CHAPTER VI. 

 THE EYE AND EAR. 



A. The Eye of the Frog. 



1. Remove the eye from a freshly killed frog : snip off with 

 scissors the muscles of the eyeball : note the following points : 



i. The shape. The eyeball is flattened on its outer 

 side, more convex on the inner or deeper side. 



ii. The sclerotic is the firm outer wall of the eyeball, 

 formed of hyaline cartilage, and dense white 

 connective tissue. 



iii. The cornea is the transparent patch on the outer 

 side of the eye through which the light enters : 

 it is continuous at its margin with the sclerotic. 



iv. The iris is a pigmented ring placed behind the 

 cornea and seen through it : it acts as a dia- 

 phragm, limiting the amount of light that enters 

 the eye. 



V. The pupit is the aperture surrounded by the iris, 

 which serves to admit the light to the interior 

 of the eye. 



vi. The optic nerve is seen piercing the sclerotic to 

 enter the eyeball on its inner side. 



2. Place the eye under water atid divide it with scissors into 

 two halves by a cut passing through the middle of the cornea and 

 through the sclerotic dose to the optic nerve, so as to lay open com- 

 pletely the interior of the eye : note the following points : 



i. The lens is a firm, solid, transparent body, just 

 behind the iris and attached to its outer margin : 

 it is more convex on its inner than on its outer 

 surface. 



