564 



THE SKIN. 



The hair, therefore, is a solid elongation of the hollow inner root- 

 sheath, and produced by the inner root-sheath alone. The outer 

 root-sheath has nothing to do with the formation of the hair. 

 At the bottom of the pouch there is a knob composed of living 

 epithelia, resembling those of the inner root-sheath in the same 

 situation. This knob is called the bulb of the root of the hair, and 

 directly surmounts the papilla of the hair. Higher up the epi- 

 thelia again become horny, and enter into the construction of 

 the root and the shaft of the hair. 



Imagine, lastly, that, on the side of the acute angle of the 

 obliquely implanted pouch, the outer root-sheath, which is, as 



FIG. 234. DIAGRAM OF THE IMPLANTATION OF THE HAIR. 



E, epidermis; RM, rete mucosum ; PL, papillary layer ; IS, inner root-sheath; OS, outer 

 root-sheath ; F, follicle ; D, derma ; M, arrector pili muscle ; P, papilla of the hair ; B, bulb ; 

 C, cuticle ; R, root ; 8, shaft ol the hair ; SG, sebaceous gland. 



said before, an offshoot of the rete mucosum, be pushed laterally 

 and downward by a pin, the result will be a third elongation, 

 produced by the outer root-sheath, a small pouch itself, bearing 

 the name sebaceous gland. According to this diagram, the seba- 

 ceous gland is an exclusive formation of the outer root-sheath, while 

 the inner root-sheath takes no part in the formation of the gland. 

 (See Fig. 234.) 



