By using the Watson transformation the heavy-ion optical-potential scattering amplitude is decomposed in the sum of a Regge-pole and a saddle point contribution. Outside a critical angular interval the saddle point contribution can easily be evaluated by using nonuniform asymptotic techniques and it is possible to assign a simple physical interpretation to each individual contribution: the Regge pole retains the contribution from generalized diffracted trajectories and the saddle point retains the contribution of traiectories either reflected or unperturbed by the nuclear part of the interaction. In the critical angular interval uniform asymptotic techniques must be applied and the above interpretation of individual contribution is no longer possible. The results are checked by analysing the16O or28Si cross-section, atEc.m.=35 MeV, obtained by using the so-calledE18 optical potential.