What you show in the photos appear to be ferrules with the antler inside. Most often on old knives, this was done when using a hidden tang. On full tang knives the bolsters are two piece and meet with the grip scales. Very seldom if ever will you see a solid bolster butt joined to antler or bone, on old knives anyway. The ferrule, while adding to the appearance of the knife, also aids in preventing the grip from splitting or cracking in use.