It appears that in the adhesion of the colic tube to the parietal peritoneum the dorsal ileo-colic vessels find an element favorable to their more complete development and extension, replacing in part or entirely the ventral caecal artery which becomes limited in distribution to the region of the ileo-colic junction. The adhesion and fixation of the dorsal wall of the intestine seems to afford an advantage to the dorsal vessel, whereas the greater mobility and the alternating conditions of distension and contraction, with variations of intracaecal pressure, depending upon the contents of the pouch, appear to operate unfavorably upon the development of the ventral vessel. This view is borne out by the conditions observed in the exceptional instances in which in the human subject the ventral artery assumes the large share in the supply of caecum and appendix (cf. p. 276). In all the cases observed the type of the caecum indicated delayed or imperfect colic adhesion, and the ascending mesocolon remained partially free. If we now compare the conditions above described for _Ateles_, _Mycetes_, _Cercopithecus_ with those usually found in man and in the anthropoid apes, we may appreciate the significance of the structures encountered by beginning the investigation with a type in which the derivation of the different parts is still quite evident. Such a condition is presented by the preparation shown in Fig. 563, taken from a child one year of age. Here the descent of the caecum has evidently been quite rapid and uniform without dorsal adhesion. The caecum and ascending colon remain free and can still be lifted away from the ventral facies of the right kidney and turned toward the median line to a point somewhat beyond the renal hilus. The caecum hangs downward vertically and the appendix arises from the funnel-shaped apex of the pouch. [Illustration: FIG. 563.--Human; child one year old. Caecum and ileo-colic junction; ventral view. (Columbia University, Study Collection.) 1. Ventral caecal artery, surrounded by epiploic appendages. 2. Dorsal vascular fold, forming appendicular mesentery. 3. Intermediate non-vascular fold.]