438 A MANUAL OF ANATOMY 



Action. — Acting from its origin the muscle is an extensor of the 

 hip- joint and a flexor of the leg upon the thigh, and, having flexed 

 the knee-joint, it acts as an internal rotator of the leg. Acting from 

 its insertion it is an extensor of the pelvis upon the thigh. The semi- 

 tendinosus is intimately connected with the long or ischial head of 

 the biceps femoris in the upper fifth of the thigh, and its belly is 

 crossed at its centre by an oblique tendinous intersection. In the 

 lower third of the thigh the muscle has a long, narrow, round 

 tendon, which broadens out at its insertion, and crosses the internal 

 lateral ligament of the knee-joint. A bursa intervenes between it 

 and that ligament, and also between it and the tendon of the 

 sartorius. 



Semimembranosus — Origin. — By means of a broad, flat tendon 

 from the upper and outer impression on the posterior surface of the 

 tuber ischii. 



Insertion. — The insertion is threefold, as follows : (i) the chief 

 insertion is by means of a strong tendon into the horizontal groove 

 on the posterior surface of the internal tuberosity of the tibia ; 

 (2) by an expansion which passes upwards and outwards to the upper 

 and back part of the external condyle of the femur, and which forms 

 a large part of the posterior ligament of the knee-joint, known as 

 the ligamentum posticum Winslowii ; (3) by a broad expansion, 

 which passes downwards and outwards to the oblique or popliteal 

 line on the posterior surface of the shaft of the tibia. This ex- 

 pansion covers the popliteus muscle, and is called the popliteal 

 fascia. 



Nerve-supply. — Great sciatic nerve. The branches come from 

 the internal popliteal part of the nerve. 



Action. — Acting from its origin the muscle is an extensor of the 

 hip- joint and a flexor of the leg upon the thigh, and, having flexed 

 the knee-joint, it acts as an internal rotator of the leg. Acting 

 from its insertion it is an extensor of the pelvis upon the thigh. 



The strong tendon of origin is prolonged downwards for some 

 distance upon the outer side of the muscle, and the chief tendon of 

 insertion is prolonged upwards for some distance upon its inner side 

 The belly of the muscle is composed of short, oblique fasciculi, an 

 arrangement which gives it great power of action, but a limited 

 range of movement. The chief tendon of insertion is under cover 

 of the posterior border of the internal lateral ligament of the knee- 

 joint. Previous to this it is separated from the interned head of the 

 gastrocnemius by the popliteal bursa, which frequently communi- 

 cates with the synovial membrane of the knee-joint through an 

 opening often present in the posterior ligament. The chief tendon 

 of insertion is also separated by a bursa from the upper lip of the 

 groove on the posterior surface of the internal tuberosity of the 

 tibia. 



The hamstring muscles descend in close contact through the 

 upper three-fourths of the thigh, being held together by the fascia 

 lata. When, however, they reach the lower fourth, they part 



