316 



EXCRETION BY THE SKIN AND KIDNEYS. 



2 7 3 il 



to the free border. This portion of the nail, with the root, is closely adher- 

 ent by its under surface to the true skin. It is marked by fine but distinct 



longitudinal stria} 

 and very faint 

 transverse lines. 

 It usually is red- 

 dish in color on ac- 

 count of the great 

 vascularity of the 

 subjacent struct- 

 ure. At the pos- 

 terior part, is a 

 whitish portion, of 



FIG. 105 Anatomy of the nails (Sappey). 



A, nail in situ : 1, cutaneous fold covering the root of the nail ; 2, section 



of this fold, turned back to show the root of the nail ; 3, lunula ; 4, nail. 



B, concave or adherent surface of the nail : 1, border of the root; 2, lunula 



and root ; 3, body ; 4, free border. 



C, longitudinal section of the nail : 1, 2, epidermis ; 3, superficial layer of 



the nail ; 4, epidermis of the pulp of the finger ; 5, 6, true skin : 7, 11, rpnranr>p 

 bed of the nail ; 8, Malpighian layer of the pulp of the finger ; 9, 10, true r ec 

 skin on the dorsal surface of the finger ; 12, true skin of the pulp of the 

 finger ; 13, last phalanx of the finger. 



, 



a Semilunar shape, 



liinVi Via a 

 WHICH lias 



ap- 



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 it receives into its grooves corresponding 

 ridges on the under surface of the nail. 



The free border of the nail begins 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 an inch and a half to two inches (40 to 50 mm.). 



On examining the nail in a longitudinal section, the horny layer, which is 

 usually regarded as the true nail, is found to increase progressively in thick- 

 ness from the root to near the free border. If the nail be examined in a 

 transverse section, it will also be found much thicker in the central portion 

 than near the edge, and that part which is received into the lateral portions 

 of the fold becomes excessively thin like the rest of the root. The nail be- 

 comes somewhat thinner at and near the free border. 



Sections of the nails show that they are composed of two layers, which 

 correspond to the Malpighian and the horny layers of the epidermis, although 

 they are much more distinct. The Malpighian layer is applied directly to 

 the ridges of the bed of the nail and presents upon its upper surface ridges 

 much less strongly marked than those of the underlying true skin. This 

 layer is rather thinner than the horny layer, is whitish in color, and is com- 

 posed of a number of strata of elongated, prismoidal, nucleated cells, arranged 

 perpendicularly to the matrix. 



The horny layer, which constitutes the true nail, is applied by its under 

 surface directly to the ridges of the Malpighian layer. It is dense and brittle 

 and is composed of strata of flattened cells which can not be isolated without 



