604 A MANUAL OF ANATOMY. 



tain the knee in that position and to resist flexion, yet after 

 flexion is once started its action (if any) is as indicated 

 above. 



(4) Upon the trunk. Taking its fixed point from below 

 the muscle will extend the trunk upon the thighs as in 

 assuming an upright position after stooping forward. 



The action of the gluteus maximus and tensor vaginae 

 femoris, through the attachment of the iliotibial band is 

 very necessary in the maintenance of the trunk erect when 

 standing upon one leg. They act here like the guy rope 

 to a derrick in lifting a weight, the femur being the up- 

 right, the pelvis the cross beam, and the body the weight ; 

 the centre of motion being at the hip joint. 



The Small Sciatic Nerve. Fig. 126. 



The small sciatic nerve is formed by branches from the 

 second and third sacral nerves, passes through the great 

 sacrosciatic foramen under the pyriformis muscle, then be- 

 neath the gluteus maximus and behind the fascia lata 

 through the middle of the thigh into the popliteal space, 

 where it pierces the deep fascia and supplies the integu- 

 ment over the popliteal space and the upper third of the 

 calf of the leg. 



Its Branches are : 



(1) Recurrent cutaneous branches to the integument 

 over the gluteus maximus. 



(2) The inferior pudendal. This branch turns inward 

 under the gluteus maximus, pierces the deep fascia about 

 an inch external to the tuberosity of the ischium (see page 

 406,) and runs forward to supply the inner side of the 

 thigh and the scrotum (or the labium majus). 



(3) The femoral cutaneous branches supply the skin 

 over the back of the thigh and popliteal space. 



