Boundaries

It has the following boundaries:

Apex: Union of the sternocleidomastoid and the trapezius muscles at the superior nuchal line of the occipital bone

Occipital bone

The occipital bone, a saucer-shaped membrane bone situated at the back and lower part of the cranium, is trapezoidal in shape and curved on itself...

Anterior: Posterior border of the sternocleidomastoideus

Posterior: Anterior border of the trapezius

Base: Middle one third of the clavicle

Clavicle

In human anatomy, the clavicle or collar bone is a long bone of short length that serves as a strut between the scapula and the sternum. It is the only long bone in body that lies horizontally...

Divisions

The posterior triangle is crossed, about 2.5 cm above the clavicle, by the inferior belly of the Omohyoideus, which divides the space into two triangles:

• an upper or occipital triangle
  Occipital triangle
  The occipital triangle, the larger division of the posterior triangle, is bounded, in front, by the Sternocleidomastoideus; behind, by the Trapezius; below, by the Omohyoideus....
  
  
• a lower or subclavian triangle
  Subclavian triangle
  The subclavian triangle , the smaller division of the posterior triangle, is bounded, above, by the inferior belly of the Omohyoideus; below, by the clavicle; its base is formed by the posterior border of the Sternocleidomastoideus.Its floor is formed by the first rib with the first digitation of...
  
   (or supraclavicular triangle)

Contents

A) Nerves and Plexuses:

• Spinal accessory nerve (Cranial Nerve XI)
• Branches of cervical plexus
  Cervical plexus
  The cervical plexus is a plexus of the ventral rami of the first four cervical spinal nerves which are located from C1 to C4 cervical segment in the neck. They are located laterally to the transverse processes between prevertebral muscles from the medial side and vertebral from lateral side...
  
  
• Roots and trunks of brachial plexus
  Brachial plexus
  The brachial plexus is a network of nerve fibers, running from the spine, formed by the ventral rami of the lower four cervical and first thoracic nerve roots...
  
  
• Phrenic nerve (C3,4,5)

B) Vessels:

• Subclavian artery
  Subclavian artery
  In human anatomy, the subclavian arteries are two major arteries of the upper thorax , below the clavicle . They receive blood from the top of the aorta...
  
   (Third part)
• Transverse cervical artery
• Suprascapular artery
  Suprascapular artery
  The suprascapular artery is a branch of the thyrocervical trunk.-Course:At first, it passes downward and laterally across the scalenus anterior and phrenic nerve, being covered by the sternocleidomastoid muscle; it then crosses the subclavian artery and the brachial plexus, running behind and...
  
  
• Terminal part of external jugular vein
  External jugular vein
  The external jugular vein receives the greater part of the blood from the exterior of the cranium and the deep parts of the face, being formed by the junction of the posterior division of the retromandibular vein with the posterior auricular vein.-Path:...
  
  

C) Lymph Nodes:

• Occipital
• Supraclavicular

D) Muscles:

• Inferior belly of omohyoid muscle
  Omohyoid muscle
  The omohyoid muscle is a muscle at the front of the neck that consists of two bellies separated by an intermediate tendon. It belongs to the group of infrahyoid muscles...
  
  
• Anterior Scalene
• Middle Scalene
• Posterior Scalene
• Levator Scapulae Muscle
• Splenius Muscle

Clinical significance

The Accessory Nerve (CN XI) is particularly vulnerable to damage at lymph node biopsy, where damage results in an inability to shrug the shoulders or raise the arm above the head (eg, for brushing hair).

The external jugular vein's superficial location also makes it vulnerable to injury.

External links

- "Identification of the muscles associated with the posterolateral triangle."