system
Given the following post, respond as if you're commenting on Reddit:
human
What's on the other side of a belly button?

If someone was to cut open my abdomen, what would they find on the inside of my navel?

What would they have found if they looked when I was just born?
gpt
When you were a fetus, the placenta contained the umbilical vein for nutrients and all that goody stuff.

The umbilical vein runs from the navel to the fetal liver and through a vessel to the fetal heart. After you're born, it closes up and basically becomes a twisted fibrous cord.