## **Core Concept**
The question tests knowledge of cranial nerve anatomy, specifically those involved in tongue movement, and the potential complications of surgical procedures in the submandibular region. The deviation of the tongue to the affected side post-surgery suggests damage to a nerve responsible for tongue protrusion.

## **Why the Correct Answer is Right**
The correct answer, **C. Hypoglossal nerve**, is implicated because the hypoglossal nerve (cranial nerve XII) is responsible for the motor innervation of the tongue muscles, except for the palatoglossus. Damage to this nerve results in weakness of the tongue on the affected side. When attempting to protrude the tongue, the weakened side is pushed back by the stronger, unaffected side, causing the tongue to deviate towards the side of the lesion. The hypoglossal nerve runs close to the submandibular gland and can be at risk during surgical procedures in this area.

## **Why Each Wrong Option is Incorrect**
- **Option A:** The **Glossopharyngeal nerve (cranial nerve IX)** primarily carries sensory fibers from the posterior one-third of the tongue and is not responsible for tongue movement. Damage to this nerve would not cause deviation of the tongue.
- **Option B:** The **Vagus nerve (cranial nerve X)** has various functions, including parasympathetic innervation of several organs, but it does not directly control tongue movement. It is not related to the deviation of the tongue.
- **Option D:** The **Mandibular nerve (V3, a branch of the Trigeminal nerve)** provides sensory innervation to the lower face and motor innervation to the muscles of mastication. It does not control tongue movement.

## **Clinical Pearl / High-Yield Fact**
A key point to remember is that the hypoglossal nerve has a long and winding course, making it susceptible to injury in various clinical scenarios, including surgical procedures in the neck and submandibular region. The classic presentation of hypoglossal nerve damage is deviation of the tongue to the side of the lesion upon protrusion.

## **Correct Answer:** C. Hypoglossal nerve