608 A MANUAL OF ANA TOMY. 



Nerve Supply. A branch from the sacral plexus, see 

 page 612. 



Action. To rotate the thigh outward and adduct it when 

 the limb is extended. If the thigh is flexed it acts as an 

 external rotator and abductor of it. 



Acting from the femur, it will depress the opposite side 

 of the pelvis and carry it backward. 



Obturator Externus. See page 582. 



Biceps Plexor Cruris (Femoris) (Biceps Femoris). 



Origin. (i) The long head, in common with the semi- 

 tendinosus from the (anterior) lower and internal facet upon 

 the tuberosity of the ischium. (2) The short head, from 

 the whole length of the external lip of the linea aspera and 

 the upper two-thirds of the external condyloid ridge, and 

 from the external intermuscular septum. 



Insertion. Into the head of the fibula at the base of the 

 styloid process, by a prolongation of some of the anterior 

 fibres of the tendon into the external tuberosity of the 

 tibia, and by others from the back of the tendon into the 

 deep fascia of the leg. 



Nerve Supply. The great sciatic (from the first, second, 

 and third sacral nerves). 



Action. (i) Upon the leg (both heads) the biceps is a 

 flexor of the leg, and in a flexed position becomes an ex- 

 ternal rotator (supinator). (2) Upon the thigh (the long 

 head) the muscle is an extensor for all the ordinary pur- 

 poses of locomotion and the like, the gluteus maximus 

 being only called into action by some heavier work to be 

 done. It also has a slight action as an external rotator of 

 the thigh. (3) Upon the body, it is used in raising it from 

 a stooping position (an extensor of the pelvis). 



