328 THE SPINAL NERVES. 



(b) The inferior pudendal nerve (rr. perineales] turns inwards below the ischial 

 tuberosity, giving offsets (sometimes separate branches of the nerve) to the skin ot 

 the upper and inner part of the thigh, and is continued forwards to the outer part of 

 the scrotum (or external labium pudendi), where its terminal filaments are 

 distributed, after forming communications with the external superficial perineal 

 branch of the pudic nerve. 



(c) The femoral cutaneous branches are numerous, and arise from both sides of 

 the nervj while it lies beneath the fascia : they supply the skin of the back of the 

 thigh, the larger number passing to the inner side. 



Varieties. In cases of separate origin of the internal and external popliteal nerves 

 (p. 324), the small sciatic nerve also arises from the sacral plexus in two parts. The ventral 

 portion descends with the internal popliteal nerve below the pyrif ormis. and gives off the inferior 

 pudendal and inner femoral branches, while the dorsal portion passes through that muscle with 

 the external popliteal nerve, and furnishes the gluteal and outer femoral branches. The 

 inferior pudendal nerve sometimes pierces the great sacro-sciatic ligament. The small sciatic 

 may be joined on the back of the thigh by a branch of the great sciatic nerve (p. 331). In 

 some cases the small sciatic nerve ends behind the knee, its place in the leg being then taken 

 by a branch of the external popliteal (p. 336). 



. The perforating cutaneous nerve (fig. 215, 10) is a slender branch which 

 arises most frequently from the second and third sacral nerves, and passes backwards 

 through the great sacro-sciatic ligament : it then turns upwards round the lower 

 border of the glutens maximus, and is distributed to the skin over the inner and 

 lower part of that muscle. 



Varieties. A perforating cutaneous nerve arising as above stated was found by Eisler 22 

 times in 34 plexuses : in three of these it was conjoined at its origin with the pudic nerve. 

 Instead of piercing the great sacro-sciatic ligament it may run with the pudic nerve between 

 the great and small ligaments, or it may pass between the great ligament and the gluteus 

 maximus muscle. In other cases a nerve having a similar distribution (. jwrfontHx <!><< t/i/nix 

 major. Eisler) arises from the third and fourth (fig. 210), or fourth and fifth nerves (fig. 204. 

 10), and pierces the coccygeus muscle on its way backwards. Its place may also be supplied 

 by a branch of the small sciatic. 



B. TERMINAL BRANCHES. 



Pudic nerve. The pudic nerve (n. pudendus) is a short plexiform trunk, .which 

 is given off from the lower part of the sacral plexus, and distributes branches to the 

 perineum and external organs of generation. Its chief root is usually derived from 

 the third sacral nerve. To this are added others from the fourth and second nerves ; 

 and according to Eisler it also receives fibres from the first sacral nerve. The upper 

 roots spring from the front of the ventral divisions of the corresponding sacral 

 nerves. Passing out of the pelvis between the pyriformis and coccygeus muscles, it 

 turns forwards over the attachment of the small sacro-sciatic ligament to the ischial 

 spine, where it is placed on the inner side of the pudic vessels, to the small sacro- 

 sciatic foramen. Having thus arrived at the hinder part of the ischio-rectal fossa, 

 the trunk ends by dividing into the following three branches, viz., the inferior 

 hsemorrhoidal nerve, the perineal nerve, and the dorsal nerve of the penis, or clitoris, 

 according to the sex. 



(a) The inferior hcemorrhoidal nerve (4, 3, (2) s) is sometimes derived separately 

 from the sacral plexus ; it inclines inwards towards the anus and divides into 

 numerous branches which supply the skin of the hinder part of the perineal space 

 and the external sphincter muscle. The most anterior branches form communica- 

 tions with the interior pudendal and superficial perineal nerves. 



(b) The perineal nerve (3, 2, 4 s) is the largest of the three divisions of the pudic 

 nerve. It runs forwards along the outer wall of the ischio-rectal fossa, being con- 



