  We show that the solutions of the Yang--Baxter equation invariant under the
action of the Yangian $Y(sl_2)$ lead to inhomogenous vertex models. Starting
from a four dimensional representation of $Y(sl_2)$ we obtain an integrable
family of coupled Heisenberg spin-$1\over2$ chains. Some thermodynamical
properties of this model are studied by means of the algebraic Bethe Ansatz.
