Author: Dr Peter de Souza
Last modified: 2 January 2023

The peroneus tertius (fibularis tertius) is one of the muscles within the anterior compartment of the leg. Collectively, the muscles of the anterior compartment act to extend the toes, dorsiflex the ankle and invert the foot.

The leg is comprised of anterior, lateral and posterior compartments.

The anterior compartment consists of four muscles:


  • Distal part of medial fibula


  • Dorsomedial surface of base of 5th metatarsal


  • Dorsiflexion of foot
  • Eversion of foot


  • Deep fibular nerve: L5,S1

Blood Supply

  • Anterior tibial artery