Quadratus plantae, also called the flexor accessorius is one of the central plantar muscles of the foot. Observing the foot muscles horizontally, quadratus plantae comprises the second layer of plantar foot muscles, together with the lumbricals. The function of this muscle is to facilitate walking by shortening the flexor digitorum longus’ tendons when the foot is in plantar flexion. Hence its other name; flexor accessorius. Origin: Medial surface of calcaneus bone, lateral process of calcaneal