THE SKIN. 



tion parallel with the surface of the skin and are surrounded by a retic- 

 ulum of rather coarse elastic fibers. In that portion of the pars papil- 

 laris bordering upon the epidermis, the interlacing strands ofr'eon- 

 nective tissue, as well as the surrounding reticulum of elastic fibers, 

 are finer, so that the whole tissue is denser. This stratum supports 

 the papillae knob-like or conical elevations of still denser tissue end- 

 ing in one or more points. We accordingly speak of simple or com- 

 pound papillae. These structures are especially numerous and well 

 developed in the palm of the hand and sole of the foot, where they 

 are from 1 10 /J. to 220/1 long. Here they rest upon ridges of the 

 corium, which are nearly always arranged in double rows. Accord- 

 ing to whether the papillae contain blood-vessels alone, or special 

 nerve-endings also, they are known as vascular or tactile papillae. 



Stratum 

 corneum. 



Lower border ~"'~ 

 of stratum, 

 lucidum. 

 Stratum granu- 



losum. 



Stratum Mal- 

 pighii. 



Fig. 306. Cross-section of human epidermis ; the deeper layers of the stratum 

 Malpighii are not represented ; X 75- 



The smallest papillae are found in the mammae and scrotum from 

 30 /J. to 50 n long. The surface of the pars papillaris is covered by 

 an extremely delicate membrane the basement membrane. Accord- 

 ing to most authors, the basal cells of the epidermis are simply 

 cemented to this structure. Others believe that the epithelial cells 

 are provided with short basilar processes which penetrate into the 

 basement membrane and meet here with similar structures from the 

 connective-tissue cells of the corium. This would give the base- 

 ment membrane a fibrillar structure (Schuberg). 



The subcutaneous layer contains numerous more or less verti- 

 cal strands of connective tissue, containing numerous large elastic- 

 tissue fibers and joining the stratum reticulare of the corium to the 



