MOVEMENTS OF THE ALIMENTARY CANAL. 737 



Movements of the Large Intestine. The opening from the 

 small intestine into the large is controlled both by the ileocecal 

 valve and by a sphincter, the ileocecal or ileocolic sphincter. 

 It is stated that this sphincter is normally in tonus and that 

 its condition of tonus is regulated through the thoracic autonomic 

 fibers received by way of the splanchnic nerve and superior mesen- 

 teric ganglion. Stimulation of the splanchnic nerve is said to cause 

 contraction of the ileocolic sphincter.* The musculature in the 

 large intestine has the same general arrangement as in the small, and 

 the usual view has been that the movements are similar, although 

 more infrequent, so that the material received from the small intes- 

 tine is slowly moved along while becoming more and more solid 

 from the loss of water. The contents of the ascending colon are 

 soft and semiliquid, but in the distal end of the transverse colon 

 they attain the consistency of the feces. Bayliss and Starling 

 state that their law of intestinal peristalsis holds in this portion of 

 the intestine, that is, local excitation causes a constriction above 

 and a dilatation below the point stimulated. Cannon, f from his 

 studies of the normal movements in cats, as seen by the Roentgen 

 rays, comes to the conclusion that the movements in the proximal 

 portion of the large intestine show a marked peculiarity. He 

 divides the large intestine into two parts; in the second, correspond- 

 ing roughly to the descending and distal portion of the transverse 

 colon, the food is moved toward the rectum by peristaltic waves. 

 A number of constrictions may be seen simultaneously within a 

 length of some inches. In the ascending colon and cecum, on the 

 contrary, the most frequent movement is that of antiperistalsis. 

 The food in this portion of the canal is more or less liquid and its 

 presence sets up running waves of constriction, which pass toward 

 the ileocecal valve. These waves occur in groups separated by 

 periods of rest. They seem to originate from a constricted ring 

 which pulsates, each contraction starting an anastaltic wave. 

 The presence of the ileocecal valve prevents the material from 

 being forced back into the small intestine. The value of this 

 peculiar reversal of the normal movement of the bowels at this 

 particular point would seem to lie in the fact that it delays the 

 passage of the material toward the rectum, and by thoroughly 

 mixing it gives increased opportunities for the completion of the 

 processes of digestion and absorption. In animals with a saccu- 

 lated colon the separate sacs or haustra may exhibit rhythmic 

 contractions somewhat similar to the rhythmic segmentations 

 in the small intestine. J These movements (haustal churning) 



* Elliott, "Journal of Physiology," 1904, 31, 157. 



t Cannon, loc. cit. 



t Elliott and Barclay-Smith, "Journal of Physiology," 31, 272, 1904. 



47 



