From 
MSNBC:
Two Brazilian doctors and amateur art lovers believe they have uncovered a secret lesson on human anatomy hidden by Renaissance artist Michelangelo in the Sistine Chapel’s ceiling. Gilson Barreto and Marcelo de Oliveira believe Michelangelo scattered his detailed knowledge of internal anatomy across 34 of the ceiling’s 38 panels. The way they see it, a tree trunk is not just a tree trunk, but also a bronchial tube. And a green bag in one scene is really a human heart.
More here.