298 ADAPTATIONS TO SPACE AND MOTION 



as are also the majority of frontolateral-eyed carnivores such as the mus- 

 telids and viverrids. Among the carnivores, the domestic cat is preem- 

 inent with (according to ThieuUn) a binocular field of 130° and a total 

 visual field of 287° — thanks to the large, prominent, and strongly curved 

 cornea. 



Of course, the binocular field of any animal is more narrow above and 

 below than it is straight ahead, and it is ordinarily pear-shaped. Again, 

 the cone of binocular space does not necessarily begin immediately at the 

 eyes — there is often a blind region, in front of the snout (Fig. 128, p. 

 376), which may extend forward for a fraction of an inch, or for a foot 

 or more as in Varanus and in large fishes. In chicks, it has been claimed 

 that it is just this distance (a couple of inches) from which the bird 

 regards each kernel before pecking at it. 



Pisa has studied the domesticated mammals and has mapped the form 

 of their binocular fields. These tend to be tall, narrow pear-shaped areas 

 unlike the roundish one of man. In man, the uniocular fields are reduced 

 to a pair of crescents which are but 30° wide in the horizontal meridian 

 and taper to points above and below the binocular field. Some of Pisa's 

 values for the divergence of the optic axes and the maximal width of the 

 binocular field are given in the accompanying table: 



Table X 

 VISUAL FIELDS IN DOMESTIC MAMMALS (After Pisa, rearranged) 



Horse 



(Foal). 



Cow 



Goat 



Dogs 



Setter 



Greyhound. . 

 Fox Terrier. 



Rattler 



Guinea-pig 



Rabbit 



At rest 



Aroused 



Posterior binocular field. 



