THE SKIN AND SKELETON 



345 



Hairs, the characteristic clothing of mammals, are 

 elongated horny cones, composed of "pith" and "crust." 

 The latter is an outer layer of 

 minute overlapping scales, which 

 are directed toward the point, so 

 that rubbing a human hair or fiber 

 of wool between the thumb and 

 finger pushes the root end away. 

 The root is bulbous, and is con- 

 tained in a minute depression, or 

 sac, formed by an infolding of the 



FIG. 301. Section of the Root and part 

 of the Shaft of a Human Hair, highly 

 magnified : it is covered with epidermic 

 scales, b, the inner layer, c, forming the 

 outer covering of the shaft, e, being im- 

 bricated; the root consists of angular 

 cells loaded with pigment ; d, bulb. 



FIG. 302. Parts of a Feather: 

 a, quill, or barrel; b, shaft; c, 

 vane, or beard; d, accessory 

 plume, or down ; e, f, lower 

 and upper umbilicus, or orifice, 

 leading to the interior of the 

 quill. 



skin. Hairs are usually set obliquely into the skin. 

 Porcupine's quills and hedgehog's spines make an easy 

 transition to feathers, which differ from hairs only in 

 splitting up into numerous laminae. They are the most 



