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THE PUDENDAL PLEXUS. 615 
The internal branch passes forwards to the interval between the fourth and fifth 
toes, where it becomes cutaneous, and divides into two plantar digital branches for 
the supply of the adjacent sides of these toes. It communicates with the fourth 
terminal branch of the internal plantar nerve. 
The deep branch (r. profundus) of the external plantar nerve, passing deeply 
along with the external plantar artery, extends inwards towards the great toe, 
beneath the accessorius and adductor obliquus hallucis. It gives off articular 
branches to the tarsal and tarso-metatarsal articulations, and muscular branches 
to the interossei of each space (except in some cases the muscles of the fourth 
space): the adductor obliquus and adductor transversus hallucis, and the outer 
three lumbrical muscles. These nerves enter the deep surface of the muscles, that 
to the second lumbrical reaching its muscle after passing forwards beneath the 
adductor transversus hallucis. 
THE PUDENDAL PLEXUS. 
The pudendal plexus constitutes the third and last subdivision of the lumbo- 
sacral plexus. It is composed for the most part of the spinal nerves below those 
which form the sacral plexus; but, as already stated, there is no distinct point of 
separation between the two plexuses. On the contrary, there is considerable over- 
lapping, so that two and sometimes three of the principal nerves derived from the 
pudendal plexus have their origin in common with nerves of the sacral plexus. 
The plexus is formed by fibres from the anterior primary divisions of the first 
three sacral nerves, and by the whole of the anterior primary divisions of the fourth 
and fifth sacral and coccygeal nerves. The size of the nerves diminishes rapidly 
from the first sacral to the coccygeal, which is extremely slender. 
Position and Constitution.—The plexus is formed on the back wall of the 
pelvis. Of the nerves forming it, the upper ones emerge from the anterior sacral 
foramina ; the fifth sacral nerve appears between the last sacral and first coccygeal 
vertebra ; and the coccygeal nerve appears below the transverse process of that 
vertebra. The nerves of distribution derived from the plexus are the following :— 
1. Visceral branches. 4. Pudie nerve. 
2. Small sciatic nerve. 5. Muscular branches. 
3. Perforating cutaneous nerve. 6. Sacro-coccygeal nerve. 
Omitting the visceral branch, all the nerves are distributed to the permeum. 
Only two, the small sciatic and perforating cutaneous nerves, send branches to the 
lower limb. 
Visceral Branches.—Like the other spinal nerves, the fourth and fifth sacral 
and coccygeal nerves are provided with fine gray rami communicantes from 
the sacral ganghated cord, which joins them after a short course on the front of 
the sacrum. The third (along with the second or fourth) sacral nerve in addition 
sends a considerable white ramus communicans or visceral branch inwards to the 
pelvic plexus and viscera. 
Small Sciatic Nerve (n. cutaneus femoris posterior)—This nerve is complex 
both in origin and distribution (Fig. 446, p. 614). Springing from the junction of 
the sacral and pudendal plexuses, it is derived from the first three sacral nerves. It 
is distributed to both 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 pudic nerve. It enters the buttock through the great sciatic notch below the 
pyritormis, along with the sciatic artery and inferior gluteal nerve. Proceeding 
downwards behind the great sciatic nerve, it enters the thigh at the lower border 
of the gluteus maximus muscle, where it gives off considerable branches. Becoming 
gradually smaller as it courses downwards over the hamstring muscles to the popliteal 
space, it finally pierces the popliteal fascia in one or more cutaneous branches, which 
supply the skin over the calf of the leg fora variable distance (Fig. 444, p. 611). 
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