304 N. W. INGALLS 



in tlio Prosimiae — a relationship which undergoes a progressive modi- 

 fication in tlie higher Cebidae and the C'ercopithecidae as the result of 

 the differentiation of the neopallial areas fringing the area striata and the 

 deepening of the sulcus lunatus to accommodate these expanding stripes 

 of cortex. In other words the sulcus lunatus (postlateralis) of the Prosi- 

 miae, while retaining its similitude to and real identity with the post- 

 lateral sulcus of the mammals, presents a much nearer approximation 

 to the condition found in the lowlier Cebidae than the latter presents to 

 the state of affairs met with in, say, Cercopithecus. 



As we gather from the description of Kohlbrugge, his Affen- 

 spalte owes its existence to the sinking in of the first annectant 

 gyrus -and has, consequently, as little to do with the Affenspalte 

 (sulcus lunatus) as that term is usually employed (Elliot Smith, 

 Cunningham, Retzius, Brodmann and with certain modifications, 

 Zuckerkandl) , as the sulcus in question has to do with the first 

 annectant gyrus. 



The sulcus occipitalis inferior (occipitalis lateralis of Retzius, 

 occipito-temporalis lateralis of Brodmann) is always very well 

 marked. Its first beginnings seem to be rather indefinite but we 

 are inclined to look for them in the small groove figured in the 

 left hemisphere of Pithecia just lateral to the lunate. Typically 

 it begins in advance of, and above the lower end of the lunate, 

 passes downward and backward bending around the lunate and 

 extends for a variable distance toward the occipital pole. That 

 portion behind the lunate is the more variable, it may be entirely 

 on the lateral aspect of the hemisphere, approximately parallel 

 with the margin or its course may be be more oblique carrying it 

 onto the tentorial surface. Its relations to the lunate are quite 

 constant and it will be found nearer or farther from the margin 

 depending upon the downward extent of the lunate. Occasionally 

 its anterior part, in front of the lunate, may be separated and the 

 remainder of it joined to the middle temporal. Its posterior ex- 

 tremity may also be bent upward so that the sulcus describes a 

 sharper curve around the lunate. As a rule it is quite deep, even 

 as deep as the lunate and its superior lip is operculated. As will 

 be seen later, the sulcus occipitalis of the Simiidae and of man 

 cannot be derived from the sulcus just described. It is evident 

 therefore that a new term is required and in referring to that 



