470 



THE INTERMEDIATE PRIMATES 



progressive advance which has taken place in telencephalization, a process 

 which is one of the outstanding features in the evohition of the brain. Its 

 consequences are seen in the adxancement to the cerebral hemispheres of 

 functions formerly vested in lower primordial portions of the neuraxis. The 

 coeflicients of the inferior coiiiculi are appended in the following tabulation: 



Coefficients of the Inferior Colliculi in the Intermediate Primates 



A comparison of the inferior coUicuIus of the intermediate group with that 

 of the lower primates shows in even more striking manner the recession of 

 this formerly prominent midl^rain structure. It bears out the idea of a pro- 

 gressive evohition in the sense of hearing. This is indicated by the steady 

 advance which the neural organization of this special sense has made in 

 transferring its activities from a lower more limited area of the nervous sys- 

 tem to a higher and more expansible territory. 



The superior colliculus, somewhat less emphatically, gives similar evi- 

 dence of gradual, progressive delegation of a highly specialized sensory func- 

 tion from lower to higher centers in the brain. The superior colliculus in the 

 gibbon is smaller than either in macacus or baboon. This fact finds substantial 

 conllrmation in the external configuration of the occipital lobe where the 

 fissural pattern in gibbon is richer and the convolutions more ample than in 

 the other intermediate primates. The occipital area of the cerebral cortex in 

 gibbon thus appears to be more actively concerned with the visual function 

 than in macacus or baboon. The coeflicients of the superior colliculus of 

 macacus, baboon and gibbon are appended in the following tabulation: 



