A Bonechewer a doctor, or at least what "nautical types" call them, according to Yu Song. Presumably, each individual specializes in different things.
Bonechewers special in a number of surgical practices, though presumably skill varies from practitioner to practitioner and isn't limited to just lyons. They even preform things like amputation, can put animals under while the process is being done, and use the acrid smell of citrus to wake them up.
- Modak is an old bonechewer.