420 -SACRAL PLEXUS. 



with the fourth, the other with the sixth. The sixth sacral nerve is 

 exceedingly small ; it gives off an ascending filament which is con- 

 tinuous with the communicating branch of the fifth ; and a descend- 

 ing filament which passes downwards' by the side of the coccyx 

 and traverses the fibres of the great sacro-ischiatic ligament to be 

 distributed to the gluteus maximus and to the integument. All the 

 anterior sacral nerves receive branches from the sacral ganglia of 

 the sympathetic at their emergence from the sacral foramina. 



The Sacral plexus is formed by the lumbo-sacral, and by the 

 anterior branches of the four upper sacral nerves. The plexus is 

 triangular in form, the base corresponding with the whole length of 

 the sacrum, and the apex with the lower part of the great ischiatic 

 foramen. It is in relation behind with the pyriformis muscle, and 

 in front with the pelvic fascia which separates it from the branches 

 of the internal iliac artery, and from the viscera of the pelvis. 



The Branches of the sacral plexus are divisible into the internal 

 and the external ; they may be thus arranged : 



Internal. External. 



Visceral, Muscular, 



Muscular. Gluteal, 



Internal pudic, 

 Lesser ischiatic, 

 Greater ischiatic. 



The Visceral nerves are three or four large branches which are 

 derived from the fourth and fifth sacral nerves : they ascend upon 

 the side of the rectum and bladder ; in the female upon the side of 

 the rectum, the vagina and the bladder ; and interlace with the 

 branches of the hypogastric plexus, sending in their course numerous 

 filaments to those viscera. 



The Muscular branches given off within the pelvis are one or two 

 twigs to the levator ani ; an obturator branch which curves around 

 the spine of the ischium to reach the internal surface of the obturator 

 internus muscle ; and an hsemorrhoidal nerve which descends to 

 the termination of the rectum to supply the sphincter and the in- 

 tegument. 



The Muscular branches supplied by the sacral plexus externally 

 to the pelvis are, a branch to the pyramidalis ; a branch to the 

 gemellus superior ; and a branch of moderate size which descends 

 between the gemelli muscles and the ischium, and is distributed to 

 the gemellus inferior, the quadratus femoris, and to the capsule of 

 the hip-joint. 



The Gluteal nerve is a branch of the lumbo-sacral ; it passes out 

 of the pelvis with the gluteal artery, through the great sacro-ischiatic 

 foramen, and divides into a superior and an inferior branch. The 

 superior branch follows the direction of the superior curved line of 

 the ilium, accompanying the deep superior branch of the gluteal 

 artery, and sending filaments to the gluteus medius and minimus. 



