  We extend a previous analysis of the lowest-lying octet baryon masses in
covariant baryon chiral perturbation theory (ChPT) by explicitly taking into
account the contribution of the virtual decuplet baryons. Up to
next-to-next-to-next-to-leading order (N$^3$LO), the effects of these heavier
degrees of freedom are systematically studied. Their effects on the light-quark
mass dependence of the octet baryon masses are shown to be relatively small and
can be absorbed by the available low-energy constants up to N$^3$LO.
Nevertheless, a better description of the finite-volume corrections of the
lattice QCD data can be achieved, particularly those with small $M_\phi L$
($<4$), which is demonstrated by a careful study of the NPLQCD and QCDSF-UKQCD
small-volume data. Finally, we show that the predicted pion- and
strangeness-baryon sigma terms are only slightly changed by the inclusion of
the virtual decuplet baryons.
