  (Abridged) A robust analysis of galaxy structural parameters, based on the
modeling of bulge and disk brightnesses in the BVRH bandpasses, is presented
for 121 face-on and moderately inclined late-type spirals. Each surface
brightness (SB) profile is decomposed into a sum of a generalized Sersic bulge
and an exponential disk. The reliability and limitations of our bulge-to-disk
(B/D) decompositions are tested with extensive simulations of galaxy brightness
profiles (1D) and images (2D). Galaxy types are divided into 3 classes
according to their SB profile shapes; Freeman Type-I and Type-II, and a third
``Transition'' class for galaxies whose profiles change from Type-II in the
optical to Type-I in the infrared. We discuss possible interpretations of
Freeman Type-II profiles. The Sersic bulge shape parameter for nearby Type-I
late-type spirals shows a range between n=0.1-2 but, on average, the underlying
surface density profile for the bulge and disk of these galaxies is adequately
described by a double-exponential distribution. We confirm a coupling between
the bulge and disk with a scale length ratio r_e/h=0.22+/-0.09, or
h_bulge/h_disk=0.13+/-0.06 for late-type spirals, in agreement with recent
N-body simulations of disk formation and models of secular evolution. This
ratio increases from ~0.20 for late-type spirals to ~0.24 for earlier types.
The similar scaling relations for early and late-type spirals suggest
comparable formation and/or evolution scenarios for disk galaxies of all Hubble
types.
