SCALP

The scalp extends from the top of the forehead in front to the superior nuchal line behind. Laterally it projects down to the zygomatic arch and external acoustic meatus. It consists of five layers: skin, subcutaneous tissue, occipitofrontalis (epicranius) and its aponeurosis, subaponeurotic loose areolar tissue and periosteum of the skull (pericranium).

The skin of the scalp is hairy and rich in sebaceous glands: it is the commonest site for sebaceous cysts. The dense subcutaneous connective tissue has the richest cutaneous blood supply in the body. The anterior and posterior muscular bellies of occipitofrontalis are connected by a tough, fibrous, epicranial aponeurosis, and this layer is therefore often called the aponeurotic layer (galea aponeurotica). These three upper layers of the scalp can easily slide on the underling layer of loose connective tissue. A scalp flap can be raised within the plane between the galea and the pericranium without compromising either the blood or nerve supply of the scalp, because all of these structures lie in the subcutaneous layer (superficial fascia). Anteriorly based subgaleal scalp flaps (bicoronal) provide excellent access to the craniofacial skeleton for the correction of congenital deformity such as craniosynostoses; treatment of craniofacial fractures involving the frontal bone, nasoethmoid complex, orbit or zygomatic arch; skull base surgery or craniotomies. Pericranial flaps can be used to separate the frontal sinus floor from the nasal cavity in the management of fractures of the posterior wall of the frontal sinus (frontal sinus cranialization). Traumatic scalp avulsion may occur if hair becomes trapped in moving machinery or a shearing force is applied in the subgaleal plane during a road traffic accident or fall injury.

The arterial blood supply to the scalp is particularly rich, and there are free anastomoses between branches of the occipital and superficial temporal vessels. Scalp lacerations continue to bleed profusely because the elastic fibres of the underlying galea aponeurotica prevent initial vessel retraction. Their repair requires a two-layer closure technique to approximate the galea aponeurotica and skin layers. The pericranial layer, if involved, cannot usually be closed because it retracts.

EYEBROWS

The eyebrows are two arched eminences of skin which surmount the orbits. Numerous short, thick hairs are set obliquely in them. Fibres of orbicularis oculi, corrugator and the frontal part of occipitofrontalis, are inserted into the dermis of the eyebrows.

BUCCOLABIAL TISSUE

RELAXED SKIN TENSION LINES AND SKIN FLAPS ON THE FACE

The direction in which facial skin tension is greatest varies regionally. Skin tension lines which follow the furrows formed when the skin is relaxed are known as ‘relaxed skin tension lines’ (Borges & Alexander 1962). In the living face, these lines frequently (but not always) coincide with wrinkle lines (Fig. 29.1) and can therefore act as a guide in planning elective incisions.

Fig. 29.1 A, Distribution of relaxed skin tension lines (Kraissl’s lines) lateral view. B, Anterior view.

When lesions on the face such as scars, pigmented lesions and skin cancers are excised, the dimensions of these lesions often require excision as an ellipse, so that the resulting defect can be closed as a straight line. If the resulting scar is to be aesthetically acceptable it is important to make the long axis of the ellipse parallel to the natural relaxed skin tension lines, so that the scar will look like a natural skin crease. If the excision line runs contrary to the skin tension lines, the scar may be more conspicuous and will tend to stretch transversely as a result of natural expressive facial movements.

When larger lesions are excised it may be necessary to advance or rotate adjacent soft tissue to fill the defect. The ability to raise these skin flaps is entirely dependent on the regional blood supply and both random pattern and axial pattern skin flaps are used surgically. Because of the richness of the subdermal plexus in the face, random pattern flaps can be raised with a greater length : breadth ratio than in any other area of the body.

The following are examples of axial pattern flaps that can be used to reconstruct defects on the face and scalp. Supratrochlear/supraorbital arteries support forehead flaps that are useful for nasal reconstruction: there is usually enough skin laxity to allow the majority of the donor site to be closed directly. The frontal branch of the superficial temporal artery anastomoses in the midline with its opposite number, and consequently the entire forehead skin can be raised on a narrow pedicle based on just one of the superficial temporal arteries. These flaps can be used to repair many facial defects and also intraoral defects, but the donor site defect cannot be closed directly and must be covered by a skin graft. The parietal branch of the superficial temporal artery and the occipital artery can support hair-bearing flaps from the scalp which are useful for reconstructing defects involving the scalp. The nasolabial flap utilizes the lax skin just lateral to the nasolabial groove. It is not supplied by a named axial artery but rather its blood supply is provided by many small branches from the underlying facial artery. These branches run perpendicular to the skin surface. Nasolabial flaps can be either superiorly or inferiorly based.

FASCIAL LAYERS

PARIETAL BONE

The two parietal bones form most of the cranial roof and sides of the skull. Each is irregularly quadrilateral and has two surfaces, four borders and four angles (Fig. 29.2).

Fig. 29.2 Left parietal bone. A, External view; B, Internal view.

The external surface is convex and smooth, with a central parietal tuber (tuberosity). Curved superior and inferior temporal lines cross it and form posterosuperior arches. The temporal fascia is attached to the superior line or arch and temporalis is attached to the inferior line or arch. The epicranial aponeurosis lies above these lines, and part of the temporal fossa lies below. Posteriorly, close to the sagittal (superior) border, an inconstant parietal foramen transmits a vein from the superior sagittal sinus and sometimes a branch of the occipital artery.

The internal surface is concave and marked by impressions of cerebral gyri and by grooves for the middle meningeal vessels. The latter ascend, inclining backwards, from the sphenoidal (anteroinferior) angle and posterior half (or more) of its inferior border. A groove for the superior sagittal sinus lies along the sagittal border, and is completed by the groove on the opposite parietal bone. The falx cerebri is attached to the edges of the groove. Granular foveolae for arachnoid granulations flank the sagittal sulcus, and are most pronounced in old age.

The dentated sagittal border, longest and thickest, articulates with the opposite parietal bone at the sagittal suture. The anterior part of the squamosal (inferior) border is short, thin and truncated, bevelled externally and overlapped by the greater wing of the sphenoid. The middle part of the inferior border is arched, bevelled externally and overlapped by the squamous part of the temporal bone. The posterior part of the inferior border is short, thick and serrated for articulation with the mastoid part.

The frontal border is deeply serrated, bevelled externally above, internally below, and articulates with the frontal bone to form one half of the coronal suture. The occipital border, deeply dentated, articulates with the occipital bone, forming one half of the lambdoid suture.

The frontal (anterosuperior) angle, which is approximately 90°, is at the bregma, where sagittal and coronal sutures meet, and marks the site of the anterior fontanelle in the neonatal skull. The sphenoidal (anteroinferior) angle lies between the frontal bone and greater wing of the sphenoid. Its internal surface is marked by a deep groove or canal that carries the frontal branches of the middle meningeal vessels. The frontal, parietal, sphenoid and temporal bones usually meet at the pterion, which marks the site of the sphenoidal fontanelle in the embryonic skull. The frontal bone sometimes meets the squamous part of the temporal bone, in which case the parietal bone fails to reach the greater wing of the sphenoid bone. The rounded occipital (posterosuperior) angle is at the lambda, the meeting of the sagittal and lambdoid sutures, which marks the site of the posterior fontanelle in the neonatal skull. The blunt mastoid (posteroinferior) angle articulates with the occipital bone and the mastoid portion of the temporal bones at the asterion. Internally it bears a broad, shallow groove for the junction of the transverse and sigmoid sinuses.

FRONTAL BONE

The frontal bone is like half a shallow, irregular cap forming the forehead or frons (Fig. 29.3). It has three parts, and contains two cavities, the frontal sinuses.

Fig. 29.3 Frontal bone. A, anterior view; B, inferior view, including the articulations between the frontal, ethmoid and nasal bones.

(From Sobotta 2006.)

ETHMOID BONE

The ethmoid bone is cuboidal and fragile (Fig. 29.3B, Fig. 29.4, Fig. 29.5, Fig. 29.6). It lies anteriorly in the cranial base and contributes to the medial walls of the orbit, the nasal septum and the roof and lateral walls of the nasal cavity. It has a horizontal perforated cribriform plate, a median perpendicular plate, and two lateral labyrinths that contain the ethmoidal air cells.

Fig. 29.4 Sagittal view of the facial skeleton, viewed from the right side of the nasal septum, looking towards the left.

(From Sobotta 2006.)

Fig. 29.5 A, B Sagittal view of the facial skeleton, showing the floor of the anterior cranial fossa, the lateral wall of the nasal cavity, the hard palate and the sphenoidal air sinus. In B, the middle concha in the lateral wall of the nasal cavity has been removed to reveal the uncinate process.

(From Sobotta 2006.)

Fig. 29.6 A, Sagittal view of the facial skeleton, showing the bones forming the lateral wall of the left orbit and the maxillary air sinus. B, The bones forming the medial wall and the floor of the left orbit.

(From Sobotta 2006.)

INFERIOR NASAL CONCHA

The inferior nasal conchae are curved horizontal laminae in the lateral nasal walls (Fig. 29.5) (see also Ch. 32). Each has two surfaces (medial and lateral), two borders (superior and inferior) and two ends (anterior and posterior). The medial surface is convex, much perforated, and longitudinally grooved by vessels. The lateral surface is concave and part of the inferior meatus. The superior border, thin and irregular, may be divided into three regions: an anterior region articulating with the conchal crest of the maxilla; a posterior region articulating with the conchal crest of the palatine bone; and a middle region with three processes, which are variable in size and form. The lacrimal process is small and pointed and lies towards the front. It articulates apically with a descending process from the lacrimal bone, and at its margins with the edges of the nasolacrimal groove on the medial surface of the maxilla, thereby helping to complete the nasolacrimal canal. Most posteriorly, a thin ethmoidal process ascends to meet the uncinate process of the ethmoid bone. An intermediate thin maxillary process curves inferolaterally to articulate with the medial surface of the maxilla at the opening of the maxillary sinus. The inferior border is thick and spongiose, especially in its midpart. Both the anterior and posterior ends of the inferior nasal concha are more or less tapered, the posterior more than the anterior.

LACRIMAL BONE

The lacrimal bones are the smallest and most fragile of the cranial bones and lie anteriorly in the medial walls of the orbits (Fig. 29.5B). Each has two surfaces (medial and lateral) and four borders (anterior, posterior, superior and inferior). The lateral (orbital) surface is divided by a vertical posterior lacrimal crest. Anterior to the crest is a vertical groove whose anterior edge meets the posterior border of the frontal process of the maxilla to complete the fossa that houses the lacrimal sac. The medial wall of the groove is prolonged by a descending process that contributes to the formation of the nasolacrimal canal by joining the lips of the nasolacrimal groove of the maxilla and the lacrimal process of the inferior nasal concha. A smooth part of the medial orbital wall lies behind the posterior lacrimal crest: the lacrimal part of orbicularis oculi is attached to this surface and crest. The surface ends below in the lacrimal hamulus which, together with the maxilla, completes the upper opening of the nasolacrimal canal. The hamulus may appear as a separate lesser lacrimal bone. The anteroinferior region of the medial (nasal) surface is part of the middle meatus. Its posterosuperior part meets the ethmoid to complete some of the anterior ethmoidal air cells. The anterior border of the lacrimal bone articulates with the frontal process of the maxilla, the posterior border with the orbital plate of the ethmoid bone, the superior border with the frontal bone, and the inferior border with the orbital surface of the maxilla.

NASAL BONE

The nasal bones are small, oblong, variable in size and form, and placed side by side between the frontal processes of the maxillae (Fig. 29.4, Fig. 29.5, Fig. 29.6B). They jointly form the nasal bridge. Each nasal bone has two surfaces (external and internal) and four borders (superior, inferior, lateral and mesial). The external surface has a descending concavo-convex profile and is transversely convex. It is covered by procerus and nasalis and perforated centrally by a small foramen that transmits a vein. The internal surface, transversely concave, bears a longitudinal groove that houses the anterior ethmoidal nerve. The superior border, thick and serrated, articulates with the nasal part of the frontal bone. The inferior border, thin and notched, is continuous with the lateral nasal cartilage. The lateral border articulates with the frontal process of the maxilla. The medial border, thicker above, articulates with its fellow and projects behind as a vertical crest, thereby forming a small part of the nasal septum. It articulates from above with the nasal spine of the frontal bone, the perpendicular plate of the ethmoid bone, and the nasal septal cartilage.

VOMER

The vomer is thin, flat, and almost trapezoid (Fig. 29.4). It forms the posteroinferior part of the nasal septum and presents two surfaces and four borders. Both surfaces are marked by grooves for nerves and vessels. A prominent groove for the nasopalatine nerve and vessels lies obliquely in an anteroinferior plane. The superior border is thickest, and possesses a deep furrow between projecting alae which fits the rostrum of the body of the sphenoid bone. The alae articulate with the sphenoidal conchae, the vaginal processes of the medial pterygoid plates of the sphenoid bone, and the sphenoidal processes of the palatine bones. Where each ala lies between the body of the sphenoid and the vaginal process, its inferior surface helps to form the vomerovaginal canal. The inferior border articulates with the median nasal crests of the maxilla and palatine bones. The anterior border is the longest, and articulates in its upper half with the perpendicular plate of the ethmoid bone. Its lower half is cleft to receive the inferior margin of the nasal septal cartilage (see Ch. 32). The concave posterior border is thick and bifid above and thin below: it separates the posterior nasal apertures. The anterior extremity of the vomer articulates with the posterior margin of the maxillary incisor crest and descends between the incisive canals.

ZYGOMATIC BONE

Each zygomatic bone forms the prominence of a cheek, contributes to the floor and lateral wall of the orbit and the walls of the temporal and infratemporal fossae, and completes the zygomatic arch. Each is roughly quadrangular and is described as having three surfaces, five borders and two processes (Fig. 29.7).

Fig. 29.7 Zygomatic bone. A, Anterolateral aspect. B, Posterolateral aspect. Muscle attachments shown in A.

The lateral (facial) surface is convex and is pierced near its orbital border by the zygomaticofacial foramen, which is often double and occasionally absent, and transmits the zygomaticofacial nerve and vessels. This surface gives attachment to zygomaticus major posteriorly and zygomaticus minor anteriorly. The posteromedial (temporal) surface has a rough anterior area for articulation with the zygomatic process of the maxilla, and a smooth, concave posterior area that extends up posteriorly on its frontal process as the anterior aspect of the temporal fossa. It also extends back on the medial aspect of the temporal process as an incomplete lateral wall for the infratemporal fossa. The zygomaticotemporal foramen pierces this surface near the base of the frontal process. The smooth and concave orbital surface forms the anterolateral part of the floor and adjoining lateral wall of the orbit, and extends up on the medial aspect of its frontal process. It usually bears zygomatico-orbital foramina which represent the openings of canals leading to the zygomaticofacial and zygomaticotemporal foramina.

The smoothly concave anterosuperior (orbital) border forms the inferolateral circumference of the orbital opening, and separates the orbital and lateral surfaces of the bone. The anteroinferior (maxillary) border articulates with the maxilla. Its medial end tapers to a point above the infraorbital foramen. A part of levator labii superioris is attached at this surface. The posterosuperior (temporal) border is sinuous, convex above and concave below, and is continuous with the posterior border of the frontal process and upper border of the zygomatic arch. The temporal fascia is attached to this border. There is often a small, easily palpable, marginal tubercle below the frontozygomatic suture. The posteroinferior border is roughened for the attachment of masseter. The serrated posteromedial border articulates with the greater wing of the sphenoid bone above, and the orbital surface of the maxilla below. Between these serrated regions a short, concave, non-articular part usually forms the lateral edge of the inferior orbital fissure. Occasionally absent, the fissure is then completed by the articulation of the maxilla and sphenoid (or with a small sutural bone between them).

The frontal process, thick and serrated, articulates above with the zygomatic process of the frontal bone and behind with the greater wing of the sphenoid bone. A tubercle of varying size and form, Whitnall’s tubercle, is usually present on its orbital aspect, within the orbital opening and about 1 cm below the frontozygomatic suture. This tubercle provides attachment for the lateral palpebral ligament, the suspensory ligament of the eye, and part of the aponeurosis of levator palpebrae superioris. The temporal process, directed backwards, has an oblique, serrated end that articulates with the zygomatic process of the temporal bone to complete the zygomatic arch.

MAXILLA

The maxillae are the largest of the facial bones, other than the mandible, and jointly form the whole of the upper jaw. Each bone forms the greater part of the floor and lateral wall of the nasal cavity, and of the floor of the orbit, contributes to the infratemporal and pterygopalatine fossae, and bounds the inferior orbital and pterygomaxillary fissures. Each maxilla has a body and four processes, namely the zygomatic, frontal, alveolar and palatine processes (Fig. 29.6, Fig. 29.8).

Fig. 29.8 Maxilla and palatine bone. A, Maxilla. B, Maxilla and palatine bone.

(From Sobotta 2006.)

PALATINE BONE

The palatine bones are posteriorly placed in the nasal cavity, between the maxillae and the pterygoid processes of the sphenoid bones. They contribute to the floor and lateral walls of the nose, to the floor of the orbit and the hard palate, to the pterygopalatine and pterygoid fossae, and to the inferior orbital fissures. Each has two plates (horizontal and perpendicular) arranged as an L-shape, and three processes (pyramidal, orbital and sphenoidal) (Fig. 29.9).

Fig. 29.9 Palatine bone, posterior view.

FRACTURES OF THE FACIAL SKELETON

Fractures affecting the facial bones are common. They occur in road traffic accidents, sports injuries, accidents at work and, increasingly, as a consequence of interpersonal violence, often alcohol-related. Given that most people are right-handed, fractures resulting from assault occur more commonly on the left side of the facial skeleton. Skull fractures tend to adopt well-recognized patterns reflecting the shape and structure of the facial bones, local anatomical factors, and stress points which constitute sites of weakness.

Frequently these fractures do not occur as bilateral symmetrical fractures but occur in various combinations, e.g. both together, on the same side, and involving both sides. Typically these fractures arise from force applied anteriorly over a wide area. Such injuries are seen in road traffic accidents where, e.g. a driver or passenger is thrown forwards on to the steering wheel or dashboard. The direction of the applied force determines the displacement of these fractures. With the possible exception of the relatively weak lateral pterygoids, muscle pull plays a relatively small role. As the fractures are generally displaced backwards, because of the angulation of the strong skull base, there is also a downward component, which results clinically in a lengthening of the face and a dished-in appearance. There may be airway obstruction if this downwards and backwards displacement is severe.

Although the fractures that occur in severe injuries are often complex, it is convenient to describe them as arising in the upper, middle and lower thirds of the face, even though fractures may involve one or more of these areas. Upper third fractures involve the frontal bones. Middle third fractures involve the nasoethmoidal complex, orbit, zygomatic complex and maxilla. Lower third fractures correspond to fractures of the mandible.

SKELETAL ACCESS SURGERY

The craniofacial skeleton has an excellent blood supply, and so can be dismantled as a series of osteoplastic flaps. The surgical disarticulation of the craniofacial skeleton has been used to gain access to otherwise inaccessible sites in order to allow the surgeon to attend to pathology in the skull base, cervical spine and anterior and posterior cranial fossae. The aim is to provide increased and more direct exposure of both the pathology and the adjacent vital structures without the need to resect uninvolved structures. The craniofacial skeleton can be divided into a series of modular osteotomies, which permit both independent and conjoined mobilization.

The zygomatic and nasal bones and the maxilla may be exposed and mobilized, pedicled on the overlying soft tissues either unilaterally or bilaterally. These approaches improve access to the nasal cavity, maxillary, ethmoid and sphenoid sinuses, the soft palate and nasopharynx, and the infratemporal fossa and pharyngeal space. The exposures may be extended to gain access to the anterior and middle cranial fossae, cavernous sinus, clivus, craniocervical junction and upper cervical vertebrae.

A variety of different access osteotomies have been described and found to be useful in specific clinical situations. Most of the osteotomies described follow the conventional patterns of facial fractures described above. The entire hemimaxilla and zygoma can be mobilized, and pedicled on the soft tissues of the face by making bone cuts that follow the lines of a Le Fort II fracture on one side. The osteotomy is completed by dividing the upper alveolus and palate just to the side of the nasal septum and perpendicular plate of the vomer. The maxilla may be mobilized at the Le Fort I level and downfractured, pedicled on the palatoglossal muscles and soft tissue attachments. This gives good access to the nasopharynx, clivus and upper cervical spine, particularly if the palate is divided in the midline.

Lateral zygomatic osteotomies may be performed to gain access to the orbital apex and infratemporal fossa. The surgical approach is from behind using a hemi- or bicoronal flap. The zygomatic complex is mobilized inferiorly pedicled on masseter. When combined with a mandibular ramus osteotomy, access is gained to the retromaxillary area and pterygoid space as well as to the infratemporal fossa. In combination with a frontotemporal craniotomy, the zygomatic osteotomy has been used for access to the middle cranial fossa, cavernous sinus, apex of the petrous temporal bone and the interpeduncular cistern.

Dividing the lower lip in the midline, and dividing the mandible either in the midline or just in front of the mental foramen, allows the hemimandible to be swung laterally. The technique is used to give improved access to the floor of the mouth, the base of the tongue, tonsillar fossa, soft palate, oropharynx, posterior pharyngeal wall, supraglottic larynx and pterygomandibular region. By extending the dissection laterally access is gained to the pterygoid space, infratemporal fossa and parapharyngeal space. By dissecting more medially access is gained to the nasopharynx, lower part of the clivus and all seven of the cervical vertebrae. A modification of the mandibular swing procedure increases access up to the skull base, by combining the classic mandibular swing with a horizontal osteotomy of the mandibular ramus above the level of the lingula.

EPICRANIAL MUSCLE GROUP

CIRCUMORBITAL AND PALPEBRAL MUSCLE GROUP

The circumorbital and palpebral group of muscles are orbicularis oculi, corrugator supercilii and levator palpebrae superioris. The first two are described here; levator palpebrae superioris is described in Chapter 39.

NASAL MUSCLE GROUP

The nasal muscle group, which consists of procerus, nasalis and depressor septi, is described in Chapter 32.

BUCCOLABIAL MUSCLE GROUP

The shape of the mouth and the posture of the lips are controlled by a complex three-dimensional assembly of muscular slips. These include elevators, retractors and evertors of the upper lip (levator labii superioris alaeque nasi, levator labii superioris, zygomaticus major and minor, levator anguli oris and risorius); depressors, retractors and evertors of the lower lip (depressor labii inferioris, depressor anguli oris, and mentalis); a compound sphincter (orbicularis oris, incisivus superior and inferior); and buccinator.

MOVEMENTS OF THE FACE AND LIPS

Direct labial tractors

Direct labial tractors, as their name suggests, pass directly into the tissues of the lips and not via the modioli. In broad terms, the force exerted by tractors is directed vertically at an approximate right angle to the oral fissure. Their action will therefore elevate and/or evert the whole, or part, of the upper lip and depress and/or evert the whole, or part, of the lower lip. The tractors are, from medial to lateral, the labial part of levator labii superioris alaequae nasi; levator labii superioris and zygomaticus minor in the upper lip; depressor labii inferioris and platysma pars labialis in the lower lip.

In both upper and lower lips the tractors blend into a continuous sheet that divides into a series of superimposed coronal sheets which are anterior to the muscle bundles of pars peripheralis orbicularis oris as they enter the free lip. The sheets may be divided into three groups at increasing depths from the skin surface, each with a distinct zone of attachment (Fig. 29.12). The superficial group comprises a succession of fine fibre bundles which curve anteriorly a short distance before attaching in a series of horizontal rows to the dermis between the hair follicles, sebaceous glands and sweat glands. The intermediate group attaches to the dermis of the vermilion zone, which they reach by two routes: the more superficial bundles continue past the skin/vermilion junction, then curve posteriorly over pars marginalis orbicularis oris to punctate attachments on the ventral half of the dermis of the vermilion zone, while the deeper bundles first pass posteriorly between pars peripheralis and pars marginalis, then curve anteriorly to punctate attachments on the dorsal half of the dermis of the vermilion zone. The deep group is closely applied to the anterior surface of pars peripheralis orbicularis oris, and sends fine tractor fibres between its parallel bundles to attach posteriorly into the submucosa and periglandular connective tissue.

Fig. 29.12 A, Sagittal section of the upper lip in repose. On the left is thin skin with oblique hair follicles; on the right is thick mucosa with mucous glands and mucosal shelf; between them is the vermilion zone. B, as A but slightly contracted, forming a narrowed profile (labial cord).

Movements of the lips

The various groups of direct labial tractors may act together or individually, and their effects may involve a complete labial quadrant, or be restricted to a short segment. For example, partial contraction of the superior labial tractors can result in localized elevation of a segment of the upper lip, in a postural expression reminiscent of the ‘canine snarl’. Normally, however, the activity of the tractors is modified by the superimposed activity of orbicularis oris and the modiolar muscles. The resultant actions range from delicate adjustments of the tension and profile of the lip margins to large increases of the oral fissure with eversion of the lips.

Lip protrusion is passive in its initial stages. It may be suppressed by powerful contraction of the whole of orbicularis oris or enhanced by selective activation of parts of the direct labial tractors. However, lip movements must accommodate separation of the teeth brought about by mandibular depression at the temporomandibular joints. Beyond a certain range of mouth opening, labial movements are almost completely dominated by mandibular movements. Thus over the last 2.5–3 cm interincisal distance of wide jaw separation, strong contraction of orbicularis oris cannot effect lip contact, and instead it causes full-thickness inflection of upper and lower lips, including the vermilion zone, towards the oral cavity, wrapping them around the incisal edges, canine cusps and premolar occlusal surfaces. The involvement of the lips in speech is described in Chapter 34, but some aspects relevant to the actions of orbicularis oris pars marginalis will be described here. Contraction of marginalis is considered to alter the cross-sectional profile of the free margin of the vermilion zone such that both the gentle bulbous profile of the upper lip and the smooth posterosuperior convexity of the lower lip change to a narrow, symmetrical triangular profile. The transformed rims, whose length and tension can be delicately controlled, have been named labial cords. They are known to be involved in the production of some consonantal (labial) sounds. A labial cord may also function as a ‘vibrating reed’ in whistling or playing a wind instrument such as the trumpet.

The modiolus and its role in facial movements

On each side of the face a number of muscles converge towards a focus just lateral to the buccal angle, where they interlace to form a dense, compact, mobile, fibromuscular mass called the modiolus. This can be palpated most effectively by using the opposed thumb and index finger to compress the mucosa and skin simultaneously. At least nine muscles, depending on the classification employed, are attached to each modiolus. Moreover, the muscles lie in different planes, their modiolar stems are often spiralized, and most divide into two bundles, some into three or four, each of them interlacing and attaching in a distinctive way. Not surprisingly, therefore, the three-dimensional organization of the modiolus has proved difficult to analyse.

The shape and dimensions of the modiolus are given approximately because they are subject to individual, age, sexual and ethnic variation. Furthermore the modiolus has no precise histological boundaries, and is an irregular zone where dense, compact interlacing tissue grades into the stems of individually recognizable muscles. The modiolus has the rough form of a blunt cone. The base of the cone (basis moduli) is adjacent and adherent to the mucosa. It is roughly elliptical in outline and extends vertically 20 mm above and 20 mm below a horizontal line through the buccal angle. It also extends laterally a similar distance from the angle. The blunt apex of the cone (apex moduli) is 4 mm across, and is centred approximately 12 mm lateral to the buccal angle. From mucosa to dermis the thickness of the mass is usually 10 mm, divided approximately equally into basal, central and apical parts. The central body has an oblique fibrous cleft or channel that transmits the facial artery, an arrangement that may limit the extent to which it is compressed by contraction of the buccolabial musculature. The cone shape is modified by two round-edged flanges (or cornua) that extend into the lateral free lip tissues above and below the corner of the mouth. The tip of the superior cornu extends 5.5 mm medial to the buccal angle, the tip of the inferior cornu only 3.5 mm. With these additions, the modiolar base becomes kidney-shaped, with the buccal angle projecting towards the hilum.

The apex of the modiolus is deep and adherent to the panniculus carnosus, which extends posteromedially as a thin sloping sheet down to the buccal angle. There, its free border forms a crescentic, narrow, flexible, subcutaneous fibroelastic cord that accommodates the varying postures of the modioli, lips, mouth and jaws.

Controlled three-dimensional mobility of the modioli enables them to integrate the activities of the cheeks, lips and oral fissure, the oral vestibule and the jaws. Such activities include biting, chewing, drinking, sucking, swallowing, changes in vestibular contents and pressure, the innumerable subtle variations involved in speech, the modulation (and occasional generation) of musical tones, production of harsher sounds in shouting and screaming, crying, and all the permutations of facial expression, ranging from mere hints to gross distortion, symmetrical or asymmetrical. Major modiolar movements appear to involve many, if not all, of its associated muscles, and there is little value in considering the actions of the individual muscles in isolation. While the most obvious determinant of modiolar position and mobility is the balance between the forces exerted by muscles that are directly attached to it, another influential factor is the degree of separation or ‘gape’ between the upper and lower teeth. Starting from the occlusal position, and with the lips maintained in contact, the teeth can be separated by approximately 1.25 cm near the midline, and the mentolabial sulcus descends by a similar distance. With further separation the lips part, and as gape increases to its maximum, interlabial and interdental distances approach 4 cm, at which point the mentolabial sulcus has descended a further 2 cm. In this posture the modiolus has descended about 1 cm to lie over the interdental space, into which its basal and surrounding buccal mucosa projects a few millimetres, and its cornua diverge into their respective lips at an obtuse angle to each other, the dispositions of the modiolar muscles being correspondingly modified. The general hexagonal shape of the labial area changes as the mouth and jaws open progressively. In maximal opening, the distance between the superior and inferior boundaries has increased by 3–3.5 cm at the centre; the transverse distance between its lateral angles has decreased by 1 cm and the angles are obtuse; the nasolabial sulci are longer, straighter and more vertical; and the inferior buccolabial sulci are less deep and curved. These soft tissue changes radiate from the bilateral modioli.

With the lips in contact and the teeth in tight occlusion, the modiolus can move a few millimetres in all directions. However, mobility is maximal when there is 2–3 mm clearance between the teeth: the apex of the modiolus may then move vertically upwards 10 mm, downwards 5 mm, posterolaterally 10 mm, and anteromedially 10 mm, these movements occurring in the curved planes of the cheek and lips. Specific movements of the modiolus may occur to any point, and along any path, within the boundaries of the envelope of movement thus defined. When the mouth is opened wide, the modiolus becomes immobile. From the neutral position the modiolus may be displaced superficially along its apicobasal axis for up to 5–10 mm by liquids or solids in the vestibule, or by an increase in air pressure that ‘balloons’ the cheeks and lips.

Many activities take place in three phases. Initially, a particular modiolar muscle group becomes dominant over its antagonists and the modiolus is rapidly relocated. Next, the modiolus is transiently fixed in this new site by simultaneous contraction of modiolar muscles, principally zygomaticus major, levator anguli oris, depressor anguli oris, platysma pars modiolaris, and this provides a fixed base from which the main physiological effectors, buccinator and orbicularis oris, carry out their specific actions. These actions are usually integrated with partial separation or closure of the jaws, and with varying degrees of activity in the direct labial tractors. All these factors combine to determine the positions of the lips and oral fissure from moment to moment. Modiolar movements may be bilaterally symmetrical, unilateral or asymmetrical.

MUSCLES OF MASTICATION

Masseter and temporalis, two of the muscles of mastication, are seen on the face. Masseter covers the ramus of the mandible, and temporalis lies over the temporal fossa. These muscles are described in detail with the other main muscles of mastication in Chapter 31.

ARTERIAL SUPPLY TO THE FACE

The main arterial supply to the face is derived from the facial and superficial temporal arteries, with additional supply from branches of the maxillary and ophthalmic arteries. The back of the scalp is supplied by the posterior auricular and occipital arteries. There are numerous anastomoses between the branches.

Facial artery

The facial artery arises in the neck from the external carotid artery (see Ch. 28). It initially lies beneath platysma, passing onto the face at the anteroinferior border of masseter, where its pulse can be felt as it crosses the mandible. The artery is deep to skin, the fat of the cheek and, near the angle of the mouth, zygomaticus major and risorius, and superficial to buccinator and levator anguli oris. It may pass over or through levator labii superioris, and pursues a tortuous course along the side of the nose towards the medial corner of the eye. At its termination it is embedded in levator labii superioris alaequae nasi.

Occasionally, the facial artery barely extends beyond the angle of the mouth, in which case its normal territory beyond this region is taken over by an enlarged transverse facial branch from the superficial temporal artery and by branches from the contralateral facial artery. The facial vein is posterior to the artery, and runs a more direct course across the face. At the anterior border of masseter, the two vessels are in contact, whereas in the neck the vein is superficial to the artery.

The facial artery supplies branches to the muscles and skin of the face (Fig. 29.13). Its named branches on the face are the premasseteric artery, the superior and inferior labial arteries and the lateral nasal artery. The part of the artery distal to its terminal branch is called the angular artery.

Fig. 29.13 The arteries and veins of the left side of the face, head and neck and their main branches. The infraorbital artery is shown in Fig. 25.1.

Premasseteric artery

The premasseteric artery is small and inconstant. When present, it passes upwards along the anterior border of masseter and supplies the surrounding tissues.

Inferior labial artery

The inferior labial artery arises near the angle of the mouth, passes upwards and forwards under depressor anguli oris, then penetrates orbicularis oris to run sinuously near the margin of the lower lip, between the muscle and the mucous membrane. It supplies the inferior labial glands, mucous membrane and muscles, and anastomoses with its contralateral fellow and with the mental branch of the inferior alveolar artery.

Superior labial artery

The superior labial artery is larger and more tortuous than the inferior labial artery. It pursues a similar course along the superior labial margin, between the mucous membrane and orbicularis oris, anastomoses with its contralateral fellow, and supplies the upper lip. It gives off an alar branch and a septal branch, which ramifies anteroinferiorly in the nasal septum.

Lateral nasal artery

The lateral nasal artery is given off by the side of the nose, supplies the dorsum and alae of nose, and anastomoses with its contralateral fellow. The lateral nasal artery may be replaced by a branch from the superior labial artery.

VEINS OF THE FACE

The veins of the face are subject to considerable variations: the following description concerns those that are relatively constant (Fig. 29.13).

LYMPHATIC DRAINAGE OF THE FACE AND SCALP

Lymph vessels from the frontal region above the root of the nose drain to the submandibular nodes (Fig. 29.14; see Fig. 28.15). Vessels from the rest of the forehead, temporal region, upper half of the lateral auricular aspect and anterior wall of the external acoustic meatus drain to the superficial parotid nodes, which lie just anterior to the tragus, either on or deep to the parotid fascia. These nodes also drain lateral vessels from the eyelids and skin of the zygomatic region, and their efferent vessels pass to the upper deep cervical nodes. A strip of scalp above the auricle, the upper half of the cranial aspect and margin of the auricle, and the posterior wall of the external acoustic meatus all drain to the upper deep cervical and posterior auricular nodes. The posterior auricular nodes are superficial to the mastoid attachment of sternocleidomastoid and deep to auricularis posterior, and drain to the upper deep cervical nodes. The auricular lobule, floor of the external acoustic meatus and skin over the mandibular angle and lower parotid region all drain to the superficial cervical or upper deep cervical nodes. Superficial cervical nodes lie along the external jugular vein superficial to sternocleidomastoid. Some efferents pass round the anterior border of sternocleidomastoid to the upper deep cervical nodes, others follow the external jugular vein to the lower deep cervical nodes in the subclavian triangle.

Fig. 29.14 The lymphatic drainage of the face and scalp. Arrows indicate direction of flow.

(From Drake, Vogl and Mitchell 2005.)

The occipital region of the scalp drains partly to the occipital nodes, and partly by a vessel that runs along the posterior border of sternocleidomastoid to the lower deep cervical nodes. Occipital nodes are commonly superficial to the upper attachment of trapezius, but occasionally lie in the superior angle of the posterior triangle.

There are usually three submandibular nodes, internal to the deep cervical fascia in the submandibular triangle. One lies at the anterior pole of the submandibular gland, and two flank the facial artery as it reaches the mandible. Other nodes are often embedded in the gland or deep to it. Submandibular nodes drain a wide area, including vessels from the submental, buccal and lingual groups of nodes, and their efferents pass to the upper and lower deep cervical nodes. The external nose, cheek, upper lip and lateral parts of the lower lip drain directly to the submandibular nodes; the afferent vessels may have a few buccal nodes along their course and near the facial vein. The mucous membrane of the lips and cheek drains to the submandibular nodes and the lateral part of the cheek drains to the parotid nodes. The central part of the lower lip, buccal floor and tip of the tongue all drain to the submental nodes which lie on mylohyoid between the anterior bellies of the digastric muscles. These nodes receive afferents bilaterally, some decussating across the chin; their efferents pass to the submandibular and jugulo-omohyoid nodes.

TRIGEMINAL NERVE

Three large areas of the face can be mapped out to indicate the peripheral nerve fields associated with the three divisions of the trigeminal nerve. The fields are not horizontal but curve upwards (Fig. 29.15), apparently because the facial skin moves upwards with growth of the brain and skull. Embryologically, each division of the trigeminal nerve is associated with a developing facial process which gives rise to a specific area of the adult face: the ophthalmic nerve is associated with the frontonasal process, the maxillary nerve with the maxillary process, and the mandibular nerve with the mandibular process.

Fig. 29.15 Cutaneous innervation of the face and neck, showing dermatomes (in bold).

(Adapted from Drake, Vogl and Mitchell 2005.)

FACIAL NERVE

The facial nerve emerges from the base of the skull at the stylomastoid foramen and almost immediately gives off the nerves to the posterior belly of digastric and stylohyoid, and the posterior auricular nerve, which supplies the occipital belly of occipitofrontalis and some of the auricular muscles (Fig. 29.16A).

Fig. 29.16 Distribution of the facial nerve. A, The branches given off immediately after the nerve exits the stylomastoid foramen. B, The branches of the nerve on the face.

(From Drake, Vogl and Mitchell 2005.)

The nerve next enters the parotid gland high up on its posteromedial surface and passes forwards and downwards behind the mandibular ramus. Within the substance of the gland it branches into superior (temporofacial) and inferior (cervicofacial) trunks, usually just behind and superficial to the retromandibular vein. The trunks branch further to form a parotid plexus (pes anserinus). Five main terminal branches arise from the plexus, they diverge within the gland and leave by its anteromedial surface, medial to its anterior margin, to supply the muscles of facial expression (Fig. 29.16B). Six distinctive anastomotic patterns were originally classified by Davis et al (1956) and these are illustrated in Fig. 29.17. Numerous microdissection studies have demonstrated that branching patterns and anastomoses between branches, both within the parotid and on the face, exhibit considerable individual variation (e.g. Lineaweaver et al 1997; Kwak et al 2004): the account that follows is therefore an overview. In surgical terms these anastomoses are important, and presumably explain why accidental or deliberate division of a small branch often fails to result in the expected facial nerve weakness. The surface anatomy of the facial nerve is described in Chapter 25.

Fig. 29.17 Pattern of branching of the facial nerve.

(Modified with permission from Berkovitz BKB, Moxham BJ 2002 Head and Neck Anatomy. London: Martin Dunitz, and from Davis RA, Anson BJ, Budinger JM, Kurth IE 1956 Surgical anatomy of the facial nerve and parotid gland based upon a study of 350 cervicofacial halves. Surg Gynecol Obstet 102: 385–412, with permission from the American College of Surgeons.)

The temporal branch usually divides into anterior and posterior rami soon after piercing the parotidomasseteric fascia below the zygomatic arch; there is often a middle (frontal) ramus. These rami cross the arch in subcutaneous tissue and above the arch lie in the subgaleal space, where their course is extremely variable. Twigs supply intrinsic muscles on the lateral surface of the auricle, and the anterior and superior auricular muscles, and communicate with the zygomaticotemporal branch of the maxillary nerve and the auriculotemporal branch of the mandibular nerve. The more anterior branches supply the frontal belly of occipitofrontalis, orbicularis oculi and corrugator, and join the supraorbital and lacrimal branches of the ophthalmic nerve.

Zygomatic branches are generally multiple. They cross the zygomatic bone to the lateral canthus of the eye and supply orbicularis oculi: they may also supply muscles innervated by the buccal branch. Twigs communicate with filaments of the lacrimal nerve and the zygomaticofacial branch of the maxillary nerve.

The buccal branch is usually single. It has a close relationship to the parotid duct for about 2.5 cm after emerging from the parotid gland, and typically lies below the duct. Superficial branches run beneath the subcutaneous fat and superficial musculo-aponeurotic system (SMAS). Some branches pass deep to procerus and join the infratrochlear and external nasal nerves. Upper deep branches supply zygomaticus major and levator labii superioris, and form an infraorbital plexus with the superior labial branches of the infraorbital nerve. They also supply levator anguli oris, zygomaticus minor, levator labii superioris alaequae nasi and the small nasal muscles: these branches are sometimes described as lower zygomatic branches. Lower deep branches supply buccinator and orbicularis oris; they communicate with filaments of the buccal branch of the mandibular nerve.

There are usually two marginal mandibular branches. They run forwards towards the angle of the mandible under platysma, then turn upwards across the body of the mandible to pass under depressor anguli oris. The branches supply risorius and the muscles of the lower lip and chin, and filaments communicate with the mental nerve. The marginal mandibular branch has an important surgical relationship with the lower border of the mandible (see Ch. 25).

The cervical branch emerges from the lower part of the parotid gland and runs anteroinferiorly under platysma to the front of the neck. Typically single, it supplies platysma and communicates with the transverse cutaneous cervical nerve.

Cutaneous branches of the facial nerve accompany the auricular branch of the vagus; they are believed to innervate the skin on both auricular aspects, in the conchal depression and over its eminence.

STRUCTURES WITHIN THE PAROTID GLAND

The external carotid artery, retromandibular vein and facial nerve, either in part or in whole, traverse the gland and branch within it. The external carotid artery enters the posteromedial surface, and divides into the maxillary artery, which emerges from the anteromedial surface, and the superficial temporal artery, which gives off its transverse facial branch in the gland and ascends to leave its upper limit (Fig. 29.16). The posterior auricular artery may also branch from the external carotid artery within the gland, leaving by its posteromedial surface.

The retromandibular vein, formed by the union of the maxillary and superficial temporal veins (which enter near the points of exit of the corresponding arteries), is superficial to the external carotid artery. It descends in the parotid gland and emerges behind the apex of the gland, where it usually divides into an anterior branch, which passes forwards to join the facial vein, and a posterior branch, which joins the posterior auricular vein to form the external jugular vein. Occasionally it is not connected to the external jugular vein, which is then small, and the anterior jugular vein is enlarged.

PAROTID CAPSULE

The parotid gland is enclosed within an unyielding parotid capsule derived from the investing layer of deep cervical fascia. Acute inflammation of the parotid gland (acute sialadenitis) may cause exquisite pain in the preauricular region as a result of stretching of the capsule and stimulation of the great auricular nerve. The pain is usually exacerbated at mealtimes when the gustatory stimulus to the gland results in further turgor within the capsule. Causes of acute sialadenitis include parotid duct obstruction (calculus, mucus plug and duct stricture) and mumps.

PAROTID DUCT

The average dimensions of the parotid duct are 5 cm long and 3 mm wide (although it is narrower at its oral orifice). It begins by the confluence of two main tributaries within the anterior part of the parotid gland: the duct appears at the anterior border of the upper part of the gland and passes horizontally across masseter, approximately midway between the angle of the mouth and the zygomatic arch (Fig. 29.16). If the duct arises lower down, it may run obliquely upwards. It crosses masseter, turns medially at its anterior border at almost a right angle, and traverses the buccal fat pad and buccinator opposite the crown of the upper third molar tooth. The duct then runs obliquely forwards for a short distance between buccinator and the oral mucosa before it opens upon a small papilla opposite the second upper molar crown. The submucosal passage of the duct serves as a valvular mechanism preventing inflation of the gland with raised intraoral pressures. While crossing masseter, the duct lies between the upper and lower buccal branches of the facial nerve, and may receive the accessory parotid duct.

The accessory part of the gland and the transverse facial artery lie above the parotid duct; the buccal branch of the mandibular nerve, emerging from beneath temporalis and masseter, lies just below, at the anterior border of masseter. The parotid duct may be crossed by anastomosing branches between the zygomatic and buccal branches of the facial nerve.

The ramifications of the ductal systems, and their patterns and calibres, can be demonstrated radiographically by injecting a radio-opaque substance into the parotid duct via a cannula. In a lateral parotid sialogram the main duct can be seen to be formed near the centre of the posterior border of the mandibular ramus by the union of two or three ducts which ascend or descend respectively at right angles to the main duct. As it crosses the face, the main duct also receives from above five or six ductules from the accessory parotid gland (Fig. 29.19). As it curves round the anterior border of masseter it is often compressed and its shadow is attenuated. Deep lacerations of the cheek where the integrity of the parotid duct is in doubt should be explored and repaired using microsurgical techniques, to prevent saliva leaking into the soft tissues of the cheek and subsequent sialocele formation.

Fig. 29.19 Oblique lateral radiograph showing normal parotid duct outlined after injection of radiopaque contrast medium (sialogram). Note that here the main duct is formed by the union of three smaller ducts at the posterior border of the ramus of the mandible.

(By courtesy of Dr N Drage.)

VASCULAR SUPPLY AND LYMPHATIC DRAINAGE

The parotid gland receives its arterial supply from the external carotid artery and its branches within and near the gland. The veins drain to the external jugular vein via local tributaries.

Lymph nodes occur in the skin overlying the parotid gland (preauricular nodes) and in the substance of the gland. There are usually 10 lymph nodes present in the gland, the majority lie in the superficial part of the gland above the plane related to the facial nerve. Lymph from the parotid gland drains to the upper deep cervical lymph nodes.

INNERVATION

Preganglionic nerves travel in the lesser petrosal branch of the glossopharyngeal nerve and synapse in the otic ganglion. Postganglionic secretomotor fibres reach the gland via the auriculotemporal nerve.