606 



PHYSIOLOGY 



CHAP. 



qualities of sensations, it would have to be admitted that all 

 mental activities from the most complex to the simplest, including 

 the visual reflexes, must have their seat in the cerebral cortex a 

 conclusion that contradicts all that has been set forth in the 

 previous chapters as to the functions of the cerebrospinal axis. 



Let us see if Minkowski's theory is, partly at any rate, 

 applicable to the visual centres of the monkey. Munk, as we 

 have seen, left his researches incomplete as regards the visual 

 sphere in apes. The sole fact which he demonstrated, and which 

 we fully confirmed, was that bilateral homonymous hemianopsia 

 occurs after extirpation of a whole occipital lobe. But while he 

 took this to be a permanent symptom, we showed that it is 

 temporary, and that it may be reproduced by successive operations 



on the same hemisphere. This proves 

 that in monkeys, too, the visual 

 sphere extends beyond the limits of 

 the occipital lobe. Munk did not 

 adduce a single experiment in sup- 

 port of his hypothesis of retinal 

 projection on the cortex, or show 

 that partial extirpation produces 

 partial blindness of one or the other 

 portion of the retina. 



The experiments on the cortical 

 visual sphere of the monkey were 

 continued by Schafer and Sanger- 

 Brown in 1888. Extirpation of one 

 occipital lobe (Fig. 302) produces 

 bilateral homonymous hemianopsia 

 in monkeys : extirpation of both 

 occipital lobes produces total blind- 

 ness, which, however, is not permanent if these lobes alone are 

 injured. To produce permanent blindness it is necessary that 

 the lesion should extend beyond the occipital lobes, particularly 

 on the inner and lower surface, and include part of the cortex 

 of the temporal and parietal lobes (Fig. 303). Contrary to 

 Ferrier and Yeo, Schafer and Sanger-Brown exclude the cortex 

 of the angular gyrus from the visual area. The hemiopic 

 symptoms sometimes seen after removal of the cortex from 

 that gyrus disappear after a few days, and may depend on shock 

 extending to the contiguous occipital lobe. But this interpreta- 

 tion will not hold in view of the fact established by us, that the 

 residual disorders of vision due to extirpation of the occipital 

 lobes become aggravated after injury of the angular gyri. 



Schafer and Sanger-Brown accepted projection from the retina 

 on the cortical centre of vision in monkeys, which Munk already 

 held for dogs. But in the monkey central vision i.e. the area 



Fio. 302. Brain of Macacus from which 

 one occipital lobe had been entirely 

 removed, but the angular gyrus left 

 intact. (Schiifer and iSanger-Brown.) 



