Accessory Supinator

The accessory supinator was found in 21 of 63 forearms, bilaterally in 8 of 27 cadavers, and in 8 of 20 males and in 7 of 16 female cadavers. With only one exception, the muscle was always found lateral to the annular ligament. The muscle originates from the coronoid process of the ulna just lateral to the ulnar tuberosity, and inserts onto the radial tuberosity, posterior to the insertion of the biceps tendon. Its action is to assist in the supination of the forearm.

LeDouble mentions that these accessory supinator muscles have been overlooked by recent, nineteenth century, anatomists. See Supinator.

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Reference

LeDouble, A.F. (1897) Traité des Variations du Système Musculaire de l'Homme et Leur Signification au Point de Vue de l'Anthropologie Zoologique. Libraire C. Reinwald, Schleicher Freres, Paris.