Anatomy Atlases: Illustrated Encyclopedia of Human Anatomic Variation: Opus I: Muscular System: Alphabetical Listing of Muscles: P: Piriformis

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

Piriformis

Ronald A. Bergman, PhD
Adel K. Afifi, MD, MS
Ryosuke Miyauchi, MD
Peer Review Status: Internally Peer Reviewed

The most frequent variation is the division of the muscle into two parts. This is usually associated with a high division of the sciatic nerve, with the peroneal portion of the sciatic emerging between the two parts. The muscle is rarely divided by the tibial division of the sciatic, or by the entire sciatic nerve. The cleavage generally affects only the muscle belly, but may involve the entire muscle. Subdivision into several fascicles has also been reported. The muscle has been reported absent as well. Fusion frequently takes place between piriformis and gluteus medius, gluteus minimus, superior gemellus, or in rare cases even the internal obturator muscle. Its digitations of origin may be reduced to two or increased to four. It may insert into the capsule of the hip joint.

Syn.: m. pyramidalis, iliacus externus (Riolan), Birnmuskel.

References

Anson, B.J., Ed. (1966) Morris' Human Anatomy,12th ed., The Blakiston Division, McGraw-Hill Book Company, New York.

Beaton, L.E. and B.J. Anson. (1938) The relation between the sciatic nerve and of its subdivisions to the piriformis muscle. Anat. Rec. 70:1-5.

Celli, E. (1914) Sur la morphologie du M. Piriformis. Arch. Ital. Biol. 41:132-133.

Fredericq, H. (1908) Un cas de division complete du nerf grand sciatique accompagnee d'une duplicite complete du muscle pyramidal. L'Assoc. Anatomistes, Comptes Rendus 10:168-170.

Henle, J. (1871) Handbuch der Muskellehre des Menschen, in Handbuch der systematischen Anatomie des Menschen. Verlag von Friedrich Vieweg und Sohn, Braunschweig.

Kawano, M. (1930) On the M. piriformis. Kaibogaku Zasshi 2:1017-1021. In Japanese.

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

Moore, A.T. (1922) An anomalous connection of the piriformis and biceps femoris muscles.Anat. Rec. 23:307-309.

Wood, J. (1864) On some variaties in human myology. Proc. Roy. Soc. Lond. B 13:299-303.

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