THE FIELD OF VISION 33 



is the head, and so far back are the eyes set, that it is 

 impossible for any such overlapping to occur (Fig. 6). In 

 rodents, such as rabbits and hares, which also have their 

 eyes set far back, the overlapping of the fields anteriorly 

 cannot exceed more than 15°. 



It has been suggested by Grossman and Meyerhausen 8 

 that in these animals some overlapping of the fields may 

 occur posteriorly, and that in them a certain amount of pos- 

 terior binocular vision may be present. As all sportsmen 

 know, rabbits and hares see very imperfectly when danger is 

 immediately in front of them, and will run straight forward 



Fig. 6. — Sperm whale. 



toward a gun. I am told that it is a general belief in the 

 country, that if a hare lies in a furrow with the nose pointing 

 down it, you can walk up the furrow to the hare's head. 



In connection with the binocular vision of mammals it 

 is important to note the observations of Kalt 7 as to the size 

 of the angle y in the different species. He states that "in 

 the human species the visual axis pierces the cornea 5° 

 inside its center. In the higher monkeys it is almost the 

 same, but one sees this angle increase as one descends the 

 animal scale. It is 15° in the Lemuridse, 20° to 26° in the 

 Carnivora, and it varies between 55 ° to 63 ° in the Herbivora." 

 The increase of the angle tends to balance to some extent 

 3 



