The structure indicated is the tibialis posterior muscle of the leg.
The muscles of the leg consist of the three compartments:
The muscles in the posterior compartment of the leg are separated into a superficial group and a deep group.
The superficial group consists of the following leg muscles:
The deep group consists of the following leg muscles:
- Flexor hallucis longus
- Flexor digitorum longus
- Tibialis posterior
Generally speaking, the muscles of the posterior compartment serve to plantarflex at the ankle joint, invert the foot and flex the toes. The posterior leg muscles are innervated by the tibial nerve, a branch of the sciatic nerve.
The tendon of the tibialis posterior runs behind the medial malleolus, deep to the tendon of the flexor digitorum longus. The tibialis posterior muscles serves to invert and plantarflex the foot, and additionally provides support to the medial arch of the foot, together with the tendons of the peroneus longus and tibialis anterior, which insert medially on the foot
Origin: Posterior surfaces of interosseous membrane and adjacent regions of tibia and fibula
Insertion: Tuberosity of navicular and adjacent region of medial cuneiform
Action: Inversion and plantarflexion of foot. Support of medial arch of foot during walking
Innervation: Tibial nerve
Learn more about the anatomy of the leg muscles in this tutorial.