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Posterior triangle


  • posterior border of the stern-cleido-mastoid
  • anterior border of the trapezius and clavicle
  • The floor of the triangle consists of several muscles
  • Three, known as prevertebral muscles, are important as landmarks
  • They are, from superior to inferior
    1. levator scapulae
    2. scalenus medius
    3. scalenus anterior

Blood supply

Subclavian artery

  • enters the triangle deep to the scalenus anterior muscle
  • Its course in the posterior triangle is short, soon crossing the lateral border of the first rib to enter the upper limb

Subclavian vein

  • a continuation of the axillary vein at the lateral border of the first rib
  • It has a short course in the posterior triangle before passing superficial to the scalenus anterior
  • Within the triangle, it receives the external jugular vein.

External jugular vein

  • there is considerable individual variation in the arrangement of the superficial veins of the neck
  • The most prominent are the external jugular veins
  • Each crosses the sterno-cleido-mastoid in the superficial fascia to enter the posterior triangle
  • here it pierces the investing fascia and drains into the subclavian vein


Cutaneous branches of the cervical plexus

  • anterior primary rami of spinal nerves C1-C4
  • A number of branches pierce the investing fascia posterior to the sternocleidomastoid to become superficial
  • They radiate throughout the anterior and lateral parts of the neck and over the shoulder, on to the thorax
  • One branch, the great auricular nerve (C2,C3), extends up over the lower jaw on to the lower part of the face

Phrenic nerve (C3-C5)

  • a branch primarily from the cervical plexus
  • It crosses the anterior surface of the scalenus anterior, deep to the sternocleidomastoid, to enter the thorax

Accessory nerve (CXI)

  • enters the posterior triangle from beneath the sterno-cleido-mastoid, which it supplies
  • It crosses the triangle, superficial to the levator scapulae, to supply the trapezius

Brachial plexus

  • the roots of the plexus emerge from between scalenus anterior and medius, while the trunks lie in the lower part of posterior triangle