DIGESTION OP POOD. 336 



was absent have been known to swallow fairly well. The / 

 ascent of the larynx any one may feel for himself ; and the be- 

 havior of the pharynx and larynx, especially the latter, may 

 be viewed by the laryngoscope. The grip of the pharyngeal 

 muscles and the oesophagus may be made clear by attaching a 

 piece of food (meat) to a string and allowing it to be partially 

 swallowed. 



The upward movement of food under the action of the 

 constrictors of the pharynx is anticipated by the closure of 

 the passage by the palato-glossi of the anterior pillors of the 

 fauces. t. 



The circular muscular fibers of the gullet are probably the 

 most important in squeezing on the food by a peristaltic move- 

 ment, passing progressively over the whole tube, though the 

 longitudinal also take part in swallowing, perhaps, by steady- 

 ing the organ. 



Deglutition can take place in an animal so long as the 

 medulla oblongata remains intact ; and the center seems to lie 

 higher than that for respiration, as the latter act is possible / 

 when, from slicing away the medulla, the former is not. An- / 

 encephalous monsters lacking the cerebrum can swallow, suck/ 

 and breathe. 



Food placed in the pharynx of animals when unconscious'] 

 is swallowed, proving that volition is not essential to the act;] 

 but our own consciousness declares that the first stage, or the' 

 removal of the food from the mouth to the pharynx, is volun- 

 tary. 



When we seem to swallow voluntarily there is in reality a 

 stimulus applied to the fauces, in the absence of food and drink, 

 either by the back of the tongue or by a little saliva. 



It thus appears that deglutition is an act in the main reflex, 

 though initiated by volition. The afferent nerves concerned 

 are usually the glosso-pharyngeal, some branches of the fifth, 

 and of the vagus. The efferent nerves are those of the numer- 

 ous muscles concerned. 



When food has reached the gullet it is, of course, no longer 

 under the control of the will. 



Section of the vagus or stimulation of this nerve modifies 

 the action of the oesophagus, though it is known that contrac- 

 tions may be excited in the excised organ ; but no doubt nor- 

 mally the movements of the gullet arise in response to natural 

 nerve stimulation. 



