Editor-In-Chief: C. Michael Gibson, M.S., M.D. 
The scalene muscles are a group of three pairs of muscles in the lateral neck, namely the scalenus anterior, scalenus medius, and scalenus posterior. They originate from the transverse processes from the cervical vertebrae of CII to CVII and insert onto the first and second ribs. Thus they are called the lateral vertebral muscles. They are innervated by the spinal nerves C3-C7. The action of the anterior and middle scalene muscles is to elevate the first rib and rotate the neck to the opposite side; the action of the posterior scalene is to elevate the second rib and tilt the neck to the same side.
The scalene muscles have an important relationship to other structures in the neck. The brachial plexus and subclavian artery pass between the anterior and middle scalenes. The subclavian vein and phrenic nerve pass anteriorly to the anterior scalene as it crosses over the first rib.
They also act as accessory muscles of inspiration, along with the sternocleidomastoids.
The passing of the brachial plexus and the subclavian artery through the space of the anterior and middle scalene muscles constitute the scalene hiatus. The region in which this lies is referred to as the scaleotracheal fossa. It is bound by the clavicle inferior anteriorly, the trachea medially, posteriorly by the trapezius, and anteriorly by the platysma muscle. If you look closely, you can also see the branches off that subclavian which will form the common carotid artery, which will further go up and split into the two branches, internal and external located at the junction of the carotid sinus. With these you will also see the Vagus Nerve (Cranial nerve X)
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- ↑ Henry Gray (1913). "Anatomy: Descriptive and Applied".