130 THE LOWER PRIMATES 



Dr. John Hunter to the effect that the nucleus of Perha, although present 

 in tarsius, is extremely small. The inference to be drawn from these cor- 

 related facts again indicates an animal poorly equipped in the neural mech- 

 anisms necessary for binocular stereoscopic vision. Hence in the organization 

 of visual function the tarsier occupies a position below the lemurs and 

 new-world monkeys. 



The importance of that ocular advance which distinguishes the primates 

 from all other mammalian orders cannot be overestimated. It has been a 

 momentous factor in the e\'olutionary process. What effects must have been 

 produced in consequence of forward-looking eyes — eyes so related to each 

 other that both visual axes could be directed upon an object cither nearby 

 or at a distance, eyes which no longer looked more or less independently to 

 one side or to the other — it is difficult to estimate in measurable terms. In 

 the final outcome of constructive development this new ocular relation 

 must have borne in the weightiest manner upon that enormous super- 

 structure of skilled movements which has had its supreme expression in 

 the achievements of man. Whether tarsius represents the earliest hesitating 

 steps in this direction, or whether it has made real progress over some 

 even simpler prototype in visual organization, is a question beside the 

 point. This animal is illustrative of one of those early steps, if not 

 the earliest, toward that inestimable consummation of visual activity in the 

 acquisition of skilled movements which at length came to be the distinguish- 

 ing feature in the neokinetic progress of the primates. 



Lateral to the nucleus of the third nerve is an extensive fasciculus 

 longitudinalis posterior (PL) whose ventral extremity borders upon the 

 large collection of fibers constituting the predorsal bundle (PD). In the 

 concavity of this extensive collection of axons is the central tegmental 

 tract (Ctt) now drawn closely in toward its ultimate position of contact 

 with the central gray matter. Bordering this substance in its more dorsal 



