;^0 HANDBOOK OF I'HYSIOLOO Y. 



charged from the gland cells. Other stimuli, however, besides that of 

 the food, and other sensory nerves besides those mentioned, may pro- 

 duce reflexly the same effects. For example, saliva may be caused to 

 flow by irritation of the mucous membrane of the mouth with mechani- 

 cal, chemical, electrical, or thermal stimuli, also by the irritation of the 

 mucous membrane of the stomach in some way, as in nausea, which 

 precedes vomiting, when some of the peripheral fibres of the vagi are 

 irritated. Stimulation of the olfactory nerves by smell of food, of the 

 optic nerves by the sight of it, and of the auditory nerves by the sounds 

 which are known by experience to accompany the preparation of a meal, 

 may also, in the hungry, stimulate the nerve centre to action. In addi- 

 tion to these, as a secretion of saliva follows the movement of the mus- 

 cles of mastication, it may be assumed that this movement stimulates the 

 secreting nerve fibres of the gland, direct or reflexly. From the fact 

 that the flow of saliva may be increased or diminished by mental emo- 

 tions, it is evident that impressions from the cerebrum also are capable 

 of stimulating the centre to action or of inhibiting its action. 



Salivary secretion may also be excited by direct stimulation of the 

 centre in the medulla. 



On the Submaxillary (Hand. The submaxillary gland has been the 

 gland chiefly employed for the purpose of experimentally demonstrating 

 the* influence of the nervous system upon the secretion of saliva, because 

 of the comparative facility with which, with its blood-vessels and nerves, 

 it may be exposed to view in the dog, rabbit, and other animals. The 

 chief nerves supplied to the gland are (1) the chorda tympani, a branch 

 given off from the facial (or portio dura of the seventh pair of nerves), 

 in the canal through which it passes in the temporal bone, in its passage 

 from the interior of the skull to the face; and (2) branches of the sym- 

 pathetic nerve from the plexus around the facial artery and its branches 

 to the gland. The chorda (fig. 238, ch. /.), after quitting the temporal 

 bone, passes downward and forward, under cover of the external ptery- 

 goid muscle, and joins at an acute angle the lingual or gustatory nerve, 

 proceeds with it for a short distance, and then passes along the submax- 

 illary gland duct (fig. 238, sm. (L), to which it is distributed, giving 

 branches to the submaxillary ganglion (fig. 23S,sm. #/.),and sending others 

 to terminate in the superficial muscles of the tongue. It consists of fine 

 medullated fibres which lose their medulla in the gland. If this nerve 

 be exposed and divided anywhere in its course from its exit from the skull 

 to the gland, no immediate result will follow, nor will stimulation 

 either of the lingual or of the glosso-pharyngeal produce a flow of saliva. 

 But if the peripheral end of the divided nerve be stimulated, an abundant 

 secretion of saliva ensues, and the blood supply is enormously increased, 

 the arteries being dilated. The veins even pulsate, and the blood con- 

 tained within them is more arterial than venous in character. 



