semispinalis capitis

noun

semispinalis cap·​i·​tis -ˈkap-ət-əs 

: a deep longitudinal muscle of the back that arises especially from the transverse processes of the upper six or seven thoracic and the seventh cervical vertebrae, is inserted on the outer surface of the occipital bone between two ridges behind the foramen magnum, and acts to extend and rotate the head

called also complexus