THE VISUAL AREA. 



753 



that destruction of the cortex of the angular gyrus and occipital lobe of 

 one hemisphere produces not amblyopia but hemiopia, i.e. not blindness 

 of the whole of the retina of the opposite eye, but blindness of the same 

 side of the retina in both eyes. It was, however, shown by H. Munk * 

 that removal of the occipital lobe alone, in the monkey, produces 

 homonymous hemiopia (blindness of the corresponding half of both 

 retime), and that removal of both occipital lobes causes complete 

 blindness, even although the angular gyri are intact ; by Munk, there- 

 fore, the visual centre was located in this lobe alone. Subsequently the 

 subject was investigated by me in conjunction with Sanger Brown"' 

 by the method of extirpation. The result of our experiments was to 

 show that, as stated by Munk, removal of one occipital lobe causes 

 homonymous hemiopia, and of both lobes at first complete blindness ; 

 but the blindness was not permanent, unless the lesion extended some- 

 what in advance of what is generally taken to be the limit of 

 A. B. 



Fig. 344. — Views from above, A, and from below, B, of the brain of a monkey, from 

 which both occipital lobes, and, on the under surface, part of the temporal lobes 

 had been cut away. This animal was completely blind for several months, 

 although both angular gyri were intact. 



the lobe, on the inner and lower surface. The explanation of the 

 difference between these results and those of Ferrier and Yeo is 

 probably to be found in the fact that in their cases the removal is 

 less complete — this is manifest from their figures. And the same 

 remark applies to some experiments of Horsley and myself on this 

 region. 3 With regard to the angular gyrus, the experiments with 

 Sanger Brown were entirely contradictory to those of Ferrier and Yeo. 

 In animals in which the grey matter of this convolution was destroyed 

 on one or both sides we could discover no defect of vision. If it were 

 done on one side, there was neither blindness of the opposite eye nor 

 hemiopia ; if the eye of the same side were bandaged, the animal saw 

 perfectly well with the opposite eye. In one case only, in which we 

 scooped the whole of the convolution away, after opening up the fissures 



1 "Die Functionen der Grosshirnrinde," 1890, S. 293. See also Sitzungsb. d. k. AJcad. 

 d. Wisscnsch., Berlin, 1890, S. 53. 



2 Sanger Brown and Schiifer, Phil. Trans., London, 1888, B, p. 303; Schafer, Brain, 

 London, 1887, vol. xi. p. 362 ; ibid., vol. xi. p. 145. 



3 Phil. Trans., London, 1888, B. 



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