Uninorms on bounded lattices

We study uninorms on bounded lattices. We show the existence of uninorms with the neutral element which is different from the top element and the bottom element using the fact that the t-norms and t-conorms on arbitrary lattice L always exist. As a by-product we give a method of constructing uninorms. Using this method, we obtain also the smallest uninorm and the greatest uninorm with a given neutral element e.