The ventral vascular fold (Fig. 460, 3), containing epiploic fat, descends over the ileo-colic junction nearly to the level of the lower ileal margin. The intermediate non-vascular fold (Figs. 460 and 461, 2), derived from the ileum opposite to the mesenteric border, passes to the ventral and left aspects of the caecum and meets, near the root of the appendix, the dorsal vascular fold (Fig. 461, 3) carrying the dorsal caecal branch of the ileo-colic artery, which ramifies over the caecum and supplies the appendix. The appendix measures 12.3 cm. and presents a terminal hook, slightly dilated. The appendicular mesentery terminates within the concavity of this hook and measures 1.5 cm. in width at the broadest part, about 4.5 cm. from the root of the appendix. Figs. 462 and 463 show the caecum of the adult chimpanzee in the ventral and dorsal view. The ventral vascular fold (Fig. 462, 1) is well developed, heavily fringed with epiploic appendages. The non-vascular fold is extremely short and tense, fusing with the short appendicular mesentery near the point where in the dorsal view (Fig. 463) the appendix is seen bent at its origin sharply to the right. Fig. 464, also taken from an adult specimen of the same animal, shows a very well-developed dorsal vascular fold, which fuses with the intermediate fold to limit a distinct ileo-caecal recess. The chimpanzee, therefore, agrees closely with the human subject in the arrangement of the folds. (2) _Orang, Simia satyrus._ In Figs. 458 and 459 the arrangement of the folds in an adult specimen of the orang is shown. The ventral caecal artery (Fig. 458) is well developed, forming with the peritoneal fold and epiploic appendages surrounding it, a sharp sickle-shaped edge which descends over the ventral surface of the ileo-colic junction following the curve of the left caecal margin, and turning its concavity to the left toward the entering ileum. The ventral caecal artery follows the left margin of the caecum below the ileo-caecal junction and passes for 0.5 cm. upon the portion of the pouch which turns up behind the terminal ileum.