MUSCLES OF THE LEG.—The muscles lying on the bones of the leg, both before and behind, are, with the exception of one, pro perly muscles of the ankle-joint and foot, since their primary action is exclusively upon these parts. (See article FOOT, MUSCLES oF.) For the convenience, however, of description they will here be demonstrated according to their si tuation.
The muscles of the leg may be classed into anterior, external, and posterior. The anterior lying in the space between the tibia and fi bula are four in number, consisting of tibialis anticus, extensor proprius pollicis, extensor longus digitorum, and peroneus tertius. The tibialis anticus and extensor longus alone are seen at the upper part of the leg on removing the deep fascia ; the extensor proprius pol 1 licis emerging from between these muscles about one-third down the leg, and the peroneus I tertius shewing itself as a separate slip of the extensor longus, about the same height, and at its fibular side.
1. Tibialis anticus lies upon the fibular and anterior surface of the tibia; arises, principally muscular, from the fibular side of the tibia, through its two upper thirds, from its tuber osity and spine, and from a small portion of the interosseous ligament, from the fascia of the leg, and from an aponeurotic septum placed between it and the extensor digitorum longus. The muscle is larger above than below ; its fleshy fibres converge to a strong tendon which crosses from the outside to the fore part of the tibia, passes through a distinct ring of the annular ligament near the ankle, runs over the astragalus os naviculare, and is inserted into the upper part of the os cuneiforme in ternum, and base of the metatarsal bone of the great toe. The insertion of the tendon is con cealed in part by the adductor and flexor brevis of the great toe. Between the tendon of this muscle and the os cuneiforme we find a small bursa mucosa. This muscle is covered in front by the fascia of the leg, to which it adheres superiorly ; behind it is in contact with the tibia and interosseous ligament, on the fibular side with the extensor digitorum communis, and extensor proprius pollicis. Its action is to flex the foot upon the leg by elevating the an terior part of the foot.
2. Extensor longus digitorum.—This mus
cle occupies the fibular side of the tibio-fi bular fossa, as the last filled the inner side. This is a tapering muscle also ; it arises ten dinous and muscular from the fibular or outer part of the head of the tibia, from the head of the fibula, and from the anterior angle of that bone almost its whole length, and from part of the tibial side of it also ; it also takes origin from the interosseous ligament, from the fascia of the leg, and from the aponeurotic septum situated between this muscle and the last. Below the middle of the leg it .splits into four tendons. These pass under the ante rior annular ligament in one common sheath with the peroneus tertius. They then run along the dorsum of the foot, spreading as they go, and are inserted into the root of the first pha lanx of each of the four smaller toes. To wards their termination each of the tendons ex pands into an aponeurosis, covering the upper surface of the phalanges, and this is strengthened by the tendons of the extensor brevis and gives attachment to the lumbricales and interossei.
This muscle is covered in front by the fascia of the leg, the annular ligament and the in tegument; posteriorly it rests upon the fibula, the interosseous ligament, and the tibia; exter nally it is in relation with the peronei muscles, internally with the tibiars anticus, and extensor proprius pollicis; along its lower and fibular border lies the peroneus tertius. On the dor sum of the foot its four tendons cross obliquely over those of the flexor brevis digitorum.
Action. To extend all the joints of the four smaller toes, and to bend the ankle-joint.
3. Extensor proprius pollieis lies between the two last muscles. Its origin is hidden by them. It commences about one-third down the leg, from the smooth surface of the fibula, between the anterior and tibial angles of that bone, of which surface it occupies part, through the middle third of its length, also from the lower two-thirds of the interosseous ligament. The fleshy fibres run obliquely forward into a tendon placed at the anterior border of the muscle, which after passing beneath the an terior annular ligament, and along the dorsum of the foot, is inserted into the bases of the first and second phalanges of the great toe.