258 IMPORTANCE OF OUR EYES 



eye can be turned in different directions, due to the little 

 paired muscles which serve to move the eyeball. 



If we study a section as shown, by cutting the eyeball 

 in halves from front to back, we find that it is more like the 



camera than it is on the 

 surface. In the front there 

 is a transparent lens which 

 makes a little picture at 

 the back of the eye, just as 

 the camera lens makes a 

 picture. This lens, how- 

 ever, is not fixed in shape 

 like that of a camera, Lut 



Section of the eye. Find the parts which J c fl^viKlA anrl ic mxr\p> 

 correspond to those in a camera. 



thicker or thinner by move- 

 ment of delicate muscles, thus doing away with the ne- 

 cessity of moving the lens forward or backward in order 

 to get a picture in focus. 



The main portion of the eye is filled with a colorless 

 substance, the vitreous humor, while back of this lies a 

 pigmented receiving organ connected by nerves with the 

 brain, known as the retina. It is on this sensitive surface 

 that our images are received and sent to the brain by the 

 optic nerve, so that we really see in the brain, although the 

 picture is received on the retina. There are three coats 

 covering the eyeball, a tough outer coat, the sclerotic, a 

 middle coat, the choroid, while the inner coat is the retina. 

 These coats are open at the front, and the choroid, which 

 is filled with pigment, or color-bearing material, makes a 

 kind of curtain. It is this curtain, called the iris, which 

 gives the color to a person's eye. The iris controls the 

 amount of light which passes through the hole, or pupil, 



