THE BRAIN 699 



.and cortico-pontine fibres. From the cells arise the transverse fibres, 

 which cross the middle line, and pass by the middle peduncle to the 

 verinis of the cerebellum. 



The Superior Olive is a small mass of grey matter closely associated 

 with the co-ordination of the movements of the eyes with the 

 mechanism of equilibration. 



The Nuclei of the Cranial Nerves. The eighth nerve is a wholly 

 afferent nerve. It consists of two portions the cochlear and the 

 vestibular. The cochlear portion is concerned with hearing. Its 

 cell-station is in the spiral ganglion of the cochlea. Peripherally, the 

 nerve processes arborize around the hair cells of the organ of Corti. 

 Centrally, the axons pass into the uppermost part of the medulla 

 oblongata. They branch on entering ; one set of branches ends in a 

 nucleus the accessory nucleus just anterior to the restiform body 

 {Fig. 426); the other around cells in what is known as the tuber- 

 culum acusticum, or acoustic tubercle, a mass of grey matter resting 

 upon the outer aspect of the restiform body. From the cells of these 

 nuclei arise fibres which go to form the lateral fillet (Fig. 426). The 

 fibres from the accessory nucleus pass transversely across in the tract 

 known as the trapezium, making in their course connection with the 

 superior olive and trapezoid nucleus of the same and opposite sides, 

 and then turning upwards in the lateral fillet to reach the nucleus 

 of the lateral fillet and the inferior corpus quadrigeminum. The 

 fibres from the tuberculum acusticum cross the floor of the fourth 

 ventricle superficially as the striae acusticse, and, dipping inwards 

 at the middle, pass with those of the trapezium to the superior 

 olive of the opposite side, and thence to the lateral fillet and inferior 

 corpus quadrigeminum. 



The vestibular portion of the eighth nerve is concerned with the 

 mechanism of equilibration. It arises from the cells of Scarpa's ganglion 

 in the vestibular portion of the internal ear. The ingoing fibres 

 divide into ascending 'and descending branches. The ascending 

 branches connect with the principal vestibular nucleus (Fig. 427), 

 a mass of grey matter situated just external to the nucleus of Deiters, 

 with which it makes intimate connection by means of collaterals. 

 The descending fibres end in the descending vestibular nucleus, which 

 lies below the principal nucleus. Many fibres of the vestibular nerve 

 pass directly by way of the restiform body to the roof nuclei of the 

 cerebellum. 



The seventh nerve is mainly motor in function. It arises from a 

 group of cells the seventh nucleus which lies in the recticular forma- 

 tion just below and somewhat external to the nucleus of the sixth 

 nerve. The fibres pursue a somewhat devious course inside the pons. 

 At first they pass inwards towards the middle line; then dorsally 

 towards the floor, and upwards to a slightly higher level of the pons ; 

 then, encircling the sixth nucleus, they turn outwards, and emerge 

 from the lateral margin of the pons (Fig. 428). The fibres supply 



