Between Sternocleidomastoid and Trapezius
Sternocleidomastoid and trapezius lie over deeper muscles in the neck. Between the posterior border of the fomer and the anterior border of the latter runs a gap with roughly parallel sides. In this gap portions of these deeper muscles can be seen, though not usually singly. In a lateral view, they seem to run at a mirror-image angle to the parallel sides just described.
The most distinct form in this region, potentially, is levator scapulae (
leh-VAY-tor SCAP-you-lee), literally the lifter of the scapula. It originates on the lateral processes of cervical vertebrae #1-4, and inserts on the medial border of the scapula above its spine.
Above levator scapulae lies splenius capitis (
SPLEEN-ee-us CAP-it-iss) and semispinalis (
sem-ee-spine-NAL-iss). These two muscles form a wall on the upper column of the neck, and assist in the lifting and rotation of the head. Both orginate on the base of the skull and insert on the spine. Semispinalis is responsible for filling out the neck at the base of the skull, and for forming a columnar ridge under trapezius. This ridge on either side of the spine puts the highest cervical vertebrae into a protective furrow similar to the one that can be found on the lower back.
Below levator scapulae lies scalenus (
scale-LEE-nus), which is responsible for bending the cervical vertebrae towards its attachment on a lateral part of the first rib. Below scalenus lies the lateral portion of omohyoid (
oh-moh-HIGH-oid), which runs at a distinctly more horizontal angle as it goes from a deep point on the scapula towards the throat.
A thin sheet of muscle called platysma (
plat-TIZ-muh) covers the front of the neck with its lower portion. Its medial edge runs from the hyoid bone to the medial end of the clavicle. Its lateral edge runs from just below the angle of the mandible to just short of the lateral end of the clavicle. Within these edges it covers the lower part of the mandible, the neck, and the clavicle before attaching to the upper border of pectoralis.
When tensed, the lower portion of platysma forms a great number of dramatic, slender, rounded bands, especially towards the clavicle. When relaxed, it cannot be detected, and the deeper muscles show through.