Where does the sternocleidomastoid insert?

• A. Mastoid process of temporal bone
• B. Lateral portion of the superior nuchal line
• C. Mastoid process and the lateral portion of the superior nuchal line
• D. Mastoid process of temporal bone and the lateral portion of the superior nuchal line of occiput

Answer: (D)

The insertion points of the sternocleidomastoid are where the muscle attaches to the skull after it runs from its two origins. It attaches to the mastoid process of the temporal bone and to the lateral portion of the superior nuchal line on the occipital bone. This combination of insertions is what lets the muscle pull the head toward the chest and rotate it to the opposite side.

This is the best answer because it names both insertion sites and clearly identifies that the nuchal line is on the occipital bone. The other options miss one of the insertion points or don’t specify the bone for the nuchal line, making them incomplete.