THE SKIN. 



351 



Nail wall. 



Fig. 248. Cross section of nail. 



is exclusively due to epithelial proliferation from the 

 Malpighian layer at the root of the nail and from 

 that part directly under each lunula already de- 

 scribed. A stratum granulosum is present in the 

 upper portion of the matrix and absent in the 

 other portions of the nail. 



The external cor- 

 nified layer consists 

 of flat epithelial 

 scales in which rem- 

 nants of a nucleus 

 may frequently be 

 found. These scales 

 are derived from 

 epithelial cells and 



overlie each other, forming hardened lamellae called 

 nail leaves. 



The hoof of the horse corresponds to the finger- 

 nail of man, and is divided for descriptive purposes 

 into the wall, the sole and the frog. The part which 

 is visible when the foot rests on the ground is the 

 wall, while the sole and frog are invisible in this 

 position. As the human nail rests on a grooved 

 matrix, so the inner surface of hoof wall is extensively 

 folded into leaf-like structures which interlock or 

 digitate with like growths from the enclosed con- 

 nective tissue, those from the wall being called horny 

 or insensitive lamina, and those from the connective 

 tissue or dermis the sensitive or vascular lamina. 



Horny Lamina. These are known collectively as 

 the kerqphyllous tissue, and clothing the inner sur- 

 face of the wall dovetail with the sensitive laminae 



