The two auricles are demarcated externally from the ventricle by an irregular groove called

Options

A. Inter-auricular septum
B. Inter-ventricular septum
C. Coronary sulcus
D. Inter-ventricular groove

Answer

To solve the question regarding the external demarcation of the two auricles from the ventricles, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Structure of the Heart**:
- The heart consists of four chambers: two atria (auricles) and two ventricles. The atria are located at the top, while the ventricles are at the bottom.

2. **Identify the Grooves of the Heart**:
- The heart has several grooves that separate its chambers. These include the interauricular septum, interventricular septum, coronary sulcus, and interventricular groove.

3. **Analyze the Options**:
- **Interauricular Septum**: This is a wall of tissue that separates the left and right atria. It does not separate the atria from the ventricles.
- **Interventricular Septum**: This is the wall of tissue that separates the left and right ventricles. It does not separate the atria from the ventricles.
- **Coronary Sulcus**: This is a transverse groove on the outer surface of the heart that marks the division between the atria and the ventricles. It surrounds the heart and separates the atria from the ventricles.
- **Interventricular Groove**: This is a shallow groove that contains blood vessels and marks the separation between the ventricles, but it does not separate the atria from the ventricles.

4. **Select the Correct Answer**:
- Based on the analysis, the correct answer is **Coronary Sulcus**, as it is the groove that demarcates the two auricles from the ventricles.

5. **Conclusion**:
- Therefore, the two auricles are demarcated externally from the ventricle by an irregular groove called the **Coronary Sulcus**.