The crop (in front) is where food is stored temporarily. Sometimes called, colloquially, the "craw." Food is digested in the proventiculus and gizzard, aka the equivalent of the stomach. Grit in the gizzard grinds grain and seeds, because chickens don't have teeth. You should always provide a separate bowl or dish of crushed granite grit for your chickens for this reason. Also, in another vessel, crushed oyster shell, for making strong egg shells. Only laying hens will eat that. Forgive me if you already know some of this.