What are the two heads of the sternocleidomastoid muscle?

The correct choice identifies the two heads of the sternocleidomastoid muscle as the sternal and clavicular heads. This muscle, located in the neck, is divided into these two distinct origins. The sternal head originates from the manubrium of the sternum, while the clavicular head originates from the medial portion of the clavicle.

Understanding the anatomy of this muscle is crucial, as it plays a significant role in head movement and stabilization. When both heads contract, they flex the neck forward; individually, the right head rotates the head to the left, and the left head rotates the head to the right. This division into sternal and clavicular heads is a key feature that helps identify the muscle's structure and function in anatomical discussions.