SUMMARY OF STRUCTURES 283 



oculomotor nucleus. This at once indicates a group of nuclei which have much 

 closer internuncial relation by means ot the decussatinjj; and commissural 

 fibers. Mycetes exceeds lemur, tarsius and marmoset in its range of acquired 

 skilled movements. It has a much more hand-hke disposition in the motor 

 adaptations of its forcHmbs. The tabulation of the longitudinal coeflicients 

 of the oculomotor decussation is: 



The Important Factor in Progressive Development 

 OF Behavioral Activity 



If the progressive development in behavioral activity traced through 

 these lower primates could be attributed to a single factor it might be 

 ascribed to an increase in discriminative sensibility. The evidence of such 

 an increase is apparent in comparing lemur, tarsius, marmoset and mycetes. 

 The influx of new volumes of sensory stimuli from such an organ as the 

 developing hand or incident to the progressive differentiation of the pre- 

 hensile tail could not fail to introduce new powers for the direction of motion. 

 It would inevitably expand kinesthetic memories and associations. By enrich- 

 ing the entire field of somesthetic sensation it supplies the basis for new 

 motor activities. This expansion in discriminative sensibility is not limited 

 to those impulses arising from the somesthetic receptors alone. Vision and 

 hearing have likewise undergone a similar extension. The combinations and 

 intercombinations among these several types of sensory perception thus 



