MOVEMENTS OF THE ALIMENTARY CANAL. 649 



small intestine is slowly moved along while becoming more and 

 more solid from the absorption of water, until in the form of feces 

 it reaches the sigmoid flexure and rectum. 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,* however, 

 from his studies of the normal movements in cats, as seen by the 

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

 large intestine show a marked peculiarity previously overlooked. 

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

 responding roughly to the descending 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 and transverse 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, beginning somewhere in the 

 colon, pass toward the ileocecal valve. These waves occur in groups 

 separated by periods of rest. The presence of the ileocecal valve 

 prevents the material from being forced back into the small in- 

 testine. The value of this peculiar reversal of the normal move- 

 ment 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. As the 

 colon becomes filled some of the material penetrates into the 

 descending part where the normal peristalsis carries it toward the 

 rectum. 



The large intestine particularly the descending colon and 

 rectum receives its nerve supply from two sources: (1) Fibers 

 which leave the spinal cord in the lumbar nerves (second to fifth 

 in cat), pass to the sympathetic chain, and thence to the inferior 

 mesenteric ganglia, which probably forms the termination of the 

 preganglionic fiber. From this point the path is continued by fibers 

 running in the hypogastric nerves and plexus. Stimulation of these 

 fibers has given different results in the hands of various observers, 

 but the most recent work f indicates that they are inhibitory. (2) 

 Fibers that leave the cord in the sacral nerves (second to fourth) 

 form part of the nervi erigentes and enter into the pelvic plexus. 

 When stimulated these fibers cause contractions of the muscular 

 coats; they may be regarded, therefore, as motor fibers. As in the 



* Cannon, loc. cit. 



t Langley and Anderson, "Journal of Physiology," 18, 67, 1895. Bay- 

 liss and Starling, ibid., 26, 107, 1900. Also Wischnewsky, in Hermann's 

 " Jahresbericht der Physiologie, " vol. xii, 1905. 



