236 



THE NAILS AND HAIE. 



Fig. 103. 



The nails. 



The NAILS constitute one of the appendages 



of the epiderma. They are horny 



coverings protecting the extremities 

 of the fingers and the toes. They originate 

 in a fold of the cutis, and become free at their 

 outer extremity. The nail grows from its 

 roots, increasing in length, and simultaneously 

 in thickness. Its rate of growth depends upon 

 the general rate of nutrition. During periods 

 of sickness or abstinence, its growth in both 

 directions is retarded, as is indicated by a mark 

 or impression on its surface, and so the nail 

 becomes a register of the condition of nutrition 

 during the period of its own existence. The 



thumb nail is Said tO OCCUpy about 20 Weeks Skin of palm, magnified 20 diameters. 



in its growth from the root to the extremity ; that of the great toe about 

 two years an estimate which is probably too long. 



THE HAIE. Each hair originates in a flask-shaped follicle, formed by 

 a depression of the cutis, and lined by a continuation of the cu- 

 ticle, and, like it, presenting scales on its superficies and round 

 cells beneath. The bottom of the follicle is the place of origin. The 

 hair consists of two portions, the outer or cortical, and the inner or me- 

 dullary, the proportions of which differ very much in different cases. 

 The surface of the hair presents a layer of imbricated scales, within which, 

 at the lower part, are minute cells, but farther from the root the cells be- 

 come larger and begin to contain pigment, the coloring matter being dis- 

 tributed unequally, sometimes producing a tubular appearance in the axis. 

 The hair grows by constant prolongation from 

 the follicle, its color being due to a peculiar col- 

 ored oil ; and in the black varieties, iron predom- 

 inates. The diameter of the hairs varies from 

 rh> to TsVo of an inch. 



In Fig. 104, the structure of the root of a hair 

 and part of its shaft is displayed. Bulb of a 

 small black hair from the scrotum, seen in sec- 

 tion : # , basement membrane of the follicle ; &, 

 layer of epidermic cells resting upon it, and be- 

 coming more scaly as they approach c, a layer of 

 imbricated cells forming the outer lamina or cor- 

 tex of the hair : they are more flattened and com- 

 pressed the higher they are traced on the bulb. 

 Within the cortex is the proper substance of the 

 Human hair in section. hair, consisting, at the base, where it rests on 



Fig. 104. 



