POSTURAL COORDINATION 



919 



tain the original point of fixation. On rotating the head to one side, 

 the eye of that side is turned upward, that of the other side downward 

 in compensation. Similar movements can be induced by stimulating the 

 sense organs in the semicircular canals directly. Stimulation of the hori- 



A 



^\ 



I) 



Fig. 228. Compensatory movements of the eyes and fins of the dogfish. A and C illustrate the 

 position of the fish when at rest. B shows the compensatory movements of the eye. c w.hich occur 

 during swimming, or on bending the tail into the position indicated. D illustrates the compensatory 

 movements which occur on rotating the fish about its horizontal axis. 



Fig. 229. The semicircular canals of the ear, showing their arrangement in the three planes of 

 space. (From Howell's Physiology.) 



zontal canal, Avhich is normally excited by a movement in its plane, i. e., 

 by turning the head to one side, causes the eye of the same side to turn 

 forward; similarly the anterior vertical canal causes a rotation of the 

 eye upward and forward, the posterior vertical canal a rotation upward 

 and backward (Lee 28 ). Appropriate movements of the fins accompany 



