1. DEEP MUSCLES
There are five muscles in the deep compartment of the posterior forearm – the supinator, abductor pollicis longus,
extensor pollicis brevis,
extensor pollicis longus and
extensor indicis.

3. SUPINATOR
The supinator, along with the brachialis muscle, forms the floor of the cubital fossa. The deep branch of the radial nerve lies between the two heads.
Attachments: It has two heads of origin. One originates from the lateral epicondyle of the humerus, the other from the posterior surface of the ulna.
They insert together into the posterior surface of the radius, just proximal to the attachment of the pronator teres muscle.
Actions: Supinates the forearm
Innervation: Radial Nerve

4. ABDUCTOR POLLICIS LONGUS
This muscle lies just distal to the supinator, on the lateral side of the forearm.
Attachments: Originates from the interosseous membrane and the adjacent posterior surfaces of the radius and ulna.
Attaches to the lateral side of the base of metacarpal I, contributing to the lateral border of the anatomical snuffbox
Actions: Abducts the thumb
Innervation: Radial Nerve

5. EXTENSOR POLLICIS BREVIS
The extensor pollicis brevis can be found medial and deep to the abductor pollicis longus.
Attachments: Originates from the posterior surface of the radius and interosseous membrane.
Attaches to the base of the proximal phalanx of the thumb.
Makes up most of the lateral border of the anatomical snuffbox
Actions: Extends the MCP and carpometacparal joints of the thumb
Innervation: Radial nerve

6. EXTENSOR POLLICIS LONGUS
The tendon of the extensor pollicis longus travels medial to the dorsal tubercle at the wrist (the extensor pollicis brevis and abductor pollicis longus travel laterally). This allows the muscle to use the tubercle as a trochlea, increasing its force.
Attachments: Originates from the posterior surface of the ulna and interosseous membrane.
Attaches to the distal phalanx of the thumb
Actions: Extends all joints of the thumb
Innervation: Radial Nerve

7. The tendon of the extensor pollicis longus lies in a groove on the medial aspect of the dorsal tubercle of the radius. Inferior to this, digital twigs of the superficial branch of the radial nerve can be felt crossing the tendon.

8. When the thumb is extended, a hollow known as the anatomical snuff-box appears between the tendon of the extensor pollicis longus medially and those of the extensor pollicis brevis and abductor pollicis longus laterally.
Its floor is formed by the scaphoid and trapezium bones and is crossed by the radial artery.
The hollow is limited superiorly by the styloid process of the radius.

9. EXTENSOR INDICIS
This muscles allows the index finger to be independant of the other fingers during extension.
Attachments: Originates from the posterior surface of the ulna and interosseous membrane, distal to the extensor pollicis longus. Attaches to the extensor hood of the index finger
Actions: Extends the index finger
Innervation: Radial Nerve

10. RADIAL NERVE
in the forearm, it branches into a superficial branch (primarily sensory) and a deep branch (primarily motor).

11. The superficial branch of the radial nerve descends in the forearm under the brachioradialis.
It crosses brachioradialis to enter posterior of forearm near the back of the wrist and supply dorsum of hand.
It gives nerve supply to dorsal aspect of thumb ,index finger,and radial side of middle finger except the nail beds,which are supplied by proper digital branches of median nerve.

12. The deep branch of the radial nerve has a muscular and articular distribution. It winds laterally between the superficial and deep layers of the supinator and often makes direct contact with the radius, being vulnerable in fractures.

13. At the lower border of the supinator, it meets the posterior interosseous vessels.
For the rest of its course, the deep branch of the radial nerve is then termed the posterior interosseous nerve, a name that is sometimes applied to the entire course of the deep branch.
The posterior interosseous nerve reaches the interosseous membrane distally and ends in an enlargement from which twigs are distributed to adjacent joints

14. The superficial branch of the radial nerve provides sensory innervation to much of the back of the hand, including the web of skin between the thumb and index finger.
The radial nerve (and its deep branch) provides motor innervation to the muscles in the posterior compartment of the arm and forearm, which are mostly extensors.

15. The superficial branch is the continuation of the radial nerve, and its distribution is cutaneous and articular.
It accompanies the radial artery, lying lateral to it, and then winds dorsally deep to the brachioradialis, to become subcutaneous and supply the lateral part of the dorsum of the hand.
Its terminal branches usually supply two and a half fingers but generally reach no further than the proximal phalanges of the index and middle fingers. (The dorsal innervation here is completed by digital branches of the median nerve.)
Several cutaneous branches of the radial nerve can be felt by stroking a fingernail down the taut tendon of the extensor pollicis longus

16. The radial nerve innervates the muscles that extend at the wrist, and these are paralysed. The flexor muscles are innervated by the median nerve, and are unaffected. The wrist undergoes unopposed flexion, and wristdrop results

17. ARTERIES OF POST.FASCIAL COMPARTMENT POST INTEROSSEOUS A.
It passes backward above the upper margin of the interosseous membrane between the radius and the ulna. It then pass down ward between the supinator and abductor pollicis longus and reach the interval betweenn the superficial and deep group of muscles .
Branches: 1-muscular branches 2-recurrent branch takes part in the anastomosis around the elbow. It ends by anastomosis with the ANTERIOR INTEROSSEIOUS arteryand taking part in the anastomosis around the wrist joint.

18. ANT. INTEROSSEOUS A.
It descend in the front of interosseous membrane and pierces it in the lower third of the membrane to reach the post.compartment