Yes! Another Fibularis muscle! Fibularis referring to the fibula bone the muscles attach to.
Fibularis Tertius lives in anterior compartment of the lower leg (the front of the body) whereas Fibularis Longus and Brevis live in the lateral compartment.
Fibularis Tertius Muscle Attachments
ORIGIN: distal 1/3 of the anterior fibula and the distal 1/3 of the interosseous membrane
INSERTION: dorsal surface of the base of the 5th metatarsal
Fibularis Tertius is actually an extension of Extensor Digitorum longus ( a muscle we haven't covered yet!) - also of course in the anterior compartment of the lower leg/ankle. In fact, Fibularis Tertius may not even be present in some folk!
Fibularis Tertius Muscle Actions
a) DORSI-FLEXION of the foot at the ankle joint
Dorsiflexion is when your bring your foot UP (heel down -toes up)
Dorsi refers to the dorsal surface of your foot (aka the the top of you foot).
b) EVERSION of the foot at the sub-talar joint
TERTIUS comes from the latin word meaning "third" - because this muscle is the third 'fibularis' (aka Peronneal) muscle.
But when I hear Tertius all I can think about is.....