(c) The provisions for these two accessory functions may be combined in the same stomach.

(a) Many of the higher vertebrates possess in connection with the alimentary tract additional reservoirs for the storage of food until used. Such reservoirs are found in mammals and birds connected with the oral cavity, as cheek-pouches, or with the œsophagus, such as the crop of the birds ([Fig. 88]). Fig. 80 shows the development of the cheek-pouches in one of the primates, Macacus nemestrinus.

In many mammals reservoirs of similar import are added directly to the stomach and form an integral part of the organ. Examples are furnished by the compound stomachs of many rodents, ruminants, cetaceans and herbivorous edentates. The peculiar appearance of these stomachs is explained if the additional reservoirs are in imagination removed and the digestive stomach proper restored so to speak to the type-form. The proximal or cardiac portion of the stomach in many rodents is devoid of gastric glands and must be interpreted as a storage chamber for food (Fig. 81). The same significance attaches to the corresponding portion of the manatee’s stomach ([Fig. 68]).

Similar contrivances are found in the ruminant stomach. The first and second divisions (rumen and reticulum) are nothing but sac-like gastric reservoirs or pouches, in which the food is collected, to be subsequently returned to the mouth for mastication. When swallowed for the second time the bolus is carried, by the closure of the so-called œsophageal gutter, past the first and second stomach into the digestive apparatus proper (the abomasum) (Figs. 82 and 83). Many ruminants (e. g., Moschus) only have these three compartments. Most, however, have four, the leaf stomach or psalterium being intercalated between the retinaculum and the abomasum. The psalterium contains no digestive glands. It may possibly serve for the absorption of the liquid portions of the foods.

Fig. 82.—Stomach of Ovis aries, sheep. (Columbia University Museum, No. 1807.) Fig. 84.—Mucous membrane of stomach of Camelus dromedarius, dromedary, showing water-cells. (Columbia University Museum, No. 1123.)
Fig. 83.—Scheme of ruminant compound stomach. (Nuhn.) Fig. 85.—Stomach of Phocæna, porpoise. (Nuhn.)

The rumen or first stomach of the camels and llamas is provided with so-called “water-cells,” for the storage of water. These cells are diverticula lined by a continuation of the gastric mucous membrane. The entrance into these compartments can be closed by a sphincter muscle after they are filled with water (Fig. 84).

Fig. 86.—Stomach of Urinator imber, red-throated loon. (Columbia University Museum, No. 1808.)

Fig. 87.—Scheme of stomach of granivorous bird. (Nuhn.)