412 PHYSIOLOGY 



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 acousticse 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. 378. 



The ventral division of the eighth nerve, or vestibular nerve, originates 

 in the bipolar cells of the vestibular ganglion or ganglion of Scarpa. These 

 cells, like those of the spiral ganglion, retain the primitive bipolar character. 

 The fibres divide into ascending and descending 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 ventrally and 

 internally to the vestibular nucleus, both nuclei being in close relation to the 

 roof nuclei of the cerebellum. Many fibres of the vestibular nerve pass 

 apparently through these various nuclei on the inner side of the restiform 

 body into the cerebellum, where they make connection with the roof nucleus 

 or nucleus fastigii. By the nuclei of Deiters and Bechterew the vestibular 

 nerve is connected through the dorsal longitudinal bundle and the descending 

 vestibulo-spinal tract with the motor nuclei of the cranial and spinal nerves. 



The use of the vestibular nerve is entirely connected with the function 

 of equilibrium. It is probably not concerned in conveying auditor} im- 

 pressions, all its nerve fibres being derived ultimately from the ner\ e-endiugs 

 in the saccule and utricle and semicircular canals. 



The siTi'Ht/t c.ritniul nerve or facial nerve emerges from the bruin at the 

 interior margin of the pons, lateral to the point of exit of the sixth nerve, 

 almost entirely a motor nerve, but carries also some sensorv fibres 

 for taste and general sensibility which it receives from the nervus win mnlmx 

 of Wrisberg. The motor nucleus of the seventh nerve lies in the reticular 

 formation, dorsal ly to the superior olive, at some depth below the floor 

 of the fourth ventricle. From this nucleus the fibres first pass inwards 

 and dorsally towards the floor of the ventricle, where they collect to form 

 a bundle which runs upwards in the grey matter for a short distance and then 

 t urns sharply in a v.-nt ro-latera! direction to emerge on the lateral aspen of 

 the pons. The fibres from tin- motor nuele us supply the muscles of the lace. 

 the scalp, and the ear. Secretory fibres also run in the chorda tympani, 

 which is a branch of the facial. These aiv probably derived, like the 

 sensory libre>. hum the nerve of \Vri>| M -r.u. The sensorv fibres of the 

 ner \ e il' \\Yi-sbrnj iris/mate in the nerve cells of t In- IMMI'II ulat e ^uu'lion. and 



