

SKIN AND ITS APPETOAGES. 151 



are required to those of the skin ; the use of dilute 

 solution of potassa is required to separate the cells 

 of the horny lamina. 



SECT. III. HAIR, The hairs, like the nails, are Hair, 

 composed of epithelium. A hair is a delicate cylin- 

 der, generally more or less flattened, variable in its 

 dimensions, and consisting of two distinct portions: 

 the shaft, which projects beyond the surface of the 

 skin, and the root which'is imbedded in a sheath,* or 

 follicle, furnished by the skin. This latter terminates 

 by a bulbous enlargement, at the extremity of which 

 is a deep excavation, which is occupied by one of the 

 papillae of the skin (germ, pulp, papilla of the hair, 

 PL XXIV. fig. IV. 3, 7). 



The surface of the hair is formed by a single layer structure. 

 of epithelium, called the epidermis of the hair (PI. 

 XXIV. fig. VII. 1) ; immediately beneath this is 

 found a material arranged in longitudinal striae which 

 constitutes almost the entire bulk of the hair, and 

 which is known as its cortical substance (fig. VII. 2) ; 

 finally, in the centre of the shaft there is generally, 

 but not always, a canal filled by cells of a peculiar 

 shape, which forms its medullary substance (fig. 

 VIL 3). 



The epidermis is composed of a single layer of scaly Epidermis, 

 cells, presenting an imbricated arrangement, so that 

 their superior margins are free (PL XXIV. fig. V.). 

 On treating this layer with acetic acid, or caustic 

 potash, its -cells swell out and become more trans- 

 parent, so that it can be seen that their contents 

 consist of fine granules, and that their nuclei have 

 disappeared (fig. VI.). The epidermis is found only 



