An anomalous muscle in the canal of Guyon (a possible ulnar nerve compression).
D000013:Congenital Abnormalities / Q000150:complications; D006801:Humans; D009132:Muscles / Q000002:abnormalities*; D009408:Nerve Compression Syndromes / Q000209:etiology*; D014459:Ulnar Nerve; D014953:Wrist