The Lymphatic System.in Humxn Embryos, Yith J a Consideration of the Morphology of the System as a Whole

When we consi$er the history of our knowledge of the lymphatic system, it is clear that there have been two wholly different lines of thought with regards to our general conceptions. To establish its general morphology is the fundamental task for each of the systems of the body, and upon such a general conception is based all future elaboration of the system. I need only to refer to the neurone theory as establishing such a foundation for our knowledge of the nervous system. In connection with the lymphatic system, the idea that it arises from mesenehyme spaces dominates anatomical and .zo6logical literature as is evidenced by examining most of the text books. This conception is based on the work of Budge, Sala, Gulland, and many others. It allies the lymphatic system with tissue spaces and serous cavities. The other theory, which seems in a fair way to displace the earlier conception, is that the lymphatics are derived from the veins, that they are vascular rather than mesenchymal in origin. This theory, only recently crystallized, has had an interesting evolution; beginning with Langer and Ranvier, it has been formulated and developed by a group of American anatomists. In this paper I hope to add evidence for this theory and give a genera1 picture of the primitive lymphatic system as a whole. The great”usefulness of this t.heory, aside from the fact that we believe it to be true, is that it gives a key by which to work out the entire development of the lymphatic system down to its ultimate capillaries, and it will bc readily conceded that the old theory of the relation of the lymphatics to the tissue spaces gave us no such point of attack.