The splenius cervicis is a minor muscle located deep in the back of the neck that helps extend, laterally flex, and rotate the neck. It originates in the upper thoracic vertebrae and attaches to the transverse processes of the top two or three cervical vertebrae. It works in conjunction with the larger splenius capitus muscle to assist in the function of the head and neck.
The splenius cervicis is a minor muscle located deep in the back of the neck. A continuation of the splenius capitus above it, this muscle sits under the upper trapezius, which is a large superficial shrug muscle of the neck and back. In the layer of muscles below the trapezius, the splenius cervicis is sandwiched between the rhomboids minor and major, which are just below it and more medial to the spine, and the levator scapulae, which are slightly above it and more lateral to the spine on the side of the neck. Its function is to extend, laterally flex or laterally bend and rotate the neck.
Originating in the thoracic spine in the upper back, this muscle starts at three of the upper thoracic vertebrae, T3-T6. It arises specifically from the spinous processes of these vertebrae, which are the pair of bony eminences projecting backwards from the body of the vertebra that are visible as bumps along the spine. From here the splenius cervicis rises, its fibers curve slightly outwards and then retract to insert themselves high up on the cervical spine. Instead of attaching by a tendon, the muscle forms fascicles, or small bundles of muscle fibers wrapped in connective tissue, which attach the muscle to the transverse processes of the top two or three cervical vertebrae. The transverse processes are small lateral protrusions from the body of the vertebra, meaning that the muscle ends along the side of the neck.
In anatomy drawings, the splenius cervicis is somewhat continuous with the larger splenius capital directly above it. The principal extensor of the head and neck, the capital is flat and broad and extends upward and slightly laterally from the cervical and upper thoracic spine to the base of the skull. In other words, its origins correspond to those of the cervix, but it superficially crosses the cervix towards the head, with the fibers of the smaller cervix crossing below it towards their point of attachment on the upper cervical spine. This integration means that the splenius cervicis assists in the function of the capitis in extension, lateral flexion, and rotation of the head, but to a lesser extent.
While the cervix may act bilaterally to extend the neck and head, meaning both sides contract at the same time, it acts unilaterally, or one side at a time, to laterally flex and rotate the head. In doing so, he moves his head to the side on which the contraction is occurring. During contractions on the right side of the neck, therefore, the splenius cervicis can tilt its head to the right and turn its head to the right on the neck.
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