This document describes the muscles of the forearm, which are divided into anterior and posterior compartments separated by septa. The anterior compartment contains flexor muscles in superficial, intermediate, and deep layers. The posterior compartment contains extensor muscles in superficial and deep layers. Key muscles are described in each layer, including their origins, insertions, innervation and functions. The document provides an anatomical overview of the major muscles of the forearm.

1. FOREARM MUSCLES
The muscles of the anterior of the forearm
The muscles of the posterior of the forearm

2. The forearm
• The forearm is divided into anterior and posterior
compartments.
• In the forearm, both compartments are separated by:
– A lateral intermuscular septum, which passes from the
anterior border of the radius to deep fascia surrounding
the limb.
– By an interosseous membrane, which links adjacent
borders of the radius and ulna along most of their
length.
– The attachment of deep fascia along the posterior
border of the ulna.

8. ANTERIOR COMPARTMENT OF THE
FOREARM
• Muscles in the anterior (flexor) compartment of the
forearm are in three layers:
– Superficial ,
– Intermediate ,
– Deep .
• Generally, these muscles are associated with:
– Movements of the wrist joint;
– Flexion of the fingers including the thumb;
– Pronation .
• All muscles in the anterior compartment of the forearm are
innervated by the median nerve, except for the flexor carpi ulnaris
muscle and the medial half of the flexor digitorum profundus
muscle, which are innervated by the ulnar nerve.

9. Anterior compartment of the forearm
.
• The five muscles of the superficial group cross
the elbow joint; the three muscles of the deep
group do not.
• The flexor compartment is much more bulky
than the extensor compartment, for the
necessary power of the grip.

10. SUPERFICIAL MUSCLES OF THE FRONT OF THE FOREARM

11. SUPERFICIAL MUSCLES OF THE FRONT OF THE FOREARM

12. Five superficial muscles
With the heel of the hand placed over the opposite
medial epicondyle, palm lying on the forearm, the
digits point down along the five superficial muscles:
• Thumb for pronator teres;
• Index for flexor carpi radialis;
• Middle finger for flexor digitorum superficialis;
• Ring finger for palmaris longus; and
• Little finger for flexor carpi ulnaris.

13. Five superficial muscles
• These five muscles are distinguished by the fact
that they possess a common origin from the medial
epicondyle of the humerus.
• Three of the group have additional areas of origin.
• The common origin is attached to a smooth area
on the anterior surface of the medial epicondyle.

15. PRONATOR TERES
• Pronator teres is smallest and
most lateral of the shallow flexors
of the forearm.
• It forms the medial boundary of
the cubital fossa.

19. ANTERIOR COMPARTMENT OF THE FOREARM
Muscle Origin Insertion Innervation Function
Flexor carpi ulnaris Humeral head-medial
epicondyle of humerus; ulnar
head-olecranon and posterior
border of ulna
Pisiform bone, and then via
pisohamate and
pisometacarpal ligaments
into the hamate and base of
metacarpal V
Ulnar nerve [C7,C8, T1] Flexes and adducts the wrist
joint
Palmaris longus Medial epicondyle of
humerus
Palmar aponeurosis of hand Median nerve [C7,C8] Flexes wrist joint; because
the palmar aponeurosis
anchors skin of the hand,
contraction of the muscle
resists shearing forces when
gripping
Flexor carpi radialis Medial epicondyle of
humerus
Base of metacarpals II and
III
Median nerve [C6,C7] Pronation
Pronator teres Humeral head-medial
epicondyle and adjacent
supraepicondylar ridge; ulnar
head-medial side of coronoid
process
Roughening on lateral
surface, mid-shaft, of radius
Median nerve [C6,C7] Flexes and abducts the wrist

20. Palmaris longus
• Morphologically, palmaris longus is a deteriorating
muscle with small short belly and a long tendon.
The palmar aponeurosis expresses the distal part of
the tendon of palmaris longus.
– The palmaris longus corresponds to the plantaris
muscle on the back of the leg.
– It is missing on one or both sides (usually on the left) in
approximately 10% of people, but its actions are not
overlooked. Hence, its tendon is often used by the
surgeons for tendon grafting.

21. The flexor carpi ulnaris
• The flexor carpi ulnaris (FCU) is
most medial of the shallow
flexors of the forearm

23. Intermediate layer of muscles in the
anterior compartment of the forearm
Muscle Origin Insertion Innervation Function
Flexor digitorum
superficialis
Humero-ulnar head-medial epicondyle
of humerus and adjacent margin of
coronoid process; radial head- oblique
line of radius
Four tendons, which attach
to the palmar surfaces of the
middle phalanges of the
index, middle, ring, and little
fingers
Median nerve [C8,T1] Flexes proximal interphalangeal
joints of the index, middle, ring,
and little fingers; can also flex
metacarpophalangeal joints of the
same fingers and the wrist joint
The flexor digitorum superficialis (FDS) is the biggest muscle of the
superficial group of muscles on the front of the forearm. Effectively
speaking, it develops the intermediate muscle layer between the
superficial and deep groups of the forearm muscles.

25. Deep layer of muscles in the anterior
compartment of the forearm
Muscle Origin Insertion Innervation Function
Flexor digitorum
profundus
Anterior and medial
surfaces of ulna and
anterior medial half
of interosseous
membrane
Four tendons, which
attach to the palmar
surfaces of the distal
phalanges of the
index, middle, ring,
and little fingers
Lateral half by
median nerve
(anterior
interosseous nerve);
medial half by ulnar
nerve [C8,T1]
Flexes distal
interphalangeal
joints of the index,
middle, ring, and
little fingers; can
also flex
metacarpophalange
al joints of the same
fingers and the wrist
joint
Flexor pollicis longus Anterior surface of
radius and radial half
of inter-osseous
membrane
Palmar surface of
base of distal
phalanx of thumb
Median nerve
(anterior
interosseous nerve)
[C7,C8]
Flexes
interphalangeal joint
of the thumb; can
also flex metacarpo-
phalangeal joint of
the thumb
Pronator quadratus Linear ridge on distal
anterior surface of
ulna
Distal anterior
surface of radius
Median nerve
(anterior
interosseous nerve)
[C7,C8]
Pronation

26. Space of Parona
• In front of pronator quadratus there is a space (of
Parona) deep to the long flexor tendons of the fingers
and their synovial sheaths.
• The space is limited proximally by the oblique origin of
flexor digitorum superficialis.
The space becomes involved in proximal extensions of
synovial sheath infections; it can be drained through radial
and ulnar incisions to the side of the flexor tendons.

27. Flexor digitorum profundus
• It is most powerful and large muscle of the forearm.
• It has double innervation by median and ulnar
nerves.
• It offers most of the gripping power to hand.
• It forms four tendons which go into the hand by
passing deep to flexor retinaculum, posterior to the
tendons of FDS in a common synovial sheath– ulnar
bursa.
• It forms most of the surface elevation medial to the
palpable posterior border of the ulna.
• It supplies origin to the lumbrical muscles in the
palm.

28. Deep layer of muscles in the anterior compartment of the forearm

29. POSTERIOR COMPARTMENT OF THE
FOREARM
• Muscles in the posterior compartment of the
forearm occur in two layers:
– A superficial and
– A deep layer.
• The muscles are associated with:
– Movement of the wrist joint;
– Extension of the fingers and thumb;
– Supination .
• All muscles in the posterior compartment of the
forearm are innervated by the radial nerve.

31. POSTERIOR COMPARTMENT OF THE
FOREARM
At the upper part are anconeus (superficial) and supinator (deep).
From the lateral part of the humerus arise three muscles that pass along the radial
Side:
– Brachioradialis ,
– Extensors carpi radialis longus
– Extensors carpi radialis brevis),
Three that pass along the posterior surface of the forearm
– Extensors digitorum,
– Digiti minimi and
– Carpi ulnaris.
At the lower end of the forearm these two groups are separated by three muscles
that emerge from deeply in between them and go to the thumb
– Abductor pollicis longus
– Extensors pollicis longus and
– Extensors pollicis longus brevis.
Finally, one muscle for the forefinger runs deeply to reach the back of the hand:
– Extensor indicis.

34. SUPERFICIAL MUSCLES OF THE BACK
OF FOREARM
• The superficial muscles of the back of forearm
are seven in number.
• From lateral to medial these are:
1. Brachioradialis.
2. Extensor carpi radialis longus (ECRL).
3. Extensor carpi radialis brevis (ECRB).
4. Extensor digitorum (ED).
5. Extensor digiti minimi (EDM).
6. Extensor carpi ulnaris (ECU).
7. Anconeus.

35. SUPERFICIAL MUSCLES OF THE BACK
OF FOREARM
• The superficial muscles of the back of the forearm are further
categorized into two groups: lateral and posterior. Each group
consists of three muscles:
• Lateral group of superficial extensors
1. Brachioradialis.
2. Extensor carpi radialis longus.
3. Extensor carpi radialis brevis.
• Posterior group of superficial extensors
4. Extensor digitorum.
5. Extensor digiti minimi.
6. Extensor carpi ulnaris.
7. Anconeus.

36. SUPERFICIAL MUSCLES OF THE BACK
OF FOREARM
• Tendon from the tip of lateral epicondyle of
the humerus (known as common extensor
origin) commonly give origin to four of the
superficial muscles
– Extensor carpi radialis brevis,
– Extensor digitorum,
– Extensor digiti minimi, and
– Extensor carpi ulnaris).
• All the seven muscles cross the elbow joint.

37. SUPERFICIAL MUSCLES OF THE BACK OF FOREARM

38. Superficial layer of muscles in the
posterior compartment of the forearm
Muscle Origin Insertion Innervation Function
Brachioradialis Proximal part of
lateral
supraepicondylar
ridge of humerus
and adjacent inter-
muscular septum
Lateral surface of
distal end of radius
Radial nerve [C5,C6]
before division into
superficial and deep
branches
Accessory flexor of
elbow joint when
forearm is mid-
pronated
Extensor carpi
radialis longus
Distal part of lateral
supraepicondylar
ridge of humerus
and adjacent
intermuscular
septum
Dorsal surface of
base of metacarpal II
Radial nerve [C6,C7]
before division into
superficial and deep
branches
Extends and abducts
the wrist
Extensor carpi
radialis brevis
Lateral epicondyle of
humerus and
adjacent
intermuscular
septum
Dorsal surface of
base of metacarpals
II and III
Deep branch of
radial nerve [C7,C8]
before penetrating
supinator muscle
Extends and abducts
the wrist
CONTINUED

39. Superficial layer of muscles in the posterior compartment of the
forearmExtensor digitorum Lateral epicondyle
of humerus and
adjacent
intermuscular
septum and deep
fascia
Four tendons, which
insert via 'extensor
hoods' into the
dorsal aspects of
the bases of the
middle and distal
phalanges of the
index, middle, ring,
and little fingers
Posterior
interosseous nerve
[C7,C8]
Extends the index,
middle, ring, and
little fingers; can
also extend the
wrist
Extensor digiti
minimi
Lateral epicondyle of
humerus and
adjacent
intermuscular
septum together
with extensor
digitorum
Dorsal hood of the
little finger
Posterior
interosseous nerve
[C7,C8]
Extends the little
finger
Extensor carpi
ulnaris
Lateral epicondyle of
humerus and
posterior border of
ulna
Tubercle on the base
of the medial side of
metacarpal V
Posterior
interosseous nerve
[C7,C8]
Extends and adducts
the wrist
Anconeus Lateral epicondyle of
humerus
Olecranon and
proximal posterior
surface of ulna
Radial nerve [C6 to
C8] (via branch to
medial head of
triceps brachii)
Abduction of the
ulna in pronation;
accessory extensor
of the elbow joint

40. Deep layer of muscles in the posterior compartment of the forearm

41. Deep layer of muscles in the posterior compartment
of the forearm
Muscle Origin Insertion Innervation Function
Supinator Superficial part-lateral
epicondyle of humerus, radial
collateral and anular ligaments;
deep part-supinator crest of
the ulna
Lateral surface of radius
superior to the anterior
oblique line
Posterior interosseous
nerve [C6,C7]
Supination
Abductor pollicis longus Posterior surfaces of ulna and
radius (distal to the
attachments of supinator and
anconeus), and intervening
interosseous membrane
Lateral side of base of
metacarpal I
Posterior interosseous
nerve [C7,C8]
Abducts carpometacarpal
joint of thumb; accessory
extensor of the thumb
Extensor pollicis brevis Posterior surface of radius
(distal to abductor pollicis
longus) and the adjacent
interosseous membrane
Dorsal surface of base of
proximal phalanx of the
thumb
Posterior interosseous
nerve [C7,C8]
Extends
metacarpophalangeal joint
of the thumb; can also
extend the
carpometacarpal joint of
the thumb
Extensor pollicis longus Posterior surface of ulna (distal
to the abductor pollicis longus)
and the adjacent interosseous
membrane
Dorsal surface of base of
distal phalanx of thumb
Posterior interosseous
nerve [C7,C8]
Extends interphalangeal
joint of the thumb; can also
extend carpometacarpal
and metacarpophalangeal
joints of the thumb
Extensor indicis Posterior suface of ulna (distal
to extensor pollicis longus) and
adjacent interosseous
membrane
Extensor hood of index
finger
Posterior interosseous
nerve [C7,C8]
Extends index finger

42. DEEP MUSCLES OF THE BACK OF FOREARM
• There are five deep muscles of the back of forearm, from
above these are:
1. Supinator.
2. Abductor pollicis longus(APL).
3. Extensor pollicis brevis (EPB).
4. Extensor pollicis longus (EPL).
5. Extensor indicis.
• The three deep extensors of the forearm, which function on
thumb (abductor pollicis longus, extensor pollicis brevis, and
extensor pollicis longus) are located deep to the superficial
extensors and in order to acquire insertion on the three
bones of thumb crop out e erge fro the furrow i the
lateral element of the forearm between lateral and posterior
groups of superficial extensor. These three muscles are
therefore called outcropping muscles.

43. Clinical Relevance: Wrist Drop
• Wrist drop is a sign of radial nerve injury that has occurred
proximal to the elbow.
• There are two common characteristic sites of damage:
• Axilla – injured via humeral dislocations or fractures of the
proximal humerus.
• Radial groove of the humerus – injured via a humeral shaft
fracture.
• The radial nerve innervates all muscles in the extensor
compartment of the forearm. In the event of a radial nerve
lesion, these muscles are paralysed. The muscles that flex
the wrist are innervated by the median nerve, and thus are
unaffected. The tone of the flexor muscles produces
unopposed flexion at the wrist joint – wrist drop.