Splenius capitis
An oblique band reaches from the back of the neck to the skull behind the ear.

Attachments & illustration source
Lower posterior neck/upper thoracic midline and nuchal ligament to mastoid/lateral occipital skull base.
Original anatomical illustration. Fine attachment boundaries are simplified.
UAMS Department of Neuroscience — Muscles of the Back RegionElliott et al. (2018), cervical musculature anatomical cross-reference