9. _The horse possesses forty teeth_, viz., twelve incisors, four tushes, and twenty-four molars. The _incisors_, sometimes called _nippers_, are those which, situated in front of the mouth, are seen when the lips are parted. They are the instruments, by means of which the animal bites its food, and are placed six in the upper, and six in the lower jaw. They are classed as pairs, being generally cut or developed after that fashion. The middle two, in both jaws, are called the _centre_ incisors; the two most backward, on either side of the mouth, the _corner_ incisors; and the teeth, by which the corners and centres are separated, the _lateral_ incisors. Of the _tushes_, the two placed in the lower jaw are the most forward. These teeth, which are sometimes termed canines, and sometimes cuspidati, (from _cuspis_, a point,) are isolated, appearing in the space which divides the incisors from the molars. They are only fully developed in the male, the mare often being without any indication of them, and never displaying them in so prominent a degree as the horse. Their use is not very apparent, but they certainly would be employed in those combats to which stallions seem naturally predisposed, and would render the grasp, and the wound it could inflict, more severe. Because the mare is of a more pacific temperament, Nature seems to have denied to her a perfect tush, by the presence or absence of which, the sex is indicated by the mouth, and upon which castration appears to exercise no influence, since the gelding has as well-formed a tush as the perfect male. The _molars_ are ranged in companies of six, one company on either side of the upper, and a like number similarly situated in the lower jaw. The molars are the instruments which enable the horse to grind down the fibrous and hard food upon which it subsists, and they are distinguished by their locality, as first, second, third, fourth, fifth, or sixth molar tooth of the near or off side in the upper or lower jaw; the first being that growing in front, or nearest to the incisors, and the sixth that placed most backward in the cavity of the mouth. 10. _Three substances enter into the composition of the horse's tooth._ Each of these substances is distinct, and can be distinguished from either of the others. The names given to the various parts are--1, crusta petrosa, or hard crust; 2, enamel; and 3, ivory.