Arising from the common extensor origin the muscle expands into a rounded belly in the middle of the forearm, diverging from the three muscles on the radial side and separated from them by the emergence of the thumb extensors. The four tendons that develop pass under the extensor retinaculum crowded together, and overlying the tendon of extensor indicis. On the back of the hand the tendons spread out towards the fingers. Commonly the fourth tendon is fused with that to the ring finger, and reaches the little finger only by a tendinous band that passes across near the metacarpophalangeal joint. Other bands join adjacent tendons in a variable manner. The extensor expansions and their insertions into the phalanges are considered with the hand.
Nerve supply of extensor digitorum:
By the posterior interosseous nerve on the back of the forearm (C7, 8).
Action of extensor digitorum:
It is an extensor of the digits.