368
UNIT 2
Covering, Support, and Movement of the Body
10
MUSCLE
DESCRIPTION
ORIGIN (O) AND
INSERTION (I)
ACTION
NERVE
SUPPLY
Obturator externus
(ob
0
tu-ra
9
tor ek-ster
9
nus)
(
obturator
5
obturator
foramen;
externus
5
outside)
Flat, triangular muscle deep
in superomedial aspect of
thigh
O—outer surfaces of
obturator membrane,
pubis, and ischium,
margins of obturator
foramen
I—by a tendon into
trochanteric fossa of
posterior femur
As for piriformis
Obturator nerve
Obturator internus
(in-ter
9
nus)
(
internus
5
inside)
Surrounds obturator
foramen within pelvis;
leaves pelvis via lesser
sciatic notch and turns
acutely forward to insert
on femur
O—inner surface of
obturator membrane,
greater sciatic notch, and
margins of obturator
foramen
I—greater trochanter in
front of piriformis
As for piriformis
L
5
and S
1
Gemellus
(je
˘
-me
˘
9
lis)—
superior and inferior
(
gemin
5
twin, double;
superior
5
above;
inferior
5
below)
Two small muscles with
common insertions and
actions; considered
extrapelvic portions of
obturator internus
O—ischial spine
(superior); ischial
tuberosity (inferior)
I—greater trochanter of
femur
As for piriformis
L
5
and S
1
Quadratus femoris
(
quad
5
four-sided square)
Short, thick muscle; most
inferior lateral rotator
muscle; extends laterally
from pelvis
O—ischial tuberosity
I—intertrochanteric crest
of femur
Rotates thigh laterally
and stabilizes hip joint
L
5
and S
1
MUSCLE GALLERY
Table 10.14
Muscles Crossing the Hip and Knee Joints: Movements of the Thigh and Leg
(Figures 10.20 and 10.21)
(continued)
Superior
gemellus
Obturator
internus
Inferior
gemellus
Gluteus medius
(cut)
Gluteus minimus
Piriformis
Obturator
externus
Quadratus
femoris
Gluteus maximus
(cut)
(c)
(d)
Obturator
externus
Figure 10.21
(continued)
Posterior muscles of the right hip and thigh.
(c)
Deep muscles
of the gluteal region, which act primarily to rotate the thigh laterally. The superficial gluteus
maximus and medius have been removed.
(d)
Anterior view of the isolated obturator externus
muscle.
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