To explore the interior of the eyeball, you need to cut it open. If you pinch the end of the optic nerve, you might be able to make it fray and ooze a little bit and you might be able to observe individual fibers. These are the remnants of the muscles that moved the eye (the extraocular muscles). In the side and rear views, you can see a ring of pink material around the waist of the eyeball. When you are finished trimming, you should have something more or less like this: A Trimmed Eyeball The most efficient way to remove the connective tissue is therefore to cut with a scissors in a circle around the middle of the eyeball. The connective tissue grows from the eyeball more or less in a circle around the “waist” or middle of the eyeball, and extends backwards forming a cylinder around the optic nerve. (Although in a way, the kids were right - the word “nerve” actually derives from a Greek root word meaning “sinew” or “tendon”.) The optic nerve sits opposite to the cornea and marks the back of the eyeball. The official modern name is the optic nerve. But it does not grow out of a muscle and it does not pull on a bone, as a tendon is supposed to do. It certainly resembles one, because it is tough and cord-like. Students will often identify the cord on the other end as a tendon. The clear (or cloudy) dome on one side is the cornea, and marks the front of the eyeball. Thus the first job of the dissector is to remove the connective tissue to produce a neatly trimmed eyeball, leaving the eyeball itself and the rear cord intact. (Depending on how the eye was removed, this cord may be long and dangly or it may be a mere stub.) A cow's eye, as normally provided, will not be a neatly trimmed eyeball but a messy agglomeration of flesh. There is also a thick, tough cord extending from the back end of the eyeball. They are sewn in and turned around by various kinds of connective tissue, padding, and muscle. Living eyeballs do not float loose within their sockets. In any case, it is possible to obtain cow eyeballs without too much trouble, and we can gain a pretty good idea what our own eyeballs are like by dissecting them. You can also buy sheep eyeballs, which are cheaper, but also smaller, and I think the larger cow eyeballs are better for most purposes. I recommend buying the eyeballs in bulk pails, especially if you are buying enough for an entire classroom. I thought they were stiff and rubbery and hard to dissect well. (One is reminded of a witch's cauldron when one opens the pail.) I once ordered them individually wrapped in plastic, but I didn't like those as well. Also, I usually purchased my eyeballs submerged in liquid preservative, in bulk pails from Carolina. Apparently, if you can obtain eyeballs soon enough after removal, perhaps by obtaining them fresh from processing plants, the corneas and lenses will still be clear, but I have never been able to do this. The cornea and lens of long-deceased animals are usually cloudy, but the interior of the eyeball is still intact, and quite fascinating, and even pretty in its own way. Cow eyes are also readily available, as a byproduct of beef production, and can be purchased inexpensively from science supply companies, such as Carolina Biological Supply. As a fellow mammal, we can expect that a cow has an eyeball that is pretty much like our own. Compared to an octopus or a beetle, a cow seems like merely a variation on the same design as people. Look inside the mammalian organ of vision with this popular and easy dissection activity.Ĭows have four limbs, two ears and two eyes, and a chest and a belly, much like we do.
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