20 ELEMENTS OF MAMMALIAN ANATOMY. 
variety of the cat. The Mombus cat of Africa has short 
stiff hair, while the Angora or Persian cat is remarkable for 
the length and delicacy of its soft fur. The hair, like the 
nails, is an extreme modification of the epidermis. Each 
hair grows from a papilla at the bottom of a small sac, the 
follicle, which 1s a depression in the corium. The central 
part of the hair is the pith, and the external portion, formed 
of thin overlapping scales, the cuticle. The coloring-matter 
lies in the superficial scales, and may be disposed in such an 
irregular manner that one-half of a hair is white, and the 
other half yellow. 
The large hairs on either side of the nose are known 
as vibrisse. Their roots are provided with delicate nerve- 
endings of touch, so that the animal may find its way with 
ease through dark narrow passages. There are a few long 
hairs above the eyes, forming the eyebrows, but no eye- 
lashes are present. 
Most of the hairs are inserted obliquely into the skin, 
but when angered the cat can erect them by the contraction 
of a small muscle passing from the skin to the hair-bulb. 
On some mammals the hairy covering is partial and 
limited to particular regions; in others, as the hippopotamus 
and the Sirenia, it is very scanty, but scattered over the 
whole surface; while in the Cetacea it is reduced to a few 
small bristles about the mouth. 
Some kinds of hair, as those of the mane and tail of the 
horse, are shed and renewed annually. Most mammals 
have a long hairy coat in winter which gives place in spring 
to a short coat. The Arctic fox, hare, ermine, and numer- 
ous other animals of the colder regions undergo a complete 
change of color in the two seasons, being white in winter 
and brown or gray in summer. By this protective colora- 
tion they escape many of their enemies. 
