42 PHYSIOLOGY OP FARM ANIMALS [CH. 



and after being carried down the oesophagus passes along the 

 oesophageal groov^e and enters the omasum or third stomach, 

 frequently called the manyplies owing to the wall bemg thrown 

 into folds which resemble the leaves of a book. Some of the 

 food, however, may return once more to the rumen. Whether 

 the food is to enter the rumen or the omasum appears to be 

 determined by its condition. It is only allowed to pass into the 

 third stomach if it is in a sufficiently divided condition. Its 

 entry is effected by the contraction of the lips of the groove. In 

 this way the rumen and reticulum are shut off and the oesophagus 

 communicates directly with the omasum. 



Fig. 26. Stomach of ox (from Smith, Messrs Bailliere, 

 Tindall and Cox). ,il and B rumen, C oesophagus, 

 IJ reticulum, E omasum, F abomasum. 



This compartment is not concerned in the process of rumina- 

 tion. Its chief characteristic is its strong muscular leaves lined 

 with coarse stratified epithelium. These act as a triturator and 

 strainer, and prevent food substances passing into the abomasum 

 or fourth stomach until they are in a sufficiently fine state of 

 division. 



The abomasum is the true digestive stomach corresponding 

 with the fundus portion of the horse's or pig's stomach. In it 

 are the glands which secrete the gastric juice containing pepsin, 

 and the other substances which are present in the gastric juice 

 of the horse. It is interesting to note that in the sucking rumi- 

 nant (e.g. the calf and lamb) the abomasum is the only compart- 

 ment which is functional, the first three stomachs being com- 



