136 



NORMAL HISTOLOGY. 



FIG. 161. 



CHAPTER IX. 



MUCOUS MEMBRANES AND GLANDS. 



ALL passages and cavities directly or indirectly communicating 

 with the exterior of the body and the atmosphere are lined by 

 mucous membranes. 



These structures consist of two parts : the connective-tissue 

 stroma, or tunica propria, and the epithelial covering; the 

 outer surface of the connective-tissue layer is quite usually special- 

 ized to form an extremely delicate basement-membrane, or mem- 

 brana propria, which thus separates the epithelium from the under- 

 lying tissue and forms a third constituent of the mucous membrane. 



The basement-membrane is often scarcely 

 demonstrable as a distinct layer, while 

 in certain organs, as many glands or the 

 hair-follicles, it is highly developed. 



The epithelium of mucous surfaces 

 varies both in character and in arrange- 

 ment, as already described in Chapter II. 

 The proper substance or stroma of the 

 mucous membrane consists of a felt-work 

 of bands of fibrous connective tissue 

 together with net-works of elastic fibres ; 

 these latter may be so plentiful that an 

 especial elastic layer is formed, as in parts 

 of the respiratory tract. Numerous con- 

 nective-tissue cells lie between or upon 

 the fibrous bundles, the flattened plate- 

 like cells forming in many places par- 

 tial linings for the interfascicular lymph- 

 spaces found throughout this layer. 



Not infrequently the surface of the 

 connective-tissue stroma is beset with numerous elevations or papillae, 

 over which the epithelium extends. Such irregularities, when slight, 

 may be present without impressing the free surface of the mucous 

 membrane, since the epithelial layer completely fills the depres- 

 sions between the elevations : when very pronounced, the papillae 

 or folds of the connective tissue produce such conspicuous sculpt- 

 urings of the surface as the papillae of the tongue or the rugae of 

 the vagina. 



Diagram of a typical mucous mem- 

 brane : e, epithelium of free surface con- 

 tinuing into the glandular depression 

 to become the secreting cells ; />, base- 

 ment-membrane separating epithelium 

 and connective-tissue stroma ; s, s, 

 fibre-elastic tissue of tunica propria ; 

 v, blood vessels forming net-works 

 beneath epithelium and around gland. 



