114 



ANATOMY FOB, NUKSES. 



[CHAP. IX. 



network of connective tissue containing a variable amount of white and 

 elastic fibres. Where the membrane is thick, this ground substance contains 

 blood-vessels and lymphatics, the lymphatics being exceedingly abundant. 



Serous membranes form closed sacs, one part of which is attached to the 

 walls of the cavity which it lines, the parietal portion, whilst the other 

 is reflected over the surface of the organ or organs contained in the cavity, 

 and is named the visceral portion of the membrane. In this way the viscera 

 are not contained within the sac, but are really placed outside of it, and 

 some of the organs may receive a complete, while others receive only a par- 

 tial or scanty, investment. 



In passing from one part to another the serous membrane in the abdomen 

 frequently forms folds, some of which are designated by special names, such 

 as the mesentery, meso-colon, and omentum. 



FIG. 87. PORTION OF ENDOTHELIUM OF PERITONEUM. (Klein.) a, larger cells ; 

 6, smaller ones, with here and there a pseudo-sterna between. 



The chief serous membranes are the peritoneum, the largest of all, lining 

 the cavity of the abdomen; the two pleurae, lining the chest and covering 

 the lungs ; the pericardium, covering the heart. 



The peritoneum in the female is an exception to the rule that serous 

 membranes are perfectly closed sacs, as it has two openings by which the 

 Fallopian tubes communicate with its cavity. 



The inner surface of a serous membrane is free, smooth, and polished; 

 the inner surface of one part is applied to the corresponding inner surface 

 of some other part, a very small quantity of fluid only being interposed 

 between the surfaces. The organs situated in a cavity lined by a serous 

 membrane, being themselves also covered by it, can thus glide easily against 

 its walls or upon each other, their motions being rendered smoother by the 

 lubricating fluid. 



