The paired scalenus anterior muscles elevate the first pair of ribs and are also used to rotate the neck and move it laterally (to the side) and forward.
The muscle starts at the anterior tubercles of the third cervical vertebra (the third vertebra from the top of the spine) and runs down through to the sixth cervical vertebra (the sixth vertebra from the top of the spine) before attaching to the scalene tubercle on the first rib. The anterior tubercles are areas of the vertebrae that stick out of the bone, on the left and right sides of its front aspect. The scalene tubercle is a small bump on the inside of the first rib.
The scalenus anterior is located in front of the subclavian artery and behind the subclavian vein, with the phrenic nerve crossing over this muscle's front. The phrenic nerve is the only nerve that controls the movement of the diaphragm, which is vital to breathing.
The scalenus anterior muscle is an important landmark in the neck and is used to find the supraclavicular triangle, which is located near the collarbone.
The scalenus anterior muscle is a muscle of inspiration (breathing in). Its primary job is to rotate and flex the bones of the neck unilaterally (using only one muscle of the pair), as well as to raise the first rib. When the muscle is moving bilaterally, or using both muscles of the pair, it flexes the neck forward.