754 



THE CEREBRAL CORTEX. 



which bound it, we produced hemiopia, which lasted for a few days, 

 gradually passing off. But in this case a considerable disturbance must 

 have been mechanically produced in the occipital lobe by the operation, 

 and this would be quite sufficient to explain the hemiopia. In no single 

 instance in which 1 have performed a lesion in this, or any other part 



of the hemisphere, has the 

 visual disturbance which 

 resulted been confined to 

 the opposite eye ; it is 

 invariably of a hemiopic 

 character, producing par- 

 tial blindness of both re- 

 tinae. 1 Eemoval of the 

 angular gyrus has no effect 

 upon the sensibility of the 

 opposite eyeball. 2 After 

 removal of the occipital 

 lobe in a monkey, all op- 

 tical reflexes, except the 

 pupillary reflex, are abol- 

 ished, so far as the blind 

 side of the retina is con- 

 cerned (Munk). 



M'Kendrick 3 found that 

 destruction of the occipital 

 lobe in the pigeon did not 

 produce blindness of the 

 opposite eye; it was neces- 

 sary to remove the whole 

 hemisphere. 



Localisation within 

 the visual area. H. 

 Munk attempted to deter- 

 mine this in the dog and 

 monkey by effecting large 

 partial extirpations of the 

 occipital cortex. 4 As the 

 result of these experi- 

 ments, he came to the con- 

 clusion that in the dog the 

 upper zone of the retina 

 corresponds with the an- 

 terior part of the visual 



FIG. 345. Diagram showing the connection between 

 several parts of the retina and occipital lobes in the 

 dog. H. Munk. 



1 As already stated, temporary hemiopia may be produced by extensive lesions of almost 

 any part of the hemisphere, the cause being doubtless the vascular and mechanical disturb- 

 ance which the removal occasions. It is, however, more apt to occur from these causes when 

 the lesions are in the neighbourhood of the occipital lobe. 



2 Contrary to H. Munk, "Ueber die Functionen der Grosshirns, Gesammelte Mittheil- 

 lungen," 4te Mittheilung, 1878. See further on the effects of removal of the occipital lobe 

 in animals, Oilman Thompson and S. Brown, Hep. Loomis Lab., New York, 1890; also 

 Vitzou, Arch, de physiol. norm, etpath., Paris, 1893, p. 678 ; and "Proc. Physiol. Cong.," 

 1892, Cenlralbl.f. Physiol., Leipzig, u. Wien, Bd. vi. S. 400. 



3 " Recent Researches on the Nervous System," Edinburgh, 1874. 



4 "Gesammelte Abhandlungen," 1890; and Sitzungsb. d. Jc. Akad. d. Wissensch., 

 Berlin, Jan. 1890, translated in Brain, London, 1890, vol. xiii. 



