208 



THE LOWER PRIMATES 



The flocculus in these monkeys, as well as in Atelcs and Lagothrix, all species 

 in which the prehensile tail has i)ecome highly specialized, reaches a higher 

 point of development than in any other primates. Whether this prominence 



FIG. I 15. VENTRAL SURFACE OF BRAIN STEM, MYCETES SENICULUS. 



[Actual Length, 34 mm.| 



Key to Diagram, cereb. peduncle, Cerebral Peduncle; opt. ped. space, Opticopeduncular Space; pvr. 

 DEC, Pyramidal Decussation; trap, body. Trapezoid Body; ventro. med. sulc, Ventromcdian Sulcus. 



of the flocculus is due, as has been thought to be the case by several author- 

 ities, to the additional responsibilities imposed upon the coordinative 

 mechanism in response to the prehensile tail is a question needing further 

 investigation. 



THE BRAIN STEM 



The surface markings of the brain stem in mycetes are more pronounced 

 than in lemur or marmoset, although in only a few instances do they attain 

 the prominence obser\ed in the higher apes. The oblongata upon its ventral 



