Fig. 363.—Arctopithecus marmoratus, three-toed sloth. Ileo-colic junction. (Columbia University Museum, No. 1479.)
1. This type may be considered as being inaugurated by the form of ileo-colic junction found in the Manidæ or Pangolins, as illustrated by Figs. 361 and 362, taken from the long-tailed pangolin, Manis longicauda. There is no cæcum and only a slight differentiation in caliber between the small and large intestine. The gut in all the forms examined shows a very characteristic bend at the ileo-colic junction, being twisted into a figure of 8 and held in place by mesenteric folds.
2. The second stage, illustrated by Arctopithecus (Bradypus) marmoratus, the three-toed sloth (Fig. 363), reveals a distinct increase in the caliber and convexity of the large intestine opposite the mesenteric border immediately beyond the ileo-colic junction.
3. This leads in the third stage, represented by Tamandua bivittata, the Tamandua ant-eater (Figs. 364 and [365]), to the development of a distinct lateral cæcal pouch. I have had no opportunity of examining the structures in Orycteropus, but from the published descriptions[8] the large cæcum of this animal would form the final link in this series.
Fig. 364.—Tamandua bivittata, Tamandua ant-eater. Ileo-colic junction and cæcum. (Columbia University Museum, No. 1590.)
Fig. 365.—Tamandua bivittata, Tamandua ant-eater. Ventral view of abdominal viscera from the left side. (Study Collection, Columbia University.)