  We present a set of detailed, self-consistent, isotropic dynamical models for
disc galaxies. We start from the hypothesis that each galaxy can be decomposed
in a bulge, following the r^{1/4} law, and a disc with an exponential projected
density profile; and that the isodensity surfaces of each component can be
represented by similar concentric spheroids. Under these conditions we produce
the rotational velocity and velocity dispersion profiles, after taking into
account both the asymmetric drift effects and the integration along the line of
sight. The model is successfully applied to reproduce the stellar kinematic and
photometry of the bulge of the 4 lenticular and early-type spiral galaxies NGC
4565, NGC 7814, NGC 5866 and NGC 4594. For these galaxies detailed stellar
kinematical data are available at different positions across the galaxy. The
application of our models shows that: 1) For all the galaxies considered in
this work, an isotropic model is able to reproduce the whole dynamical data.
This is surprising in the special case of NGC 4565, for which previous models
were unable to reproduce the velocity distribution without introducing strong
anisotropies. 2) We do not need a dark mass halo to reproduce these data. This
do not mean that a dark halo is not present, but just that its dynamical
effects in these inner regions of the galaxies are negligible.
