212 THE MUSCLES. 



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 (/). Near 

 the malleolus it ends in a strong tendon which passes beneath 

 the transverse ligament along with the tendon of the extensor 

 longus (/). 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 (/), 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. ex- 

 tensor brevis digitorum (Fig. 90, ?/). — 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. 



li 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 ex- 

 tensor 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 metatarsophalan- 

 geal 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 con- 

 tinuation 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 



