2. Proximal branch of the same vessel, turning downward to caecum and root of appendix. 3. Intermediate non-vascular fold.] Fig. 567 shows the dorsal view of such a preparation. The caecum is funnel-shaped with the apex, carrying the root of the appendix, turned upward and to the left, the sacculation to the right of the ventral muscular band being somewhat dilated. The appendix--7.2 cm. long--turns sharply upward and to the left, closely applied to the left caecal sacculation, passes dorsad to the ileo-colic junction and lies in its terminal part under cover of the ileo-colic mesentery. The ventral branch of the ileo-colic artery descends over the ileo-colic junction, supplying the ventral wall of the caecum. The intermediate non-vascular fold (3) is 3.9 cm. long and entirely free. The dorsal vascular fold contains the large dorsal branch of the ileo-colic artery, dividing into two main branches. The first of these (1) passes distally in the free edge of the fold to the terminal part of the appendix. The other proximal branch (2) turns downward to the root of the appendix and the adjacent wall of the caecum, aiding materially in holding the proximal upturned segment of the appendix in contact with the left caecal sacculation. The intermediate fold, short in its caecal attachment, does not meet the dorsal vascular fold at any point, consequently the ileo-caecal fossa is not limited caudad toward the root of the appendix. The conditions presented by this specimen correspond exactly to those found in the gorilla (Fig. 457) and in the human infantile preparation (Fig. 563). In comparing Figs. 564 and 567 it will be noticed that the line of fusion between the intermediate fold and the dorsal vascular fold (Fig. 564, 4) corresponds to the point where the dorsal ileo-caecal artery divides into its proximal and distal branches (Fig. 567, angle between 1 and 2). Fig. 567 shows that the proximal arterial twig, even without fusion with the intermediate fold, suffices to influence to a considerable degree the curves and position of the appendix, inasmuch as it serves to hold the proximal segment of the tube closely applied in the erected position to the surface of the left caecal sacculation. The intermediate segment of the appendix, between the points of accession of the two arterial branches, is most prone to develop spiral twists and bends, especially when the usual fusion of the two folds takes place and still further fixes the parts, while the distal segment, carrying the narrow crescentic terminal appendicular mesentery, remains free. [Illustration: FIG. 568.--Human adult. Ileo-colic junction and caecum. (Drawn from preparation in Columbia University, Study Collection.) 1. Distal and 2. Proximal branch of dorsal ileo-caecal artery running in dorsal vascular fold. 3. Intermediate non-vascular fold fusing with 2 and forming a narrow caudal limit to the posterior ileo-caecal fossa.]