\begin{table}%t1
\caption{\label{234para}The parameters of the best fitting models: the initial radius, $R_{i}$, the start azimuthal angle, $\theta_{i}$, and the pitch angle, $\psiup_{i}$, for the $i$th arm.}
%\centering
\small
\begin{tabular}{clclclclclclcc}
\hline
\hline
Model & $R_{1}$&$\theta_{1}$& $\psiup_{1}$ & $R_{2}$ & $\theta_{2}$ &
$\psiup_{2}$ & $R_{3}$ & $\theta_{3}$ & $\psiup_{3}$ & $R_{4}$ &
$\theta_{4}$& $\psiup_{4}$& $Z$  \\
  & (kpc)&$(^{\circ})$& $(^{\circ})$ & (kpc) & $(^{\circ})$ &
$(^{\circ})$ & (kpc) & $(^{\circ})$ & $(^{\circ})$  &
$(^{\circ})$& $(^{\circ})$& (kpc)& \\
\hline
%&&&&&&&&&&&&& \\[-8pt]
\multicolumn{10}{l}{For distribution of tracers with $R_{0}=8.5$~kpc and $\Theta_0=220$~km~s$^{-1}$} \\
2-arm model & 4.2 & 147& 5.3 & 4.0 & 297 & 5.2& & & & & & &0.47 \\
3-arm model & 3.8 & 40 & 7.8 & 3.6 & 195 & 9.9 & 4.0 & 303 & 7.5& & & &0.45  \\
4-arm model & 3.7 & 40 & 9.6 & 4.5 & 205 & 10.7 & 4.4 & 290 & 11.4 & 3.9 &
309 & 8.7 & 0.35 \\
\hline
%&&&&&&&&&&&&& \\[-8pt]
\multicolumn{10}{l}{For distribution of tracers with $R_{0}=8.0$~kpc and $\Theta_0=220$~km~s$^{-1}$} \\
2-arm model & 4.0 & 151& 5.1 & 3.9 & 315 & 5.0& & & & & & &0.43 \\
3-arm model & 3.6 & 40 & 8.0 & 3.5 & 195 & 9.6 & 3.9 & 303 & 7.4& & & &0.41  \\
4-arm model & 3.6 & 40 & 9.2 & 3.7 & 205 & 12.5 & 4.2 & 290 & 11.1 & 3.8 &
309 & 8.4 & 0.33 \\
\hline
\end{tabular}
\end{table}