Insertion: First metatarsal, medial cuneiform
Artery: Fibular (peroneal) artery
Nerve: Superficial fibular (peroneal) nerve
Action: Plantarflexion, eversion
Antagonist: Tibialis anterior muscle
The Fibularis longus (Peronaeus longus) is situated at the upper part of the lateral side of the leg, and is the more superficial of the two muscles. It arises from the head and upper two-thirds of the lateral surface of the body of the fibula, from the deep surface of the fascia, and from the intermuscular septa between it and the muscles on the front and back of the leg; occasionally also by a few fibers from the lateral condyle of the tibia. Between its attachments to the head and to the body of the fibula there is a gap through which the common peroneal nerve passes to the front of the leg. It ends in a long tendon, which runs behind the lateral malleolus, in a groove common to it and the tendon of the Peronaeus brevis, behind which it lies; the groove is converted into a canal by the superior peroneal retinaculum, and the tendons in it are contained in a common mucous sheath. The tendon then extends obliquely forward across the lateral side of the calcaneus, below the trochlear process, and the tendon of the Peronaeus brevis, and under cover of the inferior peroneal retinaculum. It crosses the lateral side of the cuboid, and then runs on the under surface of that bone in a groove which is converted into a canal by the long plantar ligament; the tendon then crosses the sole of the foot obliquely, and is inserted into the lateral side of the base of the first metatarsal bone and the lateral side of the first cuneiform. Occasionally it sends a slip to the base of the second metatarsal bone. The tendon changes its direction at two points: first, behind the lateral malleolus; secondly, on the cuboid bone; in both of these situations the tendon is thickened, and, in the latter, a sesamoid fibrocartilage (sometimes a bone), is usually developed in its substance.
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.