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).
There are here two large reservoirs, which correspond to the rumen and retinaculum of the ruminants, and a digestive compartment containing gastric glands, which corresponds to the ruminant abomasum, and is connected by an œsophageal gutter directly with the œsophagus. At the pyloric extremity the muscle wall is greatly increased and the mucous membrane of this portion carries a thick horny covering, forming a masticatory stomach greatly resembling the corresponding structure in the bird. Its function is evidently to complete the mechanical division of the food which has only been partly masticated in the mouth.
The same significance is probably to be attached to the thickened muscular walls which the pyloric segment of the stomach in Tamandua bivittata, another edentate, presents (Fig. 96), in strong contrast with the thinner walled cardiac segment and fundus.
Fig. 96.—Stomach of Tamandua bivittata, collared ant-eater, (Columbia University Museum, No. 68/1485.)
INTESTINE.
Continuing our consideration of the development of the alimentary canal we find that changes from the simple primitive straight tube below the stomach depend upon two factors:
1. The increase in the length of the intestinal tube, which exceeds relatively the increase in the length of the body cavity in which it is contained.
2. The differentiation into small and large intestine, the development of the cæcum and ileo-cæcal junction, and the development of the accessory digestive glands, liver and pancreas, by budding from the proximal portion of the primitive entodermal intestinal tube.