282 



DIGESTION 



folds are applied to the posterior side of the epiglottis (Fig. 112, B). The 

 epiglottis itself cannot play any great part in the closure of the pharynx; for 

 it can be extirpated without interfering with the act of swallowing. Nor do the 

 muscles of the epiglottis appear to be of any importance. 



This extremely complicated process of swallowing is in all probability 

 presided over and controlled by the medulla. According to Marckwald the 

 center lies lateral to and above the summit of the ala3 cinerse. 



When the bolus has reached the lower end of the oesophagus it is forced 

 into the stomach. The cardia is normally closed by tonic contraction of its 

 sphincter muscle, as is evident from the fact that no regurgitation of food 

 takes place even when the pressure in the abdominal cavity is very greatly 



Mcuc, M.sternd,. 



FIG. 113. The motor nerves of the throat and palate of the monkey, after Rthi. 1, upper; 

 2, middle; 3, lower bundle of roots. Gl-ph., glossopharyngeal nerve; Va, vagus; Lar.s, 

 superior laryngeal ; Ac. accessory nerve; R. ph., v. pharyngeal root of the vagus; St. ph., the 

 motor nerves of the stylopharyngeal muscle; P. gl., motor nerves of the palatoglossal muscle; 

 P. ph., the motor nerves of the palatopharyngeal muscle; C., motor nerves of the constrictor 

 muscles of the pharynx; L., motor nerves of the levator veli palatini; Az., those of the azygos 

 uvulse. 



increased. The cardia is opened by the action of its dilator nerves (cf. 4), 

 and the bolus of food is pushed into the stomach by contraction of the lower- 

 most section of the oesophagus. When the oesophagus is paralyzed by section 

 of its nerves, food remains in it, and may be sucked into the lungs, producing 

 inflammations which result fatally. 



By auscultation of the region over the cardia in man two sounds may be 

 heard after deglutition, the one almost immediately after the inception of the 

 act, the other some six to seven seconds later. The first sound is seldom heard 

 and appears to be caused by an abnormal gaping of the cardia. In this case 

 the food is probably spirted by contraction of the muscles in the upper passages^ 

 directly into the stomach. The second sound corresponds in its occurrence to 

 the time when the food is being forced into the stomach, and it is probably 

 caused by this procedure. 



