I have encountered one instance of this arrangement in an infant, whose cæcum and ileo-colic junction is shown in Fig. 580. Both the ventral and dorsal arteries in this case were equally developed, and shared equally in the supply of cæcum and appendix. Both vascular folds fused with the intermediate fold, thus producing two typical ileo-cæcal fossæ, one ventral, the other dorsal.
(D) Abnormal positions of the appendix due to variations in the arrangement and tension of the intermediate fold.
[Fig. 510] shows a fœtal cæcum in the ventral view. The ventral vascular fold (3) is well developed. The non-vascular fold is short, arising from the ventral surface of the ileum, instead of from the free border of the intestine opposite to the mesenteric attachment. It fuses with the ventral vascular fold a short distance below the ileo-colic junction, thus limiting a small ventral ileo-cæcal fossa. The dorsal cæcal artery in this specimen was large, but the fold carrying it extremely narrow.
The preparation illustrates the type resulting from the reduction in size and extent of the non-vascular and mesenteric folds. The intermediate fold is reduced to a short and narrow band. Compared with the usual infantile type the cæcum lacks the characteristic turn upwards and to the left, possibly in consequence of the slight traction caused by the rudimentary intermediate fold. The pouch occupies a nearly vertical pendent position, which the appendix, arising from the lowest point of the cæcal funnel, shares. The appendix is not drawn into the retro-ileal position by the dorsal vascular fold, which is much reduced.
In [Fig. 511], representing the cæcum and appendix of a fœtus at term, the effect of the tense non-vascular intermediate fold (2) is seen in the sharp turn to the left which it imparts to the nearly transversely directed funnel-shaped cæcum. The appendix (1) is coiled spirally for 1¾ turns behind the ileo-colic junction, with the tip directed upward behind the mesentery of the terminal ileum. The non-vascular intermediate fold (2) extends to the rest of the appendix. It appears short in its cæcal attachment, on account of the turn of the cæcum backwards and to the left and the close connection between the adjacent margins of the ileum and cæcum.
In Fig. 581—a fœtal preparation at term—the cæcum is turned to the left, below and behind the terminal ileum. The non-vascular fold (2) is well developed as regards length of ileal attachment, but is very narrow and tense, passing between ileum and the proximal curve of the cæcum behind the ileo-colic junction, where it merges with the dorsal vascular fold. The appendix takes a sudden turn caudad at this point and then continues up ventrad to the ileo-colic junction, the proximal portion being kept firmly in contact with the dorsal and caudal circumference of the ileum by the tension of the non-vascular band. It is quite evident that this peculiar turn of the appendix is directly due to the confining influence of the non-vascular band—which passes from its ileal attachment almost directly dorsad to the point of fusion with the dorsal vascular fold, causing the sharp downward and forward turn of the proximal segment of the appendix. Similar cases with ventral position of the appendix are shown in [Figs. 545] and 582.