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(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.



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.

References in periodicals archive ?
33185918G>A) was extremely significantly associated with carcass and meat quality, and particularly with the weight of the omasum and the pH of beef.
George Sun said Omasum has a big demand in China due to its nutritious and medicinal value.
The omasum of ruminant animals is a many-walled organ where part of the water is removed from the mass leaving the rumen and reticulum.
The omasum uses muscle action to press and further break down chewed grass cud into smaller pieces and squeeze out excess water.
Studies on the development of omasum in West African Dwarf goat (Capra hircus).
Omasum in bovines is a spherical to ovoid organ situated, right of midline in middle third of abdomen (Nickel et al.
Goats have a four-chambered stomach consisting of the rumen the reticulum the omasum and the abomasum.
Weights of the right and left halves of hot carcass, hide, head, shanks and tail, liver, heart, lung, kidneys, spleen, rumen-reticulum, omasum, abomasum, small intestine, and large intestine as well as internal adipose tissues were recorded.
Their digestive system includes a multi-chambered stomach including the reticulum, rumen, omasum, and abomasum.
Having just studied bovine anatomy in a veterinary technology program, I'd like to point out that the order of the four stomachs of the cow (from esophagus to small intestine) are: 1: Reticulum (the honeycombed texture); 2: Rumen (actually has a texture similar to short pile chenile and is called papillae); 3: Omasum (the folds); and 4: Abomasum (mucous-lined and most similar to what a human stomach would look like).
Therefore, whenever possible, entire carcasses or appropriate samples, including fixed and fresh specimens of liver, rumen, abomasum, omasum, reticulum, small intestine, large intestine, and brain, and when possible, whole blood, serum, feces, and rumen contents, should be submitted to a diagnostic lab for investigation.
Finally, feed material may be reduced in size to small and dense particles that pass out of the reticulum and rumen into the omasum.