Belgian doctors have just announced that the leg has a part that nobody had noticed before. The researchers say that the anteriolateral ligament, a tiny band of connecting tissue on the back of the knee, explains certain knee injuries. It also explains why some people don’t get better after surgery: This whole time surgeons have been missing this tiny but crucial piece of tissue. (UPDATE: It had been noticed before, but never considered important enough to actually make it into any anatomy books)
Last year, doctors announced that they’d discovered a razor-thin sixth layer of the cornea that had gone unnoticed through all of human history before that.
Part of the reason why these things can continue to escape our notice is that too often, we assume that everything important has already been mapped. Things look so clean and obvious in a textbook diagram, but the real world is messy and bizarre. We’re still just beginning to open our eyes.