72 GLANDS; MUCOUS AND SEROUS MEMBRANES. 



Fatty glands : The sebaceous and mammary glands produce 

 the fatty constituents of their secretions by a fatty degenera- 

 tion or infiltration of the protoplasm of the gland-cells. The 

 cell-bodies become swollen and infiltrated with globules of 

 fat, which are later discharged into the lumen. 



Mucous membranes : The mucous membranes are those 

 lining the spaces within the body that communicate directly or 

 indirectly with the exterior. There are three distinct continu- 

 ous tracts of mucous membrane : the respiratory-alimentary, 

 the genito-urinary, and the mammary. At the orifices and 

 along portions of these tracts the mucous membrane is a con- 

 tinuation of and similar in structure to the skin. In some situ- 

 ations the function of mucous membrane, like that of the skin, is 

 chiefly protective, and in these places it most resembles the 

 skin. In other situations mucous membrane has special 

 functions, and its structure varies accordingly. 



Mucous membrane is usually described as being, in general, 

 composed of two layers, the mucosa and the submucosa, 

 which are commonly situated on a muscular or fibrous bed. 



The mucosa consists of : (a) a superficial layer of epithelium, 

 stratified squamous, columnar, or ciliated, corresponding to 

 the epidermis of the skin. Beneath the epithelium is (6) the 

 tunica propria, a layer of connective tissue, white-fibrous or 

 elastic, corresponding in general to the corium of the skin, but 

 varying greatly in different situations. Its upper or outer 

 surface is condensed to form a basement-membrane for the 

 support of the overlying epithelium. Beneath the tunica 

 propria in many places is (c) the muscularis mucosce, a thin 

 sheet of involuntary muscle-cells, some longitudinally arranged, 

 some transverse ; it separates the mucosa from the submucosa, 

 and has no analogue in the skin. 



The submucosa is a layer of areolar tissue underneath the 

 mucosa, corresponding to the areolar subcutaneous tissue ; it 

 contains the larger vascular, lymphatic, and nerve branches, 

 which send smaller twigs and capillaries into the tunica 

 propria. The looseness of the subrtiucosa permits some play 

 or movement of the mucous layer on the layers beneath. 

 Lymphoid tissue, diffuse or circumscribed, is present in many 

 situations in the submucosa or tunica propria. 



