116 UniversUy of California Puhlications in Anatomy [^^ol. 2 



fibers and small fascicles of these turn from the common bundle 

 ventrally and again obliquely laterally along the inner contour of the 

 lateral ventricle before they actually enter the cortex in the most ante- 

 rior portion of the striate area where they just reach the floor of the 

 fissure (figs. 55, 56) . They must describe a turn of about two hundred 

 and seventy degrees or more which they complete by a spiral course 

 ascending first caudally, then turning medially around the posterior 

 horn of the lateral ventricle, and descending toward the upper lip of 

 the calcarine fissure. The ventral segment of the visual radiation must 

 have a similar spiral course occipitalward, although in none of the 

 present experiments was that portion of the radiation demonstrated by 

 degeneration. It is this ventral visual bundle which forms the ventral 

 horizontal branch of the external sagittal stratum (rhi in fig. 55), the 

 latter, however, passing ventrally below the posterior horn on its way 

 to the lower lip of the fissura calcarina (as a few solitary degenerated 

 fibers demonstrate). The remaining intermediate bundles of the 

 visual radiation composing the vertical (perpendicular) branch of the 

 external sagittal layer (rvert in fig. 55), for example, the two compact 

 bundles degenerated in Experiment I, and the bundle M in fig. 13 of 

 the Experiment V-a, have a more direct longitudinal course toward 

 the operculum occipitale and the occipital pole, as described in the 

 preceding experiment, and as it will be described later. 



Within the upper lip of the calcarine fissure, in the present experi- 

 ment, the visual fibers enter the cortex medially toward the edge of 

 the lip only as far as the stripe of Gennari or Vicq d'Azyr is visible. 

 The limit between the supplied and unsupplied cortex corresponds 

 here, as in other experiments where a "boundary segment" of the 

 visual radiation degenerated, exactly to the limit of the striate cortex 

 (figs. 55-57, 65). 



Since the degenerated bundle represents a comparatively small 

 portion of the entire visual radiation — sufficiently and clearly demon- 

 strated by the fact that in the present experiment the perpendicular 

 and ventral horizontal branch of the external sagittal layer remained 

 normal — it was not unexpected to find that the portion of the striate 

 area supplied by degenerated fibers was also a narrow strip. This 

 strip stretches along the entire calcarine fissure from its oral begin- 

 ning (where the striate area appears) as far caudalward as the upper 

 end of the ascending branch of the calcarine fissure (in front of the 

 latter branch). The narrow shaded area in figure 2, along the hori- 

 zontal portion of the calcarine fissure (Fcalc), indicates here, as in 



