I find this weirdly amazing, as to this day I was reading some medical news and documentaries where it was said that entire human bodies were sliced by millimetre slices. So, somehow I always imagined that each part of body and tissue is 100% known and that only left is to find out what are inner workings on the nano-meter scale, deep molecular levels or genetic level.
But in 2018 there was a similar news about Interstitium: https://www.livescience.com/62128-interstitium-organ.html
In 2017 there was mesentery: https://www.livescience.com/57370-mesentery-new-organ-identi...
Now we have this. So, reading this left me with one though "hidden in plain sight" and wondering what else is there.