NERVES OF THE SKIN. 231 



the skin that possess long papillae, between which the mucous 

 layer exhibits a remarkable thickness, whilst it is relatively 

 very thin over them. 



The thickness of the mucous layer, according to Krause, is 

 from l-65th to l-20th of a line ; on the other hand the epider- 

 mis varies from l-65th to 1 line. 



The two together frequently measure 3' 7 millimeters, but the 

 usual thickness is from 0'05 to 0'25 of a millimeter. 



The dark colour of the skin that in some individuals is 

 general, but in others appears only in certain parts of the 

 body, as in the area around the nipple, the scrotum, etc., 

 depends on the presence of pigment in the cells of the mucous 

 layer. In the coloured parts the lowermost cells of the rete 

 mucosum contain fine granular brownish-yellow pigment cor- 

 puscles in proportions varying with the depth of the cutaneous 

 tint. In the cells lying immediately above these are a few 

 pigment granules giving an uniform light-yellow colour to the 

 protoplasm, the colour diminishing in intensity in the upper- 

 most cells of this layer and in the scales of the epidermis, so that 

 the discoloration of these latter can only be perceived by direct 

 comparison with perfectly colourless cells. The black colour 

 of the skin in the negro depends also upon the pigment contained 

 in the cells of the mucous layer. In pathological formations 

 as in conical condylomata (Biesiadecki), the above-described 

 vagrant or migrating cells also contain pigment corpuscles. 



NERVES OF THE SKIN. 



Up to a late period medullated fibres with their peculiar 

 terminations, the corpuscles of Pacini and Meissner, were alone 

 known to exist in the skin. More recent researches have 

 demonstrated, in addition, the presence of an abundant non- 

 medullated nervous plexus ending by free extremities between 

 the cells of the mucous layer. 



The subcutaneous nerve trunks divide at the inferior surface 

 of the corium into several branches that accompany the larger 

 bloodvessels, and are composed of both medullated and non- 

 medullated nerve fibres. The nerves of those parts of the 

 skin in which the tactile and Pacinian corpuscles are especially 



