SCA MORBID ANATOMY OF THE SKIN. 



Onychogryphosis (VircJiow) or the claw-like deformity of 

 the nails which is associated with their simultaneous detachment 

 from their bed, depends upon a hyperplastic state of the entire 

 matrix of the nail. First stands that portion of its bed which 

 forms the lower boundary of the onjchial fold (Nagelfalz). 

 The long, horizontal papillae of this region furnish nearly all the 

 substance of the nail, since this is no thicker at the finger-tip 

 than it is at the edge of the lunula, up to which the papillae in 

 question extend. This gives the nail its ridged appearance, very 

 apparent by reflected light ; each ridge corresponding to a single 

 papilla in the same way as the vertical fibres of the ichthyotic 

 scale. Irregularities in the rate of growth, which may be 

 alternately accelerated and retarded, give rise to transverse 

 ridges and furrows. I ha\'e repeatedly observed that the 

 remissions and renewals of nutritive activity during subacute 

 pyrexial disorders leave traces of their presence by little trans- 

 verse grooves and ridges upon the nails. The anterior part of 

 the bed of the nail yields a thin layer of loosely-connected epi- 

 dermic cells, upon which the body of the nail glides forward as 

 upon a cushion ; it may be assumed as highly probable that 

 these cells likewise contribute, though in trifling measure, to the 

 growth of the nail in thickness ; this is rendered likely by the 

 close adhesion of the nail to its bed : but it Is far from beinor 

 proved, and Is even totally denied by Henle. 



Now if the matrix of the nail l^ecome hyperplastic, the 

 anterior part of its bed furnishes layer upon layer of these 

 loosely- connected epidermic cells ; the layers accumulate one 

 ujion the other, they raise the nail from its bed, and compel it to 

 assume a more or less upright position ; the hinder part of its 

 bed, on the other hand, produces a thick and shapeless claw, 

 several inches in length, spirally twisted, and somewhat incurved 

 at its edges. Both of these conditions, which are so Intimately 

 related, may occur together ; more usually, however, only one 

 of them is present. 



§ 307. Warts may be broadly defined as hyperplastic over- 

 growths of the epidermis, in which the papillary body shares 

 more or less ; we will begin therefore with a few introductory 

 observations on the mode of growth of the papillary bod}^ It 

 has already been stated that the very same cells which, after 

 their migration from the connective tissue, are converted into 



