THE SKIN AND ITS APPENDAGES. 263 



recently formed and most actively growing elements, the deepest of 

 which, next the corium, are perpendicularly placed and possess a 

 distinct columnar character. The irregular and often slightly 

 expanded bases of the deepest cells rest upon the thin basement- 

 membrane, while their outer ends are surrounded by the more poly- 

 hedral elements. 



Next the layer of columnar cells the elements become broader and 

 polyhedral in form and possess the delicate protoplasmic spines 

 characteristic of prickle -cells. 



The elements of the succeeding horny layer stand in marked 

 contrast to those of the soft underlying Malpighian stratum, owing 

 to the production of keratin within the protoplasm and the desicca- 

 tion of the cells. These influences are seen in the superficial layers, 

 in the disappearance of the nucleus, and in the reduction of the once 

 large polyhedral cells into the thin compressed horny plates of the 

 outer layer. 



At the inner border of the horny layer lies a thin band of cells, 

 conspicuous on account of the marked granular appearance of their 

 protoplasm ; these constitute the stratum granulosum, and con- 

 tain .granules of eleidin, a peculiar substance, staining intensely in 

 certain dyes, and bearing a close relation to the keratin of the more 

 superficial layers. 



At the outer border of the granular stratum the horny elements 

 begin ; those lying next the stratum granulosum, however, are in- 

 completely transformed into horny substance, and appear as an ill- 

 defined narrow zone, the stratum lucidum, which contrasts strongly 

 with the darker granular layer. Superficial to the clear zone lie the 

 characteristic cells of the stratum corneum ; these epithelial ele- 

 ments are enlarged and without nuclei, the outermost cells being 

 compressed flattened horny scales, which after desiccation un- 

 dergo desquamation and mechanical abrasion. 



Over those parts of the cutaneous surface where the epidermis is 

 well developed and destitute of hairs, the stratum corneum differs 

 somewhat from its usual condition in being composed chiefly of large 

 distended bladder-like cells, which probably represent the superficial 

 epitrichial layer of the embryonal skin. Where the epidermis is 

 thin the stratum granulosum is very imperfect, while the stratum 

 lucidum is wanting; under these conditions the superficial cells 

 rapidly dry and become thin horny plates. 



Pigment-granules are widely distributed throughout the epider- 

 mis, but it is especially within the deeper layers of the stratum Mal- 

 pighii that the larger accumulations are found to which the dusky hue 

 of the skin of many races is due. The pigment-granules do not origi- 

 nate within the epithelial elements, but are conveyed to the epidermis 



