  The matrix elements of the $2\times 2$ fusion of Baxter's elliptic
$R$-matrix, $R^{(2,2)}(u)$, are given explicitly. Based on a note by Jimbo, we
give a formula which show that $R^{(2,2)}(u)$ is gauge equivalent to Fateev's
$R$-matrix for the 21-vertex model. Then the crossing symmetry formula for
$R^{(2,2)}(u)$ is derived. We also consider the fusion of the vertex-face
correspondence relation and derive a crossing symmetry relation between the
fusion of the intertwining vectors and their dual vectors.
