THE OBTURATOR NERVE 1003 



The anterior (middle and internal) cutaneous nerves are best described separately. The 

 middle cutaneous nerve soon divides into two branches, medial and lateral. The lateral branch 

 pierces the sartorius and both branches become cutaneous about the junction of the upper and 

 middle thirds of the thigh (figs. 766, 768). They descend along the medial part of the front of 

 the thigh to the knee, supplying the skin in the lower two-thirds of the medial part of the front 

 of the thigh, and their terminal filaments take part in the formation of the patellar plexus. 

 About the middle of the thigh the middle cutaneous is often joined by a twig with the lumbo- 

 inguinal nerve (crural branch of the genito-crural nerve). The medial or internal cutaneous 

 nerve runs downward and medialward along the lateral side of the femoral artery, to the apex of 

 the femoral trigone (Scarpa's triangle), where it crosses in front of the artery and divides into an 

 anterior and a posterior terminal branch. Before this division takes place, however, two or 

 three collateral branches are given off from the trunk. The highest of these passes through the 

 fossa ovalis (saphenous opening), or it pierces the deep fascia immediately below the opening, and 

 supplies the skin as low as the middle of the thigh. The lowest pierces the deep fascia at the 

 middle of the thigh and it descends in the subcutaneous tissue, supplying the skin on the medial 

 side of the thigh from the middle of the thigh to the knee (figs. 768, 769). This nerve frequently 

 varies in size inversely with the cutaneous branches of the obturator and saphenous nerves. 

 The anterior branch of the internal cutaneous nerve passes vertically downward to the 

 junction of the middle and lower thirds of the thigh, where it pierces the deep fascia. It 

 still continues downward for a short distance, then it turns lateralward and passes to the 

 front of the knee, where it enters into the patellar plexus. 



The posterior branch descends along the dorsal border of the sartorius, and it gives off a 

 branch which passes beneath that muscle to unite with twigs from the saphenous and from the 

 superficial division of the obturator nerve, forming with them the subsartorial plexus which 

 lies on the roof of the adductor (Hunter's) canal. At the medial side of the knee the nerve 

 pierces the deep fascia and it descends to the middle of the calf (figs. 766, 768). 



The deep terminal branches of the femoral nerve are six in number, one 

 cutaneous branch, the saphenous, and five muscular branches. The branches 

 radiate from the termination of the trunk of the femoral nerve, and they are 

 arranged in the following order from medial to lateral: — the saphenous nerve, 

 the nerve to the vastus medialis, the nerve to the articularis genu (subcrureus), 

 the nerve to the vastus intermedins (crureus), the nerve to the vastus lateralis, 

 and the nerve to the rectus femoris. 



The saphenous nerve passes down through Scarpa's triangle along the lateral side of the 

 femoral artery. At the apex of the triangle it enters the adductor (Hunter's) canal and descends 

 through it, lying first to the lateral side, then in front, and finally to the medial side of the artery 

 (fig. 767). After emerging from the lower end of the canal, accompanied by the superficial 

 branch of the genu suprema (anastomotic) artery, it passes between the dorsal border of the 

 sartorius and the anterior border of the tendon of the gracihs, and, becoming superficial, it 

 enters into relationship with the great saphenous vein and descends with it along the inner border 

 of the upper two-thirds of the tibia (fig. 768). It crosses the medial surface of the lower third 

 of the tibia, passes in front of the internal malleolus, and runs forward along the medial border 

 of the foot to the ball of the great toe. 



While it is in the adductor (Hunter's) canal it gives off a twig to the subsartorial plexus. 

 Before it passes from under cover of the sartorius it gives off an infra-patellar branch, which 

 pierces the sartorius just above the knee and passes outward to the patellar plexus. After it 

 becomes superficial it supphes the integument on the medial side of the leg and foot, and it 

 anastomoses, in the foot, with the medial dorsal cutaneous branch of the superficial peroneal 

 (musculo-cutaneous) nerve. 



The nerve to the vastus medialis accompanies the saphenous nerve in the femoral trigone 

 (Scarpa's triangle), lying to its outer side. At the upper end of the adductor canal it passes 

 beneath the sartorius, external to the roof of the canal, and enters the medial surface of the vas- 

 tus medialis. It sends a twig down to the knee-joint. 



The nerve to the articularis genu (subcrureus), usually a terminal branch of the femoral, 

 frequently arises from the nerve to the vastus intermedins. It passes between the vastus 

 medialis and the vastus intermedins to the lower third of the thigh, where it supphes the artic- 

 ularis genu and sends a branch to the knee-joint. 



The nerve to the vastus intermedins (crureus) is represented by two or three branches which 

 enter the upper part of the muscle. One of them frequently sends a twig to the knee-joint. 



The nerve to the vastus lateralis passes downward behind the rectus and along the anterior 

 border of the vastus laterahs accompanied by the descending branch of the lateral circumMex 

 artery. It also sends a branch to the knee-joint. 



The nerve to the rectus femoris (fig. 767) enters the deep surface of that muscle, having 

 previously given off a twig to the hip-joint which accompanies the ascending branch of the 

 external circumflex artery. 



The obturator nerve contains fibres from the anterior primary divisions of the 

 second, third, and fourth lumbar nerves, but its largest root is derived from the 

 third nerve (figs. 765, 769). It sometimes receives fibres from the first and third 

 lumbar nerves. It emerges from the medial border of the psoas at the dorsal 

 part of the brim of the pelvis, where it lies in close relation with the lumbo-sacral 

 trunk of the plexus, from which it is separated by the ilio-lumbar artery. Im- 

 mediately after its exit from the psoas it pierces the pelvic fascia, crosses the 



