TRIANGLES OF THE NECK
A common method used to assist in the understanding and locating different structures in the neck is to geometrically separate the neck into triangular components and noting the contents and their relationships.
The mastoid process located immediately posterior to the external ear (auricle) marks the superior attachment for the large sternocleidomastoid muscle as it passes to its attachment on the clavicle and sternum. This muscle separates the posterior triangle from the anterior triangle of the neck. It is best palpated by turning the head against pressure to one side and palpating the opposite side of the neck.