gizzard

n. second stomach of a bird; digestive organ found in certain animals

A gizzard is a specialized stomach with a thick, muscular wall used for grinding up food. It is found in birds, reptiles, earthworms, some fish, insects, mollusks, and other creatures. In certain insects and mollusks, the gizzard features chitinous plates or teeth. The gizzard is also known as a ventriculus, a gastric mill, or a gigerium.
See more at Wikipedia.org...

Gizzard the muscular stomach of the bird, separated from the more cranial proventriculus or glandular stomach by a constriction. [more]Gizzard - Community and Resources

Noun
1. thick-walled muscular pouch below the crop in many birds and reptiles for grinding food
(synonym) ventriculus, gastric mill
(hypernym) pouch, pocket

(n.)
The second, or true, muscular stomach of birds, in which the food is crushed and ground, after being softened in the glandular stomach (crop), or lower part of the esophagus; the gigerium.
  

(n.)
A thick muscular stomach found in many invertebrate animals.
  

(n.)
A stomach armed with chitinous or shelly plates or teeth, as in certain insects and mollusks.