EUMINATION. 325 



■walls are proportionately weak. On the other hand, the reticulum is the 

 smallest of the four gastric compartments ; its muscles are, compara- 

 tively speaking, strong, and under stimulation of the pneumogastric 

 nerve it has been found to decrease one-third in volume. Furthermore 

 the oesophagus communicates more directly with the second than with 

 the first stomach, its opening into the reticulum having somewhat the 

 shape of a funnel. The lips of the oesophageal gutter are not essential 

 to the formation of the cud, for Colin found that stitching the lips of 

 this canal together with wire sutures did not interfere with rumination ; 

 so, also, the reticulum has been found not to be solely concerned in this 

 operation, for Flourens excised a portion of this organ and sewed the 

 remainder to the abdominal walls in a sheep, and yet rumination was 

 possible. Colin has shown that the gradual insertion of food between 

 the pillars of the gullet is sufficient for the regurgitation essential to the 

 act of rumination. Moreover, that the oesophageal pillars are not essen- 

 tial to the formation of the cud is proved by comparative anatomy, 

 where we find rumination occurring in the llama and dromedary, where 

 only a single pillar is present. The contents of the first two stomachs, 

 as already mentioned, are subjected to a gentle churning motion, and the 

 tendency of the food is to strike forward against the pillars of the 

 oesophagus. As it presses forward by its own weight, and the slight degree 

 of impulse which the contractions of the rumen and reticulum give to it, 

 there is a contraction of the diaphragm and abdominal muscles, and this 

 causes a portion of the contents of these two compartments to engage in 

 the infundibular orifice of the gullet, whence they are carried upward by 

 reversed peristalsis. 



The action of the abdominal muscles and diaphragm are necessary 

 to permit of rumination, for when, as was proved by Flourens, the 

 diaphragm is paralyzed by section of the phrenic nerves, although 

 rumination may take place, the abdominal muscles will be called upon to 

 make an extra effort. When the abdominal muscles are paralyzed, as by 

 section of the spinal cord, rumination is then impossible. This is also 

 the case when both pneumogastric nerves are divided. That the 

 diaphragm and abdominal muscles are the organs whose contraction 

 determines the act of regurgitation is probable on other grounds. The 

 muscular fibres of the rumen and reticulum are largely of the pale, 

 nnstriped variety, and their contraction is slow and prolonged. The 

 rapidity of the act of regurgitation points to its being produced by red, 

 striped, voluntary muscles. When the cud engages in the oesophagus, a 

 constant movement may be seen in the flank, more sensible than the 

 other respiratory movements, and which is due to contraction of the 

 abdominal muscles, an inspiration being followed by a rapid expiration. 

 This movement is coincident with the entrance of the bolus into the 



