32 THIRD LECTURE. 



sometimes indented (Lott, Langerhans). This was first seen 

 in the epithelium of the urinary bladder. When the epithe- 

 lial stratification is more developed, the cells of the lower 

 and middle layers lock into each other with their enormous 

 spines and ridges, like two brushes pressed together (Fig. 37). 



These "spinous and dentate cells" 



J$^&J$i£% (Schultze) lead to an intimate clinching. 



a t'M$^:fi$% This connection is, however, again dis- 



^*§6§'£0^iii$ solved upwards, and their deciduousness 



d^^ip-fT^v-'i is thus promoted. 



^^"^''•# The most dense formation of flattened 



epithelium covers the human corium. It 

 b v ^'^ ; ''-*.!t^ nas l° n g been known under the name of 



the epidermis. 



This corium projects in small papillae of 



various shapes. They are called the sensi- 

 JE? %*£?*?££ tive or tactile papillae. The epidermis 

 mf"\°ceii hu f™m a'p'S" forms a smoother covering over the whole ; 

 'tongue™ " ° f ** human its deeper cell layers must, therefore, fill 



up the valleys between these papillae. 

 These younger cell layers, which have a not inconsiderable 

 thickness between the papillae, while they are but slightly 

 developed over their apices, present all the characteristics of 

 a stratified epithelial mucous membrane. Collectively, it is 

 called the Malpighian rete mucosum, or rete Malpighii. 

 The layers of old cornified cells make their appearance by an 

 abrupt transition. They bear the name of the epidermis in 

 the strict sense of the word. Its thickness varies considera- 

 bly ; it may exceed a Paris line. The number of layers 

 varies, in consequence, extraordinarily. The latter are the 

 same scales as those on the surface of the mucous membranes, 

 though the cells in contact with the atmospheric air have be- 

 come dryer and harder. The nucleus, which these cells for- 

 merly possessed, has likewise been lost by the old, effete 

 epidermis scale. They measure 0.0285 to °- 45° mm.; in the 

 mucous epithelium of the mouth, 0.0425 to 0.075 mm. 



We will speak of the color of the human skin. If we 



