536 A MANUAL OF ANATOMY. 



by the gap in the upper margin of the obturator membrane. 

 It is accompanied in its course by the artery of the same 

 name if it is a branch from the internal iliac. In the thigh 

 the nerve issues from the obturator canal above or through 

 the upper part of the obturator externus muscle, where it 

 divides into two branches. The anterior branch descends 

 between the pectineus and adductor longus in front and 

 the adductor brevis behind, supplying these muscles and 

 terminating in the gracilis. It also sends a cutaneous 

 branch to the lower and inner third of thigh. The posterior 

 branch goes behind the adductor brevis and supplies the 

 adductor magnus, continues downward, pierces the adduc- 

 tor magnus just above the femoral opening, joins the pop- 

 liteal vessels, and ends in the posterior part of the knee- 

 joint. 



The obturator externus receives its nerve supply from 

 the posterior division of the nerve. A filament is also sent 

 to the hip-joint. 



(7) The obturator accessory. When present arises from 

 the third and fourth lumbar nerves. Descends between 

 the psoas and internal iliac artery (behind both) over the 

 anterior border of the pubes to the pectineus, which it sup- 

 plies, then communicates with the obturator nerve and con- 

 tinues to the hip-joint. 



DISSECTION. 



Inflate the bladder. Dissect the peritoneum from it and the rectum. Clean 

 the internal iliac vessels and their branches, also the sacral plexus. In doing 

 this notice the pelvic fascia, the so-called " white line," and the rectovesical 

 fascia. 



To dissect the pelvic cavity and viscera requires that the lateral wall shall 

 be removed from one side as represented in the plates ; as this destroys the side 

 removed for dissection of the gluteal region, it is not practicable, and the dis- 

 sector must do the best possible with the pelvis intact. 



Trace the ureters, vasa deferentia, and expose the seminal vesicles. In 



