The descending mesocolon turns its original right leaf ventrad, its left leaf dorsad, and the latter adheres to the primitive parietal peritoneum covering the left lumbar region and ventral surface of left kidney. This area of adhesion extends up to and usually involves the dorsal surface of the descending colon, anchoring the same in the left lumbar region, down to the point where the sigmoid flexure begins and where the original mesocolon again appears free. In the cat, therefore, with the intestines arranged to correspond to the course of the human large intestine after rotation has been accomplished, the lines representing the peritoneal human adhesions should be fixed, as shown in the schema, Fig. 159: AB, line of secondary attachment after rotation resulting in the formation of the "root" of a free transverse mesocolon. BC, line of limit of secondary adhesion to the original parietal peritoneum involving the entire left (now dorsal) layer of the descending mesocolon and the dorsal surface of the descending colon, resulting in the fixation of the latter part of the large intestine. 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.