278 FASCIA AND MUSCLES OF THE HORSE 



which passes over the convexit}" 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 fascise, the tensor 

 fascise latae, 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, ciuadrilateral 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 fascise, 

 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 ex- 

 ternal 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 pro- 

 pelling 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. 



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, 



* By some anatomists the portion inserted into the crest is termed the gkiteus accessorius, 

 but Lesbre considers this the deep ghiteus, homologous with the ghiteus minimus of man. The 

 portion inserted into the trochanteric ridge apparently represents the piriformis of man. 



'■* Apparently the muscle represents the biceps, together with part of the gluteus super- 

 ficialis of man. Hence the names gluteo-biceps and paramero-biceps have been suggested. 



