\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}