J'HYSIOI.CKiY FOR RKdIXXKRS 



FIG. 79. A hair in its fullicle. 

 a, Shaft of hair above the skin ; />, 

 the hair in its follicle ; c, newest 

 portion of the hair growing on 

 the papilla /; </, cuticle of hair ; 

 e, cavity of hair follicle ; f, 

 epidermis of follicle correspond- 

 ing to HI, the epidermis at the 

 surface ; g, division between 

 dermis and epidermis ; //, 

 dermis of follicle corresponding 

 t j dermis, /, near the surface ; 

 A, mouths of sebaceous glands ; 

 n, horny eprdermis at surface. 



of the skin, becoming massed to- 

 gether to form a stout horny 

 plate. Underneath the hind part of 

 the nail, at what is called the " bed 

 of the nail," is a very vascular 

 dermis, thrown up into ridges bear- 

 ing papilla? ; from this bed the 

 horny plate of the nail grows. The 

 cells of the deeper, softer layers of 

 the epidermis, just over the dermis 

 of the bed, multiply rapidly, and the 

 cells so formed are thrust forward 

 and become horny and compressed 

 together as new ones are formed 

 behind. 



Hairs. A hair is composed of 

 horny cells, and is formed from the 

 epidermis. It lies in a deep pit, 

 called the hair follicle, from the 

 bottom of which it springs. The 

 wall of the hair follicle which passes 

 deep into the skin, is formed of 

 dermis, lined throughout by epi- 

 dermis. This epidermis forms the 

 sheath of the root of the hair. At 

 the bottom of the pit the dermis rises 

 up into a vascular papilla, and it is 

 by the multiplication of the cells of 

 the epidermis immediately over the 

 papilla that the hair grows. As new 

 cells are formed the older ones, 

 which join together and become 

 corneous, are thrust outwards, and 

 so the shaft of the hair is formed. 

 The shaft of a fully-formed hair con- 

 sists of a pith or medulla, loose in 

 texture, enclosed by a cortex formed 

 of united, dry, horny cells, which is 

 covered by a cuticle consisting of 

 overlapping scales. 



