Chapter IV: The Internal Muscles of the Thigh

The muscles of this group are arranged in three layers.

FIRST LAYER

1. =Sartorius= (Figs. 180, 202, 203).—This long and rather narrow muscle is the most anterior one of the first layer. It extends from the sublumbar region to the lower and inner part of the stifle.

_Origin._—The iliac fascia and the tendon of the psoas minor.

_Insertion._—The internal straight ligament of the patella and the adjacent part of the tuberosity of the tibia.

_Action._—To flex the hip joint and adduct the limb.

_Structure._—The muscle is very thin at its origin, but becomes thicker and narrower as it passes downward and a little backward. It terminates near the stifle joint on an aponeurosis which blends with that of the gracilis and with the fascia of the leg.

_Relations._—Superficially, the inguinal (Poupart’s) ligament, the abdominal muscles, the skin and fascia, and the saphenous vessels and nerve; deeply, the ilio-psoas, quadriceps femoris, and adductor. It forms the anterior boundary of the femoral canal, in which the femoral artery and vein and the deep inguinal lymph glands are situated (Fig. 451).

_Blood-supply._—Femoral artery.

_Nerve-supply._—Femoral and saphenous nerves.

2. =Gracilis= (Figs. 186, 199, 202, 203).—This is a wide, flat, quadrilateral muscle, situated behind the sartorius, which it exceeds greatly in extent.

_Origin._—The middle third of the pelvic symphysis, the prepubic tendon and pubo-femoral ligament, and the ventral surface of the pubis behind the prepubic tendon.

_Insertion._—The internal straight ligament of the patella, the internal surface of the tibia in front of the lateral ligament of the stifle joint, and the fascia of the leg.

_Action._—To adduct the limb. It may also rotate it inward.

_Structure._—The muscle arises by a strong tendon, chiefly in common with the opposite muscle. Its direct attachment to the ventral surface of the pelvis is not so extensive as a superficial inspection would suggest. The origin of the muscle presents anteriorly a round perforation for the passage of the external pudic vein. The belly is composed of parallel bundles, and is marked by a superficial furrow which, however, does not indicate a muscular division. It terminates on the inner surface of the stifle on a thin wide tendon which blends in front with that of the sartorius, below with the crural fascia.

_Relations._—Superficially, the skin and fascia, the penis or mammary gland, and the saphenous vessels and nerve; deeply, the pectineus, adductor, semimembranosus and semitendinosus, and, at the middle of the femur, the femoral vessels; anteriorly, the sartorius. In the upper third of the thigh the sartorius and gracilis are separated by a triangular interval (femoral triangle), in which lie the deep inguinal lymph glands and the femoral vessels.

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

_Nerve-supply._—Obturator and saphenous nerves.

SECOND LAYER

1. =Pectineus= (Figs. 180, 451, 456).—This muscle is fusiform and extends from the anterior border of the pubis to the middle of the inner border of the femur.

_Origin._—The prepubic tendon, the pubo-femoral ligament, and the anterior border of the pubis.

_Insertion._—The middle of the internal border of the femur, near the nutrient foramen.

_Action._—To adduct the limb and flex the hip joint.

_Structure._—The belly is cylindrical and contains little fibrous tissue. Its origin is perforated by the pubo-femoral ligament, and is thus divided into two unequal parts. The large upper part arises mainly from the prepubic tendon—only a very small part gaining direct attachment to the pubis. The small lower part does not reach the bone. The insertion is pointed and tendinous.

_Relations._—Superficially, the gracilis; deeply, the femur, the vastus internus, the terminal tendon of the psoas major and iliacus, and the deep femoral artery; anteriorly, the sartorius, the femoral vessels, the saphenous nerve, and the deep inguinal lymph glands; posteriorly, the adductor, obturator externus, and quadratus femoris, and the obturator nerve (anterior division).

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

_Nerve-supply._—Femoral and obturator nerves.

The _femoral canal_ is exposed in the dissection of the preceding
muscles (Figs. 200, 451). It is bounded anteriorly by the sartorius,
posteriorly by the pectineus, and externally by the iliacus and vastus
internus. Its internal wall is formed by the femoral fascia and the
gracilis. Its upper or abdominal opening (Lacuna vasorum) lies behind
and a little internal to the internal inguinal ring and is bounded
anteriorly by the inguinal ligament, posteriorly by the anterior
border of the pubis, and externally by the tendon of the psoas minor.
The canal terminates below at the insertion of the pectineus. It
contains the deep inguinal lymph glands, the femoral artery and vein,
and the saphenous nerve.

2. =Adductor=[66] (Figs. 179, 186, 451) (Great and small adductors of the thigh).—This fleshy, prismatic muscle lies behind the pectineus and vastus internus. It extends downward and forward from the ventral surface of the pelvis to the internal condyle of the femur.

_Origin._—The ventral surface of the pubis and ischium and the tendon of the gracilis.

_Insertion._—(1) The posterior surface of the femur from the level of the external trochanter to the groove for the femoral vessels; (2) the internal epicondyle of the femur and the internal lateral ligament of the stifle joint.

_Action._—To adduct the limb and assist in extending the hip joint. It may also rotate the femur outward.

_Structure._—It is almost entirely fleshy, and is composed of parallel bundles united rather loosely. It is usually possible to separate from the principal mass a small anterior short portion,[67] which is inserted into the femur behind the pectineus. The principal mass[68] is perforated below its middle by the femoral vessels, and is thus divided into two branches. The outer branch is inserted into the back of the femur with the short portion, while the inner branch is attached to the internal epicondyle and lateral ligament. There is often a superficial slip which reaches the internal straight patellar ligament. Some fibers pass under the lateral ligament and end on the tendon of the semimembranosus.

_Relations._—Internally, the gracilis, and branches of the femoral artery and of the obturator nerve; externally, the femur, the obturator externus, quadratus femoris, biceps femoris, and gastrocnemius, and the femoral, deep femoral, and obturator arteries; anteriorly, the pectineus, vastus internus, and a large branch of the obturator nerve; posteriorly, the semimembranosus and the great sciatic nerve.

_Blood-supply._—Femoral, deep femoral, and obturator arteries.

_Nerve-supply._—Obturator nerve.

3. =Semimembranosus.=—Described on p. 280.

THIRD LAYER

1. =Quadratus femoris= (Ischio-femoralis).—This is a narrow, flat muscle, which lies under cover of the upper part of the adductor (Figs. 455, 456).

_Origin._—The ventral surface of the ischium, just in front of the semimembranosus.

_Insertion._—An oblique line on the posterior surface of the femur, near the lower part of the internal trochanter.

_Action._—To extend the hip joint, and to adduct the thigh and rotate it outward.

_Structure._—It is composed of parallel bundles of fibers directed downward, forward, and outward.

_Relations._—Internally, the adductor, semimembranosus, and the obturator vessels; externally, the obturator externus and biceps femoris, the deep femoral artery, and the great sciatic nerve.

_Blood-supply._—Deep femoral and obturator arteries.

_Nerve-supply._—Great sciatic nerve.

2. =Obturator Externus= (Fig. 456).—This is a pyramidal muscle which extends across the back of the hip joint from the obturator foramen to the trochanteric fossa.

_Origin._—The ventral surface of the pubis and ischium, and the margin of the obturator foramen.

_Insertion._—The trochanteric fossa.

_Action._—To adduct the thigh and to rotate it outward.

_Structure._—It is almost entirely fleshy, the muscle-bundles being rather loosely connected. The insertion is pointed, flattened, and partly tendinous. The origin is perforated by the obturator vessels and nerve.

_Relations._—Internally, the adductor and quadratus femoris and the deep femoral vessels; externally, the gemellus, the tendon of the obturator internus, the biceps femoris, and the great sciatic nerve; anteriorly, the hip joint, the pectineus, and the external pudic vein.

_Blood-supply._—Deep femoral and obturator arteries.

_Nerve-supply._—Obturator nerve.

3. =Obturator internus= (Fig. 451).—This arises by two heads within the pelvic cavity, the tendon emerging through the lesser sciatic foramen.

_Origin._—(1) The pelvic surface of the pubis and ischium around the obturator foramen; (2) the pelvic surface of the shaft of the ilium and the wing of the sacrum.

_Insertion._—The trochanteric fossa.

_Action._—To rotate the femur outward.

_Structure._—The ischio-pubic head lies on the pelvic floor and covers the obturator 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 foramen to be inserted into the trochanteric fossa. A synovial bursa facilitates the play of the tendon over the external border of the ischium.[69]

_Relations._—The pelvic surface is covered by the pelvic fascia and 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.

_Blood-supply._—Obturator and internal pudic arteries.

_Nerve-supply._—Great sciatic nerve.

4. =Gemellus=[70] (Fig. 455).—This is a thin, triangular muscle, which extends from the external border of the ischium to the trochanteric fossa.

_Origin._—The external border of the ischium near the ischiatic spine.

_Insertion._—The trochanteric fossa.

_Action._—To rotate the femur outward.

_Structure._—Fleshy, some fibers being inserted into the tendon of the obturator internus.

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

_Blood-supply._—Obturator artery.

_Nerve-supply._—Sciatic nerve.