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(also paunch), the first and largest section of the four-chambered stomach of ruminants. The rumen occupies almost the entire left half of the abdominal cavity. In adult animals its volume equals four-fifths the volume of the entire stomach. In newborns, which are fed only milk, the rumen is half the size of the abomasum. The first section of the rumen is connected to the reticulum and the esophagus. The rumen’s walls consist of the serous membrane (exterior membrane), the muscular membrane (middle membrane), and the mucous membrane (interior membrane). The interior wall has bands that divide the rumen into sacs, which slow down the movement of food. The interior epithelial surface, except for the bands, has processes, or papillae. In camels and llamas the walls of the rumen have deep cells, in the floors of which open cardiac glands. Such glands are absent in the rumens of other ruminants.
Decomposition of plant substances through bacterial and protozoan activity occurs in the rumen. Volatile acids are assimilated through the surface of the mucous membrane. The food is subjected to the action of enzymes and is mixed. From the rumen the food enters the reticulum or is regurgitated into the mouth, where it is masticated again. The food then passes into the omasum through the esophageal groove.
T. B. SABLINA [22–10101]