360
UNIT 2
Covering, Support, and Movement of the Body
10
In this table we consider the small muscles that lie entirely in the
hand. All are in the palm, none on the hand’s dorsal side. All move
the metacarpals and fingers. Small, weak muscles, they mostly control
precise movements (such as threading a needle), leaving the powerful
movements of the fingers (“power grip”) to the forearm muscles.
The intrinsic muscles include the main abductors and adductors
of the fingers, as well as muscles that produce the movement of
opposition—moving the thumb toward the little finger—that
enables you to grip objects. Many palm muscles are specialized to
move the thumb, and surprisingly many move the little finger.
Thumb movements are defined differently from movements of
other fingers because the thumb lies at a right angle to the rest of
the hand. The thumb flexes by bending medially along the palm,
not by bending anteriorly, as do the other fingers. (To demonstrate
this difference, start with your hand in the anatomical position or
this will not be clear!) The thumb extends by pointing laterally (as in
hitchhiking), not posteriorly, as do the other fingers. To abduct the
fingers is to splay them laterally, but to abduct the thumb is to point
it anteriorly. Adduction of the thumb brings it back posteriorly.
The intrinsic muscles of the palm are divided into three groups,
those in
1. The
thenar eminence
(ball of the thumb)
2. The
hypothenar eminence
(ball of the little finger)
3. The midpalm
Thenar and hypothenar muscles are almost mirror images of each
other, each containing a small flexor, an abductor, and an opponens
muscle. The midpalmar muscles, called
lumbricals
and
interossei
,
extend our fingers at the interphalangeal joints. The interossei are
also the main finger abductors and adductors.
MUSCLE GALLERY
Table 10.13
Intrinsic Muscles of the Hand: Fine Movements of the Fingers
(Figure 10.19)
MUSCLE
DESCRIPTION
ORIGIN (O) AND
INSERTION (I)
ACTION
NERVE
SUPPLY
THENAR MUSCLES IN BALL OF THUMB
(the
9
nar) (
thenar
5
palm)
Abductor pollicis brevis
(
pollex
5
thumb)
Lateral muscle of thenar
group; superficial
O—flexor retinaculum
and nearby carpals
I—lateral base of
thumb’s proximal
phalanx
Abducts thumb
(at
carpometacarpal joint)
Median nerve (C
8
, T
1
)
Flexor pollicis brevis
Medial and deep muscle of
thenar group
O—flexor retinaculum
and nearby carpals
I—lateral side of base
of proximal phalanx of
thumb
Flexes thumb
(at
carpometacarpal and
metacarpophalangeal
joints)
Median (or
occasionally ulnar)
nerve (C
8
, T
1
)
Opponens pollicis
(o-po
ˉ
n
9
enz) (
opponens
5
opposition)
Deep to abductor pollicis
brevis, on metacarpal I
O—flexor retinaculum
and trapezium
I—whole anterior side of
metacarpal I
Opposition
: moves thumb
to touch tip of little
finger
Median (or
occasionally ulnar)
nerve
Adductor pollicis
Fan-shaped with horizontal
fibers; distal to other
thenar muscles; oblique
and transverse heads
O—capitate bone and
bases of metacarpals II–
IV; front of metacarpal III
I—medial side of base
of proximal phalanx of
thumb
Adducts and helps to
oppose thumb
Ulnar nerve (C
8
, T
1
)
HYPOTHENAR MUSCLES IN BALL OF LITTLE FINGER
Abductor digiti minimi
(dı˘
9
jı˘-ti min
9
ı˘-mi)
(
digiti minimi
5
little finger)
Medial muscle of
hypothenar group;
superficial
O—pisiform bone
I—medial side of
proximal phalanx of little
finger
Abducts little finger
at
metacarpophalangeal
joint
Ulnar nerve
Flexor digiti minimi brevis
Lateral deep muscle of
hypothenar group
O—hamate bone and
flexor retinaculum
I—same as abductor
digiti minimi
Flexes little finger
at
metacarpophalangeal
joint
Ulnar nerve
Opponens digiti minimi
Deep to abductor digiti
minimi
O—same as flexor digiti
minimi brevis
I—most of length
of medial side of
metacarpal V
Helps in opposition
:
brings metacarpal V
toward thumb to cup the
hand
Ulnar nerve
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