SACRAL NERVES. 419 



another from the fourth lumbar nerve. It passes downwards in the 

 fibres of the psoas muscle through the angle of bifurcation of the 

 common iliac vessels, and along the inner border of the brim of the 

 pelvis, to the obturator foramen, where it joins the obturator artery. 

 Having escaped from the pelvis it gives off two small branches to 

 the obturator externus muscle and divides into four branches, 

 three anterior, which pass in front of the adductor brevis, supplying 

 that muscle, the pectineus, the adductor longus, and the gracilis ; 

 and a posterior branch which passes downwards behind the adductor 

 brevis, and ramifies in the adductor magnus. 



From the branch, which supplies the adductor brevis, a communi- 

 cating filament passes outwards through the angle of bifurcation of 

 the femoral vessels to unite with the long saphenous nerve. From 

 the branch to the adductor longus a long cutaneous nerve proceeds, 

 which issues from beneath the inferior border of that muscle, sends 

 filaments of communication to the plexus of the short saphenous 

 nerve, and descends to the inner side of the knee, where it pierces 

 the fascia and communicates with the long saphenous nerve. It is 

 distributed to the integument upon the inner side of the leg. From 

 the posterior branch an articular branch is given off which pierces 

 the adductor magnus muscle, accompanies the popliteal artery, and 

 is distributed to the synovial membrane of the knee-joint on its pos- 

 terior aspect. 



The Lumbo-sacral nerve. The anterior division of the fifth lum- 

 bar nerve, conjoined with a branch from the fourth, constitutes the 

 lumbo-sacral nerve which descends over the base of the sacrum into 

 the pelvis, and assists in forming the sacral plexus. 



SACRAL NERVES. 



There are six pairs of sacral nerves ; the first escapes from the 

 vertebral canal through the first sacral foramina, and the two last 

 between the sacrum and coccyx. The. posterior sacral nerves 

 are very small and diminish in size from above downwards ; they 

 communicate with each other immediately after their escape from 

 the posterior sacral foramina, and divide into branches which are 

 distributed to the muscles and integument in the sacral and gluteal 

 region. The anterior sacral nerves diminish in size from above 

 downwards ; the first is of large size and unites with the lumbo- 

 sacral nerve ; the second, of equal size, unites with the preceding ; 

 the third, which is scarcely one-fourth the size of the third, also 

 joins with the preceding nerves in the formation of the sacral plexus ; 

 the fourth is about one-third the size of the preceding sacral nerve, 

 it divides into several branches, one of which is sent to the sacral 

 plexus, a second to join the fifth sacral nerve, a third to the viscera 

 of the pelvis, communicating with the hypogastric plexus, and a 

 fourth to the coccygeus muscle, and to the integument around the 

 anus. The fifth anterior sacral nerve presents about half the size of 

 the fourth ; it divides into two branches, one of which communicates 



