The mastoid part of the cleidocephalic muscle is the ventral part of this muscle, from clavicular intersection to the mastoid process. In bo, it inserts also on the muscular tubercle of the occipital bone. This part is sometime called "cleidomastoid muscle".
Origin: clavicular tendon/clavicular intersection/vestigial clavicle
Insertion: mastoid/occipital bone
Action: draw the limb cranially and, acting bilaterally, to fix the neck
Nerve: accessory nerve, ventral branches of cervical nerves