The peroneus muscles (also called fibularis muscles or peroneals or peronæus) are a group of muscles in the leg. While the muscle group exists in many variations, it is normally composed of three muscles: peroneus longus, brevis and tertius. The peroneus muscles all originate from the fibula and insert onto the metatarsals.
The peroneus longus and brevis are much more similar to each other than they are to the peroneus tertius. The longus and brevis are both located in the lateral compartment of the leg, supplied by the fibular artery and innervated by the superficial fibular nerve, while the tertius in located in the anterior compartment, supplied by the anterior tibial artery and innervated by the deep fibular nerve. Another difference between the longus, brevis and tertius is that while they all evert the foot; the peroneus longus and brevis plantarflex the foot, while the peroneus tertius dorsiflexes it.
The peroneus muscles are highly variable and several variants have been noted as being occasionally present, such as peroneus digiti minimi and peroneus quartus. The quartus is more closely associated with the tendons of the extensor digitorum longus, and may send a small tendon to the fifth digit.