The anatomy of the facial nerve.

The facial (seventh cranial) nerve arises from the pontomedullary junction by two roots: (1) the motor root conveying fibers to muscles derived from second branchial arch mesoderm and (2) the nervus intermedius conveying visceral sensory fibers from the tongue and palate, and preganglionic parasympathetic fibers to the pterygopalatine and submandibular ganglia. The roots pass into the internal acoustic meatus where they join. At the lateral end of the meatus, the facial nerve passes into the facial canal. The nerve then turns sharply posteriorly at the geniculum. The geniculate (sensory) ganglion is situated here, and the greater petrosal nerve to the pterygopalatine ganglion arises from this region. The facial canal continues posteriorly on the medial wall of the tympanic cavity, passing above the fenestra vestibuli and arching downward and laterally to emerge at the stylomastoid foramen just after giving off the chorda tympani nerve. The posterior auricular nerve and the nerves to the stylohoid and posterior digastric muscles arise before the facial nerve enters the substance of the parotid gland. In the gland, the nerve divides into five groups of branches (temporal, zygomatic, buccal, mandibular, and cervical) that supply the muscles of facial expression.