Three horizontal axes OR Two axes on same side?

Dear list:

I need to reproduce a plot with three different horizontal axes.

I know how to make plot with two different horizontal axes (one
above, one below) using axis():
   axis(1, ....)
   axis(3, ....)

However, I don't know how to produce two axes on the same side of the
plot.

Any pointers or examples?
  

Try this, and I think you'll see the light:

plot(0)
axis(1, line=-3)

O__  ---- Peter Dalgaard             ?ster Farimagsgade 5, Entr.B
  c/ /'_ --- Dept. of Biostatistics     PO Box 2099, 1014 Cph. K
 (*) \(*) -- University of Copenhagen   Denmark          Ph:  (+45) 35327918
~~~~~~~~~~ - (p.dalgaard at biostat.ku.dk)                  FAX: (+45) 35327907

However, I don't know how to produce two axes on the same side of the
plot.

Any pointers or examples?

Try manually drawing the axis using lines() or segments() or arrows() and 
text() or mtext()

?axis says that this function has the logical parameter outer "indicating 
whether the axis should be drawn in the outer plot margin, rather than the 
standard plot margin".
You could try two calls to it with different outer values.

axis(1, line=-3)

I have just come to this solution.
However, it seems, I don't understand the meaning of the outer parameter.
What is it for?