CUTANEOUS APPENDAGES 



275 



the horny layer of the subjacent epidermis forms the so-called hypony- 

 chium. 



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

 stratum lucidum and the deeper germinal layer. These are continuous 

 at the border of the nail with the corresponding layers of the epidermis 

 which lines the nail groove. At the distal border, however, the nail 



FEN H 



268. TERMINAL PHALANX OF FINGER OP HUMAN FETUS. 



Showing A", nail; F, nail fold; H, hyponychium; E, eponychium; developing 

 sudoriparous glands, and developing bone. 



proper or thickened stratum lucidum ends in a free margin. 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 excessive 

 eleidin production that it is impossible to distinguish their outlines. 

 By maceration in alkaline solutions, however, the outlines of both cells 

 and nuclei may be caused to reappear. In the nail root the stratum 

 lucidum increases rapidly in thickness as it grows distalward; in the 

 body of the nail this layer is not very materially thickened as it ap- 

 proaches the distal or free margin. 



The stratum germinativum is of nearly equal thickness in all por- 

 tions of the nail body. In the nail root it is somewhat thicker and 



