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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 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.

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.