Figs. 517 and 518 illustrate this form of the pouch, which, in our experience, is frequently associated with the retro-caecal erect position of the appendix (cf. infra, p. 251). Fig. 472 shows this type in the adult with pendent appendix. =II. Adult Caeca Derived from Type II.= (schema, Figs. 509 and 511).--From this more commonly observed type of foetal caecum the following adult forms are developed: 1. The general shape and trend of the foetal caecum is preserved. The pouch turns sharply to the left, carrying the apex with the root of the appendix upward toward the ileum, the appendix itself being frequently placed under cover of the terminal coil of the small intestine (schema, Fig. 509, _II^b_). [Illustration: FIG. 519.--Human adult (Smith's Sound Eskimo). Ileo-colic junction and caecum. (Columbia University Museum, No. 59/1483.)] [Illustration: FIG. 520.--Human adult. Ileo-colic junction and caecum. (Columbia University, Study Collection.)] [Illustration: FIG. 521.--Human adult. Ileo-colic junction and caecum. (Columbia University, Study Collection.)] [Illustration: FIG. 522.--Human adult (Smith's Sound Eskimo). Ileo-colic junction and caecum. (Columbia University Museum, No. 56/1571.)] The apex of the caecal pouch is either conical, narrowing gradually toward the root of the appendix (Figs. 520 and 521), or blunt and more sharply defined against the appendix (Fig. 522). Mr. Treves encountered this "persistent foetal type" in two per cent. of his series. The caecum is frequently sharply bent on itself in making the turn upward and to the left, resulting in a deep indentation of the concave border and producing a corresponding projecting fold in the interior of the pouch (Fig. 523). The ventral longitudinal muscular band follows the crescentic sweep of the caecum to the root of the appendix. [Illustration: FIG. 523.--Human adult. Ileo-colic junction and caecum; dorsal view; dried preparation. (Columbia University Museum, No. 200.)] [Illustration: FIG. 524.--Human foetus at term. Ileo-colic junction and caecum; ventral view. (Columbia University Museum, No. 1717.)] [Illustration: FIG. 525.--Same preparation as Fig. 524; dorsal view.] Figs. 524_a_ and 525_b_, representing the caecum of a foetus at term in the ventral and dorsal view respectively, show very clearly the arrangement of the foetal pouch from which the adult type with sharp angular bend is derived. This type of adult caecum is found in certain of the anthropoid apes. In the orang (Figs. 458 and 459) the caecum turns sharply upward and to the left, gradually narrowing in caliber to the root of the appendix which is coiled behind the termination of the ileum. The same type is seen in Figs. 462 and 463, taken from a preparation of the adult chimpanzee. Fig. 463 shows especially well the sharp bend between the caecum and colon by means of which the apex of the pouch is carried cephalad behind the ileo-colic junction.