Part 94

Relations.—Dorsally, the tendon of the obturator internus and the gluteus profundus; ventrally, the obturator externus.

Blood-supply.—Obturator artery.

Nerve-supply.—Sciatic nerve.

III. ANTERIOR MUSCLES OF THE THIGH

This group consists of the sartorius, quadriceps femoris, and capsularis.

1. =Sartorius.=—This is described on p. 281.

2. =Quadriceps femoris= (Figs. 179, 186, 200) (Crural triceps).—This constitutes the large muscular 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 outer one is a =bursa=. 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 furnishes insertion to fibers of the vasti. The tendon of insertion is formed by the fusion of these tendinous layers on the lower part of the muscle. The lower portion of the muscle is pennate, the fibers on either side converging on the tendon at an acute angle.

Relations.—Internally, the iliacus, sartorius, and vastus internus; externally, the tensor fasciæ latæ, glutei, and vastus externus; posteriorly, the hip joint and the vastus intermedius; anteriorly, the fascia lata and the skin. The anterior femoral artery and branches of the femoral nerve descend into the interspace between the upper part of the rectus and the vastus internus; similarly, the iliaco-femoral artery dips in between the rectus femoris and vastus externus.

Blood-supply.—Femoral and iliaco-femoral arteries.

Nerve-supply.—Femoral nerve.

(2) =Vastus externus= (s. lateralis).—This lies on the outer surface of the thigh, extending from the great trochanter to the patella. It is thick and wide in its upper part, and becomes much thinner and narrow below.

FIG. 200.—CROSS-SECTION OF MIDDLE OF RIGHT THIGH OF HORSE. ]

Origin.—The external border and surface of the femur, from the great trochanter to the supracondyloid fossa.

Insertion.—(1) The outer part of the anterior surface of the patella; (2) the tendon of the rectus femoris.

Action.—To extend the stifle joint.

Structure.—The fibers are directed downward and forward, many being inserted into the tendinous sheet which covers the side of the rectus. A =bursa= is often found between the distal end and the patella.

Relations.—Externally, the fascia lata and skin, tensor fasciæ latæ, superficial gluteus, and biceps femoris; internally, the femur and femoro-patellar joint capsule, the rectus femoris, vastus intermedius, and the iliaco-femoral artery.

Blood-supply.—Iliaco-femoral artery.

Nerve-supply.—Femoral nerve.

(3) =Vastus internus= (s. medialis).—This is smaller than the preceding muscle, and lies in a similar position on the inner side of the thigh.

Origin.—The internal surface of the femur, from the neck to the distal third.

Insertion.—(1) The upper part of the inner border of the patella and its cartilage; (2) the tendon of the rectus femoris.

Action.—To extend the stifle joint.