202 



THE SKIN 



within the cells of the horny layer, which is apparently the re- 

 sult of certain of those degenerative changes which characterize 



this portion of the 

 epidermis. 



The peculiar ab- 

 sence of the osmic re- 

 action in the mid-por- 

 tion of the horny layer 

 can only be explained 

 by the supposition that 

 the osmium solution is 

 unable to penetrate the 

 dense horny layer ex- 

 cept for a short dis- 

 tance from the free 

 / surface, from the free 

 margins of the tissue, 

 and from the more eas- 

 ily penetrated rete mu- 

 cosum. The presence 

 of the fatty material in 

 the deeper part of the 

 horny layer is not in 

 accord with the idea 

 that it is derived from 

 the secretion of the 

 various cutaneous glands, i. e., the sudoriparous and sebaceous 

 glands. 



It is the thicker portions of the epidermis only, which possess 

 all the characteristic layers above described. In other portions of 

 the body the horny layer is much thinner (Fig. 181). In these 

 thinner parts the cuticle of the epidermis consists of a prominent 

 rete mucosum which is covered by a relatively very thin layer of 

 horny cells. The stratum granulosum, in such portions, is not 

 usually demonstrable, the stratum lucidum is absent or indistinct, 

 and the entire horny layer consists only of flattened cornified 

 cells, the more superficial of which form a very thin scaly layer. 



THE DERMA 



The derma or corium (derma vera, cutis vera) forms a connect- 

 ive tissue bed or matrix upon which the epidermis lies. It is 



FIG. 180. TKANSECTION OF THE EPIDERMIS OF THE 

 FOOT. 



a, superficial scaly layer; J, layer of flattened 

 cells, the inner and outer portions of which have 

 been characteristically blackened by osmium tet- 

 roxid; c, stratum lucidum; d, granular layer; e, 

 prickle cells ; /, cylindrical cells ; <7, papillary layer 

 of the derma. Osmium tetroxid, carmin. Moderate- 

 ly magnified. (After Eanvier.) 



