What is precaval and post postcaval vein?

I believe you might be referring to the "pre-caval" and "post-caval" veins, which are terms related to the circulatory system in animals, specifically vertebrates, including humans. These terms describe the veins that lead into or away from the heart.

Pre-caval Vein (Anterior Vena Cava): The pre-caval vein, also known as the anterior vena cava, is a large vein that carries deoxygenated blood from the upper part of the body back to the heart. In humans, the superior vena cava is the major pre-caval vein. It collects blood from the head, neck, arms, and upper chest regions and delivers it to the right atrium of the heart.

Post-caval Vein (Inferior Vena Cava): The post-caval vein, also known as the inferior vena cava, is another large vein responsible for carrying deoxygenated blood. It collects blood from the lower part of the body, including the abdomen, pelvis, and legs, and returns it to the right atrium of the heart.

These veins play a crucial role in the systemic circulation, which involves the transport of oxygen-depleted blood from the body's tissues back to the heart for eventual oxygenation in the lungs and recirculation through the body. The distinction between the pre-caval and post-caval veins is based on their positions in relation to the heart.