THE CRANIAL NERVES. 595 



and which descending in the aqueduct of Fallopius are continued as the 

 chorda tympani. The nerve impulses developed in the peripheral termina- 

 tions of this nerve by the action of organic matter in solution are transmitted 

 through the chorda tympani, along the facial nerve as far as the geniculate 

 ganglion. The exact pathway for these afferent or gustatory fibers beyond the 

 geniculate ganglion has long been a subject of much discussion. According 

 to some observers these fibers enter the great petrosal nerve, pass forward as 

 far as the spheno-palatine ganglion, then into the superior maxillary division 

 of the trigeminal, and so to the brain. According to others, these fibers 

 pass into the pars intermedia, into the pons, where they terminate around 

 the sensor end -nucleus of the glosso-pharyngeal. The evidence for and 

 against either of these two views is most conflicting and insufficient to justify 

 positive statements one way or the other. To the writer the weight of evi- 

 dence seems to favor the view that the gustatory fibers have their origin in the 

 geniculate ganglion; that they pass centrally through the pars intermedia; 

 that they are similar in function to the glosso-pharyngeal ; and that they are 

 indeed but aberrant branches of this nerve. 



Division of the chorda tympani nerve is also followed by a contraction of 

 the blood-vessels in the neighborhood of and a diminution in the secretion 

 from the submaxillary and sublingual glands. Stimulation of the peripheral 

 end of the divided nerve gives rise to a dilatation of the blood-vessels and an 

 increased production and discharge of saliva from these glands. (See page 

 150.) From these results it is certain that the chorda tympani contains both 

 vaso-dilatator and secretor fibers. Nicotin applied to the submaxillary 

 and sublingual ganglia abolishes the effects of stimulation of the chorda 

 tympani. It does not prevent the same effects when the ganglia themselves 

 are stimulated. It is clear, therefore, that the vaso-dilatator and secretor 

 fibers arborize around the cells of the ganglia and are not distributed directly 

 to the gland structures. It is highly probable that the vaso-dilatator and 

 secretor fibers in the chorda tympani are the continuations of the efferent 

 fibers found in the pars intermedia and that they too have their origin in the 

 nucleus salivatorius. 



EIGHTH NERVE. THE ACOUSTIC. 



The eighth cranial nerve, the acoustic, consists of the centrally coursing 

 axons of neurons which connect the essential organ of hearing with sensor 

 end-nuclei in the pons Varolii. This nerve consists of two portions: viz., 

 a cochlear or auditory and a vestibular or equilibratory. 



Origin. The axons comprising the cochlear portion have their origin 

 in the bipolar nerve-cells of the spiral ganglion located in the spiral canal near 

 the base of the osseous lamina spiralis (Fig. 279). From this origin they 

 pass centrally into the central canal of the modiolus, at the base of which 

 they emerge in well-defined bundles and enter the internal auditory meatus. 

 Dendritic processes from these cells pass peripherally to terminate on the 

 ciliated epithelial cells of the organ of Corti. 



The axons comprising the vestibular portion have their origin in the 

 bipolar nerve-cells of the ganglion of Scarpa located in the internal auditory 

 meatus. From this origin they pass centrally in connection with the cochlear 



