The stomach and greater part of the intestinal tract move freely within the abdomen, being covered by the smooth serous lining of that cavity, which also keeps in position, so as to restrict their movements, those parts, such as the duodenum, into which the ducts of large glands open. When the stomach is empty it hangs with the great curvature downward, and the muscular coats are quiescent. On being filled it is passively rotated on its long axis, so that the greater curvature is turned forward, here meeting with Jess resistance, and the lesser curvature is turned backward to its line of attachment. In the main, the motions of the stomach are peristaltic. They become very active about fifteen minutes after the introduction of food, and gradually become more and more energetic until the end of stomach digestion, which lasts about five hours.

The result of the peristaltic motion is to move the food, particularly the part next the gastric wall, along the great curvature toward the pylorus. A back current toward the cardiac extremity has been noticed running along the lesser curvature and the median axis of the food mass. At the same time a peculiar rotatory motion of the gastric wall takes place, similar to that of rolling a ball between the palms of the hands, so that the food is twisted in a given direction, and the deeper lying portion is brought into contact with the mucous membrane.

While the fundus keeps up considerable pressure on the contents of the stomach, the indistinct peristaltic action of the central parts is intensified, on nearing the pylorus, into a strong circular contraction, which proceeds as a definite wave toward the pyloric valve, through which it gradually forces the more or less digested food. At first only the fluid parts are allowed to pass, but toward the later stages of digestion the fatigued pyloric muscle admits solid masses into the duodenum.