A system of interconnected, fluid-filled compartments lies below the skin’s surface, lining the digestive tract, lungs and urinary systems, and around arteries, veins, and the space between muscles, according to a research team from the Perelman School of Medicine at the University of Pennsylvania, Mount Sinai Beth Israel Medical Center, and the New York University School of Medicine. This system is a previously unknown feature of human anatomy and is described in Scientific Reports.