DEGLUTITION. 189 



After mastication has been completed, the mouth is closed 

 and the tongue, collecting with the point aided by the cheeks 

 all the particles of food into a single mass, becomes slightly 

 increased in width, and with the alimentary bolus behind 

 it, is pressed from before backward against the roof of the 

 mouth. The act of swallowing is always performed with 

 difficulty when the mouth is not completely closed ; for the 

 tongue, from its attachments, must follow, to a certain extent, 

 the movements of the lower jaw. The first part of the first 

 period of deglutition is thus simple ; but when the food has 

 passed beyond the hard palate, it comes in contact with the 

 hanging velum, and the muscles are brought into action 

 which render this membrane tense, and oppose it in a cer- 

 tain degree to the backward movement of the base of the 

 tongue. This is effected by the action of the tensor-palati 

 and the palato-glossus. The moderate tension of the soft 

 palate admits of its being applied to the smaller morsels, 

 while the opening is dilated somewhat forcibly by masses of 

 greater size. 



It is easy to appreciate, in analyzing the first period of 

 deglutition, that liquids and the softer articles of food are as- 

 sisted in their passage to the isthmus of the fauces by a slight 

 suction force. This is effected by the action of the muscles of 

 the tongue, elevating the sides and depressing the centre of the 

 dorsum, while the soft palate is accurately applied to the base. 



The importance of the movements of the tongue during 

 the first period of deglutition is evidenced by experiments on 

 the inferior animals, and by cases of loss of this organ in the 

 human subject. In the experiments of Panizza, which have 

 already been referred to in connection with mastication, it 

 was found that paralysis- of the tongue, by section of the 

 hypoglossal nerves in dogs, deprived the animals of the power 

 of swallowing, even when a bolus of meat or bread was put 

 upon its anterior surface. 1 "We have now a young dog under 



1 PANIZZA, Nouvelles Recherches Experimentales sur Ics Nerfs. Gazette Midi- 

 cole de Paris, 1835, p. 419. 



