Definition: the posterior triangle of the neck is formed by
the sternocleidomastoid trapezius muscles and the clavicle.
Boundaries:
Anterior boundry: is formed by the posterior boarder of the sternocleidomastoid
muscle.
Posterior boundary: this is formed by the anterior border of
the trapezius muscle.
Base: formed by the middle one third of the clavicle
Apex: this is formed where the anterior border of trapezius
and the posterior boarder of the sternocleidomastoid muscle meet on the
occipital bone of the skull.
Roof: this is formed by deep fascia of the neck which cover
the space between trapezius and sternocleidomastoid.
Floor: the floor is formed from the superior to the inferior
by splenius capitis, levator scapulae, scalenus medius and posterior muscles. These
muscles are covered by the prevertebral fascia.
Content:
Veins:
1.      
The external jugular vein
2.      
Subclavian vein
Arteries:
1.      
Third part of subclavian artery
2.      
The thyrocervical trunk
3.      
The suprascapular artery
4.      
The occipital artery.
Nerves:
1.      
The accessory nerves
2.      
The cervical plexus
3.      
The phrenic nerves.
Lymph nodes: the superficial and deep groups of cervical
lymph nodes.