The Muscular System 221
Table 9- 9 Muscles Moving the Knee Joint
Muscle FunctionBiceps femoris (two heads)^ Flexes leg; rotates laterally after flexed^
Semitendinosus^ Flexes leg, extends thigh^
Semimembranosus^ Flexes leg, extends thigh^
Popliteus^ Flexes leg, rotates it^
Gracilis^ Adducts thigh, flexes leg^
Sartorius^ Flexes thigh, rotates it laterally^
Quadriceps femoris: (four heads)^ Extends leg and flexes the thigh^
Rectus femoris^
Vastus lateralis^
Vastus medialis^
Vastus intermedius(^) ®
Learning
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to suspend the hams during curing or smoking. Many
predators bring down their prey by biting through these
hamstrings. When persons “pull a hamstring,” they have
torn the tendons of one of these muscles.
The quadriceps femoris muscle consists of four
parts that extend the knee. They are the rectus femoris,
the vas-tus lateralis, the vastus medialis, and the
vastus interme-dius. The vastus medialis and vastus
lateralis are easily seen superficially on the anterior thigh
(see Figure 9-11). The sartorius muscle is the longest
muscle of the body and is known as the “tailors” muscle. It
flexes the thigh and leg and rotates the thigh laterally for
sitting cross-legged, a position some tailors sit in while
hand sewing to hold their materials in their lap.
Muscles Moving the Foot
Five muscles plantar flex the foot or bring it downward.
They are the gastrocnemius (gas-trok-NEE-mee-us) or
calf muscle, the tibialis posterior, the soleus (SO-lee-
us), the peroneus (payr-oh-NEE-us) longus, and the
plan-taris (plan-TAH-ris). Two muscles dorsally flex the
foot or bring it upward. They are the tibialis anterior and
the peroneus tertius. Table 9-10 lists the muscles
involved in moving the foot and toes.
Muscles Moving the Toes
Two muscles flex the great toe: the flexor hallucis
(FLEKS-ohr HAL-uh-kiss) brevis and longus; one muscle
extends the great toe, the extensor hallucis (see Table 9-
10). The flexor digitorum muscles flex the toes while the
extensor digitorum extends the toes. The abductor-
hallucis abducts the great toe and the -abductor digiti
minimi abducts the little toe. A total of 20 intrinsic
muscles- of the foot move the toes to flex, extend,- adduct,
and abduct.