of the Arm
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of the pectoral, back and shoulder regions | Main Anatomy Index | The cubital fossa
Last updated 30 March 2006
Muscles of the Arm
- There are four muscles
in the arm: three flexors
in the anterior fascial compartment supplied by the musculocutaneous
nerve and one extensor
supplied by the radial
- The anconeus muscle is located chiefly in the forearm,
but it is described with the brachial muscles because it
is morphologically and functionally related to the triceps brachii muscle.
The Biceps Brachii Muscle (pp. 539, 541)
- As its name "biceps" indicates, the proximal
attachment of this long fusiform muscle has two heads (bi, two + cipital,
from L. caput, head).
- The two bellies of the muscle unite just distal to the
middle of the arm.
- The biceps is located in the anterior aspect of the arm
in the anterior fascial compartment.
- Proximal attachments are: short
head-tip of coracoid process of scapula; long head-supraglenoid
tubercle of scapula.
- Distal attachments are: tuberosity of radius and fascia
of forearm via bicipital aponeurosis.
- Innervation: musculocutaneous nerve (C5 and C6).
- When the elbow is extended, the biceps is a simple flexor of the forearm.
- It is also a powerful supinator
when the forearm is flexed and when more power is needed
- The biceps barely operates at all during flexion of the
- The tendon of the long head of biceps crosses the head of
the humerus within the capsule of the shoulder joint and
descends in the intertubercular
groove of the humerus.
- The bicipital aponeurosis
is a triangular membranous band that runs from the biceps
tendon across the cubital fossa and merges with the deep
fascia over the flexor muscles in the medial side of the
- The proximal part of the bicipital aponeurosis can be
easily felt where it passes obliquely over the brachial artery and
- This aponeurosis affords protection for these and other
structures in the cubital fossa. It also helps to lessen
the pressure of the biceps tendon on the radial
tuberosity during pronation and supination of the
Injuries involving the Biceps Brachii
- Sometimes the tendon of the long head biceps brachii is
dislocated from the intertubercular groove in the
- This may occur during traumatic separation of the
proximal epiphysis of the humerus.
- When this occurs, the arm is fixed in the abducted
position and the head of the humerus can be felt in its
Brachialis Muscle (p. 541)
- This is a flattened, fusiform muscle that lies posterior
to the biceps brachii.
- Proximal attachments are: distal half of anterior surface
- Distal attachments are: coronoid process and tuberosity
- Innervation: musculocutaneous nerve (C5 and C6)
- The strong brachialis is the main
flexor of the forearm. It flexed the forearm
in all positions and in slow or quick movements.
- When the forearm is being extended slowly, the brachialis
steadies the movement by slowly relaxing.
- It always contracts during flexion of the elbow joint and
is primarily responsible for maintaining flexion. Because
of this, it is the workhorse among
the flexor muscles if the elbow joint.
The Coracobrachialis Muscle (p. 541)
- This is an elongated, narrow muscle in the superomedial
part of the arm and is important mainly as a landmark
(e.g., the musculocutaneous
nerve pierces it).
- Proximal attachments are: tip of coracoid process of
- Distal attachments are: middle third of medial surface of
- Innervation: musculocutaneous nerve (C5, C6, and
- The coracobrachialis helps to flex
and adduct the arm at the shoulder joint. It
also helps to stabilise this joint.
The Triceps Brachii Muscle (p. 541)
- This is a large, fusiform muscle and is located in the
posterior fascial compartment of the arm.
- It is associated with the small
anconeus muscle at the elbow.
- As its name "triceps" indicates, it has three
heads of proximal attachment: long, lateral, and medial.
- Proximal attachments are: long head-infraglenoid
tubercle of scapula; lateral head-posterior
surface of humerus, superior (and lateral) to the radial
groove; medial head-posterior
surface of humerus, inferior (and medial) to the radial
- Distal attachments are: proximal end of olecranon and
superior part of posterior surface of ulna.
- Innervation: radial nerve (C6, C7, and C8)
- The triceps is the main extensor or
- Because the long head of the triceps crosses the shoulder
joint, it also aids in extension
and adduction of the arm.
- Its long head also steadies the head of the abducted
Anconeus Muscle (p. 547)
- This is a small triangular muscle and is on the lateral
part of the posterior aspect of the elbow.
- It is usual blended with the triceps and should be
considered part of the medial head of this muscle.
- Proximal attachments are: lateral epicondyle of the
- Distal attachments are: lateral surface of olecranon and
superior part of posterior surface of ulna.
- Innervation: radial nerve (C7, C8, and T1)
- It helps the triceps to extend the forearm. It also abducts the ulna during pronation of
forearm and contracts whenever this joint
needs to be stabilised against flexion.