THE LUMBAR NERVES 953 



major just below the iliohypogastric, and, passing obliquely across the Quadratus 

 lumborum and Iliacus, perforates the Transversus abdominis, near the anterior 

 part of the iliac crest, and communicates with the iliohypogastric nerve between the 

 Transversus and the Obliquus internus. The nerve then pierces the Obliquus 

 internus, distributing filaments to it, and, accompanying the spermatic cord through 

 the subcutaneous inguinal ring, is distributed to the skin of the' upper and medial 

 part of the thigh, to the skin over the root of the penis and upper part of the scrotum 

 in the male, and to the skin covering the mons pubis and labium ma jus in the fema|f. 

 The size of this nerve is in inverse proportion to that of the iliohypogastric. Occa- 

 sionally it is very small, and ends by joining the iliohypogastric; in such cases, a 

 branch from the iliohypogastric takes the place of the ilioinguinal, or the latter 

 nerve may be altogether absent. 



The Genitofemoral Nerve (n. genitofemoralis; genitocrural nerve) arises from the 

 first and second lumbar nerves. It passes obliquely through the substance of the 

 Psoas major, and emerges from its medial border, close to the vertebral column, 

 opposite the fibrocartilage between the third and fourth lumbar vertebrae; it 

 then descends on the surface of the Psoas major, under cover of the peritoneum, 

 and divides into the external spermatic and lumboinguinal nerves. Occasionally 

 these two nerves emerge separately through the substance of the Psoas. 



The external spermatic nerve (n. spermaticus externus; genital branch of genito- 

 femoral) passes outward on the Psoas major, and pierces the fascia transversalis, or 

 passes through the abdominal inguinal ring; it then descends behind the spermatic 

 cord to the scrotum, supplies the Cremaster, and gives a few filaments to the skin 

 of the scrotum. In the female, it accompanies the round ligament of the uterus, 

 and is lost upon it. 



The lumboinguinal nerve (n. lumboinguinalis; femoral or crural branch of genito- 

 femoral) descends on the external iliac artery, sending a few filaments around it, 

 and, passing beneath the inguinal ligament, enters the sheath of the femoral vessels, 

 lying superficial and lateral to the femoral artery. It pierces the anterior layer of 

 the sheath of the vessels and the fascia lata, and supplies the skin of the anterior 

 surface of the upper part of the thigh (Fig. 825). On the front of the thigh it 

 communicates with the anterior cutaneous branches of the femoral nerve. A few 

 filaments from the lumboinguinal nerve may be traced to the femoral artery. 



The Lateral Femoral Cutaneous Nerve (n. cutaneus femoralis lateralis; external 

 cutaneous nerve} arises from the dorsal divisions of the second and third lumbar 

 nerves. It emerges from the lateral border of the Psoas major about its middle, 

 and crosses the Iliacus obliquely, toward the anterior superior iliac spine. It then 

 passes under the inguinal ligament and over the Sartorius muscle into the thigh, 

 where it divides into two branches, an anterior and a posterior (Fig. 825). 



The anterior branch becomes superficial about 10 cm. below the inguinal ligament, 

 and divides into branches which are distributed to the skin of the anterior and 

 lateral parts of the thigh, as far as the knee. The terminal filaments of this nerve 

 frequently communicate with the anterior cutaneous branches of the femoral nerve, 

 and with the infrapatellar branch of the saphenous nerve, forming with them the 

 patellar plexus. 



The posterior branch pierces the fascia lata, and subdivides into filaments which 

 pass backward across the lateral and posterior surfaces of the thigh, supplying 

 the skin from the level of the greater trochanter to the middle of the thigh. 



The Obturator Nerve (n. obturatorius) arises from the ventral divisions of the 

 second, third, and fourth lumbar nerves; the branch from the third is the largest, 

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

 of the Psoas major, and emerges from its medial border near the brim of the pelvis; 

 it then passes behind the common iliac vessels, and on the lateral side of the hypo- 

 gastric vessels and ureter, which separate it from the ureter, and runs along the 



