THE SKIX AND ITS APPF-XDACES 



401 



Development of the Skin, Xails, and Hair 



The epidermis is, as already noted, of ectodermic origin. It consists at first 

 of a single layer of cuboidal cells. This soon differentiates into two layers — 



a 



1 





^ 



'> 



a 



r^. 





Fig. 283. — Five stages in the development of a human hair. (Stohr.) a, Papilla; 

 b, arrector pili muscle; c, beginning of hair shaft; d, point where hair shaft grows through 

 epidermis; e, anlage of sebaceous gland; /, hair germ; g, hair shaft; h, Henle's layer; 

 i, Huxley's layer; k, cuticle of root sheath; /, inner root sheat; m, outer root sheath in 

 tangential section; 11, outer root sheath; 0, connective-tissue follicle. 

 26 



