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The scalenus anterior, also known as the anterior scalene muscle or scalenus anticus, is one of the three scaleni, or scalene muscles. These are pairs of neck muscles that function as lateral structures in this part of the body. The scalenus anterior, which is the mid-sized one of the three, is named for its location, which is near the front of the neck, flanking it. The scalenus anterior is clinically significant due to its association with certain muscular disorders such as scalenus anterior syndrome and thoracic outlet syndrome, which involve compression of nerves or blood vessels.
The scaleni are also called lateral vertebral muscles because they arise from the lateral process of the cervical vertebrae, the section of the backbone or spine immediately below the skull. This process is known as the transverse process, which is responsible for attaching ligaments and muscle. The specific vertebral area of origin is the second to the seventh vertebrae, or C2 to C7. From there, the scalene muscles go onto the body’s first two ribs. It is placed behind the sternocleidomastoid muscle, which joins the scaleni in giving the neck the ability to be flexible and to rotate.
The scalenus anterior in particular comes from the anterior tubercle sections of the transverse processes of the C3 to C6. Going downward and almost vertically, it is guided by a tendon into the scalene tubercle that the first rib has on its inner border. It is also inserted into the section of this rib’s upper surface right behind the clavicle, or collar bone. The C5's and C6’s anterior arms supply the nerves of this muscle.
There are two important functions that the scalenus anterior carries out. First, it contributes to the stabilization of the first rib, into which it is inserted. Second, in cases where other muscles fix the first rib, the scalenus anterior counters such a condition by assisting in the neck’s flexion and rotation.
The other scalene muscles are the scalenus medius and the scalenus posterior. The scalenus medius is the largest of the three, and its place of origin is the C2 to C7’s posterior tubercle sections of the transverse processes. It is mainly responsible for contributing to normal respiration, since it provides elevation to the upper ribs. The smallest of the scaleni is the scalenus posterior, also known as the scalenus posticus. This one comes from the posterior tubercles at the C4 or C5 to C7’s transverse processes, and it goes into the second rib.