M. tibialis anterior ([Fig. 90], n).—This is the superficial muscle covering the lateral side of the tibia.
Origin by fleshy fibres from the proximal one-sixth of the lateral surface of the shaft of the tibia, from the proximal third of the medial border of the shaft and head of the fibula, and from the intervening interosseous ligament. The triangular body of the muscle covers the lateral surface of the tibia and the outer surface of the extensor longus digitorum (p). Near the malleolus it ends in a strong tendon which passes beneath the transverse ligament along with the tendon of the extensor longus (p). The tendon crosses the dorsal surface of the foot obliquely toward its medial side.
Insertion into the outer surface of the first metatarsal.
Relations.—Outer surface with the superficial fascia and the tendon of the biceps femoris. Inner surface with the extensor longus (p), the tibia, and the interosseous membrane.
Action.—Flexor of the foot.
4. Muscles of the Foot.
A. Muscles on the Dorsum of the Foot.
—M. extensor brevis digitorum ([Fig. 90], u).—A broad thin muscle covering the tarsus and part of the metatarsus on the lateral side of the dorsum of the foot. It may be divided into three slips.
Origin from the distal border of nearly the whole calcaneal annular ligament (5), and from the proximal end of the dorsal surface of the three lateral metatarsals. At the middle of the metatarsals the muscle ends in three flat tendons which pass into the three interspaces between the four tendons of the extensor longus. Each tendon is divided into two branches.
Insertion.—The lateral branch of each tendon is inserted into the cartilaginous plate which lies in the metatarsophalangeal articulation of the digit on the outer side. The medial branch joins the lateral side of the extensor longus tendon on the dorsum of the first phalanx.