SUMMARY' OF STRUCTURES 721 



luiutional signilifaiK'c, this (limmutinii 111 tlu' auclitmy cdlliculus ot gorilla 

 suggests that all motor responses to suclckai soiiiuls ha\c less ol an iinnu-cliatc 

 ri-lli'\ c|Lialit \ and more ot ack'lihtral ixc element m tluu'exeeution. Such ohser- 

 \ations as ha\e been made on tlu' annual, partieidarl\ tlu' adult male, would 

 seem to indieate that \\ Iumi disturhi'd hy tlu' luinttr, it does not take to 

 niimediati' iliylit. It rist-s up to stand ereet, endea\ ormg to dc'termnu- the 

 souree whence the sounds arisi', and haxing suHieientl\ miormed itsell eon- 

 eernmg the nature ot its danger, otten |)reters to attack ratlur than si'ek safety 

 in retreat. Tlu' planinu-trie and longitudinal eot-llieieiits ol the interior 

 collieulus m the orang, chimpanzi'e and gorilla are gi\en in the following 

 tabulation : 



COEFIK.IF.NTS OF IMF InFFKIOK CoLI ICL I I 1\ IMI lIlCHEH AnTMKOI'OIDS 



Species Pianimetrie Longitudinal 



ridrilla ' .III I .070 



Chimpanzee ; .132 • .100 



Orang-outang 131 0-0 



COMPAKISUN Ol- THE I.NFEKIOK COLLICL LI OF THE GKEA 1 APES AND THE 



INTERMEDIATE PRIMATES 



It is, howe\er, when the comparison is made between the great a|)es and 

 the intermediate primates that the detloreseent [)roeess m the interior eollie- 

 Lihis becomes most coiniiicmg. The plammetric coellicients m all ol the 

 higher anthropoids are less than m the intermediate primates. I he general 

 signilicance ol the gradual decrease in size ot the interior colhcuhis is not 

 ditlicult to a|)preciate. It becomes conclusi\c' when the interior collieulus ot 

 the lower primates is compared with that ol the great anthropoids. I he 

 meaning ol this decline is not obscure, lor 111 proportion as the interior 

 collieulus diminishes m size, b\ just so much are com|)ensatory e\|}aiisions 

 pro\ Ided tor the auditory lunctioii in the temporal lobes of the cerebral 



