The other day I came across this word when I was searching for something completely unrelated on the Web of Science.

Anastomosis

1. a natural connection between two tubular structures, such as blood vessels
2. the surgical union of two hollow organs or parts that are normally separate
3. the separation and rejoining in a reticulate pattern of the veins of a leaf or of branches

– From the World English Dictionary

So this is a leaf with lots of anastomoses:

Courtesy Wikipedia