... dilatation, in which the food is retained for a considerable time, mixed with a slight mucous secretion, and softened and partly macerated by the heat of the body. Many birds feed their young from the soft contents of the crop, and in pigeons, at the breeding season, the cells lining the crop proliferate rapidly and are discharged as a soft cheesy mass into the cavity, forming the substance known as pigeon's milk. Amongst Mammalia, in Rodentia, Carnivora, elephants and ruminants, the wall of the oesophagus ... — Project Gutenberg Encyclopedia
...
