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The insertion of the inferior rectus muscle is around 6 mm from the insertion of the medial rectus muscle, and around 8 mm from the insertion of the lateral rectus muscle. [2] A parasympathetic branch that supplies the ciliary muscles of the pupil passes close to the inferior rectus muscle. [1]
The last muscle is the inferior oblique, which originates at the lower front of the nasal orbital wall, passes inferiorly over the inferior rectus muscle on its path laterally and posteriorly, and inserts under the lateral rectus muscle on the lateral, posterior part of the globe. Thus, the inferior oblique pulls the eye upward and laterally.
Oblique Superior and inferior 2 1 rectus, inferior: head, eye, orbit (left/right) annulus of Zinn at orbital apex 6.5 mm inferior to corneal limbus: ophthalmic artery: oculomotor nerve [CNIII], inferior branch: adducts and depresses eye: Oblique Superior and inferior 2 1 rectus, medial: head, eye, orbit (left/right) annulus of Zinn at orbital apex
The common tendinous ring spans the superior orbital fissure and can be described as having two parts – an inferior tendon which gives origin to the inferior rectus muscle, and to part of the lateral rectus muscle; and a superior tendon which gives origin to the superior rectus muscle, and to part of the medial and lateral recti muscles.
The inferior oblique muscle or obliquus oculi inferior is a thin, narrow muscle placed near the anterior margin of the floor of the orbit.The inferior oblique is one of the extraocular muscles, and is attached to the maxillary bone (origin) and the posterior, inferior, lateral surface of the eye (insertion).
Rectus capitis posterior minor goes from the middle of the posterior arch of the atlas to the occiput. Obliquus capitis superior goes from the transverse process of the atlas to the occiput. Obliquus capitis inferior goes from the spine of the axis vertebra to the transverse process of the atlas. They are innervated by the suboccipital nerve.
The levator palpebrae superioris originates from inferior surface of the lesser wing of the sphenoid bone, just above the optic foramen. It broadens and decreases in thickness (becomes thinner) and becomes the levator aponeurosis. This portion inserts on the skin of the upper eyelid, as well as the superior tarsal plate. It is a skeletal muscle.
Hence, when inferior rectus contracts so we look down, superior oblique also contracts to prevent extorsion of the eye, and when superior rectus contracts so we look up, inferior oblique contracts to prevent intorsion, thus the undesired rotatory actions of the inferior and superior recti about the long axis of the eye are cancelled out.