1932] Poliak: Afferent Fiber Systems, PHniate Cerebral Cortex 35 



especially characteristic of the cingulum. The caliber of the somato- 

 sensory fibers of the post- and precentral convolutions respectively, 

 differs only slightly, being in the latter a trifle less coarse. The inter- 

 hemispheric cortex reached by the afferent somato-sensory fibers 

 corresponds to the paracentral lobule and the praecuneus of the 

 human brain. 



In the present experiment, as also in Experiments I, III, and V-a, 

 no thalamo-cortical fibers whatever are seen to enter the corpus cal- 

 losum in order to invade the opposite hemisphere. Special emphasis is 

 laid upon this observation because of the almost complete degeneration 

 of the thalamo-cortical radiation and because, in the present experi- 

 ment, the capsular lesion approaches the dorsal corner of the thalamus. 

 The lesion thus transects all thalamo-cortical fibers emerging from the 

 dorso-lateral nucleus, fibers which some investigators have claimed 

 course toward the opposite hemisphere. Upon the present observa- 

 tions as a basis, as well as on Experiments I, III, and V-a, sufficient 

 justification exists for definitely dissenting from the asserted existence 

 of thalamo-cortical fibers decussating to the opposite hemisphere. 



The bulk of thalamo-cortical fibers (sr in corresponding figures) 

 undoubtedly reaches both the anterior and posterior central convolu- 

 tions, especially the entire cortex lining the sulcus centralis (figs. 

 45-53). Caudally and orally from that sulcus the number of fibers 

 quite gradually decreases. How far in both directions these regions 

 extend and what parts of the cortex, especially those concealed within 

 the various furrows, receive thalamic fibers, can be easily seen from 

 the accompanying illustrations. The illustrations show also the 

 approximate numerical distribution of fibers (compare Chapter VI), 

 and indicate in the corresponding figures the cortical termination of 

 all the degenerated fibers found. 



Within the white substance of the hemisphere, the thalamic fibers 

 exhibit great variety in their course. In the main, they do not adopt 

 the shortest path to their respective cortical destinations. A division 

 of the most direct fibers is represented by bundles arising from the 

 dorsal portion of the dorso-lateral nucleus. That part of the thalamo- 

 cortical radiation remains necessarily most distant from the convex 

 face of the hemisphere, a frequent seat of pathological processes. 

 (Compare identical observation in the foregoing experiment.) Yet, 

 even these medial (internal) fiber groups show one or two slight 

 curvatures when passing beneath the sulci. Sometimes, however, such 

 curv^es are sharp and rather sudden, for example, in the more laterally 



