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The Neck

787

A

Figure 8-4. Lateral aspect of the neck (right side), showing the cervical nangles that are used for descriptive purposes. A, The boundaries of ■e posterior triangle are: the clavicles, the posterior border of the ster-ocleidomastoid muscle, and the anterior border of the trapezius muscle. The boundaries of the anterior triangle are: the anterior border of the emocleidomastoid muscle, the inferior margin of the mandible, and

the anterior median line of the neck. B, Subdivisions of the cervical triangles. O indicates omohyoid; D, digastric; T, trapezius. Observe that the accessory nerve (CN XI) divides the posterior triangle into superior and inferior parts. Observe also that the inferior belly of the omohyoid muscle divides the posterior triangle into a large occipital triangle (su­ periorly) and a smaller supraclavicular triangle (inferiorly).

Occasionally the sternocleidomastoid muscle is injured at birth, resulting in a condition known as congenital torticollis or wryneck (Fig. 8-9). There is fixed rotation and tilting of the head owing to contracture of this muscle. Stiffness of the neck results from fibrosis and shortening of the muscle on one side. Because torticollis is a correctable condition, it is not usually seen in a more advanced form than that illustrated in Figure 8-9. Most cases of congenital torticollis result from fearing of fibers of the sternocleidomastoid when pulling the infant’s head excessively during a difficult birth, particularly in a breech presentation.

Triangles of the Neck
Each side of the neck is divided into two triangles, anterior and posterior, by the sternocleidomastoid muscle (Fig. 8-4). These cervical triangles, which are useful for descriptive pur­ poses, have a common boundary, the sternocleidomastoid.

The Neck

789

Auricularis posterior

Occipital lymph node Great occipital nerve

0
-

Occipital artery

Sternocleidomastoid

Great auricular nerve"] External jugular v e i n l

Lesser occipital nerve “Fascial carpet” of posterior triangle Accessory nerve (CN XI) Cervical branch of facial nerve Transverse cervical nerve

Platysma Nerve to trapezius from C3, C4 edial supraclavicular nerve

Lateral supraclavicular nerve

Intermediate supraclavicular nerve

Figure 8-7 .

Superficial dissection of the right side of the neck, pri­

marily to illustrate the posterior cervical triangle and its contents (Fig.

i-4). The superficial fascia and the superficial layer of the deep fascia

have been removed. The deep layer of cervical fascia forms a ‘T is: carpet” for the floor of the posterior triangle. Note the accessor* r.cr. the only motor nerve superficial to this “ carpet.”

Posterior Triangle of the Neck
B oundaries of the P osterior C ervical Triangle (Figs. 8* 8-7, and 8-8). This triangle is bounded: anteriorly by the x-sterior border of the sternocleidomastoid; posteriorly by the ulterior border of the trapezius muscle, and inferiorly by the rid d le third of the clavicle. The clavicle forms the base of the in te rio r triangle; its apex is formed where the borders of the ^emocleidomastoid and trapezius muscles meet on the superior wtchal line of the occipital bone of the skull (see Fig. 7-3). The : :pital artery passes through the apex of the posterior triangle before it ascends over the posterior aspect of the head.

Roof of the Po sterio r C ervical Triangle (Figs >-5 8). The posterior triangle is covered by deep fascia. .*r e ­ covers the space between the trapezius and sternocleidomastoid muscles. Superficial to the deep fascial roof are the fascia, platysma, superficial veins, cutaneous nerves, arc Floor of the Po sterio r C ervical Triangle Fig> vv 8-10, 8-28, and 8-31). The fascial and muscular floor of mis triangle is formed (superior to inferior) by the splemiis cap:;:>. levator scapulae, scalenus medius, and scalenus posterior mus­ cles (Table 8-1). These muscles are covered by the prevertebral layer of deep cervical fascia. This “ fascial carpet" is a lateral prolongation of the prevertebral fascia.

790

Clinically Oriented Anatomy

Semispinalis capitis l is Occipital artery j ry

Splenius capiti

Sternocleidomastoid

t

Great auricular ner* External jugular ve ?

Nerves to levator scapulae

Transverse cervical nerve Supraclavicular nerves

Accessory nerve Internal jugular vein Nerve to rhomboids Scalenus medius Nerve to serratus anterior Transverse cervical artery Phrenic nerve deep to “fascial carpet” I Brachial plexus |_Scalenus anterior Omohyoid

Pectoralis major

Figure 8-8. Deeper dissection of the right side of the neck than that shown in Figure 8-7. Observe the nerves that are deep to the “ fascial carpet” covering the muscular floor of the posterior triangle.

Contents of the Posterior Triangle The posterior cervical triangle contains mostly vessels and nerves that connect the neck and upper limb (Fig. 8-12). V eins in the Posterior C ervical Triangle (Figs. 8-7, 8-8, and 8-12). The external jugular vein begins near the angle of the mandible, just inferior to the lobule of the auricle, by the union of the posterior division of the retromandibular vein with the posterior auricular vein. It crosses the sternocleidomastoid muscle in the superficial fascia and then pierces the deep fascial roof of the posterior cervical triangle at the posterior border of this muscle, about 5 cm superior to the clavicle. The external

jugular vein passes obliquely through the inferior part of posterior triangle and usually ends by emptying into the sub. vian vein about 2 cjn superior to the clavicle. The external jugi vein drains most of the scalp and face on the same side. The subclavian vein is the major venous channel draining upper limb. It lies posterior to the clavicle and so is not re in the posterior triangle, but it may rise as far superiorly as subclavian artery. When venous pressure is within the normal range, the external jugular vein is either invisible or observable for onh a short distance superior to the clavicle. However, when ven-

794

Clinically Oriented Anatomy

Splenius capitis

Levator scapulae Nerves to levator scapulae Accessory nerve — Supraclaviculc' Scalenus medius I ius Nerve to rhomboidss j id Phrenic nerve Scalenus ante - : Accessory phrenic Transverse cervical arten

Scalenus posterior

Serratus anterior and nerves C5, C6

- Omohyoid fascia

Suprascapular

*

Axillary arte". ¿

Figure 8-11. Dissection of the right side of the neck and superolateral part of the thorax, showing the muscles forming the floor of the posterior cervical triangle. The deep fascia (“ carpet” ) covering the floor and part

of the clavicle have been removed. Note that the phrenic nerve is related to the anterior surface of the scalenus anterior muscle

paralyzed by a cervical nerve block, this procedure is not performed on patients with pulmonary or cardiac disease. Brachial Plexus Block (Figs. 8-8, 8-11, and 8-12). For anesthesia of the upper limb, the anesthetic agent is injected around the supraclavicular part of the brachial plexus of nerves. The subclavian artery is located by palpation before making the injection to avoid entering it. The main site of injection is superior to the midpoint of the clavicle. The needle is directed inferomedially toward the first rib (see Fig. 1-5).

M uscles in the P osterior C ervical Triangle (Figs. 8-8, 810 to 8-12, and 8-16 to 8-18; Table 8-1). As described (p. 789), four muscles form the floor of the posterior triangle. From superior to inferior they are: splenius capitis, levator scapulae, scalenus medius, and scalenus posterior. The Splenius Capitis Muscle (Figs. 8-10A and 8-11; see also Fig. 4-41). This is the larger superior part of the splenius mus­

cle. Its attachments, nerve supply, and main actions are in Table 8-1. The splenius (G. splenion, a bandage) sen “ bandage” that covers and holds the deeper muscles of th in place. The Levator Scapulae (Figs. 8-105 and 8-11; see aL 6-40). This thick straplike muscle is composed of four k bound slips. Its attachments, nerve supply, and main act: given in Table 8-1. It is partially covered by the stemo mastoid and trapezius muscles. As its name levator iL indicates, this muscle elevates the scapula. The Scalenus Medius Muscle (Figs. 8-10 to 8-12. 34). This is the longest and largest of the scalene mu>c attachments, nerve supply, and main actions are given 8-1. The middle scalene muscle is perforated by the don, pular nerve and the superior two roots of the long thoracic In Figure 8-11, note that the scalenus medius lies p o su the ventral rami (roots) o f the brachial plexus and the tin

The Neck

795

Trapezius Sternocleidomastoid Levator scapulae Branches of C5

[

Phrenic nerve Accessory phrenic nerve

Scalenus pos teriori "sverse cervical artery Branch of C6

Scalenus anterior

Internal jugular vein Serratus anterior Brachiocephalic vein Suprascapular nerve, artery, and vein

Subclavian vein

Deltoid

Axillary artery and vein

Figure 8-12. Close up of a dissection of the right side of the neck and superolateral part of the thorax. Observe the brachial plexus of nerves passing to the upper limb and the parts of the subclavian vessels that ire in the posterior cervical triangle. Compare with Figure 8-11, noting

the the omohyoid muscle and its fascia have been removed to show the third part of the subclavian artery and the subclavian vein. Note that the internal jugular vein (usually the largest vein in the neck) is not in the posterior triangle, but it is very close to it.

of the subclavian artery. A detailed discussion of the brachial plexus appears in Chapter 6 (pp. 512-525). The Scalenus Posterior Muscle (Figs. 8-11 and 8-12). This muscle is not completely separated from the scalenus medius muscle. Its attachments, nerve supply, and main actions are given in Table 8-1. This is the smallest and most deeply situated of ihe scalene muscles. The slender inferior belly of the straplike omohyoid muscle G. om os, shoulder), which is described with the infrahyoid muscles (Fig. 8-16; Table 8-3), also passes through the inferior part of the posterior triangle (Figs. 8-45 and 8-11). The omohyoid muscle is an important landmark in the neck; it can often be seen contracting when some people speak, especially those with thin necks. Lym ph N odes in the Posterior C ervical Triangle (see Fig. ~-32). There is a superficial group of cervical lymph nodes along the external jugular vein and a deep group accompanying the internal jugular vein. These nodes receive afferent lymph

vessels from the parotid, occipital, and mastoid lymph nodes and from vessels in the muscles and skin. Efferent lymph vessels pass to the supraclavicular lymph nodes in the supraclavicular (subclavian) triangle of the neck (Fig. 8 - 4 5 ) . Subdivisions of the Posterior Cervical Triangle The inferior belly of the omohyoid muscle divides the pos­ terior cervical triangle into a large superior occipital triangle (Fig. 8-45) and a small inferior supraclavicular triangle. The occipital triangle (Fig. 8-45) was given its name because the occipital artery appears in its apex (Fig. 8-8). The most important nerve crossing the occipital triangle is the accessory nerve (CN X I) . The supraclavicular (subclavian) triangle is the smaller sub­ division of the posterior cervical triangle (Fig. 8-45). Its location is indicated on the surface of the neck by the supraclavicular fossa (Fig. 8-1). The external jugular vein and suprascapular

The Neck

799

Great auricular nerve

Accessory nerve ™ Sternocleidomastoid branch of occipital artery____

Digastric, anterior belly Facial vein Facial artery Facial nerve, cervical branch Submandibular gland

Retromandibular vein Facial vein

Internal jugular vein | Superior root of ansa cervic alisj Inferior root of ansa cervicalis

o

Thyrohyoid Superior thyroid vein Sternocleidomastoid branch of superior thyroid artery

Figure 8-16. Superficial dissection of the anterior triangle of the neck. Observe the submandibular gland, lymph nodes (green), and the cervical

branch of the facial nerve in the subdivision of the anterior triangle called the submandibular triangle (Fig. 8-42?).

the ‘ ‘digastric triangle. ’ ’ The flo o r o f the submandibular triangle is formed, from anterior to posterior, by the following muscles: mylohyoid, hyoglossus, and middle constrictor of the pharynx. Contents of the Submandibular Triangle (Figs. 8-14, 816, and 8-17). The submandibular gland nearly fills this tri­ angle. It wraps itself around the free posterior border of the mylohyoid muscle, not unlike the capital letter U on its side. It sends a thin sheet of muscle superior to this muscle. This deep process separates the superficial and deep parts of the subman­ dibular gland. About half the size of the parotid, this salivary gland is usually palpable as a soft mass between the body of the mandible and the mylohyoid muscle. It is easily felt when the mylohyoid muscle is tensed by forcing the tip of the tongue against the maxillary incisor teeth. In Figure 8-16, note the position of the submandibular lymph nodes. They lie on the submandibular gland and along the inferior border of the man­ dible. The submandibular duct, about 5 cm in length (Fig. 8-14), passes from the deep process of the gland, parallel to the tongue, to open by one to three orifices into the oral cavity. The sub­ mandibular duct opens on an elevation, the sublingual papilla, which is produced at the side of the lingual frenulum by the sublingual gland (see Figs. 7-85 and 7-102). The hypoglossal nerve (CN XII), which is motor to the intrinsic and extrinsic muscles of the tongue, passes into the

submandibular triangle, (Figs. 8-14 and 8-17). The nerve to the mylohyoid m uscle, a branch of the inferior alveolar nerve (Figs. 7-25 and 8-17), and parts of the facial artery and vein also pass through the submandibular triangle (Fig. 8-16). The submental artery is a branch of the facial artery (Fig. 8-18). The submandibular gland, along with the parotid gland, may become inflamed (e.g., owing to mumps). The swelling formed by the enlarged gland can be seen easily and palpated. Because of the location of these glands (Fig. 8-16), it becomes painful to open the mouth and to eat.

The C arotid T riangle (Figs. 8-4 and 8-16 to 8-22). This vascular area is bounded by the superior belly of the omohyoid, the posterior belly of the digastric, and the anterior border of the sternocleidomastoid muscle. The carotid triangle is an important area because the common carotid artery and its branches ascend into it (Fig. 8-17). Its pulse can be auscultated (L. to listen to) with a stethoscope, or it can be palpated by placing the digits in the triangle and compressing the artery lightly against the transverse processes of the cervical vertebrae. At the level of the superior border of the thyroid cartilage, the common carotid artery divides within the carotid triangle (Fig. 8-24) into the internal and external carotid arteries. The Carotid Sinus (Figs. 8-19 and 8-24). This is a slight

800

Clinically Oriented Anatomy

Common trunk of facial and lingual arteries Fascia enveloping submandibular gland Stylohyoid

External carotid artery Occipital artery — Hypoglossal nerve | Accessory n e r v e l Superior root of ansa cervicalis” I Sternocleidomastoid artery Internal carotid artery | External carotid a r t e r y l Ansa cervicalis I Common carotid a r t e r y l Internal jugular vein | _ _ Sternocleidomastoid b ran ch ! Sternocleidomastoid “Fascial carpet” of posterior triangle

_

C [bnl Smt uea
_ Hyoid bone Mylohyoid

Facial artery arte'"* Nerve to mylo h.a

I Internal laryngeal nerve [infe rior constrictor - Thyrohyoid

t
#

External laryngeal nerve Superior thyroid artery

Transverse cervical vein — --------- — —

Jm

m

I f ^

..... ^Sternothyroid |_Sternohyoid

Omohyoid fascia

Anterior jugular vein Sternocleidomastoid

Figure 8-17. Deeper dissection of the right side of the neck than that shown in Figure 8-16. Observe that the facial and lingual arteries in this dilation of the proximal part of the internal carotid artery; it may involve the common carotid. A blood pressure regulating area, the carotid sinus is innervated principally by the glossopharyn­ geal nerve (CN IX) through a branch called the carotid sinus nerve (see Fig. 7-74). The sinus is also supplied by the vagus nerve and the sympathetic division of the autonomic nervous system (Figs. 8-22 and 8-28). The carotid sinus reacts to changes in arterial blood pressure and effects appropriate modifications reflexly. The carotid triangle provides an important surgical ap­ proach to the carotid arterial system (Fig. 8-17). It is also

person arise by a common trunk that passes deep to the stylohyoid digastric muscles to enter the submandibular triangle. important for approaches to: (1) the internal jugular vein; (2) the vagus (CN X) and hypoglossal (CN XII) nerves; and (3) the cervical sympathetic trunk (Figs. 8-21, 8-22, and 8-28). The carotid sinus responds to an increase in arterial pres­ sure by slowing the heart, owing to the parasympathetic out­ flow from the brain through the vagus nerve (Fig. 8-33). Pressure on the carotid sinus may cause syncope (fainting), and if the person happens to have a supersensitive carotid sinus, it may cause cessation of the heart beat (temporary or permanent). Although the common carotid artery can be oc­ cluded by compressing it against the carotid tubercle of the C6 vertebra (Fig. 8-29), e.g., for control of hemorrhage in the neck, it is recommended that you not practice this on your

The Neck

803

Esophagus---------------—----------- —

^

— — --------------- Vertebral body

Thyr0id 9'and
carotid artery-----------------------Anchoring b a nd--------------------------------------' Trachea ------------------------- Pretracheal fascia ------------------------------------Left recurrent laryngeal nerve

Figure 8-21.

Transverse section of the neck showing, in particular, the relations of the thyroid gland and carotid sheath.

Internal carotid artery Digastric, posterior belly. External carotid artery Facial artery Hyoglossus Mylohyoid CN XI Lingual artery

CN XII Internal jugular vein

Carotid sheath

Common carotid artery CN X

Figure 8-22. Structures in the carotid triangle, a subdivision of the anterior cervical triangle (see also Fig. 8-45). Observe the carotid sheath and its contents (see also Fig. 8-21). Note the key position of the posterior belly of the digastric muscle, running from the mastoid process of the

temporal bone to the hyoid bone. Note that the intermediate tendon of the digastric muscle is attached to the hyoid bone by a fascial sling. Observe that all the vessels and nerves cross deep to the posterior belly of the muscle (see also Figs. 8-17 and 8-18).

(Table 8-3) and the neck viscera (e.g., the thyroid and parathy­ roid glands). The S u hm ental T riangle (Figs. 8-4B, 8-16, 8-17, 8-20, and 8-23). This unpaired suprahyoid area is bounded inferiorly by the body of the hyoid bone and laterally by the right and left anterior bellies of the digastric muscles. The flo o r o f the sub­ mental triangle is formed by the two mylohyoid muscles, which meet in a median fibrous raphe. The apex o f the submental triangle is at the symphysis menti (see Fig. 7-2), and its base is formed by the hyoid bone. The submental triangle contains the submental lymph nodes, which receive lymph from the tip of the tongue, the floor of the mouth, the mandibular incisor teeth and associated gingivae, the central part of the lower lip, and the skin of the chin. Lymph from the submental lymph nodes drains into the submandibular and deep cervical lymph nodes

(Figs. 8-16 and 8-31; see also Fig. 7-32). The submental triangle also contains small veins that unite to form the anterior jugular vein (Fig. 8-17; see also Figs. 6-33 and 7-29). The muscular triangle (Fig. 8-4#) is used surgically for approaches to the thyroid and parathyroid glands and for exposure of the trachea, esophagus, and inferior levels of the carotid-jugular vascular system (Figs. 8-25, 8-32, and 8-36). Most cancers of the lip occur on the lower lip and tend to spread through the lymphatic system. Depending on the site of the lesion, metastases spread to the submental nodes from the central part of the lower lip and to the submandibular nodes from other parts of the lip. In advanced cancers of the central part of the lip, the submandibular and deep cervical lymph nodes would also be involved because they receive lymph from the submental nodes (see Fig. 7-32).

804

Clinically Oriented Anatomy

Submental lymph node Submental branch of facial artery

—— -“Digastric, anterior belly Mylohyoid

Fascia covering submandibular gland

Omohyoid Laryngeal prominence

Sternohyoid

Cut edge of investing layer of deep cervical fascia

Vein connecting facial and anterior jugular veins

Pretracheal fascia

Sternal head Clavicular h e a d j

Sternocleidomastoid

Sternothyroid

Jugular venous arch

Suprasternal space

Figure 8-23. Superficial dissection of the anterior aspect of the neck. Note the submental triangle, bounded inferiorly by the body of the hyoid bone and laterally by the right and left anterior bellies of the digastric Most arteries in the anterior cervical triangle arise from the common carotid artery or one of its branches, the internal or external carotid arteries.

muscles (see als6 Fig. 8-4Z?). Observe that it contains some submenu! lymph nodes and that the floor of the submental triangle is formed b> the two mylohyoid muscles. it supplies structurej within the skull. The internal carotid ar­ teries are two o f the fo u r major arteries that supply blood to the brain (see Fig. 7-54). Each artery arises from the common carotid artery at the level of the superior border of the thyroid cartilage and passes superiorly, almost in a vertical plane, to enter the carotid canal in the petrous part of the temporal bone (see Figs. 7-65 and 7-42). A plexus of sympathetic fibers accom­ panies it. During its course through the neck, the internal carotid artery lies on the longus capitis muscle and the sym­ pathetic trunk. The vagus nerve (CN X) lies posterolateral to it (Fig. 8-22). The internal carotid artery enters the middle cranial fo ssa beside the dorsum sellae of the sphenoid bone (see Fig. 7-42). W ithin the cranial cavity, the internal carotid artery and its branches supply the hypophysis cerebri (pituitan gland), the orbit, and most of the supratentorial part of the brain (see Fig. 7-54).

The C om m on C arotid A rteries (Figs. 8-17 to 8-22, 8-24, 8-25, 8-28, and 8-29). The right common carotid artery begins at the bifurcation of the brachiocephalic trunk, posterior to the right sternoclavicular joint. The left common carotid artery arises from the arch of the aorta and ascends into the neck, posterior to the left sternoclavicular joint. Each common carotid artery ascends within the carotid sheath to the level of the superior border of the thyroid cartilage, where it terminates by dividing into the internal and external carotid arteries. The Internal Carotid Artery (Figs. 8-17 to 8-22 and 824). This is the direct continuation of the common carotid artery; it has no branches in the neck. As its name indicates,

806

Clinically Oriented Anatomy

Internal laryngeal nerve Thyrohyoid membrane Superior laryngeal artery Inferior constrictor

External laryngeal nerve Sternothyroid, reflected Superior thyroid vessels

Right and left cricothyroids

Fascial band

[Trachea I Recurrent laryngeal nerve

Common carotid artery Vagus nerve Internal jugular vein

Common carotid artery Vagus nerve Internal jugular vein Thoracic duct

Subclavian artery

Sternothyroid

Clavicle

Jugular notch

Figure 8-25.

Dissection of the anterior aspect of the neck. The isthmus of the thyroid gland is divided and its left lobe is retracted. arises from it at the superior border of the posterior belly of the digastric muscle. It ascends posterior to the external acoustic meatus and supplies adjacent muscles, the parotid gland, the facial nerve, structures in the temporal bone, the auricle, and the scalp. Most of the veins in the anterior cervical triangle are tri­ butaries of the large internal jugular vein.

Table 8-4. Branches of the External Carotid Artery
Surface Branches Figure R eferences

Anterior1 Posterior Medial

Superior thyroid a. Lingual a. Facial a. Occipital a. Posterior auricular a. Ascending pharyngeal a.

8-18 8-22 8-17 8-17 8-18 8-18

and and and and and and

8-25 8-24 8-18 8-24 8-24 8-24

'The three anterior branches o f the external carotid artery are o f major im portance.

between the trapezius and sternocleidomastoid muscles. During this course, it passes superficial to the internal carotid artery and three cranial nerves (CN IX, CN X, and CN XI). The posterior auricular artery (Figs. 8-18 and 8-24; see also Fig. 7-35) is a small posterior branch of the external carotid. It

The Internal Ju g u lar Vein (Figs. 8-8, 8-12, 8-16, 8-17, 821, and 8-22; see also Fig. 7-43). Usually the largest vein in the neck, the internal jugular drains blood from the brain and superficial parts of the face and neck. Its course corresponds to a line drawn from a point immediately inferior to the external acoustic meatus to the medial end of the clavicle. This large vein commences at the jugular foramen in the posterior cranial fossa, as the direct continuation of the sigmoid sinus (see Fig. 1-41A and C). From the dilation at its origin, called the superior bulb

Figure 8-31.

Dissection of the left side of the root of the neck, showing the deep cervical lymph nodes and the termination of the thoracic duct (see also Fig. 8-29).

angle between and posterior to the internal jugular vein and carotid artery. On the right side, CN X crosses the origin of the subclavian artery, posterior to the brachiocephalic vein and the sternoclavicular joint, to enter the thorax. The recurrent laryn­ geal nerve, a branch of CN X, loops around the subclavian artery on the right side and around the arch of the aorta on the left side. After looping, both recurrent laryngeal nerves pass superiorly to reach the posteromedial aspect of the inferior pole of the thyroid gland, where they ascend in the tracheoesophageal groove to supply all the intrinsic muscles of the larynx except the crico­ thyroid (Table 8-6). The cardiac branches o f CN X (cardiac nerves) also originate in the neck and thorax (Fig. 8-33) and run along the arteries to the arch of the aorta and the cardiac plexuses of nerves (see Figs. 1-62, 1-68, and p. 106). The Phrenic Nerve (Figs. 8-12, 8-26, 8-28, 8-29, 8-31, and 8-34; see also Fig. 1-42). This nerve, which is about 30 cm long, is the sole motor nerve to the thoracic diaphragm (p. 224). It arises chiefly from the fourth cervical nerve (with contributions from C3 and C5). The phrenic nerve is formed at the superior part of the lateral border of the scalenus anterior muscle, at the

level of the superior border of the thyroid cartilage and super­ olateral to the internal jugular vein. It descends obliquely with this vein across the scalenus anterior muscle, deep to prevertebral fascia and the transverse cervical and suprascapular arteries. On the left, the phrenic nerve crosses the first part of the subclavian artery, but on the right, it lies on the scalenus anterior muscle that covers the second part of this artery. The phrenic nerve crosses posterior to the subclavian vein on both sides and anterior to the internal thoracic artery to enter the thorax. The unexpected innervation of the diaphragm by cervical nerve roots has an embryological basis and clinical signifi­ cance (Moore, 1988). During the fifth week of development, the ventral rami from C3, C4, and C5 grow into the septum transversum, the primordium of the central tendon of the diaphragm when it is in the cervical region. As the developing diaphragm migrates caudally, it carries the phrenic nerves with it. Injuries to the inferior cervical region of the spinal cord (e.g., C l segment) that are severe enough to cause paralysis

814

Clinically Oriented Anatomy

rior constrictor External laryngeal nerve Superior thyroid artery and vein

Thyroid cartilage

Sympathetic trunk Cricothyroid Cricoid cartilage----------Contents of carotid sheath (common carotid artery, internal jugular vein, vagus nerve) Ascending cervical branch Inferior thyroid artery

Inferior thyroid vein

Thoracic duct Esophagus Recurrent laryngeal nerve Trachea

Sternothyroid Anterior sternoclavicular Articular disc

Figure 8-32. Dissection of the left side of the root of the neck. Note the recurrent laryngeal nerve ascending beside the trachea, just anterior

to the angle between the trachea and esophagus. Observe the conic of the carotid sheath (see also Figs. 8-21 and 8-22).

of the upper limbs have little effect on breathing because the phrenic nerves arise from more cranial segments (C3, C4, and C5). Breathing would not be normal however, because the intercostal muscles would be paralyzed. Severance o f a phrenic nerve in the root of the neck (or elsewhere) results in paralysis of the corresponding half of the diaphragm. To produce temporary therapeutic paralysis of one half the diaphragm (e.g., to interrupt a severe case of hiccoughs [spasmodic sharp contractions of the diaphragm]), a phrenic nerve block is sometimes done. The anesthetic solution is injected around the phrenic nerve where it lies on the anterior surface of the middle third of the scalenus anterior muscle, about 3 cm superior to the clavicle (Fig. 8-31). To produce a longer period of paralysis of half of the diaphragm, (e.g., for several months after the surgical repair of a dia­ phragmatic hernia), a phrenic nerve crush may be performed. In such cases, the phrenic nerve is crushed with a hemostat for up to 1 cm of its length. In other cases, a phrenicotomy is performed during which the phrenic nerve is sectioned. An accessory phrenic nerve (Figs. 8-11 and 8-12) occurs in 20% to 30% of persons. It is frequently derived from C5 as a branch of the nerve to the subclavius muscle. It lies lateral to the main phrenic nerve and usually joins it in the root of the neck or in the superior part of the thorax. If an

accessory phrenic nerve is present, section or crushing of the phrenic nerve will not produce complete paralysis of the cor­ responding half of the diaphragm.

The S ym pathetic Trunks (Figs. 8-26, 8-28, 8-30. anc * 32). These longitudinal strands of autonomic nerve fibers ¿7 their associated sympathetic ganglia are located in the neck _ terolateral to the vertebral column from the level of the f. cervical vertebra. These trunks receive no \vhite rami com* * nicantes in the neck, but they contain three cervical sym pathe: ganglia (superior, middle, and inferior). These ganglia rece their preganglionic fibers from the superior thoracic spinal ner*: through white rami communicantes, the fibers of which k the spinal cord in the ventral roots of thoracic spinal nerv es ? Fig. 26, p. 30). From these sympathetic trunks, fibers cervical structures as postganglionic fibers in cervical spinal ner or leave as direct visceral branches (e.g., to the thyroid glanc Branches to the head run with the arteries, especially the i n l ­ and external carotid arteries. The Inferior Cervical Ganglion (Figs. 8-26, 8-30. anc 1 34). This collection of nerve cells lies at the level of the super border of the neck of the first rib, where it is wrapped ar : _~ the posterior aspect of the vertebral artery. It is usually fjs t

816

Clinically Oriented Anatomy

Sternohyoid Sternothyroid

[

Vocal told (cord) Roof of infraglottic region [ Fascial band I Recurrent laryngeal nerve Middle thyroid vein

Sternocleidomastoid Platysma

Common c a r o : : a* I Internal jugula' Left vagus ne*v?

Omohyoid

Omohyoic Lymph nodes Scalenus anterior Brachial plexus Left phre~ k nerve

Inferior cervical ganglion Scalenus medius Vertebral vein and artery Longus colli Inferior thyroid artery Esophagus Retropharyngeal space

C6 and C5

Figure 8-34.

Transverse section of the neck at the level of C7 vertebra. Observe that the thyroid gland is asymmetrically enlarged.

thoracic duct enters the left brachiocephalic vein at the junction of the subclavian and internal jugular veins. It drains lymph from the entire body, except the right side of the head and neck, the right upper limb, and the right side of the thorax (Fig. 24, p. 25). These areas drain through the right lymphatic duct, a vessel 1 to 2 cm long, which empties into the venous system at or near the junction of the right internal jugular and right subclavian veins. Blockage o f the thoracic duct (e.g., by tumor cells) usually produces no symptoms. The lymph apparently enters the ven­ ous system through other lymphatic channels. Malignant tu­ mor cells pass (e.g., from an abdominal cancer) through the thoracic duct into the root of the neck. Some tumor cells enter the venous system and others extend by retrograde permeation into the inferior deep cervical lymph nodes or supraclavicular nodes. The cancer cells proliferate here, forming metastases (new malignant tumors). The supraclavicular nodes, partic­ ularly on the left side, may be enlarged when there is a carcinoma of the bronchus (p. 77), stomach, or any other abdominal organ.

layer containing the larynx and trachea; and (3) a deep alimentar layer containing the pharynx and esophagus. The Esophagus This thick, distensible muscular tube extends from the phar­ ynx to the stomach (about 25 cm). It begins in the median plam at the inferior border of the cricoid cartilage (Fig. 8-40) and enc? at the cardiac orifice of the stomach (see Fig. 2-34). It lies between the trachea and the anterior longitudinal ligament e the surfaces of the vertebrae (Figs. 8-21, 8-29, and 8-34: sr= also Fig. 4-26). On the right side, the esophagus is in contaa: with the cervical pleura at the root of the neck (see Fig. 1-72 whereas on the left side, posterior to the subclavian artery, the thoracic duct lies between the pleura and the esophagus (see Fiz 1-73). The esophagus is also discussed in Chapter 2 (p. 160» The Trachea The trachea (windpipe) is a fibrocartilaginous tube that is supported by incomplete cartilaginous tracheal rings. These rings, which keep the trachea patent, are deficient posteriori} where the trachea is related to the esophagus (Figs. 8-21 and S34). Hence, the posterior wall of the trachea is flat. The trachea extends fro m the larynx to the roots o f the lungs, a distance oi about 12 cm (see Fig. 1-25). The isthmus of the thyroid glanc usually lies over the second and third tracheal rings (Figs. 8-35

The Cervical Viscera
The cervical viscera are disposed in three layers (Figs. 8-21 nd 8-34): (1) a superficial endocrine layer containing the thyid, parathyroid, and thymus glands; (2) a middle respiratory

818

Clinically Oriented Anatomy

Nerve to thyrohyoid Internal laryngeal nerve External carotid artery Sternohyoid, reflected

External laryngeal nerve | Superior thyroid a rte ry !

Thyrohyoid

Sternocleidomastoid branch

Cricothyroid Superior thyroid vein

Sternothyroid

Middle thyroid vein Thyroid gland Internal jugular vein Vagus nerve Common carotid artery

Subclavian arte

Sternohyoid, reflected Inferior thyroid vein— Brachiocephalic trunk

Figure 8-36.

Dissection of the anterior aspect of the neck. In this specimen there is an accessory thyroid gland on the right, lying on the thyrohyoid muscle, lateral to the thyroid cartilage.

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