The Digestive System. 29 



Mucous and Serous Membranes. Widely differing as 

 these membranes do in their location and functions, for 

 our purposes we may consider them somewhat alike in 

 construction. Mucous membranes may be said to line 

 open cavities or tubes, such as the nose, mouth, the entire 

 digestive tract, the breathing (respiratory tract), and 

 the genito-urinary tract (containing the organs of repro- 

 duction and the kidneys, bladder, urethra, etc.) The 

 main point of interest regarding the mucous membranes 

 probably relate to that part of the intestinal tract in 

 which absorption takes place, and under which heading 

 the forms taken by the mucous membrane, for short often 

 written m. m., will be described. 



Serous membranes, on the other hand, consist of two 

 layers, and line closed cavities, parts of the animal body 

 not communicating with the outside world. "While ser- 

 ous membranes have a wide distribution in the body, 

 yet in that distribution they lose their identity, becom- 

 ing known according to their location, e. g. , the serous 

 membrane of the abdominal cavity is termed the peri- 

 toneum, in it are suspended the intestines ; the inner 

 layer of the peritoneum is in one part named the omen- 

 tum, at another the mesentery. The serous membrane 

 of the lung cavity is the pleura, that of the heart the 

 pericardium. As a result of inflamation of serous mem- 

 branes, fluid is thrown out between the layers, e.g., water 

 in the chest (hydrothorax) after pleurisy. The serous 

 membranes should always be examined in post mortems 

 of suspected tuberculous animals. 



The digestive tract is practically a long hollow tube 

 running from one end of the body to the other, having 



