323
CHAPTER NINE
Muscular System
walks, runs, or climbs. It is also used to raise the body from a
sitting position (see F
g. 9.38).
The
gluteus medius
(gloo
te-us me
de-us) is partly cov-
ered by the gluteus maximus. Its F bers extend from the ilium
to the femur, and they abduct the thigh and rotate it medially
(see F
g. 9.38).
The
gluteus minimus
(gloo
te-us min
ı
˘-mus) lies beneath
the gluteus medius and is its companion in attachments and
functions (see F
g. 9.38).
The
piriformis
(pir-ı˘-for
mis) is shaped like a pyramid
and located inferior to the gluteus minimus. It abducts and
laterally rotates the thigh and is part of the posterior group of
muscles that stabilizes the hip.
The
tensor fasciae latae
(ten
sor fash
e-e lah-te
¯) connects
the ilium to the iliotibial tract (fascia of the thigh), which con-
tinues downward to the tibia. This muscle abducts and fl
exes
the thigh and rotates it medially (see F
g. 9.38).
The gluteus medius and gluteus minimus help support and maintain
the normal position of the pelvis. If these muscles are paralyzed as a
result of injury or disease, the pelvis tends to drop to one side when-
ever the foot on that side is raised. Consequently, the person walks
with a waddling limp called the
gluteal gait
.
Thigh Adductors
The
pectineus
(pek-tin
e-us) muscle runs from the spine of the
pubis to the femur. It fl exes and adducts the thigh (see F g. 9.37).
The
adductor brevis
(ah-duk
tor brev
ı˘s) is a short, tri-
angular muscle that runs from the pubic bone to the femur.
It adducts the thigh and assists in fl
exing and rotating it later-
ally (see F
g. 9.37).
The
adductor longus
(ah-duk
tor long
gus) is a long, tri-
angular muscle that runs from the pubic bone to the femur. It
adducts the thigh and assists in fl
exing and rotating it later-
ally (see F
g. 9.37).
The
adductor magnus
(ah-duk
tor mag
nus) is the largest
adductor of the thigh. It is a triangular muscle that connects
Muscles That Move the Thigh
The muscles that move the thigh are attached to the femur
and to some part of the pelvic girdle. (An important exception
is the sartorius, described later.) They can be separated into
anterior and posterior groups. The muscles of the anterior
group primarily fl
ex the thigh; those of the posterior group
extend, abduct, or rotate it. The muscles in these groups are
shown in
figures 9.37, 9.38, 9.39
, and
9.40
, in reference
plates 71 and 72, and are listed in
table 9.12
. Muscles that
move the thigh include the following:
Anterior Group
Posterior Group
Psoas major
Gluteus maximus
Iliacus
Gluteus medius
Gluteus minimus
Piriformis
Tensor fasciae latae
Another group of muscles, attached to the femur and pelvic
girdle, adducts the thigh. This group includes the following:
Pectineus
Adductor magnus
Adductor brevis
Gracilis
Adductor longus
Anterior Group
The
psoas
(so
as)
major
is a long, thick muscle that con-
nects the lumbar vertebrae to the femur. It fl
exes the thigh
(see F g. 9.37).
The
iliacus
(il
e-ak-us), a large, fan-shaped muscle, lies
along the lateral side of the psoas major. The iliacus and the
psoas major are the primary flexors of the thigh, and they
advance the lower limb in walking movements (see F g. 9.37).
Posterior Group
The
gluteus maximus
(gloo
te-us mak
si-mus) is the largest
muscle in the body and covers a large part of each buttock. It
connects the ilium, sacrum, and coccyx to the femur by fas-
cia of the thigh and extends the thigh. The gluteus maximus
helps to straighten the lower limb at the hip when a person
TABLE
9.11
|
Muscles of the Pelvic Outlet
Muscle
Origin
Insertion
Action
Nerve Supply
Levator ani
Pubic bone and
ischial spine
Coccyx
Supports pelvic viscera and provides
sphincterlike action in anal canal and vagina
Pudendal n.
Coccygeus
Ischial spine
Sacrum and coccyx
Same as above
S4 and S5 nerves
SuperF
cial transversus perinei
Ischial tuberosity
Central tendon
Supports pelvic viscera
Pudendal n.
Bulbospongiosus
Central tendon
Males: Urogenital diaphragm and
fascia of penis
±emales: Pubic arch and root of clitoris
Males:
Assists emptying of urethra and assists
in erection of penis
±emales:
Constricts vagina and assists in
erection of cltoris
Pudendal n.
Ischiocavernosus
Ischial tuberosity
Pubic arch
Males: Erects penis
±emales: Erects clitoris
Pudendal n.
Sphincter urethrae
Margins of pubis
and ischium
±ibers of each unite with those from
other side
Opens and closes urethra
Pudendal n.
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