Chapter 10
The Muscular System
363
10
The muscles fleshing out the thigh are difficult to segregate into
groups on the basis of action. Some thigh muscles act only at the
hip joint, others only at the knee, while still others act at both
joints. However,
most anterior
muscles of the hip and thigh flex
the femur at the hip and extend the leg at the knee, producing the
foreswing phase of walking. The
posterior
muscles of the hip and
thigh, by contrast, mostly extend the thigh and flex the leg—the
backswing phase of walking. A third group of muscles in this region,
the
medial
, or
adductor
, muscles, all adduct the thigh; they have no
effect on the leg.
In the thigh, the anterior, posterior, and adductor muscles are
separated by walls of fascia into
anterior
,
posterior
, and
medial
compartments
(see Figure 10.26a). The deep fascia of the thigh, the
fascia lata
, surrounds and encloses all three groups of muscles like
a support stocking.
Movements of the thigh (occurring at the hip joint) are
accomplished largely by muscles anchored to the pelvic girdle. Like
the shoulder joint, the hip joint is a ball-and-socket joint permitting
flexion, extension, abduction, adduction, circumduction, and
rotation. Muscles effecting these movements are among the most
powerful muscles of the body.
For the most part, the thigh
flexors
pass in front of the hip
joint. The most important thigh flexors are the
iliopsoas
(the prime
mover),
tensor fasciae latae
, and
rectus femoris
(Figure 10.20a).
They are assisted in this action by the
adductor muscles
of the
medial thigh and the straplike
sartorius
.
Thigh
extension
is effected primarily by the massive
hamstring
muscles
of the posterior thigh (Figure 10.21a). During forceful
extension, the
gluteus maximus
of the buttocks is called into play.
Buttock muscles that lie lateral to the hip joint (
gluteus medius
and
minimus
)
abduct
the thigh (Figure 10.21c).
Thigh adduction is the role of the adductor muscles of the medial
thigh. Abduction and adduction of the thighs are extremely important
during walking to shift the trunk from side to side and balance the
body’s weight over the limb that is on the ground. Many different
muscles bring about medial and lateral rotation of the thigh.
At the knee joint, flexion and extension are the main movements.
The sole knee
extensor
is the
quadriceps femoris
muscle of the
anterior thigh, the most powerful muscle in the body (Figure 10.20a).
The quadriceps is antagonized by the hamstrings of the posterior
compartment, which are the prime movers of knee flexion.
Table 10.17 (Part I) summarizes the actions of these muscles.
MUSCLE GALLERY
Table 10.14
Muscles Crossing the Hip and Knee Joints: Movements of the Thigh and Leg
(Figures 10.20 and 10.21)
MUSCLE
DESCRIPTION
ORIGIN (O) AND
INSERTION (I)
ACTION
NERVE
SUPPLY
PART I: ANTERIOR AND MEDIAL MUSCLES
(Figure 10.20)
Origin on the Pelvis or Spine
Iliopsoas
(il
0
e-o-so
9
us)
Iliopsoas is a composite of two closely related muscles (iliacus and psoas major) whose fibers pass under the
inguinal ligament (see Figure 10.12) to insert via a common tendon on the femur.
Iliacus
(il-e-ak
9
us)
(
iliac
5
ilium)
Large, fan-shaped, more
lateral muscle
O—iliac fossa and crest,
ala of sacrum
I—lesser trochanter
of femur via iliopsoas
tendon
Iliopsoas is the
prime
mover for flexing thigh,
or for flexing trunk on
thigh
as during a bow
Femoral nerve
(L
2
and L
3
)
Psoas major
(so
9
us)
(
psoa
5
loin muscle;
major
5
larger)
Longer, thicker, more
medial muscle of the pair
(butchers refer to this
muscle as the tenderloin)
O—by fleshy slips from
transverse processes,
bodies, and discs of
lumbar vertebrae and T
12
I—lesser trochanter
of femur via iliopsoas
tendon
As above; also flexes
vertebral column laterally
;
important postural
muscle
Ventral rami (L
1
–L
3
)
Sartorius
(sar-tor
9
e-us)
(
sartor
5
tailor)
Straplike superficial muscle
running obliquely across
anterior surface of thigh
to knee; longest muscle in
body; crosses both hip and
knee joints
O—anterior superior iliac
spine
I—winds around medial
aspect of knee and
inserts into medial aspect
of proximal tibia
Flexes, abducts, and
laterally rotates thigh
;
flexes knee (weak) as in a
soccer kick; helps produce
the cross-legged position
Femoral nerve
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