IOO NAILS. [SECT. 52. 



resemble very much those of the horny layer of the epidermis, and, 

 in the most inferior layers, are thicker and smaller than in the 

 upper and most superficial. Those of 0012" to o'oi6'" may he 

 considered as of a medium size, — such as are seen on the addition 

 of sulphuric acid, which otherwise has but little action, and at the 

 commencement of the action of potass and soda. 



§ 52. With regard to the relation of the nail to the epidermis, I 

 refer especially to the perpendicular and transverse sections given 

 in figs. 40 and 43. They show, in the first place, that the epi- 

 dermis lies upon the root, the posterior part of the body, and 

 the borders of the nail, and is connected with it under the free 

 border and on the anterior portions of the lateral margins. That is, 

 whilst the mucous layer of the epidermis passes continuously, and 

 without any boundary line, into that of the nail, the horny layer is 

 never properly continued immediately into the true substance of the 

 nail, but partly lies with its lamella? parallel to it, partly meets it 

 at various oblique angles. At the root, the horny layer of the epi- 

 dermis extends more or less deeply into the fold of the nail, and 

 may here reach back to the posterior border of the root ; it advances, 

 also, as a thin layer towards the termination of the lunula, or the 

 commencement of the body, where it becomes very fine. In this 

 situation, the cells are, anteriorly and posteriorly, placed parallel to 

 the surface of the nail ; but in the middle, where the nail is thickest, 

 they are set obliquely or perpendicularly upon it. The relation 

 is similar at the free border of the nail, where the horny layer 

 abuts, partly with more horizontal, partly with oblique lamella?, 

 upon the end of the lower surface of the body of the nail, and is, 

 perhaps, continued upon the commencement of its free border. 

 Lastly, on the lateral borders, the horny layer anteriorly lies under 

 the nail in the form of horizontal layers, and, more posteriorly, 

 presents the same relations as at the i"oot, or is simply applied to 

 the border of the nail. The horny layer of the epidermis thus 

 forms a sort of sheath for the nail, which somewhat resembles the 

 sheath of the hair, although it is much more incomplete. If we 

 compare the nail with the epidermis, we find, in the structure of 

 its mucous layer, no peculiarity of any consequence; but it is 

 different with the horny layer, which is distinguished from the 

 epidermis by its more consistent, more flattened, and intimately 

 coherent as well as nucleated cells, which are also chemically dif- 

 ferent. Nevertheless, the agreement of the latter structure is so 

 great, that the proper nail may be, as, indeed, it has long been, 



