670 THE SACRAL PLEXUS. 



unite into one broad flat cord. To the place of union the nerves proceed in 

 different directions, that of the upper ones being obliquely downwards, while 

 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. 



MUSCULAR BRANCHES. 



a. To the pyriformis muscle, one or more branches are given, either from the plexus 

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



b. The nerve of the internal obturator muscle arises from the part 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 directed forwards 

 through the small sacro-sciatic foramen to reach the inner surface of the obturator 

 muscle. 



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



d. The superior 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 capsule of the hip-joint, and reaches the deep 

 (anterior) surface of the quadratus. It furnishes a small articular filament 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 the small sacro- 

 sciatic foramen, where it usually gives off the inferior hsemorrhoidal 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 perinseal nerve and the dorsal nerve of the penis. 



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

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

 superficial and muscular branches. 



a. The superficial perinceal branches are two in number, anterior and posterior. 

 The posterior branch, which first separates from the perinseal nerve, reaching the back 

 part 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 

 forwaids with the superficial perinaeal 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 perinseal nerves are accompanied to the scrotum by the 

 inferior pudendal branch of the small sciatic nerve. The three branches are some- 

 times named long ncrotal nerves. 



In the female, both the superficial perinaeal branches terminate in the external 

 labium pudendi. 



b. The muscular branches generally arise by a single trunk, which is directed 

 inwards under cover of the transversalis perinaei muscle, and divides into offsets which 



