(a) The source of supply of the gastric juice is increased by adding to the usual gastric glands of the stomach a special accessory glandular compartment, either placed at the cardia, where the œsophagus enters, as in Myoxus or Castor (Fig. 67) or attached to the body of the stomach to the left of the cardia, as in the manatee (Fig. 68). The first arrangement is similar to the universal position of the glandular stomach of birds (Fig. 69). In birds, however, the glandular proventriculus is the only source of the gastric juice, while in the above-mentioned mammalia (myoxus and beaver) the accessory glandular stomach is merely an addition to the supply derived from the usual gastric glands situated in the body of the organ.
(b) The increase of the length of time during which the food remains in the stomach subject to the action of the gastric juice can be accomplished in one of several ways.
1. The stomach, while it retains its general tubular form increases considerably in length and assumes the shape and structure found in the human large intestine. It is partially subdivided by folds projecting into the interior and separating compartments resembling the colic cells of the human large intestine. The time required for the passage of food through the stomach is thus increased and the action of the gastric juice is prolonged and rendered more intense.
Such modifications of the structure of the stomach are encountered in Semnopithecus among the monkeys and in the kangaroo, among marsupials (Figs. 70 and 71).
2. The same purpose is accomplished by the development of diverticula from the stomach, in which the food is retained and acted on by the gastric juice for longer periods.
| Fig. 70.—Stomach of Halmaturus derbyanus, rock kangaroo. (Columbia University Museum, No. 582.) | Fig. 71.—Stomach of Semnopithecus entellus, entellus monkey. (Columbia University Museum, No. 62/1805.) |
Fig. 72.—Alimentary canal of Anguilla anguilla, eel. (Columbia University Museum, No. 1271.)
The herbivora, omnivora and such carnivora as live on animal food difficult of digestion furnish examples of this type of stomach. The same is also found in most teleosts. In the latter the cæcal gastric pouch lies in the long axis of the body, opposite the entrance of the œsophagus. A marked example of this arrangement is seen in the stomach of the eel, Anguilla anguilla (Fig. 72).
In other forms, and in the mammalia especially, the blind pouch is developed from the portion of the stomach lying to the left of the œsophageal entrance at the cardia, and is hence placed transversely to the long axis of the body.