SUMMARY OF STRUCTURES 471 



Coefficients of the Superior Colliculi in the Intermediate Primates 



The comparison of the lower primates with those in the intermediate 

 group develops a signihcant fact, nameljs that the superior eoUieuIus in 

 baboon is more prominent, by virtue of its larger size, than in any ot the 

 other species. Although not aiming to over-estimate the vahie of a purely 

 mensurational observation, it seems hkely that the baboon, whose Hfe is 

 adapted to the open phiins where danger may approach it from all directions 

 and where the safeguarding by the visual as well as the auditory lookout 

 becomes correspondingly important, requires a visual mechanism with greater 

 possibilities for immediate rellex responses. In this way visual impressions 

 from all sides may at once produce such protective attitudes and defense reac- 

 tions as to guarantee the animal's safety in its more exposed habitat. In the 

 comparison of the lo\\Tr primates with the intermediate group, the plani- 

 metric estimations do not give quite so convincing an account ot tclencephali- 

 zation as is the case with the inferior colliculus; nevertheless, the evidence of 

 such a process may be clearly discerned. This portion of the midbrain is to 

 be regarded as one of the important indices disclosing a definite line of 

 evolutional modification. 



Mil. The OcuLOiMOTOR Decussation in Relation to Binocular and 

 Stereoscopic Vision 



This decussation between the oculomotor nuclei on the two sides of the 

 brain forms one of the significant criteria indicative of the progressive adap- 

 tation of skilled acts. The connection between these two nuclei becomes 



