82 THE FROG 



Observe carefully the shape of the eye-ball. In the living 

 frog it is nearly spherical but slightly top-shaped; in pre- 

 served material it may be slightly flattened on the outer side 

 where it is covered by the cornea. Make an outline (8 cm. 

 in diameter) showing the shape of the eye-ball as viewed 

 from its side (i. e., viewed at right angles to the axis passing 

 from the center of the pupil through the center of the eye). 

 This outline is later to be filled in to show the structure of 

 the eye. 



The sclerotic is the firm outer wall of the eye, composed 

 of hyaline cartilage and dense white connective tissue; it 

 covers all that part of the eye-ball not covered by the cornea. 

 The optic nerve may be seen piercing the sclerotic to enter 

 the eye-ball on its proximal side. 



With scissors divide the eye into two unequal parts by an 

 incision passing a little to one side of the pupil and the optic 

 nerve, so as to lay open completely the interior of the eye. 

 Observe the sudden collapse of the eye-ball as soon as its 

 fluid contents are allowed to escape. Remove the other eye- 

 ball and divide it into two parts by an incision separating 

 proximal and distal halves. Place the parts of both eye-balls 

 in water and observe the following features : 



i. The crystalline lens is a solid body, transparent in 

 ^ situated just behind the iris and attached to the iris by 



its outer margin. It is more convex on its inner than on its 

 outer surface. 



2. The anterior chamber of the eye is the space between 

 the cornea and the lens; it is small, and in life contains a 

 watery fluid, the aqueous humor. 



3. The posterior chamber of the eye is a large space be- 

 hind the lens; in life it is filled with a grayish gelatinous 



