The document describes the triangles of the neck, including the anterior, posterior, and subtriangles. The anterior triangle is bounded by the median line anteriorly, sternocleidomastoid muscle posteriorly, and inferior mandible superiorly. It contains structures like the carotid sheath and is further divided into subtriangles. The posterior triangle is bounded by trapezius muscle posteriorly and sternocleidomastoid muscle anteriorly, and contains nerves like the spinal accessory nerve and branches of the brachial plexus. Both triangles and their contents are important for surgical approaches in the neck.

1. Triangles of neck
ANTERIOR & POSTERIOR
Dr M Idris Siddiqui

2. Side of neck
• The quadrangular area is on the side of
the neck and is bounded superiorly by
the lower border of the body of the
mandible and the mastoid process,
inferiorly by the clavicle, anteriorly by a
midline in front of the neck, and
posteriorly by the trapezius muscle.

4. Anterolateral aspect of neck
• A qudrilateral field divided into two larger
triangles by sternocleidomastoid muscle.
• The posterior triangle is subdivided by the
inferior belly of omohyoid into
– The occipital triangle (above)
– The subclvian triangle/
omoclavicular/supraclavicular (below)
• The anterior triangle is subdivided into
– The digastric triangle or submandibular triangle
– The carotid triangle
– The muscular triangle or omotracheal triangle
– The submental triangle

13. Anterior triangle of neck

15. Anterior triangle of Cervical Region
anterior boundary formed by the median line of
the neck
posterior boundary formed by the anterior
border of the SCM
superior boundary formed by the inferior border
of the mandible
apex located at the jugular notch in
the manubrium
roof formed by subcutaneous
tissue containing the platysma
floor formed by the pharynx, larynx,
and thyroid gland

16. Subtriangles of Anterior cervical region
(contents)
Submandibular
(digastric)
triangle
Submandibular gland almost fills triangle; submandibular lymph
nodes; hypoglossal nerve; mylohyoid nerve; parts of facial artery
and vein
Submental
triangle
Submental lymph nodes and small veins that unite to form anterior
jugular vein
Carotid triangle Carotid sheath containing common carotid artery and its branches;
internal jugular vein and its tributaries; vagus nerve; external
carotid artery and some of its branches; hypoglossal nerve and
superior root of ansa cervicalis; spinal accessory nerve (CN XI);
thyroid gland, larynx, and pharynx; deep cervical lymph nodes;
branches of cervical plexus
Muscular
(omotracheal)
triangle)
Sternothyroid and sternohyoid muscles; thyroid and parathyroid
glands

17. Anterior Triangle of the Neck
• This triangular region is used for approaching many important
structures in the neck (e.g., larynx, trachea, and thyroid gland).
• Using the digastric and omohyoid muscles, it is common to
divide the anterior triangle into smaller submandibular,
submental, carotid, and muscular triangles to descriptive
purposes.
• Floor of the Anterior Cervical Triangle
• The floor of the anterior triangle of the neck is formed mainly
by the pharynx, larynx, and thyroid gland.
• Deep to these structures is the prevertebral fascia covering
the prevertebral muscles.
• Contents of the Anterior Cervical Triangle
• This triangle contains the suprahyoid and infrahyoid muscles,
arteries, veins, nerves, lymph nodes, and viscera (e.g., thyroid
gland).

22. The submental triangle
• Inferior to the chin,this is an unpaired 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.
This triangle contains several small submental lymph nodes
and small veins that unite to form the anterior jugular vein

23. The submandibular triangle
• It is a glandular area between the inferior border of the mandible and the
anterior and posterior bellies of the digastric muscle.
• The floor is formed by
– The mylohyoid and
– The hyoglossus muscles and
– The middle constrictor muscle of the pharynx.
Contents:
• The submandibular gland nearly fills this triangle.
• 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,
• 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,
• The submental artery (a branch of the facial artery).

24. The carotid triangle
• This is a vascular area bounded by the
superior belly of the omohyoid, the
posterior belly of the digastric, and the
anterior border of the SCM.
– This triangle is important because the common
carotid artery ascends into it. Its pulse can be
auscultated or palpated by compressing it lightly
against the transverse processes of the cervical
vertebrae.
– At the level of the superior border of the thyroid
cartilage(C3), the common carotid artery divides
into the internal and external carotid arteries.

25. Contents
• Carotid sinus: A slight dilation of the proximal part of the internal
carotid artery, which may involve the common carotid artery. Innervated
principally by the glossopharyngeal nerve (CN IX) through the carotid sinus
nerve, as well as by the vagus nerve (CN X), it is a baroreceptor
(pressoreceptor) that reacts to changes in arterial blood pressure.
• Carotid body: A small, reddish brown ovoid mass of tissue in life that
lies on the medial (deep) side of the bifurcation of the common carotid artery
in close relation to the carotid sinus. Supplied mainly by the carotid sinus
nerve (CN IX) and by CN X, it is a chemoreceptor that monitors the level of
oxygen in the blood. It is stimulated by low levels of oxygen and initiates a
reflex that increases the rate and depth of respiration, cardiac rate, and
blood pressure.
• Carotid sheath: The neurovascular structures of the carotid triangle
are surrounded by the carotid sheath: the carotid arteries medially, the IJV
laterally, and the vagus nerve posteriorly. Superiorly, the common carotid is
replaced by the internal carotid artery. The ansa cervicalis usually lies on (or
is embedded in) the anterolateral aspect of the sheath. Many deep cervical
lymph nodes lie along the carotid sheath and the IJV.

29. The muscular triangle or
omotracheal/tracheal/inferior
carotid triangle
• The muscular triangle is bounded by the
superior belly of the omohyoid muscle, the
anterior border of the sternocleidomastoid,
and the median plane of the neck.
• This triangle contains
– The infrahyoid muscles and
– Viscera (e.g., the thyroid and parathyroid glands).

32. Posterior triangle of neck

34. The posterior triangle is covered by deep fascia, which covers
the space between the trapezius and the sternocleidomastoid

36. These muscles are covered by the prevertebral layer of
deep cervical fascia. This "fascial carpet" is lateral
prolongation of pretracheal fascia.

39. Posterior triangle of neck
( Lateral cervical region)
Occipital triangle Part of external jugular vein;
posterior branches of cervical plexus of
nerves;
spinal accessory nerve (CN XI);
trunks of brachial plexus;
transverse cervical artery;
cervical lymph node
Omoclavicular
(subclavian)
triangle
Subclavian artery (third part);
part of subclavian vein (sometimes);
suprascapular artery;
supraclavicular lymph nodes

40. Contents of the Posterior Triangle
Veins of the Posterior Cervical Triangle
• 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 in the superficial
fascia and then pierces the deep fascial roof the
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 the posterior triangle and usually ends by
emptying into the subclavian vein about 2 cm
superior to the clavicle.

42. Arteries of the Posterior Cervical Triangle
• The third part of the subclavian artery(vertebral A.,internal thoracic
A.,thyrocervical trunk,costocervical trunk) begins about a fingerbreadth superior
to the clavicle, opposite the lateral border of the scalenus anterior muscle.
• It is hidden in the inferomedial part of the triangle and barely qualifies as one
of its contents.
• The artery is in contact with the first rib posterior to the scalenus anterior
muscle and can be compressed against this rib to control bleeding in the
upper limb.
• The transverse cervical artery arises from the thyrocervical trunk (inferior
thyroid A.,transverse cervical A.,suprascapular A.), a branch of the subclavian
artery.
• It runs superficially and laterally across the posterior triangle, 2 to 3 cm
superior to the clavicle.
• The occipital artery, a branch of the external carotid artery, enters the apex
of the posterior triangle before ascending to the posterior aspect of the head.

43. Nerves in the Posterior Cervical Triangle
• The accessory nerve (CN XI) divides the posterior
triangle into nearly equal superior and inferior parts.
– It enters the posterior triangle at or inferior to the junction of
the superior and middle thirds of the sternocleidomastoid
muscle.
– It runs between the trapezius and the sternocleidomastoid
muscles and supplies motor fibres to them both.
– It disappears deep to the anterior border of the trapezius at
the junction of its superior 2/3 and inferior 1/3.
• The superior part of the posterior cervical triangle
contains only the lesser occipital nerve.
• The inferior part contains numerous important nerves
(e.g., the ventral rami of the brachial plexus).

44. The Cervical Plexus of Nerves
This is a network of nerves formed by the communications between the ventral rami of
the superior four cervical nerves.
•The plexus lies deep to the internal jugular vein and the sternocleidomastoid muscle.
Cutaneous branches emerge around the middle of the posterior border of the SCM to
supply the skin of the neck and scalp, between the auricle and the external occipital
protuberance.
1. The lesser occipital nerve (C2, and sometimes C3) ascends a short distance along the
posterior border of the SCM before dividing into several branches .
2. The great auricular nerve (C2 and C3) curves over the posterior border of the
SCM and ascends vertically towards the parotid gland.
3. The transverse cervical nerve from C2 and C3 curves around the posterior border of
the SCM near its middle, and then passes transversely across it.
4. The supraclavicular nerves (C3 and C4) arise as a single trunk, which divides into
medial, intermediate and lateral branches.
5. The phrenic nerve is the sole motor nerve supply of the diaphragm.
• It arises from the ventral primary rami of C3 to C5 and is an important muscular branch of the cervical plexus.
The phrenic nerve curves around the lateral border of the scalenus anterior muscle. It
then descends obliquely across its anterior surface, deep to the transverse cervical and
supracervical arteries.

45. The Ansa Cervicalis
• It is formed by branches from
C1-3 and a branch of the
hypoglossal nerve (which contains
fibres from C1).
• It descends anterior to or in the
carotid sheath.
• It supplies the infrahyoid muscles.

46. • A triangular interval (inverted V) or pyramidal
gap.
• It is triangle of vertebral artery.
• Its lateral margin is medial border of scalene
anterior.
• Its medial margin is lateral border of longus
colli.
• Apex lies at carotid tubercle(on transverse
process of C6)
• The base is subclavian artery which is divided
into 3 parts
– Part 1: medial to Scalene anterior
– Part 2: behind Scalene anterior

48. Triangle of the vertebral artery
• Scalenus anterior muscle
• Longus colli muscle
• The superior aspect of the subclavian
artery
• The space between these scaleni muscles is
called the interscalene triangle.
• Its base is formed by the groove for the
subclavian artery on the 1st rib.

50. Contents of the triangle of the vertebral artery
1. The vertebral artery and vein ascend to the apex of triangle and enter the foramen
transversarium of C6.
2. The sympathetic trunk (on the anterior aspect of longus colli) with associated
middle (at the level of the inferior thyroid artery) and inferior cervical ganglia (on the
posterior aspect of the origin of the vertebral artery).
3. The common carotid artery runs on the anterior aspect of the triangle to lie anterior
to the origins of scalenus anterior. It can be compressed on the transverse process
of C6 (the carotid tubercle).
4. The carotid sheath contains the common carotid artery, internal jugular vein and
vagus nerve. It is located on the medial border of the scalenus anterior.
5. The right recurrent laryngeal nerve arises from the vagus and loops under the
right subclavian artery to ascend to the larynx between the trachea and the
esophagus.
The most inferior aortic arch retained in embryonic development on the right is
the 4th aortic arch and it forms the initial segment of the right subclavian artery.
On the left side, the 6th aortic arch is retained as the ductus arteriosus and the
left recurrent laryngeal nerve loops around it.
6. The phrenic nerve lies in the inferolateral corner of the triangle on the anterior
surface of the subclavian artery. It crosses the anterior surface of the subclavian
artery and the apex of the lung to enter the thorax.
7. The left phrenic nerve is crossed by the thoracic duct which joins the bifurcation
of the left brachiocephalic vein.
8. The right lymphatic duct joins the bifurcation of the right brachiocephalic vein