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In this article Florence Sabin discusses in detail her observations about the development of the lymphatic system, and argues that the lymphatic structures are derived from the veins, not from mesenchyme (the undifferentiated connective tissue in the embryo, from which connective tissues, blood vessels, and other structures develop).
Periodical. Sabin, Florence R. "The Lymphatic System in Human Embryos, with a Consideration of the Morphology of the System As a Whole." American Journal of Anatomy IX, 1 (1909): 43-91. Article. 49 Images.. American Journal of Anatomy