Proximal Attachment
It is attached proximally to the lower half of the ligamentum nuchae, spinous processes of C7 to T4 and intervening supraspinous ligaments.  

Distal Attachment
Splenius capitis passes supero-laterally to attach to the mastoid process and occipital bone below the lateral third of the superior nuchal line, deep to sternocleidomastoid.