The TEETH vary a good deal according to the kind of food on which the animal is destined to live; but in man and the higher orders of animals they may be divided into three distinct groups:--_1st_, The _incisor_ or _cutting_ teeth, being the eight broad and flat teeth with a sharp cutting edge seen in front of the upper and lower jaws, and marked I in the subjoined wood-cut, which represents one-half of the lower jaw, and consequently only one-fourth of the whole number of teeth. Thus we find only two incisors marked in the wood-cut, although there are eight of them in all, viz. two more are on the other side of the lower jaw, and four corresponding ones in the upper. _2d_, The _cuspidati_, _canine_, or _dog_ teeth, being the sharp-pointed roundish-bodied teeth, four in number, one, C, in contact with each of the outer incisor teeth, and called _canine_ from being large in the dog and carnivorous animals, and used by them for the purpose of _seizing_ and _tearing_ their food; and, _3d_, The _molares_ or _grinders_, B G, twenty in number situated at the back part of the jaw, and so called from their office being to grind or bruise the food subjected to their action.[13] The term _grinders_, however, is sometimes restricted to the three back teeth on each side, marked G, and seen to have double roots and a broad grinding surface; and the two, B, intervening between them and the _cuspidati_ are styled _bicuspidati_ or _double-speared_, from bearing a greater resemblance to a double-headed canine tooth than to the other grinders. The teeth are modified in different animals to suit their habits of life. In herbivorous animals, the canine teeth, for which they have no use, are comparatively undeveloped; whereas in carnivorous animals, which tear their prey in pieces, the canine teeth are large, powerful, and pointed, and the incisors comparatively small. In these animals they constitute what are properly called the _tusks_, and in some species they are of a truly formidable character. The molar or grinding teeth differ in like manner according to the nature of the food. In herbivorous and granivorous animals they are large and powerful, and to increase their efficiency the lower jaw admits of considerable lateral motion in a horizontal direction; whereas, in carnivorous animals, it admits of motion only upwards and downwards, as in opening and shutting the mouth. The lateral grinding motion is very evident in _ruminating_ animals, such as the cow, which, after having filled its stomach with provender, is generally seen to lie down and _ruminate_, or _chew the cud_ as it is called--the rumination consisting in bringing up small masses of herbage from the stomach, and submitting them to a thorough mastication or grinding between its molar teeth before being again swallowed and digested.