The Longissimus Capitis is a muscle located in the back of the neck. It is part of the larger erector spinae muscle group, which helps maintain posture and support the spine. This muscle originates from the upper thoracic vertebrae and inserts into the mastoid process of the skull, allowing for head extension and rotation. Functionally, the Longissimus Capitis plays a crucial role in movements such as tilting the head backward and turning it to the side. It works in conjunction with other neck muscles, including the splenius capitis and semispinalis capitis, to facilitate these actions and maintain head stability.