and is more developed than in egg-laying amniotes. In many placental mammals, the uteri of each side become partially or wholly fused into a single organ, although in marsupials they remain completely separate.

For birds, the oviduct is composed of:
# Infundibulum (formation of chalazae, place of fertilisation)
# Magnum (formation of egg white)
# Isthmus (formation of the shell membrane)
#