THE NECK AND PROPORTIONS OF THE HEAD

 The  Neck

Primarily responsible for holding the head up is the nuchal ligament. This ligament is connected to the back of the head and all seven vertebrae of the neck. It functions as the cable that pulls the weight of the head back. A ligament serves the function of holding the head up well: it is strong and flexible and unlike a muscle, does not tire. Like all ligaments and tendons it does not have the power of self motion. 

The muscles of the neck are responsible for the positioning of the head, which can tip forward and back and to which side, and can turn right and left. 

The Backward tip of the head is accomplished by the trapezius, which is inserted into the base of the skull. When the cervical or neck position of the trapezius contracts, it pulls the back of the head downward. To tip the head forward, since the head is balanced toward the front, all that is usually necessary is for the trapezius to relax and gravity will pull the head down. But, if there is resistance, for example if one is lying on their back, we must act against gravity. Here a pair of muscles comes into play: the sterno-clio-mastoid muscles. Each is attached to either side of the head just behind the ear to a bony lump called the mastoid process. They then descend the column of the neck to attach to the sternum via a prominent cylindrical tendon and to the clavicle via a less obvious flat tendon. Pulling the chin toward the chest is accomplished by the interaction of both sterno-clio-mastoid muscles. To rotate the head only one of them contracts, pulling the back of the head toward the contracting side and the chin away from it. 

The rotations of the head from left to right bear close examination. Looking at yourself in the mirror with your neck and shoulders exposed, turn your neck to the left. In doing so place both your fingertips on your sterno-clio mastoid muscles and feel the muscle bulge as it contracts. You will notice as you turn to the left it is the right side that is contracting and as you turn to the right side it is the left. The sterno-clio mastoid is a diagonal muscle that links the front of the chest to the back of the skull. When it contracts the muscle pulls the ear towards the front of the chest. Thus the diagonal sterno-clio mastoid is repositioned to be vertical above the front of the chest. 

Between the two sterno-clio mastoids are the larynx and the trachea connecting the nose and mouth to the lungs.Lower down the cartilaginous trachea is partially obscured by the thyroid gland. Between the sides of this V, the larynx emerges, slanting forward towards the chin. Keeping the slant from being a straight diagonal is the hybrid bone, which is strung under the chin a the top front of the neck which pulls the tissues there. Tipping the head from side to side is performed by one side of the trapezius in the neck acting in conjunction with the sterno-clio mastoid of the same side.