Variants of the supernumerary orbital muscles, lateral view

Variants of the supernumerary orbital muscles reported in the literature. For ease of comparison and increased transparency, the same side has been presented on all schemes. Terminology applied by Lüdinghausen and colleagues has been taken into account. (Lüdinghausen M, Miura M, Würzler N. Variations and anomalies of the human orbital muscles. Surg Radiol Anat 1999;21[1]:69-76.)

(a) Anatomical variation described in this report—an accessory muscle observed on a 68-year-old cadaver with no eye movement abnormalities reported in the medical history. The accessory muscle is divided into two delicate slips (heads): superior (marked by black asterisk)—forming a muscular bridge connected to the superior rectus muscle (SR); and inferior—corresponding to accessory rectus muscle (AR) and attached in the anterior half of the inferior rectus muscle (IR). (b) Supernumerary orbital muscle (AR) with a broad muscular bridge (marked by black asterisk) to the SR and attachment to the anterior part of the IR. The accessory muscle was well-separated from the IR. (c) Supernumerary orbital muscle (AR) with a thin muscular bridge (marked by black asterisk) to the SR and close attachment to the anterior part of the IR. Variants (b) and (c) were described by Lüdinghausen and colleagues on the adult cadaver with no problems with mobility of the eyeball in the medical history.

Abbreviation: II, optic nerve.

(Source: Haładaj R, Wysiadecki G, Polguj M, Topol M. Bilateral muscular slips between superior and inferior rectus muscles: case report with discussion on classification of accessory rectus muscles within the orbit. Surg Radiol Anat 2018;40[7]:855-62. Creative Commons Attribution 4.0 International [CC BY 4.0] license, creativecommons.org/licenses/by/4.0.)