  The gas distribution and dynamics in the inner Galaxy present many unknowns
as the origin of the asymmetry of the longitude-velocity (lv) diagram of the
Central Molecular Zone (CMZ). On the other hand, there are recent evidences in
the stellar component of the presence of a nuclear bar that could be slightly
lopsided. Our goal is to characterize the nuclear bar observed in 2MASS maps
and to study the gas dynamics in the inner Milky Way taking into account this
secondary bar. We have derived a realistic mass distribution by fitting 2MASS
star counts maps with three components (disk, bulge and nuclear bar) and we
have simulated the gas dynamics, in the deduced gravitational potential, using
a sticky-particles code. Our simulations of the gas dynamics reproduce
successfully the main characteristics of the Milky Way for a bulge orientation
of 20-35 deg with respect to the Sun-Galactic Center (GC) line and a pattern
speed of 30-40 km/s/kpc. In our models the Galactic Molecular Ring (GMR) is not
an actual ring but the inner parts of the spiral arms, while the 3-kpc arm and
its far side counterpart are lateral arms that contour the bar. Our simulations
reproduce, for the first time, the parallelogram shape of the lv-diagram of the
CMZ as the gas response to the nuclear bar. This bar should be oriented by an
angle of ~60-75 deg with respect to the Sun-GC line and its mass amounts to
(2-5.5)10e9 Msun. We show that the observed asymmetry of the CMZ cannot be due
to lopsidedness of the nuclear bar as suggested by the 2MASS maps. We do not
find clear evidences of lopsidedness in the stellar potential. We propose that
the observed asymmetry of the central gas layer can be due to the infalling of
gas into the CMZ in the l=1.3-complex
