Muscular stomach

Overview of the muscular stomach or gizzard of a chicken (HE)

The gizzard (ventriculus) is a large, firm organ with a flattened spherical shape. It can be filled with grit or small stones, the gizzard stones or gastroliths, swallowed by the bird to break down hard food. Not all birds have gastroliths in their gizzard. The gizzard of Falconiformes, Stringiformes and gulls is not as well developed but forms a thin walled, poorly muscular pouch.