This difference in the position of the cul-de-sac is explained by the small transverse measure of the body in teleosts, while the greater amount of available space in the abdominal cavity of mammalia permits of the transverse position of the entire stomach and of the development of the diverticulum from its left extremity.

Most mammals have only a single pouch, whose size varies with the digestibility of the food habitually taken. It is greater in herbivora ([Figs. 64] and 73) than in omnivora and carnivora (Figs. 74 and 75). In some of the latter, as Lutra ([Fig. 63]), the cul-de-sac is almost wanting.

Fig. 73.—Stomach of Lepus cuniculus, rabbit. (Nuhn.)   Fig. 76.—Stomach of Erethizon dorsatus, American porcupine. (Columbia University Museum, No. 358.)
Fig. 74.—Stomach of Nasua rufa, coati. (Nuhn.)   Fig. 77.—Stomach of Cercopithecus cephus, moustache monkey. (Columbia University Museum, No. 158.)
Fig. 75.—Stomach of Felis leo, lion. (Nuhn.)   Fig. 78.—Stomach of Sus scrofa, pig. The fundus of the stomach carries a cæcal appendage separated in the interior by a spiral fold of the mucous membrane from the gastric cavity.

In some forms, as the pig, the left extremity of the stomach carries a cæcal appendix with a spiral valve in the interior separating its lumen from the general gastric cavity (Fig. 78). Others have two such cæcal appendices added to the left end of the stomach (Peccary, Fig. 79). These cæcal pouches may arise from the body of the stomach, instead of from the left extremity. An example of this condition is furnished by the American manatee ([Fig. 68]).

Fig. 79.—Stomach of Dicotyles torquatus, peccary. The fundus is a capacious pouch prolonged ventrally and dorsally into two cæcal appendages resembling the single appendage of the pig’s stomach. (Columbia University Museum, No. 1806.)

5. Variations in the Form of the Stomach Depending upon the Assumption by the Stomach of Special Functions, which are Usually Relegated to other Organs.—These functions are the following:

Fig. 80.—Macacus nemestrinus, pig-tail macaque monkey; cheek-pouches. (From a fresh dissection.)
Fig. 81.—Stomach of Cricetus vulgaris, hamster. (Nuhn.)

(a) Storage of food in special receptacles or compartments for subsequent use.

(b) Mastication of the food is in some animals accomplished only partly or not at all in the mouth, and is then performed in the stomach. A portion of the stomach is thus converted into an apparatus for mastication.