NAILS; 



ccvii 



Posteriorly the matrix forms a crescentic groove or fold, deep in the 

 middle but getting shallower at the sides, which lodges the root of the 

 nail ; the rest of the matrix, before the groove, is usually named the bed of 

 the nail. The small lighter-coloured part of the matrix next the groove 

 and corresponding with the lunula of the nail, is covered with papillae 

 having no regular arrangement, but the whole remaining surface of the 

 matrix situated in front of this, and supporting the body of the nail, is 

 marked with longitudinal and very slightly diverging ridges cleft at their 

 summits into rows of papillae. These ridges, or lamina, as they are some- 

 times, and perhaps more suitably, named, fit into corresponding furrows on 

 the under surface of the nail. The cuticle, advancing from the back of the 

 finger, becomes attached to the upper surface of the nail near its posterior 

 edge, that is, all round the margin of the groove in which the nail is 

 lodged ; in front the cuticle of the point of the finger becomes continuous 

 with the under surface of the nail a little way behind its free edge. 



The nail, like the cuticle, is made up of scales derived from flattened 

 cells. The oldest and most superficial of these are the broadest and 

 hardest, but at the same time very thin and irregular, and so intimately 

 and confusedly connected together that their respective limits are scarcely 

 discernible. They form the 



exterior, horny part of the Fig. CXII. 



nail, and cohere together in 

 irregular layers, so as to 

 give this part a lamellar 

 structure. On the other 

 hand, the youngest cells, 

 which are those situated at 

 the root and under surface, 

 are softer and of a rounded 

 or polygonal shape. The 

 deepest layer differs some- 

 what from the others, in 

 having its cells elongated, 

 and arranged perpendicular- 

 ly, as in the case of the 

 epidermis. Thus the under 

 part of the nail (fig. cxn. B) 

 corresponds in nature with 

 the Malpighian or mucous 

 layer of the epidermis, and 

 the upper part (c) with the 

 horny layer. As in the 

 case of the epidermis, the 

 hardened scales may be made 

 to reassume their cellular 

 character by treatment with 

 caustic alkali, and after- 

 wards with water ; and 

 then it is seen that they 

 still retain their nuclei. In chemical composition the nails resemble epider- 

 mis ; but, according to Mulder, they contain a somewhat larger proportion 

 of carbon and sulphur. 



The growth of the nail is effected by a constant generation of cells at the 



Fig. CXII. VERTICAL TRANSVERSE SECTION THROUGH 



A SMALL PORTION OF THE NAIL AND MATRIX, 



LARGELY MAGNIFIED (after Kolliker). 



A, corium of the nail-bed, raised into ridges or 

 laminae, a, fitting in between corresponding laminae, b, 

 of the nail; B, Malpighian, and C, horny layer; d, 

 deepest and vertical cells ; e, upper flattened cells of 

 Malpighian layer. 



