modifying the course through the water. The fore limbs 
 were shorter, and tlie hind limbs longer in the extinct Crocodilia 
 of marine habits. The stiffness of the neck, produced liy the 
 overlapping of the expanded cervical ribs, adds to the power of 
 the head in overcoming the resistance of the water ; but detracts, 
 
 163 
 
 Flying Uzai-d f Z)/'flro ?'n/(riis\ Linn. cciv. 
 
 with the almost inflexible cuirassed trunk, from the capacifv to 
 capture prey on land, which is seldom overtaken, cxccjit by a 
 
LOCOMOTION OF LIMBED REPTILES. 265 
 
 straip;lit-forward vusli : tliis, for a short extent, is dangerously 
 ra])id ; but the Crocodiles are most formidable and agile in their 
 hahitual element the water. 
 
 The little Draco voJans has a body which rarely exceeds 
 110 grains in weight; the delicate tegumentary parachute, sustained 
 by the long slender ribs, fig. 16.3, like the nervures of the insect's 
 wing, measures about five square inches — its area Ijeing as great 
 in proportion to the Aveight of the animal as that of the wings in 
 many birds. But the muscular api)aratus, a, a, sidoserves only 
 the expansion and folding up of the membrane, which would 
 seem, therefore, to act, if the animal ever leaps into air or darts 
 through that element, merely as a sustaining parachute to break 
 the fall. 
 
 The Kcptilia in which the fore limb was developed and modified, 
 in order to work membranous expansions with sufficient force to 
 raise and move the body in air, ceased to exist, apparently, during 
 the deposition of the cretaceous Ijeds, prior to the tertiary epoch 
 in Geology. We learn from the fossilized remains of Ptero- 
 dactyles, that the weight of the body, compared to the area of 
 their outspread wings, must have been very small, fig. Ill, A; 
 that the bones were light, of a thin but compact osseous texture, 
 permeated by air. The digit, so enormously developed for 
 sustaining the main part of the wing, fig. Ill, 5, was restricted, 
 like the antlbrachium in birds, to movements of abduction and 
 adduction, lying along the ulnar side of the fore-arm, and reaching 
 beyond the sacrum, when the wing Avas folded. Tlie proportion 
 of the area of the outstretched wings to the body was greater in 
 Pterodactyles than in most birds, and equalled that in the bats ; 
 like which, the Pterodactyles would alter the alar area by alternate 
 abduction and adduction of the sustaining digit, combined with 
 flexion and extension of the arm and fore-arm. 
 
 The large head and strong neck of the Pterodactyle seem to 
 have called for that extension and forward direction of the anti- 
 brachirun, which would cause the centres of gravity and magnitude 
 to l^e more in advance than in either Inrd or bat. Their pelvic 
 limbs were little more developed than in Bats — must have been 
 unequal to sustain the body — may have concurred Avith the short 
 unfuiculate digits of the fore limb, fig. Ill, i, 2, 3, 4, in a crawling 
 in'ogress along the ground — and, being terminated by toes of 
 equal length, probably served, as in bats, to suspend the body, 
 head downward, during sleep. 
 
26G ANATOMY OF VERTEBRATES. 
 
 CHAPTER IV. 
 
 NERVOUS SYSTEM OF EiEMATOCRYA. 
 
 § 51. Nervous tissues. — Nervous sii'ostance, like muscular, 
 ranks with the most complex of animal tissues in chemical con- 
 stitution, and possesses the greatest atomic weight : but the albu- 
 minous form of proteine here prevails. Nervous tissue presents 
 two formal characters ; one -^'csicular and grey in colour, the 
 other fibrous and white : but the neurine inclosed by neurilemma 
 being softer than myonine, and less definite in arrangement after 
 death, the nerve-fibre usually appears as a tube with white contents. 
 
 Nervous siibstance has two principal dispositions ; one in 
 masses, called ' centres,' the other in threads, called ' nerves.' 
 The centres in Vertebrate animals constitute, according to their 
 relative size or position, the spinal chord (myelon), the brain 
 (encephalon), and ganglions. In these the vesicular, grey, or 
 dynamic form of tissue is associated with the fibrous, white, or 
 conductive form. Most nerves consist of the wliite filjres, and all 
 are internuncial in office, establishing a communication between 
 the centres and the various parts of the body. 
 
 The centres, and their grey or vesicular constituent more 
 especially, appear to originate the nervous force : certain nerves 
 conduct it to the tissues, princi]ially muscular, on which it acts 
 by producing contraction ; other nerves carry the impressions 
 received at their distal ends to the centres : the first are termed 
 ' motory,' from the function they excite, and ' efferent,' from the 
 direction of conduction : the second are termed ' sensorv ' and 
 ' afferent.' Sensation, or the appreciation of the impression by the 
 individual, seems to follow only when the 'afferent' nerve conveys 
 its impressions to the brain ; when it stojis short in the myelon, 
 or ends in a ganglion, it may excite a corresponding or connected 
 'efferent' nerve to ])roduce motion, or a 'reflex' action, which 
 may then take place without sensation or volition. 
 
 The myelon, the enceplialon, and their nerves, constitute tlie 
 'myelencephalous' or ' cere))ro-si)inal ' system, to which belong 
 the ganglions on the sensory roots of the spinal and trigeminal 
 nerves, and tliose in the glosso-pliaryngcal and vao-al nerves. 
 
NERVOUS TISSUES. 
 
 267 
 
 IGl 
 
 A chain of ganglions is situated on each side, near the vertebral 
 foramina, through whicli the cerehro-S2)ii)al nerves issue. These 
 ganglions radiate many nerves, connecting them one with another 
 and with the cerebro-spinal nerves, and ramifying in a plexiform 
 way upon the viscera and coats of the blood-vessels : they con- 
 stitute the 'sympathetic' or 'ganglionic' system in Vertebrates. 
 
 In the cerebro-spinal nerves the primitive fibre consists of a 
 transparent elastic homogeneous tubular 
 mcmlu-ane (neurilemma), fig. 164, a; its 
 contents arc pulpy, homogeneous in the 
 living or recently dead state, and may bo 
 pressed out of the sheath ; when treated 
 with water, as in fig. 164, a, or with alco- 
 hol, they Condense into a white layer, 
 giving that colour to the tnbe : within the 
 vvduto substance Rcmak defines a 'flattened 
 l)and,' and Purkinje an ' axis-cylinder.' 
 "\Mien treated with ether, oil-globules co- 
 alesce in the interior, and accumulate around 
 the exterior of the tube, fig. 164, h. 
 
 The delicacy of the neurileumia, and 
 mobility of its contents, lead, in many cases, 
 to partial dilatations of the tube, of a ' vari- 
 cose' character, jiroljably d\ie to post-mortem 
 influences : in the living or natural state, the primitive nerve- 
 tube or fibre appears to be perfectly cylindrical. 
 
 The follo^ 
 diameter 
 
 Xcrvc tulles nltorcil lij 
 
 CUV. 
 
 The following are results of Todd's admeasurements of their 
 
 in the different vertebrate classes : — 
 Fishes (Eel) j-tj^ts o^ ^^ inch. 
 Reptiles (Frog) -^iwo ^^ ttifVtt of f^i^ inch. 
 Birds ., ,,"'„ n to Wtttt of an inch. 
 
 ;i 
 leVs- tOlTToo of an inch.' 
 
 2 
 
 IMammals 
 
 Primitive nerve-fibres do not divide or branch ; they are 
 associated together, in simple juxtaposition, supported by fine 
 layers of areolar tissue, which condense at the periphery into a 
 common sheath, to which the term ' neiu'ilemma ' is commonly, 
 but not properly, given : it answers to the sheath which surrounds 
 a muscle, similarly binding the constituent fibres of the nerve 
 together, and supporting their nutrient capillaries. These are the 
 smallest in the body ; they run chiefly i)arallel with the nerve- 
 fibres, forming oblong meshes, completed at intervals by cross- 
 vessels. Sometimes the nerve-fibres have a wavy course within 
 
 In a few instances they have been 
 
 cov. p. 593. 
 
 the general sheath, fig. 165 
 
268 
 
 ANATOMY OF VERTEBEATES 
 
 observed to decussate, 
 
 as in fig. 166, changing their relative 
 
 po.sition within the slieath. 
 
 The termination of efferent nerves on 
 sentient surfaces of the skin appears to 
 be plexiform : but they have been seen 
 to enter the bases of the tactile papilla3 
 in the form of loops. The looped termi- 
 nation has been distinctly seen by Henle upon the membrana 
 nictitans of the frog, and by Valentin on parts of the formative 
 matrix of teeth, fig. 167. 
 
 166 
 
 165 
 
 "Wavy course of nerve fibres, "n-ithin 
 the common slieath. ccv. 
 
 167 
 
 Diagram to show the derussntion of the primitive tibres within 
 the tnmlv of a !Ri-\ e. t'Cy. ccvi. 
 
 Amongst the nerve-fibres of the sympathetic system are some 
 of a grey colour, sometimes called ' soft fibres,' vs'hich are flattened, 
 
 homogeneous, more minute than the 
 primitive fibres of the cerebro-spinal 
 system, and characterised by small 
 multinucleate bodies upon their sur- 
 face, fig. 168. 
 
 § 52. Mi/elencephalon of Fishes. — In 
 the cold-blooded Vertebrates the pro- 
 portion of the mass-form, or centres, to 
 the thread-form, or conductors, of the 
 nervous system is less than in the 
 warm-blooded classes. 
 
 In the Lancelet (^Branchiostoma), 
 fig. 169, the neural axis, m d, shows 
 no distinction between brain and 
 myelon ; it is a slender tract of nu- 
 cleated cells, inclosed in a delicate 
 pia mater, constituting a continuous 
 chord, of opaline sub-transparency, 
 ductile and elastic. It is depressed 
 or band-lilcc along its middle third, 
 which is slightly grooved along the 
 medial line of the dorsal surface, 
 
 Tcnninul iicrvca on the s;io n[ tlio p 
 iinil;ir tuoUi of Uie Imvcr j;iw i 
 BlK'cp, sliitwiiig llie ju'rantrt'iiiei 
 Jonp.s. C'l.^vi. 
 
 riHid 
 
MYELENCEPHALON OF FISHES. 
 
 269 
 
 and tapering to both ends, but more gradually to the hinder 
 one, the fore-end being less acute. A streak of pigment- 
 cells marks the middle of the iipper surface : darker cells mark 
 the origins of the nerves. These number from fifty to sixty 
 
 168 
 
 ^i} n «fx?«i 
 
 Ncr\'iins fltiros; from n sitft. or irrey nerve iu tlic 0;iir. ccvrr, 
 A, llbre resolving itself iiitu tll:iritice. li, a llln-e duubied on itseif, 
 sliowinff tlie flattened cbanicter. C, Two fibres lying in juxtaposi- 
 tion, a, a, o, nuclei, c, a nuclear fibre {Kerii/aser). d, a Ubrilla. 
 
 pairs, and appear to come off as simple chords, fig. 170. They 
 perforate the memljranous neural canal, and accompany the inter- 
 muscular septa, dividing into two principal branches — one to the 
 neural or dorsal, the other to the hajmal or ventral, muscular 
 
 109 
 
 Diagr.am of Anatomy of tbc Lancelot, Dnrnchiostoma 
 
 se^fments. The first pair of nerves, fig. 170, h, which Professor 
 Goodsir' thinks might correspond to the 'trifacial,' passes to the 
 membranous parts above the mouth : it may be the homologue of 
 that which, when a part of such membrane becomes specialised 
 as an olfactory sac, becomes the olfactory nerve, as, e. g., iu the 
 
270 
 
 ANATOMY OF VERTEBRATES. 
 
 Lamprey. The second pair is niucli larger ; it passes out of the 
 neural canal, anterior to the first myocomma, and sends a branch, 
 170 c, fig. 170, upward and backward toward the front 
 
 edge of that segment, which communicates with 
 the dorsal branches of several successive nerves of 
 its own side, like the liranch from the coml^ined 
 trifacial and vagal nerves, marked i in fig. 204 : 
 the main trunk of the second nerve curves 
 downward and backward, d, fig. 170, communi- 
 cating with the corresi)onding jiwcis of the suc- 
 ceeding nerves of its own side, to some way 
 beyond the vent, fig. 169, a s : this portion answers 
 to the branches 3 and 4 of the ' nervus lateralis ' 
 in fig. 204. From the princip)al function of the 
 second (conspicuous) pair of nerves in the Laneelet, 
 as a ' nerve of association,' it probably answers to 
 both the trigeminal and vagal, which in most 
 higher fishes combine to form the ' lateral nerve,' 
 with the same relations to the spinal nerves and 
 median fins as the nerves c and d, fig. 170, show 
 in the Laneelet. 
 
 Costa ' describes and figures ' la macchla bruna 
 degli occhi ' (p. 14), ' I'opacita corrispondente 
 sopra e dietro degli occhi' (ib.), '^ and 'talvota i 
 gangli olfattori ' (Tab. i., fig. 2, r/y). Eetzius' re- 
 discovers the ocellus ; and KoUiker'' has more 
 particularly described the sub-terminal ciliated 
 depression, described as an ' olfactory sac,' and 
 indicated in the diagram, fig. 169, ol. According 
 to those observations, olfiictory and optic ner^c- 
 filaments may be inferred ; and the fore part of 
 the neural axis, including the trigemino-vagal 
 nerves, c b, fig. 169, will answer to the brain. 
 
 The succeeding; nerves divide, soon after cmero-- 
 ing, into dorsal and ventral branches, as in higher 
 fishes, corresponding in number Avith the muscnlar 
 segments. The nerves consist of the primitive 
 cylindrical fibres. 
 
 This is the most simple persistent condition of 
 the central organs of the nervous system known 
 
 ln'iicculnliuit. 
 
 XXX. 
 
 ( XXT, 
 
 " Qiicri/, can tliis opako spot be an acoustic sac? 
 
 ' XNXII, 
 
MYELON OF FISHES. 271 
 
 in the Ycrtebrato siibkingxloin. In all other Fishes the fore part 
 ol the neural axis receives the vagal, trigeminal, and special sense 
 ucrvcs, and developes and supports ganglionic masses, principally 
 disposed in a linear series parallel with the axis : this part is the 
 ' hrain ' (encephalon) ; the rest of the axis retaining its columnar 
 or chord-like character is the ' myclon,' and being lodged in the 
 canal ol tlie spinal column, it is usually defined as the medulla 
 spinalis (spinal marrow, or sjiinal chord). 
 
 In the Lamprey the myelon is flattened, opaline, ductile, and 
 clastic, as in the Lancclet and other Dermoytcri : in typical 
 Fishes it is inelastic and oj)aque, cylindrical or sub-depressed ; 
 of nearly uniform diameter, gradually tapering in the caudal 
 region to a point in hcterocercal Fishes, but swelling into a small 
 terminal ganglion' in most homocercal Fislies. 
 
 The Hunterian preparation of the skate {Ruia Batisf shows 
 a slight (brachial or ])ectoral) enlargement of the myelon, where 
 the nnmci-ous large nerves are sent off to the great pectoral fins : 
 a feebler brachial enlargement may be noticed in the Sharks. 
 I have not recognised it in Osseous Fishes, not even in those with 
 enormous pectorals adapted for flight, e. g. Exocatns and Dac- 
 fj/loptcriis : in the latter the small ganglionic risings ujion the 
 dorsal columns of the cervical region of the myelon receive nerves 
 of sensation from the free soft rays of the pectorals, and the 
 homologous ganglions are more marked in other Gurnards 
 (^Trijjlce), which have from three to five and sometimes six paii's^, 
 e. g. in Trujla Adrintica. Similar mj'elonal cervical ganglions 
 are present, also, in Poh/nemiis. In the hcterocercal Sturgeon 
 there is a feeble expansion of the myelim at the l)eginning of the 
 caudal region, whence it is continued, gradually diminishing to a 
 point along the neural canal in the upper lobe of the tail. In 
 some bony fishes (Trout, Blenny) the caudal ganglion is not cpiite 
 terminal, and is less marked than in the Cod or Bream, in which 
 it is of a hard texture, but receives the last pair of spinal nerves. 
 The absence of this ganglion in the Shark shows that it relates 
 not to the strength of the tail but to its form, as depending on 
 the concentration and coalescence of the terminal -^^ertebra; ; 
 except, indeed, Avhere such metamorphosis is extreme, as, e. g. in 
 Orihaqnriscus mola, and where it affects the entire condition of 
 ihc m\'elou, which has shrunk into a short, conical, and, according 
 
 1 LHi. p. 6; Liv. p. 20 (in the Cod). 
 
 - XX. vol. iii. p. 40, pi'op. No. 1347. 
 
 3 LV. pi. 2, fig. 4, p. 106; and Lui. p. G, pi. 2, fig. 24, 2.5. 
 
272 
 
 ANATOMY OF VERTEBRATES. 
 
 to Arsaki (liii. tab. iii. fig. 10), gangliated appendage tc th" 
 encephalon. A like singular modification, but without tlie 
 ganglionic structure, obtains in Tetrodon and Diodon, in a species 
 of wliich latter genus 1 found the myelon, fig. 171, M, only four 
 lines long, in a fish of seven inches in length and mea- 
 '^'^^ surino- three inches across the head. The neural canal 
 
 in these Plectognathic fishes is chiefly occupied by 
 a long "^ Cauda equina,' ib. c e. But, insignificant as 
 the myelon here seems, it is something more than 
 merely unresolved nerve-fibres : transverse white 
 strice are discernible in it, with grey matter, showing 
 it to be a centre of nervous force, not a mere con- 
 ductor. In the Lojohius a long cauda equina jiartly 
 conceals a short myelon, which terminates in a point 
 at about the twelfth vertebra. In other fishes the 
 myelon is very nearly or quite co-extensive with 
 the neural canal, and there is no cauda equina, or 
 bundle of nerve-roots, in the canal : a tendinous 
 thread sometimes ties the terminal ganglion to the 
 end of the canal. 
 
 A shallow longitudinal fissure divides the -N'entral 
 surface, and a deeper one the dorsal siu'face, of 
 the myelon, into equal moieties : a feeble longi- 
 tudinal lateral impression (Sturgeon) subdivides 
 these into dorsal and ventral columns ; in other fishes 
 (Cod, Herring) these are separated by a lateral tract, and six 
 columns or chords may be distinguished in the myelon — two 
 dorsal or sensory, two ventral or motory, and two lateral or 
 restiform tracts. A minute cylindrical canal extends from the 
 fourth ventricle, beneath (ventrad of) tlic bottom of the dorsal 
 fissure, along the entire myeton ; this canal is not exposed in the 
 recent fish by merely divaricating the dorsal columns. Both, 
 lateral halves of the myelon have grey matter in their interior, 
 and white transverse strite. Although many fishes (Bream, 
 Dorsk) show a slight enlargement at each junction of the ner\-c- 
 roots with the myelon, the anatomical student will look in ^-ain in 
 the recent Eel, or Lump-fish, for that ganglionic structure of the 
 myelon which the descriptions of Cuvicr ' might lead him to 
 expect. 
 
 As the myelon a])in-(iachcs the encephalon, It expands; and the 
 following changes may be here observed in the Cod and Shark: — 
 
 Bniiii juid my 
 loll, Dio'ioii, 
 liatui-al size 
 
 xxiii , i ji. 323; XJII. iii. ji. 170. 
 
Section of medulla 
 
 ENCEniALON OF FISHES. -273 
 
 in the ventral cohnnns a short longitndhial groove divides a 
 .larrower median 'pre-pyramidal' tract, fig. 172, a, from a broader 
 lateral ' olivary ' tract, ib. h : in the dorsal columns a median 
 ' funicular ' tract, ib. e, is similarly marked off from a lateral 
 ' post-pyramidal ' tract, d : this is now, also, distinguished by a 
 deeper fissure from the true lateral or ' restiform ' tract, c, at the 
 inferior part of which a distinct slender portion is 
 also sometimes defined. The post-pyramidal tracts ' "^ 
 
 diverge, expand and blend anteriorly with the 
 similarly bulging restiform tracts, forming the sidc- 
 ■\valls of a triangular or rhoniboidal cavity, called the 
 ' fourth ventricle,' fig. 173,7: the pre-pyramidal and 
 olivary tracts, forming the floor of the ventricle, are 
 covered below by a thin superficial layer of trans- 
 verse ' arciform fibres ' ' ib. m, concealing their 
 boundary fissures. At the bottom, of the ventricle "Uongata, cure/w- 
 
 . rtus 
 
 the myelonal canal is exposed, and its sides swell 
 and rise as rounded or ' teretial ' tracts,^ ib. /, from the floor of 
 the ventricle, diverging slightly as they ad^■ance, and exposing an 
 intermediate ' nodular ' tract ; this structure is well seen in the 
 basking shark ( Sdache) : two lateral prominent ' vagal ' cokunns 
 also project inwards into the ventricle, from the conjoined resti- 
 form and post- pyramidal tracts ; these ^"agal columns present a 
 series of nodules, fig. 173, t, corresponding with the fasciculi of 
 the roots of the Q;reat vagal nerve in Selache.^ 
 
 In the Cyprinoid Fishes the median inferior tract rises into the 
 ventricle, and is develoiJed into a smooth hemispheric mass, the 
 ' nodulus,' fig. 178, k: the conjoined post-pyramidal and restiform 
 walls swell outwards, and form lateral 'vagal' lobes, large and 
 nodulated in the Carp, fig. 178, h, which is so tenacious of life. The 
 vagal lobes are enormously developed in the Torpedo ; they join the 
 trigeminal lobes, and present a yellowish colour in the recent fish : 
 many non-nucleated cells are present in their substance ; they give 
 origin to the nerves of the electric organs, and have been called 
 ' loin electrici ; ' but the vagal lobes are scarcely less remarkable 
 for their size in the Gymnotus, where they have no direct con- 
 nection with any of the nerves of the electric organs. In the 
 Cod the vagal ganglions are obsolete, and the nodulus slightly 
 swells above, and obliterates the ' calamus scriptorius.' In the 
 Luciopcrca the vagal lobes are not very distinct, but they mark 
 
 1 Plomologous with the 'filamcnti arciformi ' of RoUindo, lviii. p 170, t. i. fig. 2. 
 - These .ire called ' vorrlero pyramiden ' by Dr. Stannius. lti. p. 43. 
 ' XX. vol. in. p. 22; Prep. no. 1311 A. 
 VOL. I. T 
 
'2H 
 
 ANATOMY OF VERTEBRATES. 
 
 173 
 
 the commencement, and form the broadest part, of the very long 
 medulla oblongata, the restiform tracts diminishing in size as they 
 ' advance. In no other Vertebrates save Fishes are the vagal lobes 
 and the nodulus present. 
 
 The posterior pyramids, which are the anterior continuation of 
 the posterior myelonal columns, diverging as they are pushed 
 aside by the deeper-seated tracts that form the floor of the fourth 
 ventricle, and combining with the lateral columns to form the 
 corpus restiforme and the basis of the vagal lol^es, again quit 
 those columns, cowvergc, ascend, and unite together above the 
 anterior opening of the fourth ventricle : they there form either 
 a simple bridge or commissure, fig. 173, C, or are developed 
 upwards and backwards into a ganglionic mass, overarching the 
 ventricle ; this mass is the 'cerebellum,' figs. 174 — 179, C. It is 
 formed chiefly by the post-pyramidal columns, 
 but doubtless derives some share of the proper 
 lateral or restiform fibres, as the result of the 
 previous confluence of these with the post- 
 pyramids. 
 
 Tlie cerebellum retains its earliest emliryouic 
 form of a simple commissural bridgeorfold in the 
 parasitic suctorial Cyclostomes, in the hea-sily- 
 laden Sturgeon, fig. 173, C, and Polypterus,' 
 and in tlie almost finless Lepidosiren,- fig. 186, 
 C : it attains its highest developement, in the 
 jiresent class, in the Sharks, where it not only 
 covers the fourtli ventricle, but advances over 
 the optic lobes, and in the Saw-fish extends 
 beyond them to rest upon the cerebrum ; its 
 surface is further extended in these active 
 predaccous fishes by niunerous transverse 
 folds, fig. 187, C. Inmost Osseous Fishes the 
 cerebellum is a smooth convex body, liemisphcroid, fig. 17o,C, or 
 transversely subelliptic (Eel, fig. 176, c), or longitudinally subel- 
 liptic (Lepidosteus), fig. 174, c ; but it may be an oblong body 
 (Diodon), fig. 171, C, or l)e dcin-esscd and tongue-shaped (Cod, 
 fig. 183,/), or oval, or pyramidal (Perch, fig. 182, cr) ; it is very 
 rarely found extending forward, as in Echeiicis andAinbli/opsis, fig. 
 175, C, over any part of the optic lobes ; Init often backward 
 over the wliolc fourth ventricle, as in tlic Cod, fig. 183, f, and the 
 Diodon, fig. 171,0; or over the major part of the ventricle, as in the 
 
 ' XXV. p. 24, pi. ii. figs. 5, 7, 
 
 k. 
 
 iaJ i « ^-■ 
 
 '' xxxm. p. 339, pi. 27. 
 
 ..' • .9 < 
 
 ^■..i f-,i^Ci'^^-i 
 
ENOEPHALON OF FISHES. 
 
 275 
 
 Herring, fig. 1 84, c ; but sometimes covering only a small portion, as 
 in the Chub, fig. 177, c, the Lumi)-fish, and the Lepidosteus, fig. 
 174, c. The relative size of the cerebellum, accordingly, varies 
 
 ^-•■•-1'i.j-- 
 
 175 
 
 Brain ; 
 
 Lei.>ldosteus 
 
 BraiQ; Amblj'opsi3 
 magnllled 
 
 Brain ; Eel. CCii. 
 
 greatly In difFcreiit bony fishes ; it is very small in tlie lazy Lnmp- 
 fish, and extremely large in the active and "\varm-l:>h)oded Tunny, 
 where, also, its surface shows transverse j^-roovings. 
 The cerebellum is unsymmetrically placed in the 
 Pike and some Flat-fish {Plevronectida), and is 
 unsymmetrically shaped in the Sharks : it presents 
 a longitudinal groove in the Diodon, and a pos- 
 terior notch in the Herrino- : a transverse notch di- 
 vides it into an anterior and posterior lobe in the 
 Lophius : it bears a crucial depression in the Skate. 
 The cerebellum presents in many fishes a small 
 cavity or fossa at its under part, continued from 
 the fourth ventricle, fig. 178, c: it is solid in the 
 Tench, the Garpike, and the common Eel : some 
 grey matter is usually found in its interior, with 
 feeble indications of vphite stria3 ; but there is no 
 ' arbor vitas,' except in the Tunny and Sharks. 
 
 The posterior ' crura cerebelli ' are formed by 
 the posterior pyramids, fig. 172, d, with part of the restlform 
 tracts, ib. c ; vertical fibres from the sides of the cerebellum 
 continue to attach it to the 
 sides of the restiform or trige- 
 minal lobes, and some of these 
 are continued as arciform fila- 
 ments upon the under surface 
 of the medulla oblongata : they 
 answer to the ' crura cerebelli ad j)ontem ' of Mammalia ; but, as 
 
 T 2 
 
 ]Jra1n and portion of 
 spinal marrow of 
 Cliub {LcitclHcus) 
 
 Scctiou of Biaiii, Carp 
 
27G 
 
 ANATOMY OF VERTEBRATES. 
 
 179 
 
 there are no lateral lobes in the cerebellum in Fishes, these crura 
 are rudimentary, and the ' pons ' is absent. In the Shark they 
 connect the sides of tlie liase of the cerebellum with the ' restiform 
 commissure,' figs. 172 & 187, I. In most Fishes two fasciculi of 
 medullary fibres proceed, as ' anterior crura,' from the under and 
 fore part of the cerebellum, or converge from the lateral and fore- 
 part forward, to form the inner wall or septum, fig. 184, r, of the 
 optic lobes : these answer to the ' processus ii cerebello ad testes ' 
 of the himiau brain : tliey are connected below their origin at the 
 under part of the ccreljellum by one or two trans%'erse fasciculi of 
 white fibres, forming the ' commissura ansulata,' which crosses the 
 pre-pyramids just behind the ' hypoaria,' fig. 185, n. The inferior 
 white surface of the cerebellum, which forms the roof of the fourth 
 ventricle, is called ' discus cerebelli,' and from this part small tuljer- 
 cles project in a few fishes (e. g. Blennius and Sturio, fig. 173, c). 
 The restiform columns, quitting the post-pyramidal crura of 
 the ccreliellum, and liaving elfected hj their previous confluence 
 therewith some interchange of filaments, swell 
 out at the anterior lateral parts of the medulla 
 oblontrata, and cive orifrin to the ajreat trio-eminal 
 nerve. They here form considerable 'trigeminal 
 lobes' in the Loach and Herring, fig. 184, /, and 
 are folded or 'fimbriate 'in C/H'mffir«,fig. 179, dd, 
 and most Plagiostomes, where they are closely 
 connected with a thick vascular mass of pia 
 mater and arachnoid. The trigeminal lobes are 
 convolute in the Skate ; enormous and blended 
 with the vagal lobes in the Torpedo ; but in most 
 Osseous Fishes (Lepidosteus, Cod) they are not 
 developed so as to merit tlie name of lobes. In 
 the Cod the inner surfaces of the restiform bodies 
 project into the fourth ventricle, and obliterate 
 the fore part of the calamus by meeting above 
 it ; this commissure, which is beneath the cere- 
 bellum, is the ' commissura restiformis,' fig. 182. 
 It is remarkably developed in Carcharias, where 
 it seems to form a small supplemental cerebellum 
 "' '" '" '""■ beneath the larc;e normal one: in fio-. 172 
 
 the medulla oblongata is cut across, the fourth 
 ventricle cxjioscd from behind, and tlie restiform eonnnissure, /, is 
 raised: it has an anterior and posterior median notch. 
 
 The priuiary division of the brain, which consists of tlie medidla 
 oblongata with the cerebellum and other less constant appendages 
 
ENCEPHALON OF FISHES. 
 
 277 
 
 (if r,T[-li, upper eiirfacc. xxui. 
 
 in Fishes, is called the ' epencephalon,' fig. 179,/, C, fig. 178, g, c ; 
 it is relatively larger, occupies a greater j^roportion of the cranium, 
 and is more complex and diversified in this than in any of the 
 higher classes of Vertebrata. 
 
 The next succeeding primary division of the brain is called the 
 ' mesenceplialon,' figs. 180 & 18J, b, e,f: it is usually the largest 
 division in Osseous Fishes, and con- 
 sists of two upper spheroidal bodies, 
 called 'optic lobes," figs. 176, 177, 
 180, /; (in most of the figures, o), 
 of two lower subspherical bodies. 
 
 called ' hypoaria,'^ figs. 178, 185, n, 
 fig. 181, e, with intervening con- 
 necting walls enclosing a cavity, 
 called the ' third ventricle,' wliich 
 is prolonged downward into the pedicle of the 'hypophysis,' or 
 pituitary gland, fig. 185, p, and u})ward into that of the ' cona- 
 rium' or pineal gland, fig. 175, zo. The prepyramidal columns 
 are continued forwards, along the floor of the fourth ventricle, 
 where they are covered by a thin layer of medullary fibres, to the 
 hypoaria and prosencephalon : some fibres Idending with the wall 
 of the third ventricle and the base of the optic lobes. The 
 transverse 'ansulate' commissure,' which unites or crosses the pre- 
 pyramids Ijcfiire they penetrate the hypoaria, may be regarded as 
 the most anterior of the arciform fila- 
 ments, wliich feebly represent the 
 pons Var(jlii in Fislies. The restiform 
 columns are exjiended chiefly in form- 
 ing the walls of the third ventricle and 
 the Ijase and exterior walls of the optic 
 lobes, a small part only being con- 
 tinued forwards to the cerebrum in most Osseous Fishes. The 
 anterior cerebellar crura are chiefly lost in the inner walls or 
 seiitum of the optic lobes. , 
 
 These lobes are commonly of a sulispherical figure, and larger 
 than the cerebral lobes, as in figs. 177, 180, h, 171, 184, o; they are 
 often larger than the cerelDcUum, ib. ib. ; l:)ut of nearly equal size 
 with the cerebellum in the Eel, fig. 176; they are smaller than 
 the cerebral lobes, but larger than the cerebellum, in the Polypterus 
 and Lepidosiren, fig. 186, O; they are smaller than either the 
 cerebrum or cerebellum in the Amblijopsis spelmus, fig. 175, o, in 
 
 181 
 
 fir- 
 
 I rif Percli, lindor surface. 
 
 ' Lobes crcux,' Ciivier. 
 
 ' Lobes inferieuis,' Ib. 
 
 LVii. pi. ir., fig. 7, /. 
 
278 
 
 ANATOMY OF VERTEBRATES. 
 
 the Chimasra, fig. 179, o, and in the Sharks, fig. 187, O. In 
 the latter they bear the same proportion to the optic nerves 
 and eyes as in other fishes, their small relative size depending 
 on the advanced developement of both cerebellura and cere- 
 brum : in the blind Amblyojjs of the svibterraneous waters, 
 the diminution of the optic lobes relates to the almost total 
 abrogation of the visual organ ; but since both in the Amblyops 
 and the equally blind Myxine these lobes are present, they 
 cannot be exclusively the central ganglion of the optic nerve, nor 
 their sole function that of receiving the impressions of the sense 
 of sight, and making them jjerceptible as ideas by the animal. 
 
 The optic lobes are hollow in most Fishes, fig. 182, b. The 
 exterior surface shows Ijlended grey and white matter, the white 
 182 fibres usually converging to the optic 
 
 nerves ; some of the fibres unite with 
 the anterior crura of the cerebellum 
 to form the septum of the optic lobes, 
 fig. 184:, r, which consists of two or 
 four medvdlary fasciculi, decreasing in 
 the Tench, increasing in the Cod, as 
 they pass forward. On divaricating 
 the optic lobes. from above, as in fig. 
 182, or by a horizontal section, as in fig. 183, their cavity, d, or 
 ventricle, is exposetl : it communicates with the expanded myelen- 
 cephalous canal, called ' third ' and ' fourth ' ventricles, as shown 
 by the bristle, q. Its floor is variously configurated in dift'erent 
 fishes. There are one or two small white tubercles, ' tiiberculi 
 optici,' figs. 182, 183, c, on each side of the back part of the septum; 
 the Cod, Salmon, Pike, and Perch, show four of these bodies ; the 
 Carp and Herring, fig. 18-1, t, two: in the Carp they are oblong, 
 juxtaposed, and were called 'tuberculura cordiforme' by Haller;' 
 they are not present in the Polypterus, Lepidosiren, Sturgeon, or 
 Plao'iostome fishes. External to these tubercles the floor of the 
 ventricle usually rises into a curved eminence, with its convexity 
 outwards ; this is the ' torus semicircularis ' of Haller,^ fig. 18-4, u\ 
 It is not homologous with either the ' thalamus opticus ' or the 
 ' corpus striatum ' of the mammars brain. In the Carp, where 
 the great physiologist first described and named them, the ' tori ' 
 are large, and much curved; in general they describe only a 
 
 ' In Salmo Umhla Ilallcr calls tlicm 'coipora ciuadrigeniiua,' as ilocs Ciivior, in 
 Perca flmiatiUs : they arc analogous in foim to the pai'ts so named, in JUamnials; 
 but are not homologous therewith. 
 
 - nx. t. iii. p. 201. - 
 
 Brain of Terrli, with tlic optic 
 open, and tlie certbcilum turned to the 
 right side, xxiii. 
 
ENCEPHALON OF FISHES. 
 
 '279 
 
 small portion of a circle, fig. 182, li ; and in some bony fisli, as tlio 
 Cxarpikc, Loach, and Lumpfish, they are scarcely raised a1)ove 
 the level of the floor of the ventricle. They are not deve- 
 lojied in the Polypterns, the Lei:)idosiren, 
 or the higher Plag-iostomcs ; and both tori 
 and tnberculi are peculiar ichthyic develope- 
 mcnts in the ventricles of the optic lobes. 
 The bottom of the 0]rtic ventricle, fig. 184, v, 
 anteri(3r and external to the 'tori,' is grey, and 
 usually prominent, with white fibres radiating 
 through it to rise and expand upon the walls 
 of the lobes. The fiptic lolies have almost 
 coalesced in the Sturgeon, fig. Xh't, o, Poly- 
 pterns, Lepidosiren, Amblyopsis, and Loach 
 ( Cohitis). Where they are quite distinct 
 externally, as in most Osseous Fishes, they 
 are brought into mutual communication by one 
 or two commissures ; the anterit^ir ' commissura 
 transversa ' is the most constant ; it is shown 
 in the Perch, fig. 182, and in tlie Plerring, 
 fig. 184, s; it passes in front of the entry to 
 the third ventricle. 
 
 In the Myxine and Lepidosiren the prepyramidal fibres curve 
 suddenly forward and upward before expanding into the 
 floor and sides of the third ventricle, and they thus form a 
 small protuberance beneath the basis of the optic lobes, fig. 
 186, n. In the Shark the same columns swell out laterally, 
 and form two small protuberances, fig. 187, a, separated below 
 by the vascular (hypophysial)" floor of the third ventricle. In 
 most Osseous Fishes the corres- 
 ponding fibres of the prepyrami- 
 dal tracts swell out suddenly, be- 
 neath the optic lobes, into two 
 protuberant well - defined oval 
 ganglions ('hypoaria,' fig. 185, ii, 
 iig. 181, e) : their bulk is increased 
 l)y added grey matter, whicli 
 variegates their outSr surface ; 
 they are well developed in tlie 
 common Cod, in which, as in some 
 other fishes, they contain a cavity (hypoarian ventricle). In some 
 Sahiiorddce their surfirce is striated ; in some Cjiprinida: (Tench) 
 they are confluent ; but commonly they are distinct, and liavc in 
 
 184 
 
 optic ventricles; 
 Ileriin'^r 
 
280 ANATOMY OF VERTEBRATES. 
 
 their inferior interspace a vascular medullary depressed sac (the 
 ' ha;matosac,' fig. 185, o), usually oblong, as in the Cod, rarely 
 bifid or cordiform, as in the Lumpfish. These prominences from 
 the floor of the mesencephalon, posterior to the infundibulum and 
 hypophysis, ib. p, are peculiar to the brain of fishes, and, in their full 
 developement, are restricted to the typical osseous member of the 
 class ; they are absent in the lowest, and disappear in the highest 
 orders ; tliey are mere rudiments, or are wanting, in the Poly- 
 pterus, as in the still more amphilnoid Lepidosiren. 
 
 The true vasculo-membranous infundibular downward pro- 
 longation of the third ventricle exists in all Osseous Fishes, and 
 extends from the anterior angle of the hypoaria, where these 
 exist : the infundibulmn is commonly short and thick, so that the 
 hypjophysis is almost sessile, as in the Cod ; but in the Lophius, 
 the infundibulum is longer than the entire brain, and the hypo- 
 physis lies at the fore-part of the cranial ca-sity, far in advance of 
 the cerebral lobes.' In the Cod the hypophysis, fig. 180,7;, ^^ ^ 
 subspherical mass, with an irregular or slightly nodulated surfiice, 
 almost half the size of the human, so called, ' pituitary gland,' 
 and illustrating the A'ast proportional size of this constant 
 appendage to the brain of Fishes. In the Lepidosiren the infun- 
 dibulum is wide, and the hypophysis a white flattened discoid 
 body, fig. 186, 0.^ In all Fishes it is richly supplied with vessels, 
 and is closely attached to the flo(_ir of the cranium ; but, although 
 its early developement checks or modifies that of the cranial 
 vertebra;, it is not provided with a special chamber or ' sella.' 
 The prolongations of the fibres from the mcsencejihalon which 
 expand into the proscncep)halic or proper cerebral lobes rarely 
 show any preliminary developement of ' thalami ; ' but the parts 
 homologous with those recruiting ganglia are constantly indicated 
 by the attachment of the conarium, or upper prolongation cif the 
 third ventricle. 
 
 The conarium, figs. 175, 186, 187, »', is as constant an append- 
 age of the eucephalon in Fishes as the hypophysis ; but it is com- 
 monly oidy a vaseido-membranous pyramidal sac continued from 
 the third ventricle, the base expanding from between the anterior 
 interspace of the optic lobes, and the apex directed forward and 
 attached to the roof of the cranium. Some medullary matter 
 mingles with the membranous walls of the conarium in the 
 Clu]>eoid and Cy]irinoid Fishes: in some Fishes there is grey 
 matter in the conarium: in most it is membranous only, as in the 
 
 ' LX. p. Sfi, t. ii. ftix. 1. 
 
 ^ The Iiypopliysis is murkeil fj in xxxiii. pi. 27, fig. 4; ami is cilU'd ' mammiUary 
 body' ill Lcjiidosircn annectcns, ib. p. 3G1. 
 
ENCEPHALON OF FISHES. 281 
 
 Leiiidosiren, Sturgeon, and Sliark : in all it is highly vascular. 
 In the Bream the conarium shows an analogous peculiarity to 
 that of the hypophysis in the Angler, viz. in the length and 
 tenuity of its attachment ; hut this consists of two distinct crura. 
 The value of the constancy of the hypfipliysis and conarium con- 
 sists chietly in their marking the boundary line between the mes- 
 and pros-encephala, although they belong to the mesencephalon, 
 and arc both essentially vertical prohingations of the third ven- 
 tricle through an interspace produced by the divarication of the 
 main lateral columns of the encephalon. 
 
 The fasciculi continued forward from the parietes of the third 
 ventricle or mesencephalic basis, are principally those which may 
 be traced back through the epencephalon to the anterior and 
 lateral m^yelonal tracts, augmented by fibres from the grey centres 
 or lobes through which they have passed, and retaining a small 
 admixture of post-pyramidal fibres from the optic septum, 
 fig. 184, r. In Osseous Fishes the two cerebral crura, so con- | 
 stituted, rarely undergo any enlargement, homologous with the I 
 ' thalanii,' where they form the anterior boundary of the third 
 ventricle ; but after a very brief course, as ' crura cerebri,' fig. 178, 
 X, radiate into two small subspherical ' prosencephalic ' masses of 
 grey matter, ib. P, situated anterior to the optic lobes, and there 
 in great part terminate. A few of the medullary fibres extend 
 along the base of the prosencephalon, receive a small tract of its 
 grey matter, converge to the anterior interspace of its lobes, and 
 either expand there into ' rhinencephala,' figs. 174, 175, 186, k, 
 or are continued fjrward and outward, as ' rhinencephalic crura,' 
 fin-s. 178, 187, r, to form the olfactory lobes or ganglia, ib. K, 
 at some distance from the brain. Although the prosencephalic 
 lobes are commonly in contact with the optic lobes, yet something 
 analogous to the displacement of the rhinencephalon may be seen 
 in the prosencephalon of the Chimwra, in which the cerebral 
 crura, fig. 179, b, advance some way before they expand into the 
 prosencephala, P : in the Plagiostomes, also, the prosencephalic 
 crura, fig. 187, x, have a short independent tract in advance of 
 the optic lobes. 
 
 The prosencephala, figs. 177, a, 180 and 182, c, 183, a, h, in 
 other figs. P, are distinguished from the optic lobes by their 
 grey pinkish exterior, and, generally, also by their fissured 
 or nodulated surface. The first of these characters must be 
 looked for in recent fish: the second is more permanent.' With 
 
 ' XX. vol. iii. it may be seen in preparations of the brain of the Eel (Anguilla acidi- 
 rostris, No. 1309, B); of the Lump-fish {Ctjcloptcrus, No. 1309, C); of the Gurnard 
 (Trigla lyra, No. 1309, C); and especially in this specimen of the brain of the Cod 
 
nraiil nf Leiiiiln.sircii 
 
 282 ANATOMY OF VERTEBRATES. 
 
 regard to the ' cerebrum ' of the Cod, a median tract or con- 
 volution is marked off by a longitudinal fissure, which extends 
 alono- the back of each prosencei^halon, defining a posterior and 
 inferior convolution ; the median convolution is vertically fissured 
 on its inner side. In the Amblyopsis, fig. 175, p, it is cleft 
 anteriorly ; and here, as in most fishes, the median longitudinal 
 tract is the most constant subdivision of the prosencephalic 
 superficies. 
 
 The laro-e elongated prosencephala are smooth in Chimfera, 
 fig. 179, p, Polypterus, and Lepidosiren, fig. 186, p, and in the 
 
 still more develoj^ed confluent mass 
 in the Sharks, fig. 187, p ; the 
 prosencephala are, also, smooth in 
 the Myxines, where they are rela- 
 tively smallest. The comparative 
 anatomists, who have failed to 
 recognise the true homology of the prosencephalon in Osseous 
 Fishes, appear to have been misled chiefly by its small proportional 
 size, which is commonly that exhibited in the brain of the Cod, 
 the Carp, and the Globe-fish ; in some species the prosencephalon 
 is even smaller, as in the Gar-fish, the Herring, or the Lump-fish. 
 The prosencephalon equals the cerebellum in size, but is less than 
 the optic lobes in the Perch and Bream ; it equals the optic lobes, 
 but is less than the cerelicllum, in the Eel ; in the Stickleback 
 and Gurnard the prosencephalon exceeds the cerebellum, still 
 more so in the Lepidosteus, but is less than the optic lobes ; in the 
 Lncioperca, the Amblyopsis, the Chimera, and the Skate, neither 
 the cerebellum nor the optic lobes are so large as the prosence- 
 phalon ; in the large Sharks their united size scarcely equals that 
 of the prosencephalon ; and in the Salamandroid Polypterus and 
 the Lepidosiren the prosencephalic lobes surpass all the rest of 
 the brain, and vindicate their true cerebral character and impor- 
 tance. In the Amblyopsis the relative magnitude of the prosen- 
 cephalon is due to the diminution of the optic lobes in that blind 
 fish ; in the Plagiostomes it is due to absolute developement ; as it 
 is, also, in the Polypterus and Lepidosiren, where the prosence- 
 phalon presents the closest similarity in form and structure to that 
 division of the brain in the Batrachian Reptiles : each lobe, for 
 
 CNo. 1300), wliich Hunter truly, though briefly, deseribos as follows :— " The cerebrum 
 fissured; tiic ccrcOdliim. a loiiy; projecting body, also fissured in a less degree; the 
 vnirs two projecting bodies: the optic nerves decussate one another." This is the 
 earliest recognition of the homology of the optic lobes with the anterior of the bigemi- 
 nal bodies of the human brain. 
 
ENCEPHALON OF FISHES. 
 
 283 
 
 Brain of Shark, CarcharUis 
 
 example, is elongated in the axis of tlie skull, and is of a sub- 
 ccimpressed oval form, and has a large ' lateral ventricle ' in its 
 interior in the Lciiidosiren, fig. 186, I v. In the Skate, tlie pros- 
 encephala coalesce into a subdepressed transversely elongated 
 mass, their essential distinction Ijeing indicated by a mere super- 
 ficial median fissure ; in Carcharias, fig. 187, the jjrosencephalon 
 forms an almost ghjbular mass, with scarcely a trace of a median 
 
 fissure. Amouo- Ijony fishes the 
 
 ^ -' 187 
 
 lirosencephalic lobes are more 
 
 or less confluent in Luciuperca 
 Sdiidrti, Tracliimis draco, S//r- 
 f/us, Mullus, Scomher trachiims, 
 Belone, Cliipea harengus, and 
 Chipea sprruttus ; they appear 
 distinct symmetrical spheroids 
 in most other fishes, their union 
 being reduced to a small trans- 
 verse medullary band (iirosencephalic commissure).' The sym- 
 metrical character of the prosencephala, as of the optic lobes, is 
 Avanting in most Pleuronectida. 
 
 The grey vascular neurine forms the greatest part of tlie pros- 
 encephalon inmost Osseous Fishes; the white fibres radiate through 
 this, and rarely appear on any part of the exterior surface ; the 
 white substance, however, predominates in the Plagiostomcs and 
 Lepidosiren. As a rule, the proseneephalic lobes are solid ; but 
 the l^rain of Carcharias ^ shows a deep ventricular fissure at the 
 anterior and under part of the prosencephalon, with a vascular 
 fold of membrane or ' choroid plexus ' penetrating the fissure, 
 wdiich is continued forward into the orus of the olfactory lobe. 
 The lateral ventricle is more extensive in the Lepidosiren, and is 
 continued directly into the olfactory lobe. 
 
 The ' rhinencephalon ' figs. 173 — 176, R, consists of two always 
 distinct lobes of grey matter, which receive the prolongations 
 of chiefly white fibres from the prosencephalon and its crura, and 
 give off the nerves to the olfactory caj^sule, whence they are 
 termed ' olfactory lobes,' ' tuliera,' or ' ganglia.' The rhinence- 
 phala are solid l)odies, always distinct, wide apart from each other 
 when remote from, and in mutual contact when near to, the rest 
 of the brain, but never united by a commissure. The rhinence- 
 
 ' Carus wcU recognises the homology of this commissure with that of tlic corims 
 striatum, called ' anterior commissure ' in the human brain, i. p. 24. 
 - (No. 1310, a), XX. Yol. ill. 
 
284 ANATOMY OF VERTEBRATES. 
 
 phalic crura, figs. 171, 175, 178, 187, z, vary exceedingly in length. 
 In the Lepidosiren, fig. 186, they are feebly indicated by a con- 
 tinuous indentation circumscribing the base of the rhinencephalon, 
 E, and defining it from the anterior end of each prosencephalic 
 lobe, p ; in Polypterus and Lepidosteus the indentation is deeper, 
 and the attachment of the base of the now pyriform rhinence- 
 phalon, fig. 174, E, sinks to the prolonged crus or basis of the pros- 
 encephalon. From this substratum the rhinencephalic crura are 
 prolonged in all Osseous Fishes : in some they are so short that the 
 rhinencephala are partly overlapped by the prosencephala ( Trigla), 
 or rise into view immediately in front of them {Ambhjopsis, 
 Anguilla,iig. 176, E, Cottus, Cydoptems) ; but in many fishes the 
 rhinencephala are developed far in advance of the rest of the 
 brain, and their crura are prolonged close to the olfactory cap- 
 sules. Tliis has led to a denial of the existence of olfactory lobes 
 in such fishes ; but the rhinencephala are truly present in both 
 the Cod and Carp, fig. 178, E ; they are merely removed to juxta- 
 position with the olfactory capsules, with a concomitant pro- 
 longation of their crura. These crura, so prolonged, ib. z, have 
 been called ' olfactory nerves ' by those who, fiiiling to appreciate 
 the true homology of the remote ' rhinencephala,' have described 
 them as ganglionic swellings of the ends of the olfactory nerves.' 
 These ganglions, wherever situated, consist of proper nervous 
 matter over and above the mere radiation or expansion of the 
 fibres of the so-called ' olfactory nerves.' The true olfactory 
 nerve quits the rhinencephalon as a plexiform chord, or as a group 
 of distinct fibres. If the thick olfiictory nerve of tlie Gurnard be 
 compared with the thick rhinenceiilialic crus of the Skate, or if the 
 long olfactory nerve fif the Eel be compared with the long rhin- 
 encephalic crus of the Chub, fig. 177, /(, their respective difi'erence 
 of structure will be readily appreciated. The crus is a compact tract 
 of medullary with a small proportion of grey matter ; the nerve 
 is a bundle of nerve filaments : the medullary tract of the crus 
 is fibrous, but the fibres are as fine as in the crus cerebri, and 
 much more niunerous and less easily separable than in the true 
 olfactory nerve. In this there is no grey tract : it consists wlioUy 
 of C(jmparati-\-ely large and readily separable white fibres, which 
 radiate at once upon the olfactory ca]isulc ; the divergence and 
 radiation of tlic true end of the olfactory nerve is well seen in 
 the Le])idosircn, fig. ISO, \,ol. In Sharks "a ventricle is continued 
 to each rhinencephalon along its crus from the prosencephalon. The 
 
 ' (Jaininr, Lxi. p. 05; Cuvicr, xxui. p. 321. 
 
ENCEPHALON OF FISHES. 285 
 
 olfactory nerve never forms a ganglion before spreading npon 
 tlie olfactory capsule ; the rliincnceplialic cms, when prolonged 
 to the capsule, always expands into a ' tuberculum olfactorinm,' 
 or rhinencephalon, before it transmits the true olfactory nerves to 
 the capsule. In other words, the olfactory nerve conveys im- 
 pressions to a proper centre or lobe, wliich, in Fishes, may Ijc 
 situated close to the capside, or close to the rest of the brain, (i 
 and the length of its crus will be inversely as that of the nerve. ^ •■ 
 The olfactory lobes or rliinencepliala are serially homologous with 
 the optic lol)cs. As to the prosencephalon, since this does not 
 immediately receive or transmit any nerve, it resembles in this j] 
 important character the cerebellum, and ])roceeds, even in the , 
 present class, to be developed to a degree beyond the ganglions 
 of any special nerves or organs of sense. 
 
 The more special homology of the prosencephalio lobes, 
 under their normal j^roportions and solid structure in Osseous 
 Fishes, with the parts of the complex and fully developed prosen- 
 cephalon in Mammals, will be made manifest as we trace the 
 jirogress of that complication synthetically. Cuvier had already, 
 by the opjiosite course of analysis, reduced the hemispheres 
 in birds to the ' corpora striata,' with their commissures and a 
 thin su])raventricular covering. ' Le corps caunele,' he says, 
 ' forme a lui seul presque tout rhuniisphere.' ' But he failed 
 to recognise the ' homology of the prosencephala in Fishes. 
 Since Arsaki's time ^ their homology witli the cerebral lobes of 
 IJejitiles, Birds, and Mammals has been generally recog- 
 nised. Girgensohn ^ says they may well be compared with 
 the ' corjiora striata ; ' but he notes the important difference, 
 that, whereas these ' transmission ganglia ' {dia-cligangsknoten) 
 give 25assage to the radiating fibres of the cerebral crura in 
 their course to other parts of the cerebrum in Mammals, those 
 fibres terminate in the solid prosencei^hala of Fishes. The 
 establishment of the lateral ventricles in the prosencephala of the 
 Plagiostomes and Lepidosiren also show them to be something 
 more than ' corpora striata.' 
 
 It now becomes important to note the mode of establishment 
 of these cerebral ventricles : they are not formed by the super- 
 addition of a layer or film of neurine overlapping parts answerable 
 to the solid hemispheres in other Fishes, but are either central 
 excavations, as in the elongated prosencephala of the Lepi- 
 dosiren, fig. 186, Iv. or they are deep fissures towards the under 
 part, as in the coalesced hemispheres of the Shark; whence I 
 
 ■ CC. t. ii. 1799, p. 162. ^ lui. 1813. ^ Lxni. p. 155. 
 
286 ANATOMY OF VERTEBRATES. 
 
 conclude that the solid prosencephalon of Osseous Fishes is not 
 a mere representative of a basal ganglion forming the floor of the 
 ventricle of the hemispheres in the higher Vertebrates, where such 
 ganglion is a medium of transmission or source of accession to 
 the cerebral fibres ; but that the fish's prosencephalon is the seat 
 of the terminal expansion of the radiatinij; medullary fibres of the 
 cerebral crura. Dissection of the recent brain shows, as in 
 fig. 178, p, that these fibres, besides being blended with grey 
 matter, as in the corpora striata, are thickly covered with a 
 layer of the same grey and highly vascular neurine, of which the 
 hemispheric convolutions in Mammals are chiefly formed ; and it is 
 interesting to perceive on the superficies of the solid prosence- 
 phalon in many fishes the foreshadowing of the convolutions, 
 which are not fully established until an advanced Mammalian 
 grade is attained. The prosencephalon of the fish is far from 
 being a miniature model, but it may be regarded as the potential 
 representative, of the complex cerebral hemispheres of man. 
 
 The average proportional weight of the brain to the rest of 
 the bodjr in Fishes is as 1 to 3000. In a chub (Leucisciis Cy- 
 jmnuH) weighing 842 scruples, the brain, exclusive of the olfactor^^ 
 lobes, weighed one scruple; in a carp (^Cyjyrinus Carpio), weigh- 
 ing 11,280 grains, the brain weighed 14 grains; in a lamprey 
 weighing 750 grains, the brain weighed half a grain. A certain size 
 seems to be essential to the performance of its functions, as a 
 recijiicnt of the impressions from the organs of sense ; and it 
 does not, therefore, vary in difi^erent species so as to accord pre- 
 cisely with the general bulk of the body. The size of the optic 
 lobes, e.g. has a more constant and direct relation to that of the 
 eyes, which soon acquire their full developement. We find the 
 entire brain proportionally greater in young than in old fislios : 
 it acquu-es its full size long before the termination of the 
 growth of the fish, if this lias a fixed period. But as the 
 head must grow with the growth of the fish, under the con- 
 ditions of its progressive motion, provision for occupying the 
 increasing capacity of the cranium is made by a concomitant 
 developement of the light cellular arachnoid, which has the 
 further advantage of regulating the specific gravity of the head. 
 
 As the branchial respiration is a peculiarly active and im- 
 portant function in Fishes, and has an extraordinary a]iparatus of 
 bony or gristly arches with their muscles, we may associate there- 
 with the ))eculiar developement and complexity of the medulla 
 oblongata, as the centre of the vagal or respiratory nerves. The 
 Carp and other Cyprinoid Fishes, which have not the mechanical 
 
BNCBPIIALON OF FISHES. 287 
 
 modifications for retaining water in contaet witli the gills, so 
 cliaractcristic of the Apodal, the Lophioid, and Lal)yrinthi-branch 
 fishes, are remarkable, nevertheless, for their tenacity of life out 
 of water ; and the peculiarly developed vagal lobes may relate to 
 this maintenance of the power of the respiratory organs during a 
 suspension of their natural actions. 
 
 The extensive gradation of the cerebellum between the ex- 
 tremes of structure presented by the Myxine and the Shark, 
 as might be expected, throws more direct light upon its function. 
 "\^^ith regard to this, two views have been taken. According to 
 one it is the organ of amativeness ; according to the other it is 
 the seat of the muscular sense, or the regulator of voluntary 
 motion. Many experiments in which the cerebellum has been 
 mutilated or removed in warm-l>looded animals support the idea 
 of its intimate relation with the locomotive powers. But to the 
 conclusions from these experiments has been objected the pos- 
 sibility of the convulsive muscular phenomena having arisen from 
 the stimulus on the remaining centres, occasioned by the mutilation 
 or destruction of the one in question ; and it may well be doubted 
 whether Nature ever answers so truly when put to the torture, 
 as she does when speaking voluntarily through her own experi- 
 ments, if we may so call the aljlation and addition of parts which 
 comparative anatomy offers to our contemplation. 
 
 If, in reference to the sexual hypothesis of the cerebellum, we 
 contrast the Lamprey with the Shark, we shall be led, by the 
 much larger ]5roportional size of the generative organs in the 
 lower cartilaginous Fish, and from the observed fact of the male 
 and female Lampreys entwining or wreathing themselves entirely 
 about each other, mutually aiding in the expulsion of their 
 respective generative products, and so absorbed in the passion as 
 to permit themselves to be taken out of the water and replaced 
 tliere, without interruption of the act, to expect a larger cere- 
 licllum in the Lamprey than in the Shark. But the very re- 
 verse of this is the fact : the Lamprey has the smallest, and 
 the Shark the largest, cerebellum in the class of Fishes. If, 
 on the other hand, we compare the Cyelostome and Plagio- 
 stome Cartilaginous Fishes, in reference to their modes and 
 powers of locomotion, we shall find a contrast which directly 
 accords with that in their cerebellar developement. The Myxine 
 commonly passes its life as the internal parasite of some higher 
 organised fish : the Lamprey adheres by its suctorial mouth 
 to a stone, and seldom moves far from its place : neither fish 
 possesses pectoral or ventral fins. The Shark, on the contrary. 
 
288 ANATOMY OF VERTEBRATES. 
 
 unaided by an air-bladder, sustains itself at the surface of tlie 
 sea, by vigorous muscular exertion of well-developed pectoral 
 and caudal fins, soars, as it were, in the uj^per regions of its 
 atmosphere, is proverbial for the raj^idity of its course, and sub- 
 sists, like the Eagle, by pursuing and devouring a living prey : 
 it is the fish in which the instruments of voluntary motion are 
 best developed, and in which the cerebellum presents its largest 
 size and most complex structure. And this structure cannot be 
 the mere concomitant of a general advance of the organisation to 
 a higher type, for the sluggish Rays, that grovel at the bottom, 
 though they copulate, and have in most other resjoects the same grade 
 and type of structure as the more active Squaloid Plagiostomes, 
 yet have a much smaller cerebellum, with a mere crucial in- 
 dentation instead of transvei'se lamina. A more decisive instance 
 of the relation of the cerebellum to the power of locomotion is 
 given by the Lepidosiren in which, with a more marked general 
 advance of organisation than in the Ray or Shark, the cerebellum 
 has not risen above the simple commissural condition wliich it 
 presents in the Lamprey ; the generative system, however, of the 
 Lepidosiren is as complex as in the Plagiostomes, and is more 
 extensive : but the fins are reduced to mere filaments, and the 
 fish is known to pass half the year in a state of torpid inactiA'ity. 
 The cerebellum is large in the Chimera, fig. 179, c. In the heavy 
 laden ganoid fishes, the cerebellum is smaller than in the ordinary 
 Osseous Fishes : the imbricated armour of dense enamelled bony 
 scales must limit the lateral inflections of the tail ; so we find in 
 Polypterus the cerebellum hardly more developed than in Lepido- 
 siren, whilst in the somewhat more active and predaceous Lepi- 
 dosteus it is the smallest of all the segments of the brain. In 
 the grovelling Sturgeons the cerebellum ofters a grade of develope- 
 ment above that in the Lepidosiren. Finally, amongst the normal 
 Osseous Fishes, the largest and highest organised cerebellum has 
 been found in the Tunny, whose muscular system approaches, in 
 some of its physical characters, most nearly to that of the warm- 
 blooded classes. 
 
 If we could enter the sensorium of the fish, and experience 
 the kind of sensations and ideas derived from the inlet of their 
 peculiarly developed and enormous eyes, we might be enabled to 
 understand the office of the peculiar complexities of their 
 large optic lolies: without such experience, we can at best 
 only indulge in vague conjecture from the analogy of our own 
 sensations. We find, when Nature reduces the organs of 
 sight to such minute specks as can give but a feeble "idea of 
 
ENCEPIIALON OE FISHES. 289 
 
 tlie presence of light, sufficient, perhaps, to warn the Ambly- 
 opsis to retreat to the darker recesses of its subterranean 
 abode, that the optic h)bes are not reduced in the same proportion, 
 but retain a form and size, which, as compared with their homo- 
 logues in other animals, are sufficiently rcmarkaljle to suggest a 
 function over and above that of receiving the impressions of 
 visual spectra, and forming the ideas consequent thereon. 
 
 The anatomical condition of the prosencephalon, and its 
 homology with the hemispheres of the bird's brain, experimented 
 on by Flourens,' would lead to the belief that it was in this 
 division of the fish's brain that impressions become sensations, and 
 that here was the seat of distinct and tenable ideas : of such, for 
 example, as teach the fish its safest lurking-places, and give it that 
 degree of caution and discernment which requires the skill of the 
 practised angler to overmatch. If different parts of the prosence- 
 phalon were special seats or organs of different psychical phenomena, 
 such phenomena are sufficiently diversified in the class of Fishes, 
 and are so energetically and exclusively manifested, as to justify the 
 expectation, on that physiological hypothesis, of corresponding 
 modifications in the form and developement of the homologues of 
 the cerebral hemispheres. Some species, as, for example, the 
 Shark and Pike, are predatory and ferocious : some, as the Angler 
 and the Skate, are crafty : some, as the Sword-fish and Stickle^ 
 back, are combative : some, as the Carp and Barbel, are peaceful, 
 timid browsers : many fishes are social, especially at the season 
 of oviposition : a few are monogamous and copulate ; still fewer 
 nidificate and incubate their ova. 
 
 Now, if Ave compare the prosencephala of the Shark and Pike, 
 fishes equally sanguinary and insatiable, alike unsocialjle, the 
 tyrants respectively of the sea and lake, we find that those parts 
 of the brain differ more in shape, in relative size, and in struc- 
 ture, than in any two fishes. The prosencephalon of the Pike 
 is less than the cerebellum, much less than the optic lobes ; in 
 the Shark it exceeds in size all the rest of the brain : in the Pike, 
 the prosencephalon consists of two distinct lobes brought into 
 communication only by a slender transverse commissure ; in the 
 Shark, the hemispheres are inchstinguishably blended into one 
 large subglobular mass. If we compare the prosencephala of the 
 Pike with those of the Carp, we find them narrow in the de- 
 vourer, broad in the prey. 
 
 The Lophius lurks at the bottom, hidden in the sand, waiting, 
 like the Skate, for its prey to come within the reach of its jaws : 
 
 ' LXIV. 
 
 VOL. I. U 
 
fcl 
 
 290 ANATOMY OF VERTEBRATES. 
 
 the difference in the shape, size, and structure of their prosence- 
 phala is hardly less than that between the Shark and Pike. The 
 combative Stickleljack has longer and narrower prosencephala 
 than the cowardly Gudgeon. The nidificative and philo-pi'O- 
 genitive CalUchfhi/s has neither the antero-lateral nor the posterior 
 regions of the cerebrum more developed than in bony fishes 
 generally. 
 
 § 53. Alyelcnccphalon of Rcptilef:. — The perennibranchiate Ba- 
 trachia lead sluggish lives in swamps and pools ; their senses arc 
 as little developed as those of the Lepidosiren, and their mus- 
 cular movements are perhaps even more restricted : hence, if the 
 cerebral lobes seem to preponderate, in pro])ortion to other jiarts 
 of the brain, over tlie prosencephalon of Osseous Fishes, it is 
 rather by contrast with the rudimentary condition of the mes- and 
 ep-enccphala than in the relative size of the prosencephalon to tlie 
 entire body. 
 
 In a Newt, weighing 39 grains, the brain weighs one-seventh 
 of a grain : and in the large Sirens, Amphiumcs, and Menopomes, 
 the proportion of the brain to the body is less than in the 
 Newts. 
 
 The medulla oblongata slightly expands ; the post-pyramidal 
 and restiform tracts diverge and expose a long and simple ' fourth 
 ventricle,' with a median fissure : the convergence and confluence 
 of the borders at the fore part of the ' calamus ' offer a feeble 
 rudiment of cerebellum. The optic lobe in the Axolotl is a long 
 elliptical body, two-thirds the breadth of the epeueephalon. A 
 slight swelling below gives off the small optic nerves, and is 
 produced anteriorly into a vascular ' hypophysis ' : a larger }iineal 
 body extends from before the optic lobe upon the jjosterior inter- 
 space of the cerebral lobes, completing the mesencephalon, which 
 is the smallest of the primary divisions of the brain. The 
 cerebral hemispheres, twice the length and breadth of the optic 
 lobe, are smooth and hollow, like those of Lepidosiren. The 
 olfactory lobes are pyriform, with the base sessile on the fore 
 and outer part of the licmisphcrcs ; the nerve is shorter than in 
 Lepidosiren. The cerebral ventricles are continued into the 
 olfactory lobes. 
 
 The small and simple brain may be wliollv removed from a 
 tor])id batracliian in the winter season, the medulla oldongata 
 included, by section of the myelim in front of the roots of the 
 second ])air of cervical nerves ; and, nevertheless the animal 
 survives many weeks, jircserving the reflex actions of (he myclou 
 iuid nerves, the contractility of the nuiscular fibre, and the 
 
ENCEPHALON OF REPTILES. 
 
 '291 
 
 functions of organic life. In the active state of the summer 
 season, suoli mutilation is followed by death in one or two hours, 
 rarely more.' 
 
 In serpents, the cerebellum, fig. 188, c, ex])ands into a depressed 
 semicircular lobe directed backward from the confluence of the 
 restiform crura and overlapping tlie major part of the fourtli 
 ventricle, which appears as a short median fissure. The optic 
 lobes, ib. b, now expanded 
 to the breadth of the cere- 
 bellum, show both a longi- 
 tudinal and a transverse 
 fissure, the latter crossing 
 near the hinder Ijorder, and 
 giving to this j^art of the 
 
 , brain a close resemblance 
 
 ■ to its homoloijue the ' biffe- 
 
 || minal bodies ' in Mammals. 
 
 ' The optic lobes are hollow : 
 the cerebral crura show 
 sliijht enlargements, like 
 optic thalami, anterior to 
 the optic lobes, before ex- 
 i:ianding into the hemi- 
 spheres. These are pressed 
 into close contact medially, 
 and comjDOse a prosence- 
 phalon nearly as broad as 
 long, and double the 
 breadth and length of the 
 mesencephalon. The outer 
 svirface of the hemisjiheres 
 is smooth, composed of a 
 thin layer of vascular or 
 grey neurine. Into their 
 cavity or ventricle a ' cor- 
 pus striatum' projects from 
 the under and outer side ; beneath or raesiad of which is a minor 
 prominence. The septum, formed by the thin mesial wall of 
 each hemisphere, is perforated for tlie passage of a ' clioroid 
 plexus.' The ventricles are continued forward into the olfactory 
 lobes, fig. 188, 1 ; each is marked off by an oblirpie fissure from 
 the fore part of the hemisphere, which it equals in breadth ; 
 
 ' CCI. 
 u 2 
 
 ll Nihls III B i( uslnit 1 I IV 
 
292 
 
 ANATOMY OF VERTEBEATES. 
 
 189 
 
 and after a short curve, resolves itself into a close fasciculus of 
 
 olfactory nerves. 
 
 In the Lacertilia, the eyes being relatively larger 
 and more active in function than in Serpents, the 
 optic lobes, fig. 189, b, show corresponding increase 
 of proportional size to other parts of the brain. The 
 cerebellum, ib. c, is still smooth, depressed, semi- 
 circular, and leaves more of the fourth ventricle, e, 
 exposed than in Python. The ojitic lobes cease to 
 show the transverse fissure, and form a pair of hemi- 
 spherical hollow bodies. The cerebral hemispheres, 
 ib. a, form an elongate oval body, more contracted 
 anteriorly than in Python. The olfactory lobes, ib. (f, 
 
 Brain ol a "^ , i ■ • • • i i i • i 
 
 Lizard (iarrrtti are coutractcd at their junction with the hemispheres 
 view^'ccxyr' into the resemblance of ' crura rhinencephali.' 
 
 191 
 
 190 
 
 Bniili ul Tdrlui^o, Ijase view. 
 
 CCVIII. 
 
 Brain oi: Tnrllo iOi,7„„c), upper \lcw. 
 
 CCXVI. 
 
 Tn the base view of tlic brain of the Tortoise, given in fio-. 190 
 the absence of ' pons Varolii' and of olivary or pyramidal bodies 
 
ENCEPHALON OF REPTILES. 293 
 
 IS shown in the medulla oblongata, which is indicated by a slight 
 tumefaction giving off the fifth, 3, 4, 5, 6, seventh, 7, eighth, 8, and 
 ninth pairs of cerebral nerves : the tract is bounded anteriorly 
 by the hypophysis covering the origin of the optic nerves. 
 The continuation of the basal fibres of the hemispheres, p, 
 into the rhinencephalon, E, is shown. 
 
 In a side view, the several primary divisions of the chelonian 
 brain present the shapes and proportions shown in fig. 192, in Avhich 
 C is the epencephalon, o, the mesencephalon, p the prosence- 
 phalon ; E, the rhinencephalon. The epencephalon includes the 
 medulla oblongata, with the cerebellum. 
 
 .-.:k 
 
 Brain of a Turtle iCIidonc), side view. ecu. 
 
 In the turtle ( Chelone, fig. 191) the cerebelkmi, c, is slightly 
 raised by the bristle, o, to expose the fourth ventricle, /*, in which 
 the sides of the calamus rise into ' teretial tracts.' The cere- 
 belluna is subelongate in its form, consisting of an arched layer 
 of neurine, smooth externally, of equal thickness throughout, 
 which spreads over a portion of the ventricle. The remainder 
 of that cavity is covered by a vascular plexus, derived from 
 the sides of the medulla oblongata, which forms a sort of valve, 
 and by becoming united to the margin of the cerebellum, com- 
 pletes the roof of the fourth ventricle, which is large and jjro- 
 longed very far back. The optic lobes, O, are smooth, sphe- 
 roidal bodies, on a plane inferior to the cerebellum and cere- 
 brum. Each lobe has its ventricle, c* , which communicates, as 
 shown by the bristle, m, with the fourth ventricle, and likewise 
 with the third ; the ' iter ' to which may be seen by divaricating 
 the optic lobes, covered by pia mater reflected down the intersjDace, 
 and by a very thin layer of neurine. From the third ventricle a 
 canal, or ' infundibulum,' is continued down to the hypophysis, and 
 another upward to the ' pineal ' body, which is pyriform, hollow, 
 and highly vascular : it occupies the interspace between the 
 optic, O, and cerebral lobes, p. These form the largest of the 
 
294 ANATOMY OF VERTEBRATES. 
 
 primary divisions of the brain, but retain the form and character 
 of simple smooth nodules. Each lobe has its ventricle, fig. 191, 
 p, containing a ' corpus striatum,' fig. 193, i, in which 
 the ' crus cerebri,' fig. 194, i, principally expands; also a 
 smaller oblong eminence connected with the ' thalami optici,' 
 fig. 19.3, 2; and a transverse body extending anteriorly to the 
 mesencephalon from the base of one lateral ventricle to the 
 other. The choroid plexus is shown in the left ventricle of 
 fig. 193. The olfactory lobes, of a pyramidal form, have their 
 base defined by a fissure from the hemispheres ; each has 
 its ventricle, fig. 191, k, which communicates with the 'lateral' 
 one, P. 
 
 The my clonal canal, fig. 191, g, is continued along all the 
 encephalic masses, in which it expands, and assumes the name 
 of 'ventricles,' the narrower intercommunicating canal being 
 the 'iter.' The 'fourth' or epencephalic ventricle is single: the 
 hypoarian ventricles, in fishes, form a pair ; as do, likewise, 
 the mesencephalic, prosencephalic, and rhinencephalic ventricles. 
 The ' iter ' or common passage between the ep- mes- and pros- 
 encejihalic ventricles, includes the cavity called 'third ventricle' 
 in Aiathropotomy : to which cavity the mesencephalic ven- 
 tricles are 'reduced by the consolidation of the optic lobes in 
 Mammals.' 
 
 The epencephalic or 'fourth ' ventricle,, exposed in figs. 193, and 
 194, c, shows the ' teretial ' columns bounding the 'calamus' or 
 median fissure : external to these are ' funicular ' and ' j^re- 
 pyramidal tracts : the rcstiform columns, forming the sides and, 
 anteriorly, the i-oof of the ventricle show grey and white striaj 
 on their inner svirface ; the cerebellum is removed from their 
 anterior union at 3, fi^. 194. The mesencephalic base which 
 
 ' The influence of the nomenclature of human anatomy, reflected downward upon 
 the dawning structures of the lower animals which culminate in Man, is nowhere more 
 obstructive to a plain and true indication of the nature of parts than in regard to those 
 of tlie brain. The ventricles, for example, were indicated by numbers, or by position. 
 But four of the primary ventricles, viz., the mesencephalic or optic pair, and the 
 rhinencephalic or olfactory pair, which are present in the majority of vertebrates, are 
 obliterated in Man; whilst the interspace of commissural lamella^, exceptionally deve- 
 loped in the complex cerebrum of Man, and some higher Mammals, is made a 'fifth 
 ventricle,' as if it were a structure of correlative significance and importance with the 
 ventricles properly so called. Those cavities moreover in the human prosencephalon 
 are specialized as ' lateral, ' being the only ventricles retaining the parial state which 
 is shown by the mes- and rhin-encephalic ventricles in all oviparous Vertebrates. 
 Whoever will eari7 out the application of neat subst.antivo names to the homologous 
 parts and structures of the encephalon, as they may be ascensively determined, will 
 perform a good work in true Anatomy. 
 
MYELON OF KEPTILES. 
 
 295 
 
 193 
 
 194 
 
 of llTllllli {11,1 I 
 
 supports tlie optic loljcs, is exposed from above, by their removal, 
 in fig. 194, o, showing the continua- 
 tion of the ventricular cavity through 
 that segment of the brain. The base 
 of the excised ' corpus striatum ' into 
 which the ' crus cerebri ' expands, is 
 shown at i, fig. 194. The prohniga- 
 tion of the optic lobe crosses the 
 cerebral crus, externally, in its way 
 to the optic tract, fig. 195, d\ a por- 
 tion has been removed in this figure 
 to expose the crus ccrel>ri in its ascent 
 to the hemisphere. Three tracts of 
 neurine may be traced from the jjros-, 
 enceplialon to the rhinenceplialon, of 
 which the inferior one is the most 
 distinct, fig. 190.' 
 
 In the brain of the Crocodile a marked advance is seen in the 
 relative size of the cereln-al lobes, especially in regard to their 
 breadth and height posteriorly, giving a pyriform sliapc to the 
 prosencephalon ; the optic lobes, also, are 
 not inferior in bulk to the cerebellum, and 
 this body sliows a transverse fissure on its 
 exterior. The olfactory loljes, which arc 
 situated near the hemispheres in the newly 
 hatched Crocodile, recede therefrom, and 
 advance, with a proportional prolongation 
 of the rhinencephalic crura. The optic 
 lobe shows a convex body projecting into 
 the ventricle from its posterior wall, which 
 body is serially homologous with the ' cor- 
 jTi_is striatum ' in the ventricle of the cere- 
 Ijral hemisphere. In other respects the 
 brain of the Crocodile closely conforms with that of the Turtle. 
 
 With the exception of the anourus Batrachia, the myelon 
 (spinal chord) is continued into the tail, gradually decreasing to a 
 point, and is not resolved into a ' cauda equina.' Such, indeed, 
 is its condition in the tadpole state of the frogs and toads ; but, 
 with the acquisition of the mature form, the myelon shrinks in 
 length, and terminates midway between the fore and hind limbs, 
 being resolved in the frog, into the three pairs of nerves which 
 
 195 
 
 i^^sertions of the hr;ii 
 Turtle tClahii'i). LIV. 
 
 XX. vol, iii. p. 22, No. J31£ 
 
296 ANATOMY OF VERTEBRATES. 
 
 form the sciatic, and into a few filaments passing on to the 
 sacrum, fig. 208, /. 
 
 In all Reptiles there is an anterior and a posterior longitudinal 
 fissure and a central canal dilating into the epencephalic ventricle. 
 The myelonal canal is surrounded by a thin layer of grey 
 neurine, and, in Lacertians and Crocodilians, it extends as far as 
 the first caudal vertebra : in Ophidians, which have the longest 
 spinal chord, the canal is continued to near the end, which 
 goes as far as the penultimate caudal. The enlargements 
 eivincc orisin to the nerves of the limbs are best marked 
 in Chelonia, owing to the relative slenderness of the myelon 
 in the trunk. In the Lizards and Crocodiles with nearly 
 equally developed limbs, the more muscular trunk and tail 
 demand a myelonal mass wliich renders the brachial and iliac 
 enlargements less conspicuous. There are no partial enlargements 
 of the myelon in Serpents ; the nerves, as numerous as the 
 vertebr;i3, are given off at short and regular distances, as in 
 fig. 188, m. 
 
 § 54. Membranes of the Myelencephalon in Hannatocrya.- — Both 
 brain and myelon are immediately invested by a thin but firm and 
 vascular membrane, the outer surface of which, in most Fishes and 
 many Reptiles, bears a stratum of pigment-cells belonging properly 
 to the central layer of the arachnoid, which has here coalesced 
 with the pia mater. This vascular membrane seems, therefore, to 
 be coloured with dark points, and sometimes to be minutely 
 speckled upon a silvery ground ; and the pigmental stratum often 
 accompanies the processes of the pia mater into the ventricles of 
 the brain. There is commonly a remarkable developement of the 
 vascular and pigmental membrane over the fourth, or epencephalic 
 ventricle ; it is largely developed in the Sturgeon, and conceals 
 the rudimental cerebellum in the Lepidosiren. In the Axolotl 
 calcareous particles are superadded to this covering of the epen- 
 cephalon. In Osseous Fishes the commonly considerable space 
 between the brain and cranial walls is occupied by a peculiar loose 
 cellular structure, filled by gelatinous or albuminous fluid, and by 
 oily matter : in the Perch and Bream it seems to consist of an 
 aggregate of minute spherical cells filled with fine colourless 
 oil, the mass being traversed by blood-vessels. Cuvier ' found 
 the cells, which he compares to a kind of arachnoid, filled by a 
 compact adipose matter in the Tunny and Sturgeon. This modified 
 arachnoid exists, but in less quantity, in the spinal canal, and 
 
 ' XXIII, i. p. 309. 
 
NEKVES OF FISHES. 297 
 
 even accompanies the cerebral nerves in their exit from the skull 
 in some fishes with large nerve-foramina. There is much cellular 
 arachnoid above the cerebral lobes in the Lepidosiren. A large 
 arachnoid is abundantly interposed between the dura mater and 
 pia mater in the Turtle ( Chelone), where two ligaments converge 
 Irom the arachnoid at the sides of the epencephalon to be attached 
 to a cartilaginous tubercle on the basioccipital. A number of 
 filamentary processes pass from the space between the cerebral 
 and optic lobes to the arachnoid above, like a rudimentary 
 ' falx.' 
 
 The primitive fibrous capsule of the neural axis, the unossified 
 or unchrondrified remains of which, or of its inner layer, form 
 the so-called ' dura mater,' is most distinct in the low-organised 
 Dermopteri ; in the Plagiostomi it is reduced to a few thin shining 
 aponeurotic bands closely adherent to the inner surface of the 
 cartilaginous walls of the cranium and spinal canal ; svich traces 
 of dura mater are more feeble and indistinct in Osseous Fishes, 
 in which no proper continuous fibrous membrane can be dis- 
 tinguished from the inner periosteum of the walls of the cerebro- 
 spinal cavity : no curtains of dru-a mater divide the cerebral from 
 the acoustic compartments of the cranium in the Osseous Fishes. 
 The dura mater, as a distinct fibrous membrane, lines the cavity 
 of the skull and spinal column in Reptiles. 
 
 § 55. Nerves of Fishes. — First pair or Olfactory nerves. — The 
 head is short and obtuse in the embryo fish ; the ganglionic 
 centres of the olfactory nerves are always originally developed 
 in close contiguity with the prosencephalon ; they are protected, 
 pi-imarily, by the rhinencephalic arch ; and, as this advances 
 in the elongation of the skull, and recedes from the prosence- 
 phalic arch, two modes of growth take place in the contained 
 nervous axis : either the brain is co-elongated, the rhinence- 
 phalon retaining its primitive relation with its vertebra, and the 
 prolonged crura occupying the narrow interorbital tract of the 
 cranial cavity, or the rhinencephalon retains its prunitive juxta- 
 position with the prosencephalon, and the olfactory nerves, figs. 
 180 — 182, 0, 203, 0, are prolonged through the interorbital space, 
 perforate or traverse a notch in the prefrontals, and expand, as a 
 resolved plexus, upon the pituitary plicated sac. 
 
 The rhinencephalon accompanies its vertebra and recedes from 
 the rest of the brain in Salmo, Cyprinus proper, Brama, Tinea, 
 Gadus, Lota, Hippoglossus, Clupea, Belone, Lucioperca, Cobitis, 
 Plectognathi, and Plagiostomi; it retains its primitive contiguity 
 with the prosencephalon in Perca, Scomber, Esox, Pleuronectes, 
 
298 
 
 ANATOMY OF VERTEBRATES. 
 
 Blenr, 
 
 Anguilla, Cyclopteri 
 
 19G 
 
 G aster osteus, Eperlanus, Coi- 
 tus, Tricjla, Amblyopsis, 
 Echeneis, the Ganoidei, 
 and Lepidosiren. 
 
 As the crus of the 
 rhinencephalon is formed 
 not only of fibres con- 
 tinued from the f)rosen- 
 cephalon, but also, and 
 in some fishes chiefly, of 
 distinct white and grey 
 
 « T^ i n ifflt flPji S™* ^!^ tracts, traceable along the 
 
 K SaSki ^InwMH^ base of the mesencepha- 
 
 ^S^hnf' nl % .VmF 'Hnk ion, in part as far back as 
 
 the prcpyramidal bodies, 
 so the origin of the olfac- 
 tory nerve has been de- 
 scribed as characterised 
 3iJL twK \!^ liH Wm '^y ^^"'^ complexity and 
 
 JiUiIvIm fHB |B| extent; and it is true 
 
 ^/■H v^Aiw^fJ^nn Wmak \\i&± in some instances 
 
 (e. g. in the Perch), 
 here the rhinence- 
 1 halon, figs. 180—182, 
 is in contact with the 
 1 rosencephalon, ib. c, a 
 nail portion of the true 
 [factory nerve may be 
 listinctly traced back- 
 ard as far as the mesen- 
 sjihalon : just as we find 
 I some fishes (e. g. 
 VW H C'^HB* '' II iimUIW "^turgeon) a portion of 
 
 7 I » \. ^E n fjlilR '^"^ optic nerve traceable 
 
 '. n m M «» t\\. JiUlHi 5 far back as the cere- 
 
 bellum, and in the Eel 
 to the hypoaria, and not 
 exclusively terminating 
 in the optic lobe. IMost 
 of the characteristics of 
 origin and course attri- 
 buted in works of Comparative Anatomy to the olfactory nerves 
 are to be understood of the 'crura rhincnceiihali.' In the 
 
 Uraiu ,111(1 ccrfl.ni] nr. 
 
NERVES OF FISHES. 
 
 '299 
 
 Lancelet the little ciliated olfactory sac is brought into close 
 contact with the rhinencephalic extremity of the neural axis. 
 AVhen the olfactory lobe or ganglion, in other Fishes, is near 
 the organ of smell, as in the Cod, fig. 196, o, it sends off the 
 nerves by numerous very short fasciculi. This multiplicity of 
 virtual origins of the proper nerve is less conspicuous vs^liere 
 the rhinencephalon is near the rest of tlie brain ; but a careful 
 analysis of the long olfactory nerve in the Eel, fig. 176, will 
 show that it is a fasciculus of filaments distinct from their 
 origin. 
 
 The optic nerves, like the eyes, are of large relative size in most 
 fishes ; but where the organs of sight are small, the nerves are 
 slender, as in the Silurus : they arc still more slender in the 
 Myxinoids, and they are scarcely discernible filaments in the 
 
 197 *, ' - 198' 
 
 Brain of Skate IJiaia), base 
 view. ecu. 
 
 Brain of a Halibut (TTippoglossi(^<), A uii|)C'r, B under 
 view. ecu. 
 
 Amblyopsis, fig. 175, 2. In the Plagiostomes, fig. 197, Holoce- 
 phali, Ganoidei, and Protopteri, the optic nerves, ib. a, a, arise in 
 part from the optic lobes, ib. d, in part from the hypoaria, ib. c, c, 
 closely adhering to the fore part of the base of the mesencephalon, 
 and are there connected together by a transverse commissure, ib. b, 
 or close interblending of substance : they do not freely cross each 
 other. In ordinary Osseous Fishes, figs. 181, 185, the exterior white 
 fibres of the optic lobes converge to their under and anterior part, 
 to form the chief part of the origin of the optic nerves ; but a portion 
 of the origin may be traced through the septum opticum to the 
 cerebellum ; and in the Eel, the Garpike, and the Lump-fish, a 
 portion may be traced to the hypoaria: in the Cod, fig. 185, and 
 
300 
 
 ANATOMY OF VERTEBEATES. 
 
 Hake some fibres of the optic nerve, ib. 2, are derived from both 
 the hypoaria, ib. n and fig. 199, d, and from the wall of the third 
 ventricle. The relation of the hypoaria to the nerves of sight is 
 illustrated in the fishes with unsymmetrical heads and eyes, e. g. 
 Pleuronectida ; in fig. 198, the optic lobe, e, and hypoarion, g, 
 giving origin to the larger optic nerve, c, are larger than the optic 
 lobe,/, and hypoarion, g, giving origin to the smaller optic nerve, d. 
 The nerves cross one another without interchange of fibres ; some- 
 times the right nerve in its passage to the left eye passes under, 
 fig. 199, 6, a, fig. 201, sometimes over, figs. 185, 198, the left nerve:' 
 rarely does one nerve perforate the other, as, e. g. in the Herring. 
 The nerves are flattened where they decussate. In most Osseous 
 Fishes the structure of the optic nerve is peculiar ; it consists of 
 a folded plate of membrane and neurine, fig. 200, a, which usually 
 prevails throughout the length of the nerve, from its cerebral 
 
 attachment to the eyeball : 
 
 ^^^ in some instances the inner 
 
 — surface of the optic lobe is 
 
 also folded : and, in all, the 
 
 plaits may be observed to 
 
 be faintly continued upon 
 
 the retina, which is formed 
 
 by the unfolding of the 
 
 nerve. The optic nerve escapes, in Osseous Fishes, either through 
 
 the anterior fibrous wall of the cranium beneath the orbito- 
 
 sphenoid, or through a notch or a foramen 
 
 in that bone. In the PleuronectidcE one optic 
 
 nerve is usually shorter, as well as smaller, 
 
 than the other, fig. 198. In the Eel the 
 
 nerves form, after decussation, a very acute 
 
 angle in the axis of the body, fig. 176, a: in the 
 Lump-fish they form an obtuse open angle. 
 
 Since there are no muscles of the eyeball 
 in the Lancelet, the Myxinoids, the Am- 
 blyopsis, and the Lepidosiren, there are no 
 motory nerves of the orbit. In the Lamprey 
 a small third nerve and a fourth nerve, wliioli 
 arc closely connected where they quit the 
 cranium, again separate, the one to supply 
 the rectus superior and rectus intcrnus, the 
 other the obliquus superior; the filaments supplying the other 
 
 ' The writer has seen both varieties in difl'crciit inOividuals of Gadm morrlwa. 
 
 Brain of a Hake (ilcrluccim) with tlic base upward, cuii. 
 
 200 
 
 Plaited optic nerve of a Mullet. 
 a, o]>tio nerve deprived uf it3 
 elieath, exhibiting tlie pliiited 
 
 ■disposition; b, scler.iiir cuat 
 of the eye tlirougli wliicli the 
 nerve is paSBing ; r, retina, 
 In ■\vliit'li tlie nerve termi- 
 nates, ecu. 
 
NERVES OF FISHES. 
 
 301 
 
 muscles of tlie eyeball cannot be separated from tlie fifth pair. In 
 all other fishes the sixth or abduce?it nerve, fig. 185, g, has its proper 
 origin, as well as the fovirth and third. The third, or oculomo- 
 torius, ib. 3, rises from the base of the mesencephalon, behind the 
 hypoaria, ib. n, or from the commissura ansulata ; it escapes through 
 the orbito-sphenoid (Carp), or the unossified membrane beneath it 
 (Cod, fig. 196, 3), and is distributed constantly to the recti superior, 
 inferior, and internus, and to the obliqu.us inferior ; it also sends 
 filaments into the eyeball : the ciliary stem, or a branch of it, 
 usually unites with a branch of the fifth nerve, and sometimes, 
 as in the Mackerel, Gar-pike, and Lump-fish, developes a small 
 ciliary ganglion at the point of communication. 
 
 The fourth nerve, or trocldearis, fig. 196, 4, rises from the back 
 of the base of the optic lobes, between these and the cerebellum ; 
 
 201 
 
 Brain anil origins of tlic llftii norvcs of tlio Cod. CCVIII. 
 
 it escapes either through the orbito-sphenoid (Carp), or the con- 
 tiguous membrane (Cod), and is constantly and exclusively dis- 
 tributed to the superior oblique eye-muscle, ib. g. 
 
 The sixth, or abducent, nerve, figs. 185, 196, 6, rises from the 
 prepyramidal tracts of the medulla oblongata, fig. 185, a, beneath 
 the fifth, and, in most Osseous Fishes, by two roots, as in the Cod, 
 ib. 6. It usually closely adheres to the ganglionic origin of the 
 fifth. In the Carp and Lump-fish it receives a filament from the 
 sympathetic, before its final distribution to the rectus externus, 
 
302 
 
 ANATOMY OF VERTEBEATES. 
 
 fig. 196, h: it escapes by the foramen or anterior notch of the 
 alisphenoid, in advance of the fifth nerve. 
 
 This nerve, the trigeminal, enormous in all Fishes, from the 
 Lancelet to the Lepidosiren, rises, often by two or more roots, from 
 the restiform, or from the anterior angle between the olivary and 
 restiform tracts ; in some fishes from a special ganglion or enlarge- 
 ment of that part of the medulla oblongata, as in the Herring, fig. 
 184, i: in a few (Conger, Lump-fish) by a smaller origin resolved 
 into several roots. The trigeminus shows well its spinal (myelonal) 
 character in Fishes, only its double root is more deeply buried in 
 the medulla oblongata. In the Cod, fig. 201, the non-ganglionic 
 portion is shown at i, the roots of the ganglionic portion at 2, 2. 
 On the left side the non-ganglionic portion is separated and turned 
 back : on the right side its divisions are seen accompanying the 
 first, a, second, b, and third, c, branches of the trigeminal. The 
 fourth branch, d, is also composed of both portions of the nerve : 
 the fifth branch, e, is exclusively from the ganglionic portion. 
 The trigeminal is in close contact with tlie acoustic nerve, at their 
 
 202 
 
 Brain ;uKl flfUi nerves iif the Ray. CO'III. 
 
 origins. In Cottus, Blennius, Cubitis, and I^aiciscus, the ganglionic 
 or dorsal roots recede from the ventral ones, as they penetrate the 
 medullary substance. The non-ganglionic roots in the Blcnny 
 join the facial and glossopharyngeal. Of the five roots of the 
 trigeminal in the Sturgeon, the first, second, and fourth form a 
 
NERVES OF FISHES. 303 
 
 ganglion (Gasseriarmm). In the Skate (Raia) the roots of the 
 two ganglionic portions, fig. 202, a, b, of the trigeminal, arise from 
 the restiform tract : the non-ganglionic part, c, from the folded or 
 iimliriate part of the tract. A pin is passed between the second 
 ganglionic and the non-ganglionic portion ; the latter, c, being re- 
 Hcctcd back on the left side of the figure ; on the right side the 
 non-ganglionic bi'anches, e, f, are left, accompanying the corre- 
 si)onding branches of the ganglionic portion, «, e,f. The acoustic 
 nerve, 7, comes off as a branch of the second ganglionic part of 
 the trigeminal. 
 
 In Osseous Fishes the hindmost branch of the fifth nerve divides, 
 one part descending to the ' opercular' nerve, fig. 203, t, the other 
 ascending to the ' lateral ' nerve, ib. m ; but both receiving an acces- 
 sion from other sources to form those nerves respectively. A branch 
 of the vagus, fig. 202, t, ascends forward to join the fifth in 
 forming the dorsal division of the ' nervus lateralis,' ib. m, which 
 escapes by a foramen in the parietal bone ; the rest of the fifth 
 emerges from the skull by a hole (Carp), or a notch (Cod), of the 
 alisphenoid. The lateral nerve in the Cod is formed chiefly by 
 the fifth, fig. 196, 5, and receives only a slender filament of the 
 vagus. In the Carp the vagus chiefly forms the lateral nerve. 
 In the Cod, fig. 205, the lateral nerve first sends off a branch, ib. i, 
 which runs along the sides of the iuterneural spines, receiving 
 branches from all the spinal nerves ; it then curves down along 
 the scapular arch, gives branches to the pectoral, ib. p, and ven- 
 tral, ib. V, fins, supplies the great lateral muscular masses, ib. 2, 
 and the mucous canal, ib. 3, and sends a nerve, ib. 4, to the inter- 
 hajmal sjiines, which communicates with filaments from the corre- 
 sponding spinal nerves : both iuterneural and iuterha3mal branches 
 terminate in the plexus supplying the caudal fin : thus all the 
 locomotive members are associated in action by means of the 
 nervi laterales. The mandibular division of the fifth (ramus man- 
 dihularis, sen maxillaris inferior) consists chiefly of motory filaments 
 which supply the muscles of the hyoid and mandibular arches, 
 and the '■ramus opercularis seu facialis,' fig. 202, t, to those of the 
 ('ill-cover ; the sensory filaments go to the teguments of the sides 
 of the head, ib. r, and under jaw, enter the dental canal, supply 
 the teeth, and, in the Cod, the symphysial tentacle.' The maxil- 
 lary division (r. maxillaris) bifurcates behind the orbit, one branch 
 ])asses outward to supply the suborbital mucous canals and integu- 
 ments on the sides of the head ; the other, after sending a branch 
 obliquely outward, curves forward along the floor of the orbit, 
 
 ' ccxxvi. p. 45, fig. 2. 
 
304 
 
 ANATOMY OF VERTEBRATES. 
 
 ib. V, gives off a palatine nerve (r. pterygo-palatinus), and supplies 
 the integuments, mucous tubes, and teeth of the upper jaw. The 
 super-orbital division, ib. e, gives off the two ciliary nerves, one 
 
 203 
 
 Cerebral nerves, rercb. XXIII. 
 
 of which joins the ciliary branch of the third ; it supplies the 
 olfactory sacs, and the integuments of the upper and fore part of 
 the head. 
 
 In the Skate the large sensory branches of the fifth, sent to the 
 integuments, and to the singularly developed mucous canals, have 
 ganglionic enlargements near their origins, fig. 202, a, b, where 
 they leave the main trunk. The first electric nerve is given off 
 by the fifth in the Torpedo, fig. 139, 5, and many of the terminal 
 filaments of the tegumentary branches of the fifth are connected 
 with the peculiar muco-ganglionic corpuscles, described at p. 324, 
 fig. 215.' In the Sturgeon the snout and its tentacula are sup- 
 plied by branches of the infra-orbital, not from the supra-orbital, 
 division of the fifth ; the opercular or facial branch supplies, in 
 addition to the gill-cover, the integuments and lips of the pro- 
 tractile mouth, and the pseudobranchia : it communicates with 
 the glosso-pharyngcal. 
 
 In the Lancelot the fifth nerve, fig. 169, ob, distributes many 
 filaments to the expanded sensitive integument which represents 
 
NERVES OF FISHES. 305 
 
 tlie head, and forms the sides of the wide oval opening ; it also 
 sujiplies the oral tentaciila. In the Myxinoids the same nerve 
 supplies both the muscles and the integuments of the head, the 
 tentacnla, the nasal tube, the mucous mcml)rane of the mouth 
 and tongue, the hyoid and jialatal teeth, and the pharynx. The 
 trigeminus supplies the same j^arts in the Lamprey, but in a more 
 compact manner, i. e. by fewer primary branches : that which 
 sends filaments to the rectus externus and rectus inferior of the 
 eyeliall is continued forward beneath the skin and resolves itself 
 into a rich plexus, which supplies the thick cirrate border of the 
 suctorial lip : the nerves to the muscular parts of the jaws and 
 tongue arise distinct from the fifth, and their trunk may be 
 regarded as a ' facial ' nerve ; one of the filaments of this joins a 
 branch of the A'agus to form a short ' ncrvus lateralis.' 
 
 Thus in reference to the motor filaments of the trigeminus or 
 great spinal nerve of the head, those that form the portio dura or 
 facial nerve in higher Vertebrata are not distinct from the rest of 
 the trigeminus at its apparent origin, except in the Lamprey ; in 
 which, on the other hand, the motory filaments of tlie rectus 
 externus, forming the sixth nerve of higher Fishes and Vertebrates, 
 retain an associated origin with the trigeminal. The ' facial ' part 
 of the operculo-lateral division of the fifth, in the Perch,' is that 
 which supplies the mandibular, opercular, and branchiostegal 
 muscles. In the extended medulla oblongata of the Sander 
 {Lucioperca) the facial nerve has a distinct origin between the 
 trigeminal and acoustic. 
 
 The acoustic nerve appears to be a jjrimary branch of the fifth, 
 ill the Skate, fig. 201, 7: its distribution on the labyrinth is beau- 
 tifully shown by Swan in Liv. pi. x. fig. 2. It communicates on 
 tlie great otolithic sac with a motor branch from the vagus, which, 
 after giving filaments to the posterior semicircular canal, passes 
 out to supjily the first and the adjacent sarface of the second gill, 
 and the faucial membrane. Swan calls this branch the ' glosso- 
 pharyngeal,' and says, ' this nerve, on being touched near its 
 origin in a recently-dead animal, immediately produces a contrac- 
 tion of the muscular appendages of the gills ' (ib. p. 41). In the 
 Cod the acoustic nerve, fig. 185, 7, which here as in all fishes 
 above the Dermopteri is of large size, rises close behind, but 
 distinct from, the fifth pair, ib. 5, between it and the vagus, ib. 8 : 
 the acoustic nerve receives a filament from the vagus, extends in 
 a cresceutic form, fig. 196, 8, upon the labyrinth, expands upon 
 
 ' xxni. torn. i. p. 325, pi. vi. fig. v. |U. 
 VOL. I. X 
 
306 ANATOMY OF VERTEBRATES. 
 
 the large sac of the otolite, ib. i, and sends filaments to the 
 ampulliform ends of the semicircular canals. In other Osseous 
 Fishes (Pike, Blenny) the acoustic blends at its origin with the 
 back part of that of the fifth : it sometimes communicates with 
 the opercular branch of the fifth, as well as with the glosso- 
 pharyngeal of the vagus. Its division on the acoustic sac is 
 shown, in the Perch, at s, s, fig. 203. 
 
 The nervus vagus, ib. t, has a developement proportional to 
 the extent and complexity of the l^ranchial apparatus in Fishes, 
 and is usually larger than the trigeminal : it rises, fig. 185, 8, from 
 the restiform tract forming the side of the medulla oblongata, and 
 commonly from a sj^ecially developed lobe ; and is distributed to 
 the branchial apparatus, the pharynx and pharyngeal arches, the 
 ossophagus and stomach ; it sends filaments to the heart, and to 
 the air-bladder when this exists ; and it forms, or helps to form, 
 the ' nervus lateralis.' In the Lamprey a portion of the vagus 
 combines with branches of the facial and hypoglossal nerves to 
 form a short side-nerve extending to the middle third part of the 
 body. In Salmo, Clujoea, Acipenser, the 'nervus lateralis' is formed 
 exclusively by the vagus : in the latter, as in Chimcera, Balistes, 
 Diodon, Cydopterus, this nerve is a single longitudinal one : in 
 most bony fishes there are two which run parallel or nearly so. 
 In all these fishes it is continued very far back along the lateral 
 or latero-dorsal region of the body ; sometimes lodged deeply in 
 the lateral mass of muscles, e. g. Belonc, Clupca, and Scomber,^ 
 but more commonly the nerve or a main branch lies just under 
 the skin, and in the course of the lateral mucous line, as in the 
 Salmon and Sturgeon ; in the Flat-fish and Bull-heads it has both 
 a deep-seated and a superficial branch. In Upeneus the super- 
 ficial Ijranch is sent off", dorsad, at an open angle from the main 
 trunk, to the lateral line, above which it runs in the Belone, the 
 superficial liranch descends to gain the lateral line. In the 
 Carp and Herring the vagal ' ramus lateralis ' sends ofl:' a strong 
 branch to the dorsal fin ; in the Garpike it sends, as in the Cod, 
 branches to tlie pectoral and ventral fins ; it distriljutes other 
 branches to the skin and mucous ducts; and some of these, in 
 most fishes, anastomose with branches of the spinal nerves, fig. 
 205. In the Perch there are two 'nervi laterales' on each side; 
 the dorsal one, fig. 203, m, above described, and the proper lateral 
 nerve, ib. I : this is formed exclusively by the vagus, and divides 
 into a superficial branch, supplying the lateral line, and a deep- 
 
 ' XX. vol. iii. p. 49, iircp. no. 1381 (mackerel). 
 
NERVES OF FISHES. 307 
 
 seated branch, coinmiinicating with the spinal nerves, and sup- 
 plying the myocommatal aponeuroses and the skin.' Whether 
 the vagus forms the whole or a part of the ' nervus lateralis,' tliis 
 does not arise like the ' nervus accessorius ' of higher Vertebrates, 
 from a motory tract of tlie myelon, but from a ganglionic part of 
 the vagus. Tlic 'nervus lateralis' chiefly supplies the skin, 
 mucous line, intermuscular septa, and vertical fins, most of them 
 liecullarly ichthyic parts, either by their preponderating develope- 
 ment, or their very existence. 
 
 The vagus sends supra-temporal l)ranclies to the head, and 
 opercular In-anches to the gill-covers. The usually doulile roots of 
 tlie nervus vagus ])ass out, in most Fislies, by a single foramen in 
 tlie exoccipital Ijone. Tlie fore part of the root is the largest, and 
 is ganglionic : it is the true pneumo-gastric, supplying the gills, 
 pdiarynx, heart, and stomach, and sending filaments to the sep- 
 tum dividing the branchial from the abdominal cavity. In the 
 Tunny the branchial nerves are remarkaljle for their size and 
 their radical ganglions. The liindcr second origin is the sovirce of 
 the glosso-pharyngeal and lateral nerves. The former, which 
 has a distinct ganglion in the Herring and some other fishes, 
 supplies the first gill and contiguous parts, and thence passes 
 forward to the tongue. Some filaments rising Ijehind tlie vagus 
 have been traced to the parts surrounding the brain within the 
 cranial cavity.- Each vagal nerve of the Sturgeon equals the 
 spinal chord in size, and rises by numerous roots. The nerve 
 has a like extensive tract of origin in the Sharks ; in which a 
 posterior fasciculus, fig. 187, 8, representing the 'nervus acces- 
 sorius,' can be best demonstrated. 
 
 There is no ' nervus lateralis ' in the Myxinoids, but the gastric 
 Isranches of the vagus are continued, united as a single ner^'e, 
 along the intestine to the anus. The vagus is represented in the 
 Branchiostoma by a branch sent from the fifth to the pliarynx. 
 In the Myxine its origin is close to that of the fifth. The 
 erectile palatal organ of the Cyprinoids is wholly, and the electric 
 organs of the Torpedo are, in great part, supplied by this remark- 
 able vagal nerve. The proportion of grey to white filaments 
 in the vagus of Fislies is greater than in that nerve in higher 
 Vertebrates, which illustrates the progressive diflPerentiation of 
 the great sympathetic.^ 
 
 The,^r5^ spinal, or my clonal, nerve rises usually by two roots, 
 the dorsal one having a ganglion, rarely by non-ganglionic roots 
 exclusively from the prepyramidal tracts : it usually emerges 
 
 ' XXIII. torn. i. pp. 325-27. - ccxxvii. ' coxii. 
 
 X 2 
 
303 
 
 ANATOMY OF VEKTEBRATES. 
 
 between the ex-occipital and tlie atlas, and divides into a small 
 dorsal and a larger ventral branch : this communicates with the 
 ventral branch of the next spinal nerve, and supplies the pectoral 
 fin-muscles, the subcoradoideus, i, the retractor hyoidei, c, and 
 geniohyoidei, 27, fig. 135: It is called 'hypoglossal nerve' by 
 some lehthyotomists ; but this name more properly applies to a 
 nerve which, in some fishes, arises from the medulla oblongata 
 behind the vagus, is distributed to the muscles between the scapular 
 and hyoid arches, and unites with the first spinal nerve. 
 
 Each of the spinal nerves has a dorsal or sensory, and a ventral 
 or motory origin ; sometimes each rises singly ; sometimes, as in 
 the Cod, by two or more filaments, fig. 196. Both sensory and 
 motory roots are long in most fishes : the sensory root is the 
 largest, arises by more filaments, and further back than the 
 motory roots, in the Sturgeon. 
 
 In most Osseous Fishes one dorsal root goes to form the dorsal 
 branch of the S23inal nerve, and the other dorsal root joins the 
 ventral branch of the same nerve : sometimes the ganglion is 
 formed on the dorsal root of the dorsal branch, as in the Cod ; 
 more commonly upon the whole sensory origin of the nerve, 
 where it emerges from the neural canal. In some fishes (Bream 
 and Garj)ike) the ganglions on the dorsal root are situated in the 
 spinal canal : more commonly (as in the Cod, the Ling, the 
 Sander) the ganglions are external to the spinal 
 canal. In both cases the nerve is increased in size 
 beyond the ganglion and the union of the ventral 
 root. This is well seen in the Skate, in which the 
 ganglions are situated beyond the holes of emer- 
 gence, and the junction of the two roots takes 
 place quite exterior to the neural canal. 
 
 The connection of the roots with the myelon 
 is weaker in Fishes than in air-brcathino- animals: 
 it is so easily broken in the Dcrmopteri as to have 
 led to a denial of its existence.' The pecidiar 
 combination of the dorsal and ventral roots of tlie 
 spinal nerves in Osseous Fishes is well seen in the 
 Cod.^ Tlie dorsal root sends a filament, fig. 204, a, 
 upward, which joins a ventral filament, h, from 
 the preceding nerve, and forms the ramus dor- 
 salis, d; the dorsal root sends two filaments, c, downward, which 
 unite together, and with a ventral filament, c, of the same nerve 
 
 204 
 
 C'unTioitiuni nf pplii il 
 and Iitr 1 a iKi\(.^, 
 
 ( 11,1 Ll\ 
 
 Lxxix. ii. p. 47'J. 
 
 LIV. pi. X. 
 
 Jj 
 
NERVES OF REPTILES. 
 
 309 
 
 to form the 'ramus ventriilis,' v. The filament of the ventral 
 root sent to the ramus dorsalis of the succeeding nerve perforates 
 the lower division of the dorsal root of its own ner^'e. 
 
 Thus each spinal nerve forms a ' ramus dorsalis,' fig. 205, lo, 
 and a ' ramus ventralis,' ib. 8 ; the ramus dorsalis includes a 
 sensory filament of its own nerve, and a motory filament of the 
 antecedent ner^'c : the ' ramus ventralis ' is fijrmed by a motory 
 
 
 A" 
 
 •• - ' 
 
 '-*»:" T ^zs^t^^jS^"^"" ''' 
 
 
 JO'' 
 
 \ *-.."?• 
 
 '■**^5^>^ 
 
 LnLeral ucvve ami IjraucljeB, Cod. LTV. 
 
 and a sensory filament of its own nerve ; both rami ' A'enti-ales ' 
 and ' dorsales ' are associated together, and with the vagal and 
 trigeminal nerves through the medium of the great ' nervus 
 lateralis,' fig. 205, i, 8. 
 
 The dorsal roots of the nerves distributed to the free, explora- 
 tory, pectoral rays of the Gurnards, rise from special ganglionic 
 swellings of the cervical portion of the dorsal myelonal columns. 
 
 § 56. Nerves of Rejjtiles. — The olfiictory nerves are continued 
 in Reptiles, for a greater or less extent, from the rhinencephalon, 
 figs. 188, 191, to the olfactory sacs; the white and grey tracts 
 beneath the proscnceiihalon, fig. 190, p, descrilied as roots of this 
 nerve, belong to the rluncncephalic crura : the true olfactory 
 nerves are less distinct from their centres than in other Ver- 
 tebrates. In the Python, fig. 188, the nerves, i, of equal 
 diameter with their centres, gradually expand, by resolution of 
 their fibres, as they aj^proach the olfactory sacs, ib. d, and are 
 joined by part of the first division of the ' fifth.' The olfactory 
 
310 
 
 ANATOMY OF VERTEBRATES. 
 
 nerves progressively increase in length in the Turtle, Iguana, and 
 Crocodile. The distrilnition of their tihres u])on the vascular 
 pituitary membrane, supported by the turbinal cartilage, is well 
 displayed in a Hunterian preparation of the Turtle.' 
 
 The optic nerves, corresponding in size with that of the eyes, 
 
 200 
 
 are smallest in the fish-like Batrachians. They arise from the 
 optic Idbcs, fig. 192, (), tlialami, and o]itic tracts, ib. d, and blend, 
 by a few decussating lamina\ into a chiasma, ib. /*, before diverg- 
 ing to the visual organ : their course is shown, in the Python, at 
 2, fig. 188. Tlie position of the 'third' or oculo-motor nerve is 
 
 ' XX. vol. iii. p. 89. iios. 1.532, l.lIiS. 
 
NERVES OF REPTILES. 311 
 
 sliown at 3, fig. 188. The course of the 'fourth' to the upper 
 ol)liquo muscle is shown at 4, fig. 188. This nerve does not 
 exist, separately, in the fish-like Batrachians. 
 
 The fifth or trigeminal nerve shows its double (ganglionic and 
 non-ganglionic) origins in all Reptiles, and its threefold primary 
 division very distinctly, in all above the Perennibranchiates. In 
 the Serpent the first division is shown at 5, fig. 188, extending 
 forward beneath the ' fourth ' nerve and upper oblique muscle, 
 and above the olfiictory nerve and capsule. The second division, 
 fig. 188, 6, fig. 206, 4, alter communicating with the sympathetic 
 nerve, divides : one branch supplies the membrane of the mouth 
 and palate ; the other passes out by canals in the upper jaw, and 
 terminates on the follicles and suljstance of the upper lip. The 
 third division, fig. 188, 7, fig. 206, 5, sends branches of its non- 
 ganglionic part to the muscles of the jaws ; a large branch enters 
 the dental canal of the maudil^le, supplies the tooth-capsules, and 
 emerges by three or more divisions : two of these, emerging at 
 the lower part of the mandible, communicate with branches of the 
 'eighth' and 'ninth' nerves, to be distril)uted to the muscles and 
 p)arts beneath the mandibular arch : another gives filaments to the 
 membrane of the mouth as far as the sheath of the tongue ; the 
 main continuation, emerging at a foramen near the symjjhysis, 
 supplies the lower lip. 
 
 In the Turtle the first or ophthalmic division of the fifth 
 advances some way in the substance of the dura mater before 
 entering the orbit ; it sends a filament to combine with one of the 
 third, to sn2:)ply the ciliary nerves, without forming a ganglion : it 
 supplies the lacrymal and harderian glands, and is continued to 
 the olfactory fossa. The second or maxillary division quits the 
 third on entering the floor of the orbit, along which it cur\-es, 
 sending from its concavity filaments to the lacrymal glands, and 
 dividing into two chief branches ; the internal branch, answering 
 to the spheno-palatine and suborbital, supplies the palate and floor 
 of the nasal cavity, and emerging at the fore-part of the orbit, it 
 spreads upon the maxillary tegument : the external branch jjasses 
 along the floor of the orbit, and emerges upon the face. The 
 third or ' mandibular ' division descends at the back-part of the 
 orbit, in front of the tympanic bone, supplies the temporal and 
 i:>teryo'oid muscles, enters the mandibular canal, and distributes 
 Ijranches inwardly to the tongue and floor of the mouth, outwardly 
 to the mandibular follicles and tegument. 
 
 In the Frog the maxillary and mandibular divisions of the 
 trigeminal, arising distinctly from the ganglion, diverge to their 
 
312 ANATOMY OF VERTEBEATES. 
 
 respective destinations at the middle of the floor of the orbit : 
 the hindmost branch, continuous with a filament from the 
 acoustic nerve, unites with a branch of the vagus, and is distributed 
 like the ' portio dura ' of the ' seventh ' nerve. The distinct 
 origin of this nerve, between the ' fifth ' and acoustic, is shown 
 in the Python, fig. 188, 8 ; it communicates, fig. 206, 6, with 
 the ganglion, ib. i, of the sympathetic, then passes through the 
 ' apertor oris,' to which it gives a branch ; communicates with 
 the first spinal nerve, and terminates on the ' costo-mandibularis ' 
 muscle. The acoustic nerve, fig. 188, 9, soon divides, and enters 
 the labyrinth by two or more foramina. The glosso-pharyngeal, 
 fig. 188, 10, is distinct at its origin in Serpents and higher Reptiles. 
 In Batrachia it issues from the ganglion of the vagus. In the 
 Python the glosso-pharyngeal passes chiefly to the ganglion, 
 fig. 206, I, of the sympathetic. The ' nervus vagus,' fig. 188, ii, 
 arises by several filaments, and in the Chelonian and Crocodilian 
 reptiles is recruited by an ' accessorius,' arising from the tract of 
 the first and second spinal nerves. In the Python, fig. 206, 8, 
 the vagus communicates with the sympathetic, and then receives 
 the continuation of the glosso-pharyngeal from the ganglion, i. 
 It sends a branch to communicate with the ' ninth,' and to be 
 distributed to the muscles and membrane of the fauces. The 
 trunk is then continued down or back, close to the trachea and 
 jugular vein: on the left side it also accompanies the carotid 
 artery : it sends filaments along the large vessels to the heart, and 
 others behind each aorta, similar to the recurrent nerves, to be 
 distributed upon the trachea and oesophagus : each trunk for a 
 short space accompanies the corresponding pulmonary artery to 
 the lung. Before reaching the liver it passes vcntrad of the 
 lung for a short distance, and joins its fellow to form a single 
 nerve. This is continued under the capsule of the \i\ev supplying 
 that organ, the lungs, and oesophagus. Near the end of the liver 
 the vagus sends a large liranch, which communicates freely with 
 the sympathetic, to the left surface of the stomach, and this also 
 gives filaments to the contiguous part of the lung. The trunk, 
 on the right of the stomach, communicating with the sympntlietic, 
 and with the division on the left, is continued a short wav on the 
 membrane connecting the viscera, gives branches to the right side 
 of the stomach, and terminates on the bcu'innino- of the intestine, 
 at the pancreas. 
 
 In the Chdonia and CroeodlUa the -S'agus quits the skull bv two 
 or three of its roots, which unite outside to form the trunk of tlic 
 nerve ; its communication with the glosso-pharyngeal, the ninth. 
 
NERVES OE EEPTILES. 313 
 
 and the sympatlictie, together witli its ultimate distril^ution, are 
 ill the main like those in Ophidia; it exclusively supplies the 
 heart. In the Ainpliubmia the accessorius is ]5art)ally blended 
 with the vagus, and separates from it to be distributed to the 
 cervical muscles, joining branches of the first two spinal nerves. 
 In Chdonid, and CrocodlUa the accessorius blends with the gan- 
 glion of the vagus : its continuation may be recognised in the 
 posterior branch sent by the vagus to the nuchal muscles. 
 
 The 'ninth' or hypoglossal nerve, fig. 188, 12, arises from the 
 motory tract, behind the vagus, from the trunk of which it receives 
 a branch ; it receives a smaller branch from the facial nerve ; com- 
 municates with the anterior cervical nerves ; and is distributed to 
 the muscles of the ]iliarynx and tongue, to the forked end of which 
 the lingual liranch may be traced. It sends a communicating 
 branch to those of the mandibular nerve, which are distributed to 
 the muscular floor of the mouth. In the Tortoise tlie liyp(_)glossal 
 escapes )jy two precondjdoid foramina ; after the union of these 
 origins the trunk communicates, as in Ophidia, with the vagal 
 and glosso-pharyngeal nerves : it sends a branch to the hyoid 
 muscles, a branch forward to the tongue, and a third downward 
 to the omohyoideus : the latter accompanies the vagus as far as 
 the fifth cervical. 
 
 The vagus enters in a larger jiroportion into the formation of 
 the nerve, or rather plexus, distributing brandies to the parts to 
 which tlie source of nervous supply is ascrilicd to the hypo- 
 glossal ; but this nerve has a distinct origin by two roots in the 
 Turtle. 
 
 The first and second spinal nerves arise, in Chelone, like the 
 hypoglossal, by motory roots only ; the sensory or dorsal roots in 
 the other cervicals are smaller than the motory ones. The skin 
 of the neck is not very sensitive : the muscles are large and 
 numerous. In the back, where muscles are few and small, the 
 sensory roots of the spinal nerves exceed the motory ones in size. 
 
 The nerve which emerges between the first and second trunk- 
 vertebra; in Batrachia supplies the muscles and integuments of 
 the subjacent part of the throat, and sends a few filaments to 
 those of the scapula. Four of the succeeding spinal nerves 
 combine in the Salamander to form the brachial plexus : two only 
 form tliat plexus in the Frog, that emerging between the second 
 and third vertebra; being the largest. In the Crocodile the sixth 
 and seventh cervical nerves, with the two following, combine to 
 form the brachial plexus. In the Turtle the sixth, seventh, 
 eio'hth, and ninth spinal nerves constitute the brachial plexus. 
 
314 ANATOMY OF VERTEBRATES. 
 
 This distributes a ' circumflex ' or axillary, an ulnar, a radial or 
 ' musculo-spiral,' and a median nerve. The circumflex supplies 
 the latissimus dorsi, claviculo-brachialis, supercoracoideus and 
 teres minor, and terminates on the integument at the back of the 
 arm. The ulnar nerve divides at the upper third of the humerus 
 into a branch sujoplying the extensor communis digitorum, ex- 
 tensor proprius pollicis, and ulnaris externus, a branch for the 
 triceps brachii, and a superficial cutaneous nerve distributed to 
 the intesument on the back of the fore-arm and hand. The 
 radial nerve passes to the outer side of the humerus, distributing- 
 muscular branches in its course, winds to the inner side, descends 
 in front of the elbow-joint, and terminates in muscular and 
 cutaneous branches. The median nerve passes along the back- 
 part of the scapula, giving branches to the pectoralis major, to 
 the shoulder-joint and siuTounding skin : passes between the 
 humeral tuberosities, supplying the triceps brachii and brachialis 
 internus : then divides into an external branch, passing between 
 the pronator teres and radialis internus, and supplying the flexors 
 of the digits, and into an internal branch, gliding between the 
 radius and ulna, and ultimately forming the volar arch. 
 
 In the Frog the axillary nerve sends a branch to the muscles 
 and skin above the scapula : it is continued into the brachial, 
 which bifurcates. One branch winds round the humerus, like the 
 ' musculo-spiral,' sends a branch to the extensor cubiti, and passing 
 in front of the elbow-joint penetrates the mass of flexor muscles, 
 and reappears at the outer side of the fore-arm : it sends one 
 branch to the skin, and another to the back of the hand, which 
 divides to supply the same aspect of the digits. Tlie other 
 division of the brachial nerve represents the ' median ; ' it divides 
 into a larger branch, running along the interosseous furrow of the 
 ulno-radial bone, which supplies the palm and palmar surf\ice of 
 tlie digits, and into a smaller branch, which supplies the flexor 
 muscles of the digits. 
 
 The spinal nerves of the Serpent difler from those of the Eel 
 in the more distinct ganglion on the posterior root, and this rises 
 closer to the anterior root, which is rather larger. Each spinal 
 nerve communicates with the sympathetic, and accompanies 
 the rib, to be distributed to the vertebral muscles and integu- 
 ment, fig. 206. '^ 
 
 In the Tortoise, nerves, analogous to the phrenic, are sent from 
 the first three dorsal ].airs to tlie sheets of the diaplu-agmatieus, 
 fig. 150, i2. Succeeding dcn-sal nerves connnunicato with the 
 sympathetic, and send filaments into the substance oi' the carajiace. 
 
NERVES OE RErTILES. 3)5 
 
 most of Avhich pass through, and terminate in the vascular beds of 
 the horny scutes. 
 
 The seventh and eiglith dorsal nerves, and the three consecutive 
 pairs, contribute to the formation of the crural plexus. The 
 sciatic nerve is formed by the last dorsal and the first two sacral 
 nerves. In the Crocodiles and Lizards the sciatic is formed by 
 but two spinal nerves : in the Frogs and Toads by three, 
 figs. 207, 208. 
 
 The crural plexus in the Tortoise sends filaments to the trans- 
 versalis, fig. 150, 4i, and obliquus abdominis, fig. 151, 40 ; to some 
 of the pelvic muscles and the glutasi ; it is then continued into the 
 limb as the 'crural nerve.' The obturator nerve is a direct branch 
 of the last dorsal. The sciatic nerve gives a filament to the 
 second gluticus and to the obturatorius, and continues, as a 
 large trunk, to behind the knee-joint, where it divides into 
 the tibial and peroneal nerves. The tibial subdivides into a 
 popliteal branch, supplying the muscles at the back of the leg 
 and the sole or plantar side of the foot, and into an external 
 branch to the external muscles and integument. In the Turtle 
 (Chelone),^ one division of the sciatic gives branches to the 
 muscles of the thigh, and is continued to the plantar surface 
 of the foot, dividing into digital nerves, terminating on 
 the skin ; the other division, after giving off some muscular 
 branches, passes to the skin on the dorsal surface of the fin. 
 
 In Lizards the crural nerve is formed by the two lumbar nerves, 
 and is distributed to the muscles on the fore-part of the thigh ; 
 the sciatic nerve is formed by the last lumbar, the two sacral 
 nerves, is continued along the inner side of the thigh, supjjlying 
 the muscles as far as the digits, and branching to accompany them. 
 
 In the Frog a pearly vesicle, with calcareous molecules, covers 
 each spinal nerve where it comes out of the spinal canal. Of the 
 four pairs of nerves which proceed from the termination of the 
 short myelon, three constitute on each side the ' sciatic plexus,' 
 which unites into a single large nerve opposite the acetabulum. 
 The sciatic nerve enters the muscles at the back-part of the thigh, 
 supplies them, and divides near the knee-joint into an external 
 and internal branch, distributed to the muscles, digits, and skin of 
 the hind-leg and foot. 
 
 The tenacity of vital force in Hamatocrya, and the seemingly 
 peculiar susceptibility to the voltaic current in the Frog, have 
 made that animal the usual subject of the experiments exemplifying 
 
 ' Liv. pi. xvi. 
 
316 
 
 ANATOMY OF VERTEBRATES. 
 
 relations between the electrical, nervous, and mnscular forces. It 
 may be convenient, therefore, to some readers to find here, in con- 
 nection with the nervous 
 207 sjstemof the JBatrachia, 
 
 an account of the chief 
 modes of preparing it 
 for the purpose of such 
 experiments. Galvani 
 removed the skin from 
 the hinder part and limbs 
 of the frog, exposed the 
 lumbar plexus, leaving 
 it in connection with the 
 part of the spine from 
 which the nerves issued, 
 and cut away all the 
 parts save the trunks of 
 the sciatic nerves, be- 
 tween the spine, S, and 
 the hind limbs, A & B, 
 fig. 207. So prepared, 
 it is usually called ' Gal- 
 vani's frog.' 
 
 The ' galvanoscopic leg,' fig. 207, C, is prepared by skinning it, 
 dissectino; out the sciatic nerve from among the muscles at the 
 posterior part of the thigh, then amputating the leg just above 
 the knee-joint, leaving the nerve connected with the leg, c. 
 
 If the nerve of c be laid upon the muscles of either leg of 
 Galvani's frog, A or B, and if these muscles are excited to contrac- 
 tion, by pricking the myelon in s, the muscles of the galvanoscopic 
 leg, C, will be simultaneously contracted. If a second galvano- 
 scopic leg be prepared, and the nerve be laid upon the muscles of 
 the first, and a third be placed in the same relation with the 
 second, contractions will take place in all three legs, when the 
 thigh-muscles of the Galvani's frog, A & B, are excited to contract. 
 This ' induced contraction ' cannot be extended to a fourth gal- 
 vanoscopic leg. 
 
 If the nerve of the galvanoscopic leg be left in connection with 
 the rest of the frog's body, and the nerve be laid across the thighs 
 of a ' Galvani's frog,' as in fig. 208 ; these being excited to con- 
 tract, not only the galvanoscopic leg, c, but tiie oiiposite leg, F, 
 contract; the one l.ty direct slinuilus of tlie sciatic nerved the 
 other by stimulus of the myelon from the inierent or ' sensitive ' 
 
 Galvatii'g frog, and the galvanoscoiiic leg. cuv. 
 
NERVES OF REPTILES. 
 
 317 
 
 fibres of the nerve, c, reflected upon the limb, f. In short, that 
 muscle will contract when the stimulating current has its origin 
 in a source external to that body. 
 
 208 
 
 Calvauoscopic leg, G, iu cniiiicction wiUi Ihc rest of the frog, f, laid across a 'Clalvani's frog.' ccv. 
 
 Immerse each leg of a ' Galvanl's frog' in a cup of water, 
 the positive Avire, P, of a voltaic battery being placed in one 
 cup, the negative wire, n, in the other, as in fig. 209. In 
 
 209 
 
 Frog, as propaitd t-i t-. ilvani. p, positive wire : N, negative wire : of tire liattery ; 0, connecting wire of 
 
 the two vessels. 
 
 the limb A the current runs in the reverse direction of that 
 of the volitional nervous force : in the limb B it runs in the 
 same direction. After the voltaic current has passed a short 
 time through the nerves, contractions occur in the limb b, not in 
 
318 ANATOMY OF VERTEBRATES. 
 
 the limb A, in ' making ' the current, or completing the circuit ; 
 whilst contractions occur in the limb A in ' breaking ' the current, 
 as by removing one of the wires : the limb in which the current 
 is direct contracts on making the current ; the limb in which the 
 current is inverse contracts on breaking the current. It needs 
 only to leave one wire in the water, and to remove or introduce 
 the other, in order to ' break ' or ' make ' the current. If the two 
 vessels be further connected by a conductor of copper wire, as at 
 o, fi"-. 209, contractions of both limbs take place on both making 
 and breaking the connection. 
 
 Neuricity ' is not electricity, any more than is myonicity ; 
 both are peculiar modes of polar force. Any point of the surface 
 of a nerve is positive in relation to any point of the transverse 
 section of the same nerve, just as any point of the surface of 
 a muscle is positive in relation to any point of the transverse 
 section of the same muscle.^ Ligature of a nerve arrests the 
 nervous current, not the electric current ; a divided nerve con- 
 nected by an electric conductor transmits the electric current ; 
 but the nervous current excited by stimulus above the section 
 is arrested by the electric conductor. Neuricity is convertible 
 into myonicity and into other forms of polar force, just as 
 myonicity or the muscular force may be disposed of by conver- 
 sion into heat,' electricity,'' and chemicity, the latter shown by the 
 evolution of carbonic acid.'^ Molecular change, in nervous and in 
 muscular fibre, attends the exercise of their respective forces. 
 
 § 57. Sympathetic system. — This consists of one or more ganoiia, 
 usually a series of such arranged on each side of the vertebral 
 centres from near the occiput to the opposite end of the abdominal 
 cavity, or to the anterior caudal vertebras. Where the ganglia are 
 numerous they are connected in each lateral series by a band of 
 nervous fibres, and resemble a pair of gangliated cords. Tliese 
 communicate with the contiguous spinal nerves, and with the 
 cranial nerves, usually through small ganglia in different parts of 
 the head, fig. 206. At the caudal end the two sympathetic cords 
 usually unite with a single ganglion in the under or fore part of 
 the body of the anterior caudal vertebra. 
 
 A sympathetic ganglion is a body connected with bundles of 
 nerve-fibres, the chief proceeding to or from it in the direction of 
 its axis, the smaller nerves diverging more or less transversely. 
 
 ' 'Vis nci-vosn,' 'Nervous force,' ' Nervous fluitl;' it is in relation to the latter name, 
 expressive of an exploded idea, that the term 'current' is still used in reference to the 
 course of the polar force, whether nervous, magnetic, or electric. 
 
 '' ccxi. •' ccix. 1 lb. a lb. 
 
SYMrATIIETIC SYSTEM. 
 
 319 
 
 210 
 
 From the sympnthctic fpr;istiic) gaiigliuii of the Ray. 
 
 CCXXII. 
 
 211 
 
 It consists of ' ganglionic corpuscles,' or ganglion-vesicles, fig. 210 
 a, h, c, and nerve-fibres, imbedded in a nucleated fibrous tissue. 
 
 The ganglion vesicle may be 
 circumscribed, or be continued 
 into a nerve-fibre, or into two 
 nerve-fibres from opposite poles 
 of tlie vesicle ; it is termed ac- 
 cordingly 'apolar,' 'unipolar,' and 
 ' bi-polar : ' the last is the most 
 common form, the first probably 
 a c'cnctic stase. When a ffan- 
 glion-ccU is connected by more 
 than two processes with nerves, 
 it is a ' multipolar cell : ' these 
 are most common in the ganglia 
 of the main cord of the symjDa- 
 thetic ; the bipolar cells prevail in the ganglia of the posterior 
 roots of the spinal nerves, fig. 
 201. The nerve-fibres in ganglions 
 consist of the ' white ' or Jjroadcr 
 kind,and of the 'grey'or finer kind; 
 there are also still more minute 
 but solid or homogeneous fibres, 
 surrounding and connecting the 
 true nervous constituents of the 
 ganglion. A nerve on entering 
 a ganglion breaks up into its 
 component fibres, which interlace 
 about the ganglion-cells, some- 
 times winding roimd them, with 
 plexiform interchanges of fibres 
 from other entering nerves and 
 from the cells. 
 
 Bidder and Volkman' give the 
 subjoined magnified view, fig. 
 212, of the 'intercommunicating' 
 nerve-fibresbetween a sympathetic 
 o-ano'lion and a spinal nerve in the 
 Fro"-. H p is the sympathetic, n 
 showing the part next the head ; 
 c p is the spinal nerve, C showing 
 the part next the myelon ; « is a portion of the communicatin 
 
 A. Spinal g.aiiglion of tlie Ray, 40 diameters. 
 B. Portion of the same, dissected, ccxxil. 
 
320 
 
 ANATOMY OF VERTEBRATES. 
 
 branch passing to the myelon ; h, a portion passing to the peri- 
 phery ; c, fibres of the communicating nerve passing in the 
 sympathetic towards the head ; d, similar fibres passing towards 
 
 212 
 
 Coimnuuicatiou ht'twofii tlic syinpafhetic and third spiual none in the Frog- ccxii. 
 
 the pelvis ; g, g, are ganglion-cells ; /«, specks of pigment, which 
 mark the ganglions in the Frog. 
 
 § 58. Sipnpathetic of Fishes. — This system, as being an off- 
 shoot or subordinate clement of the general myelencephalous 
 series of nerve-organs, is differentiated by progressive steps. In 
 the Myxinoid Fishes it is represented by the intestinal branch 
 continued from the confluence of the two nervi ^'agi. In Osseous 
 Fishes the visceral plexuses are continued into or connected with 
 slender nerves, accompanying the aorta along the hremal canal, 
 and representing the trunks of the sympathetic in higher Verte- 
 brates. The first or anterior communication of this nerve, in the 
 Cod, is with a branch of tlio fifth, and a fllament is sent forward 
 to the ciliary ganglion : in the Carp a filament joins the abducent 
 nerve, to which Cuvicr thouglit he had also traced a filament of 
 tlie sympathetic in the Cod ; the sympathetic next communicates 
 with that anterior portion of the vagus (the glosso-pharyngeal) 
 which joins part tif the acoustic nerve, and supplies the first par- 
 tition of flic gills ; the sympathetic trunks also receive accessions 
 from the trunks of the vagus, and, converging, intercomnumicate 
 
SYMPATHETIC OF REPTILES. 321 
 
 hy a cross l)rancli : tliey then send nerves whieli join the gastric 
 branches of the vagi, in order to form or join a sphmchnic ganglion 
 and plexus on the mesenteric artery, from which plexus branches 
 are sent to the intestines, pancreas, and spleen. The sympathetic 
 trunks are continued on each side of the aorta, along the hack of 
 the ahdomen, into the haemal canal ; communicate, in their course, 
 with the ventral branches of each of the spinal nerves ; supply by 
 filaments, usually accompanying the arteries, the kidneys, the 
 generative glands, and the urinary bladder, where this exists ; 
 and often, finally, blend together into a common trunk beneath 
 the tail. Ganglions are sometimes found at the junction of the 
 S3'mpathetic with the fifth, as well as at that with the glosso- 
 pharyngeal and with the vagus, bcibre the great splanchnic is 
 formed : small ganglions are more rarely discernible at the junction 
 of the sympathetic with the spinal nerves. 
 
 The splanclmic ganglion of the Skate is a large fusiform body, 
 of an ash-red coloiu- ; the succeeding ganglia on the trunks of 
 the S3'mpathetic arc larger and more constant than in Osseous 
 Fishes ; Ijut the intervening elmrds are semi-transparent. 
 
 § 59. St/mpfi.thetic of Reptiles. — The trunks of the sympathetic 
 appear, in the Frog, to be formed in a great proportion by con- 
 triljutions from or communications with the s})inal nerves ; there 
 are, however, slight enlargements at the points of connection, 
 often marked by pigment-cells, in which true ganglion-cells 
 occur, as shown in fig. 212, h. 
 
 In Ophidia the trunks of the sympathetic, conspicuous at the 
 anterior part of the truidv-cavity, on each side the vertebra, 
 bodies, show as little any enlargements where they receive the 
 communicating branches of the spinal nerves as in Batraclda. 
 They slightly diverge as they approach the basis cranii, and are 
 reflected outwards to the vagus, forming a conspicuous ganglion 
 at the junction. From this ganglion the S3'nipathetic is continued 
 forward in a canal of the basisphenoid, and forms a small ganglion 
 with a branch of the second di^dsion of the fifth ; it sends fila- 
 ments to the membrane covering the posterior part of the mouth 
 and palate, one of which communicates again with the maxillary 
 nerve. From the last ganglion there proceeds ' another branch 
 forward to form another ganglionic union ' (spheno-palatine) ' with 
 a branch of the second trunk of the fifth, and from this a branch 
 is sent to the posterior part of the nose, to ramify on the schnei- 
 derian membi-ane ; other branches are given to the membrane 
 covering the mouth and palate, and one passes forward and com- 
 municates again with a branch of the second trunk of tire fifth, 
 
 VOL. I. Y 
 
322 ANA'J'OMY OE VERTEBRATES. 
 
 and is distributed on the membrane covering the anterior part of 
 the month and palate. It is worthy of remark that the nerves 
 distributed on tlie membrane of the mouth and nose communicate 
 so many times with branclres of the second trunk of the fifth, and 
 their connection is so much greater than in the Turtle ; but in 
 this creature the palate is horny, and not so extensive in propor- 
 tion to the size of the head. 3, jjrolongation of the sympathetic 
 connected with the trunk of the Y>ar vagum, but not directly with 
 the ganglion of the sympathetic ; it communicates with the ninth 
 nerve, then passes down the spine, and communicates with the 
 eleven superior spinal nerves ; it emei'ges on each side at the 
 place the superior branches of the vertebral artery enter to dis- 
 tribute branches in the intercostal spaces ; it is continued down- 
 wards in a very fine plexiform prolongation with the vertebral 
 artery, as far as the origin from the right aorta ; it then branches 
 to each side beneath the membrane connecting the viscera with 
 the ribs and spine, and communicates with filaments of the par 
 vagum ; it is afterwards continued downwards, receiving a fila- 
 ment from each spinal nerve ; in its course it is a very fine nerve, 
 and has not any more ganglia than the first, and those communi- 
 cating with the second trimk of the fifth ; but at different points 
 from which the nerves pass to the viscera, there is an appearance 
 of a delicate plexus : this plexiform structure varies in diftorent 
 parts, and becomes much greater about the beginning of the 
 intestine, where it resembles that corresponding with the semi- 
 lunar ganglion in the Turtle : near the kidney it assumes the 
 form of a nervous membrane or retina, before it is distributed on 
 the urinary and generative organs. Branches pass from the 
 plexuses with the arteries to the difterent viscera."' 
 
 Bojanus describes the sympathetic nerve of the Eimjs Eiiropcza 
 as accompanying the carotid artery into the cranium, and uniting 
 with the vidian and the facial nerves. On issuing from the 
 cranium it is closely connected with the vagus and with the 
 glosso-pharyngeal nerves, so that it is difficult to say whether a 
 superior cervical ganglion exists or not ; and as the cervical 
 vertebra are ribless, there is no ' vertebi-al canal,' and the nerve 
 is closely connected with the vagus throughout the whole length 
 of the neck. Below the sixth cervical vertebra the sympathetic 
 nerve separates itself from the sheath of the vagus, and becomes 
 connected with a middle cervical ganglion, whence issue filaments 
 that are distributed to the aorta, the cardiac plexus, and the cwliac 
 plexus. Between the seventh and eighth cervical vertebnc is 
 situated the inferior cervical ganglion, like an elongated swelling 
 
 ' XLIV. p. CO. 
 
APPENDAGES OF THE NERVES. 323 
 
 of the nerve ; subscqaentlv two dorsal ganglia occur, and further 
 down, towards the middle of the back, there occurs a third and last 
 ganglion, which furnishes the splanchnic nerve: the remainder of 
 the sympathetic is made up of one or two cords, which, in the 
 sacral region, give off a great numl)er of branches, the divisions of 
 which form the renal, hypogastric, and sacral plexuses. 
 
 In tlie Turtle ( Cheloiie) the cervical portion of the sympathetic 
 has the same exposed position, and communications, with the vagus 
 above and the axillary plexus below, sending off filaments also to 
 the arteries. The branch accompanying a division of the carotid 
 in a canal at the base of the skull gives a filament to the portio 
 dura, and communicates with the niaxUlary part of the fifth, to 
 terminate on the back part of the palate. Another branch enters 
 with another division of the carotid into the reticular sinus close 
 to the auditory meatus, and communicates with the portio dura, 
 glossopharyngeal, and ninth nerves. lu the trunk-cavity, the 
 sympathetic passes from ganglion to ganglion as two cords, a thick 
 and a fine one, neither of which passes behind tlie neck of the 
 rib ; the intercommunicating branches with the spinal nerves are 
 perforated by an anterior branch of the intercostal artery. The 
 chief nerves given off from the sympathetic form two plexuses, in 
 the place of the ' semilunar ganglia ' of mammals : the smaller 
 plexus sends filaments along the coeliac artery to the stomach, the 
 larger plexus along the mesenteric artery to the intestines. Other 
 branches j)ass to the kidneys, and the communications with the 
 spinal ]ierves mark out the delicate prolongation of the symp)a- 
 thetic to Ijehind the rectum. 
 
 In the Crocodile the cervical part of the sympathetic lies in 
 the ' vertebral canal,' or l^etween the neck and tubercle of the rib, 
 and the ganglions are more distinct where the communications 
 with the spinal nerves occur, from the cervical to the lumbar 
 region. The intergano-lionic lono-itudinal trunks are two, one 
 passing behind the neck of the rib where it exists, at the fore-part 
 of the chest. The longitudinal trunks converge, and unite u])on 
 the Ijeginning of the caudal artery. Tliere is much pigmental 
 matter upon the sheaths of the ganglions and nerves. 
 
 § 60. Appendages of the Nervous Si/stein. — Certain nerves, as 
 those of the palm and sole in Man, and those of the mesentery in 
 other mammals, have peculiar corpuscles appended to them, called 
 'pacinian,' after their discoverer. Fig. 213 shows one of the nerves 
 of the palm with the corpuscles appended, of the natural size. 
 Those in the mesentery of the cat are numerous, conspicuous, and 
 favourable subjects for microscojoical investigation. They show 
 
 Y 2 
 
324 
 
 ANATOMY OF VERTEBRATES. 
 
 a pedicle and capsule, with a canal and central cavity. A single 
 213 nervous fibre, fig. 214, n, leaves its fasciculus witb 
 
 a portion of the nerve-sheath, ib. h, and proceeds 
 to the centre of a series of concentric capsules, 
 of a nucleated fibrous tissue. The nerve, n, on 
 entering the central cavity, loses its white sub- 
 stance, and, at the opposite end of the axial cavity, 
 terminates by a tubercular enlargement. An 
 arterial twig, a, accompianies the nerve-fibre along 
 the pedicle, and divides into capillaries, which form 
 loops in some of the intercapsular spaces. The 
 central cavity contains a clear fluid : it varies much 
 in shape. 
 
 Analogous bodies were discovered by Savi, 
 arranged in linear series, bordering the anterior 
 part of the mouth and nostrils, and extending 
 over the surface of the fore-part of the elec- 
 trical organs in the Torpedo; they arc appended 
 to and appear to be terminal dcvelopemcnts of the filaments of 
 
 the fifth pair of ner\'es. Each 
 follicle, fig. 215, is formed of two 
 larger capsules, f and g, which 
 adhere together near the fil^rous 
 band, r, c, supporting and fixing 
 the organ ; it contains a granular 
 sulistance, e, on which lies the 
 nerve-twig, h, d, transmitted from 
 the nerve, a. This twig commonly 
 receives a smaller anastomosing 
 filament, /(, from a contiguous 
 follicle. Sometimes two nerve- 
 twigs pass from the main brancli 
 to the same follicle, in which case 
 it contains two distinct granular 
 masses. These follicles arc de- 
 veloped from ganglionic or sensory 
 branches of the fifth nerve. No 
 proper pacinian corpuscles have 
 been observed in connection with 
 this nerve, nor with the glosso- 
 I)hnryngeal, the jxirtio dura, or 
 any jnu'cly motor nerve. 
 
 15csides the savian corpuscles 
 
ORGAN OF TOUCH IN FISHES. 
 
 325 
 
 Jncot thcfciUiciil^ii 
 
 , r 111 '1 1.1 |i. do. 
 
 the Tor])edo has a system of mucous organs in ultimate connec- 
 tion with nerves of sensation : hut this is common to it with other 
 Plagiostomes. The system 
 commences, in the Torpedo, 
 hy groups of globuLxr vesicles, 
 fig. 139, M, arranged sym- 
 metrically, outside the elec- 
 trical organs, from which 
 tiihes are continued in parallel 
 hviudles until they separate 
 themselves to perforate the 
 skin, and terminate l)y ori- 
 fices, some at the dorsal, some 
 at the ventral surface of the 
 head. A branch of the gang- 
 lionic part of the fifth expands 
 upon the ampulliform com- 
 mencement of each of the muciferous tubes. Similar organs 
 exist in Sharks. Hunter ])laced first in the series of specimens 
 of organs of touch in Fishes the snout of the Spotted Dog-fisli 
 ( Scyllium), ' to show the manner of the nerves ramifying, as also 
 their apparent termination in this part, each ultimate nerve 
 appearing to terminate in the bottom of a tube or duct, the sides 
 of which secrete and convey a thick mucus to the skin.' ' 
 Jacobsoii compares them to the whiskers in the Cat. Besides the 
 rostrum, these nervo-mucous organs are situated upon the sides 
 and under part of the liead, and on the fore part of the trunk ; 
 they are crowded between the massetcr, fig. 132, I, and the 
 branchial openings, ill. q, where they separate into two groups, 
 one diverging downward, forward, and backward, to beneath the 
 pectoral fin ; the other directed upward, forward, and backward, to 
 the occiput. 
 
 § 61. Oi-f/an of Touch in HcEniatocri/a. — In the Deriiiopteri, 
 the AruiuiUidcB, Silurfiids, and a few other Fishes, with the in- 
 tegument wholly or in part scaleless, or with very minute and 
 delicate scales, lubricated with mucus, the whole or major part of 
 the external surface may lie susceptiljle of impressions from the 
 surface of extraneous bodies coming in contact therewith. But 
 in the majority of the class the exercise of any faculty of touch 
 must be limited to the lips, to parts of certain fins, or to the 
 specially developed organs called ' barbules.' 
 
 ' xx. vol. iii. p. 55, prep. no. 1395. 
 
326 ANATOMY OF VERTEBRATES. 
 
 Such an organisation of a fold of skin bordering the mouth as 
 implies the tactile faculty is rare in Fishes ; the Cyfjrinoids 
 exemplify it, and more especially many of the Indian species : 
 also the marine family of Labroids. In the Sturgeon the lip has 
 numerous papillas, and more minute papilhe occur on the lips of 
 many fresh-water fishes. In tlie Eels the upper lip is richly 
 supplied by the fifth nerve, and the upper lip of the Lepidosiren 
 is papillose. The soft skin of the sucking-lip of the Lamprey is 
 well supplied with a reticulate arrangement of sensitive filaments 
 from the fifth ; its margin is papillose, fig. 277. The associated 
 pectoral and ventral fins, forming the sucker in the Lnmp-fishes, 
 have a texture of the applied surface, which seems adapted to 
 receive impressions from the part it touches, whereby the fish 
 may ascertain its fitness or otherwise for the application of the 
 anchorintr orsan. 
 
 The pectoral fins seem to be applied occasionally to explore the 
 nature of the bed of the water inhabited by the fish ; and in the 
 Gurnards ( Tru/Udce) three soft flexilile rays are detached from the 
 fin, like fingers, fig. 82, and the large nerves supplying them have 
 cjano'lionic enlargements at their origins. The filiform radial 
 appendages of the Pulynemidce, and the prolonged ventral fins of 
 Osjjhromenus, Trichogaster, and other Labyrinthibrauchs, and of 
 the Ophidiida3, enter into the present class of organs. The 
 barbules are long, slender, pointed processes of the skin, either 
 median or in pairs: the former arc limited to the imder jaw, as in 
 the Cod ; the latter may be developed from both jaws, and are 
 called, according to their position, ' prcmaxillary,' ' angular,' 
 ' nasal,' &c. They are commonly found in the grovelling fishes, 
 such as the Sheat-fishes, Loaches, Barbels, Sturgeons, tig. 123, A, 
 or in the parasitic Myxines, fig. 248. The nerves supplying the 
 barbules are large and derived from ganglionic di^•isions of the 
 fifth pair. A Cod, blind by absence or destruction of both 
 eyeballs, has been captured in good condition ; and it may be 
 supposed to have found its food by exploring with the symjihysial 
 barbule, as well as by the sense of smell' The sublingual fila- 
 ment of many UrdnoscopincE, and the rostral tentacle of Malthe 
 and Haheuta-a,^ may also exercise a tactile faculty. The limbs 
 of Lepidosiren, fig. 100, have the general form rather of organs 
 of exploration than of locomotion. 
 
 The scalcless condition of the skin in Batracliia makes it more 
 
 ' xcriii. p. 72. 
 
 ■' CLXXiv. iii. p. 'M\. The homologous organs in Lo,,hh,s scorn to act as bail, to 
 attract small (ishcs. 
 
ORGAN OF TASTE IN EErTILES. 327 
 
 susceptible of Impressions than in higher Beptllia ; the discoid 
 cxpiinsions of the toe-ends in Ilyla, and the filamentary appen- 
 dages of the toes in Pipn, may have more sense of feeling than 
 other parts, but seem not to be applied in active touch. The 
 labial papillte of larval Frogs are so placed and supplied by nerves 
 as to suggest a tactile function. Certain Ophidians, e. g. Herpeton 
 tentacidatum, have a jiair of tentacular appendages upon the 
 snout : but the long, extensile, forked, filiform tongue seems to 
 1)6 used rather as an organ of exploration than of taste in most 
 Serpents, and in the slender-tongued Lizards. The expanded 
 toes of Geckos, fig. 162, the short, thick, scansorially-opposed 
 digits in Chameleons, and the concave surface of their prehensile 
 tail, although mainly modifications for locomotive purjioses, may 
 well be supposed to have a surfiice more sensitive than other 
 parts of the body. The snout-like production of the upper lip 
 in TrioHychidcE and Cheli/s, with the subsidiary tegumentary jjro- 
 duotions of the head in the latter, are probably more direct and 
 active instruments of tactile exploration in these soft-skinned, 
 mud-haunting, and chiefly nocturnal Chelonia. Some noctiu'nal 
 Tree-Snakes {Driiophijs, Passerita) have a prolonged snout. 
 
 § 62. Organ of Taste in Reptiles. — The glosso-liyal, fig. 85, 42, 
 does not support, in Fishes, an organisation of soft parts for a 
 special sense of taste : and the description of the tongue and other 
 projections and structures in the interior of the mouth will be 
 given in connection with the preparatory digestive organs. A 
 tongue, as a gustatory organ, is as little developed in the perenni- 
 branchial Reptiles, and is absent in the marsupial Toads [Pipa). 
 There is as little trace of tongue during most of the larval period 
 in other Anura ; but, about the time when the fore limbs are in 
 bud, the membrane covering the basihyal begins to develope vas- 
 cular fungiform jiiapillsc, with looped capillaries and muscular filu'c : 
 the whole mass growing and extending from l^efore backward, and 
 constituting the retroflexed tongue, by the time the tail is atrophied. 
 The free part is usually bifid or bilobed. It is mainly an organ 
 of prehension, and will be described as such, together with the 
 tongue of the Chameleon, in connection with the organs of nutri- 
 tion. In the thick-tongued Lizards, e. g. Iguana tuberculata, the 
 dorsum and sides of the tongue are minutely jiapillose ; in Tiliqna 
 scincoidcs they are coarsely papillose : both the food and the teeth of 
 these Sauria indicate a certain amount of mastication, with which 
 the sense of taste is correlated. In most Reptilia the food is bolted 
 entire. In the Tortoise ( Testudo indica) the tongue is beset with 
 numerous elongated and pointed papilla; : in the Turtle ( CUelone 
 
328 ANATOMY OF VERTEBRATES. 
 
 mi/das) the tongue is wrinkled and devoid of papillae. In the 
 Crocodiles the tongue has no projecting extremity, and is but 
 slightly raised above the level of the membrane which attaches its 
 circumference to the mandible : but its dorsum is marked by a 
 group of follicles and increased vascularity of that part of its 
 svu'face. 
 
 § 63. Organ of Smell in Hamatocryn. — The essential character 
 of the organ of smell, in Fishes, is the jntuitary membrane lining 
 a sac with one or more apertures upon the external surface ; and 
 that, in the few exceptions in which it is extended into a canal 
 communicating with the mouth or fauces, such naso-palatine canal 
 is never traversed by the respiratory medium in its course to the 
 respiratory organs. 
 
 The extremities of the olfactory nerves, fig. 20.3, o, expand 
 upon the pituitary membrane, which is highly vascular, and is 
 covered by ciliated epithelium : its extensive surface is packed 
 into the small compass of the olfactory capsule by numerous folds. 
 The capsule is formed by a fibrous membrane, which is sometimes 
 supported by a cartilaginous, and more frequently by an osseous, 
 basis, called the ' turbinal bone,' fig. 81, 19.' 
 
 In the Dennopteri the olfixctory organ is single : Kolliker ^ 
 regards as such a small, blind, tegumentary depression, fig. 169, ol, 
 beset with vibratile cilia, and connected with the anterior end of 
 the quasi-brain of the Brnnehioxtoma. The more obivious and 
 satisfactorily determined olfactory organ of the Ammoccfe is in the 
 median line, opening above the mouth in front of the brain-sac, 
 fig. 59, 19, whence a narrow canal is produced backward from the 
 bottom of the sac to the base of the skull. In the ]Myxine the 
 parietes of the olfactory canal arc similarly situated, lined by a 
 longitudinally-plicated pituitary membrane, and are strengthened 
 by cartilaginous rings, like a trachea. The naso-]>alatinc tube 
 opens backward upon the roof of the mouth, and this opening is 
 provided with a \'alve. In the Lamprey the flask-shaped nasal 
 sac, fig. 61, It, opens upon the top of the head: a simple mem- 
 branous tube is continued from the expanded bottom of the sac, 
 Avhich dilates as it descends, but terminates in a Idind end at the 
 hypophysial vacuity, fig. 60, /(//, of the base of the skull, where 
 the mucous membrane of the palate passes over it entire and 
 im])erforate.'' 
 
 In all Fishes, save the Dermoptcri, the olfactory cn-gans are 
 double, and they have no communication with the mouth. In 
 
 ' nv. - .XXXII. [1. 32, pi. ii. lijj. 5, A. ■' XXI. pi. .13, ligs. ii. & iv. 
 
ORGAN OF SMELL IN FISHES. 329 
 
 Osseous Fislies tliey are isituated cm the sides of the snout, in a 
 cavity formed l)y the nasal, fig. 75, 15, the prefrontal, u, the 
 lacrymal, 73, the premaxillary, 22, and the vomer. The capsules 
 arc covered externally by the skin, which is usually jjierced hy 
 two openings for each sac : the Chromides, and all the Wrasses 
 with ctenoid scales, have a single opening for each nose-sac ; 
 where there are two ncistrils the posterior is usually o])cn, the 
 anterior ch)sed, as liy a sphincter or a valve : the anterior aperture 
 IS often produced into a tubular jirocess, as in tlie Loach, which 
 acts, either by muscular i)Ower or by some modification of form, 
 as a valve. Both apertures in S(nne Lophioid Fishes are bell- 
 shaped and 2'ediinciilate. In some Siluri a tentacle is continued 
 from the external nasal tulie. Wlien the nasal sac is round, the 
 pituitary plicaj radiate fi-om its centre : when the sac is elongated, 
 it is usually traversed by an axial jiartition with a row of folds on 
 each side ; and tliere are transitional arrangements, as in the 
 Perch, figs. 131, ol, & 134. In a few Fishes these folds are 
 further complicated by secondary processes. The Sturgeon pre- 
 sents the radiated type of the olfactory organ with secondary folds, 
 fig. 125, 10, but, like the Polypterus and Lepidostciis, each nasal 
 sac has a double aperture : the Le]iidosireii has an ehmgated nasal 
 sac, with the biserial arrangement of jiituitary folds, and with two 
 apertures, fig. 186, ol, upon the iiiider jiart of the thick upper lip, 
 but neither of these communicate with the moiitli. In some 
 Osseous Fishes the olfactory sac is divided into a jilicated and a 
 smooth jiart : the former exercising the sense-function, the latter 
 that of a reservoir. In the Mackerel this extends down to the 
 palate : in the Wolf-fish the reservoir passes liackward, expanding, 
 as far as the back part of the palate, where it ends blindly. The 
 prolongation of the single nasal cavity in tlie Lamprey is analogous 
 to this. 
 
 In the Plagiostomes the nasal cavities are situated beneath the 
 snout, in the Sharks, figs. 30 & 63, h : lieneath the fore part of 
 the head, behind the base of the rostrum, in the Saw-fish {Fristis), 
 fig. Gl) : or near the angles of the mouth, as in the Chimcera and 
 the Rays, where a groove extends to the mouth. Each olfactory 
 cavity h^s a single and commonly wide opening, defended by 
 valvular processes, sujjported by peculiar cartilages more or less 
 intimately connected with the proper olfactijry cartilaginous sacs, 
 and representing the superadded cartilages of the ' ala3 nasi ' in 
 higlier Vertebrata.' They have their proper muscles : whence we 
 must conclude that these Fishes scent as well as smell, i. e. actively 
 ' Sec tlie descripliou of these 'naseutlugclknorpel ' in xxi. p. 171. 
 
330 ANATOMY OF VERTEBRATES. 
 
 search for odoriferous impressions by rapidly changing the current 
 of water through the olfactory sac' 
 
 The Protopteri show no outward signs of olfactory organs : the 
 thick upper lip must be raised to bring the j)licated sac, with its 
 two remote orifices, into view. In AmjMuma the external nostrils 
 are minute, approximate, and near the end of the snout. In the 
 Siren and Axolotl the external nostril is conspicuous on each 
 side the snout : the internal one opens outside the series of 
 pterygo-vomerine teeth. In the Siren the maxillary does not 
 extend back so as to divide the internal nostril from the inner or 
 under part of the lip : in the Axolotl it is so extended, and the 
 opening is situated between the maxillary and palatine series of 
 teeth. In these, as in the Proteus, the olfactory membrane is 
 plicated at right angles to a longitudinal seam. In the Newts 
 and Salamanders the olfactory membrane is smooth, and lines an 
 oval cavity with an external nostril and a palatal one, the former 
 defended by a little fold of skin. 
 
 In tailless Batrachia the external nostril has an inferior flap, 
 endowed with a slight movement : the palatal is widely open, 
 between the palatine and maxillary bones, near the fore part of 
 the mouth. The olfactory membrane is not augmented by any 
 folds or prominences. In the Pipa it presents a cylindrical form, 
 and its outer ojiening is much nearer that of the opposite side 
 than in other Anoura. In Ophidia the external nostrils are 
 double ; the internal nostril is single and median : the bone and 
 gristle supporting the olfactory sac make some prominences in it ; 
 the pituitary membrane is almost black in some Colubers. In 
 Aiujvh, and other snake-like Lacertians, the palatal nostrils open 
 separately. 
 
 In the Iguana a single broad turbinal cartilage extends into the 
 olfactory cavity from the outer side, terminating l.)elow in two 
 tuberosities. The meatus extends at first longitudinally back- 
 ward, then bends downward to oi)en upon the palate between the 
 anterior maxillary and the pterygoid teeth. The turbinal projects, 
 with slight modifications of proportion and form in the "nasal 
 cavity of other Lacertians. The external nostrils offer varieties 
 of relative size, shape, and position, seldom receding far from the 
 muzxle in existing species. In the extinct Saurians of marine 
 habits, lehtln/osanrus and Pksiosnurus, the external nostrils 
 opened near the orlnts, at a distance from the muzzle. In Chchmia 
 
 ' 'Is tlic niorU. of smelling i„ Fishes siniihu- to tasling i„ other aninials? Of is 
 tlie a.r containca .n water iiupregnatccl with the oiloriferoiis i.arts, ami is it this air 
 wliieh tlic lish smells? ' — John J/iinlcr, in ix. vol. iii. n. 88. 
 
ORGAN OF SIGHT IN FISHES. 331 
 
 and CrocodiUa, the external opening to tlie nasal organ in the skull 
 is single and median, situated at or near the end of the muzzle. 
 -But in the Chelonia the mistrils are distinct, although approximate, 
 on the integument : in Trionyx and Chelijs they are tubular, con- 
 tinned along a short proboscidiform production of the integument. 
 The sei)tum narium is gristly. In the Turtle (yChelone) the nasal 
 cavity suddenly expands to contain the turbinal cartilage. The 
 y)eriosteum of the cavity and the pituitary membrane are both 
 coloured by dark pigment, and the latter is thick and vascidar. 
 The palatal orifice is median and single, towards the fore part of 
 the roof of the mouth. In the Crocodilia the tegmuentary nostril, 
 like the osseous one, is single, crescentic, with the concavity 
 backward, and closed by the fleshy posterior valvular lobe : in the 
 Clavial the tegument surrounding the nostril is thick, abundant, 
 and can be raised from tlie lionc, or erected, to bring the orifice to 
 the surface of the water without exposure of other j)arts of the 
 bead. The nasal cavltv is of g-reat lenii'tli, commencinjr at the 
 fore part of the muzzle, and terminating beneath the occiput, also 
 Ijy a single aperture, close to which the nasal septum terminates. 
 The anterior third part of the meatus is most expanded : the 
 pituitary membrane is extended ujion a bilobed tiu-binal, partly 
 bony and [lartly gristly : the meatus also communicates with 
 large cells or sinuses. 
 
 § 64. Or(/an of Sit/ht in. Fishes. — The organ of sight makes its 
 appearance in the lowest of Fishes, e. g. the Lancelet and Myxine, 
 under as simple a form as in the Leech: a minute teginnentaiy 
 Ibllicle is coated by dark pigment, which receives the end of a 
 special cerebral nerve. This simple eyespeck, the first mechanism 
 for the appreciation of light, is repeated in the AmJAi/opsis spelaus, 
 fig. 175, o. Eudimental eyeballs covered by the skin exist in tlie 
 AjiU'i-iciitJu/s ca'ciis : the small, but more complex, e}'es of the 
 Lepidosiren, with crystalline and vitreous humours, choroid and 
 sclerotic tunics, are also covered by the skin, l^ut this Ijecomes 
 transparent where it passes over them, and, adliering to the 
 sclerotic, forms a ' cornea.' The eyes of the Eel tribe and the 
 Siluroid Fishes are small : they are of moderate size in the 
 Plagiostomes and Ganoids ; but in most Osseous Fishes the eyes 
 are remarkable for their large size, which becomes enormous in 
 some, e. g. Orthagoriscus, Mijripristis, Priacanthus. The eyes 
 are usually placed in orbital cavities, one on each side of the 
 head ; only in the unsymmetrical Flat-fish are they both jilaced 
 on the same side : in the Stargazer ( Uranoscopus) the eyes are 
 approximated on the upper surface of a nearly cubical head, and 
 
33-2 ANATOMY OF VERTEBRATES. 
 
 are directed towards the heavens : in the Hammer-headed Sharks 
 they are supported on long outward-projecting pedicles. 
 
 The optic nerve, fig. 216, a, usually perforates the eyeball 
 oljlifiuely out of its axis, but sometimes directly in its axis. In 
 Osseous Fishes it is compressed where it 
 216 passes through the sclerotic and choroid, 
 
 and then forms the retina by unfolding 
 itself, like a fan spread out and bent into 
 the form of a cone, leaving a fissure, 5, where 
 tlie free lateral borders meet after lining 
 about two-thirds of the hollow globe. This 
 fissure extends from the entry of the nerve 
 to the anterior margin of the retina, and 
 through it a fold of the innermost layer of 
 Eye or s»ord-nsh ; ouc-uiird tlic clioroid passcs iuto tlic vltrcous humour, 
 sometimes accompanied by the dark pig- 
 mental Ruyschian layer.' The fold of the vascular choroid, 
 whetlicr accompanied by the pigmental layer or not, is called the 
 ' lalciform process,' c ; it carries before it a fold of the proper 
 tunic of the vitreous humour ('membrana hyaloidea'), and usually 
 extends to the capstde of the lens, d, to which it is attached by 
 means of a clear but firm substance, called the 'campanula 
 Ilallcri.' 
 
 The posterior or outer layer of the retina consists of the cel- 
 lular basis, supporting the stratimi of cylindricules, standing 
 vertically upon its concave surface, with the interblended twin- 
 fusifiirm corpuscles, both of which microscopic structures are more 
 easily demonstrated in the present than in the higher classes of 
 Vertclirata. Each twin-cor])uscle is surromuled by a circle of 
 cyli)Klricules. TIic ])rimitive nerve-fibres radiate over the cylin- 
 dricules, without anastomosing, and terminate in free ends, not by 
 loops, at tlie Ijasis of the ciliary zone. A delicate but well- 
 defined raised rim or ' bead' runs alone; both the anterior margins 
 of the retina, and along those which form the falciform slit. 
 
 The crystalline lens {d) is spherical, or nearly so, large, firm, 
 with a dense nucleus : it is almost luiried in the \ itrcous hinuour, 
 where it is steadied liy the attachment of the falcifiirm ligament 
 to its tliin ca]isule: the fore part projects through the pupil 
 against Ihe fiat cornea, and so nearly fills the anterior chamlier, 
 that but a very small space is left for ' aqueous humour.' In the 
 cod and other Ciidiiliv the fibres of the lens converge, like the 
 
 ' .\,x. vol. iii. p. lU; cju uf the Bouito, ])rcii. no. 1G51. 
 
ORGAN OF SIGHT IN FISHES. 
 
 333 
 
 217 
 
 P 
 
 c: 
 c 
 
 L. 
 
 
 :i.^nilled, showing inter- 
 Lied margiDS. ccxiii 
 
 meridians of a globe, to two opposite points or poles of tlie sphe- 
 roid : in the Sahnonidce and Shark, they converge to a linear tract 
 or septum at each pole, as in fig 
 218. In the fibres of the lens 
 of a cod Brewster discovered 
 the marginal teeth, like those of 
 rack-work, by which the fibres 
 are interlocked together, as in 
 fig. 217. 
 
 This acute observer computes 
 five millions of fibres and sixty- 
 two thousand five hruidred mil- 
 lions of teeth in the lens of a cod : 
 yet in the living and fresh state 
 this organ is transparent. 
 
 The radiatino; fibres and elona:- 
 ated cells of the hyaloid tissue,' 
 with the interstitial ' vitreous 
 hiunour,' present a firmer con- 
 sistency than in the human eye, 
 and show their intimate structure and arrangement more clearly 
 under the microscope than in Mammalia. 
 
 The membranes situated between the retina and sclerotica, 
 called collectively ' choroid 
 tunic,' are three in num- 
 ber : the external layer in 
 Osseous Fishes, called ' mem- 
 hrana argentea^ fig. 216, e, is 
 composed chiefly of micro- 
 scopical acicular crystals 
 reflecting a silvery, or some - 
 times a golden lustre, with a 
 delicate cellular basis, which 
 assumes more firmness where 
 it is continued upon the iris. 
 The second or middle layer 
 is the ' membrana vasculosa,'' 
 seu ' Halleri,^ ib. f, and, as 
 its name implies, is the chief 
 seat of the ramifications of 
 the choroid vessels : it also supports the ciliary nerves. The 
 
 218 
 
 Arrangem 1 1 f 
 
034 ANATOMY OF VERTEBRATES. 
 
 innermost layer is the ' memhrana -picta^ seu ' TLiajscliiana^ g, 
 also called ' uvea,' wliicli is composed of hexagonal pigment-cells, 
 usually of a deep Ijrown or black colour. In the Grey Shark 
 (Galeiis), the silvery layer is laid upon the central surface, not 
 the i^eriphery of the choroid.' 
 
 The formation of the iris, h, by the production of all these mem- 
 branes is well shown in the eye of the Sword -tish Xiphios, fig. 216, 
 where its thick base or ' ciliary ligament ' h overlaps the con- 
 vex border of the bony sclerotic.^ The membrana argentea upon 
 the front of the iris gives great brilliancy to the eye, in many 
 fishes. The pupil, i, is large and iisually round : in many Pla- 
 giostomes it is elliptic ; in Galeus it is quadrangular ; in the flat- 
 bodied Skates and Pleuronectidje, that grovel at the bottom and 
 recei's'e the rays of light from above, a fringed process descends 
 from the upper margin of the pupil, and regulates tlie quantities 
 of admitted light by being let down or drawn up like a l)lind. 
 
 The muscular structure of the iris is very feebly de^-eloped in 
 most fishes : it is best seen in the pupillary curtain of the Skate, 
 the plicated anterior border of the uvea forms the so-called 
 ' ciliary zone, or processes,' k : they are the most complicated in 
 the great Shark (Selache) where each process ' consists of two or 
 three minute folds, which, as they run forward, unite into one, 
 and terminate in a point at the circumference of tlie iris :'' but 
 they do not, as yet, project freely inward and forward from the 
 surface of the uvea. 
 
 The subordinate and accessory character of the sclerotic caji- 
 sule, fig. 216, Z, Z, fig. 219, f,f, is illustrated inmost Osseous Fishes 
 by its deviation from the sub-spherical form of the true eveljall 
 which it protects, and by the great quantity of cellular, and often 
 also of adijjose tissue, fig. 216, which fills the wide inters})aee be- 
 tween the sclerotic and the choroid. In the filirous tissue of the 
 sclerotic are usually developed the two cartilaginous or osseous 
 hemispheroid cups already described (p. 115, fig. 81, 17); but in 
 place of these, in the Orthaiioriscus, as in the Plagiostomes, the 
 capsule is strengthened liy a single hollow, cartilaginous, perforated 
 spheroid. This varies in tliickness at ditl'crent parts, being usually 
 thickest behind, and particularly so in the Sturgeon. The ante- 
 rior aperture is closed hj the cornea w, which is essentially a 
 modified ]iortion of the corium o, adlicring to, as it passes over, 
 the usually thickened borders of that aperture. In tlie eve of the 
 Xiphias-^ may be traced an accession to the cornea from the outer 
 
 > XX. vol iii. p. 147, prep, no. lC(i<.). = Ih, jircp. no. KiGl. 
 
 ' lb. prop. no. 1C70, A. < Jb. prep. no. lOi'.I. 
 
 A 
 
ORGAN OF SIGHT IN FISHES. 335 
 
 fibrous layer of the sclerotic, wlucli undergoes the same change 
 of tissue, and forms the posterior layer of tlie cornea. This 
 transparent window of the eye-capsule is quite flat : its laminated 
 strTicture is well displayed in the cornea of the Orthafiorixnis,^ 
 and a dark-brown pigment here stains the soft integimient or 
 ' conjunctive membrane' {o), continued from the perijjhery of the 
 cornea. In the eye of the same fish,^ a very delicate layer or 
 lining membrane is reflected from the posterior surface of the 
 cornea, answering to the 'membrane of the aqueovis humour' of 
 land animals : this humour exists in very small quantity, just 
 enough to lultricate the iris in the eyes of Fishes : the medium 
 through which the rays of light reach the eye needs no refractive 
 aid from au aqueous fluid interposed before the lens in the globe 
 itself 
 
 Amongst the most characteristic peculiarities of the eye in 
 the typical or Osseous Fishes is the so-called ' choroid gland ' 
 fig. 216, o, fig. 219, li; this is of the class of bodies called ' vaso- 
 ganglions : ' it usually presents a dark red colour, and lies between 
 the ' silvery' and ' vascular ' layers of the choroid, more or less 
 encompassing, in the shape of a horse-shoe or bent magnet, the 
 entry of the optic nerve. Dr. Albers' discovered the rich marginal 
 plexuses of vessels, ' the roots of which have their origin in this 
 body,' and the body itself be believed to consist also of a convolu- 
 tion of ))lood-vessels. Ordinary dissection, however, shows its 
 compact substance to be arranged in parallel straight lines running 
 between the convex and concave borders, and it has been called a 
 ' muscle ; ' but the supposed ' fibres consisted, in reality, of minute, 
 parallel, and closely-disposed vessels, both arteries and veins. '^ 
 Professor Midler has detected a relation of coexistence between 
 the choroid vaso-ganglion and the pseudo-branchia, to which the 
 Sturgeon, Lepidosiren, and the Plagiostomes are amongst the 
 exceptions, having the pseudo-branchias but not the vaso-ganglia ; 
 Silurvs, Pimdodus, Sijnodon, Cohifk, and all the Eel-tribe, have 
 neither jiseudo' branchire nor clioroid vaso-ganglia. 
 
 The most remarkable exception in the structure of the eye in 
 the present class is jn-esented by the Anableps, the comea of 
 which is bisected by an O20aque horizontal line, and the iris per- 
 forated by tw(5 pupils. 
 
 The general form of the eyeball, or rather its capsule, in Fishes, 
 is a spheroid, flattened anteriorly, around which part the integu- 
 ments commonly form a circular fold, yielding to the movements 
 
 ' XX. vol. iii. p. 147, prep. no. 1665. ^ lb. prep. no. 1649. 
 
 ' Lxxvi. ■' XX. vol. iii. (1836); p. 145, prep. 1656; and Lxvii. 
 
.336 
 
 ANATOMY OP VERTEBRATES. 
 
 219 
 
 of the globe. In Ortlia.fjoriscus the circular palpebral fold is 
 deeper, and is provided with a sphincter : in most Scomberoid and 
 Clupeoid Fishes there is an anterior and a posterior vertical trans- 
 parent fold or eyelid. In the eye of the tope and blue Shark, 
 there is a nictitating membrane superadded to a well-developed 
 circular palpebral fold of the skin. A conjunctive membrane is 
 reflected from the circular eyelid over the 
 third eyelid, which is placed at the nasal side 
 of the orbit, and then passes over the anterior 
 half of the eyeball. A strong ' nictitator ' mus- 
 cle rises from the temjwral side of the orbit, and 
 passing through a muscular and ligamentous 
 loop, descends obliquely to be inserted into the 
 lower margin of the third lid. The trochlear 
 muscle has an insertion into the upper part of 
 the circular lid, and depresses that part siuuil- 
 taneously with the raising of the third lid.' The 
 jiroper muscles of the eyeball exist in all fishes 
 except the Myxinoids and Lepidosireu, and 
 consist of the four recti, fig. 219,1,2,3,4, and two 
 oliliqui, ib. «, h : the latter rise from the nasal 
 side of the orbit, and are inserted most favour- 
 ably for eflPecting the rotatory movements of 
 the eyeball : but the superior oblique, a, has 
 not its direction changed by a trochlea in the 
 2)rcsent class. In the Gahnis there is a special 
 ])rotuberance of the upper part of the carti- 
 laginous sclerotic for the common insertion of 
 the rectus siiperior and obliqiD/s superior ; 
 and a second protuberance below for the c<:iniinon insertion of 
 the ohliquus infer/or and rectus inferior. The recti muscles 
 rise in many Osseous Fishes from the sub-cranial canal ; '^ 
 the origin of the rectus e.rtermis being prolonged furthest liack. 
 But the recti muscles are most remarkable for their length 
 in the Hammer-headed Sharks, since they rise from the basis 
 cranii, and extend ak)ng the lateral processes or peduncles, at the 
 
 cil lliCCyoof the Tel 
 XXIIJ. 
 
 ' The family of Sharks, inclmliiig Gulciis, Carcharias, with this grade of ]ialpcbral 
 structure, arc called ' nictitantcs ;' thej' are amongst the most active and formidable 
 of these great predatory Irishes. 
 
 - If, therefore, wo regard this canal as part of the orliits, we must add the alisphciioid. 
 basisphenoid, and even the basioccipital, to the bones eimnieratcd at p. 1 1 6, as forming 
 the chambers for the eyeballs and their appendages in Pishes; and this nuiltiplieity of 
 orbital bones interestingly ic)icats or jiarallels the characteristic formation of the 
 otocranes or car-chambers in the ja'cscnt class. 
 
ORGANS OF SIGHT IN REPTILES. 337 
 
 free extremities of which the eyeballs are situated. In all 
 Plagiostomes the eyeball is supported on a cartilaginous peduncle : 
 this is short and broad in the Kays ; longer and cylindrical in the 
 Sharks ; in Selache it is articulated by a ball and socket synovial 
 joint to a tubercle above, and external to the entry of the optic 
 nerve.' A fibrous ligament attaches the sclerotic to the wall of 
 the orbit in the Sturgeon and the Salmon. 
 
 The space between the eyeball and the orbit contains a soft bed 
 of gelatinoiis and adipose substance : but there is no lacrymal 
 gland in Fishes. An apparatus to moisten the cornea was, of 
 course, unnecessary in animals perpetually moving in a liquid 
 medium. The cornea, which in most fishes is always exposed to 
 that medium, is flat ; it is, therefore, less liable to injury in the 
 raj^id movements of the fish, and lacing level with the side of the 
 head, oflfers no impediment to those movements. This form of 
 cornea diminishes the cajjacity of the aqueous chamber ; but the 
 aqueous humour is needed only to float the free border of the iiis ; 
 and to make up for the small quantity of that humour, the refrac- 
 tive power of the lens is maximised by its spherical form. To 
 compensate for the deviation from the spherical form of the eye- 
 ball, produced by the flattening of its fore-part, and the consequent 
 loss of power to resist external pressure, the sclerotic capsule is 
 cartilaginous or bony. 
 
 § 65. Organs of Sight in Reptiles. — The eyes are very small, 
 of simple structure, and concealed by the skin, which passes 
 smoothly over them with little other change than subtransparency 
 of texture, in both the ichthyo- and ophio-morphons Batrachia. 
 The sclerotic, in Proteus, is lined by some dark pigment, and 
 contains a minute spherical lens. It may serve to warn the 
 animal, wandering into light, to retreat to the safe darkness of its 
 native subterranean waters. The Axolotl has the eyeball better 
 developed, and provided with muscles ; but devoid of lids. In 
 the Newts there is a horizontal fold of integument over each eye- 
 ball : the retina is thick, although the optic nerve is small : the 
 choroid shows pigment : the pupil is transverse ; the lens is 
 spherical. The cornea is convex in the Land Salamander. In 
 Newts the eyeballs are retracted in water, and are less prominent 
 than in air ; for this purpose there is a kind of choanoid muscle, 
 besides the ordinary recti and obliqui. The eyeball is very small 
 in Pipa, and has no eyelid. In the Frog, the eyeball is propor- 
 tionally large, and is prominent; the globe is siiherical; the 
 sclerotic of subcartilaginous hardness anteriorly ; elsewhere it 
 
 ' XX. vol. iii, p. 175, prep. no. 1762. 
 VOL. I. Z 
 
338 
 
 ANATOMY OF VERTEBRATES. 
 
 220 
 
 allows the colour of tlie choroid to be seen through it : the cornea 
 is very convex. The choroid has an argentine or nacreous layer 
 externally, and a dark pigment internally ; the former gives the 
 bright colour to the iris in both Frogs and Toads. The pupil is 
 subrhomboidal. A slightly j^licated ciliary circle adheres to the 
 capsule of the lens. Tiae retina is thick, and is continued to the 
 capsvile of the crystalline, which forms a small spheroid lens. 
 Besides the usual muscles of the eyeball, there is a choanoid 
 muscle ; the eyes are strongly retracted when the Frog dives. 
 The chief nictitating lid is the lower one ; the upper eyelid merely 
 follows the movements of the eyeball when it is turned down. A 
 small mviscle arising from the lower and back part of the eyeball sends 
 two tendons through the choanoid, which wind over the sides of 
 the ball to a pulley at each angle of the orbit, through which they 
 ])ass to beattached to the anglesof the lower lid: this is transparent. 
 The eyes are small in Serpents: the sclerotic is fibro-carti- 
 lngino\is, but tliin : the choroid resemldes that in the Frog, but 
 with less brilliancy of the argentine 
 layer: the ciliary plica; are small and 
 feeble : there is a delicate falcifonii pro- 
 cess, without pigment : the lens is more 
 spheroid than in Lizards : the pupil is 
 round in most Serpents; but is a ver- 
 tical slit in venomous Snakes, in Boidcp, 
 and in the nocturnal species of Dipsa- 
 (lidce ; and is horizontal in most species 
 oi Drijoplds, especially those which have 
 tlie muzzle pointed and prolonged. But 
 the chief pecidiarity in the ophidian 
 oro-an of vision is in its defensive part, fi"'. 220. The intesru- 
 ment, c, is continued from the surrounding circles of scales, 
 d, directly over the eye: it consists of a layer of transparent 
 epiderm, and a thin layer of chorium, which adheres to the outer 
 ])art of the conjunctive sac,/. At the exuviating period, the c]u- 
 derm, c, becomes opake, and is shed in connection with that of the 
 head and body. The conjunctiva covers a great proportion of the 
 (>ycbull, a, before it is reflected, as at c, r, forward to line the 
 autocnlar tegument, r. The cavity, /", is large, and receives the 
 lacrymal secretion. In the Pythons and Colubers, a pore at the 
 lower and forepart of the cavity, very minute in many species, 
 Init admitting a bristle in Pi/tlioii, leads to a slender membranous 
 duct, which dilates into a pouch conununicating with the mouth 
 ))eliind the iiremaxillary. In the Viper and other ^■onomous 
 Scrpcnis, tlie lacrymal cnn:il opens into the nasal mealus. The 
 
OKGASS OF STGIIT IN RErXILES. 
 
 339 
 
 221 
 
 Sct^Llon of eyo, 
 
 Jlotllti.r iVarun^i, 
 
 co.xxx. 
 
 lacrymal gland is large, especially in the Constrictors, and eon- 
 tribntcs its secretion to that of otlicr sources of luhrication of tlie 
 mouth during the lon<r and diflSeult act of deglutition. 
 
 It is interesting to note the correspondence of condition between 
 the eye and ear, in regard to the fore court of each organ, whicli Ser- 
 pents exclusively exemplify, among air-breathing Vertebrates. Tlie 
 tympanic chamljer parallels the conjunctive chamber ; both are closed 
 externally, — the one by the ear-drum, the other by the antocular 
 membrane : the lacrymal canal is the homotype of the eustacliian. 
 
 In Lizards, fig. 221, the eyeball is less globular, more flattened 
 anteriorly than in Serpents, and the sclerotic is strengthened near 
 the cornea l)y a circle of small sub-imljricate osseous 
 plates, d. Tlie lens, ib. i, is more con^'ex behind than 
 in front ; a ' falciform i)rocess,' ib. p, is connected 
 with its capsule ; and in the Iguanas and IMonitors 
 it has a delicate layer of pigment-cells. The 
 ciliary folds are more marked tlian in Serpents. 
 In the Geckos the pupil is vertically oval : the 
 retina shows a spot in the axis of vision. In the 
 Chameleon the cornea is small; an antocular fold of skin is con- 
 tinued in front of the globe, but it is opake and perforated in the 
 middle: it moves with the eyeball; the conjunctiva attaching it 
 to the fore-part of the ball, and the integument at its junction 
 with the skin of the head, being very thin, yielding, and wrinkled. 
 Tlie sclerotic is so thin that the dark colour of the choroid appears 
 through it : it becomes thicker antei'iorly, especially at the inser- 
 tion of the cornea. The retina shows tlie ' macula centralis,' or 
 ' foramen Samimerringi,' on the nasal side and a little above tlie 
 termination of the optic nerve, fig. 221, oJ The pupil is round ; 
 the lens is very small and almost spherical. The muscles ha'\'e the 
 usual disposition and number ; but each eye cnjoj-s an independent 
 motion. The great extinct marine Lizards {IcJitlii/osauriis) had very 
 large eyes, fig. 105, with the sclerotic plates de-^-eloped even iu 
 greater projiortion than in \i\o- 
 dern Lizards. 
 
 In the fresh-water Tortoise 
 {Emys, fig. 222, h), tlie chief 
 part of the eyeball is oblately 
 s])heroid, with the segment of a 
 smaller sphere at the fore-part; 
 a circle of sclerotic plates, c, 
 being imbedded at tlie junction, and sustaining 
 
 ' ccxY. ]i]>. 1, 101; x\-, toni. iii. ]i. 15fi. 
 Z 2 
 
 , T.iinymnl mid IT ml 
 :■, SdcroticrhilLs L 
 
 lie cornea. 
 
340 
 
 ANATOMY OF VERTEBRATES. 
 
 223 
 
 In tlie Turtle the sclerotic is cartilaginous, tlilckest behind, 
 and thicker at the temporal than at the nasal side of the globe. 
 The cornea is flatter than in the Emys or Land-Tortoise. 
 The optic nerve penetrates the sclerotic, as in other reptiles, extei-- 
 nally to the axis of vision, fig. 222, b, and makes a conical projection 
 in the interior of the eyeball, from -which 
 the thick retina expands and extends to the 
 ciliary circle, fig. 223 : there is no falciform 
 liframent. The choroid is thick, and 
 coloured by a deep-brown pigment. The 
 ciliary plicae are neatly defined, but do not 
 project freely from the surface. The pupil 
 is round ; the crystalline is more convex in 
 the Turtle than in the fresh-water or land- 
 Tortoises. The short ciliary arteries form a 
 plexus round the optic nerve in Chelone. 
 The cornea is more convex in the Tortoise, 
 fig. 222, than in the Turtle. The lacrymal glands are two, fig. 222, 
 a ; the smaller (harderian) one is internal and inferior in position ; 
 the larger is external, applied to the eyeball, fig. 224, and sending 
 its ducts to a deep fossa in the outer angle of the eyelids. These, 
 fig. 225, are thick, opake, covered by polygonal epidermic scales ; 
 the lower lid is largest, most moveable, and has fewest scales 
 
 Section of the cyc-li.Tll of the 
 Emi/s l^uwjjcea. xxx\-|ii. 
 
 221 
 
 225 
 
 Ej-c-ball of Eiini^ ICinopa'i : ^^hewitl^.' the external 
 l,uT.\ni-tl u'limd. X.VXVIII. 
 
 Eye-lids of Emiis: 
 EnropiV'T. XXXYIII. 
 
 upon it in Chclone : there is also a nictitant membrane situated 
 vertically at the inner canthus, and having a horizontal motion. 
 The duct of the harderian gland opens on its internal surface 
 near the line of reflection of the conjuncti\'e membrane upon it ; 
 and the secretion subserves the movements of the third lid. Be- 
 sides the four recti and two obliqui muscles of the eyeball, there 
 is a choanoid or retractor muscle divided into fovir fasciculi. 
 
 In the Crocodile, the sclerotic plates are not developed : the 
 membrane, fig. 226, ,c, ii, is of a firm fibro-cartilaginous tissue, 
 allowing the dark hue of the choroid to appear through it : the 
 cornea, f, is large and convex. The choroid is thinner and with 
 
ORGANS OF SIGHT IX RErTILES. 
 
 341 
 
 22G 
 
 .1 hlacker pigment, than in otlier Reptiles, and the ciliary plica; are 
 
 longer and more distinct, extending beyond the origin of the iris. 
 
 Tins is anteriorly of a pale yellow colour ; the pupil is vertical. 
 The eye of the Crocodile is chiefly peculiar for the massive and 
 
 complex character of its appendages, fig. 22G, to whicii the eye- 
 ball itself, x, u, t, bears but a small 
 
 proportion. No other or higher 
 
 animal ofters such a structure : it 
 
 was one of the discoveries of 
 
 Hunter, who left a drawing of it, 
 
 which was engraved, and, with his 
 
 preparation, no. 1770, described in 
 
 XX. vol. iii. In the copy of this 
 
 drawing, fig. 226, the upper, e, and 
 
 lower, h, eyelids are severed at the 
 
 outer canthus, and drawn apart to 
 
 show the third or nictitant eyelid, //, 
 
 and the extent of the conjunctiva. Of 
 
 this membrane e is the free surfiice of 
 
 the part which lines the ordinary 
 
 eyelids, whence it is reflected over 
 
 the nictitant lid at ij, li, k ; and then 
 
 upon the cornea at the line maidvcd e' , u]>on the part of the 
 
 circumference next the outer canthus. The free margins of 
 
 the upper and lower lids are marked c ; they arc devoid of cilia, as 
 
 in all Ilcematocrya : h is the free margin of the third lid. The 
 glands sending their secretion to the conjinictival space are the 
 proper lacrymal and the harderian ; the duct of the latter termi- 
 nates on the inner surface of the base of the nictitant lid, at /■. 
 From the conjunctival chamber the secretion of both glands is 
 conveyed by the two puncta lacrymalia, f, to the duct termin- 
 ating in the nasal cavity. The muscles are divisible into those of 
 the eyelids and those of the eyeball. The nictitator, fig. 226, z, 
 arises from the inner and upper part of the ball, proceeds outward 
 and downward, winding round the optic nerve and choanoid muscle 
 (which protects the nerve from the pressure of the nictitator in 
 action), and is inserted into the inferior angle of the third lid. 
 "Whilst the muscle draws this outward over the eyeball, it at the 
 same time rotates the ball inward beneath the third lid, being 
 attached to movable points at both extremities. The upper eyelid 
 has a levator muscle, m, chiefly inserted into the palpebral ossicle, 
 but also sending a few fibres, n, to be attached to the paliiebral 
 conjunctiva near its angle of reflection. The under lid has a 
 
312 
 
 ANATOMY OF VERTEBRATES. 
 
 depressor muscle, o. Of the muscles of the eyeball, p mai'ks the 
 rectus superior ; q the rectus inferior ; r the rectus externus ; s 
 the obliquus inferior : tlie rectus internus and obliquus superior 
 are likewise present. The letter x marks the insertion of the 
 choanoid muscle or retractor of the eyeball, which consists of four 
 portions surrounding the optic nerve, v. Counting these with the 
 other muscles of the eyeljall and lids, there are not fewer than 
 thirteen; and the eye of the Crocodile has its special skeleton as 
 well as muscles, represented by the super-palpebral ossicle. 
 
 In both Keptiles and Fislies the range of gradations of dioptric 
 structures is very great ; and the number of species in which the 
 eye is a mere passive recii>ient of the stimulus of light, and uniit 
 tor sight, or the discernment of outward objects, is greater in the 
 air-breathing tlian in the water-breathing H<zmatocrya. 
 
 § 66. Or<jan of Hcarbuj in Fishes. — The cartilaginous capsules 
 of the acoustic organs are precociously developed in all Fishes : in 
 the Myxinoids and Ammocetes they retain their primitive exterior 
 ]iositi(jn at the isides of the base of the proper cranium, fig. 58, lo; 
 they arc less cons])icuous in the Lamprey, fig. 60, 16 ; they 
 l)CComc involved in the tliick cartilaginous walls of the cranium in 
 the Plaglostomes ; and, in Osseous Fishes, are Availed up exter- 
 nally cither by the surrounding cranial bones, or by a special 
 
 Otocranc aiij labjriiilh tif rt'i-rh. xxiir. 
 
 ossification of the exterior part of the ca]isule itself, forming an 
 ' OS pctrosum,' as c. g. in tlie Carp, fig. 83, i6, and Perch, figs. 
 85, 84, 10. In the dry skull the ear-chamber appears as a large 
 lateral compartment of tlie cranial cavity, fig. 227, o ; and is 
 formed as described in p. 115. 
 
 In the INIyxmiiids tlie membranous labyrinth is a simple annular 
 tube, lined by vibi'atile cilia, filled with fluid, and supporting 
 the ramifications of the acouslic uerAc. In tlie Ammocete and 
 Lam]M-ey the labyrintli is specially attached to its cartilaginous 
 capsule, and consists of a ' vestibule ' and two ' semicircular Janals,' 
 
ORGAN OF IIEAraNG IN FISHES. 343 
 
 eacli of wlucli dilates, at. its origin, into an ' ampulla,' wliicli lias 
 some processes from its inner surface. The two canals again 
 communicate with the vestibule, where they cross each other : the 
 two divisions of the acoustic nerve first surround the ampulhe 
 before they spread over the rest of the labyrinth. The acoustic 
 communicates with the cranial cavity by two openings : the ini'crior 
 and larger is oval and closed by membrane : the superior gi\'e8 
 passage to the acoustic nerve. 
 
 In all other Fishes the memln'anous labyrinth, fig. 229, «, o, 
 consists of a vestibule, ib. «, and three semicircular canals, o ; the 
 vestibule dilating into one or more ' sacculi,' separated by a con- 
 striction, or by a narrow canal, from the ' alveus communis,' and 
 containing, besides the iiuid called ' endolymph,' two or more 
 masses of carbonate of lime, called ' otolites.' ' These are com])act 
 and crystalline in Osseous Fishes. The largest, fig. 81, ig", is an 
 oval or round flattened body, striated and indented at the margins ; 
 convex, and sometimes grooved {Ejildypus), on one side, more or 
 less excavated on the other. The smaller otolite is less regular in 
 its shape: there are often two of these. Each semicircular canal 
 rises by an ampulliform end, fig. 229, e,f,g, ivoxn the 'alveus 
 communis,' a, and communicates, by the opposite end, either with 
 another canal, or with the vestibule separately, without previous 
 dilatation: two of the canals are subvertical in their course, and 
 are anterior, e, and j^ostcrior, g, in relative position : the third 
 canal, /^, is external and horizontal. A septum is continued across 
 the amjjulla from the line where the division of the acoustic nerve 
 enters : a large proportion of the nerve expands upon the sac of 
 the otolites. In some fishes this communicates with the vestilralc 
 by a narrow canal. All the j^arts of the laljyrinth are of large 
 size ; yet the compartments of the otocrane which the semicircular 
 canals, fig. 229, e,f,g, traverse, 'are much too wide for them, 
 and they are supported in these passages by a very fine cellular 
 membrane.'^ In the Pike {Esox lucius) a pyriform membranous 
 sac, lodged in the commencement of the spinal canal, ojtens into 
 the vestibule near the entrance of the posterior semicircular canal. 
 
 The Plectognaths, Lophobranchs, Holocephali, and Sturgeons 
 resemble the bony fishes in the form and position of the labyrinth ; 
 but the otolites are represented by cretaceous particles ; and in 
 the Chimtera the communication between the cranium and otocrane 
 begins to contract. The otolites are a hard chalky substance in 
 
 ' Figures of these bodies will be found in xx. vol. iii, pi. 35; in LXvni., lxxi., and 
 in Lxxii., with microscopic figures of the crystals. 
 " Hunter, vii. iii. p. 101. 
 
344 
 
 ANATOMY OF VERTEBRATES. 
 
 228 
 
 Organ of hearing, Skate. LXA'ill, 
 
 the Lepiclosiren, in wliicli, as well as in the Plagiostomes, the 
 whole labyrinth is buried in the thick basi-lateral walls of the 
 cranivnii. In Plagiostomes the capsule conforms more closely in 
 size and configuration to the membranous 
 labyi-inth; its passages and compartments 
 are lined by a delicate perichondrium, from 
 which filaments are detached to support 
 the semicircular canal. The vestibule is 
 divided in the Skate and Tope into three 
 compartments, — the ' alveus communis,' 
 fig. 228, « ; the sac, ib. b, and the cysticule, 
 ib. c ; and it has also a small ca3cal append- 
 age, called the ' utricule,' ib. d : the otolitic 
 contents are like soft chalk, and are dis- 
 posed in two masses ; one very large, occu- 
 pying the sac and the cysticule, the other 
 small, and lodged in the utricule. A canal extends in Sharks 
 from tlie vestibular capsule to a foramen at the upper part of 
 the occiput, which is closed by the skin. In the Pays, besides 
 this ' fenestra capsula3,' ib. v, a membranous canal, ib. o, p, is pro- 
 duced from the vestibule itself, and, as Hunter well describes, 
 ' from the union of the two perpendicular canals, fig. 228, p ; 
 which is the case with all the Ray kind, the external orifice 
 ])eing small, and placed on the upper flat surface of the head.' 
 So minute and approximated are these ' outer ears,' ' that Scarpa 
 may be pardoned for overlooking them, though scarcely for 
 the warmth with which he repudiates their existence.^ The 
 '■'meatus vestibuli' is provided at its bent extremity, fig. 228, o, 
 witli a special muscle, ib. u\ 
 
 A true tympanic cavity and membrane, together with a cochlea, 
 are absent in all Fishes. But in many osseous sjiecies a com- 
 munication is established, either by tubular prolongations, or by 
 chains of ossicles, between the acoustic labyrinth and the air- 
 bladder. Weber ^ discovered the latter interesting structure in 
 the Carp, Loach, and Sheat-fish. A canal is sent from the sac of 
 each vestibule, fig. 229, h, to a common 'sinus impai-,' ib. //, in 
 the substance of the basi-occipital ; this communicates on each 
 
 ' xcn. p. 296. Hunter's ovigiiinl memoir 'On tlic Organ of Iloaring in Fislics ' was 
 printed in tho volnnio of tlie Pliilosopliical Transactions for 1782, not, as Broscliet 
 states, in the year 1786. (lviii. p. TiS.) 
 
 ■^ 'Huntcrum antcm atqnc Monroum vehcmcnter super liac re sibi hallneinatos 
 fnisse.' (lx. jip. 1, 2.) 
 
ORGAN OF HEARING IN FISHES. 
 
 34,5 
 
 side by a small orifice with 
 of the atlas, close to the 
 foramen magnum, which 
 ' atria ' are supported ex- 
 ternally by the ossicles I 
 aud m, and, by means of 
 the large ossicle o, arc 
 brought into commnnica- 
 tion with the fore part of 
 the air-bladder, j). Both 
 the atria and common 
 sinus are filled by the 
 endolymph, and from the 
 fore part of the sinus a 
 ' canalis furcatus,' ib. /, 
 is produced, the blind 
 ends of which penetrate 
 the alisphenoids. In the 
 grovelling Loach ( Cobitis 
 barhatula), the air-bladder 
 would seem to exist 
 chiefly in subserviency 
 to the organ of hearing. 
 It is so small as to be 
 wholly included within 
 the singularly modified 
 parajjophyses of the se- 
 cond and third cervical 
 vertebras, which are ex- 
 panded and coalesced so 
 as to form a large ' bulla 
 ossea ' beneath their cen- 
 trums.' The three ossicles 
 on each side, which bring 
 the air-bladder into com- 
 munication with the ' atria' 
 of the labyrinth, are also 
 concealed by the fore part 
 of the parapophysial bul- 
 lae : it is plain, therefore, 
 that they are not dis- 
 memberments of those 
 
 two subsphcrical ' atria,' on the body 
 
 229 
 
 Organ of Heariug m situ ^\ th i i 1 1 Uder and l ssides, Carp. 
 Lwm 
 
 XXXIX. i. p. 380. 
 
346 ANATOMY OF VERTEBRATES. 
 
 lateral or transverse apophyses of the vertelara; ; and, with regard 
 to their relation to the ' ossicula anditus ' of the tympanic cavity 
 in Mftinmalia, Welder mistook a relation of analogy for one of 
 homology, when he called them ' mallens,' ' incus,' and ' stapes.' 
 They belong, like the capsules of the special organs of sense, to 
 the ' splanchnoskeleton.' And since the vestibule is prolonged 
 by the ' atria ' into the neural canal of the atlas, this -^'crtebra 
 must be added, in the Cyprinoid and Siluroid Fishes, to the 
 parts of the cranial vertebra enumerated at p. 115, as entering 
 into the formation of the chamber of the acoustic organ. In tlie 
 Herring a tubular prolongation of the fore part of the air-bladder 
 advances to the basioccipital, and bifurcates ; each branch pene- 
 trates the side of tlie base of the skidl, again bifurcates, and 
 terminates in two blind sacs, which are in contact with smiilar 
 caical processes of .the labyrinth. In the Holocentrura and 
 Sargus, cajcal processes of the swim-bladder also diverge, to 
 attach themselves to the membrane closing the part of the oto- 
 crane containing the sac of the great otolite. 
 
 In Osseous Fishes the sonorous vibrations of their liquid clement 
 is communicated by the medium of the solid parts of their body, 
 and in some species, also, through the vibrations of the air in the 
 air-bladder, to the liquid contents of the labyrinth. In the Plaglo- 
 stomous Fishes the resonance in the walls of their cartilaginous 
 cranium is less than in the bony skull of ordinary fishes; but the 
 labyrinth is wholly inclosed in the cartilage ; and a further com- 
 pensation is made by the prolongation of its chamber to the siirface 
 of the body in some, and by a similar prolongation of the mem- 
 branous labyrinth itself in others. The position of the external 
 orifices on the top of the head in the Skate tribe, may relate to 
 the commonly prone position of these flat fishes at tlie liottom of 
 the sea. Professor Miiller concludes, from his experiments, ' that 
 the air-bladder in fishes, in addition to other uses, serves the 
 purpose of increasing by resonance the intensity of tlie sonorous 
 undulations communicated from water to the body of the fish."' 
 The vibrations thus commimicated to the peri- and endo-l}mph of 
 the labyrinth are doubtless made to beat more strongly upon the 
 delicate extremities of the acoustic nerve, in Osseous Fishes, by 
 their effect upon the suspended otolites : and it will be observed, 
 that the chief ])ortions of the nerve expand u]ion those chambers 
 of the vestibule, which contain the otolites. The large size of the 
 organ of hearing, and es])ecially Ihat of the hard otolites, also relate 
 to the meilium through which the sonorous vibrations arc propagated 
 
 ' i.xxin. p. 124 5. 
 
ORGAN OF HEARING IN REPTILES. 347 
 
 to tlic fish, and to the mode in which they are transmitted to the 
 organ; in lilve manner as the eyeballs are expanded, in order to 
 take in the ntmost possible amount of light. The contracted 
 encephalon harmonises with and suffices for the sensations and 
 volitions, and the simple series of ideas daily repeated in the 
 monotonous existence of the scaled inhabitants of the waters. 
 
 § 67. Organ of Henring in Reptiles. — The otocrane is large iii 
 jn'oportion to the cranium, in the Perennibranchs, but is distinct 
 from it : it is cliietly excavated in the alisphenoid and exoccipital. 
 It includes a vestibule, three semicircular canals (Proteus, Axelotes), 
 and the otolithic sac containing a cretaceous matter, which has 
 more shape and consistency in the Axolotl than in the Newts and 
 Salamanders. The external orifice of the acoustic capsule can 
 now be recognised as a ' vestibular ' one, or ' fenestra ovalis,' and 
 it is closed by a cartilaginous plate representing the base of the 
 stapes, connected with a slender ossicle in the Axolotl : but as yet 
 there is no trace of tympanic cavity. The analogy of the ear to 
 the eye, by the absence of the tympanic and conjunctivo-lacrymal 
 forecourts in the respective organs of Fishes, is still kept up in the 
 fish-like Reptilia. 
 
 The tympanic adjunct to the organ of hearing makes its first 
 appearance, sunultaneously with the developement of eyelids and 
 lacrymal organs, in the Batrachia which have quitted their aquatic 
 for an aerial existence. Beyond the vestibular foramen is 
 continued a short but wide jjassage outward, or ' meatus,' closed 
 from the external air by a thin transparent vibratile membrane — 
 the ' tjanpanum ' or ear-drum. From the gristly plate closing 
 the vestibular foramen a slender bony style is continued across 
 the ' tympanic cavity ' to a drum, to which it is attached by a 
 capitular or spatulate cartilage, in which a small muscle is inserted. 
 A wide vertical [jassage from the tympanic cavity to the fauces 
 preserves the equilibrium between the air in that cavity and the 
 atmosphere outside : it is called ' eustachian tube.' This tulie 
 will be found to bear relation to the size and exposed condition of 
 the ear-drum, and perhaps, also, to its form, which, in the Frog 
 and other air-breathing Ovipara., is convex externally. In the 
 Fipa the bony meatus is long and tubular in shape, the eustachian 
 tubes terminate by a single median and minute orifice on the 
 palate : the ear-drum is concealed by a partial covering of skin. 
 It is less conspicuous external^ in all Toads than in Frogs: a small 
 muscle acts on the cartilage connected with the ear-drum, and a 
 second lono-er muscle is attached to the discoid piece closing the 
 vestibular orifice. The labyrinth consists of alveus communis. 
 
348 ANATOMY OF VERTEBRATES. 
 
 three semicircular canals, and otolitliic sacculus containing a semi- 
 fluid cretaceous substance : it is proportionally smallest in Pipa. 
 
 All serpents have the internal organ of hearing, similar in the 
 main to the above : the base of the stapes closing the foramen 
 vestibuli, is connected, in most serpents, by a long slender bony 
 style, fig. 97, 16, through the medium of a cartilage and liga- 
 mentous fibres to the skin, which sliows no sign of ear-drum or 
 external meatus. No air is admitted by an eustachian canal to 
 the cellular substance traversed by the tympanic ossicle ; and of 
 this there is no trace in Tythlops and Rhinojjhis. 
 
 In Lacertians, the modification of part of the integument for 
 the special reception of sonorous vibrations is resumed. In the 
 Iguana, the ear-drum is partially protected by its oblique jjosition 
 and by a rising or fold of the skin at the back part of its circum- 
 ference. It consists of the proper fibrous tissue of the tympanic 
 membrane, covered externally by a thin layer of epithelium, and 
 internally by the lining membrane of the tympanic cavity. The 
 communication between the membrana vestibuli and membrana 
 tympani is by the stapedial disc, the columelliform ossicle and the 
 terminal or ' malleal ' cartilage. The eustachian canal is rela- 
 tively narrower, and its course more oblique than in the Frog : the 
 otolite is a lenticular calcareous body, fimier than in the Frog. 
 
 In the Chelonia the ear-drum is again masked by unmodified 
 integument ; in the Turtle ( Chelone mi/das) it is covered by the 
 second scale counting upward from the articulation of the lower 
 jaw. The membrana tympani is, however, distinctly formed, 
 thicker and more opake than in Batrachia or Lacertia, and con- 
 vex outwardly. The long columelliform ossicle fig. 92, ig', is 
 connected with it by a discoid cartilage, and, at the opposite end, 
 penetrates and closes the vestibular orifice by a sub-cartilaginous 
 plate. The tympanic cavity is divided into two parts by a bonv 
 sei)tum, intercommunicating at the coluraellar canal : the inner 
 or antevestibular part also communicates with cells on the mastoid. 
 The eustachian canal is narrow, and descends behind the arti- 
 culation of the mandible ; its palatal opening is more remote from 
 that of the opposite ear than in other Reptilia. The proper cap- 
 sule of the labyrinth is cartilaginous : besides the three semi- 
 circular canals and tlie otolithic capsule, there now buds from the 
 vestibule a beginning of a cochlea, with a corresponding small 
 opening into the tympanic cavity. 
 
 These approximations to the higher structure of the internal 
 car are more conspicuous in Crocodilia. The cochlear process is 
 conical, with the apex, fig. 230, «, slightly bent; its cavity is 
 
ORGAN OF HEARING IN REPTILES. 
 
 349 
 
 230 
 
 Orgiiii of bfnring-, Crocodile. 
 
 flap of the integument, 
 and accurately closing the 
 
 divided into two compartments by a double cartilaginous septum, 
 lb. h, except at the apex, where they communicate; whilst, at the 
 base, one compartment, ' scala vestibuli,' communicates with the 
 Ycstibule, the other, ' scala tympani,' 
 by a small orifice (foramen cochlea3, 
 sen rotundum), with the tympanic 
 cavity, in the dry skull, but closed 
 by membrane in the living animal. 
 The cochlear division of the acoustic 
 nerve is shown at v, fig. 2.30. The 
 semicircular canals are small com- 
 pared with those of fishes : c is the 
 anterior perpendicular, d the pos- 
 terior perpendicular, and e the ex- 
 ternal or horizontal, canal which 
 curves over the 'foramen ovale,'/. 
 The membrana tympani, g, is lodged 
 at the bottom of a deep fissure, 
 and is protected by an opercular 
 h, fitting to a smaller fold below, i, 
 
 l^assage. This is the sole approach to an external ear known 
 in existing Ref)tLHa. The ear-drum is inclined downward and 
 outward, adapted to the reception of sound from alcove, and also 
 to the position of the overhanging flap. The gristly rei^resen- 
 tation of the malleus, k, is well-marked, and the ear-drum is 
 thickened at its place of attachment : the columellar part of the 
 stapes, I, extends obliquely downward to the foramen ovale, sen 
 vestibuli, f. The tympanic cavity, in, is singularly extended 
 by air-cells, not only developed in the mastoid, but in the 
 basi-, par-, and super-occipitals, fig. 94, 3, in the alisphenoid and 
 parietal, ib. 7, bones. The communications between the tympanic 
 cavity and fauces are more comj)lex than in other animals,' 
 although the eustachian fauoial opening, n, is single, median, and 
 common to both ears. It is situated a short way behind the pos- 
 terior nostril ; and from it is continued a median, o, and two lateral, 
 p, canals. The median canal rises and enters a bony canal between 
 tlie basioccipital and basisphenoid, which bifurcates, one branch, q, 
 inclining forward into the basisphenoid, the other, r, continued ver- 
 tically into the basioccipital, both in the medial j^lane. Each of 
 these branches again bifurcates, ti-ansversely, one to the right, 
 tlic other to the left, opening upon the floor of the tympanic cavity. 
 
350 ANATOMY OF VERTEBRATES. 
 
 The lateral membranous canals, 7:1,73, from the eustachian outlet, 
 diverge to the orifices of corresponding lateral bony canals, which 
 ascend between the basioccipital and basisphenoid, and communi- 
 cate each with the transverse subdivision, s, of the posterior or 
 occipital branch of the median eustachian canal: a small rhomboidal 
 sinus is formed at the point of union, from wliich a short canal, 
 t, is continued to the tympanic cavity. The common inferior 
 outlet, situated on a prominence, is partly closed by a valve, n, 
 reducing its area to a crescentic form.' 
 
 § 68. Electric Orf/ans of Fishes. — Besides the modifications and 
 appendages of the peripheral extremities of the nerves consti- 
 tuting organs of special sense, and those of which the function is 
 still conjectural, there are nerves in fishes subject to more extra- 
 ordinary combinations, and forming instruments, unknown in the 
 liigher vertebrate classes, having the property of accumulating 
 and concentrating the subtle mode of force applicable to the com- 
 munication of electric shocks. The faculty is limited to few 
 genera, the most remarkable being Torpedo and G//ninotiis, tlie 
 species of which possess the electric organs in the highest state of 
 devclopement. In a minor degree the organs and power exist in 
 Malupterurus elcctricus, 3Ial. Beninensis, Bloninirus lonf/ipinnis, 
 Mor. oxyrhynchus, Mor. dorsalis, Trichiiirus elcctricus, Gyinnarclu/s 
 iiiloticus, and Tetraodon electricms. 
 
 In the Torpedo Galvanii the organs are two in number, are 
 large, flattened, reniform bodies, lodged on each side of the head 
 and gills, and encompassed by these and by the anterior borders 
 of the pectoral fins (fig. 1.39, e) : they consist of a mass of ver- 
 tical, for the most part hexagonal, prisms, the ends of which are 
 covered lay the doi-sal and ventral integuments. Beneath these 
 the organs are immediately coated liy a thin glistening aponeu- 
 rosis, which sends down partitions forming the chambers of the 
 ])rismatic columns. Eacli column, when insulated in the recent 
 fish, seems like a mass of clear trembling jelly; but consists of a 
 series- of delicate membranous plates inclosed by, or adherent by 
 their margins to, a proper cai)sule, and separated from each other 
 Ijy a small quantity of a limpid albuminous fluid. Each flattened 
 cell thus formed is lined by an epithelium of nucleated cells : 
 \\\<i fibrous tissue of the jilatcs and common capsule presents the 
 microscopic characters of elastic tissue ; between it and the cpi- 
 tiielnun is a clear unorganised layer, the scat of the ultinnUe 
 ]-araifications of the vessels and nerves. The ]>roper capsule 
 adheres to the apoucurolic partition-walls wliich support the 
 
 ' Cl.NXII. |X V21, 111?, xl. Nli. Xlii. 
 
ELECTRIC OIIGANS OF ELSHES. 
 
 351 
 
 columns and the larger branches of the nerves and vessels of the 
 orn'an. Some of the vertical cohmms do not extend through the 
 entire thickness of the organ ; but are intcrru]ited where the 
 deep-seated nerves traverse the sidistancc of the l)attery, fig-. 2.31, 
 A, 1). The transverse })latcs of the vertical columns are shown 
 
 231 
 
 Tliu 1-ittlitclcctr 
 
 grin, divided liurizoiitally, ;it 11. t' iJj'-C whcrr llic nerves enter, T.iirdh,. i.xwi. 
 
 at E. Hunter, who counted 470 columns in each organ, describes 
 the ]iartitlons as being very vascidar : — 'The arteries,' he says, 
 'are branches from the vessels of the gills, which convey the 
 blood tliat has received the iniiuence of respiration." But the 
 
 ' I XXXI. 
 
352 
 
 ANATOMY OF VERTEBRATES. 
 
 most characteristid feature of tlie organisation of the electric 
 battery is its enormous suj^ply of nervous matter. Each organ 
 derives tliis supply from one branch of the trigeminal, fig. 231, a, 
 and from four branches of the vagal nerves, ib., b, c, d ; the four 
 anterior nerves are each as thick as the sjDinal cord : the last 
 nerve is a feeble branch of the vagus. The trigeminal and 
 vagal enlargements of the olivary and restiform tracts coalesce on 
 each side, forming the so-called ' electric lobes ' of the medulla 
 oblongata. The electric branch of the fi.fth nerve may be defined 
 even at its origin, from the true ganglionic part of that nerve ; 
 and both this and the vagal branches consist entirely of the pri- 
 mitive nerve-fibres of animal life, as in fig. 164. The nerve- 
 trunks are distributed by successive resolution into smaller and 
 smaller fasciculi, until they finally penetrate tlie septa of the 
 columns, and terminate thereon by meshes formed by loops, or by 
 the return and anastomosis of the primitive nerve-fibres.' 
 
 In the eel-like Gymnotus the electric organs are four in 
 number, and are situated two on each side the body, extending 
 from behind the pectoral fins to near the end of the tail, fig. 232, 
 
 232 
 
 Right electrical organs, G;/7)nio/»s (reduced), ccxvil. 
 
 /(, I. They occupy and almost constitute the whole lower half of 
 the trunk, fig. 233 ; the upper organ, ib. h, being much larger than 
 the lower one, ib. i, from which it is separated by a thin muscular 
 and aponeurotic stratum. The organs of one side are separated 
 from those of the other, above by the vertebral column and its 
 muscles, ib. c, then by the air-bladder, ib. d, and below this by 
 an aponeurotic septum, ib. /(. From this septum, and from that 
 covering the air-bladder, there extend outward, to be attached to 
 tlie skui, a series of horizontal, or nearly horizontal, membranes, 
 arranged in the longitudinal axis of tlic Ijody nearly parallel to 
 one another ; they are of great but varying "length," some beino- 
 co-extensive with the whole organ, fig. 232, k : their breadth i^ 
 almost that of the scmidiametcr of the jtlanc of the body in 
 
ELECTRIC ORGANS OF FISHES. 
 
 353 
 
 whicli tliey are situatea, fig. 233, /(. Tliese membranes are about 
 half a line apart at their outer borders ; but, as they pass from 
 the skin towards their inner attachments, tliey approach one 
 
 233 
 
 I 
 
 
 / 
 
 Vci'tical transverse section, Gi/^nnotnf, natural size. coXT. 
 
 another. They are intersected transversely by more delicate 
 vertical plates, extending from the skin to the median aponeu- 
 rosis, and coextensive in length with the breadth of the septa 
 between which they are placed. Hunter counted about 240 of 
 these plates in a single inch of length of the horizontal mem- 
 brane.' He compares those stronger mcml:)ranes to the aponeu- 
 rotic walls of the prisms of the Tor})edo, and the inter- 
 secting delicate plates to the partitions of the prisms ; and if 
 we admit the analogy of these plates, and (.)f these of the Tor- 
 pedo, to the plates of the voltaic pile, we perceive that, in the 
 
 VOL. I. 
 
 ' LXXX. 
 
 A A 
 
354 ANATOMY OF VERTEBRATES. 
 
 Gymnotus, the batteries are horizontal aad the plates vertical, 
 fig. 233, h, whilst in the Torpedo the batteries are vertical and 
 their plates horizontal, fig. 231, E. The situation of the organs 
 is also very difl^erent in the two fishes ; they extend from before 
 the pectoral fins to the anterior part of the head in the one, 
 fig. 139, E, and from behind the pectoral fins to near the end of 
 the tail in the other, fig. 232, k. But a more important difference 
 exists in the condition of the interspaces between the delicate 
 transverse plates. In the Torpedo they simi^ly contain a fluid. 
 In the Gymnotus two strata of pyramidal cells diverge from a 
 common basis traversing each interspace, and terminate freely, 
 the one towards one plate, the other towards the opposite plate, 
 and divide the fluid into a ' pre-cellular ' and 'post-cellular' 
 portion. The cellular basis is ' jjositive,' the post-cellular fluid 
 and the partition-jilate is negative, constituting the ' voltaic 
 couple;' whilst the j^re-cellular fluid is the conducting element 
 between one ' coujdIc' or plate and the next: the whole represents 
 the ternary type of the voltaic pile. The Torpedo's structure is 
 according to the binary type. Another remarkable diflerence 
 is in the source of the nervous supply. In the Gymnotus the 
 electric organs are supplied by the 'rami ventrales' of all the 
 spinal nerves, about 200 pairs, that issue in the course of 
 their extent ; some of the filaments ramify upon the horizontal 
 membranes from their cutaneous margins ; but the greater part of 
 the nerves come from the deeper-seated branches wliich descend 
 upon the median aponeurotic i^artition-wall, and spread upon the 
 septa of the organ from within outwards. Yet the nervus late- 
 ralis, which is derived from the same cerebral nerves as those 
 which, in the Torpedo, supply the electric batteries, and which is 
 formed by similar proportions of the trigeminal and vagus, ex- 
 tends tlie whole length of the electric organs in the Gymnotus 
 without rendering them a filament; it is situated nearer the 
 sj)ine, and is of larger size than usual, but Hunter Avas not 
 al)lc to trace any nerves going from it to join those of the 
 medulla spinalis, which rim to the organ.' The quantity of 
 nervous matter svipplied to the batteries of the Gymnotus is 
 less than in the Torpedo : but more substance enters into their 
 composition. 
 
 The proportional size of the electric organs is also much 
 greater in the Gymnotus than in the T<u-pedo : indeed, the proper 
 body of the Gyuniotus is, as it were, a mere ajipendage tacked on 
 
ELECTRIC ORGANS OF EISHES. 
 
 35.5 
 
 234 
 
 Sectiun of Maldplerurus d'iciricns. ccxrx. 
 
 to the fore j^art of tlie enormous batteries ; for the digestive and 
 generative viscera, with the respiratory and circulating organs, 
 the hrain and organs of sense, — 
 all, in fact, that constitute the 
 proper animal, — are confined to 
 that small segment of the entire 
 Ijody which is anterior to the elec- 
 trical apparatus, fig. 232, b. The 
 vent even opens beneath the head, 
 in advance of the pectoral fins. 
 
 The electric organs of the Ma- 
 lapterurus electricus ' form a layer 
 fig. 234, A, immediately beneath 
 the skin, enveloping the whole 
 body except the head and fins, and sei)arated from the muscles, 
 ib. G, by a fiiscia with vessels and nerves, ib. B, and by a layer 
 of adipose tissue, ib. E. The electric organ is divided by fine 
 decussating membranes into minute lozenge-shaped cells, about a 
 third of a line in diameter, fig. 235, u. It is snpp)lied b)^ a large 
 nerve issuing from the beginning of the myelon and arising from 
 a mass, in its substance, of ganglion-cells, like those in the electric 
 lobes of the Torpedo. A considerable ganglion is also formed npion 
 the nerve beyond its origin, from which the trunk is continued 
 ahnig the side of the body, like a ' nervus lateralis,' and distriljutes 
 l^ranches to the diffused organ. The structure of the organ is such 
 that the electric currents run in all directions, and 
 a discharge would take jilace from any point of 235 
 
 its surface, whence, jjerhaps, the necessity fV>r a 
 layer of nonconducting substance, E, between 
 the proper body of the fish and the organ. The 
 shock delivered, wanting the concentration re- 
 sulting from the structure in the Torpedo, is 
 comparatively feel^le, but suffices for defence ; 
 the fish being protected by its electrifying coat, 
 as is the hedgehog by its spines. 
 
 In the Mormyrus longijnnnis the electric organ 
 consists of four series of membranous septa 
 placed longitudinally on the tail, two on each 
 side. Each series consists of about 150 septa 
 with intervals of -i^th. of a line, filled by albu- 
 minous fiuid. The septa are stronger than 
 those in tlie hexagonal columns of the Torpedo." 
 
 Seotionof tloctric organ, 
 MalapUrurus, ccxvilj. 
 A, skill ; B, electric ceils 
 c, fascia : ij, cellular tis- 
 sue, with a, artery, v, 
 vein, n, nerve : e, adi- 
 pose tissue. 
 
 ' xcii. and coxix. 
 
 A A 2 
 
3,56 ANATOMY OF VERTEBRATES. 
 
 An animal must be in communication with the Torpedo by 
 two distinct points, in order to receive the shock.' If an insulated 
 frog's leg, fig. 20*7, C, touches the Toi'pedo by the end of the nerve 
 only, no muscular contractions ensue on the discharge of the bat- 
 tery ; but a second contact by a portion of muscle, or any other 
 part of the leg, immediately produces them.^ 
 
 The dorsal surface of the electric organ is positive, the ven- 
 tral sui-face negative. The Torpedo has no power of otherwise 
 directina: the electric currents ; but Matteucci found that wound- 
 ing the electric lobes of the brain sometimes reversed the direc- 
 tion.^ These currents, besides their effects on the living body, 
 exercise all the other known powers of electricity ; they render 
 the needle magnetic,"* decompose chemical compounds, and emit 
 the spark. '^ The discharge of strong currents is usually accom- 
 ])anied by visible contraction of parts of the body, usually )jy a 
 retraction of the eyes of the Torpedo, and one muscle, fig. 139, 
 0, is arranged so as to constrict part of the circumference of each 
 battery ; but such consentaneous muscular action, though it may 
 add to the force of the discharge, is not essential to its produc- 
 tion. The beniunbing effect seems to be produced by the rapid 
 succession of shocks delivered by the recent and -^-igorous fish, 
 Matteucci ascertained that, during the discharge, the nerves of 
 the organ were not traversed by any electric current. Pacini,'' 
 from a minute comparison of the organs, deduces that the elec- 
 tricity in the Torpedo is j^roduced by the dynamical conflict 
 between the two polarities inherent in two sorts or diflerent 
 degrees of innervation, as it is evolved in the thermo-electric pile 
 by the conflict of two polarities inherent in two diflerent degrees 
 of temperature ; whilst in the Gymnotus it is produced, as in 
 the voltaic pile, by the chemical conflict between the materials 
 of the elements excited by the nervous influence. 
 
 Humboldt has given a lively narrative of the mode of capture 
 
 ' When the Neapolitan fishermen pull their nets to shore, their first act usually is 
 to wash the captured lislies by dashing over them hueketfuls of sea-water ; and if a 
 Torpedo be amongst tliem it makes its presence instantly felt by the slioek transmitted 
 to the arm discharging the bucket. If the fish he handled, tlie sliock is too strong 
 and piiinful to lie willingly encountered a second time, and the arm continues Icmg be- 
 nundied. Each repetition of the discharge, however, enfeebles its force, and the 
 surlaee of the fish capable of comnuinienting the shock progressively contracts, as 
 life departs, to the region of the organs themselves. When the fisherman dashes 
 the stream of water o\'er the Torpedo, tlie electric current passes up from the 
 dorsal surface of the batteries against the stream to the man's baud, and the circle 
 is completed by the earth extending from the man's feet to the ventral surface of the 
 jirone (isli. 
 
 ^ ],XXVII. p. M8. ■' lb. ' LXXXII. = I.XXVIT. « CCXVIII. 
 
ELECTRIC ORGANS OE EISHES. 3o7 
 
 of the Gymnoti, employed hy the Indians of South America,' and 
 all its circumstances estal)lish the close general analogy between the 
 Gynmotus and Torpedo in the vital phenomena attending the ex- 
 ercise of their extraordinary means of offence. It is voluntary and 
 exhaustive of the nervous energy ; like voluntary muscular eft'ort, 
 it needs repose and nourishment to produce a fresh accumulation. 
 In the experiments performed by Professor Faraday on a large 
 living Gymnotus,^ the most powerful shocks were received when 
 one hand grasped the head and the other hand the tail, of which 
 I had painful experience ; especially at the wrists, the elbows, 
 and across the back. But the nearer the hands were together 
 within certain limits, the less powerful was the shock. It was 
 demonstrated hj the galvanometer that the direction of the elec- 
 tric current was from the anterior parts of the animal to the i)os- 
 terior parts, and that the person touching the fish with both hands 
 received only the discliarge of the yiarts of the organs included 
 between the points of contact. Needles were converted into 
 magnets : iodine was obtained by polar decomposition of iodide 
 of potassium ; and, availing himself of this test, Faraday showed 
 that any given jjart of the organ is negative to other parts before 
 it, and positive to such as are behind it. Finally, heat was 
 evolved, and the electric spark obtained. The delicate plates 
 
 ' They rouse the Gymnoti by driving horses and mules into the ponds which those 
 fish inhabit, and harpoon them when they luive exhausted their electricity upon tlie 
 unhappy quadrupeds; * I wished,' says Humboldt, 'that a elever artist eould have 
 depicted the most animated period of the attack: the groups of Indians surrounding 
 the pond, the horses with their manes erect and eyeballs wild with pain and fright, 
 striving to escape from the electric storm which they had roused, and driven back by 
 the shouts and long whips of the excited Indians : the livid yellow eels, like great 
 water-snakes, swimming near the surface and pursuing their enemy: all these objects 
 presented a most picturesque and exciting ensemble. In less than five minutes two 
 horses were killed. The eel, being more than five feet in length, glides beneath the 
 body of the horse, and discharges tlie whole length of its electric organ. It attacks, 
 at the same time, the heart, the digestive viscera, and, above all, the gastric ple.xxis of 
 nerves. I thought the scene would have a tragic termination, and expected to see 
 most of the qu.adrupeds killed; but the Indians assured me the fishing would soon tie 
 finished, and that only the first attack of the Gymnoti was really formidable. In fact, 
 after the conflict had lasted a quarter of an hour, the mules and horses appeared less 
 alarmed ; they no longer erected their manes, and their eyes expressed less pain and 
 terror. One no longer saw them struck down in the water; .and the eels, instead of 
 swimming to the attack, retreated from their assailants, and approached the sliore.' 
 The Indians now began to use their missiles; and, by means of the long cord attached 
 to the harpoon, jerked the fish out of the water, without receiving any shock so long 
 as the cord was dry; but a less cautious assailant, who had climbed an overhanging 
 bough, was brought down into the water, airiidst the laughter of his companions, by 
 the shock sent upwards from the wounded Gynmotus, along the wetted cord attached 
 to the harpoon, cvii. p. 55. 
 
 - LXXXIII. 
 
358 ANATOMY OF VERTEBRATES. 
 
 siistaiiiing the terminal meshes of the nerves and vessels are hori- 
 zontal in the Torpedo ; the course of the electric current is 
 from above downwards. The corresponding plates in the Gym- 
 notus are vertical ; the direction of the electric current is from 
 before backwards : i. e. it is vertical to the planes of the pjlates in 
 both cases. 
 
 The row of compressed cells constituting the electric prism of 
 the Torpedo offers some analogy to the row of microscopic discs 
 of which the elementary muscular filament appears to consist, 
 fig. 128, B. The looped termination of the exciting nerve is 
 common to muscular tissue and that of the electric organ. The 
 electric, like the motory nerves, rise from the anterior myelonal 
 tracts ; and, though they have a special lobe at their origin, beyond 
 that origin, in the Torpedo, they have no ganglion. An impression 
 on any jiart of the body of the Torpedo is carried by the sensory 
 nerves either directly, or through the posterior myelonal tracts, to 
 the brain, excites there the act of volition, which is convej'ed 
 along the electric nerves to the organs, and ])roduces the shock : 
 in muscular contraction, the impression and volition take' the same 
 course to the muscular fibres. If the electric nerves are divided 
 at their origin from the brain, the course of the stimulus is inter- 
 ruj)ted, and no irritant to the body has any efl^ect on the electric 
 organs any more than it would have under the like circumstances 
 on the muscles. But, if the ends- of the nerves in connection 
 witli the organ be irritated, the discharge of electricity takes pjlace, 
 just as irritating the end of the divided motor nerve in connection 
 with the muscle would induce its contraction. If part of the 
 electric nerves be left in connection with the brain, the stimulus 
 of volition cannot, through these, excite the discharge of the 
 whole organ, but only of that part of the organ to which the 
 undivided nerves are distributed. So, likewise, the irritation of 
 the end of a divided nerve in connection with the electric appa- 
 ratus, excites the discharge of only that part to which such nerve 
 is distributed. We have seen that the power of exciting the 
 electric action, like that of exciting the muscular contraction, is 
 exhausted by exercise and recovered by repose : it is also augmented 
 by energetic circulation and respiration ; and what is more signi- 
 ficative of their close analiigy, both powers are exalted by the 
 direct action, on the nervous centres, of the drug ' strychnine : ' 
 its application causes simultaneously a tetanic state of the muscles 
 of the fish, and a rapid succession of involuntary electric dis- 
 charges.' 
 
 ' I.X.WH. \i. U'.2. 
 
359 
 
 CHAPTER V. 
 
 DIGESTIVE SYSTEM OE HiEMATOCRYA. 
 
 § 69. Denial Tissues. — A tooth is a hard body attached to the 
 mouth or commencement of the ahmentary canal, partially exposed, 
 when developed. Calcified teeth are jieculiar to the Vertebrates, and 
 may be defined as bodies primarily, if not permanently, distinct from 
 the skeleton, consisting of a cellular and tubular basis of animal 
 matter containing earthy particles, a fluid, and a vascular pulp. 
 
 In general, the earth is present in such quantity as to render 
 the tooth harder than bone, in which case the animal basis is gela- 
 tinous, as in other hard parts where a great proportion of earth is 
 combined with animal matter. In a very few instances, among the 
 vertebrate animals, the hardening material exists in a much 
 smaller proportion, and the animal liasis is albuminous ; the teeth 
 here agree, in both chemical and physical cj^ualities, with horn. 
 
 True teeth consist commonly of two or more tissues, character- 
 ised by the proportions of their earthy and animal constituents, 
 and by the size, form, and direction of the cavities in the animal 
 basis which contain the earth, the fluid, or the vascular i:)ulp. 
 
 The tissue which forms the body of the tooth is called ' dentine,' 
 (^dentinum, Lat. ; zahiibein, zahnsubstanz, Germ. ; Tivoire, Fr., 
 fig. 236, d). 
 
 The tissue which forms the outer crust of the tooth is called 
 ' cement ' (ceementum, crusta petrosa, Lat., ib. e). 
 
 The third tissue, when present, is situated between the dentine 
 and cement, and is called 'enamel' {encavstmn, adamas, Lat,, ib. <?). 
 
 ' Dentine ' consists of an organised animal basis and of earthy 
 particles : the basis is disposed in the form of compartments or 
 cells, fig. 2.37, h, and extremely minute tubes, ib. a : the earthy 
 particles have a twofold arrangement, being either blended with 
 the animal matter of the interspaces and parietes of the tubes, or 
 contained in a minute granular state in their cavities. The density 
 of the dentine arises principally from the proportion of earth in 
 the first of these states of combination. The tubes contain, near the 
 formative pulp, filamentary processes of that part' ; and convey a 
 
 ' CCXLVI. vol. iv. \>. 929. 
 
360 
 
 ANATOMY OF VERTEBEATES. 
 
 colourless fluid, proliably transuded ' plasma ' : they thus relate 
 not only to the meclianical conditions of the tooth, but to the 
 vitality and nutrition of the dentine. This tissue has few or no 
 canals large enough to admit capillary vessels with the red 
 
 particles of blood, and it has been 
 therefore called ' unvascular dentine.' 
 ' Cement ' always closely corres- 
 ponds in texture with the osseous tissue 
 of the same animal ; and wherever 
 it occurs of sufficient thickness, as 
 upon the teeth of the horse, sloth, or 
 ruminant, it is also traversed, like 
 bone, by vascular canals, fig. 2.36, c 
 When the osseous tissue is excavated, 
 as in dentigerous Vertebrates above 
 fishes, b)' minute radiated cells, form- 
 ing with their contents the ' cor- 
 puscles of Purkinje,' fig. 15, these are 
 likewise present, of similar size and 
 form, in the 'cement,' and are its 
 chief characteristic as a constituent of 
 the tooth. The hardening material 
 of the cement is partly segregated 
 and combined with the parietes of the 
 radiated cells and canals, and is partly 
 contained in disgregated granules in 
 the cells, which are thus rendered 
 white and ojiaque, viewed by reflected 
 light. The relative density of the 
 dentine and cement varies according 
 to the ]iroportion of the earthy material, and chiefly of that jDart 
 which is combined with the animal matter in the walls of the 
 cavities, as compared with the size and number of the cavities 
 themselves. In the complex grinders of the elephant, the masked 
 boar, and the capybara, the cement, which f(_)rms nearly half the 
 mass of the tooth, wears down sooner than the dentine. 
 
 The ' enamel,' fig. 23.5, r, is tlie hardest constituent of a tooth, 
 and, consequently, the hardest of animal tissues; but it consists, 
 like the other dental substances, of earthy matter arranged by 
 organic forces in an animal matrix. Plere, however, the earth is 
 mainly contained in the canals of the animal mcmltranc ; and, in 
 mammals and rc])ti]es, completely fills those canals, which are com- 
 ])aratively wide, whilst (licir parietes are of extreme tenuity. The 
 
 Magnified section of incisor. Horse ; 
 c comeut, d dentine, e enamel, v. 
 
DENTAL TISSUES. 
 
 3G1 
 
 2-7 
 
 hardening salts of the enamel are not only present in far greater 
 j)roportiou than in the other dental tissues ; but, in some animals, 
 are peculiarly distinguished by the presence of fluate of lime. 
 
 Teeth vary in number, size, form, structure, modifications of 
 tissue, position, and mode of attach- 
 ment, in ditferent animals. They 
 are principally adapted for seizing, 
 tearing, dividing, pounding, or grind- 
 ing the food ; in some they are 
 modified to serve as weapons of 
 offence and defence ; in others, as 
 aids in locomotion, means of anchor- 
 age, instruments for uprooting or 
 cutting down trees, or for transport 
 and working of building materials ; 
 
 ihey are characteristic of age and " '" ^ ^ 
 
 sex ; and in man they have secondary relations sulDservient 
 beauty and to speech. 
 
 Teeth are always most intimately related to the food and habits 
 of the animal, and are therefore highly interesting to the physiol- 
 ogist. They form for the same reason most important guides to 
 the naturalist in the classification of animals ; and their value, as 
 zoological characters, is enhanced by the facility with which, from 
 their position, they can be examined in living or recent animals. 
 The durability of their tissues renders them not less available to 
 
 238 
 
 to 
 
 Magnified section uf niolai", Megathei-iuni ; v vasotlentiue, t dentine, c cement, vi. 
 
 the palaeontologist in the determination of the nature and affini- 
 ties of extinct species, of whose organisation they are often the 
 sole remains discoverable in the deposits of former jieriods of the 
 earth's history. 
 
 The simplest modification of dentine is that in which capillary 
 tracts of the primitive vascular pulp remain uncalcified, and per- 
 
362 
 
 ANATOMY OP VERTEBRATES. 
 
 239 
 
 1 of tooth of Cachalot, half natural 
 size. y. 
 
 manently carry red blood into the 
 substance of the tissue. These 
 so-called ' medullary ' or ' vascu- 
 lar' canals present various dis- 
 positions in the dentine which 
 they modify, and which is called 
 ' vaso-dentine.' It is often com- 
 bined with true dentine in the 
 same tooth ; e.g. in the scalpri- 
 form incisors of certain Rodents,' 
 the tusks of the Elephant,^ the 
 molars of the extinct Megathe- 
 rium, fig. 238, V. 
 
 A third kind of dentine is 
 where the cellular basis is ar- 
 ranged in concentric layers around 
 the vascular canals, and contains 
 ' radiated cells ' like those of the 
 osseous tissue : it is called ' osteo- 
 dentine,' fig. 2.39, o. The transi- 
 tion from dentine to vaso-dentine, 
 and from this to osteo-dentine, is 
 gradual, and the resemblance of 
 osteo-dentine to true bone is very 
 close. 
 
 The chemical comjiosition of 
 teeth is exemplified in the sub- 
 joined analyses of those organs 
 and their tissues from species of 
 the different vertebrate classes : — 
 
 
 MAN' 
 
 [,TOX 
 
 ox 
 
 diOCOI-nLE 
 
 PIKE 
 
 
 _S 
 
 " 
 
 i 
 
 s 
 
 g 
 
 S 
 
 
 c- 
 
 s 
 
 h. 
 
 
 
 rt 
 
 
 
 
 
 
 c 
 
 S 1 o b rt 
 
 
 
 
 
 
 
 
 
 
 
 
 P 
 
 W 
 
 k-i 
 
 H 
 
 Q 
 
 H 
 
 O 
 
 ft 
 
 o 1^^. 
 
 
 
 
 
 
 
 
 
 
 
 
 of fiiKite of lime . 
 
 
 
 S3-3:l 
 
 fiS-oT 
 
 81 -Sn 
 
 SS-7:i 
 
 63-i;i) 
 
 53-3n 
 
 63-98; 
 
 (';irb(iii;Tte of lime . 
 
 :;■:;!; -i-:i7 
 
 ;MKi 
 
 2-ilJ 
 
 7-00 
 
 !)■:!:! 
 
 1-n 
 
 11-30 
 
 fi"2i) 
 
 2-.V1 
 
 riiosjiliate of magnesia . 
 
 l-lis |-:i| 
 
 ■I-lM 
 
 3'7ll 
 
 0-<13 
 
 1-20 
 
 O-llll 
 
 10-2-) 
 
 D-1)0 
 
 n-73 
 
 SllltK 
 
 O's:; (i-s> 
 
 O'Ti 
 
 (l-lij 
 
 0-1)1 
 
 IVIM 
 
 O-S-J 
 
 1-34 
 
 1-4-2 
 
 0-97 
 
 f 'tiomlrinc .... 
 
 'Jciill :[-;iii 
 
 :ll'.-.7 
 
 ll';l!l 
 
 .■SO-71 
 
 C-ii(i 
 
 31 -SI 
 
 ■27 -in; 
 
 •2S-1S 
 
 30-(;0| 
 
 
 D-m! (I'-iii 
 
 il-r.' 
 luo-iin 
 
 a 1 race 
 
 IVSL' 
 
 0-OL' 
 
 0-113 
 100-00 
 
 0-711 
 100-00 
 
 0-7li 
 
 1-18' 
 
 liin-ni) 
 
 mO'Or 
 
 lim-oo 
 
 10()a)0 
 
 100 a 111 
 
 100-00 
 
 100-00 
 
 ' V. J). Wo. 
 
 V. p. 043. 
 
DENTAL TISSUES. 
 
 363 
 
 The examples arc extremely few, and peculiar to the class 
 Pisces, of calcified teeth wliich consist of a sing-lc tissue, and this is 
 always a modification of dentine. Tlie large pharyngeal teeth oF 
 the AVrassc (Lahrus) consist of 
 a very hard kind of unvascular 
 
 2^0 
 
 ,,flr|Wfff'1"IWmir»(»,,,,^^ 
 
 til rM 
 
 I th rl Hill us 
 
 dentine. Fig. 240 shows a ver- 
 tical section of one of these teeth, 
 supported upon the vascular 
 osseous tissue of the pharyngeal 
 bone : p is the pidp cavity. 
 
 The next stage of complexity 
 is where a portion of the dentine 
 is modified by vascular canals. 
 Teeth, thus composed of dentine 
 and vaso-dentine, are very com- 
 mon in fishes. The hai'd dentine 
 is always external, and holds the 
 place, and performs the office, of 
 enamel in the teeth of higher 
 animals ; but it is only analogous 
 to enamel, not the same tissue. 
 Fig. 241 exemplifies this struc- 
 ture in a longitudinal section of the tooth of a Shark (Lriiuna). 
 
 The mtilars of the Dugong (^HaUcore) are coni])osed of dentine 
 and cement . the latter substance forming a thick outer layer, 
 fig. 242, c. 
 
 In the teeth of the Cachalot (Phi/scter) the pulp-ca\ ity of the 
 growing tooth becomes filled up by osteodentine, the result of a 
 modified calcification of the dentinal pulp ; when the tooth presents 
 three tissues, as shown in fig. 239, in which c is the thick external 
 cement, d the hard dentine, and o the osteodentine ; sometimes 
 developed in loose stalactitie-shaped nodules. 
 
 In the teeth of the Sloth, and its great extinct congener, the 
 Megatherium, the hard dentine is reduced to a thin layer, fig. 2.38, 
 t, and the chief bulk of the tooth is made up of a central body of 
 vaso-dentine, ib. v.. and a thick external crust of cement, ib. c. 
 
 Besides the number of constituent tissues teeth become 'complex' 
 in structure by the proportion and disposition, chiefly inflection, 
 of more or fewer of those tissues. 
 
 Certain fishes and the extinct ' Labyrinthodont ' reptiles ex- 
 hibit this complexity in a remarkable degree. In fig. 243, the 
 tooth of tlic Lahj/rinthodon salainandro'idcs feel)ly indicates its 
 singular structure by the longitudinal striie. But every streak is 
 
364 
 
 ANATOMY OF VERTEBRATES. 
 
 241 
 
 a fissure, into which a thin outer layer of cement, fig. 244, c, is 
 reflected into the body of the tooth, following the sinuous wavings 
 
 of the lobes of dentine, d, which 
 diverge from the central pulp-cavity, a. 
 The inflected fold of cement, c, runs 
 straight for about half a line, and then 
 becomes wavy, the waves rapidly in- 
 creasing in breadth as they recede from 
 the periphery of the tooth ; the first two, 
 three, or four undulations are simple ; 
 then their contour itself becomes 
 broken by smaller or secondary waves 
 these become stronger as the fold ap- 
 proaches the centre of the tooth, when 
 it increases in thickness, and finally 
 terminates by a slight dilatation or 
 loop close to the pulp-cavity, from 
 which the free margin of the inflected 
 fold of cement is separated by an 
 extremely thin laj^er of dentine. The 
 number of the inflected converrrino; 
 folds of dentine is about fifty at the 
 middle of the crown of the tooth 
 figured, but is greater at the base. 
 All the inflected folds of cemeut at 
 the base of the tooth have the same 
 complicated disposition with increased 
 extent ; but, as they approach their ter- 
 mination towards the upper part of the tooth, they also gradually 
 diminish in breadth, and consequently penetrate to a less distance 
 into the substance of the tooth. Hence, in such a section as is 
 delineated, fig. 244, it will be observed that some of the convo- 
 luted folds, as those marked c, extend near to the centre of the 
 tooth ; others, as those marked c', reach only about half way to 
 the centre ; and those folds, c" , which, to use a geological ex- 
 pression, are ' cropping out,' penetrate to a very short distance 
 into the dentine, and resemble, in their extent and simplicit}^ the 
 converginc; folds of cement in the fanirs of the tooth of tlie 
 Ichthyosaurus and Lepidostcns. 
 
 The disposition of the dentine is still more complicated than 
 that of the cement. It consists of a slender, central, conical 
 column, excavated by a conical pulp-ca^'ity for a certain distance 
 from the base of the tooth ; and this column sends radlatinn; out- 
 
 section of tooth of a Shark (Lamna), 
 
 magn. ; v vaso-4entiiie, d gano-dentine. 
 
DENTAL TISSUES. 
 
 3C5 
 
 wards, from its circumference, a scries of vertical plates, wliicli 
 divide into two once or twice before tliey terminate at the 
 peri])licry of the tooth. 
 
 Each of these diverging and dichotomising plates gives off 
 throughout its course smaller processes, which stand at right 
 
 242 
 
 .Section of tootii of IJugong ; A, n.atura] size; It, niagilifl(?Ll ; c/, dentil 
 
 angles, or nearly so, to the main plate ; they are generally oppo- 
 site, but sometimes alternate ; many of the secondary plates or 
 processes, which are given off near the centre of the tooth, also 
 divide into two before they terminate; and their contour is seen, 
 in the transverse section, to jjartake of all the undulations of the 
 folds of cement which invest and divide the dentinal plates and 
 processes from each other. 
 
 The dental pulp-cavity is reduced to a mere line about the 
 upper third of the tooth, but throughout its whole extent fissures 
 radiate from it, corresponding in numljcr with the radiating plates 
 of dentine. Each fissure is continued along the middle of each 
 plate, dividing where this divides, and extending along the middle 
 of each bifurcation and process to within a short distance of the 
 line of cement. The pulp-fissure commonly dilates into a canal 
 
3G6 
 
 ANATOMY OF VERTEBRATES. 
 
 243 
 
 at the origin of the lateral processes of the radiating plates, before 
 it divides to accompany and penetrate those processes. 
 
 The main fissures or radiations 
 of the pulp- cavity extend to with- 
 in a line or half a line of the 
 periphery of the tooth, and sud- 
 denly dilate at their terminations 
 into spaces, which, in transverse 
 section, are subcircular, oval, or 
 piyriform, p : the branches of the 
 radiating lines, which are conti- 
 nued into the lateral secondary 
 plates or processes of the dentinal 
 lamella3, likewise dilate into simi- 
 lar, and generally smaller spaces. 
 All these spaces, or canals, in the 
 living tooth, must have been oc- 
 cupied by corresponding processes 
 of the vascular pulp : they consti- 
 tute as many centres of radiation 
 of the fine tubes, which, with 
 tlieir uniting clear substance, 
 constitute the dentine. ' 
 
 An analogous complexity is 
 produced by numerous fissures, 
 radiating from a central mass of 
 vasodentine, which more or less 
 fills up the pvilp cavity of the 
 
 TooLll ..[aL:ili,\ 
 
 inilrin, natural pi/.e; a line i 
 LtUjn. V. 
 
 seemingly simple conical teeth. 
 
 fig. 245, of the extinct ' Dendro- 
 dont ' fishes. 
 
 A portion of the transverse section, a, fig. 245, magnified, 
 fig. 24G, shows the fissures diverging from the pulp-cavity, /', and 
 its reticulate extensions, and sending small branches into the den- 
 tinal lamella;. 
 
 These lateral offsets subdivide into a few short ramifications, 
 like the branches of a shrub, and terminate in irregular and 
 somewhat angular dilatations, simulating Ica-^-es, but which resoh-e 
 themselves into radiating fasciculi of dentinal tubes. There are 
 from fifteen to twenty-ti\e or thirty-six of these short aud small 
 lateral brauelies on each side of the main ravs. 
 
 V. I']), mr. -217, pi. C,4a, 04n. 
 
DENTAL TISSUES. 
 
 3G7 
 
 Purtion of tvansvL^ 
 
 .sc sectinii 
 mtigu. 
 
 (if luoLh of LribyriliUiddo 
 
 A third kind of complication is pr(xliiced by an aggregation of 
 many simple teeth into a single mass, fig. 247. 
 
 The examjjlcs of these 
 truly compound teeth are 
 most common in the class 
 of Fishes, but the illustra- 
 tion here selected is from 
 the Mammalian class. 
 Each tooth of the Cape 
 Ant-cater ( Orifcteropus) 
 presents a simple form, is 
 deeply set in the jaw, 
 but without dividing into 
 fangs ; its broad and flat 
 base is porous, like the 
 section of a common cane. 
 The canals to which these 
 jiores lead contain pro- 
 cesses of a vascular pulp, 
 and are the centres of ra- 
 diation of as many independent series of dentinal tulniles. Each 
 tooth consists of a congeries of long and slender prismatic 
 columns of dentine, cemented together by their ossified ca])sules. 
 Fig. 247 is part of a transverse secti(.)n of such compound tooth, 
 showing c the cement, d the dentine, p the 
 pidji-cavity of the denticles, and d' a section 
 of one of the denticles just Ijeyond its bifur- 
 cation. 
 
 In the series of tissues, ' cement ' and 
 ' dentine,' under its diverse modifications, 
 rank with osteine. Enamel is a tissue per 
 se : it might he compared to calcified cpi- 
 derm ; but, in the teeth of Fishes, there are 
 intermediate gradations of structure which 
 link enamel to dentine, and this to bone. 
 
 The general form of the matrix or forma- sul i 
 
 tive organ of teeth, and the relative position of the dentinal pulp 
 to its product, liear a close resemldance to tlic foimative organ 
 of hair and bristle. In these, however, the papilla or pulp is 
 de^'eloped from the skin, in teeth from the mucous membrane. 
 
 Teeth further agree with the extravascular appendages of the 
 skin in being shed and reproduced, sometimes once, sometimes 
 frequently, during the lifetime of the individual. In some 
 
 245 
 
 € ® i 
 
368 
 
 ANATOMY OP VERTEBRATES. 
 
 instances, as with certain dermal appendages, the reproduction of 
 the tooth is uninterrupted, or continuous. A tooth, when fully 
 formed, is subject to decay, but has no inherent power of 
 reparation. 
 
 246 
 
 Portion of transverse section of tooth of a Denilroi-lus, mapil. T. 
 
 Thus teeth are analogous to epidermal and horny parts in their 
 mode of developement, in their shedding and reproduction, and 
 in their exjjosure to outward influences ; but the antlers of deer 
 are similarly exposed, and are likewise shed and renewed, yet, 
 lilvc the teeth and horn-cores of the ox, they are classed with 
 the osseous tissues. 
 
 § 70. Teeth of Fishes. — In this class of Vertebrates the teeth, 
 whether we study them in regard to their number, form, substance, 
 structure, situation, or mode of attachment, offer a greater and 
 more striking series of varieties than do those of any other class 
 of Animals. 
 
 As to number, they range from zero to countless quantities. 
 The Lancelet, the Ammocete, the Sturgeon, fig. 125, 22, 32, the 
 Paddle- fish, and the whole tmler of Lo/i/io/jnnie/i ii , avc edentulous. 
 The Myxinoids, fig. 248, have a single pointed tooth, «, on the 
 roof of the mouth, and two serrated dental jilatcs, h, on the 
 tongue. The Tencli has a singk^ grinding-tooth on the occijiut, 
 
TEETH or FISHES. 
 
 309 
 
 »&- 
 
 /.i 
 
 .?ff-* 
 
 fig'. 250, c, opposed to two dentigerous pharyngeal jaws, d, d, 
 below. Ill the Lcpidosircu a single maxilhuy dental plale, 
 hg. 251, II, is o]i[)osed to a single mandibular one, h, and there are 
 two small dentieles on the nasal bone, c. In the extinet Sharks 
 with crushing teeth, called Ceratudus and Ctenodus, the jaws were 
 armed with four teeth, two above and 217 
 
 two below.' In the Chim;\;r;c two £s:y<;rS^\ 
 
 mandibular teeth are opposeil to four . ^ 
 
 maxillary teetli.^ From this low point 
 the number in ditferent Fishes is })ro- 
 gressively multiplied until, in the 
 Pike, the Siluroids, fig. 252, and many 
 other fishes, the mouth becomes 
 crowded with innmnerable teeth. 
 
 With respect to form, I may pre- 
 mise that as organised beings with- 
 draw tliemselves UKH'e and more, in 
 their ascent in the scale of life, from 
 the influence of common physical 
 agents, so their parts progressively 
 deviate from geometrical figures : it 
 is only, therefore, in the lowest ver- 
 tebrated class that we find teeth in the 
 f(.)rm of perfect cubes, and of j)rlsms 
 or jilates with three sides (^Blijlcfes), four sides ( Scancs), five, or six 
 sides (^MijUohutcs, fig. 249). The cone is the most connnon form in 
 Fishes: such teeth may be slender, sharj)- ojg 
 
 pointed, and so minute, numerous, and closely 
 aggregated, as to resemble the plush or pile 
 of A'eh'ct ; these are called ' villifbrm teeth ' 
 (di'/ifes villiformes, dents en velours^); all the 
 teeth of the Perch arc of this kind : when the 
 teeth are equally fine and numerous, but 
 longer, they are called ' ciliiform ' {denies 
 ciliifunnes) : when the teeth are similar t<^, but t "' ^ ^' ' "^^f 
 rather stronger than these, they are called ' setiform ' (denfes siii- 
 fornies, dents en hroase) : conical teeth, as close set and sharp 
 pointed as the villiform teeth, but of larger size, are called ' rasp- 
 teeth ' (dentes riiduliformes, dents en I'ape or en cardes, fig. 252 ) ; 
 the Pike presents such teeth on the back part of the vomer : tlie 
 teeth of tlie Sheat-fish {Silurus glanis) jiresent all the gradations 
 
 ' Y. pi. 22. = V. fil, 28. 
 
 ' The French terms are those us&l l>y Ciivicr in xxiii. passim. 
 
 VOI-. I. B H 
 
 s^J*.-- 
 
 ■ J. •' i» J » 
 
 octiou i>f 1,1. nth Of Onjdcrojiii!' 
 mayn. v. 
 
370 
 
 ANATOMY or VERTEBRATES. 
 
 249 
 
 Jaws and teeth iMijUohdcs). 
 
 between the villiform and raduliform types. Setiform teeth 
 are common in the Fishes thence called Clifetodonts;' in the 
 
 genus Citharina they bifurcate at 
 their free extremities ; in the genus 
 Platax they end there in three di- 
 verging points, and the cone here 
 merges into the long and slender 
 cylinder, fig. 253. 
 
 Sometimes the cone is compressed 
 into a trenchant blade : and this may 
 be pointed and recurved, as in the 
 Murana ; or barbed, as in Tricldurus, 
 and some other Scomberoids ; or it 
 may be bent upon itself, like a tenterhook, as in the fishes thence 
 called Goniodouts.^ In the Bonito may be perceived a progressive 
 
 thickening of the base of 
 2»'^ the conical teeth : and this 
 
 beinor combined in other 
 predatory fishes with in- 
 creased size and recurved 
 direction, they then resem- 
 ble the laniary or canine 
 teeth of carnivorous quad- 
 rupeds, as we see in the 
 large teeth of the Pike, in 
 the Lophius, fig. 260, and 
 in certain sharks, fig. 263. 
 The anterior diverging 
 ,j,jj ^ grajipling teeth of the wolf- 
 
 fish form stronger cones ; 
 blunting, flattening, and expansion of the 
 apex, observable in different fishes, the 
 cone gradually changes to the thick and 
 short cylinder, such as is seen in the back 
 teeth of the wolf-fish, and in similar grind- 
 ing and crushing teeth in other genera, 
 whether feeders on sea-weeds or on crusta- 
 ceous and testaceous animals. The grind- 
 ing surface of these short cylindrical teeth 
 may be convex, as in the Sheep's-head 
 fish {Sarffus); or flattened, as in the 
 pharyngeal teeth of the A\'rasse {TMbnis, fig. 25-4). Sometimes 
 tlie hemispheric teeth arc so numerous, and spread over so broad a 
 
 ' Xahri, a bristle ; uSois, a tooth. = Voivta. nii niiglc ; nSovs, n tooth. 
 
 and by 
 
 Tcctli (.f Lopkl.i.<ln 
 
TEETH OE FISHES. 
 
 371 
 
 252 
 
 surface, as to resemble a pavement, as in tlie pharyngeal bones of 
 
 the Wrasse or Rock-fish (Lahrus, fig. 254) ; or they may be 
 
 so small, as well as numerous {denies (/run/formes), as to give a 
 
 granvilated surflice to the part of the mouth 
 
 to which they are attached (premaxillaries 
 
 of Cossj/phus).^ A progressive increase of 
 
 the transverse over the vertical diameter may 
 
 be traced in the molar teeth of difixjrent 
 
 fishes, and sometimes in those of the same 
 
 individual, as in Lahrus, until the cylindrical 
 
 form is exchanged ibr that of the depressed 
 
 plate. Such dental j)lates {dentes luinelU- 
 
 formes) may be found, not only circular, 
 
 [)ut elliptical, oval, semilunar, sigmoid, ol)- 
 
 long, or even square, hexagonal, pentagonal, 
 
 or triangular ; and the frrindino- surface may 
 
 present various and beautiful kinds of sculj)- 
 
 turino-. The broadest and thinnest lamelli- 
 
 form teeth are those that form the complex 
 
 grinding tubercle of the Diodon, fig. 257, 
 
 b. The front teeth of the Flounder and Sai-gus 
 
 present the form of compressed plates, at 
 
 least in the crown, and are dentes incisivi. 
 
 Palatine bone ri 
 {Silai-as). 
 
 Numerous wedjie- 
 
 shaped dental plates {denies cuneati) are set vertically 
 
 25t 
 
 th 
 
 253 
 
 Handibulnrteolli. 
 liiau'iiillcd iJ'kitiu:!. \ 
 
 Inferior uliaryii)joall)ono and teeth {LabrnsL v. 
 
 upper pharyngeal bone of the Parrot-fish {Scants, fig. 255). 
 A thin lamella, slightly curved like a finger-nail, is the singular 
 form of tooth in an extinct genus of fishes, thence called 
 Fetalodus. Sometimes the incisive form of tooth is notched 
 in the middle of the cutting edge, as in Sarr/iis unimaculatus. 
 Sometimes the edge of the crown is trilobate {Aplodactijhis, 
 fio-. 256V Sometimes it is made nulnquelobate by a double 
 
 I V. pi 45, fig, 1. 
 
 11 15 2 
 
372 
 
 ANATOMY OF VERTEBRATES. 
 
 ii]iC'rior lii]£ir.\ 
 t(.'Otli i.-v 
 
 Botcli on each side of tlie large middle lobe (Boops). In the 
 li)i'niidable Sca-jiikc (S])/i>/ra'ria Barracuda) the crown of each 
 tooth, large and small, is produced into a compressed and sharp 
 2.5,3 point, and resembles a lancet. Sometimes 
 
 the edges of such lancet-shaped teeth are 
 finely serrated, as in Priodon, and the great 
 Sharks of the genus Curcharias, the fossil 
 teeth of which indicate a species ( Carch. 
 3[i'r/alodon) sixty or seventy feet in length. 
 The lancetted form is exchanged for the 
 stronger spear-shaped tooth in the Sharks 
 of the eenus Lamna, fi<x. 260 ; and in the 
 allied great extinct Otodus, as in the small 
 Porbeagle, similarly shaped, but stronger, 
 piercing and cutting teeth were complicated 
 by one or more accessory compressed cusps on 
 each side of their base, like the jMalay crease. 
 With respect to situation, the teeth, in 
 Sharks and Hays, are limited to the bones 
 (maxillary and mandibular), which form the 
 anterior ajicrture of the mouth : in the 
 Carp and cnlicr Cyprinoids the teeth are confined to the bones 
 (pharyngeal and Ijasioccijiital) which circumscribe the posterior 
 aperture of the mouth. The \yrasses {Lahruf:) and 
 the Parrot-fishes (^S'cflrM*) have teeth on the pre-max- 
 illary and pre-maudibular, as well as on the upper 
 and lower pharyngeals ; both the anterior and 
 piMtcrior apertures of the mouth being thus pro- 
 vided with instruments for seizing, dividing, or com- 
 minuting the food, the grinders being situated at 
 the pharynx. In most fishes teeth are developed 
 also in the intermediate parts of the oral ca^itv, 
 as on the palatines, the vomer, the hyoid bones, 
 the Ijrancliial arches ; and, though less commonly, on the pte- 
 rygoids, the entojitcrygoids and 
 the sphenoids. It is very rare to 
 find teeth developed on the true 
 superior maxillary bones ; but the 
 Herring and Salmon tribes, some 
 of the Ganoid Fishes, and the 
 great Sudis, fig. 86, i>i, arc ex- 
 ani]ilcs of this ajiproaeh to the 
 higher Vertebrates. Among the 
 anomalous positions of teeth may 
 
 2J6 
 
 Frmil (I'cMi of -\ 
 tlnrtylus. v. 
 
TEETH OF ELSUE;: 
 
 373 
 
 1)C cited, besides tlic nasal teeth of the Lepidoshcn, fig. 251, e, 
 and the occipital alveolus of tlie Carp and Tencli, fig. 250, the 
 marginal alveoli of the prolonged, depressed, well ossified rostrum 
 of the Saw-fish (PHstls, fig. 65). In the I..ampreys, fig. 1.38, and 
 in Hcloxtuniiift (an osseous fish), most t>f tlie teeth are attaclied to 
 the lips. Lastly, it is peculiar to tlic class /-"/.sees, amongst A^crte- 
 hrates, to offer examples 
 
 of teeth develo]>ed in the '-"^ 
 
 median line of the mouth, 
 as in the pal.ite of the 
 JNIyxincs, fig. 248, «; 
 or crossing the symphy- 
 sis of the jaw, as in 
 KoUdanns, Hcjjiiiiius, and 
 jSL/Vwhah'x, fig. 2-49. 
 
 Nor is the mode less 
 varied tlian the place of 
 attachment. Tlie teeth 
 of Lojiluns, Pieciliii., 
 Anabh-ps, are always 
 moveable. In most 
 fislies they are anchy- 
 losed to the jaws by con- 
 tinuous ossificatiou from 
 the base of the dental ^ - —- 
 
 pulp. Sometimes we "- n.-akurr.u-r.,t-r,.h „..,„„,, „„„.,v»^„.o. r. 
 find, not tlic base, but 
 one side, of the tooth anc]i3'loscd to the al\e(jlar border of the 
 
 ^' 
 
 
 
 4 
 
 ; t 
 ^ 
 
 
 w 
 
 ^v 
 
 ■•■•.^ 
 
 \ 
 
 y, 
 
 i 
 
 n 
 
 25a 
 
 J 
 
 Kriiinii ,.r llic Jiiiv "]' llic-' raiTiil-ii.^li, slld^ilrj I lie ] in >s IVfS . ll dull i i Utlll. V. 
 
 law ; and the teeth oppose each other by their sides instead 
 
&74 
 
 ANATOMY OF VERTEBRATES. 
 
 260 
 
 PorLioli of tlie jaw of Lopliiiis pisratnring, showing the lign- 
 mciitons attaclimcnt of tlic tot'tli. v. 
 
 of tliciv summits (^Sca?-?is, fig. 2,59); in Pimelodus, however, 
 where the tcetli are thus attached, the crown is bent down 
 in the upper teeth, and bent up in the lower ones, at right angles 
 
 to the fang, so that they 
 oppose each other by the 
 normal surfaces. Certain 
 teeth of recent and fossil 
 cartilaginous fishes have 
 their base divided into 
 processes like fangs, but 
 these serve for the attach- 
 ment of ligaments, and 
 are not set in bony sockets 
 like the true fangs or 
 roots of the teeth of Mam- 
 mals. 
 
 The base of anchylosed 
 teeth is, at first, attached 
 to the jawbone by liga- 
 ment; and in the Cod-fish, AYolf-fish, and some other spe- 
 cies, as calcification of tlie tootli })rogresses towards its base, 
 the sul)jacent portion of the jawbone receives a stimulus, and 
 
 developes a process corres- 
 ponding in size and form 
 with the base of the tooth : 
 for some time a thin layer 
 of ligamentous substance 
 intervenes, but anchylosis 
 usually takes pdace to a 
 greater or less extent before 
 the tooth is shed. Most of 
 
 nhriis). \. 
 
 the teeth of the Lophius re- 
 tain the primitive connection ; the ligaments, fig. 260, f?, of the large 
 internal or posterior teetli of the upper and lower jaws, radiate on 
 tlie corresponding sides of the bone, the base of the tooth resting 
 on a conformable alveolar process. The ligaments do not permit 
 tlic tooth to be bent outward beyond the vertical position, but 
 yield to pressure in the contrary direction, by which the point of 
 the tootli may be directed towards the back of the mouth, as at c; 
 tlie instant, however, tliat the jiressnre is remitted, the tootli 
 returns tlirongh the elasticity of the bent ligaments, as by the 
 action of a spring, into its usual erect position, h ; tlio deglutition 
 of the prey of this voracious Ksh is thus facilitated, and its escape 
 
 201 
 
 Tcolh of tho Wrasse (Cr. 
 
TEETH OF FISHES. 375 
 
 prevented. The broad and generally bifureate bony base of the 
 teeth of Sharks is attached by lig-ament to the semiossified crust 
 of the eartilaghious jaws, fig. 263 ; but they have no power of 
 erecting or depressing the teeth at will. The small and closely 
 crowded teeth of Rays are also connected by ligaments to the 
 subjacent maxillary and mandibular membranes. The broad tes- 
 selated teeth of the ALijVtdhates have their attached surface longi- 
 tudinally grooved to afford them better hold-fast, and the sides of 
 the contiguous teeth are articulated together by serrated or finely 
 undulating sutures, a structure unique in dental organisation. 
 The teeth of the Spliyrana are examples of the ordinary im- 
 plantation in sockets, with the addition of a slight anchyhjsis of the 
 base of the fully-formed tooth with the alveolar parietes ; and the 
 compressed rostral teeth of the Saw-fisli, fig. 65, are deeply 
 implanted in sockets. In the latter the hind margin of their base 
 is grooved, and a corresponding ridge from the back part of the 
 socket fits into the groove, and gives additional fixation to the 
 tooth. Some implanted teeth in the present class have their 
 hollow base further supported, like the claws of the feline tribe, 
 upon a bony process arising from the base of the socket ; tlie in- 
 cisors of the Balistes, e. g. afford an example of this double or 
 reciprocal gomphosis.' In fact, the whole of this pai't of the 
 organisation of fishes is replete with beautiful instances of design 
 and instructive illustrations of animal mechanics. The vertical 
 section of a pharyngeal jaw and teeth of the ^Vrasse (Labnis) 
 would afford the architect a model of a dome of unusual strength, 
 and so supported as to relieve from pressure the floor of a vaulted 
 chamber beneath. The base of the dome-shaped tooth, fig. 2-iO, 
 ]j, is slightly contracted, and is implanted in a shallow circular 
 cavity ; the rounded mai-gin of which is adapted to a circular 
 groove in the contracted part of the base ; the margin of the 
 tooth which immediately transmits the pressure of the bone, is 
 strengthened by an inwardly projecting convex ridge. The 
 masonry of this inner buttress, and of the dome itself, is composed 
 of hollow columns, every one of which is placed so as Ijcst to 
 resist or transmit in the due direction the external pressure. 
 The floor of the alveolus is thus relieved from the office of sus- 
 taining the tooth : it forms, in fact, the roof of a lower vault, in 
 which the germ of a successional tooth, fig. 261, b, is in course of 
 developcment. The superincumbent pressure is exclusively 
 sustained by the border of the alveolus, whence it is transferred to 
 
 ' V. \t. b-2, pi. 40. 
 
37G ANATOMY OP VERTEBRATES. 
 
 the Wcills diviJing the vaulted cavities containing the germs of the 
 new teeth ; the roofs of these cavities yield to the absorljcnt 
 process consequent on the growth of the new teeth without 
 materially weakening the attachment of the old teeth, and without 
 the new teeth Ijcing subjected to any pressure until their growth 
 is sufficiently advanced to enable them to bear it with safety; by 
 this time the sustaining borders of the old alveolus are under- 
 mined, and the old worn-down tooth is shed. 
 
 The dental system of tlie Vv^olf-fish {^Anarrhidias Lupus), is 
 adapted for feeding on hard Crustacea and testacea. But, in 
 order to secure the capture of the shell-fish, the teeth of the 
 Wolf-fish are not all crushers ; some present the laniary type, 
 with the apices more or less recurved and blunted by use, 
 and consist of strong cones spread abroad, like grappling-hooks, 
 at the anterior jiart of the mouth.' 
 
 Tlic premaxillary teeth are conical, and arranged in two rows. 
 There are three large, strong, diverging laniaries at the anterior 
 end of each premandibular bone, and immediately behind these 
 an irregular nnmljcr of shorter and smaller conical teeth, which 
 gradually excliange this form for that of large obtuse tubercles; 
 these extend Iwckward, in a double alternate series, along a great 
 part of the alveolar border of the bone. Each palatine bone 
 su]:)ports a double row of teeth, the outer ones being conical and 
 straight, and from four to six in number ; the inner ones two, 
 tliree, or four in number, and tuljerculate. The lower surface of 
 the vomer is covered l)y a double irregularly alternate series of 
 the same kind fif large crushing teeth as those at the middle of 
 the premandibular. All the teeth are anchylosed to more or less 
 developed alveolar eminences, like the anterior teeth of the 
 Lop]dus. 
 
 From the enormous develojiement of the muscles cif the jaws, 
 and the strength of the shells of the whelks and other testaeca 
 whicli are cracked and crushed Ity the teeth, their fracture and 
 displacement must obviously be no unfrequent occurrence ; and 
 most specimens of the jaws of the AVolf-fish exhibit some of the 
 teeth separated at the line of ancliylosis, or broken oif above the 
 base. 
 
 Willi regard to the tiuhstcnicc of the teeth of Fishes, the 
 modifications of dentine, called vaso-dentine and osteo-dentine, 
 ])rcdominate mueli more tlian in tlic higher Vertcl.)rates, and tliey 
 thus more closely resemble the bones which support them. The 
 
 ' V. pi. r,n, ei. 
 
TEETH OF FISHES. 377 
 
 teeth of most of the Chfctodonts are flexible, cL-istic, and composed 
 of a yellowish subtransparent albuminous tissue ; such, likewise, 
 are the labial teeth of the Ilelostome, the premaxillary and 
 mandibular teeth of the Goniodonts, and of tlie percoid genus 
 Trtchiidon. In the Cyclostomes the teeth consist of a denser 
 albuminous sidjstance. The upper pharyngeal molar of the Carj) 
 consists of a peculiar brown arid semitransparcnt tissue, hardened 
 by salts of liine and magnesia. The teeth of the Flying-fish 
 {E.ioca'tus) and Sucking-fish ( Rcmora) consist of osteo-dentine. 
 In many Fislies, e. g. the Acfmtliurus, S'jiki/ircna, and certain 
 Sharks {Lanina, fig. 241), a base, or body of osteo-dentine, is 
 coated l.\y a layer of true dentine, d, but of unusual liardness, like 
 enamel: in Prloiu>doii this hard tissue predominates. In tlic 
 Liihriis the i)haryngeal crushing teeth consist wholly of hard or 
 unvascidar dentine, fig. 240. In most Pyenodonts and Ccstra- 
 ciouts, and many other Fishes, the body of the tooth consists of 
 ordinary unvascular dentine, covered by a modification of gano- 
 dentine. In Sartpix and Baliste-^ the body of the tooth consists 
 of true dentine, and the crown is covered by a thick layer of a 
 denser tissue, differing from the ' enamel ' of Mammalia only in 
 tiic more complicated and organised mode of de})osition of tlie 
 earthy salts. The ossification of the cajisulc of the complex 
 matrix of these teeth covers the enamel vtdth a thin coating of 
 ' cement.' In the pharyngeal teeth of the Scarus a fourth sido- 
 stanee is added by the ossification of the base of the pulji after 
 its smnmit and periphery have been converted into hard dentine ; 
 and the teeth, fig. 262, thus composed of cement, c, enamel, c, 
 dentine, d, and osteo-dentine, are the most complex in regard to 
 their substance that have yet been discovered in the aiumal 
 kingdom. 
 
 The tubes wliich convey the capillary vessels through tlie 
 substance of the osteo- and vaso-dentine of the teeth of Fishes 
 were early recognised, on account of their comparatively large 
 size; as by Andre, e.g. in the teeth of Araiithurus,^ An({ by 
 Cuvier and Von Born in the teeth of the Avolf-fish and other 
 si)eeies. Lecuwenlioek had also detected the much finer tid>es 
 of the peri])heral dentine of the teeth of the haddock.^ These 
 'dentinal tubnli ' are given oft' from the parietes of the vascular 
 canals, and bend, divide, and subdivide rapidly in the hard Ijasis- 
 tissue of the interspaces of those canals in osteo-dentine ; the 
 dentinal tubuli alone are found in true dentine, and they have a 
 
 ' cc-XLvn. " cciLVjii., p luO:j. 
 
378 ANATOMY OF VERTEBRATES. 
 
 straighter and more parallel course, usually at right angles to the 
 outer surface of the dentine. Those conical teeth which, when 
 fully formed, consist wholly or in great part of osteo-dentine or 
 vaso-dentine, always first appear with an apex of hard or true 
 dentine. In some Fishes the simple central basal pulp-cavity of 
 such teeth, instead of breaking up into irregular or parallel 
 canals, sends out a series of vertical plates from its periphery, 
 which, when calcified, give a fluted character to the base of the 
 tooth, e. g. in Lepidosteus oxpn'usJ This is the first step in the 
 pattern of complication which attains its maximum in Labyrinth- 
 odonts and Dendrodonts, figs. 244, 246. 
 
 Thus, with reference to the main tissue of tooth, we find not 
 fewer than six leading modifications in Fishes : hard or true 
 dentine {Sparoids, Lahroids, Lophius, Balistes, Pycnodonts, 
 Piionodon, Sphi/rcena, Megaliclithys, Rhizodus, Diodon, Scants), 
 osteo-dentine ( Cestracion, Acrodus, Lcpidosiren, Ctenodus, Hyhodus, 
 Percoids, Scmnoids, Cottoids, Gobioids, and many others), vaso- 
 dentine (^Psammodus, ChimcBroids, Pristis, Myliohates), plici-dentine 
 {Lophius, Holoptychius, Lepidosteus oxi/urus, at tlie base of the 
 teeth), labyrintho-dentine [Lepidosteus platijrldnus, Botliriohqns), 
 and dcndro-dentine (Dendrodus) ; besides the compound teeth of 
 the Scnrus and Diodon. 
 
 One structural modification may prevail in some teeth, another 
 in other teeth, of the same fish ; and two or more modifications 
 may be present in the same tooth, arising from changes in the 
 process of calcification and a persistency of portions or processes 
 of the primitive vascular pulp or matrix of the dentine. 
 
 The dense covering of the beak-like jaws of the Parrot-fishes 
 {ScarKS, figs. 258, 259) consists of a stratum of prismatic denticles, 
 standing almost vertically to the external surface of the jaw-bone. 
 It is peculiarly adapted to the habits and exigences of a tribe of 
 Fishes wliich browse upon the lithophytes that clothe, as with a 
 richly tinted carpet, the bottom of the sea, just as the Euminant 
 quadrupeds crop the herbage of the dry land. 
 
 The irritable bodies of the gelatinous polvpes which constitute 
 t!ic food of these Fishes retract, when touched, into their star- 
 shaped stony shells, and the Scari consequently rccjulre a dental 
 apparatus strong enough to break oif or scoop out these calcareous 
 recesses. The jaws are, therefore, prominent, short, and stout, 
 and the exposed portions of tlie premaxillaries and premandibulars 
 
 ' Wyman, American Journal of Natural Sciences, Oct. 1843. Cuvier lias given 
 an accurate view of tlio plaited structure of the base of the Wolf-iisli's teeth in pi. 3'.', 
 lif:^. 7, of his Lc(^ons il'Analomie CunniarOe, 180.*). 
 
TEETH OF FISHES. 379 
 
 are encased by the above-described complicated dental covei-ing. 
 The polypes and their cells are reduced to a pulp by the action of 
 the pharyngeal jaws and teeth, that close the posterior aperture of 
 the mouth. The superior dentigerous pharyngeals, fig. 255, present 
 the iorm of an elongated, vertical, inequilateral, triangular plate : 
 the upper and anterior margin forms a thickened articular surface, 
 convex from side to side, and playing in a corresponding groove or 
 concavity upon the base of the skull ; the inferior boundary of the 
 triangle is the longest, and also the broadest ; it is convex in the 
 antcro-posterior direction, and flat from side to side. On this 
 surface the teeth are unplanted, and in most species they form 
 two rows : the outer one consisting of very small, the inner one 
 of large, dental plates, which are set nearly transversely across 
 the lower surface of the upper pharyngeal bones and teeth, 
 in close apposition, one behind the other : their internal angles 
 are ])roduced beyond the margin of the bone, and interlock with 
 those of the adjoining bone when the pharyngeals are in 
 their natural position ; the smaller denticles of the outer row 
 are set in the external interspaces of those of the inner row. 
 The single inferior pharyngeal bone consists principally of an 
 ol^long dentigerous plate,' supported by a strong, slightly curved, 
 transverse, osseous bar, the extremities of which cxj^and into thick 
 obtuse processes for the implantation of the triturating muscles. 
 A lontritudinal row of small oval teeth alternatino- witli the 
 large lamelliform teeth, like those of the superior pharyngeals, 
 bounds the dentigerous plate on each side ; the intermediate space 
 is occupied exclusively by the larger wedge-shaped teeth, set 
 vertically in the bone, and arranged transversely in alternate and 
 pretty close-set series. 
 
 The dental plates are developed in wide and deep cavities in 
 the substance of the posterior part of the lower, and of the ante- 
 rior part of the upper pharyngeal bones. The teeth exhibit 
 progressive stages of formation as they approach those in use ; and, 
 as their formation advances to completion they become soldered 
 too-ether by ossification of their respective capsules into one com- 
 iiound tooth, which soon becomes anchylosed by ossification of the 
 dentinal pulp to the pharyngeal bone itself. 
 
 In the dentine of the pharyngeal teeth of the Scarus the 
 dentinal tubes average a diameter of .j^lo i) of an inch, and are 
 seiiarated by interspaces equal to twice their own diameter. The 
 course of these tubes is shown in fig. 262, (/, in which they are 
 
 ' V. pi. 51, fig. 3. 
 
380 
 
 ANATOMY OF VERTEBRATES. 
 
 exposed by a vertical section through the middle of two of 
 tlio superior denticles. Each tube is minutely undulated: 
 it dichotomises three or four times near its termination, sends 
 off many fine lateral branches into the clear uniting sub- 
 stance, and finally terminates in a scries of minute cells and 
 inosculating loops at the line of junction with the enamel. 
 This substance, fig. 202, e, is as thick as the dentine, and 
 consists of a similar comljination of minute tubes and a clear 
 connecting substance. The tubes may be described as com- 
 mencing from the peripheral surface of the tooth to which they 
 
 stand at right angles, and, having ]n'oceedcd parallel to each otlier 
 Iialfway towards the dentine, they then begin to divide and sub- 
 divide, tlie branches crossing each other obliquely, and finally 
 terminating in the cellular boundary between the enamel and 
 dentine. 
 
 In the progress of attrition, tlie thin coat of cement resulting 
 from the ossification of the capsule is first removed i'rom tlic apex 
 of the tootli, tlien (lie enamel constituting tliat a])ex, next the 
 dentine, and, finally, the coarse central ccllnlar bone, supporting 
 tlic holliiw tddth : and thus is jiroduced a triturating surface of 
 foiu- sul)s(ances oi' dillerent derives cif dciisitv. 'I'lie enamel. 
 
TEETH OF EISIIES. 381 
 
 being the haixlcst element, appears in tlie form of elliptical trans- 
 Tcrse ridg'cs, inclosing the dentine and central bone : and external 
 to the enamel is the cement, c, which Ijinds together the different 
 denticles. 
 
 There is a close analogy between the dental mass of the Scarns 
 and the complicated grinders of the Elephant, both in form, 
 striieturc, and in the reproduction of the component denticles in 
 horizontal succession. But in the iish the ct.nnplexity of the 
 tiituratiiig surface is greater than in the mammal, since, from the 
 mode in which the wedge-sliapcd denticles of the Scarus arc 
 im])lanted upon, and anchylosed to, the processes of the sup)portlng 
 bone, this likewise enters into the formation of the masticatoiy 
 surface when the tooth is worn down to a certain point. 
 
 The proof of the efficacy of the complex masticatory apparatus 
 above descriljcd is aftbrded by the contents of the alimentary 
 canal of the Scari. The intestines arc usually laden with a chalky 
 })ulp, to which the coral dwellings have been reduced. 
 
 Dcrelopunicnt. — As might l^e supposed, by the above-defined 
 'S'aried and predominating vascular organisation in the teeth of 
 Fishes, and the jjassage from non-vascular dentine to vascular 
 dentine in the same tooth, the developement of dentine by centri- 
 petal metamorpliosis and calcification of the pulp was determined 
 by oliservations made on the developement of the teeth in the 
 present class.' 
 
 It is interesting to observe in it the process arrested at each of 
 the well-marked stages through which the developement of a 
 ]Mamn)alian tooth passes. In all Fishes the first step is the simple 
 production of a soft ^'ascular piapilla fr(jm the free surface of the 
 buccal mendjrane : in Sharks and Rays these papiilaj, fig. 382, c, 
 do not proceed to sink into the substance of the gum, but are 
 covered by caps of an opposite free fold of the buccal memljrane : 
 these cai)s do not contract any organic connection with the papilli- 
 form matrix, but, as this is converted into dental tissue, ib. h, the 
 tooth is gradually withdrawn from the extraneous protecting cap, 
 to take its place and assume tlie erect position on the margin of 
 the jaw, fig. 2G.3, a. Here, therefore, is represented the first and 
 transitory ' papillar)' ' stage of dental developement in j\Iammals : 
 and the simple crcscentic cartilaginous maxillary plate, d, with 
 the open groove behind containing the germinal papiila3 of the 
 teeth, offers iu the Shark a magnified representation of the earliest 
 condition of the jaws and teeth in the human cinbryo. 
 
 In manv Fishes, e. g. Loplvins, li!sox, the dental pa[)ill;e become 
 
 ' L>cxxix, p. 7S-!. 
 
ANATOMY OF VERTEBRATES. 
 
 263 
 
 buried in the membrane from which they rise, and the surface 
 to which their basis is attached becomes the bottom of a 
 
 closed sac : but this sac 
 does not become inclosed in 
 the substance of the jaw ; 
 so that teeth at diiferent 
 stages of growth are 
 brought away with the 
 thick and S(jft gum, when 
 it is stripped from the 
 jaw-bone. The final fixa- 
 tion of teeth, so formed, 
 is effected by the develope- 
 ment of ligamentous fibres 
 in the submucovis tissue be- 
 tween the jaw and the base 
 of the tooth, which fibres 
 become the medium of con- 
 nection between those parts, 
 either as elastic ligaments 
 or by continuous ossifica- 
 tion. Here, therefore, is 
 represented the ' follicular ' 
 stage of the developement 
 of a Mannnalian tooth : 
 but the ' eruptive ' stage 
 takes place without pre- 
 vious inclosure of the follicle and matrix in the substance of the 
 jaw-bone. 
 
 In BaUstes, Scarus, Sphyraiia, the Sparoids, and many other 
 Fishes, the formation of tlie tcctli presents all the usual stages 
 which have been observed to succeed each other in the dentition 
 of the higher Vertebrates : the papilla sinks into a follicle, becomes 
 surrounded by a capsule, and is then included within a closed 
 alveolus of tlie growing jaw, figs. 259, 261, c, where the develope- 
 ment of the tooth takes place and is followed by the usual eruptive 
 stages. A distinct enamel-pulp is developed from the inner 
 surface of the capsule in BaUstes, Scarus, Sarffus, and Chri/so- 
 jihi'i/s. 
 
 In the formidable Barrncada {Sj)Ii>/>-ana) the loss or fracture of 
 the lancet-shaped teeth, in the conflict witli a struggling ]irey, is 
 re|iaired by an uninterrupted succession of new puljis and toctli. 
 The existence of these is indicated by tlie foramina, which are 
 
 Verticnl section of jaw and tuL'tb [Laii, 
 
TEETH OE FISHES. 383 
 
 situated immediately posterior to, or on the inner margin of, the 
 sockets of the teeth in jjlace : these foramina lead to alveoli of 
 reserve, in which the crowns of the new teeth, in different stages 
 of developement, are loosely embedded. It is in this position of 
 the germs of the teeth that the Sphyrasnoid fishes, both recent 
 and fossil, mainly differ, as to their dental characters, from the rest 
 of the Scomberoid family. 
 
 It is interesting to observe that the alternate teeth are, in 
 general, contemporaneovisly shed: so that the maxillary armour is 
 thus preserved in an effective state. The relative position of 
 the new teeth to their predecessors, and their influence vij)on 
 them, resembles, in the Sphi/rccna, some of the jihenomena which 
 will be dcscril:)ed in the dentition of the Crocodilian Reptiles. 
 To the Crocodiles the jiresent voraciovis Fish also approximates in 
 the alveolar lodgement of the teeth : but it manifests its ichthyic 
 character in the anchylosis of the fully-developed teeth to tlieir 
 sockets, and still more strikingly in the intimate structure of the 
 teeth. 
 
 In all Fishes the teeth are shed and renewed, not once only, as 
 in JMammals, but frequently, during the whole course of their 
 lives. The maxillary dental plates of Lepidosrren, the cylindrical 
 dental masses of the Chlmajroid and Edaphodont Fishes, and the 
 rostral teeth of Pristis (if these modified dermal spines may be so 
 called), are, perhaps, the sole examples of ' permanent teeth ' to 
 be met with in the whole class. 
 
 When the teeth are developed in alveolar cavities, they are 
 usually succeeded by others in the vertical direction, as in the 
 pharyngeal bones of the Labroids, fig. 261 : but sometimes 
 they follow one after the other, side by side, as in the Scarolds, 
 fig. 259, c. In Eeptlles and Mammals the successional teeth 
 owe the origin of their matrix to the budding out from the cap- 
 sule of their predecessors of a ctecal process, in which the 
 papillary rudiment of the dentinal pulp is developed ; but, in 
 the great majority of Fishes, the germs of the new teeth are 
 developed, like those of the old, from the free surface of the 
 buccal membrane throughout the entire period of succession : 
 a circumstance peculiar to the present class. The Angler, the 
 Pike, and most of our common Fishes, illustrate this mode of 
 dental reproduction ; it is very consincuous in the cartilaginous 
 Fishes, figs. 263 and 264, in which the whole phalanx of their 
 numerous teeth is ever marching slowly forwards in rotatory 
 progress over the alveolar border of the jaw, the teeth being 
 successively cast off as they reach the outer margin, and new 
 
384 
 
 ANATOMY OF VERTEBRATES. 
 
 teeth rising from the mucuous membrane behind the rear rank of 
 the phalanx. 
 
 This endless succession and decadence of the teeth, together 
 with the vast numbers in which they often coexist in the same 
 
 264 
 
 Skull and ja^vs of Pnit Jufk.soii shrirlc (Cc-<lrac:nii PjiiH/ipin, ^bowinij the furiii.^ anj ai'raiic-cment of 
 
 Fish, illustrate the law of Vegetative or Irrelative Eopctition,' as 
 it manifests itself on the first introduction of new organs in the 
 Animal Kingdom, under which light we must view the aljovc- 
 described organised and calcified preparatory instrviments of 
 digestion in the lowest class of the vertebrate series. 
 
 At the extreme limit of the class of Fishes, and connecting 
 that class with the Reptiles, stands the very remarkable genus, 
 the dental system of which is figured in cut 251. This consists 
 of two small, slender, conical, sharp-pointed, and slightly recurved 
 teeth, Avhich project downward from the nasal bone, c, and of 
 str(mg trenchant dental jdates, anchylosed with the alveolar border 
 of the upper, a, and lower, h, jaws, in each of which the plate 
 is divided at the middle, or symphysial line, so as to form two 
 distinct lateral teeth. The office of the two laniariform teeth is 
 to pierce and retain the nutriti\o substance or prey which is 
 
TEETH OF REPTILES. 385 
 
 afterwards divided and comminuted by the strong maxillary 
 dental g^^)lates. 
 
 § 71. Teeth of Reptiles. — If we compare tlie dental system 
 of Lepidosiren with that in Batrachia, it is to the larval state 
 of the Anourans that an analogy may be found: the tadpole of 
 the Frog having its maxilla and mandibula each sheathed with a 
 continuous horny trenchant covering. Were this sheath actually 
 dentinal in tissue and united to the jaw-bone, the resemblance to 
 the Lepidosiren would be closer : but it is never calcified, and is 
 shed during the progress of the metamorphosis.' The Siren 
 alone, among the perennibranchiates, retains the sheath upon 
 the extremity of the upper and lower jaws ; it consists of a firm 
 albuminous tissue, and becomes harder than horn. But these 
 trenchant mandibles, which play upon one another like the blades 
 of a pair of curved scissors, are associated with numerous small 
 but distinct true teeth, which are grouped together to form a 
 rasp-like surface on each half of the divided vomer, and which 
 beset the alveolar border of the splenial element of the mandible 
 below. 
 
 The whole order of Chelonia is edentulous, as well as the family 
 of Toads {Bufonid(B) in the order Batrachia ; certain extinct 
 genera of Saurians were likewise edentulous, e. g. Rliynchosaurus 
 and Oudenodon.'^ 
 
 In the Tortoises and Turtles the jaws are covered by a sheath 
 of horn, which in some species is very dense ; its working surface 
 is trenchant in the carnivorous species, but is thick, variously 
 sculptured, and adapted for both cutting and bruising in the 
 vegetable feeders. The developement of the continuous horny 
 maxillary sheath commences, as in the Parrot tribe, from a 
 series of distinct papillas, Avhich sink into alveolar cavities, 
 regularly arranged (in Trionyx) along the margins of the upper 
 and lower jaw-bones : these alveoli are indicated by the persist- 
 ence of vascular canals long after the originally separate tooth- 
 like cones have become confluent, and the horny sheath com- 
 pleted. 
 
 The teeth of the dentigerous Saurian, Ophidian, and Batrachian 
 Reptiles are, for the most part, simple and adapted for seizing 
 and holding, but not for dividing or masticating, their food. The 
 Siren alone combines true teeth with a horny maxillary trenchant 
 sheath, like that of the Chelonian Eeptiles. 
 
 1 The lart'e dental plates of Lepidosiren have their nearest homologues in those of 
 the extinct fish called Ceratodus (v. pi. 22, fig. 2). 
 
 2 ccxxiii. p. 54, pi. I. fig. 1. 
 
 VOL. I. *^ *^ 
 
386 ANATOMY OF VERTEBRATES. 
 
 With respect to number, in no existing Reptile are the teeth 
 reduced so low as in certain Mammals and Fishes ; nor, on the 
 other hand, are they ever so multiplied as in many of the latter 
 class. Myohatrachus paradoxus, an Australian Frog, has but two 
 teeth in the premaxillary bones. The extinct Dicynodont Reptiles 
 of South Africa had two long tusks implanted in the upper jaw, 
 fig. 271.' Some species of Amphisbana {A. alba), with fifteen 
 teeth in the upper jaw and fourteen in the lower jaw, and certain 
 Monitors ( Varanus), with sixteen teeth in the upper and fourteen 
 in the lower jaw exemplify a low number of teeth amongst 
 existing Reptiles ; and certain Batrachians, with teeth ' en cardes ' 
 at the roof of the mouth, or which have ujDwards of eighty teeth 
 in each latei'al maxillary series, present the opposite extreme. 
 Rarely, however, is the number of the teeth so fixed and 
 determinate in any Reptile as to be characteristic of the 
 si^ecies, and still more rarely have the individual teeth such cha- 
 racters as to be determined homologically from one species to 
 another. 
 
 With respect to situation, the teeth may be present on the jaws 
 only, i. e. the maxillary, the premaxillary, and mandibular bones, 
 as in tlie Crocodiles, fig. 95, and many Lizards : or upon the jaws 
 and roof of the mouth : and here either upon the pterygoid bones, 
 as in the Iguana, fig. 98, D, 24, and Mosasaur; or upon both 
 palatine and jiterygoid bones, as in most Serpents, fig. 266, 20, 24; 
 or upon the vomer, as in most Batrachians, fig. 265, I; or upon both 
 vomerine and pterygoid bones, as in the Axolotl ; or upon the 
 vomerine and sphenoid bones, as in Salamandra glutinosa. With 
 respect to the marginal or jaw teeth, these may be absent in the 
 premaxillary bones, as in many Serpents, fig. 266, 22 : or they 
 may bo present in the upper and not in the lower jaw, as in most 
 Frogs: or in both upper and lower jaws, as in the tailed 
 Batrachians : and among these they may be supported, upon the 
 lower jaw, by the prcmandibular or dentary piece, as in the 
 Salamanders, Menopome, Amphiume, Proteus : or upon the 
 splcnial piece, as in the Siren: or upon both splcnial and pre- 
 mandibular bones, as in the Axolotl. The palatine and pterygoid 
 teeth may, in the Batrachians, be arranged in several rows, like 
 the ' dents en cardes ' of Fishes. The sphenoid and splcnial teeth 
 are always so arranged in the few species that possess them. The 
 intermaxillary, maxillary, and prcmandibular teeth are uniscrial, 
 or in one row, with the exception of the Crecilia and the extinct 
 
 ' ci.viii. vo). vii. ]i, 59. 
 
TEETH OF REPTILES. 387 
 
 Labyrinthoclonts, which have a dolible row of teeth at the anterior 
 part of the lower jaw. 
 
 riie teeth of Reptiles, with few exceptions, present a simple 
 conical form, with the crown more or less curved, and the apex 
 more or less acute. The cone varies in length and thickness ; its 
 transverse section is sometimes circular, but more commonly 
 elliptical or oval : and this modification of the cone may be traced 
 through every gradation, from the thick, round, eanine-like tooth 
 of the Crocodile to the sabre-shaped fang of the Varanus, the 
 Megalosaur, and the Cladeiodon.' Sometimes, as in the fully 
 formed teeth of the Megalosaur, one of the margins of the com- 
 pressed crown of the tooth is trenchant, sometimes both are so ; 
 and these may be simply sharp-edged, as in the Varanus of Timor, 
 or finely serrated, as in the great Varanus, the Cladeiodon, and 
 the Megalosaur.^ 
 
 The outer surface of the crown of the tooth is usually smooth ; 
 it may be polished, as in the Leiodon, or imijressed with fine 
 lines, as in the Labyrinthodon, fig. 243, or raised into many 
 narrow ridges, as in the Pleiosaur and Polyptychodon, or 
 broken by a few broad ridges, as in the Iguanodon, fig. 27.3, or 
 grooved by a single longitudinal furrow, as in some Serpents, 
 fig. 269, C.3 
 
 The cone is longest and its summit sharpest in the Serpents : 
 from these may be traced, chiefly in the Lizard tribe, a pro- 
 gressive shortening, expansion of the base, and blunting of 
 the apex of the tooth, until the cone is reduced to a hemi- 
 spherical tul)ercle, or plate, as in Oijdodus, fig. 272, and, in a more 
 remarkable degree, in the extinct shellfish-eating Saurian, called 
 Placodus.'^ 
 
 In the Pleiosaur the dental cone is three-sided, with one of the 
 angles rounded off. The posterior subcompressed teeth of the 
 Alligator, fig. 275, present a new modification of form ; here they 
 terminate in a mammillate summit, suj^ported by a slightly con- 
 stricted neek. In the tooth of the Hylajosaur the expanded 
 summit is flattened, bent, and spear-shaped, with the edges 
 blunted. But the expansion of the crown is greatest in the 
 subcomijressed teeth of the extinct Cardiodon and the existing 
 lo-uanas, the teeth of which are farther complicated by having 
 the margins notched. The great Iguanodon had the crown of 
 the tooth expanded both in length and breadth, and combining 
 
 ' V. pi. 62 a, fig. 4. ^ lb, pi. 65. COL. vol. iv. figs. 209, 210. 
 
 - lb. fig. 6 c. ' CXLIII. p. 169. 
 
 c c 2 
 
388 ANATOMY OF VEETEBEATES. 
 
 marginal dentations with longitudinal ridges: this tooth, fig. 273, 
 j)rescnts the most complicated external form as yet discovered in 
 the class of Reptiles. 
 
 In no Reptile does the base of the tooth ever branch into fangs. 
 
 Attachment. — As a general rule, the teeth of Reptiles are 
 anchylosed to the bone which supports them. When they con- 
 tinue distinct, they may be lodged either in a continuous groove, 
 as in the Ichthyosaur,' or in separate sockets, as in the Plesiosaur 
 and Crocodilians, fig. 275. The base of the tooth is anchylosed 
 to the wall of a moderately deep socket in the extinct Megalosaur 
 and Thecodon. In the Labyrinthodonts and CteciliEe, among the 
 Batrachians, in most Ojihidians, and in the Geckos, Agamians, 
 and Varanians, among the Saurians, the base of the tooth is 
 imbedded in a shallow socket, and is confluent therewith. 
 
 In the Sciucoids, the Safeguards ( Tejus), in most Iguanians, in 
 the Chameleons and many Lacertian reptiles, the tooth is anchy- 
 losed by an olilique surface extending from the base more or less 
 upon the outer side of the crown to an external alveolar plate of 
 bone,^ the inner alveolar plate not being developed. In the Frogs 
 the teeth are similarly but less firmly attached to an external 
 parapet of bone. The Lizards which have their teeth thus 
 attached to the side of the jaw are termed ' Pleurodonts.' In a 
 few Iguanians, as the Istiures and Rhynchocephalus, the teeth are 
 soldered to the margins of the jaws ; and in some large extinct 
 Lacertians, e. g. the Mosasaur and Leiodon, each tooth is fixed 
 ujion a conical process of the alveolar border : these Sauria are 
 termed ' Acrodonts.' 
 
 Such modifications of the attachment of the teeth of Reptiles 
 are adapted to the habits and food of the species ; and they likewise 
 ofi'er an analogy to some of the transitory conditions of the human 
 teeth. There is a period, for example, when the primitive dental 
 papillaj are not defended by either an outer or an inner alveolar 
 process, any more than their calcified homologues, which are con- 
 fluent with the margin of the jaw in the Rhynchocephalus.^ 
 There is another stage in which the groove containing the dental 
 germs is defended by a single external cartilaginous alveolar 
 ridge ; this condition is permanently typified in the Ci/clodus, 
 fig. 272, and most existing Lizards. Next there is developed in 
 the liuman embryo an internal alveolar plate, and the sacs and 
 j)ulps of the teeth sink into a deep but continuous groove, in 
 which traces of trans-^'crsc partitions soon make their appear- 
 
 ' V, pi. 13, lig. 9. = V. pi. 67. 
 
 ' CLViii. pt. 2, jil. 6, figs. 5 & 6, p. 83. 
 
TEETH OF REPTILES. 389 
 
 ance; in the ancient Iclitliyosaur tlie relation of the jaws to 
 the teeth never advanced beyond this stage. Finally, the dental 
 groove is divided by complete partitions, and a separate socket is 
 formed for each tooth ; and this stage of developement is attained 
 in the highest-organised Reptiles, e. g. the Crocodiles, figs. 95, 
 275. 
 
 Substance. — This may be four-fold, and a single tooth may be 
 composed of dentine, cement, enamel, and bone : but the dentine 
 and cement are present in the teeth of all Reptiles. 
 
 In the Batrachians and Ophidians a thin layer of cement 
 invests the central body of dentine, and, as usual, follows any 
 inflections or sinuosities that may characterise its surfiice. Be- 
 sides the outer coat of cement, which is thickest at the base, a 
 generally thin coat of enamel defends the crown of the tooth in 
 most Saurians, and the last remains of the pulp are not tuifre- 
 c^uently converted into a coarse bone, both in the teeth which 
 are anchylosed to the jaw, and in some teeth, as those of the 
 Ichthyosaur, which remain free. The modification called ' vaso- 
 dentine ' is peculiar in the present class to the teeth of the 
 Iguanodon.' 
 
 Structure. — The varieties of dental structure are few in the 
 Reptiles as compared with Fishes or Mammals, and its most com- 
 plicated condition arises from interblending of the dentinal and 
 other substances rather than from modifications of the tissues 
 themselves. In the teeth of most Reptiles the intimate strricture 
 of the dentine is of the hard or unvascular kind, presenting only 
 plasmatic or dentinal tubes, diverging from the pulp cavity, at 
 right angles to the external surface of the tooth. Such dentine 
 may be folded inwardly upon itself, so as to produce a deep longi- 
 tudinal indentation on one side of the tooth ; it is the expansion of 
 the bottom of such a longitudinal deep fold that forms the central 
 canal of the venonr-fang of the Serpent : but its structure remains 
 unaltered ; and although the pulp-cavity, fig. 270, p, is reduced 
 to the form of a crescentic fissure, the dentinal tubes contiime to 
 radiate from it according to the usual law. By a similar inflection 
 of many vertical longitudinal folds of the cement and external 
 surface of the tooth at regular intervals around the entire cir- 
 cumference of the tooth, and by a corresponding extension of 
 radiated processes of the pulp-cavity and dentine into the inter- 
 spaces of such inflected and converging folds, a modification of 
 dental structure is established in certain extinct Reptiles, which, 
 
 ' V. pt 71, Iguanodon. 
 
390 
 
 ANATOMY OF VERTEBRATES. 
 
 TfCLli of Mcuoiiomc ; fc prcmaxiJlniy, I vomerine, 
 X raaxlllaTy 
 
 by the various sinuosities of the interblended folds of cement and 
 processes of dentine, with the partial dilatations of the radiated 
 pulp-cavity, produces the complicated structure which is described 
 at p. 365, and figured in cut 244. 
 
 Developement. — The teeth of Eeptiles are never completed at the 
 
 first or pajiillary stage ; the pulp 
 265 sinks into a follicle, and becomes 
 
 inclosed by a capsule ; and in 
 certain reptiles this becomes 
 more or less surrounded by bone ; 
 but the ' eruptive ' stage, in the 
 sense in which this is usually 
 understood, as signifying the ex- 
 trication of the young tooth from 
 a closed alveolus, is not exem- 
 plified in recent Reptiles, and 
 was rare in extinct ones.' 
 
 The completion of a tooth, 
 with the exception of the Dicy- 
 nodont Reptiles, is soon fol- 
 lowed by preparation for its 
 removal and succession ; the faculty of developing new tooth- 
 germs seems to be unlimited in the present class, and the phe- 
 nomena of dental decadence and replacement are manifested at 
 every period of life ; the number of teeth is generally the same in 
 each successive series, and the diflPerence of size presented by the 
 teeth of different and distant series in the same individual is 
 considerable. 
 
 The new germ is always developed, in the first instance, at 
 the side of the base of the old tooth, never in the cavity 
 of the base ; the crocodiles form no exception to this rule. 
 The poison-fangs of serpents succeed each other from behind 
 forwards ; in almost every other instance the germ of the succes- 
 sional tooth is developed at the inner side of the base of its 
 predecessor. In the Frog the dental germ makes its appear- 
 ance in the form of a papilla developed from the bottom and 
 towards the outer side of a small fissure in the mucous membrane 
 or gum that fills up the shallow groove at the inner side of the 
 alveolar parapet and its adherent teeth : the papilla is soon 
 enveloped l)y a capsular process of the surrounding membrane. 
 vVs the tooth ac(|uires hardness and size, it presses against the 
 
 cxLin. p. 178, pi. ix., liy. 4, (/. 
 
TEETH OF REPTILES. 391 
 
 base of the contiguous attached tooth, causes a progressive 
 absorption of that part, and finally undermines, displaces, and 
 replaces its predecessor. The numlier of nascent matrices of the 
 successional teeth is so great in the Frog, and they are crowded so 
 close together, that it is not unusual to find the capsules of con- 
 tiguous tooth-germs becoming adherent together, as their ossifi- 
 cation proceeds. After a brief maceration, the soft gum may be 
 stripped from the shallow alveolar depression, and the younger 
 tooth-germs in different stages of growth are brought away 
 with it. 
 
 The mode of development of the teeth of serpents does not 
 differ essentially from that of the teeth of the Batrachian above 
 described, except in the relation of the papillaj of the suc- 
 cessional poison-fangs to the branch of the poison-duct that 
 traverses the cavity of the loose mucous gum in which they are 
 developed. 
 
 Some of the peculiarities of the dentition of the Batrachians 
 ha^'e already been noticed, as in the comparison of the Siren 
 with the Le-pidosiren, in which the true amphibian was shown 
 to have numerous teeth on the palate and lower jaw.' The 
 piscine character of rasp-like teeth aggregated in numerous 
 series, is manifested also in the Axolotl,^ upon the palatal region 
 of the mouth, and uj)on the sjilenial or opercular element of the 
 lower jaw ; but the superior maxillary bones are here developed, 
 and also support teeth. The premandibular and the liremaxillary 
 bones, instead of preserving the larval condition of the horny 
 sheath, have their alveolar border armed with a single row of 
 small, equal, fine and sharp-pointed denticles, which are continued 
 above, along the maxillaries ; thus establishing the commence- 
 ment of the ordinary Batrachian condition of the marginal teeth 
 of the buccal cavity. The dentigerous bones of the palate consist 
 of two plates on each side, as in the Siren ; the anterior pair, or 
 vomerine bones, converge and meet at their anterior extremities ; 
 the minute denticles which they support are arranged quincun- 
 cially ; the posterior pair of bones are continued backwards 
 according to the usual disposition of the pterygoids, to abut 
 against the tympanic bones ; the denticles are confined to the 
 anterior part of their oral surface, and resemble in their arrange- 
 ment and anchylosed attachment those of the vomerine series, of 
 which they form the posterior termination. 
 
 In the Menopome, fig. 265, the teeth are small, pointed, in a 
 
 1 V. pi. 62, figs. 5 & 6. Mb. pi. 02, fig. 4. 
 
392 ANATOMY OF VEETEBRATES. 
 
 single row, in each bone ; describing a semicircle, upon the pre- 
 maxillary, k, and maxillary, x, bones : a shorter parallel series is 
 supported on the vomerine bones, U The mandibular series is 
 received into the interspace of the two rows in the upper jaw. 
 
 The Frogs {Ranaf have no teeth on the lower jaw ; but in 
 some species the alveolar edge of this bone is finely notched or 
 dentated, as in the horned Frogs ( Ceratophrys). Dactylethra has 
 maxillary teeth only ; Myohatrachus has but two horizontal pre- 
 maxUlary teeth. Both premaxillary and maxillary bones usually 
 support a long, close-set, single series of small, conical, hollow 
 teeth, of which the apices only jiroject beyond the external alveo- 
 lar ridge to which they are attached. A short transverse row of 
 similar but smaller teeth extends along the posterior border of each 
 vomer. Other dispositions of the vomerine teeth helj) to charac- 
 terise the genera of RanidcB, in a few of Avhich they are wanting ; 
 as, e.g., in Uperoleia, in the slender-armed Frogs (Leptohraclduni), 
 in Oxyglossus, and in some of the Tree Frogs (e.g. Eucnemis), in 
 which the roof of the mouth is edentulous. 
 
 Amongst the most extraordinary examples of extinct reptUes 
 are those which are characterised by the labyrinthic modification 
 of the dental structure above described, and winch, with some 
 affinities to Saurians, combine characters which are essentially 
 those of the order Batrachia. In Labyrinthodon lejjtognuthus, the 
 upper jaw contains a single row of small teeth, about sixty in 
 number, anterior to which are three or four large conical tusks. 
 The apical two thirds of each tooth is smooth, but the basal third is 
 fluted and anchylosed to the outer wall of the socket. The osseous 
 roof of the mouth is principally composed of a pair of broad and 
 flat bones, homologous with the divided vomer in Batrachia, but of 
 much greater relative extent. Each bone supports anteriorly three 
 median small teeth and two outer larger ones, from which a longi- 
 tudinal row of small and equal-sized teeth is continued Ijackward 
 along the exterior margin of the vomer. The whole of this series 
 of vomerine teeth is nearly concentric with the maxillary teeth. 
 
 In Lacertinc reptiles the examples of a row of palatal teeth are 
 rare, and, when present, it is short, and situated upon tlie i^tery- 
 goid Ijoncs, as in the Iguana and INIosasaur. In Batrachians the 
 most common disposition of the palatal teeth is a transverse row 
 placed at the anterior jiart of the divided vomer, as in Frogs, and the 
 Menopome. In the Ampliiumc, the vomerine teeth form a nearly 
 longitudinal scries along the outer margin of the i)alatlno bones. 
 
 ' V. pi. 02, lig. 10. - lb, jil. 62, fig. 10. 
 
TEETH OF EEPTILES. 393 
 
 Tlie Labyrintliodon combines both these dispositions of the joalatal 
 teeth. The lower jaw, like the upper, contains a series of small 
 teeth, with a few larger tusks anterior to them. The sockets of 
 the teeth are shallower than in the upper jaw ; the outer wall is 
 more developed than the inner, and the anchylosed bases of the 
 teeth more nearly resemble, in then- oblique position, those of 
 existing Batrachia. Between the apex and the part where the 
 inflected vertical iblds of the cement commence, the tooth of the 
 Labyrinthodon resembles, in the simplicity of its intimate struc- 
 ture, that of the entire tooth of ordinary Batrachia and most 
 reptiles ; and in the lower or basal half of the tooth the lal^yrinthic 
 structure above described commences, and gradually increases in 
 complexity. 
 
 In the genus Deirodon,^ the teeth of the ordinary bones of the 
 mouth are so small as to be scarcely perceptible ; and they appear 
 to be soon lost. An acquaintance with the habits and food of this 
 species has shown how admirably this apparent defect is adapted 
 to its well-being. Its business is to restrain the undue increase of 
 the smaller birds by devouring their eggs. Now if the teeth had 
 existed of the ordinary form and proportions in the maxillary and 
 palatal regions, the egg would have been broken as soon as it was 
 seized, and much of the nutritious contents would have escaped 
 from the lipless mouth of the snake in the act of deglutition ; Ijut, 
 owing to the almost edentulous state of the jaws, the egg glides 
 along the expanded ojjcning unbroken ; and it is not until it has 
 reached the gullet, and the closed mouth prevents any escape of 
 the nutritious matter, that the egg becomes exposed to instru- 
 ments adapted for its perforation. These instruments consist of 
 the hypapophyses of the seven or eight posterior cervical vertebrce, 
 the extremities of which are capped by a layer of hard cement, 
 and penetrate the dorsal parietes of the oesophagus.^ They may 
 be readily seen, even in very small subjects, in the interior of that 
 tube, in which their points are directed backwards. The shell 
 being sawed open longitudinally by these vertebral teeth, the 
 egg is crushed by the contractions of the gullet, and is carried to 
 the stomach, where the shell is no doubt soon dissolved by the 
 acid gastric juice. 
 
 In the Boa and Pythons, fig. 2G6, the teeth are slender, conical, 
 bent backward and inward above their base of attachment. The 
 premaxillary bone in some, ib. 22, is edentulous ; in most it 
 supports four small teeth; each maxillary bone, ib. 21, has a row 
 
 ' The Coluher scaler of Linna3us ; an arboreal serpent of South Afriea. 
 ^ Jourdan, in ccxlii. t. vi. p. 100. 
 
394 
 
 ANATOMY OF VEKTEBRATES. 
 
 of larger ones, which gradually decrease in size as they are placed 
 further back. There are teeth of similar size and proportions in 
 each j)remandibular bone. These teeth are separated by intervals. 
 
 266 
 
 Dentitinu, upppi" j;iw. Python. ccL. 
 
 from which otlier teeth, similar to those in place, have been 
 detached. Tlie base of each is anchylosed to a shallow alveolus, 
 extending obliquely across the alveolar groove, of which the outer 
 is higher than the inner wall. 
 
 The palatine teeth, ib. 20, are as 
 
 large 
 
 267 
 
 Hoof uf tlic 11 
 
 as the maxillary, and 
 are similarly attached. The 
 pterygoid teeth, ib. 24, 
 which complete the inter- 
 nal dental series on the 
 roof of the mouth, are of 
 smaller size, and gradually 
 diminish as they recede 
 backward. In the inter- 
 spaces of the fixed teeth 
 in both of these bones, the 
 places of attachment of the 
 shed teeth are alwaj's visi- 
 ble ; so that the dental for- 
 mula, if it included the 
 vacated with the occupied 
 sockets, would express a 
 greater number of teeth 
 than arc ever in place and 
 use at the same time. 
 
 Tlie smaller iion-vcno- 
 mous serpents, Co/ithr/do', 
 c. g. ha\'e two rows of teeth 
 on the roof of the mouth. 
 
TEETH OF EEPTILES. 
 
 395 
 
 extending along the palatines and pterygoids. The genus Oli- 
 godon appears to form the sole exception to this rule. In the 
 Dryinus nasutus, a few small teeth are present on the ecto- 
 pterygoid as well as on the pterygoid. 
 
 In Dryoj)M^, Dipsus, and Bucephalus, in which the maxillary 
 teeth increase in size towards the posterior part of the bone, the 
 large terminal teeth of the series are traversed along their anterior 
 and convex side by a longitudinal groove. In the Bucephalus 
 capensis, the two or three posterior maxillary teeth present this 
 structure, and are much larger than the anterior teeth, or those of 
 the palatine and premandibular series. They add materially, 
 therefore, to the power of retaining the prey, and may conduct into 
 the wounds which they inflict an acrid saliva ; but they are not 
 in connection with the duct of an express poison-gland. The 
 long grooved fangs are either firmly fixed to the maxillary bones, 
 or are slightly moveable, according to their period of growth. 
 They are concealed by a sheath of thick and soft gum, and tlieir 
 points are directed backward. The sheath always contains loose 
 recumbent grooved teeth, ready to succeed those in place. 
 
 In most of the Coluhri, each maxillary and premandibular bone 
 includes from twenty to twenty-five teeth. They are less numerous 
 in the genera Tortrix and Homalopsis, and are reduced to a still 
 smaller nimiber in the poisonous serpents, in the typical genera 
 of which the short maxillary 
 bone supports only a single 
 perforated fang. 
 
 The maxillary, fig. 268, p, 
 diminishes in length with the 
 decreasing number of teeth 
 which it supports : the ecto- 
 pterygoid, rJ, elongates in the 
 same ratio, so as to retain its 
 position as an abutment against 
 
 the shortened maxillary ; and ^^_^^^^^_^^ ^^^ ^^^^ p„i,„n.tec.u „r u,c Rau,i.-,™»,.e 
 the muscles implanted into 
 
 the ectopterygoid communicate through it to the maxillary 
 bone the hinge-like movements backward and forward upon the 
 ginglymoid articulations connecting that bone with the prefrontal 
 and" palatine bones. As the fully developed poison-fangs are 
 attached by the same firm basal anchylosis to maxillary sockets, 
 which forms the characteristic mode of attachment of the simple 
 or solid teeth, they necessarily follow all the movements of the 
 superior maxillary bone. When the external pterygoid is rc- 
 
 268 
 
396 ANATOMY OF VERTEBRATES. 
 
 tracted, the superior maxillary rotates backward, and the poison- 
 fanf is concealed in the lax mucous gum, with its point turned 
 backward, fig. 267, lo. When the muscles draw forward the 
 external pterygoid, the maxillary bone is pushed forward, and the 
 recumbent fang withdrawn from its concealment and erected. 
 
 In this power of changing the direction of a large tooth, so that 
 it may not impede the passage of food through the mouth, we may 
 perceive an analogy between the viper and the Lophius ; but in 
 the fish the movement is confined to the tooth alone, and is de- 
 pendent on the mere physical property of the elastic medium of 
 attachment ; in the serpent the tooth has no independent motion, 
 but rotates with the jaw, whose movements are governed by 
 muscular actions. In the fish the great teeth are erect, except 
 when pressed down by some extraneous force. In the serpent 
 the habitual position of the fang is the recumbent one, and its 
 erection takes place only when the envenomed blow is to be 
 struck. 
 
 A true idea of the structure of a poison-fang will be formed 
 by supposing the crown of a simjile tooth, as that of a boa, to 
 be pressed flat, and its edges to be then bent towards each other, 
 and soldered together so as to form a hollow cylinder, or rather 
 cone, oi^en at both ends. The flattening of the fang and its 
 inflection around the poison-duct commences immediately above 
 the base, and the suture of the inflected margins runs along the 
 anterior and convex side of the recurved fang, as shown in 
 fig. 269, A : the poison-canal is thus in front of the pulp-cavity, as 
 shown in the longitudinal section of the fang, fig. 268, y, and 
 fig. 269, B. The basal aperture of the poison-canal, ib. v, is oblique, 
 and its opposite outlet v' is still more so, presenting the form of a 
 narrow elliptical longitudinal fissure, terminating at a short dis- 
 tance from the apex of the fang. In fig. 268, a fine hair is repre- 
 sented as passing through the poison-canal by the duct of the fang. 
 
 The secretion of the poison-gland is conveyed to the basal apertvire 
 of the poison-canal of the fang. AVe may suppose, that as the 
 analogous lacrymal and salivary glands in other animals are most 
 active during particular emotions, so the rage which stimulates the 
 venom-snake to use its deadly weapon must be accompanied with 
 an increased secretion and great distension of the poison-glands ; 
 and as the action of the compressing muscles is contemporaneous 
 with the blow by which the serpent inflicts the wound, the poison 
 is at the same moment injected with force into the Avound from 
 the apical outlet of tlic perforated tang. 
 
 The duct which conveys the poison, althougli it runs throuo-h 
 
TEETH OF REPTILES. 
 
 397 
 
 the centre of a great part of the tooth, is really on the outside of 
 the tooth, the canal in which it is lodged and protected Ijeing 
 formed by a longitudinal inflection of the dentinal parietes of the 
 pulp-cavity, fig. 270, c. This 269 
 
 inflection commences a little 
 beyond the base of the tooth, 
 where its nature is readily 
 apjireciated, as the poison- 
 duct there rests in a slight 
 groove or longitudinal inden- 
 tation on the convex side of 
 the fang, fig. 269, A, B, v ; 
 as it proceeds it sinks deeper 
 into the substance of the 
 tooth, and the sides of the 
 groove meet and seem to 
 coalesce, so that the trace of 
 the inflected fold ceases, in 
 some species, to be percej^ti- 
 ble to the naked eye ; and the fang appears, as it is commonly 
 described, to be jJerforated by the duct of the poison-gland. In 
 the Hi/drophis the groo^'c remains permanently ojien, as in 
 269, C. 
 
 poison-canal it follows that 
 
 roison-faiigs of A, vipi?r ; b, Oulira fin section) ; 
 c. Hyai-oiibi,?. V. 
 
 fig. 
 
 the 
 
 270 
 
 From the position of the 
 transverse section of the 
 tooth varies in form in dif- 
 ferent parts of the tooth : at 
 the base it is oblong, with a 
 large pulp-cavity of a cor- 
 responding form, with an 
 entering notch at the ante- 
 rior surface, fig. 268, c; 
 farther on, the transverse 
 section presents the form of 
 a horseshoe, and the pulp- 
 cavity that of a crescent, the 
 horns of which extend into 
 the sides of the deep cavity 
 of the poison-fang : a little 
 beyond this part the sec- 
 tion of the tooth itself is 
 crescentic, with the horns obtuse and in contact, so as to circum- 
 scribe the poison-canal ; and along the Avhole of the middle four 
 
 Section oj; poison-fang of Cobra, magn. 
 
398 ANATOMY OF VERTEBRATES. 
 
 sixths of the tooth, the section, of which a magnified view is given 
 in fig. 270, shows the dentine of the fang inclosing the poison- 
 canal, and having its own centre or pulp-canal, p, p, in the form 
 of a crescentic fissure, situated close to the concave border of the 
 inflected surface of the tooth. The pulp-cavity disappears, and 
 the jioison-canal again resumes the form of a groove near the apex 
 of the fang, fig. 269, A, B, v' , and terminates on the anterior surface 
 in an elongated fissure. 
 
 The venom-fangs of the viper, rattle-snake, and the Fer-de- 
 lance are coated only with a thin layer of a subtransparent and 
 minutely cellular cement. The disposition of the dentinal tubes 
 is olicdient to the general law of verticality to the external 
 surface of the tooth ; it is represented as seen in the trans- 
 verse section from the middle of the fang in fig. 270. Since 
 the inflected surface of the tooth can be exposed to no other 
 pressure than that of the turgescent duct with which it is 
 in contact, the tubes which jjroceed to the central surface, 
 while maintaininjT their normal relation of the right angle to 
 it, are extremely short ; and the layer of dentine se^oarating the 
 poison-tube from the pulp-cavity is proportionally thin. The 
 dentinal tubes that radiate from the opposite side of the pulp- 
 cavity to the exposed surface b of the tooth are disproportionately 
 long. 
 
 The teeth of Ophidians are developed and completed in that 
 part which forms the original seat of the tooth-germs in all 
 animals ; viz. the mucous membrane or gum covering the alveolar 
 border of the dentigerous bones. The primitive dental papilla in 
 the common harmless snake very soon sinks into the substance of 
 the gum, and becomes enclosed by a capsule. As soon as the 
 deposition of the calcareous salts commences in the apex of the 
 papilla, the capsule covering that part becomes ossified and 
 adherent to the dentine, and the tooth begins to pierce and 
 emerge from the gum before its mould, the pulp, is half com- 
 pleted. Fresh layers of cells are successively added to the base 
 of the pulp, and converted, by their confluence and calcification, 
 into the tubular dentine, until the full size of the tooth is 
 attained, when its situation in the gum is gradually chano-ed, 
 and its base becomes anchylosed to tlie shallow cavity of the 
 alveolar surface of the bone. In the posterior part of the large 
 mucous sheath of the poison-fang, the successors of this tooth 
 are always to be found in difterent stages of developement ; 
 the pulp is at first a simple papilla, and when it has sunk into 
 the gum the succeeding portion presents a depression alon"- its 
 
TEETH OF REPTILES. 
 
 399 
 
 inferior surface, as it lies liorizontally, with the apex directed 
 backward ; tlie capsule adheres to this inflected surface of the 
 pulp ; and the Ijase of the groove of the loose growing poison- 
 lang is brought into the same relation with the duct of the 
 poison gland as the displaced fang, which has been severed from 
 the duct. 
 
 The existing species of Lizards difl:er from those of Crocodiles 
 in the anchylosed condition of the teeth, which present few modi- 
 fications of importance : those that yield most fruit to physiology, 
 and which have most expanded our ideas of the extent of the 
 
 271 
 
 Skull of Dicyiiodnn iaccrticeps, cue .i^.^v. .„^^...^., ,^i,.., 
 
 resources of Nature and the exceptional deviations from what 
 was deemed the rule of structure in the Saurian dentition, 
 have been discovered by the study of the fossil teeth of extinct 
 forms of the order. Amongst these the most extraordinary are 
 those called ' Dicynodonts," from their dentition being reduced 
 
 k 
 
 to one long ana large canine tootn on eacn sicie oi tne upper 
 jaw. These teeth recall, at first sight, the character which the 
 long poison-fangs give, when erected, to the upper jaw of 
 the Rattle snake. The alveolar border of the lower jaw and of 
 the premaxillary p)art of the upper jaw is trencliant, and seems 
 to have been sheathed with horn. The maxillary, fig. 271, 
 21, is excavated by a wide and deep) alveolus, with a circular 
 area, and lodges a long and strong, slightly curved, and sharp- 
 pointed tusk, which projects about two thirds of its length from 
 
 ' From Sis, two, and kw6Sous, the name given by Hippocrates to the canine teeth, 
 and signifying the same idea as their common English denomiuation. 
 
400 ANATOMY OF VERTEBRATES. 
 
 the ojien extremity of the socket ; the two converging, as they 
 descend along the outer side of the compressed symphysis of 
 the lower jaAV. The tusk is principally composed of a body of 
 compact unvascular dentine. The base is excavated by a wide 
 conical pulp-cavity with the apex extending to about one half 
 of the implanted part of the tusk, and a linear tract is continued 
 along the centre of the solid part of the tusk. 
 
 The enamel is thinner than in the teeth of the Crocodile. 
 There is a trace of cement on the exterior of the sections of the 
 implanted base of the tusks. In the lower jaw, ib. 25, 23, the 
 alveolar border of the dentary element presents a smooth and even 
 edge, which seems to have jDlayed like a scissor-blade upon the 
 inner side of the corresponding edentulous border of the upper 
 jaw. In some Dicynodonts {Ptychognatliiis) the symphysis was 
 singularly produced ujJward. 
 
 Until the discovery of the Rlujnchosaurus'^ and Oudenodon, this 
 edentulous and horn-sheathed condition of the jaws was supposed 
 to be peculiar to the Chelonian order among reptiles.^ In the 
 Saurian Dicynodon we find, superadded to the horn-clad man- 
 dibles of the Tortoise, a pair of tusks, borrowed as it were from 
 the mammalian class, or rather foreshadowing a structure which, 
 in the actvial creation, is peculiar to certain members of the 
 hishest-organised warm-blooded anunals. 
 
 In the other Eeptilia, recent or extinct, which most nearly 
 approach the INIammalia in the structure of their teeth, the dif- 
 ference characteristic of the inferior and cold-blooded class is 
 manifested in the shape, and in the system of shedding and suc- 
 cession, of the teeth: the base of the implanted tooth seldom 
 becomes consolidated, never contracted to a point, as in the 
 fangs of most mammalian teeth ; and at all periods of growth 
 one or more germs of teeth are formed Avithin or near the base 
 of the tooth in use, pre2)ared to succeed it, and progressing 
 towards its displacement. The dental armature of the jaws is 
 kept in serviceable order by uninterrupted change and succes- 
 sion ; but the matrix of the individual tooth is soon exhausted, 
 and the life of the tooth itself may be said to be comparatively 
 short. 
 
 The Dicynodonts not only manifest the higher type of free 
 implantation of the base of the tooth in a deep and complete 
 socket, common to Crocodilians, INIegalosaurs, and Thecodonts, 
 but make an additional step towards the mammalian type of 
 
 ' Transactions of the Cambridge Pliilosoiihical Society, vol. vii. part iii. = CLviii. 
 
TEETH OP RErTILBS. 401 
 
 dentition, by maintaining the serviceable state of the tnsk by 
 virtue of constant renovation of the .substance of one and the 
 same matrix, according to tlie principle manifested in the long- 
 lived and ever-growing tush:s of the Walrus, and the scalpriform 
 incisors of the Kodentia. 
 
 Naturalists have availed themselves of characteristics of the 
 dental system to arrange the genera of the squamate Laccrtians. 
 In the first group, the teeth are solid, or without any perma- 
 nent internal cavity, and are anchylosed by their base to the 
 alveolar groove. The species which present this character are 
 called ' Pleodonts.' In the second group, the teeth are excavated, 
 or retain the pulp-cavity, and are less firmly fixed to the jaws, 
 being applied vertically, like piles or buttresses, against the outer 
 alveolar parapet, but not adhering by their base. This grouj) is 
 called ' Coclodonts.' 
 
 The Monitor of South America ( Ttipinanihis teguixiii) is 
 an example of the Pleodont group, in which the premaxillary 
 teeth are ten in number. The maxillary teeth vary from ten 
 to fifteen on each side, and increase in size as they are placed 
 farther back : the hindmost teeth are tricuspid in young indi- 
 viduals, and present the form of simple tubercles in the old 
 Monitors. The mandibular teeth, fifteen to eighteen in number 
 in each ramus, correspond in size and form with those above. 
 In the Coelodont group, the ' Swift lizards ' ( Tachydromus) have 
 the pterygoid bones armed with minute teeth. The teeth on both 
 upper and lower jaws are of larger size, and the hinder ones are 
 tricuspid. The true Lizards {Lacerta) have two kinds of teeth 
 quoad form ; the anterior small, conical, and recurved : the pos- 
 terior larger, and bi- or tri-cuspid. Some species have also 
 pterygoid teeth ; as the common Lacerta agilis. 
 
 In the gigantic fossil Sea-monitor of Maestricht (Mosasaurus) 
 the teeth combine the ' Pleodont ' with the ' Acrodont ' characters. 
 All the teeth are slightly recurved, and their peripheral surface 
 is smooth : the crown is pyramidal, with the outer side nearly 
 plane, or slightly convex, and separated by two sharp ridges from 
 the remaining surface, which forms a half-cone. The larger teeth 
 are implanted upon the premaxillary, maxillary, and premandibular 
 bones ; a series of similarly shaped but much smaller teeth are 
 placed upon the pterygoid bones. 
 
 Most of the smooth-scaled Lizards have small mouths and 
 slender sharp teeth, fitted best for insect food : they are usually 
 confined to the upper and lower jaws ; but the medicinal Scink of 
 ancient pharmacy ( Scincus officinalis) has four or five small obtuse 
 
 VOL. T. D D 
 
402 ANATOMY OF VERTEBRATES. 
 
 teeth upon each pterygoid bone. The chief exception, to the 
 typical dentition of the present family is made by the large 
 scincoid lizards of Australia, which, on that account, have received 
 the generic name of Cycloclus. The dentition of the Cyclodus 
 nigroluteus is exemplified in the lower jaw, fig. 272. In the upper 
 jaw, the single premaxillary bone has depressions for twelve teeth, 
 
 272 
 
 Lowov jaw anj tcctb of Cijd(^(luf; nliiroliLteus. v. 
 
 of which only the alternate ones are usually in place ; they are of 
 very small size, with the fang compressed laterally, and the crown 
 antero-posteriorly, so as to resemble a true incisor in form, the 
 summit sloping to an edge from behind forwards, with the middle 
 of the cutting surface a little produced. Each superior maxillary 
 bone has depressions for fourteen teeth ; the}' quickly increase in 
 size, and exchange their conical for a sub-hemispherical crown ; 
 the eighth to the thirteenth inclusive are the largest teeth ; they 
 are set obliquely, and pretty close together. In the lower jaw 
 there are two small incisors, at the anterior part of each jire- 
 mandibular bone corresponding with those of the premaxillary ; 
 these are succeeded by five or six conical teeth, and the rest 
 correspond in size and form with the tubercvdate molars of the 
 up)per jaw. All the teeth are attached, after the Pleurodont type, 
 by their base and outer margin to shallow depressions on the 
 outer side of the external alveolar parapet. The germs of the 
 successional teeth, c, fig. 272, are developed at the inner side of the 
 base of their predecessors, a, which they excavate, undermine, 
 and displace in the usual manner. 
 
 Certain genera of the Iguanian family of Lizards, e. g. Isfiuriis, 
 Lophyrn.s, Calutes, and Otocri/ptis, have the teeth soldered, like 
 those of Mosnscmrus, to the summit of the alveolar ridge, and 
 thence are called ' Acrodonts : ' in all these lizards the maxillary 
 and mandibular teeth may be divided into anterior laniary and 
 posterior molary teeth. In other Iguanians the teeth are lodged 
 in a common shalloAV oblique alveolar groove, and are soldered 
 to excavations on the inner surface of the outer wall of the 
 groove : these are called ' Plcurodonts.' Most of them possess 
 pterygoid as well as maxillary teeth : bnt the following genera. 
 
TEETH OF EEPTILES. 403 
 
 Hyperanodon, Tropidolejns, Plirynosoma, and CaJlisaurus, are 
 exceptions. 
 
 In the Pleurodont Iguanians, the teeth never present the true 
 laniar_y form ; and, if simply conical, as at the extremes of the 
 maxillary series, the cone is more or less obtuse ; but, in general, 
 it is expanded, more or less trilobate, or dentated along the margin 
 of the crown. The Amhhjrhynchus , a genus remarkable for the 
 marine habits of at least one of the species {Amlilyrlvynclius ater), 
 whose diet is sea-weed, has the tricuspid structure well developed 
 in the posterior teeth. The tj^iical genus of the present family 
 of Saurians {Jguana tuhercidatct) is characterised by the crenate 
 or dentated margin of the crown of the maxillary and premandi- 
 bular teeth, a few of the anterior small ones excepted. The ptery- 
 goid teeth are arranged in two or three irregular rows, resembling 
 somewhat the ' dents en cardes ' of Fishes. In the full-grown 
 Iguana tuherculata there are from forty-seven to forty-nine teeth 
 in both U2)per and lower jaws. The number is less in young- 
 subjects. The two rows of pterygoid teeth are in close order 
 on each side. In the horned Iguana {Metopuceros cornutus) there 
 is a single row of small teeth implanted in each pterygoid bone, 
 
 fig. 98, D, 24. 
 
 The teeth of the Iguanodon, though resembling those of the 
 Iguana, do not present an exact magnified image of them, but 
 dilfer in the greater relative thickness of the crown, its more 
 complicated external surface, and in a modification of the internal 
 structure, by which this huge herbivorous extinct lizard deviates 
 from every other known reptile. 
 
 As in the Iguana, the base of the tooth is elongated, contracted, 
 and subcylindrical ; the crown expanded, and smoothly 273 
 
 convex on the inner side. When first formed, it is 
 acuminate, compressed, its sloping sides serrate, and 
 its external surface traversed by a median longitu- 
 dinal ridge, and coated by a layer of enamel ; but, 
 beyond this point, the description of the tooth of the 
 Iguanodon indicates characters peculiar to that genus. 
 Three longitudinal ridges, fig. 273, traverse the outer 
 surface of the crown, one on each side of the median 
 primitive ridge ; these are separated from each other, 
 and from the serrated margins of the crown, by four 
 wide and smooth longitudinal grooves. In the upper jaw the 
 teeth are less curved, and are thicker transversely to the jaw : 
 the primary ridge is much more prominent. The marginal ser- 
 rations present, under a low magnifying power, the form of 
 
 D D 2 
 
404 ANATOMY OF VERTEBKATES. 
 
 transverse ridges, themselves notched, so as to resemble the mam- 
 mjllated margins of the nnworn plates of the elephant's grinder. 
 These ridges or dentations do not extend beyond the expanded 
 part of the crown : the longitudinal ridges are continued farther 
 down, especially the median ones, which do not subside till the 
 fang of the tooth begins to assume its subcylindrical form. 
 
 At the earlier stages of abrasion, a sharp edge is maintained at 
 the external part of the tooth by means of the enamel which 
 covers, and is restricted to, that surface of the crown. The 
 prominent ridges upon that surface give a sinuous contour to the 
 middle of the cutting edge, whilst its sides are jagged l^y the 
 lateral serrations. The dentine next the enamel is harder than 
 the vaso-dentine of the opposite half of the crown. When the 
 crown is worn away beyond the enamel, it presents a broad and 
 nearly horizontal grinding surface, and another dental substance 
 is Ijrought into use to give an inequality to that surface ; this 
 is the ossified remnant of the pulji, which, being firmer than 
 the surrounding dentine, forms a slight trans\'erse ridge in the 
 middle of the grinding surface. The tooth in this stage has 
 exchanged the functions of an incisor for that of a molar, and is 
 prepared to give the final compression, or comminution, to the 
 coarsely divided vegetable matters, such as might be afforded by 
 the Clafhrarice and similar fossil plants, which are found buried 
 with the Iguanodon. 
 
 In the Crocodilian Monitor ( Varanus hivittatus) the large fixed 
 compressed teeth, of which there may be about seven in each 
 upper maxillary bone and six in each premandibular, are anchy- 
 loscd by the whole of their base and l^y an oblique surfiice leading 
 upwards on the outer side of the tooth to a slight depression on 
 the alveolar surface. The base of the tooth is finely striated, the 
 lines being produced by inflected folds of the external cement, as 
 in the Ichthyosaur and Labyrinthodon, but they are short and 
 straight, as in those of the former genus. The great Varmuts, 
 like the variegated species, manifests its affinity to the Crocodiliaus 
 in the number of successl^'e teeth which are in progress of growth 
 to replace each other ; but, from the position in which the germs 
 of the successional teeth are developed, the more advanced teeth 
 in this species, as in the Varanus varieffafits, do not exhibit the 
 excavations that characterise the same parts of the teeth of the 
 Enaliosaurs and Crocodiles. 
 
 In some extinct Saurians, which, in other parts of their organi- 
 sation, adhere to the Lacertine division of the order, the teeth were 
 implanted in sockets, cither loosely or confluent with the bony walls 
 
TEETH OF BEPTILES. 405 
 
 of the cavity : tliesc are termed the ' Thecodont ' Lacertiaiis : their 
 dental character is seen in the oldest known of all Saiiriaus, viz. the 
 (Frotnrnsaurv,s of tlie Thuringian copper-slates), and the Palao- 
 ■sdiirns of the dolomitic conglomerates near Bristol. The com- 
 pressed Varan ian form of tooth, with trenchant and finely dentated 
 margins, wliicli characterised these ancient Lizards, is continued 
 in the comparatively more recent and gigantic species called Mer/a- 
 /(isiinrua. In this terrestrial carnivorous Reptile tlie teeth, when 
 first protruded above the gum, ]}resentcd a doidDle cutting edge of 
 serrated enamel; the position and line of action were nearly vertical, 
 and, like the two-edged point of a sabre, the teetli cut equally on 
 each side. As the tooth advanced in jirowtli it l)ecame curved 
 jjackward, in the form of a pruning-knife, and tlie edge of serrated 
 enamel was continued downward to the base of the inner and 
 cutting side of the tooth, whilst on the outer side a similar edge 
 descended but a short distance from the point, and the convex 
 ]»n-tion of the tooth became Ijlunt and thick, as the back of a 
 knife is made thick for the purpose of jiroducing strength. The 
 strengtli of the tooth was further increased by tlie expansion of 
 its side. ' In a tooth thus formed for cutting along its concave 
 edge, each movement of the jaw comliined tlie power of the knife 
 and saw : Avhilst the apex, in making the first incision, acted like 
 tlie two-edged point of a sabre. The backward curvature of the 
 full-grown teeth enabled them to retain, like barbs, tlie prey 
 wliich tliey liad penetrated. In these adaptations we see con- 
 trivances wliicli human ingenuity has also adopted in the prepara- 
 tion of various instrimients of art.'' 
 
 The teeth of tlie Mef/alosam- consist of a central body of 
 dentine, with an investment of enamel upon the crown, and of 
 cement over all, but thickest upon the fang. Tlie marginal 
 serrations are formed almost entirely liy the enamel. The remains 
 of the dentinal pulp are converted into a coarse bone in the coni- 
 j)letely formed tooth. 
 
 In most Pterodactyles the teeth arc of one kind, few and far 
 apart, fig. Ill, witli long, slender, compressed, slightly recurved, 
 pointed crowns ; l)ut some, from the more ancient secondary 
 deposits, show, behind a few teeth of tlie above iireliensile 
 cliaracter, a close-set row of small lancet-shaped teeth : such 
 modification characterises the genus DiinorjilKidon. 
 
 The teeth of the Ichtliyosaur have a simple more or less 
 acutely conical form, with a long and, usually, expanded or 
 
 ' Biicklantl, Bridgcwatcr Treatise, vol. i. p. 237. 
 
406 ANATOMY OF VEKTEBRATES. 
 
 ventricose base, or implanted fang. They are confined to the 
 premaxillary, maxillary, and premandibular bones, in which they 
 are arranged in close series, and of nearly equal size. They 
 consist of a body of unvascular dentine, invested at the base by a 
 thick layer of cement, and at the crown by a layer of enamel, 
 which is itself covered by a very thin coat of cement ; the pulp- 
 cavity is more or less occupied in fully formed teeth by a coarse 
 bone. The external surface of the tooth is marked by the longi- 
 tudinal impressions and ridges, but the teeth vary both as to 
 outward sculpturing and general form in the different species.' 
 The chief peculiarity of the dental system of the Ichthyosaur 
 is the mode of the implantation of the teeth : instead of being 
 anchylosed to the bottom and side of a continuous shallow groove, 
 as in most Lacertians, or implanted in distinct sockets, as in the 
 Thecodon, Megalosaur, or Pterodactyle, they are lodged loosely 
 in a long and deep continuous furrow, and retained by slight 
 ridges between the teeth, along the sides and bottom of the 
 furrow, and by the gum and organised membranes continued into 
 the groove and upon the base of the teeth. The germs of the 
 new teeth are developed at the inner side of the base of the 
 old ones. 
 
 The best and most readily recognisable characters by which 
 the existing Crocodilians are grouped in appropriate genera are 
 derived from modifications of the dental system. 
 
 In the Caimans (genus Allir/ator) the teeth vary in number 
 
 „ 18—18 ^ 22—22 , . , , ^ , , 
 
 irom — — — to — — — ■ : the lourth tooth oi the lower jaw, or 
 io — io .^2 — 22 
 
 canine, is received into a cavity of the palatal surface of the upper 
 
 jaw, where it is concealed when the mouth is shut. In old 
 
 individuals the upper jaw is perforated by these large inferior 
 
 canines, and the fossaj are converted into foramina. 
 
 In the Crocodiles (genus Crocodilus) the first tooth in the lower 
 jaw i)erforates the palatal process of the ]iremaxillary bone when 
 the mouth is closed; the fourth tooth in the lower jaw is received 
 into a notch excavated in the side of the alveolar border of the 
 upper jaw, and is visible externally when the mouth is closed. 
 
 In the two preceding genera the alveolar borders of the jaw 
 have an uneven or wavy contour, and the teeth are of an unequal 
 size. 
 
 In the Gavials (genus Gavialis) the teeth are nearly equal in 
 size and similar in form in both jaws, and the first as well as the 
 
 ' V. pi. 73. 
 
TEETH OF REPTILES. 
 
 407 
 
 274 
 
 fourtli tooth in tlie lower jaw passes into a groove in tlie margin 
 ol the upper jaw when the mouth is closed. 
 
 In the Alligators and Crocodiles the teeth are more unequal in 
 size, and less regular in arrangement, and more diversified in 
 form, than in the Gavials : witness the strong thick conical 
 laniary teeth as contrasted with the blunt mammlllate summits of 
 the posterior teeth in the Alligator, fig. 275. The teeth of the 
 Gavial are sidje(|ual, most of them present the form of a crown, 
 shown in fig. 274, long, slender, pointed, svxhcompressed from 
 before backward, with a trenchant edge on the right and left 
 sides, between which a few faint longitudinal ridges traverse the 
 basal part of the enamelled crown. 
 
 In the black Alligator of Guiana the first fourteen teeth 
 of the lower jaw are implanted in distinct sockets, the re- 
 maining posterior teeth are lodged close to- 
 gether in a continuous groove, in which the 
 divisions for sockets are faintly indicated by 
 vertical ridges, as in the jaws of the Ichthyo- 
 saiu'S. A thin compact floor of bone separates 
 this groove, and the sockets anterior to it, from 
 the large cavity of the ramus of the jaw ; it is 
 pierced by bloodvessels for the supply of the 
 pulps of the growing teeth and the vascular 
 dentiparous membrane which lines the alveolar 
 cavities. 
 
 The tooth-germ is developed from the mem- 
 brane covering the angle between the floor and 
 the inner wall of the socket. It becomes in 
 this situation completely enveloped by its cap- 
 sule, and an enamel-organ is formed at the 
 inner surface of the capsule before the young 
 tooth penetrates the interior of the pulp-cavity 
 of its predecessor. 
 
 The matrix of the young growing tooth 
 affects, by its pressure, the inner wall of the 
 socket, as shown in fig. 275, and forms for itself 
 a shallow recess: at the same time it attacks 
 the side of the base of the contained tooth ; 
 then, o-alnino- a more extensive attachment by 
 its basis and increased size, it penetrates the large pulp-cavity 
 of the previously formed tooth, either by a circular or semi- 
 circular perforation. The size of the calcified part of the 
 tooth-matrix which has produced the corresponding absorption of 
 
 TeetU in different stages of 
 formatiou from one alve- 
 olus of the Gavial : a is 
 the base partly absorbed 
 by tbe pressure of b, the 
 successional tooth ; below 
 wliich is Ilgiired c, the 
 germ of the next tooth 
 to follow. V. 
 
408 
 
 ANATOMY or VEETEBEATES. 
 
 St'ftloti of lower jaw, with four alveoli nnd teeth, ol the black 
 Alligator. V. 
 
 the previously formed tooth on the one side, and of the alveolar 
 
 process on the other, is 
 represented in the ex- 
 posed alveolus of fig. 
 275, the tooth a hav- 
 ing been displaced and 
 turned round to show 
 the effects of the stimu- 
 lus of the pressure. The 
 size of the perforation 
 in the tooth, and of the 
 depression in the jaw, 
 jjroves them to have 
 been, in great j^art, 
 caused by the soft ma- 
 trix, which must have 
 produced its effect not 
 by mere mechanical 
 force. The resistance 
 of the wall of the pulp- 
 cavity having been thus overcome, the growing tooth and its 
 matrix recede from the temporary alveolar depression, and sink 
 into the substance of the pulp contained in the cavity of the 
 fully formed tooth. As the new tooth, ib. c, grows, the pulp of the 
 old one is removed ; the old tooth itself is next attacked, and, 
 the crown ])eing imdermined by the absorption of the inner sur- 
 face of its base, may lac broken off by a slight external force, 
 when the point of the new tooth is exposed. The frail remains 
 of the old tooth are sometimes lifted off the socket upon the 
 crown of the new one, as in fig. 275, b, when they are speedily 
 removed by the action of the jaws. 
 
 No sooner has the young tooth penetrated the interior of the 
 old one than another germ begins to be developed from the angle 
 between the base of the young tooth and the inner alveolar 
 process, or in the same relative position as that in which its 
 immediate predecessor began to rise, and the processes of succes- 
 sion and displacement are carried on, uninterruptedly, throughout 
 the long life of these cold-l:)looded carnivorous Reptiles. 
 
 From the period of exclusion from the egg, the teeth of the 
 Crocodile succeed each other in the vertical direction ; none are 
 added from behind forward, like tlie true molars in Mammalia. 
 It follow.i, therefore, that tlio number of the teeth of the Croco- 
 dile is as great Avhcn it first sees the light as when it has aciiuired 
 
ALIMENTARY CANAL OF FISHES. 409 
 
 its full size ; and, owing to the rapidity of the succession, the 
 cavity at the base of the fully formed tooth is never consolidated. 
 
 The fossil jaws of the extinct Crocodilians demonstrate that the 
 same law regulated the succession of the teeth at the ancient 
 epochs when those highly organised Reptiles prevailed in greatest 
 numbers, and under the most varied generic and specific modifica- 
 tions. Of these the most remarkable, in reference to the dental 
 system, is the Galconanriis, in which the well-marked differences 
 of size and shape permit the division of the teeth, in both upper 
 and lower jaws, into incisors, canines, and molars. This is the 
 nearest approach to a mammalian type of dentition hitherto ob- 
 served in the lleptilian class.' 
 
 § 72. Alimentary canal of Fishes. - — The cavity, commonly 
 termed ' abdominal,' which lodges the main part of the alimentary 
 canal and its ajipendages, seems to occupy a smaller proportion of 
 the trunk in Fishes, fig. 276, /, h, i, than in Reptiles, fig. 292, 
 d, IV, l_iy reason of the slight and gradual contraction of the liody 
 beyond the vent to form the muscular organ of the tail-fin : the 
 greater and more abrupt contraction of the answerable part in 
 Reptiles distinguishes it more plainly as the ' tail ' ; the ' trunk ' 
 is usually a longer segment of the body than in Fishes. In these, 
 however, the abdominal cavity commences immediately behind the 
 head : in most Reptiles a ' neck ' intervenes. In Fishes a thoracic 
 or pericardial cavity, fig. 276, o, is partitioned oft' from the fore- 
 part of the proper abdominal one : and tliere are in this class 
 exceptional examples of the shortest abdominal cavity in pro- 
 portion to the length of the body kn(.iwn in the Vertebrate 
 province, as e. g. in Gymnotiis, fig. 2.32, in which the aljdomcn does 
 not extend into the compartment, h, much beyond the vent, 
 which is seen near the angle of the cut integument, beneath the 
 mandible. 
 
 The cavity containing the beginning of the alimentary canal is 
 called the ' mouth.' This, in Fishes, is the common entry and 
 vestibule to both the digestive, fig. 276, d to g, and the respi- 
 ratory, ib. t, V, organs ; it is, therefore, of great capacity : and, as 
 the transmission of the food to the stomach and of the respiratory 
 currents to the gills is performed by similar acts of deglutition, 
 the bony arches which surround the mouth are not only large, 
 but are complicated by a mechanism for regulating the transit 
 of the nutritious and oxygenating media, each to its respective 
 locality. The branchial slits, in most Fishes, are provided with 
 
 ' cfcxxm. p. 58, pi. II. 
 
410 
 
 ANATOMY OF VERTEBRATES. 
 
 denticles and sieve-like plates or processes, fig. 85, 6?, to prevent 
 the entry of food into the interspaces of the gills, and the branchial 
 
 276 
 
 Digestive organs in situ., Planirostra. 
 
 ,v t'^; •-- 
 
 outlets are guarded by valves which reciprocally prevent the 
 regurgitation of the respiratory streams back into the mouth. 
 
 The necessary cooperation of the jaws with the hyoid arch in 
 the rhythmical movements of respiration is incompatible with 
 protracted maxillary mastication ; and, accordingly, the branchial 
 apparatus renders a compensatory return by giving up, as it were, 
 the last pair of its arches to the completion of the work which the 
 proper or anterior jaws were compelled by their services to re- 
 spiration to leave unfinished : and thus the mouth of typical Fishes 
 is closed at both ends by dentigerous jaws.' 
 
 The first joortal to the alimentary tract is usually formed by the 
 ujjper and lower jaws, fig. 276, «, b, and their teeth: the Gym- 
 nodonts are so called on account of their conspicuous manifestation 
 of tliis character, fig. 258. In most Fishes the jaws are covered 
 by the skin, which, in passing into the mouth, takes on the 
 character of the mucous membrane. In some Fishes the inteeu- 
 ment is folded before passing over the jaws, and the arched 
 and fortified barrier is preceded by a fosse inclosed by fleshy lips. 
 The Wrasses (Lahrida;), Mullets (^JMugiliclcE), and the Carp-tribe 
 (^Cyprinidce) exemplify this character. In Crenilabrus, Champs, 
 and Julis, the lips are plicated. In Mi/r/il laheosus the thick upper 
 lip has a transverse fold. In some Ci/prinida the laliial organs 
 are developed to excess, as, for example, in the genus thence 
 termed Labeoharhua, in which the lips are not only unusually thick 
 and fleshy, but the lower one is produced downward like a pointed 
 beard : it forms a long cone in Mormi/rus Pctcrsii. The labiated 
 Fishes have not, however, so distinct a ' sphincter oris ' as 
 
 ' The Mullets ' take in a quantity of sand and mud, and after having worked it 
 for some time between the pharyngeal hones, they eject the roughest and indigestible 
 portion of it.' CLXxiv. iii. p. 411. 
 
ALIMENTARY CANAL OF FISHES. 411 
 
 Mammals : nor does the skin, continued from the lip over the jaw, 
 show so well the character of the ' gum.' Many Fishes, esioecially 
 those of the Cyprinoid, Mugiloid, and Siluroid families, have 
 fleshy and sensitive labial barbs or cirri ; those of the Siluroids 
 being supported by bony or gristly stems. Tentacles depend 
 from the rostral prolongation of the Sturgeon, and from the man- 
 dibular symphysis of the Cod. The Lej^idosiren and Cod have 
 fringed processes or filaments between the teeth and lijos, which 
 seem designed to assist in testing and selecting tlie food.' The 
 lips of most Sharks and Rays are partially supported by labial 
 cartilages. 
 
 The edentulous Sturgeon is compensated by a produced cartila- 
 ginous snout, with which it upturns the mud in quest of food at 
 the bottom of the rivers it frequents. The allied Spatiilaria, in 
 wliich a minutely shagreened surface on the jaws represents the 
 whole dental system, has had the force of developement of subsi- 
 diary organs of alimentation expended in the production of the 
 still more remarkable rostrum, fig. 276, y, which is broad and flat, 
 like the mandible of a spoonbill, and is more than half the length 
 of the entire body. Other modifications and actions of the mouth 
 have been noticed in the description of the jaws. 
 
 The conical lip of the suctorial Mj^xinoids, fig. 248, sends off 
 from its anterior expanded border six or eight long tentacida : this 
 border is fringed by numerous cirri in the Lamprey, fig. 277, the 
 inner surface of the lips is beset with short branched tentacles in 
 the Amniocete : the Lancelot has more simple, but highly vascrilar 
 intra-buccal processes, fig. 169, g,g, and the vertically fissured 
 aperture of its mouth is provided on each side with a series of 
 long slender jointed and ciliated tentacula, ib./,/, which mainly 
 tend, by the perpetual vortex they cause in the surrounding 
 water, to bring the auimalcular nutriment within the grasp of the 
 pharynx, ph, the orifice of which is also surrounded by vibratile 
 cilia. There is no tongue in this rudimentary fish : that organ is 
 often absent or very small in the typical members of the Class ; 
 its basis, the glossohyal, when it projects at all into the mouth, as 
 in fio-. 276, c, is rarely covered by integuments so organised as to 
 suo-o-est their being endowed with the sense of taste. In Anguil- 
 lid(B the lingual membrane is raised by some adipose and muscular 
 
 > Mr. Couch narrates an instance of a largo Cod, in good condition, talcen on a 
 line at Polperro, Cornwall, in which the orbits contained no eyeballs, but were covered 
 with an opako reticulated skin. So that he felt convinced that ' eyes never had 
 existed ;' yet the fish was in good condition, and must have depended on the tactile 
 oro-ans .about the mouth for the discovery of its food, xcvni. p. 72. 
 
412 
 
 ANATOMY OF VERTEBRATES. 
 
 tissue. But the surface of the prominent tongue is generally 
 callous, and either smooth and devoid of papilhis, or, if the repre- 
 
 277 
 
 Vertical scrtidu of iinaitli, Lniiijn-ey. v. 
 
 sentatives of these be jiresent, they are calcifiod and the tongue is 
 beset with teeth. It, then, seizes and ]iasses the food on to the 
 gullet; but the supporting arch of the tongue, fig. 85, .38-40, works 
 chiefly for respiratory purposes. In the Lamprey, the tongue, fig. 
 277, d, is more exclusively related to the digestive function than 
 in higher Fishes : it can be protruded and retracted, like a piston, 
 when the sucker is attached to the prey ; and it is armed by small 
 serrate teeth for tearing the flesh. In a few Fishes the integu- 
 ment of the palate presents that degree of vascularity and supply 
 of nerves which indicates some selective sense, analogous to taste. 
 In the Cyprinoids tlie palate is cushioned with a thick soft 
 vascular substance, exuding mucus by numerous minute pores, 
 but more remarkable for its irritable erectile or contractile 
 property : ' if any part of this Ijc pricked in a live Carp, the part 
 rises immediately into a cone, which slowly subsides ; this peculiar 
 tissue is richly supplied by branches of the glosso-pharyngeal 
 nerves : it may assist in the rcrpiisitc movements of the vegetable 
 food, as well as add to it an animalising and solvent mucus, whilst 
 it is undergoing mastication by the ])haryngeal teeth. In the 
 Gymnotus there are four scries of Ijranehed fleshy processes in the 
 mouth, one upon the dorsum of the tongue, a second depending 
 from the palate, and one along each side of the mouth. 
 
 ■ The only representatives of a salivary system in Fishes are the 
 mucous follicles that communicate with tlic mouth.^ The chief of 
 
 2 Tho reddish vascular body, discovered by Kelzius (cxxi.) between the basi- 
 
ALIMENT AEY CANAL OF FISHES. 413 
 
 these, in the Lamprey, open into a pair of membranous pouches, 
 wliieli discharge the secretion each by a small orifice below the 
 side of the tono-uc' 
 
 O 
 
 Tlicre are neitlier tonsils nor velum palati in Fishes : the folds 
 of membrane behind the upper and lower jaws, of Avhich ' internal 
 lips' the Sword-fish and Dory afford good exami)les, seem intended 
 to prevent the reflux of the respiratory streams of water rather 
 than the escape of food from the mouth. In the Lepidosiren these 
 folds or inner lips are papillose and glandular. That of the 
 upper jaw in the Ray has a marginal fringe. 
 
 In the aberrant Dermopteri and FLaijiostomi, at the two extremes 
 of the class, in which there are numerous branchial apertures on 
 each side, and the respiratory streams do not necessarily enter by 
 the mouth, the last pair of branchial arches are not metamorphosed 
 into pharyngeal jaws, and the entry to the gullet is simply con- 
 stricted by a sphincter ; in the Lepidosiren it is further defended 
 by a soft valvular fold like an epiglottis.^ 
 
 The alimentary canal is usually short, simple, but capacious, in 
 Fishes ; in a few instances, e.g. Br ancldo stoma (fig. 169, ph, as), 
 Myxinoids,' Exocetus, Lepidosiren,^ it extends in almost a straight 
 line Irom the pharynx to the anus : l3ut it is generally disposed in 
 folds and sometimes in numerous convolutions. In Dermopteri 
 the stomach is hardly defined : in the rest of the class the alimen- 
 tary canal is primarily divided into a gastric and an intestinal 
 portion by the constriction called ' pylorus,' fig. 28 1, e. The gastric 
 portion is subdivided into ' oesophagus,' i)3. a., and stomach, ib. h, 
 the boundary line being more commonly indicated by a change of 
 structure of the lining membrane than by a cardiac constriction : 
 the intestinal portion is suljdivided into a ' small ' and a ' large 
 intestine ; ' the latter usually answering to the ' intestinum 
 rectum,' and the boundary, when well defined, being a constric- 
 tion and an internal valvular fold ; Ijut very rarely marked by 
 an external Cfccum. From the ocsopliagus the alimentary canal is 
 situated wholly or in part in the abdominal cavity, to the walls of 
 which it is usually suspended by mesogastric and mesenteric 
 duplicatures of the peritoneal lining memljrane of the abdomen. 
 When not wholly so situated, the part extends beyond the peri- 
 toneal region into the muscidar mass of the tail ; a portion of the 
 
 branchials and the sterno-hyoid muscles in Cartilaginous Fishes, and which exists also 
 in Gadus, Salmo, and some other Osseous Fishes, has been compared to a sublingual 
 salivary gland: but it is a " vaso-ganglion " like the thyroid. 
 
 ' ccxxiT. '' XXXIII. p. 342, fig. j, d. 
 
 ' XXI. Neurologie, tab. iii. fig. 6. ^ xxxiii. pi. 2.5. 
 
414 ANATOMY OF VERTEBRATES. 
 
 intestine, for example, lies between the right myocommata and 
 the htemal spines in the Sole. The peritoneal serous membrane, 
 which defines the abdominal cavity, extends anteriorly to the 
 pericardium, from which it is separated by a double aponeurotic 
 septum, fig. 276, o: it is continued along the back over the ventral 
 surface of the kidneys and the air-bladder, when this exists, a little 
 way beyond the anus, and is reflected upon the alimentary canal, 
 ib. d, I, the liver, I, I, the spleen, n, the pancreas, k, or its ctecal 
 substitutes, the ovaria or testes, and the urinary bladder, if this be 
 present. In many Fishes the peritoneum does not form a shut 
 sac, but communicates with the external surface, by one orifice 
 (Bra/ichiostoma, fig. 169, od, Lepidosiren, xxxiii. pi. 25, fig. 1, 
 a), or two (Lamprey, Eel, Salmon, Sturgeon, Planirostra, 
 Chimasra, and Plagiostomes, fig. 352, p, p), situated, except 
 in the Lancelet, in or near the cloaca : the membrane in the 
 neighbourhood of these orifices is beset with vibratile cilia.' 
 The peritoneal orifices give exit to the generative products 
 (milt or roe) in the Lancelet, Myxinoids, Lam25reys, Murffinidce, 
 and Salmonidaj, Ijut not in the Lepidosiren and Plagiostomes. 
 In the Myxinoids, Aramocetes, Sturgeons, Chinifer^ and Pla- 
 giostomes, the peritoneum comnuiuicates also with the peri- 
 cardium.^ 
 
 The jaws and mouth are subservient in most Fishes to the 
 respiratory as well as the digestive functions : in the Lancelet, 
 this community of offices extends through a great part of the 
 alimentary canal, which is dilated into a capacious sac, and is 
 richly provided with branchial vessels and vibratile cilia arranged 
 along transverse linear clefts, by which the water escapes into a 
 surrounding cavity : (the arrow a extends from the pharynx into 
 the intestine in fig. 169 :) the oesophageal portion of the alimen- 
 tary canal is here seen to be longer than the whole gastric and 
 intestinal portions. In the Cyclostomes lateral diverticula are 
 derived from the oesophagus and metamorphosed into special 
 respiratory sacs, communicating by narrow canals both with the 
 oesophagus and with the external surface, fig. 315,/, m, h: in other 
 Fishes the respiratoiy apparatus is more concentrated and brought 
 more forward, so as to communicate with the pharynx, and to 
 leave the oesophagus free for the exclusive transmission of food to 
 the stomach. 
 
 The oesophagus, fig. 279, d, is usually a short and wide funnel- 
 shaped canal with a thick, muscular coat and a smooth epithelial 
 
 ' ccxxxiv. p. aoo. 2 i.xix. pi. 8. 
 
ALIMENTARY CANAL OF PISHES. 4L5 
 
 lining, more or less longitudinally folded to admit of increased 
 capacity for the deglutition of the often unmasticated or undivided 
 food. The muscular fibres are arranged in different fasciculi, the 
 oviter ones being usually circular, the inner ones longitudinal. 
 Some fasciculi from the abdominal vertebra} are attached to the 
 oesophagus in the Cottus scorpius.^ The cardiac half of the 
 a?sophagus is characterised by increasing width in most Cyprin- 
 idce, and by a more vascular or otherwise modified texture in 
 the Pharyufiognathi, Lophohrancldi, the Gobioids, Blennies, 
 Flying-fish, Garfish, and some others. The inner surfiice of the 
 a?sophagus sends oft' short jirocesses, papilliform in Box and Ccasio, 
 obtuse in Acipenser,'^ hard and almost tooth-like in Rhombus xan- 
 thunis, Stromatoius fiutola, and Tetragov.urus. The inner surface 
 of the gullet presents longitudinal papillose ridges in Plavirostra. 
 But the most striking peculiarities of the asophagus are met with 
 in the Plagiostomes. A layer of grey parenchymatous substance 
 is interposed between the muscular and inner coats at the cardiac 
 half of the oesophagus in the Torpedo. Numerous pyramidal 
 retroverted processes, jagged or fringed at their extremity, project 
 from tlie inner surface of the oesophagus in the Dog-fish {Spinax 
 acmithias),^ and some other Sharks, fig. 278, «. In the great Basking 
 Sliark (SelacJw) the homologous processes near the cardia acquire 
 unusual length, dividing and subdividing as they extend inwards, 
 so that the cardiac opening is surrounded by ramified tufts directed 
 towards the stomach."' This valvular mechanism, fig. 278, b, would 
 prevent the return of such fishes or mollusks as may have been 
 swallowed alive and uninjured by the small obtuse teeth of this 
 great Shark. In many Osseous Fishes we may, finally, notice 
 the communication of the ' ductus pneumaticus ' with the oeso- 
 phagus, usually by a small simple foramen ; lout provided with 
 special muscles in the Lepidosteus, where it opens upon the 
 dorsal aspect of the oesophagus, and with a spliincter and cartilage 
 in the Polypterus, and Lepidosiren, where it communicates like a 
 true glottis with the ventral surface of the beginning of the 
 oesophagus. In the Globe-fishes {Dlodon, Tetrodoii) the great 
 air-sac seems to be a more direct developement, as a cul de sac, 
 of the a^sophagus.® These singular fishes blow themselves up 
 by swallowing the air, which escapes through a large anterior 
 oblique orifice into the sac : and this again communicates with 
 
 1 xcix. ^ 5X. vol. i. p. 126. prep. no. 463. 
 
 / ^ lb. prep. no. 66-t. ' Ib."prep. no. 464. A. 
 
 = lb. vol. Jii. p. 271, pi. 47, preps, nos. 2093—209.5. 
 
 'it 
 
 ■\VS h^. . t^Q.'w '■ 
 
 
 i -C: ! I ' ,1 Ml '. 
 
416 
 
 ANATOMY OF VERTEBRATES. 
 
 the forepart of tlie oesophagus by a second orifice much smaller 
 than the first, and having a tumid valvular margin. 
 
 The cardiac orifice of the stomach is occasionally defined by a 
 constriction, as in the Planirostra and Mormyrus, fig. 280 : but 
 an increased expansion with increased vascularity and a more 
 delicate epithelial lining of the mucous membrane more usually 
 indicate, in Fishes, the beginning of the digestive cavity. The 
 stomach is a simple and commonly an ample cavity, with a 
 great disproportion in the diameters of the cardiac and pyloric 
 orifices ; in the Cornish Porbeagle- Shark, for example, the cardiac 
 entry will readily admit a child's head, whilst the pyloric outlet 
 will barely allow of the passage of a crow-quill. 
 
 There are two predominant forms of the stomach in Fishes, viz. 
 the ' siphonal ' and the ' crecal.' In the first it presents the form of 
 a bent tube or canal, as in the Turbot, fig. 287, a, b, Flounder, 
 Sole, Cod, Haddock, Salmon, fig. 286, a, h, Carp, Tench, Ide, Lump- 
 fish, File-fish, Lepidosteus, Sturgeon, Paddle-fish, and most Plagio- 
 
 Alliiiriihiry cixiial of Sliark. CCLXVI. 
 
 stomcs, fig. 278 : in the second form the cardiac division of the 
 stomach terminates in a blind sac, and the short pyloric portion is 
 continued from its right side, as in the Porch, the Scorpajna, the 
 Gurnards, the Bull-licads, the Smelts, the Whiting, fig. 285, the 
 Angler, the Pike, tlic Lucioperca, the Sword-fish, fig. 282, the 
 Silurus, the Herring, the Sprat, fig. 288, the Pilchard, the 
 Conger, the Murrena, and the Polyjiterus, fig. 279. A transi- 
 tional form, in which the pyloric end is bent so abruptly upon 
 
ALIMENTARY CANAL OF FISHES. 
 
 417 
 
 279 
 
 Stomach and pan- 
 creas, PoJyptenit^. 
 
 the cardiac as to make the crecal character of the latter doubtful 
 IS presented by the short and capacious stomach of tlie Burbot, the 
 Blenny, and the Gymnotus. In the Mormyrus 
 the stomach presents the rare form of a globular 
 sac, fig. 280, e. In the siphonal stomach of the 
 Oi/prhndcB and JJalixtidai the pylorus is little if at 
 all discernible, and the transition into intestine is 
 gradual. In the Salmon tlie intestine is indicated 
 by the pyloric appendages, fig. 286, c: in the 
 Sharks there is a true pylorus, and in Selache, fig. 
 278, an interposed pouch. Where the cajcal cha- 
 racter of the stomach is well marked, the length of 
 the blind end of the cardia varies considerably. 
 In the Turbot it is wide and short, fig. 287, b : 
 in the Sand-lance {Ammodytes) it is very large : in 
 the Polypterus, fig. 279, e, Conger, and Sword- 
 fish, fig. 282, it forms almost the whole of the 
 elongated stomach, the short pyloric portion, fig. 279,y, being 
 continued from near its commencement : in the equally elongated 
 stomach of the Pike, the pyloric portion is continued from the 
 cardiac sac at a little distance from its blind end ; the Herring, 
 Sprat, fig. 288, Whiting, fig. 285, Gurnard, and Scorprena show 
 an intermediate position of the pyloric portion, and this is usually 
 attended with a shorter and wider form of the cardiac crecuni. 
 The pyloric portion is iisually slender, fig. 278, c, or conical, figs. 
 28.5, 287 ; but it dilates into a wide sac in Sargus and Lophius ; 
 and forms a small oval pouch in Trachypterus. 
 
 In certain Fishes the stomach deviates from the typical forms 
 either into the extreme of simplicity or the 
 converse, without, however, attaining in any 
 species that degree of complexity which 
 characterises some of the higher-organised 
 Vertebrates. A proper gastric compartment of 
 the alimentary canal cannot be said to exist in 
 the Lancelot : the long cascum, fig. 169, hd, I, 
 continued from it just beyond the cardia, 
 appears to be a simple form of liver. In the higher Dermoptm, 
 as the Sand-prides, the Myxines, and the Lampreys, as also 
 in Cobitis and Lepido.nre7i, the stomach is continued straight 
 from the oesoiihagus to the intestine. I have found the capa- 
 cious cardiac division of the stomach of tlie Lophius partially 
 divided into two sacs; the unusually wide and short pyloric 
 portion forming a third sac : there may also be observed a few 
 
 VOL. I. E E 
 
 280 
 
 stomach and pancreas, 
 Murmyrus, 
 
418 ANATOMY OF VERTEBRATES. 
 
 obtuse processes from the inner side of the cardia in this fish. In 
 the Gillaroo Trout the ascending or pyloric half of the bent or 
 siphonal stomach has its muscular parietes unusually thickened, 
 by which it is enabled to bruise the shells of the small fluviatile 
 testaceans that abound in the streams to which this variety of 
 trout is peculiar.' The pyloric portion of the stomach is very 
 muscular in the Indian Whiting {Johnius), and in some species of 
 Scomber : but the modification which gives the stomach the true 
 character of a gizzard is best seen in the Mullets {Mur/il). The 
 cardiac portion here forms a long cul de sac ; the pyloric part is 
 continued from the cardiac end of this at right angles, and is of a 
 conical figure externally ; but the cavity within is reduced almost 
 to a linear fissure by the great developement of the muscular 
 parietes, which are an inch thick at the base of the cone ; and this 
 part is lined by a thick horny epithelium.' In the Herring the ductus 
 pneumaticus of the swim-bladder is continued from the attenuated 
 extremity of the cardiac end of the stomach, fig. 281, h. In the 
 Basking-shark the contracted pyloric division of the stomach, figs. 
 278, c, and 284, /" comnumicates by a narrow aperture with a 
 second small rounded cavity, fig. 284, f, which opens by a narrow 
 pylorus into the short and capacious duodenum, fig. 278, f, 284, ff. 
 
 Such arc the observed extremes of the modifications of the 
 stomach in Fishes, which it will be seen, therefore, are far from 
 according with or paralleling those of the dental system. There 
 is often, indeed, no essential difterence of form in the stomach of 
 a fish with exclusively laniary teeth, e. g. the carnivorous Salmon, 
 and in that of one with exclusively molar teeth, e. g. the herbi- 
 vorous Carp. The 2Etobates, whose teeth form a crushing 
 pavement, has a stomach similar in shape and size to that in the 
 common Ray, in which every tooth is conical and sharp-pointed. 
 
 The inner surface of the stomach presents few modifications in 
 Fishes : it is usually smooth ; rarely reticulate, as in the Gym- 
 notus ; still more rarely papillose. The lining membrane is 
 thrown into wavy longitudinal rugre in the cardiac portion of 
 the stomach of most Sliarks, fig. 278. The gastric follicles are 
 cons])icuous, especially in the pyloric portion of the stomach in 
 many Fislies, as, e. g., the Gurnards, Blennies, and Lump-suckers. 
 The circular pyloric valve is commonly well develo])ed, and has 
 sometimes a fimln-iatcd margin. Tlic solvent power of the gastric 
 secretion is conspicuously exemplified in Fislics : if a voracious 
 species be captured after having swallowed its prey, the part lodged 
 in the stomach is usually found more or less dissolved, whilst 
 
 ' ^'-ii- P- l-G. - XX. vol. i. p. 141. prep. no. 502. 
 
ALIMENTARY CANAL OF FISHES. 419 
 
 that wliicli is in the a?sophagus may be entire ; and, in specimens 
 dissected some hours after death, one may observe wlaat Hunter 
 so well describes, ' the digesting part of the stomach itself reduced 
 to the same dissolved state as the digested part of the food.'' 
 
 The muscular action of a fish's stomach consists of vermicular 
 contractions, creeping slowly in continuous succession from the 
 cardia to the pylorus ; and impressing a twofold gyratory motion 
 on the contents : so that, while some portions are proceeding to 
 the pylorus, other portions are returning towards the cardia. 
 More direct constrictive and dilative movements occur, with in- 
 tervals of repose, at both the orifices, the vital contraction being 
 antagonised by pressure from within. The pylorus has the power, 
 very evidently, of controlling that pressure, and only portions of 
 completely comminuted and digested food fchyme) are permitted 
 to pass into the intestine. The cardiac orifice appears to have less 
 control over the contents of the stomach ; coarser portions of the 
 food from time to time return into the oesophagus, and are brought 
 again within the sphere of the pharyngeal jaws, and subjected to 
 their masticatory and comminuting operations. The Fishes which 
 afford the best evidence of this ruminating action are the Cy- 
 prinoids, (Carp, Tench, Bream,) caught after they have fed 
 voraciously on the ground-bait previously laid in their feeding 
 haunts to insure the angler good sport. A Carp in this predica- 
 ment, laid oj^en, shows well and long the peristaltic movements 
 of the alimentary canal ; and the successive regurgitations of the 
 gastric contents produce actions of the pharyngeal jaws as the 
 half-ln'uised grains come into contact with them, and excite the 
 singular tumefaction and subsidence of the irritable palate, as 
 portions of the regurgitated food are pressed upon it. The 
 shortness and width of the ccsoj^hagus, the masticatory me- 
 chanism at its commencement, and its direct terminal con- 
 tinuation with the cardiac portion of the stomach, relate to the 
 combination of an act analogous to rumination, with the ordinary 
 processes of digestion, in all Fishes possessing those concatenated 
 and peculiar structures. Sometimes the Fishes, as, for example, 
 the Sturgeon, the Paddle-fish, the Dog-fish, and the Selache, 
 whose a?sophagus is best organised to prevent regurgitation from 
 the stomach, are devoid of the pharyngeal jaws and teeth. 
 
 Fishes disgorge the shells and other indigestible parts of their 
 food : and when hooked or netted, sometimes empty their stomach 
 by an instinctive act of fear, or to facilitate escape by lightening 
 their load. 
 
 ' xcii. p. 120. 
 
 E E 2 
 
420 
 
 ANATOMY OF VERTEBRATES. 
 
 The intestinal canal is shorter in Fishes generally than in the 
 hjoher Vertebrates: in the Derinopteri,Plagiostomes, Holocephali, 
 Sturionidas, Paddle-fish, fig, 276, / to i, the Lepidosiren,' the 
 Flyino--fish, the Loach, the Garpike, the Wolf-fish, the Salmon, 
 
 281 
 
 282 
 
 Abdominal viscera. Herring. CXVI. 
 
 the Plerring, fig. 281, and the apodal fishes, it is shorter than the 
 body itself: in some of the above-cited examples the intestine 
 extends in a straight line from the pylorus to the anus, fig. 281, 
 c, e, f; in most fishes it presents two or three folds ; the Sun-fish 
 ( Orthar/oriscus) shows about six longitudinal ones : the intestine 
 is sinuous in the Sword-fish, fig. 282, e, f; concentrically and 
 subspirally wound in the Mullet, in which the convolutions are 
 numerous and form a triangular mass ; and it is in this fucivorous 
 fish, in the Chretodonts, and the Carp-tribe, that the intestinal 
 canal attains its greatest length in the present class. 
 
 Witli a few exceptions, of which the 
 Dcrmopteri and the Lepidosiren are 
 cxamjjles, the intestines are divided 
 into ' small,' and ' large.' The begin- 
 ning of the small intestine, to which is 
 arbitrarily given the name of ' duode- 
 num,' fig. 278, (, fig. 281, c, e, is usually 
 wider than the rest of that di-sasion 
 of the canal : it receives the ducts of 
 the liver and pancreas ; and, in most 
 Osseous Fishes, that of the cajca, fig. 
 281, d, which are usually termed, from 
 their communication with, or devclope- 
 ment from, the commencement of the 
 small intestine, ' appendices pylorica\' 
 The termination of the small intestine 
 is commonly marked by a circular 
 valve. In the Bogue-brcam {Box 
 
 Nxxin. pi. a.'i, lig.ii. 1 mid 2. 
 
 ». Xii.ln, 
 
ALIMENTARY CANAL OF FISHES. 4:21 
 
 vulgaris) and the Flounder, there is a small ctecal j)rocess at 
 the commencement of the large intestine ; there are two short 
 ciuca at the same part in Box SalpaJ The large intestine is 
 usually short and straight in Fishes, answering to the rectum 
 of higher animals, fig. 282, f,f/. In some Fishes, e. g., Salmo, 
 Clupcii, Esiix, Anahleps, AnarrJiichas, _ and the Gymnodonts, it 
 preserves the same diameter as the small intestine, and the 
 tenn ' large ' becomes arbitrary: va. Gasterosteus, Cadrhcus, Ostra- 
 clon, Balistes, and HijngnutUus, it is even narrower than the 
 ' small intestine ; ' but most commonly it is wider, as in the 
 Percoid family, the Gurnards {Triglida:), the Breams (Spar idee), 
 Sciama, Scomber, Cottus, Lahrus, Pleuroncctes, Gadus, JLophius, 
 Ci/cloptcrus, the Siluridce, the Pla.giostomi, and the Planirostra, 
 fig. 276, h. 
 
 The tunics of the intestinal canal consist in Fishes, as in other 
 Vertebrates, of the peritoneal or serous, the muscular, and the 
 mucous coats, with their intervening ccllidar connecting layers, 
 and the epithelial lining ; the muscidar and mucous coats are 
 commonly thicker and of a coarser character than in the warm- 
 blooded classes ; pigmental cells are not unfrequently developed 
 in the serous coat ; the epithelial scales of the intestine of the 
 Lancelet support vibratile cilia. 
 
 The muscular fibres are arranged in a thin outer longitudinal and 
 a thick inner circular stratum (Sturgeon) ; ^ the elementary fibres 
 in general present the smooth character of those of the involun- 
 tary system ; but Reichert '^ has detected the transversely striated 
 fibre in the muscvdar tunic of the whole tract of the intestine 
 in the Tench. 
 
 The mucous membrane presents numerous modifications, some 
 of them more complex and remarkable than in any of the higher 
 Vertebrates. It is commonly thick and glandular, and always 
 liighly vascular. In the small intestines it presents, in some 
 Fishes (Cod), ^ a smooth and even surface; in some it is 
 ])roduced into obliquely longitudinal or wavy folds ; ■' in the 
 Herring it presents feeble transverse rugaj ; in many Fislies it is 
 reticulate, as in the Wolf-fish ^ and ^lurcena ; ' this character is 
 iiresent in the peculiarly thick and parenchymatoid mucous tunic 
 of the small intestine of the Sturgeon, where the larger meshes 
 include irregular spaces, subdivided into smaller cells.* In a few 
 Fishes the mucous membrane is coarsely villose or papillose. In 
 
 ' XXXIII. t. vi. pp. 624, 270. ^ XX. vol. i. p. 200, preps, nos. 637, 639. ' xciii. p. 26. 
 ' XX. vol. i. p. 199, prep. no. 633. '' lb. Turbot, prep. uo. 634, Salmon, ])rep. no. 635. 
 " lb. prep. no. 630. ' lb. prep. no. 631. » lb. prep. no. 638. 
 
42-2 ANATOMY OF VERTEBRATES. 
 
 Orthagoriscus it is both reticulate and -villous, the villi being 
 longest at the beginning of the canal. There is often a well- 
 marked difference in the character of the lining membrane of the 
 small and large intestines : thus, in the Salmon, the rugse become 
 fewer, larger, and less oblique as they approach the rectum ; the 
 commencement of this intestine is marked by a large transverse 
 fold or circular valve, which is succeeded by several others less 
 produced, and resembling the valvula3 conniventes in the human 
 jejunum.' The straight 'large intestine,' which is relatively 
 longer in the Amia, Polypterus, Paddle-fish, fig. 276,^, i, Sturgeon, 
 and Chimasrse, is characterised by the continuity of such transverse 
 folds as those in the Salmon, producing an uninterrupted spiral 
 valve of the mucous membrane. In the Lepidosiren the entire 
 tract of the straight and short intestine is traversed by this piecu- 
 liarly piscine extension of the inner coat.^ The spiral valve 
 characterises the large intestine, fig. 278, k, in all the Plagiostomes, 
 and establishes the essential difference between the short and 
 apparently simple intestinal canal of these cartilaginous fishes, and 
 that of the low-organised Myxinoid species. 
 
 The true homologue of the small intestine is extremely short in 
 the Plagiostomes ; it is narrow in the Pays, expanded and some- 
 times sacciform, fig. 284, fj, in the Sharks, where it seems to form 
 the commencement of the suddenly expanded large intestine : 
 this is straight, and though constituting the chief extent of the 
 intestinal canal, it is very short in proportion to the body ; not 
 exceeding, for example, one eighth of the entire length of the 
 body in the Alopias or Fox-shark. The economy of spiace in 
 the abdominal cavity is, however, effected at the expense of the 
 serous and muscular coats, not of tlie mucous membrane. The 
 required extent of secreting and absorbing superficies is gained 
 by raising or drawing inwards, from the intestinal parietes, the 
 mucous membrane in a broad fold at the beginning of the large 
 intestine, and continuing it in spiral volutions to near the anus. 
 The coils may be either longitudinal and wound vertically about 
 the axis of the intestinal cylinder, or they may be transverse to 
 that axis. In the first case, when the gut is slit open lengthwise, 
 tlie whole extent of the fold may be uncoiled and spread out as a 
 broad sheet; and, if the gut be divided transversel)^, the cut 
 edges of the valve present a spiral disposition, as in fig. 283. 
 The longitudinal form of the spiral valve may be seen in the 
 squaloid genera Carcharia.'<, S'coliodon, Gnleocerdo, ThaJassorhinns, 
 
 ' XX. vol. i. p. 199, pixp. no. G35. = xxxm. p. 343, pi. 25, Jig. 2. 
 
ALIMENTARY CANAL OF FISHES. 
 
 423 
 
 283 
 
 SpnilvalM, Zi/t/fnia. 
 
 284 
 
 and Z^r/cena.^ In the second and more common modification, the 
 fold of mucous membrane is disposed in close 
 transverse coils, as shown in the longitudinal 
 section of the Selachc's gut, fig. 284, h ; and a 
 transverse section exposes only tlie fiat surfirce of 
 one of the coils. In the Fox-shark (Alopias 
 I ulpes) ; the valve describes thirty-four circum- 
 gyrations within seven inches' extent of the 
 intestine ; the mucous membrane is minutely honeycombed : a 
 few scattered fibres of elastic or involuntary muscular tissue may 
 be traced in the vasculo-cellular 
 layer included within the mucous 
 fold, and they form a slender band 
 within the free border of the valve, 
 retaining much elasticity in the dead 
 intestine, and drawing that border 
 into festoons. Besides Seladie, fio;. 
 284, li, and Alopias, the spiral valve 
 is transverse in Galeus, Lamna, and 
 all the Dog-fishes {^Scylliidce and 
 SpinacidfE). The trunk of the ' arteria 
 meseraica intestinalis,' and that of 
 the corresponding veins of the longi- 
 tudinally convoluted valve, run along 
 its free thickened border, and the 
 vein quits its commencement to join 
 the vena porta; : ^ the arterial and venous trunks of the trans- 
 versely spiral valve are external to the gut. 
 
 One may connect the peculiarity of the spiral valve with the 
 necessity for reducing the mass and weight of the abdominal 
 contents in the active high-swimming Sharks, which have no 
 swim-bladder : the essential part of an intestine being its secern- 
 ing and absorbing surface, we see in them the requisite extent of 
 the vasculo-mucous membrane packed in the smallest comp)ass, and 
 associated with the least possible (tuantity of accessory muscular 
 and serous tunics, by the modifications above described. Analogous 
 ones exist, however, in other Plagiostomes, and in the Lamprey, 
 to which the above physiological exijlanation will not ajiply ; and 
 the spiral valve is associated with the air-bladder in some of the 
 highly organised Ganoids, and in the Lepidosiren. Nevertheless, 
 
 ' XLVI. t. iv. p. 314 ; t. xcvi. p. 277, pi. 2 and 3. See also, xx. prep. no. 645 ; 
 probably from ScoUodon. 
 
 - Duvernoy, xcvui. p. 274, pi. 10. 
 
424 ANATOMY OF VERTEBRATES. '. - . 
 
 it is to be remarked that the intestinal canal is shortest, and 
 the spiral valve most complex and extensive, in the Sharks. 
 In both these and the E.ays, the valve subsides at a short distance 
 from the anus ; and into the back part of this terminal portion of 
 the rectum an elongated cajcal process with a glandular inner 
 surface opens fig. 352, i. The anus itself communicates with the 
 fore part of a large cloacal cavity in the Plagiostomes. In other 
 Fishes, where it opens distinctly upon or near the external surface, 
 it is anterior in position to the orifices of oviducts, or sperm- 
 ducts, fig. 281, /, and of the uterus or urinary bladder; the 
 Lepidosiren has the peculiarly ichthyic arrangement of the anal, 
 genital, and urinal outlets.' 
 
 In the Dermopteri the intestinal canal is rather closely attached 
 to the back of the abdomen, though the primitively continuous 
 mesenteric fold becomes reduced in the Lampreys to filamentary 
 processes accompanying the mesenteric vessels. A similar reduc- 
 tion of the mesentery to detached membranous bands occurs in 
 the Syngnathi and Cyprinidaj. The mesentery is entire in the 
 Lepidosiren, the Plagiostomes, and many other Fishes : it is 
 usually single and continuous from the stomach to the end of the 
 intestine : there are two parallel mesogastries in the Eel, and a 
 kind of omental accumulation of adipose matter is sometimes 
 found along the ventral surface of the intestines : a second mesen- 
 tery is continued from this part of the intestine to the ventral 
 parietes of the abdomen in the Murasna. 
 
 The position of the cloacal outlet varies much in Fishes : in 
 some of the jugular species it follows the ventral fins to the 
 region of the throat ; and in the apodal Gymnotus, fig. 232, it is 
 placed so far forward as to remind us of the position of the 
 excretory outlet in the Cephalopods. It is beneath the pectorals 
 in the Amhlyojnis speloMs : but the more normal posterior position 
 of the vent obtains in most abdominal and all cartilaginous 
 Fishes. 
 
 Petrified fieces or ' coprolites ' give some insight into the struc- 
 ture of the intestinal canal in extinct species of Fishes : some 
 that have been found in the skeleton of tlic abdomen of the 
 great Macropoma of the Kentish Chalk, and detached coprolites 
 associated with the scales and hemes of the more ancient 
 Megalichtliys, indicate by their exterior spiral grooves that these 
 
 ' xxxiii. pi. 25, iig. 1, m, n, u, I. Tlio Biaiichiostoma ofi'ers no exception to fliis 
 rule ; tlic opcnint; by which the ova antl scnicu arc cxpelleJ is a comniou peritoneal 
 outlet. 
 
^ LIVER OF FISHES. 425 
 
 ancient Ganoids, like their modern representative, the Polypterus, 
 possessed the spiral valve. 
 
 § 73. Liver of Fishes. — The liver makes its first appearance 
 in the lowest vertcbrated, as in the lowest articulated, species, 
 under the form of a simple cajcal production from the common 
 alimentary canal. Commencing in the Lancelet, fig. 169, Jul, 
 a little beyond the orifice py, the hepatic CcGcum, /, extends 
 forward from its place of communication with the canal ii, and 
 terminates in a blind end. In the Myxinoids the liver, as in 
 all higher Fishes, fig. 282, «, is a well-defined conglomerate, or 
 acinous, parenchymatoid organ, with a portal and an arterial 
 circulation, with hepatic ducts, and generally a gall-bladder and 
 cystic duct, ib. c, by which the bile is conveyed to the duodenum, 
 from wliich the stomach is divided by a pyloric valvular ori- 
 fice. 1 
 
 The texture of the liver is soft and lacerable ; its colour usually 
 lighter than in higher Vertebrates, being whitish in the Lophius, 
 and in many other Fishes of a yellowish grey or yellowish brown: 
 it is, however, reddish in the Bream, of a bright red in the 
 Holocentrum orientale, orange in Holocentrum hastatum, yellow in 
 Atherina ipreshyter, green in Petroniyzon marinus, reddish brown 
 in the Tunny, dark brown in the Lepidosiren, almost black in 
 the Paddle-fish. In the Sihtridm a portion of the liver, usually 
 forming a middle lobe, thinner than the rest and of a lighter 
 colour, has been described as the ' pancreas : ' it has a distinct 
 duct, opening near that of the ductus choledochus. In most Fishes 
 the liver is remarkable for the quantity of fine oil in its substance, 
 under which form almost the whole of the adipose matter is there 
 concentrated in the Cod tribe, the Eays, and the Sharks.^ Fishes 
 which, like the Salmon and Wolf-fish, have oil more diffused 
 through the body, have comparatively little oil in the liver. 
 
 The liver is generally of large proportional size : it is attached at 
 the fore-part of the abdomen to the aponeurotic wall partitioning 
 off the pericardium, fig. 276, I, o, and extends backward, with a 
 few exceptions, further on the left than on the right side : in the 
 Carp, the Bream, and the Stickleback, the right lobe is longest. 
 Its shape varies with that of the body or of the abdominal cavity ; 
 it is broadest, for example, in the Kays, longest in the Eels ; not, 
 
 ' The Bream is the only fish in which I have found the cystic duct terminating 
 directly in the stomach. 
 
 The myriads of Dog-fish captured and commonly rejected on our coasts sliow 
 that the fishermen have not yet taken full advaut.Tgc of this anatomical fact, which 
 exposes to them au abundant source of a pure and valuable oil. 
 
426 ANATOMY OF VERTEBRATES. 
 
 however, elongated in the Gymnotus, in which apodal fish, by 
 reason of the peculiar aggregation of the organs of vegetative 
 life in the region of the head, the liver is divided into two short 
 and broad lobes connected by a transverse lobule. The liver 
 consists of one lobe in most Salmonoid and Lucioid Fishes, in 
 the Gymnodonts and Lophobranchs, in the Mullets, Loaches, 
 and Bullheads. It is long and simple in the Lamprey and 
 Lepidosiren ; long and bilobed in the Conger. The Lump-fish 
 has a lobulus besides the chief lobe, which is round and flat. 
 There is a short thick convex lobe to the right of the long left 
 lobe in the Lophius. In many Fishes the two lobes are subequal : 
 they are rarely quite distinct, as in the Myxinoids ; but commonly 
 confluent at their base, as in the Wolf-fish, or connected by a 
 short transverse portion, as in most Sharks, the Siluroids, the 
 Polypterus, the Dory, the Coryphene, the Chsetodonts, and the 
 Cocl tribe. In the Whiting the two chief lobes extend the whole 
 length of the abdomen; in the Shark about half tlie length, 
 fig. 352, h (in which the left lobe is cut away). The liver is 
 trilobed in the Corvina, the Clupeoid, and the Cyprinoid Fishes : 
 in many of the latter family it almost conceals the convoluted 
 intestinal canal. The broad and flat liver of the Eaiidffi is tri- 
 lolsed. The liver is much subdivided in the Sandlance and in 
 the Tunny, in which latter fish it presents remarkable modifica- 
 tions of the vascular system.' There are few well-established 
 exceptions to the general rule of the presence of a gall-bladder 
 in the class of Fishes. My dissections confirm the statement of 
 its absence in the Lump-fish by Cuvier^ and Wagner.^ Cuvier 
 did not detect a gall-bladder in Lates niloticus, Holoce/itr/im Sogho, 
 SphyrcBna Barracuda, Trigla lyra, Trigla cuculus, Corvina dentex, 
 Glyphisodon saxatilis, Lepidopus argentcus, Lahriis turdus, Ammo- 
 dytes, and Echineis reinora. Tlie gall-bladder is wanting in the 
 Ammocete and Lamprey, but exists in the jNlyxinoids ; it is absent 
 in Pristis, Zygana, and Selache, but is present in Galeus, and 
 others of the Shark tribe. The rich scries of observations 
 recorded by Cuvier'' and liis able Editors''' on the gall-bladder 
 and gall-ducts in Fishes have not afl:'orded a clue to the law of 
 the developement of the special receptacle of the biliary secretion 
 in Fishes. The pouch in which the aggregated hepatic ducts 
 terminate in the Selac/ie maxima, may compensate for the absence 
 of the gall-bladder in that Shark ; these ducts are enclosed in a 
 broad flat band of dense cellular tissue, fig. 284, /, which passes 
 
 ' cm. ■' xii. t. iv. p. 551. ' xlvii. 
 
 ' xxm. passim. ■• xii. t. iv. \A. ii. p. 559-569. 
 
LIVER OF FISHES. 427 
 
 obliquely clown in front of the stomach as fiir as the duodenum, 
 when each of the ducts opens by a separate oblique orifice into a 
 common cavity, ib. m, of an oval form, communicating with the 
 duodenum by a single opening. 
 
 The gall-bladder is usually situated towards the fore-part of 
 the liver, and attached to the right lobe when this exists, as in 
 fig. 276, m. In some Cyprinoids and Kays, and in the Sturgeon, 
 it is imbedded in the substance of the liver. In many Chajtodonts 
 and Salmonoids, in the Sword-fish, fig. 282, c, in the Eel and the 
 MuKBna, it hangs freely at some distance from the liver. I found 
 the gall-bladder three inches from the liver in a Lophius of two 
 feet in length. The size of the gall-bladder varies in diflPerent 
 Fishes ; it is very small in most Kays : in Osseous Fishes it 
 usually bears a direct relation to that of the liver itself. It is 
 pyriform in the Lophius, Mullet, Sea-perch (Sebastes), Pike, 
 Sturgeon, Planirostra, and most other Fishes : it is subspherical 
 in the Grey-shark ( Galeus), and in the Wolf-fish : it is like a 
 long-necked flask in Poli/pterus ; is bent like a retort in Xljjhiaa, 
 ib. c : and is remarkably long and slender in Scicena, Upeneus, 
 Lutes nohilis, and in the Bonito, the Tunny, and other Scombridce. 
 The bile is sometimes conveyed to the gall-bladder, fig. 291, c, by 
 hepato-cystic ducts, ib. d, d, and thence by a cystic duct, ib. e, into 
 the duodenum (Wolf-fish, Erythrinus, Lepidosiren) : or it passes at 
 once to the intestine by a single hej^atic duct, formed by the union 
 of several branches fi'om the liver (yZygmna, where the duct is very 
 long) : or by two hepatic ducts ojDening separately into the intestine, 
 as in Pristls : or an hepatic duct from the left lobe joins a cystic duct 
 from the bladder, receiving the gall from the right lobe, and the 
 secretion is conveyed by a ' ductus communis choledochus ' into the 
 duodenum, as in Pinielodus : or the bile is conveyed to the duode- 
 num partly by a cystic duct and f)artly by a distinct hepatic duct 
 as in the Salmon, in wliich the latter dilates before it terminates. 
 In the Lojjhius three hepatic ducts join the very long cystic, which 
 duct sometimes dilates where it receives them. In the Sword- 
 fish three or four hepatic ducts communicate with the cystic, 
 to form the ductus communis, fig. 282, b. In the Turbot there 
 are more numerous hepatic ducts, some of which communicate 
 with different parts of the cystic duct, and four open into the 
 dilated termination of the ductus communis.' In the Galeus the 
 cystic duct runs some way through the substance of the liver, and 
 sometimes between the tunics of the pyloric canal of the stomach, 
 
 ' XX. vol. i. prep. no. 811a. 
 
428 
 
 ANATOMY OF VERTEBRATES. 
 
 before it enters the commencement of the wide intestine, near the 
 beginning of the spiral valve. The gall-duct in the Sturgeon and 
 Planirostra terminates at a greater distance above the valvular 
 intestine. The ordinary position of the entry of the bile into the 
 alimentary canal in Osseous Fishes is at the commencement of the 
 small intestine near the pylorus. The terminal part of the gall- 
 duct is usually slightly expanded, fig. 291, e, and its orifice is often 
 supported on a papilla, as in the Sturgeon, the Skate, and the 
 Labrax lupus. 
 
 § 74. Pyloric Appendages and 
 
 285 
 
 Alimentary cimiil nf tl 
 siliowing Uir I'lle (if I'll 
 
 Dermopteri sluiw 
 canal is simple : 
 
 no 
 the 
 
 trace 
 
 Pancreas of Fishes. — In most 
 Osseous Fishes the intestine 
 buds out at its commencement 
 into long and slender pouches, 
 or ca3ca, fig. 281, d, into which 
 it ajjpears that the food does 
 not enter, and which, there- 
 fore, increase the direct secre- 
 ting surface of the alimentary 
 tract, over and above the ex- 
 tent of the mechanism for 
 pounding and propelling the 
 chyme, or of the vascular sur- 
 face which selects and absorbs 
 the chyle. By a very gradual 
 series of changes of these cascal 
 processes, within the limits of 
 tlie class of Fishes, they be- 
 come massed into a body, fig. 
 282, d, like the conglomerate 
 gland, called ' pancreas' in Man. 
 The secretion of the rudimen- 
 tal representatives of this gland 
 is so like the fluid which the 
 ordinary mucous surfiice of the 
 intestine eliminates and sets 
 free from its capillary system, 
 that conditions of the ordinary 
 alimentary tract exist in some 
 Fislies which render needless 
 
 "■ the devclopemeut of the spe- 
 cial accessory surfaces. The 
 
 pancreas ; their whole digestive 
 for which that canal is the 
 
PYLORIC APPENDAGES OF FISHES. 
 
 42!) 
 
 commissariat is the most simple in the Piscine class. The 
 Lamprey, at the head of the Dermoiiterous order, derives from 
 the slight spiral extension of its intestinal mncous coat the 
 
 28G 
 
 PorLidi] oi tlie alinictitnry caii.'il of tho Salinoii {SuJ/iio salur), showJnQ: one double row of ca^csil 
 jiplienilji^a^s iiiul iioitioiis or Llie other, ccxxxr. 
 
 required concomitant complexity of the digestive canal. In 
 several Osseous Fislies, either the inactive nature of the species, 
 or the extent or special modifications (the long intestine and 
 glandular palate of tiic Carp, the thickened mucous memhranc 
 
430 
 
 ANATOMY OF VERTEBEATES. 
 
 of the dyodenum of the Eel, for example) of the ordinary tract 
 of the alimentary canal, render unnecessary the presence of a 
 
 pancreas. Thus there is 
 no csecal production of the 
 duodenum in the Ambas- 
 sis. Wolf-fish, Warty Agrio- 
 pe, nor in most Labroids, 
 Cyiirinoids, Lucioids, Silur- 
 oids, nor in the ajDodal Mala- 
 copteri, nor in the Lopho- 
 branchsandPlectognats; nor 
 in the genera Antennarms, 
 MalthcBus, and Batrachus. 
 The pancreas is represented 
 by a single pyloric cascum 
 in the Sandlance and Poly- 
 pterus, fig. 279, h: by two 
 creca in most Labyrinthi- 
 branohs, in many species of 
 Amphiprion, in theLophius, 
 the Turbot, fig. 287, and 
 the Mormyrus, fig. 280, k: 
 by three creca in the Perch, 
 the percoid Popes (Acerina), the Asprodes, and Diploprions : of 
 from four to nine cteca in the genus Cottus : of from five to nine 
 
 cajca in the genus Trinla : 
 
 28s 
 
 of six cfeca and upwards in 
 Scorpcena and Holocentrum : 
 of nine creca in the Sprat, 
 fig. 288 : and so on, increas- 
 ing to a numerous group of 
 pendent pyloric j^ouches, as 
 we find in the Scomberoids, 
 Chaitodonts, Gadoids, fig. 
 285, Halecoids, fig. 286, 
 Cyclopterus, and Lepidos- 
 teus. There is a difference, 
 however, worthy of note, in 
 the mode and extent of at- 
 tachment of these numerous 
 ca3ca: in the Salmon, fig. 286, Herring, fig. 281, (/, Sprat, fig. 
 288, and Haddock, they rank almost in a line along the whole 
 duodenum : in the Gymnotus, Lump-fish, and Whiting, fig. 
 
 Pyloric coeca of the Turbot {liliornhus maximns). ccxxxi. 
 
 Pyloric cEcca of tlio Sprnt iClupcii, sprattii-i) 
 
PYLORIC APPENDAGES OF EISIIES. 431 
 
 285, they form a circular cluster around the distal side of the 
 
 pylorus. Even in the longitudinally arranged ca3ca the principle 
 
 of concentration dawns ; thus the fifty pan- gsg 
 
 creatic creca of the Pilchard communicate 
 
 with the duodenum by thirty orifices : hut 
 
 the fifty attenuated terminal blind sacs in 
 
 the pancreas of the Lump-fish unite, reunite, 
 
 and discharge their secretion bv a circle „ , „ , ^ , 
 
 & ^ One of the fnur bundles of 
 
 of six orifices around the duodenal side of vyiom appemiaEes ot the 
 
 . X 1 m WTilting, isolated; showing 
 
 the pyloric valve. In the Tunny a more "'<:"■ "lion and reunion to 
 
 ,,.*., T , , p . form a single tube, coxxsi. 
 
 subdivided buncii of pancreatic caica empty 
 
 themselves by five orifices : in the Whiting about one hundred 
 and twenty peripheral cicca progressively unite into four groups 
 or bunches, fig. 289, communicating, each by a single duct, with 
 the duodenum: in the Sword-fish, fig. 282, d, a more compact 
 gland-like mass pours its secretion into the gut by two orifices, e : 
 and, finally, in the Sturgeon and Paddle-fish, fig. 276, k, by a 
 single opening of what now becomes the short and wide duct of 
 the gland. The interposition of cellular tissue binding together 
 longer, more slender, and more ramified ca3ca, with a concomitant 
 increase of the vascular supply, and a common covering or 
 capsule, finally converts the accessory intestinal growths into a 
 parenchymatous conglomerate gland, as we see in the Sword-fish, 
 Sturgeon, Holocephali, and Plagiostomes ; the iiapillifonn ter- 
 mination of the duct of such a pancreas is shown in the Selache, 
 at fig. 284, ?'. It sometimes exceeds the liver in weight. 
 
 The existence of this developed form of secreting organ, over 
 and above the spiral intestinal valve, may relate to the high 
 organisation of these Cartilaginous Fishes, and to the great 
 develojoement of the organs of locomotion, occasioning the neces- 
 sity for rapid and complete digestion. But if we compare the 
 few existing species of heavily laden Ganoid fishes, we shall 
 again find good evidence of the compensation for a f)ancreas by 
 the extension of the intestinal mucous membrane within the 
 canal, the circumstances calling for a more complete develojDement 
 of the digestive system in the predatory Sharks and large- 
 finned liays not being present. Thus the Polypterus, which has 
 a spiral intestinal valve, has only one short pyloric ca;cum, 
 fig. 279, k; whilst the Lepidosteus, which has no spiral valve, 
 has a compact group of above a hundred small cajca, which unite 
 and reunite to communicate by a few apertures with the com- 
 mencement of the duodenum. 
 
 The inner or mucous surface of the pyloric cfeca is laminated 
 
432 
 
 ANATOMY OF VERTEBRATES. 
 
 in some Fishes : in others it is villous, with orifices of crypts at the 
 Ijasal intervals of the flattened villi : in the Herring, fig. 290, the 
 surface is minutely honeycombed ; the cells or crypts being about 
 -L-^ of an inch in diameter, and each is filled with a mass of 
 epithelial cells, as seen in the section B, fig. 290. The basis of 
 
 290 
 
 291 
 
 Crypts of pyluric c;i?ca, llciTing. CCXXXI. 
 
 Pancreas (/) of a Floimder. ccxxxil- 
 
 the crypts is fibrous and projects between and often beyond the 
 level of their openings. The masses of epithelium resemble one 
 of the stages of the contents of the ultimate follicles of the 
 pancreatic acinus of a Mammal. The relation, however, of the 
 ])yloric appendages of the Fish to that of the pancreatic gland of 
 the higher Vertebrates may be but one of analogy. 
 
 There is a minute, but more constant glandular body present 
 both in fishes which possess (^Salnio, Gadtis, Perca) and those 
 that do not possess (Flatessa, Belone, Brama, e.g.) the pyloric 
 cfeca. It is too small, fig. 291,/, for the performance of the pan- 
 creatic function in digestion ; but the contiguity of the terminal 
 dilatation of the duct, ib. g, with that of the ductus choledochus, 
 ib. e, and of their respective openings into the duodenum, suggests 
 that this glandule may be the rudimental homologue of the 
 pancreas of air-breathing Vertebrates. 
 
 In the Lepidosiren the body imbedded between the musciilar 
 and serous coats of the stomach, and referred to as probably 
 ' splenic ' in CXLV. p. 271, sends its secretion by ducts converging 
 to one canal which opens beyond the pylorus, close to the orifice 
 of the hepatic duct.' 
 
 ' Accoriling to ocxxxni. p. 10. 
 
 / 1^' 
 
 ,J ., 
 
 I 
 
ALIMENTARY CANAL OF REPTILES. 
 
 433 
 
 292 
 
 § 75. Alimentary canal of Reptiles. — The cavity containing, as 
 in Fislies, the alimentary 
 canal, Avith the kidney s and 
 principal organs of gene- 
 ration, also lodges in Rep- 
 tiles, fig. 292, the heart, a, 
 b, c, and lungs, h, i. In 
 most the whole cavity is 
 lined by the peritoneum, 
 which is reflected upon the 
 several viscera. In the 
 transA'erse section of the 
 cavity, fig. 293, the thick 
 line diagrammatically 
 shows the peritoneum re- 
 flected from the vertehral 
 centrum upon the aortal 
 and caval trunks, h, the 
 sj)leen, b, and stomach, a, 
 whence it is continued to 
 form the omental fold, e, c : 
 from the ventral surface 
 the peritoneum is reflected 
 at one small part upon the 
 remains of the umbilical 
 vein, forming the so-called 
 ' falciform,' ff, and ' round,' 
 d, ligaments of the liver. 
 In the Crocodilia the peri- 
 toneum does not extend forward beyond the stomach and liver, 
 but is reflected upon the posterior (sacral) surface s93 
 
 of both organs,' circumscribing a smaller ' abdo- 
 minal' cavity, and including fewer viscera, than in 
 IMammals. 
 
 In female Keptiles, the serous membrane of 
 the abdomen is continuous with the mucous mem- 
 brane of the oviducts ; the subhexagonal or poly- 
 gonal flattened cells of its epithelium giving place 
 to the ciliated epithelial cells at the margin of the 
 oviducal aperture. In both male and female 
 Chelonia, the peritoneum is continued, as an in- iransvei 
 
 Abdominal cavity and visCL-ra, Lrnco voknis. ccl. 
 
 verse sectiou of 
 
 fundibular canal, into the ' corpus cavernosum' ""' ^-Moniinai cavtv 
 
 Lizard, ccxxxv. 
 
 VOL. I. 
 
 ' ccxxxvi. voL ii. p. 336. 
 F F 
 
434 
 
 ANATOMY OF VERTEBRATES. 
 
 294 
 
 of the penis ' and clitoris : in the Crocodilia, besides com- 
 municating with that structure, the peritoneal canals open out- 
 wardly upon papillae, situated on each side of the base of the 
 penis ^ and clitoris. These are the exceptions, in the reptilian 
 class, to the typical character of the jDeritoneum as a closed 
 ' serous ' sac. In most Rejitiles pigmental cells are blended with 
 or supersede the ordinary tessellated lining of epithelial cells in 
 certain parts of the peritoneal surface. 
 
 The mouth in Reptiles gives passage to respiratory currents 
 as well as to the food in the Perennibranchiates, and in all 
 the air-breathers along that extent of the cavity which is poste- 
 rior to the palato-nares, fig. 294, b, h -. the Crocodilia alone 
 having the nasal distinct from the oral passage. 
 
 In Chelonia, the jaws 
 with their horny covering 
 form, as in Gymnodont 
 fishes, the first portal to 
 the alimentary canal: in 
 many Batrachia the in- 
 tegument passes evenly 
 over the alveolar margins 
 of the jaws, as in fig. 294, 
 a, a : in Ophidia, Saiiria, 
 and Crocodilia, a narrow 
 tract of soft and vascular 
 integument intervenes be- 
 tween the scale-cladborder 
 of the mouth and the jaws ; 
 sinking into a more or less 
 shallow groove, which de- 
 fines the lips and receives the secretion of a row of mucous 
 crypts : but such lips are hard and inflexilile : in certain Frogs and 
 Toads they are of softer texture : but in none are produced or 
 jirehensile. 
 
 The walls of the mouth expand into pouches in certain 
 Reptiles, as e. g. at the sides of the face in male Frogs, below the 
 tongue in Hyla, and produced from the same part into a cons]iicu- 
 ous gnlar bag, as in the Draco volans, fig. 303, d. But these 
 pouches receive air, not, as in some higher Vertebrates, food ; and 
 usually relate to the powers of voice. 
 
 Tlic Ijony walls of the mouth have been already described ; the 
 
 ' XX. vol. iv. p. 62, preps, nos. 2448 — 2451. 
 
 '' lb. vol. iv. p. PO, prep. no. 2439 ; and ocxxxvii. p. 153. 
 
 Ciliated surface of tlie nioufd and gullet, Trlioii 
 (:t'XX.\"\'III. 
 
ALIMENTARY CANAL OF REPTILES. 
 
 435 
 
 lining membrane retains the ciliated epithelium in most Batrachia. 
 In fig. 294, E shows the roof of the mouth of a Newt, of the 
 natin-al size and magnified : A shows the floor of the mouth with 
 the oesophagus, d, laid open from above, the stomach, e, and lungs, 
 f,f. a is the lower jaw, h the tongue, c the glottis. The currents 
 jiroduccd by the vibratile cilia are made visible by powdered 
 charcoal, and their course is indicated by the arrows, beginning at 
 the symphysis and extending to the cardiac end of the cesophagus. 
 The ciliary movement ' is remarkably vivid in the mouth of the 
 Serpent ; and in the Tortoise it endures for several days after death, 
 not ceasing till the parts arc destroyed by putrefaction.' ' Fig. 
 295 gives a magnified view of some of the ordinary nucleated 
 epithelial scales, a, b, c, and of some ciliated scales, c/, e, f, g, 
 from the mouth of the Frog. 
 
 The tongue, as an organ of taste in 295 
 
 Reptiles, has been noticed, p. 327. In _ ^ 
 
 Newts it is usually small, as at h, fig. 
 294. In most tailless Batrachians it is 
 large: attached to the floor of the month, 
 a little behind the symphysis of the 
 mandible, with its free border directed 
 
 Kucleatefl nnrl ciliated epithelial scales 
 mouth of Frog 
 
 backward.^ This part can Idc raised 
 
 and thrown out of the mouth hy a 
 
 rotatory movement, as on a hinge, with 
 
 a certain elongation, equaling in some 
 
 Toads two thirds or more of the length 
 
 of the body. A glutinous saliva is 
 
 spread over the surface : both the pro- 
 
 trusile and retractile movements are executed with extreme 
 
 velocity, and thus the insect is seized and swallowed more 
 
 quickly than the eye can follow, when the Batrachian has 
 
 brought its mouth within the distance at which the tongue can 
 
 reach the fly. 
 
 The hyoid being raised and the mandible depressed, the genio- 
 o-lossi, having their fixed point at the symphysis, raise and jerk 
 forward the free part of the tongue ; at the same instant the 
 tono-ue is narrowed and lengthened by the action of transverse 
 fibres in its substance : the return movements are due to the 
 hyoo-lossi, acting from the hyoid arch, while this is at the same 
 time depressed and retracted. In most Frogs the back part of 
 the tono-ue is bifurcate, fig. 350, a, or bilobed {Polypedates) : in 
 
 ' ccxxxviii. vol. i. p. 631. 
 
 ■^ In Hctcroylossus the tongue is attached by a central pedicle. 
 
 F F 2 
 
436 ANATOMY OF VERTEBRATES. 
 
 Oxi/glossus it is rounded, as in Toads and some Hylida;, e. g. 
 Elosia ; but here the whole margin adheres : the rarest form, in 
 anourous Batrachians, is that of Rhinophrynus, in which the fore 
 part of the tongue is free.' In Serpents the tongue takes no other 
 share in the prehension of food than by the degree in which it may 
 assist in the act of drinking ; it is very long, slender, cylindrical, 
 protractile, consisting of a pair of muscular cylinders, in close 
 connection along the basal two thirds, but liberated from each 
 other, and tapering each to a point at the anterior third : these 
 are in constant vibration when the tongue is protruded, and are in 
 great part withdrawn, with the undivided body of the tongue, into 
 a sheath when the organ is retracted. This act is performed by 
 the ' glossohyoidei,' fig. 147, A ; protrusion is effected by the genio- 
 hyoidei, ib. z, z' . The orifice of the sheath is strengthened by a 
 pair of cartilaginous plates, on which other muscles act.^ The 
 ununited symphysis of the mandible leaves a passage for the 
 tongue without the need of ' opening ' the mouth : and the acts 
 of protrusion and retraction are usually seen to be frequently 
 repeated. The Amphishanidai and Anguida have short, thick, 
 hardly protractile, and sub-bifurcate tongues. 
 
 The arboreal Chameleons, clinging on all fours to their tree 
 branch, depend wholly on their singularly extensile tongue for 
 the prehension of their volatile insect food. The movements of 
 this organ are as instantaneous as in the Toad and Frog, and 
 
 296 
 
 ToTiguo of tlio C'liamclcon pnrtially extended, ccl. 
 
 are due to combined muscular and elastic forces, actino- within 
 the tongue and upon its supporting bones, with concomitant 
 modifications of the hyoid arch. The glosso-hyal is produced 
 into a long and cylindrical, fibro-cartilaginous style ; it penetrates 
 a fibrous sheath in the substance of the tongue, which, when 
 
 ' It affords the character of Dr. Gi'mther's section Pivhroglossa, clxxv. 
 = CCXLI. p. 368, pi. 46, fig. l.'j. 
 
ALIMENTARY CANAL OF REPTILES. 
 
 437 
 
 retracted, fig. 297, A and C, is almost wholly supported thereby, 
 and, when witlidrawn, the cavity of the sheath is occupied by 
 a ductile cellulosity. The bulbous end of the tongue, fig. 296, 
 and fig. 297, a, b, is divided by a transverse ciirved groove into 
 a shorter upper, ib. a, and a longer lower lobe, ib. d, resembling the 
 prehensile part of the Elephant's proboscis ; the surface is finely 
 rugous, and bedewed by adhesive secretion. Between the bulb 
 and the base the glossohyal sheath is immediately surrounded by 
 fibrous, degenerating into lax elastic, tissue, covered by the lingual 
 skin, which is thrown into circular ruga3 or rings, in the contracted 
 state (as in fig. 297, A, b, and in c, where this part of the tongue 
 is exposed by divaricating the geniohyoid muscles, c). The tissue 
 of the glossohyal sheath consists chiefly of unstriped muscular fibres, 
 arranged transversely. The longitudinal fibres are those of a pair 
 of ' glossohyoidei,' extending along the sides of the annular exten- 
 sile part, and S2:»reading out at the bulbous part, of the tongue. 
 The circular fibres, strongly contracting, diminish the thickness, 
 increase the length, and, sc[ueezing the smooth supporting style, slip 
 off the elongated part of the tongue from its fore part with a certain 
 
 297 
 
 Tonsue of the Chameleon, ccxl. 
 
 jerk. But with this action is associated a more powerful propeller 
 of the weighted bulbous end of the tongue, exercised by the 
 muscles of its bony support. The geniohyoidei, fig. C, c, and A, f , 
 
438 ANATOMY OF VERTEBRATES. 
 
 draw forward the basiliyal upon the ends of the ceratohyals, /*, 
 which are steadied by the slender muscles ' ceratomandibularis,'/, 
 and ' ceratosternalis,' h : so that the inverted bony arch, from 
 being vertical, as at A, k, is made horizontal, as at B, li ; the basi- 
 liyal being brought forward about an inch, and with a force and 
 precision, due to the fixation of the ceratohyal tips, by their guy- 
 rope-like mviscles, / and h, which adds greatly to the propelling 
 force. This force, added to, and acting consentaneously with, the 
 elongation of the annulose part of the tongue, b, A and B, jerks 
 out the swollen prehensile end of the tongue to the full extent 
 allowed by its elastic yielding tissue, which, on the cessation of 
 the muscular actions and their momentum, retracts the bulb ; and 
 the drawing back of the tongue is effected by the contraction of 
 the glossohyoidei, and of the elastic cellular tissue, readjusting 
 the sheath upon the glossohyal : also by the retraction of the hyoid, 
 through the sternohyoidei muscles, fig. 297, A, C, g. These are 
 assisted by the omohyoidei, ib. A, i; and the actions of e and g are 
 made more effective by the cooperation of / and A, in steadying 
 the points of the inverted arch upon which the swinging move- 
 ments to and fro of the basi- and glosso-hyals take place. The 
 mechanism and forces of the extension and contraction of the 
 Chameleon's tongue are essentially the same as those of the 
 tongue in Toads and Geckos, among which those species can 
 most elongate the organ, when the hyoid muscles jerk it out of 
 the mouth, which have the greatest projjortion of ' linguales ' fibres 
 arranged so as to contract its breadth.' 
 
 The styliform glossohyal, besides supporting the retracted 
 tongue and increasing the force of the constricting ' linguales ' 
 fibres, enables aim to be taken at the object to be reached. The 
 Chameleon, having discerned its jirey, brings its head into position, 
 opens the mouth to the extent reqviired for the tongue's passage : 
 then, steadying the apparatus 'by a sort of tremulous rio-id 
 movement,' shoots out the tongue, and retracts it with the fly, 
 the velocity of the action being such as to ' startle one afresh 
 every time it is witnessed.'^ 
 
 The tongue of the Crocodile, fig. 298, c, is slightly raised by 
 its fleshy portion aljove the level of the memliranous "floor of the 
 
 ' The explanation aljovc given agrees in essentials with that proposed by Hunter 
 (XX. vol. iii. p. G8), anil Cuvier (xii. etl. 1, torn. iii. p. 273) ; other hypotheses are 
 cited in ccxxxix. torn. vi. p. 76, and ccxl. vol. iv. p. 1147. 
 
 2 coxt>. p. 1150. The whole of Dr. Salter's execllent article is well worth carefnl 
 study. A previous dissection of a Gecko's tongue, after maceration, as the Chame- 
 leon's ought to be, in alcohol, lacilitatcs the recognition of the circular arr.angcnieut 
 of non-striped ' linguales ' fibres, described by Hunter and Cuvier. 
 
ALIMENTARY CANAL OF REPTILES. 
 
 439 
 
 e ; 
 
 moutli, but is not prolonged freely beyond it ; 
 
 appears to rise, l:iut this is due to tlie 
 
 continuation of the niemljrane from the 
 
 base of the tongue over a transverse 
 
 cartilaginous plate, formed by the Ijasi- 
 
 liyal, which, abutting against the velum 
 
 palati, ib. d, can close the back part 
 
 of the moutli. So that, when the 
 
 Crocodile holds submerged a drowning 
 
 prey, the water traversing the mouth 
 
 has no access to the glottis.' 
 
 Tlie membrane covering the dorsum 
 of the tongue is beset by mucous 
 crypts ; the ' ceratoglossi ' divide into 
 fasciculi, which decussate across the 
 median line. 
 
 A salivary apparatus is as little 
 specialised in Batrachians as in Fishes. 
 Mucous crypts upon the tongue or 
 palate subserve the need of lubricating 
 the quickly swallowed and unmasti- 
 cated food. In Lizards a series of 
 orifices of raucous crypts extend 
 along the lip-groove of both jaws. In 
 the Crocodile, besides the lingual fol- 
 licles, there are groups of more com- 
 plex ones on each side, behind the 
 palato-nares, ojjening into the meshes 
 of the plicated faucial membrane. In 
 Chelonians there are groups of mucous 
 follicles below the tongue, representing 
 the sublingual glands of Mammals. 
 The labial glands are abundantly de- 
 veloped in O^jhidians. The secretion 
 of the lacrymal glands is added to the 
 lubricating fluid of the mouth. The 
 poison-gland of venomous Serpents 
 may be regarded as a specially de- 
 veloped parotid, but will be described 
 in another section. In all Reptiles 
 the secretions entering the mouth are 
 rather mucous and mechanical in func- 
 
 its back part 
 
 298 
 
 Jlontli, gullet md stomach, Cioc ) lile. CCL. 
 
 ' .X5. vol. iii, p. 72, prep. no. 1466. 
 
440 
 
 ANATOMY OF VERTEBRATES. 
 
 tion than truly salivary, as exercising any alterant influence on 
 the nature of the food. 
 
 A ' velum palati ' is developed only in the Crocodilia : an 
 epiglottis is not present in any Reptile : the basihyal valve of the 
 Crocodiles is analogous to one, and some lizards show a rudiment of 
 epiglottis. The sides of the pharynx are cleft by the gill-slits in the 
 perennibranchlate Batrachia ; and one slit on each side remaing 
 open in some of the caducibranchiate species, as, e. g., in Menopoma. 
 In the Siren there are three clefts on each side, defended by inter- 
 locking pointed processes, closely resembling the narrower of the 
 five lateral branchial clefts in the Lepidosiren, fig. 316, i, 3, 4, 5. 
 The oesophagus is short and wide in Batrachia, fig. 294, d, c, 
 
 long and wide in Ophidia, fig. 300, d, 
 e, f, of moderate length and width in 
 Chelonia, narrower in Crocodilia, fig. 
 298, e, and still more so in insecti- 
 vorous Lacertilia, fig. 303, e. It is 
 remarkably dilatable and thin-coated 
 in Snakes, as at fig. 300, f, in which 
 its intrinsic propelling power is sup- 
 plemented by the constriction of the 
 surrounding trunk-muscles during 
 the deglutition of bulky prey. The 
 other chief peculiarities in the struc- 
 ture of this part of the alimentary 
 canal of Reptiles are, the perforation 
 of its walls by certain elongated and 
 enameled hypapophyses in Z>e!>orfo72,' ante, p. 393, and the produc- 
 tion of the lining memljrane into pointed processes, directed to the 
 stomach, and covered by thick epithelium in the Turtles ( Chelonc).'^ 
 These aid in the deglutition of the long slippery seaweeds on 
 which the Turtle feeds ; in carnivorous Chelonia they are not 
 present; the lining membrane in Tesfiido indica, e. g., is thrown 
 into longitudinal ruga3 when undistended, and presents a fine 
 reticular and porous surface. The ciliated epithelimn is con- 
 tinued along the gullet in Triton, fig. 294, d, and in the larva; of 
 Toads and Frogs. ^ The muscular tunic of the gullet is strongest 
 in the Turtles. 
 
 Tlie stomach presents, in Reptiles, its most simple form in the 
 Ophidian and Batrachian orders, especially in the ichthyo- and 
 
 Ucti-nvci'k'il iirnci^sscs in a-S(llill;lgU3 of 
 Turtle (C/it/oJJi',). CCL. 
 
 ' .Tnniilan, in ccxi.tt. torn. ri. p. 160. 
 
 '^ XX. tpm. i. p. 12(), preps, no.s. 4(30, 4G1 ; xr.Iii. pt, iv. pi. v, fig 7. 
 
 " CCXUII. toiTi. 1. p. 191. 
 
ALIMENTARY CANAL OF REPTILES. 
 
 441 
 
 ophio-morphous kinds of tlio latter. The transition from the 
 gullet to the stomach is scarcely indicated externally. On the 
 inner surface it is shown, in the Python, by the more vascular 
 and rugous character of the longitudinal folds continued into it 
 from the oesophagus, the interspaces of the folds being reticulate. 
 The stomach, which is straight, as in the Rattlesnake, fig. .300, (f, 
 contracts at first gradually, then quickly, to the „qq 
 
 pylorus, whence a narrow canal, of about an inch 
 in length in a Python of ten feet long,' conducts 
 to the suddenly expanded intestine. In the 
 Proteus, Siren, and Amphiiima the stomach is 
 long, cylindrical, and nearly straight ; there is 
 no intervening canal between pylorus and in- 
 testine. The stomach is distinguished from the 
 cesophagus by the thickness of its coats, and by 
 the spongy and vascular character of the lining- 
 membrane. In the Siren and Triton, fig. 294, 
 the pyloric end bends a little to the right ; this 
 bend is more marked in Salamandra. In the 
 Frog, the stomach, fig. 305, a, c, is jiyriform, 
 placed on the left side of the abdomen, with a 
 slight curve to the right side. In the Lizard the 
 stomach, fig. 301, a, is fusiform, with a similar 
 130sition : but, iu curving to the right, it ad- 
 vances from behind forward. In the Flying 
 Lizard {Draco volaiis), fig. 303, f, and the 
 Iguana, the stomach is rather pyriform, I^nt the 
 shaj^e varies with the state of the contents. 
 
 In the Chelonia the stomach so far accords 
 with the broad and flattened form of trunk that 
 it is placed more transversely, bending as it passes 
 from the left to the right side. In fia;. 302 the 
 gradual passage from the oesophagus, T, to the 
 stomach, K, is shown in the fresh-water Tortoise, 
 Emys europaa, in which the stomach is cylin- 
 drical and elongated, curving behind, and in a 
 deep groove of tlie left lobe of the liver, i, to 
 the right, where the pyloric portion of the 
 stomach, k', becomes narrower and thicker in its 
 coats. Tlie muscular fibres of the layer 
 aponeurotic part on each side, at the chief bend. 
 
 viscera, in lore pnrt of 
 
 the abdomen, of tlic 
 
 KattlesiiJike. fCL. 
 
 radiate from an 
 The mucous 
 
 XX. vol. i. p. 143, no. .'504 A. 
 
442 
 
 ANATOMY OF VERTEBRATES. 
 
 301 
 
 membrane is disposed in longitudinal rugge, most marked at the 
 cardiac half; the orifices of gastric follicles are numerous at the 
 pyloric portion. Here Hunter noticed ' a glandular part on one 
 side, a little way from the pylorus, with many orifices.' ' In the 
 Turtle ( Chelone) the muscular tunic of the stomach becomes, in 
 the adult, remarkably thick, for due compression of the veo-etable 
 contents ; in the young animal the coats are as thin as in Emys."^ 
 In this genus, and other carnivorous Chelonia, the cardiac orifice 
 is very wide compared with the pyloric. 
 
 The Crocodilia present the most complex stomach known in 
 
 existing members of the Rej^tilian 
 class. The principal cavity is of a 
 rather flattened sub-circular or full 
 oval shape ; there is a tendon, fig. 
 298, i, at the middle of each side, 
 better defined than in Chelonia, and 
 the muscular fibres radiate therefrom, 
 \h. f, f. It communicates by a wide 
 aperture with the oesophagus, and by 
 a very narrow one with the pyloric 
 portion, ib. g, which is a small sub- 
 spherical pouch with a still smaller 
 oblique aperture into the intestine, 
 ib. k. The analogy to the gizzard of 
 the bird is further shown by the fre- 
 quent occurrence of stones in the 
 stomach of the Crocodile.' In all 
 carnivorous Reptiles the prey is swal- 
 lowed whole, and its entry into the 
 stomach is easy : but nothing is per- 
 mitted to pass out into the intestine 
 except the chyme and other fluids. 
 In herbivorous Reptiles the pylorus gives passage to vegetable 
 matters whose digestion is completed in the colon. 
 
 In the disposition and attachment of the intestinal canal, the 
 
 AbJomlnal \ iscei-a of a Llzai d. ccx^xxv. 
 
 ' ccxxxvr. vol. ii. p. 357. 
 
 ^ XX. torn. i. p. 146, preps, nos. 514-516. 
 
 ' XX. vol. i. p. 146, prep. no. 518 A. In the stomiielv of a Crocodllim aciitus, from 
 Jamaica, Hunter ' fouml the whole of the feathers of a binl, with a lew of the bones 
 which h;id lost all their earth, exactly similar to a bono which has been steeped in an 
 
 acid There were stones in the stomach of considerable size, larger, e. "■. than the 
 
 end of a man's thumb.' ccxxxvi. vol. ii. p. 337. Dr. Jones (ccxlv. p. 94") found in 
 the stomach of an Alligator 'the bones, teeth, hoofs, and hair of a pig; the tlesh had 
 been entirely digested.' 
 
ALIMENTARY CANAL OF REPTILES. 
 
 443 
 
 CrococUHa again offer the chief exception to Reptiles in general ; 
 in these the mesogastcr, fig. 301, h, is directly and broadly con- 
 tinued into the mesentery, as this is into a mesocolon ; they 
 are nominal distinctions of the same simple duplicature of the 
 peritoneal membrane. In the Crocodile the intestine, after 
 
 302 
 
 Viscera of the Female Tortoise (Emys ettropcea) seen from Ijebina ; tlic Imigs liavc Ijeen removed. 
 
 forming the duodenal loops, passes back to cross the spine to the 
 left, in close connection thereto : and, descending, again becomes 
 loose, and defines a 'root ' or beginning of a distinct 'mesentery' ; 
 in no Reptile is there a separate mesocolon. Thus, it is only 
 in Crocodilia that a ' duodenal ' portion of the intestine can be 
 
444 ANATOMY OF VERTEBRATES. 
 
 distinctly defined ; in other Reptiles it is indicated by its relation 
 to the pancreas and to the ducts of this gland and the liver, as at 
 e, f, fig. 301 {LacertcL), fig. 306, c,d{Rana), and fig. 305 (Chelone). 
 The large intestine is definitely marked ofi^ in all Reptiles, but is 
 short and, in most, simple, straight, and without caecal production 
 at its beginning;. 
 
 In no Reptile is the intestine so short and straight, or so 
 long and convoluted, as in certain Fishes ; as a general rule, 
 it is shorter in proportion to the trunk than in warm-blooded 
 Vertebrates. 
 
 In the Siren and Amphiume the intestine makes a few short 
 turns in its longitudinal course, and expands into a straight and 
 wide colon or rectum.' In the Menopome^ the convolutions are 
 more numerous, and the rectum is relatively wider. In Ccecilia 
 the intestine is continued in a slightly convoluted manner to the 
 short rectum which opens near the hinder extremity of the snake- 
 like body. The Newts and Salamanders have short intestines, 
 with few coils ; so likewise have the Toads and Frogs ; but, in 
 tlie lar\'al state of the latter, the intestine is very long, and forms 
 a double series of spiral coils, fig. 42, i ; and the modification by 
 absorption of this lierbivorous type of gut to the carnivorous one is 
 not amono; the least of the marvellous changes which the anourous 
 Batraehian undergoes in passing to its adult condition. In most 
 Serpents the short intestinal folds are packed closely together in a 
 long mass by connecting cellular tissue. In Sea-snakes (Hi/drophis) 
 the convolutions are more free. In Lizards the intestinal con- 
 volutions are commonly few, fig. 301, i, fig. 303, g, and free. In 
 the Chelonia, figs. 302 and 304, the convolutions of the small gut 
 are larger and more numerous; they are also well marked" in 
 the Crncodilia. 
 
 The muscular tissue of the intestine shows an external layer of 
 longitudinal fibres, and an internal layer of circular ones ; the 
 latter is remarkably thick in Chelorie. In gillcd and tailed 
 Batrachia the mucous membrane presents fine undulatory longi- 
 tudinal rugffi, not parallel, but often uniting. In Toads the ruga? 
 are transverse at the jejunum : in Frogs the ruo-a; are zio-zan-. 
 The mucous membrane of the intestine presents, in the Python, 
 small, flattened, scale-like processes ; in some Serjients they are 
 longitudinally extended, and fringed at the margin ; the appearance 
 of circular or 'connlvent' valves is due to the close coils of the 
 gut within a common peritoneal slieath. In the Chamarleon tlic 
 intestinal rugro are rhomboidal, and their free border is minutely 
 
 ' XX. vol. i. p. 122, prep. r.o. 444. -- n,. ,,. 003, p,op. ,»,. ,-,.'i4. 
 
ALIMENTAEY CANAL OF REPTILES. 
 
 445 
 
 fimbriate. In a Tortoise ( Testudo indica) the inner surface of the 
 small intestine is reticulate : in Testudo tabulata and in the Emys 
 furopcca it is disposed in small and numerous longitudinal ruga3 : 
 in Cheloiie iinbricata and Cludone Midas the jirincipal rugaj have a 
 wavy and slightly zigzag disposition. In the Crocodile the lining 
 niemhrane of the ieiunum is finely reticulate : 
 
 . . . . . 303 
 
 in the ileum it rises into longitudinal folds : in 
 the colon it again becomes minutely reticulate, 
 and is thrown into irregular rue;a3. 
 
 The intestinal tube usually somewhat dimi- 
 nishes in diameter as it approaches the colon. 
 The Batrachia have no ciecum ; the small in- 
 testine, in the Frog, makes a sudden bend, to 
 terminate obliquely in the short and wide colon.' 
 The more oblique entry of the ileum into the 
 colon of the Crocodile gives the appearance of a 
 short pouch on one side : some of the circular 
 fibres of the muscular tunic enter the ileo-colic 
 valve. ^ 
 
 In the Python the large intestine begins by 
 a subelongate, jiointed cascum, marked oft" from 
 the colon by a plaited valvular fold ; ^ a succes- 
 sion of such folds occurs in the rest of the large 
 gut. In some land and fresh-water Tortoises 
 ( Testudo tabulata, Testudo grceca, Emys europeeci) 
 the ileum opens obliquely into the side of the 
 l^eginning of the colon, leaving a short and 
 simple ' Cfecal ' summit of that gut ; "• the mar- 
 gins of the ileo-cffical orifice are p)uckercd into 
 folds, two of which, in Testudo grcEca, are continued into the 
 colon, the intervening groove extending for a short distance 
 along the curve of the colon. The colon is longer and wider 
 in the herbivorous Tortoises, and usvially contains grass, leaves, 
 or other vegetable substances, the small intestines being 
 empty. In some sjjecies of Agama (^Ai'discosoma), Galiotes, 
 Stellio, Monitor, and in the Draco volans, fig. 303, k, there is a 
 small caecum at the beginning of the colon, ib. i: and this gut, 
 when distended, seems distinguishable from the narrower rectum. 
 But the most complex large intestine has been met with in the 
 herbivorous Iguanas."' The ileum terminates by a slit on a ridge 
 
 Alimentary canal, 
 Draco volana. CCL. 
 
 ■ XX. vol. i. p. 204, 110. 669. ^ Ib. no 670. ^ Ib. no. 671 A. ' Ib. no. 671. 
 ^ XX. vol. i. p. 206, no. 671 B. 
 
446 
 
 ANATOMY OF VERTEBRATES. 
 
 projecting into the ca3cum, which is continued beyond, spirally, 
 and contracting to open into the colon by a rounded puckered 
 aperture, at the end of a conical valvular prominence. Valvular 
 folds of the mucous membrane j^roject into the colon from its 
 concave side, decreasing in breadth as they descend. The coats 
 of the intestine make smaller indentations from the convex side, 
 opposite the intervals of the larger folds. Beyond these folds the 
 colon diminishes in diameter, and makes a sudden turn upon 
 itself before becoming the ' rectum.' The cfficum is, here, not a 
 mere ' caput coli,' but a distinct segment of the alimentary canal, 
 having an orifice for ingress, and a second for egress, of contents, 
 analogous to the cardia and pylorus of the stomach, with parietes 
 more muscular than either of the intestines with which it com- 
 municates.' 
 
 It would seem, from jietrified contents or excretions of the 
 intestine, that some part, probably the terminal one, of this canal 
 had been provided, in the extinct Ichthyosaur, with a spiral valve, 
 fig. 105 ('coprolite' figured below the j^elvis). 
 
 The rectum does not open directly upon the exterior of the 
 body in any Reptile, but into a cavity, or ' cloaca,' common to it 
 
 The following Table (ccxlv. p. 92) gives the weight of the body, in grains, and 
 the lengths of the alimentary canal, in inches, in various Reptiles. 
 
 
 LeiifTtll 
 
 Weight ot 
 
 Length of 
 
 
 of body 
 
 the body 
 
 the canal 
 
 inclics 
 
 grains 
 
 inches 
 
 Menopnma alleghaniejisis ..... 
 
 
 
 24 
 
 Bana Cateabiana (Bullfrog) .... 
 
 
 9,800 
 
 34 
 
 Heterodon niger (Black viper) .... 
 
 32 
 
 4,620 
 
 26 
 
 Psammophls JlagelUjormis (Coaclnvhip snake) 
 
 68 
 
 .5.141 
 
 42 
 
 Coluber guttatus (Corn snake) .... 
 
 54 
 
 9, GOO 
 
 54 
 
 Coluber constrictor (Black snake) .... 
 
 54 
 
 5, 100 
 
 36 
 
 Crotalus adamantetis (Rattlesnake) 
 
 4S 
 
 6, 180 
 
 42 
 
 Alligator viississiirpiensis (Alligator) 
 
 
 211,940 
 
 147 
 
 Chelone caretta (Loggerhead turtle) 
 
 
 36,985 
 
 102 
 
 Chelydra serpentina (Snapping turtle) . 
 
 
 16,2.35 
 
 46 
 
 Eniys reticulata (Chicken terrajjin) 
 
 
 8,400 
 
 38 
 
 Emijs serrnta (Yellow-bellied terrapin) . 
 
 
 27, 172 
 
 66 
 
 Tesl.iiilo Pohiphemus (Gopher) .... 
 
 
 45, 500 
 
 78 
 
 Trionyx ferox (Soft turtle) 
 
 
 
 48 
 
 
 Loncrth 
 
 Length of 
 
 Length 
 
 
 oC tlie 
 
 Pliiall in- 
 
 of large 
 
 
 sto- 
 
 testine 
 
 iiites- 
 
 Menopoma. alleyhaniensis ..... 
 
 mnch 
 
 
 tinos 
 
 inches 
 3i 
 
 inche.s 
 16 
 
 inches 
 6 
 
 liana. Caiesbiana ....... 
 
 4 
 
 30 
 
 
 Chelydra serpentina . . ... 
 
 4 
 
 32 
 
 10 
 
 Testndo Polyphemus 
 
 8 
 
 24 
 
 46 
 
ALIMENTARY CANAL OF REPTILES. 447 
 
 with the urinai'y, genital, and allantoic orifices, when the latter 
 bladder persists in any degree. 
 
 In the BatracTda^ the allantois opens into the fore part of the 
 cloaca, or, as it seems, into that part of the rectum ; behind the 
 rectal outlet are the orifices of the two sperm-ducts or oviducts : 
 behind these are the orifices of the ureters ; the genital and 
 urinavjr outlets arc usually prominent. The rectal orifice is less 
 distinct and constricted, and the cloaca seems more a continuation 
 of the gut than in higher Reptiles. In the male Triton the 
 rectum forms a valvular projection into the cloaca, after it has 
 received the orifices of the vasa deferentia. 
 
 In true Ophidia there is no remnant of allantois opening into 
 the fore part of the rectum or cloaca ; in Aufjuis a small bladder 
 remains in that connection,^ which expands, in limbed Lizards, to 
 larger proportions. In Coluber, as in other Serpents, the terminal 
 orifice of the rectum is well marked ; behind it is a semilunar 
 fissure, receiving the outlets of the oviducts, and behind that is 
 the bilobed prominence on which the ureters open.^ The cloaca 
 in Lizards shows the valvular fold between the intestinal orifice 
 and those of the genital and renal conduits, together with the 
 orifice of tJie allantois at the fore part of the rectum. In the 
 Chelonia the allantois, fig. 302, u', ojiens into the fore part of the 
 cloaca, below or beyond the rectal orifice : this has a distinct 
 sphincter ;•■ the compartment of the cloaca receiving the terminal 
 orifices of the genital and urinary canal, and of the allantois, is also 
 divided by a projecting border, like a distinct orifice, from the 
 outer compartment, in which the clitoris, fig. 302, ii, or penis lies : 
 the former is termed the ' urogenital,' the latter the ' vestibular,' 
 part of the cloaca ; the urogenital orifice is transverse or semi-lunar. 
 In Cltel;/dra serpentina the o-vidncal orifices are immediately behind 
 the rectal one : the allantoic orifice is in front of it ; behind the 
 oviducts are the terminations of the ureters, and behind these, 
 Avithin the vestibule, are the wide orifices of two cloacal sacculi,^ 
 each of which exceeds the allantois in size. In Emys en.ropaa, 
 fiiT. 302, u, U, they equal the allantoic bladder, u'. The allantois 
 in the CrocodiUa is reduced to a urinary bladder-like dilatation of 
 the fore part of the cloaca, into which the rectum opens obliquely, 
 and by a valvular protrusion ; the genital orifices are behind this, 
 
 ' Siren, XX. vol. iv. no. 269.5 ; Amphiuma, ib. no. 2397; Menopoma, ib. no. 2.39 ; Tor- 
 toise, ib. n03. 2401, 2699; Salamandra, ib. no. 2407; Bana, ib. nos. 2409, 2702; Pipa, 
 ib, no. 2707. 
 
 = XX. vol. iv. p. 57, no. 2422. = Ib. no. 2708. ■" Ib. vol. i. no. 751. 
 
 5 'Anal sacculi,' xx. vol. iv. (1838) p. 147, no. 2722 e. 'Vessies auxiliares,' 
 coxLiv. (1839), p. 456. 'Vessies lombaircs,' ccxxxix. torn. vi. p. 363. 
 
448 AJSTATOMY OF VERTEBKATES. 
 
 and then come those of the ureters.' The urogenital compart- 
 meut opens into the vestibule by a narrow fissure, the lower part 
 of which is continued into the groove of the penis or clitoris 
 lying in the vestibule. 
 
 The cloacal outlet, commonly termed the ' anus,' varies in shape 
 in Reptilia, but is more constant in position than in Pisces ; it is 
 never so far forward as in some of that class. In tailed Batrachia 
 it is a longitudinal slit in the axis of the trunk ; in anourous 
 larva3 it is protected by folds of membrane, which unite to form 
 the lower border of the tail-fin ; during the progress of absorption 
 of this natatory organ the anus is somewhat advanced, and assumes 
 a rounded form with a sphincter. In the Sea-snake (^Pelamys) 
 the anus is longitudinally bilabiate, but the anterior part of the 
 fissure is crossed by a semilunar fold or ridge. In Lizards the 
 corresponding fold, with its scaly covering, is larger, covers more 
 of the orifice, and gives it a transverse semilunar shape. It has a 
 similar form in the Turtle. In Emys it is a puckered apertvire, 
 with a tunical border beneath the base of the tail ; in Trionyx it 
 is a longitudinal orifice, and nearer the end of the short tail. In 
 the Iguana the posterior valve of the cloacal opening is approxi- 
 mated, and applied to the anterior one by a muscle which arises 
 from each angle of the fissure or fold between the tail and the 
 thighs. The dilatation of the orifice is produced by two pairs of 
 muscles, attached, the one to the femoro-caudal fold, the other to 
 the lower surface of the tail. 
 
 § 76. The Liver of Reptiles. — This organ is proportionally 
 large in all Reptiles : its form is mainly governed by that of the 
 body. In Serpents, fig. 300, o, it is unilobate, long, and slender ; 
 in Tortoises, fig. 302, i, it is short and broad, chiefly composed of 
 two subequal lobes; in Lizards, fig. 292, h, it offers an inter- 
 mediate form. 
 
 In the Lepidosiren the liver consists of one long lobe, with a 
 transverse notch on the left side, lodging the gall-bladder. In 
 the Siren the liver presents a similar form, with the addition of a 
 small left lobe at the anterior end. In the Amphiume the lono- 
 and slender subtrihedral liver extends through nearly two thirds 
 of the abdominal cavity, and the gall-bladder is an inch distant 
 from the lower end. In the Menopome the liver is shorter and 
 broader, with the gall-bladder lodged in a fissure which makes 
 the posterior end bifurcate. In the Newt the liver has a smiilar 
 terminal notch into which a peritoneal fold eitters. In the Froo- 
 
 ' XX. vol i. no. 747, vol. iv. no. 2-43S. 
 
LIVER OF REPTILES. 
 
 449 
 
 the liver is divided into a right and left lobe, with subdivisions of 
 the latter. In the Pipa the right and left divisions are quite 
 distinct, and each is subdivided. In Cceciliu the elongated liver 
 is divided into several small flattened lobes. The liver, in the 
 Chameleon, consists of one lobe ; in the Gecko {Plutijdactylus 
 yuttatus) and the Draco volans, fig. 292, k, it is triangular: the 
 
 304 
 
 Viscera of the Female Tortoise (TJ/^yseuropwiO. xxxviii. 
 
 anterior angle accompanies the vena cava towards the heart : a 
 second angle, m, m, enters the curve of the stomach : the third is 
 directed backward, along the right side : the gall-bladder lies in a 
 notch between the last two angles. In some other Lizards this 
 notch is deeper, and the increased size of the left process gives the 
 liver a bilobed character ; the vena portje enters the fissure, the 
 vena cava enters the longer right lobe. In the Iguana the liver 
 extends from right to left, with a convexity forward, and with a 
 VOL. I. G G 
 
450 
 
 ANATOMY OF VERTEBRATES. 
 
 slender prolongation along the right side, into the apex of which 
 the postcaval vein enters. It has a narrow ' falciform ' ligament. 
 
 In the Crocodile the liver is divided into a right and left lobe, 
 anteriorly, by the heart, which almost wholly enters the fissure. 
 The right lobe is the largest, with the gall-bladder on its concave 
 side. The liver is more equally divided in Chelonia, fig. 304, I, I, 
 and chiefly also by the heart, ib. a', b'. The stomach, ib. k, 
 deeply imi)resses the left lobe, and is buried in it in some species 
 {Emys serrata). In many there is a process, like the ' lobulus 
 Spigelii,' entering the curve of the stomach. In the higher 
 Reptiles the liver is contained in a peritoneal pouch ; in Chelonia 
 and Crocodilia each lobe has its pouch more or less distinct. In 
 the Crocodile the capsule becomes aponeurotic, whence it is con- 
 tinued from the sterno-sacral border of the gland to the abdominal 
 parietes, to be connected, like a diaphragm, with the transversus 
 abdominis muscle.' 
 
 The lobes of the liver are subdivided into numerous and minute 
 lobules, compactly united by interlobular cellular tissue. The 
 lobules themselves are composed of corpuscles, or ' acini,' occupy- 
 ing the meshes of the vascular network pervading the lobule ; 
 these ' acini ' are larger in Reptiles than in Fishes. Their 
 secretion finds its way into biliary canals, distinguishable as 
 such, with proper walls, on the exterior of the lobule ; these 
 ducts anastomose in the interlobular spaces, and form larger 
 canals, accompanying the hepatic vessels, and, after repeated 
 unions, issuing, as the ' hepatic ducts,' from the portal fissure. 
 The walls of the ducts have no follicular glandules. The hepatic 
 tissue in Reptiles is usually softer than in warm-blooded Yerte- 
 
 ' rir. Jones, ccxlv. p. 113, ascertained the weight of the body and of the liver in the 
 following Rcptiliu, and gives the relative weight of the latter in the subjoined form. 
 
 
 
 Kuniber of 
 
 
 Weight at 
 
 times the 
 
 
 the body 
 
 "weight of 
 its liver 
 
 m gi-ains. 
 
 
 Rana Cateshiana (Bullfrog) 
 
 9,800 
 
 55 
 
 Heterodon niger (Black viper) 
 
 
 
 4,620 
 
 26 
 
 Psnmmophisjfinjellifonnis (Coachwhip snake) 
 
 
 
 5, 141 
 
 71 
 
 Coluber guttafus (Corn-sniike) 
 
 
 
 9, GOO 
 
 64 
 
 Cohiber constrictor (Black snake) 
 
 
 
 5, 100 
 
 57 
 
 Crotalus adamanteus (Rattlesnake) ' , 
 
 
 
 6, 180 
 
 55 
 
 Alligator mississippiensis {A\\\gi\tor) . 
 
 
 
 76, 507 
 
 73 
 
 Chelone caretla (Loggerhead Turtle) . 
 
 
 
 36,985 
 
 47 
 
 Chehjdra serpentina (Snapping turtle) 
 
 
 
 16,985 
 
 42 
 
 Eniijfi terrapin (Salt-water terrapin) 
 
 
 
 11,937 
 
 53 
 
 Emys reticulata (Chicken terrapin) 
 
 
 
 8, 400 
 
 18 
 
 Etni/s serrata (Yellow-bellied terrapin) 
 Testudo Polyphemus (Gopher) 
 
 
 
 23, 100 
 
 48 
 
 
 
 45, 500 
 
 50 
 
LIVEK OF REPTILES. 451 
 
 brates, and firmer than in Fishes. It never contains so large a 
 proportion of oil as in plagiostomous and some other Fishes. 
 
 A gall-bladder exists in all Rejttiles. It lies in a notcli on the 
 left side of the elongated liver in the Lepldosiren, Siren, Proteus, 
 and Amphiume, and in a notch at the hind eiid of the liver in 
 Meuopoma, Triton, and Salamundra. In Anourous Batrachia the 
 gall-bladder is imbedded in the right lobe. In the Chameleon 
 the gall-bladder is at the hind border of the liver; in Draco 
 volans, fig. 292, m, it lies in the notch between the left and hinder 
 angle ; in the Cyclodus and Iguana in the notch between the two 
 hinder divisions of the liver. The gall-bladder is deeply im- 
 bedded in the substance of the ri^ht lobe of the liver in Testudo : 
 it adheres by about one third of its length to the right lobe in 
 CheJone : it has a similar attachment in Crocodilus, but is less 
 closely connected, and sometimes quite detached, in Allujator and 
 Gavialis. In true Ophidiathe gall-bladder, fig. 300, p, is removed 
 beyond the liver to the side of the narrow canal connecting the 
 stomach with the intestine. In the snake-like Lizards (^Angids, 
 AmphisbcBna) the gall-bladder is in contact with the liver. 
 
 In Lrpidosiren, Siren, and Ampkiuma, the hepatic ducts com- 
 municate with the cystic, or with the gall-bladder {Siren~), and 
 the bile is conveyed directly by the cystic duct to the beginning 
 of the intestine. In the Iguana there is a distinct hepatic duct 
 which enters the duodenum about an inch from the pylorus, 
 a cyst-hepatic duct which enters the side of the gall-bladder, and 
 cystic ducts which leave the globose bladder abruptly. In Clie- 
 lonia the hepatic ducts unite with the cystic : but sometimes one 
 is continued directly to the intestine ( Testudo graca). In Chelone 
 Midas a long hepatic duct from the left lolje unites with a shorter 
 one from the right lobe, and the trunk joins the cystic near its 
 entrance into the duodenum. The cystic is very short and wide, 
 and runs obliquely through the thick walls of the duodenum. 
 In the Crocodile the hepatic duct sends a branch to the gall- 
 bladder, and goes to terminate in the duodenum, distinct from the 
 cystic. This arises from the apex of the bladder, and is long and 
 straight. In Ophidia the hepatic duct is of great length, and 
 unites with the cystic in the substance of the pancreas, near 
 the termination of the common duet. In some species (^Dispho- 
 lidus) it previously sends a branch directly to the gall-bladder. 
 The cystic duct in PtjtUon, single at its commencement, divides 
 into numerous branches, which penetrate the pancreas, and re- 
 unite with each other and the hepatic before terminating in the 
 duodenum. The advantage of this modification of the l^iliary 
 
 G G 2 
 
452 ANATOMY OF VERTEBEATES. 
 
 receptacle and ducts is obvious. Had the gall-bladder been 
 attached to the liver, as in insectivorous Anguida and Lizards, 
 it would have been compressed by the prey, which in true 
 Serpents is usually of large bulk when introduced into the 
 stomach. The stimulus of such pressure would have led to the 
 expulsion of the contents of the gall-bladder into the intestine 
 before the chyme had been prepared, and passed on into the 
 gut : the relative position of the liver to the stomach subjects 
 the gland to such stimulus to secrete whilst the contents of the 
 distended stomach are undergoing digestion. The bile is con- 
 veyed away by the long hepatic duct, but is reflected along 
 the branching cystic ducts to the gall-bladder, which has been 
 transferred to a jDosition beyond the pressure of the stomach. It 
 is so placed, however, as to be affected liy the distension of the 
 narrow canal which conveys the chyme to the duodenum, and is 
 thus stimulated to render up the bile to the gut, just at the time 
 when it is wanted for the sejiaration of the chyle from the chyme. 
 This fact in comparative anatomy is significant of the share taken 
 by the biliary secretion in the act of chyliiication. 
 
 The gall-bladder is not, however, a simple reservoir ; its vascular 
 and secreting inner surface can operate upon the bile by both 
 subtraction and addition : the more watery part may be diminished 
 by absorjjtion : the cylindrical epithelial cells which form the 
 innermost layer of the mucous membrane may be shed into the 
 liquid, with the contents of mucous follicles which are more or 
 less developed in that membrane. The mucous surface is 
 augmented by minute furrows in the Crocodile : in the Testudo 
 elephantopus it is nearly smooth. 
 
 The bile in Chelonla and most Reptiles is green : Hunter 
 notices its pale yellow colour in the ' Water-snake,' and its want 
 of bitter taste in the Chameleon.^ Chemical researches on the 
 nature of bile have been almost exclusively confined to that of 
 Mammals, in connection with which class the chief results will 
 be noted. Tlie glycocholic acid is wanting in the bile of the 
 Boa, as in that of the Dog. As might be supposed, from the 
 prevalent colour of the bile in Reptiles, the 'biliverdine' primarily 
 exists in it, not as a transformation of ' eholepyrrhine,' which is 
 the primary colouring ])rhicii)lc in most INIammals. The propor- 
 tion of taurocholate of soda in the bile of a Python is estimated 
 at 8-46 in 100, and in that of a Boa to 6-2 in 100 ; a trace of the 
 same princii>lc has been detected in the bile of a Tortoise. In 
 
 ' ccxxxvi. Yol. ii. pp. 373, 378. 
 
PANCREAS OF REPTILES. 
 
 453 
 
 305 
 
 all E-eptile.s the bile is poured into the gut near to, sometimes 
 close to, the pylorus.' 
 
 § 77. Pancreas of Reptiles. — ^ The pancreas in Reptiles is a 
 light grey or yellowish, sometimes pinkish, coloured gland, con- 
 sisting of numerous ' acini,' giving origin each to a duct, the 
 acini Ijcing united by them, like the short stalks of grapes, in 
 Inmches, about a larger duct; 
 such aggregates or ' lobules' 
 further uniting into ' lobes,' 
 and their ducts into a com- 
 mon canal, wliich terminates 
 either with, or close to, the 
 biliary duct in the intestine. 
 The lobes are separate in 
 Pi/tlwn, of a subcircular 
 flattened form, suspended 
 cluster-wise by ducts of from 
 six to twelve lines in length, 
 before uniting into the com- 
 mon canal. 
 
 The pancreas has a close 
 texture in herbivorous Clie- 
 lonia, forming a tliin layer, 
 spread out in the duodenal 
 mesentery, fig. 305, where 
 it branches into numerous 
 lobes. In most Ophidians 
 and in many Lizards it pre- p.™n™s,inri spiecnoi thf.Tm-tie,f7,c;™..v/rf»si. rrxxxi. 
 
 sents a more compact form, fig. 301, f. There are intermediate 
 conditions of structure in the present class. The pancreas is 
 ramified in Blenohranchn.s : it is more circumscribed in Menopoma, 
 where it forms a long, slender, yellow gland. It is rather broader 
 in Amphiuma and Triton. In the Frog, fig. 306,7?, it i^ flattened, 
 elongate, narrowest at the emergence of the duct (opposite c), and 
 sending a process, which snrroimds the gall-duct, as far as the gall- 
 l^ladder. In the Salamander it is long and narrow. It is thick and 
 pyramidal in Ccccilia albiventer ; straight, elongate, and slightly 
 forked in Cacilia interrupta : it is ovoid in most Colubridce ; of a 
 
 ' The i-elative size of the liver in Replilia Joes not relate to, or throw light on, its 
 probable accessory function as an claborator of the albumen and disc-cells of the 
 blood, or as helping to maintain animal temperature by the formation of grape-sugar 
 out of the nitrogenized elements. Dr. Jones, however, detected the presence of grape- 
 sugar in the liver of cold-blooded Animals at all periods of starvation. 
 
454 ANATOMY OF VERTEBEATES. 
 
 compact triangular form in the Rattlesnake,' where it is closely 
 attached to the commencement of the intestine, and is perforated Vjy 
 the biliary ducts. The pancreas is small and flattened in Lizards, 
 usually dividing as it recedes from the attachment by the duct to 
 the duodenum into a portion accompanying 
 30G the biliary duct, and another extending to 
 
 or towards the spleen. It is very small in 
 the Iguana. In the Crocodile the pan- 
 creas Is divided into two elongated lobes, 
 and sometimes sends its secretion into the 
 duodenum by two ducts. In Chehjdra 
 serpentina the pancreas extends from the 
 pylorus some inches along the duodenum, 
 dividing and again uniting, forming a loop, 
 and giving off a process which extends to 
 the spleen. In the Turtle ( Chelone Midas) 
 the pancreatic duct terminates on a pa- 
 pilla, whicli projects into the terminal ex- 
 pansion, or 'ampulla,' of the bile-duct. 
 The pancreas in carnivorous Terrapins {Emijs) is more bulky 
 and com])act in form than in the fucivorous Turtles ( CAefowe). 
 
 Thus in the vegetable-feeding Gopher the pancreas is -^^ of 
 the total weight of the animal : whilst in the carnivorous Snapper 
 it is -.\-^ of the total weight of the animal. As the proportion 
 of fat consumed by Carnivora must be greater than that by 
 Herbivora, the results of the above comparative observations 
 accord with the view of the use of the pancreas in preparing 
 fatty matters for absorption.^ 
 
 ' XX. vol i. p. 235, no. 778. 
 
 - Dr. Jones, ccxLV. p. 107, ascertained the weight of the body and of the pancreas 
 in several American ReptiUa, and gives the relative weight of the latter in the sub- 
 joined form. 
 
 Number of times 
 
 the "weight 
 of its pancreas. 
 
 Rana Cateshiana (Bull-frog) . . . . 
 
 
 
 
 
 1088 
 
 Helerodon niger (Black viper) 
 
 
 
 
 
 537 
 
 Psammopldsflagelliformis (Coaehwhip snake) 
 
 
 
 
 
 1353 
 
 Coluber guttatus (Corn snalie) . 
 
 
 
 
 
 1371 
 
 Coluber constrictor (Black snake) 
 
 
 
 
 
 472 
 
 Crotaliis ilurissux CBnndvi rattlesnake) 
 
 
 
 
 
 965 
 
 Chelone carelta (Loggerhead turtle) . 
 
 
 
 
 
 518 
 
 Cliebfdra serpentina (Snapping turtle) 
 
 
 
 
 
 630 
 
 Eimjs terrapin (Salt-water terrapin) . 
 
 
 
 
 
 994 
 
 Enn/s retieiihiia (Chicken terrapin) 
 
 
 
 
 
 7C3 
 
 Einys serriila (Yellow-bellied terrapin) 
 
 
 
 
 
 10G7 
 
 Tesfudo Poli/phemus (male Gopher) . 
 
 
 
 
 
 3500 
 
455 
 
 CHAPTER VI. 
 
 ABSOEBENT SYSTEM OF IIjEMATOCHYA. 
 
 § 78. All the definite structures of soft parts — acini and 
 simpler gland-follicles, their prolonged outlets or ' ducts,' — com- 
 pacted sheets or strata called ' skin ' and ' membranes,' mucous or 
 serous, — bladders, sinuses, and tubes, arterial or venous, — threads 
 or fibres, muscular, ligamentous, or nervous — are covered, coated, 
 or lined, by a loose or soft elastic substance, which, as it con- 
 nects the better-defined structures together, and fills up their 
 interspaces, is termed ' connective tissue ' (tela conjunctiva, tela 
 cclbdosa). It is dispersed in irregular jjlates, with intervals, cells, or 
 ' lacuniB,' and the plates consist of delicate and extremely minute 
 fibrils. The intervals contain a fluid called ' serous,' varying 
 in quantity, and also in quality, according to circumstances : 
 and they intercommunicate freely. These cavities are the seat 
 of a transudation from ' vessels ' and other more definite fluid- 
 holding structures during life : and recijiirocally the ' sercjsity ' is 
 resumed by the beginnings or pores of sinuses and canals. 
 
 The scrosity of the cavities of the connective tissue usually 
 consists of — 
 
 Water 975-20 
 
 Albumen .......... .5'42 
 
 Extractive matters and fat . . . . . . . 076 
 
 Mixed salts 15-62' 
 
 But it is subject to varieties from many causes, mechanical and 
 chemical, operating both within and out of the body. 
 
 The vessels or canals which seem to be most closely connected 
 with, or to be most directly traceable from, the connective 
 tissue and its lacunge are those called lymphatics, lacteals, and 
 absorbent vessels. This system exists as a separate organic 
 vascular apparatus only in the Vertebrate sid^kingdom : it was 
 first observed in Mammalia,^ was discovered by John Hunter in 
 
 ' CCLII. 
 
 - In the dug, by Aselli, in 1622 : at least the part of the absorbent system called 
 ' lacteals,' in the mesentery of the animal, ccmi. 
 
456 ANATOMY OF VERTEBRATES. 
 
 Birds' and Ilej)tiles,^ and afterwards described by Mr. Hewson 
 and Dr. Monro in Fishes. The most systematic and detailed 
 descriptions of the absorbent system of the Oviparous Animals, 
 jiublished in the last century, are those of Hewson.^ 
 
 §79. Absorbents of Fishes. — The lacteal system in Fishes 
 commences by a reticulate or plexiform layer of vessels attached 
 to the connective tissue on the outer or cellular side of the mucous 
 coat of the stomach and intestines : in the Skate '' the network is so 
 coarse that, when inflated, dried, and cut open, it a2)pears like a 
 subdivided cellular or areolar receptacle. The chyle is conveyed 
 thence in all Fishes by more vasiform lacteals, situated immediately 
 beneath the serous covering of the intestines, to large reticulate re- 
 ceptacles, one in the mesenteric angle along the junction of the small 
 and large intestines, the other extending along the duodenum, its 
 pancreatic appendages, and the jiyloric j)art of the stomach, and 
 often also surrounding the spleen. The presence of the mesentery 
 in the Myxinoids, and its alisence in the Lampreys, involve corre- 
 sponding differences in their lacteal systems : in the Myxinoids 
 the lacteals are supported and conveyed by the mesentery to the 
 dorsal region of the abdomen, and empty themselves into a 
 receptacle above the aorta and the cardinal veins, between these 
 and the vertebi-al chord : in the Lamprey the lacteals pass 
 forward, and enter the aljdominal cavernous sinus beneath the 
 aorta. 
 
 The lymphatic system is best demonstrated by injecting the 
 large absorbent trunk which runs upon the inner surface of the 
 
 ' 'It is but doing justice to tlie ingenious Mr. John Hunter to mention here, that 
 these lymphatics in the nccl;s of fowls were first discovered by him many years ago.' 
 (Hewson, civ. 1768, p. 220.) 
 
 - Hunter's account of this discovery is as follows: — ' In the beginnin"- of the winter 
 1764-.5, Igot a crocodile, which hail been in a show for several years in London 
 before it died. It was, at the time of its death, perhaps the largest ever seen in this 
 country, having grown, to my knowledge, above three feet in length, and was above 
 five feet long when it died. I sent to Mr. Hewson, and, before I opened it. I read over 
 to him my former descriptions of the dissections of this animal relative to the 'absorbing 
 system,' both of some of the larger lymphatics and of the lacteals, with a view to sec 
 how far these descriptions would agree with the appearances in the animal now before 
 us; and, on comparing them, they exactly corresponded. This was the crocodile 
 from which Mr. Hewson took his observations of the colour of the chyle.' Hunter 
 here alludes to the note appended to Mr. Ilewson's paper on the 'Lymphatic System 
 in Amphibious Animals,' Philosophical Transactions, vol. li.x. 1769, p. 199 a- 'In 
 a crocodile which I lately saw by favour of Mr. .John Huutcr, the chyle was 
 white.' 
 
 = CIV. 1768, 1769. 
 
 ' In this and other Plagiostomcs the gastric lacteals are confined chiefly to the 
 contracted pyloric canal. 
 
ABSOKBENTS OF FISHES. 457 
 
 ventral pavietes of the abdomen, along the median line from the 
 vent forward to the interspace of the pectoral fins, where the 
 size of the vessel best favours the insertion of the injeoting-pipe. 
 It receives the lymphatics of the pectorals, and (in thoracic and 
 jugular Fishes) of the ventral fins : then, advancing forward 
 through the coracoid arch, it spreads out into a rich network, 
 which almost surrounds the pericardium. The lymphatic plexus 
 which covers the heart of the Sturgeon and Paddle-fish presents 
 a spongy and almost glandular appearance when uninjected : the 
 tissue between the muscular and mucous coats of the gullet in 
 the Kays,' the gland-like mass in the orbit and palate of the 
 Chimffirae, and that lodged in a peritoneal fold of certain Sharks, 
 may likewise be appendages to the lymphatic system.^ Large 
 lymphatic trunks from the upper (dorsal) part of the circum- 
 cardial plexus receive the lymphatics of the myocommata by a 
 deeja-seated trunk which runs along the ribs, and the lymphatics 
 of the mucous ducts and integuments by a superficial trunk Avhich 
 extends along the lateral line, and gets a penniform character by 
 the regular mode in which its tributary lymphatics join it. 
 
 In the Wolf-fish {Anarrhichas) the lacteals commence in pro- 
 cesses of the edges of the mucous folds by cells or blind ends, 
 from which the vessels proceed to form a close plexus on the 
 outer surface of the intestine, and accompany in a plexiform 
 manner the bloodvessels. In the Turbot there are similar 
 plexiform surroundings of the bloodvessels of the stomach : and 
 in Silurus glanis the lacteal network covers all the stomach.-^ 
 
 In the Eel the gastro-enteric absorbent plexus communicates 
 with a cavernous sinus ujion the lower surface of the stomach, 
 and with a larger one which accompanies the intestinal canal, 
 whence other plexuses pass to the great subvertebral lym^jhatic 
 trunks. Along the free border of the intestinal spiral valve, in 
 Plagiostomes, there is a varicose lacteal reservoir, from which 
 proceed the vessels fonning the reticulate layer beneath the 
 miicous membrane. The lymphatics of the head form minor 
 plexuses at the bases of the orbits, and in the Carp they extend 
 into the basi-cranial canal ; those from the cellular arachnoid j)ass 
 through the occipital foramen to join the lymphatics of the spinal 
 canal, and terminate in the cervical and sub-occipital trunks, 
 which receive the lymphatics from the upper extremities of the 
 gills: these, with the deep-seated lymphatics from the kidneys, 
 join the single or double trunks at the under part of the vertebral 
 
 1 XX. vol. i. p. 126, no. 462. ^ colxi. p. 269. 
 
 = cv. pp. 27, 30, pi. 6, figs. 1 and 2 ; pi. 7, figs. 3 and 4. 
 
458 ANATOMY OF VEBTEBRATES. 
 
 column, which combine with the lacteal plexiform trunks con- 
 tinued forward along each side of the stomach and oesophagus, 
 to form a large, short, common lacteo-lymphatic trunk on each 
 side, which terminates in the jugular vein near its junction with 
 the short precaval vein. Fohman ' describes other and minor com- 
 munications between the absorbent and venous systems of Fishes, 
 as, e. g., in the gastric and intestinal plexuses in the Sheat-fish 
 and Turbot. The lymphatic system of the caudal portion of the 
 body is chiefly received by two caudal sinuses, intercommunicating 
 by a transverse canal, which sometimes perforates the base of the 
 anchylosed compressed terminal tail-vertebra. 
 
 The lymphatics of Fishes consist generally of a single tunic : 
 a most delicate epithelial lining may be distinguished in the 
 larger trunks. The only situations where valves have been seen 
 in these vessels are at the terminations of the trunks in the 
 caudal and the jugular veins. There are no lymphatic glands : 
 these are represented by the large and numerous plexuses, and 
 possibly by the gland-like layers or substances above-mentioned. 
 The chyle as well as the lymph of Fishes is colourless and 
 transparent : the plasmic corpuscles or lymph-cells are few in 
 number.^ The analysis of the lymph in Fishes is still a 
 desideratum. 
 
 § 80. Absorbents of Reptiles. — In the intestines of the Frog 
 and Salamander the lacteals form a network of large canals, 
 with minute or close meshes coextensive with the mucous 
 membrane ; the vessels continued therefrom accompany the 
 mesenteric arteries, sometimes forming a pair, running along 
 ojjpositc sides, with occasional connecting cross-branches ; more 
 commonly having these so numerous as to constitute a continuous 
 reticulate sheath about the artery, the cavity of which sheath 
 seems, in some parts, to be only partially divided by cross 
 threads.^ These lacteals, or intestinal lymphatics, open into a 
 receptacle at the dorsal line of reflection of the mesentery, of 
 large size in the Frog, but contracted and assuming rather the 
 
 cv. 
 
 man 
 
 '- In CXLV. these lymph-corpuscles are descrihed as ' centres of assimilative force, 
 lanifesting inherent power of developcment and change, some being granular, others 
 ith a capsule and in the condition of nucleated cells,' p. 249 (1846'). Prof. KoUiker 
 testifies to the fissiparous multiplication of the lymph-corpuscles in the lacteals of the 
 dog, cat, and rabbit. The corpuscle, in the condition of the nucleated cell, elongates, 
 the nucleus divides into two ; between which the cell contracts and tinally divides 
 (ccLxii. p. C3I)). In Fishes the nucleus undergoes further subdivision before the 
 fission of the cells takes ])lacc. 
 " CCLVI. p. 249. 
 
ABSORBENTS OF REPTILES. 459 
 
 form of a ' thoracic duct ' in the Newt ; it proceeds along the aorta 
 in both, communicating with lymphatic canals near the liver, and 
 dividing anteriorly, to accompany the right and left aortic arches, 
 and to receive the lymphatic conduits from the head and fore-limbs, 
 before terminating in the subclavian veins. Some of the vessels, 
 both arteries and veins, of the trunk have a similar lymphatic 
 sheath, but the principal conduits of the lymph, in the Batruchia, 
 have the form of irregular sinuses or lacunas, of great capacity 
 between the skin and flesh, and of smaller size in the inter- 
 muscular spaces of the limbs.' Air or liquid introduced into 
 these lymph-receptacles finds its way into the veins by the above, 
 and perhaps other, communications. The lymphatics of the 
 hind-part of the body and limbs communicate with a pair of 
 subcutaneous receptacles, with contractile walls, behind each 
 femoral joint ; there is a similar pair in front of the scapulie.^ 
 Tlicse receptacles have a subrhythmical action, not synchronous 
 with one another, or with the pulsations of the heart, or with 
 any of the movements of respiration, which in Batrachia are 
 deglutitional chiefly. The muscular fibres of these ' lymph- 
 hearts ' are of the strip)ed kind.^ The cervical pair transmit 
 their lymph into the jugular veins, and distend them at each 
 systole. The pelvic lymph-hearts have been seen to pulsate 
 sixty times in the minute in a frog.* In tlie large Ceratophrijs 
 cornuta two pairs of ischiadic lymph-hearts have been found. ^ 
 
 In the Tortoise the pelvic lymph-hearts are two, of a more 
 circumscribed rounded form, situated on each side of the bodies 
 of the vertebraj, between the femoral joints and the hind-border 
 of the carapace ; the valves at the inlets and outlets of the 
 lymph conduits, impressing the course of motion of the fluid, 
 are here readily seen.*^ In Lizards and Crocodiles the pelvic 
 lymph-hearts are situated near or upon the diapophyses of the 
 first caudal vertebra. In Pseudopus Pallasii they lie between 
 the muscles upon the sacral diapophyses, receiving the lymph 
 each by a single conduit from the great abdominal sinus, and 
 transmitting it to the umbilical veins ; they pulsate about fifty 
 times in the minute.^ In true Serpents {Python, e. g.) the 
 lymph-hearts are elongate, and situated behind the last pair of 
 ribs and upon the rib-like diapophyses of the anterior caudal 
 vertebrse; they receive the lymph by three orifices at one end, 
 and transmit it by two opposite orifices, to conduits com- 
 
 ' CCLTII. p. 28. ^ OCLV. p. 89. = cOLvni. p. 58. 
 
 ' LXXIV. '■" lb. " CCLV. pi. 1. ' CCLIX. p. 25, pi. 3. 
 
460 ANATOMY OF VERTEBRATES. 
 
 municating with the caudal vein. The three tunics of tliese 
 hearts, of which the middle one is muscular, with the inferent 
 and afferent valvular structures, are well displayed in the 
 Python.' 
 
 The intestinal lymjihatics, in Serpents, open into a large 
 receptacle, extending along the root of the mesentery, beginning 
 near the vent where it is narrow, receiving the lymphatics of 
 the tail, and extending forward, greatly expanded, as far as the 
 stomach, where it forms a cul-de-sac. This receptacle is reflected 
 about the aorta, which seems included in it, and receives the 
 lymphatics of the genital organs, kidneys, and intestines. Before 
 reaching the stomach, it sends off a plexifonn conduit, which 
 receives the lymphatics of the jiancreas, spleen, stomach, and 
 liver, the latter gland being more or less comjoletely sheathed by 
 the lymphatic receptacle ; this then contracts into an irregular 
 canal as it approaches the pericardium, where it terminates in a 
 cul-de-sac, but transmits the lymph l^y several lateral vessels to 
 a large plexus near the great vessels of the heart. The above 
 continuation of the abdominal receptacle has l)een called the 
 ' right ' or ' inferior ' thoracic duct. The ' left ' or ' sujJerior ' or 
 ' dorsal ' thoracic duct leaves the great receptacle nearer its 
 anterior extremity, by three or four conduits, and advances along 
 the (Esophagus to the pericardium, anastomosing with the rio-ht 
 duct, by transverse channels. On reaching the pericardium, the 
 left duct divides into two channels, which reunite in front of 
 the pericardium, and join the lymphatic plexus about the great 
 vessels, from which the lymph is conducted by two or three 
 terminal trunks to the two great prccaval veins. - 
 
 In Chehmia the chyle is absorlied into a stratum of intestinal 
 lymphatics, which, in the form of a close network, lies between 
 the muscular and mucous coats ; ^ from this the conduits iiierce 
 the muscular tunic, and affect a longitudinal course on the 
 exterior of the gut until they quit it, accompanying the me- 
 senteric bloodvessels to the great chyle- and lymph-receptacle, 
 fig. 307, C, C, which extends from the middle of tlie dorsal part 
 of the abdomen backward to l^ctween the ^'ertelira3 and rectum. 
 Here it receives the lymphatics of the hinder limbs and tail, and, 
 in succession forwards, those of the cloaca and its appendages, ib. 
 u, U, of the kidneys, ib. O, of tlic genital organs, ib. H, and intes- 
 tines, ib. V ; it presents the same quasi-capsular relation to the 
 
 ' CCLX. p. 538, pi. 13, figs. 7, 8, 9. ■ ccLYIi. p. 15. 
 
 ' XX. vol. ii. p. 17, nos. 850-858. 
 
ABSORBENTS OF REPTILES. 
 
 4G1 
 
 aorta as in Batrachin, and bifurcates anteriorly, the divisions 
 inclosing the right and left pulmonary arteries and aort«, and 
 
 
 • '] \- ;T "!■ '^^■ 
 
 «» 
 
 .w,<^ 
 
 A'iriccm ill situ, seen frniii hcliiiKl, witb tlic lyiuph-receiitacle iE}ii!/s eurojxuo). xxxvill. 
 
 terminating at the beginning of the two precaval veins, by 
 elliptical orifices guarded by valves. The lymphatic system of 
 the trunk and limbs affects the form of irregular plexuses and 
 dilatations. 
 
 The lymphatic system in Lacertilia resembles in the main 
 that of Oplddia and Chdonla. In CrocudiUa there are several 
 signs of advance. Hunter' noted the white colour of the chyle : 
 the ' receptaculum ' is more circumscribed ; its anterior divisions 
 are more vasiform, more like ' thoracic ducts ; ' there is a compact 
 gland-like plexus of lacteals at the root of the mesentery. At 
 the base of the tail the lymphatics surround the artery and vein 
 
 ' ccxxvi. vol. ii. p. .335. 
 
462 ANATOMY OF VEETEBRATES. 
 
 by a large plexns, filling up the haemal canal ; they present also 
 a plexiform character at the axillai and base of the neck, about 
 the jugular veins ; but the vasiform character is generally better 
 marked in the lymphatics of the Crocodile than in lower Reptiles, 
 and the valves occur more frequently. 
 
 The lymph-corpuscles are very few, and rarely visible in the 
 lymphatics of the tail of the Tadpole, but were numerous in the 
 lymphatic canals near the liver in Salamandra. By carefully 
 puncturing the large subcutaneous lymph-reservoirs of the Frog, 
 at the uj^per part of the thigh, the pure fluid may be obtained 
 from the living animal : but analysis of lymph has chiefly been 
 performed on the larger quantities discharged from artificial 
 fistula3 of the thoracic duct in the Horse and Cow, and its results 
 will be given in connection with the Mammalian class. 
 
463 
 
 CHAPTER YII. 
 
 CIRCULATING AND RESPIKATOET SYSTEMS OF IliEMjVTOCETA. 
 
 its 
 
 i 81. Blood of Fishes. — The red blood of Vertebrates owes 
 colour to the albuminoid substance called ' hajmatosine. 
 
 existing in the discoid corpuscles called ' blood-globules,' ' blood- 
 cells,' or ' blood-discs.' These float in the light straw-coloured 
 fluid called ' plasma,' which consists of water holding in solution 
 proteine principles, hydrocarbonates of the fatty nature, saccharine, 
 and saline matters. The watery solvent predominates in the 
 blood of Fishes and Batrachians. The 'proteine' basis exists 
 under the combinations termed ' albumen ' and ' fibrin.' 
 
 The blood-discs in Fishes are commonly of a full elliptic shape, 
 as in the Cod, fig. 8, ff, and Skate, fig. 8, h, p. 4 : but in the 
 Lamprey and Ammocete they are nearly circular. In the Myxine, 
 however, they are elliptic, and some are fusiform. They present 
 the largest size in the Sharks, but are smaller in them in projiortion 
 to the body, or mass of blood, than in Batrachia.' Besides the red 
 discs there are the larger white corpuscles in the Ijlood of Fishes as 
 in that of higher Vertebrates, but in less proportion than in Sau- 
 rians. Birds, or Mammals. 
 
 The comparison of main physiological importance between the 
 blood in different groups of Vertebrates, is that which relates to 
 the jjroportion of the organic matters contained in the water. 
 
 Prevost and Dumas expressed the general results of this com- 
 parison of the blood of the cold-blooded classes in the followino- 
 
 TABLE OF THE PROPORTION OF "WATER, CLOT (bLOOD-DISC'S AND FIBRIN), 
 ALBUMEN, AND SALT&i. 
 
 H.E^tATOCRTA 
 
 Water 
 
 Clot 
 
 Altiumen 
 and Salts 
 
 Hana esculenta (Frog) 
 
 Salmo fario (Trout) 
 
 Lota molva (Burbot) 
 
 Anguilla latirostris (Eel) 
 
 884 
 864 
 886 
 846 
 
 69 
 
 64 
 48 
 94 
 
 46 
 
 72 
 66 
 60 = 
 
 ' See ccxxxix. torn. i. 
 blood-discs of Fishes. 
 = CCLXV. p. 64. 
 
 p. 89, for the dimensions, in fractions of a millemeter, of the 
 
464 
 
 ANATOMY OF VERTEBRATES. 
 
 Dr. Joseph Jones ' has pushed this kind of analysis further, as 
 shown by the subjoined table. 
 
 Zyg(Bna malleus (Hammer-shark) 
 Lepidosteus ossens (Gar-fish) . 
 Salmo fario (Trout). 
 Lota molva (Burbot) 
 Anguilla latirostris (Eel) . 
 
 MoitfT Blood-discs 
 
 Plasma 
 
 Total 
 Weight 
 
 Water 
 
 Solid 
 Hatters 
 
 Total 
 Weight 
 
 Water 
 
 Solid 
 Matters 
 
 293-44 
 229-00 
 275-20 
 192-40 
 240-00 
 
 220-08 
 171-75 
 206-40 
 144-30 
 180 00 
 
 73-36 
 57-25 
 68-80 
 48-10 
 60-00 
 
 706-56 
 771-00 
 
 641-06 
 714-95 
 
 65-50 
 56-05 
 
 § 82. Veins of Fishes. — As the blood moves in a circle, it 
 signiiies little at what point we commence the description of the 
 parts in which it flows. But as, in tracing the jirogress of the 
 nutriment through the organs concerned in its chylification and 
 sanguification, we were led by the lymphatics to the veins, we 
 begin with them the account of tlie circulating system in the 
 present class. 
 
 The tunics of the veins of Fishes are unusually thin, and their 
 valves few : though commonly in the form of tubes, yet they more 
 frequently dilate into sinuses than in the higlier classes, and traces 
 of the diffused condition of tlie venous receptacles, so common in 
 the Invertebrates, are not wanting in Fishes ; as, for example, in 
 the fissures of the renal organs, where the veins seem to lose their 
 proper tunics, or to blend them with the common cellular tissue 
 of the part; and in the great cavernous sinus beneath the abdo- 
 minal aorta, receiving the renal and genital veins in the Lamprey. 
 The jugular veins of Osseous Fishes and the hepatic veins of the 
 Rays form remarkable sinuses. The very delicate fibres of the 
 proper venous tunic aifect a longitudinal disposition : and in many 
 of the veins of Fishes the walls show pigment, usually in the form 
 of stellate cells. 
 
 The veins of Fishes constitute two well-defined systems ; viz. 
 the ' vertebral ' and the ' visceral,' answering to the division of the 
 nerves and muscles into those of ' animal ' and ' organic' life : the 
 portal system is a subdivison of the visceral one, but also fre- 
 quently includes part of the vertebral system of veins, especially 
 in the Myxines, in which the portal sinus forms a common ineetiug- 
 j)oint between portions of both systems.^ 
 
 The capillary system of vessels consists in Fishes, as in other 
 Vertebrates, of minute but similar-sized tubules, capable of carrying 
 
 ' COXLV. p. 27. 
 
 - Rcl'/,ius, in x.Ki. ' Gcfiisssystcm,' 1841, p. 16. 
 
 ' .^f 
 
VEINS OF FISHES. 
 
 465 
 
 308 
 
 a single file of blood-discs, and connecting the termination of the 
 arteries with the commencement of the veins, figs. 328, 329. 
 
 The vertebral system of veins commences by a series of capil- 
 lary roots in the integnmcnts and muscles, which unite to form 
 branches corresponding with the muscular and osseous segments 
 of the body : these ' segmental ' veins consist, in the tail, of upper 
 or neural, and lower or htemal 
 branches; in the abdomen, of 
 upper and lateral branches ; in 
 the head, where the vertebral 
 segments are more modified, the 
 veins manifest a less rcgndar 
 and apprccialjle correspondence 
 with these segments. The ce- 
 phalic veins, returning the blood 
 from the cranial vertebrae, their 
 apjiendagcs and surrounding 
 soft parts, from the brain, the 
 organs of special sense and their 
 orljits or proper cavities, from 
 the mouth and pharynx, and, 
 receiving also the whole or part 
 of the ' vena3 nutritire ' from the 
 branchial arches, unite together 
 on each side to fovea a pair of 
 ^jugular' veins, fig. 308,7;*, each 
 of which usually t[ilates into a 
 larger sinus, and aeain contracts 
 and resumes the vasiform cha- 
 racter, as it descends to beneath 
 the parapophyses of the atlas 
 and axis, in order to join the 
 corresponding trunk of the ver- 
 tebral veins of the liody. ' This 
 great trunk, called ' vena cardi- 
 nalis,' ^ fig. 308, v, commences L^' 
 
 at ■ the base of the tail-fin, 
 where it receives blood, and some affirm also lymph, from the pul- 
 sating sac there present in the Eel-tribe. The vein-trunk is 
 
 ' 111 tlie Lamprey the corresponding jugular trunks lie above the aponeurotic repre- 
 pentatiyes of the vertebral parapophyses, 
 
 ^ ' La vcine cave ' of Cuvier; but it is not homologous with either the ' inferior ' or 
 * superior vcnaj cava; ' of Man. 
 
 VOL. I. n II 
 
 Circulation of the l>lood in the FJsb. ccLxvr. 
 
466 ANATOMY OE VERTEBRATES. 
 
 double, there being one for each side of the body, and both right 
 and left ' venaj cardinales ' extend forward, in cloae contact, along 
 the hicmal canal in the tail, then through the abdomen, and in both 
 regions immediately beneath the aorta and vertebral bodies, to near 
 the first vertebra, where each trunk diverges and descends to join 
 its corresponding ' vena jugularis,' fig. 308, v, forming the short 
 ' precaval ' vein,' ib. v, which empties itself in the great auricular 
 sinus between the aponeurotic layers of the pericardial and abdo- 
 minal septum. In the Lamprey the vena cardinalis is single along 
 the tail, but it bifurcates on entering the abdomen into two veins, 
 each of which is six times as large as the aorta. The left cardinal 
 vein is larger than the right in the Myxinoids : but the symme- 
 trical disposition of the vertebral venous system is more disturbed 
 in many Osseous Fishes, at the expense of the right side ; the right 
 cardinal vein, after some transverse connecting channels with the 
 left, finally terminating or losing itself therein anteriorly : part of 
 the right jugular vein, also, in this case enters the left or common 
 cardinal vein.^ In the Tunny the two ' vena3 jugulares ' unite and 
 form a common trunk, which enters the auricular sinus indepen- 
 dently.' The Shad, the Pike, and the Lucioperca are examples 
 where the jugular veins are symmetrical, and terminate distinctly 
 in the precaval veins. With regard to the vertebro-veual system 
 of the trunk, not all the segmental branches terminate in the 
 ' vena cardinalis ; ' the neural twigs form with the myelonal veins 
 a trunk which runs parallel with the cardinal veins, but above 
 the vertebral Ijodies in the neural canal. This trunk, the ' vena 
 neuralis,' communicates by short lateral aud vertical canals with 
 the venffl cardinales, and in the region of the abdomen these short 
 anastomising veins perforate the substance of the kidneys, and 
 receive the ' renal veins ' before terminating in the abdominal 
 cardinal veins. The neural vein gradually exhausts itself by 
 these descending branches, and does not extend to or terminate 
 anteriorly in the precaval trunk. Jacobson, observing that the 
 abdominal anastomotic l^ranches of the neural vein, in transferrino- 
 its contents to the cardinal veins, perforated the kidneys, thouo-ht 
 
 ' Diicius Ciwieri, Eatlike; quervenenstlimme, Miiller. Tlic precaval veins arc tho 
 homologiies of the two ' superior cava; ' in Reptiles and Birils, which receive the so- 
 called 'azygos' veins or reduced homologues of the ' venai cardinales' of Fishes: in 
 tlic liigher Mammals and in Man tliey are concentrated into a single ' superior vena 
 cava,' receiving the ' vena; cardinales ' by a common trunl<, thence called 'azygos ' in 
 Antliropotomy. The anatomical student is usually introduced to the cardinal veins, 
 as represented by their single honiologuo in tlie liuman siilyect, where their normal 
 symmetrical character becomes masked by an extreme modification, aud where the 
 name ' azygos ' is applicable only to so exceptional a condition. 
 - XXI. p. 38. 3 lb. p. 37. 
 
VEINS OF WSHES. 407 
 
 that those branches ramified in the renal tissue, like the portal 
 veins in the liver ; hut my observations eoncur witli those of 
 Meekel and Cuvier,' in showing tliat they rather receive or com- 
 municate with the renal veins in transitu in Osseous Fishes. In 
 the Lamprey the renal vein assumes tlie form of a cellular or 
 cavernous sinus, of a very darlv colour, extending along the 
 mesial margin of the kidney, uniting with its fellow joosteriorly, 
 and communicating by small orifices with the contiguous cardinal 
 vein. 
 
 The visceral system of veins commences in Osseous Fishes by 
 the capillaries of the stomach and intestines, of the pancreatic 
 ca!ca and spleen, of the generative organs and air-bladder : these 
 by progressive union and reunion, constitute either a single trunk 
 which forms the i)ortal arterial vein, fig. 308, L, of the liver ; or, 
 as in the Perch, a second trunk, the true homologuc of the ' in- 
 ferior vena cava ' which returns the blood from the ffenital organs 
 and air-bladder to the auricular sinus, without previous ramifica- 
 tion in the liver ; the portal trunk being formed only by the veins 
 of the alimentary canal and its appendages. The portal trunk is 
 single in the Ling, the Burbot, the Pope, the Eel, the Lamprey, 
 and the Plagiostomes ; but, in'the Carp, where the lobes of the 
 liver interlace with the convolutions of the intestine, the veins of 
 this canal pass directly into the liver by several small branches, 
 which ramify therein without forming a portal trunk. 
 
 In the Plagiostomes with the longitudinal spiral valve the main 
 root of the portal vein is concealed in the free, thickened, muscu- 
 lar margin of that valve : ^ the trunk of the intestinal vein is 
 lodged also in an internal fold of the mucous coat in the Lamj^rey : 
 in the Plagiostomes and Ganoids with transverse coils of the spiral 
 valve, the venous Idood is collected into an external intestinal vein. 
 In the Paddle-fish this vein joins the vein of the spleen (fig. 276, 
 h), and then, with the duodenal, pancreatic, and gastric veins, 
 forms the portal trunk. 
 
 Professors Eschricht and Miiller ' found, in the Tunny, tliat 
 the veins of the stomach, intestine, pyloric appendages, and 
 spleen, respectively srd:)dividcd into numerous minute venules, 
 which interlaced with corresponding ' retia mirabilia ' of the 
 arterial branches sent from the cocliac axis to the same viscera, 
 and formed pyriform masses of vessels before entering the liver. 
 
 In a few Osseous Fishes, as the Shad, some of the caudal 
 branches of the vertebral system of veins anastomose with the 
 
 > ixili. p. 381. ^ xoviii. p. 274. " cm. 
 
 H H 2 
 
468 
 
 AI^ATOMY OF VERTEBRATES. 
 
 veins of the rectum, and thus form part of the roots of the portal 
 system. But the most interesting modification of the portal 
 system of Fishes is that discovered by Eetzius in the Glutinous 
 Hag. In this and also in other Myxinoids, the genital and intes- 
 tinal veins form a coinmon trunk along the line of attachment of 
 the mesentery : all the gastric veins that do not empty themselves 
 into the cardinal vein also join the great mesenteric vein. This 
 vein advances to the S23ace between the jiericardiuni and the right 
 suprarenal body, receives the anterior vein of that body (its posterior 
 one joining tlie cardinal vein), and dilates into an elongated sinus, 
 which is said to contract, as if it were a portal heart. The ante- 
 rior part of this sinus receives a vein from the right anterior 
 parietes of the body, which is formed by the union of all those 
 of the muscular parts there which do not join the right jugidar 
 vein : the portal arterial vein is sent off from the posterior end of 
 the pulsating sac, near the entry of the mesenteric vein, and goes 
 backward to Ijeueath the two livers, and there divides, enters, and 
 ramifies in each. The hepatic vein of the hinder and larger liver 
 enters the common trunk or sinus formed by the union of the two 
 cardinal veins with the left jugular : the hejiatic vein of the smaller 
 liver joins the termination of the left jugular vein, and they to^'C- 
 ther end in the opposite side of the same common sinus. 
 
 lu the Plagiostomes the right jugular and cardinal veins unite, 
 and, receiving the vein of the pectoral fin (brachial vein), and a 
 superficial vein from the head (external jugular), form a short 
 transverse ' precaval ' trunk. A corresponding precaval trunk is 
 formed in the same way on the left side, and tlie great auricular 
 sinus is constituted by these and hj the wide hepatic veins, which 
 contract before they terminate. In many Osseous Fishes, as 
 
 Salmo, Silurus, 
 
 309 
 
 lldfll VCIKIU.S lio.lft Of Krl 
 CULXIV. 
 
 Bdone, Amjuilla, Ammodijtes, and Accipenscr, 
 the hepatic veins terminate in the 
 common sinus by a single trunk ; 
 in others, as Tlii/ninis, Gadiis, 
 HJ.io.v, and Plctiroitecfcs, by two 
 trunks ; and in a few Fishes, as 
 Clujica, Coftiis, and certain Cy- 
 prininds, by three or more trunks. 
 The pulsatile sac in the Eel, 
 fig. 309, is situated near the 
 beginning of the cardinal vein 
 on the ha;mal side of tlie caudal 
 vertebrae at the end of the tail. 
 It is of a yellowisli colour, 
 
VEINS OP FISPIES. 4G9 
 
 cliecqiicrecl more or less witli stellate pigment ; in shape fusiform, 
 fii;-. 309, A, or pyriform, ib. B ; at the distal end it is connected 
 with a small vein, c, which collects the hlood from the capillaries 
 of the tail, d, d' : at its proximal end it is connected with the 
 commencement of the carduial vein, h. The Idood, wliich is deep 
 red, ap]iears to flow into the sac in a continnons stream from c ; it 
 is forced out at each contraction in an interrupted current, f^nickly, 
 in successive portions, into h, where the movement soon subsides 
 into a continuous stream. During the systole the veins c and h 
 are lengthened, being drawn out ; in the diastole they resume 
 their size, and assist in elongating the sae ; which, both by 
 its contents and connections, is to be regarded as a ' venous 
 heart.' ' 
 
 Thus in Fishes the chyle, having already begun to manifest its 
 independent life liy the developement of disthict microscopic 
 granular corpuscles, as primitive centres of assimilative force, 
 before it enters the lacteals, undergoes in those vessels and their 
 receptacles a furtlier stage of conversion into blood by the reaction 
 and, as it were, impi'egnation of the lymj)!!, and by the interchange 
 of properties therewith : the vitalising stimidus of which inter- 
 change and reaction is manifested by the repeated spontaneous 
 fission of the corpuscles, many of which now acquire a capsule, 
 and thus become nuclei of cells. Then the mixed chyle and 
 cliyme enter the veins, where a further interchange of properties 
 with the venous blood and a new course of action and reaction 
 takes place. The primitive pale chyle-corpuscles are here few in 
 ninnber ; they have a capsule, and the granidar character of their 
 contents shows them to be in the course of change. Tire venous 
 Idood undergoes some change, probaldy, in its passage through the 
 kidneys, l)y virtue of the anastomoses of the renal vascular 
 system : it undergoes further change in its circulation througli 
 tiie liver, in so far as the l^ile, a fluid highly charged with 
 carbon and hydrogen, is eliminated from it : that in some fishes 
 {Myxinc, Bddlostonia) a contractile receptacle accelerates its 
 course through the portal circulation. The venous blood now 
 shows a marked accession of coloured corpniscles ; and it has 
 finally to be submitted to the influence of the atmosphere, and 
 especially to the reaction of the oxygenous element ; and for this, 
 the most important and efiicient cause of its conversion into 
 arterial l)lo(xl, a contractile cavity, with strong muscular walls, is 
 iirovided, in order to impel the l^lood to the organs especially des- 
 tined to effect its decarbonisation and oxygenation. 
 
 ' CXLV. p. 253 (18JG). 
 
470 ANATOMY OF VERTEBRATES. 
 
 § 83. Heart of Fishes. — The propelling organ is called the 
 ' heart,' fig. 308, H ; the respiratory organs the ' gills ' or branchias, 
 ib. B, h ; fig. 312, i, 6 ; fig. 323, 2,. 3, 4, 5 ; they submit the blood 
 to the influence of the air through the medium of the water in 
 which it is suspended or dissolved. 
 
 There is only one known fish, viz. the Lancelet, in which a 
 venous or branchial heart is not developed as a compact and pre- 
 dominant muscular organ of circulation : a great vein answering 
 to the ' vena cardinalis ' extends forward along the caudal region, 
 beneath the chorda dorsalis, above the kidney, fig. 169, h ; and as 
 it extends along the branchial oesophageal sac gives vessels to or 
 receives them from the ciliated vertical bands or divisions of that 
 sac, which vessels communicate with a vascular trunk along the 
 inferior part of that sac. Tliis trunk at its posterior end dilates 
 into a small sinus, ov, which pulsates rhythmically, and represents 
 rudimentally the branchial heart of the Myxinoids : the cardinal 
 vein, ba, divides anteriorly, and supplies the short vascidar pro- 
 cesses, f/ff, which project above the pharyngeal orifice, ph, into the 
 wide buccal cavity : the blood oxygenized in these processes is 
 transmitted to the cerebral portion of the neural axis, to the 
 organs of sense, especially the sensitive integument of the head, 
 and to the jointed labial tentacula, y, /', whence it returns to the 
 pharynx by the labial vessels which there unite together, and with 
 the inferior trunk of the vascular system, or arches, of the branchial 
 pharynx. 
 
 In the Myxinoids a heart consisting of an auricle and a ven- 
 tricle is situated, like the pulsating tube or sinus of the Lancelet, 
 far back from the head, in tlie beginning of the abdomen, where 
 it is inclosed by a fold or duplicature of the jieritoneum, extending 
 between the cardiac end of the oesophagus above, and the anterior 
 liver below, and forming the homologue of the pericardiimi, which 
 sac communicates freely by a wide opening with the common 
 peritoneal cavity. The auricle is much longer than the ventricle : 
 it receives the blood from the common sinus by an orifice defended 
 by a double valve. The auricle communicates with the left side 
 of the rounded ventricle, the ' ostium venosum ' having also a double 
 valve. There are no ' columna; carnea; ' or ' chorda3 tcndinea;.' The 
 artery, single here as in all Fishes, rises from the fore-part of the 
 ventricle with a pair of semilunar valves at the ' ostium arteriosum ' 
 behind its origin, beyond which it slightly dilates, but has no 
 muscular parictcs constituting a ' bulbus arteriosus.' In a large 
 Myxinold {Bdello stoma cirratinn, Dum.) tlie vessel from the heart 
 divides at once into two branchial trunks, reminding one of the 
 
HEAKT OF FISHES. 
 
 471 
 
 310 
 
 separate branchial arteries of the Cephalopods.' In other species 
 of Bdelloxtoma the artery extends beyond two or three pairs of 
 gills before it bifurcates ; and MuUer^ saw one instance in the 
 Mijxine (jlutinosa, where the branchial artery 
 continued single as far a.s the anterior gills. 
 
 The i^ericardium of the Ammocete com- 
 municates by one wide orifice with the peri- 
 toneum : that of the Lamprey is a shut sac, 
 and is supported by a perforated case of 
 cartilage, formed by the last modified pair of 
 liranchial arches, fig. 3 10, m. Not any of the 
 Dermopteri possess the ' bulbus arteriosus : ' 
 this is present, and forms, as it were, a 
 third compartment of the heart, 311, n, 
 beyond the ventricle, ib. A, and auricle, ib. 
 c, in all other Fishes : nay, if we include 
 the great ' sinus communis,' ib. D, as part of 
 the heart, then we may reckon four cham- 
 bers in that of Fishes ; but these succeed ' 
 each other in a linear series, like the centres 
 of the brain, and their valves are so disposed 
 as to impress one course upon the same cur- 
 rent of blood from behind forward, driving 
 it exclusively into the branchial artery and 
 its ramifications. This is very ditferent 
 irom the arrangement and relations of the 
 four compartments of the Inunan heart. 
 Physiologically the heart of Fishes answers 
 to the venous or pulmonary division, viz. 
 the right auricle and ventricle of the mammalian heart, and 
 its quadripartite structure in Fishes illustrates the law of vege- 
 tative repetition, rather than that of true physiological compli- 
 cation. The auricle and the ventricle are, however, alone proper 
 to the heart itself: the sinus is a developement of the termination 
 of the venous system, as the muscular bulb is a superaddition to 
 the commencement of the arterial trunk. The heart of Fishes 
 with the muscular branchial artery is the ' homologue ' of the left 
 auricle, ventricle, and aorta in higher Vertebrates ; Ijut it performs 
 a function ' analogous ' to that of the pulmonic auricle and ventricle 
 in them. 
 
 Some of the higher organised Fishes, which present the normal 
 structure of the heart, have, like the Myxinoids, a perforated 
 ' ix. vol. ii. p. 78, prep. no. 1018. - xxi. p. 9. 
 
 IlLni t .md gills, L:ini]iU'y 
 
472 
 
 ANATOMY OF VEETEBEATES. 
 
 pericardium. In the Sturgeon the communication with the peri- 
 toneum is by a single ehjngated. caual extending along the ventral 
 surface of the ccsophagus. In the Planirostra and Chimseroids 
 the pericardio-peritoueal canal is^also single. In the Plagiostomes 
 
 311 
 
 TTcrirt and trill-archer, Per(^,^ XXIII. 
 
 it bifurcates, after leaving the j^ericardium, into two canals, which 
 diverge and open into the jjeritoneum, opposite the end of the 
 oesophagus : no ciliary movements have l^een noticed on the 
 surface of these remarkable conduits. The serous layer of the 
 pericardium is defended by an outer aponeurotic coat in Osseous 
 Fishes and Plagiostomes, which adheres to the surrounding parts. 
 In the Sturgeon, Wolf-fish, Loach and Mura^na, short fil)rous 
 bands supporting vessels pass from different parts of the peri- 
 cardium to the surface of the heart : in most other lishes the heart 
 hangs freely except at the two opposite poles, viz. where the 
 sinus communicates with the auricle, and wliere the biillius 
 arteriosus is continued into the branchial artery. 
 
 In the Plagiostomes the sinus itself is situated within the peri- 
 cardium ; but in Osseous Fishes between the lavers of the posterior 
 aponeurotic partition between it and the abdomen. Tlie heart is sit- 
 uated below the hind-part of the gills, and , as these are more concen- 
 trated in the head in all Fishes above the Dermopteri, so the position 
 of the heart is more advanced, fig. 308, ii. In the Plagiostomes. the 
 Sturgeons, and many Osseous Fishes, e.g. the Porcli, the Angler 
 (L(i])hius), and the Sun-fish (Orth(/qorisais),ti\eoiiiiQ(!hy which the 
 great sinus communicates witli the auricle isgnardcd by twoscmihmar 
 valves; Init these are I'ar from being constant in the Telcostomi. 
 The auricle, when distended, ia larger in proportion to the -ventricle 
 
HEART OF FISnES. 473 
 
 in Fishes than in higher Vertehrates. Its relative position to the 
 vcuti-icle varies in different species, and permanently represents as 
 niany similar variations displayed temporarily during the course of 
 the heart's developement in birds and mammals ; thus in the heart 
 of Scorpa27ia scrofu, as in the Myxinoids, the auricle is posterior to 
 and in the same longitudinal line with the ventricle : in the 
 Perch, fig. 311, c, Carp, Sole, and Eel, it has advanced to the 
 same transverse line, on the dorsal and left side of the ventricle : 
 \n the Sturiouidaj and other Ganoids it extends more forward, 
 dorsad of both ventricle and bulbus arteriosus, and the heart, 
 including the venous sinus, is now bent into a sigmoid form. The 
 walls of the auricle are membranous, with thin muscular fasciculi 
 decussating and forming an open network ; but these are closer 
 and stronger in the Sun-fish, Sturgeons, and Plagiostomes. The 
 cavity is simple, ]jut its inner surface is much fasciculated in the 
 Sun-fish and Sturgeon, where the ends of the valves of the sinus 
 are attached to the strongest muscular bands. Only in the 
 Lepidosiren is there any vestige of a septum, and this is reticu- 
 late. The auricle communicates by a single orifice, commonly 
 with the dorsal or the anterior part of the ventricle : this is 
 guarded usually by two free semilunar valves ; but in tlie 
 Sturgeon, their margins and their surfece next the ventricle are 
 attached to numerous ' chordaj tendinea?.' In the Orthagoriscus 
 the auricular aperture is guarded by four semilunar valves, the 
 two smaller ones Ijeing placed at right angles with and on the 
 auricular side of the two larger and normal valves : their margins 
 are free. 
 
 The ventricle, fig. 311, A, usually presents the form of a four- 
 sided pja-amid, one side dorsad toward the auricle ; one angle 
 ventrad, and the liase forward. In the Lcpidosteus and Poly- 
 pterus, however, it is pyriform : in the Pike it is lozenge-shaped : 
 in the Lophius, as in the Myxinoids and Lampreys, it is oval : in 
 most Plagiostomes its transverse diameter is the longest, as if 
 preparatory to a division. Its cavity is, however, simj)le in all 
 fishes. The parietes of the ventricle are very muscular, and the 
 fibres are redder than those of any other part of the muscular 
 system ; but the colour is less deep in the ground-fisJies than in 
 those that swim nearer the surface, and enjoy more active loco- 
 motion and respiration. The exterior muscular fibres decussate 
 and interlace together irregularly and inextricably ; but the 
 deeper-seated ones form more regular layers, the innermost being- 
 transverse and circular, and separating readily by slight decom- 
 iiosition from the outer and more longitudinal layers. Some of 
 
474 ANATOMY OP VERTEBRATES. 
 
 the internal fasciculi send off the ' chordee tendinece ' above men- 
 tioned in the Sturgeon ; but in almost all other fishes those 
 ' chords ' are absent, and the auricular valve is free. In most 
 Osseous Fishes the orifice at the base of the bulbus arteriosus is 
 provided with a pair of semilunar valves : the Sun-fish ( Orthago- 
 riscus) }\a,s, four such valves there.' But the Ganoids, Holocephali, 
 and Plagiostomes have two or more transverse rows of semilunar 
 valves attached to the inner surface of their long and muscular 
 bulbus arteriosus. There are two rows of three valves in the 
 Grey Shark {Galeus), in the Blue Shark (Carchai-ias), in the 
 Dog-fish ( Scyllium), and in the Chimasroids : the Amia has two 
 rows of six valves : in the genera S-phyrna, Mustelus, Acanfhias, 
 Alojnas, Lamna, Rhinohatus, Torpedo, and Accipenser, there are 
 three rows of valves: the Sturgeon's heart ^ shows five valves in 
 the anterior row, and four valves in each of the other rows ; and 
 the free margins of the valves are connected by short ' chordas 
 tendineaj ' to the parietes of the bulb. The genera Hexanthus, 
 Hcptanchus, Centrophorus, and Tri/gon have four rows of valves. 
 The heart of the Raia Batis ^ shows five rows, the valves 
 increasing in size to the last row, which is at the termination of 
 the bulb. Scymnus, Squatina, and Myliobat's have also five 
 rows of valves. In Cephaloptera the large bulbus arteriosus ■* 
 presents internally three longitudinal angular ridges, at the sides 
 of which are small valves disposed in pairs, and in foiu- or five 
 rows : besides these there are three larger valves at the beo-in- 
 ning, and three at the end of the bulb. The valves are still more 
 numerous in lepidoganoid fishes, and are arranged in longitudinal 
 rather than in transverse rows : the Polypterus shows three such 
 rows of nine or ten larger semilunar valves alternating with as 
 many rows of smaller valves. The Lepidosteus has five longi- 
 tudinal rows of sub-equal valves : those at the end of the bulb 
 being always the largest and most eflBcient. In the Lepidosircn 
 the place of valves is supplied in its long and twisted bulbus 
 arteriosus by two longitudinal ridges, fig. 312, c ; ^ the interestino- 
 stages, which we have been tracing through the highly organised 
 Ganoids and Plagiostomes, in the partition of the bulb into 
 distinct arterial trunks for the systemic and pulmonic circidation, 
 being most advanced in this amphibious fish. 
 
 The auricle in the Lepidosiren anncctcns, ib. a, is essentially 
 single, but has two car-like appendages." The venous sinus 
 
 ■ XX ii. p. 37, rrcp. no. 905. = lb. p. 38, prep. no. 908. » lb. p. 38, prep. no. 909 
 
 I found Its cavity more capacious than that of the oontraetcd ventricle 
 " XXXIII. p. 3-13. p. pi. xxvi. lig. 2. c. « lb. p. 345. 
 
GILLS OE FISHES. 
 
 475 
 
 312 
 
 communicates with it witliout any intervening valve ; the auricle 
 receives the vein frt)m the air-bladder by a distinct aperture, close 
 to the o]3ening into the ventricle ; regurgitation into the vein 
 being prevented by a hard valvular 
 tubercle, which also projects into the 
 ventricle. The ventricle (fig. h) is 
 single, like the auricle; its inner 
 parietes are very irregular : a ' tra- 
 becula ' projects from the lower 
 part of the cavity, like a rudimental 
 septum : a smaller transverse ' tra- 
 becula ' arches over and acts as a 
 valve to the single auriculo- ventri- 
 cular opening, but there are no 
 proper membranous semilunar 
 valves. 
 
 The muscular parietes of the 
 ' l:)ull)us arteriosus ' are distinct in 
 all fishes from those of the ventricle ; 
 they may be overlapped by these, 
 but an aponeurotic septum inter- 
 venes between the origin of the bulb 
 and the overlapping ventricular 
 fibres.' 
 
 § 84. Gills of Fishes. — The primary division of the branchial 
 artery in the Myxinoids has been already described. Each gill- 
 sac receives, either from tlie trunk or its bifurcations, its proper 
 artery. The leading condition of the gills in other fishes may ha 
 understood by supposing each compressed sac of a Myxine, fig. 
 
 CirculatiDg and respiratory organs, 
 LepiUusin;li 
 
 313 
 
 314 
 
 Two gill-sacs, SdcUo- 
 stoma 
 
 Two gill-sacs, Lamprey 
 
 313, m, to be split through its plane, and each half to be glued by 
 its outer smooth side to an intermediate septum, which would then 
 support the opposite halves of two distinct sacs, and expose their 
 vascular mucous surface to view. If the septum be attached by 
 
 XX. vol. ii. p. 39, prep. no. 910. 
 
476 
 
 ANATOMY OF VERTEBEATES. 
 
 its entire margin, the condition of the plagiostomous gill is effected. 
 If the septum be liberated at the outer part of its circumference 
 and the vascular surfaces are produced into pectinated lamelli- 
 gerous processes, tufts, or filaments, proceeding from the free arch, 
 the o'ill of an ordinary osseous or teleostomous fish is formed. 
 Such a gill is the homologue, not of a single gill-sac, but of the 
 contiguous halves of two distinct gill-sacs, in the Myxines. 
 Already, in the Lampreys, the first stage of this bi-partition may 
 be seen, fig. 314, vi, and the next stage in the Sharks and Rays: 
 consequently in these fishes, a different artery goes to the anterior 
 branchial surface of each sac or fissure from that which supplies 
 the posterior branchial surface of the same fissure ; whilst one 
 branchial artery is appropriated to each supporting sejitum or 
 arch between the fissures, as it is to the liberated sejjtum or 
 l^ranchial arch in the Teleostomi} Before describing the branchial 
 vessels it will be necessary to describe the organs upon Avhicli 
 they ramify. 
 
 In the Lampreys and Plagiostomes each supporting septum of 
 the two (anterior and posterior) branchial mucous surfaces is 
 attached to the pharyngeal and dermal integu- 
 ments by its entire peripheral margin, and the 
 streams of water fiow out by as many fissures 
 in the skin, ib. h, as those by which they enter 
 from the pharynx, ib./: these are called ' fixed 
 gills,' and the sjiecies possessing them are cha- 
 racterised as ' p>isces branchiis fixis.' In the 
 Teleostomi = Osseous, Plectognathic, Lopho- 
 branchiate. Ganoid, and Holocephalous fishes, 
 the outer border of the supporting brancliial 
 arch is unattached to the skin, and plays freely 
 backward and forward, with its gill-surfirccs, 
 in a common gill-ca-\'ity which has a single 
 outlet, usually in the form of a vertical fissure : 
 with this structure are called ' pisccs branchiis 
 
 Brancli ial organs, 
 
 the species 
 liberis.' 
 
 In tlic IMyxine the outlets of the six lateral branchial sacs, fig. 
 315, m, on each side are produced into short tubes, which open 
 into a longitudinal canal, /(, directed backward, and discharging 
 Trof. Milne Edwards lias exemplified this homology hy the sub- 
 
 ' CXLV. p. 258. 
 joined formula ; — 
 
 Osseons Fishes 
 
 ria"iustomous Fishes 
 
 h.hx h 
 
 B 2 
 
 h \h I \ h. 
 
GILLS OF FISHES. 
 
 316 
 
 tlic bvancliial stream by an orifice, h, near the middle line of the 
 ventral surface : between the two outlets of these lateral longi- 
 tudinal canals, but nearer the left one, is a third larger opening, 
 /, which communicates by a short duct with the end of the long 
 ttsophagus, I, and admits the water, which passes from that tube 
 by the lateral orifices, y, leading into the branchial sacs. This is 
 the first step in devclopcment beyond that simjiler condition which 
 prevails in the Lancelot, where the whole parietes of a much 
 dilated (xsojihagus, fig. 169, rr, are organised for res}>iration ; and 
 besides the pharyngeal ojiening, ph, the sac communicates by a 
 short and wide ' ductus cesophago-critaneus,' ib. od, with the 
 external surface, and also with the peritoneal cavity. The 
 common resjnratory surface of the (lesophagus is ciliated in the 
 Lancclct. The sacs developed from the oesophagus, and specially 
 set apart for respiration in the Myxinoids, have a highly vascidar, 
 but not a ciliated mucous surface : this is disposed in radiated 
 folds, and is further increased by secondary plicjc. The seven 
 branchial sacs on each side of the oesophagus 
 have short external ducts, fig. 313, /(, which 
 open by as many distinct orifices in the skin 
 in a species of Bdellostoma hence called liep- 
 tatreuta : the internal branchial ducts com- 
 municate by as many openings, ib. /, witli 
 the oesophagus. In the Lampreys there are, 
 also, seven stigmata on each side ; but another 
 stage in the separation of the respiratory from 
 the digestive tract is here seen, for each in- 
 ternal duct communicates with a median 
 canal, fig. 310, d, beneath and distinct from 
 the oesophagus, terminating in a blind end 
 behind, and communicating anteriorly with 
 the fauces by an opening guarded l^y a double 
 membranous valve. 
 
 In all higher fishes the inlets to the branchial 
 interspaces are situated on each side the 
 fauces, and are equal in number with those 
 interspaces, fig. 316, i — 5. The outlets are, 
 with the exception of the Plagiostomes, single 
 on each side : they vary much in size ; are 
 relatively largest in the Herring and Mackerel 
 families, smallest in the Eels and Lophioid 
 fishes ; in some of the small Frog-fishes, 
 Antennarius, the circular branchial pore is produced into a 
 
478 ANATOMY OF VERTEBEATES. 
 
 short tube above each pectoral fin. The power of existing 
 long out of water depends chiefly on these mechanical modi- 
 fications for detaining a quantity of that element in the 
 branchial sacs ; for fishes perish when taken out of water, chiefly 
 by the cohesion and desiccation of their fine vascular branchial 
 processes, through which the blood is thereby prevented from 
 passing.' If suflScient water can be retained to keep the gill- 
 plates floating, the oxygen which is consumed by the capillary 
 branchial circulation is supplied to the water retained in the 
 branchial sac directly from the air. In some of the Eel tribe the 
 small branchial outlets are closely approximated below, as in 
 Sphagehranclius ; and they are blended into a single orifice in 
 Symbranchus, analogous to that in the Myxine. In some Ganoids, 
 many Plagiostomes, fig. 13/, br, and all Sturgeons, a canal leads 
 from the fore part of each side of the branchial chamber to the 
 top of the head ; the outlets are called ' spiracles,' the canals 
 ' spiracular.' The nasal sac communicates in the Lamprey with 
 the single homologous canal, the inner or faucial aperture of 
 which is shown at c, fig. 277. 
 
 The branchial chamber is largest in the fishes which have the 
 smallest outlets, as, e.g., in the Eel tribe, the Uranoscopi, the 
 Blennies, and especially the Lophioids : extending backward in the 
 Angler (^Lophius piscatorius) towards the hind part of the abdomen, 
 with a proportional elongation of the branchiostegal rays ; and 
 still further back in lialieutea. The opercular flaps formincr the 
 outer wall of the gill-chambers are described at pp. 123, 124, 
 fig. 84 ; the branchial arches at p. 106, fig. 85. The basi- 
 branchials are usually present only in the two or three anterior 
 arches, the others joining below directly, or by the medium of a 
 gristly plate ( Trigla) to the last basibranchial ; or terminating 
 loosely, as in Murenophis. The hypobranchials are usually 
 present only in the first or second arches : the most constant 
 elements, both as to existence and shape, are the ceratobranchials, 
 fig. 85, 47, and epibranchials, ib. 48. The pharyngo-branchials, 
 ib. 49, vary in shape and tissue ; they attach the arches to the 
 base of the skull, and develope, with the anterior epibranchials, 
 fig. 325, the complex labyrinthic appendages of the branchial 
 apparatus in the Climbing Perch (Aiiabas) and its allies. In 
 Lophius and Diodou there are only three pairs of branchial arches. 
 The fissures between the arches become shorter as they recede in 
 position, the last being commonly a mere foramen : their vertical 
 extent shows an agreement with that of the outer gill-slit: they 
 
 ' CVI. j). 124. 
 
GILLS OF FISHES. 
 
 479 
 
 317 
 
 are long, e.g. in the Mackerel ; short in the Eel : in the Lopho- 
 hranchs they are one -third the length of the arches: in the 
 Plectogonaths they are half that length ; in the Carji-tribe they 
 are nearly as long, in the Salmon-tribe quite as long, as the 
 branchial arches themselves. 
 
 The main purpose of the gills of fishes being to expose the 
 venous blood in a state of minute sul)division to streams of water, 
 the branchial arteries rapidly divide and subdivide until they 
 resolve themselves into mi- 
 croscopic capillaries. These 
 constitute a network in one 
 plane or layer, fig. 317, 
 supported hj an elastic 
 plate, and covered by a 
 tessellated and non-ciliated 
 epithelium. This covering 
 and the tunics of the capil- 
 laries are so thin as to 
 allow the chemical inter- 
 change and decomposition 
 to take place between the cai-bonated blood and the oxygenated 
 water. The requisite extent of the respiratory field of capillaries is 
 gained by various modes of multiplying the surface 
 within a limited space. In the Marsipobi-ancldi 
 and Plagiostomi, for example, by folds of mem- 
 brane on plane surfaces : in the Lophohranddi by 
 clavate processes grouped into tufts : in the Pro- 
 topteri, by double or single fringes of filaments : 
 in the rest of the class by the production of the 
 capillary-supporting plates from each side of long, 
 compressed, slender, pointed processes, extending, 
 like the teeth of a comb, but in a double row, fiij. 
 3 1 8 , fZ, d, from the convex side of each branchial arch, 
 fio;. 311, h. 
 
 Each pair of processes has its flat sides turned 
 toward contiguous pairs, and the two processes of 
 each pair stand edgeways toward each other, and 
 are commonly united for a greater or less extent 
 from their base : hence Cuvier describes each pair 
 as a single bifurcated plate, ' feuillet.' ' 
 
 In the Swordfish {Xiphlas), the processes of the 
 same pair stand quite free from each other ; whence 
 Aristotle described this fish as having double the 
 
 ' XXIII. i. p. 379. 
 
 Abrauclijalloaf, ^vith the reppiratory caiiillarics on side, 
 Ood. CCLX"\'I1j[. 
 
 318 
 
 Diac^ram of tkc cii- 
 culatloii of tlie blood 
 through the bran- 
 chial leaflets, I'ish. 
 
 Xilll. 
 
480 ANATOMY OF VERTEBRATES. 
 
 usual number of gills.' But to compensate for tins independ- 
 ence, and to prevent the inconvenience of mutual pressure, the 
 processes of the same scries are united together by little vascular 
 lamella3, so that tlie surface of the gill is reticulate rather than 
 pectinate. In the Orthufjoriscus the processes of each series are 
 not opposite, but alternate. In a few species the processes of 
 each pair are joined together to near their apices, as in the 
 Sturgeon, in which the musculo-membranous medium of union 
 extends from pair to pair throughout the entire gill, forming a 
 true ' septum branchiale,' and presenting a transition to the more 
 complete septum which divides the respiratory vascular surfaces 
 in the Plajriostomcs. 
 
 In fig. 318, the course of the blood through a i:>air of lu'anchial 
 processes is diagrammatically shown : a is a section of the 
 branchial arterj' ; d is the branch sent along the outer margin of 
 the process ; e is the vessel receiving the blood from the capil- 
 laries after the respiratory change has been effected, and returning 
 it, along the inner liordcr of the process, to the l^ranchial vein, the 
 sectional area of which is shown at c. In fig. 319 arc shown the 
 vascular plates or lamella;, h, of the branchial processes, a', in the 
 Cod (^Morrhua vulgaris), in which they are confined to the inner 
 half or two-thirds of the process. Fig. 317, representing a trans- 
 A'crse section of the process, shows the degree and form in which 
 the plates extend from it on each side : the arrows indicate the 
 course of the blood from the outer to the inner liorder of the 
 plate-bearing process. Fig. 320 represents the frame-work 
 supporting the vascular structure of the gill : a is a section of the 
 branchial arch; h is the base of the branchial jirocess attached to 
 but distinct from the arch : c its outer obtuse Ijorder ; d its inner 
 border, from which are continued the elastic cords, f, exteudino- 
 along the outer margin of the lamella;, fig. 317, i, and maintainiii'T 
 them outstretched.^ The number of plates on one process has been 
 estimated at 55 in the Gudgeon, 96 in the Tench, 106 in the 
 Barbel, 135 in the Carp, 700 in the Eel, 1000 in tlie Cod, 
 1400 in the Salmon, 1600 in the Sturgeon. 
 
 In some Osseous Fishes certain of the branchial arclics support 
 only one series of processes ; such are called ' uniscrial," or ' half 
 gills ; but, as a general rule, they support ' biserial,' or ' whole ' 
 gills. Most of tlic Labroids, the genera Coitus, Scorjxrna, 
 Sehastcs, Ajnstcs, Zens, Antcnnarius, Foh/ptcrns, Gohicso.r, 
 
 ' XXIII. t. Tiii. p. 192. 
 
 2 For the Iiistolony of Uk'sc stnicturos, slx^ Dr. Williams's miiuitc Ocscriplion in 
 ochnyni. pp. 288-29U. 
 
GILLS OF FISHES. 
 
 481 
 
 LepadoriaHtcr, and tlie Ci/flopterus liparis have tlircc biscrial gills 
 anil one nniscrial gill; the genera Lopliivs, Bafr/icli/is, DioiJon, 
 Tetrodon, Monopfcriis, Coti/lis, have three hiserial gills ; Maltlicea 
 and Lepidosiren have two biserial gills and one uniserial gill ; the 
 
 319 
 
 320 
 
 Section ct brnnr-liial arch with a pair of processes 
 A', supporting the branchial plates, b, Cod. 
 ccLxyiii. 
 
 Section of branchial arch, a, with snpportint,' frame- 
 work of Uie iilate-bearing jirocesses. Cod. 
 
 CCLXYIII. 
 
 Ciicliia (AmpJiipmous) has only two gills. The above ennmeration 
 refers to the branchial organs of one side ; they are symmetrical 
 in all fishes, and the uniserial ojiercular gill is not counted, as not 
 being attached to a proi)er branchial arch. 
 
 The Ijranchial processes are bony, at least along the outer and 
 thicker border, in most Osseous Fishes (e.g. Salmo, Alosa, Gadus). 
 They are gristly, like the arches which support them, in the 
 Sturgeon, where they break up into delicate branched fringes, 
 along their outer margin. Small ' interbranohial ' muscles extend, 
 through the uniting septum, between the bases of the processes, 
 for effecting slight reciprocal movements.' 
 
 ' CXII. CXIII. 
 
 VOL. r. I I 
 
482 ANATOMY OF VEKTEBRATES. 
 
 The concave borders of the branchial arclies are usually beset 
 Avith defensive processes, fringes, or tubercles, and these sometimes 
 support small teeth which aid in deglutition ; but the chief office 
 of these appendages, which project inward toward the mouth, is to 
 prevent the passage of any particles to the interspaces of the gills, 
 which might injure or irritate their delicate texture. In the 
 edentulous Sturgeon andPaddlefish each arch supports a close-set 
 series of such retroverted slender tapering filaments, fig. 276, 
 which are longer than the opposite branchial processes, ib. u : 
 they are developed even from the fifth or pharyngeal arch, wliich 
 has no gill. Similar fringes of extreme delicacy defend the 
 branchial slit in the Gray Mullet. Frequently such a fringe is 
 developed only from the first branchial arch, Mackarel, Perch, 
 fig. 85, 6.1, the rest supporting dentated tubercles, fig. 321, and 
 the last or pharyngeal arch being beset with teeth only. In the 
 Rcmora and many other Fishes, the defensive tubercles on 
 opposite sides of the same branchial fissure interlock, like the 
 teeth of a cog-wheel. In the Lcjiidosiren armectens, fig. 316, 
 short valvular processes are developed from the sides of those 
 branchial fissures only which lead to the gills, the first and second 
 arches having no gills. In the Conger, all the brancliial arches 
 are devoid of defensive fringes or tubercles.' 
 
 The immediate force of the heart's contraction is applied by a 
 short and rapidly divided arterial trunk, fig. 308, B, upon the 
 branchial circvilation. Only in a few fishes is the heart removed 
 backward from the close jn'oximity of the gills, and then the 
 branchial artery is proportionally elongated ; as in the Eel tribe, 
 especially the Si/nhranchidce : the artery is long in the Planirostra, 
 fig. 276, .5. The primary branches are always opposite and sym- 
 metrical, but vary in number in different species. Very commonly, 
 as in the Perch, they are three in number on each side ; the first 
 branch dividing, as in fig. 308, B B, to supply the fourth and third 
 gills, the second going to the second, and the third to the first 
 gill, ib. h, be. In the Polyjyterus and Skate there are only two 
 primary branches on each side : the first supplies the three poste- 
 rior gills ; the second, formed by a terminal bifurcation of the 
 In-anchial trunk, su]iplics the anterior gill in the Polypterus, and 
 in the Skate bifurcates to su]>ply also the uniserial, opercular, or 
 hyoid gill. Tlic Fox-Shark (.lAyi/V/.s-) and the Lcitidosteus give 
 examples of four pairs of ])rin\ary branches from the branchial 
 
 So 
 
 pi-L'p. 1038. (Con;;cr), .Tiid its lU'Scription, XX. 18.34, p. 83. 
 
GILLS OF FISHES. 
 
 483 
 
 tniiik. In the Shark the first jiair come off close too-ether from 
 the dorsal part of the ti-uiik : tlic arteries of the last pair rpiickl}' 
 Liturcate, and thus each of the five branchial fissures receives its 
 artery. The Myxinoids offer the exceptional instances of the 
 bifurcation of the branchial trunk by a vertical division into two 
 lateral forks, extended in one species to near its base: the 
 Lepidosteus presents the still rarer example of the trunk being 
 cleft horizontally into an upper and lower primary division ; the 
 upper or dorsal division sends off two branches on each side, tlie 
 posterior dividing to supply the fourth, fig. .323, 5, and third, 
 ib. 4, gills, tlie anterior going to the second gill, ib. 3: the lower 
 division sends off the pair of arteries to the first pair of gills, 
 ib. 2, then extends forward and l)ifurcates to snyiply the iinisei'ial 
 opercular gills, ib. i, which are ja-cscnt in this ganoid genus, as 
 in the Sturgeon.' In the Cod 
 and other Osseous Fishes the 2'-' 
 
 vessels on each side, which are 
 analogous to the pulmonary 
 veins in man, unite to form the 
 ' aortic circle,' fig. 321, «, which 
 encompasses the basisphenoid,ii. 
 The current of arterialiscd blood 
 fldws forvrard at the fore-part of 
 this circle into the hyo-oper- 
 cidar, e', and orbito-nasal, b, 
 arteries ; but the main streams 
 are directed backward, and con- 
 verge in the direction of the 
 
 arrows to the aortic trunk. The carotids, c, tlie homologues of the 
 subclavians, d, sent t(j the pectoral fins, and sometimes the coro- 
 narjr vessels of the heart, are sent off from the aortic circle. Ikit 
 no systemic heart or rudiment of a propelling receptacle is de- 
 veloped in any fish at the point of confluence of the branchial 
 veins. 
 
 Small vessels are sent off from tha marginal l)ranchial venules 
 by short triuiks, which ramify beneath the branchial membrane, 
 and become the ' arterias nutritiro ' of the gills : their capillaries 
 are collected into venous trunks, which quit the gills commonly 
 at both their extremities, those from the dorsal ends joining 
 the jugular veins, those from the ventral ends emptying 
 
 Intiuii, Dor^G 
 
 ' XXV. 
 
 I I 2 
 
484 
 
 ANATOMY OP VERTEBRATES. 
 
 themselves into the prtecavals, or directly into the great aiiricnlar 
 sinus.* 
 
 Such is the outline of the general structure of the beautiful 
 and complex mechanism of the normal or pectinated gills of fishes. 
 Of this there are many minor modifications ; some of which receive 
 explanation from known phenomena in the developement of the 
 gills ; ^ others, teleogically, from the habits of the species. 
 
 Five brancliial arches and arteries, or vascular hoops, are 
 developed on each side in the embryo of all fishes above the Der- 
 mopteri, as a general rule.^ At first the trunk of the branchial 
 arteries simply bifurcates, the divisions passing round the pharynx 
 
 and reuniting on its dor- 
 s' 2 sal surface, to form the 
 aorta. Behind this pri- 
 mary circle, which cor- 
 resi)onds with the fold 
 developing tlie liyoid and 
 mandibular arches, four 
 additional arterial hoops 
 
 are sent off, fig. 
 
 ;'22 
 
 Eiuln-j'o Osseous Fi^li 
 
 ■I, n, 
 wliicli traverse, without 
 further ramifications, the 
 couA'cx side of the four 
 anterior simple Ijranchial arches, and reunite above in the aortic 
 trunk, ib. in. If a sixth arterial arch be developed, correspond- 
 ing with the fitth branchial arch, as its presence in the Le2n- 
 dosiren would indicate, it has not been observed, and must 
 soon disappear in most Osseous Fishes. In these the gills make 
 their appearance as leaflets budding out from the con\exity of 
 the four anterior branchial arches, each leaflet supporting a 
 corresponding loop of the branchial artery ; and, as the bifur- 
 cation and extension of the primary leaflets and the pulhilation 
 of secondary laminje and loops proceed, the vascvilar arch Ijcgins to 
 scj)arate itself lengthwise into two channels, traversed by ojiposite 
 currents, and therel)y establishing an arterial, fig. 318, d, and a 
 venous, ib. c, trunk in relation to the loops and their vascular 
 developcments on tlie branchial processes. In Osseous Fishes 
 
 ' These ' YCiitc nutriiiii!' arc uiuisiuilly largo in the Carp; but are not, as l)u Vcrncy 
 suiiposed (cviu.), <lirectly eoiitinued from the true ' \cn:e braiichiales;' iiuil they Jo 
 not, therefore, divert any of the stream of arierialised blood from the aorta to pour it 
 directly into the venous sinus. Sec Midler, xxr. 1S41, ji. 28. 
 
 ^ CXI. exit. oxui. 
 
 ■' The .six-giUcd Shark (//(mkhcAw.v) and the seven-gilled Shark (l/,j<laiicl(iis) are 
 among the few exceptions. 
 
GILLS OF FISHES. 
 
 4S£ 
 
 324 
 
 tlic primary arterial arch, corresponding with the anterior or 
 hyoid one, developes either a simple 
 (iiniscrial) gill, or a plexiform, plu- 
 mose, rudiment of a gill, or both, or 
 neither. In the Lepidostcus this arch 
 retains its primitive connection witli 
 the extremity of the branchi-arterial 
 trunk, and developes on each side a 
 small uuiserial pectinated gill, fig. 32.3, 
 1, from the membrane clothing the 
 inner surface of the cerato-hyoid and 
 preopercular bones : the vein or effe- 
 rent vessel, e, of this gill goes to a smaller 
 pectinated organ, ib. R, consisting like- 
 wise of one series of vascular filaments, whicli agrees witli the 
 ' pscudoliranchia ' of other fislies in being supjilied with arterial 
 blood. In the Sturgeon, the Lepidosiren, and tlie Plagiostomes the 
 representative of the primary vascular arch has bec(.)me, by partial 
 bifurcation of the branchi-arterial 
 trunk, a secondary branch, sent otf 
 by the artery of tlie first branchial 
 arch: but it nevertlielcss developes 
 a simple gill, of one series of filaments 
 in the Lepidosiren, fig. 324, i, and of 
 tlie anterior scries of lamella; in the first 
 gill-bag of the Plagiostomes : and this 
 series is attached, like the opercular 
 gill of tlie Lepidostcus and Sturgeon, 
 to the membrane supported by the 
 hyoid arch. 
 
 In most Osseous Fishes we recognise 
 the reduced homologue of the anterior 
 primary vascular arch in that vessel, 
 fig. 321, e, which is continued from the 
 venous or refluent division of the 
 second jii'imary vascular arch ; not, as 
 in the foregoing fishes, from tlie ar- 
 terial division of that arch, or from 
 tlie liranchial trunk. Tlie vessel in 
 question carries, therefore, arterial 
 blood : it manifests its primitive 
 character by returning into the circulus aorticus, as at <■ , fig. 
 321, but now receives blood from it, and is called ' arteria 
 
 irNlili.M . 1- 
 
486 ANATOMY OF VEKTEBRATES. 
 
 liyo-opercularia : ' tlie pseiido-lDranchia, wlieii present, as at 
 fig. 321, E, is developed from it. 
 
 In Osseous Fishes the four normal biserial pectinated gills are 
 developed only from the four anterior branchial arches ; the fifth 
 and last arch has no gill developed from it, but is converted, as we 
 have seen, into a pair of accessory jaws. In the Lepidosiren, as 
 in Hexanchus, the fifth arch supports a uniserial gill, fig. 324, 6. 
 In the Planirostra, although the branchial pecten is not developed 
 from it, yet the same kind of long slender filamentary processes 
 project inwards from its concavity, as from that of each of the 
 anterior four pairs of branchial arches. The five interspaces 
 between the hyoid arch and the five branchial arches are originally 
 exposed on the sides of the head of the embryo osseous fish; the 
 opercular and Ijranchiostegal appendages are later developements, 
 and the single brancliial outlet is the result of the formation of the 
 gill-cover. Thus the numerous branchial apertures in the carti- 
 laginous fishes, like the suljstance of their skeleton, are retentions 
 of embryonic structures. Very interesting arrests of developement 
 arc also found in bony fishes. We have seen that the primary vas- 
 cular hoops sweep over their respective arches without sending off 
 any branches, the (subsequently) bi'anchial veins being, in the 
 embryo, direct continuations of the branchial arteries. This 
 ])rimitive condition is persistent in the fourth branchial arch of 
 certain MuriBnoid fishes of the Ganges, Bloiioptcrus, Syinhranchus; ' 
 it is persistent in the first and second brancliial arches of the eel- 
 like Lepidosiren, fig. 324. 2, 3. Such arches are, therefore, gill- 
 less, and a certain proportion only of the blood transmitted from 
 the heart is aerated in the gills : about one fourth, e. g. in Mono- 
 ptcrus, goes directly to the aorta in its venous state ; a larger 
 quantity would pass into the roots of the aorta, fig. 312, o, o, and 
 mix with the general circulation in the Lepidosiren, were no part 
 of the current diverted by the vessels /, /', into the lung-like 
 modification of its air-bladder. 
 
 A tuft of filaments, snpporting each a single vascular loop, and 
 covered with non-ciliatc ejiithelium, extends from each branchial 
 plate, protruding from the outer slit, in the embryo of the Plagio- 
 stomes ; ^ and a similar tuft also extends from tlie spiracle in those 
 species which possess it, c. g. I\[i(xtcJns and Acaiithias ; but 
 these preliminary brancliial organs soon disaiipear.' Three seem- 
 ingly analogous filaments are retained on cacli side, for a longer 
 period, in the Lcpuhisiii'ii. inairvtrns ; but lose tliat vascular and 
 
 ' oxix. - xx. vol V. p. 7l>. ■' i.xix. p. 88, pi. 14. 
 
 ' Lxxxu. exxv. exni. p, 1)7. 
 
GILLS OF FISHES. 487 
 
 respiratory character before they are absorbed. Accessory 
 respiratory organs, acting chiefly as a reservoir or filter of 
 water,' are developed from the npper part of the pharynx 
 in the Climbing Perch [Auahus scandms) and allied fishes of 
 aniphibions habits ; they are complex folds of slightly yascidar 
 membrane supported on sinuous plates developed from the 
 pliaryngo- and epi-branchials of the ante- 305 
 
 rior branchial arches, fig. .325, 4S ; whence 
 this family of fishes is called Lahjjrhithi- 
 hruncldi. An accessory branchial ramified 
 vascular organ is similarly situated in the 
 gciuis thence called Ileterobraackus. It re- 
 sembles a miniature ti-ec of red coral, is 
 hollow and muscular, and serves not only for 
 resjiiration, but, as Cuvier suggests, to aid in 
 propelling the arterialised blood into the liianchiaiardiesm.ii lai.jrin- 
 
 ■ T j_l i~\ ^ ' / A 1 ' \ llfic reservoir, Amaf'a.s. xxiii 
 
 aorta. in the L-uchia (Amp/npnous), a 
 
 finless snake-like fish, which lurks in holes in the marshes of 
 Bengal, the second branchial arch supports a few long fibrils, and 
 the third a simple lamina fringed at its edge; the first and fourth 
 arches have not even the rudiment of a gill. The branchial 
 function is transferred to a receptacle on each side of the head, 
 above the branchial arches, covered by the upper part of the oper- 
 cular membrane ; these receptacles have a cellular and highly 
 vascular internal surface ; the cavity communicates with the 
 mouth by an t)pening between the hyoid and first branchial arch, 
 and receives its blood from the terminal bifurcation of the 
 branchial artery, and also from the efferent vessels of the rudi- 
 mental gills. Those from the supplemental lung-like vascular 
 sacs are collected into two trunks, which unite with the posterior 
 unbranched branchial arteries to form the aorta. Thus about one 
 half of the volume of blood transmitted from the heai't is con- 
 veyed to the aorta without being exposed to the action of the air. 
 This amphibious fish is, as might be ex2>ected, of a sluggish and 
 torpid nature, and remarkable for its tenacity of life. The liomo- 
 logues of the superior branchial sacs extend in a Gangetic Siluroid 
 fish, the Singio, beyond the cranium, backward beneath the dorsal 
 myocommata upon the neural arches of tlie vertebra; to near the 
 end of the tail, where they terminate in blind ends. The inner 
 tunic of the sacs is a delicate vascular membrane, supplied by a 
 continuation of the posterior branchial artery. The position of 
 the i)alatal opening of the sac, in relation to the lamina; of the 
 
 ' CLxiiv, Yol. iii. p. 372. 
 
488 ANATOMY OF VERTEBRATES. 
 
 second and third arches, is such that water can with difficulty 
 penetrate them, and tliey are usually found to contain air. They 
 are not, however, the hoiuologues of the air-bladder or of lungs, 
 though they are analogous to the latter in function. By this 
 extreme modification of the opercular gill the Singio {Sacco- 
 branclius, Cuv.) is enabled to travel on land to a great distance 
 from its native rivers or marshes, and, like the Cuchia, is remark- 
 able for surviving the infliction of severe wounds.' In most fishes 
 a rich developemcnt of follicles on the walls of the gill-chamber 
 supplies the branchial machinery with a lubricating mucus. 
 
 The mechanism of branchial resj^iration differs from that of 
 swallowing, only in the streams of water Ijcing jirevented from 
 entering the gullet, and being diverted to the branchial slits on 
 each side the pharynx. 
 
 The mouth opens by the retraction of the prcmaxillary and the 
 depression of the mandible. Almost simultaneously the mandi- 
 Ijiilar rami are divaricated behind by the action of tire ' levatores 
 tympani,' fig. 134, 24, upon their pedicles; the opercular flajxs are 
 drawn outward by the ' levatores operculi,' ib. 25 ; the branchio- 
 stegal membrane is dilated by divarication of the rays, the ' leva- 
 tores branchiostegarum,' fig. 1.35, 28, opposing the ' depressorcs,' 
 ill. d, in this action ; the branchial arches are successively drawn 
 forward and outward by the ' branchi-levatorcs,' fig. 137, 3, and 
 ' mastobranchiales,' ib. 26 ; and the branchial chamber being thus 
 expanded, the water rushes in through the sieve-like inner slits, 
 and fills the chambers, floating apart the gills and filteriug 
 Ijctwecn every branchial process and fold. The inner slits are, 
 then, closed ))y the protraction of the hyoid and depression of the 
 branchial arches, the ' geniohyoidei,' fig. 135, coojierating with 
 the ' branclii-dcpressorcs,' fig. 137, f 5, in this action ; the branchial 
 2)roccssos arc approximated and divaricated liy special muscles, 
 and elastic parts. The respiratory currents are driven out liy the 
 contraction of the branchiostegal membranes and the depression 
 and adduction of the opercular flaps, which, on the expulsion of 
 the currents, close like a door upon the ' sill ' formed by the 
 sca[iular arch. In the Plagiostomes the branchial currents are 
 moved and directed by muscles, combined with elastic structures, 
 more inunediately acting on the inner and outer slits and the 
 intermediate clianfljcrs. 
 
 § 85. Arteries nf Fishes. — Tlic first structure to be n<iticcd in 
 connection with the arterial system, is the \'ascular body already 
 alluded to under tlienamcof' [iscudobranchia.' JLiniii/riis, Tinea, 
 
ARTERIES OF FISHES. 480 
 
 Cohitis, JVaiuhts, Sihiriis, Batraclius, Gi/mnotiis, Murcenophis, and 
 Murcena are examples of genera in which it has not been deteeted. 
 In aUnost all other Osseous Fisiies it is present, situated on each side 
 of the head, in advance of the dorsal end of the first biserial gill, 
 under the form either of a small exposed row of vascular filaments, 
 like a uniserial gill (as in all Sciaiuoids and many other Acantho- 
 pter!, the Pleiirmicctida!, and the Lcpidostcvji, fig. 323, n) ; or, like 
 a vaso-ganglionic body, composed of parallel vascular lobes, and 
 covered by the membrane of the branchial chamber (as in Esux, 
 Cyprinus, Gadiis, fig. 321, r). In both cases the vein or efferent 
 vessel of the pseudol)ranchia becomes the ophthalmic artery, ib. k, 
 and the choroid ' vaso-ganglion,' when present, is developed from 
 it. The Sturgeon, like the Lepidosteus and Lepidosiren, has a 
 uniserial ojiercular gill, the homologue of the first so-called 'half- 
 gill ' of the Plagiostomes ; and, on the anterior wall of the ' sj)ira- 
 cular canal,' a small vascular lamellate body receives arterialised 
 blood by a vessel sent off from the vein of the first biserial gill ; 
 which Idood, after being subdivided amongst innumeraljle pinna- 
 tifid capillaries is collected again into the efferent vessel of that 
 body, and divides into the artery for the lirain (encejihalic), and 
 that ibr tlie eye (ophthalmic). The pseudobranchia is thus a kind 
 of ' rete mirabile ' for both the cerebral and oplithalmio circidation 
 in the Stiirgeon ' : in Osseous Fishes it stands in that relation to the 
 eye oidy, and is most generally associated with the more immediate 
 ophthalmic 'rete mirabile,' called 'choroid gland,' fig. 2Ifi, o. 
 The pseudobrancliia, in the Plagiostomes that have the spiracnla, is 
 developed, as in the Sturgeon, on the anterior wall of each of those 
 temporal outlets from the branchial cavity : its ' vena arteriosa ' 
 supplies the eyes and part of the brain : it coexists in the Plagio- 
 stomes, ChiniKroids, Sturgeons, and some Osseous Fishes, witli 
 the vaso-wanglion supplied by vessels from the anterior branchial 
 veins, whichliesbetween the anterior basi-branchials and the sterno- 
 hyoid muscles. Besides the small nasal and orliital arteries, and 
 the hyo-opereular, from which the proper ophthalmic artery is 
 derived, the carotids are usually sent off from the ' circulus 
 aorticus.' In the Chima^ra the carotids are transmitted directly 
 from tlie anterior branchial veins ; and, in the Pike, the artery of 
 tlie iiectoral fins (brachial) is. transmitted from the common trunk 
 of the two anterior branchial veins. In the Myxines an anterior, 
 as well as a posterior, aorta is continued from the common conflu- 
 ence of the branchial veins. In all higher fishes the posterior 
 aorta is the only systemic trunk so formed. 
 
 ' XXI. pp. 41-G7, 75. 
 
490 ANATOMY OE VEETEBRATES. 
 
 Tliis aorta extends beneath the bodies of the vertebra3 along the 
 abdomen and through the hasmal canal to the end of the tail. In 
 many Cyprinoid fishes it dilates beneath each abdominal vertebra 
 into a sinus. It gives off intercostal arteries, which in many 
 adult fishes become fewer in number than the intercostal spaces ; 
 it sujjplies numerous small branches to the kidneys. In the 
 Syngnathi the aorta grooves the kidney in its course, and in the 
 Anchovy sinks into the renal substance. The first principal 
 visceral branch is the ' cceliac ; ' which sometimes, as in the 
 Burbot, is sent off from the posterior part of the ' circulus 
 aorticus,' and in some Sharks by two trunks from the same part. 
 The next branch is a posterior mesenteric, which varies in size 
 according to the extent of the intestinal canal supplied by the 
 cocliac. Between these, in some fishes, the brachial arteries are 
 sent off from the abdominal aorta : these vessels in the large- 
 finned Tor])edos and Chimrera! have a partial investment of 
 muscular fibres, like secondary builds, but without any valvular 
 structure to give effect in onward flow to their action.' 
 
 In the Porbeagle Shark (yLcnnna cornuhica) the two cceliac 
 arteries each split into a bundle of small arterioles, which inter- 
 lace Avith a similar resolution of the hepatic veins to form a mixed 
 fasciculate ' plexus mirabilis ' between the pericardial septum and 
 the liver. The arterial blood is collected again into a trunk on 
 the outer side of each plexus ; and is distributed by the ramifi- 
 cations of those trunks in the ordinary way to the stomach and 
 intestines.^ The arterial branches to the spiral valve in the Fox 
 Shark are rcmarkal)lc for the rich bundles of twigs hj which they 
 distriliute the blood to that production. In the Mediterranean 
 Tunnies (Thi/nnus and A/i.vis) the branches of the ci"eliaco-mescn- 
 teric artery sent to the stomach, the pancreas and the intestines, 
 severally split up into similar fasciculate plexuses, which are 
 interlaced with corresponding plexuses of the veins from those 
 viscera prior to the formation of the portal trunk. 
 
 But the most common modification of the visceral vascular 
 system is the sudden division and termination of a branch, usually 
 of the gastric artery, in a small body chicfiy composed of the 
 cellular beginnings of the returning veins, forming the vaso- 
 ganglion so constant in all higher Vertebrates, and called the 
 ' spleen,' fig. 276, ;/ ; fig. 281, r/. It is not jiresent in the Lancelet ; 
 and the gland-like Imdics near the cardla in tlic C'ycloftomes, and 
 near the pylorus in tlio Lc)iidosiroii, whicli some have called 
 ' spleen,' are more like the recognised remnants of the vitellicle in 
 Osseous Fishes, where a trite spleen is actually present. The 
 ' -xcvui. 2 XXI. !>. 'J'.l, pi. r>. 
 
AIR-BLADDER OF FISHES. 401 
 
 veil! of tlie siileen always contributes to form the ' vena porlffi ; ' 
 but it is Important to note that it is not essential to the formation 
 of that vessel. The absence of the spleen in fishes is concomitant 
 with the absence of the pancreas ; and the increased size and 
 complexity of the spleen is associated in some fishes with a cor- 
 responding developement of the pancreas. Thus there is an 
 accessory spleen in the Sturgeon ; and the spleen is diwlcd into 
 numerous distinct lobules in Lamna, Selache, fig. 278, d, and 
 some other highly organised Plagiostomes. In most Osseous 
 Fishes the spleen is appended l)y its vessels, and a meso-splenic 
 fold of peritoneum to the hinder end or bend of the stomach, or 
 to the beginning of the intestine : it is of variable but connnonly 
 triangular shape; of a deep red or brown-red colour, and soft 
 and spongy : the venous cells of which it is chiefly composed are 
 filled with granular corpuscles. 
 
 § 86. Air -Madder of Fishes. — The organ so denominated is found, 
 in most Osseous Fishes, in the form of an elongated bladder, tensely 
 filled by air, extending along the back of the abdomen, between the 
 kidneys and the chylopoietic viscera, fig. 281, k, and sometimes 
 (^Gi/mnotiis, fig. 233, d, Ophiocephalus, Coins) beneath the caudal 
 vertebme to near the end of the tail. It is sometimes bifurcate (as 
 we see it in most Scomberoids and Carangoids,' in some species of 
 Diodon, Tctrodon, (A Dactijlopterns, I'imelodus, Prionotus) ; seldom 
 divided lengthwise into two bladders (Arius, Gagora, Fohjpterus, 
 Lcpidosircn, fig. 324, p, p) : more often divided crosswise into 
 two compartments, which intercommunicate by a contracted 
 orifice (^Ci/piinid(B, fig. 229, j' 1; Characinidxe), or are quite 
 separate {Bar/rus filamentosus, Gymnotus equilahintus). In the 
 Siluroid genus Fmie/asius the air-bladder is divided into four 
 longitudinally succeeding portions. In the TrirjJa hirundo the 
 swim-bladder is notched anteriorly by one indent, and posteriorly 
 by two indents, from which notches septa project inwards : some- 
 times the air-bladder is divided partially, both lengthwise and 
 crosswise {Colitis fossilis, Auchenipterus furcatus, some species of 
 Fiinelodus). Sometimes the bladder sends forward two blind 
 iirocesses from its forepart {Splujrcena harracudu, T right cuculiis, 
 Conodon aiitillaims, some species of Micropotjon and Otolithus) ; 
 sometimes from its hind part {Canthurls vtdgaris, Lethrinus 
 atlunticiis, HeUases insolatiis, some species of Sillatjo, Mana, and 
 Srnaris) ; sometimes from both ends (Dules macidatus, Fiinelipteriis 
 
 ' Dr. Giintlier tells mc that all the species of these families with a shurt and 
 elevated body, with a short abdominal cavity, and with strong first ha;mal and inter- 
 haiinal spines, have the air-bladder bifurcate behind, extending backward between the 
 muscles of the tail, to or beyond the middle of its length. 
 
402 
 
 ANATOMY OF VERTEBRATES. 
 
 326 
 
 altijjenuis, Lactttrius delicatulus). Corvina trispinosa, fig. 326;, lias 
 two slender caical processes from each side of its air-bladder ; the 
 Bearded Umbrina has three such processes ; the 
 allied ' Maigre ' and other species of Sciasna, 
 with most of the CorvincB, have very numerous 
 lateral pneumatic cajca, which, as in Johnius 
 lohatus, fig. 327, are more or less ramified.' In 
 some species of Cheilonemus and Gadus blind 
 processes are continued from both the sides and 
 ends of the air-bladder (see the anterior ones 
 in Gadus callarias, fig. 321, A, p). In Gadus 
 Navavarja. the lateral productions expand, and 
 line corresponding expansions or excavations of 
 the abdominal parapophyses, thus foreshadow- 
 ing the pneumatic bones of birds. In Kvrtus the 
 air-bladder is encircled by expanded ribs, curvi)ig 
 and meeting below it.' 
 
 The proper walls of the air-bladder of ordi- 
 nary Osseous Fishes consist of a shining silvery 
 fibrous tunic, the fibres being arranged for the 
 most part trans-\'erscly or circularly, and in two 
 layers fig. 229, q r; they arc contractile and elastic; but 
 the walls of the anterior compartment of the air-bladder of 
 Cyprinoids, ib. p, are much more elastic than 
 those of the posterior one. The air-lJadder 
 is lined by a delicate mucous membrane, with a 
 ' plaster epithelium ;' it is more or less co\cred 
 by the peritoneum. Its cavity is commonly 
 sim])le ; in the iSheat-fish it is divided by a 
 vertical longitudinal septum along three-fourths 
 of its posterior part.-' The lateral compart- 
 ments arc subdivided by transverse septa in 
 mtuiy other Siluroids (e. g. genus Barp-Ks) : the 
 large air-bladder of some species of En/fhrimis 
 (c. g. E. salvus, E. twniaf/is) is partially subdi- 
 vided into smaller cells. Tiie cellular subdivi- 
 sion is such in the air-bladder of the Amia, that 
 Cuvicr compared it to the lung of a reptile' ; 
 M<-hi:„M.r..ini,i,h,.,M,„i,^3 and the transition from the air or swim-bladder 
 
 ' XXXIX. i. p. 0-1, after Ciivicr anil Valinicicnncs, xxin. ]il. 138, l."9. Tho most 
 iMimplcx form is that descrihcil l>y GiiiitlH-r (or.xxiv, vol. ii. p. ni:Miii C',illic/il/ii/s 
 liicliki, wlicro the air-l)laiUlcr forms a secoml invcsliiiciU of llic ahdoiiiiiial viscera, 
 witliin lliu pcritoiiouin. 
 
 = CLxsiv. vol. ii. p. lu. •' oxvi. vol. ii. (.. as, pi. 0, tig. I. ' XXIV. vol. ii. p. 377. 
 
 327 
 
 
AIll-BLADDER OF FISHES. 493 
 
 to the king is comjjleted in tlie Lepidosircn, in which the 
 celluhir subdivision and niuUiplicatiijn oi' the vascukir surface are 
 comhined witli a complete hilatcral partition of the bhidder into 
 two elongated sacs, with a supjdy of venous blood from a true 
 pidmonary artery, and with the connnunication of the ductus 
 l)neumaticus, as in the Polypterus, with the ventral surface of the 
 tt'sophagus. 
 
 At the first introduction into the Animal Kingdom of a true 
 lung, or air-ljreathing organ communicating with the pharynx or 
 oesophagus, much variety of form and structure, much inconstancy 
 even as to existence, might be expected, especially in that class in 
 which the normal function of the new organ could be so seldom in 
 any degree exercised, and in which, therefore, different accessory 
 or subordinate (offices predominate in such rudimental represen- 
 tative of the pulmonary organ. There is no swim-bladder, for 
 example, in the orders Denno]/teri, Iloloo-pliali, and Plagiostomi ; 
 it is present in one of the families ( Gudidce) of the thoracic sub- 
 order of Anacantldni, and not in the other family {Plcuronectldoi) ; 
 here we can associate its absence with the peculiar flattened 
 form and grovelling habits of the species. In lilce manner we may 
 account for the absence of the air-bladder in the A)igler (^Lopluun), 
 which lialntually keeps the sea-bottom : Ijut the mechanical expla- 
 nation of the absence or rudimental condition of the swim-bladder 
 is not S(j obvious in regard to the Acanthopteroiis genera Fercis, 
 Percophis, Elegmus, Auxis, TracliyiiteruH, and GymvetruH. A 
 large and often comjilex aii'-ldadder exists in most of the Siluroid 
 fishes ; but the genera Loricuria, Blihtelepis, and Hi/postonui. are 
 exeejitions in that family, having no air-bladder. What is more 
 inexplicable is, that while some spiecies of the same genus, 
 Pohjnemus and Scomber for example, have a large swim-bladder, 
 others want it, or have it of extremely small size. 
 
 The variation in respect to the presence or absence of an air- 
 duct {ductus pueumaticus) is expressed in the characters of the 
 orders in the Classification of Fishes, pp. 10 — 12. The duct, 
 wliich is shown by its place of communicaticm with the beginning 
 of the oesophagus, and by the rudimental larynx, in Polypterus 
 and Lepidosiren, fig. 316, e, to be the homologue of the trachea 
 of air-breathing Vertebrates, is a simple and delicate membranous 
 tube ; but it presents considerable variation in its length, diameter, 
 and j)lace of communication with the alimentary tract. In the 
 Herring the ductus pncumaticus is produced from the posterior 
 attenuated end of the cardiac division of the stomach, fig. 281, i, 
 and opens into the fusiform air-bladder at the junction of the 
 
494 ANATOMY OF VERTEBRATES . 
 
 middle and posterior thii-ds of that organ.' The long, narrow, 
 and flcxuous ductus pneumaticus is continued from the forepart 
 of the posterior division of the air-bladder in the Cyprinoids, and 
 opens into the dorsal part of the oesophagus, fig. 229, su : the 
 short, straight, and wide ductus pneumaticus, in the Lepidosteus, 
 opens also into the dorsal part of the ccsophagus, the oi-ifice being 
 served by a sphincter: in the Erythririus the air-duct commu- 
 nicates with the side of the oesophagus ; in Polijpterus, as in 
 Lepidosiren, with the under or ventral part of the beginning of 
 the oesophagus. ^ 
 
 The principal seat of the vascular ramifications in the air- 
 bladder, like that in a true lung, is the mucous lining membrane ; 
 but the modes of ramification in the primitive jiiscine form of the 
 air-breathing organ are as variable as any of its other properties. 
 The arteries of the air-bladder are derived sometimes directly 
 from the alidominal aorta, sometimes from the co^liac artery, 
 sometimes from the last branchial vein ; and in the Lepidosiren 
 they are continued from the aortic termination of the two non- 
 ramified branchial arteries, fig. 312, I', and therefore convey 
 venous blood to the cellular, lung-like, double air-bladder. The 
 veins of the air-bladder return, in some fishes, to the portal vein ; 
 in some, to the hepatic vein ; in some, to the great cardinal vein ; 
 and, in the Lepidosiren, ib. p , they penetrate, by a common 
 trunk, the great post-caval vein, ib. e, formed by the confluence 
 of the visceral and vertebral veins of the trunk ; but instead of 
 terminating there, the pulmonary venous trunk passes forward, 
 through the sinus and auricle, to the entry into the ventricle, and 
 there terminates above the valvular cartilaginous tuliercle. Thus 
 the aerated blood from the lungs enters the ventricle directly, 
 instead of being previously mixed with the venous blood in the 
 auricle. 
 
 The vascular system of the lung-like air-bladders of the 
 Protoptcrons and Ganoid Fishes forms no ' rctia mirabilia ' or 
 vaso-ganglions, but resolves itself into a generally diffused 
 reticular ca])illary system, which is much richer and closer in 
 the more subdivided and thicker cellular structure of the anterior 
 than of the ]iostcrior ])arts of tlie bladders in the Lepidosiren. 
 
 In the Osseous Fishes the ])rinciiial An-ms of the terminal 
 divisions of the arteries of the air-bladder arc as follows: — 1. A 
 resolution of the smaller ramifications' into fan-like tufts of 
 cajiillaries over almost every part of the inner surface (Carp). 
 2. The formation of similar, but larger and more localised, 
 
 ' cxiv. vol. ii, pi. viii. fig. 1. 2 XXI, 18J1, p. 19.1. 
 
AIR-BLADDER OF FISHES. 
 
 495 
 
 radiating tufts (Pilcc) ; in both without any special aggregation 
 of tlie capilhiries to form a ' vaso-ganglion.' 3. The conversion 
 of the tufts by rapid subdivision into capillaries aggregated so as 
 to form red gland-like bodies ; the capillaries reuniting into larger 
 vessels, which again ramify richly round the border of the gland- 
 like body ; the rest of the inner surface of the air-bladder liaving 
 tiie ordinary simple capillary system (Perch and Cod). In the 
 Cod-fish, a large artery, a branch of the cocliac, and a still larger 
 vein, winch empties itself into the mesenteric, perforate together 
 tlic fibrous tunic of the swim-bladder. Before they reach the 
 inner surface, they divide into some branches, which then radiate 
 and srdjdivide upon the mucous membrane : the arterioles 
 freijuently anastomose together, and the venules as frequently 
 anastomose with each other: both are inextricably interwoven, 
 and form the basis of the so-called 'air-gland,' whicli is essentially 
 a large ' bipolar rete mirabile,' or vaso-ganglion. The ultimate 
 vessels of this body form loops, 
 where the arteries return into 
 veins, fig. 328, and these loops 
 are covered by a layer of vessels 
 and epithelium, a, a. This organ, 
 however, is further composed of 
 a number of peculiarly arranged, 
 elongated cor2)uscles, which de- 
 pend in two rows from each 
 vascular branch, and are bound 
 together l^y a loose cellulai 
 tissue : the corjmscles are beset 
 with fine villiform processes. 
 The blood returns from the vaso- 
 ganglions by small veins which rarely accompany, more commonly 
 cross, the arteries. 4. The two chief ' retia mirabilia,' or vaso- 
 ganglions, in the air-bladder of the Eel and Conger, which are 
 situated at the sides of the opening of the air-duct, are also 
 'bipolar,' and consist of both arterioles and venules: they consist 
 of straight parallel cajiillaries, as in fig. 329 : their efferent trunks 
 do not ramify in the immediate margin of the vaso-ganglion from 
 which they issue, as in the vaso-ganglions of the Cod, Burbot, 
 Acerlne, and Perch, but run for some distance before they 
 again branch to form the common capillary system of the lining 
 membrane of the air-lsladder. 
 
 Kathkc ' failed to detect the opening of the air-duct with the 
 ' CXI. ' Ucber die Schwimm-Uase cinigcr Fischc,' p. 98. 
 
 Superllcial nnd lonpcd vessels uf the \asu-g;ni'-,']ien 
 air-liladtler, Cua. cci.xvni. 
 
496 
 
 ANATOMY or VEUTEBRATES. 
 
 329 
 
 oesophagus in the Eel ; but De la Roche had well describccl the 
 ol>li(|ne aperture,' and accurately cites the whole family of the 
 Eels as fishes havinij both the so-called 'air-gland' and the 
 pneumatic duct. It had been sup])0sed that the vascular ' air- 
 gland ' was jircsent only in those fishes which could not derive 
 the gaseous contents of their swim-bladder from without; and 
 unquestionably in those fishes wliich have the shortest and 
 widest ducts ( Sturgeon, Amia, Erythrinus, Lepidosteus, Lepido- 
 siren, Polypterus) the supposed air- secreting vaso-ganglions are 
 not developed. Since Professor Magnus has determined the 
 
 existence of free carbonic 
 acid gas, of oxygen, and of 
 azote in the blood, and dis- 
 solved in differci^t jiropor- 
 tions in the venous and the 
 arterial blood, it may be 
 readily conceived that the 
 venules of the vaso-ganglions may withdraw carbonic acid gas 
 from the arterioles, and that these may reach the inner surface of 
 the air-bladder richer in oxygen and poorer in carbonic acid than 
 when they penetrated the vaso-ganglions.^ 
 
 The air-duct may allow the gas to escape under certain circum- 
 stances ; and the small size and obliquity of its orifice in many 
 Osseous Fishes (Carp, Eel) seem only to adapt it to act as a 
 safety-valve against sudden expansion of the gas when the fish 
 rises to the surface : ^ but in the higher organised species above- 
 cited, with short and wide air-ducts, these may, likewise, convey 
 air to the bladder. 
 
 Tlie contents of the air-bladder consist, in most freshwater- 
 fishes, of nitrogen, and a very small quantity of oxygen, with a 
 trace of carbonic acid gas : but in the air-bladder of sea-fishes, 
 and especially of those which frequent great depths, oxygen 
 predominates.'' 
 
 In tlie genera Avchenipterus , Si/nodon, Alalapterurus, and some 
 other Siluroids, the axis vertebra sends out on each side a slender 
 
 ' cxvii. p. 201. = .\xi. 1841, p. 98. See also Pr. J. IlaTy, in Phil. Trans, 1S38. 
 
 " Neither the air-duct nor the elasticity of the air-blacklor are equal to jnevcnt the 
 consequences of ii too rapid removal from the enormous pressure which fishes sustain 
 at great depths in the sea; those that are drawn up quickly by tlic hook arc often 
 found to have the air-bladder ruptured, and sometimes tlic stomach is protruded from 
 the mouth by the pressure of the suddenly extricated and expanded gas. 
 
 ' Humboldt found the gas in tl)B air-bladder of the electric Gynmotus to consist of 
 90° of nitrogen and 4^ of oxygen. Biot found 8?° of oxygen in some of tlie deep- 
 sea Mediterranean lislies, the rest nitrogen, witli a trace of carbonic acid. No Iwdro- • 
 gen has over been delected in the air-l)laddcrs of lishcs. 
 
AIR-BLADDER OF FISHES. 497 
 
 process, which expands at its end into a large round plate : this is 
 ajiplied to the side of the air-bladder, and can be made to press 
 iipon it, and expel the air through the duct by the action of a 
 small muscle arising from the skull. In some species of Gadus 
 muscular fibres extend from the vertebral column upon the air- 
 bladder. The nerves of the air-bladder are derived from the vagus 
 after it has received organic fibres from the sympathetic, fig. 229, t. 
 
 Viewing the general modifications and relations of the air- 
 Ijladder throughout the class of Fishes, we cannot but discern and 
 admit, notwithstanding some seeming capricious varieties, that its 
 chief and most general function is a mechanical one, serving to 
 regulate the specific gravity of the fish, to aid it in maintaining a 
 particular level in its element, and in rising or sinking as occa- 
 sion may serve. The general law of its absence in the parasitic and 
 suctorial Dermoj)teri, and in all ground-fishes, as the Pleuronectida 
 and llay-tribe, su])ports the above conclusion, Borelli' found 
 that those fishes whose air-bladders were burst sank to the bottom 
 and were unable to rise. Nor does the absence of the air-bladder 
 in the surface-swimmino- Sharks militate against this view of its 
 physical function: for though the air-bladder serves, it also 
 enslaves. It oj^poses, for example, those Fishes that possess it in 
 their endeavours to turn on one side, and it demands a constant 
 action of the balancing fins to prevent that complete upsetting of 
 the body which it occasions from the weight of the superimposed 
 vertebral column and muscles when life and action are extinct. 
 The Sharks require, by the position of their mouth and in their 
 common pursuit of living prey, freedom in turning and great 
 variety as well as jrower of locomotion : if they are not aided 
 by a swim-bladder, neither are their muscular exertions impeded 
 by one ; whilst their swimming organs acquire that degree of 
 developement and force wliich suffices for all the evolutions they 
 are called upon to perform. With i-egard to the accessory offices 
 of the air-bladder in relation to the sense of hearing, the chief of 
 these remarkable modifications by which it is brought into com- 
 munication with the acoustic laljyrinth have been already described, 
 p. 344. In a few genera ( Trigla), the air-bladder and its duct 
 are subservient to the production of sounds. 
 
 Under all its diversities of structure and function the homology 
 of the swim-bladder with the lungs is clearly traceable ; and 
 finally, in those orders of Fishes which lead more directly to the 
 Keptilia, as, for example, the salamandroid Ganoidei and Protoptcri, 
 those further modifications are superinduced upon the air-bladder, 
 
 ' cxxxi. cap. 23. 
 VOL. I. K K 
 
498 ANATOMY OF VERTEBRATES. 
 
 by which it becomes also analogous in function to the lungs of 
 the air-breathing Amphibia. 
 
 The Lepidosiren annectens ' inhabits a part of the river Gambia, 
 which in the rainy season overflows extensive tracts, that are 
 again left dry in the dry season. Those which do not follow the 
 retreating waters escape from the scorching rays of the African 
 sun by burrowing in the mud, which is soon baked hard above 
 them; but they maintain a communication with the air by a 
 small aperture, and, coiling themselves up in their cool chamber, 
 clothe themselves by a layer of thick mucous secretion, and 
 await, in a tor^Did state, the return of the rains and the over- 
 flowing of the mud-banks. The advent of their proper element 
 wakes them into activity : they then emerge from the softened 
 mud, swim briskly about, feed voraciously, and propagate. 
 
 The peculiar modifications of the gills and air-bladder of the 
 Lej^idosiren are precisely those which adapt them to the peculiar 
 conditions of their existence. In the inactive state into which 
 they are thrown by their false position as terrestrial animals, the 
 circulation, which would have been liable to be stopped had all 
 the branchial arteries developed gills, as in normal fishes, is 
 carried on through the two j)ersistent primitive vascular channels, 
 fig. 312, 2 and 3. Whatever amount of respiration was requisite 
 to maintain life during the dry months is effected in the pulmonary 
 air-bladders ; its short and wide duct or trachea, the oesophageal 
 orifice of which is kept open by a laryngeal cartilage, fig. SIG,/", 
 introduces the air directly into the bladders : the blood transmitted 
 through the branchial arches to the pulmonary arteries, fig. 312, 1', 
 is distributed by their ramifications over the cellular surface of 
 the air-bladders, and is returned artei'ialised by the pulmonary 
 veins, ib. p, p'. A mixed venous and arterial blood is thence 
 distributed to the system, and again to the air-bladders. True 
 arterial blood exists only in the pulmonary veins, and unmixed 
 venous blood only in the system of the venaj cavte ; whence the 
 necessity, apparently, for that jJcculiar arrangement by which the 
 arterial blood is conveyed directly to the ventricle by the pul- 
 monary vein. When the Lepidosiren resumes its true position as 
 a fish, the branchial circulation is vigorously resumed, a larger 
 proportion of arterialised blood enters the aorta, and both the 
 nervous and muscular systems receive the additional stimulus and 
 support requisite for the maintenance of their energetic actions. 
 
 Anatomists and physiologists have expressed different views as 
 to the homologies and analogies of the respiratory organs of 
 
AIR-BLADDER OF FISHES. 409 
 
 fishes. Indeed the essential distinction of those relations has 
 seldom been clearly kept in view. When we read in the 
 latest edition of the Comj^arative Anatomy of Cuvier : ' the 
 giUs are the lungs of animals absolutely aquatic ; ' ' and, with 
 regard to the cartilaginous or osseous supports of the gills, 
 ' they are in our opinion, to the gills of fishes, what the carti- 
 laginous or osseous tracheal rings are to the lungs of the three 
 suj^erior classes:'^ we are left in doubt whether it is meant 
 that the gills and their mechanical supports merely perform the 
 same function in Fishes which the lungs and windpipe do in 
 Mammals, or whether they are not also actually the same jDarts 
 dilFcreutly modified in relation to the different respiratory media 
 of the two classes. Greoffroy St. Hilairc leaves no doubt as to 
 his meaning where he argues that the branchial arches of fishes 
 are the modified tracheal rinss of the air-breathing classes : we 
 perceive that he is enunciating his belief in a relation of homo- 
 logy. The truth of his proposition will be best tested hj first 
 considering the homologies of the air-ljladder of fishes. In the 
 Lcp)idosiren the notochord, the parajiophyses, the attachment of 
 the scapulfe to the occiput, the brancliiostegal covering of the 
 permanent gills, the opercular bones, the presence of a spiral in- 
 testinal valve, the relative position of the anus, the extra-oral 
 nasal sacs, the scaly integuments, the mucous tubes on the head, 
 tlie ' lateral line,' in short, the totality of the organisation of 
 the Lepidosircu, exemplify its fundamental ichthyic nature. It 
 is extremely interesting to find the Ganoid Pohjpterus, which 
 of all osseous fishes most closely resembles the Lepidosiren in its 
 sjiiral intestinal valve, in the bipartition of the long air-bladder, 
 the origin of the arteries of that part, and the place and laryngeal 
 mode of communication of the short and wide air-duct or wind- 
 pijie, also presenting the closest agreement with the Lepidosiren 
 in the important character of the form of the brain. The common 
 objection to the view of the air-bladder of fishes being the rudi- 
 raental homologue of the lungs of air-breathing Verteljrates has 
 been, that the artery of the air-bladder carries arterial blood, that 
 of the lungs venous blood. But in the Polypterus and Lej)ido- 
 siren, in reference to this character, the arteries of air-bladders 
 are derived from the returning dorsal portions of the branchial 
 vascular arches before their union to form the aorta. In the 
 
 ' 'Les branchies sont les poumons cles animaux absolument aquatiques.' (sin. 
 t. Tii. p. 164.) 
 
 ^ ' Elles sont, a notre avis, aux branchies des poisson?, ce que les cerceaux carti- 
 lagineux ou osseux des voies acriennes sont aux poumons des trois classes supu- 
 rieurcs.' (lb. p. 177.) 
 
 K K 2 
 
500 ANATOMY OF VEBTEBHATES. 
 
 Polypterus the artery of each air-sac is formed by the union of 
 the efferent vessels of the last gill : the blood is, therefore, 
 arterialised before entering the artery of the air-sac. In the 
 Lepidosiren, by reason of the non-developement of gills on two 
 of the branchial arches, the blood transmitted to the air-sac is 
 venous. But this difference relates only to the presence or 
 absence of a particular developement of the branchial vascular 
 arches, from which the air-bladders of the two species are supplied 
 with blood : it is a difference which modifies the function withovit 
 at all chano-ing; the essential nature of the air-bladders themselves : 
 the relative position of these vascular sacs, their form and size, 
 their mode of communication with the oesophagus, — in short, 
 every character by which relations of homology are determined, 
 ■ — are the same in both Polypterus and Lepidosiren.' The lungs 
 of the Lepidosiren being, then, unequivocally the homologues of 
 the air-bladder of the Polypterus, it follows that they must be 
 homologous with the air-bladders of other fishes, whatever be the 
 modifications of form or function of such air-bladders. Between 
 the completely divided air-bladder of the Polypterus and the un- 
 divided air-bladder of the Lepidosteus there are numerous degrees 
 of bifurcation in the series of fishes : it is to the undivided state 
 of the air-bladder in the Lepidosteus that its more strictly dorsal 
 position, and its communication with that aspect of the asophagus, 
 are due : these modifications, however, do not affect its relation 
 of homology with the divided air-bladder of the allied genus 
 Polypterus, any more than with the divided air-bladders of the 
 Cohitis barhatula or Arius gatjora, in which the divisions are con- 
 fined to the fore part of the abdomen, and arc inclosed in osseous 
 cups developed from anterior trunk-vertebraj. Thus, the series 
 of transitions traceable in the air-bladders of fishes proves those 
 of the Lepidosiren to be the homologous organs ; whilst the 
 developement, relative position, and connection of the lungs of 
 the Batrachia equally prove those lungs to be the liomologues of 
 the air-bladders of the Lepidosiren. Consequently, the air- 
 bladder of the Fish is homologous with the lungs of the Batrachian 
 and of all air-breathing Vertebrates ; although the air-bladder of 
 the fisli does not perform the function of a lung, but is analo- 
 gous to the air-chambers in the Nautilus shell. 
 
 § 87. Bhxid of Reptiles. — The blood of Reptiles has red cor- 
 2)iiscles of a flattened sub-biconvex elliptical shape ; proportionally 
 smallest in Ophidia, roundest in Chdonia, and largest in Batrachia : 
 
 ' Compare xxxiii. pi. xxvii. figs. 3 and •!, witli xxv. pi. ii. figs. 5 iviul 6, and fig. 54, 
 XXXIII. p. 182, with xxY. pi. ii. fig. 7. 
 
BLOOD OF REPTILES. 501 
 
 in these the size is greater in the ratio of the persistence of tlie 
 branchial apparatus ; and the perennibranchiates joresent the 
 biggest blood-discs absolutely, as well as in proportion to the size 
 of the body, of all vertebrate animals. The two extremes in the 
 relative size of the blood-discs in pulmonated Hatmatocrya are 
 shown in those of a Crocodile, which was twenty feet in length, 
 p. 4, fig. 8, e, and in those of a Siren laccrtiiia, which was two 
 feet in length, ib. f. The latter, which are just visil^le to the 
 naked eye, serve to demonstrate the highly refractive divisions of 
 the nucleus, and the nuclear capsule.' 
 
 There is less blood in cold-blooded than in warm-blooded 
 animals, and more blood in some fishes, the Tunny, e. g., than in 
 any reptile. Dr. Joseph Jones ^ estimates the average quantity 
 of blood to be : — 
 
 In Serpents . . . i to i of the weight of the body. 
 
 Emys terrapin . . rt '° 13 " " 
 
 Emys serrata . . i to Jj „ „ 
 
 Tesiudo pohjphemns , ^i to yy „ „ 
 
 Blood drawn from a living Batrachian is of a purplish red 
 colour, and coao'ulates ijito a clot includincr the discs, floating in 
 clear serum. The clot is firmer than that of fishes, but less firm 
 than in allantoic reptiles ; in a few hours the clot dissolves and 
 liberates the discs. In the recently drawn blood of Clieloida 
 most of the discs settle at the bottom of the vessel, and are not 
 included in the clear clot which forms above them. The filjrin in 
 this clot speedily passes into albumen. The colour of the serum 
 in most reptiles, e. g. Batrackia, Ophidia, Crocodilia, and some 
 Chelonia ( Testudo polypliemus), is a light yellow : in many carni- 
 vorous Chelonia (^Emys serrata, E. reticulata, E. terrajjin), it is of 
 a golden colour. When treated with a droj) of sulphuric acid, 
 and gently heated, the peculiar smell of the sj^ecies, due, e. g. in 
 the Alligator, to the musk-glands, and in the Rattlesnake to the 
 anal glands, is plainly developed. 
 
 The blood of Ophidia, contains the greatest proportion of solid 
 constituents, in the cold-blooded Vertebrates.' 
 
 § 88. Veins of Reptiles. — The capillary blood-vessels having a 
 calibre proportionate to the diameter of the blood-discs which 
 flow along them in single file, are largest in the Batrachia, in 
 which class the best examj^les are aflbrded for demonstrating to 
 
 ' cCLXXiii. and cclxxiv. ^ ccxLV. 
 
 ^ Dr. Joseph Jones, from whose cxeellent and original worlc (ccxly. ) most of the 
 above particulars are taken, suggests that the richness of the ophidian blood may be 
 due to the fact of serpents seldom, if ever, drinking. The comparatively unimportant 
 details of the diameters of reptilian blood-discs may be seen in ccxxxix. tome i, 
 p. 89. 
 
502 
 
 ANATOMY OF VEETEBEATES. 
 
 330 
 
 Cnitlllaries with blnod-Jiecs of tlie ^veb of the foot, 
 Frog, magu. CCLXVII. 
 
 331 
 
 the eye the circulatory motion of the blood, flowing constantly 
 from the arteries to the veins, as seen, e. g. by transmitted light 
 
 in a membranous part of 
 the frog's or newt's struc- 
 ture, under the micro- 
 scope, fig. 330. 
 
 The venous system of 
 Batrachians resembles that 
 of Fishes in the degree in 
 which the species retain 
 the piscine character. The 
 cardinal veins, essentially 
 those which return the 
 blood from the osseous and 
 muscular segments of the 
 trunk, are largest in the 
 Perennibranchs, and de- 
 crease, as the hind-Hmbs 
 acquire more size and 
 power, in the Newts and 
 Land -Salamanders, until, 
 in the tail-less and long- 
 legged Frogs and Toads, 
 the primitive venous trunk 
 of the body is reduced 
 to the condition of the 
 'azygos' vein in Mammals, 
 and the great bulk of the 
 blood is submitted to the 
 influence of the kidneys 
 and liver before it is re- 
 turned to the heart. 
 
 In the Frog, fig. 331, the 
 blood being collected from 
 each liind-limb into an is- 
 chiadic and iliac vein, these 
 unite into a common iliac 
 vein, winch divides. One 
 branch joins that of the 
 opposite iliac, and receives 
 the vein of the great allan- 
 toic bladder, to form the 
 unil)ilical vein,' fig. 331, u: the other branch, K, goes to the 
 
 CircahiUdii hi (lie Frog. Cfl.xvil. 
 
VEINS OF BEPTILES. 503 
 
 kidney of its own side. It inclines to the outer border of the 
 gland, and divides into two branches, which ramify in the renal 
 tissue. The vein of the sjenital glands and conduits, and a vein 
 from the lumbo-dorsal segments, also enter and ramify in the 
 kidneys. The blood of this ' reni-portal ' system is collected into 
 a sinus at the inner border of each gland, and is conveyed 
 by the vein, k, into the postcaval trunk, v. The iimbilical vein 
 ascends along the ventral aspect of the abdomen, attached to the 
 mid-line of the muscular walls of the cavity : as it approaches 
 the liver it sends branches which penetrate directly the hepatic 
 tissue, and a branch which receives the veins of the intestines, 
 sj)leen, and stomach ; but, before completing the portal system, L, 
 it sends a small vein directly to the postcaval, near the auricle. 
 The hepatic vein, I, joins the postcaval trunk, v. The blood 
 from the head and fore-limbs is collected into a right and left 
 jugular and axillary trunk, which unite to form a precaval vein, 
 o, on each side. The postcaval vein, in the Perennibranchs, after 
 receiving the renal veins, is suspended by a duplicature of peri- 
 toneum to the back of the abdomen, the fold being continued 
 from the vein to the mesentery : it enters a groove or canal in the 
 liver, and receives the hepatic veins and the left precaval, before 
 terminating in the auricular sinus. There are a few valves in 
 the venous trunks of Batrachia ; but their chief characteristic is 
 the presence of ' striped fibre ' in the muscular coat.' This is 
 associated with the faculty of rhytlnuical pulsation in the post- 
 caval, axillary, and iliac trunks, independently of the pulsations 
 of the heart. ^ The abdominal venous trunks traverse wide lymph- 
 reservoirs ; and their exterior is here and there roughened by 
 little vascular loops, floating in the lymph, but communicating 
 exclusively with the mother-vein.^ 
 
 In Oplddia the cutaneous veins of the trunk and intercostal 
 veins communicate with a large abdominal vein which runs along 
 the under part of the abdominal walls, and answers to the umbi- 
 lical vein in Batrachia. The caudal vein bifurcates on entering 
 the abdomen, each division after receiving blood from the genital 
 ducts and contiguous intestine, attaches itself to the kidney, and 
 ramifies upon its several overlapping lolies : the efferent renal 
 veins unite to form a trunk, which, on emerging from the innci- 
 and fore-part of the kidney, joins its fellow to form the postcaval 
 vein. The veins of tlie intestinal canal, genital glands, and fatty 
 appendages, which have not contributed to the reni-portal system, 
 unite with those of the pancreas and spleen to form the hepato- 
 
504 
 
 ANATOMY OF VERTEBRATES. 
 
 332 
 
 portal vein : this dilates and describes a spiral curve on entering 
 the liver, and has a valvular structure ensuring the onward flow 
 of blood to the elongated gland, during the compression exercised 
 in the contortions of the Snake. The hepatic veins enter the 
 
 j^ostcaval, and this large trunk 
 terminates in the hind end of 
 the long auricular sinus. 
 
 The blood from the head and 
 fore-part of the body is re- 
 turned to the fore-part of the 
 sinus by a jugular vein and an 
 inferior azygos vein, each of 
 which has a pair of valves at 
 its termination : and by a su- 
 perior azygos vein, which has 
 three valves at its termination: 
 there is a fourth vein, answer- 
 ing to the left precaval, which 
 passes behind the left auricle 
 to terminate in the right sinus 
 auricula? near the postcaval 
 orifice : it receives the coronary 
 vein before its termination. 
 
 In Lacertians the blood 
 from the liind limbs is partly 
 conveyed by a reni-portal 
 vein, fig. .3.32, K, to the kid- 
 neys, and partly by a trunk, 
 which communicates with the 
 caudal vein to an umbilical 
 or sub-abdominal vein, L : this, 
 as it advances, collects blood 
 from the ventral walls of the 
 trunlc, and receives a recur- 
 rent thoracic vein : it then 
 communicates with the trunk 
 of the gastro-intestinal, pan- 
 
 Olrculatioii III aLiznra{Xr(aii'/ 0C(7/a^(). CCI.XVU. CrCatic and Sl^louic VoluS 
 
 to form the great portal vein which penetrates the liver. The 
 renal veins, li, unite to form the postcaval, v, which afterwards 
 receives the hepatic veins, and proceeds to the auricular sinus. 
 A small cardinal or azygos vein, returning part of the blood 
 from the tail, advances along the back part of the abdominal 
 
VEINS OF REPTILES. 505 
 
 cavity, receiving the segmental or vertebral veins, and terminates 
 in the left precaval vein. The jugular and the axillary trunks 
 unite to form a precaval vein, fig. 332, v*, on each side, the left of 
 which as usual passes behind the auricles to the postcaval orifice 
 of the sinus. 
 
 In the Chelonia the blood from the tail and hind limbs is 
 conveyed along the plastron by a pair of ' umbilical ' or sub- 
 abdominal trunks, which receive the veins of the large allantoic 
 bladders, and the meseraic veins, to form the great portal trunk. 
 A small derivative branch from the posterior jiart of each umbi- 
 lical communicates with lumbo-dorsal vertebral veins, and with 
 some veins from the genital organs to form the reni-portal veins. 
 The renal veins vmite with the ovarian or testicular veins to form 
 the postcaval, which traverses the liver and receives there the 
 hepatic veins : the wide and short trunk, fig. 336, v, then termi- 
 nates in the auricular sinus. The lilood is returned from the 
 head and fore-limbs by the jugulars, figs. 302 and 30-1, i, i, and 
 from the axillary veins, ib. h, h. Each axillary unites with the 
 jugular of its own side to form a precaval vein : the right and left 
 precavals enter separately the auricular sinus, the left precaval 
 opening near the postcaval vein. 
 
 In the Crocodile, the caudal vein, on entering the abdomen, 
 divides into two trunks : each unites with the ischial and iliac 
 veins of its own side and advances towards the kidney. Here 
 the trunk sends off a reni-portal vein, and is then continued 
 towards the hepato-portal system. The renal veins from the inner 
 side of the kidneys unite to form the jiostcaval, fig. 339, V, 
 which receives the left precaval, fig. 340, v**, at its entry into the 
 auricular sinus, ib. s : the hepatic veins open separately into the 
 contiguous end of the sinus, fig. 339, S. The blood from the head 
 and forelimbs is conveyed to the heart, as in other Reptiles, by a 
 pair of precavals, of which the right, ib. V, terminates in the fore- 
 part of the sinus, and the left traverses the back part of the heart, 
 receiving the coronary veins, to join the postcaval or to terminate 
 near its auricular orifice. 
 
 § 89. Heart of Reptiles. — -In Lepidosireu the vein from the lung- 
 like air-bladders traverses the auricle and opens directly into the 
 ventricle. In >Siren the pulmonary vein dilates, before commu- 
 nicating with the ventricle, into a small auricle, which is not 
 outwardly distinct from the much lai-ger auricle receiving the 
 veins of the body.' This is remarkable for its large size, thin 
 walls, and hollow, fimbriated processes, which overlap and almost 
 
506 ANATOMY OP VERTEBRATES. 
 
 conceal the ventricle. The two precavals and the postcaval 
 terminate in a sinus, which the pulmonary venal trunk seems to 
 enter, but to the inner surface of which it adheres in its course to 
 its proper auricular chamber. The ventricle is obtuse and some- 
 times sub-bifid at the apex : it is connected to the pericardium by 
 the usual reflection of the serous layer upon the bulbus-arteriosus, 
 and also by a fold reflected from the apex upon the coronary vein, 
 which is thence continued to the venous sinus. The muscular 
 parietes of the ventricle are about a line in thickness, and loosely 
 fasciculate. The cavity is partially divided by an incomplete 
 septum, terminating by a concave border opposite the orifice of 
 the artery, on each side of which are the valves closing the two 
 auriculo-ventricular orifices. The aorta, narrow, and with thin 
 walls at its commencement, after a short subspiral course, thickens 
 into an elongate ' bulbus arteriosus,' which includes a longitudinal 
 valvular prominence, grooved at its fore-part in correspondence 
 with the origins of the branchial arteries. There is a pair of 
 valves at the origin of the aorta, and a second pair near the 
 beginning of the bulb. The distinction of the pulmonary from 
 the systemic auricle, first observed in Siren, has been since deter- 
 mined in Mcnobranchus^ , Axolotes"^, Amphiuma, and Menopoma.^ 
 In Proteus, in which some of the blood of the puny lungs is con- 
 veyed to systemic veins, the auricular septum is not complete, 
 according to Hyrtl.'' In Amphiuma the auricle is smaller and 
 less fimbriated than in Siren. The ventricle is similarly connected 
 to the pericardium by the apex, as well as by the artery. This 
 forms a half spiral turn at its origin, and dilates into a broader 
 and shorter bulb than in Siren. 
 
 In Mcnopoma the auricles are still more reduced in size, and lie, 
 as in Salamandra, fig. 333, a, when undistended, to the left of the 
 ventricle: their outer sui'fiice, as in Menohranchus, is entire. The 
 ventricle is of a flattened triangular form : its cavity is occupied 
 by the loose fasciculate muscular structure through Avhich the 
 blood filters, as through a sponge, from the small contiguoiis 
 auricular apertures, each of which has a simple valve, to the 
 ' ostium artcriosum.' The artery inclines, with a slight twist, to 
 the left, and swells into a subspherical bulb. The valves are 
 confined to the narrower part, and are in two transverse rows, 
 four in each row, each valve of a conical shape, pointing forward.'^ 
 The first row is just aliove the ostium : the second is haliVay 
 between this and the bull). 
 
 ' CCLXXVIII. p. 73. = coLxxix, p. 45. ^ cci-xix. p. 215. 
 
 * ccuoix. p. 258. » XX. ii. p. 45, pi. xxiii. fig. 2. 
 
HEAKT OF REPTILES. 
 
 507 
 
 333 
 
 Ilearb, vascular arches, and hyo-branchlal 
 aiiparatus, Salamander 
 
 The pulmonic auricle augments in size with the more exclusive 
 share taken by the lungs in respiration : but the auricular part 
 of the heart shows hardly any outward sign of its division in 
 Batrachians. It is small, smooth, and 
 situated to the left and in advance 
 of the ventricle, in Newts and Sala- 
 manders, fig. 333, a. In Frogs and 
 Toads the auricle is applied to the base 
 of the ventricle, and to the back and 
 side of the aorta and its bulb. The 
 ventricle, usually of a more rounded 
 form than in fig. 331, H, is occupied 
 by the muscular fasciculi, except at a 
 small part between the auriculo-ven- 
 tricular and aortal orifices. The bulbus 
 arteriosus is incompletely divided by 
 opjiosite longitudinal folds,the margins 
 of which meet, but remain free. 
 
 In Serpents the heart agrees with 
 other organs in its elongate form. The 
 auricles are in advance of the ventricle, 
 their lower obtuse ends slightly overlapping its base : they arc sepa- 
 rated anteriorly by the co-elongate intrapericardial origins of the 
 arteries called ' conus arteriosus,' answering to the bulbous part in 
 Batrachia ; a slight ' auricidar ' production of the right auricle is 
 tied down to the arteries by the serous layer of the jjcricardium. 
 
 The right auricle consists of a sinus and auricle proper. The 
 sinus receives three veins at its fore part ; the orifice of the right 
 jugular and of the inferior azygos is guarded by a pair of valves: 
 in the orifice of the superior azygos I found three semilunar 
 valves ; two veins o^tQn at the back or hind part of the sinus, the 
 largest being the postcaval, the smaller one the left precaval. 
 The aperture of communication with the auricle is longitudinal, 
 near the middle of the sinus, of a full elliptical shape, guarded by 
 a pair of membranous valves, situated within the proper auricle. 
 The sinus has the structure of the large veins, with the serous 
 layer of the pericardium reflected over it. The auricle has a 
 finely fasciculate muscular wall, thickest at its lower and fore 
 part. The auriculo-ventricular aperture is a semilunar slit, 
 opening into the base of the ventricle, near the origin of the 
 pulmonary artery, and defended by a short membranous valve, 
 havino- one or two chordce tendinete attached to its free maro-in. 
 The left auricle is shorter than the right, but of equal breadth 
 
508 
 
 ANATOMY OF VERTEBRATES. 
 
 334 
 
 when distended, and without a sinus. The pulmonary veins 
 form a common trunk, about half the size of the postcaval, 
 which advances, in contact with and to the left of the post- 
 caval, to open into the hind end of the left auricle, without 
 any valvular structure. The auriculo-ventricular orifice, shaped 
 like that of the right auricle, is close to the termination of 
 the pulmonary vein : it is guarded by a short valve, at the 
 back of the base of the ventricle, to which chordse tendinete are 
 attached. 
 
 The ventricle is conical, with an obtuse apex. More than half 
 the ca^dty, including the apical part, is occupied by a fasciculate 
 decussating muscular structure, from which rises an incomf)lete 
 septum, supporting that between the origins of the pulmonary 
 artery and left aorta. The upper or fore part of the ventricular 
 cavity is formed by a flat sort of platform or roof, supporting the 
 auricular septum, and having the curved auriculo-ventricular slits 
 and valves on each side, with the concavities opposite each other, 
 giving the roof a circular shape. 
 
 The incomplete septum divides the anterior or sternal (pulmonic) 
 
 cavity, whence the pulmonary artery 
 arises, from that at the posterior or 
 dorsal part leading to the orifice of 
 the left aorta, and receiving the blood 
 from the auricles : this ventricular 
 cavity does not extend so near to the 
 apex as the pulmonic cavity does. 
 Tlie part of the ventricle whence the 
 right aorta rises is a still smaller 
 space. A jjair of semilunar valves 
 guards the origin of each artery. 
 
 The heart in Lacertilia essentially 
 resembles that in Opludia, but is 
 shorter in proportion to its breadth. 
 The right auricle, fig. 334, h', is 
 divided by a bivalved orifice from the 
 sinus ; the left auricle, ib. h, has no sinus : it is smaller than the 
 right. Each auriculo-ventricular orifice or slit is guarded by a single 
 valve. The pulmonic cavity of the veutricle, fig. 334, ri, p, is 
 divided from the aortic cavity, ii', by a partial septum, indicated 
 by the dotted outline. The cavity li' receives, as in Opludia, tlie 
 blood from the auricles, and gives oft' the left aorta, a, the right 
 aorta, a', rising from its back part. 
 
 In Chelonia the heart, following, as in Opludia, tlie general 
 
 Heart of Laceria occllata. COLXVII. 
 
HEART or REPTILES. 
 
 509 
 
 335 
 
 shape of tlie body, shows its greatest breadth, figs. 304, a, .335. 
 The two auricles, when distended, are of nearly equal size, and 
 of a subquadrate form, fig. 336, M, o. The bivalvcd orifice 
 between the sinus and the auricle, ib. 
 V, o, is a transverse slit. The white 
 arrow, o, shows the course of the blood 
 from the right auricle, past the valve 
 supported by the base of the auricu- 
 lar septum, into the aortic cavity of 
 the ventricle. In fig. 337 a bristle 
 passes through the orifice left by the 
 incomplete septum between the aortic 
 and pulmonic cavities into the latter, 
 which is the largest in Emijs, as in 
 Opliidia and Lacertilia : the bivalved 
 orifice of the pulmonary artery, P, is 
 shown. In fig. 338 that of the left aorta, 
 A, is similarly exposed, and the in- 
 complete septum is cut through : the 
 
 root of the right aorta, a', is beliind 
 
 Heart of T^studij {jrcica 
 
 336 
 
 that of the left. The relative position 
 of the origins of the three arteries from the chelonian ventricle 
 is shown in fig. 336, where P is the pulmonary, a the left aorta, 
 a' the right aorta, the most posterior, or dorsal, of the three 
 arteries. The ventricle is almost wholly occupied by a spongy 
 muscular structure, and the cavities 
 are smaller in Testudo than in ISmi/s. 
 The left auricle, fig. 336, M, receives 
 the arterial blood from the lungs by 
 a single vein, the common trunk of the 
 ])ulmonary veins, ib. I, I: it opens into 
 the back part of the auricle near the 
 septum, and is guarded by a single 
 oblique membranous fold, ib. m. Each 
 auriculo-ventricular orifice is guarded 
 by a fold which extends across it from 
 either side of the base of the inter- 
 auricular septum ; to that of the left 
 auricle a small part of the muscular 
 structure is attached by chordas tcndineje. Opposite to the right 
 valve a semilunar ridge projects, in Testudo indica, which is the 
 rudiment of the second auriculo-ventricular valve in the Cro- 
 codile, and of the fleshy valve of tliat orifice in the right ventricle 
 
 StrucLure of auricles: heart of C7ic/j/s 
 fimbriata 
 
510 
 
 ANATOMY or VERTEBRATES. 
 
 of Birds. ' The apex of the ventricle is attached by a short fold 
 of the serous membrane to the pericardium, fig. 336, t. 
 
 337 
 
 338 
 
 339 
 
 structure of ventricle, Etnyji europma. sxxviir. 
 
 In all the foregoing modifications of the reptilian heart the 
 venous blood from the general system and the arterialised blood 
 from the lungs are transmitted by distinct auricular reservoirs 
 
 into the ventricle, where, 
 through the sjoongy character 
 of the receptacle, and the free 
 intercommunication between 
 the basal spaces into which 
 the auricles open and from 
 which the arteries proceed, the 
 blood is transmitted, in a more 
 or less mixed state, to the 
 lungs and to the general sys- 
 tem. 
 
 In the Crocodilian order a 
 marked advance is made in the 
 structure of the heart. The 
 blood from the general system 
 is poured by the veins iuto a 
 sinus, fig. 339, S, whence it 
 passes iuto a right auricle, ib. 
 o, by tlic usual bivalved aper- 
 ture. The auricle has a more 
 distinct ' appendix,' and its mus- 
 cular walls are thicker than in 
 lower reptiles. The auriculo- 
 Eifiit.'iuricicaiia veiiwcie. oviciii.insncutaa vcutricular orificc is defcudcd 
 
 \ Crricntliln/; acvtns 
 
 ' XX. vol. ii. p. 48, prep. no. 920, 
 
HEART OF REPTILES. 
 
 511 
 
 not only by the ordinary valve on its left side, which is attached 
 to the base of the auricular septum, but by a similar though 
 smaller fold on the opposite or right side : this fold becomes the 
 fleshy auriculo-ventricular valve in birds. To the junction of the 
 two valves at their lower angle a fleshy column is attached. The 
 ventricular cavity, ib. E, which receives the venous blood, propels 
 it to the left aorta. A, and to the pulmonary artery, P : tlie origin 
 of each is guarded by a pair of semilunar valves. Immediately 
 above the larger of those of the left aorta is an orifice leading 
 into the right aorta : in fig. 339, a bristle is passed from 
 the left aorta throuo;h this 
 orifice into the right axil- 
 lary branch, a, of the right 
 or brachio-cephalic aorta. 
 In the figure, the valve is 
 drawn down to show the 
 orifice ; in its natural state, 
 it conceals and woidd cover 
 the orifice as the blood 
 flowed from the ventricle 
 into the left aorta. Some 
 openings lead from the pul- 
 monic cavity of the ventri- 
 cle into a spongy structure, 
 which has been defined as 
 a particular cavity (^spatium 
 iiiterventriculare) of the 
 ventricle ; but it is essenti- 
 ally a part of the pulmonic 
 chamber: bristles are passed 
 through the orifices or in- 
 tercolumnar spaces, leading 
 from E to this structure, in 
 fig. 339. The left auricle, 
 fig. 340, M, when distended, is smaller than the right, and of a more 
 transverse form : its muscular part is produced into an appendao-e, 
 which almost meets that of the right auricle in front of the ' conns 
 arteriosus,' embracing the ' sulcus coronalis ' of the heart. There 
 is a small pulmonary sinus receiving the short trunks of the 
 pulmonary veins, fig. 340, I, I. The left auriculo-ventricidar 
 aperture is defended by a broad membranous fold continued into 
 the ventricle from the middle of the base of the interauricular 
 sejjtum : to its margin are attached a few chords teudinea3 : the 
 
 Left auricle ajid vcntritlc, Crocodilus acutus 
 
512 ANATOMY OF VERTEBRATES. 
 
 cavity into which it opens, fig. 340, L, is distinct from the 
 pulmonic cavity, tlie septum being complete : its walls are smooth, 
 or less broken by ' columnas carnete ' than in other Eej)tiles ; and 
 the free walls of this ventricle are more compactly muscular. The 
 ventricle is produced in a subcorneal form, from its base to the 
 origin of the right or brachiocephalic aorta : the auriculo-ventri- 
 cular valve is slit, in fig. 340, to show the course of the ventricle 
 to the origin of that aorta : this has a pair of semilunar valves, 
 above which is the intercommunicating orifice with the left 
 aorta. 
 
 Thus the heart, in Ci-ocodilia, consists of two auricles and two 
 ventricles, corresponding to the ' right ' and ' left ' auricles and 
 ventricles of Mammals. But, through the origin of an aorta from 
 the right as well as from the left ventricle, and their intercom- 
 munication, it follows that whenever, from an impeded state of the 
 pulmonary circulation, the right ventricle and its arteries become 
 over-distended, the venous blood flows through the inter-aortic 
 orifice into the arterial trunk, which, after supplying the head 
 and fore-limbs, bends, at a', over the right bronchus and effects 
 an union at a", fig. 339, with the left aorta, A, h. Such a state of 
 the circulation coincides with and facilitates the long submersion 
 of the Crocodile. When the animal is on land and breathing the 
 air directly, the arterialized blood flows freely into the ventricle, fig. 
 340, L, and the synchronous currents from this and the opposite 
 ventricle throw forward the valves at the respective origins of the 
 two aorta; and close the interaortal orifice. The arterial and venous 
 streams flow on unmixed ; the former to the brain and other parts 
 of the head and fore-limbs ; the latter, by the branch, /;, fig. 339, 
 chiefly to the liver and contiguous viscera ; a small part mixing 
 with the arterial blood in a', to be transmitted by a" to the other 
 abdominal viscera, hind limbs, and tail. To convert the heart of 
 the Crocodile into that of the bird, it needs only to obliterate the 
 left aorta; fig. 339, R, to ajipropriate the right or pulmonic ven- 
 tricle, exclusively to the service of the pulmonary artery ; and the 
 ' left ' or systemic ventricle to the service of the aorta, which in 
 Hainatotherma is the exclusive distributor of arterial blood, in an 
 unmixed state, to the general system. 
 
 § 90. Gills of Batrachia. - The blood is conveyed in all Reptiles 
 from the ventricular part of the heart, really or apparently by a 
 single trunk, which, in the one case, is called the ' bulbus arte- 
 riosus,' in the other the ' conus arteriosus.' The interior developc- 
 ments by which the ' bulbus ' is converted into the ' conns,' are 
 interestingly gradational, and the insulation of the pulmonary 
 
GILLS OF BATRACIIIA. 
 
 313 
 
 341 
 
 artery to its ventricular origin is not effected until the batracliian 
 type is passed. 
 
 In the lower or percnnibranchiate members of the order, the 
 single artery from the ventricle sends, as in Fishes, the whole of 
 the Ijlood jn-imarily to branchial organs, throughout life, and, in 
 all Batradiia, at the eaidier aquatic period of existence ; a 
 description of the gills, permanent or deciduous, will, therefore, 
 be premised. At page 87 are described and figured, fig. 69, the 
 hyo-branchial arch and appendages of the larva of the Fmg. 
 The basihyal, h, suspended l)y cera- 
 tohj'als, a, to the tympanic pedicle, 
 e, supports a pair of cerato-branohials, 
 c, which each send off four branchial 
 arches. All these parts are cartilao-e. 
 The heart distributes the blood by a 
 short trunk througli four pairs of vas- 
 cular arches, wliich, bending round 
 the gullet, reunite behind to form the 
 aorta. Before the larva quits the egg, 
 a tegumentary tubercle buds OTit in 
 front of the branchial cleft, and soon 
 shoots into a trifid appendage, fig. 341, 
 A and B, each process lengthening and 
 is extricated. These filaments, of cylindrical shape, ib. C, each 
 suj^port a single cajiillary 
 
 loop, pushed out from the S'i2 
 
 primitive vascular arch, and 
 are covered by ciliated epi- 
 thelium, producing the cur- 
 rents indicated by the arrows 
 in c. The branchial cavity 
 communicates at first, as in 
 Br and do stoma, with the 
 abdominal one, as well as 
 with the outer surface by 
 the branchial clefts. About 
 the fourth day these simple 
 outer gills begin to shrink ; 
 they are absorbed by the 
 seventh day. The cartilaginous arches, also beginning to shrink, 
 become more internal by the progressive growth of the head. 
 
 In the Newt ( Triton, fig. 342), three pairs of external gills are 
 developed, at first as simple filaments, each with its capillary 
 
 VOL. I. L L 
 
 Ifurcating after the lar 
 
 •va 
 
 Head ami bvancliial aiipeiidagcs of the larvaof a Newt 
 iTritoJi) magn. ccLxviir. 
 
514 
 
 ANATOMY OF VERTEBRATES. 
 
 One of the gills of the Newt, magn. ccLxvill. 
 
 344 
 
 loop, but speedily expanding, lengtliening and brandling into 
 lateral processes with corresponding looplets ; these blood-channels 
 intercommunicating by a capillary network, as at d, fig. 343. The 
 
 gill is covered by ciliated 
 343 scales, ib. e, which change 
 
 into nonciliated epithe- 
 lium, /, shortly before the 
 gills are absorbed. 
 
 The size of the gills is as 
 the proximity of their deve- 
 loping vascular arch to the 
 propelling organ of the 
 blood. In the Proteus 
 anguhius three pairs only 
 of branchial and vascular arches are developed, corresponding 
 with the number of external gills. In Siren lacertina, as in 
 caducibranchiate Batrachians, there are four pairs of branchial 
 arches ; the first and fourth being fixed, the second and third free : 
 
 their contiguous borders on the 
 concave side are provided with 
 small interlocking processes. The 
 gills are in three pairs, increasing 
 in size, according to the above- 
 stated dynamic condition, from 
 the first to the third, which is 
 attached to both the third and 
 fourth arches : the upper or outer 
 surface is entire and covered by 
 ordinary integument ; the under 
 or inner surface is produced into 
 pinnatifid fringes, supporting the 
 capillary branchial vessels and 
 covered by thin epitlielivim. Each 
 gill is attached by its base an- 
 terior to and above the gill-slit, 
 which it overhangs. In the Axolotl, 
 fia;. 344, the friu2;cs of the gills are 
 longer and more slender. In the 
 3feiiohronchHS they resemble those 
 of the Triton. In the Siren, Pro- 
 tens, and Menobranchns the outer 
 gills are persistent, and. perhaps, 
 
 Ciirculfitlng and respiratory nrpiins. A\olul.I, '^ . - . i , -r i <• ji 
 
 AMMe^w^ica„,i... wiLxvn, also lu Axolotcs. in cach ot tliesc 
 
GILLS OF BATRACUIA. 515 
 
 ' pcrennibrancliiate ' Batrachians, arteries are developed from tlie 
 last pair of branchial vascular arclies, as at p, fig. 344, to convey 
 blood to the hmgs. 
 
 In Menoporna and Amplduma tlie gill-opening persists on each 
 side ; hut of the original four pairs of vascular arches only the 
 second and third accompany remains of l)ranchial arches, circum- 
 scribe the gullet, and reunite behind to form the beginning of 
 the aortic trunk. The extent of the ossification of the hyo- 
 branchial framework in some measure corresponds with the degree 
 in which the branchial organs of respiration are retained. In 
 Proteus the ceratohyals, urohyal, two pairs of basibranchials, and 
 three pairs of ceratobranchials become bony. In the Siren the 
 ceratohyals, urohyal, one pair of basibranchials, and two pairs of 
 ceratobranchials are bony. The Menopomc and Cryptobranchus 
 agree with the Newts and Salamanders (fig. 3.33), in having the 
 basihyal, ui, the ceratohyals, x, x, and two pairs of cerato- 
 branchials, y and z ; but the latter pair is projiortionally longer 
 and shows two elements of the arch, on each side, ossified. In 
 the Anourous Batrachians the branchial arches are reduced to the 
 basal portions of a single pair of ceratobranchials (ji. 91, fig. 74), 
 which persist, in most higher Vertebrates, as the ' posterior 
 cornua ' of the ' hyoid bone.' 
 
 The \)nxis of the branchial framework in immediate relation 
 with the support of the deciduous gills never pass beyond the 
 cartilaginous stage ; and a histological test is thus aftbrded of the 
 temjDorary or permanent character of the branchiffi in a Batrachian 
 presenting them. The deciduous gills offer many modifications 
 in the larva3 of the caducibranchiate species. In a tropical South 
 American Frog (^OpisthodelpJujs ovifcra), e. g., the external gills 
 are formed before the larva is excluded, and expand into a broad 
 membranous disc at their extremity. 
 
 But whatever the form or structure of the external gills, they 
 are fitted only to their office as such : that being discharged, they 
 turn to no other use, but lose their ciliated and vascular structure, 
 and disappear. The Tadpole, meanwhile, being subject to a 
 series of changes in evciy system of organs concerned in the daily 
 needs of the coming aerial and terrestrial existence, still passes 
 more or less time in water, and supplements the early attcmjits 
 at pulmonary respiration by pidlulating loojis and looplets of capil- 
 laries, fig. 345, a, from the branchial vessel, b, e, supported by the 
 cartilaginous arch, c, and coated by delicate non-ciliated epithe- 
 lium : the terminal processes of these ' internal gills ' support a 
 single capillary loop, d. They resemble the commencing gills of 
 
516 
 
 ANATOMY OF VERTEBRATES. 
 
 .r( s^a 
 
 )Vj, 
 
 
 Teleostomous Fishes, especially of the Lophobranchs ; and the 
 analogy to the piscine respiratory structures is enhanced by the 
 growth of an opercular fold of membrane, protecting the branchial 
 
 chamber; but this, by pro- 
 "■•■' gressive adhesion of its 
 
 posterior border to the cer- 
 vical integument, reduces 
 the lateral fissures to one 
 inferior foramen. In the 
 Xewts, the side-slits are 
 longer retained. The 
 y(3ung of CiEcUia show a 
 branchial pore on each 
 side, with traces of bran- 
 chial fringes. The embryo 
 Salamander shows exter- 
 nal gills while ' in the 
 womb ; and, when these 
 disa])pear, the branchial 
 arches adhere to the oper- 
 cidar fold of skin, the 
 external outlet beino; an 
 inferior transverse slit. 
 In Newts, Salamanders, Ca3cilia3, and Anourans, the branchial 
 orifices become obliterated after the absorption of tlie internal 
 gills. The gigantic Newt of Japan (Cn/ptohranchus) equally 
 differs from Menopoma and Amphiuma in the closure of those 
 orifices. Their retention in these large American Newts, with 
 the superadded persistency of the brancliire themselves in Minio- 
 branchus, Siren, and Proteus, are amongst the most significant 
 evidences of the manifestation of generic characters through 
 arrested stages of one general course of transmutational 
 developement. 
 
 § 91. Arteries of Reptiles. — In the Axolotl, fig. 344, the three 
 anterior pairs of vascular arches rise distinctly from the ' bulbus,' 
 A ; the fourth pair blend their origins with those of the third : 
 the three anterior pairs are, functionally, branchial arteries, ib. B, 
 course along the corresponding branchial arches to the sides of 
 the neck, and then quit them to enter the base of the pendent 
 gill, nmning along the antcro-infcrior border : they there send off 
 a double scries of branches, which penetrate and ramify in the 
 branchial fringes, and constitute at their end and margin'a capil- 
 lary net-work, like that in fig. 34.3. From this the returning 
 
 The iiiternixl liraiichite of the- TaOpole of tbe Frog, magn. 
 CCI.XVIII. 
 
ARTERIES OF REri'lLES. .517 
 
 cliannels converge to fomi the 'branchial veins,' ib. h, which 
 re-enter the neck, course along the dorsal walls of the pharynx, 
 and unite to form the rig-ht and left aortro, or roots of the common 
 median arterial trunk, ib. A. From the first or foremost branchial 
 vein is given oiF the carotid or cephalic artery, a*. The fourth 
 pair of vascular arches pass outward and backward, and each 
 divides, the larger portion, p, going to the lungs, the smaller 
 division pursuing its course to the back of the rrsophagus, where it 
 unites with the third ' branchial vein,' and adds a small proportion 
 of unrespired blood to the contents of the aorta. 
 
 lu the Frutcus the bulbus arteriosus divides into a pair of 
 vessels, each of which, as it diverges, again divides ; the anterior 
 division supplies the anterior gill : the posterior division bifurcates, 
 to supply the second and third gills. But, before distributing 
 the branchial capillaries, each artery communicates by a direct 
 anastomosing channel with the branchial vein ; in other words, 
 only a portion of each j^rimary vascular arch is appropriated to 
 the gills, and a certain proportion of the blood goes from the 
 heart to the aortic trunk without being submitted to the respira- 
 tory process. The small artery to the slender simple pulmonary 
 sac is sent off from the hindmost branchial vein. The cephalic 
 arteries arise from the foremost branchial veins, and consequently 
 supply the brain with jjurer arterial blood than that which goes 
 to the body. 
 
 The changes in the vascrdar arches, consequent on absorption 
 of the gills, are chiefly due to the enlargement of anastomosing 
 channels, between the infereut and efferent branchial triudis, like 
 those in Proteus. The course of these changes reduces the 
 arterial system in Menopoma to the condition of which Hunter 
 left the illustrations published in xx. vol. ii. The bulbus is 
 shortened, and the origins of the primary vascular arches 
 approximated : those of the third and fourth are blended together. 
 The foremost arch is smaller than the second or third : it sends off 
 an artery to the intermandibular space, a second to tlie side of the 
 head, a third to the pharynx, beyond which it bends aljruptly 
 Ijack, to enter the aortal root. The second and third vascular 
 arches are of equal size, wind round the wide pharjaix, anterior 
 to the branchial opening, and unite on reaching its back part to 
 form the aortal root : this sends forward a small artery to the side 
 of the mouth, and, a little further on, the main carotid artery, 
 Ijeyond which the roots converge back^vard, and unite to form 
 the aortic trunk. The hindmost vascular arch is the smallest, 
 and courses round the oesophagus, below or behind the branchial 
 
518 ANATOMY OF VERTEBRATES, 
 
 opening, behind which it sends off the pulmonary artery, and 
 retvirns, at an acute angle, to join the third vascular arch near its 
 termination in the aortic root ; or, the pulmonary artery may be 
 said to be formed by a small Ijranch from the third arch, in con- 
 junction with the fourth arch. The branchial arteries are sent oiF 
 from the aortic trunk, about an inch l^eyond its origin. 
 
 In the Newt the small anastomosing vessel at the base of each 
 eill, between the ingoino; and outcoming trunks, enlarcres as the 
 flow of blood is checked by the stunting of the gill in the course 
 of its absorption ; so that, when this is complete, the blood flows 
 from the ' bulbus ' round to the aorta in a continuous unchecked 
 stream, fig. .333, as at its first appearance. 
 
 In the Frog this course of change issues in the following per- 
 sistent disposition of the primitive vascular arches : — The anterior, 
 originally the fourth, pair, which have their origins brought back 
 so as to seem to rise from the pair preceding, are sometimes called 
 its ' carotid branches : ' they diverge outward, as in their primitive 
 course, have a partial enlargement, and send oft' the ' lingual,' 
 pharyngeal, and entocarotid arteries. The next pair of vascular 
 arches, answering to the third of the jirimitive pairs, sends off 
 the laryngeal and brachial arteries, also a tiibutary to the sub- 
 cutaneous cervical, and are continued backward and inward, 
 supplying the oesophagus in this course, to form by their union 
 the aorta, A. The first pair, answering to the second and first 
 of the primitive pairs, send oft' the second root of the artery 
 which ramifies on the subcutaneous cervical gland, and the 
 pulmonary artery ; the dorsal part of the second primitive arch 
 now appears as the accessory root of the subcutaneous cervical 
 artery given off from the aortic root, as above mentioned. 
 
 The brachial artery sends oft' an external thoracic, distributed 
 to tlie muscles of the fore-part of the abdomen, a subscapular 
 branch, a circumflex artery, supplying the muscles of the shoulder, 
 and is then continued to the fore-arm, where it becomes ' radial,' 
 sends oft' a recurrent branch, and divides near the wrist into a 
 dorso-carpal and palmar branch, which terminates in the digital 
 arteries and the intervening web of capillaries. 
 
 The aortic trunk gi\'es oft' the gastro-mesenteric artery, dividing 
 into ' cceliac ' and mesenteric branches ; then the suprarenal and 
 renal arteries, the lumbar, and the genital arteries (spermatic or 
 ovarian), and bifurcates to form the common iliacs. From each 
 of these are sent off" a vesico-ej)igastric artery continued from the 
 allantoic bladder forward upon tlic abdominal walls, the external 
 and internal circuuiflex arteries, and the femoral, which, ou reaching 
 
ARTERIES OF REPTILES. . 519 
 
 the leg, divides into posterior and anterior tibial, terminating in the 
 digital arteries and capillaries of the webs. 
 
 In Ophidian, Lacertian, and Chelonian Reptiles the ' bulbns ' 
 of the embryo heart becomes divided into three distinct tubes, 
 which remain closely united together by their outer fibrous tissue, 
 and covered anteriorly by the reflected serous layer of the peri- 
 cardium. The extent of this union, or length of the ' conus 
 vascidosus,' is greatest in the Serpents. In the Python it may 
 exceed two inches in length ; and, when the serous and fibrous 
 tunics are dissected away, the origin of the ])ulmonary artery is 
 seen to the left, next to it is the origin of the left aorta, and to 
 the right of this, about an inch above the ventricle, the trunk of 
 the right aorta appears, which, as it diverges from the left, sends 
 off the single carotid artery. This artery is the remnant of the 
 anterior of three primitive vascular arches. The right aortic 
 arch and the left aortic arch, which unite behind and beyond the 
 pericardium to form the abdominal aorta, are the proceeds of the 
 middle primitive arches : the pulmonary artery is the issue of the 
 changes of the posterior or first pair of vascular arches. 
 
 In the Lacertilia the extent of modification is somewhat less. 
 Looking on the sternal surface of the heart, the pulmonary trunk 
 is the foremost, the left aorta is the next, the right aorta is the 
 hindmost. The left and right aortic arches converge, and unite or 
 intercommunicate, behind and usually below or beyond the heart, 
 to form the abdominal aorta. In Lacerta ocellata, fig. 33-i, P 
 marks the origin of the pulmonary artery, which ascends and 
 divides : the left branch, P, passing in front of the left descending 
 aorta, with which it is connected by a ductus arteriosus, D, before 
 proceeding to the left lung, p, fig. 332 ; the right pulmonary 
 artery, fig. 334, p', passes behind the ' arterial cone,' and in front 
 of the right descending aorta, a', with which it communicates, 
 or is connected, by a ductus arteriosus before jiroeeeding to the 
 right lung. These ' ductus arteriosi ' exist in the Python, are 
 shown in the Tortoise, fig. 335, D, D, and in the Crocodile, 
 fig. 340, D, d'. The third primitive arterial trunk, called ' right 
 aorta,' divides into the right arch (below a' in fig. 334), and 
 into the common trunk of the two cephalic or carotid arteries, 
 ib. a, «*, describing the upper arches : the common trunk of 
 the brachial arteries is usually given off from the right aortic 
 arch. In Psamviosaurus griseus the common trunk of the carotid 
 does not bifurcate until it has ascended the neck as far as the 
 origin of the bronchial tubes : and not until after the rieht aorta 
 has arched over the right bronchus does it send offj at an acute 
 
520 ANATOMY OF VERTEBRATES. 
 
 angle, the common trunk of the right and left brachials. The 
 left aortic arch, in Psammosaurus, sends off a gastric and mesen- 
 teric artery before it joins the right aortic arch ; and this is the 
 case also in the Tortoise, fig. 335, I, and Crocodile, fig. 339, h, 
 the left aorta being then so reduced in size as to resemble a 
 ' ductus arteriosus.' 
 
 In the Tortoise the right aorta, soon after its origin, sends off 
 a common trunk, which quickly subdivides into the carotids, 
 fig. 335, a", a, and brachials, ib. a, a; and the same is the case 
 with Eimjs, in which the four arteries are seen cut short near their 
 origins, between a' and A, figs. 337 and 338. 
 
 In the Crocodile the two ' arteri^e innominataj,' figs. 339, 340, b,b, 
 are longer before they divide into the brachial, «, and carotid, a' : 
 both innominate* arise by a short common trunk from the right 
 aorta, which divides, soon after its origin, into that trunk and the 
 right aortic arch, ib. a'. This arch winds over the right pul- 
 monary artery, fig. 339, p', with which it is connected by a 
 ' ductus arteriosus ' (the arch is reflected ujiward and the ' ductus ' 
 d', severed from the pulmonary artery, p', in fig. 340). The 
 origin of the riglit or brachi-cephalic aorta is hidden by that 
 of the left aorta, fig. 339, A, which is anterior, or on the sternal 
 side of it. The left aorta, as it winds over the left 2iulmonary 
 artery, is attached to it by a ' ductus arteriosus,' the remnant of 
 the channel by which the first vascular arch originallv com- 
 municated with the second, to aid in forming the aorta, before its 
 current of blood was diverted to the uses of the well-developed 
 lung, after exclusion. Tlie continuation of the main part of the 
 left aorta into the great visceral artery, fig. 339, /;, reduces its 
 original union with the right aortic arch, a', a", to a small anas- 
 tomotic channel. 
 
 The following particulars arc notable with regard to the dis- 
 tribution of arterial blood by the right aorta in Reptiles. The 
 anterior vascular arch, in Ophidia, is converted into a pair of 
 cephalic or carotid arteries in the young Snake, and this structure 
 is retained in the common Suake (Cohihef i/ntri.i); in Pi/flion 
 tii/rif; I found the right carotid much reduced in size ; in the 
 Viper ( V. vrnis), and some other Serpents, the cervical part of 
 the right carotid is obliterated: but the cephalic portion remains, 
 and receives blood by the anastomosis of one of its branches 
 with the left carotid.' In the AHper, and some other venomous 
 Serpents, the internal maxillary branch of the carotid forms a 
 retc mirabile behind the poison-gland.'- The right aortic arch, 
 
 ' CCLXXX[. ! CCLXXXII. p. 260. 
 
LUNGS 01? REPTILES. 
 
 521 
 
 soon after it has curved over the right puhiionary artery, sends oft 
 the trunk of the vertebral and anterior intercostal arteries : in its 
 origin aud position, this trunk resemljles the common brachial 
 trunk in Lizards. 
 
 The relation of the orio-iu of the ri<ilit aorta to the ventricular 
 compartment, first receiving the arterialised blood from the 
 pulmonary auricle, and the distribution of the branches of the 
 right aorta, are such, that the head, neck, and fore-liinbs receive 
 chiefly arterialised blood, and the abdominal viscera, the trunk, 
 hind-limbs, and tail, are supplied with mixed venous and arterial 
 blood. But this localised distribution of the two kinds of blood^ 
 is more completely effected in the Cro- -. -»? 
 
 codiles, through the modification of the 
 heart and arteries before described. 
 
 § 92. Lungs of Reptik-s. — An opening 
 on the midline of the ventral side of the 
 pharynx, fig. .346, c, receives air introduced 
 into the mouth, and conveys it to the 
 receptacles which, in lleptiles and all 
 higher Vertebrates, are called ' lungs,' ilj. 
 f, f. Tlie opening, usually a short longi- 
 tudinal slit, leads, in the Newt and Pro- 
 teus, to a small crescentic membranous 
 sac, from the angles of which are pro- 
 duced the long slender pulmonic bags. In 
 the Axolotl a short tube, strengthened by 
 a few feeble subannular cartilages, con- 
 ducts the air to the lungs, which com- 
 mence just beyond the heart : in the Siren and Land-Salamander 
 a similar trachea divides into two branches, one to each lung.' In 
 all these tailed Batraclua the pulmonai'y bags have simple or even 
 walls. The artery, formed as above described, from the hindmost 
 vascular arch, joined by a branch from the next arch, runs along 
 one side or border, and the vein returns along the opposite border 
 of the lung. The branches proceed from the arterj', fig. .348, 
 a, transversely, with regular intervals, midway in which the 
 venules are formed which course half-round the cylinder to open 
 into the longitudinal vein : fibres of elastic tissue accomj^any the 
 arterioles and venules. The intervening capillaries constitute a 
 re^'-ular network, uniformly o\ex the pulmonary surface ; they 
 seem to be mere channels for the passage of the blood discs, fig. 
 347, with intervals or islets of compacted cells, containing nuclei 
 
 XCIV. p. 39 5. 
 
 iitory Migaiis, Ncnvl. 
 <_'CXXX\'1II. 
 
522 
 
 ANATOMY OF VEETEBEATES. 
 
 and granules, ib. a. This vascular surface is covered by a delicate 
 carpet of epithelial cells, fig. 348, certain linear tracts of which, 
 
 347 
 
 Respiratory surface, lung of Newt, magnified, with the epithelium 
 
 out of focus. COLXVIH, 
 
 ib. h, b, are ciliated. The exterior of the lung is covered by 
 delicate peritoneal nonciliated scales. 
 
 348 
 
 ■/ 
 
 E ^ 1 
 
 in luiii, . cci.w III. 
 
 1 1 Unl criiig 
 
 111 tlic Siren the lungs are narrow bags, coextensive with the 
 
LUNGS OE REPTILES. 
 
 523 
 
 349 
 
 long trunk ; and the ciliated tracts upon the inner surface begin 
 to be raised therefrom, and to mark out shallow depressions on 
 the vascular surface, at least along the anterior half of the sac. 
 In the Axolotl, in which the lungs terminate at the hinder third 
 of the abdomen, the alveolar depressions or cells are more marked. 
 In the Amphiume the lungs are narrow, and terminate in a point, 
 within a short distance of the anus : on the inner surface elastic 
 bands are developed in the inter-alveolar partitions, and the alveoli 
 begin to be subdivided into smaller cells. In the Menopome the 
 lungs have a similar structure, but are proportionally smaller, and 
 with larger alveolar depressions. 
 
 The lungs of the Frog, fig. 349, are wider in projiortion to 
 their length, and extend along the 
 dorsal part of the abdominal cavity, 
 with the vertebral bodies and vascu- 
 lar trunks interiifening. They are 
 continued by short bronchia; or bron- 
 chial apertures, fig. 350, f, directly 
 from the larynx. The proper tissue 
 of the bag is composed of very elastic 
 fibre, covered by peritoneal epithe- 
 lium, and lined by the capillary net- 
 work and its epithelial covering ; 
 the pulmonary artery takes its course 
 beneath the peritoneal layer, the pul- 
 monary vein runs beneath the inter- 
 nal epithelium ; the one on the fore 
 and outer part, the other nearer the 
 inner or mesial side of the lung. The 
 whole inner surface is honeycombed, 
 and the alveoli are subdivided into 
 smaller cells. The arterioles run 
 along the attached borders of the septa, the venules along the 
 free borders. The ciliary epithelium is limited to the margins 
 of the alveoli supporting the larger venules: the capillary net- 
 work, covered by non-ciliated delicate epithelial scales. Is 
 disposed upon the sides and bottom of the ultimate cells, the 
 septa having a layer of the capillary network on each side. 
 Thus the lungs of the tailless Batrachla, and more especially of 
 the Pipa, In which they are very broad and the bronchial tubes 
 long, have a more extensive respiratory surface in proportion to 
 their size than in the tailed species. 
 
 But the puluionary artery is not exclusively distributed to the 
 
 Heart and lungs. Frog, cclxviii. 
 
524 ANATOMY OF VERTEBRATES. 
 
 lung : it sends a branch to the ' rete mirabile ' of the parotoid, or 
 group of subcutaneous cervical glands, and, in the Frog, the 
 branch from the pulmonary artery joins one from the aorta to 
 form a large subcutaneous artery, more extensively distributed 
 upon the skin, which exercises a respiratory office in these 
 naked Batrachia. In the Siren, Menopome, and Amphiume, 
 the pulmonary artery distributes some small twigs to the oeso- 
 phagus. 
 
 In the poisonous, colubrine, and marine Snakes the lung is, 
 functionally, single, one only being developed, but of great length, 
 for the respiratory purpose, the other becoming aborted into a 
 small or scarcely discernible rudiment. The trachea, fig. 300, a, 
 has numerous and entire cartilaginous rings along a certain pro- 
 portion of its course, and the lung, ib. B, seems to be formed by 
 a dilatation of the membranous part of the tracheal tube, after 
 the rings become incomplete : but these may be traced sujiporting 
 a narrow and shallow kind of air-canal to the hind end of the 
 luno' in Pclamis bicolor.^ A similar structure has been observed 
 in Vijiers {^Echidna arietans), and, for a shorter extent, in Kattle- 
 snakes, in which the trachea is shorter than in non-venomous 
 Snakes. The expanded membranous part of the lung is honey- 
 combed, Avith subdivisions of the alveoli at the fore-part of the 
 lung, for a varying thickness and extent in different species. The 
 rudiment of the atrophied lung is often indicated by an orifice in 
 the trachea, at or near its entry into the functional lung, leading 
 to a small pouch. This adheres to the terminal whole-rings of 
 the trachea in Coluber natrix and Naja tripudians. In the great 
 constricting Serpents both lungs are functionally Init Tincqually 
 developed. In Pijthon tigris the left lung is nearly half as lono- 
 as the right : but, by its structure, it takes almost an equal share 
 in the respiratory function, the vascular and honeycombed parietes 
 being of nearly the same extent as in the right luno;. So much 
 of this as is prolonged beyond the left lung has thin, simple, and 
 comparatively unvascular walls, performing the office of a reservoir 
 of air, which may be useful during the period, when the delicate 
 windpipe is squeezed flat by a large prey in progress of slow 
 deglutition.^ The proper parietes of the lungs almost every- 
 where adheres, by lax cellular tissue, to the contiguous oro-ans. 
 In the Slow-worm {Aiir/uis fraflil/s) the lungs are relatively 
 shorter than in true Ophidia, but the left is only half the length 
 of the right lung. A similar diftercnce is presented by the lungs 
 
 ' xx. vol. ii. p. 93, iircp. no. 1089. '' Ib. p 94, prep, no 1093 A. 
 
LUNGS OF REPTILES. 52,5 
 
 of Bipes lepidopus. In Pseudopus Pallasil the lungs are of nearly 
 equal length. 
 
 In most Laccrtian Reptiles the lungs are equal, are broader 
 in proportion to their length, and the short bronchus terminates 
 abruptly in the single pulmonary cavity. The parietes are honej'- 
 combed and 'vascular, but in a less degree as they extend from the 
 heart : in Geckos and Agamas the alveoli are deepest on the 
 mesial side of the lungs. In the Iguana the pulmonary cavity is 
 divided by a few deep partitions into primary lodges, the parietes 
 of which are honeycombed by secondary and tertiary cells.' In 
 a Monitor {Jlegmia ocellata) the bronchus is continued some way 
 along the interior of the lung.^ The lungs of the Chameleon are 
 remarkable for their great extent, for the delicacy of their 
 parietes, and tlic number of c;vcal processes continued from their 
 anterior and inferior margins. Each lung is partially divided 
 longitudinally at its fore ]iart into two cavities, which have their 
 vascular surface increased by subdivision into cellular alveoli ; 
 the posterior appendiculated part of the lung is of a simpler 
 and loss vascular structure, and may serve as a reservoir of 
 air. Marginal ca3cal productions of the pulmonary bag exist also 
 in the Geckos (e. g. Ptijodacfijlus Jindjriatiis) and in Pohjchrus 
 marmoratus. In Geckos and Scinks the trachea terminates in 
 the lungs without dividing into bronchi. 
 
 In the Chelonia the lungs present a further stage of complica- 
 tion, and are adherent to the surrounding parts. In those of 
 Chehjdra serpentina, e.g. the general cavity of each lung is divided 
 into eight compartments, the walls of which are honeycombed 
 and vascular, especially at their fore part. The bronchial tube 
 extends to the hindmost compartment of the lung,'^ communi- 
 cating l^y special orifices with the anterior ones, and sending 
 continuations of its fibrous structure along the free border of 
 the septa. 
 
 In the Sea-Turtles ( Chelone) the lungs extend over the back 
 part of the abdomen to the pelvis, and must act as an air-bladder 
 during their swimming : 4 the bronchial tubes are continued, 
 gradually decreasing, to near the end of the lungs, and retaining 
 cartilaginous rings or half-rings along three-fourths of their 
 course. They communicate with numerous primary divisions of 
 the pulmonary cavity, each of which is divided into cells, which 
 are subdivided to the third or fourth degree, with proportionate 
 extension of the vascular respiratory surface. The ultimate cells 
 
 ' XX. ib. p. 96. ■ cccxxi. p. 525. 
 
 ' Ib. p. 96, prep. no. 1109 A. ' Ibid. p. 96, prep. no. 1110. 
 
526 
 
 ANATOMY or VEKTEBRATES. 
 
 are the largest and tlieir 
 
 along the outer margin of the lung 
 parietes the least vascular. 
 
 Subjoined is a tabular view ' of the capacity of the lungs in 
 examples of different families of the Chelonian order, ' obtained 
 by pumping out the air of the lungs, then pumping in water, 
 then pumping out the water again and measuring its amount in 
 cubic inches.' ^ This table shows that aquatic Chelonia require 
 less air in their lungs, in proportion to the weight of the body, 
 than land Chelonia ; and that in mud-dwellers and the soft-turtles 
 ( Trionycida) other parts are auxiliary to the lungs in the act of 
 breathing. Thus the more permeable texture and minor thick- 
 ness of the epiderm in the Trionycidm suggest the aptness of the 
 skin for respiratory influence on the blood, analogous to that of a 
 gill. The integument of the under side of the body in these 
 estuary turtles, which seldom leave the water except to lay their 
 eggs, is highly vascular. 
 
 Dr. Sager found ' arranged along the surface of the tongue of 
 Trionyx, and somewhat in rows, as well as on the fauces and 
 about the rima glottidis, and also over the edges of the cornua 
 hyoidea, a number of delicate fringes, resembling, especially on 
 the hyoid arches, the fimbriated gills of the Menobranchus.' ^ 
 Professor Agassiz remarks that, ' after seeing this Turtle remain- 
 ing under water for half-an-hour without showing the least sign 
 of oppression, it seems plausible to assume that these fringes may 
 be similar to the internal gills of Tadpoles, not only in their 
 shape but also in their function.' '' 
 
 In the Crocodile ( Crocodilus acutus) the bronchial tube enters 
 the middle of the lung and is continvied for a short distance into 
 its substance before losing the cartilaginous annular structure, 
 
 TABLE SUOWINO THE CAPACITY OF THE LUNGS COMPARED TVITH THE TVEICnT 
 OF THE BODY. CCC. p. 283. 
 
 Sj-ieoioa 
 
 Mode of Lite 
 
 Wfipllt of 
 liody 
 
 Capacity of 
 tlie lungs 
 
 Length of 
 Carapace 
 
 Testudo polyphemiis, foom. 
 
 On dry groimd and 
 
 OlUlCi'S 
 
 culiic inches 
 
 illOlK'S 
 
 
 in sand holes 
 
 95 
 
 35 
 
 loi 
 
 Cistado trinngids, foem. . 
 
 In dry woods, under 
 
 
 
 
 
 leaves 
 
 19 
 
 17J 
 
 6J 
 
 Phjchemys rvijosa, foem. . 
 
 In water and on land 
 
 G2 
 
 221 
 
 11 
 
 Cirwslernon pennsijlvaniciim. 
 
 
 
 
 
 fcem. 
 
 In wafer and mnd 
 
 8 
 
 i 
 
 4V 
 
 Chelydra serpentina, mas. 
 
 In water and nind 
 
 6.5 
 
 f 
 
 10 
 
 Triont/a: ferox, fccm 
 
 In water and nuid 
 
 7fi 
 
 4i 
 
 13 
 
 CCC. vol. i. p. 284. '' cccii. quoted in ccc. pp. 277, 284. 
 
 ' Iliid. p. 284. 
 
LARYNX 01'' REPTILES. 
 
 527 
 
 sending off lateral branches : it then abrnptly terminates in a 
 dilated elongated passage, similar to those in which the side- 
 branches open. These passages correspond with the primary 
 divisions of the pulmonary cavity in the Turtle, and the air 
 passes from them Ijy numerous round apertures into the smaller 
 subdivisions forming the cellular structure of the lung.' 
 
 § 9 5. Larynx of Reptiles. — In perennibranchial and tailed 
 Batrucliia the glottis is a simple longitudinal fissure, fig. 346, &, 
 in the middle of the ventral walls of the pharynx, each side of 
 which is commonly strengthened by a slender portion of fibro- 
 cartilage (Amphiuma), or so divided as to represent an ' arytenoid ' 
 and a ' laryngo-tracheal ' cartilage (Proteus). The slit 02iens 
 into a small membranous cavity, usually kept patent by lateral 
 cartilages, from which the lungs diverge directly in Proteus, 
 Amphiuma, and Triton, and with a short trachea intervening in 
 Siren, Axolotes, Mcnopoma, and Salamandra, the trachea being 
 either membranous or with feeble rudiments of cartilaginous rings. 
 
 In tailless Batrachia the larynx is well developed, esjoecially 
 In the males. There is, in most, an annular thyrocricoid cartilage, 
 which supports in all a pair of large arytenoids, of a triangular 
 shape, the apex forming the upjaer and lateral boundary of the 
 larynx, fig. 351, a: the ohordas vocales 
 stretch transversely from one end of the 
 base to the other, and are wanting only in 
 Pipa and Dactylethra. Above and below 
 the vocal chords, fig. 350, c, there is a 
 mucous pouch ; and between the chords 
 there is, in some species, a cartilage. The 
 muscles are a ' dilator ' and a ' constrictor 
 rimas glottidis,' and a ' compressor glottidis,' 
 arising from the cerato-branchials, fig. 74, 
 p. 91, and inserted into the posterior angle 
 of the arytenoid : by bending this angle 
 outward, it stretches the vocal chords, and, 
 both muscles acting, they compress the 
 larynx. This is an influential muscle in 
 regard to the voice or croak, and varies with 
 its quality in different species ; it is want- 
 ing in the mute Pipa. In Bomhinator igneus 
 and Hyla verrucosa the arytenoids are ob- 
 tuse-angled and nearly equilateral triangles. In Bufo cinereus 
 
 350 
 
 Tongue, larj-nx, and lungs, 
 
 male Prog, Rrnin temporaria, 
 
 cccxx. 
 
 XX. vol. ii. p. 97, prep. no. 1118. 
 
528 
 
 ANATOinr OF VERTEBRATES. 
 
 tliey are more acute-angled and directed backward. In the Toad 
 
 (Bufo) the chordfe vocales are thin 
 elastic membranes, and in two pairs, fig. 
 .351, a and h : the saccidi are seen to be 
 lodged in the large arytenoid cartilages. 
 The males of the common and edible 
 Frogs {Rana) have two submandibular 
 sacs, the male Tree-Frog {Hyla) has 
 one such sac, opening by a straight canal 
 into the larynx, and susceptible of con- 
 siderable distension by air during the 
 croak. All these diversities of laryngeal 
 structure affect the loudness, deepness, 
 or sharpness of the peculiar vocal notes 
 of Frogs and Toads. The air passes 
 to the lungs, fig. 350, (j, 351, c, d, by 
 short bronchi, fig. 350,/!, save in the 
 Plpa, in which the broncliial tubes are long, especially in the 
 female. 
 
 The glottis in Serpents can be drawn forward and protruded 
 from the mouth by the action of the rjcniotracheales muscles, 
 fio-. 147, 7j, p. 229. In marine serpents the glottis is situated 
 very near the forepart of the mouth, and the air can be inspired 
 at the surface without exposure of the jaws. The upper rings 
 of the trachea coalesce to form a cricothyroid cartilage, sending 
 forward two processes which represent the arytenoids in many 
 Ophidia ; but which are freely articulated therewith in the great 
 constrictors. The ' processus epiglotticus ' is subquadrate in 
 Boa. True ' chordaj vocales ' are alisent ; and the voice is 
 reduced to a hissing sound produced by the action of the exjiired 
 air upon the margins of the glottis. The rings of the trachea 
 are entire, and the trachea varies in length in different ser- 
 pents before it reaches the lung. Along this it continues, of 
 decreasing breadth, with portions of the rings, as if incrusted in 
 the pulmonary parietes, for an extent varying in different 
 serpents. 
 
 In Laccrfians a cricothyroid cartilage supports a pair of 
 arytenoid cartilages : in most there is a cartilaginous or osseous 
 'processus epiglotticus,' M'hich, in a few, 'coexists with an incom- 
 plete epiglottis. The mucous membrane of the glottis is reflected 
 over the arytenoids, forming a depression beneath them, and folds 
 with free margins : these ' vocal chords ' arc broad in the Chame- 
 leon and Gecko, and stretch from the base of the arytenoid to the 
 
LARYNX OF REPTILES. 529 
 
 inner surface of tlie cricothyroid. In Lacerta and Ascalahotes 
 the corresponding fokl is very narrow, and the chirping call-note 
 of the Gecko may depend rather on the vibration of the margins 
 of the glottis than on the vocal folds, which cannot be brought 
 into contact or be made tense. In the Chameleon, the lining 
 membrane of the larynx is produced between the cricothyroid and 
 first tracheal ring into a pouch. In the Stellio of the Levant the 
 tracheal rings are osseous : in most Lizards they are cartilaginous. 
 The trachea is remarkable for its width in Platydactylus guttatus, 
 but the diameter is reduced to one half in Platydactylus vittatus. 
 In the Chameleon and most other Lacertians it is still narrower. 
 
 Amongst the Chelonia the Hawksbill Turtle ( Chelone imhricata) 
 shows a glottis undefended by retroverted papilla3, or by an epi- 
 glottis, but capable of being accurately closed by its constrictors. 
 The thyroid cartilage in all Chelonia is distinct from the cricoid : 
 the arytenoids are triangular, and their inner facet is large in 
 Emys and Testudo. The ordinary sound produced by the larynx 
 of the Chelonia is a sort of hiss. The European fresh-water Tor- 
 toise emits a low piping note, and Agassiz records the same fact in 
 regard to some North Amei'icanEmydians.^ In Chelone my das iho. 
 ' rima glottidis ' supports on each side a mucous fold, which serves 
 to produce a low grunt or bark at certain seasons. In some Tor- 
 toises ( Testudo tabulata, T. clephantopus) a triangular membrane 
 ascends from the base of the larynx to the ' rima,' dividing it into 
 two parts. The rings of the trachea are entire and cartilaginous : 
 in some species the trachea bifurcates half way towards the 
 lungs, the bronchi being of great length, and one of them usually 
 describing a large curve : in Testudo grcBca the left bronchus is 
 three fourths longer than the tracheal trunk ; but in Testudo 
 coue'i the trachea is one fourth longer than the bronchi. The 
 production of the snout in the Trionycidce enables the terminal 
 nostrils to be raised above the surface of the water, to respire, 
 without exposure of the animal. 
 
 In the Nilotic Crocodile the mucous membrane is produced into 
 a fold on each side the 'rima glottidis : ' the folds deepen as they 
 extend backward, and are produced into a pair of j^ointed pro- 
 cesses above the arytenoids. The broad cartilaginous plate of 
 the basihyal rises in front of the glottis like an epiglottis. On 
 divaricating the rimal folds they are seen to bound a wide pouch 
 anterior to and aljovc the true ' aditus laryngis,' which is much 
 shorter than the ' rima.' The thyroid and cricoid coalesce to form 
 one annular cartilage supporting the pair of arytenoids. The 
 
 ' ccc. vol. i. p. 284. 
 VOL. I. M M 
 
S30 ANATOMY OF VERTEBRATES. 
 
 membrane covering these forms a wide depression anterior to and 
 below them, before being continued as chordas vocales, along the 
 posterior half of each side the ' aditus laryngis.' These ' chordse ' 
 operate in producing the ' bellow ' of the Crocodile, a loud sound, 
 between barking and roaring. 
 
 The trachea in the Nilotic and some other kinds of Crocodile 
 forms a bend or loop before dividing into the bronchi : this loop 
 is not found in the Alligator or Gavial. The erectile structure of 
 the single tegumentary nostril in the Gavial, serves, like the short 
 proboscis of the Trionyx, to enable the aquatic reptile to breathe 
 the air with more safety. 
 
 § 94. Respiratorij actions of Reptiles. — The lungs in Batrachia 
 being suspended in a common thoracic-abdominal cavity, without 
 the costal or diaphragmatic mechanism of expansion, are filled 
 with air by acts of deglutition. 
 
 The hyoid, fig. 350, b, is depressed ; the pharynx, ib. e, is 
 dilated : the air enters by the nostrils, and its return is prevented 
 by their internal valvular folds, and by the application of the 
 tongue, ib. a, against their palatal openings. The contraction of 
 the throat-muscles and retraction of the eyeballs send the air 
 backward, the gullet contracts, the glottis opens, and the air is 
 driven through the bronchi,/, into the lungs, f/. If the movith of 
 a Frog be kept forciljly open it is soon asphyxiated, the essential 
 respiratory acts being prevented : if a breach be made in the 
 abdominal walls, and the act of deglutition can be performed, the 
 lungs are inflated. Exjiiration is performed by the elasticity of 
 the pulmonary parietes, which is such as to quite empty the lung 
 and reduce it to the size of a small pea, the abdomen being 
 opened. 
 
 The lungs of Chelonia being lodged in a cavity, the capacity of 
 which is only affected by the retraction and protrusion of the 
 limbs and tail, appear, also, to be filled with air, chiefly by acts 
 of deglutition. These are so habitual that ' the working of the 
 throat ' continues when the Turtle is immersed in water; and 
 Hunter was led by observing this circumstance, to relinquish the 
 idea of its being a respiratory act. It is, in iiict, in the Chelonia 
 in which the plastron remains unfixed by bone to the carapace 
 ( Clielone, Trionyx) that respiratory acts due to movements of the 
 thoracic-abdominal walls arc most consiiicuous. ' If a Turtle be 
 thrown iipon its liaclc, and makes an inspiration, we may observe 
 that its four fins are, as it were, erected ; the brcast-boue is pushed 
 forward, and the cavity swells out wherever the parts are soft. All 
 tliis is done, I conceive, by the uuiscles of the extremities moving 
 
RESPIRATORY ACTIONS OF REPTILES. .'531 
 
 their respective bones in an inverted order: instead of their 
 moving the extremity, the extremity becomes tlie fixed point : 
 the bones answering to the clavicles are moved forward, and the 
 bones of the pelvis at the lower part are pushed against the inside 
 of the breast-bone, so that the whole bone is pushed out. They 
 appear to draw in their breath but once in twenty minutes or 
 half-an-hour, and often at a much longer interval.' ' 
 
 It is probable that such respiratory actions could not be per- 
 formed by the animal when swimming and diving ; and it is 
 certain that such actions of the limb-muscles could not effect 
 any motion of the breast-bone in the great proportion of the 
 Chelonian order, in which the plastron is fixed. The capacity 
 of the thoracic-abdominal cavity may be slightly affected by the 
 movements of the limits acting on the soft walls at its fore and 
 and back parts, fig. 149, p. 233 ; the diaphragmatic muscles, 
 figs. 150, 151, 42, may cooperate; but respiration goes on when 
 the limbs are motionless, and ajjparently by acts of deglutition, as 
 indicated by the 'working of the throat.' 
 
 In Ophidia, Lacertilia, and CrocodiUa, respiration is performed 
 by the expansion and contraction of the more movable parts of 
 the parietes of the cavity containing the lungs : for this being 
 dilated the air rushes in by the only availaljle passage, viz. the 
 glottis and windpipe, to the lungs. The articidations of the ribs 
 in servients allow of their rotation forward and backward, and 
 even of a slight divarication of the two ribs of each pair. This 
 mechanism and the muscles concerned in working it are described, 
 pp. 55, 56, 224, figs. 143, 144. To whatever degree the visceral 
 cavity may be so expanded, the air enters by the nostrils or 
 glottis, if they be open and free ; and a general expansile or 
 inspiratory movement may then be noticed.^ But the great 
 length of the thoracic-abdominal cavity and the numlaers of pairs 
 of moveable ribs — in some serpents three hundred pairs — are 
 associated with partial enlargements and contraeti(jns of the 
 cavity, effecting corresponding changes in the long pulmonary- 
 bag, without affecting the total volume of air in it, if the glottis 
 be not in communication with the outward air, either directly or 
 through the medium of the nostrils. Schlegel has observed about 
 thirty such partial dilatations of the trunk and lung between two 
 inspirations.^ When the Constrictors swallow their prey the 
 glottis is protruded from the mouth : this may be a consecjuence of 
 the pressure exercised on the parietes of the greatly distended 
 mouth, and may not relate to the necessity of directly receiving 
 
 • ccxxxvi. vol. ii. p. 348. ^ ccLXxxv. ' ccixxiv. torn. i. p. 53. 
 
 M M 2 
 
532 ANATOMY OF VERTEBRATES. 
 
 air during the period occupied by the rotatory transit of the prey 
 to the gullet : it is more proljable that at this time the trachea is 
 squeezed flat, and the air In the hinder reservoir of the largest 
 lung may serve- to keep up the small amount of respiration needed 
 during the passage of the prey to the stomach, the snake being 
 then at rest and almost torpid. 
 
 In Lizards and Crocodiles certain pairs of vertebral ribs 
 (pleurapophyses) at the forepart of the thoracic-abdominal cavity 
 articulate with sternal ribs (hajmapoiDhyses), the bony arches being 
 completed by the sternum below. The i:ileurapophysis, fig. 49,/' 
 (p. 57), forms an angle directed backward at the joint with the 
 hfcmapophysis, ib. 6, the muscles raising or drawing outward and 
 forward the upper rib open the angle between it and the lower 
 one ; and the head of the rib being fixed to the vertebra, the 
 sternum yields, is depressed, and both the vertical and transverse 
 diameters of the cavity containing the lungs are increased. 
 Consequently the air enters the pulmonary ca-^-ities. By the 
 contrary actions, the thoracic-abdominal cavity is contracted, and, 
 the elasticity of the i^ulmonary parietes aiding, the air is expelled. 
 
 In the Crocodile the Increase in the number of the complete 
 sterno-costal arches, fig. 56, i, 2, 3, &c. (p. 68), gives greater efi:ect 
 to their respiratory movements : and the muscular fibres attached 
 to the midriff-like sheets expanded ujjon the hepatic lobes, may aid 
 in making the general exjiansion of the thoracic-abdominal cavity 
 tell more directly upon the lungs. 
 
 Almost all the Lacertilia and Batrachia have the peculiarity 
 of inflating their lungs, when they are under the influence of fear 
 or of some other excitement : in the Chama3leon, as well as in 
 Polychrus and many other Iguanoids, the expansion of the trunk 
 consequent thereon aids in producing the remarkable change of 
 colours to which we shall recur in the cha})ter on the integu- 
 ments. 
 
633 
 
 CHAPTER VIII. 
 
 URINARY SYSTEM OF HJSMATOCRYA. 
 
 § 95. Kkhieys of Fishes. — In all Vertebi'ates an excretory 
 organ is very early developed in the form of a tvibe, extending 
 from each side of the cloaca forward, along the dorsal region of 
 the abdomen, close to the spine, where it communicates with a 
 number of slender blind tubes jdaced at right angles to it ; the 
 longitudinal trunk- tube serving as the excretory duct of the 
 shorter transverse secerning ca3ca. These glands are transitory in 
 the air-breathing Vertebrates and are called, from their discoverer, 
 ' corpora WolfKana ; ' they are persistent in fishes ' and are 
 called ' kidneys,' fig. 352, n : in both they are renal organs and 
 secrete urine. 
 
 A slightly oj^aque, slender, elongated glandular body, in the 
 situation marked /* in fig. 169, may represent the renal organ in 
 Brancliiostoma. The structure of this organ is more obvious in 
 the Myxinoids : it is double : each long duct, fig. .353, i, a, as it 
 extends from the cloaca through the abdominal cavity, sends off, 
 at regular but distant intervals from its outer side, a short wide 
 tube, ib. h, which communicates by a narrow opening with a blind 
 sac, ib. d. At the bottom of this sac or caicum there is a small 
 vaso-ganglion, fig. 353, 2, d, free on all sides save that by which 
 the vessels, ib. a, enter, and ib. J,^ quit it : there are no urini- 
 ferous tubes in this vaso-ganglion : the contents of the ca3Ciim 
 must react through its thin parietes and those of the capillaries 
 with which it is in contact upon the blood in those capillaries, and 
 extract therefrom the azotised uric princiiile. Analogous vascu- 
 lar bodies, formed chiefly by convoluted tufts of arterial capilla- 
 ries, are present in the Wolffian bodies of Mammals, and in the 
 persistent renal organs of all Vertebrates. They are called, after 
 their discoverer, ' Malpighian corpuscles,' and the uriniferous 
 tubes take their rise by a sacciform blind beginning applied over 
 the vascular tuft or ganglion.^ 
 
 The combined secerning ca3ca and vaso-ganglia form in tlie 
 
 ' cxxx. ii. p. 314. ^ SXT. p. 13. = cxxxvii. 
 
534 
 
 ANATOMY OF VERTEBEATES. 
 
 Lampreys ' a continuous narrow elongated gland, which extends in 
 their young or Ammocete condition throughout the abdomen, but in 
 the full-grown fish {Petromyzori) along the posterior two thirds : in 
 
 both being confined to the 
 352 dorsal part of the cavity, 
 
 fig. 354, g. The ureters, 
 ib. e, open into the short 
 canal leading to the pa- 
 pillary production of the 
 peritoneal outlets close 
 to the anus.^ 
 
 In most Osseous Fishes 
 the kidneys are long and 
 narrow, and extend 
 throush the whole or a 
 great part of the dorsal 
 region of the abdomen, 
 firmly attached to the 
 vertebral column ; they 
 are usually broadest and 
 thickest anteriorly,where 
 they sometimes present 
 a lobulated surface ; they 
 contract, approximate, 
 and frequently blend to- 
 gether as they extend 
 backwards ( Cydopterus) ; 
 sometimes penetrating 
 the ha3mal canal in the 
 tail. In the Gymnotus 
 the kidneys are distinct 
 and thickest at their pos- 
 terior ends, as they are 
 in the Gurnard, fig. 379, 
 k, and in most Sharks. 
 The kidneys have not 
 a well-defined capsule 
 in Osseous Fishes, but 
 their ventral surface is immediately covered by an aponeurotic 
 membrane, against which the peritoneiun, and the air-bladder 
 when present, arc applied. The renal tissue is soft and spongy, 
 
 ' In Petromi/zon marinns tlio ili.anictor of the tubuli uriiiifcii is ^l:;!!! of an inch, tliiit 
 of tlio ciiiiilhiries of tlio kijncys bciii^ Tmro'h of -in im'li. ' -^x. iv. pi. 50, fig. \,c. 
 
 "^'iscL'ia ol itiaU' iSluirk, showing kidiu 
 
KIDNEYS or FISHES. 
 
 535 
 
 firmest at tlie fore-part of the gland ; visually of a reddisli-brown 
 colour; sometimes soaked, as it were, with dark pigment' It is 
 supplied by numerous small arteries from the abdominal aorta,^ 
 which form Malpighian corpuscles ; but these are fewer in 
 number and less complex than in the true kidneys of higher 
 Vertebrates. The primary branches of the tubuli uriniferi, gi^'cn 
 off from the long ureter, are extremely numerous ; their divisions 
 in the renal substance are comparatively few ; they are in most 
 fishes convoluted and of equal 
 diameter, extending through the 
 wliole renal substance, which 
 shows no distinction of cortical 
 and medullary jiarts, and has 
 neither ' pelvis ' nor ' mammil- 
 Ire : ' they are lined by a ciliated 
 epithelium. Sometimes a single 
 common ureter quits the coa- 
 lesced hinder ends of the kid- 
 neys, as in the Pike, and termi- 
 nates in a urinary bladder. More 
 frequently the essentially duplex 
 nature of the kidneys is mani- 
 fested by the emergence of two 
 ureters from the ventral surflice 
 of their posterior ends when these 
 have coalesced : in some fishes the 
 ureters unite together after quit- 
 ting the kidneys, and terminate by 
 a common gradually widening canal in the urinary bladder ; some- 
 times they enter the urinary bladder separately, as in the Wolf- 
 fish, where they both terminate on its left side, half an inch above 
 tlie cervix: rarely are any smaller accessory ureters seen, as e.g. 
 in the Stickleback, to terminate also, separately, in the bladder. 
 This, in aquatic animals apparently needless, receptacle of a fluid 
 excretion is, nevertheless, rarely absent in Osseous Fishes ; the 
 Pilchard, the Herring, and the Loach are among the few instances 
 where it is not developed. In the Loach a vei-y short, in the 
 Herring a long, common ureter terminates behind the anus. In 
 the Gymnotus the common ureter is so wide as to serve as a 
 receptacle, and it is directed forward to reach its termination 
 immediately behind the advanced vent. 
 
 The urinary bladder is sometimes round, fig. 379, h, sometimes 
 ' As in Lepidosiren, xxxiii. p. 349. ^ Hunter, vii. vol. ii. p. 112. 
 
 1. The anterior extremity of the kiiliiey, 
 /.");m. XXI. 2, Malpighian body and its 
 csscls, BdeUostviua. xxi. 
 
 Bih-no- 
 bluud- 
 
536 
 
 ANATOMY OF VERTEBRATES. 
 
 354 
 
 oval or pyriform, often bifid at Its fundus, or two-horned ; it is 
 largest in those fishes, as the PleuronectidcB, LopMus, Orthagoriscus, 
 ancl Cydopterus, in which the air-bladder is absent. In Callyowj- 
 mus the bifid urinary bladder extends the whole length of the 
 abdomen. It always lies behind the rectum, generally receives 
 the ureter or ureters nearer its fundus than its cervix, and the latter 
 is prolonged usually into a prominent papilla behind the vent. 
 The long cervix vesicaj in the Salmon is surrounded by a venous 
 
 plexus. In the Sturgeon the wide 
 ureters extend along the outer 
 borders of the kidneys, and re- 
 ceive the vasa deferentia or the 
 oviducts in their course towards 
 the cloaca, where they unite into 
 a short duct which forms the com- 
 mon outlet of the urinary and 
 generative products. 
 
 The kidneys are long, narrow, 
 but distinct from each other in 
 all the Ganoid Fishes and in the 
 Lepldosiren. In the Lophius the 
 kidneys present a more compact 
 form, and are situated wide apart, 
 far forwards in the abdomen, in 
 depressions on either side of the 
 origins of the ' retractores palati.' 
 The kidneys of the Plagiostomes 
 are also of a more compact form 
 than in Osseous Fishes, and are 
 always distinct, and generally 
 show a cerebriform convoluted or 
 lobulated exterior : the primary 
 branches of the uriniferous tubes are fewer, and their dichotomous 
 ramifications niorenumerous:' the ureteric trunk becomes superficial 
 along the inner and fore-part of the hinder half of each kidney ; 
 after quitting which it dilates in the Grey Shark (^Galeus) into a 
 kind of receptacle, fig. 352, m, behind each oviduct or vas deferens, 
 and communicating with its fellow near the cloaca, terminates by 
 a single urethral canal upon a kind of penis or clitoris, ib. o, 
 at the back of the anus, within a large common cloaca. In the 
 Torpedo, the ureters terminate on the cloacal papilla by two dis- 
 
 ' In tlio Ray, tlio ilinmetcr of the tcnniiial branches of the tuhuli uriniferi nrc mth 
 of an inch, that of the cninllarj renal arteries being ,,,'juth of an inch. 
 
 Kidney and peiicmtivo organs, Lauijirey {Petro- 
 myzon inarlnus). XK. 
 
KIDNEYS OF REPTILES. 537 
 
 tinct orifices.' In the Skate and Thornback each ureter terminates 
 in the neck of a short Ijifid ))Ux(l(ler : these open hj a common urethra 
 upon the cloacal papilla. The Lepidosiren has a small urinary 
 bladder situated behind the rectum and in front of the oviducts : the 
 ureters do not communicate directly with it, but terminate sepa- 
 rately on small papilla; in the oviducal compartment of the cloaca.^ 
 
 With regard to the circulation in the kidney of those Fishes, as 
 e. g. the Plagiostomes, the Lophius, and the Lepidosiren, in which 
 the organ is best defined, the vein on the outer side of the kidney 
 which receives blood from the tail, the abdominal parietes, and the 
 generative organs has so far the aspect of a ' portal ' or inferent 
 vessel, that a second and larger vein, whose roots take their rise 
 in part from the renal substance, extends from the inner and fore- 
 part of the kidney to convey its blood to the postcaval vein. The 
 exterior vein is not, however, completely expended in the kidney, 
 but is also continued forward from the anterior end to join the 
 veins from the anterior abdominal parietes, and sometimes those 
 from the pectoral fins. In all Fishes the kidneys maintain the same 
 relations with the cardinal veins that their transitory homologues 
 the ' Wolffian bodies ' do in the embryo of higher Vertebrates. 
 
 § 96. Kidneys of Reptiles. — In this class the kidneys are always 
 a distinct pair, and are more circumscribed in form, and more 
 compact in structure than in Fishes ; but, as in them, the renal 
 tissue is uniform, not divided into ' cortical ' and ' medullary ' parts. 
 
 In the Siren each kidney is a long, oval, subcompressed body, 
 tapering anteriorly to a point situated in the hind part of the 
 abdomen, dorsad of the rectum, with an entire investment of 
 peritoneum reflected upon their inner edges, where they receive 
 small arteries. The ureters enter the back pai-t of the cloaca, from 
 the fore part of which is developed a small allantoid or urinary blad- 
 der. The kidneys of Amphiuma resemble those of Sirent.^ In the 
 Meno-poma the kidneys are relatively longer, extending nearly the 
 whole length of the abdomen on each side of the vertebral bodies. 
 
 In the Newt the kidneys are less elongate, and their forepart 
 becomes so thin and transparent that it lends itself favourably to 
 microscopical examination. The ciliated epithelium continued 
 from the uriniferous tubule, terminates abruptly shortly after 
 entering the Malpighian capsule, fig 355, ep : the basilemma 
 of the capsule, bin, beyond the termination of the ciliated 
 epithelium, appears to be unclothed : it is a homogenous, trans- 
 parent, structureless substance, perforated by the inferent and 
 cflcrent vessels, and not reflected over them. The inferent 
 
 ' CXX5VI. ^ XXXIII. pi. 27. 
 
538 
 
 ANATOMY OP VERTEBRATES. 
 
 vessel dilates on entering, 
 
 355 
 
 Malpigliian body, ^'e\vt. ccLX\xyi. 
 
 meters, the part where the 
 
 356 
 
 I®^"^''i4 
 
 MiiUiitfliiau h^>lly, Fro;?, cxxxvii. 
 ' CXXXVII. 
 
 forms a few coils, again contracts, and 
 becomes the efferent vessel.' In the 
 Frog the kidneys present a more 
 comjoact form ; they are flattened, 
 suhelongate, with a convex outer 
 border and a nearly straight inner 
 one, fig. 331, K, k. They are situated 
 at the pelvic end of the abdominal 
 cavity behind the rectum and allantoid 
 bladder : the peritoneum covering 
 only their sternal surface. The renal 
 capillaries, derived from the renijjortal 
 vein, ib. K, ramify through the gland to 
 reach the Malpighian capsule, fig. 356, 
 f: in the specimen figured, by Bowman,^ 
 under the magnifying power of 320 dia- 
 capillaries enter (near t) is obscured by 
 an uriniferous tube. On enter- 
 ing, the capillary enlarges and 
 forms a few coils, m, which lie 
 bare in the capsular cavity. The 
 lemma begins to receive an epi- 
 tlielial lining at f, f, which 
 increases in thickness to the neck 
 of the tubule, d, d, and is covered 
 by cilia: these may maintain 
 their motions hours after the 
 death of the Frog. The urini- 
 ferous tubules form by succes- 
 sive unions the ureter, which 
 opens into the urogenital com- 
 partment of the cloaca, opposite 
 the orifice of the large bifid al- 
 lantoid bladder, the contents of 
 which are mainly water. 
 
 In Serpents the kidneys, fig. 
 357, t, t, partake of the usual 
 elongated form of the viscera, 
 and are subdivided into numerous 
 ilattcned, overlapping lobes, so 
 as readily to accommodate them- 
 selves to the flcxuositics of tlie 
 part of tlic trunk in which they 
 ■ lb. 
 
KIDNEYS OF REPTILES. 
 
 539 
 
 357 
 
 are lodged. In most Serpents they are unsyrametrically situated ; 
 the left in Coluber natrix, e.g., being one-fourth of its length 
 nearer the cloaca than the right kidney ; and they are loosely 
 attached to the dorsal abdominal walls. Each renal lobe is so 
 distinct that it may be regarded as a separate kidney or renule : 
 it is reniform in PijtJion and Boa, and is principally composed of 
 the ramifications of the renal artery, the 
 reni20ortal and renal veins, and the urini- 
 ferous tubules with their initial (Malpi- 
 ghian) capsules. -The artery of the renule, 
 entering at the notch or ' hilum,' repre- 
 senting the pelvis, distributes its branches 
 fanwise through the middle of the sub- 
 stance : each branch, fig. 358, a, sends 
 twigs to the Malpighian capsule which 
 form within it the dilated plexus, ana- 
 logous to that in fig-. 356, whence the 
 l)lood is returned by the efferent vessel, 
 in the direction of the arrow, to the 
 branch of the reniportal vein, fig. 358, 
 p, V : these branches being distributed 
 fan-wise over both surfaces of the flat- 
 tened renule. In this course they com- 
 municate with, or help to form, a rich 
 venous plexus, ib. p, surrounding the 
 tubuli uriniferi, ib. t, and commrmicating 
 with the branch of the renal or emulgent 
 vein, ib. e, v, which accompanies the 
 artery, in the mid-substance of the 
 renule. 
 
 The tubuli, lb. t, continued, as in fig. 
 356, from the capsule of the 'Malpighian 
 body,' after some convolutions, pass to the 
 surface next which the ' body ' is placed, 
 and terminate in a branch of the ureter, 
 ur, there situated : these superficial 
 branches are dispersed fan-wise, converg- 
 ing to the ' hihuTQ,' and are often seen 
 injected, as it were, by the opake white pultaceous urinary 
 excretion. The Malpighian bodies diminish in size and the tubuli 
 in length, towards the thin edge of the renule. 
 
 Thus, on each superficies of the flattened renule are the radiatino' 
 ramuli of the ureters, ur, and rcni-portal veins, pv ; whilst alonr' 
 
 Kidneys and small organs, llaltle- 
 Buake iCrotalus). CCL. 
 
540 
 
 ANATOMY OF VERTEBRATES. 
 
 the plane, midway between these surfaces, are the similarly 
 disposed branches of the renal artery, a, and renal vein, v. The 
 material of the urinary excretion thrown by the epithelial cells or 
 bags from the inner surface into the cavity of the uriniferous 
 
 tubules, t, is derived from 
 the rich venous plexus, j^, 
 everywhere in contact with 
 their outer surface : the sero- 
 sity exuded from the dilated 
 arterial plexus in the Malpi- 
 ghian capsule, propelled by 
 the ciliary action, dilutes and 
 washes out the excretion 
 from the tubuli, whence it is 
 conveyed by the superficial 
 branches of the ureters to 
 the trunk, or ureter, com- 
 mon to the several renules, 
 and, by the ureters, is dis- 
 charged into the cloaca.' 
 There is no urinary or allan- 
 toid bladder in Serpents. 
 
 The kidneys in Lacertians, 
 fig. 301, h, fig. 332, are 
 shorter, broader, and less 
 subdivided than in Serpents ; 
 situated close to the verte- 
 bral bodies at the hinder part of the abdominal cavity ; they 
 are usually pointed at their forepart ( Cyclodus). In the Iguana 
 they are of an oblong, subdej^ressed form : their structure is 
 essentially that above described in the Boa. The ureter runs 
 superficially, as it collects its tributaries, along the free or ventral 
 surface of the kidney, and terminates in a slight eminence, papilla or 
 ridge, close to the genital orifice, in the urogenital compartment 
 of the cloaca, behind or dorsad of the anus. Anterior to, or stcrnad 
 of, the terminal orifice of the rectum, is that of the urinary or 
 allantoid bladder, of large size in the Iguana. In this reptile 
 Hunter found the Ijladder ' filled with a white fluid,' and ' there 
 were small calculi in it.' '^ In the same reptile he records the pre- 
 sence of 'one brown calculus in each ureter, almost filliu'T the 
 duct.''-' 
 
 ' The ingenious and lucid explanation of the functions of the luinuto stiuctnrcs 
 given by their discoverer, Mr. Bowman, in cxxxvii. 
 '' ccxxxvi. vol. ii. p. 307. '' Ibid. 
 
 Plan of ijispositirin of b]noi]-vp?!?ol5 anj tulmll in the 
 rcnulu of Boil. cxxxTll. 
 
KIDNEYS OF REPTILES. 
 
 541 
 
 The fatty appendages which are attached to the kidneys or 
 urinary bladder in Batrachia, Ophidia, and Lacertilia, attain a 
 remarkable size in some members of the latter order ; in the 
 L/uana tuherculata they are attached by a narrow process to the 
 sides of the bladder, near its neck.' 
 
 In the Chelonia the kidneys present a more compact form, 
 and their surface is convoluted through the disposition of the 
 component lobes. They have the same low pelvic position as 
 in Lizards, but are smaller in proportion, and are outside the 
 })eritoneum. In the Tortoise {Testudo tcdiulata) they are oblong, 
 broad, thick, subtrihedral bodies : in the Turtle ( Chelone viydus) 
 they are flattened anteriorly, or towards the abdominal cavity, 
 convex where they rest upon 
 the dorsal wall. In Emys, 
 figs. 307 and 359, O, they are 
 semioval. The tubuli urini- 
 feri pass to the superficies of 
 the lol^ules and there form the 
 branches of the ureter, which 
 unite towards the mesial border 
 with the becfinning- of the main 
 duct, ib. N ; this is short, and 
 terminates, with the sperniduct, 
 C, in the male, in the uroge- 
 nital cavity at f. The rectal 
 orifice intervenes between this 
 and the wide opening of the urinary bladder, ib. M, m". This 
 receptacle is proportionally smallest in the marine Chelonia 
 ( Chelone, Trionyx) : in its contracted state it presents, in Chelone 
 mydas, thick muscular parietes and a corrugated internal surface. 
 In terrestrial and fresh-water Chelonia the bladder is relatively 
 much larger, and with thinner walls. In many it is bifid. In 
 Emydians, besides the ordinary bladder, fig. 304, tr, a pair of 
 other bladders, ib. u', u", communicate by wide orifices, behind 
 the ureters, with the cloaca (p. 447). 
 
 In the Crocodilia the kidneys are of an oblong oval form ; the 
 forepart is thickest or largest, and is sternad of the psoas muscle, 
 the hind part extends into the side of the pelvis ; they are in 
 contact with each other at the mid-line. The surface is convo- 
 luted, like the brain, but with smaller and more numerous gyraj ; 
 the colour of the kidney is usually a deep brown. The ureters 
 terminate in low papilla;, in the urogenital compartment of the 
 
 ' sx. vul, iii. p. 221, prep. no. 1820 A. 
 
 Male organs of generation, anrl kidney of Ewys 
 europ(^a. xzxviii. 
 
542 ANATOMY OF VERTEBRATES. 
 
 cloaca behind the genital orifices; the forepart of the cloaca 
 is slightly dilated, and the rectum opens therein by a valvular 
 protrusion. 
 
 The formation and disposition of the reniportal and renal or 
 emulgent veins have been previously described. 
 
 § 97. Adrenals of Hamatocrya. — The bodies called ' suprarenal 
 capsules,' 'renes succenturiatag," capsulaj atrabiliarise,' &c., in Man, 
 may be represented in the lowest Vertebrates, e.g. the Myxinoids, 
 in the form of a pair of small oval lobulated bodies situated in 
 advance of the kidneys, and close or adherent to the portal sinus. 
 In the lamprey a glandular body lies between the aorta and car- 
 dinal vein, adhering to the coats of the latter ; but it has not the 
 characteristic structure of the adrenals in higher Vertebrates. In 
 ordinary Osseous Fishes the adrenals have been recognised as 
 roundish bodies of a light grey colour ; commonly two, rarely 
 three or more in number, situated sometimes near the middle, 
 oftener at the hinder ends of the kidneys, at or near the entry of 
 the hajmal canal ; but in the Eel they are found where the two 
 kidneys unite. They are commonly symmetrical in position ; 
 but in the genus Scomber one adrenal is in advance of the other ; 
 and in Phuronectidce they lie both on the same side of the body. 
 Sometimes they lie free, sometimes they are imbedded in the renal 
 tissue : they usually possess a proper capsule, and present a 
 minutely granular texture without distinction of cortical and 
 medullary parts. Their surface is smooth in some Fishes, irregular 
 in others ; in large and old Pike three adrenals have been seen ; 
 but in the young (' Jack,' one foot long), the kidney has been 
 found to be beset with a number of small adrenals.' The yellow- 
 ish adrenals of the Sturgeon occur as numerous small glandular 
 bodies studding the dorsal surface of the kidney. Four or five 
 similar bodies are sometimes found in the Skate ; but more com- 
 monly in Plagiostomes, the adrenals are represented by a single 
 elongated narrow yellowish and lobulate body, situated behind the 
 kidney, and sometimes extending behind the dilated ureter.^ The 
 adrenal in Fishes, whether compacted or subdivided, consists of an 
 aggregate of lobules, with proper capsules, connected by looser 
 connective tissue : each lobule consists of cells of about ^juVo tli of 
 an inch in diameter, containing nuclei, fiit-globules, and molecular 
 particles, tlie latter being mostly aggregated about the nucleus. 
 Processes from the lobular capsule pass" inward and insulate the 
 multinucleate cells. In the young Pike the moleciilar-clothod 
 nuclei acquire a cell-wall, become liberated, and converted into 
 
 ' COLXXiVU. •-• OXXI. 
 
ADEENALS OF HiEMATOCRYA. 543 
 
 new multinucleate cells. In old Pike this multiplication is 
 arrested : the connective tissue increases in quantity and density, 
 and the multinucleate cells are more separated from each other. 
 'Jlie connective tissue and the capsules whlcli it forms for the 
 adrenal and its subdivisions, are richly supplied with blood-vessels. 
 
 The structure of the adrenals, however, is subject to great 
 variation within the limits of one and the same species in the 
 piscine class. The following modifications have been observed in 
 the Cod-fish ' : 1. Very rarely the adrenals are entirely absent. 
 2. They are semifluid, very vascular, not encased in a capsule, 
 and without defined form ; the blood-corpuscles are extremely 
 nmnerous, aggregated in small lumps, and in various stages of 
 transmutation. 3. They possess a proper capsule, being more or 
 less vascular. 4. They are shrunk, with but a few, or without 
 any blood-vessels. 5. Not rarely a part of an adrenal is composed 
 of cells and lobules, whilst another part is a formless conglomera- 
 tion of molecular particles, fat-globules, &c. 
 
 Adrenals are entirely absent in the Herring and in the Launce 
 (^Ammodi/tes Tobianus). 
 
 The fish-like Batrachia resemble some Fishes in the subdivided 
 condition of the adrenals ; twenty or more lobules, showing the 
 above-described structure, may be found partly imbedded in the 
 substance of the kidney, at its mesial border, partly between tlie 
 kidney and the renal and postcaval veins, surrounding the coats 
 of the eiferent veins (^Siren, Triton). In the Frog and Toad the 
 adrenals appear as a yellow streak on the sternal aspect of tlie 
 kidney, arching from about one line from the fore end to within 
 two lines of the hind end of the gland ; it shows a lobular struc- 
 ture, and surrounds the eiferent emulgent veins, closely adhering 
 to or imbedded in the coats, as they leave the kidney to join or 
 form the postcaval vein. The lobules consist of groups of multi- 
 nuclear cells, containing a greater proportion of oil-globules than 
 in Fishes : but both the free nuclei and granules are present, the 
 former sometimes showing stages of developement into nucleate 
 cells. The blood is supplied chiefly by branches of the reniportal 
 vein. 
 
 In the Ophidia the adrenals are long, slender, lobulate bodies, 
 closely adherent to the coats of the emulgent veins, in advance of 
 the kidneys : in a Python of ten feet in length they measure 
 nearly one inch. The adrenals are rather less elongated in Anrjuis 
 fnujills. The adrenals are supplied by minute branches from the 
 
 ' cccsxxi. ' Fische,' p. 258. 
 
544 ANATOMY OF VERTEBRATES. 
 
 aorta, and more abundantly by vessels sent to them from the 
 jolexiis veuosus of the neural canal ; both kind of vessels ramify 
 in their substance, forming a fine capillary network upon the 
 capsules of the multinucleate cells. The blood is returned from 
 the right adrenal directly to the postcaval vein, and from the left 
 adrenal to the corresponding emulgent vein. In Lacerta ocellata, 
 each adrenal is about one sixth of an inch in length, and one- 
 eighth of an inch in breadth, adherent to the emulgent vein, 
 where it forms the joostcaval : upon which the right and usually 
 the larger adrenal sometimes lies. In the male Lizard it is 
 situated between the vein and the vas deferens : in the female, 
 between the vein and the ovary. The adrenals are lobulated, 
 and well supplied with blood ; their minute structure is essentially 
 the same as that in Oplddia and Batrachia. 
 
 Hunter left preparations of two glandular bodies, with a con- 
 volute exterior surface, and a homogenous parenchyme, similarly 
 disposed, which he called ' supra-renal glands ' of a Tortoise ; ' 
 and, in his ' Anatomy of a Land-Tortoise,' he writes, ' The 
 capsula renalis is large and flat, situated above the kidneys : it 
 looks like a pancreas, being conglomerated, but, when cut into, 
 appears to be all of the same substance.'^ Bojanus regarded two 
 long bodies, situated at the inner margin of the kidneys of Emys 
 curopcEa as the adrenals ; but, according to Ecker, the adrenals 
 of Testudo f/rcEca lie on the abdominal (sternal) surface of the 
 kidney, imbedded in its substance, extending almost the whole 
 length of the gland, as in the Frog.' Under the microscope they 
 appeared as aggregates of yellow granules, each inclosed by a 
 proper capsule, and containing nuclei, oil-globules, and molecular 
 particles. 
 
 Hunter describes the adrenals in the Crocodile as ' two oblong 
 bodies, darker on their exterior surface than internally, and iii 
 some places little yellow bodies are to be seen upon them, as in 
 the kidney ; and on the outer edge is a very small yellow thread 
 passing down, which is continued along the broad ligament its 
 whole length towards the anus.' " This might be the remnant of 
 the duct of the primordial kidney. 
 
 '^ XX. vol. iii. p. 1,30, pi-cps. nos. 1277, 1278. ■' ccxxxvi. vol. ii. p. 364. 
 
 ccLxxxvii. 1 ccx.<ixvi. vol. ii. p. 340. 
 
515 
 
 CHAPTEE IX. 
 
 TEGDMENTARY SYSTEM OF HiEMATOCKYA. 
 
 § 98. Composition of Tegument. — The tegumentary organs of 
 Vertebrates, where they do uot happen, as in exceptional instances 
 or^parts of the body, to blend with the periosteum of the endo- 
 skeleton, are defined from subjacent structures by loose or yielding 
 connective tissue : hence the facility with which Vertebrates of 
 all classes can be 'skinned.' The part so removed is the 'tegu- 
 ment,' and constitutes the outermost of the organs differentiated 
 in the course of emljryonal developement from what has been 
 termed the 'serous' or ' anhnal ' layer of the blastoderm. 
 
 Tegument mainly consists of an outer epithelial layer, called 
 ' epiderm,' and an inner fibrous or areolar layer, called ' derm.' 
 The tissue of tlie derm includes 'white fibres' and 'yellow fibres.' 
 The white element forms bands of unec[ual thickness, striated 
 longitudinally, but irregularly, and breaking up into fibrils of 
 different width, the finest being too minute for micrometry. The 
 white bands interlace in various directions, with a wavy course, 
 frequently subdividing, and joining those near them. The yellow 
 fibres are solitary, very clastic, disposed to curl, branching at 
 intervals of variable length, and the branches, usually as large as 
 the trunk, uniting with contiguous ones. A drop of acetic acid, 
 which instantly swells the white bands and makes them trans- 
 parent, produces no change on the yellow filaments.' Into the 
 derm enter bloodvessels, absorbents, and nerves : it never contains 
 fat. Epiderm consists of epithelial cells of every form — caudate, 
 tessellate, rarely ciliate — and in all stages of developement, 
 increasing in density, horizontality, and overlappingness as they 
 approach the outer surface of the skin, and blended with pigment- 
 cells and pigment-particles in proportion as they are near the derm : 
 but many other parts are specialised in the tegumentary area of the 
 Idastoderm than those which, from their greater abundance and 
 constancy, give the character to the two best defined layers. 
 
 Bulbs or pulps of hairs and feathers, bony scutes, and fish-scales 
 
 ' ccxc. i. p. 491. 
 VOL. I. N N 
 
546 
 
 ANATOMY OP VBKTEBEATES. 
 
 — sebaceous, sudoriparous, and mucous follicles — may be developed 
 in or from the derm : the epiderm may be condensed into nails, 
 claws, hoofs, horns and horny scales. The warm-blooded are dis- 
 tinguished from the cold-blooded classes by the non-conducting or 
 heat-retaining nature of the superficial covering of the tegument. 
 
 360 
 
 Diagrammatic section of skin of Dsti, 
 
 § 99. Teguments of Fishes. — The skin in fishes is more tensely 
 stretched over the body, and often more closely united to the sub- 
 jacent fascia or flesh, than in other Vertebrates : consequently it 
 enjoys less mobility. The constituent fibres of the derm or 
 corium are so disposed as to give it a laminated structure, fig. 
 360, a ; the horizontal layers being connected by vertical sub- 
 elastic fibres,' ib. b. The numerous papillte or processes from the 
 skin of the under part of the head of the Sole (^Solea vulgaris) 
 give it a villous character : other instances where the derm deve- 
 lopes tactile pajiilloe in fishes are indicated at pp. 326,411. 
 
 In the Lancelot the dermal fibres are minute, and compacted 
 into two planes, one nearly at right angles to the other. In the 
 Lamprey the derm consists of two layers of flattened fibres cross- 
 ing each other at right angles. The epiderm exhibits numerovis 
 large stellate pigment-cells. In the Eel, the epiderm is soft and 
 thick, consisting of many layers of cells, caudate and tessellate, 
 those next the derm showing pigment in stellar masses : the 
 
 granular pigment-ceUs look like black 
 spots in the epiderm. On removing 
 this, narrow oblong scales, two lines 
 
 361 
 
 
 to three lines long, fig. 361, a, are seen 
 imbedded in depressions of the derm. 
 They consist of a finely reticulate car- 
 tilage, the long axis of the meshes, 
 which may be cells with confluent 
 walls, running nearly parallel to the 
 contour of the scale, as shown in the 
 magnified section taken at the line marked in fig. 361, o. In the 
 Blenny (^Zoarces) the skin presents circiilar depressions which arc 
 
 • ' Arctuous bands ' of Claik (ccxcii, p. 148), who well distinguishes tlicm IVom 
 llio gliind-ducts pcrfonitiiiy Uio skin in ccrtuin llshos, o. g., miintMO. 
 
 BcaloofEi-l ((, nit size, ^n(^ ptntion 
 111 l-'l) ci.\cii] 
 
TEGUMENTS OF FISHES. 
 
 547 
 
 362 
 
 Cycloid scale, xxii. 
 
 due to the presence of small round scales, about y^^tli in. diameter, 
 with concentric and radiating lines: they are set deep in the 
 derm. In the Sand-eel (^Aiitmodi/tes), the 
 scales are proportionally larger, and one 
 margin rises from the derm and pushes out- 
 ward the portion of epiderra covering it : the 
 dermal depression is limited to the oj^posite 
 margin, and is deeper than in the Eel. The 
 free part of the scale retains the reticular 
 structure ; in the imbedded part the areola; 
 are obliterated in the direction from the centre 
 to the circumference ; the radiating lines preserve their distance, 
 but, being united by cross fibres close set, the structure appears 
 to be laminated. The majority of flexible scales present the 
 same pattern of concentric and radiating lines : the concentric 
 lines are the finest, most numerous, and constant ; they repeat 
 the contour of the scale, and with most regularity at the anterior 
 imbedded and covered part, where growth chiefly takes place, 
 the stages of which are marked by these lines. The ' nucleus ' or 
 beginning of the scale is usually excentric, fig. .362, n. The ra- 
 diating lines, fig. 362 and 363, r, r, are larger and fewer : they 
 are most numerous in the Loach ( Cobltis), are sometimes confined 
 to the forepart of the scale, fig. 363, or may be absent {Sulmo): 
 they are furrows. The parts of the scale-margin between the 
 ends of the radiating lines usually project in different degrees 
 from a slight convexity, as in figs. 362, 363, to the form of pro- 
 cesses. The latter are most common at the anterior implanted 
 border of the scale (JEsox) : in many fishes the opposite or free 
 border has numerous tooth-like processes, and 
 similar parts may project from the adjacent 
 periphery of the scale in two or more rows. 
 Such scales with a comb-like free border, fig. 
 363, t, characterise the fishes thence called 
 ' ctenoid : ' where the free border of the scale 
 is rounded or simjDly undulated, fig. 362, it 
 characterises the ' cycloid ' fishes of Agassiz. ' 
 The seat of chief vascularity and greatest 
 activity and variety of developement is at the 
 periphery of the derm, between it and the 
 epiderm. Here are formed the scales, constituting an imln-i- 
 catc covering of the body in most fishes ; but, in a few, contiguous 
 or scattered. According to their structure and shape, scales are 
 
 ' XXII. 
 
 N N 2 
 
 363 
 
 ctenoid .'-rcale. xxii. 
 
548 
 
 ANATOMY OF VERTEBnATES. 
 
 364 
 
 Ganoid scales, AMblppkrus. 
 
 termed ' placoid,' fig. 365, 'ganoid,' fig. 364, 'cycloid,' fig. 362, 
 ' ctenoid,' fig. 363. In the first and second kinds bone-earth ^jredo- 
 minates, and tlie scales arc as hard as teeth ; in the two latter kinds 
 
 the earth is in less quantity, so that 
 the scale is flexible : it is rarely want- 
 inw. The kinds of scale graduate 
 into each other. Most flexible scales 
 present two structures : one next the 
 derm is composed of gristly laminte, 
 usually firm and elastic, fig. 360, c ; 
 the superficial portion, ib. d, is 
 laminated and hardened by interla- 
 mellar calcareous granules." In the posterior or exposed part 
 of the scale of a Carp there is a peripheral osseous layer, deve- 
 loping the outer markings or projections of the scale, fig. 360, c?; a 
 
 middle laminated layer, with 
 365 calcareous granules, ib. e ; 
 
 and the internal layer of 
 laminse of structureless car- 
 tilage, ib. c. 
 
 In the Tunny (Thi/imus 
 vulgaris) the scales are com- 
 posed of fine, partially ossi- 
 fied, laminre, between which 
 are elongated ' lacunas ' or 
 bone-cells: thescaleis cancel- 
 lous atitsmiddlepart.^ In Z-e- 
 pidosteus the scale is thicker, 
 is composed of very thin ossi- 
 fied layers, fig. 3 6 6, a, perfo- 
 rated by vertical tubes about 
 -!-thin. diameter, and having 
 
 tut in ^ o 
 
 numerous lacunaj in their 
 interspaces,' the radiating 
 canals of which communicate 
 with a more minute series of vertical branched tubules, called ' Le- 
 pidinc ' by their describer.' These, in most ganoid fishes, have a 
 less general distribu.tion through the scale thair the larger and less 
 branched scries, which, from their analogy to dentinal tubes, I have 
 called ' plasmatic,' conceiving them to relate to the nutrition and 
 vitality of the scale, as doubtless also do the ' lepidine ' tidnilcs in 
 
 ' ' Corpuscles of MaiuU,' ccciii.: ' Ijcnticiihir liojics' of Williamson, ccxcii. 
 ^ ccxoiii. vol. ii. p. 70. = V. p. It. 1 coxin. p, 4rty. 
 
 Phiciiid scale A, n, Eat. size ; c, magn. section, xxil. 
 
TEGUMENTS OF FISHES. 5-49 
 
 the parts of the scale to which they are limited. The peripheral 
 surface of the scale is coated Ijy a layer of hard transparent lami- 
 nated substance, ih. Z/' (' email,' Ag. ; ' ganoin,' ' ^Vilk.'^). In Lejn- 
 dostcus and Puhjptcrus the ganoin is usually confined to two-thirds 
 of the outer surfiice of the scale. In both existing Ganoids the 
 scale is perforated vertically by a few larger 
 tubes, analogous to the ' vascular canals ' of __^^^ _^ ^^^ 
 Ijone, and conveying blood from the derm to 
 the delicate layer of membrane extending from 
 the scale-pit, fig. 360, f, upon the ganoin. 
 In the scales of extinct Gunoidei a portion 
 of the deeper layer of ganoin traversed by 
 minute branching tubuli, and devoid of 
 lacunffi, has received the name of ' kosmin.'^ sinirturcnisaudid scales. 
 This tissue constitutes the chief part of the 
 tooth-shaped bodies of the ' shagreen ' of the Dog-fish and many 
 other Placoids ; in which it cannot be histologically distin- 
 guished from hard dentine.'' In fig. 3G5 are given a side view. A, 
 and upper view, B, of one of the ' placoid scales,' or spiny tubercles 
 of the Thornback {Raia clavata) : C is a magnified section of the 
 scale. The substance of the spine consists of superimposed conical 
 lamelliB, having, in the Thornback, a widely oi)en pulp-cavity, 
 ib. 7?, from which proceed vascular canals, resolving into plasmatic 
 tubes, radiating and ramifying through the suljstance as in ordi- 
 nary teeth. The base of the si:)ine-bearing scale, ib. h, is imbedded 
 in the derm ; and, as the ' haversian canals ' of the jaw pass into 
 the ' medullary canals ' of the teeth thereto anchylosed, so do the 
 capillaries of the derm j^ass directly into the ' vascular ' canals 
 and pulp-cavity of the dermal dentine in all the various forms of 
 jilacoid scales, many of which have a coating of true ' ganoin ' 
 over the fine-tubed dentine or ' kosmin.' Other modifications of 
 the dermoskeleton, such as the placoganoid and acanthogauoid, 
 are noticed at pp. 193-198, and illustrated in figs. 124-127. 
 
 The calcification of scales, as of teeth, fig. 242, and bone, fig. 
 15, takes place in layers of the organic basis successively formed: 
 but the primitive lamellate condition is most conspicuous in fish- 
 scales. The idea of excretion, or the throwing out of such layers 
 from a secreting surface, is, however, as Inadequate to represent 
 the facts of the formation and structure of the exoskeleton as of 
 the cndoskeleton of fishes.'^ 
 
 ' XXII. vol. i. p. 74. ' ccxci. p. 438. = Ib. p. 444. " v. p. 14. 
 
 * Tlie microscopical obscrrations on the structures of recent and fossil teeth, with 
 incidental notices of corresponding organisation in ossified scales, communicated by 
 
550 ANATOMY OF VERTEBRATES. 
 
 The varied and often brilliant colours of fishes are due to 
 pigment-cells at different depths of the skin, but chiefly in the 
 active or differentiating area : those of silvery and golden lustre 
 are mostly on the surface of the scales : the silvery pigment, called 
 ' argentine,' is an article of commerce, used for the colouring of 
 factitious pearls, and offers a crystalline character under the 
 microscope. The blue, red, green, or other bright-coloured pig- 
 ment is usually associated with fine oil, and occujjies areolaj 
 favouring accumvilation at, or retreat from, the sujoerficies, and 
 thus effecting changes in the colours of the fish, harmonising 
 their exterior with the hue of the bottom of their haunt.' 
 
 The surface of the body is lubricated in most Fishes l^y 
 mucus, sometimes, as in the Eel and Burbot, forming a thick 
 layer. The skin of the Eel is perforated by numerous ducts 
 or follicles, wliich contribute to this excretion.^ In the Pike the 
 scattered ducts notch the border of the scales, near their termina- 
 tion : one series of follicles represents the lateral line, as in the 
 Eel. In most Fishes the follicles of the lateral row are connected 
 liy a longitudinal canal, of which they appear to be branches ; more 
 jiarticularly so in those species (Dory, Opah) in which the follicles 
 are produced into secondary tubes, and open at some distance 
 from, usually beneath, the lateral canal. In the Mugil ceplialus 
 there are several lateral canals, giving off the follicles which 
 tunnel the scales in their outward course. The lateral canal 
 itself so marks the scales along which it runs, its follicular outlets 
 perforating them. The ' nervus lateralis' sends a filament to 
 each scale-follicle or tunnel ; ^ the cephalic system of well-nerved 
 raucous canals excavates oddly superficial bones of the head in 
 many Tdcostomi:^ this system is noticed in Plagiostomi, at p. 225. . 
 The nervous structure connected with the system of the lateral 
 line suggests a stimulus to active excretion from emotional causes, 
 as in the skin-glands of Batrachia. 
 
 § 100. Teguments of Reptiles. — The derm in i?a^?'ac/»'a presents 
 
 mo lo the meeting of the British Association in Angust 1S38, and to the Academy of 
 Sciences, Institute of Fiance, December 1839, established the ' conversion-theory,' and 
 compel any one attempting to revive the ' excretion theory ' to substitute a definition of 
 the process wholly different from that towhicli De Blainville and other supporters of the 
 theory held in 1838-9. Prof. Williamson, who has pursued microseopieal investigations 
 into the scales of recent and fossil fishes with perseverance and success, afSrms the facts 
 which ho brought forward (ccxci. p. 437) 'to be, at least, sufliciently conclusive to 
 settle the question, by showing that, whilst the scales are formed, as originally stated 
 by M. Agassiz, by the apposition of successive layers, these layers are not generated 
 by any process of secretion, but by the calcification of an organised basis, resembling 
 that of bones and teeth, as asserted by Prof. Owen.' 
 
 ' ccxciv. p. 327, 2 ccxcii. = Lcydig (cci.xxvn. p. 203, fig. 108) describes 
 
 it as ending in a kind of ganglion. ' ccciv. p. 171. 
 
TEGUMENTS OF REPTILES. 
 
 551 
 
 367 
 
 a lamellate structure, fig. 368, g, like that of Fishes, but with the 
 direction of the fibres, in succeeding layers, more regularly alter- 
 nating. In most parts of the trunk of the Anoura the skin is 
 separated by wide lymphatic lacuna;, fig. 367, P, from the subcuta- 
 neous fascia, ib. E. Marsupial pouches, one for each larva, ib. B, c, 
 are temporarilydeveloped in 
 the skin of the back of the fe- 
 male Pipa : a common dorsal 
 pouch for eggs and larvre is 
 present in the female Noto- 
 trema viarsupiatuin, Gnth., 
 and in Opisthodelphys. Tlie 
 epiderm in Perennibranchi- 
 ates resembles that of mu- 
 iiEnoid Fishes : in most A- 
 noura the constituent nucle- 
 ate cells are more condensed, 
 fig. 368, h : in many Toads 
 the epiderm is tuberculate ; 
 rarely are scales, and scutes 
 never, present in the exist- 
 ing Hatrachia. In Cacilia 
 the skin is ringed by trans- 
 verse rugte. In the Ameri- 
 can Newts, of the genus 
 Plestiodon, the small scales 
 present a reticulate struc- 
 ture. In Bufo tuberosus the ejiiderm forms on the dorsal tuber- 
 cles a horny spine in the centre, surrounded by a ring of 
 smaller sj^ines : Bufo asp)er has conical spine-bearing tubercles 
 on the back and sides of the trunk : those on the upper eye- 
 lids of certain Toads have earned for them the generic name 
 Ceratiphrys (jRana cornuta, Linn.). In 8alamandra unguiculata, 
 and in Dactylethra among the Toads, the epidei'm is condensed 
 into a claw at the end of some of the digits : in D. Midleri it 
 also forms a spur at the base of the first hind-toe. In Pipa the 
 skin is produced at the end of each fore-toe into a 3- or 4-forked 
 appendage, fig. 367. As a rule, the Batrachia are without claws. 
 Pigment-cells, fig. 368, a, are developed in various degrees, and 
 of diverse shades of colour, commonly of a dull and neutral or 
 mixed tint, but giving to parts of the skin of the land Salamander 
 a yellow or orange hue, and painting the surface of the Tree- 
 Frog (//yfo) a bright polished green. 
 
 Female Pipa, or Surinam Toad, 
 
552 
 
 ANATOMY OF VERTEBRATES. 
 
 368 
 
 Mucous follicles abound in the skin of all the BatracMa : they 
 are found in linear rows in parts of the Siren : ' are more generally 
 diffused in the Axolotl.^ In the Frog they are spheroidal/ fig. 
 .".68, d, or subdepressed/ situated in the superficies of the derm, c; 
 their ducts perforate the epiderm, h, and terminate by rounded'* 
 or triradiate'' orifices, ib. B. Like the lateral canals of Fishes, 
 they usually contain a clear fluid, which they expel on irritation 
 of their nerve, ib. /.'' This fluid, in the Newts and Toads, 
 
 appears to possess an acid or 
 irritating property. A stork will 
 swallow a frog, but rejects a toad, 
 if picked up by mistake. The 
 cutaneous follicles are more local- 
 ised in the land Salamander, 
 and their secretion is whitish and 
 opake, of an acrid nature, and 
 poured out abundantly when the 
 animal is alarmed or irritated. 
 The cutaneous follicles are nu- 
 merous and close-set in the 
 American Newts of the genera 
 Amhij&toma and Plethodon, in 
 which they exude a milky fluid.' 
 Special aggregates of cutane- 
 ous follicles occur in most 
 Batrachia. In the land Sala- 
 mander they form a porous 
 tubercle behind each eye. In 
 many Anoura the homologous 
 glandular tubercles (' parotoids ' 
 of Giinther') are conspiciious 
 above the tympanum {Ah/tidm, BufonidcB) : they are enormous in 
 Btifo aqua, and arc situated on each side of the neck in UperoUidw. 
 In Bufo calamitu, besides the ordinary parotoids, there is a similar 
 glandular tubercle on the upper side of the legs. The skin of 
 the l.)ack in Kalojdirjpius is thick and glandular, like a parotoid. 
 In Jli/larana the skin has two glandular folds, one on each side of 
 the back, usually of a white colour. Platijmantis ph'cifera has 
 several pairs of such longitudinal folds or ridges.'" In Foh/pcdafes 
 
 Scctfiin of tcf^umcnt and cutaneous glands of 
 the Frog, magnJlied. ccxcv. 
 
 ' XX. vol. iii. p. 277, prep. no. 2108. - cCLxxix. tav 
 
 ii. fif;. 10. - lb. ii- 7. ' Ib. fig. 2. « lb. fi 
 
 " ccxcvi. p. 281. '• rriiitcd by mutalio 
 
 '" CT.xxv. p. nCi, pi. viii. Tifj; 11. 
 
 g. 7. ' ccxcv. tnf. 
 
 3. ■ Ih. (6S41), p. civi. 
 
 ' p;u-.itoi(l ' in Iiis cxccllont Ciitiiloeuc. 
 
TEGUMENTS OP EEPTlLESc 55.3 
 
 a glandular fold curves from above the tympanum to the axilla or 
 shoulder. 
 
 The skin takes an important share in respiration in the 
 Anourous Batrachia,' and there is a relation of ' supply and 
 demand ' Ijctween the cutaneous follicles and the large allantoic 
 liladder : the latter would seem to receive water directly by the 
 cloaca, when the Frog may be in that element, and to serve as a 
 reservoir for the supply of cutaneous transpiration when the 
 batrachian is on dry land.^ 
 
 The cpiderm is periodically shed in Butrachia. It comes away 
 in shreds in the aquatic kinds. In the Toad the old epiiderm 
 sjdits along the middle line of both back and belly, and each 
 lateral half is wriggled off in folds towards the sides. It is then, 
 l)y contortions of the trunk and limbs, loosened from the hind- 
 limbs, and removed from them by the animal bringing first one and 
 then the other leg forward under the arm, when, by withdrawing 
 the hind-leg, its cuticle is left under the fore-leg. The two 
 jiortions are now pushed forward to the mouth, by the help of 
 which the anterior extremities are also divested of their cuticle. 
 The whole mass is finally pushed by the hands into the mouth, 
 and swallowed at a single gulp. The new cuticle is bright, soft, 
 and covered with a colourless niucus.^ 
 
 In Serpents the epiderm is shed, usually entire, and the animal, 
 ]>artially blindfolded hj the opacity of the layer passing over the 
 cornea, fig. 220, c, seeks an obscure retreat ; but I have watched 
 the process of exuviation in a captive snake. It rubs the front 
 and sides of the mouth against its prison wall, thus detaching and 
 reflecting the cuticle from the oral margin, until it is turned back 
 from over the whole head : the snake then brings forward its tail 
 and coils it transversely round the head, and by pushing the head 
 through the coil turns the cuticle back upon the neck ; then 
 tightening the coil and renewing the forward movement, threading 
 the body, as it were, through the caudal ring, the cuticle is 
 jtushed further and further back until the eversion has been 
 carried so near the end of the tail as prevents the further action 
 of the coil; the animal finally glides along dragging behind the 
 whole of the loosened epiderm, and a few wriggling actions of the 
 tail serve to completely detach it. Thus, the entire outer skin of 
 the snake may be found shed and turned inside out, the process of 
 exuviation being like the turning off a stocking from the leg and 
 foot. The Avhole of the exuviable epiderm in Ophidia has l^een 
 condensed into the form of scales : these are small and pretty 
 ' ccxcvn. ° lb. ' ccxcviii. vol i. p. 102. 
 
554 ANATOMY OP VERTEBRATES. 
 
 regular in size and shape along the back and sides of the body ; 
 but are large and transversely extended across the under part, 
 forming what are termed the ' ventral scutes,' ' scuta ventralia,' 
 the use of which in locomotion is explained at p. 259. All or 
 most of the scutes below the tail (' scuta eub-caudalia ') are single 
 in Crotalus, Bungarus, Boa ; in Pytlion, the ColuhridcB, and most 
 other serpents they are ' paired,' or divided along the middle line. 
 In most sea-snakes the abdomen is compressed and keeled below ; 
 in Pelami/s the keel is bordered by two rows of scales ; in Hydro- 
 jyhys it is formed by large bituberculate scales ; Platurus has the 
 venter scutate, with the caudal scales in pairs. Larger scales 
 occur in the head of most serjients, and serve as zoological cha- 
 racters, being defined as ' scuta marginalia labii superioris seu in- 
 ferioris,' 'scutum labiale medium,' 'scuta mentalia,' ' scuta ocularia,' 
 ' scuta frenalia,' ' scuta nasalia,' &c. The scales of serpents may 
 be smooth or carinate, they are rarely tuberculate (dorsal scales of 
 Xcnodermus) ; and in their disposition they may be either ' con- 
 tiguous,' or ' imbricate.' 
 
 The epidcrm is condensed into claws or hooks (' calcaria ') ujion 
 the rudiments of hind limbs that border the vent : these are best 
 seen in Boa, Python, Eryx, Tortrix ; it is developed into small 
 horns above the eyes in Vipera cerastes. In the Rattlesnake the 
 cpiderm forms a series of hard moveable rings at the end of the 
 tail, twenty to thirty in number in full-grown specimens, 
 decreasing in size to the end of the series. The terminal (3 to 8) 
 caudal vertebra; coalesce into a long conical bone, covered by 
 thick, soft, vascular derm, divided by two deep annular grooves 
 into three transverse swellings : the basal ring of one joint grasps 
 the projecting second ring of the preceding joint, and this 
 incloses the third ring of the joint next but one in advance. 
 Since the second rounded annular portion of each joint is thus 
 securely grasped by the first rounded annular portion of the piece 
 behind it, and the third by the second, and yet all of them so 
 loosely as to leave room for motion, it has been supposed that 
 when the foremost piece has been completed, and a new piece in 
 advance is about to be formed, the skin which is to secrete it is so 
 modified that its first swelling, which secreted the first projection 
 of the former piece, assumes that shape and size which are 
 accommodated to the shape and size of the second projection of 
 the new piece, whilst the second swelling which secreted the 
 second projectio]! of the piece takes the dimensions suited to 
 the third projection of the future new ring. The basal projections 
 of the successive rings arc chiefly visible externally, only tlie first 
 
TEGUMENTS OF REPTILES. 555 
 
 ring lias a vital connection with the derm : it is caused to vibrate 
 by the muscles of the tail, and its vibration communicates a 
 quivering motion, accompanied by a rattling noise, to the dry 
 horny pieces behind it.' 
 
 The pigment-cells are mostly combined with the epidermal 
 ones to form the deeper layers of the scales, and ornament the 
 skin of snakes with various and sometimes brilliant colours. The 
 poisonous serpents are mostly of a sombre hue. The periphery of 
 the derm is modelled according to the pattern, contiguous or im- 
 bricate, of the epiderm, the scales of which are evolved thereupon. 
 The blood-vessels form a beautiful and regular network, the area 
 corresponding with the shape of the scales, being lozenge-shaped, 
 e. g. in Coluber natrix^ with the uniting angle at the centre of 
 each scale. 
 
 The skin of the snout developes tentacular appendages in Her- 
 jieton tentaculatum. The integument in the Cobras (^Naja) 
 expands into a broad fold on each side the neck : the folds are 
 supported by correspondingly elongated ribs, p. 55, fig. 46, pi. ; 
 when these are drawn forward an oval disc of skin is caused, sur- 
 passing the head in breadth, and usually rendered more conspicuous 
 by well-defined tracts of jMgment. The name of ' spectacle- 
 snake ' refers to the jiair of circidar spots connected by a ciu-ved 
 streak on the hood of the JVaia trijnidians. 
 
 The secreting follicles of the skin in Serpents are chiefly con- 
 fined to certain depressions or inverted folds of the derm. These 
 in Crotalus and Trigonoccphalus constitute a pit between the 
 nostril and eye on each side of the head. The hinder scutes of 
 the lower lip have pits in Pi/thon Scldegelii ; as have those of both 
 lips in Python ametlujstinus. In AmphislxBna alba and in Chirotes 
 there is a row of pores in front of the vent. 
 
 The skin in most Lacertians resembles that of Serpents : the 
 scales are thickened epiderm or horn ; in most imbricate, in a 
 few (yZonosaurus, V. der H.) verticillate ; usually smooth, but 
 in some carinate, and in some tubercvdate or gibbous : in a few 
 they support a spine at certain parts of the body, as, e. g. the 
 caudal scales of Zonurus, both dorsal and caudal scales of Tr- 
 bolonotus, the circumtympanic scales of Agama, the occipital 
 scales of Phrynosonia, and scattered dorsal and lateral scales in 
 the Australian Lacerta muricata of White. Bone is developed 
 at the base of the scale forming part thereof, or combining scute 
 and scale, in Ophisaurus, Tribolonotus, Tracliysaurus. In the 
 Chameleons the scales are small and thin, like grains. The 
 
 ,. , , ' coxcix. p. 294, pi. xii. « ^x. vol. iii. p. 241. 
 
556 ANATOMY OF VERTEBRATES. 
 
 pigmental system of the skin is remarkably developed in this 
 family : it is of various colours — red, blue, yellow, brown ; each 
 colour is lodged in contractile areolar spaces, and can be accu- 
 mulated near or withdrawn from the surface. When the Chame- 
 leon is kept long in a cold dark place all the pigment subsides 
 into the derm, the superficial pale grey colour of which appears 
 throvigli the thin epiderm. When brought into the light and 
 warmth the pigments flow to the surface, in harmony with the 
 colour of that on which the animal rests, which usually in this 
 arboreal reptile is green. If, however, the Chameleon be irri- 
 tated, the colour may change to a vinous red, or deepen almost to 
 black : commonly the surface is more or less mottled, grey, yellow 
 and green. These phenomena, which have made a proverb of 
 the Chameleon, are manifested in a minor degree by some other 
 lleptiles, by most Fishes, and by Cephalopods. 
 
 The integument, besides covering the surface of the body, 
 extends, in many Lacertians, from various parts, in different 
 forms and degrees. In Basiliscus and Histiurus calotes it forms a 
 compressed fold or crest along the midline of the back and tail. 
 In Crocodilnrus the tail has a double crest above : in PhjUurus 
 platurus the lateral expansions of the skin of the short tail give it 
 a leaf-shape. In Hoplurus and Tropidurus cyclura the skin of the 
 throat is folded transversely : in Agama the transverse fold is asso- 
 ciated with a longitudinal fold beneath the under jaw. The jugular 
 fold is longitudinal and pendulous, like a dewlap, in Iguana, 
 Corythophanes, and SemiopJwrus. In Chlamydosaurus a very 
 broad transverse fold of skin extends from above each tympanum 
 across the lower part of the neck : it is partly supported and 
 moved by much elongated cerato- and thyro-hyals, and can be 
 expanded and brought forward or erected, so as to give a formid- 
 able aspect to this Lizard, when it is attacked or alarmed. 
 
 In the small insectivorous Draco volans of Linnaius a broad 
 fold of skin, on each side of the body, fig. 163, is supported by 
 five pairs of slender elongated free ribs, fig. 50, by the movement 
 of which the folds can be expanded into a sort of parachute, as 
 explained at p. 265. The special modification of the tegument 
 of the toes in the Geckos is described at p. 263, fig. 162. In 
 the extinct Ptcrodactyles still more extensive duplicatures of skiu 
 were supported on a much elongated digit, and constituted true 
 wings, as in the Bats, p. 265, fig. Ill, a. In many Lizards, on 
 the inside of the thigh, there is a row of tubcrculate perforated 
 scales, beneath each of which lies a pedunculate gland, studded 
 with marginal follicles: the presence and position "of these ' pori 
 
TEGUMENTS OF llEPTILES. 557 
 
 fcmoralcs ' afford generic characters. They are wanting in tlic 
 Chameleons. Certain male Geckos have both femoral and siilj- 
 anal pores. In Pij(jopus leimloiwdus the subanal pores arc dis- 
 posed in a single series, but in Liulis in pairs, on each side. 
 
 In the Crocudillu the conversion of parts of the integument into 
 bone is constant, and the osseous structure shows interlaced or 
 crossing fibres, like that of tlie derm in and from which the 
 scutes are developed. The arrangements and forms of these 
 scutes in different eenera of recent and fossil Crocodilia are 
 described at pp. 198, 199. As in Fishes, the dcrmoskeleton was 
 most developed in the extinct secondary species. In modern 
 Crocodiles a serrated crest extends above the tail, which divides 
 at the base of that organ. 
 
 A section of the dorsal integument of Trionyx ferox shows a 
 thin epiderm, then a thicker layer of elastic fibres, next many 
 layers of fibres crossing each other regularly, and producing 
 seeming layers of the derm. In Spliargis a superficial portion of 
 the derm is ossified, so as to form a kind of girdle to the trunk, 
 beneath which is a felt of soft corium, and under this the eudo- 
 s]<eleton. In all other Chelonia the derm adheres to the periosteum 
 of certain neural spines and pairs of pleur- and hoem-apophyses, 
 whence ossification extends in different degrees into the substance 
 of the derm. In most Chelonia a series of bones are developed 
 independently in the derm, at the circumference of the trunk, 
 and also above certain neural spines, with which they may or 
 may not become anchylosed.' 
 
 The dermal bones connate with neural spines are those above 
 the nine dorsal vertebra;, figs. 370, 371, eli, si-ss. : they arc 
 termed ' neural plates.' The dermal bones connate with ])lcura- 
 ])0])hyses are those which take ossification from near the heads of 
 the second to the ninth, inclusive of the dorsal ribs, ib. ph-ph. 
 The dermal bones connate with ha^mapophyses are those which 
 start from the sternal or abdominal ribs, or coalesced groups of 
 ribs, figs. 372, 373, called hyosternal, hs, hyj^osternal, ps, and 
 xiphisternal, xs. Occasionally, ossification extends into the skin 
 from the entosternal, s {Emyda ceylonensis), and from the e})i- 
 sternals, es ( Cryptopus Petersu). The dermal bones are least 
 developed in the Triunycida, and are not covered by horny epi- 
 derm. ' Neural ' and ' costal ' plates are present in all. One 
 i)air of dermal bones is developed from the hyosternals in Trionyx 
 suIiploMUs ; in Trionyx iiiloticus and some otlier species dermal 
 bLincs are developed from the hyo-, hypo- and xiphi-steruals, the 
 
 ' CLXii. p. 165. 
 
558 
 
 ANATOMY OF VEBTEBRATES. 
 
 hyo- and hypo-sternal plates on each side being naturally united 
 to"-ether ; in Emyda ceylonensis dermal bones are developed from 
 the epi-, hypo- and xiphi-sternals, and from the entosternal or 
 sternum proper, forming seven pieces : the skin of the hinder 
 margin of the broad depressed trunk is strengthened in Emyda 
 
 IlilL 
 
 r a 
 
 rn ■ \ Tj 
 
 Inner surface, Caraliacc, young Tortoide. Outer surface, Carapace, yoimg Tortoise. 
 
 by a few dermal ossicles ; much of the skin of the trunk, where 
 not ossified, in Triunycida, has the dermal tissue of cartilaginous 
 hardness. 
 
 In the Turtles, or marine Chelonia, besides the eight connate 
 neural plates, fig. 52, si-.s-s (p. 61), dermal bones are developed 
 in advance of and behind them, and are commonly unattached 
 to the subjacent vertebra). The anterior one, ib. ch, is the 
 ' nuchal ' plate : the posterior one, ib. py, is the ' pygal ' plate ; 
 the costal plates, ph-pls, articulate suturally with the neural 
 plates, but do not extend to the end of the ribs ; the marginal 
 plates, 7W1-W212, are articulated witli cacli other and with the 
 nuchal and pygal plates suturally, and eight on each side receive 
 the ends of the eight ribs supporting tlie costal plates. Two 
 
TEGUMENTS OF REPTILES. 
 
 559 
 
 pairs of dermal bones are developed from the liyo- and hypo- 
 stcrnals, fig. 53, hs and ps: but these do not articulate with the 
 marginal series. In Freshwater and Land Tortoises the dermal 
 ossifications spread further, uniting all the parts of the plastron 
 
 371 
 
 372 
 
 Outer surface, plastron, young Tortoise. 
 
 Inner surface, plastron, young Tortoise. 
 
 into one more or less flat floor, and all the parts of the carapace 
 into one more or less convex roof, fig. 5 1 ; side-walls being like- 
 wise now formed by the union of the hyo- and hypo-sternals 
 with the coextensive marginal plates. In all Chelonia, save the 
 TrionycidcB and Sphargis, the epiderm of the- trunk is condensed 
 into large horny scales, usually contiguous, more rarely imbricate, 
 and then only on the carajiace. They may be keeled, or rugous, 
 or scabrous, but are commonly smooth and polished, or marked 
 only by concentric lines of growth. Their growing margins 
 indent the dermal bones supporting them, forming the triradiate 
 grooves, e. g. u^ion the beginnings of the costal ■ plates in the 
 young Tortoise, fig. 370, jih, and those marked si-s5 on the 
 neural and costal plates in the Turtle, fig. 52. The large epi- 
 dermal plates of the carapace and plastron are termed ' shields ' 
 and ' tortoise-shell : ' most of them have special names in Zoology, 
 as they afford useful characters in the discrimination of genera 
 and species ; whilst the impressions they leave upon the subjacent 
 bones give similar light in the interpretation of fossil remains. 
 
560 ANATOMY OF VEllTEBEATES. 
 
 after the horny shields themselves have perished. The ej)iderm 
 is disposed upon the head in various forms : in most freshwater 
 Chelonia it is a continuous thin hard layer on the top and sides of 
 the head : in marine and terrestrial Chelonia it is usually in the 
 form of large plates, leaving marginal unpressions on the skull, 
 and distinguished by special names : they are more symmetrical in 
 Chelone than in Testudo. The skin of the neck and of the limbs 
 is covered by small contiguous scales : some of these are of 
 larger size on parts of the feet. The epiderm is thickened and 
 condensed into a beak in all Chelonia, and into claws in most. 
 In Sphargis, however, the claws are replaced by small coriaceous 
 scales : in Chelone only one digit on each foot supports a claw : 
 in Caretta two digits, and in Trionycidae three digits, support 
 claws : in some Tortoises ( Testudo) there are four claws on 
 each foot : in most Tortoises and Terrapins (Emys) there is an 
 additional claw on the fore-foot: in the heavy Land Tortoises 
 the claws assume the form of hoofs. The epiderm of the tail is 
 usually wrinkled, and covered only by small scales : in the 
 Snapper i^Chelydra?) it supports a row of hard compressed 
 tuljercles ; in some Tortoises the end of the tail has a thick 
 epidermal sheath, which, in the male Cinosternon, is armed with a 
 pointed tip. 
 
 The large imbricate plates of the carapace of CAeZo?iehave their 
 fore border imbedded in a matrix of the derm, and here receive 
 their chief increase, the older parts moving backward, and being- 
 worn off. The plates with contiguous borders receive increase 
 at their under surface and entire circvimferencc ; the concentric 
 lines of growth may be marks of annual increment : ' but these 
 usually show a greater ratio of growth at the front and sides than 
 at the back The old and dull superficial layer is worn away, or 
 thrown off from time to time, leaving the rest of the epidermal 
 shield of a bright colour : the smooth or seal)' epiderm of the 
 limbs and neck is usually shed entire. 
 
 The skin of the neck developes fimbriate processes and 
 caruncles in Chclys Jimhriata : that of the nose is produced into a 
 short snout in most Trionycidce. 
 
 Tlie deeper stratum of soft, usually imbricate, epithelial cells 
 of the epiderm are intermixed with jiigmental cells, mostly dark 
 l>rown or black; abundant pigment-particles are also suspended 
 in an oily fluid, occu]iying areolar spaces of the deep epiderm, 
 and usually of the brighter yellow, red, or green colours. Such 
 
 ' As coiijoctiucd by Agassiz, ccc. vol. i. pt. ii. p. 259. 
 
TEGUMENTS OF KEPTILES. 561 
 
 pigmental cells are blended with the tissue of the shields and 
 scales, and may ornament the former with well-marked patterns, 
 e.g. in Testudo areolata, Ernys ornata, Emijs picta, &c. 
 
 Cutaneous glands or follicles open between the warts of the 
 skin in Chdydra, and probably occasion their musky odour : but 
 this, in other Clielonia, appears to 1)6 due to larger, more com- 
 pact, and more localised glands. Beneath the epiderm of the 
 skin of the under part of the body, in the Soft- Turtles, is an 
 extensive network of vessels, spreading into dendritic ramifica- 
 tions, too numerous and large for the mere nutritive purposes of 
 tlic skin or sujiply of epithelial cells, and therefore probably ' 
 subservient to respiratiou. 
 
 Viewing the integuments in their relations to the external 
 influences from which they defend tlie body, and by which they 
 are themselves affected, we may remark that most of the housc- 
 Ijearing Reptiles which have the surface of their abode habitually 
 in contact with air or water have the epiderm hard and thick, 
 whilst those living in ooze or mud have it soft and thin. In the 
 sea the horny scutes may be partially loosened, and grow over 
 one another : in the air they condense upon the surface with the 
 margins in contact : in the mud the skin is lubricous : the only 
 known scaleless species of marine habits (Sjiharyis coriacc(i) has 
 the tegument tough and leathery. In the most vagrant and widely 
 diffused Turtle (Chelone imliricaUi) the separation of the scales 
 takes place at a part of their circumference, which makes the 
 direction of iml^rication the most favourable ti.i their aquatic 
 movements. Growing and projecting from before l^ackward, the 
 one in front overlapping the next behind, the polished shields 
 offer no resistance to the forward movement impressed upon the 
 body by the oar-shaped limbs ; whilst the scutal interspaces, 
 widening as the trunk tends to recede during the preparation for 
 the next stroke, oppose the backward slipping, and take hold, so 
 to speak, upon the wave, retaining the advantage of one stroke 
 until the next is played. 
 
 ' As conjectured by Agassiz, ccc. vol. i. pt. ii. p. 284. 
 
 VOL. I. 
 
562 
 
 ANATOMY OF VERTEBRATES. 
 
 CHAPTER X. 
 
 rECULIAK AND DUCTLESS GLANDS. 
 
 § 101. Scent-glands of Reptiles. — The Chelonia, like most 
 Reptiles, have scent-glands, with periodical access of activity, 
 enabling and exciting, as it seems, the sexes to find each other at 
 the pairing season. In Tortoises the gland, fig. 373, a, is situated 
 beneath tlie skin of the mentum ; its duct, h, in a Testudo indica 
 of two feet long, opens about an inch and a half behind the 
 symphysis of the mandible, and about half an inch from the 
 
 373 
 
 Section of niaiidihle Miowiiig tlic sceiu-glaiKi. TcsivJo indica. 
 
 mesial line. In the Turtle the glands excrete at the base of the 
 neck ; in the Kinosternon a gland is situated near the fore and 
 hind margins of the side-walls, uniting the carapace and plastron : 
 the duct perforates the bone, and opens by a fine slit in the wall. 
 In the Crocodilia a small sinus is formed bj^ an inward fold of 
 integument near the inner side of the mandibular ramus, into 
 which sinus opens the dilated duct of a gland, which is surrounded 
 by a muscle, detached from the back part of the pharynx, and 
 proceeding along the outer side of the ceratohyal to expand upon 
 the gland and reservoir.' Cuvier^ describes its contents as being 
 unctuous, of a dark grey colour, with a strong nmsky odour. 
 
 XX. vol. iii. p. 272; prep. no. 2106. 
 
 XII. torn. y. 
 
 p. 252 (1S05). 
 
POISON-GLANDS OF REPTILES. 563 
 
 The Crocodiles have glandular follicles, which open at the 
 anus. Hunter preserved ' a section of the skin of a Turtle 
 {Chelone), to show a gland situated near its anus.'' There is a 
 glandular fossa which opens into the dorsal part of the cloaca, 
 close to the termination of the rectum in most Emydians. 
 
 The anal bags in Serjients are two in number, of an elongate 
 form, fig. 357, m : they are lodged in the base of the tail, and 
 open into the back part of the cloaca : their excretion has a 
 strong, disagreeable, nauseating odour. 
 
 § 102. Poison-glands of Reptiles. — The gland which secretes 
 the poison in ordinary venomous Serj)ents is situated on each side 
 the head, anterior to the tympanic pedicle, inclosed in a strong 
 capsule, fig. 145, a (p. 227), and partly 
 covered by the muscle analogous to 
 the masseter, ib. e, some of the fibres 
 of which, fig. 374, a, are attached to 
 the capsule, ib. b. On reflecting these, 
 as in fig. 374, the gland, ib. c, is seen /J 
 comjjosed of a series of elongated 
 narrow lobes, extending from the main 
 duct at the lower border of the gland 
 
 upward and backward. Each lobe poiaon apnnti i u \ir Mpera 
 gives off a series of lobules, which are 
 
 again subdivided into smaller cteca. Their secretion is collected 
 into the dilated beginning of the duct which conveys it to the base 
 of the poison-fang, f; the bristle e passes from the duct into the 
 j3oison-canal of the fang, the structure of which is described, pp. 
 396-398 : the gum-capsule, d, of the reserve-fangs, g, is laid open. 
 In Hydrophis the poison-gland is of smaller size, narrow, elongate, 
 broadest beliind, and extended upon the maxillary and ecto- 
 pterygoid bones, in advance of the masseter : its capsule is 
 attached to the tendinous tract (p. 228) detached from the 
 digastricus and ectopterygoid : its duct enters the foremost of the 
 series of four to six small fangs attached to the maxillary. The 
 bite of these iuferiorly endowed venomous Sea-Snakes has proved 
 fatal : they are said to occasionally climb along the hawser into 
 ships at anchor ; and as they may be drawn in, adhering to it by 
 their prehensile tail, or be caught in the fishing-net and hauled 
 on board, it is well that their dangerous property should be 
 known. 
 
 The secretion of the poison-gland is a tasteless fluid, drying 
 under exposure to air into small scales : it is soluble in water, 
 
 ■ XX. vol. iii. p. 279, prep. no. 2130. 
 o o 2 
 
564 
 
 ANATOMY OF VERTEBRATES. 
 
 375 
 
 insoluble in alcohol, and slightly reddens litmus paper : it long 
 retains its noxious property. Against this the mucous surface of 
 the alimentary tract is proof: the poison, to take effect, must 
 enter the current of the blood. Here it is ordinarily introduced 
 by the puncture of the poison-fang, but it takes effect by applica- 
 tion to an abraded surface. The poison affects the nervous 
 system ; death is usually preceded by spasmodic convulsions, and 
 followed by speedy putrefaction. 
 
 § 103. The Thyroid Body or Gland of Hamatocrya. — In the 
 Skate {Raia) the body which seems to have best claim to be 
 regarded as a thyroid is situated sternad 
 of the terminal division of the branchial 
 artery, of a reddish-grey colour and con- 
 glomerate exterior. It consists of nmne- 
 rous, mostly subspherical, vesicles, of from 
 "sV to xla- iiich diameter, fig. 375, having 
 a structureless tunic. A, lined by a thick 
 stratum of epithelial substance, consist- 
 ing of nuclei and granular matter, b. Dr. 
 Handfield Jones, who has given the above 
 result of microscopical investigation of this 
 ductless gland, also found, in the Skate, 
 ' at some distance behind it, just at the 
 junction of the branchial arches anteriorly, 
 a small light reddish mass, which was 
 covered by a thin fascia, and by mucous membrane.'' It consisted 
 ' of vesicles about -pio to -^ inch diameter,' fig. 376, ' formed 
 
 by a structureless " limitary " 
 tunic, thickly lined by epithelial 
 substance, and containing abund- 
 ance of nuclei and granular matter, 
 with a few cells. The pseudo- 
 branchia, situated on the anterior 
 wall of the spiracnlar canal, is 
 manifestly of entirely different 
 structure to the organs described. 
 It consists of small plic;\3 of mucous 
 membrane, covered by a kind of 
 pavement epithelium.' - 
 the Menobrancluis the thyroid is represented liy two 
 symmetrical bodies, situated at the sides of the liasibranchlals. 
 
 Tesicle from thyroid of Skate. 
 
 CCLXXXIX. 
 
 376 
 
 side from arccsHory thyroid nf Skate, diam, 
 j^ In. CCLXXXIX. 
 
 In 
 
 ' OCI.XXXIX. p. 1 no. = lb., an.l see oxlv. p. 
 
 thyroid nature of the pscmlo-hrancliias in other fishes. 
 
 70, with reference to the non- 
 
THYMUS OF REPTILES. 5G5 
 
 In the Frog they lie on the carotids, also close to tlie basi- 
 branchialsj or thyrohyals. 
 
 In a Python of ten feet in length tlie thyroid was an oval body, 
 ten lines by six lines in the two diameters, lodged in the fork 
 made by the divergence of the large and small carotids, and 
 having the smaller thymus bodies, one on each side. 
 
 In the true Lizards {LacerUt) the thyroid is single, but broader 
 than it is long ; in the Monitor it is double : it is single in Geckos, 
 Skincs, and Chameleons, but has a more advanced 2;)osition in the 
 latter, where it is underlapj^ed, or covered, by the laryngeal pouch. 
 
 In Chelonia the thyroid, as in Serpents, lies between the two 
 carotids, but is usually covered by the pericardial part of the 
 thymus. The constituent vesicles are from -^-g to Jj inch diameter, 
 closely aggregated : the epithelial lining contains a row of nuclei 
 imbedded in the granular substance, fig. 
 278. Among the contents of the vesicles 377 
 
 were found, in most, ' one to three yellow- ^..j^sfs^ps^^s--.^ 
 ish, coarsely granular globules, ^^ to f^Pl^^lSl^- 
 ToV ™cli diameter.' ' A fine large octo- j,„.j. „^ ^, „,„ „.^,i „j ^ vosi^ie'from 
 hedral crystal was also seen in one of the "icibyvom of a Tortoise, colxxxix 
 cavities.'' 
 
 § 104. The Thymus Body or Gland of Reptiles. — The ductless 
 gland- like tubulo-vesicular body to which the name ' thymus ' 
 can, with any homological probability, be given makes its first 
 appearance in the Vertebrate series with the establishment of 
 lungs as the main or exclusive respiratory organ. ^ Thus in Siren 
 and Proteus the thymus is wanting, as in all Fishes : in tailed 
 Batrachia (^Menopoma, Triton) it is represented by a pair of 
 bodies situated, one on each side, near the origin of the pulmonary 
 artery. They make their appearance near the same part, but 
 ratlier more in advance of the pericardium, in the larvaj of 
 anourous Batrachia, and often degenerate into fat in the old Frog 
 or Toad. In most Ophidia the thymus lies on each side of the 
 carotid, of elongate form and unequal size : sometimes in two or 
 more distinct parts : usually associated with, and concealed by, 
 fatty matter. In a Python of ten feet in length I found the 
 thymus in two bodies, each about the size of a pea, of a yellowish 
 colour, one situated on the termination of the right jugular, the 
 other between the origin of the larger carotid and the left jugular. 
 Between the thymus bodies was the much larger single thyroid. 
 In the Psammosaur and Iguana the thymus is broad and flat, 
 covers stcrually the thyroid, extends along the common trunk of 
 
 ' CCLXXIX. p. 1100. ^ CXVIII. 
 
566 ANATOMY OF VERTEBRATES. 
 
 the carotids, and divides to accompany them a short distance. In 
 the young Crocodile' the thymus is relatively larger, thicker, 
 subtrihedral, extending backward upon the pericardium, as well 
 as forward along the carotids to the basis cranii. In young 
 Chelonia an elongate body, of a yellowish white colour, lies 
 between the carotid and axillary trunks on each side : it presents 
 lateral cavities, defined by limitary membrane, and containing 
 nuclei, oil-drops, and fine molecular matter. In older Chelonia it 
 seems to degenerate into fat. 
 
 § 105. Reproducible Parts in Ilcamatocrya. — One effect of life 
 is the reproduction of the parts of the body as they pass away 
 through unfitness for the required actions : this mainly takes 
 place molecularly and invisibl}' ; but parts of the integument, hairs, 
 teeth, antlers, may be cast off en masse, and reproduced on a scale 
 which catches the ordinary attention as a new growth. Certain 
 animals have the fxculty of reproducing organs and compound 
 parts of the body which may have been removed by violence : 
 amongst Vertebrates the property is greatest in the cold-blooded 
 series ; and here, so far as experiment yet shows, is most conspi- 
 cuous in the tailed species and larvas of the batrachian order. In 
 the JS^ewt ( Triton) the tail, amputated at any distance from the 
 base, is reproduced : the same with respect to the fore-limb and 
 hind-limb, the reproduced member having the digits, but with 
 diminished j)ower of movement. The same member has been, in 
 young Newts, removed and restored four times successively. In 
 the experiments recorded by Bonnet,^ it was found that warmth 
 promoted, and cold retarded, the regeneration of the part. An 
 eyeball of a Newt was extirpated, and, in the course of a year, it 
 was restored with the usual organisation. Dumeril cut off about 
 three-fourths of the head of a Triton marmoratus, and deposited 
 the animal at the bottom of a large vessel, having half an inch 
 depth of water, which was constantly renewed. The Newt con- 
 tinued to live, and to move slowly. The nostrils, the tongue, the 
 eyes, and the ears were gone, and the senses reduced to that of 
 touch. It crept slowly, and Dumeril imagines cautiously, about, 
 occasionally raising the neck to the surlacc, as if to breathe. The 
 process of cicatrisation at length completely closed the aperture of 
 respiration and deglutition ; and so it survived for three months 
 after the operation, when it died from accidental neglect. This 
 experiment exemplifies chiefly the power of endurance of mutila- 
 tion, and, collaterally, the respiratory function of the skin. In 
 
 ' I Iiavc not liad an opportunily of examining this structuic in a full-grown speci- 
 men of Crocodilian. ' coci. torn. xi. pp. G2-179, 
 
REPRODUCIBLE PARTS IN REPTILES. 567 
 
 the young larvse of Rana temporaria and Bomhinator igneus, Dr. 
 Glinther cut off the tail, and it was reproduced before the time 
 when its absorption normally commences : it was transj)arent and 
 colourless, a small Cjuantity of pigment being dejoosited at its root 
 only. ' Larva3 from fourteen to twenty days old did not survive 
 the loss of the entire tail, probably because they are disabled from 
 obtaining the requisite food ; but if only a portion of the tail be 
 cut off, it is more or less completely reproduced until its growth 
 is arrested by the commencement of the last stage of metamor- 
 phosis. If a hind limb be cut off when the larva is about two 
 lines long it is reproduced. No part of an Anourous Batrachian 
 is reproducible after completion of the metamorjohosis, not even 
 the interdigital web.'' 
 
 In Reptilia the power of local reproduction has been exemplified 
 chiefly in respect of the tails of Lizards. Hunter's preparations, 
 nos. 2208-222.3, are all from this order, and include species of 
 Arneiva, Gecko, and true Lacerfa. No instance of the restored 
 tail shows ossified vertebras, and some exemplify the tendency to 
 greater abnormality in the reproduced part. A structure of the 
 normal caudal vertebrte, related apparently to this property, is 
 noticed at p. 59 : the caudal muscles, by their proportions and 
 interlocking arrangement, seem likewise to favour the rupture of 
 the tail. When it is cast off, it continues to writhe for some 
 time, and, when these motions have ceased, exemplifies the reflex 
 function on being pricked or otherwise irritated. 
 
 The degree in which the reproduction of parts is exemplified 
 in Fishes awaits the results of experiments. Van der Hoeven^ 
 affirms that parts of the fins are restored after amputation, and 
 that the power is limited to this extent. Amputation of the 
 small adipose dorsal fin has, however, served to mark an individual 
 Salmon from its ' parr ' state to that of the ' grilse ; ' ' and it appears 
 that only the peripheral (dermoneural or dermohffimal) rays are 
 reproducible, and to this the hard ones in Acanthopterans form 
 an exception. ' The modified dermoneurals forming the cephalic 
 tentacles of Lophius and Antennarius are as frequently repro- 
 duced as they are injured, to meet the particular use which these 
 ano-ling fishes make of them : they may be observed in every 
 stao-e of growth. Lost parts of fins appear to be more easily 
 reproduced in young than in old fishes.' "* 
 
 ' MS. Notes by Dr. A. Giinther. ' cccv. vol. ii. p. 52. 
 
 ^ cccxxxiv. ' The wound caused by marking was covered with skin, and in some 
 a coating of scales had formed part.' Page 5. * MS, Notes by Dr. A. Giinther, 
 
5()S ANATOMY OF VERTEBRATES. 
 
 CHAPTER XI. 
 
 GENERATIVE SYSTEM OF IliEMATOORYA. 
 
 § 106. Male Organs of Fishes. — All Fishes are dicecious, or ot 
 distinct sex. The male parts of generation present a progressive 
 gradation of complexity from the essential gland, or testis, as a 
 single organ distinguishable only by microscopic examination of 
 its contents from an ovarium, to a more definite and concentrated 
 form of testis with complete bijjartition ; then to the developement 
 of a proper duct or ' vas deferens,' next of a vesicula seminalis 
 and prostate, afterwards of an intromittent organ, and finally of 
 superadded ' claspers,' or mechanical instruments for retention 
 of the female in coitu. In Petromyzon marinns the testis is a 
 long thin plate, disposed in the form of a series of folds, closely 
 attached by a duplicature of the peritoneum to the median line of 
 the back of the abdomen, between the kidneys ; the extension of 
 the overlapping oblique folds to the right and left of the line of 
 attachment feebly indicates the duplex character of the gland.' 
 Its tissue consists of small spherical cells filled with spermatozoa, 
 fig. 402. These escape, by dehiscence of the cells and rupture 
 of the peritoneal covering, into the abdominal cavity, and are 
 expelled by reciprocal pressure of the intertwined sexes from the 
 peritoneal outlets at the cloaca. The Eel closely resembles the 
 Lamprey in the general form and condition of the male organs ; 
 but the right and left sides of the plicated testis are more distinct, 
 and the spermatic cells are more numerous and minute. 
 
 The Sand-Eel (Ainmodytes)- has a single testis, compacted into 
 an elongated triedral form, and impressed by a median longitudinal 
 fissure : it usually inclines a little to the right side. In the Perch 
 the single testis inclines to the left : in the Blenny and the Loach 
 it lies in the middle line. In these osseous fishes the glandular 
 part of the testis is inclosed in a proper fibrous capsule, which is 
 continued from tlic posterior end of the gland, with its serous 
 covering, into a sliort and simple si)erm-duct, or ' vas deferens,' 
 whicli opens usiially into, or receives, the urethral prolongation 
 of the urinary ))ladder. In tlic Gurnard the testes, fig. 378, «, 
 
 ' xs. vol. iv. \\ 48, \m-\K no. 'J.IT.'i. -' II.. p. 4!), |.rep. no, 237S. 
 
MALE ORGANS OF FISHES. 
 
 5G9 
 
 Renal and malo organs : 
 Trujla ii/ra, Carua 
 
 arc distinct from each other, but their ' vasa deferentia' ahnost 
 immediately unite into a common duct, e, which joins the urethra, 
 c, behind the rectum, /(, and terminates at the 
 outlet, ff. In the Salmon and the Herring the 
 ' vasa deferentia ' do not unite together until 
 near their termination in the urethra. In the 
 Cod and the Bull-head (Cottiis) the common 
 portion of the efferent duct is much dilated : 
 it forms a saccular seminal reservoir in the 
 Sole. The canal common to the ureter and 
 vas deferens is of great length in the Sturgeon : 
 a valve prevents the regurgitation of the iirine 
 into the spermatic duct. The urethra is usually 
 produced into a f)f''Pill*j which projects con- 
 spicuously from the back part of the cloaca in 
 the viviparous Pcecilia, Anableps, and Blenny : 
 it is large also in the Lump-fish. The testes are almost 
 entirely extra-abdominal in the Flounder and some other Pleii- 
 ronectidoe, extending backward into a kind of concealed scrotum 
 between the integuments 
 and muscles on each side 
 above the anal fin. The 
 testes differ much in form 
 in different Osseous Fishes, 
 but are remarkable in all 
 for their enormous seasonal 
 increase : when fully deve- 
 loped, they are commonly 
 known as the ' milt ' or ' soft 
 roe.' In Gymnotus they are 
 two oblong triedral bodies, 
 attenuated at both ends. 
 In the Pipe-fishes {Syn- 
 gnatld) they present the form 
 of two simple elongated 
 straight tubes, fig. 427 , 
 y3.' In the Lump-fishes 
 {Cyclopteri) they are di- 
 vided by incisions into 
 lobes: in the Cod a vast 
 extent of the vascular sur- 
 face of the glandular substance is packed into 
 
 ' XX. vol. iv. p. 48, prep. no. 2375. 
 
 structure of the testis iji Clupea Alosa. g.xxit 
 
 a small com- 
 
570 
 
 ANATOMY OF VERTEBRATES. 
 
 380 
 
 pass, by being disposed in convolutions upon the edge of the 
 ' mesorchium.' The primitive spermatic cells, which are per- 
 sistent in the Cyclostomes, have coalesced into tubes (tubuli 
 seminiferi) in Osseous Fishes ; the tubes open at one end in the 
 wide and sometimes saccular commencement of the vas deferens, 
 and terminate at the other, either by blind free extremities or 
 by reticulate anastomoses.' In the Herring, Shad, 
 and other Clupeoids, the secerning tubes ramify 
 and anastomose in the substance of the testicle, 
 and from this plexus, fig. 379, the initial cffica 
 are prolonged to the surface of the gland, where 
 their obtuse blind ends give a granulated apiDear- 
 ance to the exterior. 
 
 In the Plagiostomes the testes, figs. 352, k, 
 380, «, are always distinct from one another, and 
 usually of a circumscribed compact form, situated 
 far forward in the abdominal cavity. They have 
 a proper capsule, or ' tunica albuginea,' and a 
 peritoneal covering ; the capsule sends many ' septa' 
 into the substance of the gland, and the lobes thus 
 formed consist chiefly of the tulDuli testis, and 
 their expanded cell-like extremities, filled with 
 tlie spermatozoa : the convolutions of the ' tubuli ' 
 are plainly discernible in the portion of the testis 
 of the Basking Shark {^Sdache maxima) preserved 
 in the Huuterian iSIuseinn, London, prep. no. 
 2396, A.^ Numerous ' vasa efterentia' convey 
 the ' semen ' to the beginning of the ' vas deferens,'' which forms 
 a large ' epididymis,' fig. 380, h, by its manifold convolutions. 
 These gradually decrease as the duct, ib. e, approaches the cloaca, 
 when it becomes straight, and expands into an elongated reservoir, 
 ib. /, the mucous surface of which is commonly increased by 
 numerous transverse plicaj, as in Spinax and Selache. Behind 
 the termination of the rectum the ' vasa deferentia ' suddenly 
 diminish, approximate, communicate with the ureters, and ter- 
 minate upon the cloacal penis, fig. 352, o. This is hardly visible, 
 and the testes are very small, except at the breeding season, in 
 the Piked Dog-fish (Sjmiax). 
 
 The claspers are present in the Chimwroid Fishes as well as in 
 the Plagiostomes. They project backward, as appendages to the 
 bases of the anal fins, and are sometimes bent inward at their 
 free extremities, figs. 352, q, 380, m. Near this part mav be 
 
 ' cxxii. ]). 105. - XX. vol. iv. p. M '■' cxxxiv. 
 
 orpniis, left sije: 
 ,'^j>inax. 
 
FEMALE ORGANS OF FISHES. 
 
 571 
 
 381 
 
 discerned a fissure, which is the outlet of a blind sac, extending 
 forward from the base of the clasper, beneath the muscles and 
 skin, at the sides of the cloaca. The inner surface of the cavity 
 is smooth, and lubricated by a fluid mucus : the attached vascular 
 surface is richly supplied with vessels, especially with veins : in 
 the Rays a glandular body adds its secretion to that of the surface 
 of the cavity. 
 
 § 107. Female Organs of Fishes. — The gradations of structure 
 of the female organs correspond very closely 
 with those of the male. In the young Lam- 
 jirey the ovarium is a simple longitudinal mem- 
 branous plate, fig. 381, c, suspended by a fold 
 of the peritoneum (mesoarium) along the under 
 part of the vertebral column : it increases in 
 breadth and thickness as the ova are developed 
 in it, and still more so in length, being accom- 
 modated to its locality by numerous folds, fig. 
 .382. But no superadditions are made to this 
 primitive structure : the ova, d, escape by 
 rupture of their capsules into the abdomen, h, 
 and are excluded by the peritoneal aperture, 
 ib. I. In all other Fishes in which vasa 
 deferentia are absent in the male, oviducts are 
 absent in the female. But it does not always 
 
 happen, where vasa deferentia are developed in the male, that 
 
 the liomotypal ducts exist in the female : the Salmon is an 
 
 example in which the ova are discharged by dehiscence into the 
 
 abdominal cavity, and escape 
 
 by jieritoneal oiitlets, as in 
 
 the Eel and Lamprey. 
 
 With this exception, the 
 
 parallelism of the male and 
 
 female organs is very close. 
 
 Thus the ovarium is single 
 
 in those bony Fishes, as the 
 
 Perch, the Blenny, the 
 
 Loach, and the Ammodyte,' 
 
 in which the testis is single : 
 
 the median cleft of the ovary 
 
 of the Ammodyte is decider 
 
 than that of the testis, but the continuity of the two seemino-ly 
 
 distinct glands is obvious at the ujoper and lower ends. In 
 
 ' XX. vol. iv. p. 133, prep. no. 2675, A. 
 
 Renal and female oi-gans 
 I'eiromiizov. xx. 
 
 An ovarian fold of the Lamprey. 
 
57-2 
 
 ANATOMY OF VERTEBRATES. 
 
 383 
 
 most Osseous Fishes the ovaria, fig. 383, a, form two elongated 
 sacs of mucous membrane, with a tliin fibrous tunic and a perito- 
 neal covering, closed anteriorly, but produced posteriorly into a 
 short, straight, and commonly wide oviduct, terminating behind 
 the anus, and commonly before the urethra, fig. 281, i. In the 
 
 Pipe-fishes the oviducts con- 
 tinue distinct to the cloaca. 
 In most Fishes the oviducts 
 coalesce, after a brief course, 
 as in the Herring, or after a 
 longer course, into a single 
 tube before arriving at the 
 cloaca : the common terminal 
 portion becomes much dilated 
 in the Cod-fish, the Lump-fish, 
 and- some others. The ' stroma,' 
 or cellular tissue, which is the 
 seat of developement of the 
 ova, is interposed between the 
 mucous and fibrous tunics of 
 the ovarian sac : it sometimes, 
 though rarely, is coextensive 
 with the mucous membrane. 
 In the Lophius the two ovaria 
 are long and large plicated 
 tubes, flattened when empty, 
 cylindrical when inflated, with 
 the ovigerous stroma lining, as 
 it were, only the ventral half 
 of the walls of the cylinder, and terminating where the oviducal 
 portions of each sac unite together to form the common short 
 efferent canal. The inner surface of the ' stroma ' is beset with 
 small tubercles, arranged in interrupted linear series, each tubercle 
 supporting four or five papilliform ovisacs. In the Pike the stroma 
 forms a longitudinal strip, in short transverse plaits, along the 
 median side of the long ovarian sacs: fig. 383, B, shows two of the 
 ovarian plaits, from which the developed ova hang in subpediui- 
 cidate ovisacs. In the Wolf-fish the stroma extends over the 
 whole of the internal surface of the ovary, into the cavity oi 
 which it projects in the form of numerous oval compressed 
 processes. In general, its superficies is extended by being plaited 
 into numerous folds, which are transverse in the Cod and Salmon, 
 oblique in the Mackerel, and longitudinal in some other Fishes. 
 
 Ovarlea and oviduct of an Osseous Fish. 
 
FEMALE ORGANS OF FISHES. 
 
 573 
 
 In the Salmon the free surface of the stroma is exposed. In the 
 Osseous Fishes that retain and hatch their ova the stroma does 
 not extend to the posterior part of the ovarian sac, but this 
 
 384 
 
 Viscera of female Shark, xx. 
 
 h^f 
 
 j..\- 
 
 serves as a kind of uterus, and contains an abundant albuminous 
 secretion at the season of the internal incubation. The viviparous 
 
574 ANATOMY OF VERTEBRATES. 
 
 Blenny (Zoarces), the Anableps, the Poecilia, and Embiotoca ' 
 are examples of ovo-viviparous Osseous Fishes, and at the same 
 time manifest naturally, what occurs as a rare adnormality in 
 higher Vertebrates, viz. ovarian gestation. In the Plaice and 
 other Pleuronectida; the parallelism between the male and female 
 organs is so close that the ovaria also escape from the abdomen, 
 and become lodged in greater or less proportion in subcutaneous 
 scrotal cavities above the basis of the anal fin.^ 
 
 In the Lamprey the short and narrow lateral infundibuliform 
 passages behind the rectum, into which the ureters open, and 
 which terminate in the peritoneal outlets, fig. 381, e, I, have been 
 compared to short oviducts. In the Sturgeon actual oviducts 
 are continued from the ureters forward, which open by wide 
 infundibular apertures, comparable to the ' morsus diaboli ' of 
 anthropotomy, into the general jjeritoneal cavity, and receive the 
 ripe ova as they burst from the ovarium. The urine is prevented 
 from regurgitation into the serous cavity through the same 
 passage lay a valve which only allows the passage of the ova 
 backward into the common urogenital duct. 
 
 The higher grade of the sexual organisation of the female 
 Plagiostome, as compared with the cartilaginous Ganoid fish, is 
 manifested chiefly by modification of the oviducts : they are 
 always two in numbei-, fig. 384, q, r, and distinct from one end 
 to the other, but they are brought into close proximity, or 
 coalesce at both ends : they are always distinct from the ureters, 
 which terminate on the prominent urethral clitoris, ib. t, between 
 the oviducal outlets, ib. ,?, s. Different parts of the oviducts are 
 modified, moreover, for special functions, superadded to that of 
 effecting the safe transit of the generative product. The ovaria 
 of Plagiostomes, fig. 384, n, are relatively much smaller than in 
 other Fishes, of a more compact form, and confined to the fore 
 part of the abdominal cavity : they are sometimes blended into a 
 single Iwdy. The stroma is not spread over the walls of a cavity, 
 but is collected into a loose cellular mass, circumscribed by a 
 fibrous membrane, and suspended by a duplicature of peritoneum 
 to the dorsal parietes of the abdomen, at the sides of the 
 oesophagus. The ova are much fewer in number than in the 
 'roe' of Osseous Fishes, and are seen in different stages of 
 growth, being developed more consecutively. The approximate 
 or confluent abdominal apertures of the oviduct, ib. (j, are anterior 
 to the ovarium, between the liver and the pericardial septum; 
 they form togetlier a heart-shaped opening, with entire margins, 
 
 ' ccoxxxv -• xLHi. V. pi. 4, fig. 1. 
 
FEMALE ORGANS OF FISHES. 57.5 
 
 attached by two diverging ligaments to the abdominal walls. If 
 a little powdered charcoal be sprinkled on the ovarian orifices and 
 ligamejits exposed by opening the abdomen in a fresh caught 
 female Dog-fish, the particles will be seen to move towards and 
 enter the connnon oviducal aperture, indicative of a ciliated 
 epithelium in the serous membrane, which may aid in the 
 transport of the ova to that aperture. The oviducts, narrow, 
 and with thin tunics at their commencement, diverge from each 
 other, arching over the fore part of the ovaria, and then descend 
 along the ventral surface of the kidneys, to terminate at the 
 lateral and posterior parts of the cloaca, ib. ,5. A glandular body, 
 ib. o, is developed in their coats, after the first, fifth, or sixth part 
 of their extent, and their terminal half or third part, ib. r, is 
 dilated; the sizes of the glandular and of the uterine parts of 
 the oviduct are usually in inverse proportion : in the oviparous 
 Plagiostomes the gland is large, the uterus small, and the reverse 
 obtains in the viviparous species, fig. 384. The inner surface of 
 the Fallopiian portion of the oviduct presents longitudinal or very 
 oblique folds of the delicate mucous membrane : but near the 
 aperture the folds resolve themselves into minute compressed villi. 
 The glandular part varies in structure as well as in size in different 
 species. In the vivij^arous Dog-fish ( Spinax acanthias) it consists 
 of two elliptic flattened lobes, of laminated structure, the free 
 surface presenting minute transverse stria;, beset with pores, the 
 orifices of secerning tubes, the aggregate of which composes the 
 layer of glandular substance. In the oviparous Homelyn {Raia 
 maculata) the lobes of the large rudimental glands are reniform, 
 and consist of close-set layers of secerning tubes. In the Tope 
 {Galeus) the lobes of the gland present the same essential 
 structure, but are conical, subspiral, and hollow. The uterine 
 part of the oviduct in the viviparous Dog-fish, fig. 384, r, has 
 the lining membrane produced into longitudinal folds, with wavy 
 margins, each of which contains a single vessel following its 
 sinuosities, and sending ofP branches to the parietes of the 
 oviduct : the folds gradually subside at the outlet of the oviduct. 
 In the oviparous Dog-fish (^Scylliuni) the folds of the lining 
 membrane of the corresponding part of the oviduct are oblique, 
 and their vessels are derived from trunks in the walls of the 
 oviduct, and are distributed in minute and tortuous ramifi- 
 cations on the folds.' The uterus of the Smooth Docf-fish 
 (^ScoUodon, M. ; Emissole lisse, Cuv.) shows several uterine 
 
 ' XX. vol. iv. p. 136. 
 
576 ANATOMY OF VERTEBRATES. 
 
 cotyledons developed from the internal surface of the dilated part 
 of the oviduct: corresponding foetal cotyledons are developed 
 fi'om the vitellicle of the embryo. 
 
 Thus the various forms of the generative organs of Fishes 
 resolve themselves into four well-marked grades of complexity. 
 First, the essential gland, testis or ovariiun, without excretory 
 canal. Second, the same, with a simple duct, continuous with 
 testis or ovarium. Third, a partial oviduct, not continuous with 
 the ovarium, and not separated from the ureter. Fourth, testis 
 or ovarium, of a more compact form, each with a long and 
 complex duct, distinct from the ureter ; the beginning of the 
 vas deferens convoluted into an epididymis, and its end dilated 
 into a seminal reservoir, with a plicated glandular inner surface ; 
 the oviduct not continuous with the ovarium, but with a nida- 
 mental gland near its commencement, and dilating into a 
 receptacle, with a plicated surface, at its terminal half. Besides 
 the ' claspers ' of the Plagiostomes, there are other accessory 
 organs of generation, viz. the subcaudal marsupial tegumentary 
 folds in the male of some species of Sijngnathus, fig. 427, o,' and 
 the subabdominal marsupial pouch in the male Hippocamps.^ 
 
 § 108. Male Orf/ans of Batracliians. — These consist of testes, their 
 ducts and appendages, the seminal reservoir, and the common ex- 
 cretory canal and terminal papilla : there is no intromittent organ. 
 
 The testes, though in some Batrachia subdivided, resemble in 
 their relative size and compactness of form and tissue tliose of the 
 Plagiostomes. In the Froteus anf/uiniifs the testis is long, cylin- 
 drical, with obtuse ends, slightly fissured lengthwise by the 
 insertion of the suspensory ligament : they sometimes show in- 
 efpiality of size, and the right is usually about three vertebra? 
 in advance of the left. In Amphiuma the testis is subcylin- 
 drical, and tapers at both extremities : adipose appendages project 
 from their free or ventral surface. In the Axolotl the ' mesor- 
 chium,' or suspensory duplicature of peritoneum, is broader, and 
 permits the vessels and ducts to be readily seen as they traverse 
 it transversely. Tlic adipose appendages are branched In the 
 Mcnopome the testes arc rather broader than in the Amphiume, 
 approaching the oval shape. This is likewise the case with 
 one or both testes of the great Japan Newt (Sicboldfia or 
 Crypfohrrnichns), which are suspended by a broad mcsorchium 
 on each side of tlic aorta and narrow remnants of the Wolffian 
 bodies, between the ends of the lungs and the beginnings of the 
 kidneys. 
 
 ' XX. vol. V. p. G7, preps, iios. .'1226 3228. - lb. p. 68, preps, nos. 3230 and 3231. 
 
MALE ORGANS OF BATRACHIANS. 
 
 377 
 
 385 
 
 In most Newts the testis is divided into two lobes, fig. 387, u, 
 one, usually the larger, in advance of the other : I have observed 
 three detached lobes or testes on each side. In the Salamander 
 there may be one or two smaller lobes or accessory testes, besides 
 the two chief divisions of the gland.' 
 
 In tailless Batrachians the testes, in accordance with the shajDe 
 of the body, jDresent a full oval form, compact and undivided : they 
 are situated, as shown in the Frog, fig. 385,_/, /, on the ventral 
 side of the anterior half of the kidneys, g, g, having an entire 
 investment of peritoneum, often deei:ily or brightly coloured by 
 pigmental cells, which forms a broad and short mesorchium, 
 suspending them to the renal glands and supporting the blood- 
 vessels and efferent ducts. Processes of peritoneum, filled with 
 fat, ib. I, I, diverge from the fore part of both bodies. 
 
 In all Batrachians the testis consists of seminiferous caaca, more 
 elongated than the sperm-follicles of Fishes, shorter and straighter 
 than in higher Reptiles, having their blind ends next the capsule. 
 This consists of a fibrous or ' al- 
 bugineous ' tunic, beneath the 
 serous one : both have been re- 
 moved to show the tubuli testis 
 in Swammerdam's accurate figure, 
 fig. 386. The semen is conveyed 
 hj short transverse efferent ducts, 
 h, to a common longitudinal canal, 
 i. In the Menopome about ten 
 vasa elFerentia quit the elong- 
 ated testes and enter the common 
 canal, which extends along the an- 
 terior three-fourths of the kidney, 
 and at its fore-end is connected 
 with the ligamentous remnant of 
 the duct of the Wolffian body : it 
 is thence reflected back along the 
 outer border of the kidney, receiv- 
 ino; in its course toward the cloaca 
 the ureters, which are short 
 transverse or oblique tubes, from ten to twenty in number : the 
 urino-seminal canal, supported by a narrow fold of peritoneum, 
 forms a few slight bends, and gradually expands as it approaches its 
 termination at the back part of the cloaca. In Sieboldia maxima 
 the longitudinal canal which receives the short efferent ducts is 
 
 ' XX. vol. iv. p. 53. 
 VOL. I. P P 
 
 Cienprative organs of male Frog. COLXX. 
 
578 
 
 ANATOMY OF VERTEBRATES. 
 
 386 
 
 continued forward to the Wolffian ligament, far in advance of 
 the testes, contracting to a point : in its backward course, between 
 the testis and remnant of the Wolffian 
 gland, it receives a few short transverse 
 ducts therefrom, which come from small 
 masses of convoluted tubes, still pervious 
 to mercurial injection in the male dissected 
 by Dr. J. Van der Hoeven : continuing its 
 descent, the longitudinal duct gradually 
 exjjands, describing convolutions, and re- 
 ceiving in its course along the outer side 
 of the kidneys the excretory ducts, two or 
 ^ ,. ,„ three in number, of those glands. Each 
 
 Testis ol Frog. CCLXX. ^ ^ ' t) 
 
 urino-seminal canal expands into a simple 
 oblong reservoir, with thickened glandular coats, at the ter- 
 mination of the rectum, and communicates with the cloaca 
 by a papilliform orifice, a little in advance of the blind end of 
 the reservoir. The slender elono-ated 
 remnants of the Wolffian glands are direct 
 continuations from the fore part of the 
 kidneys. 
 
 In the Newt ( Triton tceniatus) from four 
 to five effijrent tubes, fig. 387, c, c, quit 
 each of the two chief divisions of the testis, 
 ib. a, and terminate in tlie common longi- 
 tudinal canal, ib. d, wliich extends forward 
 to the Wolffian ligament, and backward to 
 the anterior end of the kidney, ib. c : in this 
 course it sends off" about ten short trans- 
 verse branches, which, after dilating and 
 convoluting, ib. i, severally terminate in 
 the beginning and fore part of the urino- 
 seminal canal, ib. /. The small dilatation 
 and larger mass of convolutions on each of 
 the transverse branches of the longitudinal 
 duct are retentions of modified parts of the 
 Wolffian or primordial urogenital gland. The 
 urino-seminal duct, f, forms many close 
 coils, like an epididymis, as it approaches 
 the kidney : it receives directly one or two uriniferous tubes, ib. I, 
 and communicates, near its termination, with the orifices of a 
 series of modified ureters, ib. g, which receive the rest of 
 
 Mfiic orffiins. Newt. Triloi 
 tiisakitiis. (.:cc^\.XII. 
 
MALE ORGANS OF REPTILES. 
 
 579 
 
 the urine as well as the semen. Each uriniferous duct dilates 
 into a long reservoir, describing a curve external to the kidney, 
 the first or anterior being the longest, the rest successively shorter : 
 they are connected together, eight to ten in numljer, so as to 
 form, in appearance, a flattened semi-oval ' vesicula seminalis,' and 
 terminate by a short wide canal, ib. m, common to them and the 
 vas deferens, in the l)ack part of the cloaca. 
 
 In the Frog about six transverse efferent ducts, fig. 385, A, 
 enter the longitudinal one, g, extending along the inner (mesial) 
 side of the kidney, which is reflected round tlie fore end of that 
 gland to form the beginning of the urino-seminal canal, ib. i, 
 which courses along the outer (lateral) side of the kidney. This 
 canal does not describe convolutions : it enlarges as it progressively 
 receives the ureters, and suddenly expands beyond the kidney 
 into a semi-oval ' vesicula seminalis,' ib. k, the outer half of which 
 has folliculo-glandular walls, the inner half being smooth and 
 with the character of a reservoir. A short duct conveys the 
 contents of the vesicle to the back of the cloaca, ib. b ; at the 
 fore part is the orifice, c, of the allantoid bladder, e. 
 
 No Batrachlan has the intromittent organ, or a vas deferens 
 distinct from an ureter: a stage in the substitution of kidneys 
 for Wolffian bodies is hereby obviously indicated. 
 
 § 109. 3Iale Organs of Reptiles. — In the scaled Eeptiles the 
 conduits from the kidney and the 
 testes are distinct to the cloaca, and 
 terminate there on separate jjapilliB. 
 The testes, fig. 389, b, are compara- 
 tively small and comjiact : they are 
 always abdominal, with a complete 
 investment of peritoneum, fre- 
 quently coloured by pigment-cells. 
 They have a strong albugineal 
 tunic, and consist of blind semini- 
 ferous tubes, fig. 388, much longer 
 and more slender than in Batra- 
 chians, and packed up in close 
 convolute folds, in ill-defined loculi 
 of the gland. From these tubes a 
 variable number of efferent canals 
 proceed, which are inclosed in a prolongation of the tunics of the 
 testis for a brief course, and then unite into a vas deferens. 
 
 In the Ophidia the testes, fig. 357, h,h, are of a more elongate 
 
 388 
 
 TuliuU semiuLferi ; testis of Lizard. 
 
580 ANATOMY OF VERTBBKATES. 
 
 form than in other Reptiles. In the common harmless Snake 
 ( Coluber natrix) they are oblong, subcompressed, in advance of the 
 Isidneys, the right about an inch more forward than the left, 
 corresponding to the difference in the relative position of the 
 kidneys. In the Rattlesnake the testes arc more symmetrical 
 in position. The vas deferens, disposed in short undulations, 
 goes along the kidney to the cloaca, the papillas terminating near 
 the beginning of the urethral groove. The intromittent organs 
 are two in number, and consist of invertible sheaths, or long 
 narrow bags, with a highly vascular papillose lining membrane, 
 bifurcate at their blind end, to which are attached the muscles, 
 fig. 357, I, for inverting and keeping them retracted and hidden 
 in the base of the tail. By tumefaction of the vascular portions 
 of the bags, and the action of the ' constrictor basis caudte ' and 
 ' sphincter cloaca^,' they are everted. In the Rattlesnake the 
 blind end of each inverted pouch bifurcates, and the vascular 
 membrane is thickened and produced into many processes near 
 the bifurcation : when eversion with erectile tumefaction of the 
 parts takes place, each penis presents a papillose and bifurcate 
 glans, as in fig. 357, k. In Elaphis quadrilineatus the body of 
 the penis presents large retroverted papilla3, and the glans is 
 beset with small flattened wrinkled processes. 
 
 In the Slow-worm (^Anguis) the testes are situated a little 
 anterior to the dilated rectum, the right in advance of the left ; 
 the sperm-duct simulates a long epididymis by its initial convolu- 
 tions or transverse folds. The intromittent organs are invertible 
 and evertible pouches, as in Serpents, but are shorter. 
 
 In a Scinc-lizard ( Tiliqua) the right testis is more advanced 
 in position than the left. The body of the penial pouch, when 
 everted, shows transverse rugte, and the sub-bifurcate glans short 
 retroverted papillaj. In Lacerta ocellata, as in Draco volans, 
 fig. 389, the testes, b, show a similar degree of unsymmetrical 
 position. The sj)erm-ducts form, by a series of short transverse 
 folds, a long body or band, like an epididymis : but there is no 
 structure properly so called consisting of the convolutions of 
 several efferent tubes prior to their union to form the vas 
 deferens, ib. e. In the interspace of the orifices of the ureters 
 a ridge is continued backward, on each side of which is the orifice 
 of the vas deferens, whence is continued the urethral groove 
 extending along the penial sheath to the papillose blind end or 
 glans. 
 
 The peritoneal covering of the testes shows in some Lizards 
 
MALE OKGANS OF KEPTILES. 
 
 581 
 
 stellate pigment-cells : in the Chameleon they give a Mack colour 
 to the gland. 
 
 The short and outwardly extended legs of Lizards serve for 
 progression, not for support, and the animal rests with its belly 
 on the ground, as in Serpents : 
 hence the necessity not only for "S9 
 
 the internal position of the testes, 
 but for the mechanism by which 
 the intromittent organs can be 
 inverted, and safely lodged out 
 of sight, in the base of the tail, 
 when not in use. 
 
 In the Turtle {Chelone mi- 
 das) each testis is an elongate, 
 cylindrical, slightly bent body, 
 decreasing in size at the end next 
 the cloaca : the efferent tubes 
 leave it near the fore or upper 
 part of its concavity, and soon 
 join the vas deferens, which 
 forms a large and compact body 
 by numerous convolutions, situ- 
 ated between the testis and 
 kidney. Each vas deferens ter- 
 minates, with the ureter, in a 
 papilla, the sjoermatic orifice 
 being nearer the bladder. The penis is short, and is indicated, 
 in the unexcited state, chiefly by the urethral groove ; only the 
 glans and the pointed end of the fibrocartilaginous body imme- 
 diately above it jjroject from the cloacal surface, and these are 
 partly enclosed by a thick duplicature of the cloacal membrane, 
 representing a preputium : in the erection of the organ this fold 
 is everted and obliterated. 
 
 In the Emys europaa the testes, fig. 390, y, and convoluted 
 siierm-duct, ib. c, are separated from the kidneys, ib. o, by the 
 peritoneum, which, after giving an entire investment to the testes, 
 is simply reflected over the contiguous surface of the kidney : 
 an artery, I, s, runs between the two glands. The testis presents 
 a full elliptic figure : its peritoneal covering is usually stained 
 with a dark pigment : x is the spermatic artery, z the spermatic 
 vein. The sjjerm-duct opens, close to the ureter, upon a papilla, 
 fig. 391, F, at the commencement of the urethral groove, ib. G. 
 The penis, in both freshwater and land Chelonia, is longer and 
 
 Male nj-gniiB, Draco vohnis 
 
582 
 
 ANATOMY OF VERTEBRATES. 
 
 ortriii^ of Emus cuyojKca. xxxviir. 
 
 391 
 
 larger than in the marine species : it is sul^cylindrical, with an 
 expanded terminal glans, il:). I, usually ending in a point. The 
 
 urethral groove, ib. G, 
 ^ ^° extends along the mid- 
 
 dle of the dorsal surface, 
 and becomes deeper as 
 it approaches the glans : 
 in erection the tumefac- 
 tion of its borders con- 
 verts the groove into a 
 temporary canal, and it 
 then a}i2'>ears to end by 
 an orifice, k, which is 
 usually divided by a 
 jiapillary eminence. The 
 l)enis consists of two ' corpora cavernosa,' il:). ir, wliich are firm 
 fil)rous Ijodies, cohering raesially and attached to the ventral surface 
 
 of the cloaca; and of two median 
 tracts, fig. 392, 4, of a more vas- 
 cular erectile tissue, forming; the 
 walls of the mediangroove, 5, and 
 covered by a soft quasi-nracons 
 membrane. Each vascular tract 
 commences by an enlargement, 
 fig. 390, E, analogous to the bul- 
 hus iift'fhra'. The erectile tissue 
 is continued forward, thinly at 
 first, but afterwards increasing 
 in thickness, to the glans, figs. 
 391, I, and 392, which it chiefly 
 constitutes. On each side of 
 the mid-line of the penis is a 
 canal, fig. 392, /, wliich at one 
 end communicates with the 
 cavity of the peritoneum, and 
 by the other end is prolonged 
 into the substance of the glans, 
 where it terminates, blindly or 
 by a kind of reticulate sinus.' 
 The penis is provided with 
 two retractors, fig. 391, 55, 
 . .xxxvHT. fig. 392, 55', arising from the 
 
 XX. vol. iv. p. 02, ]irep. no. 2450. 
 
FEMALE ORGANS OF REPTILES. 
 
 5(53 
 
 392 
 
 
 I. 
 
 
 ■ifconeni can.ils of jionis ; 
 e"ropa'a. xxxviir. 
 
 393 
 
 ischium, and extended along the under (ventral) surface of the 
 penis to the glans. This muscle folds up the penis in retracting it 
 within the cloaca, and at the same time closes thereby the orifice 
 of the rectum, fig. 390, A, and that of the 
 allantoic bladder, ib. M. Erection is fol- 
 lowed by eversion of the cloaca, effected 
 by its ' sphincter.' The developement of 
 the jjenis bears relation to the physical 
 imjjedimcnts to coitus, caused by shape, 
 extent, and completeness of the shell, and 
 by the medium in which the act takes 
 place : thus the penis is least develojied 
 in the marine sp)ecies, with a flattened 
 carapace and incomplete plastron. The 
 glans penis is trilobate in Trioiiyx. 
 
 In the Crocodile the testes are longer 
 than in Chelonia, and rather more in 
 advance of the kidneys. The penis is single, with a dorsal groove, 
 continued forward on a slender conical jji'ocess. 
 It consists of a firm fibrous cavernous structure, 
 commencing by two crura, and becoming softer 
 towards the glans, which consist of vascular and 
 erectile tissue : this is prolonged beyond the apex 
 of the corpus cavernosum, so that two points are 
 thus seen, one above the other: these points are 
 united together on each side, and also in the middle, 
 by a vertical septvun, which divides the intersijace 
 between them into two culs-de-sac. The urethral 
 groove is continued as far as the extremity of the 
 upper jDoint, The peritoneal canals do not pene- 
 trate the cavernous structure, but lead to and op>en 
 outwardly on papilla3, situated on each side the 
 base of the penis, within the cloaca. 
 
 As Lizards are allied to Serpents by the 
 double extra-cloacal penis, so Tortoises are allied 
 to Crocodiles by the single intra-cloacal penis : 
 the structure of this organ also presents two 
 types, respectively characterising the scaled and 
 scuted groups of Repitilia. 
 
 § 110. Female Organs of Reptiles. — In the Axolotl, fig. 
 393, and Siren lacertina, the ovaries, ib. _/, are granular elongated 
 bodies, situated on each side of the root of the mesentery. They 
 
 Female or.^ans; Axoloil. 
 
584 ANATOMY OF VERTEBRATES. 
 
 consist of delicate folds of membrane, inclosing stroma studded 
 with ovisacs, of two grades of size, the larger with ova for the 
 present season, the smaller for the following one. In a Siren 
 with enlarged ovaries I observed them bearing impressions of 
 the intestinal convolutions. The oviducts, ib. i, are external to 
 the ovaria, and are attached to the sides of the spine, each by a 
 broad duplicature of peritoneum. Tliey commence anteriorly by a 
 simple slit-like aperture, with entire borders, Ji, are attenuated at 
 their commencement, and soon begin to be disposed in short parallel 
 transverse folds, in the Axolotl about twelve, in the Siren twenty, 
 in number, which gradually diminish near the cloaca, where the 
 oviducts 023en behind the rectum upon small prominences. Above 
 the kidneys, g, a linear tract, k, indicates the remnant of the 
 Wolffian body. 
 
 Tlie foregoing type of female organs is closely followed in 
 all the perennibranchiate Batrachia. In the Newt the ovaries, 
 as they expand, assume a lobulated exterior and greater relative 
 breadth, especially at their hinder end, than in the Axolotl. 
 Each oviduct begins by a simple slit-shaped aperture, Ijetween 
 the pericardium and liver, and passes backward in a wavy course, 
 which becomes irregular as it approaches the kidneys : here the 
 oviducts diverge from each other, then approximate at the medial 
 line, and again diverge, describing a regular ciu-ve outward, and 
 again converge to their cloacal terminations. 
 
 In the Salamander { Salamandra maculosa) the oviduct is more 
 definitely divided into an oviducal, or ' fallopian,' and a uterine 
 part: the former, fig. 394, a, is slender, and before impregnation 
 is convoluted to within a short distance of the cloaca, where it 
 suddenly expands into the uterine part, b : this part curves for- 
 ward and outward before terminating in tlie cloaca at c. The 
 young are developed in this expanded part of the oviduct, which 
 is much enlarged after impregnation, as in the figure. 
 
 In the tailless Batrachia the ovary, in its quiescent state, fig. 
 395, 0, has the fonu of an irregularly plicated membranous sac, 
 with thin and transparent parietes. The initial aperture of the 
 oviduct, ib. a, is situated close to the base of the heart : the tube 
 is disposed in many, usually transverse, folds or coils, before its 
 termination in the dilatable terminal part, in which the ova to be 
 impregnated and discharged in tlie same season arc accumulated, 
 as in fig. 395, b. lu tlie cloaca the following outlets are seen: — 
 in front, that of the allantoic bladder, behind it that of the 
 rectum, then the oviducal outlets, ib. c, and lastly those of the 
 ureters. 
 
FEMALE ORGANS OF REPTILES. 
 
 585 
 
 In scaled Reptiles there is a clitoris or some representative 
 trace of the intromittent orean of the other sex. 
 
 In Ophidia the ovaries, like the testes, are long, slender, and 
 disposed one, usually the right, in advance of the other, and 
 the ovisacs are developed for impregnation, in a single longitudinal 
 series in most species. The ovaries are connected with the begin- 
 ning of the oviducts by a broad fold of peritoneum. Each oviduct 
 commences by an expanded ostium, with a wide fissure, fig. 396, 
 a ; its tunics, at first delicate and transjJarent, increase in thickness 
 as the tube contracts : here its course is slightly wavy, but it soon 
 becomes straight, and, in the viviparous Serpents, expanded, ib. h : 
 
 394 
 
 395 
 
 Ovidiirts aiiQ uteri, SalamaiKlar. 
 
 0\-i(Tucts and utori, Fr 
 
 in the Rattlesnake the lining membrane of the oviduct, prior to 
 the expansion, is disposed in minute parallel longitudinal rugte. 
 The correspondence of the ostia of the oviducts, a, with the 
 ovaries in jjosition renders the left shorter than the right, and 
 in vivijDarous Serpents it usually contains fewer ova or young, as 
 in fig. 396. The cloacal tei'minations of the oviducts are in a 
 semilunar fissure, behind the orifice of the rectum. 
 
 In the Lacertians the ovaria usually manifest a slight want of 
 symmetry in position, the right being a little more advanced than 
 
586 
 
 ANATOMY OF VERTEBRATES. 
 
 the left. In the Lacerta hilineata each ovary shows about a 
 dozen visible ovisacs : the oviducts are plicated throughout their 
 course. In Agama atra there are seven or eight equally developed 
 ovisacs in each ovary. In an Iguana the left ovary exceeded the 
 
 right in size, and the imma- 
 ^^^ ture ovisacs appeared as 
 
 flattened discs overlapping 
 each other. The duplica- 
 ture of peritoneum which 
 connects the oviduct to the 
 side of the vertebrse is con- 
 tinued beyond the canal, 
 and terminates in afree edge. 
 In the ovoviviparous Lizard 
 (^Lacerta \_Zootoca\ muralis^ 
 the part of the oviduct in 
 which embryonal develope- 
 ment proceeds is very ex- 
 pansile, as in the Vipier ; in 
 the specimen figured, fig. 
 397, the right oviduct con- 
 tained three ova, ib. e, the 
 left two ova: the ovaria are 
 shown at a, the abdominal 
 aperture of the left oviduct 
 at c, the fallopian jiart of 
 the tube at d, the uterine 
 jiart at e, the terminal part 
 at f: the peritoneal fold, 
 attaching the oviduct to the 
 ovary and to the spine, is 
 marked h, the rectum g, 
 and the cloaca h. 
 
 In Chelonia the ovaries 
 are sjanmetrically disposed, 
 and placed far bade in the 
 abdomen. The female or- 
 gans of the Turtle ( Chcloiic 
 midas^, in the quiescent 
 state, show the ovaries in tlie form of a broad, flattened, variously 
 folded sul)stancc, thickly studded with innumerable ovisacs, like 
 white S])ecks : cacli ovary is attached by a peritoneal fold, ' meso- 
 nrium,'' to the sides of vertebrav, lietwccn the rectum and the 
 
 ;ins iiniiregiiaterl, VipiT. 
 
FEMALE ORGANS OF REPTILES. 
 
 587 
 
 397 
 
 Brick view of female organs inipregnateil ; 
 Zootoca. 
 
 oviducts. The oviduct commences by a simple elongated slit, 
 opening upon the free margin of the 
 mesoary ; the duct soon contracts to 
 almost capillary tenuity, and gradually 
 expands as it approaches the cloaca, 
 contracting again before its termi- 
 nation. 
 
 In the Snapper (^Chdi/dra) the ovi- 
 duct Is disjDosed in short transverse 
 folds, between the layers of a broad 
 duplicature of peritoneum, gradually 
 diminishing in width, and increasing in 
 the thickness of its parietes as it ap- 
 proaches the cloaca. The inner sur- 
 face of the initial part of the duct 
 presents a series of oblique folds, which gradually become more 
 produced and more longitudinal. Tiie oviducts terminate between 
 two diverging folds of the 
 lining membrane of the 
 cloaca, which folds gradu- 
 ally subside as they con- 
 verge to meet and termi- 
 nate in the sinus of the 
 ' glans clitoridis.' In the 
 Euroijean Freshwater Tor- 
 toise the inner surface of 
 the initial, narrow, and thin- 
 walled part of the oviduct, 
 a", 7), fig. .398, is disposed 
 in fine longitudinal folds, 
 and is lined by ciliate epi- 
 thelium : beyond these, for 
 a short space, ib. o, the walls 
 of the oviduct are glandu- 
 lar : in the exjtanded part 
 (containing an egg in the 
 example figured) the rugfe 
 of the lining membrane are 
 feeble and sinuous. Ex- 
 ternal to the mucous mem- 
 brane there is a stratum of 
 muscular fibres, by the con- 
 tractions of which the ovum is propelled along the oviduct: 
 
 Descent of tlie Gixg in the oviduct of Emys. One oviduct, 
 tlie cloaca and parts orening therein, xxxtiii. 
 
588 ANATOMY OF VERTEBRATES. 
 
 at the termination, F, where the egg-shell is secreted, the 
 membrane is vascular, and thrown into broad irregular rugae, 
 which are continued as far as its termination, n, in the cloaca. 
 The ureter, e, opens behind the oviduct, a : the allantoic bladder, 
 B, and rectiun, m, in front. 
 
 In Crocodilia the ovaria are more advanced in position, and more 
 compact in form and structure, presenting, in the unexcited state, 
 a surface granulated by minute ovisacs. The abdominal orifice of 
 the oviduct has an entire margin ; the duct maintains a more 
 uniform diameter, and sooner gets upon the edge of the supporting 
 fold of peritoneum than in Chelonia. The lining membrane of 
 the liind part of the oviduct is puckered uj) into close-set undu- 
 lating transverse rugfe : but these subside gradually toward the 
 terminal shell-forming segment, where the membrane shows minute 
 longitudinal puckerings. The outlet projects into the cloaca. 
 The clitoris arises by two crura, and is imjjressed by a longitudinal 
 groove. 
 
 Of parts in female Reptiles accessory to generation, the most 
 remarkable are the temporary tegumentary pouches on the back 
 of the female Pipa, fig. 367, B, c, which, receiving the impregnated 
 ova, retain the young until the metamorjDhosis is comjilete. In 
 Nototrema and Opisthodelpkys there is a large single pouch in 
 the middle of the back, with the entrance above the vent. It 
 serves for the recej^tion of the ova, which are hatched tlierein. 
 This pouch is peculiar to the female, which attains nearly to its 
 full size before the pouch is developed. After the reception of 
 tlie ova, it extends nearly over the whole back of the animal, 
 whilst it is shrunk and scarcely visible when the season of pro- 
 pagation has passed. 
 
.589 
 
 CHAPTER XIL 
 
 GENERATIVE TKODUCTS AND DEVELOPEMENT OF 
 H^EMATOCRYA. 
 
 The functions of the above-described Generative Organs are 
 ' semination,' ' ovulation,' ' fecundation,' and ' exclusion,' to which 
 is added, in some Ha3matocrya, that of ' foetation.' Semination, 
 or the production of sperm-cells, is peculiar to the testis ; ovula- 
 tion, or the production of germ-cells and vitellus, is peculiar to 
 the ovary : fecundation is the combined act of the male and 
 female. A part of the oviduct is usually modified to add 
 accessory parts to the ovum, or in subserviency to foetation in the 
 viviparous Htematocrya : but, in a few instances, the protective 
 and portative functions are relegated to tegumentary wombs or 
 marsujna, whichmay be developed in either sex. Exclusion of the 
 male generative product is called ' emission,' that of the female 
 generative product ' oviposition : ' but if the ovum be arrested for 
 the process of foetation, the exclusion of the foetus is then termed 
 ' birth.' Sometimes the male assists in the process of exclusion. 
 
 § 111. Semination of Hamatocrya. — The product of the testis 
 in Fishes consists of ' sperm-cells,' ' spermatoa,' and 'spermatozoa,' 
 with very scanty fluid medium of suspension : the function is 
 seasonal, and attended by 
 rapid increase of the glands. 
 This is greatest in Osseous 
 Fishes, in the testes of which, 
 at the besinning of their 
 enlargement, the sperm-cells 
 (cysts or 'mother-cells') are 
 seen, fig. 399, a, containing sri-rm-i-eiiswitusrenrntuii, Brea.u. recvi. 
 
 one or more spermatoa (' cells 
 
 of developement '), ib. b. These usually escape from the sperm-cell 
 as such, and then undergo some change of shape, through the deve- 
 lopement of the spermatozoa within them. The rupture of the 
 spennatoon gives issue to the extremely fine capillary appendage, 
 or ' tail,' the movements of which extricate the nuclear mass forming 
 the so-called ' body ' of the spermatozoon. In most Osseous 
 
 399 
 
.590 
 
 ANATOMY OF VERTEBRATES. 
 
 Fishes the spermatozoa resemble those of the Perch, fig. 400 : but 
 in some, e. g. the Loach, there is a small swelling at the insertion 
 of the appendage, as in fig. 401. In a few the ' body ' is scarcely- 
 indicated, e. g. in the river Lamprey, fig. 402 : in the Petromyzon 
 marinus the body expands into an egg-shape. 
 
 400 401 -102 
 
 Sliemixitozoa of Pcrca 
 JlavlatiUs. CC(T\'X. 
 
 Spermatozoa of Coxitis 
 fossilU. cccvi. 
 
 Spermatozoon of Petvfinnjzon 
 fliiviattlvi. CCCT'I. 
 
 The spermatozoa in the Plagiostomes are very long, with an 
 anterior cylindrical body. This is proportionally shortest in 
 ChimcBru monstvosa, and is disposed in three spiral coils : in 
 Scyllium canicula it is about half the length of the spermatozoon. 
 
 403 
 
 404 
 
 405 
 
 A. Siiermatuzoa of 
 
 B. .Spermatozoon of 
 Ttjrpcdo Narce. cccn'l. 
 
 Spermatozoa within tbe 
 
 sperm-cell {.Torpedo Narc£). 
 
 CCCVI. 
 
 is straight, and tapers at botli ends: in Sci/m)H(s nicaensis, fig. 
 403, it is spirally disposed. In Spinax acaiitliias, the Rays and 
 Torpedos, fig. 404, tlic spiral coils are rather closer, usually four 
 in number: in Haia oxijrhi/nchus the coils are more numerous, 
 but only afi^ect the anterior half of the body. 
 
 In the Plagiostomes tlie spermatoa appear as one or more nuclei 
 witliin tlie sperm-cell, like those in fig. 399, h : but they are not, 
 as in Osseous Fishes, excluded in that state. ' In each spermatoon 
 
 ' cocvi. vol. iv. p. 484. 
 
SEMINATION OF HiEMATOCRYA. 
 
 591 
 
 106 
 
 Bundle of Spf?rmatozoa 
 
 witliin the speriu-cell. 
 
 TorpcdoNarcn. cccvr. 
 
 a spermatozoon is developed, which escapes by solution of the 
 spermatoal wall into the sperm-cell, as in fig. 405.' At this stage 
 the body does not show the spiral disposition. 
 If the sperm-cell has contained numerous 
 spermatoa, the resulting spermatozoa group 
 themselves into a bundle, as in fig. 406 : their 
 bodies are contiguous and acquire the spiral form 
 before escaping from the dilated sperm-cell. 
 
 The spermatozoa are developed in most 
 Batrachiii as they are in the Plagiostomi ; a 
 sperm-cell may contain from ten to twenty 
 spermatoa, in each of which the spermatozoon 
 is developed, as in fig. 407, and through solu- 
 tion of the spermatoal membrane the sperma- 
 tozoa become free in the cavity of the sperm- 
 cell, where they usually aggregate into a bundle, pressing the sperm- 
 cell into a pear-shajie, which bixrsts at its small end, and liberates 
 either the filamentary appendages, as in the Frog, or the spiral 
 bodies,as \i\Pelohates : in either case the remains of the 
 sperm-cell continue recognisable, for some time, at the 
 non-liberated ends of the spermatozoa, as in fig. 408, n. 
 
 In the igneous Toad {Bomhinator ir/neys') the 
 spermatozoa lie confusedly within the sperm-cell : 
 the remains of the spermatoon long adhere, like a 
 pectinate appendage, to the spermatozoon. When 
 fully develoiied and liberated, the spermatozoa show 
 a long cylindrical body, attenuated towards the head, 
 which is again slightly enlarged, and more gradually shrinking 
 
 408 409 410 
 
 407 
 
 Rpeniiatonn 
 ^vith its con- 
 tained sperma- 
 tozoon, from 
 the sperm-cell 
 of a Frog, 
 cccvil. 
 
 Bundle of Spermatozoa, e, 
 escaping from the sperm- 
 cell, fl. Pdobates. ccovi. 
 
 Spermatozoa of BomhbwVjr 
 igneiis. 
 
 Part of Spermatozoon of 
 Triton. 
 
 into the filamentary tail, which is reflected and coiled in narrow 
 
 ' "Sometimes the entire nucleus becomes a coil of fibre." — Barry, cvn. 1842, pis. 
 
 V. VI. XI. 
 
592 
 
 ANATOMY OF VERTEBRATES. 
 
 spirals about the body, fig. 409. The spermatozoa of the 
 Salamander and Newt have a similar form and disposition, and the 
 coils of the reflected tail present the appearance of a crenate 
 fringe or ridge, as in fig. 410. The fully-developed spermatozoa 
 oi Pelohatesfuscus have a long spirally disposed body, gradually 
 attenuating into the filamentary appendage, fig. 411; the total 
 length is about ^^V of a line : the looser anterior end has a constant 
 vibratile motion. 
 
 In the Frog, fig. 412, the body of the spermatozoon is long, 
 cylindrical and straight, and is terminated by a straight capillary 
 
 411 
 
 412 
 
 413 
 
 ■Spermatnzi^;! rif Pilcbat'-^ 
 
 Spermatozoou of 
 Rana temporaria. 
 
 Srerniatozoa of Laccvtn 
 
 Sperm-cell, n, with 
 four spermatoa, b, 
 and their contained 
 spermatozoa, Tcs- 
 tii'lo grff:ca. CCCVII. 
 
 appendage. In the Coluber natrix the body of the spermatozoon 
 is pointed anteriorly : in Lizards it is shorter and more obtuse, 
 fig. 413. The spermatoa rarely exceed eight in number in the 
 sperm-cell, from which they usually escape prior to the full 
 developement and extrication of the spermatozoa. The same 
 is the case also in Testudo tjraca : but here the sperm-cell, 
 fig. 414, a, remains longer than in Lizards and Snakes, and 
 spermatoa, ib. h, with developed spermatozoa, may be observed 
 within it. 
 
 § 112. Ovulatum in Osseous Fishes and Bafrachiaiis. — In 
 Cyclostomous and Tcleostomous Fishes, and in Batrachians, the 
 ova are developed almost simultaneously at each breeding season : 
 whilst in Chimwroid and Plagiostomous Fishes, as in scaled 
 Keptiles, the ova are successively developed, or come to perfection 
 at longer or shorter intervals. In Osseous Fishes, however, 
 besides the ova of the present season, there arc the germs of 
 those of the next, often studding the o^■isacs of the former. In 
 the ovary of the Frog, before pairing-time, three sets of ova are 
 
OVULATION IN OSSEOUS FISHES AND BATBACIIIANS. 593 
 
 distinguished : those about to be discharged are large and dark- 
 coloured, those intended for the next season are also of uniform 
 size, but smaller, and partially coloured, and the rest are much 
 smaller, colourless, and varying in minuteness. In Plagiostomes 
 the ova are fewer in number than in the 'roe-fish.' From four 
 to fourteen ova, for example, may be developed at one season in 
 the Torpedo (T. marmorata?),^ whilst in the Herring 
 2.5,000 ova, in the Linn])-fish lo5,000 ova, in the 
 Ilolibnt, 3,500,000 ova, have been estimated to fill 
 the enlarged ovarian sacs. In a Lmnp-fish, the 
 total weight of which was 9 lbs. 8 ounces, or 66,500 
 grains, the ovaries weiglied 3 lbs. 3 ounces, or 22,300 
 grains : thus they were to the body as 1 to 3. Each osseous FiSii 
 ovum weighed one-seventh of a grain.^ uuignined. 
 
 In all Fishes the ova are formed in chambers of the ovary, 
 called ' ovisacs.'' In Osseous Fishes the ovisac consists of a 
 delicate membranous hollow sphere, fig. 415, a, lined by 
 epithelial nucleate cells, and surrounded by a tliin layer of the 
 proper tissue, or ' stroma,' b, of the ovary ; which, as it protrudes 
 with the growth of the ovum into the ovarian cavity, carries 
 before it a covering of the delicate mucous membrane lining 
 that cavity. This tunic is not present in Cyclostomes and Pla- 
 giostomes. The first-formed and essential part of the ovum 
 is the germ-cell, or ' germinal vesicle,' c, which, in Osseous 
 Fishes, shows several nuclei, macula3, or ' germ-spots,' d, but in 
 Plagiostomes only a single nucleus. Around the germ-cell there 
 accumulates a collection of minute yolk-corpuscles and albuminous 
 granules, e, with oil-like globules, /", and in some species (Carp) 
 flat angular corpuscles are added : all are suspended in a clear 
 gelatinous yolk-fluid, and are ultimately circimiscrilicd by a delicate 
 yolk-membrane, g, devoid of visible structure. The increase of 
 the ova is due chiefly to the accumulation of the yolk, and its 
 colour to that which the oil-globules acquire as the ova approach 
 matiu'ity. Finally is formed the external tunic, or ' ectosac.'' At 
 
 ' CXSXII. 
 
 ^ cccviii. p. 49. The periodical, but r.apid and enormous increase of the hard and 
 soft roes in osseous fishes admits of no rigid cinctures, no unyielding bony hoops 
 around the abdominal eaTity, such as would have resulted from a conversion of the 
 ])Ieurapophyses, by their junction with liaimapophyses and a sternum, into ' true ribs.' 
 We sec, therefore, in the fecundity of fishes — in this compensation for their limited 
 intelligence and numerous foes— the physiological condition of their free or 'floating' 
 ribs. ' xs. iv. 1838, p. 131. 
 
 ■* As the homology of this tunic is not clearly determinable either with the vitelline 
 membrane of the ovum of the Bird, or with the chorion of that of the Mammal, it \3 
 indicated by the above term in the description of the ovum of the Osseous Fish. 
 VOL. I. Q Q 
 
594 ANATOMY OF VEETEBEATES. 
 
 this period the ova in Osseous Fishes escape into the cavity of 
 the ovarium, and the ectosac then receives its villi, or appendages 
 for adhesion, in the Fishes possessing them. The ovisac remains 
 behind, and coalesces with the stroma of the ovigerous layer, to 
 form, according to Barry, a ' vesicle analogous to the Graaffian 
 vesicle of Mammals ; ' ' but the evacuated ovisacs collapse and 
 speedily disappear, after the discharge of the ova, in the shrunken 
 ovarium of Dermopteri and in the collapsed ovarian bag of Osseous 
 Fishes : they are longer recognisable iu the more comjiact and 
 solid ovaries of the Plagiostomes. 
 
 The earlier stages of the developement of the ovum within the 
 ovisac are illustrated in figs. 1 a-d (pp. 1 and 2), from Ransom's 
 observations on the Stickleback (^Gasterosteus aculeatus). In 1 A 
 the o\dsac, <?, has a diameter of -^^-^ inch : the germinal vesicle, d, 
 appears as a gelatinous spheroid, with few 'maculas' and a scarcely 
 definite wall : a slightly turbid fluid, a, fills the space between 
 the vesicle and the ovisac, from the inner siirface of which a few 
 delicate epithelial cells, b, project. In B, with a diameter of 
 — 1-^ inch, the macular have increased in number, and the germinal 
 vesicle in size : fine yolk -granules have begun to aggregate near 
 the periphery, but there is no vitelline membrane : on the exterior 
 of the ovisac are the nuclei of flattened cells. In C, with a 
 diameter of -j-^^q- inch, the macula; have become more numeroiis 
 and distinct : the yolk-granules more abundant and opake : the 
 yolk-mass is now moi-e circumscribed, and a clear space intervenes 
 between it and the ovisac. In D, with a diameter of y~ inch, 
 the germinal vesicle has more macuhc, but has ceased to grow : 
 the yolk-granules are much increased in number, and a clear 
 peripheral space indicates the beginning of the formation of the 
 external membrane, ch. 
 
 The ' roe,' or ova, of Osseous Fishes, being usually shed iu or 
 on the sediment of shores, are subject to the action of the flow of 
 streams or break of waves upon their sandy or gravelly bed, and 
 these pellucid and seemingly delicate vesicular spherules are 
 accordingly provided with a very elastic and resisting outer coat, 
 constructed on a principle analogous to that by which a tooth 
 sustains and exerts its pressure. This coat is composed of a 
 close-set series of hollow columns, set perpendicularly to the sur- 
 face, fig. 416, /i : the part of the outer surface turned into A'iew, at 
 c, shows the pores, or ' lumina,' of the tubules. Tiie yolk, a, with 
 its granules, granular and nucleated corpuscles, and oil-globides, 
 now shows its delicate structureless membrane, which is partly 
 ' cix 1st Series, p. 814. 
 
 ! ) < 
 
OVULATION IN OSSEOUS FISHES AND BATRACHIANS. 
 
 416 
 
 detached from the cctosac, as it becomes after impregnation. 
 Against the ectosac, h, are closely applied the flattened epithelial 
 cells, (/, which line the ovisac and probably contribute to the 
 growth or thickening of the external membrane. lu the Perch 
 the ectosaccal tubes have a 
 slightly spiral course, and 
 the peripheral end of each 
 is set in a small hexagonal 
 prism : this outer stratum 
 serves to connect the ex- 
 cluded ova in groups. The 
 ova of the Stickleback have 
 villi developed for this pur- 
 pose from one part of the 
 exterior, figs. 417 and 421. 
 
 The structure of the outer 
 coat of the ova of Fishes re- 
 lates not only to the accidents 
 of appulse, but to the act of 
 imj^regnation, which takes 
 place after exclusion and 
 exposure. Besides the pores, 
 or tubular orifices, of the 
 
 ectosac, there has been observed, in the ova of G aster osteus,^ 
 Sulmo^ Blennius,^ Esox, Trigla,^ a foramen homologous with the 
 micropyle of the invertebrate ovum. Dr. Ransom, its discoverer, 
 has observed the passage of the sj^ermatozoa through this foramen 
 into the ovum. Fig. 417, A, gives a magnified view of a portion 
 of the surface of a mature ovarian ovum of the Stickleback, 
 showing the funuel-shaped depression leading to the aperture of 
 the micropyle, with a few of the flask-shaped villi of the outer 
 membrane : B represents diagrammatically a section of the ectosac 
 and funnel of the micropyle : C is a portion of the membrane 
 at the apex of the funnel, with the aperture of the microj)ylu 
 jiressed flat, of the Trout's egg, magnified 500 diameters : d is 
 a similar portion, magnified 1,000 diameters, showing the 'lumen' 
 of the ectosaccal tubules, and the hexagonal division of the spaces 
 between them.^ 
 
 In the Batrachia (Frog) a greater proportion of the ovarian ova 
 show different states of developement, previous to sexual pairing, 
 than in Osseous Fishes, although all those destined for impreg- 
 
 ' OLxxvi. - cccvni. and cccix;. p- (101). ' cxxx. pt. ii. p. 4. 
 
 * cccx p. 37G, fi^'. 6. * cccviii. p. (101), 
 
 QQ2 
 
 Part o£ Uic ovarian ovum of tbo Salmon, cccvui, 
 
596 
 
 ANATOMY OF VERTEBRATES. 
 
 nation at the same season are simultaneously ripened. As soon 
 as tlie germ-cell is recognisable, it is contained in a delicate ovisac, 
 and speedily exhibits several nuclei, or maculaj, fig. 418, B, ^ : it is 
 
 417 
 
 418 
 
 i: 
 
 
 » Q o o « *x>y-c^- 
 
 , a o ©XW'X^ •.■.■--.-.-.--■.-.;-.-.■ 
 
 » e V^i^JEw otoXSQ' •.•■■■.■•- ^^ ■ 
 o o o ® © sjoja 
 
 ID Q O O O «X®X 
 
 * » ® » •^'5Y&X'a»~ 
 
 Jllcvupjio of Llic ovum in Osseous I'^ish. cccvTil. liatnichian ovum in liio o\isar. y^^.lli iiK'ii diam. cccTlil 
 
 surrounded by a clear albuminous yolk fluid, vj), which gradually 
 becomes opake, and about which the yolk-granules accumulate, 
 among which is the opake or dark aggregate peculiar to Batraclna, 
 and called the yolk-nucleus, ib. vn. This body disappears as the 
 yolk-mass ajjproachcs its mature bulk, and acquires the larger 
 quadrilateral or quadrangular particles. The smooth and well- 
 
OVULATION IN CARTILAGINOUS FISHES. 5D7 
 
 defined periphery of the yolk-mass is in close contact with the 
 layer of nucleated cells lining the ovisac, ib. s : and at a later 
 stage of developement, when the jiigment-cells have been applied 
 to the surface of the germinal portion of the yolk, a distinct 
 external membrane is present. In the month of February the 
 maculaj of the germ-cell multiply and form aggregates, with 
 envelopes, representing cells with a granular nucleus, which 
 nucleus finally disappears, and the so-rendered clear cells escape 
 by solution of the coat of the germ-cell into the surrounding 
 yolk-substance, this rupture or disappearance of the germ-cell 
 preceding, as in some Osseous Fishes, the reception of the matter 
 of the spermatozoon. The ripe ovarian ovum of the Frog (^Rana 
 temporaria') is from -^^ to jV inch diameter. The outer membrane 
 (ectosac) of the ovum, after quitting the ovarium, is surrounded 
 and defended, before exclusion, by the gelatinous secretion of the 
 oviduct : it does not show the structure of that of the Fish. If 
 a'micropyle' exist prior to impregnation, as Prevost and Dumas 
 record,' it has escaped the express research of some later observers.^ 
 The full-sized ovum of the oviduct retains its spherical form, fig. 
 420, A. In the Newts the ectosac of the ovum is elliptical, 
 fig. 420, B, and a clear albuminous fluid intervenes between it 
 and the yolk. In Triton cristatus the yolk is bright yellow : in 
 Lissotriton punctatus it is ash-coloured : in the Land-Salamander 
 it is orange. In tailless Batraclda the colour is limited to the 
 surface of the yolk, which is grey beneath : in the Toad the 
 pigment is almost black, in the Frog it is dark brown : in both 
 it covers all the surface, save one small round spot ; in Ali/tes 
 obstetricans it covers half the yolk : it stains vertically frona -J- 
 to -j-V of ^^ diameter of the yolk : in all it defines the germinal 
 part of the yolk. 
 
 § 113. Ovulation in Cartilaginous Fishes and Scaled RejMes. — 
 If the generative organs and jDroducts were exclusively to govern 
 the classification of Animals, the Chima3roids and Plagiostomes 
 would be separated from other Anallantoids, and be combined 
 with scaled Reptiles, with which they agree in the type and 
 grade of their generative organs, and in the more important 
 characters of the structure of the ovum. Its essential con- 
 stituent, the germ-cell, has a single nucleus, and it becomes 
 surrounded, while in the circumscribed ovary, with a large mass 
 of vitelline substance, consisting in great part of oily and 
 albuminous matter, inclosed in delicate vesicles. Besides these, 
 there is a small proportion of the yolk, consisting of minute 
 ' In the centre of the brown hemisphere, ccosi. p. 104. ^ cccxiii. 
 
598 
 
 ANATOMY OF VERTEBRATES. 
 
 granules and granular cor]nxscles, more immediately surrounding 
 the germ-cell ; which, moving from the centre to the periphery 
 of the yolk, there forms the ' cicatricula,' the exclusive seat of 
 subsequent developement. In the cartilaginous Fishes the im- 
 pregnating influence is received before the ovum quits the ovarium, 
 
 or shortly after. In the 
 ^'9 egg's passage through the 
 
 oviduct the yolk is sur- 
 rounded by fluid albumen, 
 and finally by a case of 
 the denser albuminous 
 secretion of the nida- 
 mental gland. The form 
 of the egg when thus 
 invested is remarkable, 
 and different in diflerent 
 genera. 
 
 In the Skate, fig. 419, 
 A, it is an oblong quad- 
 rangular flattened case, 
 with the angles prodixced 
 forward and backward, 
 like those of a butcher's 
 tray. In the Spotted 
 Dog-fish, ib. B, the ova 
 are also quadrangular, 
 but longer, and the angles 
 are extended into filamen- 
 tary tendrils, which attach themselves to floating bodies, and thus 
 keep the ovum near the surface, where the influence of solar heat 
 and light is greatest. In Ahtidanus, vfith a similarly shaped cirri- 
 gerous egg, the anterior and posterior surfaces are crossed by 
 about twenty parallel transverse ridges.' In Cestracion the egg 
 is pyriform, with a broad ridge, or plate, wound edge-wise round 
 it in five spiral volutions. The eggs of Callorhpichus resemble a 
 broad-leaved fucus, in the form of a long depressed ellipse, with 
 a plicated and fringed margin.^ The ovum of the Myxinc 
 (jluthwsa, fig. 419, C, is a long ellipse, terminated at each end by 
 a tassel of slender tubular filaments, twenty-five to thirty in 
 number, expanding at their free end (opposite d) into a funnel- 
 shaped process.' 
 
 ' XX. vol. T. p. 70, preps, nos. 3245, 3246. 
 
 '^ XX. vol. V. p. 69, prcjis, nos. 3235, A. iind is. » cocviir. p. 51. 
 
 External form of ova of Oviparous CartCaginous Fisbeg. 
 
 CCCVIII. 
 
FECUNDATION IN FISHES. 
 
 5!j9 
 
 420 
 
 The structure and foi-mation of the ovum in scaled and scuted 
 Reptiles are essentially the same as in the cartilaginous Fishes. 
 Tlie germ-cell, with a single nucleus, is first formed in a delicate 
 OA'isac imbedded in the stroma of a solid ovarium. A yolk of 
 large size is added, of which 
 the greater jDart consists of 
 large non-nucleated oil-vesi- 
 cles, and the smaller part 
 of the vitelline granules and 
 cells with a granulated nu- 
 cleus ; these originally sur- 
 round the germ-cell, then 
 indicate its tract from the 
 centre to the periphery of 
 the yolk, and form with the 
 matter of the germ-cell the 
 cicatricula, or blastoderm. 
 This occupies a much smaller 
 extent of the surface of the 
 yolk than in the small- 
 yolked eo;2;s of Batrachians 
 and Osseous Fishes, and 
 segmentation is limited 
 thereto, the rest of the yolk being nutritive. The ovum, con- 
 sisting of the above parts, inclosed in a vitelline membrane, quits 
 the ovary and is received into the oviduct : here it accjuires a 
 certain proportion of soft albumen, upon which is condensed a 
 thin tough layer, called ' chorion.' In the ovo-viviparous Snakes 
 (^Vipcra) and Lizards (^Zootoca) this membrane is thin: in the 
 oviparous species it acquires a crust of calcareous matter before 
 exclusion. This crust is very thin and scanty in most Serpents 
 and Lizards, but is thicker in Cheloiiia and Crocodilia, forming a 
 shell. The egg is spherical in some Chclonia, spheroidal in others, 
 fig. 420, r, ellijitical in Emys, fig. 399 : in the Crocodiles the egg 
 is a long ellipse, fig. 420, e. In no reptile does it show the 
 oval form which prevails in Birds, ib. C and D. 
 
 § 114. Fecundation in Fishes. — Certain changes and peculiar 
 phenomena attend the increase of size of the soft and hard roes 
 during these primary processes of generation. The colours of 
 the fish become more marked and brilliant: the different sexes 
 are often distinguished by peculiar tints, as the male Stickleback 
 by his bright red throat, for example. The cutaneous crest on 
 the head is developed in Salarias and many other Blennioids, e.g.. 
 
 Estcrn;il forms of different eggs of Reptiles and Birds. 
 
 COCViH. 
 
GOO ANATOMY OF VERTEBRATES. 
 
 in the male viviparous Blenny, wliicli, by eversion of the 
 terminations of the sperm-canals, impregnates internally. The 
 claspers in the male Plagiostomes then acquire their full deve- 
 lopement and force: the basal glands in those of the Rays 
 enlaroje. In Osseous Fishes the whole abdomen swells, and the 
 viscera are displaced by the prodigious bulk of the germinal and 
 seminal matter. 
 
 As the period of ' fecundation ' approaches, the female osseous 
 fish seeks a favourable situation for depositing her spawn, usually 
 in shoal water, where it can be most influenced by solar warmth 
 and light. The marine Herring, Mackerel, and PUchard approach 
 the shore in shoals : the fluviatile Salmon quits the estuary to 
 ascend the river, overcoming, with astonishing perseverance and 
 force, the rapids or other mechanical difficulties ' that impede its 
 migration to the shallow sources, w'hither the sexual instinct 
 imj)els it as the fit place for oviposition. The female fish is 
 closely pursued by the male, sometimes by two : in the Capelin 
 (^Mallotus) these swim on each side of her, aiding by their 
 pressure in the expulsion of the spawn, and at the same time 
 impregnating it by diffusing over it the fluid of the milt : thus 
 absorbed in the sexual passion, they have been seen, on the 
 shores of Newfoundland, to rush ou land in their sjiasmodic 
 course over the shallows, which they strew with the fecundated 
 ova. In some genera violent combats take place between the males. 
 Mr. Shaw,^ a close observer of the habits and developement of 
 the Salmon, states: — ' On January 10, 18.36, I observed a female 
 Salmon of about 16 lbs., and two males of at least 25 lbs., engaged 
 in depositing their spawn. The two males kept up an incessant 
 conflict during the whole day for possession of the .female, and, 
 in the course of their struggles, frequently drove each other 
 almost ashore, and were repeatedly on the siirface, displaying 
 their dorsal fins and lashing the water with their tails. The 
 female throws herself at intervals of a few minutes upon her side, 
 and, while in that position, by the rapid action of her tail, she 
 digs a receptacle for her ova, a portion of which she deposits, 
 and, again turning upon her side, she coders it up by the renewed 
 action of the tail, thus alternately digging, depositing, and covering 
 tlie ova, until the process is completed by the laying of the whole 
 mass, an operation which generally occupies three or four days.' 
 
 In tlie ovo-viviparous Osseous Fishes the well-developed cloacal 
 papilla, in which the sperm-ducts terminate, doubtless serves to 
 
 ' Save those erected by stupid ciiiiidity to effectually bar the s.almon's progress. 
 ^ cxxiv. p. 551. 
 
FECUNDATION IN FISHES. 
 
 601 
 
 421 
 
 ensure intromission. The superadded claspers in the male Plagio- 
 stomes lend more effectual aid in the act of internal impregnation, 
 for in those species that are oviparous the ova are impregnated and 
 covered by a nidamental coat, or ' shell,' prior to exclusion. 
 
 In Osseous Fishes, where exclusion usually precedes impregna- 
 tion, the first change observed in the 
 ovum after entering the water is its im- 
 bibition, causing a separation of the outer 
 tunic from that of the yolk, fig. 421, A. 
 Dr. Ransom connects the phenomenon 
 with the passage of the spermatozoa 
 through the micropyle, which he ob- 
 served in his experiments on the ova 
 of the Stickleljack.^ In these ova, 
 about three minutes after impregnation, 
 the funnel of the micropyle, which had 
 descended into a depression on the 
 upper surface of the germinal part, fig. 
 421, B, began to be withdrawn by the 
 recession of the external memlu'ane from 
 the surface of the yolk and the forma- 
 tion of the intervening clear space. 
 About ten minutes after impregnation 
 the clear respiratory space is more 
 marked : the germinal layer, with a few 
 large oil-globules, is distinguishable by 
 its opacity from the clearer part of 
 the yolk, ib. a. In the Perch it presents a greyish, in the Pike 
 a yellowish, tint. The germinal vesicle, which had previously 
 become filled and obscured by granules and granular corpuscles, 
 breaks up to form, or contribute to form, the germinal layer, 
 which now becomes more circumscribed and distinct : the process 
 of segmentation, which follows that of impregnation, is limited 
 to the germinal portion of the yolk, with which it is co-extensive. 
 In the Perch the ova assume a greenish tint shortly after imjweo-- 
 nation. There is reason to suppose that impregnation of the 
 eggs of both Sharks and Hays takes place in the ovarium or the 
 contiguous part of the oviduct, for they become enveloped in the 
 dense albuminous secretion of the nidamental glands after bavin"- 
 passed that part, which covering would prevent the subsequent 
 influence of the spermatozoa. 
 
 § 115. Develope7ne7it of Fishes. — The germinal layer consists of 
 ' Cited in cccvni. p. 98. 
 
 Ovum of tlie Oastcrnstens at the timo 
 of imiircguatiuu. 
 
602 ANATOMY OF VERTEBRATES. 
 
 a minutely granular matter, with clear corpuscles, vitelline cells, 
 and oil-particles : it projects from the surface of the yolk, fig. 
 422, a, and becomes transparent : the vitelline and oil-globules, 
 aggregating at its base, buoy it up. The formation of two 
 hyaline centres is followed by the cleavage of the germinal layer 
 into two equal parts, ib. h, and these are next cleft at right angles 
 into four, ib. c. In the Tench this occurred about half an hour 
 after the rising of the germ-layer. Each of the four divisions 
 undergoes subdivision, but irregularly, ib. d : further sub- 
 division gives the surface a mulberry character, ib. e, and 
 
 finally the parts are broken up to 
 Such a dcffree of minuteness that 
 the surface is again made smooth. 
 The hyaline principle, which is the 
 centre and cause of these successive 
 divisions, is thus diffused through, 
 or assimilated by, the whole germinal 
 First steps In the devoinpemont of a Tench. layer, which has thereby become 
 °^''^'' the ' germ-mass.' It now subsides 
 
 to the form of a circular disc, separated by a layer of oil-globules 
 from the yolk. The process occupies about three days in the 
 Salmon, and from fifteen to twenty hours in the Pike : ' before it 
 is completed in the latter fish the yolk rotates within the ectosac.^ 
 A cavity is formed in the centre of the germ-mass, which, as 
 the mass subsides and extends over the yolk, is obliterated by the 
 contact of the outer and inner layers. It clothes half the yolk 
 by about the end of the third day, and when it covers two-thirds 
 or more, the rotation ceases. The margin of the germ-mass 
 encompassing the uninclosed part of the yolk is tumid. No 
 rotation takes place in the ovum of the Perch,^ and the germ- 
 mass incloses the whole vitellus, as in the Cyprinoids. 
 
 The jjeripheral layer in the Pike begins to rise from the tumid 
 margin of the germ-mass, as from a base, and extends, contracting, 
 towards the opposite pole : this tract of germ-substance is the ' em- 
 liryonal ' or ' primitive trace.' It next sinks in along the median line, 
 forming a furrow, which stops short of the two ends of the trace : 
 that end opposite the point from which the germ began, swells into 
 the head, and the median furrow expands ujwn it ; the cephalic 
 borders are next united by a thin layer of eiiithclial cells above the 
 furrow, converting it into a cavity or ventricle, and the myelonal 
 furrow is similarly covered by a layer, uniting the lateral columns. 
 The embryonal trace liecomes longer, narrower, and beuds round 
 
 ' ccoxix. p. 486. 2 cxxxi. ' Ib. p. 512. 
 
DEVELOPEMENT OF FISHES. 603 
 
 half the vitellus, fig. 422,/. A layer of epithelial cells forms a 
 net-work over the whole dorsal (upper) surface of the embryo. 
 In the germ-mass broadening from the primitive trace oblique 
 strlre ajjpear, indicating its division into segments : these begin- 
 nings of aponeurotic septa probably accompany and support ner- 
 vous productions from the myelonal columns. 
 
 Two transverse constrictions begin to divide the cephalic 
 enlargement into three lobes, the second and third of which 
 expand into vesicles : an accumulation of cells at the sides of the 
 middle expansion ajipears to add greatly to its breadth, but forms 
 the basis of the eyes. A similar accumulation of darkish granular 
 matter on each side of the third enlargement lays the foundation 
 of the acoustic vesicles. 
 
 The differentiation and confluence of the cell-constituents of 
 the primitive trace have previously led to the formation of a 
 pair of albuminous chords along the sides of the median furrow, 
 forming the myelon proper ; the cells exterior to and above them 
 are converted into muscle and fibrous septa, whilst beneath the 
 columns is the jelly-filled cylinder, with a transversely striate 
 sheath, pointed at both ends, forming the ' notocliord,' fig. 423, cA : 
 its anterior point passes a little 
 in advance of the acoustic vesi- 
 cles, ib. f. Beneath the note- 
 chord and surrounding blastema 
 is stretched the vegetative or 
 mucous layer of cells, in contact 
 with the yolk. Both head and 
 tail of the now cylindrical em- 
 bryo are liberated from the sur- Head or embryo pikc. cccxi.. 
 face of the yolk. A fold of 
 
 blastema, reflected from the under part of the head, sinks, like a 
 pouch, ib. I, into the yolk, and soon includes the rudiment of the 
 heart, like a bent cord, ib. k, which begins to oscillate about the 
 seventh day. From the mid-line of the inferior surface of the 
 embryo, or its mucous layer, two longitudinal plates descend, 
 diverging into the yolk-substance, and form the primitive intes- 
 tinal groove. 
 
 The ophthalmic vesicle, ib. g, elongates and curves outward, until 
 the two ends almost come into contact : between those ends and 
 beneath the delicate tegumentary layer connecting them the 
 crystalline lens, ib. h, is formed. About the same time, the 
 otolites appear in the acoustic vesicles, ib. f, and these have now 
 acquired a cartilaginous case. The cerebral lobes, p, begin to 
 
 423 
 
604 ANATOMY OF VERTEBRATES. 
 
 be formed by small folds, rising laterally, and overlapping the 
 fore-part of the second enlargement, ib. O, which has exjianded to 
 greater breadth. The olfactory cavities appear as small cutaneous 
 depressions or follicles, ib. r. 
 
 The two myelonal columns, expanding between the ear-sacs, 
 and receding so as to show the notochord beneath, bend upward 
 and inward, and unite, to be continued into the back part of 
 the optic lobes, thus commencing the cerebellar bridge, ib. C, 
 across the epencephalic ventricle. The encei:)halic vacuities have 
 begun to be filled by the granular basis of the cerebral fibre or 
 substance. The intestinal groove begins to be converted into a 
 canal at its two ends, which are closed : beneath the anterior end, 
 and behind the heart, progressively accumulates the cellular basis 
 of the liver. The free caudal end of the embryo grows rapidly ; 
 muscular heavings of the body occur before the heart beats, and 
 pulsation begins before the cavity is visible in the cell-mass. 
 The heart appears first as a cylinder of cells, changing in its 
 movements from a straight to a bent fissure, fig. 423, k, and jiro- 
 pclling only colourless jilasma ; a canal is next seen, along which 
 the blood-particles traverse the cylinder, from the yolk below to 
 the head above : these blood-particles are sjjherical or polyhedral, 
 coloiu-lcss and homogeneous, and are more minute than the 
 germinal cells. The cardiac cylinder is next divided by a con- 
 striction into an auricular and a ventricular compartment. The 
 blood, in which the discs soon acquire increased size and a pale 
 red colour,^ is propelled from the ventricle by channels encom- 
 passing the fore part of the alimentary canal into a dorsal trunk, 
 which, after a short course, bends down, and returns as a vein to 
 the vitellus, over which the blood at first courses in undeterminato 
 streams, but which converge to enter the auricular division of 
 the heart. As the abdominal cavity, intestine, and body elongate, 
 a succession of such vertical loops is formed, receding from the 
 first, with corresponding elongation of the aorta and 2:)ostcaval, or 
 cntero-vitelline, vein. The aorta soon sends off pairs of trans- 
 verse loops, corresponding with the vertebral segments, the 
 returning channels of which ojien into or constitute the cardinal 
 vein. The embryo now encompasses the yolk, as in fig. 422, q. 
 
 In the eye the crystalline, developed from the epithelial laver 
 uniting the two ends of the bent ophthalmic vesicles, sinks deeper 
 
 ' Lcrebouillct observed in embrvo-fishes raised in tanks from arfifieial iiupro'^na- 
 tion, that tho bloud-paitick's were later in formation, and more scantj' than in the 
 embryos derived from tho free streams : a remark worthy the attention of the breeder 
 offish, ccoxix. 580. 
 
DEVELOPEMENT OF FISHES. 605 
 
 as those ends approximate each other. The choroid appears in tlie 
 form of an inner cyhnder, applied to the snnlv back-part of the 
 lens, and its extremities, approximating and uniting, jn-odnce the 
 choroidal fissure : the eye is now the most conspicuous part of 
 the embryo, especially in the ovum of the Salmoiddm, and is a 
 useful sign to the pisciculturist of the impregnation and vitality 
 of the egg. 
 
 The hinder cascal part of the intestine rapidly elongates, fi-om 
 behind forward, the yolk advancing in jjosition. The anterior 
 ciccum also elongates from Ijefore backward : the open part of 
 the intestine, which communicates with the vitelline sac, becomes 
 in the same measure constricted. 
 
 When the two divisions of the heart arc bent upon one another, 
 the liver shows several small cfcca, which rapidly multijdy, and 
 become op)ake : it is situated, fig. 424, I, behind the heart and 
 above the yolk, now becoming reduced to a globule of oil, which 
 is long retained in the young Perch. 
 
 The primordial kidneys appear as two p)arallel rows of rounded 
 cells, above the liver, their ducts uniting to form a tulje, which 
 runs above the intestine, and dilates above the hinder caical end 
 of the gut. 
 
 The pectoral fins begin to bud forth : the protocercal mem- 
 branous fin-fold commences at the middle of the back, borders 
 the tail, and returns along the belly as far as the vitellus. Large 
 pigment-cells arc spread over the yolk-sac, which become stel- 
 late. IMuscular fibres appear in the myocommata as transparent 
 cylinders, without the transverse stria; : they move the tail 
 vigorously, and cause the embryo and its yolk-sac, in the Perch, 
 to rotate in the egg. This has increased in size by imbibition 
 of water, and its external coat is thinned by stretching; it now 
 gives way, and the embryo is extricated, about the tenth day in 
 the Pike and the twelfth day in the Perch. The size and shape of 
 the yolk-sac, fig. 424, c, vary in clltferent kinds of Osseous Fishes.' 
 
 The vitelline vascular network, ib. d, is the first respiratory organ 
 of the fish : its divisions carry the blood-discs only in single files. 
 The outer tunic covering the vascular one permits the interchange 
 of gases between the blood and the water outside. This respired 
 or arterial blood is mixed with the venous blood which is returned 
 to the heart by the cardinal veins, and is distributed, so mixed, 
 by the arteries. The vitelline capillaries gi-adually exchange a 
 reticulate for a parallel longitudinal course, with diminution of 
 
 ' In artificial liatching, young trout, and especially char, show a diflBeulty iu extri- 
 cating the yolk-sac, and many perish from inability to liberate themselyes. 
 
60G 
 
 ANATOMY OF VERTEBEATES. 
 
 numbers and increase of size : and as the fitness of the vascular 
 surface for respiration decreases, the developement of the gills 
 progresses. The branchial arches appear, three in quick succes- 
 sion, from behind forward, and branchial tubercles bud from them 
 in like order. The mouth and the branchial slits being now 
 opened, the arches move rythmically, so as to produce branchial 
 currents : the blood is yellowish, and the discs begin to show the 
 flat oval shape. As the vitellicle decreases, its circulation is 
 changed, or merged into the portal hepatic system ; and now that 
 through the branchial buds begins. The change of the vitelline 
 for the branchial circulation relates, in a general way, to that 
 from the confined to the free state of the young fish: but no 
 such alterations of the circulating or breathing systems attend 
 the escape of the fisli from the egg as mark extrication in the 
 Reptile and Bird, or birth in the Mammal. Vitelline respiration, 
 carried on in ovo by means of the imbibed water between the outer 
 and vitelline tunics, continues to operate for a longer or shorter 
 jieriod after the little fish is free, according to the species, and also 
 according to the indi'^'idual constitution in the same species. 
 
 Each branchial bud is at first a solid cell-mass, and is excavated 
 to receive the blood with blood-discs in single file : secondary 
 tubercles bud forth at right angles to the primary ones, through 
 which similar blood currents flow : the primary buds become the 
 stems of the leaflets into which the secondary ones are developed, 
 and the cartilaginous axis of the arch and stems next appears. 
 The pseudo-branchia also shows itself behind the eye, in the form 
 of flattened elongated folds, through which the blood courses at 
 first in a few vascular loops. In the Anabas, and probably other 
 Labyrinthibranchs, the 
 epibranchial reservoir, 
 fig. 325, retains a com- 
 parative degree of sim- 
 plicity until the fish is 
 full-grown. 
 
 The intestinal canal, 
 after the formation of the 
 mouth and vent, retains 
 its uniform diameter, ex- 
 cept where it is jiartly 
 surrounded by a mass of 
 the cells, in which the 
 
 liver, fig. 424, /, is developed : the gall-bladder appears to be a ca^cal 
 piroduction from the intestine, independently of the liver. Opposite 
 
 424 
 
 Vore Part of enibvio Os; 
 
DEVELOPEMENT OF EISHES. 607 
 
 the liver a tubercle of cells buds out, which elongates, enlarges, 
 and then acquires a cavity : this is the beginning of the air- 
 bladder, ib. s. Many Fishes retain the tubular connection with 
 the alimentary canal, and those which ultimately lose the ' ductus 
 pncumaticus ' usually retain for a longer or shorter period that 
 evidence of the place and mode of origin of the air-bladder. 
 The posterior compartment of the air-bladder is first developed 
 in the Cyprinoids, which accounts for the connection of the 
 air-duct with that part : the whole posterior compartment disap- 
 pears with the duct in the Loach. In the Herring the primitive 
 place of its connection with the alimentary canal is retained. 
 
 The ureter, q, developed from the intestine before the embryo 
 quits the ovum, communicates with the extremities of the trans- 
 verse parallel tubuli, f, formed by confluence of primitive cells in 
 the renal blastema. The cardinal veins traverse or groove the 
 renal organs, as they do the Wolflfian bodies in the embryos of 
 higher Vertebrates \ and this primitive relation of the vascular to 
 the renal system is not changed in Fishes by the substitution of 
 true kidneys for the primordial renal organs. In many Fishes a 
 cajcal process is developed from the fore, or ventral, surface of 
 the termination of the intestine, and extends forward, as a i 
 
 bladder : its growth is arrested at various stajres in different I 
 
 . . . . . 
 
 sjiecies, and it is termed 'urinary bladder,' but it is the homologue l| 
 
 or besinnino; of the allantois. 
 
 The intestinal wall is completed, and the fissure behind the 
 liver closed, by the time the yolk is consumed. The vent opens, 
 in the Pike, on the fourth day after extrication : in the Perch 
 coloured i^articles added to the water were seen to traverse the 
 intestine, and escaj^e ' per anum ' on the sixth day.' Previously 
 the mucous walls of the gut are in contact, although the peri- 
 staltic movements are active. About the eighth day the j^resence 
 of bile is indicated by the colour of the gall-bladder and ducts. The 
 stomach expands, and divides the oesophagus from the intestine. 
 
 After extrication the eye loses the choroidal fissure : the iris ac- 
 quires the silvery pigment. The ear-sacs assume a triangular form : 
 the two otolites grow unequally by additional calcareous layers. 
 
 The primary enlargements of the encephalon are connected, 
 respectively, with the acoustic, optic, and olfactory nerves : the 
 anterior one, fig. 424, P, becomes chvided into prosencephalon and 
 rhinencei^halon ; the second, O, ra^ndly gains superior bulk in 
 connection with the large eyeballs, and its pineal and jiituitary 
 appendages appear as vascular membranous canals. The cere- 
 
 ' CCCXIX. p. 483. 
 
 \m 
 
608 ANATOMY OF VERTEBRATES. 
 
 bellum is the last part which is formed by reflection upon the 
 upper and fore part of the epencephalon, A. 
 
 The mode of developement of the cartilaginous cranium is 
 described at pp. 71-74. In the Perch a layer of cartilage-cells 
 beneath the fore-part of the head is continued down on each side 
 into the front border of the inferior transverse mouth : a second 
 cartilaginous arch extends from the side of the cranium, behind 
 the eyes, and supports the hinder and more j^rominent border of 
 the mouth : a delicate cartilaginous filament from each side of the 
 occiput seeks an attachment with the basis of the rapidly vibrating 
 pectoral fin, and proceeds to curve beneath the cardiac chamber. 
 Between this basis of the scapular arch and the mandibular arch 
 are discernible several smaller arches, beneath the large ear-sacs, 
 of which three are conspicuous as ' branchial arches,' but the 
 foremost acquires the most decided gristly structure, and is 
 proximally attached to the origins of the mandibular arch : it 
 becomes the hyoid arch. The first and second inferior or hasmal 
 arches, called ' maxillary ' and ' mandibular,' rotate forward upon 
 their piers, or points of attachment, and from being vertical 
 become more and more oblique, until the opening of the mouth is 
 brought to the fore-part of the head, and becomes terminal in 
 position : the third, or hyoid, arch, in a minor degree, takes the 
 same forward inclination : the arches between this and tlie 
 scapular one are monopolised by the branchial organs, which are 
 transitory or undeveloped in the higher Hasmatocrya. Ossifica- 
 tion in the proto-cranial cartilage begins in the four pairs of 
 neurapophyses, answering to the four hremal arches below, and to 
 the four primary divisions of the encephalon : the four vertebral 
 segments composing the head are as instructively illustrated by 
 the develoj)ement of the skull as by that of the brain. 
 
 The scales are formed late in all Osseous Fishes : their inteo-u- 
 mcnts remain smooth and lubi'icous, as in the Dermopteri, some 
 time after the disappearance of the viteUus. 
 
 After tlie formation of the embryonal, continuous fin-fold 
 blastema accumulates in its dorsal, anal, and caudal regions ; 
 and, as the rays are here formed, the intervening membrane 
 begins to be absorbed. Tlie fin-rays (dcrmo-ueurals and -hifmals) 
 connnencc near the free border, and elongate by approacliino- the 
 neural spines : they there meet the intcr-neurals and -hxmals, 
 whlcli grow in the opposite direction. During tlic formation of 
 the caudal rays, the end of the notocliord, in the Pike, Perch 
 and Salmon, bends upward, or 'neurad:' the heterocercal tvpc 
 succeeds tlic protocovcal one, and is followed by tlic resumption 
 of synnnetry under the more advanced ' homocercal ' condition. 
 
DEVELOPEMENT OE FISHES. 
 
 609 
 
 TTcll as the internal 
 
 425 
 
 This, as a rule, is the form antl structure acquired by the tail in 
 existing Teleostomous Fishes: but the 'heterocercal ' modification 
 does not intervene between the proto- and homo-cereal ones in 
 the GadidcR. 
 
 The pectoral fins are developed usually before extrication, and 
 are often of large relative size : in this respect, as well as in the 
 inferior position of the mouth, in the unsymmetrical form of the 
 tail, in the gristly skeleton, and uncovered gill-slits, the embryo 
 Salmon, Pike, Perch, &c., manifest transitory characters which 
 are permanent in Sharks. 
 
 The singular productions of the rostrum in most Plagiostomes, 
 like the elongation of the jaws in osseous species, are later 
 phenomena of developement. It is interesting to find the broad, 
 depressed, obtuse embryonic form of head common to many of the 
 Fishes of the old red-sandstone. M. Agassiz thus accounts for the 
 extreme rarity of the Ichthyolites of this formation presenting a 
 profile view of the head : it lies in most cases upon the upper or 
 the under surface of the body. 
 
 All the Plagiostomes have the external as 
 division of the vitcllicle, fig. 425 ; 
 the peduncle of the external one 
 d, is longer, in some species con- 
 siderably so, than in Osseous 
 Fishes, and it is beset with villi 
 in Carcliarias and Zygana} 
 The tegumcntary covering of the 
 outer yolk, ib. d! , is denser and 
 more ojiake in Plagiostomes : 
 the inner yolk, ib. e, is co- 
 vered only by the proper vitel- 
 line tunic, which is thin and 
 transparent : it communicates 
 with the short tract of small 
 intestine which intervenes be- 
 tween the pylorus and the val- 
 vular straight gut, li : it receives 
 the external yolk, d', as this is 
 ijroo-ressively squeezed into the abdomen by the contraction 
 and interstitial absorj)tion of its tunics, c' : and, as no part of the 
 fo3tal abdominal appendage is cast off, nor the chord divided, there 
 is no cicatrix — no umbilicus. The arterial vessels of the yolk are 
 derived, not from the mesenteric vein as in Osseous Fishes, but 
 
 ' cxsiii. tf. iii. 
 
 VOL. I. E R 
 
 Eiiibvyo Cartilaginous flsli, Si-'ijUUnn. 
 
CIO •« ANATOMY OF VERTEBRATES. 
 
 from ramifications of a branch of the mesenteric artery, and the 
 blood is returned to the mesenteric vein. Hunter's preparations 
 of the embryo Carcharias (No. 1061), Scyllium (No. 3250), 
 Spinax (No. .3255), and Alopias (No. 3261) ', demonstrate another 
 foetal j)ecullarlty which later researches ^ have shown to be pro- 
 bably common to all Plagiostomes, viz. the external fringe of 
 filaments developed from the branchial surfaces, b : a tuft extends 
 out of each aperture, and even from the spiracula, a, in the genera 
 with those accessory openings. Each filament contains a single ca- 
 pillary loop : ' they disapjiear early, being removed by absorption. 
 The last remnants may be seen in the preparation of the fcetal Saw- 
 fish {Pristis, No. 3263),'' which is eight inches in length, including 
 the saw, and has the duct of the external vitellicle attached. In 
 the oviparous Sharks, the branchial filaments 
 '*-*' react on the streams of water admitted into the 
 
 egg by the apertures, fig. 426, c. In the ovo- 
 viviparous Sharks the size and position of the 
 cloacal apertures of the uteri would seem adapted 
 to allow free ingress of sea-water; so that, 
 whilst the vitellicle, ib. i, administers to the nutri- 
 ment of the embryo, a, the external branchia; may 
 perform the respiratoiy function. In the smooth 
 Emissole {Mustclus levis), vascular cotyledons are 
 developed from the vitelline (omphalo-mesen- 
 teric) capillaries, which are firmly connected to 
 the viterine cotyledons ; so that here the vitel- 
 licle, like a true placenta, may perform both the 
 nutrient and respiratory functions : the external 
 branchiaj disappear some time before the exclusion of the embryo 
 and the aljsorption of the yolk. In the Lcpidosircn annectms^ 
 three small external branchial filaments project from the single 
 opercular aperture on each side, and are long retained. 
 
 Some of the Plagiostomons Fishes are oviparous, but not as in 
 the majority of Osseous Fishes ; a remarkable transposition in the 
 times of the processes of fecundation and exclusion marks the 
 distinction. In the oviparous Osseous Fishes the ova are first 
 excluded, then impregnated: in the oviparous Plagiostomes im- 
 pregnation is internal, and precedes oviposition. The eggs arc 
 much fewer in nmuber, but their impregnation is more certain 
 than in the scattered indiscriminate act of spawning of the 
 Osseous Fishes, where the countless numbers of the ova seem to 
 
 ' XX. vols. ii. and v. 
 
 - Kiuloljihi, Lxxvi. ; Ratlikc, cxi. ; Lcuckart, cxxv. ; J. Davy, lxxxit. 
 
 ' A. Thompson, cxj. ' xx. vol. v, » Jaraiuc, cxxxv.j Peters, cxxxvi. 
 
GROWTH AND NESTS OF FISHES. 611 
 
 compensate for the chances that may intervene to prevent the 
 contact of the milt. 
 
 § 116. Growth and Nests of Fishes. — "VYlien developement has 
 stamped the Fish with its specific characters, growth proceeds at 
 various rates and to different degrees, according to tlie species 
 — viz., from the size of tlie Sticlileback to that of the Sharif 
 of thirty-five feet long ( Selache muxima). Carp, Pike, and some 
 other Fishes, which may live in ponds or lakes under circum- 
 stances favourable for continuous observation of the same in- 
 dividual, show that growth is not definitely arrested as an adult 
 character ; few Fishes, perhaps, can be called ' full-grown ' in 
 the sense in which the term is applied to warm-blooded Verte- 
 brates : but, after attaining the average size characteristic of the 
 species, individuals under favourable circumstances continue to 
 increase, though very slowly, in size. Growth is accompanied in 
 many species by changes of colour, in some by a greater propor- 
 tional size of the head, or by elongation or curvature of the mandi- 
 ble, or by increased length of a rostral prolongation — sword or 
 saw : other special weapons, as the dorsal spines of Cestracionts, 
 File-fish, and Dog-fish, and both dorsal and pectoral spines of Sheat- 
 fish, acquire length and hardness, or dentate borders, in the course 
 of growth. External sexual characters are assumed, as shown in 
 the form and structure of the ventral fins in some Osseous Fishes', 
 in the growth of the ' claspcrs ' of Plaglostomes, and of the mar- 
 supial folds or pouches of Lophobranchs. In the Dolphin ( Cory- 
 plicBna), the cranial crest and fore-part of the dorsal fin gain so 
 much proportional height that young individuals of even two 
 feet in length were referred by Cuvier to a distinct genus 
 {^Lamjrugus)."^ 
 
 In a few instances the changes accompanying growth amount to 
 a metamorphosis. The edentulous state of the young Lamprey, 
 and the semicircular form of the upper lip, are exchanged for the 
 suctorial multidentate mouth, shown in fig. 277. The external 
 branchial apertures enlarge, and the furrow in which they at first 
 open disappears. The perfect form of the Lamprey is not attained 
 until the fourth year. During lialf or two thirds of that time, the 
 growing Petromyzon presents a form which passes as that of a 
 distinct genus of Cyclostomes (AimnoccEtes).^ The Leptocephali 
 are probably larvaj of some larger known fish : they have never 
 been observed with roe or milt : the same may prove to be the 
 case with ErancMo stoma. 
 
 ' In almost all the Teleostomes the body of the young is more 
 
 ' cocxxxvni. "^ CLxxiv. ii. p. 405. ' cccxxvii. p. 323. 
 
 K K 2 
 
612 ANATOMY OF VERTEBRATES. 
 
 slender tlian that of the mature fish, or the height of the body is 
 less in comjiarison with its length. The eye ceases to grow long 
 before the individual has attained its full size ; so that old fishes 
 have comjiaratively smaller eyes than young ones. The form of 
 Fishes is altered by changes in the shape of fins, by the develope- 
 ment or by the loss of spines belonging to the opercular apparatus 
 or to the fins ; as in the following examples. 
 
 ' a. Some of the fin-rays are prolonged with age into long 
 filaments : species of Antldas, Pagrus, Ephijipus, CalUonymus. 
 
 ' h. Some of the fin-rays are prolonged in young individuals, 
 Ijut the filaments are worn off with age : Lophius, Echeneis, 
 Tracliynotus. 
 
 ' c. Cephalacantlius is merely the young of Dactylopterus ; 
 the pectoral fins are short in the young, and become with 
 age so long as to serve for an organ of flying in the adult 
 (JDuctyloptcrus). 
 
 ' d. In some species of Thyrsites and Gempylus the ventral fin 
 is reduced to a very small spine, which in the young is very 
 long, nearly half as long as the head. Sometimes the young 
 has ventral fins, whilst they are entirely absent in the adult: 
 Stromatcus. 
 
 ' e. The young of almost all the Carangidoi have the pra>oper- 
 culum armed, like a Percoid : this bone is entirely smooth in the 
 mature fishes. The same in Labrus. 
 
 '/. Some fish have no visible, or but a rudimentary, spinous 
 dorsal fin ; this fin is very distinct in the young : Brama, Platax, 
 Stromateus. 
 
 ' g. Large prominences of the skin are developed, which arc 
 absent in the young : Cyclopterus. 
 
 ' h. Llany of the well-armed Siluroids have the osseous carapace 
 on the head and neck more or less covered with skin in early 
 age : the dorsal and pectoral spines are more feeble in the young 
 than in the old.' ' 
 
 There arc few fields of Natural History that return more mate- 
 rial reward for scientific labour than that relating to the generation 
 and growth of Fishes. The mercantile value of the Salmon, 
 and the necessity for basing laws that arc to operate in its 
 preservation upon a knowledge of its natural history, have led to 
 interesting observations on its growth and migrations. 
 
 Mr. Shaw,^ observing ova spawned on January lOtli, no- 
 ticed dark eye-specks and some movement of the embryo in 
 
 ' For tlio above examples I am imlebtcd to my colleague, Ur. A. Giiiitlier. 
 
 '' cxxiv, 
 
GROWTH AND NESTS OF FISHES. 613 
 
 the ovnm on February 26th, that is, forty-eight days after being 
 deposited ; and on April 8 th, or ninety days after impregnation of 
 the ova, the young were excluded. They measured |-ths of an 
 inch in length; the vitellicle being |ths of an inch in length, 
 oblong in form, and of a light red colour : the tail was margined 
 like that of the tadpole, with a continuous fin running from the 
 dorsal above to the anal beneath. The vitelline sac and its con- 
 tents were absorbed by May 30th, or in about fifty days, until 
 which time the young fish did not leave the gravel of the hatch- 
 ing-2>ond. This quiescent state in their place of concealment, from 
 the period of exclusion to the absorption of the yolk, seems to 
 be common to Osseous Fishes; but the time varies in different 
 species : it is much shorter in the Tench, Perch, or Pike, for 
 example, than in the Salmon. When the young Salmon mea- 
 sures an inch in length, the vertical fin begins to divide itself into 
 the dorsal, adipose, caudal and anal fins ; and the transverse bars 
 on the sides of the body make their appearance. It is very active, 
 and continues in the shallows of its native stream till the fol- 
 lowing spring, when it has attained the length of from three to 
 four inches, and is called the ' May-parr.' In this state the 
 ' parr ' descend into deeper parts of the river, and are believed by 
 Mr. Shaw to remain there over the second winter. The weaker 
 ones do so, but the stronger fish proceed to the estuary at 
 once. In April, the caudal, pectoral, and dorsal fins assiune a 
 dusky margin ; the lateral bars begin to be concealed by a silvery 
 jiigment ; and the migratory dress, characteristic of the stage 
 called ' smolt,' is assumed. Such fish begin in April and INIay 
 to congregate in shoals and to migrate seaward : they return in 
 July and August, of a size proportionate to the length of 
 their stay in the estuary. A smolt may not exceed two ounces 
 in weight when it goes to sea : after a few mouths there it may 
 have grown to a ' grilse ' of eight or ten pounds' weight : ' at 
 two years and eight months old it becomes a Salmon of from 
 twelve to fifteen pounds' weight.' ' It may subscfjuently acquire 
 a bulk of forty pounds' weight, and upwards. 
 
 In the Syngnathus acus the sexes come together in the month 
 of April, and the ova jjass from the female and are transferred 
 into the subcaudal pouch of the male, fig. 426, n, being fecundated 
 ill transitu, and the valves of the jjouch immediately close over 
 them. In the month of July the young, ib. o, o, are hatched and 
 quit the pouch ; but they follow their father, and return for shelter 
 
 ' cccxxv. p. 120. Experiments ou marked frsh hiivc proved tliis cxtraordiii.-try 
 rale of growtli. cccxxxiv. p. 57. 
 
■614 
 
 ANATOMY OF VERTEBRATES. 
 
 427 
 
 S9- 
 
 into their nursery when clanger threatens.' In Syngnathns 
 ophidion the male carries the eggs under the flat abdomen in cells 
 placed lengthwise in three rows.^ In the 
 male Hippocamp the marsupium is subcau- 
 dal, opening by a vertical fissure just below 
 the vent.' In the Holconoti the young ac- 
 quire full developement, perfect gills, and a 
 size one third that of the parent, before 
 quitting the ovarian marsupium.'' 
 
 Both Salmon and Trout excavate the 
 gravelly bed which they select for spawning ; 
 and the ova may be found from one to two 
 feet deep in this stony nest. The Stick- 
 leback (^Gasterosteus aciileatus) fabricates a 
 more artificial nest. Aristotle signalises the 
 Plnjcis, since recognised as a Mediterranean 
 sjiecies of Gohhis, as the only sea-fish that 
 makes a nest and deposits its spawn therein. 
 Olivi confirmed the statement, and describes 
 the nest as being composed of sea-weeds 
 (alga3 and zostera), adding that the male fish 
 guards the female during the act of oviposi- 
 tion, and the young fry during their deve- 
 lopement.^ 
 
 Dr. Hancock has observed similar habits 
 in certain fresh-water Siluroid Fishes of De- 
 merara called ' Hassars,' which belong to the 
 genus CalUclitlnjs : the Kound-hcaded Has- 
 sar forms its nest of grass ; the Flat-headed 
 Hassar of leaves. ' They are monogamous : 
 both male and female remain by the side of 
 the nest till the spawn is hatched, with as 
 nivich solicitude as a hen guards her eggs, 
 and they courageously attack any assailant. 
 Hence the negroes frequently take them 
 by putting their hands into the water close 
 to the nest ; on agitating which, the male 
 Hassar springs furiously at them, and is 
 ,ihiis thus captured.''' 
 
 § 117. Fcciaidafion of Ilcptilcs. — Sala- 
 Frogs, and Toads arc generally apt for breeding 
 
 Eckstroem (1831), quoted in xxxix. ii. p. 327. 
 
 XX vol. V. p. 67, prep. no. 322y. " lb. no. 3223. * cccxxxv. 
 
 SXiii. t. xii. p. L-. " cccxxvi. p. 244, 
 
 Marsiuilnl piui. 
 
 mandcrs. Newts 
 
FECUNDATION 01? REPTILES. 615 
 
 when they have attained their third year. As the season of impreg- 
 nation approaches, the expansicjn of the abdomen, unfettered by 
 costal hoops, becomes enormous, especially in the females. The 
 nuptial tints are assumed, the yellows and pinks being Ijrightest. 
 The males of certain Newts acquire the dorsal crest and a broader 
 tail-fin, aiding in the manojuvres required for the internal impreg- 
 nation. The male of the large Warty-Newt ( Triton cristatus) in 
 the spring season seeks the female and pursues her, vibrating his 
 tail with a motion like that of cracking a whip, and, witli a rapid 
 evolution the tumid lal^ia of the cloaca in the two sexes are 
 brought into contact, and the spermatozoa get access to the 
 oviduct : the pair sink to the bottom. The Salamandra japonica 
 ol Houttuyn (^Sal. unguiculata, Schleg.) at this season has a claw 
 on each digit of the fore limb. The male Frog acquires the 
 dark-coloured swelling of the radial digit or thuml:i, by which 
 he is better able to retain the female in his grasp during the long 
 protracted business of impregnation. The larynx of the Toads, 
 and especially of the male Pipa, now gains its fullest develope- 
 ment and loudest power of croak. Lizards and Serpents exhibit 
 their brightest colours : in the male Constrictors the copulatory anal 
 hooks become consjncuous. The anal scent-glands are in active 
 function in both groups. The male Crocodile, like certain fishes, 
 fights for the female : the musky odour emitted by the submaxil- 
 lary glands pervades their haunts at this time. Many Clielonia 
 show sexual difference of form. In Land-Tortoises the plastron is 
 concave in the male and flat in the female. In the Cinostcrnoida: 
 the fore ^Jart of the carapace is broader in the female, and the tail 
 is longer and stronger in the male, wliich has also a patch of 
 rough scales between the thigh and leg, not present in the female. 
 In the Trionyeida; the tail extends beyond the rim of the shell in 
 the males only : it is a mere stump in the females: besides this differ- 
 ence, the male of Trionyx (^Asjndonectcs spiuifer) shows a sliglitly 
 oval f(")rm ; and the spines along the front margin, and the tubercles 
 behind them and on the hind part of the carapace, are less promi- 
 nent. In Trionyx {Platy peltis) fcrox the latter character is reversed. 
 In the Emydians tlie body of the male is usually flatter and 
 longer than in the female. In copulation the male mounts on the 
 back of the female : Emys picta performs the act when seven 
 years of age ; the female does not begin to oviposit befln-e her 
 eleventh year. Additional ova are developed in the ovary after 
 the first copulation, and a certain number of those already formed 
 begin to acquire a larger size, and ' go on growing for four successive 
 years before they are laid : ' thus the species is enabled to lay 
 annually from five to seven eggs after it has reached its eleventh 
 
61 G ANATOMY OF VERTEBRATES. 
 
 year.' ' Although the Emydians lay once every year, soon after the 
 period of copulation in the spring, the coitus is repeated a second 
 time every year in the autumn, shortly before the species return to 
 their winter quarters : and Agassiz concludes that in Emydians ' a 
 repetition of the act twice every year, for four successive years, is 
 necessary to determine the final developement of a new individual. 
 
 § 118. Oviposition of Reptiles. — I do not know particulars of 
 this process in the Perennibranchiates. Some Newts ( Triton 
 cristatus, e. g.) deposit the eggs upon aquatic plants i^Pohjgonum 
 Persicaria, e. g.), folding the leaf by means of the hind feet in 
 such a way that its under surface is turned inward, and the fold 
 made to stick by the adhesive coating of the egg whicli she inserts 
 in the fold. Our smaller Newt {LiHsotriton punctatus, Bell) fre- 
 quently glues the egg in the axilla of the leaf.^ 
 
 Oviposition of the Frog takes place during the sexual embrace 
 at the bottom of the water : as each egg is extruded, it is fertilised, 
 and, the chorion absorbing water, the egg acquires a diameter of 
 about three lines, the coloured vitellus appearing as a dot in the 
 middle of the transparent jelly: the ova adhere together in a 
 mass, and this is usually floated to the surface by disengagement 
 of gas in the substance of the glairy envelope. 
 
 The ova are excluded under similar circumstances in the Toad; 
 but in a long string of jelly, in which they are arranged alter- 
 nately in a double series ; the string may be a sixth of an inch in 
 diameter and from three to four feet in length. In the obstetric 
 Toad (Ali/tes), the male impregnates in water, assists in the exclu- 
 sion of the eggs, causes them to adhere to his own hind legs by 
 small i^cdicles, and then seeks the laud: onl}' when embryonic 
 developement is sufficiently advanced does he leave his place of 
 concealment, and betake himself to the water with the young brood 
 with which he has charged himself. The male Pipa is asserted to 
 place the eggs upon the back of the female, which give the stimulus 
 to the formation of the cutaneous cells in which the whole course 
 of metamorphosis is completed, fig. 367. In Ojiisfhodelphi/s and 
 Nototrema, tlie ova ai'e transferred to the common pouch of the 
 dorsal integmnent, described at p. 588. 
 
 The common Ringed Snake (^Natrix torqiiata) excludes the eggs, 
 sixteen to twenty in number, connected together by a glutinous 
 coating, visually in some fermenting mass of decaying organic 
 matter, whereby they are often transported and spread abroad in 
 the manuring of fields and gardens. The Viper is not subject to 
 this ovipositing cause of dis])crsion, and the confinement to a limited 
 locality would seem to be the condition of the viviparity of most 
 ' ceo. Piu-t iii. p. 4"J1. - cooxvii. 
 
OVIPOSITION OF REPTILES. 617 
 
 or all poisonous serpents. It affects, however, the harmless Slow- 
 worm {AnfjuisfraijiKs) and nimhle Lizard {Zootoca vivlpara), both 
 of which usually produce their yoiTug alive. An American Boa 
 Constrictor brought forth living young, and also eggs, in the Zoolo- 
 gical Gardens of Amsterdam.' The old world constricting serpents 
 would seem all to be oviparous ; but instead of excluding the eggs 
 where they would have the advantage of extraneous heat, they are 
 arranged by the female in a heap around which she coils herself 
 in a series of progressively decreasing sjjirals, constituting a 
 pyramid of wliich the head of the Pytlion forms the apex. 
 
 The fact has been observed in respect to species of Python in 
 India : Col. Abbott, in a communication on this suljject to the 
 London Zoological Society, states that the incubation lasted more 
 than three months.^ More exact observations have been made on 
 captive Pythons. In the Pytlion bivittatus, in the ' Jardin des 
 Plantes,' at Paris, copulation took place on the 22nd of January, 
 and the act was often repeated until the end of February. On 
 the 5tli of May, the female excluded fifteen eggs, between 6 a.m. 
 and 9'30 a.m. The eggs were all separate, of an elongate oval at 
 the moment of exclusion, with a flexible greyish-coloured shell : 
 they soon swelled into an elliptic shape, both ends becoming equal 
 in size, and the shell, as it dried, became hard and of a pure 
 white. The temperature of the female augments several degrees 
 above that of the surrounding atmosphere, and is very sensible to 
 the touch when she has disposed herself in incubating coils ahout 
 her eggs. Between the 3rd and 7th of July the eggs were 
 hatched. The mother did not eat during the incubating i)criod, 
 l)ut several times drank with avidity water whlclr was (iffered 
 to her, indicative of a sort of febrile state. The heat of the body 
 gradually fell towards the end of incubation.^ 
 
 A similar phenomenon in the case of a Python Sehce excited 
 the public curiosity at the Zoological Gardens of London in 1861 ; 
 the temperature of the body rose to 96° Fahr. between the incu- 
 bating coils. "^ 
 
 The Lacerta agilis lays her eggs, from twelve to fourteen in 
 number, in hollows which she prepares in the sand, and, having 
 deposited the eggs, covers them with sand, and leaves them to be 
 hatched by solar heat. The Iguana oviposits in the hollows of trees ; 
 the eggs, about forty in number, are oblong, about an incli in 
 leniTfli.'' Most of the Lacertilia are oviparous ; but the details as 
 to their oviposition are scanty : the shell is slightly calcareous. 
 
 All the Chelonians are oviparous, and the shell is calcified 
 
 ' cccxxxvii, p. 368. - lb. p. 188. ' occxxiv. 
 
 ' cocxxxvii. p. .367. ' cccxxxix. 
 
618 ANATOMY OF VERTEBRATES. 
 
 almost as completely as in the bird, tliough in most retaining 
 some flexibility. In the Painted Terrapin (^Emys picta) the ova- 
 rian effffs do not show much difference in size until the seventh 
 year, and oviposition does not begin before the eleventh year. 
 Agassiz is of opinion that all American Emydians begin to lay 
 eggs from the eleventh to the fourteenth year, when individual 
 growth is checked and proceeds more slowly. Each species 
 makes a single nest, and lays the eggs of that season at one time.' 
 Eimjs picta digs with the hind legs a perjiendicular hole near the 
 stream she frequents, and may repeat the operation several times 
 before selecting one as fit for oviposition : in this she deposits 
 from five to seven eggs. The Snapper ( Chelydra serpentincC) exca- 
 vates at first directly downward and then laterally, making the 
 widest part of the hole where the eggs are deposited on one side 
 of the external oisening. When the eggs are laid, the female 
 tramples down and smooths over the earth, so that, when dry, 
 the place is hardly noticeable. She laj^s from twenty to forty, 
 aljout the size of a walnut. Cinostenwn lays only from three to 
 five eggs. Naneim/s guttata is usually limited to two or three 
 eggs. Land Tortoises rarely lay more than four or five eggs at a 
 season, and make the nidamental burrow in dry ground. The 
 Gopher ( Testudo Carolina, L.) has a dwelling burrow, but forms a 
 separate cavity near its mouth for oviposition : in this the female 
 lays five eggs, then fills the nest up with earth, and flattens it 
 down smoothly by her own weight. 
 
 The TrionycidcE lay from twelve to twenty eggs, or more, of 
 the shape and size of a musket-ball, in a hole in the sand near the 
 water's edge. The shell is thick and brittle. 
 
 The Sea Turtles ( Chelone, Spihargis) are the most pi'olific of the 
 order. They oviposit in INIay or the beginning of June, in dry 
 sand, on the shore above high-water mark. The female selects a 
 still moonlight night, when her senses of hearing and seeing may 
 best avail her to detect an enemy. If satisfied, she proceeds to 
 scoop out the sand with her hind fins, using them alternately, and 
 when the sand has accmnulated behind her, she scatters it abroad 
 by violent jerks of the paddles ; a hole being made between one 
 and two feet in depth, the eggs are dropped in one by one, and 
 disposed in regular layers to the number of from 150 to 200. 
 The period of the entire operation may be lialf an hour. AYhcu 
 concluded, the Turtle scrapes the loose sand back over the eggs, 
 and makes the surface level and smooth. She then retreats totlic 
 water, and leaves the hatching of the eggs to the heat of the sand.^ 
 
 ' ceo. Part iii. p. 500. - Audubon, quoted iu cccxvii. p. 4, and ccc. Pint ii. p. 32S. 
 
DEVELOPEMENT OF BATEACHIA. 619 
 
 The Crocodilians, like the Chelonians, are all oviparous, and 
 the process of oviposition is very similar. The eggs, of an ellip- 
 tical form and w^ith a firm calcareous shell, are buried on the 
 shore, and left to hatch by extraneous heat. 
 
 § 119. Dcvelopement of Batrachiu. — After impregnation of the 
 batrachian ovum the dark or germinal part of the yolk is always 
 iippermost, and its central point may be defined as the germinal 
 pole. Here begins, iisually about three hours after impregnation 
 in the Frog, fig. 452, a, the process of segmentation,' by a fissure 
 which passes in a determinate direction through the canal of the 
 yolk, dividing it into two ellipsoid masses, ib. h. About the fifth 
 hour a second cleft appears, near the point where the first com- 
 menced, crossing the first at right angles. If an ovum in this state 
 be frozen, it splits into four segments of a sphere. Fissures next 
 appear, which, in relation to the two foregoing, might be termed 
 ' equatorial,' but with varieties exemplified in e,f, (j, fig. 452. New 
 ' meridional ' furrows follow, ib. li, crossed again by other ' equa- 
 torial ' ones, until the surface of the yolk jjresents the form of a 
 blackberry. Further subdivision proceeds to such an extent as to 
 render the surface again apparently smooth. This series of pheno- 
 mena, resulting in the formation of the germ-mass, occvrpies about 
 twenty-four hours, or less, according to the temperature. The 
 fissures at their first appearance show minute lines at right angles, 
 indicative of the molecular movements causing them. After the 
 surface of the yolk has resumed its smoothness on the completion 
 of the germ-mass, peripheral cells become filled with dark pigment, 
 and constitute a general ' cambium' or outer investment, fig. 428, a. 
 At the point where the formation of this investment, as well as of 
 the germ-mass, began, an eminence appears by the dcvelopement 
 of new cells beneath the investment, which loses its colour at this 
 part, indicating the first rudiment of the embryo as an oval clear 
 spot, divided at its hinder end by a crcscentic fissure from the 
 contifuous yolk, and with its anterior end sunk therein. The 
 embryonal cells, as they accumulate, assume a polyhedral figure, 
 and their different strata are seen by transverse sections. The 
 first superficial appearance of the embryo is an oblong rising, 
 
 ' The phenomenon of the division and sulidivision of the yolk in animals was first 
 ohserved by Prevost and Dumas in the ovum of the Prog (Annalcs des Sciences 
 Nat. t. ii., May 182-1, p. 112). Pranz Bauer, in the same year, delineated partially 
 tlio same important phenomenon, in the beautiful drawings which he prepared for 
 Sir Ev. Home (cccxvi. pis. v. and vi.); but his emjiloycr had no appreciation or 
 comprehension of what was thus shown him. Bergmann detected, in 18-11, the 
 hyaline nucleus in the centre of each subdivision of the yolk ; and the combination 
 of tlie spermatiscd cell progeny of the germinal vesicle with other elements of the 
 yolk- substance appears to bo a necessary prelude to segmentation. 
 
0-20 
 
 ANATOMY OF VERTEBRATES. 
 
 428 
 
 largest at one end, and impressed by a slight longitudinal fissure. 
 The rudiments of the neural axis are first recognisable in the two 
 parallel longitudinal elevations (' primitive trace ' or ' laminaj 
 dorsales,' ib. m, n) bordering the fissure. Beneath these is at the 
 same time forming the notochordal rudiment of the vertebral 
 column, ib. c. The albuminous principle is concentrated in 
 m, the gelatinous one in c : this chemical differentiation does 
 not aifect n. The polyhedral cells extend the vertebral layer 
 on each side of the ' primitive trace,' which also increases 
 in length : the neural columns, at first flat and horizontal, 
 rise at their outer margins, approximate, and ultimately unite 
 aljove, where they are covered by the peripheral cell-layer, a : 
 they are also defended by the nascent ncurapophyses, ib. n. 
 Meanwhile the ' animal ' layer is extending laterally, ib. h, beneath 
 the investing membrane, a ; and tlie cephalic 
 end of the embryo enlarges and raises itself 
 from the yolk-bed. A section of the ovum 
 just jirior to the coalescence of the ' lamina} 
 dorsales ' to form the neural axis, as in fig. 
 428, shows, a, the dark investing membrane, 
 or ' cambium : ' b, the museulo-tegumentary 
 layer, inclosing the whole yolk, v ; m, the 
 myelonal columns ; c, the notochord ; n, the 
 blastema, in which cai'tilaginous rudiments 
 of the ncurapophyses begin ; /(, the cavity, 
 beneath the germ due to solution of the 
 yolk-sul)stance. On the ventral aspect of the embryo lavers of 
 cells have been forming two parallel ridges projecting into the 
 yolk ; and the intermediate space is converted by liquefaction of 
 
 cells into a primitive alimentary 
 groove. But all the systems and 
 organs for the support of the 
 cmliryo begin to be developed 
 after the main basis of tlie neural 
 and vertebral parts has been 
 establislicd. 
 
 Figure 429, a, gives a view of 
 
 the embryo of the Frog from 
 
 the dorsal aspect, showing the 
 
 myelonal cohunns at the jieriod 
 
 of their meeting above the myelonal canal and tlie commcncino- 
 
 cnceplialic expansion, tlie extension oi" the neuro-vcrtebral tract's 
 
 outward, and the indication of luemal arches of the cephalic 
 
 clioTi nf yi)]]; anil cinl)i-yo, 
 Froi:', iiia:^'u. lxxi\'. 
 
 429 
 
 Embryo oi: Iho Fnig. coxxxvut. 
 
DEVELOPEMENT OF BATEACIIIA. 
 
 621 
 
 segments. In b, the cervical constriction begins to define the 
 head from the trunk : the complete coalescence of the myelonal 
 tracts obliterates the linear trace of the median furrow, and the 
 neurapophysial rudiments border the myelon. The embryo and 
 its supporting yolk-mass are separated from the chorion by a clear 
 fluid ; and in the above-figured stages of devehjpement the ciliated 
 epithelium begins to act upon the fluid in the direction indicated 
 by the arrows, proceeding backward and downward along the 
 sides : the currents are strongest on the hasmal arches, from which 
 the branchlaj are about to be developed. In the mass of em- 
 bryonal cells Ijetwecn the cephalic enlargement of the embryo 
 and the yolk, the heart, fig. 4.31, r, is formed, which becomes 
 hollow, and pulsates before the red blood appears ; when the 
 communication with the system of vessels is established, the 
 heart propels blood, at first pale and with spherical corpuscles, 
 in channels formed by liquefaction of cells in the blastema of 
 the second ha3mal arch ; and these primary vascular arches esta- 
 blish the communication with the longitudinal aortic trunk simi- 
 larly formed along the under part of the notoehord. The blood 
 returns by venous channels along the yolk, now progressively 
 becoming inclosed by the lateral intestinal plates, and the simple 
 clrcnlatlon is complete. 
 
 From the substance around the vascular arches are formed as 
 many branchial arches, as subordinate developcmeuts from the 
 second primary hfcmal or visceral arch ; 
 and from the branchial arches are 
 budded the succession of vascular loops 
 and coextended ciliated integument, 
 constitutlnjr the outer irills on each 
 side of the batrachian larva, fig. 430. 
 In the magnified portion of the gill, c, 
 the arrows indicate the direction of the 
 ciliary currents. Soon after the ap- 
 pearance of the heart, and of the arches 
 which encompass the primitive bucco- 
 branchial cavity, a pericardium, lined 
 with epithelial cells, is formed around 
 the heart. Between the cephalic hcemal arches interspaces are 
 opened, communicating with the bucco-branchial cavity, and from 
 one of these the budding gills begin to protrude. 
 
 The growth of the neurovertebral axis is chiefly lengthwise, 
 and, as it proceeds, its two extremities lift themselves above the 
 level of the rest of the germinal basis ; the shorter and more 
 
 430 
 
 Larva oi Frog ; A, nat. 
 
 ccxxxTirr. 
 
622 
 
 ANATOMY OF VERTEBRATES. 
 
 Longitudinal scclion, Einliryo of Frog. LXXIT. 
 
 obtuse as the head, the more acute and longer free part as the 
 tail. In this growth the amiDhibian passes from a state in wliich 
 a longitudinal section would show it supported by a spherical 
 yolk, to that represented in fig. 431, in which the vitelline, or 
 
 ' ha3mal,' portion pre- 
 sents a semioval section, 
 hv: it is inclosed, as in 
 fig. 428, by the hsemal 
 prolongations of the or- 
 ganic layer forming the 
 alxlominal parietes, a, 
 and lined by the 'mu- 
 cous ' layer, i : this be- 
 comes differentiated as the tunics of the alimentary canal, inclosing 
 the vitellus as the primary contents of such canal in all Batrachia. 
 The canal now communicates with the bucco-branchial cavity; 
 and this opens externally on the lower part of the head by a 
 vertical fissure, on each side of which a small protuberance buds 
 out, forming a special organ of adhesion— a pair of temporary 
 cephalic limbs. A pair of branchiae budding out from the gill- 
 aperture, the whole yolk being now closed in by both the in- 
 testinal and cutaneous layers, and the tail having gained its 
 muscular segments and cutaneous border-fin, the little tadpole, 
 by increasing vigour of its movements, bursts the egg-mem- 
 branes and comes forth. The external stimulus which most 
 influences this stage is warmth. In Italy, Eusconi observed 
 the eggs of the Frog to be hatched in four days ; Bauer 
 figures one extricating itself, in a warm spring, at Ivew, after 
 the fifth day : ' in a cold spring, it may be prolonged through 
 four weeks. In Ahjtes ohstetricans, the developement of the 
 'mucous' layer proceeds to form a convoluted intestinal canal 
 before ' extrication.' In Bana esculenta, and probably other 
 Frogs, the vegetative organs are later in developement, and the 
 cavity, fig. 431, liv, has not assumed the intestinal form when 
 the embryo quits the egg : but in all Batrachia the whole yolk is 
 wanted for the formation of their long spirally wo\md larval gut. 
 Herein is a diftcrential character between the Batrachian and the 
 Fish. In the latter, the supply for the mid-period of develope- 
 ment is ]'cceived, primarily, from the vascular rather than from 
 the digestive system, and a part only of the yolk is required for 
 tlie formation of the straight and simple intestinal canal. Ac- 
 cordingly, the mucous layer, as in the diagram, fig. 432, /, in 
 
 ' CCCXVI. pi. vi., fig. 1 A. 
 
DEVELOPEMENT OE BATEACHIA. G23 
 
 fovining the intestinal canal, h., excludes a portion of the yolk, v : 
 
 the tegumcntary or 'serous' lay- ^3^^ 
 
 er, a, accompanies the ' mucous ' 
 
 layer, i, in the process of severing 
 
 the vitelline from the intestinal 
 
 cavities, and an outer yolk, or ' vi- 
 
 tcllicle,' results. 
 
 The embryo of the Frog is ex- 
 tricated at a less advanced stage 
 of developement than that of any 
 other vertebrate animal: the neu- 
 ral laminoj have united along the i-»"eitnJ""iscctiu„,EmiHToorFi8h. lxx.v. 
 
 trunk, and two of the hromal arches have become complete 
 below the head, but, in other parts, the neural and hremal canals 
 are closed only by the corresponding laminaj in a state of mem- 
 brane, the original investing membrane of the yolk lacing retained 
 over all. 
 
 After extrication, the tadpole rapidly grows, and the chief 
 change of form is witnessed in the gills : each of the two lateral 
 gills puts forth four plates, which have vascular and richly ciliated 
 surfaces, fig. 430, c : a short additional leaflet is sometimes deve- 
 loped from the base of the hinder gill. ' The current of the 
 blood poured in regvdar pulsations at each contraction of the 
 heart passes up each stem or main branch of the branchiffi, and a 
 distinct stream is given off to each leaf; it is propelled to the 
 extremity, and then returns down the opposite sides in the most 
 regular manner, and the parts are so transparent that every 
 globule of blood is distinctly and beautifully visible." 
 
 The first cutaneous mouth is defined by epidermal jaws, in the 
 form of a very short transversely extended beak, fig. 433, 22, sur- 
 rounded by a lip armed with minute rasp-like denticles, and aided 
 by the pair of cephalic suckers projecting behind the mouth. Tlie 
 wide pharynx, communicating also with the outer world by the 
 lateral branchial slits, is extended posteriorly by a short ccsopliagns 
 to a simple gastric enlargement, beyond which an equally simjde 
 intestinal sac, laden with the remnant of the vitellus, gives issue 
 to a short and straight rectum, which is continued to the long 
 teo-mnentary and transitory cloacal canal at the fore-part of the 
 subcaudal fin. The contained yolk, fig. 431, hv, is not, as in Fishes, 
 fio-. 432, V, a mere 'food-yolk :' it is part of the germ-mass, and 
 consists of the embryonal cells, with their nutritious oil-globules. 
 Whilst, therefore, it serves to nourish the growing embryo, it also 
 
 ' cccsvii. p. 101. 
 
624 
 
 ANATOMY OF VEETEBEATES. 
 
 contiiivies to be the seat of progressing developement, and coil 
 after coil of intestine is formed between the duodenum before, 
 and the rectum behind the primitive simple vitelline sac, the 
 coils being disposed in a close double spiral, fig. 433, I. Thus, 
 the fully developed larva is provided with an alimentary canal, 
 
 433 
 
 Diagram of the anatomy of the Tadpole. 
 
 adapted, by its length and complexity, for the assunUation 
 of the decaying vegetable matters which chiefly constitute its 
 food. In the conversion of this digestive apparatus into that 
 of the purely carnivorous Frog, the horny cutaneous beak is 
 changed into a wide mouth formed by well-ossified jaws, the 
 lower one armed witli sharp teeth. The branchial pharynx is 
 contracted and closed at the sides, except where it communicates 
 
 with the ears. The a;sopha- 
 gus and stomach are elong- 
 ated ; the intestine is marvel- 
 lously shortened ; the rectum 
 contracts, and is found to 
 open, after the absorption of 
 the tail and cutaneous anal 
 fold, just in front of the 
 symphysis pubis, now com- 
 pleted by the developement 
 of the hind limlis. Whilst 
 the heart, as a bent tube, fig. 
 434,/", sends ofi:" the branchial 
 arteries from its fore part, it 
 is connected behind with ves- 
 sels ramifying on the vitel- 
 llcle, ib., b : a portion of this 
 is soon seen to be marked 
 off from the rest, as the 
 basis of the future liver and pancreas. 
 
 TuJpole of To;k1, inapn. fxxu. 
 
DEVELOPEMENT OE BATEACHIA. 625 
 
 The embryonal cells that lay the foundatiou of these glands, 
 fig, 434, e, are situated in the angle between the intestinal yolk- 
 mass, ib. b, and the stomach, ib. c ; not behind it, as in Fishes, 
 fig. 435. They form a hollow gland or cfecum with a wall of com- 
 pacted cells ; and, after a communication has been established with 
 the gut, other cavities or ca3ca pullulate in the cell-blastema, and 
 the liver becomes conspicuous. ' Nowhere,' says Eeichert, ' is the 
 new generation of cells within parent-cells so obvious as in the 
 blastema of the liver and pancreas.' ' The primordial kidneys, or 
 de-azotising organs, have now begun to be developed between 
 the aorta and the intestinal plates, and the ducts of these, 
 together with the anal prolongation of the intestinal tube, open 
 upon the temporary tegumentary vent. In the Tadpole, as in a 
 Fish, the mouth is destitute of tongue, but at the entrance of the 
 mouth over the lips we find among the cartilaginous teeth at 
 that region numerous conical-shaped bodies. These labial pa2:iilla3 
 consist of an external border of prismatic epithelial cells provided 
 with cilia. The tongue makes its appearance when the fore limbs, 
 fig. 433, 5-t, 55, are evolved. The habits now alter : the Tadpole 
 no longer feeds on decomposing substances, and cannot live long 
 immersed in water. As the tail of the Tadpole atrophies, the 
 fungiform papillaj appear upon the nascent tongue, increase in 
 size, and acquire the permanent complex form. 
 
 Soon after the external gills have reached their full develope- 
 ment, they begin to shrink, and finally disappear ; but the 
 branchial circulation is maintained some time longer ujoon the 
 internal gills (p. 516, fig. 345); these consist of numerous short 
 tuft-like i^rocesses from the membrane covering the cartilaginous 
 branchial arches, fig. 433, 47 : they are protected by the growth 
 of a membranous gill-cover, which, as the external branchite are 
 absorbed, leaves only one small external orifice, by which the 
 branchial streams admitted by the mouth continue to be expelled. 
 This orifice may be very plainly seen like a crescentic cicatrix, 
 a little behind and below the left eye, in the larva of the Rana 
 paradoxa.''' 
 
 The chief distinction between the fully developed branchial 
 circulation in the Batrachian larva and that of the Fish consists in 
 the presence of small anastomosing channels, between the branchial 
 artery and vein of each gill, proximad of the gill itself. 
 
 The part which these anastomoses play will be understood by 
 the following description and figures of the vascular transformation 
 as observed in the Newt. When the gills are in full developement 
 
 > cccxxYin. ^ xx. vol. v. p, 77, preps, nos. 3286-32S7, E. 
 
 VOL. I. ■ S S 
 
626 
 
 ANATOMY OF VERTEBRATES. 
 
 4.35 
 
 Draiichial circulatinn ; IniTal Newt {Triton). ccl-.xxxil. 
 
 and activity, the principal circulating vessels present the arrange- 
 ment shown in fig. 435. 
 
 The vessel, ib. 4, originally distinct and large before the deve- 
 lopement of the gills, is now very small, and so close to the 
 origin of 3 as to appear to be its first branch : it anastomoses 
 with the branch 21 from the aortal root of its own side, and 
 proceeds to the nascent lung 19. The artery 3 supplies the hind- 
 most gill, and distri- 
 butes its branches to 
 the several branchial 
 leaflets, 5, where they are 
 resolved into the capil- 
 lary network, fig. 343, 
 ji. 514 ; the blood is re- 
 turned by the branchial 
 veins, fig. 435, 7, 8, to the 
 trunk 9, which at 16 joins 
 the corresponding vein of 
 the middle gill to form 
 the aortal root or arch of 
 that side : this receives 
 the anastomosing vessel 13, from the branchial vein of the first gill, 
 and then sends off the accessory origin, 21, of the pulmonary artery, 
 1 n. The third primary vascular arch, 2, is the branchial artery of 
 tlie middle gill : it effects a small anastomotic communication, 14, 
 with the vein of the gill before proceeding to expend itself upon the 
 branchial lamella;, c ; the returning trunk, 9, after receiving the 
 anastomotic twig, 14, joins the vein, 16, of the third gill to form 
 the aortic arch. The foremost primary vascular arch, i, before 
 going to the first gill, anastomoses by a small channel, 5, with the 
 vein, 9, of that gill ; which vein, after the above anastomosis, 
 sends off the vessel 1 1 to the head : before the anastomosis it 
 passes back and di^■idcs into the vessel 13, joining the beginning 
 of the aortal arch, and the recurrent branch 12, which also conveys 
 arterialised blood to the head. 
 
 As absorption of the branchia3 proceeds in the jn'ogressing 
 metamorphosis, the following changes are observed in the above 
 described vessels, fig. 43G : the anastomosing channel, s, between 
 the roots of the artery and vein of the first gill, dilates as the cir- 
 culation through that gill is checked, and sends more blood into 
 the artery 11, into the anastomotic channel 13, and into the arterv 
 1 L'. In like manner the lilood of the second gill begins to be diverted 
 liy the anastomotic t'luuuiel asi(sl)ase leading to ic, which assumes 
 
DEVELOrEJIENT OF BATRACIIIA. 
 
 G27' 
 
 Newt I^Triton). CCLXXXII. 
 
 f gills ; larval 
 
 a size that gives it the character of the aortic arch. The pul- 
 monary vessel, 4, now 
 equals in size the trunk, 
 3, of which it was a 
 branch ; and it exceeds 
 the tributary 21. 
 
 With the total disap- 
 pearance of the gills the 
 blood of the foremost 
 vascular arch is carried 
 into the two chief ar- 
 teries of the head, fig. 
 437,12,1s; either directly, 
 or by the transformation 
 of the anastomotic channel into a recurrent origin of one of these : 
 it is thus converted into the carotid arteries. In higher Eeptilcs 
 the origins of 1, 1, are blended or produced into a common trunk 
 of the carotids. 
 
 The next vascular arch, 2, 2, is now transformed into the right 
 and left arch of the aorta, by the enlargement of the anastomotic 
 channel u, fig. 435; with changes in length and position by which 
 it gives off the cutaneous artery of the neck, 15. The tributary, 21, 
 to the pulmonary artery, 4-19, is now shortened, and transverse in 
 position : in higher Reptiles it is still more shortened, and finally 
 obliterated as the ' ductus arteriosus ' on each side. The orljital 
 arterjr, is, fig. 436, and 11, fig. 437, continues to be sent off from 
 the aortic arch. 
 
 The first or hindmost of the primitive vascular arches is now 
 converted into the pulmonary artery, 
 and the blood which was transmitted 
 by 3, figs. 435 and 436, is now diverted 
 from the largest of the gills to the 
 lungs. 
 
 The blastema, which lays the foun- 
 dation of the lungs, is situated behind 
 and at the sides of the fore part of 
 the alimentary canal, where it enters 
 the bucco-branchial cavity. The 
 lunf^s begin to be formed as soon as 
 the intestine behind has taken on its 
 first sigmoid curvature. They are 
 not developed from the alimentary 
 canal, but communicate with it soon 
 
 437 
 
 Changes in In ancbi.il vessels after aljsorp 
 
 tion of KllK: Newt. CCLXX7T. 
 
 after the establishment 
 
628 ANATOMY OF VERTEBRATES. 
 
 of the respiratory cavity in their primitive and independent 
 blastema : their communicating duct advances with the elonga- 
 tion of the oesophagus, and at the point of its communication 
 therewith the larynx is ultimately developed. The lungs them- 
 selves extend, as simple elongated sacs slightly reticulated on the 
 inner surface, backward into the abdominal cavity. These recep- 
 tacles are no sooner formed than the larva rises to the surface 
 and swallows air, which passes into and expands the prepared 
 cavity. When the pulmonary respiration has regularly begun, the 
 fore-limbs are liberated from the branchial chamber, which now 
 beo-ins rapidly to contract its dimensions, and to be completely 
 partitioned off from the abdominal cavity with which it had pre- 
 viously communicated. 
 
 The changes in the hyo-branchial ajiparatus, accompanying 
 those of the breathing organs, are defined at p. 90, and illustrated 
 in figs. 69-71 and 74. The developement of the vertebrse is 
 attended with the conversion of biconcave into cup-and-ball 
 joints, by ossification of the substance of the cavities, a, fig. 433, 
 and its coalescence either with the fore {Pipa) or back {Rana) 
 part of the centrum, c. The chief facts in the formation of the 
 skull are stated at p. 86, figs. 68-71. 
 
 About the middle period of aquatic life, the true or permanent 
 kidneys begin to be formed from and upon the primordial ones ; 
 and the basis of the ovaria, or testes, may now be discerned. The 
 oviduct is soon distinct from the ureter ; but the testes retain the 
 same excretory duct as the kidnej'S : their vasa deferentia com- 
 municate with retained ca3ca of the primordial kidneys before 
 jienetrating the later glands : the upj^er or anterior ends of the 
 first remain for some time behind the heart. 
 
 In the often-c[uoted experiments of Edwards,' it is not clearlv 
 shown that the Tadpoles of the Frogs were constantly supplied 
 with proper temperature and food, and therefore it is not satisfac- 
 torily proved that the arrest of the metamorphosis was due solely 
 to the absence of light. INIere absence or diminution of this 
 stimulus does not in all cases check the progress of the tadpole to 
 the Frog-state. Ova of a Frog, deposited on ]\Iarch 11, were 
 placed in a vessel covered witli six or eio-lit folds of black adazed 
 calico in a dark pai'tof a room, but in a temperature of from 55° to 
 65° Falirenheit, and supplied with proper food.'^ The larva? were 
 hatched on March 20 ; attained the length of an inch on ]May 1, fig. 
 438 ; had pushed out tlicir hind-logs, fig. 439, on IMay io, and 
 their fore-legs, fig. 440, on J\Iay 16 : the tail began to be absorbed 
 
DEVELOPEMENT OF BATRACIIIA. 
 
 629 
 
 at that date, was reduced to a stump, fig. 441, on the 18th, and was 
 removed by May 20 ; the metamorphosis behig fully completed, as 
 in fig. 442, in ail the tadpoles by May 22. 
 
 4.3S 
 
 440 
 
 =^^ 
 
 Aii,,dalT;uliiolc. 
 
 (^luadruiiodni Tadpule. 
 
 44 1 
 
 442 
 
 Bipedal Tadiiule. 
 
 Young Frogs. 
 
 Itinui tr-nii'ornna. 
 
 The figures 438 to 441 illustrate the chief outward changes which 
 accompany the batrachian metamorphosis, as exemplified in Runa. 
 
 In Bufo the tadpole is smaller and blacker in all the stages of 
 growth and metamorphosis. In both genera of Anourans the 
 growth is greatest at the phase figured in 439 ; with the subse- 
 quent phases the bulk of the l>ody is diminished : and this is 
 remarkably the case in the Rana paradoxu. 
 
 In the Newts {Triton) the gills are in three pairs, larger and 
 more complex than in the Frog : the fore-limbs are the first to 
 emerge, and the gills persist long after the hind-limbs are deve- 
 loped. If late hatched and in a cold season, the gills may be re- 
 tained through the ensuing winter : they are absorbed before the 
 next breeding season comes on. 
 
 Much ingenious conjecture has been expended on the influence 
 of external circumstances and internal volitions and eftbrts during 
 the struggles for existence in the origin of species by progressive 
 transmutation ; and their succession on this planet has been 
 speculatively assigned to such causes. In the metamorphoses of 
 the Batrachia we seem to have such process carried on before our 
 eyes to its extremest extent. Xot merely is one specific form 
 changed to another of the same genus ; not merely is one generic 
 modification of an order substituted for another; the transmu- 
 tation is not even limited by passing from one order ( Urodela) to 
 another (Anoura): it affects a transition from class to class. The 
 Fish becomes the Frog ; the aquatic animal changes to the terres- 
 trial one ; the water-breather becomes the air-breather ; an insect 
 diet is substituted for a vegetable one. And these changes, more- 
 over, proceed gradually, continuously, and without any interruption 
 
G30 ANATOMY OF VERTEBRATES. 
 
 of active life. The larva having started into independent ex- 
 istence as a fish, does not relapse into the passive torpor of the 
 ovum, to leave the organising energies to complete their work 
 untroubled by the play of the parts they are to transmute, but 
 step by step each organ is modified, and the behaviour of the 
 animal and its life-sphere are the consequence, not the cause, of 
 the changes. 
 
 The external gills are not dried and shrivelled by exposure to 
 the air, nor does the larva gain its lungs by eiforts to change its 
 element and inhale a new respiratory medium. The beak is 
 shed, the jaws and tongue are developed, and the gut shortened, 
 before the young Frog is in a condition to catch a single fly. 
 The embryo acquires the breathing and locomotive organs — 
 gills and compressed tail — while imprisoned in the ovum ; and 
 the tadpole obtains its lungs and land-limbs while a denizen of 
 the pool : action and reaction between the germ and the gela- 
 tinous atmosphere of the yolk, or between the larva and its 
 aqueous atmosphere, have no part in these transmutations. The 
 Uatrachian is compelled to a new sphere of life by antecedent 
 obliterations, aljsorptions, and developements, in which external 
 influences and internal eftbrts have no share. 
 
 The phenomena of batrachian metamorphosis, that each spring 
 are observable wherever there is a pool of water in a green field 
 of England, are amongst the most suggestive and instructive 
 which the animal economy affords. 
 
 § 120. Developenient of Scaled Reptiles. — From the difference in 
 tlie structure of the ovum in the scaled and naked Reptiles, the pro- 
 portion of the food-yolk to the germ-yolk is much greater in the 
 former, and the formation of a germ-mass l^y the diffusive process 
 of successive fissions is restricted to a smaller pi-oportion of the 
 ovum than in Fishes. The formation of the embryonic trace closely 
 resembles that in the Fish and Frog ; but, instead of rising above 
 the yolk-ball, the embrj^o sinks into it ; first by the head, which, 
 as it plunges in, gets covered by a fold or hood of the ' serous ' or 
 outer embryonal cell -layer, drawn progressively over the body 
 imtil it is sheathed to beyond the heart ; then the tail, bending 
 down, acquires a caudal sheath ; and the rest of the trunk sinking, 
 the margins of the serous bed are produced over it continuouslj' 
 with the bodies of the cephalic and caudal sheaths, contracting 
 concentrically until the wliole embryo is inclosed in a ' serous ' bag, 
 reflected, as it seems, from the umbilicus, and thus the ' amnios,' 
 fig. 445, a, is constituted. The embryo being imprisoned in the 
 scrum of tliis bag, brancliiie could not act, and arc not dc\elopcd ; 
 
DEVELOPEMENT OF REPTILIA. C31 
 
 but a temporary air-breathing organ is substituted to remove the 
 carbon as the organic machine becomes more complex, and Its 
 actions more vigorous and various. From the fore-part of the 
 cloaca a vesicle is protruded which elongates, escapes by the um- 
 bdicus, and, carrying along with it blood-vessels, applies their 
 ramifications to the inner side of the shell : this is the ' allantois,' 
 figs. 445 and 450, h. 
 
 On the part of the yolk supporting the embryo blood-channels 
 appear which form a circular canal called ' vena terminalis ; ' it 
 l)ends towards the embryo at the part near tlie head, and passes 
 through the opening of the cephalic hood to a transverse canal, 
 ' vena afferens,' behind the heart: this is now an obliquely bent tube, 
 which pulsates and sends the circulating fluid to a dorsal vessel, 
 which soon distributes vessels, right and left, in the abdominal 
 region to the ' vena terminalis,' towards which numerous chan- 
 nels pass from the included space, fig. 450, c, the whole now 
 forming the ' area vasculosa ' upon the yolk. The fluid first 
 circulated in this system of channels is pale plasma with granules. ' 
 The first circulation in an amniotic embryo may be described as 
 passing from the heart-tube by vascular arches to the ' dorsal 
 artery,' which supplies the parts of the embryo, and sends ' om- 
 phalo-meseraic ' branches to the ' area vasculosa,' from the ' vena 
 terminalis' of which area the blood returns by the 'vena afferens ' 
 to the heart. The dorsal artery bifurcates posteriorly, and returns 
 along the abdomen as the ' vena; cardinales : ' the arteries to the 
 head also return as ' precaval veins,' and all these terminate in 
 the 'vena afterens.' Dilatations of the heart-tube indicate a 
 ventricle, fig. 443, a, and a ' bulbus arteriosus, lb. h : ' the latter is 
 more prominent at first. An auricular dilatation behind the ven- 
 tricle next appears. A protuberance in advance of the caudal 
 curvature is formed by what soon is recognisable as a hollow sac, 
 lb. d; which, as it expands, carries with it branches from the 
 dorsal artery : these are the ' umbilical ' or ' allantoic ' arteries, 
 fig. 450, /, which convey, as the bag protrudes and expands, part 
 of the circulation to receive the influence of the air through the 
 pores of the shell ; and, the blood -returning by the ' rnnbilical ' or 
 ' allantoic veins,' a subsidiary circulation to the vitelline, ib. c, is 
 established, analogous to the branchial one of Batrachians and 
 Fishes. The blood has now become red, and of shades indicating 
 its arterial and venous conditions. The blood-corpuscles, at first 
 "■lobular, become slightly flattened, but the discs are circular be- 
 fore acquiring their elliptical form.^ The omphalo-mesenteric 
 
 ' Hunter, cclxxx. (1794) p. 45, and xx. vol. v. p. xxiv. 
 
 ^ When the heart begins to lose its tubular shape the blood-partielcs arc minute 
 
632 ANATOMY OF VERTEBRATES. 
 
 arteries diverge from a common trunk, and the venous channels 
 become more concentrated towards the heart. A venous sinus is 
 formed l)ehind the auricle, and this is divided by a valvular struc- 
 ture from the ventricle, which now is larger than the bulbus. 
 
 The changes of the primitive vascular arches into the arterial 
 trunks arising from the adult heart are effected more speedily and 
 directly in allantoic Reptiles than in Batracliia, pp. 519, 520, 
 because no branchial organs and vessels are developed : such spe- 
 cial respiratory apparatus for a temporary aquatic existence is 
 interposed in the anallantoic species, and interrupts, so to speak, 
 the course of the transformation which is now to be described. 
 
 The primitive distribution of blood from the ' bulbus ' of the 
 embryonal heart in ' Vertebrates ' is by a series of symmetrical 
 arches on each side the alimentary canal, dorsad of which those 
 loops or arches unite to form or join the aortic trunk : they relate 
 to the primitive segmental character of the embryo, co-existing 
 with maxillary, mandibular, hyoidean, and scapular segments, all 
 of which at this period are unclosed arches on the sternal aspect 
 of the fore-part of the body. 
 
 The four or five primitive vascular arches have no essential 
 relation to gills, any more than the clefts or de])ressions between 
 the budding piers of the maxillary, fig. 444, a, mandibular, ib. b, 
 and hyoidean, ib. c, arches are necessarily the precursors of the 
 branchial openings. Both primary structures exist in the embryo 
 of those vcrteljrate classes that never possess the true branchial 
 organs : these are superadded developements upon the common 
 segmental type of pleurapophysial and pleurarterial parts, which 
 developements are peculiar to Fishes and Batrachians, persistino- 
 in the first, and vanishing in most of the latter Vertebrates. 
 Of the three vascular arches on each side by which the blood 
 passed from the bulbus to the dorsal vessel, the hindmost are 
 progressively converted, with the growth of the lungs, into the 
 ' pulmonary arteries,' each retaining a connection with the second 
 pair of vascular arches; the third, or anterior pair, with the 
 developement of the head and fore-limbs, in like manner become 
 diverted to their exclusive service, but for a time retain a con- 
 transparent globular cells, with a large granulated nuclons (mcsoblast, Ag.), attached 
 to the wall. ' By the application of water the nuelens bursts and the whole granular 
 contents come out, but still retain their globular state and appear to have a membrane 
 about them. From this it would appear that the apparently granular contents of the 
 mesoblast cmstituto, in reality, an cntoblast (nucleolus), which fills the mcsoblast.' 
 The ilat elliptic form is not attained until very late. The mcsoblast is taint and 
 
 homogeneous to within a short lime before extrication of the turtle: in the adult it 
 contains a darker euloblast. ceo. y>. ('.17. 
 
DEVELOPEMENT OF REPTILIA. 
 
 033 
 
 nection with the mid-pah-, as shown in fig. 332, p. 504, at a. 
 The returning blood from the expanding lungs leads to the deve- 
 lopement of a distinct chamber in the auricle, which finally be- 
 comes the left auricle. Partitions in the bulbus arteriosus efl'ect 
 a distinct communication of the pulmonary arteries with the 
 ventricle, and a division of what now becomes ' aorta ' into two 
 trunks. Of these one is appropriated to the left of the primitive 
 pair of middle arches ; the other becomes the trunk of the right 
 arch of that pair, and also of the anterior pair in course of change 
 into brachial and carotid arteries. The ' ductus arteriosi,' between 
 the anterior and middle arches (fig. 332, a), arc usually absorbed 
 (as at D, tig. 334) : those between the posterior and middle arches 
 (d, fig. 335) are longer retained through the same course of change. 
 The trunk, which gives off the carotids either exclusively or in 
 common with the brachials, is posterior in Heptiles to the trunk 
 of the left aorta, and to that of the pulmonary artery. With the 
 dcvelopement of septa in the bulbus, there proceeds a like change 
 in the ventricle itself, but it does not reach the condition of a 
 complete ' sei)tum ventriculorum ' until the crocodilian type of 
 Iliematocrya is attained (figs. 339, 340). 
 
 The suljstitution of kidneys for Wolffian bodies is preceded by 
 an enlargement of the latter, tig. 443, /, at their middle part, 
 Avith attenuation of their ends : the 
 true kidneys begin to be formed at 
 the upper medial part, and their uri- 
 niferous tubes are larger and more 
 convoluted. The genital organs 
 appear as a narrow white band upon 
 the ventral side of the Wolffian body. 
 
 The developement of the brain 
 closely resembles that in the Fish 
 (pp. 604, 607), but it soon bends 
 down at a stronger angle with the 
 myelon. The cerebellar fold is first 
 distino'uishable ; afterwards the de- 
 fleeted anterior part of the encepha- 
 lon becomes divided into mesen- 
 cephalon, cerebrum, and olfactory 
 lobes, and the cerebrum speedily 
 attains the sujjeriority of size which 
 distin<Tuishes the brain of the liejDtile from that of the Fish. The 
 ijineal gland shows a large proportional size in the embryo Turtle, 
 as does also the ' thalamus ' or lower lobe of the mesencephalon. 
 
 443 
 
 Embryo vtLoccrto. l 
 
C34 
 
 ANATOMY OF VERTEBRATES. 
 
 444 
 
 in which the optic nerves chiefly originate: the ventricles are 
 large in each mass. The eye-ball is formed, as in Fishes, by the 
 bending of a sausage-like bag about the lens, and the coalescence 
 of the ends brought into contact. The cicatrix, shown in fig. 443, 
 soon disappears. The capsule is next differentiated from the lens 
 proper. The eye-ball is, at first, unprotected, as in Fishes ; but 
 the contiguous skin-border begins to encroach upon its fore part, 
 with modified growth, to form the eyelids. 
 
 After the developement of the labyrinth from the primitive 
 ear-capsule, a tympanic cavity is formed, in which the ' stapes ' 
 appears as a short thick cartilaginous 
 cylinder in the Chelonia, in which the 
 ' meatus auditorius ' broadens outwards 
 to a trumpet shape, which it retains. In 
 the Ofihidia the ' stapes,' fig. 444, B, e, is 
 similarly developed, independently of the 
 tympanic and mandibular (or so-called 
 jMeokel's) cartilage, ib. d, as shown by 
 Rathke, in Nutrix torquata. The nostrils 
 appear as deep depressions at the fore end 
 of the head, the margins of wliicli Ijecome 
 incurved, and the bottom of the sac is 
 produced into a canal communicating with 
 the mouth. 
 
 In and from the membrane of the 
 notochord, continued along the basis cranii, is developed the 
 cartilage of the basi-prcsphenoid, blending laterally with the 
 ear-capsules : the l^asal cartilage bifurcates anteriorly, and re- 
 imites surrounding the hypophysial fissure : it is then continued 
 singly forward, and expands anteriorly in connection with car- 
 tilaginous plates from which, in Chelonia and Ophidia, the 
 profronto-nasal bones arc developed. In Lacertdia the large 
 ' lacrymal ' bones grow from the same embryonal cartilage. 
 Behind these foremost representatives of ncurapophyses are 
 three pairs, more clearly showing the neurapophysial characters : 
 the pair resting on the bifurcated prcsphenoidal part of the 
 basal cartilage, in relation to the optic nerves, become ' orbito- 
 sphcnoids;" the next pair, in relation to the trigeminal nerves, 
 situated anterior to the ' ear-capsules,' become the ' alisphe- 
 noids;"* the pair behind the ear-capsules, resting on the 
 basioccipital, beeouic the ex- and par-occipitals.' Thus the 
 
 ' cucxxx, taf. vii. iig. 17,/, ' vnnleror KiMllioinllu.iiol.' ' 111. c, ' liiiitcrcv KcilboiiitUigcl. 
 ■' Ib. b, ' SeUciUlnjil dcs IIiiitcili;uiplbi.iin.'S.' 
 
 ivclios of cniiiinni ; 
 Sriiikc. cccxxx. 
 
DEVELOPEMENT OF REPTILIA. 635 
 
 neural arches of four vertebral segments are plainly indicated iu 
 tlie developement of the rei)tilian cranium. The hremal arches 
 make their first appearance as pairs of slender rib-like bones : 
 the foremost, fig. 444, a, becomes the palato- maxillary arch ; ' the 
 next early shows more clearly its division into the pleur- and 
 lixm-apophysial parts of the tympauo-mandibular arch, ib. b ; the 
 third, ib. c, is the hyoid arch : the fourth has no longer the 
 cephalic relation which it shows in Fishes ; and the four neura- 
 pophyscs are matched below by only three hajmapophyses in the 
 reptilian cranium. 
 
 In the oviparous Snakes, Natrix torquata, e.g., a certain 
 progress in the developement of the embryo is found to have 
 been made when the egg is laid, and the rest is completed and 
 the young extricated in the course of about two months, sooner 
 or later, according to the surrounding temperature. 
 
 When developement has ad^^anced to the formation of the 
 amnios about the embryo, the head is distinct, and shows the eye- 
 ball and ear-sac ; also the maxillary and mandibular processes and 
 the beginning of the hyoid, with the intervening depressions, mis- 
 called ' branchial clefts : ' the heart, as a sigmoidally bent tube, 
 fills the concavity between the frontal process and the chest: 
 the allantois has protrvided, as a globrdar vesicle, about the size 
 of the head ; and beyond its emergence the tail forms a single 
 spiral coil : the vascular area on which the vitelline vessels ramify 
 co^'ers half the food-yolk. The long trunk of the Serpent grows 
 in a series of decreasing spirals, and when five or six are formed, 
 the rudiment of the liver and the primordial kidneys are dis- 
 cernible. Fig. 444 shows the em):)ryo at this period magnified 
 four times : a is the amnios, h 
 the allantois, d its tubular stem, 
 produced from the cloaca, or 
 ' urachus : ' the front view of the 
 head shows the ' frontal process,' 
 0, and the bases, n, of the palato- 
 maxillary hajmal arch. The pri- 
 mordial kidneys are remarkable 
 for their length : c indicates a 
 portion of the vitellicle. With 
 
 the dilatation of the fore-part_ of E,o„n„s„a,.e ,.-.,„-,.,., cccxxx. 
 
 the alimentary canal indicating 
 
 the stomach, a small appendage, the i)ancreas, appears, marking 
 the beginning of the intestine. The lungs are next seen as a 
 
 ' cccxxx. taf. vii. fig. 11, e, ' Obcikicfcr.' 
 
G3S 
 
 ANATOMY OF VERTEBRATES. 
 
 446 
 
 symmetrical pair of longisli simple sacs, extending from the 
 pharynx on each side of the cjesojthagus to tlie beginning of the 
 liver : the left division soon begins to exceed the right in length, 
 and then seems to monopolise the power of growth. The common 
 stem or neck of the pulmonary sacs elongates, contracts, and 
 Ijegins to show traces of the transverse cartilages ; and at about 
 the latter third of the developemental period the right lung appears 
 as a mere appendage to the beginning of the left. The appear- 
 ance of malpighian bodies, as minute red points on part of the 
 surface of the primordial kidneys, is the first indication of the 
 developement therefrom of the kidneys : these grow between 
 the jH'imordial kidneys and the vertebra? at the hindmost end of 
 the abdominal cavity. The testis, or ovary, is differentiated from 
 the ventral surface of the fore-part of the primordial glands : at 
 
 one period of developement the primor- 
 dial ducts coexist with the sperm-duct 
 and ureters. Four or five ducts emerge 
 from the liver and unite into a com- 
 mon one before communicating with 
 the intestine ; a similar duct, proceed- 
 ing from the common one, expands at 
 its opposite end into the gall-bladder. 
 This remains near the pylorus : the 
 hepatic ducts elongate as the intestine 
 recedes on the growth of the snake. 
 The spleen first appears as an append- 
 age to the narrow end of the j^ancreas. 
 In the male embryo, the two bifurcate 
 penes project from the cloaca before 
 the period of extrication. 
 
 Figure 446 shows the posterior half 
 of the embryo of the Viper at a late 
 period of developement. The yolk 
 bag, fl, is mucli reduced in size, but 
 is not yet taken into the abdominal 
 cavity ; h is the portion of the amnios 
 adherent to the vitclliclo ; c is the 
 short pedicle, including part of (/, the 
 ductus Aitcllo-intestinalis, which as- 
 cends to terminate at e, lietween the 
 longitudmal folds of the mucous mem- 
 brane of tlie small intestine,, f. The continuation of the intestine to 
 the cloaca, /, is shown at v, li ; tlie ovaria at /, / ; the kidnevs at /(, h. 
 
DEVELOPEMENT OE KEPTILIA. 
 
 637 
 
 tfllirlc i)f a Viper at a more advanced period, showing the 
 yulk partially taken into tlie abdominal cavily. XLiii. 
 
 448 
 
 Tn figure 447, the vitel- 
 liclc of a Viper, at a more 
 advanced period, shows part 
 of the food-yolli entering 
 the abdominal cavity, at u: 
 the ductus vitello-intesti- 
 nalis, d, is reduced to a 
 thread : g is the intestine, 
 and /{ the kidney. 
 
 Figure 448 shows the 
 body of a Viper just before 
 the period of extrication 
 Irora the egg - coverings ; 
 the parictcs of the abdomen 
 are partly removed to show 
 the vitellicle, b, which has 
 now become inclosed in 
 that cavity, with almost 
 complete obliteration of the 
 umbilical cicatrix : a, the 
 remains of amnios and al- 
 lantois : d, the much short- 
 ened ductus vitello-intesti- 
 nalis : g, the liver : ff, the 
 stomach : f, the duodenum: 
 n, the small intestine : the 
 other letters indicate the 
 same parts as in the pre- 
 ceding fio'ures. 
 
 The gravid Viper is more 
 than usually sluggish, and 
 loves to bask in the hot 
 sunshine, turning her belly 
 as if to court the aid of the 
 extraneous warmth in ac- 
 celerating the internal in- 
 cubation of her eggs. 
 
 Figure 449 shows the 
 Q(i-(y and embryo of the 
 jMonitor Lizard near the 
 iieriod of extrication: a is Body oi;a\-iperjustiieroreiti.siiatciicd. .\liii. 
 
 tlie remnant of the food-yolk : b the amnion laid open to show the 
 embryo, d; its long tru'nk aud tail arc packed in spiral folds as 
 
638 
 
 ANATOMY OF VERTEBRATES. 
 
 449 
 
 in the embryo Seqient : c is the leathery and partially calcified 
 egg-shell. An embryo Lizard, at an earlier period of develope- 
 ment, is shown in fig. 44.3. 
 
 Hunter left the following preparations illustrative of the 
 
 developement of the Cro- 
 codile. No. 3364 shows the 
 calcareous outer crust of 
 the inner 'membrana puta- 
 minis' of the egg : No. 3365 
 shows the attachment of the 
 vascular allantoisto that shell 
 membrane in an embryo in 
 wliich part of the yolk has been 
 received within the abdomen. 
 In No. 3366 the hinder half 
 of the Crocodile is dissected 
 to show the condition of the 
 vitelline and allantoic sacs at 
 the close of foetal develojie- 
 ment : the vitellicle presents 
 an irregular lobated form, 
 and its short and narrow 
 duct communicates with the 
 small intestine a little below 
 the duodenum: the allantois 
 communicates with the lower 
 and fore part of the cloaca 
 by means of a long and slender duct homologous with the urachus : 
 but no part is dilated, as in certain Lizards, to form the urinary 
 
 bladder. In No. 3370 is sliown the 
 vitellicle, after inclusion within the 
 abdominal walls ; it is much reduced 
 in size, and its contents are hard and 
 stringy. 
 
 The period of external incubation 
 hj the action of the sun's rays upon 
 the sand-nest of the eggs of tlic 
 Turtle {ChcJonc Midas) has been 
 ascertained to be seven weeks. 
 
 Figure 450 shows the embryo 
 
 of a Snajiping Turtle (Chch/dra 
 
 siTjinifinn) from an egg laid June 21st and opened Sc]>fenibcr 21st 
 
 of the same year. The anniios Is cut away : c shows the' area vascu- 
 
 Egg anr] unibryo of (he Jloiiitoi- T,izard. xliii. 
 
 450 
 
DEVELOPEMENT OF REPTILIA. 
 
 639 
 
 losa,' with the omphalo-mesenteric vessels ; b is part of the allantois 
 with tlie aUantoic or ' umbilical ' vessels, i. The outline of the cara- 
 pace is just marked on the back of the embryo, and the proportion 
 of the vertebral column not so moditied appears to be greater, as 
 is its resemblance to the type-form of Reptile, than in the adult. 
 
 The condition of the carapace and the outward form of a P'resh- 
 Water Tortoise {Emys) is shown in figure 451. The amnios, a, is 
 turned back to show the posi- 
 tion of the limbs and head in '*■''' 
 the egg : b is the part of the 
 allantois ; c the remnant of the 
 yolk. The central opening of 
 the plastron, which is perma- 
 nent in the marine Ohelonia, 
 is seen at this period in all the 
 order, but is quickly filled up 
 in the land and fresh-water 
 species. The chief speciality 
 in the developement of the 
 scaled Eeptiles, compared with 
 each other, relates to that of 
 the carapace and plastron of 
 the Chelonia : and this has 
 been explained at pp. 557-9, 
 and illustrated in figs. 369-72. 
 
 When the Turtle is hatched, 
 the bones of the head show 
 different degrees of ossification. 
 The premaxillary and preman- 
 dibular are most advanced for the purposes of feeding ; the maxil- 
 lary, the back part of the mandible, the prefronto-nasal, frontal, 
 and parietal come next in hardness. The superoccijoital shows an 
 outer layer of bone, the rest being gristle; the basioccipital and 
 basisphenoid begin to be ossified from the centre ; the alisphenoids 
 and exoccipitals are still cartilaginous. 
 
 The limbs begin to show the digital divisions soon after the 
 carapace is outlined, and the cartilages of the metacarpals and 
 metatarsals are first discernible ; the phalanges are composed of 
 compacted polygonal cells at near the term of incubation, which 
 then become ' cartilage cells,' widely divided by blastema. The 
 lone bones of the limbs show a thin outer crust of bone inclosing 
 cartilage, which is progressively ossified, solidifying the shaft, 
 without subsequent excavation of any medullary cavity. 
 
 VOL. I. TT 
 
 Embryo of an Emys. 
 
G40 
 
 ANATOMY OP VERTEBRATES. 
 
 In the cold-blooded reptiles, hatched by external heat, indepen- 
 dentlj' of incubation, the course of developement may be inter- 
 rupted for longer periods, without hurt to the embryo, than in the 
 warm-blooded Ovipara. Agassiz states that in Testudincda the 
 common period of hatching may be 'postponed for months.' 
 
 In Snakes and Lizards a sharp tooth is developed in the pre- 
 maxillary of the embryo, towards the close of incubation, where- 
 with they cut through the tough egg-shell.' The operation of this 
 transitory and purposive weapon has been observed by Weinland ;^ 
 it totally disappears in the adult of most Ophidia. For breaking- 
 through the more brittle shell in Chelouia the embryo is provided 
 with a sort of horn or hard excrescence above the end of the upper 
 jaw : this afterwards disappears. In the Crocodilia the snout of 
 the nearly hatched young is sufficiently hard to break the egg- 
 shell ; but there is no distinct tubercle, nor any jDrecociously 
 developed premaxillary tooth.^ 
 
 CCCXXXI'I. 
 
 cccxxxvr. 
 
 ccc. p. 288. 
 
 452 
 
 Initial step? oi Vcriebvato DfvdoiicTiiont. ricrni-yolJ; ot 
 R((iuf lrw}wrin'ia. rrrxxWT. 
 
WORKS 
 
 RErERRED TO BY ROHAN NUJIERALS IN THE FIRST VOLUME. 
 
 I. Carus. Urtheilen dfs Knochen- unci Schalengerilstos. Fol. 1828. 
 II. Geoffeot St. HiLAiEE. Mimoires du Museum. 4to. t. ix. 1822,p. 119. 
 
 III. Von Eaee. Meckel's Ai'chiv fiir Physiologie. 1826. Ileft iii. 
 
 IV. BiBiiA. Chemische Uutersuelmngen iiljer die Knoclien unJ Zuhne. Svo. 
 
 1844 
 V. OwEK, E. Odontograijhy. 4to. 1840-1845. 
 VI, Owen, R. Fossil Mammalia, Zoology of the Vogagc of the Beagle. 4to. 
 11 art i. 1838. 
 VII. Hunter. Manuscripts printed in the Catalogue of the Physiological Series 
 in tlie Museum of tlie lioj-al College of Surgeons. 4to. o toIs. 1S32- 
 1840 
 VIII. PuRKiNJE and Deutcsu. Do Penitiori Structura OLiserrationes. 4to. 1834. 
 IX. Teevieanus. Beytrage des Organisclien Lebens. Bremen, 1835. 
 X. Mtn:.LEH, luo. Ueberdie Structur, &e., der Knorpel und Knochen, Poggen- 
 
 dorf's Annalender Physik, 1836, Tol. yiii. p. 295. 
 XL HuNTEB, Jno. Transactions of a Society for the Improrement of Medical 
 and Cliirurgical Kno"vrledge, vol. ii. p. 277. 
 XII. CxJTiBB. Lemons d'Anatomie Comparec. Svo. Ed. 1835-1846. 
 XIII. lb. 8vo. Ed. 1799. 
 
 XIV. Geoffeot St. IIiLAiEE. Annales des Sciences Naturelles, t. iii. Svo. 1824. 
 XV. Geoffroy St. Hilaiee. Principes de Philosophic Zoologicjue. Svo. 1S30. 
 XVI. Barclay, in Monro on the Bones. Svo. Ed. 1820. 
 XVII. Baecl-iy, in Miteliel's Plates of the Bones. 4to. 1824. 
 XVIII. Seeees. Des Lois de I'Osteogenie, Extrait de 1' Analyse des Travaux do 
 I'Academie Eoyale des Sciences pendant I'annee 1819. Svo. 
 XIX. 0%™n, E. Geological Transactions. 4to. 1838. 
 XX. O-^^TSN, E. Catalogue of the Physiological Series in the Museum of the 
 Eoyal College of Surgeons. 4to. 5 vols. 1832-1840. 2nd ed., vol. i. 
 1852. 
 XXL MiJia.EE, J. Verglcicliende Anatomic der Mj-xinoiden. Abliand. Altad. der 
 Wissenschaften zu Berlin, 1834-1843. 
 XXII. Agassiz. Hist oire des Poissons Eo.s.siles. 4to. 4 vols. 1833-1845. 
 XXIIX. CuviEE and Vaeenciennes. Histoire Naturelle des Poissons. 4to. 1828- 
 
 1845. 
 XXIV. Ctjviee. Eegno Animal. Svo. 5 vols. 1829. 
 XXV. MuLLEE. J. Ueber den Ganoiden und das natiirliclie System der Fische. 
 
 4to. 1846. 
 XXVI. De Bi.AiNTiLLE. Annales des Sciences Naturelles. Svo. 1S37. 
 XXVII. Geant, Prof. E. Outlines of Comparative An.atomy. Svo. 1835-1841. 
 
 T T 2 
 
C42 
 
 WORKS EEFEEEED TO BY IIOMAN NUMERALS 
 
 XXVIII. 
 
 XXTX. 
 
 XXX. 
 
 XXXI. 
 
 XXXII. 
 XXXIII. 
 
 XXXIV. 
 XXXV. 
 XXXVI. 
 
 XXXVII 
 
 XXXVIII. 
 
 XXXIX. 
 
 XL. 
 
 XLI. 
 XLII, 
 XLIII. 
 
 XLIV. 
 
 XLV. 
 
 XL VI. 
 
 XLVII. 
 
 XL VII I, 
 
 XLIX. 
 
 L. 
 
 LI. 
 
 LII. 
 
 LIII. 
 
 LIV, 
 
 LV. 
 
 LVI. 
 
 LVII. 
 
 LVIII, 
 
 LIX. 
 
 LX. 
 
 LXI. 
 
 LXII. 
 LXIII. 
 
 LXIV. 
 
 LXV, 
 
 — LXVI. 
 
 LXVII. 
 
 LXVIII. 
 
 LXIX. 
 
 LXX. 
 LXXL 
 
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IN THE FIRST VOLUME. 
 
 6-io 
 
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