OCR Text |
Show 42 MAMMALIA. . d . .t me and being a character peculiar to this class erives I s na ' . l ( it, they dt.s tm. gm.s h 1't b e tter than any other that IS externa. 1) Division of the Mammalia into Orders. The variable characters which form essential differences among t h e M ammar I a are taken from the organs of toudc hf, on which depends their degree of ability or ~ddress, an rom the organs of rna nducation ' which determme the nature . of t l1 e·i r al 't men t , and are all closely connecte.d , not only W.i th th. g relative to the function of digestion, but also With every m . h · · ll' a multitude of other differences relatmg even to t eir mte I· gence. h · · The degree of perfection of the organs of touc 1s estt-rna t ed by the number and the pliability of. the finge. r.s , and from the greater or less extent to which their extremities are enveloped by the nail or the hoof. A hoof which completely envelopes 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 del~cacy. The nature of the food is known by the grmders, to the form of which the articulation of the jaws universally corres-ponds. To cut flesh, grinders are required as trenchant as a saw, an~ jaws fitted like scissars, having no other motion than a verb· cal one. For bruising roots or grains, fiat-crowned grinders are ne· cessary, and jaws that have a lateral motion; in order th~t inequalities may always exist on the crown of these teeth, rt is also requisite that their substance be composed of parts of unequal hardness, so that some may wear away faster than others. Hoofed animals are all necessarily herbivorous, and have (1) We shall find, however, in the sequel some doubts on this subject, arising from certain points in the family of the Monotremata . MAMMA~IA. 43 fiat-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 CARNARIA, the thumb is not free, and cannot be opposed to the anterior extremities. Each of these orders has the three sorts of teeth, grinders, canini, and incisors or cutting teeth. In a fourth order, that of the RODENTIA, the toes differ but little from those of the Caruaria, but there are no canine teeth, and the incisors are placed in front of the mouth, and adapted to a very peculiar sort of manducation. Then come those animals whose toes are much cramped, and deeply sunk in large nails, which are generally curved; they have no incisors, and in some the canines disappear, while others have none of any description. We comprise them all under the title of the EDENT AT A. This distribution of the unguiculated animals would be perfect, and form a very regular series, were it not that New Bolland has lately furnished us with a little collateral one, |