GLUTEAL EEGION. 235 



OBTURATOR INTERNUS. 



{Suhpuhio-trocJianteruLs Internus.) 



(Fig. 83. c.) 



Situated on the floor of the pelvic cavity, covering the obturator 

 foramen, and corresponding to the externus ; it is fan-shaped, 

 with a delicate, fleshy belly, terminating in a flat tendon. 



Origin. — From the border of the obturator foramen and its 

 ligament ; it passes through the lesser sciatic notch, behind the 

 acetabulum, where its tendon joins that of the pyriformis. 



Insertion. — In the trochanteric fossa. 



Relation. — Superiorly with the pelvic fascia ; inferiorly with 

 the obturator ligament, ischium, and pubis ; outside the pelvis, 

 with the sciatic nerve above, and the externus below. 



Action. — To rotate the femur outwards, and perhaps to abduct 

 it slightly. 



PYRIFORMIS. 



{Sacro-trochanterius.) 



(Fig. 83. c.) 



Situated laterally in the pelvic cavity, this is a flat, elongated, 

 semipenniform muscle, with a small tendon of insertion. 



Origin. — From the transverse processes of the sacral vertebrae, 

 and the inner surface of .the iliac shaft ; lying along the inner 

 side of the sacro-sciatic ligament, it passes through the lesser 

 sciatic notch to join the tendon of the obturator internus. 



Insertion. — In the trochanteric fossa. 



Relation. — With the pelvic fascia internally ; externally with 

 the OS innominatum ; outside the pelvis it is crossed by the 

 sciatic nerves ; the obturator vessels and nerves pass along its 

 lower border. 



Action. — To rotate the femur outwards. 



GEMELLUS ANTICUS AND POStlOUS. 



( Gemini — Ischio-trochanterii. ) 



(Fig. S3, d d.) 



A pair of very delicate muscles, variable in form, and usually 



situated one above and before, the other below and behind the 



obturator internus tendon, with fleshy bellies and tendinous 



insertions. 



