On the [Wikipedia article for Passacaglia](https://en.wikipedia.org/wiki/Passacaglia), there is an excerpt of a piece by 17th-century composer Bernardo Storace.  It has a 6-line staff with both G and C clefs above a 7 line staff with both C and F clefs.

It seems obvious how to read this, but I had never encountered it before.  Was it something that saw frequent use in the era?

[![Storace Passagagli 1][1]][1] 

One answer mentioned a connection to the harpsichord, and it seems plausible— could it be that the staves are expanded to match the ranges of the upper and lower manual on a 2-manual instrument?

However, another part of this score suggests that it might just be a way to write for four parts on two staves that is more readily accessible to musicians accustomed to reading soprano and tenor clef:

[![Storace Passagagli 2][2]][2]


  [1]: https://i.sstatic.net/OZYpg.png
  [2]: https://i.sstatic.net/PJfNJ.png