**Core Concept**
The external anal sphincter is a striated muscle that plays a crucial role in voluntary control of defecation. Its innervation is essential for coordinating the process of passing stool.

**Why the Correct Answer is Right**
The external anal sphincter is primarily innervated by the inferior rectal nerve, which is a branch of the pudendal nerve. The pudendal nerve arises from the S2-S4 nerve roots of the sacral plexus. The inferior rectal nerve carries both motor and sensory fibers, providing voluntary control over the external anal sphincter and sensation to the anal region.

**Why Each Wrong Option is Incorrect**
**Option A:** The internal anal sphincter, on the other hand, is innervated by the sympathetic nervous system, which is not responsible for voluntary control.
**Option B:** The superior rectal nerve, a branch of the inferior mesenteric plexus, provides parasympathetic innervation to the rectum and is not directly involved in the innervation of the external anal sphincter.
**Option C:** The perianal skin is innervated by the inferior rectal nerve, but the external anal sphincter is primarily responsible for voluntary control, not the skin.

**Clinical Pearl / High-Yield Fact**
The pudendal nerve is vulnerable to injury during childbirth, which can result in anal incontinence. This is a classic exam trap, as it highlights the importance of pudendal nerve function in maintaining continence.

**Correct Answer: C. The pudendal nerve.**