## **Core Concept**
The interventricular septum is a wall of tissue that separates the left and right ventricles of the heart. It has a muscular part and a membranous part. The membranous part is a thin, non-muscular region.

## **Why the Correct Answer is Right**
The membranous part of the interventricular septum is located between the right atrium and the left ventricle. It is situated adjacent to the **tricuspid valve** (which is between the right atrium and right ventricle) and the **mitral valve** (which is between the left atrium and left ventricle), specifically being part of the **interatrial septum** and **interventricular septum** junction. This area is crucial for the conduction system of the heart.

## **Why Each Wrong Option is Incorrect**
- **Option A:** This option is incorrect because it does not accurately describe the location of the membranous part of the interventricular septum.
- **Option B:** This option is incorrect because, similar to option A, it does not correctly identify the chambers or structures between which the membranous part of the interventricular septum is situated.
- **Option D:** This option is incorrect as it also fails to accurately describe the anatomical relationship of the membranous part of the interventricular septum.

## **Clinical Pearl / High-Yield Fact**
A key clinical point to remember is that the membranous septum is a common site for **ventricular septal defects (VSDs)**, which are openings in the septum between the ventricles. This can lead to shunting of blood between the ventricles.

## **Correct Answer:** . right atrium and left ventricle