428 



PHYSIOLOGY 



or second cervical nerve. This nerve gives common sensation to 

 practically the whole of the head. 



It is doubtful in what group we should place the fibres of the eighth 

 nerve. This nerve really consists of two parts very different in func- 

 tion, the cochlear or auditory nerve, and the vestibular or labyrinthine 

 nerve. The fibres of each are derived from ganglion-cells in the 

 internal ear, pass to the medulla at its widest part, and then, dividing 



rab.a 



FIBRES TO NUCL.LEMNISCI 

 &CORPORA QUAORIGEMINA 



FIBRES OF 

 COCHLEAR 

 ROOT 



GANGLION 

 COCHLE/E 



A.'tr. 



NERVE-ENDINGS 



iN ORGAN OF CORTI 



FIG. 194. Plan of the course and connections of the fibres forming the 



cochlear root of the auditory nerve. (SCHAFER.) 



r, restif orm body ; V, descending root of the fifth nerve ; tub.ac, tuberculum 

 acusticum ; n.acc, accessory nucleus ; so, superior olive ; n.tr, nucleus 

 of trapezium ; n. VI, nucleus of sixth nerve ; VI, issuing root-fibre of sixtli 

 nerve. 



into two, terminate in masses of grey matter situated at the extreme 

 lateral part of the floor of the fourth ventricle. 



The branches of the cochlear nerve (Fig. 194) make connection 

 with two collections of cells, the dorsal nucleus, apparently embedded 

 in the fibres of the root itself, and the accessory nucleus, a little trian- 

 gular mass of grey matter situated in the angle between the cochlear 

 and vestibular nerves. From these nuclei fibres are given off which 

 take two courses. Some, following the previous course of the cochlear 

 nerve, pass across the surface of the fourth ventricle as the strice 

 medullares or strice acousticce, and then bending inwards pass into 

 the tegmentum of the opposite side. Others pass deeply and form 

 a mass of transverse fibres in the ventral part of the tegmentum, the 

 corpus trapezoides or trapezium. After making connections with the 

 superior olivary body and a special nucleus, they join the superficial 

 set of fibres, and run up in the tegmentum to the inferior corpora 

 quadrigemina, forming the lateral fillet. 



