## **Core Concept**
The hypoglossal nerve, also known as the 12th cranial nerve, primarily provides motor innervation to the muscles of the tongue. It is responsible for controlling the movements of the tongue, including protrusion, retraction, and changes in shape.

## **Why the Correct Answer is Right**
The hypoglossal nerve supplies all the intrinsic and extrinsic muscles of the tongue except for one key muscle. The muscles innervated by the hypoglossal nerve include the genioglossus, hyoglossus, styloglossus, and all the intrinsic muscles of the tongue. However, the **palatoglossus muscle**, which is one of the muscles of the palate and contributes to elevating the posterior part of the tongue, is not innervated by the hypoglossal nerve. Instead, the palatoglossus muscle is innervated by the **vagus nerve (cranial nerve X)** through the pharyngeal plexus.

## **Why Each Wrong Option is Incorrect**
- **Option A:** This option is incorrect because the muscle it refers to is indeed innervated by the hypoglossal nerve, but without the specific muscle name provided, we acknowledge that the hypoglossal nerve does supply several muscles of the tongue.
- **Option B:** Similar to Option A, this is incorrect because it implies a muscle innervated by the hypoglossal nerve, but specifics are needed for a detailed explanation.
- **Option C:** This option would also be incorrect for implying innervation by the hypoglossal nerve, assuming it refers to another muscle of the tongue supplied by this nerve.

## **Clinical Pearl / High-Yield Fact**
A key clinical point to remember is that the hypoglossal nerve's function can be tested by asking a patient to stick their tongue out. If the tongue deviates to one side, it indicates weakness on that side, suggesting a lesion of the hypoglossal nerve on the side to which the tongue deviates. This is because the genioglossus muscle, which is responsible for tongue protrusion, is primarily innervated by the hypoglossal nerve.

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