582 A MANUAL OF ANATOMY. 



which is called the fourth perforating artery. It passes 

 through a similar gap in the adductor magnus close to its 

 insertion and just above the opening for the femoral artery, 

 to the back of the adductor magnus, where it forms an 

 anastomosis with the third perforating, and the superior 

 muscular and articular branches of the popliteal. All the 

 perforating arteries supply the muscles near them. 



Subcrureus. 



The innermost fibres of the crureus which pass to the 

 synovial membrane of the knee joint. Its function is to 

 keep the synovial membrane raised up out of the way of 

 the patella. 



Obturator Externus. Fig. 1 20. 



Origin. From the inner portion of the external surface 

 of the obturator membrane, and from the adjacent portions 

 of the rami of the pubes and ischium. 



Insertion. Into the digital fossa of the great trochanter. 



Nerve Supply. Posterior division of the obturator nerve. 



Action. To adduct the thigh, to rotate the thigh out- 

 ward, to flex the thigh. This is the muscle which should 

 have been called the " sartorius " as it is the muscle which 

 crosses the legs. 



The Obturator Nerve. Figs. 119, 120. 



For its formation, and course through the pelvis, see 

 page 534. 



The nerve emerges into the thigh through the obturator 

 gap in the obturator membrane along with the obturator 

 artery. It divides into two branches, an anterior and a 

 posterior. The anterior branch passes over the upper mar- 

 gin of the obturator externus, over the adductor brevis, 

 and under the pectineus and adductor longus muscles. 



