• (n.) A flat muscle of the back of the neck.
Sple'ni·us noun [ New Latin ] (Anat.) A flat muscle of the back of the neck. 
(muscles) Type: Term Definitions: 1. splenius muscle of head, splenius muscle of neck. Synonyms: musculi spleniiType: Term Pronunciation: splē′nē-ŭs See: splenius muscle of head, splenius muscle of neck
splenius muscle noun either of two flat muscles that extend from the upper vertebrae to the base of the skull and serve to rotate or flex or extend the head and neck
Greek splenion = a bandage. Hence, splenius capitis muscle, with its finely-woven fibres and its quarter-spiral twist from a coronal to a sagittal plane.