CHAPTER XXVIII 



Ciliary Muscle 



THE HUMAN EYE 



192. Structure of the Eye. The complete eye consists 

 of three parts, namely, the eyebrows, which prevent per- 

 spiration and dust from touching the eyeball; the eyelids, 

 which protect the eyeball and keep out dust; and the 

 eyeball itself. The normal eyeball is nearly spherical and 

 the outer part is composed 

 of three layers; the inner 

 part is filled with three 

 transparent substances, two 

 of which are almost like thin 

 jelly in texture. 



The illustration shows the 

 parts of the eye. The front 

 part is a very tough sub- 

 stance called the cornea. 

 The cornea has the power 

 of refracting light and acts 

 as a converging lens. Just 

 back of the cornea is a watery liquid called aqueous humor. 

 It is transparent and helps to hold the cornea in position. 

 Back of this aqueous humor is a thin muscle called the 

 iris. The iris is the middle layer of the outer part, and 

 it goes all around the eyeball. The color of the iris in 

 front gives the various colors to the eyes, such as gray, 

 blue, or brown. The iris has a round hole in it which is 

 called the pupil of the eye. The iris, a muscle, changes 



SECTION THROUGH THE EYE 

 Showing the parts. 



