206 CLINICAL APPLIED ANATOMY. 



complex connections explain the extreme vertigo and inco-ordina- 

 tion induced by sudden lesions of the vestibular nerve. 



The fibres of the cochlear or auditory portion of the nerve 

 commence in Corti's organ in the cochlea and join the spiral 

 ganglion of the latter. Thence fibres traverse the meatus in 

 company with the vestibular portion of the nerve. Diverging 

 finally from the vestibular nerve and passing dorsal to the resti- 

 form body, the fibres terminate in a couple of ganglia closely 

 applied to the latter and known as the acoustic tubercle and the 

 ventral cochlear nucleus. 



In localising the position of a lesion in the pons or higher 

 parts of the brain which causes deafness, a knowledge of the 

 course taken by the auditory impulses from the nuclei in the pons 

 to the auditory perceptive centres in the temporal lobes is 

 essential, since it is only by the associated symptoms that the 

 localisation can be effected. 



Most of the fibres from the nuclei, bat not all, cross to the 

 opposite side of the pons, some passing dorsally through the 

 striae acusticse which are visible on the floor of the fourth ventricle 

 and other passing more ventrally in the trapezoid body. Uniting 

 in the lateral fillet this double set of crossed fibres passes through 

 the internal geniculate body, traverses the sensory limb of the 

 internal capsule and passes thence by the corona radiata to the 

 superior temporo-sphenoidal convolution. The afferent tracts 

 are also connected with the superior olivary bodies and the 

 posterior corpora quadrigemina. The whole tract consists of an 

 elaborate system of nerve cell relays. It will be gathered that 

 each ear is connected not only with the auditory centre of the 

 opposite side but also with that of the same side. 



The association of word deafness with a certain amount of 

 defect of hearing in the right ear points to the left temporal lobe 

 as the seat of disease. Deafness from a lesion of the internal 

 capsule is associated with hemianopia and hemianaesthesia since 

 the auditory fibres are in immediate relation here with the 

 visual tract and the fibres of common sensation. 



Deafness from a lesion in the corpora quadrigemina or from 



