Name __________________________ Date ___________________ Period _____ Score out of 25 _____
Corrected by ___________________________
The Cow Eye Dissection Lab
What are the structures of the mammalian eye and how do they function?
The mammalian eye consists of many specialized cells and tissues that make up several different
structures. The structures have certain functions and together, they form images that are interpreted by
the brain. In this investigation, you identify the structures of a cow eye and learn their functions.
Materials
• Safety goggles
• Preserved cow’s eye
• Forceps
• Dissection probes
• Dissection scissors
• Dissection tray
• Vinyl or latex gloves
• Apron or tee-shirt
• Paper towels
• Plastic trash bag
External features of the eye
A. Locate the cornea, sclera, and optic nerve.
a. The white part of the eye, the sclera, is a tough, outer covering
of the eyeball. The sclera gives the eye its shape and helps to
protect the delicate inner parts.
b. The blue covering over the front of the eye is the cornea.
When the cow was alive, the cornea was clear. Together with
the lens, the cornea refracts light and helps the eye to focus.
The cornea gives a larger contribution to the total refraction
than the lens. The curvature of the cornea is fixed while that of
the lens is changeable. In your cow’s eye, the cornea may be
cloudy.
c. You may be able to look through the cornea and see the iris,
the colored part of the eye, and the pupil, the dark oval in the
middle of the iris. At the back of the eye is the optic nerve.
To see the separate fibers that make up the optic nerve, pinch
the nerve with a pair of scissors or your fingers. If you squeeze
the optic nerve, you may get some white goop. That is myelin,
the fatty layer that surrounds each fiber of the nerve. It is the
nerve that transmits visual information from the eye to the brain.
1. List two functions of the sclera.
•___________________________ •_____________________________
2. The cornea covers and helps protect the eye. List two other functions of the cornea.
•___________________________ •_____________________________
3. What is the function of the optic nerve?
___________________________________________________________
B. Examine the fat and muscle surrounding the eyeball.
a. Without moving your head, look up. Look down. Look all around. Six muscles attached to your
eyeball move your eye so you can look in different directions. Cows have only four muscles that
control their eyes. They can look up, down, left, and right, but they can’t roll their eyes like you
can. Locate the externally attached muscles. These muscles control eye movement and help focus
images.
b. Although the muscles of each individual eye work as a team, the eyes themselves do not focus or
work together until months after birth. However, one eye remains dominant. Form a circle with
your thumb and index finger. Hold that position and place your hand in front of you. With both
eyes, look at something through the circle. Continue to hold that position and close one eye; then
open it. Close the other eye. The eye which is still able to view the object through the circle is your
dominant eye.
