232 MUSCLES OF THE LOWER LIMB. 



Actions. — The glutens maximus muscle is the chief extensor of the hip-joinw 

 By means of it the bent thigh is brought into a line with the bodj'. It is not in 

 action in the ordinary movements of walking or in standing on level ground, but 

 it is so in ascending an incline or a stair, and in the exercises of leaping or 

 dancing, and in rising from the sitting posture. Its most powerful action, and 

 that in connection with which it is so largely developed in the human subject, is 

 to extend the trunk upon the high when bent forward. The muscle acts also as 

 an adductor and external rotator of the limb. But although the full contraction 

 of the glutei maximi is required to bring the body into the erect postui'e, it is 

 not necessary for its maintenance when complete, that being effected chiefly by 

 the tension of certain ligaments and fascia^ passing over the joints, while the body 

 is so poised that the centre of gravity of the trunk is placed slightly behind the 

 A-ertical plane passing through the middle of the hip-joints. The glutcu.'i wrtlius- 

 and mi III III us are powerful abductors of the thigh, and along with the tensor 

 ^■agina3 femoris, come principally into action in supporting the body on one 

 limb, and in the rotation of the pelvis on the two liml:)s alternately which takes 

 lA^CQ in walking. Their anterior fibres draw forwards the great trochanter, and 

 rotate the limb inwards, while the posterior part produces outward rotation. 



The j)i/rif(inni.s\ ohtiirafor intern us. f/riiirUi and quad ratiis fcmori.s muscles sup- 

 port the hip-joint posteriorly, and rotate tlie limb outwards. These muscles may 

 also act as extensors when the thigh is strongly flexed. 



The ohturator cxtrrnus, besides being an external rotator, is also a flexor and 

 adductor of the thigh, as is the case in the uppermost of the two limbs when we 

 cross the knees in sitting. It supports the hip-joint posteriorly and inferiorly. 



POSTERIOB FEMORAL OR HAMSTRING MUSCLES. 



At the back of the thigh are three long flexor muscles of the knee- 

 joint; viz., the biceps, semitendinosns, and semimembranosus. 



The biceps flexor cruris muscle consists of two parts, arising one 

 from the hip-bone, tlie 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 most prominent part of the 

 ischial tuberosity ; the short head arises from the outer lip of the linea 

 aspera in its whole extent, from the upper part of the line leading 

 thence to the outer condyle, and from a part of the adjacent external 

 intermuscular septum. The muscular fibres from both heads end in 

 a common tendon, which is inserted into the head of the fibula by two 

 portions, one on each side of the external lateral ligament of the knee- 

 joint. Some of the fibres of the tendon, passing forwards and down- 

 Avards, are inserted into the front of the tibia, and others passing 

 backwards strengthen the fascia of the leg. 



Relations. — The origin of the biceps is covered by the gluteus maximus, the 

 rest of the muscle is subcutaneous. It rests upon the head of the semimembra- 

 nosus, the great sciatic nerve, and the adductor magnus : its inner border is in 

 contact with the semi-tendinosus and at its lower end it forms the upper and 

 outer boundary of the popliteal space. 



^'arieties. — The short head may be absent, or there may be an additional long 

 head arising from the tiiber ischii, or from the linea aspera. or from the inner 

 condjiar ridge of the femur, or from various other parts. A slip has been found 

 passing from the long head to the tendo AchilLis (Otto). 



The semitendinosus muscle, closely united f)t its origin with the 

 biceps, arises from tlie 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 below the middle in a long, 

 rounded, and slender tendon, which passes along the inner side of the 



