VISION. 221 



(^) Do all of these muscles seem to act perfectly in 



all of the subjects examined ? If not; describe any 



variation. 



(0) Convergence, (a) Let the subject direct his gaze at 

 the tip of the observer's ear, and without warning 

 change his point of binocular fixation to some distant 

 object in the same line of vision. What change in 

 the eyes of the subject is noticeable by the observer ? 

 What muscles were involved in producing the change ? 

 (/) Hold an object in front of the subject and 1 m. 



distant. Move it directly toward the subject's eyes 



and note the convergence of the lines of vision of 



the two eyes. What muscles perform the act ? 

 (/) Through how short a distance may the object be 



moved in the direct line of vision without causing a 



discernible change of the angle of convergence of 



the two eyes. 

 (</) From the central, 1 m. position, carry the object 



to a point about ^ m. to the right, and ^ m. 



above the eyes of the subject. What muscles are 



involved in the act of convergence ? 

 (>) Is the power of convergence apparently normal in 



all members of the class ? If not, describe minutely 



any variations. 



