MOTIONS OF THE EYE. 169 



MOTIONS OF THE EYE. 



510. The socket of the eye is considerably larger than 

 the ball itself, the space between them being lined with 

 a soft cellular substance, in which the eye easily turns in 

 all directions. At the anterior part of the cavity are in- 

 serted the muscles which give motion to the ball. 



5 11. A view of these muscles with their attachments 

 to the different parts of the ball, but separated from the 

 other parts, is given in Fig. 103. Four of these proceed 



Fig. 103 



in a straight course from the bottom of the orbit, arising 

 from the margin of the aperture through which the optic 

 nerve passes, and are inserted by a broad tendinous ex- 

 pansion in the forepart of the sclerotic coat. Three of 

 these are marked a, 6, c, in the figure ; the edge of the 

 fourth being seen above and behind b. These straight 

 muscles, as they are called, surround the optic nerve and 

 the eye-ball, forming four longitudinal bands ; one, a, being 

 situated above, for the purpose of turning the eye upward ; 

 a second, c, situated below, for turning the ball downward ; 

 the two others, 6, and its antagonist, perform the lateral 

 motions from right to left. 



512. Beside these straight muscles, the figure shows two 

 others, s and i, termed, from the manner in which they 

 act, oblique muscles. When these act together, they draw 



What are the directions in which the straight muscles move the eye 

 ball ? What motion do the oblique muscles give the eye-ball ? 



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