THE LOWER EXTREMITY, POSTERIOR. 603 



Insertion. Into the iliotibial band over the great tro- 

 chanter of the femur. Into the gluteal (vertical) ridge 

 which extends from the posterior surface of the great tro- 

 chanter to the outer bifurcation of the linea aspera. A 

 distance of about two inches. 



Nerve Supply. The inferior gluteal branch of the sacral 

 plexus. This nerve is usually included within the sheath 

 of the small sciatic and consequently is said to be a branch 

 of that nerve. See page 552. 



Action. The attachments of all the posterior muscles 

 of the thigh should be very carefully determined, then 

 their action when the thigh is in an extended position, and 

 finally when it is flexed at various angles. It will only be 

 by such careful study that the complex actions of these 

 gluteal and external rotator muscles will be understood. 



To attempt to commit to memory the action of muscles 

 from the book is all wrong, unless the demonstration is 

 carried out upon the subject (living or dead) and by the 

 use of the skeleton. 



Action of the gluteus maximus. 



(1) When the thigh is extended, it acts as an external 

 rotator ; its upper fibres will assist abduction, and its 

 lower fibres will assist adduction ; the action of the whole 

 muscle neutralizes these movements. 



(2) When the thigh is flexed. The muscle is a power- 

 ful extensor of the thigh, it is also a strong abductor (in 

 flexion) ; abduction diminishes as flexion decreases and ex- 

 tension increases (in other words, as the individual assumes 

 an upright position). 



(3) Upon the leg, it will assist flexion when once started, 

 and external rotation, through the iliotibial band, along 

 with the tensor vaginae femoris. 



In full extension of the leg the muscle helps to main- 



