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

• bran flake
• bran muffin
• bran-new
• branch
• branch line
• branch out
• branch water
• branched
• branched chain
• branched chain ketoaciduria
• branchia
• branchial
• branchial arch
• branchial cleft
• branchiate
• branching
• Branchiobdella
• Branchiobdellidae
• branchiopod
• branchiopod crustacean
• Branchiopoda
• branchiopodan
• branchiopodous
• Branchiostegidae
• Branchiostomidae