In the circulatory system of a frog, the triangular structure known as the sinus venosus directly joins which of the following chambers of the heart?

Step-by-step solution

The heart of a frog is a muscular structure situated in the upper part of the body cavity. It has three chambers, two atria and one ventricle. The sinus venosus is a triangular structure attached dorsally to the heart. It receives deoxygenated blood from the major veins called vena cava. The sinus venosus opens directly into the right atrium. The right atrium then pumps this deoxygenated blood into the ventricle. Answer: Right atrium