Maternal blood supply to the coneptus.

This presentation gives an unorthodox account of the relationship of uteroplacental vessels to the structural units of the placenta, the lobules, and its development. Contrary to current opinion, neither the villous stems nor the ostia of maternal arteries have a one-to-one relation to placental lobules. Both are interlobular, and thus supply portions of adjacent lobules. The involvement of whole lobules, usually multiple, in degenerative processes such as infarction as is seen particularly in the placentas of stillborn infants, may indicate a general lowering of perfusion pressure in the intervillous space rather than occlusion of one artery. Just how maternal blood circulates within a lobule, is not known. In visualizing the development of the lobule it is only necessary to realize the commonly observed fact that anchoring points of large villi coming down along the sides of the lobules, are frequently if not regularly associated with the convolutes and ostia of maternal arteries. The areas containing both, form a network; how the intervening areas are formed into lobules is unknown.