MOTIONS OF THE EYE. 173 



MOTIONS OF THE EYE. 



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. 



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 pro- 

 Fig. 104. 



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

 arising from the margin of the aperture through which 

 the optic nerve passes, and being inserted by a broad 

 tendinous expansion into the fore part of the sclerotic 

 coat. Three of these are marked a, b, 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 upwards ; a second c, situated below, 

 for turning the ball downwards ; the two others, b, and 

 its antagonist, perform the lateral motions from right to 

 left. 



Besides 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 



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

 ball 1 What motion do the oblique muscles give the eye ball ? 



15* 



