PARIETAL REGION IN THE PRIMATE BRAIN 313 



we mean that it must be based on such fundamental genetic 

 principles as will render it applicable to the greatest number of 

 cases, will give it the greatest heuristic value without its invalida- 

 tion as an expression of homology. 



To begin with, the term ' ' Affenspalte " is open to objection 

 and the same criticism naturally applies to such designations as 

 the sulcus simiarum of Retzius and the sulcus simialis of Brod- 

 mann, for the simple reason that the sulcus is not peculiar to any 

 Ape. This is a point however of minor importance, the sulcus cer- 

 tainly reaches its greatest development in the. lower Old World 

 Apes and as names these have much more to recommend them than 

 many of definitions which have been fabricated for them. We 

 would define therefore, the fissure to which we shall hereafter ap- 

 ply the term sulcus lunatus, as that fissure in the primate brain, 

 which, be it operculated or not, and be its relation to other fissures 

 what they may, is situated immediately in front of that portion of 

 the area striata which is located on the lateral aspect of the hemi- 

 sphere. In the definitely operculated forms of the sulcus, a char- 

 acteristic and quite distinctive feature is the extension of the 

 area striata almost to the free edge of the operculum and this 

 relation is causally related to the development of the operculum. 

 In proportion as the operculum is ill-developed the less exact 

 becomes the coincidence of the anterior limit of the area striata 

 with the margin of the operculum. We are well aware of the 

 grounds upon which this definition is based, but there can be 

 no doubt that the occipital operculum and with it the sulcus lu- 

 natus are directly and genetically related to the development of 

 the area striata and that the relations of these to any neighboring 

 structures are secondary and therefore of secondary importance. 



The conception of Kohlbrugge, referred to above, is altogether 

 impossible since its restricts the term to a quite fortuitous com- 

 bination of furrows which is only found in certain forms and even 

 in them with individual variations. Zuckerkandl's view, which 

 is accepted by Sergi, is more acceptable, it nevertheless suffers 

 from his defining the essential in terms of the non-essential and 

 has made, as it were, the sulcus lunatus a function of the ever- 

 varying first, second and third annectant gyri. It seems that 



