TROGLODYTES GORILLA 68 1 



lower vertebrates. Their reduction is clearly shovNTi in gorilla by a demon- 

 strable decrease in size and by the vestigeal condit " neir stratification. 

 A few layers of cells and fibers, rather indiscr; j:ed, may still 

 be observed up)on high magni: " ajray matter (Cen) 

 surrounds the aqueduct of Sylvius, and in its ventron a contains 

 one of the largest of the cranial nuclei, the nucleus oculomotorius ( Noc). 

 This nucleus is important not only because of the extremely delicate muscu- 

 lature which it controls, ' :e as much because of the close internuclear 

 relation which is maintained between the two n ecussating 

 and commissural fibers. No other structures in y are more cnt 

 upon mutual cooperatio: - :ghtest deflection in their 

 adjustment produces gross defects in visual percep" 't only 

 disorganize the appreciation of objects. -o disturb many ot the reac- 

 tions of the animal in relation to its exter ations. It is the promi- 

 nence of these internuclear com _ - which makes 

 the nucleus oculomotorius in go: picuous. 



The emergent fibers of the oculomotor ner\"e pass forward, some of them 

 p>enetrating the inner margin - NRu), some of them 



skirting its margin, to reach the sulcus oculomotor: - c optic - ^""J" 



lar space. The nucleus ruber i N R u ) is a large and highly differentiated 

 structure in the tegmentum, acting as a relay station in the efferent course 

 of impulses from the cerebellum. The marki :s nucleus, 



combined with the increased definition in the size of the dentate nucleus and 

 the expansion of " oerior cerebellar p>eduncle, indicates to what degree 



functional accessions have been made in co ve control in the animal's 



muscular system. Such additional coordinati' c muscular activity' of 



the gorilla is primarily determined by the develo; if greater adapta- 



bilrt\' of the upper extremity and especially ot e feet and 



legs have shown relatively less increase of sp>eciaIization over ver 



