VISION. 



545 



to the direction and degree of tlie movement — i. e., the move- 

 ments of the eyes are affected by very nice muscular co-ordina- 

 tions. 



PiQ. 393.— View of the two eyes and related parts (after Helmholtz.) 



Fig. 394 is meant to illustrate diagrammatically the move- 

 ments of the eyeball. 



While the several recti muscles elevate or depress the eye, 

 and turn it inward or outward, and the oblique muscles rotate 

 it, the movements produced by the superior and inferior recti 

 always corrected by the assistance of the oblique muscles, since 

 the former tend of themselves to turn the eye somewhat in- 

 ward. In like manner the oblique muscles are corrected by 

 the recti. The following tabular statement will express the 

 conditions of muscular contraction for the various movements 

 of the eye in man : 



Straight 

 move- 

 ments. 



' Elevation Eeotus superior and obliqnus in- 

 ferior. 

 Depression Rectus inferior and obliquus su- 

 perior. 

 Adduction to nasal side. . .Rectus intemus. 

 . Adduction to malar side. . . Rectus extemus. 

 35 



