Answer
The two muscles are the splenius capitis and the splenius cervicis.
Work Step by Step
The large splenius capitis originate in on the vertebrae T4-C7, and rise to insert on the mastoid process and the occipital bone. The smaller splenius cervicis originates on vertebrae T6-T3 and rises to insert on C1-C4.; they insert into the mastoid process of the temporal
and occipital bones and the transverse processes of vertebrae C2--C-4. They act to extend or hyperextend the neck, rotate the head , and laterally rotate it.
