THE PUDENDAL PLEXUS. 1349 



from only the second and third, sacral nerves, the upper root usually being associ- 

 ated with one of the roots of the inferior gluteal nerve, and the lower root with the 

 perforating cutaneous or the pudic nerve. Leaving the pelvis through the great 

 sacro-sciatic foramen below the pyriformis, it descends in the gluteal region between 

 the tuber ischii and the great trochanter, posterior to the great sciatic nerve and 

 anterior to the gluteus maximus, accompanied by the inferior gluteal nerve and the 

 sciatic artery. Emerging into the thigh at the lower border of the gluteus maximus 

 it continues downward beneath the deep fascia and superficial to the hamstring 

 muscles to a short distance above the knee, where it pierces the deep, and becomes 

 an occupant of the superficial, fascia. Thence it passes downward through the roof 

 of the popliteal space and through the upper part of the calf, in the latter situation 

 accompanying the external saphenous vein and inosculating with the external 

 saphenous nerve. It rarely extends beyond the middle of the calf, tapering off into 

 tiny threads which are distributed to the skin of the posterior surface of the upper 

 half or two thirds of the leg (Fig. 1125.) 



Branches of the small sciatic nerve are : (a) the iiiferior piidendal, {b) the 

 gluteal, {c) the /emora/ and (d) ihe sura/. 



a. The inferior pudendal or perineal branch (rr. perineales) (Fig. 1 126) leaves the parent 

 nerve at the lower margin of the gluteus maximus, curves mesially below the tuberosity of the 

 ischium and over the origin of the hamstrings and courses through the groove between the 

 thigh and the perineum. Piercing the deep fascia lateral to the pubic ramus, it enters tlie 

 perineum and supplies the integument of the scrotum and base of the penis, or of the labium 

 majus and clitoris. Branches are distributed to the skin of the upper mesial portion of the 

 thigh and to the perineal body and anus. This nerve communicates with the ilio-inguinal 

 nerve and with the perineal and inferior hemorrhoidal brandies of the pudic nerve. It may 

 pierce the great sacro-sciatic ligament. 



b. The gluteal cutaneous branches (rr. clunium inferiores) (Fig. 1124) consist of two, 

 three or more stout filaments which arise from the small sciatic a short distance above the 

 inferior margin of the gluteus maximus, around which they wind. Piercing the fascia lata 

 individually they turn upward over the lower portion of the gluteus maximus and are dis- 

 tributed to the skin of the inferior gluteal region, as far externally as the great trochanter and 

 internally almost to the coccyx. The outer branches overlap the terminal twigs of the posterior 

 branch of the external cutaneous nerve and the posterior primary divisions of the first, second 

 and third lumbar nerves. The inner branches sometimes pierce the great sacro-sciatic liga- 

 ment ; they reinforce or may replace the perforating cutaneous nerve. 



c. The femoral branches (Fig. 11 24) consist of two series of twigs, an internal and an 

 external, which pierce the fascia lata of the posterior aspect of the thigh and supply the integu- 

 ment of that region. 



d. The sural branches (Fig. 1125) are usually two terminal twigs which innervate to 

 a- varying extent the integument of the back of the leg, sometimes not extending beyond 

 the confines of the popliteal space and sometimes continuing all the way to the ankle. They 

 inosculate with the external saphenous nerve, and when they are lacking their place is taken by 

 the external saphenous. 



Variations. — In those cases in which the internal and external popliteal nerves are separate 

 from their incipiency, the small sciatic also is double. The ventral portion accompanies 

 the internal popliteal and gives off the inferior pudendal and internal femoral branches, while 

 the dorsal portion accompanies the external popliteal and gives off the gluteal and external 

 femoral branches. Sometimes the small sciatic is joined in the thigh by a branch from the great 

 sciatic. 



5. The Pudic Nerve. 



The pudic nerve (n. pudendus) arises from the front of the second, third and 

 fourth sacral nerves, its main root coming from the third and there being a doubtful 

 root from the first. Leaving the pelvis by way of the great sacro-sciatic foramen 

 between the pyriformis and the coccygeus and below the great sciatic nerve, it passes 

 forward, with the internal pudic artery and the nerve to the obturator internus, over 

 the base of the lesser sacro-sciatic ligament to the spine of the ischium (Fig. 1126). 

 Reaching the small sacro-sciatic foramen internal to the internal pudic artery, 

 the nerve traverses this opening and enters the ischio-rectal fossa, where it gives off 

 the inferior hemorrhoidal nerve. The main trunk courses forward in a canal 

 (Alcock's) in the obturator fascia on the outer wall of the ischio-rectal fossa 



