PHYSIOLOGICAL ANATOMY OF THE NAILS 309 



subjacent structure. At the posterior part, is a whitish portion, of a semi- 

 lunar 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. The skin beneath the root 

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

 papillae arranged in longitudinal rows, and it receives into its grooves 

 corresponding ridges on the under surface of the nail. 



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

 found to increase progressively in thickness from the root to near the free 

 border. Examined in transverse section, the nail 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 thin like the rest 

 of the root. The nail becomes thinner at and near the free border. 



Fig. 65. Anatomy of the nails (Sappey). 



A, nail in situ : i, 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 : i, border 

 of the root ; 2, lunula and root ; 3, body ; 4, free border. C, longitudinal section of the nail : i, 2, epi- 

 dermis ; 3, superficial layer of the nail ; 4, epidermis of the pulp of the finger ; 5, 6, true skin ; 7, n, bed 

 of the nail; 8, Malpighian layer of the pulp of the finger; 9, 10, true skin on the dorsal surface of the 

 finger ; 12, true skin of the pulp of the finger; 13, last phalanx of the finger. 



The two layers correspond to the Malpighian and the horny layers of 

 the epidermis, although they are more distinct. The Malpighian layer 

 is applied directly to the ridges of the bed of the nail and presents 

 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 composed 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 com- 

 posed of strata of flattened nucleated cells which can not be isolated 

 without the use of reagents. After boiling in a dilute solution of sodium 

 or potassium hydrate, it becomes evident that here, as in the horny layer 

 of the epidermis, the lower cells are rounded and those nearer the 

 surface are flattened. The thickness of this layer varies while that of 

 the Malpighian layer is nearly uniform. This layer is constantly grow- 

 ing, and it constitutes the entire substance of the free borders of the nails. 



