  the superior oblique muscle, or obliquus oculi superior, is a fusiform muscle originating in the upper, medial side of the orbit (i.e. from beside the nose) which abducts, depresses and internally rotates the eye. it is the only extraocular muscle innervated by the trochlear nerve (the fourth cranial nerve). ==structure==  the origin for the superior oblique is the annulus of zinn. it loops through a pulley-like structure (the trochlea of superior oblique) and inserts into the sclera on the posterotemporal surface of the eyeball. it is the pulley system that gives superior oblique its actions, causing depression of the eyeball despite being inserted on the superior surface. thumb|300px|superior oblique nerve the superior oblique arises immediately above the margin of the optic foramen, superior and medial to the origin of the superior rectus, 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 caudally, laterally, and inferiorly beneath the superior rectus to the lateral part of the bulb of the eye, and is inserted onto the scleral surface, behind the equator of the [[human eyeball|eyeb
Human_eye_anatomy Muscles_of_the_head_and_neck