120 



NORMAL HISTOLOGY. 



The epithelium may be squamous or columnar, simple or stratified. 

 Its character is determined largely by the conditions to which it is subjected 

 or by its function. Thus, where a mucous membrane is exposed to the 

 mechanical influences of foreign bodies, the epithelium is commonly strati- 



Epithelium 



Papilla with 

 capillaries 



Tunica proprla 



Epithelium 



Muscularis 

 mucosae 



FIG. 159. Section of oral mucous membrane, showing epithelium and tunica propria. X 300. 



fied squamous, as in the upper part of the digestive tract. Where concerned 

 in facilitating absorption, as in the intestinal tube, it is simple columnar in type. 

 In localities in which the existence of a current favors the function of an 

 organ, either as a means of freeing the surface from secretion or particles of 

 foreign matter, as in the respiratory tract, or of propulsion through a tube, 



as in the oviduct, the epi- 

 thelium is of the ciliated 

 columnar variety. Modi- 

 fications of the epithelial 

 cells, owing to the presence 

 of pigment or of secretion, 

 distinguish certain mucous 

 membranes, as those of the 

 olfactory region and the 

 large intestine respectively. 

 The tunica propria 

 consists of a stroma of inter- 

 lacing bundles of fibro- 

 elastic connective tissue, 

 supporting spindle-shaped 

 or stellate connective tissue 

 cells. The latter commonly 

 lie against the walls of the 

 interfascicular lymph-spaces 

 that occur between the bun- 

 dles of stroma-tissue. In many localities the outer surface of the tunica 

 propria is beset with elevations, the papilla, over which the epithelium 

 extends. When slight, such irregularities may not modify the free surface 

 of the mucous membrane, since the epithelium completely fills the depres- 

 sions between the elevations. When more pronounced, the papillae or 

 folds of connective tissue produce conspicuous modelling of the surface, 



Submucous 

 glands 



FIG. 160. Section of mucous membrane of ossophagus. X 55. 



