3. THE MUSCLES OF THE GLUTEAL REGION (figs. 648, 649)
| Gluteus maximus | Obturator internus |
| Gluteus medius | Gemellus superior |
| Gluteus minimus | Gemellus inferior |
| Piriformis | Quadrates femoris |
| Obturator externus |
The Gluteus maximus (fig. 648), the largest and most superficial muscle in the gluteal region, is a broad and thick fleshy mass of a quadrilateral shape, and forms the prominence of the buttock. Its large size is one of the most characteristic features of the muscular system in wan, connected as it is with the power he has of maintaining the trunk in the erect position. The muscle is remarkably coarse in structure, being made up of fasciculi lying parallel with one another, and collected into large bundles separated by fibrous septa. It arises from the posterior gluteal line of the ilium, and the rough portion of bone, including the crest, immediately above and behind it; from the aponeurosis of the Sacrospinalis; from the posterior surface of the lower part of the sacrum and the side of the coccyx; from the sacrotuberous ligament, and from the fascia (gluteal aponeurosis) covering the Gluteus medius. The fibers run obliquely downwards and laterally; those forming the tipper and larger portion of the muscle, together with the superficial fibers of the lower portion, end in a thick tendinous lamina, which passes across the greater trochanter, and is inserted into the iliotibial tract of the fascia lata; the deeper fibers of the lower portion of the muscle are inserted into the gluteal tuberosity of the femur between the Vastus lateralis and Adductor magnus.
Relations.—Its superficial surface is in relation with a thin fascia which separates it from the subcutaneous tissue; its deep surface, with the ilium, sacrum, coccyx, and sacrotuberous ligament, part of the Gluteus medius, Piriformis, Gemelli, Obturator internus, Quadratus femoris, the tuberosity of the ischium, greater trochanter, the origins of the Biceps femoris; Semitendinosus, Semimembranosus and the Adductor magnus. The superficial part of the superior gluteal artery reaches the deep surface of the muscle by passing between the Piriformis and the Gluteus medius; the inferior gluteal and internal pudendal vessels and the sciatic, pudendal, and posterior femoral cutaneous nerves and muscular branches from the sacral plexus, issue from the pelvis below the Piriformis. The first perforating artery and the terminal branches of the medial circumflex femoral artery are also found under cover of the lower part of the muscle. Its upper border is thin, and is connected with the Gluteus medius by the gluteal aponeurosis. Its lower border is free and prominent.
Nerve-supply.-The Gluteus maximus is supplied by the inferior gluteal nerve (L. 5 and S. 1 and 2).
Actions.–When the Gluteus maximus takes its fixed point from the pelvis, it extends the thigh and brings it into line with the trunk. Taking its fixed point below, it supports the pelvis and the trunk upon the head of the femur. Its most powerful action is to raise the trunk after stooping by drawing the pelvis backwards. It is a tensor of the fascia lata, and through the iliotibial tract it steadies the femur on the tibia during standing, when the extensor muscles are relaxed.
The Gluteus medius is a broad, thick, muscle which is situated on the outer surface of the pelvis. Its posterior one-third is covered by the Gluteus maximus, its anterior two-thirds by the gluteal aponeurosis, which separates it from the superficial fascia and skin. It arises from the outer surface of the ilium between the iliac crest and posterior gluteal line above, and the middle gluteal line below; it also arises from the strong fascia which covers the upper part of its outer surface. The fibers converge to a flattened tendon, which is inserted into the oblique ridge directed downwards and forwards on the lateral surface of the greater trochanter of the femur. A bursa (trochanteric bursa of Gluteus medius) separates the tendon from the anterosuperior part of the lateral surface of the trochanter, over which it glides.
The Gluteus minimus (fig. 649), the smallest of the Glutei, is placed immediately beneath the preceding. It is fan-shaped, arising from the outer surface of the ilium, between the middle and inferior gluteal lines, and, behind, from the margin of the greater sciatic notch. The fibers converge to the deep surface of an aponeurosis, and this ends in a tendon which is inserted into a ridge on the lateral part of the anterior surface of the greater trochanter of the femur, and gives an expansion to the capsule of the hip-joint. A bursa (trochanteric bursa of Gluteus minimus) is interposed between the tendon and the medial part of the anterior surface of the greater trochanter.
Between the Gluteus medius and Gluteus minimus are the deep branches of the superior gluteal vessels, and the superior gluteal nerve. The reflected tendon of the Rectus femoris and the capsule of the hip-joint are placed deep to the Gluteus minimus.
Nerve-supply.-Both the Gluteus medius and the Gluteus minimus are supplied by the superior gluteal nerve (L. 4 and 5 and S. 1).
Actions.-Both the preceding muscles, acting from the pelvis, abduct the thigh and rotate it medially. Acting from the femur, they produce the slight rotation of the pelvis which occurs in walking and. running, and keep the transverse axis of the pelvis horizontal, or nearly horizontal, while the opposite limb is unsupported, e.g. when the foot is off the ground in walking or running.
The Piriformis (fig. 649) lies almost parallel with the posterior margin of the Gluteus medius. It is situated partly within the pelvis on its posterior wall, and partly at the back of the hip-joint. It arises from the front of the sacrum by three fleshy digitations, attached to the portions of bone between the anterior sacral foramina, and to the grooves leading from the foramina (fig. 273) : a few fibers also arise from the margin of the greater sciatic foramen, and from the upper part of the anterior surface of the sacrotuberous ligament. The muscle passes out of the pelvis through the greater sciatic foramen, and is inserted by a rounded tendon into the upper border of the greater trochanter of the femur, behind and above; but often partly blended with, the common tendon of the Obturator internus and Gemelli.
Actions.-The Piriformis rotates the thigh laterally.
The obturator membrane (fig. 650) is a thin, fibrous sheet which nearly closes the obturator foramen. Its fibers are arranged in interlacing bundles mainly transverse in direction; the uppermost bundle is attached to the obturator tubercles and completes the obturator canal for the passage of the obturator vessels and nerve. The membrane is attached to the sharp margin of the obturator foramen except at its lower lateral angle, where it is fixed to the pelvic surface of the ramus of the ischium, i.e. within the margin of the foramen. Both Obturator muscles take origin from this membrane, and some of the fibers of the pubofemoral ligament of the hip-joint are attached to its inferior surface.
The Obturator internus (fig. 651) is situated partly within the true pelvis, and partly at the back of the hip-joint. It arises from the inner surface, of the anterolateral wall of the pelvis, where it surrounds the greater part of the obturator foramen, being attached to the inferior ramus of the pubis, the ramus of the ischium and to the inner surface of the hip-bone below and behind the pelvic brim, reaching from the upper part of the greater sciatic foramen above and behind, to the obturator foramen below and in front. It also arises from the medial part of the pelvic surface of the obturator membrane, from the tendinous arch which completes the canal for the passage of the obturator vessels and nerve, and to a, slight extent from the obturator fascia, which covers the muscle. The fibers converge rapidly towards the lesser sciatic foramen and end in four or five tendinous bands in the deep surface of the muscle; these bands are reflected at a right angle over the grooved surface of the ischium between its spine and tuberosity. The grooved surface is covered by smooth cartilage, which is separated from the tendon by a bursa, and presents one or more ridges corresponding with the furrows between the tendinous bands. These bands leave the pelvis through the lesser sciatic foramen and unite into a single flattened tendon, which passes horizontally across the capsule of the hip-joint, and, after receiving the attachments of the Gemelli, is inserted into the fore part of the medial surface of the greater trochanter of the femur, above and in front of the trochanteric fossa. A bursa, narrow and elongated in form, is usually found between the tendon and the capsule of the hip-joint; it occasionally communicates with the bursa between the tendon and the ischium.
Nerve-supply.-The nerve to Obturator internus derives its fibers from L. 5 and S. 1 and 2.
Action.—The Obturator internus rotates the thigh laterally.
The Gemelli (fig. 649) are two small muscular fasciculi, accessories to the tendon of the Obturator internus, which is received into a groove between them.
The Gemellus superior, the smaller of the two, arises from the outer surface of the spine of the ischium, blends with the upper part of the tendon of the Obturator internus, and is inserted with it into the medial surface of the greater trochanter of the femur. It is sometimes wanting.
Nerve-supply.-The Gemellus superior is supplied by the nerve to the Obturator internus (L. 5 and S. l and 2).
The Gemellus inferior arises from the upper part of the tuberosity of the ischium, immediately below the groove for the Obturator internus tendon. It blends with the lower part of the tendon of the Obturator internus, and is inserted with it into the medial surface of the greater trochanter.
Nerve-supply.-The Gemellus inferior is supplied by the nerve to the Quadratus femoris (L. 4 and 5 and S. 1)
Actions.-The Gemelli superior et inferior rotate the thigh laterally.
The Quadratus femoris (fig. 649) is a flat, quadrilateral muscle, between the Gemellus inferior and the upper margin of the Adductor magnus; it is separated from the latter by the transverse branch of the medial circumflex femoral artery. It arises from the upper part of the external border of the tuberosity of the ischium, and is inserted into a small tubercle on the upper part of the trochanteric crest of the femur, and for a short distance into the bone below. As it passes to its insertion the muscle lies posterior to the articular capsule of the hip-joint and the neck of the femur, but it is separated from them by the tendon of the Obturator externus and the ascending branch of the medial circumflex femoral artery. A bursa is often found between the front of this muscle and the lesser trochanter.
Nerve-supply.–The nerve to Quadratus femoris derives its fibers from L. 4and 5 and S.1.
Action. The Quadratus femoris is a lateral rotator of the thigh.
The Obturator externus (fig. 652) is a flat, triangular muscle which covers the outer surface of the anterior wall of the pelvis. It arises from the margin of bone immediately around the medial side of the obturator foramen; viz. from the rami of the pubis, and the ramus of the ischium; it also arises from the medial two-thirds of the outer surface of the obturator membrane, and from the tendinous arch which completes the canal for the passage of the obturator vessels and nerves. The fibers springing from the ramus of the ischium extend for a short distance on to the pelvic surface of the bone, where they obtain a narrow origin between the margin of the foramen and the attachment of the obturator membrane. The fibers converge and pass backwards, laterally and upwards, and end in a tendon which runs across the back of the neck of the femur and lower part of the capsule of the hip-joint and is inserted into the trochanteric fossa of the femur. The obturator vessels lie between the muscle and the obturator membrane; the anterior branch of the obturator nerve reaches the thigh by passing in front of the muscle, and the posterior branch by piercing it.
Nerve-supply.- The Obturator externus is supplied by the posterior branch of the obturator nerve (L. 3 and 4).
Action.-The Obturator externus is a lateral rotator of the thigh.
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