Which nerve supplies the posterior belly of the digastric muscle?

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Two bellies of the digastric have different nerve supplies because they arise from different pharyngeal arches. The posterior belly gets its motor innervation from the facial nerve via its digastric branch, which also supplies the stylohyoid. The anterior belly, by contrast, is supplied by the nerve to the mylohyoid from the mandibular division of the trigeminal nerve. So, the nerve responsible for the posterior belly’s motor function is the facial nerve. The other nerves listed don’t innervate this part: hypoglossal to tongue muscles, glossopharyngeal to a pharyngeal muscle and other roles, and trigeminal only to the anterior belly via the nerve to mylohyoid.