HAIR-FOLLICLES. 



155 



A human hair is round or flat- 

 tened an.i made up of three parts, 

 a cuticle, a cortex, and a medulla. 



The cuticle is a thin outer cov- 

 ering composed of thin non- 

 nucleated horny plates or cells, 

 imbricated or overlapping ; their 

 edges form irregular transverse 

 markings on the surface of the 

 hair. 



The cortex,, making up the 

 bulk of hair, consists of slender, 

 elongated, fusiform, horny nu- 

 cleated cells, arranged longi- 

 tudinally and closely packed and 

 cemented together. 



The medulla is not always 

 continuous or present ; it con- 

 sists of nucleated polyhedral cells 

 loosely aggregated in the axis of 

 the hair; these cells often con- 

 tain air, giving them an opaque 

 appearance. 



Hairs often contain pigment, 

 deposited in the cortex ; to this 

 pigment and the air in the med- 

 ulla the color of hair is due. 



The hair-follicles (Fig. 64), 

 which support the hairs and pro- 

 vide for their growth, are sheaths 

 formed by downward projections 

 of the epidermis and corial tis- 

 sue. They lie perpendicular or 

 oblique to the surface, and into 

 their upper half the sebaceous 

 glands open. A small band of 

 involuntary muscle extends from 

 the lower part of the follicle to 

 the corium across the obtuse- 

 angled side, forming the erector 



FIG. 64. 



ep 



Longitudinal section of hair-follicle 

 (Biesiadecki). r. bulb of hair ; d, e, 

 sheaths derived from the corium ; 

 /, outer root-sheath ; <7, inner root- 

 sheath ; h, hair ; k, medulla of hair ; 

 n, erector pili muscle ; p, papilla of 

 hair : .*. rete mucosum ; ep, stratum 

 corneum ; t, sebaceous gland. 



