Now that which is spread over the omasum (Heb. These are the rumen, reticulum, omasum, and abomasum. The function of the omasum is not completely understood. The laminae greatly increase the surface area of the omasum. "Gannap" are usually made of beef liver, omasum, or fish. The oesophageal groove, which links the oesophagus and the omasum, is located in the reticulum. Compared with domestic cattle, the rumen of yaks is unusually large, relative to the omasum. The omasum is known as the "many plies". The omasum also absorbs volatile fatty acids and ammonia. The omasum comes after the rumen and reticulum and before the abomasum.