62 PSYCHOLOGY. 



ing way how numerous the associative paths are which all 

 end by running out of the brain through the channel of 

 speech. The hand-path is open, though the eye-path be 

 closed. When mental blindness is most complete, neither 

 sight, touch, nor sound avails to steer the patient, and a sort 

 of dementia which has been called asymholia or apraxia is 

 the result. The commonest articles are not understood. 

 The patient will put his breeches on one shoulder and his 

 hat upon the other, will bite into the soap and lay his shoes 

 on the table, or take his food into his hand and throw it 

 down again, not knowing what to do with it, etc. Such dis- 

 order can only come from extensive brain-injury.* 



The method of degeneration corroborates the other evi- 

 dence localizing the tracts of vision. In young animals one 

 gets secondary degeneration of the occipital regions from 

 destroying an eyeball, and, vice versa, degeneration of the 

 optic nerves from destroying the occipital regions. The 

 corpora geniculata, thalami, and subcortical fibres leading 

 to the occipital lobes are also found atrophied in these 

 cases. The phenomena are not uniform, but are indispu- 

 table ; f so that, taking all lines of evidence together, the 

 special connection of vision with the occipital lobes is per- 

 fectly made out. It should be added that the occipital 

 lobes have frequently been found shrunken in cases of in- 

 veteratfi blindness in man. 



Hearing. 



Hearing is hardly as definitely localized as sight. In the 

 dog, Luciani's diagram will show the regions which directly or 

 indirectly affect it for the worse when injured. As with sight, 

 one-sided lesions produce symptoms on both sides. The 

 mixture of black dots and gray dots in the diagram is meant 

 to represent this mixture of ' crossed ' and ' uncrossed ' con- 

 nections, though of course no topographical exactitude is 

 aimed at. Of all the region, the temporal lobe is the most 

 important part ; yet permanent absolute deafness did not 



* For a case see Wernicke's Lclirb. d. Gehirnkrankheiten, vol. ii. p. 

 554 (1881). 



f The latest account of them is the paper ' Uber die optischen Centren 

 11. Bahnen' by von Monakow iu the Archiv filr Psychiatrie, vol. xx. p. 714. 



