DIGESTION IN THE MOUTH. 



303 



as when the same products (compounds of lactic or phosphoric acid 

 with lime) are directly brought into contact with the muscles. Indeed, 

 we may carry the parallelism still further, for we know that curare, 

 by destroying the irritability of the motor nerves, will prevent contrac- 

 tion of all the muscles when their nerves are stimulated, in the same 

 manner that atropine will prevent the secretion of the gland when its 

 secretory nerve is stimulated. In both instances the vaso-motor phe- 

 nomena remain. 



In the case of the parotid gland the circulation during secretion 

 undergoes the same changes as in the case of the submaxillary. Here, 

 also, secretory and circulatory 

 nerves have been determined. Vaso- 

 constrictor fibres have been found in 

 the sympathetic branches distrib- 

 uted to the parotid gland, while 

 the glossopharyngeal, according to 

 Heidenhain, contains fibres whose 

 stimulation leads to a dilatation of 

 the parotid blood-vessels. Both the 

 facial and the glossopharyngeal 

 nerves contain fibres whose stimu- 

 lation leads to parotid secretion, 

 and if the auriculotemporal nerve 

 is stimulated the secretion at once 

 commences ; if divided the secretion 

 stops. It has been found, however 

 that the trigeminal nerve is not the 

 source of these secretory fibres, for 

 when the trigeminal is stimulated 

 within the cranium no parotid secre- 

 tion results. They are consequently 

 derived from the facial nerve, and 

 when this latter nerve is stimulated 

 within the cranium parotid secretion 

 results (Fig. 124). The passage of these glandular fibres from the facial 

 into the auriculo-temporal nerve has been explained in the following 

 manner by Bernard : If the facial nerve is divided at its exit from the 

 stylo-mastoid foramen, and the central end divided, parotid secretion is 

 produced, while stimulation of its peripheral extremity is without effect. 

 The secretory fibres do not pass through the chorda tympani, as was 

 formerly believed, for section of the chorda in the tympanum does not, 

 as in the case of submaxillary secretion, arrest the flow of parotid 

 saliva. Nor do they pass through the greater superficial petrosal nerve, 



Fig. 123.— Diagram op Nerves Supply- 

 ing the Parotid Gland. (Yeo.) 

 The dark lines indicate the course of the nerves of 



the gland. V, inferior division of fifth cranial nerve ami 



its (AT) auriculo-temporal branch; VII, portio dura; 



SCG, superior cervical ganglion sending a branch to the 



carotid plexus around the artery. 



