DISSECTION OF THE POSTERIOR LIMB. 65 



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 anteiior 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 Semitbndinosus (Plate 15). This muscle is placed at the 

 posterior border of the hip and thigh, where it occvipies 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-sciatic 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, apparent^, 

 the muscles of the same name in man, plus portions of the gluteus 

 maximus. Percivall describes the semitendinosus as representing also 

 the semimembranosus of man. 



Directions. — The biceps mvist 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 turn- 

 ing forwards round the middle gluteus. Both branches of the super- 

 ficial gluteus should then be thrown downwards in order to fully 

 expose the next muscle. 



The Middle Gluteus (Glnietis 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-sciatic ligaments, and from the gluteal fascia. It has three distinct 

 and constant insertions: 1. By a tendon, into the swnmit of the great 

 trochanter. 2. By another tendon, which plays over the convexity of the 

 same trochanter by means of a synovial bursa, and becomes inserted into 

 the crest. 3. By a triangular fleshy slip, into the back of the trochan- 

 teric ridge. 



Action. — To extend and abduct the hip. In the former of these 



F 



