9 8 



NAILS. 



[sect. 51 



layer lines the entire under surface of the body and root of the nail, 

 often, also covers a small portion of the upper surface of the root, 

 Fig. 43. and alone forms the above- 



mentioned laminae on the 

 lower surface of the nail. 

 Its thickness varies from 



C032 to O 20 . 



^<? The mucous layer of the 

 nail consists, like that of 

 the epidermis, entirely of 

 nucleated cells, and agrees 

 with it in all essential 

 points, except that in the 

 deep portions it contains 

 several layers of elongated 

 (CT004" to o # oo7"') perpen- 

 dicular cells, which give rise 

 to a striated appearance. In 

 the negro, and, also, not 

 unfrequently in Europeans, 

 the cells of the mucous 

 layer of the nail contain 

 pigment. 



In certain cases, rounded groups of the cells of the mucous layer 

 under the nail are converted into horny plates {Amnion), which, 

 even, may lie entirely in the substance of the cutis ( Virchoiv) ; and 

 this has led to the assumption of special follicles . under the bed of 

 the nail {JRainey). 



The horny layer, or the proper nail substance, is the hard and 

 dry part of the nail which forms its free border and upper 

 portion. The under surface posteriorly at the root is even; more 

 anteriorly, it presents sharp ridges separated by broad grooves, 

 which fit into the furrows of the mucous layer of the nail. These 

 ridges of the proper nail substance appear in cross sections, as 

 pointed processes, of 001" to 002'" in length, which, in general, 

 are most strongly marked at the borders of the nail (o"04"' to 

 o - o6'"), and correspond exactly in number to the laminae on the 

 lower surface of the mucous layer. The upper surface of the 

 substance of the nail is, upon the whole, smooth, yet there are 

 often found, even here, parallel, longitudinal streaks or stripes, as 

 the last and nearly effaced indications of the inequalities of its 

 bed. 



Transverse section through the body of the nail ; mag- 

 nified 2!iO diameters. A. ( litis of the bed of (he nail ; B. 

 mucous layer of the nail ; C. horny layer of it, or proper 

 nail-substance, a. Laminae of the bed of the nail; b. la- 

 minae of the stratum Malpighii of the nail; c. ridges of the 

 nail itself; </. deepest elongated cells of the mucous layer 

 of the nail ; e. upper flat-cells of it ; /. nuclei of the proper 

 substance of the nail. 





