PITHECUS RHESUS, MACACUS RHESUS 377 



The principal Icatuif illustrated by this region is the ditluse character 

 of the cerebellar nuclei. This condition at once indicates an animal poorly 

 provided with coordinative control over its skilled acts. This view of the 

 behavior of macacus is further supported by the relatively small size of the 

 lateral cerebellar lobes. The animal is noted, and even notorious, for its 

 prankishness and its giTat agility as a climber. It is possible to teach these 

 monkeys many amusing tricks, so that the conception of them as limited in 

 their neokinetic performances perhaps does them injustice. On the other 

 hand, the fact should not be overlooked that howe\'er much they may 

 improve by training, these animals use their new accjuisitions but little in 

 the ordinary routine of their lives, and escaping from captivity, relapse to 

 the simpler motor patterns essential to their primitive arboreal adaptations. 

 It must, therefore, be accepted from such evidence as is elicited from the 

 cerebellar nuclei and their connections, that the macacus species are, in 

 fact, capable of a very limited range of skilled learned performances which 

 they habitually employ in the pursuits of their daily lives. 



LEVEL OF EMERGENCE OF SLXTH CRANIAL NERVE, NER\'US ABDUCENS (FIG. 1 77) 



At this level the section has undergone considerable change due to 

 the appearance of the caudal portion of the pons Varolii (PN). This 

 structure now adds a basal element to the neuraxis and makes distinguishable 

 in it the basis and the tegmentum pontis. The pons here consists of but 

 a few transverse fibers constituting the stratum superficiale pontis, and 

 the caudal extremity of the pontile nuclei contained within which latter are 

 the somewhat scattered libers of the pyramidal system (Py). The lateral 

 continuation of the superhcial stratum of the pons enters into and forms part 

 of the massive middle cerebellar peduncle (Mcp). The tegmentum at this 

 level is separated from the basis by a number of transverse decussating 

 fibers constituting the trapezoid body (Trp) in whose lateral extremity is the 



