## **Core Concept**
The digastric muscle is a muscle of the neck that consists of two bellies: anterior and posterior. The posterior belly of the digastric muscle is involved in the process of swallowing and elevation of the hyoid bone. The question tests knowledge of the nerve supply to this muscle.

## **Why the Correct Answer is Right**
The posterior belly of the digastric muscle is supplied by the **facial nerve (cranial nerve VII)**, specifically through its **digastric branch**. This branch arises from the mastoid segment of the facial nerve and supplies the posterior belly of the digastric muscle. The facial nerve is responsible for controlling muscles of facial expression and also provides motor innervation to the stapedius muscle, stylohyoid muscle, and the posterior belly of the digastric muscle.

## **Why Each Wrong Option is Incorrect**
- **Option A:** The **trigeminal nerve (cranial nerve V)** primarily supplies muscles of mastication and is not responsible for innervating the posterior belly of the digastric muscle.
- **Option B:** The **glossopharyngeal nerve (cranial nerve IX)** supplies stylopharyngeus muscle and provides sensory innervation to the pharynx but does not innervate the posterior belly of the digastric muscle.
- **Option D:** The **mandibular division of the trigeminal nerve** supplies the anterior belly of the digastric muscle, not the posterior belly.

## **Clinical Pearl / High-Yield Fact**
A useful clinical correlation to remember is that the **digastric muscle** has two bellies with different nerve supplies: the **anterior belly** is supplied by the **mylohyoid nerve** (a branch of the inferior alveolar nerve, which is part of the mandibular division of the trigeminal nerve), while the **posterior belly** is supplied by the **facial nerve (cranial nerve VII)**.

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