You searched for: “rumen”
rumen (s) (noun), rumina (pl)
The large first chamber of a cud chewing animal's stomach in which microorganisms break down plant cellulose before the food is returned to the mouth for additional chewing: In the rumen, food is collected and then it is returned to the mouth as cud for chewing.

The rumen contains bacteria that can break down cellulose or the substance that forms the outer layer of plant cells and plant fibers.

Partially digested food from the rumen is digested further in the second chamber, or the "reticulum", and then regurgitated to be chewed as the cud.

When swallowed again, the food passes directly to the third and fourth chambers (the "omasum" and the "abomasum") which are considered to be the true stomachs for further digesting.

—Compiled from information that is presented in
The Osborne Illustrated Dictionaryi of Science;
by Corinne Stockley, Chris Oxlade, and Jane Wertheim;
Usborne Publishing, Ltd; London; 2001; page 271.
This entry is located in the following unit: rumin-, rumina- (page 1)