5: The Head and Neck

Part 5
The Head and Neck

Surface anatomy of the neck


The differential diagnosis of lumps in the neck and the effective clinical and surgical management of pathological lesions in the neck require a sound knowledge of the surgical anatomy of the head and neck. From a practical perspective, it is helpful to picture the neck as being made up of two parts:

  1. a posterior portion – comprising the cervical vertebral column, the cervical segment of the spinal cord and the postvertebral musculature;
  2. an anterior portion – which includes the prevertebral musculature draped in prevertebral fascia, in front of which lies the centrally located visceral compartment; this portion includes also the right and left carotid sheaths, the submandibular glands and the anterior cervical musculature.

In the midline, from above down, can be felt (Fig. 186):

  1. the hyoid bone – at the level of C3;
  2. the notch of the thyroid cartilage – at the level of C4;
  3. the isthmus of the thyroid cartilage – at levels C4 and C5
  4. the cricothyroid ligament – important in cricothyroid puncture;
  5. the cricoid cartilage – continuous with the trachea at the level of C6;
  6. the rings of the trachea, over the 2nd and 3rd of which lies the isthmus of the thyroid gland (sometimes palpable);
  7. the suprasternal notch.
Image described by caption and surrounding text.

Fig. 186 Structures palpable on the anterior aspect of the neck, together with their corresponding vertebral levels.

Note that the lower border of the cricoid is an important level in the neck; it corresponds not only to the level of the 6th cervical vertebra but also to:

  1. the junction of the larynx with the trachea;
  2. the junction of the pharynx with the oesophagus;
  3. the level at which the inferior thyroid artery enters and the middle thyroid vein leaves the thyroid gland;
  4. the level at which the vertebral artery enters the transverse foramen in the 6th cervical vertebra;
  5. the level at which the superior belly of the omohyoid crosses the carotid sheath;
  6. the level of the middle cervical sympathetic ganglion;
  7. the site at which the carotid artery can be compressed against the transverse process of C6 (the carotid tubercle).

Pressing the jaw laterally against the resistance of one’s hand causes the contralateral sternocleidomastoid to become tense. This muscle demarcates the posterior triangle of the neck (bounded by sternocleidomastoid, trapezius and the clavicle) from the anterior triangle (bounded by the right and left sternocleidomastoids on either side and by the mandible superiorly (Fig. 187).

Diagram of the triangles of the neck displaying a man turning his head leftward having his chin upward, with lines marking the posterior triangle, carotid triangle, muscular triangle, digastric triangle, etc.

Fig. 187 The triangles of the neck.

Clench the jaws vigorously; the platysma then comes into view as a sheet of muscle, passing from the mandible down over the clavicles, lying in the superficial fascia of the neck. The external jugular vein lies immediately deep to the platysma, crosses the surface of the sternocleidomastoid into the posterior triangle, perforates the deep fascia just above the clavicle and enters the subclavian vein. It is readily visible in a thin subject when the latter is straining and is often seen from the audience on a singer’s neck when the singer hits a sustained high note or on the neck of an orthopaedic surgeon when the latter strains to reduce a difficult fracture!

The common carotid artery pulse can be felt by pressing backwards against the prominent anterior tubercle of the transverse process of C6. The line of the carotid sheath can be marked out by a line joining a point midway between the tip of the mastoid process and the angle of the jaw to the sternoclavicular joint. Along this line, the common carotid bifurcates into the external and internal carotid arteries at the level of the upper border of the thyroid cartilage; at this level, the vessels lie within the carotid sheath beneath the investing layer of the deep cervical fascia, where their pulsation is palpable and sometimes visible.

The fascial compartments of the neck (Fig. 188)

A thorough appreciation of the topographical arrangement of the fascial and muscular planes in the anterior aspect of the neck is fundamental to accuracy in the clinical diagnosis of neck lumps, besides being an essential prerequisite to safety and precision in neck surgery.

Transverse section of the neck through C6 displaying the fascial planes and also the contents of the pretracheal fascia, with lines marking the sternothyroid, omohyoid, sternohyoid, investing fascia, etc.
CT scan through the C6 level with lines marking the body of C6, internal jugular vein, common carotid artery, left lobe of thyroid, and trachea.

Fig. 188 (a) Transverse section of the neck through C6, showing the fascial planes and also the contents of the pretracheal fascia (or ‘visceral compartment of the neck’). (b) Computed tomography (CT) scan through the C6 level; compare this with (a).

Tissue planes and fascial layers in the anterior part of the neck

Deep to the skin of the neck is the superficial fascia or panniculus adiposus, which is essentially a layer of subcutaneous fat, more or less homogeneous. The degree of adiposity in this layer varies between individuals; it also varies, to some extent, between the anterior and posterior aspects of the neck in the same individual, being generally somewhat thinner in the front of the neck than in the back. Lying immediately deep to the subcutaneous fat, on either side of the anterior midline, is the platysma, a relatively thin but wide sheet of muscle. The platysma is a feature of the anterolateral part of the neck and does not extend to the back of the neck. Above the level of the hyoid, the medial borders of the right and left platysma muscles are contiguous, whereas, below the hyoid level, they are separated from each other by an interval of 2.5 cm (1 in). The deep fascia can be classified into four parts: investing layer of deep cervical fascia, pretracheal fascia, prevertebral fascia and carotid sheaths (right and left).

Immediately deep to the platysma is the investing layer of deep cervical fascia, the most superficial of the multiple layers of the deep cervical fascia. It invests the neck like a collar. Superiorly, its attachment may be traced circumferentially along the entire length of the lower border of the mandible, the mastoid processes and superior nuchal lines on either side and to the external occipital protuberance in the posterior midline. In the interval between the angle of the mandible and the mastoid process, the investing layer of deep cervical fascia encloses the parotid salivary gland as the parotid fascia.

Inferiorly, the circumferential attachment of the investing layer of deep cervical fascia is to the sternal notch (i.e. the notched, thick upper border of the manubrium sterni), and in continuity, on each side, to the upper surface of the clavicle, the acromion and the corresponding spine of the scapula and thus to the posterior midline. Traced laterally from the anterior midline, between its upper and lower attachments, the investing layer of deep cervical fascia meets, on each side, the medial border of the corresponding sternocleidomastoid muscle and splits to enclose the muscle. Thereafter, it continues posterolaterally as the fascial roof of the posterior triangle of the neck, and, upon reaching the anterior edge of the trapezius muscle, it splits to enclose the trapezius.

In its descent from the lower border of the mandible, the investing layer of deep cervical fascia is firmly adherent to the front of the hyoid body and to the lateral aspects of the greater horns of the hyoid. Thus, all the cervical viscera, major blood vessels and nerves of the neck and all the cervical muscles (with the sole exception of the platysma) come to lie within the sweep of the investing layer of deep cervical fascia.

The external jugular vein runs in the plane between the platysma and the underlying investing layer of deep fascia. It pierces the latter above the clavicle. If the vein is divided here, it is held open by the deep fascia that is attached to its margins, air is sucked into the vein lumen during inspiration and a fatal air embolism may ensue.

Lying immediately deep to the investing layer of deep cervical fascia and running longitudinally on either side of the anterior midline of the neck are the infrahyoid anterior cervical muscles, also known as the strap muscles. On each side of the vertical midline, the strap muscles are disposed in two planes. The superficial plane consists of the sternohyoid and omohyoid muscles lying side by side (sternohyoid medial to omohyoid), and the deep plane consists of the sternothyroid muscle, which extends vertically from the posterior surface of the manubrium sterni to the oblique line of the thyroid cartilage. Extending upwards from the oblique line of the thyroid cartilage to the greater horn of the hyoid is the thyrohyoid muscle, generally regarded as the upward continuation of the sternothyroid muscle.

The deepest layer of the deep cervical fascia is the prevertebral fascia, a relatively dense layer that covers the anterior aspects of the prevertebral musculature and the cervical vertebral column. The prevertebral fascia passes across the vertebrae and prevertebral muscles behind the oesophagus, the pharynx and the great vessels. Above, it is attached to the base of the skull. Laterally, the fascia covers the scalene muscles together with the phrenic nerve, as this lies on scalenus anterior, and the emerging brachial plexus and subclavian artery. These structures carry with them a sheath formed from the prevertebral fascia, which becomes the axillary sheath.

Inferiorly, the fascia blends with the anterior longitudinal ligament of the upper thoracic vertebrae in the posterior mediastinum.

Pus from a tuberculous cervical vertebra bulges behind this dense fascial layer and may form a midline swelling causing the posterior wall of the pharynx to bulge anteriorly. The abscess may also track laterally, deep to the prevertebral fascia, to a point behind the sternocleidomastoid. Rarely, pus has tracked down along the axillary sheath into the arm.

Deep to the strap muscles, and anterior to the prevertebral fascial layer, is the centrally located visceral column of the neck.

Lying lateral to the cervical visceral column, and in front of the prevertebral fascia, are the right and left carotid sheaths. Situated posteromedial to each carotid sheath and anterior to the prevertebral fascia is the ganglionated, cervical sympathetic chain.

The cervical visceral column flanked by the right and left carotid sheaths comprises, most posteriorly, the pharynx and its distal continuation – the oesophagus. The pharyngo‐oesophageal junction, as has been noted, is typically at the level of the lower border of the cricoid cartilage (corresponding to the level of the lower border of the 6th cervical vertebra). Situated in front of the pharynx and oesophagus are, respectively, the larynx and trachea; the laryngotracheal junction being at the same horizontal level as the pharyngo‐oesophageal junction. Lying astride the anterior aspect of the upper trachea is the thyroid isthmus, which on either side of the midline is confluent with the corresponding thyroid lobe. The entire thyroid gland is enveloped in a further layer of deep cervical fascia termed the pretracheal fascia. The pretracheal fascia is itself firmly adherent to the front of the upper trachea behind the isthmus, and, elsewhere, to the sides of the cricoid and thyroid cartilages. Indeed, the encasement of the thyroid by the pretracheal fascia, and the attachment of the latter to the trachea and laryngeal cartilages, is the anatomical basis to the clinical observation that all thyroid swellings move upwards during the second phase of swallowing. During this phase of swallowing, the larynx and trachea ascend. The thyroid gland contained within the pretracheal fascia thus moves upwards obligatorily.

Inferiorly, the pretracheal fascia continues as a thin layer to fuse with the anterior surface of the fibrous pericardium.

The cervical lymph nodes may be broadly categorized into two sets:

  1. superficial cervical lymph nodes (i.e. those that are superficial to the investing layer of deep cervical fascia);
  2. deep cervical lymph nodes (i.e. those that are deep to the investing layer of deep cervical fascia).

Each of these categories is further subdivided into groups based on location and territory of drainage.

The fascial planes of the neck are of considerable importance to the surgeon; they form convenient lines of cleavage through which the surgeon may separate the tissues in operative dissections. Also the fascial layers may serve to delimit the spread of pus in neck infections.

(Additional points of clinical significance concerning the deep cervical fascia are to be found on page 281.)

The thyroid gland

The thyroid is made up of (Fig. 189):

  1. the isthmus – overlying the 2nd and 3rd rings of the trachea;
  2. the lateral lobes – each extending from the side of the thyroid cartilage down to the level of the 6th tracheal ring;
  3. an inconstant pyramidal lobe projecting upwards from the isthmus, usually on the left side, which represents a remnant of the embryological descent of the thyroid.
Thyroid and its blood vessels with lines marking the internal carotid artery, external carotid artery, superior thyroid artery, left lobe of thyroid, middle thyroid vein, interior thyroid artery, etc.

Fig. 189 The thyroid and its blood vessels.

Relations (Fig. 188)

The gland is enclosed in the pretracheal fascia, in turn covered by the strap muscles and overlapped by the sternocleidomastoids. The anterior jugular veins course over the isthmus. When the thyroid enlarges, the strap muscles stretch and adhere to the gland so that, at operation, they often appear to be thin layers of fascia.

On the deep aspect of the thyroid lie the larynx and trachea, with the pharynx and oesophagus behind and the carotid sheath on either side. Two nerves lie in close relationship to the gland; in the groove between the trachea and oesophagus lies the recurrent laryngeal nerve, and deep to the upper pole of the thyroid lies the external branch of the superior laryngeal nerve passing to the cricothyroid muscle.

Blood supply

The endocrine glands, gram for gram, have the richest blood supply of any tissue in the body; the thyroid gland is no exception to this rule.

Three arteries supply and three veins drain the thyroid gland (Fig. 189):

  • the superior thyroid artery – arises from the external carotid and passes to the upper pole;
  • the inferior thyroid artery – arises from the thyrocervical trunk of the 1st part of the subclavian artery and passes behind the carotid sheath to the back of the gland;
  • the thyroidea ima artery – is inconstant; when present, it arises from the aortic arch or the brachiocephalic artery and runs upwards to the inferior aspect of the gland;
  • the superior thyroid vein – drains the upper pole to the internal jugular vein;
  • the middle thyroid vein – drains from the lateral side of the gland to the internal jugular;
  • the inferior thyroid veins – often several; drain the lower pole to the brachiocephalic veins.

As well as these named branches, numerous small vessels pass to the thyroid from the pharynx and trachea so that, even when all the main vessels are tied, the gland still bleeds when cut across during a partial thyroidectomy.


The thyroid develops from a bud, which pushes downwards from the fetal tongue (see Fig. 199). This outgrowth, termed the thyroglossal duct, then descends to its definitive position in the neck. The lower end of the thyroglossal duct proliferates to become the thyroid gland, while the rest of the thyroglossal duct disintegrates and disappears. The origin of the thyroid is, however, commemorated by the foramen caecum, the midline punctum at the junction of the middle and posterior thirds of the tongue, and by the inconstant pyramidal lobe on the isthmus (Fig. 190).

Image described by caption.

Fig. 190 The descent of the thyroid, showing possible sites of ectopic thyroid tissue or thyroglossal cysts, and also the course of a thyroglossal fistula. (The arrow shows the further descent of the thyroid that may take place retrosternally into the superior mediastinum.)

The parathyroid glands (Fig. 192)

These are usually four in number, a superior and inferior on either side; however, the numbers vary from two to six. Ninety per cent are in close relationship to the thyroid, 10% are aberrant, the latter most commonly being the inferior glands.

Posterior aspect of the parathyroid glands depicting its normal sites with lines marking the superior and inferior parathyroid glands, thyroid gland, inferior thyroid artery, trachea, oesophagus, etc.

Fig. 192 The normal sites of the parathyroid glands (posterior aspect).

Each gland is about the size of a split pea and is of a yellowish‐brown colour. The superior parathyroid is more constant in position than the inferior gland. It usually lies at the middle of the posterior border of the lobe of the thyroid above the level at which the inferior thyroid artery crosses the recurrent laryngeal nerve. The inferior parathyroid is most usually situated below the inferior artery near the lower pole of the thyroid gland. The next commonest site is within 1.25 cm (0.5 in) of the lower pole of the thyroid gland. Aberrant inferior parathyroids may descend along the inferior thyroid veins in front of the trachea and may even track into the superior mediastinum in company with thymic tissues, for which there is an embryological explanation (see next section). Less commonly, the inferior gland may lie behind and outside the fascial sheath of the thyroid and be found behind the oesophagus or even in the posterior mediastinum. Only on extremely rare occasions are the glands actually completely buried within thyroid tissue (Fig. 193).

Lateral view of the parathyroid glands with lines marking the abnormal sites of inferior parathyroid, superior parathyroid, usual site of inferior parathyroid in relation to in relation to inferior thyroid artery.

Fig. 193 Normal and abnormal sites of the parathyroid glands (lateral view).


The superior parathyroids differentiate from the 4th pharyngeal (branchial) pouch. The inferior glands develop from the 3rd pouch in company with the thymus (Fig. 194; see Table 4, page 332). As the latter descends, the inferior parathyroids are dragged down with it.

Diagram depicting the derivatives of the branchial pouches with lines marking the Eustachian tube and middle ear (Pouch I), tonsil (Pouch II), inferior parathyroid and thymus (Pouch III), thyroid, etc.

Fig. 194 The derivatives of the branchial pouches. Note that the inferior parathyroid migrates downwards from the 3rd pouch, whereas the superior parathyroid (4th pouch) remains stationary.

Table 4 Derivatives of the branchial system (note the 5th arch disappears).

Arch Nerve Visceral External cleft Internal pouch Floor Cartilage Muscle Artery
I V Lower face External auditory meatus Eustachian tube, middle ear and mastoid antrum Anterior 2/3 tongue Meckel’s, incus and malleus; sphenomandibular ligament Muscles of mastication, anterior belly digastric, tensor palati, tensor tympani Disappears
II VII Grows down to cover remaining clefts to form skin of neck
Palatine tonsil Contributes to anterior tongue; thyroid forms as outgrowth between I and II Stapes, styloid, stylohyoid ligament, upper body and lesser horn of hyoid Muscles of facial expression, posterior belly digastric, stylohyoid, stapedius Disappears

Thymus, inferior parathyroid Posterior 1/3 tongue Greater horn and lower part of body of hyoid Stylopharyngeus Common and internal carotids
IV X (superior laryngeal)

Superior parathyroid
Thyroid cartilage Muscles of pharynx, larynx and palate Right, subclavian; left, aortic arch
VI X (inferior laryngeal)

Outgrowth of lung buds Cricoid cartilage
Pulmonary artery and ductus arteriosus

It is thus easily understood that the inferior parathyroid may be dragged beyond the thyroid into the mediastinum and explains why, although very rarely, parathyroid tissue is found actually within the thymus.

The palate

The palate separates the nasal and buccal cavities and comprises:

  1. the hard palate – which is vault‐shaped and made up of the palatine plate of the maxilla and the horizontal plate of the palatine bone; it is bounded by the alveolar margin anteriorly and laterally, and merges posteriorly with:
  2. the soft palate – hanging as a curtain between the naso‐ and oropharynx; centrally, it bears the uvula on its free posterior edge; laterally, it blends into the palatoglossal and palatopharyngeal arches (respectively, the anterior and posterior pillars of the fauces).

The hard palate is made up of bone, periosteum and a squamous mucosa in which are embedded tiny accessory salivary glands.

The framework of the soft palate is formed by the aponeurosis of the tensor palati muscle, which adheres to the posterior border of the hard palate. To this fibrous sheet are attached the palatine muscles covered by a mucous membrane, which is squamous on its buccal aspect and ciliated columnar on its nasopharyngeal surface.

The sensory supply of the palate is largely from the maxillary division of V, but fibres of IX supply its most posterior part.

Motor innervation to the palatine muscles is from vagus (X) fibres in the pharyngeal plexus (with the qualification that the vagus derives these motor nerve fibres from XI, the cranial accessory nerve). The tensor palati is the exception to this rule and is supplied by the mandibular division of V.

In speaking, swallowing and blowing, the soft palate closes off the nasopharynx from the buccal cavity. If the palate is paralysed, as may occur in brainstem lesions or after diphtheria, the voice is impaired and fluids regurgitate through the nose on swallowing.

The development of the face, lips and palate with special reference to their congenital deformities (Fig. 195)

Around the primitive mouth, or stomodaeum, develop the following:

  1. the frontonasal process, which projects down from the cranium. Two olfactory pits develop in it and rupture into the pharynx to form the nostrils. Definitively, this process forms the nose, the nasal septum, nostrils, the philtrum of the upper lip (the small midline depression) and the premaxilla – the V‐shaped anterior portion of the upper jaw which usually bears the four incisor teeth;
  2. the maxillary processes on each side, which fuse with the frontonasal process and become the cheeks, upper lip (exclusive of the philtrum), upper jaw and palate (apart from the premaxilla);
  3. the mandibular processes, which meet in the midline to form the lower jaw.
Image described by caption and surrounding text.

Fig. 195 The ventral aspect of a fetal head showing the three processes, frontonasal, maxillary and mandibular, from which the face, nose and jaws are derived.

Abnormalities of this complex fusion process are numerous and constitute one of the commonest groups of congenital deformities. It is estimated that one child in 600 in England is born with some degree of either cleft lip or cleft palate (Fig. 196).

Illustration displaying unilateral cleft lip, bilateral cleft lip, facial cleft, and cleft lower lip (top) and partial clefts of palate, unilateral complete cleft palate, and bilateral complete cleft palate (bottom).

Fig. 196 Types of (a) cleft lip and (b) cleft palate.

Frequently, these anomalies are associated with other congenital conditions such as spina bifida or syndactyly (fusion of fingers or toes). Indeed, it is good clinical practice to search a patient with any congenital defect for others.

The following anomalies are associated with defects of fusion of the face:

  1. Macrostoma and microstoma are conditions in which either too little or too great a closure of the stomodaeum occurs.
  2. Cleft upper lip (or ‘hare lip’) – this is only very rarely like the upper lip of a hare, i.e. a median cleft, although this may occur as a failure of development of the philtrum from the frontonasal process. Much more commonly, the cleft is on one or both sides of the philtrum, occurring as failure of fusion of the maxillary and frontonasal processes. The cleft may be a small defect in the lip or may extend into the nostril, split the alveolus or even extend along the side of the nose as far as the orbit. There may be an associated cleft palate.
  3. Cleft lower lip – occurs very rarely but may be associated with a cleft tongue and cleft mandible.
  4. Cleft palate is a failure of fusion of the segments of the palate. The following stages may occur (Fig. 196):

    1. bifid uvula, of no clinical importance;
    2. partial cleft, which may involve the soft palate only or the posterior part of the hard palate also;
    3. complete cleft, which may be unilateral, running the full length of the maxilla and then alongside one face of the premaxilla, or bilateral, in which the palate is cleft with an anterior V separating the premaxilla completely.

  5. Inclusion dermoids may form along the lines of fusion of the face. The most common of these is the external angular dermoid at the lateral extremity of the upper eyebrow. Occasionally, this dermoid extends through the skull to attach to the underlying dura.

The tongue and floor of the mouth

The tongue

The tongue consists of a buccal and a pharyngeal portion separated by a V‐shaped groove on its dorsal surface, the sulcus terminalis. At the apex of this groove is a shallow depression, the foramen caecum, marking the embryological origin of the thyroid (see page 288; Fig. 194). Immediately in front of the sulcus lies a row of large vallate (circumvallate) papillae.

The under‐aspect of the tongue bears a median fold, the frenulum linguae; the mucosa is thin on this surface and the lingual veins can thus be seen on either side of the frenulum. The lingual nerve and the lingual artery are medial to the vein but not visible. More laterally can be seen a fringed fold of mucous membrane termed the plica fimbriata. On either side of the base of the frenulum can be seen the orifice of the submandibular duct on its papilla. Inspect this in a mirror and note the discharge of saliva when you press on your submandibular gland just below the angle of the jaw.


The thick stratified squamous mucosa of the dorsum of the tongue bears papillae over the anterior two‐thirds back as far as the sulcus terminalis. These papillae (particularly the vallate) bear the taste buds. The posterior one‐third has no papillae but carries numerous lymphoid nodules which, with the palatine tonsils and adenoids, make up the lymphoid ring of Waldeyer.

Small glands are scattered throughout the submucosa of the dorsum; these are predominantly serous anteriorly and mucous posteriorly.

The tongue is divided by a median vertical fibrous septum, as indicated on the dorsum by a shallow groove. On each side of this septum are the intrinsic and extrinsic muscles of the tongue (Fig. 197).

Lateral view of the tongue with lines marking the lingual branch of V, stylohyoid and styloglossus, XII, submandibular duct, lingual artery, hyoid, hyoglossus, geniohyoid, genioglossus, and sublingual gland.

Fig. 197 Lateral view of the tongue, its extrinsic muscles and its nerves.

The intrinsic muscles are disposed in vertical, longitudinal and transverse bundles; they alter the shape of the tongue.

The extrinsic muscles move the tongue as a whole. They pass to the tongue from the symphysis of the mandible, the hyoid, styloid process and the soft palate; respectively, the genioglossus, hyoglossus, styloglossus and palatoglossus. The functions of the individual extrinsic muscles can be deduced from their relative positions (Fig. 197). Genioglossus protrudes the tongue, styloglossus retracts it and hyoglossus depresses it. Palatoglossus is, in fact, a palatal muscle and helps to narrow the oropharynx in swallowing.

Blood supply

Blood is supplied from the lingual branch of the external carotid artery. There is little cross‐circulation across the median raphe, which is therefore a relatively avascular plane.

Lymphatic drainage (Fig. 198)

The drainage zones of the mucosa of the tongue can be grouped into three:

  1. the tip drains to the submental nodes;
  2. the anterior two‐thirds drains to the submental and submandibular nodes and thence to the lower nodes of the deep cervical chain along the carotid sheath;
  3. the posterior one‐third drains to the upper nodes of the deep cervical chain, and also to the deeply situated parapharyngeal and retropharyngeal nodes.
Diagram illustrating the lymphatic drainage of the tongue, with lines marking the submental nodes, submandibular nodes, digastric muscle, jugulodigastric node, deep cervical chain, etc.

Fig. 198 The lymphatic drainage of the tongue. Note two points. (i) The anterior part of the tongue tends to drain to the nodes farthest down the deep cervical chain, whereas the posterior part drains to the upper chain. (ii) The anterior two‐thirds of the tongue drain unilaterally, the posterior one‐third bilaterally.

There is a rich anastomosis across the midline between the lymphatics of the posterior one‐third of the tongue so that a tumour on one side readily metastasizes to contralateral nodes. In contrast, there is little cross‐communication in the anterior two‐thirds, where growths more than 1.25 cm (0.5 in) from the midline do not metastasize to the opposite side of the neck until late in the disease.

Nerve supply

The anterior two‐thirds of the tongue receives its sensory supply from the lingual branch of V, which also transmits the gustatory fibres of the chorda tympani (VII).

Common sensation and taste to the posterior one‐third, including the vallate papillae, are derived from the glossopharyngeal nerve (IX). A few fibres of the internal laryngeal branch of the superior laryngeal nerve (branch of X) carry sensory fibres from the very posterior part of the tongue.

All the muscles of the tongue except palatoglossus are supplied by the hypoglossal nerve (XII); palatoglossus, a muscle of the soft palate, is innervated by the pharyngeal branch of the vagus (X).

Development (Fig. 199)

A small nodule, the tuberculum impar, is the first evidence of the developing tongue in the floor of the primitive pharynx. This is soon covered over by the lingual swellings, one on each side, derived from the first branchial arch. These fuse in the midline to form the definitive anterior two‐thirds of the tongue supplied by the lingual nerve (V) and reinforced by the chorda tympani.

Diagram illustrating the stages in the development of the tongue with lines marking the copula, entrance to larynx, tuberculum impar, etc. (left), and foramen caecum and circumvallate papillae (right).

Fig. 199 Stages in the development of the tongue.

Posteriorly, this mass meets the copula (or hypobranchial eminence), a central swelling in the pharyngeal floor that represents the conjunction of the 2nd, 3rd and 4th arches and which forms the posterior one‐third of the tongue (nerve supply glossopharyngeal (IX) and vagus (X)).

The tongue muscles develop from the occipital myotomes, which migrate forwards, dragging with them their nerve supply (XII, the hypoglossal nerve).

The floor of the mouth

The floor of the mouth is formed principally by the mylohyoid muscles. These stretch as a diaphragm from their origin along the mylohyoid line on the medial aspect of the body of the mandible on each side, to their insertion along a median raphe and into the hyoid bone. Thus, together, the right and left mylohyoid muscles form a curved, sheet‐like sling that supports the tongue (Fig. 200). The mylohyoid muscle is an important surgical landmark insofar as it constitutes the boundary between the neck and oral region.

Coronal section of the floor of the mouth with lines marking the mylohyoid, geniohyoid, lingual artery, tongue, hyoglossus, sublingual gland, lingual nerve, anterior bell of digastric, etc.

Fig. 200 Coronal section of the floor of the mouth.

On the lower aspect of this diaphragm, on each side, are the anterior belly of the digastric muscle, the superficial part of the submandibular gland and the submandibular lymph nodes, all covered by the investing layer of deep cervical fascia and platysma.

Lying above mylohyoid are the tongue muscles, as a central mass, with the sublingual salivary gland and the deep part of the submandibular gland and its duct lying beneath the mucosa of the mouth floor on either side.

The pharynx

The pharynx is a musculofascial tube, incomplete anteriorly, which extends from the base of the skull to the oesophagus and which acts as a common entrance to the respiratory and alimentary tracts.

From above downwards, it is made up of three parts (Fig. 201):

  1. the nasopharynx – lying behind the nasal fossae and above the soft palate, its vertical extent being from the basiocciput above to the uvula below;
  2. the oropharynx – lying behind the palatoglossal folds (anterior pillars of the fauces), from the tip of the uvula above to the upper margin of the epiglottis below;
  3. the laryngopharynx – lying behind the larynx, from the level of the upper margin of the epiglottis above to the commencement of the oesophagus below.
Schematic sagittal section through the head and neck depicting the subdivisions of the pharynx, with lines marking the nasopharynx and opening of Eustachian tube, oropharynx, and laryngopharynx.
Interior of the pharynx viewed from behind after removing the posterior wall, with lines marking the piriform fossa, inferior constrictor, tip of hyoid, uvula of soft palate, tensor veli palatini, etc.

Fig. 201 (a) Schematic sagittal section through the head and neck to show the subdivisions of the pharynx. (b) Interior of the pharynx viewed from behind after removing the posterior wall of the pharynx.

The nasopharynx

The nasopharynx lies above the soft palate, which cuts it off from the rest of the pharynx during deglutition and therefore prevents regurgitation of food through the nose.

Two important structures lie in this compartment.

The nasopharyngeal tonsil (‘the adenoids’) consists of a collection of lymphoid tissue beneath the epithelium of the roof and posterior wall of this region. It helps to form a continuous lymphoid ring with the palatine tonsils and the lymphoid nodules on the dorsum of the tongue (Waldeyer’s ring).

The orifice of the pharyngotympanic or auditory tube (Eustachian canal) lies on the side‐wall of the nasopharynx level with the floor of the nose. The posterior lip of this opening is prominent, due to the underlying cartilage of the Eustachian tube, and is termed the Eustachian or pharyngeal cushion, behind which lies the slit‐like pharyngeal recess.

The oropharynx

This part of the pharynx lies behind the mouth and tongue. Its anterior boundaries are the right and left palatoglossal arches (anterior pillars of the fauces) and it extends from the uvula of the soft palate above to the tip of the epiglottis below. Its most important contents are the palatine tonsils, situated in the lateral wall on either side.

The palatine tonsils

The palatine tonsil lies in the tonsillar fossa between the palatoglossal and palatopharyngeal arches (anterior and posterior pillars of the fauces, respectively). The anterior pillar, or palatoglossal arch, forms the boundary between the buccal cavity and the oropharynx; it fuses with the lateral wall of the tongue and contains the palatoglossus muscle. The posterior pillar, or palatopharyngeal arch, blends with the wall of the pharynx and contains the palatopharyngeus (Fig. 202).

Diagram of the palatine tonsil in horizontal section with lines marking the superior constrictor muscle, tonsillar capsule, ascending palatine artery, tonsil, ascending pharyngeal artery, etc.

Fig. 202 Diagram of the palatine tonsil and its relations – in horizontal section.

The floor of the tonsillar fossa is formed by the superior constrictor of the pharynx separated from the tonsil by the tonsillar capsule, which is a thick condensation of the pharyngeal submucosa (the pharyngobasilar fascia). This capsule is itself separated from the superior constrictor by a film of loose areolar tissue.

The palatine tonsil consists of a collection of lymphoid tissue covered by a squamous epithelium, a unique histological combination which makes it easy to ‘spot’ in examinations. This epithelium is pitted by crypts, up to twenty in number, and often bears a deep intratonsillar cleft in its upper part.

The lymphoid material may extend up to the soft palate, down to the tongue or into the anterior faucial pillar. From late puberty onwards this lymphoid tissue undergoes progressive atrophy.

Blood supply is principally from the tonsillar branch of the facial artery entering at the lower pole of the tonsil, although twigs are also derived from the lingual, ascending palatine and ascending pharyngeal arteries.

The venous drainage passes to the pharyngeal plexus. An important constant vein, the paratonsillar vein, descends from the soft palate across the lateral aspect of the tonsillar capsule. It is nearly always divided in tonsillectomy and may give rise to troublesome haemorrhage.

Lymphatic drainage is via lymphatics that pierce the superior constrictor muscle and pass to the nodes along the internal jugular vein, especially the tonsillar or jugulodigastric node at the angle of the jaw. Since this node is affected in tonsillitis it is the most common lymph node in the body to undergo pathological enlargement.

Embryologically, the tonsil derives from the second branchial pouch (Fig. 194).

The laryngopharynx

The laryngopharynx extends from the level of the tip of the epiglottis to the termination of the pharynx in the oesophagus at the level of C6.

The inlet of the larynx, defined by the epiglottis, aryepiglottic folds and the arytenoids, lies anteriorly. The larynx itself bulges into this part of the pharynx leaving a deep recess anterolaterally on either side, the piriform fossa, in which ingested sharp foreign bodies (for example, fish bones) may lodge.

The structure of the pharynx

The pharynx is made up of mucosa, containing mucus‐secreting goblet cells, submucosa, muscle and a loose areolar sheath. The mucosa is a ciliated columnar epithelium in the nasopharynx but elsewhere it is stratified and squamous. Beneath this, the submucosa is thick and fibrous (the pharyngobasilar fascia) and it is this layer which forms the capsule of the tonsil.

The three pharyngeal constrictor muscles (superior, middle and inferior) are arranged like flower pots placed one inside the other, but are open in front at the entries of the nasal, buccal and laryngeal cavities.

Each constrictor muscle is attached anteriorly to the side‐wall of these cavities and fans out to insert into a median raphe along the posterior aspect of the pharynx, extending from the base of the skull to the oesophagus (Fig. 203).

Constrictor muscles of the pharynx with lines marking the oesophagus, inferior constrictor, middle constrictor, superior constrictor, lateral pterygold plate, mylohyoid, cricothyroid muscle, etc.

Fig. 203 The constrictor muscles of the pharynx.

Covering these muscles is a thin areolar layer continuous with that covering the buccinator and hence is termed the buccopharyngeal fascia.

Blood supply

The pharynx receives its arterial supply mainly from the superior thyroid and ascending pharyngeal branches of the external carotid.

A pharyngeal venous plexus lies in the areolar tissue that covers the pharynx and drains into the internal jugular vein.

Nerve supply

The pharyngeal branches of IX and X constitute the principal sensory and motor supply of the pharynx, respectively. The maxillary division of V supplies the sensory innervation of the nasopharynx.

The mechanism of deglutition

The act of swallowing not only conveys food down the oesophagus but also disposes of mucus loaded with dust and bacteria from the respiratory passages. Moreover, during deglutition, the Eustachian auditory tube is opened, thus equalizing the pressure on either side of the ear drum.

Deglutition is a complex, orderly series of reflexes. It is initiated voluntarily but is completed by involuntary reflex actions set up by stimulation of the pharynx. If the pharynx is anaesthetized then normal swallowing cannot take place. The reflexes are co‐ordinated by the deglutition centre in the medulla, which lies near the vagal nucleus and the respiratory centres.

The food is first crushed by mastication and lubricated by saliva. It is a common experience that it is well‐nigh impossible to swallow a pill when the throat is dry. The bolus is then pushed back through the oropharyngeal isthmus by the pressure of the tongue against the palate, assisted by the muscles of the mouth floor.

During swallowing, the oral, nasal and laryngeal openings must be closed off to prevent regurgitation through them of food or fluid; each of these openings is guarded by a highly effective sphincter mechanism.

The nasopharynx is closed by elevation of the soft palate, which shuts against a contracted ridge of superior pharyngeal constrictor, the ridge of Passavant. At the same time, the tensor palati opens the ostium of the Eustachian tube. The oropharyngeal isthmus is partially blocked by contraction of palatoglossus on each side, which narrows the space between the anterior faucial pillars. The residual gap is closed by the dorsum of the tongue wedging into it.

The protection of the larynx is a complex affair, brought about not only by closure of the sphincter mechanism of the larynx but also by tucking the larynx behind the overhanging mass of the tongue and by utilizing the epiglottis to guide the bolus away from the laryngeal entrance. The central nervous component of the swallowing reflex is depressed by narcotics, anaesthesia and cerebral trauma. In these circumstances aspiration of foreign material into the pulmonary tree becomes possible, particularly if the patient is lying on his back or in a head‐up position, an all too common cause of death in these patients

The laryngeal sphincters are at three levels:

  1. the aryepiglottic folds, defining the laryngeal inlet, which are apposed by the aryepiglottic and oblique arytenoid muscles;
  2. the walls of the vestibule of the larynx, which are approximated by the thyroepiglottic muscles;
  3. the vocal cords, which are closed by the lateral cricoarytenoid and interarytenoid muscles.

The larynx is elevated and pulled forwards by the action of the thyrohyoid, stylohyoid, stylopharyngeus, digastric and mylohyoid muscles so that it comes into apposition with the base of the tongue, which is projecting backwards at this phase. While the larynx is raised and its entrance closed there is reflex inhibition of respiration.

The action of the epiglottis has been the subject of much speculation. As the head of the bolus reaches the epiglottis, the latter is first tipped backwards against the pharyngeal wall and momentarily holds up the onward passage of the food. The larynx is then elevated and pulled forwards, drawing with it the epiglottis so that it now stands erect, guiding the food bolus into streams along both piriform fossae and away from the laryngeal orifice, like a rock sticking up into a waterfall. Finally, the epiglottis is seen indeed to flap backwards as a cover over the laryngeal inlet, but this occurs only after the main bolus has passed beyond it. The epiglottis acts as a laryngeal lid at this stage to prevent deposition of fragments of food debris over the inlet of the larynx during re‐establishment of the airway.

The cricopharyngeus then relaxes, allowing the bolus to cross the pharyngo‐oesophageal junction. Fluids may shoot down the oesophagus passively under the initial impetus of the tongue action; semi‐solid or solid material is carried down by peristalsis. The oesophageal transit time is about 15 seconds, relaxation of the cardia occurring just before the peristaltic wave reaches it. Gravity has little effect on the transit of the bolus, which occurs just as rapidly in the lying as in the erect position. It is, of course, quite easy to swallow fluid or solids while standing on one’s head, a well‐known party trick; here, oesophageal transit is inevitably an active muscular process.

Jun 28, 2019 | Posted by in ANATOMY | Comments Off on 5: The Head and Neck
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