  Observations reveal that mature spiral galaxies consist of stars, gases and
plasma approximately distributed in a thin disk of circular shape, usually with
a central bulge. The rotation velocities quickly increase from the galactic
center and then achieve a constant velocity from the core to the periphery. The
basic dynamic behavior of a mature spiral galaxy, such as the Milky Way, is
well described by simple models balancing Newtonian gravitational forces
against the centrifugal forces associated with a rotating thin axisymmetric
disk. In this research, we investigate the effects of adding central bulges to
thin disk gravitational models. Even with the addition of substantial central
bulges, all the critical essential features of our thin disk gravitational
models are preserved. (1) Balancing Newtonian gravitational and centrifugal
forces at every point within the disk yields computed radial mass distributions
that describe the measured rotation velocity profiles of mature spiral galaxies
successfully. (2) There is no need for gravity deviations or ``massive
peripheral spherical halos of mysterious Dark Matter''. (3) The calculated
total galactic masses are in good agreement with star count data. (4) The
addition of central bulges increases the calculated total galactic masses,
possibly more consistent with the presence of galactic gases, dust, grains,
lumps, planets and plasma in addition to stars. (5) Compared with the light
distribution, our mass distributions within the disk are larger out toward the
galactic periphery which is cooler with lower opactiy/emissivity (and thus
darker). This is apparent from edge-on views of galaxies which display a dark
disk-line against a much brighter galactic halo.
