chorionic villus tertiary chorionic villus NCIT:C34310 Tertiary chorionic villi contain embryonic blood vessels that develop from mesenchymal cells in the loose connective tissue core. These blood vessels connect up with vessels that develop in the chorion and connecting stalk and begin to circulate embryonic blood about the third week of development in humans. UMLS:C1515280 UBERON:0009995