324 HUMAN ANATOMY. 



The first intercostal nerve is not distributed to the skin, but 

 crosses the axilla under the name of the intercosto-humeral 

 nerve; it joins the brachial plexus. The six lower dorsal nerves 

 have received the name of lower, or abdominal intercostal nerves, 

 from their distribution. The last dorsal one is of large size, and 

 gives off a branch, the dorsi lumbar nerve, to join the lumbar 

 plexus. 



LUMBAR NERVES. The posterior divisions of the lumbar 

 nerves have the same distribution as the other spinal nerves. The 

 anterior divisions of the upper four lumbar nerves unite to form 

 the lumbar plexus. The fifth, with a branch from the fourth, 

 joins the sacral nerves to form the lumbo-sacral cord. 



THE LUMBAR PLEXUS is formed by the communicating loops 

 from the anterior branches of the first four lumbar nerves and a 

 branch from the last dorsal. 



Its branches are : 



1. Ilio-liypogastric, divides into two branches : 



(a) Iliac branch, supplies the skin of the gluteal region and the 

 oblique muscles of the abdomen ; 



(b) Hypogastric branch, supplies the skin of the hypogastric region 

 and the oblique muscles. 



2. Ilio-inguinal, supplies the skin of the inner and upper 

 part of the thigh, the scrotum, and labium (in female). 



3. Genito-crural, passes through the psoas muscle and di- 

 vides into two branches: 



(a) Genital branch, follows the spermatic cord to supply the cre- 

 master muscle ; in female, supplies round ligament ; 



(b) Crural branch, descends in the sheath of the femoral vessels to 

 supply the skin in front of the thigh. 



4. External cutaneous emerges below the anterior superior 

 spine of ilium and divides into : 



(a) Anterior branch, to skin of outer and front aspect of thigh ; 



(b) Posterior branch, to skin of outer and back aspect of thigh. 



5. Obturator, follows the brim and outer wall of pelvis to 

 foramen (obturator), which it pierces to enter thigh. 



(a) Anterior branch, supplies the femoral artery; 



(b) Posterior branch, supplies the adductor muscles ; 



(c) Articular branch, supplies the synovial membrane of knee-joint. 



6. Accessory obturator, sends a branch to the hip- joint and 

 one to join the anterior branch of the obturator nerve. 



7. Anterior crural, the largest branch of the lumbar plexus, 

 descends through the psoas muscle, beneath Poupart's ligament, 



