THE PERCEPTION OF SPACE 



691 



postiaral in nature, designed to maintain the visual field constant in 

 spite of the movements of the animal ; the primary function of the 

 extra-ocular muscles, to put the matter paradoxically, was to keep the 

 eyes immobile in sjxice. In Cyclostomes and most Fishes this is the only 

 type of movement which exists, and every movement of the head is 



Figs. 840 to 842. — Posttjeal Reflexes. 



Fig. 840. — Tonic labjrinthine reflexes. 



The rabbit on the left is in the nor- 

 mal position ; the rabbit on the right 

 has been rotated so that its right 

 side becomes lower, and the movements 

 of the eyes are indicated by the 

 arrows (after Magnus). 



Fig. 841. — Tonic neck reflexes. 



On rotation of the head upon the 

 trunk the movements of the eyes are 

 indicated by arrows. 



Fig. 842. — Compensatory movements of the eyes on inclination 



of the head. 



associated with a compensatory movement of the eyes. For this 

 reason the extra-ocular muscles of Fishes have a uniquely simple 

 arrangement designed merely to accomplish horizontal, vertical or 

 wheel rotatory movements, the recti taking origin from the apex 

 of the orbit and rotating the globe around the vertical and transverse 

 axes, the obliques arising from the orbital margin and rotating the 

 globe around the antero-posterior axis (Fig. 293). Such movements 



