II HAIR 7. 
reduced to as few as two bristles on the lips. The term “ hair,” 
however, 1s apt to be somewhat loosely applied; it has been 
made use of to describe, for example, the slender processes of the 
Sch 
—~\ 
Fic. 1.—A, Section of human skin. Oo, 
Dermis ; D, sebaceous glands; /, fat 
in dermis ; G, vessels in dermis; GP, 
vascular papillae ; H, hair ; NV, nerves 
in dermis ; VP, nervous papillae ; Sc, 
horny layer of epidermis ; SD, sweat 
gland ; SD!, duct of sweat gland ; SJ/, 
Malpighian layer. B, Longitudinal sec- 
tion through a hair (diagrammatic). A), 
Band of muscular fibres inserted into the 
hair-follicle ; Co, corium (dermis) ; /, 
external longitudinal ; /, internal cir- 
cular, fibrous layer of follicle; /'%t, fatty 
tissue in the dermis; GH, hyaline 
membrane between the root-sheath and 
the follicle; HBD, sebaceous gland ; 
HP, hair-papilla with vessels in its in- 
terior ; J/, medullary substance (pith) 
of the hair; O, cuticle of root-sheath ; 
FR, cortical layer ; Sc, horny layer of 
epidermis ; Sch, Hair shaft ; SJ, Mal- 
pighian layer of epidermis ; WS, WS}, 
outer and inner layers of root-sheath. (From Wiedersheim’s Comparative 
Anatamy.) 
chitinous 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 in this being 
