170 University of California PuhlicaUons in Anatomy [Vol.2 



mediate perpendicular branch (forming in reality the "middle" or 

 axial segment or "rib" of the external geniciilo-cortical fiber "fan") 

 has its own course and terminates in the pole of the occipital lobe 

 (Experiments I, IV, and especially V-a), (4) further from the fact 

 that the intermediate segment of the external geniculat'C body degen- 

 erates after the destruction of the macular portion of the striate area 

 (Experiment V-d), and also considering other factors with which 

 I will deal later/ I feel entitled to conclude that the intermediate 

 vertical branch of the visual radiation transmits impulses from the 

 homonymous halves of both maculae upon the pole of the occipital 

 lobe and, in the monkej^, to its external face called the occipital 

 operculum (figs. 22, 23 ; for arguments against the so-called bilateral 

 cortical representation of the macula see this discussion later). 



The lower horizontal branch of the external sagittal layer has not 

 been injured in any of the present experiments. Nor, except for a 

 few solitary fibers, has any degenerated bundle been seen to enter the 

 lower lip of the fissura calcarina. This negative result valued in its 

 proper significance in connection with the positive results in the 

 present experiments appears really as a positive result. We would 

 appear to be amply justified in accepting the termination of the lower 

 horizontal branch of the external sagittal layer as being in the lower 

 lip of the fissura calcarina and it is safe to regard these ventral bundles 

 of the visual radiation as reaching the lower lip in a similar way, 

 though in reversed fashion, as has already been described for the 

 dorsal bundles. The ventral bundles bend gradually in a spiral sense 

 in their course occipitalward below the posterior horn of the lateral 

 ventricle, at the same time approaching medially the lower lip of the 

 fissura calcarina. They have their separate course, as described, since 

 the dorsal horizontal and the perpendicular branches, degenerated in 

 the present experiments, do not mix with them ; and no degenerated 

 bundles from the dorsal or from the perpendicular branches have been 

 seen to descend toward the lower lip. The only possible origin of the 

 bundles which form the ventral portion or ventral "rib" of the fiber 

 "fan" of the visual radiation is the external or lateral segment of 

 the external geniculate body.^ This is well ascertained by our 

 Experiment V-b. 



4 Compare also Brouwer-Heuven-Biemond, Heuven, Brouwer, 1930; R. A. 

 Pfeifer, 1930 ; Foerster, 1929, and Foerster-Penfield. 



5 That the lateral segment stands in connection with the lower lip has been 

 lately proved by experiments of Heuven. 



