They are located laterally to the transverse processes between prevertebral muscles from the medial side and vertebral (m. scalenus, m. levator scapulae, m. splenius cervicis) from lateral side.
Showing the arrangement of the fascia coli (scalenus medius visible at center left in green).
It projects outward medially and is the site of insertion for scalenus anterior.
This is in contrast to the subclavian vein, which travels anterior to the scalenus anterior.
The phrenic nerve is then isolated under the scalenus anticus muscle.
It is bounded in front by the scalenus medius and behind by splenius cervicis.
