The "maternal arterial space" in the center of rats' placenta may be venous, not arterial.
Khera
K S
KS
D000818:Animals; D001158:Arteries; D004622:Embryo, Mammalian / Q000098:blood supply; D005260:Female; D010920:Placenta / Q000098:blood supply* / Q000502:physiology; D011247:Pregnancy; D051381:Rats; D014680:Veins