ig8 A MANUAL OF VETERINARY PHYSIOLOGY 



warty. Ellenberger, who has specially worked out the physi- 

 ology of this organ, and whose description we intend to follow, 

 describes the anterior papillae as resembling the teeth of a 

 harrow, the posterior papillae those of a file. In all cases the 

 papillae are arranged with their free end pointing towards the 

 abomasum, the object of this being to direct the food towards 

 the abomasum, and prevent its reflux towards the reticulum 

 when the walls of the organ contract. 



|The food may find its way into the omasum, either directly 

 from the oesophagus after remastication, or from the first or 

 second compartments. It is probable that its chief source of 

 supply is directly from the oesophagus, the omasum being drawn 

 forwards towards it by a contraction of the pillars of the oeso- 

 phageal groove, by which means communication with the rumen 

 and reticulum is cut off. Normally the reaction of the contents 

 of the omasum is neutral ; if found acid, it is due to regurgitation 

 from the true stomach. 



|We have the authority of Ellenberger for saying that the 

 organ secretes no digestive fluid, nor does it absorb. It is 

 peculiar in possessing a separate source of nerve-supply, stimula- 

 tion of the pneumogastric producing contraction of all the other 

 compartments but this. 



Further evidence of an independent nerve-supply is furnished 

 by the fact that after death the walls of the other stomachs relax, 

 but that of the omasum remains contracted. 



When the food arrives at the omasum the opening leading to 

 the abomasum is closed, and by means of the horny papillae at 

 the reticulum end of the organ the material is divided and directed 

 towards the leaves, the oesophageal groove at the same time 

 closing in order to prevent a reflux. The presence of the food 

 then causes a reflex contraction of the leaves, by which they are 

 rendered rigid and tense, and advance to meet the mass. The 

 leaves having been drawn forward, the fibres now relax, by which 

 movement the food is carried back with them. The direction 

 of the papillae on the leaves prevents the material from falling 

 out of the chambers formed between the leaves, while the curve 

 of the organ enables the leaves to give each other mutual support, 

 like the bricks in an arch, so that no muscular effort is required 

 to maintain the food in position . The walls of the omasum are 

 strong, the circular fibres being three or four times as thick and 

 powerful as those longitudinally placed ; contraction of the walls 

 is almost constantly occurring. In this way the contents of the 

 omasum are moved towards the fourth stomach, the position 

 and direction of the papillae preventing them from' travelling in 

 the other direction. Each contraction drives the ingesta not 

 only towards the omasum, but more completely between the 



