Chapter 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.
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_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.

_Structure._—This is very similar to that of the vastus externus. It is, however, more difficult to separate from the intermedius, because many fibers of the latter arise on the tendinous sheet which covers the contact surface of the inner vastus. Its insertion into the patella is chiefly by means of a broad strong tendon. From the deep face fleshy fibers are inserted also into the femoro-patellar capsule.

_Relations._—Internally, the skin and fascia lata, the iliacus, sartorius, pectineus, and adductor, the femoral vessels and saphenous nerve; externally, the femur, femoro-patellar joint capsule, rectus femoris, and vastus intermedius, the anterior femoral artery, and branches of the femoral nerve.

_Blood-supply._—Femoral and anterior femoral arteries.

_Nerve-supply._—Femoral nerve.

(4) =Vastus intermedius= (Crureus).—This muscle is deeply situated on the anterior face of the femur, and is entirely covered by the preceding heads.

_Origin._—(1) The anterior and external surfaces of the femur, from the proximal to the distal fourth; (2) the aponeurosis of the vastus internus.

_Insertion._—(1) The base of the patella; (2) the femoro-patellar joint capsule.

_Action._—(1) To extend the stifle joint; (2) to tense (raise) the femoro-patellar capsule during extension of the joint.

_Structure._—The muscle is usually quite difficult to isolate from the other vasti, so that many since Günther have declared it an artefact.[71] It is entirely fleshy, and is small at its proximal end, but when traced downward increases in bulk by the accession of fibers arising on the femur and the tendinous covering of the vastus internus. The terminal part is intimately adherent to the femoro-patellar joint capsule, where the latter bulges upward above the level of the patella.

_Relations._—Internally, the vastus internus; externally, the vastus externus; anteriorly, the rectus; posteriorly, the femur and femoro-patellar capsule.

_Blood-supply._—Iliaco-femoral and anterior femoral arteries.

_Nerve-supply._—Femoral nerve.

The straight ligaments of the patella are to be regarded as tendons of
the quadriceps which communicate the action of the latter to the
tibia, the patella being intercalated as a sesamoid bone.

3. =Capsularis= (Fig. 154) (Rectus parvus).—This is a small muscle (scarcely as large as one’s finger), which arises on the ilium immediately above the outer tendon of the rectus femoris, and passes down between the vastus internus and externus to be inserted into the anterior surface of the femur. It passes over the front of the hip joint, to the capsule of which some fibers are attached. Sometimes the muscle has two distinct heads, in which case the additional head arises between the two tendons of origin of the rectus femoris. Its action may be to raise the capsule during flexion of the joint.