76 



The occipital operculum in this specimen is a semilunar fold of 

 cortex which extends forward so as to overlap an area more than 

 1 cm across (at its mid-point). The crescentic furrow which limits 

 this semilunar strip in front may be distinguished as the "sulcus 

 occipitalis lunatus''. All of the terms "Attenspalte", "fissura perpendi- 

 cularis externa" and "sulcus occipito-parietalis lateralis" are not only 

 obviously inappropriate but also have been employed in very different 

 senses by various writers. Thus most writers include (under these 

 designations) the furrow which in this specimen passes sagittally forward 

 (on the dorso-mesial edge of the hemisphere) from the inner extremity 

 of the lunate sulcus to cut into the posterior lip of the sulcus parieto- 

 occipitalis. This furrow [hitherto nameless, so far as I am aware ^)] 

 may be called the "sulcus occipitalis paramesialis". Some writers, 

 again, still include in the "Aftenspalte" (or the two alternatives) the 

 sulcus occipitalis transversus and even the sulcus parieto-occipitalis. 

 Hence there is an urgent need for some new and exactly-applied terms 

 for these definite sulci. 



The sulcus occ. paramesialis is often visible on the surface in the 

 brains of the Gorilla and Gibbon and occasionally in the Orang. In 

 the Chimpanzee and all of the Cercopithecidae it is bidden under the 

 mesial extremity of the occipital operculum. In the human brain the 

 anterior part of this furrow is often pushed on to the mesial surface 

 of the hemisphere ; and both in Man (Fig. 5) and the large Apes it 

 often becomes broken up into two parts. In several instances I have 

 seen an operculation of its mesial lip overlapping the parieto-occipital 

 sulcus like the mesial extremity of the Chimpanzee's operculum. 



Below the lunate sulcus there is a typical horizontally-placed 

 Y-shaped sulcus occipitalis superior, such as is found in all the larger 

 Cercopithecidae and the Simiidae. It is the sulcus occipitalis of 

 ZucKERKANDL. In the Catalogue of the Royal College of Surgeons 

 I called this furrow (in the Apes) "sulcus occipitalis lateralis" 2) and 

 I now discard it in order to avoid the confusion which would result 

 when we recognise the fact that the furrow commonly called "lateral 

 occipital" in the human brain is the homologue of the sulcus lunatus 

 (i. e. it is the "Atfenspalte"), as I hope to be able to demonstrate. 



In Fig. 1 I have represented the dorsal limb of the bifid caudal 



1) It may be Zuckeekandl's Aufsteigender Ast der AiFenspalte 

 (op. cit. supra). 



2) My reason for such usage of Euerstali.er's term will be found 

 in the statement made by Cunningham (Surface Anatomy of the Cerebral 

 Hemispheres). Mem. of the Royal Irish Academy, 1892, No. 7, p. 70. 



