CH. XXXVIIL] 



THE NAILS AND HAIES 



577 



The Nails are thickenings of the stratum lucid um. Each lies in 

 a depression called the led of the nail, the posterior part of which is 

 overlapped by epidermis, and called the nail-groove. The dermis 

 beneath is beset with longitudinal ridges instead of papillae; these 

 are very vascular ; but in the lunula, the crescent at the base of the 

 nail, there are papillae, and this part is not so vascular. 



The Hairs are epidermal growths, contained in pits called hair 

 follicles. The part within the* follicle is called the root of the hair. 



The main substance of the hair is composed of pigmented horny 

 fibrous material, in reality long fibrillated cells, It is covered by a 



FIG. 440. Transverse section of a hair and hair follicle made below the opening of the sebaceous gland, 

 a, medulla, or pith of the hair ; b, fibrous layer ; c, cuticle ; d, Huxley's layer ; e, Henle's layer of 

 internal root-sheath ; /and g, layers of external root-sheath, outside of g is the basement membrane 

 or hyaline layer ; h, dermic (fibrous) coat of hair follicle ; i, vessels. (Cadiat.) 



layer of scales imbricated upwards (hair cuticle). In many hairs the 

 centre is occupied by a medulla, formed of rounded cells containing 

 eleidin granules. Minute air-bubbles may be present in both medulla 

 and fibrous layer, and cause the hair to look white by reflected light. 

 The grey hair of old age, however, is produced by a loss of pigment. 



The root is enlarged at its extremity into a knob, into which pro- 

 jects a vascular papilla from the true skin. 



The hair follicle consists of two parts, one continuous with the 

 epidermis, called the root-sheath, the other continuous with the dermis, 

 called the dermic coat. The two are separated by a basement mem- 

 brane called the hyaline layer of the follicle. The root-sheath con- 



2 O 



