THE MAMMALS 



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the face and images seen by the two eyes are superimposed. This gives 

 binocular vision, that is, both eyes see the same thing, but from slightly 

 different angles which gives depth to images and aids greatly in judging 

 distances. The three-dimension movies show how much more natural 

 things appear when seen with depth. The arboreal habits are closely 

 correlated with this accurate eyesight, for it would hardly lead to sur- 



Courtesy Chicago Natural History Museum 

 Fig. 28.27. Sportive lemur. The lemurs are the most primitive of the primates. 



vival if a primate jumped for a limb only to find that he had miscalcu- 

 lated the distance. We see tiny details with our eyes far better than 

 lower mammals due to the development of a spot of clearest vision, 

 called the fovea, in the center of the retina. In other mammals smell 

 is often the dominant sense — a dog recognizes his friends by smell 

 rather than by sight and some dogs have even learned to follow the 

 scent of an animal while running at a high speed. The sense of smell, 

 on the other hand, is very poorly developed in the primates, although 



