118 EXCRETION. 



consider briefly the general arrangement of the cuticular 

 appendages. 



The nails are situated on the dorsal surfaces of the distal 

 phalanges of the fingers and toes. They serve to protect 

 these parts, and in the fingers, are also quite important in 

 prehension. The general appearance of the nails is so famil- 

 iar that it requires no special description. In their study, 

 anatomists have distinguished a root, a body, and a free 

 border. 



The root is thin and soft, terminating in rather a jagged 

 edge, which is turned slightly upward and is received into a 

 fold of the skin extending around the nail to its free edge. 

 The length of the root of course varies with the size of the 

 nail, but it is generally from one fourth to one third of the 

 length of the body. 



The body of the nail extends from the fold of skin which 

 covers the root to the free border. This portion of the nail, 

 with the root, is closely adherent by its under surface to the 

 true skin. It is marked by fine but distinct longitudinal 

 striae and very faint transverse lines. It is usually reddish 

 in color, from the great vascularity of the subjacent structure. 

 At the posterior part is a whitish portion of a semilunar 

 shape, called the lunula, which has this appearance simply 

 from the fact that the corium in this part is less vascular, and 

 the papillae are not so regular as in the rest of the body. 

 That portion of the skin situated beneath the root and the 

 body of the nail is called the matrix. It presents highly 

 vascular papillae, arranged in regular, longitudinal rows, and 

 receives into its grooves corresponding ridges on the under 

 surface of the nail. 



The free border of the nail begins at the point where the 

 nail becomes detached from the skin. This is generally cut 

 or worn away, and is constantly growing ; but if left to itself, 

 it attains in time a definite length, which may be stated, in 

 general terms, to be from an inch and a half to two inches. 



Examining the nail in a longitudinal section, the horny 



