## **Core Concept**
The circumvallate papillae are small projections on the tongue that contain taste buds. They are part of the tongue's surface anatomy and play a crucial role in taste sensation. The sensory innervation of the tongue, including the circumvallate papillae, is essential for understanding their function.

## **Why the Correct Answer is Right**
The circumvallate papillae are supplied by the **chorda tympani nerve**, a branch of the facial nerve (cranial nerve VII). The chorda tympani nerve carries taste fibers from the anterior two-thirds of the tongue, including the circumvallate papillae. This nerve is responsible for transmitting taste sensations from these areas to the brain.

## **Why Each Wrong Option is Incorrect**
- **Option A:** The **lingual nerve**, a branch of the mandibular division of the trigeminal nerve (cranial nerve V), provides general sensory innervation (touch, pressure, temperature) to the anterior two-thirds of the tongue but does not carry taste sensation.
- **Option B:** The **glossopharyngeal nerve** (cranial nerve IX) does carry taste sensation, but it supplies the posterior one-third of the tongue, not the circumvallate papillae.
- **Option D:** The **vagus nerve** (cranial nerve X) carries taste sensation from the epiglottis and the back of the throat but not from the circumvallate papillae.

## **Clinical Pearl / High-Yield Fact**
A key clinical correlation is that damage to the facial nerve (cranial nerve VII), specifically the chorda tympani branch, can lead to loss of taste sensation in the anterior two-thirds of the tongue. This can be tested clinically using taste strips or other methods to assess taste function.

## **Correct Answer:** B. Chorda tympani nerve.