THE MUSCLES ON THE POSTEEIOE ASPECT OF THE THIGH. 421 



The membranous origin of the muscle is concealed by the proximal parts of the 

 semitendinosus and long, head of the biceps. The insertion covers the origin of 

 the inner head of the gastrocnemius. 



Nerve- Supply. It is innervated by the nerve to the hamstring muscles (L. 5. S. 1. 2.). 

 Actions. A flexor of the knee, a medial rotator of the tibia, and an extensor of the hip. 



Actions of the Muscles of the Thigh and Buttock. 



Most of the above muscles act on the pelvis and on the hip- and knee-joints. The psoas 

 major muscle in addition assists in the movements of the vertebral column (p. 411). 



1. Movements at the Hip- Joint. The movements of the thigh at the hip-joint are flexion 

 and extension, adduction and abduction, medial and lateral rotation. The following table 

 gives the muscles producing these movements : 



a. Flexion and Extension. 



Sartorius 

 Iliacus 



major 

 Rectus femoris 

 Pectineus 

 Adductor longus 

 Gracilis 

 Obturator externus 



Glutaeus maximus 

 medius 

 minimus 



Biceps femoris 

 S emitendinosus 

 S emimembranosus 

 Adductor magnus 



c. Medial Rotation and Lateral Rotation. 



Tensor fasciae latse 

 Glutseus medius (anterior fibres) 

 minimus 



Obturator externus 



Glutaeus maximus (lower fibres) 



Quadratus femoris 



Glutaeus medius \ (posterior 



minimus /fibres) 

 Piriformis ] -, 



Otorator interne | e S on 



Sartorius 

 Ilio-psoas 

 Pectineus 

 Adductor longus 



brevis 



magnus 

 Biceps femoris 



2. Movements of the Pelvis on the Thigh. It is to be noted that the several movements 

 tabulated above refer to the movements of the femur at the hip-joint. The contraction of the 

 same groups of muscles produces similar movements of the pelvis on the femur, exemplified in 

 the various changes in the attitude of the pelvis in relation to the thigh and the vertebral 

 column, which occur in locomotion. 



3. Movements at the Knee-Joint. The movements at the knee-joint are mainly flexion 

 and extension. Flexion is much more powerful than extension. There is also a limited amount 

 of rotation of the tibia. The movements are produced by certain of the muscles described above, 

 associated with certain of the muscles of the leg. 



