Temporalis muscle

The temporalis muscle is a large, fan-shaped muscle that fills much of the temporal fossa (Fig. 8.134). It originates from the bony surfaces of the fossa superiorly to the inferior temporal line and is attached laterally to the surface of the temporal fascia. The more anterior fibers are oriented vertically while the more posterior fibers are oriented horizontally. The fibers converge inferiorly to form a tendon, which passes between the zygomatic arch and the infratemporal crest of the greater wing of the sphenoid to insert on the coronoid process of the mandible.

Fig. 8.134 Temporalis muscle. Lateral view.

The temporalis muscle attaches down the anterior surface of the coronoid process and along the related margin of the ramus of mandible, almost to the last molar tooth.

The temporalis is a powerful elevator of the mandible. Because this movement involves posterior translocation of the head of mandible from the articular tubercle of the temporal bone and back into the mandibular fossa, the temporalis also retracts the mandible or pulls it posteriorly. In addition, the temporalis participates in side-to-side movements of the mandible.

The temporalis is innervated by deep temporal nerves that originate from the mandibular nerve [V₃] in the infratemporal fossa and then pass into the temporal fossa.

Blood supply of the temporalis is by deep temporal arteries, which travel with the nerves, and the middle temporal artery, which penetrates the temporal fascia at the posterior end of the zygomatic arch.

Deep temporal nerves

The deep temporal nerves, usually two in number, originate from the anterior trunk of the mandibular nerve [V₃] in the infratemporal fossa (Fig. 8.135). They pass superiorly and around the infratemporal crest of the greater wing of the sphenoid to enter the temporal fossa deep to the temporalis muscle, and supply the temporalis muscle.

Fig. 8.135 Nerves and arteries of the temporal fossa.

Zygomaticotemporal nerve

The zygomaticotemporal nerve is a branch of the zygomatic nerve (see Fig. 8.81, p. 884). The zygomatic nerve is a branch of the maxillary nerve [V₂], which originates in the pteryatine fossa and passes into the orbit.

The zygomaticotemporal nerve enters the temporal fossa through one or more small foramina on the temporal fossa surface of the zygomatic bone.

Branches of the zygomaticotemporal nerve pass superiorly between the bone and the temporalis muscle to penetrate the temporal fascia and supply the skin of the temple (Fig. 8.135).

Deep temporal arteries

Normally two in number, these vessels originate from the maxillary artery in the infratemporal fossa and travel with the deep temporal nerves around the infratemporal crest of the greater wing of the sphenoid to supply the temporalis muscle (Fig. 8.135). They anastomose with branches of the middle temporal artery.

Middle temporal artery

The middle temporal artery originates from the superficial temporal artery just superior to the root of the zygomatic arch between this structure and the external ear (Fig. 8.135). It penetrates the temporalis fascia, passes under the margin of the temporalis muscle, and travels superiorly on the deep surface of the temporalis muscle.

The middle temporal artery supplies the temporalis and anastomoses with branches of the deep temporal arteries.

Sphenomandibular ligament

The sphenomandibular ligament is an extracapsular ligament of the temporomandibular joint. It is attached superiorly to the spine of the sphenoid bone and expands inferiorly to attach to the lingula of the mandible and the posterior margin of the mandibular foramen (Fig. 8.137).

Fig. 8.137 Medial pterygoid muscle.

Medial pterygoid

The medial pterygoid muscle is quadrangular in shape and has deep and superficial heads (Fig. 8.137):

the deep head is attached above to the medial surface of the lateral plate of the pterygoid process and the associated surface of the pyramidal process of the palatine bone, and descends obliquely downward, medial to the sphenomandibular ligament, to attach to the roughened medial surface of the ramus of mandible near the angle of mandible;

the superficial head originates from the tuberosity of the maxilla and adjacent pyramidal process of the palatine bone and joins with the deep head to insert on the mandible.

The medial pterygoid mainly elevates the mandible. Because it passes obliquely backward to insert into the mandible, it also assists the lateral pterygoid muscle in protruding the lower jaw.

The medial pterygoid is innervated by the nerve to medial pterygoid from the mandibular nerve [V₃].

Lateral pterygoid

The lateral pterygoid is a thick triangular muscle and like the medial pterygoid muscle has two heads (Fig. 8.138):

the upper head originates from the roof of the infratemporal fossa (inferior surface of the greater wing of the sphenoid and the infratemporal crest) lateral to the foramen ovale and foramen spinosum;

the lower head is larger than the upper head and originates from the lateral surface of the lateral plate of the pterygoid process, and the inferior part insinuates itself between the cranial attachments of the two heads of the medial pterygoid.

Fig. 8.138 Lateral pterygoid muscle.

The fibers from both heads of the lateral pterygoid muscle converge to insert into the pterygoid fovea of the neck of mandible and into the capsule of the temporomandibular joint in the region where the capsule is attached internally to the articular disc.

Unlike the medial pterygoid muscle whose fibers tend to be oriented vertically, those of the lateral pterygoid are oriented almost horizontally. As a result, when the lateral pterygoid contracts it pulls the articular disc and head of mandible forward onto the articular tubercle and is therefore the major protruder of the lower jaw.

The lateral pterygoid is innervated by the nerve to lateral pterygoid from the mandibular nerve [V₃].

When the lateral and medial pterygoids contract on only one side, the chin moves to the opposite side. When opposite movements at the two temporomandibular joints are coordinated, a chewing movement results.

Mandibular nerve [V₃]

The mandibular nerve [V₃] is the largest of the three divisions of the trigeminal nerve [V].

Unlike the ophthalmic [V₁] and maxillary [V₂] nerves, which are purely sensory, the mandibular nerve [V₃] is both motor and sensory.

In addition to carrying general sensation from the teeth and gingivae of the mandible, the anterior two-thirds of the tongue, mucosa on the floor of the oral cavity, the lower lip, skin over the temple and lower face, and part of the cranial dura mater, the mandibular nerve [V₃] also carries motor innervation to most of the muscles that move the mandible, one of the muscles (tensor tympani) in the middle ear, and one of the muscles of the soft palate (tensor veli palatini).

All branches of the mandibular nerve [V₃] originate in the infratemporal fossa.

Like the ophthalmic [V₁] and maxillary [V₂] nerves, the sensory part of the mandibular nerve [V₃] originates from the trigeminal ganglion in the middle cranial fossa (Fig. 8.138):

the sensory part of the mandibular nerve [V₃] drops vertically through the foramen ovale and enters the infratemporal fossa between the tensor veli palatini muscle and the upper head of the lateral pterygoid muscle;

the small motor root of the trigeminal nerve [V] passes medial to the trigeminal ganglion in the cranial cavity, then passes through the foramen ovale and immediately joins the sensory part of the mandibular nerve [V₃].

Branches

Soon after the sensory and motor roots join, the mandibular nerve [V₃] gives rise to a small meningeal branch and to the nerve to medial pterygoid, and then divides into anterior and posterior trunks (Fig. 8.139):

branches from the anterior trunk are the buccal, masseteric, and deep temporal nerves, and the nerve to lateral pterygoid, all of which, except the buccal nerve (which is predominantly sensory) are motor nerves;

branches from the posterior trunk are the auriculotemporal, lingual, and inferior alveolar nerves, all of which, except a small nerve (nerve to mylohyoid) that branches from the inferior alveolar nerve, are sensory nerves.

Fig. 8.139 Mandibular nerve [V₃]—meningeal nerve and nerve to medial pterygoid.

Nerve to medial pterygoid

The nerve to medial pterygoid also originates medially from the mandibular nerve [V₃] (Fig. 8.139). It descends to enter and supply the deep surface of the medial pterygoid muscle. Near its origin from the mandibular nerve [V₃], it has two small branches:

one of these supplies the tensor veli palatini;

the other ascends to supply the tensor tympani muscle, which occupies a small bony canal above and parallel to the pharyngotympanic tube in the temporal bone.

Auriculotemporal nerve

The auriculotemporal nerve is the first branch of the posterior division of the mandibular nerve [V₃] and originates as two roots, which pass posteriorly around the middle meningeal artery ascending from the maxillary artery to the foramen spinosum (Fig. 8.140).

Fig. 8.140 Mandibular nerve [V₃]—posterior trunk. A. Lateral view.

Mandibular nerve [V₃]—posterior trunk. B. Anterior view. C. Anteromedial view.

The auriculotemporal nerve passes first between the tensor veli palatini muscle and the upper head of lateral pterygoid muscle, and then between the sphenomandibular ligament and the neck of mandible. It curves laterally around the neck of mandible and then ascends deep to the parotid gland between the temporomandibular joint and ear.

The terminal branches of the auriculotemporal nerve carry general sensation from skin over a large area of the temple. In addition, the auriculotemporal nerve contributes to sensory innervation of the external ear, the external auditory meatus, tympanic membrane, and temporomandibular joint. It also delivers postganglionic parasympathetic nerves from the glossopharyngeal nerve [IX] to the parotid gland.

Lingual nerve

The lingual nerve is a major sensory branch of the posterior trunk of the mandibular nerve [V₃] (Fig. 8.140). It carries general sensation from the anterior two-thirds of the tongue, oral mucosa on the floor of the oral cavity, and lingual gingivae associated with the lower teeth.

The lingual nerve is joined high in the infratemporal fossa by the chorda tympani branch of the facial nerve [VII], which carries:

taste from the anterior two-thirds of the tongue; and

parasympathetic fibers to all salivary glands below the level of the oral fissure.

The lingual nerve first descends between the tensor veli palatini muscle and the lateral pterygoid muscle, where it is joined by the chorda tympani nerve, and then descends across the lateral surface of the medial pterygoid muscle to enter the oral cavity.

The lingual nerve enters the oral cavity between the posterior attachment of the mylohyoid muscle to the mylohyoid line and the attachment of the superior constrictor of the pharynx to the pterygomandibular raphe. As the lingual nerve enters the floor of the oral cavity, it is in a shallow groove on the medial surface of the mandible immediately inferior to the last molar tooth. In this position, it is palpable through the oral mucosa and in danger when operating on the molar teeth and gingivae.

The lingual nerve passes into the tongue on the lateral surface of the hyoglossus muscle where it is attached to the submandibular ganglion (see p. 936), which contains the secondary cell bodies for the parasympathetic nerves of the chorda tympani nerve carried from the infratemporal fossa into the floor of the oral cavity on the lingual nerve.

Inferior alveolar nerve

The inferior alveolar nerve, like the lingual nerve, is a major sensory branch of the posterior trunk of the mandibular nerve [V₃] (Fig. 8.140). In addition to innervating all lower teeth and much of the associated gingivae, it also supplies the mucosa and skin of the lower lip and skin of the chin. It has one motor branch, which innervates the mylohyoid muscle and the anterior belly of the digastric muscle.

The inferior alveolar nerve originates deep to the lateral pterygoid muscle from the posterior trunk of the mandibular nerve [V₃] in association with the lingual nerve. It descends on the lateral surface of the medial pterygoid muscle, passes between the sphenomandibular ligament and the ramus of mandible, and then enters the mandibular canal through the mandibular foramen. Just before entering the mandibular foramen, it gives origin to the nerve to mylohyoid, which lies in the mylohyoid groove inferior to the foramen and continues anteriorly below the floor of the oral cavity to innervate the mylohyoid muscle and the anterior belly of the digastric muscle.

The inferior alveolar nerve passes anteriorly within the mandibular canal of the lower jaw. The mandibular canal and its contents are inferior to the roots of the molar teeth, and the roots can sometimes curve around the canal making extraction of these teeth difficult.

The inferior alveolar nerve supplies branches to the three molar teeth and the second premolar tooth and associated labial gingivae, and then divides into its two terminal branches:

the incisive nerve, which continues in the mandibular canal to supply the first premolar, incisor, and canine teeth, and related gingivae.

the mental nerve, which exits the mandible through the mental foramen and supplies the lower lip and chin.

The mental nerve is palpable and sometimes visible through the oral mucosa adjacent to the roots of the premolar teeth.

Chorda tympani and the lesser petrosal nerve

Branches of two cranial nerves join branches of the mandibular nerve [V₃] in the infratemporal fossa (Fig. 8.141). These are the chorda tympani branch of the facial nerve [VII] and the lesser petrosal nerve, a branch of the tympanic plexus in the middle ear, which had its origin from a branch of the glossopharyngeal nerve [IX] (see Fig. 8.111, p. 907).

Fig. 8.141 Chorda tympani and lesser petrosal nerves. A. Course after emerging from the skull.

B. Course of parasympathetic fibers.

Chorda tympani

The chorda tympani (Fig. 8.141) carries taste from the anterior two-thirds of the tongue and parasympathetic innervation to all salivary glands below the level of the oral fissure.

The chorda tympani originates from the facial nerve [VII] within the temporal bone and in association with the mastoid wall of the middle ear, passes anteriorly through a small canal, and enters the lateral aspect of the middle ear. As it continues anterosuperiorly across the middle ear, it is separated from the tympanic membrane by the handle of malleus. It leaves the middle ear through the medial end of the petrotympanic fissure, enters the infratemporal fossa, descends medial to the spine of the sphenoid and then to the lateral pterygoid muscle, and joins the lingual nerve.

Preganglionic parasympathetic fibers carried in the chorda tympani synapse with postganglionic parasympathetic fibers in the submandibular ganglion, which “hangs off” the lingual nerve in the floor of the oral cavity.

Postganglionic parasympathetic fibers leave the submandibular ganglion and either:

re-enter the lingual nerve to travel with its terminal branches to reach target tissues; or

pass directly from the submandibular ganglion into glands.

The taste (SA) fibers do not pass through the ganglion and are distributed with terminal branches of the lingual nerve.

In the clinic

Lingual nerve injury

A lingual nerve injury proximal to where the chorda tympani joins it in the infratemporal fossa will produce loss of general sensation from the anterior two-thirds of the tongue, oral mucosa, gingivae, the lower lip, and the chin.

If a lingual nerve lesion is distal to the site where it is joined by the chorda tympani, secretion from the salivary glands below the oral fissure and taste from the anterior two-thirds of the tongue will also be lost.

Maxillary artery

The maxillary artery is the largest branch of the external carotid artery in the neck and is a major source of blood supply for the nasal cavity, the lateral wall and roof of the oral cavity, all teeth, and the dura mater in the cranial cavity. It passes through and supplies the infratemporal fossa and then enters the pteryatine fossa, where it gives origin to terminal branches (Fig. 8.142).

Fig. 8.142 Maxillary artery.

The maxillary artery originates within the substance of the parotid gland and then passes forward, between the neck of mandible and sphenomandibular ligament, into the infratemporal fossa. It ascends obliquely through the infratemporal fossa to enter the pteryatine fossa by passing through the pterygomaxillary fissure. This part of the vessel may pass either lateral or medial to the lower head of lateral pterygoid. If it passes medial to the lower head, the maxillary artery then loops laterally between the upper and lower heads of lateral pterygoid to access the pterygomaxillary fissure.

Branches

Branches of the maxillary artery are as follows:

the first part of the maxillary artery (the part between the neck of mandible and the sphenomandibular ligament) gives origin to two major branches (the middle meningeal and inferior alveolar arteries) and a number of smaller branches (deep auricular, anterior tympanic, and accessory meningeal);

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the second part of the maxillary artery (the part related to the lateral pterygoid muscle) gives origin to deep temporal, masseteric, buccal, and pterygoid branches, which course with branches of the mandibular nerve [V₃];

the third part of the maxillary artery is in the pteryatine fossa (see p. 946).

Pterygoid plexus

The pterygoid plexus is a network of veins between the medial and lateral pterygoid muscles, and between the lateral pterygoid and temporalis muscles (Fig. 8.143).

Fig. 8.143 Pterygoid plexus of veins.

Veins that drain regions supplied by arteries branching from the maxillary artery in the infratemporal fossa and pteryatine fossa connect with the pterygoid plexus. These tributary veins include those that drain the nasal cavity, roof and lateral wall of the oral cavity, all teeth, muscles of the infratemporal fossa, paranasal sinuses, and nasopharynx. In addition, the inferior ophthalmic vein from the orbit can drain through the inferior orbital fissure into the pterygoid plexus.

The pterygoid plexus connects:

posteriorly, via a short maxillary vein, with the retromandibular vein in the neck; and

anteriorly, via a deep facial vein, with the facial vein on the face.

Pterygoid canal

The pterygoid canal is a bony canal opening onto the posterior surface of the pterygoid process and then continuing superomedially for a short distance in the cartilage that fills the foramen lacerum and surrounding the posterior opening of the pterygoid canal. The pterygoid canal opens into the middle cranial fossa just anteroinferior to the internal carotid artery as the vessel enters the cranial cavity through the carotid canal (Fig. 8.145B).

Maxillary nerve [V₂]

The maxillary nerve [V₂] is purely sensory. It originates from the trigeminal ganglion in the cranial cavity, exits the middle cranial fossa, and enters the pteryatine fossa through the foramen rotundum (Fig. 8.147). It passes anteriorly through the fossa and exits as the infra-orbital nerve through the inferior orbital fissure.

Fig. 8.147 Maxillary nerve [V₂]. A. Terminal branches. B. In relationship to the pteryatine ganglion.

While passing through the pteryatine fossa, the maxillary nerve [V₂] gives rise to the zygomatic nerve, the posterior superior alveolar nerve, and two ganglionic branches. The two ganglionic branches originate from its inferior surface and pass through the pteryatine ganglion.

Postganglionic parasympathetic fibers, arising in the pteryatine ganglion, join the general sensory branches of the maxillary nerve [V₂] in the pteryatine ganglion, as do postganglionic sympathetic fibers from the carotid plexus, and the three types of fibers leave the ganglion as orbital, palatine, nasal, and pharyngeal branches.

Branches

Orbital branches.

The orbital branches are small and pass through the inferior orbital fissure to contribute to the supply of the orbital wall and of the sphenoidal and ethmoidal sinuses.

Greater and lesser palatine nerves.

The greater and lesser palatine nerves (Fig. 8.147) pass inferiorly from the pteryatine ganglion, enter and pass through the palatine canal, and enter the oral surface of the palate through the greater and lesser palatine foramina.

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The greater palatine nerve passes forward on the roof of the oral cavity to innervate mucosa and glands of the hard palate and the adjacent gingiva, almost as far forward as the incisor teeth.

In the palatine canal, the greater palatine nerve gives origin to posterior inferior nasal nerves, which pass medially through small foramina in the perpendicular plate of the palatine bone and contribute to the innervation of the lateral nasal wall.

After passing through the lesser palatine foramen, the lesser palatine nerve passes posteriorly to supply the soft palate.

Nasal nerves.

The nasal nerves (Fig. 8.147), approximately seven in number, pass medially through the sphenopalatine foramen to enter the nasal cavity. Most pass anteriorly to supply the lateral wall of the nasal cavity, while others pass across the roof to supply the medial wall.

One of the nerves passing across the roof to supply the medial wall of the nasal cavity (the nasopalatine nerve) is the largest of the nasal nerves and passes anteriorly down the nasal septum, through the incisive canal and fossa in the hard palate to enter the roof of the oral cavity and supply mucosa, gingiva, and glands adjacent to the incisor teeth.

Pharyngeal nerve.

The pharyngeal nerve passes posteriorly from the pteryatine ganglion, and leaves the fossa through the palatovaginal canal, which it then exits to supply the mucosa and glands of the nasopharynx.

Zygomatic nerve.

The zygomatic nerve (Fig. 8.147) originates directly from the maxillary nerve [V₂] in the pteryatine fossa, which it leaves to enter the orbit through the inferior orbital fissure. It passes forward on the lateral orbital wall and divides into zygomaticotemporal and zygomaticofacial branches:

the zygomaticotemporal branch continues forward at the base of the lateral orbital wall, passes through a small bony canal in the zygomatic bone to enter the temporal fossa through a small foramen in the lateral orbital margin on the posterior surface of the frontal process of the zygomatic bone, and passes superficially to supply skin over the temple;

the zygomaticofacial branch also passes forward at the base of the lateral orbital wall, leaves through a small bony canal, in the orbital margin, which opens via multiple small foramina on the anterolateral surface of the zygomatic bone, and its branches supply the adjacent skin.

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Posterior superior alveolar nerve.

The posterior superior alveolar nerve (Fig. 8.147) originates from the maxillary nerve [V₂] in the pteryatine fossa and passes laterally out of the fossa through the pterygomaxillary fissure to enter the infratemporal fossa. It continues laterally and inferiorly to enter the posterior surface of the maxilla through a small alveolar foramen approximately midway between the last molar tooth and the inferior orbital fissure. It then passes inferiorly just deep to the mucosa of the maxillary sinus to join the superior dental plexus.

The posterior superior alveolar nerve supplies the molar teeth and adjacent buccal gingivae, and contributes to the supply of the maxillary sinus.

Infra-orbital nerve.

The infra-orbital nerve (Fig. 8.147) is the anterior continuation of the maxillary nerve [V₂] that leaves the pteryatine fossa through the inferior orbital fissure. It lies first in the infra-orbital groove in the floor of the orbit and then continues forward in the infra-orbital canal.

While in the infra-orbital groove and canal, the infra-orbital nerve gives origin to middle and anterior superior alveolar nerves, respectively, which ultimately join the superior alveolar plexus to supply the upper teeth:

the middle superior alveolar nerve also supplies the maxillary sinus;

the anterior superior alveolar nerve also gives origin to a small nasal branch, which passes medially through the lateral wall of the nasal cavity to supply parts of the areas of the nasal floor and walls.

The infra-orbital nerve exits the infra-orbital canal through the infra-orbital foramen inferior to the orbital margin and divides into nasal, palpebral, and superior labial branches:

nasal branches supply skin over the lateral aspect of the external nose and part of the nasal septum;

palpebral branches supply skin of the lower eyelid;

superior labial branches supply skin over the cheek and upper lip, and the related oral mucosa.

Nerve of the pterygoid canal and the pteryatine ganglion

The nerve of the pterygoid canal (Fig. 8.148) is formed in the middle cranial fossa by the union of:

the greater petrosal nerve (a branch of the facial nerve [VII]); and

the deep petrosal nerve (a branch of the internal carotid plexus).

Fig. 8.148 Nerve of the pterygoid canal. A. Overview. B. In relationship to the pteryatine ganglion.

The nerve of the pterygoid canal passes into the pteryatine fossa and joins the pteryatine ganglion. It carries mainly preganglionic parasympathetic and postganglionic sympathetic fibers.

Greater petrosal nerve

The greater petrosal nerve, which originates from the geniculate ganglion of the facial nerve [VII] in the temporal bone, exits the temporal bone through a small canal that opens via a fissure onto the anterior surface of the petrous part of the temporal bone. It passes anteromedially along the posterior margin of the middle cranial fossa and then under the internal carotid artery to reach the superior surface of the cartilage filling the foramen lacerum.

As the greater petrosal nerve passes under the internal carotid artery, it is joined by the deep petrosal nerve to form the nerve of the pterygoid canal.

The greater petrosal nerve carries parasympathetic innervation to all glands above the oral fissure, including:

mucous glands in the nasal cavity;

salivary glands in the upper half of the oral cavity; and

the lacrimal gland in the orbit.

The greater petrosal nerve also carries some taste (SA) fibers from the soft palate in the lesser palatine nerve.

Maxillary artery

The maxillary artery is a major branch of the external carotid artery in the neck. It originates adjacent to the neck of mandible, passes forward through the infratemporal fossa, and then enters the pteryatine fossa through the pterygomaxillary fissure (Fig. 8.149).

Fig. 8.149 Maxillary artery in the pteryatine fossa.

The part of the maxillary artery in the pteryatine fossa (the third part) is anterior to the pteryatine ganglion and gives origin to branches that accompany branches of the maxillary nerve [V₂] and the pteryatine ganglion.

Branches of the maxillary artery include the posterior superior alveolar, infra-orbital, greater palatine, pharyngeal, and sphenopalatine arteries, and the artery of the pterygoid canal. Collectively, these branches supply much of the nasal cavity, the roof of the oral cavity, and all upper teeth. In addition, they contribute to the blood supply of the sinuses, oropharynx, and floor of the orbit.

Branches

Posterior superior alveolar artery.

The posterior superior alveolar artery originates from the maxillary artery as it passes through the pterygomaxillary fissure. It meets the posterior superior alveolar nerve, accompanies it through the alveolar foramen on the infratemporal surface of the maxilla, and supplies the molar and premolar teeth, adjacent gingiva, and the maxillary sinus.

Infra-orbital artery.

The infra-orbital artery passes forward with the infra-orbital nerve and leaves the pteryatine fossa through the inferior orbital fissure. With the infra-orbital nerve, it lies in the infra-orbital groove and infra-orbital canal, and emerges through the infra-orbital foramen to supply parts of the face.

Within the infra-orbital canal, the infra-orbital artery gives origin to:

branches that contribute to the blood supply of structures near the floor of the orbit—the inferior rectus and inferior oblique muscles, and the lacrimal sac; and

anterior superior alveolar arteries, which supply the incisor and canine teeth and the maxillary sinus.

Greater palatine artery.

The greater palatine artery passes inferiorly with the palatine nerves into the palatine canal. It gives origin to a lesser palatine branch, which passes through the lesser palatine foramen to supply the soft palate, and then continues through the greater palatine foramen to supply the hard palate. The latter vessel passes forward on the inferior surface of the palate to enter the incisive fossa and pass superiorly through the incisive canal to supply the anterior aspect of the septal wall of the nasal cavity.

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Pharyngeal branch.

The pharyngeal branch of the maxillary artery travels posteriorly and leaves the pteryatine fossa through the palatovaginal canal with the pharyngeal nerve. It supplies the posterior aspect of the roof of the nasal cavity, the sphenoidal sinus, and the pharyngotympanic tube.

Sphenopalatine artery.

The sphenopalatine artery is the terminal branch of the maxillary artery. It leaves the pteryatine fossa medially through the sphenopalatine foramen and accompanies the nasal nerves, giving off:

posterior lateral nasal arteries, which supply the lateral wall of the nasal cavity and contribute to the supply of the paranasal sinuses; and

posterior septal branches, which travel medially across the roof to supply the nasal septum—the largest of these branches passes anteriorly down the septum to anastomose with the end of the greater palatine artery.

Artery of pterygoid canal.

The artery of pterygoid canal passes posteriorly into the pterygoid canal. It supplies surrounding tissues and terminates, after passing inferiorly through cartilage filling the foramen lacerum, in the mucosa of the nasopharynx.

Veins

Veins that drain areas supplied by branches of the terminal part of the maxillary artery generally travel with these branches back into the pteryatine fossa.

The veins coalesce in the pteryatine fossa and then pass laterally through the pterygomaxillary fissure to join the pterygoid plexus of veins in the infratemporal fossa (Fig. 8.150).

Fig. 8.150 Veins of the pteryatine fossa.

The infra-orbital vein, which drains the inferior aspect of the orbit, may pass directly into the infratemporal fossa through the lateral aspect of the inferior orbital fissure, so bypassing the pteryatine fossa.

Suprahyoid muscles

The four pairs of suprahyoid muscles are in the submental and submandibular triangles (Fig. 8.157). They pass in a superior direction from the hyoid bone to the skull or mandible and raise the hyoid, as occurs during swallowing.

Stylohyoid

The stylohyoid muscle arises from the base of the styloid process and passes anteroinferiorly to attach to the lateral area of the body of the hyoid bone (Fig. 8.158). During swallowing it pulls the hyoid bone posterosuperiorly and it is innervated by the facial nerve [VII].

Fig. 8.158 Suprahyoid muscles. A. Lateral view. B. Inferior view.

Digastric

The digastric muscle has two bellies connected by a tendon, which attaches to the body of the hyoid bone (Fig. 8.158):

the posterior belly arises from the mastoid notch on the medial side of the mastoid process of the temporal bone;

the anterior belly arises from the digastric fossa on the lower inside of the mandible.

The tendon between the two bellies, which is attached to the body of the hyoid bone, is the point of insertion of both bellies. Because of this arrangement, the muscle has multiple actions depending on which bone is fixed:

when the mandible is fixed, the digastric muscle raises the hyoid bone;

when the hyoid bone is fixed, the digastric muscle opens the mouth by lowering the mandible.

Innervation of the digastric muscle is from two different cranial nerves.

The innervation of the posterior belly of the digastric muscle is by the facial nerve [VII], whereas the anterior belly of the muscle is innervated by the mandibular division [V₃] of the trigeminal nerve [V].

Geniohyoid

The geniohyoid muscle is the final muscle in the suprahyoid group (Fig. 8.158). A narrow muscle, it is superior to the medial part of each mylohyoid muscle. The muscles from each side are next to each other in the midline.

The geniohyoid arises from the inferior mental spine of the mandible and passes backward and downward to insert on the body of the hyoid bone.

It has two functions depending on which bone is fixed:

fixation of the mandible elevates and pulls the hyoid bone forward;

fixation of the hyoid bone pulls the mandible downward and inward.

The geniohyoid is innervated by a branch from the anterior ramus of C1 carried along the hypoglossal nerve [XII].

Infrahyoid muscles

The four infrahyoid muscles are in the muscular triangle (Fig. 8.157). They attach the hyoid bone to inferior structures and depress the hyoid bone. They also provide a stable point of attachment for the suprahyoid muscles. Because of their appearance, they are sometimes referred to as the “strap muscles.”

Sternohyoid

The sternohyoid muscle is a long, thin muscle originating from the posterior aspect of the sternoclavicular joint and adjacent manubrium of sternum (Fig. 8.159). It ascends to insert onto the body of the hyoid bone. It depresses the hyoid bone and is innervated by the anterior rami of C1 to C3 through the ansa cervicalis.

Fig. 8.159 Infrahyoid muscles.

Omohyoid

Lateral to the sternohyoid muscle is the omohyoid muscle (Fig. 8.159). This muscle consists of two bellies with an intermediate tendon in both the posterior and anterior triangles of the neck:

the inferior belly begins on the superior border of the scapula, medial to the suprascapular notch, and passes forward and upward across the posterior triangle ending at the intermediate tendon;

the superior belly begins at the intermediate tendon and ascends to attach to the body of the hyoid bone just lateral to the attachment of the sternohyoid;

the intermediate tendon is attached to the clavicle, near its medial end, by a fascial sling.

The omohyoid depresses and fixes the hyoid bone. It is innervated by the anterior rami of C1 to C3 through the ansa cervicalis.

Carotid system

Common carotid arteries

The common carotid arteries are the beginning of the carotid system (Fig. 8.160):

the right common carotid artery originates from the brachiocephalic trunk immediately posterior to the right sternoclavicular joint and is entirely in the neck throughout its course;

the left common carotid artery begins in the thorax as a direct branch of the arch of the aorta and passes superiorly to enter the neck near the left sternoclavicular joint.

Fig. 8.160 Origin of common carotid arteries.

Both right and left common carotid arteries ascend through the neck, just lateral to the trachea and esophagus, within a fascial compartment (the carotid sheath). They give off no branches as they pass through the neck.

Near the superior edge of the thyroid cartilage each common carotid artery divides into its two terminal branches—the external and internal carotid arteries (Fig. 8.161).

Fig. 8.161 Carotid system.

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The superior part of each common carotid artery and its division into external and internal carotid arteries occurs in the carotid triangle (Fig. 8.162), which is a subdivision of the anterior triangle of the neck (see Fig. 8.157).

Fig. 8.162 Carotid triangle.

At the bifurcation, the common carotid artery and the beginning of the internal carotid artery are dilated. This dilation is the carotid sinus and contains receptors that monitor changes in blood pressure and are innervated by a branch of the glossopharyngeal nerve [IX].

Another accumulation of receptors in the area of the bifurcation is responsible for detecting changes in blood chemistry, primarily oxygen content. This is the carotid body and is innervated by branches from both the glossopharyngeal [IX] and vagus [X] nerves.

External carotid arteries

The external carotid arteries begin giving off branches immediately after the bifurcation of the common carotid arteries (Fig. 8.161 and Table 8.13) as follows:

the superior thyroid artery is the first branch, arises from the anterior surface near or at the bifurcation, and passes in a downward and forward direction to reach the superior pole of the thyroid gland;

the ascending pharyngeal artery is the second and smallest branch—it arises from the posterior aspect of the external carotid artery and ascends between the internal carotid artery and the pharynx;

the lingual artery arises from the anterior surface of the external carotid artery just above the superior thyroid artery at the level of the hyoid bone, passes deep to the hypoglossal nerve [XII], and passes between the middle constrictor and hyoglossus muscles;

the facial artery is the third anterior branch of the external carotid artery, arises just above the lingual artery, passes deep to the stylohyoid and posterior belly of the digastric muscles, continues deep between the submandibular gland and mandible, and emerges over the edge of the mandible just anterior to the masseter muscle, to enter the face;

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the occipital artery arises from the posterior surface of the external carotid artery, near the level of origin of the facial artery, passes upward and posteriorly deep to the posterior belly of the digastric muscle, and emerges on the posterior aspect of the scalp;

the posterior auricular artery is a small branch arising from the posterior surface of the external carotid artery, and passes upward and posteriorly;

the superficial temporal artery is one of the terminal branches and appears as an upward continuation of the external carotid artery—beginning posterior to the neck of mandible, it passes anterior to the ear, crosses the zygomatic process of the temporal bone, and above this point divides into anterior and posterior branches;

the maxillary artery is the larger of the two terminal branches of the external carotid artery—arising posterior to the neck of mandible, it passes through the parotid gland, continues medial to the neck of mandible and into the infratemporal fossa, and continues through this area into the pteryatine fossa.

Table 8.13 Branches of the external carotid artery

Branch	Supplies
Superior thyroid artery	Thyrohyoid muscle, internal structures of the larynx, sternocleidomastoid and cricothyroid muscles, thyroid gland
Ascending pharyngeal artery	Pharyngeal constrictors and stylopharyngeus muscle, palate, tonsil, pharyngotympanic tube, meninges in posterior cranial fossa
Lingual artery	Muscles of the tongue, palatine tonsil, soft palate, epiglottis, floor of mouth, sublingual gland
Facial artery	All structures in the face from the inferior border of the mandible anterior to the masseter muscle to the medial corner of the eye, the soft palate, palatine tonsil, pharyngotympanic tube, submandibular gland
Occipital artery	Sternocleidomastoid muscle, meninges in posterior cranial fossa, mastoid cells, deep muscles of the back, posterior scalp
Posterior auricular artery	Parotid gland and nearby muscles, external ear and scalp posterior to ear, middle and inner ear structures
Superficial temporal artery	Parotid gland and duct, masseter muscle, lateral face, anterior part of external ear, temporalis muscle, parietal and temporal fossae
Maxillary artery	External acoustic meatus, lateral and medial surface of tympanic membrane, temporomandibular joint, dura mater on lateral wall of skull and inner table of cranial bones, trigeminal ganglion and dura in vicinity, mylohyoid muscle, mandibular teeth, skin on chin, temporalis muscle, outer table of bones of skull in temporal fossa, structures in infratemporal fossa, maxillary sinus, upper teeth and gingivae, infra-orbital skin, palate, roof of pharynx, nasal cavity

Veins

Collecting blood from the skull, brain, superficial face, and parts of the neck, the internal jugular vein begins as a dilated continuation of the sigmoid sinus, which is a dural venous sinus. This initial dilated part is referred to as the superior bulb of jugular vein and receives another dural venous sinus (the inferior petrosal sinus) soon after it is formed. It exits the skull through the jugular foramen associated with the glossopharyngeal [IX], vagus [X], and accessory [XI] nerves, and enters the carotid sheath.

The internal jugular vein traverses the neck within the carotid sheath, initially posterior to the internal carotid artery, but passes to a more lateral position farther down. It remains lateral to the common carotid artery through the rest of the neck with the vagus nerve [X] posterior and partially between the two vessels.

The paired internal jugular veins join with the subclavian veins posterior to the sternal end of the clavicle to form the right and left brachiocephalic veins (Fig. 8.160).

Tributaries to each internal jugular vein include the inferior petrosal sinus, and the facial, lingual, pharyngeal, occipital, superior thyroid, and middle thyroid veins.

Facial nerve [VII]

After emerging from the stylomastoid foramen, the facial nerve [VII] gives off branches that innervate two muscles associated with the anterior triangle of the neck:

the posterior belly of the digastric;

stylohyoid.

The facial nerve [VII] also innervates platysma muscle that overlies the anterior triangle and part of the posterior triangle of the neck.

Glossopharyngeal nerve [IX]

The glossopharyngeal nerve [IX] leaves the cranial cavity through the jugular foramen. It begins its descent between the internal carotid artery and the internal jugular vein, lying deep to the styloid process and the muscles associated with the styloid process. As the glossopharyngeal nerve [IX] completes its descent, it passes forward between the internal and external carotid arteries, and curves around the lateral border of the stylopharyngeus muscle (Fig. 8.163). At this point, it continues in an anterior direction, deep to the hyoglossus muscle, to reach the base of the tongue and the area of the palatine tonsil.

Fig. 8.163 Glossopharyngeal nerve [IX] in the anterior triangle of the neck.

As the glossopharyngeal nerve [IX] passes through the area of the anterior triangle of the neck it innervates the stylopharyngeus muscle, sends a branch to the carotid

sinus, and supplies sensory branches to the pharynx.

Vagus nerve [X]

The vagus nerve [X] exits the cranial cavity through the jugular foramen between the glossopharyngeal [IX] and accessory [XI] nerves.

Outside the skull the vagus nerve [X] enters the carotid sheath and descends through the neck enclosed in this structure medial to the internal jugular vein and posterior to the internal carotid and common carotid arteries (Fig. 8.164).

Fig. 8.164 Vagus nerve [X] in the anterior triangle of the neck.

Branches of the vagus nerve [X] as it passes through the anterior triangle of the neck include a motor branch to the pharynx, a branch to the carotid body, the superior laryngeal nerve (which divides into external and internal laryngeal branches), and possibly a cardiac branch.

Accessory nerve [XI]

The accessory nerve [XI] is the most posterior of the three cranial nerves exiting the cranial cavity through the jugular foramen. It begins its descent medial to the internal jugular vein, emerging from between the internal jugular vein and internal carotid artery to cross the lateral surface of the internal jugular vein as it passes downward and backward to disappear either into or beneath the anterior border of the sternocleidomastoid muscle (Fig. 8.165).

Fig. 8.165 Accessory nerve [XI] in the anterior triangle of the neck.

The accessory nerve gives off no branches as it passes through the anterior triangle of the neck.

Hypoglossal nerve [XII]

The hypoglossal nerve [XII] leaves the cranial cavity through the hypoglossal canal and is medial to the internal jugular vein and internal carotid artery immediately outside the skull. As it descends, it passes outward between the internal jugular vein and internal carotid artery (Fig. 8.166). At this point it passes forward, hooking around the occipital artery, across the lateral surfaces of the internal and external carotid arteries and the lingual artery, and then continues deep to the posterior belly of the digastric and stylohyoid muscles. It passes over the surface of the hyoglossus muscle and disappears deep to the mylohyoid muscle.

Fig. 8.166 Hypoglossal nerve [XII] in the anterior triangle of the neck.

The hypoglossal nerve [XII], which supplies the tongue, does not give off any branches as it passes through the anterior triangle of the neck.

Transverse cervical nerve

The transverse cervical nerve is a branch of the cervical plexus arising from the anterior rami of cervical nerves C2 and C3. It emerges from beneath the posterior border of the sternocleidomastoid muscle, near the middle of the muscle, and loops around the sternocleidomastoid to cross its anterior surface in a transverse direction (Fig. 8.167). It continues across the neck and provides cutaneous innervation to this area.

Fig. 8.167 Transverse cervical nerve in the anterior triangle of the neck.

Ansa cervicalis

The ansa cervicalis is a loop of nerve fibers from cervical nerves C1 to C3 that innervate the “strap muscles” in the anterior triangle of the neck (Fig. 8.168). It begins as branches from the cervical nerve C1 join the hypoglossal nerve [XII] soon after it leaves the skull.

Fig. 8.168 Ansa cervicalis.

As the hypoglossal nerve [XII] completes its descent and begins to pass forward across the internal and external carotid arteries, some of the cervical nerve fibers leave it and descend between the internal jugular vein and the internal, and then common, carotid arteries. These nerve fibers are the superior root of the ansa cervicalis and innervate the superior belly of the omohyoid muscle, and the upper parts of the sternohyoid and sternothyroid muscles.

Completing the loop is a direct branch from the cervical plexus containing nerve fibers from the second and third cervical nerves C2 and C3 (Fig. 8.168). This is the inferior root of the ansa cervicalis. It descends either medial or lateral to the internal jugular vein before turning medially to join the superior root. At this location, the ansa cervicalis gives off branches that innervate the inferior belly of the omohyoid, and the lower parts of the sternohyoid and sternothyroid muscles.

Thyroid gland

The thyroid gland is anterior in the neck below and lateral to the thyroid cartilage (Fig. 8.169). It consists of two lateral lobes (which cover the anterolateral surfaces of the trachea, the cricoid cartilage, and the lower part of the thyroid cartilage) with an isthmus that connects the lateral lobes and crosses the anterior surfaces of the second and third tracheal cartilages.

Fig. 8.169 Thyroid gland in the anterior triangle of neck. A. Anterior view. B. Transverse view. C. Ultrasound scan—compound axial view of the neck. D. Ultrasound scan—axial view of the neck. E. Nuclear medicine scan—normal thyroid uptake of pertechnetate in the neck.

Lying deep to the sternohyoid, sternothyroid, and omohyoid muscles, the thyroid gland is in the visceral compartment of the neck. This compartment also includes the pharynx, trachea, and esophagus and is surrounded by the pretracheal layers of fascia.

The thyroid gland arises as a median outgrowth from the floor of the pharynx near the base of the tongue. The foramen cecum of the tongue indicates the site of origin and the thyroglossal duct marks the path of migration of the thyroid gland to its final adult location. The thyroglossal duct usually disappears early in development, but remnants may persist as a cyst or as a connection to the foramen cecum (i.e., a fistula).

There may also be functional thyroid gland:

associated with the tongue (a lingual thyroid);

anywhere along the path of migration of the thyroid gland; or

extending upward from the gland along the path of the thyroglossal duct (a pyramidal lobe).

Arterial supply

Two major arteries supply the thyroid gland.

Superior thyroid artery.

The superior thyroid artery is the first branch of the external carotid artery (Fig. 8.170). It descends, passing along the lateral margin of the thyrohyoid muscle, to reach the superior pole of the lateral lobe of the gland where it divides into anterior and posterior glandular branches:

the anterior glandular branch passes along the superior border of the thyroid gland and anastomoses with its twin from the opposite side across the isthmus;

the posterior glandular branch passes to the posterior side of the gland and may anastomose with the inferior thyroid artery (Fig. 8.171).

Fig. 8.170 Vasculature of the thyroid: anterior view.

Fig. 8.171 Superior and inferior thyroid arteries and left and right recurrent laryngeal nerve: posterior view.

Inferior thyroid artery.

The inferior thyroid artery is a branch of the thyrocervical trunk, which arises from the first part of the subclavian artery (Figs. 8.170 and 8.171). It ascends along the medial edge of the anterior scalene muscle, passes posteriorly to the carotid sheath, and reaches the inferior pole of the lateral lobe of the thyroid gland.

At the thyroid gland the inferior thyroid artery divides into an:

inferior branch, which supplies the lower part of the thyroid gland and anastomoses with the posterior branch of the superior thyroid artery; and

an ascending branch, which supplies the parathyroid glands.

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Occasionally, a small thyroid ima artery arises from the brachiocephalic trunk or the arch of the aorta and ascends on the anterior surface of the trachea to supply the thyroid gland.

Venous and lymphatic drainage

Three veins drain the thyroid gland (Fig. 8.170):

the superior thyroid vein primarily drains the area supplied by the superior thyroid artery;

the middle and inferior thyroid veins drain the rest of the thyroid gland.

The superior and middle thyroid veins drain into the internal jugular vein, and the inferior thyroid veins empty into the right and left brachiocephalic veins, respectively.

Lymphatic drainage of the thyroid gland is to nodes beside the trachea (paratracheal nodes) and to deep cervical nodes inferior to the omohyoid muscle along the internal jugular vein.

Parathyroid glands

The parathyroid glands are two pairs of small, ovoid, yellowish structures on the deep surface of the lateral lobes of the thyroid gland. They are designated as the superior and inferior parathyroid glands (Fig. 8.171). However, their position is quite variable and they may be anywhere from the carotid bifurcation superiorly to the mediastinum inferiorly.

Derived from the third (the inferior parathyroid glands) and fourth (the superior parathyroid glands) pharyngeal pouches, these paired structures migrate to their final adult position and are named accordingly.

The arteries supplying the parathyroid glands are the inferior thyroid arteries, and venous and lymphatic drainage follows that described for the thyroid gland.

External jugular vein

One of the most superficial structures passing through the posterior triangle of the neck is the external jugular vein (Fig. 8.174). This large vein forms near the angle of mandible, when the posterior branch of the retromandibular and posterior auricular veins join, and descends through the neck in the superficial fascia.

Fig. 8.174 External jugular vein in the posterior triangle of the neck.

After crossing the sternocleidomastoid muscle, the external jugular vein enters the posterior triangle and continues its vertical descent.

In the lower part of the posterior triangle, the external jugular vein pierces the investing layer of cervical fascia and ends in the subclavian vein.

Tributaries to the external jugular vein while it traverses the posterior triangle of the neck include the transverse cervical, suprascapular, and anterior jugular veins.

Subclavian artery and its branches

Several arteries are found within the boundaries of the posterior triangle of the neck. The largest is the third part of the subclavian artery as it crosses the base of the posterior triangle (Fig. 8.175).

Fig. 8.175 Arteries in the posterior triangle of the neck.

The first part of the subclavian artery ascends to the medial border of the anterior scalene muscle from either the brachiocephalic trunk on the right side or directly from the arch of the aorta on the left side. It has numerous branches.

The second part of the subclavian artery passes laterally between the anterior and middle scalene muscles, and one branch may arise from it.

The third part of the subclavian artery emerges from between the anterior and middle scalene muscles to cross the base of the posterior triangle (Fig. 8.175). It extends from the lateral border of the anterior scalene muscle to the lateral border of rib I where it becomes the axillary artery and continues into the upper limb.

A single branch (the dorsal scapular artery) may arise from the third part of the subclavian artery. This branch passes posterolaterally to reach the superior angle of the scapula where it descends along the medial border of the scapula posterior to the rhomboid muscles.

Transverse cervical and suprascapular arteries

Two other small arteries also cross the base of the posterior triangle. These are the transverse cervical and the suprascapular arteries (Fig. 8.175). They are both branches of the thyrocervical trunk, which arises from the first part of the subclavian artery.

After branching from the thyrocervical trunk, the transverse cervical artery passes laterally and slightly posteriorly across the base of the posterior triangle anterior to the anterior scalene muscle and the brachial plexus. Reaching the deep surface of the trapezius muscle, it divides into superficial and deep branches:

the superficial branch continues on the deep surface of the trapezius muscle;

the deep branch continues on the deep surface of the rhomboid muscles near the medial border of the scapula.

The suprascapular artery, also a branch of the thyrocervical trunk, passes laterally, in a slightly downward direction across the lowest part of the posterior triangle, and ends up posterior to the clavicle (Fig. 8.175). Approaching the scapula, it passes over the superior transverse scapular ligament and distributes branches to muscles on the posterior surface of the scapula.

Veins

Veins accompany all the arteries described previously.

The subclavian vein is a continuation of the axillary vein and begins at the lateral border of rib I. As it crosses the base of the posterior triangle, the external jugular, and, possibly, the suprascapular and transverse cervical veins enter it (Fig. 8.175). It ends by joining with the internal jugular vein to form the brachiocephalic vein near the sternoclavicular joint. In the posterior triangle it is anterior to, and slightly lower than, the subclavian artery and passes anterior to the anterior scalene muscle.

Transverse cervical and suprascapular veins travel with each of the similarly named arteries. These veins become tributaries to either the external jugular vein or the initial part of the subclavian vein.

Accessory nerve

The accessory nerve [XI] exits the cranial cavity through the jugular foramen. It descends through the neck in a posterior direction, to reach the anterior border of the sternocleidomastoid muscle. Passing either deep to or through and innervating the sternocleidomastoid muscle, the accessory nerve [XI] continues to descend and enters the posterior triangle (Fig. 8.176). It crosses the posterior triangle, still in an obliquely downward direction, within the investing layer of cervical fascia as this fascia crosses between the sternocleidomastoid and trapezius muscles. When the accessory nerve [XI] reaches the anterior border of the trapezius muscle, it continues on the deep surface of the trapezius and innervates it.

Fig. 8.176 Accessory nerve in the posterior triangle of the neck.

Cervical plexus

The cervical plexus is formed by the anterior rami of cervical nerves C2 to C4, and possibly a contribution from the anterior ramus of cervical nerve C1 (Fig. 8.177).

Fig. 8.177 Cervical plexus.

The cervical plexus forms in the substance of the muscles making up the floor of the posterior triangle within the prevertebral layer of cervical fascia, and consists of:

muscular (or deep) branches;

cutaneous (or superficial) branches.

The cutaneous branches are visible in the posterior triangle emerging from beneath the posterior border of the sternocleidomastoid muscle.

Muscular branches

Muscular (deep) branches of the cervical plexus distribute to several groups of muscles. A major branch is the phrenic nerve, which supplies the diaphragm with both sensory and motor innervation (Fig. 8.177). It arises from the anterior rami of cervical nerves C3 to C5. Hooking around the upper lateral border of the anterior scalene muscle, the nerve continues inferiorly across the anterior surface of the anterior scalene within the prevertebral fascia to enter the thorax (Fig. 8.175). As the nerve descends in the neck, it is “pinned” to the anterior scalene muscle by the transverse cervical and suprascapular arteries.

Several muscular branches of the cervical plexus supply prevertebral and lateral vertebral muscles, including the rectus capitis anterior, rectus capitis lateralis, longus colli, and longus capitis (Fig. 8.178 and Table 8.16).

Fig. 8.178 Prevertebral and lateral vertebral muscles supplied by cervical plexus.

Table 8.16 Prevertebral and lateral muscles

The cervical plexus also contributes to the formation of the superior and inferior roots of the ansa cervicalis (Fig. 8.177). This loop of nerves receives contributions from the anterior rami of the cervical nerves C1 to C3 and innervates the infrahyoid muscles.

Cutaneous branches

Cutaneous (superficial) branches of the cervical plexus are visible in the posterior triangle as they pass outward from the posterior border of the sternocleidomastoid muscle (Figs. 8.176 and 8.177):

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the lesser occipital nerve consists of contributions from cervical nerve C2 (Fig. 8.177), ascends along the posterior border of the sternocleidomastoid muscle, and distributes to the skin of the neck and scalp posterior to the ear;

the great auricular nerve consists of branches from cervical nerves C2 and C3, emerges from the posterior border of the sternocleidomastoid muscle, and ascends across the muscle to the base of the ear, supplying the skin of the parotid region, the ear, and the mastoid area;

the transverse cervical nerve consists of branches from the cervical nerves C2 and C3, passes around the midpart of the sternocleidomastoid muscle, and continues horizontally across the muscle to supply the lateral and anterior parts of the neck;

the supraclavicular nerves are a group of cutaneous nerves from cervical nerves C3 and C4 that, after emerging from beneath the posterior border of the sternocleidomastoid muscle, descend and supply the skin over the clavicle and shoulder as far inferiorly as rib II.

Brachial plexus

The brachial plexus forms from the anterior rami of cervical nerves C5 to C8 and thoracic nerve T1. The contributions of each of these nerves, which are between the anterior and middle scalene muscles, are the roots of the brachial plexus. As the roots emerge from between these muscles, they form the next component of the brachial plexus (the trunks) as follows:

the anterior rami of C5 and C6 form the upper trunk;

the anterior ramus of C7 forms the middle trunk;

the anterior rami of C8 and T1 form the lower trunk.

The trunks cross the base of the posterior triangle (Fig. 8.175). Several branches of the brachial plexus may be visible in the posterior triangle (see Fig. 7.52). These include the:

dorsal scapular nerve to the rhomboid muscles;

long thoracic nerve to the serratus anterior muscle;

nerve to the subclavius muscle; and

suprascapular nerve to the supraspinatus and infraspinatus muscles.

Subclavian arteries

The subclavian arteries on both sides arch upward out of the thorax to enter the root of the neck (Fig. 8.180).

Fig. 8.180 Vasculature of the root of the neck.

The right subclavian artery begins posterior to the sternoclavicular joint as one of two terminal branches of the brachiocephalic trunk. It arches superiorly and laterally to pass anterior to the extension of the pleural cavity in the root of the neck and posterior to the anterior scalene muscle. Continuing laterally across rib I, it becomes the axillary artery as it crosses its lateral border.

The left subclavian artery begins lower in the thorax than the right subclavian artery as a direct branch of the arch of the aorta. Lying posterior to the left common carotid artery and lateral to the trachea, it ascends and arches laterally, passing anterior to the extension of the pleural cavity and posterior to the anterior scalene muscle. It continues laterally over rib I, and becomes the axillary artery as it crosses the lateral border of rib I.

Both subclavian arteries are divided into three parts by the anterior scalene muscle (Fig. 8.180):

the first part extends from the origin of the artery to the anterior scalene muscle;

the second part is the part of the artery posterior to the anterior scalene muscle;

the third part is the part lateral to the anterior scalene muscle before the artery reaches the lateral border of rib I.

All branches from the right and left subclavian arteries arise from the first part of the artery, except in the case of one branch (the costocervical trunk) on the right side (Fig. 8.180). The branches include the vertebral artery, the thyrocervical trunk, the internal thoracic artery, and the costocervical trunk.

Thyrocervical trunk

The second branch of the subclavian artery is the thyrocervical trunk (Fig. 8.180). It arises from the first part of the subclavian artery medial to the anterior scalene muscle, and divides into three branches—the inferior thyroid, the transverse cervical, and the suprascapular arteries.

Inferior thyroid artery.

The inferior thyroid artery (Fig. 8.180) is the superior continuation of the thyrocervical trunk. It ascends, anterior to the anterior scalene muscle, and eventually turns medially, crossing posterior to the carotid sheath and its contents and anterior to the vertebral artery. Reaching the posterior surface of the thyroid gland it supplies the thyroid gland.

When the inferior thyroid artery turns medially, it gives off an important branch (the ascending cervical artery), which continues to ascend on the anterior surface of the prevertebral muscles, supplying these muscles and sending branches to the spinal cord.

Transverse cervical artery.

The middle branch of the thyrocervical trunk is the transverse cervical artery (Fig. 8.180). This branch passes laterally, across the anterior surface of the anterior scalene muscle and the phrenic nerve, and enters and crosses the base of the posterior triangle of the neck. It continues to the deep surface of the trapezius muscle, where it divides into superficial and deep branches:

the superficial branch continues on the deep surface of the trapezius muscle;

the deep branch continues on the deep surface of the rhomboid muscles near the medial border of the scapula.

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Suprascapular artery.

The lowest branch of the thyrocervical trunk is the suprascapular artery (Fig. 8.180). This branch passes laterally, crossing anterior to the anterior scalene muscle, the phrenic nerve, the third part of the subclavian artery, and the trunks of the brachial plexus. At the superior border of the scapula, it crosses over the superior transverse scapular ligament and enters the supraspinatus fossa.

Costocervical trunk

The final branch of the subclavian artery in the root of the neck is the costocervical trunk (Fig. 8.180). It arises in a slightly different position, depending on the side:

on the left, it arises from the first part of the subclavian artery, just medial to the anterior scalene muscle;

on the right, it arises from the second part of the subclavian artery.

On both sides, the costocervical trunk ascends and passes posteriorly over the dome of the pleural cavity and continues in a posterior direction behind the anterior scalene muscle. Eventually it divides into two branches—the deep cervical and the supreme intercostal arteries:

the deep cervical artery ascends in the back of the neck and anastomoses with the descending branch of the occipital artery;

the supreme intercostal artery descends anterior to rib I and divides to form the posterior intercostal arteries for the first two intercostal spaces.

Veins

Numerous veins pass through the root of the neck. Small veins accompany each of the arteries described above, and large veins form major drainage channels.

The subclavian veins begin at the lateral margin of rib I as continuations of the axillary veins. Passing medially on each side, just anterior to the anterior scalene muscles, each subclavian vein is joined by the internal jugular vein to form the brachiocephalic veins.

The only tributary to the subclavian veins are the external jugular veins.

The veins accompanying the numerous arteries in this region empty into other veins.

Phrenic nerves

The phrenic nerves are branches of the cervical plexus and arise on each side as contributions from the anterior rami of cervical nerves C3 to C5 come together. Passing around the upper lateral border of each anterior scalene muscle, the phrenic nerves continue inferiorly across the anterior surface of each anterior scalene muscle within the prevertebral layer of cervical fascia (Fig. 8.181). Leaving the lower edge of the anterior scalene muscle each phrenic nerve passes between the subclavian vein and artery to enter the thorax and continue to the diaphragm.

Fig. 8.181 Nerves in the root of the neck.

Vagus nerves [X]

The vagus nerves [X] descend through the neck within the carotid sheath, posterior to and just between the common carotid artery and the internal jugular vein.

In the lower part of the neck, the vagus nerves [X] give off cardiac branches, which continue downward and medially, passing posterior to the subclavian arteries to disappear into the thorax.

In the root of the neck, each vagus nerve [X] passes anterior to the subclavian artery and posterior to the subclavian vein as it enters the thorax (Fig. 8.181).

Recurrent laryngeal nerves

The right and left recurrent laryngeal nerves are visible as they originate in (the right recurrent laryngeal nerve), or pass through (the left recurrent laryngeal nerve), the root of the neck.

The right recurrent laryngeal nerve is a branch of the right vagus nerve [X] as it reaches the lower edge of the first part of the subclavian artery in the root of the neck (Fig. 8.181). It passes around the subclavian artery and upward and medially in a groove between the trachea and the esophagus as it heads to the larynx.

The left recurrent laryngeal nerve is a branch of the left vagus nerve [X] as it crosses the arch of the aorta in the superior mediastinum. It passes below and behind the arch of the aorta and ascends beside the trachea to the larynx.

Sympathetic nervous system

Various components of the sympathetic nervous system are visible as they pass through the root of the neck. These include:

the cervical part of the sympathetic trunk;

the ganglia associated with the cervical part of the sympathetic trunk; and

cardiac nerves branching from the cervical part of the sympathetic trunk (Fig. 8.182).

The sympathetic trunks are two parallel cords that run from the base of the skull to the coccyx. Along the way they are punctuated by ganglia, which are collections of neuronal cell bodies outside the CNS.

Ganglia

Three ganglia are usually described along the course of the sympathetic trunk in the cervical region, and in these ganglia ascending preganglionic sympathetic fibers from the upper thoracic spinal cord levels synapse with postganglionic sympathetic fibers. The postganglionic sympathetic fibers are distributed in branches from these ganglia.

Superior cervical ganglion.

A very large superior cervical ganglion in the area of cervical vertebrae CI and CII marks the superior extent of the sympathetic trunk (Figs. 8.182 and 8.183). Its branches pass to:

the internal carotid and external carotid arteries, forming plexuses around these vessels;

cervical spinal nerves C1 to C4 through gray rami communicantes;

the pharynx; and

the heart as superior cardiac nerves.

Fig. 8.182 Components of the sympathetic nervous system in the root of the neck.

Fig. 8.183 Cervical part of the sympathetic trunk.

Middle cervical ganglion.

A second ganglion inferior to the superior cervical ganglion along the course of the sympathetic trunk (the middle cervical ganglion) is encountered at about the level of cervical vertebra CVI (Figs. 8.182 and 8.183). Branches from this ganglion pass to:

cervical spinal nerves C5 and C6 through gray rami communicantes; and

the heart as middle cardiac nerves.

Inferior cervical ganglion

At the lower end of the cervical part of the sympathetic trunk is another ganglion (the inferior cervical ganglion), which becomes very large when it combines with the first thoracic ganglion and forms the cervicothoracic ganglion (stellate ganglion). The inferior cervical ganglion (Figs. 8.182 and 8.183) is anterior to the neck of rib I and the transverse process of cervical vertebra CVII, and posterior to the first part of the subclavian artery and the origin of the vertebral artery.

Branches from this ganglion pass to:

spinal nerves C7 to T1 through gray rami communicantes;

the vertebral artery, forming a plexus associated with this vessel; and

the heart as inferior cardiac nerves.

This ganglion may also receive white rami communicantes from thoracic spinal nerve T1, and occasionally, from T2.

Thoracic duct

The thoracic duct is a major lymphatic channel that begins in the abdomen, passes superiorly through the thorax, and ends in the venous channels in the neck. It passes through the lower thoracic cavity in the midline with:

the thoracic aorta on the left;

the azygos vein on the right; and

the esophagus anteriorly.

At about the level of thoracic vertebra TV the thoracic duct passes to the left and continues to ascend just to the left of the esophagus. It passes through the superior mediastinum and enters the root of the neck to the left of the esophagus (Fig. 8.184). Arching laterally, it passes posterior to the carotid sheath and turns inferiorly in front of the thyrocervical trunk, the phrenic nerve, and the vertebral artery.

Fig. 8.184 Thoracic duct in the root of the neck.

The thoracic duct terminates in the junction between the left internal jugular and the left subclavian veins. Near its junction with the venous system it is joined by:

the left jugular trunk, which drains lymph from the left side of the head and neck;

the left subclavian trunk, which drains lymph from the left upper limb; and

occasionally, the left bronchomediastinal trunk, which drains lymph from the left half of the thoracic structures (Fig. 8.185).

Fig. 8.185 Termination of lymphatic trunks in the root of the neck.

A similar confluence of three lymphatic trunks occurs on the right side of the body. Emptying into the junction between the right internal jugular and right subclavian veins are:

the right jugular trunk from the head and neck;

the right subclavian trunk from the right upper limb; and

occasionally, the right bronchomediastinal trunk carrying lymph from the structures in the right half of the thoracic cavity and the right upper intercostal spaces.

There is variability in how these trunks enter the veins. They may combine into a single right lymphatic duct to enter the venous system or enter as three separate trunks.

Superficial lymph nodes

Five groups of superficial lymph nodes form a ring around the head and are primarily responsible for the lymphatic drainage of the face and scalp. Their pattern of drainage is very similar to the area of distribution of the arteries near their location.

Beginning posteriorly these groups (Fig. 8.186) are:

occipital nodes near the attachment of the trapezius muscle to the skull and associated with the occipital artery—lymphatic drainage is from the posterior scalp and neck;

mastoid nodes (retroauricular/posterior auricular nodes) posterior to the ear near the attachment of the sternocleidomastoid muscle and associated with the posterior auricular artery—lymphatic drainage is from the posterolateral half of the scalp;

pre-auricular and parotid nodes anterior to the ear and associated with the superficial temporal and transverse facial arteries—lymphatic drainage is from the anterior surface of the auricle, the anterolateral scalp, the upper half of the face, the eyelids, and the cheeks;

submandibular nodes inferior to the body of mandible and associated with the facial artery—lymphatic drainage is from structures along the path of the facial artery as high as the forehead, as well as the gingivae, the teeth, and the tongue;

submental nodes inferior and posterior to the chin—lymphatic drainage is from the center part of the lower lip, the chin, the floor of the mouth, the tip of the tongue, and the lower incisor teeth.

Lymphatic flow from these superficial lymph nodes passes in several directions:

drainage from the occipital and mastoid nodes passes to the superficial cervical nodes along the external jugular vein;

drainage from the pre-auricular and parotid nodes, the submandibular nodes, and the submental nodes passes to the deep cervical nodes.

Superficial cervical lymph nodes

The superficial cervical nodes are a collection of lymph nodes along the external jugular vein on the superficial surface of the sternocleidomastoid muscle (Fig. 8.186). They primarily receive lymphatic drainage from the posterior and posterolateral regions of the scalp through the occipital and mastoid nodes, and send lymphatic vessels in the direction of the deep cervical nodes.

Deep cervical lymph nodes

The deep cervical nodes are a collection of lymph nodes that form a chain along the internal jugular vein (Fig. 8.186). They are divided into upper and lower groups where the intermediate tendon of the omohyoid muscle crosses the common carotid artery and the internal jugular vein.

The most superior node in the upper deep cervical group is the jugulodigastric node (Fig. 8.186). This large node is where the posterior belly of the digastric muscle crosses the internal jugular vein and receives lymphatic drainage from the tonsils and tonsillar region.

Another large node, usually associated with the lower deep cervical group because it is at or just inferior to the intermediate tendon of the omohyoid muscle, is the jugulo-omohyoid node (Fig. 8.186). This node receives lymphatic drainage from the tongue.

The deep cervical nodes eventually receive all lymphatic drainage from the head and neck either directly or through regional groups of nodes.

From the deep cervical nodes, lymphatic vessels form the right and left jugular trunks, which empty into the right lymphatic duct on the right side or the thoracic duct on the left side.

In the clinic

Clinical lymphatic drainage of the head and neck

Enlargement of the neck lymph nodes (cervical lymphadenopathy) is a common manifestation of disease processes that occur in the head and neck. It is also a common manifestation of diffuse diseases of the body, which include lymphoma, sarcoidosis, and certain types of viral infection such as glandular fever and human immunodeficiency virus (HIV) infection.

Evaluation of cervical lymph nodes is extremely important in determining the nature and etiology of the primary disease process that has produced nodal enlargement.

Clinical evaluation includes a general health assessment, particularly relating to symptoms from the head and neck. Examination of the nodes themselves often gives the clinician a clue as to the nature of the pathological process.

Soft, tender, and inflamed lymph nodes suggest an acute inflammatory process, which is most likely to be infective.

Firm multinodular large-volume rubbery nodes often suggest a diagnosis of lymphoma.

Examination should also include careful assessment of other nodal regions, including the supraclavicular fossae, the axillae, the retroperitoneum, and the inguinal regions.

Further examination may include digestive tract endoscopy, chest radiography, and body CT scanning.

Most cervical lymph nodes are easily palpable and suitable for biopsy to establish a tissue diagnosis. Biopsy can be performed using ultrasound for guidance and good samples of lymph nodes may be obtained.

The lymphatic drainage of the neck is somewhat complex, clinically. A relatively simple “level” system of nodal enlargement has been designed that is extremely helpful in evaluating lymph node spread of primary head and neck tumors. Once the number of levels of nodes are determined, and the size of the lymph nodes, the best mode of treatment can be instituted. This may include surgery, radiotherapy, and chemotherapy. The lymph node level also enables a prognosis to be made. The levels are as follows:

Level 1—from the midline of the submental triangle up to the level of the submandibular gland.

Level 2—from the skull base to the level of the hyoid bone anteriorly from the posterior border of the sternocleidomastoid muscle.

Level 3—the inferior aspect of the hyoid bone to the bottom cricoid arch and anterior to the posterior border of the sternocleidomastoid up to the midline.

Level 4—from the inferior aspect of the cricoid to the top of the manubrium of sternum and anterior to the posterior border of the sternocleidomastoid muscle.

Level 5—posterior to sternocleidomastoid muscle and anterior to the trapezius muscle above the level of the clavicle.

Level 6—below the hyoid bone and above the jugular (sternal) notch in the midline.

Level 7—below the level of the jugular (sternal) notch.

First part

On each side, the anterior line of attachment of the lateral pharyngeal wall begins superiorly on the posterior edge of the medial pterygoid plate of the sphenoid bone just inferior to where the pharyngotympanic tube lies against this plate. It continues inferiorly along the edge of the medial plate of the pterygoid process and onto the pterygoid hamulus. From this point, the line descends along the pterygomandibular raphe to the mandible where this part of the line terminates.

The pterygomandibular raphe is a linear cord-like connective tissue ligament that spans the distance between the tip of the pterygoid hamulus and a triangular roughening immediately posterior to the third molar on the mandible. It joins a muscle of the lateral pharyngeal wall (superior constrictor) with a muscle of the lateral wall of the oral cavity (buccinator).

Second part

The second part of the line of attachment of the lateral pharyngeal wall is related to the hyoid bone. It begins on the lower aspect of the stylohyoid ligament, which connects the tip of the styloid process of the temporal bone to the lesser horn of the hyoid bone. The line continues onto the lesser horn and then turns and runs posteriorly along the entire upper surface of the greater horn of the hyoid where it terminates.

Third part

The most inferior and third part of the line of attachment of the lateral pharyngeal wall begins superiorly on the superior tubercle of the thyroid cartilage, and descends along the oblique line to the inferior tubercle.

From the inferior tubercle, the line of attachment continues over the cricothyroid muscle along a tendinous thickening of fascia to the cricoid cartilage where it terminates.

Constrictor muscles

The three constrictor muscles on each side are major contributors to the structure of the pharyngeal wall (Fig. 8.190 and Table 8.17) and their names indicate their position—superior, middle, and inferior constrictor muscles. Posteriorly, the muscles from each side are joined together by the pharyngeal raphe. Anteriorly, these muscles attach to bones and ligaments related to the lateral margins of the nasal and oral cavities and the larynx.

Fig. 8.190 Constrictor muscles of the pharynx. A. Lateral view. B. Posterior view.

Table 8.17 Constrictor muscles of the pharynx

The constrictor muscles overlap each other in a fashion resembling the walls of three flower pots stacked one on the other. The inferior constrictors overlap the lower margins of the middle constrictors and, in the same way, the middle constrictors overlap the superior constrictors.

Collectively, the muscles constrict or narrow the pharyngeal cavity.

When the constrictor muscles contract sequentially from top to bottom, as in swallowing, they move a bolus of food through the pharynx and into the esophagus.

All of the constrictors are innervated by the pharyngeal branch of the vagus nerve [X].

Longitudinal muscles

The three longitudinal muscles of the pharyngeal wall (Fig. 8.191 and Table 8.18) are named according to their origins—stylopharyngeus from the styloid process of the temporal bone, salpingopharyngeus from the cartilaginous part of the pharyngotympanic tube (salpinx is Greek for “tube”), and palatopharyngeus from the soft palate. From their sites of origin, these muscles descend and attach into the pharyngeal wall.

Fig. 8.191 Longitudinal muscles of the pharynx. A. Stylopharyngeus muscle. B. Medial view.

Table 8.18 Longitudinal muscles of the pharynx

The longitudinal muscles elevate the pharyngeal wall, or during swallowing, pull the pharyngeal wall up and over a bolus of food being moved through the pharynx and into the esophagus.