636 ABDOMINAL SPINAL NERVES. 



superior lumbar nerves, and is the largest nerve of the lum- 

 bar plexus. It passes behind, and sometimes through the 

 psoas muscle, and descends to Poupart's ligament, beneath 

 which it passes about half an inch to the outside of the 

 femoral artery, where it divides into numerous muscular 

 and cutaneous branches. In the pelvis it distributes fila- 

 ments to the psoas and iliac muscles. 



The obturator nerve comes from the third or fourth lum- 

 bar, passes through the psoas muscle, and descends along 

 the inner edge of the latter to the obturator foramen, 

 through which it passes to the inner side of the thigh, 

 where it divides into an anterior and posterior branch, which 

 supply the muscles chiefly on the inner thigh, the adduc-. 

 tors, gracilis, vastus internus, &c., as well as the integu- 

 ments, and anastomoses with the vaginal branches of the 

 crural ; one long branch is traced as low down as the po- 

 piteal space, to the back part of the knee joint. 



The lumbo-sacral nerve comes from the fourth and fifth 

 lumbar, and descends into the pelvis to join the sacral 

 plexus. 



The posterior divisions of the lumbar nerves pass back- 

 ward between the transverse processes, and supply the 

 multifidus spinae, longissimus dorsi, and sacro-lumbalis 

 muscles, and the integuments. Varieties will be seen in 

 the number and distribution of the branches of the lumbar 

 plexus. 



The sacral nerves (Fig. 204) consist of six pair. They 

 divide within the spinal canal into anterior and posterior 

 branches, which pass out at the anterior and posterior 

 sacral foramina. The posterior are quite small, and supply 

 the muscles and integuments on the back of the sacrum. 



The anterior are large, the four superior of which, with 

 the last lumbar uniting together, constitute the sacral 

 plexus. These nerves all receive branches from the sacral 

 ganglia of the sympathetic. The fifth and sixth are very 

 small, sometimes absent, and escape between the sacrum 

 and coccyx 



The sacral or sciatic plexus is situated upon the side of 



