THE MUSCULAR SYSTEM 8 1 



trunk erect, extends, abducts, and rotates the thigh 

 outward. Nerve, inferior gluteal. 



Gluteus Medius. Arises from the outer surface of the 

 ilium. It is inserted into the great trochanter. Action, 

 supports the trunk, flexes and abducts the thigh, and ro- 

 tates it inward. Nerve, superior gluteal. 



Gluteus Minimus. Arises from the outer side of the 

 ilium, and is inserted in the great trochanter. Action, 

 flexes, abducts, and rotates the thigh inward; it also assists 

 in holding the trunk erect. Nerve, superior gluteal. 



The pyriformis is a flat muscle, arising by three digita- 

 tions from the sacrum and ilium. It is inserted into the 

 great trochanter. Action, rotates thigh outward, abducts 

 it as well, and draws the pelvis forward. Nerves, branches 

 of sacral plexus. 



The obturator internus is situated partly in the pelvis, 

 and arises from the margin of the obturator foramen. 

 It is inserted into the inner part of the great trochanter. 

 Action, draws the pelvis forward and assists in external 

 rotation and abduction of the thigh. Nerve, branch of the 

 sacral plexus. 



Gemellus Superior. Arises from the ischium, and is 

 inserted into the inner part of the great trochanter. 

 Action, rotates the thigh outward. Nerve, branch of 

 sacral plexus. 



Gemellus Inferior. Arises from the ischium, and is 

 inserted into the great trochanter of the femur. Action, 

 external rotator of thigh. Nerve, branch of sacral plexus. 



The obturator externus is a flat, triangular muscle, 

 situated on the outside of the pelvis. Arises from the 

 margin of obturator foramen, and is inserted into the 

 femur. Action, rotates thigh outward. Nerve-supply, 

 from branch of obturator. 



The quadratus femoris is a short, flat muscle, quadri- 

 lateral in shape. Origin, from the tuberosity of the 

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