From Embryology

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Fig. 501. Vertical section through wall of uterus and placenta in situ about seven months' development


In the fully developed placenta, the chorionic villi lie either free (floating villi) or attached to the decidua (fastening villi) in what are known as intervillous spaces (Fig. 500). In sections the villi are, on account of their structure, cut in all directions, many sections of villi being entirely free from their basal connections. The villi thus present the appearance of projections, peninsulas, or islands lying in spaces filled with blood (Fig. 501).

Branches from the arteries of the uterine muscularis enter the decidua basalis. They take very tortuous courses through the latter and in it lose their connective tissue and muscular coats, and, while of considerably larger diameter than most capillaries, become reduced to endothelial tubes. These follow the intervillous (placental) septa in which they branch and from which they finally open directly into the intervillous spaces along the edges of the cotyledons. The maternal blood is thus poured into the intervillous spaces at their periphery. After flowing through them it passes into veins which leave the intervillous spaces near the center of the cotyledons (Fig. 500).

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Bailey FR. and Miller AM. Text-Book of Embryology (1921) New York: William Wood and Co.

Cite this page: Hill, M.A. (2024, February 26) Embryology Bailey501.jpg. Retrieved from

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current00:47, 2 February 2011Thumbnail for version as of 00:47, 2 February 2011688 × 1,093 (276 KB)S8600021 (talk | contribs){{Template:Bailey 1921 Figures}} Category:Coelom Category:Placenta