Top:mean position-velocity diagrams across the north, north-west, south-east and north-east filaments (from left to right), where position denotes the length of a perpendicular slice relative to the central spine pixel in parsec, and the velocity are relative to the peak velocity of each slice. The overplotted black line shows the trend of the intensity-weighted mean offset velocity at each position along the radial slice. Mean radial gradients were computed within the inner 0.2 pc width around the spinal pixel. Bottom: mean variation in the velocity width in the radial direction, in km s⁻¹.