162 TEXT-BOOK OF PHYSIOLOGY. 



laryngeal nerves, a touch of the palate excited the same phenomenon. Under 

 such circumstances the closure of the glottis must have been due to the con- 

 traction of its own intrinsic muscles and in consequence of a reflex action 

 through the inferior laryngeal nerves. 



The Nerve Mechanism of Deglutition. Deglutition is almost exclu- 

 sively a reflex act throughout its entire extent, and requires for its inaugura- 

 tion merely a stimulus to some portion of the mucous membrane of the deglu- 

 titory canal. The first stage is primarily voluntary, but from inattention to 

 the process may become secondarily reflex. The origin and course of the 

 afferent nerves, stimulation of which excite reflexly the movements of the 

 pharynx and esophagus, however, are practically unknown. In the rabbit 

 deglutition can be excited by stimulating the anterior central part of the soft 

 palate; in man it has not yet been possible to locate an area stimulation of 

 which will give rise to a reflex deglutitory act. Though electric stimulation 

 of the superior laryngeal nerve will cause reflex deglutitory movements, it is 

 obvious that the terminals of this nerve cannot be the source of the natural 

 afferent impulses. Stimulation of the glosso-pharyngeal nerve causes an 

 inhibition of the movements. 



The center from which emanate nerve impulses which excite the various 

 muscles to action has been located experimentally in the medulla oblongata 

 just above the alae cinereae. The efferent nerves comprise branches of the 

 facial, hypoglossal, motor filaments of the third division of the fifth nerve, 

 motor filaments of the glosso-pharyngeal and vagus nerves derived in all 

 probability directly from the medulla oblongata. Inasmuch as the different 

 mechanisms of this reflex, act not only in a coordinate but sequential manner, 

 it would appear as if the deglutition center sent out, in response to the nerve 

 impulses coming from a single peripheral area, a series of nerve impulses 

 successively to successive portions of the canal, through the groups of nerve- 

 cells corresponding to the origins of the efferent nerves. That this orderly and 

 progressive peristalsis usually observed is due to a sequence of changes in the 

 central nerve system is shown by the fact, that if the esophagus is divided or 

 a ring of it excised, the extremity in connection with the stomach will exhibit 

 a well-marked peristalsis after a short interval, when an act of deglutition is 

 excited in the customary manner. The efferent nerve fibers, which stimulate 

 the esophageal muscles to action are contained in the trunk of the vagi nerves 

 for after their division the peristalsis is abolished. 



In addition to this primary reflex mechanism, the esophagus appears to 

 possess a secondary reflex mechanism consisting of a series of reflex arcs, 

 whose afferent and efferent paths are found in the trunk of the vagus and 

 both connected with successive portions of the esophagus. The first mechan- 

 ism is temporarily suspended during deep anesthesia while the second per- 

 sists. (Meltzer.) 



Though the peristalsis of the esophagus is excited by nerve impulses 

 coming through the vagus nerves and is abolished by their division, Cannon 

 has shown by means of the Rontgen rays that this effect for the lower portion 

 of the esophagus, at least in the cat and monkey, is of a temporary duration 

 only, lasting from one to several days, after which a peristalsis again develops 

 with sufficient vigor to force food through the cardiac orifice into the stom- 

 ach. The muscle coat of this portion of the esophagus is composed of non- 



