[OS X TeX] pictures in plain TeX

[juan tolosa]

I have just installed MacTeX, and it is wonderful. I have a question about pictures. How do you insert a figure in Plain TeX
using MacTeX? Previously I used TeXtures in my old mac, and the command looked like
\special{picture figure27 scaled 400}
I also tried PCTeX in a PC, and the command was something like
\special{bmp: figure27.jpf  y=2in}

What is your advice for inserting pictures in Plain Tex, using MacTex?

Thanks,
                    Juan Jose