THE PELVIS. 



289 



acic and all the lumbar vertebrae, and from their intercentral cartilages ; from 

 the lower border of the transverse processes of the lumbar vertebras. The 

 nerve-supply is from the lumbar plexus. The nerve-supply of the iliacus is from 

 the anterior crural part of the lumbar plexus. 



The Iliacus. Detach from its origin and turn it down to its insertion into 

 the lesser trochanter of the femur with the psoas magnus. This is a flexor of 

 the thigh on the abdomen. Its synergist is the psoas. It also pulls the body 

 forward, when the thigh is made the fixed point, antagonizing the gluteus maxi- 

 mus. Its nerve-supply is from the anterior crural of the lumbar plexus. 



Origin. (i) The upper surface of the ala of the sacrum ; (2) the front of the 

 ilio-lumbar, lumbo-sacral, and anterior sacro-iliac ligaments ; (3) the upper and 

 outer half of the venter of the ilium ; (4) the origin of the upper tendon of the 

 rectus femoris and the ilio-femoral ligament near the anterior inferior spine of 

 the ilium. 



The Psoas Parvus. Usually absent. Inserted into the ilio-pectineal line. 

 Origin : Side of twelfth thoracic and first lumbar and disc of cartilage between 



... Transversalis 



-! Internal oblique 



" External oblique 



Sacro-lumbalis 



LatiBSimus dorsi 



Quadratus lumborum 



FlG. 1C 



Longissiinus dorsi 

 Psoas magnus 



. ARRANGEMENTS OF LUMBAR APONEUROSIS AT LEVEL OF THIRD LUMBAR VERTEBRA. 



the two. Synergistic to psoas magnus. Its nerve-supply is from the first nerve 

 of the lumbar plexus. 



The obturator internus may now be removed from its origin. (Fig. 196.) 

 Trace the same through the lesser sacro-sciatic foramen. Study the origin from 

 the marein of the obturator foramen, the obturator membrane, and the inner 



o 



surface of the body of the ischium. Its nerve-supply is from the first and second 

 nerves of the sacral plexus ; it passes through the lesser sacro-sciatic foramen. 



Obturator Externus. Detach the muscle from the bony margin of the 

 obturator foramen ; from the obturator membrane. It^s inserted into the digital 

 or trochanteric fossa. It is supplied by the obturator nerve. Now you can see 

 and study the obturator membrane. See the obturator nerve coming through a 

 notch on under surface of the horizontal ramus of the os pubis. 



Locate on tlie sacrum (Fig. 199) : (i) The bodies ; (2) the anterior sacral fora- 

 mina ; (3) the transverse lines ; (4) the ala or wing ; (5) the sacro-coccygeal artic- 

 ulation ; (6) the origin of the pyriformis ; (7) the grooves leading to the foramina. 



The pyriformis arises from the anterior surface of the sacrum by three 



