THE LOWER EXTREMITY, POSTERIOR. 605 



DISSECTION. 



Divide the gluteus maximus at its outer and middle thirds and reflect the 

 two portions. 



The outer portion is to be carefully dissected to demonstrate the double 

 insertion of the muscle and the bursa between it and the great trochanter, 

 and the inner portion is to be lifted up and turned back on to the sacrum to 

 show its extensive origin and the bursa which intervenes between the muscle 

 and the tuberosity of the ischium. 



Divide the nerve and arterial supply close to the muscle. 



Remove entirely the inner portion of the muscle by cutting it away from 

 its origins. 



A large multilocular bursa will be found between the 

 tendon of the gluteus maximus and the great trochanter 

 of the femur. A second one intervenes between the muscle 

 and the tuberosity of the ischium. 



Gluteus Medius. Figs. 118, 126, 127. 



Origin. From the external surface of the ilium between 

 the middle curved line below and the superior curved line 

 and the anterior four-fifths of the external lip of the iliac crest 

 above, from the deep surface of the fascia lata covering it. 



Insertion. Into the oblique line upon the outer surface 

 of the great trochanter. The direction of this oblique line 

 is from above and behind, downward and forward. 



Nerve Supply. The superior gluteal (fourth and fifth 

 lumbar, and first sacral nerves). 



Action. At all times the muscle acts as an abductor of 

 the thigh, and serves to maintain the pelvis level when 

 standing upon one foot, as in walking, etc. 



The anterior portion of the muscle acts as an internal 

 (forward), the posterior, as an external (backward) rotator 

 of the thigh. 



Pyriformis. Figs. 114, 126, 127. 



Origin. From the front of the lateral margin of the 



