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Anatomy Atlases: Illustrated Encyclopedia of Human Anatomic Variation: Opus I: Muscular System: Alphabetical Listing of Muscles: R: Rectus Inferioris (Inferior Rectus)<br>Rectus Lateralis (Lateral Rectus) Rectus Medialis (Medial Rectus) Rectus Superioris (Superior Rectus) Obliquuis Inferior (Inferior Oblique) Obliquuis Superiorus (Superior Oblique)

Illustrated Encyclopedia of Human Anatomic Variation: Opus I: Muscular System: Alphabetical Listing of Muscles: R

Rectus Inferioris (Inferior Rectus)
Rectus Lateralis (Lateral Rectus)
Rectus Medialis (Medial Rectus)
Rectus Superioris (Superior Rectus)
Obliquuis Inferior (Inferior Oblique)
Obliquuis Superiorus (Superior Oblique)

Ronald A. Bergman, PhD
Adel K. Afifi, MD, MS
Ryosuke Miyauchi, MD

Peer Review Status: Internally Peer Reviewed


The four recti may be poorly developed and may be connected to each other by muscular slips. The inferior rectus may provide a large muscular bundle passing lateral to the optic nerve to join the superior rectus. A fasciculus of the lateral rectus may pass to the inferior rectus. Two additional fasciculi sometimes occur: one passing forward to end on the inferior tarsal plate and another inserting on the lateral wall of the orbit.

The lateral rectus may also provide a fascicle that passes across the posterior third of the orbit, beneath the optic nerve, to fuse with the belly of the medial rectus. A bifid insertion of the medial rectus has been reported.

The superior rectus may provide a muscular slip, which may also arise from the annulus of Zinn; it passes downward and forward across the lateral aspect of the optic nerve, to join the inferior rectus.

An anomalous muscle bundle from the inferior oblique (obliquus accessorius inferioris [Rex]) has been found passing from the apex of the orbit to join the inferior rectus.

The superior oblique may be closely accompanied by an offshoot from the levator palpebrae superioris, the comes obliqui superioris. The lateral and medial recti may be absent.

Occasionaly, slips corresponding to a retractor bulbi muscle are found; these may be supplied by the abducens and oculomotor nerves. In its simplest form the retractor may arise from the lateral rectus. In some reported instances, it forms a muscular funnel around the optic nerve and is inserted onto the back of the eyeball. It may be found divided into four slips that attach to the posterior hemisphere of the globe behind and between the four recti. It may also be represented by a single muscle bundle between the lateral and superior recti. A fibrous ring with four muscular slips joined to the deep surface of the four recti has been reported.

The inferior oblique and the lateral rectus may be doubled.

Abouna cites Campbell attributes to Avicenna the discovery of the "six motor muscles for the globe, four of which are inserted by a common band in the fundus of the orbit and the other two are the small and great oblique".

Image 24

Retractor Bulbi
from Posey

Image 25

Gracillimus (Albinus) or Anomalous Transversus (Bochdalek, Jr.) (right) and Accessory Inferior Oblique (left) Muscles.
from Posey.

Image 39

Accessory Muscle from Levator Palpebrae Superioris and an "Accessory Lateral Rectus."
from Posey.


References

Abouna, G.M. (1980) Arabian contribution to medical science. J. Kwt. Med. Assoc. 14:46-57.

Campbell, D. (1926) Arabian Medicine and its Influence on the Middle Ages. 2 vols., Paul, Trench, Trubner and Co. Ltd., London.

Fujita, T. (1938) Eine Muskelanomalie in der orbita. Okajimas' Folia Anat. Jap. 16:301-302.

Isomura, M. (1977) Nerve supply for anomalous ocular muscle in man. Anat. Anz. 142:255-265.

Macalister, A. (1875) Observations on muscular anomalies in the human anatomy. Third series with a catalogue of the priincipal muscular variations hitherto published. Trans. Roy. Irish Acad. Sci. 25:1-130.

MacEwen, E.M. (1930) Orbital variations. Anat. Rec. 46:223-232.

Rex, H. (1887) Uber einen abnormen Augenmuskel (Musc. obliquuis accessorius inferior). Anat Anz. 2:625-630.

Schaefer, E. A., Symington, J. and T.H. Bryce, Eds. (1923) Quain's Elements of Human Anatomy, 11th ed. Longmans, Green and Co., London.

Strangeways, T. (1868) On a supernumerary oblique muscle of the eyeball. J. Anat. Physiol. 2:245-246.

Whitenall, S.E. (1912) An instance of the retractor bulbi muscle in man. J. Anat. Physiol. 46:36-40.

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