## **Core Concept**
The genioglossus muscle is one of the extrinsic muscles of the tongue, primarily responsible for protruding the tongue. It is innervated by the **hypoglossal nerve (CN XII)**, which is a motor nerve. The genioglossus muscle plays a crucial role in maintaining the tongue's position within the oral cavity.

## **Why the Correct Answer is Right**
Palsy of the right genioglossus muscle, which is caused by damage to the right **hypoglossal nerve (CN XII)**, results in weakness of the muscle. This weakness leads to difficulty in protruding the tongue, and when the patient attempts to protrude the tongue, it deviates to the **weak side**, in this case, to the right. This occurs because the healthy side (left) pushes the tongue to the right as it protrudes.

## **Why Each Wrong Option is Incorrect**
- **Option A:** This option is incorrect because deviation to the opposite side (left) would occur if the left genioglossus was weak, not the right.
- **Option B:** This option is incorrect as the deviation to the right does not relate to a bilateral weakness or another unrelated cause.
- **Option C:** This option might seem plausible but does not accurately describe the deviation caused by a unilateral weakness of the genioglossus muscle.

## **Clinical Pearl / High-Yield Fact**
A key clinical point to remember is that when assessing a patient with suspected **hypoglossal nerve palsy**, asking the patient to protrude their tongue can help diagnose the condition. The tongue will deviate towards the side of the lesion when protruded, indicating weakness on that side.

## **Correct Answer:** D. Deviation of tongue to right.