The maternal vascular architecture of the dog girdle placenta from 30 to 63 (full term) days of pregnancy was investigated on corrosion casts by means of scanning electron microscopy. Each zone in the zonary girdle of the dog placenta was supplied by the radial arteries which were emitted from the arcuate arteries. The radial arteries branched three to five times giving off arterioles in the middle of the labyrinth which reached the allantochorionic side of the labyrinth. Subsequently, the

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... ioles emitted capillaries which formed a network in the labyrinthine zone. The capillary network was oriented in feto-maternal direction. Venules originating from the network converged into the radial veins near the junctional zone. Finally the radial veins joined the arcuate veins. At 30 days of pregnancy, the capillary network of the labyrinthine zone had a basic architecture. It developed remarkably in quantity from 30 to 45 days of pregnancy, with prominent development from 40 to 45 days. Though the network continuously developed from 45 days onward, the rate of development was lower than before. In the placenta of 45 days, the capillary network of the labyrinthine zone completed its development as well as its arrangement.