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The external anal sphincter is the ring of skeletal muscle surrounding the distal anal canal. Its contraction helps maintain faecal continence; its motor neurons allow voluntary squeezing as well as reflex control. It works alongside the smooth muscle of the internal anal sphincter, so continence depends on coordinated structures rather than one isolated ring.^[ref]

Branches of the pudendal nerve supply the external anal sphincter. Dissection of 28 cadavers found a local nerve plexus near the sphincters in five, illustrating why a schematic nerve route need not capture every individual's branching. Preserving muscle alone therefore does not guarantee preservation of its motor supply.^[ref]

The pudendal canal is a passage in the fascia of obturator internus along the lateral perineal region. It carries the pudendal nerve and internal pudendal vessels. Their common route explains how a local anatomical lesion can affect both neural supply and vascular structures.

The pudendal nerve is a mixed nerve of the sacral plexus, usually receiving fibers associated with S2–S4 spinal nerves. It carries sensory information from much of the perineum and motor signals to skeletal muscles involved in continence, including the external anal sphincter and external urethral sphincter. Its route includes the pudendal canal.

A description of anatomy is a pattern with variation, not a guarantee that every individual has identical branching. Dissection of 28 cadavers documented additional branches and interconnections near the external anal sphincter in some specimens.^[ref] The study also illustrates the difference between a skeletal muscle being structurally intact and its nerve supply being intact: coordinated contraction depends on both the skeletal muscle and the arriving motor signals.

The sacral plexus is a network of anterior spinal nerve rami, usually incorporating L4–S4 spinal contributions, lying against the anterior surface of the piriformis muscle. It distributes sensory and motor fibres to much of the pelvis and lower limb. Major branches include the sciatic nerve and the pudendal nerve.^[ref]

Its mixed origins explain an otherwise puzzling arrangement: the sciatic nerve carries fibres associated with several spinal nerves, and fibres from one spinal level can leave through different peripheral branches. A nerve plexus is therefore a redistribution network, rather than a new set of neurons inserted into each pathway.

Steven E. Schraffordt led a dissection study of the pudendal nerve and its terminal branches. Examination of 28 cadavers documented variations relevant to the motor supply of the external anal sphincter. In five specimens, interconnecting inferior rectal and perineal branches formed a local nerve plexus near the sphincters.^[ref]

This is a practical contribution of anatomical observation: an intact muscle can lose function if its nerve supply is injured. A schematic branching pattern therefore needs to be interpreted alongside documented variation when considering pelvic anatomy.