OF THE NAILS. 101 



itself with its latnelhe parallel upon the nail, partly abuts 

 upon it at various oblique angles. At the root, the horny 

 layer passes more or less deeply into the fold of the nail, and at 

 the same time runs, in a thin layer which becomes very 

 fine anteriorly, upon the upper free part of the nail, as far as 

 the end of the lunula or the beginning of the body. Ante- 

 riorly and posteriorly, in which latter region this layer not 

 uncommonly reaches the posterior margin of the root, its cells 

 lie parallel to the upper surface of the nail; while in the 

 middle, where it is thickest (fig. GO i), they are oblique or 

 perpendicular to it. At the free edge of the nail the relations 

 of the parts are similar, where the horny layer meeting the 

 end of the under surface of the body of the nail, partly with 

 more horizontal, partly with oblique lamellae, is perhaps also 

 continued upon the commencement of the free edge. On the 

 lateral edges, again, the horny layer passes anteriorly, in hori- 

 zontal strata, under the nail ; more posteriorly it is arranged as 

 upon the root, or simply rests against the edge of the nail. 

 The horny layer thus forms a kind of sheath for the nail, which 

 bears some resemblance to the sheath of the hair, though it is 

 much more imperfect. If we compare the nail with the 

 epidermis, we find, in the structure of its mucous layer, not the 

 slightest peculiarity of any importance, while the horny layer 

 is distinguished from that of the epidermis by its cells being 

 nucleated, harder, and chemically different; by their flattening 

 and intimate union. For the rest, the agreement of the two 

 structures is so close, that the proper nail may justly be con- 

 sidered, as it has long been, a modified portion of the horny 

 layer of the last joints of the fingers and toes. 



[According to the chemical investigations of Scherer and 

 Mulder, the nails agree very closely with the epidermis; and, 

 according to Mulder, they are distinguished from it, only by 

 their somewhat greater proportion of sulphur and carbon. 

 In his last essay, he considers them to be composed of 

 protein + sulphamid (0-8 per cent, of the latter). This 

 agrees with the observed action of reagents, with which the 

 plates of the nail behave almost exactly like horny plates, only 

 they are attacked with more difficulty and possess nuclei. 

 According to Lauth, the nails contain more phosphate of lime 



i. 11 



