Binsol, Paula Danika
Small Group Discussion, No. 8
Gross Anatomy
Section A, Table 21
Posterior Forearm and Dorsum of the Hand
1. Discuss the skin, superficial fascia and cutaneous innervation of the forearm and
dorsum of the hand
Skin: innervated by the anterior and posterior branches of the lateral cutaneous nerve and the
anterior and posterior cutaneous nerves of the forearm. The skin in this area is vascular and is
sensitive to touch, pressure, pain, vibration and other similar sensory stimulation. The skin of
the dorsum of the hand is thin, hairy and freely mobile on the underlying tendons and bones. Its
sensory supply comes from the superficial branch of the radial nerve and the posterior
cutaneous branch of the ulnar nerve.
Fascia: the forearm is enclosed in a deep fascial sheath, which is attached to the periosteum of
the posterior subcutaneous border of the ulna. The interosseous membrane and fibrous
muscular septa divide the forearm into several compartments. In the superficial fascia of the
forearm, the superficial veins of the forearm—the cephalic and basilica veins—are present. In
the dorsal surface of the hand, the deep fascia thickens to form the flexor retinaculum and the
palmar aponeurosis.
2. Discuss the formation of the dorsal venous arch.
The dorsal venous arch is formed by the joining of the dorsal metacarpal veins lying in the
subcutaneous tissue. The dorsal venous arch also gives rise to the basilic and cephalic veins
and drains most of the region, including the interosseous spaces.
3. Discuss the muscles in the posterior compartment of the forearm as to its attachments,
innervation and action with demonstration.
Muscle Origin Insertion Nerve Supply Action
Posterior surface of
Extensor carpi Extends and abducts
the base of the third
radialis brevis hand at the wrist joint
metacarpal bone
Middle and distal
Extends fingers and
Extensor digitorum phalanges of the Deep branch of hands
medial four fingers radial nerve
Lateral epicondyle
Extends metacarpal
Extensor digiti of the humerus Extensor expansion
phalangeal joint of little
minimi of little finger
finger
Extensor carpi Base of fifth Extends and adducts
ulnarus metacarpal bone hand at wrist joint
Lateral surface of
Anconeous olecranon process Radial nerve Extends elbow joint
of the ulna
Lateral epicondyle
of the humerus,
Neck and shaft of
Supinator anular ligament of Supination of forearm
the radius
proximal radioulnar
joint and ulna
Posterior surface of
Abductor pollicis Base of first Abducts and extends
shafts of radius and
longus metacarpal bone thumb
ulna Deep branch of the
Base of proximal radial nerve Extends
Extensor pollicis Posterior surface of
phalanx of the metacarpophalangeal
brevis shafts of the radius
thumb joints of the thumb
Base of distal
Extensor pollicis Extends distal phalanx of
phalanx of the
longus Posterior surface of the thumb
thumb
shaft of the radius
Extensor expansion Extends index finger
Extensor indicis
of the middle finger metacarpophalangeal joint
4. Discuss the radial nerve and its branches in the forearm up to its terminal branches in
the hand.
The radial nerve pierces the lateral intermuscular septum in the lower part of the arm and
passes forward into the cubital fossa. As it passes downward in front of the lateral epicondyle of
the humerus, it lies between the brachialis and the brachioradialis and the extensor carpi
radialis longus laterally. At the lateral epicondyle, it divides into superficial and deep branches.
The muscular branches innervate the brachioradialis to the extensor carpi radialis longus and a
small branch goes to the lateral part of the brachialis muscle. The articular branches supply the
elbow joint. The deep branch of the radial nerve winds around the neck of the radius and within
the supinator muscle and enters the posterior compartment of the forearm. The superficial
branch of the radial nerve passes backward under the tendon of the brachioradialis and divides
into the terminal branches that supply the skin on the lateral two thirds of the posterior surface
of the hand and the posterior surface of the phalanges of the lateral three and a half fingers at
the posterior surface of the wrist.
5. Discuss the extensor retinaculum and the structures passing through it.
The extensor retinaculum is a thickening of deep fascia; it stretches across the back of the wrist
and holds the long extensor tendons in position. It converts the grooves on the posterior surface
of the distal ends of radius and ulna into six separate tunnels for the long extensor tendons.
Tunnels are separated from one another by fibrous septa that pass from the deep surface of the
retinaculum to the bones. It is attached medially to the pisiform bone and the hook of the
hamate and laterally to the distal end of the radius. The upper and lower borders are continuous
with the deep fascia of the forearm and hand. From medial to lateral: extensor carpi ulnaris
tendon, extensor digiti minimi tendon, extensor digitorum and extensor indicis tendons, extensor
pollicis longus tendon, extensor carpi radialis longus and brevis tendons, abductor pollicis
longus and the extensor pollicis brevis tendons.
6. Discuss the extensor expansion and its significance.
The extensor expansion is the point on the posterior surface of each finger where the extensor
tendon joins the fascial expansion. The extensor expansion splits into three parts: a central part
and two lateral parts; all converge to insert into the base of the distal phalanx. The dorsal
extensor expansion receives the tendon of the insertion of the corresponding interosseous
muscle on each side and farther distally receives tendons of the lumbrical muscles on the lateral
sides. These extensor expansions play a crucial role in coordinating movement between the
proximal and distal interphalangeal joints.
7. Discuss the anatomical snuffbox and its significance.
The anatomical snuffbox is a triangular depression in the lateral aspect of the dorsum of the
hand. It has three boundaries: Ulnar (medial) border: Tendon of the extensor pollicis longus.
Radial (lateral) border: Tendons of the abductor pollicis longus and extensor pollicis brevis.
Proximal border: Styloid process of the radius. Floor: Carpal bones; scaphoid and trapezium.
Roof: Skin. Its main contents include the radial artery, a branch of the radial nerve and the
cephalic vein. The radial pulse can be palpated in the proximal portion of this space in some
individuals.
