Spectra extracted towards the four directions defined in Fig. 2b. The dashed curves show the fitted Gaussian components listed in Table 1. The solid line in each panel represents the sum of the fitted components, which are to be compared with the observed spectra in black steps. The vertical dotted lines show the velocities for the two components fitted to CO(2-1) by Costagliola et al. (2013). For reference, the systemic velocity of NGC 4418 has been measured as 2088 km s^-1 by Sakamoto et al. (2013).