Vimo-Sensory an<f Vi*>io-Pxychic Areas [CHAP. 



however, which I think this histological investigation definitely settles is the debated question 

 of the affinity between the sulcus occipitalis secundus vel sulcus occipitalis lateralis of Eber- 

 staller and this anthropoid fissure, for a close comparison of these two sulci proves that 

 with the single exception of agreeing roughly in regard to position they have no cor- 

 respondence whatever. Thus, we find, first, that the anthropoid fissure is not only a 

 relatively deep one but its course and position appear to be fixed, definite, and invariable. 

 And while Eberstaller gives the sulcus occipitalis lateralis a position of high importance in 

 the human adult brain and considers that it should be held to form the inferior boundary 

 of the occipital lobe, on the outer surface of the hemisphere, I have convinced myself from 

 a careful examination of over 200 hemispheres that this limit, on account of the extreme 

 variability of the position and general representation of the fissure, is an unsatisfactory one, 

 added to which there is no gainsaying the observation that in all cases the sulcus is rela- 

 tively shallow. But my second reason for discrediting the homology between the two fissures 

 is that which to my mind dispels all doubt on the point, it is the histological truth 

 that what I have called the calcarine type of cortex closely follows the anthropoid fissure, 

 while in the human cerebrum the sulcus lateralis occipitalis lies well without the area 

 covered by a similar type of cortex, in fact its walls and the convolutions which border 

 it are clothed by a totally dissimilar type, and this it must be granted is an extremely 

 important point of difference. 



Having arrived at the decision that this curious simian fissure does not correspond 

 with the human lateral occipital sulcus, and that its affinity with the transitory human 

 external calcarine fissure is not wholly proved, we have next to consider whether evidence 

 exists to suggest that it has any other human equivalent. 



In this connection there is one point which occurs to me and it bears upon the 

 " Affenspalte." Xow it is not my desire to enter the arena with those who have studied 

 and discussed the vexed question of the homology of this great and important fissure ; I 

 wish merely to submit a hypothesis and indicate what might happen if, in the human brain, 

 the convolutions and sulci were to be so altered as to allow of the deposition of a fissure 

 corresponding in length, depth, and position with the " Affenspalte." 



In this event I venture to say that it would be surprising if all the occipital fissures, 

 and the calcarine fissure in particular, did not undergo marked alterations in arrangement, 

 and one could imagine that the sequence of events would be as follows. To supply a 

 covering for the deep opercular posterior wall of the " Affenspalte," the external occipital 

 convolutions would be drawn forward and absorbed, the posterior calcarine fissure, along 

 with the fissura extrema of Seitz, would be pulled out on to the convexity of the hemi- 

 sphere, the cuneo-lingual gyrus would share the change and be brought to the surface, and 

 the general tension would impart a smooth and flattened appearance to the occipital lobe 

 on its external face. In this way we should obtain a simian distribution of the calcarine 

 type of cortex, and the flattened appearance which is so characteristic of the ape's cerebrum 

 in this part. 



The alternative suggestion, therefore, which I have to offer in explanation of the 

 singular distribution of the calcarine type of cortex in the anthropoid cerebrum is, that 

 the deep horizontal sulcus on the outer surface of the occipital lobe in the higher apes, 

 and possibly in other varieties of simiadae, may represent the dislocated fissura calcarina 

 posterior of the human brain. 



