162 



SQUINTING. 



made too high they almost touched the chins of the 

 smaller boys. In cases of this kind, the defect may be 

 easily remedied if attended to in season, by obliging the 

 child to look frequently at distant objects, and never 

 permitting him to hold his book so near his eyes as he 

 generally wishes. 



Emily. How is it, Dr. B., that the eyes are able to 

 move in such a variety of directions, and move too so 

 exactly together, as always to be directed towards the 

 same objects ? 



Dr. B. It is by the aid of several little muscles, that 

 ihe eyes are made capable of every possible movement 

 and can take cognizance of ob- 

 jects in every direction not abso- 

 lutely behind. These muscles 

 are six in number ; two inserted 

 into the superior, two into the in- 

 ferior side of the eye-ball. These 

 four by their various combina- 

 tions of actions, roll the eye in 

 every direction, but at the same 

 time, have a tendency to draw 

 the eye backwards a little. The 

 two others counteract this ten- 

 dency ; one of them as you will 

 observe in this figure, produces 

 this effect by a curious arrange- 

 ment. It passes through a loop in the bone in advance 

 of the level of the eye, and of course draws the eye for- 

 ward, when it contracts. When both eyes are turned 

 in precisely the same direction, the image is formed on 

 corresponding points of the retina, and the mind per- 

 ceives but one object. When however, the muscles of 

 the eyes contract unequally, we observe that their mo- 

 tions do not correspond ; the eyes are turned in differ- 

 ent directions, and the person seems to be looking at 

 two objects. 



Emily. This then constitutes the affection called 



