THE POSTERIOR TRIANGLE
OF THE NECK
Using a simplified lateral view of the neck we can once again easily
identify the Borders of the posterior triangle of the neck:
- Sternocleidomastoid anteriorly
- Trapezius posteriorly
- Clavicle inferiorly
Roof of the posterior triangle: Platysma and superficial
layer of the deep cervical fascia (Only platysma
covers the vulnerable spinal accessory nerve crossing the posterior triangle)
Floor of the posterior triangle:
A muscular floor and consists of the following muscles which are arranged, in
order, from posterosuperior to anteroinferior:
1. Splenius capitis - ligamentum nuchae and upper thoracic spinous vertebrae
to the mastoid process and occipital bone (draws head backward or to the respective
2. Levator scapulae - processes of C1-C4 to the superior aspect of the
medial border of the scapula (elevates scapula).
3. Scalenus muscles
a. scalenus anterior - anterior tubercles of the transverse cervical
processes to the scalene tubercle of the 1st rib.
b. scalenus medius - posterior tubercles of all of the transverse
cervical processes to the first rib.
c. scalenus posterior - posterior tubercles of the transverse cervical
processes to the 2nd rib.
All muscles of the posterior triangle, whether boundary or floor muscles,
are enclosed by separate subdivisions of the deep investing fascia of the neck.
The posterior triangle of the neck can be further subdivided into:
- Occipital triangle lying above the inferior belly of the omohyoid
- Supraclavicular (Omoclavicular) triangle inferior to this muscle.
BOUNDARIES OF THE OCCIPITAL
- Posterior Boundary: Trapezius m.
- Anterior Boundary: Sternocleidomastoid m.
- Inferior Boundary: Omohyoid m.
- Floor: Splenius Capitus m, Levator Scapulae m, Scalenus Medius, and a portion
of Scalenus Anterior.
- Roof: superficial layer of Deep Investing Fascia.
CONTENTS OF THE OCCIPITAL TRIANGLE:
- Spinal Accessory nerve
(XI) - crosses the upper half of the triangle diagonally and, passing from
the deep surface of sternocleidomastoid inferiorly on levator scapulae to
reach the deep surface of trapezius, innervates sternocleidomastoid and trapezius.
- Superficial cervical cutaneous branches of Cervical
plexus - formed from ventral primary rami of spinal
nerves C2-C4, which emerge from posterior border of sternocleidomastoid
- Lesser Occipital (C2) – follows posterior border
of SCM to innervate the scalp behind and above the ear.
- Great Auricular Nerve (C2,3) - crosses superficial
to SCM and innervates the skin over the parotid gland, angle of the jaw
and the posterior ear
- Transverse Cervical Cutaneous Nerve of the neck (C2,3)
- crosses SCM superficially and, is cutaneous for the skin of the front
and side of the neck (anterior triangle).
- Supraclavicular Nerves (C3,4) - divides into medial,
intermediate, and lateral branches, which supply sensation
over the shoulder(from the sternoclavicular joint to the acromion process),
lateral neck and anterior upper thoracic wall.
- Part of the occipital and parts of the transverse cervical and suprascapular
arteries are also found in the occipital triangle.
Some words about the Brachial Plexus and its
relevance in the Occipital Triangle…..
The lower four cervical nerves (C5,C6,C7,C8) are found in the scalene gap
(space between scalenus anterior and scalenus medius muscles) and they, along
with the first thoracic nerve (T1), make up the brachial plexus. Cervical nerves
C5, C6, join to form the superior (upper) trunk of the brachial plexus, and
these nerves as well as part of the superior trunk are found in the occipital
triangle. Branches from the roots of C5, C6, and C7, as well as from the superior
- Dorsal scapular nerve - from the root of C5, pierces scalenus
medius, and continues caudally on the deep surface of levator scapulae.
This nerve innervates levator scapulae, rhomboids and it is
accompanied by the dorsal scapular artery (deep branch of the transverse
- Long thoracic nerve - from the roots of C5, C6, C7. Once formed,
it passes posterior to the brachial plexus and then along the chest wall (close
to the mid-axillary line) to innervate serratus anterior.
- Superior trunk of the brachial plexus – Present in both triangles,
this trunk will be discussed in detail in the next section
THE SUPRACLAVICULAR (Omoclavicular) TRIANGLE
- Inferior Boundary: Clavicle.
- Superior Boundary: inferior belly of Omohyoid m.
- Anterior Boundary: Sternocleidomastoid m.
- Floor: Splenius Capitus m, Levator Scapulae m, Scalenus Medius m, and a
small portion of the Scalenus Anterior m.
- Roof: superficial layer of Deep Investing Fascia.
CONTENTS OF THE SUPRACLAVICULAR (Omoclavicular)
- Superior trunk of the
brachial plexus - this trunk
is formed by the union of C5 and C6 and two nerves come from this trunk. (Also
present in Occipital Triangle)
- Suprascapular - through the suprascapular foramen to innervate
supraspinatus and infraspinatus
- Suprascapular - through the suprascapular notch to innervate supraspinatus
b. Nerve to subclavius - innervates subclavius
- Middle trunk of the brachial plexus
- this trunk is the continuation of the anterior primary division of the 7th
- Lower trunk of the brachial plexus
- this trunk is formed from the anterior primary division of the 8th cervical
and 1st thoracic nerves.
- Subclavian artery (3rd part) - the first part of the subclavian artery
lies medial to scalenus anterior, the second part lies posterior to
this muscle, and the third part lies lateral to the scalenus anterior.
The thyrocervical trunk arises from the first part of the subclavian,
and two of its several branches (transverse cervical, suprascapular),
pass through both the supraclavicular and occipital triangles in route to
their destinations. The transverse cervical supplies trapezius, subscapularis,
levator scapulae and the rhomboids, while the suprascapular supplies
supra and infraspinatus. Occasionally there are no branches from the
third part of the subclavian. An exception is when the descending scapular
(dorsal scapular) arises from the second or third part of the artery (deep
part of the transverse cervical artery).
- External Jugular Vein: Derived from the Following Overview of venous
drainage in the head and neck.
- Superficial Temporal and Maxillary veins unite to form Retromandibular
- Retromandibular vein divides at angle of mandible into Anterior and Posterior
- Anterior division joins Facial Vein to form Common Facial vein which drains
into Internal Jugular vein.
- Posterior division joins Posterior Auricular vein to form External Jugular
- External Jugular vein descends across Sternocleidomastoid muscle to drain
into Subclavian vein.
- Anterior Jugular vein forms from small veins below mandible;descends to
join Ext. Jugular vein above clavicle. After lying superficial to the sternocleidomastoid
muscle, the external jugular vein descends to the anterior angle of the
posterior triangle where it enters the subclavian vein.
Region Anterior to Supraclavicular Triangle
An important landmark in this region is the scalenus
anterior muscle which passes from the anterior tubercles of C3 - C6 to its
attachment at the scalene tubercle on the first rib.
- Around this muscle from lateral to medial passes
nerve (C3-C5) which is the sole motor
innervation to the diaphragm.
- Also in this region is the subclavian artery and vein. The vein lies
anterior to the scalenus anterior while the artery is posterior to it.
Using scalenous anterior as a landmark Subclavian
Artery is divided into three main parts with several important
First - lies medial to scalenus anterior
- Vertebral artery - arises from its upper posterior surface
- passes into the foramen transversarium of C6 and ascends, winds behind
the lateral mass of the atlas and enters the skull at the foramen magnum.
It unites with the vertebral artery from the opposite side to form the basilar
- important since its has branches that also supply the cervical spinal cord
- Internal thoracic artery - arises opposite the vertebral artery posterior
to the subclavian vein
- Runs in the pleura and enters the thorax on the posterior aspect of the
- supplies anterior intercostal branches (running between the ribs) and terminates
as the musculophrenic artery which supplies the diaphragm and superior
epigastric artery which runs in the anterior abdominal wall.
- Thyrocervical trunk - Lateral to the musculophrenic artery
and superior, breaks into inferior thyroid artery, suprascapular
artery, and transverse cervical artery.
- Inferior thyroid artery passes upwards and medially toward the inferior
pole of the thyroid gland. Immediately anterior to it lies the carotid sheath
and, somewhat more medially, the middle cervical ganglion of the sympathetic
trunk. It anastomoses with the superior thyroid artery coming from the external
carotid artery. It supplies the scalenus anterior and the longus colli muscles
by its ascending cervical artery.
- Suprascapular artery passes laterally across the posterior triangle
to the upper border of the scapula. This artery may arise from the third part
of the subclavian and in this situation may separate the superior from the
middle and inferior trunks of the brachial plexus.
- Transverse (or Superficial) Cervical along with the suprascapular
a. initially passes anterior to scalenus anterior and clamp down the phrenic
nerve as they run into the posterior triangle of the neck
Second - lies posterior to scalenus anterior
- Costocervical artery: (on the left it generally arises from the first
part) passes posteriorly over the apex of the lung to give 2 branches:
- Superior/Highest Intercostal artery to supply first two intercostal spaces
with Posterior Intercostal arteries
- Deep Cervical Artery to deep musculature for the back of the neck.
Third - lies lateral to the lateral border of scalenous
anterior as far as the outer border of the first rib
- Dorsal scapular artery passes laterally through the brachial plexus
and passing deep tot he levator scapulae it reaches the scapula and descends
deep to the rhomboids with the dorsal scapular nerve. This artery may arise
from the thyrocervical trunk as the deep portion of the transverse cervical