**Core Concept**
The larynx is innervated by several nerves, including the recurrent laryngeal nerve, which supplies muscles involved in vocal cord movement and tension. However, there is one muscle that is innervated by a different nerve due to its unique embryological origin.

**Why the Correct Answer is Right**
The cricothyroid muscle is responsible for tensing and lengthening the vocal cords. Unlike other intrinsic laryngeal muscles, it is innervated by the external branch of the superior laryngeal nerve, rather than the recurrent laryngeal nerve. This is because the cricothyroid muscle is derived from a different embryological precursor than the other intrinsic laryngeal muscles, which are innervated by the recurrent laryngeal nerve.

**Why Each Wrong Option is Incorrect**
**Option A:** Vocalis is one of the muscles of the vocal cord and is innervated by the recurrent laryngeal nerve. It plays a role in adjusting the length of the vocal cord.

**Option B:** Thyroarytenoid is another intrinsic laryngeal muscle that regulates vocal cord tension and is also innervated by the recurrent laryngeal nerve.

**Option D:** Interarytenoid is a muscle that separates the two arytenoid cartilages and is innervated by the recurrent laryngeal nerve. It is involved in the closure of the posterior glottis.

**Clinical Pearl / High-Yield Fact**
It's essential to remember that the cricothyroid muscle is the only intrinsic laryngeal muscle not innervated by the recurrent laryngeal nerve, which is a crucial detail for laryngeal surgery and anesthesia.

**✓ Correct Answer: C. Cricothyroid**