MOVEMENTS OF THE EYEBALL. 



131 



toward any particular object. We 'have already seen that 

 the centre of exact vision is in the f ovea ; and it is evident 

 that, in order to see any object distinctly, it is necessary 

 to bring it within the axes of vision of both eyes. As the 



FIG. 8. 



Muscles of the eyeball. 1. attachment of the tendon connected with the inferior rectus, inter- 

 nal rectus. and external rectus ; 2, external rectus divided and turned downward to expose 

 the inferior rectus ; 3. internal rectus ; 4, inferior rectus ; 5, superior rectus : 6, superior 

 oblique; 7, pulley and reflected portion of the superior oblique; 8, inferior oblique; 9, leva- 

 tor palpebri superioris; 10, 10, middle portion of the levator palpebri superior-is; 11, optic 

 nerve. (SAPPEY, Traite (Tanatomie, Paris, 1868, tome ii., p. 118.) 



globe is so balanced in the orbit as to be capable of rotation, 

 within certain limits, in every direction, we have only to 

 note the exact mode of action of each of the muscles, in 

 order to comprehend how the different movements are ac- 

 complished. 



It is sufficient for our purposes to admit that, approxima- 

 tively, there is a common axis of rotation for each pair of 

 muscles ; but the movements of the globe have been studied 

 much more minutely than this, with reference particularly to 

 the effects of paralysis of different muscles. The points thus 



