Extensor Digitorum Brevis
The structure indicated is the extensor digitorum brevis muscle.
This muscle is the only intrinsic muscle of the foot located on the dorsal aspect, and serves to extend digits 2 to 4.
Origin: Superolateral calcaneus
Insertion: Base of proximal phalanx of great toe, lateral portion of tendons of extensor digitorum longus of toes 2 – 4.
Action: Extension of great toe at MTP joint. Flexion of toes 2 – 4.
Innervation: Deep fibular nerve.
Learn more about the anatomy of the foot muscles in this tutorial.