THE LUMBAR PLEXUS. 785 



the back part of the spermatic cord to the scrotum, and supplies, in the male, the 

 Cremaster muscle. In the female, it accompanies the round ligament, and is lost 

 upon it. 



The crural branch descends on the external iliac artery, sending a few filaments 

 round it, and, passing beneath Poupart's ligament to the thigh, enters the sheath 

 of the femoral vessels, lying superficial and a little external to the femoral artery. 

 It pierces the anterior layer of the sheath of the vessels, and, becoming superficial 

 by passing through the fascia iata, it supplies the skin of the anterior aspect of the 

 thigh as far as midway between the pelvis and knee. On the front of the thigh it 

 communicates with the outer branch of the middle cutaneous nerve, derived from 

 the anterior crural. 



A few filaments from this nerve may be traced on to the femoral artery ; they 

 are derived from the nerve as it passes beneath Poupart's ligament. 



The External Cutaneous Nerve arises from the second and third lumbar nerves. 

 It emerges from the outer border of the Psoas muscle about its middle, and crosses 

 the Iliacus muscle obliquely, toward the anterior superior spine of the ilium. It 

 then passes under Poupart's ligament and over the Sartorius muscle into the thigh, 

 where it divides into two branches, anterior and posterior. 



The anterior branch descends in an aponeurotic canal formed in the fascia 

 Iata, becomes superficial about four inches below Poupart's ligament, and divides 

 into branches which are distributed to the integument along the anterior and 

 outer part of the thigh, as far down as the knee. This nerve occasionally com- 

 municates with a branch of the long saphenous nerve in front of the knee- 

 joint. 



The posterior branch pierces the fascia Iata, and subdivides into branches which 

 pass backward across the outer and posterior surface of the thigh, supplying the 

 integument from the crest of the ilium as far as the middle of the thigh. 



The Obturator Nerve supplies the obturator externus and Adductor muscles of 

 the thigh, the articulations of the hip and knee, and occasionally the integument 

 of the thigh and leg. It arises by three branches from the second 1 , the third, and 

 the fourth lumbar nerves. Of these, the branch from the third is the largest, 

 while that from the second is often very small. It descends through the inner 

 fibres of the Psoas muscle, and emerges from its inner border near the brim of 

 the pelvis ; it then runs along the lateral wall of the pelvis, above the obturator 

 vessels, to the upper part of the obturator foramen, where it enters the thigh, and 

 divides into an anterior and a posterior branch, separated by some of the fibres of 

 the Obturator externus (Fig. 257), and lower down by the Adductor brevis muscle. 



The anterior branch (Fig. 419) passes down in front of the Adductor brevis, 

 being covered by the Pectineus and Adductor longus, and at the lower border of 

 the latter muscle communicates with the internal cutaneous and internal saphenous 

 nerves, forming a kind of plexus. It then descends upon the femoral artery, upon 

 which it is finally distributed. The nerve, near the obturator foramen, gives off an 

 articular branch to the hip-joint. Behind the Pectineus it distributes muscular 

 branches to the Adductor longus and Gracilis, and usually to the Adductor brevis, 

 and in rare cases to the Pectineus, and receives a communicating branch from the 

 accessory obturator nerve. 



Occasionally the communicating branch to the internal cutaneous and internal 

 saphenous nerves is continued down, as a cutaneous branch, to the thigh and leg. 

 When this is so, this occasional cutaneous branch emerges from beneath the lower 

 border of the Adductor longus, descends along the posterior margin of the Sartorius 

 to the inner side of the knee, where it pierces the deep fascia, communicates with 

 the long saphenous nerve, and is distributed to the integument of the inner side 

 of the Feg as low down as its middle. When this communicating branch is small, 

 its place is supplied by the internal cutaneous nerve. 



The posterior branch of the obturator nerve pierces the Obturator externus, 

 sending branches to supply it, and passes behind the Adductor brevis on the front 

 of the Adductor magnus, where it divides into numerous muscular branches, which 



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