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

• susceptible
• susceptibleness
• susceptive
• sushi
• sushi bar
• Susian
• Susiana
• suslik
• suspect
• suspected
• suspend
• suspended
• suspended animation
• suspender
• suspender belt
• suspense
• suspense account
• suspenseful
• suspension
• suspension bridge
• suspension point
• suspension system
• suspensive
• signally
• signalman