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

• auxiliary
• auxiliary airfield
• auxiliary boiler
• auxiliary cell
• auxiliary engine
• auxiliary equipment
• auxiliary operation
• auxiliary pump
• auxiliary research submarine
• auxiliary storage
• auxiliary verb
• auxin
• auxinic
• Av
• avadavat
• Avahi
• Avahi laniger
• avail
• availability
• available
• availableness
• avalanche
• avalanche lily
• Avalokiteshvara
• Avalokitesvara