52 



NORMAL HISTOLOGY. 



is no sharp structural line separating cubical from pavement-epithe- 

 lium. Functionally, pavement-epithelium is a much less active 

 tissue than the cubical variety. 



3. Columnar Epithelium (Figs. 31, 32, 33). The cells of this 



FIG. 31. 



Columnar epithelium. From tongue of pseudopus. (Seiler.) a, three cells with intact cyto- 

 plasm, except the central one, which contains a vacuole ; 6, three cells of which the dis- 

 tal ends contain drops of fluid (vacuoles) or of metaplasm. 



form of epithelium are of a general columnar or prismatic shape 

 and possess a single nucleus and a cytoplasm that is usually dis- 

 tinctly granular. They are arranged with their long axes parallel 

 to each other, so that their free ends form the surface of the epithe- 



FIG. 32. 



FIG. 33. 



Columnar epithelium. 

 Fig. 32. From small intestine of the mouse. (Paneth.) a, pyramidal reserve cell, nucleus not 



included in section ; b, "goblet" cell, enclosing a large drop of secretion. 

 Fig. 33. From small intestine of the mouse. (Paneth.) Columnar epithelial cells seen from 



above : b, goblet-cell, the mucous contents darkened by the hardening process ; s, s, highly 



granular cells which have recently discharged their secretion. 



lium, while their deeper ends either rest upon the tissues beneath 

 the epithelium or upon other epithelial cells of diiferent shape 

 which form one or more layers between the columnar cells and the 

 underlying tissues. When they rest directly upon the tissues 

 beneath there are usually other epithelial cells of a pyramidal or 

 oval shape which may be regarded as immature cells ready to take 

 the place of such fully developed cells as may become detached or 

 destroyed. The presence of these cells occasions a narrowing of 



