A few measures with a different number of lines

Hello,
I want to know how to change the number of lines of just one (or a few) measures. For example: a 50 measures sheet music for flute (5 lines) but for measure 18 to 25 each measure has just 1 line (so, from 18 to 25 it isn't a pentagram but a "monogram", if the word is correct).
How can I do this?
Thanks in advance (and sorry for my English, I'm not a native speaker)