Fibularis brevis muscle

Origin: Fibula

Insertion: Fifth metatarsal

Artery: Fibular (peroneal) artery

Nerve: Superficial fibular (peroneal) nerve

Action: Plantarflexion, eversion

Description:
The Fibularis brevis (Peronaeus brevis) lies under cover of the Peronaeus longus, and is a shorter and smaller muscle. It arises from the lower two-thirds of the lateral surface of the body of the fibula; medial to the Peronaeus longus; and from the intermuscular septa separating it from the adjacent muscles on the front and back of the leg. The fibers pass vertically downward, and end in a tendon which runs behind the lateral malleolus along with but in front of that of the preceding muscle, the two tendons being enclosed in the same compartment, and lubricated by a common mucous sheath. It then runs forward on the lateral side of the calcaneus, above the trochlear process and the tendon of the Peronaeus longus, and isinserted into the tuberosity at the base of the fifth metatarsal bone, on its lateral side.
On the lateral surface of the calcaneus the tendons of the Peronaei longus and brevis occupy separate osseoaponeurotic canals formed by the calcaneus and the perineal retinacula; each tendon is enveloped by a forward prolongation of the common mucous sheath.

Variations.—Fusion of the two peronaei is rare. A slip from the Peronaeus longus to the base of the third, fourth or fifth metatarsal bone, or to the Adductor hallucis is occasionally seen.
- Peronaeus accessorius, origin from the fibula between the longus and brevis, joins the tendon of the longus in the sole of the foot.
- Peronaeus quinti digiti, rare, origin lower fourth of the fibula under the brevis, insertion into the Extensor aponeurosis of the little toe. More common as a slip of the tendon of the Peronaeus brevis.
- Peronaeus quartus, 13 per cent. (Gruber), origin back of fibula between the brevis and the Flexor hallucis, insertion into the peroneal spine of the calcaneum, (peroneocalcaneus externum), or less frequently into the tuberosity of the cuboid (peroneocuboideus).

Nerves.—The Peronaei longus and brevis are supplied by the fourth and fifth lumbar and first sacral nerves through the superficial peroneal nerve.

Actions.—The Peronaei longus and brevis extend the foot upon the leg, in conjunction with the Tibialis posterior, antagonizing the Tibialis anterior and Peronaeus tertius, which are flexors of the foot. The Peronaeus longus also everts the sole of the foot, and from the oblique direction of the tendon across the sole of the foot is an important agent in the maintenance of the transverse arch. Taking their fixed points below, the Peronaei serve to steady the leg upon the foot. This is especially the case in standing upon one leg, when the tendency of the superincumbent weight is to throw the leg medialward; the Peronaeus longus overcomes this tendency by drawing on the lateral side of the leg.