430 THE INTERMEDIATE PRIMATES 



which has been likened to the most skillful attainment of expert trapeze per- 

 formers. The execution of such acts would require most active and precise 

 visual supervision, both in the recognition of distance as well as in the selec- 

 tion of adequate supports to sustain the weight of the body as the animal 

 makes its prodigious swinging flights through space from one limb to another. 

 Inaccuracy in visual judgment and particularly in the simultaneous adjust- 

 ment of head, eye and hand in the execution of such acts could not fail to be 

 attended with catastrophe. Hence it is that the simultaneous movements of 

 head, eye and hand become of greater importance to the gibbon than to the 

 ground-living baboon or in the more conservative aerial feats of the macacus 

 and allied monkeys. 



The pyramid (Py) occupies its characteristic position in the ventral 

 area of the cross section, but from its general dimensions, it appears to 

 show no marked increase over this structure in the macaque and baboon. 

 The cross section bears out the general impression conveyed by the appear- 

 ance on the external surface of the oblongata. It seems probable that, despite 

 the high development of the hand and especially of the forearm in the adjust- 

 ment to its arboreal locomotion, the gibbon has shown no great specialization 

 in its skilled movements, generally speaking. The proficiency which the 

 animal exhibits in the hindlimb would indicate less need for the volitional 

 control in these parts of the body than that possessed by many of the other 

 primates. 



Dorsolateral to the olive is the reticular formation (Rcf) through 

 which pass many of the internal arcuate fibers. Its definition is less well 

 marked than in the other intermediate primates. At the lateral extremity of 

 the section is a bundle of fibers constituting the restiform body (ICP) 

 which is carrying spinocerebellar and other ascending cerebellar fibers 

 upward toward the cerebellum. 



