THE LUMBAR PLEXUS 367 



The external cutaneous crosses the iliacus and enters the 

 thigh through the notch below the anterior superior spine of 

 the ilium, superficial to the sartorius, dividing into an anterior 

 and a posterior branch. The former runs in a canal within the 

 fascia lata, and becomes cutaneous four inches below Poupart's 

 ligament. It supplies the front and outer part of the thigh 

 to the knee, sometimes joining in the patellar plexus. The 

 posterior branch supplies the skin of the outer and back part 

 of the thigh halfway to the knee. 



The obturator nerve emerges from the inner border of the 

 psoas at the pelvic brim. It runs above the obturator vessels 

 to escape at the upper part of the obturator foramen, dividing 

 into two branches separated by the adductor brevis. The 

 anterior runs beneath the pectineus and adductor longus, 

 joining at the lower part of the latter with branches of the 

 long saphenous and internal cutaneous nerves to form a plexus. 

 A branch supplies the hip-joint; muscular branches to gracilis 

 and adductor longus, sometimes to the adductor brevis and 

 pectineus; the terminal branch to the femoral artery. 



The posterior branch pierces the obturator externus and 

 runs behind the adductor brevis on the adductor 'magnus, 

 and supplies these muscles (the adductor magnus only in 

 part). A branch to the knee-joint pierces the magnus, lies 

 on the popliteal artery, sending branches to it, and pierces 

 the ligamentum Winslowii to supply the synovial membrane. 



The accessory obturator is inconstant; when present it arises 

 by branches from the second, third, and fourth nerves, or is 

 a branch of the obturator. It runs along the inner border 

 of the psoas, and, crossing the pubes, divides beneath the 

 pectineus into three branches one to the anterior branch 

 of the obturator, another to the hip-joint, and a third to the 

 pectineus. It is not constant. 



The anterior crural nerve is the largest branch of the lumbar 

 plexus. It enters the thigh between the psoas and iliacus, 

 external to the femoral artery, and divides into an anterior 

 (mainly cutaneous) and a posterior (mainly muscular) portion. 



BRANCHES. Within the abdomen, three or more branches 

 to the iliacus, and a branch to the femoral artery. 



ANTERIOR PORTION. (a) The middle cutaneous pierces the 

 fascia lata four inches below Poupart's ligament, and divides into 

 two branches which run on the front of the thigh to the patella. 



