SPLANCHNOLOGY 



157 



visceral portion; the two surfaces contacting, and gliding upon each 

 other, are lubricated by a fluid secretion contained in the sac; hence 

 one use of these membranes is to prevent friction between the walls 

 of cavities and the organs contained therein. - Serous membranes 

 line the abdominal cavity, pericardium, cavities of the 'heart and is 

 continuous throughout the vascular structures. 



Fig. 39. — A transverse section of body of hen through 15, Pig. 34. R, Right 

 side. L, Left side. 1, Spinal cord. 2, Esophagus. 3, Trachea. 4, Skin. 5, 

 Pectoral muscles. 



The serous membrane besides covering the external surface of the 

 viscera, double folds pass from one organ to another, or from an 

 organ to the parietes of the cavity. These double folds of the 

 peritoneum are known as ligaments, or as mesenteries. In Ugaments 

 the two folds are strengthened by an interposed layer of fibro-elastic 

 tissue. A mesentery is a broad, double fold of peritoneum, attached 

 to the abdominal parietes above, and containing a portion of the 

 intestine in its free or remote extremity. Between its folds we find 

 blood-vessels, nerves, and lymphatics or lacteals, hence it permits 



