THE PERITONEUM. 



The hepatic artery reaches the duodenum through its mesentery, and crosses the 

 left side of the gut, to which it gives branches. Thence it runs in or near the edge 

 of the lesser omentum at the foramen of Winslow to the portal fissure. 



FIG. 1476. 



Gastro-pancreatic fold 



Vestibule of lesser sac 



Lesser or gastro-hepatic 

 omentum. 



Lieno-renal fold 



c 



Lesser sac of 

 . peritoneum 



Gastro-splenic omentum 



' Greater omentum 



Schematic reconstruction, showing relations of peritoneal layers in vicinity of lesser sac. Upper surface of duo- 

 denum (>) at floor of foramen of Winslow lies at deeper level than plane of section. It is to be noted that only that 

 art of peritoneum covering posterior wall of lesser sac is derived from greater omentum which lies to left of aorta, 

 eginning at gastro-pancreatic fold. /., liver ; St, stomach ; Sp, spleen ; /*, pancreas ; A", kidney. 



The Posterior Mesentery: Part II. This is that part of the peritoneum 

 derived from the original mesentery of the jejuno-ileum, the caecum, and the ascend- 

 ing and transverse colon. Its artery is the superior mesenteric. If the transverse 

 colon with the greater omentum be turned upward and the small intestine to the right, 

 the left side of the mesentery of the jejuno-ileum is seen running from the left of the 

 top of the body of the second lumbar vertebra to the right sacro-iliac joint. At 

 the beginning this is attached to the lower side of the gut, where it makes a sharp 

 flexure at the origin of the jejunum from the end of the duodenum. This flexure 

 lies directly in front of the aorta, which usually lies covered with peritoneum at the 

 back of the abdomen, with the fourth part of the duodenum to the right of it. (This 

 relation is more fully described with the duodenum (page 1647). The line of attach- 

 ment of the mesentery (Fig. 1477) descends over the fourth part of the duodenum, 

 crossing the third part and the inferior vena cava. The greatest breadth of the mes- 

 entery to the free border is from 20-23 cm - (8-9 in.). It reaches its full breadth 

 almost at once after its origin. Usually it becomes very narrow perhaps only 1 2 mm. 

 at its termination ; but this varies much,, as does also the point of that termina- 

 tion. The connective tissue between the layers is thickest and the lymph-nodes most 

 numerous near the attached part. Except in very fat subjects, there is little between 

 the layers of peritoneum besides the vessels, within an inch or so of the gut. The 

 superior mesenteric artery can be felt at the top, entering it from under the lower 

 border of the pancreas. The peritoneum can be followed at any point across from 

 the left to the right side of the mesentery. From the latter it is followed along the 

 posterior wall to the kidney and the ascending colon, lying on the front of the 

 latter, where they are in contact. The membrane crosses the ascending colon, 

 leaving its posterior surface without covering attached to the parts behind it, and 

 completely envelops the caecum, passing on the left into the mesentery. Very 

 often the peritoneum is carried for an inch or two behind the lower part of the 

 ascending colon. It then passes into the left flank and the pelvis without incident. 

 . Development shows that this is a departure from the original condition, in which the 



