The tongue-body outline is represented as a circle with a moving center and fixed radius. The position of the tongue-body C is given with reference to the jaw-based line FJ by polar coordinates (Sc, Øc). Since the jaw rotates about point F, the angular coordinate with respect to the fixed system Øjc is given by the sum Øj + Øc.

The coordinates specify the position of the tongue with respect to the fixed reference system and the jaw. Identification of variables with unique muscles is not intended. This is a purely functional assignment of coordinates permitting descriptions of movement as fixed relative to the moving jaw and as moving relative to a fixed jaw.