Though the general shape of the 'boughs' is similar, GD33-type glyphs have longer arms ending in backwardturning claws. Possibly the left glyph therefore really depicts female breasts, whereas GD33 should be explained in some other way. I have tried to explain the shape as due to an open bivalve shell. But why then the claws? One answer is that viri means a clew.

These two clews could signify the points (like spurs) where one year ends and another begins. The open space would then mean the five extracalendrical nights. It is as if the sun totally disappeared those five nights, which of course in reality would not happen below the polar circle.

Furthermore, I believe that there is a connection in thought between those five nights (the open space between the spurs) and the apex at left (summer solstice). Symmetry calls for that.