Chapter 1. Anatomy

The anatomy of the head and neck is rich in complexity as it is populated with motor and sensory organs, cranial nerves, major arterial and venous structures in a compact three dimensional space. This chapter provides a broad and concise overview to familiarize the novice and yet detailed enough to serve as a reference for the more knowledgeable clinician.

Muscles

The muscles of facial expression develop from the second branchial arch and lie within the skin of the scalp, face, and neck (Figure 1–1).

Occipitofrontalis Muscle

The occipitofrontalis muscle, which lies in the scalp, extends from the superior nuchal line in the back to the skin of the eyebrows in the front. It allows for the movement of the scalp against the periosteum of the skull and also serves to raise the eyebrows.

Orbicularis Oculi Muscle

The orbicularis oculi muscle lies in the eyelids and also encircles the eyes. It helps to close the eye in the gentle movements of blinking or in more forceful movements, such as squinting. These movements help express tears and move them across the conjunctival sac to keep the cornea moist.

Orbicularis Oris Muscle

The orbicularis oris muscle encircles the opening of the mouth and helps to bring the lips together to keep the mouth closed.

Buccinator Muscle

The buccinator muscle arises from the pterygomandibular raphe in the back and courses forward in the cheek to blend into the orbicularis oris muscle in the lips. It helps to compress the cheek against the teeth and thus empties food from the vestibule of the mouth during chewing. In addition, it is used while playing musical instruments and performing other actions that require the controlled expression of air from the mouth.

Platysma Muscle

The platysma muscle extends from the skin over the mandible through the superficial fascia of the neck into the skin of the upper chest, helping to tighten this skin and also to depress the angles of the mouth. Although lying primarily in the neck, it is grouped with the muscles of facial expression.

Arteries

The blood supply of the face is through branches of the facial artery (Figure 1–2). After arising from the external carotid artery in the neck, the facial artery passes deep to the submandibular gland and crosses the mandible in front of the attachment of the masseter muscle. It takes a tortuous course across the face and travels up to the medial angle of the eye, where it anastomoses with branches of the ophthalmic artery. It gives labial branches to the lips, of which the superior labial artery enters the nostril to supply the vestibule of the nose.

The occipital, posterior auricular, and superficial temporal arteries supply blood to the scalp. They all arise from the external carotid artery. The superficial temporal artery gives a branch, the transverse facial artery, which courses through the face parallel to the parotid duct.

Veins

The superficial temporal and maxillary veins join within the substance of the parotid gland to form the retromandibular vein (Figure 1–3). The facial vein joins the anterior division of the retromandibular vein to drain into the internal jugular vein. Additional details about the venous drainage pattern of the scalp and face are provided in the discussion of the veins of the neck. The facial vein communicates with both the pterygoid venous plexus and the veins in the orbit. Each of these has connections to the cavernous sinus, thus allowing infections to spread from the face into the cranium.

Innervation

Sensory Innervation

The sensory innervation of the face is through terminal branches of the trigeminal nerve (V) (Figure 1–4). Two imaginary lines that split the eyelids and the lips help to approximately demarcate the sensory distribution of the three divisions of the trigeminal nerve.

In addition to the skin of the face, branches of the trigeminal nerve (V) are also responsible for carrying sensation from deeper structures of the head, including the eye, the paranasal sinuses, the nose, and the mouth. The details of this distribution are discussed with the orbit and the pterygopalatine and infratemporal fossae.

Ophthalmic Division of the Trigeminal Nerve

The ophthalmic division of the trigeminal nerve (V1) carries sensation from the upper eyelid, the skin of the forehead, and the skin of the nose. Its cutaneous branches, from lateral to medial, are the lacrimal, supraorbital, supratrochlear, and nasal nerves.

Maxillary Division of the Trigeminal Nerve

The maxillary division of the trigeminal nerve (V2) carries sensation from the lower eyelid, the upper lip, and the face up to the zygomatic prominence of the cheek. Its cutaneous branches are the infraorbital, zygomaticofacial, and zygomaticotemporal nerves.

Mandibular Division of the Trigeminal Nerve

The mandibular division of the trigeminal nerve (V3) carries sensation from the lower lip, the lower part of the face, the auricle, and the scalp in front of and above the auricle. Its cutaneous branches are the mental, buccal, and auriculotemporal nerves.

Motor Innervation

The muscles of facial expression are innervated by branches of the facial nerve (VII). After emerging from the stylomastoid foramen, the facial nerve lies within the substance of the parotid gland. Here, it gives off its five terminal branches: (1) The temporal branch courses up to the scalp to innervate the occipitofrontalis and orbicularis oculi muscles. (2) The zygomatic branch courses across the cheek to innervate the orbicularis oculi muscle. (3) The buccal branch travels with the parotid duct and innervates the buccinator and orbicularis oris muscles, and also muscles that act on the nose and upper lip. (4) The mandibular branch innervates the orbicularis oris muscle and other muscles that act on the lower lip. (5) The cervical branch courses down to the neck and innervates the platysma muscle.

The Nasal Cavity

The nose is bounded from above by the cribriform plate of the ethmoid bone and from below by the hard palate. It extends back to the choanae, which allow it to communicate with the nasopharynx. The nasal septum is formed by the perpendicular plate of the ethmoid and the vomer bones. The lateral wall of the nose has three bony projections, the conchae, which increase the surface area of the nasal mucosa and help to create turbulence in the air flowing through the nose. This allows the nose to humidify and clean the inhaled air and also to change the air to body temperature. The spaces between the conchae and the lateral wall of the nose are called the meatuses. The middle meatus typically has a bulge in its lateral nasal wall, the bulla ethmoidalis, which is created by the presence of ethmoidal air cells. This bulge is bounded from below by a groove, the hiatus semilunaris. The mucous membrane of the nasal cavity is primarily ciliated columnar epithelium and is specialized for olfaction in the roof of the nose and on the upper surface of the superior concha.

The Paranasal Sinuses

Several bones that surround the nose are hollow, and the spaces contained within, the paranasal sinuses, are named for the skull bones in which they lie. They are lined by a mucous membrane that is continuous with the nasal mucosa through openings with which the paranasal sinuses communicate with the nose. The presence of the sinuses decreases the weight of the skull and provides resonant chambers for voice. The secretions of the sinuses are carried into the nose through ciliary action.

The frontal sinus drains into the anterior part of the hiatus semilunaris via the infundibulum. The maxillary sinus also drains into the hiatus semilunaris, as do the anterior and middle ethmoidal sinuses. The posterior ethmoidal sinuses drain into the superior meatus. The sphenoid sinus drains into the space above the superior concha called the sphenoethmoidal recess. The inferior end of the nasolacrimal duct opens in the inferior meatus, allowing tears from the conjunctival sac to be carried into the nose. The maxillary sinus lies between the orbit above and the mouth below. The roots of the upper premolar and molar teeth project into the maxillary sinus, often separated from the contents of the sinus only by the mucous membrane that lines the sinus cavity.

Sensory Innervation

The olfactory nerves (I) pass through the cribriform plate of the ethmoid bone into the olfactory bulb lying in the anterior cranial fossa, carrying the sensations of smell from the olfactory mucosa in the roof of the nose (Figure 1–5). General sensory fibers to the nose are provided by the ophthalmic (V1) and maxillary (V2) divisions of the trigeminal nerve. Specifically, the sensory innervation of the mucosa lining the anterior part of the nasal cavity, as well as that surrounding the olfactory mucosa in the roof of the nose, is by the ethmoidal branches of the ophthalmic division of the trigeminal nerve. Sensation from the lateral wall of the nose is carried by the lateral nasal branches of the maxillary division of the trigeminal nerve. Sensation from the nasal septum is carried by the nasopalatine branch of the maxillary division of the trigeminal nerve.

The sensory innervation of the lining of the frontal sinus is by the supraorbital branch of the ophthalmic division of the trigeminal nerve (V1). Sensory innervation of the sphenoid and ethmoid sinuses is by the ethmoidal branches of the ophthalmic division of the trigeminal nerve. Sensory innervation of the maxillary sinus is by the infraorbital branch of the maxillary division of the trigeminal nerve (V2).

Arteries

The rich blood supply of the nasal cavity is primarily from the sphenopalatine branch of the maxillary artery that enters the nose from the pterygopalatine fossa (Figure 1–6). The superior labial branch of the facial artery supplies the vestibule of the nose. In addition, the ophthalmic branch of the internal carotid artery supplies the roof of the nose. All of these vessels anastomose with each other.

Parotid Gland

The parotid gland is wedged into the space between the mandible in front and the temporal bone above and behind. It lies in front of the external auditory meatus. It extends as deep as the pharyngeal wall and is enclosed within a sheath formed by the investing fascia of the neck, which is attached to the zygomatic arch above. The parotid duct passes forward over the masseter muscle and can be palpated just in front of the clenched muscle, about half an inch below the zygomatic arch. It passes into the oral cavity by piercing the buccinator muscle and opens in the buccal mucosa opposite the upper second molar tooth.

Several important structures lie within the capsule of the parotid gland (Figure 1–7). The facial nerve (VII) enters the gland after emerging from the stylomastoid foramen and gives off its terminal branches within the substance of the gland. The external carotid artery ascends up the neck, into the gland, and gives off its two terminal branches—the maxillary and superficial temporal arteries—within the gland. The superficial temporal and maxillary veins come together in the substance of the gland to form the retromandibular vein, which divides into its anterior and posterior divisions as it emerges from the gland.

Submandibular Gland

The submandibular gland lies in the digastric triangle of the neck, below the mylohyoid muscle. Like the parotid gland, it is enclosed within a sheath formed by the investing fascia of the neck that is attached to the mandible above. A part of the gland extends around the posterior, free edge of the mylohyoid muscle to lie above the muscle in the floor of the mouth. The submandibular duct arises from this deep portion of the gland and extends forward, alongside the tongue, to open at the base of the frenulum of the tongue on the submandibular caruncle.

Sublingual Gland

The sublingual gland lies below the tongue in the floor of the mouth. It creates a fold of mucous membrane, the sublingual fold, which lies along the base of the tongue, above the mylohyoid muscle. The gland has multiple ducts that open along the sublingual fold.

Innervation

Secretomotor Innervation

Although the facial nerve (VII) is responsible for almost all the parasympathetic secretomotor innervation of the head, it is interesting to note that the one gland to which it does not provide secretomotor innervation is the very gland in which it is buried. The secretomotor innervation of the parotid gland is by fibers carried on the glossopharyngeal nerve (IX). The preganglionic parasympathetic fibers originate in the inferior salivary nucleus and join the glossopharyngeal nerve (Figure 1–8). They course through the lesser superficial petrosal nerve and the foramen ovale to synapse at the otic ganglion. The postganglionic fibers now join the auriculotemporal branch of the mandibular division of the trigeminal nerve to reach the parotid gland.

The secretomotor innervation of the submandibular and sublingual glands is by fibers carried on the facial nerve (VII). The preganglionic parasympathetic fibers originate in the superior salivary nucleus and join the facial nerve (Figure 1–9). They course through the chorda tympani nerve and the petrotympanic fissure to join the lingual branch of the mandibular division of the trigeminal nerve (V3) in the infratemporal fossa, and they synapse at the submandibular ganglion. Postganglionic fibers coursing to the submandibular gland usually reach the gland directly from this ganglion. Postganglionic fibers coursing to the sublingual gland reach the gland on branches of the lingual nerve.

Sympathetic Innervation

The sympathetic innervation to the salivary glands controls the viscosity of the glandular secretions. The preganglionic neurons originate in the thoracic spinal cord and ascend in the sympathetic trunk to synapse in the superior cervical ganglion in the neck. From here, postganglionic sympathetic fibers travel as plexuses on the external carotid artery and its branches to reach the salivary glands.

The mouth is bounded by the palate above, the mylohyoid muscle below, the buccinator muscles in the cheek on each side, and the palatoglossal arches behind. In addition to the oral cavity proper, the mouth includes the vestibule, which is the space between the cheek and the teeth.

Palate

The hard palate is formed by the palatal process of the maxilla and the horizontal process of the palatine bone, which are covered by a mucous membrane. The soft palate is formed by contributions from a number of muscles.

Muscles of the Soft Palate

Tensor Veli Palatini Muscle

The tensor veli palatini arises from the scaphoid fossa of the sphenoid bone and descends in the lateral wall of the nose, narrowing to a tendon that turns medially around the pterygoid hamulus. It then fans out to become the palatine aponeurosis and attaches to the muscle of the opposite side. Together, the two muscles tense the soft palate for other muscles to act upon it.

Levator Veli Palatini Muscle

The levator veli palatini arises from the petrous part of the temporal bone near the base of the styloid process and from the cartilage of the eustachian tube. It passes between the lowest fibers of the superior pharyngeal constrictor muscle and the highest fibers of the middle pharyngeal constrictor muscle, attaching to the upper surface of the palatine aponeurosis. It helps to elevate the soft palate and, together with the palatopharyngeus and superior pharyngeal constrictor muscles, it closes off the nose from the oropharynx during swallowing.

Palatoglossus Muscle

The palatoglossus muscle arises from the lower surface of the palatine aponeurosis and passes down, in front of the palatine tonsil, to attach to the side of the tongue. It pulls the back of the tongue upward and approximates the soft palate to the tongue, closing off the mouth from the pharynx.

Palatopharyngeus Muscle

The palatopharyngeus muscle also arises from the lower surface of the palatine aponeurosis and passes down, behind the palatine tonsil, to blend into the longitudinal muscle layer of the pharynx. It helps to pull the pharyngeal wall upward during swallowing, and together with the levator veli palatini and superior pharyngeal constrictor muscles, it closes off the nose from the oropharynx.

Musculus Uvulae

The musculus uvulae is a small muscle that helps to elevate the uvula.

Arteries

The blood supply of the palate is from the ascending palatine branches of the facial artery as well as from the palatine branch of the maxillary artery, both of which drop down to the palate from the pterygopalatine fossa by passing through the palatine canal.

Tongue

The anterior two-thirds of the tongue develop separately from the posterior third, and the two parts come together at the sulcus terminalis. The surface of the anterior two-thirds of the tongue is covered by filiform, fungiform, and vallate papillae. The posterior third of the tongue contains collections of lymphoid tissue, the lingual tonsils.

Muscles

The mass of the tongue is made up of intrinsic muscles that are directed longitudinally, vertically, and transversely; these intrinsic muscles help to change the shape of the tongue. Several extrinsic muscles help to move the tongue (Figure 1–10).

Genioglossus Muscle

The genioglossus arises from the genial tubercle on the inside surface of the front of the mandible and passes upward and backward into the tongue. It acts to protrude and depress the tongue.

Hyoglossus Muscle

The hyoglossus arises from the hyoid bone and passes upward to attach to the side of the posterior part of the tongue. It acts to depress and retract the back of the tongue.

Styloglossus Muscle

The styloglossus arises from the styloid process and passes downward and forward through the middle pharyngeal constrictor muscle to attach to the side of the tongue. It acts to elevate and retract the tongue.

Palatoglossus Muscle

The palatoglossus muscle (described previously) acts on the tongue but is considered a muscle of the palate.

Arteries

The blood supply of the tongue is from the lingual branch of the external carotid artery. The lingual artery reaches the tongue by passing behind the posterior edge of the hyoglossus muscle and turning forward into the substance of the tongue, thus coursing medial to the hyoglossus. In contrast, all the other nerves and vessels of the tongue pass forward lateral to the hyoglossus before entering the tongue.

Floor of the Mouth

The floor of the mouth is formed by the mylohyoid muscle upon which lie the geniohyoid muscles (Figure 1–11). The digastric muscle lies immediately below the mylohyoid muscle. Both the geniohyoid and the digastric muscles are discussed with the suprahyoid muscles of the neck. The mylohyoid arises from the similarly named line on the inside surface of the mandible and attaches to the front of the hyoid bone. It is the main support of the structures in the mouth. It helps to elevate the hyoid bone during movements of swallowing and speech. Also, with the infrahyoid muscles holding the hyoid bone in place, the mylohyoid and digastric muscles help to depress the mandible and open the mouth.

The deep part of the submandibular gland and the duct that emerges from it lie above the mylohyoid muscle. The sublingual gland also lies above the mylohyoid. The hypoglossal nerve (XII) enters the mouth from the neck by passing lateral to the hyoglossus muscle and above the free posterior edge of the mylohyoid muscle. It continues in the mouth, inferior to the submandibular duct, and enters the substance of the tongue at its side. The lingual branch of the mandibular division of the trigeminal nerve (V3) enters the mouth from the infratemporal fossa by passing medial to the lower third molar. It initially lies above and lateral to the submandibular duct and then spirals under the duct as it comes to lie above and medial to the duct, where it gives off its terminal branches to the tongue and the floor of the mouth. The glossopharyngeal nerve (IX) passes from the pharynx to the mouth, lies lateral to the bed of the palatine tonsil, and courses into the posterior third of the tongue.

Innervation

Sensory Innervation

Sensation from the palate is carried by branches of the maxillary division of the trigeminal nerve (Figure 1–12). From the front of the hard palate, just behind the incisors, sensation is carried by the incisive branch of the nasopalatine nerve. From the rest of the hard palate and the mucosa lining the palatal aspect of the upper alveolar margins, sensation is carried by the greater palatine nerve. From the soft palate, sensation is carried by the lesser palatine nerve.

Sensation from the tongue is carried by nerves predicated upon the development of the tongue. There are general sensory fibers that carry sensations of touch, pressure, and temperature. In addition, there are special sensory fibers that carry the sensation of taste.

General sensation from the anterior two-thirds of the tongue is carried by the lingual branch of the mandibular division of the trigeminal nerve (V3). General sensation from the posterior third of the tongue is carried by the glossopharyngeal nerve (IX). Taste sensation from the anterior two-thirds of the tongue is carried by the chorda tympani branch of the facial nerve (VII). Taste sensation from the posterior third of the tongue is carried by the glossopharyngeal nerve (IX).

Sensation from the floor of the mouth and the mucosa lining the lingual aspect of the lower alveolar margins is carried by the lingual branch of the mandibular division of the trigeminal nerve (V3). Sensation from the buccal mucosa and the mucosa lining the buccal aspect of the upper and lower alveolar margins is carried by the buccal branch of the mandibular division of the trigeminal nerve (V3). Sensation from the mucosa lining the anterior part of the vestibule, inside the upper lip, and the adjacent mucosa lining the labial aspect of the upper alveolar margins is carried by the infraorbital branch of the maxillary division of the trigeminal nerve (V2). Sensation from the mucosa lining the anterior part of the vestibule, inside the lower lip, and the adjacent mucosa lining the labial aspect of the lower alveolar margins is carried by the mental branch of the inferior alveolar branch of the mandibular division of the trigeminal nerve (V3).

Motor Innervation

All the muscles of the palate are innervated by branches of the vagus nerve (X) except the tensor veli palatini, which is innervated by the mandibular division of the trigeminal nerve (V3). All the muscles of the tongue, extrinsic and intrinsic, are innervated by the hypoglossal nerve (XII) except the palatoglossus muscle, which is considered a muscle of the palate and is therefore innervated by the vagus nerve (X). The mylohyoid muscle and anterior belly of the digastric muscle are innervated by the nerve to the mylohyoid muscle, a branch of the mandibular division of the trigeminal nerve (V3). The posterior belly of the digastric and the stylohyoid muscle are innervated by the facial nerve (VII). The geniohyoid muscle is innervated by fibers from the cervical spinal cord (C1), which are carried to it by the hypoglossal nerve (XII).

The pharynx is a muscular tube that both lies behind and communicates with the nasal, oral, and laryngeal cavities (Figure 1–13). It lies in front of the prevertebral fascia of the neck and is continuous with the esophagus at the level of the cricoid cartilage. From within, it is made of mucosa, pharyngobasilar fascia, pharyngeal muscles, and buccopharyngeal fascia.

The mucosa is lined by ciliated columnar epithelium in the area behind the nasal cavity and by stratified squamous epithelium in the remaining areas. The pharyngobasilar fascia, a fibrous layer, is attached above to the pharyngeal tubercle on the base of the skull. The muscles of the pharynx consist of the circular fibers of the constrictor muscles that surround the longitudinally running fibers of the stylopharyngeus, salpingopharyngeus, and palatopharyngeus muscles.

The buccopharyngeal fascia is a layer of loose connective tissue that separates the pharynx from the prevertebral fascia and allows for the free movement of the pharynx against vertebral structures. This layer is continuous around the lower border of the mandible with the loose connective tissue layer that separates the buccinator muscle from the skin overlying it.

Muscles

The muscular layer of the pharynx is made of inner longitudinal and outer circular layers (Figure 1–14). The longitudinally running muscles help to shorten the height of the pharynx. As the pharyngobasilar fascia is attached to the skull, this shortening results in an elevation of the pharynx and larynx during swallowing. The salpingopharyngeus, stylopharyngeus, and palatopharyngeus muscles contribute to this layer.

The circularly running muscles help to constrict the pharynx, and their sequential contractions propel food downward into the esophagus. The superior pharyngeal constrictor muscle arises from the pterygomandibular raphe, the middle pharyngeal constrictor muscle from the hyoid bone, and the inferior pharyngeal constrictor muscle from the thyroid and cricoid cartilages. From these narrow anterior origins, the fibers of the constrictor muscles fan out as they travel back around the pharynx and attach to the corresponding muscles of the opposite side at the midline pharyngeal raphe. The pharyngeal raphe is attached along its length to the pharyngobasilar fascia and is thus anchored to the pharyngeal tubercle on the base of the skull. The orientation of the constrictor muscle fibers is such that the inferior fibers of one muscle are overlapped on the outside by the superior fibers of the next muscle down, producing a “funnel-inside-a-funnel” arrangement that directs food down in an appropriate fashion.

The narrow anterior attachments of the constrictor muscles, compared with their broad posterior insertion, create gaps in the circular muscle coat that surrounds the pharynx. Structures from without can pass into the pharynx through these gaps.

The gap between the base of the skull and the upper fibers of the superior inferior constrictor muscle allows the eustachian tube and the levator veli palatini muscle into the nasopharynx.

The gap between the lower fibers of the superior pharyngeal constrictor muscle and the upper fibers of the middle pharyngeal constrictor muscle allows the stylopharyngeus muscle and the glossopharyngeal nerve (IX) into the oropharynx.

The gap between the lower fibers of the middle pharyngeal constrictor muscle and the upper fibers of the inferior pharyngeal constrictor muscle allows both the internal laryngeal branch of the vagus nerve (X) and the superior laryngeal branch of the superior thyroid artery into the laryngopharynx and the larynx.

The gap between the lower fibers of the inferior pharyngeal constrictor muscle and the upper fibers of the circular muscle of the esophagus allows both the recurrent laryngeal branch of the vagus nerve (X) and the inferior laryngeal branch of the inferior thyroid artery into the larynx.

Innervation

The innervation of the pharynx is by a group of nerves whose branches form a meshwork of neurons, the pharyngeal plexus, which lies in the wall of the pharynx. The glossopharyngeal nerve (IX), the vagus nerve (X), the maxillary division of the trigeminal nerve (V2), and postganglionic fibers from the sympathetic trunk all contribute to the formation of the pharyngeal plexus.

Sensory Innervation

The sensory innervation of the upper part of the nasopharynx is carried by branches of the maxillary division of the trigeminal nerve (V2). The sensory innervation of the lower part of the nasopharynx, the oropharynx, and the laryngopharynx is carried by the glossopharyngeal nerve (IX). The internal laryngeal branch of the vagus nerve (X) carries sensation from the piriform recesses of the laryngopharynx.

Motor Innervation

Motor innervation of all the muscles of the pharynx, circular and longitudinal, except the stylopharyngeus, is by the pharyngeal branch of the vagus nerve (X), which carries motor fibers that originated in the cranial component of the accessory nerve (XI). The stylopharyngeus muscle is innervated by the glossopharyngeal nerve (IX).

Nasopharynx

The nasopharynx extends from the base of the skull to the level of the soft palate (Figures 1–15 and 1–16). It is continuous with the nasal cavity through the choanae. In its lateral wall, the cartilage of the eustachian tube creates a bulge, the torus tubarius, below which is the opening of the tube. Above and behind this bulge lies a depression called the pharyngeal recess. A collection of lymphoid tissue, the pharyngeal tonsil, lies in the posterior wall and the roof of the nasopharynx. Additional lymphoid tissue, the tubal tonsil, is found around the opening of the eustachian tube. A fold of mucous membrane created by the salpingopharyngeus muscle extends down from the torus tubarius. The nasopharynx is continuous with the oropharynx below.

Oropharynx

The oropharynx extends from the soft palate to the epiglottis (Figures 1–15 and 1–16). It is continuous with the mouth through the oropharyngeal isthmus formed by the palatoglossal muscles on each side. The anterior wall of the oropharynx is formed by the posterior third of the tongue. The mucous membrane of the tongue is continuous onto the epiglottis and creates three glossoepiglottic folds—one in the midline and two placed laterally. The space on either side of the median glossoepiglottic fold is the vallecula.

The lateral wall of the oropharynx has two folds of mucous membrane, the palatoglossal and palatopharyngeal, created by the muscles of the same name, which are described with the muscles of the palate. An encapsulated collection of lymphoid tissue, the palatine tonsil, lies in the triangular recess between these two folds. The blood supply of the palatine tonsil is by a branch of the facial artery. Additional lymphoid tissue, the lingual tonsil, is located under the mucous membrane of the posterior third of the tongue. Together, the tonsillar tissues of the nasopharynx and oropharynx form a ring of lymphoid tissue—Waldeyer's ring—that surrounds the entrances into the pharynx from the nose and the mouth. The oropharynx is continuous with the laryngopharynx below.

Laryngopharynx

The laryngopharynx extends from the epiglottis to the cricoid cartilage (Figures 1–15 and 1–16). It is continuous with the larynx through the laryngeal aditus, which is formed by the epiglottis and the aryepiglottic folds. On either side of these folds and medial to the thyroid cartilage are two pyramidal spaces, the piriform recesses of the laryngopharynx, through which swallowed food passes into the esophagus. The piriform recesses are related to the cricothyroid muscle laterally and the lateral cricoarytenoid muscle medially. The laryngopharynx is continuous with the esophagus below.

Triangles of the Neck

Bounded by the mandible above and the clavicle below, the neck is subdivided by the sternocleidomastoid muscle into an anterior and a posterior triangular region, each of which is further divided into smaller triangles by the omohyoid and digastric muscles (Figure 1–17). The surface markings of these muscles help to visibly define the borders of the triangles of the neck.

Posterior Triangle

The posterior triangle is bounded by the sternocleidomastoid muscle in front, the trapezius muscle behind, and the clavicle below. It is divided by the omohyoid muscle into an occipital triangle and a supraclavicular triangle.

Occipital Triangle

The occipital triangle has a muscular floor formed from above, downward by the semispinalis capitis, splenius capitis, levator scapulae, and scalenus medius muscles. After emerging from behind the sternocleidomastoid muscle, the spinal accessory nerve (XI) courses across the muscular floor of the posterior triangle to pass deep to the trapezius muscle. In addition, the cutaneous nerves of the neck, discussed below, course through the deep fascia of the neck that covers the posterior triangle.

Supraclavicular Triangle

The supraclavicular triangle lies above the middle of the clavicle. It contains the terminal portion of the subclavian artery, roots, trunks, and divisions of the brachial plexus, branches of the thyrocervical trunk, and cutaneous tributaries of the external jugular vein. The cupola of the pleural cavity extends above the level of the clavicle and is found deep to the contents of the supraclavicular triangle.

Anterior Triangle

The anterior triangle is bounded by the sternocleidomastoid muscle behind, the midline of the neck in front, and the mandible above. It is subdivided into submental, digastric, carotid, and muscular triangles.

Submental Triangle

The submental triangle is bounded by the anterior belly of the digastric muscle, the midline of the neck, and the hyoid bone. The mylohyoid muscle forms its floor.

Digastric Triangle

The digastric triangle is bounded by the mandible above and the two bellies of the digastric muscle. In addition, the stylohyoid muscle lies with the posterior belly of the digastric muscle. The mylohyoid and hyoglossus muscles form the floor of this triangle. The submandibular salivary gland is a prominent feature of this area, which is also referred to as the submandibular triangle. The hypoglossal nerve (XII) runs along with the stylohyoid muscle and posterior belly of the digastric muscle, between the hyoglossus muscle and the submandibular gland, on its course into the tongue. The facial vessels course across the triangle, with the facial artery passing deep to the submandibular gland while the facial vein passes superficial to it.

Carotid Triangle

The carotid triangle is bounded by the sternocleidomastoid muscle behind, the posterior belly of the digastric muscle above, and the omohyoid muscle below. Its floor is formed by the constrictor muscles of the pharynx. It contains the structures of the carotid sheath—namely, the common carotid artery as it divides into its external and internal carotid branches, the internal jugular vein and its tributaries, and the vagus nerve (X) with its branches.

Muscular Triangle

The muscular triangle is bounded by the omohyoid muscle above, the sternocleidomastoid muscle below, and the midline of the neck in front. It contains the infrahyoid muscles in its floor. Deep to these muscles are the thyroid and parathyroid glands, the larynx, which leads to the trachea, and the esophagus. The hyoid bone forms the superior attachment for the infrahyoid muscles, and the prominent thyroid cartilage and cricoid cartilage are also contained in this region.

Muscles

Sternocleidomastoid Muscles

The sternocleidomastoid muscles act together to flex the cervical spine while extending the head at the atlantooccipital joint. Acting independently, each muscle turns the head to face upward and to the contralateral side. By virtue of their attachment to the sternum, the sternocleidomastoids also serve as accessory muscles of respiration.

Trapezius Muscles

The trapezius muscles have fibers running in several directions. The uppermost fibers pass downward from the skull to the lateral end of the clavicle and help to elevate the shoulder. The middle fibers pass laterally from the cervical spine to the acromion process of the scapula and help to retract the shoulder. The lowest fibers pass upward from the thoracic spine to the spine of the scapula and help to laterally rotate the scapula, making the glenoid fossa turn upward. This action assists the serratus anterior muscle in rotating the scapula when the arm is abducted overhead.

Scalene Muscles

The scalene muscles attach to the cervical spine and pass downward to insert on the first rib. They are contained within the prevertebral layer of deep fascia and help to laterally bend the cervical spine. The roots of the brachial plexus and the subclavian artery pass between the anterior and middle scalene muscles on their course to the axilla. In contrast, the subclavian vein passes anterior to the anterior scalene muscle as it leaves the neck to pass behind the clavicle and reach the axilla. Also, the phrenic nerve lies immediately anterior to the anterior scalene muscle as it runs down the neck into the thorax.

Infrahyoid Muscles

The infrahyoid muscles, the omohyoid, sternohyoid, sternothyroid, and thyrohyoid, are named for their attachments. Together, they act to depress the hyoid bone and the thyroid cartilage during movements of swallowing and speech.

Suprahyoid Muscles

The suprahyoid muscles, the mylohyoid, stylohyoid, geniohyoid, and digastric, act together to elevate the hyoid bone during movements of swallowing or speech. In addition, with the infrahyoid muscles holding the hyoid bone in place, the suprahyoid muscles help to depress the mandible and open the mouth.

Arteries

The arch of the aorta has three branches: (1) the brachiocephalic artery, (2) the left common carotid artery, and (3) the left subclavian artery. The brachiocephalic artery branches into the right subclavian and right common carotid arteries.

Subclavian Artery

The subclavian artery gives off the vertebral artery, the internal thoracic artery, the thyrocervical trunk, and the costocervical trunk (see Figure 1–2).

Vertebral Artery

The vertebral artery courses up through the transverse foramina of the upper six cervical vertebrae. It enters the vertebral canal, passes through the foramen magnum, and goes on to supply blood to the hindbrain, the midbrain, and the occipital lobe of the forebrain.

Internal Thoracic Artery

The internal thoracic artery leaves the root of the neck and passes into the thorax, where it supplies blood to the anterior chest wall and eventually to the upper part of the anterior abdominal wall through its superior epigastric branch.

Thyrocervical Trunk

The thyrocervical trunk gives off the following branches: (1) the inferior thyroid artery, which supplies blood to the thyroid gland; (2) the transverse cervical artery, which passes backward across the neck to supply blood to the trapezius and rhomboid muscles; and (3) the suprascapular artery, which courses laterally across the neck toward the suprascapular notch and participates in the elaborate anastomosis of vessels that surround the scapula. The inferior thyroid artery has a branch, the inferior laryngeal artery, which enters the larynx by passing between the lowest fibers of the inferior pharyngeal constrictor muscle and the upper fibers of the circular muscle of the esophagus. The inferior thyroid artery anastomoses with the superior thyroid artery, a branch of the external carotid artery.

Costocervical Trunk

The costocervical trunk gives off branches that supply blood to the first two intercostal spaces and the postvertebral muscles of the neck.

Common Carotid Artery

The common carotid artery courses up into the neck and terminates at the level of the thyroid cartilage by dividing into the internal and external carotid arteries. It has no branches.

Internal Carotid Artery

The internal carotid artery also has no branches in the neck. It travels up to the base of the skull, where it enters the carotid canal and passes through the petrous part of the temporal bone and the cavernous sinus before turning sharply upward and backward at the carotid siphon to pierce the dura mater. It supplies blood to the frontal, parietal, and temporal lobes of the forebrain. Its main branch to the head is the ophthalmic artery, which supplies blood to the orbit and the upper part of the nasal cavity.

External Carotid Artery

The external carotid artery is the main source of blood supply to the head and neck (see Figure 1–2). In the neck, it has a number of branches.

Superior Thyroid Artery

The superior thyroid artery passes downward to supply blood to the upper part of the thyroid gland. It has a branch, the superior laryngeal artery, which pierces the thyrohyoid membrane to pass into the larynx. The superior thyroid artery anastomoses with the inferior thyroid artery, a branch of the thyrocervical trunk of the subclavian artery.

Ascending Pharyngeal Artery

The ascending pharyngeal artery supplies blood to the pharynx.

Posterior Auricular Artery

The posterior auricular artery passes upward, behind the auricle, and supplies blood to the scalp.

Occipital Artery

The occipital artery passes upward and backward to supply blood to the scalp on the back of the head.

Facial Artery

The facial artery passes upward and forward, deep to the submandibular salivary gland. It then crosses the mandible, where its pulsations can be palpated just in front of the masseter muscle, to supply blood to the face.

Lingual Artery

The lingual artery passes upward and forward, behind the posterior edge of the hyoglossus muscle, and into the substance of the tongue, to which it supplies blood.

Terminal Branches

The external carotid artery then ascends into the substance of the parotid gland, where it gives off two terminal branches.

Superficial Temporal Artery

The superficial temporal artery crosses the zygomatic arch just in front of the auricle, where its pulsations can be palpated. It then goes on to supply blood to the scalp.

Maxillary Artery

The maxillary artery passes medially into the infratemporal fossa and is responsible for the blood supply to the deep structures of the face and the nose.

Veins

The venous drainage of the head and neck is best understood by comparing it with the arterial distribution described above. Many variations exist in the pattern of venous drainage, but each of the arteries has a vein that corresponds to it (see Figure 1–3).

Retromandibular Vein

The veins that correspond to the two terminal branches of the external carotid artery, the superficial temporal and maxillary veins, come together within the substance of the parotid gland to form the retromandibular vein. At the angle of the mandible, the retromandibular vein divides into an anterior and a posterior division.

External Jugular Vein

The two veins that correspond to the arteries that pass backward from the external carotid artery, the posterior auricular and occipital veins, join the posterior division of the retromandibular vein and become the external jugular vein. In addition, the suprascapular and transverse cervical veins drain into the external jugular vein.

Internal Jugular Vein

The two veins that correspond to the arteries that pass forward from the external carotid artery, the facial and lingual veins, join the anterior division of the retromandibular vein and drain into the internal jugular vein. The internal jugular vein drains blood from the areas to which the internal carotid artery supplies blood. In addition, the superior and middle thyroid veins drain into the internal jugular vein.

Inferior Thyroid Veins

The inferior thyroid veins lie in front of the trachea and drain blood from the isthmus of the thyroid gland into the left brachiocephalic vein as it lies behind the manubrium of the sternum.

Brachiocephalic Vein

The external jugular vein drains into the subclavian vein, which joins the internal jugular vein at the root of the neck to become the brachiocephalic vein. The two brachiocephalic veins come together to form the superior vena cava.

Lymphatics

The superficial lymph nodes of the head and neck are named for their regional location (Figure 1–18). The occipital, retroauricular, and parotid nodes drain lymph from the scalp, auricle, and middle ear. The submandibular nodes receive lymph from the face, sinuses, mouth, and tongue. The retropharyngeal nodes, although not truly superficially located, receive lymph from deeper structures of the head, including the upper parts of the pharynx. All of these regional nodes drain their lymphatic efferents into the deep cervical nodes, which lie along the internal jugular vein. Two of these deep nodes are commonly referred to as the jugulodigastric and the juguloomohyoid nodes. They lie at locations at which the internal jugular vein is crossed by the digastric and omohyoid muscles, respectively. The jugulodigastric node is concerned with the lymphatic drainage of the palatine tonsil; the juguloomohyoid node is concerned primarily with the lymphatic drainage of the tongue. The deep cervical nodes drain their lymph into either the thoracic duct or the right lymphatic duct. The thoracic duct empties into the junction of the left internal jugular vein and the left subclavian vein. The right lymphatic duct drains into a similar location on the right side of the root of the neck.

Innervation

Sensory Innervation

The cutaneous innervation of the anterior skin of the neck is by the ventral rami of cervical spinal nerves that form the cervical plexus (C2–4), whereas the posterior skin of the neck is innervated by the dorsal rami of cervical spinal nerves (C2–5) (see Figure 1–4). The cutaneous branches of the cervical plexus emerge from just behind the sternocleidomastoid muscle, at a point about halfway between its attachments to the sternum and the mastoid process. They are named for the areas of skin from which they carry sensation.

Transverse Cervical Nerve

The transverse cervical nerve turns forward and courses across the neck, with its branches carrying sensation from the anterior neck.

Supraclavicular Nerves

The supraclavicular nerves course down toward the clavicle and carry sensation from the skin of the lower neck, extending from the clavicle in front to the spine of the scapula behind.

Greater Auricular Nerve

The greater auricular nerve courses up toward the auricle, with its branches carrying sensation from the skin of the upper neck, the skin overlying the parotid gland, and the auricle itself.

Lesser Occipital Nerve

The lesser occipital nerve courses upward to carry sensation from the skin of the scalp that lies just behind the auricle.

Motor Innervation

The infrahyoid muscles are innervated by branches of the ansa cervicalis, which is formed by the descending cervical nerve and the descending hypoglossal nerve. The descending cervical nerve (C2 and 3) arises from the cervical plexus. The descending hypoglossal nerve contains fibers from the first cervical spinal nerve, some of which initially joined the hypoglossal nerve (XII) before dropping from that nerve to form the ansa cervicalis (Figure 1–19). Other fibers from the first cervical spinal nerve continue on the hypoglossal nerve and later branch off to supply the thyrohyoid muscle.

Of the suprahyoid muscles, the mylohyoid muscle and the anterior belly of the digastric muscle are innervated by the nerve to the mylohyoid muscle, which is a branch of the inferior alveolar nerve from the mandibular division of the trigeminal nerve (V3). The stylohyoid muscle and the posterior belly of the digastric muscle are innervated by the facial nerve (VII). The geniohyoid muscle is innervated by C1 fibers carried by the hypoglossal nerve (XII).

The prevertebral musculature and the scalene muscles receive motor innervation from direct branches of the cervical plexus. The sternocleidomastoid muscles and the trapezius muscles are innervated by the spinal accessory nerve (XI).

Vagus Nerve

The vagus nerve (X) travels in the carotid sheath with the internal jugular vein and the carotid artery (Figures 1–20 and 1–21). In the neck, it has branches to the larynx, the pharynx, and the heart. The laryngeal and pharyngeal branches of the vagus nerve carry motor fibers that originate in the cranial component of the accessory nerve (XI).

Superior Laryngeal Nerve

The superior laryngeal nerve gives off two branches, the external and the internal laryngeal nerves. The external laryngeal nerve provides motor innervation to the cricothyroid muscle. The internal laryngeal nerve pierces the thyrohyoid membrane to enter the larynx. It carries sensation from the part of the larynx that lies above the vocal folds and also carries sensation from the piriform recess of the laryngopharynx.

Recurrent (Inferior) Laryngeal Nerve

The recurrent (inferior) laryngeal nerve provides motor innervation to all the muscles of the larynx, with the exception of the cricothyroid muscle, as previously described. In addition, it carries sensation from the part of the larynx that lies below the vocal folds and from the upper part of the trachea. It courses up the neck in the groove between the trachea and the esophagus. As a result of the differing development of the aortic arches on the right and left sides of the body, the right recurrent laryngeal nerve passes in front of the right subclavian artery and turns up and back around this vessel to course toward the larynx. In contrast, the left recurrent laryngeal nerve passes into the thorax and lies in front of the arch of the aorta before turning up and back around the aorta, behind the ligamentum arteriosum, to reach the larynx.

Pharyngeal Branches

The pharyngeal branches provide motor innervation to all the muscles of the pharynx, with the exception of the stylopharyngeus muscle, and to all the muscles of the palate, with the exception of the tensor veli palatini muscle.

Thoracic Branches

The cardiac branches descend into the mediastinum and provide parasympathetic innervation to the heart. Additional branches arise in the chest to provide parasympathetic innervation to the lungs.

Sensory Branches

The vagus has sensory branches that serve the meninges and the external ear.

Phrenic Nerve

The phrenic nerve arises from the ventral rami of cervical spinal nerves C3–5 and courses down in the prevertebral fascia, in front of the anterior scalene muscle, into the thorax between the subclavian artery and vein. It provides motor innervation to the diaphragm. In addition, it carries sensation from the mediastinal and diaphragmatic parietal pleura, the pericardium, and the parietal peritoneum under the diaphragm.

Sympathetic Trunk

The sympathetic trunk in the neck is an upward continuation of the thoracic part of the trunk and reaches the base of the skull, lying medial to the carotid sheath in the prevertebral fascia. Unlike the thoracic part of the trunk, which has a sympathetic ganglion associated with each spinal nerve, the cervical part of the trunk has only three ganglia. The inferior cervical ganglion lies near the first rib and is frequently fused with the first thoracic ganglion to form the stellate ganglion. The middle cervical ganglion lies at the level of the cricoid cartilage. The superior cervical ganglion lies at the base of the skull, just below the inferior opening of the carotid canal. The cervical sympathetic ganglia get preganglionic input from fibers that originate in the upper thoracic spinal cord and ascend in the sympathetic trunk to reach the neck. Postganglionic outflow from these ganglia passes to the cervical spinal nerves, the cardiac plexus, the thyroid gland, the pharyngeal plexus, and the neurons that form plexuses around the internal and external carotid arteries as those vessels course up to the head.

Fascial Planes

The deep fascia of the neck is thickened into several well-defined layers that are of clinical significance (Figure 1–22).

Investing Fascia

The investing fascia surrounds the neck, attached below to the sternum and the clavicle, and above to the lower border of the mandible, the zygomatic arch, the mastoid process, and the superior nuchal line of the occipital bone. The fascia splits to enclose the sternocleidomastoid and trapezius muscles and the submandibular and parotid salivary glands.

Prevertebral Fascia

The prevertebral fascia surrounds the prevertebral and postvertebral muscles, and is attached to the ligamentum nuchae in the back. It is attached to the base of the skull above and extends down into the mediastinum below. There is a potential space, the retropharyngeal space, between this fascial layer and the pharynx and esophagus, allowing for the free movement of these structures against the vertebral column. However, this arrangement also provides a communicating space that extends from the base of the skull down into the mediastinum, allowing for infections to easily track in either direction.

Carotid Sheath

The carotid sheath surrounds the carotid arteries, the internal jugular vein, the vagus nerve (X), and the deep cervical lymph nodes.

Visceral Fascia

The visceral fascia surrounds the thyroid and parathyroid glands and the infrahyoid muscles. It extends from its attachment to the thyroid cartilage above to the pericardium below and is fused with the carotid sheath and the investing fascia.

The larynx extends from the epiglottis and the aryepiglottic folds to the cricoid cartilage (Figure 1–23). It communicates with the laryngopharynx above—through the laryngeal aditus—and with the trachea below. Its lateral walls have two infoldings of mucous membrane: the vestibular folds above and the vocal folds below. The space between the two vestibular folds is called the rima vestibuli, and the space between the two vocal folds is called the rima glottidis. The part of the larynx that extends from the aditus to the rima vestibuli is called the vestibule of the larynx, and the part that lies between the rima vestibuli and the rima glottidis is called the ventricle of the larynx. The ventricle has a lateral extension, the saccule, between the vestibular fold and the thyroid cartilage. The mucous membrane of the larynx is primarily ciliated columnar epithelium. The larynx is made of cartilages and ligaments that are essential to its role in phonation.

Cartilages

Thyroid Cartilage

The thyroid cartilage (Adam's apple) makes up the bulk of the larynx, but is deficient posteriorly. It articulates with the cricoid cartilage below, which is narrow in front but taller in the back.

Arytenoid Cartilages

Articulating with the posterior lamina of the cricoid cartilage and lying directly behind the thyroid cartilage are the paired arytenoid cartilages. These cartilages have laterally extending muscular processes that allow for the attachment of several muscles of vocalization, and anteriorly extending vocal processes that allow for the attachment of the vocal ligaments.

Corniculate and Cuneiform Cartilages

The epiglottis forms the roof of the larynx. The aryepiglottic folds contain two additional pairs of cartilages, the corniculate and cuneiform, which add support to the folds.

Ligaments

Thyrohyoid Ligament

The thyrohyoid ligament extends from the upper border of the thyroid cartilage to the hyoid bone above, anchoring the larynx to the hyoid bone and its associated muscles.

Quadrangular Ligament

The quadrangular ligament lies within the aryepiglottic folds, and its lower edge extends into the vestibular folds of the larynx.

Cricothyroid Ligament

The cricothyroid ligament (triangular ligament) extends upward from the upper border of the cricoid cartilage. However, it is not attached to the lower border of the thyroid cartilage. Instead, it ascends medial to the thyroid cartilage and is compressed sagittally, with its top edges forming the vocal ligaments that are attached to the inside of the thyroid cartilage in front and the vocal processes of the arytenoid cartilage behind.

Muscles

The muscles of the larynx change the spatial relationships of the laryngeal cartilages during speech and swallowing.

Posterior Cricoarytenoid Muscle

The posterior cricoarytenoid muscle arises from the posterior aspect of the cricoid cartilage and courses upward and laterally to attach to the muscular process of the arytenoid cartilage. Its contraction pulls the muscular process backward and rotates the arytenoid cartilage around a vertical axis so that the two vocal processes are abducted and the size of the rima glottidis is increased. In addition, the two arytenoid cartilages are approximated, an action that is similar to that of the transverse arytenoid muscle.

Lateral Cricoarytenoid Muscle

The lateral cricoarytenoid muscle arises from the front of the arch of the cricoid cartilage and courses upward and backward to attach to the muscular process of the arytenoid cartilage. Its contraction pulls the muscular processes forward and rotates the arytenoid cartilage around a vertical axis, in a direction opposite to the movement created by the contraction of the posterior cricoarytenoid muscle so that the vocal processes are adducted and the rima glottidis is closed. Additional contraction of the lateral cricoarytenoid muscle from this adducted position of the vocal ligaments, coupled with a relaxation of the transverse arytenoid muscle, pulls the two arytenoid cartilages away from each other, positioning the vocal folds for whispering, with approximated vocal ligaments but an open posterior rima glottidis.

Transverse Arytenoid Muscle

The transverse arytenoid muscle extends between the bodies of the two arytenoid cartilages, bringing them together by its contraction.

Thyroarytenoid Muscle

The thyroarytenoid muscle has fibers that run parallel with the vocal ligaments, attaching to the deep surface of the thyroid cartilage in front and the muscular process of the arytenoid cartilage behind. Its contraction brings the arytenoid and thyroid cartilages closer, decreases the length and tension of the vocal ligaments, and lowers the pitch of the voice. A part of the thyroarytenoid muscle that lies adjacent to the vocal ligament is called the vocalis muscle. Because its fibers attach to the vocal ligaments, this muscle can provide fine control of the tension in the vocal ligaments, allowing for rapid alterations in the pitch of the voice. When the vocalis muscle contracts by itself, without an accompanying contraction of the thyroarytenoid muscle, it can pull on the vocal ligaments, increase the tension in them, and raise the pitch of the voice.

Cricothyroid Muscle

The cricothyroid muscle arises from the front and side of the cricoid cartilage and courses upward and backward to attach to the inferior border of the posterior part of the thyroid cartilage. Its contraction produces a rocking movement at the joints between the thyroid and cricoid cartilages, so that the front of the cricoid is pulled upward and the cricoid cartilage is tilted backward. This moves the arytenoid cartilages farther from the thyroid cartilage and increases the tension in the vocal ligaments, raising the pitch of the voice.

Aryepiglottic Muscle

The aryepiglottic muscle arises from the muscular process of the arytenoid cartilage and extends into the epiglottis within the opposite aryepiglottic fold. Its contraction decreases the size of the laryngeal aditus and, combined with an elevation of the larynx by the suprahyoid muscles and longitudinal muscles of the pharynx as well as the push of the tongue on the epiglottis from above, prevents food from entering the larynx.

Innervation and Blood Supply

The vagus nerve (X) provides sensory and motor innervation to the larynx. These details are discussed with the vagus nerve in the neck. Briefly, sensation from the vestibule and ventricle of the larynx, above the vocal folds, is carried by the internal laryngeal branch of the vagus nerve, and sensation from below the vocal folds is carried by the recurrent laryngeal branch of the vagus nerve. Motor innervation of all the muscles of the larynx is by the recurrent laryngeal branch of the vagus nerve, except the cricothyroid muscle, which is innervated by the external laryngeal branch of the vagus nerve.

The superior laryngeal branch of the superior thyroid artery, a branch of the external carotid artery, supplies blood to the upper half of the larynx. The inferior laryngeal branch of the inferior thyroid artery, a branch of the thyrocervical trunk from the subclavian artery, supplies blood to the lower half the larynx.

The orbit lies between the frontal bone with the anterior cranial fossa above and the maxilla and maxillary sinus below. The sphenoid bone lies behind and separates the orbit from the middle cranial fossa. The zygomatic and sphenoid bones lie lateral to the orbit, and the ethmoid and sphenoid bones lie medial to it. The orbit communicates with the infratemporal fossa through the lateral end of the inferior orbital fissure and with the pterygopalatine fossa through the medial end of this fissure. In addition, the orbit communicates with the middle cranial fossa through the superior orbital fissure and the optic canal, and with the nose through the nasolacrimal canal. The structures in the orbit receive their blood supply from the ophthalmic branch of the internal carotid artery. The corresponding veins form the ophthalmic venous plexus, which communicates in front with the facial vein, behind with the cavernous sinus through the superior orbital fissure, and below with the pterygoid venous plexus through the inferior orbital fissure. The orbit contains the eye surrounded by orbital fat, the lacrimal gland, which lies above and lateral to the eye, the muscles that help move the eye, and the nerves and vessels related to these structures.

Muscles

All of the muscles of the orbit, with the exception of the inferior oblique, arise from the sphenoid bone at or near the opening of the optic canal behind the eye (Figure 1–24). They pass forward to attach to the sclera of the eye, except for the levator palpebrae superioris muscle, which inserts on the upper eyelid. The inferior oblique arises from the anterior and medial part of the floor of the orbit.

Levator Palpebrae Superious Muscle

The levator palpebrae superioris passes over the eye and attaches to the tarsal plate of the upper eyelid. It helps to elevate the eyelid and keep the eye open. A part of this muscle is made of smooth muscle fibers that get sympathetic innervation.

Superior Rectus Muscle

The superior rectus muscle passes over the eye and helps to turn the eye upward. It is assisted in this action by the inferior oblique muscle.

Inferior Rectus Muscle

The inferior rectus muscle passes below the eye and helps to turn the eye downward. It is assisted in this action by the superior oblique muscle.

Medial Rectus Muscle

The medial rectus muscle passes medial to the eye and helps to turn the eye medially.

Lateral Rectus Muscle

The lateral rectus muscle passes lateral to the eye and helps to turn the eye laterally.

Superior Oblique Muscle

The superior oblique muscle first passes around a fibrous pulley, the trochlea, which lies above and medial to the front of the eye. It then turns backward, downward, and laterally to attach to the sclera. Its contraction places the eye in a position of a downward and lateral gaze. In addition, the superior oblique muscle produces torsion of the eye around an anteroposterior axis such that the upper part of the eye is turned medially.

Inferior Oblique Muscle

The inferior oblique muscle passes upward, backward, and laterally from its origin to insert on the sclera. Its contraction places the eye in a position of an upward and lateral gaze. In addition, it produces torsion of the eye around an anteroposterior axis such that the upper part of the eye is turned laterally.

Muscle Testing

During clinical examination, the rectus muscles are tested by asking a patient to follow a target with her or his eyes in the directions of the expected actions of each muscle. The superior oblique muscle is tested for its ability to turn the eye downward, but the eye is first turned medially so that the inferior rectus muscle is unable to participate in this downward movement. Similarly, the inferior oblique muscle is tested by asking a patient to first turn the eye medially and then upward. With the eye placed in a direction of medial gaze, the superior and inferior rectus muscles are unable to assist the obliques as they normally would. In this situation, the superior and inferior oblique muscles are the only muscles that are optimally situated to turn the eye downward or upward, respectively, and are thus isolated and individually tested.

Innervation

The orbit is the location in which the ophthalmic division of the trigeminal nerve (V1) divides into its terminal branches after leaving the middle cranial fossa through the superior orbital fissure (Figure 1–25). The orbit also contains branches of the maxillary division of the trigeminal nerve (V2) and nerves that provide parasympathetic innervation to the lacrimal gland.

Sensory Innervation

Lacrimal Nerve

The lacrimal nerve passes above and lateral to the eye and carries sensation from the lateral part of the upper eyelid.

Frontal Nerve

The frontal nerve passes over the eye and divides into the supratrochlear and supraorbital nerves. The supratrochlear nerve exits the orbit above the trochlea and carries sensation from the skin of the forehead. The supraorbital nerve exits the orbit through the supraorbital notch (foramen) and carries sensation from the skin of the forehead that lies lateral to the area served by the supratrochlear nerve. The supraorbital nerve also carries sensation from the frontal sinuses.

Nasociliary Nerve

The nasociliary nerve passes above and medial to the eye before giving off branches to the nose and the eye. The nasal component is made of the ethmoidal and nasal nerves that carry sensation from the roof of the nasal cavity, the skin of the bridge of the nose down to its tip, and the sphenoid and ethmoid sinuses. The ciliary component is made of the long and short ciliary nerves that carry sensation from the eye and cornea.

Motor Innervation

The orbit also contains nerves that enter the orbit through the superior orbital fissure and innervate the muscles of the eye.

Oculomotor Nerve

The oculomotor nerve (III) innervates the levator palpebrae superioris; the superior, inferior, and medial rectus muscles; and the inferior oblique muscles.

Trochlear Nerve

The trochlear nerve (IV) innervates the superior oblique muscle.

Abducens Nerve

The abducens nerve (VI) innervates the lateral rectus muscle.

Optic Nerve

The optic nerve (II) enters the orbit through the optic canal and is surrounded by the meninges, which fuse with the sclera. As a result of this arrangement, the cerebrospinal fluid in the subarachnoid space can extend up to the back of the sclera along the optic nerve. The nasal retina, which has a temporal field of view, transmits its visual information through optic nerve fibers that decussate at the optic chiasm to the optic tract of the opposite side. The temporal retina, which has a nasal field of view, transmits its visual information through optic nerve fibers that remain in the ipsilateral optic tract. Thus, the left optic tract contains fibers from the temporal retina of the left eye and the nasal retina of the right eye; it is responsible for carrying the visual information of objects that lie to the right of the body. Similarly, the right optic tract contains fibers from the temporal retina of the right eye and the nasal retina of the left eye; it is responsible for carrying the visual information of objects that lie to the left of the body.

Autonomic Nerves

Parasympathetic Nerves

The ciliary muscle and the sphincter pupillae muscle of the eye receive parasympathetic innervation from the oculomotor nerve (III). The preganglionic fibers arise in the Edinger–Westphal nucleus of the oculomotor nerve in the midbrain, travel on that nerve, and reach the ciliary ganglion in the orbit at which they synapse. From the ciliary ganglion, the postganglionic fibers travel on the short ciliary branches of the ophthalmic division of the trigeminal nerve (V1) and reach the eye and its intrinsic muscles. Contraction of the sphincter pupillae muscle decreases the size of the pupillary opening, diminishing the amount of light entering the eye, while at the same time increasing the depth of field through which the eye remains focused. Contraction of the ciliary muscle relieves the tension in the suspensory ligaments of the lens, allows the lens to become more convex, and increases its power. Together, the actions of the intrinsic muscles help with accommodation of the eye.

Sympathetic Nerves

The dilator pupillae muscle of the eye and a part of the levator palpebrae superioris muscle receive sympathetic innervation. The preganglionic neurons originate in the thoracic spinal cord and ascend in the sympathetic trunk to synapse in the superior cervical ganglion in the neck. Postganglionic neurons leave the superior cervical ganglion to ascend as a plexus around the internal carotid artery and then around its ophthalmic branch to reach the orbit. In the orbit, the sympathetic neurons travel on the ciliary branches of the ophthalmic division of the trigeminal nerve (V1) to reach the eye and its dilator pupillae muscle, while the sympathetic neurons to the levator palpebrae superioris muscle reach it on further branches of the ophthalmic artery. Contraction of the dilator pupillae muscle increases the size of the pupillary opening, increasing the amount of light entering the eye. Contraction of the levator palpebrae superioris elevates the upper eyelid; therefore, the loss of either its sympathetic innervation or its innervation by the oculomotor nerve produces ptosis.

The pterygopalatine fossa is a small space that lies directly in front of the pterygoid plates of the sphenoid bone and behind the maxilla. Its floor is formed by the upper end of the palatine canal, its roof by the medial half of the inferior orbital fissure, its lateral wall by the pterygomaxillary fissure, and its medial wall by the sphenopalatine foramen and perpendicular plate of the palatine bone. Through the palatine canal, which opens in the hard palate, the pterygopalatine fossa communicates with the oral cavity below; through the inferior orbital fissure, which opens behind the floor of the orbit, the pterygopalatine fossa communicates with the orbital cavity above; through the pterygomaxillary fissure, the pterygopalatine fossa communicates with the infratemporal fossa that lies lateral to it; and through the sphenopalatine foramen, which opens near the roof of the back of the nose, the pterygopalatine fossa communicates with the nasal cavity that lies medial to it. The maxillary sinus lies in front of the pterygopalatine fossa, whereas the foramen rotundum and the pterygoid canal lead into it from behind.

The maxillary artery enters the pterygopalatine fossa after branching from the external carotid artery in the substance of the parotid gland and passing through the infratemporal fossa and the pterygomaxillary fissure. The pterygopalatine fossa is the location at which the maxillary division of the trigeminal nerve (V2) divides into its terminal branches after it leaves the middle cranial fossa through the foramen rotundum (Figure 1–26). The branches of the maxillary artery essentially match the branches of the maxillary division of the trigeminal nerve that originate in and travel out of the pterygopalatine fossa.

Maxillary Nerve Branches

The branches of the maxillary nerve are all named for the area from which they carry sensation.

Greater Palatine Nerve

The greater palatine nerve courses down through the palatine canal and, on reaching the palate, turns forward to carry sensation from most of the hard palate with the exception of a small area behind the upper incisor teeth. While in the palatine canal, it sends branches that pierce through the bony medial wall of the canal, formed by the perpendicular plate of the palatine bone, and carries sensation from the lateral wall of the nose. These are the lateral nasal nerves.

Lesser Palatine Nerve

The lesser palatine nerve also courses down through the palatine canal, but on reaching the palate, it turns backward to carry sensation from the soft palate.

Infraorbital Nerve

The infraorbital nerve courses up through the inferior orbital fissure and on reaching the orbital floor, it turns forward and runs in a bony canal in the floor of the orbit to emerge on the face through the infraorbital foramen. While running forward in the floor of the orbit, the infraorbital nerve lies in the roof of the maxillary sinus and gives branches that carry sensation from the roots of the upper premolar teeth, the middle superior alveolar nerve, and the roots of the upper canines and incisors, the anterior superior alveolar nerve. Once it reaches the face, the infraorbital nerve carries sensation from an area of skin that extends from the lower eyelid to the upper lip.

Zygomatic Nerve

The zygomatic nerve courses up through the inferior orbital fissure and up the lateral wall of the orbit. It then branches into the zygomaticofacial and zygomaticotemporal nerves, which pierce through the zygomatic bone, turning forward onto the skin of the face and backward onto the temple, respectively, from where they carry sensation.

Posterior Superior Alveolar Nerve

The posterior superior alveolar nerve courses laterally through the pterygomaxillary fissure and, on reaching the infratemporal fossa, pierces the back of the maxilla and carries sensation from the roots of the upper molars.

Nasopalatine Nerve

The nasopalatine nerve courses medially through the sphenopalatine foramen and then over the roof of the nose to reach the nasal septum. Here, it turns forward and downward and travels along the septum to reach the incisive canal, emerging behind the upper incisors. It carries sensation from the nasal septum and the anterior part of the hard palate in an area just behind the upper incisors.

Autonomic Nerves

The pterygoid canal allows the carotid canal behind to communicate with the pterygopalatine fossa in front. It passes forward in the floor of the sphenoid sinus and transmits the nerve of the pterygoid canal (Vidian nerve), which has both sympathetic and parasympathetic components.

Deep Petrosal Nerve

The sympathetic component of the nerve of the pterygoid canal is the deep petrosal nerve, which is composed of postganglionic sympathetic neurons. The preganglionic neurons originate in the thoracic spinal cord and ascend in the sympathetic trunk to synapse in the superior cervical ganglion in the neck. Postganglionic neurons leave the superior cervical ganglion to ascend as a plexus around the internal carotid artery. Some of these postganglionic sympathetic neurons branch off the carotid plexus, in the carotid canal, and form the deep petrosal nerve, which enters the pterygoid canal to reach the pterygopalatine fossa. These sympathetic neurons then join branches of the maxillary artery and travel on their walls. Because these are postganglionic neurons that reach the pterygopalatine fossa, they do not synapse in the pterygopalatine ganglion.

Greater Superficial Petrosal Nerve

The parasympathetic component of the nerve of the pterygoid canal is the greater superficial petrosal nerve, which is composed of preganglionic parasympathetic neurons. These originate in the lacrimal nucleus of the facial nerve (VII) and course within the petrous part of the temporal bone before emerging on its superior surface as the greater superficial petrosal nerve, which then turns down into the carotid canal and forward into the pterygoid canal to reach the pterygopalatine fossa (Figure 1–27). There, the preganglionic parasympathetic neurons synapse in the pterygopalatine ganglion. The postganglionic parasympathetic neurons then join branches of the maxillary division of the trigeminal nerve (V2) and reach mucous secreting glands in the paranasal sinuses, the palate, and the nose, to which they are secretomotor. Some postganglionic parasympathetic neurons travel on the zygomatic branch of the maxillary division of the trigeminal nerve (V2) as it courses up the lateral wall of the orbit. When the zygomatic nerve leaves the orbit by piercing through the zygomatic bone, the postganglionic parasympathetic neurons leave the zygomatic nerve, continue up the lateral wall of the orbit, and join the lacrimal branch of the ophthalmic division of the trigeminal nerve to reach the lacrimal gland, to which they are secretomotor.

The infratemporal fossa lies between the mandible laterally and the lateral pterygoid plate of the sphenoid bone medially. The maxilla lies in front and the petrous part of the temporal bone behind. It is bounded above by the base of the skull and extends down to the level of the angle of the mandible. It communicates with the temporal fossa above and with the pterygopalatine fossa medial to it. The maxillary sinus lies in front of it and the temporomandibular joint behind. The maxillary artery gives off several branches here, before passing into the pterygopalatine fossa. The infratemporal fossa is the location at which the mandibular division of the trigeminal nerve (V3) divides into its terminal branches after leaving the middle cranial fossa through the foramen ovale (Figure 1–28).

Muscles

The muscles of the infratemporal fossa are responsible for movements of mastication (Figure 1–29).

Temporalis Muscle

The temporalis muscle arises from the temporal bone and passes medial to the zygomatic arch to attach to the coronoid process of the mandible. Its anterior fibers elevate the mandible, and its posterior fibers retract the mandible.

Masseter Muscle

The masseter muscle arises from the lower border of the zygomatic arch and attaches to the lateral aspect of the angle of the mandible. Its contraction elevates the mandible.

Lateral Pterygoid Muscle

The lateral pterygoid muscle arises from both the lateral aspect of the lateral pterygoid plate and the sphenoid bone above, attaching to the neck of the mandible and the articular disc of the temporomandibular joint. Its contraction protracts the mandible along with the articular disc.

Medial Pterygoid Muscle

The medial pterygoid muscle arises from the medial aspect of the lateral pterygoid plate and attaches to the medial aspect of the angle of the mandible. Its contraction, like the masseter muscle, elevates the mandible.

Temporomandibular Joint

The temporomandibular joint lies between the head of the mandible and a fossa in the temporal bone. The capsule of the joint is attached to the neck of the mandible below and the margins of the mandibular fossa above. The joint is strengthened on its medial side by the sphenomandibular ligament, on its lateral side by the temporomandibular ligament, and behind by the stylomandibular ligament.

The joint contains a fibrocartilaginous, intracapsular articular disc that divides the joint into upper and lower synovial cavities. Translational movements of the joint, produced by the protraction and retraction of the mandible, occur in the upper joint cavity such that the articular disc moves with the head of the mandible. Rotational movements of the joint, produced by elevation and depression of the mandible, occur in the lower joint cavity such that the mandibular head rotates while the articular disc remains stationary.

Protraction of the mandible is produced primarily by the lateral pterygoid muscle, assisted by the medial pterygoid and masseter muscles, whereas retraction is produced by the posterior fibers of the temporalis muscle. Elevation of the mandible (clenching the teeth) is produced by the anterior fibers of the temporalis, the masseter, and the medial pterygoid muscles. Depression of the mandible (opening the mouth) is produced by the suprahyoid muscles—namely, the geniohyoid, mylohyoid, and digastric muscles, with the infrahyoid muscles serving to hold the hyoid bone in place. As the mouth opens wide, the head of the mandible must be protracted out of the mandibular fossa; this movement is brought about by the lateral pterygoid muscle. Closing the mouth from this position requires an initial retraction of the mandible so that the head of the mandible and the articular disc are replaced into the mandibular fossa by the posterior fibers of the temporalis muscle. Side-to-side movements of the mandible are produced by contractions of the medial and lateral pterygoid muscles from one side, joined by the posterior fibers of the temporalis muscle of the other side, alternating with the opposite set of muscles.

Mandibular Nerve Branches

Unlike the ophthalmic (V1) and maxillary (V2) divisions of the trigeminal nerve, which are purely sensory in their roles, the mandibular division of the trigeminal nerve (V3) has both sensory and motor functions. Its motor branches supply all the muscles of mastication, and also the tensor veli palatini muscle, the tensor tympani muscle, the mylohyoid muscle, and the anterior belly of the digastric muscle. These are all muscles that develop from the first branchial arch. The mandibular division of the trigeminal nerve reaches the infratemporal fossa through the foramen ovale and gives off branches that carry sensation from the areas for which they are named.

Buccal Nerve

The buccal nerve, which courses into the cheek, pierces the buccinator muscle but does not innervate it. This nerve carries sensation from the skin over the cheek and the mucous membrane within.

Lingual Nerve

The lingual nerve courses into the tongue and carries general sensation from the anterior two-thirds of the tongue. The chorda tympani branch of the facial nerve (VII) reaches the infratemporal fossa by passing through the petrotympanic fissure and joins the lingual nerve. It contains preganglionic parasympathetic fibers from the superior salivary nucleus that are secretomotor to the submandibular and sublingual salivary glands. It also contains fibers that carry the sensation of taste from the anterior two-thirds of the tongue. Additional details of the chorda tympani and the lingual nerve are described in the sections on the salivary glands and the mouth.

Inferior Alveolar Nerve

The inferior alveolar nerve courses into the mandibular canal and carries sensation from the roots of the lower teeth. It emerges onto the face through the mental foramen as the mental nerve and carries sensation from the lower lip and the skin of the chin. Before it enters the mandible, the inferior alveolar nerve gives off a motor branch, the nerve to the mylohyoid muscle, which innervates the mylohyoid and anterior belly of the digastric muscles.

Auriculotemporal Nerve

The auriculotemporal nerve courses backward, deep to the temporomandibular joint, and ascends onto the scalp, in front of and above the auricle, to carry sensation from that area. In the infratemporal fossa, the auriculotemporal nerve is split by the middle meningeal branch of the maxillary artery. The preganglionic parasympathetic fibers for the secretomotor pathway to the parotid gland originate in the inferior salivary nucleus, travel on the lesser superficial petrosal branch of the glossopharyngeal nerve, and synapse at the otic ganglion. Postganglionic fibers from the otic ganglion, which lies just below the foramen ovale, join the auriculotemporal nerve to reach the parotid gland. Additional details are described in the section on salivary glands.

Maxillary Artery

The maxillary artery, a branch of the external carotid artery, courses into the infratemporal fossa and passes through the pterygomaxillary fissure to reach the pterygopalatine fossa. It can pass either superficially or deep to the lateral pterygoid muscle and supplies blood, through several branches, to the structures that lie in the infratemporal fossa.

One branch, the inferior alveolar artery, enters the mandibular canal with the corresponding nerve. Another branch, the middle meningeal artery, splits the auriculotemporal nerve and passes through the foramen spinosum to enter the middle cranial fossa. The deep temporal arteries course up to the temporalis muscle, lying between the muscle and the skull.

Pterygoid Venous Plexus

The veins that correspond to the branches of the maxillary artery form a plexus in the infratemporal fossa, which is continuous with the plexus of veins in the pterygopalatine fossa, and is collectively called the pterygoid venous plexus. The pterygoid venous plexus communicates with the ophthalmic venous plexus through the inferior orbital fissure and with the cavernous sinus through the foramen ovale and rotundum. The interconnections of these venous plexuses among themselves and with the facial vein are described in the section on the face.

The cranial nerves are depicted in Figure 1–30.

Olfactory Nerve

The olfactory nerve (I) carries the sensation of smell. It is solely a sensory nerve. Its fibers pass through the cribriform plate of the ethmoid bone into the olfactory bulb lying in the anterior cranial fossa, carrying the sensations of smell from the olfactory mucosa in the roof of the nose. From the olfactory bulb, the olfactory tracts pass back to the cerebrum.

Optic Nerve

The optic nerve (II), which is also only a sensory nerve, carries visual information from the eye. Its fibers originate from the ganglion cells of the retina and leave the orbital cavity through the optic canal. Fibers from the nasal retina decussate at the optic chiasm, which lies just above the pituitary gland. The optic tract passes backward from the chiasm and around the midbrain to reach the lateral geniculate body, from where most fibers pass to the visual cortex.

Oculomotor Nerve

The oculomotor nerve (III) innervates muscles that move the eye. It is solely a motor nerve. In addition, it has a parasympathetic role as described below. Its fibers originate in the midbrain and pass medial to the cerebral peduncles, through the interpeduncular cistern and between the posterior cerebral and superior cerebellar branches of the basilar artery. It then passes through the lateral wall of the cavernous sinus and enters the orbit through the superior orbital fissure, where it innervates the levator palpebrae superioris, the inferior oblique, and the superior, medial, and inferior rectus muscles.

Trochlear Nerve

The trochlear nerve (IV) innervates one muscle, the superior oblique, which moves the eye. It is solely a motor nerve. It is the only cranial nerve that arises from the posterior aspect of the brain and it has a long intracranial course. It runs forward around the cerebral peduncles, lying medial to the tentorium cerebelli. It then passes through the lateral wall of the cavernous sinus and enters the orbit through the superior orbital fissure, where it innervates the superior oblique muscle.

Trigeminal Nerve

The trigeminal nerve (V) is the main sensory nerve for the face and deeper structures. It is both a sensory and a motor nerve. It innervates all the muscles of mastication and other muscles that are derived from the first branchial arch, including the tensor tympani muscle. In addition, it allows postganglionic parasympathetic fibers to travel on its branches to reach their target organs in the head. Its fibers arise from the anterolateral surface of the pons and course forward through the posterior cranial fossa to the trigeminal ganglion, which lies at the apex of the petrous part of the temporal bone in a dural cave. It is here that the cell bodies of the first-order sensory neurons from all sensory branches of the trigeminal nerve are located. The three divisions of the trigeminal nerve separate at the trigeminal ganglion.

Divisions of the Trigeminal Nerve

Ophthalmic Nerve

The ophthalmic division of the trigeminal nerve (V1) continues forward in the lateral wall of the cavernous sinus and passes through the superior orbital fissure to enter the orbit.

Maxillary Nerve

The maxillary division of the trigeminal nerve (V2) also continues forward from the ganglion and leaves the middle cranial fossa through the foramen rotundum to enter the pterygopalatine fossa.

Mandibular Nerve

The mandibular division of the trigeminal nerve (V3) continues downward and leaves the middle cranial fossa through the foramen ovale to enter the infratemporal fossa. In addition to the sensory fibers, the motor fibers of the trigeminal nerve leave the pons and, at the trigeminal ganglion, join the mandibular division to course out of the foramen ovale and reach the infratemporal fossa.

Abducens Nerve

The abducens nerve (VI) innervates one muscle that moves the eye. It is solely a motor nerve. Its fibers originate just above the medullary pyramids, have a long intracranial course, and pass into the cavernous sinus. It courses through the middle of the sinus with the internal carotid artery, to which it is approximated. The abducens nerve enters the orbit through the superior orbital fissure, where it innervates the lateral rectus muscle.

Facial Nerve

The facial nerve (VII) innervates the muscles of facial expression and all other muscles that are derived from the second branchial arch. It carries the sensation of taste from the front of the tongue. It is both a sensory and a motor nerve. In addition, it has a parasympathetic role as described below. Its fibers originate at the pontomedullary junction, leave the posterior cranial fossa through the internal acoustic meatus, and enter the facial canal in the petrous part of the temporal bone. It has a motor root, and another part, the nervus intermedius, which is responsible for carrying the sensation of taste and for parasympathetic innervation to glands of the head.

Motor Root of Facial Nerve

The motor root travels through the facial canal and innervates the stapedius muscle. Then, the motor root turns down to emerge from the stylomastoid foramen. Here, it gives off branches to the posterior belly of the digastric and the stylohyoid muscles, whose posterior attachments are adjacent to the stylomastoid foramen. From here, the motor root lies in the substance of the parotid gland and gives off branches to the muscles of facial expression.

Nervus Intermedius

The nervus intermedius part of the facial nerve gives off two branches.

Chorda Tympani

The chorda tympani courses laterally through the petrous part of the temporal bone, enters the middle ear, and courses forward on the inner surface of the eardrum. It leaves the middle ear by turning down through the petrotympanic fissure and reaches the infratemporal fossa. It plays a role in carrying the sensation of taste from the anterior two-thirds of the tongue. In addition, it is secretomotor to the submandibular and sublingual salivary glands. The sensory ganglion for the facial nerve (VII) is the geniculate ganglion, which lies in the petrous part of the temporal bone.

Greater Superficial Petrosal Nerve

The greater superficial petrosal nerve, after coursing laterally in the facial canal, turns medially in the petrous part of the temporal bone and emerges on its superior surface. Then it turns down into the carotid canal and forward into the pterygoid canal to reach the pterygopalatine fossa. It is secretomotor to the mucous glands of the sinuses and also to the lacrimal gland.

Vestibulocochlear Nerve

The vestibulocochlear nerve (VIII) carries sensory information from the vestibule and the cochlea. It is solely a sensory nerve. The vestibular fibers arise from the vestibular ganglion while the cochlear fibers arise from the spiral ganglion, in the petrous part of the temporal bone. The vestibular fibers carry sensory information about the position and angular rotation of the head, both necessary to maintain equilibrium. The cochlear fibers carry the stimuli of hearing. The sensory fibers emerge from the internal acoustic meatus and reach the brain at the pontomedullary junction.

Glossopharyngeal Nerve

The glossopharyngeal nerve (IX) carries sensation from the pharynx and tongue. It also innervates one muscle of the pharynx that develops from the third branchial arch. It is both a sensory and a motor nerve. In addition, it has a parasympathetic role as described below. Its fibers arise from the medulla and leave the posterior cranial fossa through the jugular foramen. Behind the pharynx, it lies with the stylopharyngeus muscle, which it innervates. In the pharynx, the glossopharyngeal nerve contributes to the pharyngeal plexus, carrying sensation from most of the pharynx and the posterior third of the tongue. In addition, as it emerges from the jugular foramen, the glossopharyngeal nerve gives off a branch that enters the petrous part of the temporal bone and reaches the tympanic cavity to form the tympanic plexus which carries sensation from the middle ear. These fibers then emerge on the surface of the petrous part of the temporal bone in the middle cranial fossa as the lesser superficial petrosal nerve which exits the skull through the foramen ovale and is secretomotor to the parotid gland. The sensory ganglia for the glossopharyngeal nerve lie just below the jugular foramen.

Vagus Nerve

The vagus nerve (X) innervates the muscles of the palate, the pharynx, and the larynx, with some exceptions. It carries sensation from the larynx. It is both a sensory and a motor nerve. In addition, it has a parasympathetic role as described below. Its fibers arise from the medulla, are joined by the cranial root of the accessory nerve, and leave the posterior cranial fossa through the jugular foramen. Thus, the laryngeal and pharyngeal branches of the vagus nerve carry motor fibers that originated in the cranial component of the accessory nerve (XI).

Innervation

Motor Innervation

Palate

All the muscles of the palate, except for the tensor veli palatini, are innervated by the vagus nerve (X). The tensor veli palatini is innervated by the mandibular division of the trigeminal nerve (V3).

Pharynx

All the muscles of the pharynx, except for the stylopharyngeus, are innervated by the vagus nerve (X). The stylopharyngeus muscle is innervated by the glossopharyngeal nerve (IX).

Larynx

All the muscles of the larynx, except for the cricothyroid muscle, are innervated by the recurrent laryngeal branch of the vagus nerve (X). The cricothyroid muscle is innervated by the external laryngeal branch of the vagus nerve.

Sensory Innervation

The sensory ganglia for the vagus lie just below the jugular foramen. The superior laryngeal branch of the vagus nerve carries sensation from the upper part of the larynx, above the vocal folds, whereas the recurrent laryngeal branch of the vagus nerve carries sensation from the lower part of the larynx.

Accessory Nerve

The accessory nerve (XI) innervates two muscles in the neck and is solely a motor nerve. It has a cranial root and a spinal root. The fibers of the cranial root arise from the medulla. The fibers of the spinal root originate from the upper spinal cord segments (C1–5) and ascend into the skull to join the cranial root. The two roots separate almost immediately. The fibers of the cranial root join the vagus nerve (X) in the posterior cranial fossa, exit through the jugular foramen, and are distributed in the motor branches of the vagus nerve to the pharynx, the larynx, and the palate. The fibers of the spinal root reach the neck by passing through the jugular foramen and innervate the sternocleidomastoid and trapezius muscles.

Hypoglossal Nerve

The hypoglossal nerve (XII) innervates the muscles of the tongue and is solely a motor nerve. Its fibers arise from the medulla, leave the posterior cranial fossa through the hypoglossal canal, and go on to innervate the extrinsic and intrinsic muscles of the tongue.

Autonomic Innervation

Sympathetic Innervation

The sympathetic innervation of the head and neck is from the thoracic sympathetic outflow. The preganglionic neurons originate in the thoracic spinal cord and ascend in the sympathetic trunk to synapse in the middle and superior cervical ganglia in the neck. From here, postganglionic sympathetic fibers travel as plexuses on the branches of the internal and external carotid arteries to reach target structures in the head and neck.

Parasympathetic Innervation

The oculomotor (III), facial (VII), glossopharyngeal (IX), and vagus (X) nerves are the four cranial nerves that carry the parasympathetic outflow from the brain to most of the body. Parasympathetic innervation of the pelvic organs and lower gastrointestinal tract is from the sacral parasympathetic outflow (S2–4).

Ciliary Ganglion

Preganglionic parasympathetic fibers from the Edinger–Westphal nucleus travel on the oculomotor nerve (III) and synapse at the ciliary ganglion (see Figure 1–24). Postganglionic fibers from the ciliary ganglion join the short ciliary branches of the ophthalmic division of the trigeminal nerve (V1) to reach the ciliary muscle and the sphincter pupillae muscle of the eye.

Pterygopalatine Ganglion

Preganglionic parasympathetic fibers from the lacrimal nucleus travel on the greater superficial petrosal branch of the facial nerve (VII) and synapse at the pterygopalatine ganglion (see Figure 1–27). Postganglionic fibers from the pterygopalatine ganglion join branches of the maxillary division of the trigeminal nerve (V2) to reach the lacrimal gland and the mucous secreting glands of the nose and mouth.

Submandibular Ganglion

Preganglionic parasympathetic fibers from the superior salivary nucleus travel on the chorda tympani branch of the facial nerve (VII) and synapse at the submandibular ganglion (see Figure 1–9). Postganglionic fibers from the submandibular ganglion join the lingual branch of the mandibular division of the trigeminal nerve (V3) to reach the submandibular and sublingual salivary glands.

Otic Ganglion

Preganglionic parasympathetic fibers from the inferior salivary nucleus travel on the lesser superficial petrosal branch of the glossopharyngeal nerve (IX) and synapse at the otic ganglion (see Figure 1–8). Postganglionic fibers from the otic ganglion join the auriculotemporal branch of the maxillary division of the trigeminal nerve (V3) to reach the parotid salivary gland.

Visceral Ganglia

The vagus nerve (X) is the only cranial nerve that leaves the head and neck. It carries preganglionic parasympathetic fibers to the rest of the body, with the exception of the pelvic organs and organs associated with the hindgut. These fibers synapse at ganglia in the walls of the organ being innervated, from where short postganglionic fibers serve their secretomotor role.