Floor of posterior triangle of neck is formed by
Muscles forming floor of posterior triangle of neck :

 Semispinalis capitis.
 Splenius capitis.
 Levator scapulae.
 Scalenus posterior.
 Scalenus medius.
Semispinalis capitis, elevator scapulae, scalenus anterior, scalenus medius
Levator scapulae, splenius capitis, scalenus medius, scalenus anterior
Semispinalis capitis, scalenus anterior, splenius capitis, sternocleidomastoid
Levator scapulae, scalenus posterior, semispinalis capitis,scalenus medius