PUDENDAL PLEXUS. 737 



the sacrum. The third (along with the second or fourth) sacral nerve, in addition, 

 sends a considerable white ramus communicans or visceral branch direct to the 

 pelvic plexus and viscera. 



N. Cutaneus Femoris Posterior Posterior Cutaneous Nerve of the Thigh 

 (O.T. Small Sciatic). This nerve is complex both in origin and distribution 

 (Fig. 631, p. 736). Springing from the junction of the sacral and pudendal 

 plexuses, it is derived from the first three or second and third sacral nerves. It 

 is distributed to the lower limb and perineum, and is associated with other nerves 

 belonging to both regions. It arises from the back of the roots of the sacral 

 plexus in the pelvis. Its higher roots from the first and second sacral nerves 

 are intimately associated with the origin of the inferior gluteal nerve-; its lowest 

 root from the third sacral nerve is associated with the origins of the perforating 

 cutaneous or of the pudendal nerve. It enters the buttock through the greater 

 sciatic notch, below the piriformis, along with the inferior gluteal artery and nerve. 

 Proceeding distally, posterior to the sciatic nerve, it enters the thigh at the 

 lower border of the glutseus maximus muscle, where it gives off considerable 

 branches. Becoming gradually smaller as it courses distally over the hamstring 

 muscles to the popliteal fossa, it finally pierces the popliteal fascia in one or more 

 cutaneous branches, which supply the skin over the calf of the leg for a variable 

 distance (Fig. 629, p. 733). 



Branches. The nerve is purely cutaneous. It supplies branches to the 

 perineum, buttock, thigh, and leg. 



Kami Perineales. The perineal branch arises at the lower border of the 

 gluteeus maximus muscle (Fig. 631, p. 736). It sweeps in a medial direction to 

 the perineum, lying on the origin of the hamstring muscles, distal to the ischial 

 tuberosity; and becoming subcutaneous after passing over the pubic arch, its 

 terminal branches supply the skin of the scrotum and root of the penis, or, in the 

 female, the labium inajus and clitoris, some of them being directed backwards 

 towards the anus and central point of the perineum. They communicate with 

 the inferior hsemorrhoidal and perineal branches of the pudendal nerve, and with 

 the ilio-inguinal nerve. In its course to the perineum the nerve gives off 

 collateral branches to the skin of the proximal and medial part of the thigh. 



Nn. Clunium Inferiores. The inferior gluteal branches are large and numerous 

 (Fig. 631, p. 736). They arise from the nerve beneath the glutaeus maximus, 

 and become subcutaneous by piercing the fascia lata at different points along its 

 lower border. They supply the skin of the lower half of the buttock. The most 

 lateral branches, reaching to the back of the greater trochanter, overlap the terminal 

 filaments of the gluteal branches of the lateral cutaneous nerve of the thigh, 

 and the posterior rami of the first three lumbar nerves. The most medial branches, 

 which may pierce the sacro-tuberous ligament, reach nearly to the coccyx, and 



are co-extensive in their distribution with the branches of the perforating cutaneous 



nerve, which they reinforce and not infrequently replace. 



The femoral branches are divisible into two sets medial and lateral. They 



pierce the fascia lata of the thigh at intervals, and supply the skin of the back of 



ihe thigh. 



The sural branches are two or more slender nerves which pierce the fascia 



)ver the popliteal fossa, and are distributed for a variable extent to the skin of 



;he back of the leg. They may stop short over the popliteal fossa, or may extend 



is far as the ankle. Usually they innervate the skin as far as the middle of the 



ialf. They communicate with the nervus suralis. 



In cases where the sciatic nerve is naturally divided at its origin into tibial and common 

 >eroneal nerves (e.g. by the piriformis muscle), the posterior cutaneous nerve also is separated into 

 wo parts : a posterior part, associated with the common peroneal nerve and arising in common 

 ath the lower roots of the inferior gluteal nerve (usually from the first and second sacral nerves), 

 , nd comprising the gluteal and lateral femoral branches ; and an anterior part, associated with 

 lie tibial nerve and arising usually from the second and third sacral nerves, along with the 

 erforating cutaneous and pudendal nerves, and comprising the perineal and medial femoral 

 ranches. 



Perforating Cutaneous Nerve (n. perforans ligamenti tuberoso - sacri 

 Schwalbe), n. cutaneus clunium inferior medialis (Eisler)). This nerve arises 



48 



