Final answer:
The Splenius Capitis muscle primarily assists in the rotation of the neck. It contributes to neck movements such as rotation, extension, and lateral flexion of the head.
Step-by-step explanation:
The primary function of the Splenius Capitis muscle is B) Rotation of the neck. This muscle is one of the back and neck muscles that move the vertebral column. It originates at the midline and runs laterally and superiorly to its insertion, helping in the movements necessary for the extension, lateral flexion, and rotation of the head.
When this muscle contracts on one side (unilaterally), it allows for rotation of the head to the opposite side. When it contracts on both sides (bilaterally), it assists in the extension of the head. Therefore, option B is correct as the Splenius Capitis plays a critical role in neck movements, especially in rotating the head.