804 NERVOUS SYSTEM OF THE HORSE 
through the lamina cribrosa to the labyrinth, 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 ganglion. The peripheral processes (dendrites) of the cells 
form arborizations about the deep ends of the hair-cells of the macule and criste acustice 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 tuberculum 
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 strize acusticee) 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 part of the cerebral hemisphere. 
THE GLOSSO-PHARYNGEAL NERVE 
The glosso-pharyngeal nerve (N. glossopharyngeus) 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 
cornu 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 ganglion of the vagus nerve 
and with the anterior cervical ganglion 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 onits 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 ganglion appears to be equivalent to the jugular or superior and petrous ganglia of man. 
