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Anatomy of the Neck

Sources: Gray's Anatomy for Students; Fischer's Mastery of Surgery, 8th ed.

1. Overview and Surface Landmarks

The head is in the anatomical position when the inferior margins of the bony orbits and the superior margins of the external acoustic meatuses lie on the same horizontal plane (the Frankfort plane).

Key palpable landmarks of the head and neck include:

Mastoid process - posterior to the external acoustic meatus; the sternocleidomastoid (SCM) attaches here
Zygomatic arch - from the temporomandibular joint to the zygomatic bone
External occipital protuberance - marks the junction of the neck and head posteriorly
Vertex - highest point of the head; marks the transition from trigeminal (anterior) to cervical (posterior) scalp innervation

Head and neck surface anatomy with landmarks labeled - Gray's Anatomy for Students

Fig. 8.286 - Anatomical Position of the Head and Major Landmarks (Gray's Anatomy for Students)

2. Key Vertebral Levels

Two cervical levels serve as major anatomical reference points:

Level	Landmark
CIII/CIV	Upper margin of thyroid cartilage; bifurcation of common carotid artery
CVI	Inferior margin of cricoid cartilage; junction of pharynx-esophagus and larynx-trachea

Lateral neck showing CIII/IV and CVI vertebral levels with key structures labeled

Fig. 8.287 - Vertebral Levels of the Neck (Gray's Anatomy for Students)

3. Fascia of the Neck

Superficial Fascia

Loose areolar connective tissue containing the platysma muscle (a muscle of facial expression, innervated by the cervical branch of CN VII)
Contains: external and anterior jugular veins, branches of the superficial cervical plexus, and superficial lymph nodes

Deep Cervical Fascia - Three Layers

Investing layer - deepest layer of subcutaneous tissue; encircles the entire neck; splits to envelop the SCM and trapezius
Pretracheal layer - muscular part envelops the infrahyoid (strap) muscles; visceral part envelops thyroid gland, trachea, and esophagus
Prevertebral layer - surrounds the vertebral column and its musculature; contains the cervical sympathetic trunk

Carotid Sheath

A tubular fascial compartment extending from the cranial base to the root of the neck. It contains:

Common and internal carotid arteries
Internal jugular vein
Vagus nerve (CN X)
Sympathetic nerve fibers
Carotid sinus nerve and lymph nodes

Retropharyngeal Space

Lies between the prevertebral layer and the buccopharyngeal fascia - a clinically important potential space for spread of infection.

Cross-section and lateral view showing all layers of cervical fascia and the triangles of the neck (SCM = sternocleidomastoid; TRAP = trapezius)

Figure 38.2 - Fascia of Neck (A) and Triangles of Neck (B) - Fischer's Mastery of Surgery

4. Triangles of the Neck

The SCM and trapezius divide each side of the neck into anterior and posterior triangles.

Anterior and posterior triangles of the neck - 3D anatomical and schematic views

Fig. 8.17 - Anterior and Posterior Triangles of the Neck (Gray's Anatomy for Students)

Fig. 8.288 - Outlining the Anterior and Posterior Triangles of the Neck (Gray's Anatomy for Students)

Anterior Triangle

Boundaries:

Medial: midline of neck
Superior: inferior border of mandible
Lateral/posterior: anterior border of SCM
Apex: inferiorly at the suprasternal notch

Function: Contains airway, digestive tract, thyroid/parathyroid glands, and neurovascular structures passing between head and thorax.

Subdivisions (by the digastric and omohyoid muscles):

Sub-triangle	Boundaries	Key Contents
Submental (unpaired)	Hyoid, anterior bellies of both digastrics	Small lymph nodes, small veins
Submandibular	Inferior mandible, anterior and posterior bellies of digastric	Submandibular gland, facial artery/vein, CN XII (hypoglossal)
Carotid	Posterior belly of digastric (sup.), omohyoid (inf.), SCM (post.)	Common/internal/external carotid arteries, internal jugular vein, CN X (vagus), CN XI, CN XII, ansa cervicalis
Muscular (omotracheal)	Midline, omohyoid, SCM	Infrahyoid muscles, thyroid gland, trachea, esophagus

Posterior Triangle (Lateral Cervical Triangle)

Boundaries:

Anterior: posterior border of SCM
Posterior: anterior border of trapezius
Inferior: middle third of clavicle
Apex: posteroinferior to the mastoid process

Subdivisions (by the inferior belly of omohyoid):

Occipital triangle (larger, superior)
Omoclavicular / subclavian triangle (smaller, inferior)

Floor muscles (anterior to posterior):

Anterior scalene (C3-C6 → 1st rib)
Middle scalene (C5-C7 → 1st rib)
Posterior scalene (C5-C7 → 2nd rib)
Levator scapulae
Splenius capitis / semispinalis capitis (at apex)

5. Nerves of the Neck

Superficial Cervical Plexus (Sensory)

All branches emerge at the nerve point (posterior border of SCM, midpoint). They include:

Nerve	Root	Area Supplied
Lesser occipital nerve	C2	Scalp posterior to ear
Greater auricular nerve	C2-C3	Skin over parotid, mastoid, ear
Transverse cervical nerve	C2-C3	Anterior neck skin
Supraclavicular nerves (medial, intermediate, lateral)	C3-C4	Clavicular and deltoid region

Deep Motor Branches

Ansa cervicalis (C1-C3) - innervates infrahyoid strap muscles (except thyrohyoid which is C1 via CN XII)
Phrenic nerve (C3,4,5) - sole motor supply to the diaphragm; descends on the anterior scalene muscle deep to prevertebral fascia

Cranial Nerve XI (Spinal Accessory)

Emerges at the junction of middle and superior thirds of the lateral SCM border ("nerve point")
Courses superficial to prevertebral fascia, deep to investing fascia, to reach trapezius
Most superior nerve in the posterior triangle - important surgical landmark

Lateral neck dissection showing superficial cervical plexus branches, CN XI, external jugular vein, and posterior triangle

Figure 38.3A - Posterior Triangle Superficial Dissection (Fischer's Mastery of Surgery)

Brachial Plexus (in posterior triangle)

Roots emerge between anterior and middle scalene muscles:

C5 + C6 → Superior trunk
C7 → Middle trunk
C8 + T1 → Inferior trunk

6. Vascular Anatomy

Arteries

Common carotid artery: Right originates from brachiocephalic; left from aortic arch. Both travel in the carotid sheath. No branches in the neck.
Bifurcation at the superior margin of thyroid cartilage (CIII/CIV) into:
- Internal carotid artery - no neck branches; enters carotid canal
- External carotid artery - multiple neck branches:
  - Anterior: Superior thyroid, lingual, facial arteries
  - Posterior: Sternocleidomastoid, occipital, posterior auricular arteries
  - Medial: Ascending pharyngeal artery
  - Terminal: Superficial temporal + maxillary (at neck of mandible)
Carotid sinus - dilation at proximal internal carotid; baroreceptor
Carotid body - ovoid mass at bifurcation; chemoreceptor

Veins

Internal jugular vein - begins at jugular foramen; runs in carotid sheath lateral to carotid arteries; joins subclavian to form brachiocephalic vein
External jugular vein - crosses the superficial surface of SCM; drains into subclavian vein lateral to clavicular head of SCM
Anterior jugular vein - runs in anterior neck

7. Carotid Triangle - Deep Dissection

The carotid triangle contains the major neurovascular bundle of the neck. Key relationships within it:

Deep dissection of carotid triangle (A) and superficial dissection (B) showing carotid arteries, internal jugular vein, ansa cervicalis, CN XI, CN XII, and submandibular structures

Figure 38.4 - Carotid Triangle Deep (A) and Superficial (B) Dissection (Fischer's Mastery of Surgery)

8. Lymph Nodes of the Neck

The cervical lymph nodes are classified into 7 levels (surgical levels):

Level	Location
I	Submental (Ia) and submandibular (Ib)
II	Upper jugular (above hyoid)
III	Middle jugular (hyoid to cricoid)
IV	Lower jugular (cricoid to clavicle)
V	Posterior triangle nodes
VI	Central compartment (between carotid sheaths)
VII	Superior mediastinum (suprasternal notch to brachiocephalic artery)

All surgically relevant nodes lie deep to the platysma, along nerves, vessels, and viscera.

9. Clinical Summary

Structure	Clinical Relevance
Carotid sinus	Carotid sinus hypersensitivity; palpation can cause reflex bradycardia
Carotid body	Carotid body tumor (paraganglioma) at bifurcation
Retropharyngeal space	Spread of deep neck infections; retropharyngeal abscess
Phrenic nerve on scalenus anterior	At risk during central venous catheter insertion and thoracic procedures
Marginal mandibular nerve	Can lie 2.5 cm below mandible; at risk in submandibular dissection
Spinal accessory nerve (CN XI)	Injury causes trapezius palsy and dropped shoulder
Ansa cervicalis	Used for nerve grafting/reinnervation procedures
Median cricothyroid ligament	Emergency surgical airway access point (cricothyrotomy)

Sources: Gray's Anatomy for Students (9780323934237); Fischer's Mastery of Surgery, 8th ed. (9781975176433)

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