It is located dorsally to the trachea so that it appears behind the trachea when the throat is opened ventrally in the abattoir. In poultry, just before the esophagus enters the thoracic cavity, there is a large sack-like expansion on the right side known as the crop . The crop is a temporary storage area for feed. The stomach differs in structure between pigs, ruminants, and poultry. Cattle and sheep have three additional chambers before the true stomach.
Poultry have a second chamber after the true stomach.
The stomach has complex glands in its wall. This is the stomach of a pig on the floor of our abattoir, with some of the small intestines showing in the top right corner. In cattle and sheep, instead of opening directly into a glandular stomach where digestion begins , the esophagus leads to a series of three extra compartments, the rumen, the reticulum and the omasum. These compartments are lined with stratified squamous epithelium. In young lambs and calves that are still drinking milk, the rumen and reticulum may be by-passed .