THE EYEBALL AND EYELIDS. 321 



pression of the object on the retina has not time to 

 vanish in the interval. The motions of the eyeball 

 for directing the eye to objects are strictly volun- 

 tary, and are always connected with the exercise 

 of the sense of vision. 



It will now be admitted that the variety of the 

 motions of the eye requires the complication of 

 muscles which we find in the orbit, and unless the 

 various offices and different conditions of the eye 

 be considered, it will be in vain to attempt an ac- 

 curate classification of the muscles or nerves of 

 the orbit. 



