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Medical Definition of Maternal cotyledon
1. A unit of the placenta made up of trophoblastic cells, fibrous tissue, and abundant blood vessels, which is visible grossly on the maternal surface as an irregularly shaped lobe circumscribed by a deep cleft and made up of a stem villus with numerous branching free villi and anchoring villi; placental vessels in the chorionic plate supply the stem villus and its branches, allowing gas and metabolite exchange across the trophoblastic layer with maternal blood in the intervillous space; traditionally called clinicians' cotyledon. (05 Mar 2000)