The sternocleidomastoid muscle is a prominent muscle used as a landmark in the anterior neck. The proximal attachments are on the sternum (manubrium) and clavicle. Distally, it is attached to the mastoid process of the temporal bone. When one side is activated, sternocleidomastoid rotates the head to the opposite side (nose away from the muscle) and laterally flexes the neck. When both sides contract together, sternocleidomastoid flexes the neck. Sternocleidomastoid is innervated by CN XI Accessory n. Model created using files from BodyParts3D (lifesciencedb.jp/bp3d), Life Sciences Integrated Database Center licensed by CC Attribution-Inheritance 2.1 Japan, 2008 and edited using Blender