130 Visuo-Semory and Visuo-Psychic Areas [CHAP. 



by the margin of the hemisphere and the parieto-occipital fossa, was left uncovered, in fact 

 it seems to be the rule for this type of cortex to recede from the parieto-occipital fossa in 

 this situation. And, as a further consequence, when we inspect the margin of the hemisphere 

 from the dorsal aspect, we find that the external prolongation of the parieto-occipital fossa 

 lies in some cases anterior and in others posterior to the margin of the area, therefore, it 

 also cannot be regarded as a fixed boundary. 



Continuing our examination of the distribution of the area on the postero-lateral surface 

 of the hemisphere, we find that the outer edge assumes the form of a curve, running more 

 or less parallel with and at a distance of 1'4 to 2 cms. from the margin of the calcarine or 

 visuo-sensory area. 



To the visuo-sensory area, therefore, it bears a definite relation, but it cannot be said 

 that its distribution in like manner is influenced or regulated, with any degree of constancy, 

 by the fissures which cut up this portion of the occipital surface ; thus, concerning its relation 

 to the ramus occipitalis transversus of Ecker, anteriorly the area usually crosses the upper- 

 half of that sulcus and spreads for a varying extent over the convolution which is known 

 by the name of the superior parieto-occipital annectant gyms, while lower down the border 

 does not reach so far forwards as the lower half of the same sulcus, accordingly the area 

 does not touch the inferior parietal lobule. And concerning its relations to the lateral occipital 

 sulcus of Eberstaller, when this sulcus is present in typical form, the line of demarcation 

 merely cuts across its posterior extremity. 



Coming lastly to the under surface of the hemisphere, we find that the boundary of the 

 area still closely follows the visuo-sensory outline. Posteriorly it lies lateral to the hinder 

 extremity of the collateral fissure, but it soon crosses this fissure and curves upwards to end 

 in the stem of the calcarine fissure, at a point a few mm. anterior to the commencement 

 of the visuo-sensory area; and here it may be noted, that although the visuo-psychic and 

 hippocampal fields converge at this point, there is not the least difficulty iu discriminating 

 between the two types of cortex. 



Summed up, therefore, the visuo-psychic area may be described as a zone of cortex 

 from 1-3 to 2 cms. broad, investing the visuo-sensory area on all sides, that part above the 

 stem of the calcarine fissure excepted. 



STRUCTURE AND DISTRIBUTION OF THE VISUO-PSYCHIC CORTEX IN THE 

 ANTHROPOID BRAIN. (Text-figure 11.) 



It is unnecessary to enter into details concerning the structure of the visuo-psychic 

 cortex in the anthropoid ape's brain, because here again we have a reproduction of the 

 human arrangement. The subject can be dismissed with the statement that the grouping 

 and formation of the elements follow the human plan, but on a reduced scale, and that 

 the presence of an abundance of large fibres in the racliary zone again constitutes the 

 most important guide in defining the area. 



The distribution of the area, also, need not be discussed at length, because it, likewise, 

 resembles the human arrangement in forming a border zone for the visuo-sensory area, also, 

 because many of the topographical peculiarities which I referred to when discussing the 

 anthropoid visuo-sensory field may be reapplied. 



