image matrix in tabular

\documentclass{article}
\usepackage{ifthen}
\usepackage[pdftex]{graphicx}
\begin{document}
\begin{center}
\begin{tabular}{@{}ccccc@{}}
  \newcounter{k}%
  \setcounter{k}{1}%
  \newcounter{i}%
  \setcounter{i}{1}%
  \whiledo{\thek<19}{%
    \rule[-3em]{0pt}{0pt}%
    \begin{minipage}{.158\hsize}
      \centering
      \includegraphics[clip,width=\hsize]{./M\thek.eps}\\
      \(M_{\thek}\)\\
    \end{minipage}%
    \ifthenelse{\thei=5\OR\thek=18}{\setcounter{i}{0}\\}{&}
    \stepcounter{k}\stepcounter{i}}
\end{tabular}\\
\end{center}
\end{document}