a<-c(1,2,3,4,5,6,4,5)
b<-c(1,7,7,8,5,6,4,5)

par(mfrow=c(1,2), mar=c(5,4,1,2),
    oma=c(0,0,2,0))
hist(a, main=NA)
hist(b, main=NA)
mtext("histograms", outer=T, font=2,
      family="mono")