1. Membranous structure that functions as the circulatory system in mammalian embryos until the heart becomes functional
   - yolk sac, umbilical vesicle, vesicula umbilicus

Derived forms: vitelline sacs

Type of: sac

• HydroDIURIL
• hydrodynamic
• hydrodynamics
• hydroelectric
• hydroelectric turbine
• hydroelectricity
• hydroflumethiazide
• hydrofluoric acid
• hydrofluorocarbon
• hydrofluosilicic acid
• hydrofoil
• hydrogel
• hydrogen
• hydrogen atom
• hydrogen azide
• hydrogen bond
• hydrogen bromide
• hydrogen carbonate
• hydrogen chloride
• hydrogen cyanide
• hydrogen fluoride
• hydrogen iodide
• hydrogen ion
• hydrogen ion concentration
• hydrogen peroxide