MOVEMENTS OF THE ALIMENTARY CANAL. 713 



it was found that food introduced into this opening was not 

 moved toward the stomach until the patient ^made a swallow- 

 ing movement.* The afferent nerves concerned in this reflex 

 are the sensory fibers to the mucous membrane of the pharynx 

 and esophagus, including branches of the glossopharyngeal, 

 trigeminal, vagus, and superior laryngeal division of the vagus. 

 Artificial stimulation of this last nerve in the lower animals 

 is known to produce swallowing movements. Several observers 

 have attempted to determine the precise area or areas in the 

 pharyngeal membrane from which the sensory impulses lib- 

 erating the reflex normally start. According to Kahn,f the 

 most effective areas from whose stimulation the reflex may be 

 produced vary in location in different animals. In the rabbit the 

 reflex is originated most easily by stimulation at the entrance to 

 the pharynx — the soft palate — along the fine extending from the 

 posterior edge of the hard palate to the tonsils (superior maxil- 

 lary branch of trigeminal); in the dog irritation of the posterior 

 pharyngeal wall is most effective (glossopharyngeal nerve); in 

 monkeys the area is approximately as in rabbits, — that is, in the 

 region of the tonsils. The motor fibers concerned in the reflex 

 comprise the hypoglossal, the trigeminal, the glossopharj^ngeal, 

 the vagus, and the spinal accessory. For an act of such complexity 

 and such perfect co-ordination it has been assumed that there is a 

 special nerve center, the swallowing or deglutition center, which has 

 been located in the medulla at the level of the origin of the vagi. 

 There is little positive knowledge, however, concerning the existence 

 of this center as a definite group of intermediary nerve cells, after 

 the type of the vasoconstrictor or respiratory center, which send 

 their axons to the motor nuclei of the several efferent nerves con- 

 cerned. As in the case of other complicated reflex acts, we can only 

 say that the deglutition reflex is controlled by a definite nervous 

 mechanism the final motor cells of which are scattered in the several 

 motor nuclei of the efferent nerves mentioned above. 



So far as the esophagus is concerned, the motor fibers are 

 received from the vagus, and in normal swallowing these fibers are 

 excited reflexly from the pharynx at the beginning of the act. 

 That is to say, the initial sensory stimulus in the pharynx hberates 

 a series of reflex movements which begin with the contraction of the 

 mylohyoid muscle and end with a peristaltic wave that progresses 

 in orderly fashion along the esophagus. It has been shown, 

 however, that the bolus when it reaches the esophagus may start 

 a different order of reflexes by local stimulation of the sensory fibers. 

 These stimuli lead to reflex contraction of the musculature above 

 the bolus, and thus a series of reflexes are liberated which are suffi- 

 cient to move the bolus downward. If the primary reflex initiated 



* Quoted from Cohnheim in Nagel's "Handbuch d. Physiologie." 

 t Kahn, "Archiv f. Physiologie," 1903, suppl. volume, 386. 



