GLUTEAL REGION. 235 



OBTURATOR INTERNUS. 



(Subpubw-trochanterius Internus.) 

 (Fio. 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. ) 



(Fie. 83. c.) 



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

 semi pen niforrn 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 POST1CUS. 



(Gemini Ischio-trochanterii.) 



(FiG. 83. 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. 



