262 SKIN, HAIR, AND NAILS, BY ALFRED BIESIADECKI. 



The posterior part of the nail bed, provided with papillae, 

 and lying in the fold of the nail, must therefore be regarded as 

 the exclusive seat of formation of the nail, and is properly 

 termed the nail matrix. 



It corresponds to the papilla of the hair, whilst the nail fold 

 is equivalent to the hair follicle, and occasions the forward 

 growth of the nail; for the nail cells, as they become more 

 superficial, become constantly broader; but since they are unable 



Fig. 204. 



Fig. 204. Transverse section of a nail, made through the proper 

 bed of the nail, a, Nail ; 6, loose horny layer beneath it ; c, mucous 

 layer ; d, transversely divided nail ridges, with injected bloodvessels ; 

 e, nail fold, destitute of papillae ; /, the horny layer of the nail fold 

 which has been deposited upon the nail ; g, papillae of the skin of the 

 back of the finger. 



to expand equably, on account of the posterior angle of the nail 

 fold, they must necessarily press forward, and be pushed still 

 further forward by those that succeed them. 



It is on this account that the nail cells are arranged in an 

 imbricated manner, the upper covering the greater part of the 

 lower, and only leaving their posterior border free.* 



Where the nail fold is deficient, i.e., simply the nail wall, 

 as frequently occurs with the little toes, the nail only increases 

 in thickness, and forms a horny eminence, that attains a certain 

 height, and then breaks off. 



* "Virchow, Zur normal und pathologischen Anatomie der Ndgel. "On 

 the normal and pathological Anatomy of the Nail." Wurzburg. Verhand. t 

 Band v. 



