480 THE TISSUES. 



especially those clustered round the nuclei of the cells. In the 

 white races, the granules are also darker in certain parts of the 

 body, and the cells become pigment- cells, therefore, as already de- 

 scribed; as in the areola and the nipple (especially during preg- 

 nancy and after bearing children), in the linea alba, and the face 

 during pregnancy, &c. (p. 136). In the negro, even the horny layer 

 (cuticle) is also inclined to yellow or brownish ; while in the white 

 races it is entirely colorless, except in the parts and circumstances 

 just mentioned. It consists usually of many layers of horny plates, 

 the lowermost of which suddenly merge into the subjacent upper- 

 most cells of the rete Malpighii. That these plates are still flat- 

 tened cells, and contain a very minute quantity of viscid fluid, is 

 proved by the addition of acetic acid and potassa, which cause 

 them to swell up and assume the form of vesicles, sometimes, though 

 seldom, containing a rudimentary nucleus. In the lower and mid- 

 dle parts of the cuticle, these plates are pretty regularly polygonal 

 (4, 5, or 6 sided) ; in the upper layers they present more irregular 

 outlines, and often appear wrinkled and folded. They vary from 

 TS'UU to 750" f an i nc h m diameter. Upon the glans penis and the 

 outer side of the labia minora, the largest are 7 J to s 7 of an inch, 

 and on the labia majora T,^ to T Jo of an inch in diameter. All 

 these larger cells are distinctly nucleated. 



These plates being applied to each other horizontally, give the 

 cuticle a distinct lamination. The most superficial laminae are 

 parallel to the general surface of the corium, while the deepest take 

 a direction parallel to the surface of the papillae. Thus depressions 

 corresponding to the papillae in form appear on the inner surface of 

 the cuticle (Figs. 321 and 328), and into which the papillae, covered 

 by the stratum Malpighii, projected. 



The thickness of the entire epithelium of the skin varies in differ- 

 ent parts; viz., it is 9 ^ to 5 o of an mcn on tne CD i n ? cheeks, and 

 brow, on the eyelids, and in the external auditory passage; ^Q to 

 g^ of an inch on the bridge of the nose, the breast and nipple of 

 a female, the back of the toes and the fingers, on the neck and back, 

 on the inner and outer side of the thigh, the scrotum, and the labia 

 minora. 



It is 3-^ to T | 3 of an inch on the edge of the eyelids, the male 

 chest and nipple, the hairy scalp, the chin, penis, prepuce, and glans 

 penis; y^ to T |o of an inch on the red external portion of the lips, 



