Which of the following statements is not true?

Options

A. Heart is ectodermal in origin
B. In human beings heart is situated in the thoracic cavity, in between the two-lungs slightly. lifted to the left
C. Human heart has the size of a clenched fist.
D. Double wall membranous bag (pericardium) with pericardial fluid protects heart

Answer

To determine which statement is not true regarding the heart, we can analyze each statement provided.

1. **Statement 1**: "The heart is ectodermal in origin."
- This statement is incorrect. The heart is actually derived from the mesoderm, not the ectoderm. The cardiac muscles that make up the heart originate from the mesodermal layer during embryonic development.

2. **Statement 2**: "The human heart is situated in the thoracic cavity in between two lungs slightly lifted to the left."
- This statement is true. The human heart is located in the thoracic cavity, positioned between the lungs, and it is indeed tilted slightly to the left.

3. **Statement 3**: "The human heart has the size of a clenched fist."
- This statement is also true. The size of the human heart is approximately that of a clenched fist.

4. **Statement 4**: "The heart is a double-walled membranous bag with pericardial fluid protecting it."
- This statement is true as well. The heart is surrounded by a double-layered membrane called the pericardium, which contains pericardial fluid that helps protect and lubricate the heart.

After analyzing all the statements, we find that the first statement is the only one that is not true.

**Final Answer**: The statement that is not true is: "The heart is ectodermal in origin."