126 DEGLUTITION. 



mucous membrane is so ample, that when the gullet is at 

 rest and closed, its lining is thrown into longitudinal folds, 

 which are readily distended by the food swallowed. 



From the foregoing description, it will be understood that 

 the food has to pass from the mouth into the pharynx or 

 throat, from this into the gullet, and from the gullet into the 

 stomach. Muscular power is exerted for this purpose, and in 

 the first step the will controls the act, so that deglutition is 

 effected, or not, according to the animal's desire. In the 

 second effort, the will is only partially capable of influencing 

 the movement, and beyond this the act is perfectly in- 

 voluntary. 



When I say that the first effort in swallowing is voluntary, 

 it must not be- understood that, in the ordinary process of 

 feeding, a special act of the will induces the animal to pass 

 the food into the throat. We find, in ourselves, that it is 

 difficult to resist swallowing food which has been sufficiently 

 masticated; and the marvellous feature of an act which calls 

 into play so many organs as that of deglutition is, that they 

 all co-operate under the influence of the nervous system. 

 When a bolus is formed, independently of the will and by reflex 

 action, the mouth, throat, and gullet act in succession, and 

 force the morsel into the stomach. 



In considering the three stages in the process of deglutition, 

 I refer the reader to Pig. 65 to see how favourably situated 

 the throat and oasophagus are for the passage of substances 

 from the mouth to the stomach. The tongue and cheeks press 

 the food back through the pendulous soft palate 3, and at 

 the same time, from the active muscles being connected with 

 the hyoid bone supporting the tongue, the larynx and the 

 windpipe are drawn upwards. The throat, in fact, advances, 

 and opens for the reception of the food. The larynx closes, 

 and this is effected by a lateral contraction, as well as by a 



