CHAPTER XXV 

 IMPEESSIOXS OF SIGHT AND HEARIXG 



The two other senses, sight and hearing, which gain an 

 early neopallial representation in the Mammals become 

 of enhanced value to the arboreal animal. Their in- 

 creasing importance in this stock is, in the first place, 

 largely the outcome of the diminishing dominance of the 

 sense of smell. When an animal ceases to find its way 



« 



about the world guided almost entirely by olfactory 

 impressions it begins to rely more and more upon other 

 senses for its guidance. It is not that the sense of smell 

 or its pal Hal representation becomes lost, but it ceases 

 to be the main channel through which the animal gains 

 knowledge of its surroundings. Sight, especially, becomes 

 the principal guiding sense of the arboreal animal. 



Both visual and auditory neopallial areas are well 

 developed in terrestrial Mammals. There is nothing 

 whatever distinctive of arboreal life in the mere cortical 

 representation of these senses, but the arboreal life has 

 a ver}' definite influence upon the development of these 

 areas. 



Two essentially physical factors come prominently 



into play in the elaboration of the neopallial areas devoted 



to sight and hearing in arboreal animals. The first is 



one to which reference has been already made, and which 



ma}^ be termed the increased mobilit}^ of the poise of 



the head. There are obvious educational possibilities for 



the animal which can turn head and eyes and ears all 



together, and Avith the greatest rapidity, towards an}* 



object which attracts its attention h^^ any sensory 



channel. 



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