2. The appendix is erected vertically behind the caecum and ascending colon and closely attached to the dorsal wall of the large intestine. In some instances the caecum and colon, with the adherent vertical appendix, possess a free serous dorsal surface, not adherent to the parietal peritoneum (Figs. 529, 538, 539 and 540). In other cases the ascending colon is fixed and the greater part of the retro-colic appendix is buried in the connective tissue which attaches the large intestine to the abdominal parietes (Fig. 517). Even in these cases, however, the dorsal surface of the caecum and the root of the appendix retain their free serous investment. [Illustration: FIG. 538.--Human juvenile. Caecum _in situ_ lifted up to show vertical course of appendix, situated behind caecum and ascending colon. The large intestine has a free peritoneal dorsal surface, and the appendix is held in position by adhesion to the large intestine. (Columbia University, Study Collection.)] [Illustration: FIG. 539.--Human adult. Ileo-colic junction and caecum; dorsal view. (Columbia University Museum, No. 1594.)] [Illustration: FIG. 540.--Human adult. Ileo-colic junction and caecum; dorsal view. (Columbia University Museum, No. 1850.)] 3. The proximal part of the appendix turns upward and to the left in continuation of the caecal curve, but the distal portion is directed downward and inward, hanging over the brim of the pelvis (Figs. 505, 541 and 542). 4. The appendix is directed downward, pendent from the lowest point of the conical caecal pouch, and hangs free over the pelvic brim. This type is encountered at times in foetal and infantile subjects (Figs. 516 and 543). [Illustration: FIG. 541.--Human infant. Ileo-colic junction and caecum; ventral view. (Columbia University, Study Collection.)] [Illustration: FIG. 542.--Human infant. Ileo-colic junction and caecum; dorsal view. The dorsal surface of caecum as far as root of the appendix is adherent to the parietal peritoneum of the iliac fossa. (Columbia University Museum, No. 394.)] [Illustration: FIG. 543.--Human foetus at fifth month. Abdominal cavity and viscera; liver and greater part of small intestine removed. (Drawn from preparation in Columbia University Museum, No. 1814.)] [Illustration: FIG. 544.--Human foetus at term. Abdominal cavity and viscera; greater part of small intestine removed. (Drawn from preparation in Columbia University Museum, No. 1813.)] [Illustration: FIG. 545.--Human foetus at term. Ileo-colic junction and caecum. (Columbia University Museum, No. 998.)] 5. The position of the appendix is variant and abnormal, as _e. g._ placed to the right of caecum and colon (Fig. 544) or turned up ventrad of the ileo-colic junction (Fig. 545). These variations in the position of the appendix and the resulting peritoneal relations of the structure depend upon the following factors.