POSTERIOR PART OF LOWER EXTREMITY. 371 



above muscles back, not to injure the vessels and nerves, upon which both 

 the beauty and benefit of your dissection depend. You have exposed to view 

 now these structures : 



1. The greater sacro-sciatic foramen. (Fig. 226.) 



2. The lesser sacro-sciatic foramen. (Fig. 226.) 



3. Sacro-sciatic ligaments greater and lesser. (Fig. 258.) 



4. The three gluteal muscles. 



5. The pyriformis muscle. 



6. The obturator externus muscle. 



7. The obturator intern us muscle. 



8. The gemelli superior and inferior. 



9. The quadratus femoris muscle. 



10. The superior gluteal nerve and artery. 



1 1. The small sciatic nerve and its branches. 



Sciatic artery 



INFERIOR GLUTEAL NERVE 

 Gluteal artery 



Gluteus 



medius 



Gluteus maximus 



BRANCH TO GLl'- 

 TEUS MAXIMUS 



Tendon of obturator externu3 



Vastus externus Gluteus maximus 



FIG. 258. A DISSECTION OF THE NERVES IN THE GLUTEAL REGION. 

 (The gluteus maximus and glutens medius have been divided near their insertions, and thrown upward.) 



12. The sciatic artery and its branches. 



13. The great sciatic nerve and its relations. 



14. The internal pudic nerve and artery. 



15. The origin of the biceps, semitendinosus, and semimembranosus. 



1 6. The gluteus medius muscle. 



17. The gluteus minimus muscle. 



1 8. The subgluteal bursa over the greater trochanter. 



The gluteus medius arises from the outer lip of the iliac crest for the anterior 

 four-fifths ; from the outer surface of the ilium, between the superior and middle 

 gluteal curved lines (Fig. 226) ; from the dense aponeurosis covering the muscle 

 and separating the same from the gluteus maximus. The muscle is inserted into 

 the oblique line of the greater trochanter of the femur. (Fig. 227.) Nerve-supply 

 is the superior gluteal from the lumbo-sacral cord of the sacral plexus. (Fig. 193.) 



The gluteus minimus arises from the outer surface of the ilium, between the 



