The main stem of the facial nerve [VII] then gives off another branch, which innervates the posterior belly of the digastric muscle and the stylohyoid muscle. At this point, the facial nerve [VII] enters the deep surface of the parotid gland (Fig. 8.66B).
Once in the parotid gland, the main stem of the facial nerve [VII] usually divides into upper (temporofacial) and lower (cervicofacial) branches. As these branches pass through the substance of the parotid gland they may branch further or take part in an anastomotic network (the parotid plexus).
Whatever types of interconnections occur, five terminal groups of branches of the facial nerve [VII]—the temporal, zygomatic, buccal, marginal mandibular, and cervical branches—emerge from the parotid gland (Fig. 8.66A).
Although there are variations in the pattern of distribution of the five terminal groups of branches, the basic pattern is as follows:
Temporal branches exit from the superior border of the parotid gland to supply muscles in the area of the temple, forehead, and supra-orbital area.
Zygomatic branches emerge from the anterosuperior border of the parotid gland to supply muscles in the infra-orbital area, the lateral nasal area, and the upper lip.
Buccal branches emerge from the anterior border of the parotid gland to supply muscles in the cheek, the upper lip, and the corner of the mouth.
Marginal mandibular branches emerge from the anteroinferior border of the parotid gland to supply muscles of the lower lip and chin.
Cervical branches emerge from the inferior border of the parotid gland to supply the platysma.
The arterial supply to the face is primarily from branches of the external carotid artery, though there is some limited supply from a branch of the internal carotid artery.
Similarly, most of the venous return is back to the internal jugular vein, though some important connections from the face result in venous return through a clinically relevant intracranial pathway involving the cavernous sinus.
The facial artery is the major vessel supplying the face (Fig. 8.67). It branches from the anterior surface of the external carotid artery, passes up through the deep structures of the neck, and appears at the lower border of the mandible after passing posterior to the submandibular gland. Curving around the inferior border of the mandible just anterior to the masseter, where its pulse can be felt, the facial artery then enters the face. From this point the facial artery runs upward and medially in a tortuous course. It passes along the side of the nose and terminates as the angular artery at the medial corner of the eye.
Along its path the facial artery is deep to the platysma, risorius, and zygomaticus major and minor, superficial to the buccinator and levator anguli oris, and may pass superficially to or through the levator labii superioris.
Branches of the facial artery include the superior and inferior labial branches and the lateral nasal branch (Fig. 8.67).
The labial branches arise near the corner of the mouth:
The inferior labial branch supplies the lower lip.
The superior labial branch supplies the upper lip, and also provides a branch to the nasal septum.
Near the midline, the superior and inferior labial branches anastomose with their companion arteries from the opposite side of the face. This provides an important connection between the facial arteries and the external carotid arteries of opposite sides.
The lateral nasal branch is a small branch arising from the facial artery as it passes along the side of the nose. It supplies the lateral surface and dorsum of the nose.
Another contributor to the vascular supply of the face is the transverse facial artery (Fig. 8.67), which is a branch of the superficial temporal artery (the smaller of the two terminal branches of the external carotid artery).