3. The descending duodenum is now situated dorsad to the colon.
4. The original left leaf of the mesentery has become the right, and _vice versa_.
5. The superior mesenteric artery crosses over the transverse portion of the duodenum, and with the exception of the inferior pancreatico-duodenal artery the original right-sided branches now arise from the left side of the vessel and _vice versa_.
It is now time to compare the conditions established in the cat by the manipulations just detailed with the arrangement of the adult human intestinal tract and peritoneum below the level of the transverse colon and mesocolon.
I. The shortness of the large intestine in the cat will require careful manipulation in order to produce a disposition in conformity with the arrangement of this portion of the human intestinal tract. By stretching the gut somewhat and pulling it well out of the pelvis sufficient length will be obtained to establish an ascending, transverse and descending colon. Move the cæcum from the subhepatic position which it occupies immediately after rotation (Fig. 145) down to the lower and right-hand corner of the abdomen. Pull the distal portion of the large intestine well out of the pelvis and obtain thus sufficient length to establish an ascending, transverse and descending division each provided with a free mesocolon (Fig. 146). In the formation of the three definite main segments of the human large intestine, ascending, transverse and descending colon, the following stages may be recognized:
[Illustration: FIG. 146.--Abdominal viscera of cat, with the intestines rotated to correspond to the adult human disposition, with ascending, transverse, and descending segments of the colon. (From a fresh dissection.)]
1. Immediately after rotation the large intestine lies transversely along the greater curvature of the stomach, with the cæcum on the right side in front of the duodenum and closely applied to the caudal surface of the right lobe of the liver (Fig. 147).
[Illustration: FIG. 147.--Human fœtus, 6.6 cm., vertex-coccygeal measure; liver removed. (Columbia University Museum, Study Collection.) × 4.]
PERSISTENCE OF SUBHEPATIC POSITION OF CÆCUM IN ADULT.--The period at which the cæcum descends into the iliac fossa is liable to a considerable range of variation.