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

Type of: sac

• extracellular fluid
• extract
• extractable
• extractible
• extraction
• extractive
• extractor
• extracurricular
• extracurricular activity
• extraditable
• extradite
• extradition
• extrados
• extradural
• extragalactic
• extragalactic nebula
• extrajudicial
• extralegal
• extralinguistic
• extramarital
• extramarital sex
• extramundane
• extramural
• extraneous
• extraneousness