32 PHYSIOLOGY AT THE FAKM. 



the pharynx ; in the third stage, it is transmitted through the 

 gullet to the stomach. 



The collecting of the masticated food on the tongue is 

 accomplished by the complicated movements of the tongue 

 itself, and by the contraction of the fore part of the cavity 

 of the mouth. In like manner the bolus is driven backwards 

 on the tongue by the contraction of the back part of the 

 cavity of the mouth. In the second stage of deglutition the 

 act is somewhat complex. It begins as soon as the bolus 

 has arrived at the back part of the tongue. It may be re- 

 marked that, except in drinking, the mouth during deglutition 

 is always closed. This, then, is a first step in the second stage 

 of deglutition. Then the hyoid bone is drawn upwards and 

 forwards by muscular contractions, and along with the hyoid 

 bone the larynx and pharynx, which are connected with that 

 bone, are made to move upwards and forwards the epiglottis 

 or lid of the larynx is at the same time depressed so as to 

 close the larynx. Now a kind of convulsive movement occurs, 

 during which the bolus is precipitated across the epiglottis 

 into the pharynx. The pharynx, being a muscular organ, con- 

 tracts, and transmits the bolus onwards to the gullet, and the 

 gullet being also muscular, propels, by its movements, the 

 bolus into the stomach. The mouth is shut in order to fix the 

 lower jaw, from which the principal muscles concerned in 

 raising the hyoid bone originate. 



The whole act of deglutition is an involuntary act, belonging 

 to that description of acts technically known as reflex acts. 

 The second stage of deglutition is indeed a remarkable illustra- 

 tion of acts of that kind. As soon as the bolus arrives at the 

 back part of the tongue, it stimulates the extremities of the 

 afferent nervous filaments distributed there ; this stimulus or 

 impression is, by these nervous filaments, conveyed to the 

 nervous centre within the skull, where an effect is produced 



