In Galen's own time, some proponents of venesection believed that it was immaterial which vein was opened, since the same effect could equally well be obtained by using any of them; others, Galen among them, thought that it made a great deal of difference which vessel was used. Hippocrates and the most celebrated physicians, he says, were of this opinion also. This is not an isolated opinion of Galen's; he expresses it in all three of his works on venesection, and he makes further mention of specific sites for bloodletting in the De Sanitate Tuenda, the De Methodo Medendi, Ad Glauconem de Methodo Medendi, and his commentary on the Aphorisms. Now Galen was an expert anatomist, and his view of the structure (as distinct from the function) of the vascular system was, except in insignificant detail, that of the anatomist of today; yet he approved of practices of revulsive phlebotomy which, it would seem, must be quite inconsistent with such a view of vascular anatomy. To try to understand why he did this it will be necessary to summarise not only his own anatomical opinions, but also those of some of his predecessors, particularly those who offered clear accounts of the peripheral vessels.

Since the vessels contain blood, and since blood has been a subject of interest to man from the earliest times, we find some reference to blood-vessels in the earliest Western literature. Homer describes how Antilochus, leaping on Thoon from behind, cut right through the vein that runs straight along the back till it arrives at the neck.