SENSE AREAS AND ASSOCIATION AREAS. 



211 



of the auditory tract of fibers cannot be determined with cer- 

 tainty, but it seems probable that it lies mainly in the superior 

 temporal gyrus and the transverse gyri extending from this into 

 the lateral fissure of the cerebrum (fissure of Sylvius). 



The Histological Evidences. — On the histological side the paths 

 of the auditory fibers have been followed with a large measure of 

 success, although in many details the opinions of the differ- 

 ent investigators vary considerably. The eighth cranial nerve 



Posterior nucleus. 



Deiters's nucleus. 



Fig. 94. — The medullary nuclei of the eighth nerve. — (From Poiner and Charpy.) 



arises from the medulla by two roots: the external and the 

 internal. The former has been shown to supply, mainly at 

 least, the cochlear portion of the internal ear, and is, there- 

 fore, the auditory nerve proper. This division is spoken of 

 as the cochlear branch. The internal root supplies mainly the 

 vestibular branch of the internal ear, and is, therefore, spoken 

 of as the vestibular branch (see Fig. 94). It seems certain that 

 the latter is not an auditory nerve, but is concerned with pe- 

 cuhar sensations from the semicircular canals and vestibule 

 that have an important influence on muscular activity, especially 

 in complex movements. The central course of these two roots is 



