The correct answer is Option B: muscle fibres found only in the ventricle wall.

Let's elaborate on the nature and function of the Bundle of His to clarify this answer. The Bundle of His, also known as the Atrioventricular Bundle (AV Bundle), is a crucial part of the electrical conduction system of the heart. It is not a network of nerve fibers but rather specialized muscle fibers.

The heart's electrical conduction system is responsible for coordinating the heartbeat, ensuring that blood is pumped efficiently throughout the body. The sequence of the conduction system goes as follows: from the sinoatrial (SA) node, located in the right atrium, the electrical impulse travels to the atrioventricular (AV) node. From the AV node, the impulse passes down through the Bundle of His, which then divides into the right and left bundle branches that run along the sides of the ventricular septum.

The Bundle of His is specifically located between the atria and the ventricles within the heart's septum—the wall dividing the right and left sides of the heart. Its role is critical for transmitting electrical impulses from the atria to the ventricles, a process essential for maintaining a synchronized heartbeat. After the impulse moves through the Bundle of His, it travels down through the right and left bundle branches and into the Purkinje fibers, spreading throughout the ventricles and causing them to contract.

Thus, the Bundle of His is comprised of specialized cardiac muscle fibers, not nerve fibers, and is found specifically in the heart's ventricular walls, bridging the electrical conduction between the atria and the ventricles. This corrects the common misconception that it might be composed of nerve fibers or distributed throughout the entire heart, including the atrial walls.