It had always seemed to me that since the slide sackbut technology was already available in the Renaissance, then the use of a soprano sackbut (trombone) to play the high end in works by Gabrielli etc. would have been a natural  development.  My misconception has now beeen corrected by Arnold Meyers of the Edinbrough Museum of Musical Instruments, as well as by Jeff Nussbaum, President of the Historical Brass Society, that the high end was always played by cornetti.  Arnold contends: "Venetian music by the Gabriellis (uncle and nephew), Monteverdi and their contemporaries can be effective played on modern brass instruments, but are more satisfying when played on the original instruments with cornetti as the soprano-register "brass"instruments alongside the trombones. Having played this repertoire now with good cornett players, I wouldn't want to be bothered any more with valve trumpets. "

To emphasize this point, listen here to a Montiverdi piece played by the English Cornett and Sackbut Ensemble

This fact was brought home to me dramatically when  "Dr Hank" Meredith (University of Western Ontario Faculty of Music and the Director of the Plumbing Factory Brass Band) visited my collection and picked up and played this cornetto - and produced a loud and distinctive trumpet-like sound! See a short clip of Dr Hank "having a go" at the Cornetto.   The tiny mouthpiece  makes playing the cornetto very difficult - and musicians sometimes played from the side of the mouth.

Cornetti were made of wood and wrapped in leather- with the interior hollowed out in a conical shape with 6 finger holes (one in back) placed to permit clear chromatic scales and most importantly- a small cup mouthpiece. This Cornetto was made by Christopher Monk UK in resin .