The triangles of the neck are bounded by neck muscles and divided by the sternocleidomastoid muscle. The anterior triangle contains structures like the thyroid gland and carotid artery. The posterior triangle contains the brachial plexus and subclavian artery. Knowledge of the neck triangles is important for procedures like evaluating jugular venous pressure, palpating carotid pulses, and performing emergency cricothyroidotomy access to the airway.

1. Triangles of Neck

2.  The triangles of the neck are the topographic areas of the neck bounded by the
neck muscles.
 The sternocleidomastoid muscle divides the neck into the two major neck
triangles:-
1. The anterior triangle
2. The posterior triangle
 The triangles of the neck are important because of their contents, as they house all
the neck structures, including glands, nerves, vessels and lymph nodes.

3. Anterior and Posterior Triangle of Neck

4. Anterior Triangle
 The anterior triangle is situated
at the front of the neck. It is bounded:
 Superiorly
inferior border of the mandible (jawbone).
 Laterally
anterior border of the sternocleidomastoid.
 Medially
sagittal line down the midline of the neck.
 Investing fascia:
covers the roof of the triangle,
while visceral fascia covers the floor.

5. Division of Anterior
Triangle
 It can be subdivided
further into four
triangles:-
1. Muscular (omo-
tracheal) triangle
2. Carotid triangle
3. Submandibular triangle
4. Submental triangle

6. Contents of Anterior Triangle
 Muscles: thyrohyoid, sternothyroid, sternohyoid muscles
 Organs: thyroid gland, parathyroid glands, larynx, trachea,
esophagus, submandibular gland, caudal part of the parotid gland
 Arteries: superior and inferior thyroid, common carotid, external
carotid, internal carotid artery (and sinus), facial, submental, lingual
arteries
 Veins: anterior jugular veins, internal jugular, common facial, lingual,
superior thyroid, middle thyroid veins, facial vein, submental vein,
lingual veins

Nerves: vagus nerve (CN X), hypoglossal nerve (CN XII), part
of sympathetic trunk, mylohyoid nerve

7. Muscular (Omotracheal) Triangle
 The muscular (omotracheal) triangle
shares one margin with the anterior triangle
– the median line of the neck.
 The muscular triangle begins
at the inferior border of the body of the hyoid bone.
 It has two posterior borders –
 the proximal part of the anterior
border of sternocleidomastoid inferiorly
 the anterior part of the superior belly of
omohyoid superiorly

8. Borders of Muscular Triangle
 Superior - hyoid bone
 Lateral - superior belly of omohyoid
and anterior border of sternocleidomastoid
 Medial - midline of neck

9. Contents of Muscular Triangle
 Muscles: thyrohyoid, sternothyroid, sternohyoid
 Vessels: superior and inferior thyroid arteries, anterior jugular veins :
 Viscera: thyroid gland, parathyroid glands, larynx, trachea, esophagus

10. Carotid Triangle
 Similar to the muscular triangle,
the carotid triangle has the
omohyoid and
sternocleidomastoid muscles
as parts of its borders

11. Borders of Carotid Triangle
Anterior
- superior belly of omohyoid muscle
Superior
- stylohyoid and posterior belly of digastric muscles
Posterior
- anterior border of sternocleidomastoid muscle
Floor:
the inferior and
middle pharyngeal constrictors,
hyoglossus and parts of thyrohyoid.
Roof: deep and superficial fascia,
platysma and skin

12. Contents of Carotid Triangle
Arteries: common carotid, external carotid (and branches except maxillary, superficial
temporal and posterior auricular), internal carotid artery (and sinus)
Veins: internal jugular, common facial, lingual, superior thyroid, middle thyroid veins
Nerves: vagus nerve (CN X), hypoglossal nerve (CN XII), part of sympathetic trunk

13. Submandibular (Digastric) Triangle

14. Borders of submandibular Triangle
Superior
- inferior border of mandible
Lateral
anterior belly of digastric muscle
Medial
- posterior belly of digastric muscle
Inferiorly:
formed by the posterior belly of the
digastric and stylohyoid muscles posteriorly,
and the anterior belly of the digastric muscle anteriorly.
Apex: of the triangle rests at the
intermediate tendon of the digastric muscle.
Floor: is formed by the mylohyoid and hyoglossus,
while it is roofed by skin, fascia and platysma

15. Contents of submandibular Triangle
 Viscera:
submandibular gland and lymph nodes (anteriorly), caudal part of the parotid gland
(posteriorly)
 Vessels:
facial artery and vein, submental artery and vein, lingual arteries and veins
 Nerves:
mylohyoid, hypoglossal (CN XII)

16. Submental Triangle

17. Contents of Submental Triangle
 Anterior jugular vein,
 submental lymph nodes

18. Posterior Triangle
 The posterior triangle is a
triangular area found posteriorly
to the sternocleidomastoid muscle.
 It has three borders;
 Anterior border
posterior margin of the sternocleidomastoid muscle.
 posterior border
is the anterior margin of the trapezius muscle,
 inferior border
is the middle one-third of the clavicle.

19. Posterior Triangle
 Roof:
The investing layer of deep cervical fascia
 Floor:
covered with the prevertebral fascia along with levator scapulae, splenius capitis and
the scalene muscles.
 The inferior belly of omohyoid subdivides the posterior triangle into a small
supraclavicular, and a large occipital, triangle

20. Division of Posterior Triangle
 The posterior Triangle is divided into:-
 Occipital Triangle
 Supraclavicular (Omoclavicular) Triangle

21. Occipital Triangle
 The anterior and posterior margins
of the occipital triangle are the same
as those of the posterior triangle

22. Borders of Occipital Triangle
 Anterior
- posterior margin of sternocleidomastoid muscle
 Posterior
- anterior margin of trapezius muscle
 Inferior
inferior belly of omohyoid muscle
 Floor:
splenius capitis, levator scapulae and middle scalene
 Roof:
(from superficial to deep)
skin, superficial and deep fascia

23. Contents of Occipital Triangle
 Accessory nerve (CN XI),
 branches of the cervical plexus,
 upper most part of brachial plexus,
 supraclavicular nerve

24. Subclavian(Omoclavicular) Triangle

25. Borders of Subclavian Triangle
 Superior
inferior belly of omohyoid muscle
 Anterior
- posterior edge of sternocleidomastoid muscle
 Posterior
- anterior edge of trapezius muscle

26. Contents of Subclavian Triangle
 Third part of the subclavian artery,
 brachial plexus trunks,
 nerve to subclavius muscle,
 lymph nodes

27. Clinical Significance
 Important for clinical examinations and surgical procedures. These clinical and
surgical procedures include,
 Evaluation of the jugular venous pressure
 Evaluation of the pulses in a cardiovascular examination
 Emergency airway management

28. Jugular Venous Pressure
 Jugular venous pressure (JVP) is an indirect measurement of the pressure within the
venous system.
 This is possible because the internal jugular vein has valveless communication with
right atrium, therefore blood can flow backward into the vessel.
 With the patient lying at a 30 - 45 degree angle and their head turned to the left, an
elevated JVP will appear as a collapsing pulsation between the distal parts of the
sternocleidomastoid in the supraclavicular triangle and can extend as far as the lobule
of the ear.
 The JVP is measured as the vertical distance from the sternal angle of Louis to the top
of the pulsation. An elevated JVP (greater than 3 cm) is indicative of several
pathologies, including but not limited to pulmonary hypertension, hepatic congestion
and right heart failure

29. Jugular Venous Pressure

30. Carotid Artery Pulsation
 Identification of the carotid artery pulsation is important in the examination of the
cardiovascular system
 . It is often compared with the pulsation of the radial artery.
 The pulsation of the carotid artery can be appreciated by palpating the region of
the carotid triangle.

31. Carotid Artery Pulsation

32. Cricothyroidotomy
 A cricothyroidotomy is an emergency procedure used to establish a patent airway
when other less invasive procedures (endotracheal intubation, laryngeal mask
airway, etc) are contraindicated or would provide suboptimal care.
 It is a sterile procedure that involves incision of the cricothyroid membrane
 The membrane is an avascular plane deep to the region of the muscular triangle
that allows for quick access to the airway until a formal tracheostomy can be
performed

33. Cricothyroidotomy

34. Muscles of Neck
 Platysma
 Sternocleidomastoid
 Suprahyoid Muscles
1. -Digastric Muscle (anterior & posterior
belly)
2. -Stylohyoid
3. Mylohyoid
4. Geniohyoid
 Infrahyoid Muscles
1. Sternohyoid
2. Sternothyroid
3. Thyphyoid
4. Omohyoid (Inferior & Superior belly)
 Scalene Muscles
1. Scalenus anterior
2. Scalenus medius
3. Scalenus posterior

35. Platysma Muscle
 The platysma is a thin sheet-like muscle that lies superficially within the anterior
aspect of the neck
 lie deep to the subcutaneous tissue, the platysma is situated within the
subcutaneous tissue of the neck (superficial layer of the cervical fascia).

36. Platysma Muscle
Origin: Skin/fascia of infra- and supraclavicular
regions
Insertion: Lower border of mandible, skin of
buccal/cheek region, lower lip, modiolus,
orbicularis oris muscle
Innervation: Cervical branch of facial nerve (CN
VII)
Blood Supply: submental artery (facial artery),
suprascapular artery (thyrocervical trunk
Action: Depresses mandible and angle of
mouth, tenses skin of lower face and anterior
neck

37. Sternocleidomastoid Muscle
 The sternocleidomastoid muscle is a two-headed neck muscle,
 name bears attachments to the manubrium of sternum (sterno-),
 the clavicle (-cleido-),
 the mastoid process of the temporal bone (-mastoid).

38. Sternocleidomastoid Muscle
Origin: Sternal head: superior part of anterior surface of
manubrium sterni
Clavicular head: superior surface of medial third of the
clavicle
Insertion: Lateral surface of mastoid process of the
temporal bone, Lateral half of superior nuchal line of the
occipital bone
Innervation: Accessory nerve (CN XI), branches of
cervical plexus (C2-C3)
Function:
Unilateral contraction: cervical spine: neck ipsilateral
flexion, neck contralateral rotation
Bilateral contraction: atlantooccipital joint/ superior
cervical spine: head/neck extension; Inferior cervical
vertebrae: neck flexion; sternoclavicular joint: elevation of
clavicle and manubrium of sternum

39. Clinical Significance of SCM

40. Suprahyoid Muscles
 The suprahyoid muscles are a group of four muscles located superior to
the hyoid bone of the neck.
 They all act to elevate the hyoid bone – an action involved in swallowing.
 The arterial supply to these muscles is via branches of the facial artery, occipital
artery, and lingual artery

41. Stylohyoid Muscle
 The stylohyoid muscle is a thin muscular
strip, which is located superiorly to the
posterior belly of the digastric muscle.
 Attachments: Arises from the styloid
process of the temporal bone and attaches
to the lateral aspect of the hyoid bone.
 Actions: Initiates a swallowing action by
pulling the hyoid bone in a posterior and
superior direction.
 Innervation: Stylohyoid branch of the facial
nerve (CN VII). This arises proximally to
the parotid gland.

42. Digastric Muscle
 Two muscular bellies present connected by tendon
 Attachments:
 The anterior belly arises from the digastric fossa of the
mandible.
 The posterior belly arises from the mastoid process of the
temporal bone.
 The two bellies are connected by an intermediate tendon,
which is attached to the hyoid bone via a fibrous sling.
 Actions: Depresses the mandible and elevates the hyoid
bone.
 Innervation:
 The anterior belly is innervated by the inferior alveolar
nerve, a branch of the mandibular nerve (which is derived
from the trigeminal nerve, CN V).
 The posterior belly is innervated by the digastric branch of
the facial nerve.

43. Mylohyoid Muscle
 The mylohyoid is a broad, triangular shaped
muscle. It forms the floor of the oral cavity
and supports the floor of the mouth.
 Attachments: Originates from the
mylohyoid line of the mandible, and attaches
onto the hyoid bone.
 Actions: Elevates the hyoid bone and the
floor of the mouth.
 Innervation: Inferior alveolar nerve, a
branch of the mandibular nerve (which is
derived from the trigeminal nerve)

44. Geniohyoid
 The geniohyoid is located close to the
midline of the neck, deep to the
mylohyoid muscle.
 Attachments: Arises from the inferior
mental spine of the mandible. It then
travels inferiorly and posteriorly to attach
to the hyoid bone.
 Actions: Depresses the mandible and
elevates the hyoid bone.
 Innervation: C1 nerve roots that run
within the hypoglossal nerve

45. Infrahyoid Muscles of Neck
 The infrahyoid muscles are a group of four muscles that are located inferiorly
to the hyoid bone in the neck. They can be divided into two groups:
 Superficial plane – omohyoid and sternohyoid muscles.
 Deep plane – sternothyroid and thyrohyoid muscles.
 The arterial supply to the infrahyoid muscles is via the superior and
inferior thyroid arteries, with venous drainage via the corresponding veins.

46. Omohyoid Muscle
 Comprised 02 bellies connected by muscular
tendon
 Attachments:
 The inferior belly of the omohyoid arises from
the scapula. It runs superomedially underneath
the sternocleidomastoid muscle.
 It is attached to the superior belly by an
intermediate tendon, which is anchored to
the clavicle by the deep cervical fascia.
 From here, the superior belly ascends to attach to
the hyoid bone.
 Actions: Depresses the hyoid bone.
 Innervation: Anterior rami of C1-C3, carried by a
branch of the ansa cervicalis

47. Sternohyoid Muscle
 The sternohyoid muscle is located within
the superficial plane.
 Attachments: Originates from the
sternum and sternoclavicular joint. It
ascends to insert onto the hyoid bone.
 Actions: Depresses the hyoid bone.
 Innervation: Anterior rami of C1-C3,
carried by a branch of the ansa cervicalis

48. Sternothyroid Muscle
 The sternothyroid muscle is wider and
deeper than the sternohyoid. It is located
within the deep plane.
 Attachments: Arises from the manubrium
of the sternum, and attaches to the
thyroid cartilage.
 Actions: Depresses the thyroid cartilage.
 Innervation: Anterior rami of C1-C3,
carried by a branch of the ansa cervicalis

49. Thyrohyoid Muscle
 The thyrohyoid is a short band of muscle,
thought to be a continuation of the
sternothyroid muscle.
 Attachments: Arises from the thyroid
cartilage of the larynx, and ascends to
attach to the hyoid bone.
 Actions: Depresses the hyoid. If the hyoid
bone is fixed, it can elevate the larynx.
 Innervation: Anterior ramus of C1, carried
within the hypoglossal nerve.

50. Scalene Muscles of Neck
 The scalene muscles are three paired muscles (anterior, middle and posterior),
located in the lateral aspect of the neck.
 Collectively, they form part of the floor of the posterior triangle of the neck.
 The scalenes act as accessory muscles of respiration, and perform flexion at the
neck

51. Scalenus Anterior
 The anterior scalene muscle lies on the
lateral aspect of the neck, deep to the
prominent sternocleidomastoid muscle.
 Attachments: Originates from the anterior
tubercles of the transverse processes of C3-
C6, and attaches onto the scalene tubercle,
on the inner border of the first rib.
 Function: Elevation of the first rib. Ipsilateral
contraction causes ipsilateral lateral flexion
of the neck, and bilateral contraction causes
anterior flexion of the neck.
 Innervation: Anterior rami of C5-C6

52. Scalenus Medius
 The middle scalene is the largest and longest of
the three scalene muscles.
 It has several long, thin muscles bellies arising
from the cervical spine, which converge into one
large belly that inserts into the first rib.
 Attachments: Originates from the posterior
tubercles of the transverse processes of C2-C7, and
attaches to the scalene tubercle of the first rib.
 Function: Elevation of the first rib. Ipsilateral
contraction causes ipsilateral lateral flexion of the
neck.
 Innervation: Anterior rami of C3-C8

53. Scalenus Posterior
 The posterior scalene is the smallest and
deepest of the scalene muscles.
 Unlike the anterior and middle scalene
muscles, it inserts into the second rib.
 Attachments: Originates from the posterior
tubercles of the transverse processes of C5-
C7, and attaches into the second rib.
 Function: Elevation of the second rib, and
ipsilateral lateral flexion of the neck.
 Innervation: Anterior rami of C6-C8