  We analyse IRAS and COBE DIRBE data at wavelengths between 2.2 and 240 mu of
the central 500pc of the Galaxy and derive the large-scale distribution of
stars and interstellar matter in the Nuclear Bulge. Models of the Galactic Disk
and Bulge are developed in order to correctly decompose the total surface
brightness maps and to apply proper extinction corrections. The Nuclear Bulge
appears as a distinct, massive disk-like complex of stars and molecular clouds
which is, on a large scale, symmetric with respect to the Galactic Centre. It
is distinguished from the Galactic Bulge by its flat disk-like morphology, very
high density of stars and molecular gas, and ongoing star formation. The
Nuclear Bulge consists of an R^-2 Nuclear Stellar Cluster at the centre, a
large Nuclear Stellar Disk with radius 230+-20 pc and scale height 45+-5 pc,
and a Nuclear Molecular Disk of same size. Its total stellar mass and
luminosity are 1.4+-0.6 10^9 M_sun and 2.5+-1 10^9 L_sun, respectively. The
total mass of interstellar hydrogen in the Nuclear Bulge is 2+-0.3 10^7 M_sun.
Interstellar matter in the Nuclear Bulge is very clumpy with ~90% of the mass
contained in dense and massive molecular clouds with a volume filling factor of
only a few per cent. This extreme clumpiness enables the strong interstellar
radiation field to penetrate the entire Nuclear Bulge and explains the
relatively low average extinction towards the Galactic Centre. In addition, we
find 4 10^7 M_sun of cold and dense material located outside the Nuclear Bulge,
which gives rise to the observed asymmetry in the distribution of interstellar
matter in the Central Molecular Zone.
