1932] Poliak: Afferent Fiber Systems, Primate Cerebral Cortex 85 



of them preserves its relative position Avith respect to its neig^hbor 

 during its entire course up to its cortical termination. In particular, 

 the dorsal and at the same time the most caudal bundles of the 

 auditory radiation are destined for the most caudal segments of the 

 auditory projection cortex coating the posterior corner of the Sylvian 

 fossa. The most ventral and at the same time the most oral bimdles 

 of the radiation reach the most oral or rostral segments of the audi- 

 tory projection cortex. The remaining intermediate bundles are dis- 

 tributed in a regular way to intermediate segments of that cortex. 

 From such an arrangrement of the fibers of the auditory radiation, it 

 is permissible to suppose a similar arrangement of the indi\'idual seg- 

 ments of the auditory^ projection cortex paralleling' one another and 

 strung along^ a line approximately parallel to the long axis of the 

 superior temporal convolution (in the human brain somewhat obliquely 

 across the posterior Sylvian fossa, corresponding^ to the axis of the 

 transverse temporal convolution of Heschl). 



The fiber fan or the lamina formed by the auditory radiation 

 shows, in addition to the above features, another peculiarity. The 

 anterior or oral ribs of that fan are lowered ventrally, and the posterior 

 ribs lifted a little dorsalward, thus indicating^ a spiral rotation of the 

 radiation for approximately ninety degrees around one of the central 

 ribs or radii (compare Pfeifer, 1920). This can be explained by the 

 auditory fiber lamina being: at the point of its cortical termination 

 originally situated in a vertical or nearly vertical position, correspond- 

 ing" with the planes vertical to the long axis of the hemisphere, and 

 with the oblong auditory projection cortex also having originally an 

 almost perpendicular position (gyrus sylvius in camivora for exam- 

 ple). With the changing of the position of this cortical region into one 

 more horizontal-longitudinal, as encountered in primates, the lateral 

 portion of the auditory fiber lamina where it leans toward the cortex 

 also gradually came to occupy a more horizontal position approxi- 

 mately parallel to the lower or ventral wall of the Sylvian fossa ; the 

 bundles of the auditory radiation orig^inally ventral, becoming more 

 oral or rostral ; and the bundles originally dorsal, remaining or becom- 

 ing caudal. This rotation of the auditory radiation as described, seems 

 to have been attained in greater degree closer to the cortex, while its 

 portion nearer the internal geniculate body has accomplished a lesser 

 rotation. In addition to this transverse rotation of the auditory radia- 

 tion another point must be considered : the shifting of the internal 

 geniculate body from its original ventral position to an internal posi- 

 tion in relation to the external geniculate body ; that is, the rotation 



