Teeth are arranged in three different ways, serrated, in one continuous row, or else protruding from the mouth. When serrated they unite together, just like those of a comb, in order that they may not be worn by rubbing against one another, as in serpents, fishes, and dogs,[218] for instance. In some creatures they are set in one continuous row, man and the horse, for instance; while in the wild boar, the elephant, and the hippopotamus, they protrude from the mouth.[219] Among those set in one continuous row, the teeth which divide the food are broad and sharp, while those which grind it are double; the teeth which lie between the incisive and the molar teeth, are those known as the canine or dog-teeth; these are by far the largest in those animals which have serrated teeth. Those animals which have continuous rows of teeth, have them either situate on both sides of the mouth, as in the horse, or else have no fore-teeth in the upper part of the mouth, as is the case with oxen, sheep, and all the animals that ruminate. The she-goat has no upper teeth, except the two front ones. No animals which have serrated teeth, have them protruding[220] from the mouth; among these, too, the females rarely have them; and to those that do have them, they are of no[221] use: hence it is, that while the boar strikes, the sow bites. No animal with horns has projecting teeth; and all such teeth are hollow, while in other animals the teeth are solid. All[222] fish have the teeth serrated, with the exception of the scarus,[223] this being the only one among the aquatic animals that has them level[224] at the edges. In addition to this, there are many fishes that have teeth upon the tongue and over the whole of the mouth, in order that, by the multitude of the bites which they inflict, they may soften those articles of food which they could not possibly manage by tearing. Many animals, also, have teeth in the palate, and even in the tail;[225] in addition to which, some have them inclining to the interior of the mouth, that the food may not fall out, the animal itself having no other means of retaining it there. CHAP. 62.—THE TEETH OF SERPENTS; THEIR POISON. A BIRD WHICH HAS TEETH.