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

• thalamostriate vein
• thalamus
• Thalarctos
• Thalarctos maritimus
• thalassaemia
• thalassaemia major
• thalassemia
• thalassemia major
• thalassic
• Thalassoma
• Thalassoma bifasciatum
• thalassotherapy
• thaler
• Thales
• Thales of Miletus
• Thalia
• Thaliacea
• Thalictrum
• thalidomide
• Thalidone
• thallium
• thalloid
• Thallophyta
• thallophyte
• thallophytic