144 Visuo-Sensory and Visuo-Psyehic Areas [CHAP. 



of the occipital lobe in two cases of blindness, that the large and prominent pyramidal cells 

 which I have noticed as characterising the visuo-psychic field undergo regressive changes in 

 such cases : also I venture to say that the atrophy and disappearance of a considerable number- 

 might occur without occasioning a laminar alteration demonstrable by a relatively coarse method 

 such as that of measurement. Here, however, we tread on debatable ground, for it is really 

 not known what cortical cells constitute the termini of the optic radiations, and although 

 S. Ramiin y Cajal, von Monakow, Leonowa, Tanzi and others have made propositions on this 

 point, it cannot be denied that it is one on which we require further enlightenment. 



With the exception of this work of Dr Bolton I can find none giving a definition of the 

 visual area on a histological basis, for while many writers I need only mention Meynert, Betz, 

 S. Ramon y Cajal, and the late Carl Hammarberg present excellent accounts of the cell- 

 lamination in this district, none of them have approached the subject from the localisation 

 point of view. So likewise with the admirable monographs of Kaes on the medullated nerve 

 fibres of the human cerebral cortex, it is impossible to glean from his diagrams the exact 

 distribution of the occipital types of cortex to which he alludes. 



Berger also, who has examined portions of the calcarine cortex from cases of blindness, does 

 not assist us in localisation, and as regards the pathological changes found, he seems only to 

 have confirmed Bolton's work. 



SUMMARY AND CONCLUSIONS. 



Convinced from my histological investigations that two definite and distinct areas, each 

 bearing a specialised type of cortex, can be mapped out in the occipital lobe, I am now 

 satisfied, after a consideration of most of the recorded work on this subject, that these two fields 

 have different physiological functions to perform. And joining hands with those who hold the 

 belief that in the occipital lobe there exist two distinct cortical centres, one specialised for the 

 primary reception of visual sensations, the other constituted for the final elaboration and 

 interpretation of these sensations, I would go a step further and affirm that the area of cortex 

 in the calcarine region, which I have mapped out and termed visuo-sensory, represents the 

 exact limits of the first-mentioned centre, while the investing field, which I have designated 

 visuo-psychic, represents the precise extent of the second centre. 



In previous sections, I have alluded casually to most of the grounds for assuming that 

 the area in the calcarine region represents the part where visual sensations first impinge, and 

 here I will offer a collective recapitulation of this evidence. 



From the records of experiments on the lower animals there is nothing to be gained in 

 favour of the point in question, but at the same time I find little that can be urged as 

 antagonistic. The reasons why such experiments must yield negative or doubtful results 

 concerning differential localisation are several ; to begin with, ablational procedures are, of 

 necessity, coarse; in the second place, it is difficult, almost impossible, to effect a psychic 

 analysis of the conscious perceptions of dumb animals, which will be sufficiently thorough to 

 meet the demands of scientific accuracy; thirdly, caution must be exercised in deriving con- 

 clusions, applicable to the human being, from operations on creatures the brains of which are 

 morphologically different (this even applies to the brains of the higher apes); and, lastly, the 

 calcarine area is so awkwardly placed (judging from the arrangement in the chimpanzee and 



