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

by George S. Huntington

In comparing [Figs. 564] and 567 it will be noticed that the line of fusion between the intermediate fold and the dorsal vascular fold ([Fig. 564], 4) corresponds to the point where the dorsal ileo-cæcal artery divides into its proximal and distal branches (Fig. 567, angle between 1 and 2). Fig. 567 shows that the proximal arterial twig, even without fusion with the intermediate fold, suffices to influence to a considerable degree the curves and position of the appendix, inasmuch as it serves to hold the proximal segment of the tube closely applied in the erected position to the surface of the left cæcal sacculation. The intermediate segment of the appendix, between the points of accession of the two arterial branches, is most prone to develop spiral twists and bends, especially when the usual fusion of the two folds takes place and still further fixes the parts, while the distal segment, carrying the narrow crescentic terminal appendicular mesentery, remains free.

Fig. 568.—Human adult. Ileo-colic junction and cæcum. (Drawn from preparation in Columbia University, Study Collection.)

1. Distal and

2. Proximal branch of dorsal ileo-cæcal artery running in dorsal vascular fold.

3. Intermediate non-vascular fold fusing with 2 and forming a narrow caudal limit to the posterior ileo-cæcal fossa.

Finally, in a certain number of cases, an intermediate condition between the types presented by [Figs. 564] and [567] is encountered. In Fig. 568 the general arrangement of the parts corresponds pretty accurately to that seen in [Fig. 566], but the transition from a completely free intermediate non-vascular fold to one which has begun to fuse with the dorsal vascular fold is evident. The cæcum is bent upward and to the left, the caput coli being formed by the right sacculation. The appendix, 7.8 cm. long, takes a wide ≀-shaped curve. The convexity of the proximal curve corresponds to the point where the proximal appendicular artery (2) passes to the tube. The non-vascular intermediate fold (3), measuring 2.2 cm., fuses with the dorsal vascular fold at this point.

The three preparations illustrate serially the share which the peritoneal folds take in the formation of the posterior ileo-cæcal fossa.

In [Fig. 566] the failure of the intermediate fold to meet and fuse with the dorsal vascular fold has left the caudal boundary of the fossa (between 2 and 3) incomplete, the ventral and dorsal walls being formed by the folds in question. Fig. 568, in which fusion between the non-vascular and the dorsal vascular folds has commenced, shows the shallow form of the complete fossa under these conditions, while in [Fig. 567], with extensive union of the folds, the fossa has correspondingly increased in depth.