Answer
The renal portal system in frogs is a specialized venous connection that links the kidney and the lower part of the body. This system is designed to carry blood from the posterior parts of the body (such as the hindlimbs and tail) to the kidneys before the blood returns to the heart. This serves as a functional adaptation, allowing blood to be filtered by the kidneys before re-entering systemic circulation. The renal portal system is unique to amphibians and some reptiles and plays a crucial role in waste filtration and osmoregulation.
✅ Correct Option: (4) Kidney and lower part of body