Syennesis (Ancient Greek: Συέννεσις) of Cyprus was a physician, who must have lived in or before the fourth century BCE, as he is mentioned by Aristotle, who quotes from his writings a passage on the origin of the veins.[1] This fragment also forms part of the treatise De Ossium Natura in the Hippocratic Corpus,[2] which is in fact composed entirely of passages taken from different ancient writers.