MAN'S NEAR RELATIVES {MAMMALS). 229 
Growth from the Epidermis. Hair, claws, hoofs, 
and horns are all made of the same substance as our 
own finger-nails. All are modifications of the epider¬ 
mis or outer skin. In its growth a hair dips down into 
the true skin, forming a papilla which is sunken into 
the dermis or true skin. This papilla is provided at 
its base with glands for oiling the hair, muscles for 
erecting, blood-vessels for nourishing, and nerves for 
Fig. 192.— Growth of Hair. A , hair-rudiment; B, hair-rudiment with 
young hair formed, but not yet risen through the cuticle; C, hair 
protruded. 
warning. When the hair is long and twisted we call 
it wool, when smooth, fine, and soft we call it fur. 
On the pig the coarse, straight hairs are called bristles. 
The quills of a porcupine are stout hairs with sharp 
points, very useful to the animal in defending itself from 
enemies. Hairs are colored by pigment-cells found in 
each hair. Commonly among wild animals the color 
of the hair serves to conceal the wearer from enemies; 
