376
UNIT 2
Covering, Support, and Movement of the Body
10
MUSCLE GALLERY
Table 10.16
Intrinsic Muscles of the Foot: Toe Movement and Arch Support
(Figure 10.25)
MUSCLE
DESCRIPTION
ORIGIN (O) AND
INSERTION (I)
ACTION
NERVE
SUPPLY
MUSCLES ON DORSUM OF FOOT
Extensor digitorum brevis
(Figures 10.22a and 10.23a)
Small, four-part muscle
on dorsum of foot;
deep to the tendons of
extensor digitorum longus;
corresponds to the extensor
indicis and extensor pollicis
muscles of forearm
O—anterior part of
calcaneus bone; extensor
retinaculum
I—base of proximal
phalanx of great toe;
extensor expansions on
toes 2 to 4 or 5
Helps extend toes at
metatarsophalangeal
joints
Deep fibular nerve (L
5
and S
1
)
MUSCLES ON SOLE OF FOOT—FIRST LAYER (MOST SUPERFICIAL)
(Figure 10.25)
Flexor digitorum brevis
Bandlike muscle in middle
of sole; corresponds
to flexor digitorum
superficialis of forearm and
inserts into digits in the
same way
O—calcaneal tuberosity
I—middle phalanx of
toes 2–4
Helps flex toes
Medial plantar nerve
(a branch of tibial
nerve, S
1
and S
2
)
Abductor hallucis
(hal
9
yu-kis)
(
hallux
5
great toe)
Lies medial to flexor
digitorum brevis (recall
the similar thumb muscle,
abductor pollicis brevis)
O—calcaneal tuberosity
and flexor retinaculum
I—proximal phalanx of
great toe, medial side,
in the tendon of flexor
hallucis brevis)
Abducts great toe
Medial plantar nerve
Abductor digiti minimi
Most lateral of the three
superficial sole muscles
(recall similar abductor
muscle in palm)
O—calcaneal tuberosity
I—lateral side of base
of little toe’s proximal
phalanx
Abducts and flexes little
toe
Lateral plantar nerve
(a branch of tibial
nerve, S
1
, S
2
, and S
3
)
MUSCLES ON SOLE OF FOOT—SECOND LAYER
Flexor accessorius
(quadratus plantae)
Rectangular muscle just
deep to flexor digitorum
brevis in posterior half of
sole; two heads (see also
Figure 10.25c)
O—medial and lateral
sides of calcaneus
I—tendon of flexor
digitorum longus in
midsole
Straightens out the
oblique pull of flexor
digitorum longus
Lateral plantar nerve
Lumbricals
Four little “worms” (like
lumbricals in hand)
O—from each tendon of
flexor digitorum longus
I—extensor expansion on
proximal phalanx of toes
2–5, medial side
By pulling on extensor
expansion,
flex toes at
metatarsophalangeal
joints and extend toes at
interphalangeal joints
Medial plantar nerve
(first lumbrical) and
lateral plantar nerve
(second to fourth
lumbrical)
The intrinsic muscles of the foot help to flex, extend, abduct, and
adduct the toes. Collectively, along with the tendons of some leg
muscles that enter the sole, the foot muscles help support the arches
of the foot. There is a single muscle on the foot’s dorsum (superior
aspect), and several muscles on the plantar aspect (the sole). The
plantar muscles occur in four layers, from superficial to deep.
Overall, the foot muscles are remarkably similar to those in the palm
of the hand.
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