In order to classify an animal, and place him in his proper division, it is necessary first of all to make a careful examination of his physical structure, and examine his organs in turn and severally, with the utmost care; when, by a comparative study of his organs, and by comparing them with those of other animals, living upon other foods, we shall be enabled to classify man properly—at least, so far as the evidence afforded by comparative anatomy enables us to reach a decisive conclusion one way or the other. There are numerous other facts and arguments to be taken into consideration; but, as said before, the argument drawn from comparative anatomy is the most complete and convincing of all—since that alone practically settles the case for all other animals. Let us, therefore, consider the structure or anatomy of man, from this point of view; and see how far these arguments lead us, and to what class we should naturally assign man, from a study of these facts alone. I shall take up for discussion first of all the teeth. THE TEETH _The Herbivora._—Let us consider first the teeth of the herbivorous animal. The horse, the ox, and the sheep are typical of this class of animals—living, as they do, almost entirely upon grass and herbs. The character of their food is peculiar. It is bulky, coarse, and covered with sharp, cutting edges—ill suited for tender mouths and gums. It must be mashed and ground thoroughly between the teeth and in the mouth before it is fit to be swallowed; and teeth of a peculiar construction and mutual relation are necessary in order properly to perform this function. Just such teeth they possess. There are twenty-four molars, six on each side in each jaw; and in the lower jaw, in front, eight incisors, or cutting teeth, with none on the upper jaw. In place of any of these teeth on the upper jaw, there is simply a horny plate upon which the long incisors of the lower jaw impinge when the jaws are closed. This renders possible the tearing, grinding motions necessary for biting off and masticating the food upon which these animals live. Not only that. The actual _structure_ of their teeth is peculiarly suited to their food and its mastication. Unlike our teeth, they are not covered with enamel, but are composed of alternate layers of enamel and dentine—a soft, bony substance lying between the layers of enamel, and wearing away more rapidly than it does. The result is that there is soon formed a series of jagged edges, which form cutting, grinding surfaces, and are especially adapted for the food which these animals feed upon. No such formation is present in any other class of animals, since their food is different from that of the herbivora. It is a wise provision of nature, precisely adapted to the desired ends.