The scalene muscles are three paired muscles positioned deeply to the sternocleidomastoid muscle in the lateral compartment of the neck. Therefore, these muscles are also known as the lateral vertebral muscles of the neck. Each side of the neck presents with the following scalene muscles:

All scalene muscles extend between the anatomical features of the cervical vertebrae and the upper two ribs. Overall, the scalenes are involved in lifting the first two ribs. These muscles are also classified as the accessory muscles of inspiration, and they act during forced inspiration.

Note: A variant anatomy of the scalene muscles can be present, and some people have four instead of three scalene muscles. In this case, the fourth muscle is called the scalenus minimus muscle. It is positioned between the anterior and middle scalene muscles posterior to the groove for the subclavian artery found on the superior surface of the first rib. It stretches from the anterior tubercle of the transverse process of the seventh cervical vertebra (C7) to the first rib. Also, it inserts into the suprapleural membrane. Sometimes, this muscle is mistaken for the transverse pleural ligament.

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Scalene muscles