ABDOMINAL CAVITY 313 



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. 145) and the coiled condition of the gut is due to 

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

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

 its longest part, is about 15 cm. (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, 

 called lacteals, passing from the gut, and numerous lymph 

 glands. The jejunum and ileum lie in the free anterior 

 border of the fold. 



The amount of fat between the two layers of the mesentery 

 varies, not only in different subjects but also in different 

 parts of the mesentery. The amount is greatest near the 

 root of the mesentery and smallest near the gut. The 

 difference referred to is most marked in the upper part of the 

 mesentery, near the duodena -jejunal flexure, where the 

 amount of fat is so small that semi-translucent areas or 

 peritoneal windows are recognisable between the loops of 

 anastomoses formed by the jejunal branches of the superior 

 mesenteric artery ; near the lower part of the ileum, where 

 the fat is more abundant, the " windows " cannot be seen. 

 The difference is taken advantage of by the operating surgeon 

 who wishes to know whether he is dealing with an upper or 

 a lower coil of the small intestine. 



Occasional Peritoneal Fossae. Before the dissection of the mesentery 

 is commenced the dissector should look for certain peritoneal fossce which 

 are occasionally present. Some of the 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 dttodeno-jefunal, 

 the superior duodenal, the inferior duodenal, the para- 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 superior and the inferior duodenal 

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

 passing upwards and the lower passing downwards. 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 



