158 SPECIAL HISTOLOGY. 



misled Giinther, and probably Rainey also, 1 into supposing the 

 existence of peculiar glands under the nail. In the Negro, 

 according to Beclard (Anat. Generale, p. 309), the stratum 

 Malpighii of the nail is black ; and according to Krause 

 (1. c, p. 124), its cells would in this case appear to contain 

 dark-brown nuclei, as well as yellowish-brown ones, in dark 

 Europeans. According to Hassall (p. 252), the younger cells 

 of the nail (*. e., those of the stratum mucosum), generally con- 

 tain pigment, which I can confirm, at least in some cases. 



The horny layer of the nail, or its proper substance 

 (figs. 58 f; 60 k, I, m; 61 c), is that hard brittle portion 

 which forms its upper part and its free edge. The under 

 surface of this layer is quite smooth, posteriorly at the root ; 

 further forwards it exhibits sharp ridges separated by broad 

 furrows, which are inserted into the furrows of the mucous layer 

 of the nail. These ridges of the proper nail substance appear 

 in transverse sections (figs. 58, 61), as pointed processes of 

 0-01 — 0-02'" in length, which, as a rule, are most strongly 

 developed at the edges of the nail, even to 0'04 — 006'", and 

 answer precisely in their number to the laminae of the under 

 side of the stratum Malpighii. The upper surface of the sub- 

 stance of the nail is smooth, taken as a whole, yet sometimes 

 even here, very distinct, parallel, longitudinal streaks appear 

 as the last, almost effaced indications, of the inequalities of 

 its bed. 



Usually, the thickness of this part of the nail continually 

 increases from the root to near the free edge, so that the body 

 of the nail is, anteriorly, at least three times thicker (from 

 0*3 — 0'4>'") than the former ; at the free edge, again, it becomes 

 somewhat less. In its transverse diameter also, with the excep- 

 tion of the posterior edge of the root, the substance of the nail 

 is not everywhere equally thick ; it thins considerably towards 

 the lateral edges, so that at last the nails, where they lie in 

 the fold, measure not more than 0-06 — 0*1 2'", and finally ter- 

 minate quite sharply. 



1 [With respect to Rainey 's observations, Reichert, in his Report for 1849-50 

 ('Miill. Arch.,' 1850-51), says that the observation as to the follicles is quite cor- 

 rect, and that with Dr. Amraons, who had studied the growth and regeneration of 

 the nails for some years, he had seen such capsules containing horny cells, with 

 especial distinctness upon the bed of the nail of the great toe. — Eds.] 



