392 ZOOLOGY. 
VERTEBRATA. 
Crass IV. Mammaria (Mammats). 
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 animal creation. att 
The mammals are vertebrates 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 mamme 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 with 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 
harder in those parts than where it is covered with hairs. These bald 
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