Origin Medial head from posterior nonarticular surface of medial femoral condyle; Lateral head from lateral surface of femoral lateral condyle Insertion The two heads unite into a broad aponeurosis which eventually unites with the deep tendon of the soleus to form the Achilles tendon, inserting on the middle 1/3 of the posterior calcaneal surface Action Powerful plantar flexor of ankle Innervation Tibial nerve (S1, S2) (S1, S2) Arterial Supply Each head supplied by a sural branch of the popliteal artery