**Core Concept**
Lateral medullary syndrome, also known as Wallenberg syndrome, is a neurological disorder caused by a lesion in the lateral part of the medulla oblongata, which is located in the brainstem. This syndrome results from a vascular event, such as a stroke, and leads to a specific set of symptoms due to the damage to the surrounding neural structures.

**Why the Correct Answer is Right**
The 12th cranial nerve, also known as the hypoglossal nerve, is primarily responsible for controlling the movements of the tongue. In contrast to the other cranial nerves listed, the hypoglossal nerve is not directly affected in Wallenberg syndrome. The lateral medulla is primarily responsible for the nuclei and tracts of the 5th (trigeminal nerve), 7th (facial nerve), 8th (vestibulocochlear nerve), 9th (glossopharyngeal nerve), and 10th (vagus nerve) cranial nerves, but not the hypoglossal nerve.

**Why Each Wrong Option is Incorrect**
**Option A:** The 5th cranial nerve, or trigeminal nerve, is involved in Wallenberg syndrome due to its close proximity to the lateral medulla. Damage to this nerve can result in facial pain, numbness, and weakness of the muscles of mastication.
**Option B:** The 9th cranial nerve, or glossopharyngeal nerve, is also affected in Wallenberg syndrome. This nerve is responsible for swallowing, taste, and salivation, and damage to it can result in dysphagia and decreased salivation.
**Option C:** The 10th cranial nerve, or vagus nerve, is involved in Wallenberg syndrome. This nerve is responsible for various functions, including swallowing, voice production, and heart rate regulation, and damage to it can result in dysphonia and bradycardia.

**Clinical Pearl / High-Yield Fact**
A key feature of Wallenberg syndrome is the presence of a crossed pattern of weakness, where the weakness of the limbs is on the opposite side of the body from the lesion. This is due to the decussation of the corticospinal tracts in the medulla, which results in the contralateral control of the limbs.

✓ Correct Answer: D. 12th cranial nerve.