form like that of the two-edged point of a sabre, cutting equally on each side. As the tooth advanced in growth, it became curved backwards, in the form of a pruning knife, (Pl. 23, Figs. 1. 2. 3.) and the edge of serrated enamel was continued downwards to the base, of the inner and cutting side of the tooth, (Fig. 1, B. D.) whilst, on the outer side, a similar edge descended, but to a short distance from the point (Fig. 1, B. to C.) and the convex portion of the tooth (A.) became blunt and thick, as the back of a knife is made thick, for the purpose of producing strength. The strength of the tooth was further increased by the expansion of its sides, (as represented in the transverse section, Fig. 4, A. D.) Had the serrature continued along the whole of the blunt and convex portion of the tooth, it would, in this position, have possessed no useful cutting power; it ceased precisely at the point, (C.) beyond which it could no longer be effective. In a tooth thus formed for cutting along its concave edge, each movement of the jaw combined the power of the knife and saw; whilst the apex, in making the first incision, acted likes the two-edged point of a sabre. The backward curvature of the full-grown teeth, enabled them to retain, like barbs, the prey which they had penetrated. In these adaptations, we see contrivances, which human ingenuity has also adopted, in the preparation of various instruments of art.
In a former chapter (Ch. XIII.) I endeavoured to show that the establishment of carnivorous races throughout the animal kingdom tends materially to diminish the aggregate amount of animal suffering. The provision of teeth and jaws, adapted to effect they work of death most speedily, is highly subsidiary to the accomplishment of this desirable end. We act ourselves on this conviction, under the impulse of pure humanity, when we provide the most efficient instruments to produce the instantaneous, and most easy death, of the innumerable animals that are daily slaughtered for the supply of human food.
