TISSUES OF THE BODY. 



1G3 



shape. It is more strongly doubled down at the sides than in the 

 middle; and at the anterior free edge is thicker than posteriorly. 



Fig. 154. Noil and matrix in transverse section, a, the matrix with the 

 ridges of the cutis; 6, side portion of the same, forming the groove of 

 the nail ; c, rete Malpighii ; e, homy layer; d, rete Malpighii of the nail, 

 dipping in between the papillae of the matrix ; /, the homy substance of 

 the nail. 



Of the edges only the anterior is exposed, while the lateral ones are 

 concealed in a fold of the skin (fig. 154, b) which commences at the 

 point of the finger as a flat groove, and becomes deeper and deeper 

 behind. The posterior portion of the nail finally disappears in a very 

 deep furrow of about 4'5 mm, in depth (fig. 154, a left), in which, a con- 

 siderable proportion of the whole nail is contained, known as the " root " 

 (fig. 155, Z), while the lateral grooves have received the name of "the 

 fold,"and the portion of skin concealed by the nail, that of "the matrix" 

 (fig. 154, a; 155, a). 



Fig. 155. Nail and matrix divided vertically and longitudinally, cr, the matrix, forming at the left 

 hand side the deep fold for the root, /; k, the horny part of nail; in, its anterior free edge; /, epi- 

 dermal layer on the point of the finger; g, its termination towards the rail; 6, rete Malpighii of the 

 same, which becomes that of the nail at c, and of the fold of the nail and root at d ; while at e, it is 

 continuous with that of the dorsum of the finger; A, epidennal layer on the di>,nm of the latter; ', 

 termination of the same towards the nail. 



The nail, which determines, roughly taken, the form of the matrix in 

 conjunction with the lateral fold, is so closely adherent to the first of 

 these that, like the rete Malpighii on other parts of the fibrous tissue of 

 the cutis, it can only be separated from it by maceration or boiling. 



If we examine the surface of a matrix so exposed, we find it marked 

 by a number of longitudinal ridges. These, as Henle has demon- 

 strated, commence at, the posterior border of the matrix as from 

 one pole, and, in the middle portions, pass directly forwards to the 

 anterior edge, while at the sides they maintain a course convex exter- 

 nally. On these ridges are' situated, more or less isolated, the papillse of 

 the cutis. Fig. 154, d, represents the former, of which from 50 to 90 

 may be reckoned on one matrix. They are arranged much closer to- 

 gether under the root of the nail than elsewhere, but are, at the same 

 time, much less elevated there. Both parts of the matrix are usually 



