94 THE LOWER PRIMATES 



Surface Appearance of the Brain in Tarsius 



The cerebral hemisphere of tarsiers is hssencephalic, the iissure of 

 Sylvius lacing the sole indication of sulcal marking. In general contour the 

 brain of tarsius is elongate, its greatest length being 21 mm., its greatest 

 width 20 mm. The length is further augmented by the addition of a pro- 

 nounced bulbus olfactorius which projects forward for a consideralale distance 

 beyond the frontal region. In this regard the tarsial brain is as primitive as 

 many of the lower mammals and even approaches reptilian conditions. None 

 of the primates possesses a bulbar development comparable in prominence 

 to that of tarsius. In fact, it is in exactly this olfactory detail that all of the 

 Anthropoidca manifest that marked involution significant of a progressive 

 microsmatic development. 



THE LISSENCEPHALIC CHARACTER OF THE CEREBRAL CORTEX 



The Sylvian fissure, although clearly distinguishable, has none of those 

 features which characterize it in the apes and man. It unquestionably corre- 

 sponds to that suprarhinal fold which forms the mammalian pseudo-Sylvian 

 fissure. Lobation of the tarsicr's hemisphere is almost negligible. The Sylvian 

 indentation separates a poorly developed frontal lobe from a feebly delin- 

 eated temporal area. The occipital pole has extended caudad so that the 

 cerebral hemisphere covers a large portion ot the tentorial surface of the 

 cerebellum. This is a definitely pithecoid character. On the other hand, that 

 total absence of boundary between the occipital and parietal as well as between 

 the parietal and frontal areas bespeaks a neopallium of such pronounced 

 generalization that it might well serve for the lowest of mammalian forms. 

 With the exception of the marmoset, no such Hssencephalic condition of the 

 cerebral cortex is encountered among the primates. In the Hapalidae, how- 



