6o8 ABDOMEN 



the sciatic trunk out of the pelvis, and supplies not only 

 the quadratus femoris but also the inferior gemellus and the 

 hip-joint. 



The Perforating Cutaneous Nerve springs from the back of 

 the plexus and contains fibres of the second and third sacral 

 nerves. It pierces the sacro-tuberous ligament, winds round 

 the lower border of the glutseus maximus, and supplies the 

 skin over the lower and medial part of that muscle. 



The Twigs to the Piriformis spring usually from the 

 first and second sacral nerves. 



The Visceral Branches (white rami communicantes) are 

 derived mainly from the third and fourth sacral nerves. 



The Coccygeal Plexus. This is a small, looped plexus. 

 It is formed by the lower branch of the fourth sacral nerve, 

 the fifth sacral nerve, and the coccygeal nerve. Besides join- 

 ing with the fifth, the fourth sacral nerve gives branches 

 to the coccygeus and the levator ani, the latter branch being 

 known as the perineal branch of the fourth sacral. It also 

 supplies white rami communicantes which join the pelvic 

 plexuses of the sympathetic and supply the pelvic viscera. 



The fifth sacral nerve enters the pelvis by piercing the 

 coccygeus. It communicates with the fourth sacral and the 

 coccygeal nerves and gives branches to the coccygeus muscle. 



The coccygeal nerve also enters the pelvis by piercing the 

 coccygeus muscle. Having communicated with the fifth 

 sacral nerve it runs downwards and leaves the pelvis by again 

 piercing the coccygeus muscle. It ends in the skin in the 

 neighbourhood of the tip of the coccyx. 



Pelvic Plexuses of the Sympathetic. It has already been 

 noted that the hypogastric plexus, which lies in front of the 

 last lumbar vertebra, ends below by dividing into the two 

 pelvic plexuses. These are prolonged downwards, one on 

 each side of the rectum. Each pelvic plexus receives 

 numerous branches from the third and fourth sacral nerves 

 and from the pelvic portion of the sympathetic cord of the 

 same side. The points at which these unite with the plexuses 

 are marked by minute ganglia. 



Prolongations from each pelvic plexus are sent along the 

 various branches of the hypogastric artery of the same side. 

 There are thus formed various secondary plexuses, viz. the 

 vesical plexus associated with the bladder, the seminal vesicles, 

 and the vas deferens ; the hczmorrhoidal plexus distributed to 



