320 THE INTERMEDIATE PRIMATES 



quadruped type. The dentate nueleus of the baboon belongs to this latter 

 group. It is typical of an animal with strong quadrupedal tendencies and 

 possessed of no very wide range of highly skilled, learned motor performances. 



Mesial to the dentate nucleus is another collection of nerve cells. This 

 is the nucleus fastigii. The fibers arising and terminating in this nucleus 

 in the main make their way by the juxtarestiform body to connections 

 with nuclei m the lloor ol the fourth ventricle, especially those which 

 receive impulses from the semicircular canals, utricle and saccule. The 

 nucleus tastigii is in this sense a structure most intimately concerned with 

 the function of balancing and may be regarded as one of the higher stations 

 for equilibratory control. Its comparatively large size in baboon has a sig- 

 nilieanee not unlike that ot Deitcrs' nucleus, indicating a considerable need 

 on the part of the animal for a highly organized balancing mechanism. 



The vermis of the cerebellum (^Ver) is primarily concerned with the 

 coordinative control of those muscles of the body \\hich surround the axis 

 and are immediately adjacent to it. This part of the cerebellum varies least 

 phyletically, in this respect being cjuite unlike the lateral lobes which show 

 in marked degree a variability in size, in richness of foliation, in expansive 

 tendency, all of which appear to bear a direct relation to the degree of 

 functional capacity manifested by the upper and lower extremites. 



LEVEL OF THE EMERGENT FIBERS OF THE SIXTH NERVE AND 

 THE CAUDAL FIBERS OF THE PONS \'AROLII (FIG. I50) 



At this level certain striking changes have occurred, more particularly 

 those marked by the presence of many transversely disposed libers crossing 

 the ventral surface of the axis and forming the pons Varolii. Chief among these 

 fibers, and the most ventral in position, are those forming the stratum super- 

 ficiale pontis, dorsal to which are the scattered fasciculi of the pyramidal 

 system (.Py). Dispersed among the bundles of the pyramidal tract is the 



