140 



SPECIAL HISTOLOGY. 



more marked elevations and depressions, such as the ridges of the palm 

 of the hand and of the sole of the foot, the folds at the joints, muscular 

 insertions, &c. are expressed in it, the latter even more strongly ; on 

 the other hand, the papillae produce either no perceptible projection, or 

 hardly any. 



The epidermis consists of two layers, chemically and morphologically 

 distinct, and which are separated by a tolerably sharp line of demarca- 

 tion, viz., the mucous layer and the horny layer. 



41. The mucous layer, stratum Malpighii, rete or mucus Malpighii 

 (rete mucosum), of many authors, is that part of the epidermis which lies 

 immediately upon the corium, and almost everywhere appears undulated; 

 in many places it is distinguishable even to the naked eye by its color, 

 which is whitish or variously tinged with brown, and it is further cha- 

 racterized by its small, soft, easily destroyed, peculiarly disposed cells. 

 Fig. 555. The form of these cells and their dispo- 



sition are not the same in all localities. 

 The innermost of them (Fig. 55 5), which, 

 without interspersed free nuclei or semi- 

 fluid substance, form a single layer resting 

 immediately upon the free surface of the 

 coriutn, are elongated, and not unfre- 

 quently resemble the cells of cylinder- 

 epithelium ; they are placed perpendicu- 

 larly upon the corium ; their length is 

 about from 0-0033-0-006, their breadth 

 0-0025-0-003 of a line. Upon these im- 

 mediately follow in most places, elongated 

 or even round cells of 0-003-0-004 of a 

 line in many layers ; but in a few locali- 

 ties, as in the hand and foot, at the free 



margin of the eyelids, in the mucous layer of the nails and hairs (vide 

 infra), there are interposed here and there, between the rounded and 

 elongated cells, one, two, or even three layers of similarly elongated and 

 perpendicularly disposed elements, so that the mucous layer, on account 

 of the numerous strata of perpendicular cells, has a striated appearance 

 in its deepest part, under a low power. This character is the more 

 striking, since the other elements of the mucous layer, the further they 

 are followed from the first, round cells outwards, become thinner in 

 another direction, i. e. become horizontally flattened (Fig. 55 c), and 

 finally in the uppermost layers are transformed into thick vesicles, 

 0-006-0-016 of a line broad, and 0-002-0-008 of a line thick. At the 



FIG. 555. Perpendicular section of the skin of the Negro (from the leg), a a, cutis- 

 papillse; b, deepest intensely-colored layer of perpendicularly elongated cells of the stratum 

 mucosum; c, upper layer of the stratum mucosum: rf, horny layer. Magnified 250 diameters. 



