OF THE NAILS. 167 



the plates of the proper nail which border upon the mucous layer are 

 much less flattened than in the interior and on the surface, which also 

 indicates that they are developed upon the spot. In conclusion I must 

 add, in support of my view, that it is only in this way, that it becomes 

 explicable why the under surface of the proper nail substance upon the 

 root of the nail is almost smooth, while on the body of the nail it pre- 

 sents more or less prominent ridges. The origin or increase of these 

 ridges demonstrates clearly that nail-substance is also formed here. 

 Corresponding with these ridges and with the grooves between them, we 

 also find that the lowest layers of the nail plates, which are quite hori- 

 zontal upon the root, run with an undulating course upon the body (Fig. 

 61). The general result then is, that whilst the formation of the nail 

 goes on especially at its root, yet that plates are added to the body of 

 the nail from below, though more slowly and scantily, thus producing the 

 anterior thickening, or at least preventing the necessary thinning of the 

 nail anteriorly. It is to be remarked further, that the development of 

 nail-substance takes place in all parts of the middle line of the nail 

 more rapidly than in the lateral portions, which, anteriorly, are almost 

 as thin as in the root, though they possess longer processes below. But 

 even there, substance must be added to the body of the nail, because it 

 becomes broader anteriorly. 



The plates of the substance of the nail once formed, alter in certain 

 respects, as they are pushed forwards and upwards by those which come 

 after them. In the first place, their nature becomes altered in a man- 

 ner which is little understood, the change consisting partly in the depo- 

 sition of more phosphate of lime, partly in a solidification (conversion 

 into horn) of their organic elements, particularly of the cell-mem- 

 branes, in consequence of which, from being soft, as at the root and 

 under surface of the nail, they become gradually harder and harder. 

 In the second place, like the horny cells of the epidermis, they are 

 very considerably flattened, and at the same time increase somewhat in 

 their longitudinal and' transverse diameters ; finally, they coalesce more 

 completely, so that they cannot be separately recognized, without the 

 action of reagents, in the upper and anterior parts of the nail, which 

 appear to be composed of nothing but a homogeneous substance which 

 tears in all directions; whilst in the lower parts the separate nail- 

 plates are, at least, indicated, and are occasionally tolerably distinct. 

 On the other hand, the nuclei of the nail-plates do not disappear, and 

 in this lies a characteristic distinction between the horny layer of the 

 nail and that of the epidermis. They are to be seen in perpendicular sec- 

 tions, of fresh nails, and after treatment with caustic soda, and even in 

 the most superficial layers, though somewhat smaller and flatter than in 

 the deep layer. It follows then, that certain metamorphoses go on in 

 the proper substance of the nail, which as in the epidermis, are to be 

 ascribed to a peculiar growth and vital process in the nail-cells them- 



