What changes in the respiratory system were brought about by the entry of animals on land?

Previously, amphibians could only get oxygen from water through gill respiration. After they went on land, lungs appeared due to protrusion of the intestinal tube. With the help of the lungs, it became possible to absorb oxygen from the air. But the surface of the lungs is so small that they are poorly ventilated. Therefore, the skin still takes part in the respiratory process – through it, the blood is additionally saturated with oxygen.