The Anatomy of the Human Peritoneum and Abdominal Cavity / Considered from the Standpoint of Development and Comparative Anatomy

by George S. Huntington

This establishes, as already stated, a secondary parietal peritoneal surface in the left lumbar region derived from the original right leaf of the descending mesocolon. Inasmuch as the inferior mesenteric vessels originally passed to the descending colon between the layers of the mesocolon they will now apparently be placed beneath the (secondary) parietal peritoneum of the left lumbar region.

If now the duodenal fold in the cat be examined after rotation of the intestine it will be found presenting the original relations ([Figs. 160] and 163), viz., passing from the convex margin of that portion of the duodenal loop which would correspond to the human fourth or ascending portion, to the original right layer of the mesocolon, which in man becomes secondarily converted into the parietal peritoneum of the left lumbar region. Hence the connections of the fold are as follows:

On the right: ventral surface of the ascending duodenum.

On the left: right layer of mesocolon (secondary lumbar parietal peritoneum in the adult human subject).

Cephalad it abuts against the caudal layer of the transverse mesocolon along the line which would correspond to the root of the mesocolon in the adult human subject.

The concave caudal edge is free and bounds the entrance into a fossa, the “superior duodenal fossa” of anthropotomy. This fossa opens caudad and extends cephalad to the root of the transverse mesocolon. The ventral and left wall of the fossa is formed by the fold in question, its background by the mesocolon (right leaf); to the right the left circumference of the ascending duodenum enters into the formation of the fossa, and its fundus is formed by the confluence of the fold and of the caudal layer of the transverse mesocolon. The inferior mesenteric vessels are found near the left margin of the entrance into the fossa.

Fig. 164.—Abdominal viscera of Nasua rufa, the brown coaiti, showing the position of the duodenal fold after rotation of the intestine. (From a fresh dissection.)

Fig. 165.—Abdominal viscera of human fœtus at term, arranged to show duodenal folds and fossa. The jejuno-ileum, ascending and transverse colon have been removed. (Columbia University Museum, No. 1819.)