The Sense of Sight. 



253 



Movements of the Eye. There are six pairs of muscles which move 

 the eyes to right and left, up and down, and give rotary movements. 

 The two eyes move in the same direction at the same time, though in 

 looking at near objects the two eyes both point inward, so that one 

 appears cross-eyed. 



Dissection of an Eye. The muscles and external parts of the eye 

 may readily be seen by examining the eye of a rabbit in its natural 

 position and then dissecting it out. A beef eye should be obtained 

 from the butcher and the structure of the eye learned by following the 

 description. 



Ciliary Muscle 



Optic Nerve Choroid 



Fig. 96. Horizontal Section of Right Eye. 



The Coats of the Eye. There are three coats, the outer 

 or sclerotic, the middle or choroid, and the inner or retina. 



The Sclerotic Coat. This is of a dull white color, con- 

 stituting the "white of the eye." It is thick and tough, 

 holding all the contained parts firmly and furnishing suffi- 

 cient strength for the attachment of the muscles that move 

 the eyeball. 



