Why was galen wrong in many of his statements about the human body even though he was a careful observer?

It is because Galen based his information about anatomy on what he had found out during dissecting the bodies of animals. This created mistakes on his claims in human anatomy. Some of these anatomical errors were the following:

1.       He thought muscles are attached to the bone just like in dogs.

2.       He thought that the liver produces blood. He then realized that it flowed around the body, but he claimed that is burned fuel for the muscle.

3.       He thought that there are holes through the septum, which allowed the blood to flow from one side to another of the heart.

4.       He thought that there are blood vessels in the brain.

5.       He thought human’s jaw was made up of two bones just like a dog’s.

6.       He made mistakes about the liver’s shape.