## **Core Concept**
The tongue muscles are primarily derived from the **somites**, specifically the occipital somites. These somites give rise to the intrinsic and extrinsic muscles of the tongue, except for one muscle.

## **Why the Correct Answer is Right**
The correct answer, **.**, indicates that the tongue muscle derived from a source other than somites is the **palatoglossus muscle**. The palatoglossus muscle is one of the muscles of the tongue but is unique because it is derived from the **pharyngeal mesenchyme** or more specifically, it is innervated by the **cranial nerve X (vagus nerve)** via the pharyngeal plexus, unlike the other tongue muscles which are derived from somites and innervated by the **hypoglossal nerve (cranial nerve XII)**.

## **Why Each Wrong Option is Incorrect**
- **Option A:** This option is incorrect because the majority of tongue muscles are indeed derived from **somites**, specifically the occipital somites.
- **Option B:** This option is incorrect as there is no commonly recognized contribution to tongue muscles from the **neural crest** in the context provided.
- **Option C:** This option might seem plausible because **somites** do give rise to tongue muscles, but it does not specifically address the exception.

## **Clinical Pearl / High-Yield Fact**
A key point to remember is that while most muscles of the tongue are innervated by the **hypoglossal nerve (CN XII)**, the **palatoglossus muscle** is innervated by the **vagus nerve (CN X)**. This is a critical distinction for understanding the innervation and, by extension, the potential deficits seen with lesions affecting these nerves.

## **Correct Answer:** . Palatoglossus.