The facial nerve motor nucleus is in the mid-lower pons. The axons from this nucleus go backwards encircling the abducent nucleus and then forward to exit through the lateral surface of the pons (Figure 176.1). After exiting the pons, they travel in the subarachnoid space until they enter the internal auditory canal. They travel in the auditory canal for a short distance and then bend backward and downward into the facial canal.

Figure 176.1.— Schematic representation of the intrapontine trajectory of the facial nerve. N: nucleus; CN: cranial nerve.

The facial nerve travels in the facial canal and exits through the stylomastoid foramen (Figure 176.2). Shortly after exiting through the stylomastoid foramen, the facial nerve divides into five branches to innervate the mimetic facial muscles: temporal, zygomatic, buccal, mandibular, and cervical.

Figure 176.2.— Facial motor system. T: thalamus; AC: internal auditory canal; FC: facial canal; SMO: stylomastoid orifice; BB: buccal branch; MB: mandibular branch; TB: temporal branch; OOM: orbicularis oculi muscle; RM: risorius muscle; DAOM: depressor angularis oris muscle; BM: buccinator muscle; MM: mentoris muscle. Light blue line indicates components of the facial nerve that have ipsilateral (hence bilateral) cortical innervation; dark blue line indicates components of the facial nerve that have contralateral innervation.