omasum

thumb|right|The ruminant digestive systemThe omasum, also known as the green, the fardel, the manyplies and the psalterium, is the third compartment of the stomach in ruminants. The omasum comes after the rumen and reticulum and before the abomasum. Different ruminants have different omasum structures and function based on the food that they eat and how they developed through evolution.

== Anatomy == thumb|The 'leaflets' of the omasumThe omasum can be found on the right side of the cranial portion of the rumen. It receives food from the reticulum through the reticulo-omasal orifice and provides food to the abomasum through the omaso-abomasal orifice. The omasum is spherical to crescent shape and has multiple leaflets similar to a book, called omasal laminae. The omasal laminae are made of thin muscular layers covered with a nonglandular mucous membrane. The omasal laminae come from the sides of the large curvature and project towards the inside of the omasum, extending from the reticulo-omasal orifice to the omaso-abomasal orifice. They greatly increase the surface area of the omasum. The laminae are covered in omasal papillae that are claw-like in some ruminants or blunt cones in others. These papillae further increase the surface area, and also provide increased friction against the food particles.