Usually tops and backs are just glued directly to the ribs and linings, nothing fancy. At various places and times in the past, though, sometimes makers locked the top and back in place. This is seen in very old French violins and Dutch, also, but usually just as a thin groove slotted into the back or top, the width of the rib thickness, into which the rib is glued. Though this is mostly hidden, there are two nearly invisible clues that a back has the ribs set in. The first is that in spite of their great age, the margins of these backs and tops are usually flawlessly even all around. Where normal ribs can move and bulge, ribs set in a groove can’t. The other clue is to look at the back and rib junction right at the tops of the corners–the area in the photo above. Usually the fit isn’t perfect right at the point and a bit of the groove will commonly be visible there. You can see in this photo how that spot would be easily visible on this corner. While you’re noticing things, observe how the shape of the corner blocks was cut after the blocks were in place: you can see the arc-shaped cuts in the back that the gouge made in the process of shaping the blocks in place!
In this Dutch violin the maker has taken it one step farther, cutting a ramp with some unusual characteristics.
First, in gluing on the plates notice how the ramp routes the rib automatically, sliding it out to the upright cut. Second, just to make sure it doesn’t come apart, the maker has undercut the outside upright cut so that the rib curls outward in the groove and locks itself in place. This undercut warps the edge of the rib, resulting in a flange that locks into the groove’s undercut, as you can see along the top edge of the rib in the photo below:
Now, referring back to the opening photo, try to imagine what the lining, just inside the rib, is sitting on–a slanted ramp. In this violin the lining was not fit to the slope of the ramp. All it was doing was covering a puddle of glue hidden under the lining. Because of the undercut flange, this didn’t matter, and the rib was well held in place.
The only reason I had to see any of this was that the edge in the lower bout had been worn down from the outside to the bottom of the slanted groove by the players shoulder and was falling off. The back and rib had to be separated to repair this edge.