SENSE ORGANS. IO i 



then through a loop on the inside which acts like a pul- 

 ley, then back obliquely over the upper side of the ball, 

 to attach itself on the outside a little behind the equator. 

 Its pull being from the loop, it turns the eye downward 

 and outward and rotates it on its axis inward. The in- 

 ferior oblique arises from the lower part of the inside of 

 the orbital opening, runs under the eye obliquely back- 

 ward and outward across the equator, to attach itself on 

 the outside of the ball a little behind the equator. Its 

 action, therefore, is to turn the eye outward and up- 

 ward and rotate it on its axis outward. 



The use of these oblique muscles is much more ob- 

 scure; their full explanation would carry us too far. 

 For this we would refer the reader to the author's book 

 on Sight (pages n and 12 and page 210). 



In the normal condition, looking forward, the axes 

 of the eyes are either parallel or equally convergent, so 

 as to bring their axes together on the object looked at. 

 Any deviation from this position is quickly detected by 

 an observer as a squint or a cast. These malpositions 

 of the eyes are often, but not always, caused by too 

 great action of some one of the muscles, and are cor- 

 rected by cutting the muscle and allowing it to attach 

 itself to a new point on the ball. 



Coats of the Ball. — Take the ball out of the socket. 

 Dissect away the muscles. The ball, except the front 

 part, is seen to be invested with a strong white coat of 

 fibrous tissue. This is the sclerotic. It gives form to 

 the eye and serves as attachment of the muscles. The 

 front or more protuberant part is covered with an 

 equally strong but perfectly transparent coat, appar- 

 ently continuous with the sclerotic. This is the cornea. 

 Its function is to retain the form of this part of the eye, 

 and at the same time to freely admit the light. Look- 

 ing through the transparent cornea, we see a little way 



