**Core Concept**
The motor supply to the muscles of the tongue is primarily provided by the hypoglossal nerve (cranial nerve XII), which is responsible for controlling the movements of the tongue. This nerve innervates all the extrinsic and intrinsic muscles of the tongue, enabling functions such as speaking, swallowing, and manipulating food in the mouth.

**Why the Correct Answer is Right**
The hypoglossal nerve originates from the brainstem, specifically from the lateral medullary pyramidal tract, and exits the skull through the hypoglossal canal. It then descends into the neck, where it synapses with the motor neurons that innervate the muscles of the tongue. The hypoglossal nerve is a mixed nerve, containing both motor and sensory fibers, and is responsible for the motor functions of the tongue, including protrusion, retraction, elevation, and depression. The hypoglossal nerve also receives input from the trigeminal nerve (cranial nerve V) for sensory innervation of the tongue.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because the facial nerve (cranial nerve VII) primarily supplies the muscles of facial expression, not the muscles of the tongue.
**Option B:** This option is incorrect because the glossopharyngeal nerve (cranial nerve IX) primarily supplies sensory innervation to the tongue, as well as motor innervation to the stylopharyngeus muscle, but not the intrinsic muscles of the tongue.
**Option D:** This option is incorrect because the vagus nerve (cranial nerve X) primarily supplies parasympathetic innervation to various organs, including the tongue, but not motor innervation to the muscles of the tongue.

**Clinical Pearl / High-Yield Fact**
The hypoglossal nerve is unique in that it is the only cranial nerve that does not cross over (decussate) at the level of the medulla oblongata, allowing it to innervate both sides of the tongue. This is why lesions of the hypoglossal nerve can cause atrophy of the tongue on the affected side.

**Correct Answer: C. The hypoglossal nerve (cranial nerve XII).**