STRUCTURE OF NAILS. 343 



moulded the epidermal cells of which the nail is made up 

 (Fig. 119). 



The growth of the nail, like that of a hair, or of the epi- 

 dermis generally, is effected by a constant production of cells 

 from beneath and behind, to take the place of those which are 

 worn or cut away. Inasmuch, however, as the posterior edge 

 of the nail, from its being lodged in a groove of the skin, can- 

 no. 119. 



Vertical transverse section through a small portion of the nail and matrix largely 



magnified (after Kolliker). 



A, corium of the nail-bed, raised into ridges or laminie a, fitting in between cor- 

 responding laminae ft, of the nail. B, Malpighian, and C, horny layer of nail; d, 

 deepest and vertical cells ; e, upper flattened cells of Malpighian layer. 



not grow backwards, on additions being made to it, so easily 

 as it can pass in the opposite direction, any growth at its 

 hinder part pushes the whole forwards. At the same time 

 fresh cells are added to its under surface, and thus each por- 

 tion of the nail becomes gradually thicker as it moves to the 

 front, until, projecting beyond the surface of the matrix, it can 

 receive no fresh addition from beneath, and is simply moved 

 forwards by the growth at its root, to be at last worn away or 

 cut off. 



