Discovery of the valves of the lymphatic vessels

The valves of the lymphatic vessels were demonstrated by the Dutch anatomist Frederik Ruysch, whose Wikipedia article credits him with the proof of valves in the lymphatic system. His treatise Dilucidatio valvularum in vasis lymphaticis et lacteis, an elucidation of the valves in the lymphatic and lacteal vessels, appeared at The Hague in 1665, and his injection and embalming methods later allowed anatomists to follow the smallest vessels. The finding added to the anatomy of the lymphatic system that Thomas Bartholin and Olof Rudbeck had opened up a decade earlier.