v] Summary amf Conclusions 14.") 



orang) that its satisfactory ablation without injury to other structures would baffle the skill 

 of the most dexterous operator. 



Analysing the clinico-pathological records, we find that, although the evidence concerning 

 the delimitation of the yisuo-sensory area is perhaps not so conclusive as it might be, there 

 still exists a sufficiency of data to justify the statement that a pure, unmixed hemianopic 

 condition is most readily brought about by a lesion in the neighbourhood of the calcarine 

 fissure. At least this is the impression which we receive from a perusal of cases reported 

 by Henschen. Huguenin, Hun, and other authorities : and while, on the contrary, Monakow, 

 Starr, Vialet, Mills, and others would not confine the visuo-sensory area within such narrow 

 limits, they unanimously recognise the calcarine fissure and its lips as an essential part of 

 their field. 



But, of course, the same difficulties concerning precise differential localisation which beset 

 the experimental investigator prove a stumbling-block to the clinico-pathologist ; for the arrange- 

 ment of parts is such that it is almost impossible for nature to restrict a damaging lesion 

 to the cortex, and the cortex only, of the area in question. Hence definite confirmation or refu- 

 tation of this point will not be forthcoming until the positive and negative facts adduced 

 from the careful analysis and digestion of many more cases are weighed and sifted. 



It seems to nie that one of the strongest pieces of evidence in favour of a limitation of 

 the visuo-sensory area to the calcarine region is that provided by the embryological studies 

 of Flechsig. 



According to the Leipzig professor the only fibres in the optic radiations, and even in the 

 whole occipital lobe, which have acquired their myelinic investment at the time of full foetal 

 maturation are those derived from the corpora geniculata externa, and it is plainly and un- 

 equivocally demonstrable that these fibres are distributed to the cortex coating the lips and 

 walls of the calcarine fissure. 



Needless to say this is in agreement with physiological fact; for in early infancy the 

 tracts for the conveyance of visual impulses to the primary cortical centre are obviously 

 active, but visuo-psychic processes being in abeyance, there is no demand for association 



fibres. 



There is a point in the behaviour of the large medullatecl fibres in the radiary 

 of the calcarine cortex which lends support to the thesis that this region constitutes the 

 arrival platform to use Mutt's expressive simile for visuo-sensory impulses, it is that in 

 specimens treated for the display of nerve fibres, the above-mentioned large tubules, after 

 gaining the cortex, pursue a curious oblique course, crossing and tending to avoid the 

 vertically-placed radiations of Meynert instead of finding a place in these bundles. Now 

 S. Ramon y Cajal has already drawn attention to this feature in his examination of the 

 calcarine cortex, and I have noticed its occurrence in two other parts of the brain besides the 

 calcarine region, namely, the transverse temporal and the postcentral convolutions ; and having 

 strong reasons for believing that the two last-named parts constitute cortical stations for sensory 

 impulses, I am led to assume that the oblique course of a large fibre in the radiary zone is an 

 index of its corticipetal character, and that in the case of the calcarine cortex these fibres are 

 probably seeking the large supra- and sub-stellate cells. On the other hand, in fields of cortex 

 such as that coating the precentral convolution, in which we suppose that the large fibres 



c. 19 



