**Core Concept**
The interarytenoid muscle plays a crucial role in the regulation of the glottis, and its unique innervation pattern sets it apart from other laryngeal muscles. The laryngeal muscles are responsible for controlling the opening and closing of the glottis, which is essential for breathing, speaking, and protecting the airway.

**Why the Correct Answer is Right**
The interarytenoid muscle is the only laryngeal muscle that receives bidirectional innervation from the recurrent laryngeal nerve (RLN) and the superior laryngeal nerve (SLN). This dual innervation allows for precise control over the glottis, enabling the interarytenoid muscle to contract and relax in response to both the RLN and the SLN. The RLN provides motor innervation to the posterior cricoarytenoid, lateral cricoarytenoid, and other intrinsic muscles of the larynx, whereas the SLN provides motor innervation to the cricothyroid muscle and sensory innervation to the larynx.

**Why Each Wrong Option is Incorrect**
**Option A:** The vocalis muscle is innervated by the RLN, but it does not receive bidirectional innervation from both the RLN and the SLN.

**Option B:** The posterior cricoarytenoid muscle is the only abductor of the vocal cords and is primarily innervated by the RLN, making it an unlikely candidate for bidirectional innervation.

**Option C:** The lateral cricoarytenoid muscle is also innervated by the RLN and is involved in adduction of the vocal cords, but it does not receive bidirectional innervation from both the RLN and the SLN.

**Clinical Pearl / High-Yield Fact**
The interarytenoid muscle is a crucial structure in the larynx, and its unique innervation pattern highlights the importance of precise control over the glottis in maintaining airway patency and facilitating speech and breathing.

**✓ Correct Answer: D. Interarytenoid**