POSTERIOR FEMORAL REGION. 339 



from the femur, the Glutei muscles act upon the pelvis, supporting it and the whole 

 trunk upon the head of the femur : this is especially obvious in standing on one 

 leg. In order to gain the erect posture after the effort of stooping, these muscles 

 draw the pelvis backwards, assisted by the Biceps, Semi-tendinosus, and Semi- 

 membranosus muscles. The remaining 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 FEMORAL REGION. 



Biceps. Semi-tendinosus. Semi-membranosus. 



Dissection (fig. 189) . 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. A third incision 

 should then be made transversely at the junction of the middle with the lower third of the thigh. 

 The integument having been removed from the back of the knee, and the boundaries of the pop- 

 liteal 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 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, from 

 an impression at the upper and back part of the tuberosity of the ischium, by a 

 tendon common to it and the Semi-tendinosus ; the femoral or short head, from 

 the outer lip of the linea aspera, between the Adductor magnus and Vastus ex- 

 ternus, extending from two inches below the insertion of the Gluteus maximus, 

 to within two inches of the outer condyle ; it also arises from the external inter- 

 muscular septum. The fibres of the long head form a fusiform belly, which, 

 passing obliquely downwards and a little outwards, terminates in an aponeurosis 

 which covers the posterior surface of the muscle, and receives the fibres of the 

 short head ; this aponeurosis becomes 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 portions, 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 ham-string. 



^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 

 Semi-membranosus, 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, and superior external articular artery. 



The Semi-tendinosus, 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 from 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 ; curving around the inner tuberosity of the tibia, it 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. 



Relations. By its superficial surface, with the Gluteus maximus and fascia lata. 



