1146 



DIGESTIVE SYSTEM 



its arrangement as made evident in transverse sections of the abdomen at certain 

 levels. 



The first section to be described shows the peritoneum in its simplest condition. 

 This is a transverse section through the body, at about the level of the upper sur- 

 face of the fourth lumbar vertebra, and therefore about the site of the umbilicus 

 (fig. 902). 



Starting on the inner surface of the anterior abdominal wall, the peritoneum is seen to 

 cover the transversalis fascia, and indirectly the anterior abdominal muscles; then, passing 



Fig. 902. — Diagram of Cross-section of the Abdomen, SHO"mNG the Peritoneal 

 Relations AT THE Level OF THE Umbilicus. J.0, Aorta. yl>S. COL., Ascending colon. DES. 

 COL., Descending colon. MES.,_ Mesentery. M. COL., Descending mesocolon. SI, Small 

 intestine. V.C., Vena cava inferior. 



to the left, it lines the side of the abdomen, until it reaches the descending colon. This it covers, 

 as a rule, in front and on the sides, though occasionally it forms a mesocolon. Then it passes 

 over the bodies of the vertebrae with the large vessels upon them, and leaves the back of the abdo- 

 men to run forward and enclose the small intestine, returning again to the spine. The two 

 layers thus form the mesentery, having between them a middle layer [lamina mesenterii propria] 

 containing the terminal branches of the superior mesenteric vessels. It then passes over the 

 right half of the posterior abdominal wall, covering the ascending colon in front and at the 

 sides'only (unless there be a mesocolon), and then passes on to the side and front of the abdomen 

 to the point from which it was first traced. 



Fig. 903. — Diagram of Cross-section of the Abdomen, Showing the Peritoneal Rela- 

 tions AT THE Level of the Foramen of Winslow. (F. of W.) 



Gastro-hepatic omentum 



Gastro-splenic 

 omentum 



In tracing the peritoneum in a section of the body opposite the stomach (fig. 

 903), on a level with the first lumbar vertebra, its course becomes more com- 

 plicated and difficult to follow. 



In the section already given the peritoneum as a simple closed sac can be readily con- 

 ceived; but at the level now expo.sc(l the serous membrane has been so introverted that there 

 appear to be two sacs, one leading from the other, and known respectively as the greater and 

 the lesser sac of the peritoneum. They communicate through the ei)ii)luic foramen (of Winslow). 

 The le.sser .sac [bursa omentalis] is situated behind the stomach, so that on first opening the 

 abdomen no trace of it is to be seen. It extends downward [recessus inferior] between the layers 

 of the great omentum (though this part of the le.sser sac is largely obliterated by adhesion 



