HAIR 



reduced to as few as two bristles on the lips. The term "hair," 

 however, is apt to be somewhat loosely applied ; it has heen 

 miifle use of to desfrihe, for example, the slender ])rocesses of the 



SM 



Fig. 1. — A, Section of human skin. Co, 

 Dermis ; T), sebaceous glands ; /■', fat 

 in dermis : G, vessels in dermis ; GP, 

 vascular papillae ; //, hair ; iV, nerves 

 in dermis ; NP, nervous papillae ; Sc, 

 horny layer of epidermis ; SD, sweat 

 ^land; .S/)!, duct of sweat gland : SM, 

 Malpighian layer. B, Longitudinal sec- 

 tion through a hair (diagi-amniatie). Ap, 

 Band of muscular filires inserted into tliu 

 hair-follicle ; Co, corium (dermis) ; F, 

 e.icternal longitudinal ; 7''', internal cir- 

 cular, fibrous layer of follicle ; Ft, fatty 

 tissue in the dermis ; GH, hyaline 

 membrane between the root-sheath and 

 the follicle ; HBl), sebaceous gland ; 

 HP, hair-papilla with vessels in its in- 

 terior ; ^1/. medullary substance (pith) 

 of the hair ; 0, cuticle of root-sheath : 

 R. cortical layer ; Sc, horny layer of 

 e]iidermis ; Sch, Hair shaft ; SM, Mal- 

 pighian layer of epidermis ; \vs, ir.s'', 

 outer and inner layers of root-sheath. 

 A natomy. ) 



^^ 



B 



(From Wieiierslieim's Co'iivparative, 



cliitinous skin of the Crustacea. It will be necessary, therefore, 

 to enter into the microscopical structure and development of the 

 mammalian hair. Hair is found in every mammal. The first 

 appearance of a hair is a slight thickening of the stratum 

 Malpighii of the epidermis, the cells taking part iu this being 



