Which structure is the insertion point for the splenius capitis muscle?

The splenius capitis muscle is primarily involved in extending, rotating, and laterally flexing the head and neck. Its insertion is specifically at the mastoid process of the temporal bone, which is a prominent bony structure located behind the ear. This relationship is crucial for the muscle's function, allowing it to pull on the mastoid process to facilitate the movements of the head.

Choosing the mastoid process as the insertion point highlights the anatomical relevance to muscle function. The mastoid process provides a strong and effective attachment for muscles that need to control the position of the head, making the splenius capitis effective in its role of neck extension and rotation.

The other structures mentioned, such as the superior nuchal line or the spinous processes, are connected to neck muscles but do not serve as the insertion for the splenius capitis. The base of the cervical vertebrae is also not a site for this muscle's attachment, further emphasizing the specific role of the mastoid process in facilitating the actions performed by the splenius capitis.