[R] Plot multiple lines, same plot, different axes?

[zack holden]

Dear list,
 
I would like to plot 2 series of numbers with very different ranges/scales as lines on the same plot. I assumed this is commonly done and easy, but I have not found any help files (e.g. axis() or matplot() that show how. I've searched many old posts to no avail. 
 
I'll be very grateful for any suggestions on how this is done. 
 
Best,
 
Zack