  In this paper we propose an Outer space analogue for the principal stratum of
the unit tangent bundle to the Teichm\"uller space $\mathcal{T}(S)$ of a closed
hyperbolic surface $S$. More specifically, we focus on properties of the
geodesics in Teichm\"uller space determined by the principal stratum. We show
that the analogous Outer space "principal" periodic geodesics share certain
stability properties with the principal stratum geodesics of Teichm\"uller
space. We also show that the stratification of periodic geodesics in Outer
space exhibits some new pathological phenomena not present in the Teichm\"uller
space context.
