824 A MANUAL OF PHYSIOLOGY 



thicker than the other. Many of the thicker branches terminate 

 by arborizing around the cells of the accessory auditory nucleus, 

 whose position is indicated by a swelling on the ventral surface of 

 the restiform body at the junction of the dorsal and ventral roots ; 

 but some pass over the restiform body to end in another nucleus 

 (lateral nucleus), also indicated by a swelling (tuberculum acusticum) 

 lying over the restiform body. The nerve-cells of the accessory 

 nucleus and the acoustic tubercle, therefore, constitute nuclei of 

 reception for the dorsal root-fibres. The more slender branches 

 of the cochlear root-fibres run downwards for some distance before 

 breaking up into fibrils. 



The path to the high parts of the brain is continued by the axons 

 of nerve-cells in the accessory nucleus and the acoustic tubercle. 

 The fibres from the accessory nucleus pass into the trapezium, a 

 mass of transverse fibres lying in the pons behind the pyramidal 

 fibres. In their course through the trapezium some of the fibres 

 terminate around the cells of the nucleus of the trapezium, others 

 run into the superior olive of the same side, and end there ; but 

 most of them cross the middle line, and enter the trapezoid nucleus 

 and superior olive of the opposite side, where many of them ter- 

 minate. Others, however, run through those nuclei and pass into 

 the lateral fillet, to end in its nucleus or in the posterior corpora 

 quadrigemina. The path of the fibres which terminate in the nuclei 

 of the trapezium, superior olive, and lateral fillet, is continued by 

 another relay of fibres, which link them also to the posterior corpora 

 quadrigemina. The axons of the cells of the acoustic tubercle 

 enter for the most part the stria acusticte, a series of prominent 

 strands that run transversely across the floor of the fourth ventricle. 

 Passing across the raphe, they join the fibres from the accessory 

 nucleus on their way to the superior olive, and accompany them into 

 the lateral fillet, which terminates in the grey matter of the posterior 

 corpus quadrigeminum. We must assume, from clinical and 

 experimental data, that the dorsal root is ultimately connected with 

 the first, or first and second temporo-sphenoidal convolutions on 

 the opposite side. From the posterior corpora quadrigemina the 

 auditory path to the convolutions seems to run in the brachium to 

 the internal or mesial geniculate body, whence it is continued in 

 the posterior extremity of the internal capsule. 



The fibres of the ventral root of the eighth nerve, better termed the 

 vestibular nerve, after entering the medulla oblongata, pass to a 

 nucleus called the principal nucleus of the vestibular division. 

 Here each bifurcates into a descending and an ascending branch. 

 The descending branches running down in the medulla terminate 

 at different levels around cells in the principal nucleus, and the grey 

 matter continued down from it (descending vestibular nucleus}. 

 The ascending branches run up on the inner side of the restiform 

 body towards the nucleus of the roof (nucleus tecti] in the cerebellar 

 worm. On their course they enter into relation through their col- 

 laterals with the nuclei of Deiters and Bechterew. The nucleus 

 of Deiters, as already stated, sends fibres into the posterior longi- 

 tudinal bundles. Through ascending branches of these fibres a 

 communication is established with the nuclei of the third and sixth 

 nerves, and through descending branches that pass into the antero- 

 lateral descending tract of the cord with the anterior horn cells. 

 It is obvious that through these connections which link the vestibule 

 with the cerebellum, the nuclei of the motor nerves of the eyeball 

 and the motor cells of the cord, the nucleus of Deiters has an 



