STRATIFIED EPITHELIUM 



43 



II. STRATIFIED EPITHELIUM 



1. STRATIFIED SQUAMOUS EPITHELIUM 



This variety of epithelium occurs as a membrane of varying thickness 

 but always comprising several cell layers. A straight line perpendicular 

 to its free surface would penetrate from five to thirty or more epithelial 

 cells. But while there is a wide diversity in the thickness of the epithelial 

 layers, the character of the cells at any given level is very nearly con- 



FIG. 49. STRATIFIED EPITHELIUM FROM THE HUMAN ESOPHAGUS. 

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



stant. Thus the deeper cells, those nearest the basement membrane, are 

 nucleated, of soft consistence and may contain mitotic figures, indicating 

 that it is at this level that cell reproduction is most active. Toward the 

 surface of the membrane the cells become progressively of firmer con- 

 sistence, so that the most superficial ones present a horny appearance as 

 a result of the gradual keratization of the cytoplasm during the progress 



