DIGESTION OF FOOD. 



329 



The abomasum or rennet resembles other forms of true 

 digestive stomachs in all essential particulars. 



While the opening between the flrst and second stomachs is 

 large enough to allow of free intercommunication, the reverse 

 applies to the entrance into the third stomach. 



The rumen is nearly always tolerably well filled with food, a 

 condition of things favorable to its return for remastication. 



Fig. 273. — Stomach of horae (after Chauveaii). A, cardiac extremity of cesophagns; 

 B, pyloric ring. 



We may conclude that only food in a proper form for the 

 action of the fourth stomach passes to any extent beyond the 

 first two. 



After the food has been duly softened and has undergone 

 some fermentative changes in the rumen, leading to the evolution 

 of gases (COa, HaS) and certain organic acids (acetic, butyric), 

 it is regurgitated by a process that closely resembles vomiting. 



In this the diaphragm and the abdominal muscles, as well 



