Each side of the neck contains two triangular sections created by the major deep muscles. The sternocleidomastoid muscle separates the sections, known as the anterior and posterior triangles.

Located in the front of the neck, the anterior triangle includes four smaller triangles. They are:

  • Submental: This triangle is located directly under the jaw at the front of the neck. The main muscle here is the mylohyoid muscle, which helps in swallowing as well as closing the mouth.
  • Submandibular: This triangle includes the deep muscles below the jawbone, or mandible. These include the digastric and stylohyoid muscles.
  • Muscular-visceral: Located just to the side of the lower center portion of the neck, this triangle involves the sternohyoid and sternothyroid muscles. These hold thyroid cartilage, hyoid bone (a curved bone in the neck between the chin and the thyroid cartilage), and the larynx.
  • Carotid: Located on the side of the neck, the carotid triangle includes the digastric, omohyoid, and sternomastoid muscles. These help flex the neck, anchor the hyoid bone, and flex the jaw.

The posterior triangle is a large section of muscles on the back of the sternocleidomastoid muscle that extends from behind the ear to the top of the shoulder on each side of the neck. The muscles involved here include the anterior, middle, and posterior scalene muscles. They work to elevate the first rib bone.

Also included in the posterior triangle muscle group are the levator scapulae and splenius muscle The splenius capitis muscles runs from the back of the skull to the spinal column and form a V shape in the back of the neck. They flex the head and help stabilize it. The levator scapulae function just as their name suggests: they help elevate the scapulae, or shoulder blades.

The erector spinae are long muscles of the back that run down a groove on each side of the vertebral column. They begin in the back of the neck and extend down to the pelvic area. These erector spinae are divided into three muscles on each side. These include the iliocostalis, longissimus, and spinalis. All of these muscles help move and stabilize the spine.