i68 THE LOWER PRIMATES 



occupies its usual position dorsal to tiie pyramidal bundles. It is of relatively 

 small size and irregular outline. While it has nearly the same prominence as 

 in lemur, in many respects it seems more poorly delined as a distinctive 

 structure in the oblongata. Its edges are not so clearly demarcated. This 

 holds true of the olivary body at all levels in the marmoset, in which it 

 appears to be a poorly developed constituent indicating a low degree of 

 organization m the olivary sphere of action. Its function, as already 

 described, is related to the automatic control of simultaneous movements of 

 the hand, head and eye in the performance of skilled acts. Certainly there are 

 no acts executed by this animal which indicate the necessity of any very 

 close coordinative cooperation between eye, head and hand. 



The pyramid (Py) here reveals its dimensions in the cross section 

 and again signifies a conduction bundle with rather low capacity for dis- 

 tributing volitional motor impulses. Dorsal to the pyramidal fibers and 

 adjacent to the midline arc the first aggregations of iibers which enter into 

 the mesial fillet (Mf). This bundle is formed by decussating arcuate fibers 

 arising in the nuclei of Goll and Burdach which sweep forward across the 

 midline where they take a cephalic course toward the higher levels of the 

 brain. It furnishes some idea as to the extensivencss of the secondary sensory 

 pathway. 



LEVEL THROUGH THE MIDDLE OF THE INFERIOR OLIVE (FIG. 82) 



At the level through the middle of the inferior olivary body, although 

 this body appears in its greatest dimensions, it gives the impression of a 

 poorly developed structure. Its relatively small size supports the supposi- 

 tion that the coordinative control of simultaneous movements of head, eye 

 and hand and the coordination of all skilled learned performances are com- 

 paratively slight in this animal. The relative functional significance of the 

 nucleus of Goll as compared with that of Burdach is obvious by the con- 



