continually growing. ‘Thus provision is made to meet the loss by wearing down, which otherwise would very soon result from the use to which they are constantly applied: for the action of these teeth is not that of biting, as in the Apes, nor of tearing, as in the Cats, nor of cropping as in the Ruminants, but of gnawing, as the name Rodentia implies ; a patient scraping, filing, or nibbling away the surface of the substances which they attack, often the bark or wood of trees, or the shells of nuts, of almost a stony hardness. The hinge-joint of the lower-jaw is of such a character as to allow of no other horizontal motion than forwards and backwards; and hence the flat crowns of the molar teeth have their enamel ridges set transversely; so that the motion of the jaw brings their surfaces into more effectual contact for the purpose of grinding. In general the teeth are of a frugivorous character; but some have the molars set with blunt tubercles, or sharp points, and these are less restricted in their diet; the latter manifesting, indeed, more or less appetite for animal food. The canine teeth are always wanting.
“The structural organization of the Rodents,” observes Mr. Martin, ‘‘ as evidenced by the characters of the skull, the bird-like condition of the brain, and by other points, is at a low par, and the ratio of their intelligence is in a parallel degree. We may tame them, but we cannot educate them. They are all timid and feeble, and trust for self-protection to flight or concealment. The prey of ferocious beasts, and birds, and reptiles, their fertility, by a wise provision, counterbalances their annual diminution. Spread over the earth, from
