MOKPHOLOGT OF THE BKAIX IN THE MA^r^IALIA. 



8fil 



The first cerebral hemisphere of the Aye-aye, which I cxamiiicd, is tliat represented 

 in fig. 38. At that time I had just coniph>ted an investigation into flie morphology of 

 the calcarinc sulcns, and had come to the conehision that tlie homologuo of the [anterior] 

 calcarine sulcus of tlie Primates was to be found in the retrosplenial part of the splenial 

 sulcus of Krueg in the brains of Carnivora, Ungulata, Ivlentata, Chiroptera, and 

 jMarsupialia (Proc. Anatomical Soc. of Gt. Britain and Ireland ; Journ. Anat. and Phys., 

 189!)). In tliis particular hemisphere of Cliiroinijii there seemed, at a casual glance, to 

 be one great arcuate sulcus (such as we find in Tapinis, for example) rei3resenting a 

 fusion of the genual, intercalary, and calcarine sulci ; and so, occurring in a Lemur, 



Pig. 38a. 



Fig. 37. — Chiromi/s madar/ascni-ieiisls. Mesial aspect of the brain cut in sagittal section. 

 Fig. 38. — Chifomi/s madar/ascariensis. The mesial aspect of the right cerebral hemisphere. 

 Figs. 38 «, h. — Chironiiis. Modifications of the calcarine group of sulci, delineating the variations as if they 

 occurred in the /-ir/ht hemisphere, so as to be more directly comparable with figs. 37 and 38. 



there seemed to be a striking confirmation of the hypothesis I then put forward. 

 However, upon separating the lips of the sulcus in the region immediately behind the 

 splenium, the great arcuate sulcus was found to be interrupted by a small narrow 

 submerged gyrus, so that the essential relations of the two furrows were thos(i 

 diaEcrammaticallv shown in fiij. 38. Examination of the other hemisphere showed the 

 existence of a broader bridge, and thus exj)0sed a state of affairs which is essentially 

 identical (fig. 38 b) with that found in other Lemurs. The subsequent examination of .i 

 second brain still further confirmed this view. In these four hemispheres of Cltiromyi 

 we find therefore every gradation of form between a condition which dilFers in the very 



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