\version "2.18.2"

incipit =
#(define-music-function (parser location incipit-music) (ly:music?)
   #{
     \once \override Staff . InstrumentName . self-alignment-X = #RIGHT
     \once \override Staff . InstrumentName . self-alignment-Y = ##f
     \once \override Staff . InstrumentName . padding = #0.5
     \once \override Staff . InstrumentName . stencil =
     #(lambda (grob)
        (let* ((instrument-name (ly:grob-property grob 'long-text)))
          (set! (ly:grob-property grob 'long-text)
                #{ \markup { 
                  \score
                  {
                    { \context PetrucciStaff \with {
                      instrumentName = #instrument-name                      
                      \once \override Staff . KeySignature #'X-offset = #-1.2
                      } $incipit-music            
                    } 
                    \layout { $(ly:grob-layout grob)
                              line-width = \indent
                              indent =
                              % primitive-eval is probably easiest for
                              % escaping lexical closure and evaluating
                              % everything respective to (current-module).
                              #(primitive-eval
                                '(or (false-if-exception (- indent incipit-width))
                                     (* 0.5 indent)))
                              ragged-right = ##f
                              ragged-last = ##f
                              system-count = #1 }
                  } 
                  \hspace #0.5                  
                   }
                #})
          (system-start-text::print grob)))
   #})

music_incipit = {
  \override Staff . Accidental #'glyph-name-alist = #alteration-mensural-glyph-name-alist
  \override Staff . KeySignature #'glyph-name-alist = #alteration-mensural-glyph-name-alist
  \override Staff . TimeSignature #'glyph-name-alist = #alteration-mensural-glyph-name-alist
  \override Staff . BassFigure #'glyph-name-alist = #alteration-mensural-glyph-name-alist
  \override Staff . BarLine . transparent = ##t
  \override Staff . Rest . style  = #'mensural  
  \override Staff . TimeSignature #'stencil = #ly:text-interface::print
  \override Staff . TimeSignature #'text = \markup \musicglyph #"timesig.mensural22"
  \key f \major 
  s4
  }
\score {
  \keepWithTag #'Cond
  \new GrandStaff
  <<
    \new PianoStaff
    <<
      \new Staff
      <<        
        \incipit { \clef "petrucci-c1"  \music_incipit a'4 c' s4}
        \set Staff . instrumentName =  \markup\center-column { "Viola" "Prima"  }
        \set Staff.shortInstrumentName = \markup { "Vn. I" }
        \new Voice { \autoBeamOn \clef treble a'4 c' }
      >>
      \new Staff
      <<
        \incipit { \clef "petrucci-c1"\music_incipit c'4 a' s4 }
        \set Staff . instrumentName =  \markup\center-column { "Viola" "Secunda"  }
        \new Voice { \autoBeamOn  \clef treble c'4 a' }
      >>
    >>
  >>
  \layout
  {
    indent = 4.5 \cm
    short-indent = 0.5\cm
    incipit-width = 1.6\cm
  }
}