Longissimus capitis is located between longissimus cervicis laterally and semispinalis capitis medially.  

Proximal Attachment
It arises by tendons from the posterior surfaces of the transverse processes of T1 to T5 and the articular processes of C4 to C7.  

Distal Attachment
The muscle passes superiorly to attach to the posterior margin of the mastoid process deep to splenius capitis and sternocleidomastoid.  It usually has a transverse tendinous intersection close to its upper attachment.

Nerve Supply
Longissimus capitis is supplied by the dorsal rami of C4 to T5.

Action
Longissimus capitis extends the head on the neck and turns the face to the same side.