334 ANIMAL PHYSIOLOGY. 
pharynx seize it and press it on into the gullet; when the mor- 
sel is small or liquid is swallowed, it is rapidly propelled on- 
ward by the tongue, the cesophagus and pharynx being largely 
passive at the time, though contracting slowly afterward ; at 
the same time the larynx as a whole is raised, the epiglottis 
pressed down, chiefly by the meeting of the tongue and itself, 
while its cushion lies over the rima glottidis, which is closed or 
all but closed by the action of the sphincter muscles of the 
larynx, so that the food passes over and by this avenue of life, 
not only closed but covered by the glottic lid. The latter is 
not so essential as might be supposed, for persons in whom it 
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 esophagus 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 con- 
strictors of the pharynx is anticipated by the closure of the 
passage by the palato-glossi of the anterior pillars of the fauces. 
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. 4 
Swallowing will 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, 
