The alimentary canal is simple and usually comparatively short. There is no cæcal pouch. Differentiation of mid- and endgut is usually marked externally by a constriction and by the increased caliber of the terminal intestinal segment.

Fig. 318.—Rana catesbiana, bull-frog. Alimentary canal and ap­pend­ages. (Columbia University Museum, No. 1454.)   Fig. 319.—Necturus maculatus, mud-puppy. Alimentary canal and appendages. (Columbia Uni­ver­sity Museum, No. 1582.)   Fig. 320.—Cryptobranchus alleghaniensis, hellbender. Ileo-colic junction. (Col­um­bia Uni­versity Mu­seum, No. 1711.)

Fig. 318 shows the alimentary canal of the bull-frog, Rana catesbiana, Fig. 319 that of a Urodele Amphibian, Necturus maculatus, and Fig. 320 the ileo-colic junction isolated in Cryptobranchus alleghaniensis, the hellbender.

III. REPTILIA.

In reptiles a well-marked differentiation of small and large intestine is the rule.

Four types of ileo-colic junction are encountered in this class:

1. The transition from small to large intestine is marked by the greatly increased caliber of the latter and by an annular valve in the interior. An example of this type is furnished by Alligator mississippiensis (Fig. 321) and a similar form is encountered in some lizards, as Heloderma suspectum, the Gila monster (Fig. 322).

Fig. 321.—Alligator mississippiensis, alligator. Ileo-colon; dried prep­aration. (Columbia University Museum, No. 179.)   Fig. 322.—Heloderma suspectum, Gila monster. (Columbia University Museum, No. 69/1536.)

2. The large intestine immediately beyond the ileo-colic junction protrudes along the convex border to form a rudimentary lateral cæcum. This type is found in many Chelonians, e. g., in Pseudemys elegans, the pond turtle (Figs. 323 and 324) and Chelydra serpentaria, the snapping turtle (Fig. 325).

Fig. 323.—Pseudemys elegans, pond-turtle. (Columbia UniversityMuseum, No. 1069.)

 

Fig. 325.—Chelydra serpentaria, snapping turtle. Intestinalcanal, pancreas, and spleen. (Columbia University Museum,No. 1369.)

Fig. 324.—Pseudemys elegans, pond-turtle. Ileo-colic junction, opened.(Columbia University Museum, No. 1524.)

 
 

Fig. 326.—Iguana tuberculata, iguana. Ileo-colic junction and cæcum;dried preparation. (Columbia University Museum, No. 243.)