218 



THE SKIN. 



Fi-. 145. 



The part of the corium to which the nail is attached, and by which 

 in fact it is secreted or generated, is named the nuifn'x. This portion of 

 the skin is highly vascular and thickly covered Avith large vascular 

 papillae. Posteriorly the matrix forms a crescentic groove or fold, deep 

 in the middle but getting shallower at the sides, Avliich 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 papillfe 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 papilla3. These ridges, or 

 lamiiuc, as they are sometimes, 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 tiie 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 epithelial 

 cells. The oldest and most 

 superficial of these are the 

 broadest and hardest, but 

 at the same time very thin 

 and irregular, and so inti- 

 mately and confusedly con- 

 nected together that then 

 respective limits are scarcely 

 d ! B jernible. They form th( 

 exterior, horny part of th( 

 nail, and cohere together ir 

 irregular layers, so as t( 

 give this part a lamellai 

 structure. On the othe: 

 hand, the youngest cells 

 which are those situatec 

 at the root and under sur 

 face, are softer and of i 

 rounded or polygonal shape 

 The deepest layer differ: 

 somewhat from the others 

 having its cells elon 



-_ Q^ 



a. 



Fig. 145. — Vertical Ti!Ansverse Section through 



A SMALL PORTIO>f OF THE NaIL AKD JIaTRIX, 

 HIGHLY MAGNIFIED (Kolliker). 



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

 laminn3, a, fitting in between corresponding laminie, 

 h, of the nail ; 1], Malpighian, and C, horny layer ; 

 d, deepest and vertical cells ; e, upper flattened cells 

 of Jlalpighian layer. 



ni 



gated, and arranged per 

 pendicularly, as in the cas( 

 of the epidermis. Thus th( 

 under part of the nail (fig 

 145, B) corresponds ii 

 nature with the Malpi 

 ghian or mucous layer o 

 the epidermis, and the upper part (c) with the horny layer. As in th< 

 case of the ei)idermis, the hardened scales may be made to reassum( 

 their cellular character by treatment with caustic alkali, and after 



