THE CO A TS OF THE EYE. 22/ 



The front part of the outer coat is the transparent por- 

 tion above mentioned. It is called the cornea (3). 



The middle coat is colored. Its hinder portion, 10, is 

 black, and lies close against the sclerotic; it is called the 

 choroid. Its front part separates from the outer coat, and 

 instead of lying close against the cornea, turns in a little 

 way behind it, 14, so as to leave a space, 30, between. 

 This part of the middle coat is called the iris. Its color 

 varies; we see it through the cornea, and say the eye is 

 brown, or blue, or gray, or black, according to the color 

 of the iris. In the middle of the iris is a hole, the pupil 

 of the eye. It looks black, just as a hole opening into a 

 box whose inside was painted black would, if you viewed 

 it from outside, although the hole would let light into 

 the box. The dark choroid answers to the black paint 

 inside the box; in some animals, as dogs and cats, part 

 of it is not black, and so the inside of the eyes of those 

 animals, seen through the pupil, often looks shining. In 

 bright light, the pupil becomes smaller, so as to protect 

 the nerves inside the eye from being over-stimulated and 

 dazzled: when there is not much light the pupil becomes 

 larger. If you stand in front of a mirror and close your 

 eyes for half a minute, and then open them and let light 

 get into them, you can watch your pupils getting 

 smaller. 



The inside coat of the eyeball is the retina, 15. It is 

 very thin, and is transparent so that the dark color of 

 the choroid shows through it. The retina only lines the 

 hinder half of the eyeball. It is the sensitive part of 



does the pupil look black ? What is said of its expansion and con- 

 traction ? How can you see the contraction of your own pupil ? What 

 is the retina? Describe it. Its position ? Of what does it consist ? 

 Illustrate the connection of optic nerve and retina. 



