The neck muscle that lowers and rotates the head is called the __________.

The sternocleidomastoideus muscle is responsible for lowering and rotating the head. It is a key muscle located in the lateral aspect of the neck. This muscle originates from the manubrium of the sternum and the clavicle and inserts into the mastoid process of the temporal bone. When this muscle contracts on one side, it causes the head to turn toward the opposite side and can also assist in lowering the head when both sides are engaged.

In contrast, other muscles listed serve different functions: the trapezius, which is a large muscle that extends from the back of the head and neck down to the thoracic region, is primarily involved in the movement of the shoulders and neck stabilization. The deltoid muscle, located in the shoulder, is responsible for the movement of the upper arm. The pectoralis major, a muscle in the chest, is involved in the movement of the shoulder and arm but does not play a role in head movement. Therefore, the role and positioning of the sternocleidomastoideus make it the correct choice for this question regarding head movement.