432 



THE SKIX. 



posterior edge of the nail, from its being lodged in a groove 



Fig. 119.' 



v 



of the skin, cannot 

 grow backwards, 

 on additions be- 

 ing made to it, 

 so easily as it 

 can pass in the 

 opposite direc- 

 tion, any growth 

 at its hinder 

 part pushes the 

 whole forwards. 

 At the same time 

 fresh cells are 

 added to its un- 

 der surface, and 

 thus each portion 

 & of the nail be- 



comes gradually thicker as it moves to the front, until, 

 projecting beyond the surface of the matrix, it can receive 

 110 fresh addition from beneath, and is simply moved for- 

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

 cut off. 



Excretion by the Skin. 



The skin, as already stated, is the 'seat of a two-fold 

 excretion ; of that formed by the sebaceous glands and hair- 

 follicles, and of the more watery fluid, the sweat or perspira- 

 tion, eliminated by the sudoriparous glands. 



The secretion of the sebaceous glands and hair -follicles 



* Fig. 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 laminte , fitting in 

 betAveen corresponding laminae b, of the nail. B, Malpighian, and C, 

 horny layer of nail : d, deepest and vertical cells ; c, upper flattened 

 cells of Malpighian layer. 



