904 THE ORGANS OF DIGESTION. 



est in connection with the possibility of the occurrence of retro-peritoneal hernia. 

 One of these is the lesser sac of the peritoneum, which may be regarded as a recess 

 of peritoneum through the foramen of Winslow, in which a hernia may take place, 

 but there are several others, of smaller size, which require mention. 



These recesses of fossae may be divided into three groups, viz. : (1) the duodenal 

 fossae ; (2) pericaecal fossae ; and (3) the intersigmoid fossa. 



1. Duodenal Fossce. Moynihan has described no less than nine fossae as occur- 

 ring in the neighborhood of the duodenum. Three of these are fairly constant, and 

 are the only ones which require mention, (a) The inferior duodenal fossa is the 

 most constant of all the peritoneal fossae in this region, being present in from 70 to 

 75 per cent, of cases. It is situated opposite the third lumbar vertebra on the left 

 side of the ascending portion of the duodenum. The opening into the fossa is 

 directed upward, and is bounded by a thin sharp fold of peritoneum with a concave 

 margin, called the inferior duodenal fold. The tip of the index finger introduced 

 into the fossa under the fold passes some little distance up behind the ascending or 

 fourth portion of the duodenum. (6) The superior duodenal fossa is the next most 

 constant pouch or recess, being present in from 40 to 50 per cent, of cases. It 

 often coexists with the inferior one, and its orifice looks downward, in the opposite 

 direction to the preceding fossa. It lies to the left of the ascending portion of the 

 duodenum. It is bounded by the free edge of the superior duodenal fold, which 

 presents a semilunar margin ; to the right it is blended with the peritoneum cover- 

 ing the ascending duodenum, and to the left with the peritoneum covering the peri- 

 renal tissues. The fossa is bounded in front by the superior duodenal fold ; behind 

 by the second lumbar vertebra ; to the right by the duodenum. Its depth is 2 cm., 

 and it terminates in the angle formed by the left renal vein crossing the aorta. This 

 fossa is of importance, as it is in relation with the inferior mesenteric vein : that is 

 to say, the vein almost, always corresponds to the line of union of the superior 

 duodenal fold with the posterior parietal peritoneum, (c) The duodeno-jejunal fossa 

 can be seen by pulling the jejunum downward and to the right, after the transverse 

 colon has been pulled upward. It will appear as an almost circular opening, look- 

 ing downward and to the right, and bounded by two free borders or folds of perito- 

 neum, the duodeno-mescocolic ligaments. The opening admits the little finger into 

 the fossa to the depth of from 2 to 3 cm. The fossa is bounded above by the 

 pancreas, to the right by the aorta, and to the left by the kidney ; beneath is the 

 left renal vein. The fossa exists in from 15 to 20 per cent, of cases, and has never 

 yet been found in conjunction with any other form of duodenal fossa. 



2. Periccecal Fossce. There are at least three pouches or recesses .to be found 

 in the neighborhood of the caecum, which are termed periccecal fossae. (1) The 

 ileo-colic fossa (superior ileo-caecal) is formed by a fold of peritoneum, the ileo-colic 

 fold, arching over a branch of the ileo-colic artery, which supplies the ileo-colic 

 junction, and appears to be the direct continuation of the artery. The fossa is a 

 narrow chink situated between the ileo-colic fold in front, and the mesentery of the 

 small intestine, the ileum, and a small portion of the caecum behind. (2) The 

 ileo-ccecal fossa (inferior ileo-caecal) is situated behind the angle of junction of the 

 ileum and caecum. It is formed by a fold of peritoneum (the ileo-caecal fold or 

 bloodless fold of Treves), the upper border of which is attached to the ileum, oppo- 

 site its mesenteric attachment, and the lower border, passing over the ileo-caecal 

 junction, joins the mesentery of the appendix, and sometimes the appendix itself; 

 hence this fold is sometimes called the ileo-appendicular. Between this fold and 

 the mesentery of the vermiform appendix is the ileo-caecal fossa. It is bounded 

 above by the posterior surface of the ileum and the mesentery ; in front and below by 

 the ileo-caecal fold, and behind by the upper part of the mesentery of the appendix. 

 (3) The subccecal fossa (retro-caecal) is situated immediately behind the caecum, 

 which has to be raised to bring it into view. It varies much in size and extent. In 

 some cases it is sufficiently large to admit the index finger, and extends upward 

 behind the ascending colon in the direction of the kidney : in others it is merely a 

 shallow depression. It is bounded and formed by two folds : one, the parieto-colic, 



