1396 



HUMAN ANATOMY. 



from above downward and forward, parallel to the shelving under surface beneath the 

 white area that rests upon the matrix. Minute air-vesicles, imprisoned between the 

 horny scales, are constant constituents of the nail-substance. When these occur in 

 unusual quantities, they give rise to the white spots in the nail above mentioned. 



Corresponding respectively to the colored zones — the white, rosy and yellow — 

 seen on the dorsal surface of the nail, the nail-bed is divided into a proximal, 



Fig. ii6o. 



Subcutaneous tissue 

 Stratum germinativum 

 Stratum corneum 



Eponychium 



Nail-plate 

 Epidermis 



and 



Corium 

 of nail-bed 



"" ,^^«»s Transformation 

 ^ zone 



%x^,X^^^Z''-t I ' ''■ ^ Matrix 





Longitudinal section of proximal part of nail lying within the nail groove. X 30. 



a middle and a distal region, each of which exhibits structural differences. The 

 most important of these regions is the proximal, known as the matrix, which lies 

 beneath the white area and alone is concerned in the production of the nail. 



The corium of the nail-bed varies in the different regions in the arrangement and size of its . 

 elevations. Within the proximal third of the matrix, these elevations occur in the form of low 

 papilke, which decrease in height and number until they disappear, a smooth field occupying 

 the middle of the matrix. This even field is succeeded by one possessing closely set, low, 

 narrow longitudinal ridges, that at the distal margin of the lunula suddenly give place to more 

 pronounced, but less numerous broader, linear elevations. These continue as far as the distal 

 end of the nail-bed and are then replaced by papillae. Owing to the strong fibrous bands and 

 the absence of the usual layer of fatty subdermal tissue, the corium of the nail-bed is closely 

 attached tc^ the bone. The fibrous reticulum formed by the interlacing of the longitudinal with 

 the vertical bundles contains few elastic fibres, since these are entirely wanting beneath the body 

 of the nail and only present in meagre numbers- within the matrix. 



bi view of its genetic activity, the relations of the epiderinis underlying the nail are of 

 especial interest. While the stratum germinativum of the skin covering the finger tip passes 

 directly and insensibly onto the nail-bed, the entire extent of wliich it invests (stratum germina- 

 tivum unguis), the stratum corneum ends on reaching the under surface of the nail-plate, the line 

 of apposition corresponding to the narrow yellow zone which defines the distal boundary of the 

 rosy area. Beneath the latter, therefore, the epidermis of the nail-bed consists of the stratum 

 germinativum alone, which, without cornification of any of its cells, rests against the under sur- 

 face of the nail. Beneath the white zone, that is, within the matrix, the epidermis includes a half 

 dozeivor more layers of the usual elements of the stratum germinativum, surmoiinted by a like 

 number of strata of cells distinguished by a peculiar brownish color. On reaching the nail these 

 modified epithelial elements, which appear white by reflected light, are not circumscribed, but 

 pass over into the substance of the nail, into the constituent cells of which they are directly con- 

 verted. Their cytoplasm presents a marked fibrillation to which, according to Brunn, the light 

 appearance of the cells is referable as an interference phenomenon and not as a true pigmenta- 

 tion. This pecuHarity of the cells, coupled with the relatively small size of subjacent capillaries, 



