THE ANTERIOR TRIANGLE OF THE NECK
Using a simplified lateral view of the neck we can easily identify the
Borders of the anterior triangle of the neck:
- Midline of the neck from chin to manubrium
- Posterior border of the sternocleidomastoid
- Inferior border of the mandible
The Investing layer of deep cervical fascia anteriorly covers the anterior
triangle of the neck and fuses with the opposite fascia in the midline.
Contains the Suprahyoid and the Infrahyoid muscles:
Omohyoid-Inf A (actually
in the posterior triangle but included here for the sake of comparison)
Origins, Insertions and Actions can be reviewed
in the text.
= Ansa Cervicalis (c1, c2, c3)
Nerve from the Inferior Alveolar Nerve of V3
The anterior triangle of the neck can be further subdivided
Triangle: between the anterior belly of the digastric, superior
to the hyoid bone, and the midline of the neck
- Floor is formed by the mylohyoid muscle
- Most noted for the presence of several submental lymph
nodes which drain the floor of the oral cavity, tip of the tongue and
middle lower lip and central incisors
- Anterior jugular veins: Lying in the midline,
running from the submental triangle, they pierce the deep fascia above manubrium.
They pass between the posterior border of the sternocleidomastoid muscle and
the upper border of the clavicle to drain into the external jugular veins
in the posterior triangle of the neck.
(Digastric) Triangle: between the posterior and anterior bellies
of the digastric muscle and inferior border of the mandible. Its floor is formed
by the mylohyoid, hyoglossus and middle constrictor muscles.
- Continuous with the fossa for the parotid gland
- Mylohyoid muscle lies superior to the anterior
belly of the digastric
- Forms a sling passing from side to side from its
attachment to the internal surface of the mandible (mylohyoid line)
- Forms the floor of mouth: It is attached from the
mylohyoid line to the superior aspect of body of hyoid bone and the midline
- Around the free edge of this muscle lies the duct
of submandibular salivary gland which occupies a significant part of the
- Associated with the anterior belly of digastric,
as both are derived from the 1st Branchial Arch and therefore
share the same innervation: Mylohyoid Br. of the Inferior Alveolar
N. of V3
- Hypoglossal nerve (CN XII) also passes into the
triangle as it goes to the tongue between Hyoglossus and mylohyoid close to
the hyoid bone
- Facial artery, arising from the external carotid,
passes superiorly deep to the posterior belly of digastric, follows the floor
of the triangle and winds posteriorly over the submandibular gland and "grooves"
the inferior edge of the mandible at anterior-inferior angle of the masseter
muscle to reach the face
- Posterior belly of the digastric:
- Originates from the digastric fossa medial to the
- Attaches to the anterior belly of digastric by the
intermediate tendon which is tied down by a fascial sling to the body
of the hyoid.
- Associated with the stylohyoid, which arises
from the lateral surface of the styloid process and it splits around the
Common tendon of the digastric to insert into the hyoid bone.
- Both muscles are derived from the 2nd Branchial Arch
and therefore share the same innervation: Facial N. (CN VII)
Triangle: between the superior belly of the omohyoid, lower anterior
margin of the sternocleidomastoid and the median line of the neck.
Medially contains infrahyoid muscles.
- As stated, these strap muscles lie between the
investing deep fascia and the visceral fascia covering the thyroid gland,
trachea and esophagus.
- Are depressors of the larynx and the
- Except for Thyrohyoid, they are all innervated by the
motor plexus from the ventral rami of C1, 2, 3 and 4) discussed in the Carotid
Triangle Section in detail.
- Deep in the Muscular Triangle it contains visceral structures
of the neck including the thyroid gland, larynx, trachea and esophagus.
- Also includes the recurrent
laryngeal nerve, inferior laryngeal artery, and external laryngeal nerve
parallel to superior laryngeal nerve
- Sternohyoid m.: lying close to the midline
- The superior belly of the omohyoid lies lateral
- Muscles pass from the posterior surface of the
manubrium of the sternum to insert on the hyoid bone.
- Sternothyroid m.: deep to sternohyoids
- Also pass from the posterior sternum but insert onto the oblique line
of thyroid cartilage
- The superior belly of the omohyoid lies lateral to it
- Splits both the anterior and posterior triangles
- Two bellies united by an intermediate tendon which is connected to
the clavicle by a fascial sling
- Thyrohyoid m.: above the thyroid cartilage
- Completes the gap from thryoid cartilage to hyoid bone
- Innervated by fibers from C1 which have piggybacked onto the hypoglossal
nerve (CN XII) and subsequently jump off that nerve twice: Once to supply
this muscle, and a second time in the floor of the mouth to supply the
- Covers visceral structures of the neck including the thyroid gland,
larynx, trachea and esophagus.
Triangle: between the posterior
belly of the digastric, superior belly of the omohyoid and deep to the sternocleidomastoid
As the vascular area of the neck, it is most noted
for the carotid sheath and its contents:
The Common Carotid
Artery arises in the base of the neck from the brachiocephalic artery
on the right side and directly from the arch of the aorta on the left
side in the superior mediastinum of the thorax. It passes into the base of the
neck through the thoracic inlet bounded by T1 vertebral body, the sternum and
first rib and ascends into the carotid triangle
- Medial to the artery is the esophagus and trachea
- Internal jugular vein lies lateral to it
- It can be compressed on the transverse process
of C6 (the carotid tubercle).
- CN IX and the pharyngeal btranches of IX and
X run between the internal and external carotid arteries
- Both CN Xl and XII run laterally to the internal
and external carotid arteries
- Bifurcation into the internal and external
carotid arteries occurs at the level of the upper border of the thyroid
Gives no branches in neck and simply ascends to enter
the base of the skull into the carotid canal
Has the carotid sinus (baroreceptors associated
with CN IX) at its beginning
The carotid body is present at the bifurcation
and has chemoreceptors.
The carotid sinus and body are for mechanisms controlling
Lies posterolateral to the external carotid artery.
Cranial nerve IX or glossopharyngeal nerve
runs anterior to the internal carotid artery and penetrates the lateral
pharyngeal wall with the stylopharyngeus muscle. It is motor to this
muscle and sensory to the mucosa of posterior 1/3 of tongue, mucosa
of pharynx, palatine tonsil and soft palate.
Main arterial supply to structures of the neck and superficial
Gives off several branches, some of which originate in
or pass through the carotid triangle.
Lies inferior to (I), deep to (D) or superior to (S)
the posterior belly of the digastric.
Branches of the External Carotid Artery
can be described through SALFOP | S-MAX
Superior thyroid artery
(I) arises close to the carotid bifurcation. It descends anteriorly
across the triangle to enter the superior pole of the thyroid gland anastomosing
with its opposite counterpart and the inferior thyroid artery.
Its branches are:
- The superior laryngeal artery supplying the inner aspect
of the larynx
- The cricothyroid branch running with the external laryngeal
- The muscular branch to the sternocleidomastoid muscle.
Location Tip: Seen running with the internal laryngeal nerve
piercing thyrohyoid membrane
Ascending pharyngeal artery (I) arising near
the carotid bifurcation from the posterior surface of the external carotid
and passing posteriorly to the back of the pharynx. It supplies the pharyngeal
constrictor muscles (lateral wall of the pharynx and the nasopharynx)
and gives off small branches that supply the prevertebral muscles, middle
ear and meninges, tonsil (palatine)
Lingual artery (DI) passes superiorly deep
to the suprahyoid muscles to enter and supply the tongue. It also gives
branches to the suprahyoid muscles and the sublingual gland (tonsil)
Facial artery (D) arises Immediately above
the level of the hyoid bone and dips into the digastric triangle and around
the submandibular gland. It ascends and crosses over mandible to supply
the anteromedial aspect of the face (incl. lips, nose). It also sends
branches to the palatine tonsil (tonsillar br.), the submandibular gland
and on the face, to both the lips and the nose. It ends as the angular
artery which anastamoses with the infraorbital
Occipital artery (D) arises on posterior side
of ext. carotid, opposite facial artery, above the ascending pharyngeal,
sends branches to the SCM, the dura mater, and then courses to the back
of the head to supply the scalp
Location Tip: found by identifying the hypoglossal nerve
(CN XII) which loops around it from posterior to anterior.
Posterior Auricular (S) courses behind the
external ear and helps to supply the scalp, the middle ear, and the auricle.
Neuritis of CNVII might be due to compression of this artery due to proximity
to the nerve. In general, palsy of CNVII is termed Bell's palsy.
Superficial Temporal (S) Large terminal branch
arising opposite external auditory meatus supplying the scalp on the lateral
side of the head and giving off the transverse facial artery which courses
across the face. Splits into parietal and temporal branches(Temporalis
Maxillary artery (S) second large terminal
branch, is the principal artery of the deep face. It has 3 divisions and
many branches in each division. It supplies the tympanic membrane, gives
rise to the middle meningeal artery, supplies the muscles of mastication,
all lower and some upper teeth, the infraorbital region, the hard and
soft palate, and the walls of the nasal cavity. More information regarding
the maxillary artery can be found in its dedicated section.
Branches of the External Carotid
Artery can also be described using the following diagram:
Note how the structures are physically placed
- which ones are posterior, anterior, etc- and use that as a guide not only
for locating them on the cadaver, but also for memorizing the structures themselves.
Jugular Vein collects blood from the brain, face and neck
- Usually the largest vein in the neck
- As a direct continuation of the sigmoid sinus
and the inferior petrosal sinus, it begins after exiting the jugular foramen.
It is usually larger on the right, since the superior sagittal sinus drains
to the right transverse and sigmoid sinuses in most people.
- Passes inferiorly through the carotid triangle
receiving many tributaries from surrounding structures.
- At the base of the neck it unites with the subclavian
vein on either side to form right and left brachiocephalic veins which in
turn form the superior vena cava.
- Deep cervical lymph nodes lie along its course
The vagus has an extensive distribution as it conveys
voluntary motor and sensory nerve fibers to structures in the neck, and viscero-motor
fibers to thorax and abdomen. It enters the neck by exiting the skull through
the jugular foramen. In the carotid triangle it lies behind and between the
carotid and jugular vessels. Several branches are present.
A pharyngeal branch passes between the internal and external carotid
vessels to the middle constrictor of the pharynx to join branches from the
glossopharygeal nerve to form the pharyngeal plexus.
A superior laryngeal nerve arises below the pharyngeal branch and
passes to the side of the larynx deep to both External and Internal Carotid
The superior laryngeal nerve from X divides into:
- The internal laryngeal branch which pierces the thyrohyoid membrane,
is sensory to the piriform fossa of the pharynx and laryngeal mucosa above
vocal cords and is involved in the coughing reflex.
- The external laryngeal branch which runs on the lateral aspect
of the larynx to innervate the cricothyroid muscle (the only laryngeal
muscle outside the larynx) which tenses vocal cords during vocalization.
Outside the triangle the important recurrent
laryngeal branches arise.
Other branches in the neck region include:
- (upper branches) voluntary motor nerves to the muscles of palate (except
for the tensor veli palatini muscle which is innervated by V3), to the
pharynx (except for the stylopharyngeus muscle which is innervated by
CN IX) and to the larynx.
- (lower branches) parasympathetic preganglionic fibers to the cardiac,
thoracic and abdominal regions
- sensory fibers to the inferior sensory ganglion lying in jugular fossa.
- sensory fibers to the skin of the external auditory canal with cell
bodies lying in the superior sensory ganglion in the jugular fossa.
Sympathetic Trunk – Autonomic Nerve Fibers
- Lies posterior to the carotid sheath in the carotid
triangle on the anterior aspect of longus coli (prevertebral muscle).
- May occur as a single band or as web-like filaments
passing upward and therefore may be difficult to differentiate from fascia
of the sheath.
- Preganglionic fibers arise from the superior thoracic
spinal nerves T1-T4 to the sympathetic chain, which leave the thorax through
the inlet and travel to cervical structures.They reach the trunk via white
- 3 Cervical Sympathetic
Inferior: At the level of the 1st rib/C7
Middle: At the level of cricoid cartilage (C6)/Inferior thryoid
- Wrapped around the posterior aspect of the vertebral artery
- May be fused with the 1st thoracic ganglion to form the stellate ganglion
- Post-ganglionic fibers pass to C7, C8, heart, and vertebral plexus around
the vertebral artery
Superior: At the level of C1/C2, Largest
- Anterior to the vertebral artery
- Post-ganglionic fibers pass to C5 &C6, heart and the thyroid gland
- Postganglionic fibers enter the cranial cavity
via the internal carotid plexus and sends branches to the internal and external
carotid artery, c1-c4, and the upper cardiac plexus