BACK OF THE THIGH 321 



about the middle of the thigh ; the other branches arise about 

 the level of the ischial tuberosity. 



As the nerves to the muscles are being followed ; arteries will 

 be found piercing the adductor magnus and passing into the 

 hamstring muscles ; they are branches of the profunda artery. 

 As many of them as possible should be preserved and cleaned. 

 After the nerves and arteries have been secured, pull the long 

 head of the biceps and the semitendinosus laterally, and clean 

 the semimembranosus, which lies on a deeper plane. 



M. Biceps Femoris. The biceps femoris arises by two 

 heads a long or ischial^ and a sfwrt or femoral^ and is 

 inserted, chiefly, into the head of the fibula. The long head 

 arises from the ischium by a tendon, common to it and the 

 semitendinosus (Fig. 128, p. 286), which is implanted into the 

 medial of the two impressions on the upper part of the 

 ischial tuberosity. Some fibres from the sacro- tuberous 

 ligament are continued into it. The short head arises from 

 the back of the femur, distal to the insertion of the glutaeus 

 maximus, viz., from the lateral lip of the linea aspera, from 

 the proximal half of the lateral supracondylar ridge, and 

 from the lateral intermuscular septum. Its parallel fibres 

 run obliquely distally and laterally, and join the anterior and 

 medial surface of the tendon of insertion. This tendon, on 

 the lateral aspect of the knee joint, is split into an anterior 

 and a posterior part by the fibular collateral ligament. Both 

 parts are inserted into the upper aspect of the head of 

 the fibula anterior to the apex capituli, but, in addition, the 

 posterior part sends an aponeurotic expansion to the deep 

 fascia of the leg, and by means of a similar expansion the 

 anterior part gains attachment to the lateral condyle of the 

 tibia. Each head of the biceps femoris receives its nerve 

 supply from the sciatic nerve. The twigs to the long head 

 are derived from the tibial part of the sciatic nerve, and 

 that to the short head from the common peroneal part. 

 Both heads flex the knee joint and rotate the leg laterally. 

 The long head is also an extensor of the hip joint. 



M. Semitendinosus. The semitendinosus muscle arises 

 from the medial impression on the superior part of the tuberosity 

 of the ischium by a tendon common to it and the long head of 

 the biceps femoris (Fig. 128, p. 286). The muscular belly 

 ends, in the distal third of the thigh, in a long cylindrical tendon 

 which passes downwards on the semimembranosus muscle. 

 At the medial side of the knee the tendon bends forwards, 



VOL. i 21 



