The sternocleidomastoid muscle is a prominent muscle located in the neck. It originates from the sternum and clavicle and inserts into the mastoid process of the temporal bone of the skull. This muscle is responsible for rotating and flexing the head, allowing for movements such as turning the head side to side and tilting it forward. In addition to its role in head movement, the sternocleidomastoid muscle also assists in breathing by elevating the sternum during deep inhalation. It is easily identifiable on the surface of the neck, especially when the head is turned, making it a key landmark in anatomy and clinical assessments.