DEGLUTITION OR 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 esophagus or gullet ; this 
cavity, termed the pharynz, communicates above with the 
nostrils, and in front with the larynx, which is at the top of 
the trachea or windpipe. The esophagus 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 
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, im 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 fiuid particles from entering it. But it sometimes 
happens that, if the breath be drawn-in at the moment or 
y almost suffocating cough (§ 342) ; the effect of which 
sometimes to drive it up through the glottis, and thus to 
rid of the source of irritation. 
| 194. The act of swallowing is itself involuntary, and may 
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