MOVEMENTS OF THE ALIMENTARY CANAL. 727 



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 con- 

 traction starting an anastaltic wave. The presence of the ileo- 

 cecal 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, 

 but from the reports received from x-ray examinations in man it 

 is doubtful whether this kind of movement is usual in the human 

 being. These observers lay stress upon a different kind of move- 

 ment which they designate as mass peristalsis, that is, strong 

 peristaltic movements which last only a few seconds, but move the 

 contents from one division to another, from ascending to trans- 

 verse colon, etc. These movements occur only rarely, three to 

 four times a day. Hurst connects them with the act of eating, 

 assuming the existence of a gastrocolic reflex which is set into play 

 by the entrance of food into the stomach. According to this view 

 the food is moved along the colon at long intervals by the sudden 

 displacements caused by the mass peristalsis. In between the 

 contents are not moved except for the local agitation caused by 

 the rhythmic contractions of the haustra (haustral churning). 



The large intestine receives its nerve supply from two sources 

 (Fig. 287): (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 form 

 the termination of the preganglionic fibers. 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 general view * is that they 

 are inhibitory. (2) Fibers that leave the cord in the sacral nerves 

 (second to fourth) form part of the nervi erigentes or pelvic nerves 

 and enter into the hypogastric plexus. When stimulated these 

 fibers cause contractions of the muscular coats; they may be re- 

 garded, therefore, as motor fibers. As in the case of the small 

 intestine and stomach, we may assume that these motor and in- 

 hibitory fibers serve for the reflex regulation and adaptation of the 

 movements. In this connection attention may be called to the 

 difference in innervation between the stomach and small intestine, 

 on the one hand, and the colon and rectum on the other. The 



* Langley and Anderson, "Journal of Physiology," 18, 67, 1895. Bayliss 

 and Starling, ibid., 26, 107, 1900; Gaskell, "The Involuntary Nervous System," 

 1916. 



