478 THE HUMAN BODY 



tex; while, in hairs with a medulla, the middle cells retain pretty 

 much their original form and size. Pulled apart by the elongating 

 cortical cells, these central ones then form the medulla with its air- 

 cavities. The innermost layer of the epidermis lining the follicle, 



has its cells projecting, with over- 

 lapping edges turned downwards. 

 Accordingly these interlock with 

 the upward directed edges of the 

 cells of the hair-cuticle; conse- 

 quently when a hair is pulled out 

 the epidermic lining of the follicle 

 is usually brought with it. So long 

 as the dermic papilla is left intact 

 O a new hair will be formed, but not 



FIG. 143. Parts of two hairs em- ,, . 01 , , ,, f 



bedded in their follicles, a, the skin, otherwise, blender bundles ot un- 



which is seen to dip down and line afrinprl miT?plp '^ T?i0- 14^O nin frrvm 

 the follicle; 6, the subcutaneous tis- l6 ( C '^ 1 S- 1*>J ^ 



sue; c, the muscles of the hair-follicle, the dermis to the side of the hair- 



which by their contraction can erect ,,. , _. , 



the hair; o, sebaceous gland. follicles. The latter are in most re- 



gions obliquely implanted in the skin so that the hairs lie down on 

 the surface of the Body, and the muscles are so fixed that when 

 they shorten, they erect the hair and cause it to bristle, as may be 

 seen in an angry cat, or sometimes in a greatly terrified man. 

 Opening into each hair-follicle are usually a couple of sebaceous or 

 oil-glands. Hairs are found all over the skin except on the palms of 

 the hands and the soles of the feet ; the back of the last phalanx of 

 the fingers and toes, the upper eyelids, and one or two other regions. 



Nails. Each nail is a part of the epidermis, with its horny 

 stratum greatly developed. The back part of the nail fits behind 

 into a furrow of the dermis and is called its root. The visible part 

 consists of a body, fixed to the dermis beneath (which forms the bed 

 of the nail), and of a, free edge. Near the root is a little area whiter 

 than the rest of the nail and called the lunula. The whiteness is 

 due in part to the nail being really more opaque there and partly to 

 the fact that its bed, which seen through the nail causes its pink 

 color, is in this region less vascular. 



The portion of the corium on which the nail is formed is called its 

 matrix. Posteriorly this forms a furrow lodging the root, and it is 

 by new cells added on there that the nail grows in length.' The part 

 of the matrix lying beneath the body of the nail, and called its bed, 



