SUMMARY OF STRUCTURES 467 



intimating that the rehiying structure in the efferent pathway of impulses 

 out of the cerebelhim varies with the dentate nucleus from which these 

 impulses arise. The planimetric coefficients of the red nucleus are shown 

 in the appended tabuhitions: 



As compared with the similar structure in the lower primates, the red 

 nucleus is in general larger in the intermediate primates, with one exception, 

 namely, Mycetes seniculus, which has a planimetric coefficient greater than 

 in all of the other forms thus far described. 



VI. The Pontile Nuclei and Their Relation to the Control of 

 Skilled Movements, Especially Complex Manual Performances 

 A comparison of the pontile nuclei, those structures of the brain to which 

 such importance has been attached as indicative of the animal's capacity for 

 acquiring skilled motor performances, shows that the gibbon is slightly more 

 advanced in the line of this development. This fact does not accord with 

 the observations with reference to the nucleus of Burdach which furnishes 

 the basis for estimating the volume of discriminative inllux from the upper 

 extremity and hand. It will be recalled that in this review, the macacus was 

 accredited with a higher degree of manual differentiation than the other 

 intermediate primates. On the other hand, the pontile nuclei seem to indicate 

 that the gibbon is endowed with a high degree of specialization in its skilled 

 movements, and is thus capable of a wider range of behavioral adaptation. 

 It is difficult to reconcile this apparent discrepancy, since the macacus, by 



