102 NAILS. [SECT. 54. 



would appear, indeed, as Pecliliii relates, that such a regeneration can take 

 place periodically, inasmuch as a boy every autumn lost his nails, which first 

 became dark blue, together with the epidermis (horny layer?), and they were 

 subsequently reproduced. In such a case, the entire bed of the nail, according 

 to Lauth and Ili/rtl, becomes covered with soft horny plates, which gradually 

 harden, and are transformed into a real nail, which finally projects with its 

 free border over the point of the finger. After loss of the distal phalanx of 

 the finger, rudimentary nails are, in many cases, developed on the dorsal 

 surface of the second, and even on that of the proximal phalanx. As the 

 formation of the substance of the nail depends upon the vessels of its bed, 

 we may, with Ilcnle, assume, that varying conditions of the latter may often 

 occasion an irregular growth, in some places thickening, in others thinning of 

 the nail, and even its entire detachment ; and that the deformities of the 

 nails in cyanosis and phthisis also depend upon this. Very frequently, how- 

 ever, as I have observed, the thickening and malformation proceed from 

 partial impermeability of the capillaries of the bed of the nail. After 

 section of the nervus isehiadieus in rabbits, Stcinruch observed a shedding 

 of the hair and nails, which is to be ascribed to the influence of the nerves 

 upon the vessels. Lastly, the shape of the bed of the nail also influences its 

 formation. It is thus explained how, after inflammation and closure of the 

 fold of the nail, the formation of new nail at the posterior border ceases, so 

 that the nail does not grow furwards any more, but remains covering its bed 

 and closely applied to it at its borders (see Ilenle, I.e.). Mcissncr, and espe- 

 cially Yirchorv, have described many cases of cryptogamic productions {J'unyi) 

 in the nails. 



§ 54. The development of the nail begins in the third month of 

 intra- uterine life with the formation of the bed and the fold, which 

 are marked off from the other parts by the gradual growth of skin 

 into the wall of the nail. The bed of the nail, is, at first, covered 

 by the same cells which, in other parts, form the epidermis, except 

 that by the third month the cells of the mucous layer are already 

 characterised by their elongated and polygonal shape (length, 

 0'004'" ; breadth, 0001'" to o - ooi6'"). In the fourth month, there 

 appears between the mucous and horny layers of the epidermis on 

 the bed of the nail, — the latter of which is formed by a single stratum 

 of polygonal, distinctly nucleated cells, — an intermediate layer of 

 pale, fiat, likewise polygonal and nucleated, cells, crooa/" in diameter, 

 which are firmly connected with each other, and may be considered 

 as the first indication of the proper nail-substance. At the same 

 time, the stratum Malpighii under these cells becomes thickened, 

 so that it is decidedly composed of, at least, tw r o layers. The nail, 

 accordingly, is at first entirely enclosed within the epidermis, it is 

 formed over the whole surface of the bed of the nail, in the shape 

 of a quadrangular plate, and arises between the embryonic mucous 

 layer and horny layer, undoubtedly by a transformation of the 



