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 (f). 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 (f), 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. 
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 
