1932] PoUak: Afferent Fiber Systems, Primate Cerelral Cortex 119 



bundle changes its position (figs. 69, 70) . From then on occipitalward 

 it occupies the dorsal horizontal branch of the external sagittal layer 

 jcorresponding with the upper lip of the calcarine fissure. Its fibers in 

 their course occipitalward gradually shift medially and soon, in sec- 

 tions showing the oral segment of the striate cortex lining the bottom 

 of the fissura calcarina, begin to descend ventrally by bending around 

 the hook-shaped bundle of the callosal fibers (tapetum, Tap in fig. 70) 

 near the dorsal corner of the lateral ventricle, and penetrate as indi- 

 vidual fibers and as thin fascicles of these into the upper lip of the 

 calcarine fissure (in figs. 69 and 70 the small branch of the common 

 degenerated bundle directed medially and pointing toward the edge of 

 the upper lip does not actually enter the cortex here, but on more 

 caudal sections where the striate cortex extends more medially; see 

 figs. 71, 72). Since the oral segments of the striate cortex are con- 

 fined to the bottom of the calcarine fissure, the individual visual fibers 

 and bundles of these have to describe a spiral turn of scarcely less 

 than three hundred and sixty degrees before they can reach the striate 

 cortex (see Experiment II). Farther up caudad the striate cortex 

 gradually extends more medially toward the inner face of the hemi- 

 sphere, approaching but not quite reaching the edge of the upper lip 

 of the calcarine fissure (see figs. 71-73, and lower degenerated bundle 

 in fig. 74). In the same way the degenerated visual fibers shift 

 medially with the changing boundary of the striate cortex. Yet the 

 incoming afferent visual fibers never overstep that boundary. To 

 demonstrate the strict congruence of the boundaries of both the striate 

 cortex and the cortical segment receiving degenerated visual fibers in 

 the present experiment, two illustrations have been prepared of the 

 dorsal lip of the fissura calcarina of figure 71 under a higher magnifi- 

 cation clearly illustrating the actual conditions (figs. 72, 73 ; the latter 

 figure is turned almost ninety degrees in comparison with figs. 71, 72). 

 The striate cortex is indicated here by the presence of a double or a 

 triple horizontal intracortical stripe, the closest to the surface of the 

 cortex being the stria Gennari or Vicq d'Azyr. The striate cortex, as 

 can be seen, ceases quite abruptly at the points indicated by the arrow. 

 In the same way the entering cortico-petal visual fibers, black lines 

 and dots in the figures, stop at the limit of the stripes. A similar 

 strict observance of the boundaries of the striate cortex by the afferent 

 visual fibers exists in the entire present series as well as in the remain- 

 ing series whenever a "boundary bundle" degenerated (compare 

 especially fig. 76 in Experiment IV). No visual fibers whatever enter 



