Chapter 50: The neck
The sternocleidomastoid, or more simply sternomastoid, muscle arises by two heads from the front of the manubrium sterni and the upper surface of the medial third of the clavicle (see figs. 6-2, 19-2, and 50-8). It ascends obliquely in the neck (figs. 50-1 and 50-2) and is inserted into the lateral surface of the mastoid process (see fig. 42-10) and the lateral part of the superior nuchal line on the occipital bone (see fig. 42-14). A variable interval between the two heads of origin (fig. 50-1) lies over the termination of the internal jugular vein.
The sternomastoid muscle lies deep to the platysma and the external jugular vein, and it covers the great vessels of the neck, the cervical plexus, and the cupola of the parietal pleura.
The trapezius muscle (see fig. 8-4) arises from the superior nuchal line, the external occipital protuberance, the ligamentum nuchae, and the spinous processes of the last cervical and all the thoracic vertebrae. The upper fibers are inserted into the superior surface of the lateral third of the clavicle, and the remaining fibers go to the scapula, as described with the upper limb.
The sternomastoid and trapezius muscles are supplied mainly by the accessory nerve (cranial nerve XI). Cervical nerves 2-4 also contribute.
The sternomastoid muscles, acting together, flex the head and neck forward against resistance. Flexion of the head is usually performed by gravity, however. One sternomastoid muscle inclines the head ipsilaterally while the head is rotated contralaterally. Spasm of a sternomastoid produces a wry neck (torticollis). The trapezius elevates the scapula. The accessory nerve (external branch) is tested by asking the subject to shrug the shoulders (trapezius) and then to rotate the head (sternomastoid).
The sternomastoid divides the quadrilateral area of the side of the neck into anterior and posterior triangles (fig. 50-2). The posterior triangle is bounded by the sternomastoid, the trapezius and by the clavicle. The anterior triangle is bounded by the sternomastoid, the anterior median line of the neck, and the inferior border of the mandible.
Posterior triangle (fig. 50-3)
The posterior triangle is divided by the inferior belly of the omohyoid muscle into an occipital triangle superior to it and a supraclavicular triangle inferior to it (fig. 50-2C).
The roof of the posterior triangle consists of fascia and the platysma muscle. The floor is formed by a series of longitudinal muscles - the splenius capitis, levator scapulae, and the middle and posterior scalenes - all covered by the prevertebral fascia.
The most important contents of the posterior triangle are the accessory nerve (cranial nerve XI), brachial plexus, third part of the subclavian artery, and lymph nodes. The accessory nerve (external branch), which crosses the transverse process of the atlas, either pierces or runs deep to the sternomastoid, which it supplies. At the middle of the posterior border of the sternomastoid, the accessory nerve crosses the posterior triangle obliquely (fig. 50-3B). It then passes deep to the anterior border of the trapezius and supplies that muscle.
The brachial plexus is formed by the anterior primary rami of cervical nerves 5-8, and the first thoracic nerve, which are sandwiched between the anterior and middle scalene muscles. In the posterior triangle, the brachial plexus is found in the angle between the posterior border of the sternomastoid and the clavicle, where it can be "blocked" by injection of a local anesthetic, thereby rendering insensitive all the deep structures of the upper limb and the skin distal to the middle of the arm.
The cervical plexus (see table 50-5) is situated deeply in the upper part of the neck, under cover of the internal jugular vein and the sternomastoid. Formed by the anterior primary rami of cervical nerves 1-4, it gives rise to superficial branches, which emerge near the middle of the posterior border of the sternomastoid (fig. 50-4). The branches are (1) the lesser occipital nerve, which hooks around the accessory nerve and ascends to the auricle; (2) the great auricular nerve which ascends superficial to the sternomastoid and toward the parotid region; (3) the transverse cervical nerve, which crosses the sternomastoid into the anterior neck; and (4) the supraclavicular nerves, which descend as three nerves that cross the clavicle and supply the skin over the shoulder.
The external jugular vein drains most of the scalp and face and also contains a significant amount of cerebral blood. It begins near or in the parotid gland by a highly variable union of smaller veins (fig. 50-5). It descends under cover of the platysma and obliquely crosses the sternomastoid muscle, where it is frequently visible. It empties into the subclavian or internal jugular vein. The tributaries of the external jugular vein, which are very variable, include communications with the internal jugular and an inconstant anterior jugular vein that descends anterior in the neck.
The anterior triangle is bounded by the sternomastoid, the anterior median line of the neck, and the inferior border of the mandible. The anterior triangle is crossed by the digastric and stylohyoid muscles and by the superior belly of the omohyoid. These muscles allow further subdivisions of the triangle to be made, such as the carotid triangle, which is bounded by the sternomastoid, the posterior belly of the digastric, and the superior belly of the omohyoid (see fig. 50-2B).
The roof of the anterior triangle consists of fascia and the platysma. The platysma (see fig. 50-24) is a subcutaneous, quadrilateral muscular sheet. It arises from the skin over the deltoid muscle and the pectoralis major and is inserted into the lower border of the mandible and the skin around the mouth. It is supplied by the cervical branch of the facial nerve. It raises the skin, thereby probably relieving pressure on the underlying veins.
The floor of the anterior triangle is formed by a series of muscles, including the mylohyoid and hyoglossus, infrahyoid muscles, and the constrictors of the pharynx. The carotid triangle contains a portion of the external carotid artery and its branches. The common and internal carotid arteries and the internal jugular vein tend to be overlapped by the anterior border of the sternomastoid (see fig. 50-12).
The infrahyoid "strap" muscles (fig. 50-6 and table 50-1) are four strap-like muscles that anchor the hyoid bone. They are arranged in (1) a superficial plane comprising the sternohyoid and omohyoid muscles and (2) a deep plane comprising the sternothyroid and thyrohyoid muscles. The first three muscles are innervated by the ansa cervicalis and its superior root, whereas the thyrohyoid muscle is supplied by cervical fibers carried in the hypoglossal nerve. All the fibers to the infrahyoid muscles are derived ultimately from cervical nerves l-3. The muscles act, according to circumstances, either to depress the larynx, hyoid bone, and floor of the mouth or to resist their elevation.
The omohyoid muscle consists of two bellies, an inferior belly from the scapula, which ends in a middle tendon, and a superior belly, which continues from the tendon to the hyoid bone. The middle tendon, situated deep to the sternomastoid, is attached by fascia to the manubrium, first costal cartilage, and clavicle.
The cervical vertebrae (fig. 50-7) are described with the back. The lower part of the neck is a transitional region between the thorax and the upper limbs (fig. 50-8). The inlet (superior aperture) of the thorax is a kidney-shaped opening bounded by the T1 vertebra, the first ribs and costal cartilages, and the manubrium sterni. The chief structures that pass through the inlet are vessels (brachiocephalic trunk and left common carotid, left subclavian, and the internal thoracic arteries), nerves (phrenic, vagus, recurrent laryngeal, and sympathetic trunk), the trachea and esophagus, cupola of the parietal pleura, apex of the lung, and thymus. The apex of the axilla is bounded by the upper border of the scapula, the external border of the first rib, and the posterior surface of the clavicle. The chief structures that pass through this interval are the brachial plexus, the axillary artery and vein and lymph vessels.
The thymus, described with the thorax, has a cervical part anteriorly on the trachea, posterior to the sternohyoid and sternothyroid muscles.
The thyroid gland is an endocrine organ in the neck; it may become enlarged to form a goiter. The gland is covered by (1) an adherent, fibrous capsule and (2) a sheath ("false capsule") derived from the deep cervical fascia.
The thyroid gland, seen from the front, is H or U shaped, consisting of right and left lobes connected by an isthmus (figs. 50-9, 50-10 and 50-11). The lobes can be palpated. Each lobe has an apex, which ascends between the sternothyroid muscle and the inferior constrictor of the pharynx; a base directed inferiorward; and three surfaces. The lateral surface is covered by infrahyoid muscles; the medial surface is related to the larynx, pharynx, trachea, and esophagus; the posterior surface (fig. 50-9B) is related to the carotid sheath and its contents and to the pre vertebral muscles. The isthmus connects the right and left lobes and lies anterior to rings 2 to 4 of the trachea. The inconstant pyramidal lobule (or "lobe") ascends from the isthmus (fig. 50-9A) and may be anchored to the hyoid bone by fibrous or muscular tissue (levator glandulae thyroideae).
Blood supply (fig. 50-11).
The thyroid gland is highly vascular and is supplied mainly by the superior thyroid artery (from the external carotid) and the inferior thyroid artery (from the thyrocervical trunk of the subclavian). The thyroidea ima artery is an inconstant branch of variable origin (e.g., from the brachiocephalic trunk) that ascends to the isthmus. The thyroid gland is drained by superior and middle thyroid veins into the internal jugular vein and by inferior thyroid veins into the brachiocephalic vein.
The lymph vessels drain (1) upward to the deep cervical nodes and (2) downward to the paratracheal nodes. The isthmus drains into the prelaryngeal and pretracheal nodes.
Development. The thyroid gland develops largely as a median diverticulum from the tongue (foramen cecum). Parts of the embryonic thyroglossal duct may remain as cysts, the pyramidal lobule, and accessory thyroid tissue.
The parathyroid glands are small endocrine organs that are essential to life and that therefore must not be removed during thyroidectomy. They usually lie outside the thyroid capsule and on the medial half of the posterior surface of each lobe of the thyroid gland. Although usually four (superior and inferior on each side), they vary from two to six in number.
The trachea, with its incomplete rings of hyaline cartilage (see fig. 53-9), lies partly in the neck and partly in the thorax. The trachea extends from the level of the C6 vertebra to about T6 or 7. The cervical part (see fig. 50-9) is related in front to infrahyoid muscles, the thyroid isthmus (generally over rings 2 to 4), and vessels (e.g., inferior thyroid veins). Tracheotomy, the making of an artificial opening in the trachea, is sometimes necessary for treating respiratory obstruction. For non-surgeons, however, cricothyrotomy is safer and preferable.
The esophagus lies in the neck, thorax, and abdomen (q.v.). The esophagus extends from the C6 vertebra to about T11. Its narrowest point is adjacent to the inferior constrictor of the pharynx, about 15 cm from the upper incisor teeth. The cricopharyngeal fibers of the inferior constrictor hav a sphinctor-like effect. The upper part of the esophagus consists of skeletal muscle that is attached to the lamina of the cricoid cartilage. The esophagus is posterior to the trachea and anterior to the longus colli and vertebral column.
The main vessels of the head and neck (fig. 50-12) are the right and left common carotid arteries, each of which divides in the carotid triangle into (1) an external carotid artery, which supplies the structures external to the skull as well as the face and most of the neck, and (2) an internal carotid artery, which is distributed within the cranial cavity and the orbit. The common and internal carotid arteries lie in a cleft bounded by (1) the cervical vertebrae and their attached muscles, (2) the pharynx and esophagus, larynx and trachea, and thyroid gland, and (3) the sternomastoid (see fig. 50-29C).
The carotid arteries ascend along a line from (1) the sternoclavicular joint, along the anterior border of the sternomastoid muscle, to (2) a point medial to the lobule of the auricle. The left common carotid has also a thoracic part. Each common carotid artery is crossed by the corresponding omohyoid muscle opposite the cricoid cartilage (the C6 vertebral level), and this is the site for compression. The common carotid artery divides usually at the level of the upper border of the lamina of the thyroid cartilage. The pulsation of the common and external carotid arteries can be felt along the anterior border of the sternomastoid muscle.
The right common carotid artery arises from the brachiocephalic trunk (posterior to the right sternoclavicular joint), whereas the left common carotid is a branch of the arch of the aorta and hence has a thoracic portion before it reaches the neck (posterior to the left sternoclavicular joint). The common carotid artery is crossed by the omohyoid at the level of the cricoid cartilage (C6), and then lies under cover of the anterior border of the sternomastoid. The artery is related to the cervical vertebrae. The common carotid artery can be compressed against the transverse processes of the cervical vertebrae by pressing medially and posteriorly with the thumb. The common carotid usually gives off no named branches in the neck. Each common carotid artery divides usually at the level of the upper border of the lamina of the thyroid cartilage (the C4 vertebral level).
External carotid artery (see fig. 50-14)
The external carotid artery extends from the bifurcation of the common carotid artery in the carotid triangle to the retromandibular area. The external carotid artery is crossed by the hypoglossal nerve and passes deep to the posterior belly of the digastric and the stylohoid muscle. The constrictors of the pharynx lie medially. The external carotid divides in the substance of the parotid gland into the superficial temporal and maxillary arteries.
The eight branches of the external carotid artery are described in the following paragraphs and summarized in table 50-2. The first four generally arise in the carotid triangle.
1. The superior thyroid artery (see fig. 50-11) arises in the carotid triangle, descends deep to the infrahyoid muscles to enter the apex of the corresponding lobe of the thyroid gland, where it divides into glandular branches. It generally gives off the superior laryngeal artery, which accompanies the internal laryngeal nerve.
2. The lingual artery (see fig. 49-4) may arise in common with the facial artery. Its description in three parts is based on its relationship to the hyoglossus muscle. The first part forms a loop in the carotid triangle and is crossed by the hypoglossal nerve. The second part passes deep to the hyoglossus and lies on the middle constrictor. The third part (deep lingual artery) runs along the inferior surface of the tongue.
3. The facial artery (see fig. 47-5B), in its cervical part, ascends in the carotid triangle and enters a groove on the posterior aspect of the submandibular gland. It then descends to wind around the inferior border of the mandible at the anterior margin of the masseter muscle. The facial artery, in its facial part, proceeds superior and anterior in a tortuous course on the face. It supplies the muscles of facial expression, to which it is variably related. The facial artery ends at the medial angle of the eye by anastomosing with branches of the ophthalmic artery. The facial vein is posterior and straighter. The cervical part of the facial artery gives off palatine, tonsillar, glandular (submandibular), and muscular branches. The facial part gives off the inferior and superior labial arteries and a nasal branch and ends as the angular artery.
4. The occipital artery (fig. 50-12C) arises from the posterior aspect of the external carotid artery. Its description in three parts is based on its relationship to the sternomastoid muscle. In the carotid triangle, the hypoglossal nerve hooks around the artery, which ascends deep to the lower border of the posterior belly of the digastric muscle. Deep to the sternomastoid, the artery occupies a groove medial to the mastoid process. Behind the sternomastoid, the occipital artery divides into branches to the scalp. The most important branch descends (as superficial and deep divisions) to anastomose with transverse and deep cervical branches of the subclavian artery (see fig. 50-21). The descending branch of the occipital artery provides the chief collateral circulation after ligation of the external carotid or the subclavian artery.
6. The ascending pharyngeal artery (see fig. 49-4) arises medially and ascends on the wall of the pharynx.
The internal carotid artery begins at the level of the upper border of the lamina of the thyroid cartilage. It enters the skull through the carotid canal of the temporal bone, and it ends in the middle cranial fossa by dividing into the anterior and middle cerebral arteries.
The internal carotid artery has no named branches in the neck. Its course may be considered in four parts: cervical, petrous, cavernous, and cerebral. The last three have been described already.
The internal carotid artery begins in the carotid triangle, which it exits by passing deep to the digastric and stylohyoid muscles. The vessel is closely related to cranial nerves IX, X, and XII and to the sympathetic trunk. The internal carotid artery lies on the transverse processes of the cervical vertebrae and against the wall of the pharynx.
The carotid sinus (fig. 50-13) is a slight dilatation of the internal carotid artery or jointly of the common and internal carotid arteries near the bifrucation. Its wall contains receptors sensitive to changes in blood pressure. The carotid body lies in the angle of bifurcation of the common carotid artery and is sensitive to hypoxemia.
The glossopharyngeal nerve (cranial nerve IX) contains afferent nerve fibers from the tongue and pharynx (hence its name) and efferent fibers to the stylopharyngeus muscle as well as parasympathetic preganglionic secretomotor fibers to the parotid gland. It emerges from the brain stem (medulla) and passes through the jugular foramen, where it has superior (jugular) and inferior (petrous) ganglia containing the cell bodies of the afferent fibers. The nerve then passes between the internal jugular vein and the internal carotid artery and descends deep to the styloid process and muscles. The glossopharyngeal nerve curves anteriorly around the stylopharyngeus, runs deep to the posterior border of the hyoglossus (see fig. 49-2), and passes between the superior and middle constrictors of the pharynx.
The branches of the glossopharyngeal nerve are described in the following paragraphs:
1. The tympanic nerve is secretomotor and vasodilator to the parotid gland. It enters the bone (tympanic canaliculus) to reach the tympanic cavity, where it divides to form the tympanic plexus on the promontory on the medial wall of the middle ear (see fig. 44-5). Having supplied the adjacent mucosa, the plexus forms the lesser petrosal nerve, which traverses the temporal bone, passes through or near the foramen ovale, and synapses in the otic ganglion. Postganglionic secretomotor fibers arise there and reach the parotid gland by the auriculotemporal nerve (see fig. 48-9).
2. A communicating branch joins the auricular branch of the vagus.
3. The branch to the carotid sinus (see fig. 50-13) supplies the carotid sinus and body with afferent fibers.
4. The pharyngeal branches unite on the middle constrictor with vagal and sympathetic branches. They are sensory to the pharyngeal mucosa.
5. The motor branch to the stylopharyngeus arises at that muscle.
6. Tonsillar branches are sensory to the mucosa.
7. Lingual branches supply taste and general sensory fibers to the posterior third of the tongue and the vallate papillae. The ninth cranial nerve is tested by tactile sensation in the pharynx and sometimes by taste on the posterior tongue. Touching the posterior wall of the oropharynx normally induces elevation of the palate and contraction of the pharyngeal constrictors (gag reflex).
The vagus nerve (cranial nerve X), which is mostly afferent, is "vagrant" in the head, neck, thorax, and abdomen. It is both afferent and efferent to the pharynx and larynx. It emerges from the brain stem (medulla) and passes through the jugular foramen, where it has superior (jugular) and inferior (nodose) ganglia containing the cell bodies of the afferent fibers. The vagus is then joined by the internal branch of the accessory nerve, the fibers of which are distributed with branches of the vagus.
The vagus descends within the carotid sheath, between the internal jugular vein and the internal and common carotid arteries. The vagus then crosses anterior to the first part of the subclavian artery; its subsequent course is described with the thorax and abdomen.
The branches of the vagus are described in the following paragraphs:
l. The meningeal branch, which contains spinal fibers (cervical nerves 1 & 2), supplies the dura of the posterior cranial fossa.
2. The auricular branch passes through the temporal bone (tympanomastoid fissure) and supplies the auricle and external acoustic meatus.
3. The pharyngeal branches are the chief motor nerves to the pharynx and soft palate. Along with glossopharyngeal and sympathetic nerve fibers, these branches form the pharyngeal plexus on the constrictors of the pharynx. The plexus supplies most of the muscles of the pharynx and soft palate. Accessory fibers in the vagus are tested by asking the subject to say" ah": the uvula should proceed backward in the median plane.
4. The superior laryngeal nerve descends along the side of the pharynx and divides into internal and external branches. The internal laryngeal branch (or nerve) is afferent from the mucosa of the larynx superior to the vocal folds. The nerve pierces the thyrohyoid membrane, divides into terminal branches and communicates with the recurrent laryngeal nerve. The external laryngeal branch (or nerve) pierces the inferior constrictor of the pharynx and enters the cricothyroid, supplying both muscles.
5. Depressor nerves (carotid branches) assist the glossopharyngeal nerve in supplying the carotid sinus and body.
6. Cardiac branches arise in the neck and thorax and are often considered in superior, middle, and inferior groups. They end in the cardiac plexus.
7. The recurrent laryngeal nerve supplies the mucosa of the larynx inferior to the vocal folds and all the intrinsic muscles of the larynx except the cricothyroid. As a result of the embryologic development of the aortic arches, the right and left recurrent nerves arise at different levels, the right nerve hooking inferior to the first part of the subclavian artery and the left nerve to the arch of the aorta and the ligamentum arteriosum (fig. 50-17). Both recurrent nerves ascend in or near the groove between the trachea and the esophagus, and both are closely related to the thyroid gland and inferior thyroid artery; therefore they are in danger in thyroid operations. Damage to one recurrent nerve renders the ipsilateral vocal fold motionless and results in alteration of the voice. The recurrent nerve gives off cardiac, tracheal, and esophageal branches and a sensory branch to the laryngopharynx. It divides into two or more branches before passing deep to the lower border of the inferior constrictor of the pharynx and behind the cricothyroid joint to gain the larynx.
Accessory nerve (fig. 50-19)
The accessory nerve (cranial nerve IX) arises by the union of a cranial and a spinal part. The cranial roots emerge from the medulla. The spinal roots emerge from the spinal cord (sometimes as far inferior as the seventh cervical segment) and form a trunk that ascends in the vertebral canal, passing through the foramen magnum. Both parts, cranial and spinal, exit through the jugular foramen. After traversing the jugular foramen the cranial part, or internal branch, joins the vagus. It contains motor fibers to skeletal muscles and is best regarded as a portion of the vagus. By means of the pharyngeal and laryngeal branches of the vagus, it is distributed to the soft palate, constrictors of the pharynx, and larynx. The spinal part, or external branch, of the accessory nerve is distributed to the sternomastoid and trapezius muscles. It crosses the transverse process of the atlas, descends deep to the styloid process and the posterior belly of the digastric, and usually pierces the sternomastoid, which it supplies. At the middle of the posterior border of the sternomastoid muscle, the accessory nerve crosses the posterior triangle of the neck obliquely (see fig. 50-3B), lying on the levator scapulae and in relation to lymph nodes. It passes deep to the anterior border of the trapezius and supplies that muscle. The nerve communicates with cervical nerves 2-4. The spinal part of the accessory nerve is tested by asking the subject to shrug the shoulders (trapezius) and then to rotate the head (sternomastoid).
Hypoglossal nerve (fig. 50-20)
The hypoglossal nerve (cranial nerve XII) is chiefly the motor nerve to the tongue. It emerges from the brain stem (medulla) and traverses the hypoglossal canal of the occipital bone. It then descends between the internal carotid artery and the internal jugular vein, deep to the posterior belly of the digastric. The hypoglossal nerve loops anteriorly around the occipital artery and crosses the internal carotid, external carotid, and lingual arteries (see figs. 49-4 and 50-14). It courses lateral to the hyoglossus and passes deep to the digastric and mylohyoid muscles (see fig. 49-2).
Most of the branches of the hypoglossal nerve are hypoglossal in origin, whereas others are spinal and are merely travel with the hypoglossal nerve for a short distance. The meningeal branches, the superior root of the ansa cervicalis, the nerve to the thyrohyoid muscle, and the branch to the geniohyoid muscle consist of cervical fibers. The branches of the hypoglossal nerve are described in the following paragraphs:
1. Meningeal branches supply the dura of the posterior cranial fossa.
2. The superior root of the ansa cervicalis descends from the hypoglossal nerve to the ansa cervicalis and supplies infrahyoid muscles (see fig. 50-6B).
3. The thyrohyoid branch arises in the carotid triangle and supplies the thyrohyoid muscle.
4. The terminal lingual branches supply the extrinsic (except the palatoglossus) and all intrinsic muscles of the tongue and communicate with the lingual nerve. The hypoglossal nerve is tested by asking the subject to protrude the tongue (genioglossus and intrinsic muscles). A lesion of one hypoglossal nerve would result in deviation of the protruded tongue toward the affected (same) side.
The main artery to the upper limb is called by various names (subclavian, axillary, and brachial) during its course. The territory supplied by the subclavian artery extends as far as the forebrain, abdominal wall, and fingers. The left subclavian artery arises directly from the arch of the aorta, whereas the right subclavian is from the brachiocephalic trunk. The course of each subclavian artery may be considered in three parts: (1) from the origin of the vessel to the medial border of the anterior scalene muscle, (2) behind that muscle, and (3) to the lateral border of the first rib, where the subclavian changes name to the axillary artery.
The first part arches superiorly and laterally from posterior to the sternoclavicular joint and is deeply placed under cover of the sternomastoid, sternohyoid, and sternothyroid muscles. The second part of the subclavian artery extends a few centimeters superior to the clavicle. It lies anterior to the apex of the lung and cupola of the parietal pleura. The third part of the subclavian artery is the most superficial, and its pulsations can be felt on deep pressure. It lies mainly in the supraclavicular triangle, on the first rib (see fig. 8-7), and anterior to the lower trunk of the brachial plexus. It can be compressed against the first rib by pressing downward, backward, and medially in the angle between the clavicle and the posterior border of the sternomastoid muscle (see fig. 50-3B). This is also the site of ligation, after which the collateral circulation to the upper limb is generally adequate.
The subclavian vein, which is the continuation of the axillary vein, passes anterior to the anterior scalene and unites with the internal jugular vein to form the brachiocephalic vein.
Most of the branches arise from the first part of the subclavian artery. They are described in the following paragraphs:
1. The vertebral artery (fig. 50-23), despite its name, supplies chiefly the posterior part of the brain. Arising medial to the anterior scalene, it ascends through the foramina transversaria of the C6 to C1 vertebrae, passes posterior to the lateral mass of the atlas (see fig. 39-3) and along the posterior arch of the atlas. It penetrates the posterior atlantooccital membrane and enters the cranial cavity by passing superiorly through the foramen magnum. At the lower border of the pons, it unites with the vessel of the opposite side to form the basilar artery, which ends by dividing into the two posterior cerebral arteries. The course of the vertebral artery may be considered in four parts: cervical, vertebral, suboccipital, and intracranial. The cervical part ascends posterior to the common carotid artery in the pyramidal space between the longus colli and anterior scalene (see Fig. 50-28B). The vertebral part ofthe artery, accompanied by a venous plexus and sympathetic nerve fibers, gives branches to the spinal cord and vertebrae. The suboccipital and intracranial parts of the vertebral artery have been described already.
(a) The inferior thyroid artery ascends anterior to the anterior scalene and arches medially anterior to the vertebral vessels and posterior to the carotid sheath. It is closely related to the middle cervical ganglion and the recurrent laryngeal nerve. It enters the posterior surface of the thyroid gland. The inferior thyroid artery gives branches to the vertebrae (ascending cervical artery), larynx (inferior laryngeal artery), trachea, pharynx, esophagus, and thyroid gland.
(b) The suprascapular artery passes laterally across the anterior scalene and phrenic nerve and then across the subclavian artery and cords of the brachial plexus, finally contributing to the anastomoses around the scapula. It gives off suprasternal, acromial, and articular branches.
(c) The transverse cervical artery passes laterally (more superior than the suprascapular artery) across the anterior scalene and phrenic nerve and then across the trunks of the brachial plexus in the posterior triangle. It supplies the trapezius (as the superficial cervical artery).
4. The costocervical trunk arches over the cupola of the parietal pleura to reach the neck of the first rib, where it divides into two branches: (a) the deep cervical artery, which ascends to anastomose with the descending branch of the occipital artery, and (b) the highest intercostal artery, which descends posterior to the pleura and usually gives off the first two posterior intercostal arteries.
5. The dorsal scapular artery generally passes between the trunks of the brachial plexus and accompanies the dorsal scapular nerve to the rhomboid muscles. It may, however, be replaced by a deep branch of the transverse cervical artery.
Abnormal compression of the subclavian or axillary vessels, the brachial plexus, or both produces the signs and symptoms of the "neurovascular compression syndromes" of the upper limb (often generically called "thoracic outlet syndromes"). The features of vascular compomise may include pain, paresthesia (prickling), numbness, weakness, discoloration, swelling, ulceration, and gangrene, may be produced also by other causes. The neurovascular bundle to the upper limb is liable to be compressed: (1) between the scalenus anterior and the middle scalene (see fig. 50-28B), where the compression may be produced or accentuated by a cervical rib (fig. 50-22); (2) between the first rib and the clavicle (see fig. 8-5); or (3) near the coracoid process, where the neurovascular bundle is crossed by the pectoralis minor muscle (see fig. 8-7).
Cupola of pleura (see fig. 50-28A)
The cupola is the cervical pleura, i.e., the continuation of the costal and mediastinal pleura over the apex of the lung. It begins at the inlet of the thorax along the sloping internal border ofthe first rib (see fig. 8-5). The cupola and apex of the lung project into the root of the neck up to about 3 cm above the medial third of the clavicle. The cupola is covered by fascia, the suprapleural membrane (attached to the first rib and to C.V.7 and T.V.1); muscle fibers (scalenus minimus) are sometimes present. The cupola and apex of the lung occupy the pyramidal interval between the scalene muscles and the longus colli and are posterior to the subclavian vessels and anterior scalene.
The sympathetic supply to the head and neck arises in segments spinal segments T1 and T2 (and sometimes C8) of the spinal cord. The preganglionic fibers leave in the ventral roots and pass through rami communicantes to the thoracic part of the sympathetic trunk. They then ascend to the cervical part of the sympathetic trunk, where they synapse. Postganglionic fibers are distributed to the blood vessels, smooth muscle, and glands of the head and neck.
The cervical part of the sympathetic trunk consists of three or four ganglia connected by an intervening cord or cords. Postganglionic fibers leave the trunk by gray rami communicantes and also in branches that go directly to blood vessels or viscera. Any cause of interruption of sympathetic nerve impulses to the head, including damage to the cervical part of the sympathetic trunk, produces Horner's syndrome: constriction of the pupil (meiosis, caused by unopposed parasympathetic action), drooping ofthe upper eyelid (ptosis, caused by paralysis of smooth muscle), an illusion that the eye has receded (enophthalmos), redness and increased temperature of the skin (vasodilatation), and absence of sweating (anhidrosis). The preganglionic fibers for the eye and orbit are probably from T1 (range: C8 to T4), and they probably enter the cervicothoracic ganglion. A local anesthetic injected near the cervicothoracic ganglion will "block" the cervical and upper thoracic ganglia (stellate ganglion block), thereby relieving vascular spasm involving the brain or an upper limb.
1. The superior cervical ganglion lies inferior to the base of the skull and posterior to the internal carotid artery. It distributes postganglionic fibers to cranial nerves IX-XII and cervical nerves 1-4, the carotid sinus and body, the pharyngeal plexus and larynx, and the heart. A plexus on the external carotid artery is continued on its branches to the salivary glands. A large ascending branch from the ganglion, the internal carotid nerve, accompanies the internal carotid artery and forms a plexus that contributes to several cranial nerves, the tympanic and greater petrosal nerves, the ciliary ganglion (pupillodilator fibers), and the anterior and middle cerebral arteries.
2. The middle cervical ganglion, usually superior to the arch of the inferior thyroid artery, is very variable.
3. The vertebral ganglion generally lies anterior to the vertebral artery and inferior to the arch of the inferior thyroid artery. Cords connect this ganglion with those above and below, and another cord, the ansa subclavia, loops around and forms a plexus on the first part of the subclavian artery.
4. The cervicothoracic (stellate) ganglion comprises two variably fused components: inferior cervical and first thoracic ganglia. It lies posterior to the vertebral artery and anterior to the C7 transverse process and the neck of the first rib. Preganglionic rami come from the T1 nerve, and postganglionic (gray) rami go to cervical nerves 6-8 and the T1 nerve. These fibers enter the brachial plexus and are distributed to the upper limb. Other branches of the ganglion go to the heart and to the subclavian and vertebral arteries. The vertebral plexus is ultimately distributed along the basilar artery. The plexuses on the posterior cerebral arteries may be derived from the vertebral or internal carotid plexuses.
Internal jugular vein (fig. 50-25)
The internal jugular vein drains the brain, neck, and face. It commences in the jugular foramen as the continuation of the sigmoid sinus. At the base of the skull, the internal carotid artery (in the carotid canal) lies anterior to the internal jugular vein (in the jugular foramen), and the two vessels are there separated by cranial nerves IX-XII (see fig. 48-2B). The internal jugular vein descends in the carotid sheath and is hidden by the sternomastoid muscle. The internal and common carotid arteries accompany the vein medially, and the vagus lies posterior to and between the vein and the arteries. The deep cervical lymph nodes lie along the course of the internal jugular vein. The vein passes deep to the interval between the two heads of the sternomastoid muscle (see fig. 50-12B) and ends posterior to the medial end of the clavicle by uniting with the subclavian vein to form the brachiocephalic vein. Dilatations are found at its beginning and near its end (superior and inferior bulbs).
The tributaries, which are variable, include the inferior petrosal sinus and the pharyngeal, lingual, and superior and middle thyroid veins. The right lymphatic duct or (on the left) the thoracic duct opens usually into the internal jugular vein at or near its junction with the subclavian vein.
The thoracic duct receives the lymph from most of the body, including the left side of the head and neck. The duct (fig. 50-26), on leaving the thorax, arches laterally anterior to the left vertebral artery, phrenic nerve, and anterior scalene and posterior to the carotid sheath. It receives the left jugular trunk and ends variably anterior to the first part of the left subclavian artery in or near the angle between the left internal jugular and subclavian veins. The right lymphatic duct receives the lymph from the right side of the head and neck, right upper limb, and right side of the thorax. This duct, which is seldom present as a single structure (fig. 50-27B), has components (the right jugular, subclavian, and bronchomediastinal trunks) that usually drain separately into the right internal jugular vein, the subclavian vein, or both.
All the lymphatic vessels from the head and neck drain into the deep cervical nodes, either (1) directly from the tissues or (2) indirectly after traversing a more superficial group of nodes. Several of these groups of lymph nodes form a "pericervical collar" at the junction of the head and neck (fig. 50-27A): these are the occipital, retro-auricular (mastoid), parotid, submandibular, buccal (facial), and submental nodes. The superficial tissues drain into these groups and also into the superficial cervical nodes.
The superficial cervical nodes are in (1) the posterior triangle along the external jugular vein and (2) the anterior triangle along the anterior jugular vein.
The deep cervical nodes include several groups, the most important of which forms a chain along the internal jugular vein, mostly under cover of the sternomastoid muscle. The jugulodigastric node lies on the internal jugular vein immediately inferior to the posterior belly of the digastric. It receives important afferents from the posterior tongue and from the tonsils. The jugulo-omohyoid node lies on the vein immediately superior to the middle tendon of the omohyoid. It receives afferents from the tongue. One group of deep nodes is found in the posterior triangle and is related to the accessory nerve. Other groups are prelaryngeal, pretracheal, paratracheal, and retropharyngeal. These take part in the drainage of deeper structures (e.g., middle ear and nasal cavity). The efferent vessels from the deep cervical nodes form the jugular trunk, which usually joins the thoracic duct on the left and enters the internal jugular-subclavian junction on the right.
The ventral rami of cervical nerves 1-4 unite to form the cervical plexus, whereas those of cervical nerves 5-8 and the first thoracic nerve form the brachial plexus. The cervical plexus is an irregular series of loops from which the branches arise. Cutaneous areas and muscles are thereby supplied by more than one spinal nerve (table 50-5). The cutaneous branches all emerge near the middle of the posterior border of the sternomastoid muscle (see fig. 50-4). The cervical plexus lies anterior to the levator scapulae and middle scalene, under cover of the internal jugular vein and the sternomastoid. The ventral rami receive postganglionic rami communicantes from the cervical sympathetic ganglia.
The ansa cervicalis is a loop on or in the carotid sheath. It is formed by fibers of cervical nerves 1-3 (see figs. 50-6B and 50-20). It has a superior root, which descends from the hypoglossal nerve (but consists of spinal fibers), and an inferior root, which connects the ansa with cervcial nerves 2 and 3. The ansa and its superior root supply the infrahyoid muscles (but the thyrohyoid receives its cervical fibers directly from the hypoglossal nerve).
The phrenic nerve arises chiefly from C4 and supplies the diaphragm and the serosa of the thorax and abdomen. It often has a root from C3 and usually an accessory root from C5 (see fig. 50-24) that may reach the phrenic through the nerve to the subclavius. The phrenic nerve, formed at the lateral border of the anterior scalene, descends on the anterior surface of that muscle (see fig. 50-8) under cover of the internal jugular vein and the sternomastoid. It lies deep to the prevertebral fascia, is crossed by the transverse cervical and suprascapular arteries (fig. 50-28B), and is accompanied by the ascending cervical artery from the inferior thyroid. It passes between the subclavian artery and vein (see fig. 50-17), crosses the internal thoracic artery, and proceeds through the thorax. Damage to the phrenic nerve collapses a lung by paralyzing and thereby elevating the hemidiaphragm.
The anterior scalene (except at its insertion) lies entirely under cover of the sternomastoid.
The subclavian artery passes posterior to the anterior scalene, whereas the phrenic nerve lies on the muscle. The anterior scalene arises from the anterior tubercles; the middle and posterior scalene (the latter often absent or blended with the middle) arise from the posterior tubercles of the cervical transverse processes. The ventral rami of the cervical nerves emerge between the anterior and posterior tubercles; hence the brachial plexus emerges between the anterior scalene and the middle scalene. The scalenes may act as muscles of inspiration even during quiet breathing; they become active during strong expiratory effects, and they may be important in coughing and straining. A pyramidal interval occurs between the scalemes laterally and the longus colli medially, and into this the pleura and apex of the lung project upward (fig. 50-28A).
Cervical fascia (fig. 50-29)
The cervical fascia "affords that slipperiness which enables structures to move and pass over one another without difficulty, as in swallowing, and allowing twisting of the neck without it creaking like a manilla rope Ð a looseness, moreover, that provides the easiest pathways for vessels and nerves to reach their destinations" (Whitnall).
The fascia of the neck comprises three layers: the investing, visceral (pretracheal), and prevertebral layers.
The investing layer is attached to the major bony prominences: the external occipital protuberance, superior nuchal line, ligamentum nuchae, cervical spinous processes, mastoid and styloid processes, lower border of the mandible, zygomatic arch, hyoid bone, acromion, clavicle, and manubrium. The layer surrounds the trapezius, roofs the posterior triangle, surrounds the sternomastoid, and roofs the anterior triangle. It forms the sheaths of the parotid and submandibular glands. At the manubrium, it bounds the suprasternal space, which encloses the sternal heads of the sternomastoid and the jugular venous arch.
The visceral (pretracheal) layer, limited to the anterior neck, is more extensive than its name suggests. It lies inferior to the hyoid bone and is attached to the oblique lines of the thyroid cartilage and to the cricoid cartilage. It surrounds the thyroid gland, forming its sheath, and it invests the infrahyoid muscles and the air and food passages. Infections from the head and neck can spread anterior to the trachea or posterior to the esophagus and reach the superior mediastinum in the thorax.
The prevertebral layer is attached to the base of the skull and to the transverse processes of the cervical vertebrae. It covers the pre vertebral muscles, scalenes, phrenic nerve, and deep muscles of the back, and therefore the floor of the posterior triangle. Anterior to the subclavian artery, it is prolonged laterally as the axillary sheath, which also invests the brachial plexus.
The carotid sheath, which is fused with all three layers of the cervical fascia, is a condensation around the common and internal carotid arteries, internal jugular vein, and vagus nerve.
Prevertebral muscles (see table 50-6)
The longus capitis, which covers the superior part of the longus colli, extends from the inferior cervical vertebrae to the occipital bone. The longus colli (see fig. 50-28) consists of a vertical bundle spanning vertebral bodies and of oblique fasciculi that connect cervical transverse processes to- vertebral bodies. The recti capitis anterior and lateralis connect the atlas to the occipital bone. The longus colli is active during talking, coughing, and swallowing. The pre vertebral muscles and sternomastoid muscles act with, and as antagonists to, the upper deep muscles of the back.
50-1 Why is the sternomastoid known officially as the sternocleidomastoid muscle?
50-2 How is the accessory nerve tested?
50-3 What are the most important contents of the posterior triangle?
50-4 Why is the carotid triangle so called?
50-5 What is the significance of "oid" in thyroid?
50-6 What are the coverings of the thyroid gland?
50-7 What is a goiter?
50-8 Why may the voice be affected by thyroid surgery?
50-9 List some anomalies of thyroid development.
50-10 At which level is tracheotomy performed?
50-11 What is the line of the carotid arteries in surface anatomy?
50-12 List the branches of the external carotid artery.
50-13 How is the glossopharyngeal nerve tested?
50-14 What is the relationship between cranial nerves X and XI?
50-15 How is the hypoglossal nerve tested?
50-16 Between which two muscles is the middle (second) part of the subclavian artery lodged?
50-17 Where is the site of compression and ligation of the subclavian artery?
50-18 Which important structures are found in the pyramidal interval between the scaleni and longus colli?
50-19 How do sympathetic fibers reach the cervical ganglia?
50-20 What is the stellate ganglion?
50-21 Where are most of the deep cervical lymph nodes concentrated?
50-22 Which important nerve crosses the front of the anterior scalene?
50-23 Which are the three main layers of the cervical fascia?
50-24 What are the contents of the carotid sheath?
Figure 50-1 Surface anatomy of the neck. The sternal and clavicular heads of the sternomastoid muscles are clearly visible. On each side, the anterior triangle of the neck is bounded by the anterior border of the sternomastoid, the anterior median line of the neck, and the lower border of the mandible. (From Royce, J., Surface Anatomy, Davis, Philadelphia, 1965, courtesy of the author and publisher.)
Figure 50-2 Triangles of the neck. A shows the platysma, which roofs parts of both the anterior and posterior triangles. B shows the division of the neck by the sternomastoid into anterior and posterior triangles. C and D show the subdivisions of the triangles.
Figure 50-3 Posterior triangle of the neck. A, Floor. B, Chief contents. The brachial plexus meets and follows the subclavian artery. The third part of the subclavian artery is the site for compression.
Figure 50-4 The cutaneous branches of the cervical plexus. The vertical line represents the posterior border of the sternomastoid: the branches of the plexus emerge from the middle of this border. e.A., great auricular nerve; L.O., lesser occipital nerve; S.C., supraclavicular nerves. T.C., transverse cervical nerve; 1 to 4, cervical nerves. (After von Lanz and Wachsmuth.)
Figure 50-5 Superficial veins of the head and neck. Variations are very common. The internal jugular vein can be seen deep to the sternomastoid.
Figure 50-7 Cervical vertebrae. A, Anteroposterior view. Note the translucency of the larynx and trachea. B, Lateral view. Note the anterior and posterior arches of the atlas, the curve of the cervical column and the slopes of the articular facets. The teeth display metallic fillings.
Figure 50-8 The main structures that cross the thoracic inlet. See text. In addition to various vessels, note the recurrent laryngeal nerves and (on the left side) the thoracic duct. (After von Lanz and Wachsmuth.)
Figure 50-9 A, The thyroid gland, anterior aspect. B, Horizontal section through the line shown in A, showing the relationships of the thyroid gland, (after von Lanz and Wachsmuth.)
Figure 50-10 Scintigram of the thyroid gland produced by uptake of a radioisotope. The right and left lobes are united by the isthmus. (from DeLand, F.H., and Wagner, H.N., Atlas of Nuclear Medicine, vol. 3, W.B. Saunders Company, Philadelphia, 1972, courtesy of the authors.)
Figure 50-11 The blood supply of the thyroid gland. Only the arteries are shown on one side and only the veins on the other. Most anastomotic vessels are omitted.
Figure 50-12 The carotid arteries in the neck. A, Important bony landmarks. B, The sternomastoid and underlying great vessels. Note the internal jugular vein in the interval between the heads of the sternomastoid below. C, The carotid arteries. Note the branches of the external carotid artery.
Figure 50-13 The carotid sinus and its innnervation from the glossopharyngeal and vagus nerves and from the sympathetic trunk.
Figure 50-14 The last four cranial nerves below the base of the skull. The glossopharyngeal nerve passes between the carotid arteries. The vagus descends between the jugular vein and the internal and common carotid arteries, the accessory nerve crosses the internal jugular vein. The hypoglossal nerve, superficial to the great vessels, winds around the origin of the occipital artery. The maxillary artery disappears deep to the neck of the mandible.
Figure 50-15 Summary of the branches of the last four cranial nerves in the head and neck.
Figure 50-16 The glossopharyngeal nerve.
Figure 50-17 The vagus and phrenic nerves, anterior aspect. Note the different levels of origin of the right and left recurrent laryngeal nerves. The anterior scalene muscle is depicted on each side. The thoracic duct can be seen terminating on the left side of the body.
Figure 50-18 The vagus nerve.
Figure 50-19 The vagus and accessory nerves. The superior and inferior ganglia of the vagus are shown above and below the jugular foramen, respectively.
Figure 50-20 The hypoglossal nerve.
Figure 50-21 The branches of the subclavian artery: vertebral, internal thoracic, thyrocervical trunk, costocervical trunk, and descending scapular. The second part of the subclavian artery is shaded.
Figure 50-22 Cervical ribs. A, An unusually long transverse process of C7 (arrow). B, A minute cervical rib with head, neck, and tubercle. C, A cervical rib bound to the first rib: in other instances it may end freely. (After von lanz and Wachsmuth.)
Figure 50-23 The vertebral artery, a branch of the subclavian, presents cervical, vertebral, suboccipital, and intracranial parts. It unites with its fellow of the opposite side to form the basilar artery, which divides into the right and left posterior cerebral arteries.
Figure 50-24 The right sympathetic trunk in the neck, lateral aspect. Only cervical nerves 1 to 5 are shown. The numerals on the left side of the drawing refer to those cervical and thoracic nerves to which rami communicantes (postganglionic fibers) are given. The numerals on the right side refer to the cervical vertebrae. The subclavian (in transverse section) and vertebral arteries are shown.
Figure 50-25 The internal jugular vein and its tributaries. Note the valves at the terminations of the subclavian and internal jugular veins: these are the last valves before the blood reaches the heart. (After Grant.)
Figure 50-26 A, A horizontal section in which the arch formed by the thoracic duct is seen between the anterior scalene muscle (posterior) and the internal jugular vein and common carotid artery (anterior) The phrenic nerve is visible on the anterior scalene. B, The termination of the thoracic duct, anterior aspect.
Figure 50-27 The lymphatic drainage of the head and neck. A, The superficial groups of cervical lymph nodes. The wide, shaded band indicates the "pericervical collar" of nodes. Each circle represents a group of nodes. The arrows show the direction of drainage. B, The deep cervical lymph nodes. The drawing at the lower right shows one of many patterns that may be found on the left side of the body.
Figure 50-28 A, The cupola of the pleura, anterior scalene, and longus colli; anterior aspect and slightly from the right side. The cupola projects upward between the scalenes and the longus colli, about 3 cm above the medial third of the clavicle (interrupted line). B, The third part of the subclavian artery and the brachial plexus between the anterior scalene and the middle scalene. The lower trunk of the plexus lies posterior to the artery. The phrenic nerve, which descends almost vertically on the obliquely set anterior scalene, is bound to the front of the muscle by the transverse cervical and suprascapular arteries. The anterior scalene, longus colli, and first part of the subclavian artery form a triangle. The carotid tubercle of C6 lies at the apex, and the vertebral artery ascends through the triangle to reach the foramen transversarium of C6. (A is based on von Lanz and Wachsmuth.)
Figure 50-29 Horizontal sections illustrating the cervical fascia. A shows the general arrangement of the three layers. B presents the pretracheal layer at the level of C7. C shows the three layers at the level of C6, on the right. (C is based on Truex and Kellner.)