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Figures from The Sourcebook of Medical Illustration (The Parthenon Publishing Group, P. Cull, ed., 1989). Retrieved Nov 27, 2007 from Jensen, M., 2007. Webanatomy Image Bank at http://msjensen.cehd.umn.edu/webanatomy If you just print this out, you'll miss some of its function. As you review it online, you can put the cursor on parts of the eye and they will be identified for you. |
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Dissecting the cow eye |
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Look into the cow eye. You are looking through the conjunctiva and the cornea at the iris and the pupil. Around the cloudy cornea you can see the white sclera. You should be able to identify the white optic nerve coming out of the back of the eye. Now use scissors to remove the cornea by cutting around its edge and lifting it away from the iris. You have opened the anterior chamber of the eye; the fluid spilling out is the aqueous humor. You can now look more closely at the iris and see see the lens just behind it, filling the pupil. Cut around the eye behind the iris and try to lift it off the back of the eye without tearing it loose from the sclera. On the back side of the iris, where it joins the sclera, it is thickened into the ciliary body. This area produces aqueous humor and contains muscles that control the shape of the lens. The ciliary muscles (colored pink on the figure) are connected to the lens by suspensory ligaments (colored blue on the figure) , which hold the lens in position. When you lifted the iris and lens off, you opened the posterior chamber. It is filled with the vitreous humor, a jelly-like substance that helps maintain the shape of the eye and press the retina against the choroid. The retina is the inner soft, pale layer of nerve cells and photoreceptors lining the posterior chamber. It is pale because the rhodopsin inside the cells has been bleached, and since the cow is dead there is no ATP being produced to unbleach the rhodopsin. Behind the retina, you will see an iridescent layer. This is the tapetum corneum, on the inside of the sclera, and it is present in animals that need to see better in the dark. It reflects light that has entered the eye and passed through the retina back into the retina, so it has a second chance to stimulate photoreceptors. This layer is what makes a cow's or deer's eyes shine in the headlights. |
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