POSTERIOR FEMORAL REGION. 417 



by the Biceps, Semitendinosus, and Semimembranosus muscles. The remain- 

 ing muscles are powerful rotators of the thigh outwards. In the sitting posture, 

 when the thigh is flexed upon the pelvis, their action as rotators ceases, and 

 they become abductors, with the exception of the Obturator Externus, which 

 still rotates the femur outwards. When the femur is fixed, the Pyriformis and 

 Obturator muscles serve to draw the pelvis forwards if it has been inclined 

 backwards, and assist in steadying it upon the head of the femur. 



POSTEEIOR FEMOKAL EEGION. 

 Biceps. Semitendinosus. Semimembranosus. 



Dissection (Fig. 256). Make a vertical incision along the middle of the thigh, from the lower 

 fold of the nates to about three inches below the back of the knee-joint, and there connect it 

 with a transverse incision, carried from the inner to the outer side of the leg. Make a third 

 incision transversely at the junction of the middle with the lower third of the thigh. The in- 

 tegument having been removed from the back of the knee, and the boundaries of the popliteal 

 space examined, the removal of the integument from the remaining part of the thigh should be 

 continued, when the fascia and muscles of this region will be exposed. 



The Biceps (Fig. 257) is a large muscle, of considerable length, situated on 

 the posterior and outer aspect of the thigh. It arises by two heads. One, the 

 long head, arises from an impression at the upper and back part of the tube- 

 rosity of the ischium, by a tendon common to it and the Semitendinosus. The 

 femoral, or short head, arises from the outer lip of the linea aspera, between 

 the Adductor Magnus and Vastus Externus, extending from two inches below 

 the insertion of the Gluteus Maximus, to within two inches of the outer con- 

 dyle ; it also arises from the external intermuscular septum. The fibres of the 

 long head form a fusiform belly, which passing obliquely downwards and a 

 little outwards, terminate in an aponeurosis which covers the posterior surface 

 of the muscle, and receives the fibres of the short head; this aponeurosis be- 

 comes gradually contracted into a tendon, which is inserted into the outer side 

 of the head of the fibula. At its insertion, the tendon divides into two por- 

 tions, which embrace the external lateral ligament of the knee-joint, a strong 

 prolongation being sent forwards to the outer tuberosity of the tibia, which 

 gives off an expansion to the fascia of the leg. The tendon of this muscle 

 forms the outer hamstring. 



Relations. By its superficial surface with the Gluteus Maximus above, the 

 fascia lata and integument in the rest of its extent. By its deep surface, with 

 the Semimembranosus, Adductor Magnus, and Vastus Externus, the great 

 sciatic nerve, popliteal artery and vein, and near its insertion, with the external 

 head of the Gastrocnemius, Plantaris, the superior external articular artery, 

 and the external popliteal nerve. 



The /Semitendinosus, remarkable for the great length of its tendon, is situated 

 at the posterior and inner aspect of the thigh. It arises from the tuberosity 

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

 also arises from an aponeurosis which connects the adjacent surfaces of the 

 two muscles to the extent of about three inches after their origin. It forms a 

 fusiform muscle, which, passing downwards and inwards, terminates a little 

 below the middle of the thigh in a long round tendon which lies along the" 

 inner side of the popliteal space, then curves around the inner tuberosity of 

 the tibia, and is inserted into the upper part of the inner surface of the shaft 

 of that bone, nearly as far forwards as its anterior border. This tendon lies 

 beneath the expansion of the Sartorius, and below that of the Gracilis, to 

 which it is united. A tendinous intersection is usually observed about the 

 middle of the muscle. 



delations. By its superficial surface, with the Gluteus Maximus and fascia 

 lata. By its deep surface, with the Semimembranosus, Adductor Magnus, inner 

 head of the Gastrocnemius, and internal lateral ligament of the knee-joint. 



The Semimembranosus, so called from the membranous expansion on its 

 27 



