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THE LATERAL MUSCLES OF THE HIP AND THIGH 321 
Action.—To tense the fascia lata, flex the hip joint, and extend the stifle joint. 
Structure—The muscle arises by a rather small head, about two inches (ca. 
5 em.) wide, on the antero-inferior eminence of the tuber cox. Below this the 
belly spreads out and terminates in the aponeurosis about midway between the 
point of the hip and the stifle. Many fibers arise from an intermuscular septum 
between this muscle and the superficial gluteus; this septum is attached to the lat- 
eral border of the ilium. The aponeurosis fuses with the fascia lata, which may be 
regarded practically as the tendon of insertion; it detaches a lamina which passes 
with the tendon of insertion of the superficial gluteus to the lateral border of the 
femur. 
Relations.—Laterally, the skin and fascia; medially, the obliquus abdominis 
externus, the iliacus, superficial gluteus, rectus femoris, and vastus lateralis, branches 
of the circumflex iliac, ilio-lumbar, and iliaco-femoral arteries, and the anterior 
gluteal nerve; anteriorly, the prefemoral lymph-glands. A considerable quantity 
of connective tissue is found between the deep face of the muscle and the abdominal 
wall. 
Blood-supply.— Cireumflex iliac, ilio-lumbar, and iliaco-femoral arteries. 
Nerve-supply.—Anterior gluteal nerve. 
2. Gluteus superficialis (Fig. 267)—This muscle lies behind and _ partly 
underneath the tensor fascie late. It is triangular and consists of an anterior and 
a posterior head united by the gluteal fascia. 
Origin.—(1) The tuber cox and the adjacent part of the lateral border of 
the ilium; (2) the gluteal fascia. 
Insertion —The third trochanter of the femur. 
Action.—To abduct the limb, flex the hip joint, and tense the gluteal fascia. 
Structure-—The anterior head of the muscle is not completely separable (ex- 
, cept artificially) from the tensor fasciz late, since both muscles are attached to an 
intermuscular septum. The attachment to the border of the ilium is by means of 
an intermuscular septum, which passes beneath the thick lateral border of the 
gluteus medius and furnishes origin to fibers of both muscles. The posterior head 
arises from the deep face of the gluteal fascia, and so indirectly from the dorsal 
sacro-iliac ligament. The two heads unite and terminate on a strong flat tendon, 
which is inserted into the edge of the third trochanter of the femur, under cover of 
the biceps femoris. 
Relations.—Superficially, the skin, fascia, and biceps femoris; deeply, the 
gluteus medius, iliacus, rectus femoris, and branches of the iliaco-femoral vessels; 
in front, the tensor fascize latee; behind, the biceps femoris. 
Blood-supply.—Gluteal and iliaco-femoral arteries. 
Nerve-supply.—Anterior gluteal nerve. 
3. Gluteus medius (Figs. 268, 580) —This is a very large muscle which covers 
the gluteal surface of the ilium and the greater part of the lateral wall of the pelvis, 
and extends forward also on the lumbar part of the longissimus dorsi. 
Origin.—(1) The aponeurosis of the longissimus dorsi, as far forward as the 
first lumbar vertebra; (2) the gluteal surface and tubera of the ilium; (3) the dorsal 
and lateral sacro-iliac and sacro-sciatic ligaments, and the gluteal fascia. 
Insertion —(1) The summit of the trochanter major of the femur; (2) the crest 
below the trochanter; (3) the lateral aspect of the trochanteric ridge. 
Action.—To extend the hip joint and abduct the limb. By its connection 
with the longissimus a muscular mass is formed which is one of the chief factors in 
rearing, kicking, and propulsion. 
Structure —The anterior extremity of the muscle is narrow and thin, and lies 
in a depression on the surface of the longissimus, from the strong aponeurosis of 
which the fibers take origin. The pelvic portion of the muscle is very voluminous, 
and forms the bulk of the muscular mass which gives the haunch its rounded con- 
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