176 University of California Puhlications in Anatomy ["^'ol. 2 



perpendicular branch, a fact quite in accord with the greater import- 

 ance of "central" or macular vision and with the greater number of 

 ganglion cells of the fovea centralis (compare Woollard). Macular 

 fibers form the perpendicular branch interposed between both hori- 

 zontal branches. They enter neither the upper lip, nor the lower lip 

 of the fissura calcarina but the pole and the operculum of the occipital 

 lobe (figs. 13, 22, 23). It is also true that the visual fibers which enter 

 the occipital pole and the operculum are of a more delicate caliber 

 than those terminating in the lips of the fissura calcarina (its anterior 

 portion). This harmonizes well with the delicate discriminating func- 

 tion of the macula and the more summary, reflex function of the 

 "peripheral portion of the retina." 



Besides this direct proof, still another consideration leads us to the 

 same conclusion. Since the number of macular fibers in the optic 

 nerve and tract exceeds that of the extramacular fibers and since the 

 macular segment of the external geniculate body represents more than 

 half of that nucleus, the macular cortex must be proportionally large, 

 probably larger than the entire extramacular cortex. It is logical, 

 therefore, to search for the macular cortex in the far more extensive 

 region of the striate area which covers the occipital pole and, in the 

 monkey, the occipital operculum, than in the narrow strip of the 

 striate cortex lining the fissura calcarina. In the monkey's brain, the 

 striate cortex which remains hidden in the fissura calcarina represents 

 only about a half of the whole striate area (field 17 in fig. 7, compare 

 with figs. 4, 21, 24). Evidently there is not enough room for the 

 extensive macular projection in the fissura calcarina, certainly not in 

 the brain of the monkey. (Compare also Brodmann, 1909, p. 218.) 



In the human brain the conditions are somewhat different from 

 those in the monkey, though not essentially. Less of the human striate 

 area extends over the occipital pole and still less over the convex face 

 of the occipital lobe (according to Brodmann in 10 per cent of cases; 

 see also Goldstern and Economo) . The greater portion of the human 

 striate area remains hidden in the fissura calcarina and extends but 

 slightly into the immediate neighborhood. There is, therefore, in the 

 human brain proportionately less of the macular cortex on the convex 

 face of the occipital pole than in the monkey, a part of the human 

 macular cortex being buried in the most posterior portion of the 

 fissura calcarina. But in both man and the monkey the anterior por- 

 tion of the fissura calcarina represents the extramacular portion of 

 the retinae. (Compare also Heuven, p. 60.) 



