Chapter 7The Head by Regions

1 The Face and Scalp

The face is that part of the head visible in a frontal view, that is, all that is anterior to the external ears and all that lies between the hairline and the chin. Clustered in this region are the various facial openings and their associated sensory structures.

The scalp covers the forehead, the superior aspect of the cranial vault, and the occipital region above the superior nuchal line. Laterally, the scalp blends in with the temporal area.

REGIONS OF THE FACE

The facial region may be subdivided into a number of areas (Figure 7-1): (1) the forehead, extending from the eyebrows to the hairline; (2) the temples or temporal area anterior to the ears; (3) the orbital area containing the eye and covered by the eyelids; (4) the external nose; (5) the zygomatic (malar) area (prominence of the cheek); (6) the mouth and lips; (7) the cheeks; (8) the chin; and (9) the external ear.

Figure 7-1 Regions of the face. A, At rest. B, Smiling.

SKELETON

The anterior, superior, lateral, and posterior aspects of the skull are discussed in Chapter 6.

SKIN AND FASCIA

SENSORY (CUTANEOUS) NERVES OF THE FACE

The facial cutaneous nerve supply is principally derived from the trigeminal nerve (cranial nerve V) (Figure 7-2). Within the skull, the trigeminal nerve divides into three parts: (1) the ophthalmic nerve (cranial nerve V-1), a sensory nerve associated mainly with the orbit and its contents; (2) the maxillary nerve (cranial nerve V-2), a sensory nerve associated with the nasomaxillary complex; and (3) the mandibular nerve (cranial nerve V-3), a sensory and motor nerve associated with the lower jaw and the muscles of mastication. Only the mandibular nerve contains motor as well as sensory fibers. Each division of the trigeminal nerve contributes sensory cutaneous branches to the face.

Figure 7-2 A, Cutaneous nerves of the face. V-1 (ophthalmic nerve): SO, Supraorbital nerve; ST, supratrochlear nerve; L, lacrimal nerve; IT, infratrochlear nerve; EN, external nasal nerve. V-2 (maxillary nerve): IO, Infraorbital nerve. V-3 (mandibular nerve): AT, Auriculotemporal nerve; B, buccal nerve; M, mental nerve. Spinal nerve: GA, Great auricular nerve. B, Motor nerves to the muscles of facial expression. Facial branches of CN VII: T, Temporal branches; Z, zygomatic branches; B, buccal branches; M, mandibular branches; C, cervical branches.

Facial Branches of the Ophthalmic Nerve

The ophthalmic nerve contributes several branches to the upper eyelid, the forehead and scalp, and the external nose.

Supraorbital Nerve

The supraorbital nerve emerges from the roof of the orbit through the supraorbital foramen, or notch. It travels to and supplies a small portion of the frontal sinus, a large portion of the upper eyelid, and a large portion of the forehead and scalp.

Supratrochlear Nerve

The supratrochlear nerve within the orbit passes over the pulley, or trochlea, of the superior oblique muscle. It emerges from the medial aspect of the superior orbital margin to supply the medial portion of the upper eyelid and adjacent forehead.

Infratrochlear Nerve

The infratrochlear nerve passes under the trochlea in the orbit and emerges near the medial angle of the eye; this nerve supplies the medial angle of the upper lid and the lacrimal sac.

Lacrimal Nerve

The lacrimal nerve is a tiny branch that emerges from the lateral aspect of the superior margin of the orbit to supply a small, lateral portion of the upper eyelid.

External Nasal Nerve

The external nasal nerve surfaces on either side of the midline at the junction of the nasal bone and nasal cartilages. It supplies a median strip of external nose below the nasal bones.

Facial Branches of the Maxillary Nerve

Infraorbital Nerve

The infraorbital nerve is the large, terminal branch of the maxillary nerve. The infraorbital nerve passes through a bony canal in the orbital floor to emerge onto the face through the infraorbital foramen. On the face, it immediately breaks up into three sets of branches.

1. Inferior palpebral branches, which convey sensation from the skin and conjunctivum of the lower lid

2. Lateral nasal branches, which convey sensation from the lateral aspect of the external nose

3. Superior labial branches, which convey sensation from the skin and mucous membrane of the upper lip.

Zygomaticofacial Nerve

The zygomaticofacial nerve is a small branch of the zygomatic nerve, which, in turn, is a branch of the maxillary nerve. It emerges onto the face through the zygomaticofacial foramen to supply skin of the zygomatic prominence.

Zygomaticotemporal Nerve

The zygomaticotemporal nerve is another branch of the zygomatic nerve, which passes through the zygomaticotemporal foramen and ascends to supply skin of the anterior aspect of the temporal fossa and scalp.

Facial Branches of the Mandibular Nerve

The cutaneous contribution of cranial nerve V-3 to the face is fairly widespread, ranging from the temples to the chin.

Auriculotemporal Nerve

The auriculotemporal nerve surfaces between the temporomandibular joint and the tragus of the ear. It ascends to supply the skin of a portion of the external ear and ear canal, the temporal region, and the lateral aspect of the scalp.

Buccal Branch of Cranial Nerve V-3

The buccal branch of cranial nerve V-3 appears on the face from under the cover of the ramus of the mandible. It spreads over the cheek and conveys sensation from the skin and mucous membrane of the cheek. In addition, it conveys sensory information from the vestibular (buccal) gingiva of the mandibular molars.

CLINICAL NOTES

Dental Anesthesia

Various facial branches of the trigeminal nerve are anesthetized following routine local anesthetic injections for dental procedures. Anesthesia of the mandibular teeth will also result in anesthesia of the mental nerve supplying the chin and lower lip. Anesthesia of the maxillary anterior teeth will also block sensation from the lower eyelid, lateral nose, and the upper lip. Numbness in these areas indicates successful local anesthesia.

Trigeminal Neuralgia (Tic Douloureux)

Disorders of the trigeminal ganglion, within the skull, can give rise to paroxysms (sudden, severe bouts of pain) along the pathways of the sensory facial branches of the trigeminal nerve. Trigeminal neuralgia occurs more often in territories supplied by the maxillary (cranial nerve V-2) or mandibular (cranial nerve V-3) nerves. These episodes of pain can be triggered by just a light touch to the face or hot or cold foods in the mouth. Treatment sometimes consists of resection of the maxillary or mandibular division. Following resection, patients must chew very carefully to prevent biting the cheek. Patients who have undergone such a resection should visit their dentists frequently to monitor possible intraoral problems that the patient can no longer detect because intraoral pain is no longer a warning that something is wrong.

Mental Nerve

The mental nerve is a cutaneous branch of the inferior alveolar nerve. The mental nerve leaves the mandibular canal through the mental foramen and exits onto the face lateral to the chin. It immediately breaks up into three sets of branches.

1. Mental branches supply the skin of the chin.

2. Inferior labial branches supply the skin and mucous membrane of the lower lip.

3. Gingival branches supply the vestibular (labial) gingiva of the mandibular anterior teeth.

ARTERIES OF THE FACE

The face is richly supplied with blood from various arteries, and the terminal branches of these various arteries anastomose freely (Figure 7-3). The entire blood supply is derived from either the internal or the external carotid arteries. Their facial branches travel as companion arteries to the sensory facial nerves described previously and, in general, carry the same names as the facial sensory nerves.

Figure 7-3 A, Superficial arteries of face. SO, Supraorbital artery; ST, supratrochlear artery; L, lacrimal artery; EN, external nasal artery; ZF, zygomaticofacial artery; ZT, zygomaticotemporal artery; IO, infraorbital artery; S, superficial temporal artery; M, mental artery; F, facial artery. B, Superficial veins of face. SO, Supraorbital vein; ST, supratrochlear vein; L, lacrimal vein; EN, external nasal vein; ZF, zygomaticofacial vein; IO, infraorbital vein; S, superficial temporal vein; M, mental vein; F, facial vein; DF, deep facial vein.

Facial Branches of the Ophthalmic Artery

The facial branches arise directly or indirectly from the ophthalmic artery of the orbit and stream out of the orbit as five branches.

Supraorbital Artery

The supraorbital artery, along with its companion cutaneous nerve, leaves the orbit through the supraorbital notch, or foramen, to supply the upper eyelid, forehead, and scalp.

Supratrochlear Artery

The supratrochlear artery emerges medial to the supraorbital artery and supplies the upper lid, forehead, and scalp.

Dorsal Nasal Artery

The dorsal nasal artery is the companion artery to the infratrochlear nerve. It emerges from the medial-superior angle of the orbit to supply the medial upper lid, the lacrimal sac, and the bridge of the nose.

Lacrimal Artery

The lacrimal artery is the small terminal portion of the ophthalmic artery, which emerges at the lateral aspect of the supraorbital margin to supply the lateral aspect of the upper lid.

External Nasal Artery

The external nasal artery surfaces on either side of the midline at the junction of the nasal bone and nasal cartilages. It supplies a median strip of external nose below the nasal bones.

Zygomatic Artery

The zygomatic artery passes through the zygomatic canal in the lateral wall of the orbit and divides into two terminal branches that emerge on the face. The zygomaticofacial artery emerges through the zygomaticofacial foramen to supply the skin of the prominence of the cheek. The zygomaticotemporal artery emerges through the zygomaticotemporal foramen to supply the skin of the anterior temporal region.

Facial Branches of the Maxillary Artery

Infraorbital Artery

The infraorbital artery issues from the infraorbital foramen below the orbit and immediately breaks up into (1) inferior palpebral branches to the lower eyelid, (2) nasal branches to the lateral aspect of the nose, and (3) superior labial branches to the upper lip.

Buccal Artery

The buccal artery appears from under the cover of the ramus and masseter muscle. It spills onto the cheek, supplying the skin and mucous membrane of the cheek and vestibular gingiva of the mandibular molar area.

Mental Artery

The mental artery branches from the inferior alveolar artery within the mandibular canal of the mandible. It exits through the mental foramen, along with the mental nerve, to supply the chin, lower lip, and vestibular gingiva of the mandibular anterior teeth.

Branches of the Facial Artery

The facial artery, a collateral branch of the external carotid artery, leaves the submandibular region of the neck and ascends over the inferior border of the mandible through the antegonial notch. As the facial artery ascends obliquely on the face, it follows a somewhat tortuous route toward the medial angle of the eye. It passes between the more superficial and the deeper muscles of facial expression and supplies several branches to the face that anastomose freely with terminal branches of the maxillary and ophthalmic arteries.

Superior and Inferior Labial Branches

As the facial artery travels diagonally toward the medial angle of the mouth, it gives off the inferior labial artery to the lower lip and the superior labial artery to the upper lip. The pulsations of the labial arteries may be felt in your own lip by grasping the lip between the thumb and forefinger.

Lateral Nasal Branches

Lateral nasal branches are given off to the side of the nose; these anastomose with nasal branches of the infraorbital artery and the external nasal artery.

Angular Artery

The facial artery ends at the medial angle of the eye as the angular artery. It provides branches to the nose and medial aspect of the lids.

Facial Branches of the Superficial Temporal Artery

The superficial temporal artery is a terminal branch of the external carotid artery that emerges onto the face between the jaw joint and the ear to ascend on the scalp. Just below the ear, it sends a branch forward as the transverse facial artery immediately below the zygomatic arch. It accompanies the auriculotemporal nerve on the side of the head.

CLINICAL NOTES

Pulse Points on the Face

It is occasionally convenient for the dentist to take a patient’s pulse in the head region. Two areas in the face where the pulse may be taken are (1) the facial artery as it passes through the antegonial notch and (2) the superficial temporal artery as it passes immediately anterior to the ear, above the tragus.

Ligation of Arteries

The face is profusely supplied by blood vessels. The areas of the external nose and lips receive a dual arterial supply from branches of both the facial and maxillary arteries. Facial lacerations bleed profusely, and occasionally branches of the external carotid artery or the external carotid itself must be ligated (tied off) to control hemorrhage.

The facial artery is vulnerable in oral surgery procedures on the buccal aspect of the mandibular molar region. Excessive force and improper techniques can sever the facial artery as it ascends onto the mandible in the antegonial notch.

To prevent excessive hemorrhage, major arteries are sometimes ligated or tied off as a preventative measure before major oral surgery procedures.

VEINS OF THE FACE

The veins of the face follow somewhat the same pattern of distribution as the arterial supply, except for a few small but important differences (see Figures 7-3 and 7-4). Veins generally show more variability in their distribution than do arteries.

Figure 7-4 Lateral view of the facial artery and vein.

Veins that Accompany Cutaneous Nerves and Arteries

For each of the named arteries described previously as facial branches of the ophthalmic artery or maxillary artery, there are corresponding veins of the same name that flow in the opposite direction. The veins of the forehead, scalp, and upper lid flow to the superior ophthalmic vein in the orbit; the veins of the upper lip, lateral nose, and lower lid flow via the infraorbital vein to the pterygoid plexus of veins in the infratemporal region.

The Facial Vein

The facial vein roughly parallels the route of the facial artery. However, it is more posterior, takes a straighter and less tortuous course, and travels in the opposite direction. The facial vein originates and gathers tributaries in the following manner:

1. The angular vein forms at the medial angle of the eye by the union of the supraorbital and supratrochlear veins. The angular vein divides, and one division passes into the orbit to drain to the superior ophthalmic vein. The other division remains superficial and passes inferiorly as the facial vein.

2. The facial vein angles posteriorly toward the angle of the jaw and, as it descends, picks up several tributaries.

3. Nasal veins drain the side of the nose and communicate with tributaries of the infraorbital vein.

4. The deep facial vein communicates with the pterygoid plexus of veins deep within the infratemporal region.

5. Labial veins drain the upper and lower lips: the superior labial vein communicates with the infraorbital vein; the inferior labial vein communicates with the mental vein.

The facial vein then descends over the inferior border near the antegonial notch to enter the submandibular region of the neck. Unlike the facial artery, the vein takes a superficial course through the submandibular region.

The Retromandibular Vein

The retromandibular vein is formed from two sources. The superficial temporal vein drains the scalp and side of the head. It descends anterior to the ear and plunges into the substance of the parotid gland. Here it unites with the maxillary vein from the infratemporal region.

The retromandibular vein continues inferiorly, picking up glandular tributaries, and leaves the gland at its inferior border. At the angle of the mandible, the retromandibular vein divides into an anterior and a posterior division in the neck. The posterior division of the retromandibular vein unites with the posterior auricular vein from behind the ear to form the external jugular vein.

The anterior division of the retromandibular vein joins the facial vein in the neck to form the short common facial vein. The common facial vein drains deep to the internal jugular vein (see Chapter 5).

CLINICAL NOTES

Spread of Infection

Infections arising from the face or the orbit can spread through these venous communications to the cavernous sinus and cause an infective intracranial thrombus (clot). The condition is termed cavernous sinus thrombosis, is difficult to eradicate even with extensive antibiotic therapy, and may be fatal. Organisms in the blood from infections on the face could, therefore, be swept through the orbit to the cavernous sinus, where a secondary, more dangerous site of infection could develop.

Venous Communications

The facial vein contains no valves and communicates with relatively small tributaries of the infraorbital, zygomatic, and mental veins. In addition, two major communications are highly significant.

1. The facial vein communicates directly with the superior ophthalmic vein via the angular vein. Venous drainage from the angle of the eye may travel down the facial vein to the neck or may track into the orbit via the superior ophthalmic vein. The superior ophthalmic vein, in turn, drains to the cavernous sinus within the skull, where venous blood pools and flow is sluggish.

2. Venous drainage may back along the deep facial vein to the pterygoid plexus of veins in the infratemporal region. The plexus, in turn, communicates with the cavernous sinus within the skull.

MUSCLES OF THE FACE

The muscles of the face, or muscles of facial expression, are derived from the second branchial arch and are supplied by the cranial nerve of the second arch, the facial nerve (cranial nerve VII) (Figure 7-5 and Table 7-1). The muscles of the scalp and the platysma muscle of the neck belong to the same muscle group.

Figure 7-5 Muscles of facial expression. A, Anterior view. Superficial muscles are shown on right; deeper muscles are shown on left. B, Lateral view.

TABLE 7-1 Muscles of the Face

In general, the muscles are found within the superficial fascia around the facial orifices. They perform two functions: (1) as dilators and sphincters they control the openings of the orifices, and (2) as movers of overlying skin they reflect the various facial expressions.

Most facial muscles originate from bone or from fascia, and all insert into the skin of the face. Upon contraction, therefore, they move the facial skin into various attitudes that reflect emotions, such as smiling, grinning, frowning, and forehead wrinkling of puzzlement. The muscles are grouped by regions.

Mouth

Orbicularis Oris

The orbicularis oris muscle is the sphincter of the oral aperture and lies within the upper and lower lips, encircling the mouth. Its fibers originate mainly from contributions of other facial muscles that converge on the mouth. A few intrinsic fibers arise from labial alveolar bone overlying the upper and lower incisors.

The orbicularis oris muscle closes the oral aperture, presses the lips against the teeth, and protrudes the lips.

Levator Anguli Oris

The levator anguli oris muscle originates from the canine fossa of the maxilla immediately inferior to the infraorbital foramen. It inserts into the angle of the mouth, blending with fibers of the orbicularis oris muscle. The function is self-descriptive; the muscle lifts the angles of the mouth.

Depressor Anguli Oris

The depressor anguli oris is a triangular muscle, the base of which originates from the external oblique line of the mandible. The ascending fibers converge at the apex to insert into the angle of the mouth from below and blend with the fibers of the orbicularis oris muscle. The depressor anguli oris muscle pulls the angles of the mouth downward.

Zygomaticus Major

The zygomaticus major muscle arises from the facial aspect of the zygomatic bone. Its fibers angle downward and medially to insert into the angle of the mouth and blend with the orbicularis oris muscle. It is the “laughing” muscle of the face, drawing the angle of the mouth upward and backward.

Risorius

The risorius muscle is a thin, wispy muscle that arises from parotid and masseteric fascia, plus a small contribution from upper fibers of platysma muscle sweeping up from the neck. Risorius muscle inserts transversely into the angle of the mouth and retracts the angle posteriorly, as in grinning.

Lips

Levator Labii Superioris

The levator labii superioris muscle has three origins that blend and pass into the upper lip.

1. The angular head (levator labii superioris alaeque nasi) arises from the frontal process of the maxilla.

2. The infraorbital head, the largest component, originates from the inferior orbital margin.

3. The zygomatic head (zygomaticus minor) originates from the facial aspect of the zygomatic bone.

All three origins insert as one into the upper lip and, upon contraction, raise the upper lip. A slip of the angular head inserts into the ala of the nose and helps to dilate the nostril.

Depressor Labii Inferioris

The depressor labii inferioris muscle arises from the lowest portion of the oblique line of the mandible, inserts into the lower lip, and depresses the lower lip.

Cheek

Buccinator

Origin

The buccinator muscle arises from three areas (Figure 7-6).

1. The pterygomandibular raphé is a thin, fibrous band running from the hamulus of the medial pterygoid plate down to the mandible, just behind the last mandibular molar. The raphé is actually a shared attachment with the superior constrictor muscle of the pharynx, the fibers of which interdigitate with those of the buccinator muscle as a common origin. The buccinator sweeps anteriorly into the wall of the cheek; the superior constrictor sweeps posteriorly into the wall of the pharynx.

2. The lateral aspect of the maxillary alveolar process in the molar region provides attachment for the superior muscle fibers of the buccinator muscle.

3. The lateral aspect of the mandibular alveolar process in the molar region provides attachment for the inferior muscle fibers of the buccinator muscle along the posterior half of the external oblique line.

Figure 7-6 Attachments of the buccinator muscle.

Insertion

The muscle fibers sweep anteriorly through the cheek as a flattened sheet. On approaching the angles of the mouth, the upper fibers sweep inferiorly and the lower fibers sweep superiorly to blend with the orbicularis oris muscle.

Function

The buccinator muscle presses the cheek against the vestibular surfaces of the molar teeth. In doing so, it aids in mastication by pushing food onto the occlusal surfaces of the teeth in opposition to the tongue, which pushes the food in the opposite direction. The buccinator muscle also prevents the cheeks from expanding when forcefully expelling air from the oral cavity against resistance, as in playing wind or brass musical instruments.

Eye Region

Orbicularis Oculi

The orbicularis oculi muscle is contained within the upper and lower eyelids (palpebrae). It is a sphincteric muscle and helps close the eyelids. The orbicularis oculi muscle originates as three components.

Attachments

The orbital portion originates from bone of the upper medial orbital margin, encircles the orbital margin, and inserts from below into the prominent medial palpebral ligament. The ligament, in turn, is anchored to the anterior lacrimal crest of the maxilla.

The palpebral portion arises from the medial palpebral ligament and arches laterally within the upper and lower eyelids. The fibers of the upper and lower lids interdigitate laterally at the less prominent lateral palpebral ligament.

The lacrimal portion is small and originates from the lacrimal bone deep behind the lacrimal sac. It inserts into the medial portions of the lids.

Actions

The palpebral portion lightly approximates the lids, as in light blinking or during sleep. The orbital portion, because of its attachment to bone of the orbital periphery, is in a good mechanical position to forcibly squeeze the lids tightly to block out foreign objects or intense light. The lacrimal portion holds the lids against the globe of the eyeball for more even distribution of moistening tears and guiding tears to the small openings, or puncta, of the nasolacrimal apparatus for tear removal to the nasal cavity.

Chin: Mentalis

The mentalis muscle is a conical muscle, the apex of which arises from the mandibular incisive fossa. The fibers converge as the base to insert into the skin of the chin superficially. Contraction of the fibers puckers the skin overlying the chin and helps the orbicularis oris muscle in clearing food from the mandibular labial vestibule.

Nose: Nasalis

The nasalis muscle is the main muscle of the nose, and it arises as two parts.

The transverse portion (compressor nares) arises from the upper portion of the canine ridge of the maxilla. It arches upward and medially to insert along with its counterpart in a midline aponeurosis overlying the nasal cartilages.

CLINICAL NOTES

Facial Muscles and Orthodontics

The actions of the nasalis muscle are insignificant, yet to the observant clinician, they are of diagnostic value. A true nasal breather can quite visibly flare the nostrils. Habitual mouth breathing caused by nasal obstruction decreases, if not eliminates, the ability to flare the nostrils. Mouth breathing is a cause of some dental malocclusions in children.

In children with class II malocclusions (small mandible in relation to the maxilla), the mentalis muscles are hyperactive when the lips are closed. The dimpling of the chin indicates hyperactive mentalis muscles.

The alar portion (dilator nares) arises from the nasal margin of the maxilla and inserts into the skin of the nostril. It acts to “flare” the nostrils. Some alar fibers sweep up to the ala and septum as the depressor septi muscle. These fibers tend to pull down on the septum and ala during nostril dilation.

Forehead

Procerus

The procerus muscle arises as small slips from fascia overlying the dorsum of the nose. The fibers sweep upward to insert into the skin overlying the glabella. Contraction produces transverse wrinkles over the bridge of the nose.

Corrugator

The corrugator is a small muscle slip that originates from the medial supraorbital margin. The fibers travel laterally to insert into the skin underlying the eyebrow. It produces vertical wrinkles over the glabella in certain individuals.

Frontalis

The frontalis muscle is the anterior component of the occipitofrontalis muscle of the scalp. It originates from a membranous sheet, or aponeurosis, on the scalp and inserts into the skin of the frontal region above the eyebrows. Contraction produces transverse wrinkling of the brow, as in worrying, or raising of the eyebrows, as in surprise.

MOTOR NERVES OF THE FACE: THE FACIAL NERVE

The facial nerve exits from the skull through the stylomastoid foramen at the base of the skull (see Figure 7-2). It passes inferiorly and anteriorly for several millimeters, enters the substance of the parotid gland, and here breaks up into five main groups of branches that radiate from the anterior margin of the gland and travel to various areas of the face.

Superficial Branches

Many facial muscles are supplied by more than one of the five branches of the facial nerve.

Temporal Branches

The temporal branches travel superiorly and anteriorly to supply facial muscles situated above the zygomatic arch, including the orbit and forehead. They innervate the anterior and superior auricular muscles, the frontalis muscle, and the superior portion of the orbicularis oculis muscle.

Zygomatic Branches

The zygomatic branches travel transversely across the face to supply facial muscles in the zygomatic, orbital, and infraorbital areas. They supply the inferior portion of the orbicularis oculis muscle, and the superior portions of the zygomaticus major, levator labii superioris, levator anguli oris, nasalis and orbicularis oris muscles.

Buccal Branches

Buccal branches supply muscles of the cheek and circumoral muscles. They innervate the buccinator and orbicularis oris muscles, and the inferior portions of the zygomaticus major, levator labii superioris, levator anguli oris, nasalis, and orbicularis oris muscles.

Mandibular Branches

The mandibular branches supply muscles of the chin and lower lip. Specifically they pass to the depressor anguli oris, depressor labii inferioris, and to the mentalis muscle.

Cervical Branches

Cervical branches descend to the neck to supply platysma, posterior belly of the digastric, and stylohyoid muscles. Cervical branches also pass posteriorly to supply the occipitalis and posterior auricular muscles.

Sensory Nerve Communications

The motor branches of the facial nerve communicate with cutaneous branches of the trigeminal nerve on the face and cutaneous branches of spinal nerves in the neck. It is likely that these communications represent sensory proprioceptive contributions, which distribute with the facial nerve branches to the various facial muscles.

CLINICAL NOTES

Facial Paralysis

Damage to the facial nerve results in some form of facial paralysis (Figure 7-7). The type of paralysis is dependent upon where the lesion (damage) occurs.

Figure 7-7 Facial paralysis resulting from damage to lower motor neurons of the facial nerve (cranial nerve VII).

(Redrawn from Wilson-Pauwels L, Akesson EJ, Stewart PA: Cranial Nerves: Anatomy and Clinical Comments. Toronto, 1998, BC Decker).

Lesions of the upper motor neuron

Axons of the upper motor neurons of the facial nerve cross the midline of the brainstem to supply facial muscles of the contralateral side. The upper facial muscles (frontalis and orbicularis oculi) also receive axons from the same or ipsilateral side. Damage to the upper motor neurons of the facial nerve results in paralysis of the lower facial muscles on the contralateral side. The upper facial muscles continue to receive an ipsilateral nerve supply. Strokes are the most common cause of this type of facial paralysis.

Lesions of the lower motor neuron

Damage to the lower motor neurons at any point along their path results in paralysis of the upper and lower facial muscles on the ipsilateral side. The causes of lower motor neuron damage are varied.

The mastoid process, at birth, is small and offers little protection to the facial nerve that emerges through the stylomastoid foramen. The nerve can be crushed in a forceps delivery.

Viral infections can cause inflammation of the facial nerve as it passes through the facial canal. Swelling of the nerve in the enclosed bony canal causes pressure and a temporary facial paralysis or Bell’s palsy.

A local anesthetic mistakenly injected into the parotid gland anesthetizes the facial nerve within the gland and results in a temporary facial paralysis. (See page 269.)

Effects of facial paralysis

Each muscle of facial expression can be affected but the most disabling and distressing effects are those on eyelids and those on the mouth and oral cavity.

The eyelids cannot close to lubricate the eye because the orbicularis oculi muscle is inactive and the levator palpebrae muscle, the opener of the upper eyelid acts unopposed. Tears fall onto the face because the punctum of the lower eyelid (hole that drains tears) is no longer applied closely to the eye (paralysis of the lacrimal portion of the orbicularis oculi).

Saliva may dribble from the mouth, and food cannot be chewed properly on the affected side because of paralysis of the buccinator and orbicularis oris muscles. In addition, expressive lines produced by facial muscles are obliterated, and facial distortion may occur because of contractions of unopposed contralateral facial muscles.

FEATURES OF THE FACE

Lips (Labia)

The upper and lower lips surround the mouth, or entrance to the oral cavity (Figure 7-8). The upper lip lies between the nose above and the opening of the mouth below. Laterally, the lips are separated from the cheeks by the nasolabial groove, a furrow extending from the ala of the nose to approximately 1 cm lateral to the angle of the mouth. The philtrum is a wide (6 to 7 mm), shallow trough extending from the nose to the red (vermilion) border of the upper lip. Superiorly, the philtrum ends at the columella, the fleshy external partition between the nostrils.

Figure 7-8 External features of the lips.

The lower lip lies between the mouth above and the labiomental groove below. This groove separates the lower lip from the chin below.

The upper and lower lips are continuous at the angles of the mouth and blend laterally with the cheeks.

Layers

The lip consists of several layers sandwiched between the skin externally and oral mucous membrane internally (Figure 7-9).

Figure 7-9 Sagittal section through the lower lip to demonstrate layers.

Skin

The skin of the lip exhibits all the general features of thin skin, such as hair, sweat, and sebaceous glands. As the skin of the lip approaches the mouth, it changes color abruptly to red. The point at which this change occurs is the vermilion border and marks the beginning of the red transitional zone between the external skin and the internal mucous membrane. The skin of the transitional zone is extremely thin and hairless, allowing the redness of the underlying capillary bed to show through.

Muscle

The muscle of the lip is the orbicularis oris muscle, the sphincter of the mouth. In addition, the circumoral muscles, which contribute to the orbicularis oris muscle, occupy this layer. The muscles lie within the superficial fascia.

Glands

Within the submucosa lie numerous labial mucous glands, or labial glands. These can be felt by running the tongue against the bumpy internal surface of your own lips. These glands open directly through tiny duct openings to the vestibule of the mouth.

Mucous Membrane

The transitional zone sweeps into the mouth and is transformed into true, moist, nonkeratinizing mucous membrane. The mucous membrane coats the intraoral vestibular portion of the lip and then reflects down from the upper lip or up from the lower lip onto the alveolar process. The fold is the vestibular, or mucolabial, fold. The mucous membrane ascends on the alveolar process and turns abruptly to gingiva (gums). The demarcation is abrupt, with the gingiva assuming a lighter color and a stippled surface. The gingiva is firmly attached to the underlying alveolar bone. The gingiva is described in greater detail in section 8 of this chapter.

Labial Frenula

These are folds of mucous membrane that run in the midline of the upper lip and the lower lip from the mucosa to the labial gingiva. Secondary frenula are found in the molar and premolar areas as well.

CLINICAL NOTES

Labial Frenectomy

Occasionally, an overly large frenulum must be resected. Excessively large frenula may cause spacing between the central incisors in children. In adults, large frenula may contribute to gingival recession.

CLINICAL NOTES

Lesions of the Lips

Even before the dentist examines the oral cavity, the lips are examined because they are targets for many types of lesions and diseases.

Angular cheilosis is an inflammation and cracking of the skin and transition zone at the angles of the mouth. It is a condition that is usually associated with a B vitamin deficiency. It may also be infected with bacteria and/or fungi and is called perlèche. Treatment consists of a regimen of antibacterial and antifungal medication. This condition is common in older edentulous patients with angular wrinkling and leakage of saliva contributing to irritation and inflammation. Restoration of facial contours with dentures helps rectify this problem.

Herpes labialis, or cold sores, are painful vesicular lesions (watery blisters) at the vermilion border of the lip that are caused by the herpes simplex virus. The vesicles rupture and form yellow crusted lesions that last about 10 days. Primary infections occur in early childhood and, after remission, the virus remains dormant in the trigeminal ganglion. The virus is opportunistic and can recur with fever-producing diseases, onset of menstruation, anxiety, exposure to sun, and occasionally dental treatment.

A labial mucocele or mucous retention cyst is a labial mucous gland with a blocked secretory duct that causes the gland and the overlying epithelium to bulge and assume a bluish tinge. Mucoceles usually occur on the lower lip. Large or noticeable cysts can be surgically removed.

Squamous cell carcinoma is a type of cancer. An ulcerated (cratered) lesion on the vermilion border of usually the lower lip that does not appear to heal over a reasonable period of time should be under suspicion and investigated.

Arteries

The upper lip is supplied by superior labial branches of the facial and infraorbital arteries. The lower lip is supplied by inferior labial branches of the facial and mental arteries.

Sensory Nerves

The upper lip is supplied by the superior labial branch of the infraorbital nerve. The lower lip is supplied by the inferior labial branch of the mental nerve.

Functions

The lips are used for grasping food, sucking liquids, clearing the labial vestibule of food, forming speech, and osculation.

Cheeks (Buccae)

The cheeks form the lateral movable walls of the oral cavity (Figure 7-10). Externally, the cheek includes not only the movable portion but also the prominence of the cheek over the zygomatic arch. This terminology, however, is from common usage, and our definition of cheek is confined to the movable portion.

Figure 7-10 Coronal section through the cheek to demonstrate layers.

Layers

The cheek layers are similar to those of the lip and from superficial to deep are (1) skin, (2) the buccinator muscle, (3) molar glands within the submucosa, and (4) buccal mucous membrane.

The mucosa of the cheek ends in a mucobuccal fold superiorly and inferiorly, that sweeps onto the alveolar process. As the mucosa ascends to the alveolar crest, it becomes firmly attached to the bone as the gingiva.

Occupying the space superficial to the buccinator muscle is a collection of fat, that is continuous with fat deposits deep to the ramus of the mandible and deep to the zygomatic arch lateral to the orbit. This fat depot is relatively larger in the infant, presumably to reinforce the cheeks and keep them from collapsing during sucking actions. Hence its name—the buccal sucking fat pad.

The parotid duct opens intraorally through the mucosa of the cheek at the occlusal level of the second maxillary molar.

Blood Supply

The cheek is supplied by the buccal branch of the maxillary artery.

Nerve Supply (Sensory)

The cheek is innervated by the buccal branch of the mandibular nerve (long buccal nerve).

Functions

The cheeks and lips really function as a single unit and act as an oral sphincter to push food from the vestibular area to the oral cavity proper. In addition, they act together with the lips during sucking and blowing actions.

External Nose

Framework

The framework of the external nose consists of the paired nasal bones superiorly and a movable hyaline cartilage and fibroareolar portion below (Figure 7-11).

1. The nasal bones are described with the skull in Chapter 6.

2. The septal cartilage is a midline plate of hyaline cartilage that posteriorly forms a portion of the movable nasal septum.

3. The lateral cartilages are winglike anterior extensions of the septal cartilage; they flare to the right and left and are firmly attached to the nasal bones superiorly and the nasal notch of the maxilla laterally.

4. The alar cartilages lie below the lateral cartilages like backward Cs. They are anchored to the lateral cartilages above by areolar tissue. Fibroareolar tissue completes the deficiency of the C laterally to create the oval openings of the external nares.

Figure 7-11 Skeleton of external nose.

Skin

The skin of the nose continues beyond the opening of the external nares into the vestibule of the nose. Within the vestibule, the skin is less keratinized but contains hair follicles and sebaceous glands. Nasal hairs are long (more prominent in the adult male) and act to filter larger particles of dust from the inhaled air.

The bulge of the alar cartilages into the floor and lateral wall of the vestibule marks the transition of skin to the respiratory nasal mucosa of the nasal cavity within.

Muscles

The muscle of the nose is the nasalis muscle, consisting of two sets of fibers: (1) the dilator nares, which flare the nostrils, and (2) the compressor nares, which flatten the nostrils (see Figure 7-5).

Blood Supply

The external nose is supplied by (1) the dorsal nasal branch of the ophthalmic artery, (2) the external nasal branch of the anterior ethmoidal artery, (3) the nasal branch of the infraorbital artery, and (4) the nasal branch of the facial artery.

Sensory Nerve Supply

The external nose is supplied by (1) the external nasal nerve (cranial nerve V-1), (2) the infratrochlear nerve (cranial nerve V-1), and (3) the nasal branches of the infraorbital nerve (cranial nerve V-2).

External Ear (Auricle)

Cartilage

A single elastic cartilage provides support for the external ear (Figure 7-12). The pendulous lower portion, or earlobe, contains no cartilage but does contain fibroareolar tissue. The cartilage of the ear is continuous with the cartilage of the external auditory meatus (canal), leading within the petrous temporal bone to the middle ear.

Figure 7-12 Features of the right external ear (auricle).

Muscles

The muscles of the ear are the superior, anterior, and posterior auricular muscles, which wiggle the ear (see Figure 7-5).

Skin

The skin of the auricle is tightly bound to the cartilage, with no intervening subcutaneous layer. The skin funnels into the opening of the external auditory meatus and lines the canal and the lateral aspect of the tympanic membrane (eardrum).

Ceruminous glands resembling sweat glands lie within the skin of the ear canal. These glands, along with secretions of sebaceous glands, produce cerumen, or earwax.

Prominent hair is not generally visible on the auricle. In older men, however, coarse tufts of hair appear on the tragus of the ear, guarding the entrance of the meatus.

Features

The cartilage and skin of the ear are thrown into several folds. The names of these resulting ridges and depressions are found in Figure 7-12.

Blood Supply

The external ear is supplied by (1) branches of the superficial temporal artery and (2) branches of the posterior auricular artery.

Sensory Nerve Supply

The sensory innervation of the ear is from (1) the auriculotemporal nerve (from cranial nerve V-3), (2) the great auricular nerve (from anterior primary rami [APR] of C2 and C3), and (3) the lesser occipital nerve (from APR of C2 and C3).

In addition, small sensory contributions arise from the vagus (cranial nerve X) and the facial (cranial nerve VII) nerves.

Eyelids (Palpebrae)

The upper and lower lids form a curtain for the ocular globe, or eyeball. When closed, the lids protect the eye from light and harmful objects.

External Features (Figure 7-13)

1. The palpebral fissure is the transverse, elliptical opening between the upper and lower lids.

2. The palpebral commissures are the lateral and medial junctions of the upper and lower lids.

3. The superior palpebral margin covers the superior one fifth of the iris when the lids are open.

4. The inferior palpebral margin cuts across the lower border of the iris when the lids are open.

5. Cilia, or eyelashes, project from the palpebral margins in two or three irregular rows; the medial one sixth of each palpebral margin is devoid of cilia.

6. The plica semilunaris is a crescent fold at the medial angle of the eye that separates the white of the eye from the medial, reddish-colored lacus lacrimalis.

7. The lacus lacrimalis (lake of tears) is a small, raised, triangular area bordered by the plica semilunaris and the medial converging margins of the lid; a raised, reddish area within the lacus is the caruncle.

8. Superior and inferior papillae appear as small, raised bumps at the junction of the ciliated and hairless margins of the lids; the apex of the papilla presents a small opening, or punctum, which sucks up excess tears.

9. A mucous membrane inner lining of the eyelid, the conjunctivum, is seen when the eyelid is everted; the conjunctivum reflects up onto the eyeball to cover its anterior aspect. The conjunctival layer of the eyeball is reduced to a single layer of cuboidal epithelium, which is transparent. The space between the red conjunctivum of the lid and the transparent conjunctivum of the eyeball is termed the conjunctival sac.

Figure 7-13 Surface features of the left eye and eyelids.

Layers

Skin

Extremely thin skin covers the lids of the eye (Figure 7-14). At the margins of the eye, prominent hairs, or cilia, form two or three irregular rows along the lateral five sixths of the margin. Associated with the cilia are large sebaceous glands, or ciliary glands (glands of Zeis). Infected ciliary glands result in the common stye.

Figure 7-14 Sagittal section through eyelids and orbit to demonstrate layers of eyelids.

Muscular Layer

The palpebral portion of the orbicularis oculi muscle occupies the muscular. The fibers act as a sphincter and approximate the lids.

Fibers of the levator palpebrae superioris muscle pass through the orbicularis oculi muscle to insert superficially into the skin of the upper lid. This muscle opens the lid.

The motor nerve of the orbicularis oculi is the facial nerve; the motor nerve to the levator palpebrae superioris consists of the oculomotor nerve and some sympathetic fibers.

Orbital Septum and Tarsi

The orbital septum and tarsi form the “skeleton” of the eyelid (see Figure 7-14 and also Figure 7-34 later in this chapter). The orbital septum is a membranous connective tissue sheet that attaches to the periphery of the orbital margin. Medially, it attaches to the posterior lacrimal crest. The septum forms a curtain with an elliptical transverse opening, the palpebral fissure.

Figure 7-34 The orbital septum and lacrimal apparatus.

The margins of the septum around the palpebral fissure are thickened as tarsal plates, or tarsi. The tarsi are half-moon in outline, and the lower tarsus is not as large as the upper one. Medially, the tarsi attach to the anterior lacrimal crest via the stout medial palpebral ligament. The lateral anchorage is weaker via the less prominent lateral palpebral ligament to the lateral margin of the orbit.

The tarsi contain large tarsal glands, seen as yellowish streaks shining through the conjunctivum in the everted lid. The ducts open to the margins of the lids and secrete an oily substance.

Conjunctiva

The conjunctiva is the special name given to the mucous membrane of the lids. It lines the inner aspect of the lid as palpebral conjunctiva and then at the base of the conjunctival sac reflects back onto the eyeball as transparent bulbar conjunctiva.

2. Connective tissue. A thick, dense, subcutaneous connective tissue is anchored firmly to the skin above and the membranous layer below.

3. Aponeurosis. The membranous aponeurosis (galea aponeurotica) is an intermediate tendon for the two fleshy bellies of the occipitofrontalis (epicranius) muscle (see Figure 7-5, B). The occipitalis portion originates just above the superior nuchal line and inserts into the aponeurosis. It pulls the scalp and the attached superficial layers back. The frontalis portion originates from the aponeurosis and inserts into skin above the eyebrows. It pulls the scalp forward and produces transverse wrinkling of the brow.

4. Loose connective tissue. The fourth layer consists of loose areolar tissue and allows freedom of movement of the superficial three layers over the top of the skull.

5. Periosteum. The periosteum is firmly anchored to the underlying bone.