  Bipartite entanglement in the ground state of a chain of $N$ quantum spins
can be quantified either by computing pairwise concurrence or by dividing the
chain into two complementary subsystems. In the latter case the smaller
subsystem is usually a single spin or a block of adjacent spins and the
entanglement differentiates between critical and non-critical regimes. Here we
extend this approach by considering a more general setting: our smaller
subsystem $S_A$ consists of a {\it comb} of $L$ spins, spaced $p$ sites apart.
Our results are thus not restricted to a simple `area law', but contain
non-local information, parameterized by the spacing $p$. For the XX model we
calculate the von-Neumann entropy analytically when $N\to \infty$ and
investigate its dependence on $L$ and $p$. We find that an external magnetic
field induces an unexpected length scale for entanglement in this case.
