Bone has been used to make buttons for a few centuries and is still being used today.
Moulds were used to wind thread or braid around in a decorative way to form a button. Rings were also used for the same purpose (especially Dorset buttons) I think it was very time consuming. My first picture shows wooden button moulds as well as some bone rings.
The second picture has a group of utility bone buttons, while the third one is of underwear buttons. Note the large holes enabling narrow tape to be threaded through which was then sewn onto the garment so the size could be adjusted around the waist. We use elastic these days.