542 APPENDIX. 



Structure of the Nails. 



" If a thin vertical section be made lengthways through a finger-nail 

 from its posterior to its anterior or free margin, the external or dorsal 

 surface of that portion of it which was lodged in the groove between 

 the matrix and the semilunar fold of skin projecting from the dorsum of 

 the finger, is seen covered by a thin layer of cuticle, which extends 

 backwards as far as its posterior border, which is generally jagged and 

 uneven, and forwards upon its dorsum. This portion of cuticle is im- 

 mediately continuous with that overhanging the root of the nail, and 

 although it is not inseparably blended with its horny substance, yet it is 

 sufficiently adherent to be carried forward with it during its growth and 

 to remain intimately attached to its dorsal surface until it is worn off by 

 friction or some other mechanical cause. The palmer surface, near to its 

 free border, is also- seen covered by cuticle, which in like manner divides 

 into two parts, the one becoming continuous with the cuticle covering 

 the end of the finger ; the other passing backwards along the palmer 

 surface of the nail as far as the lunula, where it imperceptibly terminates. 

 This portion of cuticle gradually diminishes in thickness as it extends 

 backwards, and is more intimately connected with the horny part of the 

 nail than was the cuticle on its dorsal surface. Between these layers of 

 cuticle the proper or horny matter of the nail can be distinguished, pre- 

 senting fine, nearly parallel, and generally semi- elliptical lines, with their 

 concavity looking in different directions in different parts of the same 

 section, and also a multitude of darkish-looking corpuscles, when viewed 

 by transmitted light, of various forms and sizes. These compose the 

 substance of the horn of the nail, and the lines are the cut edges of the 

 lamina? of which it is made up. The horny part of the nail does not 

 increase in thickness after it has extended beyond the lunula, the ap- 

 parent increase of the nail anterior to this point being derived from the 

 cuticle formed upon the anterior part of the matrix. 



The Matrix of the NaiL 



" A mere inspection, even in the living subject, of the parts situated 

 beneath the nail, is, in consequence of its transparency, sufficient to give 

 a general idea of the relative vascularity of the various parts of its 

 matrix. The upper part of the matrix is seen to present a pale, semi- 

 lunar space, called the lunula. The greater part of the lunula is con- 

 cealed by the semilunar fold of integument which projects over it ; but 

 extending a little below this fold the lower portion of the lunula is 

 visible, presenting a curved border, with its convexity looking down- 

 wards^. Immediately below the lunula, and circumscribing its inferior 



