[Illustration: FIG. 10.--A section of the wall of the rumen and reticulum,
showing the oesophageal groove: lips of groove; opening from
oesophagus; and opening into omasum.]

RUMINANTS have a compound stomach (Figs. 9 and 10). The capacity of the
stomach of the ox is between twenty and thirty gallons. The four
compartments into which it is divided are the rumen, reticulum, omasum, and
abomasum or true stomach. The rumen is the largest compartment, with a
capacity of more than twenty gallons. The reticulum is the smallest, with a
capacity of about one-half gallon.

After a brief mastication, the food passes directly to the _rumen_. Here it
is subjected to a churning movement that mixes and presses the contents of
the rumen forward in the direction of the oesophageal opening, where it is
ready for regurgitation. It is then carried back to the mouth, remasticated
and returned to the rumen. This is termed rumination. All food material
that is sufficiently broken up is directed toward the opening into the
third compartment by the oesophageal grove (Fig. 10), a demi-canal that
connects this with the oesophageal opening.

The third compartment, the _omasum_, communicates anteriorly with the
second and first, and posteriorly with the fourth compartment or true
stomach. The interior arrangement of this compartment is most singular. It
is divided by a number of large folds of the lining membrane between which
are smaller folds. It is between these folds that the contents pass.

The first three compartments possess no glands capable of secreting a
digestive juice. However, important digestive changes occur. The
carbohydrates are digested by means of enzymes contained in the feed. The
most important function of the rumen and omasum is the maceration of the