Digestion. 139 



stomachs, the choice of stomach being determined, as we 

 shall presently point out, by the condition in which the 

 food is swallowed. 



The oesophageal groove possesses two so-called lips or 

 pillars, the anterior being formed by the reticulum, the 

 posterior by the rumen. These pillars are composed of 

 involuntary muscular fibres arranged longitudinally and 

 transversely, by which means the groove can be shortened 

 and constricted. By a contraction of the pillars the third 

 stomach may be shut off from the first and second, and 

 the opening into it brought nearly into apposition with the 

 • esophagus ; when the pillars are relaxed the oesophagus 

 communicates more directly with the first and second 

 stomachs. Another function of the groove is to cut off a 

 pellet of food pressed into it by the contraction of the 

 rumen and reticulum, the pellet or bolus being then passed 

 into the oesophagus for remastication. 



The food which has been lightly crushed in the mouth 

 enters the rumen, meeting there with material from the 

 last meal, as the rumen never empties itself. Here the 

 maceration previously spoken of occurs, the food the whole 

 time being slowly and deliberately churned. In the second 

 stomach the same changes are occurring as in the rumen. 



In rumination the oesophageal groove has been con- 

 sidered to play an important part ; but Colin has shown 

 that even if the lips be stitched together rumination may 

 occur, so that the theory that the bolus is formed between 

 the lips of the canal, and forced up the oesophagus by the 

 powerful contraction of the rumen, is not correct according 

 to this observer. What he says occurs is, that during the 

 churning movement the food is gently pressed against the 

 lips of the groove, when, by a spasmodic contraction of 

 the diaphragm and abdominal muscles, some of the liquid 

 from the reticulum and some of the solid from the rumen 

 is carried up the oesophagus, which latter by the contrac- 

 tion of its funnel-shaped extremity cuts off the bolus, and 

 by its reversed peristaltic action conveys it to the mouth. 

 In passing under the velum palati the liquid portion is 



