How doctors inspect skull fractures before x-ray was invented?

500 years before x-rays were invented, Italian surgeon Guido Lanfranc would place a violin string between a patient's teeth.

When the string was plucked, it would cause the skull to vibrate in a musical note. If the sound was bright and clear, the skull was intact and healthy.

If the sound was dim and muffled, it indicated that a fracture was likely present. His results were surprisingly accurate.