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The peroneus brevis muscle arises from the lower two-thirds of the lateral surface of the fibula and inserts, via its tendon, into the tubercle on the base of the fifth metatarsal bone.
The peroneus longus muscle takes origin from the upper two-thirds of the lateral surface of the fibula and inserts into the medial cuneiform and the base of the first metatarsal. Follow the tendons of peroneus longus and brevis muscles as far distally into the foot as your dissection will allow. Pull on these tendons to demonstrate that the principle function of the peroneus longus and brevis muscles is to evert the foot (which aides in stability of the foot when walking on uneven terrain).Links and References:
Grant's: 5.77
Netter (1ed.): 490 (2ed.): 486
Rohen/Yokochi: 433