306 DEGLUTITION. 



(2.) The jaws are pressed against each other by the muscles of 

 mastication (N. trigeminus), while at the same time the lower jaw 

 affords a fixed point for the action of the muscles attached to it and the 

 hyoid bone. 



(3.) The tip, middle, and root of the tongue, one after the other, are 

 pressed against the hard palate, whereby the contents of the mouth are 

 propelled towards the pharynx. 



(4.) When the bolus has passed the anterior palatine arch (the 

 mucus 'of the tonsillar glands making it slippery again), it is prevented 

 from returning to the mouth by the palato-glossi muscles which lie in 

 the anterior pillars of the fauces, coming together like two side-screens 

 or curtains, meeting the raised dorsum of the tongue (Stylo-glossus 

 Dzondi, 1831). 



(5.) The morsel is now behind the anterior palatine arch and the 

 root of the tongue, and has reached the pharynx, where it is subjected 

 to the successive action of the three pharyngeal constrictor-muscles 

 which propel it onwards. The action of the superior constrictor of 

 the pharynx is always combined with a horizontal elevation (Levator 

 veli palatini; N. facial is), and tension (Tensor veli palatini; X. frige- 

 minus, otic ganglion} of the soft palate (Bidder, 1838). The upper 

 constrictor presses (through the pterygo-pharyngeus) the posterior and 

 lateral walls of the pharynx tightly against the posterior margin of the 

 horizontal tense soft palate (Passavant), whereby the margins of the 

 posterior palatine arches (palato-pharyngeus) are approximated. The 

 pharyngo-nasal cavity is thus completely shut off, so that the bolus 

 cannot be pressed backwards into the nasal cavity. In cases where 

 the soft palate is defective, part of the food usually passes into the 

 nose. 



(6.) The bolus is propelled onwards by the successive contractions 

 of the constrictors of the pharynx until it passes into the oesophagus. 

 At the same time the entrance to the glottis is closed, else the morsel 

 would pass into the larynx. 



Falk and Kronecker assert, that by the rapid contraction of the transversely 

 striped muscles which diminish the aperture of the mouth, the bolus is projected 

 into the oesophagus, so that peristalsis of the pharynx and oesophagus only occurs 

 during forced deglutition. 



If we make a series of efforts to swallow, one after the other, con- 

 traction of the oesophagus takes place only after the last attempt. 

 Kronecker and Meltzer found that stimulation of the glosso-pharyngeal 

 nerve inhibited the act of deglutition and the propagation of the move- 

 ment through the oesophagus. Section of both nerves causes tonic 

 epasm of the oesophagus and cardia. 



