**Core Concept**
The vocal cord muscles play a crucial role in voice production, respiration, and swallowing. The muscles responsible for the movement of the vocal cords are innervated by the recurrent laryngeal nerve, a branch of the vagus nerve. The specific muscle responsible for abduction of the vocal cords is essential for maintaining a patent airway.

**Why the Correct Answer is Right**
The posterior cricoarytenoid muscle is the only muscle responsible for the abduction of the vocal cords. This muscle rotates the arytenoid cartilages laterally, thereby moving the vocal cords apart. This action is crucial for opening the glottis and maintaining a patent airway. The posterior cricoarytenoid muscle is innervated by the recurrent laryngeal nerve, which provides the motor innervation for all the intrinsic muscles of the larynx.

**Why Each Wrong Option is Incorrect**
**Option B:** The lateral cricoarytenoid muscle is responsible for adduction of the vocal cords, not abduction. It helps to approximate the vocal cords and is also innervated by the recurrent laryngeal nerve.

**Option C:** There is no muscle called the "cricoarytenoid" in the larynx. The cricoarytenoid muscle is actually a combination of the posterior and lateral cricoarytenoid muscles.

**Option D:** The transverse arytenoid muscle is a small muscle that helps to approximate the arytenoid cartilages, but it is not responsible for the abduction of the vocal cords.

**Clinical Pearl / High-Yield Fact**
The posterior cricoarytenoid muscle is the only muscle that can move the vocal cords apart, and its paralysis can lead to bilateral vocal cord fixation, which can result in respiratory distress.

**✓ Correct Answer: A. Posterior cricoarytenoid**