CETOLOGY.
Among the REPTILES, frogs and toads have no teeth, but the edges of their jaws are denticulated, like those of many birds. In lizards, however, there are numerous teeth, which have a peculiarity of structure for the pur pose of facilitating their change. The permanent teeth are inclosed within the temporary, as in a shell, and this shell slips off at the time of change.
The teeth of SERPENTS in general resemble those of the lizard tribe among REPTILES; but many of those animals, viz. the venomous serpents, are provided with two conical fangs, perforated in the middle with a tubu lar cavity, reaching through the whole length. By this structure they are enabled to infuse into the wound in flicted by their bite, the poisonous fluid contained in a bag at the root of each fang. See OPHIOLOGY.
A great variety takes place in the teeth of Fisuas. Their most common appearance is that of simple teeth, formed of a bony substance, covered by enamel, as in most of the mammalia, though in fishes the root is firmly united to the socket. In other cases, the teeth adhere only to the gum, or to a firm cartilaginous substance covering the jaw, as in the shark. These teeth appear to be formed, not as in the mammalia, by a deposition of of successive bony layers, but by the gradual ossification of a cartilaginous substance. Most fishes have teeth attached to the palate as well as the jaws.
Among the invertebral animals, there are very few instances of their possessing teeth. The crustacea and some others are remarkable in this respect, as they are provided with bony processes that serve the purpose of teeth, and are found between the membranes of the in testines and integuments of the body. Some of the worms have also teeth, as the ajzhrodit.e, the nereis, and espe cially the leech, in which last the mouth is furnished with three semicircular projecting bodies, having a sharp denticulated edge. The echini are furnished with teeth, which consist of five hard bodies, filling up the aperture in the shell through which the food enters, and set in motion by means of numerous muscles.
Several of the mammalia have attached to their cheeks a membranous cavity, serving as a pouch or reservoir for keeping the food which they do not immediately devour. These cheek pouches are found in several apes, in the hamster, (mus cricetus), and some other spe cies of rats.
The salivary glands, and those organs which in other animals supply their place, will be noticed under the comparative anatomy of the organs of secretion.
-Of the Organs of Deglutition.
Among the organs of deglutition in the inferior ani mals, we shall first describe the tongue, as in the second chapter of this part we declined considering this organ, as chiefly belonging to the sense of tasting. A tongue
iS found in all MAMMALIA and CETACEA ; all BIRDS, REPTILES, SERPENTS, and FISHES, but is scarcely found in any of the invertehral animals.
The tongue of MAMMALIA differs in some respects from that of man, and in some species its form and situ ation are peculiar. Most herbivorous quadrupeds have the tongue covered with a firm and thick cuticle, beset with numerous pointed papilla directed backwards. In many of the carnivorous mammalia, especially those of the cat tribe, these papill2e are exchanged for sharp and strong prickles, also directed backwards. In the cdentata, the tongue is cylindrical, extremely long, and capable of being thrust out to considerable distance ; its surface is moistened with a very glutinous mucus, which enables the animals the better to secure their prey.
Among the cetacea some species, as the porpoise and grampus, have the tongue of a firm texture ; while in others, as the spermaceti whale, its texture is loose and spongy, so that their tongue is not unaptly compared to a feather-bed.
The only BIRD in which the presence of the tongue has been denied, is the pelican, which has merely the rudiment of that organ. In a few of these animals, as the parrots, and some predacious and swimming birds, the tongue is soft, muscular, covered with papilla, and moistened with a mucous fluid ; but in most cases this organ in birds is stiff, dry, and horny. There are some peculiarities in the tongues of particular species, as in the toucan, where it is extremely long and narrow; the wood-peckers, which have it attached to a very com plex os hyoides, furnished with elastic cartilages, which enable these birds to dart out their tongue with great force into the clefts of trees ; and in the cock of the woods, whose tongue generally lies deep in the gullet, and is occasionally thrust forward.
There are several peculiarities in the tongue of REP TILES and SERPENTS. In many of the former, especially the frogs, and in all the latter, the tongue is situated within the mouth, in such a manner, that its free ex tremity is turned towards the gullet. In some of the lacertx, especially the crocodile, the tongue is extremely small, and possesses very little motion ; but in one spe cies, the cameleon, it is long, fleshy, enlarged at the tip, and extremely moveable. In serpents it is usually round and slender, with its point forked, and its root resting in a kind of fleshy sheath.
There is little peculiar in the tongue of FISHES. It is in general very small, and has no papillx but in several instances it is covered with teeth.