804 NERVOUS SYSTEM OF THE HORSE 



through the lamina cribrosa to the labjrrinth, and is distributed to the organ of 

 Corti in the cochlea. 



The fibers of the vestibular nerve arise from the vestibular ganglion as central processes 

 (axones) of the bipolar cells of the ganghon. The peripheral processes (dendrites) of the cells 

 form arborizations about the deep ends of the hair-cells of the maculse and cristse acustieae of the 

 utriculus, sacculus, and semicircular ducts. The fibers enter the medulla, pass between the 

 restiform body and the spinal tract of the trigeminus, and spread out to end in the vestibular 

 nucleus in the floor of the fourth ventricle. Among the central connections of the vestibular 

 nerve are: (1) fibers which connect its nucleus with centers in the cerebellum (chiefly of the oppo- 

 site side) ; (2) the vestibulo-spinal tract, which conveys impulses to the motor cells of the ventral 

 columns of the spinal cord ; (3) fibers which connect the nucleus with those of the abducent nerve 

 of the same side, the third and fourth nerves, and the motor part of the trigeminus of both sides. 



The fibers of the cochlear nerve are the central processes of the bipolar cells of the spiral 

 ganglion of the cochlea. The peripheral processes of these cells end in relation to the hair-cells 

 of the organ of Corti. Some of the nerve-fibers enter the ventral cochlear nucleus in the medulla 

 close to the superficial origin of the nerve; others end in the dorsal nucleus of the tuberoulum 

 acusticum at the lateral angle of the floor of the fourth ventricle. From the ventral nucleus 

 fibers pass in the corpus trapezoideum to the anterior olivary nucleus of the same and of the 

 opposite side. Thence tracts pass to the nuclei of the motor nerves of the eye, and through the 

 lateral fillet to the posterior quadrigeminal body and the medial geniculate body. The axones 

 of the cells of the dorsal nucleus pass largely (as the strife acusticse) over the restiform body and 

 across the floor of the fourth ventricle toward the median plane. They then turn ventrally, 

 cross to the opposite side, and are continued by the lateral fillet. From the mid-brain a tract 

 proceeds to the cortex of the temporal lobe of the hemisphere. 



THE GLOSSO-PHARYNGEAL NERVE 



The glosso-pharyngeal nerve (N. glossopharjoigeus) is attached to the anterior 

 part of the lateral aspect of the medulla by several filaments (Fig. 629). The root- 

 bundles enter the furrow ventral to the restiform body; they are separated by a 

 short interval from the origin of the facial nerve, but are not marked off behind from 

 the roots of the vagus. The bundles converge laterally to form a nerve which per- 

 forates the dura mater and emerges through the foramen lacerum posterius just 

 in front of the tenth nerve (Fig. 647). As it issues from the cranium the nerve 

 bears a considerable ovoid gray enlargement, the petrous ganglion (G. petrosum).' 

 It then curves downward and forward over the guttural pouch and behind the great 

 comu of the hyoid bone, crosses the deep face of the external carotid artery, and 

 divides into pharyngeal and lingual branches (Fig. 562). The collateral branches 

 are as follows: 



1. The tympanic nerve (N. tympanicus) (Fig. 647) arises from the petrous 

 ganglion and passes upward between the petrous and tympanic parts of the temporal 

 bone to reach the cavity of the tympanum. Here it breaks up into branches to 

 form, along with branches from the carotid plexus of the sympathetic, the tympanic 

 plexus. From the plexus branches pass to the mucous membrane of the tympanum 

 and the Eustachian tube. The continuation of the nerve issues from the plexus 

 and unites with a filament from the geniculate ganglion of the facial to form the 

 small superficial petrosal nerve; this runs forward and ends in the otic ganglion. 



Filaments also connect the petrous ganglion with the jugular ganghon of the vagus nerve 

 and with the anterior cervical ganghon of the sympathetic. 



2. A considerable branch runs backward on the guttural pouch, contributes 

 filaments to the pharyngeal plexus, and concurs with twigs from the vagus and the 

 sympathetic in forming the carotid plexus on the terminal part of the carotid 

 artery and on its chief branches. In this plexus is the small ganglion intercaroticum. 



3. The very small nerve to the stylo-pharyngeus muscle (N. stylopharyngeus) 

 arises from the dorsal border of the nerve. 



The pharyngeal branch (R. pharyngeus) (Fig. 562) is the smaller of the two 

 terminal branches. It runs forward across the deep face of the great cornu of the 



1 This ganghon appears to be equivalent to the jugular or superior and petrous ganglia of man. 



