cardinal vein sprouting

During human embryogenesis, lymphatic progenitor cells emerge primarily from mesodermal tissues, with paraxial mesoderm serving as the principal source. By approximately week 6-7 of human gestation (equivalent to E12.5 in the comparative mouse model shown in the right side of the image), a significant milestone in lymphatic development occurs as initial lymphatic endothelial cells (LECs) begin sprouting from the cardinal vein and organizing into primitive lymphatic structures.