OF THE SKIN. 133 



there, between the rounded and elongated cells, one, two, or 

 even three layers of similarly elongated and perpendicularly 

 disposed elements, so that the mucous layer, on account 

 of the numerous strata of perpendicular cells, has a striated 

 appearance in its deepest part, under a low power. This 

 character is the more striking, since the other elements of 

 the mucous layer, the further they are followed from the 

 first, round cells outwards, become thinner in another direction, 

 i. e., become horizontally flattened (fig. 55 c), and finally in 

 the uppermost layers are transformed into thick vesicles, 

 0-00G— 001 6"' broad, and 0-002— 0008'" thick. At the same 

 time, from their mutual pressure, they acquire a polygonal 

 form, which may even be recognised in isolated cells. 



All the cells of the mucous layer agree, inessential points, in 

 their structure, and are nucleated vesicles distended with fluid. 

 Their membrane is pale, often difficult of demonstration in the 

 smallest, frequently quite distinct, always delicate, thicker in the 

 larger ones, yet by no means to be compared to that of the cells 

 in the horny layer. The contents are never quite fluid; but also, 

 excepting in the coloured epidermis (vide infra), never normally 

 contain larger particles, granules or fat-drops for example ; but 

 are finely granulated, with more or less clearly-defined granules, 

 which invariably diminish in number in the more external 

 cells. The nucleus, lastly, is small in the smallest cells 

 (0-0015 — 00025'"), in the large, of greater size (0003 — 

 0-005"'); globular or lenticular, in the round and flattened 

 cells; elongated, in the elongated cells. In the larger cells it 

 appears obviously vesicular, often with a nucleolus, and lies 

 centrally in the midst of the contents ; in the smaller it is 

 apparently more homogeneous, without any visible nucleolus, 

 and so disposed that it is not unfrequently in contact with one 

 part or other of the cell-walls. 



§ 42. 



The horny, layer (stratum comeum), forms the external semi- 

 transparent part of the epidermis, which in white people is 

 colourless, and is composed almost wholly of uniform cells 

 metamorphosed into plates. The deepest plates are still very 

 similar to the uppermost cells of the stratum mucosum; but 

 evcu in the second or third layer we find the widely different 



