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. i i 60. 



Subcutaneous tissue 

 Stratum germinativum 

 Stratum corneum 



v -x 



Eponychium 



and 



Corium 

 of nail-bed 



Nail-plate 



Epidermis- 



.Transformation 

 zone 



^Matrix 



Longitudinal section of proximal part of nail lying within the nail groove. X 3- 



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 si/e of its 

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

 papillae, 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 papilla?. 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 to 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 

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



In view of its genetic activity, the relations of the epidermis 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 which it invests (stratum 

 liviim unguis), the stratum corneum ends on reaching the under surface of the nail-plate, the Hi 

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

 rosy area. Heiieath tin- latter, therefore, the epidermis of the nail-bed consists of the strati 

 germinatn urn alone, which, without cornification of any of its cells, rests against the under snr- 

 f the nail, llenrath the white /one, that is, within the matrix, the epidermis includes a halt 

 do/en or more layers of the usual elements of the stratum germinativum, surmounted 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 siibst;uice of the nail, into the constituent cells of which they are directly con- 

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

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

 tion. This peculiarity of the cells, coupled with the relatively small size of subjacent capillii 



