1. Antebrachium Extensors

2. Extensor retinaculum
thick fibrous fascia band at wrist -holds forearm tendons in place
from lateral radius to medial ulna (styloid process), triquetrum & pisiform bones

4. Extensor Canals six osteofibrous canals: post side of bones
extensor tendons pass through to dorsal hand

6. Extensor Canals
a. abductor pollicis longus, \ extensor pollicis brevis / in #1: most lateral
b. extensor carpi radialis longus \ extensor carpi radialis brevis / in #2
c. extensor pollicis longus - in #3
d. extensor digitorum \ extensor indicis / in #4
e. extensor digiti minimi - in #5
f. extensor carpi ulnaris - in #6

7. Anatomical snuff box
depression on dorsolateral wrist bounded by tendons of:
abductor pollicis longus, extensor pollicis brevis & extensor pollicis longus (where the scaphoid bone lies in the floor here, most likely be fractured, local tenderness, death & absorption of the bone later)

10. Muscles Muscles 3 Functional groups + brachioradialis & supinator
i) extend hand at wrist = the 3 extensor carpi's - radialis longus & brevis; & ulnaris
ii) extend medial 4 digits (fingers) = extensors digitorum; indicis; digiti minimi
iii) extend thumb (1st digit) = abductor pollicis longus; extensor pollicis longus & brevis

11. Muscles Extensor are arranged in three anatomical layers
Superficial layer
brachioradialis
extensor carpi radialis longus
extensor carpi radialis brevis
extensor digitorum
extensor digiti minimi
extensor carpi ulnaris

13. BRACHIORADIALIS
ORIGIN proximal two thirds of lateral supracondylar ridge of humerus, and lateral intermuscular septum
INSERTION lateral side of base of styloid process of radius
ACTION flex the elbow joint, and assists in pronating and supinating the forearm when these movements are resisted
NERVE radial nerve C5, C6

14. EXTENSOR CARPI RADIALIS LONGUS
ORIGIN Distal one third of lateral supracondylar ridge of humerus, and lateral intermuscular septum
INSERTION dorsal surface of base of second metacarpal bone, radial side
ACTION extends and abducts the wrist, and assists in flexion of the elbow
NERVE radial nerve C5, C6, 7, 8

15. EXTENSOR CARPI RADIALIS BREVIS
ORIGIN common extensor tendon from lateral epicondyle of humerus, radial collateral ligament of elbow joint, and deep antebrachial fascia
INSERTION dorsal surface of base of third metacarpal bone
ACTION extends and assists in abduction of the wrist
NERVE radial C6, 7, 8

16. EXTENSOR DIGITORUM
ORIGIN Common extensor tendon fromlateral epicondyle of humerus, and deep antebrachial fascia
INSERTION By four tendons, each penetrating a membranous expansion on the dorsum of the second to fifth digits and dividing over the proximal phalanx into medial and two lateral bands. The medial band inserts into the base of the middle phalanx while the lateral bands reunite over the middle phalanx and insert into the base of the distal phalanx.
ACTION Extends the metacarpophalangeal and, in conjunction with the lumbricals and interossei, extends the interphalangeal joints of the second through fifth digits. Assists in abduction of the index, ring, and little fingers; and assists in extension and abducting of the wrist.
NERVE Radial nerve, C6, 7, 8

17. EXTENSOR DIGITI MINIMI
ORIGIN Common extensor tendon from lateral epicondyle of humerus, and deep antebrachial fascia
INSERTION Into extensor expansion of little finger with extensor digitorum tendon
ACTION Extends the metacarpophalangeal joint and, in conjunction with lumbricals interosseus, extends the interphalangeal joints of the little finger. Assists in abduction of the little finger
NERVE radial nerve C6, 7, C8

18. EXTENSOR CARPI ULNARIS
ORIGIN Common extensor tendon fromlateral epicondyle of humerus, by aponeurosis from posterior border of ulna, and deep antebrachial fascia
INSERTION base of fifth metacarpal bone, ulnar side
ACTION extends and adducts the wrist
NERVE radial nerve C6, 7, C8  

19. Deep layer Supinator abductor pollicis longus extensor pollicis brevis
extensor pollicis longus
extensor indicis

21. SUPINATOR
ORIGIN Lateral epicondyle of humerus, radial collateral ligament of elbow joint, annular ligament of radius, and superior crest of ulna
INSERTION Lateral surface of upper one third of body of radius covering part of anterior and posterior surfaces
ACTION supinates the forearm
NERVE radial nerve C5, C6, C(7)

23. ABDUCTOR POLLICIS LONGUS
ORIGIN posterior surface of body of ulna distal to origin of supinator, interosseus membrane, and posterior surface of middle one third of body of radius
INSERTION base of first metacarpal bone, radial side
ACTION Abducts and extends the carpometacarpal joints of the thumb; abducts (radial deviation) and assists in flexion the wrist
NERVE Radial nerve C6, 7, C8

24. EXTENSOR POLLICIS BREVIS
ORIGIN Posterior surface of body of radius distal to origin of abductor pollicis longus, and interosseus membrane
INSERTION Base of proximal phalanx of thumb, dorsal surface
ACTION Extends the metacarpophalangeal joint of the thumb, extends and abducts the carpometacarpal joint, and assists in abduction (radial deviation) of the wrist
NERVE Radial nerve C6, 7, C8 

25. EXTENSOR POLLICIS LONGUS
ORIGIN Middle one third of posterior surface of ulna distal to origin of abductor pollicis longus, and interosseus membrane
INSERTION Base of distal phalanx of thumb, dorsal surface
ACTION Extends the interphalangeal joint and assists in extension of the metacarpophalangeal and carpometacarpal joints of the thumb. Assists in abduction and extension of the wrist.
NERVE Radial nerve, C6,  C7, C8 

26. EXTENSOR INDICIS
ORIGIN posterior surface of body of ulna distal to origin of extensor pollcis longus, and interosseus membrane.
INSERTION Into extensor expansion of index finger with extensor digitorium longus tendon
ACTION Extends the metacarpophalangeal joint and, in conjunction with the  lumbricals and interossei, extends the interphalangeal joints of the index finger. May assist in adduction of the finger
NERVE Radial nerve C6, 7, C8