150 DIGESTION. 



with the anterior fibres of the temporal. By the combined 

 action of the posterior fibres of the temporal, the digastric, 

 mylo-hyoid, and genio-hyoid, the jaw is brought back to its 

 position. By the same action it may also be drawn back 

 slightly from its normal position while at rest. 



Action of the Tongue, Lips, and Cheeks, in Mastication. 

 Experiments on living animals and phenomena observed in 

 cases of lesions of the nervous system in the human subject 

 have fully demonstrated the importance of the tongue and 

 cheeks in mastication. The following observations of Pa- 

 nizza on the effects of section of both hypoglossal nerves in 

 dogs show the importance of the tongue, both in mastication 

 and deglutition : " After the section of the hypoglossal the 

 movements of the tongue cease immediately, but the gen- 

 eral sensibility of that organ and the taste was not less 

 marked. Indeed, if milk, or bread moistened in the 

 liquid, were presented to the dog, he made ineffectual efforts 

 to lap and to masticate, moving the head and the lower jaw; 

 the tongue, when displaced, remaining in the same position, 

 and even when a bolus of meat or bread was put on its an- 

 terior surface, it was found for a long time after in the same 

 place, which proves that section of the hypoglossals destroys 

 not only the movements necessary to mastication, but also 

 those of deglutition." * "We have lately had occasion to ver- 

 ify most of these observations by Panizza in a dog in which 

 both sublingual nerves were divided. The experiment, how- 

 ever, was made chiefly with reference to the action of the 

 tongue in deglutition. 



Section of the facial nerves is now a common physiolo- 

 gical experiment ; and operations of this kind, with cases of 

 facial palsy, which are not uncommon in the human subject, 

 show that when the cheek is paralyzed the food accumulates 

 between it and the teeth, producing great inconvenience. 



1 PANIZZA, Nouvelles Recherches Experimentales sur les Nerfs. Gazette Mcdi- 

 cale de Paris, 1835, p. 419. 



