The second or muscular stomach, devoid of gastric glands, functions merely as a masticating apparatus for the mechanical division of the food. The thick muscular walls of this compartment may measure several inches in diameter and carry on the opposed mucous surfaces lining the cavity a hard horny plate with corrugated and roughened surface (Fig. 88). These hard plates are designed to crush the food between them, as between two mill stones. The muscle stomach is best developed in herbivorous birds, while both the muscular wall and the horny plate are much weaker and thinner in carnivore wading and swimming birds (Fig. 89). [Illustration: FIG. 88.--OEsophagus and stomach of _Gallus bankiva_, hen. (Columbia University Museum, No. 1809.)] [Illustration: FIG. 89.--Stomach of _Botaurus lentiginosus_, bittern. (Columbia University Museum, No. 23/1810.)] In birds of prey, especially in the owls, the stomach walls are scarcely more massive than in other animals, and the mucous membrane is soft and devoid of a horny covering. The glandular and masticatory stomachs are less sharply divided from each other in these forms, and the entire organ conforms more to the general vertebrate type (Fig. 90). [Illustration: FIG. 90.--Stomach of owl sp. (Nuhn.)] In some birds (herons, storks, etc.) a small rounded third stomach, the so-called pyloric stomach, is placed between the muscle stomach and the pylorus (Fig. 91). It contains no gastric glands, and possibly may function as an additional absorbing chamber. [Illustration: FIG. 91.--Stomach of _Ardea cinerea_, heron. (Nuhn.)] [Illustration: FIG. 92.--Stomach of crocodile. (Nuhn.)] Among reptiles the stomach of the crocodile resembles the organ in birds (Fig. 92). It is flat and rounded in shape, the muscle wall carries a tendinous plate, and there is a pyloric stomach. There is, however, no glandular stomach or proventriculus, as in birds, and the mucous membrane is not covered by a horny plate, but is soft and contains the peptic glands. Figs. 93 and 94 show the stomach of _Alligator mississippiensis_, in the ventral view and in section. [Illustration: FIG. 93.--Stomach of _Alligator mississippiensis_. (Columbia University Museum, No. 1811.)] [Illustration: FIG. 94.--Same in section. Thin-walled cardiac segment continues into cavity of pyloric ventriculus.] [Illustration: FIG. 95.--Stomach of _Bradypustridactylus_, three-toed sloth. I. First stomach, devoid of gastric glands, corresponding to rumen of ruminants. II. Second stomach, the homologue of the ruminant reticulum. III. Digestive stomach proper, provided with gastric glands connected by a gutter with the oesophagus. IV. Muscular stomach, the walls formed by a thick muscular plate and provided on the mucous surface with a dense corneous covering for purposes of trituration.] (_c_) The combination of the two accessory functions just described in the same stomach is found in the three-toed sloth (Fig. 95).