118 University of California Puhlications in Anatomy [Vol.2 



Experiment III 



In this experiment by a direct lesion of the visual radiation while 

 still in the internal capsule, at the level corresponding with tig'ure 52 

 of Experiment II, an almost identical portion of the radiation as in 

 Experiment II, and partly corresponding with the degenerated seg- 

 ments in Experiments I and IV (namely with those supplying the 

 dorsal lip of the calcarine fissure) was caused to degenerate and was 

 traced up to its termination in the visual cortex {vr in figs. 66-74). 

 This bundle represents here, as well as in Experiment II, the dorsal 

 rib or radius of the whole visual radiation, appearing on all sections 

 through the parieto-occipital lobe as the dorsal horizontal branch of 

 the external sagittal stratum. The number of degenerated fibers in 

 the present experiment must be almost equal to that in the foregoing 

 experiment since the degenerated area of the external sagittal layer 

 has about the same extent and position. (Compare figs. 69 and 71 

 with fig. 55.) 



The course, position, and termination of the single degenerated 

 bundle is in all details the same as in Experiment II. The caliber of 

 its fibers is fairly coarse and also of medium size ; yet the visual fibers 

 do not attain the caliber of the coarse somatic sensory fibers. The 

 latter {sr in the figs.) accompany the degenerated visual bundle on its 

 dorsal side to a longitudinal distance of about one centimeter and 

 turn toward the dorsal segments of the postcentral and superior 

 parietal convolution {P8 in figs. 69, 71) ; whereas the degenerated 

 visual fiber bundle proceeds occipital ward (a few callosal and other 

 fibers degenerated in the present experiment will be neglected ; they 

 can easily be distinguished from the proper visual bundle by their 

 position in the tapetum). The visual bundle in question degenerated 

 almost completely. It formed in all sections a sharply defined area 

 close to the lateral margin of the sagittal layers. The degenerated 

 area or its fibers do not appreciably mingle with the bundles remain- 

 ing normal. (Compare especially fig. 72"). This is especially e\adent 

 in sections through the occipital lobe where both the internal sagittal 

 stratum and the tapetum, as well as the entire remaining white sub- 

 stance of the hemisphere laterally from the external sagittal layer, 

 remain completely free from degenerations. 



On levels behind the splenium of the corpus callosum as soon as the 

 calcarine fissure takes its proper shape, the degenerated visual fiber 



