Final answer:
An accessory peroneal nerve, when present, would innervate the fibularis longus or fibularis brevis muscle, which are responsible for plantar flexing the foot at the ankle and everting it at the intertarsal joints.
Step-by-step explanation:
An anomalous accessory peroneal nerve, when present, typically innervates muscles within the lateral compartment of the leg. The muscles in this compartment are the fibularis longus and the fibularis brevis. These muscles are responsible for plantar flexion of the foot at the ankle joint and eversion of the foot at the intertarsal joints. Therefore, an accessory peroneal nerve would innervate either one of these muscles to perform these functions.