DIGESTION 155 



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

 ocated 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 

 ;he course stated above. 



The Glosso-pharyngeal Nerve. The autonomic 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 auriculo-temporal 

 nerve. The trunk of this latter nerve contains therefore post-ganglionic 

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

 that the post-ganglionic 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 autonomic nerve-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 ganglion non-medullated nerve-fiberssympathetic nerves proper 

 follow the branches of the external carotid artery to the different glands. 

 There is no evidence that these fibers have any connection, anatomic 

 physiologic, with local ganglia at or near the submaxillary, sublmgual, or 

 parotid glands. If the sympathetic nerve in the neck, especially in the dog, 

 be divided and the peripheral end stimulated with induced electric currents, 

 there is at once a contraction 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 pou 

 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 

 the transformation of starch into sugar. 



Stimulation of the sympathetic fibers passing to the parotid glan 

 followed by contraction of the vessels and an abolition of the secretion; but 

 at the same time there is an increased activity of the secretor cells, for sub- 

 sequent stimulation of the auriculo-temporal nerve not only caus 

 increase in the amount of water and inorganic salts, but an increase also in 



