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).
| Fig. 63.—Stomach of Lutra vulgaris, otter. (Nuhn.) | 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.
| Fig. 65.—Stomach of Lophius piscatorius, angler. (Nuhn.) | 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.
| Fig. 67.—Stomach of Castor fiber, beaver. (Nuhn.) | Fig. 68.—Stomach of Manatus americanus, manatee. (Nuhn.) |
Fig. 69.—Stomach of Phalacrocorax dilophus, double-crested cormorant; section. (Columbia University Museum, No. 67/1804.)