inches long. (See Fig. 89.) Like the rest of the food tube, it is lined with mucous membrane. It has two layers of muscles in its walls, the fibers of one layer running lengthwise, and the fibers of the other layer being circular. In swallowing, the food does not fall down the gullet of its own weight, but the circular bands of muscle in front of the food relax, and those behind it contract and push it on into the stomach. This wavelike motion is called peristalsis.
The stomach, the greatest enlargement of the food tube, is like a large bag lying sideways. It lies to the left side of the abdomen. The walls of the stomach consist chiefly of muscular fibers which run lengthwise, crosswise, and slantwise, making three coats (Exp. 7, also Fig. 95). As soon as the food reaches the stomach, the layers of muscles begin to contract, changing the size of the stomach, first in length, then in breadth, thus churning the food to and fro, and mixing it with the gastric juice, a fluid more active than the saliva. For as the food enters the stomach, the mucous membrane lining it turns a bright red, and many little gastric glands in the lining begin to secrete gastric juice.
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Fig. 95.—Muscular and Other Layers in Wall of Stomach.
1, mucous lining; 2, layer of blood vessels and connective tissue; 3, muscular layers (involuntary muscles); 4, connective-tissue fibers. (Peabody.)
Digestion in the Stomach.—The stomach churns the
food from two to four hours after the meal, according to
