THE SKIN 199 



they are thus irregularly cylindrical in shape. It is these cells 

 which in the pigmented portions of the body, i. e., areolae of the 

 nipples, scrotum, circumanal region, etc., and in the skin of bru- 

 nettes and the colored races contain the pigment which gives rise 

 to the darkened color of the skin. The processes of mitotic cell 

 division are very active in these columnar cells, and they, with the 

 adjacent portion of the prickle cell layer, form the stratum germi- 

 nativum of Fleming, in which the regeneration of the epidermis 

 occurs. The cylindrical cells are firmly united to the basement 

 membrane by delicate cytoplasmic fibrils, the intercellular bridges. 

 Their nuclei are ovoid in shape, and vesicular in appearance. 



Prickle Cell Layer (Stratum Spinosum, Stratum Filamentosum 

 of Ranvier). Superficial to the cylindrical cells is a stratum of 

 polyhedral epithelium which extends inward between the adjacent 

 papillae of the corium (interpapillary region of the epidermis), and 

 is therefore thick in these portions, but is relatively much thinner 

 over the apices of the dermal papillae (suprapapillary portion of 

 the epidermis). 



The polyhedral cells of this layer contain a soft granular cyto- 

 plasm and a very chromatic, though vesicular, spheroidal nucleus. 

 They are separated from one another by narrow intercellular 

 spaces which are bridged across by innumerable delicate cyto- 

 plasmic fibrils. These fibrils connect adjacent cells and are fre- 

 quently continued without interruption through one, two, or even 

 three or four neighboring cells. Their course is characteristically 

 curved, the convexity being directed toward the nucleus. Those 

 portions of the numerous cytoplasmic fibrillae which span the 

 intercellular spaces form the so-called intercellular bridges. It is 

 because of the resulting spinous appearance that the polyhedral 

 cells have been termed prickle cells (Schultze). 



In the thinner portions of the epidermis the prickle cells are 

 immediately covered by several layers of hard flattened cells whose 

 nuclei have partially or wholly disappeared, and whose cytoplasm 

 has been changed into a horny, keratin containing mass. The 

 flattening and desiccation of these cells becomes more pronounced 

 as they approach the surface. In the thin portions of the epi- 

 dermis the change from the prickle cell layer to the horny layer 

 is abrupt. 



In the thicker portions of the epidermis, as in the palms of the 

 hands, the change is more gradual, and results in the appearance 

 of two additional cell layers, in the cytoplasm of whose cells are. 



