Triangles of the Neck

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Last updated 1 April 2006

Posterior Triangle of the Neck

Boundaries of the Posterior Cervical Triangle (p. 789)

The clavicle forms the base of the posterior triangle.
The apex is formed where the borders of the sternocleidomastoid and the trapezius muscles meet on the superior nuchal line of the occipital bone.
The occipital artery passes through the apex of the posterior triangle before it ascends over the posterior aspect of the head.

Roof of the Posterior Cervical Triangle (p. 789)

The posterior triangle is covered by deep fascia, which covers the space between the trapezius and the sternocleidomastoid.
Superficial to the deep fascia are the superficial fascia, platysma, superficial veins, cutaneous nerves, and skin.

Floor of the Posterior Cervical Triangle (p. 789)

Click here for a diagram of the floor of the posterior cervical triangle.

The fascial and muscular floor of this triangle is formed (superior to inferior) by the splenius capitis, levator scapulae, scalenus medius, and scalenus anterior muscles.
These muscles are covered by the prevertebral layer of deep cervical fascia. This "fascial carpet" is a lateral prolongation of the prevertebral fascia.

Contents of the Posterior Triangle

Veins of the Posterior Cervical Triangle (p. 790)

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.

Arteries of the Posterior Cervical Triangle (p. 791)

The third part of the subclavian artery 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, 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.

Nerves in the Posterior Cervical Triangle (p. 791)

Click here for a diagram of the superficial nerves of the neck.

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).

The Cervical Plexus of Nerves (pp. 792-3)

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.

The lesser occipital nerve (C2, and sometimes C3) ascends a short distance along the posterior border of the SCM before dividing into several branches that supply the skin of the neck and scalp posterior to the auricle.

The great auricular nerve (C2 and C3) curves over the posterior border of the SCM and ascends vertically towards the parotid gland.
It supplies branches to the skin of the neck and then divides into anterior and posterior branches
These supply the skin on the inferior part of the auricle on both surfaces, and an area extending from the mandible to the mastoid process.

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.
Its branches supply the skin over the anterior triangle of the neck.

The supraclavicular nerves (C3 and C4) arise as a single trunk, which divides into medial, intermediate and lateral branches.
They send small branches to the skin of the neck and then pierce the deep fascia just superior to the clavicle to supply the skin over the anterior aspect of the chest and shoulder.
The medial and lateral supraclavicular nerves also supply the sternoclavicular and acromioclavicular joints, respectively.

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.
The phrenic nerve enters the thorax by crossing the origin of the internal thoracic artery between the subclavian artery and vein.

The Ansa Cervicalis

Click here for a diagram of 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.

Anterior Triangle of the Neck

Boundaries of the Anterior Cervical Triangle (p. 796)

Its apex is at the jugular notch.
Its base is formed by the inferior border of the mandible and a line drawn from the angle of the mandible to the mastoid process.

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 (p. 796)

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 (p. 796)

This triangle contains the suprahyoid and infrahyoid muscles, arteries, veins, nerves, lymph nodes, and viscera (e.g., thyroid gland).