The extensor hallucis longus muscle has its origin in the middle of the fibula, running along the inside of that bone and over the ankle to insert on the distal phalanx. It extends the big toe (straightens it) and assists in the ankle’s dorsal flexion. The hallux (plural, hallucis) are muscles pertaining to the big toe. The extensor hallucis longus are muscles used in extending the toe; the flexor hallucis longus are used in flexing it and moving it to the side.