BICEPS FEMORIS 3G3 



THE HAMSTRING MUSCLES 



The hamstring muscles form a group at the back of the thigh, separated l)y 

 inter^m^c•ular septa from the vastus externus on the outer, and the adductor 

 magnus on the inner side. They consist of the biceps, semi-tendinosus and semi- 

 membranosus, and are supplied by the great sciatic nerve. Like the gluteus 

 maximus their action is to extend the hip. 



L BICEPS FEMORIS 



The biceps femoris (figs. 288 and 290) — named from its two heads — consists 

 of two parts; the longer head being somewhat fusiform, and the shorter a triangular 

 sheet. 



Origin. — The long head from (1) the lower and inner facet at the back 

 of the tul)er ischii by a tendon common to it and the semi-tendinosus; (2) the 

 lower part of the great sacro-sciatic ligament. The short head from (1) the outer 

 lip of the linea aspera from a point just above the middle of the bone down to the 

 bifurcation; (2) the uj^per two-thirds of the outer condylar ridge; (3j the external 

 intermuscular septum. 



Insertion. — (1) A fossa below and in front of the styloid process of the head 

 of the tiljula; (2) the deep fascia covering the peronei muscles; (3) the outer 

 tuberosity of the til)ia. 



Structure. — The origin of the long head is by a short tendon which is con- 

 tinued down to the middle of the thigh by a sej^tum which divides this muscle 

 from the semi-tendinosus. From this tendon and the outer surface of the septum 

 the muscular filjres arise in penniform fashion and form a fusiform belly, which 

 receives at the junction of the middle and lower thirds of the thigh the thick sheet 

 of muscular fibres derived from the short outer head. The tendon commences 

 upon the posterior surface of the muscle near its outer border about the middle 

 of the thigh. At the back of the external condyle the fleshy fi])res cease. The 

 roitnded tendon here widens into a thick aponeurosis, which embraces the anterior 

 portion of the external lateral ligament at the point of its insertion into the outer 

 and anterior facet of the head of the fibula. Between this tendon and the external 

 lateral ligament is a bursa. From the borders of the tendon at this point a thinner 

 aponeurosis is given off to the outer tuberosity of the tibia in front and the deej) 

 fascia of the leg liehind. 



Nerve-supply. — From the first, second and third nerves of the sacral j^lexus by 

 the great sciatic nerve which sends branches to the anterior and inner surfaces of 

 the muscle about the middle of the thigh. The short head of the biceps receives 

 its supply from the external popliteal nerve. 



Action. — To extend the hip and flex the knee. Its shorter head acts U])on the 

 knee only. A\'hen the knee is flexed, both heads will unite in rotating the leg out- 

 wards. When the knee is extended, the long head will have a slight influence in 

 rotating the hip outwards. Acting from below, the long head Avill assist in raising 

 the brxly from the stooping position. 



Relations. — Behind, the gluteus maximus, the plantaris, the outer head of 

 the gastrocnemius, gluteus maximus, fascia lata, and the small sciatic nerve. In 

 front, the tendon of the semi-memVtranosus, the adductor magnus, and the great 

 sciatic nerve. Upon its inner Ijorder lie the semi-tendinosus, scmi-membranosus, 

 and the external popliteal nerve. Beneath the lower tendon is a bursa which sep- 

 arates it from the external lateral ligament of the knee-joint. 



Variations. — The short head of the biceps may be absent. Accessory heads may be derived 

 from tlie tuber ischii, tlie upper part of the linea aspera, the fascia lata, or the iimer surface of 

 the tendou of insertion of the gluteus maximus. It may send a sHp to the gastrocnemius. 



