SUMMARY" OF STRUCTURES 723 



COMPARISON OF THE SLPEKIOK COI.LICL LI IN THE GREAT ANTHROPOIDS AND 



THE INTERMEDIATE PRIMATES 



As compared with tlic iiitrrnu'chatc- primates, tln' sLii^enor colliculus in 

 the great anthropoids is eonsiderahly smaller. This is likewise the case when 

 comparison is made w itii the lower primates, w ith a single notable exception, 

 namely, in the lenuir. That animal, in the eot'llleients of its superior collic- 

 ulus, ec|uals the gorilla. The meaning of this discre]:)ancy must still he leit 

 in doubt, since the special mlluences which condition \isual expansion can- 

 not yet be e\aluated as a w hole, and many details of the j:)rocess rec|uirc 

 further iiuestigation. In the main, the progressive denorescence in the supe- 

 rior colliculus shows a steady advance m that process which proxides cortical 

 representation lor \isual lunctions formerly vested in lower midbrain le\els, 

 and hence denotes evolutional development. 



\Tii. The Oculomotor Decussation in Rel.\tion to Binocilar V^ision 



The progress in organization of the visual function has also shown a con- 

 stant achance in the matter of tlu' internuclear decussations and connnissural 

 connections ol the luicK'us oculoniotorius. The necessity of such close asso- 

 ciation in the interest of coniugate eye mo\ements, whose ultimate object is 

 the production and maintenance of binocular vision, has already been dis- 

 cussed, in the case ol the great anthropoids, there is the additional light shed 

 upon this held b\ tlu' rtsearches ol Prolessor Kohler in tests made upon 

 chimpanzee. From tht^se investigations it was concluded that the anthropoid 

 has developed to a considerable extent the powers of stereoscopic visual 

 perception. The gorilla shows the greatest internuclear communication, and 

 appears to be proxided with a more ample means to maintain conjugated eye 

 movements. The coenicients of the gorilla and the chimpanzee exceed those 

 of the orang. These coellicients of the oculomotor decussation are given in 

 the following tabulation : 



