_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. _Action._--Extensor of the digits. B. MUSCLES OF THE SOLE OF THE FOOT.--=M. flexor brevis digitorum= (=pedis perforatus=).--This is the direct continuation of the tendon of the plantaris. It lies immediately beneath the superficial plantar fascia. The flat belly of the muscle has its medial border attached by an oblique tendinous band to the medial surface of the scaphoid and the medial cuneiform. It divides into four slips which diverge to the four toes, each ending in a flat tendon. The slips decrease in size from the lateral to the medial side. The three lateral ones overlap one another proximally. _Insertion._--Each tendon expands at the distal end of the metatarsal and is wrapped about the tendon of the deep flexor which perforates it. The two halves unite beneath the perforating tendon and pass together with the perforating tendon through fibrous rings, the annular ligaments. One of these is attached to the sesamoids at the base of the phalanx. The other is attached to the head of the first phalanx. The tendons are finally inserted into the bases of the second phalanges. The two annular ligaments are connected by fascia so as to form a continuous canal for the tendons. This canal is lined by a synovial membrane. Covering this canal is a more superficial layer of fascia. Before passing into the proximal annular ligament the two middle tendons unite each with the tendon of the corresponding lumbrical muscle. Each also gives off a branch, the lateral one on its lateral side and the medial one on its medial side. These branches, like those of the two middle ones, are inserted into the common phalangeal fascia. _Action._--Flexor of the second phalanges of the digits.