The variable characters which form essential differences among the mammalia are taken from the organs of touch, on which depends their degree of ability or address, and from the organs of manducation, which determine the nature of their ailment, and are all closely connected, not only with everything relative to the function of digestion, but also with a multitude of other differences relating to their intelligence. The degree of perfection of the organs of touch is estimated by the number and the pliability of the fingers, and from the greater or less extent to which their extremities are enveloped by the nail or the hoof. A hoof which completely envelops the end of the toe blunts its sensibility, and renders the foot incapable of seizing. The opposite extreme is when a nail, formed of one single lamina, covers only one of the faces of the extremity of the finger, leaving the other possessed of all its delicacy. The nature of the food is known by the grinders, to the form of which the articulation of the jaws universally corresponds. To cut flesh, grinders are required as trenchant as a saw and jaws fitted like scissors, having no other motion than a vertical one. For bruising roots or grains flat-crowned grinders are necessary, and jaws that have a lateral motion; in order that inequalities may always exist on the crown of these teeth, it is also requisite that their substance be composed of parts of unequal hardness, so that one may wear away faster than others. Hoofed animals are necessarily herbivorous, and have flat-crowned grinders, inasmuch as their feet preclude the possibility of their seizing a living prey. Animals with unguiculated fingers were susceptible of more variety; their food is of all kinds, and independently of the form of their grinders, they differ greatly from each other in the pliability and delicacy of their fingers. There is one character with respect to this which has immense influence on their dexterity and greatly multiplies its powers; it is the faculty of opposing the thumb to the finger for the purpose of seizing minute objects, constituting what is properly called a hand, a faculty which is carried to its highest perfection in man, in whom the whole anterior extremity is free and capable of prehension. These various combinations which strictly determine the nature of the different mammalia have given rise to the following orders: Among the unguiculated animals, the first is Man, who, in addition to privileges of other descriptions, possesses hands at the anterior extremities only, the posterior being designed to support him in an erect position. In the order next to man, that of the Quadrumana, we find hands at the four extremities. In another order, that of the Carnivora, the thumb is not free, and can not be opposed to the anterior extremities. Each of these orders has the three sorts of teeth, grinders, canini, and incisors, or cutting teeth.