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

by George S. Huntington

We may judge from this series that the following factors are capable of materially modifying the definite arrangement of the structures:

1. The vascular folds are capable of reduction until the vessels run close to the intestinal surface, merely covered by somewhat redundant peritoneum containing epiploic appendages. (Cercopithecus.)

2. The dorsal cæcal artery tends to assume in all three forms the greater share in the cæcal vascular supply. This tendency is slightly developed in Ateles, becomes more pronounced in Mycetes, and is well marked in Cercopithecus, in which animal the dorsal vessel nearly replaces the ventral branch, the latter confining itself to the ventral surface of the ileo-colic junction and the adjacent ventral parts of the cæcal wall.

3. The intermediate non-vascular fold is placed nearer to the dorsal larger than to the ventral smaller cæcal artery. This condition, present in both Ateles and Cercopithecus, foreshadows the fusion of the intermediate and dorsal vascular folds at the lower border of the ileo-colic junction, as seen in Mycetes.

4. This fusion of the two folds named in Mycetes results in giving different values to the dorsal vascular fold in its proximal and distal segments. The proximal segment descends from the ileo-colic notch behind the ileo-colic junction to its lower border as a distinct fold. Beyond this point its fusion with the distal (cæcal) segment of the intermediate fold rounds out a fossa, the inferior or posterior ileo-cæcal, which is consequently bounded in front by the intermediate vascular fold, behind by the proximal segment of the dorsal vascular fold, to the right side by the inner wall of the cæcum, between the intermediate and dorsal vascular folds, above by the lower border of ileum and ileo-colic junction, and below by the fusion of the two folds.

This pocket or fossa which is the most important and constant of the peritoneal recesses in the neighborhood of the cæcum, opens upward and to the left.

5. A superior or anterior ileo-cæcal fossa, formed in cases of well-developed ventral vascular fold between the same and the ventral wall of the ileo-colic junction, is of small size and shallow.

The cause of the greater development of the dorsal as compared with the ventral cæcal artery is probably to be sought in the adhesion of the colon to the dorsal parietal peritoneum. In Cercopithecus the dorsal surface of the ascending colon is adherent to the parietal peritoneum down as far as the iliac region and beginning of the cæcum, whereas in Mycetes the entire cæcum, as well as the ascending colon, are free and non-adherent to the abdominal parietes. The influence of this adhesion on the arrangement of the vascular supply of the lower portion of the ascending colon and cæcum appears to be important. Some of the departures from the Ateles type presented by Cercopithecus become still better developed in the human subject, where the adhesion of the ascending colon and the obliteration of the apposed serous surfaces of ascending mesocolon and parietal peritoneum is normally complete, even if the cæcum remains entirely free, or only adheres to the iliac parietal peritoneum in the proximal part of its dorsal surface. Comparison with forms presenting non-adherent colic and cæcal tubes indicates that the adhesion determines the relative size and arrangement of the ileo-colic vessels.

Thus the partially adherent colon and cæcum of Cercopithecus presents, compared with the free tube of Ateles and Mycetes, a marked reduction of the ventral and a corresponding enlargement of the dorsal cæcal artery. Further progress in the same direction is noted in the human subject where normally the ascending colon and at times the proximal portion of the cæcum are adherent to the dorsal parietal peritoneum.