250 THE LOWER PRIMATES 



a portion which is more recent, the neo-ohve. Each of these subdivisions has 

 been accredited with special connections in the ccreijcilum. This question, 

 however, does not necessarily concern the phyletic problem at present under 

 consideration. Discrete differentiation of ohvary segments and the significance 

 of their connections are matters needing further investigation before their real 

 value as to the function of this nuclear structure is determined. Although 

 there is undoubted significance underlying the distinction between the 

 phyletically old and new portions of the inferior olivary body, attention is 

 here directed to the evolutional unfolding which has involved the structure 

 as a whole rather than any changes affecting its individual parts. 



EVE. HEAD AND HAND MOVEMENTS, AND THEIR CONTROL 



As the hand gains in its capacity to utilize motor patterns, the wider 

 becomes its range of purposive reactions. The process of acquiring manual 

 performances, as well as the actual execution of them once they have been 

 acquired, necessitates certain directive influences. Vision especially becomes 

 an important supplementary and even dominating factor. Without the aid 

 of sight many complex movements of the hands could not be learned, and 

 quite as certainly many acts would be deprived of their full efTectiveness if 

 the eyes did not supply the proper idea of distance and perspective. 



Accepting the cooperation of vision as essential to the organization and 

 performance of many highly skilled acts acquired by the animal, especially 

 those resulting in the movements of the hands and fingers, it becomes clear 

 that a close functional inter-relation between the movements of the eyeball 

 and of the hand must exist. It is necessary that the visual axes hold in focus 

 the movements of the hand during the performance of acts which have been 

 acquired with the supplementary cooperation of the visual function. In this 

 sense the eye and the hand become essentially one organ, since the move- 

 ments in the one must follow and harmonize with the movements 



