66 THE ANATOMY OF THE HORSE. 



Action. — It is an abductor at the hip-joint. 



The Biceps Femoris (Plate 15). This is one of the largest muscles 

 in the body. It arises from the sacral spines, the fascia enveloping the 

 muscles of the tail, the sacro-sciatic ligament, the tuber ischii, and the 

 gluteal fascia. Inferiorly it has three divisions, one of which is inserted 

 into the anterior surface of the patella, a small synovial bursa being 

 interposed between the tendon and the bone, another into the tibial 

 crest, and the third into the fascia of the leg. Besides these, the muscle 

 has an insertion into the circular mark behind the third trochanter of 

 the femur, by means of a fibrous band detached from the deep surface 

 of the muscle. 



Action. — The anterior half of the muscle, in virtue of its attachment 

 to the patella, is an extensor of the stifle, and an abductor at the hip. 

 The posterior half of the muscle, with its insertions into the tibia and 

 fascia of the leg, is a flexor and an outward-rotator at the stifle. When the 

 stifle-joint is kept extended the lower end of the muscle becomes its fixed 

 point, and it then extends the pelvis on the femur, and aids in rearing. 



The Semitendinosus (Plate 15). This muscle is placed at the 

 posterior border of the hip and thigh, where it occupies a position 

 between the last-described muscle and the semimembranosus. The 

 muscle is bifid superiorly, where it arises by one division from the 

 sacral spines and sacro-soiatic ligament, and by another and shorter 

 branch from the tuber ischii. Inferiorly it has a flat tendon, which is 

 inserted into the tibial crest, and whose posterior border blends with 

 the fascia of the leg. 



Action. — To flex the stifle and rotate the leg inwards. When the 

 stifle is fixed it can aid in rearing. 



The biceps femoris and semitendinosus muscles represent, apparently, 

 the muscles of the same name in man,^jte portions of the gluteus maximus. 



Directions. — The biceps must be carefully severed at its origin, and 

 pulled downwards. This will expose the aponeurotic layer that passes 

 beneath it from the superficial gluteus. A branch from the posterior 

 gluteal nerves should be found entering the last-named muscle by 

 turning forwards round the middle gluteus. Both branches of the 

 superficial gluteus should then be thrown downwards in order to fully 

 expose the next muscle. 



The Middle Gluteus {Gluteus maximus of Percivall) (Plate 15) is a 

 muscle of great size and strength. It was partly exposed before the 

 removal of the superficial muscle. The fibres of the muscle arise from 

 the aponeurosis of the common mass of the loins (longissimus dorsi), 

 from the gluteal surface of the ilium, from the two ilio-sacral and the 

 sacro-soiatic ligaments, and from the gluteal fascia. It has three 

 distinct and constant insertions : 1. By a tendon, into the summit of 

 the great trochanter. 2. By another tendon, which plays over the 



