DISSECTION OF THE ABDOMEN. 309 



extending between this membrane and the spinal column, that is, ontsich 

 the serous sac. Conceive next this tube of intestine let gradually down 

 until It extended through the cavity about its centre. In this descent 

 the nitestme would first surround itself with peritoneum ; and then, as 

 It sank farther, it would stretch the membrane so as to form a kind of 

 slmg passnig iipwards to the point from which it started. The membrane 

 would now have lost its simplicity, for it would have a parietal division 

 contmumg to line the abdominal walls, and a visceral portion surround- 

 ing the tube of intestine. Moreover, these two portions would be con- 

 tinuous with each other along the sling-like portion suspending the tube. 

 Lastly, imagine the tube of intestine to grow and branch, so as to com- 

 pletely fill up the abdominal cavity, and obliterate the space between 

 the parietal and visceral peritoneum. This, of course, would not destroy 

 the continuity of the serous sac, although it would complicate it so that 

 Its continuity would be difiicult to trace. 



All the organs, then, that actually project into the abdominal cavity 

 get a more or less complete investment of visceral peritoneum ; and, in 

 the case of each organ, this visceral covering is traceable on to a neigh- 

 bouring organ, or on to the walls of the abdomen. Where organs are 

 contiguous to each other or to the abdominal parietes, the peritoneum 

 may pass directly from the one organ to another or to the abdominal 

 parietes ; but, at other times, the connection between the parietal and 

 visceral peritoneum is traceable along bands or folds analogous to the 

 sling-like membrane that was formed in the imaginary case. These 

 folds constitute the various mesenteries, omenta, and peritoneal liga- 

 ments that will hereafter be described. 



Although there is but a single peritoneal sac, this sac is so disposed 

 that it forms two compartments, termed respectively the greater and 

 lesser cavities of the peritoneum, the latter being also known as the 

 cavity of Winsloiv. The greater cavity is that which is exposed when 

 the inferior wall of the abdomen is removed, the lesser cavity is situated 

 behind the stomach, and is separated from the greater cavity mainly by 

 the omentum. 



The Great or Gastro-colic Omentum. — Passing backwards among the 

 intestines, on the left side of the abdomen, there will have been noticed 

 a large lace-like membrane, which is the rp-eat omentum, epiploon, or web. 

 In order to examine its connection, the caecum and double colon should 

 be thrown backwards over the right flank, and the coils of the single 

 colon arranged over the left flank. The coils of small intestine should 

 at the same time be gathered backwards and to the right. The omen- 

 tum is composed of two layers of peritoneum, which include between 

 them vessels and a varying quantity of fat. This fat is deposited 

 mainly along the course of the vessels, leaving, except in obese subjects. 

 Intervening transparent areas that are free from fat ; and it is from this 



