DIGESTION. 101 



ulla oblongata where they are transformed into motor impulses 

 which are then transmitted through efferent nerves to the blood- 

 vessels and epithelium of the glands. 



Stimulation of the auriculotemporal branch increases the flow of 

 saliva from the parotid gland ; division arrests it. 



Stimulation of the chorda tympani is followed by a dilatation of 

 the blood-vessels of the submaxillary and sublingual glands, an in- 

 creased flow of blood and an abundant discharge of a thin saliva ; 

 division of the nerve arrests the secretion. 



Stimulation of the cervical sympathetic is followed by a contrac- 

 tion of the blood-vessels, a diminished flow of blood, and a diminu- 

 tion of the secretion, which now becomes thick and viscid ; division 

 of the sympathetic is not, however, followed by complete dilatation 

 of the vessels. There is evidence of the existence of a local vaso- 

 motor mechanism, which is inhibited by the chorda tympani, and 

 augmented by the sympathetic. 



DEGLUTITION. 



Deglutition is the act of transferring food from the mouth into 

 the stomach, and may be divided into three stages : 



1. The passage of the bolus from the mouth into the pharynx. 



2. From the pharynx into the esophagus. 



3. From the esophagus into the stomach. 



In the first stage, which is entirely voluntary, the mouth is closed 

 and respiration momentarily suspended ; the tongue, placed against 

 the roof of the mouth, arches upward and backward, and forces the 

 bolus into the fauces. 



In the second stage, which is entirely reflex, the palate is made 

 tense and directed upward and backward by the levatores palati and 

 tensores palati muscles ; the bolus is grasped by the superior con- 

 strictor muscle of the pharynx and rapidly forced into the esophagus. 



The food is prevented from entering the posterior nares by the 

 uvula and the closure of the posterior half-arches (the. palatopharyn- 

 geal muscles) ; from entering the larynx by its ascent under the base 

 of the tongue and the action of the epiglottis. 



In the third stage the longitudinal and circular muscle-fibers, con- 

 tracting from above downward, strip the bolus into the stomach. 



