466 PHYSIOLOGY 



The fifth is also said to be the nerve of taste for the anterior third 

 of the tongue, but it is probable that the taste fibres which run in 

 the fifth are derived from the glossopharyngeal or from the nervus 

 intermedius. 



The eighth nerve and its connections have been discussed already 

 on several occasions. We may here briefly summarise what has already 

 been stated. In describing the eighth nerve it is necessary to consider 

 separately its two divisions, the dorsal or cochlear division and the 

 ventral or vestibular nerve. The fibres of the cochlear nerve originate 

 in the bipolar cells of the spiral ganglion of the cochlea. They carry 

 impulses from the auditory end-organ. On entering the medulla they 

 bifurcate into ascending and descending branches which terminate in 

 two nuclei, the ascending branches in the ventral nucleus, the descend- 

 ing branches in the dorsal nucleus. The ventral or accessory nucleus 

 lies between the cochlear and vestibular divisions ventrally to the 

 restiform bodv. The dorsal nucleus, often called the acoustic tubercle, 



/ * 



forms a rounded projection on the lateral and dorsal aspects of the 

 restiform body. From these two nuclei new relays of fibres start, pass 

 to the other side, and cross the median raphe (where they form the 

 trapezium) to run up in the lateral fillet of the opposite side. From 

 the ventral nucleus the fibres pass directly to the opposite side, forming 

 the greater part of the trapezium, making connection on their way with 

 the nucleus of the trapezium and with the superior olive. From the 

 dorsal nucleus most of the axons pass dorsally, forming the striae 

 acousticae at the middle of the floor of the fourth ventricle. On 

 arriving at the middle line they dip down and join the fibres of the 

 trapezium of the opposite side. The further course of these fibres 

 up to the internal geniculate body, the posterior corpora quadrigemina, 

 and the auditory radiations of the cerebral cortex, have been described 

 on p. 436. 



The ventral division of the eighth nerve, or vestibular nerve, origi- 

 nates in the bipolar cells of the vestibular ganglion or ganglion of 

 Scarpa. These cells, like those of the spiral ganglion, retain the primi- 

 tive bipolar character. The fibres divide into ascending and descend- 

 ing branches which become connected with two nuclei. The dorsal 

 or vestibular nucleus, or principal nucleus, which receives the ascending 

 fibres, is a mass of grey matter lying laterally of the vago-glosso- 

 pharyngeal nucleus and corresponding to the lateral triangular area, 

 the trigonum acoustici, which is seen on the surface of the fourth 

 ventricle outside the ala cinerea. The descending vestibular nucleus, 

 receiving the descending branches of the vestibular nerve, lies below 

 but continuous with the principal nucleus. The fibres of the vestibular 

 nucleus send also collaterals to the nucleus of Deiters and the nucleus 

 of Bechterew, two accumulations of large multipolar cells lying 



