FIG. 162. 



MUCOUS MEMBRANES AND GLANDS. 



Mucous membranes may be invaded to a greater or less degree 

 by lymphoid cells, as in many localities in the digestive tract ; 

 sometimes, as in the villi of the small intestine, the tissue assumes 

 still more closely the lymphoid type, a delicate connective-tissue 

 reticulum supporting the lymphoid cells. 



The membrana propria, or basement-membrane, usually 

 appears as a delicate homogeneous line beneath the 

 epithelium. It must be regarded as a modification 

 of the connective tissue, and when well developed, 

 after suitable staining with silver, appears as a more 

 or less complete covering of flattened, endothelioid 

 cell-plates. The deeper layers of the mucous mem- 

 brane fade away into the surrounding areolar tissue 

 or into the adjacent submucosa ; sometimes, how- 

 ever, the mucosa is limited by a delicate zone of 

 involuntary muscle, the muscularis mucosae, 

 consisting often of two distinct, although delicate, 

 layers of muscle-cells. 



Mucous membranes are usually provided with 

 glands, which in their simplest type are depressed portions of the 

 general mucous surface, lined with modified epithelium the secreting 

 cells. A single cell may constitute an entire gland, instances of such 

 arrangement being found in the unicellular glands of the lower 

 forms ; the familiar goblet-cells are, in fact, such structures ; it is, 

 however, the more developed forms of secreting apparatus which 

 the term ' ' gland' ' usually represents. 



Glands are of two chief varieties, tubular and saccular, each 

 of these occurring as simple and compound. Simple tubular 



Plate-like endothe- 

 lioid connective-tissue 

 cells constituting base- 

 ment-membrane. 



Diagram illustrating the forms of glands : A , simple tubular ; B, compound tubular ; C, modified 

 (coiled) tubular; D, simple saccular; E, compound saccular, or racemose. 



glands are frequent, the peptic glands and the mucous follicles of 

 the intestines being well-known examples. Compound tubular 

 glands vary in complexity, from a simple bifurcation of the fundus, 



