1932] Poliak: Ajj event Fiber Systems, Primate Cerebral Cortex 113 



radiation degenerated, no evidence was found of afferent fibers cross- 

 ing through the corpus callosum to the opposite hemisphere. (See the 

 same observation in the following experiments.) 



Experiment II 



In Experiment II, so far as the visual system is concerned, the 

 lesion (L) is strictly limited to the internal segment of the external 

 geniculate body (Cgl), close to the thalamus, as figure 51 clearly 

 demonstrates. (For other details on the lesion see Chapter V and X.) 

 The remaining and by far the larger portion of the external genicu- 

 late body, its intermediate and its external segments as well as the 

 entire visual radiation including its beginning (Wernicke's triangular 

 field), entirely escaped direct injury (figs. 52-57). Also no callosal, 

 association, or any other fibers of the parietal and occipital lobes were 

 damaged in this experiment. 



From the sharply localized lesion of the external geniculate body, 

 one single compact bundle of the visual radiation degenerated occi- 

 pitalward; namely, that originating from the damaged inner and 

 somewhat oral segment of the body. On well stained sections of our 

 uninterrupted series it was possible to study the bundle in question 

 from its origin, along its entire course, to its termination in a definite 

 portion of the visual cortex (figs. 51-57, 65). 



The origin of the degenerated bundle was clearly discernible. Fine 

 bundles of degenerated fibers, all of about equal size and lying strictly 

 parallel to each other, spring from the internal contour (these fibers 

 being somewhat stronger) and from the dorsal margin of the external 

 geniculate body (these fibers being somewhat thinner). At the begin- 

 ning the degenerated fibers when passing the internal capsule neces- 

 sarily mix with other fibers that remain normal (callosal, associational, 

 efferent, and so forth), and also gradually change from an ascending 

 to a sagittal direction (vr in fig. 52). 



Some of the degenerated fascicles ascending from the damaged 

 portion of the external geniculate body turn medially and dorsally 

 close along the thalamus and pulvinar forming a narrow sickle-shaped 

 bundle. Unfortunately it was impossible to ascertain whether these 

 fine medial fibers belong to the cortico-petal visual path or whether 

 they enter the thalamus, or pulvinar, or anterior colliculus. Thus the 

 question of a possible connection between the external geniculate body 



