THE SKIN. 



135 



hair-bulb being now attached at its sides as well as below to the 

 epithelium of the follicle (fig. 158). The hair then ceases to grow, and 

 eventually becomes lost, but its place may be again supplied by a new 

 hair, which becomes formed in a downgrowth from either the bottom or 

 the side of the hair-follicle, a new papilla first becoming formed at the 



FIG. 159. REPLACEMENT OF OLD HAIR BY A NEWLY-DEVELOPING ONE IN 

 THE HUMAN SCALP. (Ranvier.) 



p, papilla of the new hair ; i, its inner root-sheath ; e, its outer root-sheath ; 

 p', attached lower extremity of the old hair ; r, epithelial 



insertion of arrector pili, 



projection at 



extremity of the downgrowth (fig. 159). If not previously detached, 

 the old hair may be pushed from out the follicle by the one which 

 replaces it. 



The hairs are originally developed in the embryo in the form of 

 small solid downgrowths from the Malpighian layer of the epidermis 

 (fig. 160). The hair-rudiment, as it is called, is at first composed 

 entirely of soft, growing cells ; but presently those in the centre become 

 differentiated, so as to produce a minute hair invested by inner root- 

 sheath, and its base resting upon a papilla which has grown up into 

 the extremity of the hair-rudiment from the corium (fig. 161 p). As 



