568 DIGESTION. 



cision, and yet he never remarked that their mastication experienced 

 the slightest modification, or that they swallowed inopportunely. Our 

 experience corresponds with that of M. Magendie. We know of more 

 than one individual in whom there is not the slightest vestige of uvula, 

 yet they taste, chew, and swallow like other persons. 



d. Deglutition. 



The act of swallowing, although executed with extreme rapidity, 

 and apparently simple, is the most complicated of the digestive opera- 

 tions, and requires the action of mouth, pharynx and oesophagus. It 

 has been well analyzed by M. Magendie, first of all in a thesis, main- 

 tained at the Ecole de Medecine of Paris, in 1808, and subsequently, 

 in his Precis Elementaire de Physiologie^ To facilitate its study, he 

 divides it into three stages. In the first, the food passes from the 

 mouth into the pharynx; in the second, it clears the apertures of the 

 glottis and nasal fossse, and attains the oesophagus; and, in the third, 

 it clears the esophagus and enters the stomach. 



1. When the food has been sufficiently masticated and imbued with 

 saliva, it is collected by the action of the cheeks and tongue upon the 

 upper surface of the last organ ; the mass being more or less rounded, 

 and hence usually termed alimentary bolus. Mastication now stops; 

 the tongue is raised and applied against the bony palate in succession 

 from the tip to the root, and the alimentary bolus, having no other 

 way of escaping from the force pressing it, is directed towards the 

 pharynx. Previous to this, the pendulous veil of the palate had been 

 applied to the base of the tongue. The bolus now raises it to the hori- 

 zontal position: the circumflexus palati muscles render the velum tense, 

 so that the food cannot pass into the nasal fossse ; and the muscles that 

 constitute the pillars of the fauces palato-pharyngei and glosso-sta- 

 phylini contribute to this effect. By this combination of results, the 

 food is impelled into the pharynx. The muscles, which, by their action, 

 apply the tongue to the roof of the mouth and to the velum palati, are 

 the proper muscles of the organ, aided by the mylo-hyoidei. In this 

 first stage of deglutition, the motions are voluntary, except those of the 

 velum palati. The process is not executed with rapidity, and is easily 

 intelligible. Such is not the case with the second stage. The actions 

 in it are complicated, and executed with so much celerity, that they 

 have been regarded as a kind of convulsion. 



2. The distance, over which the bolus has to travel, in the second 

 stage, is trivial ; the rapidity of its course is owing to the larynx or 

 superior aperture of the windpipe, which opens into the pharynx, 

 having to be cleared instantaneously, otherwise respiration might be 

 arrested, and serious effects ensue. The mode, in which the second 

 stage is accomplished, is as follows. As soon as the alimentary bolus 

 comes in contact with the pharynx all is activity ; the pharynx con- 

 tracts, embraces, and presses the bolus; and the velum pendulum, drawn 

 down by the palato-pharyngei and glosso-staphylini muscles, fulfils a 

 similar office. At the same time, the genio-glossus, by applying the 



1 Edit, cit., ii. 63. 



