718 



STRUCTURE OF EPIDERMIS. 



398). In Serous membranes, on the other hand, whose function is 

 simply protective, the supply of Blood-vessels is more scanty. 

 561. Epidermic and Epithelial Cell-layers. — The Epidermis or 



' Cuticle ' covers the -whole 

 ■p IG 3 H.g exterior of the body, as a thin 



semi-transparent pellicle, which 

 is shown by Microscopic ex- 

 amination to consist of a series 

 of layers of Cells, that are 

 continually wearing-off at the 

 external surface, and renewed 

 at the surface of the True 

 Skin ; so that the newest 

 and deepest layers gradually 

 become the oldest and most 

 superficial, and are at last 

 thrown-off by slow desquama- 

 tion. In their progress from 

 the internal to the external 

 surface of the Epidermis, the 

 cells undergo a series of well 

 marked changes. When we 

 examine the innermost layer, 

 we find it soft and granular ; 

 consisting of germinal cor- 

 puscles in various stages of 

 development into cells, held- 

 Vertical Section of Skin of Finger : together by a tenacious semi- 

 — a, Epidermis, the surface of which fluid substance. This was 

 shows depressions a, a, between the formerly considered as a dis- 

 eminences b, b, on which open the ti t t[ and supposed 



Perspiratory Ducts s; at m is seen , , ., ' ,. , ^ ., 



the deeper layer of the Epidermis, to be the peculiar seat of the 

 or Stratum Malpighii :— b, Cutis colour of the skin ; it received 

 Vera, in which are imbedded the the designation of Malpighian 

 Perspiratory Glands d, with their , J f . _ BW)BM1 r S> 



Ducts e, and aggregations of Fat- la y er or ? ete mucosum - ra! f- 

 cells /,• g, Arterial twig supplying ing outwards, we find the cells 

 the Vascular papillae p ; t, one of the more completely formed ; at first 

 Tactile papillae with its Nerve. near]y spherical in shape , but 



becoming polygonal where they 

 are flattened one against another. As we proceed further towards 

 the surface, we perceive that the cells are gradually more and more 

 flattened until they become mere horny scales, their cavity being 

 obliterated ; their origin is indicated, however, by the Nucleus in 

 the centre of each. This change in form is accompanied by a 

 change in the Chemical composition of the tissue, which seems to 

 be due to the metamorphosis of the contents of the Cells into a 

 Horny substance identical with that of which Hair, Horn, Nails, 

 Hoofs, &c, are composed. — Mingled with the Epidermic cells, we 



