OF THE NAILS. 163 



[The mode in which the plates of the nail arise from the 

 cells of the mucous layer, is easily demonstrable at the root 

 of the nail. Here, in fact, the uppermost cells of the mucous 

 layer are constructed very differently from the deeper ones ; 

 they arc more or less flattened, and closely resemble the cells 

 of the epidermis, but they possess a nucleus, which, however, is 

 only to be discovered by adding caustic soda, and then with 

 difficulty. If we follow these cells, which form a layer of 006 

 — - 12'" in thickness, towards the proper substance of the 

 nail, we find that they become more and more flattened, and at 

 last pass without any defined boundary into the latter, uniting 

 together more closely, and taking on a more transparent ap- 

 pearance. 



In the body of the nail, the formation of nail substance is 

 demonstrated with more difficulty, yet here, in opposition to 

 Reichert, we must assume that it does take place, because the 

 nail almost invariably increases in thickness even in the body, 

 from behind forwards. However, there is unquestionably, in this 

 part, a sharper demarcation between the two layers of the nail, 

 than in the root ; but in fine sections it appears by no means so 

 sharp as in those which are commonly examined, and I find, in 

 fact, that the transition of the cells of the mucous layer into the 

 plates upon the body of the nail, is demonstrable with tolerable 

 readiness, particularly on the addition of alkalies, where the ridges 

 of the under surface of the proper nail are well developed. 

 Between the ridges also, though no direct transition is recog- 

 nisable, yet it may be observed that the plates of the proper nail 

 which border upon the mucous layer are much less flattened than 

 in the interior and on the surface, which also indicates that they 

 are developed upon the spot. In conclusion I must add, in 

 support of my view, that it is only in this way, that it becomes 

 explicable why the under surface of the proper nail substance 

 upon the root of the nail is almost smooth, while on the body 

 of the nail it presents more or less prominent ridges. The 

 origin or increase of these ridges demonstrates clearly that 

 nail-substance is also formed here. Corresponding with these 

 ridges and with the grooves between them, we also find that 

 the lowest layers of the nail plates, which are quite horizontal 

 upon the root, run with an undulating course upon the body 

 (fig. 61). The general result then is, that whilst the formation 



