418 



THE SKIN. 



The part of the corium to which the nail is attached, and by which in fact it is 

 secreted or generated, is named the matrix. This portion of the skin is highly 

 vascular and thickly covered with large vascular papilla?. Posteriorly the matrix 

 forms a crescentic groove or fold, deep in the middle but| getting shallower at the 



Fig. 476. SECTION ACROSS THE MIDDLE OF THE NAIL OF A CHILD OF 8 DAYS. (Ranvier.) 



e, body of the nail ; I, nail-bed with its papillated ridges and rete muoosum ; d, corium under nail- 

 bed ; p, fold at edge of nail : here the horny layer is separated from the mucous layer by a well marked 

 stratum granulosum, which is altogether lacking over the nail-bed ; a, skin of finger at side of nail. 



sides, which lodges the root of the nail ; the rest of the matrix, before the groove, 

 is usually named the led of the nail. The small lighter-coloured part of the matrix 

 nearest the groove and corresponding with the lunula of the nail, is covered with 

 papillae having no regular arrangement, but the whole remaining surface of the 



Fig. 477. SECTION ACROSS THE NAIL AND NAIL- 

 BED. (Heitzmann). 



P, papillae ; B, rete mucosum of nail-bed ; 

 N, nail. 



matrix situated in front of this, and 

 supporting the body of the nail, is 

 marked with longitudinal ridges. 

 These ridges are cleft at their sum- 

 mits into rows of papillae, which 

 are directed obliquely forwards and are 

 better marked towards the distal end of 

 the nail. The ridges, or lamince, as 

 they are sometimes, and perhaps more 

 suitably, named, fit into corresponding 

 furrows on the under-surface of the 

 nail-epidermis. At the posterior part 

 of the matrix they are low, but increase 

 in height anteriorly. 



The nail, like the cuticle, is made 

 up of epithelial cells. The oldest and 

 most superficial of these are the broadest and hardest, but at the same time very thin, 

 and so intimately connected together that their respective limits are scarcely 

 discernible. They form the exterior, horny part or nail proper, and cohere together 

 in irregular layers. On the other hand, the youngest cells, which are those 

 situated at the root and under-surface, are softer and of a polygonal shape. The 

 deepest layer differs somewhat from the others, in having its cells elongated, and 



