The Hand

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Muscles of the forearm | Main Anatomy Index | The anatomical snuff-box

Last updated 30 March 2006

The Hand

The hand (L. manus) forms the distal part of the upper limb.
It contains the metacarpal bones and the phalanges.

Fascia of the Palm (p. 595)

The deep fascia of the palm is continuous proximally with the antebrachial fascia (fascia of the forearm) and at the borders of the palm, with the fascia on the dorsum of the hand.
The fascia is thin over the thenar and hypothenar eminences, but it is thick in the palm where if forms the palmar aponeurosis.
The fascia in the digits forms the fibrous digital sheaths.

The Palmar Aponeurosis (p. 595)

This is a strong, well-defined, triangular part of the deep fascia of the hand.
It covers the soft tissues and overlies the long flexor tendons of the palm.

The proximal end of the palmar aponeurosis is continuous with the flexor retinaculum and the tendon of the palmaris longus muscle.

The distal end of the aponeurosis divides at the roots of the digits into 4 longitudinal bands.
Each band is attached to the base of the proximal phalanx and is fused with the fibrous digital sheath.

Muscles of the Hand

The intrinsic muscles of the hand are on the palmar aspect and are innervated by branches of the ulnar and median nerves.

They can be divided into 3 groups: (1) the thumb or thenar muscles in the thenar compartment; (2) the little finger or hypothenar muscles in the hypothenar compartment; and (3) the lumbrical muscles in the central compartment and the interosseous muscles between the metacarpal bones.

The long flexor tendons of the extrinsic muscles of the hand, arise in the forearm and pass to the digits.
These are located in the central compartment with the lumbrical muscles.

The Thenar Muscles

These muscles (abductor pollicis brevis, flexor pollicis brevis, and opponens pollicis) produce the thenar eminence.

They are chiefly responsible for the movement known as the opposition of the thumb.
The pressure that the opposed thumb can exert on a fingertip is enhanced by the reinforcing action of the adductor pollicis and flexor pollicis longus muscles.

The thenar muscles are supplied by the recurrent branch of the median nerve.

The Abductor Pollicis Brevis Muscle (p. 597)

This is a thin, short, and relatively broad muscle.
It forms the anterolateral part of the thenar eminence.

Proximal attachments are: flexor retinaculum and the tubercles of the scaphoid and trapezium bones.
Distal attachments are: lateral side of the base of the proximal phalanx of the thumb.
Innervation: recurrent branch of median nerve (C8 and T1).

It abducts the thumb at the carpometacarpal joint and assists the opponens pollicis muscle during the early stages of opposition by rotating the proximal phalanx slightly medially.

The Flexor Pollicis Brevis Muscle (p. 597)

This is a short, wide fusiform muscle.
It is located medial to the abductor pollicis brevis.

Proximal attachments are: flexor retinaculum and tubercle of the trapezium bone.
Distal attachments are: lateral side of the base of the proximal phalanx of the thumb.
Innervation: recurrent branch of the median nerve (C8 and T1).

It flexes the thumb at the carpometacarpal and metacarpophalangeal joints and aids in opposition of the thumb.

The Opponens Pollicis Muscle (p. 597)

This is a quadrangular muscle that lies deep to the abductor pollicis brevis and lateral to the flexor pollicis brevis.

Proximal attachments are: flexor retinaculum and the tubercle of the trapezium bone.
Distal attachments are: lateral side of the 1^st metacarpal bone.
Innervation: recurrent branch of the median nerve (C8 and T1).

It opposes the thumb.
The tip of the thumb is brought in contact with the palmar surface of the 5^th digit.
The thumb can also be opposed to other digits.
Opposition is the most important movement of the thumb.
It involves extension initially, then abduction, flexion, medial rotation, and usually adduction.

The Adductor Pollicis Muscle (p. 599)

This is a fan-shaped muscle and is located in the adductor compartment of the hand.
It has 2 heads that are separated by a gap through which the radial artery passes.

Proximal attachments are: oblique head-bases of the 2^nd and 3^rd metacarpals, the capitate and adjacent carpal bones, transverse head-anterior surface of the body of the 3^rd metacarpal bone.
Distal attachments are: medial side of the base of the proximal phalanx of the thumb.
Innervation: the deep branch of the ulnar nerve (C8 and T1).

It adducts the thumb and gives power to the grasp.

Hypothenar Muscles

These muscles deal with the movement of the 5^th digit.
They lie in the hypothenar compartment of the palm with the 5th metacarpal bone.

The hypothenar muscles produce the hypothenar eminence, or ball of the 5^th digit.
They are all supplied by the deep branch of the ulnar nerve.

The Abductor Digiti Minimi Muscle (p. 600)

This is a short, wide, fusiform muscle.
It is the most superficial of the three muscles forming the hypothenar eminence.

Proximal attachments are: pisiform bone.
Distal attachments are: medial side of the base of the proximal phalanx of the 5^th digit.
Innervation: deep branch of the ulnar nerve (C8 and T1).

It abducts the 5^th digit and helps to flex the proximal phalanx.

The Flexor Digiti Minimi Brevis Muscle (p. 600)

This is a short, wide, fusiform muscle that is variable in size.
It lies lateral to the abductor digiti minimi muscle.

Proximal attachments are: hook of the hamate bone and the flexor retinaculum.
Distal attachments are: medial side of the base of the proximal phalanx of the 5^th digit.
Innervation: deep branch of the ulnar nerve (C8 and T1).

It flexes the proximal phalanx of the 5^th digit at the metacarpophalangeal joint.

The Opponens Digiti Minimi Muscle (p. 600)

This is a quadrangular muscle and it lies deep to the abductor and flexor muscles of the 5^th digit.

Proximal attachments are: hook of the hamate bone and the flexor retinaculum.
Distal attachments are: medial border of the 5^th metacarpal bone.
Innervation: deep branch of the ulnar nerve (C8 and T1).

It draws the 5^th metacarpal bone anterior and rotates it laterally, thereby deepening the hollow of the palm, and bringing the 5^th digit into opposition with the thumb.

The Lumbrical Muscles (p. 600)

There are 4 slender lumbrical (L. lumbricus, earthworm) muscles-one for each digit.

Lumbricals 1 and 2

Proximal attachments are: lateral two tendons of flexor digitorum profundus.
Distal attachments are: lateral sides of extensor expansions of the 2^nd and 3^rd digits.
Innervation: median nerve (C8 and T1).

Lumbricals 3 and 4

Proximal attachments are: medial three tendons of flexor digitorum profundus.
Distal attachments are: lateral sides of extensor expansions of the 4^th and 5^th digits.
Innervation: deep branch of the ulnar nerve (C8 and T1).

The lumbrical muscles flex the digits at the metacarpophalangeal joints and extend the interphalangeal joints.
They place the digits into the writing position.

The Interosseous Muscles (p. 600)

There are 7 interossei muscles located between the metacarpal bones.
They are arranged in 2 layers: 3 palmar and 4 dorsal muscles.

Dorsal interossei 1 to 4

Proximal attachments are: adjacent sides of two metacarpal bones.
Distal attachments are: extensor expansions and the bases of the proximal phalanges of the 2^nd to 4^th digits.
Innervation: deep branch of the ulnar nerve (C8 and T1).

Palmar interossei 1 to 3

Proximal attachments are: palmar surfaces of 2^nd, 4^th and 5^th metacarpal bones.
Distal attachments are: extensor expansions of digits and the bases of the proximal phalanges of the 2^nd, 4^th and 5^th digits.
Innervation: deep branch of the ulnar nerve (C8 and T1).

The dorsal interossei abduct the digits (DAB: Dorsal ABduct).
The palmar interossei adduct the digits (PAD: Palmar ADduct).

They also assist the actions of the lumbrical muscles.
These are important movements in typing, writing, and playing the piano.

The Long Flexor Tendons of the Extrinsic Muscles (pp. 600, 602)

The tendons of the flexor digitorum superficialis and flexor digitorum profundus enter a common synovial sheath deep to the flexor retinaculum.
They pass deep to the palmar aponeurosis and enter osseofibrous digital tunnels.
There are 2 tendons in each tunnel.

To enable the two tendons slide freely, they are covered with synovial membrane.

Near the base of the proximal phalanx, the tendon of the flexor digitorum superficialis splits and surrounds the tendons of the flexor digitorum profundus.
The halves of the tendon of the flexor digitorum superficialis are attached to the margins of the middle phalanx.
The tendon of the flexor digitorum profundus, after passing through the slit, attaches to the base of the distal phalanx.