1884.] The Effects of Lesions of the Cerebral Hemispheres. 223 



Among the more important results arrived at are the following : — 



Lesions of the occipito-angular region (occipital lobes and angular 

 gyri) cause affections of vision, without affection of the other sensory 

 faculties or motor powers. 



The only lesion which causes complete and permanent loss of vision 

 in both eyes is total destruction of the occipital lobes and angular 

 gyri on both sides. 



Complete extirpation of both angular gyri causes for a time total 

 blindness, succeeded by lasting visual defect in both eyes. 



Unilateral destruction of the cortex of the angular gyrus causes 

 temporary abolition or impairment of vision in the opposite eye — not 

 of a hemiopic character. 



Deep incisions may be made in both occipital lobes at the same 

 time, or the greater portion of one or both occipital lobes at the same 

 time may be removed without any appreciable impairment of vision. 



Destruction of the occipital lobe and angular gyrus on one side 

 causes temporary amblyopia of the opposite eye and bomonymous 

 hemianopia of both eyes, towards the side opposite the lesion. 



As in none of the cases recorded, either of partial unilateral or 

 bilateral destruction of the occipito- angular region, were the amblyopic 

 or hemianopic symptoms pei'manent, it is concluded that vision is 

 possible with both eyes if only portions of the visual centres remain 

 intact on both sides. 



Destruction of the superior temporo-sphenoidal convolution on both 

 sides causes complete and permanent loss of hearing, without other 

 sensory or motor defect. Hearing is not impaired by lesions of any 

 other part of the temporal lobe. 



Destructive lesions of the Rolandic zone (convolutions bounding 

 the fissure of Rolando) cause motor paralysis, without loss of sensation, 

 limited (monoplegia) or general (hemiplegia), according to the posi- 

 tion and extent of the lesion. 



Lesions of this region are followed by descending degeneration of 

 the pyramidal tracts of the spinal cord. 



Lesions of the frontal region vary according as they affect the post- 

 frontal (base of the frontal convolutions) or pre-frontal (anterior two- 

 thirds of the frontal convolutions) region. 



Lesions of the pre-frontal regions alone do not produce any dis- 

 coverable physiological symptoms. 



Lesions of the post-frontal regions cause temporary paralysis of 

 the lateral movements of the head and eyes. 



As the symptoms are only temporary so long as any portions of the 

 frontal lobes remain intact, it is concluded that the post-frontal and 

 pre-frontal regions have essentially the same physiological significa- 

 tion, and that portions only of the frontal lobes are sufficient for the 

 exercise of their functions. 



