The opening of superior vena cava is guarded by

Options

A. Semilunar valves
B. Columnae carnae
C. Principal septum
D. None of these

Answer

To answer the question, "The opening of superior vena cava is guarded by," we will analyze the options provided and understand the anatomy of the heart.

### Step-by-Step Solution:

1. **Understanding the Superior Vena Cava**:
- The superior vena cava is a major vein that carries deoxygenated blood from the upper parts of the body (head, neck, arms, and upper chest) back to the heart, specifically into the right atrium.

2. **Identifying the Options**:
- The options given are:
1. Semi-lunar valve
2. Columnar carnae
3. Principal septum
4. None of these

3. **Evaluating Each Option**:
- **Option 1: Semi-lunar valve**:
- This valve is found at the opening of the pulmonary artery and the aorta, preventing backflow of blood but is not related to the superior vena cava.
- **Option 2: Columnar carnae**:
- These are muscular ridges found in the ventricles of the heart, specifically in the right and left ventricles, and do not guard the opening of the superior vena cava.
- **Option 3: Principal septum**:
- The septum refers to the wall dividing the right and left sides of the heart, but it does not guard the opening of the superior vena cava.
- **Option 4: None of these**:
- Since none of the previous options correctly describe what guards the opening of the superior vena cava, this option must be correct.

4. **Conclusion**:
- The opening of the superior vena cava is not guarded by any valve or structure, making the correct answer **Option 4: None of these**.

### Final Answer:
The opening of the superior vena cava is guarded by **none of these**.