[Illustration: FIG. 59.--Stomach of _Phoca vitulina_, harbor seal. (Columbia University Museum, No. 600.)] [Illustration: FIG. 60.--Stomach of _Pseudemys elegans_, pond turtle. (Columbia University Museum, No. 1710.)] [Illustration: FIG. 61.--Stomach of _Chelydra serpentina_, snapping turtle. (Columbia University Museum, No. 1852.)] [Illustration: FIG. 62.--Same in section.] =2. Stomach Forms Depending on the Influence Exerted by the Volume and Digestible Character of the Foods.=--Vegetable substances usually have a large volume in proportion to the amount of nutritive material which they contain. Meat, on the other hand, contains considerable nutriment in a comparatively small bulk. Hence carnivora (Fig. 63) usually have a smaller stomach than herbivora (Fig. 64). [Illustration: FIG. 63.--Stomach of _Lutra vulgaris_, otter. (Nuhn.)] [Illustration: FIG. 64.--Stomach of _Equus caballus_, horse. (Nuhn.)] =3. Stomach Forms Influenced by Size and Shape of the Abdominal Cavity in which they are Contained.=--In animals whose bodies are long and slender, as in snakes (Fig. 52), most saurians (Fig. 56), many tailed batrachians and perennibranchiates (Figs. 50 and 51), many teleosts (Fig. 48), the stomach is likewise usually long and slender in shape, unless special modifying conditions exist. When on the other hand the body is broad and short, as in Lophius (Fig. 65), Pipa (Fig. 66), and most higher vertebrates, the stomach is also broader and more sac-like. [Illustration: FIG. 65.--Stomach of _Lophius piscatorius_, angler. (Nuhn.)] [Illustration: FIG. 66.--Stomach of _Pipa verucosa_. (Nuhn.)] =4. Stomach Forms Depending on Structural Modifications Designed to Increase the Action of the Gastric Juice on the Food.=--This purpose is accomplished: (_a_) By increasing the source of supply of the gastric juice. (_b_) By increasing the length of time during which the food remains in the stomach. (_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 oesophagus 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. [Illustration: FIG. 67.--Stomach of _Castor fiber_, beaver. (Nuhn.)] [Illustration: FIG. 68.--Stomach of _Manatus americanus_, manatee. (Nuhn.)] [Illustration: FIG. 69.--Stomach of _Phalacrocorax dilophus_, double-crested cormorant; section. (Columbia University Museum, No. 67/1804.)]