34 



EPIDERMIC TISSUE. 



[SECT. 20. 



Fig. 5. 



2 



tion and absorption. All epidermic structures are non-vascular, 

 and are maintained by a plasma passing into them from the sub- 

 jacent vessels. In most cases, when the older parts of their tissue 

 wear away, it is renewed with extreme facility by the formation of 



new elements in the deeper layers; and 

 even after complete destruction, they are 

 readily reproduced. The epidermic tissue 

 appears in the following forms : — 



A. As proper epidermic tissue. To this 

 division belong — 



i. Horny tissue. — This always consists 

 of compact masses of cells, which are soft 

 in the neighbourhood of the vascular 

 matrix, but when further removed from 

 it, become more firm and hard (cornified), 

 and often lose their original cellular cha- 

 racter and their nuclei, and become ce- 

 mented into horny plates. To this division 

 belong the following organs : — 



a. The Epidermis, or Scarf-skin, which 

 covers the outer surface of the body, and, 

 at the large openings of the internal ca- 

 vities, is continued into their epithelial 

 lining. — It consists of two rather distinctly 

 defined layers, the mucous layer, with soft, 

 roundish, polygonal, sometimes coloured 

 cells, which adapts itself accurately to all the' inequalities of the 

 subjacent corium (which nourishes the epidermis), and passes ex- 

 ternally into the polygonal plates of the horny layer (fig. 5) . 



b. The Nails. — These may be regarded as a modified part of the 

 epidermis, the horny layer of which has attained a still greater 

 degree of firmness, and lies together with the mucous layer upon 

 a special depressed surface of the corium — the bed of the nail 

 — and is, in part, lodged on a special groove — the fold of the 

 nail. 



c. The Hairs. — Filiform epidermic structures, seated upon a 

 vascular papilla, in a special sac — the hair follicle — derived from 

 the corium, and lined by a continuation of the epidermis. The 

 elements in the immediate neighbourhood of this papilla are soft 

 and vesicular, whilst those farther removed from it are transformed 



Scales of the horny layer of the 

 human epidermis, magnified 350 

 times. 1,2,3, from the arm; 2 

 and 3, treated with water; 4, from 

 tha glans penis, with a nucleus. 



