The eyes one procures from a butcher or a slaughter house will always have the extrinsic tissues so badly cut and torn that identification of the various parts and their relations is impossible. Therefore, it is best to supply one’s self with the head of an animal, such as a sheep or a calf, and dissect an eye with all its extrinsic tissues intact. For this dissection, a hammer and a chisel are necessary in addition to the tools needed for doing the previous dissections.
Fig. 47—Showing method of making the initial cuts in the skin. (Page 97.)
Fig. 48—Part of calf’s head, showing the first cut to be made in the bones of the orbit. (Page 102.)
Fig. 49—Showing all the cuts to be made through the bones of the orbit. (Page 102.)
Using the left orbit, begin the dissection by making an incision directly over the supra-orbital ridge, extending from over the inner to the outer canthus. At the middle of that line, make an incision, and cut at right angles upward to the top of the head. Next make a cut below the eye, extending from the outer to the inner canthus. (Fig. 47.) Loosen the skin from the bone with the scalpel, and lay bare the skull immediately over the orbit. Fold the flaps of the skin back and fasten them down to the skull with pins or tacks so they will not interfere with the work.
Fig. 50—Showing how to pry the cut bone loose. (Page 102.)
Fig. 51—“In removing orbital contents dissect close to the bone.”
Fig. 52—Showing excavated orbit. (Page 105.)
Using the hammer and the chisel, cut through the roof of the orbit at the middle of the supra-orbital ridge, and continue upward for about two and one-half inches. Do not strike hard blows, or the chisel may be driven through the underlying tissues. Listen for the peculiar sound that is heard when the bone has been completely penetrated; then remove the chisel. Continue until the full distance of two and one-half inches of bone has been separated. (Fig. 48.) Now, begin at the upper end, and cut through the bone downward to the right for about two inches toward the outer canthus. A similar line should be cut on the right of the centre line toward the inner canthus. This will mark out two irregular, triangular-shaped pieces of bone. (Fig. 49.) Remove the piece on the right-hand side by prying it off. (Fig. 50.) The left-hand piece should be pried loose and then carefully cut away with the scalpel, so that the pulley through which the superior oblique muscle runs its tendon, will not be injured. In removing the orbital contents, dissect close to the bone (Fig. 51), so that the periosteum will also be removed, and form a sort of sac or capsule in which will be contained the eye with all its extrinsic tissues. If difficulty is experienced in getting at the posterior parts of the orbit, it will be best to cut away as much more of the obstructing bone as is necessary. In this way the “capsule” containing the eye, its six muscles, the lacrimal gland, and both eyelids, all in situ, will be removed. (Fig. 54.) As the orbital entrance of the optic nerve is neared, care must be exercised not to cut into this “capsule,” or sever any of the muscles. (Fig. 52 shows the excavated orbit. Fig. 53 shows an anterior view of the enucleated eye. Fig. 54 is a side view of the enucleated eye.)
Fig. 53—Anterior view of the enucleated eye.
Fig. 54—Showing the enucleated eye, its muscles, and its accessories, all in situ.
