  This work present high-precision measurements of the specific baryon angular
momentum jb, contained in stars, atomic gas, and molecular gas, out to ~10
scale radii, in 16 nearby spiral galaxies of the THINGS sample. The accuracy of
these measurements improves on existing studies by an order of magnitude,
leading to the discovery of a strong correlation between the baryon mass Mb,
jb, and the bulge mass fraction B/T, fitted by
B/T=-(0.34+-0.03)*log(jb/Mb/[1e-7 kpc km/s/Msun])-(0.04+-0.01) on the full
sample range of B/T=0.00-0.32 and Mb/Msun=1e9-1e11. The corresponding relation
for the stellar quantities Ms and js is identical within the uncertainties.
These M-j-B/T relations likely originate from the proportionality between j/M
and the surface density of the disk that dictates its stability against
(pseudo-)bulge formation. Using a CDM model, we can approximately explain
classical scaling relations, such as the fundamental plane of spiral galaxies,
the Tully-Fisher relation, and the mass-size relation, in terms of the M-j-B/T
relation. These results advocate the use of mass and angular momentum as the
most fundamental quantities of spiral galaxies.
