DEGLUTITION OB SWALLOWING. 179 



in Birds and other animals that do not masticate their food, 

 hangs from the arch and sides of the palate, so as to touch 

 the tongue by its lower border ; but it can be lifted in such a 

 manner as to give the food free passage beneath it, into the 

 top of the gullet. When mastication is completed, the food 

 is collected on the back of the tongue into a kind of ball ; 

 and this, being carried backwards by the action of its muscles, 

 presses against the partition just mentioned, and causes it to 

 open. The food thus passes into a sort of funnel, formed by 

 the expansion of the top of the oesophagus or gullet; this 

 cavity, termed the pharynx, communicates above with the 

 nostrils, and in front with the larynx, which is at the top of 

 the trachea or windpipe. The oesophagus is a long and narrow 

 tube, which descends from the pharynx to the stomach, lying 

 just in front of the vertebral column, and behind the heart 

 and lungs. It is surrounded by muscular fibres, disposed in 

 various ways ; by the action of which the food that has once 

 passed into the pharynx is propelled downwards to the 

 stomach. 



193. But in order to reach this tube, the alimentary ball 

 must pass over the glottis or aperture of the larynx. With 

 a view to prevent its falling-in, the larynx is drawn, in the 

 very act of swallowing, beneath the base of the tongue ; and 

 this action presses down a little valve-like flap, the epiglottis, 

 upon the aperture, so as in general effectually to prevent any 

 solid or fluid particles from entering it. But it sometimes 

 happens that, if the breath be drawn-in at the moment 01 

 swallowing, a small particle of the food, or a drop of fluid, is 

 drawn into the glottis ; and this action (commonly termed 

 "passing the wrong way,") excites a violent coughing, the 

 object of which is to drive up the particle, and to prevent it 

 from finding its way into the lower part of the windpipe. It 

 may also happen that a larger substance may slip backwards, 

 by its own weight, into the glottis, when there was no 

 intention of swallowing, and when the larynx was conse- 

 quently not drawn forwards beneath the tongue. The presence 

 of such a substance in the windpipe excites a violent and fre- 

 quently almost suffocating cough ( 342) ; the effect of which 

 is sometimes to drive it up through the glottis, and thus to 

 get rid of the source of irritation. 



194. The act of swallowing is itself involuntary, and may 



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