ANATOMY, COMPARATIVECOMPARATIVE ANATOMY.

PART I.

ANATOMY OF THE ORGANS OF RELATION. CHAP. I.—COMPARATIVE OSTEOLOGY.

RED-BLOODED ANIMALS only can be said to possess that assemblage of bones denominated skeleton; and as in these the most constant part is the vertebral column, it furnishes the general character of Vertebrated. The shells of the Mollusea and the Crustacea have been generally regarded as a species of internal skeleton; and in the circumstance of affording mechanical support and external protection, they indeed resemble the skeleton of the Vertebrata. But neither in mode of developement nor in chemical constitution can they be regarded as of the same nature. Hence it is only in the vertebrated classes that it is requisite to study the peculiarities of the skeleton.

In general characters the bones of the Mammalia resemble those of the human subject. Like them, they are white, firm, elastic, and incompressible. They consist also of compact and reticular or cancellated tissue. In the lower animals the latter kind of structure is in general coarser and looser than in man; and in the Cetacea especially the cavities are large. In the carnivorous animals the compact structure is exceedingly dense, and gives the bone much greater weight than in other animals. In the Cetacea also the acoustic or lithoid portion of the temporal bone is of a marble hardness.

The bones of the Mammalia may, like those of man, be distinguished, according to their mechanical form, into long, flat, and short bones. Though the first class in general possess a medullary canal, this cavity is imperfect or wholly wanting in the bones of the Cetacea and Amphibia.

The cavities denominated sinuses are much more completely developed in several of the Mammalia than in the human skeleton. In the pig these cavities extend into the occipital bone; in the elephant they not only give the frontal bone extraordinary protuberance, but they extend into the parietal, temporal, and even the occipital bones, and contribute much to augment the volume of the head. In the ox, deer, and sheep, they communicate with the cavity of the horns.

The bones of Birds are in general whiter, firmer, and smoother than those of the Mammalia ; and they consist of a firm, compact substance, which is elastic and hard in the bones of the trunk, and extremely brittle in those of the extremities. With the exception also of some of the thin, flat bones, as the sternum, they consist of thin, compact walls, inclosing large capacious cavities, which contain not marrow, but air, and which communicate by one or more minute holes with the windpipe and lungs. While these cavities, which may be regarded as the most perfect and advanced form of sinuses, diminish considerably the weight of the whole skeleton, by the density and completely cylindrical shape, they rather augment the strength. In the chick, and at birth, the bones are homogeneous and without cavities; afterwards they contain marrow; and eventually this disappears and gives place to air.

The bones of the Reptiles are not remarkable in any respect, unless in being void in general of medullary cavity. The absence of this canal was originally observed by Caldesi, and afterwards by Cuvier, in the tortoise; by Troja in the bones of the frog and toad; and by Carus in those of the turtle. In the crocodile, however, and in several of the lizard family, they are large and distinct. The bones of Reptiles also are less firm than those of Birds and Mammals.

The bones of Fishes are remarkable for great softness, flexibility, and elasticity. Those of the lamprey, shark, ray or skate, and sturgeon family, are soft, flexible, sectile, of a bluish white colour, translucent, and so elastic that a cutting instrument forced into them is speedily re-truded by the resilient nature of the bony matter. From these characters, the bones of these families have been regarded as cartilaginous, and the fishes themselves have been distinguished by this character. (Pisces cartilainci, pisces cnondropterygn.) In the other fishes, the bones, though softer than those of Mammals, Birds, and Reptiles, present a greater degree of firmness and solidity, are whiter and more opaque, and are much less sectile, than those of the cartilaginous division. As in this respect, therefore, they approach the genuine bone of the Mammals, these are distinguished as fishes with osseous skeletons. (Pisces ossei.)

The bones of both classes of fishes consist of a large quantity of gelatine, with a small proportion of phosphate [7:3:2]of lime. In the osseous fishes, however, the latter substance is most abundant. .

The colour of the bones of fishes, though in general whitish gray, is observed to vary in certain genera. In the gar-pike (esox belone), for instance, they are green, and in the viviparous blenny (biennius viviparus), the sand launce (ammodytes tobianus), and two species of labrus (the l. lapina and aeruginosa), they assume a green colour after boiling. The causes of these varieties in colour are unknown.

SECT. 1. OSTEOLOGY OF THE MAMMIFEROUS ANIMALS.

The skeleton of the Mammalia bears a general rĉsem-blance to that of the human subject, in the construction, shape, and disposition of its component pieces. Distinguished, like that, into head, trunk, and extremities, we recognise the importance of the trunk, and especially of the spine, in the different classes of mammiferous animals.

The spine consists of separate vertebrae, which are conveniently distinguished, as in man, into cervical, dorsal or costal, lumbar, sacral, and coccygeal or caudal.

The number of cervical vertebrae is the same in animals with the longest and shortest necks,—in the horse, camel, and giraffe, and in the mole and ant-eater. They are always seven. The only exception is observed in the Ai or three-toed sloth (bradypustridactyla), which has 9 cervical vertebrae (Cuvier); and an apparent exception is presented in the dolphin and porpoise, in which the first two are consolidated into one; and in the cachalot or large-headed whale, in which the last six, sometimes the whole seven, are united or ankylosed. The last six are also united in the ant-eater and manis (Cuvier). Even in this state, however, the traces of the original separation are distinct.

In the ape the cervical vertebrae are distinguished from those of man chiefly by the spinous processes being stronger and not biful, and in their bodies being projected more over each other before, so as to support the head more perfectly. In the Zoophaga the transverse processes of the cervical vertebrae are flattened from behind backwards, and those of the atlas are very large, both for supporting the head and giving attachment to the strong muscles employed in defence, attacking prey, or bearing it off. For the same purpose the spinous process of the axis is very prominent, while the others are short and directed towards the head. In the mole and shrew the cervical vertebrae, which are void of spinous processes, are simple osseous rings, which move easily on each other, probably to facilitate the frequent motions requisite in these animals in burrowing. In the hog the cervical transverse processes are compressed and broad before, so as to appear double. In the elephant the cervical vertebrae have short single spinous processes, and the bodies projecting over each other as in the ape. In the Ruminants the length of the spinous processes diminishes as the neck is elongated. Thus they are almost wanting in the camel and giraffe, in which the arched neck is much retro-flected; and the same peculiarity is recognised in those of the’ horse.

From these facts it results that the length of the neck depends not on the number, but on the longitudinal extent, of the cervical vertebrae.

The dorsal, thoracic, or costal vertebrae are distinguished by forming the central fixed basis of the ribs; and their number depends on that of the latter class of bones, which is very variable. The number of costal vertebrae varies from 11, which is that of the Chinese monkey, commonbat, armadillo, helmet-headed dolphin (delphinus glo-bteeps), and Gangetic dolphin, to 23, which is that of the Unau (Ι3radypus didactylus). The most common number is 12, which is that not only of man, but of the ourang-outang, silky monkey (simia marikina), patas (s. patas), maimon (simia maimon), macaca (simia cynomolgus), baboon (s. sphynx), magot (s. inuus), mandrill (s. maimon), pongo (s. pongo), macauco (lemur catta), vampyre, great and horse-shoe bat, colugo (galeopithecus), shrew, hare and rabbit, agouti, flying squirrel, mouse and field rat, and camel and dromedary. The next most frequent number is 13, which is that of the mole, white bear, civet, the cat tribe (selis), the dog, wolf and fox, the didelphis tribe, the cavy, guinea pig and paca, the mouse tribe, excluding the two exceptions already mentioned, the longtailed manis, the stag, the antelope genus, the goat, sheep, and ox, and the dolphin and porpoise. The number is 14 in the gibbon, coaïta, and weeping monkey, in the howling ape (simia beelzebuľ), the tarsius, the brown bear, raccoon and coati, the weazel genus, the porcupine, hog, and giraffe. It is 15 in the lori, hedgehog and tenrec, in the badger, pangolin, and seal. The number is 16 in the glutton, hyena, ant-eater, American lamantin, and megatherium. In the horse, quagga, and dugong, they are 18; in the rhinoceros 19; in the Indian elephant and tapir 20; and in the Unau or two-toed sloth 23, which, as already stated, is the greatest number yet known.

In the ape family the dorsal vertebrae resemble those of the human subject, but their spinous processes are long, and erect in the macaca and magot. In the bats, instead of spinous processes, which are wanting, there are minute tubercles. The want of these, however, in sundry species, leaves the column comparatively smooth behind. In the proper quadrupeds these processes arc larger, straighter, and stronger, as the head is weighty or supported on a long neck, in order to give attachment to the strong yellow cervical ligament. This peculiarity is very distinct in the giraffe, camel, ox, rhinoceros, and elephant. In the dolphin they are straight, and smaller than those of the loins.

The lumbar vertebrae vary in number still more, perhaps, than the cervical and dorsal; and this variety may occasionally be traced to the greater or less distinctness with which the sacral and coccygeal are distinguished. The smallest number is 2, which is that of the two-toed anteater, ornithorhyncus, and American lamantin; and the greatest 9, which is that of the lori. The most frequent number is 7, which is that of the greater part of the monkeys, the macauco, the great bat (noctula), the hedgehog, shrew, raccoon; the tiger, panther, puma, and cat, in the feline genus; the wolf and fox in the dog; the hare and rabbit; the whole murine genus except the hamster; and in the camel and dromedary. The next number in frequency is 6, which is that of the horse-shoe bat, the colugo (galeopithecus), the white and brown bear, the coati, the weasel genus, the civet, the lion, among the feline, and the dog among the canine genus, the didelphis and cavy genera, the hamster, the stag, antelope, goat, sheep, ox, horse, and quagga. The gibbon, coaïta, Ai, Echidna or Ornithorhyncus hystrix of English zoologists, six-banded armadillo, and dugong, have only 3 lumbar vertebrae; the ourang-outang, pongo, and howling ape, 4; the vampyre bat 4; the hyena, armadillo, Unau, and tapir, 4; the jocko, tarsier, and common bat, 5; the badger and glutton, the porcupine, beaver, pangolin, long-tailed manis, hog, giraffe, gazelle, chamois, and seal, all 5; and the agouti and flying squirrel have 8. j ° 1

In theQüADRUMANA and Zoophaga generally the outer Side of each posterior articular process presents an apex turned backward, so that the anterior articular process of the next vertebra is locked between two eminences, which confine its movement much. Though this apex is found [7:3:3] in the Rodentia, it is there shorter; and the arrangement is wanting in the other tribes. The size of the transverse processes indicates the strength of the loins,—a fact which is evinced especially in the instance of the horse, porpoise, &c.

The number of sacral vertebrae is still more various, even in the species of the same genus. Thus, while in several of the ape genus., in the lori, in the vampyre bat, the colugo (galcopitaccus), the coati, and two of the didelphis, there is one sacral vertebra only, most of the apes have sacra consisting of 2, 3, 4, 5, or 6 pieces; the majority of other animals have 3 sacral vertebrae; the hedgehog, porcupine, guinea pig, paca, hare, tiger, several of the murine genus, the ant-eater, rhinoceros, camel, dromedary, chamois, goat, sheep, and ox, have 4; the elephant has 5; the Ai 6; the Unau Ί ; and in the mole, white bear, and quagga, they also amount to 7. The frequency of the three sacral vertebrae in the lower animals shows that Galen, who ascribes only 3 to the human subject, must have derived this inference from the former.

These vertebrae are in the mammalia narrower than in man, and their direction forms with the spine, instead of receding backwards, a straight line; an arrangement evidently connected with the horizontal position of the former. The shape of the sacrum in the lower mammals is that of an elongated triangle; and it is further remarkable, that in those species which occasionally assume the erect attitude on the hind leg, as apes, bears, and sloths, the width of the sacrum is proportionally greater. The sacral spines, which are short in man and the ape, become longer in the Zoom aga, and form a continuous ridge in the rhinoceros, most ruminants, and especially in the mole. In the vampyre bat the sacrum forms a long compressed cone, the extremity of which is united to the ischial tuberosities, without sustaining a coccyx. The seal has two sacral bones; but the Cetacea, e. g. the dolphin and porpoise, are void both of sacrum and coccyx.

The coccygeal bones constitute the tail of the lower animals, and in many instances they are extremely numerous. The smallest number is 3, which is that of the magot (simia sylvanus, pitheciis, et ìnuus) or Barbary ape; and the greatest yet known is that of the ant-eater, in which they amount to 40, and the long-tailed manis, in which they amount to 45. Next to these may be placed that of the coaïta 32, the baboon 31, the phalangcr (didelphis orientalis') 30, the marmoset (didelphis murina) 29, the pangolin 28, the silky monkey (simia rosalia) and black rat 26, the weeping monkey and howling ape 25; the panther, mouse, dormouse, and elephant, 24; the lion, beaver, water-rat, Norway rat, and field-rat, 23; the flyingcat, puma, cat, dog, marmot, and rhinoceros, 22; the otter, 21; the Chinese monkey, raccoon, civet, hare, and rabbit, 20; the tiger and wolf, 19; the macauco, glutton, marten, fat dormouse, dromedary, giraffe, and quagga, 18; the tarsier, shreŵ, camel, and horse, 17; and other genera and species, without any determinate order, descending so low as to 9, 8,7, 6, and 4. The quilled duckbill (echidna, ornithorhyncus hystrix) has only 12 caudal vertebrae, while the common one (ornithorhyncus paradoxus) has at least 20. The gibbon and vampyre bat are the only mammiferous animals, excepting the Cetacea, in which there are no coccygeal bones. It sometimes happens that a monkey or opossum loses a portion of its tail, when the truncated end is converted into a knotty excrescence, sometimes carious, always different from the taper point of the last coccygeal vertebra; and in this case it is difficult to determine the exact species.

In the Cetacea, in which the absence of pelvis affords no mark to distinguish the lower vertebrae into lumbar, sacral, and coccygeal, those below the dorsal may be regarded as lumbo-cθccygeal ; and their number is estimated by deducting that of the cervical and costal from the total number. The following table, which shows the number of the costal, the lumbo-coccygeal, and the total number of vertebrae, indicates that their number varies much in various genera of this family.
[table]

In general, however, if we reckon the first 2, 3, or 5 vertebrae after the costal as lumbar, it may be said that the caudal vertebrae of the Cetacea vary from 22 or 25, which are the numbers respectively in the lamantin and dugong, to 34, 38, and 42, at which they may be estimated in the dolphin. We shall see that, in the dugong at least, we arc guided in this estimate by the rudimental bones of the pelvis.

The coccygeal or caudal vertebrae of the Mammalia may be distinguished into two kinds; those which contain a canal in continuity with that of the vertebral column and sacrum, and those in which the pieces are solid. The first, which are next the sacrum, have articular, transverse, and spinous processes, distinct in proportion as the animals move their tails. The latter are generally prismatic in shape, diminish in size towards the extremity, and have only slight tubercles for muscular attachments. Animals with prehensile tails, as the American ape (sapajous), have above, at the base of the body of each vertebra, two small tubercles, between which pass the tendons of the flexor muscles. By means of this mechanism these animals can twine the tail round the branch of a tree with sufficient force to support the weight of the body.

The Mammalia with long mobile tails have often two or three small supernumerary bones placed on the lower surface of the junctions of several of the coccygeal vertebrae, from the 3d or 4th to the 7th or 8th. These sesamoid bones give attachment to muscles. In the beaver, which employs its tail as a trowel, the transverse processes are remarkable for size, while the lower spinous processes are larger than the upper ones,—an arrangement which enables it to depress the tail forcibly when it beats the ground.

The shape of the chest in the Mammalia varies in general as the clavicles are present or wanting. In animals provided with clavicles, as the Quadrumana, bats, the squirrel, beaver, mole, ant-eater, hedgehog, and sloth, the shape of the chest approaches to the human, or is conoidal, and flattened before and behind. In those void of clavicles it is compressed laterally, from the smaller incurvation of the ribs; and the sternum makes a remarkable prominence, so that the transverse or intercostal diameter is less proportionally, and the sterno-vertebral· is greater proportionally, than in man and the claviculated animals. In the long-legged animals, as the giraffe and those of the stag kind, this prominence of the sternum is sufficient to give it a keel-like appearance (thorax carinatus). In the carnivorous animals the chest presents its greatest longitudinal extent.

The number and shape of the ribs varies in the different tribes. In number, indeed, the ribs always correspond with that of the costal vertebrae. Thus, in the Quadruma-na,Zoopnaga, Rodentia, Edentata, and Ruminantia, they vary from 12 to 15 pair, with only three exceptions, the glutton, hyena, and ant-eater. In the Chinese monkey, common bat, and armadillo, they are a pair less than in [7:3:4]man. While the quilled duckbill (echidna, ornithorhyncus hystrix) has only 15 ribs, the common duckbill (ornithorhyncus paradoxus) has 17; the horse and quagga have 18, the rhinoceros 19, the elephant and tapir 20, and in the Unau or two-toed sloth they amount to 23, which is the greatest known number. On the whole, the most prevalent number is 13. In the carnivorous animals they are narrow and dense in structure. In the herbivorous they are large, broad, and thick. In the armadillo the two first ribs are large compared with the others. In the two-toed ant-eater, which has 16 pairs, they are so broad that they are imbricated over each other like the plates of a corslet, and render the parietes of this animal’s chest exceedingly solid. In the two species of duckbill (ornithorhyncus paradoxus and hystrix ; echidna of Cuvier), the true ribs, in number 6, consist of two portions—a long or vertebral joined to the spine, and a short or sternal attached to the sternum. These portions are united by cartilage, so as to resemble the ribs of birds. The 9 or 10 false ribs terminate before in broad, flat, oval plates of bone, which are mutually connected by elastic ligaments.

The sternum, which is broad in the ourang and pongo, is narrow in the other species of ape, and consists of seven or eight pieces. In the vampyre and all the bat family it is narrow, but presents before or below rather a prominent azygous ridge or keel (carina), and an anterior extremity, broad on the sides, like a T, for receiving the clavicles. In the mole the clavicular extremity of the sternum is continued before the ribs, and is flat on the sides for receiving the two short clavicles. In the hog the sternum is broad behind and narrow before. In the rhinoceros, horse, and elephant, it is prolonged before and flat on the sides. In the Cetacea it is broad and thin, especially before.

Though the Quadrumana have 8 cranial bones, the sphenoid often consists of two portions, one forming the orbitar wings and the anterior clinoid processes, the other the temporal or large wings, the posterior clinoid processes, and the basilar fossa. The two parietal bones are early united into one in the Chiroptera and the other Zoo- phaga, in which, however, the frontal remains biparted by a middle suture. The temporal tympanum is separated from the rest of the bone by a suture, which is seldom obliterated in the feline, canine, and viverra genera. The temporal tympanum is also separate in the Rodentia, and the frontal ununited. The parietal is united in some, as the hare, the porcupine, cabia, marmot, rat, and squirrel; separate in the mouse, fat dormouse, and rabbit. The frontal and parietal bones of the elephant are early united with the other cranial bones, find form a vault without trace of suture. In the hog, tapir, and ’ hippopotamus, the two parietal bones form one piece, while the frontal bone is biparted; and though in the rhinoceros both are biparted, the frontal is early united into one portion. The sphenoid bone of the animals of this tribe long consists of two pieces, one forming the orbitar wing; the other the temporal wings, which, it is to be further observed, are the smallest, in opposition to their proportional dimensions in man. In the Ruminantsand Solidungula the frontal remains long parted by its middle suture; but the two parictals are represented by a single bony vault. The tympanum is always distinct from the temporal bone. In the seal and walrus the parietal and the frontal consist of two pieces. The lamantin has only one bony arch, representing the two parietal and the squamous part of the temporal bones, while the temporal tympanum is detached from the rest of the bone. In the other Cetacea the. parietal bones are at an early period united to the occipital and temporal bones, so that the five form one solid portion. The auditory or pyramidal bone is always detached from the temporal, and adheres to the cranium by soft parts only. The sphenoid is not only long separate, but consists of several portions.

Though, among the Quadrumana, the cranium oţ the ourang-outang approaches that of man in shape, it differs nevertheless in the connections of the constituent bones. The temporal wing of the sphenoid bone is very narrow, does not reach the parietal, and touches the frontal only by its upper extremity, so that the temporal bone is partly articulated with the frontal. The temporal suture is not imbricated, but serrated. The same mode of connection is observed in the mandrill, macaca (s. cynocephalus), magot, and guenon ( Cercopithecus), or tailed monkey tribe. In the American monkey the temporal wing of the sphenoid touches neither the frontal nor the parietal bones; but the temporal bone is articulated directly with the malar by its flat portion. In the American monkeys the frontal bone does not touch the temporal wing of the sphenoid, and the parietal is articulated to the malar. In the howling ape (simia beelzebuι) the connections are as in man.

The connections of the cranial bones are in the Zoo-PHAGA the same as in man. In the Rodentia the sphenoid is joined to the frontal and temporal, without touching the parietal; and the orbitar and temporal fossae are very small. In the armadillo, pangolin, and sloth, the connections are as in the Rodentia ; but in the ant-eater the parietal bone, continued below the cranium, is united to the sphenoid at the posterior part of the orbito-temporal fossae.

In the elephant, though the cranial bones are at an early period consolidated into one, the auditory is always distinct from the temporal bone. In the hog, tapir, rhinoceros, and hippopotamus, the sphenoid is united to the parietal bone, and its temporal wings occupy a small space only of the orbitar and temporal fossae. The orbitar wings, though larger, appear small externally. The auditory bone, though distinct, is, however, united by its base to the margin of the auditory canal of the temporal bone. The sphenoid of the ruminants is articulated, as in man, with all the cranial bones; but its orbitar wing, which is extensive, is principally concealed within the cerebral cavity, and covered by the orbital part of the frontal bone. In the Cetacea generally, all the sutures which remain after early life are squamous or imbricated.

The outline of the frontal bone in the ourang-outang is more irregular than in man, and the orbitar arches are less surbased. In the American monkeys its outline is triangular, and terminates in a point towards the vertex. In the others of this family (Simia), this bone is almost elliptical, and the orbitar arches arc nearly straight; and in the whole family these arches form, as in man, the anterior border of the frontal bone, in consequence of the narrowness of the root of the nose. In the makis it begins to widen, and the eyes become oblique,—a circumstance which gives their frontal bone a rhomboidal shape.

The frontal bone in the Zoophaga, and in all the subsequent Mammalia, except the Cetacea, forms an irregular prismatic or cylindrical surface with three faces—a superior, bounded before by the muzzle, behind by the cranial convexity and two lateral, descending into the or-bitar and temporal fossae on each side. The hedgehog, mole, shrew, ant-eater, some of the phocae, the morse or walrus, and the rhinoceros, have no proper orbitar arches; and the frontal bone, though broad behind, is contracted and nearly cylindrical between the orbits. In the hippopotamus, the ruminants, and the one-hoofed animals, it enlarges, and forms a vault over each orbit. Lastly, in t ιe Cetacea it is narrow from before backward, resembling a fillet stretched across the cranium, but descends beneath the maxillary bones to form the floor of the orbit.
[7:3:5]

The parietal bones of the ourang-outang differ from those of man only in their temporal margin being nearly straight. Those of the ape are narrower, and become more oblique-angled as the cranium is flattened. Tn the Zoo-PHAGA and Edentata they are almost rectangular. The single parietal of the Rodentia is nearly quadrilateral; but it is sometimes flat, sometimes rounded, sometimes surmounted by a crest. Of the single parietal bone of the ruminants, that of the stag, most of the antelope genus·, the sheep and the goat, is broad, and sends on each side a narrow process into the temporal fossa before the occipital arch; in the camel it is narrower, and bears a longitudinal crest; and in the ox and antilope bubalus it is placed behind the occipital crest, and resembles a fillet surrounding the back of the head transversely. In the Solidungula the single parietal is nearly quadrilateral, and placed before the occipital crest.

The occipital bone in the lower mammalia is remarkable for five characters. 1. The proper occipital surface, instead of being oblique or horizontal, and inferior or basilar, becomes vertical and posterior. 2. The plane of the occipital hole forms with that of the orbits an angle constantly diminishing, becomes parallel to the orbitar plane, and at length crosses it above the head. 3. The plane of the occipital condyles, instead of being transverse and horizontal, becomes oblique, and at length vertical. 4. The basilar or cuneiform process is not only horizontal, but forms with the occipital a right angle. And, 5. The mastoid process, which in man and the ape forms part of the temporal, belongs in the other mammalia to the occipital. In the polar bear, however, the mastoid process constitutes part of the temporal bone.

From the 1st, 2d, and 3d characters, it results that the head of quadrupeds is not balanced on the spine, but is suspended by muscles, tendons, and ligaments, especially the strong cervical, which connects the occipital spine to the spinous processes of the cervical and dorsal vertebrae. This ligament, therefore, though feeble and indistinct in man, is strong, particularly in quadrupeds with heavy head or long neck, in order to counteract the disadvantage of the long lever. It is strongest in the elephant, and is almost wholly ossified in the mole—a condition requisite for the burrowing faculty exercised by that animal.

The temporal bone is naturally distinguished in the •Mammalia into two parts; a flat or proper temporal, corresponding to the squamous part of the human temporal bone, and the pyramidal, acoustic, or auditory, corresponding to the pyramidal or lithoid portion of the human subject. The first only, which is proper to the scull, claims attention here. In the ourang-outang and most of the genus simia it forms a trapezium with the longest side above, and the height of which varies with that of the scull. In the American apes it is smallest in this direction. In the Zoophaga the proper temporal bone is as in the ape. Being narrow in the Rodentia behind, it is a little rounded in the short-muzzled Edentata, the Ruminantia, and Paciiydermata.

The ethmoid is, strictly speaking, the olfactory bone, and shall be mentioned under the organs of sense. The sphenoid, among other offices, may be regarded as the essential ophthalmic bone.

The facial bones of the lower Mammalia differ from those of man; first, in the number of separate pieces; and, secondly, in the form and proportional horizontal extent.

The difference in number consists in each superior maxillary bone being divided into a maxillary bone proper, and an anterior or labial portion; which being interposed between the proper maxillary, are commonly denominated the intermaxillary (ossa intermaxillaria). As it bears also the superior incisors, it is named by Haller the incisive bone (os incisivum) ; but since it is found not only in the ruminants, which, excepting the camel, are void of incisors, but in the Edentata and Cetacea, this denomination is less applicable than the former. It may be doubted whether these should be regarded as additional bones, as they are generally represented by zootomists; for they are in truth merely the incisive or anterior portion of the superior maxillary bones. In other respects, the difference between the human and the animal superior maxillary bone is, that in the former each bone is in one piece, in the latter it is in two. Even in the human foetus the trace of the separation may be recognised; and we have seen it in the human scull some years after birth. Conversely, it is early obliterated in some quadrupeds. Thus, though distinct in the ourang-outang seen by Cuvier, it was not found by Tyson or Daubenton, and is wanting in one preserved in the Hunterian museum. In a young specimen of the jocko also, noticed by Cuvier, no trace of the intermaxillary suture was observed. It appears also to be wanting in the perforated bat, the horse-shoe bat, and the three-toed sloth.

Mutually united on the mesial plane, the intermaxillary bones are united to the maxillary by sutures, which pass from the outer angles of the latter, near the incisive holes, towards the palate, where they intersect. In form and size it varies in the different orders and genera. Small in many of the Zoophaga and the walrus, it is large in the Rodentia, in the hippopotamus, porpoise, and cachalot, and prominent in the wombat. In the duckbill’ it consists of two unciform portions, united by a broad intermediate cartilage.

The peculiarity of the animal face consists in the horizontal elongation of the two jaw-bones. In the monkey tribe this elongation is trifling; and all that is remarked is, that the palate and maxillary bones are more elongated in proportion to their height, and that their anterior part, instead of being vertical, is more or less inclined forwards. The degree of this elongation, which differs in different genera, may be estimated by the acuteness of the facial angle.

The narrowness of the interorbital space is another character of the animal countenance. In the guenon and American ape it is a mere septum ; but in the ourang-outang, magot, and howler, it is larger, by reason of the nasal fossae ascending to this height. From these the face of the Zoophaga is distinguished by the following circumstances. 1. The breadth of the ascending maxillary processes throws the orbits to the sides; 2. these orbitar surfaces form the anterior wall instead of the floor of the orbit; 3. the malar bone is united neither to the frontal nor to the sphenoid bone, and forms only the zygomatic arch and the lower margin of the orbit; 4. the orbit, closed neither behind nor below, communicates freely with the temporal fossa ; and, 5. the palate bones are much elongated and form a considerable space of the internal wall, to which the ethmoid bone does not contribute. In the Rodentia the interorbital space is still larger, by reason of the size of the intermaxillary bones throwing the maxillary backwards and to the sides, where they form the inner orbitar wall, in which the palate bones occupy only a small space. The anterior wall is formed by a process of the maxillary, which contributes to form the zygomatic arch, while the malar is suspended in the middle between the process and that of the temporal bone. Very similar is the face of the elephant, except that the height of the alveoli from the tusks, thrusting the nose upwards, and shortening its bones, alters entirely the expression of the head of this animal.

In the sloth, in which the face is short in proportion to [7:3:6]the scull, the malar bone attached to the maxillary only, is not united to the zygomatic process of the temporal. In the long-muzzled Edentata, in which the face is conoulal, the maxillary bones extend to the orbits, and are scpaiat-ed by a broad lacrymal bone, while a long palate bone forms the inner wall of these fossae. The zygomatic arch, which is interrupted in the ant-eater and pangolin, is completed in the Cape ant-eater and the armadillo. In the tapir and rhinoceros the maxillary bone passes beneath the orbit; and the nasal bones form a sort of vault, which supports in the first animal the trunk, and in the second the horn. . 1 ,

In the Cetacea the maxillary and intermaxillary bones form a sort of flattened beak, distinguished into four parallel bands, of which the maxillary, which are external, alone bear teeth in three genera, provided with the latter organs. The nasal fossa is a vertical opening before the cranium, surrounded before and laterally by the intermaxillary bones. The maxillary ascend in the same manner, and cover that part of the frontal bone which forms the orbitar vault, but do not themselves contribute to the formation of this cavity. The nasal bones are two minute tubercles implanted on the frontal bone above the narrow aperture. The malar is in the shape of a style, suspended by cartilages beneath the orbit; and the latter cavity is completed behind by a process of the frontal, which joins the zygomatic of the temporal bone, and below which the orbitar and temporal fossae communicate.

The direction of the orbits, the shape of their base or facial border, and their relation to the temporal fossa, are important circumstances in the animal face and cranium. In the simiae the angle of the orbitar axes is rather smaller; and the shape of the margin, which is quadrilateral in the jocko, becomes oval in the ourang-outang and American monkeys. The angle of the axes enlarges in the other Mammalia; and the base or anterior margin becomes nearly circular in the Zoopiiaga, Rodentia, Edentata, and Pachydermata ; but the arch is incomplete behind. In the Ruminants and Solidipeda, however, in which it is also circular, the border is complete. In the Cetacea the orbitar vault is semicircular, their axes are rectilineal, and there is no floor.

In the human scull the junction of the malar bone with the frontal and.sphenoid completes the orbit externally, and prevents it from communicating with the temporal fossa ; and the same arrangement is observed in the simiae. In the Carnivora, Rodentia, Edentata, and Pachydermata, however, in which the malar bone is united neither to the frontal nor the sphenoid, the orbit is not only incomplete on the external posterior border, but communicates freely with the temporal fossa. In the Ruminants is observed an arrangement intermediate between that of the Quadrumana and that of the Carnivora. The malar bone, united to the frontal, completes the orbitar ring; but as it is not united to the sphenoid, it allows the orbits and temporal/ossAE to communicate. The orbit of the mole is so superficial, that it can scarcely be said to exist.

The lower jaw of the mammiferous quadruped differs from that of man chiefly by the following circumstances. The triangular flat surface which constitutes the chin,.and which is most distinct in the Caucasan race, begins to become faint in the negro, and is altogether lost in the monkey tribe. In the ourang-outang, indeed, the animal character of the lower jaw appears distinct in the vertical convexity of the anterior arch of the jaw, and the retreating of its lower margin. In the lower Quadrumana the anterior maxillary arch is still more retreating, and the maxillary rami form a more acute and elongated angle. These animal characters are still more conspicuous in the Car nivora, most of the Pachydermata, Ruminants, Solidungula, and Rodentia. The ascending ramus also becomes short in the Pachydermata and several of the Cetacea, more so in the Zoophaga, and is almost extinct in several of the Rodentia, for instance the paca, beaver, and porcupine, and the armadillo, ant-eater, and duckbill, among the Edentata. In the Zoophaga, however, in which the prehensile and masticatory muscles are large and powerful, the ramus becomes broad, and its coronoid process is extensive. The angle which the ramus forms with the body of the jaw, and which is almost right in the adult human subject, becomes obtuse in the lower animals, nearly at the same rate at which the rannts disappears; and indeed the transition of the angle into a straight line implies the disappearance of the ramus. This, therefore, is the character in the Edentata and Cetacea, in which there is neither ramus nor coronoid process, after thesie parts have been seen for the last time in the amphibious Mammalia.

When the mammiferous cranium is considered generally, and the relative direction and proportion of the cranial and facial part of the head examined, we recognise more distinctly the characters by which the lower orders of that class arc distinguished from man. This character consists in the position of the occipital bone and hole, the position and direction of the facial bones in relation to the frontal, the elongation of the former, and large size which they present in relation to the cranial.

In the human subject, it has been already observed, the position of the occipital bone is oblique and horizontal, and the plane of the occipital hole is horizontal, while its position is anterior. In most quadrupeds, while the bone assumes a vertical position, the hole becomes posterior, and its plane vertical or oblique, in proportion as the face is elongated. The plane of the occipital hole forms with that of the horizontal a considerable angle, which Daubenton undertook to determine, by drawing one line through the plane of the aperture, and another from its posterior margin through the lower edge of the orbit. (J∕e⅛. de l’Acad, des Sciences de Paris, 1764, p. 568.) In the horse this angle is about 90°, while in the ourang-outang it is only 37°, and in the lemur 47°. In other respects, however, it furnishes an imperfect result, since in most quadrupeds which differ very much it ranges between 80° and 90°.

The direction of the face in relation to that of the< cranium, determined according to the method of Camper,] furnishes more accurate results. While in the human i subject it varies, according to the races, from 70° to 80°, in the ourang-outang it is only 65°; in the American and long-tailed monkeys about 60°; in the macaca and baboon about 45°; and, lastly, in the mandrillo, the most vicious and ferocious of the monkey tribe, only 30°. In some species in which the ear is elevated and the guttural fossa deep, for instance in the pongo and alouate or howler, the small size of this angle does not indicate proportional elongation of muzzle; and to rectify this inconvenience, it is requisite to draw the basilar line of the facial angle parallel to the base of the nostrils. With this modification, however, the Camperian line admits of correct application to the human race and Quadrumana only, in which the frontal sinuses are small and not prominent. In quadrupeds, for instance the carnivora, several of the ruminants, and in the elephant, the frontal sinuses are so large and prominent as to affect the results given by the facial angle very materially. In other orders, again, for instance the Rodentia and the morse, the nose occupies so much space that the cranium is inclined backwards without its walls being free before; and it is impossible to know where the facial line passes. These, therefore, must be measured by the inner surface. Lastly, [7:3:7]in the Cetacea the pyramidal elevation of the cranium above an elongated but flattened face renders the facial line much more vertical than it ought to be. The following measurements show the angle subtended by a line drawn parallel to the base of the nostrils, and another passing by the anterior margin of the alveoli, and touching the convexity of the cranium, whether the point of contact be concealed by the face or not.
[table]

Aware of the imperfect results obtained in this method of measurement, Cuvier proposes to estimate the relative proportion of the cranial and facial part of the head, by comparing the respective areas exhibited by a longitudinal and vertical section of both. In this section the area of the cranium is to that of the face sometimes in a ratio of majority, sometimes of minority, occasionally of equality.

In the European the area of the cranial section is about four times that of the face, excluding that of the lower jaw. In the negro the cranial area remaining the same, that of the face augments about one fifth, whereas in the Calmuck it augments only one tenth. In the ourang-outang the proportion is still less. In the American ape the facial is almost half the cranial area. The ratio is that of equality in the mandrill and most of the Carnivora, except the varieties of short-muzzled dogs, as the pug, in which the facial is rather less than the cranial area. In the Rodentia, Pachydermata, Ruminants, and Solidungula, the facial is larger than the cranial area. Among the Rodentia, in the hare and marmot, it is a third larger; in the hedgehog double; in the Ruminants almost double; in the pig a little more than double; nearly triple in the hippopotamus; and almost four times in the horse. In the morse and elephant the face is rendered large by the height of the alveoli; and it may be regarded as augmenting the organs of the senses. The cranium of the Cetacea is very convex, and the face very flat, and the proportional area of the latter is thereby diminished. The facial area of the dolphin may be a third larger than the cranial.

The outline of the cranial section in the human subject is oval, that of the facial section forms a triangle, with the longest side contiguous to the cranium, and the smallest without, while the angle formed by the latter with the third side or palate is the facial. In the lower animals, this triangle, which may be named the facial, becomes so much elongated, that the cranial side, which is the longest in man, becomes the shortest of the three in the cynocephalus and mandrill, and continues so in the other quadrupeds.

The basin {pelvis') of the Mammalia in general agrees with that of man in forming a part common to the trunk and the lower extremities. It differs, however, altogether in the direction which it takes, which is obliquely backwards, with its anterior opening or brim forwards and downwards, and in the bones being smaller and much narrower; both of which characters are connected with its not being used in the lower animals to oppose the gravitating weight of the abdominal and pelvic viscera,. In the apes, most similar to man, the coxal bones are much elongated; and in the Zoophaga, their superior or ilial part is not much broader than their pubal. In the Ruminants, the Pachydermata, and Solidungula, the ilial portions again become broad; and in the elephant and rhinoceros especially, this width, combined with the length of the ilio-pubal rami and the concave abdominal surface, concurs to give the pelves of these animals the prodigious capacity by which they are distinguished. The pelvis of the amphibious Mammalia differs from that of the Zoopiiaga only in being narrow and elongated, and in the pubis being thrown behind. In the ant-eater, mole, and shrew, the pubal junction is open as in birds; and in the two latter genera, the bones are so narrow that the sexual and urinary organs are placed without its circumference. In the sloth genera, e. g. the Ai and Unau, the pelvis is wide, the cotyloid cavities turned upwards, and the ischial tuberosity is united with the sacrum, so as to convert the ischiatic notch into a hole. This sacro-ischial junction is also observed in others of the Edentata, as the ant-eater and armadillo, and in the phascoloma {didelphis ursina). The marsupial animals present two minute bones, one on each side, connected by movable articulation to the pubis, and which are employed to sustain the mammillary pouch {marsupium) or nipple-bag, in which the young are reared after exclusion from the uterus. These bones, which are distinguished by the name of marsupial {ossa marsupialia), are oblong and flattened. Lastly, in the Cetacea, in which the pelvic extremities are wanting (Plate XXXIV. fig. 2), the pelvis is also so far deficient, that instead of consisting of the sacrum and coxal bones, it is represented by a small bony appendage, suspended in the soft parts on each side of the anus, and which, meeting at angles on the mesial plane so as to form a bone like the letter V, are merely a rudiment of the ischial bones.

The shoulder of the Mammalia generally differs from that of man by the absence or the proportions of the collarbone, and by the shape of the scapula.

The collar-bone exists in the Quadrumana nearly as in man; but it is wholly wanting in the three orders of Ungulata — Pachydermata, the Ruminants, and the Solidungula— and in all the Cetacea. Between these extremes it is found in various forms in the intermediate orders of the Unguiculata. Among the Zoophaga it exists in the Ciiiroptera, especially the bats proper, in which it is strong and large; the Insectivora, as the hedgehog, shrew, and mole genera ; and in the didelphis or opossum among the marsupial animals. In the others of this order, as the bear, raccoon, coati, weasel, otter, dog, cat, and seal, the collar-bone is represented by clavicular bones, suspended among the muscles, touching neither the sternum nor acromion; and in some species it is altogether wanting. The Rodentia may be distinguished into two subdivisions, as they are provided with or void of collarbones. The first comprehends the squirrel, beaver, and mouse, with the helamys, marmot, and aye-aye or cheiro-mys genera. The second consists of the porcupine, hare, and cavy genera, as the guinea-pig and paca, in which the collar-bone is rudimental only, suspended among the soft parts. It exists in most of the Edentata, as the sloth, armadillo, ant-eater, and the gigantic fossil animal named megatherium ; but it is wanting in the pangolin, and was believed to be wanting in the echidna and duckbill till Cuvier demonstrated its existence. In the Cetacea there is no vestige of collar-bone.

From these facts it results that the clavicle exists in all animals, the fore legs of which are frequently or habitually protruded, either to seize, as apes and the Rodentia ; or to fly, as bats; or to dig and burrow, as the mole; or to rake the ground, as the hedgehog and ant-eater. In the mole particularly, the collar-bone, instead of being long, is [7:3:8]a broad, thick, short, quadrangular bone; and while it is connected to the acromion by a ligament, it is articulated to the humerus by a large facette. The collar-bone 'of the echidna and ornithorhyncus is very singular. It consists of a broad central bone, surmounted by two transverse branches spreading out on each side, so as to give the whole bone some resemblance to the letter T, but sinuated so as to make the diverging branches like the Greek υ. In young animals this bone consists of three portions. The two diverging branches are genuine collarbones, and may be regarded as a bifurcated bone; while the middle is supported on the sternum, and has articulated to each side a part of the scapula, corresponding to the coracoid process. The collar-bone, indeed, is a power? ful buttress, which prevents the arm-bone from being thrust too much forward.

Of the shoulder-blade or scapula, which is present in all red-blooded animals with thoracic extremities, and hence in all the Mammalia, the principal point is to remark the varieties which its shape presents. Though in man, most of the Quadrumana, the Chiroptera, and the elephant, the vertebral margin or base of several authors on human anatomy is the longest, it becomes the shortest in most quadrupeds, especially those which, like the Ruminants and the Solidungula, have long legs and narrow chest. In most of them, also, this margin, instead of being straight, is rounded,as in theCARNivoRAandllθDENriA. In theCAR- nivora without collar-bone, the hedgehog and dideiphis, the acromion is less prominent; there is another eminence directed backwards, almost perpendicular to the spine. The coracoid process, also, which is present in the Cm-ROPTEiiA, the hedgehog, and dideiphisgenus, is wanting in most of the zoophagous tribe. In the hare the acromion terminates in a long slender process, rising at right angles and bending backwards, which may be named the recurrent. In the Ruminantsand Solidungula, notonly are this and the acromion, but even the coracoid, wanting. The scapula, again, of the hog and rhinoceros is remarkable for the disappearance of the spine at the glenoid angle; while from its middle proceeds a prominent process towards the costal or inferior margin. In the mole the scapula is long and narrow, like a cylindrical bone, placed parallel to the spine,—an arrangement which, together with the shortness and thickness of the clavicle, already mentioned, is evidently connected with the burrowing habits of this animal. Lastly, in the echidna and ornithorhyncus, which in so many characters of organization approach the Amphibia on the one side, and the Birds on the other, the scapula is a single sinuous bone, attached by one extremity to the sternum and middle part of the clavicular bone, with the other loose; and in the middle an articular cavity, in which the head of the humerus is plaçed, and which evidently corresponds to the glenoid. In this instance, therefore, the clavicle and scapula may be regarded as united into a single bone.

The humerus, which exists in all the animals with thoracic extremities, undergoes considerable variations. In the lower animals generally it is much shorter than in man; and .it is invariably shorter in proportion as the, metacarpus is elongated. Thus, in animals with what is named a cannon bone, that is, one metacarpal, as in the horse and the ruminants, the humerus is so short that it is concealed in the soft parts as far as the cubit. In the Cetacea it may be said to attain its maximum of brevity. In the bat and sloth it is long in proportion to the rest of the body.

The humerus of the mole is perhaps the most extraordinary of all those of the mammiferous animals. Not only is it articulated with the scapula by a small head, but it is connected with a facette of the clavicle by another belonging to the great tuberosity, and between which and the head is a deep pit. Tile crest of the small tuberosity is so large, that it represents a square placed vertically, so that the ĩinea aspena, is above. The rest of the body of the bone, which is very short, is arched above, so that the cubital extremity is directed upwards. From this arrangement it results that the cubit is elevated above the shoulder while the palm is turned downwards,—a disposition necessary for the burrowing habits of the animal.

In the simiae the radius and ulna are arranged as in man, except that in the cynocephalus, mandrill, magot, and guenon, the coronoid process of the ulna is narrower, and the radial facette deeper. In the other Mammalia the ulna very generally disappears or becomes rudimentary only. In the bat family and the colugo {galeopithecus) the ulna is wanting or is represented by a slender style placed below the radius. These animals are therefore destitute of the power of pronation and supination. In the Zoophaga, the radius and ulna, though separate, are void of rotatory motion; and the olecranon is compressed, and continued farther back than in man. In the Paciiy-dermata the radius is before and the ulna behind, and, though distinct, there is no rotation. In several of the Rodentia, for instance the marmot, porcupine, &c. the coronoid process is small, and in others, e. g. the cavy, hare, and mouse family, it is altogether effaced. In the Ruminants the ulna is united immovably to the radius; and in the Solidungula it is represented by an olecranon adhering to the posterior surface of that bone. In the Cetacea, though both bones are present, they are much flattened.

The carpus of the ape genus contains one bone more than that of man, situate between the pyramidal and large bone, and which seems to result from the trapezium being divided into two parts. Conversely, in the Zoophaga, but especially in the dog, cat, hedgehog, shrew, bear, and seal, the scaphoid and semilunar are united into one large bone. Those which have a vestige of thumb, as the hyena and glutton, have the trapezium very small. The mole has not only 9 carpal bones, as the ape, but a large sickje-shaped bone, which is attached to the radial margin of the fore paw, and which gives it the shape proper to the habits of the animal. The toes are further very short. Of the Rodentia, the hare resembles the ape; but in the beaver, marmot, squirrel, and cat, the scaphoid and semilunar make one bone; while in the porcupine the supernumerary bone is between the pisiform and metacarpal of the fifth toe. In the two-toed ant-eater there are only 6 carpal bones, 4 in the first row and two in the second; in the three-toed sloth there are only 5, 3 in the first row and 2 in the second; the pangolin has 7; the cachecame 8 and a rudimental small toe; the elephant 8, 7 wedge-shaped and one elongated, corresponding to the pisiform; and the other Pachydermata 8. In the rhinoceros, which has only 3 toes, the trapezium only is wanting; but there is a supernumerary bone on the margin of the scaphoid, and on that of the unciform, as in the porcupine. The first range consists, in the Ruminants and Solidungula, of 4 bones; in the former, excepting the camel, the second consists of 2, and the latter of 3. Those of the Cetacea, which are much flattened, are 3 in the first row and 2 in the second.

Ιhe Mammalia generally have as many metacarpal bones as toes, that is, never fewer than 3 or more than 5, with the exception of the Ruminants, in which these bones are in early life consolidated into one named the cannon bone. In animals which walk on the tips of the toes, or which use them as organs of prehension, the metacarpal bones are lengthened·to nearly double; and hence in all hese animals the metacarpus is erroneously named the. tore leg, and therefore it has been imagined, that in several [7:3:9]of our domestic animals the different parts of the lower extremity are articulated in opposite directions to those of; man. Thus the fore leg of the horse, deer, sheep, and dog are in truth the metacarpus of these animals; and what is vulgarly named the fore knee or cannon bone of the horse, is actually the carpus or wrist-joint. It is therefore convex on the dorsal, and concave and inflected on the palmar aspect, exactly as the carpus of the human subject.

In the three-toed sloth, the three bones of which the metacarpus consists are mutually consolidated at the base and with the rudiment of a fourth toe. In the Cetacea, the metacarpal bones, which are much flattened, are also mutually united.

In the Mammalia generally, if we include imperfect or rudimental phalanges concealed in the skin, there are never fewer than 3, nor more than 5. The Unguiculated animals generally have 5, perfect and imperfect· The character of the perfect fore toe or finger is to consist of 3 rows or phalanges, excepting the first of the radial side, which has only 2. In the Quadrumana this is separate, and opposable to the other toes, constituting a thumb, and giving this tribe of animals a prehensible organ entitled to the epithet of hand. It is, however, shorter and less perfect in other respects than the genuine thumb of the human hand. In the coăìta (simia paniscus) it is converted into a rudimental bone, concealed under the skin.

In the Zoophaga, which have no power of grasping minute objects, the thumb or first toe is parallel to the others, and, though equal in length to these in the ursine family, it is shorter in the mustela, viverra, canine and feline genera. In the latter, which have the power of erecting the claws, to prevent them from being blunted in walking, the shape of the middle and unguinal phalanx is remarkable. The former is triangular prismatic, with two lateral and a plantar or palmar inferior surface. The third or unguinal phalanx is shaped like a hook, consisting of two parts. One, directed forwards, sharp and pointed, receives the nail or claw, in a long groove like a sheath. The second part of the hook, which is behind, rises vertically from the lower part by which it is articulated, and is produced into two processes, to which are attached the erecting muscles of the claw, which are flexors of the phalanx.

Among the Rodentia there is a perfect but short thumb in the hare, beaver, and jerbois; a two-phalanx but concealed one in the squirrel, mouse, and rat family, porcupine, paca, agouti; and a one-phalanx concealed one in the cavy, guinea-pig, marmot, &c. In the Edentata the number of fore toes varies much; in the Tamanoir, and Tamandua or four-toed ant-eater, the thumb· toe is obliterated; in the Ai or three-toed sloth, both that and the fifth toe are obliterated; and in the two-toed ant-eater, and Uhau or two-toed sloth, these, with the second toe also, are obliterated.

The elephant has 5 perfect toes, all concealed under the thick, callous hide of the foot. In hoofed animals with 4 toes, for instance the hog, tapir, and hippopotamus, the thumb-toe is in the shape of a śmall rudimental bone.

In the Ruminants the single metacarpal bone (Chesel-den’s figure of the Deer, Plate I.) is articulated with two digital phalanges, which constitute one of the distinguishing characters of this order—the cloven foot. In some genera, at the root of these two perfect toes are two small bones, often covered with horn, which represent two other toes. The last or unguinal phalanx is always trilateral in shape. In the horse and the Solidungula generally, the two lateral toes are represented only by two bony styles, named the splint bones, situate on the two sides of the metacarpal or cannon bone. The three phalanges of the single toe which constitutes the foot are distinguished as the pastern bone, which is the first phalanx; the coronet, which is the middle or second; and the coffin bone, which is the third or unguinal phalanx, which has the shape of the hoof, rounded before, convex above, and flat below. To the back of the pastern joint are connected two sesamoid bones; and to the coffin bone is attached another, named the shuttle bone. In the Cetacea, all the phalanges, which are flattened, and often cartilaginous, are united in the fin or paddle.

The thigh-bone, which is single in all the classes, follows the type of that of the human frame in general figure and parts. In the Mammalia it is, however, proportionally shorter, and its length diminishes as that of the metatarsus augments. In the Ruminants and Solidungula, for instance, it is so short that it is concealed by muscles against the belly; and hence it is too often overlooked and confounded with the leg. In other respects the general characters are, that it is not arched; that, excepting in the bear and some of the simia genus, e. g. the ourang-outang, it is shorter than the leg-bones; that its neck is very short, and more perpendicular to the axis of the diaphysis than in man; and that the great trochanter is raised above the head, which is directed inwards. In the simiae it is quite cylindrical, and void of linea, aspera. In the tapir the middle part is found flattened; and at the external margin there is a prominent crest, terminating in an unciform process. In the rhinoceros the great trochanter and the unciform process are so elongated as to unite almost, and form a hole between them and the diaphysis. The unciform process is observed also in the horse, beaver, and armadillo. The thigh-bone of the seal is so short, that the half of its length consists of the two articular extremities.

Though the leg-bones of the Mammalia bear a general similitude to those of man, the tibia alone is constant; and the fibula, after becoming unusually slender, and changing its position from the outside to the posterior part of the tibia, is converted into a mere appendage, and at length disappears entirely. Thus, though it is distinct, and occupies its usual position in the simiae, in the Chirop-tera it is extremely slender; and since the femora are directed backward, the fibulae are turned towards each other. In several of the Edentata, for instance the pha-tagin, armadillo, and sloth, it is large, curved, and remote from the tibia. In the dog family and the Rodentia it is altogether behind the tibia. In the mole and murine genus it is consolidated to the lower third of the tibia, leaving an empty trilateral space above. In the rhinoceros, elephant, and hog, the fibula is flattened and united to the whole length of the tibia. In the ruminants it is represented by a small bony appendage, placed on the outer margin of the astragalus, below the tibia, and forming the external or fibular ankle. Lastly, in the horse and Solidungula, the fibula is reduced to a styloid rudimental pro-, cess, which is firmly consolidated in the adult animal to the upper part of the tibia.

Between the tarsus of man and that of the other Mammalia the following are the principal differences.

In the simiae the fibular facette of the astragalus is nearly vertical, and the tibial is very oblique; and the calcaneum wants the tuberosity, except in the pongo. In the ordinary bat family the calcaneum is elongated into a styloid process, concealed in the substance of the membranous ubiform expansions; but in the roussette (pteropus) the tuberosity projects beneath the foot.

In the Rodentia the calcaneum is produced considerably backwards, while the scaphoid, which consists of two parts, forms a tubercle on the sole. Among the Edentata the three-toed sloth is peculiar in having a tarsus, [7:3:10]consisting of four bones only, the astragalus, calcaneum, and two cuneiform bones, the first of which is articulated not only with the tibia, fibula, and calcaneum, but with the 'large cuneiform bone, without any intermediate scaphoid bone. Its connection with the tibia is by means of a convex articular surface, which rolls on the external part of the tarsal end of the tibia. From this mode of articula φ - tion it results that the foot of the sloth admits neither of being elevated nor depressed, but simply of performing lateral motions of adduction and abduction, to which it owes the power of clasping the trunks of trees and climbing, but which renders progression difficult and laborious.

¾ιe hog has a scaphoid with three ordinary cuneiform bones, and a rudimental great-toe bone beneath the first. In the tapir and rhinoceros there are only two cuneiform bones. All the animals already enumerated have the same number of metatarsal bones as of toes. .

In the Ruminants the cuboid and scaphoid bones are united, unless in the camel, in which they are distinct. At the outer margin of the pulley of the astragalus is a bone which represents the lower head of the fibula, and which is farther articulated to the upper surface of the os calcis. In this side also there are only two cuneiform bones, which are united in the giraffe. The two metatarsal bones are always united, as in the metacarpus, into one, which forms a posterior cannon bone. The Solidungula resemble the camel in this, that the scaphoid is distinct from the cuboid bone, and that there are two cuneiform bones, while the peroneal rudiment and the corresponding articular surface of the calcaneum are wanting. The metacarpal arc also consolidated into a single piece, named the hinder cannon bone, each side of which is provided with a minute bony style.

The toes of the Quadrumana and the Marsupialia are longer than those of man; but the great toe is shorter than .the others, and its metatarsal bone is susceptible of separation and opposition, as the thumb or thumb-toe of the hand. Hence Cuvier, in his first classification, distinguished the latter by the name of Pedimana. The Aie-are among the Rodentia appears to possess the same faculty. Among the Zoopiiaga the great toe remains always conjoined with and parallel to the others; and in the canine and feline genera it is obliterated. Among the Rodentia, that of the beaver is nearly equal to the other toes; those of the marmot, porcupine, and the murine genus, are shorter; in the paca it is almost obliterated; it is reduced to a single bone in the Cape gerboa; and the leporine genus have no trace of it. In the cavy, agouti, and guinea-pig, the great and small toes are each reduced to one bone. In the gerboa (mus jaculus) and alactaga (mus sagitta) the three middle metatarsal bones are united into a single one similar to the cannon bone of the Ruminants and Solidungula ; and while the two lateral toes are distinct, though short, in the former animal, they are obliterated altogether in the latter.

Among the Edentata, the ant-eater, orycteropus, pangolin, and armadillo, have five toes, of which the great is the shortest in all. In the sloth the great and small toe are reduced to one small bone. The other metatarsal bones are united at their base. The toes have only two phalanges, of which the unguinal are the largest.

In the subsequent, families the metatarsal bones deserve particular attention, In the elephant and Pach yder-mata, their tarsal extremity has a flat surface, and the phalangeal consists of a convex tubercle, which presents below a prominent line in the middle of the bone. In the Solidun t gula this line is above and below both. In the Ruminants, in which the cannon bone consists of the two metatarsal bones, the line of union is represented by a deep line like the tract of a saw. The elephant has 5 perfect toes; the hog 4; the tapir and rhinoceros 3; the Ruminants have two perfect toes on one metatarsal bone, and two small ones attached behind its .base, lhe ðo- lidungula have one perfect toe, and two imperfect, which are reduced to a single styloid bone. In these animals the body is supported in walking by the last or unguinal phalanx alone; and hence the term foot is not of the same import as in the human subject and animals similarly constructed. While indeed man supports his person in progression on the os calcis and the poster ior. or metatarsal phalanges, in the other mammiferous animals the former bone touches not the ground, but is always elevated above it a considerable height. All the .zoophagous or unguiculated animals, excepting the plantigrade, support themselves chiefly on the unguinal and middle phalanges both of the fore and hind foot; and neither the posterior phalanges nor the calcaneum touch the ground, as is easily demonstrated on observing the gait of the hedgehog, dog, fox, cat, or similar individuals of the same family. The animals distinguished by the name of Plantigrade are believed to support themselves on the entire foot. But though the foot is certainly spread on the ground more freely than in those already mentioned, by the bear, glutton, badger, and others, it appears that not the heel, but the metatarsus, is allowed to touch the ground in progression. In the Ruminants and Solidungula, as already mentioned, the only part of the foot which is applied to the ground is the unguinal phalanx; and it is well known that the horse supports himself on the plantar surface of the coffin bone only.

Lastly, in the Amphibious Mammals, while the extreme brevity of the humerus and femur unfit them for progression on land without extreme awkwardness and difficulty, the expanded shape and oblique position of the metacarpal bones and phalanges, the length of the tibia and fibula, and the greater length of the first and last than the middle metatarsal phalanges, all concur to give these animals great facility in swimming. (Cuvier, Ossemens Fossiles, tome V. partie i. septième partie.) In the Cetacea, again, while the total want of pelvic extremities renders motion on land quite impracticable, the fin-like disposition of the metacarpus and metacarpal phalanges, with the great strength of the lumbar, and the length of the coccygeal vertebrae, peculiarly qualify them for locomotion in the waters.

sect. ii. — osteology of birds.

The number of vertebrae of which the different regions of the spine consist, is not less variable in Birds than in the Mammalia. Some idea of these variations may be formed from the number exhibited in the following table by Cuvier.
[table]
[7:3:11]
[table]

In this table the most remarkable circumstance is the great number of ćervical vertebrae, which are much more numerous than in the Mammalia. They vary from 9, the number in the sparrow, to 23, which is that of the cervical vertebrae of the swan. The most common number is 11, which is that of 10 genera. The next most frequent is 12, 13, and 14, which are equally the numbers of 9 genera. The next is 15, which is that of 8; 10 occurs in 6, 18 in 4, and 16 in 3. In the stork and crane they are 19.

The next remarkable circumstance is, that the dorsal or costal vertebrae are greatly fewer than in the Mammalia, never exceeding the number of ll,.and being more frequently about 7 or 8. Thus, while they arc 11 in the cassowary, swan, and sheldrake, 10 in the goose, bernacle, and grebe, and 9 in the sparrow, lark, humming-bird, parrot, crane, avoset, oyster-catcher, cormorant, and blackdiver, they are 7 or 8 in all the other genera, and only 6 in the bullfinch.

’ There are no lumbar vertebrae strictly so named, for those which extend from the chest to the' tail are· consolidated into one piece with the iliac'bones. The tail, which iŝ short, consists of from 7 to 9 vertebrae.

j The part most variable in proportional length is the neck. It is .so much .longer as-the feet arcelevated, except in some of the swimmers, in which it is greatly longer, because they require to seek their food below the surface of the waters on which they float.

The bodies of the cervical vertebrae are articulated not by plane facettes, which would admit obscure motion only, but by portions of cylinders, which allow extensive motion. The 3d, 4th, or 5th superior vertebrae allow of anterior inflection only, and the others of posterior inflection. This gives the necks of birds an alternate serpentine in-flectiön; and it is by rendering the two arches, of which this curvature consists, straight or convex, that the animal elongates or shortens his neck. The articular processes of the superior vertebrae are directed upwards and downwards; those of the lower are turned anteriorly and posteriorly.

Instead of transverse processes, the cervical vertebrae of birds are provided with a tubercle above, and the anterior extremity of which terminates in a narrow style, descending parallel to the body of the vertebra.

Only the most superior and inferior vertebrae have distinct spinous processes, and these have anterior as well as posterior ones. The middle ones have before two crests, which form a half-canal, and.behind a tubercle, often biful, or, when they are elongated, two rough lines. The atlas, which is articulated with the occipital bone by a single facette, has the shape of a minute ring.

As the neck of birds is movable, the back is fixed. The spinous processes of these vertebrae are in mutual contact, and they are connected by strong ligaments. Most of these processes are generally consolidated into a single continuous crest, extending along the whole back. The extremities of the transverse processes terminate in two apices, one directed forwards, the other backwards; and occasionally they are consolidated into a continuous mass like the spinous. That this arrangement is requisite for the trunk to remain fixed during the violent motions which take place in flying, is rendered probable by the fact, that in birds which do not fly, as the ostrich and cassowary, the spinal column retains its mobility.

The last dorsal vertebrae are often placed on the crest of the iliac bones, and they are then united, as the lumbar, on the large piece of the iliac bones, from which it results that the number of vertebrae can often be estimated in no other mode than by that of the holes of the nerves which issue from the chord.

The caudal vertebrae are most numerous in the species which move the tail with most energy; for instance, the magpie and swallow. They have spinous processes below as well as above, and very long transverse processes. The last of all, to which the pinions are attached, is longest, and has the shape of a ploughshare or a compressed quoit. In the cassowary, which has no visible tai), the last bone is conical; in the peacock, on the contrary it has the shape of an oval plate, situate horizontally.

It was early observed by the original zoologist and traveller Pierre Belon, that the crania of birds were void of sutures; and that in a few only were these lines of distinction into separate bones recognised. The explanation of this peculiarity is found in the history of the ossification of the head in young birds, which shows that the cranium consists at that period of separate bones, corresponding in number and situation to those of quadrupeds. Thus, there are two frontal bones, which are continued forwards to form the vault of the orbits; two small parietal bones behind the frontal; a temporal bone on each side of the ścull; a sphenoid united to the occipital, even in subjects in which the other sütures are distinct; or a sphello-occipital bone, which is early united with the temporal.' ,

These sutures, however, are distinctly seen only in [7:3:12]young birds and those recently hatched; for the bones are very early united, and in the adult bird the cranial sutures are invariably obliterated. Thus, in the domestic fowl and turkey the scull is one piece; and the only trace of suture that remains is a linear depression in the middle of the frontal bone, indicating the original formation in two halves. In the recently hatched bird, also, the sphenoid is separated from the occipital bone by a transverse suture, extending from the one ear to the other. The occipital bone is at the same time a ring, consisting of four parts; a superior, two lateral, and an inferior which is small. The sphenoid, which forms the greater part of the base of the cranium, is nearly trilateral, with a small anterior process, to which the palatine arches are articulated. It has no pterygoid processes, and does not touch the posterior aperture of the nostrils. The temporal bone, though void of zygomatic process, has a pointed style, which contributes to form the posterior margin of the orbit. The frontal bone, after covering part of the cranium, is continued forwards in a broad, thin plate, which forms the vault of the orbits, while these cavities are separated by a thin vertical bony plate which descends at right angles from the frontal bone, and is connected behind with the sphenoid. The long eminences observed on the heads of the cassowary, curlew, pintado, and some species of hocco, are produced from this supraorbital part of the frontal bone; and their interior, which consists of loose diploe, communicates with that of the same bone.

The face in birds is rarely so firmly consolidated as the cranium. It is composed of two lacrymal bones, forming the anterior margins of the orbits, and united on the mesial plane; two nasal bones anterior to the lacrymal; two bones corresponding to the superior maxillary, and forming the external lateral parts of the upper half of the bill; two inter-maxillary bones; two anterior palate bones, corresponding to those of the Mammalia ; two posterior palate. bones corresponding to the pterygoid processes of the sphenoid; and the lower jaw a paraboloid bone, consisting of twortroi united before, where they are covered by the horn of the lower half of the bill. Besides these, there is in the whole class an irregular-shaped bone, common to the Cranium and lower jaw, and connecting these two together. This bone, which has been rather improperly named the square, quadrangular, or quadrilateral bone (os quadratum), consists of a body with curvilinear hollow margins, terminating in two elevated and rather pointed processes, one of which is connected with the cavity named tympanum, while the other, projecting into the orbit, affords attachment to several muscles. The anomalous character of this bone has perplexed several of the most distinguished zootomists; and while Geoffroy gives it the name of os Tympano-styloideum, Spix considers it analogous to the annular process of the temporal bone, which in the human foetus is separate; and Carus regards it as representing the incus, to which it bears a remote resemblance in shape and in one of its connections.

Both maxillae are void of teeth; but the hard, horny matter of the bill covering the margins and extremities of each jaw, and constituting the mandibles (mandibula), is manifestly constructed to perform for Birds what teeth do for the Mammalia. But the most remarkable peculiarity of the, facial bones of this class is, that the upper jaw admits of more or less motion. In the majority of instances this is effected by the jaw being united to the cranium by means of thin, flexible, elastic, bony plates; but in the parrot family the upper jaw is entirely distinct, and is connected by a proper articulation.

The base of the palatine surface of the upper jaw is divided into 4 branches, which diverge backwards. The two external ones, which correspond to the zygomatic arches of the Mammalia, and which are very slender, are articulated to the quadrangular bone which moves on the temporal before the ear. The two intermediate ones, which have been already stated to correspond to the pterygoid processes, and which are parallel, are placed beneath the septum of the orbits, and are articulated by their posterior extremities with a small bone, variable in shape, but named omoid by Hérissant, which is also articulated with the quadrilateral. From this arrangement results a singular species of broken lever, not dissimilar to the parallel joint of the piston and lever of the steam-engine, and the effect of which is, that whenever the lower jaw is depressed by its proper muscles, it necessarily causes the quadrilateral bone to perform a slight rotatory motion, in consequence of which, by means of the omoid bone, the upper jaw is at the same time elevated on the elastic plates; and as soon as the lower jaw is raised, the elasticity of these plates forces down the superior one.

The upper jaw is immovable in a few instances only, and of these the calao or rhinoceros bird is one.

The breast bone (sternum) is a trilateral, boat-shaped bone, concave internally, convex with a middle longitudinal crest externally, with the base of the triangle above, and the apex, which is also incurvated backwards, below. The middle longitudinal crest, which is occasionally named the keel (carina), is shaped something like a spherical triangle, with the broadest side above, the base before, and the apex behind; and its prominence forms large spaces on each side for the attachment of the pectoral and other muscles used in flight. In the male wild swan (anas cygnus), in some sjpecies of curlew, in the crane, and in the guinea-fowl, this crest forms a cavity for the reception of the windpipe. In the ostrich and cassowary, which do not fly, the sternum is void of crest, and is merely arched strongly.

The ribs, which rarely exceed 10 pairs, may be distinguished into sterno-vertebral and vertebral. Though the latter are generally before, they are sometimes also behind. The vertebral end terminates in two diverging processes, one of which is articulated with the vertebral body, the other with the transverse process. The sternal extremity consists of a bony process, which performs the part of the sterno-costal cartilages of the Mammalia by uniting the rib to the sternum. The ribs of birds, however, are further distinguished by presenting near their middle a flat long process, projecting from the rib backwards at an acute angle, and resting on the rib immediately below, so that each rib is supported not only on the vertebrae and sternum, or the vertebrae alone, but on the next rib below. These processes are obliterated in the lower ribs.

The coxal bones constitute one piece with the sacrum and lumbar vertebrae. The ischial portion is united with the sacrum, and the ischiatic notch is converted into a hole. The part which corresponds to the os pubis of the Mammalia is not consolidated before so as to form a symphysis, but proceeding directly backwards, terminates in a styloid process, variable in length and slenderness. The only exception to this mode of structure occurs in the ostrich, in which the pubal bones are united below. The infra-pubal or oval hole is present in the whole class notwithstanding. It is worthy of remark, however, that in young birds this and the ischial aperture are still notches, in consequence of the deficient ossification of the parts.

The direction of the pelvis in birds is nearly that of the spine, that is, obliquely backwards, and deviating but little from the horizontal line.

The wings or thoracic extremities are connected to the trunk by three bones, the collar-bone or clavicle, the scapula, and the bifurcated bone. The collar-bones, which [7:3:13]are straight, strong, and cylindrical, are articulated by a large head with the anterior and lateral part of the sternum, in which its motion is rather limited. It forms before and laterally two short processes, one anterior-inferior and internal, articulated with the bifurcated bone; the other posterior-superior and external, uniting with the scapula, and forming a cavity, in which the head of the humerus is lodged. ’

The scapula is a long bone, flattened, but narrow, and slightly incurvated, with the convex side turned towards the spine, to which it is nearly parallel in position. The head or anterior extremity is thick and extensive, oblique from before backwards, and is articulated behind with the clavicle, before with the humerus. The free extremity is thin, flattened, and sharp. The whole bone is not dissimilar in shape to a scimitar.

Besides these, which Birds possess in common with the Mammalia, we find an azygous bone, situate on the mesial plane, denominated in ordinary language the Merry thought, and, from its shape, the fork-like or bifurcated bone. It consists of two long, rounded, converging branches, united at an acute angle, and forming a broad process, flat in the vertical direction, and by which it is articulated to the anterior extremity of the crest or carinated part of the breast-bone. To the posterior or free extremities of the divergent branches are articulated the humeral ends of the collar-bones, which are thus enabled to sustain the violent motions of the humerus during flight. The branches of the bifurcated bone are separate in the ostrich, and each is united with the clavicle and scapula of the same side, so that the three bones form only one, much flattened, and with a hole towards the sternal extremity. In the cassowary the bifurcated bone is reduced to a mere rudimental process at the inner margin of the head of the clavicle. From these facts it results, that the bifurcated bone is particularly useful in the energetic and continued efforts of the wings in flight, and not only serves to keep the clavicles apart, but, by lengthening the distance between the collar-bones and sternum, enables the animal to use a longer lever. It is freest, strongest, and most elastic in the birds which fly best. In birds which do not fly, and which use the wings merely to sustain the equilibrium, as the ostrich and cassowary, it is reduced to almost nothing, or it is in such a rudimental and imperfect form, that it cannot keep the collar-bones apart.

The bones of the thoracic extremities, or those of the wings, correspond in general to those of the Mammalia. They consist of a single cylindrical humerus, articulated with the scapula and collar-bone above, two bones of the fore wing corresponding to the ulna and radius, two bones of the carpus, two of the metacarpus, consolidated by their extremities, one styloid bone as a thumb, a long finger consisting of two phalanges, and a short one consisting of one. The thumb supports the bastard pinions, the large finger and metacarpus the primaries, while the small one, which is covered by the skin, is destitute. In several of the webfooted divers, for instance the duck and penguin (alca im-pennis and spheniscus), these bones are flattened like thin plates.

In the pelvic extremities the thigh-bone is provided with one trochanter only, is shorter than that of the leg, and is almost invariably straight; and is arched only in the cormorant, duck, and dobchick. In the ostrich its diameter is about four times that of the humerus. The tibia differs from that of the Mammalia chiefly at its lower extremity. While the fibula adheres to it like a slender appendage as far as the middle, the tarsal extremity terminates in two trochlear condyles, with an intermediate pulley-like groove. The tarsus and metatarsus are represented by a single bone of considerable length, and the head or tibial end of which consists of a middle prominence and two lateral depressions, and which, therefore, χ moves in cardinal opposition, but does not admit of extension beyond the straight line. Though variable in proportion to the length in different orders, this bone is very long in the order Grallae (Grallatores). It terminates below in 3 pulley-shaped processes, to which are attached the bones of the 3 anterior toes, with an internal margin for that of the great toe. In the ostrich there are 2 processes only, corresponding to the two toes. In the penguin tribe, however, the tarsus and metatarsus consist of 3 bones, separate from each other in the middle, but united at the tibial and digital extremities. To the tarso-metatarsal bone of the cock, and others of the Gallinaceous tribe, is attached the spur, a conical pointed excrescence of hard horny matter.

SECT. III.—OSTEOLOGY OF THE REPTILES.

The number of vertebrae, and all the other attributes of the spinal column, vary more in this class than in all the others.

In the Cheloniad or Tortoise family there are 7 cervical, 8 dorsal, connected with the shell in an immovable piece, so as to have neither processes nor articular facettes; from 3 to 5 lumbar and sacral,· consolidated in like manner; and about 20 caudal or coccygeal. (Plate XXXIV. fig. 5.)

In the Saurial or Lizard tribe, the number 7 predominates in the cervical, being that of the crocodile and most lizards. In several, however, there are 8, as in two of the monitor genus, the American safeguard, the lizard of Fontainebleau, the dragon, the iguana, the anolis, and the gecko and seine; and in a few, as the Nilotic monitor, and an undetermined species of monitor, they amount to 9. In the chameleon there are only 5 cervical vertebrae. Here, however, a singular peculiarity is observed. Instead of the cervical vertebrae being, as in the Mammalia, distinguished by being unconnected with ribs, to those, from the third to the seventh inclusive, short ribs, unconnected with the sternum, are attached. The atlas and axis, therefore, alone are proper cervical vertebrae; but the general analogy is observed in the cervical ribs being exceedingly short and almost rudimental. The dorsal vary from 11, which is that of the crocodile and iguana, to 29 and 30, which are the numbers in the New Holland seine and Nilotic monitor. In the American safeguard, cordy-lus, stellio, crested basilisk, dragon, guana, and great anolis, they are 16; in the chameleon, black safeguard, and ameiva, 17; in the tupinambis, spotted gecko, and golden seine, 18; in the green lizard and spotted guana (poly-chrus) 19; in the Fontainebleau and gray lizard 20; 21 in the Levant seine and undetermined monitor; and 22 in the Java and New Holland monitor.

TheBATRACHoiD or Ranine reptiles are void of ribs, and it is impossible therefore to distinguish the first three orders of vertebrae from each other. In general, however, there are from the nape to ¢ae pelvis 8 vertebrae, all provided with long transverse processes, and which are longest in the last. The sacrum is represented by a long flattened but pointed bone, without coccyx. In the Surinam toad (rana pipa) the last vertebra is consolidated with this bone; and the transverse processes of the second and third vertebrae are so much larger than the others, that they resemble rudimental ribs. In the Salamander family there are from the head to the sacrum 14 vertebrae, all alike in shape except the first, which receives the occipital bone, and the last, which is articulated with the sacrum. These two are distinguished by wanting rudimental ribs, which are small elongated bones, movable, and articulated with the trans [7:3:14]verse processes,'which are directed backwards. The articular processes are large and imbricated, the posterior resting on the anterior, so as to resist the motion of the spine backwards. The sacrum consists of one vertebra only, but the coecyx or tail is composed of 27.

In the Serpentine tribe the vertebrae may be said to attain the most extensive numerical developement. With the exception of the head and rudimental ribs, they constitute the whole skeleton. (Fig. 3.) From the head to the tail their shape is the same, and may be distinguished into body, articular and transverse spinous processes. In some species, for instance the boa, the spinous processes of the back are so much separated as to allow mutual motion to a considerable extent. In others, conversely, for instance the rattlesnake, these processes are so long and broad as to touch each other, while the oblique proeesses, which form their bases, are imbricated over each other. In consequence of this arrangement the motion of the spine is limited behind, but more extensive on the ventral surface. The vertebral bodies, whieh move easily on each other, are provided with a sharp spine directed towards the tail, which somewhat limits motion in this direction.

The first vertebra differs from those of the rest of the body in supporting short or rudimental ribs; there are therefore no cervical vertebrae and no proper neck in the serpent family. The caudal vertebrae are distinguished by not supporting ribs, and by their spines both dorsal and ventral being double, and forming two rows of tubereles. The articulation of the bodies of these vertebrae is peculiar. On the anterior part of the body is a round hemispherical tubercle, while the posterior presents a corresponding cavity, so that each vertebra forms a cup and ball joint with the following one.

The number of costal vertebrae varies from 32, which is that of the blind worm (Anguis fragilis), to 204 in the ringed snake (Coluber natrix), 244 in the snake, and 252 in the Boa constrictor, and which is perhaps the greatest known number. Of intermediate numbers, the Amphisbaena has 54, the viper (Coluber berus) has 139, the rattlesnake 175, and the cobra di capello 192. The caudal vertebrae vary in number from 7, which is that of the Ampkisbaena, to 112, which is that of the Coluber natrix. Of intermediate numbers, the blind worm has 17, the rattlesnake 26, the boa 52, the viper 55, and the cobra 63; from which it appears that the number of the caudal is not in proportion to that of the costal vertebrae.

Of the heads of the Ciieloniads, the most remarkable characters are, that the facial line is horizontal, and quite continuous with the cranial line; that the orbits, though complete without, are continuous behind with the temporal fossae; that the parietal and occipital bones are compressed laterally, while the latter terminates above in a sharp spine, projecting behind. The occipito-parietal and occipito-temporal sutures are distinct. The cranial cavity is small compared with the volume of the scull.

These characters are not less remarkable in the Saurial or Lacertine Reptiles. The cranium of a erocodile measuring from 13 to 14 feet is scarcely capacious enough to admit the thumb; and Cuvier estimates the area of the cranial section, which is oblong, at about ģ¾ of that of the whole head. In these animals, indeed, the bones of the superior and inferior jaws are so much prolonged, and occupy so large a proportion of the head, that small space is left for the proper cranial cavity, which indeed is an immediate continuation of the vertebral. In these animals, also, the anatomist can trace, much more distinctly than in the more perfect, the resemblance between the cranial bones and the vertebral. In the Ciieloniads, and Saurial especially, the occipital bone is very distinctly a cephalic vertebra.

Still more manifest is this arrangement in the Ranine or Batrachoid and Serpentine or Ophidial Reptiles. In the former, as exemplified in the frog, the occipital bone, which forms the posterior cranial vertebra, consists of four pieces, and has two articular proeesses. The middle cranial vertebra is represented by the parietal bones above and the posterior part of the sphenoid below, while between it and the occipital or posterior is contained the temporal as the organ of hearing. The third or anterior cranial vertebra is represented by the anterior part of the sphenoid bone below and the two narrow frontal bones above. The sace, which may be regarded as the organ of the senses, is elongated anterior to the head, somewhat after the manner of the Cheloniad family; while an approximation to the Birds is indicated in the articulation of the lower jaw, which is connected to the head by the intervention of a quadrilateral bone.

In the Serpentine family, the cranium of which is very similar in other respects, the most remarkable deviation is in the want of ethmoid bone. .The lower jaw is connected to the cranium by an intermediate bone, corresponding to the quadrilateral, but of an oblong shape, and something like a collar-bone.

The chest of the Reptile class varies much in the mode of formation. While true ribs are recognised in the Saurial family only, the Batraciioið reptiles have a sternum without ribs, the Serpentine ribs without sternum, and the Ciieloniad ribs united into the dorsal shell, and a sternum expanded into the abdominal one.

In the Saurial family the ribs correspond in number to that of the costal vertebrae already mentioned, that is, 12 in the crocodile and iguana, two of which are not connected to the sternum, 17 in the chameleon, 18 in the tupinambis, and 27 in the monitor. The Saurial reptiles, however, are peculiar in having from 1 to 6 ribs attached to the eervical vertebrae, and the opposite ends of which are not connected to the sternum. These, which have been named eervical ribs, form a transition to the rudimental ribs of the Serpentine family, which are larger in the neck than elsewhere. The sternum of the crocodile consists of two parts,—an anterior or thoracic, which is osseous, supporting the two collar-bones,—and a posterior or abdominal, which is cartilaginous, and extends to the pubis, and furnishing to the abdominal parietes eight cyhndrical eartilages. In the East India erocodile it appears that these lateral processes are converted into a single broad piece of cartilage on each side. (Fig. 4.)

The ribs of the Ciieloniad family are represented by the dorsal shell, which consists of eight broad incurvated plates, identified behind with the dorsal vertebrae, and terminating before in the margin of the shell, and which are doubtless genuine ribs. In the ordinary land-tortoise (Testudo Groeca) these are seen in the shape of elevated bonyridges, proceeding from the head of each rib in atrans-verse concave bend to the margin of the dorsal shell. On each side of these ridges the bone is depressed, and is united at its lowest point by a genuine suture with the adjoining ones. These sutures, however, are not continuous with those of the sterno-abdominal shell, but meet it in the intermediate points. (Fig. 5.) The sterno-abdominal shell consists, in like manner, of several transverse pieces consolidated into one. The ordinary number is eight on each side of the mesial plane, and a ninth azygous, generally placed in the centre of the shell. In a specimen, however, of the tabular tortoise (Testudo tabulata), in our possession, the number of the sterno-abdominal pieces is 11, of which 8 are in pairs, united on the mesial line from before backwards, and 3 azygous at the posterior tip of the shell. In young animals it is easy to recognise the unions of these constituent bones, which consist of suturesex-actly[7:3:15] similar to those of the cranium in the Mammalia. So feeble is the union, that it often happens that the ab- l dominai shell especially separates at the lines of junction, in the attempt to detach it from'the dorsal.

The Batraciioid Reptiles, though void of ribs, are provided with a sternum, which before is a cartilaginous process, terminating on a disc placed below the larynx, where it receives the collar-bones, and forms behind a broad plate placed below the abdomen, and giving attachment to the muscles. In the Salamander tribe, which are without stermιm, the ribs consist of twelve pair of small rudimental processes, articulated with the vertebrae, but admitting of very limited motion.

Lastly, in the Serpentine family, though there is no sternum, the upper vertebrae are provided with costal processes, quite rudimental. The great number of these costal rudiments, amounting in the rattlesnake to 175, in the cobra di capello to 192, in the coluber natrix to 204, and in the boa constrictor to 252, and the freedom of their anterior extremities, enable the animals of this tribe, which are destitute of locomotive members, thoracic or abdominal, to employ the spinal column and the ribs as organs of progressive motion. On this point the reader will find some interesting observations by Sir Everard Home (Phil. Trans. 1812, p. 163). In the region of the neck, where the ribs acquire peculiar length, they are employed in erecting that region, and producing the expansive swelling peculiar to this tribe of animals. It is an important link in the same series of facts, that in the animal absurdly named the flying lizard (draco volans), the five posterior ribs are recurvated and elongated to form the bony skeleton of the membranous sails by which the animal supports itself in its desultory flight from tree to tree.

It is in the Saurial family that the locomotive extremities of Reptiles ought first to be studied. In these we -find an elongated scapula without spine, and one short flat bone, constituting the clavicle, united to the sternum. In the iguana and chameleon this bone is broad and nearly quadrilateral, while in the tupinambis it is large and oval-šhaped, with its greatest length from before backwards, •and with two unossified points.

In the Ranine tribe, while the scapula consists of two articulated pieces, the upper towards the spine, each shoulder is provided with two collar-bones attached to the two extremities of the sternum, and the two anterior of which correspond to the bifurcated bone of birds. The sternum, collar-bone, and first part of the scapula, form one piece. In the salamander, in which the same consolidation is observed, the scapular portion is most distinct and directed to the spine, while of the clavicular portion the part connected to the sternum stretches below the chest, but, without uniting with that of the opposite side, the right glides over the left,—an arrangement which facilitates the dilatation of the chest during inspiration.

A nearer approach still to the bifureated bone than is seen in the Ranine may be recognised in theCHELONiAD family. In these animals three bones are united to form the humeral cavity. The first is a flat, trilateral bone, situate below the abdominal and thoracic viscera, close to the abdominal shell, and which, notwithstanding its situation, is evidently the scapula. The second is a bone about the same length, flat, and like the feather of an oar at one extremity, which is free, round in the middle, and flattened in the opposite direction at the other end, which is firmly united at a right angle to a long slender cylindrical bone. At the angle of union of these two bones is part of the glenoid cavity, which is complete in the small end of the scapula. The first of the two bones is the collarbone proper; the second is the lateral branch of the bone, which forms the bifurcated, and which is occasionally united with its fe 1 Jow. (Plate XXXIV. fig. 5.) The abdominal shell we have already stated to represent the sternum or breast-bone.

The humerus in the Saurial and Cheloniad family is arched and incurvated in a serpentine direction. It is articulated with a radius and ulna, which are succeeded by three rows of carpal bones, one row of four metacarpal bonès and digital phalanges, varying in number in different genera. In the skeleton of a fossil animal belonging to the Saxjrial tribe, originally delineated by Collini, and afterwards by Cuvier, and named by him the Ptérodactyle or Wingtoe (Pterodactylus, 0ssemens Fossiles, tome v.), the metacarpal bone and phalanges of the index are prolonged to about twenty times the ordinary length, for the purpose, apparently, of giving attachment to the membranous web by which the animal occasionally elevated itself into the atmosphere. This animal, which, like the dragon (draco volans) of modern times, must have combined the contradictory characters of a flying reptile, may be regarded as forming the link between the Reptiles and Birds, as the Ichthyosaurus does between Reptiles and Fishes.

In the pelvis of the Cheloniad family it is remarkable that the pubal and iliac bones appear to change places. Thus the ilium on each side is a narrow bone proceeding backwards to the sacral part of the spine, which is received between its posterior aperture; while the pubis appears in the shape of a broad, trilateral, flat bone, uniting before with its fellow on the mesial plane, behind with the ilium, and below with a flat, thin, quadrilateral bone, corresponding to the ischium, with which it forms the oval aperture. The inner of these three bones presents, as usual, the cotyloid cavity. It is further to be observed, that the two iliac bones, and consequently the whole pelvis, are movable on the vertebral column. (Plate XXXIV. fig· 5∙)

In the Saurial Reptiles the pelvic bones are arranged and shaped nearly as in the Cheloniad. In the Ranine ’ the iliac bones are much elongated, and the pubal and ischial are consolidated into one piece, the symphysis of which forms a rounded crest.

The femur is short, thick, and incurvated sinuously, with the convexity before towards the tibial end, and the concavity towards the pelvic. Trochanters, though present in the Ciieloniad, are wanting in the Saurial and Ranine Reptiles. In the leg we find both tibia and fibula distinct, and of nearly equal size, in the Cheloniad and Saurial family, but conjoined in the Ranine family. The tarsus consists of five bones, and sustains four or five metatarsal ones, on which are supported three rows of phalanges. The metatarsal bones, which vary in length, are longest in the crocodile and others of the Lacertine tribe. In the Ranine, again, the astragalus and calcaneum are the bones of greatest proportional length.

The anatomical characters now enumerated are proper to the skeletons of Reptiles at present existing on the surface of the earth or in its waters; and in these we find a gradual transition from the Saurial and Cheloniad, by means of the Serpentine, to the finny inhabitants of the ocean. Even the Batrachoid Reptiles, in the early period of their existence while tadpoles, we shall have occasion to see, approach to the Fishes ; and in one singular genus, if not two, the Proteus anguinus and Siren Lacertina, the characters of the Reptile are combined with those of the Fish, in having at once lungs or internal respiratory cells, and gills or external ciliated branchiae. The transition thus indicated is still more strongly demonstrated in the osteological characters of two Genera of animals now extinct, so far as is yet known,—the Ichthyosaurus and the Plesiosaurus.
[7:3:16]

From the specimens of the Ichthyosaurus hitherto discovered, it appears that the number of vertebrae varies from 80 to 90 or more; in one entire specimen they amounted to 104 (Conybeare and De la Beche); that they are flattened, with the transverse diameter greater than the longitudinal, and the two articulating surfaces of the bodies calycoid or cup-shaped as in Fishes. Though the annular 3 part is distinct from the body, it is united to its sides. The spinous processes, which are long and prominent, form a continuous ridge above the spine, and are connected to each other by a process from the front of the one spine, which is inserted into a pit in the back of the other. Instead of proper transverse process, a certain number of the vertebrae are provided with two tubercles on each side of the body, of which the superior, convex, is articulated to the tubercle of the rib, while the other, which is concave, receives the head. In the inferior part of the vertebral column, these two tubercles, after approximating, are eventually identified into one.

The ribs, which are numerous, and extend from the occiput to the pelvis, are slender and trilateral in shape, bifurcated above, and attached to the vertebrae by a head and tubercle. In the perfect specimen of Mr de la Beche they amount to 31, and of these 17 appear to be cervical or anterior false ribs, with single tubercles; thus affording another mark of resemblance to the Saurial family in osteological characters.

The bones of the head, distinguished by the extraordinary size of the orbit, are similar to those of the Saurial Reptiles. The sternum, collar-bone, and scapula, though also similar to those of this family, bear a much closer resemblance to the figure of these parts in the Echidna and Ornithorhyncus. The humerus is short, thick, and sinuated; the bones of the fore arm flat, and probably constituting part of the fore or thoracic fin. The Carpus consists of three rows, the first containing three bones, the other two, four each. These are followed by five or six rows of flattened, irregularly cuboidal bones, gradually diminishing in size and number to the tips, and which represent at once the metacarpus and phalanges of the fore paw, used apparently chiefly as a fin or paddle. The pelvic extremities appear to have been less strong and perfectly constructed than the thoracic. The femur is smaller and shorter than the humerus ; the tibia and fibula are flattened like the ulna and radius ; the tarsus consists of two rows only, the first containing three, and the second five bones; and this in like manner terminates in five ranges of flattened bones, gradually diminishing in size, and which represent the metatarsus and metatarsal phalanges of the hind paw or paddle.

From the specimens hitherto discovered of the Plesiosaurus, it appears that the total number of vertebrae amounts to 90, of which 35 appear to be cervical, while the other 55 are dorsal and caudal, the regions of which are proportionally short. The head of this animal also is small and compressed, nor has it the large orbit of the Ichthyosaurus. Each rib consists of a vertebral and sternal portion, united at an obtuse angle, the former articulated by a single head to the transverse process, and the latter connected with its fellow by a transverse slip, so that the lower or abdominal ribs appear to have surrounded the abdomen with a complete cincture. The anterior part of the chest is occupied by two trilateral bones uniting in the middle, which, from their connection with the scapula, are believed to be the coracoid bones; and above these is a transverse piece, with a middle notch and lateral sinuated elevations, which is regarded as the sternum; while the scapula extends on each side like a buttress be? tween the two. It is. not improbable, nevertheless, that the middle portions named coracoid bones are the sternum, and the transverse bone the clavicles; and it is worthy of remark, that not only this bone, but the middle piece, closely resembles in figure and disposition those of the Echidna and Ornithorhyncus. The pelvis consists of three bones, a vertebral or superior, corresponding to the ilium, narrow and slightly incurvated; an anterior, ascending forwards, and broad, separating the pubis ; and a posterior, short, forming the ischium. The humerus and femur are longer than in the Ichthyosaurus. There is a very short radius and ulna, and tibia and fibula, articulated with five carpal and tarsal bones; and the rest of both paddles consists of successive rows of flattened but long bones, contracted in the middle, and expanded at the extremities, representing the metacarpal and metatarsal digital phalanges. (Home, Phil. Trans. 1816, 1818, 1819, 1820; De la Beche and Conybeare, Geological Transactions, vol. V. p. 559; and Cuvier, Ossemens Fossiles, vol. v. part ii.)

SECT. IV. OSTEOLOGY OF THE FISHES.

' The Serpentine or Ophiad Reptiles present in their osteological characters an approximative transition to those of Fishes. While in the former order the skeleton is reduced to the spinal column, ribs, and head, in the latter class the spine and head only are left; and in some tribes the transition is still more distinctly marked by the presence of ribs.

The vertebra of a fish is distinġuished from that of any other animal by the shape of its body. The cephalic and caudal, or anterior and posterior surfaces, are hollow cuplike cones, so that the union of each two vertebrae forms a double conical cavity, united by the base, containing a substance composed of concentric fibro-cartilaginous layers, with intermediate albuminous or gelatinous matter. By this cartilage the vertebral bodies are united; and on this the motions of the spine are effected. This motion, however, is chiefly lateral; for the spinous processes are so long, and the articulation so complex, that antero-posterior inflection or extension is nearly impracticable.

In the cartilaginous fishes, for instance the shark, sturgeon, and lamprey, the vertebral bodies form simple tubes, which, from the extreme elasticity of the constituent cartilage, propel the contained fluid to a considerable distance. Thus Sir E. Home saw the fluid.projected to the height of four feet from the intervertebral cavities of the shark. {Phil. Trans. 1809.) In this order, also, the spine is infinitely more flexible, and its resilient power, when bent by the muscles, is almost incredible. On each side, also, the vertebrae are excavated, to form a canal for lodging the large blood-vessels.

The vertebrae of fishes are numerous, and not easily distinguished into classes. They may, however, be distinguished into two, according as the spinous process is above only, or above and below at once. Those with the dorsal spine only are denominated dorsal or abdominal verte-broe, and have commonly at the sides transverse processes for the attachment of the ribs. Those with the dorsal and ventral spines are distinguished as the caudal vertebrae. The last caudal vertebra is generally trilateral, flattened in the vertical direction; and its tip is marked with articular pits, which indicate the attachment of the small elongated bones which sustain the caudal fins.

The number of vertebrae varies. In the uranoscopus or star-gazer there are only 25, in the balista 17, and in the four-spined trunk-fish (pstracion) only 13; while in the sturgeon the number is 84, in the eel 115, and in the shark 207.

Ţhough'FiSHEs have no chest, and require none, since their respiratory organs are gills, all of them are not void of ribs. The ray, shark, syngnathus, tetraodon, diodon, cy- [7:3:17] clopterus, fistularia, &c. have indeed no vestige of rib. But in the sturgeon, balista, eel, uranoscopus, pleuronectes, sea-wolf, and dory, they are in the shape of short rudimental processes; in the7r⅛⅛ and loricaria their sides are horizontal; in the perch, carp, pike, and chetodon, they encompass nearly the whole upper region of the abdominal cavity; and, lastly, in the silver-fish (zcus vomer), the herring, rhomboidal salmon, &c. they are united to a sternum. In the little animal named sea-horse (syngna-thus hippocampus), several series of osseous tubercles of the skin, surrounding the body like belts, are supposed to represent false ribs. The sternum is limited to a small number of Fishes. Besides those already mentioned, in the dory there is a series of minute flat bones disseminated along the lower edge of the belly, which is supposed to represent a rudimental sternum.

In size and number the ribs vary, though in the silurus, carp, and chetodon they are of largest proportional size; in the herring they are as fine as hairs.

The head in the finny tribes is more an object of zoological than anatomical description. The chief points to be remarked are, that the cranium forms but a small part of the head; that the orbits are separated by a septum, sometimes membranous, occasionally, as in the wolf-fish, bony; and that there is on each side a large movable bone, corresponding to the quadrilateral of Birds, not square, however, but oblong, which supports not only the lower jaw and palatine arches, but the gill-cover. In the cartilaginous fishes the sutures are early obliterated, and the cranium consists of an inseparable mass of cartilage. In the bony fishes the cranium is separable into numerous pieces, and in the perch they amount to 80. In the cranium of fishes the anatomist recognises more distinctly than in the superior orders the formation according to the vertebral type. Small in proportion to the whole head, the cranium appears like a direct continuation of the vertebral column. In the osseous division of the class especially, the cranium may be distinguished into the occipital or posterior vertebra, the spheno-parietal or middle, and the frontal or facial vertebra. The cavity thus formed is very small; yet small as it is, it is not exactly filled by the brain, between which and the bones there is interposed a pellucid fluid, contained in fine cellular tissue. The cranium of the osseous fishes also is widest between the ears, because the organ of hearing is contained within its cavity with the brain. In the cartilaginous it is quite different.

Though Fishes are destitute of extremities similar to those possessed by the other three classes of the Vertebrata, they are not, however, without locomotive members. The thoracic extremities are represented by the pectoral fins, and the pelvic by the ventral. In short, it may be said that the bones of the thoracic and abdominal extremities are converted into osseous rays in the finny tribes.

In the Bay genus, in which the wing-like disposition of the pectoral fins gives the body a rhomboidal shape, they consist of numerous radiating cartilaginous lines, all attached to a cartilage parallel to the spine, divisible into two or three others, and articulated above to another adherent to the spine. Below there is a strong transverse bar common to the cartilages of both fins, and separating at once the sternum and clavicle. This transverse bar is also seen in the shark tribe; but their pectoral fins, which are much smaller, are not articulated with the spine.

In the osseous fishes, and in many others usually referred to the cartilaginous division, e. g. the balista, the pectoral fins are fixed to an osseous belt, which surrounds the body behind the gills, and which supports the posterior margin of their aperture. This belt consists of a single bone on each side, articulated to the posteriorsuperior angle of the cranium, and uniting below the breast with that of the opposite side. This bone, which - may be regarded as a scapula, varies in shape and the angle which it forms with its fellow in different species. In fishes flattened vertically, the angle of union is acute; in those which are depressed, the angle is so obtuse as to' form nearly a straight line. In many fishes, especially those of the order Thoracici, e g. pleuronectes, cottus, zeus, chetodon, perch, <⅛c., in the small unicon (balista), and others, the superior part forms a large spine, which descends immediately behind the fin, and to which the adductor muscles are attached. This spine, which is movable, has been improperly named a clavicle.

The rays by which the membrane is supported are not directly articulated to this belt, but are connected by a row of minute flat bones, which may be compared to the carpus in the other three classes. When the first ray of the pectoral fin, however, is thorny, as in the harness-fish (loricaria), and some species of silurus, it is articulated directly with an osseous belt; and it is remarkable that some fishes, as the silurus and stickle-back, have the power of retaining this spinous ray erected against the body as a means of defence. This is effected by a cylindrical tubercle, on which the spinous ray is articulated by a hollow, bounded before and behind by an elevated process. When the spine is erected, the anterior process, entering a hole in the cylindrical tubercle, is locked in it by the spine revolving slightly on its axis, so that it cannot be inflected unless by the spine revolving in the opposite direction.

The pectoral fins are so long that they answer the purpose of wings in several species of trigla, the trigla hirundo, the flying gurnard (trigla volitans), the springing gurnard (trigla evolans,) in the scorpaena volitans, the tropical flying fish (exocoetus volitans), and some others. Their situation also is liable to vary. In the exocoetus they are near the gills, but in the biennius and others they are remote. Lastly, they are totally wanting in a small number only, as the lamprey (petromyzon), the hag-fish (myxine, Lin.; gastróbranchus), the muroena, the eel genus, the sphagobranchus, &c.

The abdominal or ventral fins, which correspond to the pelvic extremities of the other classes, are so denominated because in the majority of fishes they are situate below the belly, and nearer the anal outlet than the pectoral. By this circumstance a numerous order are distinguished by the name of Abdominal Fishes (Abdominales).

In a small number of fishes, comprehending the gadus, biennius, kurtus, callionymus, trachinus, and uranoscopus, the ventral fins are placed under the throat, below the aperture of the gills, and before the pectoral fins. This order is therefore distinguished by the name of Jugulares.

In the most numerous order of all, the ventral fins are situate behind and below the pectoral fins. These have therefore been denominated Thoracic Fishes (Thoracici).

The ventral fins consist of two parts—one formed of rays covered by a double membrane, apparent externally, and constituting the proper ventral fin; the other internal, representing the coxal bones of the pelvis, always supporting the pinnal rays, and often articulated with the bones of the trunk. It is never articulated, however, with the spine, nor does it form an osseous belt round the abdomen. The bones of which it consists are generally flattened, varying in shape, and in mutual contact by the internal margin. In the shark and ray genera only is there a single transverse bone, nearly cylindrical, to the extre-inities[7:3:18] of which the fins are attached. The direction of the pelvic plane to the walls of the abdomen varies according to the shape of the body of the fish. In the flat fishes they are directed obliquely, and their inner margin forms the keel of the belly. In fishes with a broad or cylindrical belly they form a plane more or less horizontal.

. In the Jugular and Thoracic Fishes, the pelvic bones are always articulated with the base of the belt which sustains the pectoral fins; and they vary much in shape and situation.

In the trachinus, uranoscopus, cottus, sçioena, chetodon, and perch, these two bones are united by their inner margin. In the cuckoo-gurnard, in which they are united by the posterior tip only of their internal margin,.they are broad, flat, and oval. In the sole and flounder genus (pleuronectes), in which the fins are attached to their anterior tip, they are united in a quadrangular pyramid, the apex of which is directed backwards and upwards, and the base forwards. In some of the stickle-backs these bones are altogether separate, and being long, receive in their middle a movable spine, which supplies the place of the ventral fin. In the dory (zeus faber, L.) they are flat and triangular, in mutual contact by their whole surface. In the silver-fish (zeus vomer) they are small and cylindrical.

In the whole of the Abdominal order, on the contrary, the pelvic bones are equally unconnected with the bones of the shoulder and with the osseous belt of the pectoral fins, and are confined to the middle-inferior part of the belly, not far from the anus. In general these two bones are separate from each other, and are retained in their situation by ligaments. In the carp,. in which they are elongated, they touch only by their posterior third. In the herring, in which they are small and approximated, they are continuous with the minute bones of the sternum. In the pike they are broad and trilateral, approximated by their anterior tips, separate behind where the fin is attached. In the silurus, in which they are united, they form a round and often spinous shield before, while the fins are attached to the exterior-posterior margin. Lastly, in the cuirassier or harness-fish (loricaria), the pelvic bones are united in one piece, the posterior notch of which forms the anal aperture, while the fins are attached to its external margin.

The proper fin consists of a certain number of osseous rays, simple or biful, supported by one or two rows of ιni- ∙nute bones placed between them and the pelvic bones. On these small bones the constituent rays move, diverging or converging like the rods of a fan, while the whole fin maybe inflected or extended by the minute bones moving on the pelvic, so as to adduct or abduct the fin.

’ In the cartilaginous fishes the structure is different. To the tip of each pelvic bone are articulated two principal cartilages, one external, forming a kind of toe with seven or eight joints; the other internal, supporting all the other rays of the fin, which often exceed thirty in number.

r If we suppose these bones, like the minute ones of the 1 pectoral fin, to represent the tarsus of the other three l classes, it must follow that, in the locomotive extremities, the humerus, with the ulna and radius, and the femur, with the tibia and fibula“, are obliterated. It is not en-important to observe, that the general structure of l the Vertebrata tends through various transitions to this termination. In the Amphibia the long bones of the extremities are shortened by removing the diaphysis, and leaving their articulating ends only. In tha Cetaçea the pelvic •extremities are removed altogether. In the Cheloniad and Saurial Reptiles the same long bones of the extremities are much abridged; and in the Ichthyoid.Reptiles,· now extinct, but sharing by their structure a form of animal existence partaking, of the. reptile and fish at once, and perhaps intermediate between the two, this abbreviation is carried perhaps to its greatest possible degree, in leaving the articular ends only of the four locomotive extremities. Lastly, this reduction is merely preparatory to that exhibited in the whole class of Fishes, in which the three longitudinal bones so conspicuous in the higher classes of animals are completely obliterated, and those representing the hand or forepaw and foot are articulated directly to the shoulder and pelvic bones.

Besides the bones already mentioned as constituting the skeleton, there are observed in the osseous fishes minute bones, generally fork-like in shape, disseminated through all the muscular parts of the body. The purpose of these bones, which, as being totally insulated from the other parts of the skeleton, arc denominated ossicula musculorum·, is chiefly to afford points of support; and they are probably to be regarded as rudimental representatives of osseous parts, more completely developed in the higher animals.

It is further a curious circumstance, that the skeleton, which is so symmetrical in all the other classes and orders, begins to exhibit a deviation from this first in the skeleton of the finny tribes. In the Sole genus (Pleuronectes) this deviation is very conspicuous. Both eyes are placed on the same side of the mesial plane; and the side on which the eyes are placed is broader than the opposite one. The former is bounded by a convex margin, the latter by a concave one. The orbit towards the former is large, the other small and imperfect. Conversely, it is to be observed, that in the latter the maxillary and intermaxillary bones are larger than in the former. The sides of the inferior jaw are less discordant; and though in the Sole and Plaice those of the eyeless side arc more straight and elongated than those of the other, in the Turbot (Pleuronectes maximus) they are nearly symmetrical,

CHAP. II.—COMPARATIVE MYOLOGY.

Though this is the proper place to consider the peculiarities of the muscular system of animals, the limits assigned to this sketch will not allow us to enter into details. We shall merely, therefore, take a cursory view of those points in which the myology of the lower animals differs from that of the human subject.

In general, in the lower animals, especially the Mammalia, Birds, and Reptiles, the muscles correspond in situation to those of the human subject; and whatever modifications they undergo consist in changes of figure, and in some few instances in changes in attachment. The former kind of changes may be in all cases pretty accurately estimated by the osteological characters of the class, order, or genus; for when the position, shape, or direction of, a bone is altered, in the same proportion nearly are the attached muscles altered in their attributes.

Though in the lower animals, however, the zootomist traces muscles in general quite analogous to those of the human subject, in several instances this analogy ceases to be observed. In general the muscles of the lower animais are less numerous than those of the human subject; and this, deficiency in number, though not much observed in the Quadrumana, is very remarkable in all the inferior orders of the Mammalia, and still more in the Birds and Reptiles. In general, also, these variations are most conspicuous in the locomotive extremities. Thus the small; pectoral muscle, which is present in the Quadru-mana, is; wanting in the Camivqra and the whole of the. Ungulated Animals and the Reptiles. The short supinator is present in the Canine and Feline genera, but the long is wanting; and both are absent in the CiiiROP- tera, Rodentia, Pachydermata, Ruminantia, and [7:3:19] Solidungula, and în the whole class of Birds. Both pronators (teres and quadratus) are present in the Quadrumana and Carnivora, but wanting in the Chirop-tera, Ruminants, and Solidungula. The Rabbit, and perhaps the Rodentia generally, have the pronator teres ; but as the radius is not very movable, its influencé is trifling. ' ∙

In the mole the rhomboideus is inserted into the ćervical ligament, which is ossified; and it therefore elevates the head and neck On the scapula with singular force. This is effected still more remarkably by the occipital ‘part of the rhomboideus, the fibres of which being parallel to the spine, pass below the proper rhomboideus to be attached to the transverse ligament and the middle of the Cranium. The strong, thick, quadrangular collar-bone has two muscles, a supraclavius and a subclavius. The large pectoral is very’ thick, and nearly as large as in birds.

The common extensor of the fingers or fore toes is the only muscle which is common to man and all the quadrupeds. Of the proper extensors the horse has two on the side of the common extensor, but acting as an extensor of the fore pastern; another between the common extensor and the extensor of the pastern, and which seems merely an appendage to the former. The proper extensor of the index is wanting in the Rodentia, Ruminants, and Solidungula ; and while the two latter orders are destitute of the long and short extensors of the thumb, and the feline, canine, ursine, and leporine genera have the former,· they are destitute of the latter. Lastly, the lower animals are wholly destitute of the short muscles of the hand, which in man produce flection, abduction, adduction, and opposition. In the Chiroptera only is there one extensor, and flexors of the fore toes.

’ Among the muscles of the pelvic extremities the glutaeus maximus, or large muscle of the buttock in man, diminishes much in the Quadrumana ; and in the other orders is reduced to a very small size. The buttock in the Mammalia generally consists chiefly of the glutaeus medius and minimus ; and while the glutaeus maximus is in the horse in a great part aponeurotic, the g. medius is so largé as to produce those forcible and sudden extensions of the hind leg which constitute the kićk.

In the leg the sartorius of the horse, the animal in which the muscles have been most studied/ is-large, and is distinguished by the name of the long adductor, in opposition to the gracilis, which constitutes the short ad-ductor. ’ The muscle representing the biceps of man is in all quadrupeds a uniceps, and the single head is attached to the ischium’only. In-the horse and dog i it has been denominated the vastus loñgus. .' (·.·

The gastrocnemius externus et internus (gemellus), which constitute the calf of the human subject, diminish consi∙∙ 'derably in the lower animals; and the solaeus, which is Ĩ»laced belotv them,’also becomes small,* and is-particu-arly slender in the Ruminants and Solioungula.

The following’musclés are wanting in the'whole class of Bird’s.’. The diaphragm, the recti abdominis, and the py ramidales; the muscles of the dorsal part of the spine, the splenius, the brachialia externus, or third head" of the triceps ; the supinators of the fore ⅛rm or wing, as already mĕntioneá, all those corresponding - to the short m i uscles of' the hand and 'fingers; the quadratuà lumborum, the psoas parvus, the pšŏas magňuš, iliacus intermis, obturator externus, and the extensor longus pollicispedis.

' 'Two muscles, which 1 occupy the Situation of the;pronators;’ácţ as flekòrs, showing the connection between the actions 1 of inflection and prpnatioit’, and*the occasional substitution of the lattér for the former. ’

‘•‘In this class, r also,"the gľútoeiis ŉiaxiríius is of'a pyramidal shape, while lhe l trno pyriformis is-wanting. ’ The glutaeus minimus, which is attached to the anterior edge of the iliac bones, is the iliacus. In place of the pectineus there is a slender muscle, which extends to the knee, over which its tendon passes, and gliding behind the leg, its tendon is bifurcated, One slip going back to be inserted into the posterior part of the metatarsus, the other to be united to the perforated flexor of the first and last toe. This muscle, which 1 is ńaméd the accessory femoral flexor, is the one by which birds are enabled to clasp a perch during sleep.

’ In Birds the great pectoral is a remarkable muscle in point of size. It consists indeed of three muscles, the large pectoral, the middle, and the small, which occupy the sides of the vertical crest of the sternum, and constitute what is named the breast of the animal; and which are chiefly employed in the energetic motion of the wings in flying. Thèse muscles are sometimes so large that they weigh more than all the other muscles of the animal together. In birds which fly much they are dark coloured and firm ;· in those which fly little, as the domestic poultry, they are white coloured,' and in general soft. The ⅛ame distinction is observed in the muscles of the two extremities. In birds much on the wing these muscles are dark Coloured and firm, while those of the legs are comparatively lighter and more tender; and, conversely, in birds little on the wing and mostly on the legs, as the domestic poultry and many of the Gralloe, the waders, swimmers, &c. the muscles of the wings are light coloured and tender, while those of the legs are dark coloured, firm, and strong.

The flexor muscles of the leg and toes of Birds merit notice. They consist of muscles corresponding to the long flexors, which are divided into three masses. The first consists of· five portions, three of which may be regarded as constituting a single common perforated flexor. It rises by tWo bellies, one attached to the external condyle of· the femur, forming a perforated tendon, which receives one of those of the muscle corresponding to the peronoeus ; the other to the posterior surface of the femur,. forming the tendons of the index and small toe. This muscle is further connected by intermediate fibres with the accessory femoral flexor,—a muscle placed on the internal surface of the thigh, and sending its tendon over the knee·; 1 and as the tendons are inserted into the unguinal phalanges, when the· accessory femoral bends the thigh the flèkors of the toes inflect them also, and retain them in· the inflected position. By means of this arrangement birds are enabled to clasp a perch or other small body when roosting, without continued muscular effort, and thereby-to sleep on the perch. This mode of explanation, which was originally given by Borelli, has been controverted by Vicq d ’ Azyr; but apparently not on good grounds. ∙

Among the class of Reptiles, while the muscles of the OphiDIAL family are confined to tho⅛e∙ of the vertebrae and rudimental ribs, in the CheĺoniáD these are obliterated, and the· muscles 4 of the neck, head, and tail, and those of the locomotive'extremities alone, are left. In the other two class⅛s of reptilès the muscles are in general analogous to those' of the Mamm'aiia.

»There ate nöt many instattcés of muscles which, though unknown in foan, äre found’in ∙the lower animals. Of these the most remarkable are thecŭtaneöus muscle (panniculus carnosus), and the suspensory of: the eye. The former was absurdly maintained tó’exist in the human subject/ especially by Niċolaŭs Massa; but it is*manifest that the-assertion was derived from the dissection of tile lower animals’ only. » It was : not-long after demonstrated by Charles-Etienne, that no fleshy pannićle or cutaneous ι muscle exists,* süċh áš is found in the lower -animals; ahd [7:3:20]that the only cutaneous muscles in man are the latissimus colli, the epicranius or scalp-muscle, and those which are attached to the face, and which by their motion give expression to the countenance. The cutaneous muscle even is not found in the Qüadrumana, nor does it exist in the pig. In various other animals, however, it is found in different degrees of distinctness. It is very well marked in the hedgehog and porcupine ;—by its means they have the power of erecting their spines, and rolling themselves up ;—and in the armadillo and the anteater tribe. In the mole, also, we have seen it pretty well marked.

It is an interesting fact, that Galen originally observed that the lower animals possess a seventh muscle of the eye, or one more than man. The suspensory or infundibular muscle (musculus clioanoides), as it has been named, from its shape, especially in the Ruminants and Solidungula, has the apex fixed to the margin of the optic hole, and its base inserted a little behind the four straight muscles. In the Zoophaga and Cetacea it consists of four parts, so that these orders appear to be provided with 8 straight muscles. In the rhinoceros it consists of two portions.

There is yet another part, the muscles of which· can scarcely be said to exist in the human subject, but which attain a very great degree of developement in the lower animals. The coccyx of the human subject is expanded in the lower animals into a highly flexible prolongation denominated the tail (caudd), variable in length, but always consisting of separate vertebrae, articulated and movable on each other. While the coccyx of the human subject possesses two muscles only, the iscliio-coccygeus and sacro-coccygeus, which are so insignificant in size that they scarcely serve to move the part, the caudal vertebrae of the lower animals are moved by muscles greatly larger, more numerous, and more powerful.

The tail is to animals a much more useful and powerful organ than the coccyx to man. It is a member which peculiarly belongs to them; and though in ordinary circumstances pendulous, it is made to assume a variety of motions of which no other organ is susceptible, and to perform duties which would be otherwise impracticable. With many, as the long-tailed monkeys, the sloths, the ant-eater, and the squirrel tribes, it is indispensable as an organ of prehension. The majority of animals, as the Ruminants, Solidungula, &c. use it as a whip or lash to drive away insects. The lion, tiger, and others of the feline tribe, lash their sides with it when enraged. The Cetaceous swimmers employ it as a rudder and oar in the waters. The beaver uses it as a trowel, to enable him to construct his clay-built dwelling. An organ employed so variously must consist of a muscular apparatus rather complex.

The different motions of which the tail of the Mammalia is susceptible may be referred to three heads,—one by which it is extended or elevated, another by which it is inflected or depressed, and a third by which it is made to beat the sides. The combination or succession of these motions gives rise to secondary ones more complex in character. It may be twisted on its axis, or turned in a spiral direction. These motions are effected by three classes of muscles.

Isŕ, The muscles which raise the tail are situate above; they are musculi sacro-coccygeei superiores. Commencing at the base of the articular processes of the 3 or 4 last lumbar vertebrae, or those of the sacrum and the caudal vertebrae, by fleshy slips, they are connected to tendons, which are inserted into the base of the first of the caudal vertebrae, which are void of articular processes. The second tendon goes to the next following vertebra, and so on to the 13th, each contained in a ligamentous groove, which forms an investment. The muscles of both sides acting together, elevate or incurvate the tail up- wards.

The interspinalis and spinalis obliquus or lumbo-sacro-coccygeal are the continuations of the interspinales dorsi et lumborum. The spinous processes, however, becoming indistinct, or being represented by two tubercles, the attachments vary.

2d, The muscles which depress or inflect the tail downwards take their origin within the pelvis, and are prolonged to various extents along the inferior surface of the tail. Of these there are four pairs, the ileo-coccygeal of Vicq d’Azyr, the inferior sacro-coccygeal, the inter-coccygeal muscles, and the pubo-coccygeal of the same author. The insertions of these muscles vary in different genera, according to the number of vertebrae of which the tail consists. The pubo-coccygeal is wanting in the raccoon, but it is distinct in the dog and opossum. The effect of the ileo-coccygeal and it, is to depress the tail and apply it forcibly to the anus. 3d , There are only two muscles which carry the tail to the sides of the animal—the ischio-coccygaeus externus, and the intertransυersalis of Vicq d’Azyr; the former proceeding from the pelvic surface of the ischium below and behind the acetabulum, to the transverse processes of the caudal vertebrae, the second extending in a continued band between all the transverse processes.

The tail, therefore, in the Mammalia, consists of a series of successively decreasing vertebrae, moved by eight pairs of muscles.

In Fishes it is not easy to trace any analogy between the muscles and those of the other classes. Though the spine, head and fins, have appropriate muscular bundles, the natural or fascial distinctions are less evident than in the other three classes. It is important, however, to remark, that while the muscles which move the spinal column are placed in these classes, partly before, and chiefly behind the vertebrae, those of Fishes are placed on each side. Hence the lateral motion of the spine, which is inconsiderable in Mammiferous animals, Birds, and Reptiles, becomes very conspicuous in the finny tribes, especially in the motion of swimming, while the anteroposterior inflection or extension is altogether insignificant.

It is almost superfluous to remark, that, in the greater part of the finny tribes, the muscles are white or pale coloured. In a few only, for instance the salmon, trout, gwiniad (coregonus), herring (clupea harengus), carp (cyprinus), and some others, are the muscular fibres of a pale flesh red. The circumstances on which these differences depend arc not known; but it is supposed that in the latter sorts the proportion of oleo-albuminous matter is more abundant than in the former. The proportion of albumen, however, in the muscles of fish, seems in general to be small. They abound in gelatine and isinglass; and in some of the cartilaginous fishes especially, the greater part of the muscles seem to consist chiefly of gelatine in various degrees of consistence. This is particularly the case with the lamprey, the hag-fish (myxine glutinosa), and even with the sturgeon. The sterlet especially (acipenser Ruthenus), a small species of sturgeon found in the rivers of Russia, both European and Asiatic, abounds in gelatine; and the presence of this principle enables the inhabitants to use it in the preparation of a species of soup, the sterlet, which is esteemed a great delicacy. In some of the genus Pleuroncctes this principle is also very abundant. Thus the Plaice (Pleuronectes Platessa), sole (P. Solca), and especially the turbot (P. Maximus), contain a considerable proportion of gelatine. On the proportion of this principle depends the quality of fish used [7:3:21]as an article of food in nourishing without exciting. All fishes which abound in gelatine uncombined with oleo-albuminous matter may be safely used as articles of food; while those in which the latter ingredients predominate are invariably eaten with the risk of disordering the stomach and producing indigestion.

CHAP. III.—COMPARATIVE AESTHIOLOGY, OR THE COMPARATIVE ANATOMY OF THE ORGANS OF SENSATION.

SECT. I. THE ORGAN OF SMELL.

The organ of smell consists of the nasal cavities, those of the ethmoidal and turbinated bones, and the frontal, Sphenoidal, and superior maxillary sinuses, all of which communicate with the nasal. The whole of these parts are invested by fine periosteum, lined by mucous membrane. The ethmoid bone is the essential organ of smell; and the others appear simply to multiply the extent of the membrane.

. The ethmoid bone consists of a perforated plate, with a middle vertical one attached at right angles to it, and lateral portions composed of thin bony plates convoluted with various degrees of complexity and minuteness in different orders and genera of animals. These convoluted plates form what are denominated the ethmoidal cells. They may be represented as numerous tortuous canals, proceeding from the perforated plate forwards and outwards, approximating mutually, and forming numerous communicating cavities. Such nearly is the structure of these plates in the Edentata, Ruminantia, Solidungula, Pachydermata, and Carnivora, the last of which have more complicated cells than the first. In the dog they are numerous and extensive. In the Rodentia, for instance the porcupine, they are few—not above 3 or 4 on each side.

In Birds the internal side of each nostril is occupied by three orders of plates; the inferior turbinated or spongy bone; the middle, consisting of one plate convoluted on itself two turns and a half; and the upper, shaped like a bell, adhering to the frontal and lacrymal bones. These form three tortuous passages, varying in size and tortuosity in different genera. Though generally cartilaginous, these turbinated bones are membranous in the cassowary and albatross, and bony in the calao and toucan.

In the nostrils of Reptiles there are convoluted prominent plates, which, however, are merely membranous productions, unsupported by any bone.

In the Fishes, in like manner, there are membranous folds, the disposition of which is tortuous. They arc, however, more regularly arranged than in the other classes. In the cartilaginous fishes they consist of semilunar folds placed in parallel tracts on each side of a broad plate, which divides the one side of the nasal cavity from the other. In the sturgeon, however, they are arranged in diverging plates, which are subdivided into more minute ones, like the branches of a tree. In the osseous fishes generally they consist of radiating plates disposed round a prominent central tubercle.

In these three classes the olfactory nerve is distributed to the membrane much in the same manner. This nerve, however, does not proceed farther than the superior turbinated bones; and the middle and inferior appear to be supplied with filaments of the fifth pair, the naso-ophthalmic branch of which is distributed to the nose in all the vertebrated animals. In the Mammalia, further, the spheno-palatine ganglion sends several filaments to the posterior part of the narine membrane.

By most zootomical authors the trunk of the elephant has been described as an organ of smell peculiar to that animal. We are satisfied, however, from observing the motions of this body in the living animal, that it is an organ, not of smell, but of prehension. Cuvier, after adopting the ordinary view, has relinquished it, and, on the ground of personal inspection, admits that the sense of smell in the elephant is confined, as in other animals, to that portion of the nasal cavities which is contained within the bones of the head. The trunk of the elephant, therefore, will with greater propriety be noticed under a subsequent head.

The nasal cavities of the Cetaceous animals are not so much organs of smell as channels of respiration, and must also be noticed afterwards. It is sufficient here to remark, that in these animals the part of the cranium corresponding to the ethmoid bone is penetrated by no aperture, or, in other words, is not an ethmoid bone. It has therefore been asserted that the Cetacea have no olfactory nerve, and no sense of smell. This, however, is by no means established. Blainville and Jacobsen have observed in the dolphin nerves which they regard as olfacient; and Treviranus delineates nerves of the same character. By Otto and Rudolphi, on the contrary, who have had frequent opportunities of dissecting the dolphin and whale, the existence of these nerves is denied.

Though almost all the invertebrated animals give proofs of the existence of the sense of smell, in none of them do we find any organ in which this sensation appears with certainty to be exercised. That these animals possess the faculty of smell, is inferred from the fact, that insects recognise their food at a distance; that male butterflies scent the female even when inclosed in cages; and that the ordinary flesh-fly deposits her eggs on tainted meat, and occasionally on fetid plants, in the belief that they arc the proper nidus, though in the latter case the larvae perish for want of the necessary sustenance.

Since odorous particles are evidently applied to the olfactory membrane of all aeropnoic animals by the medium of the atmosphere, and since the organ of smell is therefore situate in connection with the wind-pipe, it was conjectured by Baster, that, in insects at least, the organ of smell is situate at the entrance of the tracheae or airtubes. This conjecture derives some probability from the fact, that the inner tracheal membrane in these animals is soft and moist, and that those in which it is expanded into convoluted lacunae and tortuous vesicles, for instance beetles, flies, and bees, are remarkable for the nicety of their sense of smell.

The antennae, in which this sense has been placed by some anatomists, appear to be rather organs of touch than of smell.

In the Mollusea the whole cutaneous covering seems to combine the character of an organ of touch or tact, and of smell. Like an extensive pituitary membrane, it is soft, villous, moist, and liberally supplied with nerves. The Articulata and Zoophytes seem much in the same state. But on all these points information is rather conjectural than positive.

SECT. II. THE EYES; THE ORGANS OF VISION.

All red-blooded animals, without exception, are provided with two movable eyes, consisting of the same essential parts as those of man, forming globular organs, and placed in the cranio-facial cavities named orbits. In none are there more or fewer; and the exceptions to the general rule, either in relation to the presence of these organs, or number, are only apparent. Among the Mammalia,: indeed, there are two instances of blindness,—in the zemni or blind rat (Mus typhlus, Lin.; Spalax typhlus, Pall.), and 1 the golden mole (Talpa Asiatica, Lin.; Chrysochloris, 1 Lacep. and Cuvier). But in neither of these animals are [7:3:22]the eyes absolutely wanting; they are merely very minute, and covered by a thin fold of hairy skin, in which there is said to be no aperture. Much in the same manner the muraena coecilia, and the hag-fish (myxine, Lin., gastrobranclius caecus), though provided with eyes, are deprived of the use of these organs by the opacity of the conjunctiva. In the Anableps ( Cobitis Anableps, Lin.), the cornea and iris are biparted by transverse bands, so as to give the animal the appearance of having two pupils in each eye, though the crystalline lens, vitreous humour, and retina, are single. This animal affords the only example of this structure among the vertebrated animals; but a similar arrangement is observed in the Cephalopodous Mollusea and cuttle-fish family.

The general shape of the eye depends on the medium in which the animal lives. It is nearly spherical, or approaching the spherical shape, in man and the quadrupeds moving along the surface of the earth; that is, in the lowest and most dense region of the atmosphere. The cornea merely forms a slight convexity, in consequence of being the segment of a smaller sphere than the rest of the eyeball; yet in the porcupine, opossum, &c., this difference is inconsiderable. To show the degree of this convexity, it is merely requisite to compare the axis or antero-posterior diameter with the transverse diameter of the ball, as exhibited in the following table :—
[table]

According to the measurements of the younger Soemmering, the axis of the human eye, taken in a beautiful Tyrolese girl of 20, is to the transverse diameter as 100 to 95; that of the eye of the magot (simia inuus) as, 85 to 84; and that of the bat (vespertilio auritus) as 12 to 11. In the raccoon (ursus lotor) and lynx (felis lynx) alone the axis is exactly equal to the diameter. In all the other vertebrated animals, it is, as in the measurements of Cuvier, less than the transverse diameter at the rate of from 9 to 33 or 45 per cent. In the horse it is as 186 to 212, in the seal as 130 to 142, in the Indian elephant as 135 to 180, and in the black whale (balaena mysticeius) as 20 to 29. In the owl it is as 17 to 18, in the golden falcon as 14½

to 16, in the ostrich as 18 to 19∣, and in the swan as 7 to 10. In the Reptiles and Fishes it is always less at the rate of from 3 to. nearly 10 per cent. In the cuttle-fish, which may be taken as a general example of the invertebrated classes, it is much greater, the axis being to the diameter as 80 to 57. (D. W. Soemmering de Oculorum Hominis Animaliumque Sectione Horizontali Commentatio. Goetting. 1818, fol.)

In Fishes and the Cetacea which inhabit the sea, the anterior part of the eyeball is much more flattened, and in many fishes it resembles a hemisphere with the plane surface before, and the convex behind. In the ray genus the superior part is also flat, so as to give the eýe the appearance of the quadrant of a sphere, cut through two large circles perpendicular to each other. In some fishes, especially the burbot (Gadus Lota), the cornea is convex.

In Birds which occupy the elevated regions of the atmosphere, the deviation from the spherical shape is in the direction opposite to that of fishes. On the anterior part, which is sometimes flat, sometimes shaped like a truncated cone, is chased a short cylinder, closed by a very con-vex, and occasionally hemispherical cornea, always belonging to a much smaller sphere than the posterior convexity.

These differences in shape depend on the proportion between the density of the medium iń which the animals live and that of the aqueous humour. In the higher régions of the atmosphere, in which the air is very much rarefied, the refracting power of the aqueous humour is much more considerable than at the surface, occupied by quadrupeds; and hence it is more abundant in the former than in the latter class. Its refracting power, however, would be almost extinguished in a watery medium, from which it could differ but little in density; and hence it is either trifling or absolutely wanting in the inhabitants of the deep. In the cuttle-fish family it is entirely wanting.

The crystalline lens in Fishes, which is nearly spherical, projects through the pupil, and leaves little room for the aqueous humour. The lens is also very convex in the Cetacea, the Amphibious Mammalia, the diving birds, as the cormorant, and the marine and aquatic Reptiles.

Affecting the oblate spheroidal shape in the Mammalia, it becomes extremely so in man, and still more in Birds. Its consistence is greatest in animals in which it is most convex; and hence it is matter of common observation, that the crystalline of fishes is particularly firm. It also contains rather more albumen than the lens of the Mammalia. The crystalline lens occupies least proportional space of the eyeball in man, and most in fishes.

The comparative spaces occupied by each of the humours may be understood from the following table, in which the axis of the eye, or the śpace occupied by the whole three humours, is represented by unity.
[table]

On the proportion of the total volume occupied by each of the three transparent parts there are few accurate facts. It may be remarked, however, that the human eye among the Mammalia is that in which the vitreous humour is proportionally most abundant. It is estimated to be twenty times more copious than the aqueous. In the ox it is only ten times, and in the sheep nine times the quantity of the aqueous.

In the Mammalia generally, the sclerotic is comparatively elastic, soft, and yielding; but in all animals in which the eye deviates from the spherical shape, as the Cetacea, Fishes, and Birds, this membrane is strengthened by greater solidity and thickness of tissue, or supported by accessory parts of a hard unyielding structure.

In the eye of the whale these two parts, the hard and soft, are naturally distinguished in a very striking manner. The lateral parts of the sclerotic are nearly an inch thick, and very hard. The posterior part is about one and a half inch thick, and softer, because the spaces between the firm fibres are filled with oily substance. The, posterior part presents Tor the optic nerve a canal one and a half inch long, the walls of which are formed chiefly by fibres in direct continuity with the durd mater, the only fact, it may be observed, which favours the statement of the ancient anatomists, that the sclerotic is derived from the dura mater. The sclerotic of the porpoise, though only two or three lines thick has the same structure as that of the whale. In the seal it is thick before and thicker behind, but the middle zone is'thin and flexible.

The sclerotic in Birds is thin flexible, and elastic behind, with a bluish glistening aspect, and without distinct fibres. The optic nerve, enters, not by a hole, but an oblique canal. The anterior part consists of two plates, between which is enchased a zone of thin, hard, oblong, osseous[7:3:23] scales, varying in number from 11 or 12 to 14 or 15, imbricated over each other so as to give the anterior part of the eyeball a great degree of hardness, and a figure unsusceptible of change. Though these plates are nearly flat in most birds, and form an annular zone slightly convex, they are broad, arched, and concave internally in the owl genus, and form a bell-shaped tube, with the posterior aperture oval and the anterior round. This may be denominated the osseous ring (annulus osseus, zona ossea). In the ostrich it is narrow and flat.

Among the Reptiles, the Cheloniads possess an osseous zone, consisting of plates inclosed in the membrane without being continuous with its substance. They are also found at the lateral part of the sclerotic in the chameleon and some of the Saurial Reptiles, as the Crocodilus Sclerops and Lucius, the monitor, and the iguana (D. W. Soemmering). It is also an important character in the structure of the eye of the Ichthyosaurus, which indicates the connection of that animal with the Saurial tribe, that its sclerotic was provided with an osseous zone, consisting, as in these, of 13 separate pieces.

In Fishes the sclerotic is cartilaginous, homogeneous, semi-translucent, elastic, and, though thin, firm enough not to collapse. In the ray it is expanded into a tubercle, by which the eye is attached to a peduncle or stalk. The sclerotic of the sturgeon is so thick that it resembles a cartilaginous sphere, with the external part hollowed for the humours and membranes.

In the Cepiialopodous Mollusea it forms behind a truncated cone, with the apex at the bottom of the orbit containing the gangliform swelling of the optic nerve, and several glandular parts, with the eye before.

The cornea has often been represented to be merely a continuation of the sclerotic; and though, this is easily disproved by accurate dissection of the human eye and that of our ordinary domestic animals, its inaccuracy is much more manifestly demonstrated in the animal world at large. In the whale and rhinoceros the margins of the two membranes penetrate reciprocally. In man and the ox the corneal margin is enchased within the sharp imbricated edge of the sclerotic. In the tope-fish (squalus milandra, Lin.; galeus, Cuv.) the cornea is observed distinctly passing within the sclerotic in the manner of imbrication. The cuttle-fish is destitute of cornea; and as there is no aqueous humour, the crystalline lens is covered by a fine thin membrane, extended beneath the conjunctiva.

In all animals provided with eyelids, the mucous membrane, after being folded behind the eyelids, is reflected forwards over the sclerotic and cornea, in the form of a thin, transparent membrane. In those void of eyelids, as most fishes are, the skin, passing into mucous membrane, is continued directly over the cornea, without forming any angular fold, and adheres strongly. This is very distinct in the eel, which may be flayed without leaving any trace at the site of the eyes, except a round, translucent spot. The same peculiarity is remarked in Serpents and in the cuttle-fish family. In the zemni, golden mole, blind eel, and hag-fish, it has been already stated that the cornea is covered by opaque mucous membrane.

The choroid coat exists in all animals yet examined. It is always very vascular. The inner layer, which has been distinguished by the name of tunica lìuyschiana, can scarcely be said to exist in man, s∏ialf quadrupeds/ and birds. In the large quadrupeds^,however, especially the Cetaceous animals, it appears in . the form of a distinct simple membrane like epidermis. The lateral and anterior parts of the membrane are/always invested by a semifluid, viscid substance, of different shades of black or brown black (pigmentum nigrum) ; chocolate'brown in.the hare, rabbit, and pig; deep red brown in some birds; and purple red in the calmar. The absence of this dark-coloured pigment, which is not unfrequent, is observed in albinos, both human and animal, for instance white rabbits and white mice. The transparency of the Ruyschian membrane then shows the choroid of its natural red colour; and the pupil is red and contracted, and the eye intolerant of light.

In the Zoopiiaga, Ruminantia, Pachydermata, Solidungula, and Cetacea, the concave or inner surface of the Ruyschian membrane is diversified with colours of metallic lustre, more or less brilliant and something iridescent. In the ox it is of bright metallic green, changing to sky-blue; in the horse, buck, buffalo, and stag, it is a silvery blue passing to violet; in the sheep of a pale golden green, sometimes bluish; in the lion, cat, bear, and dolphin, of a pale gold yellow; and in the dog, wolf, and badger, of a pure white, surrounded by blue. This coloured part of the inner choroid surface, which occupies chiefly the side opposite to that on which the optic nerve enters, is named the tapetum. The use of it is by no means obvious. The explanation of Monro in reference to the tapetum of the ox, that it represents more distinctly to that animal the colour of his natural food, is not only frivolous, but inapplicable to the other genera.

The tapetum is wanting in all Birds and Fishes, excepting the ray, in which there is at the bottom of the eye a beautiful silvery-coloured space, produced by the transparency of the Ruyschian tunic, through which the tint of the choroid is seen.

In Fishes generally the choroid consists of two distinct separable membranes; the external, the proper choroid, white, silvery, or golden, very thin and not vascular; and the inner or Ruyschian, black, and consisting of a network of vessels. Between these two membranes is a body of a bright red colour, consisting of numerous tortuous vessels, convoluted and inclosed in pulpy filamentous tissue. Its general shape is that of a thin cylinder, encompassing the optic nerve like a ring, which, however, is incomplete at one side. This is the choroid gland,—a body about which there has been some difference of opinion, but which appears to be glandular rather than any thing else. Its vascular structure is well seen in the globe-fish, perca labrax, and cod, in which they are very large, and form numerous anastomotic communications. They are generally covered by a white, opaque, viscid flüid.

The choroid gland is wanting in the Cartilaginous Fishes, the eye of which approaches more nearly to that of the Mammalia in this as in other circumstances. The choroid of the ray and shark genera is a threefold tissue of vessels, thick and consistent; the txinica Ruyscħiana is very thin and semi-transparent; and between these is a layer of silvery matter with metallic lustre.

In the cuttle-fish genus, though between the sclerotic and choroid there are several glandular bodies, there are none between the choroid and Ruyschian tunic. The choroid is thick, soft, and vascular; the Ruyschian thin, firm, and dry; and though there is no tapetum, the whole interior surface of the eye is covered by deep purple, semifluid, viscid varnish.

Ciliary processes are found in all theMAMMALiA, Birds, several Reptiles, and even in the cuttle-fish among' the Mollusea ; but they are wanting in almost all fishes.'

The indented border of these processes is more distinct, and is converted into a genuine fringe in the large animals, as the òx, horse, rhinoceros, and whale, in v¢hich the angle applied to the capsule is more acuminated than in other animals. In the Carnivora, particularly the lion, the base of the plates is shorter in proportion to the other sides than in the previously mentioned animals, so that the opposite angle is more prominent; nor is the [7:3:24]border indented. In all the species every third or fourth plate is shorter than the others, but without determinate order.

The ciliary plates of Birds are mere serrated striae, without sufficient prominence to make them undulate in fluid. In the owl they are fine, closely set, and numerous; in the ostrich they are larger and more numerous; and if t all, their extremities adhere firmly to the capsule of the lens.

In the tortoise the ciliary processes are so short that they are recognised only by the impression left on the vitreous humour; in the crocodile, however, they are distinct, and terminate each by an angle nearly right. They are indistinct in the toad, and imperceptible in the ordinary lizards and serpents.

The ciliary body and processes are large and distinct in the tope-fish; but if they are seen in any other of the cartilaginous fishes, they are wholly wanting in the osseous, in which the Ruyschian tunic is directly continuous with the uvea.

The utility of these processes in retaining the lens in its position is nowhere so distinctly seen as in the eye of the cuttle-fish family, and especially the many-feet of the ancients (polypus octopodd). In these the ciliary processes form a large diaphragm or zone, in the aperture of which the crystalline lens is truly chased. They penetrate a deep annular furrow which surrounds the lens, dividing it in two unequal hemispheres, and cannot be detached without laceration.

The iris, of the same intimate structure as in man, is of a deep tawny or brown in the Mammalia, and marked with fewer coloured striae than the human iris. In Birds it is of a uniform lustreless colour, varying according to the species, bright yellow, red, or clear blue. In the microscope it appears like a net-work formed by the intersection of numerous very minute fibres. The uvea is so fine that when the viscid varnish is removed it becomes transparent, and the iris appears of the same colour on both sides. In Fishes, conversely, the iris is so thin and transparent that the uvea is seen through it, of a golden or silvery brilliance, showing its direct connection with the choroid. Intermediate in metallic splendour is the iris of the Reptiles. The vessels, however, are greatly more conspicuous, especially in the crocodile.

The central aperture or pupil, though round in man, the Quadrumana, many of the Carnivora, and Birds, is not of that shape when contracted in all animals. In the feline family it consists of two elliptical segments, which form angles above and below, and which approach mutually so as to form a slit nearly vertical. In the Ruminants it is oblong transversely, and forms at its greatest contraction an oblong or transverse slit. In the horse, in which it is also transverse, its upper margin is distinguished by a five-pointed festoon. In the whale it is oblong transversely, and in the dolphin it is heart-shaped. The pupil of the crocodile resembles that of the cat; in the frog and gecko it is rhomboidal; and round in the tortoise, chameleon, and common lizards. In the ray among Fishes the upper margin forms several radiating slips like the branches of the palm-tree, gold-coloured without, dark within. In the dilated state these slips are folded backwards between the upper margin of the pupil and the vitreous humour; but when the eye is pressed they are erected, and close the pup'il like a blind.

The motion of the pupil is voluntary in the parroquet, and is indistinct in most of the Fishes.

The pupillary membrane is well known to exist in the foetuses of all the Mammalia ; but it is not determined whether it is found in the chick of birds.

On the subject of the retina in the lower animals the most important point is the structure of the melanoplectic or pectiniform membrane (pecten, marsupium nigrum) of Birds. In this class the optic nerve forms not a round disk as in the Mammalia, but a narrow white line, the margins, and extremity of which are in continuity with the retina. 1 Along this line is suspended a plicated or convoluted] membrane, very fine and vascular in structure, like the < choroid, from which, however, it is quite distinct, and en-J tering a depression of the vitreous humour almost like a∙i wedge. Its vessels, which proceed from a proper branch 1 of the ophthalmic artery, are distributed in a minute arborescent form, among the folds of which the marsupium consists; and from these vessels the black viscid pigment with which its folds are covered appears to be secreted. The plicae or membranous folds vary in number. In the cassowary they are only 4; in the brown owl (<S ’. aluco) 5; in the common owl, ostrich, Guiana macaw, and merganser, they are 7; in the flamingo 9; in the falcon and swan 11; in the vulture and goose 12; in the duck, large heron, woodcock, and coot, 13; in the stork and partridge 15; in the crane 17; in the pheasant 20; in the turkey 22; in the jackdaw 25; and in the thrush 28. According to the observations of the elder Soemmering, to whom we are indebted for these numbers, the number of folds, though variable in different species, is the same in the same. In most birds the folds are arranged in a pectiniform order. On the use of this organ different opinions have been entertained by Petit, Haller, and Home; but all of them are conjectural.

In the Reptiles and many Fishes, between the optic nerve and the retina is a small tubercle, from the margins of which the latter membrane appears to rise; and radiating fibres are perceived more distinctly than in most quadrupeds. In many other Fishes the connection of the retina with the optic nerves resembles that of Birds. Thus, in the salmon, trout, herring, mackarel, cod, dory, and moon-fish, the optic nerve, after passing through the Ruyschian tunic, appears to be parted into two long white processes, which, following the outline of this membrane parallel but not contiguous to each other, are connected with the retina by their opposite margins.

In all animals provided with ciliary processes the retina terminates at and is connected with the gray pulpy zone denominated ciliary ligament. In those without ciliary processes, as the Fishes, it terminates suddenly at the attached or large margin of the uvea.

In several of the reptiles the retina presents the yellow-spot of Soemmering. The principal peculiarities of the humours have been already mentioned.

Of the appendages the most important are the lacrymal gland and nictitating membrane.

In the Ruminants the lacrymal gland consists of two or J three bodies, each composed of granules, each provided £ w-ith a separate short excretory duct. In the hare and rabbit, in which the gland is large, there appears to be only one excretory duct, which perforates the upper eyelid near its posterior angle.

A gland peculiar to certain species, and wanting in man, that of Harder, is situate at the external or nasal angle, and presents an aperture under the third or nictitating eyelid, from which issues a thick viscid fluid. It is found in the. Ruminants, the Rodentia, the Pachyderm ata, and in the sloth genus.

The caruncle exists in the Ruminants as in man, and appears to consist of numerous aggregated follicles. It is wanting in the Rodentia.

In the Cetacea, as in most animals which live under water, there is neither gland nor lacrymal passages; and they are represented apparently by lacunae below the upper eyelid, which discharge a thick mucilaginous fluid.

Birds, though destitute of caruncle, have both lacrymal[7:3:25] gland and that of Harder, the latter large, oblong, and flesh-coloured, placed betwixt the levator and adductor, and discharging by a single canal, opening at the inner surface of the third eyelid, a thick yellow fluid. The lacrymal, which is small, round, and very red, is provided in general with two or three canals, which, though small, are distinct. In most of the Grallae and Palmiped Birds there is, in place of the lacrymal gland, a hard granular body, occupying the upper part of the orbit, and following in situation the curvature of the eye. It has, nevertheless, no visible excretory duct.

In the turtle there is a reddish granular tabulated body, of considerable size, extending beneath the temporal vault. In the tortoise, frog, and toad, there are two small blackish glands without apparent excretory ducts. Neither in Serpents nor Fishes has any glandular apparatus in the eye been recognised.

Though in man and the monkey tribe the eyelids consist of two semilunar cutaneo-muscular folds, with a minute mucous duplicature at the nasal angle, the latter acquires such a developement in the lower animals as to constitute a genuine third eyelid, often distinguished by the name of nictitating membrane. This duplicature is semilunar in shape in the Ruminants, Edentata, and Pachy-Dermata. In the rhinoceros it is thick and fleshy; but of this the Cetacea present no trace. In the Birds, on the contrary, in which the eye is covered by the elevation of the lower eyelid, which is also the largest, the third eyelid is large, and covers the eye like a blind drawn before it; yet it is in some degree translucent, for it is evident that birds see objects through the membrane. In the owl and goatsucker the eye is closed by the depression of the upper as well as the elevation of the lower eyelid.

Though the Serpentine reptiles are void of eyelids entirely, in the crocodile, tortoise, and Batrachoid, there are three, as in birds, the third being vertical in the two former orders, and horizontal in the latter. In the S auri al and Cheloniad, also, the third, which is translucent,moves from before backwards by means of a single muscle, and may cover the whole eye. In the lizard genus the eyelids consist of a circular veil drawn before the orbit, and perforated by a horizontal fissure, which is shut by a sphincter, and opened by a levator and depressor. The gecko has no movable eyelid.

In insects, the eye consists of innumerable hexagonal surfaces, slightly convex, and mutually separated by minute furrows, containing fine hairs variable in length. Each of these hexagonal surfaces, which constitute a hard, elastic, very transparent membrane, may be regarded as a cornea or crystalline lens, convex externally, concave within, and thicker in the centre than on the margins. Immediately behind is an opaque, viscid coating, varying in colour in the different species, analogous to the choroid pigment of the vertebrated animals, and completely obstructing the transmission of light. Beneath this varnish are short, whitish filaments, corresponding in number to the corneal surfaces, and mutually joined like mosaic or tessellated pavement, separated only by the dark-coloured pigment, and which appear to correspond to the retina of the Vertebrata. Behind these again is a delicate, darkcoloured membrane, which appears to correspond to the choroid; and exterior to this is a membrane continuous with the optic nerve, and which seems to be a general retina, forming, by subdivision of its parts on the anterior part of the choroid, the divided or multiplied retina. This is the structure of what are named compound eyes. That of the simple eyes of insects is too minute to be accurately demonstrated; but analogy gives probability to the inference that they are not dissimilar.

sect. hi. — the ear.

In warm-blooded animals generally, that is, in the Mammalia and Birds, the labyrinth or essential part of the organ consists of three semicircular canals, with a globular enlargement to each (ampulla), a cavity common to these canals named vestibule (vestibulum), and a conical tapering canal,· divided into two compartments by a longitudinal septum. This may be named the bilocular cone (conus bilocularis). These parts consist of membranous substance inclosed in the bony walls of the pyramidal or auditory bone. In all the Mammalia the bilocular conical canal is convoluted in a spiral form, and hence is denominated, as in man, the cochlea — a name, however, which is applicable to it in this class only.

The organ of hearing in the Mammalia consists of the same parts nearly as in man. In somei indeed, for instance the guinea-pig (cabiai), and porcupine, the cochlea makes three turns and a half; and, conversely, in the Cetacea only one and a half. In most of the Zoophaga, and in the hog, elephant, and horse, the cochlea is much larger in proportion than the semicircular canals; but in the hare it is small, and in the mole very small. In the Cetacea, while the cochlea is very large and fully developed, its spiral is on the same plane throughout; and the semicircular canals are so small, that their existence was tang denied by Camper, till they were demonstrated by Cuvier in a foetal whale. In general the labyrinth of the Mammalia is greatly smaller in proportion to the head than in Birds.

This part, which is membranous, is inclosed in the solid compact substance of the temporal pyramid, so closely that its existence appears to be identified with the latter. Researches, however, on the labyrinth in the foetus of the Mammalia, and especially in those of whales, demonstrate the fact that it is in a completely membranous form, dis- ∙ tinct from the bony inclosure; that in shape and constituent parts it exists previous to the bony inclosure; and that the latter is afterwards moulded round the different parts as they acquire their full developement. It is also to be observed, that in the mole the semicircular canals are seen within the cranium without preparation, and the cochlea is merely inclosed in fine cellular tissue. In the bat family, also, both parts are seen without bony inclosure.

The tympanum forms a cylindrical or spheroidal cavity in most of the^ Mammalia. In most of the Digitata the mastoid process consists of a slight prominence of the tympanum only as it is identified with the latter; but in the cabiai, guinea-pig, hog, the Ruminants, and Solidungula, it is represented by a long process of the occipital bone. In most of the Zoophaga and Rodentia the parietes of this protuberance, which are thin and hard, form by their separation a large cavity. In the hog only it is occupied by a firm cancellated structure.

All the Mammalia, except the ornithorhyncus, have the tympanal bones as in man; the hammer (malleus), anvil (incus), orbicular bone and stirrup (stapes). The lenticular bone, which is rarely found in the adult, is probably only an epiphysis of the anvil. They are articulated with each other so as to admit of motion, and are moved by the same muscles as in the human subject—the internus mallei, externus mallei, laxator tympani, and stapedius. In the ornithorhyncus, however, there are only two tympanal bones.

In all the Mammalia, except the Cetaceous, the ear is provided with a bony external canal (meatus) ; and most of the Mammalia, except the Cetaceous, have a cartilaginous funnel-shaped opening (concha) attached to the outer margin of the bony meatus, and which serves to [7:3:26]collect the sonorous vibrations, and direct them to the meatus. The other exceptions are among the Insecti-vora, the mole, and some of the shrew genus; among the Rodentia, the zemni or blind rat, and some of the ratmole genus ; among the Edentata, the pangolin or sealyant-eater; and among the Amphibia, the morse and several species of seal; and the ornithorhyncus paradoxus.

The tympanum of the Cetacea is peculiar. It consists of a bony plate, convoluted on itself like a buccinum, unless that the thick side, instead of containing a spiral cavity, is entirely solid. The opposite side is thin, with an irregular margin. The anterior extremity of the tympanum is open, and there commences the Eustachian tube, which ascends along the pterygoid process, and, penetrating the maxillary bone, terminates at the upper part of the nose. This direction of the tube and position of its orifice is so much more necessary, because, since these animals have no external bony meatus, and the ear-hole scarcely admits a pin, the vibrations of the air reach their organ of hearing entirely by the Eustachian tube, and because the Eustachian tube also in these animals conveys odorous impressions to the part in which the sense of smell appears to reside. The aperture by which it communicates with the nose is provided with a membranous valve, which prevents the water from entering when the animal expels it by his nostrils.

In Birds, of the three semicircular canals the vertical is largest, and obliquely directed forwards and outwards; the second is horizontal and turned outwards; and the third, which, like the first, is vertical, crosses the second, and is turned in the direction opposite to that of the first. The vestibule is small and nearly spherical. The bilocular cone, which is obtuse at the apex, is situate obliquely backwards and outwards below the inferior part of the cranium. The longitudinal septum consists of two narrow cartilaginous plates connected by a thin membrane. The posterior canal is short, and, as in the Mammalia, is separated from the tympanal cavity by the membrane of the fenestra rotunda; while the anterior, which is larger, communicates directly with the vestibule. The whole of these parts are inclosed, as in the Mammalia, in the compact bone of the pyramid.

The posterior and inferior .walls of the tympanal cavity are formed by part of the occipital bone; the lateral aperture is large, and the cavity superficial; and its anterior part is closed by the posterior superior cornu of the quadrilateral bone and a membrane. The inner wall presents the two apertures—the oval or vestibular, and the round or cochlear. In this class, however, while the upper is round or triangular, the lower is distinctly elliptical,—a disposition the reverse of what is observed in man. The Eustachian tube or tympano-guttural canal is entirely osseous. The tympanal cavity contains only one ossiculum, consisting of two branches; the first attached to the tympanum, corresponding to the malleus ; the second closing by an oval or triangular plate the vestibular aperture, and therefore corresponding to the stapes of the Mammalia. By Carus the incus is supposed to be represented by the quadrilateral bone.

The external meatus is short, and opened by a simple aperture, while the absence of external ear is compensated by a ring or zone of fine elastic feathers with thin barbs, between which the air passes very easily. In the owl tribe it terminates in a large cavity, the margins of which are covered by a smooth valvular fold of skin.

The ear of the Reptiles is remarkable for the last appearance of the bilocular cone, and the first of the saccular apparatus which is found in the Fishes. In the crocodile and lizard this part appears, as in Birds, in the shape of a conical tube, divided by a cartilaginous partition into a double canal, one separated by the membrane of the round hole from the tympanal cavity, the other communicating with a membranous sac containing three very small friable stones, not harder than starch. There are also three semicircular canals of considerable size, each forming a large circumference. In the frog and toad, while the three canals form almost a complete circle, the sac contains an amylaceous friable stone; but the bilocular cone is no longer observed. In the salamander, also, in which the three canals form together a sort of equilateral triangle, the sac which is below contains a single amylaceous stone. The same arrangement is observed in the Cartilaginous Fishes, unless that the sac contains two amylaceous stones, nearly oval in shape, suspended in a gelatinous semifluid pulp. In the Osseous Fishes it is a little different. The three semicircular canals terminate in a membranous sac, which is divided by septa into compartments which contain one, two, or three small stones suspended in gelatinous fluid. These minute stones, however, instead of being soft, friable, and amylaceous, as in Reptiles and cartilaginous Fishes, are as hard as rock, and white as porcelain. These parts are situate on the sides of the cranial cavity, and are fixed to it by cellular tissue, vessels, and osseous or cartilaginous processes. This sac, in the fluid of which the extremities of the auditory nerve are distributed, is believed to correspond to the bilocular cone of the higher classes.

These membranous cavities are contained, in the bony fishes, in the general cavity of the cranium; and while only the middle of the canals is inclosed in the bone of the cranium, the extremities and the sac are quite free. The sturgeon, which belongs to the cartilaginous order, is the first in which the canals are entirely inclosed in the cranial cartilage; but even in this a membrane is interposed between the cranium and sac, which is free. In the ray and shark genera, again, these organs are entirely inclosed in the cartilage of the head.

The tympanal cavity, in like manner, is modified, and eventually disappears as we descend in the scale. Though present in the tortoise, crocodile, and lizard tribe, it is superficial and open; it becomes membranous behind in the Ranine tribe, and communicates directly with the back of the mouth; and in the Serpentine reptiles it entirely disappears, so that the handle of the osseous plate by which the oval aperture is closed is suspended in the soft parts with its free extremity below the skin, near the articulation of the lower jaw. In the lizard tribe, also, the round or cochlear aperture is seen for the last time. In the Cheloniad, for instance, the Batrachoid, and the Serpentine, this aperture disappears, and the oval or vestibular alone is left; and in the salamander both disappear, and there is no communication between the external part of the cranium and the labyrinth. This arrangement is continued in the fishes.

In the molluscous animals the labyrinthine membrane is a simple sac, globular or ovoidal, containing pulpy matter, in which is suspended a small body, which is osseous in the sepia and amylaceous in the many-feet (polypus), in which the filaments of the auditory nerve are distributed.

Our limits do not allow us to enter into the detailed description of the organ in the other Invertebrated animals.

SECT. IV. THE ORGAN OF TASTE.

Though the sense of taste is seated chiefly in the tongue in animals, yet that organ performs, in all the classes, so important a part as an instrument of prehension, that it cannot with much justice be distinguished by the former title only. In the present section, therefore, we must regard it as one of prehension as well as of taste.
[7:3:27]

In the Mammalia and Birds the tongue is a muscular organ invested by mucous papillated membrane, supported by a proper bone, the hyoid, which serves as a point of support in its various motions. In the Ranine Reptiles it is also muscular, attached to the margin of the lower jaw. In the salamander, however, it is attached as far as the tip, and is movable on the sides only. In the crocodile it is attached so generally, both by tip and margins, that it was long asserted that the animal was tongueless. In the stellio and iguana it is as movable as in the Mammalia ; and in the seine and gecko to this property is added that of being biful, or divided by a longitudinal notch into two pointed tips. In the ordinary lizard, tupinambis, monitor, &c. the tongue is remarkable for its great extensibility, and terminates in two long, flexible though semi-cartiiaginous extremities. That of the chameleon is still more extensible, and forms, by a peculiar arrangement of vessels, a cup-like extremity. The tongue of the blind worm (anguis fragilis) and amphisbaena is also biful at the tip. The cartilaginous fishes are void of tongue, while in the bony division of the class this organ is represented by a hard protuberance, attached to the middle branchial bone.

In some of the Mammalia, however, the tongue is not exclusively muscular. In the singularly long, extensible, and tortuous tongue of the giraffe, Sir Everard Home describes a peculiar arrangement of vessels, which he represents as a substitute for muscular motion. Though Sir Everard does not appear to understand the exact nature of this arrangement of vessels, all the circumstances tend to •show that it is that denominated erectile. These vessels, from the account given, are large, numerous, and communicate freely; and it would be impossible to discover the reason of such a vascular system, unless for some purpose of this description. (Phil. Trans. Comp. Anat.) When the tongue is protruded it becomes perfectly black or bluish-black, evidently from the injection and detention of the blood in its elongated and anastomosing veins. By means of this mechanism the giraffe not only elongates the tongue to the distance of about twenty inches or two feet beyond the mouth, but twists it round the soft leafy twigs of the trees on which he feeds. It is not improbable that a similar vascular arrangement exists, though in less degree, in the tongue of the deer, and in the long projectile tongue of the animals of the ant-eater tribe, as the Tamanoir, Tamandua, &c.

The erectile arrangement is still more distinctly pre- . sented in the tongue of the chameleon. The researches of Mr Houston of Dublin show that the tongue of this animal consists of two parts,—a prehensile, which is anterior, and provided with a glandular apparatus for secreting the viscid fluid by which its tip is covered, and insects are entangled; and an erectile, which is posterior between the prehensile and the hyoid bone, in the form of a trellis-work of innumerable minute anastomosing bloodvessels, not very dissimilar to those of the cavernous body in animals generally, and inclosing a central tube connecting the prehensile portion to the hyoid bone. The effect of this arrangement is, that when the vascular network is injected with blood, the anterior part of the tongue is rapidly darted out at the insects on which the animal lives. The injection of these vessels, and the consequent projection of the tongue, is not independent altogether of the will of the animal; for the veins by which the blood is returned pass through a slit in the tendon of the internal cerato-maxillary muscles, which are always contracted in order to protrude the hyoid style, and thereby tend, by compressing the veins, to inject the erectile part, and project the’ tongue. (Trans. P. I. Acad. 1828, and Dublin Hospital Reports, vol. v. p. 487.) The same arrangement is in all probability found in several of the lizards, the tongues of which, like that of the chameleon, are darted out suddenly, and become of a dark-blue colour at the moment of projection.

In all the Mammalia the tongue is invested by a papillated muco-villous membrane, in which the papillae are of the same general characters as in man—granular, mushroom-like, or fungiform, tubercular or calycoid, and conical or acuminated. The only differences consist in the size and abundance of the fungiform papillae, in the number of the calycoid and the mode of their arrangement, and in the shape of the conical papillae and the mode of their termination. In the Ruminants especially, the conical papillae are numerous, long, slightly incurvated, and each terminating in a horny but flexible style slightly incurvated backwards. The tongue of the dolphin and porpoise, examined even by the microscope, presents no distinct conical papillae, but is covered by minute eminences, each penetrated by a small aperture.

In the tongue of the dog genus there is a ligamentous substance extended longitudinally from the hyoid bone to the tip of the member. This, which has been vulgarly distinguished by the name of worm of the tongue, and has been absurdly supposed to be the seat of hydrophobic rabies, is merely a central pillar of support for the muscular fibres to act with greater steadiness and effect, and which enables the animal to protrude and expand the tongue in lapping water or other fluids better than he could have otherwise done. A similar central ligament is found in the opossum.

The tongue of Birds is generally more or less horny, and almost cartilaginous. That of the woodpecker and wryneck is peculiar in consisting of two parts,—a basilar or posterior, loose and fleshy; and an anterior projectile, long, smooth, acuminated, and covered laterally with four or five stiff spines directed backwards, which make the organ a sort of barbed arrow. The soft, loose, or basilar part of the tongue contains the aperture of the glottis; and the surface is covered with minute spines pointed backwards, and each of which is placed in the centre of a fleshy papilla.

As a prehensile organ of very singular construction, the trunk of the elephant deserves particular notice; and it cannot be more conveniently introduced than under the present section, since it is used not only to convey food, but drink, into the mouth. The trunk may be described as a cylindrical tubular organ, consisting of integument, a sort of fibro-cartilage, muscles, fat, and a membrane of villous character internally. This tube contains two long canals continued from the nostrils, parallel to the axis of the trunk, and separated throughout by a partition of adipose substance about two fifths of an inch thick. From the extremity to the middle part of the intermaxillary bone, in which the tusks are fixed, these canals are nearer the anterior-superior than the posterior-inferior part of the tube, the latter wall being thickest; and their diameter is the same throughout. At this part they undergo a sudden incurvation, approaching the anterior surface of the intermaxillary bone, and form a semicircular bend with the convexity turned forwards. Here also they are so narrow that, without a muscular effort on the part of the animal to dilate them, fluids could not ascend beyond this point; and hence this forms the only valvular contrivance, either to impede the progress of fluids upwards, or to propel them downwards, at the will of the animal.

Above this curvature each canal is dilated before the upper part of the intermaxillary bone, and again is contracted where it bends back to enter the bony nostril; and the curvature is protected before by the nasal cartilage, which is oval, convex in the male, and flat in the female.
[7:3:28]

Both canals are lined by a dry, greenish-yellow coloured membrane, marked with superficial intersections (rugae), inclosing rhomboidal spaces, and some venous branches.

Though the muscular fasciculi of the trunk are numerous, they may be referred to two orders,—those forming the substance or inner part of the organ, and those by which it is invested. The former, which are transverse, and cut the axis in different directions, consist of numerous small muscular packets proceeding in various directions, some running from the inner membrane to the circumference of the tube, others directly from right to left, and others crossing the two former obliquely. All these little muscles are inclosed in cellular tissue, containing white homogeneous fat; and all of them terminate in slender tendons, some of which cross the layers of the longitudinal muscles in their course to the external covering, while others are attached to the internal membrane. Cuvier calculates the number of these minute transverse muscles in the trunk of the elephant to be not fewer than 30,000 or 40,000. (Plate XXXVĲ. fig. 13.)

The longitudinal muscles, which are external, may be distinguished into anterior, posterior, and lateral bundles. The first extend from the anterior surface of the frontal bone, above the nasal bones and cartilages, in parallel bundles, connected by tendinous intersections downwards on the trunk. The posterior extend from the posterior surface and inferior margin of the intermaxillary bones, and form two layers which meet on the median line along the lower surface of the trunk. The lateral muscles form two pairs, one of which, descending between the anterior and posterior muscles to the middle of the trunk, may be regarded as a continuation of the orbicular muscle of the lips, or the representative of the nasalis labii superioris ; while the other, which is attached to the anterior margin of the orbit, and is expanded over the root of the former, may be supposed to correspond to the levator of the upper lip.

The whole of these muscles are supplied by a very large branch of the infraorbital or second branch of the trifacial nerve, which, entering on each side between the lateral and superior muscle, is distributed to the whole of the trunk.

With such a construction, it is not difficult to understand the numerous motions of the elephant’s trunk. While the longitudinal muscles are employed either to shorten the tube, to bend it upwards or downwards or to the side, or by means of the tendinous intersections to give it peculiar inflections, it is manifest that the transverse ones, which act as antagonists to the longitudinal, may also either dilate or close the canals, or incurvate or alter the direction of particular parts.

The foot of the Lacerta Gecko and the house-fly presents a prehensile apparatus of peculiar construction for .walking along surfaces, in opposition to the action of gravity. In the former animal the plantar surface of each toe presents sixteen transverse slits, leading into an equal number of pouches, which by means of appropriate muscles are capable of forming an equal number of vacua, so that the atmospheric pressure is employed with muscular effort to support the animal in his unnatural position. A similar apparatus is found in the upper surface of the head of the sucking fish (echencis remora) ; and something approaching to it, though less distinctly, in the foot of the walrus. (Home, Phil. Trans. 1816.)

CHAP. IV.—COMPARATIVE ANATOMY OF THE ORGANS OF

VOICE.

Under this head our limits allow us to mention very few circumstances.

In the American long-tailed monkeys (sapajous) the cuneiform cartilages form, by means of adipose cellular tissue, before the upper extremity of the ventricle of the glottis, a large cushion like a spherical segment, which, touching that of the opposite side, causes the air to whistle through the canal in its course to the mouth, and occasions the flute-like voice of some of these animals, as the weeper (s. apella) and the capuchin (s. capucina). In the howler (s. seniculus), so remarkable for its morning and evening yelling, though the larynx is similar in general characters to that of the common sapajou, in having the two rounded cushions before the ventricles, the hyoid bone is arched in the form of a spherical chamber, with a large quadrilateral aperture, and each ventricle opens into a membranous sac, lying between the epiglottis and the adjoining wing of the thyroid cartilage. The air, which passes between the vocal chords, is therefore partly impelled into this osseous and elastic cavity of the hyoid bone, and probably by its resonance in this situation gives the voice of these animals the deep-toned howl by which they are known in the American forests.

Among the Zoophaga, in the dog the cuneiform cartilages are large, the arytenoid small, the vocal chords well marked, and the ventricles deep. In the feline tribe the anterior ligaments, though destitute of cuneiform cartilages, are thick, and separated from the back of the epiglottis by a broad, deep furrow. The posterior ligaments, though neither free nor sharp-edged, are distinguished from the anterior by an appearance of greater firmness, more regular fibres, and by an intermediate furrow. The approximation of the anterior ligaments towards the glottis forms a sonorous vault, in which the air may be forcibly vibrated by the posterior. In the bear the cuneiform cartilages assume the shape of styles, and their posterior extremity forms a distinct eminence, not above, but without the arytenoid cartilages, while the ventricles are merely deep fissures.

The kangaroo has neither cuneiform cartilage, anterior ligament, nor ventricle; and it may even be said to be void of vocal chord, while the margins of the glottis are much separated in the middle. This arrangement appears to indicate that the animal is almost destitute of voice. In the opossum, in which there is merely a small inferior ligament susceptible of tension, voice is limited to a whistling sound.

In the Solidungula, in which the cuneiform cartilages are completely concealed by the mucous membrane, there is neither superior ligament nor proper ventricle; but an aperture in the lateral wall of the laryngeal membrane, above the vocal chord, leads into a large, oblong, sinuous cavity, situate between this membrane and the thyroid cartilage, and covered chiefly by the thyro-arytenoid muscles, by which it may be compressed; and above the anterior commissure of the vocal chords, or below the base of the epiglottis, is an aperture on the mesial plane, leading into a cavity below the vault formed by the anterior margin of the thyroid cartilage. This cavity, which may be named the infrathyroid, is superficial in the horse, and its aperture is large; while in the ass, with a small, round aperture, the cavity is large, capacious, and globular in every direction, and allows the latter animal to make his voice re-ecħo in the singularly harsh sound denominated the bray. Conversely, though the lateral cavities are equally large in both animals, the apertures in those of the ass are small, round, and situate nearer ∖ hz. epiglottis than the vocal chord, while those of the horse are large, oblong, and situate immediately above the vocal chord on each side. On the latter peculiarity appears to depend the neigh of the horse.

In the Cetacea we recognise neither vocal chords nor glottis, that is to say, an aperture variable in size ac [7:3:29]cording to the will of the animal; but the superior part of the trachea, which represents the larynx, forms a hollow pyramid or funnel, rising into the posterior part of the nostrils, in which only it opens, while on the sides is left a passage for the food. This pyramidal funnel is formed by an elongated triangular cartilage, corresponding to the epiglottis, attached by membrane to the arytenoid cartilages, which also take the shape of scalene triangles, with the small side connected to the cricod cartilage. Strictly speaking, therefore, the Cetacea have no larynx, and probably no vocal organ; and the superior part of the trajchea, with the nostrils, serves merely to admit the atmospheric air for the purposes of respiration.

Birds are distinguished by possessing not only a glottis or laryngeal aperture similar to that of the Mammalia at the upper end of the trachea, but a second, denominated the inferior glottis or larynx, at the lower end, near its bifurcation. The former, which is composed of four cartilages, or six, according as the cricod consists of one or three pieces, on the middle of the posterior part of which is a small round bone, articulated with two oblong longitudinal bones, parallel, and forming between them in the posterior wall of the windpipe a longitudinal slit, susceptible of approximation by means of muscles, is intended merely to regulate the admission of air into the windpipe, or its expulsion from that tube, and to close more or less accurately its superior orifice.

The inferior larynx consists of a membrane projecting from each side of the inferior aperture of the trachea. This aperture is divided into two, occasionally by an osseous anterior-posterior middle bar, occasionally by the angle at which the two bronchial tubes unite. Since the first bronchial arc has the same curvature as the last tracheal ring, the second and third, which are arcs of larger circles, are less convex without, but more prominent within, than the former. Over this prominence the tracheobronchial membrane forms a fold, which, half closing on each side the inferior tracheal aperture, forms a plate susceptible of vibrating by the motion of the air, and producing sound. This apparatus, which constitutes what is named the inferior larynx, or rather glottis, is of two kinds, one void of proper muscles, the other provided with muscles.

In the former kind of larynx the state of the glottis is altered only by those muscles which depress and elevate the trachea. The depressors are two pairs, the sternotracheal and the glosso-tracheal, the latter attached to the bifurcated bone and trachea. There are no proper elevators; but the windpipe is raised by the mylo-hyoid muscle through the ligaments which connect the hyoid bone to the superior larynx. In the quiescent or relaxed state, and while the trachea is depressed, the bronchial rings approximate, and the second and third even gliding below the first, the glottis may be elongated. When the trachea is elevated by these pairs of muscles, the bronchi are at the same time dragged upwards, and the second and third arcs are separated from the first; and while the external prominence of the glottidal membrane diminishes in length, its tension is augmented. These forms of larynx without proper muscles may yet be subdivided into two sorts, as they have or have not lateral pouches, membranous or osseous. These are observed in the male duck (anas) and the merganser (mergus), but never in the female; and to this perhaps the harsh and deep tone of the voice of the male bird is to be ascribed. The larynx without muscles and without pouch is observed in all the gallinaceous order without exception.

The forriis of larynx provided with proper muscles may be distinguished into three subdivisions.

The first, which has only one proper muscle on each side, is observed in the whole of the falcon genus, e. g. the eagle, hawk, falcon, buzzard, sparrow-hawk, and goss-hawk; in the owl genus and the majority of the waders and swimmers, as the heron, bustard, woodcock, lapwing,, rail, coot, gull, cormorant, and some of the passerine birds. In these birds, in which the motions of the lower ]arynx are necessarily limited, the voice is not variable or extensive in its notes.

The second form of larynx has three pair of proper muscles, a constrictor of the glottis, an auxiliary constrictor, and a laxator or opener of the glottis. This kind of larynx is observed in the whole of the parrot genus and psittacoid birds generally, as the toucan, macaw, calao, &c.

In the third kind of musculo-membranous larynx there are no fewer than five pair of muscles, the longitudinal levator of the demiannular cartilages, the posterior levator of the same cartilages, the small levator, the oblique levator, and the transverse levator. This quinque-muscular larynx is found not only in all the birds properly named whistlers or warblers, as the nightingale, hedge-sparrow, blackbird, thrush, goldfinch, lark, linnet, canary, chaffinch, &c., but in others whose tones are more monotonous, as the swallow, sparrow, stork, crossbill, &c., and even in some the tones of which are harsh and positively disagreeable, e. g. the jay, magpie, crow, raven, &c.

The differences remarked in the notes of these three divisions of birds with the quinque-muscular larynx depend not so much on anatomical peculiarities as on the timbre of their larynx, and on the mobility of the trachea in relation to the larynx, and on the tracheal membrane having dilatations and contractions.

On the whole, the inferior larynx of birds is to be regarded in three lights: 1⅛Z, As the reed of a wind-instrument, like a hautboy or clarionet, in which the notes vary as the lower glottis varies in its position to the windpipe; 2<∕, as an instrument susceptible of uttering different tones, according to the distance between the mouthpiece and vent, or as the windpipe is elongated or shortened; and, 3d, as an instrument capable of uttering different notes by varying the diameter of the mouth-piece, or as the superior glottis is widened or contracted.

The only bird in which the inferior larynx is wanting is the vulture.

The vocal organ of the Reptiles consists of the superior larynx only, analogous to that of the Mammalia. This is a cartilaginous apparatus, composed in general of five distinct pieces at least in the large individuals of the Saurial genera, as the crocodile and alligator, and forming a broad cavity behind, before a narrow slit, bounded by two vertical pillars. The glottis, however, is entirely membranous; and there are neither vocal chords nor ventricles. There are nevertheless two muscles, one for opening and another for shutting the glottis. When these act, and the air is made to vibrate against the anterior pillars, it gives a slight whistling sound only. In the iguana, tupinambis, lizard, tortoise, and serpent, the arrangement of parts is nearly the same; and these animals, therefore, can utter only slight hissing sounds. In the chameleon the pillars are furnished with a tense, vibrating membrane, a fleshy tubercle which contracts the glottis, and a membranous pouch opening below, between the lower laryngeal cartilage and the first tracheal ring. In the frog tribe, so remarkable for their croaking noise, the vocal chords are large and prominent. The males have also two membranous pouches, opening by a small aperture, not in the larynx, but deep in the lateral part of the mouth. When the frog croaks these pouches are inflated, and swell the skin on each side below the ear. Though these sacs are wanting in the female frog, and toad both male and female, as well as the tree-frog, there is beneath the throat a single pouch on the median plane.
[7:3:30]

CHAP. V.—COMPARATIVE NEUROLOGY.

A general view of the nervous systems in different classes of animals shows that the only common part is an azygous tubercle, situate at the anterior extremity of the spinal chord, connected by means of two lateral bundles or peduncles to the rest of the system. This mass, which corresponds to what is denominated the cerebellum in man, is connected in the vertebrated red-blooded animals with several pairs of tubercles, forming generally a larger mass than itself, and connected to the rest of the system by two longitudinal bundles or limbs, which mingle with and intersect those of the cerebellum. These anterior-superior tubercles, which constitute the brain proper, present numerous modifications in figure, disposition, and magnitude, and even in presence, in the different orders of the animal world.

In the vertebrated animals the brain or central part of the nervous system consists of the vertebral or funicular portion, named the spinal chord, and the cranial or cephalic portion, properly denominated the brain.

The funicular portion has the shape of a cylinder flattened on its superior or dorsal and inferior or sternal surfaces. It consists of two similar chordiform productions, united on the mesial plane, and marked at the line of junction by linear longitudinal furrows, of which the superior is most deep and distinct. This, however, which was observed by Blasius in several animals, is denied by Bellingeri, who asserts, from various observations, that though in some parts the superior furrow penetrates more deeply than the inferior, in the general course of the chord the latter is the deepest. ( De Medulla Spinali Annotationes AnatomicoPhysiologicae. Auctore C. F. Bellingeri, Aug. Taurinorum, 1823.) This discordance appears to depend on the circumstance that the sternal or inferior furrow is in truth deeper and more distinct in man, the monkey tribe, and a few Mammalia, than the dorsal; whereas in most others/ as the coati, raccoon, horse, &c. the dorsal furrow is of the same depth as the sternal; and in the mole, murine, and leporine genera, it is deeper and more distinct than the sternal. In Birds and the cartilaginous Fishes the sternal furrow is deepest; in Reptiles the dorsal and sternal are nearly equally deep; and in the osseous Fishes the dorsal is the deepest. On each side of the chord, also, there is a slight longitudinal depression commonly called the lateral (sulcus lateralis).

The breadth and thickness of the spinal chord vary in different regions. The lower cervical portion is in general the broadest and thickest; at the upper dorsal region it is somewhat more slender, becoming thicker again at the lower dorsal region; and after again becoming more slender in the lumbar region, it is expanded into a filamentous brush-like termination of different lengths in different classes, and even in different orders. These enlargements at the superior dorsal and lumbar regions are believed by Serres to correspond with the origins of the thoracic and pelvic extremities; and each swelling he represents to predominate over the other, as the animal habitually employs the one or the other kind of members. It is remarkable in illustration of this principle, that in the Cetacea, which are void, of pelvic extremities, the lumbar enlargement is wanting; and in the amphibious Mammalia, the pelvic extremities of which are feeble, this enlargement is also inconsiderable.

The spinal or funicular brain consists of white cerebral matter on the surface and gray matter in the centre, the former being most abundant, unless in the sacral region, where both are nearly equal in quantity, or the gray rather predominates. In the Mammalia the gray matter is in greater proportion to the white than in the other three classes, in which the white matter progressively augments.

The sternal and dorsal longitudinal lines indicate the original formation of the chord in two lateral portions, with an intermediate cavity denominated the spinal canal. This exists only during the formation of the chord in the human foetus, in some of the Mammalia when adult, and in the other three classes. Its disappearance in the human foetus, and in that of various Mammalia, is represented by Serres to depend on the progressive deposition of gray cerebral matter on the inner or central surfaces of the component pillars of the chord. Though obliterated in man, in whom the gray matter is abundant, it is not hermetically sealed in the monkey tribe, in which some traces of it are left. In the Amphibia and Cetacea it is larger than in the monkey tribe; its diameter augments in the Carnivora, feline, canine, and ursine, in which the gray matter is thinner than in the former; and in the Rodentia it is said to be largest of all among the Mammalia. Lastly, in the birds, reptiles, and fishes generally, in which the gray matter is scanty and the white predominates, the spinal canal is large and distinct.

The lateral regions of the spinal chord are connected with a double series of nerves by means of two rows of nervous filaments, an anterior and posterior, separated by a longitudinal membrane of fine white tissue, with a serrated or festooned border. This membrane, which is named the denticulate, is the same in the Mammalia and Birds. That these nerves do not issue from the spinal chord, must be inferred not only from the phenomena attending the original developement of the nervous system, but especially from what is observed of their comparative size, and that of the chord in the inferior classes. In that of fishes especially, while the chord is small and slender, and by no means fills the vertebral canal, it is remarkable that the nerves which supply the voluntary muscles are exceedingly large. Thus, in many both of the cartilaginous and osseous divisions, as the sturgeon, dog-fish, ray, wolf-fish, cod, &c. the nerves which supply the pectoral fins are large, broad chords, two or three of which seem to contain more substance than the whole spinal chord itself.

The chord is expanded at its cephalic end into a thick eminence denominated the spinal bulb, the surface of which presents three pairs of eminences. These eminences are developed in various degrees in the different classes and orders. In some of the Mammalia the anterior pyramids or pyramidal bodies are more distinct than in man, for instance the ape tribe, the Cetacea, Carnivora, Ruminants, and Rodentia. They are small in most Birds, all the Reptiles, and the Cartilaginous Fishes. In the osseous division they assume the appearance of two parallel chords at the base of the brain. The olivary bodies, less prominent in the ape than in man, are still less so in the Cetacea, and progressively through the Amphibia, Carnivora, Ruminantia, Rodentia, and Insecti-vora, and the other three great classes of vertebrated animals. Conversely, the restiform bodies or posterior pyramidal eminences, from man through the ape tribe, the Cetacea, Amphibia, to the Ruminants, Carnivora, and Rodentia, increase in size.

Though the brain of the Mammalia presents the same parts, and is arranged nearly in the same order, as that of man, it varies in its proportions to the rest of the body; in its proportions to the cerebellum and spinal bulb; in general figure; in the presence, absence, and number of convolutions; in the configuration of its central surface; in the communication of its central with its external surface; and in the manner of its connections with the cerebral nerves. As it is impossible in this sketch to examine all [7:3:31]these circumstances fully, we shall confine our attention to the notice of a few only.

It is not easy to ascertain the proportion of the mass of the brain to that of the rest of the body. Excluding as much as possible the ordinary sources of fallacy, in small animals the brain is proportionally larger; yet in this respect man is surpassed only by a small number of animals, habitually lean, and with little muscle, as bats, small birds, &c. While the proportion of brain in man to that of the whole person varies from a 22d to a 35th part, that of the monkey tribe varies from a 22d to a 42d part; and in the baboon it is only the 104th part of the body. Among the Mammalia, the Rodentia have in general the largest proportion of brain, and the Pachydermata the smallest; and while the hare has a brain about the 300th part of the size of the body, that of the elephant, the most sagacious of animals, is about the 500th part the size of his body. It is also remarkable, that while the brain of the horse is only a 400th part of the size of his body, that of the ass amounts to a 254th part. The Reptile brain becomes excessively small, that of the turtle being rather more than the 5000th part the size of his body; and in some of the Fishes, not all, it appears to attain the maximum of decreasing proportion, that of the tunny being so small as the 37,000th part of his body, while the brain of the earp is so large as to approach the proportion of the elephant. It may be doubted whether, under such circumstances, any precise conclusions can be drawn from results so variable and so little to be expected.

The proportional weight of the brain to that of the cerebellum is, excepting in the ease of one species of ape, the saimiri, greater in man than in any other animal. The ox is equal to man in this respect, and the dog approaches him. The animals most remote are the Rodentia, as the beaver, rat, and mouse, &c.

The convolutions, which are so numerous and so deep in man, diminish both in number and size in the Quadrumana and Carnivora, and are nearly obliterated in the Rodentia. In the Ungulated animals, however, and especially in the Ruminants and the horse, the convolutions are numerous; and even in the dolphin among the Cetacea, they are numerous and deep. In all the Mammalia the cerebellum is foliated.

On the whole, the peculiar character of the brain of man and the ape family consists in the existence of the posterior lobe and digital cavity. The brain of the Zoo-PHAGA is remarkable for the small size of the nates or anterior pair of the bigeminous eminences in proportion to the testes or posterior pair. In the Rodentia the organ is distinguished for the large size of the nates, and the want or superficial nature of the convolutions. In the Ungulated division of animals, i. e. Pachydermata, Ruminantia, and Solidungula, the brain is remarkable for the large size of the nates combined with the number and depth of the convolutions; while that of the Cetacea is remarkable for its height and breadth, and the want of olfactory nerves. It is further to be observed as a general distinction between herbivorous and carnivorous or zoophagous animals, that in the former the nates are larger than the testes, whereas in the latter the testes are largest. Lastly, Man and the Quadrumana are the only animals which possess genuine olfactory nerves. In the other quadrupeds they are represented by the mammillary processes of the ancients; and in the Cetacea they have not yet been unequivocally demonstrated.

The brain of Birds is at once recognised by consisting of six distinct tubercles, two representing the cerebral hemispheres, two representing the optic eminences, one the cerebellum, and one the bulb of the chord. The hemispheres are void of convolutions, but the cerebellum is marked by transverse parallel striae corresponding to the lamince of the mammiferous brain. There is neither middle band (corpus callosum), vault, nor septum. The ceiling or vault of the aqueduct or passage from the third to the fourth ventriele is not, as in the Mammalia, surmounted by the bigeminous eminences, but is merely a thin plate corresponding to the valve. Each optic eminence contains a cavity communicating with the others by the Sylvian aqueduct. The anterior eminences (corpora striata) are not striated with alternate white and gray matter, as in the Mammalia. Between the anterior and the optic eminences are four rounded tubercles, best seen in the ostrich, which are to be regarded as entirely heterologous to the structure of the mammiferous brain, and connecting the cerebral structure of Birds with that of Reptiles and Fishes, in which also these tubercles are observed.

The Reptile brain is smooth and uneonvoluted. The optic eminences, which are situate behind the hemispheres, are uncovered, and contain a ventriele communicating with the third. At the extremities of the latter are the anterior and posterior commissures, but there is neither soft commissure nor bigeminous eminences. The hemisphere presents an anterior eminence, which, however, in the brain of Birds is unstriated. The cerebral valve is, like that of Birds, unsurmounted by bigeminous eminences.

In the class of Fishes the structure becomes still more simple. The tubercles of which the brain consists are placed in a row; and their increase in number only demonstrates the decomposition of the organ, and its resolution into simple integrant parts. The two representing the hemispheres are ovoidal, unconvoluted, and contain a ventriele, in which is seen the eminence analogous to the striated bodies. The optic eminences, situate beneath the hemispheres, though small, contain each a cavity, as in the two oviparous classes already noticed. Lastly, there are in several genera, under the common vault of the hemispheres, occasionally two, occasionally four tubercles, variable in shape and proportions, but which would be analogous to the bigeminous eminences, were they not, like those already mentioned in Birds, situate before and above the optic chambers. In the cartilaginous fishes, in which these tubercles are not observed, the anterior or striated eminences are obliterated. The cerebellum does not cover the fourth ventriele.

Behind the cerebellum are two tubereles, which in the ray give origin to the fifth pair, and are very distinct in the pike, trout, salmon, and perch. These tubereles are peculiar to this class.

The cavities in the interior of the optic eminences in Birds, Reptiles, and Fishes, are observed in the foetal brain of the Mammalia during its early growth.

It is almost superfluous to mention, that, in the two warm-blooded classes, Mammalia and Birds, the brain, with its investments, fills completely the cranial and vertebral cavities. In the Reptiles, however, in which the brain does not approach the cranial walls, we remark the first departure from this arrangement; and in the Fishes it is so completely violated that the brain and chord occupy but a small proportion of the cranio-vertebral cavity; and between the former and the osseous walls there is a quantity of fine but very loose filamentous tissue, containing in its cells a large quantity of pellucid fluid. Though this arrangement gives this the appearance of a white jelly-like substance; it is not gelatinous, as is generally represented, but merely a pellucid fluid, sometimes pale straw-coloured, occasionally with a reddish tint, contained in numerous communicating cavities of a tissue which appears to repre∙ sent the arachnoid of the warm-blooded animals.
[7:3:32]

The pia mater in the reptiles and fishes is reduced to a filamento-vascular web, accompanying the blood-vessels.

The dura mater undergoes some peculiar modifications in different orders. In the duckbill a bony plate is contained between the laminae of the falx; and the same structure is found in the porpoise, perhaps in the other Cetacea. An osseous tentorium with a quadrangular aperture is found in the coaïta and marten, and the feline and ursine families; and an osseous partition consisting of three parts is found in the dog, horse, Cape ant-eater (orycteropus), the wombat, and the seal. The bony tentorium îs also found in the woodcock and others of the feathered class. In the red but cold-blooded animals the dura mater forms neither falciform nor tentorial process.

On the nerves or ramified chords of the nervous system a few words must suffice. In fishes the tenth or pneumogastric consists not of a common trunk, but of three orders of filaments, the first and largest of which are distributed to the gills, and correspond to the pulmonary nerves of the Mammalia ; the second, slender, are distributed to the muscles of the tongue and the surface of the oesophagus ; and the third terminate in a large nerve which traverses the body longitudinally immediately beneath the lateral line. The phrenic nerve is wanting in birds, reptiles, and fishes.

In the Mollusea the nervous system consists of a number of whitish cerebral masses distributed in different parts of the body, with one or two more conspicuous than the rest, and supposed therefore to represent the brain, placed transversely over the oesophagus, which it encompasses with a nervous collar.

In the Articulata the nervous system consists of two long chords extending along the belly, and expanded at various intervals into gangliform knots or enlargements. The first of these, which is situate on the oesophagus, rarely exceeds the others in size. Among the Zoophytes hitherto examined the nervous system assumes either a radiated or an arborescent form.

PART II.

COMPARATIVE ANATOMY OF THE ENTROPHIC ORGANS.

CHAP. I. THE LIMITROPHIC ORGANS. SECT. I. THE ORGANS OF DIGESTION. § 1. THE TEETH.

Though genuine teeth are found in three classes of animals only, viz. the Mammalia, the Reptiles, and the Fishes, yet all the orders of these classes are not provided with teeth. Thus, among the first class, the ant-eater tribe, the pangolin, the echidna and ornithorhyncus, and the whales—among the second the cheloniads — and among the third the sturgeon—are altogether destitute of these organs. In all the invertebrated classes, the jaws, when present, are provided with notches varying in number. The echinodermata alone have genuine teeth, inserted in a mechanical apparatus very different from ordinary jaws.

Though in general structure the teeth of the lower animals resemble those of man, in some respects they differ Considerably. These varieties consist either in some change or modification of the constituent parts of the teeth, or in the addition of some other substance to those parts.

The first variety to be noticed is of the former description.

Though in the Qüadrumana and Zoophaga the bony matter of the teeth is quite similar to that of man, in Other orders this substance appears in the form of a very hard, compact, and more regularly fibrous substance than bone, and to which the name of ivory (ebur) is applied. It is chiefly in the canine or tearing teeth that this substance is found to represent the bony pillar of the teeth; and it is principally among the Pachydermata, and some of the Amphibia and Cetacea, that this change is observed.

The ivory of the elephant is the most tender, and that which most rapidly becomes yellow on exposure to air. It is readily distinguished from the ivory of other animals by the curve lines which radiate from the centre to the circumference of the tooth in various directions, and which form by intersection regular curvilinear lozenges.

The ivory of the hippopotamus is greatly harder and whiter, and is on that account preferably employed for the preparation of artificial teeth. A transverse section of this substance shows striae extremely delicate and regular. In this animal, also, not only the canine but the incisor teeth consist of this substance. The tusks of the Ethiopian boar (sus Aethiopicus) consist of ivory similar to that of the hippopotamus. In those of the ordinary boar, though no striae are recognised, there is sometimes a mixture of brown substance disposed in layers. The ivory of the teeth of the morse, though void of stnae, is compact and susceptible of polish nearly as brilliant as that of the hippopotamus; and its character is, that the central pillar of the tooth consists of minute round grains, indiscriminately aggregated, like pebbles in puddingstone. The axis or pillar of the molar teeth of this animal, which are without internal cavity, consists of similar minute grains. The ivory of the dugong is homogeneous and without striae. That of the teeth of the white whale or cachalot resembles the bone of human teeth in its satin-like appearance. The ivory of the tusk of the narwal is very compact and homogeneous in appearance.

The most singular structure of teeth among quadrupeds is observed in those of the Cape ant-eater (orycteropus). The teeth of this animal, which have the appearance of two cylinders conjoined, consist of an infinite number of minute straight parallel tubes, so that their transverse section resembles that of a rush. As these tubes are closed only at the triturating surface, it is there only that the tissue of the tooth is compact; and when the enamel is worn, the upper orifices of these tubes begin to be exposed. There is, therefore, no general cavity in the interior of the tooth. These teeth are also void of root. A similar tubular structure is observed in the two molar teeth of the ornithorhyncus, and in the teeth of some fishes.

The enamel (lamella vitrea, cortex striatus) presents peculiarities in the lower animals, as well as the bone of the tooth.

While the enamel of the human tooth is confined to the crown, in several of the lower animals, as the morse, it envelopes the tooth all round; and in the molar teeth of this animal, which, indeed, are void of cavity, it is thicker under the root than at the crown. A similar arrangement is observed in the old or adult teeth of the cachalot, which, when their cavity is obliterated by the full deposition of osseous substance, are also covered with enamel below.

The texture or constitution of the enamel is best seen in the grinders of the elephant. The section of a tooth in the germ exhibits fibres similar to those of asbestos or fine velvet. The fracture of the enamel is more distinctly fibrous than that of the bone, and the fibres are everywhere perpendicular, or nearly so, to the surface of [7:3:33]the tooth. The hardness of this substance may be inferred from the fact that it strikes fire with steel. These component fibres, however, are not always rectilineal. Most frequently they describe curves with the convexity of incurvation towards the crown and the concavity towards the root. This arrangement at least is observed in the ruminants. The distinction between the enamel and bony matter is recognised by a gray line, and another whiter which belongs to the latter substance.

The enamel varies chiefly in thickness in different animals. The tusks which project from the mouth are generally observed to be less white, less hard, and more similar to bone or ivory than the other teeth; and on this account, probably, the existence of enamel has been denied in the tusks of the elephant. It is nevertheless certain that the external layer of these tusks presents radiating fibres, though it is by no means so hard, or possesses the same grain, as the enamel of the other teeth. Enamel is more apparent, though thinner, in the tusks of the morse, dugong, and boar; and it is quite as distinct in those of the hippopotamus as in the other teeth of that animal. Lastly, the enamel of the teeth of the cachalot, which is very thick, shows in its section only striae parallel to the surface of the osseous substance.

Teeth may be distinguished according to the mode in which their component tissues are arranged into three sorts. Isŕ, When the enamel invests the axis all round, and does not penetrate the latter, the tooth is said to be simple (dens simplex). Such is the character of the human teeth, and those of the Quadrumana and Zoo- pnaga, and several other animals, and all the reptiles. [ 2d, When the enamel is folded as it were round the bony part, but without inclosing it, so that the latter forms a continuous band several times folded on itself, and sections of the tooth in every direction divide repeatedly the component substances, the tooth is said to be compound or complex (dens multiplex vel compositus). A good example of this structure is seen in the grinders of the elephant. 3d , When the base or root of the tooth is simple, and the folds of the enamel and bone penetrate only to a certain depth, they are said to be semicopound. Examples of this modification of arrangement are seen in the grinders of the ruminating animals.

In the compound, and part of the seitiicompound teeth, the enamel is covered by a third substance; and as the latter is arranged, especially in the former sort, so as to leave intervals between it and the next layer of enamel, this substance serves to fill all these intervals, and consolidates the component lobes of the tooth even before their osseous parts are united below. This substance, which is denominated by Cuvier cement, by Tenon cortex osseus, and by Blake crusta petrosa, though less firm than either bone or enamel, is dissolved by acids more slowly than the former, and sooner becomes black in the fire. In the teeth of the elephant and cabiai it forms half their mass at least. In most genera it presents no apparent organization, and resembles a sort of crystalline tartar incrusted on the tooth. In the cabiai, however, it presents numerous pores very regularly arranged. Tenon was of opinion that it arose from ossification of the membrane which enveloped the tooth; blake ascribed it to deposition from the opposite surface of the enamel membrane; but Cuvier ascertained that it is deposited by the same membrane and the same surface as the enamel. This accurate observer found, on inspecting the germs of the teeth of the elephant, that when the internal membrane of the dental capsule has deposited the enamel, it undergoes a change of structure, and becomes thick, spongy, opaque, and reddish, to furnish the cement, which is then deposited, not in regular crystalline fibres, but in random drops.

The teeth of the Reptiles consist of hard, compact, osseous matter, invested by a thin covering of enamel, and without cement.

The teeth of Fishes vary much in structure. They are either siiŉple or compound. The simple teeth are those which consist of bone invested by enamel. They may be distinguished into two species, according to their mode of attachment. The first are the simple teeth, which are not implanted in alveoli, but merely attached to the gum, or fixed by articulation to the jaw, as those of the shark tribe; the second are simple teeth growing in alveolar cavities, as is observed in the majority of fishes, the pike, dory, &c. The simple teeth attached to the gum are chiefly distinguished by their fibres intersecting in the manner of the cancellated tissue of bones, and being therefore at first light, porous, and spongy, and becoming afterwards uniformly hard and compact like ivory.

The compound teeth, which consist of an infinite number of minute tubes mutually aggregated and invested by a common covering of enamel, form plates of different sizes, adhering to the bones of the jaws or palate by an intermediate membrane only. In some they affect the disposition of the quincunx; in others they occupy the whole breadth of the upper jaw at least, as in the ray as seen on the small scale, and in the same manner in larger fishes; others are in straight transverse bars; others assume the shape of a circular segment, or the figure in heraldry denominated the chevron.

In the wolf-fish the jaws are provided with eminences composed of fibres or tubes proceeding from the base to the circumference, and which are connected to the jaw by a substance more spongy than the rest of the bone.

After their first formation the teeth retain nearly their original shape in the Zoophaga, man, and the Quad-rumana. In the two latter only their crowns begin to be worn, rendering the incisor and canine less pointed by the use of food partly vegetable; but in the zoophagous tribes they undergo no detrition whatever. In the herbivorous animals, however, the crown begins to undergo detrition more or less rapidly; and in no long time the superior layer of enamel is entirely worn off, and the surface of the tooth exposes the succession of bone or ivory, enamel, and cement. These substances are well seen in the teeth of the Rouentia, for instance the hare; those of the Pachydermata, as the elephant; the Ruminants, as the stag, sheep, and ox; and the Solldungula, as the horse. In all these animals the enamel, which is hardest, forms prominent lines or ridges; while the bone and cement are indicated by depressions.

This detrition, which is purely mechanical, might proceed to such an extent in the herbivorous quadrupeds as to destroy the whole of the crown of the tooth,'and leave the process of mastication to be performed by the jaws only. It appears to be chiefly to obviate this inconvenience that the dentition of the elephant, the Ethiopian boar, and perhaps all the Pachydermata, is conducted in a successive manner through a series of six or eight sets of teeth at least. In the former animal, in which this process has been best observed, and was ably explained many years ago by Mr John Corse Scott (Phil. Trans. 1799), each half-jaw, whatever it contains, exhibits at one time only one complete grinder and part of another behind it, the prominent parts of which are placed obliquely to the horizon, forming an inclined plane, so that the anterior parts are worn before the posterior. The anterior complete one, which is employed in mastication, undergoes progressive detrition till its anterior portion is worn down to the level of the jaw. In this state the fangs of the anterior part of the tooth begin to diminish, rendering the tooth narrow before; while the crown of the posterior[7:3:34] begins to be worn, and undergoing the same detrition, the posterior fangs also begin to give way. While this process, however, is advancing, the posterior tooth, of which only the anterior part was appearing above the gum, gradually rises, with its crown forming a plane inclined from before backwards, similar to that of the anterior grinder. When this posterior tooth has been raised sufficiently to allow its anterior margin to be used in mastication, the residue of the anterior tooth drops out altogether, and the posterior one continues to rise and advance rapidly, until it is completed, when it is found to be much larger than the previous tooth, and to consist of a greater number of plates of ivory and enamel (denticuli). In no long time this new tooth, which undergoes the same process of detrition, is succeeded by another one, the anterior margin of which rises first behind the posterior one of its predecessor, and which passes through the same stages of growth, detrition, and shedding. This process is repeated at least seven or eight times, and each succeeding tooth is larger, and contains a greater number of ivory and enamel plates than its predecessor. The elephant has thus 7 or 8 grinders in each half-jaw, or 28 or 32 grinders respectively; yet there are never more than one tooth and part of another, or at most two, that is, eight teeth in the upper and lower jaws, at the same time. Though the disappearance of the fangs of the anterior tooth is ascribed to absorption—which indeed is a good general name—yet the true reason is the fact that the maxillary or dental vessels of the elephant are unable to sustain more than one tooth in each half-jaw at once; and that since these vessels gradually transfer their blood to the new tooth, while those of the old one shrink and are obliterated, the new tooth grows as the old one is actually dehematised or atrophied. The order in which the teeth of the elephant succeed each other is nearly the following. The first or milk grinder, composed of 4 eburneo-vitreous plates (denticuli), cuts the gum eight or ten days after birth, is well formed in six weeks, and completely out in three months. The second, which consists of 8 or 9 plates, is completely exposed at the age of two years; the third, consisting of 12 or 13 plates, at six years. The fourth to the eighth grinder consist of plates varying in number from 15 to 23; but the period at which these teeth appear has not yet been determined. This process has been shown to have taken place also in the gigantic fossil animal named the mastodon.

A similar process of displacement and renovation takes place in the poison-teeth of serpents, and in the teeth of the shark, diodon, and tetraodon tribes. In the wolffish (anarrhicas lupus) the teeth are shed along with the spongy membrane in which they are contained, exactly as the horns of the stag.

In the horse, in which the process of dentition has been carefully observed, it is usefully employed to determine the age of the animal. The milk incisors appear at the end of 15 days; the four middle ones, or the nippers, are shed at 30 months; the four following ones at 42 months; and the four external, or the comer teeth, at 54 months. The permanent corner teeth do not grow so quickly as the other incisors; and by these especially the age of the horse is determined. At first they scarcely rise above the jaw. Their middle then presents a hollow filled with blackish tartar, the margins of which are worn down as the tooth rises from the gum, and is rubbed against the corresponding one; and it diminishes progressively from 54 months to 8 years, when it is altogether obliterated. The hollow of the other incisors is obliterated at a later period than that of the corner ones; and the age of the animal is then estimated from the length of the incisors, which continue to increase.

The first two molar teeth appear in each jaw and on each side about the 8th day, the next at the 20th, and the complementary or small anterior grinder about the 5th or 6th month. The first posterior molar appears about the 11th month, and the second in the 20th. At the 30th or 32d month the first two milk grinders are shed, the third in the 3d year; and about the 5th or 6th year the last posterior grinder appears. The milk grinders are longer from before backwards than the permanent ones, which are themselves contracted in this direction, as they are pressed by the posterior grinders; from which it results that the dental crowns of young horses are oblong, while those of the old are quadrangular.

In the Mammalia the teeth are always implanted in the jaw-bones, and never, as in other animals, in the tongue, palate, &c. The only exception to this rule is the echidna.

The three kinds of teeth, incisor, tearing, and grinder, are found together only in Man, the Quadrumana, the Zoop∏AGA, the Pachydermata except the elephant and two-horned rhinoceros, in the hornless Ruminants, and in the Solidungula ; but, of all these animals, in man only are the three forms of teeth arranged in an uninterrupted series, and in such a manner that those of the lower jaw are applied to those of the upper. In one other animal only, now extinct, the anoplotherium, is this continuity of arrangement observed.

In the Quadrumana and Zoophaga, and all those in which the canine are larger than the other teeth, there is a gap on each side of the jaw to receive the canine of the opposite one. In the ursine genus there is a large empty space behind each canine tooth. In the hedgehog, shrew, phalanger, and tarsier, in which the canine are shorter than the other teeth, a space is left between them and those opposite. In the maki tribe, proper bat, colugo, and camel, there is a large interval between the upper incisors. Lastly, the Ruminants want the incisors of the upper jaw, and the morse those of the lower.

Some animals provided with the three classes of teeth lose the incisors at a certain age; for instance several of the bat tribe, and the Ethiopian hog. Other Mammalia have only two sorts of teeth, for instance incisors and grinders, separated by an interval without canine, as the wombat and all the Rodentia, in which there are only 2 incisors in each jaw; the kangaroo, which has two below and 6 or 8 above; and the cavy or hyrax genus, which have 2 above and 4 below. The elephant has grinders and two tusks planted in the superior intermaxillary bone, but no inferior incisors or canine teeth.

Animals may possess grinders and canine teeth without incisors, as the sloth tribe and the dugong. The grinders, which are most essential, are most rarely wanting; and when others are deficient these are present, as in the armadillo tribe, the orycteropus, the ornithorhyncus, two-horned rhinoceros, and lamantin. The jaws of the dolphin are provided with uniform conical teeth all round, while the cachalot or white whale has them in the lower jaw only. In the narwal there are only two long spiral tusks implanted in the intermaxillary bone, and of these one is often wanting.

Lastly, teeth are entirely wanting in the ant-eater tribe, pangolin, and echidna, which are therefore arranged among the Edentata. In the whale the teeth are represented by plates of the laminated, fibrous, bluish substance distinguished by the name of whale-bone.

§ 2. organs of insalivation.

Under this head ought to be noticed the modification which the salivary glands undergo in the lower animals. Our limited space, however, obliges us to proceed immediately to notice the peculiarities of the other divisions of the alimentary canal.
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§ 3. (ESOPHAGUS, STOMACH, AND INTESTINAL TUBE.

The muscular tissue of the oesophagus consists, in most of the Mammalia, of spiral fibres twisted in two opposite directions, the external from before backwards, the internal from behind forwards. This arrangement, which was first observed in the Ruminantia, was supposed to explain the process of rumination. This opinion, however, is refuted by the fact that the arrangement is not confined to this order, but is very general among the zoopha~ fous and other animals which do not ruminate. In the angaroo the direction of these fibres is, as in man, transverse in the internal layer, and longitudinal in the external.

The oesophageal mucous membrane is covered by epidermis, which extends to the cardiac opening of the stomach in man, the Quadrumana, and all the Zoopha-ga. This membrane, as well as the mucous, is thrown, by the action of the muscular tunic, into longitudinal folds, which are effaced only when the oesophagus is distended. In the tiger, lion, and lynx, there are large transverse valvular folds, and smaller ones in the civet and couguar— an arrangement connected probably with the carnivorous habit.

The stomachs of the lower animals vary considerably in shape, in the insertion of the oesophagus, in the disposition of their muscular tunics, and in the simplicity or complication of their cavities. These characters it is impossible in such a sketch as the present to consider in detail; and we shall confine our attention to those peculiarities which are most striking in the digestive organs of the animal world.

The stomachs of the Mammalia may be distinguished into the simple and compound. Those of man, the Quad-rumana, zoophagous and most of the herbivorous tribes, belong to the former order. This simple form of stomach, however, may be generally distinguished into two parts, a cardiac and a pyloric, more or less separated from its other by a central transverse contraction of its annular muscular fibres. This is particularly seen in the horse, man, murine family, and many other animals which occasionally feed both on animal and vegetable matter. In the human stomach this contraction is represented in Plate XXXVI. fig. 4. In the porcupine, however, there are three pouches. This contraction depends on a strong annular band of muscular fibres at this part of the organ. In the pure carnivorous animals, however, as the feline family, the annular fibres, which are very thick, are nearly equally so from the cardiac to the pyloric end.

The compound stomachs, or those which contain more cavities than one, are found in the sloths, and the ruminant and cetaceous animals chiefly.

In the first tribe the stomach of the Unau, or two-toed sloth, is two-fold. The first cavity is large and globular, but tapering behind into a conical appendage, separated by a semilunar fold; while a large cul de sac on the left of the cardia opens into a canal which proceeds at first backwards, and then turning to the right, enters the second cavity by a narrow aperture. The second, which is small, tubular, and folded under the former from left to right, is distinguished by a semilunar fold into two halves, the first of which opens into a small cul de sac on the right side of the first cavity. The inner membrane of both cavities is smooth, and without villi. A similar arrangement is found in the Ai, or three-toed sloth, with this exception, that the appendage of the second gastric cavity is divided into three compartments by two longitudinal bands. This canal seems analogous to the arrangement of the ruminating stomachs, in so far as it may allow the alimentary matters to pass occasionally from the oesophagus directly into the second stomach.

The stomach of the hyrax, ashkoko, or Cape cavy, also consists of two pouches, separated by a middle partition, in which there is an aperture for mutual communication. In the hippopotamus the cardia communicates with three pouches, two of which only are cognizable without, and with a long tubular bowel, the interior of which is divided across by several valvular folds.

In the kangaroo the stomach receives the oesophagus near its left extremity, which is small and biful (Plate XXXV. fig. 8); and forming a larger cavity on the right, passes upwards, making a turn, and crosses to the left before the oesophagus, makes another turn, and again crosses the mesial plane to the right, where it terminates in a tapering cavity at the pylorus. In this course it presents internally a longitudinal band (l, l, D, extending all round to near the pyloric end, and crossed by valvular membranous folds, which divide the cavity into cells not unlike those of the colon, especially in the horse. The mucous epidermis is continued from the oesophagus over the space marked c, c.

The stomach of the Ruminants consists of four distinct but communicating cavities. The first, denominated the Paunch (×ofKia, rumen, penula, ingluvies; la panse, l’ herbier, la double), is a large bag occupying the left side of the abdomen chiefly, marked externally by two saccular appendages, and separated within into four parts. (Plate XXXV. fig. 1, A, A, a, a.) Its inner surface, upon which the epidermis is continued, is occupied by flat papillae. By a pretty wide aperture (b, b), with rounded margins, this communicates with the second cavity named the Kings-hood (%sx^υpαλoi, reticulum, le bonnet), which is distinguished by the rhomboidal and polygonal cells, into which its inner membrane is moulded. An aperture at the further end of this (c) leads into the third or smallest cavity, termed the Maniplies (sχ∕voς, omasum, le feuillet), from the numerous concentric crescentic folds formed by its inner membrane (fig. 2, c and p). These folds amount to about 40 in the sheep and 100 in the ox. The smallest of them, between the aperture from the second into the third cavity, are puckered or collected towards their further end by a transverse membranous fold, which acts as a valve to the aperture between this and the fourth cavity. This one, generally named the Red (yw<srξpv, abomasum, la caillette), is of an elongated pyriform shape, slightly incurvated on itself (fig. 2, d), and is marked internally by longitudinal folds (p) incurvated according to the curvature of the cavity itself, and terminating near the pyloric end in rugae or irregular duplicatures (r). This is the structure of the gastric cavities in the ox.

In the camel, dromedary, and lama, the stomach is equally complicated, though the structure is a little different. In the first of these animals, which may be taken as an example of the others, the Paunch or first cavity is a large bag, divided into two compartments on the posterior part; by a strong band passing from the right side of the cardiac orifice longitudinally downwards (l,l, fig. 3), and forming one border of a groove leading to the orifice of the second. From the left margin of this band proceed eight muscular bands, nearly at right angles, and intersecting with others, form cellular cavities on the left side of the paunch (n) ; while on the right side there are similar cells, though smaller, and wholly unconnected with the longitudinal band. From the left margin of the cardia, in like manner, proceeds a broad muscular band (μ, fig. 3) to the aperture (b) of the Paunch into the Kingshood, after which it takes another direction (μ, fig. 4) towards the Maniplies or third cavity, within the orifice of which it terminates (c, fig. 4). The Red or fourth chamber is much the same as that of the bullock (d, p, r, fig. 5), and the only peculiarity is, that after terminating in (∏) the pylorus, it opens in a small cavity (o) which leads into the duodenum (∆).
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From this description, for the particulars of which we are indebted to the accurate account of Sir E. Home, it results that the stomach of the camel differs from that of the ox and other horned ruminants chiefly in the possession of the quadrilateral cells in the second stomach. Into these the water is conveyed by the animal when drinking, and in these it remains. By the action of the muscular band (μ), the aperture between the Paunch and Kingshood is opened, and the water is directed into it so as to fill its cells. When these are filled the surplus runs off into those of the first stomach, where at least those on the left side of the long band may be regarded as part of the general cellular structure. These cells are represented of a large size in fig. 5, in which they appear like oblongs with rounded corners. They are always larger on the left side of the band, in the Paunch, than those in the second stomach.

Both in the bullock and in the camel, and in all the Ruminants, the first and second stomachs only are covered by mucous epidermis.

In the Cetaceous animals similar complication of the gastric cavities is observed. In the bottle-nose porpoise, which may be taken as an example, the oesophagus, which is large and capacious, terminates in a spheroidal or ovoidal flask-like bag (fig. 6, a, a) with an aperture a little below the cardiac, consisting of rose-like annular folds, and leading into a second cavity. This, which corresponds to the ruminant kingshood, is nearly spherical in shape (fig. 7, b), and presents valvular folds more circular than in the ruminants, and intersected by others so as to give it the honeycomb appearance characteristic of this cavity. From this another aperture leads into the smallest cavity of the three (c, fig. 7); and thence into the fourth, which is long, cylindrical, and slightly incurvated. The third cavity is remarkable for presenting in its inner membrane numerous apertures of mucous glands.

Birds are distinguished by possessing a stomach consisting of three cavities. The first is the crop, which may be regarded as a mere expansion of the oesophagus, and confined chiefly to land birds. It is filled not only with food, but with small stones; and its chief purpose seems, by mechanical comminution, to supply the place of the teeth in dividing the granular aliment, and bruising or killing the animals swallowed. It is found chiefly in the granivorous birds. It is wanting in the ostrich, in the piscivorous birds, and most of the Grallae.

The second is the glandular crop or subsidiary stomach (ventriculus succenturiatus, bulbus glandulosus), a mem-brano-glandular sac, which may be also regarded as an oesophageal dilatation. It is larger when the crop is wanting; and though, when conjoined with it, it is always very glandular, and may be therefore regarded as a chemical solvent of alimentary substances, it appears to supply the want of the crop, which is certainly chiefly a mechanical apparatus. The glandular crop or subsidiary stomach .is remarkable for the number and size of the glandular bodies contained between its mucous and muscular tunics. These glands, though variable in shape, are generally conical; and some consist of several glands conjoined in one common peduncle (Plate XXXVI. fig. 3). All of them are hollow, and secrete a fluid which is discharged by one or more minute apertures, and which is of essential importance in the solution of the food. In some instances, as in the American ostrich (fig. 2), they are few in number, and occupy only a small part of the posterior wall of the oesophagus.

The gizzard or proper stomach of birds may be considered as a horny mucous membrane, somewhat cartilaginous, .continuous with that of the oesophagus, and covered by two strong thick muscles, the fibres of which converge to a point. (Plate XXXVI. fig. 1.) In the carnivorous and piscivorous genera of birds, especially those in which the crop is wanting, the gizzard loses its muscular character, and is converted into a membranous pouch.

The stomach of Reptiles does not present those dilatations observed in Birds ; and when it changes its diameter or capacity, it is only progressively and insensibly. Its general diameter, nevertheless, is proportionally larger than in the two classes already noticed. Most generally without cul de sac, its shape is spheroidal, more or less oblong; its membranous walls are thin and transparent; its muscular layer almost imperceptible; the cellular identified with the mucous tissue; the situation of the cardia indeterminate; and the pylorus, without valve, is distinguished by a simple tapering contraction of the gastric walls, and the appearance of the structure proper to the intestines.

In this class of animals, further, digestion appears to be less regulated by fixed principles than in the other two. It is evidently not confined exclusively to the stomach. The oesophagus of the turtle is provided with numerous large, firm, pointed processes, which in all probability contribute to the mechanical division of the food, so much the more requisite as the Cheloniad Reptiles are toothless. Except in the crocodile, the Sau-rial Reptiles are destitute of large arch or proper cardiac cavity. In the Ophidial or Serpentine Reptiles the stomach has the figure merely of a dilated sac between the oesophagus and intestines, and presents no curvature. It is probably in connection with this modification of structure that we find animals remain for days in the oesophagus of serpents; and this tube appears to be to a certain extent capable of digesting aliment as much as the stomach. The best mark of distinction in such circumstances is the cessation of epidermis.

In no class of animals does the stomach vary more in shape, structure, and situation, than in Fishes ; and perhaps the general character of the alimentary canal in this class is most justly given by representing it as deviating from those attributes of regularity which we find in the higher classes. While in the Mammalia and Birds it is always distinguished by its spheroidal or pyriform enlargement between two tapering extremities, and by being much more dilated than any other part of the alimentary canal, in the Reptile class it begins to part with this character; and it loses it altogether in the Fishes. In most of the finny tribes it is often not more capacious than the oesophagus; and it is distinguished from this tube only by the villous character of its internal membrane. In general, also, the situation of this pyriform dilated sac is transversely across the body in the Mammiferous class. In the feathered tribes this character also is slightly set aside, and partly from the alteration in shape, partly from that of position, the stomach occupies less of the transverse diameter than of the longitudinal extent of the body. Among the Reptiles this character, though still retained in the Ciieloniad, and even in the Saurial, is gradually enfeebled in the Ophidial ; and in the Fishes it may be said to be entirely obliterated, since the organ occupies much more longitudinal extent than transverse width of the body.

The first character of the alimentary tube of fishes is the width or capacity combined with shortness of the oesophagus. The latter character is manifestly associated with the absence of lungs and consequent want of chest; so that between the throat and abdominal cavity, the interval, which corresponds only to the space occupied by the heart, is extremely abridged. The oesophagus consists, as in the other classes, of a mucous membrane surrounded by a muscular tunic; but the mucous membrane is distinguished by the firmness and whiteness of its corion, which in some genera approaches to the consistence of horn or cartilage, and by the presence of conical pa-piiloe, sometimes of great hardness, and which appear to [7:3:37]act mechanically on the food. It is almost superfluous to notice the facility which the large capacity of this tube affords fishes for swallowing their prey. Most of them ’ are voracious in the extreme; and it is not uncommon to find the stomach and oesophagus crammed to the throat.

The figure and position of the stomach of Fishes are so variable, that it is difficult to give a character of general application. Though in many genera, especially of the Jugulares, it consists of a cylindrical sac with a slight dilatation immediately below the cardia, in others it is oblong ovoidal, as the ray and shark tribe; and in others, as the sole, dory, and flat fishes generally, it is orbicular. In the sturgeon it consists of a cylindrical tube incurvated twice on itself. In none is there more than one cul de sac, the depth of which varies as the part corresponding to the pylorus is more or less remote from the fundus. When the limits of the stomach are indistinct, the situation of the cardia įs equally so. In the lamprey (petromyzon) and pen-fish (syngnathus pelagicus) the whole tube is of a -uniform size from the mouth to the anus; and much the same may be said of the carp genus. The genera in which it forms a distinct dilatation or cul de sac are chiefly the following; the eel (muraena anguilla), conger (ni. conger), the bullhead genus (coitus), the scorpeena horrida, labrus genus, perch, cuckoo gurnard, mackerel, herring, salmon, mormyrus genus, mullet, and silurus Bagre. In the anableps the dilatation disappears; and in the chaetodon ciliaris and some others it is a large sac incurvated in an arch-like bend.

The intestinal canal in most of the Mammalia is very similar to that of man; and the chief differences of different orders and genera are found in the difference of longitudinal extent either of the whole intestinal tube or the comparative lengths of its several parts.

From the time of Grew to that of Cuvier, and most 1 modern anatomists, it has been a point of some importance to determine the length of the intestinal tube in relation to that of the body. This comparative length, which is greatest in the Mammalia, diminishes successively in the Birds, Reptiles, and Fishes. It has been occasionally stated by different anatomists, that the intestinal tube is longer, coeteris paribus, in granivorous than in carnivorous animals, and conversely. When we come, however, to compare the different lengths of this tube in the several tribes, we find that this statement demands modification. In the ape family its length varies from 5 to 8 times that of the body; in several of the lemur tribe from 4 to 6 times, the smaller length being in this case compensated by the size of the ccecum ; and in others of the lemur tribe, e. g. the lori, the intestine is only three times the length of the body. Among the Chiroptera there are two examples of very great contrast in this respect. While the intestine of the noctula or great bat (vespertilio noctula, Lin.) is the shortest of all the Mammalia, and scarcely does more than exceed the length of the animal’s body, that of die roussette (pteropus) or East India bat, which lives chiefly on vegetable matter, is at least 7 times longer than its body. A similar instance of the meeting of extremes is found in the Marsupial order, in which the marmoset and cayopollin have intestines only 2⅜ times longer than the body, while that of the phalanger is more than 11 times longer. In the plantigrade or ursine family, which occasionally live on vegetable matters, the proportional length approaches to that of the ape.

In the carnivorous animals the intestine, though generally short, varies from 3 times to 8 times the length of the body. The former is the proportion in the lion, wild cat, ocelot, couguar, and weasel; and the latter in the hyena. Some of them also vary among themselves. Thus the intestine of the wild cat is greatly less than that of the domestic animal. The proportion is very great among the Rodentia, in several of which it is 8, 10,12, or 16times longer, as in the agouti, than the body of the animal. Among the murine tribe, however, it undergoes a diminution. Among the Edentata, again, especially the sloth tribe, it diminishes very much, being only about 3∣ times longer than the body in the Ai and Unau. This brevity is so much the more extraordinary that these animals are void of caecum, and live on vegetable matters; but, in all probability, the duplicature of the gastric cavities· in some degree compensates this deficiency.

The intestinal tube attains its greatest proportional length in the Ruminant animals, being at least 11 times longer than the body, as in the goat, and 28 times longer in the ram. This immense length is supposed to compensate the absence of dilatation in the large intestines, and the small size of the caecum. In the Solidungula, again, which are remarkable for the large size*of the caecum, the length of the intestine diminishes much, being 8 times longer than the body in the zebra, 9 times in the ass, and 10 times in the horse.

Lastly, it is a singular circumstance, that in different species of the same genus the comparative length varies much. We have already noticed the difference between the length of the intestine in the wild and in the domestic cat. The wild and tame boar is a similar instance of the same, the intestine being only 9 times longer than the body in the former, and so much as 13∣ times in the latter. It is possible that such differences may depend on the different habits of the animal in his wild and domestic condition. This explanation, however, is totally inadequate to account for the difference in the comparative length of the intestinal tube in the Asiatic and African elephant, being 10 times longer than the body in the former species, and only 7 times in the latter. The same may be observed of two animals very closely allied, if not of the same genus, the echidna and ornithorhyncus. The intestine of the former animal is 7 times longer than his body, while that of the latter is only 5 times.

In Birds generally the intestine is shortest among those genera which prey on animals and fish; it varies from twice to five times the length of the body. In the gallinaceous and passerine birds, which live on grains, it is always longer and more capacious than in those which live on animal substances. In the cassowary, which is granivorous with a short intestine, the intestine is divided by contractions into distinct pouches, to compensate for the brevity of the tube. It must be remarked, nevertheless, that in several birds which prey on fishes, * the intestinal tube is proportionally longer than in those which feed only on grain; and the proportional length is not diminished in birds living indiscriminately on animal and vegetable aliment.

The intestinal tube of the Reptiles is still shorter than that of Birds, and often it does not exceed twice the length of the body. It is longest in the Cheloniad, and shortest in the Ranine and Serpent tribe. In the tadpole, however, a singular peculiarity is observed. The intestinal tube of the tadpole of a frog is nearly ten times longer than the space between the muzzle and the vent (anus) ; whereas, after the animal has become a frog, the intestine is only twice as long as this space.

In the class of Fishes the intestinal tube is still shorter and more direct in its course to the vent or outlet. In a few which live chiefly on marine vegetables, for instance some of the chaetodon genus, it is about six times longer than the body of the animal; and in a few of the carp genus (viz. cyprinus capaeta) it amounts to ten or twelve times longer than the body. In others, however, of the same genus, for instance the cyprinus niursa, it is scarcely as long again, showing here once more an instance of the conjunction of extremes not easily explained.
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In most vertebrated animals the intestinal tube may be distinguished by natural marks into two divisions, one extending between the pyloric end of the stomach to a part 1 of the tube, where it becomes wider and more capacious; the other from this to the vent or outlet. In some instances, however, this distinction is very obscurely and imperfectly marked. In the Mammalia, in which-the distinction is observed, it is indicated by one or more appendages, which, if large, are denominated caeca, and if slender and long, are termed vermiform, processes. Man, the ourang, and the wombat (phascolomys), are the only animals which are possessed at once of caecum and vermiform appendage. In the other genera of the ape tribe, in the maki of the lemur, in the colugo among the Chiroptera, the ichneumon, many of the carnivorous tribe, the opossum and kangaroo, the Rodentia except the dormouse, the Cape ant-eater, the Pachydermata except the hyrax, the Ruminants, Solidungula, and Amphibia, there is only a caecum without vermiform process. The caecum is wanting in the sloths, the bat tribe, the Ursine except the ichneumon, the marten, pine-marten, weasel, &c. the dormouse, and all the Cetaceous animals.

The presence of caecum or vermiform process, however, is not necessary to distinguish the canal into two portions. The inner or mucous surface of the ileum is always villous and uniform; and the whole intestine, except its superior or pyloric portion, is convoluted in proportion to its length, and moves about freely in the abdominal cavity; whereas the colon is more or less fixed at different points, it is shorter and more capacious, andits inner membrane is merely mucous without long villi. A mark equally general is the semilunar duplicature of mucous membrane placed between the ileum and colon, and named the ileocolic valve. In the sloth and armadillo tribes, which want caecum and vermiform process, this and the slight difference of diameter are the only marks of distinction between the ileum and colon. In all the other Mammalia which are destitute of caecum the whole tube is of the same calibre, occasionally diminished towards the vent; and the division into ileum and colon is no longer cognizable.

In all the Mammalia with one caecum, it appears in the form of a production from the large intestine beyond the part at which it receives the ileum; and though variable in its diameter and structure, it bears a general resemblance to the colon in these respects. In herbivorous animals, and even in some that are omnivorous, as the ape and lemur tribes, it is generally large and puckered by tendinous bands. To this, however, an exception is observed in the Ruminants, in which the caecum is moderate in size and unpuckered. It is small and unpuckered in the kangaroo-rat and wombat; while, conversely, in the colugo and brown phalanger, which are believed to be chiefly zoophagous, it is very large and puckered.

In the zoophagous animals generally both the colon and caecum are of small calibre, little different from that of the ileum ; and both the colon and caecum are destitute of cells or compartments. In herbivorous and several omnivorous animals, on the contrary, the inner surface of the colon is divided by longitudinal and transverse bands into a number of cells or compartments. From this rule, however, there is an exception in the wombat, kangaroo, and the Ruminants. In the Rodentia the colon is cellular at its commencement only.

In birds the canal is provided with two caeca, one on each side, not far from the vent. In the omnivorous and granivorous these caeca are generally long and capacious. While they are very large in the nocturnal predatory birds, they are either obliterated or wanting in the diurnal predatory birds, in the green woodpecker, the lark, and the cormorant. In the heron, bustard, and grebe, there is a single small one; in the cassowary two very slender; and in the merganser, diver, &c. they are short and thick.

In all birds the short bowel between the insertion of the, caeca and the cloaca is a little wider and more capacious than those between the pylorus and the caeca ; and this is the only circumstance which indicates in this class the distinction of the tube into ileum and colon.

In the reptiles the intestinal tube is generally void of caeca or appendage; and the only distinction consists in the one part of the tube, which is long and slender, being joined to another which is short and thick, and in the presence of a semilunar membranous fold at the point of insertion. In the iguana alone has a genuine caecum been observed.

The distinction into small and large intestine, or ileum and colon, is still less obviously observed in the class of fishes. It sometimes happens that the difference of capacity is inverted, and that the calibre of the portion which terminates at the vent is actually smaller than that of the part connected with the stomach. This arrangement is observed in the ray, shark, sturgeon, and even the bichir; in the syngnathus, trunk-fish, and balista. In other instances the diameter is the same throughout; and the only distinction is derived from the anatomical characters of the inner membrane. In the lamprey, sea-devil, rough star-gazer, radiated sole, holocentrus sago, carp tribe, mormyrus, and mullet, it is impossible to distinguish the intestine into large and small.

Fishes resemble Reptiles in being destitute of caecum at the junction of the small and large bowel. In many of them, howe-⅛r, there is attached to the intestine, somewhere below the pylorus, a variable number of small intestines terminating in blind ends, similar in size and structure to the intestine with which they communicate. These tubes, which have been not very happily named pyloric appendages (appendices pyloricae), in so far as they are most frequently connected rather with the part of the bowel corresponding to the duodenum, vary in number from 2, 4, 6, or 8, to 80 or 180 in some genera, and even their number is not the same in different species of the same genus. Thus, while there are 6 in the smelt (salmo eperlanus), there are 68 in the s. lacustris, and 70 in the salmon (s. salar). In like manner, though there are 18 in the anchovy, (clupea encrasieous), there are 24 in the herring (c. harengus), and fourscore in the shad (c. alosa). In some, as the cod and pollach, they consist of several large trunks ramified into numerous small ones.

These appendages, however, are wanting in the cartilaginous fishes with free branchiae, in most of those with fixed branchiae, in the Apodes, and in several of the thoracic and abdominal order. In the sturgeon and some others they are represented by a series of communicating cavities inclosed in the intestinal membrane, which is covered by a cellulo-muscular tunic and peritoneum (Plate XXXVI. fig. 5), and which assumes the external appearance of a pancreas.

Among the cartilaginous fishes the brevity and directness of the intestinal tube is compensated by a peculiar disposition of the intestinal mucous membrane. This consists in part of the membrane projecting like a broad fold or process from the inner surface of the intestine, and winding round from the pyloric to the anal or lower extremity (fig. 7 and 8). This, which is denominated the spiral valve, may be easily understood from these figures, which represent the arrangement as it is observed in the shark. In the sturgeon, in which it is found in the last portion of intestine (fig. 6), its peculiarities have been described by the writer of this article in the Wernerian Transactions, vol. vi.

In all the Mammalia the intestinal tube terminates in a distinct bowel denominated the rectum, the mucous membrane of which is continuous with the skin at the [7:3:39]anus. This rule can scarcely be said to be violated in the case of the echidna and ornithorhyncus, in which there is an aperture at the lower part for the urine and the semen of the male and the ova of the female. These anomalous and singular animals form a transition to the mode in which the intestinal tube terminates in the three genuine oviparous classes. In Birds, Reptiles, and most of the cartilaginous Fishes, the intestinal tube terminates in an outlet common to it with the urinary organs, denominated generally the cloaca. In the sturgeon, however, it has been shown, in the paper already mentioned, that there is a distinct urinary outlet; and that consequently this animal cannot be said to have a cloaca. In the greater part of fishes, while there is one vent for the excrement, there is another common one for the urine, the ova, and the spawn.

On the subject of the liver, spleen, and pancreas, it is impossible to enter with any interest in this sketch.

CHAP. II. SECT. I. THE HEMATROPHIC ORGANS.

The Mammalia and Birds agree in having a heart consisting of two pairs of chambers, a venous auricle and ventricle, and an arterial auricle and ventricle. The Eustachian valve is often wanting in the Mammalia. It is wanting, for instance, in the lion, bear, and porcupine; while it is broad and muscular in the seal, and assumes a spiral direction along the upper walls of the right auricular sinus in the elephant.

It was at one time imagined that the aquatic Mammalia were distinguished from the terrestrial by the foramen ovale being open and forming a communication between the two auricles. This, however, is a mistake, at least in the adult animal; for neither in the otter, the seal, nor the porpoise or dolphin, did Cuvier find this aperture pervious; and it may be inferred, that when it is open, it is an anormal remain of the fetal structure. In the ornithorhyncus, also, according to Sir Everard Home, it is impervious. In the porcupine and elephant, in which there are two anterior venae cavae, the blood of the left anterior cava, which opens in the sinus near the auricoventricular aperture, is conveyed directly into the right ventricle.

The reptile heart, the first in the cold-blooded division, varies somewhat in the several tribes. In the first three, the Cheloniad, Saurial, and Ophidial∕ it consists of two auricles and one ventricle, divided in some instances into communicating chambers. In the Batrachoid family, on the contrary, it always consists of one auricle and one ventricle, the interior of which is unilocular or undivided. In several of the Turtle tribe, among the first family, the ventricle consists of a pulmonary chamber, in which the blood is more particularly directed to the pulmonary artery, and a general or aortic chamber, which is above, and from which the blood is conveyed into the aorta. In the crocodile the ventricle is divided into three chambers, communicating by several apertures. One is inferior and to the right, and communicates with the right auricle by a large aperture provided with two valves. On the left, and before, is the second chamber, receiving the orifice of the left descending aorta. Behind is an aperture leading into the smallest chamber of the three, situate at the middle of the base of the heart, and receiving the common trunk of the pulmonary arteries. The left chamber is above. In the Ophidial or Serpentine family the ventricle is divided into two chambers, a superior and inferior, separated by an imperfect partition, which allows the two to communicate.

The heart of the finny tribes is as simple as that of the Ranine reptiles, which indeed constitutes the preparatory step in the descending scale of organic forms. It consists, as in these animats, of two chambers only, an auricle and ventricle. The former receives the blood from the body at large, and transmits it to the ventricle, which is almost in all cases unilocular. From this a single vessel conveys it, not to the body at large, but to the gills, from which it is again collected by several branchial veins.

Of the blood-vessels of the four vertebrated classes it is superfluous to speak in any detail.

The most remarkable circumstances are the minute subdivisions which in some classes the arteries undergo previous to final distribution. In the Ruminants, and several of the Pachydermata, the branches of the carotid artery, instead of uniting by the communicating vessels, are subdivided into a great number of minute vessels, which form round the pituitary gland a communicating plexus, denominated by the ancients Pete mirabile.

In the slow lemur (lemur tardigradus) Sir A. Carlisle found the subclavian artery, after entering the axilla, divide into 23 arterial cylinders of equal size, and the iliac on the brim of the pelvis into at least 20 equal-sized tubes, which in both cases surrounded the principal artery, reduced to a small vessel, and, proceeding along the extremity, were distributed chiefly to the muscles. (Phil. Trans. 1800.) A similar arrangement, carried to a still greater extent, was found in the Ai or three-toed sloth, in which the axillary and iliac arteries were divided into about 60 or 65 cylindrical parallel tubes. In the slender lemur (Lemur loris) these vessels are subdivided into 4 or ô only.

In Fishes in which the unilocular ventricle sends its blood to the gills only, the heart is pulmonary, and the arterial system is destitute of central impulsive organ. In the sturgeon, which is one of the best examples of the distribution of the arterial system in the finny tribes, the blood, which is distributed in the branchiae by the large artery, is collected in numerous vessels, which may be regarded as analogous to the pulmonary veins of the warm-blooded classes, but which have thick parietes like arteries; and these uniting, form a large vessel, which is lodged in a cartilaginous canal formed by the continuous bodies of the vertebrae. This vessel is further void of compressive or elastic tunics, and the blood moves through it as through an immovable and inelastic tube. From its sides, however, a series of arterial vessels issue, which forthwith assume the usual characters of arterial tubes. In many other fishes the parietes of the large artery adhere in part to the semi-osseous canal in which it is lodged.

SECT. II. THE ORGANS OF AERATING CIRCULATION.

The lungs of the Mammalia are in all essential points perfectly similar to those of the human subject.

The lungs of Birds differ chiefly in not presenting distinct lobules, in having the air-vessels larger and more distinct, in the branchial tubes not becoming quite so small, and in terminating not alone in the pulmonic vesicles, but in perforated parts of the surface of the lungs, which lead into large air-sacs, communicating with all parts of the body, and forming an accessory lung. In the ostrich, which may be taken as a general example, there are four of these cells or aerolabous sacs. The first, which is anterior, extends from the apex of the chest to the iliac bones, between the first ribs and heart above, and between the lower ribs and a cell which surrounds the intestines. It is divided into four chambers, the first two communicating with the lungs by large apertures, while the fourth opens in the iliac bones. Behind this large sac are two small ones, between the iliac bones and the peritoneal sac. Before it is another small one occupying the lateral regions of the apex of the chest, and communicating with sacs in the axillae and neck. Besides these, the stomach, liver, heart, and intestines are surrounded by sacs. All of these communicate by saccular processes with the cavities of the bones. By this peculiar arrangement Birds possess the greatest extent of respiratory surface of all classes of animals.
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The lungs of Reptiles are distinguished by consisting of large sacs, subdivided by membranous partitions into polygonal cells, which again are subdivided by smaller slips into smaller cells. In these cells the bronchial tubes are not ramified, but divide abruptly in them at the surface of the lung. Some idea of this arrangement may be obtained from the lung of the ordinary land-tortoise (Testudo Groeca, Plate XXXVII. fig. 1). The sacs or large cells are smaller and more numerous in the turtle (fig. 2); but the general disposition is much the same.

The young of the Batrachoid family, and several of the water-lizard tribe, are provided with fimbriated or ciliated processes attached to the neck, and which are in all respects similar to the gills of fishes. These gills disappear as the animal grows; and when it assumes the true ranine or reptile character, vesicular lungs like those of other reptiles, and which had continued in a hitherto latent and rudimental state, are developed, and the animal breathes as others of the same tribe.

A peculiar form of respiratory organ is found in the lamprey or seven eyes, and the two species of hag-fish, (Myxine, Lin.; Gastrobranchus, Bl.; and Gastrobrauchus Dombey). The former has on each side seven apertures leading into cylindrical tubes, in which the branchiae are contained. (Plate XXXVII. fig. 3.) In the two species of hag these tubes are dilated into ovoidal cavities, in which the water is received, and on the membrane of which the branchial vessels are distributed. In this respect, therefore, the hag-fish approaches to the mode of respiration among the cephalopodous Mollusea, in which the branchiae are inclosed in a cavity. Lastly, in the Aphrodite aculeata, which may be taken as an example of the respiration of worms, there is a series of tubes like tracheae and bronchi, proceeding from the surface to the interior, and in which the water containing the air requisite for respiration is received. (Fig. 6.)

SECT. III.—SECRETORY ORGANS.

Under this head ought to be described the urinary organs of the four vertebrated classes. Those of the Mammalia agree in consisting of kidneys more or less tabulated, ureters or excretory tubes, a reservoir or urinary bladder, and a urethra opening on the same mucous surface with the organs of generation. In the three oviparous classes considerable changes are made. Though in Birds and Reptiles the glandular organs denominated kidneys are left in the shape of aggregated glands with the two excretory tubes, the bladder is withdrawn, and the ureters open in the cloaca. The only apparent exceptions are the ostrich and cassowary, in which the cloaca is so organized that it may serve as a bladder or temporary receptacle of the urinary secretion. In the Reptiles the presence of this organ is variable, being found in the Che-loniad and Batrachoid ; and the iguana, tupinambis, chameleon, stellio, and dragon, among the Saurial tribe; but wanting in the crocodile, lizard, agami, gecko, and the whole Ophidial tribe. In Fishes it is not less variable. While the ray and shark tribe are destitute of bladder, and the ureters terminate in a cloaca, this receptacle exists in the sea-devil, lump-fish, globe-fish, and others of the cartilaginous division.

A peculiar secreting organ, deserving notice, is the poison gland of the poisonous serpents. It is a glandular body situate on each side above the upper jaw, behind and below the eyes, with a considerable cavity, which opens into a tang excretory tube, lying along the outer surface of the upper jaw, and opening in the tubular tooth, represented at fig. 17 and 18; and which is movable in an articulation, and may be erected, as in fig. 18, or depressed, as in 16, at the will of the animal. The poisonous serpents are therefore distinguished from the innocuous by the presence of the erectile movable tubular fangs. Fig. 15 is the head of the innocuous, and 16 of the poisonous serpent.

PART III.—REPRODUCTIVE ORGANS.

Under this head we mention only the nipple-bag (marsupium mammillare), or secondary uterus of the Marsupial animals (Plate XXXa 7 II. fig. 7); the nipples (fig. 8); and the manner in which the foetal animal, in a very imperfect and embryal form, becomes attached by the mouth to the nipples (fig. 10). The Marsupium, therefore, ought to be regarded, not as a mere pouch in which the young may take refuge after they are grown, but as a subsidiary uterus, combining the character of the Mammoe of the other orders. «

The Mammalia are peculiar in possessing a uterus. In the other classes this organ is withdrawn, and the ovary (fig. 11) and oviduct alone are left. In the ovo-viviparous animals, as the ovo-viviparous shark, the oviduct (fig. 12) resembles that of the common fowl. In the lower classes the ova are hatched out of the body entirely.

In the space assigned to this article, it was impossible to treat fully of a subject so extensive as the structure of the animal world; and while the author has arranged its divisions in such a manner as to show in what order it may be most easily and advantageously studied, he has introduced only those topics which are most indispensable, and most require illustration. For more complete details, therefore, he refers the reader to the following works.

1. Leçons d’Anatomie Comparée de G. Cuvier, Membre de l’lnstitut National, &c.; recueillies et publiées sous ses yeux par C. Duméril, chef des Travaux Anatomiques, &c. Cinq tomes. Paris, tome i. 1799;—tome v. 1805. 2. Blumenbach’s Manual of Comparative Anatomy ; with additional Notes by William Lawrence, Esq. F. R. Š. Second edition, revised and augmented by William Coulson. Lond. 1827, 8vo. The notes are derived chiefly from the work of Cuvier and the papers of Sir E. Home in the Philosophical Transactions. 3. Gore’s Translation of Corus s Introduction to the Comparative Anatomy of Animals, Lond. 1827, 2 vols. 8vo. The arrangement of this work, in which the author examines the forms of organs as they ascend, from the lowest to the highest classes, diminishes its general interest. 4. Lectures on Comparative Anatomy, in which are explained the Preparations in the Hunterian Museum. By Sir Everard Home, Bart. Lond. 1823, 6 vols. 4to. This work consists of the papers read by the author at the Royal Society, and published in their Transactions. Though entitled, therefore, Lectures on Comparative Anatomy, it embraces a much more extensive field, and contains a great number of physiological and pathological papers. This renders it at once rather desultory and prolix. It contains, nevertheless, a-great number of facts illustrative of peculiarities of structure in the animal world; and it is particularly valuable by the number of engravings with which it is embellished. It can scarcely be said to possess any arrangement whatever. 5. Recherches sur les Ossemens Fossiles, où l’on rétablit les characteres de plusieurs animaux dont les Révolutions du Globe ont détruit les espèces. Par Μ. le Bar. G. Cuvier, &c. Nouvelle édition. Tome i. 1822, Osteology of the Elephant, Hippopotamus; tome ii. partie i. 1822, Osteology of the Rhinoceros, Horse, Hog, Daman, and Tapir; tome iv. 1823, Osteology of the Deer and Ox, the Bear, Hyena, Lion, Glutton, Wolf, and Dog; tome v. partie i. 1823, Osteology of the Reptiles, the Ichthyosaurus and the Plesiosaurus; partie ii. 1823, Rodentia, Edentata, Monotrema, Amphibia, and Cetacea. Paris, 1824. These papers contain much accurate osteological description.

(v.)