THE SKIN AND ITS APPENDAGES. 



267 



THE HAIR. 



The hairs, together with their homologues, feathers and scales of 

 the lower animals, are derived entirely from the epidermis, and 

 are therefore of ectodermic origin. These slender flexible horny 

 threads are distributed, with few exceptions, over the entire surface, 

 but differ greatly as to both size and frequency in various regions ; 

 individual and race peculiarities also greatly influence the character 

 of the hair. In general, in straight-haired races the hairs are 

 thicker and coarser and more cylindrical than in crisp-haired races ; 



Section of human scalp, showing hair-follicles and sebaceous glands : a, epi- 

 dermis ; 6, corium ; c , hair embraced within its hair-follicle ; d, fibrous sheath 

 of follicle ; e, glassy membrane ; f, outer root-sheath ; g, inner root-sheath ; h, 

 expanded terminal bulb of hair ; ', hair-papilla ; k, mouth of follicle from which 

 hair-shaft (/ ) projects ; m, adipose tissue ; n, blood vessel ; o, sebaceous glands ; 

 p, arrector pili muscle ; s , portions of sweat-gland. 



in the negro the hairs are flattened cylinders, small and oval in sec- 

 tion ; dark hair is usually coarser than that of light color. 



Every hair presents two principal divisions, the part which 

 projects beyond the surface, as the shaft, and the portion embedded 



