THE BRAIN 01 MODERN MAN 827 



LE\EL OF THE INFERIOR COLLICL LLS (FIGS. 352, 353) 

 At this Ic\c'I tlir midbrain is ciitiTrd and sliows ihv (.haracteristic- 

 modifications occunmii; m xUv roolplalc. Two svmnn-trieal t-lcxations rise 

 upon cither side fornun^' the inlerior collicuh ( IC). These structures are 

 more conical in shape than is the case m any ot tlie lower prmiates. From 

 surface appearances these primar\ way-stations in the |)atln\a\ ot hearing 

 seem to have undergone considerable reduction m the human hram. The 

 significance of such rechiction may be gauged l)y Xhv lact that hearing in 

 man has become much more dehberati\e m its reactions. Au(htor\ stimuli 

 need and recei\e more coiisidt'iatioii, greater association and mort' exact 

 evahiation before courses of action are determined in response to them. 

 The need of immediate rellex response as the rt'sult of auditory impressions 

 is much less apparent in man than in lower animals. It is probable that such 

 instantaneous reaction as man\ of the lower a[)es manilest in consequence 

 of auditory stimuli might proxe in)urioiis to man. The adage, "Look before 

 you leap," applies ec|iiall\' to the sense ol hearing. Sounds or noises arc usu- 

 ally submitted to proj)er analysis by higher centers in the neural mechanism. 

 Although a certain degree of the ancient stratification still is apparent in 

 the inferior colliculus, reminiscent of its lornu'r functional |:)romineiice among 

 various parts of the brain, this specialization is but feeble and gi\es a distinct 

 impression of definite iiuolution. Probably no other single function has 

 undergone more e\tcnsi\e elaboration than the sense ol hearing. The 

 evaluation of sounds and the production ol speech and music, as well as the 

 associations connected with the nian\ \(iiees of natiire, ha\c' formed an 

 almost inexhaustible material out of which man has constructed his wealth 

 of auditory perception and understanding. It is little wondi'r, therefore, that 

 the primitive capitol of lu-aring has \n-vn transferred to a thoroughl\ modern- 

 ized neural organization callable of meeting all ol the great variety of mocfili- 

 cation and exiirencN' m the auditor\ realm. 



