The influence of the third-order dispersion on the propagation of short pulses in optical fibres is considered. The appearance of coupled nonlinear structures consisting of dark and bright envelope solitons is described. The wavelength range is found in the vicinity of the zero-dispersion wavelength where the effect of the third-order dispersion on the pulse propagation proves to be dominant. It is shown that in this case a nonlinear structure in the form of an embedded soliton appears.