142 



SPECIAL HISTOLOGY. 



the English authors, I believe to be identical. They are but the external 

 portion of the corium, which appears, especially around and between the 

 papillae, as a structureless and homogeneous membrane. A separation 

 from the corium of this narrow, and on its under surface, by no means 

 distinctly limited membrane, ought not to be attempted ; for although a 

 distinct membrane in the embryo, it cannot be obtained as a special layer 

 in the adult. (From Kb'lliker's Microsc. Anat. vol. ii. p. 47. DaC.)] 



42. The horny layer (stratum corneum}, forms the external semi- 

 transparent part of the epidermis, which in white people is colorless, 

 and is composed almost wholly of uniform cells metamorphosed into 

 plates. The deepest plates are still very similar to the uppermost cells 

 of the stratum mucosum; but even in the second or third layer we find 

 the widely different epidermic or horny plates. They (Fig. 56, 1, 2, 3) 

 are, in fact, plates of moderate thickness, which 

 in the lower and middle parts of the horny layer 

 retain tolerably regular polygonal (4-5-6-sided) 

 and smooth surfaces ; in the upper layers, on 

 the other hand, they present more irregular 

 outlines, are variously crooked and curved, and 

 thence often appear to be wrinkled and folded. 

 These plates must be regarded as cells, com- 

 pletely flattened, and containing a very minute 

 -. quantity of viscid fluid; and not, as might at 

 \ first be imagined, as homogeneous lamellae, 

 j composed throughout of the same substance ; 

 for by the addition of various reagents, espe- 

 cially of acetic acid and potassa, they swell up 

 and assume the form of vesicles (Fig. 57) ; at 

 the same time, a rudimentary nucleus becomes 

 obvious in a few, particularly in those from the 

 middle and inner layers, but by no means in 

 the majority of them, in the form of a flat, 

 homogeneous, rounded or, elongated corpuscle, 

 0-003-0-004 of a line in length, and 0-002- 

 0-003 of a line in breadth, which, especially 

 when seen from the side, is easily recognized 

 by the dark contours which it then presents. 

 The size of the plates of the ordinary horny 

 layer varies from 0-008-0-016 of a line, and 

 in the outer layer it is commonly somewhat 



FIG. 56. Horny plates of man: 1, without addition, viewed from the surface one with a 

 nucleus; 2, from the side; 3, treated with water, granular and dark; 4, nucleated plate, 

 such as occur on the outer surface of the lalia nrinora and on the glans penis. Magnified 

 350 diameters. 



