254 



ANATOMY AND PHYSIOLOGY 



(tactile cells) supported by a fibrous and elastic network (reticular 

 layer) which contains non-striated muscle fibers and fat. In this 

 layer are the blood-vessels, nerves and lymphatics which are 

 exceedingly numerous. 



Tiny projections called papilla rise from this network portion, 

 many papilla containing special nerve-endings called touch cor- 

 puscles. They all contain at least a single loop of blood-vessels. 

 Some contain several loops these are vascular papilla. They 



are arranged in rows form- 

 ing ridges which are circular 

 on the front of the finger 

 tips. It is a remarkable fact 

 that no two fingers or toes 

 are alike in this respect, hence 

 the thumb- or finger-mark is a 

 means of identification. Its 

 value is never lost, even in 

 old age, as these ridges are 

 permanent. 



The papillae constitute a "papil- 

 lary layer." There are still other 

 nerve endings in the corium for different sensations. These are nerve 

 papillae. 



The epidermis (or cuticle) completely covers the corium. It 

 consists of layers of cells of varying character and thickness. The 

 deeper cells are soft and nucleated, but near the surface they 

 become flat and dry, until finally they are mere tiny scales. It has 

 no vessels and scarcely any nerves, consequently it is not sensitive 

 and does not bleed. It is this which comes away after the action 

 of a blister. 



The color of the skin depends partly upon the blood supply 

 and more upon pigment or coloring matter, which is deposited in 

 the deep layers of the epidermis (and the superficial layers of the 

 derma). The pigment varies in different people and races. 



In all races, the color is deeper in exposed portions of the skin 

 (face and hands), about the arms, axillae, and the areolae of the 

 mammary glands. It is lighter than elsewhere on the palms 

 and soles of the colored races. Exposure to heat as well as light 

 deepens it. 



FIG. 167. TACTILE CELLS FROM SNOUT 

 OF PIG. a. Tactile cell. m. Tactile disc. 

 n. Nerve-fiber. (Stirling.') 



