THE NAILS. 



331 



The substance of the nail -pi ate consists entirely of flattened horny 

 epithelial cells, very firmly united and containing the remains of their 

 shrunken nuclei; hence it is also called stratum 

 corneiim unguis. These cornified scales are 

 disposed in lamellae, which, in transverse sec- 

 tion, pursue a course in general parallel with 

 the dorsal surface. In nails which possess the 

 longitudinal ridges, however, the latter coincide 

 with an upward arching of the lamellae dependent 

 upon the conformation of the nail-matrix. In 

 longitudinal section the lamellation is oblique, 

 extending from above downwards and forwards. 

 Minute air-vesicles, imprisoned between the horny 

 scales, are constant within the nail-substance. 

 When these occur in unusual quantities, they 

 give rise to white spots in the nail. 



The nail-bed is divided into a proximal, 

 a middle and a distal region, each of which 

 exhibits structural peculiarities and corresponds 

 respectively to the white, rosy or yellow zone 

 seen from the dorsal surface of the nail. 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 produc- 

 tion of the nail. So long as the matrix is healthy, it is capable of replacing 

 even an enti~e lost nail by a new one. 



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 



Subcutaneous tissue 

 Stratum germinativum 

 Stratum corneum 



Eponychium 



Nail-plat 

 Epidermi 



FIG. 376. Part of finger, showing 

 relations of the nail ; a, 6, distal 

 and proximal borders of nail ; c, 

 nail-wall; rf, line along which epi- 

 dermis passes to under surface of 

 nail-plate ; e, lunula. 



Transformation 

 ;/.-;! zone 



Matrix 



. . 

 FIG. 377. Longitudinal section of proximal part of nail lying within the nail-groove. X 3. 



as low papillae, which decrease in height and number until they disappear, an even 

 field occupying the middle of the matrix. This field is succeeded by one possessing 



