392 ZOOLOGY. 



VERTEBRATA. 



Class IV. Mammalia (Mammals). 



The class of Mammalia, it is well known, stands at the head of the verte- 

 brated animals ; the decided superiority of its organization, the multiplicity 

 of its aptitudes, sensations, and motions, which other classes do not possess, 

 entitle us to consider it a step in the ascending scale of beings, and indeed 

 the last of the aninial creation. 



The mammals are vertebrj^tes whose body is covered with hairs, or 

 modified hairs, by opposition to the feathers of birds and scales of reptiles 

 and fishes ; possessing, like birds, warm and red blood ; a heart with two 

 ventricles and two auricles, and breathing by lungs. Mammals, instead of 

 laying eggs like other vertebrates, bring forth living young, which are 

 nourished by mamma? situated on the inferior surface of the female, some- 

 times on the breast and sometimes on the abdomen. 



The skin of the mammals is more or less thick, sometimes transformed 

 into a cuirass, as in the tatous, or else the upper part of the body is covered 

 by imbricated scales, as in the pangolins. Generally its exterior surface is 

 covered w»ith hairs, which sometimes appear under the form of spines, bristles, 

 or wool. The ordinary hairs are smooth, in most cases directed backwards. 

 When the hairs on the nape and neck are very long, they form a mane ; on 

 the lips and cheeks, or on the chin, they constitute a beard ; above, on the 

 top of the head, a tuft, or wig ; and on the extremity of the tail, a tuft 

 again. 



Sometimes, as in the horse, the tail is furnished with long depending 

 hairs hanging down from its very base ; at other times, long hairs hang 

 down from each side of the tail. In several mammals, as, for example, 

 squirrels, the long hairs on the head are directed towards both sides, right 

 and left. Some, again, as the lynx and squirrel, have a long bush of hairs 

 at the end of each ear. There are also mammals whose whole body is 

 covered with long hairs. The hairs are called wool when they are fine, 

 soft, and curled or crisped. In some, as the sheep, the body is only covered 

 with wool, but in many mammals the wool is found between the smooth 

 hairs, and covered by the latter, which extend beyond it. This is the 

 under-wool analogous to the down in birds. Bristles are the stiff, stout 

 hairs ; in the hog, for instance, the whole body is covered with them ; in 

 other animals they are limited to the angle of the mouth, or behind it, where 

 they are very long, and are then called moustaches or whiskers. When 

 the hairs are very thick, acute at the extremities, and horny, they are called 

 spines, as in the urchin or hedgehog, and porcupine. In some mammals 

 we find the posterior part of the body, or a part of the breast, the knees and 

 the sole of the feet, deprived of hair. Usually in such cases the skin is 

 hai'der in those parts than where it is covered with hairs. These bald 

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