DIGESTION 229 



Deglutition. 



The bolus which is formed by mastication and in- 

 salivation is pushed by the tongue to the back of the throat. 

 The cavity of the mouth is then closed by the approxi- 

 mation of the dorsum of the tongue to the palate by 

 the palato-glossal muscles, whilst the nose is shut off 

 by the elevation of the soft palate by the levator palati 

 and palato-pharyngeal muscles. This stage of deglutition 

 may be interfered with by paralysis of the tongue e.g., 

 in bulbar paralysis or of the soft palate, when fluids 

 tend to regurgitate into the nose e.g., in post-diph- 

 theritic paralysis. Food is prevented from entering the 

 larynx during deglutition by the larynx being drawn up 

 towards the base of the tongue, and by its posterior wall 

 being pulled forwards away from the back of the pharynx. 

 The bolus of food therefore glides over the posterior wall 

 of the epiglottis, which explains how it is that destruc- 

 tion of the epiglottis by disease has no effect on degluti- 

 tion a fact which was inexplicable on the old theory 

 that the epiglottis shut down on the top of the larynx 

 like a lid. Normally, respiration is reflexly inhibited 

 whilst the food is passing over the top of the larynx, but 

 if a breath be involuntarily taken during the process, food 

 enters th'e larynx, and coughing and ' choking ' result. 



In the case of fluids, the contraction of the pharyngeal 

 muscles is sufficient to force them rapidly through the 

 oesophagus until the cardiac orifice is reached, after 

 which their progress becomes much slower, and they 

 merely trickle into the stomach (Fig. 15). Hence, when 

 corrosive liquids are swallowed, it is found that the 



