NAILS. 



Longitudinal section through the middle of the nail and its matrix, a, matrix and cutis of the back and point 

 of the finger ; b, rete mucosum of the point of the finger; c, that of the nail ; d, that of the bottom of the root-fold; 

 e, the same of the back of the finger; /, epidermis of the point of the finger; g, its origin beneath the margin 

 of the nail ; h, epidermis of the back of the finger ; i, its termination at the upper surface of the root of the nail ; 

 k body, / root, TO free end of the proper nail. 



Magnified 8 diameters. 



Transverse section of the nail and its matrix, a, matrix with its ridges (black) ; b, cutis of the lateral fold ; c, rete 

 mucosum of the same ; d, rete mucosum of the nail with its ridges (white) ; e, epidermic layer of cutaneous fold ; 

 /, proper substance of the nail, with short teeth on its under surface. 



Magnified 8 diameters. 



furnished with the ridges, and is either en- 

 tirely lodged in the posterior depression of 

 the cutis, or the crescentic portion of it is 

 exposed. The body of the nail is uncovered 

 except at the sides, which are overlapped by 

 the lateral folds of the skin. 



The portion of the cutis (fig. 510 a) to which 

 the under surface of the nail, except that of 

 the anterior free portion, is attached, the 

 matrix or bed, is covered with ridges (fig. 



510 a), extending from the posterior part 

 or root of the nail to the convex margin of 

 the white crescentic portion called the lu- 

 nule, where they become larger and higher, 

 forming plates which run to the end of the 

 matrix. The margins of the ridges and 

 plates are covered with short papillae. The 

 anterior portion of the matrix of the nail is 

 very vascular. 



The under surface of the root and body 

 of the nail is covered with depressions and 

 ridges to adapt itself to those of the matrix. 



Two layers are distinguishable in the 

 nails; an under soft layer (figs. 509 d, 510 c, 



511 B), corresponding to and directly conti- 

 nuous with the rete mucosum of the skin, 



and the upper horny layer forming the true 

 nail (figs. 510/, 509 *," 511 C). The lower 

 surface of the latter is furnished with small 

 ridges (fig. 511 c), which occupy correspond- 

 ing furrows in the mucous layer. 



In minute structure the soft layer resem- 

 bles that of the cutaneous rete, except in 

 the deeper layers of cells being elongated 

 and arranged perpendicularly (fig. 511 b). 



The horny portion, or proper nail, con- 

 sists of epidermic cells, flattened and aggre- 

 gated into plates or laminae (fig. 511 C). In 

 the natural state, these cells are undistin- 

 guishable, except at the root and the under 

 surface, where the nail is in contact with 

 the mucous layer; the remainder merely 

 exhibiting shorter or longer dark lines, re- 

 presenting the flattened nuclei, or indicating 

 the existence of the laminae. But if a sec- 

 tion of nail be treated with solution of caustic 

 potash or soda, the nucleated cells swell up, 

 and resume their natural form and appear- 

 ance. 



The cutaneous epidermis (fig. 510 e) ex- 

 tends for a certain distance into the lateral 

 and posterior depressions of the skin, covers 



