90 EPIDERMIS. [SECT. 45. 



vesicles. After this, a rudimentary nucleus comes into view in a 

 few of them, but by no means in the majority, and particularly in 

 those from the middle and inner portions of the horny layer. The 

 nucleus has the form of a fiat, homogeneous, roundish or elongated 

 corpuscle, from 0"003'" to 0*004"' long, and o*oo2'" to 0003'" broad ; 

 and, on account of its dark contour, is easily perceived, especially 

 when viewed from the side. The size of the plates of the ordinary 

 horny layer varies from o'oo8'" to 0*020'", and generally measures 

 O'oio'" to o'oi6'". 



Whilst the mucous layer, the uppermost cells excepted, is only 

 indistinctly stratified, an evident stratification is found throughout 

 the horny layer, occasioned by the apposition of the surfaces of 

 the plates, which, according to the thickness of the whole, 

 form a variable number of strata, having, in the inner layers, 

 an undulating course. These strata, however, are not capable of 

 being separated from each other as simple layers of cells, but 

 cohere by their contiguous surfaces in such a way that they are 

 separable with the knife only into portions composed of several sim- 

 ple strata; and, as such, they can be readily shown, especially after 

 boiling or maceration of the epidermis. 



§ 45. With respect to the colour of the epidermis, the horny layer 

 is, as has been already mentioned, in the white races, transparent 

 and colourless, or has a slight tinge of yellow; the mucous layer, 

 yellowish-white, or with various shades of brown or blackish-brown. 

 The darker pigment, which is found on "the areola of the nipple, 

 on the genitals, and, in exceptional cases, also, in other parts of 

 the skin, is not situated in special pigment-cells, but in the or- 

 dinary cells of the mucous layer, around whose nuclei either a 

 finely granular or more homogeneous colouring matter, or actual 

 pigment- granules, are deposited. Sometimes the deepest layer of 

 these cells is alone coloured, sometimes two, three, or more layers, 

 so that the deep part appears as a dark stratum. In the negro 

 and the other coloured races of mankind, the epidermis is likewise 

 the only part which is coloured, while the corium presents entirely 

 the same characters as in the European; the pigment, however, is 

 much darker and more widely distributed. All the cells of the 

 mucous layer are, with the exception of their membranes, coloured 

 in their entire extent, and more especially in the parts surrounding 

 the nucleus, which, in the deeper strata, are by far the darkest 

 parts of the cells. The horny layer, also, has a yellowish or 

 brownish tinge. 



