THE EYE AND EAR. 91 
Chap. VIIL—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 
i. The shape of the eyeball: flattened on the outer 
side; more convex on the inner or deeper side. 
i. The sclerotic: the firm outer wall of the eyeball, 
formed of dense white connective tissue 
strengthened by hyaline cartilage. 
iii, The cornea: the transparent patch on the outer 
side of the eye through which the light enters : 
continuous at its margin with the sclerotic. 
iv. The iris: 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. 
The pupil: the aperture surrounded by the iris, 
which serves to admit the light to the interior 
of the eye. 
vi. The optic nerve: seen piercing the sclerotic to 
enter the eyeball on its inner side. 
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2. Place the eye under water and divide it with scissors into two 
halves by a cut passing through the middle of the cornea and 
through the sclerotic close to the optic nerve, so as to lay open 
completely the interior of the eye: note :-— 
i. The lens: a firm solid transparent bedy, just 
behind the iris and attached to its outer margin : 
more convex on its inner than its outer surface. 
ii, The anterior chamber of the eye: between the 
lens and cornea: small: contains the aqueous 
humour. 
iii. The posterior chamber of the eye: the large space 
behind the leus: filled by the vitreous humour, 
a gelatinous body. 
