CorneaThe clear front of the eye. A cow's is thicker than a horse's.
IrisThe colored ring that makes the pupil wider or narrower. A cow's is very dark.
PupilThe opening that lets light in. A cow's is a wide horizontal oval.
LensSits behind the iris and focuses light onto the retina.
RetinaThe light-sensing layer lining the eye's rear.
Tapetum lucidumA shiny layer that reflects light back through the retina. It makes eyes glow at night.
Optic nerveCarries signals from the retina to the brain.
The wall and the back: 6 3
ScleraThe tough white outer wall of the eyeball.
ChoroidThe dark layer of blood vessels between the sclera and retina.
Optic discWhere the optic nerve leaves the retina; it has no light sensors.
Inside the eye: 4 3
Aqueous humorWatery fluid filling the space behind the cornea.
Vitreous humorClear jelly filling the eyeball behind the lens. A cow's is firmer than a horse's.
Ciliary bodyHolds the lens by fine fibres and makes the aqueous humor.
How this list was compiled: Read 2026-09-26. Sisson, The Anatomy of the Domestic Animals (1914), https://archive.org/details/anatomyofdomesti00siss : the eye (cornea, sclera, chorioid and its tapetum, ciliary body, iris, pupil, lens, aqueous humor, vitreous body, retina, optic papilla, optic nerve) and the eye of the ox. Merck Veterinary Manual, Eye structure and function in horses, https://www.merckvetmanual.com/horse-owners/eye-disorders-of-horses/eye-structure-and-function-in-horses . Wikipedia: Eye, https://en.wikipedia.org/wiki/Eye ; Tapetum lucidum, https://en.wikipedia.org/wiki/Tapetum_lucidum ; Optic disc, https://en.wikipedia.org/wiki/Optic_disc (no rods or cones: a blind spot); Ciliary body, https://en.wikipedia.org/wiki/Ciliary_body (attached to the lens by zonule fibres; its epithelium makes the aqueous humor). Licence: own work
The drawing: Drawn for this site by script, 2026-09-26. Own work, nothing traced. Licence: own work
How it works
This unlabeled cow eye diagram has two drawings side by side: the eyeball cut across, with the front of the eye toward the left, and the eye seen from the front. Thirteen lines end in empty space for a name.
Read the full guide
Thirteen names to write
From the front of the eye to the back: cornea, aqueous humor, iris, pupil, ciliary body, lens, vitreous humor, retina, tapetum lucidum, choroid, sclera, optic disc and optic nerve.
Lines that are easy to misread
Only the pupil has its line on the front view; the other twelve are on the cut eye. Two lines stop in open space: the one in the gap behind the cornea is the aqueous humor, and the one in the large room behind the lens is the vitreous humor.
The three lowest lines reach the three bands of the wall. From the outside in, the bands are sclera, choroid, retina.
On a cow eye diagram with no labels of parts, start with the optic nerve: the one part outside the eyeball.
Questions and answers
How many parts are labeled on a cow eye diagram?
Thirteen on this sheet. The fine fibers that hold the lens and the opening of the lids are drawn but have no line, and the eyelids, the eye muscles and the fat round the eye are left off.
Where is the ciliary body on a cow eye diagram?
Behind the root of the iris. It is drawn as a small wedge above the lens and another below it, and one line reaches the upper wedge.
Where is the tapetum lucidum on the diagram?
In the choroid, the middle band of the wall. It is the stretch in the upper back of the cut eye that one line points to, and the retina lies in front of it.
Is the optic disc the same as the optic nerve?
No. The optic nerve is the thick cord that leaves the back of the eyeball. The optic disc is the spot inside the eye where that cord leaves the retina.