Sacral Plexus 379 



and emerges above the pyriformis ; it courses between the gluteus 

 medius and minimus, supplying them and the tensor fascias femoris. 

 Thus it is the motor nerve of the internal rotators of the thigh. 



The inferior gluteal comes partly from the back of the plexus, and 

 partly from the lesser sciatic ; it supplies the gluteus maximus. The 

 two gluteal nerves are named from their situation as regards the pyri- 

 formis, one leaving the pelvis above and the other below that muscle. 



The small sciatic nerve passes out below the pyriformis, under 

 cover of the glutens maximus, which it helps to supply. Its remaining 

 branches are cutaneous ; some of them curl round the lower border of 

 the gluteus maximus, to supply the skin over the buttock, whilst others, 

 descending^ pierce the fascia lata at various points to supply the skin 

 over the back of the thigh and the upper part of the calf. Another 

 branch, the long pudendal^ winds round the outer side of the ischial 

 tuberosity to the outer part of the scrotum or to the labium. Pain in 

 that region may be due to pressure upon the trunk of the long pudendal, 

 or the lesser sciatic, or upon that part of the plexus, or of the spinal 

 cord, from which the nerve-filaments arise. 



The internal pudic nerve emerges below the pyriformis from 'the 

 lower part of the plexus, and, winding round the ischial spine, enters 

 the ischio-rectal fossa, where it divides into the inferior hcemorrhoidal 

 (which supplies the external sphincter and the neighbouring integu- 

 ment), \htperineal) and the dorsal nerve of the penis or clitoris. The 

 perineal nerve runs superficial to the pudic artery, in the outer wall of 

 the fossa, and gives off t\vo superficial branches to the scrotum and 

 the penis, and motor twigs to the anterior part of the levator and 

 sphincter ani, to the transverse muscle, and to the accelerator urinae 

 and erector penis. (See fig. on p. 440.) 



The dorsal nerve of the penis ascends between the two layers of the 

 triangular ligament, where it supplies the compressor urethras, and then 

 passes through the anterior layer of the triangular ligament and the 

 suspensory ligament, and along the dorsum, to end in the glans penis 

 or clitoridis, and the prepuce. 



Peripheral annoyance of the internal pudic nerve by a long or 

 adherent prepuce may set up reflex irritation of so general and serious 

 a nature as to entail want of co-ordination of the muscles of the ex- 

 tremity, paralysis, or other obscure nervous affections. Amongst the 

 commonest of the reflex results of phimosis are priapism, incontinence 

 of urine, and nocturnal emissions of semen. 



The great sciatic nerve comes from the upper part of the plexus, 

 and, passing out below the pyriformis, and under cover of the gluteus 

 maximus, descends, shielded from pressure, in the hollow between the 

 ischial tuberosity and the great trochanter, over the small external 

 rotators, and on to the adductor magnus. It supplies the posterior 

 surface of the great adductor, and, just below the middle of the thigh, 

 divides into the two popliteal nerves. 



