1932] Poliak: Afferent Fiber Systems, Primate Cerehral Cortex 83 



dorsal half of the white substance of the superior temporal convolu- 

 tion close to the cortex of the lower w^all of the Sylvian fossa, and 

 along and within the ventral spur of the claustrum, leaving the ventral 

 half of the white substance for the most part entirely free (compare 

 a similar behavior of the visual fibers, Chapter XV). At this spot, 

 too, in so far as the auditory fibers do not enter the cortex immediately, 

 they can be seen as short, more or less parallel, oblique, or somewhat 

 obliquely horizontally arranged fiber segments, forming a thin fiber 

 sheet or lamina, each section of the series showing a few fibers which 

 actually enter the cortex on the corresponding level. The overwhelm- 

 ing majority of the auditory fibers gradually enter the cortex of the 

 covered dorsal lip of the superior temporal convolution (Tj) or, in 

 other words, the ventral horizontal wall of the Sylvian fossa {F8). 

 Only a few solitary fibers reach the convexity of the superior temporal 

 convolution on the free face of the temporal lobe. No auditory fibers 

 in any of the present experiments were seen to enter the lower, ventral 

 lip of the superior temporal convolution around the superior temporal 

 sulcus (/S'^i) or any other part of the cortex of the temporal lobe (for 

 example the middle or the inferior temporal convolution). 



Some of the auditory fibers (also some of the ventral somato-sensory 

 fibers) do not observe this course in the external capsule and penetrate 

 through the claustrum intO' the capsula extrema (fig. 33). From the 

 capsula extrema they either enter the medial (perpendicular) wall of 

 the Sylvian fossa along the claustrum or turn around and below the 

 ventral corner of the fossa eventually entering the covered portion of 

 the insulo-temporal cortex. Thus all the fibers forming the auditory 

 radiation, as the close study of both series demonstrates, no matter 

 whether penetrating directly through or avoiding the putamen from 

 behind, finally reach the Sylvian fossa and the hidden upper lip of 

 the superior temporal convolution. 



In more oral sections where the putamen increases in size before, 

 however, attaining its greatest extent, all fibers of the auditory radia- 

 tion have already passed over to the external capsule {ar in figs. 28, 

 29, 48, 49). From then on, they can be found on anterior levels only 

 lateral tOi the pntamen and constitute at that spot a portion of the 

 "sagittal stratum" of the temporal lobe immediately neighboring the 

 ventral extremity of the claustrum. From the sagittal layer where 

 they run for a longer or shorter distance in a longitudinal direction, 

 the auditory fibers deviate laterally in a definite order, bimdle after 

 bundle, to reach their respective places of termination in the more 

 orally situated segments of the auditory projection cortex. First the 



