228 DEGLUTITION. 



(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). 



(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. facialis) and tension (Tensor veli palatini ; 

 N. trigeminus, otic ganglion) of the soft palate. 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, 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 persons with congenital or acquired defects of the soft palate, or cleft-palate, during 

 swallowing, food passes into the nose. 



(6) Falk and Kronecker assert, that by the energetic contraction of the muscles 

 which diminish the cavity of the mouth, especially the mylo-hyoid, the bolus is 

 " projected " through the pharynx and oesophagus. [They even assert that the 

 bolus reaches the cardia before even the musculature of the pharynx or oesophagus 

 can contract, and further that the pharyngeal muscles of a dog may be divided 

 without making swallowing impossible.] If we make a series of efforts to swallow, 

 one after the other, as in drinking, contraction of the pharynx and oesophagus takes 

 place only after the last effort. Thus each new act of deglutition in the mouth 

 inhibits (by stimulation of the glosso-pharyngeal nerve) the movements in the parts 

 of the oesophageal tube situated below it. 



(7) The bolus is propelled onwards by the successive contraction of the upper, 

 middle, and lower 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, or, as is generally said, would " pass the wrong way." 



Duration. According to Meltzer and Kronecker, the duration of deglutition in the mouth 

 is 0'3 sec; then the constrictors of the pharynx contract 0*9 sec; afterwards, the upper part 

 of the oesophagus ; then after 1*8 sec. the middle ; and after another 3 sec. the lower constrictor. 

 The closure of the cardia, after the entrance of the bolus into the stomach, is the final act in the 

 total series of movements. 



Sounds during Deglutition. If the region of the stomach be auscultated during the act of 

 swallowing, two sounds may be heard ; the first one is produced when the bolus i3 projected into 

 the stomach ; the second occurs when the peristalsis, which takes place at the end of swallow- 

 ing, squeezes the contents of the oesophagus through the cardia {Meltzer, Zenker, Ewald). [The 

 latter occurs 4-5 mins. afterwards. In man, when water alone is swallowed, there is no sound, 

 but when it is mixed with air there is, and it is generally heard because air is usually swallowed 

 with the food or drink (Qui7icke).] 



The closure of the glottis is effected in the following manner : (a) The whole 

 larynx the lower jaw being fixed is raised ujpwards and forwards, while at the 

 same time the root of the tongue hangs over it. The hyoid bone is raised forwards 

 and upwards by the genio-hyoid, anterior belly of the digastric, and mylo-hyoid ; 

 the larynx is approximated close to the hyoid bone by the thyro-hyoid. (b) When 

 the larynx is raised, so that it comes to lie below the overhanging root of the 

 tongue, the epiglottis is pressed downwards over the entrance to the glottis, and 

 the bolus passes over it. The epiglottis is also pulled down by the special muscular 



