170 THE HUMAN BODY. 



THE EYE. 



SECTION IV. 1. The cavities in the skull which con- 

 tain the eyes are called the orbits. They are shaped like 



pyramids, pointing inward, 

 and are about an inch and 

 a half deep. At the bottom 

 of the orbits are holes, 

 through which the nerves 

 of the eye the optic nerves 

 enter them. In the inner 

 side of the orbits are open- 

 ings into a canal, called the 

 lachrymal canal, which runs 

 straight down into the nose. 



2, The orbit is lined with fat, which makes a soft 

 cushion for the eyeball. The .eyeball is nearly round, 

 and about an inch in diameter. It is attached to the 

 optic nerve behind, as to a stem. 



3, The outer coat of the eyeball is white and tough. 

 It is called the sclerotic coat. A transparent circle, like a 

 watch-glass, is set into this in front. It is called the 

 cornea. 



4, The cavity of the eyeball is divided into two cham- 

 bers by the lens. The chamber behind the lens is filled 

 with a jelly-like fluid, called the vitreous humor. The 

 chamber before the lens is filled with a watery fluid, called 

 the aqueous humor. 



The optic nerve goes to the interior of the ball, and 

 spreads out, by dividing up into fine threads, to line the 

 back part. This lining is the retina. 



SUGGESTION TO TEACHERS. Get a beefs eye from the butcher's, and dis- 

 sect it. 



