544 BINOCULAR VISION. [Boon m. 



Fig. 75. The rectus superior and the rectus inferior rotate the eye 

 round a horizontal axis, which is directed from the upper end of 

 the nose to the temple; the obliquus superior and obliquus in- 

 ferior round a horizontal axis directed from the centre of the eye- 



r.ext. r.sup. r.inf 

 r.inf. 



FIG. 75. DIAGRAM OF THE ATTACHMENTS OF THE MUSCLES OF THE EYE, AND OF THEIR 

 AXES OF KOTATION, the latter being represented by dotted lines. The axis of 

 rotation of the rectus externus and internus, being perpendicular to the plane 

 of the paper, cannot be shewn. (After Fick.) 



ball to the occiput; and the rectus internus and rectus externus 

 round a vertical axis (which, being at right angles to the plane of 

 the paper, cannot be shewn in the diagram), passing through 

 the centre of rotation of the eyeball parallel to the median plane 

 of the head when the head is vertical. Thus the latter pair acting 

 alone would turn the eye from side to side, the other straight pair 

 acting alone would move the eye up and down, while the oblique 

 muscles acting alone would give the eye an oblique movement. 

 The rectus externus acting alone would turn the eye to the malar 

 side, the internus to the nasal side, the rectus superior upwards, 

 the rectus inferior downwards, the oblique superior downwards and 

 outwards, and the inferior upwards and outwards. The recti 

 superior and inferior in moving the eye up and down also turn it 

 somewhat inward and at the same time give it a slight amount of 

 rotation; but this is corrected if the oblique muscles act at the 

 same time; and it is found that the rectus superior acting with the 

 obliquus inferior moves the eye upwards, and the rectus inferior 

 with the obliquus superior downwards in a vertical direction. In 

 oblique movements also, the obliqui are always associated with the 

 recti. Hence the various movements of the eyeball may be ar- 

 ranged as follows : 



