  We present explicit descriptions of the crystals $\mathcal{B}(\infty)$ and
$\mathcal{B}(\lambda)$ over special linear Lie algebras in the language of
\emph{extended Nakajima monomials}. There is a natural correspondence between
the monomial description and Young tableau realization, which is another
realization of crystals $\mathcal{B}(\infty)$ and $\mathcal{B}(\lambda)$.
