This is a muscle of considerable size and strength, and gives to the upper part of the arm in front its prominence and width.

Origin. - In common with the extensor pedis from the outer surface of the external condyle, and from the ridge above it.

Insertion.-By a strong tendon which, after passing over a groove on the lower part of the front face of the tibia and the knee-joint, becomes inserted into a bony prominence on the superior and anterior part of the large metacarpal or canon bone. In passing over the knee, the tendon of insertion plays through a synovial sheath, which facilitates its movements during flexion and extension of the joint.

Action. - To extend the canon and knee bones on the fore-arm.