ELEMENTARY FORMS. 25 



21. Nails, Ungues, 



are four-sided transparent plates of horn, rounded from before to 

 behind, and from side to side, which are placed upon the dorsal 

 surface of the last phalanx of the fingers and toes. They lie 

 with their lateral edges in a fold of the corium. In the same 

 manner the posterior border, the root, the length of which con- 

 tributes one-fifth to one-sixth the length of the entire nail. The 

 root extends about two lines deep into the fold, and is likewise 

 surrounded above and below by the corium. The remaining 

 portion, the body of the nail, is only united on the inferior surface 

 with the corium ; its anterior edge, the point of the nail, quite free. 



22. The epidermis turns up at the root of the nail towards 

 the fold of skin, without going deeper into it. By scalding the 

 epidermis is loosened from the corium, and the nail with it. 



23. The bed of the nail, matrix unguis, is the fold before 

 mentioned, and the surface of the cutis which is covered by the 

 nail. It determines the shape of the nail; is smooth above, below 

 striated like the culis. The striae consist of elevated ridges which 

 pass from before to behind, and upon which are placed cylindrical 

 papillae. The striae become stronger towards the point of the 

 nail and appear through, but the nail itself does not consist of 

 parallel longitudinal fibres. Anteriorly the matrix is richer in 

 vessels than at the root of the nail, where even a whitish semi- 

 lunar mark (lunula) appears, whilst the rest of the nail is pale red. 



The tissue of the nails is only distinguished from that of the Epidermis by 

 its hardness and brittleness, which depends upon Phosphate of Lime (Lauth). 

 It consists of flat, dry, non-nucleated cells, which, deposited in layers and 

 spread out like a membrane, form plates, which run longitudinally. Cor- 

 responding to the Reie Malpighi of the Epidermis, we may here also remark 

 a soft and white layer, particularly in young children. In old people in- 

 dented, undulating transverse striae appear upon the nails, particularly of the 

 toes. 



The nails are first distinguishable in the fifth month of foetal life by their 

 firmness, but even in the third month the fold fixes their limits. 



The growth of the nail takes place from the matrix, and the old parts are 

 pushed forwards by the younger, from the roots. They may reach the length 

 of two inches. In many diseases (e. g., Typhus) they fall out, in others (as 

 Phthisis pulmonalis, Plica Polonicd) they become thickened and curved. After 

 falling out, the surface of the matrix becomes covered with a thin horny layer, 

 which is always more thickened over the recess of the lunula. 



24. Granular Pigment, 



improperly denominated black pigment, is, like the preceding, a 

 nerveless and non-vascular tissue, for which the highly vascular 

 membranes upon which it appears serve as a matrix. 



