£01 
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 1899 
 
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THE LIBRARY 
 
 OF 
 
 THE UNIVERSITY 
 
 OF CALIFORNIA 
 
 PRESENTED BY 
 
 PROF. CHARLES A. KOFOID AND 
 
 MRS. PRUDENCE W. KOFOID 
 
Dunglisori } s American Medical Library. 
 
 THE 
 
 STUDENT'S COMPENDIUM 
 
 OF 
 
 COMPARATIVE ANATOMY. 
 
 BY P. EYERS, 
 
 LICENTIATE OF THE ROYAL COLLEGE OF SURGEONS IN IRELAND, &C. 
 
 Sparsa coegi."— Ovid. 
 
 PHILADELPHIA : 
 
 PRINTED AND PUBLISHED BY A. WALDIE, 40 CARPENTER ST. 
 
 1839. 
 

 TO 
 
 PHILIP CRAMPTON, M. D., F. R. S. 
 
 SURGEON GENERAL TO THE FORCES IN IRELAND, 
 
 <fcc. Sec. Sec. 
 
 AS AN INADEQUATE, BUT SINCERE TESTIMONY OF RESPECT, 
 
 TO 
 
 DISTINGUISHED SCIENTIFIC ATTAINMENTS, 
 
 AND 
 
 DESERVED PROFESSIONAL EMINENCE, 
 
 THIS VOLUME 
 
 IS INSCRIBED, 
 
 BY 
 
 HIS GRATEFUL AND OBLIGED FRIEND, 
 
 THE AUTHOR. 
 
 y&w 
 
PREFACE. 
 
 In the compilation of these pages no originality is claimed, but 
 the labours of modern authors have been freely appealed to, and 
 it is trusted, on every occasion, with due respect. A list of the 
 several authors consulted has been added at the end of the book. 
 
 I have to acknowledge several obligations to my friend Dr. 
 Houston of this city, whose scientific acquirements and connec- 
 tion with the Museum of the College, have well qualified him for 
 the many auxiliary favours he has conferred on me. 
 
 P. E. 
 
 Dublin, 33 Aungier Street, 
 September, 1838. 
 
COMPENDIUM 
 
 OF 
 
 COMPARATIVE ANATOMY. 
 
 CHAPTER I. 
 
 PRELIMINARY OBSERVATIONS. 
 
 When we turn our attention to the busy theatre of animal life, 
 we are at once attracted by scenes of wonder and delight. The 
 works of nature appear unbounded in extent, variety, and riches. 
 Wherever the eye is cast, from the icy regions of the pole to the 
 scorching sands of the line, it beholds life displayed in forms as 
 endless as they are enchanting. 
 
 Every region and every element is the abode of numerous animals, 
 and is admirably suited to their peculiar living habits and instincts ; 
 the vastness of their number may be estimated from the declaration 
 of the celebrated Ehrenberg, that a single cubic line which is less 
 than a drop of fluid contains 500,000,000 monads. 
 
 But however varied and delightful the occupations of the zoolo- 
 gist may be, his information is still defective, and he perceives that 
 the interior machinery of life is hidden from his observation, and its 
 springs concealed by clouds which nothing but the light of dissec- 
 tions can dispel. 
 
 When once engaged in this captivating department of his inves- 
 tigations, he begins to observe the beautifully progressive develop- 
 ment of organisation, varied and modified in obedience to certain 
 laws ; he will often behold the same animal, according to the parti- 
 cular epoch of its existence, undergoing metamorphosis, appearing 
 under different characters, and playing very different parts on the 
 stage of life. 
 
 Having entered a little more fully into the details of comparative 
 anatomy, he will often observe an organ which has attained a high 
 degree of development, and whose functions are perfectly under- 
 stood in one animal ; diminutive, rudimentary, and apparently use- 
 less in another. Hence it must be obvious, that he who aspires to a 
 perfect knowledge of human structure and function, must extend 
 his researches to an examination of the animal kingdom in general ; 
 and accordingly great advantage will be found in a previous ac- 
 quaintance with some one or more of the most approved classifica- 
 tions in natural history. 
 
 Every classification hitherto proposed has in some particular or 
 other its imperfections ; but it matters little what scale we adopt. 
 
8 EVERS'S COMPARATIVE ANATOMY. 
 
 or whether we make use of several, provided that our object of con- 
 veying or acquiring a knowledge of the comparative structure of 
 animal bodies be attained. This must be my excuse for appearing 
 in some places to have followed the arrangement of Cuvier, and in 
 others, that of Dr. Grant, both having their excellences, and their 
 authors holding the highest place as authorities on the subject. 
 
 Cuvier's and Grant's classifications are therefore subjoined, ac- 
 companied by familiar illustrations of each, to lead the student at 
 one glance to the objects which each subdivision embraces. The 
 examples appended to Grant's classification have been added by 
 myself, whilst those of Cuvier have been taken from Dr. Houston's 
 Descriptive Catalogue of the Preparations in the Museum of the 
 Royal College of Surgeons in Ireland, with a few additional exam- 
 ples from Roget's Bridgewater Treatise. 
 
 It might appear an omission not to make some allusion to the 
 arrangement of the animal kingdom adopted by the immortal Lin- 
 neeus, but the researches of later zoologists have proved it so defec- 
 tive, that it is not followed by any writer or teacher of the present 
 day, and needs therefore but a cursory allusion. Suffice it to state 
 that he divided the whole animal kingdom into six classes, Mam- 
 malia, Aves, Reptilia, Pisces, Insecta, Vermes, founding his classi- 
 fication mainly on the peculiarities afforded by the respiratory and 
 sanguineous systems. 
 
 OUTLINE OF CUVIER'S CLASSIFICATION OF ANIMALS. 
 
 FOUR GREAT DIVISIONS. 
 
 1. Vertebrata. 3. Articulata. 
 
 2. Mollusca. 4. Radiata. 
 
 VERTEBRATA. 
 
 Characters. — Internal skeleton — brain and spinal marrow in separate cavi- 
 ties — red blood and muscular heart — mouth with horizontal jaws — five 
 organs of sense — never more than four limbs — separate sexes. 
 
 MOLLUSCA. 
 
 Ch. — No skeleton — muscles all attached to external skin — nervous system 
 situated in the visceral cavity and composed of separate masses joined by 
 nervous filaments — taste, sight, or as in one instance, hearing, the only senses 
 — organs of circulation, respiration, and digestion very perfect. 
 
 ARTICULATA. 
 
 Ch. — No skeleton — two long nervous chords with ganglia at intervals — 
 have usually taste and sight — divided in jointed rings, soft or hard, to inside 
 of which muscles attached — sometimes lateral limbs, sometimes none — jaws 
 when present alwavs lateral. 
 
CLASSIFICATION. 
 
 RADIATA. 
 
 Ch. — Organs of movement and sense disposed circularly around a centre, 
 not symmetrically as in the preceding — no visible nerves — no organs of sense 
 or circulation — respiration by the outward integument — intestines often a 
 simple bag— sometimes the animal is but a homogeneous pulp without aper- 
 ture or cavity. 
 
 I. YERTEBRATA. 
 
 Class 1. MAMMALIA. 
 Order 1. Bimana - - Examples, Man. 
 
 2. q,cadrumana 
 
 3. Cheirotera - 
 
 4. Insectivora - 
 
 5. Plantigrada - 
 
 6. DlGITIGRADA - 
 
 7. Amphibia - - 
 
 8. Marsdpialia - 
 
 9. Edentata - - 
 
 10. Rodentia - - 
 
 11. ruminantia - 
 
 12. Pachydermata 
 
 13. Cetacea 
 
 Cl. 2. AVES. 
 
 Orel 
 
 Exam. 
 
 Orel 
 
 Orel. 
 
 1. Accipitres 
 
 2. Passeres - - 
 
 3. ScANSORES - - 
 
 4. GALLIN2B - - 
 
 5. Grallje - - 
 
 6. Palmipedes - 
 
 Cl. 3. REPTILIA. 
 
 1. Chelonia - Exam. 
 
 2. Sauria - - - 
 
 3. Ophidia - - 
 
 4. Batrachia - 
 
 Cl. 4. PISCES. 
 1. Chondropterygii Exam. 
 
 Monkey, ape, lemur. 
 
 Bat, colugo. 
 
 Hedge-hog, shrew, mole. 
 
 Bear, badger, glutton. 
 
 Dog, lion, cat, marten, weasel, otter, 
 
 Seal, walrus. 
 
 Opossum, kangaroo, wombat. 
 
 Sloth, armadillo, ant-eater. 
 
 Beaver, rat, squirrel, porcupine, hare, 
 
 Camel, deer, giraffe, sheep, ox. 
 
 Elephant, hog, rhinoceros, tapir, horse, 
 
 Dolphin, whale. 
 
 Vulture, eagle, owl, hawk. 
 Thrush, swallow, lark, crow, sparrow. 
 Woodpecker, cuckoo, toucan, parrot. 
 Peacock, pheasant, grouse, pigeon. 
 Plover, stork, snipe, ibis, flamingo. 
 Auk, grebe, gull, pelican, swan, duck. 
 
 Tortoise, turtle, emys. 
 
 Crocodile, lizard, gecko, chameleon. 
 
 Serpents, boa, viper. 
 
 Frog, salamander, newt, proteus, siren, 
 
 2. Malacopterygii 
 
 3. LoPHOBRANCHII 
 
 4. Pleclognatiii 
 
 5. Acanthopterygii 
 
 Head crowned with tenta- 
 cula which serve as feet 
 
 Progression by fins placed 
 near the head. 
 
 Head free progression on 
 the belly. 
 
 Without distinct head. 
 
 :■ 
 
 Lamprey, shark, ray, sturgeon. 
 Salmon, herring, cod, sole, eel. 
 
 Pike-fish, pegasus. 
 
 Sun-fish, trunk-fish. 
 
 Perch, mackerel, sword-fish. 
 
 II. MOLLUSCA. 
 Cl 
 
 I. Cephalopoda Exam. Cuttle-fish, cala- 
 mary, nautilus. 
 
 2. Pteropoda 
 
 3. Gasteropoda 
 
 4. Acephala 
 
 Clio, hyaloea. 
 
 Slug, snail, lim- 
 pet. 
 
 Oyster, muscle, 
 ascidia. 
 
10 
 
 EVERS S COMPARATIVE ANATOMY. 
 
 Two long arms at the mouth 
 for seizing objects. 
 
 Arms very numerous, arti- 
 culated, horny. 
 
 5. Brachiopoda Exam. Lingula, tereba- 
 
 tula. 
 
 6. Cirrhopoda Barnacle, triton. 
 
 III. ARTIOULATA. 
 CI. 1. ANNELIDA. 
 
 Ord. 1. Tubicola - - - 
 
 2. Dorsibranchia - 
 
 3. Abranchia - - 
 
 - Exam. 
 
 Serpula, sabella, amphitrite. 
 Nereis, aphrodite, lob-worm. 
 Earth-worm, leech, nais, hair-worm. 
 
 Cl. 2. CRUSTACEA. 
 
 Ord. 1. Malacostraca - - Exam. 
 
 2. Decapoda - - - 
 
 3. Stomopoda - - - 
 
 4. Amphipoda - - - i 
 
 5. LiEMODIPODA - - 
 
 6. ISOPODA - - - - , . 
 
 7. Entomostrata - - 
 
 Cl. 3. ARACHNIDA. 
 Ord. 1. Pulmonalia - - - Exam. 
 
 2. Trachealia 
 
 Cl. 4. INSECTA. 
 
 Ord. 1. Aptera - - 
 
 2. Coleoptera - 
 
 3. Ortiioptera 
 
 4. Hemiptora - 
 
 5. Neuroptera 
 
 6. Hymenoptera 
 
 7. Lepidoptera 
 
 8. Rhipiptera - 
 
 9. Diptera - - 
 
 Exam. 
 
 Lobster, crab, prawn. 
 
 Squill, phyllosoma. 
 
 Grammarus, sand-hopper. 
 
 Cyamus. 
 
 Wood-louse. 
 
 Monoculus. 
 
 Spider, tarantula, scorpion. 
 Phalangium, mite. 
 
 Centipede, podura. 
 Beetle, glow-worm. 
 Grass-hopper, locust. 
 Fire-fly, aphis. 
 Dragon-fly, ephemera. 
 Bee, wasp, ant. 
 Butter-fly, moth. 
 Xenos, stylops. 
 Gnat, house-fly. 
 
 IV. RADIATA vel Zoophyta. 
 
 ClaSS 1. ECHINODERMATA 
 
 2. Entozoa - - 
 
 3. acalephje - - 
 
 4. Polypi - 
 
 5. Infusoria - - 
 
 Exam. Star-fish, sea-urchin. 
 
 ! Fluke, hydatid, tape-worm. 
 
 Actinia, medusa. 
 
 Hydra, coral, madrepore, pennatula. 
 
 Brachionus, vibrio, proteus, monas. 
 
 GRANT'S DIVISION OF THE ANIMAL KINGDOM. 
 
 Division. Class. 
 
 f 1. POLYASTRICA 
 
 I. CYCLO-NEURAl I £° RIFE * A " " 
 
 -RAD.ATA 1 4:I or E P„T- I 
 I 5. Echinodermata 
 
 Exam. Monad, madrepore. 
 
 — Sponges. 
 
 Polypes, corals. 
 
 Medusa, actinia. 
 
 Star-fish, sea-urchin. 
 
SKELETON IN THE INVERTEBRATA. 
 
 11 
 
 Division. 
 
 II. DIPLO-NEURA 
 vel ARTICULA- 
 TA. 
 
 III. CYCLO-GAN- 
 GLIATA vel 
 MOLLUSCA. 
 
 IV. SPINI-CERE- 
 BRATA vel 
 VERTEBRATA. 
 
 Class. 
 f 6. Entozoa - 
 
 7. 
 8. 
 9. 
 10. 
 11. 
 12. 
 113. 
 fl4. 
 115. 
 {jft. 
 117. 
 
 Lis. 
 f19. 
 
 I 20. 
 <2l. 
 
 | 22. 
 123. 
 
 Rotifera - 
 
 ClRRHOPODA 
 ANiNELIDA - 
 
 Myriapoda 
 Insecta - - 
 Arachnida 
 Crustacea 
 Tdnicata - 
 conchifera 
 Gasteropoda 
 Pteropoda 
 Cephalopoda 
 Pisces - - 
 Amphibia - 
 Reptilia - 
 Aves - - 
 Mammalia 
 
 Exam. Intestinal worms, hyda- 
 tids. 
 
 Patella. 
 
 Barnacle, triton. 
 
 Earth-worm, leech, 
 
 Scolopendra. 
 
 Bee, butter-fly. 
 
 Spider, scorpion. 
 
 Lobster, crab. 
 
 Ascidia intestinalis. 
 
 Muscle, oyster. 
 
 Slug, snail. 
 
 ■ Clio, hvalosa. 
 
 Cuttle-fish. 
 
 Salmon, shark, eel. 
 
 Frog, toad, proteus. 
 
 Tortoise, lizard, serpent. 
 
 1 Eagle, heron, duck. 
 
 Man, kangaroo, whale. 
 
 Many other arrangements of the animal kingdom have been pro- 
 posed by different zoologists; some, as Linneeus, founding their basis 
 of classification on the vascular and respiratory systems, and others on 
 the peculiarities afforded by the generative organs. Aristotle divided 
 all animals into those with, and those without red blood; and 
 Lamark into the apathic, the sensitive, and the intelligent. 
 
 CHAPTER II. 
 
 SKELETON IN THE INVERTEBRATA. 
 
 General observations. — The skeleton gives figure, strength, and 
 solidity to the entire frame ; it serves as a basis of support to the 
 soft parts, forms levers of locomotion, and encloses cavities to pro- 
 tect and defend the most delicate and important organs. Its use, 
 however, being chiefly of a mechanical nature, it will be found to 
 vary much, according to the respective wants, habits, and instincts 
 of animals. In all the operations of nature we find that there is a 
 rigid economy observed ; the means employed are such only as 
 are required, and always the most simple by which the intended 
 purposes can be accomplished. Hence we shall not be surprised to 
 meet with infinitely varied modifications of skeleton throughout 
 the widely extended range of the animal world. The chemical 
 composition of this solid frame-work presents some variety. For 
 instance, silica is found in the lowest forms of the radiata ; carbo- 
 nate of lime in the molluscous animals; carbonate and phosphate of 
 lime in the articulata ; and phosphate of lime in the organised skele- 
 tons of the vetebrata. This frame-work is sometimes placed external 
 to the soft parts, and in others it is internal to them. In no instance 
 do we meet with a bony skeleton except in animals possessed of 
 
12 
 
 a regularly formed brain ; and here it is obvious to those who un- 
 derstand the difference between the growth of shell and bone that 
 the former would be unfit for the purpose, since there is no provi- 
 sion made for the enlargement of the original cavity. 
 
 Radiata, Cuvier ; Cyclo-neura, Grant. — In this acrite or 
 lowest division of the animal kingdom the skeleton generally holds 
 an internal situation, and is composed either of one large mass or 
 several smaller pieces symmetrically disposed, composed of silicious 
 or calcareous spicula. In many of the polygastrics the organ of 
 support consists in a condensation of the common integument en- 
 veloping the body — occasionally in the form. of an elastic vagini- 
 form sheath into which the animal can retreat on the approach of 
 danger, (fee, as seen in the vaginicola innata. Among the pori- 
 phera, skeletons are met with of a horny, silicious, or calcareous 
 structure, variously modified. In none does nature seem to have 
 amused herself more in the construction of skeletons than among the 
 zoophytes. Here they are met with internal or external, soft, horny, 
 or calcareous ; branched, globular, or filiform ; free or fixed. The 
 astenas and others of the echinodermata present us with skeletons 
 in the form of external crusts or shells, disposed after the manner 
 of plates, and composed of carbonate, with a trace of phosphate 
 of lime. 
 
 Articidata, Cuvier; Diplo-nerose Animals, Grant. — The bo- 
 dies of these animals are generally long, cylindrical, and divided 
 transversely into segments. Their skeletons are generally thin, 
 light, and situate externally, chiefly composed of phosphate of lime, 
 though occasionally of carbonate, as in the cirrhopoda and Crusta- 
 cea. The entozoa owe their peculiar stiffness and rigidity to the 
 tough, strong, and transparent covering enveloping their entire 
 body. In some of the inferior orders of them, as in the acanthoce- 
 phalous species, their retractile proboscis and part of their bodies 
 are set with dense, sharp spines, which enable them to move with 
 freedom and precision through the fleshy media in contact with 
 them. The rotifera are closely allied to the entozoa in their ex- 
 terior coverings. In the former, however, this texture possesses a 
 greater degree of firmness, from the attachment of numerous mus- 
 cles to it. There are no earthy deposits in any part of the body of 
 these animals. The cirrhopoda, like the mollusca, are usually 
 enclosed in shells, dense, thin, laminated, and composed of carbo- 
 nate of lime. These testaceous coverings are best developed in the 
 balani. and least in the anatiferse. The reverse order of develop- 
 ment obtains with respect to their extremities. 
 
 The amielida, or red-blooded worms, lead us a step higher in 
 the development of skeleton; for, although the halithea, the leech, 
 the nais, &c, possess a flexible membraneous covering, many others, 
 as the serpulas, are shielded by adventitious, solid, calcareous tubes. 
 The common earth-worm is provided with four pairs of sharp 
 spines, or setas, for the purpose of progression. The skeleton of 
 insects is for the greater part composed of a thin, epidermic layer, 
 
SKELETON IN THE INVERTEBRATA. l3 
 
 and a thick internal one resembling the woody fibres of plants, but 
 of an animal nature, termed chitine and coccine, blended with por- 
 tions of phosphate of lime, magnesia and iron. These animals 
 also present distinct legs and wings. 
 
 In the arachnida we meet with a more consolidated form of 
 skeleton; generally more than three pairs of legs : and, at the sides 
 of their head, a pair of sharp-pointed piercing" instruments, suited 
 to their retired, cunning, and carnivorous habits. These animals 
 throw off periodically their exterior coverings, like the larvae of 
 insects; and, like the Crustacea, they are capable of reproducing 
 their members when destroyed. The Crustacea affords us by far 
 the most solid form of skeleton met with in any of the articulata. 
 In the decapods it contains half its weight of carbonate of lime, 
 and a considerable proportion of phosphate, with traces of iron, 
 soda, and magnesia, all of which are secreted from the true skin. 
 These animals have generally five pairs of legs, two strong mandi- 
 bles, two pairs of slender maxillae, and two pairs of antennae. The 
 solid crust forming the skeleton of Crustacea is cast off periodically. 
 This is accomplished by the animal first detaching the cutis and 
 muscles from the inner surface of the old shell; "then secreting 
 from the surface of the cutis a new layer of epidermis ; next a layer 
 of colouring matter; and, within this, the calcareous materials of 
 the new shell. 
 
 Mollusca, Cuvier ; Cyclo-gangliated animals, Grant. The 
 shells of these animals are formed of carbonate of lime, without 
 the phosphate, and are remarkable for their want of symmetry on 
 the two sides of the body, and their inconstancy in animals of simi- 
 lar structure. In the tunicata we meet with an exterior cartilagi- 
 nous skeleton, in some instances thick and opaque, as in the ascidia 
 — in others more delicate and transparent, as in the cynthia papil- 
 lata. The shells of the conchifera usually consist of two movable 
 pieces placed on the exterior of the body, connected by ligament 
 and muscle. All these animals, however, are not bivalved ; some, 
 as the pholades, have additional pieces at the hinge of the valve, 
 constituting the multivalves. They have a muscular foot, and a 
 pair of tentacula. The gasterpoda possess hollow, unilocular, co- 
 nical shells. Many of them have no shell, as the tritonia and 
 doris; some have a thin calcareous lamina within the skin of the 
 back, as the aplysia; whilst others have only a partial covering of 
 shell as the testacella. In the cephalopodous mollusca we recog- 
 nise the transition from the external unorganised shells of the in- 
 vertebrated tribes to the internal organised bones of the vertebrata. 
 The shells are sometimes external, as in the nautilus, and some- 
 times internal, as in the sepia. In this complicated class of ani- 
 mals we find a near approach to the cartilaginous fishes in the pre- 
 sence of cranium, spinal column, &c, in a mdimental form. 
 
14 
 
 RECAPITULATION. 
 
 1. All animals are included under the heads vertebrata and in- 
 vertebrata. 
 
 2. Great advantage to be derived from a knowledge of arrange- 
 ment and classification. 
 
 3. The osseous system is neither the most important nor the 
 most uniformly existing. 
 
 4. Skeleton exists in every class of animals, but modified accord- 
 ing to each class. 
 
 5. Skeleton generally internal in the radiata, and external in the 
 articulata, subject to exceptions. 
 
 6. Skeleton remarkable for inconstancy and want of symmetry 
 in the mollusca. 
 
 7. Basis of skeleton — silica in the lowest radiata, carbonate and 
 phosphate of lime in the articulata, and carbonate of lime chiefly in 
 the mollusca. 
 
 8. No bony skeleton where regularly formed brain does not 
 exist. 
 
 CHAPTER III. 
 
 VERTEBRATA. 
 
 General observations. — It will appear hereafter that the principal 
 part of the nervous system consists in a single central mass extended 
 along the back, and composed of a series of distinct portions, each 
 of which, like the cerebral ganglion of one of the sepiae, is indicated 
 by its giving off one or more pairs of nerves. To coincide with such 
 a disposition, the chief portion of the skeleton is formed by a series 
 of osseous rings, which being mutually articulated and collectively 
 forming a closed cavity, compose a series of spinal vertebra? consti- 
 tuting the spinal column — the distinctive character of this division 
 of the animal sphere. The vertebral column, which is the first 
 rudiment of skeleton observed in the human embryo, is also the 
 primary and most essential portion of it in the higher classes of ani- 
 mals generally, and in many cases alone composes nearly the whole 
 of the skeleton. 
 
 Another characteristic of the skeleton in this department of ani- 
 mals is, that it is placed internal to the soft parts, and is not exuviable 
 in a mass, as it was in most of the invertebrate classes. Here 
 the phosphate of lime is the predominant ingredient, and its propor- 
 tion increases as we ascend through the vertebrated classes. 
 
 The appearance of the skeleton is greatly varied by the situation 
 of the ribs ; for instance, in fish and aquatic mammalia the thorax is 
 placed near the anterior part of the column, to allow of the mobility 
 
VERTEBRATA. 15 
 
 of the posterior portion for the purposes of swimming. In birds, 
 where the neck is used as a prehensile oro-an, the thoracic portion of 
 the column is situate near its posterior extremity. Whilst in quad- 
 rupeds aud reptiles balanced on two pairs of extremities, the solid 
 portion of their trunk is placed near the middle of their column. 
 
 PISCES. 
 
 The bones of fishes closely resemble those of the higher grades 
 of organisation in their embryotic state, not only in their soft carti- 
 laginous character, but also in the isolated condition of their several 
 centres of ossification, especially in the complicated bones of the 
 head. The bones of the cartilaginous tribes are composed of water, 
 gelatine, and the sulphate, subcarbonate and chloruret of soda; 
 whilst the more dense bones of the osseous fishes are indurated and 
 strengthened by the more insoluble phosphates. As the human 
 embryo originally consists almost exclusively of the vertebral 
 column, so also in fishes we find that the spine, and the head, which 
 is only an increased development of it, constitute the most impor- 
 tant parts of the skeleton. 
 
 Spine. — The vertebrae in this class are very numerous, and may 
 be divided into the abdominal and caudal. The bodies of the verte- 
 bras are the elements first developed ; they are the most important, and 
 form almost the entire of the skeleton in the lowest species of cartila- 
 ginous fishes. They are concave on both surfaces ; consequently 
 enclose large spaces, filled with a thin gelatinous fluid ; and in many 
 of the cartilaginous species, the inter- vertebral substances communi- 
 cate and form a continuous elastic chord passing through the entire 
 column as in the lamprey. The spinous processes of the abdominal 
 vertebras are very long superiorly, and assist, by their shanks, to 
 form the spinal canal ; whilst the caudal vertebrae are distinguished 
 by having long spinal processes both above and below. Between 
 the roots of the inferior spinous processes there is enclosed a simi- 
 lar canal, but larger for the passage of the great systemic artery. 
 
 The vertebral column in fishes is constructed in such a manner 
 as to give considerable perpendicular extent to the trunk, and thus 
 favour their horizontal mode of progression. The number of ver- 
 tebra varies greatly; thus in the carp we find 41, in the burbot 57, 
 in the eel 115. and in the shark as many as 207. In the osseous 
 fishes, the ribs form an upper and a lower range ; the latter are 
 better developed and more uniform in their existence than the former. 
 The number of ribs is generally determined by that of the abdo- 
 minal vertebrae. In some, however, as the chaetodon, scomber, &c, 
 the caudal vertebrae are furnished with ribs. These bones articulate 
 with one vertebra only, as a consequence of which they enjoy but 
 little motion, and are but slightly subservient to respiration. In the 
 shark they are cartilaginous ; in the carp they are long and firm ; 
 in the eel short and slender ; and in many genera, as the raia, fis- 
 tularia, &c., they are almost wholly absent. The sternum, when 
 
16 EVERS'S COMPARATIVE ANATOMY. 
 
 present, consists, as described by Meckel, of a variable number of 
 V-shaped pieces, pointed downwards and overlapping each other. 
 This rudimentary bone is best seen in the herring and the dory. 
 
 Head. — To the researches of Oken, Meckel, Cams, Blainville, 
 &c, we are indebted for the important fact that the cranium, is 
 nothing more than a highly developed portion of the vertebral 
 column. The composition of the cranium in the cartilaginous 
 fishes is very simple; in many, as in the skate, consisting chiefly of 
 one large piece. In the osseous tribes, on the contrary, the com- 
 ponent parts are very numerous — amounting to 80 in the head of 
 the perch. The bodies of the vertebras continue forward in a straight 
 line with the spine along the base of the scull, forming the basilar 
 part of the occipital, the body of the sphenoid, and the ethmoid 
 bones. In the bony fishes the cranium is remarkable for being thin, 
 diaphanous, elastic and having its elements united by squamous 
 sutures, which favours the extension of the period of growth of each 
 part. The cavity of the cranium is occupied chiefly by the cellular 
 tissue of the arachnoid coat; the brain occupying but a small por- 
 tion of the base of the skull. 
 
 The bones of the face present but few peculiarities. The inter- 
 maxillary bone consists of three triangular pieces inserted between 
 the vomer, the palate, the nasal, and the superior maxillary bones. 
 The central piece is generally cartilaginous. In connection with 
 the upper jaw, we have to notice the os quadratum ; this is composed 
 of several pieces, which closely resemble the ascending process of 
 the lower jaw in man. The three portions of which it is mainly 
 composed are articulated, one to the inferior maxilla and palate 
 bone, the second to the temporal bone, while the third consists of a 
 thin round plate, and is called os discoideum. Behind the lower 
 jaw, and connected to the os quadratum, is the operculum. This 
 is a plate of bone usually composed of four pieces, which have been 
 considered analogous to the bones of the tympanum, on account of 
 the absence of this cavity from the ears of fishes ; others have 
 regarded it as a portion of the lower jaw. Be this as it may we find 
 the operculum covering the respiratory apparatus in the same man- 
 ner as the shells of bivalves cover the subjacent gills. 
 
 The os hyoides reaches a high degree of development here, as in 
 all water breathing vertebrata ; it consists of a body or lingual bone, 
 and five pieces on either side of it: it is suspended from the tem- 
 poral bones ; and it is, by its free antero-posterior motions that res- 
 piration is effected in fishes, and in amphibia, as will be shown 
 hereafter. It forms an arch, having the lower jaw above it, and the 
 scapular and coracoid bones below. Its sides support the four pairs 
 of branchial arches, and externally it has attached to it the opercular 
 membrane. 
 
 Extremities. — In fishes fins supply the place of extremities ; the 
 anterior corresponding to the arms, and the posterior to the legs. 
 They are named according to the parts they are attached to, as 
 dorsal, pectoral, ventral, caudal, and anal fins. The anterior or 
 
VERTEBRATA. 17 
 
 pectoral fins are larger and more uniform in their existence than 
 the posterior; they also commence their development at an earlier 
 period; in all of which they resemble the embryo of the higher 
 classes. The ventral fins are wanting in the apodes, as well a*s in 
 several species of other orders ; whilst the pectoral fins are generally 
 present. 
 
 The anterior fins are generally joined to the back of the skull by- 
 means of an osseous belt, formed behind by the scapula, and in front 
 by the coracoid bones. A humerus, generally long and angular, is 
 attached to these above, and to the radius and'ulna below. To these 
 succeed the carpal bones, and the member is terminated by long 
 and numerous phalanges. The posterior members, or ventral fins, 
 have no connection to the spine, but are suspended from the rib-like 
 iliac bones, and placed on the lower part of the trunk, at a variable 
 distance between the head and anus. The presence of a sacrum 
 in this class would be injurious to the free motion required in 
 swimming. In the abdominal fishes the pelvic bones are uncon- 
 nected to the skeleton : and in the apodal families they are wholly 
 absent. The long phalanges of the feet are attached directly to the 
 pelvic bones, there being rarely a trace of intermediate bones 
 developed. 
 
 The want of symmetry observed in the skeletons of many fishes 
 forms a singular peculiarity in this class. In the pleuronectes, for 
 instance, one side is turned upwards, instead of the back ; both 
 eyes are placed on the same side; the cranial vertebra- seem 
 twisted in their long axis ; and the lower part of the head is imper- 
 fectly developed. The bones, especially the intermaxillary, are 
 much larger on the side opposite to that on which the eyes are 
 placed. 
 
 RECAPITULATION. 
 
 1. The bones of fishes resemble the embryotic condition of the 
 osseous system in the higher classes of animals. 
 
 2. The spine is the most important part of their skeleton. 
 
 3. The spinal column enjoys very (ree motion, chiefly in the 
 lateral direction. 
 
 4. The construction of the head is as simple in the cartilaginous 
 as it is complex in the osseous fishes. 
 
 5. The os hyoicles is greatly developed to support the branchial 
 apparatus. 
 
 6. The anterior fins are larger, earlier developed, and more uni- 
 form in their existence than the posterior. 
 
 7. The pelvic bones and posterior fins are absent from the ske- 
 letons of many cartilaginous fishes. 
 
 8. Want of symmetry is a striking peculiarity in the skeletons 
 of many fishes. 
 
 ' * evers 2 
 
18 EVERS'S COMPARATIVE ANATOMY. 
 
 AMPHIBIA. 
 
 In the Batrachia the ribs are almost wholly absent ; it is only 
 in the rana pipa and the salamanders that small cartilaginous 
 appendages are found attached to the transverse processes of some 
 of the vertebrae. In these animals the spine consists of dorsal, 
 sacral, and caudal portions — the distinction being marked by the 
 connection of one of the vertebras to the ilium on each side. The 
 salamander has fourteen dorsal, one sacral, and twenty-seven cau- 
 dal vertebrae ; in the common frog there are only nine vertebrae ; 
 and in the rana pipa but eight; whilst the siren has forty-three in 
 the trunk, and about forty-five in the tail ; from the second to the 
 eighth inclusive have rudimentary ribs attached to them. The 
 bodies of the vertebrae are concave on their surfaces; so that, when 
 in apposition, they give rise to the existence of an intervertebral 
 oval cavity filled by a gelatinous mass. 
 
 When we consider the habits, food, and mode of progression, of 
 the frog — that its movements, which are chiefly on land, are both 
 active and extensive, as well for the purpose of seizing its prey as 
 of escaping from danger — it becomes obvious why its spine should 
 be short and firmly anchylosed — how the presence of a tail would 
 be worse than useless, and why a necessity exists for a full deve- 
 lopment of the posterior extremities. The absence of ribs will 
 hereafter be accounted for by an interesting peculiarity in the func- 
 tion of respiration. 
 
 Cranium. — The elements composing this cavity are remarkable 
 for remaining permanently ununited, a state of things which is 
 strikingly imitated during the progress of the development of these 
 parts in the higher orders of animals. The maxillary, intermaxil- 
 lary, tympanic, and jugal bones are greatly expanded, in the 
 transverse direction, giving the face a flattened appearance. The 
 lower jaw consists of three pieces on each side. 
 
 Of all parts of the osseous system of this class, there is none so 
 interesting as the os hyoides, on account of the changes to which 
 it is subjected during the transit of the amphibia from the pisciform 
 to the reptile state. The branchiae are external, supported by car- 
 tilaginous arches connected with os hyoides. As the age of 
 the tadpole increases, the branchiae disappear, the lungs become 
 developed, and the os hyoides grows, from a small rhomboidal 
 point, to the large size and peculiar from which it presents in the 
 full-grown frog. 
 
 Anterior extremity. — The shoulder of a frog consists of scapula, 
 clavicle, and coracoid bone, all of which unite to form the glenoid 
 cavity. The humerus is short and thick, having a round head 
 above, received by the glenoid cavity, and also a spherical extremity 
 below, to articulate with the bones of the fore-arm, which consists 
 of radius and ulna so united that a faint line indicates their former 
 separation. The carpal bones are six ; the metacarpal, four. The 
 
VERTEBRATA. 19 
 
 middle and index fingers have each two phalanges, the others 
 three. 
 
 The posterior extremity, for reasons before assigned, reaches a 
 high degree of development. The cotyloid cavity is constituted by the 
 ilium, ischium, and pubis. The femur is long and cylindrical. The 
 tibia and fibula are consolidated into one bone, and joined inferiorly 
 to two bones representing astragalus and os calcis. Between these 
 and the long metatarsal bones are placed four small, irregular 
 bones. Of the rive toes, the internal is best developed, and sus- 
 tains three long, slender phalanges. 
 
 The structure and form of the salamander, proteus, and siren, 
 are well contrasted with those of the froo\ In the former animals, 
 the spinal column attains a high state of development : the extre- 
 mities are reduced to a rudi mental type. The bones of the fore- 
 arm and leg, instead of being anchylosed as in the frog, maintain 
 a permanent state of separation. The toes, which are four in 
 number, are but slightly developed. The whole economy of the 
 frog is admirably organised for rapid terrestrial progression, while 
 that of the other animals is designed to favour their movements 
 through a watery element. 
 
 Who can fail to observe the extreme wisdom manifested in the 
 metamorphosis of these animals? In the early part of their exist- 
 ence, and while they enjoy an aquatic mode of life, their organi- 
 sation is in due accordance ; at first their members are scarcely 
 perceptible, whilst their tail is of great length, and continues so in 
 those destined to continue their watery habitation ; but in the frog, 
 (fee, which are to breathe by lungs, the tail is gradually removed 
 by absorption, and the extremities, particularly the posterior, un- 
 dergo a rapid evolution. 
 
 REPTILIA. 
 
 Chelonia.—These reptiles present a tolerably perfect form of ske- 
 leton. Their spine consists of eight cervical, fourteen dorsal, three 
 sacral, and from twenty to thirty caudal vertebrae. There are 
 eight pairs of immovable ribs, united to each other by sutures, and 
 attached between the bodies of the vertebrae. By the union of the 
 ribs with each other, and with the spinous processes of the dorsal 
 vertebras, they form the upper shield or carapace. The nine pieces 
 of the sternum which are movable in the turtle, form the lower 
 shield or plastron. This unyielding frame-work is well suited to 
 resist pressure, as well as to favour their muscular movements on 
 land, whilst the mobility of the several elements of the sternum in 
 the aquatic species is applicable to their extensive respiration in that 
 dense element. 
 
 The bones of the head are firmly united by sutures. The occi- 
 pital condyle presents three facets, formed by the basilar and the 
 two condyloid portions. The inter-maxillary bones are narrow, 
 but present a large palatine surface. The bones of the ear are 
 
20 EVERS'S COMPARATIVE ANATOMY. 
 
 anchylosed, and the body and cornua of the os hyoides are fully 
 developed. 
 
 In the anterior extremity, which is attached to the inner side of 
 the chest, we distinguish scapula and clavicle united by suture ; 
 humerus twisted, with a large articular condyle; radius and ulna 
 short, strong, and expanded inferiorly, fixed in a state of pronation; 
 carpal bones, sometimes as many as ten, arranged in three rows; 
 five short metacarpal bones; and the phalanges, two for the thumb 
 and last finger, and three for each of the others. 
 
 The ilia are long and cylindrical in the land tortoise ; the pubis 
 and ischium broad and flat. The femur presents indications of 
 trochanters, as in man ; its head is large, and joins the shaft at a 
 right angle. There is no round ligament in the hip, though rudi- 
 ments of semilunar cartilages connected to crucial ligaments in the 
 knee. The tibia and fibula are separate. The metacarpal bones 
 are five, and the number and arrangement of the phalanges the 
 same as observed in the phalanges of the fingers, with the exception 
 of the outer toe, which is generally rudimentary. In the aquatic 
 chelonia, the bones of the extremities are longer, straighter, and 
 more slender than in the land species. 
 
 Ophidia. — The skeleton in serpents consists of little more than a 
 vertebral column, possessing such a degree of mobility as enables 
 them to creep with speed along the surface, to swim through the 
 waters, to spring into the air, to climb trees, and to combat with and 
 conquer their prey. Extremities are here wholly absent, and the 
 spinal column and ribs constitute the sole organs of progressive 
 motion. For this reason the spine is characterised by immense 
 strength and great mobility. The vertebrae are more numerous 
 in this than in any other class of animals, being 49 in the anguis 
 fragilis, or blind worm ; 201 in the crotalus horrid us, or rattle-snake ; 
 and 316 in the coluber natrix. The bodies of the vertebrae have 
 ball and socket articulations, so disposed as to admit of free lateral, 
 but limited antero-posterior motion. The ribs of serpents are tubu- 
 lar, narrow and compressed from before backwards. Their head 
 presents a broad, arched, concave surface, to articulate with the 
 rounded, prominent, transverse processes of the vertebra?, whilst 
 their ventral extremity tapers to end in a thin, flexible cartilage. 
 The ribs extend from the atlas to the anus, and are 32 pairs in the 
 blind worm, 175 in the rattle-snake, and 204 in the coluber natrix. 
 They are all of the false kind, there being no rudiment of sternum, 
 except in the ophisaurus and blind worm alone, in which also faint 
 traces of shoulder and pelvis may be discerned. 
 
 The head resembles the preceding order (or that of the chelonia) 
 in the small size of the cranium, whilst the multiplicity and detached 
 condition of its bones ally it to the fishy tribes. This loose state of 
 the component elements of the head is necessary in serpents, for, 
 being deprived of organs of prehension, they are compelled to swallow 
 their prey entire. As a consequence of the looseness of the other 
 bones, the two parietals are anchylosed along the median line, to 
 
VERTEBRATA. 21 
 
 protect the brain during the exposure of these animals to the 
 trampling of quadrupeds, &c, whilst concealed in their natural 
 haunts. Their teeth are small, conical, and sharp ; they are placed 
 in the two maxillary, the intermaxillary, and the palate bones. 
 
 Sauria. — In this order we meet with a more perfect development 
 of skeleton than in the last, as they possess a sternum, a scapular 
 and pelvic apparatus, together with atlantal and sacral extremities. 
 The lacerta iguana presents 5 cervical, 11 dorsal, 9 lumbar, 2 
 sacral, and 72 caudal vertebrae ; the crocodile of the Nile 7 cervical, 
 12 dorsal, 5 lumbar, 2 sacral, and 34 caudal — articulated by ball 
 and socket. There are false ribs behind and before the true ones. 
 In the chameleon there are 17 pairs ; in the crocodile 12. The 
 sternum is prolonged posteriorly as far as the pubis, and has attached 
 to it five pairs of cartilaginous arches, for the purpose of supporting 
 the abdomen. 
 
 The head is extended forwards in a line with the spine, as in the 
 other inferior vertebrata ; like these, also, its component elements 
 are loosely connected. As in serpents, the basilar condyle is elon- 
 gated transversely, and the parietal bones anchylosed. The lower 
 jaw consists of six pieces on each side ; and here, as in serpents, 
 the prehensile teeth are attached by broad base to the surface of the 
 jaw, and the new teeth rise by the side of the old, and not in their 
 interior as in the crocodile. 
 
 Anterior extremity. — The scapula is broad, thin, and curved. 
 The acromion is a distinct bone, and the clavicles are anchylosed 
 in form of a cross, on the front of the sternum. The humerus is 
 expanded at its extremities, and the same form as in man ; the ulna 
 is without an olecranon, stronger than the radius, and separated from 
 it below. There are from four to nine bones in the carpus, five 
 in the metacarpus; and the phalanges are, two for the thumb, 
 three for the second and last fingers, and four for each of the 
 others. 
 
 Posterior extremity. — The three portions of the os innominatum 
 contribute to the formation of the cotyloid cavity. The ossa pubis 
 and ischii form a lengthened symphisis in front; and the spine of 
 the iliac bones is extended backwards along each side of the sacrum. 
 From the front of the pubic bone a process passes up towards the 
 sternum as in the marsupiales. The head of the femur is com- 
 pressed and directed forwards ; the great trochanter is also flat and 
 turned towards the tibia. The patella is small ; the tibia short, 
 thick, and curved ; the fibula slender in the centre, expanded at its 
 extremities, and apart from the tibia. In the crocodile there are five 
 bones in the tarsus, four in the metatarsus, and the toes are so 
 arranged that the most internal sustains two phalanges, the second 
 three, and the third and fourth, four each. 
 
 In the skeletons of the nilotic crocodiles, alligators, and other 
 reptiles destined to swim by the lateral movements of a muscular 
 tail and long webbed feet, their long bones are filled with a thin 
 oily marrow, and the bones of the head firmly united. 
 
22 
 
 RECAPITULATION. — Amphibia. 
 
 1. In amphibia rudiments of ribs only are met with. 
 
 2. Vertebrae range from eight in the rana pipa to eighty-nine in 
 the siren. 
 
 3. In the frog, the extremities, especially the posterior, are fully 
 developed ; the tail is absorbed. 
 
 4. Salamander, proteus, and siren, may be well contrasted with 
 the frog ; in the former the spinal column attains and maintains a 
 high degree of development, whilst their members are reduced to a 
 mere rndimental type. 
 
 5. The bones of the cranium remain loosely united through life. 
 
 6. The os hyoides undergoes remarkable changes during the 
 metamorphosis of the animal from the pisciform to the reptile 
 state. 
 
 recapitulation. — Reptilia. 
 
 1. The vertebrae and ribs are more numerous" than in any other 
 class of animals. 
 
 2. The chelonia differ from the sauria in having immovable ribs, 
 and from the ophidia in having arms and legs. 
 
 3. The bones of the head generally maintain a permanent state 
 of separation, except the parietals which are firmly auchylosed. 
 
 AVES. 
 
 As in this department of my subject I avail myself of much of the 
 valuable matter contained in the article, Aves, in the Cyclopaedia of 
 Anatomy and Physiology, by that clear, accurate, and scientific 
 writer, Mr. Owen, it becomes necessary to state that he divides the 
 class into the following orders : — 
 
 1. Raptores, birds of prey, or raveners ; 2. Insessores, perchers ; 
 3. Scansores, climbers ; 4. Rasores, scratchers ; 5. Cursores, 
 coursers; 6. Grallatores, waders ; and 7. Natatores, swimmers. 
 
 Positive characters of the class. — Animal, vertebrated, oviparous, 
 biped: anterior extremities organised for flight; integument plu- 
 mose ; blood red and warm ; respiration and circulation double ; 
 lungs fixed and perforated. 
 
 Negative characters. — No auricles, teeth, lips, epiglottis, dia- 
 phragm, fornix, corpus callosum, or scrotum. 
 
 The bones of birds are remarkable for being permeated by atmo- 
 spheric air, for their compact and laminated texture, their white 
 colour, and their fragility, owing to a preponderance of phosphate of 
 lime. 
 
 The vertebrae are the first bones observed in the development of 
 the osseous system of birds, and of all parts of this system, they 
 present the fewest variations. The spine here consists of cervical, 
 dorsal, sacral and caudal portions. The first and last are the most 
 
VERTEBRATA. 23 
 
 movable, and in many species of the dorsal and caudal portions 
 admit of no motion at all. This fixity facilitates the flight of the 
 bird, whilst the length and mobility of the cervical portion of the 
 spine compensate, in some degree, for the unfitness of the anterior 
 members to the purposes of prehension, &c. 
 
 The cervical portion of the spine is generally composed of a greater 
 number of vertebrae than any of the other divisions ; they are not 
 fewer than nine, as observed in the sparrow, nor more than twenty- 
 three, as in the swan. 
 
 The bodies lock into each other, and are so disposed as to allow 
 the superior and inferior ones to move forwards, and the middle 
 backwards. The transverse processes are long, and have rudi- 
 mentary ribs connected to them ; these are particularly well deve- 
 loped in rapacious birds, and hence the great breadth of their necks. 
 The atlas is a simple ring, generally articulated to the occipital 
 tubercle by a single facet; but the penguin and ostrich have two 
 other facets continuous with the central one. From the dentata 
 down, a movable inter-articular cartilage is found, as in the joint of 
 the lower jaw of the mammalia. 
 
 The dorsal vertebrae range from six in the bull-finch to eleven as 
 seen in the swan. The bodies of these vertebrae are short and 
 compressed laterally, except in the ostrich. The transverse pro- 
 cesses are greatly developed. The anterior cartilaginous surface is 
 convex in the vertical direction, concave in the transverse, and 
 connected by fibrous capsules and synovial membranes. Most 
 birds have the middle and lower vertebrae anchylosed ; even the 
 transverse and spinous processes of the superior are anchylosed in 
 those birds requiring great fixation of the trunk ; while in those that 
 cannot fly, as the penguins, they are all movable. 
 
 The sacral vertebrae are firmly anchylosed with one another, 
 and with the ilia laterally; consequently it is difficult to determine 
 their real number ; it is not, however, greater than nineteen, as 
 seen in the emeu and cassowary, nor less ihan eight, as observed in 
 the hoopoe. The bodies of these vertebrae are broad, but shallow, 
 and the canal greatly enlarged, to correspond to the size of the 
 chord, which here supplies nerves to the posterior extremities. 
 When it is considered that the head, posterior members, viscera, &c, 
 are suspended in flight from this central portion of the trunk, the 
 necessity for the mechanism consolidating these vertebrae will be 
 readily appreciated. 
 
 The coccygeal vertebrae are generally movable, and from five 
 to nine in number. With the exception of the last, they are broad, 
 short, and perforated for the spinal marrow. The last has no pro- 
 cesses ; it is compressed laterally, and terminates above and below 
 in a sharp edge ; it supports the coccygeal oil-gland, and affords a 
 firm basis to the tail feathers, or retrices of Linnaeus. These bones 
 possess ligamentous connections, except the sixth and seventh which 
 re provided with a capsule and synovial fluid. 
 
24 
 
 EVERS'S COMPARATIVE ANATOMY. 
 
 TABLE OF THE VERTEBRAE IN BIRDS. 
 
 ORDER RAPTORES 
 
 VBRTEBR.K. 
 
 
 ORDER RASORES. 
 
 VERTEBRAE 
 
 
 
 Species. 
 
 Derv. 
 
 Dor. 
 
 Sac. 
 
 Cau. 
 
 Species . 
 
 Cerv. 
 
 Dor. 
 
 Sac. 
 
 Cau. 
 
 Vulture, 
 
 13 
 
 7 
 
 11 
 
 7 
 
 Crested Curas- 
 
 
 
 
 
 Eagle, 
 
 13 
 
 8 
 
 11 
 
 8 
 
 sow, 
 
 15 
 
 8 
 
 10 
 
 7 
 
 Sparrow-hawk, 
 
 11 
 
 8 
 
 11 
 
 8 
 
 ORDER CCRSORES 
 
 
 
 
 
 Kite, 
 
 12 
 
 8 
 
 11 
 
 8 
 
 Ostrich, 
 
 ' 18 
 
 10 
 
 17 
 
 9 
 
 Hawk-owl, 
 
 11 
 
 8 
 
 11 
 
 8 
 
 Cassowary, 
 
 16 
 
 10 
 
 19 
 
 7 
 
 ORDER INSESSORES. 
 
 
 
 
 Emeu, 
 
 19 
 
 9 
 
 19 
 
 9 
 
 Fly-catcher, 
 
 10 
 
 8 
 
 10 
 
 8 
 
 ORDER GRALLATORES. 
 
 
 
 
 Blackbird, 
 
 11 
 
 8 
 
 10 
 
 7 
 
 Heron, 
 
 18 
 
 7 
 
 10 
 
 7 
 
 Crow, 
 
 13 
 
 8 
 
 13 
 
 7 
 
 Crane, 
 
 19 
 
 9 
 
 12 
 
 7 
 
 Magpie, 
 
 13 
 
 8 
 
 13 
 
 8 
 
 Spoonbill, 
 
 17 
 
 7 
 
 14 
 
 8 
 
 Jay, 
 
 12 
 
 7 
 
 11 
 
 8 
 
 Avoset, 
 
 14 
 
 9 
 
 10 
 
 8 
 
 Starling, 
 
 10 
 
 8 
 
 10 
 
 9 
 
 Plover, 
 
 15 
 
 8 
 
 10 
 
 7 
 
 Bull-finch, 
 
 10 
 
 6 
 
 11 
 
 6 
 
 Woodcock, 
 
 18 
 
 7 
 
 13 
 
 8 
 
 Sparrow, 
 Goldfinch, 
 
 9 
 
 9 
 
 10 
 
 7 
 
 Curlew, 
 
 13 
 
 8 
 
 10 
 
 8 
 
 11 
 
 8 
 
 11 
 
 8 
 
 Oyster-catcher, 
 
 12 
 
 9 
 
 15 
 
 7 
 
 Lark, 
 
 11 
 
 9 
 
 10 
 
 7 
 
 Coot, 
 
 15 
 
 10 
 
 13 
 
 8 
 
 Redbreast, 
 
 10 
 
 8 
 
 10 
 
 8 
 
 Flamingo, 
 
 18 
 
 7 
 
 12 
 
 7 
 
 Swallow, 
 
 11 
 
 8 
 
 11 
 
 9 
 
 ORDER NATATORIS. 
 
 
 
 
 Humming-bird, 
 
 14 
 
 9 
 
 10 
 
 8 
 
 Pelican, 
 
 16 
 
 7 
 
 14 
 
 7 
 
 Kingfisher, 
 
 12 
 
 7 
 
 11 
 
 7 
 
 Cormorant, 
 
 16 
 
 9 
 
 14 
 
 8 
 
 ORDER "CANSORES. 
 
 
 
 
 Gull, 
 
 12 
 
 8 
 
 11 
 
 8 
 
 Woodpecker, 
 
 12 
 
 8 
 
 10 
 
 9 
 
 Catarrhactes, 
 
 13 
 
 9 
 
 13 
 
 8 
 
 Parrot, 
 
 11 
 
 9 
 
 11 
 
 8 
 
 Swan, 
 
 23 
 
 11 
 
 14 
 
 8 
 
 ORDER RASORES. 
 
 
 
 
 
 Goose, 
 
 15 
 
 10 
 
 14 
 
 7 
 
 Pigeon, 
 
 13 
 
 7 
 
 13 
 
 7 
 
 Duck, 
 
 14 
 
 8 
 
 15 
 
 8 
 
 Peacock, 
 
 14 
 
 7 
 
 12 
 
 8 
 
 Sheldrake, 
 
 16 
 
 11 
 
 11 
 
 9 
 
 Pheasant, 
 
 13 
 
 7 
 
 15 
 
 5 
 
 Mergancer, 
 
 15 
 
 8 
 
 13 
 
 7 
 
 Turkey, 
 
 15 
 
 7 
 
 10 
 
 5 
 
 Grebe, 
 
 14 
 
 10 
 
 13 
 
 7 
 
 Skull. — It has been already shown that the bones composing the 
 skull of the crocodile, and other cold blooded vertebrata, were not 
 consolidated till a late period of life, giving rise to some difficulty 
 in tracing a correspondence between their bones and those of a 
 higher order. A still greater difficulty is experienced in determining 
 the component parts of the head in birds ; for in them the bones of 
 the skull are anchylosed, and every trace of suture effaced at an 
 early epoch ; therefore, in order to accomplish their perfect separa- 
 tion, it must be undertaken at an early period of their existence. 
 
 In the majority of birds, the head is articulated to the spine, by 
 means of a single hemispherical tubercle on the basilar process of 
 the occipital bone ; but in the penguin and ostrich, the condyloid 
 portions contribute to its formation, and the articulation is such as 
 to admit of very great freedom of motion. 
 
 The occipital bone is originally composed of four pieces, basilar, 
 spinous and two condyloid. The temporal consists of the petrous, 
 squamous, and tympanic portions ; the last is movably articulated 
 to the inferior part of the squamous portion, and is sometimes called 
 osquadratum. The alae majores of the sphenoid bone remain a 
 long time separate, and are called interarticular, or omoid bones. 
 The remaining bones of the skull present no remarkable peculiarities 
 
VERTEBRATA. 
 
 25 
 
 save that they are all early and firmly anchylosed, with the excep- 
 tion of the tympanic bone. 
 
 The bones of the face correspond in number and position to those 
 of the mammalia, especially the order rodentia. They are movably 
 connected with the bones of the cranium, and remain separate to a 
 much later period. The upper mandible is chiefly characterised by 
 the presence of the intermaxillary bone. This consists of three 
 processes, a central, and two lateral ; the former passes up between 
 the superior maxillary bones, and becomes joined to the nasal and 
 ethmoid ; this union is ligamentous in the parrot, and those birds 
 that apply the upper mandible to the purposes of climbing. The 
 two lateral processes of the inter-maxillary bone, extend upwards 
 and backwards external to the superior maxillary bones, to which 
 they are firmly united. 
 
 There are few more ingenious or beautiful pieces of mechanism 
 than that by which the mouth of a bird is opened. The tympanic 
 bone as before observed, never anchyloses with the other elements 
 of the temporal; on the contrary, it articulates with the zygomatic 
 portion of the latter bone, by two transverse condyles above ; below 
 it articulates by a broad surface with the upper and back part of the 
 lower jaw, while in front and near its lower extremity, it has 
 applied to it the long, slender malar bone which reaches to the 
 superior maxilla. When the tympanic bone is drawn forwards, 
 either by the action of the pterygoid muscles attached to it, or by 
 the depression of the lower jaw, the malar bone is advanced against 
 the superior mandible, which is elevated at the same moment that 
 the lower one is depressed. The moment the pressure ceases to 
 exist below, the elasticity of the union of the intermaxillary bone 
 with the cranium restores the upper mandible to its situation. 
 
 The inferior maxilla originally consists of six pieces on each 
 side, named anterior dental, two condyloid, angular, supra-angular, 
 and opercular. As this bone, together with the upper jaw, forms 
 the chief organ of prehension in birds, it is but natural to expect 
 that it shall present numerous modifications, indicative of the food 
 and habits of each species. 
 
 There is more uniformity observed in the skulls of birds than in 
 any other class of the vertebras department. It generally presents 
 the form of a five sided pyramid, the base represented by the occiput, 
 and the apex by the bill. In the Raptores it is short, broad, and 
 deep ; nearly spherical in the Warblers ; flattened, and of great 
 breadth, in the Scansores ; narrow, and slightly raised in theRaso- 
 rial birds ; and remarkable for its great length in the Waders. 
 
 Thorax. — The extent and energy of the respiratory function of 
 birds, are clearly indicated by the peculiar and perfect condition of 
 this part of their osseous system. The ribs, as in the mammalia, 
 are arranged into true and false, with this difference, that the false 
 ribs are placed both above and below the true ones. There is 
 some, though not very great variety in the number of ribs presented 
 by this class : for instance, in the Insessores we meet with seven or 
 
26 
 
 eight pairs ; and in the willock, of the order Natatores, twelve 
 pairs; the average number is eight or nine pairs. The true ribs 
 are joined to the sternum by straight osseous portions, called ster- 
 nal ribs, instead of by elastic cartilages, and are movably connected 
 at each end. It is highly interesting to observe the mode of articula- 
 tion of the vertebral extremity of the ribs. In such as require 
 fixity of the chest, for the purposes of flight, the rib is articulated 
 to the side of the vertebra, having no connection to the inter-arti- 
 cular cartilage; but in the ostrich, and others of the cursores, 
 where the dorsal vertebras preserve their mobility, the heads of the 
 ribs are attached to the intervertebral spaces. 
 
 There is another interesting fact connected with the ribs, in 
 birds of powerful flight ; it consists in a number of small osseous 
 plates being detached from the posterior margin of each true rib, 
 and passing backwards and upwards to be connected to the suc- 
 ceeding rib, by means of strong, oblique, fibrous ligaments. In 
 the ostrich, rhea, emeu, and cassowary, these bony splints present a 
 mere rudimentary type. 
 
 Sternum. — The modifications presented by this bone, strictly 
 conform to the functions which the anterior extremities are designed 
 to execute. Hence, in the cursorial birds which do not fly, it is met 
 with in the form of a simple square plate of bone like a shield, while in 
 those birds that possess great powers of flight, it extends over the 
 whole of the lower aspect of the thorax and abdomen, even to the 
 pubic bones, and in order to afford sufficient space for the attach- 
 ment of the pectoral muscles, it is armed with a huge crest, extend- 
 ing the whole length of its lower surface. This crest, or keel, is 
 uniformly developed in proportion to the size of the pectoral mus- 
 cles, and hence declares the power of the anterior extremities. The 
 sternum is sloped obliquely on each side of its anterior extremity, 
 for the reception of the clavicle, and in the centre is connected 
 with the fork-bone, either directly or by means of ligaments; the 
 true ribs are attached to it on each side. The sternum of the crane 
 has within it a large cavity, containing several convolutions of the 
 trachea. This condition is repeated in the wild swan; but in the 
 tame swan, and some of the grallae, as the ciconia and gallinae, it 
 is but very feebly developed. 
 
 On the internal surface of the sternum, chiefly along the mesial 
 line, several apertures may be observed, for the passage of air into 
 the bone. 
 
 Anterior extremity. -—Here, as in the mammalia, the extremity 
 consists of shoulder, arm, fore-arm. and hand. In the first, we 
 recognise a scapula, a coracoid bone, and a clavicle. 
 
 The scapula is generally a long, narrow bone, increasing in 
 thickness as it approaches the shoulder joint, where it expands in 
 the transverse direction, to form the posterior half of the glenoid 
 cavity ; here also it articulates with the coracoid bone and clavicle. 
 The direction of the scapula is longitudinal. In birds with active 
 
VERTEBRATA. 27 
 
 powers of flight, it reaches to the last rib. while in the emeu it covers 
 only two. This bone is broad and flat in the penguins. 
 
 The coracoid. or posterior clavicle, is a strong bone, broad in- 
 feriorly. where it is received in a transverse groove in the sternum ; 
 it extends upwards, outwards, and forwards", to articulate with the 
 scapula and clavicle. The glenoid cavity thus resulting from the 
 union of this bone with the scapula, is often unequal to^the recep- 
 tion of the head of the humerus ; hence, in the raptores and inses- 
 sores, a small but distinct bone extends between the coracoid and 
 scapula, over the superior part of the cavity,|which it here completes. 
 It was discovered by Nitzsch, who called it the capsular bone. 
 
 The clavicles are subject to considerable variety. In the ground 
 parrots of Australia, for instance, they present only a rudimentary 
 type, while in the psittacus mitratus, &c, they are wholly absent; 
 they are feebly developed in the emeu, rhea, and cassowary. When 
 these bones are enchylosed together at their sternal extremities, as 
 they ordinarily are, they constitute a single bone, named furculum. 
 In the ostrich they do not come in contact inferiorly, although they 
 reach the sternum ; and in the toucans, they neither come "in con- 
 tact below, nor reach the sternum. It is remarkable that in the 
 ostrich they are anchylosed above with the coracoid and scapula, 
 whilst almost in every other species they either continue separate, 
 or are movably jointed superiorly. 
 
 The humerus attains its greatest length in the albatross, and is 
 shortest in the struthious birds and penguins, whilst in the swifts 
 and humming birds it is characterised by its thickness, strength, 
 and the development of its muscular processes. In the cursores it 
 is short and attenuated, resembling the corresponding part in the 
 paddle of the turtle. Its head is oblong transversely, and enlarged 
 by two lateral crests, under one of which are to be found the air 
 passages leading into the bone. The lower extremity of the hu- 
 merus is formed after the manner of a hinge, consisting of an in- 
 ternal spherical portion to articulate with the ulna, and an external 
 oblong portion for the radius. 
 
 The radius and ulna are straight and slender bones, enlarged at 
 their extremities, and placed one in front of the other, so as scarcely 
 to admit of any pronation or supination. In the penguins the bones 
 of the fore-arm are flattened, and articulated with the anterior edge, 
 and not the extremity of the humerus. 
 
 The carpus is composed of two bones only, and so wedged in 
 between the metacarpus and fore-arm, as to limit the motionsof the 
 hand to adduction and abduction. 
 
 The metacarpus is chiefly formed of two bones, a small ulnar 
 one, which supports a single phalanx, and a large radial one, which 
 sustains two phalanges. A small rudimental bone is usually an- 
 chylosed to the outer side of the proximal extremity of the radial 
 metacarpal bone. 
 
 Lower extremity. — The pelvic bones, like those of the shoulder, 
 are three in number: the ilium represents the scapula, the ishium 
 
28 EVERS'S COMPARATIVE ANATOMY. 
 
 the clavicle, and the pubis the coracoid bone. Unlike the shoulder, 
 however, these bones are always anchylosed into one piece on 
 either side, and with one exception, never join in the mesial line ; 
 this single exception is afforded by the ostrich, in which the pubic 
 bones complete the pelvic circle by anchylosing" at their inferior 
 extremities. The vulture cinereus, and some acquatic birds, form 
 the nearest approach to this last condition. In them the pubic 
 bones are often surmounted by a cartilaginous appendix at their 
 anterior extremity. 
 
 The ilium is the only bone of the pelvis that comes in contact 
 with the spine ; it is elongated in form, narrow in the centre, and 
 expanded at its extremities. This bone is anchylosed with the 
 sacrum, the ischium, and the spinous and transverse processes of 
 one or two dorsal vertebras. 
 
 The ischium lies parallel with the ilium; it is a small oblong 
 bone, not presenting any peculiarity. 
 
 The pubis unites with the ischium in a two fold manner in the 
 humming bird and some others, so as to form two foramina obtura- 
 toria, while in others, as the stork, it is only united to it at the coty- 
 loid foramen. This cavity is always incomplete at its internal part, 
 where it is closed by some fibrous bands. 
 
 The femur is short, and slightly convex anteriorly; its head is 
 hemispherical, and joined to the shaft at a right angle, without 
 the intervention of a neck. There is but one trochanter; it is of 
 a large size, continuous with the external part of the shaft, and gene- 
 rally rises above the level of the head. The lower extremity of 
 this bone presents two condyles, the inner one for the tibia, the 
 outer one, which is longer and larger, rests on the tibia and fibula; 
 it is convex from behind forwards, and terminates in a groove in 
 both these directions. 
 
 The tibia is the principal bone of the leg, the fibula ending in a 
 point inferiorly, and achylosed to the tibia for a considerable extent. 
 The lower extremity of the tibia forms a transverse trochlea, above 
 which there is a deep groove or foramen, to transmit the tendon of 
 the extensor digitorum communis. The upper and anterior part of 
 the tibia gives rise to a long pointed process, which ascends in the 
 shape of an olecranon in front of the joint, being also anterior to 
 the patella. 
 
 The tarsus can only be recognised as a distinct segment of the 
 foot, when examined at an early period of the bird's existence ; 
 then only can be found a distinct astragalus of a flattened oval form, 
 convex superiorly, and concave below, where it meets the three 
 bones of the metatarsus partially separated. A rudiment of os calcis 
 may also be found in the extensor tendons. In the penguins, the 
 three metatarsal bones are only anchylosed at their extremities ; 
 but in other birds, faint grooves alone indicate their existence. 
 The remote extremity of the metatarsus presents three convex facets 
 to articulate with the toes. These last are subject to great variety 
 as to number, being reduced to two in the ostrich, and increased to 
 
VERTEBRATA. 29 
 
 five in the gallinaceae. The phalanges bear no proportion to the 
 size or number of the toes, being found to vary from one up to five. 
 
 RECAPITULATION. 
 
 1. There is more uniformity observed in the skeleton of birds, 
 than in any other of the vertebrated classes. 
 
 2. The bones are white, thin, and brittle; in early life, filled 
 with a thin serous oil, which is subsequently removed to be replaced 
 by atmospheric air, especially in those of the high-flying kind. 
 
 3. The bones are early and rapidly ossified, particularly those of 
 the head, thorax, and pelvis. This ossification also affects the ten- 
 dons of the muscles of the leg, sclerotic tunic of the eye, inferior 
 larynx, and the rings of the trachea. 
 
 4. Arms adapted solely for flight ; legs for support. 
 
 5. Head and neck long, for the purposes of prehension. 
 
 6. The dorsal and sacral portions of the spine the most fixed. 
 
 7. Cervical vertebras more numerous than in the mammalia; 
 occasionally, three times the number. 
 
 MAMMALIA. 
 
 The number of vertebrae contained in the spine, is very variable ; 
 but the human type is by far the most generally predominant. In 
 the cetaceae there is no distinction between lumbar, sacral, and 
 caudal vertebras ; and in the porpesse, there are sixty-six posterior 
 to the dorsal : these mammalia, however, have no pelvis. The 
 cervical vertebrae are uniformly seven throughout this class, not- 
 withstanding Cuvier imagined lie had found a solitary exception in 
 the neck of the ai, bradypus tridactylus; but it has been well as- 
 certained since, that what he conceived to be the two last cervical 
 vertebrae of this animal, have two rudimental ribs attached to them. 
 When we are reminded of the localities and habits of the sloth, 
 hanging from the branches of trees, and passing from bough to 
 bough, aided by the current winds, it becomes obvious why such a 
 provision should exist, of modifying the two superior dorsal verte- 
 brae, and of consigning to them the offices of cervical, rather than 
 infringe on a law which at present seems without an exception. 
 
 The dorsal vertebrae range from twenty-three, as seen in the 
 unau, bradypus didactylus, to twelve, as presented by man, mice, 
 bats, rabbits, hares, and several apes. In the megatherium there 
 are sixteen, in the horse eighteen, and in the elephant twenty. 
 The lumbar vertebrae are generally seven; they vary, however, 
 there being two in the two-toed ant-eater, and nine in the lori. The 
 sacral vertebrae are seven in the mole ; in the vampyre bat, opossum, 
 and some apes, there is but a single sacral vertebra, the usual 
 number being three. The caudal vertebrae are four in man and 
 the ourang-outang; forty in the two-toed ant-eater; and in the 
 vampire bat they are altogether absent. 
 
30 EVERS'S COMPARATIVE ANATOMY. 
 
 In most animals, it has been said, that the head and neck together 
 equal in length the fore-feet, except where the latter are used as 
 hands, as in the apes and rodentia. The neck attains its greatest 
 length in the genus cameius, and is shortest in the order cetacea, 
 owing to the consolidation of the vertebrae. According to the 
 statement of Gore, the number of cervical vertebras in certain of 
 the cetacea, as the balaena, manatee, and dugong, amounts only to 
 six. In the rodentia, and most long necked animals, the spinous 
 processes are almost wanting. The atlas, in the carnivora, rumi- 
 nantia, solipida, pachydermata, <fec, is distinguished by its length, 
 and by its large aliform transverse processes. The free motion and 
 beautiful arch observed in the necks of some horses, camels, &c, is 
 explained by the bodies of the cervical vertebras having a perfect 
 articular head on their upper surface, and a corresponding depres- 
 sion on their lower, similar to what we observe in the necks of 
 serpents, with this difference, that the surfaces are reversed. The 
 ruminantia, rhinoceros, elephant, &c, are remarkable for the great 
 length of the spinous processes of the dorsal vertebrae. Bats have 
 scarcely any spinous processes; and, with the exception of the 
 second dorsal, they are short in the rodentia. In the lumbar ver- 
 tebrae, the form of the transverse processes is very variable — almost 
 absent in bats, very strong in the ruminantia, rodentia, and carni- 
 vora. The megatherium possesses long spinous processes. In the 
 sloth, the length, breadth, and consolidation of the sacral vertebrae 
 remind us of the sacrum of birds. The few first only of the caudal 
 vertebrae in mammalia contain a prolongation of the vertebral canal. 
 Animals with long movable tails, as the two-toed ant-eater, have 
 oblong triangular processes on the under surface of the caudal 
 vertebrae, as in the crocodile. The connection of the vertebrae is 
 almost always by means of interarticular cartilage, as in man, and 
 consists of concentric rings, most evident in the whale. In the 
 pig and rabbit the interarticular cavities are filled with an albu- 
 minous fluid, as in fishes. 
 
 Ribs. — Man has seven true and five false ribs ; the balaena 
 whale, one true and eleven false ; in the unau, or two-toed 
 sloth, there are twenty-three pairs, of which eleven are false ; in 
 the horse eighteen, and eight of them false; in wolves, cats, and 
 some apes, there are thirteen pairs, four of which are false; in the 
 guinea pig, armadillo, and porpoise, there are thirteen, of which 
 seven are false ; in the manatee, of sixteen pairs, but two are true; 
 in the dugong but three out of eighteen ; and in the ornithorhynchus 
 but six out of seventeen. The breadth of the ribs is greater in the 
 ruminantia, pachydemata, in the manatee, and especially in the 
 two-toed ant-eater, than in other mammalia. The connection of 
 the ribs with the sternum is in general effected by cartilage; but in 
 the cetacea, ant-eaters, dasypus, bradypus man is, ornithorhynchus, 
 echidna, and frequently in bats, the union is completely bony. 
 
 Sternum. — This bone, though essentially the same as in the 
 human subject, is somewhat modified in form by the shape of the 
 
VERTEBRATA. 31 
 
 chest. In ungulated animals, where there are no clavicles, the 
 sternum- is compressed laterally, and projects in the centre like a 
 ship's keel. The superior piece of the sternum is very considera- 
 ble in the mole, where it forms a distinct bone. It is proportionably 
 small in the bat, seal, horse, rhinoceros. In the cetacea it is 
 short and large, being composed of five pieces in the dugong, and 
 three in the dolphin, the porposse, and the platanist. In the bat 
 and ornithorhynchns, the upper part of the sternum is T-shaped, 
 the transverse process being for the articulation of the clavicle. 
 
 The figure of the thorax in most apes, bats, and the greater 
 number of the rodentia, and, in fact, of the class mammalia, having 
 clavicles, agrees with that of the human subject. In ungulated 
 animals, on the contrary, where there are no clavicles, the thorax 
 is laterally compressed and elongated. 
 
 The whole arrangement of the thorax proclaims man to be 
 destined to move in the erect attitude: he is the only animal in 
 which its transverse exceeds the antero-posterior diameter; even in 
 the chimpanse, which approaches nearest to him, the latter exceeds 
 the former measurement, reminding us of the form of this cavity 
 in the very young subject. Its great lateral width and inconsider- 
 able depth from sternum to spine, throw the arms apart, and in- 
 crease their sphere of motion. The reverse characters, together 
 with the absence of clavicles in quadrupeds, allow the fore legs to 
 approximate, to fall perpendicularly under the front of the body, 
 and support it with ease and security. 
 
 Head. — We shall cease to wonder at the striking" differences 
 observed in the construction of this part of the skeleton, when we 
 consider that it forms the receptacle for the brain, most of the ex- 
 ternal senses, the masticatory apparatus, &c. Man combines by 
 far the largest cranium with the smallest face; and animals deviate 
 from these relations in proportion as they increase in stupidity and 
 ferocity. In man, the area of the section of the cranium is nearly 
 four times as large as that of the face; three times as large 
 in the ourang-outang; twice as large in the sapajous; and they 
 are nearly equal in the baboons and carnivora. In the hare 
 and marmot, the face exceeds the cranium by one third; in the 
 porcupine and ruminants, by one half. The face is three times 
 as large as the cranium in the hippopotamus, and four times 
 as large in the horse. 
 
 The superior maxillary bones of the human subject are united 
 to each other, and contain all the upper teeth ; in some other 
 mammalia, however, they are separated by a coniform bone, which 
 contains the incisor teeth, and hence named os insicivum; but it 
 exists where there are no incisor teeth, as in the kerotophara, the 
 elephant, and the two-toed rhinoceros of Africa, and even where 
 there are no teeth at all, as in the ant-eater and some of the ceta- 
 ceans, for which reason Blumenbach calls it os intermaxillare. In 
 some it is a single bone, in others double; it is absent from the 
 chimpanse, though present in the ourang-outang. The former of 
 
32 
 
 these animals possesses supercilliary ridges, which are wanting in 
 the ourang. 
 
 The head of the ourang, viewed in front, is pear-shaped, expand- 
 ing from the chin upwards, the cranium being much the larger 
 end. The frontal sinuses are very large in the dog, wolf, porcu- 
 pine, sloth, sheep, bull, pig, horse, and especially in the elephant; 
 they are small in bats, rats, squirrels, ant-eaters, the hippopotamus, 
 rhinoceros, &c. In cats, martens, and bears, the parietal bones 
 give off from their inner and posterior edge a process of bone 
 which projects into the cavity of the skull, and forms a perfect 
 bony tentorium cerebelli. In the dog and horse, similar processes 
 arise from the petrous portion of the temporal bones. 
 
 The lower jaw is subject to many varieties in the mammalia. 
 In the whale it resembles two enormous ribs, united at the point, 
 without any trace of ascending rami or coronoid processes. The 
 articular head here, as well as in the porpoise, is directed back- 
 wards, and is attached to the skull by means of strong cellular 
 tissue, filled with oil. 
 
 In the hare, rabbit, and guinea-pig, of the order rodentia, the 
 coronoid process is very small; in others, as squirrels and rats, it 
 is pretty large. The condyloid, or articular process, is compressed 
 latterally, directed from behind forwards, and larger in front than 
 behind. 
 
 In the carnivora, the articular head is directed transversely, and 
 so closely adapted to the glenoid cavity of the temporal bone that 
 the jaw retains its situation after the destruction of the ligaments. 
 This is well seen in the marten and sea-otter. In the ruminants 
 the condyle is very flat, to admit of the lateral motion necessary 
 during the process of rumination. In the carnivora, rodentia, and 
 ruminantia, the two halves of the lower jaw are never firmly 
 united — in this particular affording us an instance of the perma- 
 nence of a condition in other mammalia, which in man is peculiar 
 to the earliest periods of life. 
 
 Swine have two small bones placed at the aterior openings of 
 the nares for the support of the snout. In fine, it is to be remarked 
 that the crania of all the quadrumana, together with the other 
 mammalia, are distinguished by the comparative size, great'length 
 and projection of the jaws. 
 
 Anterior extremity. — This extremity in the lower animals cor- 
 responds to the superior of the human subject, and contains all 
 the elements of it. modified according to the habits of the animal. 
 Sometimes connected to the trunk by means of muscle only, as in 
 the cetacea, pachydermata, ruminantia, and solipe a; in other in- 
 stances by ligament and muscle, as seen in the insectivora. 
 
 Clavicle. — The importance of this bone, in the motions of the 
 upper or anterior extremity, may be well estimated by the fact of 
 its being present in those animals only whose habits of life require 
 free and varied motions of the shoulder. Thus in the quadrumana 
 it is strong and curved, as in the human subject. The bat, hedge- 
 
VERTEBRATA. 33 
 
 hog, and mole, among the insectivora, afford examples of clavicle 
 in its highest degree of development. It is very perfect in the 
 rodentia, as the squirrel, beaver, rabbit, rat, &c. Among the eden- 
 tata, those animals only whose habits are fossorial possess clavicle, 
 as the ant-eater, the dasypus, and the gigantic megatherium ; in 
 the last named animal it presents the peculiarity of being articulated 
 with the first rib instead of the sternum. 
 
 Where the anterior extremity is employed merely for the purpose 
 of progression, we find no clavicle, as in the pachydermata, rumi- 
 nant ia, cetacea, and solipeda. In the carnivora. where there is a 
 slight increase in the range of motion of the anterior extremities, 
 the clavicle exists in a rudimental form, and its development is in 
 proportion to the motion enjoyed ; hence it is small and short in 
 the cat, the bear, and the dog ; in those animals it has no attachment 
 to the sternum or scapula, but lies loose among the muscles. 
 
 Scapula. — This bone forms an essential element of the thoracic 
 extremity, and exists wherever the latter is fully developed, but 
 greatly modified, according to the uses to winch the extremity is 
 applied. The cetacea, in general, have a large scapula of a trian- 
 gular form; the pachydermata, ruminantia, and solipeda, have a 
 long narrow scapula placed perpendicularly on the anterior and 
 lateral part of the chest. In the carnivora and rodentia, where 
 strength and freedom of motion are required, the scapulas are placed 
 obliquely over the ribs; and it is interesting to observe how the 
 obliquity of the glenoid cavity varies with the motions required. 
 This fact has not escaped the observation of the horse-jockey, who 
 is well aware that the upright shoulder is the mark of a stumbling 
 horse. 
 
 Humerus. — When the fore-arm and hand are used for seizing 
 objects, as in apes, many rodentia and carnivora, or for flying, as 
 in the bat, the humerus is formed essentially in accordance with 
 the human type. On the contrary, when the anterior part of the 
 member is but slightly developed, as in the cetacea, the bone is 
 short and thick; and in the whalebone whale, it is nearly as broad 
 as it is long. In the mole it is short, thick, and strong; its tuber- 
 osities greatly developed, and its upper extremity presents two arti- 
 culating surfaces, one for the scapula, and the other for the clavicle. 
 This large size of the bone prevails in all the other fossorial ani- 
 mals, as the mighty megatherium, the pangolins, beavers, ant-eaters, 
 and monotremata. The humerus of the lion is remarkable for 
 being perforated by the brachial artery and nerve, in order to avoid 
 being crushed by the huge and powerful mass of muscles exhibited 
 in this part of the economy of the king of beasts. 
 
 Fore-arm. — The radius and ulna are very short in the cetaceans, 
 and in most of them consolidated too-ether at both extremities. In 
 the cheiroptera they are long, slender, and firmly united, to accord 
 with their mode of progression by flight; in some the olecranon is 
 wholly absent, and in others, as the vampyre, it exists in the form 
 of a patella. The ruminants and solipeds have these bones con- 
 7 — ff cvers 3 
 
34 
 
 solidafed into one. The rodentia, many carnivora, pachydermata, 
 insectivora, and edentata, the bones are distinct throughout, but 
 admit of no motion. The sloth, however, among the edentata, 
 enjoys great freedom of pronation and supination ; here the bones 
 are long, arched, and widely separated in the centre. 
 
 Carpus. — The bones composing this part of the extremity are 
 usually disposed in two rows, as in man. though the number almost 
 invariably differs from that model. The following is Cuvier's 
 statement of their number: — In man and the elephant. 8; in apes, 
 the hare, and the mole, 9: in the solipeda, carnivora and several 
 rodentia, 7 ; in the ruminantia from 6 to 7 ; in the edentata, 6; and 
 in cetacea from 4 to 7. In apes, carnivora, and several of the un- 
 gulata, the pisciform bone is very large, and by affording attachment 
 to the flexor muscles of the hand, performs the office of os calcis 
 in the foot. The simise, in general, have nine bones in the carpus — 
 another distinction between their hand and that of man. In the 
 most anthropo-morphous of them, the chimpanse and the ourang- 
 outang, the ninth is a sesamoid bone in the tendon of the abductor 
 pollicis longus. 
 
 The metacarpal bones in the whale are five in number and 
 flattened in the form of phalanges. These last are, two in the 
 thumb, three in the little finger, four in the index and ring fingers, 
 and five in the middle, collectively forming a short but strong 
 paddle. The shovel-shaped hand of the mole consists of five fingers, 
 each having a metacarpal bone and three phalanges. In the 
 bat the thumb is short, and not included within the flying membrane, 
 The metacarpal bones are long, slender, and cylindrical : the distal 
 phalanx is hooked, and sustains a nail by which the animal suspends 
 itself. The simias have these parts constructed as in man, except 
 the thumb, which is small, and extends only to the metacarpopha- 
 langeal articulation. In bears and badgers the five fingers are of 
 equal length, and parallel to each other. In the endentata several 
 of the fingers disappear; for instance in the two-toed ant-eater, the 
 thumb, index, and little fingers, are merely rudimentary; the 
 middle finger, however, is proportionally developed. 
 
 Among the ungulata the hand is still more diversified ; the ele- 
 phant, for example has five fingers all united into one mass within 
 the skin. The pig almost wants the thumb; he, however, has four 
 perfect fingers, but walks only on two. The ruminantia have but 
 two fingers, each metacarpal bone supporting three phalanges. In 
 the solipeda there is but a single finger; for instance, in the horse 
 the carpus corresponds to the knee ; the metacarpal bones are con- 
 solidated into one, cannon bone, behind which there are two small, 
 splint bones, commencing broad at the knee, and terminating in a 
 pointed manner behind the lower third of the cannon bone. Here 
 we meet with three phalanges, the first called pastern, the second 
 coronet, and the third coffin bone. 
 
 Pelvis. — It has been truly asserted that in the human skeleton 
 alone, a true pelvis is to be found. This arises from the form and 
 
VERTEBRATA. 35 
 
 manner of connection of the bones entering into the formation of 
 this cavity. The chimpanse and elephant afford ns the nearest 
 approach to the human formation, even here the ilia are narrow 
 and elongated ; and the sacrum and coccyx are flat, contracted, and 
 continued in a direct line with the spine. Next in the order of 
 development may be ranked the rhinoceros, the ox, the horse, the 
 carnivora and the rodentia. In ant-eaters, moles, and shrews, the 
 symphysis pubis remains open; and in the two latter genera the 
 pelvis is so small that the pelvic viscera are placed without it. The 
 megatherium and sloth, however, have pelvis of large dimensions. 
 Some of the edentata, as the dasypus, have the ilia joined to the 
 sacrum. In others, as the sloth and some of the ant-eaters, the 
 ischium is connected with the sacrum, forming an ischiatic foramen, 
 instead of a notch. The cetacea present but slight rudiments of a 
 pelvis in the form of two small bones united to each other and to 
 one of the vertebrae by cartilage. Finally the marsupial animals 
 present a small, elongated pelvis, especially remarkable for the pre- 
 sence of two particular bones not found in any other mammiferous 
 animal even in a rudimental state, and named 0.95a marcip'ialia. 
 These bones are attached, but not articulated, to the anterior part 
 of the pubis, near the symphysis; each is about three inches long 
 in the kangaroo, flat, with anterior thin, and a posterior thick 
 edge. The bone is triangular in form, the broad end being at the 
 pubis, while the narrow has attached to it the abdominal muscles. 
 The use of these bones is to support the marsupium, or abdo- 
 minal pouch, in which the mammary apparatus is lodged, and the 
 young animal nurtured. 
 
 The posterior or abdominal extremity is altogether absent in 
 the cetacea. In the other mammalia inhabiting the sea, the seal, 
 for instance, the several elements of the posterior extremity, even 
 the toe-nails, are distinctly recognisable, but consolidated by a 
 membranous web into a kind of caudal fin. 
 
 The femur in the lower mammalia is short and straight ; the 
 neck is either absent or but little developed, the head being placed 
 vertically over the shaft. The trochanters and linea aspera are 
 badly marked. This bone is shorter than the tibia, the converse to 
 what obtains in man. In the megatherium its thickness equals 
 half its length. The trochlea is a deeper and the transverse 
 diameter of the condyles less than in man. 
 
 The patella is usually present in the mammalia; best developed 
 in the pachyderms, solipeds, and monotrems; least so in the carni- 
 vora and quadrumana; and wholly absent in the marsupiata and 
 cheiroptera. 
 
 Tibia and Fibula. — Throughout the mammalia these bones 
 coincide pretty nearly with those of the fore-arm. As in man, the 
 tibia forms the chief bone of the leg. The fibula is analogous to 
 the ulna, and is found only in a rudimentary state in the solipeds 
 and ruminants, as the latter bone was in these animals. In the 
 solipeds, the fibula is applied to nearly the upper half of the outer 
 surface of the tibia, being pretty large above, and ending in a fine 
 
36 EVERS'S COMPARATIVE ANATOMY. 
 
 point below. Ruminants, on the contrary have the fibula better 
 developed inferiorly where it forms the external malleolus and ex- 
 tends but a short way up the leg. Pachyderms, and all the ungili- 
 Gulata, possess a fibula well developed ; and in sloths its lower 
 extremity ends in a conical point, which enters a corresponding 
 cavity in the astragalus. In the rodentia, and insectivora, particu- 
 larly the mole, the tibia and fibula are united through their inferior 
 half. Carnivora have these bones fully developed and detached: 
 this is well seen in the phocidee and felina?. In the dog they are 
 united posteriorly. 
 
 Tarsus. — The bones composing this part of the foot for the 
 greater part resemble those of man. The cheiroptera present a 
 remarkable peculiarity in the formation of a long slender bone, 
 extending from the back of the os calcis half way to the tail, and 
 enclosed within the flying membrane. Cuvier and Meckel supposed 
 it to be a portion of the os calcis, whilst Daubeton conceived it to 
 be a distinct bone. On the inner side of the tarsus of the mole, a 
 sickle-like process of bone is found, similar to that observed on the 
 carpus. The metatarsus and toes in ruminants and solipeds are 
 disposed pretty nearly as in the anterior extremities. The rodentia 
 and carnivora have usually five toes, the great one being often 
 shortened, or as in cats, dogs, and hares, altogether absent. The 
 quadrumana and marsupiales have the great toe separated from the 
 rest, bearing the same relation to the foot as the thumb to the hand. 
 
 Although the disproportion in the respective size and length of 
 the upper and lower extremities of the human subject, indicate the 
 different functions they are designed to execute, yet they present 
 many similarities throughout their divisions, the construction of 
 their articulations, and the number and form of their bones. The 
 arm, fore-arm, and hand, lor instance, resemble the thigh, leg, and 
 foot; the os innominatum may be compared to the scapula; the 
 hip, knee, and ankle, to the shoulder, elbow, and wrist: and the 
 carpus, metacarpus, and fingers, to the tarsus, metatarsus, and toes. 
 Contrast. — A line falling perpendicularly from the shoulder in the 
 erect attitude, would pass behind the hip. The upper extremities 
 diverge below, whilst the inferior converge. The deep acetabulum, 
 and the strong tight capsule of the hip, may be well contrasted 
 with the shallow glenoid cavity, and weak, loose capsule of the 
 shoulder. The lower extremities are as long as the head and 
 trunk together, being only equaled in this respect by the kangaroo 
 and jerboa. 
 
 The great length of the shaft and neck of the femur, its perpen- 
 dicularity with the spine, and the depth of its internal condyle, are 
 characters peculiar to man : in the fore-arm every thing conspires 
 to procure freedom of motion; in the leg, strength and security are 
 the objects aimed at. The hand is articulated on a line with the 
 fore-arm, and enjoys free and varied motions; the leg joins the 
 foot at a right angle, and moves chiefly in the angular direction; 
 the entire surface of the tarsus, metatarsus, and toes, rests on the 
 ground : the two latter circumstances are exclusively confined to 
 
VERTEBRATA. 37 
 
 the human subject. The parts composing the hand and foot are 
 disposed inversely as regards their development and importance. 
 The solid part of the hand is small, weak, and but slightly deve- 
 loped ; that of the foot is large, firm, and ossified at an earlier 
 period of life. The fingers are long, slender, and mobile; the toes 
 are short, thick, and enjoy only a limited share of motion. But the 
 distinguishing characteristic of the human hand is due to the 
 strength, situation, and development of the thumb, which is oppos- 
 able to the fingers, and rendered useful in the thousand offices 
 which it has been designed to execute. 
 
 Man is distinguished from all other animals by the great size of 
 the cranium over that of the face. One method of expressing 
 these relative proportions, is by the course of the facial line, and 
 the number of degrees in the facial angle. A line drawn from the 
 greatest prominence of the forehead to that of the upper maxillary 
 bone, in the erect attitude, describes the direction of the face, and 
 is called the facial line ; a second line, perfectly horizontal, drawn 
 backwards from beneath the basis of the nostrils, forms with the 
 other what is termed the facial angle, and gives the measure of 
 the relative prominence of the jaws and forehead. In the adult 
 human subject the facial angle varies from 65° to 85°; in children 
 it reaches 90°; a sufficient proof of its inadequacy as a standard 
 for the measurement of intellect. The situation of the foramen 
 magnum, and occipital condyles, being but little posterior to the 
 centre of gravity, are also distinctive characters of man. Aline 
 drawn forwards parallel to the plane of the foramen magnum, will 
 come out just under the orbits. In the ourang-outang this line 
 would pass below the level of the lower jaw, and in most other 
 animals the foraman magnum is placed on the back of the head, 
 its plane being nearly vertical. The great weight of the human 
 head, the absence of ligamentum nuchas, and of the rete mirabile, 
 or some analogous provision for moderating the influx of blood to 
 the brain, coupled with other facts hereafter to be mentioned, in- 
 contestably prove that man was intended for the erect attitude, and 
 that he is quite unfit to move on all-fours, as some modern authors 
 would have it. 
 
 Nature has clad in defensive mail the armed rhinoceros, provided 
 the lion and the ti^er with weapons of defence, clothed the sheep 
 in wool, and the bear in fur; every animal she has bountifully 
 provided in all that was necessary for its subsistence, and adapted 
 to its destined mode of existence. Man alone she has abandoned, 
 weak, naked, and defenceless, unarmed in the midst of dangers, 
 and uncovered to the winds of heaven. But she has bestowed on 
 him gifts far more than equivalent to all that was denied: she has 
 given him an illimitable capacity for improvement; she has endowed 
 him with terrestrial ubiquity, or a capability of inhabiting every part 
 of the known world: and above all, she has conferred on him in- 
 tellect and inventive genius, which have raised him to a measure- 
 less superiority over the rest of created beings. By means of these 
 endowments he has made most animals subservient to his purposes, 
 
3S 
 
 and obedient to his commands ; and such as their native ferocity- 
 renders incapable of utility, or dangerous to Ii is repose, he has 
 banished to the "howling wilderness." In fine, the surface of the 
 earth attests his industry and intelligence, and nature herself is 
 delighted to obey him. 
 
 Recapitulation. — Characters Peculiar to Man. 
 
 Biped ; bimanous ; erect attitude ; great proportion in the size 
 of the cranium over that of the face; development of brain ; direc- 
 tion of facial line; articulation of the head with the spine; rational; 
 endowed with speech ; prominent chin, and teeth of peculiar cha- 
 racters ; absence of ligamentum nuchas and intermaxillary bone: 
 great transverse measurement of the chest; curved spine, sacrum, 
 and coccyx; large pelvis; short arms; long, powerful thumb, pos- 
 sessing separate flexors ; length and direction of the neck of the 
 femur ; depth of internal condyle ; the whole flat of the foot resting 
 on the ground, and the leg joining it at a right angle. Man is also 
 remarkable for the smoothness of his skin, and the slowness of his 
 growth. 
 
 The following are Camper's measurements of an ourang-outang, 
 compared with those of man : 
 
 
 
 MAN. 
 
 
 OURANG 
 
 
 Whole length of the 
 
 body 
 
 
 
 
 
 from vertex to heel 
 
 i 
 
 71 inches. 
 
 Less than 30 ii 
 
 ic\ 
 
 Superior extremity. 
 
 
 32 " 
 
 a 
 
 24| 
 
 a 
 
 Inferior do. 
 
 
 39 " 
 
 a 
 
 16 
 
 a 
 
 Humerus, 
 
 
 13 " 
 
 ii 
 
 81 
 
 a 
 
 Ulna, 
 
 
 91 " 
 
 ii 
 
 9 
 
 a 
 
 Hand, 
 
 
 8* " 
 
 ii 
 
 7 
 
 a 
 
 Thumb, 
 
 
 4i " 
 
 ii 
 
 « 
 
 a 
 
 Middle finger, 
 
 
 41 M 
 
 ii 
 
 3 
 
 a 
 
 Femur, 
 
 
 20 " 
 
 ii 
 
 7 
 
 a 
 
 Tibia, 
 
 
 16| " 
 
 ii 
 
 7 
 
 a 
 
 Foot, 
 
 
 10i " 
 
 ii 
 
 n 
 
 a 
 
 Middle toe, 
 
 
 2\ " 
 
 a 
 
 2k 
 
 a 
 
 FOSSIL BONES OF ANIMALS. 
 
 It is the undivided opinion of geologists, that there has been a 
 regular succession of deposits in the earth, and that the remains of 
 different animals (many of them long since extinct) are to be found 
 in the several strata. In the deeper strata, the remains of animals 
 low in the scale of organisation are to be met with ; in higher 
 strata, oviparous animals of large size and complex structure are 
 discovered; above these are found mammalia; and still nearer to 
 the surface, the bones of the megatherium, mastodon, rhinoceros, 
 elephant, &c. ; and it is now the prevalent opinion that man was 
 created last of all. 
 
LIGAMENTS. 39 
 
 Some bones are found with their animal ingredients remaining 
 others are fossilised. The phosphate of lime loses its phosphoric 
 acid, and the earth remains incorruptible, while the soft animal 
 matter decomposes and dissipates. The bone in this condition 
 may become fossilised ; silicious earth, or lime combined with iron, 
 may pass, by infiltration, into the interstices of the original earthy 
 matter, and in this state it is permanent as the solid rock. 
 
 There is preserved in the Royal Museum of Madrid, a skeleton 
 of the enormous megatherium of Cuvier. It is supposed that the 
 animal was seven feet in height; for its femur is three times the 
 diameter, and its pelvis twice the breadth of that of an elephant. 
 
 CHAPTER IV. 
 
 LIGAMENTS. 
 
 In the lowest grades of animal beings, cartilages, synovial mem- 
 branes, capsular or accessary ligaments, scarcely exist at the joints. 
 We here rind the movable points formed of a tough connecting 
 material, which, by its elasticity, admits of the limited motions 
 required. 
 
 No ligamentary apparatus appears in the soft, gelatinous animal- 
 cules ; but the silicious and calcareous spicula of the poripherous 
 radiata are supported by a tough, elastic species of cellular tissue. 
 The plates composing the shells of the echinida are united by 
 sutures, and the enarthroidal joints of the spine by capsules, and 
 often by a ligamentum teres, as in the cidaris. In the larger Crus- 
 tacea and coleopterous insects portions of the skeleton are locked 
 into each other, where they move securely, but to a limited extent, 
 in the angular direction without ligaments. The shells of the con- 
 chifera are united by their locking teeth, and by a strong, tough 
 ligament, which, by its elasticity, constantly tends to the separation 
 of the bivalves. 
 
 In the soft, flexible skeletons of the cartilaginous fishes, the liga- 
 ments are few, and confined to the organs for mastication and pro- 
 gressive motion. But in the osseous fishes the ligaments of the 
 spine are white, fibrous, dense, and highly elastic ; and here, for the 
 first time, we meet the contiguous ends of bones incrusted with car- 
 tilage. In the amphibia, and in the reptiles, the bodies of the vertebrae 
 are united by enarthroses, furnished with strong fibrous capsules and 
 synovial secretion. Here we have external fibrous bands, inter- 
 spinous ligaments, and occasionally loose cartilages in the joints. 
 The capsular ligaments of birds are thin and strong : their cartilages 
 of incrustation are also thin, but their joints are freely supplied 
 with synovia and their hip joint furnished with a strong ligamen- 
 tum teres. 
 
40 EVERS's COMPARATIVE ANATOMY. 
 
 In the mammalia, thick fibro-cartilages appear interposed between 
 the bodies of the vertebras, and in the carnassier and climbing 
 mammalia, the articular processes are furnished with well developed 
 synovial capsules. The tails of many quadrupeds enjoy full motion 
 from their coccygeal vertebras being united by synovial capsules. 
 The anterior and posterior common ligaments of the spine are 
 powerfully strong and highly elastic along the pliant columns of 
 the cetacea. In the large and heavy-headed herbivorous quadru- 
 peds, the ligamentous nuchas is of great size and strength, extending 
 from the occipital protuberance along the cervical and dorsal spines, 
 and in many instances, to the coccygeal and iliac spines. The 
 light-headed, and active muscular carnassier have this ligament 
 short and small, and in the quadrumana and many of the rodentia 
 scarcely a trace of it is to be found. The inter-articular cartilage 
 of the lower jaw is met with, in this, but not in the preceding classes, 
 the ligamentum teres is found in most of this class, but is said to be 
 absent from the ourangs, the elephant, the rhinoceros, the hippopo- 
 tamus, the kangaroo, the sloths, and the monotremata. The two 
 toes of those ruminants, whose habits oblige them to make rapid 
 and bounding movements, are secured by strong transverse liga- 
 ments passing between their phalanges. 
 
 CHAPTER Y. 
 
 ON THE MUSCULAR SYSTEM IN THE INVERTEBRATA. 
 
 General observations. — In the higher orders of animals, there is 
 a close relation, and a perfect mutual dependence between the 
 osseous and the muscular systems; so much so, indeed, that the 
 arrangement of one may be at once inferred by any one who pos- 
 sesses a sufficient acquaintance with the other. It is by means of 
 this system that animals are enabled to move from place to place, to 
 seize, masticate, and swallow their aliment, to circulate their fluids, 
 to expel their excretions, to produce various sounds, and to accom- 
 plish an infinitude of other purposes. A system ordained to execute 
 so many offices cannot fail to present some interesting peculiarities 
 in the animal kingdom. In obedience to a law, often alluded to, 
 we find that the muscles of the highest classes of red-blooded ani- 
 mals, during their development, pass through the soft, colourless, 
 and gelatinous condition of those of the lowest species before they 
 attain the characters peculiar to them in their highest state of 
 development. 
 
 Radlata. — No muscular fibres have been hitherto found in the 
 polygastric animalcules. Their rapid motions through the fluids 
 which they inhabit appear to be accomplished by means of the vibra- 
 tions of minute cilia (which are analogous to the villi on the mucous 
 surface of a small intestine) growing from the outer surface of their 
 
MUSCULAR SYSTEM OF THE INVERTEBRATA. 41 
 
 bodies ; the cilia which in these animalcules, serve the double pur- 
 pose of locomotive and respiratory organs, have been observed in 
 every class of animals, even the mammalia. 
 
 In the zoophytes, the soft, fleshy mass, which we have seen 
 secrete the solid matter of the skeleton, possesses distinct, but lan- 
 guid irritability: no part of these animals is, however, so irritable 
 and contractile as their prehensile sacs or polypi. It is not till we 
 arrive at the stellerida and asterias that distinct muscular fibres 
 have been satisfactorily demonstrated ; and in the echinida strong 
 adductor and abductor muscles are seen attached to, and moving the 
 jaws of several species. 
 
 Articulata. — Seeing that these animals possess an extensive sur- 
 face for respiration, and a highly developed nervous system, we are 
 prepared to meet with considerable muscular energy. Accordingly, 
 in the nematoid entozoa, strong muscular fibres are seen taking 
 different directions: the rotiferous or wheel-animals, are also re- 
 markable for the development of the muscular apparatus provided 
 for the movements of their jaws, and long vibratile cilia. The 
 common earth worm has distinct muscles appropriated to the move- 
 ments of its conical pointed feet, and its anus is well furnished with 
 levator and sphincter muscles. The insects and the air-breathing 
 arachnida possess a well marked muscular system ; but of all the 
 branchiated invertebrata, the Crustacea possess the largest proportion 
 of muscle ; this they require for the purpose of swimming, escaping 
 from danger, &c. Although these animals are provided with ex- 
 ternal organs of mastication, the interior of their stomach is set 
 with numerous teeth, and its exterior provided with a suitable 
 arrangement of muscle. 
 
 Mollusca. — The muscular system presents much greater variety 
 of form in this than in the articulate class. The tunicata possess 
 a distinct muscular coat within their cartilaginous covering, by 
 which they act on their entire body, and empty their thoracic 
 cavity; the orifice of which, as well as the anus, is provided with 
 sphinctorial muscles. The foot of the conchifera, by which they 
 swim, creep, burrow, or attach themselves, is hollow, and composed 
 almost entirely of muscular fibres, taking different directions. This 
 foot occasionally admits the water into its interior, and is absent 
 from the oyster and others where the shell is permanently fixed. 
 In the gasteropoda, the foot is the largest muscle in the body, and 
 in trachelipodous gasteropods or those residing in turbinated shells, 
 its fibres are traceable up to the neck, and backwards to be attached 
 to the shell. The predaceous gasteropods possess a powerful mus- 
 cular proboscis provided with a fleshy tongue, armed with sharp 
 conical teeth, as seen in the common whelk, (buccinum undatum.) 
 In the chephalopoda and pteropoda, muscular fins are attached to 
 the side of the trunk for progressive motion. And in the naked 
 cephalopods, a thin panniculus carnosus with interlacing fibres, is 
 spread all over the body, beneath the coloured skin of the mantle. 
 The octopus is destitute of any lateral fins, but is provided with a 
 
42 
 
 muscular membrane extended between the bases of its feet, by 
 which it is enabled to swim ; but what is curious about it is, that 
 it swims backwards by impelling the water forwards. 
 
 CHAPTER VI. 
 
 ON THE MUSCULAR SYSTEM IN THE VERTEBRATA. 
 PISCES. 
 
 In all the vertebrata the soft parts are uniformly placed external 
 to the hard resisting textures : in them the muscles of animal life 
 are generally of a red colour, and connected to bone by at least one 
 extremity, through means of tendinous or fibrous structure. In 
 fishes, the muscular fibres are soft, gelatinous, and colourless as in 
 the in vertebrata, and the embryos of the higher vertebrated classes. 
 In the salmon, however, they are of a higher red, especially about 
 the head ; and in the lamprey they are blackish gray. The 
 arrangement of the muscles in the osseous fishes is such, that a 
 large mass extends from head to tail on each side, divided by fibrous 
 bands into numerous strata. The active movements of fishes are 
 not subject to much variety ; their ascent or descent is effected 
 by the compression or expansion of the air-bladder, and by their 
 pectoral fins, whilst they are impelled forwards by the lateral motion 
 of the tail opposed by the resistance of the water. When the 
 swimming bladder is absent, as in the sole genus, or very small, as 
 in the cobitis fossilis, the animal either remains at the bottom, or 
 swims on one side by the vertical motions of the tail. The remora, 
 lump-sucker, and others are provided with a muscular disk in the 
 form of a sucker, by which they adhere to other fish or bodies 
 moving through the water: so powerful is the muscular tail of the 
 salmon, that, aided by the great elasticity of its spine, it is able to 
 mount over cataracts fifteen feet high. The shark is especially 
 remarkable for speed, so much so, that according to a calculation of 
 Sir E. Home, it would, if not compelled to rest, swim over the cir- 
 cumference of the globe in thirty weeks. 
 
 AMPHIBIA. 
 
 The proteus, siren, and the tadpoles of the higher anurous spe- 
 cies, are moved through the water by the same kind of lateral 
 motion of the spine and tail as in fishes. The oreat lateral mus- 
 cles that accomplish these motions are still pale, bloodless, and 
 feeble, and their connecting cellular tissue is soft, scanty, and 
 colourless; the muscles are slightly connected to the skin, and pre- 
 sent but little appearance of tendinous structure. So far the mus- 
 cular system closely resembles that of fishes, but in the adult state 
 
MUSCULAR SYSTEM IN THE VERTEBRATA. 43 
 
 of the anurous species, it presents characters very remote from them, 
 arising from their great extent of respiration, and their inhabiting a 
 rarer medium. The oblique caudal muscles in the tadpole of the 
 tailless tribe, become absorbed with the vertebras to which they are 
 attached, as the animal assumes its permanent form ; but its change 
 of habits is still provided for by the great development of the 
 muscles of the posterior extremity, in fact they closely resemble 
 those of the human leg; and hence the act of swimming in man 
 is an accurate imitation of that of the frog. In this animal, the 
 extensors are much stronger than the flexors of the leg, and those 
 of the arm are but feebly developed. 
 
 REPTILIA. 
 
 The rarity of the medium through which the air-breathing rep- 
 tiles move, at once declares an increased development of muscular 
 energy in this class. In the progressive motion of serpents, their 
 vertebral column forms several S-shaped lateral curves; is shortened, 
 and again stretched forwards, whilst the posterior part of the body 
 is fixed: this rapidly performed constitutes a leap or dart. The ribs 
 being free at their distal extremities, admit of extensive motion, and 
 are furnished with large intercostal muscles of various lengths, 
 some passing from rib to rib, and others over one or more to have 
 distant insertions. These muscles have small shining tendinous 
 bands, by which a great number can be attached to a small space, 
 and thus admit of great variety in the movements of the ribs, 
 which are not only subservient to respiration, but to progressive 
 motion in these animals. The muscles of the head are strong, and 
 in the rattle-snake and others, a portion of the temporal extends 
 forwards like a buccinator, to embrace the poison gland and force 
 its secretion into the perforated fang. 
 
 The saurian reptiles possess members sometimes organised for 
 progression on the surface, sometimes for climbing, sometimes for 
 swimming, and occasionally for flying ; hence their muscles are 
 more numerous and complicated than in serpents. A rudiment of 
 diaphragm may be perceived in the dragons and geckos ; and in the 
 prehensile tongue of the chameleon there resides a beautiful muscu- 
 lar apparatus ordained to govern its stealthy movements in obtaining 
 his food, and as Sir C. Bell aptly describes it, he lies more still than 
 the dead leaf, his skin is like the bark of the tree, and takes the hue 
 of surrounding objects. Whilst other animals have excitement 
 conforming to their rapid motions, the shriveled face of the cha- 
 meleon hardly indicates life ; the eyelids are scarcely parted ; he 
 protrudes his tongue with a motion so imperceptible towards the 
 insect, that it is touched and caught more certainly than by the 
 most lively action. In the chelonia, the muscles of the extremities 
 together with those of the shoulders and pelvis are well marked, 
 whilst those of the jaws, lips, and chest are almost wholly absent. 
 
44 EVERS'S COMPARATIVE ANATOMY. 
 
 AVES. 
 
 A greater degree of uniformity pervades the muscular system of 
 this than any other of the vertehrated classes, yet it will be found to 
 present many peculiarities. From the rarity of the element they 
 inhabit, as well as from their rapid and long continued movements 
 through it, their muscles require a considerable degree of vital 
 energy, hence they are red, vascular, dense, and irritable in the 
 high flying and rapacious tribes, although pale, soft, and feeble in 
 those of heavier and slower habits. The fleshy portions of the 
 muscles are short and thick, whilst the tendons are long, slender, 
 dense, and often ossified ; their trunk being almost fixed, the 
 muscles of the dorsal and lumbar regions are feeble and indistinct, 
 those of the neck, on the contrary, are well developed in accordance 
 with the perfect and varied motions of this part of the spine. The 
 muscles of the abdomen are week and feeble, and the diaphragm so 
 imperfect in the centre as to allow the heart to come in contact 
 with the liver as in reptiles. Of all the muscles, none reach so 
 great a degree of development as those of the anterior extremity, 
 especially those attached to the humerus. Birds possess three pec- 
 toral muscles, an anterior, middle, and posterior: they are all 
 attached to the sternum and the proximal extremity of the humerus. 
 In birds of flight, the great pectoral often equals in weight all the 
 other muscles of the body combined. The latissimus dorsi and 
 deltoid are feebly developed, whilst the psoEe, obturator externus, 
 and quadratus lumborum, are wholly absent. The muscles of the 
 lower extremity are remarkable for their long, slender tendons, and 
 especially for the beauty and perfection of the mechanism by which 
 they support the bird when asleep on roost, without any muscular 
 action. This is accomplished by the gracilis, which, arising from 
 the pubis, descends along the inner side of the thigh, and ends in a 
 strong tendon, which passes in front of the knee-joint, and subse- 
 quently over the projection of the heel to terminate by attaching 
 itself to the outer origin of the flexor digitorum perforatus. From 
 this disposition it results, that the more the joints are bent, the 
 firmer the twig on which the bird rests, is grasped, and the heavier 
 it sleeps, the more secure it is. Every one is familiar with the 
 fact of birds generally sleeping on one leg, this is for the purpose 
 of throwing the entire weight of their body on it, and so grasping 
 the firmer, and in order to increase the effect by adding to the 
 weight of the body, some birds are in the habit of never going to 
 roost without grasping a stone, or some ponderous body in the 
 other foot. 
 
 Flight, which is the most chracteristic mode of progression in 
 birds, is effected by the animal springing into the air ; or, where the 
 legs are so short, and the wings so Ions: that it cannot jump high 
 enough to gain the requisite space for the expansion of the wing, 
 it throws itself from some elevated point. The humerus is next 
 
MUSCULAR SYSTEM OF THE VERTEBRATA. 45 
 
 raised, and the fore-arm extended, a considerable extent of sur- 
 face thereby gained ; the entire member being then forcibly 
 depressed, the resistance which it receives from the air, effects the 
 elevation of the bird; velocity of flight depends upon the rapidity 
 with which these strokes succeed each other. The eider-duck is 
 supposed to fly 90 miles an hour; the hawk 150, and everyone 
 has heard of the falcon belonging to Henry IV. king of France, 
 flying in one day from Fontainbleau to Malta, a distance of 1350 
 miles. 
 
 MAMMALIA. 
 
 Some of the animals composing this class are destined to move 
 like fishes through a watery element, some to fly through the air 
 like the feathered tribes, some to climb treess, some to dig and 
 burrow in the earth, and others to walk upon its surface. Habits 
 so diversified bespeak corresponding diversities of muscular arrange- 
 ment. Many approximations to the human type present themselves 
 on the one hand, and indisputable recurrences of simpler forms on 
 the other. The fleshy portions of the muscles are generally large 
 and plump, proportioned to the size of the body, or the massive 
 bones of the skeleton. The respiration being here less extensive, 
 and the circulation more slow, than in birds, the temperature is 
 lower, the muscular fibre less dense, and the tendons less prone to 
 undergo ossific changes. 
 
 The arrangement of the muscles in the cetacea nearly coincides 
 with that in fishes, the latter moving horizontally, the former chiefly 
 in a verticle direction. The muscles of the ribs, spine, pharynx, 
 os hyoides, and exterior nares a are well developed, those of the pelvis 
 and posterior extremities disappear with those parts, and the muscles 
 of the anterior extremities are curtailed and simplified, least so, 
 however, in the phytophagous cetacea. The large herbivorous 
 quadrupeds require strong muscles to move their massive and 
 heavy trunks, and the active and predatory habits of the carnivora 
 demand a still greater development of this system. In theruminan- 
 tia, pachydermata, and those animals without clavicles, the anterior 
 extremities are placed under the trunk, which is suspended between 
 their long vertical scapulas by the great serrati muscles, in many 
 instances prodigiously developed. The buffalo, the bull, and others 
 of the ruminants, with many of the pachyderms, have the muscles 
 of the neck large and powerful to move their heavy heads, which 
 are often armed with large teeth, tusks, a proboscis, or huge horns. 
 The external muscles of the ear are greatly developed in many of 
 the herbivorous quadrupeds, and the muscles of the nose in the 
 hog tribe. 
 
 The panniculus carnosus. which is thin, and finely spread over 
 the trunks of the pachydermata, is strong and fleshy in the soft 
 skinned ruminantia, where it is attached to the humerus and to the 
 femur. In the mammalia covered with spines, as the echidnia, the 
 
46 
 
 hedge-hog, and the porcupine, and those covered with scales, as the 
 rnanis and the armadillo, this muscle is important in erecting or 
 moving these epidemic organs, and in coiling or uncoiling the body. 
 In the mole, and those animals that dig the earth, the flexors of the 
 arm, the pectoralis major, the latissimus dorsi, and the teres major, 
 are of vast size. In the rodentia, the muscles are pale, and those of 
 the jaws of great magnitude. The marsnpiata have the panniculus 
 carnosus extended over the pouch in such a manner as to support 
 the young abortive-like fretus, and force the mammary secretion 
 into its mouth. The arrangement of the muscles approaches nearer 
 to the human type in the quadrumana than in any others of the 
 mammalia. In them the flexor muscles are strongly developed on 
 all their extremities. The thumbs, have no long separate flexors, 
 but receive tendons from the flexors of other fingers. r ^ ne P^ an ~ 
 taris muscle, which is very fleshy in monkeys, instead of termina- 
 ting, as it does in man, by insertion in the os calcis, passes over that 
 bone to be connected with the planter fascia and flexor perforatum. 
 In other quadrupeds it passes over the os calcis to the sole of the 
 foot, and supplies the place of the flexor digitorum brevis. The 
 glutaeus maximus, which is the largest muscle of the human body, 
 is small and feeble in the simise and other animals, its chief use being 
 to support the trunk upon the lower extremity, and thus assist in 
 maintaining the erect attitude, and not, as the pious Spigelius 
 imagined, to form a soft cushion for the body to rest on during 
 divine cogitation. 
 
 Finally, the extensors of the knee, the flexors of the toes, and the 
 other muscles forming the calf of the leg. are relatively larger in the 
 human subject than in any other animal. 
 
 RECAPITULATION. 
 
 1. Muscular fibres have been satisfactorily shown to exist in the 
 higher species of the radiata. 
 
 2. Muscle is found all through the articulate and molluscous 
 classes, but better and more uniformly developed in the former. 
 
 3. The soft parts are uniformly placed external to the hard, in 
 the vertebrated classes. 
 
 4. The muscles in fishes are generally soft and pale, as in the 
 lower classes. 
 
 5. In the amphibia, the muscles present different characters in 
 the tadpole and adult state. 
 
 6. Great variety in the reptiles, chiefly referable to their diversi- 
 fied habits. 
 
 7. The muscular system in birds is characterised by great 
 uniformity throughout the class. 
 
 8. The muscles of the aquatic mammalia resemble those of 
 fishes. 
 
 9. Serrati magni greatly developed in the quadrupeds not pos- 
 sessing clavicles. 
 
NERVOUS SYSTEM IN THE INVERTEBRATA. 47 
 
 10. Panniculus carnosus best marked in the echidna, the hedge- 
 hog, the porcupine, the manis, the tatu, the marsupiata, and The 
 thin-skinned ruminants ; less so in the pachydermata, and absent 
 from some, as the hog. It is found in monkeys, but not in the 
 chimpanse. 
 
 11. Lattismus dorsi, teres major, &c, are very powerful in the 
 mole and ant-eaters. 
 
 12. The plantaris, which is rudimental in man, is large in mon- 
 keys and some quadrupeds. 
 
 13. Man is characterised by the magnitude of his buttocks, thio-hs, 
 and calves. 
 
 CHAPTER VII. 
 
 ON THE NERVOUS SYSTEM IN THE INVERTEBRATA. 
 
 This system, when perfectly developed, consists of an internal or 
 central, and an external or circumferential portion ; to the latter 
 belong the nerves and ganglions ; to the former, the spinal cord, the 
 medulla oblongata, the cerebellum, and the cerebrum. The nervous 
 system presides over the movements of our muscles and the sensi- 
 bility of our bodies; by it we are connected with surrounding 
 objects, and an injury inflicted on any part of the body, at once 
 declares the extent of its distribution, as well as the close relation 
 that subsists between its several parts. 
 
 The nervous system has been detected in every division, although 
 not in every class, of the animal kingdom : it commences its develop- 
 ment at the circumference, and grows towards the centre, and its 
 forms corresponds pretty closely with that of the body of the animal. 
 
 The nervous matter is extremely soft in the inferior grades of 
 animals, as well as in the embryo of the higher classes ; and its 
 colour presents some variety, being bright red in the helix stagnalis • 
 blackish red in the aplysias ; and bright yellow in the common fresh 
 water muscle. The nerves are composed of tubes filled with minute 
 globules. The brain is also composed of globules, eight times 
 smaller than those of the blood, larger and more numerous in the 
 medullary, than in the cineritious substance, and in the former dis- 
 posed in lines which gave it its fibrous character. 
 
 Cyclo-neura, Grant. — In the two first classes of this division, 
 the polygastrica and the porifera, no nervous filaments have been 
 detected, yet, from their active movements, their sensibility to the 
 impression of light, and their consciousness of each others approach, 
 it is but reasonable to infer the existence of a nervous system in 
 them, though from its transparency or some other cause, it cannot 
 be demonstrated. Both nerves and ganglions are found to exist in 
 the three remaining classes of the radiata. Distinct nervous fila- 
 ments surround the muscular foot of the actinia; and in the 
 
48 EVERS'S COMPARATIVE ANATOMY. 
 
 acaiephae and echinodermata, fine nervous filaments and small 
 white, ganglions surround the entrance of the alimentary canal. 
 
 Dlplo-neura, Grant.— In this great division, the nervous 
 system, presents the same extended form as the body, placed on the 
 ventral surface of the alimentary canal, and except in the higher 
 classes, not enclosed in an osseous sheath. Among the higher 
 forms of the entozoa, as the ascaris, two fine nervous filaments 
 extend along the median line of the abdomen, separating to embrace 
 the oesophagus, and the vulva of the female. In the notommata 
 clavulata of the rotifera, we find nine pairs of ganglions disposed 
 along the course of the lateral columns. Scarcely a trace of ner- 
 vous system can be perceived in the simple forms of the annelida. 
 In the nereids, however, and many others of this class, the sympa- 
 thetics become quite distinct ; and numerous nerves are seen to pass 
 off in the lateral direction. The common leech, which presents 
 about eighty rings in the trunk of its body, has five and twenty 
 ganglia placed along: the abdomen, approximated at the two extre- 
 mities of the column. In the most inferior of the diversified class 
 of the crustaceans, the nervous system presents itself in the form of 
 two slender abdominal filaments, in imitation of what we have seen 
 in the preceding classes, and by a gradual development from the 
 peripheral to the central parts, it arrives at that concentration of 
 nervous ganglia around the oesophagus, which connects the highest 
 of the articulate with the molluscous classes. 
 
 ' Cyclo-gangliata.— The greater number of the mollsuca being 
 aquatic, their nerves present the same pale and soft characters 
 observed in the other aquatic invertebrates ; hence the difficulty of 
 indicating their particular distributions. Here as in the radiata, the 
 same tendency to accumulate nerves around the entrance to the 
 alimentary canal prevails, but in this case more generally accom- 
 panied with ganglia. In the lowest classes of the division, as the 
 tunicata and conchifera, the nervous chords are placed beneath the 
 alimentary canal ; in the two next classes gasteropoda and ptero- 
 poda, they are more in the vicinity of the stomach ; arid in the ce- 
 phalopoda, which is the last and highest of the division, the nervous 
 ganglia attain a more elevated position, they cease to embrace the 
 oesophagus; and a distinct brain, as in the vertebrata, with nume- 
 rous symmetrical ganglia along the abdomen take, their place. 
 
 CHAPTER VIII. 
 
 NERVOUS SYSTEM IN THE VERTEBRATA. 
 
 PISCES. ^ 
 
 We no longer find the nervous system perforated by the alimen- 
 tary tract. On, the contrary, in all the succeeding classes, it 
 
NERVOUS SYSTEM IN THE VERTEBRATA. 49 
 
 occupies a dorsal situation, and is protected by an osseous sheath. 
 In the lowest orders of fishes, as the lamprey, and the gastrobranchus, 
 we perceive a repetition of the two nervous columns extending 
 along the back as observed in the worm. This simple condition 
 resembles the embryo state of this system in the highest grades of 
 the vertebrata, previous to the development of their extremities. 
 With kw exceptions the spinal chord extends the whole length of 
 the vertebral column ; whence, from the great number of vertebrae, 
 it attains a very remarkable length. In some, however, as the 
 lophius piscatorius, it is stated to be very short, forming a kind of 
 Cauda equina as in man. It usually terminates in a single thread, 
 presenting several enlargements throughout its tract, which corres- 
 pond very accurately with the number, magnitude, and situation of 
 the extremities. For instance, when the anterior members are very 
 large, as in rays and flying-fishes, the anterior enlargements are 
 proportionally developed ; and where a large caudal fin is to be 
 supplied, the chord presents a sensible enlargement posteriorly 
 where the nerves join it. The spinal marrow, here, as in the 
 human foetus, usually contains a canal of considerable size, and is 
 distinguished by an anterior, a posterior, and two lateral grooves. 
 From the latter, the nerves arise by two roots, the posterior or sen- 
 sitive root having a ganglion on it, receives the anterior root im- 
 mediately external to the canal. 
 
 The brain m fishes does not fill the cavity of the cranium, a 
 considerable portion of it being occupied by the soft cellular tissue 
 of the arachnoid. The medulla oblongata is of great length, lobed, 
 and deeply grooved above by the calamus scriptorius. 
 
 Tn most fishes, the optic lobes are larger than the hemispheres, 
 they are hollow and communicate freely with each other and with 
 the fourth ventricle. The earlier they are examined the larger they 
 are found to be ; their development is proportionate to that of the 
 optic nerves and eyes, and inversely to that of the cerebrum and 
 cerebellum. The cerebral hemispheres are small in the osseous, 
 apodal, and cyclostome fishes, and in the plagiostome species they are 
 larger than the optic tubercles. In the osseous fishes they resemble 
 the embryo condition of the human brain in being destitute of ven- 
 tricles, and having no convolutions on the surface. In sharks and 
 rays the hemispheres attain a large size, present irregularities on 
 the surface, and ventricles in their interior. In front of the hemi- 
 spheres are placed the olfactory tubercles, elongated transversely, and 
 exceeding in magnitude the hemispheres themselves; subject, how- 
 ever, to considerable variations, regarding form, size, and situation. 
 
 The cerebellum is scarcely to be recognised in many of the 
 cyclostome fishes. When present it appears as a transverse band, 
 rising vertically in the osseous fishes, and forming a small vermiform 
 median lobe, slightly laminated in the plagiostome fishes. In sharks 
 and rays not only does this median lobe attain considerable magni- 
 tude, but small hemispheres are developed laterally, corresponding 
 in size to that of the carpora restiformia. The pineal gland is found 
 8 — e evers 4 
 
50 
 
 in all fishes, lodged between the hemispheres and optic tubercles, 
 but so small in the osseous tribes that its existence has been ques- 
 tioned. These several lobes are covered with a layer of cineritious 
 substance, and closely invested by a delicate layer of pia mater; 
 outside of which is the soft, gelatinous, cellular arachnoid tunic, and 
 all are surrounded by an envelope of dura mater. 
 
 Nerves. — The olfactory nerves are white and fibrous ; they are 
 very large in the rays and sharks, and in many instances form a 
 ganglion before their termination ; as may be seen in the carp. 
 The optic nerves are developed in proportion to the size of the optic 
 tubercles and eyes ; hence they are large in the carp, and slender in 
 the eel. In the osseous fishes they generally cross without any in- 
 termingling of fibres; in the plagiostome fishes their fibres are 
 blended at the commissure as in the mammalia; and in the skate, 
 the right nerve goes through a fissure in the left. The third, fourth, 
 and sixth nerves are developed in proportion to the size of the 
 muscles they supply. The fifth nerve presents a greater size, and 
 gives off more branches in this class than in any other of the verte- 
 brata. The ophthalmic, superior, and inferior maxillary are dis- 
 tributed to the face, palate and lower jaw. In the rays, and many- 
 other fishes, it sends a branch to the ear, and in the torpedo, to the 
 electrical organs. These latter are composed of a series of mem- 
 branous cells occupied by a gelatino-albuminous substance, per- 
 forming the office of a Leyden jar or electrical battery. They lie 
 in the torpedo on the upper surface of the lateral fin. In the elec- 
 tric eel, on the posterior part of the abdomen ; and in the silurus 
 electricus they are situate between the muscles and skin over the 
 entire body. In the last named fish the nerves appear to be derived 
 from the pneumo gastric. Both portions of the seventh pair are 
 small and distributed without any peculiarity. The pneumo-gas- 
 tric arises from the side of the medulla oblongata, behind the fifth 
 pair ; it forms a large ganglion below its origin, from which 
 branches proceed to the branchiae, the oesophagus, the stomach, and 
 rudimentary lungs. This nerve gives off also a branch to the 
 tongue analogous to the glossopharyngeal, and one to the lateral 
 part of the body analogous to the spinal accessary, both of which 
 are rudimental in fish. The ninth pair is wholly absent and its 
 place supplied by a branch from the fifth. The distribution of the 
 spinal nerves is very simple, and their development is always pro- 
 portioned to the size of the fins ; the sympathetic is very slender, 
 and its ganglions small in fishes. It is most developed in the pla- 
 giostome chondropterygii, and least so in the cyclostome species ; it 
 receives filaments from the spinal nerves, and its meshes accompany 
 the arterial trunks in their distribution on the digestive, respiratory, 
 and generative organs. 
 
 AMPHIBIA. 
 
 The condition of the brain, the medulla oblongata, and the spinal 
 chord are nearly the same in the perennibranchiate amphibia, and 
 
NERVOUS SYSTEM IN THE VERTEBRATA. 51 
 
 in the larva state of those which undergo metamorphosis, as are 
 observed in the osseous fishes. The lobed form of the medulla 
 oblongata, the small cerebellum, the optic thalami, with the ventri- 
 cles, and the diminutive extent of the hemispheres, all evince a 
 degree of perfection not much above that noticed in fishes. The 
 spinal chord is prolonged, small and tapering into numerous coc- 
 cygeal vertebrae, and without sensible enlargements where the 
 nerves are to come off to supply the future members. The meta- 
 morphosis of the caducibranchiate species, from the pisciform to 
 the reptile state, develope an interesting series of phenomena. The 
 hemispheres become enlarged, the cerebellum, which was scarcely 
 visible, increases in size across the median line ; as the limbs begin 
 to appear, the spinal marow exhibits corresponding developments, 
 but dwindles posteriorly as the coccygeal vertebrae disappear. So 
 rapid are these changes in the nervous system of the frog, that we 
 can appreciate them from day to day. The sympathetic system is 
 more distinct in this class than in that of fishes. 
 
 REPTILIA. 
 
 In this class the cerebral hemispheres exceed in size the optic 
 lobes, and contain a distinct ventricle. The cerebellum is remark- 
 ably small ; and, in the sauria and chelonia, the spinal marrow 
 presents an obvious enlargement, opposite the attachment of each 
 nerve. The medulla oblongata is broad ; the nerves are large, 
 compared with the cerebral centres, but present no peculiarity of 
 distribution. The plexuses of the sympathetic are here more 
 closely connected with the arterial trunks, than in the preceding 
 classes. 
 
 AVES. 
 
 The brain and spinal chord are in this class developed with more 
 uniformity and perfection than in the cold-blooded reptilia ; and 
 bear a remarkable correspondence with the perfection of muscular 
 energy which they possess. In a pigeon weighing 3360 grains, 
 without the feathers, the brain weighed 37, and the spinal chord 11 
 grains=48. 
 
 The spinal chord extends from the foramen magnum to the 
 coccygeal vertebrae, where it is greatly reduced in size, and expends 
 itself in distributing a few nerves through the lateral foramina. The 
 length of the chord is considerable, compared with the size of the 
 brain ; its shape is cylindrical ; its anterior and posterior grooves 
 are very distinct, as well as a minute canal extending through its 
 whole length, arising from the union of the two halves of the 
 chord: the dilatation of this canal in the pelvic region, is called 
 "rhomboidal sinus." The spinal chord is chiefly composed of 
 white matter, but contains a small quantity of gray, internally. 
 Two enlargements occur on the chord, bearing a relative size to 
 the development and powers of the extremities: in general the 
 posterior enlargement is the greater, especially when the business 
 
52 
 
 of progression devolves on the posterior members, as in strnthious 
 birds. The form of the chord is not altered in the alar enlarge- 
 ment, but simply increased by an accession of gray and white 
 substances; — the lower one, on the contrary, not only receives 
 additional matter, but the pillars separate, so that the fluid in the 
 sinus is merely covered by pia mater. 
 
 The brain of the bird differs from that of the reptile in the 
 greater size of the cerebrum, and the more complex structure of 
 the cerebellum; it differs from the brain of a mammal in the 
 smaller size of the cerebellum, and the rudimentary state of the 
 fornix; and it differs from the brain of every other vertebrate class 
 in the inferior position of the optic lobes. The cerebral hemispheres 
 are generally of a convex condiform shape, with the apex directed 
 forwards; they are disunited through their whole extent, being 
 only joined by a round anterior commissure; they are destitute of 
 convolutions, and have a small ventricle in their interior. The 
 olfactory tubercles are greatly reduced in size, and retain their 
 tubular communication with the cerebral ventricles. The optic 
 lobes are small ; gray on the surface, white internally, and contain 
 each a small ventricle ; they are connected by transverse medul- 
 lary bands on which the pineal gland rests, with its peduncles 
 directed forwards over the optic thalami. These last bodies are 
 covered by the cerebral hemispheres, united by a commissura 
 mollis, and destitute of transverse sulci. The medulla oblongata 
 is large and wide; its components are marked on the surface, but 
 it is without tuber annulare. The cerebellum presents a median 
 vermiform lobe, and rudimentary hemispheres, sulcated trans- 
 versely, with a faintly-marked arbor vitae in the interior. The 
 membranes investing the brain differ but little from those of the 
 mammalia. 
 
 Nerves. — The nerves in this class present but few striking pecu- 
 liarities, being distributed nearly as they are in man. The olfactory 
 arise from the front of the hemispheres, pass forwards through 
 distinct osseous canals in the cribriform plate, and are distributed 
 in a radiated manner on the superior spongy bone. The large 
 optic nerves arise from the optic tubercles, and form a perfect 
 decussation in front of the infundibulum ; where, as in the iguana, 
 an incision displays a mutual intermixture of the fibres. The 
 remaining cerebral nerves are distributed pretty nearly as in mam- 
 malia ; the portio dura is, however, small in accordance with the 
 insensibility of the superficial parts of the face. The spinal nerves 
 correspond in number to the vertebrae ; they arise by two roots, the 
 posterior having a large ganglion on it. The sympathetic, which 
 is well developed, communicates through the anterior lacerated 
 opening with the fifth and sixth nerves. From the third cervical 
 vertebra to the thorax, it is contained in the canal in the transverse 
 processes, in company with the vertebral artery. It form a series 
 of ganglions, from the base of the skull to the end of the coccyx ; 
 and communicates, in its course, with every neighbouring nerve. 
 
NERVOUS SYSTEM IN THE VERTEBRATA. 53 
 
 MAMMALIA. 
 
 In this class the increased development of the nervous system is 
 marked by the size and length of the spinal chord ; the magnitude 
 of the cerebrum and cerebellum, and the number of their gray 
 deposits and commissures, as well as by the number and arrange- 
 ment of the ganglions, together with the extent and systematic dis- 
 tribution of the great sympathetic. 
 
 The spinal chord is larger in proportion to the size of the body, 
 but smaller when compared with the brain, in this than in any of 
 the preceding classes; its internal canal has almost ceased to exist, 
 and its lateral portions are more intimately united. It is shortest 
 in man, quadrumana, and the tailless cheiroptera, and longest in 
 the cetacea, where, as in apodal fishes, tadpoles, serpents, and the 
 human embryo, it presents no posterior enlargements. In the long- 
 tailed quadrupeds it extends to the sacrum; the posterior groove is 
 generally shallow, though sometimes of considerable depth, as in 
 cheiroptera and rodentia. The medulla oblongata is small : the 
 corpora pyramidalia decussate very distinctly: the olivary bodies 
 are small, and generally contain a corpus dentatum in their interior, 
 and the transverse fibres of the pons or great cerebellic commissure 
 are well seen. 
 
 Brain. — In the class mammalia, the cineritious matter bears a 
 small proportion to the white substance. The convolutions are 
 very superficial in the cetacea, edentata, ruminantia, and pachyder- 
 mata, and wholly absent in the rodentia, and monotremata, as in 
 birds; whilst they are deep in man, monkeys, and carnivorous ani- 
 mals. The optic lobes, without cavities, are smallest in man, 
 quadrumana, and carnivora, larger in the herbivora, and largest of 
 all in rodentia and edentata. A contrary ratio obtains respecting 
 the development of the cerebral hemispheres, and the olfactory 
 tubercles. The anterior and inferior cornua of the lateral ventri- 
 cles, as well as the several commissures, are always present in this 
 class. The posterior lobe of the brain, and the posterior cornua of 
 the lateral ventricle, first appear in the quadrumana ; the former 
 has no convolutions. 
 
 The vast superiority of man over all other animals in mental 
 faculties, led physiologists at a very early period to seek for corres- 
 ponding differences in the brains of man and animals. They 
 compared the weight of the brain with that of the body, and their 
 researches led them to conclude that man had the largest brain in 
 proportion to his body. Since the time of Aristotle till within a 
 late period this opinion has been received : but more modern inves- 
 tigations have proved that the proportion of the brain to the body 
 in some birds exceeds that of man, and that several of the quadru- 
 mana and some rodentia equal him in this respect. The illustrious 
 Soemmering proposed another mode of comparison, that of the 
 ratio which the mass of the brain bears to that of the nerves arising 
 from it, and in this point of view man is decidedly pre-eminent. 
 
54 
 
 The brain of man far exceeds in size that of the simiaa compared 
 with the nerves proceeding from it, and in these latter and in the 
 seal it is larger in proportion than in other animals, while it is 
 smallest in the glires, marsnpialia, cheiroptera, and edentata. The 
 largest brain which Soemmering has found in a horse weighed 
 1 lb. 4oz., and in an adult man was 2 lb. 5£oz. : yet the nerves arising 
 from the former were ten times larger than those of the latter. 
 Coeteris paribus^ small animals have a larger brain in proportion 
 to their size, than large ones, and in cold-blooded animals its di- 
 mensions are very small, compared with those of a higher tempe- 
 rature. The following table shows the relative weight of the brain 
 to that of the body in several of the vertebrate classes of animals: — 
 
 Fishes. — Silurus glanis, one-1 887th ; dog-fish, one-1344th ; shark, 
 one-2496th ; carp, one-560th. 
 
 Reptiles. — Turtle, one-5688th; colubar natrix, one-792d ; frog, 
 (amphibious,) one-172d. 
 
 Birds. — Goose, one-360th ; duck, one-257th ; eagle one-260th ; 
 falcon, one-102d ; sparrow, one-25th ; canary-bird, one-14th. 
 
 Cetacea. — Porpoise, one-93d; dolphin, one-102d, one-60th, one- 
 36th, one-25th. 
 
 Solipeda. — Ass, one-254th ; horse, one-700th; one-400th. 
 
 Ruminantia. — Ox, one-S60th; stag, one-290th; sheep, one-192d; 
 calf, one-2l9tb. 
 
 Pachydermata. — Wild boar, one-672d ; domestic, one-512th ; 
 elephant, one-500th. 
 
 Rodentia. — Beaver, one-290th ; hare, one-228th ; rabbit, one- 
 152d; rat, one-76th; mouse, one-43d; field-mouse, one-3 1st. 
 
 Carnivora. — Dog, one-305th, one-47th ; fox, one-205th ; wolf, 
 one-230th; cat, one-156th, one-82d ; ferret, one-138th. 
 
 Plantigrada. — Hedge-hog, one- 1 68th; bear, one-265th; mole, 
 one-36th. 
 
 Cheiroptera. — Bat, one-96th. 
 
 Le?nurs. — Vari, one-84th; mococo, one-61st. 
 
 Baboons. — Magot, one 105th; great baboon, one-104th ; macaque, 
 one-85th. 
 
 Apes. — Mangabey, one-48th; the monk ape. one-44lh ; malbrouk, 
 one-24th. 
 
 Sapajous. — (American apes) Coa'ita, one-41st; Sai, one-25th ; 
 Saimiri, one-22d. 
 
 Onranfr-outangs. — The gibbon, one-48th; chimpanse, 26 inches 
 in height, 11 oz. 7dr. 
 
 Child of six years, one-22d; adult man, one-35th. 
 
 The Cerebellum is smaller in proportion to the cerebrum in 
 man, the saimiri, and the ox, than in any others of the mammalia. 
 In the human subject and in ourangs only, is it covered by the 
 posterior lobes of the brain. The superior vermiform process and 
 the hemispheres of the cerebellum are developed in every class 
 in the inverse ratio of each other. In the saimiri ape, the cerebel- 
 lum is to the cerebrum as 1 to 14 ; in man and the ox, 1 to 9 ; in 
 
NERVOUS SYSTEM IN THE VERTEBRATA. 55 
 
 the monk ape and the dog, 1 to 8 ; in the magot, papio, and wild 
 boar, 1 to 7 ; in the sai and hare, 1 to 6 ; in the mole, 1 to 4 ; in 
 the rat and beaver, 1 to 3 ; and in the mouse, 1 to 2. 
 
 Nerves. — The olfactory nerves are largest in the ruminantia, 
 pachydermata, and carnivora, smaller in the cheiroptera and qua- 
 drumana, and discoverable with difficulty in many of the cetacea. 
 In the squirrel, rabbit, hare, and other large-eyed nocturnal quadru- 
 peds, the optic nerves are very large; they are small in rats, mice, 
 bats, hedge-hogs, and subterranean moles, and in the sorex arraneus, 
 mus typhlus, muscapensis. and others, they are said to be altogether 
 wanting. They unite before the infundibulum, and form a partial 
 decussation of their fibres. The third, fourth, and sixth nerves are 
 distributed as in man, and are very small in subterranean animals. 
 Of all the cerebral nerves, none reaches so great a degree of deve- 
 lopment as the fifth pair, in the inferior classes of animals and in 
 the foetal state of the human subject: it is also of enormous size in 
 most aquatic birds. Its branches are freely and extensively distri- 
 buted in those animals with proboscis, long muzzles, large lips, and 
 broad bills, as the cetacea, ruminantia. pachydermata, carnivora, 
 and ornithorhynchi, and also in those possessing horns, spines, 
 bristles, and whiskers. This nerve is supposed to preside over the 
 peculiar instinctive actions so remarkable in those grades of ani- 
 mals which indicate an inferior degree of mental endowment, and 
 this opinion receives strength from the fact of its great size in the 
 very early periods of human existence, when we know the actions 
 are purely instinctive. The remaining cerebral, the spinal, and the 
 sympathetic nerves are distributed so much after the human type 
 as to merit no particular remarks. 
 
 In most mammalia the arteries of the brain form a complicated 
 net-work around the petuitary body at the base of the cranium 
 named rete mirabile, obviously designed to impede the flow of 
 blood to the brain, in those animals with pendent heads. The 
 veins occasionally run in osseous canals in order to avoid pressure; 
 this is well seen in the cribriform plate of the mole's skull, and in 
 the bony falx cerebri of the porpoise. A bony falx cerebri is also 
 found in the ornithorhynehus, an animal which abounds in in- 
 stances of anomalous structure. Animals which possess a bony 
 tentorium are of far more common occurrence: it is well developed 
 in most species of the cat and bear kind; it is not so well marked 
 in the dog, seal, horse, and wombat, and it is merely rudimentary 
 in the pig, the rabbit, and the mouse. 
 
 It has been generally supposed that these structures exist in such 
 animals only as jump far, and that they served the purpose of pro- 
 tecting the respective portions of the cerebrum and cerebellum from 
 undue pressure during these active movements, but this opinion is 
 rendered quite untenable from the fact of their absence in many 
 animals notable for jumping, as the wild goat, (fee, and their pre- 
 sence in those animals alike remarkable for their slow and easy 
 movements, as the bear. It is more probable they exist for the 
 
56 EVERS's COMPARATIVE ANATOMY. 
 
 purpose of obviating the concussion which would arise from the 
 strong exertions in biting; for such exertions are made by all the 
 animals which possess them, even by the horse in his wild state. 
 
 RECAPITULATION. 
 
 1. A nervous system exists in every class of animals, though not 
 in all the animals of each class. 
 
 2. In the invertebrate classes it has a peculiar tendency to accu- 
 mulate around the oesophagus. 
 
 3. In all the vertebrata its principal parts are protected by osseous 
 sheaths. 
 
 4. The spinal marrow is tubular in the human embryo, and most 
 of the lower vertebrata. 
 
 5. This system undergoes remarkable changes in the amphibia, 
 during their metamorphosis. 
 
 6. It is highly developed, and with great uniformity in birds. 
 
 7. The chord presents enlargements corresponding in size to the 
 members most used. 
 
 8. The spinal chord bears a large ratio to the size of the body in 
 most mammalia. 
 
 9. Man's superiority is due to his mental faculties. 
 
 10. The brain is larger in proportion to the size of the nerves 
 connected with it in man than in any other animal. 
 
 11. The fifth cerebral, or the nerve of instinct, is very large in 
 most mammalia, and in the foetal state of the human subject. 
 
 CHAPTER IX. 
 
 ORGANS OF SENSE. 
 
 General observations. — The organs of sense are those instru- 
 ments which are placed upon the distal extremities of certain cere- 
 brospinal sensitive nerves, whose office being to establish a relation 
 between the internal sentient principle and the external objects of 
 surrounding nature, are necessarily placed in connection with the 
 external surface of animals, and generally in the neighbourhood of 
 the entrance of the alimentary canal. They are more numerous, 
 more varied, and more perfect in the higher than in the lower tribes 
 of animals, but they are more developed in the active insects and 
 others of the articulata, than in the slow and torpid mollusca, and 
 they attain their greatest degree of perfection in the vertebrata where 
 the most complicated and delicate forms of organisation are con- 
 signed to their careful watch. 
 
 Vision. — Organs of vision have been figured and minutely de- 
 
ORGANS OF SENSE. 57 
 
 scribed in many of the polygastric animalcules ; they vary in number 
 from one in the polygastrics, up to eight in the acalepha. In the 
 rotifera, optic nerves and ganglia are quite visible, and in the aca- 
 lepha a lenticular body is superadded. Visual organs are met with 
 in almost every class of the diplo-neurose division ; in some there 
 is but a single eye, in others they are more numerous, and placed 
 apart on different aspects of the head. The medicinal leech pos- 
 sesses ten prominent eyes disposed transversely, and the neiris nun- 
 tia has two large pairs placed on the upper part of the head, and 
 nearly a hundred smaller ones grouped around the mouth. Many 
 of the higher insects present in their optical apparatus all the essen- 
 tial ingredients found in the highest forms of the organ. The eyes 
 of the crustaceans, are generally compound like those of insects, and 
 in many instances are moved by distinct muscles, and covered in 
 front by a transparent layer of epidermis. In the Crustacea, as in 
 insects, the optic nerves enlarge into a ganglion in the globe of the 
 compound eye, from which small filaments radiate to the several 
 lenses of the component eyes. 
 
 Organs of vision are less required, and consequently less deve- 
 loped in the torpid mollusca than in the active articulata ; they 
 never form groups of simple eyes like the myriapods, nor compound 
 organs like the insects and Crustacea. In the acephalous mollusca 
 they are simple, separate and numerous as in worms, but in the 
 higher forms of gasteropods, pteropods, and so on, they are more 
 complicated, and but two in number, disposed on the sides of the 
 head as in the vertebrata ; and in these possessing opaque coverings, 
 as the inhabitants of bivalve shells, they are altogether wanting. In 
 those, however, which enjoy rapid motion, as the pectem maximus, 
 they are upwards of fifty in number, each being about a quarter of 
 a line in diameter. The eyes of these animals are generally flat- 
 tened in front, they possess a rudiment of membrana nicitans; the 
 iris and the lids are usually motionless, yet in the general plan of 
 their formation they form a near approach to the condition of these 
 organs in the higher vertebrated classes. 
 
 In all the vertebrata the eyes are two in number, and with the 
 exception of a few species, are symmetrically disposed on the sides 
 of the head ; the differences they present being chiefly referable to 
 the density of the media in which the various animals reside. From 
 the density of the watery element through which fish move, their 
 eyes are generally of considerable size, except in the worm-shaped 
 fishes, as the eel and the lamprey. Sometimes they are directed 
 backwards or upwards as in the star-gazer : less frequently they are 
 placed on one side, as in the sole. The eye is spherical posteriorly, 
 and flattened in front. The conjunctiva is continued across in front 
 of the cornea, and admits of easy separation from it in the eel and 
 many other species. The eyelids are merely rudimentary and the 
 lachrymal gland is wholly absent. The sclerotic tunic is thick, 
 deuse, laminated, elastic, and occasionally ossified anteriorly. The 
 choroid is divisible into three layers, the internal or tunica Ruys- 
 
58 
 
 chiaria, the middle or the membrana vasculosa Halleri, and the 
 external with its shining pearly lustre passes in front of the iris 
 and produces the gold and silver colours so much admired. The 
 cornea is remarkable for its flatness, the iris for its immobility, and 
 the crystalline lens for its density, magnitude, and sphericity. The 
 aqueous humour is scanty, the ciliary processes are rarely deve- 
 loped, and the yellow spot of Soemmerring is altogether wanting. 
 Between the layers of the choroid, and embracing the optic nerve, a 
 reddish mass of a horse-shoe shape is found in most fishes named 
 choroid gland, which, according to some, secretes the colouring 
 matter ; according to others it is a sort of rete mirabile, and others 
 again look upon it as an enlargement of the optic nerve, whilst the 
 prevailing opinion at present seems to be, that it is a muscle 
 destined to modify in some way the reflection of the rays of light. 
 From the inner layer of the choroid another body, campanula 
 Halleri, passes forwards towards the lens, somewhat analogous to 
 the marsupium of birds. The pupil in fishes is large and round, 
 and the eye is moved by four recti and two obliqui muscles. 
 
 The eyes of the amphibia are very large, and like those of 
 fishes contain a small quantity of aqueous humour, and are flat in 
 front. They enjoy great latitude of motion and are provided with 
 palpebrae and a membrana nictitans; the superior lid is small and 
 scarcely movable; the inferior large and very movable. The 
 opaque integument veils the front of the eye in the proteus ; in 
 most other characters the eyes resemble those of fishes. 
 
 The reptilia present us with characters of eyes well suited to 
 the rare medium they inhabit, such as convexity of cornea from 
 abundance of humours, and a compressed state of the lens. .Like 
 the amphibia, they are furnished with three lids, but unlike them 
 and fish, they are provided with lachrymal apparatus; they ap- 
 proximate the succeeding classes in many respects, as having ciliary 
 processes, a movable iris, generally a vertical pupil, a dark pecten 
 prolonged from the choroid into the vitreous humour, and osseous 
 plates around the anterior margin of the sclerotic. In the chame- 
 leon only a small portion of the eye is to be seen through a narrow 
 vertical slit between the margins of the lids, which conceal a large 
 membrana nictitans. 
 
 We cannot fail to observe how the remarkable peculiarities pre- 
 sented by the organs of vision in birds, coincide with the vigour of 
 their respiratory, circulatory, and locomotive systems. In all the 
 other vertebrate classes we meet with instances, where the eyes, if 
 not absent, are at least rudimentary, but in this class they are 
 remarkable not only for their uniform existence but for their great 
 size and perfect development. From the convexity of the anterior 
 segment of the eyes and their lateral location, birds command an 
 extensive sphere of vision, and in many of the high-flying rapa- 
 cious kind, the orofan is prolonged in front into a tubular form, but 
 in aquatic birds the anterior half is more flattened. The sclerotic 
 is thin, flexible, and elastic posteriorly ; it is divisible into three 
 
ORGANS OF SENSE. 59 
 
 layers, between the middle and outer of which, from 15 to 17 osse- 
 ous quadrangular plates are placed anteriorly, a repetition of what 
 we have seen in reptiles and fishes; these scales overlap each other, 
 they are connected by the sclerotic, and are capable of a limited 
 degree of motion. The cornea is dense, and possesses a consider- 
 able degree of convexity, as well from the abundant humours as 
 from the pressure of the surrounding muscles ; and, according to 
 the discovery of Crampton, it is capable of varying its convexity 
 by the action of a muscular sphincter attached to the posterior 
 layer at its circumference. The choroid is the same as in mam- 
 malia: the iris is remarkable for the freedom of its motions which, 
 in some instances, seem voluntary: the pupil is generally circular, 
 but elongated transversely in the goose and dove, and vertically 
 oval in the owl. The chief peculiarity in the eye of birds consists 
 in the marsupium nigrum or pecten plicatum ; this wedge-shaped 
 body, which in appearance simulates choroid, is composed princi- 
 pally of vessels, and extends from the entrance of the optic nerve 
 through the vitreous humour towards the lens which it sometimes 
 reaches, and gets an attachment to. Petit supposed that this sub- 
 stance rendered objects in front of the eye more distinct by absorb- 
 ing the lateral rays of light: Home, that by its muscularity it 
 retracted the lens; but this is impossible when it does not reach it. 
 
 Owen considers it an erectile organ, destined to push forward 
 the lens either directly or through the medium of the vitreous hu- 
 mour ; others look upon it as a gland for secreting the vitreous 
 humour, and many are of opinion that it is placed there for the 
 purpose of absorbing the super-abundant rays of light during the 
 exposure of the eye to the blazing sun when soaring aloft. 
 
 The aqueous and vitreous humours present no peculiarities ; 
 the lens is flat in high-flying birds of prey, and more convex in 
 the aquatic species ; it is not here as in the other classes an achro- 
 matic lens, in consequence of the absence of central nucleus. The 
 globe of the eye is moved by four recti and two oblique muscles. 
 The lower lid is the more movable in birds and is provided with a 
 distinct depressor muscle. The third eyelid, or membrana nicti- 
 tarts is a conjunctival fold connected with the inner angle of the 
 eye and capable of being moved across the organ by a peculiar 
 pair of muscles. One of these, from its shape, is named quadratics ; 
 it arises from the upper and back part of the sclerotic; its fibris 
 descend in a convergent manner towards the optic nerve, a little 
 above which they terminate in a free semilunar aponeurotic margin, 
 containing a canal. The second muscle called pyramidalis arises 
 from the inferior internal and posterior part of the sclerotic, its 
 fibres pass converging to the upper surface of the optic nerve, where 
 it forms a slender tendon, which passes though the canal in the 
 quadratus; it then passes from the outer to the lower surface of the 
 sclerotic, conducted in a cellular sheath till it gains the free margin 
 of the membrana nictitans, into which it is inserted. 
 
 By the simultaneous action of this pair of muscles the membrane 
 
60 EVERS'S COMPARATIVE ANATOMY. 
 
 is rapidly and forcibly drawn downwards and outwards over the 
 front of the eye, and is restored to its former situation by its own 
 elasticity. The lachrymal gland is situated at the external angle 
 of the eye, and at the internal angle there is another gland named 
 Harderian, from its discoverer, but is nothing more than a con- 
 geries of mucous follicles to compensate for the absence of meibo- 
 mian glands. There is a third gland in or near the orbit, called 
 nasal, its secretion being wholly destined for the nose. 
 
 In the mammalia the organs of vision are Constructed in perfect 
 accordance with the media the animals move in ; they are usually 
 placed laterally, but in the nocturnal quadrupeds they are directed 
 forwards as much as in man, and in the quadrumana even more 
 so. The eyes are of a large size in ruminantia, rodentia and many 
 pachydermata; and they are small in moles, shrews, whales, and 
 in most cheiroptera. In the mus typhlus the eye is covered by 
 hairy conjunctiva ; and in the mole of Libanus, it is so small as to 
 be almost invisible. The form of the eye is generally spherical, 
 but in the cetacea flattened anteriorly as in fish, and in bats it 
 approaches to that of birds. In the cetacea the aqueous and vitre- 
 ous humours are less abundant than in terrestrial quadrupeds, the 
 cornea is flat, the lens is large, dense, and round, and the sclerotic is 
 an inch thick posteriorly in a whale, with an eye the size of an 
 orange; the lids are imperfectly developed, the lachrymal apparatus 
 is absent, and the superior oblique muscle of the eye is destitute of 
 a pully ; but the smallness of the eye in this order of mammalia, 
 compared wi th that of fish, bespeaks a higher development of internal 
 perceptive organs. 
 
 In the carnivora the cornea is prominent, the pupil vertically 
 oval, the thick choroid without pigmentum nigum posteriorly, and 
 a blue or green tapetum glitters in the bottom of the eye. The 
 cornea covers half the eye in the rat and porcupine, and is elongated 
 transversely in the marmot, and generally in ruminants. The 
 tapetum also exists in the ruminantia, solipeda, pachydermata, and 
 cetacea. In the dog, wolf, and badger it is white, bordered by blue. 
 The iris is subject to numerous varieties as regards its colour, 
 structure, and the shape of the pupil: the latter is of a circular 
 form in the rodentia, bats, and simise ; transversely oval in the ru- 
 minantia, solipeda and cetacea ; in these instances the oval form 
 does not seem to pervade the entire thickness of the iris, but only 
 its external layer. The retina in carnivora, and many rodentia, as 
 in some birds, is confined to the posterior half of the eye: in the 
 former on account of the breadth of the corpus ciliare ; in the 
 latter on account of the width of the iris. 
 
 In the mammalia the eyelids are formed generally as they are in 
 man, the superior b«ing the larger and more movable, and the 
 membrana nictitans exist in the entire class, with the exception of 
 man, apes, and the cetacea. The ornithorhynchus histrix has but 
 a single circular lid. In addition to the lachrymal gland, which is 
 
ORGANS OF SENSE. 61 
 
 found in all mammalia, except the cetacea, the glandula Harden 
 exists in the carnivora, ruminantia, pachydermata, and some roden- 
 tia. Instead of puncta lachrymalia, the hare and rabbit have a slit 
 opening into the nasal duct ; the eye is moved by four recti and 
 two oblique muscles, and in many of the genus felis the superior 
 oblique is perforated by the rectus superior : the inferior oblique 
 has the same relation to the inferior rectus in the tiger, though not 
 in the lion. All the muscles of the eye are said to be wanting in 
 those animals in which the organ is in a rudimentary state. 
 
 Hearing. — When we consider the many services arising from 
 this sense, such as indicating the approach of danger, conducting 
 predaceous animals to their prey, the bringing together the two sexes, 
 (fee, we should expect to find, as we really do, an organ of hearing 
 in almost every division of the animal kingdom. In the radiated 
 division of animals no distinct acoustic organs have been detected ; 
 it is probable, however, that the undulations produced by the per- 
 cussion of outward bodies in the media in which these low creatures 
 reside, produce some impression, though feeble it may be, upon the 
 general surface of their bodies. It is not till we ascend in the scale 
 as high as the active air breathing insects of the articulata that we 
 meet with special organs appropriated to this sense ; and here they 
 consist of auditory nerve, vestibule, and two rudimentary semicir- 
 cular canals. In many of the inferior torpid mollusca there do not 
 seem to be any particular organs devoted to the perception of sound, 
 but in the higher cephalopods which approach the nearest to fish 
 in their general characters, the organs of hearing present a similar 
 degree of complexity. 
 
 Fishes, like the cephalopodous mollusca, receive their acoustic 
 impression by undulations through the dense medium surrounding 
 them, and in the lowest cartilaginous species, as the lamprey, the 
 organ consists of a simple vestibule, and three membranous semi- 
 circular canals, separated from the cavity of the skull merely by 
 dura mater. In the bony fishes the vestibule and semicircular 
 canals are highly developed, fenestra ovalis appears, and by and by 
 a rudimentary cochlea and tympanum without air are seen ; in the 
 cavity of the vestibule two or three small bodies are found, soft and 
 pulpy in the cartilaginous fishes, but of a stony hardness in the 
 osseous kind, and composed of carbonate of lime. 
 
 In the aquatic amphibia and in the tadpole state of the reptiliform 
 species, the organ of hearing possesses a near affinity to that of 
 fishes ; it consists of the vestibular cavity containing its cretaceous 
 bodies, the membranous semicircular canals, and fenestra ovalis 
 closed by stapes, all contained in a cavity of the temporal bone, and 
 covered externally by the common integument. But in the adult 
 state of the frog and salamander the apparatus is more complicated, 
 the semicircular canals are lodged in the temporal bone ; the tym- 
 panum is closed by membrana tympani, contains three ossicula 
 united, and communicates with the fauces by a Eustachian tube. 
 
 The reptiles present a higher development of acoustic organs ; in 
 
62 
 
 serpents, however, they closoly resemble the caduci-branchiate am- 
 phibia, and by their vestibular saculus, containing solid cretaceous 
 bodies, they resemble the osseous fishes. The cavity of the tym- 
 panum is larger in the saurian than in the ophidian reptiles. As 
 we ascend to the higher orders, we meet with a cochlea, which is 
 the last part of the internal ear that attains perfection, slightly cnrved 
 and divided into a scala tympani and scala vestibuli. 
 
 In birds the organ of hearing resembles that of the crocodile ; 
 there is no cartilaginous external ear, and but a rudimentary concha, 
 which, however, is compensated for, especially in rapacious birds, 
 by a peculiar arrangement of feathers around the external meatus, 
 which in general they can erect at will so as to catch distant sounds, 
 and by that means either flee from danger, or pursue their prey 
 through dark and gloomy places. The external ear of owls is fur- 
 nished with a crescentic fold of integument in the form of a valve. 
 The oval tympanum, surrounded by bone, communicates with the 
 air-cells of the cranium by three large openings, and with the 
 fauces by two short wide Eustachian tubes which open by a single 
 orifice in the swan at the back of the posterior nares. There is but 
 one bone in the tympanum analogous to the stapes, with processes 
 rudimentary of the malleus and incus, and moved by a single tensor 
 muscle, which comes from the occiput and increases the convexity 
 of the membrana tympani by drawing it outwards. The cochlea, 
 though more developed than in reptiles, has not yet reached perfec- 
 tion, and the other parts of the internal ear present no remarkable 
 peculiarities different from the inferior grades of the next class. 
 
 In the mnmmalia, generally, the organ of hearing is distinguished 
 by the development of a true cochlea ; by an increased number of 
 auditory hones ; by the formation of external canal, and by the 
 addition of an external movable ear. We will meet, however, with 
 evident, though gradual, transitions from the simple state of organ 
 already seen in the inferior classes, up to man, where it has attained 
 its most complex and perfect condition. The concha is very small 
 in otarite, beavers, and otters, and wholly absent in the cetacea, 
 seals, walruses, the mole, the manis, and the ornithorhynchus. The 
 aquatic shrew and other mammalia which frequently go into the 
 water, form an approach to the crocodlile in having the external 
 auditory opening furnished with a valve. This external orifice in 
 the dolphin is merely large enough to admit a pin, and from it a 
 long narrow winding passage leads to the tympanum through the 
 fat which lies under the skin. As we ascend through the mam- 
 malia, residing more exclusively on the land, the concha acquires 
 greater size, and by the development of cartilage and powerful 
 muscles it becomes to enjoy very free and varied motions. It is 
 large, movable, and directed backwards in the ruminantia, pachy- 
 dermata, cheiroptera; and especially in the timid and feeble rodentia ; 
 and in the carnivora it is small and inclined forwards. 
 
 The cavity of the tympanum communicates with the mastoid cells, 
 contains four movable ossicula and three distinct muscles ; it is 
 
ORGANS OF SENSE. 63 
 
 closed by a raembrana tympani, which is concave externally, except 
 in the whale. In the ornithorhynchus, which in so many points of 
 view constitutes the connecting link between reptiles and the higher 
 classes of animals, the external passage is long and singularly tor- 
 tuous, the ossicula auditus anchylosed, the cochlea represents a 
 curved horn, as in birds and reptiles, and the semicircular canals 
 project into the cranium. The Eustachian tube is wide in the ceta- 
 cea, it opens at the blowing hole, where it is furnished with a valve; 
 the cochlea is short and convoluted in one plane in the cetacea, long, 
 narrow, and spiral in the rodentia, and in the guinea-pig, porcupine, 
 and aguti, it forms three turns and a half; the other essential parts 
 of the labyrinth agree on the whole with those of the human 
 subject. 
 
 Smell. — No organs subservient to this sense have been detected 
 in the cyclo-neurose animals, but in the annelidesof the diplo-neura, 
 the sense is said to reside in the parietes of their mouths, or the pores 
 of their air-sacs, and in the palpi, and autennag of insects. The 
 entrance to the respiratory passages, the sensitive tentacula, and 
 even the whole surface of the body in the higher orders of the mol- 
 lusea, are capable of receiving odorous impressions. The lami- 
 nated organs of smell in fishes are placed in two small depressions on 
 the anterior part of the face ; they are protected by cartilage, lined 
 by a delicate mucous membrane disposed in radiated folds in the 
 pike: tufted in the cyprinus, and arranged like the barbs of a quill 
 in the carp, ray, and shark. These cavities have no communication 
 with the mouth or pharynx ; they are closed in front by a valve 
 formed of skin and cartilage, and a similar structure partly divides 
 each into two. 
 
 In the perennibranchiate amphibia, as the proteus and siren, the 
 organs of smell in every respect resemble those of fishes, and in the 
 more highly developed genera, as frogs and salamanders, they 
 approach in characters to those of reptiles. The nostrils are partly 
 cartilaginous, partly osseous, and open into the cavity of the mouth. 
 The olfactory nerves enter by two foramina in the ethmoid bone, 
 and are distributed to every part of the soft pituitary membrane. In 
 serpents the nasal cavities present rudimentary turbinated bones, 
 and open posteriorly by a single orifice. The turbinated bones are 
 larger and more curved in the sauna, and in the chelonia the olfac- 
 tory surface is greatly extended and concealed by a strong osseous 
 covering. 
 
 In birds the external nostrils vary much as to size, shape, and 
 situation, they are generally free and wide, but in some instances 
 very small, as in the heron and gannet. The septum narium is 
 partly bony, partly cartilaginous, and covered by a highly vascular 
 pituitary membrane in the swan. The nasal cavities in birds con- 
 tain three turbinated bones and open separately into the pharynx, 
 except in the cormorant, where they join previous to their opening. 
 The olfactory nerves are distributed exclusively to the membrane 
 covering the septum narium and superior spongy bone. It is gene- 
 
64 EVERS'S COMPARATIVE ANATOMY. 
 
 rally supposed that birds of prey are gifted with an acute sense of 
 smell, but the experiments of Mr Audubon go to prove the reverse 
 opinion ; and according to the researches of Scarpa, the following is 
 the order in which it is enjoyed, beginning with those in which it 
 is most acute ; grallatores, natatores, raptor es, scansores, inses- 
 sores, rasores. 
 
 The organs of smell in the mammalia are distinguished by the 
 more perfect formation of external nose, by the large size of the 
 nasal cavities, and by the latter receiving several new openings, 
 such as the frontal, nasal, ethmoidal, sphenoidal, and maxillary 
 sinuses. The external openings are valvular in the beavers, seals, 
 and camels, and variously modified in other animals, according to 
 their different habits, as in the hog, elephant, &c. The turbinated 
 bones are long and simple in the rodentia, ruminanlia, and pachy- 
 dermata, and they form a complicated series of labyrinths in the 
 carnivorous tribes, where an acute sense is so necessary to enable 
 them to pursue their prey through their dark retreats. The large 
 olfactory nerves pass through the numerous openings of the cribri- 
 form plate, except in the cetacea, to be distributed on the surface of the 
 turbinated bones. These nerves are large and hollow in the human 
 foetus, like the olfactory tubercles of quadrupeds, and it is interest- 
 ing to observe how the sense of smell preponderates over all others 
 in the new born child, this can be easily tested during the nuzzling 
 of the infant at the mother's breast, when the loudest sounds may 
 assail its ears without effect, and when its visual powers are limited 
 to the mere perception of intense light. 
 
 Taste. — A considerable degree of obscurity prevails, respecting 
 the enjoyment of this sense in the different classes of animals, and 
 although we cannot display any organ especially appropriated to it 
 in the inferior tribes of animals, yet it is supposed that all enjoy it, 
 from the polygastric animalcules up to man. It is generally seated 
 in, but by no means confined to the tongue, this organ being absent 
 in some instances even in the human subject, where the existence 
 of the sense has been proved; and in other cases, where the tongue 
 does exist, its dense horny nature excludes it from such an enjoy- 
 ment. The form of the tongue differs considerably in different 
 animals; in none, not even in the simiae, is it exactly like that of 
 man. In the cephalopoda distinct gustatory villi cover its surface ; 
 in many fishes it has no papillae, and in others it is set with teeth ; 
 in the chameleon it is an organ of very peculiar mechanism, and 
 admits of being protruded for several inches in pursuit of prey, with 
 amazing celerity and precision. This power, for a long period a 
 paradox with naturalists was discovered by Dr. Houston to be of an 
 erectile nature. In birds it serves chiefly as an organ of prehension, 
 in a few only does it possess papillae, being generally sheathed in 
 front by horn. With few exceptions among the edentata, the 
 tongue in the mammalia serves as an organ of taste. In the bisulca 
 it is covered with a thick epithelium ; in the bat, the opossum, and 
 
ORGANS OF SENSE. 65 
 
 especially the lion, and others of the cat kind, it is beset with strong 
 sharp prickles, for prehensile purposes. 
 
 Touch. — This is the most general as well as the most simple of 
 the senses, and the degree in which it exists has reference to the 
 state of the tegnmentary membrane, and I he condition of the nervous 
 system. In the invertebrata no organs solely devoted to the per- 
 ception of sensitive impressions have been detected, yet there is little 
 doubt but that the cilia of most poly wastries, the ten taenia of zoo- 
 phytes and mollusca, and the antennas of ray ri a pods and insects are 
 subservient to this sense. Some fishes have fleshy sensitive fila- 
 ments arranged around the month after the manner of ten taenia, 
 and others have only the skin on the abdomen, or about the mouth, 
 uncovered with scales, and capable of receiving- external impres- 
 sions. The tongue among serpents, and the tail among saurian 
 reptiles, and some mammalia, constitute their chief tactile organs. 
 The organs of touch in birds are the bills, the cire in the falconidce 
 the wattles of the cock, and the caruncles of the turkey. It must 
 be acknowledged, however, that this sense is very limited in birds, 
 which is in some degree compensated for by the free distribution of 
 the fifth pair of nerves to their horny bills, especially those of the 
 aquatic species, which procure their aliment from mud. 
 
 In many of the mammalia the skin is shielded from external im- 
 pressions by the presence of horny or spiny coverings, dense furs. 
 or thick hides; and it is not till we arrive at the higher orders of 
 quadrupeds, carnivora and quadrumana, that the organ of touch 
 makes any approach to the perfect development of it observed in 
 the human subject. 
 
 RECAPITULATION. 
 
 1. Organs of vision exist in every class of animals, and in the 
 lowest orders the eyes vary in number from one to near 100. 
 
 2. In the vertebrata the eyes are two and vary much in form and 
 situation. 
 
 3. No organs of hearing or smell have been detected in the 
 radiata. 
 
 4. Our knowledge concerning the organ of taste is involved in 
 much obscurity. 
 
 5. No organ of touch has been detected in the invertebrata. 
 
 CHAPTER. X 
 
 ORGANS OF DIGESTION IN THE INVERTEBRATA. 
 
 General observations. — The organs engaged in the function of 
 digestion may be arranged under two heads: the primary, or 
 8 — f evers 5 
 
66 EVERS'S COMPARATIVE ANATOMY. 
 
 essential — including the alimentary tract; and the secondary, or 
 tributary, embracing the liver, spleen, pancreas, salivary, and 
 mucous glands. 
 
 There is no organ so universally present, nor so essential, as an 
 internal digestive cavity, and hence so often alluded to as consti- 
 tuting a line of distinction between the animal and the vegetable 
 kingdoms ; indeed there is no class of animals without it, although 
 it is not found in every species of each class. The peculiarities 
 presented by the digestive apparatus will vary according to the 
 rank an animal holds in the scale of the creation, the kind of food 
 on which it is destined to subsist, and the elaboration that food 
 may require to undergo. The alimentary surface of a plant is the 
 exterior of its root spread out in the earth, and absorbing, by its 
 spongioles, the materials for its nutrition, but the alimentary surface 
 of an animal is internal, and continued from the skin, like the in- 
 side of a lady's muff. 
 
 Cyclo-neura, Grant — Radiata, Cuvier. — In the very low 
 tribes of animals the digestive apparatus presents characters equally 
 diversified as the forms of the creatures themselves. The aliment- 
 ary cavity has often but one orifice; there are seldom teeth or 
 glandular organs, and the food is generally of the simplest sort. In 
 the polygastrica, as the term signifies, the cavities are numerous, 
 and their various forms have been well observed by Ehrenberg, 
 who caused these transparent animalcules to swallow fluids coloured 
 with carmine, indigo, or sap-green. The monads and several other 
 genera have but one orifice which receives the openings of the several 
 cavities, and from the absence of intestine the entire group has been 
 named anentera. in the higher forms, however, the alimentary 
 canal is furnished with an oral and an anal orifice, the straight, 
 curved, or spinal intestine receives the openings of numerous ccecal 
 appendices through its whole course. In some of the small monads 
 no internal cavity has been detected, and in other genera the num- 
 ber varies from one up to two hundred, as seen in a paramascium. 
 Many species are provided with dental organs in the form of stiff 
 spines disposed around the mouth, but in none of the class have 
 tributary or glandular organs been observed. 
 
 The porifera present a very simple form of alimentary appa- 
 ratus, their absorbent canals closely resembling the ramified roots 
 of plants, and as we ascend through the diversified series of the 
 polypifera or zoophytes we perceive the system increasing in com- 
 plexity from the simple genito-digestive sac of the hydra up to the 
 complicated structure presented by the actiniform polypi, where the 
 stomach is provided with a muscular and mucous tunic lined with, 
 vibralile cilia, and communicates inferiorly with the genital cavities. 
 The greater number of the acalepha possess a simple broad and 
 radiated alimentary cavity, suited to their highly organised and 
 minutely divided food, but in the monostomatous species, which 
 live on coarser aliment, a cartilaginous masticatory apparatus and 
 biliary secretion are superadded. The torpid predaceous echino- 
 
ORGANS OF DIGESTION IN THE INVERTEBRATA. 67 
 
 dermata afford in the structure of their digestive organs, connecting 
 links of transition from the radiated to the articulated classes. In 
 the higher forms of the echinida strong masticating and salivary- 
 organs are provided, the anal orifice, which in the lower tribes is 
 placed on the inferior surface, gains a dorsal aspect, which it con- 
 tinues to hold in the holothuriae and articulated classes. Thus we 
 perceive the digestive cavity, from being a simple monostome sac, 
 gradually acquires the form of a long narrow canal, open at both 
 ends, and furnished with salivary and biliary organs. 
 
 Diplo-neura, Grant — Articulate Cuvier. — The carnivorous 
 character of this great division of the animal kingdom bespeaks an 
 alimentary canal, limited in its capacity, straight in its form, and 
 simple in its structure. This canal usually takes a horizontal 
 direction, opens at the two opposite extremities of the body, and is 
 provided at its commencement with prehensile, destructive, or mas- 
 ticating organs. In consequence of the simple nature of the food 
 on which the entozoa subsist, many of them have but a single orifice 
 to their digestive sac. In the higher and more perfect forms, how- 
 ever, of these as well as of the rotifer a, the canal passes straight 
 or slightly winding through the body, presenting an oral and anal 
 aperture, and surrounded by the genital and biliary organs. The 
 cirrhopoda are remarkable for the great size of their salivary and 
 biliary apparatus, and the wide ducts of the latter, which open into 
 the stomach, as in most of the invertebrated tribes. 
 
 Among the annelida the earth-worm is remarkable for its capa- 
 cious mouth, a small salivary gland, a sacculated stomach, consist- 
 ing of three continuous cavities, and a narrow, slightly bending 
 intestine. The leech has three horny maxillae, furnished with sharp 
 teeth, with which it inflicts its tri-radiate wound, the straight, irre- 
 gularly sacculated intestine is furnished with ten pairs of lateral 
 coeca, and enlarges into a small sac near ihe anus. The carnivo- 
 rous rnyriapods are provided with three pairs of salivary and two 
 poison-glands, by their contracted oesophagus and elongated mem- 
 branous stomach, they resemble the higher species of worms, and 
 by their small, narrow intestine, ending in a wide colon, they are 
 allied to the ophidian reptiles. 
 
 The digestive organs of the insecta present in an embryo state 
 nearly all the essential elements of the chylo-poietic system in the 
 highest classes of animals, as masticating organs, salivary and 
 mucous glands, liver, pancreas, &c. : they will be found to vary, 
 however, according to the peculiar living habits of the species, and 
 the quality of their food. The alimentary canal usually consists 
 of a wide pharynx, a narrow oesophagus, a dilated crop, a muscular 
 gizzard, provided with sharp, conical, horny teeth, a capacious chy- 
 lific stomach, a straight, narrow intestine, a short, dilated colon, 
 and a contracted cloaca. In the herbivorous insects, the alimentary 
 canal is long, capacious, and complicated. The gall-bladder is 
 usually single, but occasionally double. The cunning carnivo- 
 rous aracknida resemble the insects in the arrangement of their 
 
68 
 
 masticating organs, whilst their straight narrow alimentary canal 
 and the compact state of their liver, ally them to the Crustacea. 
 
 Like most other carnivorous articulata, the cunning, cruel, 
 aqautic crustaceans are provided with prehensile and masticating 
 organs well suited to destroy the prey in the rich element they in- 
 habit. The maxillae vary from one to five pairs, but are wanting 
 in the lower orders. The alimentary canal is generally without 
 convolutions, and opens by two apertures. The decapods present 
 a narrow oesophagus, leading to a capacious muscular stomach, 
 furnished with numerous solid calcarious teeth, and a straight in- 
 testine occupying the dorsal portion of the trunk, and receiving- 
 near its commencement the biliary and pancreatic ducts. The 
 salivary glands are absent except in the higher orders, where rudi- 
 ments of them are perceived surrounding the oesophagus. The 
 mucous membrane forms rugae in the oesophagus and stomach, 
 but not in the intestine, and the peritoneum ibrms no mesentery. 
 
 Cyclo-gangliata, Grant — Mblluscq, Cuvier. — This great divi- 
 sion of the animal kingdom being destined chiefly to subsist on 
 soft food, masticating organs are little required by them, hence they 
 are often but sliohtly developed, and in some cases wholly absent. 
 But their food is greatly varied and often coarse, so as to require a 
 complicated form of alimentary canal, and a high development of 
 glandular apparatus. The digestive organs of the tunica t a closely 
 resemble those of the conchifcra, being a little more complicated in 
 the latter. Both are destitute of prehensile or masticating organs, 
 and depend for their supply of food on the respiratory currents. 
 They possess a short wide oesophagus, opening into a capacious 
 muscular stomach, without teeth, and receiving the biliary ducts. 
 The intestine is generally short, wide, and convoluted. The con- 
 chifera differ from the tunicata by their long and convoluted intes- 
 tine passing between the two aorta?, through the fleshy substance 
 of the ventricle, and the mass of the liver. The terrestrial pulmo- 
 nated gasieropnds present a more complicated digestive apparatus 
 than the acephalous mollusca, especially those which feed on vege- 
 table substances. They are provided with a pair of horny jaws, a 
 muscular tongue and proboscis armed with sharp recurved spines, a 
 large pharynx, a long oesophagus, and a capacious stomach, divided 
 in the phytophagous species, into several compartments, fur- 
 nished internally with teeth, and receiving the biliary and pancre- 
 atic secretions. One or two pairs of salivary glands lie around the 
 oesophagus, and the liver is of considerable size. The intestine 
 is long and convoluted, and opens in common with the genital or- 
 gans on the right side, near the anterior extremity of the body. In 
 the pteropods and cephahpods, the oesophagus passes through the 
 cranial cartilage and ganglionic ring, sometimes dilating into a 
 crop before entering the muscular gizzard, which is often lined 
 with a thick coriaceous epithelium. The intestine is short and 
 wide in the carnivorous species, destitute of coecum-coli, not dis- 
 tinguished into large and small as in the vertebrata, and no where 
 
VERTEBRATA. 69 
 
 imbedded in the substance of the liver, as in many of the inferior 
 mollusca. The mollusca are without gall-bladder^ and as yet no 
 portal circulation has appeared. The entrance of the hepatic duct 
 into the stomach is guarded by a pair of prominent valves, pro- 
 longed so into the intestine as to allow of the passage of the pan- 
 creatic and biliary secretions into the gut during a state of vacuity 
 without entering the stomach or duodenum. 
 
 CHAPTER XI. 
 
 VERTEBRATA. 
 
 In this great department of the animal world the digestive appa- 
 ratus presents a higher development and a greater degree of com- 
 plexity than we have met with before. The alimentary canal 
 always swells out into a distinct gastric enlargement, and is provided 
 with a large conglomerate liver, spleen and pancreas. The duode- 
 num invariably receives the biliary and pancreatic secretions, and 
 he salivary glands are rarely absent. The teeth are generally 
 confined to the alveoli, and there are none found in the stomach. 
 As a general rule the canal is longer, larger and more sacculated, 
 and the masticating; and glandular apparatus more developed in 
 the phytophagous than in the carnivorous tribes. 
 
 PISCES. 
 
 Since vegetable food cannot be procured in the unfathomable 
 depths of the sea, we are prepared to meet with a short and simple 
 form of alimentary canal in fishes, suited to their predaceous habits. 
 Vegetable substances might even endanger their lives by an evolu- 
 tion of gas which would render them specifically lighter than the 
 water, and cause them to float upon its surface with the belly up- 
 wards. The teeth of fishes are generally numerous, destitute of 
 fangs, laminated, deciduous, thinly covered with enamel, and 
 movable on the surface to which they adhere, till maturity, when 
 they become permanently fixed. The teeth of fishes are often 
 implanted in the tongue as in many gasteropods and birds, in the 
 vomer as in amphibia, in the palate bones as in serpents, in the 
 pharyngeal bones, branchial arches and os hyoides, as well as in the 
 maxillary and inter-maxillary bones to which they are confined in 
 the saurian reptiles and mammalia; the teeth are most numerous 
 in the pike and salmon, and are altogether wanting in some genera, 
 as the sturgeon. As in serpents, crocodiles, dolphins, and other 
 predaceous non-masticating vertebrata, the teeth are not opposed to 
 each other but placed alternately, adapting them to their prehensile 
 office. 
 
70 
 
 The tongue is broad, short, and almost destitute of papillae. The 
 salivary glands are only rudimentary, and even wanting where the 
 liver and pancreas are well developed, but the mouth is well sup- 
 plied with mucus. The short, wide infundibuliform oesophagus 
 has an external circular, and an internal longitudinal layer of mus- 
 cular fibres, and is lined with a pale, villous, longitudinally plicated 
 mucous membrane provided with numerous mucciperous follicles. 
 The large gastric cavity is sometimes long and tapering as in the 
 herring, and sometimes globular as in the lophius: its two orifices 
 are closely approximated, so that the food is retained in it for a long 
 period, hence, if we feed a tame perch till it is gorged, it will not 
 eat again for ten or fourteen days ; both orifices of the stomach are 
 sphinctorial, its mucous membrane is plicated and forms a valve at 
 the pylorus with a fringed margin, surrounded by a ring of carti- 
 lage. The intestine, in many cases, does not measure more than 
 half the length of the body, in others, however, as the sword fish, it 
 forms several convolutions, but rarely does it admit of any distinc- 
 tion into large and small. In the sturgeon, ray, and shark the anal 
 is smaller than the cardiac portion, and the reverse obtains in the 
 pleuronectes, gadi, murcenae, &c. In order to compensate for the 
 shortness of the canal and the absence of valvulse conniventes, the 
 lining membrane is peculiarly disposed, being reticulated in the 
 sturgeon, forming spiral turns in the shark and ray, and serpentine 
 folds in the eel. The rectum here as in oviparous vertebrata, ter- 
 minates in the cloaca through which are discharged feces, urine, 
 semen, and ova. On either side of the anus there is an oblique 
 valvular opening, admitting of free egress, but prohibiting any 
 thing from without, and the air-sac, or rudimentary lung commu- 
 nicates by a membranous tube with the oesophagus, stomach, or 
 upper portion of the intestine. 
 
 The large elongated liver is of a soft texture, light colour, and 
 divided into many lobes, it is provided with arterial and portal cir- 
 culation, and generally with a large gall-bladder as in other pre- 
 daceous vertebrata. Several long hepatic ducts join the cystic, and 
 many short ones run at once into the fundus of the gall-bladder, 
 and the short but wide choledochus either opens separately or in 
 common with one or more of the pancreatic ducts into the upper 
 portion of the intestine. The spleen is small, of various forms, 
 attached to the side of the stomach, generally simple, but lobulated 
 in the shark and sturgeon, as in some of the cetacea, and in the 
 lamprey, which has neither pancreas nor gall-bladder, it is wholly 
 absent, as in the invertebrata. The pancreas which is wanting in 
 the centriscus, presents every stage of development, from one or 
 two simple follicles as in the lophius, choetodon, (fee, up to a large, 
 compact, reniform mass, enveloped in a muscular tunic, as in the 
 sturgeon and xiphas. The large pancreatic follicles are connected 
 by loose cellular tissue, and admit the digested food info their in- 
 terior, like the biliary tubes of some mollusca. The peritoneum 
 lines the walls of the abdomen, and surrounds the viscera in the same 
 
VERTEBRATA. 71 
 
 manner as in snails, and the sepias: it form a small mesentery and 
 a rudimentary epiploon, and it presents the remarkable peculiarity 
 of its cavity communicating with the surrounding medium by the 
 tvyo small openings, placed at the side of the anus. 
 
 AMPHIBIA. 
 
 These animals, like the fishes, are predaceous in their habits, 
 and swallow their food without mastication. The whole of them 
 have prehensile teeth in the palate ; salamanders have them in both 
 jaws, frogs in the upper only, and the toad and pipa in neither, but 
 in the toad two small transverse rows exist behind the posterior 
 nares. The teeth in the proteus nearly resemble those of the sala- 
 mander, but in the siren they are arranged in a quincunx order as 
 in many fishes, and amount nearly to two hundred. The salivary 
 glands are absent in the aquatic, and merely rudimentary in the 
 terrestrial amphibia. In the toad and perennibranchiate amphibia 
 the tongue is short, thick, and fleshy, but in the frog it is 
 long, free, bifid, covered with papillae and mucous follicles, as in 
 reptiles The short, dilatable, fleshy oesophagus, leads to a narrow, 
 transversely elongated stomach, muscular in it parietes, and over- 
 lapped by a large bilobate liver with a distinct gall bladder. In 
 the young tadpole of the frog the almentary canal is very long, the 
 intestine which is narrow and coiled, measures ten times the length 
 of the space from the mouth to the anus, but after the metamorphosis 
 has occurred, and that the mixed food of the tadpole is changed for 
 that of a more nutritious nature, as snails, worms, ccc, the canal 
 becomes gradualy shortened to one fourth of its former length. The 
 duodenum has transverse folds like valvular conniventes, and the 
 short, wide colon ends in the cloaca, together with the openings of 
 the genital and urinary organs. The mucous membrane forms 
 longitudinal folds in the proteus, the triton, the pipa, and the sala- 
 mander ; transverse folds in the froo-, and quadrangular cells in 
 the hyla. A small pyloric valve exists in the toad and pipa, and 
 the valve of the colon is distinct in the frog, the triton, and the 
 hyla. The liver, the spleen, and the pancreas are found in all the 
 amphibia, varying in shape according to the form of the animal. 
 Thus we perceive in the lower orders of amphibia, an evident 
 approach in their digestive organs to those in fishes, in the great 
 number of teeth, shortness and width of oesophagus, absence of 
 fundus to the stomach, want of distinction between large and small 
 intestine, and the magnitude of the liver. But in many we discover 
 an approximation to the higher vertebrata, in having fewer teeth, 
 an elongated tongue, fundus to the gastric cavity, distinction between 
 large and small intestine, absence of pyloric and colic valves, and 
 the development of transverse folds in the duodenum. 
 
72 EVERS's COMPARATIVE ANATOMY. 
 
 REPTILIA. 
 
 The ophidian and saurian reptiles chiefly subsist on animal food, 
 therefore their digestive apparatus will be found to differ from that 
 of the chelonia which live on vegetable substances. The teeth of 
 serpents are sharp, conical, inverted, unopposed, and set in loose, 
 movable bones, adapted for seizing and lacerating their prey, they 
 are attached to the maxillary, inter-maxillary, sphenoid, and palate 
 bones, and the poison fangs of the venomous species are perforated 
 and grooved in front to transmit, the secretion of the poison gland 
 forced out by muscular pressure. The tongue is long, smooth, 
 sheathed, and bifurcated. The salivary glands vary in the differ- 
 ent species; the sublingual is always present, and the poison gland, 
 which is analogous to the parrotid, is confined to the noxious spe- 
 cies, and is placed below and behind each orbit. The long, disten- 
 sible oesophagus, copiously supplied with mucus, leads to the long, 
 straight, capacious stomach, longitudinally plicated and capable of 
 being distended to many times the size of the body ; it tapers to the 
 pyloric orifice, which is provided with a distinct valve, and embraced 
 by sphinctorial fibres. The duodenum presents a villious surface, 
 and receives the pancreatic and biliary ducts; the remainder of the 
 small intestine is narrow and convoluted to the commencement of 
 the short, dilated colon, where there is generally a circular valve 
 and a small coecum. The colon ends in the cloaca together with 
 the ureters, oviducts, or vasa deferentia, and the male organ of 
 generation, single or divided, also passes through the cloaca, as in 
 other oviparous vertebrata. The liver, spleen, pancreas, the kid- 
 neys, the testes, and the ovaria present an elongated form conform- 
 able to the shape of the body. The small intestines are attached 
 to a mesentery, and the large are often sacculated for the purpose 
 of retarding the passage of the food. 
 
 As most of the sauria are carnivorous like the ophidia, they pre- 
 sent a form of alimentary apparatus equally simple. Their prehen- 
 sile teeth are fewer and chiefly restricted to the jaws; the stomach 
 is short and round in the form of a gizzard, with a pair of central 
 tendons ; the small intestine is long in the phytophagous species 
 as the scincus and iguana, and in all other respects they resemble 
 the ophidian reptiles. 
 
 The phytophagous chelonia present a higher development of 
 alimentary canal than the carnivorous species. The place of teeth 
 is supplied by the sharp horny margins of the jaws ; the tongue is 
 covered with long papilla?; and the salivary glands are variously 
 developed in the different species. The long, wide, muscular oeso- 
 phagus leads to a large fleshy stomach, extended transversely, and 
 without a pyloric valve. The intestine is about six times the length 
 of the body, and the colon presents a short, wide coecum, and a 
 circular valve at its commencement in the terrestrial, but not in the 
 aquatic species. The alimentary canal is wide and muscular, and 
 
VERTEBRATA. 73 
 
 the mucous membrane folded longitudinally so as to form a surface 
 of considerable extent. The rectum dilates into a cloaca which 
 receives the openings of the urinary and genital organs. 
 
 AVES. 
 
 Nothing can be more beautiful to observe than the rigid economy 
 which is displayed in the accurate adaptation of the digestive 
 apparatus of birds to the various and dissimilar kinds of iood on 
 which, from their diversified living habits they are destined to subsist. 
 The absence of teeth in this class is supplied by strong horny 
 beaks and powerful muscular gizzards, the former performing the 
 part of cutting, and the latter of grinding teeth ; the form of the 
 bill will vary according to the food of the different species of birds 
 and their mode of procuring it, thus in the climbing frugivorous 
 maccaws, parrots, and cockatoos, it is broad and powerful to break 
 the hard shelly coverings of seeds, and most of the granivorous 
 order have a similar structure. The broad bills of ducks, geese, 
 and other aquatic species are well adapted for obtaining worms and 
 other substances from watery or muddy situations, whilst the eagle, 
 the hawk, the owl, and other rapacious birds have short, strong, 
 arched, dense bills, with cutting edges, equally suited to seize, cut, 
 or tear their living prey. The tongue, which in birds serves the 
 purpose of a prehensile organ, is as variable in form as the bills, 
 being long, broad, and covered with recurved spines in the swans; 
 short, round, and flexible in the parrots and cockatoos, and short 
 and muscular in the struthious birds. The tongue of the flamingo 
 is very remarkable, it is composed of an elastic, cellulo-fatty sub- 
 stance, its form is nearly cylindrical, the pointed apex being sup- 
 ported by an osseous plate iuferiorly. A deep groove runs along 
 the centre of the upper surface with a row of recurved spines on 
 either side. The os hyoides in this class very much resembles that 
 of reptiles, and the length of its glosso-hyal element chiefly deter- 
 mines the length of the tongue. 
 
 Since the food for birds remains but a short time in the mouth 
 and undergoes very little change there, their salivary glands are 
 small. In the crow they consist of a series of conical follicles 
 situated along the sides of the mouth, and opening separately on 
 its mucous surface; in most other birds, however, there are four 
 pairs, one under the tongue, another at the junction of the angles 
 of the lower jaw, another close to the cornua of the os hyoides, and 
 the fourth is placed at the angles of the mouth: they are most 
 developed in the frugivorous species. The uvula and velum are 
 not present, and the narrow laryngeal aperture is protected by the 
 retroverted papillae at the base of the tongue, except in the coot, the 
 albatross, and a few others where the epiglottis exists merely in a 
 rudimentary form quite insufficient to cover the opening. 
 
 There is a remarkable pouch under the jaw of the pelican which 
 serves as a net for seizing fish, and is capable of containing ten 
 
74 
 
 VE ANATOMY. 
 
 quarts of water; a similar provision is found in the swift, the rook, 
 the male bustard at maturity, and other insectivorous birds. The 
 alimentary canal is much longer and more capacious, and the glan- 
 dular apparatus better developed in the phytophagous birds than 
 in those which subsist more exclusively on animal food. The long, 
 wide, fleshy oesophagus, with a cuticular lining-, passes down 
 behind and to the right side of the trachea, behind the heart 
 and between the lungs. In rapacious birds it is capable of enor- 
 mous dilatation, but in the flamingo its diameter does not exceed 
 half an inch. In the frugivorous, insectivorous, and omnivorous 
 birds, the oesophagus presents nearly a uniform capacity all through, 
 but in the raptorial eagles and vultures, which gorge themselves at 
 uncertain periods, it forms a lateral dilatation at the lower part of 
 the neck termed the ingluvies or crop. And in those birds which 
 live exclusively on, and require to take a large quantity of vegetable 
 food, the crop is large, globular or oval, single in the common fowl, 
 and double in the pigeon ; it is altogether wanting in the swan and 
 goose. The oesophagus and crop are supplied with an abundant 
 mucous secretion, and are provided with an external circular and 
 an internal longitudinal set of muscular fibres, the reverse of the 
 disposition observed in the human subject. Mr. Hunter has re- 
 corded in his animal economy, some interesting observations on 
 the crop of the pigeon, from which it appears that this macerating 
 paunch takes on a secreting function during the breeding season, 
 and supplies the young pigeons with an abundance of milk, a diet 
 suitable to their tender a^e, and the analogy of the pigeon's milk to 
 that of the mammalia has not escaped popular notice. 
 
 That part of the oesophagus which extends from the crop to the 
 gizzard, was called by Mr. Hunter the lower oesophagus ; at its in- 
 ferior part, just above the gizzard, it dilates into the glandular divi- 
 sion of the stomach, variously termed the jjroventriculus, ventri- 
 cular succenturiatus, bulbus glandulosus, echinus, infundibulum. 
 In the omnivorous and piscivorous tribes there is no perceptible 
 dilatation here, but in all it presents increased vascularity as it is 
 provided with a number of glands which secrete a fluid analogous 
 to the gastric juice. Beneath the infunbulum is the powerful 
 muscular gizzard directed transversely like the stomach of the 
 vertebrita, overlapped by the lobes of the liver, and lined internally 
 with a thick, dense epithelium. At the upper part of the gizzard 
 are two openings, one large, to the left side, and communicating 
 with the proventriculus, the other smaller, and a little to the right, 
 leads into the duodenum. In those birds which feed on grain and 
 other hard substances, the muscular fibres of the gizzard are dis- 
 tinguished by their density and red colour, they are arranged in 
 four masses, two lateral, called the digastric muscles, and connected 
 to anterior and posterior tendons, and two smaller ones between 
 these, at the end of the gizzard, termed musculi intermedii. In 
 rapacious and carnivorous birds the parietes of the gizzard are thin 
 and membranous, yet distinctly presenting the anterior and posterior 
 
VERTEBRATA. 75 
 
 tendons. The gallinaceous birds, in which the gizzard is most 
 powerful, swallow pebbles and other hard bodies, which serve the 
 purpose of reducing their food, like the gastric teeth of crustacea, 
 insects, and gasteropods ; but in the carnivorous birds, with a thin 
 membranous gizzard, no such substances are required, all the neces- 
 sary changes being effected by the activity of the gastric secretions. 
 The parietes of this organ are subservient in a remarkable manner 
 to a known law, to which the whole muscular system yields, that 
 of increasing its growth in proportion to the functions imposed on 
 it; this was strikingly illustrated in the case of a sea-gull, which 
 Mr. Hunter kept for a year, living, contrary to its nature, upon grain. 
 At the end of that period he contrasted its gizzard with that of 
 another sea gull, which had been living on fish, and found that the 
 digastric muscles of the former had acquired nearly three times the 
 development of the latter. He accomplished similar phenomena by- 
 changing the food of an eagle and of a tame kite, the former throve 
 very well on bread, but that it was dissatisfied with its fare, is to be 
 inferred from its seizing the earliest opportunity of breaking its 
 chain, and effecting its escape. These facts show in a clear manner 
 the provision of nature for the preservation of life under a variety 
 of circumstances. 
 
 The intestine is shorter in birds than in mammalia, its different 
 divisions are better marked than in the lower classes, and in the young 
 bird a remnant of the entrance of the vesicula umbilicalis may be 
 seen on the interior part of the small intestine in the form of a 
 small ccecal appendage, and in many gallinaceous and some aquatic 
 birds it remains through life. The course of the small intestine 
 varies much in the different orders of birds; the duodenum always 
 makes a long fold, which embraces the long, bilobate pancreas in 
 its concavity. The large intestine is about a tenth part of the 
 length of the body, and usually has two coeca at its commencement, 
 except in the bustard and ostrich, it runs a straight course from 
 the cceca to the cloaca ; it is generally a little larger than the small 
 intestine, and its villi are shorter, coarser, and fewer. The coeca 
 coli are of great size in the gallinaceous and other granivorous 
 birds, where they arise by two narrow canals, and enlarge into 
 wide sacs, often several times the size of the intestine, as in the 
 turkey. In the ostrich they have the mucous membrane disposed 
 in the form of a spiral fold. They are least developed in the gral- 
 latores and the nocturnal rapacious birds. In the herons and several 
 other birds there is but one, as in the invertebrate and lower ver- 
 tebrate animals, and as in the plantigrade carnivora, they are alto- 
 gether wanting in the zygodactylous birds. 
 
 The rectum terminates by a round valvular orifice in a dilatable 
 cavity, the upper part of the cloaca, which is the remains of the 
 allantois, and now forms a rudimental urinary bladder, and in the 
 ostrich it serves for the retention of the urine as in the higher 
 viviparous animals. At the lower and back part of this urinal por- 
 
76 EVERs's COMPARATIVE ANATOMY. 
 
 tion of the cloaca are the openings of the ureters, and external to 
 these, the openings of the oviducts, or vasa deferentia. 
 
 To this urethro-sexual canal, succeeds the preputial cavity, or 
 lower portion of the cloaca, which lodges the organs of excitement, 
 clitoris or penis, as in reptiles, marsupial, and monotrematous mam- 
 malia. In the median plain, and on the dorsal aspect of the prepu- 
 tial cavity is the opening of a conical sac, named Barsa Fibricii, 
 which lodge's the anal follicles, and is analogous to Cowper's glands. 
 
 The liver is large in birds, especially in the aquatic species, it 
 generally consists of two lobes, but occasionally of three, as in the 
 pigeon, goose, and swan ; the right lobe is usually larger than the 
 left, the latter, however, is larger in the bustard, where it extends 
 into the pelvis. The bile is discharged by two ducts, one goes 
 directly to the duodenum, the other to the gall-bladder, and when 
 the latter is absent, they both open separately into the duodenum, 
 but in no case is there a ductus choledochus. The pancreas, long, 
 narrow, and trihedral, is lodged in the fold of the duodenum, its 
 ducts are two, sometimes three in number, as in the pigeon, raven, 
 and common fowl, and they terminate separately in the duodenum. 
 The small, round, oval, flat, or elongated spleen is placed beneath 
 the liver, and to the right of the proventriculus; its texture is loose, 
 and the blood would seem to be deposited in cells, from which the 
 veins take it up. 
 
 When we contemplate the different lengths and forms of intestine 
 met with in this class, we cannot help attributing it to some wise 
 purpose, and a little reflection on the greatly diversified nature of 
 the food on which the various tribes of birds are destined to subsist, 
 irresistibly leads us to infer that economy seems to be the main 
 design ; for instance, the colon and coeca of the African ostrich, 
 which has to subsist on the scanty and uncertain fare of the desert, 
 are fifty times the length of the same parts in the cassowary, which 
 inhabits Java, one of the most fertile countries on the globe. 
 
 MAMMALIA. 
 
 The digestive organs vary more in this than in any other of the 
 vertebrated classes, and the varieties will be found to refer chiefly 
 to the type of development and living habits of the sundry species. 
 The teeth present infinite varieties as to form and position ; however, 
 their density and fixedness are well calculated to disintegrate ali- 
 mentary substances, and blend them with the mucous and salivary 
 secretions. The teeth are wanting in the ant-eaters, pangolins, and 
 the whalebone whale. The young ornithorhynchus paradoxus has 
 two molar teeth in each jaw on each side: these are shed in the 
 adult animal, and replaced by one large one on each side. But in 
 the hystrix there are twenty small, blunt, horny teeth, near the base 
 of the tongue, and seven transverse rows in the corresponding sur- 
 face of the palate. The incisor, canine, and molar teeth exist in 
 the quadrumana. carnivora, ruminantia, without horns, and in most 
 
VERTEBRATA. 77 
 
 of the pachydermata ; but it is only in the extinct anoplotherium 
 among mammalia, that the three kinds of teeth are arranged 
 in an uninterrupted series, as in man. The superior incisors are 
 wanting in the ruminantia, and the inferior in the walrus. The 
 Ethiopian hog and certain bats lose their incisors at a particular 
 age. The canine teeth are absent in the rodentia, some ruminants, 
 and in most of the female solipeda. The rodentia have but two 
 incisors in each jaw, with the exception of the hare and rabbit, 
 which have them double in the upper jaw; the kangaroo has two 
 below and eight above ; the daman two above and four below. The 
 molar teeth are the most essential, and are the last to disappear: 
 hence the ornithorhynchus paradoxus, the tatu, and the two-horned 
 rhinoceros, are restricted to them. The molar teeth are renewed 
 eight times in the elephant, the incisors are shed twice in many 
 rodentia ; and most of the teeth are renewed once in the other 
 orders of the mammalia. In most mammalia which feed on animal 
 substances, the crowns of the teeth are entirely covered with enamel, 
 and only partially so in the phytophagous quadrupeds. 
 
 The following is an outline of the process by which the teeth 
 are produced. About two months after conception, a gelatinous 
 substance lies alonsf each alveolar arch: at 'the third month this 
 substance is firmer, and lodged in a shallow groove in the bone. It 
 is next divided into separate pulps by transverse filaments passing 
 from one side of the alveolous to the other. These pulps are en- 
 closed in, and connected by vessels to a thin vascular membrane, 
 which, between the third and fourth month begins to secrete the 
 ossific laminae from its outer surface. This membrane, with its 
 contained pulp, is supplied from the dental vessels, and nerves, and 
 is surrounded by a thick vascular sac, separable into two layers ; 
 • he latter membrane is attached to the pulp only at its base, but is 
 firmly connected by its outer layer to the gum, from which it derives 
 its vascular and nervous supplies. It is from the inner surface of 
 the internal layer of this sac that the enamel is secreted, and at 
 this period it becomes thick and vascular, whilst the outer layer, 
 which is only rudimentary in man, secretes the crusta petrosa in 
 the graminivorous quadrupeds. After the enamel has been secreted, 
 both layers of this sac become wholly absorbed, hence they have 
 been termed the deciduous membranes, in contra-distincti< n to the 
 permanent, which are described as three in number, one being the 
 periosteum of the alveolus, another the periosteum of the root, 
 and the third the periosteum of the dental cavity, which secreted 
 the tooth. But in fact these three permanent membranes are simply 
 a continuation of the periosteum of the jaw which first lines the 
 alveolus, then descends, to form the periosteum of the root, and 
 lastly passes up in the form of a hollow cone to enclose the pulp. 
 The period at which the teeth appear in the human subject is very 
 variable, some children being born with two or more, whilst in 
 others they may not appear for two or even three years. From five 
 to eight months, however, is the most usual period ; they generally 
 
78 
 
 appear first in the lower jaw, and proceed in the following order : — 
 From 5 to 8 months, the four central incisors; from 7 to 10, the 
 lateral incisors; from 12 to 16, the four anterior molars ; from 14 
 to 20, the four cuspidati ; and from 18 to 36 months, the four pos- 
 terior molars. 
 
 The purposes of prehension are accomplished by sensitive fleshy 
 lips, as in herbivorous quadrupeds, by a long, flexible tongue, as in 
 the giraffe and ant-eaters, and by other organs such as the proboscis 
 of the elephant. The salivary glands are largest in herbivorous 
 quadrupeds, less in the carnivora, and least in the aquatic mamma- 
 lia. The sublingual glands are wanting in cats. The velum palati 
 is large, but the uvula is confined to the quadrumana. The os 
 hyoides, is most developed in the herbivorous quadrupeds, and has 
 been shown by Geoffroy to consist of twelve elements, a glosso and 
 basi-hyal piece for the body, an apo a cerato, and a styl-hyal ele- 
 ment tor each of the anterior corn u a, and an ento and uro-hyal for 
 each of the smaller posterior cornua. This condition is sometimes 
 found as an abnormal state in man. The oesophagus is wide and 
 dilatable in the carnivora, and narrow and fleshy in the herbivora. 
 The arrangement of its muscular fibres is the same as in man ; and 
 its mucous tunic, wh'ich usually forms longitudinal and but rarely 
 transverse folds, is lined with cuticle, which in the carnivora termi- 
 nates at the cardiac orifice in a fringed margin, but lines half the 
 stomach of the horse, the rat, the hog, and some others of the pecora, 
 and in the ruminantia it lines the three first cavities of the stomach. 
 The oesophagus of the ornithorynchus hystrix is furnished with a 
 peculiar valve at its commencement, and numerous papillse at its 
 termination, directed upwards, and its cuticular lining is continued 
 through the stomach. 
 
 The animal nature of the food of the carnivora bespeaks a short 
 and simple form of alimentary canal. In some, as the lion and the 
 cat, the stomach is elongated in form, and its orifices remote from 
 each other, this is particularly the case in the lynx; in others, as 
 the racoon, it is nearly globular, and in all, with the exception of 
 the seal, its interior is smooth, and almost without villi. The 
 monotremata, cheiroptera, insectivora, and marsupialia, also present 
 a simple stomach, a coecal portion being but little developed. 
 When, however, the food is of a more mixed character, the stomach 
 becomes more elongated transversely, as in the quadrumana and 
 others of the less carnivorous tribes. In most of the rodentia the 
 thin cardiac portion forms a distinct coecum, and is separated by a 
 constriction from the pyloric muscular portion. Several of the 
 pachydermata, marsupialia, edentata, and quadrumana, form a link 
 of transition to the more complex stomachs of the cetacea and 
 ruminantia in the formation of folds or coeca with cuticular linings. 
 Thy intestinal canal is very short in these animals, the whole tract 
 not exceeding three times the length of the body in the lion and 
 wild cat. In the badger there is scarcely any distinction between 
 small and large intestine: but in the lion, seal, and others, it is well 
 
VERTEBRATA. 
 
 79 
 
 marked. The coecum is small in cats, spiral in dogs, and generally 
 absent with the colic valve in the mustelidae. Valvulse conniventes 
 are scarcely developed. 
 
 In thecetacea the tongue is short, thick, fleshy, and but. little sus- 
 ceptible of motion, and in the whale it often affords three barrels of 
 oil. The teeth are prehensile, the salivary glands rudimental or 
 deficient, and the oesophagus short and wide. In the phytophagous 
 cetaceans the stomach is divided into a large cardiac, and a small 
 pyloric portion, by a contraction which gives origin to twotubiform 
 prolongations. The coecum is simple in the dugong, and bifurcated 
 in the manatee. In the zoophagous cetacea the stomach consists of 
 four or five compartments, none of which, except the first, have any 
 communication with the oesophagus, therefore no rumination can 
 occur. The first cavity is small and lined with cuticle, which ter- 
 minates abruptly at the narrow opening leading into the second. A 
 smal| pyloric orifice leads to a dilated duodenum. There is scarcely 
 any distinction between small and large intestine, and the coecum 
 coli is but little developed. Why so complicated a stomach should 
 exist in animals nourished by the most digestible and highly organ- 
 ised food, is an anomaly for which we can offer no explanation, but 
 one which, from its interest, courts early investigation. 
 
 The stomach of the kangaroo resembles the human colon and 
 caecum; the oesophagus enters near its left extremity, which is 
 small and bifid; the stomach first extends towards the right side, 
 and then upwards and to the left, in such a manner as to completely 
 encircle the entrance of the oesophagus, and terminates at the py- 
 lorus by a contracted orifice. Its cavity gradually enlarges from the 
 left extremity till it nearly reaches the pylorus, it then dilates into a 
 round cavity with two lateral processes, and finally ends by a 
 narrow orifice. It presents a sacculated appearance arising from 
 the presence of anterior and posterior bands like those of the human 
 colon, and the cuticle lines it to a certain extent on either side of 
 the entrance of the oesophagus. This animal has been known to 
 ruminate when fed on hard ifood. The kangaroO-rat and the vam- 
 pyre bat present similar modifications of stomach but have no part 
 of it lined with cuticle, and in the former there is a valve at the 
 cardiac orifice. The intestine of the kangaroo corresponds in its 
 great length and convolutions with the coarse nature of its vegetable 
 food, and the coecum is about fifteen inches long. At the cardiac 
 orifice of the stomach in the beaver and wombat there is a large 
 gastric gland, like the glandular infundibulum in birds. 
 
 The ruminating animals possess four stomachs ; the first magnus 
 venter, or paunch, receives the crude unrnasticated food, while the 
 animal is grazing. When this cavity is filled the animal retires to 
 rest, and begins to ruminate; the unmasticated food, softened in 
 the paunch, now passes in small portions into the second cavity, 
 called reticulum, or honey comb ; from this it passes as a bolus up 
 through the oesophagus to the mouth, where it is thoroughly mas- 
 ticated and insalivated ; it is next couducted by the oesophagus to 
 
80 EVERS'S COMPARATIVE ANATOMY. 
 
 the third stomach, termed mam/plies, or omasum, aid from thence 
 into the fourth stomach called abo?nasum, or rennet bag-. Of these 
 cavities, the first is the largest, and the third the smallest. The three 
 first are lined with cuticle, and the fourth, which is next in capacity 
 to the paunch is lined with a soft mucous coat folded in the longitu- 
 dinal direction. This is the proper digestive stomach, and is analo- 
 gous to the digestive sac of carnivorous and higher quadrupeds. 
 The fourth stomach of the ruminantia is the first developed ; in the 
 earlier periods of life it is the largest, and the only one employed in 
 digestion. The mechanism by which milk is transmitted directly 
 into the fourth stomach during the period of suckling is this, the 
 G3Sophagus enters just where the three first cavities approach each 
 other, here it can open directly into the first or second stomach, but 
 instead of terminating there, it is continued in the form of a groove 
 with prominent lips, which admit of being drawn together so as to 
 form a complete canal, which then constitutes a direct continuation 
 of the oesophagus into the third stomach, but this cavity not having 
 been distended with solid food in the young animal, it merely forms 
 a tube through which the milk passes into the fourth stomach. In 
 the adult animal the same mechanism continues, but here the third 
 cavity having been already distended, receives the bolus after 
 rumination. 
 
 In the ruminants without horns, as the dromedary, the camel, 
 and the lama, a somewhat different but not less beautiful mechanism 
 prevails, fitting them to live in the sandy deserts and arid plains 
 they inhabit. In these animals the paunch consists of two com- 
 partments, the first of which receives the un masticated food from 
 which it is returned to the mouth, moistened by the fluid of the 
 second or cellular compartment. After the cud has been chewed, 
 the food passes along the upper part of the second cavity into the 
 third, and from that to the fourth. When the camel drinks, the 
 water passes directly into the second cavity, and when this is full 
 it flows into the neighbouring cellular compartment of the paunch. 
 In the bullock, the three first cavities are lined with cuticle ; in the 
 camel it lines only the two first, and terminates just within the ori- 
 fice of the third, the surface of which has a faint appearance of 
 honey-comb structure. From the comparative view which has 
 been taken of the stomach of the bullock and camel, it appears, that 
 in the bullock there are three cavities formed for the preparation of 
 of the food, and one for its digestion. In the camel, the two com- 
 partments of the first cavity answer the purposes of the two first 
 stomachs of the bullock ; the second is employed as a reservoir for 
 water only ; the third is so small and simple in its structure, that it 
 is not easy to ascertain its particular office, whilst the fourth is that 
 in which the process of digestion is accomplished. 
 
 As a general rule, it may be stated that the intestinal canal is 
 long, large, and sacculated in the herbivorous tribes, and short, 
 straight, and without sacculi, in the carnivora. Some remarkable 
 exceptions, however, present themselves, for instance in makies, 
 
VERTEBRATA. 81 
 
 mice, and shrews which are purely frugivorous, and in sloths, 
 which live on vegetable food, the intestine measures only about 
 three times the length of the body; whilst in the porpoise and seal, 
 which live on animal food, it measures in the former 11 times, and 
 in the latter 28 times the length of the body. But this apparent 
 anomaly is explained by recollecting that the caecum plays a com- 
 pensating part with respect to the other portions of the alimentary 
 canal, indeed the researches of the Heidelberg professors authorise 
 us in believing that it acts the part of a second stomach, and that 
 where the latter is simple, the coecum presents a complex and 
 highly developed condition, and vice versa. Hence by a reference 
 to the highly developed coecnm and vermiform appendix of the 
 rodentia, we are enabled to reconcile their simple form of stomach 
 with their herbivorous food. In the elephant, the small intestine 
 measures 3S feet, the colon and rectum 20£ feet, and the coecum 1£. 
 In the camel, the small intestine is 71 feet, the colon and rectum 
 56, and the coecnm 3. The intestine is 10 times the length of the 
 body in the horse, and 28 times in the sheep. In an ornitho- 
 rhynchus 17£ inches long, the small intestine measured 4 feet 4 
 inches, and the colon and rectum 1 foot 4 inches. In this animal, 
 the rectum, urinary, and genital organs terminate in a cloaca, as in 
 birds and amphibia. 
 
 The solidungulous pachydermata masticate their food before it is 
 swallowed, therefore they do not ruminate, and require but a simple 
 digestive stomach ; but they have the same narrow lengthened form 
 of intestine, and a capacious sacculated coecum and colon. The 
 liver is largest in the cetacea and those animals that dive or burrow ; 
 smaller in the herbivora, and least in the carnivorous tribes. There 
 seems to be no general law for the presence or absence of the gall- 
 bladder in mammalia more than in birds and fishes ; it is for the 
 most part wanting in the herbivorous species, as the deer and 
 the camel ; it is also absent from most of the rodentia and pachy- 
 dermata ; and here the hepatic duct is generally much dilated, as in 
 the horse and elephant. In the otter a similar dilation exists in 
 conjunction with a gall-bladder. It is remarkable that all the 
 mammalia which want this reservoir, except the porpoise, are 
 phytophagous. 
 
 In the course of my dissections during my pupilage at the college, 
 I, together with my esteemed friend, Surgeon Bewley, of Moate, met 
 with a female subject about nine years of age, in which this recep- 
 tacle was absent. I invited the attention of Dr. Houston to this, I 
 believe, unique anomaly, who has prepared and deposited the 
 biliary apparatus in the museum of the college. 
 
 The spleen is long, flat, and attached to the paunch in the rumi- 
 nantia, narrow and lengthened in the carnivora, and in the porpoise 
 it consists of several portions. The pancreas is long, flat, and 
 attached to the right end of the first stomach in the cetacea, in other 
 mammalia it is longer, and often divided into several portions, its 
 8 — g evers 6 
 
82 
 
 duct, which is double in the elephant, usually opens separately into 
 the duodenum. 
 
 RECAPITULATION. 
 
 1. A digestive cavity is the most universal organ in animals, and 
 exists in all, with the exception of some of the monads. 
 
 2. Masticating, salivary, and biliary organs are found in the 
 higher radiata. 
 
 3. All these parts are more highly developed in the articulata, 
 and one or two gall-bladders are present. 
 
 4. There has been no gall-bladder found in the mollusca. 
 
 5. The stomach receives the biliary and pancreatic fluids in all 
 the invertebrata. 
 
 6. The invertebrated animals possess no portal circulation. 
 
 7. In the vertebrate the alimentary canal always swells out into 
 a gastric enlargement. The tributary organs are large and conglo- 
 merate, and the salivary glands are rarely absent. 
 
 8. The duodenum receives the biliary and pancreatic secretions, 
 and there are no teeth found in the stomach. 
 
 9. As a general rule the alimentary canal is larger and longer in 
 the vegetable-eating animals, than in those that live on flesh. 
 
 10. Fishes have a simple form of alimentary canal, their teeth are 
 often numerous, as in the pike, rarely absent as in the sturgeon, 
 their salivary glands are rudimental, or entirely wanting, and their 
 whole canal often measures but half the length of the body. 
 
 11. The digestive apparatus undergoes interesting changes during 
 the metamorphosis of the frog, &c. 
 
 12. The teeth are absent in birds, and their place supplied by bill 
 and gizzard. 
 
 13. The crop is double in the pigeon, single in the fowl, and 
 absent from the goose. The gizzard is thick and powerful in the 
 granivorous, but thin and membranous in the carnivorous species, 
 and the great intestine terminates in the dilatable rectal vestibule 
 which receives the openings of the ureters, of the oviducts, or vasa 
 deferentia, and of the Bursa Fabricii. 
 
 14. The teeth are greatly modified in the mammalia, being 
 rarely absent, as in the man is or pangolin, the myrmecophaga and 
 the echidna. 
 
 15. The digestive system is most complex in the herbivorous 
 ruminantia, and most simple in the carnivora ; in the latter the 
 food requires but little elaboration, hence the form of the teeth, and 
 the great strength of the jaws are admirably adapted for seizing and 
 tearing their living prey, here also we have a simple stomach, and 
 a short intestine, without any provision to retard its contents. In 
 the ruminantia, on the contrary, the jaws are elongated, and admit 
 of free lateral motion with flat grinding teeth, the stomach is com- 
 plicated, and the intestine long and sacculated ; in fact all things 
 
ABSORBENT SYSTEM. 83 
 
 conspire to ensure perfect comminution of the food, retardation of 
 its passage, and a due absorption of its nutritious particles. 
 
 CHAPTER XII. 
 
 ABSORBENT SYSTEM. 
 
 Although Monro, Poli, Sheldon, and Carus, have described chy- 
 liferous vessels in many of the invertebrated classes, their existence 
 in these animals has not yet been satisfactorily proved, and it is more 
 than probable that their function is performed by the veins, the white 
 blood of which resembles the chyliferous fluid of the vertebrata. 
 The chyle varies much in its composition and properties in the 
 various tribes of vertebrated animals, and even in the same animal 
 according to the sort of food it lives on, being of a pinkish tint, with 
 abundance of crassamentum in the different animals which subsist 
 on nutritious animal food, while it is limpid and pale, with a great 
 proportion of serum in the inferior animals. The chyliferous, like 
 the other systems of the body, presents different grades of develop- 
 ment in the different vertebrated classes. Thus, in fishes the 
 vessels seem to consist of a single tunic, destitute of valves, and 
 without conglobate glands ; they form two strata of vessels between 
 the coats of the intestine, and carry a limpid fluid to the recepta- 
 culum chyli, from which one or two thoracic ducts lead to the 
 jugular veins or other branches of the cavee. The lymphatics and 
 lacteals communicate frequently with one another, and with the 
 neighbouring veins, and when injected they present a beaded ap- 
 pearance owing to the presence of rudimentary valves. 
 
 The chyliferous system in the amphibia is the same as in fish, 
 but in the reptilia it presents a higher degree of formation in the 
 existence of valves, and the milkish appearance of the chyle, the 
 place of glands is still supplied by the convoluted condition of the 
 vessels as in fishes ; here also, two or more thoracic ducts, fre- 
 quently communicating, pass to the jugular or subclavian veins, or 
 the angle between them, previously receiving the lymphatics from 
 the head, neck, and arms. In the tortoise, the anastomoses of the 
 thoracic ducts nearly conceal the trunk of the aorta. This system 
 presents a somewhat higher grade of development in birds, both 
 sets cf vessels being more numerous and distinct, the valves are 
 more abundant, but yet admit of the passage of fluids from trunks 
 to branches. Glands appear now for the first time, in connection 
 with the lymphatics, but not with the lacteals. Two thoracic ducts, 
 having but few anastomoses, terminate by several openings at the 
 junction of the jugular and subclavian veins. 
 
 In the mammalia the absorbent system is better developed and 
 
84 EVERS'S COMPARATIVE ANATOMY. 
 
 mora distinct from the sanguiferous than in any of the preceding 
 classes, as manifested in the sanguineous characters of the chyle, 
 the elaborate structure of the vessels, the perfect condition of their 
 valves, the increased number of conglobate glands, and the unity 
 and distinctness of the thoracic duct. Sometimes this duct is 
 double, as in the dog, and sometimes its branches open into the vena 
 azygos, as in the hog. Occasionally its trunk divides, and having 
 enclosed a narrow elongated space, called insula Halleri, the 
 branches again unite. The mesenteric glands are of great magni- 
 tude in the cetacea, more detached in the pachydermata, and grouped 
 into a mass, named pancreas Assellii, in the carnivora. 
 
 RECAPITULATION. 
 
 1. Lymphatics have been described, but not saticfactorily demon- 
 strated, in the invertebrata. 
 
 2. No conglobate glands have been found in fishes ; their absorb- 
 ents are thin, convoluted, and furnished with rudimentary valves, 
 and occasionally two thoracic ducts exist. 
 
 3. This system is the same in amphibia as in fishes, but in the 
 reptilia the valves are more perfect. 
 
 4. In birds the absorbents are very numerous, the valves still 
 more perfect, and glands for the first time met with. 
 
 5. In mammalia the entire system is marked by a higher type of 
 formation : the thoracic duct is sometimes double as in the dog, 
 and occasionally opens into the vena azygos as in the hog. 
 
 CHAPTER XIII. 
 
 SANGUIFEROUS SYSTEM IN THE INVERTEBRATA. 
 
 The systemic, or red-blood circulation was discovered in the 
 higher animals by Harvey, in 1619; and by the researches of 
 modern comparative anatomists, it has been found to have a much 
 more extended existence ; there is a considerable number, however, 
 of the cycloneurose classes of animals, in which no distinct vascular 
 system has as yet been detected. The first appearance of it which 
 we observe in the lower animals, as in the earliest condition of the 
 human embryo, consists of vessels alone, through which the fluids 
 move in a circle, like the colourless blood in the cells of a plant. 
 In the asterias, echinus, and holothuria among the echinodermata, 
 a large vessel, in the form of a ring, surrounds the commencement 
 of the alimentary canal, from which the systemic arteries are 
 derived ; the systemic veins send branches to the gills, from which 
 the blood is returned by one large vessel to the heart. 
 
SANGUIFEROUS SYSTEM IN THE INVERTEBRATA. 85 
 
 Diplo-neura. — In the earth-worm two vessels, one above and the 
 other below, extend the entire length of the body; they communi- 
 cate by several cross branches, and join at their extremities, where 
 small dilatations are observable, supposed to aid in propelling the 
 blood, which moves in opposite directions. The large vessels of the 
 annelida are endowed with a contractile power, and in insects, 
 spiders, and the lower species of Crustacea, large dilatations occur, 
 capable of considerable contractility. 
 
 In the leech, hirudo vulgaris, the two principal vessels are placed 
 on the sides, and lesser ones above and below, all anastomosing 
 freely by transverse branches ; of these the superior longitudinal 
 and the inferior transverse only pulsate. It is the opinion of 
 Miiller that the lateral vessels alternately empty themselves from 
 behind forwards ; and others state that the blood is moved forwards 
 in the upper vessel and backwards in the lower. 
 
 The arachnidans, which breathe by means of trachae, seem to have 
 a dorsal vessel only, without any ramifications. Those, on the 
 contrary, which possess branchial lungs, have a well developed cir- 
 culatory apparatus. The blood leaving the heart by the arteries is 
 distributed to all parts of the body ; having become venous it is 
 returned to the pulmonary branchiae by sinuses which supply the 
 place of veins, and having undergone arterialisation, it is returned 
 to the heart by the branchio-cardiac vessels, again to be propelled 
 through the arteries. 
 
 In the higher Crustacea the heart consists of two sinuses and a 
 ventricle ; from the latter, in the stomopoda, six vessels arise which 
 distribute the blood to the eyes, liver, antennas, (fee. This fluid 
 is next returned to venous sinuses in the neighbourhood of the 
 branchiae, through passages without any apparent parietes ; the 
 arterialised blood is brought from the branchiae to the sinuses of the 
 heart by vessels named branchio-cardiacs, from which it is received 
 by the ventricle and sent into the arteries issuing from it, each of 
 which is provided with a valve at its origin. 
 
 Cyclo-gangliata. — The greater number of the animals which 
 compose this class are aquatic, and enjoy a branchial respiration. 
 In the ascidiae the heart is very simple, consisting merely of a thin 
 membranous ventricle destitute of valves. The conchifera have 
 two auricles and a ventricle; the gasteropoda and pteropoda possess 
 a strong auricle and ventricle provided with valves. In the cepha- 
 lopoda there is an aortic heart, and two branchial hearts, or dilata- 
 tions ; in these animals, the blood having been carried to the system 
 by the arteries is returned by the veins to the branchial fringes ; in 
 some bivalves, however, a portion of it is sent direct to the heart 
 without passing through the respiratory organ. In the gastero- 
 podous and other mollusca the rectum passes through the ventricle. 
 
86 EVERS'S COMPARATIVE ANATOMY. 
 
 CHAPTER XIV. 
 
 SANGUIFEROUS SYSTEM IN THE VERTEBRATA. 
 
 In the greater number of the invertebrate animals which we have 
 hitherto examined, the heart and principal artery were placed above 
 the alimentary canal and the chief part of the nervous system ; but 
 in the vertebrate classes the converse order obtains, the heart 
 being below the alimentary tract; in the former division the blood 
 generally arrives at the heart after having passed through the re- 
 spiratory organ, while in the latter the blood flows from the heart 
 to the respiratory organ. In the invertebrate classes, too, there is 
 no vena porta, the liver being supplied by an hepatic artery alone. 
 
 PISCES. 
 
 The gills, which are the only respiratory organs of fishes, are 
 placed in the course of the arterial circulation. The venous blood 
 from all parts of the body is conducted to a single auricle which 
 propels it into the ventricle, from which it is brought by the 
 arterial bulb to the gills, where it is arterialised, and from which it 
 is distributed by the branches of the aorta to all parts of the body. 
 The caudal vein of the eel presents a contractile dilatation, to which 
 Dr. Hall has applied the name of caudal heart; this doubtless 
 assists in promoting the circulation in the caudal branches of the 
 vena cava. Many look upon the heart of fishes and the artery 
 issuing from it as analogous to the right heart and pulmonary 
 artery of higher animals ; but it is much more just to consider the 
 heart as corresponding to the whole heart of the warm-blooded 
 vertebrata, seeing that in some of the reptiles possessing gills, the 
 blood is sent to these organs through the great systemic trunk. In 
 fact, the heart, in these animals, acts at once the part of a pulmo- 
 nary and a systemic heart in propelling the blood not only to the 
 gills, but through all parts of the aortic system. 
 
 Portal-circulation. — The porta in fishes carries to the liver the 
 venous blood from the stomach, intestines, spleen, pancreas, and 
 occasionally from the genital organs, swimming bladder, and tail. 
 In the gadus, however, as in reptiles, the venous blood from the tail 
 and the central parts of the abdomen goes to the kidneys. In the 
 silurus the blood from the posterior part of the body is distributed 
 to the liver and kidneys : and in the carp, pike and perch, to these 
 organs and to the vena cava. This vessel also receives the blood 
 from the testicle, ovary, kidneys, and frequently from the swimming 
 bladder. 
 
 AMPHIBIA. 
 
 The metamorphosis which this class of animals undergoes in 
 passing from the pisciform to the reptilian state, is strikingly 
 
SANGUIFEROUS SYSTEM IN THE VERTEBRATA. 87 
 
 illustrated in their circulatory system : beginning life with the 
 single heart of a fish, and ending it with the double heart of a 
 reptile. In the water salamanders the venous blood which has cir- 
 culated through the body, is returned to a systemic auricle, and 
 having passed through the ventricle, it is received by the bulbus 
 arteriosus, and sent by the branchial arteries to the branchial 
 leaflets. The pure blood is now received by the pulmonary veins, 
 the confluence of which constitute, as in fishes, the descending 
 aorta. 
 
 From this latter vessel a small branch passes off to the rudiment- 
 ary lung, which is afterwards to become the pulmonary artery. As 
 the animal changes from an aquatic to an atmospheric respiration, 
 the branchiag become absorbed, and the lungs proportionally deve- 
 loped. Their arteries experience corresponding changes, those of 
 the former organs diminishing, while those of the latter increase 
 with the growth of the lung. The two veins which return the 
 blood from the rudimental lung also enlarge, and as they arrive at 
 the heart, they undergo a remarkable dilatation, which constitutes 
 the left auricle. Till lately the bi-auricular form of heart was sup- 
 posed to be confined to the caducibranchiate amphibia, as frogs, 
 toads, salamanders, and tritons, but the researches of Owen have 
 proved its existence in the perennibranchiate amphibia also. 
 
 At the same time that the systemic auricle receives the impure 
 blood from the cavae, the pulmonic auricle receives the aerated 
 blood from the lungs. From both of these cavities the blood is sent 
 into, and mixed in, the single ventricle, from which it is sent by 
 the one impulse to the lungs and to the system generally. From 
 this description it is obvious that the blood is but partially purified, 
 mixed blood being sent through the pulmonary arteries, as well as 
 through the aorta and its ramifications. 
 
 REPTILIA. 
 
 In this class of animals we perceive a still higher grade of deve- 
 lopment than was met with in the amphibia; the ventricle is par- 
 tially divided by a septum into two compartments, corresponding 
 in most particulars to the two ventricles of warm-blooded animals. 
 In some the septum is so imperfect as to be incapable of preventing 
 the admixture of the blood derived from both auricles. In others, 
 however, as the crocodile, the ventricles are separated completely, 
 or communicate by a small orifice provided with a valve, which 
 prevents the blood passing from one compartment to the other. In 
 fact the heart in this singular animal is double, as in the higher 
 vertebrata, so that the venous blood returned by the cava? to the 
 right auricle, passes from the right ventricle through the pulmonary 
 artery to the lungs, while the pure blood returned from this organ 
 to the left auricle is directed from the left ventricular compartment 
 through the systemic arteries. The auriculo-ventricular orifices are 
 provided with a muscular valve, and in the crocodile there are two. 
 
88 
 
 It is curious, however, that in the whole of this class the descending 
 aorta is formed by the union of two branches, the right branch 
 arises from the left ventricular compartment, consequently carries 
 pure, or nearly pure blood, which it distributes to the head, neck, 
 chest, and upper extremities. The left branch, on the contrary, 
 arises either from the right ventricular compartment, or what is 
 tantamount to it, from the pulmonary artery. It is obvious, then, 
 that the descending aorta carries a mixed quality of blood to the 
 parts it supplies; but it is interesting to observe, that previous to 
 the junction of the two aortic arches, the left gives off the cosliac 
 axis which supplies the entire alimentary canal and digestive organs 
 with venous blood. In the turtle, lizard, and some serpents, where 
 the septum ventriculorum is imperfect, the pulmonary artery and 
 aorta at once carry mixed blood, and in some of the chelonia, 
 as the tortoise, the existence of ductus arteriosus ensures a more 
 complete mixture of venous and arterial blood. The arteries arising 
 from the ventricles are each provided wtth two valves. 
 
 Portal system. — In amphibia and reptiles, as in fishes, there 
 are two lesser venous circulations; the one belongs to the liver, 
 and the other, which does not exist in birds or mammals, belongs 
 to the kidneys. In some reptiles ail the venous blood from the 
 posterior parts of the body is distributed to the liver and kidneys, 
 while in others a portion is sent to the inferior cava ; this latter 
 vessel also receives the venous blood which has circulated through 
 the kidneys. 
 
 AVES. 
 
 The heart, in this highly organised class of oviparous animals 
 consists of four separate and distinct compartments, and indeed pre- 
 sents a more perfect typical form than is met with in even the mam- 
 malia. Its form is conical, being sometimes short and wide, as in 
 the crane, and sometimes more elongated, as in the emeu. Its 
 situation is mesial, its axis parallel to that of the trunk, and in con- 
 sequence of the partial development of the diaphragm its apex rests 
 between the lobes of the liver. The right auricle seems consider- 
 ably larger than the left, and the auricular portion is distinctly 
 divided from the sinus by two semilunar muscular valves; one 
 attached along the anterior, and the other along the posterior side 
 of the sinus. The venous blood is returned to the sinus of the 
 auricle by an inferior and two superior venas cavae, and it is re- 
 markable that the left superior cava receives the coronary vein just 
 before its termination. The orifice of this vessel is opposite to that 
 of the inferior cava, but separated from it by a semilunar mem- 
 branous valve. The auriculo-ventricular opening is a small oblique 
 slit, and reflux from the ventricle is prevented by a thick strong 
 muscular valve so disposed as to give considerable impulse to the 
 flow of blood through the pulmonary artery. There is a small 
 muscular column at the upper part of the orifice, but it is only one 
 
SANGUIFEROUS SYSTEM IN THE VERTEBRATA. 89 
 
 of the carnese columnse, of which few exist in the ventricle. In 
 the left auricle a mere rudiment of valve is found between the sinus 
 and the appendix. The parietes of the left ventricle are very thick, 
 and the auriculo-ventricular opening 1 is guarded by two mem- 
 branous folds corresponding to the mitral valve in mammalia. The 
 pulmonary artery and aorta are provided at their origins with three 
 semilunar valves, those of the former vessel being thicker and 
 stronger than those of the latter. The extremities of these valves 
 will be found by careful dissection to be attached to cartilaginous 
 or osseous points imbedded in the fibrous tunic of the vessels. 
 
 The pulmonary artery having arisen from the right ventricle at 
 once divides into two branches, one for each lung; from these or- 
 gans the blood is returned by two veins, which unite before they 
 reach the left auricle. From the left ventricle arises the aorta, 
 which immediately sends off two branches analogous to arteriae 
 innominatae, for the supply of the head and wings. It may be 
 observed that birds possess no palmar arches, nor, strictly speaking, 
 a radial artery. The cerebral, orbital, temporal, and spermatic 
 arteries are remarkable for their free and plexiform anastomoses. 
 But of all the arterial plexuses, that of the organ of incubation 
 requires special notice. It is formed by branches from the posterior 
 thoracic, abdominal, cutaneous, and ischiadic arteries, immediately 
 under the integuments of the abdomen. This plexus becomes 
 enormously enlarged during the period of incubation. 
 
 The venous system in birds is remarkable for the frequency of 
 its communications, especially one which exists between the united 
 caudal, hemorrhoidal, and iliac veins and the vena porta, by means 
 of which the blood from the viscera and posterior parts of the body 
 may flow either into the cava or porta, a disposition obviously de- 
 signed to guard against congestions: as yet it is a question con- 
 cerning which contradictory opinions prevail, as to whether the 
 branches of the pulmonary artery extend to the air-cells distributed 
 over the body, or whether the blood in the systemic capillaries un- 
 undergoes any change tending to its purification in the parietes of 
 these cells. 
 
 MAMMALIA. 
 
 The form of the heart, and the distribution of the blood vessels in 
 the whole of this class so closely resemble the human type, that it 
 becomes necessary to notice only a kw individual peculiarities ; in 
 the dugong and rytina for instance, among the cetacea, the heart is 
 cloven by the deep separation of its two ventricles, and the orifice 
 of the inferior cava is guarded by a fleshy Eustachian valve, which 
 is wholly absent in the lion, the bear, and the dog. In the mono- 
 tremata, the marsupiata, the porcupine, and the elephant, the right 
 auricle receives one inferior and two superior cavae as in birds, and 
 the coronary vein terminates in the left superior cava. In the 
 ourang-outang and the mole, only, is the apex of the heart inclined 
 
90 EVERS's COMPARATIVE ANATOMY. 
 
 to the left side as in the human subject. In the upper part of the 
 substance of the left ventricle of the pig, the stag", and other bisulea, 
 are two small flat bones, cruciformly disposed in the stag, they are 
 formed about the third year of the animal's life, and are but slightly 
 developed in the female. It has been generally supposed that the 
 foramen ovale and ductus arteriosus remain permanently open in 
 seals, otters, and cetaceans, and although the dissections of Cuvier, 
 Home, Blumenbach, and T. Bell, go to prove that they have 
 remained unclosed in a few instances, still we must look upon these 
 as exceptions, admitting, however, that these passages continue 
 longer pervious in these diving animals than in other mammalia. 
 
 As regards the arterial system some remarkable peculiarities are 
 observed in the branches arising from the arch of the aor^a, thus 
 in the horse, the camel, and many of the long necked mammalia, 
 this great trunk just after its origin divides into two branches, one 
 becomes the descending aorta, the other ascends vertically and 
 divides into a right innominata, a left subclavian and a left carotid, 
 which latter appears in direction the continuation of the trunk. In 
 the elephant there is but one coronary artery, and both carotids 
 arise by a common trunk between the two subclavians. 
 
 The dolphin has an innominata on each side, this constitutes the 
 type of the cheiroptera. In the marmot and the guinea-pig, the 
 right innominata gives rise to the two carotids, and the right sub- 
 clavian. This also is the type of the order quadrumana, and most 
 of the carnivora. Among the peculiarities in the distribution of 
 arteries we may notice the rete mirabile formed by the internal 
 carotid at its entrance into the cranium in several carnivora and 
 ruminant bisulca ; the plexifonn arrangement of arteries which 
 exists under the pleurae and between the ribs in the cetacea ; and 
 the remarkable anastomosing divisions of the arteries of the extre- 
 mities and tail in the slow moving and climbing animals as the 
 bradypus, myrmecophaga, pangolin, and stenops. This condition 
 of the arterial system doubtless has reference to the peculiar living 
 habits of the animal it exists in, thus in the cetaceans these serpen- 
 tine vessels constitute so many reservoirs for containing arterial 
 blood during the obstructions to the circulation which are almost 
 inseparably connected with the aquatic habits of these mammalia, 
 whilst in those with depending heads, the rete mirabile is admirably 
 calculated to . obviate the injurious effects of sudden influxes 
 to the brain, and in the edentata the arterial divisions alluded 
 to are no less indicated, lest the large trunks of the extremities 
 should suffer from pressure during their long continued action 
 in climbing. 
 
 The plexiform disposition, which characterises so many parts of 
 the arterial system, is no less strikingly displayed in the venous. 
 This is well seen in the tortuous sinuses which receive the inter- 
 costal veins in the porpoise, the vena azygos being absent in this 
 animal. A beautiful distribution of veins constituting the rete 
 mirabile venosum, is met with on the foot of the horse, where these 
 
SANGUIFEROUS SYSTEM IN THE VERTEBRATE. 91 
 
 vessels run in innumerable parallel branches on the anterior surface 
 of the coffin bone. Another peculiarity in this system is presented 
 by the inferior cava, in the porpoise, the seal, the common and the 
 sea otter, consisting in a considerable dilatation of this vessel 
 between the liver and the diaphragm, similar to what is observed 
 in tortoises and diving birds. 
 
 A general review of the vascular system indicates that the heart 
 in its simplest form resembles a vessel endowed with contractility, 
 as exemplified by the vessel-like multiple hearts which constitute 
 the vascular trunks of the annelides, the contractile trunks on the 
 alimentary canal of the holofhuria, the dorsal vessel of insects, &c. 
 In the embryo of the highest warm-blooded animals the heart is at 
 first tubular, and it is interesting to observe, that during the progress 
 of its development it passes through, and resembles the several forms 
 which constitute its permanent type in the adult state of fishes and 
 reptiles, even the clefts in the neck, with the arched divisions of the 
 aortic trunk, which are persistent in reptiles, may be seen in the 
 human embryo at a very early stage of its development, and the 
 ductus arteriosus, which is single in mammalia, but double in birds, 
 is the last of those arches which remains unclosed in the foetus. 
 These arches may be well seen by inspecting the embryo of a bird 
 on the third day of incubation. 
 
 The frequency of the heart's action varies much in different ani- 
 mals, and even in the human subject, from a variety of causes. 
 In a fish it beats in a minute from 20 to 24 
 In the frog, about - - 60 
 
 In birds, from - - 100—140 
 
 In the bat, - - 200 
 
 In rabbits, - 120 
 
 In the cat, - J 10 
 
 In the dog, - - 95 
 
 In the sheep, - 75 
 
 And the horse, - 40 
 
 In the human embryo, - 150 
 
 At birth, - - 130 to 140 
 
 During the first year - - 115 — 130 
 During the second year - 100 — 115 
 
 During the third year, - 90 — 100 
 
 During the seventh year, - 85 — 90 
 
 About the fourteenth year - 80 — 85 
 
 in the middle period of life, - 70 — 75 
 
 In old age, - - 50—65 
 
 RECAPITULATION. 
 
 1. The systemic circulation was discovered by Harvey in 1619. 
 
 2. In the higher radiata a large artery surrounds the beginning 
 of the alimentary canal, in the form of a ring, from which the 
 systemic branches arise. 
 
92 
 
 EVERSS COMPARATIVE ANATOMY. 
 
 3. A distinct heart is first seen in the Crustacea. 
 
 4. In the gasteropodous mollusca, as the snail, the rectum passes 
 through the heart. 
 
 5. There is no portal circulation in the avertebrata. 
 
 6. The heart of a fish consists of a single auricle and ventricle, 
 and the blood of the porta is distributed to the liver and kidneys. 
 
 7. All the amphibia have at first the single heart of a fish, but 
 the caducibranchiate species terminate life with the double heart of 
 a reptile. 
 
 8. The heart of birds consists of four distinct compartments, as 
 in mammalia, but rather more perfect, owing to the existence of its 
 fleshy valves. 
 
 9. The heart of the higher warm-blooded mammalia, even that 
 of man, in the course of its development, represents the several 
 grades which constitute the permanent types of the lower animals. 
 
 CHAPTER XV. 
 
 RESPIRATORY SYSTEM IN THE INVERTEBRATA. 
 
 The respiratory organs are sometimes placed in the interior of 
 the body in the form of lungs sometimes towards its exterior in the 
 form of lamellated, ramified, pectinated, tufted, ciliated, or pin- 
 nated processes, termed gills, or branchiae, and a third form of re- 
 spiratory apparatus is obtained by the development of a system of 
 tracheal tubes, ramified to an exquisite degree of minuteness, and 
 widely spread through all the organs of the body. Animals pro- 
 vided with lungs generally breathe atmospheric air, whilst in those 
 furnished with branchiae respiration is accomplished by means of 
 water. An exception to the former, however, is met with in the holo- 
 thuria; and to the latter, in the terrestial Crustacea. It will appear 
 in the progress of this article that some of the vertebrated animals 
 commence life by a branchial respiratory and terminate it by a pul- 
 monary, and that others enjoy a mixed form of respiratory organ all 
 through. In fact, nature seems almost to have exhausted her 
 ingenuity in the construction and development of respiratory 
 apparatus. 
 
 Cyclo-neura. — In the lowest classes of this division the only 
 respiratory organs detectible are small cilia pervading the entire 
 surface, but so minute as to require high magnifying powers to 
 render them visible. The tentacula and the whole surface of the 
 body are subservient to the function of respiration in the polypifera. 
 In the asterias and sea-urchin among the echinodermata, the water 
 passes into and out of the cavity lined by peritoneum, in which the 
 viscera are lodged. In the holothuria the water is alternately re- 
 
RESPIRATORY SYSTEM IN THE INVERTEBRATA. 93 
 
 ceived and emitted from a tube which is ramified in an arborescent 
 manner, with terminal cellules. 
 
 Diplo-neura. — The highly vascular skin of the entozoa performs 
 the function of respiration — in some, through the medium of water ; 
 and in others the blood is oxygenated on the mucous surface of the 
 animals they infest. In the cirrhopoda respiration is performed by 
 the arms and by the leaf-like fringed membranes attached to the 
 anterior part of the sides of the body. The surface of the body is 
 in general the seat of respiration among the annelida, but in the 
 lumbrici, nereides, and hirudines respiration is in part effected by a 
 series of minute membranous sacs under the skin of the abdomen, 
 each having a separate external opening. Respiration is aerial in 
 the greater number of insects, the air being received through a 
 number of stigmata, and carried by the tracheae in some cases into 
 vesicles, and in others into longitudinally ramifying trunks. 
 
 Many insects in their larval state breathe by means of branchiae 
 in the water, and some in their perfect condition breathe water, 
 although they have an internal tracheal apparatus ; from the water 
 in these branchiae the air is separated, and passed in the gaseous 
 state through the ramified tracheae. There is a very curious fact 
 connected with the eristalis, this disgusting insect has the last ring 
 of its body elongated into a membranous tube, within which there 
 is a second horny tube, which the animal can extend to the surface 
 for the purpose of respiration, whilst it lives at the bottom where it 
 procures its food in the filth of sloughs, sewers, and stinking privies. 
 The tracheary aracknida resemble insects in their tracheal tubular 
 respiration, whilst the respiratory organs of the pulmonary arachnida 
 consist of small sacs opening externally, and situated at the under 
 surface of the abdomen. Both sets of organs are enjoyed by the 
 segestria and dysdera. In tracing the progress of development of 
 the respiratory apparatus in the higher Crustacea, as the astacus 
 fluviatilis, it will be found to present four principal periods ; lstly, 
 that which precedes the appearance of this apparatus ; 2dly, that in 
 which the branchiae are not distinguishable from the organs dedi- 
 cated to locomotion or mastication ; 3dly, that characterised by the 
 transformation of these into organs wholly dedicated to respiration, 
 and distinct from the extremities ; and 4thly, that during which the 
 branchiae sink inwards, and become lodged in the branchial cavities. 
 
 By reviewing the respiratory apparatus in the different groups of 
 crustaceans, it will be found that the several stages of development 
 of the higher orders constitute the permanent types of the lower 
 series ; thus, to the first stage of organisation belong the greater 
 number of the entomostraca and copepoda ; to the second, the bran- 
 chiopoda ; to the third, the amphipoda ; and to the fourth the entire 
 order of the decapoda. The greater number of the Crustacea live 
 under water; some, however, as the gecarcini, or land-crabs, con- 
 stantly live out of water, but it is necessary t ! at their ^piratory 
 membrane shall be kept humid, and for this purpose the membrane 
 is thrown into folds in the form of reservoirs for containing water. 
 
94 EVERS's COMPARATIVE ANATOMY. 
 
 Gyclo-gangliata. — The greater number of this division breathe in 
 water, by means of gills, some however, breathe by lungs in the air. 
 The first mode of respiration is enjoyed by the tunicata, conchifera, 
 pteropoda, cephalopoda, and some of the gasteropoda, the remainder 
 of this class breathe atmospheric air, by means of a lung in the form 
 of a large cavity, placed beneath the mantle. A curious circumstance 
 connected with the conchifera is, that the eggs on escaping from the 
 ovary, are deposited between two layers of the branchial membrane, 
 where they increase in size and undergo incubation. 
 
 CHAPTER XVI. 
 
 ORGANS OP RESPIRATION IN THE VERTEBRATA. 
 PISCES. 
 
 This entire class is covered with branchiae, by means of which 
 they abstract the free oxygen contained in the water. In the sharks 
 and rays, and in all the osseous fishes there are four gills on each 
 side, supported by as many branchial arches of cartilage or bone, 
 connected to the os hyoides. 
 
 Each gill consists of a double series of lance-shaped lammellae 
 closed in by a movable cover, operculum. Generally there is but 
 a single opening for the passage of the water, but in some 
 instances, especially among the cartilaginous fishes, there are 
 several. In consequence of the swimming bladder of fish being 
 supposed by Cams, Blumenbach, and many others, to be subservient 
 to the purposes of respiration, it merits some notice in this place. 
 
 This organ, which is sometimes divided by a septum, as in the 
 genus cyprinus, and sometimes absent, as in the pleuronectes, 
 Jophius, and mackerel, is placed in the abdomen, close to the spine, 
 and below the kidney ; consists of an internal vascular lining 
 membrane, a strong fibrous tunic, and a partial investment of peri- 
 toneum. In fresh-water fishes, it has been found to contain nitrogen, 
 and in salt water fishes, chiefly carbonic acid gas. From its 
 anterior part a canal, ductus pneumaticus, passes forwards and 
 opens into the oesophagus, except in the sturgeon where it 
 opens into the stomach. This duct is double in the cod, in the 
 carp it possesses valves so disposed as to admit of the egress, but 
 prevent the ingress of air; it is absent in the sciura, cobitis, burbot, 
 and others. When we consider that this organ is largest in such 
 fishes as swim with greatest velocity, and wanting in those where 
 large fins or a powerful tail compensate for its absence, we are dis- 
 posed to agree with those who regard it as an organ of progressive 
 motion. 
 
ORGANS OF RESPIRATION IN THE VERTEBRATA. 95 
 
 AMPHIBIA. 
 
 Progs and salamanders in their tadpole state, breathe by gills, 
 which during the earliest periods of their existence are placed ex- 
 ternally; they also possess rudimentary lungs, which become deve- 
 loped as the animals change from the aquatic to the aerial respira- 
 tion. The perennibranchiate amphibia, as the proteus, siren, and 
 axolotl also possess both sets of organs, and retain them through 
 life, but here the lungs always present the rudimentary type, and 
 it is even doubted whether they subserve at all to the function of 
 respiration. In these as well as in the larval condition of the 
 caducibranchiate genera, the pulmonary organ is in the form of a 
 mere sac, and it is only during the metamorphosis that it assumes 
 the cellular character. In the adult state of all the higher orders 
 of amphibia respiration is accomplished in a manner different from 
 all other air-breathing animals, viz., the mouth being fully distended 
 by the air which enters through the nostrils, these passages together 
 with the pharyngo-oesophageal are closed, the mouth then suddenly 
 contracts by the action of the surrounding muscles, and the air is 
 forced by an effort of deglutition through the glottis and trachea 
 into the lungs. Hence, one of the most effectual ways of killing a 
 frog is to keep its mouth open for a short period ; this mode of 
 inspiration is accounted for by recollecting that the ribs are 
 absent in these animals. 
 
 REPTILIA. 
 
 In most of the amphibia the trachea is very short and perfectly 
 membranous. In this class it is somewhat longer, and cartilaginous 
 plates begin to appear in it ; these plates which are first seen in the 
 dactylethra, do not form perfect rings, but present the appearance 
 of perforated lamellse irregularly disposed. In the bronchi of the 
 casciliae, however, the cartilaginous rings are much more complete. 
 In lizards and serpents the lung is a mere cavity with cellular 
 parietes, having perforations which communicate with the neigh- 
 bouring cells. Turtles have a more complicated structure, approach- 
 ing that of warm-blooded animals. 
 
 AVES. 
 
 The lungs, in this class, are confined to the back parts of the 
 cavities of the thorax and abdomen by the serous membrane com- 
 mon to these cavities ; they are of a flattened, elongated form, smooth 
 anteriorly, and grooved posteriorly by the ribs, between which they 
 are impacted ; they are of a bright red colour, and of a loose spongy 
 texture; on the surface of the lungs there are openings through 
 which air passes from the bronchial tubes into large neighbouring 
 cells. In birds not organised for flight these cells, are confined to 
 
96 EVERS'S COMPARATIVE ANATOMY. 
 
 the abdomen, but in others they extend along the neck, and even 
 into the extremities: they also penetrate the cavities and diploe of 
 the bones, a discovery for which we are indebted to Mr. Hunter. 
 This great physiologist injected the medullary cavities of the bones 
 from the trachea: he also tied this tube, and having broken the 
 humerus of a fowl, and the femur of a hawk, he found that the 
 birds respired for a short time through the artificial openings. The 
 proportion in which the osseous system of birds is permeated by 
 air has reference to their respective modes of progression, thus 
 almost every bone in the body admits air in the kite, the hawk, the 
 eagle, and other birds of high flight; and in the hornbill even the 
 phalanges of the toes contain air. Four uses have been ascribed 
 to this extension of the respiratory system in birds — first, to sub- 
 serve the function of respiration ; secondly, to aid by mechanical 
 pressure the action of the lungs; thirdly, to render the body spe- 
 cifically lighter for the purposes of flight : and fourthly, by the dis- 
 tension of the cells in the extremities to assist in maintaining the 
 wings in a state of extension, during long-continued flight. Mr. 
 Hunter supposed it contributed to sustain the song of birds and to 
 give it strength and tone. 
 
 The air passages in birds consist of a superior larynx, a trachea, 
 and inferior larynx, and two bronchi with their ramifications. The 
 superior larynx is situated behind the root of the tongue, resting 
 on the uro-hyal element of the os hyoides ; it is composed of from 
 four to ten bony or cartilaginous pieces, and two pairs of muscles ; 
 thyro-arytenoidea and constrictores glottidis. The trachea is com- 
 posed of a series of bony or cartilaginous rings, which form com- 
 plete circles, with the exception of the two first ; they are closely 
 approximated, and sometimes overlap. Many birds, as the rasores, 
 have no inferior larynx ; in others it presents different degrees of 
 development, thus, in the genus falco there is but one pair of 
 muscles; in the parrot tribe three, and in the insessores, where this 
 organ attains its greatest decree of perfection, five. The rings of 
 the bronchi do not form complete circles, but gradually become 
 smaller, and finally disappear. 
 
 MAMMALIA. 
 
 In the entire of this class there is great similarity in the respira- 
 tory organs, not only to each other but to the human type of for- 
 mation. An epiglottis exists in all, and is divided at its superior 
 extremity in the seal, the hare, and the ant-eater. The larynx in 
 all the mammalia consists of the same parts generally as in man, 
 but occasionally modified in obedience to particular circumstances. 
 Thus, in the cetacea this organ ascends as far as the posterior 
 nares, and communicates with the spouting hole, which opens at 
 the top of the head by a single or double orifice, closed by a fleshy 
 valve in the form of two semicircles. The great size of the larynx 
 in the lion accounts for the powerful and terrific roar of that ani- 
 
ORGANS OF GENERATION IN THE INVERTEBRATA. 97 
 
 mal. The peculiar grunting voice of the pig is produced by large 
 lateral cavities communicating with the small ventricles of the 
 larynx, and the neighing of the horse results from the vibrations of 
 membranous folds connected with the chordae volcales. 
 
 The trachea varies considerably in the length, breadth, and num- 
 ber of its rings; thus, in the seal, the porpoise, the cheiroptera, and 
 several rodentia, its rings form complete circles as in birds ; their 
 number varies from 14, presented by the mouse, to 78, as seen in the 
 seal. In the sloth the trachea descends considerably in the chest, 
 and again ascends to divide into the bronchi. The lungs present 
 very few varietes in the class mammalia. In the cetacea they 
 are remarkable for their elongated, flattened form, and for the free 
 communication of their cells with each other. 
 
 RECAPITULATION. 
 
 1. The respiratory apparatus is very extensive and greatly varied 
 in the invertebrata, in the lowest orders of which it is usually con- 
 fined to the surface of the body. 
 
 2. Respiration is performed by gills in fishes, and in the caduci- 
 branchiate amphibia, during the tadpole state ; in the siren and 
 proteus it is in all probability performed all through life both by 
 gills and lungs. 
 
 3. In birds this system is extended into the bones and into the 
 large cells of the thorax and abdomen. 
 
 4. The organs of respiration throughout the class mammalia, 
 are very similar to those of man. 
 
 CHAPTER XVII. 
 
 ORGANS OF GENERATION IN THE INVERTEBRATA. 
 
 Notwithstanding the varied modifications observed in the organs 
 of generation throughout the animal kingdom, the reproductive 
 function will be found to conform to a few leading types, as the 
 fissiparous, sfemmiparons, oviparous, viviparous, and ovo-vivipa- 
 rous. Fissiparous generation consists in the division of an animal 
 into two or more, similar in every respect to the original being. In 
 this form of generation, which is met with in some of the infusoria, 
 cestoidea, and annelida. the line of separation takes different direc- 
 tions, being transverse in the paramoecuim, and vertical in the vor- 
 ticellae. In gemmiparous generation the young appear as sprouts 
 from the body of the parent: it is more extended than the last, 
 being met with in the polypine and coralline animals, in sponges, 
 cystiform entozoa, and in some acalephae. These two forms of 
 9 — e evers 7 
 
98 
 
 EVERS'S COMPARATIVE ANATOMY. 
 
 reproduction appertain to animals unprovided with special organs 
 of generation. 
 
 In oviparous generation, which belongs to birds, many reptiles 
 and fishes, the egg^ after fecundation, passes through the oviduct 
 from the body of the parent, to be hatched by the influence of 
 external agents. Most mammalia afford examples of the viviparous 
 form of generation, here the ovum remains within the uterus of 
 of the female until it is capable of independent life. Many animals, 
 however, besides mammalia, bear their young alive, examples of 
 which are to be met with among the reptiles, fishes, mulluscous 
 and articulate animals. The last form of generation above alluded 
 to is the ovo-viviparous, which implies the production of living 
 foetus, the ovum being hatched within the body of the parent; 
 but never contracting a vascular connection with the uterus, this is 
 the case with the monotremata, as the echidna, and ornithorhynchus, 
 and also with the monotrematous marsupiata, as the opossum, and 
 kangaroo. 
 
 All the higher classes of animals possess generative organs of 
 two kinds, the co-operation of which, for the purposes of reproduc- 
 tion, constitutes the distinction of sex, into male and female. 
 
 The following table exhibits a view of the reproductive process 
 in the different classes of animals, as given by Dr. Thomson, of 
 Edinburgh, in his matchless article on generation, in the "Cyclo- 
 paedia of Anatomy and Physiology." 
 
 f Parent splits, each part a new ani- 
 mal. 
 J 1. Transverse, 
 f Fissiparous . . \ 2. Longitudinal. 
 3. Irregular. 
 I Parent splits and discharges the 
 
 Non-sexual 
 
 o 
 
 O 
 
 J-H 
 
 youn< 
 
 v Sexual 
 
 I r«o™™^o™„„ $ Budding upon the parent stock. 
 ^Gemmiparous . J Separat b ed Du ds, gemmae, or sporules 
 
 1. On all parts of the body. 
 
 2. On one part or organ only. 
 
 f Hermaphrodite Both sexual organs on one individual. 
 
 1. Self-impregnation. 
 
 2. Mutual impregnation. 
 'Oviparous laying eggs which are 
 
 hatched. 
 1. External fecundation. 
 L Dioecious . . <{ 2. Internal fecundation. 
 
 Ovo-viviparous, eggs hatched within 
 
 the maternal body. 
 .Mammiferous, suckling the young. 
 
 1. Monotrematous. 
 
 2. Marsupial. 
 
 3. Placental or strictly viviparous. 
 
 Prom the above table, it appears that there are a vast number of 
 animals wholly destitute of generative apparatus, and where organs 
 first appear, the animals seem to have the power of pro*J5agati ng by 
 means of ova, without copulation ; in many of the lower animals, 
 
ORGANS OF GENERATION IN THE INVERTEBRATA. 99 
 
 however, as the annelida, the acephalous, and gasteropodous mol- 
 lusca, both sets of organs are placed on the same individual, con- 
 stituting it an hermaphrodite. Some of animals of this class, as 
 the holothuriae, possess the power of self-impregrmtion, whilst 
 others, though possessing double organs, require mutual impregna- 
 tion ; this is the case with the leech, and the common earth-worm. 
 In all the insect tribes the sexes are separate, the male organs being 
 the testicles, the vesiculae seminales, the excretory tubes, and in 
 many, the prehensores.or organs for seizing the female during 
 coitus. The female organs consist of the ovaria, the oviducts, the 
 spermotheca, or receptacle for the male semen, and the ovipositor, 
 an instrument for directing the ova to their proper location at the 
 period of extrusion. 
 
 The generative system of the arachnida and Crustacea is very 
 simple, consisting in the male, of testes and vasa deferentia, and in 
 the female, of membranous ovaries with their excretory ducts. 
 These organs are double in each sex, and quite distinct from each 
 other. 
 
 In the mollusca, the generative organs present some peculiarities; 
 there is but one testicle in the male, and one ovary in the female, 
 each placed on the right side of the neck. The penis is of huge 
 dimensions in the gasteropoda, while in the cephalopoda it is quite 
 rudimentary; but, by way of compensation, the vas deferens is 
 large, convoluted, and muscular. 
 
 When two snails amorously disposed, meet, as Professor Jones, 
 of London, lucidly observes, they begin their blandishments by 
 rubbing the surfaces of their bodies together; after some hours 
 the generative orifice on the side of the neck is seen to dilate, and 
 to display within its cavity three apertures, one from the penis, 
 another from the female organs, and the third from the sac which 
 contains a calcareous quadrangular spike, called the dart; the use 
 of which seems to be to excite to love its sluggish, sleepy, apathetic 
 associate, by pricking the surface of its body; at length his dart is 
 broken, and he becomes in turn the object of a similar attack ; both 
 the reptile cupids having thus exhausted their quivers, and received, 
 each, the love inspiring wound, the other two orifices now dilate, 
 from one the Ions: whip-like penis protrudes, and is received by the 
 vaginal orifice of the other; these phenomena being reciprocal, they 
 mutually embrace and impregnate each other. 
 
100 
 
 CHAPTER XVIII. 
 
 ORGANS OF GENERATION IN THE VERTEBRATA. 
 PISCES. 
 
 In this extensive class, the generative apparatus is comparatively 
 simple, consisting in the female osseous family of two large mem- 
 branous ovaries, with short oviducts, opening in the vicinity of the 
 anus. The ova are generally very numerous, and are deposited in 
 shallow water where they receive the fecundating influence of the 
 male, and the genial heat of the solar rays. In the males the tes- 
 ticles are of great size and composed of a congeries of convoluted 
 tubes; the semen is discharged by the vasa deferentia, and diffused 
 through the water in the neighbourhood of the ova, which are thus 
 impregnated. The presence of a penis in this class is not necessary, 
 seeing that copulation does not occur; to this, however, there are 
 a few exceptions, in which the ova are fecundated prior to their 
 discharge; and in the blennius viviparus, the young are produced 
 alive, being hatched within the oviduct. In these rare instances, 
 the vas deferens protrudes externally in the form of a little penis. 
 In the eel, the lamprey, and many cartilaginous fishes, the ova are 
 suspended in the interior of the abdomen where they receive the 
 influence of the semen, and are discharged by a simple orifice near 
 the anus. 
 
 AMPHIBIA. 
 
 The ovaria of these animals are smaller, but in other respects 
 similar to those of the lamprey ; the oviducts are long and tortuous; 
 they commence by a fimbriated extremity, and previous to their 
 termination in the cloaca they enlarge to retain the ova for some 
 time before expulson. In the frog, the testicles, which are two in 
 number, are placed on the kidneys, and their excretory tubes dis- 
 charge themselves into the ureters. In the majority of instances, 
 the ova are fecundated in exitu by the sprinkling of the semen from 
 the male which is placed on the back of his mate. In the triton, 
 and a few others, the semen diffused through the water passes into 
 the genital organs and produces internal impregnation. The sala- 
 mander alone possesses a rudimentary penis, and in this case, too, 
 the eggs are hatched within the oviduct. 
 
 The reptilia, for the greater part, possess a generative system, 
 the same as the amphibia ; the higher orders accomplish internal 
 impregnation. The males of serpents' are generally provided with 
 two penises which, instead of being perforate, are grooved for the 
 passage of the semen into the cloaca of the female. In the sauria 
 the penis is bifid, and its extremities covered with recurved spines. 
 
ORGANS OF GENERATION IN THE VERTEERATA. 101 
 
 AVES. 
 
 In the males of this class, the testes, two in number, are placed 
 high in the abdomen, beneath the kidneys; they are subject to re- 
 markable variation of size, according to the period of the year their 
 office is required; thus, in January the testicle of the sparrow is 
 about this size, o, and by April it attains the size of a large pea. 
 The vasa deferentia, seldom much curved, pass down and terminate 
 separately on a rudimentary penis in the urethro-sexual pouch. 
 The epididymis is quite rudimentary, and varies much in colour, 
 being black, yellow, or green. Coitus is usually effected simply by 
 an eversion of the cioacag, therefore the intromittent organ is only 
 rudimentary:, in those birds, however, which copulate in water, as 
 the drake, swan, &c, it necessarily attains a larger size. It is 
 sometimes double as in serpents, and is always grooved along its 
 upper surface, for the passage of the semen. The ovarium and 
 oviduct are confined to the left side, they primarily, however, exist 
 on both sides, but rarely continue their development on the ri<rht. 
 A clitoris is present in the females of those species whose males°are 
 provided with a penis. 
 
 MAMMALIA. 
 
 The male organs of generation in this class consist of the testicles, 
 vasa deferentia, penis, urethra, vesiculas seminales, the prostatic 
 and Cowper's glands, and with one interesting exception, supplied 
 by the monotremata, the genito-urinary systems are quite distinct 
 from the digestive. In by far the greater number of mammalia the 
 testicles descend into the scrotum as in man ; in some, however, as 
 the amphibious mammalia, the cetacea, the elephant, and the orni- 
 thorhynchus, they never leave the abdomen, and in others, as the 
 bat, the mole, and the hedge-hog, among the insectivora; the rat, 
 the guinea-pig, the porcupine, and the squirrel, among the rodentia, 
 they descend during the rutting season, and return into the abdomen 
 after it is over. The communication between the tunica vaginalis 
 and the peritoneum remains unclosed in those animals in which the 
 testicles descend, except man, and where these glands occasion- 
 ally pass into and out of the cavity, the communication is very 
 free. The vasa deferentia are very serpentine in those ani- 
 mals where the testicles remain in the abdomen, and in ruminants, 
 the elephant, and especially the horse, they are greatly dilated near 
 their termination in the urethra. 
 
 Vesiculce Seminales.— There seems to be no general law for the 
 presence or absence of these accessory bodies. They are met with 
 ID the camel, elephant, bull, ram, horse, boar, guinea-pig, rabbit, 
 hedge-hog, &c. In these animals they have either no communica- 
 tion, or a very imperfect one, with the vas deferens. In man and 
 the simiae only is the communication free and direct. The prostate 
 
102 EVERs's COMPARATIVE ANATOMY. 
 
 is more constant in its existence than the vesiculae, being found in 
 all orders of the mammalia, excepting perhaps the greater number 
 of the rodentia and insectivora. It is double in the elephant, the 
 camel, the horse, and some others. Compels glands, which are 
 small, and situate behind the bulb of the urethra in the human 
 subject, are large, and often increased in number in other animals, 
 thus in the opossum and kangaroo-rat there are four, and in the 
 wombat, kangaroo, and others, as many as six. They are absent 
 from the greater number of carnivora, ruminantia, and cetacea. In 
 the marsupiata they are covered by a strong muscular stratum, and 
 in the icheneumon, their ducts run forward, and open near the 
 extremity of the penis. 
 
 Penis. — This organ is modified considerably throughout the 
 class. Thus, in the digitigrade carnivora, as the dog and the lion, its 
 two crura are separated by a distinct fibrous septum, which is absent 
 in the cetacea, pachydermata, and plantigrade carnivora. In the 
 cheiroptera, qnadrumana, cetacea, rodentia, and carnivora, with the 
 exception of the hyena, and a few others, the penis is occupied by 
 a cylindrical bone occasionally grooved. Remarkable peculiarities 
 exist in the intromittent organ of the marsupiata; in the opossum 
 the glans is bifid, and has three openings, one for the urine, and 
 two for the semen. In the ornithorhynchus paradoxus the penis is 
 double anteriorly, and in the hystrix, it divides into four glands, 
 each furnished with sharp papillse perforated for the discharge of 
 the semen, but in neither of these strangely organised animals does 
 the urine pass through it, this organ being concealed within the 
 cloaca. The urethra shall be deferred till the consideration of the 
 urinary organs. 
 
 The female organs of generation in the mammalia consist of the 
 vulva, clitoris, nymphse, vagina, uterus, Fallopian tubes, and ovaries. 
 These latter organs are invariably double; in the marsupiata 
 their structure is racemose as in birds, but in all the other genera 
 they are more solid, and approach more or less the human type. 
 The Fallopian tubes present but few peculiarities, except in the 
 echidna and ornithorhynchi, where they experience a dilatation in- 
 feriorly to supply the place of a uterus, and afterwards open sepa- 
 rately into the short vagina, on each side of the orifice of the urin- 
 ary bladder. In the lower orders of mammalia the urethral and 
 sexual passages are blended together, the uterus is elongated in form, 
 and thin in its walls; in the carnivora, ruminantia, pachydermata, 
 and cetacea, a mesial cleft appears, and the cornua are greatly deve- 
 loped ; and in the marsupiata and most rodentia, the organ is 
 divided into two lateral halves, each opening separately into the 
 vagina, which, in the virgin state of the sloth, the ass, the mare, 
 the pig, and the cow, is divided by a narrow ve3itical septum. The 
 external organs of generation afford no striking peculiarities, except 
 in the deficiency of nymphae and hymen. 
 
 From a review of the above details of the generative organs in 
 the marsupial and monotrematous orders, one must expect to find 
 
ORGANS OF GENERATION IN THE VERTEBRATA. 103 
 
 some peculiarity in their mode of generation. In all the other 
 mammalia the ovum is fecundated in the ovary, from which it de- 
 scends through the Fallopian tube to the uterus, in the higher 
 orders about the twelfth day. An intimate vascular connection is 
 now established between the ovum and the uterus, by means of the 
 placenta, and continues till the embryo is fully formed, and as we 
 say, capable of enjoying an independent existence. This consti- 
 tutes the period of utero-gestation, which, in the human subject is 
 ten lunar months, but varies in almost every species of the class. 
 A very different process, however, takes place in the animals above 
 alluded to, thus in the kangaroo, the foetus, small and imperfect, 
 leaves the uterus about the thirty-ninth day after conception, and 
 is lodged by the mother in the marsupium or pouch formed for its 
 reception on the lower part of the abdomen, by a fold of integument 
 in which the mammary gland is placed. Shortly after it reaches 
 the pouch, it is found attached by its mouth to one of the nipples, 
 from which it receives a constant supply of milk ; this is rendered 
 more secure by the gland being covered over by a stratum of mus- 
 cular fibres, which enables the mother to feed the foetus at pleasure. 
 
 The mode of breeding of the monotremaia is as yet involved in 
 some obscurity. The word monotremata means animals with a 
 single outlet from the genito-urinary and digestive organs, called a 
 cloaca; and is applicable to all the marsupiata, but is at present 
 confined to the edentate species of them, as the echidna and orni- 
 thorhynchi. Previous to the late valuable researches of Mr. Owen, 
 the existence of mammary glands in these animals was denied, 
 which, combined with the structure of their ovaries, and their pe- 
 culiar development of uterus, led to the supposition of their being 
 oviparous in their generation. 
 
 Although the structure of their generative organs, the presence 
 of mammary glands, their bearing their young alive, and suckling 
 them, confer on them the ovo-viviparous type of generation, it must 
 be acknowledged they possess many characters in common with 
 reptiles. 
 
 RECAPITULATION. 
 
 1. All forms of generation conform to the fissiparous, gemmipa- 
 rous, oviparous, viviparous, and ovo-viviparous. 
 
 2. These organs are separate and distinct in the insecta, the 
 annelida, and the Crustacea. In the mollusca they are single, and 
 confined to one side. 
 
 3. This system is simple in fishes, and a rudimentary penis oc- 
 casionally present. 
 
 4. Internal impregnation rarely occurs among the amphibia or 
 reptiles. 
 
 5. In birds the size of the testicles varies according to the season, 
 and the penis is often absent. 
 
104 
 
 6. In some orders of mammalia the testicles never leave the 
 abdomen, and in others they descend at certain periods. 
 
 7. There is no general law for the presence or absence of vesi- 
 culae seminales or prostate, the latter is more generally present . 
 
 8. The penis in many instances is furnished with a bone ; in 
 some it is bifid, and in the ornithorhynchus no urine passes 
 through it. 
 
 9. The generative organs and mode of generation are peculiar 
 in the monotremata. 
 
 CHAPTER XIX. 
 
 URINARY ORGANS IN THE INVERTEBRATA. 
 
 The urinary, like the biliary and lachrymal apparatus, consists 
 of four principal parts, each having its peculiar office consigned to 
 it, and all jointly contributing to the same end — namely, the sepa- 
 ration from the blood, and the discharge from the system, of certain 
 decomposed and effete animal and saline matters. The urinary 
 organs, when complete, as they are in the higher orders of animals 
 consist of the kidneys, the ureters, the bladder, and the urethra. 
 
 Although the mollusca secrete urine, and uric acid has been de- 
 tected in the long convoluted caeca of insects, and even through 
 the bodies of cantharides ; yet no perfect urinary system has been 
 discovered in the great invertebrate division of animals. It is more 
 than probable that the function of the kidneys in the majority of 
 instances devolves on the respiratory, the cutaneous, and the biliary 
 systems, together with certain glands, many of which serve not only 
 for the elimination of noxious materials from the system, but as or- 
 gans of defence on the approach of danger; in this latter light may 
 be regarded the acrid secretions of bees, beetles, wasps, and spiders ; 
 as also the ink of the cuttle-fish which has the effect of blackening 
 a considerable extent of the surrounding water, and thus baffling 
 the attacks of its enemies : and among the vertebrata, a striking 
 example is presented by the yagouare of Azara, one of the mephitic 
 weasels of Chili, whose urine is rendered so intensely offensive by 
 the secretion of some adjoining glands, that dogs or other animals 
 which have been sprinkled with it during their pursuit of this crea- 
 ture, are said to have torn portions of their own skins off from dis- 
 gust, notwithstanding careful and repeated ablutions. 
 
URINARY ORGANS IN THE VERTEBRATA. 105 
 
 CHAPTER XX. 
 
 URINARY ORGANS IN THE VERTEBRATA. 
 PISCES. 
 
 The kidneys in this class are long and narrow, sometimes extend- 
 ing the whole length of the abdomen, as in the burbot. They 
 generally present the appearance of forming but a single mass, 
 their separation being only indicated by the presence of the ureters 
 and the cava. The ureters, which arise by numerous fine radicles, 
 soon unite in all the osseous fishes, into a single tube, which forms 
 a heart shaped dilatation previous to its termination behind the 
 anus, in common with the sexual organs. 
 
 Bladder. — This reservoir is absent from all the osseous, and 
 several of the cartilaginous fishes, as the ray and shark, in which 
 the ureters open as in birds, into a cloaca: when it is present as in 
 the lump-fish, it receives the ureters anteriorly, and opens behind 
 the anus in common with the vasa deferentia. 
 
 H 
 
 AMPHIBIA. 
 
 The kidneys are more distinct in this class than in fish. They 
 are greatly lengthened in the aquatic genera, but are much shorter in 
 the frog. The ureters convey the urine to the bladder, which is 
 situated in front of the rectum : in the frog it is of considerable size, 
 its walls are thin, and its fundus presents' two cornua. In the rep- 
 tilia the kidneys afford but few peculiarities, being elongated in the 
 lizard, as in fish, and somewhat oval in the tortoise. The ureters 
 are longer in this class than in the amphibia, and discharge them- 
 selves either into the cloaca or bladder. This organ is absent from 
 the ophidia, and several of the sauria, as the lizard, and the croco- 
 dile. It is very large in the chelonia, as the tortoise, and it is sin- 
 gular, that the ureters instead of going to it, empty themselves into 
 the urethra in front of it, so that the urine has to re-ascend to the 
 urinary reservoir. 
 
 AVES. 
 
 In this extensive oviparous class the kidneys are of great length, 
 extending along the spine, from the lungs to the lower end of the 
 rectum. These organs are relatively larger in birds than in the 
 terrestrial mammalia — a circumstance which is explained by recol- 
 lecting the nature of their integuments, and the little transposition 
 they admit of. They are of small size in the bustard and heron, 
 and their lower extremities are somewhat blended together in the 
 coot. Their structure is remarkable for the absence of cortical 
 portion ; the tubuli uriniferi run to the surface, and by their con- 
 
106- 
 
 fluence form the commencement of the ureter, which descends 
 along the surface of the kidney, and posterior wall of the rectum, 
 and terminates in that part of the cloaca called the urethro-sexual 
 cavity. The space between their termination and that of the rec- 
 tum is large in the owl and many aquatic birds, and is looked upon 
 by some as a rudiment of urinary bladder. 
 
 The supra-renal capsules are small, of a bright yellow colour, 
 and placed on the inner and upper part of each kidney, in contact 
 with the testicle or the ovary. They are erroneously supposed by 
 some to have some functional relation to the generative system. 
 
 MAMMALIA. 
 
 The kidneys are lobulated in the cetacea, seals, otters, bears, the 
 elephant, the ox, &c, as in the human foetus. In the otter each 
 kidney consists of about ten lobules; in the bear of about fifty, and 
 in the seal as many as a hundred and thirty. They present a lobu- 
 lated appearance in many other mammalia during the early periods 
 of existence. The ureters enter the bladder in an oblique direction, 
 a little behind its neck, in all the animals of this class, with the ex- 
 ception of the echidna and ornithorhynchus, in which they open 
 into the urethra near its commencement, so that the urine must ?G- 
 ascend to the bladder, as in the chelonian reptiles. In the mamma- 
 lia generally the bladder lies more loose in the abdomen than in 
 the human subject, owing to its more perfect peritoneal investment. 
 For the greater part it is more muscular and less capacious in the 
 carnivora than in the herbivorous tribes. In the rodentia, however, 
 it is small and fleshy. The shape of the bladder will be found to 
 vary in obedience to age, sex, and species, the younger the animal, 
 however, the more elongated will it be found, and in the human 
 embryo it is cylindrical, tapering towards the urachus above, and 
 the urethra below. 
 
 The renal capsules, like the kidneys, are lobulated in the cetacea, 
 and other aquatic mammalia, and are found relatively very large 
 in the young of animals possessing them. The urethra, as in the 
 human subject, consists of a membranous or muscular, and of a 
 spongy portion, the former receiving the accessory secretions. In 
 the boar and many ruminants these two portions join at an angle. 
 The corpus spongiosum arises by two roots in most of the marsu- 
 piata, and in the kangaroo, the urethra runs through the centre of 
 the penis to its extremity. 
 
 RECAPITULATION. 
 
 1. In the great invertebrate division of animals, the functions of 
 the kidneys seem to be performed by other parts, as the surface of 
 the body generally, and certain glands. 
 
 2. Kidneys exist in all fishes, but a urinary bladder is confined 
 to the cartilaginous tribes. 
 
NAMES OF AUTHORS CONSULTED. 107 
 
 3. Birds have kidneys and supra-renal bodies, but no bladder. 
 
 4. The kidneys are lobulated in the adult state of many, and in 
 the foetal state of most mammalia. 
 
 5. The ureters open into the bladder in all the mammalia, 
 excepting the monotremata. 
 
 LIST 
 OF THE PRINCIPAL AUTHORS CONSULTED. 
 
 Baron Cdvier.— Leeons D'Anatoraie Comparee— Regne Animal— Bv 
 
 Griffith, &c. 
 Linnjeus. — Systema Naturae. 
 Grant. — Outlines of Comparative Anatomy, &c. 
 Lamark.— Histoire Naturelle des Animaux sans Vertebres. 
 Owen.— Clycopaedia of Anatomy and Physiology, &c. 
 Coldstream. 
 Edwards. 
 
 Lawrence. — Zoological Lectures. 
 Bell. — Cyclopaedia of Anatomy and Physiology. 
 Auduin. 
 Todd. 
 Sir C. Bell.— Mechanism of the Human Hand— Bridgewater Treatise. 
 Blumenbach. — Comparative Anatomy, by Lawrence. 
 Deshayes.— Cyclopaedia of Anatomy and Physiology. 
 Harrison. 
 Sharpey. 
 Carus by Gore.— Introduction to the Comparative Anatomy of 
 
 Animals. 
 F. Cuvier.— Histoire Naturelle des Mammiferes. 
 
 Houston.— Descriptive Catalogue of the preparations in the 
 
 Museum. 
 Fyfe. — Outlines of Comparative Anatomy. 
 Thomson.— Cyclopaedia of Anatomy and Physiology. 
 Jacob. 
 Jones. 
 Sir E. Home.— Lectures on Comparative Anatomy. 
 Mueller. — Elements of Physiology. 
 Hunter. — Animal (Economy. 
 Roget— Bridgewater Treatise. 
 Rees. — Cyclopaedia. 
 Blainville.— De l'Organisation Des Animaux, ou Principes 
 
 d'Anatomie Comparee. 
 
CONTENTS, 
 
 CHAP. I. Preliminary Observations, 
 
 Cuvier's Classification of Animals, 
 Grant's Classification of Animals, 
 II. Skeleton in the Invertebrata — General Remarks, 
 
 III. Vertebrata — General Observations, 
 
 — Pisces, 
 
 Amphibia, 
 
 Reptilia, 
 
 Aves, ... 
 
 Mammalia, ... 
 
 Recapitulation, - 
 
 Fossil Bones of Animals, ... 
 
 IV. Ligamentary System, ... 
 
 V. Muscular System in the Invertebrata, 
 VI. Vertebrata, 
 
 VII. 
 VIII. 
 
 Pisces, 
 
 Amphibia, 
 
 Reptilia, 
 
 Aves, 
 
 Mammalia, 
 
 Recapitulation, - 
 
 Nervous System in the Invertebrata 
 
 Vertebrata, 
 
 Pisces, 
 
 Amphibia, 
 
 Reptilia, 
 
 Aves, 
 
 Mammalia, 
 
 Recapitulation, 
 IX. Organs of Sense — Vision, 
 
 Hearing, 
 
 Smell, 
 
 Taste, - 
 
 Touch, 
 
 Recapitulation, 
 X. Organs of Digestion in the Invertebrata, 
 
 XI. 
 
 Development of Teeth, 
 Recapitulation, 
 XII. Absorbent System, 
 
 Vertebrata — Pisces, 
 
 Amphibia, 
 
 Reptilia, 
 
 Aves, - 
 
 Mammalia, 
 
 PAGE 
 
 7 
 . 8 
 
 10 
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 14 
 
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 18 
 
 - 19 
 22 
 
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 38 
 
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 39 
 
 . 40 
 42 
 
 . 42 
 42 
 
 - 43 
 44 
 
 - 45 
 46 
 
 . 47 
 48 
 
 - 48 
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 . 51 
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 . 53 
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 - 63 
 64 
 
 . 65 
 65 
 
 . 65 
 69 
 
 - 71 
 72 
 
 . 73 
 76 
 
 - 77 
 82 
 
 . 83 
 
112 CONTENTS. 
 
 XIII. Sanguiferous System in the Invertebrata, 84 
 
 XIV. Vertebra ta— Pisces, - - .86 
 
 Amphibia, .... 86 
 
 Reptilia, ' - - .87 
 
 . Aves, .... 88 
 
 Mammalia . - . 89 
 
 Recapitulation, --,.... 91 
 
 XV. Respiratory Organs in the Invertebrata, - - - - 92 
 
 XVI. Vertebrata— Pisces, ... 94 
 
 Amphibia, - - . .95 
 
 Reptilia, - - - 95 
 
 Aves, - . . . .95 
 
 Mammalia, ■ . . - 96 
 
 Recapitulation, - . - - - - - 97 
 
 XVII. Organs of Generation in the Invertebrata, ... 97 
 
 XVIII. Vertebra I a— Pisces, . - - 100 
 
 Amphibia, - - 100 
 
 Reptilia, . - - - 100 
 
 Aves, . . . .101 
 
 . Mammalia, - - . - 101 
 
 Recapitulation, - - . ... . - 103 
 
 XIX. Urinary Organs in the Invertebrata, .... 104 
 
 XX. Vertebrata— Pisces, - - . 105 
 
 Amphibia, ..... 105 
 
 Reptilia, - - - - .105 
 
 Aves, . . . - .105 
 
 Mammalia, . - - .106 
 
 Recapitulation, ....... 106 
 
 Names of Authors who have been consulted, - - - 107