112 University of California Puhlicati-ons in Anatomy [Vol. 2 



the entire pole of the occipital lobe caudad to both the ascending and 

 descending branches of the calcarine fissure (Fcalc). A small number 

 of fibers enter the upper lip of the calcarine fissure, corresponding to 

 the small number of degenerated fibers in the dorsal horizontal branch 

 of the external sagittal layer. They reach the latter region by gradu- 

 ally turning around the dorsal corner of the lateral ventricle down- 

 ward where they form a thin fiber layer. This will be better demon- 

 strated by Experiments II, III, and IV (figs. 55-57, 69-72, 75, 76). 

 It was also noticed that in the calcar avis the visual fibers before 

 entering the cortex run for a distance oralward. Also the fibers 

 destined for the upper lip of the calcarine fissure are, in the present 

 experiment, not everywhere equal in number nor uniformly distri- 

 buted. (See different observation in other experiments.) This is 

 due to the fact that, unlike what was observed in Experiments II, III, 

 and IV, no compact bundle supplying the upper lip of the calcarine 

 fissure (upper horizontal branch) was caused to degenerate in this 

 experiment, but a few scattered fibers only. The relation between the 

 afferent visual fibers and the striate cortex of the upper lip of the cal- 

 carine fissure is exactly the same as described for the occipital oper- 

 culum. No afferent fibers whatsoever reach the extra-striatal cortex. 

 While on the other hand, the ventral lip of the calcarine fissure did 

 not, in this experiment, receive any such fibers. This is due, as 

 expected, to the fact that the ventral horizontal branch of the sagittal 

 layers and the lateral segment of the external geniculate body 

 remained unaltered in the present experiment. The most posterior 

 portion of the calcarine fissure, its ascending branch, however, is 

 reached by a great number of degenerated fibers. 



The caliber of the afferent visual fibers is in general considerably 

 below that of the somatic sensory and auditory fibers. (Compare 

 Somatic Sensory System and Auditory System.) There are, as men- 

 tioned, some differences in size also among the visual fibers, the 

 majority of these being fairly delicate. Also there are regional differ- 

 ences since the fibers supplying the occipital operculum are fine and 

 of about equal caliber, a few of them only being coarse ; whereas the 

 coarser fibers enter the striate cortex lining the calcarine fissure. It 

 was also noticed that individual bundles close to the external genicu- 

 late body are composed of fibers having an equal caliber, though there 

 are differences in caliber in different bundles. 



It must also be mentioned that, although in the present experi- 

 ment a considerable portion of the entire external geniculo-cortical 



