ANTERIOR MUSCLES OF THE THIGH 329 
Structure.-—The ischio-pubic head lies on the pelvic floor and covers the ob- 
turator foramen. It is thin and fan-shaped. The iliac head extends along the 
lateral wall of the pelvis, and is pennate, with a central tendon throughout. Both 
terminate on a flat tendon which passes outward through the lesser sciatic fora- 
men to be inserted into the trochanteric fossa. The tendon furnishes insertion to 
fibers of the gemellus. A synovial bursa facilitates the play of the tendon over the 
lateral border of the ischium.? 
Relations.—The pelvic surface is covered by the pelvic fascia and in part by 
the peritoneum. The obturator vessels and nerve lie between the two heads, and 
the internal pudic vessels and nerve lie along the dorsal edge of the iliac head. The 
tendon is crossed by the great sciatic nerve. 
Blood-supply.—Obturator and internal pudic arteries. 
Nerve-supply.—Great sciatic nerve. 
4. Gemellus” (Fig. 580).—This is a thin, triangular muscle, which extends 
from the lateral border of the ischium to the trochanteric fossa and ridge. 
Origin.—The lateral border of the ischium near the ischiatic spine. 
Insertion —The trochanteric fossa and ridge. 
Action.—To rotate the femur outward. 
Structure—The thin tendon of origin is attached to a line on the lateral border 
of the ischium, which begins just below the posterior end of the superior ischiatic 
spine. Many superficial fibers are inserted into the tendon of the obturator in- 
ternus. 
Relations.—Superficially, the biceps femoris, the tendon of the obturator in- 
ternus, the gluteus medius, and the great sciatic nerve; deeply, the obturator ex- 
ternus and the hip joint. 
Blood-supply.—Obturator artery. 
Nerve-supply.—Great sciatic nerve. 
IV. ANTERIOR MUSCLES OF THE THIGH 
This group consists of the sartorius, quadriceps femoris, and capsularis. 
1. Sartorius.—This is described on p. 325. 
2. Quadriceps femoris (Figs. 268, 289, 291).—This constitutes the large mus- 
cular mass which covers the front and sides of the femur. It has four heads, one 
of which, the rectus, arises from the ilium; the other three arise from the femur. 
All are inserted into the patella. 
(1) Rectus femoris.—This is fusiform and rounded. It arises by two tendons. 
Origin.—Two depressions on the shaft of the ilium above and in front of the 
acetabulum. 
Insertion.—The base and anterior surface of the patella. 
Action.—To extend the stifle joint and to flex the hip joint. 
Structure.—It has two short strong tendons of origin; beneath the lateral one 
isabursa. The belly is rounded and rests in a groove formed by the other portions 
of the quadriceps. Its sides are covered by a strong tendinous layer which fur- 
‘The iliac head has been described as a separate muscle, and termed the piriformis. This 
does not seem desirable, especially since it is probable that the homologue of the piriformis of 
man is that portion of the middle gluteus which is inserted into the trochanteric ridge. 
_ * The name is based on the arrangement in man, in whom the muscle usually consists of two 
fasciculi forming a groove between them for the tendon of the obturator internus. In the horse 
it is usually undivided at its origin, but toward the insertion the upper part is separated from the 
rest of the muscle or is readily isolated. The muscle is subject to much variation in size. When 
well developed, the insertion extends from the proximal end of the trochanteric fossa to a point 
| Just above the femoral attachment of the biceps femoris; in such cases the upper part, which 
occupies the space behind the hip joint between the gluteus profundus and obturator externus, 
is much thicker than the remainder, which covers the latter muscle. The gemellus may be re- 
garded as the extrapelvic head of the obturator internus (Gegenbaur). 
