  An extended spin-space model in $7+1$ dimensions is presented that describes
the standard-model electroweak quark sector. Up to four generations of massless
and massive quarks and two-Higgs doublets derive from the associated
representation space, in addition to the W- and Z-vector bosons. Other mass
operators are obtained that put restrictions on additional non-Higgs scalars
and their vacuum expectation value. After symmetry breaking, the scalar
components give rise to a hierarchy effect vertically (within doublets)
associated to the Higgs fields, and horizontally (within generations)
associated to the non-Higgs elements.
