When was it revealed that there was organs inside of our body?

Question: When was it revealed that there was organs inside of our body?
- Keywords:
  body,
  organ
Asked by Api to Reka, Pip on 18 Nov 2016.
- Reka Nagy answered on 18 Nov 2016:
  
  We’ve known that for thousands of years – the ancient egyptians regularly removed the organs of dead bodies, storing them in jars, as they believed these would travel with them to the afterlife.

Question: When was it revealed that there was organs inside of our body?