Peroneus tertius

The peroneus tertius (also known as fibularis tertius) is a muscle of the human body located in the lower limb.Bones of the right foot (dorsal surface).The mucous sheaths of the tendons around the ankle (lateral aspect).Dorsum of Foot. Deep dissection.Dorsum of Foot. Deep dissection. The peroneus tertius (also known as fibularis tertius) is a muscle of the human body located in the lower limb. The muscle arises from the lower third of the anterior surface of the fibula (anterior compartment of lower leg); from the lower part of the interosseous membrane; and from an intermuscular septum between it and the peroneus brevis muscle. The septum is sometimes called the intermuscular septum of Otto. The tendon, after passing under the superior extensor retinaculum of foot and inferior extensor retinaculum of foot in the same canal as the extensor digitorum longus, is inserted into the dorsal surface of the base of the metatarsal bone of the fifth digit. It is innervated by the deep fibular nerve, unlike the other peroneal muscles which are innervated by the superficial fibular nerve, since the peroneus tertius is a member of the anterior compartment. Its action is that of weak dorsiflexion of the ankle joint and to evert the foot at the ankle joint.