The most elaborate apparatus for digesting cellulose is the familiar one used by the ruminants such as antelope, deer, buffalo as well as domestic sheep and cows (order Artiodactyla). They clip grass from their pasture with the lower incisors, pressing it against the tongue or the gums of the upper jaw, which has no teeth in the front. They then swallow it immediately and it goes down to the rumen, a chamber of the stomach which contains a particularly rich brew of bacteria. There it is churned back and forth for several hours, squeezed by a muscular bag, while the bacteria attack the cellulose. Eventually, the mash is brought up the throat, a mouthful at a time, to be chewed in a particularly thorough way by the molars. Ruminants can move their jaws not only up and down but backwards, forwards and sideways. This ruminating can be done, however, at leisure and in safety, when the animal has left the exposed feeding grounds and is relaxing in the shade during the heat of the day. Eventually the mouthful is swallowed for the second time. It goes past the rumen and on to the stomach proper which has absorptive.