  Let B be the crystal basis of the minus part of the quantized enveloping
algebra of a semi-simple Lie algebra. Kashiwara has shown that B has a
combinatorial description in terms of an embedding of B into the tensor product
of B and k abstract crystals B_{i_j}, j=1,2,...,k, where the longest word in
the Weyl group is s_{i_1}...s_{i_k}. We give an explicit description of the
image of this embedding for classical Lie algebras of types A, B, C, D. This
description is in terms of semi-standard Young tableaux of types A, B, C, D
defined by Kashiwara and Nakashima.
