Part 90

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

Nerve-supply.—Anterior gluteal nerve.

3. =Gluteus medius= (Figs. 178, 179) (Middle gluteus; gluteus maximus).—This is a very large muscle which covers the dorsal surface of the ilium and the greater part of the lateral wall of the pelvis, and extends forward also on the lumbar part of the longissimus.

Origin.—(1) The aponeurosis of the longissimus, as far forward as the first lumbar vertebra; (2) the gluteal or dorsal surface and internal and external angles of the ilium; (3) the dorsal and lateral sacro-iliac and sacro-sciatic ligaments, and the gluteal fascia.

Insertion.—(1) The summit of the trochanter major of the femur; (2) the crest below the trochanter; (3) the outer aspect of the trochanteric ridge.

Action.—To extend the hip joint and abduct the limb. By its connection with the longissimus a muscular mass is formed which is one of the chief factors in rearing, kicking, and propulsion.

Structure.—The anterior extremity of the muscle is relatively thin, and lies in a depression on the surface of the longissimus, from the strong aponeurosis of which the fibers take origin. The pelvic portion of the muscle is very voluminous, and forms the bulk of the muscular mass which gives the haunch its rounded contour. This part of the muscle is intersected by several tendinous sheets. One of these is particularly distinct, and is attached to the gluteal line on the ilium. This divides the muscle incompletely into superficial and deep strata. The superficial part is inserted by a strong tendon into the summit of the great trochanter, and by a pointed fleshy mass with a tendinous border into the trochanteric ridge. The deep part (Gluteus accessorius) is smaller, and arises entirely from the ilium between the gluteal line and the external angle (Fig. 455). It has a strong flat tendon which passes over the convexity of the trochanter to be inserted into the crest below it. The convexity is covered with cartilage, and the =trochanteric bursa= (Bursa trochanterica) is interposed between the tendon and the cartilage.

Relations.—Superficially, the skin, lumbo-dorsal and gluteal fasciæ, the tensor fasciæ latæ, gluteus superficialis, and biceps femoris; deeply, the longissimus, the ilium, sacro-iliac and sacro-sciatic ligaments, the gluteus profundus, iliacus and rectus femoris, the iliaco-femoral artery, the gluteal and internal pudic vessels and nerves, and the great sciatic nerve.

Blood-supply.—Gluteal, ilio-lumbar, lumbar, and iliaco-femoral arteries.

Nerve-supply.—Gluteal nerves.

4. =Gluteus profundus= (Deep gluteus; gluteus internus; scansorius).—This much smaller, quadrilateral muscle lies under the posterior part of the preceding muscle, and extends over the hip joint, from the superior ischiatic spine to the anterior part of the great trochanter (Fig. 455).

Origin.—The superior ischiatic spine and the adjacent part of the shaft of the ilium.

Insertion.—The edge of the anterior part or convexity of the trochanter major of the femur.

Action.—To abduct the thigh and to rotate it inward.

Structure.—The muscle is short and thick and contains numerous tendinous intersections. The fibers are directed almost transversely outward over the capsule of the hip joint and converge at the convexity of the trochanter.

Relations.—Superficially, the gluteus medius and branches of the gluteal vessels and nerves; deeply, the shaft of the ilium, the hip joint, and the rectus femoris and capsularis.

Blood-supply.—Gluteal artery.

Nerve-supply.—Anterior gluteal nerve.

5. =Biceps femoris= (Gluteo-biceps s. paramero-biceps).—This large muscle lies behind and in part upon the superficial and middle glutei. It extends in a curved direction from the sacral and coccygeal spines to the outer surface of the stifle and leg (Figs. 178, 199, 200, 201, 202).

Origin.—(1) The dorsal sacro-iliac ligament, the gluteal and coccygeal fasciæ, and the intermuscular septum between this muscle and the semitendinosus; (2) the tuber ischii.

Insertion.—(1) A tubercle on the posterior surface of the femur near the external trochanter; (2) the anterior surface and external straight ligament of the patella; (3) the tibial crest; (4) the anterior and internal surface of the tuber calcis.

Action.—The action is somewhat complex, because the muscle is composed of three portions, has several points of insertion, and acts on all the joints of the limb except those of the digit. The general action is to extend the limb, as in propelling the body, rearing or kicking, and to abduct it. The anterior part, by its attachment to the posterior surface of the femur and to the patella, would extend the stifle and hip joints and abduct the limb. The middle part, being inserted chiefly on the tibial crest and the external straight ligament, would extend the hip, and, with the semitendinosus, flex the stifle. The posterior part, by virtue of its attachment to the tuber calcis, assists in extending the hock.

FIG. 199.—MUSCLES OF PELVIC LIMB OF HORSE, POSTERO-EXTERNAL VIEW.

17, Position of tuber ischii; o′, superficial gluteus; q, q′, q″, biceps femoris; r, semitendinosus; t, sacro-coccygeus lateralis; v, semimembranosus; w, gracilis; f, gastrocnemius. (After Ellenberger-Baum, Anat. f. Künstler.)] ]

Structure.—The muscle has two heads of origin: The long or vertebral head arises chiefly from the dorsal and lateral sacro-iliac ligaments, the coccygeal fascia, and the intermuscular septum. There is often a large =bursa= between this head and the trochanter major. The short or ischiatic head arises by a strong tendon from the ventral spine on the tuber ischii. They unite, and a short tendon is detached from the deep face of the muscle, to be inserted into the posterior surface of the femur near the third trochanter (Fig. 455), a =bursa= being interposed between the tendon and the bone. The muscle then divides into three portions, which terminate on a strong aponeurosis over the junction of the thigh and leg. The anterior branch is directed toward the patella, the middle toward the tibial crest, while the posterior one assists in the formation of the posterior contour of the limb. The aponeurosis blends with the deep layer of the fascia cruris, as already described. A synovial =bursa= occurs under the patellar insertion.

Relations.—Superficially, the skin and fascia; deeply, the sacro-iliac and sacro-sciatic ligaments, the coccygeal fascia, the femur, the obturator, gemellus, quadratus femoris, adductor, semimembranosus, vastus externus, and gastrocnemius muscles, branches of the lateral sacral, gluteal, obturator, femoral and deep femoral vessels, the great sciatic, tibial, peroneal, and posterior gluteal nerves; in front, the superficial and middle glutei; behind and internally, the semitendinosus.

Blood-supply.—Gluteal, obturator, and femoro-popliteal arteries.

Nerve-supply.—Posterior gluteal and great sciatic nerves.