  We derive from the subleading contributions to the chiral three-nucleon force
(short-range terms and relativistic corrections, published in Phys. Rev. C84,
054001 (2011)) a density-dependent two-nucleon interaction $V_\text{med}$ in
isospin-symmetric nuclear matter. The momentum and $k_f$-dependent potentials
associated with the isospin operators ($1$ and $
\vec\tau_1\!\cdot\!\vec\tau_2$) and five independent spin-structures are
expressed in terms of loop functions, which are either given in closed
analytical form or require at most one numerical integration. Our results for
$V_\text{med}$ are most helpful to implement subleading chiral 3N-forces into
nuclear many-body calculations.
