THE SKIN. 



129 



epidermis commences, as a layer of clear compressed cells several deep 

 (stratum lutidum, s.L). Above this comes the main part of the horny 

 layer. It is composed of a number of layers of somewhat swollen cells 

 (epitrichial stratum, sw), the nuclei of which are no longer visible. 

 These cells are replaced near the surface by thin horny scales 

 (stratum squamosum), which eventually become detached (s). The 

 epitrichial stratum is only found in certain parts which have a thick 

 epidermis and are not covered with hair (e.g. the palms and soles). 

 In the embryo it covers the whole body, but is thrown oft' when the 

 hairs are developed. 



The growth of the epidermis takes place by a multiplication of the 

 cells of the deepest layer. The newly formed cells, as they grow, push 

 towards the surface those which were previously formed, and in their 

 progress the latter undergo a chemical transformation, which converts 

 their protoplasm into horny material : this change seems to occur just 

 above the stratum granulosum (see fig. 152). The granules which 

 occupy the cells of the last-mentioned layer are composed of a substance 

 termed eleidin, which according to Ranvier is transformed into keratin. 



No blood-vessels pass into the epidermis, but it receives nerves 

 which ramify between the cells of the rete mucosum in the form of 

 fine varicose fibrils (fig. 151). 



FlG. 152. POKTION OF EPIDERMIS FROM A SECTION OF THE SKIN OF THE FINGER, 



COLOURED WITH PICROCARMINATE OF AMMONIA. (Ranvier. ) 



a, stratum corneum ; b, stratum lucidum with diffused flakes of eleidin ; c, stratum granu- 

 losum, the cells filled with drops of eleidin ; d, prickle-cells ; e, dentate projections by 

 which the deepest cells of the epidermis are fixed to the cutis vera. 



The cutis vera or corium is composed of dense connective-tissue, 

 which becomes more open and reticular in its texture in its deeper 

 part, where it merges into the subcutaneous tissue. It is thickest over 

 the posterior aspect of the trunk, whereas the epidermis is thickest on 



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