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The Fibularis Tertius is located in the Anterior Compartment of the (lower) leg. The muscles in the anterior compartment are:
- Distal anterior fibula to the base of the fifth metatarsal.
- The fibularis tertius attaches proximally onto the distal 1/3 of the anterior fibula and distal 1/3 of the interosseus membrane.
- The fibularis tertius attaches distally onto the dorsal surface of the base of the fifth metatarsal.
- Dorsiflexes the foot at the ankle joint.
- Everts (Pronates) the foot at the subtalar joint.
- The fibularis tertius is actually structurally part of the extensor digitorum longus. It has been separated from the extensor digitorum longus because it attaches onto a metatarsal, not a “digit”, i.e., not a phalanx.
- The fibularis tertius used to be named the peroneus tertius; it was renamed at an Anatomy Congress in 1999.
- Eversion is the principal cardinal-plane (frontal-plane) component of the oblique-plane motion pattern of pronation.