THE BRAIN OF MODERN MAN 815 



reticular lurniation ( Ri'f) occupies a lar<ic ])orti()ii of the si'ction but has 

 less of that (lilTuse appearance so charael eristic of it in tlie apes. Its boundaries 

 are most clearly drawn in the human bram sti-in. 



This Ie\el is of particular signilicance because of its beariny upon the 

 ixiiancing mechanism, in the apparent decrease in prominence ol the neural 

 portion ot this apparatus. 



LEVEL OF THE CEREBELLAR NUCLEI (fIG. 348) 



At this level the chief feature is the nuclear de\elopment in the medullary 

 substance of the cerebellum. This specialization appears in the extremely 

 complex dentate nucleus (Ndt) which exceeds in its complicated lorm 

 all other species. The nearest a[)proach to the dentate nuch-us m man 

 is that of the gorilla, although both the chimpanzee and orang show a marked 

 increase in complexity of this nuclear structuri'. In man tln' nucleus dentatus 

 shows a definite increase m its proportional \'olume, a greater clearness in 

 definition of its outline, and a much increased richness in its convolutional 

 arrangement. The nucleus emboliformis is somewhat larger m man than in 

 the apes, \\hile the nucleus globosus and nucleus lastigii remain about the 

 same in size as seen in tlu' lower species. Since the dentate- nucleus is the 

 linal relay station for all neural impulses ])assing irom the cerebellar lu'iiii- 

 sphercs, its expansion seems to lollow as a natural constciuence ol the 

 extension in the lateral lobes. These acKances in cerebellar organization 

 denote the increase of coordinati\e control requin-d by the human mus- 

 culature in comparison with that of the forms most nearix approaching man 

 in motor capacity. 



Such expansion of the cerebellum does not in any way signify a mere 

 extension of power in muscular contraction. Some authorities still attribute 

 to the cerebellum the function of imparting strength to muscular action (the 

 sthenic element in Luciam's cerebellar triad). The arboreal habits ol the 



