474 ABDOMEN 



second lumbar vertebra to the right iliac fossa, crossing in its 

 course the third part of the duodenum, the abdominal aorta, 

 the inferior vena cava, the right ureter, and the right psoas 

 magnus muscle. Its total length is about six inches. Its 

 anterior border, which is attached to the intestine, is necessarily 

 as long as the part of the gut to which it is attached, that is, 

 about twenty-two feet ; but this great length is not at first 

 apparent because the mesentery is thrown into folds like a 

 frill (Fig. 182) and the coiled condition of the gut is due to 

 this arrangement. Thus the mesentery is markedly fan-like, 

 and its length, from its root to its intestinal attachment, at 

 its longest part is about six inches after death and when the 

 body is hardened, but it may be considerably longer during 

 life. 



The two layers of the peritoneum of the mesentery are 

 not in apposition. They are separated by a variable amount 

 of fat and areolar tissue in which lie the superior mesenteric 

 artery and its branches to the jejunum and ileum, the corre- 

 sponding veins, the accompanying nerves, the lymph vessels 

 passing from the gut which are called lacteals, and numerous 

 lymph glands. The jejunum and ileum are generally con- 

 sidered as lying in the free border of the fold. 



Occasional Peritoneal Fossae. Before the dissection of the mesentery 

 is commenced the dissector should look for certain peritoneal fossae which 

 are occasionally present. Some of these fossae lie near the terminal part 

 of the duodenum, others near the termination of the ileum, and one is associated 

 with the root of the pelvic meso-colon. 



The chief fossae in the region of the duodenum are the duodeno-jejunal, 

 the upper duodenal, the lower duodenal, the par a- duodenal, and the retro- 

 duodenaL 



The duodeno-jejunal or meso-colic fossa lies immediately above the 

 duodeno-jejunal flexure of the small intestine and passes upwards into the 

 root of the transverse meso-colon. The upper and the lower duodenal fossce 

 lie at the left side of the terminal portion of the duodenum, the upper 

 passing upwards towards the upper end and the lower passing downwards 

 towards the lower end. The -para- duodenal fossa lies a little more to the 

 left. It is a pouch of peritoneum pushed laterally behind the inferior 

 mesenteric vein, and its mouth looks towards the terminal part of the 

 duodenum. The retro-duodenal fossa passes upwards behind the terminal 

 part of the duodenum. 



The fossae in the region of the ileo-coecal junction are the anterior ileo- 

 c&cal, the posterior ileo-ccecal or ileo-appendicular, and the retro-ccecal or 

 retro-colic. The anterior ileo-caecal fossa lies behind a small fold of 

 peritoneum which crosses the front of the ileo-ccecal junction. Its mouth is 

 directed downwards and to the left. The inferior ileo-caecal fossa also opens 

 towards the left. It is bounded to the right by the caecum, in front by the 

 terminal part of the ileum and the adjacent part its mesentery, behind by 

 the mesentery of the appendix, and below by the plica ileo-caecalis, a fold 



