Peroneus tertius muscle

Dr Craig Hacking et al.

The peroneus tertius muscle, also known as fibularis tertius muscle, is a muscle of the anterior compartment of the leg, despite its name suggesting it is in the lateral compartment. It aids in dorsiflexion and eversion of the foot.

  • origin: inferior 1/3rd of anterior surface of fibula and interosseous
    membrane; some authors describe the muscles as arising from the lateral margin of the extensor digitorum longus muscle
  • insertion: dorsal surface of the 5th metatarsal base
  • action: dorsiflexion and foot eversion
  • innervation: deep peroneal nerve

Its tendon passes anterior to the lateral malleolus (unlike peroneus brevis and longus which pass anterior), deep to the inferior extensor retinaculum to become enclosed in a common tendon sheath with the tendons of the extensor digitorum longus muscle.

It may be absent or associated with other peroneus accessory muscles.

Lower limb anatomy
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Article Information

rID: 40284
Section: Anatomy
Synonyms or Alternate Spellings:
  • Fibularis tertius muscle
  • Fibularis tertius

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Cases and Figures

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    EDL: extensor dig...
    Figure 1: peroneal tendons
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    Figure 2: Lower leg axial section - Gray's anatomy illustration
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