This prominent neck landmark has two heads of origin below: that from the sternal manubrium is a rounded tendon, that from the clavicle a flat, fleshy mass (Fig. 6.2). A triangular interval exists between the two above the sternoclavicular joint, and the lower end of the internal jugular vein lies here, where it can be entered by needle or catheter. The manubrial tendon is attached to the front of the bone below the jugular notch; the clavicular head arises from the superior surface of the medial third of the clavicle. The muscle is attached by a tendon to the lateral surface of the mastoid process and by a thin aponeurosis to the lateral half of the superior nuchal line of the occipital bone. The clavicular fibres spiral behind the sternal fibres with the deep aspect of which they blend. The clavicular fibres are directed mainly to the mastoid process, while the sternal fibres run more obliquely chiefly to the occipital bone. The spinal accessory nerve enters the muscle under cover of the lobule of the ear, about 3cm below the tip of the mastoid process, accompanied by a branch to the muscle from the occipital artery. It runs through the deep part of the muscle to emerge from between a third and a half of the way down the posterior border of the muscle.

Sternocleidomastoid is enclosed within a sheath of the investing layer of deep cervical fascia, which splits to surround it (Fig. 6.1). The muscle is crossed superficially by the great auricular nerve, the external jugular vein and the transverse cervical nerve, in that order from above downwards. Deep to the upper half of the muscle lies the cervical plexus; deep to its lower part lies the carotid sheath and its contents, overlying scalenus anterior.

The blood supply of the muscle is from branches of the occipital and superior thyroid arteries.

Nerve supply. By the spinal part of the accessory nerve, from a branch which leaves the nerve proximal to its point of entry into the muscle. The pathway for innervation by the cerebral cortex of the anterior horn cells of the segments concerned (mostly C2 and 3) is disputed; projection to the muscle from either or both hemispheres has been described. Branches from the cervical plexus (C2, 3) carrying proprioceptive fibres enter the muscle directly or by joining the accessory nerve.

Action. Contraction of one muscle tilts the head towards the ipsilateral shoulder, and rotates the head and face to the opposite side. Both muscles acting together from below draw the head forwards. With the head fixed, the muscles can assist in raising the roof of the thorax in forced inspiration.

Test. The face is turned to the opposite side against resistance and the muscle palpated.

The cervical plexus (Fig. 6.3) is formed by loops between the anterior rami of the upper four cervical nerves, after each has received a grey ramus communicans from the superior cervical ganglion. It lies in series with the brachial plexus, on the scalenus medius, behind the prevertebral fascia. It is covered by the upper part of sternocleidomastoid, and does not lie in the posterior triangle. The upper three cervical nerves have meningeal branches for the posterior cranial fossa. C1 fibres ascend with the hypoglossal nerve, C1 and 2 fibres ascend with the vagus nerve and C2 and 3 fibres ascend through the foramen magnum.

Muscular branches. Muscular branches are given off segmentally to the prevertebral muscles (longus capitis, longus colli and the scalenes). Other muscular branches are:

Cutaneous branches. Cutaneous branches of the plexus (Fig. 6.4) supply the front and sides of the neck and contribute to the supply of the scalp, face and chest.

The lesser occipital nerve (C2) is a slender branch that hooks around the accessory nerve and runs up along the posterior border of sternocleidomastoid to supply the posterior part of the upper neck and adjacent scalp behind the auricle. It may contribute to the supply of the auricle.

The great auricular nerve (C2, 3, mostly 2) is a large trunk passing almost vertically upwards over sternocleidomastoid; it is distributed to an area of skin on the face over the angle of the mandible and the parotid gland and to the parotid fascia. It also supplies the skin of the auricle over the whole of its cranial surface and on the lower part of its lateral surface below the external acoustic meatus, and skin over the mastoid region. Branches passing deep to the parotid gland supply the deep layer of the parotid fascia.

The transverse cervical nerve (C2, 3) curves round the posterior border of sternocleidomastoid, perforates the investing fascia and divides into ascending and descending branches that innervate the skin of the front of the neck from chin to sternum. The ascending branch communicates with the cervical branch of the facial nerve.

The supraclavicular nerve (C3, 4, but mostly 4) emerges with the other three nerves at the posterior border of sternomastoid and soon divides into several branches. They are distributed in three main groups (see Fig. 1.8, p. 12). The medial group supply the skin as far down as the sternal angle. The intermediate group proper pass anterior to the clavicle and supply skin as far down as the second rib. The lateral group cross the acromion to supply skin halfway down the deltoid muscle, and pass posteriorly to supply skin as far down as the spine of the scapula.

In addition to the cutaneous branches of the cervical plexus described above, which supply the anterior and lateral skin of the neck, the greater occipital and third occipital nerves from posterior rami of C2 and C3 respectively provide sensory fibres for the back of the neck (Fig. 6.15). The first cervical nerve does not supply any skin. C2 supplies most of the superior part of the neck, extending into the occipital region of the scalp and forwards to the auricle and the face over the parotid gland. C3 supplies the cylindrical part of the neck, C4 extends over the clavicle to the sternal angle, across the top of the shoulder and down to the scapular spine at the back. There is much overlap across dermatome boundary lines.

This arises as the posterior belly, from the digastric groove on the medial surface of the base of the mastoid process (Fig. 6.35). The triangular fleshy belly tapers down to the intermediate tendon, which is held beneath a fibrous sling attached to the junction of the body and the greater horn of the hyoid bone. The tendon is lubricated by a synovial sheath within the fibrous sling. The bifurcated tendon of insertion of stylohyoid which embraces the tendon plays no part in holding it down. The anterior belly lies on the inferior surface of mylohyoid, and connects the intermediate tendon to the digastric fossa on the inner surface of the mandible near the midline.

Nerve supply. The posterior belly is supplied by the facial nerve, by a branch arising between the stylomastoid foramen and the parotid gland, and the anterior belly by the nerve to mylohyoid.

Action. To depress and retract the chin, and to assist the lateral pterygoid in opening the mouth.

This arises from the back of the styloid process, high up near the base of the skull, and slopes down along the upper border of digastric. Its lower end divides to embrace the digastric tendon and is inserted by two slips into the junction of the greater horn and body of the hyoid bone.

Nerve supply. By the facial nerve, by a branch from that to the posterior belly of digastric.

Action. To retract and elevate the hyoid bone when swallowing.

The muscles of each side unite to make a thin sheet forming the ‘diaphragm’ of the floor of the mouth (Fig. 6.6). Each arises from the whole length of the mylohyoid line of its own side on the inner aspect of the mandible from as far back as medial to the third molar tooth to below the mental spines (see Fig. 8.5B, p. 510). The two muscles slope downwards towards each other, and the posterior quarter of each is inserted into the anterior surface of the body of the hyoid bone. In front of this the anterior three-quarters of each interdigitate in a midline raphe which extends from the chin to the hyoid bone.

Nerve supply. By its own nerve, a branch of the inferior alveolar (from the mandibular division of the trigeminal nerve), which arises just before the parent nerve enters the mandibular foramen, pierces the sphenomandibular ligament and runs forward on the inferior surface of the mylohyoid, supplying it and the anterior belly of the digastric.

Action. It forms a mobile but stable floor of the mouth. The two muscles together form a gutter; contraction makes the gutter more shallow, thus elevating the tongue and the hyoid bone as when swallowing or protruding the tongue.

This slender muscle extends from the inferior mental spine (genial tubercle) of the mandible (see Fig. 8.5B, p. 510) to the upper border of the body of the hyoid bone (see Fig. 8.6, p. 512). The two muscles lie side by side between the mylohyoids and the base of the tongue (genioglossus), on the floor of the mouth.

Nerve supply. By a branch from the hypoglossal nerve, consisting of fibres from the C1 nerve and not from the hypoglossal nucleus.

Action. To protract and elevate the hyoid bone in swallowing, or if the hyoid is fixed, to depress the mandible.

This flat strap of muscle is attached to the back of the upper part of the manubrium and the adjoining sternoclavicular joint and clavicle. Its upper attachment is to the lower border of the body of the hyoid bone. The two muscles lie edge to edge at the hyoid bone, but diverge from each other below.

Nerve supply. By a branch from the ansa cervicalis which enters the lower part of the muscle.

This flat strap of muscle lies edge to edge with sternohyoid at its attachment to the lateral part of the inferior border of the hyoid bone (Fig. 6.5). As it descends it diverges somewhat from the sternohyoid and, passing deep to sternocleidomastoid, it comes to lie over the carotid sheath. Where it lies over the internal jugular vein, the muscle fibres are replaced by a flat tendon, a useful guide at operation to the underlying vein. A change of direction now occurs, and the inferior belly runs almost horizontally just above the level of the clavicle to pass back to its attachment to the upper border of the scapula and the transverse scapular ligament. The intermediate tendon and supraclavicular portion of the muscle are bound down close to the clavicle in a fascial sling derived from the deep layer of the investing layer of deep cervical fascia (see Fig. 2.2, p. 39), which results in the angulated course of the muscle.

Nerve supply. The superior root of the ansa cervicalis supplies the superior belly and the ansa supplies the inferior belly.

This is a broader and shorter muscle that lies under cover of the upper ends of sternohyoid and omohyoid. It arises from the greater horn of the hyoid bone, and is inserted into the oblique line of the thyroid cartilage alongside sternothyroid.

Nerve supply. By a branch of the hypoglossal nerve, but the fibres are all ‘hitch-hiking’ from C1.

Broader than sternohyoid and lying deep to it, this muscle is attached lower down than sternohyoid to the posterior surface of the manubrium and the adjacent first costal cartilage. Its upper attachment is to the oblique line of the thyroid cartilage.

Nerve supply. By the ansa cervicalis, which gives a branch to the lower part of the muscle.

They are all depressors of the larynx. Sternothyroid acts directly on the thyroid cartilage, the others act indirectly via the hyoid bone. Depression of the larynx increases the volume of the resonating chambers during phonation and thus affects the quality of the voice. The infrahyoid muscles also oppose the elevators of the larynx (mylohyoid, palatopharyngeus, stylopharyngeus, salpingopharyngeus), enabling them to act progressively and gradually. The infrahyoid muscles prevent ascent of the hyoid bone when the digastric and geniohyoid lower the mandible.

From the facial artery, with veins draining into the facial vein.

To the submandibular lymph nodes.

Secretomotor fibres to the gland have their cell bodies in the submandibular ganglion (see p. 22), which hangs suspended from the lingual nerve on the surface of hyoglossus. The preganglionic fibres pass from cell bodies in the superior salivary nucleus in the pons by way of the nervus intermedius, facial nerve, chorda tympani and the lingual nerve (see pp. 365–366). Postganglionic fibres pass to the submandibular gland and also to the lingual nerve for transmission to the sublingual gland. Sympathetic (vasoconstrictor) fibres come from the plexus around the facial artery.

An ectodermal groove in the floor of the mouth becomes converted into a tunnel whose blind end proliferates to form the secreting acini.

The gland is exposed by a skin crease incision about 4cm below the mandible, which continues through platysma and investing fascia on to the gland, to avoid the marginal mandibular branch of the facial nerve which may lie over the gland (see p. 353). Removal of the gland requires ligation of the facial vein which lies on the gland surface. The facial artery needs to be separated from its groove on the posterosuperior part of the gland, or a segment of the artery removed with the gland. The hypoglossal nerve and lingual nerve need to be safeguarded, the latter particularly when the duct is ligated and divided. The removal of a stone from the duct is carried out from within the mouth by incising the mucous membrane and duct over the stone; the mucosal and duct incisions are not sutured.

The superior thyroid artery, the first branch from the anterior aspect of the external carotid (see p. 342), after giving off its sternocleidomastoid and superior laryngeal branches, pierces the pretracheal fascia as a single vessel to reach the summit of the upper pole. The external laryngeal nerve is immediately behind the artery as the vessel approaches the pole, but they part company as the artery reaches the gland and the nerve descends to supply the cricothyroid muscle. The artery divides on the gland into an anterior branch that runs down to the isthmus and a posterior branch that runs down the back of the lobe and anastomoses with an ascending branch of the inferior thyroid artery from the lower pole. In thyroidectomies the artery is ligated close to the upper pole, or its anterior and posterior branches are ligated instead, to avoid damage to the external laryngeal nerve.

The inferior thyroid artery, from the thyrocervical trunk (see p. 349), arches upwards and medially behind the carotid sheath and then loops downwards to the lower pole. It divides outside the pretracheal fascia into branches that pierce the fascia separately to reach the lower part of the gland. As described above, the recurrent laryngeal nerve has a variable relationship to the artery but always lies behind the pretracheal fascia. Ligating the inferior thyroid artery well lateral to the gland, or carefully ligating its small branches on the surface of the gland, helps to safeguard the nerve. The inferior thyroid artery gives off the ascending cervical artery and small pharyngeal, oesophageal, laryngeal and tracheal branches before its terminal distribution to the thyroid gland; the small inferior laryngeal artery ascends with the recurrent nerve.

A thyroidea ima artery enters the lower part of the isthmus in 3% of individuals. It arises from the brachiocephalic trunk, arch of the aorta or right common carotid artery.

From a venous plexus on the surface of the gland the superior thyroid vein follows the superior thyroid artery and enters either the internal jugular or facial vein in about equal proportions. The middle thyroid vein crosses anterior to the common carotid artery to drain into the internal jugular vein; early ligature and division of this vein during thyroid surgery facilitates mobilisation of the gland. The inferior thyroid veins are multiple and drain downwards mainly into the left brachiocephalic vein; one may enter the right brachiocephalic vein.

The lymphatics from the thyroid gland drain mainly to deep cervical nodes. A few pass into prelaryngeal, pre- and paratracheal nodes, and a few drain directly into the thoracic duct.

Sympathetic (vasoconstrictor) nerves from the superior, middle and inferior cervical ganglia accompany the thyroid arteries.

The thyroid consists essentially of a mass of more or less rounded follicles containing varying amounts of colloid produced by the single layer of epithelial (follicular) cells that form the walls of the follicles. The thyroid is unique in being the only endocrine gland to store its secretion outside the cells. The colloid is iodinated when in the follicle and reabsorbed by the cells before being discharged into blood capillaries. The main hormonal products are thyroxine (T₄) and triiodothyronine (T₃). Less than 2% of the epithelial cells are the C or parafollicular cells which secrete calcitonin. The C cells are scattered on the outer aspects of the follicles and do not reach the lumina of the follicles. The thyroid gland is highly vascular.

The gland develops as a proliferation of cells from the caudal end of the thyroglossal duct (see p. 26). The parafollicular calcitonin-producing cells develop from the ultimobranchial body (fifth pharyngeal pouch), under the influence of neural crest cells.

The thyroid gland is approached surgically through a transverse incision in a low skin crease on the front of the neck. The investing fascia is divided vertically and the sternohyoid and the sternothyroid muscles retraced, or divided at a high level, to safeguard their nerve supply and to prevent adherence of their subsequent suture line to the closure of the skin incision. The pretracheal fascia needs to be divided to expose the gland proper.

Both upper and lower parathyroids are usually supplied by the inferior thyroid artery, otherwise by an anastomosis between the superior and inferior arteries. Their minute veins join thyroid veins.

As for lymph drainage of the thyroid gland (above) and thymus see page 196.

Sympathetic vasoconstrictor fibres enter with the arteries.

The gland is a mass of small closely packed chief or principal cells which secrete the parathyroid hormone (PTH). The mass of cells bears a superficial resemblance to lymphoid tissue, but the number of blood capillaries in the gland provides a clear distinction. Scattered among the chief cells are small groups of slightly larger oxyphil cells.

The superior gland is termed parathyroid IV because it develops from the fourth pharyngeal pouch. The inferior gland is parathyroid III, developed from the third pouch, but displaced caudally by the descent of the thymus from the same pouch (see p. 26); hence its liability to end up in unusual positions.

For parathyroidectomy the lobes of the thyroid gland are exposed as for thyroidectomy, and then retracted forwards and medially so that the posterior surfaces can be inspected for the parathyroids. If not obvious, branches of the inferior thyroid artery are followed and should lead to the glands. Exposure of the thymus through a median sternotomy may be necessary.

Tracheotomy implies making an incision in the trachea; tracheostomy involves removing a small part of the wall (making a stoma), but the strict distinction between these terms is often ignored. In an emergency, laryngotomy (incising the cricothyroid ligament, see p. 393) provides a subglottic airway; the procedure also gives access to the trachea for sucking out excess secretions. Depending on the speed with which tracheostomy needs to be performed, the skin incision is vertical from the lower border of the thyroid cartilage to the jugular notch, or (preferably) transverse 2cm below the cricoid cartilage. The sternohyoid and sternothyroid muscles are retracted laterally. The isthmus of the thyroid gland is usually divided and an opening made by removing part of the second and third tracheal rings so that a tracheostomy tube can be inserted. In the narrow trachea of children only a vertical incision is made in the trachea (tracheotomy), as removal of any segment of tracheal wall tends to lead to tracheal stenosis.

The common carotid artery arises on the left side from the arch of the aorta, where it lies in front of the subclavian artery up to the sternoclavicular joint. Here the two arteries diverge. On the right the brachiocephalic trunk bifurcates behind the sternoclavicular joint into common carotid and subclavian arteries. The common carotid gives off no branches proximal to its bifurcation. It lies within the medial part of the carotid sheath, with the internal jugular vein lateral to it and the vagus nerve deeply placed between the two vessels. The sympathetic trunk is behind the artery and outside the sheath, which is overlapped superficially by the infrahyoid muscles and sternocleidomastoid. Medial to the sheath is the trachea and oesophagus and, at a higher level, the larynx and pharynx. The thyroid gland overlaps the sheath anteromedially and the inferior thyroid artery crosses from the thyrocervical trunk to the gland behind the sheath.

The common carotid artery usually bifurcates at the level of the upper border of the lamina of the thyroid cartilage (upper border of C4 vertebra) into the external and internal carotids; it may do so higher near the tip of the greater horn of the hyoid bone (C3 vertebra). The terminal portion of the artery often shows a slight dilatation, the carotid sinus, which includes the commencement of the internal carotid artery.

The carotid pulse can be felt by pressing backwards between the trachea and lower larynx medially and sternocleidomastoid laterally, pressing the artery against the anterior tubercle of the transverse process of C6 vertebra (carotid tubercle of Chassaignac). The surface marking of the common carotid artery is along a vertical line from the sternoclavicular joint to the level of the upper border of the thyroid cartilage. The vessel can be surgically exposed by retracting the lower part of sternocleidomastoid backwards and incising the carotid sheath. The middle thyroid vein is divided between ligatures.

The external carotid artery at its commencement lies against the side wall of the pharynx somewhat anteromedial to the internal carotid artery. It then ascends in front of the internal carotid deep to the posterior belly of digastric and stylohyoid, above which it pierces the deep lamina of the parotid fascia and enters the gland. It divides within the gland behind the neck of the mandible into the maxillary and superficial temporal arteries. As the external carotid artery lies in the parotid gland it is separated from the internal carotid by the deep part of the gland and its fascia, styloid process and its continuation the stylohyoid ligament, styloglossus and the ‘pharyngeal’ structures: stylopharyngeus muscle, glossopharyngeal nerve and pharyngeal branch of the vagus (and, if present, the track of a branchial fistula, see p. 26). At the commencement of the artery the internal jugular vein lies lateral, but higher up it is posterior and deep to the artery. The facial vein crosses the artery, with the hypoglossal nerve lying between. Except at its commencement the vessel lies in front of the anterior border of sternocleidomastoid.

The surface marking of the external carotid is along a line from the bifurcation of the common carotid passing up behind the angle of the mandible to a point immediately in front of the tragus of the ear.

Surgical approach. The vessel can be exposed in front of the upper part of sternocleidomastoid before it enters the parotid gland by ligating the facial vein. The hypoglossal nerve which crosses the external and internal carotids superficially must not be damaged.

Branches. Before it divides into its two terminal branches the external carotid artery gives off six branches, three from in front, two from behind and one from its deep (medial) aspect. The three from in front are the superior thyroid, lingual and facial, and they diverge widely. The two from behind are the occipital and posterior auricular, which pass up deep to and above the posterior belly of digastric respectively. The branch from the medial side is the ascending pharyngeal, which ascends to the base of the skull on the side wall of the pharynx, alongside the internal carotid artery.

The superior thyroid artery arises at the commencement of the external carotid. It runs almost vertically downwards, with the vein, to the upper pole of the thyroid gland (see p. 339), with the external laryngeal nerve close behind it, alongside the larynx (Fig. 6.24). Before reaching the thyroid gland it gives off infrahyoid, sternocleidomastoid, superior laryngeal and cricothyroid branches. The superior laryngeal artery pierces the thyrohyoid membrane with the internal laryngeal nerve. The cricothyroid artery crosses the upper part of the crico-thyroid membrane to anastomose with the contralateral artery.

The lingual artery arises from the front of the external carotid above the superior thyroid, near the tip of the greater horn of the hyoid bone. It forms a short loop (Fig. 6.22), then passes forwards along the upper border of the greater horn, deep to hyoglossus (p. 381). It is accompanied by the lingual vein. The loop of the artery is crossed laterally by the hypoglossal nerve and its companion vein, the latter opening into the facial vein.

The facial artery arises from the front of the external carotid above the lingual artery (sometimes by a common linguofacial trunk with the lingual) and runs upwards on the superior constrictor, deep to the digastric and stylohyoid muscles, then deep to the submandibular salivary gland. It grooves the posterosuperior part of the gland. As the artery lies on the superior constrictor muscle it gives off a tonsillar and an ascending palatine branch to the tonsil and soft palate. The facial artery then makes an S bend, curling over the submandibular gland (Fig. 6.7) and crossing the inferior border of the mandible, where its pulsation can be felt, at the anterior border of masseter. Before passing to the face it gives off the submental artery, which accompanies the mylohyoid nerve into the submandibular fossa and sends perforating branches through the mylohyoid to anastomose with a sublingual branch of the lingual artery.

The occipital artery arises from the back of the external carotid on a level with the facial artery. It courses backwards deep to the lower border of the posterior belly of digastric. It grooves the base of the skull at the occipitomastoid suture, deep to the digastric notch on the mastoid process (Fig. 6.35), and passes through the apex of the posterior triangle to supply the back of the scalp (see p. 356). The artery gives off two branches to sternocleidomastoid. The upper branch is a guide to the accessory nerve in front of the upper border of the muscle. At its origin the occipital artery crosses lateral to the hypoglossal nerve, which hooks around it from behind (Fig. 6.24), the nerve being held down here by the lower sternocleidomastoid branch of the artery (Fig. 6.23).

The posterior auricular artery arises above the level of the digastric muscle, often within the substance of the parotid gland. It runs up superficial to the styloid process above the digastric posterior belly and crosses the surface of the mastoid process to supply the scalp. Auricular branches supply the pinna of the ear. Its stylomastoid branch enters the stylomastoid foramen and supplies the facial nerve; this branch may arise instead from the occipital artery.

The ascending pharyngeal artery arises just above the commencement of the external carotid, from its deep aspect. It runs up along the side wall of the pharynx in front of the prevertebral fascia, deep to the internal carotid artery. It supplies the pharyngeal wall and the soft palate and sends meningeal branches through the nearby foramina in the base of the skull (foramen lacerum, jugular foramen, hypoglossal canal).

The internal carotid artery arises at the bifurcation of the common carotid (see p. 342) and continues upwards within the carotid sheath (see p. 366). At its commencement it shows a slight bulge, the carotid sinus. Here the arterial wall is thin and its contained baroreceptors are supplied by the glossopharyngeal and vagus nerves, which mediate blood pressure impulses to medullary centres. The carotid body is a small structure lying behind the bifurcation of the common carotid artery, or between its branches, from which it receives two or three very small glomic arteries. Its cells are chemoreceptors concerned (like the aortic bodies, see p. 192) with respira-tory reflexes, and are innervated by the glossopharyngeal and vagus nerves. Carotid body tumours form a swelling at the anterior border of sternocleidomastoid at the level of the carotid bifurcation, and exhibit transmitted pulsation from the arteries.

The internal carotid artery is lateral to the external carotid at its origin, but soon passes up posteriorly to a medial and deeper level. It has no branches and passes straight up in the carotid sheath, beside the pharynx, to the carotid canal in the base of the skull; its intracranial course is considered on pages 445 and 449.

Behind the internal carotid artery in the neck is the sympathetic trunk (outside the carotid sheath), pharyngeal veins and the superior laryngeal branch of the vagus. The ascending pharyngeal artery is medial to it. The internal jugular vein is lateral, with the vagus nerve deeply placed between artery and vein. Superficially near its origin it is crossed by the lingual and facial veins, the occipital artery and hypoglossal nerve. The superior root of the ansa cervicalis runs downwards along it, embedded in the carotid sheath. At a higher level it is crossed by the posterior belly of digastric and stylohyoid and the posterior auricular artery, and by the structures that separate it from the external carotid (see above).

The surface marking of the internal carotid artery in the neck is along a line from the bifurcation of the common carotid artery to the head of the mandible.

Surgical approach. The internal carotid is exposed in the neck by an incision along the anterior border of sternocleidomastoid. The muscle is retracted backwards, the facial and lingual veins divided between ligatures, and the carotid sheath is incised. The hypoglossal nerve must be safeguarded and this may require division of the lower sternocleidomastoid branch of the occipital artery. The emergence of branches from the external carotid artery ensures its differentiation from the internal carotid.

The internal jugular vein emerges from the jugular bulb at the posterior compartment of the jugular foramen (Fig. 6.35). At first behind the internal carotid artery, it lies on the transverse process of the atlas, crossed by the accessory nerve. It receives the inferior petrosal sinus as its first tributary, just below the base of the skull; the sinus passing back lateral or medial to the glossopharyngeal, vagus and accessory nerves. The vein passes down to gain the lateral side of first the internal carotid artery and then the common carotid artery, within the loose lateral part of the carotid sheath, with the vagus nerve deeply placed between the vein and the arteries. In the lower part of its course the vein is overlaid by the sloping sternocleidomastoid. Deep cervical lymph nodes within the sheath are closely adjacent to the vein throughout its course. Its posterior relations include the cervical plexus lying on levator scapulae and scalenus medius, and the phrenic nerve on scalenus anterior. The thoracic duct crosses behind the left vein at the level of C7 vertebra. The inferior root of the ansa cervicalis curls round its lateral border, to unite with the superior root (from the hypoglossal nerve) at a variable level in front of the vein. Low down the tendon of omohyoid crosses the vein, providing a useful guide to its position. The terminal part of the vein lies deep to the triangular interval between the sternal and clavicular heads of sternocleidomastoid (Fig. 6.2). It joins the subclavian to form the brachiocephalic vein behind the sternal end of the clavicle.

The tributaries of the internal jugular vein below the inferior petrosal sinus are the pharyngeal, lingual, facial and superior and middle thyroid veins. The lingual and superior thyroid veins may join the facial vein and other variations are possible.

At its commencement and termination the vein is slightly dilated to form superior and inferior bulbs. There is a pair of valves above the inferior bulb.

The surface marking of the internal jugular vein is along a line from the lobule of the ear to the sternal end of the clavicle, between the two heads of sternocleidomastoid. The jugular venous pulse is a guide to jugular venous pressure, which is the same as right atrial or central venous pressure and thus an indicator of cardiovascular function. With a patient reclining at 45° the jugular venous pulse should be visible just above the clavicle.

Catheterization. The right internal jugular vein (on a direct path to the right atrium) can be cannulated for the insertion of a central venous line, for measurements of central venous pressure, or the rapid administration of drugs when a peripheral approach would be too slow. The vein is usually approached through the centre of the triangle formed by the two heads of sternocleidomastoid and the clavicle. The needle is directed caudally, parallel to the sagittal plane at a 30° posterior angle with the coronal plane, entering the vein at about 4–5cm depth. (The subclavian vein is an alternative, see p. 348). The most common complication is haematoma formation; others include common carotid artery puncture, vagus nerve injury and pneumothorax due to pleural perforation.

The ansa cervicalis lies on the front of the internal jugular vein and gives branches to the infrahyoid muscles. It is usually embedded within the anterior wall of the carotid sheath and classified as one of its contents. It is formed by union of superior and inferior roots. The superior root is a branch of the hypoglossal nerve containing only C1 fibres, which have hitch-hiked along the hypoglossal nerve. It runs down on the front of the internal and common carotid arteries, giving a branch to the superior belly of omohyoid.

The inferior root is formed by union of a branch each from C2 and C3 anterior rami in the cervical plexus. The single nerve so formed spirals from behind around the internal jugular vein and runs down to join the superior root in a wide loop over the lower part of the vein, from which branches arise for the infrahyoid muscles (sternohyoid, sternothyroid and inferior belly of omohyoid). Sometimes the inferior root passes forwards between internal jugular vein and internal carotid artery.

The uppermost part of the hypoglossal nerve in the neck is described on page 368. It emerges between the internal carotid artery and internal jugular vein deep to the posterior belly of digastric. Hooking round the occipital artery, which runs backwards lateral to the nerve, it curves forwards lateral to the internal and external carotids and the loop of the lingual artery (Fig. 6.23). As it crosses these arteries it lies just below the posterior belly of the digastric, behind its tendon and just above the tip of the greater horn of the hyoid bone. It gives off the superior root of the ansa cervicalis as it crosses the internal carotid and the branch to thyrohyoid (C1 fibres) as it crosses the lingual artery. It passes forwards on the lateral surface of hyoglossus deep to mylohyoid to enter the mouth, giving off the branch to geniohyoid (C1 fibres) as it does so (Fig. 6.24).

Boundaries. Sternocleidomastoid, trapezius, clavicle.

Contents. Occipital, transverse cervical, suprascapular and subclavian arteries; transverse cervical, suprascapular and external jugular veins; accessory nerve; cervical plexus branches and brachial plexus trunks (deep to prevertebral fascia); inferior belly of omohyoid; lymph nodes.

Boundaries. Sternocleidomastoid, mandible, midline. Subdivided into:

Boundaries. Sternocleidomastoid, posterior belly of digastric, superior belly of omohyoid.

Contents. Bifurcation of common carotid artery and branches of external carotid (except posterior auricular); lingual, facial and superior thyroid veins; hypoglossal, internal and external laryngeal nerves, and superior root of ansa cervicalis; lymph nodes.

Boundaries. Mandible, anterior and posterior bellies of digastric.

Contents. Submandibular gland and lymph nodes; facial, submental and mylohyoid vessels; hypoglossal and mylohyoid nerves.

Boundaries. Anterior bellies of digastric, body of hyoid bone. (Triangle crosses midline.)

Contents. Anterior jugular veins; lymph nodes.

Boundaries. Sternocleidomastoid, superior belly of omohyoid, midline from hyoid bone to jugular notch.

Contents. Parts of larynx, trachea, pharynx, oesophagus, thyroid and parathyroid glands; their vessels and nerves; lymph nodes.

This flat muscle arises from the anterior tubercles of the four ‘typical’ cervical vertebrae (3–6) by four slender tendons of origin which lie end to end with those of longus capitis (Fig. 6.8). The muscle passes forwards, laterally and downwards to end in a narrow tendon attached to the scalene tubercle and adjacent ridge on the inner border and upper surface of the first rib (see Fig. 4.34, p. 218).

Nerve supply. By separate branches from the anterior rami of C4–6 nerves.

Action. It is more important as a landmark than an active muscle. It assists in flexion and rotation of the neck, and helps to stabilize the first rib. Even in quiet respiration it shows some electromyographic activity.

The phrenic nerve passes vertically down across the obliquity of the muscle, plastered thereto by the prevertebral fascia (Fig. 6.10) and a pad of fat lies in front of the prevertebral fascia. The nerve leaves the medial border of the muscle low down and crosses in front of the subclavian artery and its internal thoracic branch, behind the subclavian vein. (Occasionally the phrenic nerve may pass in front of the subclavian vein or posterior to the internal thoracic artery.) Lying on the suprapleural membrane it passes medial to the apex of the lung, crossing in front of the vagus nerve as it enters the superior mediastinum. The ascending cervical artery, a branch of the inferior thyroid artery or the thyrocervical trunk, runs up on the prevertebral fascia medial to the phrenic nerve.

In front of the prevertebral fascia the superficial cervical and suprascapular arteries lie between the scalenus anterior and the carotid sheath (internal jugular vein). The vagus nerve in the carotid sheath passes down in front of the subclavian artery, on the right side giving off its recurrent laryngeal branch. The latter hooks under the artery and passes upwards (Fig. 6.9A). The vagus nerve inclines posteriorly and runs on the medial surface of the apex of the lung to enter the superior mediastinum. The internal jugular vein has inferior deep cervical lymph nodes closely adjacent to it.

The subclavian vein lies in a groove on the first rib and, due to the slope of the rib, lies at a lower level than the insertion of scalenus anterior (Fig. 6.9A). Running medially it joins the internal jugular vein at the medial border of scalenus anterior to form the brachiocephalic vein; the thoracic duct on the left and the right lymph duct on the right enter the angle of confluence of the two veins.

Catheterization. The right subclavian vein can be used for the placement of a central venous line, instead of the internal jugular (see p. 344); it is preferred by many operators and is more comfortable for the patient. The usual approach is infraclavicular, from a point 2cm below the midpoint of the clavicle along a line that passes behind the clavicle towards the jugular notch of the sternum. The needle pierces the clavipectoral fascia and enters the vein just behind the fascia. Pneumothorax due to puncture of the pleura and lung, and puncture of the subclavian artery are complications of this procedure. The vein is also used for the placement of wires from cardiac pacemakers, which are usually implanted in connective tissue over the upper lateral part of pectoralis major.

The medial edge of scalenus anterior makes a pyramidal space with the lateral border of the lower part of longus colli. The prevertebral fascia in front of these muscles is attached to bone at their opposing margins and there is no fascial roof across the pyramidal space between the muscles. The base of the space is formed by the subclavian artery, lying on the suprapleural membrane. The apex of the space is the carotid (Chassaignac’s) tubercle on the transverse process of C6 vertebra (Figs 6.8 and 6.10).

The common carotid artery, medial to the internal jugular vein, lies deep to sternocleidomastoid immediately in front of the pyramidal space. Behind the artery and the carotid sheath, the space contains the inferior cervical sympathetic (or stellate) ganglion, with the vertebral artery and vein(s) in front of it. The inferior thyroid artery arches medially in a bold curve whose upper convexity lies in front of the apex of the pyramidal space (C6 level), with the sympathetic chain, usually the middle ganglion, in front of the artery. At a lower level, and further forward, the thoracic duct (or right lymphatic duct) makes a similar convexity behind the carotid sheath as it arches over the lung apex and subclavian artery to enter the confluence of the subclavian and internal jugular veins (Fig. 6.10).

The relationship of the scalenus anterior to the subclavian artery is used to descriptively divide the subclavian artery into three parts. The first part of the subclavian artery is medial to scalenus anterior. It arches over the suprapleural membrane and impresses a groove upon the apex of the lung. It has three branches. The vertebral artery is the first; this arises from the upper convexity of the subclavian and passes up to disappear, at the apex of the pyramidal space, into the foramen of the transverse process of C6 vertebra. The accompanying sympathetic nerve runs up behind the artery. Rarely this first part of the vertebral artery may initially enter the foramen of the transverse process of a higher vertebra than C6. A connecting loop between middle and inferior cervical ganglia passes in front of the subclavian artery and turns up behind it, forming the ansa subclavia. The recurrent laryngeal nerve recurves under the right subclavian artery, while the thoracic duct loops over the left artery. The thyrocervical trunk arises lateral to the vertebral artery from the upper surface of the subclavian. It divides immediately into superficial cervical, suprascapular and inferior thyroid arteries, which have already been noted. The proximal part of the superficial cervical is named transverse cervical artery when it gives off the dorsal scapular artery as a deep branch. The internal thoracic artery arises from the lower surface of the subclavian and passes downwards over the lung apex, crossed usually anteriorly by the phrenic nerve.

The vertebral vein emerges from the foramen in the transverse process of C6 vertebra and runs forward in front of the vertebral and subclavian arteries to empty into the brachiocephalic vein. It may be accompanied by a companion vein that passes through the foramen of the transverse process of C7 vertebra and passes behind the subclavian artery to the same destination.

Scalenus anterior is separated from scalenus medius by the subclavian artery and the anterior rami of the lower cervical and first thoracic nerves. The second part of the subclavian artery lies behind scalenus anterior. Its only branch is the costocervical trunk. It passes back across the suprapleural membrane towards the neck of the first rib and there divides into a descending branch, the superior intercostal artery, which enters the thorax across the neck of the first rib, and an ascending branch, the deep cervical artery, which passes backwards between the transverse process of C7 vertebra and the neck of the first rib to run upwards behind the cervical transverse processes.

The trunks of the brachial plexus and the third part of the subclavian artery emerge from the lateral border of scalenus anterior. They lie behind the prevertebral fascia on the floor of the posterior triangle (Fig. 6.10). The dorsal scapular usually arises from the third part. It runs laterally through the brachial plexus in front of scalenus medius and then deep to levator scapulae to take part in the scapular anastomosis (see p. 46). It is frequently replaced by the deep branch of the transverse cervical artery, and this branch then takes the name of dorsal scapular.

The surface marking of the subclavian artery in the neck is along a line arching upwards from the sternoclavicular joint to the middle of the clavicle and about 2cm above it.

Surgical approach. The artery can be exposed by dividing the clavicular head of sternocleidomastoid from the clavicle and then detaching scalenus anterior from the first rib, taking particular care not to damage the phrenic nerve.

Pressure on the subclavian artery and lowest root (T1) of the brachial plexus as they cross over a cervical rib or fibrous band, when present at the root of the neck, is described on page 422. Elevation of the first rib by scalenus anterior may also cause or aggravate such a thoracic outlet syndrome, and the muscle is usually divided close to its insertion when the syndrome is treated surgically.

Scalenus medius arises from the lateral ends of the transverse processes of atlas and axis and from the posterior tubercles of all the other cervical vertebrae and is inserted into the quadrangular area between the neck and subclavian groove of the first rib (see Fig. 4.34, p. 218).

Scalenus posterior is a small unimportant muscle that arises from the posterior tubercles of the lower cervical vertebrae, passes across the outer border of the first rib deep to the upper digitation of serratus anterior, and is inserted into the second rib.

Nerve supplies. Both muscles are supplied segmentally by the anterior rami of cervical nerves, scalenus medius by C3–8.

Actions. Scalenus medius, mainly a lateral flexor of the neck, can elevate the first rib as an accessory muscle of respiration.

The palpebral fissure is surrounded by a sphincter, the orbicularis oculi, and has a dilator mechanism consisting of levator palpebrae superioris (considered with the orbital muscles, see p. 400) and occipitofrontalis which is part of the scalp (p. 355).

Orbicularis oculi has a palpebral part, confined to the lids, and an orbital part, extending beyond the bony orbital margins on to the face. The palpebral part consists of fibres that arise from the medial palpebral ligament (see p. 398), arch across both lids, anterior to the tarsal plates, and interdigitate laterally to form the lateral palpebral raphe. Fibres of a deeper lacrimal part are attached medially to the posterior lacrimal crest and lacrimal sac; laterally they join the upper and lower palpebral fibres. The orbital part, much the larger, arises from the nasal part of the frontal bone, the anterior lacrimal crest and the frontal process of the maxilla, whence the fibres circumscribe the orbital margin in a series of concentric loops.

Nerve supply. By temporal and zygomatic (mainly) branches of the facial nerve.

Action. Contraction of the palpebral fibres closes the lids gently without burying the eyelashes. Orbital and palpebral parts contracting together close the eyelids forcibly so that the eyelashes are buried and only their tips are visible. In normal closing of the eye, the lateral part of the upper lid comes down before the medial part, so helping to spread lacrimal secretion from the gland side (lateral) towards the nose.

Levator palpebrae superioris is the opponent of the upper palpebral fibres of orbicularis oculi; occipitofrontalis opposes the orbital part.

The sphincter muscle of the nostril is the transverse part of nasalis (compressor naris), which forms an aponeurosis over the bridge of the nose with its fellow of the opposite side. Its opponent is the alar part of nasalis (dilator naris), which is inserted into the lateral part of the ala. Each arises from the maxilla. In addition, levator labii superioris alaeque nasi (see p. 352) and depressor septi contribute to widening the nostril. Depressor septi arises from the maxilla above the central incisor and is attached to the nasal septum. All these muscles are supplied by buccal branches of the facial nerve.

The sphincter is the orbicularis oris; the dilator mechanism consists of the remainder of the facial muscles, which radiate outwards from the lips like the spokes of a wheel.

Orbicularis oris consists of fibres proper to itself and fibres that are added to these from the dilators. The muscle is made up of four quadrants (upper, lower, right and left) each of which has a larger peripheral part and a smaller marginal part in the red zone of the lips. The bulk of the orbicularis muscle is formed of extrinsic fibres; most of these come from the buccinator. The fibres of buccinator converge towards the modiolus (see p. 352). At the modiolus they form a chiasma; the uppermost and lowermost fibres pass straight on into their respective lips, while the middle fibres decussate, the upper fibres of buccinator passing into the lower lip, the lower into the upper lip (Fig. 6.12).

Incisivus labii superioris and incisivus labii inferioris are attached to the incisive fossa of the maxilla and mandible, respectively, from where they arch laterally, interlacing with fibres of the peripheral part of orbicularis oris as they approach the modiolus. They are the deepest fibres in the lips and are attached to the mucous membrane.

Nerve supply. By buccal and marginal mandibular branches of the facial nerve. Damage to the latter branch (such as in the surgical approach to the submandibular gland) causes asymmetry of the mouth when speaking or smiling.

Action. Contraction of the orbicularis oris causes narrowing of the mouth, the lips becoming pursed up into the smallest possible circle (the whistling expression).

Buccinator has a bony origin from both jaws opposite the molar teeth, horizontally on the maxilla and from the oblique line of the mandible. Between the tuberosity of the maxilla and the hamulus at the bottom of the medial pterygoid plate (of the sphenoid), the muscle arises from a fibrous band (the pterygomaxillary ligament), above which the tendon of tensor palati hooks around the base of the hamulus (Fig. 6.13).

From the tip of the hamulus the pterygomandibular raphe extends to the mandible just above the posterior end of the mylohyoid line; between them the lingual nerve is in contact with the mandible where the bone is often thinned by a shallow groove (Fig. 6.22). The buccinator arises from the whole length of the raphe, along which it interdigitates with the fibres of the superior constrictor (see p. 383). The muscle converges on the modiolus, where its fibres of origin from the raphe decussate; the maxillary and mandibular fibres pass medially without decussation into the upper and lower lips respectively. The muscle is pierced by the parotid duct opposite the third upper molar tooth. The duct also passes through the buccal fat pad which lies on the outer surface of buccinator and is particularly prominent in infants, giving them their chubby cheeks. Beneath the fat lie a few small molar glands; their ducts pierce the muscle to open on the mucous membrane of the cheek, which lines the muscle’s inner surface and to which muscle fibres are attached.

Nerve supply. By the buccal branches of the facial nerve. The buccal branch of the mandibular nerve supplies proprioceptive fibres.

Action. It is essentially an accessory muscle of mastica-tion, being indispensable to the return of the bolus from the cheek pouch to the grinding mill of the molars. It is, however, classified as a muscle of facial expression on account of being supplied by the facial nerve. When the cheeks are puffed out the muscle is relaxed, and the muscle contracts in forcible expulsion of air from the mouth, as in blowing a trumpet. (Buccinator is the Latin name for a trumpeter.)

Radiating from orbicularis oris like the spokes of a wheel is a series of dilator muscles, some inserted into the lips, some into the modiolus. All contracting together open the lips into the widest possible circle, an action that is usually accompanied by simultaneous opening of the jaws. Upper and lower lips have flat sheets of elevator and depressor muscles. Other muscles converge towards the angle of the mouth, where their decussating fibres form a knot of muscle with the chiasma in the buccinator fibres, bound together by fibrous tissue; this is termed the modiolus and is situated about 1cm lateral to the angle of the mouth, opposite the second upper premolar tooth. Its position and movements are of importance in prosthetic dentistry.

Levator labii superioris alaeque nasi arises from the frontal process of the maxilla and is inserted into the ala of the nose and the upper lip; it elevates both. Levator labii superioris arises from the inferior orbital margin and is inserted into the remainder of the upper lip, which it elevates. The muscle overlies the exit of the infraorbital nerve. From the canine fossa below the infraorbital foramen arises levator anguli oris; the infraorbital nerve lies sandwiched between it and the overlying levator labii superioris. The fibres of this muscle, deep to the superficial sheet of muscle, converge to the modiolus and pass through it to become superficial. They merge into the fibres of depressor anguli oris. Zygomaticus minor from the zygomaticomaxillary suture and zygomaticus major further out on the surface of the zygomatic bone converge to the modiolus. Risorius is a variable muscle that converges on the modiolus from the parotid fascia. All these muscles are supplied by buccal branches of the facial nerve.

Depressor anguli oris arises from the mandible below the mental foramen. It lies superficial but its fibres pass through the modiolus to the deeper stratum. Depressor labii inferioris arises from the mandible in front of the mental foramen, deep to the former muscle; its fibres are inserted into the lower lip. Mentalis is a muscle that arises near the midline of the mandible. Its fibres pass downwards to reach the skin. It is an elevator of the skin of the chin (which it sometimes dimples) and its contraction may disturb a lower denture. These muscles are supplied by the marginal mandibular branch of the facial nerve.

The supply from the facial nerve to the muscles described above is motor. Proprioceptive impulses from the facial muscles are conveyed centrally by the trigeminal nerve, whose cutaneous branches connect freely with branches of the facial nerve.

The facial nerve emerges from the base of the skull through the stylomastoid foramen, near the origin of the posterior belly of digastric. It immediately gives off the posterior auricular nerve which passes upwards behind the ear to supply auricularis posterior and the occipital belly of occipitofrontalis. A muscular branch is next given off which divides to supply the posterior belly of digastric and stylohyoid. The nerve now approaches the posteromedial surface of the parotid gland. Just before entering or within the gland it divides into an upper temporofacial and a lower cervicofacial division. Within the substance of the parotid gland each divides and rejoins to divide again and finally emerge from the parotid gland in five main groups of branches (Fig. 6.14). This plexiform arrangement, the pes anserinus, lies in the gland superficial to the retromandibular vein and the external carotid artery.

The temporal branches emerge from the upper border of the gland, cross the zygomatic arch, and supply auricularis anterior and superior, and part of frontalis. They are only important for wrinkling the forehead. (A branch is also termed a frontal branch in some texts.)

The zygomatic branches cross the zygomatic arch and zygomatic bone, lying directly on the periosteum. They may be damaged in fractures or operations in this region. These branches supply orbicularis oculi. Paralysis of this muscle prevents blinking and the precorneal film of tears is no longer spread. The dry cornea easily ulcerates. The resultant scar impairs vision and this is the most serious consequence of impaired facial nerve function.

The buccal branches run forwards close to the parotid duct, often one above and one below the duct. They supply buccinator and the muscle fibres of the nose and the upper lip. Paralysis of the buccinator prevents emptying of the cheek pouch; the bolus lodges there and cannot be returned to the molar teeth. Chewing has to be performed on the other side.

The marginal mandibular branch is frequently single and runs forwards above, along, or below the lower border of the mandible. From below the mandible it crosses the inferior border of the bone to reach the face just beyond the anterior border of the masseter muscle, passing superficial to the facial artery and vein. A small lymph node lies here (Fig. 6.63). The nerve is in danger when an incision is made at or near the lower border of the mandible. This nerve does not communicate with a buccal branch and damage to the nerve invariably causes detectable paralysis of the depressors of the lower lip and mouth angle, there being no alternate pathway for motor fibres to these muscles.

The cervical branch passes downwards from the lower border of the parotid gland and supplies platysma.

The details of the pattern of branching of the facial nerve differs in different individuals and even on the two sides of the face of the same person.

Five cutaneous branches:

The lacrimal nerve supplies a small area of skin over the lateral part of the upper lid.

A third of the way lateral to the medial end of the upper margin of the orbit, the supraorbital nerve indents the bone into a notch or a foramen. The nerve passes up, breaking into several branches which radiate out and supply the forehead and scalp up to the vertex.

The smaller supratrochlear nerve passes up on the medial side of the supraorbital nerve to supply the middle of the forehead up to the hairline.

The infratrochlear nerve supplies skin on the medial part of the upper lid and, passing above the medial palpebral ligament, descends along the side of the external nose, supplying skin over the bridge of the nose.

These four branches of the ophthalmic nerve also supply upper lid conjunctiva.

The external nasal nerve supplies the middle of the external nose down to the tip. It emerges between the nasal bone and the upper nasal cartilage.

The supraorbital and supratrochlear nerves are branches of the frontal nerve (see p. 402). The infratrochlear and external nasal nerves are derived from the nasociliary (see p. 403), the former directly and the latter via the anterior ethmoidal branch; when these nerves are involved in herpes zoster infection, the cornea (supplied by the ciliary branches of the nasociliary) may also become affected and lead to dangerous corneal ulceration.

Three cutaneous branches:

The infraorbital nerve emerges through its foramen and lies between levator labii superioris and the deeper placed levator anguli oris. It is a large nerve that immediately breaks up into a tuft of branches; these radiate away from the foramen to supply the lower eyelid (including conjunctiva), cheek, nose, upper lip and labial gum.

The zygomaticofacial nerve emerges from a foramen on the outer surface of the zygomatic bone; its branches supply the overlying skin.

The zygomaticotemporal nerve emerges in the temporal fossa through a foramen in the temporal (posterior) surface of the zygomatic bone. It supplies a small area of temporal skin.

Three cutaneous branches:

The auriculotemporal nerve passes around the neck of the mandible and ascends over the posterior root of the zygomatic arch behind the superficial temporal vessels. The auricular part of the nerve supplies the external acoustic meatus, surface of the tympanic membrane and skin of the auricle above this level. The temporal part supplies the hairy skin over the temple.

The buccal nerve gives off cutaneous twigs before it pierces the buccinator muscle to supply oral mucous membrane. They supply a small area over the cheek just below the zygomatic bone, between the areas of the infraorbital nerve and the great auricular nerve (see p. 334).

The mental nerve is a cutaneous branch of the inferior alveolar nerve. Like the infraorbital nerve it breaks up into a tuft of branches; these radiate away from the mental foramen to supply the skin and mucous membrane of the lower lip and labial gum from the midline to about the second premolar tooth.

At the medial angle of the eyelids there is a communication between the angular vein and the ophthalmic veins, which drain directly into the cavernous sinus. Blood from the forehead normally flows via the facial vein; if the latter is blocked by thrombosis, blood above the obstruction will flow through the orbit into the cavernous sinus. Hence the ‘danger area’ of infection of the upper lip and nearby cheek. A further communication is the deep facial vein. This passes backwards from the facial vein, between the masseter and buccinator muscles, to the pterygoid plexus. The plexus connects with the cavernous sinus by emissary veins that pass through the foramen ovale and the foramen lacerum. The danger area of the face lies between the angular and deep facial veins.

The arteries of the scalp are derived from the external carotid artery by the occipital, posterior auricular and superficial temporal branches, and from the internal carotid artery by the supraorbital and supratrochlear branches. All these arteries anastomose very freely with each other. The arterial walls are attached to the dense connective tissue of the second layer of the scalp and tend to be held open and bleed profusely when cut. Scalping does not cause necrosis of the bones of the vault, most of whose blood comes from the middle meningeal artery.

The occipital artery emerges from the apex of the posterior triangle and runs with the greater occipital nerve to supply the back of the scalp up to the vertex. The smaller posterior auricular artery runs with the lesser occipital nerve to supply the scalp behind the ear.

The superficial temporal artery is a terminal branch of the external carotid. Running up behind the temporomandibular joint and in front of the ear and the auriculo-temporal nerve, it crosses the zygomatic arch, where its pulsation can be felt, and branches out widely into the skin that overlies the temporal fossa. One branch, the middle temporal artery, pierces the fascia, supplies temporalis and anastomoses with the deep temporal branches of the maxillary artery.

The supraorbital and supratrochlear arteries (from the ophthalmic) run with the corresponding nerves. The supraorbital is the larger and supplies the front of the scalp up to the vertex. Its anastomosis with the superficial temporal artery connects the internal and external carotid systems.

The veins of the scalp run back with the arteries. In forehead, temple and occipital regions they receive diploic veins from frontal, parietal and occipital bones.

The supraorbital and supratrochlear veins drain by the angular vein into the facial vein. The superficial temporal veins run into the retromandibular vein, and occipital veins reach the plexus around the suboccipital muscles which drains into the vertebral vein. The posterior auricular vein drains the scalp behind the ear to the external jugular vein; it also receives the mastoid emissary vein from the sigmoid sinus. Spread of infection to this emissary vein from mastoid air cells can be dangerous or fatal, from retrograde thrombosis of cerebellar and medullary veins. At the vertex a parietal emissary vein on either side of the midline connects scalp veins with the superior sagittal sinus.

There are no lymph nodes within the scalp; lymphatic channels from the posterior half of the scalp drain to occipital and mastoid nodes, and from the anterior half to preauricular (parotid) nodes. The lymph eventually reaches the nodes of the deep cervical chain.

The main sensory nerves run with the arteries. Posteriorly the greater occipital and third occipital nerves (posterior rami of C2 and C3 respectively) extend to the vertex and the posterior scalp respectively. The lesser occipital (anterior ramus of C2) supplies skin behind the ear. The temple is supplied by the auriculotemporal and the zygomaticotemporal nerves, and the forehead and front of the scalp by the supratrochlear and supraorbital nerves.

This muscle (one of the muscles of mastication) arises from the temporal fossa over the whole area between the inferior temporal line and the infratemporal crest, and from the deep surface of the temporalis fascia. The most anterior fibres are vertical and the most posterior are horizontal, turning downwards in front of the temporomandibular joint. The fan-shaped muscle converges towards the coronoid process of the mandible, becomes tendinous, and is inserted into a bevelled surface on the medial aspect of the coronoid process adjacent to its posterior border, apex and anterior border. From the anterior part of this insertion, two tendinous bands extend downwards and forwards to the posterior end of the alveolar process enclosing the retromolar fossa between them. The deep, larger tendinous band is attached to a slight (temporal) crest on the mandible, and is palpable through the vestibule of the mouth; a useful guide when performing an inferior alveolar nerve block.

The blood supply of the muscle is derived from the temporal branches of the maxillary and superficial temporal arteries.

Nerve supply. Two or three deep temporal branches of the mandibular nerve enter the deep surface of the muscle.

Action. Temporalis elevates the mandible when the open mouth is closed, and it retracts the protruded mandible.

This quadrilateral muscle of mastication arises from the lower border of the zygomatic arch and is inserted into almost the whole of the lateral surface of the mandibular ramus. Most of its fibres slope downwards and backwards at 45°. The posteriormost fibres arise from the deep surface of the arch and pass vertically downwards to be inserted into the upper part of the ramus; these fibres blend with the lower fibres of temporalis. The upper anterior part of the muscle is covered by an aponeurosis on which the parotid duct and the accessory parotid gland lie.

The muscle receives blood supply from branches of the facial artery, maxillary artery and superficial temporal artery, particularly its transverse facial artery. These vessels form an anastomotic network on the surface of and within the muscle.

Nerve supply. By the masseteric branch of the mandibular nerve, which passes through the mandibular notch to enter the deep surface of the gland.

Action. Masseter elevates and draws forwards the angle of the mandible when the jaws are approximated. The deep fibres assist temporalis in retracting the mandible.

Branches from the external carotid artery supply the gland. Venous return is to the retromandibular vein.

Lymph drains to the preauricular (parotid) nodes and thence to nodes of the upper group of deep cervical nodes.

Secretomotor fibres arise from cell bodies in the otic ganglion (see p. 22) and reach the gland by ‘hitch-hiking’ along the auriculotemporal nerve. As it passes backwards along the mandibular neck and ascends behind the temporomandibular joint, the auriculotemporal nerve is in contact with the anteromedial surface of the gland, which is penetrated by filaments from the nerve. The preganglionic fibres arise from cell bodies in the inferior salivary nucleus in the medulla, and travel by way of the glossopharyngeal nerve, its tympanic branch, the tympanic plexus and the lesser petrosal nerve to the otic ganglion. Sympathetic (vasoconstrictor) fibres reach the gland from the superior cervical ganglion by way of the plexus on the external carotid and middle meningeal arteries.

A groove that appears in the ectoderm of the mouth pit (stomodeum, see p. 28) becomes converted into a tunnel, from the blind end of which cells proliferate to form the gland.

The most common neoplasm of the parotid gland is a pleomorphic adenoma (mixed parotid tumour) which requires removal with a margin of normal parotid tissue, conserving the facial nerve and its branches. On account of the wide extent of the gland, it is approached through an S-shaped incision made from in front of the ear, backwards to the mastoid process and then downwards and forwards below the angle of the mandible. The gland is retracted forwards from the sternocleidomastoid to expose the posterior belly of digastric and stylohyoid and the cartilage of the external meatus. The facial nerve is approached along a plane in front of the anterior margin of the cartilage. The trunk emerges from the stylomastoid foramen, just deep to the junction of the cartilaginous and bony parts of the external meatus, about 1cm above and medial to the upper end of the posterior belly of digastric (Fig. 6.18). The cartilage in this region has a slight arrow-headed projection that points downwards to the emerging nerve trunk. The stylomastoid branch of the posterior auricular artery is superficial to the facial nerve and is a guide to its proximity. Once identified, the facial nerve is followed forwards into the gland and the required amount of parotid tissue removed with preservation of facial nerve branches. An alternative approach to facial nerve conservation is to first find a facial nerve branch as it leaves the gland and to follow this in a centripetal manner back to the trunk and other branches. The marginal mandibular branch may be identified as it lies superficial to the retromandibular vein or its anterior branch, aided by the colour contrast between the white nerve and the dark vein; occasionally this branch may pass behind the vein. Alternatively, the cervical branch may be followed up from its communication with the ascending branch of the transverse cervical nerve.

Its medial boundary is the lateral surface of the lateral pterygoid plate with, behind it, the tensor palati muscle and the superior constrictor. In front of the lateral pterygoid plate, between it and the maxilla, is the pterygo-maxillary fissure through which the infratemporal fossa communicates with the pterygopalatine fossa (see p. 369). The lateral wall is the ramus of the mandible and its coronoid process. The anterior wall is the posterior surface of the maxilla, at the upper margin of which is a gap between it and the greater wing of sphenoid—the inferior orbital fissure. The roof of the fossa is formed medially by the infratemporal surface of the greater wing of the sphenoid (perforated by the foramen ovale and foramen spinosum) and the adjacent squamous part of the temporal bone in front of the articular eminence (Fig. 6.19). This infratemporal surface of the sphenoid is bounded laterally by the infratemporal crest, where the bone takes an almost right-angled turn upwards to become part of the side of the skull, deep to the zygomatic arch and part of the temporal fossa. Thus the roof of the infratemporal fossa lateral to the infratemporal crest is not bony, but is the space deep to the zygomatic arch where the temporal and infratemporal fossae communicate. The posterior boundary is the styloid process with the carotid sheath behind it.

The fossa contains the deep part of the parotid gland, the medial and lateral pterygoid muscles, the insertion of temporalis into the coronoid process, the maxillary artery and its branches, the pterygoid venous plexus, the mandibular nerve and its branches together with the otic ganglion, the chorda tympani, and the posterior superior alveolar branches of the maxillary nerve.

This muscle arises by two heads: the upper from the roof of the infratemporal fossa and the lower from the lateral surface of the lateral pterygoid plate. The two heads, lying edge to edge, converge and fuse into a short thick tendon that is inserted into the pterygoid fovea on the front of the neck of the mandible. The upper fibres of the tendon pass back into the capsule and the articular disc of the temporomandibular joint (Fig. 6.20).

Nerve supply. By a branch from the anterior division of the mandibular nerve.

Action. When the muscle contracts it draws condyle and disc forwards from the mandibular fossa down the slope of the articular eminence (Fig. 6.35). It is indis-pensable to active opening of the mouth. It participates with medial pterygoid in chewing movements.

This muscle also arises by two heads. The larger deep head arises from the medial (deep) surface of the lateral pterygoid plate. The muscle diverges down from the lateral pterygoid muscle at nearly a right angle from their common origin on either side of the lateral pterygoid plate (Fig. 6.20). A small slip of muscle, the superficial head, arises from the tuberosity of the maxilla and the pyramidal process of the palatine bone which insinuates itself between the tuberosity and the lower end of the lateral pterygoid plate (Fig. 6.13). Passing over the lower margin of the lateral pterygoid muscle, the superficial head fuses with the main muscle mass. In this way the two heads, very unequal in size, embrace the lower edge of the lateral pterygoid. The muscle passes down and back at 45°, and laterally to reach the angle of the mandible. It is inserted into the rough area on the medial surface of the angle as far as the groove for the mylohyoid vessels and nerve (see Fig. 8.5B, p. 510). The muscle is characterized by tendinous intersections on its surface, which account for the roughness of the area of insertion on the mandible.

Nerve supply. By a branch from the main trunk of the mandibular nerve (Fig. 6.21).

Action. The pull of the muscle on the angle of the mandible is upwards, forwards and medially (i.e. it closes the mouth) and it moves the mandible towards the opposite side in chewing. Contracting with its opposite fellow and the two lateral pterygoids, it helps to protrude the mandible.

The maxillary artery is, with the superficial temporal artery, a terminal division of the external carotid. It enters the infratemporal fossa by passing forwards deep to the neck of the mandible, between the neck and the sphenomandibular ligament. Here the auriculotemporal nerve lies above it (Fig. 6.21), and the maxillary vein below it. It usually runs deep (sometimes superficial) to the lower head and passes forward and upward between the two heads of the lateral pterygoid muscle (Fig. 6.20). It then passes deeply into the pterygomaxillary fissure and so into the pterygopalatine fossa.

It is described conventionally in three parts, before, on and beyond the lateral pterygoid muscle and this is useful, since five branches come from each part. From first and third parts the five branches all enter foramina in bones, from the second part the branches are mainly muscular.

The five branches from the first part are the inferior alveolar, middle meningeal, accessory meningeal and two branches to the ear.

The inferior alveolar artery passes downwards and forwards (vein behind it) towards the inferior alveolar nerve and all three enter the mandibular foramen. It passes forwards in the mandible, supplying the pulps of the mandibular molar and premolar teeth and the body of the mandible. Its mental branch emerges from the mental foramen and supplies the nearby lip and skin.

The middle meningeal artery passes vertically upwards to the foramen spinosum. It is embraced by the two roots of the auriculotemporal nerve (Fig. 6.21). Its course and distribution are described on page 442. From the sympathetic plexus on the artery a branch enters the otic ganglion.

The accessory meningeal artery passes upwards through the foramen ovale and supplies the dura mater of the floor of the middle fossa and of the trigeminal (Meckel’s) cave. It is the chief source of blood supply to the trigeminal ganglion.

The remaining two arteries pass upwards to enter the ear and run superficial and deep to the tympanic membrane. The deep auricular artery is the more superficial of the two and supplies the external acoustic meatus, passing between the cartilage and bone. The deeper is the anterior tympanic artery which passes through the petrotympanic fissure to the middle ear to join the circular anastomosis around the tympanic membrane.

The second part of the maxillary artery gives off branches to the pterygoid muscles and masseter, and deep temporal branches to temporalis which ascend between the muscle and the temporal fossa. A small branch accompanies the buccal nerve.

The third part of the maxillary artery, in the pterygopalatine fossa, gives five branches (see below) which accompany branches of the maxillary nerve and the pterygopalatine ganglion (see p. 370). The artery then passes forwards, with the maxillary nerve, through the inferior orbital fissure into the orbit as the small infraorbital artery, which continues along the floor of the orbit and infraorbital canal to emerge with the infraorbital nerve on the face; its middle (occasional) and anterior superior alveolar branches supply maxillary incisor and canine teeth.

The sphenopalatine artery passes through the sphenopalatine foramen to enter the nasal cavity as its main artery of supply (see p. 374). The posterior superior alveolar artery gives branches that accompany the corresponding nerves through foramina in the posterior wall of the maxilla. The greater palatine artery gives off lesser palatine branches to the soft palate and passes through the greater palatine foramen to supply the hard palate (see p. 380). The very small pharyngeal artery enters the palatovaginal canal, and the artery of the pterygoid canal runs into its own canal.

The posterior superior alveolar nerve is a branch of the maxillary, given off in the pterygopalatine fossa and soon dividing into two or three branches which pierce the posterior wall of the maxilla separately. They are distributed to the molar teeth and the mucous membrane of the maxillary sinus. Another branch does not pierce the bone but runs along the alveolar margin of the maxilla as far forward as the first molar tooth, to supply the gingiva of the vestibule alongside the molar teeth. The posterior superior alveolar nerves can be blocked here by an injection through the vestibule of the mouth; on account of the proximity of the posterior superior alveolar vessels and the pterygoid venous plexus, a haematoma of some size may be a complication.

The pterygoid plexus is a network of very small veins that lie around and within the lateral pterygoid muscle. The veins draining into the pterygoid plexus correspond with the branches of the maxillary artery, but they do not return all the arterial blood, much of which returns from the periphery of the area by other routes (facial veins, pharyngeal veins, diploic veins). On the other hand the pterygoid plexus receives the drainage of the inferior ophthalmic vein (see p. 403), via the inferior orbital fissure, and the deep facial vein. The pterygoid plexus drains into a short maxillary vein which lies deep to the neck of the mandible. It runs back to join the superficial temporal vein and form the retromandibular vein. The plexus is valved and acts as a ‘peripheral heart’, aiding venous return by the pumping action of the lateral pterygoid muscle. Emissary veins connect the pterygoid plexus with the cavernous sinus through the foramen ovale and the foramen lacerum.

The sphenomandibular ligament is a flat band of tough fibrous tissue extending from a narrow attachment on the spine of the sphenoid. It broadens as it passes downwards to be attached to the lingula and inferior margin of the mandibular foramen (see Fig. 8.5B, p. 510). It is derived from the perichondrium of Meckel’s cartilage (see Fig. 1.20, p. 25). Between it and the neck of the mandible pass the auriculotemporal nerve and the maxillary artery and vein. Between it and the ramus of the mandible the inferior alveolar vessels and nerve converge to the mandibular foramen. Any remaining space between the ligament and the mandible is occupied by parotid gland tissue. The ligament is pierced by the mylohyoid nerve, a branch from the inferior alveolar nerve, and the accompanying small mylohyoid artery and vein.

One sensory and one motor. The meningeal branch, or nervus spinosus, re-enters the middle cranial fossa via the foramen spinosum, or the foramen ovale, supplying the meninges of the middle cranial fossa, and the mastoid air cells.

The nerve to the medial pterygoid runs forwards to the muscle, and gives a branch which passes through the otic ganglion without synapse to supply the two tensor muscles, tensor palati and tensor tympani.

This division is motor, except for one branch (the buccal nerve).

Two deep temporal branches to temporalis pass above the upper border of the lateral pterygoid muscle; one may be a branch of the buccal nerve.

The masseteric nerve, passing above the upper border of the lateral pterygoid, emerges through the mandibular notch to enter the deep surface of the masseter. It gives an articular branch to the temporomandibular joint.

The nerve to the lateral pterygoid runs with the buccal nerve and supplies both heads of the muscle.

The buccal nerve contains all the fibres of common sensation in the anterior division of the mandibular nerve. It emerges between the two heads of the lateral pterygoid (Fig. 6.20) and courses downwards and forwards on the buccinator, giving branches to the skin over the cheek. It then pierces the buccinator (giving proprioceptive fibres to it) and supplies the mucous membrane of the cheek and the gum of the lower jaw opposite the lower molars and second premolar (i.e. up to the mental foramen).

This division is sensory except for the motor fibres which are distributed via the mylohyoid nerve. There are three branches.

The auriculotemporal nerve is derived by two roots from the posterior division; they embrace the middle meningeal artery (Fig. 6.21). The nerve passes backwards between the neck of the mandible and the sphenomandibular ligament, lying above the maxillary vessels. It gives a branch to the temporomandibular joint, and ascends over the lateral aspect of the zygomatic arch behind the superficial temporal vessels (Fig. 6.11). The auricular part innervates the skin of the tragus and upper part of the lateral surface of the pinna, the external acoustic meatus and the outer surface of the tympanic membrane. The temporal part is distributed to the skin of the temple. The auriculotemporal nerve is in contact with the anteromedial surface of the parotid gland, and supplies it with postganglionic secretomotor fibres from the otic ganglion.

The inferior alveolar (dental) nerve emerges below the lower head of the lateral pterygoid and curves down on the medial pterygoid (Fig. 6.20). The nerve lies anterior to its vessels between the sphenomandibular ligament and the ramus of the mandible, and enters the mandibular foramen. It is into this region, just above the foramen, that anaesthetic solution is introduced for inferior alveolar nerve block (see p. 379). The inferior alveolar nerve lies midway between the anterior and posterior borders of the mandibular ramus at the level of the midpoint of the posterior border of the ramus. The mylohyoid nerve leaves the inferior alveolar at the foramen. It pierces the sphenomandibular ligament and lies on a groove on the mandible in front of the insertion of the medial pterygoid (see Fig. 8.5B, p. 510), accompanied by small branches of the inferior alveolar artery and vein. The mylohyoid nerve then runs forward on the superficial (cervical) surface of the mylohyoid supplying it and the anterior belly of the digastric (Fig. 6.6); the nerve often carries sensory fibres from a small area of submental skin and may participate in the sensory supply to lower incisors.

The inferior alveolar nerve runs with its vessels in the mandibular canal. It supplies the three molar and two premolar teeth. Then it divides into the mental nerve (see p. 354) and the incisive nerve. The latter nerve supplies the canine and both incisors, with some overlap into the opposite central incisor.

The lingual nerve appears below the lateral pterygoid and passes forwards and downwards on the medial pterygoid (Fig. 6.20). It then comes into contact with the mandible, where the bone is thinned to form a shallow groove below and medial to the third molar, just above the posterior end of the mylohyoid line (see Fig. 8.5B, p. 510). This groove separates the attachments of the pterygomandibular raphe above and mylohyoid muscle below (Fig. 6.22). The nerve is characteristically flattened here, rather than round, and it enters the mouth on the superior surface of the mylohyoid. It gives off a gingival branch which supplies all the lingual gum and mucous membrane of the floor of the mouth. The lingual nerve then crosses the submandibular duct (see p. 338) and runs forwards and medially to the tongue.

The chorda tympani (from the facial nerve, see p. 417) emerges through the petrotympanic fissure (Fig. 6.35), grooves the medial surface of the spine of the sphenoid, and joins the lingual nerve at an acute angle (Fig. 6.21), 2cm below the base of the skull, and is distributed with it to the anterior two-thirds of the tongue. It carries parasympathetic secretomotor fibres to the submandibular ganglion and taste fibres from the anterior two-thirds of the tongue (see p. 382).

This small body lies between the tensor palati and the mandibular nerve, just below the foramen ovale. It is a flat plaque, about 2–3mm in diameter, closely applied to the medial surface of the nerve (Fig. 6.21). It is a relay station for parasympathetic secretomotor fibres to the parotid gland; the lesser petrosal branch of the glossopharyngeal nerve brings these fibres. Postganglionic sympathetic fibres from the plexus around the middle meningeal artery, sensory fibres from the auriculotemporal nerve and a branch from the nerve to the medial pterygoid (to tensor tympani and palati) pass through the ganglion without relay. The connections of the otic ganglion are summarised on page 22.

The carotid sheath extends from the base of the skull to the arch of the aorta. In its upper part it is attached to the margins of the carotid canal and the jugular fossa. It contains here the internal carotid artery and internal jugular vein (see p. 343) and the last four (ninth to twelfth) cranial nerves. Medial to it lies the pharynx; laterally the deepest part of the parotid gland touches the sheath, partly separated by the styloid process and its three muscles. Anteriorly is the infratemporal fossa. Behind the carotid sheath lies the cervical sympathetic trunk on the prevertebral fascia.

The carotid canal lies immediately in front of the jugular foramen (which lies deep to the external acoustic meatus). The internal jugular vein lies behind the internal carotid artery at the base of the skull, but slopes as it descends, and at a lower level lies lateral to the common carotid artery as the vessels lie on scalenus anterior. At all levels the vagus nerve lies deep in the groove between the two, within the carotid sheath. The glossopharyngeal and accessory nerves emerge at the base of the skull between artery and vein and immediately curve away from each other superficial to the vessels (Fig. 6.23). The hypoglossal nerve emerges from the hypoglossal canal medial to the sheath. It passes through the sheath behind the inferior vagal ganglion and turns forwards to emerge between the artery and vein.

The glossopharyngeal nerve emerges from the anterior part of the jugular foramen on the lateral side of the inferior petrosal sinus (see p. 447). It makes a deep notch in the inferior border of the petrous bone and here its inferior ganglion bulges the nerve. The ganglion contains the cell bodies of most sensory fibres in the nerve. The nerve passes down on the lateral aspect of the internal carotid artery and curves forward around the lateral side of stylopharyngeus (Figs 6.23 and 6.41). It passes deep to the external carotid artery and continues forward deep to hyoglossus to reach the tongue (see p. 382).

The tympanic branch (Jacobson’s nerve) leaves the nerve at the jugular fossa and passes through a canaliculus on the ridge of petrous bone between the carotid and jugular foramina (Fig. 6.19) to enter the temporal bone and supply the middle ear, mastoid air cells and bony part of the auditory tube with sensory fibres. In this branch are also parasympathetic fibres from the inferior salivary nucleus. They run through the tympanic plexus on the promontory and continue in the lesser petrosal nerve. This nerve leaves the middle ear through its roof and runs along the floor of the middle cranial fossa to the foramen ovale, through which it passes to reach the otic ganglion (Fig. 6.27). The parasympathetic fibres relay in the otic ganglion for the secretomotor supply of the parotid gland and the other small glands of the vestibule of the mouth.

The motor branch to stylopharyngeus is given off as the nerve spirals around the posterior border of that muscle.

The carotid sinus nerve is the main supply to the carotid sinus and carotid body (baroreceptors and chemoreceptors.

One or more pharyngeal branches join the pharyngeal plexus on the middle constrictor muscle (see p. 386). They pierce the muscle and supply the mucous membrane of the oropharynx with common sensation and (a few) taste fibres.

The tonsillar branch supplies the mucous membrane over most of the (palatine) tonsil.

The lingual branch supplies the posterior one-third of the tongue with sensory fibres (common sensation and taste) and secretomotor fibres to the glands of the posterior third. These last relay in small ganglia in the mucous membrane.

The vagus nerve emerges through the middle compartment of the jugular foramen, in which a small enlargement constitutes the superior ganglion. Just below the base of the skull the elongated inferior ganglion dilates the trunk. The ganglia contain cell bodies of the afferent fibres of the vagus; the superior ganglion for the meningeal and auricular branches, the inferior ganglion for all the other sensory fibres. Just above the inferior ganglion the vagus is joined by a large branch from the accessory nerve (cranial part), comprising nucleus ambiguus fibres for the skeletal muscle of the soft palate, pharynx and larynx.

The nerve runs straight down the neck, within the carotid sheath, between and behind carotid (internal and common) artery and jugular vein. In the root of the neck it passes in front of the subclavian artery and so enters the mediastinum (see p. 196) to supply thoracic and abdominal viscera.

Meningeal branches pass up from the superior ganglion to supply the dura mater of the posterior fossa below the tentorium.

The auricular branch (Arnold’s nerve) runs laterally through a canaliculus in the lateral wall of the jugular fossa. It supplies the posteroinferior quadrant of the outer surface of the tympanic membrane and a small adjacent area of skin of the external acoustic meatus and a little area of skin on the cranial auricular surface.

The very fine carotid body branch forms a plexus with the carotid sinus branch of the glossopharyngeal for the supply of those structures.

The pharyngeal branch of the vagus passes forward between the internal and external carotid arteries (Fig. 6.23) and joins the pharyngeal plexus on the middle constrictor muscle. The fibres supply the muscles of the pharynx (except stylopharyngeus) and the muscles of the soft palate (except tensor palati, see p. 390).

The superior laryngeal nerve slopes downwards on the side wall of the pharynx deep to the internal carotid artery (Fig. 6.23). It divides into a large internal laryngeal nerve which pierces the thyrohyoid membrane to reach the piriform recess (see p. 388), carrying sensory fibres for the pharynx and larynx, and a small external laryngeal nerve which runs down close to the superior thyroid vessels, outside the larynx, to supply cricothyroid and contribute to the supply of the inferior constrictor.

The cervical cardiac branches are two on each side. They all pass down to the deep part of the cardiac plexus (see p. 194), except for the lower left branch which goes to the superficial part of the plexus.

The recurrent laryngeal nerve on the right hooks around the subclavian artery at the root of the neck (Fig. 6.9). On the left side the recurrent laryngeal nerve is given off in the superior mediastinum and recurves around the ligamentum arteriosum under the arch of the aorta (see Fig. 4.13, p. 192). Both nerves then ascend along the posterolateral border of the trachea, in a groove between it and the oesophagus, and pass under the lower border of the inferior constrictor. Both nerves have cardiac branches, and also supply the trachea, oesophagus and the cricopharyngeus part of the inferior constrictor, before entering the pharynx and larynx to supply the laryngeal muscles (except cricothyroid) and the laryngeal mucosa from the vocal folds downwards (see p. 396).

The accessory nerve is formed in the posterior cranial fossa by union of cranial and spinal (cervical) roots. The nerve occupies the middle compartment in the jugular foramen, just lateral to the vagus, with which it shares a meningeal sleeve. All the fibres of its cranial root leave the nerve in a branch which joins the vagus. The nerve, now consisting of cervical fibres only, runs downwards and backwards on the internal jugular vein (Fig. 6.23), where the latter lies on the transverse process of the atlas; the nerve crosses lateral (usually) or medial to the vein. It passes deep to the styloid process and posterior belly of the digastric, where it is crossed by the occipital artery. With the upper sternocleidomastoid branch of the occipital artery it reaches the sternocleidomastoid, supplies it and enters its deep surface. Emerging from the posterior border of the muscle it crosses the posterior triangle (see p. 333) to supply trapezius.

The hypoglossal nerve emerges from the hypoglossal canal. It picks up a branch from the anterior ramus of C1 and then spirals behind the inferior ganglion of the vagus to emerge between the internal carotid artery and internal jugular vein, passing through the carotid sheath. It then descends on the carotid sheath, deep to the styloid muscles and the posterior belly of digastric. It is crossed by the occipital artery and its lower sternocleidomastoid branch and then turns forwards, superficial to both carotid arteries and the loop of the lingual artery (Fig. 6.23), just above the tip of the greater horn of the hyoid bone. It continues forwards on the hyoglossus (Fig. 6.24), accompanied by veins draining the tip of the tongue, to supply tongue muscles.

The C1 fibres that join the hypoglossal nerve leave it progressively in the superior root of the ansa cervicalis and in the branches to thyrohyoid and geniohyoid. The small meningeal branch which enters the posterior fossa through the hypoglossal canal also comprises C1 fibres.

The maxillary nerve, giving a meningeal branch to the front of the middle cranial fossa, passes through the foramen rotundum in the greater wing of the sphenoid bone into the pterygopalatine fossa. Deviating laterally in the inferior orbital fissure for about 1cm, it turns forwards to enter the infraorbital groove and canal in the floor of the orbit, changing its name to the infraorbital nerve and eventually emerging from the front end of the canal at the infraorbital foramen to supply skin on the face (see p. 354). The zygomatic nerve arises from the maxillary in the fossa and runs above the maxillary in the inferior orbital fissure to enter the orbit (see p. 402). The posterior superior alveolar nerve is also given off in the fossa. It passes through the pterygomaxillary fissure on to the posterior wall of the maxilla (see p. 364).

In the fossa the maxillary nerve is connected to the pterygopalatine ganglion by two branches that carry fibres going both to and from the ganglion.

The pterygopalatine ganglion is a relay station between the superior salivary nucleus in the pons and the lacrimal gland and mucous and serous glands of the palate, nose and paranasal sinuses. It is the ganglion of hay fever (‘running nose and eyes’). Its connections are summarized on page 22.

The ganglion lies immediately in front of the opening of the pterygoid canal and the nerve of that canal runs straight into the back of the ganglion. The canal is below and medial to the foramen rotundum (Fig. 6.26), and so is the ganglion in relation to the maxillary nerve.

The autonomic root is the nerve of the pterygoid canal (Vidian nerve). This nerve is formed in the foramen lacerum by union of the greater petrosal nerve (see p. 417), containing mainly parasympathetic secretomotor fibres, with the deep petrosal nerve, containing sympathetic vasoconstrictor fibres. The former is a branch of the facial nerve and the latter is a branch from the internal carotid sympathetic plexus. The combined nerve passes forward in the pterygoid canal and joins the ganglion.

The postganglionic secretomotor fibres to the lacrimal gland leave the ganglion and join the maxillary nerve, pass in its zygomatic branch into the orbit, join the lacrimal branch of the ophthalmic nerve and so reach the lacrimal gland.

The rest of the fibres in the connections between the maxillary nerve and the ganglion are sensory and, like the sympathetic fibres in the deep petrosal nerve, they pass through the ganglion without relay. The only cell bodies in the ganglion are parasympathetic (secretomotor). The branches of the pterygopalatine ganglion are distributed to the nose, palate and nasopharynx. Every branch carries a mixture of all three kinds of fibres: sensory, secretomotor and sympathetic.

Medial posterior superior nasal nerves pass through the sphenopalatine foramen, cross the roof of the nose, and are distributed to the septum. The largest of these is termed the nasopalatine nerve, as it continues beyond the septum through the incisive canal to supply the anterior part of the hard palate.

The lateral posterior superior nasal nerves pass through the sphenopalatine foramen and turn forward to supply the posterosuperior part of the lateral wall of the nose.

The greater palatine nerve passes down through the greater palatine canal, between the perpendicular plate of the palatine bone and the maxilla (Fig. 6.27). At the greater palatine foramen it turns forward to supply the mucous membrane of the hard palate. As it descends it also supplies the posteroinferior part of the lateral wall of the nose and the medial wall of the maxillary sinus.

The lesser palatine nerves, two in number, pass down behind the greater palatine nerve and emerge through the lesser palatine foramina. They pass back to the soft palate and the mucous membrane of the palatine tonsil. They carry the only non-secretomotor fibres transmitted in the greater petrosal nerve; these are sensory (taste) fibres that have their cell bodies in the genicular ganglion of the facial nerve.

The pharyngeal nerve passes back through the palatovaginal canal (a little canal between the vaginal process of the medial pterygoid plate and the sphenoidal process of the palatine bone) and supplies the mucous membrane of the nasopharynx. A few fine orbital branches enter the orbit via the inferior orbital fissure and supply periosteum of the orbital floor and the mucous membrane of the sphenoidal and ethmoidal sinuses.

The maxillary artery passes through the pterygomaxillary fissure, enters the pterygopalatine fossa in front of the ganglion and gives off five branches. These and the artery’s further course into the orbit are described on page 363. The branches of the maxillary artery in the pterygopalatine fossa may be ligated by an approach through the maxillary sinus (see p. 376), the fossa being entered instrumentally through the posterior wall of the sinus. An alternative endoscopic approach is via the sphenopalatine foramen.

Veins accompany the above arteries and, passing through the fossa, emerge at the pterygomaxillary fissure to drain into the pterygoid plexus. In general, vessels in the fossa lie anterior to the nerves.