204 



NORMAL HISTOLOGY. 



injury sufficiently great to overcome the usual protective powers of 

 the epidermis. Thus we see that when the automatic action of the 

 skin is inadequate for the performance of its functions it calls forth 



FIG. 181. 



Hair-rudiment from an embryo of six weeks. (Kolliker.) a, horny layer of epidermis ; 6, 

 Malpighian layer, rete mucosum ; i, limiting membrane ; m, m, cells extending from the 

 rete mucosum to fill the future hair-follicles. The elongated cells near the base of the 

 sac are those from which hair is developed. The secreting glands of the body arise from 

 some epithelial layer in a similar manner. 



an auxiliary activity of other organs, through the medium of the 

 nervous system. 



The hair-follicles are developed from the rete mucosum of the epi- 

 dermis, and first appear as little masses of cells growing into the 



FIG. 182. 



ms83&SS$$wm d 



Section of developing tooth. From embryo of sheep. (Bohm and Davidoff.) a, epi- 

 thelium of the gum ; b, its deepest layer ; c, superficial cells of the enamel-pulp ; d, 

 enamel-pulp formed of modified epithelial cells ; s, cells of the enamel-pulp destined to 

 produce the enamel (" adamantoblasts ") ; p, dental papilla. 



underlying connective tissues (Fig. 181). The sebaceous glands 

 arise as oifshoots from these cellular masses. 



