[Illustration: FIG. 550.] [Illustration: FIG. 551.] [Illustration: FIG. 552.] [Illustration: FIG. 553.] [Illustration: FIG. 554.] [Illustration: FIGS. 549-554.--Schematic series illustrating the variations in the arrangement of the caecal and colic peritoneum.] Normally, however, in the human subject, even if the obliteration of the apposed serous surfaces and the resulting fixation of the ascending colon has been delayed beyond the usual period, as above indicated, adhesion takes place subsequently, involving the dorsal surface of the ascending colon between the ileo-colic junction and the hepatic flexure (schema, Fig. 550). The dorsal surface of the caecum usually retains its free serous surface in whole or in greater part. The appendix is pendent, entirely invested by peritoneum and hangs free in the abdominal cavity, directed toward the pelvic brim, illustrating the effect of delayed fixation of the colon on the position of the appendix. Examples of this condition are not frequent, and are confined almost exclusively to foetal and juvenile subjects. Illustrations are afforded by Figs. 515 and 516. We have already noted (p. 246) the resulting foetal type of pendent caecum (Fig. 510). More commonly colic adhesion before the caecum obtains its final iliac position results in imparting a backward turn to the pouch, leading to the peritoneal disposition shown in schema, Fig. 551, in which the root of the appendix is involved in the area of obliteration, while the terminal segment remains free. An example of this condition is furnished by the embryo shown in Fig. 508 (10.7 cm. vertex-coccygeal measure). The colon is already segmented into an ascending, transverse and descending portion. The caecum is retroverted and its apex with the appendix is placed under cover of the terminal ileum which enters the large intestine in the direction from below upward and to the right. In the side-figure the divided end of the ileum is displaced upward to show caecum and appendix and their relation to the ileal mesentery.