\long\def\@makecaption#1#2{%
  \vskip 10\p@
  \setbox\@tempboxa\hbox{#1: #2}%
  \ifdim \wd\@tempboxa >\hsize
      \unhbox\@tempboxa\par
    \else
      \hbox to\hsize{\hfil\box\@tempboxa\hfil}%
  \fi}