152 TEXT-BOOK OF PHYSIOLOGY. 



of the vessels and an increased blood-supply. There is thus abundant 

 proof that the chorda tympani contains two sets of fibers one regulating 

 the blood-supply to the gland, the other stimulating the secretor cells. 



The efferent fibers, vaso-motor and secretor, which constitute in part 

 the chorda tympani nerve have their origin in cells, the nucleus salivatorius, 

 located beneath the floor of the fourth ventricle, from which they emerge in 

 the nerve of Wrisberg or pars intermedia, and enter the trunk of the facial 

 nerve at the bottom of the internal auditory canal after which they pursue 

 the course stated above. 



The Glosso-pharyngeal Nerve. The nerve-fibers that conduct nerve 

 impulses outward from the medulla to the parotid gland are believed to pass 

 through the glosso-pharyngeal nerve, through the tympanic branch or nerve 

 of Jacobson, to the otic ganglion, with which they become connected. From 

 this ganglion new nerve-fibers arise which pass into the fifth nerve and 

 reach the secretor cells of the parotid gland through the auriculotemporal 

 nerve. The trunk of this latter nerve contains therefore postganglionic 

 fibers that bear the same relation to the parotid gland and blood-vessels 

 that the postganglionic fibers from the submaxillary ganglion bear to the 

 submaxillary gland and blood-vessels. 



The influence of the efferent fibers in the trunk of the glosso-pharyngeal 

 on the parotid gland is similar to the influence of the chorda tympani on the 

 submaxillary gland ; for if the glosso-pharyngeal nerve or its post ganglionic 

 continuations in the auriculo- temporal nerve be stimulated in any part of its 

 course with induced electric currents there follows a dilatation of the blood- 

 vessels and an abundant discharge of a thin saliva rich in water and salts 

 but poor in the amount of organic matter. Division of the glosso-pharyngeal 

 nerve, extirpation of the otic ganglion or division of the auriculo-temporal 

 nerve is followed by a loss of reflex secretion. Stimulation of the branch 

 connecting the glosso-pharyngeal with the otic ganglion ( Jacobson' s nerve) 

 gives rise to the secretion as shown by Heidenhain. Division of the nerve 

 is also followed by a loss of reflex secretion. 



The Sympathetic Nerves. The sympathetic fibers which influence 

 the salivary secretion emerge from the spinal cord mainly through the second, 

 third, and fourth thoracic nerves. After passing into the sympathetic chain 

 they ascend to the superior cervical ganglion, with the cells of which they 

 become connected through the intermediation of fine terminal branches. 

 From this point non-medullated nerve-fibers follow the branches of the 

 external carotid artery to the different glands. There is no evidence that 

 these fibers have any connection, anatomic or physiologic, with local ganglia 

 at or near the submaxillary, sublingual, or parotid glands. If the sympa- 

 thetic nerve in the neck, especially in the dog, be divided and the peripheral 

 end stimulated with induced electric currents, there is at once a contrac- 

 tion of the smaller blood-vessels of the submaxillary and sublingual glands 

 and a diminution of the blood-supply, a result showing the presence of vaso- 

 constrictor fibers. Nevertheless both the submaxillary and sublingual 

 glands pour out a saliva which is different from that poured out when the 

 chorda tympani is stimulated. The quantity is less, it is more viscid, richer 

 in organic matter, of a higher specific gravity, and more active in the trans- 

 formation of starch into sugar. 



