146 Visuo-Sensory and Visuo-Psi/chic Areas [CHAP. 



present are corticifugal or efferent, it is interesting to find that the radiations of Meynert 

 form their chief track to the white substance ; also, it is important to notice that in the visuo- 

 psychic cortex where large fibres are even more abundant than in the visuo-sensory cortex, many 

 exhibit the corticifugal peculiarity. 



The concluding evidence in support of a separate functional standing for the visuo-sensory 

 area is the proof adduced by Dr Bolton that in old-standing cases of optic atrophy the whole 

 of the calcarine cortex undergoes distinct secondary alterations allied in kind to Gudden's 

 atrophy, alterations by which the exact histological localisation of what he also calls the visuo- 

 sensory area can be determined. 



The grounds for a similar succinct delimitation of an area wherein visual impressions 

 are further dealt with in the process of elaboration and intellectual interpretation can hardly 

 be called definite ; at the same time we have now elicited a considerable amount of evidence, 

 both direct and indirect, which points to this simplified arrangement. 



That one or more fields exist in the occipital lobe for carrying out these psychic processes 

 concerned with vision has been amply proved by the results of experiment and clinico-pathological 

 observation, but the extreme complexity of psychic visual processes along with the extreme 

 difficulty attending the precise localisation of psychic perceptions generally, has necessarily 

 prevented the experimenter and the clinician from arriving at an exact judgment concerning 

 the orientation of this particular function. 



From the histological point of view, however, the differentiation of such an area presents 

 less difficulty ; to begin with, my own observations have definitely proved that immediately 

 investing the visuo-sensory area there exists a moderately extensive field of cortex, possessing 

 a specialised type of arrangement of nerve cells and nerve fibres, entirely different both from 

 that in the visuo-sensory area and that in the more outlying parts : and granted that the calcarine 

 area is solely devoted to the reception of primary visual stimuli, the mere existence of a second 

 area placed in such immediate contiguity suggests the likelihood that it is concerned with the 

 sorting out and further elaboration of these stimuli. 



More than this, the arrangement of fibres in this investing area suggests that they carry 

 corticifugal instead of corticipetal impressions, that they are the fibres, in other words, which 

 combine to form the strands joining the visual with other centres and helping to make the 

 visual function so complex. Then, notwithstanding that the cortical connections of the strands 

 of fibres to which I allude have not been fully worked out, yet arguing on the supposition 

 which is almost equivalent to a truth that large fibres take origin from large cells, it is reasonable 

 to assume that the fibres of these bands are derived from the giant cells which form such a 

 characteristic feature of the visuo-psychic cortex. 



Again, we can adduce Flechsig's e'vidence to the effect that in the newborn child none 

 of these fibres pertaining to association tracts possess a medullated sheath, indicating that 

 their development is delayed until the child is capable of interpreting sight stimuli. Lastly, 

 we have the extremely important information gained from clinical observation of various psychic 

 visual defects, that for the production of a psychic element in the blindness, it is necessary 

 for the occipital lesion to be widespread and not confined to the calcarine region. 



