PITHECUS RHESUS, MACACUS RHESUS 357 



fissure of Rolando and the sulcus simiarum, namely the parietal lobe, is 

 much more richly convoluted than any other portion of the surface of the 

 macacus brain. The temporal lobe, which is a continuation of the parietal 

 lobe ventrally, also has a marked degree of tissural richness. The area of 

 cortex lying in front of the iissure of Rolando, namely the frontal lobe, 

 is the least richly fissured and convoluted portion of the brain. The 

 orbital surface presents a wcll-delined interorbital keel upon either side 

 of which is a deep orbital indenture characteristic particularly of the 

 simian brain. The fissures upon this surface correspond closely to those 

 observed in the baboon. The occipital lobe, especially caudal to the sulcus 

 simiarum, shows less convolution even than the frontal area, but this lack 

 of fissural pattern, so conspicuous on the lateral convexity of this region of 

 the brain, is ofiset by the relative richness in fissures on the mesial and 

 ventral surfaces of the occipital lobe. The ventral surface presents a deep 

 cerebellar concavity. In general, it may be said that the cortex of the macacus 

 brain corresponds closely to that of the baboon, its lobation being essentially 

 the same and its fissures occupying similar positions. If there is any essential 

 difference between these two types of cerebral hemisphere, it is to be found 

 in the greater richness in convolutional pattern of the macacus. The hemi- 

 spheres of both of these species give a convincing representation of the 

 simian type of brain, even in such minor details as the temporo-sphenoidal 

 incisure and the ventral projection of the tip of the temporal lobe. In both 

 instances, the occipital lobe overhangs and completely covers the tentorial 

 surface of the cerebellum, a feature which is so typically primate that it 

 may be regarded as a primarily identifying character of this order. 



THE CEREBELLUM 



The cerebellum presents a tentorial surface which, however, is more con- 

 vex from side to side than is the case in the still higher primates. Its vermal 



