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i. Its origin is on the trapezium and the flexor retinaculum.
ii. Its insertion is on metacarpal I.
2. The hypothenar group of muscles forms the fleshy mass (hypothenar eminence) at the
base of the little finger. All three muscles are concerned with movement of the little
finger and are innervated by the ulnar nerve.
a. The abductor digiti minimi abducts the little finger, as in spreading the fingers
apart.
i. Its origin is on the pisiform and the tendon of the flexor carpi ulnaris.
ii. Its insertion is on the medial surface of proximal phalanx V.
b. The flexor digiti minimi brevis flexes the little finger at the
metacarpophalangeal joint.
i. Its origin is on the hamulus of the hamate bone and the flexor
retinaculum.
ii. Its insertion is on the medial surface of proximal phalanx V.
c. The opponens digiti minimi flexes metacarpal V and the carpometacarpal joint
when the little finger is moved into opposition with the tip of the thumb; it also
deepens the palm of the hand.
i. Its origin is on the hamulus of the hamate bone and the flexor
retinaculum.
ii. Its insertion is on the medial surface of metacarpal V.
3. The midpalmar group of muscles occupies the hollow of the palm; it has 11 small
muscles divided into three groups.
a. The dorsal interosseous muscles (four muscles) abduct the fingers and
strongly flex the metacarpophalangeal joints, but extend the interphalangeal
joints, depending on actions of other muscles. They are important for grip
strength and are innervated by the ulnar nerve.
i. Their origins, each with two heads, arise from the facing surfaces of
adjacent metacarpals.
ii. Their insertions are on proximal phalanges II–IV.
b. The palmar interosseous muscles (three muscles) adduct the fingers and have
other actions similar to the dorsal interosseous muscles. They are innervated by
the ulnar nerve.
i. Their origins are on metacarpals I, II, IV, and V.
ii. Their insertions are on proximal phalanges II, IV, V.
c. The lumbricals (four muscles) extend the interphalangeal joints and contribute
to the ability to pinch objects between the fleshy pads of the digits. They are
innervated by the median and ulnar nerves.

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i. Their origins are the tendons of the flexor digitorum profundus.
ii. Their insertions are on proximal phalanges II–V.
V. Muscles Acting on the Hip and Lower Limb
A. The largest muscles are found in the lower limb. They can be grouped into those that act on the
femur and hip joint, those that act on the leg and knee joint, extrinsic (leg) muscles that act on the
foot and ankle joint, and intrinsic (foot) muscles that act on the arches and toes.
B. Muscles acting on the hip and femur mostly originate on the hip bone.
1. The anterior muscles of the hip are the iliacus and the psoas major, collectively termed
the iliopsoas. They share a common tendon to the femur.
a. The iliacus flexes the thigh at the hip when the trunk is fixed and flexes the
trunk at the hip when the thigh is fixed. It also balances the trunk during sitting.
It is innervated by the femoral nerve.
i. Its origin includes the iliac crest and fossa, the superolateral region of
the sacrum, and the anterior sacroiliac and iliolumbar ligaments.
ii. Its insertion is on the lesser trochanter and nearby shaft of the femur.
b. The psoas major has the same action as the iliacus. It is innervated by the
anterior rami of lumbar spinal nerves.
i. Its origin includes the bodies and intervertebral discs of vertebrae
T12–L5 and the transverse processes of the lumbar vertebrae.
ii. Its insertion is on the lesser trochanter and nearby shaft of the femur.
2. The lateral and posterior muscles of the hip include the tensor fasciae latae and three
gluteal muscles.
a. The fascia lata is a fibrous sheath that encircles the thigh and binds its
muscles. It combines with the tendons of the gluteus maximus and tensor fasciae
latae to form the iliotibial tract, which extends from the iliac crest to the lateral
condyle of the tibia and braces the knee when the opposite foot is lifted.
b. The tensor fasciae latae extends the knee, laterally rotates the tibia, aids in
abduction and medial rotation of the femur, and steadies the pelvis and femur
during standing. It is innervated by the superior gluteal nerve.
i. Its origin includes the iliac crest, the anterior superior spine, and the
deep surface of the fascia lata.
ii. Its insertion is on the lateral condyle of the tibia via the iliotibial
tract.

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c. The gluteus maximus extends the thigh at the hip as in stair climbing or
running and walking, abducts the thigh, elevates the trunk after stooping, holds
the trunk erect, and helps stabilize the femur on the tibia. It is innervated by the
inferior gluteal nerve.
i. Its origins include the posterior gluteal line of the ilium on the
posterolateral surface from the iliac crest to the posterior superior spine,
the coccyx, the posterior surface of the lower sacrum, and the
aponeurosis of the erector spinae.
ii. Its insertion includes the gluteal tuberosity of the femur and the
lateral condyle of the tibia via the iliotibial tract.
d. The gluteus medius and gluteus minimus abduct and medially rotate the thigh.
During walking, they shift the weight of the trunk toward the planted limb as the
other foot is lifted. They are innervated by the superior gluteal nerve.
i. Their origins include most of the lateral surface of the ilium between
the crest and the acetabulum.
ii. Their insertions are on the greater trochanter of the femur.
3. The six lateral rotators lie inferior to the gluteus minimus and deep to the other two
gluteal muscles. They are named for their action on the femur. They oppose medial
rotation by the gluteus medius and minimus and are responsible for shifting the body
weight when walking.
a. The gemellus superior laterally rotates the extended thigh and abducts the
flexed thigh; it is sometimes absent. It is innervated by the nerve to the obturator
internus.
i. Its origin is on the ischial spine.
ii. Its insertion is on the greater trochanter of the femur.
b. The gemellus inferior has the same actions as the gemellus superior; it is
innervated by the nerve to the quadratus femoris.
i. Its origin is on the ischial tuberosity.
ii. Its insertion is on the greater trochanter of the femur.
c. The action of the obturator externus is not well understood, but is thought to
laterally rotate the thigh in climbing. It is innervated by the obturator nerve.
i. Its origins include the external surface of the obturator membrane and
the pubic and ischial rami.
ii. Its insertion is on the femur between the head and the greater
trochanter.

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d. The action of the obturator internus is also not well understood, but is thought
to laterally rotate the extended thigh and abduct the flexed thigh. It is innervated
by the nerve to the obturator internus.
i. Its origin is on the ramus of the ischium, the inferior ramus of the
pubis, and the anteromedial surface of the lesser pelvis.
ii. Its insertion is on the greater trochanter of the femur.
e. The piriformis laterally rotates the extended thigh and abducts the flexed
thigh; it is innervated by spinal nerves L5–S2.
i. Its origin is on the anterior surface of the sacrum, the gluteal surface
of the ilium, and the capsule of the sacroiliac joint.
ii. Its insertion is on the greater trochanter of the femur.
f. The quadratus femoris laterally rotates the thigh; it is innervated by the nerve
to the quadratus femoris.
i. Its origin is on the ischial tuberosity.
ii. Its insertion is on the intertrochanteric crest of the femur.
4. The medial (adductor) compartment of the thigh includes five muscles that act as
adductors, but some cross both the hip and knee joints and have additional actions.
a. The adductor brevis adducts the thigh; it is innervated by the obturator nerve.
i. Its origin is on the body and inferior ramus of the pubis.
ii. Its insertion is on the linea aspera and spiral line of the femur.
b. The adductor longus adducts and medially rotates the thigh, and flexes the
thigh at the hip. It is innervated by the obturator nerve.
i. Its origin is on the body and inferior ramus of the pubis.
ii. Its insertion is on the linea aspera of the femur.
c. The adductor magnus adducts and medially rotates the thigh, and extends the
thigh at the hip. It is innervated by the obturator and tibial nerves.
i. Its origin includes the inferior ramus of the pubis and the ramus and
tuberosity of the ischium.
ii. Its insertion includes the linea aspera, gluteal tuberosity, and medial
supracondylar line of the femur.
d. The gracilis flexes and medially rotates the tibia at the knee; it is innervated
by the obturator nerve.
i. Its origin includes the body and inferior ramus of the pubis and the
ramus of the ischium.
ii. Its insertion is on the medial surface of the tibia just below the
condyle.

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e. The pectineus flexes and adducts the thigh. It is innervated by the femoral
nerve.
i. Its origin is on the superior ramus of the pubis.
ii. Its insertion is on the spiral line of the femur.
C. Muscles acting on the knee and leg form most of the mass of the thigh and produce actions on
the knee joint. Some cross both the hip and knee joints and produce actions at both, moving the
femur, tibia, and fibula.
1. The anterior (extensor) compartment of the thigh contains the quadriceps femoris,
which is the prime mover of knee extension and the most powerful muscle in the body.
2. This compartment also includes the sartorius (tailor’s muscle), the longest muscle in
the body.
3. The four heads of the quadriceps (rectus femoris, vastus lateralis, vastus medialis, and
vastus intermedius) converge on the quadriceps (patellar) tendon that extends to the
patella and then continues as the patellar ligament that inserts on the tibial tuberosity. All
are innervated by the femoral nerve.
a. The rectus femoris extends the knee, flexes the thigh at the hip, and flexes the
trunk on the hip if the thigh is fixed.
i. Its origin includes the ilium, at the anterior inferior spine and superior
margin of the acetabulum, and the capsule of the hip joint.
ii. Its insertion is on the patella, the tibial tuberosity, and the lateral and
medial condyles of the tibia.
b. The vastus lateralis extends the knee and retains the patella in the groove on
the femur during knee movements.
i. Its origin includes the femur at the greater trochanter and
intertrochanteric line, the gluteal tuberosity, and the linea aspera.
ii. Its insertion is the same as the rectus femoris.
c. The vastus medialis has the same action as the vastus lateralis.
i. Its origin includes the femur at the intertrochanteric line, the spiral
line, the linea aspera, and the medial supracondylar line.
ii. Its insertion is the same as the rectus femoris.
d. The vastus intermedius extends the knee.
i. Its origin includes the anterior and lateral surfaces of the femoral
shaft.
ii. Its insertion is the same as the rectus femoris.
e. The sartorius aids in knee and hip flexion, as in sitting or climbing. It abducts
and laterally rotates the thigh. It is innervated by the femoral nerve.

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i. Its origin is on and near the anterior superior spine of the ilium.
ii. Its insertion is on the medial surface of the proximal end of the tibia.
4. The posterior (flexor) compartment of the thigh contains three muscles colloquially
known as the hamstring muscles.
a. The biceps femoris flexes the knee, extends the hip, elevates the trunk from a
stooping posture, laterally rotates the tibia on the femur when the knee is flexed,
laterally rotates the femur when the hip is extended, and counteracts forward
bending at the hips. It is innervated by the tibial and common fibular nerves.
i. The origin of the long head is on the ischial tuberosity; the origin of
the short head includes the linea aspera and lateral supracondylar line
of the femur.
ii. Its insertion is on the head of the fibula.
b. The semitendinosus flexes the knee, medially rotates tibia on the femur when
the knee is flexed, medially rotates the femur when the hip is extended, and
counteracts forward bending at the hips. It innervated by the tibial nerve.
i. Its origin is on the ischial tuberosity.
ii. Its insertion is on the medial surface of the upper tibia.
c. The semimembranosus has the same action as the semitendinosus.
i. Its origin is on the ischial tuberosity.
ii. Its insertion includes the medial condyle and nearby margin of the
tibia, the intercondylar line and lateral condyle of the femur, and the
ligament of the popliteal region.
5. The posterior compartment of the leg contains one muscle that acts on the knee, the
popliteus; the others act on the ankle and foot.
a. The popliteus rotates the tibia medially on the femur if the femur is fixed
(sitting down), or rotates the femur laterally on the tibia if the tibia is fixed
(standing up). It unlocks the knee to allow flexion, and may prevent forward
dislocation of the femur during crouching. It is innervated by the tibial nerve.
i. Its origin includes the lateral condyle of the femur, the lateral
meniscus, and the joint capsule.
ii. Its insertion is on the posterior surface of the upper tibia.
D. Muscles acting on the foot include the crural muscles, which are tightly bound by deep fasciae
that compress them and aid in the return of blood from the legs.
1. The fasciae separate the crural muscles into anterior, lateral, and posterior
compartments; the posterior compartment has superficial and deep groups.

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2. The anterior (extensor) compartment of the leg contains four muscles that dorsiflex the
ankle and prevent the toes from scuffing the ground during walking. Their tendons are
held tightly against the ankle by two extensor retinacula similar to those at the wrists. All
four are innervated by the deep fibular (peroneal) nerve.
a. The fibularis (peroneus) tertius dorsiflexes and everts the foot during walking
and helps the toes clear the ground during the forward swing of the leg.
i. Its origin includes the medial surface of the lower one-third of the
fibula and the interosseous membrane.
ii. Its insertion is on metatarsal V.
b. The extensor digitorum longus extends the toes, dorsiflexes the foot, and
tightens the plantar aponeurosis.
i. Its origin includes the lateral condyle of the tibia, the shaft of the
fibula, and the interosseous membrane.
ii. Its insertions are on the middle and distal phalanges II–V.
c. The extensor hallucis longus extends the great toe and dorsiflexes the foot.
i. Its origin includes the anterior surface of the middle of the fibula and
the interosseous membrane.
ii. Its insertion is on distal phalanx I.
d. The tibialis anterior dorsiflexes and inverts the foot, resists backward tipping
of the body, and helps support the medial longitudinal arch of the foot.
i. Its origin includes the lateral condyle and lateral margin of the
proximal half of the tibia and the interosseous membrane.
ii. Its insertion includes the medial cuneiform and metatarsal I.
3. The superficial group of the posterior (flexor) compartment of the leg includes three
plantar flexors; all are innervated by the tibial nerve.
a. The first two, the gastrocnemius and the soleus, are collectively known as the
triceps surae and insert on the calcaneus via the calcaneal (Achilles) tendon.
b. The gastrocnemius plantar flexes the foot, flexes the knee, and is active in
walking, running, and jumping.
i. Its origin includes the condyles, popliteal surface, and lateral
supracondylar line of the femur and the capsule of the knee joint.
ii. Its insertion is on the calcaneus.
c. The soleus also plantar flexes the foot and steadies the leg on the ankle during
standing.
i. Its origin includes the posterior surface of the head and proximal one-
fourth of the fibula, the middle one-third of the tibia, and the
interosseous membrane.

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ii. Its insertion is on the calcaneus.
d. The plantaris is a weak synergist of the triceps surae; it is absent in many
people. Its long tendon is often used for tendon grafts needed in other parts of
the body.
4. The deep group of the posterior (flexor) compartment of the leg contains four muscles,
one of which, the popliteus, is described in Table 10.14 because it acts on the knee rather
than on the foot. All are innervated by the tibial nerve.
a. The flexor digitorum longus flexes phalanges of digits II–V as the foot is
raised from the ground, stabilizes the metatarsal heads, and keeps the distal pads
of the toes in contact with the ground in toe-off and tiptoe movements.
i. Its origin is on the posterior surface of the tibial shaft.
ii. Its insertions are on distal phalanges II–V.
b. The flexor hallucis longus has the same actions as the flexor digitorum
longus, but for the great toe (digit I).
i. Its origin includes the inferior two-thirds of the fibula and
interosseous membrane.
ii. Its insertion is on distal phalanx I.
c. The tibialis posterior inverts the foot and may assist in strong plantar flexion
or control pronation of the foot during walking.
i. Its origin includes the posterior surface of the proximal half of the
tibia, the fibula, and the interosseous membrane.
ii. Its insertions are on the navicular, the medial cuneiform, and
metatarsals II–IV.
5. The lateral (fibular) compartment of the leg includes two muscles; they are innervated
by the superficial fibular (peroneal) nerve.
a. The fibularis (peroneus) brevis maintains the concavity of the sole during toe-
off and tiptoeing, and may evert the foot and limit inversion and help to steady
the leg on the foot.
i. Its origin is on the lateral surface of the distal two-thirds of the fibula.
ii. Its insertion is on the base of metatarsal V.
b. The fibularis (peroneus) longus also maintains concavity of the sole during
toe-off and tiptoeing, and everts and plantar flexes the foot.
i. Its origin is the head and lateral surface of the proximal two-thirds of
the fibula.
ii. Its insertion includes the medial cuneiform and metatarsal I.
E. The intrinsic muscles of the foot help to support the arches and act on the toes in ways that aid
locomotion. Several of them are similar in name and location to the intrinsic muscles of the hand.

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written consent of McGraw-Hill Education.
Only one of the intrinsic muscles is on the dorsal side of the foot; all remaining muscles are on the
ventral aspect and are grouped into four layers.
1. The dorsal aspect of the foot has only one muscle, the extensor digitorum brevis; the
medial slip of this muscle is sometimes called the extensor hallucis brevis.
a. The extensor digitorum brevis extends proximal phalanx I and all phalanges
of digits II–IV; it is innervated by the deep fibular (peroneal) nerve.
i. Its origin includes the calcaneus and the inferior extensor retinaculum
of the ankle.
ii. Its insertion includes proximal phalanx I and the tendons of the
extensor digitorum longus to middle and distal phalanges II–IV.
2. Ventral layer 1 (most superficial) is the first muscle layer encountered beneath the
plantar aponeurosis, a tough fibrous sheet between the skin and the muscles, that serves
as an origin for several ventral muscles.
a. The flexor digitorum brevis is a stout muscle on the midline that flexes digits
II–IV and supports the arches. It is innervated by the medial plantar nerve.
i. Its origin includes the calcaneus and the plantar aponeurosis.
ii. Its insertions are middle phalanges II–V.
b. The abductor digiti minimi, lateral to the flexor digitorum brevis, abducts and
flexes the little toe and supports the arches of the foot. It is innervated by the
lateral plantar nerve.
i. Its origin includes the calcaneus and the plantar aponeurosis.
ii. Its insertion is on proximal phalanx V.
c. The abductor hallucis, medial to the flexor digitorum brevis, abducts the great
toe and supports the arches of the foot. It is innervated by the medial plantar
nerve.
i. Its origin includes the calcaneus, the plantar aponeurosis, and the
flexor retinaculum.
ii. Its insertion is on proximal phalanx I.
3. Ventral layer 2, the next deeper layer, contains the thick quadratus plantae, and the
four lumbrical muscles located between the metatarsals.
a. The quadratus plantae has the same action as the flexor digitorum longus
and also flexes digits II–V. It is innervated by the lateral plantar nerve.
i. It has two heads with origins on the medial and lateral sides of the
calcaneus.
ii. Its insertions are on distal phalanges II–V via the flexor digitorum
longus tendons.

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b. The four lumbricals flex toes II–V. They are innervated by the lateral and
medial plantar nerves.
i. Their origin is the tendon of the flexor digitorum longus.
ii. Their insertions are on proximal phalanges II–V.
4. Ventral layer 3, next deepest, contains three muscles that serve only the great and little
toes.
a. The flexor digiti minimi brevis flexes the little toe. It is innervated by the
lateral plantar nerve.
i. Its origins include metatarsal V and the sheath of the fibularis longis.
ii. Its insertion is on proximal phalanx V.
b. The flexor hallucis brevis flexes the great toe; it is innervated by the medial
plantar nerve.
i. Its origins include the cuboid, the lateral cuneiform, and the tibialis
posterior tendon.
ii. Its insertion is on proximal phalanx I.
c. The adductor hallucis, with an oblique head and a transverse head, adducts
the great toe; it is innervated by the lateral plantar nerve.
i. The two heads have origins on metatarsals II–IV, the fibularis longus
tendon, and ligaments at the bases of digit III–V.
ii. Its insertion is on proximal phalanx I.
5. Ventral layer 4, the deepest layer, consists of only the small interosseous muscles
located between the metatarsal bones—four dorsal and three plantar. All are innervated
by the lateral plantar nerve.
a. The dorsal interosseous muscles are bipennate and abduct toes II–IV.
i. Each has two heads with origins on the facing surfaces of two
adjacent metatarsals.
ii. Their insertions are on proximal phalanges II–IV.
b. The plantar interosseous muscles are unipennate and adduct toes III–V.
i. Their origins are the medial aspect of metatarsals III–V.
ii. Their insertions are on the proximal phalanges III–V.