[An accessory muscle of the shank]

An accessory bilateral crural muscle is shown which has not yet been described. The muscle arises like the peronaeus quartus muscle at the proximal third of the flexor surface of the fibula and the interosseous membrane. The tendon runs medially to the tendon of the flexor hallucis longus muscle underneath the flexor retinaculum. On the left side, it is divided in 2 parts. The insertion lies medially to the anterior tubercle of the calcaneus. There is no phylogenetic explanation for such an accessory muscle.