Normal Anatomy and Anomalies of the Rectus Extraocular Muscles in Human: A Review of the Recent Data and Findings

Figure 2

Anatomical relationships within the orbit. The origin of the medial rectus muscle (mr) is fixed to the medial aspect of the common tendinous ring. On its further course, the muscle runs parallel to the medial orbital wall. The inferior rectus muscle (ir) runs perpendicularly to the inferior wall of the orbit. The anterior part of the muscle is separated from the orbit by the inferior oblique muscle (io). All three muscles (mr, ir, and io) are innervated by the inferior division of the oculomotor nerve (id). The nerve to the inferior oblique muscle (nio) branches off from the inferior division of the oculomotor nerve and runs parallel to the lateral border of the inferior rectus muscle. A characteristic feature of the lateral rectus muscle (lr) is the so-called “dual headed origin,” as this muscle begins from the common tendon ring with two tendinous bands. The muscle runs along the lateral wall of the orbit. It is innervated by the abducens nerve (an). The ciliary ganglion (cg) is located medially to the internal surface of the muscle. The superior rectus muscle (sr) is located under the levator palpebrae superioris muscle (lps). Both muscles (sr and lps) are innervated by the superior division of the oculomotor nerve (sd). fn: frontal nerve; ln: lacrimal nerve; ncn: nasociliary nerve; son: supraorbital nerve; stn: supratrochlear nerve, th: troch; ear nerve.