THE PERCEPTION OF SPACE 



689 



so that binocularity is attained both in front (10°) and behind (9°) 

 (Dubar, 1924 ; Pisa, 1939) (Figs. 805, 833-4). In the squirrel with its 

 protruding eyes the binocular field is more extensive and varies from 

 25-30°. The Ungulates occupy an intermediate position with a 

 binocular field varying from 60° to 80° (Kahmann, 1933). The horse 

 has a wide binocular field in front (60°-70°) and a wide panoramic 

 uniocular segment of 146° so that it sees behind along a line parallel 

 to the axis of its body (Figs. 830-1, 838) ; by adopting a number 

 of devices such as the forward prolongation of the functional retina 

 on the nasal side, and the horizontally oval puj^il, this animal thus 



Figs. 838 and 839 

 BINOCULAR FIELD 

 ■65' 



-The Binocular Fields of Placentals. 



,,x>P. fjUp 



^^'^O ARt'^ 



BLIND AREA 



Fig. 838. — The horse. Showing a small 

 binocular field, large panoramic uni- 

 ocular areas and a minute blind area. 



Fig. 839. — A primate. Showing a 

 large binocular field, small uniocular 

 areas and a large blind area. 



achieves a remarkable field, with a broad binocular area in front and 

 below to survey the ground on which it is feeding or over which it is 

 galloping, and a minimal blind area behind. The elephant has the 

 wide uniocular area of 190° and a binocular field of 67°. The goat has 

 a binocular field of 63°, the ox of 51-78° (Pisa, 1939 ; Bresson, 1955). 

 Carnivores with eyes set more frontally have larger binocular fields, 

 that of dogs varying from 80° to 116° (Thieulin, 1927) and of cats 

 extending to 120° (Fig. 806) ; while in monkeys, apes and man it 

 may extend to 140° — in this class, as we have seen, in the interests of 

 finesse in manipulation (Fig. 839). 



THE OCULAR MOVEMENTS OF VERTEBRATES 



Ocular movements in Vertebrates are of three types all of which 

 are of primary importance in spatial perceptions : 



(1) Involuntary movements, associated with the postural reflexes 



Spider 

 monkey 



