THE SKTX AND ITS APPENDAGES 



389 



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from the derma. The membrane and cells follow the elevations and 

 depressions caused by the papillae. The rest of the stratum germi- 

 nativum consists of large polygonal cells. These cells have well- 

 developed intercellular bridges, which appear as spines projecting from 



the surfaces of the cells. For this _^ _ 



reason the cells are sometimes called ^>==:f^ 3 



"prickle" cells, and the layer, the - | 



''stratum spinosum." The spines * _ ' S 



cross minute spaces between the cells, 

 which are believed to communicate 

 with the lymph spaces of the derma 

 (Fig. 274, c) . The cells of the stratum 

 germinativum are usually in a state 

 of active mitosis. 



(2) The stratum granidosum is well 

 developed only where the skin is thick. 

 It consists of from one to three layers 

 of flattened polygonal cells. The 

 protoplasm of these cells contains 

 deeply staining granules — keratohya- 

 line granules — which probably repre- 

 sent a stage in the formation of the 

 horny substance — keratin — of the 

 corneum cells. The nuclei of these 

 cells always show degenerative 

 changes, and there is reason for be- 

 lieving that this karyolysis is closely 

 associated with the formation of the 

 keratohyaline granules (Fig. 274, b). 



(3) The stratum lucidum is also 

 best developed where the skin is 

 thickest. It consists of two or three 

 layers of fiat clear cells, the outlines of 

 which are frequently so indistinct that 

 the layer appears homogeneous. The 

 transparency of the cells is due to the 



presence of a substance known as eleidin, and derived from the 

 keratohyaline granules of the stratum granulosum (Fig. 274, a). 



(4) The stratum corneum varies greatly in thickness, reaching its 

 greatest development in the skin of the palms and soles. The cells 



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Fig. 274. — ^From Vertical Section 

 through Thick Skin. (jNIerkel- 

 Henle.) a, Stratum hicidum; b, 

 stratum granulosum; c, stratum 

 germinativum, showing intercellular 

 bridges. 



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