Posterior Scalene: The posterior scalene is the smallest and deepest of the scalene muscles. It is deeply placed, lying behind Sternocleidomastoid. Unlike the anterior and middle scalene muscles, it inserts into the second rib.
Origin: Originates from the posterior tubercles of the transverse processes of C5-C7
Insertion: The anterior surface of the 2nd rib, posterior to the tubercle for serratus.
Function: Elevation of the second rib, and ipsilateral lateral flexion of the neck.
Innervation: Anterior rami of C6-C8.
Blood Supply: Ascending cervical artery and superficial cervical artery.