STKATIFIED EPITHELIUM 27 



approach the free surface; on the other hand, their transverse 

 diameter, that parallel to the surface of the epithelial membrane, 

 is correspondingly increased. The deepest cells of stratified epi- 

 thelium those which rest upon the basement membrane are 

 elongated in their vertical diameter, and possess an irregularly 

 columnar shape.* Their nuclei are likewise elongated, oval or 



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FIG. 26. STRATIFIED EPITHELIUM FROM THE HUMAN ESOPHAGUS. 

 a, basement membrane ; 6, connective tissue. Hematein and eosin. x 410. 



elliptical in shape. Superficial to these, but still in the deeper 

 layers, are polyhedral cells with spherical nuclei, which are known 

 as prickle cells because of their prominent intercellular bridges. 

 Superficial to the prickle cells, the epithelial cells become progres- 

 sively more flattened, until at the surface they are mere scales. 

 This gradual transition from columnar and polyhedral cells below, 



* In the skin of brunettes and the dark-skinned races, and in the epithelium of 

 the skin of the scrotum, peri-anal region, and areolae of the breasts, these cells 

 contain small granules of the pigment to which the color of the cuticle is due. 

 This columnar cell layer is then described as the layer of pigment epithelium. 



