THE KAILS 



former comprising the exposed, the latter the hidden portion of 

 the organ. The root of the nail is overhung by a fold of the skin, 

 the thickened horny layer at the margin of which forms an adher- 

 ent border, the eponychium. 



The nail groove or sulcus is included between the overhanging 

 skin and the root of the nail. It is deep at its proximal end but 

 is shallow at the lateral margins of the nail. The distal or free 

 border of the nail projects over the skin at the tip of the finger 

 and the thickening of the horny layer of the subjacent epidermis 

 forms the so-called hy pony Mum. 



Finer Structure. The nail consists of two layers, the superficial 

 stratum lucidum and the deeper Malpighian layer. These are 

 continuous at the border of 

 the nail with the corre- 

 sponding layers of the epi- 

 dermis which lines the nail 

 groove. At the distal bor- 

 der, however, the nail prop- 

 er or thickened stratum 

 lucidum ends in a free mar- 

 gin. The finer structure 

 of these two layers does not 

 essentially differ from that 

 of the corresponding layers 

 of the epidermis. 



The stratum lucidum 

 in the body of the nail is 

 very thick and its cells are 

 so completely blended with 

 each other through the ex- 

 cessive eleidin production 

 that it is impossible to dis- 

 tinguish their outlines. By 

 maceration in alkaline solu- 

 tions, however, the outlines 

 of both cells and nuclei 

 may be caused to reappear. 



In the nail root the stratum lucidum increases rapidly in thick- 

 ness as it grows distal ward ; in the body of the nail this layer is 

 not very materially thickened as it approaches the distal or free 



margin. 



15 



FIG. 184. TRANSECTION THROUGH THE MARGIN 



OF A FINGER NAIL. 



On the left is the skin, on the right the nail, 

 a, a', horny layer ; ft, ft', germinal layer ; c, c', 

 corium ; d, margin of the nail. Moderately 

 magnified. (After von Brunn.) 



