Histological observations on the left accessory rectus muscle

(a) Part of the superior head of the left accessory rectus muscle (marked by grey arrowheads) shown at its origin from superior rectus muscle (SR) (H&E stain, x2 objective). Fibers of striated skeletal muscle and a cross-section of small nerve (marked by white arrowhead) have been visualized. (b) Part of the tendon with visible bundles of collagen fibers (tissue sample taken from the origin of the left accessory rectus muscle) (H&E stain, x40 objective). (c) Part of the inferior head of the left accessory rectus muscle (marked by black arrowheads) shown at its origin from the inferior rectus muscle (IR) (H&E stain, x2 objective). Fibers of striated skeletal muscle and cross-section of small nerve (marked by white arrowhead) have been visualized. (d) Sample fibers of striated skeletal muscle obtained from the inferior head of the left accessory rectus muscle. The striations of skeletal muscle tissue have been visualized (H&E stain, x40 objective).

Abbreviations: An, anterior; Po, posterior.

(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.)