## **Core Concept**
The development of the tongue is a complex process involving multiple embryological structures. The tongue can be divided into two parts: the anterior two-thirds and the posterior one-third, which develop from different embryological origins.

## **Why the Correct Answer is Right**
The posterior one-third of the tongue develops from the **third pharyngeal arch**. During embryonic development, the pharyngeal arches form and give rise to various structures in the head and neck. The third pharyngeal arch specifically contributes to the formation of the posterior one-third of the tongue. This part of the tongue is primarily innervated by the **glossopharyngeal nerve (cranial nerve IX)**, which is associated with the third pharyngeal arch.

## **Why Each Wrong Option is Incorrect**
* **Option A:** The first pharyngeal arch primarily contributes to the formation of the jaw, portions of the external ear, and some structures of the mouth, but not the posterior one-third of the tongue.
* **Option B:** The second pharyngeal arch, also known as the hyoid arch, gives rise to structures including the styloid process and the anterior two-thirds of the tongue (innervated by the facial nerve), not the posterior one-third.
* **Option D:** The fourth and sixth pharyngeal arches contribute to laryngeal development and some muscles of the pharynx and larynx but are not primarily involved in the formation of the posterior one-third of the tongue.

## **Clinical Pearl / High-Yield Fact**
A key clinical correlation to remember is that the **innervation of the tongue** reflects its embryological origin. The anterior two-thirds of the tongue are innervated by the **chorda tympani (a branch of the facial nerve, CN VII)**, while the posterior one-third is innervated by the **glossopharyngeal nerve (CN IX)**. This dual innervation pattern is crucial for diagnosing and managing conditions affecting the tongue.

## **Correct Answer:** C. Third pharyngeal arch.