![]() ![]() When the eye looks up or down, the eye must also rotate slightly to compensate for the superior rectus pulling at approximately a 20-degree angle, rather than straight up. Rotation of the eye by the two oblique muscles is necessary because the eye is not perfectly aligned on the sagittal plane. When it contracts, it laterally rotates the eye, in opposition to the superior oblique. The inferior oblique muscle originates from the floor of the orbit and inserts into the inferolateral surface of the eye. The angle of the tendon through the trochlea means that contraction of the superior oblique rotates the eye medially. The tendon inserts obliquely into the superior surface of the eye. However, the tendon of the oblique muscles threads through a pulley-like piece of cartilage known as the trochlea. The superior oblique originates at the posterior orbit, near the origin of the four rectus muscles. For example, when the superior rectus contracts, the eye rotates to look up. When each of these muscles contract, the eye to moves toward the contracting muscle. ![]() They are the superior rectus, medial rectus, inferior rectus, and lateral rectus. Four of the muscles are arranged at the cardinal points around the eye and are named for those locations. Movement of the eye within the orbit is accomplished by the contraction of six extraocular muscles that originate from the bones of the orbit and insert into the surface of the eyeball ( Figure 8.14). The orbit is surrounded by cranial bones of the skull. Figure 8.13. The Eye in the Orbit The eye is located within the orbit and surrounded by soft tissues that protect and support its function.
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