108 University of California Publications in Anatomy [Vol. 2 



in the striate area; thus it was hoped to obtain an insig^ht into the 

 projection of various segments of the lateral geniculate body upon the 

 striate area on the one hand, and to prove or to disprove the existence 

 of an anatomical basis for the preserv^ation of ''figures" in the visual 

 acts on the other hand; and (&) to prove or disprove the existence of 

 the crossed connections between the lateral geniculate body and the 

 striate area ("Fasciculus corporis callosi cruciatus," and the like) ; 

 to verify the existence of other side-paths of the visual radiation, and 

 the existence of the so-called "intercalated neurons" ("Schaltzellen" 

 of Monakow) within the lateral geniculate body, and also the existence 

 of a projection of the superior colliculi of the midbrain upon the 

 cerebral cortex, and the like problems. 



Experiment I 



By the lesion in this experiment {L in figs. 36, 37), described pre- 

 viously (see Chapter V), two bundles of the external geniculo-cortical 

 radiation were interrupted (vr^ and vro in figs. 37-41). They con- 

 stitute the intermediate segment or the perpendicular branch of the 

 parieto-occipital sagittal strata. The dorso-ventral extent of each 

 bundle is about one millimeter, with an intermediate zone of about 

 one millimeter between both bundles left unaltered. Both these com- 

 pact degenerated bundles were followed up to the visual cortex. 

 However, besides these two fairly distinct bundles well separated from 

 each other, a considerable number of degenerated visual fibers were 

 seen scattered among the normal fibers of portions of the sagittal 

 strata not injured directly. Many of these were found in the vertical 

 branch of the strata {rvert in fig. 39), and a few in the dorsal hori- 

 zontal branch {rJis) while the ventral horizontal branch remained 

 almost free {rhi). This somewhat diffuse degeneration was due, it 

 must be assumed, to a slight alteration of the internal and the inter- 

 mediate segment of the external geniculate body caused by the neigh- 

 boring lesion of the diencephalon, and to the direct slight injury of the 

 posterior spur of the external geniculate body (figs. 34 and 35), 

 whereas the external segment of the external geniculate body being 

 more distant, remained unaltered. Thus, it is the middle or the per- 

 pendicular (vertical) branch of the external sagittal strata which 

 degenerated in this experiment. Callosal fibers from and to the occi- 

 pital lobe, being more dorsally situated, on the whole, escaped the 

 injury. These as well as the efferent and the association fibers were 

 neglected. 



