Human Anatomy Vol 1

Supinator

Abductor pollicis

longus

Extensor pollicis

longus

Extensor pollicis brevis

Extensor indicis

Fig. 9.58: The origin of the five deep muscles of the back of the
forearm from the posterior aspects of the radius and ulna

FOREARM AND HAND

slips. The central slip is joined by some fibres from the

margins of the expansion, crosses the proximal

interphalangeal joint, and is inserted on the dorsum of

the base of the middle phalanx. The two collateral slips

are joinedby the remaining thick margin of the extensor

expansion. They then join each other and are inserted

on the dorsum of the base of the distal phalanx.

At the metacarpophalangeal and interphalangeal

joints the extensor expansion forms the dorsal part of

the fibrous capsule of the joints.

The retinacular ligaments (link ligaments) extend

from the side of the proximal phalanx, and form its

fibrous flexor sheath, to the margins of the extensor

expansion to reach the base of the distal phalanx

(Fig. e.5e).

The muscles inserted into the dorsal digital expansions of:

lndex finger; First dorsal interosseous, second palmar

interosseous, first lumbrical, extensor digitorum slip,

and extensor indicis.

Middlefinger; Second and third dorsal interossei, second

lumbrical, extensor digitorum slip.

Ring finger: Fourth dorsal interosseous, third palmar

interosseous, third lumbrical and extensor digitorum

slip.

Little finger: Fourth palmar interosseous, fourth

lumbrical, extensor digitorum slip and extensor digiti

minimi.

Muscle

1. Supinator (Fig. 9.4)


2. Abductor pollicis longus (Fig.9.58)


3. Extensor pollicis brevis


4. Extensor pollicis longus


5. Extensor indicis

Origin

Lateral epicondyle of humerus, annular

ligament of superior radioulnar joint,

supinator crest of ulna and depression

behind it

Posterior sufface of shafts of radius and ulna

Posterior sudace of shaft of radius

Posterior suriace of shaft of ulna

Posterior sudace of shaft of ulna

lnsertion

Neck and whole shaft of upper 1/3rd

of radius

Base of first metacarpal bone

Base of proximal phalanx of thumb

Base of distal phalanx of thumb

Extensor expansion of index finger

1. Supinator (Fig. 9.4)


2. Abductor pollicis longus (Fig.9.58)


3. Extensor pollicis brevis


4. Extensor pollicis longus


5. Extensor indicis

Nerve supply

Deep branch of radial nerve

Deep branch of radial nerve

Deep branch of radial nerve

Deep branch of radial nerve

Deep branch of radial nerve

Actions

Supination of forearm when elbow is extended

Abducts and extends thumb

Extends metacarpophalangeal joint of thumb

Extends distal phalanx of thumb

Extends metacarpophalangeal joint of index finger

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