  The angular distributions and the partial branching fraction of the decay
$B^{0} \rightarrow K^{*0} \mu^+ \mu^-$ are studied using an integrated
luminosity of $0.37\,fb^{-1}$ of data collected with the LHCb detector. The
forward-backward asymmetry of the muons, $A_{\mathrm{FB}}$, the fraction of
longitudinal polarisation, $F_{\mathrm{L}}$, and the partial branching
fraction, $\mathrm{d}{\mathcal B}/\mathrm{d}q^{2}$, are determined as a
function of the dimuon invariant mass. The measurements are in good agreement
with the Standard Model predictions and are the most precise to date. In the
dimuon invariant mass squared range $1.00-6.00{\mathrm{\,Ge\kern -0.1em
V}}^2/c^4$, the results are $A_{\mathrm{FB}}=-0.06\,^{+0.13}_{-0.14} \pm 0.04$,
$F_{\mathrm{L}}=0.55\pm 0.10\pm 0.03$ and $\mathrm{d}{\mathcal
B}/\mathrm{d}q^{2}=(0.42 \pm 0.06\pm 0.03) \times 10^{-7}c^4/{\mathrm{\,Ge\kern
-0.1em V}}^2$. In each case, the first error is statistical and the second
systematic.
