THE NAILS. 



1395 



epidermis and, therefore, may be removed without mutilation when the cuticle is 

 taken off after maceration. 



The entire nail-plate is divided into the body (corpus unguis), which includes 

 the exposed portion, and the root (radix unguis), which is embedded beneath the. 

 skin in a pocket-like recess, the nail-groove (sulcus unguis). The modified skin 

 supporting the nail-plate, both the body and the root, constitutes the nail-bed 

 (solum unguis), the cutaneous fold overlying the root being the nail-wall (vallum 

 unguis). 



The sides of the quadrilateral nail-plate are straight and parallel and at their 

 distal ends connected by the convex free margin (margo liber) that projects for a 

 variable distance beyond the skin. The proximal buried border (margo occultus) is 

 straight or slightly concave, more rarely somewhat convex, and often beset with 

 minute serrations (Brunn). Both surfaces of the transversely arched nail are smooth 

 and even, with the exception of the longitudinal parallel ridges that often mark the 

 upper aspect. Inspection of the latter during life shows color-zones, the translu- 

 cent whitish crescent formed by the projecting portion of the nail being immediately 

 followed by a very narrow yellow band that corresponds to the line along which the 

 stratum corneum of the underlying skin meets the under surface of the plate. The 



FIG. 1159. 



B c 



Distal portions of fingers, showing relations of nail ; A was drawn from living subject ; B and C are lateral and 

 under views respectively of inner surface of cuticle with nail ; nothing but the epidermal structures are present, the 

 cuticle and nail having been removed together, a, 6, distal and proximal borders of nail ; c, under surface of nail ; 

 rf, nail in section ; e, line of deflection of cuticle to under surface of nail ; f, lunula ; g, nail-wall ; h, cuticle in section. 



succeeding and larger part of the nail is occupied by the broad pink zone which owes 

 its rosy tint to the blending of the color of the blood in the underlying capillaries 

 with that of the horny substance. On the thumb constantly, but on the fingers often 

 only after retraction of the cuticle, is seen a transversely oval white area, the 

 so-called lunula, which marks the position of the underlying matrix. Additional 

 white spots, irregular in position, form and size, are sometimes seen as temporary 

 markings. 



The thickness of the nail-plate greatest on the thumb and large toe and least 

 on the last digits diminishes towards the sides, but in the longitudinal direction, 

 between the lunula and the free margin of the nail, is fairly uniform ; beneath the 

 white area, however, the under surface of the nail shelves off towards the buried 

 border, where it ends in a sharp edge. 



Structure. The substance of the nail-plate (stratum corneum unguis) consists 

 entirely of flattened horny epithelial cells, very firmly united and containing the 

 remains of their shrunken nuclei. These cornified scales are disposed in lamellae, 

 which, in transverse section, pursue a course in general parallel with the dorsal sur- 

 face. 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 (Brunn). In longitudinal section the lamellation is oblique, extending 



