15thc perception on swallowtail merlons?

[CaryR]

It seems to be inconsistent, most of the merlons in Hildegard's illustrations are flat and square without decoration, and some are decorated with "Y" shaped lines inside like this:
   

So this gives them the appearance of a V-shape, but still it's contained within a square border. It seems like it's an artistic embellishment rather than a depiction of swallowtail merlons, but in that one example of the walls of heaven, it's a lot more prominent. They do look actually forked at the top. I can't find a good resolution detail though.