x THE FORE-BRAIN 601 



Another indisputable fact, in which our results agree perfectly 

 with Munk, is that in dogs extensive extirpation of one occipital 

 lobe at once produces bilateral homoiiymous hemianopsia, which is 

 somewhat more extensive in the eye of the opposite side than in 

 the hornolateral. This proves that each visual centre is in direct 

 relation with the more extensive nasal segment of the retina on 

 the opposite side, and with the less extensive temporal segment 

 of the retina on the same side. Contrary, however, to Munk's 

 theory, our experiments further bring out the following un- 

 mistakable facts : 



(a) Hemiopic defects result not only after extensive and 

 complete destruction of one occipital lobe, but also after extensive 

 removal of the cortex of either the parietal or the temporal lobe. 

 This fact shows that in the dog the visual centre is not confined to 

 the occipital lobe, but also spreads in the cortex of adjacent lobes. 



(5) Partial bilateral extirpation (outer or inner, in front or 

 behind) of the occipital lobes never produces definite symptoms 

 of partial blindness, but always more or less marked visual 

 disturbances distributed over different segments of both retinae. 

 This observation confutes the theory of retinal projection on to 

 the cortex. 



(c) Neither the hemiopic defects due to extensive unilateral 

 extirpations of the occipital, parietal, and temporal regions of the 

 cortex, nor the visual disturbances spreading over the whole 

 retinal field, which occur after bilateral extirpations limited 

 to these regions, are permanent, but both gradually disappear. 

 The hemianopsia is transformed by degrees into hemiamblyopia ; 

 the diffuse blindness into diffuse amblyopia of the whole retina ; 

 lastly, the amblyopia symptoms gradually diminish to phenomena 

 of simple psychical blindness, more or less severe and complete. 

 These facts are directly opposed to the theory of absolute and 

 permanent cortical blindness. 



The above observations, published in 1885, were substantially 

 confirmed in 1903 by Shinkichi Imamura in an important series 

 of researches carried out in Exner's laboratory at Vienna. He 

 admitted that the occipital lobe must stand in closer relation with 

 the visual function than other parts of the cerebral cortex. The 

 anatomical researches of v. Monakow and Probst show that the 

 occipital cortex is in direct connection with the subcortical visual 

 centres (external corpus geniculatum, pulvinar and anterior quad- 

 rigeminal body). Imamura was able with Marchi's method to 

 follow descending degenerations from the occipital cortex to the 

 subcortical visual centres, while this degeneration is absent when 

 the frontal lobes are destroyed. 



Contrary to Munk's view, and in accordance with the state- 

 ments of Loeb, Hitzig, and Luciani, Imamura, after extirpating 

 any portion of the occipital lobe, always found hemianopsia and 



