1932] Poliak: Af event Fiber Systems, Primate Cerebral Cortex 101 



Chapter XIII 



RESULTS OF THE PRESENT INVESTIGATIONS OF THE 

 AUDITORY SYSTEM 



1. AUDITOEY KADIATION 



The uppermost link of the central auditory path, the internal 

 g:eniculo-cortieal or auditory radiation (ar in the corresponding 

 figures), originates from the internal geniculate body. So far no evi- 

 dence exists that a portion of the auditory radiation might originate 

 elsewhere in the between-brain. This fiber system forms a thin, well 

 defined fiber lamina comparable to a "fan" with its narrow "handle" 

 placed near the internal geniculate body, and its broad wing expand- 

 ing toward the cortex. The auditory fiber sheet or lamina is continuous, 

 being interrupted only at the spot where its bundles divide to slip 

 through the gaps between the islets of the ventro-caudal putamen. 

 At first closely accompanying ventral bundles of the thalamo-cortical 

 radiation (the latter emerging from the ventro-lateral nucleus of the 

 thalamus), the auditory radiation enters the most ventral portion of 

 the internal capsule, there forming a dense sheet of oblique fiber 

 sectors immediately above the external geniculate body. Although 

 close together near their origin, the auditory and the visual pathways 

 do not ming'le with each other appreciably. The auditory radiation 

 crosses above and somewhat in front of the visual radiation where the 

 latter forms the triangular field or zone of Wernicke. The course of 

 the auditory path further laterally is partly between the islets of the 

 ventro-caudal brim of the putamen and partly caudad to it. Lateral to 

 the putamen, the auditory fibers fit at first into the stratum sagittale of 

 the temporal lobe, forming that portion of it close beneath the claus- 

 trum, and then turn gradually toward the cortex, fascicle after fascicle. 

 At first the most dorsal bundles turn ; these are at the same time the 

 most caudal; they enter the cortex in the posterior corner of the 

 Sylvian fossa. The subsequent ventral bundles of the auditory sagittal 

 stratum gradually deviate toward the more oral segments of the audi- 

 tory projection cortex. The most ventral bundles enter the most oral 

 segments of the auditory cortex. This indicates not only a regular or 

 "spatial" arrangement of individual bundles of the auditory radia- 

 tion but a similar organization of the auditory projection cortex as 



