MUSCLES OF THE PELVIC LIMBS. 21T 
Origin by a thin flat tendon from the lateral surface of the 
lateral epicondyle of the femur just dorsad of the origin of the 
popliteus. The tendon becomes narrower and thicker and 
passes through the capsule of the knee-joint and over a slight: 
groove on the tibia just dorsad of the head of the fibula. The 
belly of the muscle extends the entire length of the tibia, pass- 
ing beneath the transverse ligament (5) along with the tendon 
of the tibialis anterior (z). At the ankle it runs through a 
fibrous loop which is attached to the dorsal surface of the 
calcaneus (the annular ligament of the calcaneus); it then turns 
and passes onto the dorsum of the foot. The muscle ends in 
four slender tendons, the two middle of which begin at the 
transverse ligament, while the others begin at the fibrous loop. 
The tendons diverge to the four digits. Each tendon is con- 
nected with the fibrous sheath surrounding the base of the first 
phalanx, and each has a synovial bursa beneath it at this point. 
Near the distal end of the first phalanx the tendon is united on 
the, lateral side to the conjoined tendon of the extensor brevis 
digitorum and an interosseus muscle, and on the medial side 
to the tendon of the interosseus. The lateral side of the most 
lateral tendon is not thus united, but is joined on the outer side 
by the tendon of the peroneus tertius. 
Insertion.—The tendon thus formed on the dorsum of each 
phalanx by the junction of the two or three tendons above 
mentioned is firmly attached to the base of the second phalanx 
at its proximal end in the middle of its dorsal surface. In 
crossing the joint between the first and second phalanges the 
tendon forms a fibrous pad which protects the dorsum of the 
joint and glides over it. It then continues to be inserted into 
the base of the terminal phalanx. 
Relations. —Outer surface with the tibialis anterior (7) and 
the superficial fascia; Inner surface with a part of the tibialis 
anterior, with the bones, the interosseous membrane, and the 
peroneus brevis (s). 
Action.—Extensor of the phalanges. 
M. tibialis anterior (Fig. 90, ~).—This is the superficial 
muscle covering the lateral side of the tibia. 
Origin by fleshy fibres from the proximal one-sixth of the 
