$22 OF MASTICATION AND DEGLUTITION. 



Tides from the soft parts of the mouth, is mixed with 

 the saliva. 



345. The mixture of these fluids with a substance which 

 we are chewing, renders it not only a pultaceous and 

 easily swallowed bolus, but likewise prepares it for 

 further digestion and for assimilation. 



346. The mechanism* of deglutition, although very 

 complicated and performed by the united powers of 

 many very different parts, amounts to this. The tongue 

 being drawn towards its root, swelling and growing rigid, 

 receives the bolus of food upon its dorsum, which is 

 drawn into a hollow form. The bolus is then rolled 

 into the isthmus of the fauces, and caught with a cu- 

 rious and rather violent effort by the infundibulum of 

 the pharynx, which is enlarged and in some measure 

 drawn forward to receive it. The three constrictoresf 

 muscles of the pharynx drive it into the oesophagus. 

 These motions are all performed in very rapid succes- 

 sion and require but a short space of time. 



347. Nature has provided various contrivances for 

 opening and securing this passage.^ 



The important motion of the tongue is regulated by 

 the os hyoides. 



The smallest particle of food is prevented from enter- 

 ing the nostrils or eustachian tubes, by means of the 

 soft palate,§ which, as well as the uvula suspended from 



• Fr. Bern. Albinus, De Drglutitiont. LB. 1740. 4to. 



I'. J. Siindifort, Deglutitionis Mechanismus. LB. 1805. 4to. 



f Eustachius, Tab. xlii. fig. 4, 6. 



Santorini, Tab.Poslhum.vi. fig. 1. 



B. S. Albinus, Tab. Muscular. XII. fig. 23, 24. 



X J- C. Roscnraullcr, Icones Chirtirgico-Anatomicee. Fasc. I. Vinar. Ifc05. fol. 



§ Littre, Mem. de rAcad.Jet Sc. de Paris, 1718. tab. xv. 



