122 University of California PuhlicaUons in Anatomy [Vol. 2 



equal in size to the individual degenerated bundles in other of the 

 present experiments (Experiments II and III). It is situated at the 

 limit between the dorsal and the middle third of the vertical branch 

 of the sag-ittal strata on levels where the latter attain their usual 

 shape (parietal lobe). It accordingly corresponds to a fiber segment 

 immediately ventral to that degenerated in Experiment II (fig. 54) 

 and in Experiment III (fig. 68), or approximately to the upper 

 degenerated bundle in Experiment I (figs. 38 and 39) though it 

 extends somewhat toward upper horizontal branch. 



The degenerated zone occupies about three external quarters of the 

 sagittal strata corresponding with the external sagittal layer. The cali- 

 ber of a considerable number of the degenerated fibers is here of medium 

 size, though the coarse fibers are more conspicuous. The internal sagit- 

 tal layer, which farther up in the occipital lobe hardly exists, and the 

 tapetum remain free from degeneration a.s soon as the descending and 

 callosal fibers have disappeared. The contours of the degenerated zone 

 of the external sagittal layer are quite sharp against its dorsal and 

 ventral portions left unaltered. They become a little less sharp more 

 occipitalward when the degenerated bundle begins to approach the 

 striate cortex. Along its course occipitalward the visual bundle does 

 not give off any fibers for the parietal or for the occipital cortex until 

 it reaches the level of the striate area. 



The further course of the bundle is similar to that in the foregoing 

 experiments. It gradually ascends dorso-medially by describing a 

 spiral turn around the callosal bundle and the lateral ventricle, and 

 finally reaches the upper lip of the calcarine fissure {Ls in fig. 75). 

 Here again the degenerated fibers run for a considerable distance in 

 the oral direction inside the thin fiber layer covering the calcar avis and 

 within the white substance of the upper lip before they penetrate in 

 the striate cortex. This is especially the case with fibers destined to 

 supply the bottom of the fissura calcarina which, by running in a 

 retrograde sense, reach the oral beginning of the striate area. Thus a 

 portion of the common single degenerated bundle in this experiment 

 terminates in the upper lip of the calcarine fissure where its fibers 

 enter exclusively the striate cortex. However, in contradistinction to 

 Experiments II and III, the supplied zone in this experiment (ah in 

 fig. 75) does not coincide with the whole striate cortex of the upper 

 lip, leaving a narrow strip, the actual "boundary segment" of the 

 striate cortex in that lip (between the arrow and the letter a, in fig. 

 75), with normal fibers. The degenerated bundle of the visual radia- 



