250 THE MUSCLES OF THE LOWER LIMB. 



the fascia lata, which is attached below to the fore part of the outer tuberosity of the tibia, 

 the gluteus maximus is farther enabled to exercise an influence upon the knee, steadying and 

 supporting that joint in the extended position during standing, when the proper extensor 

 muscles are relaxed. 



The gluteus medius and minimus are powerful abductors of the thigh when the hip- joint is 

 extended, and along with the tensor vaginae f emoris, come principally into action in supporting 

 the body on one limb, and in the rotation of the pelvis on the two limbs alternately which 

 takes place in walking. Their anterior fibres draw forwards the great trochanter, and rotate 

 the limb inwards, while the posterior part of the minimus produces outward rotation. In 

 proportion as the hip is flexed, they lose their power as abductors, and become inward 

 rotators. 



The tensor vagince femoris aids the gluteus medius and minimus in rotating inwards and 

 abducting the limb, in the latter case being combined in its action with the upper part of the 

 gluteus maximus. Owing to its mode of insertion, moreover, it will assist the gluteus 

 maximus in supporting the knee in the extended position, counteracting the tendency of that 

 muscle to draw the ilio-tibial band backwards, and thus ensuring that the traction is exercised 

 upon the tibia in the direct line of the thigh. 



The pyriformis, obturator inter nus, and gemelli muscles support the hip- joint posteriorly, 

 and rotate the limb outwards when it is extended, but become abductors when the hip is 

 flexed. The quadratus femoris rotates the thigh outwards and assists in adducting. The 

 oUurator externus is also principally an external rotator, but it is farther a flexor and 

 adductor of the thigh, bringing the uppermost of the two limbs into position when the thighs 

 are crossed in sitting. It supports the hip- joint posteriorly and inferiorly. 



THE POSTERIOR FEMORAL OR HAMSTRING MUSCLES. 



At the back of the thigh are three long flexor muscles of the knee-joint, viz., 

 the biceps, semitendinosus, and semimembranosus. 



The biceps flexor cruris muscle (fig. 249, 4) consists of two parts, arising one 

 from the hip-bone, the other from the femur, which unite inferiorly to terminate on 

 the fibula. The long head arises by a tendon common to it and the semitendinosus 

 from the inner impression on the upper part of the ischial tuberosity, receiving also 

 some fibres from the great sacro-sciatic ligament ; the short head (fig. 251, 8) arises 

 from the outer lip of the linea aspera in its whole extent, from the upper two-thirds 

 of the external supracondylar line, and from the adjacent external intermuscular 

 septum. The muscular fibres from both heads end in a common tendon, which is 

 inserted into the upper and outer part of the head of the fibula by two portions, 

 which embrace the external lateral ligament of the knee-joint. Some of the fibres 

 of the tendon, passing forwards and inwards, are inserted into the outer tuberosity of 

 the tibia, and from the posterior border others are given off to the fascia of the leg. 



Relations. The upper end of the biceps is covered by the gluteus maximus ; in the rest 

 of its extent the muscle is subcutaneous. It lies upon the semimembranosus, the great 

 sciatic nerve, the adductor magnus, and the outer head of the gastrocnemius ; its inner border 

 is in contact with the semitendinosus and semimembranosus, and at its lower end it forms the 

 upper and outer boundary of the popliteal space. A bursa is generally present between the 

 tendon and the external lateral ligament, and there is sometimes another between the long 

 head and the origin of the semimembranosus. 



Varieties. The short head may be absent ; or there may be an additional head arising 

 from the ischial tuberosity, or from the linea aspera, or from the inner supracondylar ridge 

 of the femur, or from various other parts. A slip has been found passing from the long head 

 to the gastrocnemius or the tendo Achillis. 



The semitendinosus muscle (fig. 249, 5 ; 254, 12), closely united at its origin 

 with the long head of the biceps, arises from the tuberosity of the ischium, and from 

 the tendon common to it with the biceps for about three inches ; it descends 

 on the back of the thigh, and terminates in the lower third in a long, rounded, and 

 slender tendon, which passes along the inner side of the popliteal space, resting on 

 the semimembranosus, and curves forwards to be inserted in an expanded form into 

 the upper part of the inner surface of the tibia, a considerable process being sent 



