SENSE OF SIGHT. 873 



Movements of the Eye. The position of the eyeball in the orbit 



FIG. 395. DIAGRAM ILLUSTRATING IMPERFECT PERCEPTION OF SIZE. (Stirling.) 



corresponds to a ball-and-socket joint, and each eyeball is capable of 

 moving around an immovable centre of rotation, which has been found to be 



FIG. 396. DIAGRAM ILLUSTRATING RADIAL MOVEMENT. (Stirling.) 



placed a short distance behind the centre of the e}^e. The movements of 

 the eye are accomplished b}^ six muscles four straight and two oblique. 



