The muscles of the face (Fig. 8.56) develop from the second pharyngeal arch and are innervated by branches of the facial nerve [VII]. They are in the superficial fascia, with origins from either bone or fascia, and insertions into the skin.
Because these muscles control expressions of the face, they are sometimes referred to as muscles of “facial expression.” They also act as sphincters and dilators of the orifices of the face (i.e., the orbits, nose, and mouth). This organizational arrangement into functional groups provides a logical approach to understanding these muscles (Table 8.7).
Two muscles are associated with the orbital group—the orbicularis oculi and the corrugator supercilii.
The orbicularis oculi is a large muscle that completely surrounds each orbital orifice and extends into each eyelid (Fig. 8.57). It closes the eyelids. It has two major parts:
The outer orbital part is a broad ring that encircles the orbital orifice and extends outward beyond the orbital rim.
The inner palpebral part is in the eyelids and consists of muscle fibers originating in the medial corner of the eye that arch across each lid to attach laterally.
The orbital and palpebral parts have specific roles to play during eyelid closure. The palpebral part closes the eye gently, whereas the orbital part closes the eye more forcefully and produces some wrinkling on the forehead.
An additional small lacrimal part of the orbicularis oculi muscle is deep, medial in position, and attaches to bone posterior to the lacrimal sac of the lacrimal apparatus in the orbit.
The second muscle in the orbital group is the much smaller corrugator supercilii (Fig. 8.57), which is deep to the eyebrows and the orbicularis oculi muscle and is active when frowning. It arises from the medial end of the superciliary arch, passing upward and laterally to insert into the skin of the medial half of the eyebrow. It draws the eyebrows toward the midline, causing vertical wrinkles above the nose.
Three muscles are associated with the nasal group—the nasalis, the procerus, and the depressor septi nasi (Fig. 8.58).
The largest and best developed of the muscles of the nasal group is the nasalis, which is active when the nares are flared (Fig. 8.58). It consists of a transverse part (the compressor naris) and an alar part (the dilator naris):
The transverse part of the nasalis compresses the nares—it originates from the maxilla and its fibers pass upward and medially to insert, along with fibers from the same muscle on the opposite side, into an aponeurosis across the dorsum of the nose.
The alar part of the nasalis draws the alar cartilages downward and laterally, so opening the nares—it originates from the maxilla, below and medial to the transverse part, and inserts into the alar cartilage.
The procerus is a small muscle superficial to the nasal bone and is active when an individual frowns (Fig. 8.58). It arises from the nasal bone and the upper part of the lateral nasal cartilage and inserts into the skin over the lower part of the forehead between the eyebrows. It may be continuous with the frontal belly of the occipitofrontalis muscle of the scalp.
The procerus draws the medial border of the eyebrows downward to produce transverse wrinkles over the bridge of the nose.
The final muscle in the nasal group is the depressor septi nasi, another muscle that assists in widening the nares (Fig. 8.58). Its fibers arise from the maxilla above the central incisor tooth and ascend to insert into the lower part of the nasal septum.
The depressor septi nasi pulls the nose inferiorly, so assisting the alar part of the nasalis in opening the nares.