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THE ANATOMY OF THE NECK
24. October.2011 Monday
The neck is the transitional area between the base of the cranium superiorly and the clavicles
inferiorly. Neck is a passageway for many important structures extending between the head and the trunk
such as the larynx and the thyroid and parathyroid glands.
The neck is relatively slender to allow the flexibility necessary to position the head to maximize the
efficiency of its sensory organs (mainly the eyeballs but also the ears, mouth, and nose). Thus many
important structures are crowded together in the neck, such as muscles, glands, arteries, veins, nerves,
lymphatics, trachea, esophagus, and vertebrae. Consequently, the neck is a well-known region of
vulnerability. Further, several vital structures, including the trachea, esophagus, and thyroid gland, lack the
bony protection afforded other parts of the systems to which these structures belong.
The main arterial blood flow to the head and neck (the carotid arteries) and the principal venous
drainage (the jugular veins) lie anterolaterally in the neck. Carotid/jugular blood vessels are the major
structures commonly injured in penetrating wounds of the neck. The brachial plexuses of nerves originate in
the neck and pass inferolaterally to enter the axillae and continue into and supply the upper limbs.
Bones of the Neck
The skeleton of the neck is formed by the cervical vertebrae, hyoid bone, manubrium of the sternum, and
clavicles. These bones are parts of the axial skeleton except the clavicles, which are part of the appendicular
skeleton.
Cervical Vertebrae
Seven cervical vertebrae form the cervical region of the vertebral column, which encloses the spinal
cord and meninges. The centrally placed vertebral bodies support the head, and the intervertebral (IV)
articulations—especially the craniovertebral joints at its superior end—provide the flexibility necessary to
allow positioning of the head.
Hyoid Bone
The mobile hyoid bone (usually referred to as the hyoid), lies in the anterior part of the neck at the
level of the C3 vertebra in the angle between the mandible and the thyroid cartilage. The hyoid is suspended
by muscles that connect it to the mandible, styloid processes, thyroid cartilage, manubrium, and scapulae.
The hyoid does not articulate with any other bone.
It is suspended from the styloid processes of the temporal bones by the stylohyoid ligaments and is
firmly bound to the thyroid cartilage. The hyoid consists of a body and greater and lesser horns (L. cornua;
the lesser horn is the attachment for the sytlohyoid ligament.
Functionally, the hyoid serves as an attachment for anterior neck muscles and a prop to keep the airway
open.
Fascia of the Neck
The fascia of the neck has a number of unique features. Structures in the neck are surrounded by a
layer of subcutaneous tissue (superficial fascia) and are compartmentalized by layers of deep cervical
fascia. The knowledge of the organization of the cervical fascia is critical in figuring out where the
infections of this region may spread.
Superficial cervical fascia
The superficial cervical fascia is a layer of fatty connective tissue that lies between the dermis of the
skin and the investing layer of deep cervical fascia. This tissue is usually thinner than in other regions,
especially anteriorly. It contains cutaneous nerves, blood and lymphatic vessels, superficial lymph nodes,
and variable amounts of fat. Anterolaterally, it contains the platysma.
The platysma (G. flat plate) is a broad, thin sheet of muscle in the subcutaneous tissue of the neck.
The external jugular vein (EJV) and the main cutaneous nerves of the neck are deep to the platysma. The
platysma covers the anterolateral aspect of the neck. Acting from its superior attachment, the platysma tenses
the skin, producing vertical skin ridges and releasing pressure on the superficial veins. Men commonly use
this action of the platysma when shaving their necks and when easing tight collars. Acting from its inferior
attachment, the platysma helps depress the mandible and draw the corners of the mouth inferiorly. As a
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muscle of facial expression, the platysma serves to convey tension or stress. The platysma is supplied by the
cervical branch of CN VII.
Deep cervical fascia
The deep cervical fascia consists of three fascial layers (sheaths): investing, pretracheal, and
prevertebral layers support the viscera (e.g., the thyroid gland), muscles, vessels, and deep lymph nodes.
The deep cervical fascia also condenses around the common carotid arteries, internal jugular veins (IJVs),
and vagus nerves to form the carotid sheath.
These three fascial layers form natural cleavage planes through which tissues may be separated
during surgery, and they limit the spread of abscesses (collections of pus) resulting from infections. The
deep cervical fascial layers also afford the slipperiness that allows structures in the neck to move and pass
over one another without difficulty, such as when swallowing and turning the head and neck.
The investing layer of deep cervical fascia, the most superficial deep fascial layer, surrounds the
entire neck deep to the skin and subcutaneous tissue. Anteriorly, the investing fascia surrounds the
infrahyoid muscles.
The investing fascia is attached:
 superiorly to the external occipital protuberance and the superior nuchal line;
 laterally to the mastoid process and zygomatic arch; and
 inferiorly to the spine of the scapula, the acromion, the clavicle, and the manubrium of sternum.
The pretracheal layer of deep cervical fascia extends between the hyoid bone and thorax. At the
thorax it blends with the fibrous pericardium.
It has two layers: muscular layer which encloses the infrahyoid muscles and visceral layer which encloses
the thyroid gland, trachea and esophagus. Posteriorly, the pretracheal layer is referred to as the
buccopharyngeal fascia (a fascia enclosing the pharynx, superior continuation of the fascia covering the
buccinator muscle) and separates the pharynx and the esophagus from the prevertebral layer. The
buccopharyngeal fascia begins superiorly at the base of the skull and ends inferiorly in the thoracic cavity.
Laterally, it blends with the carotid sheath.
The prevertebral layer of deep cervical fascia forms a tubular sheath for the vertebral column and
the muscles associated with it. Muscles in this group include the prevertebral muscles, the anterior, middle,
and posterior scalene muscles, and the deep muscles of the back. It extends between the base of the skull and
T3 vertebra. The prevertebral fascia is attached posteriorly along the length of the ligamentum nuchae, and
superiorly forms a continuous circular line attaching to the base of the skull.
The prevertebral layer of deep fascia is fixed to the cranial base superiorly. Infero-laterally it extends
to axilla and continuous with the axillary sheath enclosing the axillary vessels and the brachial plexus.
Carotid Sheath
The carotid sheath is a tubular fascial investment that extends from the cranial base to the root of the
neck. The carotid sheath contains the:
 Common and internal carotid arteries.
 Internal jugular vein.
 Vagus nerve (CN X).
 Some deep cervical lymph nodes.
 Carotid sinus nerve.
 Sympathetic nerve fibers (carotid periarterial plexuses).
The carotid sheath and pretracheal fascia communicate freely with the mediastinum of the thorax inferiorly
and the cranial cavity superiorly. These communications represent potential pathways for the spread of
infection and extravasated blood.
Fascial spaces
Between the fascial layers in the neck are spaces that may provide a conduit for the spread of infections from
the neck to the mediastinum.
Three spaces could be involved in this process:
 the first is the pretracheal space between the investing layer of cervical fascia (covering the posterior
surface of the infrahyoid muscles) and the pretracheal fascia (covering the anterior surface of the trachea and
the thyroid gland), which passes between the neck and the anterior part of the superior mediastinum;
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

the second is the retropharyngeal space
the third space is within the prevertebral layer covering the anterior surface of the transverse processes
and bodies of the cervical vertebrae. This layer splits into two laminae to create a fascial space that begins at
the base of the skull and extends through the posterior mediastinum to the diaphragm.
Retropharyngeal space
The retropharyngeal space is the largest and most important interfascial space in the neck. It is a
potential space that consists of loose connective tissue between the visceral part of the prevertebral layer of
deep cervical fascia and the buccopharyngeal fascia surrounding the pharynx superficially. It permits the
movement of pharynx, larynx and esophagus The retropharyngeal space is closed with the skull base
superiorly and the carotid sheath laterally. It extends from the base of the skull to the upper part of the
posterior mediastinum.
.Cervical Regions
To allow clear communication regarding the location of structures, injuries, or pathologies, the neck
is divided into regions. Between the cranium (mandible anteriorly and occipital bone posteriorly) and the
clavicles, the neck is divided into four major regions based on the usually visible and/or palpable borders of
the large and relatively superficial SCM and trapezius muscles, which are contained within the outermost
(investing) layer of deep cervical fascia.
Sternocleidomastoid Region
The sternocleidomastoid (SCM) muscle is a key muscular landmark in the neck, forming the
sternocleidomastoid region. The SCM visibly divides each side of the neck into the anterior and lateral
cervical regions (anterior and posterior triangles).
The SCM is a broad, strap-like muscle that has two heads: The sternal head attaches to the
manubrium, and clavicular head attaches to the clavicle. The SCMs produce movement at the
craniovertebral joints, the cervical intervertebral joints, or at both. The cranial attachments of the SCMs lie
posterior to the axis of the atlanto-occipital (AO) joints. Bilateral contraction of the SCMs will cause
extension of the head at the AO joints, elevating the chin. Acting bilaterally, the SCMs can also flex the
neck.
Posterior Cervical Region
The region posterior to the anterior borders of (i.e., corresponding to the area of) the trapezius is the
posterior cervical region. The suboccipital region is deep to the superior part of this region.
The trapezius is a large, flat triangular muscle that covers the posterolateral aspect of the neck and thorax.
The trapezius is a:
 Superficial muscle of the back
 Posterior axioappendicular muscle, that acts on the pectoral girdle
 Cervical muscle, that can produce movement of the cranium.
The trapezius attaches the pectoral girdle to the cranium and the vertebral column, assists in suspending it.
Lateral Cervical Region
The lateral cervical region (posterior triangle) is bounded:
 Anteriorly by the posterior border of the SCM.
 Posteriorly by the anterior border of the trapezius.
 Inferiorly by the middle third of the clavicle between the trapezius and the SCM.
The lateral cervical region wraps around the lateral surface of the neck like a spiral. The region is covered by
skin and subcutaneous tissue containing the platysma.
Muscles in the Lateral Cervical Region
The floor of the lateral cervical region is usually formed by the prevertebral fascia overlying four
muscles: splenius capitis, levator scapulae, middle scalene (L. scalenus medius), and posterior scalene (L.
scalenus posterior).
Nerves of the Lateral Cervical Region
The spinal accessory nerve (CN XI) passes deep to the SCM, supplying it before entering the lateral
cervical region at or inferior to the junction of the superior and middle thirds of the posterior border of the
SCM.
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The roots of the brachial plexus (anterior rami of C5-C8 and T1) appear between the anterior and
the middle scalene muscles. The five rami unite to form the three trunks of the brachial plexus, which
descend inferolaterally through the lateral cervical region. The plexus then enters the axilla, providing
innervation for most of the upper limb.
Arteries in lateral cervical region
The arteries in the lateral cervical region include the lateral branches of the thyrocervical trunk,
the third part of the subclavian artery, and part of the occipital artery. The occipital artery, a branch of
the external carotid artery, enters the lateral cervical region at its apex and ascends over the head to supply
the posterior half of the scalp. The third part of the subclavian artery supplies blood to the upper limb.
The third part of the artery is the longest and most superficial part. It lies on the 1st rib, and its pulsations can
be felt by applying deep pressure in the omoclavicular triangle. The branches that occasionally arise from the
third part (suprascapular artery, dorsal scapular artery) are aberrant forms of more typical patterns in which
they arise elsewhere (from the thyrocervical trunk via a cervicodorsal trunk in particular).
Veins in lateral cervical region
The external jugular vein (EJV) is formed by the union of the posterior division of the
retromandibular vein with the posterior auricular vein. The EJV terminates in and drains into the
subclavian vein. It drains most of the scalp and side of the face. The subclavian vein, the major venous
channel draining the upper limb unites with the IJV to form the brachiocephalic vein.
Lymph nodes in the Lateral Cervical Region
Lymph from superficial tissues in the lateral cervical region enters the superficial cervical lymph
nodes. Efferent vessels from these nodes drain into the deep cervical lymph nodes, which form a chain
embedded in the fascia of the carotid sheath.
Anterior Cervical Region
The anterior cervical region (anterior triangle) has the following:
 An anterior boundary formed by the median line of the neck.
 A posterior boundary formed by the anterior border of the SCM.
 A superior boundary formed by the inferior border of the mandible.
 An apex located at the jugular notch in the manubrium.
 A roof formed by subcutaneous tissue containing the platysma.
 A floor formed by the pharynx, larynx, and thyroid gland.
For more precise localization of structures, the anterior cervical region is subdivided into four smaller
triangles by the digastric and omohyoid muscles: the unpaired submental triangle and three small paired
triangles—submandibular, carotid, and muscular.
Submental triangle: The submental triangle, inferior to the chin, is a suprahyoid area bounded inferiorly by
the body of the hyoid and laterally by the right and left anterior bellies of the digastric muscles. The floor of
the submental triangle is formed by the two mylohyoid muscles, which meet in a median fibrous raphe. The
apex of the submental triangle is at the mandibular symphysis, the site of union of the halves of the mandible
during infancy. Its base is formed by the hyoid.
The submental triangle contains several small submental lymph nodes and small veins that unite to
form the anterior jugular vein.
Submandibular triangle: The submandibular triangle is a glandular area between the inferior border of the
mandible and the anterior and posterior bellies of the digastric muscle. Submandibular lymph nodes lie on
each side of the submandibular gland and along the inferior border of the mandible. The hypoglossal nerve
(CN XII) provides motor innervation to the intrinsic and extrinsic muscles of the tongue. It passes into the
submandibular triangle, as does the nerve to the mylohyoid muscle (a branch of CN V3, which also supplies
the anterior belly of the digastric), parts of the facial artery and vein, and the submental artery (a branch of
the facial artery).
Muscular triangle (omotracheal triangle): The muscular triangle is bounded by the superior belly of the
omohyoid muscle, the anterior border of the SCM, and the median plane of the neck. This triangle contains
the infrahyoid muscles and viscera (e.g., the thyroid and parathyroid glands).
MUSCLES IN ANTERIOR CERVICAL REGION
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In the anterolateral part of the neck, the hyoid provides attachments for the suprahyoid muscles
superior to it and the infrahyoid muscles inferior to it. These hyoid muscles steady or move the hyoid and
larynx. For descriptive purposes, they are divided into suprahyoid and infrahyoid muscles.
 Muscles superior to the hyoid are classified as suprahyoid muscles and include:
1) stylohyoid
2) digastric
3) mylohyoid
4) geniohyoid
 Muscles inferior to the hyoid are infrahyoid muscles and include:
1) omohyoid (superficial plane)
2) sternohyoid (superficial plane)
3) thyrohyoid (deep plane)
4) sternothyroid (deep plane)
As a group, suprahyoid muscles constitute the substance of the floor of the mouth, supporting the
hyoid in providing a base from which the tongue functions and elevating the hyoid and larynx in relation to
swallowing and tone production. The difference in nerve supply between the anterior and the posterior
bellies of the digastric muscles results from their different embryological origin from the 1st and 2nd
pharyngeal arches, respectively. CN V supplies derivatives of the 1st arch, and CN VII supplies those of the
2nd arch.
The infrahyoid muscles, often called strap muscles because of their ribbon-like appearance. These
four muscles anchor the hyoid, sternum, clavicle, and scapula and depress the hyoid and larynx during
swallowing and speaking. They also work with the suprahyoid muscles to steady the hyoid, providing a firm
base for the tongue. The infrahyoid group of muscles are arranged in two planes: a superficial plane, made
up of the sternohyoid and omohyoid, and a deep plane, composed of the sternothyroid and thyrohyoid.
Arteries in anterior cervical region
The anterior cervical region contains the carotid system of arteries, consisting of the common carotid
artery and its terminal branches, the internal and external carotid arteries. It also contains the IJV and its
tributaries and the anterior jugular veins.
Common carotid artery
The common carotid artery arises from the brachiocephalic trunk on the right side and from the arch of
aorta on the left side. The common carotid artery and one of its terminal branches, the external carotid artery,
are the main arterial vessels in the carotid triangle. Branches of the external carotid (e.g., the superior
thyroid artery) also originate in the carotid triangle.
The carotid triangle is bounded:
 posteriorly by the sternocleidomastoideus;
 inferiorly, by the superior belly of the omohyoideus
 superiorly, by the Stylohyoideus and the posterior belly of the digastricus.
Each common carotid artery ascends within the carotid sheath with the IJV and vagus nerve to the level
of the superior border of the thyroid cartilage. Here, each common carotid artery terminates by dividing into
the internal and external carotid arteries. The internal carotid artery has no branches in the neck; the external
carotid has several. The right common carotid artery begins at the bifurcation of the brachiocephalic trunk.
The right subclavian artery is the other branch of this trunk. From the arch of the aorta, the left common
carotid artery ascends into the neck.
The internal carotid arteries are direct continuations of the common carotids superior to the origin of the
external carotid artery, at the level of the superior border of the thyroid cartilage. The carotid body (carotid
glomus or glomus caroticum) is located in the cleft between the internal and the external carotid arteries.
While the carotid bodies contain chemoreceptors, the carotid sinus, a slight dilatation of the proximal part
of internal carotid artery, contains baroreceptors. The carotid sinus is sensitive to blood pressure changes. It
is innervated mainly by the glossopharyngeal nerve and also by the vagus nerve.
Role of the carotid bodies
• Carotid bodies are sensitive to decreased O2 and increased CO2 content of the blood
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•
In both cases visseral reflexes are activated leading to increased ventilation (increased depth and rate
of repiration) and as well as rise of heart rate and blood pressure
• Both the afferent and efferent pathways for this reflex is through the vagus and glossopharyngeal
nerves
Internal carotid artery
The internal carotid arteries enter the cranium through the carotid canals in the petrous parts of the
temporal bones and become the main arteries of the brain and structures in the orbits. No named branches
arise from the internal carotid arteries in the neck. The internal carotid artery supplies the brain together with
the vertebral artery which is a branch of the subclavian artery. After entering the cranial vault it forms the
polygon of Willis together with the vertebral artery.
External carotid artery
The external carotid arteries supply most structures external to the cranium; the orbit and the part of
the forehead and scalp supplied by the supraorbital artery are the major exceptions. The external carotid
artery superiorly extends to the level of the parotid gland. Each external carotid artery runs terminates by
dividing into two branches, the maxillary artery and the superficial temporal artery within the tissue of the
parotid gland. Before these terminal branches, six arteries arise from the external carotid artery.
Veins in anterior cervical region
Most veins in the anterior cervical region are tributaries of the internal jugular vein (IJV), typically
the largest vein in the neck. Internal jugular vein is the main vein draining the intracranial veins, as well as
the head and neck. It commences at the jugular foramen in the posterior cranial fossa as the direct
continuation of the sigmoid sinus. IJV unites with the subclavian vein to from the brachiocephalic vein.
NERVES IN ANTERIOR CERVICAL REGION
Several nerves, including branches of cranial nerves, are located in the anterior cervical region.
Transverse cervical nerve (C2 and C3): supplies the skin covering the anterior cervical region.
Hypoglossal nerve (CN XII): the motor nerve of the tongue, enters the submandibular triangle deep to the
posterior belly of the digastric muscle to supply the intrinsic and four of the five extrinsic muscles of the
tongue. The nerve gives off the superior root of the ansa cervicalis and then a branch to the geniohyoid
muscle.
Branches of the glossopharyngeal (CN IX) and vagus (CN X) nerves: in the submandibular and carotid
triangles. CN IX is primarily related to the tongue and pharynx. In the neck, CN X gives rise to pharyngeal,
laryngeal, and cardiac branches.
ROOT OF THE NECK
The root of the neck is the junctional area between the thorax and the neck. It is the cervical side of
the superior thoracic aperture, through which pass all structures going from the thorax to the head or upper
limb and vice versa. The inferior boundary of the root of the neck is the superior thoracic aperture, formed
laterally by the 1st pair of ribs and their costal cartilages, anteriorly by the manubrium of the sternum, and
posteriorly by the body of T1 vertebra.
NERVES IN ROOT OF NECK
There are three pairs of major nerves in the root of the neck: (1) the vagus nerves, (2) the phrenic nerves, and
(3) the sympathetic trunks.
Vagus Nerves (CN X)
After its exit from the jugular foramen, each vagus nerve passes inferiorly in the neck within the posterior
part of the carotid sheath in the angle between the IJV and the common carotid artery.
The right vagus nerve passes anterior to the first part of the subclavian artery and posterior to the
brachiocephalic vein and to enter the thorax.
The left vagus nerve descends between the left common carotid and the left subclavian arteries to enter the
thorax.
The recurrent laryngeal nerves arise from the vagus nerves in the inferior part of the neck.
The cardiac branches of CN X originate in the neck as well as in the thorax and convey presynaptic
parasympathetic and visceral afferent fibers to the cardiac plexus of nerves.
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Phrenic Nerves
The phrenic nerves pass under the prevertebral layer of deep cervical fascia, between the subclavian
arteries and veins, and proceed to the thorax to supply the diaphragm. The phrenic nerves are important
because, in addition to their sensory distribution, they provide the sole motor supply to their own half of the
diaphragm.
Sympathetic Trunks
Each sympathetic trunks descend at the antero-lateral parts of the vertebral column. Sympathetic trunks are
formed of sympathetic ganglia and nerve fibers extending between them.
The cervical portion of the sympathetic trunks lies anterolateral to the vertebral column, extending
superiorly to the level of the C1 vertebra or cranial base. The sympathetic trunks receive no white rami
communicantes in the neck (white rami associated with cervical spinal nerves). The cervical portion of the
trunks includes three cervical sympathetic ganglia: superior, middle, and inferior. These ganglia receive
presynaptic fibers conveyed to the trunk by the superior thoracic spinal nerves and their associated white
rami communicantes, which then ascend through the sympathetic trunk to the ganglia. After synapsing with
the postsynaptic neuron in the cervical sympathetic ganglia, postsynaptic neurons send fibers to the:
 Cervical spinal nerves via gray rami communicantes.
 Thoracic viscera via cardiopulmonary splanchnic nerves.
 Head and viscera of the neck via cephalic arterial branches (rami).
The latter fibers accompany arteries as sympathetic periarterial nerve plexuses, especially the vertebral and
internal and external carotid arteries.
Arteries in root of neck
The brachiocephalic trunk is covered anteriorly by the right sternohyoid and sternothyroid muscles; it is the
largest branch of the arch of the aorta. It arises in the midline from the beginning of the arch of the aorta. It
passes superolaterally to the right where it divides into the right common carotid and right subclavian
arteries. The brachiocephalic trunk usually has no branches.
Subclavian artery
The subclavian arteries supply the upper limbs; they also send branches to the neck and brain. The right
subclavian artery arises from the brachiocephalic trunk. The left subclavian artery arises from the arch of the
aorta distal to the left common carotid artery.
Veins in root of neck
Two large veins terminating in the root of the neck are the external jugular vein (EJV), draining
blood received mostly from the scalp and face, and the variable anterior jugular vein (AJV), usually the
smallest of the jugular veins. The right and left AJVs commonly unite across the midline to form the jugular
venous arch.
The subclavian vein, the continuation of the axillary vein, begins at the lateral border of the 1st rib and ends
when it unites with the internal jugular vein (IJV). The internal jugular vein (IJV) is the main vein draining
the intracranial veins, as well as the head and neck. It ends posterior by uniting with the subclavian vein to
form the brachiocephalic vein. This union is commonly referred to as the venous angle and is the site
where the thoracic duct (left side) and the right lymphatic trunk (right side) drain lymph collected throughout
the body into the venous circulation. Right and left brachiocephalic veins unite to form the superior vena
cava (opens into the right atrium of the heart).
VISCERA OF NECK
The cervical viscera are disposed in three layers, named for their primary function. Superficial to deep, they
are the:
 Endocrine layer: the thyroid and parathyroid glands.
 Respiratory layer: the larynx and trachea.
 Alimentary layer: the pharynx and esophagus.
Endocrine Layer of Cervical Viscera
The cervical organs in the endocrine layer are part of the body's endocrine system of ductless,
hormone-secreting glands. The thyroid gland is the body's largest endocrine gland. It produces thyroid
hormone, which controls the rate of metabolism, and calcitonin, a hormone controlling calcium metabolism.
The thyroid gland affects all areas of the body except itself and the spleen, testes, and uterus. The hormone
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produced by the parathyroid glands, parathormone (PTH), controls the metabolism of phosphorus and
calcium in the blood. The parathyroid glands target the skeleton, kidneys, and intestine.
THYROID GLAND
The thyroid gland lies deep to the sternothyroid and sternohyoid muscles, located anteriorly in the
neck. It consists primarily of right and left lobes, anterolateral to the larynx and trachea. A relatively thin
isthmus unites the lobes over the trachea, usually anterior to the second and third tracheal rings. A pyramidal
lobe is often present, and it projects upward from the isthmus, usually to the left of the midline.
Vasculature of the Thyroid Gland
The highly vascular thyroid gland is supplied by the superior and inferior thyroid arteries. These
vessels lie between the fibrous capsule and the loose fascial sheath. Three pairs of thyroid veins usually form
a thyroid plexus of veins on the anterior surface of the thyroid gland. The lymph from the thyroid gland
drains into superficial and deep cervical lymph nodes.
Nerves of Thyroid Gland
The nerves of the thyroid gland are derived from the superior, middle, and inferior cervical
(sympathetic) ganglia. They reach the gland through the cardiac and superior and inferior thyroid
periarterial plexuses that accompany the thyroid arteries. These fibers are vasomotor, not secretomotor. They
cause constriction of blood vessels. Endocrine secretion from the thyroid gland is hormonally regulated by
the pituitary gland.
PARATHYROID GLANDS
The small flattened, oval parathyroid glands usually lie external to the thyroid capsule on the medial
half of the posterior surface of each lobe of the thyroid gland, inside its sheath. Most people have four
parathyroid glands.
Vessels of the Parathyroid Glands
Because the inferior thyroid arteries provide the primary blood supply to the posterior aspect of the
thyroid gland where the parathyroid glands are located, branches of these arteries usually supply the
parathyroid glands.. Parathyroid veins drain into the thyroid plexus of veins of the thyroid gland and
trachea. Lymphatic vessels from the parathyroid glands drain with those from the thyroid gland into deep
cervical lymph nodes and paratracheal lymph nodes.
Nerves of the Parathyroid Glands
The nerve supply of the parathyroid glands is abundant; it is derived from thyroid branches of the
cervical (sympathetic) ganglia. Like the nerves to the thyroid, they are vasomotor rather than secretomotor
because these glands are hormonally regulated.
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