THE ACT OF RUMINATION. 325 



The precise nature of the operation, the external features 

 of which have now been described, has been the subject of 

 much investigation and discussion. The following points appear 

 to have been clearly established : 



1. Rumination is altogether prevented by paralysis of the 

 abdominal muscles, and it is a good deal impeded by any in- 

 terference with the free action of the diaphragm. 



2. Neither the paunch, nor the reticulum, ever becomes 

 completely emptied by the process of regurgitation. The 

 paunch is found half full of sodden fodder, even in animals 

 which have perished by starvation. 



3. When solid substances are swallowed, they pass indif- 

 ferently into the rumen, or reticulum, and are constantly driven 

 backward and forward, from the one into the other, by peris- 

 taltic actions of the walls of the stomach. 



4. Fluids may pass either into the paunch and the re- 

 ticulum ; or into the psalterium, and thence at once into the 

 fourth stomach, according to circumstances. 



5. Rumination is perfectly well effected after the lips of 

 the oesophageal groove have been closely united by wire 

 sutures. 



It would appear, therefore, that the cropped grass passes 

 into the reticulum and rumen, and is macerated in them. But 

 there is no reason to believe that the reticulum takes any 

 special share in modelling the boluses which have to be re- 

 turned into the mouth. More probably, a sudden and simul- 

 taneous contraction of the diaphragm and of the abdominal 

 muscles compresses the contents of the rumen and reticulum, 

 and drives the sodden fodder against the cardiac aperture of 

 the stomach. This opens, and then the cardiac end of the 

 oesophagus, becoming passively dilated, receives as much of the 

 fodder as it will contain. The cardiac aperture now becoming 

 closed, the bolus, thus shut off, is propelled, by the reversed 

 peristaltic action of the muscular walls of the oesophagus, into 

 the mouth, where it undergoes the thorough mastication which 

 has been described. 



The sodden fodder is prevented from passing out of the 

 psalterial aperture of the reticulum, in part by the narrowness 

 of that aperture, and in part by the fine grating formed by the 

 edges of the psalterial laminae. But when the semifluid 

 matter, returned after mastication, once more reaches the 

 cardia, it is compelled to pass toward the psalterial end of the 

 reticulum (even apart from the guidance afforded by the lips 

 of the oesophageal groove) on account of the direction of the 



