Lateral Plates

paired structures originating in the course of embryonic development in all chordates during the separation of the middle germ layer. The lateral plates consist of two sheets: outer (parietal), adjacent to the body wall, and inner (visceral), adjacent to the intestinal wall. A secondary body cavity or coelom develops between them. The serous membranes, smooth muscles, mesenchyma, blood vessels, heart, and mesentery are derived from the lateral plates during embryonic development.