3. The ileo-colic junction is provided with a well-developed sacculated caecal pouch derived from the proximal segment of the colon and divided in the interior by folds into several secondary compartments. [Illustration: FIG. 326.--_Iguana tuberculata_, iguana. Ileo-colic junction and caecum; dried preparation. (Columbia University Museum, No. 243.)] This type is found in some of the phytophagous lizards, as _Iguana tuberculata_ (Figs. 326 and 327). The small intestine of this animal is of considerable length and of uniform caliber from the pylorus to the ileo-colic junction. The caecum is a large sacculated pouch developed chiefly along the convex border of the large intestine opposite to the mesenteric attachment. [Illustration: FIG. 327.--_Iguana tuberculata_, iguana. Mid-gut, ileo-colic junction, caecum, and end-gut; dried preparation. (Columbia University Museum, No. 178.)] [Illustration: FIG. 328.--_Iguana tuberculata_, iguana. Ileo-colic junction and caecum in section. (Columbia University Museum, No. 1321.)] [Illustration: FIG. 329.--Drawing taken from same preparation (No. 1321) to elucidate more clearly internal structure of caecal pouch.] [Illustration: FIG. 330.--_Cyclura teres_, smooth-backed cyclura. Ileo-colic junction and caecum in section. (Columbia University Museum, No. 1523.)] The examination of the interior of this pouch reveals a complicated structure (Figs. 328 and 329). Fig. 330 shows the same structures in a closely allied form, _Cyclura teres_. The entrance of the small intestine is guarded by an annular sphincter valve, whose central circular opening leads into a proximal compartment of the caecum. This compartment is in turn separated from the remainder of the caecal pouch by a second circular valvular fold with central opening. Beyond this valve the interior of the pouch carries a number of crescentic mucous folds, corresponding to the external constrictions between the caecal sacculations. The entire pouch gradually diminishes in caliber and finally passes with a sharp angular bend into the terminal portion of the endgut. At this point the lumen of the canal is slightly diminished by a sphincter-like thickening of the muscularis, producing an annular projection of the mucous membrane. The entire caecal pouch appears as a specialized segment of the large intestine interposed between the termination of the midgut and the terminal portion of the endgut, which latter is characterized by uniform caliber and increased thickness of the muscular walls.