THE MUSCLES OF THE LOWER LIMB. 



629 



Variations. — A separation of any of the adductor muscles into distinct portions may occur, 

 and indeed the upper part of the anterior portion of the magnus is usually quite separate from 

 the rest of the muscle and has been termed the adductor niininms. The posterior fibres of the 

 magnus frequently receive their nerve-supply through the great sciatic nerve. 



8. OuADRATUS Femoris (Figs. 602, 608). 



Attachments. — The quadratus femoris arises from the lateral border of the 

 tuber ischii and passes almost directly outward to be inserted into the femur along 

 the linea quadrati, which extends a short distance downward from about the middle 

 of the intertrochanteric line. • 



Nerve-Supply. — By a special nerve from the fourth and fifth lumbar and first 

 sacral nerves. 



Action. — To rotate the thigh outward. 



Relations. — The quadratus femoris is concealed by the lower portion of the 

 gluteus maximus, and its posterior surface is crossed by the great and small sciatic 

 nerves. Beneath it lie the obturator externus and the termination of the internal 



Fig. 603. 



V lumbar vertebra 



Anterior surface 

 of ilium 



Obturator foramen 



Symphysis pubis 



Femur 



\ ^Greater sacro-sciatic foramen 



Anterior sacral foramina 



Pyriformis 

 Sacral canal 



Greater sacro-sciatic foramen 

 Spine of ischium 

 -Coccygeus 



Coccyx 



Lesser sacro-sciatic foramen 

 Greater sacro-sciatic ligament 

 Obturator internus 

 Tuber ischii 



Dissection of right postero-lateral wall of pelvis from within, showing pyriformis and obturator internus muscles. 



circumflex artery. Its upper border is in contact with the gemellus inferior and its 

 lower border with the adductor magnus. 



Variations. — The muscle is not infrequently apparently absent, being fused with the 

 adductor magnus. 



9. Obturator Externus (Figs. 552, 601). 



Attachments. — The obturator externus, a thick triangular muscle, arises from 

 the anterior surface of the lower half of the obturator membrane and from the rami 

 of the pubis and ischium which bound the lower half of the obturator foramen. The 

 fibres are directed outward, and converge to a rounded tendon which is inserted into 

 the floor of the digital fossa of the femur. 



Nerve-Supply. — By the posterior division of the obturator nerve from the 

 third and fourth lumbar nerves. 



Action. — To rotate the thigh outward. 



10. Obturator Internus (Figs. 602, 603). 



Attachments. — The obturator internus arises from (i) the inner surface of 

 the rami of the pubis and ischium which bound the obturator foramen, (2) from the 



