Used on the chest wall as a platform on which to percuss with a hammer. The nature of the resulting sound could help to distinguish healthy lung from fluid or consolidation. A precursor to sonar and ultrasound. The graduated ivory and hinged wings with ornate silver work, make this a very fine example. There is a similar piece shown on page 194 of Elisabeth Bennion's book "Antique Medical instruments" which is is the Museum of historical Medicine in Copenhagen.