STRUCTURE OF THE NAILS. 261 



the corium that lies immediately upon the periosteum of the 

 phalanx, and is firmly attached to it by short and tense con- 

 nective-tissue fibres. 



The deepest cells of the mucous layer of the nail bed are 

 columnar, the intermediate ones are polygonal, whilst the most 

 superficial are tabular. All enclose a large well-defined nucleus. 



The further destiny of the cells of the mucous layers varies ; 

 on the proper bed of the nail they suddenly pass into flat epi- 

 dermal scales, as in other parts of the skin ; but on the matrix 

 of the nail they pass gradually into the nail substance. 



In vertical sections, dividing the nail into two lateral halves, 

 it may easily be seen that the layer of nucleated flattened cells 

 over the matrix of the nail is much thicker than over the nail 

 bed, and that over the nail matrix they are continuous, by an 

 oblique furrowed surface, with the horny nail substance. The 

 thickness of this layer continuously diminishes towards the 

 nail bed, whilst the thickness of the nail substance increases 

 The line of junction between the mucous layer of the true nail 

 bed and the nail substance, on the other hand, is sharp and 

 level, a thin layer (in chromic-acid preparations) of looser 

 epidermal scales existing in most cases between them, which 

 also increases in thickness towards the free border of the nail 

 (Reichert). 



Between the mucous layer of the matrix and the root of the 

 nail no sharply defined line exists, the uppermost flattened 

 cells of the nail matrix passing continuously into still more 

 flattened nucleated and distinctly contoured cells, colourable by 

 carmine (Nagel), and these again into very flat scales, in which 

 a nucleus is no longer distinguishable. 



These scales are converted, in a plane falling off anteriorly 

 towards the nail bed, into a homogeneous lustrous horny nail 

 substance, that is no longer capable of imbibing carmine, but 

 is deeply stained by chromic acid. 



The mucous layer of the under surface of the fold of the 

 nail that looks towards the nail is covered with an epidermal 

 layer, increasing anteriorly in thickness, which is applied to 

 the upper surface of the nail root, but can nevertheless be 

 easily raised from it, and consequently plays no part in the 

 formation of the nail. 



