202 THE LOWER PRIMATES 



Total weight of the brain 24 . 5 gms. 



Water displacement of the brain 24. 5 c.c. 



Weight of the forebrain 20 gms. 



Weight of the midbrain , i gm. 



Weight of the hindl^rain 3.5 gms. 



On the basis of these figures, the following indices were computed for the 

 several divisions of the brain: 



Forebrain index 81.6 per cent 



Midbrain index 4.8 per cent 



Hindbrain index 13.6 per cent 



These indices definitely place the animal in the manual group. 



Surface Appearance of the Brain in Mycetes Seniculus 



the fissural pattern 



The surface of the hemispheres of the brain is gyrenceJDhahc with the 

 most marked fissuring in the parietal, temporal and occipital regions. The 

 frontal lobe has but few sulci. The fissure of Sylvius is a prominent landmark 

 upon the hitcral surface. Below and parallel to it is the superior temporal 

 fissure, separating an inferior from a superior temporal convolution. Several 

 interrupted sulci in the parietal region occupy the position of the interparietal 

 fissure, while a small sulcus in the usual position of the fissura semilunaris 

 separates the occipital frt)m the parietal lobe. A short preccntral sulcus 

 extends horizontally from the sagittal line toward the fissure of Sylvius. The 

 ventral extremity of this fissure falls considerably short of the latter sulcus. 

 While this fissure may be easily discerned as the fissure of Rolando, its 

 perpendicular relation to the great longitudinal fissure is reminiscent of the 

 fissura cruciata of lower mammals. One deep fissure is present in the rostral 



