THE TEETH.
The jaws of the mammalia, with a very few exceptions, contain teeth. The pro per whales (balmna,) the pangolin (ma nis,) and the American ant-eaters, are the only genera entirely destitute of these organs.
Animals of the genus balmna (the pro per whales) have, instead of teeth, the peculiar substance called whalebone,' co vering the palatine surface of the upper jaw : this resembles in its composition hair, born, and such matters.
The lower surface of the upper jaw forms two inclined planes, which may be compared to the roof of a house reversed ; but the two surfaces are concave. Both these are covered with plates of the whalebone, placed across the jaws, and descending vertically into the mouth. They are parallel to each other, and exist to the number of two or three hundred on each of the surfaces. They are connect ed to the bone by the intervention of a white ligamentous substance, from which they grow ; but their opposite edge, which is turned towards the cavity of the mouth, has its texture loosened into a kind of fringe, composed of long and slender fibres of the horny substance, which therefore covers the whole surface of the jaw. This structure probably serves the animal in retaining and con fining the mollusca, which constitute its food.
The teeth of the ornithorhynchus para doxus and hystrix deviate very consider ably from those of other mammalia. In the former animal there is one on each side of the two jaws : it is oblong, flat tened on its surface, and consists of a horny substance adhering to the gum. There are likewise two horny processes on the back of the tongue : these point forwards,and are supposed by Mr. Home to prevent the fond from passing into the fauces before it has been sufficiently masticated. In the ornithorhynchus hys trix there are six transverse rows of point ed horny processes at the back of the palate, and about twenty similar horny teeth on the corresponding part of the tongue.
The teeth of the human subject seem to be designed for the single purpose of mastication, and hence an erroneous con clusion might be drawn, that they serve the same office in other animals. Many
exceptions must, however, be made to this general rule. Some mammalia, which have teeth for the office of mastication, have others, which can only be consider ed as weapons of offence and defence ; viz. the tusks of the elephant, hippopo tamus, walrus, and manati. The large and long canine teeth of the carnivora, as the lion, tiger, dog, cat, &c. not only serve as natural weapons to the animal, but en able it to seize and hold its prey, and assist in the rude laceration which the food undergoes previous to deglutition. The seal, the porpoise, and other cetacea, as the cachalot, have all the teeth of one and the same form, and that obviously not calculated for mastication. They can only assist in securing the prey which forms the animal's food.
As the number and arrangement of the teeth was made by Linnzeus the basis of his classification of animals, it may be worth while to mention, that this anato mist gives the name of primores to the front, or incisor teeth ; and of laniarii to the canine or cuspidati. The term of tusks is applied to such teeth as extend out of the cavity of the mouth.
Certain classes of the teeth are entirely wanting in some orders, classes, and ge nera of quadrupeds ; and in other in stances, the different descriptions of teeth, particularly the canine and molares, are separated by considerable intervals. There is no animal in which these parts are of such equal height and such uniform ar rangement as in man.
All the three kinds of teeth are found in the quadrumana, the carnivora, the pachydermata (excepting the two-horned rhinoceros and elephant,) the horse, and those ruminating animals which have no horns.
Cuvier states, that the teeth of an animal, whose bones are found in a fos sil state, resemble those of man, in be ing arranged in a continued and unbroken series.