338 



VETERINARY PHYSIOLOGY 



direct to the abomasum or true stomach. But when solid 

 food is taken the pillars of the oesophageal groove relax, and 

 the oesophagus then communicates with the rumen and 

 reticulum to which the food passes. The fluid part tends to 

 accumulate in the reticulum. After feeding, if the animal 

 be comfortable and undisturbed, rumination or " chewing the 

 cud " begins. By fixation of the diaphragm in the position 

 of inspiration, and the contraction of the muscular walls of 

 the rumen and reticulum and of the abdomen, some of the 

 contents of the rumen accompanied by fluid from the 

 reticulum is passed into the oesophagus. A bolus is cut off 

 by contraction of the cardiac end of the oesophagus, and by 

 a reversed peristalsis, is carried to the mouth. The fluid is 

 immediately squeezed out and reswallowed, passing along the 

 oesophageal groove to the omasum and thence to the true 

 stomach. The mass left in the mouth undergoes a second 

 process of mastication and insalivation. The finely com- 

 minuted pasty material is then reswallowed, and by a con- 

 traction of the pillars of the oesophageal groove the omasum 

 is drawn towards the oesophagus, and receives the material. 



In the omasum it is reduced to a still finer state of division 

 bv the orindinsr action of the hard leaves, between which it 

 filters throusfh to the true stomach. Even after remastica- 

 tion the food, if not in a fine enough state of division, may 

 pass again to the rumen instead of to the omasum. 



A certain degree of distension of the rumen is necessary 

 to make regurgitation possible. This is maintained by the 

 constant activity of the parotid glands, whose secretion 

 constitutes a considerable proportion of the contents of the 

 rumen. 



The flow of saliva and the process of rumination 

 cease in disease. Under these conditions the food may 

 become dry and caked and set up inflammatory changes. 

 Impaction may occur, especially in the omasum. The moist 

 mouth indicating a flow of saliva, and the commencement of 

 rumination are of great value in prognosis. 



The ox spends about seven hours out of the twenty-four 

 ruminating. A bolus of about 100 grams is regurgitated, 

 remasticated, and reswallowed in rather less than one minute. 



