268 THE SKIN 



stains. Its superficial layers stain deeply in osmic acid, indicating a 

 considerable fatty alteration. If, however, these cells are acted upon 

 by solutions of strong alkalies, soda, potassa, etc., the outlines of the 

 degenerated nuclei reappear. As the cells are pushed nearer the free 

 surface, by the process of cell division in the deeper layers and the 

 coincident desquamation of cells from the free surface, they become 

 more and more flattened and desiccated and more completely and firmly 

 fused together until at the surface they form the partially detached 

 cell masses or scales scaly layer, stratum squamosum which are 

 eventually removed by continued desquamation. 



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. 262). 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 stra- 

 tum 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 connective 

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

 two strata, a deeper reticular layer in which coarse fiber bundles inter- 

 lace to form a loose connective tissue network, and a superficial papil- 

 lary layer in which the finer bundles of connective tissue form a more 

 closely meshed network. 



The Papillary Layer (Stratum Papillare). The surface of the 

 papillary layer presents numerous conical elevations, the papillce of 

 the corium, which project into corresponding cup-shaped cavities in the 

 under surface of the epidermis. Many of the connective tissue papillae 

 contain tactile end-organs (touch corpuscles of Meissner), and terminal 

 filaments of the nerve fibers. They may therefore be regarded as the 

 special organ of tactile sensation. Other papillae contain no touch cor- 

 puscles but are richly supplied with capillary blood-vessels. Two types 

 are thus distinguished, the tactile papillce and the vascular papillce. 



Papillae are most abundant in the palms of the hands and the soles of 

 the feet, where they are mostly arranged in rows which are responsible 

 for the fine lines and ridges visible to the naked eye. In other portions 



