The superior oblique muscle, or obliquus oculi superior, is a fusiform muscle in the upper, medial side of the orbit whose primary action is intorsion and whose secondary actions are to abduct (laterally rotate) and depress the eyeball (i.e. it makes the eye move outward and downward). One of the extraocular muscles, the superior oblique is the only muscle innervated by the trochlear nerve.

The origin for the inferior rectus is the annulus of Zinn at the orbital apex. It loops through a pulley like structure (the trochlea) and inserts on the postereotemporal surface of the eyeball.

It arises immediately above the margin of the optic foramen, above and medial to the origin of the Rectus superior, and, passing forward, ends in a rounded tendon, which plays in a fibrocartilaginous ring or pulley attached to the trochlear fovea of the frontal bone.

The contiguous surfaces of the tendon and ring are lined by a delicate mucous sheath, and enclosed in a thin fibrous investment.

The tendon is reflected backward, lateralward, and downward beneath the Rectus superior to the lateral part of the bulb of the eye, and is inserted into the sclera, behind the equator of the eyeball, the insertion of the muscle lying between the Rectus superior and Rectus lateralis.

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Muscles of the head and neck | Eye

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