THE LUMBAR PLEXUS. 1327 



The accessory obturator courses downward mesial to the psoas magnus and 

 beneath the iliac fascia, and leaves the pelvis by passing over the horizontal ranjus of 

 the pubes and under the pectineus. In the latter situation it breaks up into its 

 branches, one of which (a) supplies the pectineus, another (d) the hip joint, while 

 the third (c) inosculates with the anterior division of the obturator nerve. Some- 

 times it is very small and its fibres pass only to the hip joint. By means of its in- 

 osculation with the obturator some of its fibres may reach the addi^ctores longus and 

 brevis and gracilis muscles, as well as the integument of the inner region of the thigh. 



8. The Anterior Crural Nerve. 



The anterior crural or femoral nerve (n. femoralis) (Fig. 1108), the largest 

 branch of the lumbar plexus, arises from the first, second, third and fourth lumbar 

 nerves. It passes obliquely downward and outward, posterior to the psoas magnus, 

 and emerges from beneath the middle of the lateral margin of that muscle. Thence 

 it continues its course between the outer edge of the psoas and the mesial edge of the 

 iliacus, covered by the iliac fascia, as far as Poupart's ligament, under which it passes 

 to become an occupant of the anterior portion of the thigh. The nerve lies to the 

 outer side of the external iliac and femoral vessels, in the abdomen being separated 

 from them by the psoas magnus, but, as the thigh is reached, gradually nearing them 

 until in Scarpa's triangle the nerve lies in apposition to the femoral sheath. In 

 the immediate neighborhood of Poupart's ligament, the anterior crural nerve rapidly 

 splits up into a number of 



Branches, which may be grouped into (d} a superficial divisioii, principally 

 sensory, and (c) a deep division, mainly motor. In addition there are {a) branches 

 arising from the main trunk. 



a. The branches from the main trunk consist of {aa) the muscular branches and i^bb) the 

 nerve to the femoral artery. 



aa. The muscular branches supply the iliacus, the psoas magnus and the pectineus. 



The branches to the iliacus consist of two to four filaments which arise in the abdomen, 

 pass outward and enter the inner margin of the ihacus muscle. 



The branch to the psoas magnus arises in the lower part of the iliac fossa and supplies the 

 inferior portion of that muscle. It may originate in common with the nerve to the femoral 

 artery. 



The branch to the />^r/z«^K^ leaves the anterior crural beneath Poupart's ligament, passes 

 inward posterior to the femoral vessels and enters the anterior surface of its muscle. 



bb. The nerve to the femoral artery usually takes origin in the iliac fossa, but frequently 

 arises higher, sometimes as a distinct branch from the third lumbar nerve. It accompanies the 

 anterior crural as far as Poupart's ligament, leaving the parent trunk at the lateral margin of 

 the femoral sheath. At the ligament it gives off fine twigs which ramify over the posterior part 

 of the femoral vessels, and from them tiny filaments pass to the middle of the thigh. Other 

 twigs are distributed to the deep femoral artery and from this group a fine terminal thread 

 traverses the nutrient foramen of the femur, after supplying branches to the periosteum. 



b. The anterior or superficial division is mainly cutaneous in distribution. It supplies 

 sensory twigs to the anterior and mesial surfaces of the thigh and motor twigs to the sartorius. 



Branches of this division are : (aa) the middle cutaneous and {bb) the internal cutaneous. 



aa. The middle cutaneous nerve (rr. cutaneianteriores) (Fig. mo) consists of two branches, 

 an external and an internal, both of which contain motor as well as sensory fibres. 



The external branch passes downward under the sartorius, to whose posterior surface are 

 given off a row of fine twigs which enter the upper portion of the muscle. The continuation of 

 the nerve pierces the sartorius at the junction of the upper and middle thirds, then pushes its 

 way through the fascia lata and splits into fine filaments which supply the integument over the 

 rectus femoris as far as the knee. 



The internal branch is sometimes united in the upper part of its course with the external. 

 It supplies twigs to the sartorius but seldom pierces that muscle, usually passing internal and 

 anterior. This branch, like the external, is distributed to the anterior integument of the thigh 

 as far down as the knee and frequently inosculates with the crural branch of the genito-crural. 



Variations. — Sometimes the middle cutaneous arises from the beginning of the anterior 

 crural or from the lumbar plexus and replaces in toto or in part the crural branch of the 

 genito-crural. 



