  We present a representation of skew-orthogonal polynomials of symplectic type
($\beta = 4$) in terms of a matrix Riemann-Hilbert problem, for weights of the
form $e^{-V(z)}$ where $V$ is a polynomial of even degree and positive leading
coefficient. This is done by representing skew-orthogonality as a kind of
multiple-orthogonality. From this we derive a $\beta = 4$ analogue of the
Christoffel-Darboux formula. Finally, our Riemann-Hilbert representation allows
us to derive a Lax pair whose compatibility condition may be viewed as a $\beta
= 4$ analogue of the Toda lattice.
