294 ANATOMY OF THE CENTHAL NEEVOUS SYSTEM. 



nation in the territory of the thalamus and in the corpora quadrigemina. The last 

 radiations of the occipital fibers of the corpus callosum, the forceps, are separated 

 and distinct from the gray matter of the ventricle. The fasciculus occipito-tem- 

 poralis, or longitudinalis inferior, lies now no longer lateral, but ventral, to the 

 ventricle. 



The greater part of the remaining white matter visible in the section belongs to 

 the intrinsic fibers of the occipital lobe, to the short pathways which connect its 

 various cortical areas with one another. 



It is not improbable that the fibers foiind in the optic radiation have 

 two points of origin: they may originate from the cells of the primarj' 

 ■ centers and pass to the cortex, or they may originate from cortical cells and 

 pass to these primary centers. 



In cases of destructive focal lesion in the occipital lobe and in the most 

 posterior part of the internal capsule, disturbances of sight appear that are 

 exactly similar to those where the optic-nerve tract has been injured on the 

 side involved. The outer half of the retina of the eye which is on the same 

 side as the lesion and the inner half of the retina of the opposite eye 

 degenerate. 



A fiber-tract that was discovered by Oall and Spiirzlicim probably belongs to 

 the system of the opticus also. It passes down laterally from the anterior corpora 

 quadrigemina, and at the base of the brain runs for a distance transversely^ across 

 the pes peduneuli before it sinks into the pes near to the median line. It then 

 attains a ganglion of the ventral thalamic region (KolUker). This tract — tJie 

 tractus pcduncularis trarisrcrsus — degenerates after the destruction of one optic 

 tract (Gvddeii). It is not always capable of demonstration, and is variable in its 

 development. In Fig. 141 you see it (not designated) pass over the right crus 

 cerebri. Probably this bundle is identical with that one which was described on 

 page 132 as the tractus thalamo-teetalis. 



