1. Differentiation in caliber, with direct funnel-like transition of small into large intestine. No cæcum.
Beyond the ileo-colic junction the caliber of the large intestine increases gradually. The terminal ileum is thus implanted into the apex of a funnel formed by the proximal segment of the colon.
Examples of this type are furnished by Myrmecophaga jubata, the great ant-eater (Fig. 356), and by Cholœpus didactylus, the two-toed sloth (Fig. 357).
Fig. 358.—Tatusia novemcincta, nine-banded armadillo. Ileo-colic junction. (Columbia University Museum, No. 176.)
2. Abrupt demarcation of small and large intestine, with median transition of ileum.
The caliber of the intestine enlarges rapidly immediately beyond the ileo-colic junction. This form is derived from the preceding by the substitution of the abrupt ileo-colic transition for the gradual funnel-shaped development of the large intestine.
The type is illustrated by Tatusia novemcincta, the nine-banded armadillo (Fig. 358), and is also found in two other armadillos, Tolypeutes and Xenurus.
3. The colon on each side of the ileo-colic junction is prolonged backward along the small intestine, forming two symmetrical lateral globular colic cæca.