Omasum

omasum [ō′mā·səm]

(vertebrate zoology)

The third chamber of the ruminant stomach where the contents are mixed to a more or less homogeneous state. Also known as manyplies; psalterium.

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Omasum 

one of the glandless sections in the multicompartmental stomach of ruminants (it is not present in Tragulidae and camels), located between the reticulum and abomasum. The mucous coat on the inner surface of the omasum, except for on the bottom, forms longitudinal folds of varying heights, or laminae that are similar to the pages of a book (hence the Russian name knizhka, literally “book”). These laminae are mobile, since they have smooth muscle. Thus, the cavity of the omasum is divided into narrow chambers and only at its base, which the free ends of the laminae do not reach, is there an integral cavity, the canal of the omasum. In the omasum the feed that has been swallowed again by the animal after rumination is finally ground down and converted into a gruel-like substance that passes into the abomasum. Along the bottom of the omasum there is an abomasal groove, the sulcus omasi, serving as a direct continuation of the reticular groove; liquified food can flow along it directly into the abomasum.