THE PUDENDAL PLEXUS. 615 
nerve) arises from the small sciatic nerve at the lower border of the gluteus 
maximus muscle (Fig. 447, p. 616). It sweeps inwards towards the perineum, 
lying on the origin of the hamstring muscles below the ischial tuberosity, and 
terminates by becoming subcutaneous over the pubic arch. Its terminal branches 
supply the skin of the scrotum and root of the penis, or in the female the labium 
majus and clitoris, some of them being directed backwards towards the anus and 
central point of the perineum. They communicate with the inferior heemorrhoidal 
and perineal branches of the pudic nerve and with the ilio-inguinal nerve. In its 
course to the perineum the nerve gives off collateral branches to the skin of the 
upper and inner part of the thigh. 
The gluteal branches (rr. clunium inferiores) are large and numerous (Fig. 
444, p. 611). They arise from the small sciatic nerve beneath the gluteus 
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 outermost branches, reaching to the back of the great trochanter, overlap the 
terminal filaments of the gluteal branches of the external cutaneous nerve, and the 
posterior primary divisions of the first three lumbar nerves. The innermost branches, 
which may pierce the great sacro-sciatic ligament, reach nearly to the coccyx, and 
are coterminous in their distribution with the branches of the perforating cutaneous 
nerve, which they reinforce and not unfrequently replace. 
The femoral branches are divisible into two sets—internal and external. They 
pierce the fascia lata of the thigh at intervals, and respectively supply the skin of 
the back of the thigh on its inner and outer sides. 
The sural branches are two or more slender nerves which pierce the fascia 
over the popliteal space, and are distributed for a variable extent to the skin of 
the back of the leg. They may stop short over the popliteal space, or may extend 
as far as the ankle. Usually they innervate the skin as far as the middle of the 
calf. They communicate with the external saphenous nerve. 
In cases where the great sciatic nerve is naturally divided at its origin into tibial (internal 
popliteal) and peroneal (external popliteal) nerves (eg. by the pyriformis muscle), the small 
sciatic nerve is also separated into two parts : a dorsal part, associated with the peroneal nerve 
and arising in common with the lower roots of the inferior gluteal nerve (usually from the first 
and second sacral nerves), which comprises the gluteal and external femoral branches ; and a 
ventral part, associated with the tibial nerve and arising usually from the second and third 
sacral nerves, along with the perforating cutaneous and pudie nerves, which comprises the 
perineal and internal femoral branches. 
Perforating Cutaneous Nerve (n. perforans ligamenti tuberoso - sacri 
(Schwalbe), n. cutaneus clunium inferior medialis (Kisler) )—This nerve arises 
from the back of the second and third sacral nerves (Fig. 447, p. 616). It is 
associated at its origin with the lower roots of the small sciatic nerve. Passing 
downwards it pierces the great sacro-sciatic ligament, along with the coceygeal 
branch of the sciatic artery; and after winding round the lower border of the 
gluteus maximus muscle, or piercing its lower fibres, it becomes subcutaneous a 
little distance from the coccyx, and supplies the skin over the lower part of the 
buttock and the inner part of the fold of the nates. 
The perforating cutaneous nerve is not always present. In a minority of cases it is associated 
at its origin with the pudic nerve. When absent as a separate nerve, its place is taken by (1) 
gluteal branches of the small sciatic nerve, or (2) a branch from the pudic nerve, or (3) a small 
nerve (n. perforans coceygeus major, Eisler), arising separately from the back of the third and 
fourth sacral nerves. 
Muscular Branches.—Between the third and fourth sacral nerves (occasion- 
ally reinforced by the second, Eisler) a plexiform loop is formed, from which 
muscular nerves are given off to the levator ani (supplying the muscle on its pelvic 
surface), coccygeus, and external sphincter. The nerve to the external sphincter 
(perineal branch of fourth sacral) pierces the great sacro-sciatic ligament and the 
coccygeus muscle, to which it gives offsets, and appears in the ischio-rectal fossa 
between the gluteus maximus and the external sphincter. Besides supplying the 
posterior fibres of the external sphincter, it distributes cutaneous offsets to the skin 
