THE FOOD AND DIGESTION 331 



gland is connected with a mercurial manometer, it is found 

 that the pressure of secretion may exceed the blood pressure 

 in the carotid. 



When the perivascular sympathetics, or when the sym- 

 pathetic cord of the neck is stimulated, the blood vessels of 

 the gland constrict, and a flow of very viscous saliva takes 

 place. 



On the parotid gland the auriculo-temporal nerve (Aur. T.) 

 acts in the same way as the chorda tympani acts on the 

 other salivary glands. But stimulation of the fifth nerve 

 above the otic ganglion, from which the auriculo-temporal 

 takes origin, fails to produce any effect. On the other hand, 

 stimulation of the glossopharyngeal nerve (IX.) as it comes 

 off from the brain, acts upon the parotid gland, and since the 

 glossopharyngeal is united to the small superficial petrosal 

 which passes to the otic ganglion, by Jacobson's nerve (J.N.), 

 it is obvious that these parotid fibres take this somewhat 

 roundabout course. When the sympathetic fibres to the 

 gland alone are stimulated, constriction of the blood vessels 

 but no flow of saliva occurs, but if, when the flow of watery 

 saliva is being produced by stimulating the glossopharyngeal 

 or Jacobson's nerve, the sympathetic fibres are stimulated, 

 the amount of organic solids in the parotid saliva is very 

 markedly increased. 



The nerve fibres passing to the salivary glands are pre- 

 sided over by a centre in the medulla oblongata which acts 

 reflexly. So long as this is intact, stimulation of the lingual 

 or glossopharyngeal leads to a reflex flow of saliva. Other 

 nerves may also act on this centre. Thus, gastric irritation, 

 when it produces vomiting, causes a reflex stimulation of 

 salivary secretion. 



II. Swallowing. 



The food after being masticated is collected on the surface 

 of the tongue by the voluntary action of the buccinators and 

 other muscles, and then, the point of the tongue being 

 pressed against the hard palate behind the teeth, by a 

 contraction passing from before backwards, the bolus of 

 food is driven to the back of the tongue. When this is 



