Thumbs are innervated by the superficial fibular nerve, and the flexor digitorum brevis originates on the ventral side of the fibula.
It is innervated by the anterior interosseus branch of the median nerve (C7-C8) It is a persistence of one of the former contrahentes muscles that pulled the fingers or toes together. Dorsal digital nerves of radial nerve, proper palmar digital nerves of median nerve 
