854 THE NERVOUS SYSTEM. 



crosses the Iliacus muscle obliquely, to the notch immediately beneath the ante- 

 rior superior spine of the ilium, where it passes under Poupart's ligament into 

 the thigh, and divides into two branches, anterior and posterior. 



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

 lata, 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 lata, 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, the third, and 

 the fourth lumbar nerves. 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, and 

 lower down by the Adductor brevis muscle. 



The anterior branch (Fig. 506) 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, occasionally to the Adductor brevis, 

 and rarely to the Pectineus, and receives a communicating branch from the acces- 

 sory 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 leg 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 

 supply the Adductor magnus, and occasionally the Adductor brevis. One of the 

 branches gives off a filament to the knee-joint. 



The articular branch for the knee-joint perforates the lower part of the Adductor 

 magnus and enters the popliteal space ; it then descends upon the popliteal artery 

 as far as the back part of the knee-joint, where it perforates the posterior ligament, 

 and is distributed to the synovial membrane. It gives filaments to the artery in 

 its course. 



The Accessory Obturator Nerve (Fig. 504) is not constantly present. It is of 

 small size, and arises by separate filaments from the third and fourth lumbar nerves. 

 It descends along the inner border of the Psoas muscle, crosses the horizontal 

 ramus of the os pubis, and passes under the outer border of the Pectineus muscle, 

 where it divides into numerous branches. One of these supplies the Pectineus, 

 penetrating its under surface; another is distributed to the hip-joint ; while a third 

 communicates with the anterior branch of the obturator nerve. When this nerve 

 is absent the hip-joint receives two branches from the obturator nerve. Occasion- 

 ally it is very small, and becomes lost in the capsule of the hip-joint. 



