It's entirely plausible to me that this has gone unnoticed for 200 years.
Two possibilities come to mind. First, he may have been studying a rare brain that had an enlarged system, and since he did not have preconceptions that what he found couldn't possibly be a component of the lymphatic system, he called it like he saw it. (It is also possible such brains were less rare back then or something. Many things have changed in our body's environments in the last 200 years. Random correlations abound.)
The other is that perhaps he was simply wrong. He saw something that he identified as a lymphatic component but was in fact something else. Future people didn't make the same mistake so the observation sank without a trace. 200 years later, the real and much-more-subtle lymphatic system was found.
[1] http://news.stanford.edu/news/2014/november/mystery-brain-im...
Video description:
Leonardo became obsessed with the heart in the latter period of his remarkable life. He made a prediction about the main blood vessel leaving the heart, the aorta. He had figured out how the flow of blood out of the heart actually closes the aortic valve.
Leonardo had no way of testing it and no way of seeing inside a working heart. For centuries no one else even speculated. But in the last 50 years technology has finally been invented to show that he was absolutely right.
And even practicing surgeons. Cadaver studies are hugely important for training surgeons how to implant new or new-to-the-surgeon medical devices.
Lymphatic vessels are part of the body’s circulatory system. In most of the body they run alongside blood vessels.
it's somewhat surprising (in hindsight I admit) that no-one thought to look for them there before.
How about you have a peek at the research article, think away the colors from the antibody staining and see if you still consider it strange that it could go undiscovered.
The things in question are appropriately measured on a micrometer scale, fragile to match and tightly tangled up with similar things inside jelly. And needless to say they don't come with helpful colored plastic hulls or developer defined object type annotation for inspection.
As to how the brain’s lymphatic vessels managed to escape notice all this time, Kipnis described them as “very well hidden” and noted that they follow a major blood vessel down into the sinuses, an area difficult to image. “It’s so close to the blood vessel, you just miss it,” he said. “If you don’t know what you’re after, you just miss it.”
http://neurosciencenews.com/lymphatic-system-brain-neurobiol...