  There are two fundamentally different physical origins of faint satellite
galaxies: cosmological sub-structures that contain shining baryons and the
fragmentation of gas-rich tidal arms thrown out from interacting galaxies
during hierarchical structure formation. The latter tidal-dwarf galaxies (TDG)
may form populations with correlated orbital angular momenta about their host
galaxies. The existence of TDGs is a stringent necessity because they arise as
a result of fundamental physical principals. We determine the significance of
the apparent disc-like distribution of Milky Way (MW) satellite galaxies. The
distribution of the MW satellites is found to be inconsistent with an isotropic
or prolate DM sub-structure distribution at a 99.5 per cent level including the
recently discovered UMa and CVn dwarf spheroidal galaxies. The distribution is
extremely oblate and inclined by about $88\degr$ with respect to the the MW
disc. We also apply the methods to Andromeda's (M31) satellite galaxies using
two recently published data-sets. It can not be excluded that the whole
population of M31 companions is drawn randomly from an isotropic parent
distribution. However, two subsamples of Andromeda satellites are identified
which have disc-like features. [abbreviated]
