**Core Concept:**
The hypoglossal nerve (CN XII) is a cranial nerve responsible for supplying motor innervation to the muscles of the tongue, with the exception of one muscle.

**Why the Correct Answer is Right:**
The hypoglossal nerve supplies the extrinsic muscles of the tongue, which are responsible for the movements of the tongue. These muscles are:
1. Longitudinal muscle of the tongue (also known as the anterior commissure)
2. Vertical muscle of the tongue (also known as the lingual artery, vein, and nerve)
3. Lateral lingual muscles (anterior and posterior)
4. Lateral lingual muscle (also known as the lingual nerve)

The correct answer is **D**:

**Correct Answer: Longitudinal muscle of the tongue**

The longitudinal muscle of the tongue is a part of the intrinsic muscles of the tongue, which are innervated by the lingual nerve (CN VII). The lingual nerve is a mixed nerve containing both sensory and motor fibers, which is why it supplies the intrinsic muscles of the tongue as well.

The hypoglossal nerve (CN XII) only supplies the extrinsic muscles of the tongue, excluding the longitudinal muscle. This distinction is important as it helps differentiate between the actions of the extrinsic and intrinsic muscles of the tongue in clinical examination and interpretation of tongue movements.

**Why Each Wrong Option is Incorrect:**

**Option A:** Vertical muscle of the tongue
The vertical muscle of the tongue is correctly supplied by the lingual nerve, not the hypoglossal nerve.

**Option B:** Lateral lingual muscles
The lateral lingual muscles are correctly supplied by the lingual nerve.

**Option C:** Lingual nerve (CN VII)
While the lingual nerve does contain both sensory and motor fibers, it is the motor fibers that supply the intrinsic muscles of the tongue, including the longitudinal muscle. It is the hypoglossal nerve (CN XII) that supplies the extrinsic muscles of the tongue, excluding the longitudinal muscle.

**Clinical Pearls:**
1. Understanding the anatomy and innervation of the tongue muscles is crucial for clinical examination and interpretation of tongue movements.
2. Differentiating between extrinsic and intrinsic muscles of the tongue helps in assessing tongue function and identifying potential neurological deficits.
3. Knowledge of cranial nerves and their functions is essential in neurological evaluation and differential diagnosis.

**Core Concept:**

The hypoglossal nerve (CN XII) is a mixed nerve containing motor fibers, while the lingual nerve (CN VII) contains both sensory and motor fibers. The hypoglossal nerve innervates the extrinsic muscles of the tongue, excluding the intrinsic muscles.

The longitudinal muscle of the tongue (D) is an intrinsic muscle of the tongue, which is supplied by the lingual nerve (CN VII).

1. The lingual nerve innervates the intrinsic muscles of the tongue, including the longitudinal muscle.
2. The hypoglossal nerve innervates the extrinsic muscles of the tongue, excluding the longitudinal muscle.
3. Understanding the anatomy of the tongue muscles and their innervation is vital for assessing