250 THE TISSUES. 



on the form of true lamina?, ^J n to T J(j of an inch deep. The line 

 of transition of the ridges into the laminae divides the bed of the 

 nail into two sections, differing in color and in extent; the posterior 

 smaller one underlying its root and lunula, and the other portion its 

 body. The ridges and laminae number from fifty to ninety. At 

 their edges they are beset with a series of short papillae. On the 

 little toe, however, the papillae are frequently not seated upon the 

 ridges, but are dispersed. (Kolliker.) 



The wall of the nail is the process of the skin continuous with 

 the bed of the nail, laterally and posteriorly; forming the folds on 

 the sides, by which the nail is limited. The corium of the wall and 

 of the bed of the nail contains but little fat ; but in the ridges and 

 the laminas is an abundance of fine elastic fibres. The capillaries, 

 ^ffs to TSUU f an i ncn i n diameter, form simple loops in the pa- 

 pillae; and the nerves have the same relation as in the skin. 



The nail itself is divided into the body, the root, and the free 

 edge. These are shown by Fig. 158. The lunula is the opaque 



semilunar portion of the nail (not seen 

 in all cases), at its posterior part. When 

 not Apparent, it is covered entirely by 

 the fold of the skin underneath which 

 the root of the nail lies, and which is 

 called the matrix of the nail. 



The lower surface of the nail corre- 

 sponds with the surface of the ridges and 

 laminae of the bed. Furrows and ridges 

 therefore appear on the former as upon 

 Relations of nan to the cuticle. n,n. the latter. It is by the mutual interlock - 



Cuticle and nail ; m, m. Corium and 



bod of naii. in g 0* these opposite surfaces that the 



intimate union of the nail with the co- 

 rium of the skin is effected. (Fig. 157.) 



In structure, the nails, like the epithelium of the skin, consist of 

 two layers; the deeper being soft (the Malpighian layer, sometimes 

 improperly called the stratum mucosum), and the superficial, consti- 

 tuting most of the thickness of the nail (the horny layer). This 

 stratum consists wholly of cells, like that of the epidermis (except 

 that they are nucleated) ; and in the negro is black. Hassall states 

 that the younger cells of this layer generally contain pigment in 

 the white races. The horny layer is quite smooth on its under sur- 

 face at the root, but becomes ridged further forwards; the ridges 



