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and 2. D. it will be seen to be quite separate, but in these two cases 

 it is very possible that the caudal stem of the H-shaped arrangement is 

 really formed by the superior parietal. This may not really be the case, 

 because that would place the sulcus so far forward that it could hardly 

 be fulfilling its purpose, i. e. of separating the structurally different 

 areas parietalis superior anterior and posterior from one another. 



It may well be that in these two brains the different parts of the 

 area were not sufficiently differentiated to call a limiting sulcus into 

 being. " In most specimens I have found it quite impossible to 

 distinguish the cortex of the area in front of these furrows (i. e. the 

 sul. pariet. sup. and sul. praecunei), from that placed behind them, 

 but it often happens that there is a distinct difference in the texture 

 of the two parts, the lines of Baillarger being somewhat narrower 

 and denser in the area parietalis superior anterior than in the area 

 parietalis superior posterior." (Elliot Smith, (4) p. 425). The 

 superior parietal sulcus would in such cases hardly be present. Brod- 

 MANN states that he has no hesitation in separating the superior 

 varietal field into two parts though the difference between them is 

 pery slight. The sulcus which limits the two fields is naturally not 

 a deep one, though it is fairly constant. 



A possibility is that the anterior limbs of the H-shaped arrange- 

 ment exhibited by the two specimens already referred to (Figs. 1. C. 

 and 2. D.) are really the homologue of the sulcus praeparietalis since 

 these limbs occupy a position which must be well within the confines 

 of the sensory area proper — perhaps actually between the areas 

 postcentralis caudalis and praeparietalis, as we have seen to occur in 

 pithecus. I have, at any rate, doubts in naming a sulcus " post- 

 centralis " when it lies so obviously within the sensory area. I am 

 fully aware that the sulci cannot be taken as the rigid boundaries of 

 specialised areas, as was pointed out long ago by Sherrington. But 

 at the same time I cannot conceive of sulci being far removed from such 

 boundaries, seeing that it was specialisation of cortex which produced 

 them. The second explanation then of this H-shaped arrangement ia 

 that, the anterior limb is sulcus praeparietalis, the posterior sulcus 

 postcentralis superior proprius, whilst the horizontal portion is sulcus 

 paracinguli the superior parietal sulcus being absent. I have already 

 alluded to the difficulties besetting a discussion on these points in 

 the absence of histological studies of the actual brain in question, and 

 I do not propose to treat the matter further. 



