294 N. W. INGALLS 



Potto (Perodicticus), with a smaller brain than some of the 

 animals just enumerated, has well developed and in a character- 

 istic relative position all the fundamental sulci distinctive of the 

 Primates (fig. 1). 



In Potto we meet an undoubted sulcus centralis, although in- 

 dications of it may be found in certain other Lemurs, both living 

 and extinct. The fissure of Sylvius (fissura lateralis cerebri), the 

 superior temporal and interparietal sulci are present in typical 

 form although the last named furrow is shorter and straighter 

 than the corresponding fissure in the apes, of which it represents 

 only the anterior part. This is evident from the drawing (fig. 1), 

 showing the localization, and will be indicated in the discussion 

 which is to follow. Behind the interparietal sulci and quite sym- 

 metrically placed are two small transverse fissures, the ss. lunati. 

 In addition there is to be seen in each hemisphere a short obliquely 

 placed groove, above and between the Sylvian and superior tem- 

 poral, at the junction of the temporal and parietal regions and 

 hence may be called temporo-parietal. It lies in the region where 

 areas 7, 21 and 22 (cf. also figs. 12, 13, 14) are, at this early stage, 

 more or less indistinguishably fused (cf. Brodmann 06, fig. 98, 

 Lemur). The correctness of the identification of these fissures in 

 Potto as the lunate and central sulci has been established by ex- 

 amination of the structure of the cortex (unpublished notes of 

 Elliot Smith) and also in the case of the central sulci by the re- 

 sults of C. and O. Vogt's determination of the motor area by elec- 

 trical stimulation. The arrangement of the rest of the furrows 

 resemble* so exactly that found in Lemur that the results of the 

 precise localization of the cortex in that form may be confidently 

 applied to Perodicticus. This results in the arrangement shown 

 in figure 1. The pattern of sulci thus revealed is almost identical 

 with that seen in Pitheca (fig. 2) one of the more primitive South 

 American monkeys in which the relations of the interparietal 

 and lunate form a connecting link between the Prosimiae and the 

 Apes. 



For our purpose, which is to study mainly the transition from 

 the simian to the human condition and the earlier phases of the 

 process which led up to this, it is not directly useful to discuss the 



