THE SKIN AND ITS FUNCTIONS. 



341 



which is so moulded on the imbricated scaly cuticle of the hair, that 

 its inner surface becomes imbricated also, but of course in the opposite 

 direction. When a hair is pulled out, the inner layer of the root-sheath 

 and part of v the outer layer also are commonly pulled out with it. 



Nails. A nail, like a hair, is a peculiar arrangement of epidermal 

 cells, the undermost of which, like those of the general surface of the 

 integument, are rounded or elongated, while the superficial are flattened, 



FIG. 235. 



FIG. 



FIG. 235. Magnified view of the root of a hair, a, stem or shaft of hair cut across; 6, inner, and 



c, outer layer of the epidermal lining of the hair-follicle, called also the inner and outer root-sheath; 



d, dermal or external coat of the hair-follicle, shown in part; e, imbricated scales about to form a cor- 

 tical layer on the surface of the hair. The adjacent cuticle of the root-sheath is not represented, and 

 the papilla is hidden in the lower part of the knob where that is represented lighter. (Kohlraush.) 



FIG. 236. Trans'verse section of a hair and hair-follicle made below the opening of the sebaceous 

 gland, a, medulla or pith of the hair; 6, fibrous layer or cortex; c, cuticle; d, Huxley's layer, e, 

 Henle's layer of internal root-sheath; /and #, layers of external root-sheath, outside of g is a light 

 layer, or " glassy membrane." which is equivalent to the basement membrane; h. fibrous coat of hair 

 sac; i, vessels. (Cadiat.) 



and of more horny consistence. That specially modified portion of the 

 corium, or true skin, by which the nail is secreted, is called the matrix. 



The back edge of the nail, or the root as it is termed, is received into 

 a shallow crescentic groove in the matrix, white the front part is free and 

 projects beyond the extremity of the digit. T^e intermediate portion of 

 the nail rests by its broad under-surface on the front part of the matrix, 

 which is here called the led of the nail. This part of the matrix is not 

 uniformly smooth on the surface, but is raised in the form of longitudi- 

 nal and nearly parallel ridges or laminae, on which are moulded the epi- 

 dermal cells of which the nail is made up (Fig. 237). 



The growth of the nail, like that of the hair, or of the epidermis 



