610 THE SACRAL NERVES. 



that of the lower is nearly horizontal ; and, as a consequence of this 

 difference, they diminish in length from the first to the last. The 

 sacral plexus rests on the anterior surface of the pyriform muscle, 

 opposite the side of the sacrum, and escaping through the great sacro- 

 sciatic foramen, ends in the great sciatic nerve. 



Branches. — The sacral plexus gives rise to the great sciatic nerve, 

 and to various smaller branches ; viz., the pudic nerve, the small sciatic 

 nerve, and branches to the obturator internus, pyriformis, gemelli, and 

 quadratus femoris muscles. 



Small Muscxilar branches. 



a. To tlie jfyrifprmls vmscle, one or more branches are given, either from the 

 jilexus or from the upper sacral nerves before they reach the plexus. 



li. The nerve, of the inteinial ohtnrator muscle arises from the jiart of the plexus 

 formed by the union of the lumbo-sacral and the first sacral nerves. It turns 

 over the ischial spine of the hip-bone with the pudic vessels, and is then dii'ected 

 forwards through tire small sacro-sciatic foramen to reach the inner sm-face of 

 the obturator muscle. 



c. To the levator ani one or more twigs proceed from the lower part of the plexus. 



(I. The iiq>erior gemellus receives a small branch, which arises from the lower 

 part of the plexus. 



e. The small nerve which supplies the lower gemellus and quadratus femoris 

 muscles springs from the lower part of the plexus. Concealed at first by the 

 great sciatic nerve, it passes beneath the gemelli and the tendon of the internal 

 obturator, — between those muscles and the capsrde of the hip-joint, — and reaches 

 the deep (anterior) surface of the quadratus. It fmnishes a small ai-ticular fila- 

 ment to the back part of the hip- joint. 



The Pudic Nerve. 



This nerve, arising from the lower part of the sacral plexus, turns 

 over the spine of the ischium, and then passes forwards through tlie 

 small sacro-sciatic foramen, where it usually gives off the inferior 

 hasmorrhoidal branch. It is next directed along the outer part of the 

 ischio-rectal fossa, in a sheath of the obturator fascia, along with the 

 pudic vessels, and divides into two terminal branches, the perineal 

 nerve -^nd the dorsal nerve of the penis. 



A. — The perineal nerve, the lower and much the larger of the two 

 divisions of the pudic nerve, lies below the pudic artery, and is expended 

 ia superficial and muscular branches. 



a. The .luperfieial jicrineal branches are two in number, anterior and pos- 

 terior. The jwxterior branch, which fii-st separates from the perineal nerve, 

 reaching the back i^art of the ischio-rectal fossa, gives filaments inwards to the skin 

 in front of the anus, and turns forwards in company with the anterior branch 

 to reach the scrotum. The anterior branch descends to the fore part of the 

 ischio-rectal fossa ; and, passing forn^ards with the superficial perineal artery, 

 ramifies in the skin on the fore part of the scrotum and on the penis. This branch 

 sends small twigs to the levator ani muscle. The superficial perineal nerves are 

 accompanied to the scrotum by the inferior pudendal branch of the small sciatic 

 nerve. The three branches are sometimes named long scrotal nerves. 



In tlie female, both the superficial perineal branches temiinate in the external 

 labium pudendi. 



l>. The muscular hranches generally arise by a single trunk, which is directed 

 in-n-ards vinder cover of the transversalis perinasi muscle, and divides into offsets 

 which are distributed to the transversalis perinxn, erector penis, accelerator 

 urinaj. and comnressor urethrte. 



