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 oesophageal 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. [Illustration: FIG. 82.--Stomach of _Ovis aries_, sheep. (Columbia University Museum, No. 1807.)] [Illustration: FIG. 83.--Scheme of ruminant compound stomach. (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). [Illustration: FIG. 84.--Mucous membrane of stomach of _Camelus dromedarius_, dromedary, showing water-cells. (Columbia University Museum, No. 1123.)] [Illustration: FIG. 85.--Stomach of _Phocaena_, porpoise. (Nuhn.)] The three stomachs of the cetaceans are similar to those of the ruminants (Fig. 85). The first is a crop-like reservoir for the reception of the food when swallowed. The mucous membrane is entirely devoid of digestive glands. In the dolphins the mucous membrane is provided with a hard horny covering, which serves to break up the food mechanically by trituration. The second stomach and the gut-like pyloric prolongation constituting the third stomach contain gastric glands and are hence digestive in function. (_b_) Stomach forms, in which a portion of the organ is converted into an apparatus for mastication, are seen especially in birds, in which animals, on account of the absence of teeth, mastication cannot be performed in the mouth. The stomach of the bird is usually composed of two segments, one placed vertically above the other. The first appears like an elongated dilatation of the oesophagus, forming the _Proventriculus_ or glandular stomach. The second is larger, round in shape, with very strong and thick muscular walls (Figs. 86 and 87). [Illustration: FIG. 86.--Stomach of _Urinator imber_, red-throated loon. (Columbia University Museum, No. 1808.)] [Illustration: FIG. 87.--Scheme of stomach of granivorous bird. (Nuhn.)] The proventriculus furnishes the gastric juice exclusively.